Environmentally-Compatible Food Packaging (Woodhead Publishing Series in Food Science, Technology and Nutrition)

Environmentally compatible food packaging

© 2008, Woodhead Publishing Limited

Related titles Handbook of waste management and co-product recovery

in food processing (ISBN 978-1-84569-025-0) Millions of tonnes of waste are produced every year by the agri-food industry. Disposal by landfill or incineration is already expensive and the industry faces increasing costs for the removal of refuse and remnants. The costs of energy and water are also significant for food businesses and savings can be made in these areas if the quantity of energy and water used is limited. Methods to recycle and reduce the need for disposal are therefore increasingly of interest. This comprehensive collection reviews recent research in the field, covering optimisation of manufacturing procedures to decrease waste, reduction of energy and water expenditure, methods to valorise refuse by co-product recovery and techniques to deal with wastewater and solid waste. Novel food packaging techniques (ISBN 978-1-85573-675-7) With its distinguished international team of contributors, Novel food packaging techniques summarises the key developments in the field. The first part of the book discusses general issues such as packaging design, consumer attitudes to novel packaging and the legislative context. Part II looks at new techniques such as the use of oxygen and other scavengers, freshness indicators and antimicrobial packaging. The final part of the book discusses packaging materials and considers how packaging can be used with other preservation techniques to improve the quality of particular foods. Environmentally friendly food processing (ISBN 978-1-85573-677-1) With increasing regulation and consumer pressure, the food industry needs to ensure that its production methods are sustainable and sensitive to environmental needs. This important collection reviews ways of analysing the impact of food processing operations on the environment, particularly life cycle assessment (LCA), and techniques for minimising that impact. The first part of the book looks at the application of LCA to the key product areas in food processing. Part II then discusses best practice in such areas as controlling emissions, waste treatment, energy efficiency and biobased food packaging. Details of these books and a complete list of Woodhead’s titles can be obtained by: • visiting our web site at www.woodheadpublishing.com • contacting Customer Services (e-mail: [email protected]; fax: +44 (0) 1223 893694; tel.: +44 (0) 1223 891358 ext. 130; address: Woodhead Publishing Ltd, Abington Hall, Granta Park, Great Abington,

Cambridge CB21 6AH, England)

© 2008, Woodhead Publishing Limited

Environmentally compatible food packaging Edited by Emo Chiellini

WPTF3007

Cambridge England

© 2008, Woodhead Publishing Limited

Published by Woodhead Publishing Limited, Abington Hall, Granta Park, Great Abington, Cambridge CB21 6AH, England www.woodheadpublishing.com Published in North America by CRC Press LLC, 6000 Broken Sound Parkway, NW, Suite 300, Boca Raton, FL 33487, USA First published 2008, Woodhead Publishing Limited and CRC Press LLC © 2008, Woodhead Publishing Limited The authors have asserted their moral rights. This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the authors and the publishers cannot assume responsibility for the validity of all materials. Neither the authors nor the publishers, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from Woodhead Publishing Limited. The consent of Woodhead Publishing Limited does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from Woodhead Publishing Limited for such copying. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress. Woodhead Publishing ISBN 978-1-84569-194-3 (book) Woodhead Publishing ISBN 978-1-84569-478-4 (e-book) CRC Press ISBN 978-1-4200-7789-6 CRC Press order number: WP7789 The publishers’ policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp which is processed using acidfree and elementary chlorine-free practices. Furthermore, the publishers ensure that the text paper and cover board used have met acceptable environmental accreditation standards. Typeset by SNP Best-set Typesetter Ltd., Hong Kong Printed by TJ International Ltd, Padstow, Cornwall, England

© 2008, Woodhead Publishing Limited

Contents

Contributor contact details........................................................................... xiii Preface............................................................................................................ xviii Part I 1

2

Biobased food packaging materials: new directions

State-of-the-art biobased food packaging materials........................ G. Robertson, University of Queensland, Australia 1.1 Introduction: biobased packaging, the food industry and the environment................................................................. 1.2 Classification of biobased food packaging materials ............ 1.3 Properties of biobased food packaging materials................. 1.4 Assessing the biodegradability of biobased materials for food packaging................................... 1.5 Applications and challenges for biobased food packaging .......................................................... 1.6 Future trends .............................................................................. 1.7 Sources of further information and advice ............................ 1.8 References .................................................................................. Types, production and assessment of biobased food packaging materials.............................................................................. S. Imam, G. Glenn, B.-S. Chiou, J. Shey, R. Narayan and W. Orts, USDA-ARS-PW-WRRC, USA

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Contents 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12

3

4

Introduction: rationale and need for biobased food packaging .......................................................... The environmental impact of conventional food packaging........................................................................... Opportunities for renewable polymers .................................. Production of biobased food packaging materials................ Hybrid blends and composites ................................................ New developments in the production of packaging from recycled lignocellulosic fiber and renewable materials........................................................... Assessing the biodegradability of renewable materials in food packaging ...................................................................... Biodegradable packaging life cycle assessment .................... Food safety concerns, applications and adoption by the industry ........................................................................... Future trends .............................................................................. Sources of further information and advice ............................ References ..................................................................................

Thermoplastic nanobiocomposites for rigid and flexible food packaging applications .......................................... J. Lagaron and M. Sanchez-Garcia, Institute of Agrochemistry and Food Technology, Spain; E. Gimenez, ESID, University Jaume I, Castellon, Spain 3.1 Introduction: plastic food packaging, sustainable materials and barrier properties ......................... 3.2 ‘Barrier properties’ limit the use of plastics in monolayer packaging............................................................ 3.3 Novel developments in barrier polymeric structures ........... 3.4 Polymer blends: the case of permeable fillers ....................... 3.5 Nanocomposites: the case of impermeable fillers ................. 3.6 Nanobiocomposites for monolayer packaging: polylactic acid, polycaprolactone, polyhydroxyalkanoate and starch ........................................... 3.7 Future trends and outlook ....................................................... 3.8 Nomenclature............................................................................. 3.9 References .................................................................................. Improved fibre-based packaging for food applications................... J. Poustis, JPC Packaging Institute, France 4.1 Introduction................................................................................ 4.2 Properties and uses of fibre-based food packaging .............. 4.3 Innovative methods to improve fibre-based packaging for food applications .................................................................

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29 30 32 37 41 44 46 52 53 55 56 57

63

63 65 69 71 73 78 82 82 83 90 90 93 95

Contents 4.4 4.5 4.6 4.7 4.8 5

6

Starch-based edible films..................................................................... Y. Zhang and Z. Liu, University of Manitoba, Canada; J. Han, Frito-Lay, Inc., USA 5.1 General properties and structure of starch............................ 5.2 History of edible films .............................................................. 5.3 Edible film materials and their previous applications.......... 5.4 Starch film-forming mechanisms – gelatinization and recrystallization .................................................................. 5.5 Appearance and physical properties of starch films............. 5.6 Plasticization of starch films..................................................... 5.7 Trends in starch research and applications ............................ 5.8 References .................................................................................. The use of chitin and chitosan for food packaging applications............................................................................................ I. S. Arvanitoyannis, University of Thessaly, Greece 6.1 Introduction................................................................................ 6.2 Mechanical properties............................................................... 6.3 Thermal properties .................................................................... 6.4 Gas permeability ....................................................................... 6.5 Water permeability .................................................................... 6.6 Conclusions ................................................................................ 6.7 References ..................................................................................

Part II 7

Suitability of new fibre-based packaging materials for food packaging .................................................................... Assessing the biodegradability of new fibre-based packaging materials for food packaging................................. Applications and future trends in the food industry............ Sources of further information and advice ............................ References ..................................................................................

vii 96 102 103 107 107 108 108 110 111 112 118 126 132 133 137 137 138 146 149 154 156 157

Using environmentally compatible packaging technologies in the food industry

Consumer attitude to food packaging and the market for environmentally compatible products ......................................... I. S. Arvanitoyannis and A. Kasaveti, University of Thessaly, Greece 7.1 Introduction................................................................................ 7.2 Packaging materials................................................................... 7.3 ‘Green’ packaging ..................................................................... 7.4 Disposal of packaging materials.............................................. 7.5 Recycling of packaging materials ............................................

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Contents 7.6 7.7 7.8 7.9 7.10

8

9

10

New packaging technologies.................................................... Food packaging regulation in the European Union ............. The study of consumer behaviour ........................................... Conclusions ................................................................................ References ..................................................................................

Environmental assessment of food packaging and advanced methods for choosing the correct materials.................... K. Verghese, RMIT University, Australia 8.1 Introduction................................................................................ 8.2 Modern day lifestyle conflicts and demands from the retail sector................................................................................. 8.3 Recognition of the environmental impacts of packaging in the food industry ........................................... 8.4 Environmental assessment of food packaging systems........ 8.5 Environmental assessment tools for food packaging systems ........................................................................................ 8.6 Sustainable packaging developments ..................................... 8.7 Implementing environmental assessment approaches into the product–packaging system development process......................................................................................... 8.8 Future trends .............................................................................. 8.9 Sources of further information and advice ............................ 8.10 References .................................................................................. Measuring the environmental performance of food packaging: life cycle assessment ......................................................... G. Parker, Ciba Expert Services, UK 9.1 Introduction................................................................................ 9.2 Environmental performance of biopolymers ........................ 9.3 Measuring environmental impacts: the science of life cycle assessment .................................................................. 9.4 Results of existing life cycle assessment studies of biopolymers ........................................................................... 9.5 Measuring the environmental performance of packaging: future trends ........................................................... 9.6 Sources of further information and advice ............................ 9.7 References .................................................................................. Eco-design of food packaging materials ........................................... H. Lewis, RMIT University, Australia 10.1 Introduction................................................................................ 10.2 Key drivers of eco-design of food packaging materials ....... 10.3 Eco-design strategies for food packaging materials ............. 10.4 Future trends .............................................................................. 10.5 Conclusions ................................................................................

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Contents 10.6 10.7 11

12

13

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Sources of further information and advice ............................ 259 References .................................................................................. 259

Additives for environmentally compatible active food packaging...................................................................................... S. Irmak and O. Erbatur, Cukurova University, Turkey 11.1 Introduction................................................................................ 11.2 Antimicrobial/antioxidant agents incorporated into polymers...................................................................................... 11.3 Chemical preservatives ............................................................. 11.4 Peptides and proteins................................................................ 11.5 Polysaccharides .......................................................................... 11.6 Natural antimicrobial/antioxidant compounds from plant sources............................................................................... 11.7 Extraction and fractionation techniques for antimicrobial/antioxidant compounds from plant sources......................................................................................... 11.8 Antimicrobial and antioxidant tests ....................................... 11.9 Suitability of new coatings and adhesives for food packaging .................................................................... 11.10 Incorporation of antimicrobials/antioxidants into polymer materials...................................................................... 11.11 Applications in the food industry ........................................... 11.12 Future trends .............................................................................. 11.13 References .................................................................................. Recycling of food packaging materials: an overview ...................... D. Dainelli, Sealed Air Corporation, Italy and EuPC (European Plastics Converters Association), Belgium 12.1 Introduction................................................................................ 12.2 Regulation of recycling of food packaging materials ........... 12.3 Recycling paper food packaging: collection, separation and processing............................................................................ 12.4 Recycling plastic food packaging: collection, separation and recovery ........................................................... 12.5 Recycling of other materials .................................................... 12.6 Supply chain management to reduce packaging waste........ 12.7 Conclusions ................................................................................ 12.8 References ..................................................................................

263 263 265 265 266 268 270 273 276 279 280 282 283 284 294 294 295 299 305 314 319 322 324

Recycled plastics for food applications: improving safety and quality............................................................................................. 326 V. Komolprasert and A. Bailey, Food and Drug Administration, USA 13.1 Introduction................................................................................ 326 13.2 Plastic food packaging and the environment ........................ 327

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Contents 13.3 13.4 13.5 13.6 13.7 13.8 13.9

14

Recycled paper and board for food applications: improving safety and quality............................................................... C. Nerín, I3A, CPS, University of Zaragoza, Spain 14.1 Introduction................................................................................ 14.2 The recyclability of paper and board...................................... 14.3 Improving the recyclability of paper and board packaging .................................................................................... 14.4 Testing the safety and quality of recycled paper and board.................................................................................... 14.5 Future trends .............................................................................. 14.6 Sources of further information and advice ............................ 14.7 References ..................................................................................

Part III 15

16

The recyclability of packaging plastics ................................... Recycling processes ................................................................... Improving the recyclability of plastic packaging for food use ................................................................................ The safety and quality of recycled plastics ............................ The use of recycled plastics in the food industry .................. Future trends .............................................................................. References ..................................................................................

328 330 331 336 345 346 347 351 351 352 358 359 364 365 367

Environmentally compatible food packaging for particular applications

Overview of environmentally compatible polymeric materials for food packaging............................................ E. Chiellini, A. Barghini, P. Cinelli and V. I. Ilieva, University of Pisa, Italy 15.1 Introduction................................................................................ 15.2 Polymers from renewable resources ....................................... 15.3 Multilayer packaging films ....................................................... 15.4 Technology for biobased polymer processing ....................... 15.5 Economic issues regarding biodegradable polymers...................................................................................... 15.6 Conclusions ................................................................................ 15.7 Sources of further information and advice ............................ 15.8 References ..................................................................................

371 371 372 376 377 379 388 389 390

Modified atmosphere packaging using environmentally compatible and active food packaging materials ............................. 396 C. Guillaume, P. Chalier and N. Gontard, University of Montpellier II, France 16.1 Introduction................................................................................ 396

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Contents 16.2 Modified atmosphere packaging of fruit and vegetables: using proteins to control gas transport phenomena through paper-based materials ................................................ 16.3 Antimicrobial modified atmosphere packaging: antimicrobial properties of aroma compounds and their controlled release using the paper coating agent as an inclusion matrix....................................... 16.4 Future trends .............................................................................. 16.5 References .................................................................................. 17

18

19

Active environmentally compatible food packaging ....................... R. Catalá, P. Hernández-Muñoz and R. Gavara, IATA-CSIC, Spain 17.1 Introduction................................................................................ 17.2 Basic characteristics of active packaging ............................... 17.3 Biopolymer-based active materials for food packaging .................................................................................... 17.4 Future trends .............................................................................. 17.5 References .................................................................................. Biobased intelligent food packaging.................................................. P. Taoukis, National Technical University of Athens, Greece; M. Smolander, VTT Technical Research Centre of Finland, Finland 18.1 Introduction................................................................................ 18.2 Biobased tools for the detection of quality-indicating metabolites.................................................. 18.3 Biobased tools for the detection of pathogenic and microbial contamination ................................................... 18.4 Biobased indicators for monitoring the time–temperature history ......................................................... 18.5 Other intelligent packaging systems utilising biomolecules............................................................................... 18.6 Future trends .............................................................................. 18.7 References .................................................................................. Environmentally compatible packaging of fresh agricultural and horticultural produce.................................................................... C. Bishop and S. Hanney, Writtle College, UK 19.1 Introduction................................................................................ 19.2 Specific challenges for fresh produce packaging................... 19.3 Industry response ...................................................................... 19.4 Storage of packaging material ................................................. 19.5 Supply chain ...............................................................................

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403 414 415 419 419 420 422 432 433 439

439 440 444 446 450 451 452

459 459 463 464 468 470

xii

Contents 19.6 19.7 19.8

20

21

22

Reducing the environmental impact of secondary packaging – returnable plastic crates...................................... 471 Conclusions ................................................................................ 475 References .................................................................................. 476

Biobased packaging of dairy products .............................................. M. Jakobsen, University of Copenhagen, Denmark; V. Holm, Danish Technological Institute, Denmark; G. Mortensen, Danish Dairy Board, Denmark 20.1 Introduction................................................................................ 20.2 Properties required in relation to dairy products ................. 20.3 Current applications of biopackaging of dairy products ..... 20.4 Future trends .............................................................................. 20.5 Sources of further information and advice ............................ 20.6 References .................................................................................. Environmentally friendly packaging of muscle foods ..................... P. Dawson, K. Cooksey and S. Mangalassary, Clemson University, USA 21.1 Introduction................................................................................ 21.2 Types of meat packaging materials ......................................... 21.3 Source reduction ........................................................................ 21.4 Recyclable materials ................................................................. 21.5 Biobased materials .................................................................... 21.6 Future trends .............................................................................. 21.7 References .................................................................................. Legislation and certification of environmentally compatible packaging in the European Union..................................................... C. Enguix, A. Imbernon and J. Ferrer, AINIA – Instituto Tecnológico Agroalimentario, Spain 22.1 Introduction................................................................................ 22.2 Packaging waste legislation ...................................................... 22.3 Biodegradable waste ................................................................. 22.4 Legislation on materials and articles intended to come into contact with food .................................................... 22.5 Future trends for the legislation of materials and articles intended to come into contact with food ................. 22.6 References ..................................................................................

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478 479 485 489 491 492 496 496 496 498 501 503 515 515 521 521 523 539 542 553 556

Contributor contact details

(* = main contact)

Chapter 2

Editor

S. Imam,* G. Glenn, B.-S. Chiou, J. Shey, R. Narayan and W. Orts Bioproduct Chemistry and Engineering Research USDA-ARS-PW-WRRC 800 Buchanan Street Albany CA 94710 USA

E. Chiellini Laboratorio Materiali Polimerici Bioattivi per Applicazioni Biomediche ed Ambientali UdR-Consorzio INSTM – Dipartimento di Chimica e Chimica Industriale University of Pisa Via Risorgimento 35 56126 Pisa Italy E-mail: [email protected]

E-mail: [email protected]

Chapter 3

G. L. Robertson School of Land and Food Sciences University of Queensland Brisbane QLD 4072 Australia

J. M. Lagaron* and M. D. Sanchez-Garcia Novel Materials and Nanotechnology Institute of Agrochemistry and Food Technology C.S.I.C. Apdo. Correos 73 46100 Burjassot Spain

E-mail: [email protected]

E-mail: [email protected]

Chapter 1

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xiv

Contributor contact details

E. Gimenez Department of Engineering and Design (ESID) University Jaume I Campus del Riu Sec E-12080 Castelló de la Plana Spain Email: [email protected]

Chapter 4 J. Poustis CEO JPC Packaging Institute 3 allée de Saintonge 33600 Pessac France E-mail: [email protected]

Chapter 5 Y. Zhang and Z. Liu Department of Food Science University of Manitoba Winnipeg, MB Canada R3T 2N2 E-mail: [email protected] J. H. Han* Pepsico Fruit and Vegetable Research Center Frito-Lay, Inc. 7701 Legacy Dr. Plano, TX 75024 USA Emial: [email protected]

© 2008, Woodhead Publishing Limited

Chapter 6 I. S. Arvanitoyannis Department of Agriculture, Ichthyology and Aquatic Environment School of Agricultural Sciences University of Thessaly Fytoko Street 38446 Nea Ionia Magnesias Volos-Hellas, Greece E-mail: [email protected]

Chapter 7 I. S. Arvanitoyannis* and A. Kasaveti Department of Agriculture, Ichthyology and Aquatic Environment School of Agricultural Sciences University of Thessaly Fytoko Street 38446 Nea Ionia Magnesias Volos-Hellas, Greece E-mail: [email protected]

Chapter 8 K. Verghese Centre for Design RMIT University GPO Box 2476V Melbourne Victoria 3001 Australia E-mail: Karli.Verghese@rmit. edu.au

Contributor contact details

xv

Chapter 9

Chapter 12

G. Parker Ciba Expert Services Cleeve Road Leatherhead Surrey KT22 7RU UK

D. Dainelli Analytical Department and Regulatory Affairs Sealed Air Corporation Via Trento 7-20017 Passirana di Rho (Milano) Italy

E-mail: [email protected]

E-mail: Dario.dainelli@ sealedair.com

Chapter 10 H. Lewis Centre for Design RMIT University GPO Box 2476V Melbourne Victoria 3001 Australia E-mail: [email protected]

Chapter 11 S. Irmak* and O. Erbatur Department of Chemistry Cukurova University Balcali 01330 Adana Turkey E-mail: [email protected]

Chapter 13 V. Komolprasert* and A. Bailey Division of Food Contact Notifications (HFS-275) Office of Food Additive Safety Center for Food Safety and Applied Nutrition Food and Drug Administration 5100 Paint Branch Parkway College Park, MD 20740 USA E-mail: Vanee.Komolprasert@fda. hhs.gov

Chapter 14 C. Nerín Research Institute of Engineering Research (I3A) Centro Politécnico Superior (CPS) Department of Analytical Chemistry University of Zaragoza María de Luna 3 50018 Zaragoza Spain E-mail: [email protected]

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Contributor contact details

Chapter 15

Chapter 18

E. Chiellini,* A. Barghini, P. Cinelli and V. I. Ilieva Laboratorio Materiali Polimerici Bioattivi per Applicazioni Biomediche ed Ambientali UdR-Consorzio INSTM – Dipartimento di Chimica e Chimica Industriale University of Pisa Via Risorgimento 35 56126 Pisa Italy

P. S. Taoukis* National Technical University of Athens School of Chemical Engineering Heroon Polytechniou 5 15780 Zografou Greece

E-mail: [email protected]

Chapter 16 C. Guillaume, P. Chalier and N. Gontard* UMR 1208 IATE Agropolymers Engineering and Emerging Technologies University of Montpellier II CC023, Pl. E. Bataillon, 34095 Montpellier Cedex 5 France E-mail: [email protected]

E-mail: [email protected] Maria Smolander VTT Technical Research Centre of Finland Tietotie 2, Espoo PO Box 1000 FI-02044 VTT Finland E-mail: [email protected]

Chapter 19 C. F. H. Bishop* and S. J. Hanney Writtle College Chelmsford Essex CM1 3RR UK E-mail: [email protected]

Chapter 17 R. Catalá, P. Hernández-Muñoz and R. Gavara* Institute of Agrochemistry and Food Technology IATA-CSIC Apdo. Correos 73 46100 Burjassot Spain

Chapter 20

E-mail: [email protected]

E-mail: [email protected]

© 2008, Woodhead Publishing Limited

M. Jakobsen* University of Copenhagen Department of Food Science Rolighedsvej 30 DK-1958 Frederiksberg C Denmark

Contributor contact details V. Holm Danish Technological Institute Holbergsvej 10 DK-6000 Kolding Denmark E-mail: Vibeke.Kistrup.Holm@ teknologisk.dk G. Mortensen Danish Dairy Board Frederiks Allé 22 DK-8000 Århus C Denmark E-mail: [email protected]

Chapter 21 Paul L. Dawson* Department of Food Science and Human Nutrition Clemson University 204 Poole Hall Clemson SC 29634-0316 USA E-mail: [email protected]

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Kay Cooksey and Sunil Mangalassary Department of Packaging Science Clemson University Clemson SC USA E-mail: [email protected]

Chapter 22 C. Enguix,* A. Imbernon and J. M. Ferrer Dpto. Tecnologías de Envase AINIA – Instituto Tecnológico Agroalimentario Portal Agroalimentario Spain E-mail: [email protected]

Preface

The packaging sector plays an important role in industrial activity with an estimated economic impact in developed countries and in countries in transition of about 2.5% of the average gross national product. Europe has a market share of around 150 million euros, which is more than one-third of the worldwide packaging market. About 50% of this figure is represented by food packaging and projections for the future development of the sector indicate a continuous growth in size and performance improvement. Beyond the fashionable trend of current consumers – ever more inclined to purchase packaged food products that are easy to handle, prepare and consume, while maintaining the quality and freshness of the original produce – there is mounting public concern about the environmental impact of the post-consumer packaging waste that is being generated. On the other hand, the modern vision in food packaging development is no longer focused on the passive role of packaging exploitation in the processing and preservation of foodstuffs and ensuring food integrity and safety.Today, packaging design aims for: the one-step transfer of the produce directly ‘from the field to the table’, hence guaranteeing food freshness and safety; and the preparation of ‘ready-to-eat’ food portions in microwaveable packaging containers (bowls and trays), supplying the consumer with warm food dishes. Active and intelligent packaging can be considered as a further step in the optimization of packaging efficacy. Active packaging is able to modify the condition of the packed food without provoking any substantial variation in its quality and nutritional value, while improving its shelf-life and ultimately its safety. Intelligent packaging is meant to monitor the features of the packed food to provide indications of the quality status of the food during storage and handling. A combination of these two attributes in a single packaging material would then be desirable for the maintenance and quality control of the packed food.

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Preface

xix

Among the wide variety of materials currently utilized in food packaging technology, polymeric materials are taking a major share because of the versatility of their processing methods – extrusion (bubble and cast), injection and compression moulding – and their interesting cost/performance ratios. There are various parameters determining the fortunes of natural, artificial or truly synthetic materials aiming to penetrate the food packaging market, notably parity of efficacy in food protection and hence cost/performance. One aspect that is assuming ever-increasing performance, is the environmental impact of these materials as well as the management of the post-consumer packaging waste. The present book primarily focuses on environmentally compatible packaging based on materials that are designed to achieve a low environmental burden during their formulation, processing and conversion to semi-finished and fully finished items, as well as at the end of the service life of the packaging, once it becomes a waste to be treated in appropriate infrastructures. According to the major scope of the book, its content is divided into three parts: • •

•

Part I, new directions in the utilization of biobased materials for food packaging. Part II, using environmentally compatible packaging technology in the food industry, including chapters focusing on the recycling technology related to food packaging and one chapter describing the use of additives for the development of active food packaging. Part III, environmentally compatible food packaging for particular applications, primarily the use of active and intelligent packaging systems.

The book should therefore be of interest to readers from research, industry and government institutions who are involved not only in the field of food packaging but also in the area of new materials design and the utilization of resources and technologies in keeping with the modern vision for sustainable industrial development. Finally, I wish to express my personal appreciation to all the contributors for their efforts and their willingness to share their expertise in the fields of materials science and technology, and food packaging, under the pressure of the tight schedules kindly but firmly imposed by personnel from Woodhead Publishing. Last, but not least, I wish to thank my Secretarial Assistants Maria G. Viola, Michela Bianchi and Maria Caccamo for their continuous help in keeping timely contacts with Woodhead Publishing staff and the contributors to the book. Emo Chiellini Editor

© 2008, Woodhead Publishing Limited

To my wife Teresa and my joyful grand-daughter Eugenia Emo Chiellini

© 2008, Woodhead Publishing Limited

Part I Biobased food packaging materials: new directions

© 2008, Woodhead Publishing Limited

1 State-of-the-art biobased food packaging materials G. Robertson, University of Queensland, Australia

1.1

Introduction: biobased packaging, the food industry and the environment

Biobased food packaging materials have been defined (van Tuil et al. 2000) as ‘materials derived from renewable sources’. A narrower definition (Haugaard & Mortensen 2003) which will be used in this chapter is ‘materials derived from primarily annually renewable sources’, thus excluding paper-based materials, since trees used for papermaking generally have a renewal time of 25–65 years depending on species and country. Paper-based materials have been used for food packaging for decades and account for approximately 50% of all municipal solid waste (MSW) in developed countries (wood accounts for a further 10%); they will not be discussed further in this chapter. At the beginning of the twentieth century, most non-fuel industrial products such as inks, dyes, paints, medicines, chemicals, clothing, synthetic fibres, flexible packaging and also plastics were made from biologically derived resources (Weber et al. 2002). During the twentieth century, petroleum-derived chemicals replaced these to a major extent, due largely to their better physical and chemical properties such as, in the case of packaging materials, strength, lightness and resistance to water and waterborne micro-organisms. Now at the beginning of the twenty-first century, increasing attention is being given to sustainability and the replacement of non-renewable resources (particularly those derived from petroleum) with those from renewable sources, essentially plant-derived products and byproducts from their fermentation (Mohanty et al. 2005).

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4

Environmentally compatible food packaging

It has become almost commonplace for introductory chapters in books on biobased polymers to include dire warnings about the consequences for life on Earth if a switch is not made immediately from conventional to biobased polymers. For example, Scholz and Khemani (2006) wrote ‘there is a growing general awareness among consumers and government agencies in most countries around the world that conventional plastic products, although useful, are causing tremendous damage to the environment, water supplies, sewer systems (sic) as well as to the rivers and streams’. Mohanty et al. (2005) wrote that ‘persistence of plastics in the environment, the shortage of landfill space, the depletion of petroleum resources, concerns over emissions during incineration, and entrapment by and ingestion of packaging plastics by fish, fowl and animals have spurred efforts to develop biodegradable/biobased plastics’. There is not space here to rebut these statements; a more balanced discussion of the issues can be found in Robertson (2006). A recent article (Royte 2006) questioned whether biodegradable packaging is really the answer to America’s throwaway culture and addressed various concerns about poly(lactic) acid (PLA) and in particular its inability to break down in home composting operations. Environmentalists such as Lester Brown, president of the Earth Policy Institute, question the morality of turning a foodstuff into packaging when so many people in the world are hungry. The recent increase in bioethanol production in the United States has resulted in the price of corn reaching the highest level in a decade and, as a consequence, a dramatic rise in the cost of the tortilla, a food staple in Mexico. The reality is that plastic packaging materials from petroleum sources are well established and play an essential role in the packaging of food. The global annual production of plastics exceeds 250 million tonnes and of this approximately 40% or 100 million tonnes are used for packaging. North America produces about 26 million tonnes of plastics for packaging; Europe about 28 million tonnes; Japan 7 million tonnes and Asia (excluding Japan) 34 million tonnes. Global consumption of biobased polymers was estimated to be 79 800 tonnes (starch, 44 800; PLA, 35 800) in 2005 with loose-fill foam packaging accounting for more than half of starch biopolymer volumes. By 2010, global consumption is forecast to reach 180 000 tonnes (starch, 89 200; PLA, 89 500), a compound annual growth rate of 17.7%. In 2005, global production capacity for biodegradable polymers was around 360 000 tonnes and is expected to reach 600 000 tonnes by 2008. Packaging (including rigid and flexible packaging, paper coating and food service) is the largest sector with 39% of total biodegradable polymer market volumes in 2005; loose-fill packaging was second with 24%, followed by bags and sacks with 21% (Platt 2006). Even with rapid expansion of manufacturing capacity (and assuming equivalent performance), it will be many years before the packaging industry can switch a significant quantity of its production to biobased materials.

