Green composites for automotive applications 9780081021774, 0081021771

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Green Composites for Automotive Applications

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Woodhead Publishing Series in Composites Science and Engineering

Green Composites for Automotive Applications

Edited by Georgios Koronis Arlindo Silva International Design Centre Singapore University of Technology and Design Singapore

Woodhead Publishing is an imprint of Elsevier The Officers’ Mess Business Centre, Royston Road, Duxford, CB22 4QH, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, OX5 1GB, United Kingdom Copyright Ó 2019 Elsevier Ltd. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-08-102177-4 For information on all Woodhead Publishing publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Matthew Deans Acquisition Editor: Gwen jones Editorial Project Manager: Lindsay Lawrence Production Project Manager: Sojan P. Pazhayattil Cover Designer: Greg Harris Typeset by TNQ Technologies

Contents Contributors Preface

xi xv

Part I Processing and characterization of green composites 1.

Surface modification of natural fibers in polymer composites Diana P. Ferreira, Juliana Cruz and Raul Fangueiro 1.1 1.2 1.3 1.4

1.5

1.6 1.7

2.

Introduction Properties of natural fibers Surface modification techniques 1.3.1 Physical methods 1.3.2 Chemical methods Physical and chemical methods as treatments for natural fiber polymer composites (NFPCs) 1.4.1 Effects of plasma treatment on NFPCs 1.4.2 Natural fibersdchemical treatments and their influence on NFPCs Biological methods as an alternative to chemical/physical treatments 1.5.1 Enzymatic treatment 1.5.2 Fungal treatment 1.5.3 Bacterial cellulose coating Nanoparticles deposition/functionalization Concluding remarks and future trends References

3 6 6 10 15 20 20 23 28 29 30 30 31 32 33

Flammability performance of biocomposites Maya Jacob John 2.1 2.2

Introduction Flammability testing techniques 2.2.1 Cone calorimetry 2.2.2 Pyrolysis combustion flow calorimetry 2.2.3 Limiting oxygen index

43 44 44 45 45

v

vi Contents

2.3 2.4

2.2.4 Underwriters laboratories 94 (UL94) 2.2.5 Ohio State University heat release apparatus (OSU) Case studies 2.3.1 Biopolymers and biocomposites 2.3.2 Use of green flame retardants Conclusions References

46 47 47 47 54 56 56

Part II Thermosetting and thermoplastic materials for structural applications 3.

Green thermoset reinforced biocomposites Samson Rwahwire, Blanka Tomkova, Aravin Prince Periyasamy and Bandu Madhukar Kale 3.1 3.2

3.3

4.

Introduction Vegetable oil resins and composites 3.2.1 Linseed oil thermoset composites 3.2.2 Soybean oil thermoset composites 3.2.3 Wheat gluten matrix composites 3.2.4 Castor oil resin composites 3.2.5 Bio-based polyurethanes 3.2.6 Cashew shell nut liquid 3.2.7 Zein matrix composites 3.2.8 Green epoxy composites Conclusion and challenges References Further reading

61 64 65 65 68 69 70 71 73 75 75 76 80

Green composites in automotive interior parts: a solution using cellulosic fibers N.C. Loureiro and J.L. Esteves 4.1 4.2 4.3 4.4 4.5

Introduction Natural fibers Green composites in the automotive industry Case study 4.4.1 Materials used Conclusions References Further reading

81 82 84 85 85 95 96 97

Contents vii

5.

Eco-impact assessment of a hood made of a ramie reinforced composite G. Koronis and A. Silva 5.1 5.2

5.3 5.4

6.

Introduction Materials and methods 5.2.1 Functional unit and boundary conditions for the hood 5.2.2 Natural fiber incorporation (ramie reinforcement) and alternative approaches to manufacturing 5.2.3 Materials, manufacture, end of life Results and discussion Conclusions References

99 101 102 103 104 106 111 112

Production and modification of nanofibrillated cellulose composites and potential applications Md Nazrul Islam and Fatima Rahman 6.1 6.2 6.3

6.4

6.5 6.6

6.7 6.8

Introduction Cellulose and nanocellulose 6.2.1 Architecture of cellulose 6.2.2 Structures and size of nanocellulose Pretreatment of biomass fibers 6.3.1 Enzyme 6.3.2 Alkaline-acid 6.3.3 Ionic liquids Isolation of nanofibrillated cellulose 6.4.1 Homogenization 6.4.2 Grinding 6.4.3 Ultrasonication 6.4.4 Electrospinning 6.4.5 Cryocrushing 6.4.6 Steam explosion 6.4.7 Ball milling Drying of nanofibrillated cellulose Modifications of nanofibrillated cellulose 6.6.1 Acetylation 6.6.2 Silylation 6.6.3 Application of coupling agents 6.6.4 Grafting Applications of nanofibrillated cellulose 6.7.1 General applications 6.7.2 Applications in automobile industry Conclusion References

115 116 117 118 119 119 121 121 122 122 123 123 124 125 125 126 126 126 127 128 130 130 131 131 132 133 133

viii Contents

Part III Nanomaterials and additive manufacturing composites 7.

Nanocomposites with nanofibers and fillers from renewable resources N. Saba, M. Jawaid and M. Asim 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10

8.

Introduction Nanomaterials Renewable nanomaterials Advantages over micro-sized particles 7.4.1 Nanoclays 7.4.2 Nanocellulose Applications of renewable materials Polymer composites Polymer nanocomposites 7.7.1 Characterization and applications of nanocomposites Renewable nanomaterialebased polymer nanocomposites Applications of nano fillers or nanofibers reinforced polymer nanocomposites Conclusions Acknowledgment References

145 146 147 148 148 149 154 154 157 157 158 161 162 162 163

3D printing technologies and composite materials for structural applications Rajkumar Velu, Felix Raspall and Sarat Singamneni 8.1 8.2 8.3 8.4 8.5

9.

Introduction 3D printing technologies Composites and its properties for fabrications 8.3.1 Challenges for 3D printing material properties 3D printing of composite materials 8.4.1 3D printing of green composite materials Conclusion and future directions References

171 174 177 179 183 189 190 190

Biocomposites: present trends and challenges for the future Malladi Nagalakshmaiah, Sadaf Afrin, Rajini Priya Malladi, Saı¨d Elkoun, Mathieu Robert, Mohd Ayub Ansari, Anna Svedberg and Zoheb Karim 9.1 9.2

Introduction Reinforcement phase

197 199

Contents

9.3

9.4 9.5

9.6 9.7

Polymer matrices 9.3.1 Renewable source 9.3.2 Mixed source 9.3.3 Fossil fuelebased source Bio-composites processing and properties 9.4.1 Processing techniques 9.4.2 Improved properties Bionanocomposites 9.5.1 Lignin-based bionanocomposites 9.5.2 Hemicellulose-based bionanocomposites 9.5.3 Nanocellulose-based bionanocomposites Challenges 9.6.1 Challenges at industrial scale Conclusion References

ix 201 201 202 202 202 202 202 203 206 206 207 208 209 210 211

Part IV Life cycle assessment and risk analysis 10.

Risk-sensitive life cycle assessment of green composites for automotive applications U. Go¨tze, P. Pec¸as, H.M. Salman, J. Kaufmann and A. Schmidt 10.1 10.2

10.3 10.4

10.5 10.6

11.

Introduction Green composites and their LCA: a review 10.2.1 Green composites based on natural fibers 10.2.2 Advantages and disadvantages of natural fiber-based composites 10.2.3 LCA of Green Composites Modeling risks of LCA and their management 10.3.1 Modeling risks 10.3.2 Management of modeling risks Real-world risks of green composites and their management 10.4.1 Real-world risks of green composites 10.4.2 Management of real-world risks Example from the Automotive Industry Conclusion References

219 221 221 225 228 233 233 236 239 239 241 243 246 247

Ramie and jute as natural fibers in a composite partda life cycle engineering comparison with an aluminum part P. Pec¸as, I. Ribeiro, H. Carvalho, A. Silva, H.M. Salman and E. Henriques 11.1

Introduction 11.1.1 The need to be greener 11.1.2 Motivation and contribution

254 254 254

x Contents 11.2

11.3

11.4

11.5 11.6

12.

Background 11.2.1 Natural fibers and green composites 11.2.2 Industrial applications of natural fibers 11.2.3 Life cycle analysis and case studies from literature Bonnet case study 11.3.1 Means and methods 11.3.2 Materials and assumptions 11.3.3 Requirements and FEM analysis Life cycle studies of different alternatives 11.4.1 Raw material and transport 11.4.2 Manufacturing phase 11.4.3 Use phase 11.4.4 End-of-life phase 11.4.5 Overall environmental impact and costs during whole life cycle Life cycle engineering and CLUBE analysis 11.5.1 CLUBE analysis Conclusions and outlook References

255 255 260 262 267 268 268 270 271 272 274 274 275 275 276 277 279 280

Recycling processes and issues in natural fiber-reinforced polymer composites Sibele Piedade Cestari, Daniela de Franc¸a da Silva Freitas, Dayana Coval Rodrigues and Luis Claudio Mendes 12.1 12.2 12.3 12.4 12.5

Index

Introduction Polymers recycling Polymer composites/nanocomposites 12.3.1 Natural fiber-reinforced polymer composites 12.3.2 Green automotive composites Recycling and natural fiber-reinforced composites in the automotive industry Conclusion References

285 286 287 288 295 295 296 297

301

Contributors Sadaf Afrin, Department of Chemistry, Faculty of Science, Aligarh Muslim University, Aligarh, India Mohd Ayub Ansari, Department of Chemistry, Bipin Bihari College, Jhansi, India M. Asim, Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Serdang, Malaysia H. Carvalho, IDMEC, Instituto Superior Te´cnico, Universidade de Lisboa, Lisbon, Portugal Sibele Piedade Cestari, Instituto de Macromole´culas Professora Eloisa Mano (IMA), Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil Juliana Cruz, Centre for Textile Science and Technology (2C2T), University of Minho, Guimara˜es, Portugal Daniela de Franc¸a da Silva Freitas, Instituto de Macromole´culas Professora Eloisa Mano (IMA), Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil Saı¨d Elkoun, Center for Innovation in Technological Ecodesign (CITE), University of Sherbrooke, QC, Canada J.L. Esteves, Institute of Science and Innovation in Mechanical Engineering (INEGI), Porto, Portugal; Department of Mechanical Engineering, Faculty of Engineering of University of Porto (FEUP), Porto, Portugal Raul Fangueiro, Centre for Textile Science and Technology (2C2T), University of Minho, Guimara˜es, Portugal Diana P. Ferreira, Centre for Textile Science and Technology (2C2T), University of Minho, Guimara˜es, Portugal U. Go¨tze, Chair of Management Accounting and Control, Chemnitz University of Technology, Chemnitz, Germany E. Henriques, IDMEC, Instituto Superior Te´cnico, Universidade de Lisboa, Lisbon, Portugal Md Nazrul Islam, Forestry and Wood Technology Discipline, Khulna University, Khulna, Bangladesh M. Jawaid, Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Serdang, Malaysia

xi

xii Contributors Maya Jacob John, CSIR Materials Science and Manufacturing, Polymers and Composites Competence Area, Port Elizabeth, South Africa; Department of Chemistry, Faculty of Science, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa; School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, Johannesburg, South Africa Bandu Madhukar Kale, Department of Material Engineering, Technical University of Liberec, Liberec, Czech Republic ¨ rnsko¨ldsvik AB, O ¨ rnsko¨ldsvik, Sweden Zoheb Karim, MoRe Research O J. Kaufmann, Institute of Lightweight Structures, Department of Textile Technologies, Chemnitz University of Technology, Chemnitz, Germany G. Koronis, Singapore University of Technology and Design, SUTD-MIT International Design Centre (IDC), Singapore N.C. Loureiro, Superior Institute of Douro and Vouga (ISVOUGA), Santa Maria da Feira, Portugal; Institute of Science and Innovation in Mechanical Engineering (INEGI), Porto, Portugal; Research Center of Mechanical Engineering (CIDEM), School of Engineering (ISEP), Polytechnic of Porto, Porto, Portugal Rajini Priya Malladi, Center for Innovation in Technological Ecodesign (CITE), University of Sherbrooke, QC, Canada Luis Claudio Mendes, Instituto de Macromole´culas Professora Eloisa Mano (IMA), Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil Malladi Nagalakshmaiah, Center for Innovation in Technological Ecodesign (CITE), University of Sherbrooke, QC, Canada P. Pec¸as, IDMEC, Instituto Superior Te´cnico, Universidade de Lisboa, Lisbon, Portugal Aravin Prince Periyasamy, Department of Material Engineering, Technical University of Liberec, Liberec, Czech Republic Fatima Rahman, Forestry and Wood Technology Discipline, Khulna University, Khulna, Bangladesh Felix Raspall, Singapore University of Technology and Design, Singapore I. Ribeiro, IDMEC, Instituto Superior Te´cnico, Universidade de Lisboa, Lisbon, Portugal Mathieu Robert, Center for Innovation in Technological Ecodesign (CITE), University of Sherbrooke, QC, Canada Dayana Coval Rodrigues, Instituto de Macromole´culas Professora Eloisa Mano (IMA), Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil Samson Rwahwire, Faculty of Engineering, Busitema University, Tororo, Uganda N. Saba, Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Serdang, Malaysia H.M. Salman, IDMEC, Instituto Superior Te´cnico, Universidade de Lisboa, Lisbon, Portugal A. Schmidt, Chair of Management Accounting and Control, Chemnitz University of Technology, Chemnitz, Germany

Contributors

xiii

A. Silva, Singapore University of Technology and Design, SUTD-MIT International Design Centre (IDC), Singapore; Singapore University of Technology and Design, Engineering Product Development Pillar, Singapore Sarat Singamneni, Auckland University of Technology, Auckland, New Zealand ¨ rnsko¨ldsvik AB, O ¨ rnsko¨ldsvik, Sweden Anna Svedberg, MoRe Research O Blanka Tomkova, Department of Material Engineering, Technical University of Liberec, Liberec, Czech Republic Rajkumar Velu, Singapore University of Technology and Design, Singapore

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Preface This book presents a thorough overview of recent studies and applications of green composite materials that reached momentum during the past years for the automotive sector. There is growing support in the technical and scientific literature that green composites can provide mechanical properties analogous to synthetic composites and, therefore, will replace their traditional counterparts. Up to now, composites made of renewable (green) materials have been rampantly used in interior and exterior body parts as they have significant weight reduction advantages compared with aluminum and steel. Green composites have the potential of many gains regarding economic/mechanical performance, environmental impact and public acceptance when compared with fossil-derived plastics, ferrous and traditional synthetic resourced composites. Consequently, they have found widespread applications on an industrial scale in different technological areas due to their versatile properties. In this book’s chapters, thorough reviews of latest achievements along with state-of-the-art studies and industrial applications for a number of modern examples employed by car makers and scientists are included. In addition to that, an elaborative assessment on the topic of industrial and academic applications in many dimensions such as eco-design, durability issues, environmental performance, and future trends has been taking place. The first part of this book deals with Processing and Characterization of Green Composites. Physical properties, surface modification, and flammability performance of biocomposites have been included in the chapters. Predictive modeling and experimental techniques for automotive composites are also discussed here. The second part highlights Thermosetting and Thermoplastic Materials for Structural Applications. In this part, the reader can find processes and techniques for production and modification of biobased thermosets and biothermoplastics which may combine benefits of recyclability and disposal. Part 3 is addressing Nanomaterials and Additive Manufacturing Composites. Present trends and challenges for the future are reviewed here. In this part, nanofibrillated cellulose composites and potential applications have been presented. Finally in Part 4, the Life Cycle Assessment and Risk Analysis of natural fiberereinforced composites have been discussed. This part is dedicated to life cycle analysis and recycling issues of natural fiberereinforced polymer composites.

xv

xvi Preface

The contributors of this book are recognized experts and researchers from the academia and research laboratories across the world. Each of the chapters has been presenting many of the most recent stages of techniques required for practical applications of automotive composites. Thus, it can be a suitable tool for chemical, environmental and materials science engineers and technologists. This book can also be a useful information source for undergraduate and postgraduate students in institutes of material science and researchers in R&D labs working in the green composite materials filed. This book owes its final shape to the assistance and hard work of many talented colleagues and associates. The editors want to express their appreciation to all contributors of this book for their time and efforts that went into producing this volume. They also want to thank the editorial staff of the Woodhead Publishing and Elsevier Inc, who helped them throughout all stages of this publication. Georgios Koronis Arlindo Silva SUTD-MIT International Design Centre, Singapore

Part I

Processing and characterization of green composites

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Chapter 1

Surface modification of natural fibers in polymer composites Diana P. Ferreiraa, Juliana Cruz, Raul Fangueiro Centre for Textile Science and Technology (2C2T), University of Minho, Guimara˜es, Portugal

Chapter Outline 1.1 Introduction 1.2 Properties of natural fibers 1.3 Surface modification techniques 1.3.1 Physical methods 1.3.1.1 Plasma treatment 1.3.1.2 Ultrasound and ultraviolet treatments 1.3.2 Chemical methods 1.3.2.1 Alkali treatment 1.3.2.2 Silane treatment 1.3.2.3 Acetylation 1.3.2.4 Benzoylation 1.3.2.5 Maleated coupling treatment 1.3.2.6 Graft copolymerization 1.3.2.7 Other chemical treatments

3 6 6 10 10

15 15 16 16 17 18 18 19 19

1.4 Physical and chemical methods as treatments for natural fiber polymer composites (NFPCs) 1.4.1 Effects of plasma treatment on NFPCs 1.4.2 Natural fibersdchemical treatments and their influence on NFPCs 1.5 Biological methods as an alternative to chemical/physical treatments 1.5.1 Enzymatic treatment 1.5.2 Fungal treatment 1.5.3 Bacterial cellulose coating 1.6 Nanoparticles deposition/ functionalization 1.7 Concluding remarks and future trends References

20 20

23

28 29 30 30 31 32 33

1.1 Introduction Fibers are the basic building block of many materials and despite the fact that, for years, these structures have been mainly applied in textiles manufacturing, they have strong potential for widespread applications. The most common areas of applications are: in the automotive industry, medical field, civil a.

Corresponding Author

Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00001-X Copyright © 2019 Elsevier Ltd. All rights reserved.

3

4 PART | I Processing and characterization of green composites

engineering, aerospace industries, among others [1e5]. In the last few years, the development of new materials based on fibers revealed the huge potential of these materials to improve the quality of human life. The constituents of these fibrous materials may be of natural or synthetic origin. Natural fibers, including cellulosic, protein, and mineral fibers are collected directly from nature and are considered environmentally friendly materials. On the other hand, synthetic fibers are man-made and despite being the most used fiber for new materials development, they raise several environmental issues. These nonrenewable resources generate large amounts of waste at the end of the product lifecycle and require a long time for their complete degradation [6,7]. In the last few years, there is a great deal of concern about the replacement of synthetic materials by natural ones in order to reduce the cost, the production of CO2 and oil dependence, as well as problems related to materials recycling. It is estimated that 20%e25% of the total greenhouse gas emissions in industrialized countries come from the transportation industry. Therefore, the challenge is to develop lightweight and low price composites based on natural fibers to be used in the automotive industry in order to turn automobiles more fuel efficient and environmentally friendly [8]. Many automotive components are already produced with natural composites based on fibers like flax, hemp, and sisal. Table 1.1 presents several automotive industries that are already using natural fibers in the automobile components [8]. Natural fibers have high strength, high modulus of elasticity, high moisture absorption, and low elongation and elasticity when compared to non-natural fibers [11,12]. Natural fibers can be classified according to their origin into animal, vegetable, or mineral. Animal fibers include fibers such as silk, hair, wool, and feather and are proteinaceous in nature [13]. Vegetable fibers, on the other hand, are generally based on arrangements of cellulose with lignin including cotton, hemp, jute, flax, kenaf, ramie, sisal, bagasse, abaca, pineapple, and banana [14]. Mineral fibers, unlike the animal and vegetable fibers of animal or plant origin, cannot be strictly defined as bio-based fibers. Nevertheless, as the previous ones, they are obtained from nature. Mineral origin fibers, consisting mainly of silicates, are not renewable and include materials based on clays, asbestos, and inosilicates [14]. Some advantages of natural fibers are: abundance, nontoxic nature, low density, low cost, biodegradability, high toughness, and reasonable specific strength properties [15]. However, they also possess some drawbacks when used in composites. For example, large variations in properties (like in wettability, mechanical behavior, tensile strength, etc.), flammability, poor moisture absorption, and swelling properties. These variations lead to formation of cracks and promote material defects [16,17]. The poor compatibility with different matrices especially with polymers is a major drawback due to the hydrophilic character of the fiber and the hydrophobic polymer in a natural fiberereinforced composite [18,19]. As a result, numerous techniques have been tried till date to modify the surface of

Surface modification of natural fibers in polymer composites Chapter | 1

TABLE 1.1 Automotive manufacturers and application areas of natural fibers [8e10]. Company/ manufacturer

Model applications

Automobile parts

Audi

A2, A3, A4, A6, A8, Roadster, Coupe

Seat backs, side and back door panels, boot lining, hat rack, spare tyre lining

BMW

3, 5,7 series, BMW I series

Door panels, headliner panel, boot lining, seat backs, noise insulation panels, door trim

Citroe¨n

C5

Interior door panelling

Chrysler

A, C, E, and S-class models

Door panels, windshield, dashboard, business table, pillar cover panel

Fiat

Punto, Brava, Marea, Alfa Romeo 146, 156

Door cladding, seat-back linings, door panels, seat bottoms, head restraints, back cushions

Ford

Mondeo CD 162, Focus, Freestar

Door panels, boot liner, sliding door inserts

Lotus

Eco Elise

Body panels, spoiler, seats, interior carpets

MercedesBenz

Trucks, Mercedes A

Internal engine and roof cover, sun visor, interior insulation, bumper, wheel box

Opel

Vectra

Packing trays, panel inserts

Peugeot

406

Seat backs, parcel shelf

Renault

Clio, Twingo

Rear parcel shelf

Rover

2000

Insulation, rear storage shelf/panel

Saab

e

Door panels

Seat

e

Door panels, seat backs

Saturn

L300s

Packing trays, door panel inserts

Toyota

Brevis, Harrier, Celsior, Raum

Door panels, seat backs, spare tyre cover

Vauxhall

Corsa, Astra, Vectra, Zafira

Headliner panel, interior door panels, instrument panel

Volkswagen

Golf, Passat, Bora

Door panel, seat back, boot lid finish panel, boot liner

Volvo

C70, V70

Seat padding, natural foams, cargo floor tray

5

6 PART | I Processing and characterization of green composites

natural fibers, in order to reduce their water absorption and improve their adhesion with polymeric matrices. This chapter provides an overview of natural fiber properties and the functionalization techniques available to allow their surface modification for advanced applications in the field of green composites. Several examples of natural fiber composites utilized in the automotive industry will be described.

1.2 Properties of natural fibers As shown in Table 1.2, natural fibers are mainly composed of cellulose, hemicellulose, lignin, pectin, waxes, and water-soluble substances [15,22]. The differences in the chemical composition, structural parameters, and properties of each fiber are related to the different modes of extraction, the origin of growth, the climatic conditions, and the age of the fiber plant [22]. Table 1.3 presents the mechanical properties of several natural fibers compared with synthetic ones such as e-glass, a very common inorganic synthetic fiber used in automobile parts. The properties of each fiber depend on the chemical composition, chemical structure, and cellular arrangement of the fiber. Synthetic fibers like e-glass, aramid, or carbon are commonly used, due to their good mechanical properties, as fillers and reinforcements for door panels, seat backs, dashboards, and interior automobile parts. However, these fibers are abrasive and difficult to machine; they are obtained from nonrenewable resources and present potential health hazards caused by glass fiber particles [26]. Regarding the comparison between the natural fibers and the synthetic e-glass, it is expected that the natural fibers could replace glass fiber into biocomposites due to several properties, namely, their low density, comparable specific strength, favorable mechanical properties, weight reduction potential, high stability, and wide availability [15,22,27]. They also can be produced using ecologic and lowprice methodologies contributing to the sustainability of the process.

1.3 Surface modification techniques Due to the presence of amorphous regions, hydroxyl and other polar groups, natural fibers exhibit a high propensity to absorb moisture. The increased moisture at the surface of the fiber further leads to a decrease in the mechanical properties resulting in loss of dimensional stability and leading to biodegradation. This significantly reduces the potential application of natural fibers for reinforcing polymers, since the adhesion at the interface is not suitable for the development of composites. Thus, various treatments could be applied to modify the surface of the fibers in order to make them more suitable for such applications. In general, these surface-modifying treatments can be physical, chemical, or biological, and regardless the mechanism associated with each type of treatment; the goal is similar for all of them: break the atoms bonds of some fiber surface groups in order to enable their functionalization [28,29].

Types of fiber

Cellulose

Lignin

Hemi-cellulose

Pectin

Wax

Microfibrillar spiral angle

Moisture content

Jute

61e71.5

12e13

13.6e20.4

0.2

0.5

8.0

12.6

Flax

71

2.2

18.6e20.6

2.3

1.7

10.0

10.0

Hemp

70.2e74.4

3.7e5.7

17.9e22.4

0.9

0.8

6.2

10.8

Ramie

68.6e76.2

0.6e0.7

13.1e16.7

1.9

0.3

7.5

8.0

Kenaf

31e39

15e19

21.5

e

e

e

e

Sisal

67e78

8.0e11.0

10.0e14.2

10.0

2.0

20.0

11.0

Pineapple

70e82

5e12

e

e

e

14.0

11.8

Henequem

77.6

13.1

4e8

e

e

e

e

Cotton

82.7

e

5.7

e

0.6

e

e

Coir

36e43

41e45

0.15e0.25

3e4

e

41e45

8.0

Surface modification of natural fibers in polymer composites Chapter | 1

TABLE 1.2 Chemical composition in percentage of some natural fibers and the respective structural parameters [19e21].

7

Fiber

Density (g, g/cm3)

Tensile strength (s, MPa)

Stiffness/Young’s modulus (ε, GPa)

Elongation at failure (%)

Specific tensile strength (s/g)

Specific Young’s modulus (ε/g)

Jute

1.3e1.5

393e800

10e55

1.5e1.8

300e610

7.1e39

1.3e1.45

393e773

13e26.5

1.16e1.5

e

e

1.5

345e1100

27.6

2.7e3.2

571e1071

43

1.4

800e1500

60.0e80.0

1.2e1.6

e

e

1.5

345e1830

27e80

1.2e3.2

230e1220

18e53

Cotton

1.5e1.6

287e800

5.5e13

3.0e10

190e530

3.7e8.4

Kenaf

1.5

930

53.0

1.6

e

e

1.45

930

53

1.6

641

36

e

413e1627

34.5e82.5

1.6

e

e

1.4

1020

34.0e82.0

0.8e1.6

e

e

1.5

468e640

9.4e22.0

3.0e7.0

e

e

1.2e1.5

511e700

3.0e98.0

2.0e2.5

e

e

1.3e1.5

507e855

9.4e28

2.0e2.5

362e610

6.7e20

1.4

550e900

70

1.6

392e643

50

1.5

550e1110

58e70

1.6

370e740

39e47

Flax

Pineapple

Sisal

Hemp

8 PART | I Processing and characterization of green composites

TABLE 1.3 Properties of natural fibers compared with e-glass, s-glass, aramid, and carbon fibers [8,15,19,23e25].

