Polymers From Biobased Materials

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POLYMERS BIOBASED

FROM

MATERIALS

Edited by

Helena L. Chum Solar Energy Research Institute Golden, Colorado

NOYES

DATA

CORPORATION

Park Ridge, New Jersey,

U.S.A.

Copyright @ 1991 by Noyes Data Corporation Library of Congress Catalog Card Number: 90-23203 ISBN: O-8155-1271-6 Printed in the United States Published in the United States of America Noyes Data Corporation Mill Road, Park Ridge, New Jersey 07656

by

10987654321

Library

of Congress Cataloging-in-Publication

Data

Polymers from biobased materials / edited by Helena L. Chum. p. cm. Includes bibliographical references and index. ISBN O-8155-1271-6 : 1. Polymers. 2. Biomass chemicals. I. Chum, Helena L. TP1092.P67 1991 668.9--dc20 go-23203 CIP

ACKNOWLEDGMENTS This

report

could

contributions

of

not

have

R.M.

been

Brown,

Goring,

K. Grohmann,

M.

Rowell,

V.T.

and R.A.

suggestions nesin,

have been

M.

Hearon,

Mathias, G.

Stannett,

A.

Power,

Tesoro,

Berger,

and

Himmel,

made

H.

The

N. Greer,

staff, in finalizing

Lewis,

Glasser, D.A.I.

R. Narayan, many

L. Keay,

K.

work

and

is gratefully

B. Gun-

E. Malcolm,

Sarkanen,

dedicated

R.M. helpful

Chang, J. Eberhardt,

K. Piper,

this report

the excellent

W.G.

In addition,

J. Hyatt,

Rutenberg,

S. Wolf.

B. Glenn,

N.G.

by H.M.

without

Daly,

Young.

Hergert, M.

prepared

Jr., W.H.

of

I. Anderson,

R. Texeira

This

book by

was the

United

States

any

their

of

warranty,

prepared

U.S.

appreciated.

government employees,

ity or responsibility of any

fringe

privately

name,

nor the

trademark, or

Publisher,

makes any

completeness,

apparatus,

rights.

product,

Reference

manufacturer,

or otherwise

or imply

favoring

of authors

sarily state or reflect

herein

by the

United

States

or the Publisher.

expressed

those of the United

information

plementation involve ation for

is intended of

potentially

for

to obtain

any

hazardous

of the suitability

expert

procedures

materials.

of any information

of the user.

vi

The views

purposes. advice

which

use by any user, and the manner

sole responsibility

recomgovern-

States govern-

The

is cautioned

to any

herein do not neces-

or the Publisher.

book

or

not in-

does not

its endorsement,

ment or any agency thereof,

reader

or

process, or service by trade

or any agency thereof,

and opinions

nor

or assumes any legal liabil-

product,

constitute

mendation,

the

agency thereof,

or represents that its use would owned

spon-

Neither

for the accuracy,

commercial

necessarily ment

nor any

information,

process disclosed,

of work

of Energy.

express or implied,

usefulness

specific

as an account

Department

before

might

The im-

possibly

Final determinor procedure

of that

A.

of the SERI

NOTICE

sored

L.

S. Shoemaker,

use, is the

Foreword

Polymers

from

biobased

combined

chemical

binations

of renewable

This assessment biopolymers A major

materials

produced

materials

materials

discussed are wood,

for

selected

polymers

flour

as a filler

materials

polymers

copolymers,

The book properties.

properties

materials.

including

properties

polylactide

in two

of new materials

high strength,

major

plant

such

material.

for composites.

cell wall

or with

specific

Automotive,

of materials

polymers,

with

build-

is reviewed

and protein,

can be produced (e.g.,

role

research necessary to bring

Bioproduction

materials

The conventional

with

em-

specific

en-

polyhydroxybutyrate

mechanical

properties

(e.g.,

and high

uses).

parts. Part I describes

II reviews bioproduction

with

resulting

as biodegradability

polymers)

metals. poly-

material

polymeric

perform corrosion

and lignin, related

as well as the future

other

which

light weight,

such as cellulose

are considered.

biobased

for cellulose for specific

is presented Part

applications

These

significant

tensile properties

or

such as starch, which when combined

to the

is reviewed,

such as cellulose,

phasis on silk and wool. valerate

degradability

into a higher value use as a reinforcing

vironmentally

by chemical

processes. Com-

are also biobased

which could be used to replace certain components

environmental

packaging

plastics

also exhibit

carbohydrate

plastics

ing, and

resources

in biological

resources and their

its polymeric

and other

this material

renewable

directly

is the manufacture

and which

and/or

mers such as chitin, wood

from

fossil-fuel-derived renewable

research

plastics,

resistance and biodegradability,

of inexpensive

from

derived

or produced

by plants and selected animal sources.

goal of biobased

can impart

methods,

and conventional

reviews

as well as fossil-fuel-derived

Examples

are polymers

and mechanical

materials

of materials.

from

renewable

An appendix

provides

resources and their examples

of recent

Japanese research activities. The

information

in the

Chum of the Solar Energy The table

of contents

access to the information

book

is from

Research

is organized contained

Assessment

Institute

of Biobased

Materials,

for the U.S. Department

edited

of Energy,

in such a way as to serve as a subject

index

Helena

L.

1989.

and provides easy

in the book.

Advanced composition and production methods developed by Noyes Data Corporation are employed to bring this durably bound book to you in a minimum of time. Special techniques are used to close the gap between “manuscript” and “completed book.” In order to keep the price of the book to a reasonable level, it has been partially reproduced by photo-offset directly from the original report and the cost saving passed on to the reader. Due to this method of publishing, certain portions of the book may be less legible than desired.

V

by

December

Contents and Subject Index

EXECUTIVESUMMARY Helena

..............................................

..l

L. Chum

Introduction.

.................................................

.I

.................................... Assessment of Biobased Materials. ................................... ECUT

Biobased

Materials

Materials

from

Bioproduction Conclusions References

Goals.

Renewable

Resources and Their

of Materials

.....................................

Helena

FROM

MATERIALS

FOR THE

Biobased

.I0

.I2

I

RESOURCES AUTOMOBILE

AND

THEIR

OF THE

PROPERTIES

FUTURE:

..........................................

.I6

................................................ Industry.

Materials

References.

.I9

.........................

Industry.

IN LIGNOCELLULOSIC-DERIVED of Lignocellulosic

in Properties Sorption

Dimensional Biological

COMPOSITES.

Materials

of Lignocellulosic

....................... ....................

Materials

...........................................

Stability. Resistance

PAST,

PRESENT

AND

T. Stannett

vii

.37 .37 .39

.........................................

.39

Resistance.

GRAFTING:

.35

.37

........................................

........................................ Pyrolysis Properties. ......................................... Property Enhanced Lignocellulosics ............................... Combination of Lignocellulosics with Other Materials ..................... Future Opportunities. .......................................... References. ................................................. Ultraviolet

..........

Young

Modification

Improvements

2. CELLULOSE

.26 .32

.................................................

ADVANCES

Moisture

.I6

..........................................

in the Automotive

RoweN and R.A.

Chemical

Vivian

.4 .I0

L. Chum

Introduction.

R.M.

RENEWABLE

MATERIALS.

Automobile

2. RECENT

.................

.......................................... PART

MATERIALS

COMPOSITE

.4

Properties.

................................................. and Notes.

1. STRUCTURAL

.2

FUTURE.

.44 .47 .47

.47 .53 .53

. . . . , . . . . . . . . . . . . . . .58

viii

Contents

and Subject

introduction. Earlier

Index

................................................ .....................................

.58 .58

................................................

.59

Research-1953-1984.

Synthesis.

Chain Transfer Direct

and Redox

Oxidation.

Cellulose

Methods

.............................

.59

.........................................

Initiators.

.59

.........................................

SO

..................................... Radiation Methods ........................................ Peroxide Method. ....................................... Preirradiation Method .................................... Mutual Method. ........................................ Ultraviolet-Light Grafting .................................... Other Methods of Free Radical Grafting .......................... Ionic Polymerization Methods ................................. Ring Opening Methods. ..................................... Condensation Methods. ..................................... Characterization of the Graft Copolymers ........................... Cellulosic

.60 .61 .61

Comonomers

Properties..

.61 .61

.62 .62 .62 .62 .63 .63

.............................................

..6

.............................................. Present Situation-l 985-l 988 ..................................... Future Research Needs. ......................................... International Aspects. ..........................................

4

.64 .65 .66

Applications.

.68

References...................................................6 4. LIGNIN:

PROPERTIES

Wolfgang

AND

MATERIALS

8

...............................

.70

G. Glasser

................................................ Structure and Properties. ............................. Materials ................................................... Need for Future Research. ....................................... International Activities. ......................................... Conclusions .................................................

.70 .70

Introduction.

Macromolecular

Appendix-Papers 5. MATERIALS

FROM

Presented RENEWABLE

at the Symposium RESOURCES

.71

on Lignin:Properties

and Materials

.73 .73 .74 .. .75

...........................

.78

D.A. I. Goring New Materials Priorities

from Wood.

.......................................

for Research on the Utilization

.78

of Biobased

Materials

...............

.79

Conclusions..................................................7 References. 6. CHITIN:

THE

William

9

.................................................

NEGLECTED

BIOMATERIAL

.80

..............................

.81

H. Daly

..............................................

ChitinKhitosan. Future

Developments

References.

in Chitin/Chitosan

Research.

.83 .86 .87

.......................

.................................................

7.STARCH-BASEDPLASTICS...........................................9 Ramani Narayan Introduction. Northern

0

................................................

Regional

Starch as Filler

.90

Research Center Technologies

........................

.90

.............................................

Starch-Urethanes. Starch-Polyethylene

.90

........................................... (PE) Blends with

Ethylene-Acrylic

.92 Acid Copolymer

(EAA)

..

.95

Contents and Subject Index Starch Graft Copolymerization .................................. Starch Xanthate ........................................... Processing of Ribber ....................................... Encapsulation. .......................................... St. Lawrence Starch Technology ................................... St. Lawrence and ECOSTAR. .................................. Albis Plastic GmbH ........................................ Production of Products with Albis ECOSTAR Master Batch ............. Breathable Rapidly Degradable Films-ECOLAN. ...................... The Michigan Biotechnology Institute/Purdue Technology .................. References.

.95 .I01 101

.I03 107

.I07 107 107 108 112

................................................

8. BIODEGRADATION

OF PLASTICS

ix

.I 12

...................................

.I1 5

Christopher Rivard, Michael Himmel, and Karel Grohmann Why Degrade

Plastics?

..........................................

115

History....................................................116 Biodegradation

of Standard

........................

Plastic Formulations.

116

.......................................... Photo Self-Destruction ........................................ Plastic Copolymers .........................................

Biodegradable

Microbial

Plastics

118

...................................... .................................................

.I18

Research.

PART BIOPRODUCTION 9. ADVANCES

117

.I 17

Derived Plastics ......................................

Need for Future References.

117

IN CELLULOSE

118

II OF MATERIALS

BIOSYNTHESIS

............................

.I22

R. Malcolm Brown, Jr.

................................................. .................................... New Sources of Cellulose ....................................... Pure Cellulose Synthesis from Acetobacter. .......................... Hydrophilic Nature of Microbial Cellulose ........................... Direct Synthesis of Shaped Celluloses by Acetobacter ................... Background

122

Diversity

122

and Uses of Cellulose.

.I23

Outstanding Shape Retention and Dimensional Stability of Microbial Cellulose. Microbial Cellulose Synthesis Using Natural Substrates. .................. Control of Physical Properties of Cellulose During Synthesis ............... Scale Up of Microbial Cellulose Synthesis. ........................... Concluding Remarks: The Future .................................. References. .................................................

124 124 125 .. 125 125 126 126 127 127

......

129

10. BIOGENESIS

AND

BIODEGRADATION

OF PLANT

CELL

WALL

POLYMERS.

Norman G. Lewis Introduction.

...............................................

.I29

Cellulose...................................................12

Synthesis and Structure

in Higher Plants:

9

Current Status .................

Cellulases ................................................ Future Recommendations. ..................................... Lignin.....................................................13 Synthesis and Structure in Vascular Plants: Current Status ................ Alteration/Regulation of Lignin Decomposition Processes. .............. Lignin Structure ......................................... Lignin Biodegradation ........................................

129

.I31 132 3 133 133

.I34 135

x

Contents

and Subject

Index

..................................... ...................................... Cutin and Suberin ........................................... Current Status ........................................... Future Recommendations. ................................... Hydrolyzable and Condensed Tannins. ............................. Biosynthesis and Structure ................................... Biodegradation .......................................... Future

Recommendations.

Other Aromatic

Future

Recommendations.

138 138 138 138 138

.I38

...................................

139

.............................................

Hemicelluloses Future

137

.I38

Polymers.

Recommendations.

139

...................................

139

References..................................................13 11. ADVANCES

IN PROTEIN-DERIVED

Karel Grohmann

and Michael

9

MATERIALS

.........................

Materials. ................................. .............................................. Historical. ............................................... Silk and Silk-Like Fibers. ...................................... Hair and Wool. ............................................

Why Study Current

Protein-Based

Fibers from Modified

Collagen.

Leather

........................................

Need for Future

EXAMPLES Recent

Research.

148

.148

..................................

149 .I49 .I50

......................................

................................................

References. APPENDIX:

144

.I44 .144

Status

Composites.

OF RESEARCH

Progress of Chemical

Ajinomoto

.I52

ACTIVITIES

Modification

IN JAPAN.

of Wood

.................

in Japan .................

Co., inc ..........................................

Asahi Chemical

Industry

Chisso Corporation Daicel Chemical

Co., Ltd.

158

.........................................

Industries,

Kanebo,

Kogyo Seiyaku

.I61

Ltd ...................................

162

Co., Ltd

Ltd. Research & Development

Nisshinbo

Industries,

Shin-Etsu

Chemical

Inc.

Laboratories

......................................

Co., Ltd .....................................

154 155

.I57

................................

.................................. Daiwabo Co., Ltd ........................................... Fuji Spinning Co., Ltd ........................................

Dai-lchi

.I44

E. Himmel

....................

163

.I64 .I65 166 168 169

Executive Summary Helena L. Chum Chemical Conversion Research Branch Solar Energy Research Institute Golden, Colorado

INTRODUCTION Since 1980, the Energy Conversion and Utilization Technologies (ECUT) Division of the U.S. Department of Energy (DOE) has supported generic, high-risk applied research and exploratory development pertaining to energy conservation. These activities, which have long-, mid- , and near-termelements, are ones that private enterprise cannot or will not undertake. Innovative concepts frombasic research and other fields of technology are identified and brought to a stage at which other end-use government programs or industry will carry them into more advanced technology and engineering development (Carpenter 1984). The major objective of ECUT R&D is to develop generic technologies enabling energy conversion and utilization concepts. Key to the ECUT activities is ECUT's role as a bridge between basic research (such as sponsored by the National Science Foundation or DOE Basic Energy Sciences) and end-use applied research that uncovers a wide range of concepts that, if further developed, could be used in many applications. These applications serve a variety of end-use sectors such as transportation; industry: buildings and community systems; and power generation, storage, and transport. The need for this type of government program in the DOE Office of Conservation and Renewable Energy was recognized by both the Research and Development Coordination Council in 1979 and the Energy Research Advisory Board in 1983. To bridge the gap, for instance, between materials research and materials engineering, it is necessary to a) monitor and evaluate U.S. and international basic research and exploit it for energy conservation purposes: b) expand the generic technology base, common to many end-use sectors, through the understanding of techniques, processes, and materials relevant to energy conservation; c) identify potentially revolutionary materials conservation technologies and establish concept feasibility: and d) transfer the technology to DOE end-use programs and/or to private industry. Over the years, in many technologies, this approach has been for instance, by Japanese successfully implemented, researchers, in programs that have significant contributions from government agencies. One area identified by the ECUT Materials Program is biobased materials--polymers derived from renewable resources by chemical or combined chemical and mechanical methods, or produced directly in biological processes. Combinations of renewable and conventional fossil-fuel-derived plastics are also biobased materials. One example of a biobased material is a phenolic resin made with a feedstock derived from fast pyrolysis of renewable wood or bark wastes, followed by simple chemical This feedstock replaces conventional petroleum-derived phenol. fractionation. An example of a biologically produced biobased material is microbial cellulose, known since 1886 when Adrian Brown described that it could be produced from the bacterium Acetobacterxylinum (Brown, Jr. Chapter 9). Significant basic research in

2

Polymers

from

Biobased Materials

this area has been carried out at the University of Texas, with some funding from government and U.S. industry. An example of an industrial product emerging from this research is high-tensile-strength microbially produced cellulosic fibers that have superior acoustic performance and, therefore, are being used by Ajinomoto Co., Inc. in Japan to produce acoustic diaphragm materials. Also, films of bacterial cellulose with extremely good properties such as an effective barrier to growth of pathogenic microbes and close adhesion to the wound are being marketed in Brazil for the treatment of severe burns and other wounds (Fontana et al. 1989). The United States still leads in the basic research area, but the development of new markets and applications, albeit in high-value, lowvolume, specialty areas, is primarily in foreign countries. A well established pathway for the development of innovative technologies is to focus initially on the highest value products, and then, as the technologies mature and their cost decreases, expand them into low-value, high-volume markets of interest to the program because they have the highest impact on energy conservation. approach is being used by industrial consortia described in Chapter 4.

This

In September 1986, SERI began the technical assessment of biobased materials The assessment included literature reviews; for the ECUT Materials Program. discussions with researchers from universities, research institutes, and industry: and participation in relevant meetings. After its announcement in commerce Business Daily (May 20, 19871, a Letter of Interest (LOI) was distributed to Nineteen proposals were received and 250 members of the technical community. reviewed by a panel. Five proposals were selected for funding (September 1987), and work started on four subcontracts in January-July 1988. These ongoing sublightweight biobased contracts support the area of biomass-derived plastics: composites and biobased packaging plastics. consists of a series of contributions from This report The authors were asked North American researchers in areas of their expertise. to review the topics and to present their views on directions of R&D in both the United States and other countries. They were also asked to identify "gap" areas in the R&D of biobased materials. These contributions have two companion volumes that emerged from the symposia sponsored, in part, by the ECUT Biobased Materials project, a number of industries, and the American Chemical Society, Division of These symposia took place at the 3rd North Cellulose, Paper and Textile. American Chemical Congress, Toronto, April 1988, and covered the topics: "Lignin: Properties and Materials" and "Biosynthesis and Biodegradation of Plant They were organized by W. G. Glasser/S. Sarkanen and Cell Wall Polymers." N. G. Lewis/M. G. Paice, respectively: full papers representing the bulk of the contributions to the meeting were published in 1989 as ACS Symposium Series These two volumes complement the present volumes 397 and 399, respectively. Chapters 4 assessment and summarize the state of these fields internationally. and 10 summarize these symposia and research directions worldwide.

ECUT BIOBASED MATERIALS GOALS The ECUT Biobased Materials R&D goal is the identification of new materials, or combinations of renewable and synthetic ones, that have the same level of performance as metals and plastics used in key industries such as automotive and These materials can be made to have special properties. packaging plastics. Environmental degradability, biodegradability, and photodegradability can be New composites can have high strength, light imparted to packaging plastics. weight, corrosion resistance, and sound deadening effects for the automotive and The R&D aims to identify new materials that are buildings industries. inexpensive and not energy-intensive to manufacture. To help select options that will lead to cost-effective technologies and guide limited research funds, the R&D includes techno-economic evaluations of the key concepts investigated by an

ExecutiveSummary

3

independent process engineer (Mr. Arthur Power, A. J. Power and Associates, Boulder, Colorado). In these assessments, performed with contributions from project participants and the SERI field programmanager, mass and energy balances for selected processes are prepared; equipment is sized and the associated capital costs are estimated; operating costs are evaluated; and, finally, overall costs are calculated as a function of the return on investment, to provide industry with a realistic economic assessment of the routes chosen. In addition, sensitivity analyses are performed. These assessments indicate process areas in which research improvement would have the highest impact on the materials cost and process energy use. These evaluations are performed on a case-by-case basis instead of on a global, or in principle, basis. As will be clearly seen with biobased materials, such a variety of concept3 and chemical and engineering options is involved that global assessments may not be useful. Many of the lightweight biobased composites developed can also be used in more traditional applications such as materials of construction, insulation, and other applications in buildings and community systems. The ECUT Biobased Materials R&D supports the overall conservation goal to replace plastics currently derived from fossil fuel and natural gas with renewable materials of similar or improved properties, while providing materials that are environmentally acceptable and designed for reuse or degradation. Energy is conserved directly by the reduction in energy and feedstocks derived from fossil resources, and indirectly, in various ways. For instance, for transportation applications, indirect energy savings are accrued because automobile weight reductions can increase fuel economy on the order of 0.7 mpg for every 100 pounds saved in the weight of the vehicle. Considering that in the United States in 1986, 169 million vehicles consumed roughly 124 billion gallons of motor fuels, the impact of weight reduction on overall fuel consumption can be very high indeed. Between 1978 and 1984, approximately 16% of the total 36% increase in fleet fuel economy could be attributed to automobile weight reductions (Kulkarni 1984). Strategies employed included downsizing, weight reduction by materials substitution, improved aerodynamics, and improved power train efficiencies. Plastics are not inherently environmentally degradable. In fact, polymer scientists historically have concentrated on making plastics more and more durable and reproducible. Plastics are resistant to biological degradation for many reasons. Microorganisms have not yet had time enough to adapt and synthesize polymer-specific enzymes capable of degrading and using these man-made synthetic polymer3 of recent origin. The hydrophobic character of the plastics inhibits enzyme activity and the low surface area of the plastics with its inherent high molecular weights compounds the problem further. The permanence of plastics in the environment has resulted in increasing concerns over their disposal. There is also evidence that plastic wastes present a hazard to wildlife, particularly in the marine environment (Office of Technology Assessment 1989). Hence, Congress and state legislatures are addressing mandated plastics degradability--a move that can affect significantly the plastics packaging business, mostly for consumer products, institutional products, and packaging. Overall, 4.8 billion pounds of plastics were used in 1988 to produce 38.6 billion units (Society of the Plastics Industry 1989). As many as 15 states have banned or proposed bans on nondegradable plastic products ranging from egg cartons, disposable food service items, and clam shell packaging used by fast food restaurants, to plastic grocery bags, liquor bottles, and beverage rings that keep 6-packs together. On the federal level, 10 degradable plastics bills and a concurrent resolution introduce environmental are pending before Congress. Biobasedpackagingplastics degradability into conventional plastics, such that at least the volume is reduced, thereby decreasing harm to wildlife. Usually, the current concepts impart environmental degradability but do not maintain the level of performance of conventional plastics. ECUT-identified concepts strive to make combinations

4

Polymers from BiobasedMaterials

of plastics and renewable polymers, such as those derived from starch, compatible through the design of specific graft copolymers of both entities. These copolymers would permit common plastics processing practices of making alloys between incompatible polymers possible in a cost-effective way. ASSESSbiEWT OR' BIOBASED MATERIALS The assessment addresses two areas: I. Materials from Renewable Resources and Their Promrties This area discusses major biopolymers produced by plants and selected animal sources. Figure 1 shows a simplified schematic of the flows of these materials in the industry today, and Figure 2 presents chemical formulae of the typical renewable polymers discussed in this assessment. The various chapters address the following topics: Biobased materials can contribute to materials substitution by offering low-cost options in polymer composites. Advantages of polymer composites include light weight with reasonable strength properties and cost; ease of manufacture in continuous processes that achieve parts consolidation and, therefore, lower capital cost than conventional multiple metal stamping operations: higher corrosion resistance compared to metals; increased durability; and sound deadening properties. The disadvantages of these materials are lower shatter resistance than steel for some applications; the difficulty of attaining a highquality surface finish for some types of composites: the higher temperature sensitivity of the composites: and the difficulty of attaching the composites to other materials, principally steel. Chapter 1 reviews composites in the industry, with emphasis on automative applications for conventional and emerging biobased materials. Recognizing the importance of the composites area, General Motors, Chrysler, and Ford formed the Automotive Composites Consortium to address synthetic plastics and plastics/metals composites , not biobased materials (Alper and Nelson 1989) and to conduct further research on how these materials can be incorporated into automotive design in the years ahead. Industrial efforts in the biobased materials area for automotive composites were sponsored by General Motors through Cadillac ASA; these efforts terminated soon after the formation of the consortium. Wood is the oldest composite material. Wood and other lignocellulosic materials consist of flexible cellulose fibers assembled in an amorphous matrix of lignin with the hemicellulosic polymer. These polymers make up the cell wall and are responsible for most of the physical and chemical properties of these materials. They have been used as engineering materials because they are low cost, renewable, and strong, and require low processing energy. However, they have undesirable properties such as dimensional instability caused by moisture sorption with varying moisture contents; biodegradability: flanunability; and degradability by ultraviolet light, acids, and bases. These feedstocks and their modifications that allow improvement of mechanical and chemical properties are discussed in Chapter 2 by Drs. R. Rowe11 (U.S. Forest Products Laboratory) and R. Young (University of Wisconsin). Inexpensive lignocellulosics such as wood flour and a number of lignocellulosic materials have been used as cheap fillers in many applications both in thermosets and thermoplastics. The properties of the renewable feedstock used are cost and availability. However, to use the fiber properties as reinforcements has not been successfully achieved, mainly for lack of compatibility between cellulosic fibers that are hydrophilic and the hydrophobic thermoplastic matrices (Zadorecki and Michell 1989). Increasing the compatibility between these types of polymers would greatly facilitate their incorporation

J

Marma Rn

Figure

1.

Simplified

reference

I

materials

system

6

Polymers from BiobasedMaterials

_o~07po$&03&-ok -n

Ho

\

\’

__ w

'0

CH,OH

b

/

Cellulose

I

~“z$=G&

mylopectin

HX-C-CH,

noCH,.C”

Figure 2.

two

Examples of chemical formulae of selected biobased materials

Executive Summary

7

into a number of applications. This type of R&D is conducted in industry worldwide to increase the compatibility of glass fibers with polymer matrices (Toensmeier 1987). Isolated components from wood and lignocellulosics in general, such as cellulose and derivatives, are discussed in Chapter 3 by Professor V. T. Stannett, Worth Carolina State University, who reviews past work and future directions in cellulose grafting. The bulk of the grafting R&D has been carried out based on free-radical approaches, but more controlled ionic polymerization methods are evolving that can yield grafts of better defined structures. These chemical derivations add cost to the starting inexpensive feedstocks and also increase substantially the required process energy. Thus approaches that could accomplish the desired chemical derivations at low cost and high energy efficiency would be highly desirable. In Chapter 4, Professor W. G. Glasser of Virginia Tech reviews the symposium "Lignin: Properties and Materials," which gathered the international community working in this area. Although these feedstocks are abundant, the key application today is combustion for process energy and chemicals recovery in conventional pulping processes. The main polymeric application is as an inexpensive surfactant; lignosulfonates are less expensive than petroleum sulfonates (Lin 1983, Chum et al. 1985). Other polymeric applications are evolving. Two consortia with industries are currently trying to introduce lignin-derived products into the plastics industry. One is mentioned above for the production of phenol replacements for phenol-formaldehyde thermosetting resins (Chum et al. 1989), and the other is emerging from the structure-property-performance data gathered by Glasser and coworkers at Virginia Tech on epoxylated and propoxylated lignins for use in polyurethanes. Professor D. Goring was invited to review biobasedmaterials opportunities, based on his extensive experience with the pulp and paper industry and his outstanding vision of the field. His comments are incorporated as Chapter 5. A key remark is the following: It should be noted that research in this area has been done mostly with pulps produced for papermaking, where much effort is put into making the fibers flexible with hydrophilic surfaces. In the case of mechanical pulps, a large expenditure of energy is required. It is possible to produce mechanically stiff fibers coated with lignin at much lower energy consumption than is currently used. Such pulps would be useless for papermaking but might prove to be the ideal fiber component for a composite. . .. Goring highlights a common problem of the area. The research and development carried out for the traditional applications of pulp and paper, as well as conventional construction materials, is not what is required if these materials are to fit other market areas such as the automotive industry with the development of high tensile properties fibers, of low density and low cost. The elastic modulus of bulk wood is 10 GPa. Cellulose fibers with moduli up to 40 GPa Such fibers may be can be separated from wood by chemical pulping processes. further separated by hydrolysis and comminution into microfibrils with modulus of 70-80 GPa. Theoretical calculations of the Young's modulus of elasticity for cellulose crystallites give a value of 250 GPa (Jeronimidis 1980), comparable to Kevlar and to some carbon fibers (see Chapter 1). Figure 3 illustrates the evolution of structure-process-modulus envisioned for cellulose materials compared to those of synthetic fibers. We do not have technologies at present that can achieve the theoretical values. Materials of this type could compete favorably with other reinforcing fibers of excellent properties, principally when

8

Polymers

from

Biobased

Materials

. - *. :. 9

Executive Summary

9

cost

and density are considered together. Actually, even now, some wood fibers (1.5 g/ml density and under $l/lb) compete quite favorably with E-glass, with its density of 2.5 g/ml and $1.5-$S/lb (Matsuda 1988).

Chitin (see Figure 2), poly(2-amino-2-deoxy-D-glucose), is one of the most ubiquitous natural polymers, isolated where crustacean shells are collected in large quantities. Crustacean shells are natural composites of chitin, polyChitin has peptides or proteins, and an inorganic filler, calcium carbonate. Chitin is present in been found in shells of hundreds of mollusk species. tendons and other stress-bearing fibrous portions of marine animals, where the Professor W. Daly chitin molecules adopt a highly oriented structure. (Louisiana State University) reviews in Chapter 6 the research activities, occurring primarily outside the United States, related to the many high value uses of these interesting materials. Starch is a polymer of anhydroglucose units linked by a-D-1,4-glycosidic bonds. Two distinct structural classes exist: linear and branched (see Figure 2). Amylose, the linear component, is the lower molecular weight polymer, having an Amylose makes up approxiaverage molecular weight of about one-half million. The preponderant mately one-fourth of the weight of starch for some species. polysaccharide is amylopectin, consisting, like amylose, of mostly 1,4-linked a-E-glucopyranosyl units, but with branched chains, with a molecular weight of The abundant hydroxyl groups on the starch molecules impart up to 10 million. The polymer attracts water and the characteristic hydrophilic properties. The self-attraction and crystallization tenitself through hydrogen bonding. dencies are most readily apparent for the amylose. The association between the polymer chains results in the formation of an intermolecular network that traps Precipitation is particularly evident for amylose. water and forms gels. Amylopectin association is interrupted because of amylopectin's highly branched However, at low temperatures, even amylopectin will associate, character. resulting in decreased water binding and gel formation. As would be expected from their differences in structure, amylose and amylopectin exhibit different properties. Amylose forms strong flexible films and has value as a coating agent. The branched component forma films with poor properties but finds wide usage as a thickening agent, especially in food and paper applications. Dr. R. Narayan (Michigan Biotechnology Institute) reviews in Chapter I work originated from the Northern Regional Research Center of the U.S. Department of Agriculture, the commercial technologies practiced through January 1989, and the technology he and coworkers developed while at Purdue University. Starch can introduce environmental degradability into plastics. The higher the proportion of the natural polymer present in the resulting plastic, the more true biodeHowever, starch and thermoplastic gradability is expected to be achievable. Thermoplastic amylose alone can form films for matrices are incompatible. packaging applications (Lacourse and Altieri 19891, which are currently being pursued by industry. In Chapter 8, Dr. C. Rivard and coworkers review the biodegradation of plastics. This is an area of intense research today since test methods are not yet standardized, while legislation is being created mandating biodegradation without clear definitions of parameters.

10

II.

Polymers from Biobased Materials

Bioproduction

of

Materials

This section addresses bioproduction of selected polymers such as cellulose, other plant cell wall polymers, and proteins, with emphasis on silk and wool. These materials can be produced with specific properties such as biodegradability (e.g., polyhydroxy-butyrate and valerate copolymers, polylactide polymers --see also Chapter 81, or specific mechanical properties. The following topics are addressed. Microbial cellulose production is reviewed in Chapter 9 by Professor M. Brown, Jr., of the University of Texas. It is intriguing that bacterial cellulose can have high modulus as produced or perhaps can be genetically manipulated to have very high modulus. Bacterial cellulose has several unique features not found in trees or cotton: (a) Acetobacter can synthesize pure cellulose, devoid of lignin and other polymers; (b) bacterial cellulose has a very marked hydrophilicity; (c) microbial cellulose is capable of being directly synthesized into articles of virtually any shape or size; (d) bacterial cellulose has outstanding shape retention and dimensional stability: (e) bacterial cellulose can be synthesized from a variety of inexpensive substrates: (f) the physical properties of microbial cellulose can be controlled during synthesis: and (g) expected high rates of pure cellulose synthesis could lead to efficient scale up. Understanding microbial cellulose synthesis and genetic engineering can also help the understanding of the more complex cellulose synthesis in higher plants. An authoritative review of the biogenesis and the biodegradation of plant cell wall polymers constitutes Chapter 10, written by Professor N. Lewis of Virginia Tech. This chapter is complemented by the ACS Symposium Series Volume 399, in which many outstanding worldwide contributions to these fields are made. Research and development in the United States is concentrating by far on biodegradation aspects, with major emphasis on lignin model compounds and cellulose biodegradation. Very little emphasis, by comparison, is being given to the biosynthetic work. Worldwide, more balanced research portfolios have been achieved. This trend parallels increased emphasis in other countries in emerging industries using biosynthesized polymers. Another set of interesting polymers are proteins. In fact, silk proteins have extremely high tensile properties. Drs. K. Grohmann and M. Himmel review in Chapter 11 the properties and syntheses of these materials. They also present approaches that could be undertaken to design protein fibers. The Appendix provides Examples of Research Activities in Japan through excerpts of the exposition guide distributed at the Cellucon '88 meeting in Japan. Current Japanese industry efforts are given for the various areas addressed by this assessment. CONCLUSIONS The use of the wood natural composite material is energy efficient. For instance, the production of most solid-wood products uses only 5-10 million Btu/ton (Bider et al. 1985, Gaines and Shen 1983, McRae et al. 1977). Wood, however, has limited thermoplasticity, though it can be bent under steam and chemical treatment. Ways of improving whole-wood thermoplasticity that lend themselves to heat molding, an important way of shaping materials for high-speed composite production, are key for cost-effective penetration of biobased materials into the composites markets. The low energy requirements for wood products and for the simple fractionation of the wood into its component polymers suggest that it would be possible to produce materials conserving energy from renewable resources. Fiber reinforcements for inexpensive composites for the automotive

Executive Summary

11

industry are an attractive area: one pound of a material introduced in an automobile represents a potential 10 million pounds market opportunity. Most plastics used today consume between 30-90 million Btu/ton (Bider et al. 1985, Gaines and Shen 1983, &Rae et al. 1977), but the plastics have very low density and thus a low-energy-per-unit product is achieved. The products formed are very reproducible. But they are derived from fossil resources that are finite and obtained partially from foreign sources, subject to political vulnerability in their exclusive use. Another important rationale for government programs in this area is the improved international competitiveness that could accrue to many segments of U.S. industries, primarily small businesses, in an area currently addressed by programs in other countries. In fact, the United States is currently importing biobased materials and technologies for their production from other countries (see Chapter 1). The use of starch is appealing. The feedstock is readily available; ii the 1986-1987 surplus of about 5 billion bushels of corn were used to produce starch, 195 billion pounds would be available as a feedstock (Rutenberg 1988), a number very close to the total top fifty organic compounds produced in 1986 in the United States (Anon. 1987). Cost-effective strategies that increase the compatibility between starch and thermoplastic materials could lead to the development of new materials with mechanical properties that rival those of the plastics and include environmental degradation or biodegradation. A large industry based on renewable sources of materials exists: small business industries dedicated to these technical areas are striving to survive. They can take new materials developed by government-sponsored programs into the marketplace. The R&D carried out by the large renewable resources industries is necessarily oriented toward high-value products and established product lines. There is a large gap between the current product-oriented industrial research and government programs, which consist of basic research (National Science Foundation, Biological DOE/Basic Energy Sciences) and applied end-use programs (Biofuels and Municipal Waste Technology Division, Office of Industrial Programs, and U.S. Department of Agriculture). There is also a large gap between government programs that is partially addressed by the ECUT program. There is a need to explore potential innovations that can emerge from the systematic exploration of the properties of renewable materials, which can play a major role in the future when our traditional feedstocks are depleted or when the relevant developed technologies become cost-competitive. Examples are already emerging of cost-effective biobased materials technologies. If these industries are to remain profitable and internationally competitive, there is a need for government involvement in planning and implementing such research programs, with input from industry. These government programs must be initiated and continued. The development of the necessary data base is a long-term The ability to bring together the relevant disciplines that will lead effort. to cost-effective and energy-efficient products from the most successful concepts in biobased materials requires a sustained effort. Developments are ongoing worldwide with major emphasis centered in Japan, Canada, and Sweden. Significant efforts also continue in other countries. Many strategies are identified in this report to expand biobased materials They are based on a better understanding of the beyond the current areas. In the composites area, techstarting materials and end-use applications. nologies developed for pulp and paper are not likely to be the best for the development of inexpensive fibers for reinforcement of composites: in fact, materials not suited for current conventional applications are likely to be best and will use less energy in their manufacture than kraft pulp and some high yield pulps (chemomechanical processes). Developing compatibility between hydrophilic renewable polymers and hydrophobic synthetic polymers is a theme

12

Polymers from BiobasedMaterials

throughout many chapters of this assessment. It is one of the high-priority areas of the ECUT Biobased Materials project. Designing compatible polymers and understanding the resulting properties can bring about the increased use of biobased materials into various markets--lightweight composites and packaging plastics, which will serve the transportation, buildings, and many industrial sectors. AcIcNowLEDGEMENTS

Discussions with many researchers from industry, universities, and research institutions are gratefully acknowledged. In particular, thanks to H. M. Chang, B. Gunnesin, M. Hearon, H. Hergert, J. Hyatt, E. Malcolm, A. Power, M. Rutenberg, K. Sarkanen, and S. Shoemaker for profitable discussions from the industrial point of view. Thanks are due to all contributors to the assessment: their enthusiasm for the area and encouragement are greatly appreciated. Finally, thanks are due to Drs. J. Eberhardt and Stanley Wolf of ECUT for their support and guidance. REFERENCES AND NOTES Alper J. and G. L. Nelson, PolymericMaterials, American Chemical Society: Washington DC, 1989. Anon., "Facts and Figures for the Chemical Industry," Chemical and Engineering News, 65(23), 31(1987). Bider, W. L., L. E. Seitter, and R. G. Hunt, Total Energy Impacts of the Use of Plastics Products in the United States, Franklin Associates, Ltd., Prairie Village, KS, 1985. Carpenter, J. A., Jr., "Introduction," in State-of-the-ArtReviews in Selected Areas of Materials

forEnergy Conservation, J. A. Carpenter, Jr. Ed., ORNL/ CF-83/291, Oak Ridge National Laboratories,

Oak Ridge, TN, 1984, pp. l-4.

Chum, H. L., S. K. Parker, D. A. Feinberg, J. D. Wright, P. A. Rice, S. A. Sinclair, and W. G. Glasser, 1985. The Economic Contribution of Lignins to Ethanol Production from Biomass, SERI/TR-231-2488, Solar Energy Research Institute, Golden, CO, pp. 90. Chum, H. L., J. Diebold, J. Scahill, D. K. Johnson, S. Black, H. A. Schroeder, and R. Kreibich, "Biomass Pyrolysis Feedstocks for Phenolic Adhesives," in Adhesivesfrom Renewable Resources, R. Hemingway and A. Conner, eds., ACS Symposium Series, 385, American Chemical Society, Washington, DC, pp. 135-151, 1989. The Pyrolysis Materials Research Consortium was formed on July 28, 1989, by MRIVentures, Inc., the for-profit subsidiary of Midwest Research Institute (MRI), the SERI parent company. On October 27, 1989, the consortium was registered with the Justice Department and the Federal Trade Conunission. MRI-Ventures, Inc., manages the consortium of (a) phenol producers, Allied-Signal Corp. and Aristech Chemical Corp.; (b) phenolic resin producers and/or users, GeorgiaPacific Resins, Inc., and Plastics Engineering Co.; and (c) Pyrotech Corp., a small business interested in the scale up of the technology. Fontana, J. D., J. C. Moreschi, B. J. Gallotte, A. M. Souza, G. P. Naiciso, and L. F. X. Farah, "Uses and Potential of a Native Cellulosic Biofilm from Acetobacter, ‘I Presented at the 11th Symposium on Biotechnology for the Production of Fuels and Chemicals, Colorado Springs, May 8-12, 1989, Paper Number 15. Gaines, L. L. and S. Y. Shen, Energy and Materials Flows in the Production of Olefins and Their Derivatives, ANL/CNSV-9, Argonne National Laboratory, Argonne, IL, 1983.

Executive Summary

13

Jeronimidis, G., "Wood, One of Nature's Challenging Composites," in The MechaniEds . J. F. Vincent and J. D. Currey, Cambridge University Press, Cambridge, 1980, p. 169. cal Properties of Biological Materials,

Kulkarni, S. V., "Composites," in State-of-the-ArtRev&u in Selected Areas of Materialsfor Energy Conservation, J. A. Carpenter, Jr., Ed., ORNL/CF-83/291, Oak Ridge National Laboratories, Oak Ridge, TN, 1984, pp. 185-219. Lacourse, N. L. and P. A. Altieri, "Biodegradable Packaging Material and the Method of Preparation Thereof," U.S. Patent, 4,864,655 (1989). Lin, S. Y., "Lignin Utilization: Potential and Chal.lenge,"in Progress in Biomass Conversion, Vol. 4, 1983, pp. 31-78.

McRae, A., J. Dudas, and C. Rowland, Eds., The Energy Source Book, Aspen Systems Corp., Germantown, MD, 1977, pp. 440-44s. Office of Technology Assessment, FacingAmerica’s Trash, OTA-0-424, Washington, DC, 1989. Rutenberg, M., "Corn as a Raw Material: A Retrospective and a Prospective View,‘8 Proc. of 1st Corn UtilizationConference, St. Louis, June 1987, National Corn Growers Association, St. Louis, MO and Funk Seeds International, Bloomington, IL, 1988, pp. 6-68. Society of the Plastics Industry, FactsandFiguresofthe DC, 1989.

U.S.PlasticsIndustry, Washington,

Toensmeier, P. A., Modern Plastics, May 1987, 55-56.

Zadorecki, P. and A. references therein.

J. Michell, Polym. Compos.,

10(2),

69-77 (19891, and

Part

I

Materials from Renewable Resources and Their Properties

15

1. Structural Materials for the Automobile of the Future: Composite Materials Helena L. Chum Chemical Conversion Research Branch Solar Energy Research Institute Golden, Colorado

INTRODUCTION A composite is broadly defined as a material consisting of a large number of fibers (fine filaments) embedded in a continuous phase or matrix, which gives it a definite shape and a durable surface (Phillips 1987). Matrices may consist of inorganic glasses or cements, metals, and other materials, but in this chapter they will be restricted to synthetic resins or polymers, which can be readily shaped or hardened by many different methods. Once the shaping/hardening process has taken place, the remaining function of the matrix is to distribute evenly between the fibers any structural loads imposed on the composite. The matrix can be a thermoset material such as polyester, vinylester, or epoxy, which cure (or chemically crosslink) by means of heat or catalytic hardening. Alternatively, the matrix can be of a thermoplastic material, in which case there is no cure (chemical crosslinking). Typical examples of thermoplastic are nylon, polycarbonate, polysulfone, polyethersulfone, and polyether ether ketone. (Phillips 1987). These composites can be heat reformed. The percentage of fiber (vol %) in the composite is a function of the preparation process. Many processes have been developed over the past 20 years. They range from fiber impregnation with the appropriatematrix (soaking, brushing, spraying, etc.), followed by proper fiber reinforcement orientation and lay-up against the surface of an accurate mold. Finally, heat treatment (or pressure, or the action of chemical hardeners) converts the matrix from liquid to solid, which is resistant to further softening. Such processes will yield composites with 25%-45% fiber volume. Autoclave or vacuum can increase the fiber volume substantially so that the excess resin and entrapped air are removed. More than 60% fiber volume can be achieved. In advanced composites (Fishman 19SS), resin-based composites with continuous or discontinuous fibrous reinforcements are oriented in an organized pattern; the reinforcing fibers constitute at least 60% by volume of the composition. Reinforcing fibers are high-modulus inorganic or organic materials such as carbon fibers, aramids, and glass fibers. Table 1 presents some examples of conventional fibers and their properties , along with a few properties for some biomassderived fibers, not necessarily optimized for composites. These materials penetrate three major markets--aerospace, automotive, and industrial/commercial, which cover respectively high, low, and intermediate raw materials and fabrication costs, as shown in Figure 1. A few customers in the aerospace industry buy high-performance materials, and therefore, high-value products, from many suppliers in a highly competitive business environment. The recreational/sports equipment manufacturer can easily afford the very costly advanced composites because of the performance needed. A few customers in the automotive industry (24 companies--155 car lines worldwide) would like to have high-performance materials, but usually have no or very little tolerance for cost premium in passenger cars or trucks. They need high-volume low-cost composites, in many areas of the vehicles, such as components, structures, and frames, where

16

TABLE 1 REINFORCING FIBER PROPERTIES

Density g/cm3

Material

Tensile strength GPa

Specific strength lo6 cm

Tensile modulus GPa

2.5

3.4-4.5 1.7

18-19

70-85 72

Polyacrylonitrile carbon fiber

1.7-1.9

2.3-7.1

12-39

230-490

Pitch carbon fiber

1.6-2.2

0.8-2.3

5-10

38-820

Rayon carbon fiber

1.4-1.5

0.7-1.2

7

2.4-2.8

17-19

60-200

Glass Fiber E-Type

‘34-55

Specific modulus 10' cm

2.8-3.4

13-26 2.3-38

Elongation %

4.8-5.4

Price S/lb

1.5

1.5-2.4

30-150

2.1-2.4

6-1200

2.3

30

Aramid fiber Poly(p-phenyleneterrephthalamide) (PPT) (Kevlar)

1.4

Super-drawn Polyethylene

1.0

3.0

32

175

1.8

Boron fiber

2.8

3.6

12

400

14

300

Si carbide fiber

2.6

2.8

10

190

7.3

600

fiber

Alumina fiber

2.7-3.9

Whisker

2.3-3.2

Wood fiber" Ramie, flaxb Matsuda,

:::

1.4-1.7 14-21 0 5-l 5 .' .67

1988; aWoodhams, et al., 1984;

3.6-6.3

120-380

43-91

380- 1000

10

20-80 22.5-27

4.2-14

3.8

30-60

3

4.4-9.7 12-43

90 <
1.3-6 1.5-3

bAmin et al., 1985 (See Chapter 11 for additional data.)