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There are two main driving forces behind the development of biobased packaging materials. One driver is the ambition to replace non-renewable with renewable resources, thus leading to a more sustainable packaging industry. The other driver is a desire to reduce the amount of used packaging going to landfill by converting to biodegradable and compostable packaging. Retailers are playing a leading role in encouraging the switch to biobased packaging materials, presumably because that is what their customers want. For example, the UK Courtauld Commitment agreement took shape at a ministerial summit held at the Courtauld Gallery in March 2005, where the Environment Minister met with senior representatives from the majority of the leading UK grocery retailers, as well as the British Retail Consortium. The meeting focused on engaging support to find new packaging solutions and technologies, so that less rubbish ends up in the household bin. The retailers strongly supported the development of biopolymers and compostable packaging. In the United States, Wal-Mart released their Packaging Scorecard in 2006 with a commitment of reducing packaging across its global supply chain by 5% by 2013. Although renewability as such is not explicitly mentioned, the paper-based packaging sector is working to ensure that it receives proper weighting in the scorecard, since in their view renewability is just as important as recyclability when considering the environmental impact of raw materials. From a public point of view, the main drivers for the development of biodegradable packaging are the solid waste problem (particularly the perception of a lack of landfills), the litter problem which the public feel would be solved if biodegradable packaging were used and pollution of the marine environment by non-biodegradable plastics packaging. Despite the professed public preference for biodegradable or compostable packaging, more than 50% of MSW in the United States is biowaste such as yard trimmings, food scraps and paper products (Narayan 2006). This suggests that even if part of the current 15% of MSW that is plastics were to be replaced by biobased materials, there is no guarantee that such material would be composted rather than sent to landfill. A major stumbling block is the lack of composting facilities close to major cities and towns; only 113 such facilities have been identified nationwide in the United States (Royte 2006). An alternative approach is to construct bioreactors or biologically active landfills. The situation in Europe is quite different with European legislation being the key driver for national and regional policy on composting. The 1999 EU Landfill Directive (99/31/EC) contains ambitious targets for diverting biodegradable MSW from landfills; if the targets are met, the quantity of biodegradable waste going to landfill by 2016 will be only 35% of that produced in 1995. This legislation has led to significant developments in composting infrastructures across Europe where organic matter makes up 30–40% of MSW. In The Netherlands and Germany, more than 95% and 60% respectively of all households have access to industrial composting

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plants (Platt 2006). In the United Kingdom, one-third of households actively compost their green waste at home and the potential is for more than 80% to do so. With the development of commercial composting facilities, food retailers in Europe are leading the switch to biodegradable packaging for fresh foods so that they can send ‘back of store’ waste such as product that has passed its ‘best by’ date straight to composting without the need for separation. Producing biodegradable plastics using annually renewable biomass feedstocks that end up in biodegradation infrastructures like composting is ecologically sound and promotes sustainability (Narayan 2006). Such an approach would be carbon neutral in that the inorganic carbon present in the atmosphere as CO2 is converted to organic carbon in plants using sunlight and then returned to the atmosphere as CO2 during biodegradation. However, given that the major contemporary environmental problem is an excess of CO2 in the atmosphere, a more helpful approach would be to sequester biobased packaging materials in sanitary landfills where, because of little or no moisture and negligible microbial activity, biodegradation is retarded. Landfills have been described as vast mummifiers with excavations finding that even after two decades of burial, about one-third to one-half of food and yard waste remains in a recognisable condition and newspapers can be easily read (Rathje & Murphy 1992). However, because there will be some anaerobic decomposition of organic materials in landfills leading to the production of landfill gas (c. 50% CH4 and 50% CO2), such gas should be captured using conventional gas wells and combusted to produce energy. Polyhydroxyalkanoates (PHAs) are well known to biodegrade under anaerobic conditions, in contrast with other condensation polymers including PLA and aliphatic polyesters which do not biodegrade in the absence of oxygen (Swift & Wiles 2004). The development of biobased packaging materials is predicated on a widely held belief that such materials will have lower environmental impacts than existing petroleum-derived materials. Without this advantage, there is less incentive for industry to adopt biobased packaging materials. Detailed life cycle assessment (LCA) studies on biobased products have been released and are discussed further in Chapter 9. A comparative review (Patel et al. 2003) of 20 published studies (7 dealing with starch polymers, 5 with PHAs, 2 with PLAs, 3 with other biobased polymers and 3 with composites based on natural fibres) provided some interesting conclusions. Of all the biobased polymers studied, starch polymers performed best in environmental terms, with some differences among the various types. Compared with starch polymers, the environmental benefits seemed to be smaller for PLA (LCA results were only available for energy and CO2). For PHA, the environmental advantages seemed to be very small compared with conventional polymers (LCA results were only available for energy use). For both PLA and PHA, the production method, scale of production and type of waste management treatment has a decisive influence on the

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ultimate conclusion concerning overall environmental balance. Recently Patel and Narayan (2005) stated that available LCA studies and environmental assessments strongly support further development of biodegradable and biobased polymers. However, careful monitoring of various environmental impacts continues to be necessary both for decision makers in companies and policymakers in governments. Recently, Kim and Dale (2005) reported on a detailed LCA of PHAs derived from no-tilled corn and concluded that, under the current PHA fermentation technology, PHA from corn grain does not provide an environmental advantage over polystyrene (PS). The main reason that different LCA studies arrive at different conclusions is because of variations in the approaches used to allocate the environmental burdens. In an attempt to improve its environmental profile, NatureWorksTM announced in 2005 that it will achieve a greenhouse-gas-neutral position for its PLA, making it the first, and only, commercially available greenhouse-gas-neutral polymer in the industry. This will be achieved through the purchase of renewable energy certificates, which serve as an offset to cover all of the emissions from the energy used for the production of PLA. The net result will be a 68% reduction in fossil fuel use in the manufacture of PLA compared with traditional plastics.

1.2

Classification of biobased food packaging materials

Biobased food packaging materials can be classified in a number of ways, based on their chemical composition, origin, synthesis method, economic importance, application, etc. It is important to note that biodegradable polymers such as polycaprolactones (PCLs), polyglycolic acid and polyesteramides are made from petroleum feedstocks and therefore will not be included in the classification below since they are not derived from primarily annually renewable resources. Polymers from renewable resources are distinct from natural polymers in that their synthesis has been purposely initiated. Currently there is no industrial process in place that produces plastic materials solely from renewable resources (Scholz & Khemani 2006). Due to their natural origin (i.e. an enzyme-catalysed synthesis), all natural polymers are inherently biodegradable since for every polymerase enzyme whose action leads to a natural polymer, there is a depolymerase capable of catalysing the degradation of that polymer (Scholz & Khemani 2006). However, it has recently been shown that some recombinant strains of micro-organisms capable of PHA synthesis are also able to synthesise polymers of mercaptoalkanoic acids, which are generally referred to as polythioesters. They are distinguished from PHAs solely by the occurrence of sulphur atoms instead of oxygen atoms in the linkages of the polymer backbone and are non-biodegradable (Steinbüchel 2005).

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The traditional way of classifying biobased packaging materials has been to divide them into three generations based on their historical development. A similar approach has been adopted below, with the third generation further subdivided into three main categories based on their origin and method of production. 1.2.1 First generation The first generation of biobased packaging materials were used for shopping bags and consisted of synthetic polymers such as low-density polyethylene (LDPE) with 5–15% starch fillers and pro-oxidative and auto-oxidative additives. Although these materials disintegrated or biofragmented into smaller molecules when composted, they did not biodegrade. This gave a very poor image to biodegradable products, leading to public outrage with many consumers feeling that they had been misled by the biodegradability claims. 1.2.2 Second generation Second-generation materials consist of a mixture of gelatinised starch (40–75%) and LDPE with the addition of hydrophilic copolymers such as ethylene acrylic acid, poly(vinyl alcohol) (PVOH) and vinyl acetate which act as compatibility agents. Complete degradation of the starch takes 40 days and degradation of the entire film a minimum of 2–3 years. Public reaction to these films has been similar to that described above for firstgeneration materials. 1.2.3 Third generation Third-generation materials consist of completely biobased materials and can be classified into three main categories according to their origin and method of production. 1 Polymers directly extracted from biomass. 2 Polymers produced by classical chemical synthesis from biomass monomers. 3 Polymers produced directly by natural or genetically modified organisms. A schematic presentation of these three categories is depicted in Fig. 1.1. Category 1: polymers directly extracted from biomass Most of the commonly available Category 1 polymers are extracted from marine and agricultural products: examples including polysaccharides such as cellulose, starch and chitin, and proteins such as collagen and soy. They

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Third-generation biobased polymers

Category 2

Category 1

Category 3

Polymers synthesised Polymers directly extracted from biomass from bioderived monomers

Polysaccharides

Polymers produced directly by natural or genetically modified organisms

Proteins

Polylactates Plant

Animal

Other polyesters Collagen

Starches Potato Corn Wheat Rice

PHAs

Bacterial celluloses

Soy Chickpea Gluten

Hemicelluloses Barley

Others Chitin/chitosan

Fig. 1.1 Classification of third-generation biobased polymers used for food packaging based on their origin and method of production. Adapted from van Tuil et al. (2000).

can be used alone or in a mixture with a synthetic biodegradable polymer such as PCL or other biodegradable polyesters such as PLA. The most widely used food packaging material in this category is cellulose-based paper and board which will not be discussed further since the raw material (typically trees) is not annually renewable. Regenerated cellulose film (referred to as cellophane in many countries), which has been available for just over a century, and cellulose acetate will not be discussed for the same reason. There is on-going research into the use of hemicelluloses (the second most abundant plant biopolymers on Earth) for biobased food packaging materials (Gröndahl et al. 2006) using glucuronoxylan (the primary

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Environmentally compatible food packaging

hemicellulose in hardwood) and arabinoxylan (the primary hemicellulose in annuals such as barley). Of the annually renewable raw materials, those based on starch are the most commonly used. In nature starch is found as crystalline beads of about 15–100 µm in diameter and after extraction the crystalline structure must be destroyed by pressure, heat, mechanical work or plasticisers such as water, glycerol or other polyols to make the starch thermoplastic (Bastioli 2005). Plasticised starch (known as thermoplastic starch or TPS) is most commonly obtained after disruption (destructuration) and plasticisation of native starch with water and plasticiser by applying thermomechanical energy in a continuous extrusion process. TPS can be processed in the same way as traditional plastics but its sensitivity to water vapour and poor mechanical properties make it unsuitable for many applications. TPS properties reach equilibrium only after several weeks (Avérous & Boquillon 2004). Blending of starch with aliphatic polyesters improves their processability and biodegradability, PCL and its copolymers being particularly suitable (Bastioli 2005). The combination of starch with a water-soluble polymer such as PVOH has been widely studied since 1970 and is currently used to produce starch-based loose fillers as a substitute for expanded PS, as well as sheet extrusion and thermoforming (Bastioli 2005). Italian-based Novamont is the largest producer of biodegradable blends based on starch and synthetic polymers (Platt 2006). Chitin is the second most widespread polysaccharide resource after cellulose and is particularly abundant in the cell walls of insect cuticles, many fungal species and crustacean exoskeletons, the latter being a major source. Chitosan is the deacetylated derivative of chitin (β-[1-4]-poly-Nacetyl-d-glucosamine). Although both chitin and chitosan can be extruded to make films for packaging applications, there being 63 main producers (Clarinval & Halleux 2005), their main use is as an edible coating to extend the shelf-life of fresh fruits and vegetables (Zhao & McDaniel 2005). Films made only from chitosan lack water resistance and have poor mechanical properties. Recently Xu et al. (2005) prepared chitosan/starch composite films that had decreased water vapour transmission rates (WVTRs) and increased mechanical properties. Both chitin and chitosan have antimicrobial activity against a range of food-borne filamentous fungi, yeast and bacteria which can be a useful attribute in many food packaging applications to improve quality and extend shelf-life (No et al. 2007). Two of the more common plant proteins used to produce biodegradable plastic films are chickpea and soy protein isolates; other proteins used include those extracted from wheat, pistachio, sunflower and peas (Dean & Yu 2005). Many other protein-based polymers – such as casein, albumin, fibrinogen, silks and elastins – have been considered because of their inherent biodegradability but they have not yet found widespread use as packaging materials since they are difficult to process, do not melt without decomposition, are difficult to blend with most polymers because of

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their incompatibility and are more expensive than most polysaccharides (Bhattacharya et al. 2005). Soy protein isolate films suffer from high moisture sensitivity and low strength. The addition of up to 25% stearic acid resulted in films with improved tensile and thermal properties as well as reduced moisture sensitivity (Lodha & Netravali 2005). Recently soy protein isolate, glycerol and gellan gum or κ-carrageenan were found to be suitable for the manufacture of biodegradable/edible soy-based packaging trays (Mohareb & Mittal 2007). However, a moisture barrier must be applied to the trays as they are hydrophilic in nature. Although protein materials have been studied extensively as food packaging materials with recent improvements in properties (Guilbert & Cuq 2005), a breakthrough leading to commercialisation has not yet eventuated. Collagen sausage casings remain the major commercial protein packaging material. Future packaging applications of proteins are likely to be as edible films. Category 2: polymers produced by classical chemical synthesis from biomass monomers Of all the possible biopolyesters that have been produced from biobased materials, PLA has shown the highest commercial potential and is now produced on a comparatively large scale. Lactic acid can be produced cheaply by the fermentation of glucose obtained from the starch in biomass such as corn or wheat, or from lactose in whey or sucrose in molasses. Recently, a novel oat-based biorefinery producing l(+)-lactic acid and various value-added coproducts was proposed (Koutinas et al. 2007). Lactic acid production was achieved via fungal fermentation of Rhizopus oryzae on pearled oat flour and could, it was claimed, lead to significant operating cost reduction as compared with current industrial practices for lactic acid production. The dimerisation of polycondensed lactic acid into lactide (dilactone of lactic acid) and the ring-opening polymerisation (ROP) thereof was reported by the American chemist Wallace Carothers and others from DuPont in 1932 (Södergård & Stolt 2002). However, because the polymer based on lactyl units was unstable at high humidities, it was not considered to have commercial potential until the 1960s when its advantages in medical applications became apparent (Zhang & Sun 2005). Lactic acid (2-hydroxypropanoic acid) is one of the smallest optically active molecules; it can be either an l(+) or a d(−) stereoisomer (Huang 2005). Lactide is formed by the condensation of two lactic acid molecules to give a combination of l-lactide (two l-lactic acid molecules); d-lactide (two d-lactic acid molecules) and meso-lactide (an l-lactic acid and d-lactic acid molecule). PLA can be prepared by both direct condensation of lactic acid and by the ROP of the cyclic lactide dimer. Because the direct condensation route is an equilibrium reaction, difficulties in removing trace amounts of water during the late stages of polymerisation generally limit

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the ultimate molecular weight achievable by this approach. Most work has focused on the ROP, although Mitsui Toatsu Chemicals has patented an azeotropic distillation process using a high-boiling-point solvent to drive the removal of water in the direct esterification process to obtain high molecular weight PLA (Gruber & O’Brien 2003). NatureWorks® LLC has developed a patented, low-cost continuous process for the production of lactic acid-based polymers. The process starts with a continuous condensation reaction of aqueous lactic acid to produce low molecular weight PLA prepolymer which is converted into a mixture of lactide stereoisomers using tin catalysts. The molten lactide mixture is then purified by vacuum distillation. Finally, PLA high molecular weight polymer with a repeating unit of -[O-CH(CH3)-CO]- is produced using a tin-catalysed, ring-opening lactide polymerisation in the melt, completely eliminating the use of costly and environmentally unfriendly solvents. After the polymerisation is complete, any remaining monomer is removed under vacuum and recycled to the beginning of the process (Gruber & O’Brien 2003). Category 3: polymers produced directly by natural or genetically modified organisms Category 3 polymers consist mainly of the microbial polyesters known generally as PHAs. PHAs are a family consisting of renewable, biodegradable, biocompatible, optically active polyesters that were first identified in 1925 by the French microbiologist Maurice Lemoigne. They are produced in the form of intracellular particles by many commonly found microorganisms which accumulate PHAs as a carbon and energy sink when grown under nutrient stress in the presence of excess carbon (Iwata et al. 2006). Under controlled fermentation conditions, some species can accumulate up to 90% of their dry mass as polymer (Chen 2005). There are now over 100 different types of known molecular building blocks reported for various PHA copolymers (Noda et al. 2004). PHAs are linear aliphatic polyesters consisting of homo- or copolymers of β-hydroxyalkanoic acids that can be produced from the fermentation of sugars by, for example, Cupriavidus necator (originally known as Alcaligenes eutrophus and subsequently renamed Ralstonia eutropha and then Wautersia eutropha), the sugar to polymer conversion yield being about 33%. The polymers produced are biodegradable, and due to their characteristics are suitable for the production of packaging materials. Many different prokaryotic micro-organisms are known to accumulate PHAs intercellularly under growth-limiting conditions. By manipulating the growth medium, a random copolymer containing both 3-hydroxybutyrate (HB) and 3-hydroxyvalerate (HV) is obtained. After biomass separation, the polyester is extracted from the biomass and refined. In the PHA family, poly(hydroxybutyrate) (PHB) is the most common, and is classed as a short chain length PHA (scl PHA) with its monomers containing four to five

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carbon atoms. Another important scl PHA is poly(hydroxybutyrate-cohydroxyvalerate) or PHBV. PHAs are degraded on exposure to bacteria or fungi in soil, compost or marine sediment. In composting trials up to 85% of the PHA samples degraded within 7 weeks, and PHA-coated paper was rapidly degraded and incorporated into the compost (Nayak 1999). PHAs were first developed industrially in the 1960s and commercialised by ICI in the late 1980s under the tradename Biopol®, the first commercial product being launched in Germany by Wella AG in 1990 as a biodegradable, injection blow-moulded bottle for hair and skin products; these products were introduced to the United States and Japanese markets in 1991 and 1992 respectively (Ramsay & Ramsay 2004). Monsanto acquired Biopol® technology in 1996 and focused on direct synthesis in transgenic plants but stopped production in 1998. The technology was acquired by Metabolix in 2001 who have formed a joint venture company with Archer Daniels Midland known as Telles; they will release a family of PHAs under the tradename MirelTM in late 2008. Biomer in Munich has produced PHB since 1994 using proprietary bacteria. Proctor & Gamble released NodaxTM (a family of PHA copolyesters consisting of scl HB and medium chain length (mcl) HAs) using a genetically modified Pseudomonas species in 2005 but have since withdrawn them from the market (Noda et al. 2005). Since bacterial synthesis is costly, the focus now is on producing PHA plastics and derived chemicals directly in genetically modified crops such as switchgrass, while concurrently providing biomass for alternative energy generation. Switchgrass grows with high yields in the United States on land of marginal use for other crops. It fixes 2 kg CO2 in its root system per 1 kg of biomass above ground. Sugar cane and soybean are also attractive crops for PHA production. Coproduction of energy and PHAs using biomass is seen as the most sustainable approach to biobased material production. It is hoped that direct production of PHAs in plants will achieve economics competitive with those of existing large-volume petrochemical polymers. However, the extraction of PHA accumulated in plant materials will not be as easy as extracting PHA from micro-organisms (Sudesh & Doi 2005). The numerous challenges, both technical and non-technical, associated with commercialising this technology have recently been discussed (Bohlmann 2006). One challenge is to achieve a high level of polymer production in the plant without a decrease in crop yield; another is to recover the polymer from the plant biomass economically. An analysis of the process economics for producing PHAs in agricultural crops such as soybean or switchgrass and the economics compared with those for PHA production by Escherichia coli fermentation are discussed by Bohlmann (2006). Another Category 3 polymer is bacterial cellulose which can be synthesised by bacteria belonging to the genera Acetobacter, Rhizobium, Agrobacterium and Sarcina. Its most efficient producers are the

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Gram-negative, acetic acid bacteria Gluconacetobacter xylinus (previously Acetobacter xylinum) (Bielecki et al. 2003). It is considered to have enormous potential within the food packaging industry but so far is unexploited. The cellulose is identical in chemical and physical structure to the cellulose formed in plants but has the advantage that it is not combined with lignin, hemicelluloses and pectin, and so can be extracted without the need for harsh chemical treatment.

1.3

Properties of biobased food packaging materials

Before biobased materials can be successfully utilised by the food packaging industry, their physical and mechanical properties have to be within an acceptable range, as does their cost. The key properties of interest in food packaging are briefly reviewed below. 1.3.1 Barrier properties The poor barrier properties (especially under conditions of high humidity) of the traditional and most widely used biobased materials (paper and regenerated cellulose film or cellophane) are well known and it is necessary for them to be coated with synthetic polymers in order to achieve the desired barrier properties necessary for the packaging of many foods. Polysaccharide-based films are poor barriers against water vapour and other polar substances at high relative humidity but at low to intermediate relative humidity they are good barriers against oxygen and other non-polar substances such as aromas and oils (Dole et al. 2004). WVTRs of starchbased films are 4–6 times greater than those of conventional films made from synthetic polymers. Films based on arabinoxylan from annuals such as barley have low oxygen and carbon dioxide permeabilities but high water vapour permeability; they have been made less hydrophilic by surface fluorination but are not yet commercially available (Gröndahl et al. 2006). The barrier properties of some biobased and petroleum-derived polymers are shown in Table 1.1. The wide variation in the values reported are due in large part to the physical nature of the films (e.g. some are handmade; others are extruded commercially) and variations in test methodology rather than their inherent transmission properties. In addition, many values reported in the literature could not be included in the table since their units were incomplete. All the values in Table 1.1 should be used with caution. PLA has WVTRs 3–5 times higher than PET, LDPE, HDPE and OPS; PHAs have WVTRs similar to those of petroleum-derived polymers. PLA has better O2 barrier properties than PS but not as good as PET; PHB has better O2 barrier properties than PET and polypropylene (PP) (data not shown), and adequate fat and odour barrier properties for applications with

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State-of-the-art biobased food packaging materials Table 1.1

15

Barrier properties of biobased and petroleum-derived polymers

Polymer OPLA

Water vapour Oxygen Temperature Thickness Source transmission transmission (ºC) (mm) a b rate rate 15.30

22

4.6

66c

23

0.1

PLLA-Mh

210d

25

0.25

P(LLA-DLA) (50:50) PLLAh

214d

25

0.25

31d

27

1

18d 34–40c

27 23

1 0.1

118c 118 146c 1.16

23 23 23 30

0.1 0.1 0.1 1

1.39

30

1

3.48

22

4.6

5.18 6c

22

4.6 0.1

7.9

38d

0.75

36.85

38d

0.75

PLA

PLLA + SiOx PLA/NCg PLA-PCLe PLA (IM)f PLA-PCL/NCg PHB PHBV (14% HV) PET OPS LDPE/APET

56.33 200

84–99 105 233 183

9.44 532 33

LDPE LDPE + 5% starch

Auras et al. (2005) Plackett et al. (2006) Tsuji et al. (2006) ″ Uemura et al. (2006) ″ Plackett et al. (2006) ″ ″ ″ Miguel and Iruin (1999) ″ Auras et al. (2005) ″ Plackett et al. (2006) Jagannath et al. (2006) ″

Abbreviations: OPLA, oriented PLA; PLLA-M, poly(l-lactic acid) middle molecular weight; P(LLADLA), poly(l-lactic acid) and poly(d-lactic acid); NC, nanoclay; PLA (IM), impact modified PLA; PCL, poly(caprolactone); PHB, poly(hydroxybutyrate); PHV, poly(hydroxyvalerate); PHBV, poly(hydroxybutyrate-co-hydroxyvalerate); PET, poly(ethylene terephthalate); OPS, oriented polystyrene; LDPE/APET, low-density polyethylene/amorphous poly(ethylene terephthalate). a Units: mL m−2 day−1 at 0% relative humidity (RH). b Units: g m−2 day−1 at 100% RH. c 37.8 ºC. d 90% RH. e 3–4% caprolactone. f Impact modified. g 5% nanoclay. h Poly(l-lactic acid).

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short-shelf-life products. Although the gas barrier properties of most biobased materials depend on the ambient humidity, PLA and PHA are two notable exceptions (Auras et al. 2004b). Recently the sorption of ethyl acetate and d-limonene in PLA polymers has been determined (Auras et al. 2006). Ethyl acetate permeability coefficients in PLA are lower than those for PP and LDPE and slightly higher than PET. The permeability coefficient for d-limonene in PLA is much lower than for PET, PP and LDPE, thus confirming that PLA is a good aroma barrier when used in food packaging, as shown earlier in studies on orange juice (Haugaard et al. 2002). 1.3.2 Mechanical properties The mechanical properties of most biobased materials are similar to synthetic polymers as can be seen in Table 1.2. Polysaccharide film tensile

Table 1.2 Mechanical properties of biobased and petroleum-derived polymers Glass Young’s Tensile Elongation Melting transition modulus strength at break Source Polymer temperature, temperature, (Gpa) (Mpa) (%) Tm (ºC) Tg (ºC) Starcha

0.1–0.4

24–30

200–1000

Starchb Starch

110–115

—

0.2–2.0 0.6–0.85

20–30 35–80

20–500 580–820

PLA PHA PHB PHBV PHB

130–180 70–170 140–180 100–190 180

40–70 −30 to 10 0 0–30 4

3.5 0.7–1.8 3.5 0.6–1 3.5

48–53 18–24 25–40 25–30 43

30–240 3–25 5–8 7–15 5

PHBVc PET

145 245–265

1 73–80

1.2 2.8–4.1

20 48–72

50 30–300

PS LDPE LDPE

100 98–115 110

70–115 −100 −30

2.3–3.3 0.3–0.5 0.2

34–50 8–20 10

1.2–2.5 100–1000 620

PP

176

1.7

38

400

a b c

Film grade. Injection moulding grade. 20% HV.

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0

Bastioli (2005) ″ Clarinval and Halleux (2005) ″ ″ ″ ″ Sudesh and Doi (2005) ″ Clarinval and Halleux (2005) ″ ″ Sudesh and Doi (2005) ″

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strength and elastic modulus decrease with increasing plasticiser content, while film elongation normally increases. The mechanical properties of PLA are determined by the molecular weight of the polymer, chain architecture (linear versus branched) and degree of crystallinity, the achievable crystallinity being determined by the relative proportions of l-, d- and meso-lactide in the polymer backbone (Dorgan et al. 2006). Orientation of PLA improves mechanical strength and heat stability, and varying crystallinity and molecular weight results in films ranging from soft and elastic to stiff and high strength. Some limitations do still exist, including the low melt strength (extensibility without breaking of the molten state) and the relatively low temperature at which heat distortion begins to occur. Amorphous and low-crystalline PLA are clear with a high gloss, while highly crystalline PLA is an opaque white material (Dorgan 2006). PLA has a heat seal initiation temperature of 80 ºC, and mechanical properties similar to those of PET. Recently it has been shown (Holm et al. 2006) that hydrolysis of PLA ester linkages results in a 75% decrease in molecular weight and a 35% loss of tensile strength over 130 days at 25 ºC and 98% relative humidity; no decrease was observed at 5 ºC. The physical properties of PHA copolymers can be regulated by varying their molecular structures and copolymer compositions. In general PHB is a hard, highly crystalline thermoplastic polymer that most closely resembles isotactic PP with respect to mechanical behaviour. Although PHB homopolymer is relatively stiff and brittle, introduction of HV comonomers greatly improves its mechanical properties by reducing the level of crystallinity and the melting point, resulting in a decrease in stiffness but an increase in toughness or impact resistance (Bohlmann 2005). As a consequence, the PHA family of polyesters displays a wide variety of properties, from hard crystalline plastics to elastic rubbers with melting temperatures of 50–180 ºC (Sudesh et al. 2000). A random copolymer containing both 3-HB and 3-HV is thermoplastic, being able to be formed by the same techniques as those used for synthetic polymers. By changing the ratio of HV to HB, the resulting copolymer can be made to resemble either PP (low HV) or LDPE (high HV) with regard to flexibility, tensile strength and melting point. For example, the melting temperature decreases from 179 ºC for PHB with no HV to 137 ºC with 25% HV (Hocking & Marchessault, 1998). PHBV has good chemical and moisture resistance as well as good oxygen and aroma barrier properties. PHB has a different resistance to dynamic compression than PP, its deformation value being about 50% lower indicating a more rigid and less flexible material. Under normal freezing and refrigeration conditions the performance of PHB tended to be inferior to that of PP, whereas at higher temperatures PHB performed better than PP (Bucci et al. 2005). When amorphous PLA was blended with PCL it resulted in improved mechanical properties and thermal stability without significant decrease in barrier properties (Cabedo et al. 2006). The toughness of PLA has been

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substantially increased without a reduction in optical clarity by blending a small amount of ductile PHA with PLA (Noda et al. 2004). 1.3.3 Current limitations The major limitations of most biobased packaging materials for food applications are their performance, processing and cost (Sorrentino et al. 2007). In particular, brittleness, low heat distortion temperature, poor resistance to protracted processing operations and (with the exception of PHAs) their barrier properties, in particular their barrier to water vapour, have limited their applications. Cost has declined in recent years and will decline further as production volume is increased and process optimisation and in-plant efficiencies are achieved. Limited availability is another issue although construction of additional production capacity will address this issue. However, it is unlikely that there will be sufficient PLA to meet food industry requirements for some time. 1.3.4 Methods to improve functionality It is possible to improve the barrier properties of biobased materials (as well as petroleum-derived polymers) using various techniques including plasma deposition of SiOx and the addition of nanocomposites from natural polymers and modified clays. The use of nanocomposites promises to expand the use of biobased packaging (Chiellini et al. 2004; Lagarón et al. 2005; Ray & Bousmina 2005, 2006; Lewitus et al. 2006; Okamoto 2006; Yu et al. 2006) and readers are referred to two recent reviews for details of the potential of bio-nanocomposites in food packaging applications (Rhim & Ng 2007a; Sorrentino et al. 2007). A detailed review of the current literature associated with the barrier properties of polymer/clay nanocomposites has recently been published (Sorrentino et al. 2006). To give just a few examples, an SiOx coating on PLA reduced the WVTR by 60% (Uemura et al. 2006); when 4% kaolinite nanofillers were blended with amorphous PLA, it resulted in an increase in oxygen barrier of 43% (Cabedo et al. 2006). Chang et al. (2003) reported that O2 permeability values were less than half when three types of nanoclays were incorporated into PLA. Results of a similar order of magnitude obtained by Plackett et al. (2006) are shown in Table 1.1 although they did not achieve the full potential for permeability reduction, possibly due to processing conditions, extruder characteristics and selection of the most appropriate nanoclay for a given polymer. Recently starch/clay nanocomposite films were prepared which showed improved mechanical properties (Avella et al. 2005). In a more traditional approach to improving film properties, Rhim et al. (2007b) coated a soy protein isolate film on both sides with PLA and reported up to a 6-fold increase in tensile strength and a 20- to 60-fold decrease in water vapour permeability compared with uncoated soy protein

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isolate. Coating of paperboard with up to 3 w/v% PLA resulted in an improvement in water barrier properties (Rhim et al. 2007c).