1.5

12e980

e

e

e

e

Bagasse

0.5e1.2

290

e

e

e

e

Banana

0.75e1.3

180e914

e

e

e

e

Bamboo

1.5

575

27

e

e

18

Kapok

0.38

93.3

4

e

e

12.9

Ramie

1.5

400e938

44e128

1.2e3.8

270e620

29e85

Harakeke

1.3

440e990

14e33

4.2e5.8

338e761

11e25

Alfa

1.4

188e308

18e25

1.5e2.4

134e220

13e18

Coir

1.2

131e220

4e6

15e40

110e180

3.3e5

Silk

1.3

100e1500

5e25

15e60

100e1500

4e20

Feather

0.9

100e203

3e10

6.9

112e226

3.3e11

Wool

1.3

50e315

2.3e5

13.2e35

38e242

1.8e3.8

E-glass

2.5

2000e3500

70.0

2.5

1297

28

2.6

2400

73.0

3.0

e

e

2.5

2000e3000

70

2.5

800e1400

29

S-glass

2.5

4570

86

2.8

e

e

Aramid

1.4

3000e3150

63e67

3.3e3.7

e

e

Carbon

1.7

4000

230e240

1.4e1.8

e

e

Surface modification of natural fibers in polymer composites Chapter | 1

Abaca

9

10 PART | I Processing and characterization of green composites

1.3.1 Physical methods Physical methods of processing natural fibers are mainly used to separate natural fiber bundles into individual filaments and to modify the fibers surface structure in order to improve its application on composites. Some examples of physical methods for natural fibers functionalization are related to the use of plasma, ultrasounds, and UV light.

1.3.1.1 Plasma treatment Plasma treatments are among the most common physical surface modification processes used nowadays in the industry; they are very effective in substrate surface activation, especially when applied to natural fiber modification [30]. There are mainly two different types of plasma: thermal and nonthermal. However, due to the destructive character of the thermal plasma concerning fiber-based materials, just nonthermal plasma treatments will be addressed within this book, the ones at atmospheric pressure and at low pressure or vacuum [29,31]. Plasma treatment schematically represented in Fig. 1.1 is applied in order to remove surface contaminants (cleaning effect) which will induce changes in the surface properties like wettability, dyeability, flammability, etc. This treatment can also increase the surface roughness providing better mechanical binding to the polymers and improve the adhesion at the fiberematrix interface. At the same time, the plasma can produce free radicals able to react with oxygen or other gases leading to the generation of surfaces with different hydrophilic/hydrophobic character [32,33].

Introduction of new functional groups

Plasma

COOH NH2

Fiber surface After plasma treatment

Electrode

Cleaning

OH

Fiber surface Electrode

Radicals

Electronic excited particles

Ions

Electrons

UV radiation

Contaminants

FIGURE 1.1 General scheme of the Plasma surface treatment.

Surface modification of natural fibers in polymer composites Chapter | 1

11

Plasma is partially ionized gas, composed of highly excited atomic, molecular, ionic and radical species with free electrons and photons [34]. It is generated by applying an electric field over two electrodes with gas in between at atmospheric pressure or under vacuum [35]. In both cases, the properties of the plasma will be determined by the gases used to generate the plasma, as well as by the applied electrical power and the electrodes (material, geometry, size, etc.). The plasma treatment is an example of an electric discharge treatment which includes ions (10e30 eV), electrons (0e10 eV), and UV (200>l < 400 nm) and vacuum UV (l < 200 nm) radiation (3e40 eV) [29]. Plasma vacuum requires that samples be treated in a low vacuum chamber in which a gas is introduced, causing ionization. Various gases have been used, including oxygen, nitrogen, helium, and air. The introduced gas ions strike the surface, causing chemical and topographical changes on the fiber surface. These chemical modifications are complex but generally involve removing atoms or breaking bonds that result in free radicals. However, this method is limited to the size of the vacuum chamber and is also a batch process [36]. The treatment with atmospheric plasma has attracted the researchers’ attention due to the excellent results demonstrated by several works using this treatment applied to a wide variety of fibers, polymers, ceramics, and composites [37e40]. It is a very attractive technique because it allows the sample to be treated in situ rather than restricted to a vacuum chamber [29], allows a continuous and uniform treatment, is reliable, reproducible, and is not so expensive as the low-pressure treatments avoiding the use of expensive vacuum systems. There are four main types of atmospheric plasma techniques which will be discussed in the following sections: corona treatment, dielectric barrier discharge technology (DBD), glow discharge (APGD), and atmospheric pressure plasma jet (APPJ). Corona treatment The corona treatment is one of the most interesting techniques for activating the surface oxidation of several materials and induces several changes in order to improve the compatibility between hydrophilic fibers and hydrophobic matrices [31]. Corona treatment is based on high-frequency discharges applied across electrodes and grounded metal roll as can be observed in the scheme of Fig. 1.2. These discharges between electrodes induce ionization of the surrounding atmosphere creating plasma (ionized air) and the emission of blue color as can be observed (Fig. 1.2). The sample or the substrate is placed in the gap between the electrodes and is bombarded with high-speed electrons. The energy level of these electrons is high enough to break the molecule bonds of the most substrate surfaces [41]. This process will induce the surface oxidation

12 PART | I Processing and characterization of green composites

FIGURE 1.2 Corona treatment photography.

of the materials by the oxidants present in corona discharge like: ozone, atomic oxygen, and oxygen free radicals. These oxidants in combination with free radicals of the material surface will create oxidizing groups, for example, hydroxyl, carboxyl, carbonyl, or ester groups. The introduction of polar groups on the material surface will increase the surface energy improving the wettability and adhesion properties of the materials [42]. The corona process is very successful as a pretreatment for textiles. The treatment can be used for cleaning the surface of the material improving its roughness and adhesion properties. With this method it is possible to create better surfaces without changing the mechanical properties of the whole material [43]. One of the disadvantages of corona treatment is related to the penetration depth, in some cases, the corona systems have an effect only in loose fibers and cannot penetrate deeply into the yarn or woven fabric so that their effects on textiles are limited and short-lived [44]. Nevertheless, the corona treatment presents several advantages when compared with other plasma treatments and also with other surface modification techniques. There are no requirements regarding specific conditions during modification [45] (unlike the low-temperature plasma treatment, where vacuum chambers are used). It is a low-cost process and presents low energy consumption [46]. Finally, the process can be applied in large scale and directly in a high volume of material which is very important for the application in an industrial production line. Dielectric barrier treatment The plasma dielectric-barrier discharge (DBD) technique is similar to corona treatment process, however, in the corona, the discharges are between bare metal electrodes without dielectric. The DBD plasma technique consists of two plane parallel metal electrodes with at least one of the electrodes covered by a dielectric layer which accumulates the transported charge on its surface

Surface modification of natural fibers in polymer composites Chapter | 1

13

High voltage electrode High voltage Discharge gap AC generator

Dielectric barrier Ground electrode

Dielectric barrier

Discharge gap

High voltage electrode

Ground electrode

FIGURE 1.3 Scheme of a general dielectric barrier discharge apparatus [29].

and distributes the charge over the entire area of the electrode (Fig. 1.3) [30,47,48]. The preferred materials for the application as dielectric barriers are glass or silica glass or, in special cases, ceramics and polymer layers or thin enamel [49]. If an alternating voltage ranging from low-frequency AC to 100 kHz is applied to the electrodes, breakdown processes are initiated in the gas gap and transient microdischarges are established with duration of nanoseconds and distributed over the dielectric surface [50,51]. Discharges of this type are wellknown for the treatment of surfaces for the production of ozone [52]. Regarding the surface treatment, the dielectric barrier discharges provide high-energy electrons (generated through collisions during discharge), which are able to produce radicals and electronically excited particles efficiently. The DBD can trigger different reaction paths that can lead to the production of reactive intermediates, which, in turn, will promote the surface activation of the materials [29,49]. This technology is commonly used for the treatment of textiles, polymers, plastic foils, metal surfaces, and also in the sterilization of surfaces, deposition of films, removal of components from flue gases, and conversion of greenhouse gases [53]. The major disadvantage of DBD is that the treatment or the discharge is not completely uniform and has a short duration. Atmospheric pressure glow discharge Compared with the DBD technique, the atmospheric pressure glow discharge (APGD) is very suitable for a more uniform surface treatment. Glow discharge is characterized as a uniform, homogeneous, and stable discharge usually generated in helium (sometimes argon and nitrogen can be used, but helium is the preferred gas) as we can see in Fig. 1.4 [44]. APGD is generated by applying relatively low voltages (when compared with DBD) across symmetrical conductive electrodes at higher frequencies (MHz). Plasma is homogenous across the electrodes and gives one current pulse for every half cycle [54]. The APGD plasma is characterized by high

14 PART | I Processing and characterization of green composites

HV HE gas

Air

Plasma Dielectric Conductor

Dielectric barrier discharge

Atmospheric pressure glow discharge

HV = high voltage power source FIGURE 1.4 Scheme of atmospheric pressure glow discharge (APGD) compared with dielectric barrier discharge (DBD).

electron energy and high densities of excited and charged particles at low gas temperature. Nonequilibrium glow discharge plasma provides active species that can be used for surface treatment without material overheat [55]. This treatment is used in several applications such as: surface modification, etching, thin-film deposition, ozone generation, degradation of organic compounds, sterilization, disinfection, biological and chemical decontamination, surface cleaning, food safety, and waste treatment [56]. Atmospheric pressure plasma jet (APPJ) In general, the APPJ source can contain two tubular metal electrodes separated by a gap through which a discharge current occurs as shown in Fig. 1.5. Inside the Electrodes

HE

Plasma jet

Quartz tube

FIGURE 1.5 Schematic view of one of the possible experimental set-ups of APPJ.

Surface modification of natural fibers in polymer composites Chapter | 1

15

electrodes lies a quartz cylindrical tube through which helium (or other gases) flows. To generate the plasma, several parameters can be optimized like wave pulse, the frequency of pulse, and rate of gas flow. The plasma is launched through the open end of the quartz cylindrical tube directly into the sample [57]. An APPJ can provide a local treatment with a relatively high density of charged particles, reactive oxygen and nitrogen species since the length of the plasma plume (bright region) from the opening of the APPJ can be of several centimeters. Short lifetime species such as atomic oxygen can, therefore, be involved in reactions with the target. Furthermore, a very precise treatment is possible and owing to the high gas velocity, penetration of the plasma components into small cavities can be achieved. The APPJ is suitable for industrial and research applications, such as surface modification, biological material sterilization, biomedical applications (dermatological, dental, etc.), ozone formation, and treatment of heat-sensitive materials [58].

1.3.1.2 Ultrasound and ultraviolet treatments Ultrasound treatments are not so used as the previously described plasma treatments. However, they are also effective in the rising of different substances and pollutants from the surfaces even without the use of surfactants in the rinsing bath. This effect could be attributed to the acoustic cavitation, known as the process of bubble formation and collapse, responsible for most of ultrasound’s physical and chemical effects observed in solid/liquid or liquid/ liquid systems [59]. Effects of ultrasonic treatment on natural cellulosic fibers, such as cotton, have been extensively studied and changes were found, the ultrasonic treatment can alter the crystalline morphology of cotton and subsequent mechanical and chemical properties of the fiber and fabric [60]. The ultraviolet (UV) light is an electromagnetic radiation ranging from 10 to 400 nm which can cause chemical reactions with several organic molecules, leading to effects greater than simple heating effects. The UV radiation is a potential energy source able to promote photochemical reactions in the molecular structures of natural fibers changing its mechanical properties, and simultaneously, acts as a clean method to modify the surface of natural fibers [61,62]. UV radiation has proved to be a clean and cost-effective method and is also a very promising technique to be used in industrial applications due to the economic construction and simplicity. Some examples regarding the use of these techniques for the surface modification of natural fibers in polymer composites will be shown later in this chapter. 1.3.2 Chemical methods Alternatively to the physical methods, natural fibers can also be treated with several chemical methods such as alkali treatment (mercerization), silane treatment, maleated coupling, acetylation, permanganate and peroxide treatment,

16 PART | I Processing and characterization of green composites

benzoylation, graft polymerization, etherification, isocyanate treatment, etc. These chemical processes for modification of natural fibers are used in order to improve their surface and mechanical characteristics. These chemical modifications consist of chemical reactions between the reactive constituents of the natural fibers (hydroxyl groups, for example) and a chemical reagent forming a covalent bond between the two [19]. It has been observed that some of these chemical treatments (for example, alkali treatment) can significantly improve the mechanical properties of natural fibers by modifying their crystalline structure, as well as by removing weak components like hemicellulose and lignin from the fiber structure [63]. Also, moisture absorption and subsequent swelling of natural fibers can also be reduced through selective chemical treatments (e.g., water repelling agents). Moreover, silane coupling agent treatment can also improve the fiber/matrix interface interactions through the formation of strong chemical bonding and therefore, result in considerable improvement in the mechanical performance of composites [64]. Some of the existent chemical treatments will be briefly described in the following sections.

1.3.2.1 Alkali treatment The alkali treatment also known as mercerization is one of the oldest and most used chemical treatments for natural fibers. This method consists of treating the fibers with sodium hydroxide (NaOH) in order to remove from the surface certain amounts of lignin and hemicellulose and completely remove pectin, wax, oils, and other organic compounds [65]. After this removal, it is supposed to have more cellulose molecules exposed at the surface, improving the adhesion of fibers to the polymeric matrix due to the higher number of possible reactions sites (Gandini A, 2009). In this way, the treatment influences the chemical composition of the fibers and the molecular orientation of the cellulose crystallites. The surface roughness is also increased enhancing the mechanical properties and adhesion [63]. The following Fig. 1.6 exhibits, in a general way, the alkali treatment reaction where the addition of sodium hydroxide promotes the ionization of the natural fibers hydroxyl groups to alkoxides.

O– H + NaOH

Fiber

Fiber

1.3.2.2 Silane treatment Silanes are very promising and versatile coupling agents to be used in the treatment of natural fibers in order to improve the chemical interactions between the fiber and the polymeric matrix [66]. The silane molecule should have bifunctional groups which may respectively react with the two phases thereby forming a bridge in between them [64]. As we can see in Fig. 1.7,

+ O– Na

+

H 2O

FIGURE 1.6 Mechanism of the alkali treatment of natural fibers.

Surface modification of natural fibers in polymer composites Chapter | 1

OH

OR ´R

Si

17

OR

+

3H2O

H or OH

´R

Si

OR

OH

O

O

OH2 +

3ROH

OH OH + ´R O

Si OH

H

OH

H

Fiber

Fiber

H

HO

Si

R´

OH OH O

H

HO

Si

R´

OH

FIGURE 1.7 Mechanism of the reaction between the silane groups and the functional groups of the natural fibers.

the first step of the reaction mechanism is the silane coupling agent hydrolysis. The alkoxy groups from the coupling agent under use are firstly hydrolyzed in order to generate reactive silanol groups. After this, the hydrolyzed silane solution is mixed with natural fibers. The reactive silanol groups of the silane molecule allow the silane to bind to the OH groups of the fiber surface by hydrogen bonds. On the other side, the alkyl groups connect the silicon atom to the organofunctionality of the polymer functional groups forming a siloxane bridge between the fiber and the polymer. This phenomenon increases the compatibility with organic compounds and the hydrophobic character of the surface, thus leading to an increase in the strength of the interface in the polymer matrix [67,68]. Coupling agents are normally used to improve the degree of cross-linking in the fiber/polymer interface by providing a perfect connection between the silane groups. Among the various existing coupling agents, silane is one of the most reported as more effective in modifying the fiber/matrix interface. Moreover, it has been demonstrated that the efficiency of the silane treatment can be higher when the samples are subjected to an alkali treatment before the silane one. The generation of reactive sites in the molecule increases leading to a more successful reaction with silanes. Furthermore, both treatments can be combined improving the properties of the fibers and enhancing the fiber-matrix bonding in composites [69].

1.3.2.3 Acetylation The acetylation method is very effective in modifying the surface of natural fibers in order to increase their hydrophobicity [70]. Generally, the treatment consists of applying acetic anhydride and acetic acid for plasticizing the cellulosic fibers (esterification method). The esterification occurs by reaction of acetyl groups (CH3COe) with hydroxyl groups (eOH) on the fibers as shown in Fig. 1.8 [25]. This chemical modification promotes the substitution of polar hydroxyl groups found on fiber cell wall by the less polar acetyl groups [71]. As a result, the hydrophilic nature of the fiber decreases leading to a better compatibility

18 PART | I Processing and characterization of green composites

O H+ H 3C

O O

Fiber

Fiber

O C

H2C

O C

CH3 + H2C

C OH

C O

O

FIGURE 1.8 Reaction of the acetic anhydride with the functional groups of natural fibers.

with the nonpolar matrix. The acetylation treatments are effective in reducing the moisture absorption of natural fibers and also in improving the mechanical properties of composites, such as the interfacial shear and tensile and flexural strength [72]. In some cases, the acetylation can be preceded by alkali pretreatment for better results [24].

1.3.2.4 Benzoylation Like acetylation treatment, the principal purpose of the benzoylation method also decreases the fibers’ hydrophobicity. Firstly, as Fig. 1.9 presents, the alkali pretreatment is normally used to activate the hydroxyl groups of the fiber. Secondly, the benzoylation is performed by the reaction of benzoyl chloride with the cellulosic OH groups of the natural fibers [73]. This reaction leads to the introduction of functional benzoyl groups (C6H5CO) into the fibers, improving the possible adhesion with the matrix [74]. Although there is improvement of the fiber/polymer interaction, the benzoylation process increases the thermal stability of the fibers and the strength of the generated composite [63].

O H +

NaOH

Fiber

Fiber

1.3.2.5 Maleated coupling treatment Maleated coupling method is widely used to strengthen composites based on natural fibers. The fundamental difference from other chemical treatments is that maleic anhydride (MA) is not only used to modify the fiber surface, but also the polymeric matrix, in order to achieve better interfacial bonding between them and improved mechanical properties [75]. Maleic anhydride is commonly grafted to the polymers that are used to produce the final matrix to ensure a great compatibility between the matrix and the coupling agent. One of

O– Na+ H2O

O– Na+ +

C1

O

Fiber

Fiber

O O

+ Nacl

FIGURE 1.9 Reaction of the alkali treatment followed by the reaction between the fiber and benzoyl chloride.

O H + HO O H

O

H2

C

C

C

C

O

FIGURE 1.10

H

O O

C PP

H O H

19

H2 C

C

C H

Fiber

Fiber

Surface modification of natural fibers in polymer composites Chapter | 1

CH

C O

O

PP

Reaction of maleic anhydride polypropylene with natural fibers.

the most common polymers used is polypropylene (PP), which in the presence of the maleic anhydride results in the grafted maleic anhydride polypropylene (MAPP) [25]. In this treatment, MAPP can react with the hydroxyl groups (OH) in the amorphous region of cellulose structure leading to the formation of hydrogen or covalent bonds between them [76]. The maleic anhydride could form carbonecarbon covalent bond with the polymeric matrix and also combine with hydroxyl groups of the fiber forming an efficient bridge interface. In Fig. 1.10 an example is shown of the possible reaction mechanism of MAPP with fibers [77].

1.3.2.6 Graft copolymerization The graft copolymerization of many monomers onto a cellulose backbone is a very effective method used for their surface chemical modification [78]. Due to its abundance in nature, the vinyl monomers are the most utilized for graft copolymerization. In order to graft vinyl monomers onto natural fibers, redox initiators can be used such as: ceric (IV) ion (ceric ammonium nitrate (CAN)) or cerium (IV) sulfate. However, free radical initiators such as azobisisobutyronitrile (C8H12N4: AIBN), potassium persulfate (K2S2O8: KPS), or ammonium persulfate ((NH4)2S2O8: APS) has also been used for the grafting of the different monomer onto natural fibers [79]. The use of microwave radiation to induce multicomponent polymerization reactions is also a very used technique with increasing interest [80]. Several works showed that the physicochemical properties such as chemical resistance, moisture absorption, water uptake behavior, etc., of natural fibers (jute, hemp, flax, ramie, sisal, pinus, oil palm, coir, bamboo, okra, agave, Grewia optiva, Cannabis indica, Hibiscus sabdariffa, etc.) have been improved by graft copolymerization [81]. 1.3.2.7 Other chemical treatments Many other chemical compounds could be used in order to reduce the number of hydroxyl groups and also to improve the interfacial adhesion between the fiber and polymer. The permanganate treatment leads to the development of cellulose radical through MnO3 ion formation. The peroxide functional groups could initiate free radical reactions between the matrix and the

20 PART | I Processing and characterization of green composites

cellulose fiber. The isocyanate is highly susceptible to the reaction with OH groups. Stearic acid (CH3(CH2)16COOH) and acrylic acid (CH2CHCOOH) are also employed for altering the surface topography, and sodium chlorite (NaClO2) is usually used for fibers bleaching [82].

1.4 Physical and chemical methods as treatments for natural fiber polymer composites (NFPCs) As mentioned before, in the automotive industry natural fibers are replacing the glass and other nonrecyclable fibers in many components. Their biodegradability, low cost, low weight, ecological sustainability, low energy requirements for production, end of life disposal and carbon dioxide neutrality [28] have made them particularly attractive for developing green composites in the automotive sector. However, the adhesion between the natural fibers and the polymers used in the final composites remains as a problem. All the described physical and chemical methods for treating the natural fibers’ surface could be the strategy to overcome this issue regarding the compatibility fiber/matrix and improving at the same time the mechanical properties. Among all the natural fibers, flax, hemp, jute, kenaf, sisal, oil palm, pineapple, banana, and bamboo have received a great importance for developing NFPCs with potential application in the automotive industry [83,84]. In this section, several examples will be provided regarding these fibers treatment with chemical and physical methods to be applied as reinforcements in polymer composites.

1.4.1 Effects of plasma treatment on NFPCs Recent research on banana fibers [85] demonstrated that atmospheric DBD plasma treatment represented in Fig. 1.11 effectively modified the surface of the fibers leading to the increase of tensile strength, elastic modulus, and adhesive properties of the treated banana fibers. Simultaneously, the fibers’ hydrophilicity was improved and the cross-section images of the untreated and treated fibers revealed several changes introduced by the plasma treatment as we can see in Fig. 1.11. Atmospheric glow discharge plasma was used by Ebru Bozaci et al. for jute treatment [86]. The jute fibers were pretreated by alkali treatment followed by the plasma one, exhibiting several morphological changes. The surface roughness increased, as well as wickability, with increasing plasma power and treatment time. These changes on surface properties could be very important for improving the polymer/matrix compatibility in composites production like was found by Gibeop et al. when they studied the effect of plasma treatment on mechanical properties of jute fiber/polylactic acid (PLA) composites [87]. The tensile, modulus, and flexural strength of the plasma-treated fibers increased due to the surface roughness improvement enabling a good compatibility with PLA matrix.

Surface modification of natural fibers in polymer composites Chapter | 1

21

High voltage Ceramics electrodes Banana fibers Power source

Working gas air

Continuous fabric transmission device

Rubber roll

(a)

(b)

(c)

(d)

FIGURE 1.11 Schematic apparatus of DBD treatment and images of cross-section of banana fibers untreated (a, c) and plasma treated (b, d).

Ragoubi et al. studied the effect of corona plasma treatment in hemp fibers for the combination with polypropylene [26]. The treated fibers increased the strength at break of the composites hemp/polypropylene (TF/PP) from 28.6 to 37.8 MPa as shown in Fig. 1.12. The corona treatment also improved the young modulus, stiffness, and elastic density energy properties of the composites produced with treated fibers. Furthermore, the surface modification with corona allowed a better surface contact with the polymeric matrix under study. The study performed by Seki et al. revealed interfacial adhesion fiber/ matrix improvement by using low temperature oxygen plasma in jute fibers treatment for the fabrication of high-density polyethylene (HDPE) composites. Composites with treated and untreated fibers were produced, and several properties were evaluated. The interlaminar shear strength of the oxygen plasmaetreated jute fiber/HDPE composite increased 47% (plasma power 60W) when compared with the untreated jute/HDPE composite. The flexural

22 PART | I Processing and characterization of green composites 40

TF/PP

Stress (MPa)

30

20

NTF/TPP NTF/PP

10

0 0

1

2 3 Deformation(mm)

4

5

FIGURE 1.12 Tensile curves for the different composites TF/PP (corona-treated hemp in polypropylene), NTF/PP (untreated hemp with polypropylene), and NTF/TPP (untreated hemp with corona-treated polypropylene).

TABLE 1.4 Flexural strength and flexural modulus of the developed composites. Composite

Flexural strength (MPa)

Flexural modulus (MPa)

Untreated jute/HDPE

31.4  1.4

823.6  12.7

Oxygen plasma-treated (at 30 W) jute/HDPE

39.7  1.5

965.8  13.2

Oxygen plasma-treated (at 60 W) jute/HDPE

45.6  1.8

1244.5  18.5

strength and flexural modulus also increased with plasma treatment with plasma power of 30 and 60W as can be observed in Table 1.4 [88]. Marais et al. utilized helium cold plasma treatment in reinforcing flax fibers for increasing moisture resistance and improving adhesion with the matrix. The analysis of polyester composites reinforced by flax fibers submitted to helium cold plasma revealed a reduction of water permeability of the composites and improved mechanical properties. In summary, plasma treatment of flax fibers resulted in a composite material with improved mechanical properties [89,90].

Surface modification of natural fibers in polymer composites Chapter | 1

23

FIGURE 1.13 Scanning electron microscope images at 8000 magnification of (a) untreated flax fibers, (b) flax fibers after 15 min corona treatment, and (c) flax fibers after 30 min corona treatment.

Pizzi et al. employed corona discharge treatment on flax fibers impregnated with natural resins matrices with possible application as back rebatable flap in cars. Treated nonwoven flax fiber mats significantly improved the tensile and flexural properties of the mimosa tanninehexamine biocomposites. Such as the scanning electron microscope images of Fig. 1.13 exhibit, the corona treatment turned the surface rougher which probably could increase the surface area of the substrate resulting in improved adhesion of the natural resin on the fiber substrate [91].