18

Polymers from Biobased Materials

I

b

m

Fabrkhd

Produclr

'

AEROSPACE MARKET

.

INDUSTRIAL MARKR

\/

-

AUTOhiOTlVE MARKET

106 PRODUCTION VOLUME Figure 1.

Major markets for 1988) (Fishman

structural

pound8 composites

1

Structural Materials for the Automobile of the Future-Composite

Materials

19

corrosion resistance, improved damage resistance, sound-deadening effects, and reduced weight are necessary. Military vehicles, on the other hand, can afford performance-driven increased costs (Loud 1988, Beardmore, 1988). The industrial/commercial market is highly fragmented and embryonic. It is characterized by a multitude of small-to-intermediate specific applications. The costs range from the high-value, low-volume aerospace industry to the low-value, highvolume automotive industry (Rasmussen 1988). Examples include equipment for process, agricultural and forestry, mills, mining, and medical industries (see Table 2). The world market size and projected growth of fabricated composites is shown in Table 3 (Fishman 1988). The curves that describe the volume of a product versus the time it takes for such products to become developed commodities are usually "S" shaped. The time necessary to achieve commodity status was 150 years for steel, 130 years for aluminum, and 15 years for plastics. Advanced composites have had approximately 25 years of development with roughly 64 million pounds production (see Table 3), quite far from the projected potential of these products as commodities (billion pound range). Because technological progress can occur faster now as we move into the' late 1980's, compared to early 1980's, Rasmussen suggests that 25 additional years will see advanced composites become commodity materials. This chapter addresses composites for the automobile industry in more detail. Industry trends and areas of R&D that the industry is pursuing will be identified. The role for federal government R&D, complementary to the industrial needs, will be discussed. Key references used to prepare this chapter are by Beardmore (1988); Matsuda (1988); Fatsch and Eckert (1988); and Wright, Hamblin, and Rader (1988). In addition, materials presented by W. Surber and S. H. W. Brooks of General Motors, Corp. and Cadillac/ASA, respectively, in October 1988 at the Forest Products Research Conference on Opportunities for Combining Wood with Nonwood Materials (Madison, Wisconsin), were employed. The American Chemical Society Division of Chemical Marketing and Economics held a Symposium on Marketing and Economic Aspects of Advanced Composites in Los Angeles (September 1988). Talks by Norman Fishman (SRI International), S. N. Loud, Jr. (Composite Market Reports, Inc.), and B. M. Rasmussen (BMR Associates) provided invaluable materials. General computer searches revealed hundreds of specific references for more detailed information. AUTOMOBILE

INDUSTRY

The U. S. automobile industry has begun to change its materials radically in response to energy crises, fuel economy legislation, and safety and emissions requirements since the 1970's. There were four key methods used to improve fuel economy: downsizing, weight reduction by materials substitution, improved aerodynamics, and improved power train efficiencies. In fact, the average weight of the American car decreased from about 3800 lb in 1976 to approximately 2800 lb in 1986 (Beardmore 1988). Automobile weight reduction alone can lead to an increase in fuel economy of 0.0068 km/L per kilogram saved (0.0073 mpg/lb--in a range of 0.0002-0.05 km/L/kg or 0.0021-0.053 mpg/lb). Considering that in 1986, 169 million automobiles, buses, and trucks consumed roughly 124 billion gallons of motor fuels (1986 U.S. statistics from the Federal Highway Administration: National Transportation and Safety Board), the impact of weight reduction on overall fuel consumption can be very high indeed. Between 1978 and 1984, approximately 16% of the total 36% increase in fleet fuel economy could be attributed to automobile weight reductions (Kulkarni 1984).

20

Polymers from Biobased Materials

TABLE 2 PARTIAL LIST OF INDUSTRIAL APPLICATIONS ADVANCED COMPOSITE MATERIALS

BASED ON

AoDlications

Cateqory Process Industry Equipment

Drive Shafts for Pumping Stations, Cooling Towers, 8 Chemical Mixers High Speed Print Rollers Grinding Wheels, Repler Sticks, Picki &ShuttleCocks for Weaving Equip. Shaft Couplings

Heavy Vehicle Rigging

Drive Shafts & Brake Linings Dump, & Transit Mixers Raiiroad Hopper Cars

Agricultural/Forestry

Equip.

Tractor ROP's, Light Weight Planters, 8 Harvesters Forest Flumes

for Garbage,

Parts

for

Sprayers,

Mill Equipment

Drive Shafts for Rubber, Mills

Medical/Scientific/Office

X-Ray Table Tops, Alignment Fixtures, Copy Machine Base, Ultracentrifuge Rotor Artificial Braces & Limbs, Implants

Electronic/Electrical

Lamp Poles, Ladders & Antennas Satellite Dish Antennas, Fiber Optic Cable Circuit Breaker Tubes, Circuit Boards Windmill Blades, Electromagnetic/RadioFrequency/Electrostatic Distortion Shielding

Construction

Bridges, Decks, Highways, Buildings, & Office Walls Cranes, Backhoes, & Forklifts

Mining/Oil

Well Logging Tubes, Mine Props, Off Shore Riser Pipe, Sucker Rods, Sucker Ribbons, Pump & Valve Packing, Pump Impellers, Undersea Exploration Capsules Drive Shafts for Logging & Drilling Equip.

Field

Steel, Textile,

Fire,

& Lumber

Material Handling

Robotic Arms for Point & Pick Operations

Musical

Drum Sticks, Speaker Boxes, Violin Frames, Drum Wall

Marine

Drive Shafts for Tug Boats & Barges Shipboard Handling Cranes

Other

Walking Canes, Wheel Chairs, Cryogenic Pressure Vessels, Ballistic Protection Garments, Flag Poles, Handles for Brooms and Window Cleaning Equipment

From B. Rasmussen, BMR Associates,

N.J., 1988

TABLE 3 WORLD MARKET SIZE AND ESTIMATED GROWTH FABRICATED COMPOSITES (in 1985 U.S. Dollars)

Consumption, Millions of Pounds

Dollar Value Millions of Dollars

Consumption. Milliob of' Pounds

1995 Dollar Value Millions of Dollars

5.4

1,620

12.3

3,075

2.2

440

7.2

1,225

1985 Composite Parts Based on:

Carbon fiber, advanced Aramids,

advanced

E-glass fiber, advanced

10

50

290

1,160

E-glass fiber, structural pultrusions

46

92

138

280

Total

63.6

2,200

5,740

447.5

Average Annual Growth Rate in S value, YY 1985-1995

6.67

7.6% 11% II--

!z 2 2 5 !?.

2 z. 2 v) 0" 1

10%

Assumotions: Reinforcing fibers in advanced composites constitute 65% of the composites. Average prices of fabricated composite parts are: Carbon Aramids,,advanced E-glass, fiber, advanced E-glass, fiber, structural pultrusions

$300/pound (1985) S200/pound (1985) $S/pound (1985) SZ/pound (1985)

$25O/pound (1995) $170/pound (1995) S4/pound (1995) S2/pound (1995)

Total dollar values include all other products, such as hybrids and high-strength glass fiber composites. from N. Fishman, SRI International,

1988

B 1. L In N

22

Polymers

from

Biobased

Materials

The demand for lighter vehicles is expected to continue (Beardmore 1988). Though decreases in vehicle weight will also result from the development of new engine materials, the discussion in this chapter will center primarily on body structure and components, more germane to biobaaed materials applications. The automobile body structure is composed of a body shell (Figure 2A) and the corresponding closure panels--hood, deck lid, doors, and front fenders (Figure 2B). The body shell sustains all the durability loads through the suspension and the energy absorption loads. The body shell also provides the overall vehicle atiffneaa and dynamics for'comfortable performance. The outer panels, on the other hand, provide dent resistance and should have a high surface quality so that attractive finishes can be accomplished. Reindl (1986) reviewed materials ana requirements for these structural parts extensively. As expected, steel and plastics currently compete for use in the outer skin panels. The steel-derived panels (mild steel or low-carbon) generally have a high-quality surface finish for their coat; weight and less damage resistance are the disadvantages of these metal parts. While the steel itself is relatively inexpensive on a weight basis (about SO.35/lb), the coat of the fabricated part usually involves so many operations that a true cost comparison must be done on the coat of a unit weight of the finished part (Surber 1988). Technical developments in steel manufacture are to produce higher yield strength steel (15,000 psi) such that thinner (and therefore lighter) parts can be made at the same performance. The competing materials for the outer akin panels are plastics of many different types. For instance, for the bumper systems and vertical panels, unreinforced injection-molded thermoplastics have been developed, which have comparable surface quality to steel. However, because these unreinforced materials have low stiffness and a high expansion coefficient, they are not suitable for the horizontal panel applications such as hoods, roofs, and deck lids. For these parts, the sheet-molding compounds (SMC) are preferred, though the surface quality is inferior to that of steel and the price needs to decrease for widespread use. However, the advantages are lower weight and improved damage resistance (Beardmore 1988). Thus, inexpensive materials and manufacturing technology may well be the key to success of large-scale implementation of composites in the automobile industry. Examples of process technologies employed for the fabrication of composites are: Compression moldinq is used for bodies and panels as illustrated in Figure 3 for sheet-molding compound (SMC). Fiber-reinforced plastics are fabricated in the form of sheets and then compression molded to the final shape. Injection moldinq is used for mass-produced parts; these parts are stronger and stiffer than unreinforced polymers at a reduced coefficient of shrinkage. Pultruaion produces continuous lengths of composite materials with uniform cross section; the fibers with the matrix are drawn into the die and the matrix cures. Filament windinq involves the winding of the tow and resin simultaneously onto a fonner-- shaped as a solid of revolution-- by means of a lathe-like machine. The fiber is led from a creel (adapted from the textile industry), through a resin bath via a comb fitted with a swiveling head to direct the former or mandrel. After the winding process, the resin is hot cured. It is possible to make simple shapes of great size with this technology (e.g., rocket bodies). Tape laying and braiding are also used. Reaction iniection moldina (RIM) involves polymerization of the monomers or prepolymers during the process of molding the finished parts. Reinforcement is obtained by adding suitable milled glass or other fibers (RRIM). These materials To obtain similar properties have lower strength and stiffness compared to SMC.

Structural

Materials

for the Automobile

of the Future-Composite

Materials

(sheet molding compound) Deck (sheet-molding compound)

Hood (sheet-molding compound)

Fenders (thermoplastic)

Figure 2.

(A) Body shell; (Beardmore 1988)

(B) Outer skin panel

23

24

to

Polymers

from

Biobased Materials

SMC, fibers are placed in the mold for reinforcement reaction of the matrix (structural RRIM), and

before injection

and

Hich speed processes are resin transfer molding (RTM) and high-speed resin transfer molding (HSRTM) (illustrated in Figure 4). It is estimated that with HSRTM large-scale structures could be fabricated in the form of complete front ends and complete body tubs, in which substantial parts consolidation can be achieved. In manufacturing technologies , teams of designers and manufacturers will use the best features of the composites to optimize the manufacture of parts having the appropriate strength and appearance properties. Automation and robotics can be used fully as well as computer-aided design, manufacturing, and engineering (CAD/CAM/CAE), after the scant data base that now exists is developed further. As with any new area, standards, test methods, and data bases will be necessary. Phillips (1987) points out that mechanical property tests are crucial, but not only this short-term testing (usually carried out by the companies) is important. Long-term testing that pays particular attention to fatigue (repeated *tresses), creep (continuous loading), thermal cycles, long-term weathering, water absorption, and chemical resistance is crucial to aerospace composites. The automotive industry needs some of the same testing and the corresponding data base but the teats should be performed on different composites. Phillips (1987) stresses the role of government agencies in ensuring that such a data base exists and is maintained. Because every pound of a new material introduced into an American vehicle can represent a lo-million-lb market opportunity, tailoring products to vehicle applications is a justifiable investment. But the raw material and fabrication costs have to come down for substantial penetration into the market (Fatsch and Excellent opportunities exist for new materials--carbon fibers Eckert 1988). of reasonable quality in the $5 - SE/lb range, with a minimum of 200 GPa Inexpensive fibers under $2/lb are highly desirable. In (30 M psi) modulus. summary, total system cost with acceptable performance is a key, as opposed to the performance-driven systems of the advanced aerospace, electronics, recreational, and selected industrial composites. The advantages of advanced composites include the relatively low capital investment necessary to implement many of the fabrication processes--this increases The industry would like to the manufacturer's flexibility of product design. produce complex-shaped parts for many reasons including aesthetics and aerodynamics. In addition, advanced composites offer increased flexibility in manufacturing -- large moldings can consolidate a number of parts and operations such as metal stampings into a few operations. For instance, two one-piece moldings made with a high-speed resin transfer process can make 90 steel stamping operations unnecessary and reduce weight by more than 33% in the front structure of the Ford Escort (Beardmore 1988). Ultimately, these advantage* translate into Increased durability is another char.acteri8ti.cof saving* in assembly costs. advanced composites. The corrosion-resistance of these parts relative to metals provides this key property. The main limitations of advanced composites are lower shatter resistance than steel for some applications; the difficulty of attaining high-quality surface finish for some types of composites; the higher temperature sensitivity of the composite*; and the difficulty of attaching the composites to other materials, Thus adhesives becomes a major area of activity, bonding principally steel. composites to steel and other materials, rather than welding or mechanical fastening.

Structural

Materials

Figure

for the Automobile

Schematic (Beardmore

3.

of the Future-Composite

of sheet 1988)

Materials

molding

Pwcut material

y

/

,Glass

preform Low-pressul n pm81

shaping die

Heatedateel/e!umlnum

Figure 4.

w-4

Ep0&

die

Schematic (Beardmore

of

high

1988)

speed

resin

transfer

molding

25

26

Polymers from BiobasedMaterials

Common types of reinforcements are glasses (E-, R-, S-, and T-), carbon fibers based on polyacrylonitrile and pitch, Aramid fibers, silicon carbide fibers, whiskers, particles (see Table l), and other organic fibers. To date for automobiles, the more inexpensive E-glass fibers appear to have the highest potential, whereas the higher cost carbon and aramid fibers can find only specialized applications. Note, however, that wood-fiber materials have a low density and can be made with reasonable strength properties. Mixed fiber reinforcements using properties and cost as parameters are practiced (Phillips 1987). The resin systems are dominated by low-cost polyesters and vinylesters to form the thennoset structural matrices (versus the epoxy matrices often employed the aerospace industry). In the thermoplastics area, stampable polypropylenes are very useful as well as thermoplastic elastomers (TPE). TPE can be blow molded faster than thermoset rubbers. TPE and thermoplastic olefins offer design flexibility in automotive applications (Wright, Hamblin, and Rader 1988). Other combinations such as metal matrix composites and ceramic matrix composites are being developed (see Milberg 1987, Ishikawa 1989). Again, the development of low-cost resin materials could provide the advanced composite suppliers with ways to reduce overall cost and penetrate additional automotive markets. The General Motors, Ford, and Chrysler Composites Consortium was announced on September 9, 1988. It is a 12-year agreement, with chair and secretary to rotate annually, starting with GM. It includes polymer-based and metal-plastics composites (not biobased materials) for structural uses. It will stimulate technological communication in the generic area of advanced composites to establish a network of information and protect the technological edge of U.S. companies (Loud 19RG). BIOBASED

MATERIALS IN THE

AUTOMOTIVE

INDUSTRY

Lightweight biobased composites are based on very inexpensive renewable materials such as wood (-$O.O4/lb) and wood fibers (-SO.l-0.2/lb depending on the process). Wood costs have been declining over the years (discounting the abnormal oil crisis period) and this trend is expected to continue (Comstock 1988). Wood flour has been and continues to be used as an inexpensive filler for automobiles and in thermoplastic conglomerates in general (Savonuzzi 1988). Trunk liners, mats and many other products have been made, tailored to the specific needs. Usually the thermoplastic is polypropylene because it shows good moldability, and retains its thermoplasticity, even at 33% wood incorporation. The additional advantage of the product is recyclability. Japan leads the research, development, and commercialization of such products (see Appendix on the Cellucon 88 meeting). For instance, Mitsubishi Corp. in Japan has introduced Papia", a polypropylene composite containing 50% of reclaimed newspaper fibers for injection molding and thermoforming of automotive components (Woodhams et al. 1984). These uses begin to take advantage of the fiber properties of cellulose, reinforced by the hemicellulose/lignin matrix or other biobased fibers. In Canada, Woodhams et al. (1984) have made extensive measurements of the reinforcing properties of various wood fibers in polyolefins. Woodhams et al. concluded that wood pulp fibers possessed strength and modulus properties which compared favorably with E fiber glass when the differences in fiber densities were considered. Dispersion of the fibers was accomplished with the aid of dispersing agents (carboxylic acids) leading to 50% wood fiber mixtures that could be injection molded. The best way to compatibilize wood fibers with the polyolefins has not been reached. Similar mechanical properties were obtained for kraft mechanical and chemo-mechanical fibers, as well as recycle newsprint. The wood fibers imparted equal or higher stiffness/weight compared to glass The strength properties were not as good because fibers, steel, or aluminum. of voids created in processing due to volatiles formation. The wood fibers were not abrasive such that machining was easier even at 50% loading compared to a

Structural

Materials

for the Automobile

lower level of glass fiber addition. in Figure 5.

of the Future-Composite

Materials

Examples of selected properties

27

are shown

There are many different materials to be developed for Specific automotive applications that require moderately high-temperature performance with low cost and with other specific properties such as low brittleness, high stiffness, high Ease of processing can be achieved strength, low weight, and easy processing. from simple moldings made by RIM, RTM (or HSRTM), or SRIM, or from textilederived methods such as web technologies , which lend themselves to easy manufacturability, automation and robotic control. Processing needs to lead to a surface that can be finished as metal pars can, which has been a difficult task for composites. For the past five years, GM, through the Cadillac/ASA Industries, has been involved in investigating such composites using a variety of biomass-derived fibers such as thermally processed wood from the batch steam explosion process (Figure 6) or one of its continuous versions, such as the Stake digester (Figure I), which maintains good dimensional stability (see Chornet and Overend 1986). Hammer-milled kenaf fibers, which have good sound-deadening properties have also been investigated. Using web technologies, wood-glass fiber composites have been made for the automobile panels withthermoset resins (phenolic novolaks and polyesters). Innovative approaches were used to spin the novolak fibers so that blends of the various components could be made into webs (inch thick mats). The resulting air-laid mats can be heat molded (Brooks 1988). These developments evolved form the self-supporting moldable fiber mats and processes patented by Brooks (1982) for use in automotive applications , such as dashboards andintericr door panels. An example of the flow sheet for this processing shown in Figure 8. Cadillac/ASA Industries have produced a number of car parts and have achieved some successes in parts consolidation. The major success of these experiment=: has been in meeting the strength properties required for the same surface area of material, such that lightweight biobased composites have been made that exhibit acceptable properties for several car applications. Complete crash testing has not been performed. Cost reductions are necessary in all areas, but especially in the phenolic resins. Performance improvements of the starting materials will open up new applications in this very interesting high-volume lowprice materials area. These materials can have a major impact on future petroleum savings both in transportation and in materials production. General Motors terminated the effort in 1989. Cadillac/ASA Industries have collaborated with several government institutions (USDA) Forest Products such as the United States Department of Agriculture Laboratory (FPL) (Dr. Roger Rowell), the University of Wisconsin (Professor Ray Young, Energy Conversion and Utilization Technologies [ECUTI subcontractor), and SERI. A donation of a 12-in. Rando Forming line to the FPL, to which ECUT subcontractors have access, has been instrumental in the development of new composites for testing. It is extremely important to develop these composites so that during the service life (about 10 years), mechanical properties are good, dimensional stability exists, and the composites resist biological, chemical, and photochemical degradation. However, after the useful life, easy reclaim of these parts, either through recycling or reuse of the parts, or degradation into safe degradable and biodegradable components is highly desirable. A joint venture between Magna International Inc. and the General Financing Society of Quebec (Quebec government, Canada) has been formed to produce wood fiber components for automotive application and other industries. The plant will use West German technology for mat production: mats will be shipped to the USA for use in the Nashville, IL plant to be molded into interior door, roof and instrument panels for cars and trucks (Globe & Mail, Toronto, March 9, 1989)!

9Kraft A * WNewsprint wOr AHardwoo l Talc 3 b U- OGlass S

.A .' 4l

i

n

0

’ IO

20

30

40

,I

, 50

,

,

,

,

,

OKraft ATMP nNewsprint AHardwood 0 Talc OGlass

Y Filler by Weigh:

a. Effect of Filler Level on Tenslle Strength of Polypropylene.

OKraft (MFl=4) n Kraft (~~i=i0) ATMP

0 =r

t:

G

150

I

t

Glass

0

10

1

20 X Filler

Effect of Filler Level on Flbxwal Modulus of Hlgh Oenslty Polye;hylene

Figure 5.

Effect of Filler Level on Flexural Modulus of Polypropylene

C.

b. Effect of Filler Level on Tenslle Strength of Hlgh Density Polyethylene

30

40

by Weiaht

e. Effect of Filler Level on Impact Strength of Polypropylene

0

20

UJ

%I Rdative

60

Do

loll

Weight

1. Cost versus Welght of Equlvalent-Stlffness Materials

Physical properties of polyolefins with wood fibers as reinforcing fillers and comparative costs and weights (Woodhams et al. 1984)

Structural

Figure

6.

Materials

for the Automobile

Schematic (Chornet

diagram of and Overend

of the Future-Composite

a steam 19@6)

explosinn

Materials

29

30

Polymers from Biobased Materials

Figure

I.

Configuration

of the STAKE system (Chornet and Overend 1986)

Structural

Figure

0.

Materials

for

the

Automobile

of the

Future-Composite

Materials

31

The moldable fiber mat is formed of cellulosic fibers, a small percentage of textile fibers, and a binder. Wood chips (0~ bark or refuse) are abraded and heated to about 260' to 370°C to melt the lignin in the material, depolymerize and redistribute the lignin through the fiber surfac*s. *he lignocellulosic material has 15%85% solids before the heating stage. Blending the lignocellulosic fibers with the textile ones with the binder is accomplished batchwiae

188).

the

mat can then be formed to rigid fiberboards.

mat

into

is

passed

a variety

through

a compactor

of products

frompaper

(1081.

The

products

32

Polymers

from

Biobased

Materials

To develop successfully these characteristics in materials, researchers need a data base of properties of the lightweight biobased composites that includes: modulus of elasticity; tensile, compression, and impact strength; brittleness; and processability. The data base must include data on chemical and biological degradation: dimensional stability as a function of moisture and heat; and thermal cycling. With this information, researchers from academia and industry can develop new materials that will reach the automotive industries with a host of special properties and have a major impact on vehicle weight reduction and thus fuel savings and coat. The federal government has a major role in this area. The conventional composites with all plastics components are being inveatigated by the U.S. industry; much leas effort is currently dedicated to the biobased materials role in composites. Thus, funding in this area allows a host of new materials that are inexpensive to produce to be made available for industry testing. One example of inexpensive materials aoon to be available for industrial testing stems from research at SERI in the area of waste wood and bark utilization through fast pyrolysis coupled to solvent extraction to isolate mixtures of phenolic compounds. These mixtures are likely to replace at least 50% of phenol in phenol-formaldehyde thermosetting resins in the near future. These mixtures are produced in a very simple process for which the pay back is expected to be one year (maintaining the current $0.20 difference between the highest production coat of the substitute ($0.27) and the current price of phenol (Chum et al., 1989). A consortium of industries has been formed and will help the U. S. Department of Energy through the Office of Industrial Programs to explore this 2.5-year-old process. Because the risk of these new processes and of new materials production is very high, companies will not undertake their development alone. The high pay off in terms of short pay back, independence from petroleum feedstocks, and suitable property development are not enough to allow moat of U.S. industry today to dedicate a sizable fraction of its resources to this area without continued government and SERI involvement. Government-sponsored programs can indeed lead to new technologies, economic development through the creation of new industries, and ultimately to energy conservation. Note that use of biobaaed materials provides one of the best solutions to the greenhouse effect and conservation of carbon dioxide in a material that can be used for a short or long period of time, depending on its function. Use of these materials is at least neutral (carbon dioxide fixed by plants will be eventually released in a controlled way) or very positive if strategies are made that will incorporate these products and recycle them in long-term uses. New enabling materials technologies will be generated, along with extensive data bases of properties of these new materials, so that industry can continue to develop these attractive options. Industry involvement is a key to the success of these new technologies through review boards, joint work, and true collaboration.

Very profitable discussions with H. Brooks and W. Surber are gratefully acknowledged. N. Fiahman, S. Loud, Jr., and B. Rasmussen are thanked for their willingnesa to share the materials presented at the American Chemical Society meeting.

REFERENCES Amin, M. B., Maadhah, A. G., and Usmani, A. M., "Natural Vegetable Fibers: A Status Report", in Renewable-Resource Materials - New Polvmer Sources, C. E. Carraher, Jr. and L. H. Sperling, Eda., Plenum Press: New York, (1986) pp. '29-40.

Structural

Materials

Beardmore, P., “hutomobile 599.

for the Automobile

Materials

of the Future-Composite

of the Future", Chemtech,

Brooks, S. H. W., "Self-supporting Moldable Mat," W082/DISOT, May 13, 1982 and references therein.

Materials

33

(October 1988)

PCT International

Patent

Brooks, S. H. W., "Web Products" in Forest Products Research Conference on Opportunities for Combinins Wood with Nonwood Materials (Madison, Wisconsin), October 4-6, 1988; personal discussions H. Chum with Dr. Brooks October I, 1988, Golden, Colorado. Troy, Michigan, and September 14, 1988, Chornet, E. and Overend,R. Fractionation of Lianocellulosics, Centre Quebecois de Va.lorisat.ionde la Biomasse, Sainte-Foy, Quebec, Canada, (1986) Chapter 3. Chum, H. L., and Kreibich, in Adhesives ACS Symposium

Diebold, J., Scahill, J., Johnson, D., Black, S., Schroeder, H., R. E., "Biomass Pyrolysis Oil Feedstocks for Phenolic Adhesives," from Renewable Resources, R. W. Hemingway and A. H. Conner Eds., Series No. 385, (1989) pp. 135-154.

Comstock, G., "Market Trends for Solid Wood Products," in Forest Products Research Conference on Opportunities for Combinins Wood with Nonwood Materials (Madison, Wisconsin), October 4-6, 1988. Fatsch, R. and Eckert, 1988) 408.

C. H.,

"Advanced Materials

Markets,"

Chemtech,

(July

Fishman, N. "Structural Composites in the Aerospace, Automotive, and Industrial Markets," presented at the 196th American Chemical Society Meeting, Los Angeles, September 25-30, 1988, Abstract CME Abstract 1; copies of visuals kindly provided by Dr. Fishman. Ishikawa, T. "Fiber-reinforced

Metals,”

Chemtech,

(January 1989) 38.

Kulkarni, S. V., "Composites," in State-of-the-Art Reviews in Selected Areas of Materials for Enerqv Conservation, J. A. Carpenter, Jr., Ed., ORNL/CF-83/291, Oak Ridge National Laboratories, Oak Ridge, Tennessee, (1984) pp. 185-219. Loud Jr., S. N. "Structural Composites for the Automotive Industry", presented at the 196th American Chemical Society Meeting, Los Angeles, September 25-30, 1988, Abstract CME Abstract 2; copies of visuals kindly provided by Dr. Loud. Matsuda, H. S., "Reinforcing 1988) 310.

Fibers

for Advanced

Milberg, M. E., "Ceramics for Cars," Chemtech,

Composites,"

Chemtech,

(May

(September 1987) 552.

Phillips, L. N. "Carbon Fibre Comes of Age," Endeavor, New Series, 11 (3), (1987) (1987) 127. Rasmussen, B., "Industrial Applications of Composite Materials," presented at the 196th American Chemical Society Meeting, Los Angeles, September 25-30, 1988, Abstract CME Abstract 3; copies of visuals kindly provided by Dr. Rasmussen. Reindl, J. C., "Commercial Experience with Composite Structures," from ASM International The Latest Developments Comoosites: November 18-20, 1986, Vol. 2, pp. 117-124.

in Advanced Conference,

34

Polymers

from

Biobased Materials

Savonuzzi, A., "Wood Fiber as a Filler for Thermoplastic Conglomerates" in Forest Products Research Conference on Ooportunities for Combinina Wood with Nonwood Materials (Madison, Wisconsin), October 4-6, 1988. Sperling, L. H. and C. E. Carraher, Jr., "Modern Polymers from Natural Products", in Renewable-Resource Materials - New Polvmer Sources, C. E. Carraher, Jr. and L. H. Sperling, Eds., Plenum Press: New York, (1986) pp. 3-28. Surber, W., "Automotive Composites in the Next Decade,@' in Forest Products Research Conference on Opportunities for Combinina Wood with Nonwood Materials (Madison, Wisconsin), October 4-6, 1988. Personal communication with H. Chum, October 7, 1988, Troy, Michigan. Woodhams, R. T., Thomas, G., and Rodgers, D. K., Pol. Ena. Sci., 24 (1984) 116671, and references therein. Wright, A. M., Hamblin, N. R., and Rader, C. P., Chemtech,

(June 1988) 354.

2. Recent Advances in Lignocellulosic-Derived

Composites

R. M. Rowe11 U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, and Forestry Department University of Wisconsin Madison, Wisconsin R. A. Young Forestry Department University of Wisconsin Madison, Wisconsin

Wood and other lignocellulosic materials are three-dimensional, polymeric composites made up primarily of cellulose, hemicelluloses, and lignin. These polymers make up the cell wall and are responsible for most of the physical and chemical properties of these materials. Wood and other lignocellulosic materials have been used as engineering materials because they are economical, low in processing energy, renewable, and strong. However, they have several undesirable properties such as dimensional instability caused by moisture sorption with varying moisture contents, biodegradability, flammability, and degradability by ultraviolet light, acids, and bases. Because of the undesirable properties and susceptibility to environmental degradation of lignocellulosic materials, most composites made from them have a limited service life. Most lignocellulosic composite markets are price driven; l.e., sales depend on the price of the composite. The markets for other composite materials such as metals, plastic, and glass are generally performance driven; i.e., sales depend on the way the material performs in service. Lignocellulosics are now part of multi-material composites. But in most cases, the lignocellulosics are there as filler to reduce the cost of the material, not to improve the properties of the composite. Lignocellulosic materials could be part of a performance driven composite if their undesirable properties could be improved. The undesirable properties of lignocellulosics all result fromchemical reactions involving degradative environmental agents (Figure 1). Because these types of degradation are chemical in nature, it is possible to eliminate them or decrease their rate by modifying the basic chemistry of the lignocellulosic cell wall polymers (Figure 2). The majority of research on chemical modification of lignocellulosic materials has been done on wood; this research has mainly dealt with improving either dimensional instability or biological resistance. This chapter will review the chemical modification of lignocellulosic materials, improvements in properties of lignocellulosic materials resulting from chemical modification, the combination of lignocellulosics with other materials, and opportunities for future composites using modified lignocellulosics in combination with other materials.

35

36

Polymers

from

Biobased Materials

Biological Degradation - Fungi, Bacteria, Insects, Termites Enzymatic Reactions - Oxidation, Hydrolysis, Reduction Chemical Reactions - Oxidation, Hydrolysis, Reduction Mechanical - Chewing Fire Degradation - Lightning, Sun., Man Pyrolysis Reactions - Dehydratron, Hydrolysis, Oxidation Water Degradation - Rain, Sea, Ice Wood-Water Interactions - Swelling, Shrinking, Freezing, Cracking Weathering Degradation - Sun, Water, Heat, Wind Chemical Reactions - Oxidation, Hydrolysis Mechanical - Erosion Chemical Degradation - Acids, Bases, Salts Chemical Reactions - Oxidation, Reduction, Dehydration, Hydrolysis, Acid Rain Mechanical Degradation - Storms (Wind, Rain, Hail, Snow), Loads Mechanical - Stress, Cracks, Fracture, Abrasion Figure 1.

Degradation reactions that occur when lignocellulosics are exposed to nature

Biological Degradation Hemicelluloses > > > Accessible Cellulose > Non Crystalline Cellulose > > > > Crystalline Cellulose > > > > > Lignin Moisture Sorption Hemicelluloses > > Accessible Cellulose > > > Non Crystalline Cellulose > Lignin > > > Crystalline Cellulose Ultraviolet Degradation Lignin > > > > > Hemicelluloses > Accessible Cellulose > Non Crystalline Cellulose > > > Crystalline Cellulose Thermal Degradation Hemicelluloses > Cellulose > > > > > Lignin Strength Crystalline Cellulose > > Non Crystalline Cellulose + Hemicelluloses + Lignin > Lignin Figure 2.

Lignocellulosiccell wall polymers responsible for properties

Recent Advances

in Lignocellulosic-Derived

Composites

37

CBEMICAL MGDIBICATICW OP LI~CCWIUlIQsIc WATBRIALS Reactive organic chemicals can be bonded onto hydroxyl groups on cellulose, hemicelluloses, and lignin in the lignocellulosic cell wall. Simple epoxies (Rowell, Tillman, and Liu 1966; Tillman tin press)) and water-soluble phenol formaldehyde resins (Brown, Kenaga, and Gooch 1966) have been reacted with wood flakes to improve dimensional stability in composites. By far the most research on the chemical modification of lignocellulosicmaterials, however, has been done using acetylation techniques. Acetylation reactions have been done on wood furnish to produce fiber boards (Bekere, Shvalbe, and Ozolinya 1978; Bristow and Black 1969), hardboards (Sudo 1979; Klinga and Tarkow 1966; Zhang et al. 1981; Osolinya et al. 1974; Shvalbe 1974), particle boards (Rowe11 1985; Tillman, Simonson, and Rowe11 1985; Nishimoto and Imamura 1985; Yoshida et al. 1986; Rowell, Simonson, and Tillman 1986a; Imamura et al. 1966; Rowe11 et al. 1989; Kiguchi and Suzuki 1985; Imamura and Nishimoto 19S7), and flake boards and Krzysik 1986; (Youngquist, Krzysik, and Rowe11 1986; Youngquist, Rowell, Rowe11 and Plackett [in press]), using vapor phase acetylation (Klinka and Tarkow 1966; Arora, Rajawat, and Gupta 1991; Rowell, Tillman, and Simonson 1986a,b), liquid phase acetylation (Rowell, Tillman, and Liu 1986; Rowell, Tillman,and Simonson 1986b), or reaction with ketene (ROwell, Wang, and Hyatt 1986). If the acetylation system does not include a strong catalyst or cosolvent, only the easily accessible hydroxyl groups will be acetylated. Some of us developed an acetylation system that uses no strong catalyst or cosolvent and probably acetylates only easily accessible hydroxyl groups (Rowell, Tillman, and Simonson 1986b).

Several lignocellulosic fibers were acetylated using this procedure using reaction times varying from 15 min to 4 h with southern pine, aspen, bamboo (Rowe11 and Norimoto 1987)), bagasse (Rowe11 and Keany [n press)), jute (Rowell, Simonson, and Tillman 1985), pennywort, and water hyacinth (Rowe11 and Rowe11 [in press]). All the lignocellulosic materials were easily acetylated. Plotting acetyl con-. tent resulting from the acetylation the above fibers as a function of time shows all data points fitting a common curve (Figure 3). A maximum weight percent gain (WPG) of about 18 was reached in a 2-h reaction time, and an additional 2 h increased the weight gain only by about 2% to 3%. Without a strong catalyst, acetylation using acetic anhydride alone levels off at approximately 20 WPG for the softwoods, hardwoods, grasses, and water plants. IwpmS

IN PROPERTIES 01p LI-LLULOSIC

NATERIALS

Moisture Sorntion Sorption of moisture is mainly due to hydrogen bonding of water molecules to the hydroxyl groups in the cell wall polymers. By replacing some of the hydroxyl groups on the cell wall polymers with acetyl groups, the hygroscopicity of the lignocellulosic material is reduced. Table 1 shows the equilibrium moisture content (BMC) of several lignocellulosio materials at 65% relative humidity (RR). A plot of the reductions in EWC at 65% RH of acetylated fiber referenced to unacetylated fiber as a function of the bonded acetyl content is a straight line plot (Figure 4). Even though the points shown in Figure 4 come from many different lignocellulosic materials, they all fit a common line. A maximum reduction in EWC is achieved at about 20% bonded acetyl. Extrapolation of the plot to 100% reduction in EMC would occur at about

38

Polymersfrom BiobasedMaterials

Reaction timefhrs) Figure 3.

Rate of acetylation of various lignocellulosic materials. southern pine; a, aspen; A, bamboo; ol bagasse; x, jute; +, pennywort: v , water hyacinth 100

0 .I

,/31% /I

90

/I /I

90 /

/

/I

Pwcont acetyl Figure 4.

Reduction in equilibrium moisture content (EMC) as a function of bonded acetyl content for various acetylated lignocellulosic materials. 0, southern pine: 0, aspen; A, bamboo; 0, baga==; X, jute: +, pennywort; v, water hyacinth

Recent Advances in Lignocellulosic-Derived

Composites

39

30% bonded acetyl. Because the acetate group is larger than the water molecule, not all hygroscopic hydrogen-bonding sites are covered. The fact that EMC reduction as a function of acetyl content is the same for many different lignocellulosic materials indicates that reducing moisture sorption and, therefore, achieving cell wall stability are controlled by a common factor. The lignin, hemicelluloses, and cellulose contents of all the materials plotted in Figure 4 are different (Table 2). Earlier results showed that the bonded acetate was mainly in the lignin and hexnicelluloses (Rowe11 1982) and that isolated wood cellulose does not react with uncatalyzed acetic anhydride (Rowell, n.d.). Because these materials vary widely in their lignin, hemicelluloses, and cellulose content, because acetate is found mainly in the lignin and hemicelluloses polymer, and because isolated cellulose does not acetylate by the,procedure used, acetylation may be controlling the moisture sensitivity caused by the lignin and hemicellulosic polymers in the cell wall but not reducing the sorption of moisture in the cellulose polymer. Dimensional

Stability

Dimensional instability, especially in the thickness direction, is a great problem in lignocellulosic composites because they exhibit not only reversible swelling, but also swelling caused by the release of residual compressive stresses imparted to the board during the composite pressing process (irreversible swelling). Water sorption causes both reversible and irreversible swelling with some of the reversible shrinkage occurring when the board dries. Dimensional instability of lignocellulosic composites has been the major reason for their restricted use. The rate of swelling in liquid water of an aspen flake board made from acetylated flakes and phenolic resin (Rowell, Tillman, and Simonson 1986b) is shown in Figure 5. During the first 60 min, control boards swelled 55% in thickness; the board made from flakes acetylated to 17.9 WPG swelled less than 2%. During 5 days of water soaking, the control boards swelled over 66%; the 17.9 WPG board swelled about 6%. Control boards made from bamboo particles using a phenolic adhesive swelled about 10% after 1 h, 15% after 6 h, and 20% after 5 days. Particle boards made from acetylated bamboo particles swelled about 2% after 1 h and only 3% after 5 days (Rowe11 and Norimoto 1968). Thickness changes in a six-cycle water-soaking/ ovendrying test for an acetylated aspen -flake board are shown in Figure 6 (Rowell, Tillman, and Simonson 198613). Control boards swelled over 70% in thickness during the 6 cycles as compared to less than 15% for a board made from acetylated flakes. Acetylation greatly reduced both irreversible and reversible In a similar five-cycle water-soaking/oven-drying test on bamboo swelling. particle boards, control boards swelled over 30%; boards made from acetylated particles swelled about 10%. Biolooical Resistance Chemical modification of wood composite furnish for biological resistance is based on the theory that the potentially degrading enzymes must directly contact the substrate, and the substrate must have a specific chemical configuration and molecular conformation. Reacting chemicals with the hydroxyl groups on cell wall polymers chemically changes the substrate so that the highly selective enzymatic Chemical modification also reduces the moisture reactions cannot take place.

40

Polymers

TABLE

from Biobased

Materials

Various

(FIMC) of Equilibrium Moisture Content Lignocellulosic Materials (65% FM, 27’C)

1.

Material

Reaction weight gain (74

SouthernPine

Acetyl content (XI

EMC (%I

1.4 7.0

12.0

0 6.0 14.8 21.1

Aspen

0

3.9

11.1 7.8

14.2 17.9

16.9 19.1

2::

0

3.2

8.9

10.8 14.1 17.0

13.1 16.6 20.2 3.4 14.4 15.3 19.0 3.0 16.5 1.3 14.0 1.2 10.8 17.8

2::

;.4

12.2 17.6 1i.6

Pennywort

0

10.1

TABLE 2.

2::

10.1

Bogasse

Water hyacinth

4.3

7.3

Bamboo

Jute

15.1 20.1

0 8.3 18.6

Acetylated

::;I 2:; 3.4 9.9 4.8 18.3 8.6 1.7 1.2 0.7

Chemical Composition of Some Lignocellulosic Materials Sugars

Material

Lig- Cellu- Clu- Xylose Calac- Arabi- MannoseUranic Ektr%- Ash tose

case

Southern Pine

26.6

45

49.0

5.4

2.4

--

lg.2

1.6

6.9

0.3

1.4

Aspen

18.5

49

53.3

18.5

1.0

--

1.4

2.5

4.3

0.4

4.1

Bamboo

24.2

42

52.0

21.7

--

0.8

--

0.8

11.0

0.4

3.2

Bagasse

21.1

45

47.4

27.6

--

1.7

--

1.0

8.4

1.4

3.4

Jute

13.7

58

63.8

13.1

1.2

--

0.6

3.2

3.7

1.0

3.0

Pennywort

10.3

49

39.0

3.5

2.8

0.8

2.9

9.8

38.3

11.2

1.3

Water hyacinth

8.5

58

37.2

8.7

5.0

11.4

1.4

7.1

20.5

7.9

1.2

b6 h of reflux. benzene ethanol.

acids

Acetyl

lose

4tlason.

nose

tives

*ina

Recent Advances in Lignocellulosic-Derived Composites

Figure

5.

Rate of swelling in liquid water of aspen flakeboard -de acetylated flakes. 0, control; +, 7.3 “PO; x , 11.5 WPG; A, 14.2 “Xi 0, 17.9 WFG

I Figure

6.

2

3

L

5

41

ftOm

6

Changes in ovendry (0.D.) thickness in repeated water soaking test of aspen flakeboard mdde from acatylated flakes. 0, control; c, 7.3 WPG; x, 11.5 WFGi A, 14.2 WPGi 0, 17.9 WPG

42

Polymers

from

Biobased

Materials

content of the cell wall polymers to a point where biological degradation cannot take place. Particle boards and flake boards made from acetylated flakes have been tested for resistance to several different types of organisms. In a 4-week termite test using Reticulitermes flavines (subterranean termites), boards acetylated to 1617 WPG were very resistant to attack, but not completely so (Imamura et al. This may be attributed to the 1986; Rowe11 et al. 1987; Rowe11 et al. 1988). However, because termites can live on acetic acid and severity of the test. decompose cellulose to mainly acetic acid, perhaps it is not surprising that acetylated wood is not completely resistant to termite attack. Chemically modified wood composites have been tested to decay fungi in several Untreated aspen and pine particle boards and flake boards exposed to ways. white-, soft-, and brown-rot fungi and tunneling bacteria in a fungal cellar were destroyed in leas than 6 months; particle boards and flake boards made from acetylated furnish above 16% acetyl weight gain showed no attack after 1 yr (Table 3) (Rowe11 et al. 1987; Rowe11 et al. 1988; Nilsaon et al. 1988). In a standard 12-week ainale-culture soil-block test, control aspen flake boards exposed to the white-;ot fungus Trametes versicolbr lost 34% weight; acetylated flake boards (17% acetyl weight gain) lost no weight (Rowe11 et al. 1987; Rowe11 Using the brown-rot Tvromvces oaluatris, et al. 1988; Nilsson et al.- 1988). control aspen flake boards lost only 2% weight when a phenol-formaldehyde adhesive was used but lost 30% weight when an isocyanate adhesive was used. If the flake boards are water leached before the soil-block test is run, control boards made with ohenol-fonnaldehvde adhesive lose 44% weight with the brown rot fungus Gloeoohvlium trabeum (Rowe11 n-d.: Rowe11 et al.-1987; Rowe11 et al. 1988). This shows that the adhesive can influence results of fungal toxicity, especially in a small, closed teat container. W-_Lght loss resulting from fungal attack is the method most used to determine the effectiveness of a preservative treatment to protect wood composites from decaLring. In some cases, especially for brown-rot fungal attack, strength loss may be a more important measure of attack because large strength losses are known to occur in solid wood at very low wood weight loss (Cowling 1961). A dynamic bending-creep test has been developed to determine strength losses when wood or white-rot (Imamura and fungus composites are exposed to a brownNishimoto 1985). Using this bending-creep test on aspen flake boards, control boards made with phenol-formaldehyde adhesive failed in an average of 71 days with 2. palustria and 212 days with 2. versicolor (Rowell, Youngquist, and Imamura 1988). At failure, weight losses averaged 8% for 2. palustris and 32% for x. versicolor. Zsocyanate-bonded control flake boards failed in an average of 20 days with 2. Elustris and 118 days with 2. versicolor, with an average weight loss at failure of 6% and 34%, respectively (Rowell, Youngquist, and Imamura 1988). Very little or no weight loss occurred with both fungi in flake boards made using either phenol-formaldehyde or isocyanate adhesive with acetylated flakes. None of these specimens failed during the test period. Mycelium fully covered the surfaces of iaocyanate-bonded control flake boards within 1 week, but mycelial development was significantly slower in phenolBoth isocyanateand phenolformaldehyde-bonded control flake boards. formaldehyde-bonded acetylated flake boards showed surface mycelium colonization during the test time, but the fungus did not attack the acetylated flakes, ao little strength was lost.