1.4

Assessing the biodegradability of biobased materials for food packaging

Biodegradability is a much over-used and frequently misunderstood word and has no practical meaning unless the environment, timeframe and context are specified. Biodegradable polymers constitute a loosely defined family of polymers that are designed to be degraded by biological agents. Two key steps occur in the biodegradation of polymers. First is a depolymerisation or chain cleavage step (hydrolysis and/or oxidation may be responsible) which converts the polymer chain into smaller oligomeric fragments. The hydrolytic or oxidative processes may be promoted biotically (in biological pathways) and abiotically (in non-biological pathways), oxidation usually being a slower process than hydrolysis (Swift & Baciu 2006). The second step (known as mineralisation) occurs inside the cell where oligomeric fragments are converted into biomass, minerals and salts, water and gases such as CO2 and CH4 (Bohlmann 2005). Composting is the accelerated degradation of heterogeneous organic matter by a mixed microbial population in a moist, warm, aerobic environment under controlled conditions (Narayan 2006). Temperatures in a typical compost system are in the range 40–70 ºC. A standard definition for biodegradable plastics can be found in ISO 472 Plastics vocabulary and ASTM D883 Standard terms relating to plastics: ‘Biodegradable plastic: a degradable plastic in which the degradation process results in lower molecular weight fragments produced by the action of naturally occurring micro-organisms such as bacteria, fungi and algae’. As has been clearly pointed out (Scott 2005), the development of biodegradable polymers has been beset by misinterpretation of the way in which nature deals with its waste products. In particular, the importance of abiotic (non-living) processes has not been given sufficient emphasis in the process of bioassimilation, with the consequence that standards for biodegradable polymers tend to be based on folklore rather than scientific evidence since they ignore completely the environmental role of abiotic chemistry. A number of ASTM standards address important aspects of biodegradable plastics. For example, D5338 addresses CO2 generation in aerobic environments including controlled composting, while D5511 addresses CH4/CO2 evolution in anaerobic environments such as high solids anaerobic digestion, and D5526 accelerated landfill conditions. Other relevant standards include: D6002 for assessing the compostability of environmentally degradable plastics; D6400 for compostable plastics; D6868 for biodegradable plastics used as coatings on paper and other compostable substrates; D6954 for exposing and testing plastics that degrade

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in the environment by a combination of oxidation and biodegradation; D7075 for evaluating and reporting the environmental performance of biobased products. Complete biodegradation of the product is commonly measured through respirometric tests such as ASTM D5338 which is equivalent to ISO 14852. In this method, the aerobic biodegradation of polymer materials is determined under controlled composting conditions. This test is more suitable for packaging materials as the inoculum is obtained from composted MSW. Difficulties associated with maintaining the complicated temperature profile of this test have been eliminated in ISO 14855, where a constant temperature of 58 ± 2 ºC is specified. This is the most widely used standard test method for the determination of the rate and degree of biodegradation of packaging materials under conditions simulating an intensive aerobic composting process (Jayasekara et al. 2005). The percent biodegradation does not include the carbon converted to cell biomass and not metabolised to CO2 during the course of the test. The European standard EN 13432 Requirements for packaging recoverable through composting and biodegradation – test scheme and evaluation criteria for final acceptance of packaging corresponds to D6400. It is worth noting that both the D6400 and EN 13432 standards were originally developed for starch-based biopolymers, or hydrobiodegradable polymers, where the mechanism inducing biodegradation is based on a reaction with water. The inherent biodegradation test measures the conversion of carbon to CO2 but there is one significant difference between the two standards: complete biodegradation in the compost is measured by CO2 evolution in 180 days in D6400 and 90 days in EN 13432 (Swift & Baciu 2006). The International Standards Organisation has developed ISO 17088 which specifies procedures and requirements for the identification and labelling of plastics, and products made from plastics, that are suitable for recovery through aerobic composting. It comes as a surprise to many people to learn that certain natural materials do not meet these standards, e.g. a leaf will not naturally biodegrade within the timeframe allotted by either D6400 or EN 13432. It is worth emphasising that ‘biobased’ refers to the feedstock used while ‘biodegradable’ refers to how a material acts during disposal. Of course biodegradation depends only on the chemical composition of the polymer and not on its origin (Scott 2005). A major problem with the above standards is that they evaluate samples of biodegradable materials under laboratory conditions rather than as a complete package under real commercial conditions. Recently, Kale et al. (2007b) determined the degradation process of two PLA packages (a bottle and a delicatessen container) over 30 days under real composting and ambient exposure conditions. Bottles made of 96% l-lactide exhibited less degradation than trays made of 94% l-lactide, mainly due to their highly ordered structure and, therefore, their higher crystallinity.

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The procedure to have a package certified as ‘compostable’ is very elaborate (Kale et al. 2007a). As well as passing test method D5338 or ISO 14855, it must meet various other requirements such as the disintegration test, having heavy metals below certain limits and passing the plant growth test for ecotoxicity. An LCA evaluating the environmental impacts of solid waste management alternatives concluded that diversion of organic waste from landfill to composting reduced energy recovery and increased greenhouse gas emissions of the waste management system (Barlaz et al. 2003). However, the environmental consequences of composting could not be completely characterised due to lack of data.

1.5

Applications and challenges for biobased food packaging

Despite considerable research and development, the use of the newer biobased packaging materials for the packaging of food remains limited. The major scientific studies on the packaging of foods in (partly) biobased materials have been reviewed (Haugaard & Mortensen 2003). Although the number of published papers is few, they show that there are many potential applications. For example, thermoformed PLA cups and injection-moulded PHB cups were found to be as effective as HDPE cups in protecting an orange juice simulant and a dressing from quality changes during storage (Haugaard et al. 2003). The O2 permeability of the three containers was 0.21, 0.18 and 0.26 mL cup−1 day−1 respectively. The quality changes were primarily induced by light. PLA can be made into films, co-extruded into laminates, thermoformed and injection stretch blow moulded into bottles (Auras et al. 2004a). A major application to date has been as food service containers. For example, one-way beverage cups have been used, either as 100% PLA cups or paper cups coated with PLA, to promote an environmentally friendly image. Other current uses are for thermoformed packaging for bakery products, and bags for bread, fresh pasta and salads. Small niche markets for PLA trays and films have been found in Europe, often for organically grown food. Auras et al. (2005) evaluated OPLA for fresh food service containers and compared it with PET and OPS. At ambient conditions (22 ºC) they concluded that OPLA containers provided better mechanical properties than OPS and were comparable to PET. Although the OPLA WVTR was inferior to OPS (5 times greater), the oxygen transmission rate was 10 times less and it was concluded that OPLA could easily replace OPS for fresh food containers. PLA products are fully compostable in commercial composting facilities. Provided that production costs can be reduced, PLA is expected to find packaging applications in areas such as candy twist wraps, coatings for

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paperboard beverage cartons, plastic film wraps for foods, blister packs and plastic windows in boxes. Recently Rhim et al. (2007c) showed that the optimum concentration of coating solution for improving the water resistance of paperboard was 3 w/v% of PLA solution; a reduction in water vapour permeability of almost 96% at 98% relative humidity was achieved. It was suggested that the improved water barrier properties of paperboard could be exploited in the preparation of water-resistant corrugated fibreboard boxes for storage and distribution of high-moisture foods such as fresh agricultural produce. A small but widely publicised niche market has been developed for a water-soluble, compostable, thermoformed starch tray in chocolate boxes, replacing polyvinyl chloride (PVC) and PET trays. A glassine ‘topper’ pad covers the chocolates in a paperboard box that is overwrapped with PVC film. The tray is manufactured by Plantic and is reputed to consume 50% less energy throughout its life cycle than the previous PVC tray; it has been adopted by the two major chocolate manufacturers in Europe. Haugaard and Mortensen (2003) suggested that, in the short term, biobased materials will be used for short-shelf-life foods stored at chill temperatures, due to the fact that the materials are biodegradable. Recently Holm et al. (2006) reported on the influence of temperature and humidity on the stability of copolymer PLA films with 1.8% PCL. They concluded that PLA films can be expected to be mechanically stable when packaging dry to moist foods at chill to ambient temperatures. Potential applications include fast food packaging of salads, egg cartons, fresh or minimally processed fruits and vegetables, dairy products such as yoghurt and organically grown foods. The high CO2 : O2 permeability ratio of certain biobased packaging materials suggests that they could find application in the packaging of respiring foods such as fruits and vegetables. The challenge for the successful use of biodegradable polymer products in food packaging is achieving the desired shelf-life followed by efficient biodegradation after disposal. Obviously, premature biodegradation and insect infestation must be avoided. In addition, it is imperative that biodegradable plastics do not contaminate the recycling stream for nonbiodegradable, petroleum-derived plastics.

1.6

Future trends

Numerous factors, including political and legislative changes as well as global demand for foods and energy resources, will influence the development and success of biobased packaging materials. However, there is no doubt that the use of biobased materials for food packaging will increase, partly as a result of improvements in mechanical and barrier properties, partly as a result of decreases in costs vis-à-vis petroleum-derived polymers,

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and partly as a result of their improved environmental profiles. Major supermarket chains are already leading the way by encouraging their suppliers to use biobased packaging materials and this trend is likely to accelerate. Future biobased food packaging materials are likely to be blends of polymers and nanoclays (so-called bio-nanocomposites) in order to achieve the desired barrier and mechanical properties demanded by the food industry. Already important research has been undertaken in this area with some small commercialisation; the next decade will see significant production of bio-nanocomposites for food industry use. Cost is undoubtedly a limitation to the widespread adoption of biobased packaging materials but as production capacity increases, costs will fall. One barrier to reducing costs is the increase in the production of biofuels which in many cases are competing for the same raw materials (corn and maize) as biobased packaging, putting upward pressure on raw material costs. If PHA is to be competitive with synthetic plastics economically, it must be produced on a far larger scale than any other aerobically produced microbial product. In addition, since PHAs are intracellular products, there are physical limitations to the amount that can be produced per cell (Ramsay & Ramsay 2004). The biggest unanswered question from a commercial point of view is whether the use of biobased packaging materials will be enthusiastically embraced by consumers. Only time will tell if the majority of consumers are ready for environmentally sustainable food packaging materials, and if they are, whether they insist on them being composted rather than landfilled after use.

1.7

Sources of further information and advice

• Baillie C (2004), Green Composites Polymer Composites and the Environment, Cambridge, UK, Woodhead Publishing Ltd. • Bastioli C (2005), Handbook of Biodegradable Polymers, Shawbury, UK, Rapra Technology Ltd. • Bozell JJ, Patel MK (2006), Feedstocks for the Future: Renewables for the Production of Chemicals and Materials, ACS Symposium Series No. 921, Washington DC, American Chemical Society. • Kaplan DL (1998), Biopolymers from Renewable Resources, New York, Springer. • Khemani K, Scholz C (2006), Degradable Polymers and Materials: Principles and Practice, ACS Symposium Series No. 939, Washington DC, American Chemical Society. • Mai Y-W, Yu Z-Z (2006), Polymer Nanocomposites, Cambridge, UK, Woodhead Publishing Ltd.

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• Mallapragada SK, Narasimhan B (2006), Handbook of Biodegradable Polymeric Materials and Their Applications, vol. 1, Valencia, California, American Scientific Publishers. • Mattson B, Sonneson U (2003), Environmentally Friendly Food Processing, Boca Raton, Florida, CRC Press. • Mohanty AK, Misra M, Drzal LT (2005), Natural Fibers, Biopolymers, and Biocomposites, Boca Raton, Florida, CRC Press. • Smith R (2005), Biodegradable Polymers for Industrial Application, Cambridge, UK, Woodhead Publishing Ltd. • Weber CJ (2000), Biobased Packaging Materials for the Food Industry – Status and Perspectives, Copenhagen, The Royal Veterinary and Agricultural University, Department of Dairy and Food Science.

1.8

References

auras r, harte b, selke s (2004a), ‘An overview of polylactides as packaging materials’, Macromol Biosci 4, 835–864. auras r, harte b, selke s (2004b), ‘Effect of water on the oxygen barrier properties of poly(ethylene terephthalate) and polylactide films’, J Appl Poly Sci 92, 1790–1803. auras ra, singh sp, singh jj (2005), ‘Evaluation of oriented poly(lactide) polymers vs. existing PET and oriented PS for fresh food service containers’, Packag Technol Sci 18, 207–216. auras r, harte b, selke s (2006), ‘Sorption of ethyl acetate and d-limonene in poly(lactide) polymers’, J Sci Food Agric 86, 648–656. avella m, de vlieger jj, errico me, fischer s, vacca p, volpe mg (2005), ‘Biodegradable starch/clay nanocomposite films for food packaging applications’, Food Chem 93, 467–474. avérous l, boquillon n (2004), ‘Biocomposites based on plasticized starch: thermal and mechanical behaviours’, Carbohydr Polym 56, 111–122. barlaz ma, kaplan po, ranjithan sr, rynk r (2003), ‘Evaluating environmental impacts of solid waste management alternatives’, Biocycle 44(10), 52–56. bastioli c (2005), ‘Starch-based technology’, in Bastioli C (Ed.), Handbook of Biodegradable Polymers, Shawbury, UK, Rapra Technology Ltd, pp. 257–286. bhattacharya m, reis rl, correlo v, boesel l (2005), ‘Material properties of biodegradable polymers’, in Smith R (Ed.), Biodegradable Polymers for Industrial Application, Cambridge, UK, Woodhead Publishing Ltd, pp. 336–356. bielecki s, krystnowicz a, turkiewicz m, kalinowska h (2003), ‘Bacterial Cellulose’, in Steinbüchel A (Ed.), Biopolymers, vol. 5, Toronto, Wiley-VCH, pp. 37–59. bohlmann gm (2005), ‘General characteristics, processability, industrial applications and market evolution of biodegradable polymers’, in Bastioli C (Ed.), Handbook of Biodegradable Polymers, Shawbury, UK, Rapra Technology Ltd, pp. 183–217. bohlmann gm (2006), ‘Polyhydroxyalkanoate production in crops’, in Bozell JJ and Patel MK (Eds), Feedstocks for the Future: Renewables for the Production of Chemicals and Materials, ACS Symposium Series No. 921, Washington DC, American Chemical Society, pp. 253–270. bucci dz, tavares lbb, sell i (2005), ‘PHB packaging for the storage of food products’, Polym Test 24, 564–571.

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cabedo l, feijoo jl, villanueva mp, lagarón jm, giménez e (2006), ‘Optimization of biodegradable nanocomposites based on aPLA/PCL blends for food packaging applications’, Macromol Symp 233, 191–197. chang j-h, an yu, sur gs (2003), ‘Poly(lactic acid) nanocomposites with various organoclays. 1. Thermomechanical properties, morphology, and gas permeability’, J Polym Sci: Part B Polym Phys 41, 94–103. chen g g-q (2005), ‘Polyhydroxyalkanoates’, in Smith R (Ed.), Biodegradable Polymers for Industrial Application, Cambridge, UK, Woodhead Publishing Ltd, pp. 32–56. chiellini e, cinelli p, chiellini f, imam sh (2004), ‘Environmentally degradable bio-based polymeric blends and composites’, Macromol Biosci 4, 218–231. clarinval a-m, halleux j (2005), ‘Classification of biodegradable polymers’, in Smith R (Ed.), Biodegradable Polymers for Industrial Application, Cambridge, UK, Woodhead Publishing Ltd, pp. 3–31. dean k, yu l (2005), ‘Biodegradable protein–nanoparticle composites’, in Smith R (Ed.), Biodegradable Polymers for Industrial Application, Cambridge, UK, Woodhead Publishing Ltd, pp. 289–309. dole p, joly c, espuche e, alric i, gontard n (2004), ‘Gas transport properties of starch based films’, Carbohydr Polym 58, 335–343. dorgan jr, braun b, wegner jr, knauss dm (2006), ‘Poly(lactic acids): a brief review’, in Khemani K and Scholz C (Eds), Degradable Polymers and Materials: Principles and Practice, ACS Symposium Series No. 939, Washington DC, American Chemical Society, pp. 102–125. gröndahl m, gustafsson a, gatenholm p (2006), ‘Gas-phase surface fluorination of arabinoxylan films’, Macromolecules 39, 2718–2721. gruber, p, o’brien, m (2003), ‘Polylactides “NatureWorksTM PLA” ’, in Steinbüchel A (Ed.), Biopolymers, vol. 4, Toronto, Wiley-VCH, pp. 235–252. guilbert s, cuq b (2005), ‘Material formed from proteins’, in Bastioli C (Ed.), Handbook of Biodegradable Polymers, Shawbury, UK, Rapra Technology Ltd, pp. 339–374. haugaard vk, weber cj, danielsen b, bertelsen g (2002), ‘Quality changes in orange juice packed in materials based on polylactate’, Eur Food Res Technol 214, 423–428. haugaard vk, mortensen, g (2003), ‘Biobased food packaging’, in Mattson B and Sonneson U (Eds), Environmentally Friendly Food Processing, Chapter 11, Boca Raton, Florida, CRC Press. haugaard vk, danielsen b, bertelsen g (2003), ‘Impact of polylactate and poly(hydroxybutyrate) on food quality’, Eur Food Res Technol 216, 233–240. hocking pj, marchessault rh (1998), ‘Polyhydroxyalkanoates’, in Kaplan DL (Ed.), Biopolymers from Renewable Resources, New York, Springer, pp. 220–247. holm vk, ndoni s, risbo j (2006), ‘The stability of poly(lactic acid) packaging films as influenced by humidity and temperature’, J Food Sci 71, E40–E44. huang sj (2005), ‘Poly(lactic acid) and copolyesters’, in Bastioli C (Ed.), Handbook of Biodegradable Polymers, Shawbury, UK, Rapra Technology Ltd, pp. 287–301. iwata t, tanaka t, adachi n, hasegawa m, teramachi s, doi y (2006), ‘Physical properties, structure analysis, and enzymatic degradation of poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] films and fibers’, in Khemani K and Scholz C (Eds), Degradable Polymers and Materials: Principles and Practice, ACS Symposium Series No. 939, Washington DC, American Chemical Society, pp. 61–75. jagannath jh, nadanasabapathi s, bawa as (2006) ‘Effect of starch on thermal, mechanical, and barrier properties of low density polyethylene film’, J Appl Polym Sci 99, 3355–3364.

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jayasekara r, harding i, bowater i, lonergan g (2005), ‘Biodegradability of a selected range of polymers and polymer blends and standard methods for assessment of biodegradation’, J Polym Environ 13, 231–232. kale g, kijchavengkul t, auras r, rubino m, selke s, singh sp (2007a), ‘Compostability of bioplastic packaging materials: an overview’, Macromol Biosci 7, 255–277. kale g, auras r, singh sp (2007b), ‘Comparison of the degradability of poly(lactide) packages in composting and ambient exposure conditions’, Packag Technol Sci 20, 49–70. kim s, dale be (2005), ‘Life cycle assessment study of biopolymers (polyhydroxyalkanoates) derived from no-tilled corn’, Int J LCA 10, 200–210. koutinas aa, malbranque f, wang r, campbell gm, webb c (2007), ‘Development of an oat-based biorefinery for the production of l(+)-lactic acid by Rhizopus oryzae and various value-added coproducts’, J Agric Food Chem 55, 1755–1761. lagarón jm, cabedo l, cava d, feijoo jl, gavara r, gimenez e (2005), ‘Improving packaged food quality and safety. 2. nanocomposites’, Food Additiv Contam 22, 994–998. lewitus d, mccarthy s, ophir a, kenig s (2006), ‘The effect of nanoclays on the properties of PLLA-modified polymers part 1: mechanical and thermal properties. J Polym Environ 14, 171–177. lodha p, netravali an (2005), ‘Thermal and mechanical properties of environmentfriendly ‘green’ plastics from stearic acid modified-soy protein isolate’, Indust Crops Products 21, 49–64. miguel o, iruin jj (1999), ‘Water transport properties in poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) biopolymers. J Appl Polym Sci 73, 455–468. mohanty ak, misra m, drzal lt, selke se, harte br, hinrichsen g (2005), ‘Natural fibers, biopolymers, and biocomposities: an introduction’, in Mohanty AK, Misra M and Drzal LT (Eds), Natural Fibres, Biopolymers and Biocomposites, Chapter 1, Boca Raton, Florida, CRC Press. mohareb e, mittal gs (2007), ‘Formulation and process conditions for biodegradable/edible soy-based packaging trays’, Packag Technol Sci 20, 1–15. narayan r (2006), ‘Biobased and biodegradable polymer materials: rationale, drivers and technology exemplars’ in Khemani K and Scholz C (Eds), Degradable Polymers and Materials: Principles and Practice, ACS Symposium Series No. 939, Washington DC, American Chemical Society, pp. 282–306. nayak pl (1999), ‘Biodegradable polymers: opportunities and challenges’, J Macromol Sci 39, 481–505. no hk, meyers sp, prinyawiwatkul w, xu z (2007), ‘Applications of chitosan for improvement of quality and shelf life of foods: a review’. J Food Sci 72, R87–R100. noda i, satkwoski mm, dowrey ae, marcott c (2004), ‘Polymer alloys of Nodax copolymers and poly(lactic acid)’, Macromol Biosci 4, 269–275. noda i, green pr, satkowski mm, schechtman la (2005), ‘Preparation and properties of a novel class of polyhydroxyalkanoate copolymers’, Biomacromolecules 6, 580–586. okamoto m (2006), ‘Biodegradable polymer/layered silicate nanocomposites’, in Mallapragada SK and Narasimhan B (Eds), Handbook of Biodegradable Polymeric Materials and their Applications, vol. 1, Valencia, California, American Scientific Publishers, pp. 153–197 patel m, bastioli c, marini l, würdinger e (2003), ‘Life-cycle assessment of bio-based polymers and natural fiber composites’, in Steinbüchel A (Ed.), Biopolymers, vol. 10, Chapter 10, Toronto, Wiley-VCH.

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patel m, narayan r (2005), ‘How sustainable are biopolymers and biobased products? The hope, the doubts, and the reality’, in Mohanty AK, Misra M and Drzal LT (Eds), Natural Fibres, Biopolymers and Biocomposites, Chapter 27, Boca Raton, Florida, CRC Press. plackett dv, holm vk, johansen p, ndoni s, nielsen pv, sipilainen-malm t, södergà6rd a, verstichel s (2006), ‘Characterization of l-polylactide and lpolylactone–polycaprolactone co-polymer films for use in cheese-packaging applications’, Packag Technol Sci 19, 1–24. platt dk (2006), Biodegradable Polymers Market Report, Shawbury, UK, Rapra Technology Ltd. ramsay ba, ramsay ja (2004), ‘Poly(3-hydroxyalkanoates)’, in Mark HF (Ed.), Encyclopedia of Polymer Science and Technology, 3rd Edn, vol. 3, New York, John Wiley & Sons Inc., pp. 525–544. rathje w, murphy c (1992), Rubbish! The Archaeology of Garbage, New York, HarperCollins Publishers, p. 115. ray ss, bousmina m (2005), ‘Biodegradable polymers and their layered silicate nanocomposites: in greening the 21st century world’, Prog Mater Sci 50, 962–1079. ray ss, bousmina m (2006), ‘Nano reinforcements of renewable plastics: to create the next generation of value-added novel eco-friendly nanocomposites’, in Mallapragada SK and Narasimhan B (Eds), Handbook of Biodegradable Polymeric Materials and Their Applications, vol. 1, Valencia, California, American Scientific Publishers, pp. 1–53. rhim j-w, ng pkw (2007a), ‘Natural biopolymer-based nanocomposite films for packaging applications’, Crit Rev Food Sci Nutr 47, 411–433. rhim j-w, lee jh, ng pkw (2007b), ‘Mechanical and barrier properties of biodegradable soy protein isolate-based films coated with polylactic acid’, LWT 49, 232–238. rhim j-w, lee j-h, hong s-i (2007c), ‘Increase in water resistance of paperboard by coating with poly(lactide)’, Packag Technol Sci 20, 393–402. robertson gl (2006), ‘Food packaging and the environment’, in Robertson GL, Food Packaging Principles and Practice, 2nd Edn, Boca Raton, Florida, CRC Press, pp. 503–527. royte e (2006), ‘Corn plastic to the rescue’, Smithsonian Mag, August, www.smithsonianmagazine.com/issues/2006/august/pla.php. scholz c, khemani k (2006), ‘Introduction’ in Khemani K and Scholz C (Eds), Degradable Polymers and Materials: Principles and Practice, ACS Symposium Series No. 939, Washington DC, American Chemical Society, pp. 2–11. scott g (2005), ‘Standards for environmentally biodegradable plastics’, in Smith R (Ed.), Biodegradable Polymers for Industrial Applications, Cambridge, UK, Woodhead Publishing Ltd, pp. 313–335. södergà6rd a, stolz m (2002), ‘Properties of lactic acid based polymers and their correlation with composition’, Prog Polym Sci 27, 1123–1163. sorrentino a, gorassi g, tortora m, vittoria v (2006), ‘Barrier properties of polymer/ clay nanocomposites’, in Mai Y-W and Yu Z-Z (Eds), Polymer Nanocomposites, Cambridge, UK, Woodhead Publishing Ltd, pp. 273–292. sorrentino a, gorassi g, vittoria v (2007), ‘Potential perspectives of bionanocomposites for food packaging applications’, Trends Food Sci Technol 18, 84–95. steinbüchel a (2005), ‘Non-biodegradable biopolymers from renewable resources: perspectives and impacts’, Curr Opin Biotechnol 16, 607–613. sudesh k, abe h, doi y (2000), ‘Synthesis, structure and properties of polyhydroxyalkanoates: biological polyesters’, Prog Polym Sci 25, 1503–1555.

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sudesh k, doi y (2005), ‘Polyhydroxyalkanoates’, in Bastioli C (Ed.), Handbook of Biodegradable Polymers, Shawbury, UK, Rapra Technology Ltd, 219–256. swift g, wiles dm (2004), ‘Biodegradable polymers and plastics in landfill sites’, in Mark HF (Ed.), Encyclopedia of Polymer Science and Technology, 3rd Edn, vol. 9, New York, John Wiley & Sons, Inc., pp. 40–50. swift g, baciu r (2006), ‘Biodegradable polymers: are sources and structures important?’ in Khemani K and Scholz C (Eds), Degradable Polymers and Materials Principles and Practice, Chapter 24, ACS Symposium Series No. 939, Washington DC, American Chemical Society. tsuji h, okino r, daimon h, fujie k (2006) ‘Water vapor permeability of poly(lactide)s: effects of molecular characteristics and crystallinity’, J Appl Polym Sci 99, 2245–2252. uemura y, maetsuru y, fujita t, yoshida m, hatate y, yamada k (2006), ‘The effect of coatings formed by low temperature tetramethoxysilane plasma treatment on water-vapor permeability of poly(l-lactic acid) film’, Korean J Chem Engng 23, 144–147. van tuil r, fowler p, lawther m, weber cj (2000), ‘Properties of biobased packaging materials’, in Weber CJ (Ed.), Biobased Packaging Materials for the Food Industry – Status and Perspectives, Copenhagen, The Royal Veterinary and Agricultural University, Department of Dairy and Food Science, pp. 13–44. weber cj, haugaard v, festersen r, bertelsen g (2002), ‘Production and applications of biobased packaging materials for the food industry’, Food Additiv Contam 19, 172–177. xu yx, kim km, hanna ma, nag d (2005), ‘Chitosan-starch composite film: preparation and characterization’, Indust Crops Products 21, 185–192. yu l, dean k, li l (2006), ‘Polymer blends and composites from renewable resources’, Prog Polym Sci 31, 576–602. zhang j-f, sun x (2005), ‘Poly(lactic acid)-based bioplastics’, in Smith R (Ed.), Biodegradable Polymers for Industrial Application, Cambridge, UK, Woodhead Publishing Ltd, pp. 251–288. zhao y, mcdaniel m (2005), ‘Sensory quality of foods associated with edible film and coating systems and shelf-life extension’, in Han JH (Ed.), Innovations in Food Packaging, San Diego, California, Elsevier Ltd, pp. 434–453.

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2 Types, production and assessment of biobased food packaging materials S. Imam, G. Glenn, B.-S. Chiou, J. Shey, R. Narayan and W. Orts, USDA-ARS-PW-WRRC, USA

2.1

Introduction: rationale and need for biobased food packaging

Food packaging was initially created to facilitate trade and transportation of commodities over long distances. These commodities include both perishable as well as non-perishable foods. Paper, cardboard and cellulosic fibers – as well as glass, aluminum and tin – were the materials of choice for packages such as cartons, sacks, containers, bottles, etc. Over the last few decades, the packaging industry has transformed into a highly sophisticated and intelligent service industry, particularly for perishable foods; the industry has taken advantage of the state-of-the-art in material science, manufacturing and process engineering along with ever-advancing knowledge of food science (Truong et al., 2001; Ahvenainen, 2003; Robertson, 2005). Today, food packaging has many purposes. It is designed not only to contain and protect food, but also to keep food safe and secure, to retain food quality and freshness, and to increase its shelf-life. In addition, packaging should be affordable to consumers worldwide and, more importantly, it must be naturally biodegradable upon disposal. Undeniably, packaging has become the very core of the thriving businesses of fast-foods, ready meals, on-the-go beverages, snacks and manufactured foods, and is one of the fastest growing sectors of the global economy. Names are necessary to report factually on available data; however, the United States Department of Agriculture (USDA) neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may be suitable.