1.4.2 Natural fibersdchemical treatments and their influence on NFPCs The influence of alkali treatment on hemp fibers was analyzed by [92] in a study where the hemp fibers were alkali treated with NaOH and Na2SO3 solution, while the polymer used in the final composite (polypropylene) was also modified with MAPP. The fiberematrix interfacial adhesion is usually characterized by the interfacial shear strength (IFSS) of a composite. In this investigation, the composite formed by the NaOH/Na2SO3-treated hemp fiber with polypropylene/MAPP presented an IFSS equal to 15.4 MPa, which indicates a relatively high level of interfacial bonding when compared with other literature examples.

24 PART | I Processing and characterization of green composites

Xia et al. performed the modification of flax fiber surface by alkali, corona discharge, maleic anhydride (MA) grafting, and aminopropyl triethoxysilane treatment for the combination with PLA [93,94]. The alkali treatment successfully removed hemicelluloses, lignins, waxes, and oils from the fiber surface. At the same time, maleic anhydride and the silanes reacted with fiber to form eOCOeCH]CHeCOOH and e(CH2)3eNH2 groups increasing the hydrophobic character of the fiber surface. Fig. 1.14 shows the morphology changes with the several treatments used. By analyzing the SEM images, it is clear that the surface roughness increased with alkali treatment (a) giving rise to more contacting points and improving the mechanical interlocking between

(a)

(b)

20 µm

20 µm

(c)

(d)

20 µm

20 µm

(e)

20 µm FIGURE 1.14 SEM images of (a) Untreated fiber, (b) alkali-treated fiber, (c) corona-treated fiber, (d) MA-grafted flax fiber, and (e) silane-treated flax fiber.

Surface modification of natural fibers in polymer composites Chapter | 1

25

PLA and fiber. Images (d) and (e) show the fibers’ surface covered by a coating layer promoted by MA and silane treatment acting as adhesive agents to increase the fiberematrix interaction. In a study performed by Annie Paul et al., banana fibers were subjected to different surface treatments such as: alkali, benzoylation, KMnO4, and triethoxy octyl silane (TEOS). The influence of these chemical treatments was investigated in PP composites regarding several thermophysical properties [95]. All the chemical methods enhanced both thermal conductivity and diffusivity of the composite banana fibers/PP improving the contact between the fiber and the matrix. Pineapple leaves (PALF) and Kenaf fibers were modified by alkali, silane, and combined alkali and silane treatments by Asim et al. regarding the compatibility improvement with polymer matrices. Table 1.5 summarizes several properties of untreated and treated fibers [96]. As can be observed in Table 1.5, diameters of chemically treated fibers were more uniform and smaller than untreated fibers due to the impurities removal. Tensile properties of silane-treated PALF and KF are enhanced as compared with the untreated, alkali-treated and NaOH-silaneetreated fibers. Silane-treated PALF and KF have the highest IFSS. The acetylation, isocyanate, maleic anhydride, and potassium permanganate treatments were used in kenaf fibers in order to improve the adhesion of the fibers to the polyurethane matrix by Datta and Kopczynska [97]. Once again, the mechanical properties of the polyurethane/kenaf composites were influenced with the chemical modification of kenaf fibers. As an example, the tensile strength of all the produced composites when compared with untreated fibers increased except with maleic anhydride treatment. Kushwaha and Kumar modified bamboo fibers with alkali, maleic anhydride, permanganate, benzoyl chloride, and benzyl chloride treatments for their use as reinforcements in epoxy and polyester matrices [98]. All the mentioned chemical treatments improved the mechanical as well as waterresistant properties of bamboo-epoxy composites. The tensile strength improved 25% with MA and 54% with permanganate method. Benzoylation treatment decreased the water absorption from 41% (untreated fibers) to 16% (treated fibers). As Fig. 1.15 exhibits, the combination of alkali with high intensity ultrasound (HIU) treatment was studied in sisal fibers by Krishnaiah et al. [99]. In this investigation, the effects on the morphology, thermal properties of fibers, and mechanical properties of their reinforced PP composites were studied. By the FE-SEM images presented in Fig. 1.16, it was possible to analyze the influence of each treatment on the fiber surface. The alkali treatment, as usual, removed the wax, oil, and other impurities present on the surface fibers while the ultrasounds removed the amorphous materials and also promoted the cellulose separation. This synergetic effect is very important to enhance adhesion or mechanical interlocking between the sisal fibers and the PP matrix.

Testing

Fibers

Untreated

NaOH-silane

NaOH

Silane

Fiber diameter (mm)

PALF

78.8

50.6

47.8

42.4

KF

83.5

52

46.4

39.4

PALF

290.61

424.63

432.01

629.90

KF

282.60

247.81

455.74

551.23

PALF

5,381.59

6,599.71

8,396.76

10,998.39

KF

7,132.65

11,867.02

15,247.35

19,707.86

PALF

1.70

1.93

1.81

2.35

KF

1.27

1.71

2.89

4.54

Tensile strength (MPa)

Tensile modulus (MPa)

IFSS (MPa)

26 PART | I Processing and characterization of green composites

TABLE 1.5 Values of diameter, tensile strength, tensile modulus, and IFSS of PALF and kenaf fibers.

Surface modification of natural fibers in polymer composites Chapter | 1

Alkali treatment

27

High intensity ultrasonic treatment

Raw sisal fibers

FIGURE 1.15 Alkali and HIU treatments on the sisal fibers.

FIGURE 1.16 FE-SEM micrographs of sisal fibers: (a) Untreated, (b) Ultrasound treated, (c) Alkali treated, and (d) the combination of alkali and ultrasound treated.

Orue et al. [66] also studied the effect of chemical treatments on sisal fibers, the combination of alkali and silane treatment was used for improving the connection with poly(lactic acid) composites. As expected, the treated sisal/ PLA composites showed better mechanical properties than untreated ones because the adhesion between fibers and PLA matrix was improved. The influence of fibers alkali treatment in reinforced oil palm fiber epoxy composites was investigated by Muhammad Khusairy Bin Bakri et al. [100]. Fig. 1.17 shows microscope images of oil palm epoxy composites. The composites with untreated fibers showed lower absorption of epoxy in the fibers, while the composites with treated ones showed higher absorption of

28 PART | I Processing and characterization of green composites

FIGURE 1.17 Light/optical microscope images of oil palm epoxy composites; (a) untreated, (b) treated, and (c) fracture part of oil palm fiber-epoxy.

epoxy in the fibers due to alkaline treatment. In Fig. 1.17(c) we can observe the fracture surface of oil palm fiber epoxy. The traces of epoxy on the fiber proved that fiber itself absorbed an amount of epoxy that changed its structure to become brittle. Therefore, the alkali treatment changed the structure of oil palm fiber inducing better compatibility with the matrix.

1.5 Biological methods as an alternative to chemical/ physical treatments Nowadays, chemical or physical modifications are among the most common type of surface treatments. Nevertheless, they present some disadvantages like: use of large amounts of solvents and hazardous chemicals, waste generation, pollution, high energy use, and high cost of some chemicals and equipment. Microorganisms such as fungi, bacteria, and enzymes could be used in order to overcome this issue; they can modify the natural fibers’ surface with lower energy input. Thus, greener surface treatments could be developed for the extraction and surface treatment of raw fibers or natural fibers. Enzymatic, fungal, and bacterial treatments are described in the following sections.

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1.5.1 Enzymatic treatment The enzymatic treatment is an environmental friendly and very specific technique used nowadays in the development of natural fiber/polymer composites. The process consists in using enzymes for selectively removing hydrophilic pectin, lignin, and hemicellulosic components from the fibers [101], reducing the natural cellulosic fibers’ hydrophilicity. The principal enzymes applied in this catalytic process (enzymatic hydrolysis) are hydrolases and oxidoreductases [102]. The hydrolases include amylases, cellulases, proteases, pectinases, and lipases/esterases. From the class of the oxidoreductases the tyrosinase, laccase, or peroxidase was already studied for polymer modification [19]. Enzymatic catalysis differs from chemical catalysis due to the higher velocity of the reaction; the more delicate conditions of action (temperatures below 100 C, atmospheric pressure, and pH of 4e8); and the higher specificity of the reaction [103]. It was observed in several research works that the enzymatic treatment facilitates better fiberematrix adhesion and improved mechanical properties of the composites [101,104e106]. For example, Laccase showed high selectivity to remove lignin efficiently without damaging the fiber’s surface. Novamix, a mixture of lipase, protease, and amylaseexylanase, was used to separate microfibers from wheat husks and remove unwanted materials on the fiber surfaces without causing damage [107]. Abaca fibers, modified with commercial fungamix, exhibited smoother surfaces as Fig. 1.18 shows [108]. Beyond all these advantages, the cost of using enzymes is still the most important problem and the probable reason for its limited use. However, the possibility of recycling enzymes after each use could be one the chances of reducing the associated cost.

FIGURE 1.18 Micrograph of Abaca fiber surface morphology: (a) unmodified, (b) fungamix modified.

30 PART | I Processing and characterization of green composites

1.5.2 Fungal treatment As the enzyme treatment, the fungal treatment is also an environment friendly and efficient alternative to the chemical methods. It is used to remove noncellulosic components (such as wax, lignin, or pectin) from the fiber surface by the action of specific enzymes [76]. The white-rot fungus Schizophyllum commune produces extracellular oxidases, enzymes that react with lignin constituents (lignin peroxidase). These enzymes are responsible for the lignin removal from the natural fiber surface increasing its roughness [109]. At the same time, the fungi are capable of producing hyphae which creates fine holes in the fiber surface providing roughness to the fiber surface and ultimately increases the interfacial adhesion with the matrix [110]. Hemp fibers treated with fungi Ophiostoma ulmi revealed lower percentages of impurities compared with untreated ones, due to water-soluble compounds’ removal and due to the action of fungus on the hemp fiber as SEM images of Fig. 1.19 show [111]. Another study regarding the hemp fibers showed that after fungi treatment the composite strength is 22% higher in comparison to the untreated fiber. Moreover, for hemp polypropylene thermoplastics, fungi over alkali treatment showed a 32% improvement in composite strength [111]. Fungal treatment is a low cost method and green treatment that is poised to move the composite industry from conventional synthetic materials to green and environmentally friendly products [112].

1.5.3 Bacterial cellulose coating Several methods were described in the previous sections taking into account the treatment of natural fibers by removing substances from their surface.

000322

10KV

X600

50µm

000316

10KV

X600

50µm

FIGURE 1.19 SEM picture of an untreated hemp fiber bundle (left) and Ophiostoma ulmi treated hemp fiber bundle (right).

Surface modification of natural fibers in polymer composites Chapter | 1

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The surface coating with bacterial cellulose is a recent modification technique which involves the addition of a new material onto the surface of natural fibers rather than removing. Cellulose can be synthesized by various species of bacteria, such as those of the genera Gluconacetobacter (Acetobacter), Agrobacterium, Aerobacter, Azotobacter, Rhizobium, Salmonella, Escherichia, and Sarcina [113]. When that kind of bacteria are added to an appropriate culture medium in the presence of natural fibers, they produce bacterial cellulose which is preferentially deposited in situ onto natural fibers [114]. Bacterial cellulose (BC) exhibits unique properties when compared with plant cellulose, such as: high purity, high crystallinity, excellent biodegradability, large water-holding ability, and excellent biological affinity [115]. The goal of coating natural fibers with BC is to improve interfacial adhesion between fibers and polymers and also to develop green fiberereinforced hierarchical nanocomposites with enhanced properties and much better durability [106,116]. Several methods were reported for coating natural fibers with BC, one of them regards the coating of sisal and hemp fibers with layers of BC by culturing Acetobacter xylinum. This method led to improved interfacial adhesion between the polymer PLLA and BC-coated natural sisal and hemp [117].

1.6 Nanoparticles deposition/functionalization One of the most recent strategies for the natural fibers surface treatment is the incorporation of nanoparticles. Several types of nanoparticles can be used to enhance the interaction between the natural fibers and the matrix, to improve several characteristics of the fibers, and also to introduce new properties into the fibers. As a promising surface treatment method, inorganic nanoparticles such as CaCO3 can be employed as a filler to reduce the voids in the micropore fiber cell structure and as an adhesive between the fibers and the polymer matrix [118]. The nanoparticles on the fiber surface can provide nucleation sites to initiate the crystalline formation of the polymers, which will improve the compatibility between the fiber and the polymer matrix. Generally, the fibers are impregnated with Na2CO3 and CaCl2 salts at a certain pressure and temperature and the inorganic nanoparticles of CaCO3 are formed directly. This process compared to several chemical ones, is a simple, low-cost, and environmental friendly method which improves the mechanical characteristics of the fibers [119]. In addition to the filling and compatibility properties, the incorporation of nanoparticles can reduce the air bubble formation during the composite fabrication process improving the quality of the final product. Liang et al. reported that the mechanical properties of both kenaf fibers and kenaf fiber/polymer composites were increased by impregnating calcium carbonate nanoparticles into kenaf fibers. The tensile strength of the kenaf fibers increased more than 20% after the treatment, and also the tensile

32 PART | I Processing and characterization of green composites

modulus and strength of the composite composed of polypropylene matrix and treated kenaf fibers [120]. Besides CaCO3, other types of nanoparticles can be used for functionalizing the natural fiber surface and introduce new properties, based on the type of nanoparticle used, magnetic and electrical conductivity; UV protection; self-cleaning; fire retardant; and other special properties can be achieved. Very promising results were obtained utilizing gold (Au), silver (Ag), Cu (copper), Pd (palladium), Pt (platinum), Co (cobalt), titanium dioxide (TiO2) nanoparticles in fibers [121,122]. Cellulosic fibers with incorporated Au and Ag nanoparticles are used in homogeneous and heterogeneous catalysis, biosensors, protein delivery, and optical applications. Besides these applications, the Ag nanoparticles are also used in antimicrobial systems and also in the development of conductive structures [123,124]. The titanium dioxide incorporation allows extending the cellulose fiber applications to photocatalysis, stain-proofing, and self-cleaning; gas and humidity sensors; photovoltaics; photocleavage of water; photodegradation of organic pollutants; etc [125]. Zinc oxide (ZnO) nanoparticles have excellent ultraviolet protective properties and also conductive and fire retardant characteristics which can be incorporated into the composites [126,127]. Natural fibers with magnetic properties can be obtained by introducing, for example, iron oxide nanoparticles into the structure [128]. Several other examples could be presented; however, the goal is always the same, the combination of nanoparticles with natural fibers as an emerging strategy to produce a range of multifunctional cellulosic composites.

1.7 Concluding remarks and future trends Currently, the application of natural fibers in several industrial fields is in full growth due to its environmental and economic benefits compared to synthetic materials. Natural fibers are recyclable, biodegradable, safe to use, and present high specific strength-to-weight ratio. This last parameter is of particular importance when we are dealing with automotive applications, the high specific strength-to-weight ratio of the fibers used in composites manufacturing leads to the automobile parts weight reduction, which is reflected directly in the fuel consumption reduction. However, one of the problems related to the use of natural fibers in polymeric composites is the low compatibility between the fibers and the polymeric matrix. Therefore, several fibers surface functionalization methods were described in this chapter including chemical, physical, biological, and with nanoparticles. All the examples described herein reveal that the natural fibers surface treatment is essential to reduce the hydrophilicity of the fibers, to remove surface contaminants, and to increase the surface roughness improving the fiber surface properties and providing a better mechanical bonding between the fiber and polymer.

Surface modification of natural fibers in polymer composites Chapter | 1

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In conclusion, the natural fibers are very promising materials to be used in polymer composites development using different fiber surface modification methods. The chemical treatment is still the most frequently used method followed by the physical methods which are attracting more and more attention. In the near future, we hope it will be possible to use biological methods and nanoparticles treatment to achieve better results and improve the sustainability of the processes involved in the manufacturing of natural fiber polymer composites.

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Chapter 2

Flammability performance of biocomposites Maya Jacob John1, 2, 3 1 CSIR Materials Science and Manufacturing, Polymers and Composites Competence Area, Port Elizabeth, South Africa; 2Department of Chemistry, Faculty of Science, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa; 3School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, Johannesburg, South Africa

Chapter Outline 2.1 Introduction 2.2 Flammability testing techniques 2.2.1 Cone calorimetry 2.2.2 Pyrolysis combustion flow calorimetry 2.2.3 Limiting oxygen index 2.2.4 Underwriters laboratories 94 (UL94)

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2.2.5 Ohio State University heat release apparatus (OSU) 2.3 Case studies 2.3.1 Biopolymers and biocomposites 2.3.2 Use of green flame retardants 2.4 Conclusions References

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2.1 Introduction Bio-based composites are witnessing a growth in different industrial sectors, mainly ranging from construction to aerospace industries. This recent surge in the use of biocomposites is motivated by factors such as depletion of and high cost of petroleum reserves, comparable technical properties of biocomposites, and the current shift toward environmentally friendly and sustainable materials which in turn is supported by the implementation of environmental legislation such as REACH Act (Registration, Evaluation, Authorization and Restriction of Chemical substances) and other bio-based incentives. Bio-based products have been mainly used as flexible and rigid packaging materials where stringent flammability measures did not always have to be met. As recent trends seem to dictate the growing use of biopolymers [like polylactic acid (PLA)] and biocomposites in the transportation and electronics Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00002-1 Copyright © 2019 Elsevier Ltd. All rights reserved.

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sector, it has become very relevant to formulate strategies to improve flammability by the use of flame retardants to meet the various industrial regulatory standards of these sectors. A few examples of such regulatory measures include for aerospace applications; components used as interior panels must exhibit heat release rates (total heat release and peak heat release)
65 kW/m2 when tested on a Ohio State University heat release apparatus. For the automotive sector, the Federal Motor Vehicle Safety standard 302 stipulates that horizontal burn rate of the samples must not exceed 102 mm/min. There are four main families of flame retardant (FR) chemicals: inorganic, organophosphorus, nitrogen-based, and halogenated. There are synergists that act in combination with the FRs (e.g., antimony trioxide, zinc borate). Many of the traditional FRs, however, pose environmental/ecotoxicological threats, whether it is during manufacture, application, or combustion, or at end-of-life disposal. For example, antimony trioxide is a possible carcinogen and some of brominated and chlorinated FRs may form dioxins and furans on combustion or can be persistent, bioaccumulative, and/or toxic to humans, and this has led to a market call for halogen-free FRs There is growing evidence that these FRs can accumulate in people and cause adverse health effectsdhormonal imbalances, interference with reproductive systems, thyroid and metabolic function, and neurological development in infants and childrendand this has resulted in restrictions like REACH being imposed. The full-scale implementation of REACH will affect more than 3000 chemicals across a huge range of industrial and consumer products. Another legislative measuredthe Stockholm Convention on Persistent Organic Pollutants (POPs)dhas banned the production and use of 21 chemicals of which four are brominated FRs. Consequently, new ways are being sought to find more environmentally friendly FRs or fire resistance systems. These include modifications to new inorganic-based FRs, the use of nanocomposites (e.g., nanoclays), and nontoxic “green-chemistry” solutions. Also, in the use of green/environmentally friendly FRs the biodegradable nature of the biopolymers is retained.

2.2 Flammability testing techniques 2.2.1 Cone calorimetry Cone calorimetry is one of the most common fire behavior tests used to study the rate of heat released by materials exposed to radiant heat flux. Its principle is based on the measurement of decreasing oxygen concentration in the combustion gases of the sample that is subjected to a given heat flux (10e100 kW/m2). The analysis of combustion products and gaseous species can be performed by installation of a Fourier transform infrared (FTIR) spectrometer [1]. The most important parameter obtained from cone calorimetric testing is the heat released per unit of time and surface area (heat release rate, HRR)

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expressed in kW m2. The fire properties of materials are assessed by studying the gradual development of HRR over time, that is, the value of its peak maximum (PHRR) or HRR maximum. The calculation of HRR is based on Huggett’s study on the estimation of HRR via oxygen consumption measurements [1a]. This study concluded that most organic materials release an amount of heat that is practically proportional to the amount of oxygen consumed while burning. The proportionality factor is constant from one material to another and is equal to 13.1 kJ ge1 consumed oxygen, with an accuracy of approximately 5%. The total heat release (THR) [2] is obtained by integration of the HRR versus time curve expressed in MJ me2. Cone calorimetry, in addition to the aforementioned parameters, also provides information on time to ignition (TTI), time to flame out (TFO), mass loss rate, levels of oxygen, carbon monoxide, and carbon dioxide, and total smoke released (TSR). Furthermore, it provides more detailed fire characteristics, with HRR being the most widely used parameter for evaluating the fire properties.

2.2.2 Pyrolysis combustion flow calorimetry Pyrolysis combustion flow calorimetry (PCFC) is a fire test method for evaluating the combustibility of milligram-sized samples [3]. It is also known as microscale combustion calorimetry (MCC) and is now a standardized technique classified as ASTM D7309-07. PCFC reproduces the solid state and gas phase processes of flaming combustion in a nonflaming test. This is achieved by controlled pyrolysis of the sample in an inert gas stream followed by high temperature oxidation of the volatile pyrolysis products. The heat of combustion of the pyrolysis products is measured by the use of oxygen consumption calorimetry. This method combines the constant heating rate and flow characteristics of thermal analysis (i.e., thermogravimetry) with the ability to determine the heat of combustion typical of oxygen bomb calorimetry. PCFC determines the heat release and heat release rate using an oxygen consumption method. The heat release capacity is the maximum potential of the material to release combustion heat in a fire. From the above derivation, the heat release capacity (hc) is a combination of material properties, and consequently, is itself a material property as measured in PCFC. The use of Heat release capacity (HRC) as a measure of fire risk is based on the assumption that the maximum specific heat release rate at the decomposition temperature reached at constant heating rate correlates with the mass loss rate during pyrolysis in a fire characterized by a transient temperature gradient [4].

2.2.3 Limiting oxygen index Limiting oxygen index (LOI) is the minimum concentration of oxygen in a mixture of oxygen and nitrogen that is needed to support the flaming

46 PART | I Processing and characterization of green composites

combustion of a material. It is expressed in volume percent (vol%). It was first introduced in 1966 by Fenimore and Martin and is used to indicate the relative flammability of materials. It is standardized in the United States (ASTM D 2863) and in France (NF T 51-071), as well as internationally (ISO 4589). The method involves placing a sample vertically within a controlled atmosphere and its top inflamed with a burner. LOI, the minimum concentration of oxygen in a mixture of oxygen and nitrogen that either maintains flame combustion of a material for 3 min or consumes a length of 5 cm of a sample, is expressed as: LOI ¼ 100  ½O2 ð½O2  þ ½N2 Þ

(2.1)

where [O2] and [N2] are the concentrations of oxygen and nitrogen gases, respectively. Materials with LOI values less than 21% are classified as combustible, but those with LOI greater than 21 are classed as self-extinguishing since their combustion cannot be sustained at ambient temperature without an external energy contribution. Materials with a high LOI value generally exhibit a better FR property. This method remains one of the most important screening and quality control tools in the plastics industry to characterize both the ignitability and flammability resistance. However, LOI measurements are taken at room temperature and LOI values decrease as temperature increases. This means that self-extinguishing cannot be considered a fast rule, since materials with high LOI values at room temperature may burn without self-extinguishing under intense fire conditions. It should be noted that melting and dripping of a polymer during the LOI test may cause a specimen to extinguish and thus give misleading high LOI values. In addition, LOI has a limitation as a test for nanocomposites in that organomodified nanoclayereinforced polymer nanocomposites exhibit decreased LOI values due to an increased flame spread rate over the surface of the specimen, while inside the material nanoclays form a barrier layer that limits the propagation of fire [5]. The advantages of LOI are that it provides a convenient, reproducible means of determining a numerical measure of flammability. Furthermore, the test equipment is inexpensive and only a small sample size is required for testing.

2.2.4 Underwriters laboratories 94 (UL94) UL 94 is a set of tests approved by Underwriters Laboratories Inc. as flame tests for plastics materials for parts in devices and appliances. It includes a range of tests such as small and large flame vertical (V) tests, horizontal (H) tests for bulk and foamed materials, as well as radiant panel flame spread test. The commonly used test is UL 94V in terms of practice and usage. It measures ignitability and flame spread of vertical bulk materials exposed to small flame. It is equivalent to international standard IEC 60695-11-10 (Test method B) for small flames (50W) and ASTM D3801-10 [6]. The UL 94 test is widely used both in industry and academic research centers. It is intended to

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meet industrial requirements, as well as classify polymeric materials hierarchically. The information obtained remains limited due to its basic and unrefined character.

2.2.5 Ohio State University heat release apparatus (OSU) The OSU is a technique used to measure the RHR of materials and products in a forced flaming combustion. Both heat and smoke release are measured from the moment the specimen is injected into a controlled exposure chamber. Measurements are continued during the period of ignition and to such a time that the test is terminated. Although the OSU heat release apparatus is a good tool for flammability testing, there are known limitations of this test method [7]. The heat and smoke release depend on several factors such as formation of surface char, formation of adherent ash, sample thickness, and method of mounting. Heat release values are a function of the exposed tested area of the specimen. The test method is restricted to the specified specimen size of materials, products, or assemblies. In the case of products, the test specimen (i.e., prototype) is representative of the product in actual size. At very high specimen HRR, flaming above the stack is possible making the test invalid. There is no established general relationship between HRR values obtained from horizontally and vertically oriented specimens. Specimens that melt and drip in a vertical position are tested horizontally and hence vertical testing remains a problem for testing thermoplastic materials in the OSU.