RecentAdvancesin Lignocellulosic-Derived Composites

TABLE 3.

Acetyl WPGC

Y.3 11.5 13.6 16.3 17.9

43

Fungal Cellar Tests on Aspen Flakeboards Made from Control and Acetylated Flakes"b > Rating at intervals" 2 mo

3 mo

4 mo

5 mo

6 mo

s/2

s/3 s/1 0 0 0 0

s/3 S/l S/O 0 0 0

s/3 s/2 s/1 0 0 0

s/4 s/3 s/2 S/O 0 0

S/O 0 0 0 0

12 mo

__ s/4 s/3 s/1 0 0

% onsterile soil containing brown-, white-, and soft-rot fungi and tunneling bacteria. b Flakeboards bonded with 5% phenol-formaldehyde adhesive. 'Weight percent gain. d Rating system: 0 = no attack: 1 = slight attack: 2 = moderate attack: 3 = heavy attack: 4 = destroyed: S = swollen.

44

Polymersfrom BiobasedMaterials

In similar bending-creep teats, both control and acetylated pine particle boards made using melamine-urea-formaldehyde adhesive failed because 2. palustris attacked the adhesive in the glueline (Imamura et al. [in press]). Mycelium invaded the inner part of all boards, colonizing in both wood and glueline in control boards but only in the glueline in acetylated boards. After a 16-week exposure to g. paluatris, the internal bond strength of control aspen flake boards made with phenol-formaldehyde adhesive was reduced more than 90% and that of flake boards made with iaocyanate adhesive was reduced 85% (Imamura, Niahimoto, and Rowe11 1987). After 6 months of exposure in moist unsterile soil, the same control flake boards made with phenol-formaldehyde adhesive lost 65% of their internal bond strength and those made with iaocyanate adhesive lost 64% internal bond strength. Failure was due mainly to great strength reductions in the wood caused by fungal attack. Acetylated aspen flake boards lost much leas internal bond strength during the 16-week exposure to x. palustria or C-month soil burial. The isocyanate adhesive was somewhat more resistant to funaal attack than the phenol-formaldehyde adhesive. In the case of acetylated composites, loss in internal bond strength was mainly due to fungal attack in the adhesive and moisture, which caused a small amount of swelling in the boards. Acetylated pine flake boards have also been shown to be resistant to attack in a marine environment (Johnson and Rowe11 1988). Control flake boards were destroyed in 6 months to 1 year, mainly because of attack by Limnoria tri_ punctata, while acetylated boards showed no attack after 2 years. All laboratory teats for biological resistance conducted to this point show that acetylation is an effective means of reducing or eliminating attack by soft-, white-, andbrown-rot fungi, tunneling bacteria and subterranean termites. Tests are presently under way on several lignocellulosic composite3 in outdoor environments. Ultraviolet

Resistance

There are other properties of lignocelluloaic composites that can be improved by changing the basic chemistry of the furnish (Rowe11 1984). .Acetylation also improves the ultraviolet (W) resistance of flake boards (Feiat, Rowell, and Ellis [in press]). Table 4 shows the weight loss, erosion rate, and depth of penetration resulting from 800 h of accelerated weathering. Control specimens erode at about 0.12 E/h or about 0.02 %/h. The depth of the effects of weathering is about 200 &! into the wood surface. Acetylation reduces erosion by 50%. Table 5 shows the acetyl content of the outer 0.5 mm surface before and after accelerated weathering and of the remaining specimen after the surface had been removed. In all specimens, the acetyl content was reduced about 50%. W

radiation does not remove all of the blocking acetyl group, so some stabilizing effect to photochemical degradation is still in effect. The loss of acetate is confined to the outer 0.5 mm because the remaining wood has the same acetyl content before and after accelerated weathering.

Table 6 shows that the surface layer is richer in glucose, xyloae, and mannose and lower in lignin content after photochemicaldegradation resulting from accelerated weathering. This shows that both the cellulose and hemicelluloaes are much more stable to photochemical degradation. In outdoor tests, flake boards made from acetylated pine flakes are still light yellow in color while control boards have turned dark orange to light gray during this.time.

Recent Advances

in Lignocellulosic-Derived

Composites

45

Weight Loss and Erosion of Modified Aspen After 800 Hours of Accelerated Weathering

TABLE 4.

Before weathering

Specimen

Surface

Remainder

After weathering Surface

Remainder

_____--_-----_x_________----

Control Acetylated

4.5

4.5

1.9

3.9

17.5

18.5

12.8

18.3

Acetyl Analysis Before and After 800 Hours of Accelerated Weathering

TABLE 5.

of

Modified Aspen

Specimen

Weight loss

illhr Control Acetylated

Erosion

~/hr

0.0194

0.121

.0095

.059

iCompared to control Measured in cross section

Reductiona in erosion %

Depth of penetrationbof weathering iim l&j-2i0

51

84-105

TABLE

6.

Specimen

Chemical Analysis of Modified Aspen After 800 Hours of Accelerated Weathering

Klason lignin

Soluble lignin

Glucose

Xylose

Sugars Arabinose Galactose

Mannose

----------___---____~~~~~~-~~~~~~~~~g ____________________~~~~~~~~~~~~~~~~~~~ Control (before weathering) Surface Remainder (after weathering) Surface Remainder Acetylated Surface Remainder

lg.8 20.5

2.9 2.7

50.9 49.8

24.5 23.3

0.1

1.9 17.9

1.6 1.6

82.2 52.8

10.1 22.9

0.5

4.7 15.3

;::

56.4 41.8

17.1 17.9

2:;

f

:E

1.6 2.3

Recent Advances

in Lignocellulosic-Derived Composites

47

Pvrolvsis Properties Acetylation does not change the fire properties of lignocellulosic materials. In thermogravimetric analysis, acetylated and control pine sawdust pyrolyze at the same temperature and rate (Rowe11 et al. 1984). The heat of combustion and rate of oxygen consumption are also the same for control and acetylated specimens, showing that the acetyl group added to the cell wall has approximately the same carbon, hydrogen, and oxygen content as the cell wall polymers. Reactive fire retardants can be bonded to the cell wall hydroxyl groups. The effect would be an improvement in dimensional stability, and biological resistance as well as fire retardancy.

Prooertv Enhanced Liunocellulosics In recent advancements, technology has been developed to form acetylated high yield whole lignocellulosic fiber into flexible mats using either a non-woven needling technique or a thermoplastic fiber welding technique. These fiber mats can be impregnated with an adhesive (such as a phenolic resin) at the time the mat is formed and pressed into many different shapes. This fiber mat technology allows the formation of a final product all of uniform density directly from the wood fiber. Products made thus far from this acetylation fiber technology show (1) high dimensional stability both in the thickness and lineal directions; (2) a high level of rot resistance; (3) a low d egree of thermal expansion; (4) smooth surfaces that do not require further sanding; (5) a uniform density throughout the product wall: (6) no increase in toxicity of the wood; (7) high strength--both wet and radiation stability: and, (9) no change in dry; (8) a high degree of W flammability. Acetylated veneers can be pressed along with the acetylated fiber mat to yield veneer-faced fiber-backed products (Rowe11 et al. 1989). Other face materials can also be used, such as metals, plastics, glass, or synthetic fibers. Preliminary economic analysis of producing acetylated fiber shows a cost of about $0.15 to $O.l8/lb (which includes low raw fiber cost) versus $0.05 to $O.O7/lb for the fiber. The cost of the acetylated fiber mat adds about $O.O5/lb; The cost of the acetylated fiber at roughly triple the price of unacetylated fiber directs this technology into value-added products where markets are driven by improved performance rather than cost alone. In considering cost, it must be remembered that it is possible to produce the final product from the fiber mat technology, so the price already includes part of the secondary manufacturing cost. COMBINATION OF LIGNCCELIJJLOSICS WITH OTHER MATERIALS Early work on wood fiber-- synthetic fiber composites concentrated on laminate structures. For example, Michell, Vaughan, and Willis (1976) prepared laminates containing 67% by weight of cellulose fibers by hot-pressing paper sheets coated The flexural properties of the laminates at low with low-density polyethylene. relative humidities compared favorably with those of glass filled high-density polyethylene and of paper-phenolic resin laminates; however, at higher humidities the flexural properties for the cellulose fiber laminates were diminished. Prud'homme (1977) also prepared polymer-paper laminates by hot-pressing a sandThe polymer matrices were polymethwich of paper between polymeric films. acrylate and polyethylene. The mechanical properties of Whatman paper laminates were, significantly higher that those predicted from the laws of mixtures. This

48

Polymersfrom BiobasedMaterials

indicates that the polymer increases the strength of the fiber-to-fiber bonds. Prud'homme noticed, like Michell, Vaughan, and Willis (19771, that there was a considerable decline in properties of the laminates at high moisture levels. Grafting of vinyl monomers to wood pulp has been used to create new composite materials with lignocellulosic fibers. A summary of the properties of grafted pulp and papers has been made by Phillips et al. (1972). The effect of the grafted polymer on the sheet properties is specific to each vinyl polymer-fiber substrate system. In many cases, simple admixing of the synthetic polymer with the wood pulp gave aimilar properties to the grafted product. However, both Young and Nguyen (1979) and Kokta, Daneault, and Sean (1986) found that grafting of pulps with polyacrylamide gave improved dry and wet strength values, probably because of the ability of polyacrylamide to form hydrogen bonds with cellulose. Young and Nguyen (1979) found that post-treated, hot-pressed grafted mechanical pulps, heated above the glass transition temperature of the grafted polymer, resulted in considerable increases in the dry and wet strength of the composite. Thus, to take advantage of the unique physical properties of graft copolymerized pulps, a high temperature treatment is probably necessary. Similar conclusions were reached by Kokta, Daneault, and Sean (1986) in a later study of grafted hardwood pulps in thermoplastic composites. A wide variety of other natural fibers have been incorporated into polymer composites. Paramaaivan and Kalam (1974) incorporated sisal fibers in an epoxy matrix and found that the tensile strength of the composites were 250-300 MN/m', which is about one-half that of a fiberglass-epoxy composite, but the specific strengths were roughly equivalent. Jute fiber has been extensively evaluated in composites because of the higher strength of this fiber. Jute has been incorporated into epoxy, polyester, epoxy/polyester, and phenol-formaldehyde resins. Up to 40% by weight of the jute has been incorporated into epoxy or polyester resins. Generally, strength improvement is realized with about a 25% by weight addition of the fiber. Exposure to moisture and temperature results in decreases in tensile strength of the composites. Sridhar et al. (1982) found that the moisture absorption of the composites can be reduced by coating the jute fibers with lignin and ethylene-diamine solutions. Satyanarayana and coworkers in India (1981) evaluated the properties of compoaitea of coir fibers (coconut husks) with polyester resins. Several types of molded articles were produced fromthe composites, such as helmets and mailboxes. The products held up well to weathering. However, it was noted that the incorporation of the coir fiber into the polyester resin adversely affected the mechanical properties of the polyester, roughly proportional to the amount of fiber in the matrix. It was suggested that this was due to poor compatibility and therefore limited bonding between the fiber and the resin. To improve compatibility, several different treatments were applied to the fibers. Copper coating of the fibers was found to considerably increase the tensile and flexural strength of the composites, while simple alkali treatment of the fibers resulted in a 40% increase in the mechanical properties of the polyester-fiber composite (Praaad, Pavithran, and Rohatgi 1983). Wheat straw has also been tested as the fiber component in polyester resin composites. White and Anaell (1983) incorporated up to 50% straw fiber into polyester resins and prepared molded products. Small percentages of fiber improved the properties of the resin and mechanical pretreatment of the fiber gave better performance for the composite. The stiffness of the product was 2.5 times greater than that of pure polyester but one-half a softwood fiber or glass fiber reinforced plastic material. These investigators also recognized the compatibility problems associated with composite structures.

Recent

Advances

in Lignocellulosic-Derived

Composites

49

is active on compounding of wood fibers with polyethylene Currently, research to produce a composite for molding and extrusion. Selke, Yam, and Lai (1988) incorporated aspen fibers with recycled high density polyethylene (HDPE) using a co-rotating intermeshing twin-screw extruder. Mechanical properties and dimensional stability were studied as a function of fiber properties and process variables. Inadequate compounding was found to produce poor dispersion and poor wetting of the fibers, while excessive compounding caused severe fiber damage, both of which lead to reduced mechanical properties. Kokta and coworkers in Canada (Kokta, Daneault, and Beshay 1986; Beshay, Kokta, and Daneault 1985; Raj et al. 1987) have also carried out extensive studies on incorporation of wood fibers into polyethylene composites. These investigators evaluated the use of chemithermomechanical pulp (CTMP) and modified CTMP mixed with polyethylene at 160°C and molded into shoulder type test specimens. It was found that the wood-filled composites gave decreased mechanical properties compared to unfilled polyethylene. To improve the poor interface between the wood fibers and polyethylene, several different chemical treatments of the wood fibers were explored. Surprisingly, a silane treated wood pulp did not give significant improvement of the mechanical properties of the composite. Incorporation of isocyanates was found to significantly enhance the adhesion at the fiber-matrix interface as demonstrated by the improvement in the mechanical properties (Raj et al. 1987). The stress and modulus increased 60% and 90%, respectively, in HDPE and LDPE composites depending on the type of isocyanate treatment. Raj and Kokta (1988) also studied the mechanical properties of polyvinylchloridewood fiber composites. In this work, polyvinylchloride (PVC) was reinforced/ The variables were filled with CTMP, wood flour, and steam explosion pulp. evaluated as to the effect on the mechanical properties of the composites and included the weight fraction of filler, the addition of coupling agents, and the effect of fiber length. Composites from PVC filled with isocyanate-treated steam explosion pulp (30%) exhibited a 45% increase in tensile strength and an 11% increase in modulus compared with composites prepared with unmodified pulp fiber. A higher fiber aspect ratio resulted in an increase in tensile modulus. Impact strength generally decreased as the concentration of the fiber increased in the samples. Comparison of tensile properties of PVC-wood fiber, glass fiber, and mica composites demonstrated the advantage of wood fiber as a filler in terms of reiative cost and performance. Another fiber treatment evaluated by Kokta, Daneault, and Beshay (1986) was modification of the CTMP fibers through grafting with polyethylene by the xanthate method. This resulted in considerable improvement in the compatibility with unmodified polyethylene in the composite. The energy to break was improved by lOO%, the modulus by 160%, and the stress by 133%, compared with a composite The grafted CTMP-polyethylene composites of unmodified CTMP and polyethylene. were superior to both mica and glass filled polyethylene in stress (Figure 7) and better than glass in modulus (Figure 8). Grafted CTMP The cost comparisons performed in 1986 are also worth noting. fibers were estimated to cost $250-$300/tori;;the price of mica was $700/tori and The overall mechanical properties as well as the favorable glass $2900/tan. price comparisons show good promise for use of grafted wood fibers as reinforcers in polyethylene composites. Kokta et al. are currently evaluating the use of modified sawdust as a filler (Kokta, Daneault, and Beshay 1986) which would drop the price to about $lOO/ton. In recent work in Japan, composites of polypropylene with refiner mechanical pulp (Pinus radiata) were prepared by Takase, Shiraishi, and Takahama (1988). The mixture was kneaded at 180°C at 50 rpm for 10 min. The kneaded samples were then

50

Polymers

from

Biobased Materials

Recent Advances in Lignocellulosic-Derived

Composites

51

molded into films by hot-pressing. Strips taken from the samples were tested for tensile strength. To achieve good strength, it Was necessary to modify the polypropylene to get good compatibility with wood pulp fiber. Therefore, composites of three kinds of chemically modified polypropylene were prepared by reaotion with maleic anhydride (MAW, glycidylmethacrylate (GMA), and hydroxyethylmethacrylate (HKMA). The tensile strength of the composites was found to increase in order as follows: unmodified PP < HKMA-PP < GMA-PP < MAH-PP (Mpp). It was concluded that the more reactive the modified PP with hydroxyl groups in the wood pulp, the better the tensile strength. It is believed that grafting takes place between MPP and wood pulp by esterification during the kneading process. A small amount of MPP (5%) was found to give good adhesion for a composite of refiner pulp (50%) and polypropylene (45%). Japanese investigators also produced a low density board, which consisted of wood pulp fibers, glass fibers and pulverized polyethylene manufactured by a wet forming process (Kawaguchi, Murase, and Iida 1988). The board was molded by hot pressing or preheating and successive cold pressing. The pulp fiber provided good paper machine runability, while the glass fiber provided dimensional stability to the product. The fiber component was lo%-30% and the glass/wood fiber ratio was important to the final properties of the product. A minimum of 10% glass fiber was necessary for reasonable dimensional stability. As the polyethylene content was increased from 40%-90% of the product, the bending strength and the dimensional stability decreased. The final molded product exhibited good dimensional stability, water resistance, and impact strength. Applications for automobile interiors and furniture panels were proposed by the investigators. Shiraishi and coworkers have had a 10 yr program on wood molding at Kyoto University in Japan (Shiraishi, Matsunaga, andYokota 1979a,b; Shiraishi 1980a,b; Shiraishi et a11982, 1983). Their approach to rendering wood to a thermoplastic material has been through chemical modification of wood meal. Generally, their work has emphasized esterification of wood. Thermoplasticity of esterified wood was found to depend on the acyl group, the method of preparation, and the degree of substitution. As shown in Table 7, as the size of the aliphatic group is increased, the melting temperature of the modified wood at 3 kg/cm' is decreased. Preparation of the esters by the trifluoroacetic acid (TFAA) method give lower melting points than by the chloride method. Acetylated wood samples prepared by the trifluoroacetic acid method clearly melted at 320°C under a pressure of 3 kg/cm* (Shiraishi et al. 1983). Wood samples acetylated by the chloride method or by a method using the acetic anhydride-pyridine or triethylamine-DMF system (25°C) did not undergo complete flow, but showed considerable thermoplasticity. Although wood samples fully acetylatedwith acetic anhydride-acetic acid-sulfuric acid did not show clear melting, their partially saponified samples gave thermomechanical diagrams with a sharp drop corresponding to flow. Acetylated wood samples prepared with the acetic anhydride-acetic acid-perchloric acid system did not show clear melting either. Thermal properties of the acetylated wood wtre enhanced by mixed esterification with other acyl groups. That is, wood esters containing either propionyl or butyryl groups in addition to acetyl exhibited meltable properties, if the mixing ratio was appropriate (Shiraishi et al. 1983). Shiraishi and coworkers (1982) also found that grafting can convert the unmeltable, acetylated-propionylated wood sample into more readily meltable materials, and that the apparent melting temperature decreased with an increase in the amount of attached polymer. A further striking finding was that a very small degree of grafting of polystyrene was enough to cause a drastic change in the thermoplastic property of the esterified wood. Even graft products with total weight increases of less than lo%, which were prepared by irradiation to a total dose of less than 0.2 Mrad, behaved as thermally meltable materials. The effect

52

Polymers

TABLE I.

from

Biobased

Materials

Apparent Melting Temperature of Various Higher Aliphatic Acid Eaters

of Wood Prepared by the TFAA or the Chloride Method'

Sample (awl) Butyryl Valery1 Caproyl CaprylYl Capryl Lauroyl Myristyl Palmityl Stearoyl

%easured under a pressure of 3 kg/cm2.

Melting temperature ("C) TFAA Chloride

300 235 250 210

310 305 260

205 195 200

245 290 240 __

195 __

295 220

Recent Advances

in Lignocellulosic-Derived

Composites

53

of grafted polystyrene was interpreted as effecting external plasticiration to compensate for the limited internal plasticiration obtained by acylation. Matsuda and coworkers (Matsuda 1981; Matsuda, Veda, and Haia 1984; Matsuda and Veda 1985) also extensively investigated esterified woods and were able to circumvent the complicated solvent systems employed by Shiraishi's group at Kyoto University. Matsuda easily produced esterified wood with a solvent by simply heating wood meal with succinic anhydride for 3 h to temperatures greater than 60°C. The wood meal was readily molded at high temperatures (18O'C) under pressure (570 kg/cm21 for 10 min. The moldability of various esterified woods decreased in the following order: succinic anhydride > maleic anhydride > phthalic anhydride. Hon and Ou (1988) produced a moldable product by benzylation of wood powder. The degree of substitution was varied by alterations in the reaction alkalinity, temperature, and time. Sodium hydroxide concentrations greater than 25% were necessary to obtain high weight gain, presumably related to swelling of the lignocellulosic substrate. Different species showedvariation in reaction rates. The thermoplasticized woods exhibited good melting properties and were readily moldable in bulk materials or extruded into films and sheets. A wide range of glass transition temperature, from 66'C-2SO'C,were observed for the benzylated wood, largely dependent on weight gain. The molded and extruded products exhibitedacceptablemechanioalstrength forstructuralengineering applications. FVTVRE OPPORTuNITIES Properties such as dimensional instability and susceptibility to degradation by biological organisms and ultraviolet radiation can be greatly improved by modification of lignocellulosfo cell wall polymers. These modifications result in a furnish that can be converted into composites of any desired shape, density, and size, and provide an opportunity for a manufacturer to distinguish a product line based on quality, uniformity, and performance. For some applications, the optimum composite may be a combination of materials to achieve the desired properties and performance. Property improved lignocellulosic fibers can be combined with materials such as metal, glass, plastic, natural polymers, and synthetic fiber to yield a new generation of composite materials. New composites will be developed that utilize the ..niqueproperties obtainable by combining many different materials. It is predicted that this trend will increase significantly in the future. The key to a successful composite made with a lignocellulosic material and another material is to improve compatibility between the two. Composites have beenmade using lignocellulosicmaterials in combination with plastics, synthetic fibers, or glass, but in most cases the properties of the resulting composite were not as good as they could have been. Research is under way in several laboratories in the world to make hygroscopic (polar) lignocellulosics more compatible with hydrophobic (nonpolar)materials. This is being done either by grafting onto the lignocellulosicmaterial or adding a coupling agent to the mixture to make them more compatible.

Arora, M., Rajawat, J.S., and Gupta, R.C., Holrforschuna and Holzverwertunq, a(l) (1981) a-10.

54

Polymers from Biobased Materials

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(1969) 367-374.

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Cowling, E.B., Comoarative Biochemistry of the Decav of Sweetsum Saowood & White-Rot and Brown-Rot Funuus, U.S. Department of Agriculture, Forest Serv. Technol. Bull. No. 1258 (1961). Feist, W.C., Rowell, W.C., and Ellis, W.D., Wood and Fiber Sci., (in press). Hon, N.-S. and Ou, N.-R., "Thermoplasticization of Wood. I. Benrylation of Wood," Proceedinas Tenth Cellulose Conference, Syracuse, NY, May 1988 (in press). Imamura, Y. and Nishimoto,

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Imamura, Y., Nishimoto, K., Yoshida, Y., Kawai, S., Sato. T., and Nakaji, M., Wood Res., 13 (1986) 35-43. Imamura, Y., Rowell, R.M., Simonson, R., and Tillman, A.-M., Paoeri ia Puu, (in press). Johnson, B.R. and Rowell, R.M., Material und Oruanismen, z(2)

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Kawaguchi, K., Murase, T., and Iida, K., "New Wood Fiber-Plastic Composite for Thermomoulding," presented at Cellucon '88 Meeting, Kyoto, Japan, December l-4, 1988. Kiguchi, M. and Suzuki, M., Mokuzai Gakkaishi, 3l(3) Klinga, L.O. and Tarkow, H., TaDPi, Kokta, B., Daneault, (1986) 127.

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49(l)

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Ozolinya, I.O., Shvalbe, K.P., Bekere, M.R., Shnyutsinsh, F.A., Mitsane, L.V., and Karlsone, I.M., USSR Patent 449 822 (1974). Paramasivan, T. and Abdul Kalam, A.P.J., Fiber Sci. & Technol., 1

(1974) 85.

Phillips, R.B., Quere, J., Guiroy, G., and Stannett, V., Tapoi, z Prasad, S.V., Pavithran, C., and Rohatgi, P.K., J. Mater. Sci., g Prud'homme, R.F., J. Aopl. Pol~m. Sci., 21

(1972) 858. (1983) 14443.

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Raj, R.G. and Kokta, B-V., "Studies on Mechanical Properties of PVC-Wood Fiber Composites,'* presented at Cellucon '88 Meeting., Kyoto, Japan, December l-4, 19R8. Raj, R.G., Kokta, B.V., Maldos, D., and Daneault, C., National Research Council of Canada/Industrial Materials Research Institute Symp. Series: "Composites ta7,*' November 5-6, 1987. Rowell, R.M., in Chemistry of Solid Wood, R.M. Rowell, ed., Advances in Chemistry Series No. 207; American Chemical Society, Washington, D.C., Chap. 4 (1984) pp. 175-210. Rowell, R.M., unpublished data. Rowell, Posnan, pRdla%,

in Wood Modification, (1985) pp. 358-365.

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238-266.

Rowell, R.M., Imamura, Y., Kawai, S., and Norimoto, M., Wood Fiber Sci., 21(l) (1989) 67-79. Rowell, R.M. and Keany, F., Wood and Fiber Sci.,

(in press).

Rowell, R.M. and Norimoto, M., J. Jav. Wood Res. Sot., 33(11) Rowell, R.M., Norimoto, M., Mokuzai Gakkaishi 34(7)

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Rowell, R.M. and Plackett, D., New Zealand J. Forest Sci., Rowell, R.M. and Syracuse, NY, May,

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R .,

and Tillman, A.-M., Nordic Pulp and Paper

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Satyanarayana, K.G., Kulkarni, A.G., Sukumaran, K., Pillia, S.G.K., Cheriyan, K.A., and Rohatgi, P.K., Proceedinas, International Conference on Comoosite Structures, Paisley College of Technology, Scotland, September16-18, (1981) 618. Selke, S.E., Yam, K.L., and Lai, C.C., "CompoundingWood Fibers and Recycled HDPE Using a Twin-screw Extruder," Presented at Third Chemical Congress, ACS, Toronto, Canada, June S-10, 1988, American Chemical Society Abstracts Macromolecular Secretariat #36. Shiraishi, N., Mokurai Koavo, 35 (1980b) 200. Shiraishi, N., Mokuzai Koavo, 35 (1980a) 150. Shiraishi, N., Aoki, T., Morimoto, M., and Okumura, M., Chemtech, s

(1983) 366.

Shiraishi, N., Aoki, T., Norimoto, M., and Okumura, M. in Graft Conolvmerization of Lianocellulosic Fibers, D.S. Hon, ed., ACS Symposium Series 187. American Chemical Society, Washington, D.C., (1982) p. 321. Shiraishi, N., Matsunaga, T., and Yokota, T., J. ADP~. Polvm. Sci., 24 (1979) 2347. Shiraishi, N., Matsunaga, T., and Yokota, T., J. Anal. Polvm. Sci., 24 (1979) 2361. Shvalbe, K.P., Orolinya, I.O., Bekere, M.R., Mitsane, L-v., Karlsone, I.M., and Dudin'sh, M.M., USSR Patent 478 743 (1974). Sridhar, M.K., Basavarajappa, G., Kasturi, S.G., and Balasubramanian, N., Ind. J. Text. Res., 2. (1982) 87. Sudo, K., Mokuzai Gakkaishi, 25(3) (1979) 203-208.

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Takaae, S., Shiraishi, N., and Takahama, M., "Studies on Composites from Wood and Polypropylenea," presented at Cellucon '88 Meeting, Kyoto, Japan, December 1-4, 1988. Tillman, A.-M., J. Wood Chem. Technol.,

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Yoahida, Y., Kawai, S., Imamura, Y., Niahimoto, K., Satou, T., and Nakaji, M., Mokuzai Gakkaiahi, 32(12) (1986) 965-971. Young, R.A., and Nguyen, C., Svenak Panneratidn., s;! (1979) 414. Youngquist, J.A., Krzyaik, A., and Rowell, R.M., Wood Fiber Sci. t la(l)

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90-98.

Youngquist, J.A., Rowell, R.M., Krzyaik, A., Holz ala Roh- und Werkatoff, 44(12) (1986) 453-457. Zhang, G., Yin, S., Wang, W., Xu, Forest Products, 3 (1981) 70-75.

R., and Chen, C., J. Naniins Technol. COllece

3. Cellulose Grafting: Past, Present and Future Vivian T. Stannett North Carolina State University Raleigh, North Carolina

INTRODUCTION Cellulosic graft copolymerization is of great interest with regard to the increased use of biobased materials. Indeed the graft copolymers are perhaps the clearest example of useful materials bringing together synthetic and natural polymers. These use biomass in all its many lignocellulosic varieties ranging from wood, grasses, and other plants to essentially pure celluloses such as cottons. Coupled with this aspect is the intrinsic biodegradability of the cellulosic component. The challenge of the Energy Conversion Utilization Program (ECUT) and similar programs is to expand and develop useful large scale and hi-tech smaller scale applications of such materials in an economic costeffective manner. These objectives have not yet been achieved, and increased, well-programmed research is clearly and unequivocally needed. The desperate need to produce plastics, fibers, films, and other materials with biodegradability has given a continuation to such programs, which began with the need (now longer range) of replacing all or part of petroleum and natural gas feedstocks with renewable biomass. The need for a useful degree of photo and other types of degradability should also not be overlooked. This chapter will review the present status of such research, where the future emphasis should be stressed and the relative efforts currently under way in the United States compared with the overall international effort. The author was privileged to be deeply involved in such research since July 1952, one year before the first conscious, deliberate, and successful synthesis of a cellulose graft copolymer was presented (Waltcher, Burroughs, and Jahn 1953). The preparation of this report was also based on presentations at major international meetings in 1988 (Tenth Cellulose Conference, Syracuse, N.Y., June; Cellucon '88, Kyoto, Japan, November; Nisshinbo Conference on Cellulose Utilization, Tokyo, Japan, December), and literature searches from January 1985 to December 1988 (including U.S. and foreign patents) to ensure adequate coverage of recent and present developments. EARtIER RRSRARCH - 1953-1984 Graft polymerization per se was first reported in 1946 (Carlin and Shakespeare). In 1943, however, vinyl and ally1 esters of cellulose were prepared and copolymerized in experiments conducted with them. Although only crosslinked products resulted, certainly grafting must also have taken place (Ushakov 1943). Cellulose and its derivatives have been among the most popular as grafting substrates since 1952. Perceived perhaps as the first new type of cellulose derivatives, grafting was eagerly seized upon for research. By 1984, more than 1000 papers Grafting, which is often were published and patents granted on the subject. carried out heterogeneously, is an excellent method of modifyirlg not only natural polymers but also polymers in fiber form. It was therefore even more attractive This effort is still continuing. to carry out extensive work on the subject. One excellent monograph (Hebeish and Guthrie 1981) and a number of rather thorough reviews (Krassig and Stannett 1965; Arthur 1970, 1985; Stannett and Hopfenberg 1971; Bhattacharya and Maldas 1984; Hon 1982; Samal, Sahoo, and Samataray 1986) on the subject have been published. These may be regarded as

58

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59

key references. As with polymer science in general, research in cellulose grafts synthesis, characterization, may be broken down into properties, and applications. Svnthesis Although ionic and condensation methods of grafting to cellulose have been briefly reported, the overwhelming majority of methods employed have been by free radical mechanisms. The general procedure is to generate free radicals on the The macrocellulose molecule and then to introduce a vinyl or diene monomer. The various radicals then initiate polymerization, forming graft copolymers. methods for carrying out this process via free radicals have been classified by Stannett and Hopfenberg (1971). Some notes and key references will be presented under similar headings. Chain Transfer and‘Redor Methods In these methods, a vinyl or diene monomer is polymerized in the presence of a In the chain transfer method, the growing chain can then cellulosic material. abstract hydrogen or another atom leaving behind the desired macroradical to It is clear that the process is not too efficient and also initiate grafting. Nevertheless, it has a certain pracleads to an equal amount of homopolymer. ticability and, in fact, similar methods are widely used industrially to produce heterogeneous grafts such as high-impact plastics. A useful development with this method is to introduce onto the cellulose groups that contain atoms that are readily extractable by free radicals. This was the first grafting method used, with halogens (Waltcher, Burroughs, and Jahn 1953). More recently, ethylene sulfide was reacted with cellulose to form mercaptan groups. These are very So far the growing chains from free radical efficient chain-transfer agents. polymerizations have been discussed as methods to generate the macroradicals. Radical transfer from the free radical catalysts themselves, although this is not strictly speaking chain transfer , can also be used with considerable success. To achieve this, the catalyst needs to be sorbed into the cellulose matrix A high concentration of the itself. Potassium persulfate is a good example. sulfate ion radicals are then formed, for instance, by heating persulfate, in Abstraction can then compete successfully with the cellulose matrix itself. initiation of homopolymer. An even more efficient extension of the radical transfer approach is to sorb part of a two component redox system such as ferrous ions into cellulose. The monomer is then introduced with the second component such as hydrogen peroxide. Bridgeford has discussed such methods in detail (1962). The xanthate method involves a redox system and has considerable promise for industrial exploitation. It was first reported by the Scott Paper Company in 1964 but still has not been commercialized. A number of pilot plants were built, It is possible that the method will still however, and operated successfully. be used on a large scale, but because it is tied to the xanthate rayon process, it has lost favor. However, xanthation can be carried out deliberately to low degrees of substitution. The xanthate group reacts with hydrogen peroxide to yield free radicals. The presence of ferric or ferrous ions may be necessary. Direct Oxidation A number of metallic ions have been used for the direct oxidation of cellulose to its macroradicals. The best known examples are ceric salts such as the suiThe reaction is complex and not completely understood. It fate and nitrate. is known that the ceric ion forms a complex with cellulose hydroxyl groups in The complex then dissociates in the presence of acids, into aqueous solution.

60

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Materials

a cellulose radical, a hydronium ion, and a cerous ion. The monomer is added either simultaneously or following pretreatment of the cellulose with a solution of the ceric salt. Initiation is rapid and efficient and in principle, leads to little homopolymer. In fact, some monomers themselves, notably acrylamide and acrylic acid, react with ceric ion to form radicals and homopolymers. In addition to cerium (IV) salts, vanadium (V), manganese (III), cobalt (III), and chromium (VI) salts have been used. Other oxidizing agents such as permangates, bromates, and periodates also form radical3 and initiate grafting. A considerable number of paper3 and patent3 have been published on the direct oxidation method and have been discussed and referenced in the various reviews (Hebeish and Guthrie 1981; Krassig and Stannett1965; Arthur 1970, 1985; Stannett and Hopfenberg 1971; Bhattaoharya and Maldas 1904; Hon 1982; Samal, Sahoo, and Samataray 1986). Cellulose

Initiator8

Another general method of grafting to cellulose is to form chemically an initiator, such as a peroxide or hydroperoxide, on the macromolecule. This can then decompose into radicals and initiate graft copolymerization. If a reducing agent is used, the homopolymer formation can be largely eliminated. For example, Cell-OOH t Fe"

--> Cell-O

t Fe'*+ OH-

(1)

Peroxides can be formed by ozonization, a method that has been studied chiefly in the Soviet Union, or by radiation of the substrate in air or in hydrogen peroxide solution. Similar reaction3 have been carried out with cellulose nitrate, ethylcellulose, and benzylcellulose. There is a danger with these methods that extensive degradation may occur, which has not been assessed adequately in the literature. In addition to peroxides, other initiating groups can be introduced into the cellulose molecule, such as peroxy esters. Diazonium salts have also beer synthesized and used as grafting initiators. As with the hydroperoxides, tht addition of a reducing agent such as ferrous ammonium sulfate essentially eliminates the formation of homopolymers. The use of diazonium salts has also been extensively studied in the Soviet Union. Cellulosic Cornonomars Perhaps one of the most obvious ways to synthesize graft copolymers is to form ally1 or vinyl cellulose derivatives and then copolymerize with a suitable vinyl or similar type of monomer. This was indeed probably the first, although not a conscious attempt at grafting (Ushakov 1943). Unfortunately, at that time there was no knowledge of grafting and the degrees of substitution were presumably too high and only crosslinked products were produced. With low degrees of substitution, however, and a proper choice of monomer reactivity ratios, graft polymers without much homopolymer could be prepared by this technique. To our best knowledge, there has been little progress or research on this approach. This was the earliest and perhaps one of the most obvious ways to form cellulose graft copolymers, i.e., to form vinyl or ally1 cellulose derivatives. Among the derivatives prepared have been cellulose ally1 esters, cellulose methacrylates, and cellulose ally1 ethers, as well as cellulose crotonates and maleates. More recently vinyl groups were introduced with cellulose nitrate by reacting with ally1 monocarbonate and hexamethylene diisocyanate. Grafting to these derivatives can be accomplished by direct free-radical vinyl copolymerization. It can readily be seen that if there are several unsaturated group3 on each cellulose molecule, heavy crosslinking will rapidly result. The situation is in many ways comparable to the polymerization of unsaturated polyesters. With low degrees

Cellulose

Grafting:

Past, Present and Future

61

of substitution, however, or properly balanced monomer reactivity ratios, graft copolymers that are essentially free from crosslinks can be prepared by this technique. Radiatipn Wethoda Both ultraviolet light and high-energy radiation have been used to initiate grafting to cellulose and its derivatives. The latter method has, however, been by far the most thoroughly studied. In fact, high-energy radiation grafting has probably been investigated in more detail than any other method. Because the chemistry of the process is relatively obscure, radiation initiation has been used in experiments designed to reveal details of the grafting process itself. No chemical reagents are used normally for the radiation-grafting techniques, so it is essential to make the substrate accessible to the monomer. In fact, with a suitable swelling agent only negligible degrees of grafting are possible. Three methods developed for radiation grafting have been successfully used for cellulose. Peroxide

Method. The cellulose substrate is irradiated in air to form peroxide derivatives, which can later be used for grafting as previously described. This method has been studied leas with cellulose than with many other polymers; however, preirradiation grafting in air has been frequently used. Here it seems clear that a combination of peroxide and trapped-radicalinitiation is operating. The grafting yields have been increased by first soaking the cellulose. In the case of viscose rayon fibers, for example, the fibers are soaked in hydrogen peroxide solution. Pmirradiation Method. This method involves irradiating the celluloaic aubatrate, preferably in the absence of air, and subsequently contacting the irradiated material with the monomer and swelling agent. Both liquid and vaporphase grafting has been used, and nearly every kind of celluloaic substrate has been studied. Again, a suitable swelling agent is essential for successful grafting. In general, it is better to irradiate dry to produce the maximum number of free radicals and then to admit the monomer and swelling agent together. In the case of vapor phase grafting, the swelling agent can also be in the form of vapor, such as water vapor. In addition to water vapor, methanol and acetic acid vapors were found to be effective promoters of the grafting process. In liquid-phase preirradiation grafting, these additives were also found to be effective. Generally, the same monomer-swelling agent systems were effective for both the mutual and the preirradiation techniques. These will be discussed further in the section on mutual grafting methods. With the trappedradical method as opposed to the peroxide method of preirradiation grafting, very little homopolymer is produced. A disadvantage, however, is that the degradation of the cellulosic backbone is usually greater with the preirradiation method. This is particularly true when the grafting is carried out in the presence of air or oxygen. Leas degradation is encountered with the mutual method of irradiation because of the protective action of the vinyl monomers present during the actual irradiation. Preirradiation is often carried out in air, and the combination of peroxides and grafted radicals that results is used to initiate the grafting reaction. In spite of the possibly deleterious effects of the concurrent degradation, the preirradiatior method is very attractive economically. It has been used for pilot-plant studies of the grafting of atyrene and other monomers to rayon. Mutual Method. In this method, the celluloaic substrate is irradiated directly in contact with the monomer. The celluloaic material can be actually dissolved in the monomer or monomer-solvent mixture, or simply swollen. Either a vaporphase or liquid-phase monomer can be used. The most usual technique, however, is the irradiation of the swollen cellulosic material in the liquid monomer or

62

Polymers

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Biobased

Materials

monomer solution. It is clear that much homopolymer will also be generated by direct radiolysis of the monomer, the monomer-solvent, or the monomer-swelling agent mixture, but this can be successfully controlled. The cellulose acetatestyrene system has been studied in considerable detail, and methods have been developed for separating the homopolymers from true graft copolymers. It was apparent from the results of these studies that the degree of swelling of the cellulose substrate has a profound effect on both the yield of graft and the molecular weight of the grafted side chains. Ultraviolet-Light Grafting This method of direct radical formation and grafting has received comparatively little study, although the first experiments started as early as 1959. Cellulose derivatives have been investigated more than cellulose itself. The latter normally involves the addition of photosensitizers. In principle, the preirradiation and the mutual methods can be used. It is also clear that photochemical grafting can be useful for the surface modification of grafting. Hon has described some more recent experiments on ultraviolet grafting. Other Methods of Free Radical Grafting A number of methods have been developed to form graft (and block) cellulose

copolymers. In general, they involve some mechanical breaking of the cellulosic chain such as mastication, vibratory milling, extrusion, or even ultrasonics and swelling techniques, in the presence of a vinyl monomer. Electrical discharge and plasma procedures have also been studied mainly for surface grafting. The mechanical treatments together with grafting carried out simultaneously with certain pulping processes represent less well defined but in principle practical methods capable of being scaled up for industrial exploitation. Some key workers in this approach have been Young, Hon, and their coworkers (Young, Achmodi, and Barkalow 1985; Hon 1985). Ionic Polpmriration

blathoda

These were studied very little in the early period under review. Normally such methods involve the use of nonaqueous solvents, which are less attractive to the cellulose and allied industries than aqueous methods. Nevertheless, there were a number of approaches using anionic routes, which have been discussed rather fully in the key reviews. In general, shorter grafted side chains but rather higher degrees of substitution were obtained compared with free radical methods. One very interesting cationic method has been described using boron trifluoride in nitrogen to form the cations, which were then reacted with isobutylene. Like the National Lead Process involving the Ziegler-Natta type of polymerization, it seems clear that little or no true grafting was obtained. However, in both cases the coated or encapsulated celluloses produced had excellent water resistance and other useful properties. Fling

Opening Methods

A number of reactive rings such as ethylene oxide, ethyleneimine, propiolactone, and ethylene and propylene sulfides have been reacted directly with cellulose following a suitable pretreatment. Generally, low-molecular-weightgrafted side chains but relatively high degrees of substitution were obtained. Polyamides were successfully grafted to celluloses by reacting caprolactam with suitable cellulosic acid chlorides. Again, low DP grafts were obtained.