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The packaged food industry experienced a tremendous growth in the later half of the twentieth century owing mostly to the advances made by the petrochemical industry offering new and innovative plastics with a wide range of useful properties. Such synthetic plastics not only offer large processing windows, but are physically strong, chemically and biologically inert, produced at a fraction of the cost of earlier plastics, and are adaptable to most plastic processing equipments. Of the petrochemical-based synthetic plastics, high- and low-density polyethylene (LDPE and HDPE), polypropylene (PP), polystyrene (PS), poly vinylchloride (PVC) and polyethylene terephthalate (PET), polyvinyl alcohol (PVA) and polycaprolactone (PCL) are among the major synthetic polymers routinely utilized by the food packaging industry. Synthetic plastics offer excellent barrier (to moisture and gas) and thermal insulation properties that are considered critical for packaged foods. Some examples of synthetic food-contact articles/packagings include grocery bags, packaging containers for fresh produce, dairy and meat products, clamshells for the food service industry, dinnerware and containers for hot and cold beverages. However, one drawback of synthetic plastics is that they are exceedingly recalcitrant to biodegradation, and because of that reason, these plastics have become a challenge for the municipal solid-waste (MSW) management companies, and are posing a real threat to the already rapidly shrinking capacities of landfills in the United States and Europe. Furthermore, in some developing countries, and in most under-developed countries, which lack sound MSW practices, the unregulated disposal of single-use plastic packaging has become a nuisance and is impacting the quality of life of the local populations and the health of the local environment.

2.2

The environmental impact of conventional food packaging

Synthetic plastics are the wonder material of today’s world, and life without them is unimaginable. Unfortunately, these same useful qualities are overshadowed by their steady contribution to litter worldwide and its negative consequences for the environment. The unrestricted volume generated by the single-use consumer packaging made from such plastics accumulates because they do not readily break down in nature. In fact, synthetic plastic disposed of today may still be around for hundreds of years. Because the cost of the virgin resins is so low, recycling is not an attractive option and is only limited to certain plastic types. The Food and Drug Administration (FDA) of the United States has raised many concerns regarding recycled plastics, particularly for re-use of these materials in food-contact articles. These concerns include: (a) the contaminants from the post-consumer material that may appear in the final food-contact product made from the recycled material, (b) incorporation of recycled

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post-consumer material that is not regulated for food-contact into foodcontact packaging and (c) assimilation of adjuvants/additives in the recycled plastic not approved for food-contact use. In view of the serious threat posed by synthetic plastics to marine life and the environment, in 1987 Congress enacted the Marine Plastic Pollution Research and Control Act. This law prohibits the dumping of plastics in all US waters. In an effort to further save the environment as well as marine life, in 1997 the US Congress signed the International MARPOL treaty (Marine Pollution Treaty) prohibiting all US and foreign vessels, both naval and commercial, from discarding any plastic waste overboard in US territorial waters unless it is shown to be completely biodegradable. It is estimated that about 1 million metric tons of plastics per year are dumped into the oceans and that in certain areas as many as 17 500 pieces of plastic are present per square kilometer (Narayan, 1994). The situation on land with respect to plastic waste is even worse. According to a US Environmental Protection Agency report published in 2005, roughly 24.2 million metric tons of MSW deposited in US landfills consisted of disposable consumer packaging used for both food and non-food purposes made mostly from non-renewable resources. On average, every American generates approximately 1500 pounds (680 kg) of waste per year, much of which is destined for landfills. Of this waste, single-use food and non-food consumer packaging made from synthetic polymers constitutes about 40–60% of the volume, which roughly represents about 20–30% of the size of a typical landfill. According to some estimates, industrialized nations alone generate quantities of packaging waste in a single day that if stacked-up together would fill up a space equivalent to the Sears Tower, which once was the world’s tallest building. Most of this packaging is made from synthetic plastics. The consequences of such irresponsible behavior will be of enormous proportions; continued production and accumulation of trash is not only detrimental to the environment but is also contributing to the depletion of our precious and finite natural resources. Currently, one sensible alternative is to produce biobased fuels and chemicals from renewable resources that can compete effectively with petroleum-derived synthetic chemicals in terms of both the overall cost and physical properties (Röpper and Koch, 1990; Swanson, et al., 1993; Shogren and Bagley, 1999; Chum and Overend, 2001; Chiellini et al., 2002; Stevens, 2002). This offers an excellent opportunity for biobased/renewable feedstock to be utilized as a raw material substitute for petrochemicals in the manufacturing of food packaging. Despite many challenges, there is a common belief among the scientific community worldwide that inherently biodegradable biopolymers with improved properties are poised to play a positive role in the development of environmentally compatible, single-use consumer packaging, as evidenced by the explosive increase in the number of scientific papers, patents and products that have surfaced in the last decade alone.

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2.3

Environmentally compatible food packaging

Opportunities for renewable polymers

Heightened fuel prices and the rising cost of petroleum-derived commodity chemicals have provided much of the impetus for the research and development in the field of biobased/renewable polymers. The availability of many renewable polymers in surplus quantities, problems associated with the disposal of recalcitrant plastic products and consumer demand for environmentally compatible, greener products – especially single-use packaged goods – have further helped to build the momentum to seek new uses for agriculturally derived polymers and byproducts. Generally, agriculturally derived polymers exhibit poor physical–mechanical properties, provide materials of inconsistent purity, present difficulties in material processing and perform poorly under extreme environmental conditions (Luzier, 1992; Swanson et al., 1993; Mayer and Kaplan, 1994). Nevertheless, these materials have an inherent advantage over their petroleum counterparts in that they are susceptible to biodegradation in the environment upon disposal. Renewables such as cellulose, starch, proteins, oils and, to a lesser extent, lignin, are among the most abundant agriculturally derived materials. In order to overcome many of the shortcomings in renewable materials, hybrid blends and composites, particularly made in conjunction with bio-derived and/or biodegradable polymers such as poly (lactic acid) (PLA), poly (hydroxyalcanoates) (PHAs) and PVA, along with other additives, plasticizers and compatibilizers, etc., have shown to be the most promising, and are expected to play a major role in food packaging. Figure 2.1 compares some plastic properties (modulus and elongation at break) of biopolymers with those of synthetic plastic polymers.

PHB

PLA

PS Modulus (MPa)

PET

PP HDPE STARCH LDPE Elongation (%)

Fig. 2.1 Comparison of the mechanical properties of biopolymers with those of synthetic polymers (shown in bold). PHB, poly(hydroxybutyrate).

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2.3.1 Polymer properties Some relevant information about starch, poly (hydroxybutyrate) (PHB) and PLA polymers along with the factors that influence their properties is provided below. Starch is one of the most extensively studied biopolymers derived from renewable crops grown in surplus in the world, and is naturally biodegradable (Whistler et al., 1984). It is also one of the most abundant and versatile among natural polymers, and has been extensively researched as a raw material for the development of biodegradable hybrid composites and blends (Griffin, 1971; Otey et al., 1976, 1987; Doane et al., 1998). Its structure and some relevant properties are described in the following paragraphs. The starch polymer is composed of two major components, amylose and amylopectin. The amylose is mostly composed of linear α-d-(1→4)-glucan (Fig. 2.2), whereas, amylopectin is a highly branched α-d-(1→4)-glucan with α-d-(1→6) linkages at the branch points (Fig. 2.3). The linear amylose molecules constitute about 30% of common cornstarch and have molecular weights of 200 000–700 000, while the branched amylopectin molecules have molecular weights as high as 100–200 million.

HO

O

HO HO

HO

O

HO

O OH OH

OH O HO n

OH O HO

G Gn G

Fig. 2.2

Linear amylose molecule.

G G G G G G G G G G G G G G G

O HO

OH O

HO O HO

Fig. 2.3

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O

HO O

OH O HO

O

HO

OH O HO

O OH O

Branched amylopectin molecule.

34

Environmentally compatible food packaging

Starch is stored in plants as granules comprised of molecules of both amylose and amylopectin. The granules vary in size from a few micrometers to >50 µm, depending on their botanical source. Starch granules are hydrophilic since each starch monomer unit contains three free hydroxyl groups. Consequently, the moisture content of starch changes as relative humidity (RH) changes. Cornstarch granules retain about 6% moisture at 0% RH but contain 20% moisture at 80% RH. Starch granules are thermally stable when heated in an open atmosphere to about 250 ºC. Above this temperature, the starch molecules begin to decompose. Dry granules absorb moisture when immersed in water but retain their basic structure due to their crystallinity and hydrogen bonding within the granules. Native granular starch contains crystalline areas within the amylopectin (branched) component, but the linear amylose component is largely amorphous and can be mostly extracted in cold water. The granular structure is ruptured by heating in water or treating with aqueous solutions of reagents that disrupt crystalline areas and hydrogen bonding within the granules. The constituent molecules become completely soluble in water at 130–150 ºC and at lower temperatures in alkaline solutions. Starch granules that have been ruptured in aqueous media are commonly referred to as gelatinized or destructurized starches. The temperature at which starch granules are completely gelatinized is known as the gelatinization temperature, which varies depending on the botanical source of the starch. Application of high pressure and shear to starch granules permits disruption of the organized structure at lower water contents than is possible at atmospheric pressure. Gelatinized starch also tends to swell in water leading to its hydrolytic degradation. Starch granules can be disrupted by high pressure and low shear at moisture contents below 10% (Whistler, 1984; Swanson et al., 1993; van Soest, 1996; Shogren, 1998). Starch solutions are unstable at low temperatures. On standing in dilute solutions, the linear amylose component crystallizes. Many branches of amylopectin may also crystallize. Rapid cooling of concentrated starch dispersions creates stiff gels, which crystallize more slowly. Amylose, and to a lesser degree the outer branches of amylopectin, can assume helical conformations that have a hydrophobic core (Fig. 2.4). Each turn the helix comprises six monomer units. Iodine, fatty acids, lipids, alcohols and other materials may enter the core of the helix to form stable complexes with starch. Small amounts of crystalline amylose–lipid V-type complexes are usually found in starches such as corn and wheat, which contain free fatty acids and phospholipids (Galliard and Bowler, 1987; Chinnaswamy et al., 1989; Shogren, 1992; Imam et al., 1993). Starch molecules readily depolymerize into glucose monomer units when heated in acidic solutions or when treated with a variety of amylolytic enzymes. They are generally stable under alkaline conditions at moderate temperatures. When heated with amines under alkaline conditions, they undergo complex Maillard reactions to form brown-colored products with caramel-like odors. Upon mechanical injury that alters its surface

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Types, production and assessment of biobased materials O

O

O

O

O

O O O

O O

O

O

O O

O

O O

O O

O O

O O

O O

O O O

O

O

O

O

O

35

O O

O O

Fig. 2.4 Helical conformation in amylose and the outer branches of amylopectin. Each turn of the helix comprises about six monomer units.

morphology causing starch to be exposed on the surface, starch degrades fairly quickly under ambient conditions. The presence of many hydroxyl groups on starch permits easy alteration of its properties through chemical derivatization. This provides the opportunity to improve starch properties for use in packaging. Modifications in starch polymers have yielded starches with improved properties. Acetate esters and carboxymethyl and hydroxypropyl ethers exemplify starch derivatives. Extruded acetylated starch (DS 2.23) foam, for example, has much-improved moisture barrier characteristics, mechanical properties and dimensional and thermal stability compared with unmodified starch (Xu et al., 2005). Several other starch derivatives with unique functionalities have also been reported (Imam and Harry-O’Kuru, 1991). Aging of the starch polymer at constant temperature and moisture levels results in starch embrittlement. Differential scanning calorimetric studies (Shogren, 1992) have shown that this phenomenon is due to structural relaxation of starch chains, leading to decreases in enthalpy and free volume with time. This type of aging is typical of most amorphous polymers (Hodge and Berens, 1982; Hutchinson and Kovacs, 1984). The rates of aging seem to vary with polymer structure but the reasons for such differences are not fully understood at present. In addition, starch can be crosslinked with compounds having many functional groups, such as formaldehyde, pyrophosphate and epichlorohydrin. Such modifications usually lead to improved polymer properties. In this regard, an increased tensile property and water resistance was observed in starch/cellulose/PVA crosslinked with hexamethoxymethylmelamine (Cymel 323) reagent (Imam et al., 1999b). Two other important biodegradable polymers in the context of biobased packaging are PHA and PLA. Both biopolymers have excellent physical properties, exhibit excellent compatibility with other natural polymers and,

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Environmentally compatible food packaging

more importantly, are completely biodegradable in a variety of environments. PHAs are linear polymers produced in nature and can be produced via bacterial fermentation of plant-derived feedstock such as sugars or lipids. A combination of a variety of different monomers can provide materials with variable and distinct properties. For example, with melting points ranging between 40 and 180 ºC the polymer can behave as a thermoplastic, as well as an elastomer. The most common of the PHAs is a homopolymer, PHB (Fig. 2.5), with properties quite similar to those of PP, albeit stiffer and much more brittle. A copolymer, poly (β-hydroxybutyrate-co-valerate) (PHBV) (Fig. 2.5), is ideal for packaging as it is less stiff and much tougher than PHB. PLA, on the other hand, is a condensation polymer of lactic acid produced via fermentation using renewable resources such as starch (Fig. 2.6). PLA has many useful properties similar to the petroleum-based plastics,

O

HC

CH2CH3 O

O

CH3

CH2C

HC

O

CH2C

n

n PHB

PHV

CH3 O

HC

O CH2C

CH2CH3 O O

CH

CH2C n

PHBV

Fig. 2.5

PHB and copolymer.

O H3C

Catalyst+ heat

O

O CH C

O

CH3

O Lactide

Fig. 2.6

CH3 O

CH3 O O CH C n

Polylactide

Ring opening polymerization of lactide to polylactide.

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which makes it highly suitable for a variety of applications. PLA, certified as Generally Recognized As Safe by the US FDA, is a non-volatile, odorless, clear and naturally glossy polymer. It is a versatile polymer that can be processed using a variety of conventional techniques/equipments such as injection molding, blow molding, sheet extrusion, thermoforming, film forming and fiber spinning. Furthermore, its resistance to moisture and oils along with its gas barrier properties makes it ideal for food packaging. Both PHA and PLA are still relatively expensive compared with synthetic plastics. These polymers are starting to be noticed by the food packaging industry due to their plastic-like properties, but their market penetration will be dictated mainly by their cost and product performance. In order to achieve this market penetration, the overall objective would be to seek biobased substitutes for synthetic plastics in food packaging by engineering products from renewable materials that are stable, durable, provide the required mechanical and barrier properties, improve transportation and storage, and ensure that the product biodegrades effectively when disposed of after use. In this regard, efforts are being made worldwide, including at USDA laboratories, to improve and transform agriculturally derived materials to overcome the technological barriers that are restricting their commercial potential and consumer acceptance. Biochemical and engineering tools are being used to improve and optimize the properties of biopolymers. Approaches include: chemical crosslinking, chemical grafting, chemical substitutions/derivatizations, biocatalysis, plasticization, novel processing, blending and compatibilization with other polymers and additives. Research efforts on the use of starch-, PLA- and PHBV-based blends and hybrid composites for food packaging applications will be reviewed in the subsequent sections along with the future outlook for these materials.

2.4

Production of biobased food packaging materials

2.4.1

Production, properties and functionality of biobased food packaging materials Extrusion, baking, thermoforming, casting, blow molding, injection molding, lamination, calendaring and coating are some of the major plastic processing methods that are currently utilized by the plastic industry in producing food packaging, mostly from LDPE, HDPE, PP, PS, PET, PCL, etc. With few exceptions, renewable/biobased polymers generally exhibit a great deal of adaptability for many of these plastic processing methods requiring little or no adjustments (Röper and Koch, 1990; Tomka, 1991; Doane et al., 1998; Shogren, 1998; Bastioli, 2000). Some, however, have a narrow processing window and poor mechanical and thermal properties, causing materials to be rigid, stiff and dry; others lack good gas and moisture barrier properties.

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These shortcomings in their properties need to be overcome before biobased packaging is successfully commercialized and accepted by the consumers (Zobel, 1988; van Soest, 1996). In order to overcome the brittleness and to improve the properties of biopolymers, biodegradable plasticizers are routinely used in formulations. Plasticizers include glycerol and other low molecular weight polyhydroxy compounds, polyethers and urea. During extrusion, the starch granular structure is disrupted due to high shear and temperature in the presence of plasticizers. This causes starch to plasticize and behave as a molten or viscous thermoplastic material. Plasticized starch could subsequently be used for injection-molding and for thermoforming into sheets. Thermoforming of starch into sheets for subsequent molding into products is somewhat challenging, and industrial applications are limited due to its moisture sensitivity and poor mechanical properties. Blending plasticized wheat starch with biodegradable polyester, however, has been shown to improve moisture resistance in injectionmolded packaging materials (Avérous and Fringant, 2001). In addition, blending plasticized wheat starch with cellulose fiber considerably improved stiffness and impact resistance, as well as aging behavior, of the extruded material. Such blends and composites, when processed on industrial-scale thermoforming equipment to produce packaging trays, exhibited much improved aging properties at storage temperatures ranging from ambient to 4 ºC (Avérous et al., 2001). The starch baking process is quite analogous to the process used in making waffles and wafer cookies. A predetermined amount of aqueous starch dough is placed into a preheated (120–200 ºC) mold cavity, after which the mold is closed. Upon heating, the starch in the dough is gelatinized, and steam serves as the foaming agent providing a starch product with properties similar to expanded polystyrene (EPS); the procedure is described in detail elsewhere (Glenn et al., 2001a; Shey et al., 2006). Tiefenbacher (1993) and Hass et al. (1996) demonstrated a baking process for making molded starch products as thin as 1.5 mm. An Austrian company, Biopack, was the first to produce starch-based foam trays commercially for food packaging. Currently, Apack in Germany is also producing starchbased food packaging made by a similar process. More notably, EarthShell Corporation in the United States had a much larger impact on the development of baked starch packaging as they have been able to successfully produce commercial, single-use, disposable baked trays, dinner plates, soup bowls and clamshells for the fast-food industry. These products have been sold in selected US markets for trials, and are currently being sold at Smart & Final stores. More recently, EarthShell has licensed its technology to Renewable Products, Inc. located in Lebanon, Missouri for manufacturing and distribution of EarthShell Packaging plates and bowls in the United States and to EarthShell Hidalgo S.A. de C.V. of Mexico for markets in Central and South America. As consumer demand for such products

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increases, EarthShell is poised to take a leadership role in the disposable food container market worldwide. The properties of the baked starch foams are dependent on several factors such as moisture content, starch type and the additives used in the dough formulation (Andersen and Hodson, 1996; Shogren et al., 1998; Lawton et al., 1999). Although baked starch foams have decent mechanical properties and their thermal properties are quite comparable with PS-based commercial food containers, these products are susceptible to moisture and lack the required flexibility. Starch polymers and blends have been successfully baked into foamed articles with properties similar to those of an EPS. Under dry storage conditions, starch blends and composites lose water quickly and become brittle, yielding a matrix of low modulus. Under high-moisture conditions, starch can absorb moisture, yielding a loose and flexible matrix. Thus, to obtain a starch food packaging with improved properties, other substances such as fillers, compatible additives, plasticizers and a moisture-resistant coating are generally required. Incorporating cellulose fibers as a filler material in formulations has been shown to improve both the flexibility and the strength of baked starch foams (Andersen and Hodson, 1996). For example, addition of softwood pulp fiber improved flexural properties and lowered the foam density (Glenn et al. 2001a). Foam properties can be further improved by utilizing chemically modified starches and additives such as aspen fiber, PVA and monostearyl citrate (Shogren et al., 1997, 2002; Lawton et al., 2004). Modified starches improved flexibility and aspen fiber improved strength, whereas monostearyl citrate improved water resistance. Interestingly, not all fibers improve foam properties. The addition of corn fiber in formulations had a rather negative impact on starch foam packaging trays, as it tended to decrease the mechanical properties and cause an increase in the baking time and batter volume (Cinelli et al., 2006a). Trays produced with a high fiber ratio in conjunction with PVA, however, showed improved water resistance. The addition of PVA in the formulation was also effective in providing moisture resistance to the baked foam products (Shogren and Lawton, 1998). Alternatively, protective food grade, hydrophobic and thermostable polymer laminate could also be applied directly on to the baked product to provide an effective moisture barrier (Glenn et al. 2001b; EarthShell Corporation, 2002). More recently, Shey et al. (2006) used natural rubber latex as a moisture-resistant additive for baked starch foams. Moisture resistance in starch foams improved when a small amount of latex was added in the formulation in the presence of non-ionic additives. Latex also improved the flexibility of the foam product. Such approaches to improve moisture resistance, however, add to the overall cost of the product. Among all the biodegradable polymers, starch currently represents about 85–95% of the total market share in various single-use consumer products. Current applications are mostly limited to films, sacks, garbage

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bags and as fillers. However, articles made from expanded starch foam and hybrid composites such as cups, bowls, cutlery, plates, wrapping, laminated paper and food containers are beginning to penetrate the market place (Bastioli, 2001). PLA-based hybrid materials, having properties similar to synthetic plastics like PET and PP, are well suited for processing on standard equipment used by the plastic industry. In particular, films, injection-molded and thermoformed articles such as food containers, and other types of packaging have been manufactured and are currently marketed in North America, Europe and Asia. Film wraps and containers for organic foods are two of the wellknown products made from PLA (Francia, 2000; Bastioli, 2001). CargillDow is currently the largest producer of PLA polymer under the brand name NatureWorksTM. Cargill-Dow’s new facility in Blair, Nebraska has a capacity to produce 140 000 metric tons of NatureWorksTM; expansion is expected in order to meet the demands of European and Asian markets. PLA offers a good moisture barrier, but its application in vacuumed packaged foods is limited due to its poor gas barrier properties. Because of its excellent compatibility with other biopolymers and synthetic polymers, this is not a serious impediment. DannonTM, the yogurt manufacturer, is already successfully marketing the thermoformed PLA-based yogurt containers in supermarkets in Europe and North America. Also included in the list of PLA-based products are single-use, food-contact packaging for readymade meals available in the frozen section of supermarkets. Food service wares including cups, plates and other containers laminated or extrusion-coated with PLA-based materials are available in the market for hot and cold beverages (Bastioli, 2001). These also include starch-based baked and molded soup bowls and dinner plates as well as cardboard cups laminated or coated with the PLA. Table 2.1 lists many of the commercial resins made

Table 2.1 List of major biobased/biodegradable polymers and blends produced commercially worldwide Biodegradable polymer

Trade name

Company

Starch Starch Modified starch Thermoplastic starch Starch/copolyester PHAs PHAs Copolyester Copolyester Copolyester Polylactc acid Cellulose acetate

Ecofoam Novon Evercorn Paragon Mater Bi Nature’s Plastic Nodax Ecoflex Biomax Bionelle NatureWorks ACEPLAST

National Starch, USA Ecostar GmbH, Germany Japan Corn Starch Co. Ltd Avebe, The Netherlands Novamont, Italy Metabolix, USA Proctor & Gamble, USA BASF, Germany Dupont, USA Showa Highpolymer, Japan NatureWorks (Cargill-Dow), USA Acetati, Italy

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from biobased polymers and blends that are currently available for food packaging applications. The aliphatic polyester PHB and copolymer PHBV are commercially important biobased biodegradable plastics that are well positioned to fulfill many of the food packaging industry needs. Typically, PHB is a good thermoplastic material with high crystallinity, but PHAs of medium chain length behave more as an elastomeric material having considerably lower melting points and a relatively low degree of crystallinity. A very interesting property of PHAs in the context of food packaging is their low water vapor permeability, which makes them behave like LDPE. This polymer can be blow molded, extruded or injection molded into shapes such as films, bottles, food packaging containers, etc. PHAs have proven quite useful biomaterials in biomedical applications, e.g. tissue engineering and controlled-release carriers, owing to their properties such as biodegradability, optical activity and isotacticity (Köse et al., 2003). Because of its non-toxicity and biocompatibility in humans, PHB is also being used in implants, bone plates and surgical sutures. PHB has been utilized to produce packaging for some disposable products (Rosa et al., 2004a), but information with respect to its much broader application in food packaging is limited at this point. Major impediments in the successful commercialization of PHB are its production cost and brittleness, and the resulting intolerance to high impact. Nevertheless, companies worldwide are making efforts to produce this polymer and copolymer cheaply. Particularly, both Brazil and China claim to have used sugarcane bagasse and cornstarch, respectively, as a renewable carbon source to produce PHB inexpensively. PHB produces a transparent film above 130 ºC providing a much larger window of operation for plastic processing. Additionally, PHB offers low permeability and, more importantly, biodegrades completely without leaving any visible residue. The injectionmolded food containers made from PHB showed good potential for this material in food packaging (Bucci et al., 2005). These investigators found that under normal freezing and refrigeration conditions, the performance of PHB food containers was slightly inferior compared with PP, but at higher temperatures, the performance of PHB food packaging was much superior to that of PP packaging. Sensory evaluation of food packaged in PHB containers yielded positive and encouraging results.

2.5

Hybrid blends and composites

Renewable polymers are generally sensitive to moisture and do not provide effective gas barrier properties. Hybrid blends and composites, containing renewable polymers in conjunction with other biobased or synthetic polymers and additives, have shown great potential in making up for some of these shortcomings. In fact, the majority of the consumer food packaging currently available commercially worldwide is based on hybrid materials,

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rendering the desirable properties and functionality for packaging a variety of foods such as fresh meats, dairy products, ready-meals, beverages, fruits and vegetables, snacks, and frozen and dry foods (Table 2.2). For example, multilayer films produced from plasticized wheat starch and various biodegradable aliphatic polyesters via flat film co-extrusion and compression, significantly improved mechanical performance and moisture resistance in melt blended wheat starch films (Martin et al., 2001). In this film, the properties were totally dependent on the compatibility between the respective materials without the use of any additives, compatibilizers or adhesives. Coatings of edible and biodegradable polymers have, in general, been used to achieve an improved moisture barrier and to prolong the shelf-life of perishable food products (Guilbert et al., 1996, 1997; Guilbert, 2000). Improved water permeation barrier properties were observed as a result of an in situ lamination process for baked starch foams with PVA and PVC. These foams had barrier properties similar to the EPS foams (Glenn et al., 2001a). With the addition of a small amount of cellulose fibers in wheat starchbased extruded films, increases in modulus, strength and temperature stability were observed with concomitant shifts in the glass transition (Tg) temperature. Thermoformed food trays from these hybrid blends showed greatly reduced aging compared with trays without added fibers (Averous et al., 2001). Similarly, products formed from hybrid composite foams prepared by baking granular starch in the presence of 10–30% aqueous PVA showed markedly improved strength, flexibility and water resistance (Shogren et al., 1998). More recently, these investigators have also shown that the addition of softwood fiber and monostearyl citrate in the formulations yielded baked products with sufficient flexibility and water resistance to function as clamshell-type, hot-sandwich food containers (Shogren et al., 2002); aspen fiber also had a similar effect (Lawton et al., 2004). A detailed work has been published recently on extruded and injection-molded hybrid blends and composites containing agriculturally derived fiber and PVA, and their impact on material properties (Chiellini et al., 2004, Cinelli et al., 2006a, 2006b). A laminate of chitosan-cellulose and PCL film has shown to be effective for modified atmospheric packaging of horticultural crops such as lettuce, broccoli, tomatoes and sweet corn within the 10–25 ºC temperature range (Makino and Hirata, 1997). PE film containing 6% starch has been recommended for storage of wet and dry low-lipid foods. However, significant loss of elongation was observed in these films due to possible interactions between the film and the free radicals developed during lipid oxidation in foods with higher fat content, such as ground beef, during storage under freezing conditions (Holton et al., 1994). It is interesting to note that PE– starch films neither impaired the heat sealing nor accelerated microbial growth in ground beef. Furthermore, there was no impact on color stability during refrigeration and frozen storage (Strantz and Zottola, 1992). In this

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Table 2.2 Commercial food packaging from biobased polymers, blends and composites currently in use worldwide Packaging product

Properties

Biopolymer(s)

Packaged material

Company

Trays

Convenience, moisture barrier Oxygen and moisture barrier Convenience Convenience, insulation, moisture barrier Mechanical protection, moisture barrier, carbon dioxide barrier Moisture barrier, light barrier, grease barrier Containment

Virgin pulp

Beer, chicken

PE–starch (0–28%)

Ground meat

Pactiv, Omni-Pac, Germany Europe

Coated pulp and starch Powdered starch, foam, baked foam

French fries Hamburgers/sandwiches

Belgium Apack, Germany Earthshell, USA

Cardboard/PLA

Yogurt

Dannon, Europe/ North America/ Asia

PLA–copolyester, starch–PLA, PLA–polycaprolactone

Butter/margarine

Europe

Nets of starch-based plastics, pulp trays, corrugated board trays and transport boxes NatureSEAL™ (cellulose based) Starch/starch–polycaprolactone

Fruits and vegetables

Germany, Belgium/Europe

Variety of fruits and vegetables General purpose

Europe/USA/Asia

Wrapping films Tray/container Container clamshells/ plates, soup bowls, beverage cups, etc. Container

Packaging Packaging Packaging Bags

Moisture and gas barrier Biodegradable

Data are partly selected and condensed from Haugaard et al. (2001a, 2001b). © 2008, Woodhead Publishing Limited

Europe – Finland, Italy, Denmark

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Table 2.3 Advantages and disadvantages of using cellulosic fiber in composites Advantages

Disadvantages

Renewable Strong Light weight Biodegradable Inexpensive

Poor dimensional stability Low biological resistance No thermal plasticity Low processing temperature Incompatible with hydrophobic thermoplastics

regard, an excellent review article has been written on the potential of biobased materials for food packaging (Petersen et al., 1999). Cellulose, one of the world’s most abundant and inexpensive raw materials, is problematic to use because of its hydrophilic nature, insolubility and crystalline structure. Because of its highly ordered structure, hydroxyl groups and strong hydrogen bonding yield highly crystalline microfibrils and fibers. Such fibers are already being used in numerous commercial packaging products made up of paper and cardboard. Fibers also make excellent biological fillers in many plastic wraps and films. Having biological filler in a plastic matrix is advantageous because the biological additive is readily attacked by microbes, which start the deterioration process leading to eventual composting. Waxed or PE-coated papers are commonly used in the food packaging industry. While cellulose fiber in blends offers many advantages, it can also have a negative impact on the matrix properties. Some of the advantages and disadvantages of using cellulose fiber are outlined in Table 2.3. The strengthening of the polymer matrix by the discontinuous fiber reinforcements is dependent upon the aspect ratio, geometry and orientation of the fibers, and the interface adhesion between the fiber and the matrix, as well as the microstructural features within the matrix. Dispersed microstructures offer higher elastic properties than equivalent aggregated microstructures due to the more efficient reinforcement of a dispersed system. Cellulose fibers have poor dimensional stability and offer little or no thermal plasticity. The addition of fiber in higher amounts generally results in processing difficulties and a reduction in viscosity. The strategies used to overcome this challenge are usually to increase the shear rate and to use lubricants or plasticizers to improve the flowability.