2.3 Case studies 2.3.1 Biopolymers and biocomposites The different types of FRs and their use in natural fibers and natural fibere reinforced composites has been documented in detail by Mngomezulu and John [8]. Generally it has been seen that the methods of imparting fire resistance in natural fiberereinforced composites has been through three main routes [9]: l l

l

Chemically treating the natural fibers with suitable FRs; Treating the matrix (petroleum-based/biopolymer) with suitable FR additives during melt compounding stage; Use of FR coatings on the molded natural fiber composite

The choice of the FR depends upon the type of matrix polymer and processing technique used. In the case of natural fibers, commonly used FRs include phosphorus and nitrogen-based systems, which function in the condensed phase and promote char formation by converting fiber structure into char and reduce fuel formation. The most commonly used FRs for thermoplastic polymers are metal hydroxides (aluminium hydroxide/magnesium

48 PART | I Processing and characterization of green composites

hydroxide), expandable graphite, ammonium polyphosphate, intumescent systems, and nanoclays. Metal hydroxides act by undergoing exothermic reactions at elevated temperatures releasing vapor which retards the fire-forming reactions. Metal hydroxides need to be used at high loadings and usually has an adverse effect on mechanical properties. Phosphate-based systems interfere with polymer decomposition and promote char formation. FR coatings act as a barrier coating and are more often ceramic or intumescent-based. Intumescent coatings upon exposure to fire form a carbonaceous layer which acts as a thermal barrier and protects the underlying polymer system. In recent times, the use of nanofillers in PLA has been of particular interest as researchers have found that such nanocomposites exhibit improved mechanical properties at low loadings (3%e5%) along with increased flame resistance [10]. Addition of clay has been shown to reduce the peak heat release rate (PHRR) for PLA-based nanocomposites [11]. A decrease or increase in smoke production has also been observed. It has been proposed that when the polymer matrix is exposed to heat, the clay platelets migrate to the surface providing a protective layer that delays gasification of the layer below. The clays also form a carbonaceous-silicate char which acts as a heat barrier, increasing thermal stability, and as a physical barrier to mass transport of oxygen and volatile products. Solarski et al. investigated the flammability properties of melt-spun PLA/ montmorillonite multifilament nanocomposite fibers using the cone calorimeter [12]. They found a large (38%) decrease in the PHRR of the nanocomposites when compared to the pure PLA. Tensile strength and Young’s modulus, however, decreased upon addition of clay. In addition to clay, multiwalled carbon nanotubes (MWCNTs) have also been used in PLA but limited enhancement was observed as MWCNTs were not uniformly dispersed in PLA [13]. Another nanofiller that has potential is expanded graphite (EG) which when incorporated in PLA reduced the PHRR by 30% when compared to virgin PLA [14]. The use of natural halloysite as effective green FRRRs for thermoplastic compounds was presented by Dharia and Zetoun [15]. Although PLA nanocomposites exhibit lower flammability properties in terms of cone calorimetry, they often fail in other flammability tests (limiting oxygen index and UL-94) [16]. The fire resistance of the nanocomposite can, however, be improved by combining the nanofiller with conventional FRs. When using nanofillers, the properties achieved depend not only on the properties of the nanofiller and polymer but also on interfacial characteristics and the method of preparation. Layered silicate nanocomposites, for example, result only when an intercalated or exfoliated structure is formed. An intercalated nanocomposite is one in which the polymer chains are inserted into the layered silicate structure in a crystallographically regular fashion. When the individual silicate layers are separated in a continuous polymer matrix, an exfoliated structure is obtained. When the polymer is unable to intercalate between the layered silicates, phase separation occurs and the properties

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remain the same as that for a traditional microcomposite. For particled or fibrousdreinforced nanocomposites the dispersion and nanofiller-polymer interface is crucial in determining the properties of the material. Uniform dispersion is usually attained by chemical modification of nanofillers to enhance the interfacial adhesion between the nanofillers and polymer matrix. In a recent study, PLA containing melamine grafted MWCNTs were found to exhibit a 28% reduction in PHRR. This was attributed to high level of dispersion in treated MWCNTs-reinforced PLA when compared to unmodified systems. Another interesting observation was the formation of a compact and cohesive char for the functionalized MWCNT-reinforced PLA while unmodified PLA exhibited islands of char devoid of any cohesion [17]. The use of nanoclay (C30 B) and polylactic acid grafted glycidyl methacrylate (PLA-g-GMA) on flammability properties of silane-treated banana fiberereinforced PLA composites was investigated by Sajna et al. [18] Flammability properties measured by UL-94 horizontal burning test and cone calorimetry showed that the PHRR reduced by 22.6% in the presence of nanoclay (Fig. 2.1). This was attributed to the fact that nanoclay accelerated the char formation and hence could reduce the flammability of PLA samples. Another group of FRs commonly used for natural fiber composites are the inorganic hydroxides. In a recent study, Mg (OH)2 and Al (OH)3 were used to improve the fire resistance of sisal [19] and saw-dust [20] ereinforced polypropylene composites. However inorganic hydroxides have been reported to

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700

800

FIGURE 2.1 HRR graphs of compatibilized bionanocomposites.

50 PART | I Processing and characterization of green composites

reduce the mechanical properties of composites and hence the use of Ca(OH)2 as a FR was studied by Zhao et al. [21]. for hemp-reinforced polypropylene composites. In this study, Ca (OH)2 was used to modify the hemp fiber surface and not incorporated in the compounding stage as in previous studies. Fig. 2.2 shows the LOI values of the composites, and it can be seen that the LOI values registered an increase indicating improved flame retardance, and this was attributed to the fact that Ca(OH)2 decomposed to form CaO and water which aided in fire resistance. The authors also observed that addition of ammonium polyphosphate (APP) further improved flame retardance due to synergistic interaction between CaO and APP. In a detailed study, Sypaseuth [22] observed that best flammability results are obtained when multicomponent FR systems are used. In the study dealing with kenaf fiberereinforced PLA composites, the synergistic effects of multicomponent systems of expandable graphite with ammonium polyphosphate and magnesium hydroxides with layered silicates were studied. It was observed that for both systems, excellent flame retardance was obtained at low level of FRs. In another study [23] involving synergistic systems, ammonium polyphosphate (APP) and distiller’s dried grains with solubles (DDGS) as the natural charring agent was used for polylactic acid systems. The surfaces of both APP and DDGS were coated by degradable polymeric FR resorcinol di(phenyl phosphate) (RDP). The main observation of the study was that the limited oxygen index value of the biocomposites with loading of 15 wt% CdDDGS and 15 wt% CdAPP reached 32.0%, and a ULd94 Vd0 was

25

20

F F1 F-15R F1-15R

LOI

15

10 5

0 0%

20% 30% Content of the hemp fiber

50%

FIGURE 2.2 Limiting oxygen index of the treated and untreated hemp and their reinforced composites.

Flammability performance of biocomposites Chapter | 2

51

attained. The biocomposites also exhibited good mechanical properties with the tensile strength of the samples being maintained at 57 MPa. The effect of the FR APP on the properties of a range of natural fibere reinforced polybutylene succinate composites was investigated by Dorez et al. [24]. The natural fibers chosen in this study were cellulose, hemp, flax, sugarcane, and bamboo and flammability was measured by PCFC and cone calorimetric testing. The main observations of this study were that the incorporation of fibers reduced the time to ignition in the composites but increased the char residues (Fig. 2.3), which led to reduction of PHRR values. The authors suggest that the synergistic effect of the presence of APP and natural fibers results in decrease of flammability properties. The use of glycerol phosphate and phosphorus-silane treatment on flax fibers in flax-reinforced PLA/thermoplastic starch (TPS blends) was investigated by Bocz et al. [25]. The authors observed that the multifunctional additive system resulted in reduction of flammability properties by 40%. The composites also exhibited well-balanced strength and stiffness values. In an interesting study, the effect of biochar (carbonaceous material produced when organic wastes are heated at high temperatures >500 C) on the

FIGURE 2.3 Residue of samples from cone calorimeter tests: (a) 90PBS10fl, (b) 85PBS15fl, (c) 80PBS20fl, (d) 70PBS30fl.

52 PART | I Processing and characterization of green composites

properties of polypropylene composites was investigated by Das et al. [26]. The authors observed that the both flame retardance and mechanical properties of the composites improved with the addition of biochar. With incorporation of 35% biochar, the PHRR values were found to decrease by 54% (Fig. 2.4) and time to ignition by 43%.This was attributed to the thermally stable biochar acting as an efficient barrier to transport of oxygen and reducing the flammability. As an extension of the above study, the synergistic effect of biochar and wool on polypropylene composites was investigated by the same authors [27]. Samples were prepared containing different ratios of biochar, wool, and APP. It was found that the incorporation of both biochar and wool fiber reduced the PHRR, smoke production as seen in Fig. 2.5 and resulted in improved LOI values. Composites containing higher amount of wool exhibited higher LOI values compared to composites containing biochar. Another interesting observation was that wool-containing composites exhibited minimal dripping of molten PP and negligible smoke production. This was attributed to the high fire resistance and char forming ability of wool fibers. Recently the researchers at the Council for Scientific and Industrial Research (CSIR), South Africa, have been involved in the development of woven flax fiberereinforced phenolic sandwich panels for use in aircraft as secondary structures. The research work involved imparting an aqueous-based phosphate FR treatment on the flax fabric to ensure that the composite panels comply with Federal Aviation Administration (FAA) and AIRBUS regulations.

(a)

(b)

1400

0.7

1000 800 600

0.5 0.4

0.2

200

0.1 0

0 0

200

400 600 Time (s)

800

1000

(d)

0.012

0

200

400 600 Time (s)

800

1000

120 Neat PP 15 BC 25 BC 30 BC

0.008 0.006

Neat PP 15 BC 25 BC 30 BC 35 BC

100 80 Mass loss %

0.01 COP (g/s)

35 BC

0.3

400

(c)

Neat PP 15 BC 25 BC 30 BC

0.6

Neat PP 15 BC 25 BC 30 BC 35 BC

CO2P (g/s)

2 HRR (kW /m )

1200

35 BC

0.004 0.002

60 40 20 0

0 0

200

400 Time (s)

600

800

1000

0

500

1000

1500

Time (s)

FIGURE 2.4 Flammability properties of biocomposites (cone calorimeter).

2000

Flammability performance of biocomposites Chapter | 2

(b) 1000 800

Neat PP S1 S2 S3

600 400 200

0.6 0.5

0.3 0.2 0.1

100 200

(c)

300 400 500 600 Time (s)

Neat PP S1 S2 S3

0.006 0.004

0 0

700

0.01 0.008

100 200

(d)

300 400 500 600 Time (s)

700

100 Neat PP S1 S2 S3

80 60 40 20

0.002 0

Neat PP S1 S2 S3

0.4

0 0

CO production (g/s)

CO2 production (g/s)

0.7

1200

Mass loss (%)

2 Heat release rate (kW /m )

(a)

53

0 0

100

200

300 400 Time (s)

500 600 700

0

100 200

300 400 500 600

700

Time (s)

FIGURE 2.5 Cone calorimeter results of neat PP and composites.

In addition to the primary FR, the panels contained nonfibrous natural silicate fire resistant material as well. The composite panels were reported to exhibit superior flammability, smoke, and toxicity properties for the aforementioned purposes [28]. In another study by the same group, researchers analyzed the aging and flammability behavior of woven flax fabricereinforced phenolic composites. It was observed that the phosphate-based flame retardant treatment on the woven flax fabric reduced the PHRR, SPR, and CO2 emission rates. Biocomposites being used in the transport sector are exposed to varying conditions of temperature and humidity and hence it is crucial to record the behavior of materials after aging. In this study, after aging at high temperatures, the tensile strength of both treated and untreated composites decreased, but the decrease was most prominent in fire retardantetreated composites. This was attributed to the degradation of the flame retardants when exposed to high temperature and humidity. This further indicated that the selection of flame retardants is an important criteria, especially for biocomposites to be used in advanced industrial applications. The commonly used conventional FRs in the automotive sector have been described in Table 2.1. In a recent study, researchers developed bio-based FR panels for trucks and buses from Solaris and Fiat. The biopolymers used were PHB (polyhydroxybutyrate) and PBS (polybutylene succinate), which were obtained from byproducts from the cellulose production. Sandwich panels were

54 PART | I Processing and characterization of green composites

TABLE 2.1 Flame retardants used in automotive sector. Automotive components

Polymer

Flame retardants (FRs)

Printed circuit board

Epoxy/Phenolics

Brominated FRs; Sulfonates

Housing and dashboard

HIPS/ABS/PC-ABS alloys/ PP

Brominated FRs

Wire and cables

PP copolymers/EPR

Brominated FRs

Battery casing

PP

Brominated FRs

Textile for seats

Latex backcoating

Brominated and phosphorusbased additives

Seats

Flexible PUF

Phosphorus-based additives

Connectors and underhood parts

Polyamides

Brominated FRs

Acoustic insulation

XPE foam

Brominated and mineral-based FRs

Thermal insulation

Rigid PUF/XPE foam/ Plasticized PVC

Phosphorus-based additives

Truck and boat covers

Plasticized PVC

Phosphorus-based additives

Door partition and internal panels

PP and wood polymer composites

Mineral and phosphorus-based FRs

Adapted from Fire protection for automotive and transportation. http://icl-ip.com/wp-content/uploads/2015/07/FR-Transportation-2012.pdf.

manufactured from natural fiberereinforced PHB and PBS and a cork core and had potential to be used in trains and vans [30].

2.3.2 Use of green flame retardants Global chemical regulations are on the increase and these changes impact a broad range of materials, including FRs. FRebased regulations are important to ensure fire safety in areas like electronics, automobiles, and furnishings. Currently some of the conventional FRs pose environmental/ecotoxicological threats, whether it is during manufacture, application, or combustion, or at end-of-life disposal, and are subsequently under the threat of being banned. The emergence of stringent legislative measures (like REACH) and the desire for sustainability are resulting in a focus on the need for characterizing environmental and human health impacts of all chemicals. In response to the regulatory challenges, the research community has focused attention on the

Flammability performance of biocomposites Chapter | 2

55

development of flame retardants that are safe, effective, in compliance with regulations, and are sustainable. Some of the techniques used for imparting flame resistance by green flame retardants have been used for textile fabrics. The use of deoxyribonucleic acid (DNA) and chitosan as flame retardants through the layer-by-layer technique for cotton fabrics was investigated by Carosio et al. [31]. The authors observed a reduction of HRR by 40% during cone calorimetry tests and selfextinguishing characteristics during horizontal flammability tests. This was attributed to the fact that DNA contains a precursor of phosphoric polyphosphoric acid, a polyhydric char source and an ammonia releasing base. The combination with chitosan promoted the formation of char which reduced the flammability of the system. Another study elaborated on the novel use of chitosan-based FR (urea salt of chitosan phosphate [UPCS]) on the flammability properties of polyvinyl alcohol (PVA). The authors observed a reduction of 42% in PHRRs upon the addition of 20% FR. This was attributed to the fact that UPCS accelerated the dehydration action and the formation of char at low temperatures [32]. In an interesting study, the flame retardance behavior of alginate fibers was studied by Tian et al. [33]. The authors reported the LOI results which showed that all zinc alginate fibers are intrinsically flame retardant, with LOI values of over 27.0, as compared with about 24.5 for alginic acid fiber. The HRR and total heat release values of zinc alginate fibers (obtained from cone calorimeter) were significantly less than those of alginic acid fiber, and decreased with increasing zinc ion content. The use of lignin as a flame retardant for polybutylene succinate (PBS) composites was investigated by Ferry et al. [34]. Lignin possesses intrinsic properties of high thermal stability, crosslinked chemical structure, and char forming ability indicating that it can be used as a FR additive. In this study, two types of lignin (alkali and organosolv) were used and the grafting of phosphorus on lignin was also examined. It was observed that incorporation of 20 weight% of alkali lignin reduced peak HRR by 50% (Fig. 2.6) and improved charring in the PBS system. The authors conclude that modified lignin can be used as an efficient bio-based FR. Most of the bio-based FRs developed are either expensive or affect the mechanical properties of the final product. To overcome this, in an H2020 ongoing project on bio-based FRs for consumer electronics and automotive applications, researchers are developing green FRs from a combination of a recently developed lignosulphonate flame retardant (LS-FR) and commercial ammonium polyphosphate (APP). LS-FR which is obtained as a byproduct of pulp industry has been found to be an effective and bio-based FR which complies with fire resistant standards for the consumer electronics and automobile sectors, while maintaining adequate mechanical properties.

56 PART | I Processing and characterization of green composites 600 PBS PBS-5%lig alk

500

PBS-10%lig alk PBS-15%lig alk PBS-20%lig alk

HRR (kW/m2)

400 300 200 100

0 0

100

200

300 Time (s)

400

500

600

FIGURE 2.6 HRR versus time curves from cone calorimeter test at 35 kW/m2 for the various PBS-alkali lignin blends.

2.4 Conclusions This chapter deals with studies on imparting flame retardance in biopolymers and biocomposites. The introduction section gives an overview of biocomposites and stringent flammability requirements that needs to be met for biocomposites to be used in automotive and aerospace applications. The different flammability techniques and advantages and disadvantages of certain techniques have been outlined. Case studies based on flammability studies in fibers, biopolymers, and biocomposites and the use of green FRs have been presented. As seen from the case studies, the methods of imparting fire resistance has been by treating the reinforcement (natural fibers) with suitable FRs, modifying the matrix polymers by use of FR additives during compounding, and use of FR coatings. It can be inferred that FR characteristics is a prerequisite especially in advanced industrial applications and hence novel strategies for development of environmentally friendly FRs needs to be a focus area for researchers.

References [1] [1a] [2] [3]

Lindholm, Brink A, Hupa M. Cone calorimeter e a tool for measuring heat release rate. 2009; Hugget C. Estimation of rate of heat release by means of oxygen consumption measurements. Fire and Materials 1980;4:61e5. Wichman IS. Material flammability, combustion, toxicity and fire hazard in transportation. Progress in Energy and Combustion Science 2003;29:247e99. Morgan AB, Galaska M. Microcombustion calorimetry as a tool for screening flame retardancy in epoxy. Polymers for Advanced Technologies 2008;19:530e46.

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[6]

[7]

[8] [9] [10]

[11]

[12]

[13]

[14]

[15] [16]

[17]

[18]

[19] [20]

57

Schartel B, Pawlowski KH, Lyon RE. Pyrolysis combustion flow calorimeter: a tool to assess flame retarded PC/ABS materials? Thermochimica Acta 2007;462:1e14. Chapple S, Anandjiwala R. Flammability of natural fibre-reinforced composites and strategies for fire retardancy: a review. Journal of Thermoplastic Composite Materials 2010;23:871e93. Laoutid F, Bonnaud L, Alexandre M, JLopez-Cuesta J-M, Dubois P. New prospects in flame retardant polymer materials: from fundamentals to nanocomposites. Materials Science and Engineering R 2009;63:100e25. Hirschler MM. Use of heat release measurements and/or fire hazard assessment in codes and standards in the USA. In: Fire risk & hazard assessment symposium, June 28e30, 2000. Atlantic City, NJ: National Fire Protection Research Foundation; 2000. Mngomezulu ME, John MJ, Jacobs V, Luyt AS. Review on flammability of biofibres and biocomposites. Carbohydrate Polymers 2014;111:149e82. Kandola BK. Flame retardant characteristics of natural fibre composites, natural polymers, vol. 1 composites. RSC Publishing; 2012. Alexandre M, Dubois P. Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials. Materials Science and Engineering 2000;28:1e63. Gilman JW, Jackson CL, Morgan AB, Harris R, Manias E, Giannelis EP, Wuthenow M, Hilton D, Phillips SH. Flammability properties of polymer-layered-silicate nanocomposites. Polypropylene and polystyrene nanocomposites. Chem Mater 1866e1873;12:2000. Solarski S, Mahjoubi F, Ferreira M, Devaux E, Bachelet P, Bourbigot S, Delobel R, Coszach P, Murariu M, Da Silva Ferreira A, Alexandre M, Degee P, Dubois P. (Plasticized) polylactide/clay nanocomposite textile: thermal, mechanical, shrinkage and fire properties. Journal of Material Science 2007;42:5105e17. Murariu M, Bonnaud L, Yoann P, Fontaine G, Bourbigot S, Dubois P. The production and properties of polylactide composites filled with expanded graphite. Polymer Degradation and Stability 2010;95:374e81. Bourbigot S, Fontaine G, Duquesne S, Delobel R. PLA nanocomposites: quantification of clay nanodispersion and reaction to fire. International Journal of Nanotechnology 2008;5:683e92. Dharia A., Zetoun A., AMI Flame Retardants in Plastics,http://appliedminerals.tempwebpage. com/images/uploads/eventspresentations/Applied_Minerals_-_FR_JUNE14.pdf. Sinha Ray S, Yamada K, Okamato M, Fujimoto Y, Ueda K. New polylactide/layered silicate nanocomposites. 5. Designing of materials with desired properties. Polymer 2003;44:6633e46. Bourbigot S, Fontaine G, Gallos A, Gerard C, Bellayer S. In: Wilkie CA, Morgan AB, Nelson GL, editors. Fire and polymers V e Materials and concepts for fire retardancy, vol. 1013. Washington, DC: American Chemical Society; 2009. p. 25e34. V.P. S, Mohanty S, Nayak SK. Influence of nanoclay and graft copolymer on the thermal and flammability properties of polylactic acid/banana fibre biocomposites. Journal of Vinyl and Additive Technology 2017;23:E81e91. https://doi.org/10.10002/vnl.21556. Suppakarn N, Jarukumjorn K. Mechanical properties and flammability of sisal/PP composites: effect of flame retardant type and content. Composites Part B 2009;40:613e8. Sain M, Par SH, Suhara F, Law S. Flame retardant and mechanical properties of natural fibreePP composites containing magnesium hydroxide. Polymer Degradation and Stability 2004;83:363e7.

58 PART | I Processing and characterization of green composites [21]

[22] [23]

[24] [25]

[26] [27]

[28]

[29] [30] [31] [32]

[33] [34]

Zhao WJ, Hu QX, Zhang NN, Wei YC, Zhao Q, Zhang YM, Dong JB, Sun ZY, Liu BJ, Li L, Hu W. In situ inorganic flame retardant modified hemp and its polypropylene composites. RSC Advances 2017;7:32236e45. Sypaseuth FD, Gallo E, Ciftci S, Schartel B. Polylactic acid biocomposites: approaches to a completely green flame retarded polymers. E-Polymers 2017;17:449e62. Shi X. The intumescent flame-retardant biocomposites of poly(lactic acid) containing surface-coated ammonium polyphosphate and distiller’s dried grains with solubles (DDGS). Fire and Materials 2017:1e8. https://doi.org/10.1002/fam.2479. Dorez G, Taguet A, Ferry L, Lopez-Cuesta JM. Thermal and fie behaviour of natural fibres/ PBS biocomposites. Polymer Degradation and Stability 2013;98:87e95. Bocz K, Szolnoki B, Marosi A, Tabi T, Wladyka-Przybylak M, Marosi G. Flax fibre reinforced PLA/TPS biocomposites flame retarded with multifunctional additive system. Polymer Degradation and Stability 2014;106:63e73. Das O, Bhattacharyya D, Hui D, Lau K-T. Mechanical and flammability characterisations of biochar/polypropylene biocomposites. Composites Part B 2016;106:120e8. Das O, Kim NK, Sarmah AK, Bhattacharya D. Development of waste based biochar/wool hybrid biocomposites: flammability characteristics and mechanical properties. Journal of Cleaner Production 2017;144:79e89. Anandjiwala R, Chapple SA, John MJ, Schelling HJ, Michaelis W,M, Do¨cker M. A flameproofed artefact and a method of manufacture thereof, WO 2013/084023 A1. World Intellectual Property Organization, International Bureau; 2013. Fire protection for automotive and transportation. http://icl-ip.com/wp-content/uploads/ 2015/07/FR-Transportation-2012.pdf. http://www.aimplas.net/blog/new-flame-retardant-and-biodegradable-panels-trucks-andbuses-wastes-paper-industry. Carosio F, Di Blasio A, Alongi J, Malucelli G. Green DNA-based flame retardant coatings assembled through layer by layer. Polymer 2013;54:5148e53. Hu S, Song L, Pan L, Hu Y. Effect of a novel chitosan-based flame retardant on thermal and flammability properties of polyvinyl alcohol. Journal of Thermal Analysis and Calorimetry 2013;112:859e64. Tian G, Ji Q, Xu D, Tan L, Quan F, Xia Y. The effect of zinc ion content on flame retardance and thermal degradation of alginate fibres. Fibres and Polymers 2013;14:767e71. Ferry L, Dorez G, Taguet A, Otazaghine B, Lopez-Cuesta JM. Chemical modification of lignin by phosphorus molecules to improve the fire behaviour of polubutylene succinate. Polymer Degradation and Stability 2015;113:143e235.

Part II

Thermosetting and thermoplastic materials for structural applications

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Chapter 3

Green thermoset reinforced biocomposites Samson Rwahwire1, Blanka Tomkova2, Aravin Prince Periyasamy2, Bandu Madhukar Kale2 1

Faculty of Engineering, Busitema University, Tororo, Uganda; 2Department of Material Engineering, Technical University of Liberec, Liberec, Czech Republic

Chapter Outline 3.1 Introduction 3.2 Vegetable oil resins and composites 3.2.1 Linseed oil thermoset composites 3.2.2 Soybean oil thermoset composites 3.2.3 Wheat gluten matrix composites

61 64 65 65

3.2.4 Castor oil resin composites 3.2.5 Bio-based polyurethanes 3.2.6 Cashew shell nut liquid 3.2.7 Zein matrix composites 3.2.8 Green epoxy composites 3.3 Conclusion and challenges References Further reading

69 70 71 73 75 75 76 80

68

3.1 Introduction Worldwide, researchers are embroiled in a race for niche products whereby industries can boost production processes as well as serve the needs for sustainability. The quest for environmentally friendly materials so as to mitigate the global warming effects is on the agenda of most industrialized nations, and recommendations are put forward for the production of recyclable, biodegradable products or materials with zero emissions [1]. The impact of the consequences of climate change due to an increase in Green House Gas (GHG) emissions is visible. GHG emissions from agriculture mostly come from the management of agricultural soils, livestock, rice production, and biomass burning. Plants mitigate climate change by absorbing and storing carbon; when plant biomass is effectively utilized the carbon dioxide remains stored in the products for decades. However, if the biomass is left to decompose, carbon dioxide is emitted. The Intergovernmental Panel on Climate Change’s (IPCC) Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00003-3 Copyright © 2019 Elsevier Ltd. All rights reserved.

61

62 PART | II Thermosetting and thermoplastic materials for structural applications

most recent report recommends cutting of GHG emissions by 70% and an increase of the use of clean green energy by 2050. Effective strategies such as utilization of sustainable biodegradable materials instead of synthetic materials can contribute to lowering GHG emissions, thus combating climate change [2]. The European Union (EU) guideline 2000/53/EG [3] issued by the European Commission had stipulated that 95% of the weight of a vehicle had to be recyclable by 2015. This regulation in tandem with a couple of other regional and international regulations led to a surge of utilization of green composites among the European automotive industry by designing and production of renewable biodegradable composites based on natural fibers [4e14]. Furthermore, the EU Landfill Directive 1999/31/EC whose main goal is to reduce the quantity of biodegradable municipal waste that ends up in landfill sparked research in sustainable and biodegradable materials that can be reused [15]. Production of chemicals and materials from bio-based feedstock is increased from approximately 12% in 2010 and expected to be 18% in 2020 and 25% in 2030 [16]. The need for lightweight materials with superb performance characteristics has sparked interest in composite materials’ research and practice. Early civilizations used natural fibrous materials from biblical times; Egyptians reinforced mud bricks with straw. However, at the turn of the 20th century, new fibers, largely from petrochemical sources and with exceptional strength impeded the use and production of natural fibers. With the dwindling petroleum resources, coupled with high prices, fiber from lignocellulosic materials play a major role in the transition from synthetic to environmentally friendly, biodegradable green composites whose feedstock is from wood and plants [16,17]. The ecological “green” image of cellulosic fibers is the leading argument for innovation and development of products, which are not only biodegradable but can be applied to the automotive industries [5], building and construction [18], geotextiles, and agricultural products [19,20]. Table 3.1 shows the most popular automotive companies and the respective parts where green composites are applied. Plant-based fibers like flax, hemp, nettle, and kenaf, which were previously used for fiber in the Western world, have attracted renewed interest in textile and industrial composite applications [21e23]. To mitigate climate change through a reduction of GHG, composites are being developed whereby the polymers are from biodegradable sources so as to have fully green environmentally friendly polymer resins. Green polymer resins are obtained from vegetable/plant oils. Vegetable oils are composed of triglyceride molecules containing three fatty acid chains joined by ester groups (Fig. 3.1). The fatty acids have a varied number of C]C bonds, however the double bonds needs to be conjugated so as to be able to be reactive to fillers. Although vegetable oils are derived from plant sources, the pathways involved in making thermoset resins are synthetic, and this chemical modification results in monomers or resins which are precursors for polymerization reactions [25].