Cellulose Grafting:Past, Present and Future

63

Condensation Uthods Methods of this type have received little study compared with the grafting of vinyl polymers. The most extensive studies have been made in the Soviet Union. A distinction can be made between adding an already formed polymer to a reactive functional group of the celluloaic material and using reactive groups on the cellulosic molecule to initiate condensation or ring-opening polymerization. An example of preliminary work on the former method is the reaction of a lowmolecular-weight poly(ethylene adipate) acid chloride with cellulose, using either a solvent-exchange or interfacial polymerization technique. A somewhat analogous study involved the reaction of telomers of poly(acrylic acid) having chlorine end groups with 8-aminoethylcelluloae. Only a small proportion of telomer became attached. Alkali cellulose also did not react extensively with the poly(acrylic acid) telomer. Direct polycondensation grafting of aminoenanthic acid chloride to cellulose and its derivatives has also been achieved. A low degree of substitution and molecular weight was found. An interfacial approach with cellulose xanthate gave similar results. In principle, the direct addition of a polymer with suitable functional groups could be attractive. However, the accessibility of one polymer to another except in solution and reactivity considerations has negated this method of synthesis. In conclusion, it can be said that studies of methods of synthesis of cellulosic graft copolymers (mainly free radical in nature) dominated work through 1983. Comparatively little attention has been given to characterization, properties, and applications of such products. Characterization

of the Graft Copolymers

In addition to developing methods of grafting and examining their properties, it is necessary to characterize as closely as possible the pure grafts and to estimate the extent and molecular nature of the resulting graft. In some respects, cellulosic graft copolymers are rather easy to investigate because the solubilities of the two homopolymers and the grafts themselves are often quite different from one another. Furthermore, the cellulosic backbone can be destroyed by acid hydrolysis, and the molecular weight and other properties of the isolated side chains can be determined. This has made research on the structure of cellulosic grafts attractive not only for the grafts themselves but as models for grafting in general. Whether the grafting reaction takes place in solution or within a swollen, insoluble cellulosic substrate, such as film or fiber, it seems inevitable that some homopolymera are present together with the graft and unreacted cellulose. In rather early work, the grafting of acrylamide to cellulose film was carried out by an ultraviolet-light technique. It was found that the graft copolymer, polyacrylamide, and the cellulose itself were all soluble in cuprammoniumhydroxide. On acidifying, however, only the ungrafted cellulose and the graft copolymer precipitated. By weighing the precipitate, the amount of the grafting could be measured, but the amount of ungrafted cellulose could not be determined. This simple procedure was later applied to a number of other grafting methods. It was seen that each method of grafting gave different efficiencies of grafting and that the preirradiation technique was the moat efficient. With heterogeneous grafting to semicrystalline as cotton, the morphology and orientation can greatly change the properties and will depend the choice of monomers and swelling agents and

polymers, especially fibers such This, in turn, can be changed. on the grafting method used and other additives. This aspect of

64

Polymersfrom BiobasedMaterials

the structure-property relationships of cellulose graft copolymers has been studied in depth, particularly by Arthur and his coworkers (1985). Proverties

The properties of celluloaic materiala--pulp and paper, textiles, and regenerated cellulose--and cellulose derivatives canbe dramatically changedbygraft copolymerization. Although data concerning properties and applications are scant in comparison with data concerning synthesis and phyaicochemical characterization, a sufficient technology has emerged to permit the beginning of a rational tailoring of properties in cellulosics via graft copolymerixation. Graft copolymerization has resulted in improvements in a wide variety of properties, including tensile strength; resistance to microbial degradation, abrasion, and acids; dye receptivity: wet strength of paper: and, adhesion. In addition, an entirely new spectrum of properties can be imparted, such aa changing pulp, paper, cellophane, and fibers into ion-exchange materials including membranes by the controlled grafting of anion- and/or cation-exchange groups onto the cellulose. It has been demonstratedthatmoiature regain in cellulose and cellulose acetate can be reduced by controlled radiation-inducedgrafting of atyrene. The water uptake can also be increased by grafting hydrophilic monomers including the synthesis of the so-called super water absorbing cellulosea. It has also been demonstrated that the compatibility of dissimilar polymers can be markedly improved by adding small quantities of celluloaic graft copolymers "constructed" from the two incompatible backbones. The latter observation has considerable implications regarding the formation of stable and useful "polymer alloys," or "polyblends." Cellulose itself is relatively inexpensive but cellulose derivatives are often expensive. Property improvements and alterations in properties achieved by grafting will usually be accompanied by an increase in cost. This immediately suggests that applications of some such end products will tend to be more specialized than those of the starting material. It is recognized that the grafting process results in the formation not only of true covalently bonded graft copolymers but also of residual homopolymers of the substrate polymer and newly formed homopolymers corresponding in the chemical repeat unit to the grafted aide chains. Many workers have scrupulously attempted to synthesize, isolate, and subsequently characterize the pure graft, whereas others, though acknowledging the presence of residual homopolymers, have proceeded to evaluate the end properties of the graft contaminated by the homopolymer impurities. Although a definitive study on the effect of homopolymer content in the properties of graft mixtures has not been made, it is cautioned that graft copolymers containing unextracted homopolymer will have properties that differ from those of a pure graft. Many studies have been reported on the properties of grafted cellulose fibers-mainly on cotton and rayon, but also on jute and other natural fibers (Mohanty 1987, 1988). Such studies have included water moisture regain, resistance to soil burial, dyeability, mechanical, and thermal properties. Properties of grafted pulp and paper have also been extensively studied. All the property studies are well reported in the references and need not be repeated here. The subject of biodegradability will be discussed separately.

Anplicationa A considerable number of applications have been explored. In general, researchers have concentrated on synthesis, and to a lesser extent, characterizationand properties rather than on developing suitable applications. For example, in the

Cellulose

Grafting:

Past, Present and Future

65

excellent monograph on cellulosic graft copolymers by Hebeish and Guthrie (1981), only 16 pages out of 345 are devoted to applications. Nevertheless, there were 141 references through 1979, and there have been many more since then. In more recent years, increased attention has been given to this area. The subject of applications will be discussed in the present and future sections of this review. In general, there are applications to wood itself (Cxikovsky 1968), to textile fibers (Arthur 19851, to pulp and paper (Phillips et al. 19721, and to membranes. There are also a number of miscellaneous applications. Some key references are given plus the reviews. PRESENT SITUATION - 1985-1988 About 450 papers and patents were published in this 4-year period. Of these, about 350 were concerned with grafting to cellulose itself. As with the earlier years, synthesis and research on mechanisms and variations on establishedmethods have been the major thrust. Recently, the effect of reaction variables on the composition of the grafts and the .amounts of both homopolymers has been emphasized more than in earlier years. This research has inevitably included characterization and property studies. Together, however, the three areas of synthesis, characterization, and properties make up only about 62% of the published work. The remaining 38% was concerned with papers and patents discussing possible applications. This is in marked contrast to the earlier years when synthesis probably made up at least 75% of the total effort. The contrast was even greater in 1988. In the area of synthesis, research into various features of the conventional free radical methods has continued. The effects of changes in the reaction variables on the yields, homopolymers and molecular weights of the side chains have been emphasized. The ceric ion and xanthate initiation techniques have dominated chemical methods. High energy radiation and photochemical grafting continued to be active areas of research. Studies on the latter method have increased markedly and it was by far the subject of the greatest number of publications on synthesis. This may be linked to a number of hi-tech types of imaging processes apparently under development. There has also been a sharp increase in ionic grafting. Anionic grafting which links preformed living polymers to substituted celluloses has been explored in depth by Narayan and his coworkers (Biermann, Chung, and Narayan 1987; Narayan and Shay 1986). Their methods have the advantage of being able to achieve controlled degrees of substitution, molecular weights, and molecular weight disThis is in marked contrast to the free radical tributions of the side chains. techniques developed to date. At the moment, the need for rather dry solvent systems and cellulose derivative substrates make anionic grafting economically These anionic unattractive on a large scale except for specialized products. More polymerization products could, however, be high value added materials. importantly, at the moment, they have great value for exploring propertystructure relationships of the grafts of well-defined structure. There have also been a few papers using cationic methods. Although it is difficult to envisage it being practical on a large scale, the cationic approach widens the range of side chain monomers available. One method, however, uses tosylated bleached kraft pulp to initiate the cationic grafting of 2-methyl oxazoline and is potentially more attractive for industrial exploitation (Cheradame, Ambo, and Gandini 1986). Characterization methods have continued along similar lines to those developed in the earlier years. Somewhat more attention has been given, however, to improving the acid hydrolysis of the grafts to isolate the synthetic side chains fortheir characterization.

66

Polymers from Biobased Materials

The property studies reported during the past few years have also continued along the lines developed during the previous years. But more emphasis has been given to water sorption, retention, and diffusion. There were also a few isolated studies on polymer blends used with compatibilizing grafts, on acid resistance, and on thermal and photo degradation. Various biological, bioactive, enzyme immobilization, antimicrobial, cell attachment, and related studies have been emphasized much more than in earlier years. Curiously, no studies of the biodegradability per s of the grafts were reported, in spite of its obvious importance. ::esearch into possible acvlications of cellulosic graft copolymer9 has been very active in the past 4 years' particularly in Japan. Most activity has centered on grafted cellulosic membranes for gas and other separation processes, including alcohol from water. Nearly 27% of the reports were on membranes and ion exchange materials. Applications based on water sorption were emphasized, particularly for super sorbing materials for uses such as sanitary napkins, tampons, and diapers, and for soil stabilization and other agricultural uses. Miscellaneous applica+ions such as for bandages and other medical uses were also important. Equal-j emphasized were applications for the immobilization of enzymes, antimicrobials, and for hemostatic and biomaterial related uses including controlled drug release and biocompatibility. Applications of the graft copolymers in the coatings industry have been investigated to a considerable degree to increase adhesion and to impart other useful properties. Applications in plastics were studied, including the use of grafts for compatibilizing blends, such as molding compositions and composites. Newer areas have been developed particularly in uses for diazoprinting, copying, and recording applications --some based on photosensitive materials; these were chiefly Japanese developments. Water soluble grafts and uses for the cosmetic industry have been reported. Applications to the textile and pulp and paper industries continued to be explored, but along similar lines to those developed in previous, years including waste water treatment. Minor activities included the use of cellulosic grafts for adhesives, catalyst support systems, latex coagulating agents, oil absorbers, and foaming agents.

There is a strong need for research following: 1.

in a number

of areas, which

include the

Much more work on the biodegradability of cellulosic graft copolymer? is The extraordinary fact is that in the past four years (through needed. 1988) not a single paper concerning this problem appears to have been published'. Even across all the years of research into cellulosic graft copolymers, the enzymatic and microbial degradability of such copolymers have been studied to only a small extent. With available landfill capacity rapidly diminishing, the disposal of over 160 million tons of waste annually in the United States is emerging as a key environmental problem of the future. More than half the municipal solid waste stream is made

'Editor's note: The past year (1988-1989) has seen a number of attempts to measure the biodegradability of graft copolymer9 and composite materials. However, standard methods of analyses are not yet available, making the definition and assessment of the biodegradability of materials an area of intensive and extensive research (see chapter 8).

Cellulose

Grafting:Past, Present and Future

67

of paper-based and synthetic plastic materials, which biodegrade quite The use of grafting and other chemical means slowly in the environment. to enhance the degradability of this fraction of waste will allow faster "recycling" of the landfill volume and also serve to reduce urban litter. The grafting of short chain moieties to cellulose to alter the rate of both the light-induced degradability and the biodegradability of the material Sensitized photooxidation of cellulose has been is one such possibility. extensively discussed in the literature. With judicious choice of functional groups, light-sensitive centers and even photooxidation catalysts An allied field of might be incorporated into the cellulose structure. interest is the chemical modification of the structure of cellulose itself to increase its degradability in the environment. Plastics are practically non-biodegradable in the soil. Grafting a significant fraction of the relatively more biodegradable cellulose derivatives to the synthetic polymer is likely to enhance its biodegradability. Rapidmicrobial degradation of the grafted cellulose component will in turn generate a network of voids in the plastic matrix, weakening the structure and at least causing brittleness, which will decrease the harm the plastic material may cause to the environment. Cellulose-synthetic polymer grafting reactions have been studiedby Warayan and others (see Chapter 7). Further research based on these pioneering studies may extend these techniques to achieve high levels of grafting in slurry (or solid reactant) systems in a continuous, fast process. 2.

With all the work on methods of grafting, the effect of the lignin content on grafting yields and the characteristics and properties of the resulting Most of the research has concentrated grafts have been little studied. More work is needed on on pure forms of cellulose and its derivatives. The direct use of whole wood, steam-exploded woods, and this subject. high-yield pulps as grafting substrates is clearly of considerable indusSome such studies are under way by Glasser and others. trial importance. Some work has been reported, particularly by Kokta and coworkers (see Coupled with this Chapter 2), on the effects of lignin on grafting. aspect, the possibility of grafting during the pulping process or on whole An important example is the work of wood should be further explored. Young, Rowe11 and colleagues.

3.

Work on the super water-absorbing cellulose grafts needs to be expanded. Methods of reducing the effects of salts on the water sorbency and retention need to be explored, but an initial finding of Salamone et al. (1985) is a good start on the problem. The biodegradability of the "supersorbers" is also important and should lead to a new emphasis on cellulose and starch based sorbents compared with the overwhelming use of the purely synthetic polymers currently on the market.

4.

Finally, cost-effectiveness of the resulting products are all-important. A reasonable economic analysis of the various methods of grafting with various substrates is needed. Even if somewhat tentative and speculative, such a study would be most helpful for the further development of grafting The three subjects summarized above represent examples that technology. could benefit from an economic analysis.

68

Polymers from Biobased Materials

An analysis of the research reported during the past four years, up to December 1968, showed that 28 countries had published work on cellulose grafting. Japan led the way with 50 papers and patents followed by the Soviet Union with 40 entries and the United States with 33 published works. Other active countries are Egypt, Ctechoslovakis, and Canada, but these all have less than 15 entries each.

Arthur, J. C., Ad". pp. l-87.

in "acromol.

Sci.,

of 901-r Arthur, J. C., EncvcloDedia "01. 3, Wiley-Interscience Publ., New

Bhattacharya, Biermann, Bridgeford,

S. N. and Maldas,

C. J.,

Chug,

D. J.,

York

h

., Pr

Atomic

Enarw, Review,

New York !i970)

Science and Enqineerinq, (1985) pp. 68-86.

and Narayan,

R.,

Sci.,

2

1:.

2nd Edition,

(1984) 171-270.

Maoromol.,

. R83. De"elooL,

Carlin, R. S. and Shakespeare, N., J. Cheradame, H., Rmbo, T. A., and Gandini, 6 (1986) 261. Czikovsky,

2, Academic Press,

D., Proa. 901~.

J. B.,

n . En .

Vol.

20 (1997) 954. 1 (1962) 45.

Chem. SOC,, B 11946) 876. Makromol. Chem.. Macfomol.

IIAEA-Vienna),

5 (1968)

I'., The Chernistrv Hebeish, A. and Guthrie, J. Co~olvmer*, Springer-Verlag, Berlin, 1981.

Svm~.,

3.

and Technoloav

of Cellulosic

Hon. David N. S., ed., ACS Symposium Series, No. 187: Graft CoDolvmerization of Lianocellulose Fiber%, ACS Division of Cellulose, Paper, and Textile Chemistry at the 182nd Meeting of the American Chamical Sooiety, New York, NY, August 2326, 1982. Hon. D.N.S., 'Wechanochemistry of Cellulosio Materials," Chapter 6 in Cellulose and Its Derivatives, J. F. Kennedy, 0. 0. Phillips, D. J. Wedlock, and P. A. Williams, eds., Ellis Horvood Ltd., Chichester, (1985) 71-86. Krassig,

H. A. and Stannett,

V.

Hohanty,

A. K.,

Sci.

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T., Ad". Polym. - Reviews,

a

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1 (1965) 111-156

(1987-S)

593-639.

Narayan, R. and Shay, M., in Renewable Reaovrca Materials, New Polymer Sources, C. E. Carraher, Jr. and 1. H. Sperling, eds., ~lenm, New York (1986) 137-146; Polvm. Sci. Tech., 2 (1986) 137-146. Phillips, R. (1972) 858.

B.,

Quere,

J.,

Guiroy,

Salamone, J. C., Rodriguez, E. L., Lin, Ahmed, I., 901-r. 26 (1965) 1234. Samal, R. K., 81-141.

G.,

and

Stannett,

v.

T.,

K. C., Quaoh, I+., Wattarson,

Sahoo. P. K., and Samataray,

J.,

~aoromol.

Sci.

a,

55

A. C., and

Review, ~

(1986)

Cellulose

Grafting:

Past, Present and Future

69

Stannett, V. T. and Hopfenberg, H. B., Chapter XVII in Cellulose and Cellulose Derivatives, Part V, Wiley-Interscience Publ., New York (1971) pp. 907-936.

Ushakov, S. N., Fiz-Mat. Nauk., 1 (USSR) (1943) 35. Waltcher, I., Burroughs, R., and Jahn, E. C., I.U.P.A.C. Conference, Stockholm (1953). Young, R. A., Achmodi, S., and Barkalow, D., "Direct Modification of Cellulose in Woody Biomass and Sludge,**Chapter 37 in Cellulose and Its Derivatives, J. F. Kennedy, G. 0. Phillips, D. J. Wedlock, and P. A. Williams, eds., Ellis Horwood Ltd., Chichester (1985) 417-424.

4. Lignin: Properties and Materials Wolfgang G. Glasser Department of Wood Science and Forest Products Virginia Polytechnic Institute and State University Blacksburg, Virginia

IWTRGDUCTIGW The Division of Cellulose, Paper and Textile Chemistry held a symposium at the Third Chemical Congress of North America, June 5-11, 1988, in Toronto, Canada, This symposium was jointly on the topic of "Lignin: Properties and Materials." organized by W G. Glasser of Virginia Tech, Blacksburg, Virginia and S. Sarkanen The symposium featured of the University of Minnesota, St. Paul, Minnesota. 65 scheduled presentations in nine half-day sessions. It was financially supported by six private corporations, five of which are currently marketing commercial lignin or lignin-derivative products; the American Chemical Society, Division of Cellulose, Paper and Textile, and the Energy Conversion and Utilization Technologies of the U.S. Department of Energy. The technical sessions of this symposium provided evidence for significant advances in several areas, and these are highlighted in the following report. The proceedings of this symposiumhave been published in the ACS Symposium Series The Number 391 and represent approximately two-thirds of all presentations. titles of the individual reports are given in the appendix. MACRGMOLBCULAR

STRUCTURE AND PROPERTIES

The chemistry and biochemistry of lignin in woody plant have been recognized as being related to the enzymatically triggered, free radical polymerization of p-hydroxyl cynnamyl alcohols. Although the understanding of particular physiological and biochemical circumstances during plant formation, and their effect on the process of lignification is experiencing rapid progress at the moment (see chapter lo), there is little doubt that the essential features of the chemical composition of lignin in plants is well understood. Whereas this chemistry has been recognized primarily because of analytical degradation studies, novel approaches to structure recognition are primarily based on the spectroscopic analysis of chemical features, principally "C-NMR (solid and solution state) In contrast to the understanding of the chemistry of lignin and spectroscopy. lignin formation, the recognition of the macromolecular structure and properties of lignin both in situ and in isolated form (both in solution and in solid state) has so far remained obscure. The Symposium on Lignin: Properties and Materials provided an opportunity to review the latest advances regarding the understanding of the macromolecular characteristics of lignin. Papers by Goring and Koshijima et al. focused on the issue of network architecture, lignin-carbohydrate interaction, and morphology and aggregation in micelles of lignin in plant tissue as well as in aqueous These papers raised serious doubts regarding "conventional wisdom," solution. which pictures lignin as a highly cross-linked network material of infinite The conflicting view presented is consistent with lignin molecular weight. having the nature of several types of chemically and ultrastructurally different networks (Goring); or with lignin being of relatively low molecular weight, but having strong hydrophobic and electrostatic interactions with the amorphous The concept of lignin heterogeneity was polysaccharides (Koshijima et al.).

70

Lignin:

Properties

and Materials

71

supported by the dissolution studies of Forss et al. Several unusual behaviors of lignin in solution were interpreted in terms of a not yet completely understood association behavior of lignin in solution. The behavior differs in relation to time (Siochi et al.) and molecular weight (Rudatin et al.), and interferes with the determination of molecular weights by displaying association/ dissociation-dependentanisotropy (Froment and Pla; Dutta et al.). Hypotheses advanced by Sarkanen and others hold conformational and other factors responsible for the arrangement of lignin macromolecules in solution. A series of reports dealt with the issue of molecular weight determination of isolated lignin preparations (Siochi et al., Johnson et al., Forss et al., Froment and Pla., Himmel et al., Meister and Richards). Although the final word is not yet spoken, the advances presented indicate that the characterization of (soluble)lignins by high performance liquid chromatography in a reliable manner and in a form comparable to other polymers will become available in the near future. In summary, the understanding of the macromolecular structure and properties of lignin suggests that lignin in situ and in an isolated form is often of low molecular weight: that it is intimately associated and covalently bound to carbohydrates in nature: that it is macromolecularly and ultrastructurally heterogeneous; and that it readily forms solid and dissolved associated complexes that are held together by secondary bonds and/or conformational forces. Rapid progress is recognized concerning the understanding of the nature of lignin in terms of its chemistry as well as its macromolecular character. As the secrets of this biopolymer yield to scientific investigation, lignin begins to be recognized as a molecule that can contribute unique properties to water-soluble as well as solid (structural) materials. This is the field to which approximately twothirds of the symposium's presentations were devoted. MATERIALS Reports on the use of lignin in water-soluble as well as structural materials have involved chemical polymer modification with only one exception. Research on water-soluble polymers dealt with lignin sulfonates (Hatakeyama et al.) and with a re-examination of the industrial process of sulfonation and sulfomethylation of lignin (deGrooteet al., Gratxl et al.). Novel water-soluble materials resulted from grafting with 2-propenamide (Meister et al.) and from functionalization by derivatization with multifunctional reagents (Pulkkinenet al.). Severa1 papers reported on research dealing with the synthesis of cationic, anionic, and non-ionic water-soluble lignin derivatives for use as a thickening agent and in wastewater treatment. Research on structural materials concentrated on phenolics, polyurethanes, and epoxies, and on a variety of other (specialty) polymer applications (Lindberg et al.). Among them were electrically conducting polymers (Kuuselaet al ); high performance polymers prepared from lignin degradation products (Hatakeyama et al.): carbon fibers from modified and degraded lignins (Sudo); and lignin-based materials for (bioactive) control release applications in agriculture as well as fire-resistant polymers (Struszczyk). The field of lignin-based phenolics featured several reports from industry/ university cooperative studies. Lignins from organosolv pulping were described as low-molecular-weightcomponents that have promise for partial replacement of phenol-formaldehyde resins (Lora et al., Cook and Sellers). Replacement levels were between 35% and 50%. Lignins from steam explosion attracted interest in relation to reactivity with phenol-formaldehyde resin (Cyr and Ritchie) and with phenol and formaldehyde in separate reactions (Ono and Sudo). The reaction of lignin with formaldehyde under acidic conditions produced hydroxymethylated

72

Polymers

from

Biobased

Materials

derivatives with substituents in meta-position to the aromatic hydroxy group (v. der Klashorst), and this helps overcome a reactivity handicap common to all hardwood-derived lignins. Resultsirith a novel "bio-adhesive" fromlignin demonstrated that phenoloxidases immobilized by an aqueous organic solvent were capable of serving as cure catalysts in a conventional hot-press system (Huttermann et al.). The fact that all reports on lignin-based phenolics from North America and Europe involved a strong public-private interface suggests that this type of study Research results suggest that begins to concentrate on product development. lignin can be incorporated into phenolic resins in a variety of ways, following no, limited, or extensive chemical modification: but that no compelling technical or economic reasons for industry to adopt these hybridmaterials exist. However, the future holds promise especially for novel unsulfonatedtypes of lignins, such as those commonly produced by organosolv pulping and steam explosion'. Methods for improving the performance of lignin in phenolic resins have focused on (a) phenolation and aromatic nucleus exchange, (b) on hydroxymethylation in positions 2 and 6 of the aromatic ring, and (c) on enzyme-catalyzed crosslinking reactions. Several papers dealt with the conversion of lignin into polyurethanes (Hirose Two alternative approaches became et al., Merck et al., and Kelley et al.). apparent, and these dealt with the use as polyol component of solutions of (lowmolecular-weight) lignin fractions in aliphatic glycols and of hydroxyalkylated lignin derivatives. The presence of lignin in polyurethanes was found to retard the thermal degradation in air (Hirose et al.), and this was attributed to the ability of lignin to undergo oxidative polymerization. Structure-property relationship studies of lignin-containing polurethanes in relation to soft segment content illustrated that glass transition temperature, modulus, tensile strength, and elongation at break (i.e., elastomeric behavior) could all be modified in a predictable manner by combining lignin with aliphatic or polyether glycols of variable chemistry and size (Merck et al., Kelley et al.). Hydroxyalkyl lignin derivatives received attention as star-shaped macromers (de Oliveira and Glasser) and as modulus-building components of polymer blends with a range of thermoplastic polymers including hydroxypropyl cellulose (Ciemniecki and Glasser, Rials and Glasser). Surprisingly positive intermolecular interactions were recorded for those polymer combinations that allowed hydrogen and related secondary bonds to influence material properties. The analysis of hydroxypropyl lignin was described by Hyatt. The bleaching of these derivatives with H,O, was the subject of a contribution by Barnett and Glasser. The synthesis of graft copolymers of lignin and polystyrene was accomplished by reacting polymeric styryl carbanion with mesylated lignin (Narayan et al.). Research on lignin-based epoxies involved both lignin degradation and functionalization by ozone (Tomita et al.) as well as the reaction of hydroxyaikyl lignin derivatives with epichlorohydrin (Nieh and Glasser). The importance of chemical modification and degradation on the reactivity of wood components was stressed by research on wood and lignin dissolution with phenols or polyhydric alcohols (Shiraishi). Acrylated lignin derivatives were reported

'Editor's Note: see Chapter 1 for details on wood fast pyrolysis lignins replacement of phenol in these resins without chemical modifications.

as

Lignin:

Properties

and Materials

73

to have promising copolymerization characteristics with conventional vinylmonomers (Glasser and Wang). In summary, the latest studies reported at this symposium suggest that several types of water-soluble and solid (structural) materials can be formulated on the basis of lignin. Whereas several technical problems persist, advances are being made to understand and overcome them. Because existing kraft mills in the United States have available in their spent pulping (black) liquor as much kraft lignin as polymeric materials produced in the United States annually, kraft lignin use will remainlimitedto those companies capable of developing high-volume markets. Opportunities for novel types of lignin, which are lower in molecular weight, free of sulfur, and better soluble in organic solvents, are seen especially for the lower volume but higher value materials markets. Although there are no demonstrated successes as yet, a significant public-private cooperative effort is under way in several areas of lignin-based structural materials. The greatest industrialparticipationinthe research and development of lignin-based polymers is recorded in the phenolics and polyurethane fields. The only commercial lignin products, however, are still,water-soluble polymers. NEED FOR PUTURB RESEARCH The history of the commercialization of lignin products began with the need to develop alternative disposal routes for lignin sulfonates from the sulfite pulping process. This resulted in the development of large-volume/low-value markets for ionic water-soluble polymers. With lignin sulfonates having captured a greater than 50% market share of industrial anionic water-soluble polymers, industrial research and development efforts have concentrated on improving product values via purification and chemical modification. Individual manufacturers have been able to penetrate such markets as dyestuff dispersants, drilling mud additives, and battery acid additives. The envisioned entry of lignin into markets for structural materials is likely to parallel that of the water-soluble polymers. The recovery and sale of lignin will represent an alternative to incineration, and markets will develop in size Sufficiently low prices in accordance with lignin acceptance and profitability. along with adequate quality control and predicable chemical behavior will be important parameters for success. Non-sulfonated lignin preparations from wood fractionation other than kraft pulping are likely to penetrate markets for (lowvalue) wood adhesives first. With time, these lignin sources will be upgraded and refined, and they will become acceptable for high-value, low-volume specialty materials. The rate at which this development takes place will probably depend on (a) how well structure-property relationships of lignin-based materials are understood; (b) on the ease with which performance standards can be determined and quality assured (i.e., standard techniques of analysis); and (c) on the degree to which Because a greater industry has participated in product development efforts. involvement by industry in phenolic resin projects is recognized, this is likely Polyureto be the first industrial application for lignin in solid materials. thanes are candidates for second generation structural materials. Because most non-kraft lignin producers are small in size and unsophisticated in technology, a glaring need exists for the establishment of standard and routine analysis and performance evaluation services at public institutions. INTERNATIONAL ACTIVITIES Approximately half of the 65 papers presented at the symposium on Lignins: Properties and Materials represented the work of foreign laboratories. About lO%'of the papers were from Canada. Among the foreign papers, an about equal

74

Polymers

from

Biobased Materials

number was from Japan, from Europe, and from other parts of the world. Whereas Japanese researchers emphasized technological aspects of high-value materials, such as carbon fibers and epoxy resins, European authors (mostly from Scandinavia and Eastern Europe) concentrated on fundamental properties of lignin. Only North American papers reflected close association with the private industry in several materials fields (especially phenolics and polyurethanes). CONCLUSIONS The symposium on Lignin: Properties and Materials has revealed that lignin is a reasonably well understood polymer isolated from woody plants that presents a diverse range of opportunities for industrial application. Among the few compelling economic reasons that call for lignin to be developed into a structural material of commercial importance is the fact that availability of lowcost carbohydrates (for separation and nutrients) is a facilitator of an emerging biotechnology industry. Because treatment with steam is among the most promising techniques for fractionating woody biomass into low-cost carbohydrates and lignin, lignin use plays a crucial role in the economic success of the biotechnology industry. The bulk of the research on high-value applications of lignin in specialty materials originates abroad, predominantly in Japan. For the United States to remain competitive in the field of lignin conversion to materials, incentives must be provided for cooperative studies between public and private laboratories.

This is to acknowledge with gratitude financial contributions for the organization of this Symposium by Daishowa/Beed, DOE-Energy Conversion and Utilization Technologies, Biobased Material Project, ACS Cellulose, Paper and Textile Division, ENCE, Georgia Pacific, ITT Rayonier, Vestvaco, and Weyerhaeuser Company.

Lignin:

Paper8

Presented

at the Symposium on Lignin:

Section A:

MACROMOLECULAR

Properties

Properties

STRUCTURE AND PROPERTIES TITLE

D. A. I. Goring

The Lignin Paradigm and

75

and biaterials

AUTHOR(S)

T. Koshijima, T. Watanaba, F. Yaku

and Materials

Structure and Properties of the Lignin-Carbohydrate Complex Polymer as an Amphipathic Substance

K. Forss. R. Kokkonen, and P.-E. Sagfors

The Heterogeneity of Lignin: Dissolution and Properties of Low Molar Mass Components

L. Li and E. Kiran

Supercritical Fluid Extraction Lignin from Wood

J. J. Meister and E. G. Richards

Determination of a Polymer's Molecular Weight Distribution by Analytical Ultracentrifugation

M.

E. Himnel, K. Tatsumoto, K. K. K. Grohmann, D. K. Johnson, and H. L. Chum

Oh,

Molecular Weight distribution Aspen Liqnins from Universal Calibration

of

of

E. J. Siochi, M. A. Haney, W. Mahn, and T. C. Ward

Molecular Weight Determination Hydroxypropylated Lignins

D. K. Johnson, H. L. Chum, and J. A. Hyatt

Molecular Weight Distribution Using Lignin Model Compounds

K. Forss, R. Kokkonen, and P.-E. Sagfors

Determination of the Molar Mass Distribution of Lignins by Gel Permeation Chromatography

P. Froment and F. Pla

Recent Determinations of Average Molecular We.:ghts and Molecular Weight Distributions of Lignin

S. Rudatin, Y. L. Sen, and D. L. Woerner

Associations of Kraft Lignin in Aqueous Solution

S. Dutta, T. M. Garver, Jr., and S. Sarkanen

Modes of Association Liqnin Components

K. Forss, R. Kokkonen, and P.-E. Sagfors

Reversed-Phase Chromatography Lignin Derivatives

of

Studie:

between Kraft

of

76

Polymers

from

Biobased Materials

Section B:

GENERAL MATERIALS

J. J. Lindberg, T. Kuusela, and K. Levon

Specialty Polymers from Lignin

H. Hatakeyama, T. Hatakeyama

High-Performance Polymers from Lignin Degradation Products

S. Hirose,

and

T. A. Kuusela, J. J. Lindberg, K. Levon, and J. E. Osterholm

Modification of Lignin to Electrically Conducting Polymers

R.

R. W. Thring, E. Chornet, P. Overend, and M. Heitz

Production and Hydrolytic Depolymerization of Ethylene Glycol Lignin

H. Struszczyk

New Trends in Modification

T. Elder

The Application of Computational Methods to the Chemistry of Lignin Section C:

H. Hatakeyama, T. Hatakeyama

WATER-SOLUBLE

S. Hirose, and

of Lignins

POLYMERS

DSC and NMR Studies on the WaterSodium Lignosulfonate System

E. Pulkkinen, A. Makela, and H. Mikkonen

Preparation Flocculents

J. J. Meister, D. R. Patil, C. Augustin, and J. 2. Lai

A Review of Product Synthesis, Polymer Characterization and Application Testing of Lignin Graft Copolymers Section D:

and Testing of Cationic from Kraft Lignin

PHENOLICS

J. H. Lora, C. F. Wu, E. K. Pye, and J. J. Balatinecz

Characteristics of ALCELL' J,ignin and Its Potential Applications

P. M. Cook and T. Sellers, Jr.

Organosolv Lignin-Modified Resins

H.-K. Ono and K. Sudo

Wood Adhesives from Phenolysis Lignin: A Way to Utilize Lignin from Steam Explosion Process

G. H. van der Klashorst

The Modification of Lignin at the 2and 6-Positions of the Phenyl Propanoid Nuclei

A. Huttenaann, 0. Milstein, B. Nicklas, and J. Trojanowski, A. Haars, and A. Kharazipour

Enzymic Modification of Lignin for its Technical Use: Strategies and Results

N. Cyr and R. G. S. Ritchie

A Method of Estimating the Adhesive Quality of Lignins for Internal Bond Strength

Phenolic

Lignin:

Section E:

Properties

and Materials

77

POLYOLS, POLYURETHAWES, POLYBLENDS, AND GRAFTS

S. Hirose, S. Yano, T. Hatakeyama, and H. Hatakeyama

Heat-Resistant Polyurethanes from Solvolysis Lignin

R. Merck, A. Reimann, and K. P. Kringstad

Elastomeric Polyurethanes from a Kraft Lignin-PEG-TDI System

S. S. Kelley, W. G. Glasser, and I. C. Ward

Effect of Soft Segment Content on the Properties of Lignin-Based Polyurethanes

W. de Oliveira and W. 0. Glasser

Star-Like Macromers from Lignin

0. A. Hyatt

Hydroxypropyl Lignins and Model Compounds: Synthesis and Characterization by Electron Impact Mass Spectrometry

C. A. Barnett and W. G. Glasser

Bleaching of Hydroxypropyl Lignin with Hydrogen Peroxide

S. L. Ciemniecki and W. G. Glasser

Polymer Blends with Hydroxypropyl Lignin

T. G. Rials and W. G. Glasser

Phase Morphology of Blends of Lignin with Liquid Crystal Cellulosics Engineering Ligno-Polystyrene

Ft.Narayan, N. Stacy, M. Ratcliff, and H. L. Chum Section F:

Materials

of Controlled

Structures

EPOXIES AND ACRYLICS

N. Shiraishi

Recent Progress in Wood Dissolution and Adhesives from Kraft Lignin

8. Tomita, K. Korozumi, A. Takemura, and S. Hosoya

Ozonized Lignin/Epoxy Resins: Synthesis and Utilization

W. L.-S. Nieh and W. G. Glasser

Lignin Epoxide-Synthesis Characterization

W. G. Glasser and H.-X. Wang

Lignin Derivatives Functionality

and

with Acrylate

5. Materials from Renewable Resources D. A. I. Goring University of Toronto Toronto, Ontario, Canada

In the present section, I first discuss some recent trends in the development of new materials form wood. Then my opinions on priorities for research in the overall area of the utilization of the bioresource are listed. The section ends with a paragraph of conclusions. NEWMATERIALS

FROMWOOD

Wood is natures high-tech material. It is light and strong, and it lasts, sometimes doing a demanding job for hundreds of years. When its work is finished, it biodegrades and contributes life to the soil from which it came. Wood is abundant and cheap. Its use is highly energy conservative. As a modern industrial material, wood is not uniform. Knots and other flaws predict. Second, wood is not readily by current manufacturing processes and

First, it has two major disadvantages. produce weaknesses that are difficult to molded into the complex shapes demanded products.

Many successful technologies have been developed to overcome the non-uniformity of wood. Until recently, these products have been limited mostly to sheet materIn passing, it is interesting ial such as plywood, waferboard, and hardboard. to note that plywood in the form of I-beams is being used instead of 2" X 0" support in floor joists. At the present time, however, there are several processes under development in which structural beams are being producedby reconditioning strands of wood. The most promising of these new products in the North American scene is Parallam--parallel strand lumber-- being developed by MacMillan Bloedel Ltd (1988). Strands of veneer are mixed with a small quantity of a waterproof adhesive, aligned, and then pressed together to give beams as large as 15" X 12" of any desired length. The process "edits out" weaknesses such as knots in logs and also averages out the variability between different trees. A light, strong material is produced with much closer engineering specifications than conventional dimension lumber. Parallam is expected to be used whenever the strongest and most durable beams are required in houses and light commercial buildings. Currently there are two main approaches to the development of thermoplastic materials from wood. The first involves chemical modification of the wood to In the second the wood is reduced render the polymers therein thermoplastic. to pulp either chemically or mechanically and the fibers blended with a synthetic polymer to give a thermoplastic composite. Much interesting work is going forward on the chemical modification of wood to make it thermoplastic. The concept here is to derivatize the wood polymers and The softening temperature thus to reduce the crystallinity of the cellulose. of the wood is reduced and the material can be heat formed easily. Cyanoethylation (Morita and Saka 19861, acetylation (Shiraishi and Yoshioka 1986), and other derivatizing procedures (Shiraishi et al. 1985) are now under study in Japan. A wide range of materials can be made, including a strong, low-density foam (Shiraishi et al. 1985).

78

Materials from Renewable Resources 79

Both chemical and mechanical wood pulps are proving to be excellent fiber components of composites. For materials of equivalent stiffness, pulp/high density polyethylene (HDPE) composites are superior to glass-filled or tale-filled HDPE on a cost-weight basis (Thomas, Rodgers,and Woodhams 1984). However, some problems such as low impact strength have yet to be overcome. It should be noted that research in this area has been done mostly with pulps produced for papermaking, where much effort is put into making the fibers flexible with hydrophilic surfaces. In the case of mechanical pulps, a large expenditure of energy is required. It is possible mechanically to produce stiff fibers coated with lignin at much lower energy consumption than is currently used (Kim and Goring 1974). Such pulps would be useless for papermaking but might proved to be the ideal fiber component for a composite. From the above it is clear that there are several important technologies on the horizon for producing new materials from wood. The development of reconstituted structural lumber is now in the final stage and will probably be an accepted technology soon. It is still very much at the bottom of the S-curve and we can expect both the process and the product to be improved as the use of products such as Parallam expands. A move to manufacture automobile panels from wood plastics composites has been announced for Korea. Yet many of the concepts for thermoplastic materials from wood are still in the laboratory stage. Considerably more applied research is required to bring them to the initial stages of development. However, the longterm potential of this approach for the production of a wide variety of useful products is very great indeed. PRIORITIES FOR BESEAKCB ON TKE VTILIZATIW OF BIOBASED M?LTBRIALS My personal judgment would place the following priorities for work on new methods of utilizing biobased materials: 1.

Lightweight Biobased Composites: This approach has great long-term significance. We shall always need better and more cost-effective materials for our mass-produced products.

2.

Biobased Packaging Plastics: Both the developed and developing world must cope with its wastes. This is an important route to allow wastes to be recycled and at the same time maintain and improve the convenience of our present packaging practices.

3.

Food from Wood and Other Unconventional

Biobased Resources:

This is a low priority because we have plenty of food for the world now and can produce much more if necessary. However, certain waste streams in our major industries (e.g., pulp and paper) could supply inexpensive raw material for food production.

CONCLUSIONS In conclusion, I judge that the program proposed by SERI is an excellent one. The priorities for the work are high. Both the staff and facilities on site are perfectly adequate for the job. Also SERI has developed cooperative arrangements with several other world-class laboratories. It is my opinion that this is a strong and much needed program and deserves funding at a level appropriate to the research proposed.

80

Polymers from Biobased Materials

REFERENCES

Kim, C. Y. and Goring, D. A. I., Cellulose Chemistrv and Technolosv, 1 (1974) 401. Morita, M. and Saka, I., J. Appl.

Polvmer Sci., 31 (1986) 831.

Parallam PSL, MacMillan Bloedel Ltd., Vancouver, B.C., 1988. Shiraishi, N., Onodera, S., Ohtani, M., (1985) 418.

and Masumoto, T., Mokuzai Gakkaishi, 1

Shiraishi, N. and Yoshioka, M., Sen-I Gakkaishi, 42 (1986) T-346. Thomas, G., Rodgers, D. K., and Woodhams, R. T., "Plastics in a World Economy," Proceedings of the SPE 42nd Annual Technical Conference and Exhibition, 1984.

6. Chitin: The Neglected Biomaterial William H. Daly Department of Chemistry Louisiana State University Baton Rouge, Louisiana

As

the U. S. chemical industry continues to focus on specialty chemicals especially those derived from biotechnology, the potential market for new materials derived from carbohydrates is growing rapidly. Multimillion poundper-year-sales are not required to ensure the success of a specialty product; however, the ability to tailor the product to a given customer's specific needs is vital. Although the total consumption carbohydrate polymers may be dwarfed by the production of petroleum-based polymers, i.e., 15 billion lb/yr of polyethylenes alone, the ability of natural polymers to meet the demands of specialty markets creates a growing niche for them in the marketplace'. The biodegradability and biocompatibility of polysaccharides can be exploited in the preparation of replacements for commercial hydrocarbon polymers or in the preparation of biopolymer synthetic polymer conjugates, which will have a minimum long-term impact on the environment. Currently, processed polysaccharides contribute significantly to the fiber, coatings, and water-soluble polymer markets. The diversity of natural polymers provides the chemist with a broad spectrum of materials, which allows him to meet the requirements for many specific applications by making modest modifications. Unfortunately, this same diversity complicates the controlled manufacture of a given derivative as each natural raw material requires unique processing conditions -for the conversion. Some of the recent progress in the industrial polysaccharide field has been reported in a series of monographs and conference proceedings published in the last three years (Yalpani 1987; Kennedy, Phillips, and Williams 1987; Kennedy et al'. 1985; Nevell and Zeronian 1985; Young and Rowe11 1986; Muzzarelli, Jeuniaux, and Gooday 1986). The reports reflect the vitality of the field, but unfortunately the contributions of U.S. chemists to these works is rather limited. An indication of the relative importance of the major polysaccharides can be gained by perusing the data in Table 1. The data are gathered from several secondary sources (C&E News, Chemical Week, Chemical Marketing Reporter) so the figures may not be absolutely accurate. However, one can obtain a perspective on the market. Starch and all its-derivatives clearly dominate the market. The total consumption of natural gums in the United States was only 5% of that of starch. However, the value of the natural gum market is substantial; i.e., alginates ($44 million), agar and carrageenan ($200 million), guar gum ($60-$70 million), xanthan gum ($50-$80 million) and miscellaneous natural gums ($182 million). Most of the natural gums are required by the food or pharmaceutical markets which allows them to command a rather high price. Further, the prices are subject to supply fluctuations based on harvest yield. Thus these markets

'Editor's note: Compare these figures with the paper and board production in the Just the United States of 129 billion lb including 104 lb of pulp in 1986. corn surplus in 1986-1987 would have made available 195 billion lb of starch.

81

82

Polymers from Biobased Materials

Table 1.

U.S. Consumption

Polysaccharide Starchb

of Major Polysaccharides Consumption Million lb/yr

Prices' S/lb

3,600

Cellulosics Acetate Carboxymethyl Hydroxyethyl Methyl Hydroxypropyl Microcrystalline

730 76 62 32 6 6

1.60-1.80 0.90-1.2s 2.07 2.24-2.05 2.17-3.00 0.60-0.90

Guar Gun? Hydroxypropyl

134 32

1.15-1.20 1.50-1.80

Alginates'

46

6.00-6.75

Xanthan Gum

13

4.54-7.00

Carrageenan'

12

3.00

Pectin

9.5-9.85

Agar Agarose"

10

250-2000

Locust Bean Gum

10

4.75-5.00

Chitin/Chitosan"

1-1.5

' Reference Chem. Mark. Rep., January 30, 1989. b Includes All Derivatives. ' Worldwide Consumption.