2.6

New developments in the production of packaging from recycled lignocellulosic fiber and renewable materials

Paper products – such as corrugated boxes, food wraps, bags and single-ply boxes – constitute the largest percentage of single-use items in the United States, and end up as the largest component in MSW streams. Even with

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recycling (the United States recycles ∼27% of its MSW stream), lignocellulosic material (paper) accounts for 37–40% of our landfill materials. The need for using recycled materials and renewable non-wood pulps, rather than virgin wood pulp, is clear. New twists in the traditional slurry-pulp technology provide an outlet for this recyclable fiber, creating food packaging and wraps from 100% recycled and/or non-wood pulps, such as straw and bagasse. Slurry-pulp processing has been used for years to make egg cartons, drink trays and box in-lays. In slurry-pulping, screens in the shape of the finished product are dipped into a tank holding slurry-pulp, a mixture of water (99%) and recycled fiber (1%). As vacuum is applied to the molded screen, a thin layer of fiber forms on to the screen; upon drying, this thin fiber mat, which is in the shape of the contoured mold, is then separated. Innovations in slurry-pulp processing have provided tremendous flexibility in the size and shape range of products created by innovators such as Greg Gale and colleagues, as described elsewhere (Orts et al., 2003a, 2003b). In particular, two improvements stand out: (a) use of rapid prototyping to create molds within 2 days and (b) drying of the molded package on the mold, which prevents ‘slumping’ or sagging of the piece during drying. Rapid prototyping creates a mold using designs drawn in the latest computer aided design programs: these complex designs are then sent to the rapid prototype instrument. The rapid prototyping method produces the tool, one layer at a time by depositing a thin layer of a dry polymer powder followed by application of a laser beam that fuses that layer into a solid. Once one layer is complete, a second layer of powder is deposited and fused, similar to rastering methods used in a laser printer. This layering and fusing process is repeated until the complex mold takes shape, generally within hours or days. The second feature of improved slurry-pulp processing methods is the ability to dry the fiber product while it is still on the mold. In the traditional (egg carton) process, the carton is taken off the (metal) mold while wet and passed through a drying oven. Pieces must be relatively small or they will ‘slump’ and dry unevenly. Blowing hot air under pressure through the mold dries the fiber package evenly without any change in shape, preventing the piece from sagging during drying. With this innovation, shapes can be more extreme with heights exceeding 18 in. (45.7 cm). One example of the innovative shapes that are attainable is the wine packaging/bottle shipper and some other food packaging produced by Regale, Napa, California that prevents label scuffing during transportation. Ultimately, the economics of slurry-pulp processing depend on reducing drying times to minimize energy costs. Continuing experimentation with alternative fibers has shown that agriculturally derived, non-wood pulps – such as rice straw, wheat straw, grasses, cotton linters, chicken feathers, and fibers recovered from MSW – can be used. Molded fiber packages have been created from processing slurries containing anywhere from 5 to 60%

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straws and other agriculturally derived fibers, reducing drying times by as much as 22%. A key driving force behind using agriculturally derived fibers in packaging is the need to find novel economically viable uses for crop residues, especially straws and grasses which can no longer be burned in California due to legislation. Regale’s first plant obtains most of its recycling pulp by shredding wine boxes, office waste and brochures from its wineproducing neighbors in the Napa Valley.

2.7 Assessing the biodegradability of renewable materials in food packaging Biodegradation is a process in which organic material is decomposed via natural biological activity. In this process, biochemical breakdown of an organic compound leads to smaller products (oligomers or monomers) due to the action of microbes (bacteria, fungi, yeast) or their hydrolytic enzymes. Thus, under ideal conditions, biodegradation is generally a two-step process: the polymer is first hydrolyzed into intermediate compounds, where abiotic factors such as ultraviolet light, along with microbial enzymes, may facilitate this process. This step is then followed by further metabolism of such intermediates by microorganisms. Biodegradation can occur under both aerobic and anaerobic conditions. Under aerobic conditions, the final breakdown products are H2O, CO2 and residual biomass (byproducts). Under anaerobic conditions, biogas such as methane or hydrogen gas is produced in lieu of CO2. Eventual biodegradation of renewable polymers and blends is dependent upon a wide variety of factors. Parameters that influence the biodegradation process include environmental conditions like temperature, moisture, salinity and pH, as well as geometry and surface area of the material, inoculum size, type of environment and the availability of microbes. In addition, certain chemical structures are more susceptible to microbial breakdown than others. Availability and accessibility of specific enzymes to hydrolyze a certain polymer are also critical. For example, polymers such as starch, cellulose, protein and polyester will require amylases, cellulases, proteases and esterases, respectively, to hydrolyze these individual polymers. Therefore, in hybrid blends containing two or more polymers, degradation will be influenced by the presence of the right combination of microbes or enzymes in the disposal environment. In order to assess polymer biodegradation, packaging material is generally exposed to the testing environment (such as soil, compost, seawater, sewage, sludge, etc.) containing appropriate microbes and environmental conditions that are controlled for the duration of the experiment. Sample degradation can be assessed by measuring the deterioration in the physical–mechanical properties such as tensile strength, elongation at break and decrease in molecular weight of the testing material. However, more

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commonly, polymer degradation is assessed by measuring the production and accumulation of CO2 (under aerobic conditions) or CH4 (under anaerobic conditions) as a result of enzymatic hydrolysis of the material and further assimilation of intermediate byproducts. Collected data can be useful in determining both the rate and extent of the polymer degradation and, if the exact carbon values in the initial sample are known, theoretical yields can be calculated to determine overall carbon to CO2 or CH4 conversion. The reproducibility and reliability of the test method is critical. In order to test the reliability of the system and for comparative purpose, use of a background measurement, as well as positive and negative controls are also required. There are several international organizations that are actively involved in writing, examining and establishing standards for testing polymeric materials for biodegradability. The International Organization for Standardization (ISO), American Society for Testing Materials (ASTM), European Committee for Standardization (CEN), German Institute for Standardization (DIN), Organic Reclamation and Composting Association (Belgium based) and Institute for Standards Research (ISR) are some of the leading institutions playing a major role in defining and regulating the standards to assess polymer biodegradation. Standards pertaining to biodegradable plastics put forward by these organizations differ somewhat in their definitions and specific requirements, but the ultimate approach/goal is more or less the same. Great efforts have been made by international scientists to reconcile the European and American standards with international standards. The Sturm test (or modified Sturm test), BODIS test, composting test, anaerobic test, enzyme test, soil burial test and toxicity test are some of the most relevant tests pertaining to bioplastics. No attempt will be made to provide details on the standardized tests, and a list of the most commonly used tests is provided in Table 2.4. The only exception is the ASTM D533893 test for determining the compostability of the plastic materials. This test is quite important, as most of the biodegradable single-use food packaging in future will be sent to composting facilities. Furthermore, knowing the product’s compostability will be a desirable feature for commercialization and ultimately acceptance of the product. In order to apply the ASTM D5338-93 (composting) standard, composting materials need to have both the capacity to biodegrade and to physically disintegrate. Disintegration must lead to the physical collapse of the plastic matrix yielding visually indistinguishable fragments, a requirement for composting. To achieve total biodegradability, after disintegration, polymer chains must be first broken down by microbes and their enzymes, followed by their complete mineralization, i.e. polymer conversion into CO2, H2O and minerals. Mineralization rate, however, has to be high and compatible with the composting process. Materials having a biodegradation capacity equal to or more than that of cellulose are considered compostable under this testing standard.

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Table 2.4 A list of some of the important standard tests from various organizations used to determine the biodegradability of food packaging Standards/tests

Environment

ASTM D6400

Standard specifications for compostable plastics Controlled compost Aerobic biodegradation in soil Compost Aerobic, sewer sludge Anaerobic, sewage sludge High-solids anaerobic digestion Aerobic biodegradation under controlled conditions Aerobic biodegradation in aqueous environments Anaerobic biodegradation in a high-solids sewerage environment European standard for biodegradability for polymers and packaging; incorporates other standards and tests

ASTM 5338-98 (2003) = ISO 14852 ASTM D5988-03 = ISO 17556:2003 ISO CD 14855 ASTM D5209-91 ASTM D5210-92 ASTM D5511-94 ISO 14855 ISO 14852 ISO 15985 CEN 13432 ISO 14855; ISO 14855 (respirometric); ISO 14852; ASTM D5338-92; ASTM D5511-94; ASTM D5152-92; ASTM E1440-91; modified OECD 207; CEN TC 261/SC4/WG2

Specifically, the ASTM D5338-93 standard measures compostability of plastic materials. The test method determines the aerobic biodegradation of plastic materials under controlled composting conditions. In this method, plastic is mixed with stabilized and mature compost. The CO2 evolution is compared with unsupplemented compost. Biodegradation is determined by the rate and extent of material conversion into CO2 over time. The conversion should be accompanied by weight loss in the plastic material, visible disintegration and high biological activity in the compost. According to the standard, 90% of the disintegrated material must not have any adverse effect on the quality of the compost. In particular, it must not be toxic to other plants. ISO CD 14855 and the CEN test procedures are quite similar to ASTM D5338-92. The only difference is that both ISO and CEN protocols require that the temperature profile of the compost should be continuously at 58 ºC, whereas the ASTM procedure follows a temperature profile of 35–58–50–35 ºC. In addition, for packaging to turn into visibly indistinguishable fragments in compost, different standards have put forward different requirements regarding time limitations (Table 2.5). Scores of studies have been conducted to investigate the biodegradability of starch polymer and its hybrid blends containing both syntheic and/or renewable polymers and additives (Imam et al., 1992, 1995a, 1995b, 1999a, 1999b; Shogren 1992; Ramsay et al., 1993; Lawton, 1997; Avévous

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Table 2.5 Compliance requirements of various international standards for plastic degradation Standard organization

Percentage biodegradation

Time requirement

DIN ASTM CEN OECD

60% 60% 90% 60% (for chemicals)

6 months 6 months None 28 days

OECD, Organization for Economic Co-operation and Development.

et al., 2001; Lawton and Shogren, 2004). In the 1970s, investigators from the United Kingdom (Griffin, 1971, 1977) and the United States (Otey et al., 1976, 1987; Doane et al., 1998), for the first time reported on the production of starch–PE blown films where starch was totally accessible to microbial attack, leaving behind a decomposed matrix comprising mostly of recalcitrant PE; hence, the birth of the bioplastics. Since that time, scientists worldwide have developed a variety of novel hybrid plastics containing both biodegradable as well as non-biodegradable polymers and additives. They offer novel properties and are useful for single-use packaging applications. Starch, cellulose, PLA, PHBV, PVA, PE, PP, PET and PCL are among the most prominent materials of choice for the production of these hybrid plastics and plasticizers, compatibilizers and coating materials are also used as additives to improve properties. Most of the focus of these developments has been to achieve bioplastics that are mostly biodegradable or compostable. Several excellent articles have been written on this subject (Yasin et al., 1989; Luzier, 1992; Shogren et al., 1993; Mayer and Kaplan, 1994; Koenig and Huang, 1995; Cutter, 2000; Avérous and Fringant, 2001; Chiellini et al., 2002, 2004). Hybrid plastics are a multi-component polymeric system. It is possible that, when polymers are mixed and compounded, compatibilized, plasticized or surface modified to make a hybrid blend, the properties of the individual polymer(s) may also change. As a result, blends may have biodegradation properties distinct from their individual parent polymers. For example, in PE-based blown thin films containing up to 40% thermoplastic starch (dry weight basis), most of the starch readily degraded when films were disposed of in the environment (Imam et al., 1992, 1996). However, when a similar formulation was used to produce injection-molded articles, most of the starch was found to be encapsulated in the PE matrix, severly compromising the ability of microbes and/or their hydrolytic enzymes to access the starch substrate (Imam et al., 1995a, 1995b). This clearly indicated the influence of processing technique on the biodegradability of the polymer matrix. Packaging films where starch or cellulose fiber were used as fillers in a slow-degrading polymeric matrix, showed quick degradation of these fillers, which accelerated the deterioration of the otherwise slow-degrading

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polymer and allowed for rapid compostability (Bastioli, 2001). Due to the presence of starch in a starch–PHBV blend, a significant enhancement was observed in both the rate and extent of PHBV degradation in a compost environment (Imam et al., 1998). In similar blends, where starch was precoated with polyethylene oxide to increase the compatibility between starch and PHBV, starch degradation was negatively impacted. Many biodegradation studies of starch–PHBV hybrid blends in a variety of environments have shown that PHBV and starch both degraded, albeit at different rates and to different extents (Ramsay et al., 1993; Imam et al., 1995a, 1995b, 1999a, 1999b). Blends of the aliphatic polyester PCL or aliphatic-aromatic copolyesters with starch are another important group of biodegradable plastics suitable for food packaging; it has been found that thermal behavior is dominated mainly by PCL and mechanical properties are improved by blending with starch (Rosa et al., 2004, 2007; Dean et al., 2007). Biodegradability of this blend is heavily influenced by the complex interaction between starch and the polyester not only at the molecular level, but also in the surface properties. A good example of this is seen in modified natural polymers such as starch and cellulose acetates used to improve polymer properties via esterification of hydroxyl groups of sugar residues. The increased degree of substitution (esterification) improves the properties of polymers, but greatly reduces their biodegradability. Starch and cellulose acetates containing large amounts of plasticizers are available commercially and are claimed to be biodegradable. PLA is biodegradable in compost; however, information on its biodegradation in other environments is limited. Several studies have confirmed the degradation of PLA by a variety of microorganisms (Agarwal et al., 1998; Jarerat and Tokiwa, 2001, 2003; Jarerat et al., 2003; Masaki et al., 2005). Changes in environmental factors such as humidity and temperature have been shown to influence PLA degradation (Ho et al., 1999). In one study (Shogren et al, 2003), little or no degradation was observed in injection-molded PLA samples buried in soil for a 1 year period in the Midwestern United States. The reason for the slow breakdown of PLA and other polyester-based plastics may be that the environmental degradation of PLA requires a two-step process. First, high molecular weight polyester chains need to be hydrolyzed into low molecular weight oligomers. This is a rather slow step, but the reaction can be accelerated by acids or bases and is also affected by both temperature and moisture levels of the compost. In a second step, microbes and enzymes convert the low molecular weight components into CO2, H2O and residual biomass. The synthesis and assembly of the supra-macromolecular structure of biopolymers proceeds through distinct biosynthetic pathways, requiring specific biological building blocks joined together via specific linkages or chemical bonds. Thus, specific enzymes are required to disassemble or decompose each polymer. From a biodegradation standpoint, blends containing two biopolymers are interesting materials. In starch–PHBV blends, both polymers require different enzymes to degrade effectively. Starch

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needs microbial amylases that can attack both α-1→4 and α-1→6 linkages to completely break down the polymer. On the other hand, PHBV requires esterases to break down the ester linkages in the polymer to achieve degradation. Similarly, cellulose and lignocellulose would require cellulases and lignases and protein polymer would need proteases to attack polypeptide linkages. Certain chemical modifications might improve the properties of a polymer, but it would be challenging for natural microbes as they are programmed to degrade naturally occurring polymers. Assessing the de-gradation of individual polymers in a hybrid blend is challenging. Fourier transform infrared (FTIR) spectroscopy has shown to be a very powerful technique for this purpose in some blends because certain chemical group(s) in each polymer have a characteristic infrared absorption, and the decrease of these absorption peaks or changes in their peak ratios with time can provide useful information on the extent of polymer biodegradation. For example, a hybrid blend made up of PE–starch–protein will show distinguishable peaks that are characteristic of starch, such as the hydroxyl and the fingerprint region. Similarly proteins show the amide I and amide II peaks, and PE shows characteristic C–H stretching bands and a weaker C–H bending absorbance (Imam et al., 1992; Gordon et al., 1996). The CO2 evolution, loss of polymer weight and decrease in molecular weight and tensile properties in polymers all correlated well and were in excellent agreement with the FTIR data (Imam et al., 1992; Gordon et al., 1996). Polymer degradation occurs mainly through scission of the main chains or side chains of macromolecules. In nature, in addition to biological activity (enzymes), polymer degradation is also induced by several other processes, including thermal activation, hydrolysis, oxidation, photolysis and radiolysis. Although there is little evidence that PE can be attacked directly by microbial enzymes, there are many PE-based products available in the market place that are being sold as ‘biodegradable’ materials. The primary step in the degradation consists of a chemically or physically induced reduction of the polymer chain length. Chain length reduction in biodegradable PE has also been attributed to special additives, which trigger the thermal and/or photo-oxidation causing embrittlement of the plastic, followed by enzymatic degradation. Addition of biodegradable fillers like starch or cellulose can further help in the rapid defragmentation of the PE matrix. Such PEbased plastics are termed ‘oxobiodegradable plastics’. EPI Environmental Technologies Inc., based in Vancouver, Canada is the supplier of the product TDPATM (Totally Degradable Plastic Additive, a pro-oxidant). An extruded sample of LDPE containing TDPA additive, when first thermally degraded and subjected to mature compost in respirometric studies, showed that these samples were biodegraded by micro-organisms and the mineralization rates exceeded 60%, a level typical of several natural polymers. Moreover, the rate of biodegradation was comparatively slower (Chiellini et al., 2003). This additive can also be used with other thermoplastic polymers such as

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PP, PVC, etc. Other investigators have also proposed that thermally degraded polyolefins can be mineralized by microorganisms in soil (Volke-Sepúlveda et al., 1999; Scott and Wiles, 2001). However, further research is needed; in particular, respirometric studies to confirm biodegradability and toxicity evaluations are required to ascertain the safety of the breakdown products. If the claims are confirmed, then this might be the breakthrough technology that would certainly benefit the packaging industry on a wider scale.

2.8

Biodegradable packaging life cycle assessment

A product’s life cycle starts from the moment when raw materials are harvested and processed, followed by the product’s manufacturing, transport, usage and disposal. At every stage of the life cycle, there are emissions of greenhouse gases and consumption of resources/energy. Life cycle assessment (LCA) documents the environmental profile over the life of the product, also known as ‘cradle to grave’ analyses of the environmental impact or the product’s ‘environmental footprint’. This information helps to evaluate the product’s (such as food packaging) overall sustainability and the entire environmental economy. LCA identifies and quantifies the environmental loads involved at every stage – e.g. the energy and raw materials consumed, including the emissions and wastes generated – evaluates the potential environmental impacts of these loads and assesses available options for reducing these environmental impacts. LCA is becoming so crucial that ISO has standardized this framework within the ISO 14040 series on LCA. In the future, all biodegradable packaging manufacturers will be required to conduct LCAs on their products. In this regard, Novamont in Italy has applied LCA to evaluate their product Mater-Bi bags, used for the collection of organic waste, and to compare it with paper bags and PE bags (Bastioli, 2001). Interestingly, paper bags, due to their weight, consumed much more energy in their production compared with Mater-Bi or PE bags. However, the Mater-Bi bags had a four times lower greenhouse effect than PE bags and a five times lower effect than paper bags. This is attributed to the presence of natural fillers in the MaterBi bags. Preliminary studies carried out under the European Climate Change Program indicated a primary CO2 savings potential equivalent to approximately 4 million metric tons of CO2 as a greenhouse gas. This figure is based on the assumption that the bioplastics market, given the appropriate supportive framework conditions, will have grown to around 1 million metric tons (www.european-bioplastics.org). Bioplastics, particularly for food packaging, are at a very early stage of their development, and therefore the information available on the LCA of biobased products is scarce. A comprehensive article on this subject has been published by Patel et al. (2003).

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Food safety concerns, applications and adoption by the industry

The safety of biobased food packaging has to be examined from a variety of perspectives in view of their overall LCA. Raw materials for bioplastics are derived from renewable crops and their monomers are naturally biodegradable and eventually get recycled back to the earth. Material handling, processing and product manufacturing is routine and does not raise any issues concerning workers’ health or environmental safety. The biggest concern, however, is public health, and safety and security of the packaged food. Petroleum-based packagings have contributed tremendously in this regard, improving the stability and safety of packaged foods. No less is expected from biobased packaging. With consumers demanding more environmentally friendly packaging, the question remains, can biobased polymers provide packaging products that can match the properties of petrochemical-based packaging, by delivering food safely to consumers? In this regard, some earlier developments in the biobased food packaging have already provided results that are quite encouraging. For example, with hybrid biobased packaging, improvements have been observed with regard to the handling of food, prevention of moisture loss, reduction in lipid oxidation, improvement in flavor, stabilization of microbial growth and retention of color in foods ranging from fresh fruits, vegetables, dairy products and meats, to processed food requiring modified atmospheric packaging (Petersen et al., 1999; Marron, et al., 2000; van Tuil et al., 2000; Haugaard et al., 2001a, 2001b; Weber et al., 2002). Numerous investigators have observed that biobased packaging technology improved the quality and safety of fresh processed muscle food (Cutter, 2000), enhanced color and storage life of fresh beef (Ayers, 1959; Baker et al., 1994) and provided enhanced barrier and antimicrobial properties to dairy products where stability of microbial environment and storage capacity is critical (Ahvenainen, 2003). Prolongation of the shelf-life of perishable foods using biodegradable films and coatings has also been reported (Ayers, 1959; Baker et al., 1994; Baldwin, 1995; Guilbert et al., 1996). Many biobased packagings have also been reported to offer fire-retardant capabilities. Interestingly, very few or no reports exist to indicate any negative impact on food quality resulting from biobased packaging. For example, concern has been raised with respect to petroleumbased plastics as containers (packaging) for foods that are cooked in microwave or conventional ovens. Plasticizers, unreacted monomers, mold release agents or other contaminants found in plastics may leach upon heating, and contaminants may get absorbed by foods. This may produce changes in food flavor and raise safety concerns (Brooker and Friese, 1989; Castle et al., 1992; McNeal and Hollifield, 1993). In contrast, such concerns have not been raised for the biobased packaging made of mostly renewable natural polymers.

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Biobased packaging has already been adapted and is in wide use by nonfood industries worldwide. Europe, North America and Asia have taken the lead in this regard. The items manufactured include garbage bags, shopping bags, laundry bags, agricultural mulch films, single-use consumer packaging and corrugated (KTM Industry, Lansing, MI) and loose-fill foams. KTM and Michigan State University are jointly developing ‘green’ technology-based novel industrial materials to provide innovative solutions for global packaging applications. Biodegradable starch foam packaging and insulation materials are now available commercially. Some automotive manufacturers (Toyota) as well as giant computer manufacturers (NEC) and other consumer electronics producers (HP and Dell) are using biobased packaging for their products. In particular, renewable polymers have found some useful applications in the field of biomedicine. Implants, prostheses, bone substitutes, sutures and drug delivery vehicles are examples of their applications. This is quite encouraging, as these materials have shown to be quite compatible with human tissues and blood, and no rejection of these materials or adverse effects of their use have been reported in a mammalian system. Adoption of these products by the food industry has been steady but slow due to obvious health and food safety concerns as well as regulatory hurdles. In the United States, for example, any food contact item has to pass through a stringent and lengthy process of evaluation before it can be approved by the US FDA for public use. The European Community also has similar protocols in place. For example, the EU Framework Directive 90/128/EEC requires that any biobased packaging for food contact must ensure food quality and safety. Another reason for the slow progress in incorporation of biobased packaging by the food industry concerns the fulfillment of unique and characteristic functionality requirements demanded by packaged food to provide a stable, healthy and safe food to consumers. Packaging biologically active materials in a space made up of mostly biologically active polymers is in itself a challenge. Factors such as modified atmospheres, provision of gas and water vapor barriers, microbial and thermal stability, retention of color, texture and flavor, as well as timecontrolled performance, are not trivial issues and need to be considered in the design of the food package. In the last decade, the science of biobased materials with respect to food packaging has advanced to the highest level and some great strides have been made by the food industry to embrace this new thinking on biobased food packaging. In addition, biobased packaging for foods has been reconsidered as a more environmentally responsible alternative compared with petrochemical-based counterparts. This factor, and the demand for environmentally friendly packaging from consumers and advocacy groups, concern for accumulating recalcitrant plastic waste in landfills and ever-increasing oil prices have all served as catalysts to bring about this change. Many companies worldwide are positioning themselves as leaders in developing biodegradable plastic resins as they foresee a bright future for applications of these materials (Table 2.1); this is evidenced by the food packaging products that are already in the market © 2008, Woodhead Publishing Limited

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place (Table 2.5). More details on this subject are provided elsewhere (Haugaard et al., 2001a, 2001b). There are several critically important determinants that will guide the success of renewable and biopolymers as raw materials for food packaging. First of all, the availability of material with consistent properties will be critical for the industry. Factors such as flooding, extended drought, frost, harvesting pattern and crop infestation could potentially have an impact on on both the quality and the quantity of the available raw materials. For example, harvesting a corn crop prematurely would certainly affect the quality of the starch. One consistent fear will be the presence of any chemical contaminants, or their byproducts, from the fertilizers, pesticides or herbicides used in industrialized countries. Although there seems to be no indication of this at the present time, this is one of the aspects that will be closely examined and monitored by regulatory agencies such as the FDA. Currently, most of the renewable crops are produced in surplus, and this seems to be the global trend. However, environmental factors, weather, climate change due to global warming and scarcity of water resources could change this scenario, and will threaten the abundant availability of raw materials. Yet another important aspect of renewable-based plastics is the fact that many renewable crops, for example corn and soybean, are also consumed as food. Many impoverished nations – particularly in Africa, Asia and South America – are dependent on these crops to provide food to their people. There is a fear that, when demand exceeds the supply, market forces will drive the food prices high and will place economic pressure on these countries. The world’s population is expected to double by the year 2050 and a big portion of agricultural land will presumably be lost to the urban development required to accommodate the population. This will, inevitably, provoke competition for renewable crops, i.e. crops grown for food and crops grown for use as raw materials for industrial products. One of the unintended consequences of this competition has already occurred. Many of the small family farms, once considered the backbone of American agriculture, have been replaced by corporate farming organizations. Large corporations with business interests and with intellectual property rights on many commercially important, genetically modified germplasms are positioning themselves to be the market players in the near future. The effort to produce biodegradable microbial polyesters in plants by NatureWorksTM is one such example.

2.10

Future trends

Judging from the R&D achievements of the past 10–15 years with respect to biopolymer-based plastics, the future of biobased polymers in food packaging looks quite promising. Many of the challenges posed by renewable materials have been and are being resolved, and the food industry in general is supporting the concept by moving towards the adoption of biobased packaging. Consumers have shown a strong acceptance on their part for © 2008, Woodhead Publishing Limited

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biobased products and are even willing to pay higher prices for the sake of the environment. These products will also be good for MSW management companies and composting facilities, which will generate extra revenues by converting these compostable materials into rich soil additives. This would also reduce pressure on the ever-shrinking landfill spaces. One obvious benefit will be the minimization of litter on land and sea: the litter is not only a nuisance but is also compromising the natural habitats for many animals, including marine life. Many countries and regions have already introduced legislation on the management of plastic waste and have placed incentives to promote biodegradable plastics. Likewise, many international organizations such as ASTM, ISO, CEN, DIN and OECD are coordinating testing standards, criteria and definitions for biodegradable packaging. Composting councils are active in defining what is acceptable for composting and what is not. The LCAs of several renewable and biobased products have shown very encouraging trends indicating a strong environmental benefit of such packaging. A recent EU study estimates a considerable reduction in the production of greenhouse gases as a result of the usage of biodegradable plastics (Patel, 2004). In the end, a combination of the desired properties and functionalities of the packaging materials and the commodity market price will dictate the successful adoption of renewable polymers in food packaging. If these packages do not perform at the level consumers are currently accustomed to, they will not be accepted or supported. In addition, raw materials have to be cost competitive, otherwise the industry will naturally revert to the petroleumbased chemicals. This is particularly critical for the PHB and PLA polymers, because despite having good properties, the current market price for these resins is not attractive and is keeping many manufacturers away. It is encouraging to note that consumer surveys in industrialized countries have repeatedly shown the willingness of consumers to pay a fractionally higher price for an environmentally friendly packaging derived from biodegradable and/ or renewable polymers. For now, there are strong factors in favor of renewables: an astonishing amount of per capita garbage generation in the industrialized world, rising oil prices and the production of crops in surplus quantities. This momentum needs to be sustained with commitment for the design and production of products with useful functionality, i.e., products that perform under a variety of storage conditions and that retain the ability to degrade after use. More efforts are needed globally to take advantage of the changing market trends with respect to biobased packaging.