TABLE 3.1 Examples of Green Thermoset Biocomposites. Filler

% of Filler in Resin

Production Process

Modulus [GPa]

Strength [MPa]

References

Conjugated Soybean oil (St-DVB cross-linked)

Wheat straw

75

Compression molding

1.59e2.3

5.5e11.3

[29]

Conjugated Soybean oil (DVB cross-linked)

Corn stover

80

Compression molding

0.291e1.398

2.7e7.4

[30]

Conjugated soybean oil

Soybean hulls

50

0.7

2.3

[31]

Methacrylic anhydride modified soybean oil

Regenerated cellulose (Lyocell)

Compression molding

18

144

[32]

Methacrylic anhydride modified soybean oil

Jute

Compression molding

14e19

65e84

[32]

AESO

Hemp

20

RTM

4.4 2.6 (F)

35 35.7e51.3(F)

[26]

AESO

Flax

20

RTM

4.4

35

[26]

AESO (St-cross-linked)

Chicken feathers

30

RTM

1.59

45.2

[33]

Linseed oil

Pine wood flour

40

1.5

19.9

[34]

Castor oil

Banana fiber

1.96

[35]

Castor oil

MDI-modified cellulose

25.4(MPa)

4.87

[36]

Tung oil

Pine wood flour

0.9

26

[37]

Hand lay-up 43

Green thermoset reinforced biocomposites Chapter | 3

Biopolymer Resin

63

64 PART | II Thermosetting and thermoplastic materials for structural applications O 1

H2C

O

HC

O

H2C

O 2

O

5

O

9

15

12

ω

α 3

4

6

FIGURE 3.1 A triglyceride molecule (from top to bottom: saturated palmitic acid and unsaturated oleic acid and alpha-linolenic acid), glycerol linkage (1), ester group (2), a-position of ester group (3), double bonds (4), monoallylic position (5), and bisallylic position (6) [24].

Chemical modification of the double bonds in the triglycerides leads to formation of maleates, hydroxyl, or epoxy groups [26]. Hereafter, the modified triglycerides can be used for cross-linking reactions or can be further modified. For example, when epoxy groups are reacted with acrylic acid in the presence of vegetable oil such as soybean oil, a thermoset polymerdacrylated epoxidized soybean oildis formed that can be used in green composites. Alternatively, the reaction of hydroxylated triglycerides with maleic anhydride results into maleates, whereas the use of alcoholyzed castor oil or alcoholyzed hydroxylated oils can be utilized for the production of polyurethanes obtained by polycondensation reactions with different isocyanate components. In order to improve the physical, processing, and handling properties of vegetable oil-based thermoset polymers, the resins are usually blended with diluents such as styrene, vinyl toluene, divinylbenzene, acrylates, etc. Styrene has been the preferred diluent; however, it is detrimental to human health, and therefore other diluents vinyl toluene, divinylbenzene, and acrylates among others are used instead. Vegetable oilebased resins offer specific advantages over other synthetic resins. The major advantages of these plant-based oil resins include: renewability, low environmental impact, and reduction of the dependence on the limited resources of petrochemicals. On the other hand, the traditional synthetic resins such as epoxy, phenolic, polyurethanes (PUs), polyester, and vinyl ester pose problems regarding biodegradability, initial processing cost, energy consumption, health, and environmental hazards as none of the components of these polymers come from renewable resources [27].

3.2 Vegetable oil resins and composites Bio-resins made from vegetable oils could offer a sustainable alternative to petroleum-based thermoset resins. New research has developed viable ways of making use of cost-effective green technology. Table 3.1 shows a number of examples of such material applications.

Green thermoset reinforced biocomposites Chapter | 3

65

3.2.1 Linseed oil thermoset composites Thermoset composites from linseed oil also known as flaxseed oil or flax oil, which is obtained from the dried, ripened seeds of the flax plant through pressing and sometimes followed by solvent extraction [28]. Linseed oil is chemically composed of 57% linolenic acid (C18:3), 15% linoleic acid (C18:2), 19% oleic acid (C18:1), and 4% stearic acid (C18:0). The unsaturated fatty acids which are mixtures of triglycerides can easily be converted into epoxy fatty acids by conventional epoxidation, metal catalyst epoxidation, catalytic acidic ion exchange, or other reactions [38]. Linseed oil is the most highly epoxidized oil because of its highest concentration of double bonds. In order to ensure the required reactivity, the triglyceride compound is isolated and purified carefully, followed by suitable functionalization. A number of chemical modification techniques are used for the functionalization of epoxidized linseed oil and one of the most commonly used is an epoxidation reaction [39]. Synthesis of thermoset polymers from linseed oil through epoxidation, followed by acrylation, and then maleinization produces thermosets with storage modulus of approximately 2.5 GPa at 30
C, Tg of above 100
C, flexural strength of 100 MPa, flexural modulus of 2.8 GPa [25]. Thermoset epoxidized linseed is used as an impregnator, for drying oil finish in wood finishing, as a pigment binder in oil paints, and in the manufacture of linoleum. Linseed oil has been found to exhibit the highest glass transition, high strength, and the lowest elongation at break [40]. Thermoset polymers can also be obtained from conjugated linseed oil, styrene, and divinylbenzene (DVB) via thermal polymerization [34], as well as bulk-free radical polymerization [25]. Lignocellulosic-reinforced biocomposites prepared using a free radically cured conjugated linseed oilebased resin show a tensile strength of 5.4e8.8 MPa; the addition of maleic anhydride as a compatibilizer increases the tensile strength up to 10.4 MPa [41]. The triglyceride molecules in the linseed oil can be functionalized to produce an unsaturated polyester like resin through glycerolysis to produce a monoglyceride and thereafter reaction with maleic anhydride to produce a maleinated monoglyceride that is blended with styrene, the reactive co-mononer giving rise to a cross-linked thermoset polymer with carboxyl groups that can be utilized for bonding with hydroxyl groups of lignocellulosic fibers [34].

3.2.2 Soybean oil thermoset composites Just like other vegetable oils, soybean oil contains high levels of unsaturated fatty acids, which can be easily converted into epoxy fatty acids by conventional methods mentioned above. A number of chemical modification techniques are used for the functionalization of soybean oils and one of the most

66 PART | II Thermosetting and thermoplastic materials for structural applications

O O

O

O

O

2

3 OH

O

O

O

O

OH

3

3

O

O

OH O

7

FIGURE 3.2 Methacrylated soybean oil [43].

commonly used is an epoxidation reaction [42]. In the literature, it is quite evident that the use of plant oilebased resins, for example, methacrylated soybean oil (Fig. 3.2), compared with their synthetic counterpart, leads to a reduction in the emission of some of the synthetic components; health and environmental risks associated with them thereby leading to environmentally sustainable materials [44]. The impact performance of biocomposites fabricated from jute/ methacrylated soybean oil (MSO) subjected to low-velocity impact loading was investigated by Dhakal et al. [43]. The biocomposite laminates were fabricated using compression molding; the influence of thickness and weave architectures on the impact response showed that the biocomposite reinforced with 46 yarns per 10 cm weft and 50 warp (W2-3 mm thick) exhibited the highest resistance to impact damage compared to 32 and 15 yarn per 10 cm weft samples, which was attributed to efficient fiber-to-matrix adhesion due to the fabric structure (Fig. 3.3). Furthermore, it was deduced that both fiber orientation and fabric thickness affected the impact response of the biocomposite laminate panels. Because styrene is hazardous to human health, other diluents such as vinyl monomer and N-vinyl-2-pyrrolidone (NVP) can serve the same purpose. NVP was used as a replacement for hazardous styrene in soybean oilebased thermosets to form acrylated epoxidized soybean oil (AESO) and reinforced with hemp fibers. An increase in the NVP resulted in the composites with higher tensile strength, tensile modulus, flexural strength, flexural modulus, storage modulus, and Tg compared to those with styrene as a diluent [45]. Research elsewhere shows that the addition of diluents in soybean oil resin positively influences the mechanical properties of thermoset biocomposites [46]. Liu et al. [47] presented a green thermoset resin system based on AESO and methacrylated eugenol (ME) prepared via free radical polymerization. The resin system exhibited high strength, modulus, fast curing speed within 10 min and thermally stable up to 300
C making it suitable for pultrusion and other composite manufacturing processes. Mandal and Maji [48] investigated the properties of wood polymer composites based on three types of modified soybean oils: acrylic acid (AESO), methacrylic acid (MESO), and methacrylic anhydride (MAESO) (Fig. 3.4).

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FIGURE 3.3 Different fibers (a) nonwoven jute, (b) woven fabric W1, (c) woven fabric W2, (d) woven fabric W3 [43].

OH

(a)

OH

O O

O O O

OO

O

O

OH O O

O O

O

O HO

O O O OH O

O

O

(b) O O

OH O O

FIGURE 3.4 Molecular structure of typical modified soybean oils: (a) maleinated acrylated epoxidized soybean oil (MAESO) and (b) methacrylated fatty acid (MFA) molecules [43].

68 PART | II Thermosetting and thermoplastic materials for structural applications

The MAESO-based WPC had a maximum enhancement in mechanical properties, thermal properties, flame retardancy, and water uptake resistance. Regenerated cellulose fibers utilizing nonwoven lyocell and viscose were used as reinforcement in acrylated epoxidized soybean oil (AESO) [49]. The biocomposites reinforced with lyocell fiber with 60 wt% fiber content had a high percentage elongation, good impact, and flexural strength and exhibited a tensile strength and modulus of about 135 MPa and 17 GPa, respectively. Furthermore, lyocell-reinforced AESO biocomposites showed good viscoelastic properties and excellent fiber-to-matrix adhesion.

3.2.3 Wheat gluten matrix composites Wheat gluten (WG) is mainly found in wheat as a storage protein, the protein is stored in the endosperm cells of the grain. WG protein can be generally classified into two groups based on their solubility in alcohol: the alcohol-soluble low-molecular weight gliadin and the alcohol insoluble high-molecular weight glutenin, whose proportion is typically about 45% and 55%, respectively [50]. When mixed with water, the protein cells form a viscoelastic matrix; these viscoelastic properties underpin the utilization of wheat to give bread and other processed foods. One group of gluten proteins, the HMM subunits of gluten, is particularly important in conferring high levels of elasticity (i.e., dough strength). These proteins in HMM polymers are stabilized by disulfide bonds and are considered to form the elastic backbone of gluten [51]. Green composites can be prepared by conventionally blending WG and other organic or inorganic components using conventional plastic processing equipment followed by thermo-molding of the mixture at elevated temperatures to cross-link the matrix. In order to remedy the poor toughness and water resistance properties, WG needs plasticizers such as glycerol, sorbitol, as well as saturated fatty acids such as diethanolamine, triethanolamine among others [52]. Glycerol as a plasticizer might be used to overcome the brittleness and improve toughness of the composites. Addition of a secondary component in the filler form can significantly improve Young’s modulus and tensile strength of the plasticized composites, which is accompanied by a decrease in the loss/mechanical damping factor in the glass transition temperature region of the gluten-rich phase. Synthetic biodegradable polymers have also been used for preparing WG blends by incorporation of reactive compatibilizer or by chemical modification of WG proteins. The mechanical properties, moisture absorption, and molecular relaxation of the composites could be tailored by adjusting the contents of the second component and the plasticizer, as well as the molding temperature and time [53]. Addition of plasticizers increases the mobility of the polymer chains, improves the flow characteristics, and eventually better impregnation of the fillers and the matrix; however, this produces composites with compromised mechanical properties [54].

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Thermally processed green composites based on WG show promising potential for large-scale production, and their applications will be beneficial to reduce plastic waste and improve recyclability. The structures and properties of WG composites are dependent on several parameters such as the content of plasticizers, the structure, and nature of the secondary component, the compatibilizer and the interfacial adhesion, as well as the fabrication method and condition. The processability and toughness of WG composites could be easily adjusted through use of plasticizers and appropriate processing equipment. Improvement of mechanical properties of WG composites by addition of organic and inorganic components either in the particle or the fiber forms would attract the interest of industry and consumers. Especially, the inclusion of nanoparticles or rigid microfiber in WG composites can improve tensile strength and modulus significantly [55]. Unplasticized WG is in the glassy state with Tg ranging from 124 to 145
C. Dry WG in the powder form does not flow and form a viscoelastic network during the thermal molding processing. Aqueous dispersant is usually utilized to facilitate the mixing of WG proteins with the other components used in the filler form. For the preparation of unidirectional WG/natural filler composites, WG has been dissolved in meta-cresol (0.1 g/10 mL) solution and the basalt yarn is soaked in the solution. The soaked yarns are dried in a vacuum oven to allow WG to penetrate into the yarn. Unplasticized WG/basalt composites are then made by compression molding the basalt yarns at elevated temperatures. Aqueous dispersant has also been used to mix polyvinyl alcohol (PVA) and WG for improving the mixing effect. The mechanical behavior of thermally processed WG bioplastics might be tailored by controlling the molding temperature that determines the crosslinking density of the WG matrix via disulfide formation or by addition of cross-linking agents such as aldehydes that introduce additional cross-linking bonds between protein macromolecules [56].

3.2.4 Castor oil resin composites Castor oil is a natural, viscous, pale yellow, nonvolatile and nondrying oil, with a bland taste, obtained from trees. It usually is thick with varying colors. India is the most significant producer of castor oil followed by China and Brazil, and these are responsible for 92% of the worldwide production. Castor plant grows in countries with tropical and subtropical climates with average temperatures about 20e26
C and low air humidity. The oil is obtained by extracting or expressing the seed of the Ricinus communis plant, which belongs to the Euphorbiaceae family [42]. Among various biopolymeric materials from renewable resources, castor oils represent an ideal alternative to chemical feedstock [55]. Castor oil like all other plant oils is a vegetable triglyceride. The molecule is, characteristically, formed by hydroxyl groups and applied as a polyol in the synthesis of crosslinked polyurethane (Fig. 3.5).

70 PART | II Thermosetting and thermoplastic materials for structural applications O

O

OH

O CH2 OH OH

CH

O

O C H2 O

FIGURE 3.5 General structure of castor oil.

The oil is a natural resource considered to be closer to a pure compound, where 87%e90% of the fatty acid present in its constitution is ricinoleic acid. About 10%e13% are nonhydroxylated fatty acids. Castor oil is also an unsaturated oil, but additionally, it has hydroxyl groups in its structure (the ricinoleic acid has one hydroxyl group in its chain). Unsaturated fatty acids contain a number of double or triple bonds between two carbon atoms. Derivatives of vegetable oils, such as epoxidized vegetable oils, especially castor oil, can be used as raw material for the synthesis of a variety of chemicals, including glycol, polyol, and carbonyl compounds, as well as lubricants and plasticizers for polymers [57]. Bio-based polyurethanes and polyesters are some of the polymers that can be obtained from castor oil and its derivatives. Approaches applied to obtain the polymeric materials from vegetable oils can be grouped into two categories namely: direct polymerization and chemical modification [58]. The major advantages of castor oil resins are: renewability; abundance, and therefore low cost; low environmental impact, and reduction of the dependence on the limited resources of petrochemicals; flexibility during processing and less resulting machine wear; low density; desirable fiber aspect ratio; relatively high tensile and flexural modulus.

3.2.5 Bio-based polyurethanes Polyurethanes (PU) are synthesized by the reaction of a polyol and a diisocyanate; they are important polymers in industries that produce rigid foams, elastomers, coatings, adhesives, and sealants. Polyurethanes can be thermoplastic or thermoset depending on either diols or polyols. The former results in thermoplastic PU, whereas the latter forms thermoset PU. Castor oil has naturally occurring polyols. Therefore, it offers an alternative to synthetic polyols, compared to hydrocarbon-based feedstocks for the synthesis of PU, since they are cost competitive and offer environmentally benign alternatives [24]. Castor oil has the highest concentration of ricinoleic acid, a fatty acid which is a precursor for the production of polyols. The ricinoleic fatty acid has hydroxyl groups whereas other vegetable oils do not have hydroxyl groups, rendering castor oil the best alternative for reaction with isocyanates for the production of PU. Zlatanic et al. [59] synthesized PU from different vegetable oils: mid-oleic sunflower, canola, soybean, sunflower, corn, and linseed oil with 4,4-diphenylmethane diisocyanate as the cross-linking

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71

agent. Linseed oilebased PU presented higher cross-linking density, better mechanical properties, and higher glass transition temperatures. The lowest Tg was obtained for the PU from mid-oleic sunflower oil (33
C), and the highest was observed for the linseed oilebased PU (77
C). Tensile strengths of all PU ranged from 15 to 23 MPa, except for the PU based on linseed oil, which showed tensile strength three times higher than the others (56 MPa). The tensile modulus of linseed oilebased polyurethane was nearly four times higher (2 GPa) compared to other oil-based polyurethanes. This variation in the mechanical strength was due to the different cross-linking densities and less from the position of the reactive sites in fatty acid chains. Natural oil polyols are produced commercially by several companies, Agribusiness Cargill (BiOH, soybean-based polyol), Dow Chemical (Renuva soybean-based polyols), Urethane Soy Systems Company, and BioBased Technologies (Agrol) BASF (BALANCE, castor oil-based polyol), Bayer (BAYDUR, castor oil-based polyol) and Mitsui Chemicals (castor oilebased polyols), for making polyurethane foams for the automotive, furniture, spray insulation, and other industries [24]. Lignocellulosic materials including wood and agricultural or forestry wastes contain natural polymers based on lignin, cellulose, and hemicellulose, and tannins with more than two hydroxyl groups per molecule, and can therefore be utilized for the synthesis of polyols. Lignocellulosic materials and carbohydrates are also used to obtain polyols which are precursors for the production of PU. For biomass, the process involves liquefying through chemical or thermochemical treatments at high temperatures and high pressure in the presence of alcohols such as ethylene glycol, liquefied biomass with hydroxyl content is suitable for reaction with isocyanate and polyol is obtained.

3.2.6 Cashew shell nut liquid Cashew nut shell liquid (CNSL) is a dark brown viscous liquid present inside a soft honeycomb structure of the cashew nutshell and is a very important agricultural byproduct of cashew nut and cashew apple production, produced by the cashew nut tree (Anacardium occidentale). The shell of the nut is approximately 1/8 inch thick. Cashew nut shell liquid is the pericarp fluid of the cashew nut. Natural CNSL is a mixture of phenolic compounds with aliphatic side chains, and these are 70% anacardic acid, 5% cardanol, and 18% cardol [57] (Fig. 3.6). Several methods can extract CNSL: hot oil process, solvent extraction, mechanical extraction, vacuum distillation, or supercritical fluids processes: mainly hot-oil and the local roasting in which the CNSL flows out from the shell. CNSL is typically treated with high temperatures, which decarboxylates anacardic acid, yielding cardanol; additional distillation of CNSL removes cardol leaving cardanol as the primary component in CNSL (Fig. 3.7).

72 PART | II Thermosetting and thermoplastic materials for structural applications

OH

OH

O OH HO

C15H(31–2n) Anacardic acid

C15H(31–2n) Cardol OH

OH H 3C HO

C15H(31–2n) Cardanol

C15H(31–2n) 2-methyl cardol

FIGURE 3.6 Major components of cashew nut shell liquid.

OH

OH

O OH

–CO2 •T

C15H(31–2n)

C15H(31–2n)

FIGURE 3.7 Conversion of anacardic acid to cardanol, where n ¼ 0, 1, 2, or 3 [57]. Reproduced with permission from the Royal Society of Chemistry.

The composition of CNSL can vary based on the method used for extraction, and hence they have different chemical composition which can be classified into two main types: solvent-extracted CNSL (natural CNSL) and technical CNSL (tCNSL) [60]. Natural CNSL is obtained by the utilization of some solvent extraction technique (commonly soxhlet, supercritical carbon dioxide, or subcritical water) in order to obtain its constituents under mild conditions, without promoting any chemical modification. Technical CNSL was employed as a source of phenolic compounds for the synthesis of phenol/ formaldehyde polymers. Nowadays, with the advances in the chemistry of these phenolic lipids, tCNSL appears as an economically feasible source of phenolic components. In the industry, CNSL is extracted by an automated process that employs high temperatures in order to open the shell and recover the cashew kernel [60]. The presence of aromatic rings in CSNL is an added advantage which results into thermal stability, making it to be used as a fire retardant [61]. The different constituents of CNSL, as aromatic, phenolic compounds, can react with formaldehyde to create condensation polymers, such as resole and novolac, which make excellent matrix resins for composites and also the unsaturation sites in the side chains of CNSL can also undergo addition polymerization using either free radical initiators or ionic initiators. A hexamethylenetetramine (HMTA) hardener is added to CNSL-formaldehyde

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73

TABLE 3.2 Mechanical Properties of Selected CNSL-Based Composites. CSNL resin type

Reinforcement

Modulus [GPa]

Strength [MPa]

References

Novalac

Hemp

13 (F)

91 (F)

[64]

Novalac

Kenaf

17 (F)

166 (F)

[64]

Resol

Coir

10.5 (T)

6.42 (T)

[66]

Resol

Coir

16.9 (T)

13.45 (T)

[66]

Resol

Jute

20.4 (T)

18.21 (T)

[56]

Resol

Jute

6.56 (T)

[56]

resins as a way of improving the cure characteristics [57]. The presence of aromatic and phenolic compounds enables CSNL to cross-link with formaldehyde to form novalac and resole which are usable thermoset resins for biocomposites. Novalac CNSL formaldehyde resins have long hydrocarbon chains; therefore the condensates are more flexible than the conventional phenolic resins. These resins can be used for surface coatings with or without oil modification when high chemical resistance is desired. Natural fibers have been used to reinforce CNSL-based thermosets. Research elsewhere has utilized oil palm fibers [62], sisal fibers [63], kenaf and hemp bast fibers [64,65], jute fibers [56], and coconut coir fibers [66]. Table 3.2 shows a comparison of the mechanical properties of selected CNSLbased composites.

3.2.7 Zein matrix composites Zein is a biochemical substance that belongs to prolamine proteins and is extractable from corn (maize). Prolamines are a group of proteins with high proline (C5H9NO2) content, which are found in cereal grains such as wheat, barley, and corn. Zein is insoluble in water but a lot of organic compounds, especially alcohols, ketones, and aromatic hydrocarbons, can be applied as a solvent for it either in their neat form or sometimes mixed with water [67]. Zein has been demonstrating a wide variety of applications over nearly one century as a binder, an adhesive, a plastic coating agent, film, or fiber in various industries. A comprehensive essay about zein, its properties, and applications is available in [67]. Like WG, pure zein has strong adhesive properties but it needs supplementary compounds as plasticizers in order to convert into films or fibers or act as a suitable polymer matrix. Eight groups of plasticizers have been identified by Hansen (1938) including glycols,

74 PART | II Thermosetting and thermoplastic materials for structural applications

sulfonamides, fatty acids, amides, amines, glyceryl esters, glycol esters, esters, and miscellaneous organic compounds [68]. An investigation on processing and properties of a polymer composite of zein and gluten was carried out by Sanghoon Kim in 2006 [69]. He introduced a developed process through which microscopic-scale wheat protein (gluten) material was coated with zein in room temperature and then compressed to form a rigid coherent material. The compressive strength of this polymer composite was found to be around 40 MPa comparable with polypropylene [69]. The best mechanical properties were obtained with a matrix containing 10% octanoic acid, 30% water, and 20% wood fibers, which resulted in a tensile strength and Young’s modulus of 18.7 MPa and 4 GPa, respectively. Research activities are currently under development in BBL in order to extract zein from low-cost residues of corn starch processing and utilize it in manufacturing of environmental friendly particleboards. In one of these studies, methylene dichloride was applied as plasticizer and effects of methylene dichloride content, zein content, and the temperature of making glue on the mechanical properties of zein/bamboo particleboard were investigated. The results showed that when the volume percentage of methylene dichloride was increased from 10% to 50%, the values of mechanical properties of particleboard, such as modulus of rupture, modulus of elasticity, tensile strength, and internal bond strength, were initially increased and then decreased. The optimal volume percentage was obtained about 20% corresponding to 2353.44 Pa and 15.62 MPa for TS and Young’s modulus, respectively. When the percentage of zein was increased from 20% to 40%, the values of mechanical properties of particleboard also showed initial increases and then decreases; the optimal percentage of zein was found to be of 30%. When the temperature of making glue increased from 25
C to 65
C, the value of mechanical properties of particleboard decreased; so the optimal temperature was found to be 25
C. Similar experiments have been performed using other plasticizers such as oleic acid or glycerol in this laboratory. The optimal percentage content for oleic acid and glycerol were found to be 9% and 10%, respectively. Although mechanical properties have been found satisfying in above mentioned experiments but more experiments are still needed to improve water resistance of bamboo/zein composites [70]. In the field of renewable materials, natural fiber composites demonstrate the capacity to be a viable structural material. Corn zein protein was selected as a natural bio-based coupling agent because of its combination of hydrophobic and hydrophilic properties. Zein was deposited on the surface of flax, which was then processed into unidirectional composite. The mechanical properties of zein-treated samples were measured and compared against commonly utilized synthetic treatments of sodium hydroxide and silane which incorporate harsh chemicals. Fourier transform infrared spectroscopy, chemical analysis, and scanning electron microscopy were also used to analyze zein treatments. Results demonstrate the environmentally friendly zein treatment

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successfully increased tensile strength by 8%, flexural strength by 17%, and shear strength by 30% compared to untreated samples [71]. Concerns regarding the disposal of synthetic polymers have initiated another approach to the development of novel materials from renewable resources and one of the current priorities in green polymer chemistry is the exploration of biodegradable polymers. These emerging bio-based materials have the potential to play a significant role in the next generation of material applications. Intense research efforts around the globe are ongoing to use biopolymers effectively and to successfully implement them in useful products such as in packaging and structural and biomedical applications [70].