3.00-200.00

Chitin:

could

be penetrated

by

The Neglected

Biomaterial

83

modified starches or cellulosics, or gums produced by

fermentation processes. The fluctuations and inevitable rise in petroleum prices coupled with legislated demands to reduce the impact of the polymer industry on the environment provide impetus for polysaccharide research. The recent slump in the oil industry, which is a major consumer of water-soluble polymers for drilling applications and for tertiary oil recovery, has simply delayed the growth surge expected in the field. Genetic modification of microorganisms and more efficient fermentation processes (Betlach et al. 1987) are lowering the coat of microbial polysaccharides and opening new markets. For example, xanthan gum is already replacing plant and/or seaweed extracts in the food industry and is entering into the paint industry. When the price of petroleum riaea, applications of xanthan gum in drilling fluids and in tertiary oil recovery should quadruple the market demand to 120 million lb/yr. Although the future is not as bright for moat of the remaining polysaccharides, modest growth is expected for cellulosics through the next decade, particularly if a research investment leads to the development of improved processes and products. CIW!IN/CWPOSAN One market that is still in its infancy but has very high growth potential is the sale of chitin/chitosan products. Chitin, poly(2-amino-2-deoxy-D-glucose), is one of the moat ubiquitous natural polymers; it is second only to cellulose in natural abundance and can be isolated wherever crustacean shells are collected in large quantities. Crustacean shells are very interesting composites of chitin, polypeptides or proteins, and an inorganic filler, calcium carbonate. Chitin has been found in the shells of more than 150 mollusk species in amounts varying from 0.01% to 40% of the matrix dry weight (Poulicek, Voss-Foucart,and Jeuniaux 1986). Further, chitin is an important component of tendons and other atreaa bearing fibrous portions of marine animals, where the chitin molecules adopt a highly oriented structure (Ramakrishman and Prasad 1972; Bittiger, Husemann, and Kuppel 1969; Dweltz and Calvin 1968). Chitin is also found in insects, fungi, and yeast. Completely deacetylated chitin (chitosan) is found in various fungi (Knorr 1984). The presence of chitin in microorganisms offers an opportunity to employ fermentation technology to ensure an unlimited supply of this polysaccharide. The conformation and orientation of the matrix macromolecules is intriguing; there is an association of chitin in its &form (crystalline parallel chains) with proteins that adopt an antiparallel O-sheet conformation. The chitin polymer appears to be oriented approximatelyperpendicular to the protein-polypeptide chains 30 that the crossed-chain construction produces a mesh that contributes to the strength of the matrix. Transmission electron microscopy confirms that the ultrastructure of the matrix is a micro-mesh network of dense grains united by short, straight and thin organic connections (Figure 1) (Goffinet, Gregoire, and Voss-Foucart 1977). The sheets of the matrix are composed of several different layers; the two surface layers are composed mainly of more soluble acidic constituents and the core comprises a thin layer of chitin sandwiched between two thicker layers of proteins (Nakanara, Bevelander, and Kakei 1982). The nature of the chitin-protein association is poorly understood, primarily because the form of the linkage between the two polymers has not been characterized completely. Dissolution of native chitin composites is accompanied by degradation of both the protein ar.-i chitin componenta, 30 efforts to ascertain the structure of thabinding sites uy solution techniques have failed. Brine and Austin (1981) showed that the predominant amino acids in residual chitin after

84

Polymers

from

Biobased

Materials

partial alkaline hydrolysis were aspartic acid, serine, and glycine, suggesting that these amino acids may be involved in the chitin-protein linkage. In fact, these three amino acids comprise 35%-50% of the amino acid residues in shell Recent results reported on the nature of the bond formation during matrix. sclarotization in insect cuticle are enlightening, but introduce further complexity to the protein/chitin interactions (Schaefer et al. 1987). Proteins containing histidine and to a lesser extent, lysine residues, couple via aromatic carbon-nitrogen bonds to catechol derivatives, which in turn bind to chitin. The integral part played by chitin in natural biocomposites complicates its isolation (Figure 2). Shrimp, crab or krill shells are treated with sodium hydroxide to remove the proteins, then the inorganic salts, CaCO, and Ca,(PO,),, are extracted with hydrochloric acid. Both treatments are conducted at low temperatures to minimize deacetylation and degradation of the chitin, but approximately 15% deacetylation occurs. After rinsing, the chitin can be recovered as flaked material (Sanford and Hutchings 1987). The current price of chitin is more a reflection of the highly specialized market than of the actual cost of production. As major markets are developed, the price will drop to a range more representative of commercial polysaccharides. Chitin is normally insoluble in common solvents, but dissolution in DMAc-LiCl Controlled deacetylation to produce derivatives with mixtures is possible. approximately 50% free amine can be used to produce a water-soluble chitin (Sannan, Jurita, and Iwakura 1975; 1976; 1977). The solubility is achieved by using homogeneous hydrolysis conditions to assure random distribution of the acetyl substituents. Completely deacetylated chitin, chitosan, is prepared by treating the chitin with concentrated NaOH in the presence of NaBH,, which minimixes chain scission. Chitosan is soluble in organic acids and dilute mineral In the protonated form, it acids, as one would expect from a linear polyamine. exhibits a high charge density and is very effective in interacting with negatively chargedbiomolecules and surfaces. The neutralized formcomplexes readily with a wide variety of harmful metals such as copper, chromium, cadmium, manganese, cobalt, lead, mercury, zinc, uranium, palladium, and silver (Sanford and Hutchings 1987). Thus, a major market for chitin/chitosan is the water purification industry, where the biodegradable polysaccharides can serve both as flocculents and trace metal scavengers. Chitosan can also be employed to recover proteinaceous material from food-processing wastes for animal feeds. Because it is biodegradable and innocuous, FDA approval for its presence in these feed has been obtained. Higher technology applications of chitosan include blood coagulant in wound healing (Muzrarelli 1983), artificial kidney membranes (Hirano, Tobetto, and Noishiki 1981; Chandy and Sharma 1987), sustained release of drugs (Sawayanagi, Nambu, and Nagai 1982), immobilized enzymes and cells (Muzrarelli 1980), complexed metal catalysts (Arena 1983), and encapsulation of proteins (Hwang, Rha, and Sinskey 1986; Rha, Rodriguez-Sanchez, and Kienzle-Stenrer 1985). Thin layer chromatography on ground chitin is a method for separating amino acid mixtures (Rozylo, Gwis-Chomics, and Makinowska 1986). Chitosan triacetate exhibits high chiral recognition in the resolution of some racemates (Namikoshi et al. 1987). Both chitin and chitosan adsorb polychlorinated biphenyls in water purification (Thome and Van Daele 1986). A careful analysis of the variables associated with cobalt recovery from hydrometallurgical solutions has recently been reported (Blazques et al. 187), and the most effective means for preparing a lightly crosslinked chitin to adsorb cupric ions requires homogeneous crosslinking of water soluble chitin with glutaraldehyde (Koyama and Taniguchi 1986; Kurita, Koyama, and Taniguchi 1986). Chitin is a natural flocculant and metal concentrating agent. In fact, the Japanese are using it extensively to clean their environment.

Chitin:The Neglected Biomaterial

:c

3-K

U-K

/

=o

I-2

‘1

I-2

/

Figure 1.

/

\

\

/

n=o

Crustacean shell composite

CRUSTACEAN

SHELL COMPOSITE NaOH I

I

Figure 2.

( - Proteins)

40% NaOH (NaBH4)

Isolation of chitin and chitosan

85

86

Polymers

from

Biobased

FUT'DRB DEVELOPMENTS

Materials

INCHI4IN/CHITOSANRESEARCH

The crustacean shell can be decomposed enzymatically, reformed in a soft pliable form suitable for shaping, and then hardened in situ by complexation of minerals from the environment; this sequence of events occurs during'each molting stage. Because chitin plays a vital role in the formation of this superb biocomposite, any effort to duplicate this process in the laboratory must center on either chitin or a polysaccharide derivative with similar functionality. Biocomposites based on amino polysaccharides, peptides, and mineral salts should have applications in bone prosthesis and dental fillings. We believe that materials that will duplicate the strength and durability of chitin composites can be produced from more accessible cellulose derivatives by grafting techniques. Moreover, we are interested in using the graft copolymers of amino acids onto natural and synthetic polymers as completely biodegradable carriers for pharmacons and agricultural chemicals (Daly and Lee 1998). Natural chitin-based biocomposites are the ideal model systems for this research. The area of biopolymer/synthetic polymer interpenetrating networks (IPNs) is very interesting because the unique properties of chitin allow homogeneous mixing of monomers with chitosan, gelation of the chitosan to form a stiff matrix, then polymerization of the monomer to produce the IPN. The gel can be set by acylation of chitosan with long chain fatty acid anhydrides, which could induce liquid crystalline order in the matrix. Monomers containing acidic functional groups could serve as solvents so that no volatiles would need to be removed from the IPN. The IPNs could be prepared as membranes with high chelating capacity for water purification or active ion transport. The presence of hydrocarbon-based copolymers would enhance the hydrolytic stability of the polysaccharide component. Alternatively, the gels could be molded into pellets, polymerized, and then hardened by exposure to calcium ions. These IPNs could have applications as prosthetic materials. By selecting appropriate comonomers, tough, lightweight composites, which would be formed in the gel state and then set by photopolymerization, could be developed. The affinity for metals exhibited by the chitin/ chitosan matrix should simplify the application of coatings and allow facile metallation of the composite surfaces. The most rapidly growing area of applications is that of membrane materials. Both chitosan and chitosan/polyanionic composite membranes have proved useful in a diverse range of applications including active transport of organic ions (Uragami., Yoshida, and Sugihara 1988), selective transport of alkali metal ions (Kikuchi, Kubota, and Tanaka 1986), pervaporation of aqueous alcohol solutions (Uragami, Saito, and Takigama 1988), dialysis of blood (Schmer 1985), sustained release of pharmaceuticals (Mikazalo, et al. 19881, and cell culture (Popowicz et al. 1985). Techniques for casting chitin membranes from DMAc-LiCl solutions have been developed (Aiba et al. 1985). The compatibility of chitin with natural and synthetic polymers affords many opportunities to produce composite membranes with very high selectivity for a given substance. Composite membranes of chitosan and transition or noble metals could serve as reactive catalysts; complexes with more inert metals would exhibit unique properties in separation processes. If the complexed metals would serve as nucleating agents for other metal complexes, precursors for ceramics could be produced. The high affinity of chitosan for proteins suggests that it is ideally suited for enzyme or cell immobilization in bioreactors. In fact, chitosan membranes could serve as substrates for cell cultures. New applications for chitin/chitosanappear practically every day; unfortunately, U.S. chemists and chemical engineers are not participating in this development. A Chemical Abstracts survey of the literature from 1985 to present uncovered 50 citations on chitin/chitosan membranes. Japanese scientists published 30 of

Chitin:

The Neglected Biomaterial

87

these articles or patents--a sharp contrast to the American output of 2 papers. A more general survey on applications of chitin/chitosan revealed 40 additional references. The source distribution appeared a little better, i.e., 20 Japanese to 5 American but three of the American articles were reviews. Contributions from U.S. research groups are limited and the number is continuing to diminish. While we have complacently assumed that polysaccharide technology is a mature field, our foreign competitors continue to advance at a rate that could drive us out of the market in a few years. We are allowing this very vital field to evolve overseas. REFERENCES

Aiba, S., Izume, M., Minoura, N., and Fujiwara, Y., Carbohvdr. Polvm., 5 (1985) 285; Br. Polvm. J., u (1985) 38. Arena, B. J., U. S. Patent 4,361,355, 1983. Betlach, M. R., Capage, M. A., Doherty, D. H., Hassler, R. A., Henderson, N. M., Vanderslice, R. W., Marelli, J. D., and Ward, M. B., "Genetically Engineered Polymers: Manipulation of Xanthan Biosynthesis," in Industrial Polvsaccharides, Genetic Enqineerinq, Struhture/Provertv Relations and ADDlications; M. Yalpani, ed., Proqress in Biotechnoloqy, 3, Elsevier, New York, (1987) pp. 35-50. Bittiger, H., Husemann, E., and Kuppel, A., J. Polvm. Sci., Part C, a

(1969) 45.

Blazques, I., Vincente, F., Gallo, B., Ortix, I. and Irabien, A., J. ADP~. Polvm. sci., 33 (1987) 2107. Brine, C. J. and Austin, P. R., Camp. Biochem. Phvsiol., m Chandy, T. and Sharma, C. P., Polvm. Mater. Sci. Enq., 57

(1981) 173. (1987) 299.

Chem. Mark. Rep., January 30, 1989. Daly, W. H. and Lee, S., J. Macromol.

Sci.-Chem., A25

Dweltz, N. E. and Colvin, J. R., Can. J. Chem., 45 Goffinet, G., Gregoire, C., and Voss-Foucart, Biochem., fi (1977) 849. Hirano, S., Tobetto, K., andNoishiki,

(1988) 705.

(1968) 1513.

M. F., Arch.

Internat. Phvsiol.

Y., J. Biomed. Mater. Res., 2

(1981) 903;

TransHwang, C., Rha, C. K. and Sinskey, A. J., "Encapsulation with Chitosan: membrane Diffusion of Proteins in Capsules," in Chitin in Nature and Technoloqy R. Muzzarelli, C. Jeuniaux, and G. W. Gooday, eds., Plenum, New York, (1986) pp: 389-396. Kennedy, J. F., Phillips, G. O., and Williams, P. A., eds., Wood and Cellulosics, Industrial Utilization, Biotechnoloqv, Structure and Properties, Halsted Press, New York, (1987). Kennedy, J. F., Phillips, G. O., Wedlock, D. J., and Williams, P. A., eds., Cellulose and Its Derivatives, Chemistrv, Biochemistrv, and Acplications, Halsted Press, New York, (1985). Kikuchi, Y., Kubota, N., and Tanaka, H., Nippan Abst 105, p. 75502. AI

K., K., 2

(1986) 706; A Chem

88

Polymers

from Biobased

Materials

Knorr, D., Food Technolosy, 1

(1984) 85.

Koyama, Y. and Taniguchi, A., J. Aoul. Polvm. Sci., 31 (1986) p. 1951. Kurita, K., Koyama; Y., and Taniguchi, A., J. Aool. Polvm. Sci., 31 (1986) 1169. Mikazalo, S. Yamaghuchi, H., Yokouchi, C., Takada, M. and Hou, W., Chem. Pharm. (1988) 4033. Bull., 6 Muzzarelli,

R. A. A., Carbohvdr.

Polvm., 3

Muzzarelli,

R. A. .A., Enzvme Microb. Technol., 1

Muzzarelli, R., Jeuniaux, C., and Gooday, Technolosv, Plenum, New York, (1986). Nakanara, H., Bevelander,

(1983) 53. (1980) 177.

G. W., eds., Chitin

G.,,and Kakei, M., Venus, 39

in Nature

and

(1982) 205.

Namikoshi, H., Shibata, T., Nakamura, H., Okamota, I., Shimizu, K., and Toga, "Chromatographic Optical Resolution on Cellulose and Other Polysaccharide Y DBLivatives," in Wood and Cellulosics, Industrial Utilization, Biotechnolosv, Structure and Prooerties, J. F. Kennedy, G. 0. Phillips, and P. A. Williams, eds., Halsted Press, New York, (1987) pp. 611-617. Nevell, T. P. and Eeronian, S. H., eds., Aoolications, Halsted Press, New York, (1985).

Cellulose

Chemistrv

and

its

Popowicz, P., Kurzyca, J., Dolinska, B. and Popowicz, J., Biomed. Biochim. Acta, 44 (1985) 1329. Poulicek, M., Voss-Foucart, M. F., and Jeuniaux, C., "Chitinoproteic Complexes and Mineralizati.on in Mollusk Skeletal Structures," in Chitin in Nature and Technoloav, R. Muzzarelli, C. Jeuniaux, and G. W. Gooday, eds., Plenum, New York, (1986) pp. 7-12. Ramakrishnan,

C. and Prasad, N., Biochem. Biophvs. Acta, 261

(1972) 123

Rha, C. K., Rodriguez-Sanchez, D., andKienzle-Sterzer, C., in Novel Anulications of Chitosan in Biotechnoloqv of Marine Polvsaccharides, Colwell, R. R., Pariser, E. R., and Sinskey, A,. eds., Hemisphere, Washington, D. C., (1985) pp. 283-311. Rozylo, J. K., Gwis-Chomicz, (1986) 3447.

D. and Makinowska,

I., J. Licf. Chromatour.,

Schaefer, J., Kramer, K. J., Garbow, J. R., Jacob, G. S., Stejskal, Hopkins, T. L., and Speirs, R. D., Science, 235, (1987) 1200.

2

E. O.,

Sanford, P. A. and Hutchings, G. P., "Chitosan-A Natural, Cationic Biopolymer: Commercial Applications," in Industrial Polvsaccharides, Genetic Enuineerina, Structure/Pronertv Relations and Applications; M. Yalpani, ed., Prosress in Biotechnolosy, 3, Elsevier, New York, (1987) pp. 363-376. Sannan, T., Kurita, K., and Iwakura, Y., Makromol. Chem., 176 (1975) 1191; 177, (1976) 3589; 178 (1977) 3197. Sawayanagi, Y., Nambu, N. and Nagai, T., Chem. Pharm. Bull, 30 (1982) 4213, 4216. Schmer, G., Ger. Offen. DE 3341113 Al, 23 May 1985.

Chitin:

The Neglected

Biomaterial

89

Thome, J. P. and Van Daele, "Chitosan as a Tool for the Purification of Waters," in Chitin in Nature and Technology R. Muzzarelli, C. Jeuniaux, and G. W. Gooday, eds., Plenum, New York, (1986) pp: 551-554. Uragami, T., Saito, M., and Takigawa, (1988) 361.

K.,

Makromol. Chem. Ranid Commun., 2

Uragami, T., Yoshida, F., and Sugihara, M., Sep. Sci. Technol., 23 (1988) 1067. Industrial Polvsaccharides, .Genetic Enaineerinq, Yalpani, M., ed., Structure/Propertv Relations and Avplications; Progress in Biotechnolocv, 3, Elsevier, New York, (1987). Young, R. A. and Rowell, R. M., eds., Cellulose, Structure, Modification and Hvdrolvsis, John Wiley & Sons, New York, (1986).

7. Starch-Based Plastics Ramani Narayan Michigan Biotechnology Institute Lansing, Michigan

IRl'RODUC!SION Starch is a polymer of anhydrodextrose units (Rahler and Cardus 1971). The basic repeating unit involves the linkage of successive D-glucose molecules by a-D-1,4-glycosidic bonds. Two distinct structural classes exist: linear and branched (Figure 1). Amylose, the linear component, is the lower molecular weight polymer, having an average molecular weight of about one-half million. Amylose makes up approximately one-fourth of the weight of starch. The preponderant polysaccharide is amylopectin, consisting, like amylose, of mostly 1,4-linked a-g-glucopyranosyl units, but with branched chains occurring through a-1,Glinkages at about 1 in every 25 Pglucopyranosyl units. Some measurements show amylopectin to have a molecular weight of up to 10 million. The abundant hydroxyl groups on the starch molecules impart the characteristic hydrophilic properties. The polymer attracts water and itself through hydrogen bonding. The self-attraction and crystallization tendencies are most readily apparent for the amylose or straight chain component (Wurzburg1978). The association between the polymer chains results in the formation of an intermolecular network that traps water. At sufficient starch concentrations, (>3%) gels are produced, whereas in dilute solutions, the associated forms may precipitate. Precipitation is particularly evident for amylose. Amylopectin association is interrupted because of its highly branched character. However, at low temperatures, even amylopectin will associate, resulting in decreased water binding and gel formation. As would be expected from their differences in structure, amylose and amylopectin exhibit different properties. Amylose forms strong flexible films and has value as a coating agent. The branched component forms films with poor properties but finds wide usage as a thickening agent, especially in food and paper applications. This review concentrates on work originating from the Northern Regional Research Center of the U.S. Department of Agriculture, the commercial technologies practiced through January of 1989, and the technology developed by the author and coworkers while at Purdue University. NORTHERN REGIONAL RRSRARCR CRWTRR TRCRWOIOGIES Starch as Filler Otey (1976) has reviewed the current and potential applications of starch products in plastics. He and his co-workers have evaluated starch as an inert filler in poly(viny1 chloride) (PVC) plastics, as a reactive filler in rigid urethane foams, and as a component in poly(viny1 alcohol) (PVA) films. Three techniques were evaluated for incorporating large amounts of starch as a filler in PVC plastics (Westhoff et al. 1974). In one, a starch derivative was coprecipitated with a PVC latex and the coprecipitate was filtered off, dried, hammer milled to a fine powder, blended with dioctyl phthalate (DOP), and molded in an aluminum cavity. In a second, starch was gelatinized and mixed with PVC latex,

90

Starch-Based Plastics

CH20H

Jqp+!F&$Jo_ OH

OH

a

-D-(1-34) Bond

AMYLOSE - LINEAR POLYMER

a

a

-D-(1+6) Bond

-D-(1-*4) Bond

AMYLOPECTIN - Branched Polymer Figure 1.

Chemical structure of the components of starch

91

92

Polymers

from

Biobased

Materials

and water was removed from the mixture in an oven. The dry product was milled, mixed with DOP, and molded as before. The third technique involved dry blending starch, PVC, and DOP on a rubber mill and then molding. Tensile strength remained good even with as much as 50% starch in the plastic (Table 1). Clarity of the plastics was also good except for those made by dry blending, but elongation decreased rapidly as the starch level increased. The three formulations were also blended on as rubber mill until films could be removed from the rolls. Properties of the film were measured and their longevity in Weather-0-MeteiB and outdoor exposure tests were evaluated (Table 2). By varying the composition, films were obtained that lasted from 40 h to 900 h in the Weather-O-Mete??' and from 30 days to more than 120 days in the soil. All samples tested under standard conditions with common soil microorganisms showed mold growth, with the greatest amount of growth recorded for samples containing the highest amount of starch. One area for application of biodegradable plastic films is as an agricultural mulch. Mulch is now used for many vegetable crops to control soil moisture and temperature, to reduce nutrient leaching, and to prevent weed growth. According to Otey (1976), in 1973 polyethylene served as mulch for nearly one-half of the 40,000 acres of tomatoes, and all the 2000 acres of strawberries grown in Florida. Owing to its nonbiodegradability, the polyethylene mulch must be removed between growing seasons at a cost of up to $100 per acre. The mulch cannot be reused because holes are punched in it during the planting of seedlings. Considerable interest has been expressed concerning use of a mulch film, which would degrade and thus obviate the need for removal. Griffin reported that starch can be incorporated into low-density polyethylene film to impart biodegradable properties (Griffin.1973). Based on this work, Coloroll Ltd., of England, is now producing a polyethylene bag that contains 7%-10% starch and is reportedly biodegradable. The rights to thi.stechnology were purchased by St. Lawrence Starch (Canada), which is marketing these plastics. This technology is discussed later. Otey and co-workers (Otey et al. 1974) are investigating starch-PVA films that may have application as a degradable agriculturalmulch. In preliminary studies, a composition containing 60%-65% starch, 16% PVA, 16%-22% glycerol, l%-3% formaldehyde, and 2% ammonium chloride was combined with water to give 13% solids, and heated at 95°C for 1 h. The hot mixture was then cast and dried at 130°C to a clear film. Films, on removal from the hot surface, were passed through a solution of PVC to coat the film with a water-repellent coating. Uncoated films remained water-insoluble on soaking for 16 h, but the wet strength was low. Coated films retain good strength even after water soaking. Weather-0-MeterG tests suggest that films with 15%-20% PVC coating might last three to four months in outdoor exposure. For several years, one company has been using the starch-PVA technology to produce a water-soluble laundry bag, for use by hospitals, to contain soiled'or contaminated clothing prior to washing. The bags and their contents are placed In order to provide directly into washing machines, where the bag dissolves. enhanced solubility, a derivative of the pearl starch used by Otey is substituted. Such water-soluble bags are also being suggested for packaging agricultural chemical pesticides to improve safety during handling. Starch-Urethanes Not only can starch be mixed with synthetic polymers and exhibit utility as a filler, extender, or reinforcing agent, it can also become an integral part of

Starch-Based Plastics 93

Properties of Plastics Made with Starch and 25 Parts of DOP per 100 Parts of PVC?

Table 1.

Tensile Strength psi

Starch %

Elongation %

Specific Gravity

Fungi Resistanceb

&precipitate: Starch Xanthate-PVC (Geon 151R) 2,560 133 1.27 0 2,720 66 1.23 1 2,240 8 1.36 4 1,920 5 1.35 3 Co-concentrate: Starch-PVC (Geon 151) 3,650 140 --0 3,220 44 1.24 1 3,360 13 1.31 4 Dry Mix: Starch-PVC (Geon 126) 2,600 150 1.25 0 2,170 110 1.27 1 1,370 31 1.30 4 Dry Mix: Starch-PVC (Geon 102) 3,600 140 ___ 0 2,930 104 --___ 3,040 35 ---_-

0

12.3 32.9 51.0 0 12.9 34.0 0

13.4 38.2 0

30 40

Geon is a registered trademark of B. F. Goodrich Chemical Co. (a) DOP = dioctyl phthalate: PVC = polyvinyl chloride. (b) ASTM D-1924-70, fungus growth: 0 - none; 1 = 10%; 2 = lo-30%; 4 = 60-100%. (C) Relative values: 0 = completely clear: 100 = opaque. Westhoff, R. P., Otey, F. H., Mehltretter, C. L., and Russell. C. R.. Inn. Eng.

Chem..

Prod. Res. Dev., I3.

123 (1974).

Clarityc

12 12 16 20 13 16 15

6 43 85 ___ 70 78

3 = 30-60%;

94

Polymers from Biobased Materials

Table 2. Starch Type Whole Xanthate Gelatinized Gelatinized

Properties of Starch-PVC-DOP Films' PVC Resin

%

Type

25.1 40.5 44.0 36.4

Geon 126 Geon I51 OpaIonR Geon 151

% 57.5 39.7 37.2 36.4

DGP, PHRb 25 50 50 75

Opalon is a registered trademark of Monsanto Co. (a) PVC = polyvinyl chloride: DOP = dioctyl phthalate. (b) Parts of DOP per 100 parts of PVC. (C) Films showed major deterioration after given time.

Tensile Strength, psi

Outdoor Exposure, days 120 > 150 52 66

1,720 1.860 740 420

Monsanto

Co.

Westhoff, R. P., Otey, F. H., Mehltretter, C. L., and Russelk C. R., Id. Eng, Chem., Prod. Rex Dev., 13, 123 (1974).

Starch-Based

Plastics

95

such polymers through chemical bonds. Urethane is an example of a system where Elastomers have been prepared starch has been chemically bonded to a resin. using starch as a filler and crosslinking agent for diisocyanate-modified polyesters (Boggs 1959). Dosmann and Steel (1961) reported that starch can be incorporated into urethane systems to yield shock-resistant foams. Bennett, Otey, and Mehltretter (1967) found that up to 40% starch can be incorporated into rigid urethane foam and that such foams are more flame resistant and more readily attacked by microorganisms. Starch-Polvethvlene

@lb) Blenda with Ethvlene-Acrylic

Acid Co~olvmer

(BAA)

Otey et al. (1979) discovered that compositions of ethylene-acrylic acid copolymer (EAA) and a starchy material can be formed into films that are flexible, water resistant, heat stable, and biodegradable. These films were formed by either casting, simple extruding, or milling the starch-EAA compositions. All are relatively slow processes that are considerably more expensive than the more conventional extrusion blowing technique. The relatively high processing cost coupled with the high price of EAA compared to PE tend to diminish this composition's potential for achieving large-scale commercial success. Also, at certain starch levels needed for achieving desired mechanical properties, the optimum degrees of biodegradability and ultraviolet (W) stability are compromised. They then discovered property improvements by adding an agent to neutralize part or all of the acidic portion of the EAA and by blowing the formulation at a moisture content in the range of about 2%-10%. The preferred neutralizing agent was ammonia in either its anhydrous or aqueous form. Agritech Industries based in Illinois is trying to commercialize this technology in cooperation with University of Illinois.

Starch Graft

CoDolvmerization

Another approach to chemically bond natural polymer-synthetic polymer compositions is through graft copolymerization. This technique has received considerable attention from scientists at the Northern Regional Research Center, especially for those systems where the natural polymer is starch. Basically, the procedure used for synthesizing starch graft polymers was to initiate a free radical on the starch backbone and then allow the radical to react with polymerizable vinyl or acrylic monomers. A number of free-radical initiating methods have been used to prepare graft copolymers. These may be divided into two broad categories, chemical initiation and irradiation. The choice depends in part on the particular monomer or combination of monomers to be polymerized. A conceptual structure of a starch graft polymer is shown in Figure 2. Both a chemical and an irradiation initiating system were employed, and a wide variety of monomers, .both alone and in selected combinations, were graft polymerized onto Fanta and Bagley (1977) have reviewed this work along with that of starch. others in the area of starch graft copolymers. For plastic or elastomeric copolymer compositions that can be extruded or milled, monomers such as styrene, isoprene, acrylonitrile, and various alkyl acrylates and methacrylates were employed. Starch-g-polystyrene, -poly (methyl methacrylate), -poly (methyl acrylate), and -poly (methyl acrylate-gg-butyl acrylate) polymers have been prepared with approximately 50% add-on and evaluated for extrusion processing characteristics (Gugliemelli et al. 1974). A 2O:SO (by weight) mixture of starch-g-polystyrene and commercial polystyrene produced an extrudate that was filled with particles of unfluxed graft copolymer after two passes through the extruder at 15O'C.

96

Polymers

from

Biobased

Materials

r

’

Graft Chains from Cl$ w

-

Wt. % Graft 10.50

When X = -CQH, -CCN&, -CQ(Cti&h&Ci products are 40 soluble and useful as thickeners, absorbents, and flocculants.

sizes,

adhesives,

When X = CN, -CQq products

are 40

33 insoluble

and -potentially

useful as resins and plastics. Figure 2.

Conceptual structure of starch graft polymers

Starch-Based Plastics

97

for starch did not greatly Addition of glycerol to the mixture as a plasticizer However, when the graft copolymer was extruded improve extrudate properties. at 115'C in the absence of additives, a continuous, well-formed extrudate was produced. Tensile strengths for specimens milled from the extrudate were in the range 7500 - 9100 psi (Table 3). Two starch-q-poly (methyl acrylate) products, one prepared from granular starch and other from gelatinized starch, were .processed by extrusion under various The graft copolymer prepared from granular starch was extruded conditions. (three passes) through a 1 x 0.020 in slit die at 160°C. The smooth and translucent extruded ribbon exhibited good tensile strength (3000 psi) and little die swell. Lower extrusion temperatures produced an extrudate that contained unfluxed polymer; at 125"C, only a crumbly mass was obtained. The graft copolymer prepared from gelatinized starch was extruded (one pass) at 125°C with a die temperature of 140°C to give extrudate that resembled that obtained from granular starch, but was less brittle. When extruder and die temperatures were lowered to lOO"C, a continuous plastic was still produced, although there was an appreciable amount of unfluxed polymer. Tensile strength of the higher temperature extrudate was on the order of 2500 psi, and die swell was minimal. Prolonged soaking of the extrudate in water at room temperature produced a material that was white , soft, and pliable and that showed appreciable increases in both weight and thickness (Table 4). The specimen surface, however, was not sticky, and the plastic remained continuous and showed no tendency to disintegrate. To estimate biodegradability, a portion of the extrudate was incubated for 5 days at 25°C with three different cultures in a nutrient solution Asoerqillus niser and Trichoderma viride gave as suggested by ASTM DI924-70. goodgrowth and sporulation. Penicillium funiculosumproducedlittle sporulation but gave good growth. Ceric-initiated graft polymerization of acrylonitrile, methyl acrylate, and chloroprene onto gelatinized cationic starch yields copolymers with up to 60% polyvinyl side chain (Gugliemelli et al. 1976). When starch-graft reaction mixtures of any of the copolymers are sonified at 20 KHz for l-3 min, latexes result that dry to clear adhesive films at room temperature. Viscosity of the sonified Molecular dispersions of about 0% concentration is in the range lo-40 cP. weights of synthetic side chains are influenced by the type of cationic charge on the starch and on the type of stirring action employed during the polymerizations (Table 5). Number-average molecular weight in the range of 100,000 to 1 This work has recently been extended to the million are readily obtainable. preparation of starch-q-poly (isoprene-co-acrylonitrile) latexes (Gugliemelli n.d.). Preparation of latexes with higher solids content at low viscosities and evaluation of the latexes in various end-use applications continue. A wide variety of other monomers have been graft polymerized onto granular and gelatinized starch. Several of the graft polymers show promise as, among other things, thickeners for aqueous systems, flocculants, clarification aids for wastewaters, and retention aids in paper making. The polymer that has received the most attention, and is now being marketed,by three U. S. companies, is made by graft polymerizing acrylonitrile onto gelatinized starch and subjecting the resulting starch-q-polyacrylonitrile graft copolymer to alkaline saponification to convert the nitrile functionalities to a mixture of carboxamide and alkali metal carboxylate groups (Figure 3). Removing the water from this polymer provides a solid that absorbs many hundreds of times its weight of water, but does not dissolve (Figure 4). Because of its ability to absorb such large amounts of water, and to do so rapidly, it has been named Super Slurper. As of January 1989, the U. S. Department of Agriculture has granted 21 nonexclusive licenses

Table 3.

Polysaccharide

%

Monomer,

No. 1.

Styrene

2. Styrene

g

(40) (40)

3. Methyl methacrylate (100) 4. Methyl acrylate (300) 5. Methyl acrylate (120) 6. Methyl acrylate (63.7) 7. Methyl acrylate (7.5) and Butyl acrylate (75) (a) add-on (b) (~1

Polysaccharide. g granular starch (40) granular starch (40) gelatinized starch (100) granular starch (250) gelatinized starch (100) cellulose (53.2) gelatinized starch (100)

Weight gain: 8 add-on determined by loss in UTS: Ultimate tensile Crude graft copolymer,

Water, ml

0

Graft Copolymers

Initiator

2 2 F

Add-ona

Weight Gain

Weight Loss

Graft

UT!+

MW

psi

10

6cC0, 1.0 mrad

48~

_--_

----

10

6oC0, 1.0 mrad

40

41

710,000

---

2,500

Ce+s

41

50

1,360.OOO

---

2,000

Ce+4

39

41

845,000

3,000

2,500 2,000

Ce” Ce*

44 49

42 ___

861,000 ---

2,500 ___

2,500

Ce+t

53

-__

---

___

7,500-9,100

determined by gain in weight of starch after graft polymerization. Weight loss: weight of graft copolymer after depolymerization and removal of starch. strength of the extruded plastic. homopolymer not extracted.

Gugliemelli, L. A., Swanson, C. L., Baker. F. L.. Doane, W. M., and Russell, C. R., J. Polymer Sci., Z2( 11). 2683 (1974).

%

s m & k-2 2L

Z (D 2. L VI

Starch-Based Plastics99

Effect of Water on Starch-q-Poly(Methy1Acrylate) Extrudate'

Table 4.

% Increase Immersion Time, hr

In Weight

0 22.5 476.0

In Thickness

-mm

___

54 53

41 41

In Width ___

12.5 12.5

(~1 1 X 0.222 in. extrudate from polymer 6, Tuble 3. Extruded temperature of 14OoC . Soaked in water at room temperature.

at 125OC with die

Gugliemelli, L. A.,Swanson, C. L., Baker, F. L., Doane, W. M., and Russell, C. R., J. Polymer Sci., 12(11), 2683 (1974).

Table 5.

Influence of Cationic Functionality (CR) on Starch on Number-Average Molecular Weight (y) of Grafted Polyacrylonitrile [poly(AN)]

CES

N, %

Agitator

TA”

0.42 0.42 0.39 0.39

SF SHd ST SH

;

QA

Poly(AN).

AGU/Ce(IV)

Starch Graft Product, N,%

40 40 45 45

12.25 13.50 13.07 12.81

1,094,000 506,000 232,000 178,000

M,

(a) Cationic starch (24 g), gelatinized in 600 ml of water by heating under nitrogen for 30 min. was cooled to 25oC, and reacted with AN and cerium (IV) reagent. The AN:AGU molar ratio was 3.1 and the reaction time, 3 hr. (b) Tertiary amine. (~1 Reaction was conducted in a round-bottomed flask using a rotating blade stirrer at 240 rpm. (d) Reaction was conducted in a stoppered Erlenmeyer flask-clamped to a Burrell wrist-action shaker. Gugliemelli, L. A., Swanson, C. L., Doane, W. M., and Russell, C. R.. ibid., Polymer Left. Ed., 14(4), 215 (1976). Gugliemelli. results.

L. A., Northern

Regional

Research

Center,

unpublished

100

Polymers

from

Biobased

Materials

Ce+4

Starch Free Radical + C&

-CHCN --b

[Complex]

Starch --) Free + Ce’3+ H + Radical

Starch I

Starch-polyacrylonitrile Graft Copolymer Figure

3.

St arch

Ceric

ion-initiated graft polymerization onto starch

+ NaCtl -%

Starch

Saponified Starch-polyacrylonitrile (Viscous dispersion) Figure 4.

Saponification of starch-acrylonitrilegraft copolymer

Starch-Based Plastics101

to parties interested in practicing the technology covered in the four patents (Weaver et al. 1976) issued for this work with the starch graft polymer. Aqueous dispersions of saponified starch-q-polyacrylonitrilecan be cast to yield films on drying. These films are brittle but can be plasticized to improve flexibility. They will absorb several hundred times their weight of distilled water to give clear sheets of gel, which remain strong enough to maintain their integrity. Also, despite a 3Q-fold increase in surface area in imbibing water, the exact shape of the dry film is retained (Weaver el al. 1974). Reducing the pH of the water to near 3 causes the gel sheet to retract to its original size; raising the pH back to near 7, or higher, causes the film to return to a highly swollen gel sheet. Other forms of the absorbent polymer are obtained by alternate methods of drying. Alcohol precipitation yields a granular or powdery product, whereas drum-drying affords flakes and freeze-drying gives spongy mats. Selected end-use applications may dictate the most desirable form of the product. Interest has been expressed in the powder and mat forms for application as an additive to absorbent soft goods such as disposable diapers, bandages, and hospital bed pads. The ability of the absorbent polymer to retain most of its absorbed fluid under pressure is a desirable property for such applications (Weaver, Fanta, and Doane 1974) (Table 6). Under a pressure of 45 x g, a Super Slurper product that had absorbed 640 times its weight of water still retained 409 times its weight. Cellulose fibers, on the other hand, initially absorbed 40 times their weight and retained only 2.1 times their weight under this pressure. Agricultural applications, such as seed and root coatings and water-retaining additives for fast-draining soils, appear most promising for Super Slurper. Large-scale field tests have been made and, for such applications, the powder, granular, or flake forms seem most appropriate. The utility of the salt form of the starch-q-polyacrylonitrilecopolymer as a thickening agent for aqueous systems has been evaluated (Gugliemelli et al. 1969). These early studies showed that the saponified product was readily recoverable from the saponification mass by lowering the pkl to near 3. This lowering converts the carboxylate groups to the acid form; thus, the polymer precipitates and can be easily recoveredby filtration or centrifugation. Resuspension of the dry product in water and adjustment of the pH to near neutrality produces a highly viscous dispersion at low solids content. The viscous dispersions show visible evidence of highly swollen gel particles. Taylor and Bagley (1974) confirmed the presence of a substantial gel fraction by isoionic dilution experiments, which failed to yield linear reduced viscosity-concentrationplots, and by an ultracentrifugation study, which showed that water dispersions of the polymer contained only about 20% solubles. They propose that the tremendous thickening action of the polymer in water is due to the nearly complete absorption of solvent by gel, which gives a system consisting of highly swollen, closely packed deformable.gel particles. Neither the minor amounts of graft copolymer in solution nor the size of the gel particles exerts a large influence on rheological properties. Under high-dilution or high-ionic strength conditions, solvent is in excess: the gel particles are no longer tightly packed; and the viscosity, therefore, drops sharply. Starch Xanthate Processing

of Rubber:

The use of starch as a replacement for carbon black has been studied in detail Crosslinked starch xanthate can be at the Northern Regional Research Center.

102

Polymers from Biobased Materials

Simulated Absorbency

Table 6.

of H-SPAN vs. Cellulose Fibers g Fluid/g

Absorbent Cellulose

fibers

Free Draining

Fluid

Absorbent

45 xg

Water Simulated

urine

40 32

2.1 1.8

H-SPAN (insoluble) air dried

Water Simulated

urine

648 54

409.0 40.0

H-SPAN (insoluble) drum dried

Water Simulated

urine

896 60

180 xg

H-SPAN is the starch based super slurper product (starch-g-poly propenamide-co-2-propenoic acid, mixed sodium and aluminum salts) and marketed by Grain Processing Corporation Weaver, M. O., Fanta, G. F.. and Doane, W. M., Proc. Tech. Symp., Product Technol., International Nonwovens and Disposables Assoc., Washington, DC, March 5-6, 1974, p. 169.

Nonwoven

1.05 1.0

37.0

(2-

Starch-Based

Plastics

103

incorporated into rubber to provide reinforcement to the same extent as medium grades of carbon black (265) (Table 7). Current domestic use of carbon black in rubber is about 3 billion pounds, virtually all of which is derived from petroleum. By modifying the process for incorporating the starch derivative into rubber, a simple and economically feasible process was developed for making powdered rubber, a long-sought goal of the rubber industry. A crosslinked starch xanthate-rubber coprecipitate containing 3%-S% starch and 95%-97% rubber can be readily blended with various rubber additives (Table 9) and injection-molded to finished rubber goods with good properties (Abbott, Deane, and Russel 1973; Abbott et al. 1975). Preliminary calculations, based on an estimated 50% market penetration, suggest that the United States could save 2.5 billion kWh annually by using the new process, shown in Figure 5.

Encapsulation A new technology for encapsulating

a broad range of chemical pesticides within a starch matrix, to improve safety in handling and reduce loss of pesticide in the environment because of volatility, leaching, and decomposition by light, has been published (Shasha, Deane, and Russell1976; Doane, Shasha,and Russell1977). The procedure, shown in Figure 6, is based on starch xanthate. It consists of dispersing the active agent in an aqueous starch xanthate solution and subsequently crosslinking the starch xanthate either oxidatively, with multivalent metal ions, or with dysfunctional reagents such as epichlorohydrin. Cereal flours, which contain about 10% protein along with starch, can also be xanthated and used as an encapsulating matrix. Upon crosslinking, which is effected within a few seconds under ambient conditions, the entire mass becomes gel-like. On continued mixing, for an additional few seconds, it becomes a particulate solid that can be dried to low moisture content with minimal, or no, loss of the entrapped chemical. That only a single phase is.produced on crosslinking, with no supernatant, is important in assuring essentially complete entrapment of both water-soluble and water-insoluble pesticidal chemicals. Both solid and liquid pesticides have been encapsulated by this procedure. Where the pesticide is a liquid or finely divided solid, it is added as such to the aqueous solution. For pesticides provided as granular solids, they are first We have dissolved in any appropriate solvent and then added to the solution. made formulations containing up to 55% (by weight) of liquid pesticides and even higher amounts of solid ones. Starch-encapsulated formulations have excellent shelf life: no loss of pesticide was recorded on storage in closed containers for up to a year. During storage in open containers for several weeks, loss of even volatile pesticides was neqligible. However, when products are placed in water or soil, an active agent is released from the matrix. Other polymers can be incorporated.readily into the products to modify release properties. Polymers like polystyrene, polyethylene, and PVC are dissolved in a small amount of an appropriate solvent, such as benzene or acetone, then added to the xanthate solution. Poly(styrene-butadiene), commercially provided as a latex, is conveniently added in this form. Upon crosslinking the xanthate, the other polymers are entrapped along with active agents. Another modification easily made provides products that are doubly encapsulated. This is achieved by adding more starch xanthate, either alone or containing another polymer, after the initial crosslinking reaction has been effected, and Schreiber (1976) recently reported then adding additional crosslinkage agent. results of greenhouse and field tests of two crosslinked starch xanthate-EPTC One formulation contained 14% EPTC (S-ethyl dipropylthiocarbamate) products.

104

Table

Polymers

7.

from

Biobased

Materials

Comparative

Vulcanizate Properties of Extrusion Processed StarchSBR and Black Reinforced SBR Rubbers

Vulcanizatea 50 phr starch xanthide-SBR 1,500 50.4 phr FEF black-SBR 1,500 50.4 phr SRF black-SBR 1.500 50.4 phr FT black-SBR 1,500 50.4 phr MT black-SBR 1,500 Premium grade passenger tread 100 level passenger tread First line competitive tread

Hardness Shore A

Tensile psi

Elongation %

70 63 58 51 51 . 58 56 58

2,730 2,900 2.380 1,880 1,340 2,990 2,550 2,290

310 360 480 690 510 600 620 590

(a) Blacks used were fine extrusion furnace black (FEF), semireinforcing JSRF), fine thermal black (FT), and medium thermal black (MT). The use of starch as a replacement rubber.

for carbon

black

black in processing

Abbott, T. P., Doane, W. M., and Russell, C. R., Rubber Age, IM(8). (1973).

43

Abbott, T. P., James, C., Doane. W. M., and Russell, ‘C. J.. J. Elust. Past., 7(2), 114 (1975).

Starch-Based Plastics

Table 8.

105

Formulation of a Cross-Linked Starch Xanthate Rubber Coprecipitate Containing 3%-5% Starch and 95%-97% Rubber Blended with Various Rubber Additives

Form of Polymer Base Compound Type1 I. II. III. IV. V. VI.

Shoe heel Shoe sole Tire tread Mechanical compound (mixed polymer base) Mechanical compound (SBR polymer base) White NBR compound

Slab

Powdered Rubber With 5 or 6 phr SXb

Powdered Rubber With 20 phr SX

1.s 1I.S 111:s

I.5 II.5 111.5

1.20 11.20 111.20

1V.S

IV.5

IV.20

$1:

v.5 VI.5

v.20 VI.20

(a) Roman numerals correspond to the formula type and S, 5, and 20 correspond to the nature of the raw polymer-used. S corresponds to slab rubber; 5, to powdered rubber with 5 or 6 phr SX; and 20 to powdered rubber with 20 phr SX. (b) SX = starch xanthide. Abbott, T. P.. Doane. W. M., and Russell, C. R., Rubber Age., IOS(8). 43 (1973).

Abbott, T. P., James, C.. Doane, W. M.. and Russell, C. J., J. Elast. Past.. 7(2), 114 (1975).

106

Polymers

from

Biobased

Materials

CONVENTIONAL

METHOD

POWDER METHOD

!NJEClION MOLDCA

Figure 5.

Comparison of conventional and powder methods of processing rubber

STARCi-l+NACH+cs, f STARCH a!!S Na Starch Xanthate \

/

Zn+*

HN4

\

J

S ST ARCH -&&I

STARCH -4!!S

ARCH

St arch Xant hi de

-Zn

-S

EO-STARCH

Zi nc St arch Xant hat e

STARCH XANTHATE + RESORCINOL +FORMALDEHYDE Figure 6.

S

Zn+* -0 r----) HN4 Xanthation

Starch Xanthate Resorcinol-Formaldehyde Resins

and crosslinking of starch

Starch-BasedPlastics 107

and the other was a double-encapsulated product containing 20% latex polymer and 22% EPTC. In greenhouse and field tests, both starch formulations gave better control of weeds than the commercial formulation applied at an equivalent weight of an active agent. The double-encapsulated product gave excellent control of weeds for 120 days, whereas the commercial product controlled weeds for only about 45 days. This technology has been licensed and evaluated by several companies. ET. LAWREWCE STARCH TECRWOLCGF The development of the technology for incorporating starch into the common oilderived polymers was initiated in the early 1970s when a paper bag manufacturing company, Coloroll, commissioned work at Brunel University to develop more paperlike plastic films for carrier bags. They also imposed constraints on raw material costs, processability, and performance. After starch was identified as the most cost-effective additive, it was also realized that standard starch was unsuitable. This led to the discovery of the benefits of modifying the starch/polymer interface by making the normal hydrophilic starch surface hydrophobic and the need to reduce the moisture content of the starch so that it could be processed in polymer melts typically above 16O'C.