2.11

Sources of further information and advice

Publications • Ahvenainen R (Ed.). Novel food packaging techniques. Woodland Publishing Limited, Cambridge, UK, 2003.

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• Petersen K, Væggemose Nielsen P, Bertelsen G, Lawther M, Olsen MB, Nilsson NH, Mortensen G. Potential of biobased materials for food packaging. Trends Food Sci. Technol., 1999, 10, 52–68. • Robertson GL (Ed.). Food packaging: principles and practice. CRC Press, Boca Raton, Florida, 2005. • Smith R (Ed.). Biodegradable polymers for industrial applications. Woodhead Publishing Limited, Cambridge, UK, 2005. • Truong D, Pham PSS, Dimov SS (Eds). Advances in manufacturing technology. Wiley & Sons, Hoboken, New Jersey, 2001. • Young RA, Rowell JK, Roweu RM (Eds). Paper and composites from agro-based resources. CRC Press, Boca Raton, Florida, 1996. Websites • American Society for Testing and Materials (ASTM) (www.astm.org). • European Committee for Standardization (CEN) (www.cenorm.be). • International Organization for Standardization (ISO) (www.iso.org).

2.12

References

agarwal m, koelling kw, chalmers jt. Characterization of the degradation of polylactic acid polymer in a solid substrate environment. Biotechnol. Prog. 1998, 14, 517–526. ahvenainen r. (Ed.) Novel food packaging techniques. Woodhead Publishing Limited, Cambridge, UK, 2003, p. 590. andersen pj, hodson sk. Molded articles having an inorganically filled organic polymer matrix. US Patent No. 5,545,450, 1996. avérous l, fringant c. Association between plasticized starch and polyesters: processing and performances of injected biodegradable systems. Polym. Engng Sci., 2001, 41, 727–734. avérous l, fringant c, moro l. Starch-based biodegradable materials suitable for thermoforming packaging. Starch/Stärke, 2001, 53, 368–371. ayers jc. Use of coating materials or film impregnated with chlortetracycline to enhance color and storage life of fresh beef. Food Technol., 1959, 13, 512–515. baker ra, baldwin ea, nisperos-carriedo no. Edible coatings and films for processed foods. In Edible coatings and films to improve food quality, Krochta JM, Baldwin EA, Nisperos-Carriedo MO (Eds). Technomic Publishing Company, Lancaster, Pennsylvania, 1994, pp. 89–104. baldwin ea, nisperos-carriedo mo, baker ra. Use of edible coatings to preserve quality of lightly (and slightly) processed products. Crit. Rev. Food Sci. Nutr., 1995, 35, 509–524. bastioli c. Industrial applications of bioplastics. Green Tech Conference, Utrecht, Holland, April 3–5, 2000. bastioli c. Global status of the production of biobased packaging materials. Starch/ Stärke, 2001, 53, 351–355. brooker jl, friese ma. Safety of microwave-interactive paperboard packaging materials. Food Technol., 1989, 31, 110–117. bucci dz, tavares lbb, sell i. PHB packaging for the storage of food products. Polym. Test., 2005, 24, 564–571.

© 2008, Woodhead Publishing Limited

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castle l, nichol j, gilbert j. Migration of polyisobutylene from polyethylene/polyisobutylene film into foods during domestic and microwave oven use. Food Addit. Contam., 1992, 9, 315–330. chiellini e, chiellini f, cinelli, p. Polymers from renewable resources. In Degradable polymers: principles and applications, Scott G. (Ed.), 2nd edn, Chapter 7. Kluwer Academic Publishers, Dordrecht, The Netherlands, 2002, pp. 163–233. chiellini e, corti a, swift g. Biodegradation of thermally-oxidized, fragmented low-density polyethylene. Polym. Degrad. Stabil., 2003, 81, 341–351. chiellini e, cinelli p, chiellini f, imam sh. Environmentally degradable bio-based polymeric blends and composites. Macromol. Biosci., 2004, 4, 218–231. chinnaswamy r, hanna ma, zobel hf. Microstructural physiochemical and macromolecular changes in extrusion-cooked and retrograded cornstarch. Cereal Foods World, 1989, 34, 415. chum hl, overend rp. Biomass and renewable fuels. Fuel Process. Technol., 2001, 71, 187–195. cinelli p, chiellini e, lawton jw, imam sh. Foamed articles based on potato starch, corn fibers and poly(vinyl alcohol). Polym. Degrad. Stabil., 2006a, 91, 1147–1155. cinelli p, chiellini e, lawton jw, imam sh. Properties of injection molded composites containing fiber and poly(vinyl alcohol). J. Polym. Res., 2006b, 13, 107–113. cutter cn. Opportunities for bio-based packaging technologies to improve the quality and safety of fresh and further processed muscle foods. Meat Sci., 2000, 74, 131–142. dean k, yu l, bateman s, wu dy. Gelatinized starch/biodegradable polyester blends: processing, morphology, and properties. J. Appl. Polym. Sci., 2007, 103, 802–811. doane wm, swanson cl, fanta gf. Emerging polymeric materials based on starch. In Emerging technologies for materials and chemicals from biomass, ACS Symposium Series 476, Rowell RM, Tor P, Narayan R (Eds). ACS, Washington, DC, 1998, pp. 197–230. earthshell corporation. EarthShell packaging foam laminates products. 3916 State Street, Suite 110, Santa Barbara, CA, 2002. http://www.earthshell.com/foam. html. francia c. I sistemi e I contenitori per la raccolta differenzi-ata dei rifiuti organici. FederAmbiente, November 2000. galliard t, bowler p. Morphology and composition of starch. In Starch: properties and potential, Galliard T. (Ed.). Wiley & Sons, New York, 1987, p. 55. glenn gm, orts wj, nobes gar. Starch, fiber and CaCO3 effects on the physical properties of foams made by a baking process. Ind. Crops Prod., 2001a, 14, 201–212. glenn gm, orts wj, nobes gar, gray gm. In situ process for baked starch-based foams. Ind. Crops Prod., 2001b, 14, 125–134. gordon sh, imam sh, greene rv. Starch-based plastics: measurement of biodegradability. In Polymeric materials encyclopedia, Salamone JC (Ed.), vol. 10. CRC Press, Boca Raton, Florida 1996, pp. 7885–7892. griffin gjl. Biodegradable fillers in thermoplastic. Adv. Chem. Ser., 1971, 134, 156–170. griffin gjl. Biodegradable synthetic resin sheet material containing starch and a fatty acid material. US Patent No. 4016,117, 1977. guilbert s. Edible films and coatings and biodegradable packaging. Bull. Int. Dairy Fed., 2000, 346, 10–15. guilbert s, gontard n, gorris lgm. Prolongation of shelf-life of perishable food products using biodegradable films and coatings. Lebensm.-Wiss. Technol., 1996, 29, 10–17.

© 2008, Woodhead Publishing Limited

Types, production and assessment of biobased materials

59

guilbert s, cuq b, gontard n. Recent innovations in edible and/or biodegradable packaging materials. Food Addit. Contam., 1997, 14, 741–751. hass f, hass j, tiefenbacher k. Process of manufacturing rottable thin-walled starchbased shaped elements. US Patent No. 5,576,049, 1996. haugaard vk, udsen am, mortensen g, høegh l, petersen k, monahan f. Potential food applications of biobased materials. In Biobased food packaging – status and perspectives, Weber C-J, (Ed.), Chapter 3. Royal Veterinary and Agricultural University, Copenhagen, 2001a, pp. 46–85. haugaard vk, udsen a-m, mortensen g, høegh l, petersen k, monahan f. Potential food applications of biobased materials. An EU-concerted action project. Starch/ Stärke, 2001b, 53, 189–200. ho k-lg, pometto iii al, hinz n. Effects of temperature and relative humidity on polylactic acid plastic degradation. J. Polym. Environ. Degrad., 1999, 7, 83–92. hodge im, berens ar. Effects of annealing and prior history on enthalpy relexation in glassy polymers: 2. Mathematical modeling. Macromolecules, 1982, 15, 762. holton ee, asp eh, zottola ea. Corn-starch-containing polyethylene film used as food packaging. Cereal Foods World, 1994, 39, 237–241. hutchinson jm, kovacs a. Effects of thermal history on structural recovery of glasses during isobaric heating. J. Polym. Engng. Sci., 1984, 24, 1087. imam sh, harry-o’kuru re. Adhesion of Lactobacillus amylovorus to insoluble and derivatized cornstarch granules. Appl. Envir. Microbiol., 1991, 57, 1128–1133. imam sh, gould jm, gordon sh, kinney mp, ramsey am, tosteson tr. Fate of starchcontaining plastic films exposed in aquatic habitats. Curr. Microbiol., 1992, 25, 1–8. imam sh, gordon sh, thompson ar, harry-o’kuru re, greene rv. The use of CP/MAS 13C-NMR for evaluating starch degradation in injection molded starch–plastic composites. Biotechnol. Tech., 1993, 7, 791–794. imam sh, gordon sh, burgess-cassler a, greene rv. Accessibility of starch to enzymic degradation in injection-molded starch–plastic composites. J. Environ. Polym. Degrad., 1995a, 3, 107–113. imam sh, gordon sh, shogren rl, greene rv. Biodegradation of starch–poly(βhydroxybutyrate-co-valerate) composites in municipal activated sludge. J. Environ. Polym. Degrad., 1995b, 3, 205–213. imam sh, gordon sh, greene rv. Starch biodegradation (in starch–plastic blends). In Polymeric materials encyclopedia, Salamone JC (Ed.), vol. 10. CRC Press, Boca Raton, FL, 1996, pp. 7892–7901. imam sh, chen l, gordon sh, shogren rl, weisleder d, greene rv. Biodegradation of injection molded starch–poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends in a natural compost environment. J. Environ. Polym. Degrad., 1998, 6, 91–98. imam sh, gordon sh, shogren rl, tosteson tr, govind ns, greene rv. Degradation of starch–poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) bioplastic in tropical coastal waters. Appl. Environ. Microbiol., 1999a, 65, 431–437. imam sh, mao l, chen l, greene rv. Wood adhesive from crosslinked poly(vinyl alcohol) and partially gelatinized starch: preparation and properties. Starch/Stärke, 1999b, 51, 225–229. jarerat a, tokiwa y. Degradation of poly (l-lactide) by a fungus. Macromol. Biosci., 2001, 1, 136–140. jarerat a, tokiwa y. Poly (l-lactide) degradation by Saccharothrix waywayandensis. Biotechnol. Lett., 2003, 25, 401–404. jarerat a, tokiwa y, tanaka h. Poly (l-lactide) degradation by Kibdelosporangiium aridum. Biotechnol. Lett., 2003, 25, 2035–2038. koenig mf, huang sj. Biodegradable blends and composites of polycaprolactone and starch derivatives. Polymer, 1995, 36, 1877–1882.

© 2008, Woodhead Publishing Limited

60

Environmentally compatible food packaging

köse gt, ber s, korkusuz f, hasirci v. Poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid) based tissue engineering matrices. J. Mater. Sci: Mater Med., 2003, 14, 121–126. lawton jw. Biodegradable coatings for thermoplastic starch. In Cereals: novel uses and processes, Campbell GM, Webb C, McKee SL (Eds). Plenum Press, New York, 1997, pp. 43–47. lawton jw, shogren rl, tiefenbacher kf. Effect of batter solids and starch type on structure of baked starch foams. Cereal Chem., 1999, 76, 682–687. lawton jw, shogren rl, tiefenbacher kf. Aspen fiber addition improves the mechanical properties of baked cornstarch foams. Ind. Crops Prod., 2004, 19, 41–48. luzier wd. Materials derived from biomass/biodegradable materials. Proc. Natl Acad. Sci. USA, 1992, 89, 839–842. makino y, hirata t. Modified atmosphere packaging of fresh produce with a biodegradable laminate of chitosan-cellulose and polycaprolactone. Postharvest Biol. Technol., 1997, 10, 247–254. marron v, saari l, floridi g, boelck c, innocenti f. The market of biobased packaging materials. In Biobased packaging materials for the food industry – status and perspectives, Weber CJ (Ed.). Report of EU Concerted Action Project, 2000, pp. 105–112. martin o, schwach e, avérous l, couturier y. Properties of biodegradable multilayer films based on plasticized starch. Starch/Stärke, 2001, 53, 372–380. masaki k, kamini nr, ikeda h, iefuji h. Cutinase-like enzyme from the yeast Cryptococcus sp. strain S-2 hydrolyzes polylactic acid and other biodegradable plastics. Appl. Environ. Microbiol., 2005, 71, 7548–7550. mayer jm, kaplan dl. Biodegradable materials: balancing degradability and performance. Trends Polym. Sci., 1994, 2, 227–235. mcneal tp, hollifield hc. Determination of volatile chemicals released from microwave-heat-susceptor food packaging. J. Assoc. Anal. Chem., 1993, 76, 1268–1275. narayan r. Impact of governmental policies, regulations and standards activities on an emerging biodegradable plastic industry. In Biodegradable plastics and polymers, Doi Y, Fukuda K. (Eds). Elsevier, Amsterdam, 1994, pp. 261–271. orts wj, ingelsby b glenn gm. Bringing bioproducts to market. Biocycle, 2003a, June, 25–27. orts wj, inglesby m, glenn gm. Cleaning up with bioproducts. Business, 2003b, March/April, 12–14. otey fh, westhoff rp, russell cr. Starch graft copolymers-degradable fillers for poly (vinyl chloride) plastics. Ind. Engng. Chem., Prod. Res. Dev., 1976, 15, 139–144. otey fh, westhoff rp, doane wm. Starch-based blown films. Ind. Engng. Chem. Res., 1987, 26, 1659–1663. patel m. Surfactants based on renewable raw materials: carbon dioxide reduction potential and policies and measures for the European Union. J. Ind. Ecol., Special Issue on Biobased Products, 2004, 7, 47–62. patel m, bastioli c, marini l, würdinger e. Life-cycle assessment of biobasedpolymers and natural fibers. In Biopolymers, Steinbüchel A (Ed.), vol. 10. WileyVCH, Weinheim, Germany, 2003, pp. 409–452. petersen k, væggemose nielsen p, bertelsen g, lawther m, olsen mb, nilsson nh, mortensen g. Potential of biobased materials for food packaging. Trends Food Sci. Technol., 1999, 10, 52–68. ramsay ba, langlade v, carreau pj, ramsay ja. Biodegradability and mechanical properties of poly(β-hydroxybutyrate-co-β-hydroxyvalerate)–starch blends. Appl. Environ. Microbiol., 1993, 59, 1242–1246.

© 2008, Woodhead Publishing Limited

Types, production and assessment of biobased materials

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robertson gl (Ed.). Food packaging: principles and practice. CRC Press, Boca Raton, Florida, 2005, p. 568. röpper h, koch h. The role of starch in biodegradable thermoplastic materials. Starch/Stärke, 1990, 42, 123. rosa ds, lotto nt, lopez dr, guedes cgf. The use of roughness for evaluating poly-β-(hydroxybutyrte) and poly-β-(hydroxybutyrate-co-β-valerate). Polym. Test., 2004a, 23, 3. rosa ds, gliedes cgf, pedroso ag, calil mr. The influence of starch gelatinization on the rheological, thermal, and morphological properties of poly(ε-caprolactone) with corn starch blends. Mater. Sci. Engng C, 2004b, 24, 663–670. rosa ds, lopes dr, calil mr. The influence of the structure of starch on the mechani cal, morphological and thermal properties of poly (ε-caprolactone) in starch blends. J. Mater. Sci., 2007, 42, 2323–2328. scott g, wiles dm. Programmed-life plastics from polyolefins: a new look at sustainability. Biomacromolecules, 2001, 2, 615–622. shey j, imam sh, glenn gm, orts wj. Properties of baked starch foam with natural rubber latex. Ind. Crops Prod., 2006, 24, 34–40. shogren rl. Effect of moisture content on the melting and subsequent physical aging of cornstarch. Carbohydr. Polym., 1992, 19, 83. shogren rl. Complexes of starch with telechelic poly(ε-caprolactone) phosphate. Carbohydr. Polym., 1993, 22, 93–98. shogren rl. Starch: properties and material applications. In Biopolymers from renewable resources, Kaplan DL (Ed.). Springer-Verlag, Berlin, 1998, pp. 30–46. shogren rl, bagley eb. Natural polymers as advanced materials: some research needs and directions. In Biopolymers – utilizing nature’s advanced materials, ACS Symposium Series 723, Imam SH, Greene RV, Zaidi BR (Eds). ACS, Washington, DC, 1999, pp. 2–11. shogren rl, lawton jw. Enhanced water resistance of starch-based materials. US Patent No. 5,756,194, 1998. shogren rl, lawton jw, doane wm, tiefenbacher kf. Structure and morphology of baked starch foams. Polymer, 1997, 39, 6649–6655. shogren rl, lawton jw, tiefenbacher kf, chen l. Starch–poly (vinyl alcohol) foamed articles prepared by a baking process. J. Appl. Polym. Sci., 1998, 68, 2129–2140. shogren rl, lawton jw, tiefenbacher kf. Baked starch foams: starch modification and additives improve process parameters, structure and properties. Ind. Crops. Prod., 2002, 16, 69–79. shogren rl, doane wm, garlotta dv, lawton jw, willet jl. Biodegradation of starch/polylactic acid/poly(hydroxyester-ether) composite bars in soil. Polym. Degrad. Stabil., 2003, 79, 405–411. stevens es. Biopolymers. In Green plastics. Princeton University Press, New Jersey, 2002, pp. 83–103. stranz aa, zottola ea. Bacterial survival on lean beef and bologna wrapped with cornstarch-containing polyethylene film. Food Prod., 1992, 55, 782–786. swanson cl, shogren rl, fanta gf, imam sh. Starch–plastic materials – preparation, physical properties, and biodegradability (a review of recent USDA research), J. Polym. Environ., 1993, 1, 155–166. tiefenbacher k. Starch-based foamed materials – use and degradation properties. J. Macromol. Sci., Pure Appl. Chem., 1993, A30, 727–731. tomka i. Thermoplastic starch. Adv. Exp. Med. Biol., 1991, 302, 627. truong d, pham pss, dimov, ss (Eds). Advances in manufacturing technology. Wiley & Sons, Hoboken, NJ, 2001, p. 490. van soest jjg. Starch plastics structure–property relationship. PhD thesis, Utrecht University, The Netherlands, 1996.

© 2008, Woodhead Publishing Limited

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van tuil r, fowler p, lawther m, weber cj. Properties of biobased packaging materials. In Biobased packaging materials for the food industry – status and perspectives, Weber CJ (Ed.). Report of EU Concerted Action Project, 2000, pp. 8–33. volke-sepúlveda t, favela-torres e, manzur-guzmáan a, limón-gonzalez m, trejo-quintero g. Microbial degradation of thermo-oxidized low-density polyethylene. J. Appl. Polym. Sci., 1999, 73, 1435–1440. weber cj, haugaard v, festersen r, bertelsen g. Production and applications of biobased packaging materials for the food industry. Food Addit. Contam., 2002, 19 (Suppl.), 172–177. whistler rl. History and future expectation of starch use. In Starch chemistry and technology, Whistler RL, Bemiller JN, Paschall EF (Eds). Academic Press, San Francisco, California, 1984, pp. 1–9. xu yx, dzenis y, hanna ma. Water solubility, thermal characteristics and biodegradability of extruded starch acetate foams. Ind. Crops Prod., 2005, 21, 361–368. yasin m, holland sj, jolly am, tighe bj. Polymers for biodegradable medical devices. VI. Hydroxybutyrate–hydroxyvalerate copolymers: accelerated degradation of blends with polysaccharides. Biomaterials, 1989, 10, 400–412. zobel hf. Starch crystal transformations and their industrial importance. Starch/ Stärke, 1988, 40, 1.

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3 Thermoplastic nanobiocomposites for rigid and flexible food packaging applications J. Lagaron and M. Sanchez-Garcia, Institute of Agrochemistry and Food Technology, Spain; E. Gimenez, ESID, University Jaume I, Castellon, Spain

3.1

Introduction: plastic food packaging, sustainable materials and barrier properties

Over the last few decades there has been a significant increase in the amount of plastics being used in packaging applications. In fact, the largest application for plastics today is packaging, and within the packaging niche, food packaging constitutes the largest plastics-demanding application. This is because plastics demonstrate enormous advantages, such as thermoweldability, flexibility in thermal and mechanical properties, lightness and low price.1–3 However, polymers do also have a number of limitations for certain applications when compared with more traditional materials such as metals and alloys or ceramics. Of these limitations, those relevant to this chapter are their impermeability to low molecular weight components, a comparatively low thermal resistance and a strong interdependence between the last two properties. In spite of this, use of plastic materials continues to expand and to replace the conventional use of paperboard, tinplate cans and glass, which have typically been used as monolayer systems. Initially, most plastic packaging was made of monolayer rigid or flexible materials but as the advantages of plastic packaging became more and more established and developed, the increasingly demanding product requirements found when plastics had to suit more and more different food products led, in conjunction with significant advances in plastic processing technologies, to more and more complex polymeric packaging formulations. This resulted in complex multicomponent structures such as the so-called multilayer packaging-based systems widely used today. However, there are significant advantages in terms of costs and other issues, such as ease of recycling, in

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developing packaging materials made of monolayer components. As a result, much research effort has been expended over the last decades in the study of material developments and material blends to reduce complexity in food packaging structures. On the other hand, the substantial increase in the use of plastics has also raised a number of environmental concerns from a waste management point of view. As a result, there is a strong research interest – driven by authorities at national and international levels, and a concomitant increasing demand from industry – in the development and use of materials that can disintegrate and biodegrade, through processes such as composting, into carbon dioxide and water. Among biodegradable materials, three families are usually considered. The first family are polymers directly extracted from biomass, such as the polysaccharides chitosan, starch and cellulose and proteins such as gluten and zein. A second family makes use of oil-based monomers or biomassderived monomers but uses classical chemical synthetic routes to obtain the final biodegradable polymer; this is the case for polycaprolactones (PCLs), polyvinyl alcohol (PVOH) and copolymers (ethylene vinyl alcohol, EVOH), and for sustainable monomers of polylactic acid (PLA).1–3 The third family makes use of polymers produced by natural or genetically modified microorganisms such as polyhydroxyalkanoates (PHAs) and polypeptides.4 The materials that are now attracting more commercial interest are some biodegradable polyesters, which can be processed by conventional processing equipment and are already being used in a number of monolayer and also multilayer applications, particularly in the food packaging and biomedical fields. The most widely researched thermoplastic, sustainable biopolymers for monolayer packaging applications are starch, PHA and PLA. Of these, starch and PLA biopolymers are without doubt the most interesting families of biodegradable materials because they have become commercially available (from, for instance, companies such as Novamont and Natureworks, respectively) and are produced on a large industrial scale, and also because they present an interesting balance of properties. Of particular interest in food packaging is the case of PLA due to its excellent transparency and relatively good water resistance. The water permeability of PLA is, for instance, much lower than that of proteins and polysaccharides but it is still higher than that of conventional polyolefins and polyethylene terephthalate (PET). Its relatively high stiffness is usually reduced by addition of plasticizers such as PCL and others, but these also lead to a decrease in oxygen barrier properties and in transparency. Thus, the main drawbacks of this polymer regarding performance are still associated with low thermal resistance, excessive brittleness and insufficient barrier to oxygen and to water compared with, for instance, other benchmark packaging polymers like PET. It is, therefore, of great industrial interest to enhance the barrier properties of this material while maintaining its inherently good properties such as transparency and biodegradability.5–11

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Finally, there are also other biomaterials that show a lot of potential in food packaging applications; these materials are directly extracted from biomass, for example gluten, protein zein obtained from corn and the polysaccharide chitosan typically obtained from the crustaceous chitin. These materials have excellent barrier properties to oxygen under dry conditions and are transparent (albeit zein is slightly coloured). The main drawbacks of these families of materials is their inherently high rigidity, difficult processability using conventional processing equipment and the very strong water sensitivity arising from their hydrophobic character, which leads to a strong plasticization of many properties, including the excellent oxygen barrier, as relative humidity and water sorption increase in the material. The low water resistance of proteins and polysaccharides strongly handicap their use as monolayers in food packaging and apart from a few particular cases such as starch-based materials and, on a smaller scale, gluten and zein, most proteins and polysaccharides are better suited for coatings or multilayer systems. Nevertheless, chitosan and zein biopolymers exhibit two very interesting characteristics: one is that the chitosan displays antimicrobial properties12,13 and the other is that zein shows an unusually high water resistance compared with other similar biomaterials.14 Furthermore, zein in a resin form can also be heat processed. In spite of this, and from an application point of view, it is of great relevance to diminish the water sensitivity of proteins and polysaccharides and to enhance the gas barrier properties of thermoplastic biopolyesters to make them suitable for monolayer and also for multilayer food packaging applications. The outline of the current chapter is to first introduce the general concept of barrier properties and the need for these in food packaging applications and to describe briefly the phenomenology of transport in polymers. This is followed by presentation of novel plastic strategies and technologies for monolayer packaging. The next sections introduce and review the role of the nanocomposites, and in particular the nanobiocomposites, as the most promising monolayer technology currently available for enhancing barrier properties and designing sustainable and more efficient active and bioactive systems for current and future food packaging applications.

3.2

‘Barrier properties’ limit the use of plastics in monolayer packaging

From the above introduction, it is clear that enhancing or being able to tailor the barrier properties of conventional and biodegradable polymers, but especially the latter, is essential for their competitive implementation in food packaging applications as monolayers, or even in some cases in multilayer structures. Barrier properties are concerned with the ability of a plastic material to reduce the transport of low molecular weight compounds through it; these properties strongly influence relevant, and often

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undesirable, transport phenomena in food packaging, such as the sorption of food components or scalping, migration and permeability processes. ‘High barrier’ is without doubt a highly desirable property to be retained by polymeric materials intended to be used in many packaging applications. The term ‘high barrier’ is usually referred to as the low to very low permeability of a material to low molecular weight chemical species like gases, water vapour and organic compounds. However, this property has perhaps never received as much industrial attention as it has over the last few decades, when it began to be discussed in relation to modern food and beverage packaging technologies making use of plastic materials.15–17 In this respect, high barrier has been the subject of a great deal of recent industrial and social discussion, as it has become associated with topical issues such as food commercialization, food shelf-life extension, and food quality and safety. As a consequence, polymer scientists, engineers and technologists in industry and academia have invested a great deal of effort and resources to push the limits of plastics and bioplastics performance towards impermeability, chiefly due to the overwhelming pressure exerted by an industry keen to benefit from the numerous cited advantages associated with the use of plastics in high barrier monolayer and multilayer applications. 3.2.1 Phenomenology of transport in plastics According to the above, barrier properties in polymers are necessarily associated with their inherent ability to permit the exchange, to a greater or lesser extent, of low molecular weight substances through mass transport processes such as permeation. The permeation of low molecular weight chemical species through a polymeric matrix is generally envisaged as a combination of two processes, i.e. solution and diffusion.18 A permeate gas is first dissolved into the upstream face of the polymer film and then undergoes a molecular diffusion to the downstream face of the film where it evaporates into the external phase again. A solution–diffusion mechanism is thus applied, which can be formally expressed in terms of permeability (P), solubility (S) and diffusion (D) coefficients as follows P = DS

[3.1]

This permeability coefficient derives from application of Henry’s law of solubility to Fick’s first law of diffusion as follows J=

q S∆p ql ∂c ∆p = −D =D = DS ⇒ P = DS = At l l At∆p ∂x

[3.2]

The solubility coefficient (S) is thermodynamic in nature and is defined as the ratio of the equilibrium concentration of the dissolved penetrant in the polymer to its partial pressure (p) in the gas phase (Henry’s law). In polymers, Henry’s law is usually obeyed at low penetrant concentrations, i.e.