3.2.8 Green epoxy composites Approximately 90% of all non-bio-based epoxy in the market is based on diglycidyl ether of bisphenol A (DGEBA) derived from epichlorohydrin and bisphenol A [24]. Epichlorohydrin is an epoxide whose process of production involves chlorohydrination of allyl chloride, which in turn is made by chlorination of propylene from petroleum sources. Several companies are now producing green epoxy resins through utilization of epichlorhydrin from renewable sources. Spolchemie a.s., a company in the Czech Republic, produces green epoxy resins with unique technology of epichlorhydrin production from a renewable raw material resource, one of the byproducts of biofuel productiondglycerin. Spolchemie completely replaced propylene with glycerine. The green epoxy resins produced are certified by the independent organization International EPD Consortium from Sweden and EPD (Environmental Product Declaration) certificate was obtained. It was the first time that green epoxy resin has obtained EPD certificate in the world. Solvay Chemicals produces epichlorohydrin from bio-based glycerol, a byproduct of biodiesel production using rapeseed, according to EPICEROL technology [72]. Biodegradable bark clothereinforced green epoxy composites were developed using green epoxy with view of application to automotive instrument panels. The optimum curing temperature of green epoxy was shown to be 120
C. The static properties showed a tensile strength of 33 MPa and flexural strength of 207 MPa. The dynamic mechanical properties’ frequency sweep showed excellent fiberematrix bonding of the alkali-treated fabric with the green epoxy polymer with glass transition temperature in the range of 160e180
C [73].

3.3 Conclusion and challenges Epoxidized vegetable oils (linseed oil, soybean oil, castor oil, etc.) are facing the challenge of low reactivity of the epoxy groups together coupled with a tendency for intramolecular bonding which results into a low degree of

76 PART | II Thermosetting and thermoplastic materials for structural applications

cross-linking. This low degree of cross-linking eventually leads to poor mechanical, thermal properties and highly hydrophilic composites compared to fossil epoxy systems [24]. In order to address the challenges of greenhouse gas emissions, research and development in renewable materials will increase. Fully green biocomposites will address a plethora of challenges in terms of recyclability. Although partially green epoxy matrices are currently produced whereby the percentage of fossil fuel in the material is reduced, plant-based epoxies from vegetable oils are the best candidates for the production of green thermoset composites and the mechanical properties are promising especially for interior automotive applications.

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Dong J, Dicharry R, Waxman E, Parnas RS, Asandei AD. Imaging and thermal studies of wheat gluten/poly (vinyl alcohol) and wheat gluten/thiolated poly (vinyl alcohol) blends. Biomacromolecules 2008;9:568e73. Thakur VK. Green composites from natural resources. 2014. Hong NV, Pyka G, Wevers M, Goderis B, Van Puyvelde P, Verpoest I, Van Vuure AW. Processing rigid wheat gluten biocomposites for high mechanical performance. Composites Part A: Applied Science and Manufacturing 2015;79:74e81. Ding R. ROMP-based thermosetting polymers from modified castor oil with various crosslinking agents. 2012. Barreto ACH, Esmeraldo MA, Rosa DS, Fechine PBA, Mazzetto SE. Cardanol biocomposites reinforced with jute fiber: microstructure, biodegradability, and mechanical properties. Polymer Composites 2010;31:1928e37. Quirino RL, Garrison TF, Kessler MR. Matrices from vegetable oils, cashew nut shell liquid, and other relevant systems for biocomposite applications. Green Chemistry 2014;16:1700e15. https://doi.org/10.1039/C3GC41811A. Organique LDC, Naturels P, Photochimie E. New composites based on castor oil with isophorone diisocyanate polyurethanes and cellulose fibers, vol. 4; 2013. p. 571e82. Zlatanic A, Lava C, Zhang W, Petrovic ZS. Effect of structure on properties of polyols and polyurethanes based on different vegetable oils. Journal of Polymer Science Part B: Polymer Physics 2004;42:809e19. Anilkumar P. Cashew nut shell liquid: a goldfield for functional materials. Cashew Nut Shell Liq. A Goldf. Funct. Mater. 2017. p. 1e230. https://doi.org/10.1007/978-3-31947455-7. Ravichandran S, Bouldin RM, Kumar J, Nagarajan R. A renewable waste material for the synthesis of a novel non-halogenated flame retardant polymer. Journal of Cleaner Production 2011;19:454e8. Tiamiyu AO, Ibitoye SA. Effect of clay addition on service properties of a developed OPFeCNSLeformaldehyde roofing material. Construction and Building Materials 2012;36:358e64. Barreto ACH, Rosa DS, Fechine PBA, Mazzetto SE. Properties of sisal fibers treated by alkali solution and their application into cardanol-based biocomposites. Composites Part A: Applied Science and Manufacturing 2011;42:492e500. Aziz SH, Ansell MP. The effect of alkalization and fibre alignment on the mechanical and thermal properties of kenaf and hemp bast fibre composites: part 2ecashew nut shell liquid matrix. Composites Science and Technology 2004;64:1231e8. Mwaikambo LY, Ansell MP. Hemp fibre reinforced cashew nut shell liquid composites. Composites Science and Technology 2003;63:1297e305. Barreto ACH, Junior AEC, Freitas JEB, Rosa DS, Barcellos WM, Freire FNA, Fechine PBA, Mazzetto SE. Biocomposites from dwarf-green Brazilian coconut impregnated with cashew nut shell liquid resin. Journal of Composite Materials 2013;47:459e66. Lawton J. Zein: a history of processing and use. Cereal Chemistry 2002;79:1e18. Hansen D. Plasticized prolamine base composition. U.S. Patent, U.S. Pat. 2. 1938. p. 76. Kim S. Processing and properties of gluten/zein composite. Bioresource Technology 2008;99:2032e6. Thakur VK, Thakur MK. Processing and characterization of natural cellulose fibers/ thermoset polymer composites. Carbohydrate Polymers 2014. https://doi.org/10.1016/ j.carbpol.2014.03.039.

80 PART | II Thermosetting and thermoplastic materials for structural applications [71]

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R.J. (AA(North D.S.U. Whitacre, The effects of corn zein protein coupling agent on mechanical properties of flax fiber reinforced composites, ProQuest Diss. Theses; Thesis (M.S.)eNorth Dakota State Univ. 2013.; Publ. Number AAT 1549180; ISBN 9781303605307; Source Masters Abstr. Int. Vol. 52-04.; 111 P. (2013). EpicerolÒ, n.d. https://www.solvay.com/en/markets-and-products/featured-products/epicerol. html. Rwawiire S, Tomkova B, Militky J, Jabbar A, Kale BM. Development of a biocomposite based on green epoxy polymer and natural cellulose fabric (bark cloth) for automotive instrument panel applications. Composites Part B: Engineering 2015;81:149e57.

Further reading [1] Hodzic A, Shanks R. Natural fibre composites: materials, processes and properties. Woodhead Publishing; 2014.

Chapter 4

Green composites in automotive interior parts: a solution using cellulosic fibers N.C. Loureiro1, 2, 4, J.L. Esteves2, 3 1 Superior Institute of Douro and Vouga (ISVOUGA), Santa Maria da Feira, Portugal; 2Institute of Science and Innovation in Mechanical Engineering (INEGI), Porto, Portugal; 3Department of Mechanical Engineering, Faculty of Engineering of University of Porto (FEUP), Porto, Portugal; 4 Research Center of Mechanical Engineering (CIDEM), School of Engineering (ISEP), Polytechnic of Porto, Porto, Portugal

Chapter Outline 4.1 Introduction 4.2 Natural fibers 4.3 Green composites in the automotive industry 4.4 Case study 4.4.1 Materials used

81 82 84 85 85

4.4.1.1 Polyhydroxyalkanoates 4.4.1.2 Poly(lactic acid) 4.4.1.3 Cellulosic fibers 4.5 Conclusions References Further reading

86 87 89 95 96 97

4.1 Introduction Natural fibers of vegetal origin were used for the first time around 3000 years ago. In composite systems in ancient Egypt, straw and clay were mixed to build walls. Now, the interest of natural fibers of vegetal origin in the reinforcement of polymer composite material is growing day by day. Continuous research and development efforts in bioplastics are creating high-quality products for a wide variety of industries. As far as the benefits of biologically sourced plastics are well-understood, their market share is likely to rise sharply. The ecological aspect of material selection, replacing synthetic fibers with natural ones, is only a first step. Restricting the emission of the greenhouse effect caused by gases such as CO2 into the atmosphere and increasing awareness of the finiteness of fossil energy resources are leading to the

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development of new materials that are entirely derived from renewable resources. Once the relative price and quality fulfill the requirements of the automotive industry, it is mandatory to check if these products fulfill the technical specificationsdsuch as service temperature, mechanical behavior, and dimensional stability, among others. The major problem identified with wood fibers (cellulose derived from trees) and natural vegetal fibers to reinforced polymer composite materials is the incompatibility between the hydrophilic character of the natural fibers and the hydrophilic thermoplastic matrices during incorporation, which leads to undesirable properties of the resulting composites. It is, therefore, necessary to alleviate this problem by various fiberepolymer interface modifications to improve the adhesion between fiber and matrix, which results in an improvement of performance of the resulting composite. The most critical application sectors for these biocomposites are construction (decking and siding) and automotive interior parts. Between 10% and 15% of total European composite market is covered by wood-plastic composites (WPC) and natural fiber composites (NFC) [1]. One possibility is the use of interior door trims of biodegradable polymers from renewable sourcesdsuch as polylactic acid (PLA) and polyhydroxyalcanoate (PHA)dinstead of traditional petrol-source polymersd such as polypropylene (PP), polyethylene (PE), or Acrylonitrile butadiene styrene (ABS). Among the biodegradable polymers from natural sources, PHA is the one that has best properties and is expected to be able to fulfill these requirements. However, due to its current price, the solution is not economically viable. To make the eco-solution competitive, it is necessary to reduce the price of the final polymer. One way to accomplish this is to blend it with cheaper polymers, such as PLA. In this chapter, we will present the incorporation of cellulosic fibers into a biodegradable PLA and PHA blended matrix to replace, in some applications, the petrol-based polymers used in automotive interior trims. Ultimately, various concrete applications studied during this work will be presented.

4.2 Natural fibers Natural vegetable fibers can be considered as composites designed by nature and have hollow cellulose fibrils held together by a lignin and hemicelluloses matrix. The chemical composition, as well as the structure of vegetable fibers, is relatively complicated. The fibers are basically comprised of a rigid, crystalline cellulose microfibrilereinforced amorphous lignin, and/or hemicelluloses, lignin, pectins, waxes, and several water-soluble compounds, where cellulose (a cellulose), hemicelluloses, and lignins are its major constituents.

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The main structural unit of the fibers often called the microfibrils, microfibers, or primary/elementary fibers have the shape of a cell wall of a hollow tube with four different layers: one primary cell wall, three secondary cell walls, and a lumen, which is an open channel in the center of the microfibril. Cellulose fibrils that are mechanically ground or chemically made from trees are called wood fibers. Cellulose is the most abundant natural polymer in the world and the essential component of all vegetal fibers. It is a natural linear crystalline homopolymer (polysaccharide) consisting of repeating units of D-glucopyranose rings connected to each other with 1-4 ß-D-glycosidic bonds. Cellulose molecules are randomly oriented and tend to form intramolecular and intermolecular hydrogen bonds. The packing density of cellulose is highly crystalline and may contain as much as 80% crystalline regions. The remaining portion has a lower packing density and is commonly referred to as amorphous cellulose. On a dry weight basis, most plants consist of approximately 45%e50% cellulose. The cellulose percentage can vary from a high (cotton) of almost 90% to a low of about 30% for stalk fibers [2]. The properties of natural vegetable fibers vary and will depend on the source of fiber (plant types); the position of the fiber in the plant; conditions of growth, age, and separating techniques of the fibers [3]. In order to have a

TABLE 4.1 Physical and mechanical properties of bast (b), leaf (l), and seed (s) fibers Fiber type

Apparent density (kg/m3)

Tensile strength (MPa)

Young’s modulus (GPa)

Microfibril angle (q)

Flax (b)

1500

500e900

50e70

5

Hemp (b)

1500

310e750

30e60

6.2

Jute (b)

1500

200e450

20e55

8.1

Kenaf (b)

1200

295e1191

22e60

e

Banana (l)

1350

529e914

27e32

11e12

Pineapple (l)

1440

413e1627

60e82

6e14

Sisal (l)

1450

80e840

9e22

10e22

Cotton (s)

1550

300e700

6e10

20e30

Coir (s)

1150

106e175

6

39e49

Adapted from Mwaikambo LY. Plant-based resources for sustainable composites [Ph.D. thesis]. UK: Department of Engineering and Applied Science, University of Bath; 2002.

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broader view of the mechanical and physical properties of different natural fibers, available data from several authors has been compiled as seen in Table 4.1.

4.3 Green composites in the automotive industry Henry Ford made the first attempt to use composite material combinations of plastics with natural fibers in the automotive industry in the early 1940s [4]. In 1942, Henry Ford developed the first prototype composite car made from hemp fibers [4]. The car did not go to mass production due to economic limitations at the time. The car weighed 2000 lbs., 1000 lbs. lighter than a steel car. The exact ingredients of the plastic panels are unknown because no record of the formula exists today. The real use of natural vegetal fiber composites in the automotive industry dates from 1950. The body of the East German car “Trabant” (1950e90) was a typical example of natural vegetal fibers application (cotton) embedded in a polyester matrix [2]. The last decades have seen the development of an entirely new market for textile fibers (bast and leaf fibers) for reinforcing composite products. The automotive industry used vegetal fibers for the interior trim before the 1970s. Some examples of the uses of these fibers in older car models included jute needle-felts for sound insulation placed under the carpet; wadding, made from wool and cotton for seats and door trim panels; rubberized coir upholstery for seats; and wood fibers for door trim panels. During the 1970s and 1980s, these fibers were partially replaced by petrochemical polymers like nonreinforced acrylonitrile butadiene styrene (ABS) plastic for interior car panels, because of their easier optimized properties and their faster manufacturing processes. In the mid-1980s it was thought that the use of natural fiberereinforced composites could offer an exciting alternative to these plastics because of their technical, economic, ecological advantages and social upheaval in the global balance of the food supply. Several international and national bodies, and in particular, the European Union and several of its member countries provided R&D grants aimed at investigating the technical potentials of reinforcing these panels with natural fibers, and thus, improving their performance. At about the same time and owing to the completely international nature of the automobile industry, similar work on using vegetal fibers to reinforce vehicle trim panels was being carried out in the United States and Japan. Despite encouraging results from the R&D work during this period, it produced little concrete follow-up from the automobile industry until the mid-1990s when the first bast fiber (jute)ereinforced plastic door panels were incorporated into a German standard production Mercedes-Benz model E-Class in 1996 [5]. Another example of green composites’ application appeared commercially in 2000; Audi launched the A2 midrange car where

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the door trim panels were made of polyurethane reinforced with a mixed flax/ sisal mat [4]. The advantages of these new composites in the automobile industry are: l l l l

l l

l l l

l

Lower density of fibers, leading to a reduction in weight of 10%e30% Improved mechanical and acoustic insulation properties Improved processing propertiesddecreased wear of tools The potential for one-step manufacturing, even when making complex parts Improvement accident performancedhigh stability, no splintering Improved eco-balance, during both manufacturing and vehicle use (due to lighter weight) Improved health benefit in manufacturing, compared to glass fibers No release of noxious/toxic gases Less condensation of emissions (fogging) compared to phenol-bonded composites Price and ecological advantages compared to previously used technologies using synthetic or glass fibers

Since the beginning of the new millennium, there is a renewed interest in natural fibers mainly as a glass fiber substitute in automotive industries. However, in the last two decades, the automotive applications have been mostly restricted to interior parts, such as interior trims of door panels, dashboards, rear shelves, and upholstery applications. These applications are essentially linked to excellent acoustic properties and thermal insulation, as well as the low cost of natural fibers. At the same time, some of these applications arise in the pursuit of marketing policies by exploring an environmentally friendly image and the use of materials from renewable sources. Structural applications are rare due to traditionally low-impact strength, the poor moisture resistance of natural fibers and wood fiber composites, and the scarce availability of semi-finished materials of consistent quality. Presently, the use of natural fibers and wood fibers in composite material applications is being intensively investigated. As a result, many automotive nonstructural components are now produced by natural composites, mainly based on polyester or polypropylene and reinforcements like flax, jute, and wood fibers.

4.4 Case study 4.4.1 Materials used In this section, a case study of an interior part production using natural cellulosic fibers is presented. Based on previous works [6] we defined the matrix as a blend of PLA/PHA in a 70:30 weight fraction ratio. We list the most adequate constituents (resin and reinforcement) for the production of a green composite to be applied as a trim panel. By comparing measured values

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adopted by studies regarding the mechanical performances of fibers, matrices, and identical composites, it is depicted which combination holds the best potential for a composite of fair structural performance. The fiber incorporation was determined based on the work of D. Guimara˜es [7], who stated that for PLA/cellulosic fiber composites it is not possible to incorporate more than 30% of fibers. Otherwise, the PLA matrix will not be able to accommodate all the fibers. Other researchers have reported decreased mechanical strength with higher fiber loading of approximately 30% volume fraction due to stress concentration and dispersion problems [8,9]. Therefore, based on previous works [10] we incorporated 10% and 20% of fibers (weight fraction) in the PLA/PHA blend matrix.

4.4.1.1 Polyhydroxyalkanoates In 1923, Lemoigne at the Institut Pasteur demonstrated that aerobic sporeforming bacillus formed quantities of 3-hydroxybutyric acid in anaerobic suspensions. He further investigated and was successful in quantitatively estimating the amount of 3-hydroxybutyric acid formed. Finally, in 1927, he was able to extract a substance from bacillus using chloroform and prove that the material was a polymer of 3-hydroxybutyric acid. However, it was not until the early 1960s that the production of poly (3-hydroxybutyrate) was explored on a commercial scale. The polyhydroxyalkanoates (PHAs) represent a range of polyesters produced from renewable resources via bacterial fermentation. The PHA’s family includes a wide range of polymers that depend on the carbon substrates and the metabolism of the microorganisms that produce the polymers. PHAs are semicrystalline with melting temperatures ranging from 120 to 180 C, depending on the chemical composition. In addition to biosynthesis, an enzyme-catalyzed process, PHAs have attracted much interest due to their biocompatibility and biodegradability [11]. The PHAs are fully biodegradable and are enzymatically degraded by a wide range of bacteria, fungi, and algae. A wide variety of prokaryotic organisms can accumulate PHA from 30% to 80% of their cellular dry weight [12]. Degradation times depend on the environment and material form and can range from weeks to over a year. In nature, PHAs are microbially synthesized as an energy storage compound. Therefore, the degradation by a wide range of bacteria, algae, and fungi is not surprising. Typically, this organism undergoes extracellular depolymerization, which degrades the polymer into a low molecular weight one. The degradation products vary according to the degradation environment. Under aerobic conditions, degradation produces carbon dioxide, water, and some organic material, and under anaerobic conditions, degradation produces methane and carbon dioxide. The first polymer within the PHA familyebased polymer includes the polyhydroxybutyrate (PHB), another aliphatic polyester. Some other different poly(hydroxybutyrate-co-hydroxyalkanoates) copolymers exist in this

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TABLE 4.2 PHI002dPHA technical data. Melt temperature ( C)

145e155

Degradation temperature ( C)

200

Tensile strength at break (MPa)

35

Tensile elongation at break (%)

2

Tensile modulus (MPa)

2950

HDT A (1.8 MPa) ( C)

72.5

Density

1.25 (0.05)

MFI (190 C/2.16 kg) (g/600 s)

15e30

family such as poly(hydroxybutyrate-co-hydroxyvalerate) e PHBV, poly(hydroxybutyrate-co-hydroxyhexanoate) e PHBHx, poly(hydroxybutyrate-cohydroxyoctanoate) e PHBO, among others [12]. PHB is a highly crystalline polyester with a high melting point when compared to other biodegradable polyesters [12]. The PHB homopolymer possesses a narrow window for the processing conditions. To ease the PHB processing, it is possible to plasticize the PHB with citrate ester. However, the PHB copolymer is more adapted for the process. The production of PHAs is intended to replace synthetic nondegradable polymers for a wide range of applications, in packaging, agriculture, and medicine [13] as PHAs are biocompatible. PHA used is produced by Natureplast (France) under the trade name PHI002. It is a thermoplastic resin of PHA made from bacterial fermentation and is specifically developed for injection molding process. The main properties from material datasheet are described in Table 4.2.

4.4.1.2 Poly(lactic acid) Poly(lactic acid) (PLA) polymer is a biodegradable polyester derived from lactic acid (2-hydroxy propionic acid). PLA is a rigid thermoplastic biodegradable polyester polymer that can be semi-crystalline or entirely amorphous, depending on the stereopurity of the polymer backbone. PLA is the first commodity polymer produced from annually renewable resources and is a unique polymer that in many ways behaves like PET (polyethylene terephthalate), but also performs a lot like PP (polypropylene). The properties of PLA are determined by the polymer architecture (i.e., the stereochemical makeup of the backbone) and the molecular mass, which is controlled by the addition of hydroxylic compounds. The ability to control the

88 PART | II Thermosetting and thermoplastic materials for structural applications

Article service Glassy state

Extrusion

Ductile

Physical ageing (Creep)

Strictly brittle

Processing

Foaming

–45 Tβ

Rubbery 58 Tg

Decomposition

Viscous liquid 110–150

215–285

Temperature, ºC

FIGURE 4.1 Metastable states of amorphous PLAs [14].

stereochemical architecture allows precise control over the speed of crystallization and the degree of crystallinity. This ability also allows the control of the mechanical properties and the processing temperatures of the material. It is also possible to control the degradation behavior since it is strongly dependent on the crystallinity of the polymer. Due to its excellent strength properties, film transparency, biodegradability, biocompatibility, and availability from renewable sources, PLA is commercially attractive. The physical characteristics of PLA are extremely dependent on its transition temperatures for common qualities such as density, heat capacity, and mechanical and rheological properties. In the solid state, PLA can be either amorphous or semi-crystalline depending on the stereochemistry and thermal history. For the amorphous PLA, the glass transition temperature (Tg) determines the upper use temperature for most commercial applications. Figs. 4.1 and 4.2 are showing the influence of the crystallinity on the macroscopic behavior. For semi-crystalline PLAs, both Tg (approx. 58 C) and the melting point (Tm), 130e207 C, are important for determining the temperature use across various applications. Tg and Tm are strongly affected by the overall optical composition, primary structure, thermal history, and molecular weight.

Article service

Processing

Brittle

Ductile

Limited amorphous aging

Leathery, tough

–45 Tβ

58–70 Tε

130–207 Tm

Viscous liquid

Decomposition 215–285

Temperature, °C

FIGURE 4.2 Metastable states of semi-crystalline PLAs [14].

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The PLA used is produced by NatureWorks LLC (USA) under the trade name INGEO 3251D biopolymer. INGEO 3251D is a thermoplastic resin designed for injection molding applications. This grade presents a higher melt flow capability and a higher flow capability. The main properties from material datasheet are described in Table 4.3.

4.4.1.3 Cellulosic fibers The biofiber world is full of examples where cells or groups of cells are designed for strength and stiffness. Cellulose is a natural polymer with high strength and stiffness per weight, and it is the building material of long fibrous cells. In general, the fiber consists of a wood core surrounded by a stem. Within the stem, there are a number of fiber bundles, which contain individual fiber cells or filaments. These filaments are made of cellulose and hemicellulose, bonded together by a matrix, normally lignin or pectin. The principal differences between the individual fibers are fiber qualities, lignin content, and odor. The increasing interest in lignocellulosic fibers is due mainly to their economical production with few requirements for equipment and a low specific weight, which result in higher specific strength and stiffness when compared to glass-reinforced composites. The biofibers, such as the cellulosic fibers, are nonabrasive to mixing and molding equipment, while additionally they have high thermal conductivity and acoustic insulating properties. They have a positive environmental impact and with a production that requires little energy for their production when compared to materials made of dwindling petroleum resources. They also have competitive specific mechanical properties, carbon dioxide sequestration, and lower eco-toxicity while bringing attached higher sustainability, recyclability, and biodegradability. Furthermore, they lack residues upon incineration, and the amount of energy required for the production of plant fiber textiles or fabrics is estimated to be lower than for the production of glass fibers for instance.

TABLE 4.3 INGEO 3251DdPLA technical data Melt temperature ( C)

188e210

Tensile strength at break (MPa)

48

Tensile elongation at break (%)

2.5

Density

1.24

MFI (190 C/2.16 kg) (g/600 s)

30e40

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Parallel to the advantages natural fibers bring with their use in composites constructions, they also come with inherent drawbacks regarding their performance, their behavior in polymeric matrix systems, and their processing. Similar to the case of wood composites, natural fibers and plastic are like oil and water and do not mix well. Unfortunately, the inherent polar nature (“hydrophilic,” absorbing water) of lignocellulosic fibers and the nonpolar (“hydrophobic,” repelling water) characteristics of the common thermoplastics result in compounding difficulties leading to the nonuniform dispersion of the fibers within the matrix which impairs the efficiency of the composite. This is probably one of the major disadvantages of biocomposites. Another main drawback is related to the processing temperatures that for this type of fibers are restricted to 200 C; above this limit, the fibers start to degrade and shrink which subsequently results in lower performance of the composite. The low processing temperatures are linked to limited thermal stability. An increase in temperature can create irreversible damage and leads to porosity, which reduces the mechanical properties of the fibers. Another setback is the high moisture absorption of the biofibers leading to swelling and presence of voids at the interface, which leads to reduced mechanical properties and reduces the dimensional stability of the composites. Nevertheless, it is clear that the advantages outweigh the disadvantages and most of the shortcomings have remedial measures in the form of chemical treatments as added benefits for instant enhanced environmental performance, as themass per unit volume of natural fiber is achieved. The cellulosic fibers used in this work are rejected fiber coming from the Portucel Kraft paper factory, located in Viana do Castelo, and its origin is the Eucalyptus globulus tree. The preprocessing of the fibers at the paper factory is an extremely complex and chemically demanding set of operations. In the end, a small part of the fibers will be rejected and removed from the production system. Currently, these rejected fibers are incinerated in furnaces drying raw wood for energy recovery. This means that after a set of chemical treatments, they were removed from the production line after the final chemical treatment and before entering the paper production line, the fibers will be incinerated leading to money wastage. Furthermore, not only is all the effort applied to the treatment not utilized, but the incineration also releases various harmful emissions. The bulk fibers are composed essentially of cellulose (w85%) and glucuronoxylan (w15%). The main properties are expressed in Table 4.4. Experimental study The composite mechanical properties can be optimized through the variation of neat base materialsdPLA, PHA, and cellulosic fibersdweight fraction ratio. In order to select the best cellulosic fibers weight fraction ratio, a mechanical characterization of the composites was realized.