St. Lawrence and ECOSTAR* Having acquired the rights to the technology in 1985, St. Lawrence has been developing and marketing ECOSTAR* in North America and Europe, manufacturing the modified starch at its plant just outside Toronto, and having it made under license in Europe. During the manufacture of ECOSTAR*, starch is surface modified to make it hydrophobic. It is also dried in special equipment to less than 1% moisture (in comparison to the usual lo%-12% moisture content of a normal starch powder). For most applications, the most widely available starch--corn or maize starch--is suitable, However, for some products rice starch or potato starch is used. The physical properties of ECOSTAR* are shown in Table 9. For many users in plastic processing, the starch needs to be pre-dispersed in an appropriate carrier resin to make a master batch, so that it can be incorporFor ECOSTAR*, this is ated with no or only minor changes to existing methods. carried out by Albis. Albia Plastic G&H Albis Plastic was founded in 1961 in Hamburg and supplies the plastics industry with color and additive concentrates, and a whole range of thermoplastics. Albis has factories in Germany, England and Canada. Using Albis' compounding technology, an ECOSTAR* basedmaster batch was developed during 1986. Together with St. Lawrence, Albis has been marketing and selling this master batch in Europe and North America. Production of Products with Albis ECOSTAR* Master batch Suitable master batches have been produced and are being marketed for blowing film in low density, linear low density, and high density polyethylene. With appropriate precautions, particularly to avoid moisture pickup, these are being

108

Polymers from BiobasedMaterials

used to make good quality film. Without describing all the technical details, in Table 10 is illustrated the effect of various levels of starch addition on linear low density film. To some extent, as for normal film blowing, the physical characteristics can be manipulated by adjusting blowup ratios and other processing parameters. Much of the work on this has been carried out by Windmoeller & Hoelscher at its pilot plant in Lengerich in West Germany. Apart from the environmental degradability conferred on the plastic article, ECOSTAR* inclusion has other benefits such as anti-block and its textural effect and in some cases is being used solely for these purposes. For blowing high density polyethylene bottles, a master batch based on this resin has been developed by Albis and is now being introduced to the market. Processing presents few problems and, depending on the particular parameter that is limiting in the final article, reduction in the wall thickness of the bottle Finally, Master batches for injection molding have also been can be achieved. Using ECOSTAR* has been found to improve the dimensional stability developed. of the molding. Early trials resulted in the degradation curves shown in Figure 7. Although dramatic reduction in elongations could be achieved , these were insufficient to meet the specific demands of the composting site. Further development yielded another product, DEGRASTAR*. In Figure 8, a comparison can be seen between low density polyethylene with no additive: the effect of a photodegradable additive; starch on its own; the DEGPASTAR* system at two sites; and, the DEGRASTAR* system in a laboratory simulation. As expected in the dark interior of a compost heap, the photodegrading has virtually no effect, whereas DEGRASTAR* shows rapid degradation.

additive

Compost bags based on the DEGRASTAR* system are being test marketed in Switzerland and further developments can be expected. This new system will also ,be widely marketed where a more rapid degradation rate is required. It is important to ensure that for this system, as well as for ECOSTAR* applications, careful attention needs to be paid not only to the additive but also to the basic components of the polymer or polymers and the processing into film. Breathable

F4apidlv

Films - ECOW

Another development has been of a breathable rapidly environmentally degradable film with Porvair Ltd in the UK. This film is being developed for hygiene products where a fast degrading system is wanted, and is named ECOLAN*. The manufacturing technology is very different from normal blown film and the resulting material can have a level of over 50% ECOSTAR*. The plastic polymer is polyurethane and the resulting structure is microporous with holes (or more correctly interconnecting pores) of a controlled sire. The performance characteristics of an early sample of the film are summarized in Table 11. Tensile strength is not of paramount importance because the resulting products derive much of their strength from the non-woven part to which ECOLAW* is bonded. AS would be anticipated, such a material containing 50% ECOSTAR* displays rapid environmental degradation. Preliminary results of the resulting tensile strength after exposure to two environments are shown in Table 12. The polymer used is a polyester-based polyurethane , and further developments -Y achieve accelerated degradability.

Starch-Based Plastics109

Table 9--Physical Properties of ECOSTAR* Description:

natural polymer, free flowing white powder

Granule size:

15 p for maize starch 8 k for rice starch 80 g for potato starch

Density (g/cm'):

1.28

Thermal stability:

stable to 230°C

Moisture content:

lessthan 1%

Table lo--Physical Properties Containing Various

of Linear Low Density Polyethylene Film Amaunts of ECOSTAR*

Starch Content (%) Gauge

0.0

(10

Elmendorf Tear (g) Tensile @ Yield (kg/cm') Tensile @ Break (kg/cm*) Elongation (%) Dart Impact (g)

MD TD MD TD MD TD MD TD

53 579 1190 124 128 299 286 807 889 192

3.0 56 634 1113 128 126 257 230 717 774 160

6.0 53 637 1133 126 124 260 222 734 764 174

9.0 56 797 1126 128 130 223 198 667 702 118

110

Polymers from Biobased Materials

COMPOSTING

TRIAL

loo-

I 0 A

';;I C *r(

10% STARCH. 90% LDPE 16% STARCH. 84% LDPE 24% STARCH. 76% LDPE

2 i2 % 6(

50-

.

.

: c

.

4 :

.

z

z

. I

I

0

5

I

10

Composting trial data polymers

Figure 7.

on

I

I

-

zOWeeks

15

environmental degradation of

starch

ALDPE l PHOTODEGRADABLEADDITIVE (rLDPE + STARCH 1ST GENERATION COMPOST SITE m2ND GENERATION. XZND GENERATION.LABORATORY SIMULATION

G1

I

0

Figure 0.

X

I

5

I

10

I

15

I

-

2OWeeks

Comparison of environmental degradation of starch polymers

Starch-Based

Table

thickness density

ll--Performance

Characteristics

()L)

(g/cm')

of

(g/m'/24h)

0% Starch

50% Starch

50

50 0.70

Typical PolyEthylene Film 32 0.70

3000

2400

265

7004

320

7000

(water method 37"C, 100% RH gradient) waterproofness--hydrostatic

head

(cm H,O)

(BS. 3424 method 29c) tensile strength

5.5

(N/cm width)

elonaation at break

2.5

200

(%)

170

Table 12--Tensile Strength of Exposed Polyurethane Sample as a Percentage of the Unexposed Sample 0% ECOSTAR*

111

ECOLAN*

0.55

water vapor permeability

Plastics

50% ECOSTAR

0 weeks

100.0

lake water

5 weeks

108.5

93.6

0 weeks

100.0

100.0

clav soil

5 weeks

109.5

58.9

100.0

4.75 60

112

Polymers from Biobased Materials

TXE MICHIGAN BIOTECHNOLOGY

INSTITUTE/RURJXlZ TECXNO~

Naturally occurring biopolymera like starch and cellulose are readily biodegradable (degrade only in soil, sewage, and marine environments where bacteria are active--i.e., biologically active environments only--precisely the conditions Incorporation of these types of where the onset of degradation is desired). biopolymera with the plastics (atyrenic plastics or polyethylene or polymethyl methacrylate plastics) by blending or graft copolymerization should lead to a However, preparing new type of plastics that are environmentally degradable. a new material system by mixing two incompatible polymers as in the present case Strength and toughness results in products with reduced physical properties. values are minimal and are lower for the mixture than any of the pure components. This situation arises from poor interfacial adhesion between the individual comIt is similar to trying to ponents because of their inherent incompatibility. mix or disperse oil and water. The solution to this incompatibility problem, which is widely practiced in the polymer industry, uses block or graft copolymers of the form A-B as compatibilizers or interfacial agents to improve adhesion between immiscible A-rich and B-rich phases. Baaed on the literature work, to function effectively as a compatibilizer, the following are true: 1) components of the graft copolymers must be identical with the polymers in the two phases (identical with the 2 dissimilar polymers, which need to be blended); 2) molecular weight of the segments plays an important role, and control over the molecular weights is essential; 3) molecular weights greater than 150,000 are generally poor compatibilizera; and 4) block or graft copolymers segments containing lo15 monomer units are an effective compatibilizing agent for the corresponding higher molecular weight homopolymer. Thus, the key to the incorporation of natural biopolymera like starch and cellulose in a plastics materials system to make biodegradable/biobaaed plastics is the ability to tailor cellulose/starch-synthetic polymer graft copolymer structures with control over the molecular weights of the graft, the degree (amount) of graft substitution, and the backbone-graft linkage. Current technology does not permit the making of cellulose/starch (natural biopolymers)--synthetic polymer graft copolymers with precise control over these variables. Thus, precise tailor-made cellulose/starch graft copolymers cannot be made with current technology. Narayan and coworkers have identified at Purdue University a new technology that allows us to prepare tailor-made cellulose/starch-synthetic polymer graftcopolymera with precise control over molecular weights, degree of substitution, and backbone-graft linkage. We have also demonstrated that these graft copolymers can function effectively as compatibilizing agents/interfacial agents for compounding/blending of cellulose and starch with synthetic polymers. The graft copolymer allows a fine dispersion of the natural polymer into the plastic phase without detracting from the excellent mechanical and thermal properties inherent in the plastic, while incorporating a new trait of biodegradability.

Abbott, T. P., Doane, W. M., and Russell, C. R.,Rubber Ace, 105(E)

(1973) 43.

Abbott, T. P., James, C., Doane, W. M., and Russell, C. J., J. Elast. Past., z(2) (1975) 114. Anonymous, "Making plastics biodegradable by modified starch additions," Recycle '88 Forum, Davoa, Switzerland, May 5 through June 6, 1988.

Starch-Based

Plastics

113

"Making plastics biodegradable by modified starch additions," Anonymous, Proceedinqs of Svmoosium on Degradable Plastics, The Society of the Plastics Industry, Inc., Washington D.C., June 10, 1987. Bennett, F. L., (1967) 369.

Otey,

F.

H.,

and Mehltretter,

C.

L.,

J. Cell.

Plast.,

2

Boggs, R. w., U. S. Patent 2, 908-657 (1959). Doane, W. M., Shasha, B. S., and Russell, C. R., "Encapsulation of Pesticides within a Starch Matrix," in Am. Chem. Sot., Div. of Pesticide Chem., March 1917, New Orleans, LA. Dosmann, L. P. and

Steel,

R. N., U. S. Patent 3,004,934

(1961).

Fanta, G. F. and Bagley, E. B., "Starch Graft Copolymers," Encvcl. Polvmer Sci. Technol., supplement Vol. 2 (1977) p. 665-699. Griffin, G. J. L., Am. Chem. Sot., Div. Orq. Coat. Plast. Chem., 33(2) (1973) 88. and Biodegradation of Plastics and Griffin, G. J. L., "Biodeterioration Polymers," Proceedings: Autumn Meetinq of the Biodeterioration Society, 12-13 September 1985. Griffin, G. J. L., "Degradation of Polyethylene (1976) 281. sci., 2,

in Compost Burial," J. Polvmer

Gugliemelli, L. A., Swanson, C. L., Baker, F. L., Doane, W. M., and Russell, * C. R., J. Polymer Sci., l2(11) (1974) 2683. Gugliemelli, L. A., Weaver, M. O., Russell, C. R., and Rist, C. E., J. Aool. Polvmer Sci ., z(9) (1969) 2007. Gugliemelli, L. A., Swansoni C. L., Doane, W. M., and Russell, C. R., J. Polymer sci., 14(4) (1976) 215. Gugliemelli, L. A., Northern Regional Research Center, unpublished

results.

Mahler, H. R. and Cordes, E. H., Bioloqical Chemistrv, Harper and Row, New York, (1971). Otey, F. H., Polymer Plast. Technol. Enq., z(2)

(1976) 221.

Otey, F. H. and Westhoff, R. P., U. S. Patent No. 4, 133, 784, (1979). Otey, F. H., Mark, A. M., Mehltretter, XC. L., and Russell, Chem., Prod. Res. Dev., 13 (1974) 90.

C. R., Ind. Enq.

Schreiber, M., "Efficacy and Persistence of Starch Encapsulated EPTC," presented at the North Central Weed Control Conference, Dec. 7-9, 1976, Omaha, NE. Shasha, B. S., Doane,W. M., and Russell, ,C. R, J. Polvmer Sci., Polvmer Lett. l4(7) (1976) 417.

Ed.,

Taylor, N. W. and Bagley, E. B., J. Ao~l. Polvmer Sci., u Weaver, M. O., Bagley, E. B., Fanta, G. F., and Doane, 3,935,099; 3,981,100; 3,985,616; and 3,997,484 (1976).

(1974) 2747. W. M., U.S.

Patents

114

Polymersfrom BiobasedMaterials

Weaver, M. O., Bagley, E. B., Fanta, G. F., and Doane, W. M., Aool. Polvmer Svmo., No. 25 (1974) 97. Weaver, M. O., Fanta, G. F., and Doane, W. M., Proc. Tech. Svmo., Nonwoven Product Technol., International Nonwovens and Disposables Assoc., Washington, D. C., March 5-6, (1974) 169. Westhoff, R. P., Otey, F. H., Mehltretter, C. L., and Russell, C. R., Ind. Ena. Chem., Prod. Res. Dev., 13 (1974) 123. Wurzburg, 0. B., "Starch, Modified Starch and Dextrin," in Products of the Corn Refining Industrv: Seminar Proceedinus, Corn Refiner's Association, Inc., Washington, D. C., May 9, 1978.

8. Biodegradation of Plastics Christopher

Rivard, Michael Himmel, and Karel Grohmann Biotechnology Research Branch Solar Energy Research Institute Golden, Colorado

WBY DEGRADE PLASTICS? Past research in plastic formulations has focused on extending the useful lifetime of plastic polymers. This usually means stabilizing these structures to photo- and biological-mediated degradation (Klausmeier and Andrews 1981). Commercial plastic formulations do not, in general, support microbial growth. However, with an estimated 320 billion lb of municipal solid wastes produced and discarded each year in the United States (Thayer 19891, plastic biodegradation has become an important issue. The bulk of the MSW material is either landfilled or burned. Because of public concern over hazardous emissions from combustion processes, as well as the decreased initiation or siting of new landfills and closure of mature landfill sites, interest in alternative waste disposal processes and waste reduction by recycling has increased. Although the composition of MSW varies with respect to location, season, and time of day, the major components are biodegradable. These components are cellulose (paper), lignocellulosics (sawdust, wood, grass clippings, cardboard), and food wastes (U.S.E.P.A. 1974; Hasselriis 1984a; Hasselriis 1984b; Schwartz and Brunner 1983; Evans and Milne 1987). However, a large component is composed of non-biodegradable materials, such as glass and metals, which may be removed and recycled. Plastics constitute 4%-7% of the MSW materials and are considered inert to biological degradation processes occurring naturally in landfills or in biological conversion processes designed to convert the waste to useful fuels. The plastics industry over the years has devoted a significant effort to increase the stability of plastic formulations to provide stable materials for a wide variety of applications. However, as the application of plastics in consumer throughway packaging increases, litter problems and environmental concerns also increase. Many states in the nation are currently considering or have passed legislation requiring mandatory recycling of garbage (Herr, Gold, and Bell 1987). Rhode Island was the first state to pass such legislation in 1986, requiring curbside recycling of newsprint, glass, metals, and plastic. Additionally, public concern over plastic wastes has generated movements to ban nonbiodegradable plastics. Berkeley, California, for instance, is proposing a ban on nonbiodegradable packaging in takeout food operations by 1990 (Smock 1987). Many states (11 to date) are requiring that biodegradable plastics be used in six-pack beverage carriers, which may constitute as much as 50 million pounds of polymer (Smock 1987). Such recent legislation and public concern has affected business deciRecently, McDonalds banned foam plastic sions of many major U.S. corporations. containers made with chlorofluorocarbons, Burger King switched to biodegradable paper packaging, and Coca-Cola Co. decided to postpone the use of the plastic can. These changes certainly indicate that manufacturers can be influenced by consumer attitudes (Herz, Gold, and Bell 1987).

'Accepted for partial publication

in Journal in Environmental Health

115

116

Polymers from Biobased Materials

Spokespersons for the However, not all concern favors biodegradable plastics. major plastics producers view the problem as one in which municipalities are attempting to solve the litter problem by mandating the use of plastics that are fully biodegradable (Anon 1986; Smock 1987). This is partially the case in the Italian government's ban on the sale of nonbiodegradable shopping bags by 1991. However, the design of "built-in" self destruction of plastics has uses beyond dissipating litter , as shown by interest in plastic sheeting for a variety of agricultural purposes such as mulch applications where materials with predetermined life spans are of great interest and economic significance because they avoid costly periodic removal of mulch materials (Gilead 1985). HISTORY Over the past century, plastic formulations have been developed to resist deterioration and provide long service. To'achieve the desired durability, various agents have been developed to reduce microbial degradation and photo-oxidation. In general, most plastic formulations are inert to microbial attack even though the chemical bonds in plastics are also found in biodegradable organic compounds found in nature. The resistance of plastic polymers to biodegradation may be due to several parameters, including the unavailability of chain ends for initial oxidation by microbial enzymes. Plastic formulations are hydrophobic in nature so conditions favorable to microbial enzymes, such as water absorption, swelling, and proper pH, are not present (Klausmeier and Andrews 1981). To further decrease photo-oxidation and microbial attack of plastic formulations, agents such as ultraviolet stabilizers and biocides may be added in processing. Many plastic formulations have been developed. These may be separated into three classes: polyolefins, polyesters, andpolyurethanes. Additionally, plasticizers were developed to modify the natural properties of plastic formulations. For example, polyvinyl chloride (PVC) as manufactured is hard, stiff, and strong; however, its properties can be modified by the physical incorporation of various natural or synthetic oils yielding products with improved flexibility over PVC alone and with suitability for films, insulation for electrical wire, raincoats, and other useful products. BIODEGRADATION

OF STANDAND PLASTIC FONMUT.ATIONS

Although most plastic formulations are not biodegradable to any great extent, microbial growth (especially fungal) may occur, degrading the appearance of the product and often necessitating replacement. Research has sought to develop reliable and reproducible protocols for determining the potential for biodegradation and to identify the microorganisms responsible for such activity. Most of the microorganisms responsible for plastic biodegradation are fungal and are found in soil (Gorlenko 1983). Therefore, test protocols are currently grouped as those involving the use of pure cultures of fungi (Darby and Kaplan 1968; Pathirana and Seal 1983; Shuttleworth and Seal 1986) and soil inoculum (Sugatt et al. 1984; Seal, Pantke, and Allsopp 1986). Of the standard plastic formulations used today, the potential for microbial degradation follows this order: polyurethane > polyester > polyethylene (Klausmeier and Andrews 1981). However, even the most resistant plastic formulations, such as polyethylene, may be biodegraded to some extent if the material is subjected to photo-oxidation, which produces carbonyl groups or accessible polymer chain ends, the sites for microbial attack (Albertsson, Andersson, and Karlsson 1987). Plasticizers consist of various natural and synthetic oils that are significantly more biodegradable than plastic formulations (Stahl and Pessen 1953; DeCoste 1968; Klausmeier and Jamison 1973). In general, the microbial degradation of plastic copolymers, which employ plasticizers, is due to microbial attack on the

Biodegradation of Plastics

plasticizer copolymer.

component.

117

This results in the subsequent loss Of elasticity of the

In summary, very few plastic polymer formulations can be degraded microbially, and most microbial growth is due to the utilization of plasticizers used to increase plastic elasticity. BIODEGRADABLE PLASTICS As plastics have been developed to increase their stability, plastic refuse has become a major environmental concern. It is comparatively easy to dispose of natural or man-made materials, such as paper, cardboard, wood, glass and metals, but stabilized plastic formulations are water insoluble, nonbiodegradable, and This environmental concern led to often unsinkable when 'disposed of at sea. research interest in the 1960s into biodegradable plastics. However, with the oil crisis of 1973, much of the research into biodegradable plastics was discontinued in view of plastic recycling efforts designed to reduce dependence on petroleum-based products. In the late 1980s, interest again arose in plastic disposal. This time interest was due to the cost of municipal solid waste disposal, and concern for cycling of carbon in the environment. The development of biodegradable plastics has branched into three distinct areas: photo selfdestruction, copolymers of plastic and cellulose or starch, and microbially derived materials that demonstrate high degradation rates. Photo Self-destruction The photo-oxidation and subsequent loss of durability of plastic formulations has been postulated as a mechanism for destruction of commercial plastics. Depending on temperature, normal plastic films have been estimated to take three months to three years to photo-degrade (Smock 1987). However, plastics disposed of in landfills are rarely exposed to sunlight for any appreciable period before additional garbage or soil is added for cover. Therefore, photo-oxidation often does not play an important role in plastic disposal in garbage. Plastics that photo-self-destruct are important especially in the agricultural field where plastic films serve a variety of specialized purposes, many intended to create controlled environments for growing crops. These thin plastic films incorporate a photo-stabilizing agent with a predetermined active period (Gilead 1985). After ,the predetermined period, the photo-stabilizer is inactive and further exposure to sunlight causes photo-oxidation of the plastic polymer and loss in structural integrity. Photo-oxidation results in carbonyl end formation in the polymer chains, which increases the further biological breakdown of the plastic film. Plastic Cowlwners The mixture of plastic polymers with natural polymers, known (or considered) to be readily biodegradable, such as cellulose and starch, improves the biodeqradation of the copolymer as a whole (Narayan 1988; Smock 1987). These natural polymers (cellulose and starch) are available in great supply and may therefore be competitively priced as compared to oil-derived component plastics. However, the level of natural biodegradable polymer required to achieve significant biodegradation of the copolymer, and thus pollution control, has been estimated at 30%-50% (Smock 1987). At these high natural polymer addition rates, the copolymer is difficult to process and loss of physical properties is evident. A siqnificant amount of research is necessary to determine the exact composition of natural polymer to be incorporated into the copolymer to optimize not only biodegradability, but also the retention of the desired physical properties and production parameters of this copolymer.

118

Polymers

from

Biobased

Materials

Microbial Derived Plastics A different approach is the production of engineered "new" polymers. Polyhydroxybutyrate (PHB) (Lemoigne 1927) is an aliphatic, polyester homopolymer that is stored as an energy reserve in the cells of many bacteria including Alcaliaenes eutroohus (Schlegel, Gottschalk, and Von Barta 1961). This bacterium can be grown in large fermentation vessels on a variety of substrates and the polymer The physical properties of PHB (PHB) can be easily separated from the cells. are comparable to those of polypropylene, although it is stiffer and more brittle (Westlake 1987). This drawback can be overcome by inducing the bacterium to produce copolymers of PHB and polyhydroxyvalerate (PHV) (Holmes 1985). These copolymers have a random structure, reduced stiffness, and increased impact strength. By producing copolymers with varying proportions of PHV, the stiffness and strength of the material can be exactly determined as appropriate to the application. ICI has a pilot plant operating in England that now produces PHBV copolymers for specialty applications (Smock 1987). Research in the microbial production of tailored high-value, special-property materials is ongoing both at ICI and by university-industry cooperative ventures (Ribbons et al. 1988). Today, copolymers produced vary from products similar to unplasticized PVC or polystyrene to soft and flexible products like polyethylene. The most significant property of copolymers of PHB and PHV is biodegradability. Thin films of PHBV degrade in ten days in anaerobic sewage treatment plants and one year in landfills (Smock 1987). However, current production cost at the 1000 ton/month plant is $lS/lb and the estimated industrial price is $l/lb, which is still higher than polyethylene terephthalate (PET) and polystyrene beads ($0.65-$0.70 and $0.60/lb, respectively, Smock 1987). WEED FOR PUTDRE RESEARCH Since the second World War, the plastics industry has grown by producing increasingly more durable products. The oil-derived plastic polymers are cheaper than comparable natural polymers and synthetic plastics can be produced with relative ease and consistent quality. The current requirement that these commercial plastic formulations exhibit biodegradability runs contrary to their properties as originally formulated. It has been acknowledged by the plastics industry that new chemistries are now required (Smock 1987). Obviously, there is a need for biodegradable plastics. Several avenues are currently available for their development. The production of copolymers of plastics and natural polymers provide one such mechanism (i.e., increasing the fragmentation of plastic polymers and thus increasing the subsequent plastic biodegradaAdditionally, the development of natural polymers with biodegradable tion). capabilities, such as PHB, PHV and copolymers of the two, is extremely advantageous. However, a great deal of research is needed to improve the physical properties of plastic copolymers (or natural polymers) while reducing their producwith currently used oil-based plastic tion costs to levels competitive formulations. REFERENCES

Anonymous,

Chem. Ind.

17

(1986) 564.

Albertsson, A.-C., Andersson, Stabilitv, 2 (1987) 73-87.

S.O., and Karlsson,

Darby, R.T. and Kaplan, A.M., APP~. Microbial., 16 DeCoste, J.B., Ind. Enq. Chem. Prod. Res. Dev., 1

S., Polvmer Desradation

(1968) 900. (1968) 238.

and

Biodegradation of Plastics 119

Evans, R.J. and Milne, T.A., "Liquid Fuels from the Pyrolysis of Municipal Solid Waste and Its Components: Rapid Product Characterization and Process Parameter Screening by Molecular Beam, Mass Spectrometry." Eneruv from Biomass and Wastes KI, D. Klass; ed., Chicago: Institute of Gas Technology, pp. 807-838 (1987). Gilead, D., Chemtech., 15

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5, John Wiley

and Sons, Chichester,

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Arbor

(1985) 32-36.

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in Industrial Microbioloav, 14

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and

Ribbons, D.W., Bushell, D.J., Cass, A.E.G., Rossiter, J.T., Slawin, A.M.Z., Williams, S.R., Widdowson, D.A., and Woodland, M.P., Tenth Svmposium on Biotechnolosv for Fuels and Chemicals, Gatlinburg, Tenn. (1988) May 16-20. Schlegel, H. G., Gottschalk,

G., and von Barta, R., Nature, 191

(1961) 463.

Schwartz, S.C. and Brunner, C.R., in Eneruv and Resource Recoverv Noyes Data Corp., N.J., (1983). Seal, K.J., (1986) 22.

Pantke,

M.,

and Allsopp,

D.,

Kunststoffe

Shuttleworth, W.A. and Seal, K.J., ADDS. Microbial. 407-409. Smock, D., Plastics World, 45

- German

from Waste,

Plastics,

Biotechnol., 23

76

(1986)

(1987) 28-31.

Stahl, W.H. and Pessen, H., ADDS. Microbial., 1 (1953) 30. Sugatt, R.H., O'Grady, D.P., Banerjee, S., Howard, ADDS. Environ. Microbial., 41 (1984) 601-606. Thayer, A.M., Chem. Enq. News, 61

(1989) 7-15.

P.H. and Gledhill,

W.E.,

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U. S. Environmental Protection Agency, "Resource Recovery and Waste Reduction". Third Report to Conuress, Pub. No. SW-161, Washington, DC. (1984). Westlake, R.P., Kautschuk und Gummi Kunststoffe, fi

11987) 203-204.

Part II Bioproduction of Materials

9. Advances in Cellulose Biosynthesis R. Malcolm Brown, Jr. Johnson & Johnson Centennial Chair in Plant Cell Biology Department of Botany The University of Texas Austin, Texas

BACICGROUND Cellulose is the most abundant biobased material on earth. It is estimated that 10" tons of cellulose are produced and destroyed annually (Preston 1974). Cellulose is a natural polymer of great diversity, and it has been used by mankind for thousands of years. The need to continue applied and fundamental research on cellulose structure and biosynthesis would not seem at first to be so important, for after all, we have developed very efficient methods for harvesting and producing sufficient quantities of cellulose for present use. However, we need to consider more than just harvesting trees for wood and cotton for textiles. The rivalry of natural polymers for petroleum-based materials is great, but there are compelling reasons why we must upgrade fundamental research and development on biobased materials. World competition for producing and using a broad range of natural polymer systems will increase in the future, and the United States has not yet prepared itself for this competition. In order to bring to the forefront the importance of cellulose, my first goal in this assessment will be to survey the broad diversity of cellulose products and to indicate the major problems associated with the use and harvesting of each major source (also, see Mark 1987). My second goal will be to discuss new sources of cellulose with an emphasis on some of the unique properties of this material (Brown 1989). My third goal will be to suggest future research and development in the field of cellulose biosynthesis leading to improvement in efficiency of synthesis and improvement of physical properties. The outcome of this assessment should provide to the U.S. government important directions that should be taken to ensure our leadership in this extremely important field of biotechnology development. DIVERSITY AND USES OF CELLULOSE It is quite ironic that such a simple polymer of R-1,4 linked glucose residues Most cellulose presently is, would be used in so many products and processes. harvested from two major resources: forest trees, and cotton. Because forests are abundant and harvesting techniques are streamlined, this is the major source Major uses of forest cellulose products can be classified into for cellulose. three areas: (a) renewable energy sources such as firewood and biodegradable products: (b) structural building materials: and (c) wood pulp for paper, packaging, derivatization, and food base uses. Cotton is the major resource for textiles as well as high quality rag paper. The cellulose industry is a maior worldwide industry. The impact of this one industry on the economy and environment of the entire world is significant. It is only recently that the greenhouse effect has received extensive public attention. The huge scale of forest harvests for firewood, building, and paper products is leaving a serious negative impact on the ecology of affected regions. Endangered species are being lost, cultivated lands are eroded, and perhaps most

122

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in Cellulose

Biosynthesis

123

significantly, the vast natural CO2 utilizers, the forests, are being lost. If humans are to continue harvesting cellulose on a scale indicated by past and present usage, it becomes important to consider remedies to these problems. Many are indirect and will require years of basic research before they can be used efficiently in the field.

What are the serious problems with the present major sources of cellulose? Because wood pulp can be harvested frommany sources, the tropical forests should not be used because regrowth to establish climax forest communities is difficult, if not impossible. The fragile soils in tropical regions suggest the use of other areas for scientific forest cultivation. It is not the purpose of this assessment to discuss the economics of the forest industry. Rather, we should think in terms of fundamentally new concepts to genetically engineer plants that are (a) more efficient in cellulose production, (b) adapted to a wider variety of climates and stresses, and (c) useful for specific end-product uses of the wood. The second biobased material, cotton cellulose, is a major world crop. InTexas alone, it is a billion-dollar annual crop. In the United States, cultivation of this crop has declined largely because of expansion of bollweavil overwintering. Gossvvium requires frequent fertilizing and insecticides to maintain a crop of higher standards of productivity. Inclement weather and damage caused by freezing, cold stress, hail, draught, heat, and wind have a negative impact on farming and production. Furthermore, mechanical harvesting requires expensive equipment, and logistics of transport demand storage. In addition, the cotton boll is rather inefficient in cellulose production, since only the lint fibers are used. Fuzz fibers are too short for textile or yarn formation. Thus, the need for understanding the fundamentals of cell morphogenesis in this plant is very great. We need to know more about the onset and regulation of cellulose synthesis during fiber initiation. We lack fundamental knowledge of the control of the degree of polymerization, microfibril orientation, and mechanism(s) of glucan chain crystallization. Given that forests and cotton plants are the two major worldwide source of cellulose, and that we know very little about the biochemistry of its synthesis, it is indeed surprising that more basic research has not been conducted in this field. On the other hand, biotechnology is prospering and through this avenue, it may be possible to utilize microbes and fermentations to synthesize cellulose made to specification. This will be described below. NEW SOURCES OF CELLULOSE I have briefly described the two major sources

of cellulose, trees and cotton. In addition to these sources, microorganisms can synthesize cellulose. Because microbes are the cornerstone of the biotechnology revolution, they will undoubtedly play a very important role in the commercial scale up of cellulose production. Since the days of Pasteur, production of cellulose by bacteria has been known. In fact, in 1886, Adrian Brown described bacterial celluloee from a gram negative rod later named Acetobacter xvlinum (Brown 1886). Bacterial cellulose has several unioue features not found in trees or cotton: (a) Acetobacter can synthesize m cellulose, devoid of lignin and other polymers; (b) bacterial cellulose has a very marked hydrophilicity. This microbial cellulose is never dried at the time of harvesting and can hold hundreds of times its weight in water; (c) microbial cellulose is capable of being directly synthesized into microwoven pads or membranes of virtually any shape or size; (d) bacterial cellulose has outstanding shape retention and dimensional stability; (e) bacterial cellulose can be synthesized from a variety of inexpensive

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substrates; (f) the physical properties of microbial cellulose can be controlled during synthesis; and (g) the extremely high rate of pure cellulose synthesis suggests efficient scale up of its production. These seven features deserve further comment and elaboration, since biobased materials of exceptional quality can now be produced from bacterial cellulose. Pure Cellulose Svnthesis from Acetobacter Acetobacter xvlinum is a gram negative rod. Cellulose synthesis appears to be constitutive since no true cellulose-negative mutants have been isolated. As long as the culture is grown on a simple medium consisting of yeast extract, proteose peptone, citrate, and glucose, it will synthesize cellulose. Acetobacter xvlinum is an obligate aerobe. In a standing culture, the cells proliferate near the gas/liquid interface, and cellulose synthesis is abundant in this region. Each cell synthesizes a ribbon of cellulose microfibrils tangential to the cell surface. The ribbon is directed parallel to the longitudinal cell axis. The ribbon consists of many individual microfibrils that associate by lateral intermolecular R-bonding. Imperfect associations lead to ribbon twisting. Time lapse tine and video microscopy of cellulose synthesis has demonstrated that the ribbon twists during synthesis and is not the result of drying. The directed polymerization and subsequent crystallization of cellulose leads to a forward propulsion of the cell, which rotates on its longitudinal axis when the ribbon becomes long enough to interact with other ribbons. The result is a very hydrophilic gel of pure cellulose formed at the gas/liquid interface. The most active zone of cellulose synthesis is at the top of the gel. Older cells become buried in the ribbon matrix, cease ribbon synthesis, and eventually die. The site of synthesis is an enzyme complex in the cytoplasmic membrane (Bureau and Brown 1987). In the LPS layer of the cell envelope juxtaposed with the synthesizing complexes is a row of particles and pores (Brown, et al. 1976; Zaar 1979) The components of the cell envelope are believed to assist in the directed polymerization of the glucan chain aggregates so that highly: crystalline cellulose I is formed. Recently, we have discovered mutants of Acetobacter that synthesize the cellulose II polymorph (Roberts et al. 1989). This crystalline form is synthesized in much less quantity than cellulose I, probably due to the more inefficient means to facilitate export of the glucan chains, since the particles and pores are missing in the mutants. Hydrophilic Nature of Microbial Cellulose Because the cellulose ribbons are assembled extracellularly into the liquid culquantities of the liqture medium, abundant micelles are formed that trap large In addition, the large surface area of cellulose ribbons is responsible uid. for the formation of an extremely hydrophilic yet strong membrane of pure cellulose. Once dried, however, the native cellulose can never regain its original hydrophilicity because the intermolecular H-bonds formed between microfibrils The unique feature of biosynthesis of cellulose in a cannot easily be broken. hydrophilic environment is a property that will be of great importance in subseThe hydrophilicity can be quent treatment and derivatization of the product. made even greater by addition of hydrophilic materials to the cellulose either during or after synthesis (White and Brown 1989) It is important to note that cellulose from wood and cotton must be mechanically disintegrated in order to produce sufficient surface area to impart hydrophilicity. Such processes are involved in the production of Avicel; however, hydrophilicity is gained at the loss of mechanical wet strength. This is not the case with microbial cellulose. Because the extremely long, continuous ribbons are interconnected, the high wet

Advances

strength in maintained. cellulose.

in Cellulose

Biosynthesis

125

This is a unique property, known only with microbial

Direct Svnthesis of Shaped Cellulose6 bv Aoetobacter The obligate requirement for oxygen can be put to a novel method for producing cellulose membranes of virtually any shape (Roberts, Hardison, and Brown 1986). Gas permeable membranes can be used as culture vessels for production of microbial cellulose. The cells prefer a liquid enriched in oxygen, and this is achieved as a gradient adjacent to the gas permeable surface. Thus, cellulose will be synthesized directly by Acetobacter xvlinum. Even micro devices can be made that retain their shape and dimensional stability. Using this technology, large-scale manufacture of microbial cellulose has great possibilities. These are being investigated in our laboratory. Cutstandina Shape Retention and Dimensional Stabilitv of Microbial Cellulose Because of the extensive intermolecular H-bonding network, microbial cellulose has great mechanical strength. The Japanese company, Ajinomoto, recently disclosed the production of high tensile strength microbial cellulose for use in audio speakers (see &SD?& Industrial Journal May 15, 1987). Microbial cellulose is an ideal material for superior acoustical performance. The heat pressed and cleaned microbial cellulose has a Young's Modulus in excess of 50 gigapascals. The theoretical Young's Modulus of 178 gigapascals, if achieved, would yield a product of strength rival to that of high performance fibers (see Table 1.1). Thus, it is conceivable that lightweight structural components for aircraft, spacecraft, and automobiles could be manufactured using microbial cellulose. Add to this the probability that shaoed objects can be directlv synthesized would open entirely new industries. Much research needs to be done in this area, but the possibilities are extremely attractive because of the unique properties of the cellulose as well as biotechnology manufacturing techniques that can be developed. Of all the major areas inmaterials science, this one should be given high priority and extensive research and development by the federal government. Microbial Cellulose Sathesis Uaina Natural Substrates In order to achieve large-scale manufacture of microbial cellulose, it will be necessary to develop efficient strains of Acetobacter that use economical, diverse substrates. In our laboratory, we have a number of strains that can use sucrose as the basic carbon source. Some strains effectively thrive on glycerol as the sole carbon source. In addition, vitamins, cofactors, and trace elements are required. These can be supplied by corn steep liquor, which is economical. Conversion efficiencies of carbon to cellulose range from 10% - 45% in our laboratory, but in order to manufacture large-scale commodity grade cellulose that can compete economically with wood and cotton sources, the efficiencies will need to be enhanced. Thus, U.S. laboratories need to be adequately funded to develop and optimize the nutritional requirements for microbial cellulose,production. Fundamental and basic recombinant DNA technology may help to dramatically improve conversion efficiencies. For example, if the genes for cellulose synthesis could be effectively transferred and expressed in a photosynthetic microbe, the potential conversion efficiency could increase dramatically. Because many value-added products using the unique properties of cellulose will be anticipated, the development of efficient strains will not be so important at first as selection and characterization of diverse cellulose-producing strains. It should be emphasized that many of the unique properties are linked to specific strains, and these need to be explored in greater detail. Thus, the need to acquire many diverse strains from the field should be a top priority for

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basic and applied research in the United States and federal funding should be available to support the establishment of culture collections of microbial celluIn addition to Acetobacter xvlinum, the list includes lose synthesizers. Hhixobium, Acrobacter, Pseudomonas, Sarcina, and Nostoc. Such collections are currently being implemented in other countries.

Control of Phvaical

Properties

of

Cellulose Durina Svnthesis

The pioneering work from our laboratory in 1980 (see Haigler, Brown, and Benziznan 1980) established that cellulose assembly could be modified during synthesis. Using optical brighteners such as Calcofluor White and other substantive dyes as Congo Red, the crvstallixation of the cellulose was delayed, but the polymerization of glucose into glucan chains continued. Thus, two distinct steps of microfibril assembly were dissected. The rate of cellulose polymerization increases when the constraints of crystallization are removed. The process is entirely reversible. From these studies, a better understanding of the mechanisms leading to microfibril formation has emerged; however, much more remains to be accomplished in this field. One very exciting example of the potential for modifying the physical properties of cellulose is the use of carboxymethylcellulose (CMC) to modify the microfibril size and inhibition of ribbon production (Haigler, et al. 1982; Brown 1988). Cellulose produced in the presence of CMC has more than 1000 times water-holding capacity. Extremely hydrophilic gels can be manufactured using this technology. This hydrophilicity cannot be achieved by addition of CMC to the cellulose after synthesis. Modification during synthesis is a requirement for securing this enormous hydrophilicity. This hydrophilic cellulose behaves like a nematic liquid crystal, allowing possible wet spinning of native cellulose I crystallites of high molecular weight and order. This is but one example of the economic potential for modifying cellulose physical properties during synthesis. The cellulose II polymorph mutant is another example. The structural equivalent to "rayon" can now be synthesized directly by living organisms (Roberts et al. 1989). The future seems indeed bright for direct in situ modifications of biosynthetic capacities and will require intensive basic research and federal funding to develop the technology to its full potential. Scale

UR

of

Mictobial Cellulose Svnthesis

Using time-lapse microphotography

and video microscopy, we have determined the rate of ribbon elongation from the surface of A. xvlinum. Knowing the number of glucan chains/microfibril , and the average number of microfibrils per ribbon, we can calculate the rate of glucose incorporation into cellulose on a per cell basis. More than 10' glucose molecules can be incorporated into cellulose in a single Acetobacter cell each hour! This translates to a productivity on an acre surface area basis of more than 26,000 lb of cellulose per year. When compared with cotton production in which 1 bale/acre is approximately 650 lb/acre annual production, the astounding rate of microbial cellulose production is more than 40 times that of cotton! One major drawback, however, is that the carbon for cellulose production in Acetobacter needs to be supplied in the form of glucose or some other organic compound, while cotton derives its carbon from CO, via photosynthesis. Although these are sobering facts, the high rate of cellulose synthesis in bacteria needs to be extensively compared with the rate of cellulose synthesis in trees and cotton. Further basic research on this topic will be necessary to develop economically sensible strategies for achieving efficient, competitive cellulose synthesis by bacteria. One ultimate aimwould be to transfer the genes for cellulose synthesis into a photosynthetic, nitrogen-fixing microbe that can tolerate salt water. With such an organism at hand, it might

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indeed be possible to produce microbial that from wood and cotton sources.

cellulose

on a scale competitive

with

CONCLUDING REMARKS: THE FUTURE In this brief assessment, I have attempted to present the present state of affairs in the cellulose field. With such a large and diverse area, this assessment can only be interpreted as a simple review; however, the important parameters for establishing increased federal funding in the area of cellulose biobased materials research are covered. With the potential of biotechnology and our ability to clone and express genes effectively in other organisms, there is no reason why improved cellulose biosynthesis should not be achieved. There are compelling arguments to support an immediate increase in federal funding for cellulose biosynthesis research. The possibilities for large-scale microbial cellulose production opens a vision of many new kinds of biobased materials for use by mankind. More important, long-term use of other sources of cellulose, particularly the forests, may be diverted by fermentation production of cellulose, thereby greatly helping to alleviate the destruction of invaluable tropical forests. Finally, gaining more knowledge of the basic mechanisms of cellu.lose biosynthesis will help us to develop and use a greater variety of non-microbial sources. Increasing the productivity of plant growth may lead to greater cellulose harvests from forests and cotton fields. Our basic knowledge on cellulose biosynthesis is so rudimentary that a maior research effort is now needed to keep up with the rapidly expanding pace of recombinant DNA research, which can be a most helpful tool for achieving greater cellulose productivity.

Brown, R. M., Jr., Willison, J. H. M., and Richardson, Sci. USA, 12 (1976) 4565-69. Brown, A., Trans J. Chem. Sot. London, 49

C. L., Proc. Natl. Acad.

(1886) 432.

Brown, R. M., "Cellulose Biogenesis and a Decade Perspective," J. Aopl. Polv. Svmp., (in press).

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Brown, R. M., Jr., Patent Application No. BP 260093 A2, "Micro Cellulose Modified During Synthesis." (1988). Brown, R. M., Jr., Patent Application No. EP 258038, "Use of Cellulase Preparations in the Cultivation and Use of Cellulose-Producing Micro-Organisms." (1988). Brown, R. M., Jr., and Bin, L. C., "Method for Production of Cellulose I European Patent Application EP26093, (1988). Involving In-Vitro Synthesis," Bureau, T. E. and Brown, 6985-89.

R. M.,

Jr., Proc. Natl. Acad.

Sci. USA, E

Haigler, C. H., White, A. R., Brown, R. M., Jr., and Cooper, Biol., 94 (1382) 64-69.

K. M., J. Cell.

Haigler, C. H., Brown, R. M., Jr., and Benziman, M., Science, 110 06. Japan Industrial Journal, May 15, 1987. Mark, H., Chem Enu. Proc., 83

(1987) 55.

(1987)

(1908) 903-

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Preston, London Roberts, Application Roberts,

J.

Awl.

from

R. D., (1974). E.,

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Materials

The Phvsical

Biolow

of

Hardison, L., and Brz.m, No. EP 186495 AZ (1986).

E. M., Saxena, I. M., Brown, POl. SvmD. (in press,.

White, A. R. and Brown, Bioayntheais of Microbial

R. M., Jr., Cellulose,"

the

Plant

R. M., R. M.,

Jr.,

“Prospect8

J.

Appl.

Cell

Jr.,

Wall,

Microbial

"Biosynthesis

Chapman

and fall,

Cellulose

Patent

of Cellulose

for the Conunercialiration Pal. Smp. (in press).