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when S is independent of concentration (or of the partial pressure). D characterizes the average ability of the sorbed permeate to move through the polymer chain segments and is determined from Fick’s first law of diffusion, i.e. the flux of the permeant J (q is the amount of substance expressed in mass for condensable fluids or in volume for permeant gases and A is the surface area) is proportional to the local gradient of concentration (c) through the thickness of the polymer film (l). During sorption kinetic experiments, if Fickian transport (case I) is assumed, a linear relationship in the penetrant uptake versus t1/2 (t being time) curve at small times is usually observed.19 Case II diffusion is defined when a linear relationship is observed in the uptake versus t curve. This behaviour is observed in a number of systems and is associated with large uptakes and plasticization of the structure by the penetrant. When complex sorption relationships such as sigmoidal shapes are observed, it is usually assumed that an ‘anomalous’ or non-Fickian transport has occured. Nevertheless, from recent works a better rationalization of these ‘anomalous’ relationships has been achieved, where contributions from the effect of macroscopic elastic constraints arising during the swelling process (geometrical effects) in adsorption experiments have been pointed out.20,21 Concerning the mechanisms of the mass transport process through polymeric materials, two general approaches can be found, namely: (a) molecular models studying the specific penetrant and chain motions in conjunction with the corresponding intermolecular forces and (b) ‘free-volume’ models which pay attention to the relations between the transports coefficients and the free volume existent in the polymeric matrix, without consideration of molecular-scale mechanisms.22 The structural factors determining inherent high barrier properties in polymers are fundamentally related to the chemistry, but there are also other relevant factors making a significant impact on barrier properties for a given chemistry including polymer morphology (crystallinity, thermal history, molecular orientation, etc.), polymer molecular architecture (branches, molecular weight and tacticity), polymer plasticization and others. Table 3.1 presents typical data relating to permeability to oxygen and water vapour for conventional and novel biodegradable plastics used in packaging. The differences in gas permeability, which can vary between materials by more than six orders of magnitude, are primarily related to the influence of chemistry. Plastics are either semi-crystalline or amorphous materials. Polymer crystals in semi-crystalline materials not only provide support and rigidity to hold the supermolecular structure of the materials but are in general impermeable blocks that impose some constraints on molecular mobility to the surrounding amorphous phase. Thus, the presence of crystallinity, its morphology (for instance crystal width to thickness ratio) and orientation, bring in additional considerations in terms of permeability as the penetrant molecules have to circumvent the crystallites and, thereby, travel through

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Table 3.1 Water permeability (at 38 ºC and 90% relative humidity (RH) and oxygen permeability (23 ºC) of a number of commercial plastics and multilayer structures (data were gathered, unless otherwise stated, from Reference 11)

Material

PVOH EVOH PAN PAN (70% AN) PVDC PA6 aPA (amorph.) PET PP PC LDPE LCP PET–PVDC PA–PVDC PP–PVDC PET-met. PET–AlOx–PE PET–SiOx–PE PA–SiOx–PE PP–SiOx–PE 23 PLA 24 PLA 23 PHB 24 PHB 23 PHBV 23 PCL 25 PCL 26 PCL

Water permeability (1018 kg m/(m2 s Pa))

Oxygen permeability (1021 m3 m/(m2 s Pa)) 0% RH

75% RH

485 000 17 000 2420 8250 30.53 20 600 2420 2300 726 19 400 1200 10 170 160 43 58 21 16 32 13 12 600

0.17 0.77 1.9 10.5 4.5 52 83 135 6750 10 500 21 500 0.42 17.5 18.2 25 3.5 7 4.9 7.7 81 2250

900 91

1689

230

6900 26 600

1590 4380 934 1960

31 225 60

15

2209 1750 5100 3010 7850

For abbreviations, see Section 3.8.

a more tortuous diffusive path than in a fully amorphous material. This effect is usually accounted for in the calculations of the transport coefficients (see equation [3.3] below for diffusion in which c is the crystallinity fraction) by the so-called tortuosity, detour or geometrical impedance factor (t). Thus, the tortuosity factor is in essence the path length that a permeant has to travel across the material thickness divided by the actual thickness of the material. At this point it is relevant to realize that any additional impermeable elements, such as clays or other fillers, added to the molecular structure of the polymers have an immediate impact on the tortuosity or detour factor, as will be further explained later in the chapter. Furthermore,

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and as commented above, the presence of crystalline blocks or other fillers also affects the surrounding conformationally disordered amorphous phase. The constraining effects imposed by crystals or fillers to the chain segments in the amorphous phase typically depend on factors such as crystal or particle surface area and penetrant size. This phenomenon is substantiated from extensive mechanical and transport data, which clearly indicate that the segmental mobility of the non-crystalline fraction is much less than that in the fully amorphous polymer or in unfilled materials.27,28 This effect is accounted for in the calculations of the transport coefficients (see equation [3.3]) by the so-called chain immobilization factor (b) Dsemi-crystalline =

Damorphous (1 − χ ) βτ

[3.3]

As a result of this, awareness of the effects of crystallinity or of the presence of fillers, and their morphology and distribution, on the barrier properties is, as a matter of fact, a very relevant issue, because by adequate processing (thermal history) of polymers these additional effects can be optimized to obtain specimens, based on the same matrix chemistry, with enhanced permeability.

3.3

Novel developments in barrier polymeric structures

Novel developments in plastic materials currently come mainly from five different sources, namely: (a) new synthetic polymers, (b) biomass-derived polymers, (c) polymer blends, (d) nanocomposites, and (e) surface or coating technologies. Polymeric materials for high barrier applications are challenged today with a broad range of stringent property requirements including: ease of processing; higher barrier properties to permanent gases, moisture and low molecular weight organic compounds; excellent chemical resistance; permselectivity; low relative humidity dependence for the barrier performance; and ease of recycling, biodegradability or compostability. Among the new high barrier polymers being developed are materials like the polyketone (PK) copolymers (aliphatic polyketones).30,31 These semi-crystalline materials have an outstanding range of mechanical, thermal and high barrier properties (comparable with some EVOH copolymers), chemical resistance and reduced relative humidity dependence for barrier properties, which give them significant commercial potential in a broad range of engineering, barrier packaging, fibre and blend applications. Another new range of promising materials currently being investigated for packaging applications are those derived from biomass, as mentioned above, which to a greater or lesser extent are easily biodegradable or compostable.24,32 These polymers can have excellent barrier properties to gases, as for example plasticized chitosan, albeit the barrier performance is dramatically reduced in the presence of moisture. However, other polymers

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such as the PHAs have very high water barrier properties. Therefore, in principle, one could devise a biomass-derived, high barrier multilayer system where an inner layer of plasticized chitosan could be sandwiched between high moisture barrier PHA layers. An interesting property of some of these biobased polymers, e.g. PLA and starch, is that their permeability to carbon dioxide compared with that of oxygen (permselectivity) is higher than most conventional mineral oil-based plastics. This is of interest, for instance, in some food packaging applications where a high barrier to oxygen is required, but carbon dioxide generated by the product should be allowed to exit the package head space to avoid package swelling. Some of these materials, however, still suffer from high production costs and shortcomings in certain properties and so cannot compete with other conventional plastic materials now in the market. Figure 3.1 shows a general mastercurve representing oxygen permeability versus the fractional free volume/cohesive energy density ratio for a number of plastics and the gas barrier properties at dry conditions for the bioplastics families for comparison purposes. The data indicate that some proteins and polysaccharides have excellent barrier properties under dry conditions, comparable with EVOH; however, under humid conditions these properties deteriorate to a much larger extent than for EVOH. On the other hand, thermoplastic biopolymers such as PLA or PCL are not as strongly affected by moisture but have lower barrier properties than for instance the benchmark PET. It is therefore of great interest, as explained above, to make functional monolayer food packages that reduce the moisture sensitivity of proteins and polysaccharides and increase the gas barrier properties of thermoplastic biopolyesters.

100 Thermoplastic biopolymers

10 Dry proteins Polysaccharide

1

PET PO2

HDPE

1

PVC

PA

0.

PK

0.0

EVOH

High barrier

0.00 0

0.000

0.00

0.001

0.00

0.002

FFV/CED

Fig. 3.1 Oxygen permeability (PO2) (cc mm/m2 day atm) versus the fractional free volume(FFV)/cohesive energy density (CED) ratio for a number of polymers and biopolymers typically used in packaging applications.

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There are also a significant number of technological developments making use of existing materials and associated with modern packaging technologies aiming to tailor designs to specific performance and packagedproduct requirements. These developments include: (a) multilayer systems comprising various polymeric materials and made by lamination, coextrusion or co-injection; (b) aluminium metallized polymeric films obtained by vacuum deposition technologies; and (c) oxide (AlOx or SiOx)-coated polymeric films. Multilayer systems in the food packaging field usually consist of high gas barrier polymers like EVOH or polyamide (PA) sandwiched between structural layers of other polymers which usually provide the assembly with a high barrier to moisture as well as with other properties such as thermal, mechanical, optical or processing properties, printability, thermosoldability, etc. Coating plastics with vacuumdeposited aluminium aims to increase barrier properties to gases, moisture and organic vapours; it results in better flexibility, greater appeal to consumers and lower environmental impact due to the reduction in metal consumption and better recyclability compared with conventional lamination with aluminium foil. On the other hand, the metal coating of polymeric films imposes reductions in flexibility, stretchability and thermoformability compared with the performance of the polymer films alone. Moreover, aluminium coatings render the package opaque and cannot be microwaved. In order to circumvent these problems, oxide-coated polymer films can be obtained that exhibit transparency and high barrier properties, albeit they the coating is susceptible to microcracking during processing or handling. Apart from coatings, blending with other polymers and nanocomposites are the most commonly considered technologies in the manufacture of more efficient monolayer barrier systems for packaging.

3.4

Polymer blends: the case of permeable fillers

The blending of polymers is a feasible route for achieving the desired balance of properties by controlling the polymer phase interaction and/or morphology in monolayer barrier systems.33 The most commonly used method is to blend polymers with other polymers that have higher barrier properties. The barrier properties of these blends seem to follow a relationship (see equation [3.4]) that is in good general agreement with that proposed by Maxwell and extended by Roberson (see equation [3.4] and Fig. 3.2)34 for spheres of a low oxygen barrier phase (amorphous PA (aPA) in Fig. 3.2), but with higher water resistance, dispersed in a high oxygen barrier (EVOH in Fig. 3.2), continuous matrix which has a lower water resistance.35 This simple model would appear to closely reflect, albeit with a slight positive deviation (due to orientation, see Fig. 3.2), the case of the dispersed morphology found for this EVOH–PA blend.

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aPA Simple additivity O2

PO2 (m3m/m 2s Pa)

1 × 10–19

1 × 10–20

O2 O2

1 × 10–21 0.0

EVOH blends

Maxwell equation Co-extruded multilayer EVOH32 0.2

0.4

0.6

0.8

1.0

EVOH volume fraction in the blend

Fig. 3.2 Modelling of oxygen permeability (PO2) for various EVOH–aPA blend components facing the transport of oxygen gas and as a function of volume fraction of EVOH. As an example, experimental data (see arrow) for 80/20 EVOH–PA and EVOH–ionomer melt-mixed blends developed in our laboratories are also provided.

The EVOH–ionomer blend presents even better barrier properties than predicted from equation [3.4] due to the fact that the morphology of the particles is elongated (higher aspect ratio) in the machine direction and normal to the permeation direction.  P + 2PEVOH − 2VaPA ( PEVOH − PaPA )  PEVOH/aPA = PEVOH  aPA   PaPA + 2PEVOH + VaPPA ( PEVOH − PaPA ) 

[3.4]

The permeability of blends following equation [3.4] would then approach the permeability of a co-extruded multilayer (see equation [3.5]) system comprising two layers, one made of a lower barrier disperse phase and the other of a high barrier matrix; therefore, the overall permeability will be close to the permeability of the neat high barrier matrix for a sufficiently high volume fraction of the matrix (VEVOH). Equation [3.5] is a very favourable situation in terms of permeability for a non-miscible blend. PEVOH/aPA =

PEVOH PaPA VaPA PEVOH + VEVOH PaPA

[3.5]

The circles on the graph in Fig. 3.2 represent the values of permeability obtained by application of a simple additive rule (layers parallel to permeant flow, see equation [3.6]). This case would clearly be a very unfavourable situation in terms of permeability for blends.

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Thermoplastic nanobiocomposites for rigid and flexible packaging PEVOH/aPA = PEVOHVEVOH + PaPAVaPA

73 [3.6]

Figure 3.2 shows, as an example, some modelling for the barrier properties of EVOH–aPA blends as a function of blend composition and the orientation of the blend constituents in relation to the direction of oxygen transport. High barrier blends of EVOH with an ionomer and an amorphous polyamide have recently been developed in our laboratories.36,37 These blends show excellent barrier properties to gases compared with neat EVOH (see experimental values for EVOH 80/20 blends in Fig. 3.2), and yet much better thermoformability than EVOH alone for the production of thermoformed multilayer rigid food containers.35 Curiously, when the EVOH–aPA blend, which under dry conditions presented a lower barrier to oxygen, was subjected to typical packaged food water vapour sterilization (at 120 ºC for 20 min), it demonstrated better oxygen barrier properties than EVOH due the decreased water sensitivity of the system. There are also a relatively large number of blends reported in the literature where a high gas barrier polymer like EVOH was added to improve the barrier properties of a low gas barrier material and, conversely, where a high water barrier polymer was added to a high gas barrier material to reduce the relative humidity dependence in the barrier properties of the latter.36

3.5

Nanocomposites: the case of impermeable fillers

More recently, however, there has been a significant increase in the number of research works devoted to enhancing relevant polymer properties, mainly mechanical and barrier properties – but also surface hardness, UV-VIS (ultraviolet–visible light) protection, thermal stability and fire-retardancy – by means of nanotechnology. Nanotechnology is by definition the creation and utilization of structures with at least one dimension in the nanometrelength scale and which demonstrate novel properties and phenomena otherwise not displayed by either isolated molecules or bulk materials. Among the various existing nanotechnologies available, the one that has attracted the most attention in the food packaging field is inorganic layered nanocomposites. It has been broadly reported in the scientific literature that the addition of low loadings of nanolayered particles, with thickness in the nanometre scale and with high aspect ratios, to a raw polymer can have a profound enhancing effect on some material properties – such as mechanical properties, thermal stability, UV-VIS protection, conductivity, and gas and vapour barrier properties. Figure 3.3 shows typical modelling examples of permeability reductions in nanocomposites as a result of the application of the Nielsen and Fricke models (equation [3.5]) with different aspect ratios (L/W) to layered particles. The Nielsen model38 (see equation [3.7]), and other ulterior refinements such as that of Fredrickson and Bicerano,39 describe systems in which the

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L/W = 400, Nielsen L/W = 100, Nielsen O2 at 80% RH L/W = 100, Fricke L/W = 250, Fricke L/W = 400, Fricke d-Limonene

0.9 0.8 0.7 P/P0

0.6 0.5 0.4 0.3 0.2 0.1 0.0 0.00

0.02

0.04

0.06

0.08

0.10

Volume fraction of filler

Fig. 3.3 Theoretical permeability reduction and some experimental permeability reduction values to oxygen and limonene found in poly(hydroxybutyrate) (PHB) by the authors. RH, relative humidity. P0, permeability of the unfilled material.

layered – i.e. thin, flat and squared – particles are perfectly oriented with length and width perpendicular to the permeant transport direction and are homogeneously diluted in the polymer matrix. 1 − Vclay Pnano = Pneat 1 + L V clay 2W

[3.7]

where L/W is the aspect ratio of the platelets, Vclay is the volume fraction of the clay filler, Pnano is the permeability of the nanocomposite and Pneat is the permeability of the pure material. The Fricke model40 describes oblate randomly oriented spheroids uniformly distributed across the matrix. Pnano 1 − Vclay = τ Pneat W = L

[3.8] 1

Vclay / (τ − 1) 0.785 − 0.616 − [Vclay / (τ − 1)] + 3

[3.9]

In equation [3.8], t is the tortuosity factor, which increases with increasing impedance efficiency of the clay filler. Equation [3.9] shows, in this model, the relationship between the volume fraction of clay, the aspect ratio and the tortuosity factor.

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In this regard, gas and water vapour permeabilities have been found to decrease, in some cases to a large extent, in the nanocomposites due increased tortuosity factors, among other factors.41 For example, an ethylene propylene diene monomer (EPDM)–clay nanocomposite with a 4 wt% loading was found to decrease N2 permeability by 30% compared with EPDM alone.42 Oxygen permeability decreased by a factor of three in polyester–clay nanocomposites at 2.5 wt% loading. A 60% reduction in the water permeability was measured in a 5 wt% loaded poly(vinyl alcohol)– sodium montmorillonite (MMT) nanocomposite and the material still retained its optical clarity.43 In EVOH nanocomposites, reductions in oxygen permeability of more than 75% across a range of relative humidity values have been reported44,45 and reductions in water permeability of over 90% have also been reported in some proteins and polysaccharides.46 However, in general, the experimentally measured reductions in permeability have not been in full agreement with the values expected from modelling work for most systems, due to lack of complete exfoliation, insufficient compatibility, morphological alterations, penetrant solubility effects and other factors. Figure 3.4 shows the microstructure of a nanocomposite of PE containing nanolayers of NanoterTM (clay-based, food-contact approved, commercial clay grade of NanoBioMatters Ltd, Spain), in which a myriad of highly dispersed nanoshields constitute a definitive barrier to the passage of nondesirable permeants. Depending on barrier requirements, different particulate aspect ratios and modifications should be used. These one-dimensional nanoscale structures can display a high surface to volume ratio, which is ideal for applications that involve composite materials, chemical reactions, drug delivery, controlled and immediate release of substances in active and

100 nm

Fig. 3.4

Transmission electron micrograph of nanocomposites of HDPE.

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functional packaging technologies and energy storage, for instance in intelligent packaging.44 Until recently, the most interesting packaging technology based on blending to generate barrier properties was the so-called oxygen scavenger technology. This technology is known to lead to relatively low levels of oxygen in contact with the food because it traps permeated oxygen from both the headspace and the outside. However in, for example, carbonated beverages, a barrier to carbon dioxide is also required. As most commodity plastic packaging materials, e.g. PET and its main sustainable counterpart PLA, are not sufficient barriers to these gases, multilayer structures had to be devised in which one layer (made of EVOH, aliphatic polyamide resin (MXD6), polyethylenenaphthalate (PEN), nanocomposites of PA6, etc.) needed to be high barrier to carbon dioxide and to oxygen, while the scavenger reduces oxygen levels at the package headspace. Nanobiocomposites technology can overcome this in monolayer solutions since barrier properties usually appertain not only to oxygen but also to other gases and low molecular weight components such as water vapour and food aroma components. Despite the fact that multilayer solutions are currently needed in many food packaging applications, including the above-mentioned carbonated beverages, a monolayer solution would be of great interest for many reasons, including recyclability and technology and material costs. Nanocomposites technology can also make this possible by simple melt or solution blending routes. For example, in PET bottles, the reason that nanocomposites are still devised to be used in multilayer systems is because the PET nanocomposites are extremely difficult to obtain in a monolayer form due to the high temperatures needed to process the polymer, which cause degradation of the organophilic chemical modification of the layered clay particles. Some sort of modification of the inorganic layered particles is needed in nanocomposites to facilitate exfoliation of these into nanolayers during processing and also to enhance compatibility with the polymer. In spite of this, new commercial clay formulations exist that are capable of producing high barrier PET nanocomposites by direct blending without degradation issues, therefore making monolayer formulations for PET possible.47 Another situation where ultrahigh barrier properties are needed is in high barrier food packaging applications, such as aromatic products, retortable pouches, dehydrated products and vacuum and some modifiedatmosphere packaging applications. In these and other similar applications, aluminium, EVOH or other high barrier materials and technologies are being applied. However, all of the existing technologies have associated drawbacks of some kind. While this is so, it would for instance be highly desirable to enhance the barrier properties of EVOH by 10-fold across the whole humidity range, making the material virtually impermeable in dry

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conditions and capable of acting as a substitute for typical impermeable materials or technologies in many applications where transparency or more simple packaging structures represent added value. It is also a very important concern that most of the nanocomposite formulations (first-generation nanocomposites) on the market are currently making use of non-food-contact-permitted ammonium salts as organophilic chemical modifiers, and have been devised to enhance the properties of engineering polymers in structural applications. However, for food packaging applications only food-contact-approved materials and additives should be used, and should be incorporated at below their corresponding threshold migration levels. In this context, only the so-called secondgeneration nanocomposites claim to comply with the current food-contact legislation.46,48 Second-generation nanocomposites are therefore referred to as ‘nanocomposite formulations’; they are specifically designed to comply with current regulations and at the same time are cost-effective and specifically formulated to target specific materials (including biopolymers), materials properties or production technologies. In essence, second-generation nanocomposites are materials with targeted specifications rather than widespectrum generic formulations. Most applications of nanocomposites in plastics have made use of laminar clays and carbon nanotubes. However, there are other types of reinforcing elements, such as biodegradable fibres obtained by electrospinning, that are showing promise in a number of application fields.49,50 The electrospinning method is a simple and versatile technology that can generate ultrafine fibres, typically in the range of 50–500 cm3, of many materials. The fibres produced have a very large surface to mass ratio (up to 103 higher than a microfibre), excellent mechanical strength, flexibility and lightness. The procedure for obtaining these fibres is not mechanical but electrostatic and is applied to the polymer in solution or to polymer melts. As a result of the latter, it is a very suitable technique for the generation of ultrafine fibres of biodegradable materials, which are in general easy to dissolve.51 It has been reported that around 100 different polymers (including biopolymers) and polymer blends have been nanofabricated by electrospinning. In spite of the fact that there is a significant body of scientific literature reporting the characterization of nanofibres, there are not as many works reporting on the properties of nanocomposites made from materials containing these fibres. One of the most interesting aspects of the electrospinning methodology is the possibility of incorporating various substances, including fillers such as clays and also bioactive agents, in the electrospun fibres. The advantages of this nanotechnology have already been considered in the controlled release of bioactive principles in the pharmaceutical and biomedical fields and can also be applied to the controlled release of active and bioactive food packaging applications.

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3.6

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Nanobiocomposites for monolayer packaging: polylactic acid, polycaprolactone, polyhydroxyalkanoate and starch

Of the polymer–clay nanocomposite technologies, the case of the biocomposites containing biopolymers and clays is one of the most significant novel developments. The biopolymers typically considered for thermoplastic monolayer and also multilayer applications are PLA, PCL, PHA and starch. These materials have, however, a number of property shortcomings in terms of barrier, thermal and mechanical performance when compared with the conventional plastics currently used. The use of clay-based nanoadditives to boost their performance, particularly in barrier properties, is perhaps one of the most active areas of current and future research and, therefore, we pay special attention to reviewing the current status of the literature regarding the enhancement of barrier properties of thermoplastic biocomposites. For PLA, two techniques are frequently used to produce nanocomposites of this material, namely solution casting52,53 and melt mixing.54–63 The reports claim that, compared with neat PLA, the PLA nanocomposites show improvements in material properties such as storage modulus, flexural modulus, flexural strength, and heat distortion temperature, and also show improvements in gas barrier properties.60–73 Maiti et al.64 postulated that the barrier properties of non-interacting gases in nanocomposites primarily depend on two factors: one is the dispersed silicate particles’ aspect ratio and the other is the extent of the dispersion of these particles within the polymer matrix. When the degree of dispersion of the layered organoclay is at a maximum, an exfoliated morphology is attained and the barrier properties solely depend on the particles’ aspect ratio. Table 3.2 summarizes the reported improvements in oxygen and water permeability of the nanocomposites of PLA and of other thermoplastic biopolymers. Recently, Sinha Ray et al.61 claimed reductions in oxygen permeability of c. 65% for PLA + 4 wt% synthetic fluorine mica prepared by melt mixing. Nanocomposites with similar clay contents (4–7 wt%), but using a different kind of clay, showed less improvement in oxygen permeability, i.e. ranging from 6 to 56%.45,60,61,70,72,73 In summary, the barrier properties of PLA were found to depend strongly upon clay type, organic modification of the clay, clay content, clay aspect ratio, clay interfacial adhesion and clay dispersion. In the case of PHAs, Gardolinski et al.77 described the formulation of PHB nanocomposites. However, due to the high thermal instability of the polymer, the commercial applications of PHB have been extremely limited (see Table 3.2). Sanchez-Garcia et al.74 prepared nanocomposites of PHB and PCL by melt mixing with layered phyllosilicates based on commercial organomodified kaolinite and MMT clay additives. The addition of the PCL component to the blend was seen to reduce oxygen permeability and stiffness but it was also found to stabilize the PHB polymer during processing

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Table 3.2 Reductions (%) in oxygen and water vapour permeability reported for nanocomposites of thermoplastic biopolymers

Matrix

Type of clay

PLA60 PLA60 PLA60 PLA61 PLA61 PLA61 PLA61 PLA70 PLA44 PLA72 PLA73 PLA73 PLA73 PLA73

Organically modified MMT Organically modified MMT Organically modified MMT MMT MMT-modified Saponite Synthetic fluorine mica MMT-layered silicate MMT-modified Bentonite Hexadecylamine-MMT Hexadecylamine-MMT Hexadecylamine-MMT Dodecytrimetil ammonium bromide-MMT Dodecytrimetil ammonium bromide-MMT Dodecytrimetil ammonium bromide-MMT Cloisite 25A (organically modified MMT) Cloisite 25A (organically modified MMT) NanoterTM (organically modified MMT) NanoterTM (organically modified MMT) Organomodified kaolinite-MMT NanoterTM (organically modified MMT) NanoterTM (organically modified MMT) NanoterTM (organically modified MMT) Organically modified mica-type silicate Organically modified mica-type silicate Organically modified mica-type silicate Organically modified mica-type silicate Cloisite 30B (organically modified MMT)

PLA73 PLA73 PLA73 PLA73 PLA23,46 PLA23,46 PHB74 PHBV46 PHBV46 PHBV46 PCL75 PCL75 PCL75 PCL75 PCL76

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Clay content (%)

Reduction in O2 permeability (%)

Reduction in H2O permeability (%)

4 5 7 4 4 4 4 5 5 5 4 6 10 4

12 15 19 14 12 40 65 48 46 6 42 56 58 41

6

55

10

58

6

45

10

56

1

20

27

5

32

54

4

46

Dwater 72

50

1

61

5

60

5

28

52

1.1

11

2.5

39

3.6

59

4.8

80

2

35

80

Environmentally compatible food packaging

Table 3.2 Cont’d

Matrix

Type of clay

PCL76

Cloisite 30B (organically modified MMT) Cloisite 30B (organically modified MMT) Cloisite 93B (organically modified MMT) Cloisite 93B (organically modified MMT) Cloisite 93B (organically modified MMT) NanoterTM (organically modified MMT) NanoterTM (organically modified MMT) NanoterTM (organically modified MMT)

PCL76 PCL76 PCL76 PCL76 PCL23,48 PCL23,48 PCL23,48

Clay content (%)

Reduction in O2 permeability (%)

5

50

10

57

2

21

5

34

10

44

Reduction in H2O permeability (%)

1

47

5

63

10

63

and led to a finer dispersion of the clay. The study found that MMT clays can facilitate the degradation of the material and have therefore no commercial interest whereas kaolinite-based clays influence the inherent instability of the polymer to a much lower extent and can lead to property-enhanced nanobiocomposites. The study indicated that nanocomposites of PHB– PCL–kaolinite had better barrier properties to oxygen than the petroleumbased counterpart PET. The oxygen permeability was seen to be reduced by c. 43% at 0% relative humidity and by c. 46% at 80% relative humidity. The diffusion coefficient of water in the biocomposite was seen to drop by c. 72% compared with the unfilled polymer blend and the composites also exhibited higher barrier properties to limonene. Due to the above-mentioned instability of the PBH copolymer, researchers have mainly used lower melting temperature copolymers of PHB, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), with improved chemical stability and good physical properties but with lower barrier properties. Again, solution-casting78–80 and melt-mixing74,79,80–82 routes were explored for the nanocomposites of this biopolymer, Sanchez-Garcia et al.23,46,48 reported an improvement in oxygen permeability of c. 28% in melt-mixed and casting material, compared with the unfilled material. They also reported reductions in water permeability of c. 52 and 60% for films of PHBV with 1 and 5% clay, respectively. In the case of PCL, four methodologies have been used to prepare nanocomposites containing PCL, namely polymerization in situ,83–87 solution-

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casting,88 melt mixing75,76,89–96 and the master batch method.97 Table 3.2 summarizes the reported oxygen and water barrier improvements for these nanocomposites. Gorrasi et al.94 prepared nanocomposites of PCL with MMT by melt mixing. The barrier properties were studied for water vapour and dichloromethane as an organic solvent. Although the water sorption increased with increasing MMT content, the diffusion parameters of the samples showed much lower values in exfoliated systems. Messersmith et al.75 prepared nanocomposites with an organically modified mica-type silicate. The nanocomposite exhibited a significant reduction in water vapour permeability, which showed a linear dependence with silicate content. The significant decrease in water permeability observed for this system is of great importance in evaluating PCL and PCL nanocomposites for use in food packaging, protective coatings and other applications where efficient polymeric barriers are needed. The significant improvements in both barrier and mechanical properties of PCL nanocomposites could be attributed to the fine dispersion state of organoclay in the PCL matrix and the strong interaction between the organic modifier and the matrix. In starch, solution casting98–100 and melt mixing101–106 are also the nanocomposite technologies applied. In most cases, given the higher sensitivity of this material towards water sorption, attempts have been made to reduce water sorption in starch nanocomposites. Park et al.101,102 prepared nanocomposites of starch–organoclays by melt intercalation, with different natural MMT (Na+ MMT, Cloisite Na+) and different organically modified MMTs. The barrier properties to water vapour in the nanocomposites were found to be better than in the pure starch. In general, for the preparation of nanocomposites by solution casting the addition of a plasticizer has been considered a necessary condition. Kampeerapappun et al.98 prepared starch–MMT films by casting, using chitosan as a compatibilizing agent in order to disperse the clay in a starch matrix. Other nanocomposites99,100 of starch were prepared via different addition sequences of plasticizer and clay (Na+ MMT) by the solution method. Nanocomposites of starch with clay generally led to a decrease in hydrophilicity for the systems. Huang et al.103 and Huang and Yu105 prepared nanocomposites of starch– ethanolamine-activated MMT by melt mixing. From the results, the water absorption of the nanocomposites was also found to be reduced. Bagdi et al.104 prepared nanocomposites of thermoplastic starch and layered silicates organophilized with different surfactants, by the melt-mixing method. The equilibrium water uptake in an atmosphere of 50% relative humidity decreased by about 0.5–1.0% for composites containing 5 vol% silicate. The largest decrease in water adsorption was observed in the case of the neat Na+ MMT, for which laminate exfoliation was reported. De Carvalho et al.106 prepared nanocomposites with varying amounts of kaolin in thermoplastisized starch and observed a decrease in the water uptake of the nanocomposites.

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3.7

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Future trends and outlook

Several nanotechnologies are being trialled by an increasing number of material manufacturers and packaging converters. Nevertheless, for their wide commercial implementation and success they need to comply with current and future legislation and be designed to reach specific targets in materials and properties in specific food packaging applications. It is clear that there is still a lot of missing information in the food packaging sector regarding their use and potential in finished articles. However, the various nanotechnologies being currently developed will certainly have a wide range of applications given the fact that they make use of relatively inexpensive raw materials and that can have a strong impact on, among other factors, barrier, thermal and mechanical properties, without significant losses in impact resistance and while maintaining clarity. In the future, the above nanotechnologies will also have enormous potentials and synergies in new developments, for instance in providing intelligent, active and bioactive properties in addition to the current role as a passive barrier with enhanced thermal and mechanical performance.