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TABLE 4.4 Eucalyptus Globulus fiber general properties[15,16] Average fiber diameter (mm)

10.9

Average fiber length (mm)

0.66

Tensile strength at break (MPa)

160

Tensile elongation at break (%)

5.2

Tensile modulus (GPa)

17.4

Flexural modulus (GPa)

16

Flexural strength at break (MPa)

130

3

Density (g/cm )

1.6

The envisaged tensile and flexural properties were the initial modulus and the maximum/yield stress. The tests were performed according to ASTM D638 standard [17] for tensile properties and ASTM D790 standard [] for flexural properties. The impact properties measurement was performed according to ISO 66032 standard [18]. From the force-displacement curve, the impact toughness was calculated as the area below the force-displacement graph. The heat deflection temperature (HDT) was measured according to ISO 75-2 standard [19], using the method HDT A with an applied stress state of 1.8 MPa and an increasing temperature rate of 120 C/h. All test specimens were produced via injection molding technique by a compound injection molding machine in which it was possible to adjust the feed throat of each hopper to obtain the proper weight fraction ratio. The mold temperature was set up at 20 C in order to allow successful part demolding. The injection temperature profile that combines the polymers’ melting temperatures, the degradation temperatures, and the injection molding conditions suggested by the suppliers are presented in Fig. 4.3. A constant injection velocity of 20 mm/s (corresponding to an injection flow rate of 6.3 cm3/s) was maintained. The mechanical properties obtained experimentally are expressed in Table 4.5.

170°C

180°C

160°C

160°C

140°C

FIGURE 4.3 Injection spindle temperature profile of the injection machine.

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TABLE 4.5 Experimental results Matrix [70:30] [PLA:PHA]

Biocomposite (10% fiber)

Biocomposite (20% fiber)

Tensile modulus [GPa]

3.4

4.3

5.1

Maximum tensile stress [MPa]

46.02

44.21

49.01

Flexural modulus [GPa]

3.5

4.4

5.6

Maximum flexural stress [MPa]

62.30

82.51

89.02

Absorbed energy [J]

6.7

10.5

10.5

Heat deflection temperature [ C]

62.1

49.2

56.0

The specimens are the following geometries and dimensions according to the respective standard: l l l

Flexural and HDT: 12  150  6 mm parallel piped bars Impact specimens: central gated discs of Ø60  2 mm Tensile specimens (type II): dog-bone geometry with a narrow section of 57  10  4 mm, and an overall dimension of 183  19  4 mm.

As the interior door trims are mainly injection molded into ABS or PPcopolymer, we compared the obtained results with general ABS and PP properties. Using the online databases of matweb.com, it was possible to assume the main properties of ABS and PP as seen in Table 4.6.

TABLE 4.6 ABS and PP general properties [20e22] ABS (injection grade)

PP (injection grade)

Tensile modulus [GPa]

2.33

1.72

Maximum tensile stress [MPa]

38.4

31.3

Maximum flexural stress [MPa]

68.6

48.1

Absorbed energy [J]

22.7

10.8

96

63

o

Heat deflection temperature [ C]

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Tensile modulus

HDT

Tensile stress

Flexural modulus

Impact energy

Flexural stress

FIGURE 4.4 A 6-dimension chart of a comparison of raw materials.

Based on Tables 4.5e4.6, it is possible to compare the properties of the raw materials with our cellulosic composites. The schematic presented in Fig. 4.4 emphasizes the relation of all these parameters. The 6D graphic (Fig. 4.4) correlates and compares all the obtained results.The graphic provides a comprehensive and visual comparison between the two studied biocomposites (gray shadows), the blended matrix (yellow line) and the two more common polymers used in this type of applicationd ABS (red line) and PP (blue line). It is important to know that each hexagon vertex presents a different scale regarding the values that are necessary to present. This type of representation, although hiding the figures, allows one to make a quick comparison of several different behaviors. Regarding the HDT, it is possible to see that ABS presents the highest value. However, the value presented is an average of all ABS grades currently in the market. Therefore, it is possible to have an ABS with an HDT lower than the studied composites. Based on the graphic in Fig. 4.4, it is possible to choose the best solution; to produce automotive parts, the composite that presents equal or better properties in all dimensions will be used. By analyzing the graphic, it is possible to conclude that the composite with 20% fiber (light gray shadow) fulfills the previous statement.

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FIGURE 4.5 Cabin light support produced in cellulosic composite.

After verifying that the cellulosic composite is suitable for an interior automotive application, we produced a cabin light support part from a 2008 model of a well-known OEM that was already using this composite. The original part was produced in an ABS/PA6 blend by injection molding. The aim was to verify if the injection molding process would be suitable for cellulosic fiber composite part production. It is worth mentioning that the mold used produced the original parts by ABS/PA6, whereby the mold parts produced will not be optimized for our green composite. It is possible that the thickness of the part can be adjusted and, therefore, the weight of the part can be reduced. This new composite will be produced by repeating a similar injection process used for interior automotive applications, namely the neat polymers PLA and PHA, which will both be shipped from the supplier in a pelletized form. During the injection process, the fibers will be added to the mix. The process used is compound injection molding (CIM), in which all materials are directly inserted into the fuse. The CIM machines ensure that all materials are well mixed into the fuse. In the first stage, the two polymers are mixed, and in the following stage, the cellulose fibers are added to the blend in the right ratio and at the proper time, driving a homogeneous dispersion of all materials in the fuse. The final stage is the injection into the mold. At this time, the polymer blend is perfectly mixed and the reinforce is well dispersed. Using the injection parameters already optimized in the previous works on a CIM equipment with a composite material formed by a [PLA:PHA] [70:30] matrix and a ratio of 20% fiber weight in percentage (wf) of cellulosic fiber [10], it is possible to obtain a part of equivalent performance but being manufactured by biodegradable composites. Fig. 4.5 shows the composite part produced using CIM. As one may notice, no distortion or visible injection molding defects are present. In that sense, this indication would potentially allow the replacement of the current part with parts made of cellulosic composites. Consequently, this will allow the incorporation of the systems and parts that are integrated into the cabin interior light part and other interior parts.

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FIGURE 4.6 Cellulosic composite part detail.

In a closeup in Fig. 4.6, it is possible to see that even the small details of the component can be produced with the suggested composite. The color in Fig. 4.6 is not due to lack of color additives in the composite mix. In addition, the appropriate color of the part can be later adjusted with the inclusion of pigments if necessary.

4.5 Conclusions The main expected results of this work are focused on the development of a sustainable composite suitable to be used in an automotive interior part. These sustainable composites will use 100% renewable source materials, while meeting current applicable crashworthiness standards and aesthetic requirements. The feasibility of producing interior parts on the studied ecocomposites was further investigated. Composites with a [30:70] [PHA:PLA] matrix and with a fiber weight of 10% and 20% (wf) were compared with the most used petrol-based polymers for automotive interior parts (PP and ABS). The incorporation of 20% wf fiber leads to a sustainable composite that presents the best properties. When compared with ABS and PP, this ecocomposite, normally, presents equal or better properties, excluding the impact of absorbed energy. It is possible to conclude that the suggested composite can be rendered an alternative option to replace the petrol-based polymers in some cabin interior parts applications. Although it is possible to use other biopolymers such as matrix(PHB, PGA, and PBA) and other natural fibers (coconut, flax, cotton, hemp, jute, and sisal), due to prior works and knowledge, the chosen materials were PHA/PLA and cellulosic fibers. After comparing all the results, it is possible to conclude that for interior automotive parts, the best biodegradable composite achieved by this work was a composite with a matrix composed by [PHA:PLA] [30:70] (wf) and with fiber incorporation of 20% (wf).

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Globally, a continuous growth in the incorporation of reinforced composites with natural fibers by the world automotive industry in the next decades is foreseeable. Unfortunately, in the present, the bioplastics manufacturing cost is a significant barrier for their generalized use in the automotive industry, but it is expected that soon manufacturers of these materials will turn up affordable solutions as their demand in industrial-scale applications will no doubt tend to decrease their prices to more affordable levels. The trend can also be reversed in the sense that the necessity for environmentally conscious solutions can overturn the value chain and put a premium price on the environmental impact of current solutions.

References [1]

[2] [3] [4] [5] [6]

[7] [8]

[9]

[10] [11] [12] [13]

[14]

Carus M, Elder A, Dammer L, Korte H, Scholz L, Essel R, Breitmayer E, Barth M. WPC/ NCF market study: European and global markets 2012 and future trends in automotive and construction (update 2015-06). Nova Institute for Ecology and Innovation. Bledzki AK, Sperber VE, Faruk O. Natural and wood fibre reinforcement in polymers. Rapra Review Reports 152. Rapra Technology Limited; 2002. ISSN: 0889e3144. Caroline Baillie. Green composites: polymer composites and the environment. Woodhead Publishing Ltd; 2004, ISBN 1-85573-739-6. Mohanty AK, Misra M, Drzal LT. Natural fibers, biopolymers, and biocomposites. CRC Press; April 8, 2005, ISBN 9780849317415. e CAT# 1741. Franck RR. Bast and other plant fibres. Woodhead Publishing in Textiles; 2005, ISBN 1-85573-684-5. Loureiro NC, Esteves JL, Viana JC, Ghosh S. Mechanical characterization of polyhydroxyalkanoate and poly(lactic acid) blends. Journal of Thermoplastic Composite Materials 2015;28(2). Guimara˜es D. Efeito das condic¸o˜es de injecc¸a˜o nsa propriedades de PLA reforc¸ado com fibras celulo´sicas [Master Thesis in Polymer Engineering]. Portugal: University of Minho; 2009. Mishra S, Misra M, Tripathy SS, Nayak SK, Mohanty AK. Potentiality of pineapple leaf fibre as reinforcement in PALF-polyester composite: surface modification and mechanical performance. Journal of Reinforced Plastics and Composites 2001;20(4):321e34. https:// doi.org/10.1177/073168401772678779. Yu T, Li Y, Ren J. Preparation and properties of short natural fiber reinforced poly(lactic acid) composites. Transactions of Nonferrous Metals Society of China 2009;19(Suppl. 3):651e5. https://doi.org/10.1016/s1003-6326(10)60126-4. Loureiro NC. Sustainable automotive components for interior parts: a case study. Saarbru¨cken, Germany: Lambert Academic Publishing; 2014. Gunaratne L, Shanks R. Multiple melting behavior of poly(3-hidroxybutyrate-cohydroxyvalerate) using step-scan DSC. European Polymer Journal 2005;41:2980e8. Bordes P, Pollet e E, Ave´rous L. Nano-biocomposites: biodegradable polyester/nanoclay systems. Progress in Polymer Science 2009;34:125e55. Xie Y, Kohls D, Noda I, Schaefer e D, Akpale Y. Poly(3-hydroxybutyrate-co-3hydroxyhexanoate) nanocomposites with optimal mechanical properties. Polymer 2009;50:4656e70. Auras R, Harte e B, Selke S. An overview of polylactides as packaging materials. Macromolecular Bioscience 2004;4:835e64.

Green composites in automotive interior parts Chapter | 4 [15] [16]

[17] [18] [19] [20]

[21] [22]

97

Mwaikambo LY. Plant-based resources for sustainable composites [Ph.D. thesis]. UK: Departement of Engineering and Applied Science, University of Bath; 2002. Agopyan V, Savastano Jr H, John VM, Cincotto MA. Developments on vegetable fibrecement based materials in Sa˜o Paulo, Brazil: an overview. Cement and Concrete Composites 2005;27:527e36. ASTM standard D 638 e 03. Standard test method for tensile properties of plastics. 2010. ISO standard 6603 e 2. Determination of multiaxial impact behavior of rigid plastics - Part 2: instrumented puncture test. 2000. ISO standard 75-2. Determination of temperature of deflection under load - Part 2: plastics and ebonite. 2004. Bledzki AK, Sperber VE, Faruk O. Natural and wood fibre reinforcement in polymers, Rapra review reports, report 152, vol. 13, Number 8. RAPRA Technology LTD; 2002. ISSN:0889e3144. Johnson RM, Mwaikambo LY, Tucker N. Biopolymers, Rapra review reports, report 159, vol. 14, Number 3. RAPRA Technology LTD; 2003. ISSN:0889e3144. Information on: http://matweb.com.

Further reading [1] ASTM standard D 790 e 10. Standard test method for flexural properties of unreinforced and reinforced plastics and electrical insulating materials. 2010.

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Chapter 5

Eco-impact assessment of a hood made of a ramie reinforced composite G. Koronis, A. Silva Singapore University of Technology and Design, SUTD-MIT International Design Centre (IDC), Singapore

Chapter Outline 5.1 Introduction 99 5.2 Materials and methods 101 5.2.1 Functional unit and boundary conditions for the hood 102 5.2.2 Natural fiber incorporation (ramie reinforcement) and

alternative approaches to manufacturing 5.2.3 Materials, manufacture, end of life 5.3 Results and discussion 5.4 Conclusions References

103 104 106 111 112

5.1 Introduction There is global concern regarding the damaging effect of human activity on effecting climate change along with the environment. This prompts effort to analyze the ecological burden and reduce it via eco-design methods and strategies at the early stages of product development. Specifically, the scientific area of green composites has gathered significant attention. A plethora of contributions can be found in the literature regarding their mechanical behavior in static and dynamic conditions, their aging behavior, and their environmental impact [1e7]. A typical response toward this sustainability demand is the incorporation of renewable materials in the composite mix with low embodied energy associated with their extraction and production. By the addition of renewable constituents in the part composition, the overall composite can be considered “green” with a number of benefits attached as for its cost, environmental performance, and weight. In fact, natural fibers as sustainable, annually renewable crops that are considered environmentally Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00005-7 Copyright © 2019 Elsevier Ltd. All rights reserved.

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superior to their glass-fiber counterparts [8], which are synthetic and sourced from nonreplenishable products. Researchers have explored the potential of incorporating chopped ramie mats and kenaf fibers in acrylic composites targeting the automotive industry [9]. Particular research has been accomplished on producing polylactic acid (PLA) resins by the addition of natural fiber reinforcement such as flax [10,11] or short ramie fibers [12,13]. More specifically, ramie fibers have been proven to provide excellent performance when compared to the other natural fibers [14], while being highlighted for their valuable mechanical properties [2,15,16]. On the other hand, the increment of consumer awareness regarding recycling and the impact of these materials on the environment have also played a key role in their adoption by both society and industry. The informed customers are willing to pay more as they become more ecologically conscious of green products [17]. As a result, customers are seeking to purchase eco-friendly products and services, preferring firms that are in favor of environmental practices. In enterprise perspective, major car makers such as Toyota [18], Mercedes [19], Lotus [20], Mazda [21], and Mitsubishi [22] have already adopted green composite solutions for their fleets. The automotive industry is striving to combine the optimum materials for a lightweight green composite production while promoting themselves as companies of sustainable profile and claiming a reduced impact on the environment. These factors here led to a greater impetus for the development of commercially viable green composites [23] and spurred their large-scale demands. Ultimately, there is an urgent need to develop and implement green technologies into the existing industrial facilities [24]. Following the principles above, our goal is to explore the environmental performance of a sustainable composite for its application in a buggy vehicle’s hood. The objective is to reduce its environmental footprint through strategic decisions that sequester the energy spent and the CO2 emissions in product’s life cycle. The environmental performance of the composite is quantified with the aid of the Eco-Audit tool from ©CES Selector by Granta Design [25]. The Eco-Audit tool provides a very fast and reliable way of developing an initial grasp on the problem and enables a streamlined environmental assessment of alternative scenarios at the early stage of the product development. The analysis relies on materials and processes alteration in real time while projecting a set of impacts associated with the component/product during the main stages of its life cycle. This is achieved by using few reliable impact indicators, which are adopted for this research. These are the energy consumption (energy breakdown in terms of direct and indirect contributors, expressed by megajoule MJ per functional unit), the global warming potential (in terms of CO2 per functional unit), and the end-of-life potential (in terms of effective practicable scenarios, i.e., of potential recycling). Thereafter, the phases of the product life that create the greatest burden associated with energy consumption and carbon footprint are identified by the above mentioned tool expediently. This approach is designed to simplify and reduce time, cost,

Eco-impact assessment of a hood Chapter | 5

101

and effort involved in conducting a full life cycle analysis (LCA) while still facilitating accurate and effective decisions [26]. Whereas more advanced tools like LCA are more accurate in assessing environmental impact and providing a full list of environmental indicators, they are generally extremely time-consuming to set up. There are numerous technical parameters needed by typical LCA applications, which are often unavailable or even unknown at the early design stage. A conventional LCA requires high levels of detail and is not designed to be used as a quick and practical early design tool but becomes meaningful to assess after all the early design details have been set and the product is near its production phase [27]. The Eco-Audit tool has been employed by a number of studies to evaluate sensible heat storage materials [28,29], wall hung boilers [30], and wind turbines [31] for their environmental performance. An LCA is highly desirable and can provide valuable information about the total environmental performance in a way that the Eco-Audit tool cannot do. Eco-audit is a quick, approximate assessment of the distribution of energy demand and carbon emission over life [32,33]. It identifies the phases of lifedmaterial, manufacture, transport, and usedthat carry the highest demand for energy or create the greatest burden on emissions [33]. There is, therefore, a trade-off between time to setup and accuracy of the results, which is in fact mitigated by the uncertainty regarding a number of parameters that need to be in place to use a full LCA which renders its use extremely difficult [34].

5.2 Materials and methods Using the Eco-Audit tool, one can experiment with “what-if ” scenarios during the early stages of design, before time has been spent and funds have been committed. This could provide a fast estimate of environmental impacts across the entire product life cycle with respect to life cycle energy consumption and carbon dioxide emissions. Overall, the Eco Audit Tool’s approach is developed in three components, which are briefly described below. The first step is the adoption of a single indicator of environmental stress (mainly the energy in MJ or CO2 footprint). These two, which are related, are largely acceptable measures as they are easier to monitor and measured with relative precision. Secondly, it is envisioned a breakdown of the phases of life into five stages as follows: material creation, product manufacture, transport, product use, and disposal. In that way, a fraction of the total life-energy demands is assigned to each of the phases of life to be analyzed separately. At last, the software will base the subsequent actions on the energy or carbon breakdown to identify where the most significant gains might be made. Its results guide redesign and materials selection to minimize environmental impact. A full explanation of the EcoAudit tool approach and inputs for selecting materials and eco-aware product designs can be found in ©CES EduPack Eco-Audit tool white paper [33].

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For this purpose, the bill of materials, the choice of the manufacturing process, transport requirements, and duty cycle (the details of the energy and intensity of use) are needed to be keyed in. Data for embodied energies and process energies are drawn from a database and tool (Eco-Audit) from ©CES Selector from Granta Design Ltd. [33]. The outputs are the energy or carbon footprint of each phase of life, presented as bar charts and in tabular form. The Eco-Audit is a well-known software in engineering academic curriculums, and it is also adopted by researchers to enable them to browse material data and calculate the environmental load. Recently much attention has been focused on evaluating the environmental performance on sensible heat storage materials [28,29], wall hung boilers [30], and wind turbines [31]. The tool may also be used as part of an integrated approach to assist on design decisions that are followed by further cost analysis and LCA [26].

5.2.1 Functional unit and boundary conditions for the hood In this study, we assigned the buggy’s hood as a functional unit (FU) which has an area of 0.35 m2 and yields the required mechanical and structural performance to be used in the buggy’s chassis. The equivalence performance in terms of strength and stiffness was already established in the past studies of [35] and [36]. The Brazilian company had also manufactured and tested other sets of jute and glass hoods analyzed in the study of [1]. As in the studies above the targeted stacking sequence applied is [(0/90), (45/45), (0/90)] produced by the use of ISOJET Resin Transfer Molding (RTM) unit. For the boundary conditions (BC), the baseline scenario considers the operational conditions of Ancel Ltda, Rio Claro, Brazil (composite manufacturer) facility. The hood part (functional unit) has been produced by the use of six layers of glass-fiber mats in unsaturated polyester (UP) matrix via the resin transfer molding (RTM) manufacturing technique. The finished part is of 4 mm thickness and weighs 2.44 kg out of which 0.8 kg are glass fabrics of 21% fiber volume fraction (Vf%). Ancel established its medium-term prerequisite for annual production volume (APV) at a maximum of 300 units. A number of 18 parts which are manufacturing rejects is added to the APV based on statistical data provided by Ancel Ltda when fabricating analogous parts. After the hood production and installation on the buggy vehicle’s body, it is transported to Rio de Janeiro (Brazil) at the distribution center for a distance of 560 km by a 32-ton truck. The product life of the car is assigned for a 20 years period, as is common for most Brazilian automobiles [37]. This expected product life is based on Brazilian Association of Automotive Components Manufacturers Reports (Sindipec¸as), which contain important data about the auto-parts sector in Brazil. The hood is part of a vehicle, so will relate to the mobile mode on the transportation systems. It is assumed additionally that the buggy car will be used at least once per week for a 40 km route, in a hypothetical round trip around the beaches of Rio de Janeiro city, Brazil.

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Eco-impact assessment of a hood Chapter | 5 Materials

Fibers manufacture Transportation vehicle manufacture

Use phase

End of life

Recycling Input

Input

Ceramics

RAMIE fiber fabrics

Input Refining

Input

Cultivation

Combustion Functional unit (Hood) Input

RAMIE Input

Downcycle

Polyester

Ramie plant

Input

Glass Input

Glass fiber fabrics

Recycling

Emissions

FIGURE 5.1 Boundaries of the eco-impact analysis.

Fig. 5.1 depicts the schematic diagram within the boundaries of a hypothetical life cycle scenario regarding the FU. The green color arrow shapes (inputs) are obtained by authors while the black color inputs are provided by the CES software materials database. Energy and materials are consumed in each of the five phases of life, generating gaseous emissions outlined by the arrow shape at the bottom side of the diagram.

5.2.2 Natural fiber incorporation (ramie reinforcement) and alternative approaches to manufacturing The alternative scenario in comparison with the baseline is a ramie-reinforced polyester hood part that incorporates natural biaxial woven fabrics fiber. The ramie fiber (Boehmeria nivea (L.) Gaud, Boehmeria nivea var. tenacissima), also referred as Chinese grass or white ramie, is a member of the Urticaceae family and principally produced in China, Japan, and several other South Asian countries [2]. The type of mat used is imported from a Chinese supplier (based in Shanghai) by sea freight and is expected to have more energy related to transportation than e-glass, which is fabricated by a manufacturer close to the industrial area where Ancel is located. The ramie-reinforced hood weighs 1.79 kg of which 0.4 kg is ramie and the remainder is biopolyester with fiber Vf at 18%. The resulting part is 27% lighter than the baseline scenario with comparable mechanical properties. The mechanical and weathering performance of these green composites are discussed in a past study of Koronis et al. [3], where maximum tensile stress (Ftu) of 30.38 MPa and the modulus of elasticity in bending (EB) of 5.29 GPa were targeted for equivalent

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TABLE 5.1 Mechanical properties of compositesa Sample

Resin

Vf (%)

Ftu (MPa)

EB (GPa)

RBP

BioPoli

20

27.1
1.6

5.8
0.4

GFC

Quires

21

60.5
0.5

4.6
0.1

a

Values from Koronis[35]

performance. All composites performance is presented in Table 5.1, where the RBP is ramie-reinforced bio-polyester and GFC is the e-glass fiber baseline composite. For this alternative scenario, two methods for improving the RTM baseline were considered optimizing the injector machine runs (actually converting it to RTM-Lite) and optimizing the raw materials use. By this improvement, labor use will be additionally optimized in terms of performance. The reason is that the upgraded technique requires less labor as only one worker is needed to run one part production. The process becomes slower due to its moderate pressure (assisted by vacuum). However, more precision is attained regarding surface finish and far less manual post-mold rework is required. This will subsequently mean fewer rejects and ultimately agrees with the results of [38]. To more fully explore the potential of the ramie scenarios, we generated two sets of counter-alternatives by using the same input profiles as for the ramie alternative. At this point, we investigate a set of “what if ” scenarios when altering the reinforcing element and supplier location and examining the APV limits. In the first counter-alternative scenario, the supplying site location regarding the fibers is changed while all other profiles are identical to the ramie alternative scenario. It is assumed in this case that the same quality of fabric can be found being close to the workshop, therefore minimizing the transportation impact. For the second counter-alternative scenario; a breakeven comparison is run by adjusting the APV accordingly to check the peak point for attaining the same energy demands and CO2 generation as for the baseline. For all the alternative scenarios, a novel polyester resin with the addition of renewable plant oils name BioPoli 507 [39] was used. As a result, 20% of the matrix volume is renewable, which contributes additionally by decreasing the overall impact of the material and disposal phases.

5.2.3 Materials, manufacture, end of life In a first stage, the Eco-Audit Tool assesses the inputs of the components that are involved in the parts manufacturing. In this step, the energy and CO2 profiles for the materials and processes are introduced to the project’s database. Table 5.2 presents the profile characteristics inputs regarding the two

TABLE 5.2 Components elements profile in Eco-Audit Step 1: Material and manufacturing, joining and finishing Component name

Material

Process

Mass

Secondary process

Baseline glass

Car hood, 318 units

Polyester

Molded

1.56 kg

Painting

Mat fabric, 318 units

E-Glass

Fabric production

0.88 kg

Cutting/trimming

Car hood, 318 units

Biopolyester

Molded

1.39 kg

Painting

Car hood, 318 units

Ramie

Fabric production

0.40 kg

Cutting/trimming

Alternative ramie

Step 2: Transport Stage name

Transport type

Distance (km)

Finished part to the point of sale

32 tons track

560

Raw materials (by all suppliers)

14 tons track

457

Step 3: Use Phase-Mobile Mode Fuel & mobility type

Usage (days/year)

Distance (km)

Gasoline-family car (km/day)

80

40

Eco-impact assessment of a hood Chapter | 5

Scenario

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106 PART | II Thermosetting and thermoplastic materials for structural applications

TABLE 5.3 Disposal phase (energy inputs, outputs) for reference composite Component

End-of-life option

% Recovered

Energy (MJ)

% Energy

Matrix

Remanufacture

11.0

96.04

65.4

Reinforcement

Landfill

20.0

50.88

34.6

146.92

100

Total

scenarios under comparison. In a second stage, a contradiction between alternatives on materials and choices of the supply chain are attempted. All information about allocation was taken from Ancel database. In the study of [1], mechanical recycling of the composite materials was performed successfully although at low percentages (11%e12%) due to low recycling efficiency of biaxial-reinforced composites. The remainder 80% of the fibers end up in landfills at the disposal scenarios of the composite materials. Analogous performance characteristics were assigned to this study as the referral part is essentially the same. Table 5.3 shows the energy recovery profile, according to these assumptions from experimental data.