II," of

the

IO. Biogenesis and Biodegradation of Plant Cell Wall Polymers Norman G. Lewis Departments of Wood Science and Biochemistry Virginia Polytechnic Institute and State University Blacksburg, Virginia

INTRODUCTION This chapter attempts to summarize some of the important research thrusts directed toward a detailed understanding of the processes of plant cell wall development and ultimate bioconversion. These have been classified, on a topicby-topic basis, in terms of current status and recommendations for the future. Much of the material described was presented (or discussed) at an international symposium held in Toronto, Canada from June 5-11, 1988. This symposium was organized by N. G. Lewis and M. G. Paice, as part of the American Chemical Society's (ACS) Cellulose, Paper and Textile Division Program. The contributed papers in the symposium attracted many of the foremost scientists in this field. An ACS Symposium Series Volume No. 399 entitled Plant Cell Wall Polvmers: Bioaenesis and Biodearadation has been published in 1989. The chapter is separated into four main sections:'(1) cellulose structure, biosynthesis and.biodegradation; (2) lignin biosynthesis, structure, and biodegradation; (3) other aromatic polymers; and, (4) hemicelluloses, biosynthesis, structure, and biodegradation. Some topics are covered more thoroughly (e.g., lignin), whereas others are described less extensively either to minimize overlap between contributing chapters or because certain topics were not covered in depth. CELLULOSE Smthesia and Structure in H&her

Plants: Current Statua

Cellulose is a relatively uncomplicated biopolymer in terms of its primary structure, since it is composed solely of cellobiose repeating units linked via stereoregular b-(1 -> 4) bonds (Atalla 1979). In spite of this apparent simplicity, our understanding of how it is biosynthesized in vascular plants, its secondary structure and factors controlling its degree of polymerization (DP), crystallization, and orientation within the cell wall are still far from being adequate (Hotchkiss 1989). This is all the more surprising when one reflects on the fact that this biopolymer represents about 50% of all plant biomass. It should, therefore, be self-evident that a detailed understanding of this deposition process is important, not just from the standpoint of fundamental knowledge gained, but also as regards more applied goals, e.g., the production of cellulose of specific DP or optimization of conditions for enzymic degradation. However, cellulose has not yielded its secrets easily and many studies have been thwarted in attempts to obtain unambiguous answers to questions posed. For example, in regard to biosynthesis, it has been known for some time that this occurs at the plasma membrane. The enzyme(s) involved are normally described as terminal complexes that are capable of converting UDP-glucose into cellulose (Delmer 1987). "Structures" have often been observed on plasma-membrane derived fragments (following appropriate freeze-fracture studies), and these have been

129

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Materials

as the cellulose-forming terminal complexes. Depending on the organism in question, they can be visualized as either linear arrays (as for some algae) or aggregates of rosettes and globules. Based on these distinctions, attempts at classifying organisms into different phylogenetic categories have been made (Itoh 1989). implicated

However, it cannot simply be dismissed that no enzyme, or crude preparation thereof, has ever been obtained from higher plants that catalyze the facile in vitro synthesis of cellulose (Hotchkiss 1989; Delmer 1987). Until this occurs, identification of these structures as cellulose-forming complexes should be regarded as incomplete. Indeed, all attempts thus far to isolate an enzyme capable of catalyzing the conversion of DDP glucose into a B(l -> 4) glucan have normally only been rewarded with a 011 -> 3) glucan formation: i.e., instead of cellulose synthesis, callose is formed instead. For several years now, Delmer (1987; 1989) has argued that the synthesis of both polymers (callose and cellulose) is inextricably intertwined, For example, mechanical damage (e.g., wounding) or stress to plants leads to the formation of callose [D(l -> 3) ] in place of cellulose [a(1 -> 411. She further postulated that, in vascular plants, the rosettes of rosette/globule complexes function to ensure that 8(1 -> 4), rather than 13(1-> 3), formation occurs (Delmer 1989). Upon damage or wounding to the tissue, these rosettes are presumably dislodged or inactivated in some way. The remaining globular enzyme is then only capable of forming callose. Following inhibition studies using 2,6_dichlorobenzene and 2,6- dichloronitrene (inhibitors of cellulose formation), it was proposed that an easily solubilized 18 kD protein was the dislodged "rosette" protein. Hence, difficulties encountered for in vitro cellulose synthesis are presumably due to facile removal of this rosette protein (Delmer, Read, and Casper 1987). It should be self-evident that there is an urgent need to raise antibodies against this 18 kD protein, and establish whether there is any relationship of this protein with the "rosette" structures in the plasma membrane. Northcote (1989) has also suggested that the cellulose synthase complex contains some sort of binding protein, and argues that this is able to orientate the C-4 hydroxyl group of the nonreducing end of the growing glucan chain so that it can specifically react with DDP-glucose. As regards B(1 -> 3) glucan synthesis itself, Wasserman et al. (1989) have reported that a 54 kD polypeptide isolated from red beet storage tissue may catalyze its formation. What information this will provide about cellulose synthesis is awaited with interest. However, it must be emphasized that while all these proposed models for cellulose synthesis are appealing, they must eventually yield to the rigors of experimental verification. Hence, from a purely pragmatic standpoint, much remains to be proven before the question of cellulose formation can be laid to -rest. In related areas, let us now turn our attention to cellulose structure, specifically chain orientation and factors affecting microfibril assembly. As far as the former is concerned, it has long been known that cellulose I is the native polymorph and that it contains chains that lie parallel to each other, as evidenced by interpretation of X-ray powder diffraction patterns (Sarko 1978). Additionally, it has been argued over the years that subsequent treatment of cellulose I with alkali (which results in swelling of the fibers) is accompanied by formation of cellulose II, whose chains are now antiparallel (Sarko 1978). This remarkable claim has not been without its critics. Indeed, VanderHart and Atalla (1987) have proposed that the only conformational changes are being observed instead of changes in chain alignment. Although this debate has gone on for some time, a possible solution to this controversy has appeared. Roberts (1989) recently confirmed the work bv Sisson (1938) where it was reported that

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the native polymorph of Halicystis is cellulose II. If this is correct, and if a cellulose I -> II transition has not occurred, then presumably the orientation of the chains produced by the cellulose synthase complexes are identical in both cases; i.e., that the arguments by VanderHart and Atalla (1987) are correct. If so, this result cannot be simply ignored, because this would mean that the interpretation of X-ray powder diffraction patterns of a major biopolymer has been incorrect. It has also been proposed that during cellulose synthesis, the rate-determining step controlling the rate of formation of D(1 -> 4) glucan bonds is a postsynthesis step controlling lateral fasciation of O(1 -> 4) glucan chains (Brown et al. 1983). This conclusion was based on the fact that addition of Calcofluor or Tinopal dramatically increased the rate of cellulose synthesis in Acetobacter xvlinum. This was interpreted as being due to disruption of the lateral fasciation process, which would nonna+lly lead to slower sequential crystallization. This hypothesis has been severely criticized by Reuben, Bokelman and Krakow (1989). Finally, orientation of cellulose microfibrils has often been reported as being determined by microtubular orientation. At leastin the case of the giant marine algae, Valonia ventricosa and Boerzensenia forbersii, this does not appear to be the case (Itoh 1989). In summary, much remains to be learned about cellulose formation and structure. Cellulases Unlike the cellulase-synthesizing enzyme system, much more is known about the cellulose-hydrolyzing enzymes , which are collectively known as cellulases. These can be classified as exocellulases (1,4-D-glucan cellobiohydrolases), endocellulases (1,4-13-D-glucan glucanohydrolases), etc. The first cellulase gene cloned was from Ceilulomonas fimi (Owolabi et al. 1988; Gilkes et al. 1988). ,This was one for catalytic hydrolysis, then subsequently showxo have three regions: one for substrate binding and a proline-thyrosine connection region (Gilkes et al. 1989). (Apparently, glycolysis of these enzymes prevents proteolysis and enhances binding to cellulose.) Since then several other systems have been cloned, e.g., from Trichoderma reesii where Knowles' group cloned four cellulases (two exocellulobiohydrolases and two endoglucanases) (Teeriet al. 1989). Interestingly, the amino-acid sequence of several of the exocellulobiohydrolases and endoglucanases were similar, although they have different catalytic functions. Note also that the homologous region was separated from the enzyme core by heavily glycosylated, proline-serine rich regions. Claeyssens and Tomme (1989) have carried out limited proteolytic degradation of two of the cellulobiohydrolyases (using papain) in order to separate the enzyme In this way, cellobiohydrolyases core (active site) from the other regions. (CBH I and CBH II) gave cores (active sites) of 56 and 45 kD and terminal pepA general "tadpole-like" structure for tides of 11 and 13 kD, respectively. the enzyme was proposed with an ellipsoid core region and a proline-serine rich region as the tail (See Figure 1). This was proposed following small angle X-ray scattering analysis of both the intact enzyme and its core. Interestingly, the cores remained perfectly active This was towards soluble substrates but not to microcrystalline cellulose. Following isolation of attributed to removal of the cellulose binding domains. the enzyme cores containing the active sites, these were crystallized by Jones at Uppsala. Hence, the exact nature of the tertiary structure and a more precise knowledge of intricate reaction mechanisms by which these enzymes function can be expected in the very near future.

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CBH core

Figure 1.

I

+a+a-l

Node1 structures of intact Cellobiohydrolyase I as deduced from the results of small angle X-ray scattering experiments. The arrow indicates the proteolytic scission site (papain), dividing the core protein (left) from the **binding domain" (right). A,A-domain; B,Bdomain; N,N-terminus; C,C-terminus (from Ciseyssens and Tomme 1989)

Horikoshi (1988) reported the isolation of unusual alkaline cellulases from alkalophilic Bacillus (sp N-4 and sp 1139) strains respectively. Four genes were isolated and their nucleotide sequences were determined. According to Horikoshi, these cellulases are added to laundry detergents in Japan to facilitate dirt removal from cotton fabrics, and have captured more than 50% of the market. Future Recommendations A picture now appears to be slowly emerging whereby cellulose and caliose formation in vivo are closely related. Resolution of this fascinating problem at the molecular level is eagerly awaited. Clearly, an understanding of how this process occurs may lead to the formation (synthesis) of cellulose of a specific DP or crystallinity. This could be of considerable importance in producing new cellulose or cellulose-derivedpolymers of specific physico-chemicalandmechanical properties. If one assumes that a cellulose-forming enzyme system will be isolated in the near future, then a number of studies can be undertaken and a precise understanding at the molecular level can be obtained. However, the pace is slow. Indeed, it is rather disturbing that in two recent reviews (Delmer 1987; Hotchkiss 1989), the authors call for young blood to enter the field. This presumably reflects a general level of frustration at the rate of progress, and perhaps also a need for fresh ideas. In the United States, there is essentially only one group studying the formation of cellulose, namely that of R.N. Brown, Jr. Worldwide there are a few others; they are present mainly in the United Kingdom, Israel, and Japan. This apparent lack of trained scientists in this field in the Uhited States seems very surprising given the apparent complexity of the problem and its importance as a source of biobased materials. There is also a very clear need to determine how microfibril assembly and orientation is controlled, as well as that of exactly establishing the precise difIn this arena, the United States is comferences between cellulose polymorphs. peting very favorably, as evidenced by the studies by Brown, Atalla, VanderHart, Reuben, etc.

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As far as the cellulases are concerned, their mechanism of action is steadily being determined. It appears pretty safe to state that the structure of their active centers will yield to investigation. If so, this will lead to a marked improvement of our understanding of how these enzymes function, and their intricate reaction mechanisms. The first cellulase enzyme was cloned in Canada (Owolabi et al. 1908; Gilkes et al. 1988), but some of this advantage now seems to be lost as several European groups are making very rapid progress. In terms of application, an almost unlimited use of cellulases was originally envisaged. However, no major application has yet been realized. Perhaps application in more modest arenas, such as laundry detergents and specialty products requiring some cellulase activity, will be attained. Some of the Clostridium cellulases are generating interest, where it is hoped (by some) that the properties of the purified enzymes may be of use in the bleaching of chemical wood pulps (Claeyssens and Tomme 1989): LIGNIN Svntheaia and Structure in Vascular

Plants:

Current Status

These complex aromatic polymers normally account for some 20% - 30% of woody plant tiasue, and are essential for conferring rigidity and strength to cell walls. In woody plants, lignins are moat often described as random, dehydrogenative polymers of the three monolignola, p-coumaryl, coniferyl, and sinapyl alcohols. The ratio of these monolignola in lignin is both species and tissue dependent. Annual plants such as grasses, cereals, etc., contain lower levels of lignin. As an additional complication, such plants also have hydroxycinnamic acids incorporated into the lignin framework. Note, though, that the biochemical processes affecting both initiation and regulation of lignification are poorly understood. The structure of lignin within different plants has also attracted much attention. Unfortunately, such studies have been characterized by a lack of definitive results because of a) structural complexity of lignina b) its apparent heterogeneity within the plant cell wall and c) the fact that no method is currently available to isolate lignins in their native, or intact, state. A better understanding of lignin deposition and structure is important from both fundamental and applied standpoints. This is because alteration of lignin content and/or structure may have important commercial ramifications. Two examples will suffice: (i) there is a negative correlation between ruminant digestibility of plant material and lignin content and (ii) the kinetics of delignification vary markedly depending upon the plant material being studied. Hence, if either the quantity or the structure of lignin in intact plant tissue could be altered, this could have a major impact on wood pulping operations, wood fractionalization for chemicals, fuels, lignin utilization, and ruminant digestibility. Alteration/Regulation of Lignin Decomposition Processes Jensen, Zamir and Banner (1989) reported that in many annual plants, phenylalanine and tyrosine are synthesized via arogenic acid and not phenylpyruvate or 4-hydroxyphenylpyruvateas previously thought. This is an important result, and suggests that regulation of the synthesis of these two amino acids is controlled via a central (pivotal) intermediate. Hence inhibition of arogenate formation could lead to reduced lignin levels. Beyondphenylalanine andtyrosine, the enzymatic steps leading to the monolignols are fairly well understood. However, it is this sequence of events that is being

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considered for modulating the synthesis of lignin, in terms of type and amount. For

example, Grand and Boudet (1988) have cloned and sequenced a cinnamyl alcohol dehydrogenase gene. It is hoped that such information can now be used to reduce the lignin content of wheat. This work is being carried out in cooperation with ICI. A comparable approach to alter lignification, although essentially on a conceptual basis at present, was also described by Campbell et al. (1988). They propose to transform softwoods with O-methyl transferase genes from aspen (a

hardwood). The authors suggest that increased levels of this enzyme should result in higher syringyl contents of lignins in softwoods: i.e., a hardwoodlike lignin in softwoods. Presumably this would be less extensively cross-linked and easier to pulp. This is a high risk approach. Another important and achievable goal would be to examine the effects of enhancing the synthesis of syringyl moieties in hardwood lignin thereby facilitating delignification. Lignin Structure One other means of studying the effect of altering lignin deposition and structure is through the use of mutants. In this regard, several (annual) plants, e.g., maize that produce mutants somewhat deficient in lignin content have been observed (Monties et al. 1989). By way of a detailed chemical investigation, Monties' group in Prance is attempting to ascertain the reasons for these differences. The hope exists that this will shed some light on the underlying biochemical reasons. One feature, not yet taken into account by the French group, is that of the presence and potential significance of 4,4'dihydroxytruxillic acid (and related structures) in the annual plant Loliummultiflorum (Hartley and Ford 1989; Hartley, Whattley, and Harris 1988). According to Hartley, the possibility exists that a significant amount of lignin in grasses, cereals, etc., may have This is an important distinction and needs such cyclobutane-type structures. to be evaluated. As aforementioned, there is no known method whereby lignin can be isolated in its native, or intact, state. Consequently, we have developed methodology to probe the exact bonding environments of specific carbons in lignin in situ (Lewis et al. 1987, 1988, 1989; Lewis 1988). This was attained by synthesizing lignin precursors containing specifically enriched C-13 atoms at points considered to be mainly involved in inter-unit linkages in lignin, and then administering them The specifically labeled to plants over extended periods (weeks, months). lignins so obtained were then examined by solid state C-13 nuclear magnetic resonance spectroscopy (cross-polarization magic angle spinning techniques). In this way, the specific bonding environments for both the cereal, wheat, Triticum aestivum, and the hardwood, Leucaena leucoceoohala were obtained and compared to that of a synthetic dehydrogenatively polymerized (DHP) lignin prepThese studies showed that these synthetic aration from coniferyl alcohol. preparations were not an adequate representation of lignin structure in those plants.

In related radiochemical labelling studies, Terashima (1989) and Terashima,and Fukushima (1989) have developed methodology to examine the morphological distribution of each ligninmonomer (i.e., p-coumaryl, coniferyl, and synapyl alcohols) in lignin in the developing cell wall (i.e., secondary wall, middle lamella). This approach, coupled with appropriate delignificaton experiments, permits estimation of the extent of different substructures formed during both lignin formation and lignin removal.

However, the real significance of these studies is the following: (i) methodology can now be developed for other plant species, such as gymnosperms; (ii) the exact changes that the polymer undergoes during either chemical or biochemical delignification can now be examined: (iii) the effects of chemical inhibitors, etc.,

Biogenesis and Biodegradation

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135

on lignin structure can be studied; and (iv) if lignin from different cell wall layers can be obtained (e.g. secondary wall, middle lamella), then previously reported differences in their lignin structure can be verified (Saka and Goring 1985). Note that these studies require tissue grown over extended time periods (weeks, months, and perhaps, years). Z&n&a

Biodearadation

Most woody plants contain significant amounts of lignin, and hence this material contributes extensively to organic carbon recycling. However, the rate of biodegradability of plant tissue depends, to a large extent, on the amount of lignin present, i.e., the more lignin, the more recalcitrant the tissue is to biodegradation. Recent interest in biodegradatiod has largely been spurred on by the view that an appreciation of its detailed molecular mechanism(s) will lead to new processes, such as biopulping, biobleaching, etc. However, this view is not without its skeptics, and only time will tell as to whether such processes can (or will) be implemented. One application that does seem achievable (and likely) in the near future is that of detoxifying organic pollutant streams, such as those containing chlorinated phenolics/lignins and other organics. Over the past few decades, a rather substantial effort has been placed on elucidating the mechanism(a) by which certain microorganisms degrade lignin to carbon dioxide and humus. Of these, the most widely studied organism has been the white-rot baaidiomycete, Phanerochaete chrvaoaoorium. This is known to extensively degrade lignin as well as other plant polymers. An apparent breakthrough in elucidating the medhaniam of lignin biodegradation occurred when it was reported that p. ChrvsoaDorium secreted a lignin-degrading enzyme called ligninase, now described as lignin peroxidase (Tien and Kirk 1983; Glenn et al. 1983). This was capable of partially‘depolymerizing a "CHJmethylated aqueous acetone extract of spruce wood (Tien and Kirk 1983). At this point, it is pertinent to connnenton choice of substrate for lignin biodegradation studies. Many investigations do not use lignin itself, but instead employ lignin model compounds (normally phenylpropanoid dimera), DHP lignin preparations, or soluble lignin-derived materials, such as dioxane-HCl wheat straw lignin, milled wood lignina, etc. Of these, the lignin model compounds, which more closely represent lignin structures, are the most frequently employed. A major drawback to their continued usage is the fact that experimental findings are, for the moat part, never duplicated with the lignin polymer itself. Additionally, in the examples where lignin biodegradation is described, little or no conversion yield data is ever provided. been proposed (Gold, As far as 2. chrvaoaporium is concerned, it has recently Wariahi, and Valli 1989) that much of its lignolytic activity is due to the secretion of two soluble H,O,-requiringperoxidasea [lignin peroxidase aforementioned and manganese peroxidaae] (Kuwahanaet al. 1984). 'It is currently thought that lignin peroxidaae and H,O, convert nonphenolic substrates to aryl radical cations (Gold et al. 1984; Schoemaker et al. 1985; Keratem et al 1985); the charged species so formed can then diffuse away from the enzyme, following which a variety of different reactions can occur: e.g., benzylic oxidation/ hydroxylation, C1-C,aide-chain cleavage, ether cleavage (2-O-4' or OCH,), ring opening, rearrangements, etc. On the other hand, the manganese peroxidaae functions by oxidizing Mn" to Mn"', which in turn oxidizes phenolic substrates (Gold et al. 1989). Thus, combined action of both peroxidaaea results in lignin biodegradation.

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Although this explanation is appealing in its simplicity, several disconcerting observations require substantial explanation. These observations were as fol(i) the action of lignin peroxidase & vitro on milled wood lignin lows: resulted in polymerization, not depolymerization (Haemmerli, Hersola, and Fiechter 1986); (ii) Kirk et al. (1986) reported that lignin peroxidase both oolvmerized and deoolvmerized nonmethvlated lianin; (iii) some strains of P. .chrvsosnorium, which showed lignolytic activity, did not secrete detectable amounts of peroxidase (Leisola et al. 1988). However, when lignin peroxidase was added to the cultures on its own, or in combination with veratryl alcohol, the rate of biodegradation of a soluble "C wheat straw lignin increased: (iv) & vitro, lignin peroxidase oxidized veratryl alcohol to the corresponding aldehyde, and other quinones and lactones (Leisola et al. 1988) such as: d

=h

bCH,

R =

OCH3

ocnj

COOCH3

CHpOH

RslCUO

Addition of Mn"' resulted in a higher amount of veratryl aldehyde being produced (Leisola et al. 1988); (v) In vivo, veratryl alcohol was rapidly metabolized to CO2 (Leisola et al. 1988); when veratryl aldehyde was added, a quantitative reduction to veratryl alcohol occurred, via the action of a NADP oxidoreductase. On the other hand, the quinones and lactones were quickly "consumed" by p. chrvsosporium cultures; (vi) aromatic aldehyde formation made the lignin substrate less susceptible to one electron oxidation to give the radical cation(s), and therefore less susceptible to degradation (Leisola et al. 1988; Schoemaker et al. 1989). In an effort to rationalize these observations, Leisola et al..(1988) proposed the following working hypothesis for lignin biodegradation (Figure 2). In the first instance, the lignin polymer undergoes a one-electron oxidation to generate radical cation intermediates, which then undergo C2-CI cleavage to afford the corresponding aldehyde. This electron withdrawing group reduces the susceptibility to further biodegradation. However, mediation of an aryl-alcohol oxidoreductase reduces the aldehyde to the corresponding alcohol, following which aryl radical cation formation can occur once again. In this way, quinone and lactone intermediates can eventually be formed, which are then rapidly metabolized to COI. Biodegradation of the polymer can then occur (Leisola et al. 1988; Schoemaker et al. 1989). However, it must be cautioned that most of these findings and interpretations are based on experiments with model compounds, such as veratryl alcohol. Whether this is indeed the organism's mechanism of action for lignin biodegradation remains to be established unambiguously. In spite of these limitations, there is nevertheless considerable activity in the area of lignin biodegradation in terms of (bio)chemical, enzymological, and ultrastructural studies. In terms of ultrastructure, Joseleau and Rue1 (1989) and Gallagher et al. (1989) were able to identify changes to wood cell walls, following exposure to a variety of proposed lignolytic agents. Indeed, Joseleau concluded that many of the proposed changes can be mimicked by hydroxyl radicals from Fenton's reagent.

Biogenesis and Biodegradation of Plant Cell Wall Polymers

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Lignin Peroxidase

iFungus co2

Figure

2.

Hypothetical pathway for lignin biodegradation (Modified diagram from Leisola et al. 1988)

etc.---CO, by P. chrvsosnorium.

Interestingly, Dolphin's group (Cui and Dolphin 1989) has synthesized several hemeproteins and favorably compared their mechanism of action to that of the lignin peroxidase enzymes. Future Recommendations The Department of Energy (Office of Basic Research) recently conducted a workshop in Urbana, Illinois, in an attempt to identify future direction in the area of lignin research. It was generally felt that lignin biosynthetic studies had fallen far behind that of lignin biodegradation. Our labeling studies with lignin, and the processes whereby lignification is initiated, regulated, or modified were seen to be areas where significant advances could be obtained. Additionally, now that the enzymes leading to the monolignols are being cloned, the way is open to examine the effects of genetic manipulation of lignin in plant tissue. Such studies must surely be the path of the future, and will presumably result in improving wood-processing operations, animal nutrition, lignin-derived products, etc. However, other studies must also be carried out. We need to be able to determine, at the molecular level, exactly what is occurring during the chemical and biochemical delignification of plant material. This is an urgent priority. Finally, in terms of lignin biodegradation, this research has made some inroads toward our understanding themechanismby whichg. chrvsosDoriumdegrades lignin. Unfortunately, the mechanism of biodegradation, as reactions simply catalyzed by lignin peroxidase(a), do not seem tenable as such at present. Clearly an efficient means of degrading the polymer is required, and more effort should be placed in this direction. These studies seem to be at an impasse, at present. In terms of manpower, it is mainly my own group that is studying lignin biosynthesis in the United States, although there are also smaller programs at Michigan Technological University (W. H. Campbell and V. L. Chiang), and the Oregon

138

Polymers from Biobased Materials

Graduate Center W. Pengelly). As far as biodegradation is concerned, there are numerous working grolupsin the U.S.A. (e.g., Kirk's, Gold'S, Tien's) and progress continues to be made. Lignolytic systems other than P. chrvsosoorium need to be investigated with greater emphasis. OTHER AROMATIC POLYMERS Gutin and Subetin Current Status These structural polymers have reduced levels of phenylpropanoids (as compared to Signin) and significant amounts of aliphatic (long chain fatty acid/alcohol) domains. However, very little is understood about their structures, although some lim.itedprogress using solid state Carbon-13 NMR is being made (Stark et al. 1989). These materials play important roles in both defense and as barriers to diffusion. Put-are

Reccmaendations

The structures of these polymers need to be defined. This could be done by specific labeling cutin and suberin, together with appropriate degradation studies in a manner similar to that described for lignin. In addition, an improved understanding of the exact mechanism(s) of suberin--and cutin--degrading enzymes would be useful. At present, very few groups worldwide are examining this problem. Hvdrolvzable and Condensed Tannins Although they are not structural cell wall polymers, these aromatic substances can be present in large amounts depending on the tissue in question. Although their roles as tanning agents are declining, newer applications such as in adhesives and oil drilling muds continue to improve slowly. Biosynthesis and Structure Hydrolyzable tannins are polymeric substances normally containing a polyol group glucose) to which gallic acid substituents are esterified. The enzymology (e.g., of formation of the gallotannins has been studied, and Gross' group has shown that D-glucogallin can act as both donor and acceptor in transesterification reactions leading to 8-glucopentagallin (Gross 1989). Beyond this intermediate, the mechanism of formation of depside linkages and ellagitannins remains elusive. Condensed tannins (normally called proanthocyanidins) are widespread in nature, and are found in particularly high levels in gymnosperms (Lewis and Yamamoto 1989). They are products of both the phenylpropanoid and acetate pathways respectively. Beyond the formation of flavan-3-01s or flavan-3,4 dials, the remaining steps that lead to the oligomeric and polymeric proanthocyanidins are essentially unknown. Biodegradation In the case of hydrolyzable tannins, the enzyme tannase has been isolated and its properties are fairly well established (Deschamps 1989). However, as with .theproanthocyanidins, all that has been shown is that a number of organisms can grow on these substrates. There is absolutely no knowledge as to the detailed molecular transformations that are occurring, or the enzymes that are involved.

Biogenesis and Biodegradation of Plant Cell Wall Polymers

Future

139

Recoummndations

At present there is no group in the United States working on the biosynthesis or biodegradation of these important classes of polymers. This area needs to be revitalized.

This topic was not covered adequately in the symposium, mainly because of difficulties in finding anyone working in the area of biosynthesis. As regards biodegradation, attention seems to be focussed on xylanases. In this respect, the structure and function of bacterial and fungal xylanases was described by M. Yaguchi (1988). Surprisingly, their structures from different organisms were remarkably similar. Site-directed mutagenesis of a xylanase from Bacillus circulans suggested that a conserved glutamic acid was the catalytic residue. Five xylanases with molecular weight -20,000 were compared. Their secondary structures consisted of B-sheets and random coils, with no a-helix. Apparently it was verbally mentioned during the discussion period that some Japanese researchers had apparently crystallized a xylanase, but this has not yet appeared in the literature. Dekker (1989) described different xylans from various sources, and their commercial potential was then discussed by Senior et al. (1989). Future Reccmnmdations

There is some possibility that xylanases may have some utility in bleaching chemical pulps. Several groups in North America (both academic and industrial) are currently examining this possibility. ACIWOWLEDG-S

The author wishes to express sincere thanks to the following organizations for financial assistance received to host the symposiumBiogenesis and Biodegradation of Plant Cell Wall Polymers: Department of Energy (ECUT), American Chemical Society Petroleum Research Fund, American Chemical Society (Cellulose,Paper and Textile Division), Philip Morris USA, Weyerhauser, and Abitibi-Price, Inc. REFERENCES Atalla, R. H., Adv. Chem. Ser. 181 (1979) 55. Brown, R. M., Jr., Haigler, C. H., Suttie, J., White, A. R., Roberts, E., Smith, C., Itoh, T., Cooper, K. M., J. ADDS. Polvm. Sci., ADDS Polvm. S~mr,.,31 (1983) 33 - 78 (and references therein). Campbell, W. H., Bugos, R. C., and Chiang, V.L.C., "Isolation, Characterization and Cloning of O-Methyl Transferase from Aspen," Third Chemical Congress of North America, Abstract Cell 078, (American Chemical Society, 1988, Toronto, June S-11). Claeyssens, M., and Tomme, P., "Study of Structure-Activity Relationships of Cellulolytic Enzymes,'*in Plant Cell Wall Polvmers: Bioaenesis and Biodearada&&p, N. G. Lewis and M. G Paice, eds., ACS Symposium Series No. 399, American Chemical Society, Washington, D.C. (1989).

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Terashima, N., "An Improved Radiotracer Method for Studying Formation and Structure of Lignin," in Plant Cell Wall Polvmers: Bioaenesis and Biodearadation, N. G. Lewis, and M. G. Paice, eds., ACS Symposium Series No. 399, American Chemical Society, Washington, D.C. (1989). Terashima, N. and Fukushima, K., "Biogenesis and STructure of Macromolecular Lignin in the Cell Wall of Tree Xylem as Studied by Microautoradiography," in Plant Cell Wall Polvmers: Bioaenesis and Biodearadation, N. G. Lewis, and M. 0. Paice, eds., ACS Symposium Series No. 399, American Chemical Society, Washington, D.C. (1989). Tien, M. and Kirk, T. K., Science, 221 (1983) 661. VanderHart, D. L. and Atalla, R. H., in The Structures of Cellulose, R. H. Atalla, ed., ACS Symposium Series No. 340, American Chemical Society, Washington, D.C. (1987). Wasserman, B. P., Mason, T. L., Frost, D. J., Read, S.M., Slay, R. M., and Watada, A. E., "(1,3)-I+Glucan Synthase: Subunit Identification Studies," in Plant Cell Wall Polvmers: Bioaenesis and Biodearadation, N. G. Lewis and M. G. Paice, eds., ACS Symposium Series No. 399, American Chemical Society, Washington. D.C. (1989). Yaguchi, M. A. X., "Structure and Function of Bacterial and Fungal Xylanase," Abstract Cell 127, Third Chemical Congress of North America, (American Chemical Society, 1988, Toronto June 5-11).

11. Advances in Protein-Derived Materials Rare1 Grohmann and Michael E. iiimmel Biotechnology Research Branch Solar Energy Research Institute Golden, Colorado

WHY STUDY PROTEIN-BASEDMATERIALS After the advent of numerous manmade fibers, animal fibers and materials retained a share of the market because they have comparable mechanical properties and some aspects that manmade fibers cannot yet duplicate. However, production of animal fibers, especially silk, is relatively inefficient and very labor intensive. In fact, the manufacture of silk represents the only large-scale cultivation of insects that man has successfully achieved. Therefore, some high-value fibers such as silk are produced primarily in countries where labor is very cheap and exported to the United States. Many high-quality animal fibers remain undeveloped because they require the large-scale cultivation of insects, which in the case of carnivorous spiders, may be rather difficult. In comparison, synthetic fibers are readily produced at low cost. As a result, many natural fibers cannot effectively compete today. The production of natural fibers by a combination of biotechnological and chemical methods could use a cheap domestic source of starting materials (e.g., sugars, starch, and cellulose) in a very efficient overall process. Such a process would lend itself well to large-scale processing, thus demonstrating a potential for low cost. The systematic modification of the primary sequences of these materials would allow correlation of chemical structures to physical properties and result in the development of physical properties equivalent or superior to those of natural products available today. Furthermore, it is important to note that protein fibers are fully biodegradable and, therefore, environmentally benign. Genetic and enzyme engineering technology now offers considerable potential improvements in the synthetic production of protein-based fibers. CURBENT STATUS Historical

Proteinaceous substances in fibers and cell walls perform similar functions in the animal kingdom as polysaccharides do in plants. They provide structural integrity to multicellular organisms and, in the form of skin and hair, protect internal organs from damage and attack by outside forces. Man recognized the structural qualities of these materials long ago. Animal skins provided leather and fur for clothing and other products where high tensile strength was required. Animal hair, pr!.marilyfrom sheep, goats and rabbits, was spun into fibers or matted into felt and used as woven or nonwoven woolen textiles. Fibers secreted by larvae of the moth Bombyx mori to form cocoons were separated by the Chinese more than 4000 years ago and used in the manufacture of highly prized silk textiles (Livengood 1982, Lucas and Rudal11968, Otterburn 1977, and Peters 1963a). Natural fibers like silk and wool are still used in the textile industry and successfully compete with manmade fibers like nylon or polyester because they have comparable tensile strength (Tables I and II) and some properties that

144

PROPERTIES

Name

Specific Gravity

Tensile Elongation Standard water strenoth. at break HPa - . (dry) X regain

TABLE I' OF NATURAL

Fiber diameter, cc

FIBERS

Fiber length, in

Fiber shape and kind

Resistant to

Oval, crimped scales Flexible, soft smooth, weak Flexible, soft, smooth

Age, weak acids solvents Heat, solvents acids, wear Heat, solvents, weak acids, wear

Flat, ribbon, convoluted

Age, heat, washing, solvents, alkalies, insects

ANIHAL ORIGIN Wool

1.32

1.25 Silk (silkworm) 1.25 Silk (spider dragline)

120-200

23-35

620

20-25

1420-1550

15-18 10

17-40

1.5-5

10-13

n/ah

16-30

n/ah

VEGETABLE ORIGIN 210-830

Cotton

1.54

Jute

1.5

340

Sisal

1.49

520

Flax

1.52

1.48

Heneguen Abaca

10-20

1-1.5

14

15-20

2-2.5

13

10-30

2-3

12

15-18

2

18-25

410 1.48

690

0.5-2

Woody, rough Strand 30-40 Strand 40-50

15-30

310

Kenaf Hemp

7.5-8.5

5-11

2-3

13

Strand 30-70 Strand 30-60 Strand 30-120

a - References: Handbook of Material Science (1974) and O'Sullivan b - N/A, not applicable. Very long or continuous fibers.

(1988).

T$YfSfDn straight Soft, fine

Polygon or oval Polygon or oval, irregular Finer than sisal

Age, solvents washing, insects, weak acids, and alkalies

2 s : 2

TABLE II" PROPERTIES OF MAN-MADE ORGANIC FIBERS Chemical Class: common name

Specific gravity

Tensile strength MPa

z Q)

Elongation Water Softening Melting at Regain point point break, 4: (standard) ("C) ("CX)

Flarrmability

Brittleness temp, ("C)

CELLULOSE DERIVED FIBERS

3 f ;k 5 m _.

Acetate

1.30

120-170

20-30

Triacetate

1.32

140-190

25-30

Viscose rayon

1.51

210-320

17-25

3

200

High tenacity viscose Polynosic viscose Cuprammonium rayon (cupro)

1.53

410-550

10-12

0

200

1.53

410-550

8-20

7

200

1.52

210-310

10-17

12.5

250

6.5

140

230

225

300

Melts and burns Melts and burns Burns readily Burns readily Burns readily Burns readily

0

P %

<-114

PROTEIN DERIVED FIBERS Animal: casein 1.3 (milk) Vegetable-seed: 1.3 soybeans, corn, peanuts Vegetable-latex: 1.0 rubber (vulcanized)

100

60-70

80-100

40-60

30-50

14

100

150

Slow

11-15

150

250

Slow

700-900

0

300

Burns

-60

SYNTHETIC FIBERS Polyacrylonitrile (acrylic) Polyamide (nylon) Polyester (PET dacron) Polyethylene (low density, olefin)

4 L

1.17

340-520

25-40

2

190

260

1.14 1.38

480-830 480-830

20-40 10-50

4 0.4

200 225

215-250 250-290

Slow Low

(-100

0.92

280-480

25-40

0.15

120

Slow

-114

go-120

Burns

; (D T. m z-

TABLE II’ PROPERTIES OF MAN-MADE ORGANIC FIBERS Chemical Class: comnon name

Specific gravity

Polyethylene (high 0.95 density, Olefin) 0.91 Polypropylene (olefin) 1.1 Polyurethane (spandex) 1.38 Polyvinyl chloride (PVC) Polyvinyl alcohol 1.3 (PVA) Polyvinylidene 1.7 chloride (Saran) Polytetrafluoro2.1 ethylene (PTFE)

Tensile strength MPa

Elonuation

at

break, X

410-550

10-20

310-550

15-30

50-110 80-120 410-620

(continued)

Water Softenino Melting Regain point point(standard) ("C) 0%) 0.01

120-130

140

o-o.5

145

160-170

500-700

1.0

190

loo-125

0.1

Flaamability

Brittleness temp, ("C)

Slow

-114 - 70

250

Self-ext. low Burns

70

140

No; chars

<-I00

230

240

Slow

115-135

170

No

225

300

No

15-28

5

280

20-30

0.1

230

15-30

0

1.8-1.9

2400-3300

0.6-1.4

2200

n/a

Low

1.9-2.1

1400-2200

0.3-0.9

2200

n/a

Low

2200

n/a

Low

HIGH STRENGTH FIBERS Carbon (PAN precursor) Carbon (pitch precursor) Carbon (rayon precursor)

1.6

1000

2.5

2800 3600-4100 3400

4.0 2.8 2.0

PARA-ARAMID FIBERS Kevlar 29 Kevlar 49 Kevlar 149

1.44 1.44 1.47

160 160 160

a - References: Handbook of Material Science (1974) and Engineered

Materials

500(dec) 500 500 Handbook

Low Low Low (1987)

.z ID Z. g 2 %I

148

Polymers from BiobasedMaterials

synthetic fibers cannot duplicate at the present time. Wool, for example, has a partially hydrophilic character and, therefore, can remove moisture produced by perspiration (Boston 1984, Brearley and Iredale 1977). Condensation of moisture releases heat, which accounts, in part, for the heat-retaining properties of woolen fabrics.

Silk and Silk-like Fibers Silk fibers are solidified, viscous fluids secreted by special glands of a number of insects, namely caterpillars and spiders (Lucas and Rudall 1968). The significant source for textile use is the silk-moth caterpillar, commonly known as the silkworm (Livengood 1982, Otterburn 1977). Silk consists primarily of the proteins sericin and fibroin (Lucas and Rudall 1968). The bulk of the fiber is fibroin coated with 15%-25% of sericin or silk gum. Silkworm fibroin is composed mainly of alternating sequences of two amino acids, L-alanine and glycine, with hydroxyamino acids, L-serine or L-tyrosine, at approximately every seventh position (Couble et al. 1985, Katagata et al. 1984, Manning and Gage 1980, Oshima and Suzuki 1977, Strydom et al. 1977, Suzuki and Oshima 1982, Gage and Manning 1980). The overall structure of silk is more complex, with 18 amino acids found in silk fibroin, mostly in very small amounts. The secondary amino acid structure of silk fibers is composed of antiparallel-chain pleated sheet (i.e., b-pleated sheet), where chains are held together by hydrogen bonding between amide links (Livengood 1982; and Asakura et al. 1984). The silks of other insects are not as well characterized as the silk of Bombvx a; but, in general, most have a D-pleated sheet structure and contain mainly compact amino acids, such as alanine and glycine , with lesser amounts of serine, tyrosine, arginine, and aspartic acid (Lucas and Rudall, 1968). The sulfurcontaining amino acids also occur in small amounts, if at all, in most silk fibroins. Therefore, the proteins in silk fibers are held together primarily by hydrogen bonds and by a small number of ionic interactions between acidic and basic amino acids. The compositions of silks fromdifferent organisms can differ significantly. Silk from the sawfly, Phvmatocera aterrima, is mostly polyglycine; silks of Anaohe genus are alternating alanine and glycine units, whereas the unusual silks produced by species of the Aroidae family have alternating alanine and glutamine units (Lucas and Rudall 1968). The high tensile strength silks from spiders, which are related by composition to collagens, have a high content of glycine, alanine, and proline. Silks, manufactured by insects, represent a family of high-quality fibers composed of relatively simple amino acids.

Hair and Wool The structures of hair and wool fibers are much more complex than the structure of silk. Hair fibers are composed of hair cells with properties determined by cell wall structure and composition (Peters 1963b, Boston 1984). The hair proteins are relatively complex but can be subdivided into two subgroups: fibroins, The fibroins and matrix proteins 'are which form fibers, and matrix proteins. covalently crosslinked by disulfide bridges between the many cysteine residues, Great strides were made which occur throughout these proteins (Boston 1984). in recent years in the determination of primary sequences of the wool fibroins and matrix proteins (Crewther and Lennox 1975, Dopheide 1973, Dowling, Parry, and Sparrow 1983, Dowling, Crewther, and Inglis 1986, Gouqh, Inglis, and Crewther 1978, Hogg, bowling, and Crewther 1978, Kuczek and Rogers 1987; Parry, Fraser, and MacRae 1979, Rogers 1984). Although the structure of wool fibroins is much more complex than that of their counterparts in silk, several basic features have Wool fibroins are a-helical proteins with a general repetition of emerged. seven amino acids where the first and fourth amino acids have hydrophobic side They are also characterized by repeated pairs of basic, acidic, or chains.

Advancesin Protein-Derived

Materials

149

sulfur-containing amino acids every 9 to 10 amino acids residues. The repeats of ionic or sulfur-containing amino acids provide inter-or intrachain bonding through ionic interactions and covalent disulfide bridges. The matrix proteins have similar pairs of cysteine residues which form inter- or intramolecular disulfide bridges. P&eta

from ModLfied Coll8aen

Collagen is a protein complex arranged in a fibrous form and is normally found in bone, skin, and various connective tissues of higher animals. In fact, collagen comprises 20% - 30% of the total protein weight of mamnals. This consideration has led to an impressive research effort in the leather utilization industry. Collagen ffbrils are arranged in different ways, depending on the biological function of the particular type of connective tissue. For example, in tendons, collagen fibers are,arranged in parallel bundles for strength, yet have very little or no capacity for stretching. Although denatured forms of collagen, such as gelatin, have been used extensively in the food industry, its use as a biomaterial is currently attracting significant research effort. Although collagens of different species differ in amino acid sequence, most contain about 35% glycine and 11% alanine, thus .resemblingthe B-keratins. From comparisons of the X-ray patterns of collagen and of polyproline it has been deduced that the secondary structure of collagen is that of a triple helix of polypeptide chains. Each chain is held together by hydrogen bonds. The high frequency of proline residues determines the distinctive type of helicalarrangement of the chain, whereas the smaller side groups of the glycine residues, which occur in every third position, allow the chains to intertwine. Collagen is composed of recurring subunit structures, triple-stranded tropocollagen molecules, having distinctive "heads," or telopeptide end'groups. Both structures are now known to have different primary amino acid sequences (Brennan and Ferdinand 1983). Tropocollagen is composed of three rodlike polypeptide chains arranged in a 3000~A-long, right-handed helix (Rubin and Stenzyl 19691, which has been shown by electron microscopy to be slightly flexible (Walton and Blackwell1973). These subunits are arranged head to tail in many parallel bundles with the heads staggered along the length of the bundle. As a bio-fiber, collagen has the distinct advantage over synthetic polymers of biocompatibility, especially important in the biomedical industry. It is now believed that only the telopeptide end groups are responsible for eliciting immune response from the host organism following implantation, thus rendering fibers made from modified collagen, with these groups removed, an ideal replacement material for silk or catgut sutures. Biodegradability at the site of implantation is another highly desirable property of collagen. This feature makes collagen ideal for burn-wound coverings, structural implants, and prosthetic devices. Recently, research in collagen structure has used chemical crosslinking with methyl cellulose to produce modified collagens with specific structural properties (Brennan and Rodriguez 1983). Leather Comnosites Although man has used leather and leather goods as clothing and shelter for thousands of years, these materials may be more useful as "trunk" polymers for chemical grafting or other modifications. Such materials--a composite of a renewable resource, leather (a desiccated collagen), and engineered copolymers-may be suitable for adaptation to specific functions in industry. Ultravioletand radiation-inducedpolymerization has been used successfully for the grafting

150

Polymers

from

Biobased

Materials

of styrene to native leather, for example, thus yielding modified leather materials with altered properties (Davis et al. 1983). AlSO, Jordan et al. (1983) have recently reported the preparation of leather-acrylate composites using methyl methacrylate, a mixture of n-butyl acrylate and methyl methacrylate, and pure n-butyl acrylate. Many of these leather composites show mechanical properties similar to synthetic composite materials, which have been extensively studied (Jordan et al. 1983). Although interesting and perhaps useful as a model protein-polymer matrix of known structure, vast availability, and suitability for chemical modification, leather composites show limited promise for improvement via genetic engineering. NERD FOR FUTURR RESEARCH Although silk, wool, and other natural proteinaceous polymers were used in early textile and fiber applications, these materials have been displaced substantially by synthetic polymers derived from petroleum feedstocks. Many naturally occurring fibers and materials have properties that are superior to synthetic materials, but the latter lend themselves to inexpensive mass production. The full development of natural protein fibers will require either development of largescale cultivation methods for insects or development of alternate methods of production. The objectives of future research should be focused on the development of synthetic protein materials which resemble natural protein fibers. These now materials should be subjected systematically to primary structural modification, so that characterization of these proteins generates information regarding correlations between the protein primary and secondary structures and their physicochemical properties. Ultimately, the development of synthetic protein materials incorporating these "engineered" features may be feasible. Initial research efforts should focus on the application of genetic engineering to produce silk-type proteins because of their superior mechanical properties (Tables I and II), high value , and much simpler structure when compared to wool. The synthesis of silk proteins can be performed by either purely chemical methods or a combination of biological and chemical methods. The purely chemical approach appears on the surface to be the most straightforward, since the majority of silk proteins have simple repeating sequences of two or three amino acids as primary building blocks. There are, however, several serious obstacles to chemical synthesis of proteins that still prevent commercialization of protein based materials, despite decades of synthetic efforts. These are: 1. With the single exception of glycine (a-aminoacetic acid), all amino acids are asymmetric at the a-carbon atom and therefore optically active. All natural proteins are ,made from one (primarily the -L-) form of each amino acid and are themselves asymmetric. Synthesis and separation of optically active amino acids have been a challenge which has not been satisfactorily met. Therefore, most optically active amino acids are produced by biological fermentations as secondary metabolites (i.e., in low yields and concentrations). Most amino acids are relatively expensive for these reasons. 2. The simple polymerization of unprotected amino acids does not lead to high molecular weight polymers as a major product. The major products are cyclic dipeptides (diketopiperazines). 3. Many activation procedures for the formation of peptide bonds lead to racemization. Racemization produces imperfections in the protein chains and modifies the mechanical properties of the finished material.