3.8

Nomenclature

aPA EPDM EVOH HDPE LCP LDPE LLDPE MMT PA PAN PA6 PC PCL PE PET PHA PHB PHBV PK PLA PMMA PP PS

amorphous polyamide ethylene propylene diene monomer ethylene vinyl alcohol copolymers high-density polyethylene liquid crystal polymer low-density polyethylene linear low-density polyethylene montmorillonite polyamide polyacrylonitrile polyamide 6 (Nylon) polycarbonate polycaprolactone polyethylene polyethylene terephthalate polyhydroxyalkanoates poly(hydroxybutyrate) poly(3-hydroxybutyrate-co-3-hydroxyvalerate) aliphatic polyketone copolymers polylactic acid polymethyl methacrylate polypropylene polystyrene

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Thermoplastic nanobiocomposites for rigid and flexible packaging PVC PVDC PVOH

3.9

83

polyvinyl chloride polyvinylidene chloride polyvinyl alcohol

References

1 k. petersen, p.k. nielsen, g. bertelsen, m. lawther, m.b. olsen, n.h. nilsson, g. mortensen; ‘Potential of biobased materials for food packaging’, Trends in Food Science and Technology 10, 52–68 (1999). 2 v.k. haugaard, a.m. udsen, g. mortensen, l. hoegh, k. petersen, f. monahan; ‘Food biopackaging’, in Biobased Packaging Materials for the Food Industry – Status and Perspectives, Ed. C.J. Weber, European Concerted Action Report (2001). 3 i. arvanitoyannis, e. psomiadou, c.g. biliaderis, h. ogawa, h. kawasaki, o. nakayama; ‘Biodegradable films made from low density polyethylene (LDPE), ethylene acrylic acid (EAA), polycaprolactone (PLC) and wheat starch for food packaging applications: Part 3’, Starch/Stärke 49, 306 (1997). 4 j. reguera, j.m. lagaron, m. alonso, v. reboto, b. calvo, j.c. rodriguez-cabello; ‘Thermal behavior and kinetic analysis of the chain unfolding and refolding and of the concomitant nonpolar solvation and desolvation of two elastin-like polymers’, Macromolecules 36, 8470–8476 (2003). 5 m.f. koening, s.j. huang; ‘Biodegradable blends and composites of polycaprolactone and starch derivatives’, Polymer 36, 1877 (1995). 6 c. bastiolo, v. bellotti, g.f. del tredici, r. lombi, a. montino, r. ponti; International Patent Application WO 92/19680 (1992). 7 e.s. park, m.n. kim, j.s. yoon; ‘Grafting of polycaprolactone onto poly(ethyleneco-vinyl alcohol) and application to polyethylene-based bioerodable blends’, Journal of Polymer Science Part B: Polymer Physics, 40, 2561 (2002). 8 h. tsuji, t. yamada; ‘Blends of aliphatic polyesters. VIII. Effects of poly(llactide-co-ε-caprolactone) on enzymatic hydrolysis of poly(l-lactide), poly(εcaprolactone), and their blend films’, Journal of Applied Polymer Science 87, 412 (2003). 9 s. jacobsen, ph. degée, h.g. fritz, p.h. dubois, r. jérome; ‘Polylactide (PLA) – a new way of production’, Polymer Engineering and Science 39, 1311 (1999). 10 s. jacobsen, h.g. fritz; ‘Filling of poly(lactic Acid) with native starch’, Polymer Engineering and Science 36, 2799 (1996). 11 c.c. chen, j.y. chueh, h. tseng, h.m. huang, s.y. lee; ‘Preparation and characterization of biodegradable PLA polymeric blends’, Biomaterials 24, 1167 (2003). 12 h. möller, s. grelier, p. pardon, v.y. coma; ‘Antimicrobial and physicochemical properties of chitosan-HPMC-based films’, Journal of Agricultural and Food Chemistry, 52, 6585–6591 (2004). 13 d.s. cha, m.s. chinnan; ‘Biopolymer-based antimicrobial packaging: a review’, Critical Reviews in Food Science and Nutrition 44(4), 223–237 (2004). 14 y. wang, g.w. padua, ‘Water sorption properties of extruded zein films’, Journal of Agricultural and Food Chemistry 52(10), 3100–3105 (2004). 15 g. bureau, j.l. multon, Eds; Food Packaging Technology, Vol. 1 and Vol. 2, VCH Publishers Inc., New York (1995). 16 a.l. brody, k.s. marsh, Eds; The Wiley Encyclopedia of Packaging Technology, 2nd edn, John Wiley & Sons, New York (1997). 17 j.f. hanlon, r.j. kelsey, h.e. forcinio, Handbook of Package Engineering, 3rd edn, Technomic Publishing Co. Inc., Lancaster, PA (1998).

© 2008, Woodhead Publishing Limited

84

Environmentally compatible food packaging

18 j. crank, g.s. park, Eds; Diffusion in Polymers, Academic Press, New York, (1968). 19 z. zhang, i.j. britt, m.a. tung; ‘Water absorption in EVOH films and its influence on glass transition temperature’, Journal of Polymer Science: Part B: Polymer Physics 37, 691 (1999). 20 m.a. samus, g. rossi; ‘Methanol absorption in ethylene–vinyl alcohol copolymers: relation between solvent diffusion and changes in glass transition temperature in glassy polymeric materials’, Macromolecules 29, 2275 (1996). 21 g. rossi; ‘Macroscopic description of solvent diffusion in polymeric materials’, Trends in Polymer Science 4, 337 (1996). 22 w.j. koros, Ed.; Barrier Polymers and Structures, ACS Symposium Series 423, ACS, Washington, DC, p. 23 (1990). 23 d. cava, e. gimenez, r. gavara, j.m. lagaron; ‘Comparative performance and barrier properties of biodegradable thermoplastics and nanobiocomposites versus PET for food packaging applications’, Journal of Plastics Films and Sheeting 22, 265 (2006). 24 k. petersen, p.v. nielsen, m.b. olsen; ‘Physical and mechanical properties of biobased materials,’ Starch 53(8), 356 (2001). 25 s.k. young, g.c. gemeinhardt, j.w. sherman, r.f. storey, k.a. mauritz, d.a. schiraldi, a. polyakova, a. hiltner, e. baer; ‘Covalent and non-covalently coupled polyester–inorganic composite materials’, Polymer 43, 6101–6114 (2002). 26 i. olabarrieta, d. forsström, u.w. gedde, m.s. hedenqvist; ‘Transport properties of chitosan and whey blended with poly(ε-caprolactone) assessed by standard permeability measurements and microcalorimetry’, Polymer 42, 4401–4408 (2001). 27 r.h. boyd; ‘The modulus of the amorphous component in polyethylenes’, Polymer Engineering Science 19, 1010 (1979). 28 m. hedenqvist, a. angelstok, l. edsberg, p.t. larsson, u.w. gedde; ‘Diffusion of small-molecule penetrants in polyethylene – free-volume and morphology’, Polymer 37, 2887 (1996). 29 william andrew inc. Permeability and other Film Properties of Plastics. PDL Handbook Series, Plastics Design Library, New York (1995). 30 j.g. bonner, a.k. powell; Aliphatic polyketones as high barrier materials. 213th National American Chemical Society Meeting, ACS Materials Chemistry Publications, Washington, DC (1997). 31 j.m. lagaron, a.k. powell; ‘Polyketones having improved barrier properties’, Patent WO 0042089 (2000). 32 c.j. weber, v. haugaard, r. festersen, g. bertelsen; Food Additives and Contaminants 19, 172 (2002). 33 d.r. paul, c.b. bucknall, Eds; Polymer Blends, Vol. 2: Performance, John Wiley & Sons, New York (2000). 34 h.b. hopfenberg, d.r. paul; in Polymer Blends, D.R. Paul, S. Newman, Eds. Academic Press, New York (1978). 35 j.m. lagaron, e. gimenez, v. del-valle, b. altava, r. gavara; ‘Characterization of extruded ethylene–vinyl alcohol copolymer based barrier blends with interest in food packaging applications’, Macromolecular Symposia 198, 473 (2003). 36 j.m. lagaron, e. gimenez, r. gavara, j.j. saura; ‘Study of the influence of water sorption in pure components and binary blends of high barrier ethylene–vinyl alcohol copolymer and amorphous polyamide and nylon-containing ionomer’, Polymer 42, 9531 (2001). 37 j.m. lagaron, e. gimenez, j.j. saura, r. gavara; ‘Phase morphology, crystallinity and mechanical properties of binary blends of high barrier ethylene–vinyl

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Thermoplastic nanobiocomposites for rigid and flexible packaging

38 39 40 41 42 43 44 45 46

47 48

49 50 51 52 53 54 55

85

alcohol copolymer and amorphous polyamide and a polyamide-containing ionomer’, Polymer 42, 7381 (2001). l.e. nielsen; ‘Models for the permeability of filled polymer systems’, Journal of Macromolecular Sciences (Chemistry) A1, 929–942 (1967). g.h. fredrickson, j. bicerano; ‘Barrier properties of oriented disk composites’, Journal of Chemistry and Physics 110, 2181–2188 (1999). m. krook, g. morgan, m.s. hedenqvist; ‘Barrier and mechanical properties of injection molded montmorillonite/polyesteramide nanocomposites; ‘Polymer Engineering and Science 45, 135–141 (2005). r.k. bharadwaj, a.r. hehrabi, c. hamilton, c. trujillo, m. murga, r. fan, a. chavira, a.k. thompson; ‘Structure–property relationships in cross-linked polyester-clay nanocomposites’, Polymer 43, 3699 (2002). a. usuki, a. tukigase, m. kato ‘Preparation and properties of EPDM–clay hybrids’ Polymer 43, 2185 (2002). k.e. strawhecker, e. manias; ‘Structure and properties of poly(vinyl alcohol)/ Na+ montmorillonite nanocomposites’, Chemistry of Materials 12, 2943 (2000). j.m. lagaron, d. cava, l. cabedo, r. gavara, e. gimenez; ‘Improving packaged food quality and safety. Part 2: nanocomposites’, Food Additives and Contaminants 22(10), 994–998 (2005). l. cabedo, e. giménez, j.m. lagaron, r. gavara, j.j. saura; ‘Development of EVOH–kaolinite nanocomposites’, Polymer 45(15), 5233–5238 (2004). j.m. lagaron, e. gimenez, m.d. sánchez-garcía, m.j. ocio, a. fendler; ‘Novel nanocomposites to enhance quality and safety of packaged foods’ in Food Contact Polymers 2007, Rapra Technologies, Shawbury, Shrewsbury, UK, paper 19 (2007). m.d. sanchez garcia, e. gimenez, j.m. lagaron; ‘Novel PET nanocomposites with enhanced barrier performance of interest in food packaging applications’, in ANTEC’07 Conference Proceedings, May, Cincinnati, Ohio (2007). j.m. lagaron, e. gimenez, m.d. sánchez-garcía, m.j. ocio, a. fendler; Technical Session, in The 15th IAPRI World Conference on Packaging, International Association of Packaging Research Institutes, Japan Packaging Institute, Tokyo, Japan (2006). i.s. chronakis; ‘Novel nanocomposites and nanoceramics based on polymer nanofibers using electrospinning process – a review’, Journal of Materials Processing Technology 167(2/3), 283–293 (2005). z.m. huang, y.z. zhang, m. kotaki, s. ramakrishna; ‘A review on polymer nanofibers by electrospinning and their applications in nanocomposites’, Composites Science and Technology 63(15) 2223–2253 (2003). s. torres-giner, e. gimenez, j.m. lagaron; ‘Characterization of the morphology and thermal properties of zein prolamine nanostructures obtained by electrospinning’, Food Hydrocolloids 22, 601–614 (2008). n. ogata, g. jimenez, h. kawai, t. ogihara; ‘Structure and thermal/mechanical properties of poly(l-lactide)-clay blend,’ Journal of Polymer Science Part B: Polymer Physics 35, 389–396 (1997). s. bandyopadhyay, r. chen, e.p. giannelis; ‘Biodegradable organic–inorganic hybrids based on poly(l-lactide)’, Polymer Materials Science and Engineering 81, 159–160 (1999). s. sinha ray, k. yamada, m. okamoto, k. ueda; ‘New polylactide/layered silicate nanocomposite: a novel biodegradable material’, Nano Letters 2, 1093–1096 (2002). s. sinha ray, p. maiti, m. okamoto, k. yamada, k. ueda; ‘New polylactide/layered silicate nanocomposites. 1. Preparation, characterization and properties’, Macromolecules 35, 3104–3110 (2002).

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Environmentally compatible food packaging

56 s. sinha ray, k. yamada, a. ogami, m. okamoto, k. ueda; New polylactide layered silicate nanocomposite: nanoscale control of multiple properties’, Macromolecular Rapid Communications 23(16), 943–947 (2002). 57 s. sinha ray, k. yamada, m. okamoto, a. ogami, k. ueda; ‘New polylactide/layered silicate nanocomposites. 3. High performance biodegradable materials’, Chemistry of Materials 15, 1456–1465 (2003). 58 s. sinha ray, m. okamoto, k. yamada, k. ueda; ‘New polylactide/layered silicate nanocomposites: concurrent improvement of materials properties and biodegradability’, in Proceedings of Nanocomposites 2002, San Diego, CA (2002). 59 k. yamada, k. ueda k, s. sinha ray, m. okamoto; ‘Preparation and properties of polylactide/layered silicate nanocomposites’, Kobunshi Robunshu 59, 760–765 (2002). 60 s. sinha ray, k. yamada, m. okamoto, k. ueda ‘New polylactide/layered silicate nanocomposites. 2. Concurrent improvements of material properties, biodegradability and melt rheology’, Polymer 44, 857–866 (2003). 61 s. sinha ray, k. yamada, m. okamoto, y. fujimoto, a. ogami, k. ueda; ‘New polylactide/layered silicate nanocomposites: 5. Designing of materials with desired properties’, Polymer 44(21), 6633–6646 (2003). 62 s. sinha ray, m. okamoto; ‘Biodegradable polylactide/layered silicate nanocomposites: open a new dimension for plastics and composites’, Macromolecular Rapid Communications 24, 815–840 (2003). 63 s. sinha ray, k. yamada, m. okamoto, k. ueda; ‘Biodegradable polylactide/ montmorillonite nanocomposites’, Journal of Nanoscience and Nanotechnology 3, 503–550 (2003). 64 p. maiti, k. yamada, m. okamoto, k. ueda, k. okamoto; ‘New polylactide/layered silicate nanocomposites: role of organoclays’, Chemistry of Materials 14(11), 4654–4661 (2002). 65 t.-m. wu, m.-f. chiang; ‘Fabrication and characterization of biodegradable poly(lactic acid)/layered silicate nanocomposites’, Polymer Engineering and Science 45(12), 1615–1621 (2005). 66 m. shibata, y. someya, m. orihara, m. miyoshi; ‘Thermal and mechanical properties of plasticized poly(l-lactide) nanocomposites with organo-modified montmorillonites’, Journal of Applied Polymer Science 99(5), 2594–2602 (2005). 67 a. hasook, s. tanoue, y. iemoto, t. unryu; ‘Characterization and mechanical properties of poly(lactic acid)/poly(ε-caprolactone)/organoclay nanocomposites prepared by melt compounding’, Polymer Engineering and Science, 46(8), 1001–1007 (2006). 68 m.a. paul, m. alexandre, p. degee, c. henrist, a. rulmont, p. dubois; ‘New nanocomposite materials based on plasticized poly(l-lactide) and organomodified montmorillonites: thermal and morphological study’, Polymer 44, 443–450 (2003). 69 m.a. paul, m. alexandre, p. degee, c. calberg, r. jerome, p. dubois; ‘Exfoliated polylactide/clay nanocomposites by in situ coordination–insertion polymerization’, Macromolecular Rapid Communications 24, 561–566 (2003). 70 c. thellen, c. orroth, d. froio, d. ziegler, j. lucciarini, r. farrell, n.a. d’souza, j.a. ratto; ‘Influence of montmorillonite layered silicate on plasticized poly(l-lactide) blown films’, Polymer 46(25), 11716–11727 (2005). 71 g. gorrasi, l. tammaro, v. vittoria, m.a. paul, m. alexandre, p. dubois, ‘Transport properties of water vapor in polylactide/montmorillonite nanocomposites,’ Journal of Macromolecular Science and Physics B 43(3), 565–575.

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72 l. petersson, k. oksman; ‘Biopolymer based nanocomposites: comparing layered silicates and microcrystalline cellulose as nanoreinforcement’, Composites Science and Technology 66(13), 2187–2196 (2006). 73 j.-h. chang, y.u. an, g. s. sur; ‘Poly(lactic acid) nanocomposites with various organoclays. I. Thermomechanical properties, morphology, and gas permeability’, Journal of Polymer Science Part B: Polymer Physics 41, 94–103 (2003). 74 m.d. sanchez-garcia, e. gimenez, j.m. lagaron; ‘Morphology and barrier properties of novel nanobiocomposites of bacterial poly(3-hydroxybutyrate), poly(ε-caprolactone) and layered silicates’, Polymer International in press, (2007). 75 p.b.messersmith,e.p.giannelis; ‘Synthesis and barrier properties of poly(epsiloncaprolactone)-layered silicate nanocomposite’, Journal of Polymer Science Part A: Polymer Chemistry 33(7), 1047–1057 (1995). 76 y.w. di, s. iannac, l. sanguigno; ‘Barrier and mechanical properties of poly(caprolactone)/organoclay nanocomposites’, Macromolecular Symposium 228, 115–124 (2005). 77 j.e. gardolinski, l.c.m. carrera, m.p. cantao, f. wypych; ‘Layered polymerkaolinite nanocomposites’, Journal of Materials Science 35(12), 3113–3119 (2000). 78 g.x. chen, g.j. hao, t.y. guo, m.d. song, b.h. zhang; ‘Crystallization kinetics of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/clay nanocomposites’, Journal of Applied Polymer Science 93, 655–661 (2004). 79 g.x. chen, g.j. hao, t.y. guo, m.d. song, b.h. zhang; ‘Structure and mechanical properties of poly(3-hydroxybutyrateco-3-hydroxyvalerate) (PHBV)/clay nanocomposites’, Journal of Materials Science Letters 21, 1587– 1589 (2002). 80 s.f. wang, c.j. song, g.x. chen, t.y. guo, j. liu, b.h. zhang, s. takeuchi; ‘Characteristics and biodegradation properties of poly(3-hydroxybutyrateco-3-hydroxyvalerate)/organophilic montmorillonite (PHBV/OMMT) nanocomposite’, Polymer Degradation and Stability 87(1), 69–76 (2005). 81 p. maiti, c.a. batt, e.p. giannelis; ‘Renewable plastics: synthesis and properties of PHB nanocomposites’, Polymer Materials Science and Engineering 88, 58–59 (2003). 82 w.m. choi, t.w. kim, o. ok. park, y.k. chang, j.w. lee; ‘Preparation and characterization of poly(hydroxybutyrateco-hydroxyvalerate)– organoclay nanocomposites’, Journal of Applied Polymer Science 90, 525–529 (2003). 83 p.b. messersmith, e.p. giannelis; ‘Polymer-layered silicate nanocomposites: in situ intercalative polymerization of ε-caprolactone in layered silicates’, Chemistry of Materials 5, 1064–1066 (1993). 84 d. knani, a.l. gutman, d.h. kohn; ‘Enzymatic polyesterification in organic media. Enzyme-catalyzed synthesis of linear polyesters. I. Condensation polymerization of linear hydroxyesters. II. Ringopening polymerization of ε-caprolactone’, Journal of Polymer Science Part A: Polymer Chemistry 31, 1221–1232 (1993). 85 a.s. sawhney, p.p. chandrashekhar, j.a. hubbell; ‘Bioerodible hydrogels based on photopolymerized poly(ethylene glycol)-co-poly(a-hydroxy acid) diacrylate macromers’, Macromolecules 26, 581–587 (1993). 86 p. cerrai, m. tricoli, f.a.m. paci; ‘Polyether–polyester block copolymers by noncatalysed polymerization of ε-caprolactone with poly(ethylene glycol)’, Polymer 30, 338–343 (1989). 87 d.r. wilson, r.g. beaman; ‘Cyclic amine initiation of polypivalolactone’, Journal of Polymer Science Part A: Polymer Chemistry 8, 2161–2170 (1970).

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88 g. jimenez, n. ogata, h. kawai, t. ogihara; ‘Structure and thermal/mechanical properties of poly(ecaprolactone)–clay blend,’ Journal of Applied Polymer Science 64, 2211–2220 (1997). 89 y. di, s. iannace, e.d. maio, l. nicolais; ‘Nanocomposites by melt intercalation based on polycaprolactone and organoclay’, Journal of Polymer Science Part B: Polymer Physics 41, 670–678 (2003). 90 b. lepoittevin, m. devalckenaere, n. pantoustier, m. alexandre, d. kubies, c. calberg, r. jerome, p. dubois; Poly(ecaprolactone)/clay nanocomposites prepared by melt intercalation: mechanical, thermal and rheological properties’, Polymer 43, 4017–4023 (2002). 91 i. gonzalez, j.i. eguiazabal, j. nazabal; ‘New clay-reinforced nanocomposites based on a polycarbonate/polycaprolactone blend’, Polymer Engineering and Science 46(7), 864–873 (2006). 92 l. cabedo, j.l. feijoo, m.p. villanueva, j.m. lagaron, e. gimenez; Optimization of biodegradable nanocomposites based on aPLA/PCL blends for food packaging applications’, Macromolecular Symposium 233, 191–197 (2006). 93 b.q. chen, j.r.g. evans; ‘Poly(epsilon-caprolactone)–clay nanocomposites: structure and mechanical properties’, Macromolecules 39(2), 747–754 (2006). 94 g. gorrasi, m. tortora, v. vittoria, e. pollet, b. lepoittevin, m. alexandre, p. dubois; ‘Vapor barrier properties of polycaprolactone montmorillonite nanocomposites: effect of clay dispersion’, Polymer 44(8), 2271–2279 (2003). 95 m. avella, f. bondioli, v. cannillo; ‘Preparation, characterisation and computational study of poly(epsilon-caprolactone) based nanocomposites’, Materials Science and Technology 20(10), 1340–1344 (2004). 96 g. gorrasi, m. tortora, v. vittoria, e. pollet, m. alexandre, p. dubois; ‘Physical properties of poly(epsilon-caprolactone) layered silicate nanocomposites prepared by controlled grafting polymerization’, Journal of Polymer Science Part B: Polymer Physics 42(8), 1466–1475 (2004). 97 b. lepoittevin, n. pantoustier, m. devalckenaere, m. alexandre, c. calberg, r. jerome,c.henrist,a.rulment,p.dubois; ‘Polymer/layered silicate nanocomposites by combined intercalative polymerization and melt intercalation: a master batch process’, Polymer 44, 2033–2040 (2003). 98 p. kampeerapappun, d. aht-ong, d. pentrakoon, k. srikulkit; ‘Preparation of cassava starch/montmorillonite composite film’, Carbohydrate Polymers 67(2), 155–163 (2007). 99 j.k. pandey, r.p. singh; ‘Green nanocomposites from renewable resources: Effect of plasticizer on the structure and material properties of clay-filled starch’, Starch/Stärke 57(1), 8–15 (2005). 100 h.-m. wilhelm, m.-r. sierakowski, g.p. souza, f. wypych; ‘Starch films reinforced with mineral clay’, Carbohydrate Polymers 52(2), 101–110 (2003). 101 h.-m. park, w.-k. lee, c.-y. park, w.-j. cho, c.-s. ha; ‘Environmentally friendly polymer hybrids part I. Mechanical, thermal, and barrier properties of thermoplastic starch/clay nanocomposites’, Journal of Materials Science 38(5), 909–915 (2003). 102 h.-m. park, x. li, c.-z. jin, c.-y. park, w.-j. cho, c.-s. ha; ‘Preparation and properties of biodegradable thermoplastic starch/clay hybrids’, Macromolecular Materials and Engineering 287(8), 553–558 (2002). 103 m.-f. huang, j.-g. yu, x.-f. ma, p. jin; ‘High performance biodegradable thermoplastic starch – EMMT nanoplastics’, Polymer 46(9), 3157–3162 (2005). 104 k. bagdi, p. muller, b. pukánszky; ‘Thermoplastic starch/layered silicate composites: structure, interaction, properties’, Composite Interfaces 13(1), 1–17 (2006).

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105 m. huang, j. yu; ‘Structure and properties of thermoplastic corn starch/ montmorillonite biodegradable composites’, Journal of Applied Polymer Science 99(1), 170–176 (2006). 106 a.j.f. de carvalho, a.a.s. curvelo, j.a.m. agnelli; ‘A first insight on composites of thermoplastic starch and kaolin’, Carbohydrate Polymers 45(2), 189–194 (2001).

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4 Improved fibre-based packaging for food applications J. Poustis, JPC Packaging Institute, France

4.1

Introduction

Demand for packaging for foodstuffs has soared as the agro-food industry has filled the space between agriculture and the consumer, first in the location of food processing, for example the move of butter production from farm to factory and also, more recently, in the development of pre-cooked and ready-to-heat meals. The rise in the numbers of restaurants and fastfood outlets has led to further industrialization in the food production line, and to changes in the cooking equipment used in homes. The packaging sector in Europe is estimated to produce 3 million tonnes of material per annum, and is becoming increasingly important in the agro-food and mass retailing industries – the mainstays of the food and drink sector. Food safety and quality are of paramount importance to consumers, manufacturers and regulators. Both can be influenced by the appropriateness of the packaging used and its performance throughout the logistics chain. Further development in the sector is likely to be fuelled by the higher safety standards for food and drink packaging required by EU regulations. Plastics account for 42% of total packaging materials used in Europe, followed by paper and cardboard (30%), glass (10%), steel (9%), aluminium (4.5%) and wood (3.6%). The use of plastic packaging is constantly increasing. Glass is used primarily for the beer market, particularly in the accession states, and the use of wood packaging remains small in all countries (source: http://www.foodproductiondaily.com) Some examples of packaging, taken from reference 1, are shown in Figs 4.1 to 4.3. Security, product protection, longer shelf-life and presentation are the basic requirements for packaging in the food industry. Among plastics,

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Fig. 4.1 Packaging in microflute for beer cans.

Fig. 4.2

Large range of packaging used for pet foods, from Nestlé Purina.

shrink bags and thermoformed packaging meet all of these requirements. Shrink bags have perfect shrinkage even at low temperatures, form an impermeable barrier and have a high-gloss surface printable in up to eight colours on either side. Thermoformed packaging materials represent the latest sensation. They lend themselves to transparent or glossy colours and high-quality product presentation, creating outstanding differentiation on the shelf. They are microwaveable and pasteurizable, and provide a highly impermeable barrier. They promote a long shelf-life and come in customized shapes and colours. Fibre-based packaging fulfils two main functions: • it acts as a protective and/or structural entity, particularly important in the distribution of goods; • it can display printed information. The basic function of fibreboard packaging is to protect products during distribution, right up to the point that the product is removed from the

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Fig. 4.3

Palletization of boxes.

Fig. 4.4 Regular slotted container for bottles of mineral water.

package by the consumer or user. The growing use of palletization (see Fig. 4.3) in distribution requires corrugated boxes with good stackability. Corrugated board is by far the commonest type of paper-based packaging in terms of tonnage, and is suitable for achieving high stackability. It has a lightweight rigid structure composed of liners separated by corrugated fluting papers. The pack shown in Fig. 4.4 is known as a regular slotted container. Issues in designing packaging for transport include positioning of the products within the packaging and cost-effectiveness in relation to packing and distribution logistics. Fibre-based board boxes are erected and packed manually or automatically. The packaging can be erected, filled and closed, or formed around the product and closed. Packaging today is not just about protecting and transporting products, but also about advertising and brand promotion. Printing technologies have been developed for packaging to take advantage of its potential as a communication medium, carrying information and artwork. The attractiveness of the print can be decisive in catching the customer’s eye. Of the total European production of corrugated board, 32% is used for food packaging, including transport packaging. If beverage packaging is included, this rises to 40% of the total European production. A significant

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Others 16 % Bakery and confectionery 7 %

Meat 10 % Frozen 7 %

Fig. 4.5

Fruit and vegetables 60 %

Corrugated board packaging in contact with food, data for Europe (source: FEFCO, Avenue Louise 250 B, 1050 Brussels).

proportion is used in direct contact packaging, but most of the applications are for trays for fruit and vegetables (Fig. 4.5). The volumes of corrugated board used for contact packaging vary widely by country across Western Europe, but in some areas may be as high as 20% of total production. The proportion of corrugated board used for other direct food-contact applications are for fatty/aqueous foodstuffs (pizza, burgers, french fries as fast food, fresh meat, poultry and fish), and for dry/frozen foodstuffs (bread, frozen meat, poultry and fish). Although a significant proportion of the total tonnage is not covered by legislation on direct food contact, some of this proportion may still be used in applications where food safety is critical.

4.2

Properties and uses of fibre-based food packaging

4.2.1 Standard properties Paper properties The papers used in the board industry are made from wood virgin fibres or from recovered papers. Packaging papers are defined by their structural properties, their mechanical properties and their water sensitivities. The basic properties of papers used in corrugated board are described in Table 4.1. Packaging properties The basic function of paper-based packaging is the same as for any packaging, namely to protect products during distribution up until purchase and use. Performance in areas such as stacking height or content protection are evaluated through various measurements (see Fig. 4.6); the most wellknown of these are described in Table 4.2.

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Table 4.1 Basic properties of papers Properties

Characterization

Nature of fibre Grammage Thickness Sheet density Strength Surface Orientation Water sensitivity

Virgin or recycled Basis weight (g/m²) Microns Porosity, IBT Burst, stiffness, compression, etc. Smoothness, brightness, gloss, etc. Machine/crossdirection Cobb, repellancy, etc.

IBT, internal bond test. Source: Poastis (2005).2

Table 4.2 Basic properties of packaging papers Properties

Characterization

Design Weight Stability Strength Surface Communicative Water sensitivity

Dimensions Grammage (g) Creep, fatigue Burst, stiffness, vertical compression Brightness, gloss, etc. Bar code, RFID Absorbance

Radio-frequency identification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. An RFID tag is an object that can be applied to or incorporated into a packaging for the purpose of identification using radiowaves. Some tags can be read from several metres a