Advances in Protein-Derived Materials 151

These groups must be pro4. Many amino acids contain reactive side chains. tected before formation of the peptide chain and selectively removed after the protein formation. 5. Cyclic dipeptides do not form if suitable protective groups are introduced into the amino and carboxylic-tennini of each amino acid. One of the protective groups is then selectively cleaved for the formation of the next amide (i.e., peptide) bond. Therefore, the formation of each peptide bond is a complex procedure that can be approximated by the following sequences: (a) preparation and purification of the optically active amino acid, (b) preparation and purification of the blocked and protected amino acid, (c) coupling step, and finally (d) deprotection. 6. The coupling and protection of amino acids must be performed in an anhydrous Expensive and toxic organic solvents are thus used in large environment. amounts. The net result of these complications is the limitation of chemical synthesis to short peptides of very high value in medicinal applications. All larger proteins are isolated from living organisms or produced by genetic engineering. Protein materials like silk fibroins present a unique challenge to genetic engineering: they are crystalline and insoluble in water. Therefore, they will precipitate in the cell environment and may block movement of ribosomes producing them from messenger RNA. Bacteria and other microorganisms used in recombinant DNA work are very small and do not have specialized organs for secretion of long filaments as do some insects. The relatively simple solution to these technical problems may be the use of genetically engineered bacteria to overproduce short repeating peptide units. Following the isolation of these peptides, they would Fibers or other materials be chemically coupled to form long polymer chains. would be produced from these polymers by conventional technology. The utilization of genetic engineering technology will simplify the overall Amino acids are produced from simple carbohydrates and process tremendously. ammonia in every microorganism for its own protein synthesis. The incorporation of genes for synthetic peptides will carry the step further, and the entire building block will be produced in one system. Therefore, the raw material for protein production will be cheap carbohydrate, and expensive synthesis and purification of amino acids will be eliminated. The genetically engineered bacteria will perform the whole complicated sequence from carbohydrate metabolism through amino acid synthesis to peptide production in high yield, with one simple unit The construction of the protein production system requires several operation. elements: (a) a host microorganism, (b) a vector DNA (plasmid), (c) a promoter sequence (preferably controllable), (d) a terminator sequence, and (e) a gene. Since the major building blocks in silk proteins are repeating dipeptides, the DNA synthesis will be greatly simplified because it will be mostly composed of Other DNA elements are readily available. repeating hexanucleotides. The simplest initial approach for evaluation of synthetic silks is to synthesize polyglycine, polyalanine, and alternating poly (glycine-alanine), and then evaluate the mechanical and physical properties of each polymer. Advances in the development of optical methods such as circular dichroism (Greenfield and Fasman 1969) may also be important in the evaluation of the solution structures of these new fibers or fiber-precursors. In the next step, the serine can be introduced at every seventh and adjacent positions. The hydroxy-group of serine provides a site for chemical crosslinking. The effects of the distance and the chemical character of crosslinks can thus be readily assessed. The serine can also be replaced by cysteine which can crosslink the protein chains by disulfide bridges and also offers highly nucleophilic groups for chemical crosslinking agents.

152

Polymers from Biobased Materials

The amino acid substitutions can then evolve to replacement of alanine and/or serine with glutamine and other amino acids. Such replacements may lead to materials with new thermomechanical, electrical, and chemomechanical properties as evidenced by the limited results obtained recently by Urry (1988). Besides showing high promise for structural applications requiring fibers or sheets of high tensile strength (i.e., comparable to most advanced synthetic fibers such as Kevlar and aramid), synthetic peptides and proteins can have significant applications as adhesives. A recent U.S. Patent (Waite 1986) describes novel decapeptides identified in mollusk secretions, which exhibit superior adhesive capabilities especially on surfaces submerged in water. REFERENCES Asakura,

T., Watanabe, Y., and Itoh, T., Macromolecules,

E

(1984) 2421-2426;

Boston, W.S., in Kirk Othmer Encyclopedia of Chemical Technolosv, Vol. 24, WileyInterscience Publishers, New York, (1984) pp. 612-644.

Brearley, A. and Iredale, J.A., Leeds, U.K., (1977).

"The Woolen

Industry," W.I.R.A.

Publications,

Brennan, J.M. and Rodriguez, F., "Modified Fibers from Regenerated Collagen," in Polvmer Science and Technolocv, vol. 17, C.E. Carraher and L. H. Sperling, eds., Plenum Press, New York, (1983) pp. 361-373. Couble, P., Chevillard, M., Moine, A., Ravel-Chapnis, Nucl. Acids Res., 13 (1985) 1801-1814.

P., and Prudhonrme, J.C.,

Crewther, W.G. and Lennox, F.G., J. Proc. R. Sot. N.S.W., 108

(1975) 95-110.

Davis, N.P., Garnett, J.L., Ang, C.H., and Geldard, L., "Novel W and Radiation Polymerization Methods for Modifying Polyolefins, Cellulose and Leather," in Polvmer Science and Technology Vol. 17, C.E. Carraher and L. H. Sperling, eds., Plenum Press, New York, (1983)'~~. 323-345. Dopheide,

T.A.A., Eur. J. Biochem., 2

(1973) 120-124.

Dowling, L.M., Parry, D.A.D., and Sparrow, L.G., Bioscience Reo., 2 (1983) 73-78. Dowling, L.M., Crewther, W.G., and Inglis, A.S., Biochem. J., 236 (1986) 695-703. *'Engineered Materials Handbook Volume 1. Composites," Park, OH (1987) pp 50-57. Gage, L.P. and Manning, R.F., J. Biol. Chem., 255

ASM International, Metals

(1980) 9444-9450.

Gough, K.H., Inglis, A.S., and Crewther, W.G., Biochem. J., 173 (1978) 373-385. Greenfield, N. and Fasman, G. D., Biochem., 1 (1969) 4108-4116. Hogg, D. McC., 353-363.

Dowling,

L.M.,

and

Crewther,

W.G.,

Biochem.

J., 173

(1978)

Artymyshyn,. B., Hannigan, M.V., Carroll, R.J., and Feairheller, Jordan, E.F., S.H., "Polymer-Leather Composites V. Preparative Methods, Kinetics, Morphology,

Advances in Protein-Derived Materials 153

and Mechanical Properties of Selected Acrylate Polymer-Leather Composite Materials," in Polymer Science and Technolooy, Vol. 17, C.E. Carraher, and Sperling, eds., Plenum Press, New York, (1983) pp. 407-452. Katagata, Y., Kikuchi, A., and Shimura, K., Nipcon Sashisaku Zasshi, 53, 226-236. Kuczek, E.S. and Rogers, G.E., Eur. J. Biochem., 166

(1984)

(1987) 79-85.

Livengood, C.D., in Kirk-Othmer Enovclopedia of Chemical Technology, Wiley-Interscience Publishers, New York, (1982) pp. 973-981.

Vol. 20,

Lucas, F. and Rudall, K.M., in Comorehensive Biochemistrv, Vol. 26, Part B, M. Florkin and E.H. Stotz, eds., Elsevier Publishing Co., New York, (1968) pp. 475-558. Manning, R.F. and Gage, L.P., J. Biol. Chem., 255

(1980) 9451-9457.

Oshima, Y. and Suzuki, Y., Proc. Nat. Acad. Sci. USA, 74 O'Sullivan, D., C&E News, 66

(1977) 5363-5367.

(1988) 24-25.

Otterburn, M.S., in Chemistry of Natural Protein Fibers, Plenum Press Publishers, New York, (1977) pp. 53-80. Parry, D.A.D., (1979) 17-22.

Fraser,

R.D.B.,

and MacRae,

Peters, R.H., Textile (1963a) pp. 302-314.

Chemistrv,

Vol.

Peters, R.H., Textile (196313)pp. 263-301.

Chemistrv. Vol.

Rogers, G.E., Biochem. Sot. Svmc., 49

T.P.,

R.S. Asquith,

Int. J. Biol. Macromol.,

Publishing

Co., New York,

1, Elsevier

Publishing

Co.,

New

York,

(1984) 85-108. Plenum Press, New York,

Strydom, D.J., Haylett, T., and Stead, R.H., Biochem. Bionhvs. (1977) 932-938.

Urry, D.W., Res. & Dev.,

1

1, Elsevier

Rubin, A.L. and Stenzyl, K.H., in Biomaterials,

Suzuki, Y. and Cshima, 947-957.

ed.,

Y., Cold Spring Harbor

Svm~. Quant.

(1969).

Res. Comm., 79

Biol., 47

(1982)

(August 19881, 57-64.

Waite, J.H., U.S. Patent 4,585,585, April 29, 1986. Walton, A.G. and Blackwell, (1973).

J., Biopolvmers,

Academic

Press, New York, N.Y.,

Appendix: Examples of Research Activities in Japan

CELLUCON AN

88

INTERNATIONAL

SYMPOSIUM

NEW FUNCTIONALISATION

28

NOVEMBER

6 WOOD

AND -

APPLICATIONS

1 DECEMBER,

KYOTO,

The Third International

OF FIBER SCIENCE in cooperation CELLUCON

BOOK

Cellucon

Organised SOCIETY

1988

JAPAN

EXPO GUIDE

THE

ON

DEVELOPMENTS

IN CELLULOSlCS

FUNDAMENTALS

JAPAN

Conterence

by

AND

TECHNOLOGY,

with

CONFERENCES

154

JAPAN

Appendix-Examples

RECENT PROGRESS OF CHEMICAL

of Research Activities in Japan

NODlPlCATION

OF WOOD

IN JAPAN

of

A field

in

both

Practical

we have some

“Chemical

exhibited

of

vhlch

academic

wood

have

University, vi th

and

modification

been

in

viewpoints.

products

of

in

The

is

this

important

exhibition,

cheml cal

modification

collaboration

Materials

Japan.

wood” In

of

developed

Laboratory

lndB;strtes

of

for

of

Wood

followings

Kyoto

Improvements,

are

the

products

exhibited; *Wood

phenol

*Moldings

liquid from

(Kyoto

University)

chemically

modified

*Foams

from

wood-phenol

lFi lms

from

thermal

ly

*Three-dimensionally esterifted

*Carbon

fibers

liquid

(Kyoto

Univ.)

f lowable

wood

(Kyoto

cured

wood bearing

crosslinking

wood

agent from

sheets

and

carboxyl

tOkura

lnd.

wood-phenol

vessels

gror)ps Co.,

liquid.

Univ.) from

and

epoxide

Ltd,) tO]l

Paper

Co.,

Ltd.) *Wood

fiber-polypropylene

wood

+Acetylated (Daiken

Trade

1

and

8 lnd.

*Wood-plastic-composites Ltd.

composites

its Co.,

application

(Ube

Ind., to

Ltd.) speaker

box

Ltd.) (VPC)

(Daiken

Trade

8 lnd.

Co.,

155

156

Polymers

from

Biobased

Materials

Exhibitors of CELLUCON 88 JAPAN EXPO Ajinozoto

Co.,Ltd.

Chemical

Asahl

Industry

Chlsso

Corporation

Dalcel

Chemical

Daido-Haruta

Industry Finishing

Dai-Ichi

Kogyo

Dalwabo

Co. .Ltd.

Fuji

Spinning

Jujo

Paper

Kanebo

Ltd. Co.,Ltd.

Seiyaku

Co.,Ltd.

Co.,Ltd. Co.,Ltd.

Ltd.

Nihon

Seikl

Kaisha

Nisshinbo

Industries.

Shimadzu

Corporatlon

Shin-Etsu

Chemical

Suga

Co. ,Ltd.

Test

Toyobo Shiraishi

Ltd. Inc.

Co.,Ltd.

Instruments

Co.,Ltd.

Co. #Ltd. Laboratory

CELLUCON 88 JAPAN EXPO Conmittee Chairman

Prof.

Vice

Dr.

Chairman

Member

Toshlyuki Tatsuya

Uriu

Hongu

(Univ.

Prof.

Takeaki

Miyamoto

Prof.

Hirofusa

Shirai

Assoc.Prof.

Toshio

Assoc.Prof.

Shire

Tokyo)

(Nisshinbo (Kyoto

Unive.)

(Shinshu

Univ.)

Hayashi Saka

Ind..Xnc.)

(Kyoto

(Kyoto

Univ.)

Univ.)

Appendix-Examples

AJ

inomolo

of

Co

Researcn

I nc

Activltles

in Japan

157

158

Polymers from Biobased Materials

ASAHI CHEMICAL

Bead Office

Bibiya-Mitsai

cho. Chiyoda-h

Bldg..

T&JO

100.

l-1-2

Taraka-

JAPAN

Ot?HBERG J) Hain Products Chemicals. fibers. Plastics. synthetic rubbers, coaposite materials. fine CeriuiCS. food products. pharmaceuticals. medical esuiprnt. Dcmbrane separation systems. eieCt!WiCS. infomationlcorunications systems. construction materials, housing, engineering

INDUSTRY

GO.,LTD

BmEERcclJmlPs Be&erg@ is a silky

cloths,

lingerie

years Products

Exhibited

msterial

bore from pure

cotton. Vihh its intrinsic properties, “a soft touch feeling”,“suit~bla moisture absorbency”, **sweai absorbency” and “excelleot aoti-electroBernberg@ is suitable for static property”, textile such as lining high-grade ladies’ users

tation

and nodergamots.

and customers

to Benberg@

as a reliable

There are only a few companies berg

Gmpany Profile: Throughout founding, expanded

the more than 60 years

Asahi Chemical its operations

tion

from raw material

full

utilization

lence

of

io technology

to finished

byproducts.

Sufficiency

in basic is

production

the early

further

product and

strengthened

with

petrochemical The corporate

in 1982 with

ves

the comccmplcx base was

the absorp-

tion of Asahi-Dou Ltd sod its strong cmplementaty position in resins and plastics. Today,

Asahi

Chemical

with

comprehensive

which

have

becac

Asahi Asia

Chemical in its

has

sales

cootinues

its

growth

operations

and

products

ao iotegral

part

of lve!y

day life. As far as cellolosic

products enjoyed

are cooceroed,

No.1 position

in

output.

Lint-free cottoo Class 10 cleaalioess.

vipers corresponding to made of ooowoveo fabric

of 1001 pure cotton cellulose fibers. BMXIf@ contains DO impurities such as an adhesive since

these

fibers

bind

themselves

by self-

BEMIX@ lint-free vipers are used adhesion. ia a wide range of leading-edge techoology fields including clean rooms for semiconductor production,

and pharmaceutical,bioaedical

food-processing plants. Contact:Bemliese Sales

Dept.

is

the

mterial. producing

Ben-

around the world sod Asahi Chemical

sole

success

good repo-

manufacturer

in Japan.

of Benberg fiber

“Ceaseless through innovation”. Contact:Bemberg

buisiness

techoical Sales

Our great is

and

realized

scientific

Dept.

Full stlf-

materials

1970s.

of the Hianshiu

in Okayama Prefecture.

its

based oo excel-

and development.

established pletion

since

Industry Co.,Ltd. has by vertical iotegra-

fiber

For maoy

have given

and

RhYwclRrlEs Uith. more then SO yews’ history, Asshim Wsyon ber enjoyed the world-wide reputation. Asahi@ Rayon has its wide range of uses as ladies’ knitted threads,

lining cloths, velvet, outerwears, embroidery goods, interior goods. industrial woven fabrics. The develop-

ments

towards

gress tion

under the continuous and with the crestioo

21th century

having more fascinatiog Contact: Rayon Sales

are steadily technical of

new

in proinoovaproducts

properties. Dept.

FWl:

Be&erg@ licroporoos hollow fiber meabraoe with precisely controlled pore sire is echievld through phase-separation mechmism and modificatioo of membrane surface characteristics. With a highly uniform pore size distribution, the hollow fiber membrane has good possibility for complete removal of AIDS and hepatitis-B viruses fron human blood Developcots are also application of Bt@l in tiooated blood plaza

plasma. in progress

for

the

the production of fracproducts, by utilizing

the hydrophilic nature of Be&erg@. which prevents BtM from absorbing useful protein conposents Contact:

of blood plasma. EM4Project ration

Team, Textile

Admisist-

Appendix-Examples

of Research

Activities

in Japan

ASAHI CHEMICAL INOUSTRY CO.,110 tlollw

Fiber

Artificiel

Kidney - lkmbrw

Plesu

Seplrxtor~nembnne

Component

Scparrtor

13 yews a

rrpa

fiber

AVICR@ Avicel@

is

meoufectured

ego Aexbi Medial

hollow

rypC Plmsme

Co.,Ltd.

lrtificiel

developed

kidney(AK)

mriog

cupremooiw reywfcoprr cellulose;llemberg@) for the first time in the world. Sioce then, ooder the mottos “more sefely”,‘kore cafortlbly” cod “with higher perforseoce”. we hew

nice1

cooperetion

grioed ent

crystelline Chemical

with

exhibiting

stebilirer

cellulose

under the tech-

PX Corp.

high,reputetion

disintergetion

Avicel@

es aa excellent

superior

and adsorbent grade:

field

in Commeot-

XC(registered in Staodof Drugs not in JP)

on wmbreae materiels end lpplied reeeerch om menufecturing rod hew offered the best cupre

Food ldditive grede: fD, RC-N(rdmitted oeturel food ldditive)

cellulose

AXs.

At present,

cupre cellolose

is

utilized

most world-widely

Cosmetic grade: PH-•icro(rcgistered Steoderds for Cosmetic lleteriels)

mbrene

uterisl

Industriel

grrde:

Contect:

Specielty

for

valuable knov-hovs of cuprr cellolose developing plrsme This

es l most relieble end AK. Yith verious

geiaed io the development AK, we heve succeeded in

world’s

l

separrtor

first

using

nnbrene

membrxoe type plesme

,therepy Pulmineot

scparetor

aLWlME Cellulose

Co.,Ltd.

is oo* of the most uide-

cellulose CN is

derivrtives. Among mew used in combioetion with

inks rbility,

lbility, Efforts flexibly

es

l

rxw materiel

lxcelleot

pipcnt

strong

in

Jrpea

proper ;redes:

iogs especielly for megnetic (3)CElJ4OU@ BI’Kl/& Pertielly

coetlngs. cerboxyleted

swelled by tolueoe end MgK exhibiting the improved pigment dispersing end adhesive Suiteblo

disintegretor

sales

en excellent

for’ Ac-Di-Sol,

for medicines

Ac-Di-Sol

is

l

pertielly

network weterend phercross-

linked sodium cerboxymethyl cellulose cod registered in NP in USA es Croscerullose Sodium, Type A. Cootect:

Specielty

Chemicrls

is

Div.

film

(1)HIC l/Z: Por gene& use (Z)CEUKWA@ BMI/Z: CN’swelled by tolueoe and methyl isobutyl ketone(MBK) which l re inert to isocyenetes. Suiteble for uretheoe coet-

lbilities.

Div.

dispersing

repid drying rbility end so oo. have ken udc to meet users’ demands end to develope

Chemicrls

for coetings,

end exhibits

etc.,

TC

AC-Di-Sol Asrhi Chemic81 hes en exclusive

uceuticelr.

nitrete(M)

some solvents peints, forring

es

WITRATgPw INDtCXUAL USE

ly utilized otilixetions,

in

hes opeoed trcrtmeot

insoluble tkdicel

l

type

for intrecteble diseeses such es Hepetitir end klipeot Rhrwtoid

Arthritis. Cootect:Asehi

es

cellulose-di-rcetete.

the new wry to the plesuphtresis l

xnd sod es

in food industries.

PH(rcgistered

cry of Jep. Pherm.). lrds for Ingredients

hes

excipi-

compressibility

in phermeceutical

Phwmeceuticel

ude efforts to meet the expending demands in “dielyris treetment” through l besic rereerch

micro

l

by’Asahi

for ugoetic

used for high performance ugnetic Costect: Specielty Chcmicels Div.

coetings tepes.

CN

PARMan PAP= Parchment peper is l specielized end sulfric lcid-treeted peper ude of pure plent fibers. Vith its excellent properties such es high oilend weter-resistance perchment peper has cesiog uterielr for creb, end es uteriels end so on. Contect: Specielty

xod processebility. the found its wide usage es deiry for

Chericels

products. imitation Div.

canned flowers

159

160

Polymers

from

Biobased

Materials

ASAHI CHEMICAL INDUSTRY CC.,110

Ul We-thin strength

hemp peper (6g/e*)

end dinnsionel

vi th

stebility

eyellent

ir produced

usinS hemp pulp. Ihe ultre-thin hemp paper cae be treeted by viscose reyoo eolutien to ipspire high by soy

weter- end chuicel-resistances, end resin solutions to give en excelloot

strength

end high

The

uio

useSo

Ses or liquid of

the

pemebility.

hemp pepers

l re

es

cosmetic paper. peper, tape, ceke fiber casing, cheese-dyeinS of

follows: steqcile pepers for ldhesive heir-dressing(pewent),

fiber end ueter/kitchcn refuse seperetion. Contect: Spcielty Cheeicsls Div.

CR-85: Holeculerly

disptreed

of

mixture

cellulose/sterch CR-R5 ir

the world’s

Senooue mixed product

first ude

eoleculsrly free

cellulose

homocod

exhibiting lxellent propertier es rterch, food uteriels end food sdditives. CR-85 is developed es l results of rcieotific rcscerch on supereoleculer structure of cellulose and its vent,

dissolution which is

into cepeble

l

rieple

end sefe

sol-

strrch

too.

to dissolve

M-85 is produced in the fom of fiber(uet or dry) or powdw(mt or dry). With e hmc~eaoous distribution of cellulso cod stsrch, cod l controlled porous structure, Ok85 has the following outstuadiw properties: l.Yhite

in color,

testelcss, retention

odorless

Z.Superior

weter

end oil

J.Excellent LPleeeent

diwosioml stebility when boiled texture end touch to eet

reteotion

A. Ae food edditives:

l.Prevents

the oil-water

seperetioo

of foods

b.Proaotes the smooth recovery of dehydrated foods when warmed by hot uster c.Powderites end ;leouletes highly vet foods d.Improves eeting touch for foods(fryie& noodle, meet, boiled fish peste, ltc) l.Inereeses the uhiteoees of foods f.Civee noo-celo~ cod heslthy festure B.Ae food uteriels: l.Febricetod foodsWab stick, Scellops, squid net. sherk fin, ltc) b.Non+rlory diet. Contact:

Food Div.,

Food Research Iaboretory;

Appendix-Examples

of Research Activities

in Japan

CHISSO CORPORATION Herd

Office

Capital

Employee Main Office/Branch Hain Plant Uain Product8

Tokyo Bldg., 713 Uarunouchi 2-chome Chiyoda-ku, Tokyo U7,013,960,750 1,200 Tokyo, Osaka, Nagoye, Fukuoka, Yokohama, Neu Uinamate, Uitushima Polypropylene Ffber, Polyvinyl Polypropylene, Resin, Higher Alcohols, Plasticizer, Organic Solvents, Silicon Products, Liquid Crystals, Fertilizer, Slov-release Nitrogen Fertilizer

York Chloride Acid, Compound

PRODUCTS EXHIBITED

1.

“Cellufine”

Media

for

Chromatography

Chisso has developed a nev technology to poroui spherical beads in various sizes. Three chromatography types of “Cellufine”

produce media

cellulose-based are

available.

(1 )Cel Filtration Chromatography (2)Ion Exchange Chromatography (3)Affinity Chromatography “Cellufine” is excellent chromatographic media with the followSng characteristic features. (l)Crost-linked cellulose shaped in spherical form means excellent mechanical strength and separation under higher flow rate is possible. (2)Applicable to laboratory to indhstrial scale separation. (3)Especially suitable for large-scale affinity chromatographic separation. (4)Very stable chiplically. (5)Excellent separation efficiency. 2.

Chiral

Reagents

Chlsso has develooed the outical active alcohols. These reagents ir; available as the starting substances reagents for medicine, agricultural medicine, biological subitancer, liquid crystils, etc. Examples

of Chlral Reagents

R-(-)-2-heptanol, R-(-)-2-octanol, R-(-)-2-nonanol, R-(+I-1-phenyl

S-ftl-2-heptanol S-(*)-2-octanol S-(*)-2-nonanol

ethanol, S-(-I-1-phenyl ethanol

of

chiral active

161

162

Polymers

from

Biobased

Materials

HEAD OFFICE OSAKA

: 1. Teppo-cho, Sakai, Osaka 590, Japan

HEAD OFFICE TOKYO

: 8-1, Kasumigaseki Whome, Chiyoda-ku, Tokyo 100, Japan

CAPITAL:Y25.954,882,332 EMPLOYEES: 3.041 MAIN PRODXTS:CELLULOSlC

DERIVATIVES. ORGANIC CHEMICALS.

PLASTICS AND FILMS, FUNCTIONAL PRODUCTS, PROPULSION SYSTEMS

Columns

for Optical Resolution

CHIRALPAK” CHIRALCELTROWNPAK Sor far we have developed 15 kinds of HPLC columns aiming at Chromatographic resolution of various racemates. These are on the market in United State and Europe, as well as Japan. Moreover we undertake practical preparative scale resolution of your samples with fee.

Appendix-Examples

DAI-ICHI

of Research

Activities

in Japan

163

KOGYOSEIYAKU CO., LTO.

Head office :Shin-KvotoCenterBids.7F Shiokoji-dori

Products

DAI-ICHI KOGYOSEIYAKUCG..LTG.

Exhibited is a manufacturer and mrketar

KarasunaNishi-iru.

of a wide ran96of chemicalsfor

Shiwsvo-ku.Kvoto 600 JAPAN

variousindustries.

Capital

: % 1.3 billion(Authorized

Here.we likefocal1

Nunberof

: 985(asof March3lst 1988)

Capital5.2 billion)

your

atte-

ntionto someof the productsto be usedfor %llulose " ,

Emlovees

u Wood " and "Textile" which

Branchesand : Kvoto.Tokvo.Nasoua.

Fukuoka.

are the subjects at Cellulcon-88.

offices Fukui Factories : Kvoto.Yokkaichi,Ohsata

Cellulose

CarboxvmthvlCellulose u CELLOGEN"

Scopeof our :Surfaceactiveagent.

Paper

Therm-reactivewater soluble polyurethane resin " ELASTRONPolyurethane emlsion u SUPERFLEX"

business

Polvethers.Carboxmethvl cellulose.Flamretardants,

Wood

Flocculant.Susar esters, Emulsifierfor emulsion

Textile

Polyurethane adhesive u MINOTACK-

oolvmerization. Antistatic

Surfaceactiveagents . “NGIGEN” etc.

asent(Kneadingtype).

M)NOGEN "

Resinreformer, Antioxidant. Rubbermid releasingagent. Oisoersant. Printingthickener Scouringasent. Penetrating agent. Water solubleurethaneresin. Viscosifier

At Cellulcon-88.n CELLOGEN" , Y

ELASTRON "

,

- SUPERFLEX"

and * MINOTACK " are presented for Your attention. For me

information. contact at DKS international.

inc. Overseas Division of

DAI-ICHIKOGYOSEIYAKUCO..LTD. We wish our products wuuld be of use for your reserch works.

164

Polymers from Biobased Materials

Daivabo

Head office 3-7,

:

II. Various

1-chome,

Nirhi-ku,

Tosabori.

uses

The deodorizing

Osaka

fibers

can decompose

and remove not only hydrogen

Capital

:

mercaptsns,

10,WO.000.000

(Ken)

Number of employees

indole

such as old urine

locations

:

odors,

odors and rotted

Tokyo (Branch

the targets

office)

odors, odors

water disposal

refrigerator

Osaka (Head office)

but

So bad

and feces

sewage and waste and mill

sulfide,

and skatole,

also ammonia and amines.

:

2,800 Office

Co. *Ltd.

odors, protein

facility

garbage odors

for the deodorizing

will can be fibers.

Kanazawa (Mill) Fukui

(Mill)

Hairuru

lU. Products

(Mill)

h’e have succeeded deodorizing

Wakayama (Hill)

and wool materials.

Uarima (Plant)

now marketed are exhibited

flasuda

(Plant)

Yarns,

fibers

Woven fabrics,

Made-up goods,

Knit fabrics,

Viscose

and Polypropylene

staple

staple

fibers

fibers

Deodorizing

A (Amorphous rayon)

(2) Deometafi

S (Regular

(3) Deometafi

US (Wool)

Ocodoriring

ore mnnufsctured immobilizing an srti-

fibers.

enzyme (a metal rivative)

consideration of oxidase body.

of analogcous and catalasc

be-

by Prof.

University

(4) Blanket thermal

(6) Carpet

The artificial

was developed

(3) Bed pad (5) Electric

fibers

phthalocyaninc

of Shinshu

CS (Cotton)

products

(2) FIJRIN

fibers)

enzyme on ctllulosic

and protein

rayon)

(1) Wadding of FUTON

fibers

by effectively

Shirai

3. Final

fibers

H.

In reactions

1.n a living

the

in this products booth.

2. Yarns

Exhibited

(Odor decomposing

the of cellulosic

Some of

(1) peometafi

(1) Deometafi Products

ficial

mainly

1. Fibers

:

Main products

I.

in developing

Izumo (Hi 11)

(7) Car seat (8)

Hat for

(9) Diaper (10) Shoes

cover

pets cover

insole

blanket

Appendix-Examples

of Research Activities in Japan

FUJYSphn ing Co... Hd. Head

offlce

/

Nihonbashi.

Capital

18-12,

Chuo-Lu.

1 -chose, Tokyo.

Ninpyo-cho

103

/ VS.4 billion

Esployecs Office

/ Approx.3.400

and Hi11 /

Oyaoa sill. sill.

Ohita

pill.

/

Cotton

Outline

yarns products,

srde

yarns

and

lade

It

and

chitosan.

ester

group

mild

couditiou.

superior

licroorganism.

it

porms

hydrop!li

lit

activity

imoobi I izi ng carrier. for

affinity

strength

chromato-

and conteins

reacts

with

has

large

pore

is

available

active

lisands

SUPER IIICR POROUSCHITOPEARL for

Therefore

natural

into

shows outstanding

which

sicroorganisa

a

manufactured

used as an enzyme

has high

ready-

archanical

Exhibit4

ACTIVATED CHlTOPEARL graphy

yarn

Various

parts.

demonstrates

properties rhen

and

of is

Worsted

and textile

and component

CHITOPEARL.

and

thread,

Electrical

polysaccharide.

fabrics

fabrics, Seuins

Products

beads.

goods dept. and

and fabrics

goods.

equipments

Osaka branch.

Yao nil 1. toyohaea

yarn

and

Lol

sill. Electronic

synthetic

blended

Head office,

k’ashizu

under

irmobi lized

size (5c(s). to use

a lot

Of

165

166

Polymers

from

Biobased

Materials

Kanebo. LTD. Research

IL

Development

S-90.Tomobuchi-cho Osaka

534.

Particle

a new cellulose

new technology.

It

spherical

(domestic

shape

Yiyakojisa-ku

Exhibition

C F: I I II I 0 s e

is

I-Chome

Japan

Products

BELLFINE

Laboratories

has

-ReIIfine’

particle

a precise and

which

has

distribution

foreign

been

and

patents

developed

particle

by KANEBO’s

size

yith

nun

a perfect

pending).

Properties

I.

Regenerated

2.

Perfect

3.

Microporous

4.

Iligh-pressure

5.

Large

water-absorption

6.

Safe,

harmless

I.

Column

cellulose

uniform

of

fine

spherical

particles

particles

shape (Pore

resistance

(crystal

(Uiameter

size

can

and volume

(under

the

capacity

can

mechanical

(250

and non-stimulating

type

II)

be controlled.5-ZOOurn.) be controled.) mixing

process)

wt %) (natural

polymer)

Uses

proteins. 2.

Cosmetic

grinding and of

B=30pm

film. toners,

packings enzymes

of

supports. abrasives.

liquid

and

chromatography

Solid Fillers

cores of

Slow-release-supports moldings.

for

separating

and

refining

so on.

and

Resins for

for

Microcapsules.or and Rubber.

pharmaceuticals.

paper

fi=80rm

cyliths.

Dye-supports

6= I45wJl

Binding

Fine for

fiber

additives

Appendix-Examples

Technical

Section

Polyester

Staple

2-2,UHEDA

of Research

Activities

in Japan

of Kanebo Department

I-CHOUHE,KIThKU,OSAKA

(OSAKA EKIKAE DAM1

Products

BLDG)

Exhibited

BACTEKILLER

In batter

recent in

antibacterial for

fiber

articles

through

becomes all

in

mainly

compound

effectfdurability

,

and

disintegration fiber

BACTEKIILLER

been developed

the

and articles is

organic

touching

that

during arc

an epoch-making

by Kanebo’s

accelerate

them either

organic

to

(heat

and

,

inorganic

ovn technology

give

using

research

on

treatment Their

agents, or

inhibit

or

indirectly

directly

agents

are

still the

to

vashinglfrom

resistance)

heating.

safe.

our

destroy

antibacterial due

by harmful

antibacterial

either

effect

effects

evaporation

caused

antibacterial

that

and resistance reduced

to

damage

Today’s

methods

antibacterial

the

necessary

employ such

These

their

of

fields.

sub1 imat ion.

decreased

develop

it in

understanding

concerns

an organic

unsatisfactory

in use

vill

action

vith

as our

,

treatment

bactericidal growth

,

years

increases

So it superb

separation

caused has

been

by their desirable

antibacterial

antibacterial zeolite.

their

agent

to

effect. vhich

has

167

168

Polymers

from

Siobased

Materials

NISSHINBO INDUSTRIES, NISSHINBO INDUSTRIES, INC. INC.

Head Office : 3- 10 Yokoy;tna-cho, Nihonbashi, Chuo-ku, Tokyo 103 Capital : 18,400 ai I I ion yen EwInyces : 6,600 Rranches : Osaka and 4 ot.hers Plants : Hamamatsu and IS others Products : spun yarn, textiles, rayon staple, spandex, automotti le hrahes, polyurethane, paper, machine tools, label printing, etc. Products

Euh i hi ted

1 . SAKKARAH U1tlm:tt.c superior cotton textiles. Using rSAKI;ARAHj specially selected from I.he rxtrl lnng staple Cita 45 Egyptian cotton. These are spun, vwen and finished mildly and gently as vi th hand-production. They have the superior qualities of Iust.cr, grace. natural drape and sof tness .

2.

SUPER SOFT A special finishing mcihod. Cotton fahr its prtrcssed the WJPER SOFTJ mrthod possess dimcntional stability, vrinkle-free and supple.

hy

3 . CWIFORT PROPOSAL A campaign far high-qua1 ity roitnn The campaign rmplw ises FA comfortable I itt? in CottonJ us i ng f i ne cot tons. 4 . A variety of raw cottors presenting peculiar appearance, touch and feel We have made textile saaplrs of count f ram yarn the same various raw cntl.ons. Cach textile has its mm individual appcararwe, touch and feel.

Appendix-Examples

of Research Activities in Japan

Shin-Etsu Chemical Co.,Ltd.

Shin-Etsu Chemical Co., Ltd.

Head

: 6.1.

Orficc

ku. Tokyo

2Chome

Ohtemachi.

Chiyoda-

100. Japan

Capital

: Y29.3 billionfUSS225.3

Number

of Employees : 3.394

million)

Office. 11 Branches. Sales Offices,

Facilities

: Head

5 Plants,

5 Research Center.

3 Overseas

Liaison

Offices Major Products

: PVC,

anes, Cellulose

Derivatives(Methp1

Phamaceutical

Coating).

Synthetic

Quartz

the Electronics

Silicone, PVA. Chloromelh. Gllulose

Semiconductor

Products. Organic Industry.

and

Silicon,

Materials

Rare Earth,

for

Rare Earth

Magnet

Products

Exhibited

1. High-Performance Dielectric Polymer ‘CYANORESIN’ “CYANORESIN” dielectric

is

a

high.performance

polymer developed dy Shin.Etsu

Chemi-

cal Co., Ltd. Its prades are as follows. (Grades) .CR.S......CyanocOlyl

Pullulan

-CR-C ..*..Cyanoethyl

Cellulose

4.IR.V ..--Cyanwthyl

Polyvinylalcohol

(Applications) -Organic

dispersion ilectro

*Electric

Q electronic parts that require the use

luminescenl device

of a highly dielectric material

169

Other Noyes Publications

INDUSTRIAL

SOLVENTS Fourth

HANDBOOK

Edition by

Ernest

This new Fourth Edition is completely revised, and vastly expanded by 30% over the last edition published in 1985. This well established and widely used reference volume is designed for the chemical and allied industries, the process industries, and will be found very helpful by anyone needing the most recent pertinent data on industrial solvents. This Fourth Edition is uniquely useful when it becomes necessary to select a new solvent on a competitive or comparative basis; when the customary solvent, employed hitherto, might no longer be available; or when prices have risen to such an extent that an existing process must be redesigned to make it economically feasible again. The approximately 1200 tables in this book contain basic data on the physical properties of most solvents and on the solubilities of a variety of materials in these solvents. Even phase diagrams for multicomponent systems are included. The contents of the tables were selected by the editor mainly from manufacturers' literature at no cost to, nor influence from, the manufacturers or distributors of these solvents. The vast amount of information contained in this book is shown in the condensed table of contents that follows here. The numbers in parentheses after each entry indicatethe number of tables per topic, and selected solvents, or solvent groups are shown beneath. HYDROCARBONS (146) Paraffins, Olefins, Aromatics HALOGENATED HYDROCARBONS Chlorinated, Brominated, Iodinated NITROPARAFFINS ORGANIC

SULFUR

COMPOUNDS

n-Propanol, Isopropanol Butyl and Amyl Alcohols Fatty Alcohols

0-8155-1244-9

{1990)

Flick

POL YHYDRIC

ALCOHOLS Ethylene Glycol Propylene Glycol Diols Glycols and Glycerine Triols and Sorbitol

PHENOLS

(172)

(34)

(204)

(1)

ALDEHYDES (13) Furfural Other Aldehydes ETHERS (49) Isopropyl Ether GLYCOL ETHERS (74) Ethylene Glycol Ethers Propylene Glycol Ethers Polyethylene Glycols Polypropylene Glycols Glycerine Ethers KETONES (55) Acetone and MEK Other Aliphatic Ketones Cyclohexanone ACIDS (21) Acetic Acid Fatty Acids AMINES (135) Alkyl Amines Alkylene Diamines Imines. Amides and Nitriles Heterocyclic Compounds ESTERS (85) Formates and Acetates I-ropionates and Butyrates Adipates Oxalates

(10)

MONOHYDRIC ALCOHOLS Methanol, Ethanol

ISBN

(109)

W.

and Lactates

HPLC and UV DATA COMPARATIVE DATA VARIOUS SOLVENTS

(84) FOR

REFERENCES TRADE

NAME

SY,"

INDEX

X 11

925 pages

Other Noves Publications

HANDBOOK ADHESIVES

OF

RAW

Second

MATERIALS

Edition by

Ernest

w.

This handbook contains descriptions of more than 2200 materials which are currently available to the adhesives industry. It will be of value to technical and managerial personnel in adhesives manufacturing companies and companies which supply materials or services to these companies. This book will be useful to both those with extensive experience as well as those new to the field. The data included represent selections from manufacturers' descriptions made at no cost to, nor influence from, the makers or distributors of the materials. Only the most recent information has been included. It is believed that all of the products listed here are currently available, which will be of utmost interest to readers concerned with product discontinuances. The 1988 market for adhesives and sealants was estimated at $5.1 billion, with projections for

adhesives for 1995 at $12 billion. Statistical documentation on the projections varies; however. there is no doubt about the industry's steady growth and expansion into new areas. In addition to the sections listed below, a list of Suppliers' Addresses and a Trade Name Index are included. Companies are presented alphabetically in each section and appropriate products are listed for each company. The book lists the following product information, as available, in the manufacturer's own words" .Company .Trade

1. Antifoams,

Defoamers,

Name and Product Name and Product

Category

Numbers

.Product description: a description of the product, its properties, and possible applications, as presented by the supplier

The materials have been divided Parenthetic numbers indicate the section.

2. Antioxidants

Flick

into the following 12 sections. number of products in each

Dispersants,

Surfactants

(100)

(11 )

3. Extenders,

Fillers,

4. Flame/Fire

Retardants

Pigments

(376)

(56)

5. Oils (37) 6. Polymer

Emulsions

7. Preservatives,

(300)

Bactericides,

Fungicides

(26)

8. Resins (744) 9. Rheological/Viscosity 10. Starches

Control

Agents

(78)

(41)

11. Waxes (137) 12. Miscellaneous

ISBN 0-8155-1185-X

(1989\

(260)

&"xg"

501 pages

Other Noyes Publications

HANDBOOK PAINT

RAW

OF MATERIALS

Second

Edition by

Ernest

W.

as contributing to this growth pattern are the relative strength of the U.S. economy, the recent resurgence of heavy industry, and the decline in the dollar which has made U.S. products more competitive in fQreign markets. In addition to the sections listed below, a list of Suppliers' Addresses and a Trade Name Index are included. Companies are presented alphabetically in each section and appropriate products are listed for each company. The book lists the following product information, as available, in the manufacturer's own words.

This handbook contains descriplions of nearly 4000 materials which are currently available to the paint industry. It will be of value to technical and managerial personnel in paint manufacturing companies and companies which supply materials or services to these companies. This book will be useful to both those with extensive experience as well as those new to the field. The data included represent selections from manufacturers' descriptions made at no cost to, nor influence from, the makers or distributors of the materials. Only the most recent information has been included. Lead-based chemicals and color pigments are excluded. It is believed that all of the products listed here are currently available, which will be of utmost interest to readers concerned with product discontinuances. Over one billion gallons of paints and coatings valued at $10 billion were shipped in 1987, a 10-year high for the industry; and sales in early 1988 showed continued growth. Factors cited

.Company .Trade

1. Antifoams,

Defoamers,

3. Extenders,

Fillers,

4. Flame/Fire

Retardants

5. Flatting

Agents

Name and Product Name and Product

Category

Numbers

.Product description: a description of the product, its properties, and possible applications, as presented by the supplier

The materials have been divided Parenthetic numbers indicate the section.

2. Driers and Antiskinning

Flick

into the following 13 sections. number of products in each

Dispersants, Agents

Pigments

Surlactants

{258)

{194)

{420)

{33)

{28)

6. Latex Emulsions

{102)

7. OIls {92) 8. Preservatives,

Bactericides,

Fungicides

{80)

9. Resins {2064) 10. Rheological/ViscosIty AddItives

{51)

12. TItanium

Dioxides

{33)

13. Miscellaneous

ISBN

0-8155-1184-1

Control

11. SIlicone

(1989)

Agents

{125)

{468)

6"x9'

998 pages

Other Naves Publications

ENGINEERING

RESINS

An Industrial

Guide

by Ernest This volume describes almost 2500 engineering resins which are currently available for industrial usage The definition of engineering resins differs depending on whom one asks The book contains those products which are termed "engineering plastics" as well as "upgraded commodity resins" The book will be of value to industrial technical and managerial personnel involved in the specification and use of these products. It has been compiled from information received from numerous industrial companies and other organizations The data included represent selections from manufacturers. descriptions made at no cost to, nor influence from, the makers or distributors of the materials Only the most recent information has been included Products covered include blends, composites, alloys, and resins with superior impact resistance, heat or cold resistance, and!or stiffness The products have been manufactured to meet high performance requirements in major end-use industries-automotive, packaging, electronics, compl!ters and business equipment, aerospace and medical supplies Many can be tailored to specific end-uses on request It is believed that all of the products are currently available. which will be of interest to readers concerned with product discontinuances Products are presented by company. and the companies are listed alphabetically Also included are a Trade Name Index and a list of Suppliers' Addresses. The book lists the following product information, as available. in the manufacturer's own words company name and product category, trade name and product numbers. and a description of the product as presented by the supplier Companies represented in the book are AlIi d -S. n I e Ig a Amo~o Performa~ce

Products

ApplIed ComposItes Arco Chemical Co. Ashley Polymers, Inc. Atochem, Inc. BASF Carp. Borg Warner Chemicals, Inc. The B\ldd Go. Celanese Engineering Resins Colorite Plastics Go. Contl~ental P.olymers, Inc. Cosmic PlastIcs, Inc. ISBN 0-8155-1172-8

(1988)

w.

Flick Custom Resins Dartco Manufacturing, Inc. Dexter Plastics Dow Chemical U.S.A. DuPont Co. Eagle-Picher Plastics Division Eastman Chemicals Division El Paso Products Co. Enron Chemical Co. Eval Co. of America Fiberite Fina Oil and Chemical Co. Freeman Chemical Corp. General Electric Co. Georgia Gulf Corp. B.F. Goodrich Haysite Reinforced Plastics Hexcel Huntsman Chemical Corp. ICI Americas, Inc. Industrial Dielectrics, Inc. Koppers Co., Inc. MKB Industries, Inc. Mitsui Petrochemicals(America) Mobay Corp. Mobil Chemical Co. Monmouth Plastics, Inc. Monsanto ChemIcal Co. Nuodex, Inc. Orthane Division! Ohio Rubber Owens-Corning Fiberglas Corp. Pennwalt Corp. Perstorp, Inc. Phillips 66 Co. Plaskon Electronic Materials Plaslock Corp. Plastics Engineering Co. RTP Co. Resinoid Engineering corp. Rhone-Poulenc, Inc. Richardson Polymer Corp. Rogers Corp. Rohm and Haas Rostone A. Schulman, Inc. Standard Oil Thermolil, Inc. U.S.I. Chemicals Union Carbide Corp. Valite Division! Valentine Sugars Inc Washington Penn 'Plasiic Welfman, Inc. Wilson-Fiberfillnternational 6"x9"

Co.

838 pages