5.3 Results and discussion The Eco-Audit final output of the calculations is shown in the form of detailed breakdown tables of the energy and CO2 footprint for individual life phases (material, manufacture, transport, use, and end of life) which are shown in Tables 5.4 and 5.5 respectively. In the two left-hand columns are listed the totals of their percentage values. Several observations can be drawn out of the Eco-Audit assessment regarding the MJ/kg of energy spent and the CO2 emissions generated per mass. As deduced from Table 5.4 regarding the baseline scenario, the most energy-intensive phases and overwhelmingly dominant environmental stressors (energy, CO2 footprint) are the Material (62.6%, 50.4%) followed by the Manufacture (17.7%, 27.4%), and Use Phase (18.9%, 21.2%). The Material use particularly stands out high because e-glass fibers, as well as UP (the constituents of the baseline), are synthesized from polymeric materials and therefore their production requires high embodied energy and CO2 footprint per kilo. The value for the End-of-Life potential (EoL) is not very high as composite materials and especially the ones incorporating thermosets are improbable to be recycled after their end-use, but they can partially be downcycled for their use in byproducts and/or fillings in other composites. The

TABLE 5.4 Eco-Audit report of the energy and CO2 footprint for glass composite baseline scenario Energy (MJ)

Energy (%)

CO2 footprint (kg)

CO2 footprint (%)

Material

47,383

62.6

1976

50.4

Manufacture

13,417

17.7

1073

27.4

Transport

440

0.6

31

0.8

Use

14,324

18.9

831

21.2

Disposal

146

0.2

10

0.3

Total (for first life)

75,710

100

3921

100

End-of-life potential

3278

1114

Eco-impact assessment of a hood Chapter | 5

Phase

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108 PART | II Thermosetting and thermoplastic materials for structural applications

TABLE 5.5 Eco-Audit report of the energy and CO2 footprint for the alternative ramie scenario Phase

Energy (MJ)

Energy (%)

CO2 footprint (kg)

CO2 footprint (%)

Material

30,004

60.9

1091

42.8

Manufacture

10,122

20.6

810

31.8

Transport

2825

5.7

201

7.9

Use

6152

12.5

437

17.1

Disposal

145

0.3

10

0.4

Total (for first life)

49,248

100

2548

100

End-of-life potential

2828

99

EoL represents the end-of-life savings realized in future life cycles when utilizing the recovered material or components. Table 5.5 lists the energy and carbon footprints of the materials and manufacturing processes regarding the alternative scenario, which is the ramie-reinforced biocomposite. A bar chart and summary is created according to user-choice and a report detailing the results of each step of the calculation are plotted in Fig. 5.2. The latter shows the comparison of the two tables in tabular form. The bars for the energy and carbon contributions to the first life as bars of solid colors, and show the potential energy and carbon saving (or penalty) as a separate, cross-hatched bar. After a closer look, it is observed that ramie composite is less energy- and carbon-intensive in the categories of material, manufacturing, and use. This is explicable as ramie-reinforced composites are lighter and consequently have less total product mass when compared to the ones made of e-glass. It has to be noted here that air emissions are generated during finishing processes of raw materials production which Eco-Audit takes into consideration. Specifically, glass-fiber manufacturing requires melting in a furnace, which consumes a significant amount of energy, thereby rendering the process very energy demanding. In principle, glass-fiber production requires 5e10 times more nonrenewable energy than natural fiber production [8]. In addition to that, melting raw materials in order to produce glass-fibers generates air emissions consisting of particulates,

Eco-impact assessment of a hood Chapter | 5

109

Energy (MJ) 50000 40000 30000 20000 10000 0 Material Manufacture Transport

Use

–100

Disposal EoL potential % Change

+100 0%

E-Glass hood part

–29%

Ramie hood part - sea freight

CO2 footprint (kg) 2000 1500 1000 500 0 Material Manufacture Transport –100 E-Glass hood part Ramie hood part - sea freight

Use

Disposal EoL potential % Change

+100 0% –30%

FIGURE 5.2 Eco-Audit comparison charts for fiber-glass baseline scenario against ramie alternative.

nitrogen oxides (NOx), and sulfur oxides (SOx). These particulates are generated from fuel combustion and dissociation of raw materials and are primary air pollutants. As indicated by the software tool, their values are 10 times lower when considering the ramie fabrics. On the other hand, harvesting and forming ramie into mats is a process which is less energy-intensive, compared to the emissions associated with glass-fiber production. However, the transportation profile for the ramie scenario is ranked the worst, which is 6 times higher in contrast to the e-glass baseline. This is attributed to the long distance that the ramie fabrics need to be

110 PART | II Thermosetting and thermoplastic materials for structural applications Energy (MJ) –100

% Change

+100

E-Glass hood part

0%

Ramie hood part local fiber

–32 %

CO2 footprint (kg) –100 E-Glass hood part Ramie hood part local fiber

% Change

+100 0% –35 %

FIGURE 5.3 Eco-Audit charts for glass-fiber baseline against ramie fiber acquired from local resources.

transported by sea freight. As seen in Fig. 5.2, ramie alternative will be 29% less energy demanding than baseline and generate 30% less CO2 emissions. In the first occurrence and the hypothetic modification of the supply chain from overseas to the close proximity of the manufacturing facilities (first counter-alternative), the overall impact can be further minimized. Fig. 5.3 features the impact in percentage and following in the baseline scenario shows the same composite setting by swapping the fibers’ location as if these were supplied around the industrial area that Ancel is located. The overall ramie impact is supplementary optimized by shortening the supply chain distance; a decrement of 3% in energy and 5% of CO2 emissions compared to the ramie scenario of Fig. 5.2 are observed. The question that arises at this point is whether that scenario is feasible about the local fiber quality and delivery in a reasonable timeframe, given the social and economic constraints that would potentially apply. The authors did not identify a local producer that could potentially supply fabrics of the same quantity and quality; however, they are presenting the outcome of such a comparison considering that Brazil indeed produces ramie fiber. In the last “what if ” scenario (second counter-alternative) depicted in Fig. 5.4, one may realize that even by the addition of 100 manufactured parts to the APV, the total eco-performance over life is lower by order of 6% in energy demands and 7% in CO2 emissions. In addition to that, the manufacturing phase for both scenarios have roughly the same demands in both environmental stressors under comparison while the material phase remains lower as for energy and CO2 footprint for the ramie hood. That is indeed a fascinating outcome when considering that the APV is increased by 32% while no significant difference is noticed.

Eco-impact assessment of a hood Chapter | 5

111

Energy (MJ) 50000 40000 30000 20000 10000 0 –10000

Material Manufacture Transport

Use –100

Disposal EoL potential % Change

+100

E-Glass hood part

0%

Ramie hood by sea + (100 parts)

–6%

CO2 footprint (kg) 2000 1500 1000 500 0 Material

Manufacture Transport

Use –100

Disposal EoL potential % Change

+100

E-Glass hood part

0%

Ramie hood by sea + (100 parts)

–7%

FIGURE 5.4 Eco-Audit comparison breakeven charts for glass-fiber baseline against ramie fiber when 100 additional parts are produced.

5.4 Conclusions The advantages of switching from synthetic fiber to natural fiber are evident within the scope of the Eco-Audit Tool analysis. Throughout the life cycle of a product, we identified the most relevant critical phases of a system for a set of environmental impact indicators (MJ per part and CO2 equivalent per part). Energy savings and CO2 emission reductions are among the benefits of the material during the manufacture and use phases. The more considerable savings are observed in the stage of material and use, where the type of materials and the weight of the part are showing a positive contribution to the

112 PART | II Thermosetting and thermoplastic materials for structural applications

environmental impact. The addition of biocontent and natural fibers acts as a complementary effect and optimizes its environmental performance given that both are derived from annually renewable resources. It is perceived by this study that products of biomaterial contents are less energy- and CO2-intensive as opposed to products from an entirely synthetic material (UP and glassfibers). However, the substitution of constituent materials alone might not always be capable of minimizing the environmental impact, and therefore further adjustment in the process should be considered. Under this lens, it is understood that the optimal scenario is indeed the one of ramie when considering a local fiber in the fabrication of the composite. Additionally, the locality of the fiber plays a significant role in the eco-impact assessment, which suggests that we should consider this factor along with materials substitution. It is fair to conclude that exploring green composites that match the performance of conventional counterparts while being economical and environmentally friendly is a feasible and worthwhile endeavor.

References [1]

[2]

[3]

[4] [5]

[6] [7]

[8]

[9]

[10]

Alves C, Ferra˜o PMC, Silva AJ, Reis LG,M,F, Rodrigues LB, Alves DE. Ecodesign of automotive components making use of natural jute fiber composites. Journal of Cleaner Production 2011;18:313e27. Goda K, Sreekala MS, Gomes A, Kaji T, Ohgi J. Improvement of plant based natural fibers for toughening green compositeseEffect of load application during mercerization of ramie fibers. Composites Part A: Applied Science and Manufacturing 2006;37:2213e20. Koronis G, Silva A, Dias APS. Development of green composites reinforced with ramie fabrics: effect of aging on mechanical properties of coated and uncoated specimens. Fibers and Polymers 2014;15:2618e24. Koronis G, Silva A, Furtado S. Applications of green composite materials. In: Kalia S, editor. Biodegradable green composites. New Jersey: John Wiley & Sons, Inc; 2016. Omrani E, Menezes PL, Rohatgi PK. State of the art on tribological behavior of polymer matrix composites reinforced with natural fibers in the green materials world. Engineering Science and Technology, an International Journal 2016;19:717e36. Shogren RL, Petrovic Z, Liu ZS, Erhan SZ. Biodegradation behavior of some vegetable oilbased polymers. Journal of Polymers and the Environment 2004;12:173e8. Venkateshwaran N, Elayaperumal A, Arwin Raj RH. Mechanical and dynamic mechanical analysis of woven banana/epoxy composite. Journal of Polymers and the Environment 2012;20:565e72. Joshi S, Drzal L, Mohanty A, Arora S. Are natural fiber composites environmentally superior to glass fiber reinforced composites? Composites Part A: Applied Science and Manufacturing 2004;35:371e6. Chen Y, Sun LF, Chiparus O, Negulescu I, Yachmenev V, Warnock M. Kenaf/ramie composite for automotive headliner. Journal of Polymers and the Environment 2005;13:107e14. Oksman K, Skrifvarsb M, Selinc JF. Natural fibres as reinforcement in polylactic acid (PLA) composites. Composites Science and Technology 2003;63:1317e24.

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Shanks RA, Hodzic A, Ridderhof D. Composites of poly(lactic acid) with flax fibers modified by interstitial polymerization. Journal of Applied Polymer Science 2006;99:2305e13. Yu T, Li Y, Ren J. Preparation and properties of short natural fiber reinforced poly(lactic acid) composites. Transactions of Nonferrous Metals Society of China 2009;19:651e5. Yu T, Ren J, Li S, Yuan H, Li Y. Effect of fiber surface-treatments on the properties of poly(lactic acid)/ramie composites. Composites Part A: Applied Science and Manufacturing 2010;41:499e505. Herrmann AS, Nickel J, Riedel U. Construction materials based upon biologically renewable resources - from components to finished parts. Polymer Degradation and Stability 1998;59:251e61. Angelini LG, Lazzeri A, Levita G, Fontanelli D, Bozzi C. Ramie (Boehmeria nivea (L.) Gaud.) and Spanish Broom (Spartium junceum L.) fibres for composite materials: agronomical aspects, morphology and mechanical properties. Industrial Crops and Products 2000;11:145e61. Marsyahyo E, Jamarsi, Rochardjo HSB, Soekrisno. Preliminary investigation on bulletproof panels made from ramie fiber reinforced composites for NIJ level Ii, Iia, and IV. Journal of Industrial Textiles 2009;39:13e26. Han H, Hsu LT, Lee JS. Empirical investigation of the roles of attitudes toward green behaviors, overall image, gender, and age in hotel customers’ eco-friendly decision-making process. International Journal of Hospitality Management 2009;28:519e28. Anonymous. Bioplastics in automotive applications. Bioplastics Magazine. Germany: Polymedia Publisher GmbH; 2007. Mercedes-BenzCom. Environmental certificate A-class [Online]. Stuttgart: Daimler Ag, Mercedes-Benz Cars; 2005. Available: http://www3.mercedes-benz.com/fleet-sales/en/assets/documents/Environmental_Certificate_A_Class.pdf. Malnati P. ECO elise concept: lean, speedy and green composites technology. Cincinnati, Ohio: Garder Publications Inc; 2009. MazdaCom. Mazda biotechmaterial. 2008 [Online]. Available: http://www.mazda.com/ mazdaspirit/env/biotech/material2.html. Mitsubishi-MotorsCom. Mitsubishi motors develops new eco-friendly floor mats using plant-based fibers. 2011 [Online]. Tokyo. Available: http://www.mitsubishi-motors.com/en/ corporate/pressrelease/corporate/detail1475.html. Satyanarayana KG, Arizaga GGC, Wypych F. Biodegradable composites based on lignocellulosic fibersdan overview. Progress in Polymer Science 2009;34:982e1021. Li J, Pan S-Y, Kim H, Linn JH, Chiang P-C. Building green supply chains in eco-industrial parks towards a green economy: barriers and strategies. Journal of Environmental Management 2015;162:158e70. Granta D, Ltd. CES EduPack materials selection software. Ver.15.10. 8th ed. Cambridge: Granta Design Limited; 2015. Seow Y, Goffin N, Rahimifard S, Woolley E. A ‘Design for Energy Minimization’ approach to reduce energy consumption during the manufacturing phase. Energy 2016;109:894e905. Finnveden G, Hauschild MZ, Ekvall T, Guine´e J, Heijungs R, Hellweg S, Koehler A, Pennington D, Suh S. Recent developments in life cycle assessment. Journal of Environmental Management 2009;91:1e21. Khare S, Dell’amico M, Knight C, Mcgarry S. Selection of materials for high temperature sensible energy storage. Solar Energy Materials and Solar Cells 2013;115:114e22.

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[31] [32] [33]

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[39]

Khare S, Dell’amico M, Knight C, Mcgarry S. Selection of materials for high temperature latent heat energy storage. Solar Energy Materials and Solar Cells 2012;107:20e7. DE Benedetti B, Toso D, Baldo GL, Rollino S. EcoAudit: a renewed simplified procedure to facilitate the environmentally informed material choice orienting the further life cycle analysis for ecodesigners. Materials Transactions 2010;51:832e7. Ghenai C. Eco audits and selection strategies for eco design. In: 9th Latin American and Caribbean conference for engineering and technology. Medellı´n, Colombia; 2011. Ashby M. Materials and the environment. Eco-informed material choice. Oxford: Butterworth Heinemann; 2012. Ashby M, Coulter P, Ball N, Bream C. The CES EduPack eco audit toolda white paper [Online]. Granta Design Ltd; 2012. Available: http://coral.ufsm.br/righi/Materiais/FIGS/ ch7bnotes.pdf. Koronis G, Silva AJ. Green composites reinforced with natural fabrics: process cost and eco-impact assessment. Journal of Composites Science 2, 2017. Koronis G. A green composite as a hood part of a buggy vehicle [Ph.D. dissertation]. Instituto Superior Te´cnico; 2014. Alves C. Sustainable design of automotive components through jute fiber composites: an integrated approach [Ph.D. dissertation]. Instituto Superior Tecnico; 2010. Serra B, Credidio J. Estudo da frota circulante brasileira. 2008. Available: http://www.cesvi. com.br/seguranca/biblioteca/dados_gerais/Frota_Circulante_Brasileira_SINDIPECAS.pdf. Hutchinson JR, Schubel PJ, Warrior NA. A cost and performance comparison of LRTM and VI for the manufacture of large scale wind turbine blades. Renewable Energy 2011;36:866e71. Elekeiroz. Launch of the BIOPOLI line of sustainable resins [Online]. Sao Paulo: Elekeiroz S.A; 2011. Available: http://www.elekeiroz.com.br/?s¼BIOPOLIþ.

Chapter 6

Production and modification of nanofibrillated cellulose composites and potential applications Md Nazrul Islam, Fatima Rahman Forestry and Wood Technology Discipline, Khulna University, Khulna, Bangladesh

Chapter Outline 6.1 Introduction 6.2 Cellulose and nanocellulose 6.2.1 Architecture of cellulose 6.2.2 Structures and size of nanocellulose 6.2.2.1 Cellulose nanocrystal 6.2.2.2 Nanofibrillated cellulose 6.3 Pretreatment of biomass fibers 6.3.1 Enzyme 6.3.2 Alkaline-acid 6.3.3 Ionic liquids 6.4 Isolation of nanofibrillated cellulose 6.4.1 Homogenization 6.4.2 Grinding 6.4.3 Ultrasonication 6.4.4 Electrospinning

115 116 117 118 118 119 119 119 121 121 122 122 123 123 124

6.4.5 Cryocrushing 6.4.6 Steam explosion 6.4.7 Ball milling 6.5 Drying of nanofibrillated cellulose 6.6 Modifications of nanofibrillated cellulose 6.6.1 Acetylation 6.6.2 Silylation 6.6.3 Application of coupling agents 6.6.4 Grafting 6.7 Applications of nanofibrillated cellulose 6.7.1 General applications 6.7.2 Applications in automobile industry 6.8 Conclusion References

125 125 126 126 126 127 128 130 130 131 131 132 133 133

6.1 Introduction Today, nanotechnology is recognized as one of the most promising areas for technological development in the 21st century [1] and more attention has been paid to utilize bio-based material in line with development of nanotechnology Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00006-9 Copyright © 2019 Elsevier Ltd. All rights reserved.

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and recent concern about environmental issues [2]. Natural fibers have gained much more consideration due to their promising characteristics such as biodegradability, renewability, uniformity, durability, and low cost [3]. Among the natural fibers, cellulose is one of the most plentiful biopolymers which exists in a wide variety of natural fibers such as kenaf [4], cotton [5], banana [6], wood [7], flax [8], oil palm [9], bamboo [10], and animal species like tunicate [11], and ;it has been the subject of many researches in nanotechnology. Cellulose is a linear biopolymer with b-D-glucopyranose repeating units [12] including both crystalline and amorphous region [13]. For the application of cellulose in nanotechnology, two general types of nanocellulose are recognized, namely nanofibrillated cellulose (NFC) and cellulose nanocrystal (CNC) that can be distinguished depending on their different production processes and structures [1]. Nanofibrillated cellulose (NFC) is a high aspect ratio fiber including both amorphous and crystalline regions and can be produced through some techniques such as electrospinning, refining [14], homogenization, grinding, cryocrushing [15], ultrasonication [16], and steam explosion [17]. Structures of cellulose nanofiber have gained attention as a potential material for reinforced nanocomposites [1]. By inserting these nanoscale compounds into polymers, even in small quantities, the properties of polymers improve and can be used for various applications [18]. However, NFC displays two main drawbacks which are associated with its intrinsic physical properties. The first one is the high number of hydroxyl groups which lead to strong hydrogen interactions between two nanofibrils and to the gel-like structure once produced. The second drawback is the high hydrophilicity of this material which limits its uses in several applications such as in paper coating (increase of dewatering effect) or composites (tendency to form agglomerates in petrochemical polymers). Surface modification, including grafting, silylation, acetylation, etc., is the most common way to make the surface of cellulose nanofiber hydrophobic and to incorporate it homogenously in different polymers [19]. Not only the modification processes but also the drying of nanofibrillated cellulose is another challenge, which should be considered for incorporation in polymers because the change of size of these materials after drying may affect their unique properties [1]. In this chapter, first the structures of cellulose and nanocellulose have been discussed. Then the production processes of NFC have been addressed. After that, drying and modification of NFC have been highlighted. At the end, the applications of these materials for the production of different nanocomposites to be used in the automobile industry have been discussed.

6.2 Cellulose and nanocellulose Cellulose is the most abundant renewable natural biopolymer on earth, which presents in a wide variety of living organisms including plants, animals, and some bacteria [20]. It is the main structural component of plants and is gaining

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117

importance as a renewable chemical resource to replace petroleum-based materials [21,22]. The annual production of cellulose is estimated to be over 7.5
1010 ton [23]. Nanocellulose generally refers to cellulosic materials having at least one dimension in the nanometer range. It can be isolated by different methods from various lignocellulosic sources. Recently, considerable interest has been emphasized on cellulose nanofibers due to their low thermal expansion [24,25], high aspect ratio (length to diameter ratio) [26], strengthening effect, good mechanical and optical properties, which may offer many applications in nanocomposites, paper making, coating additives, security papers, and food packaging [27]. Moreover, it has also promising applications in various electronic devices [28].

6.2.1 Architecture of cellulose Plants cell walls are divided by a middle lamella from each other followed by the primary cell wall layer [1]. Cellulose is predominantly found in the secondary wall and consists of roughly 6000 glucose units in the primary cell wall [29e31]. The degree of polymerization (DP) is up to 20,000; however, it varies widely and the value is around 10,000 in wood [32]. Fig. 6.1 represents the microstructure of wood fiber cell wall containing primary cell wall layer, and S1, S2, and S3 are the inner, middle, and outer layers of the secondary wall, respectively. This linear polymer is composed of repeated b-1,4 linked

Cambium Bark cambium Pith

Sapwood Hardwood

Sapwood Intermediate wood Hardwood

Layering of a mature cell wallt S1 S2

Secondary wall

S3 Cellulose nanofiber bundle

FIGURE 6.1 Microstructure of wood fiber cell wall [33].

Primary wall

118 PART | II Thermosetting and thermoplastic materials for structural applications

anhydroglucopyranose units that are covalently linked through acetal functions between the equatorial OH group of C4 and C1 carbon atom forming bundles of fibrils, called microfibrillar aggregates. Creation of highly ordered regions (i.e. crystalline phases) is allowed by these aggregates by alternating the disordered domains (i.e., amorphous phases) [34,35].

6.2.2 Structures and size of nanocellulose Depending on dimensions, crystallinity, functions, and processing conditions, nanocellulose can be classified into three main subcategories. Herein, the nomenclature is used as cellulose nanocrystal (CNC) and nanofibrillated cellulose (NFC), indicated in Table 6.1. Another type of nanocellulose is the bacterial nanocellulose (BNC), which is synthesized with a bottom-up method from glucose by a family of bacteria referred to as Gluconoacetobacter xylinus [36].

6.2.2.1 Cellulose nanocrystal CNC exhibits elongated crystalline rod-like shapes with a very limited flexibility compared to NFC as it does not contain amorphous regions [37]. It is also known as nanowhiskers [38e42], nanorods [34,43], and rod-like cellulose crystals [44] that are usually isolated from cellulose fibers through acid hydrolysis [45,46]. CNC possess a relatively low aspect ratio; it has typical

TABLE 6.1 Types of nanocellulose Type of nanocellulose

Synonyms

Typical sources

Average size

Cellulose nanocrystal (CNC)

Nanocrystalline cellulose (NCC), whiskers, rod-like cellulose, microcrystals

Wood, cotton, wheat straw, hemp, flax, rice straw, mulberry bark, ramie, tunicin, algae, bacteria, etc.

Diameter: 5e70 nm Length: 100e250 nm (from plant); 100 nm eseveral micrometers (from cellulose of tunicates, bacteria)

Nanofibrillated cellulose (NFC)

Nanofibrils, microfibrils, nanofibrillated cellulose, microfibrillated cellulose

Wood, potato tuber, sugar beet, hemp, flax, etc.

Diameter: 5e60 nm Length: several micrometers

Source: Klemm, D., Kramer, F., Moritz, S., Lindstrm, T., Ankerfors, M., Gray, D. and Dorris, A. Nanocelluloses: a new family of nature-based materials. Angewandte Chemi International Edition 2011;50:5438e5466.

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diameter of 2e20 nm and wide length distribution from 100 to 600 nm [47e49].

6.2.2.2 Nanofibrillated cellulose NFC refers to cellulose fibers that have been fibrillated to achieve agglomerates of cellulose microfibril units. It is described as a long and flexible cellulosic nanomaterial, which is obtained from cellulose fiber by mechanical disintegration [19]. Nanofibrillar cellulose [50,51], cellulose nanofiber [45,52], and cellulose nanofibril [50,53] are the terms used for microfibrillated cellulose in the literature. NFC is the smallest structural unit of plant fiber and consists of a bundle of stretched cellulose chain molecules [54] at approximately 1e100 nm size [55]. Fig. 6.2 shows a schematic wood hierarchical structure from biomass to CNC and NFC. Fig. 6.3 represents the morphology of CNC and NFC. As can be seen in this figure, compared to rod-like crystalline structure of CNC, NFC has long and fibrillar structure.

6.3 Pretreatment of biomass fibers Energy consumption is one of the main challenges for the production of nanofibers by mechanical isolation processes. Moreover, less energy utilization leads to less fibrillation of cellulosic fibers, as well as less production of nanofibers [59]. Pretreatment (e.g., enzyme, chemical) helps to reduce energy consumption to an amount of 1000 kWh/ton from 20,000 to 30,000 kWh/ton for cellulosic fibers [15]. On the other hand, appropriate pretreatments of cellulosic fibers promote the accessibility of hydroxyl groups, increase the inner surface, alter crystallinity, break cellulose hydrogen bonds, and boost the reactivity of the fibers [14].

6.3.1 Enzyme Enzyme is used to modify and/or degrade the lignin and hemicelluloses contents while maintaining the cellulose portion. On the other hand, it helps in restrictive hydrolysis of several elements or selective hydrolysis of specified component in the cellulosic fibers [60]. However, a single enzyme cannot degrade the cellulose fibers because they contain different organic compounds. For this reason, a set of cellulase enzymes are involved which can be categorized as below [61]: A. Cellobiohydrolases: A and B type cellulases which attack greatly the crystalline cellulose. B. Endoglucanases: C and D type cellulases which need some disordered structure in cellulose to attack it.

120 PART | II Thermosetting and thermoplastic materials for structural applications

(a)

(b)

(c)

(d)

(e)

FIGURE 6.2 A schematic of wood hierarchical structure from biomass to CNC and NFC: (a) Biomass, (b) single-fiber network, (c) microfibril, (d) cellulose nanocrystal, and (e) nanofibrillated cellulose [56].

Many investigations have been done on the production of NFC with enzymatic pretreatment [62e65]. Pa¨a¨kko¨ et al. [66] applied mild enzymatic hydrolysis combined with refining and homogenization to produce NFC from bleached softwood pulp, and found that selective and mild hydrolysis using a mono-component endoglucanase enzyme allowed a greater aspect ratio and was less aggressive compared to acid hydrolysis.

Production and modification of nanofibrillated cellulose Chapter | 6

(a)

500 nm

121

(b)

1 µm

FIGURE 6.3 Transmission electron microscopy (TEM) images of CNC [57] and NFC [58].

6.3.2 Alkaline-acid Alkaline-acid pretreatment has been used by some of the researchers before mechanical isolation of NFC for solubilization of lignin, hemicelluloses, and pectins [67,68]. This pretreatment included the following three steps [45,69]: A. Soaking fibers in 12e17.5 wt% sodium hydroxides (NaOH) solution for 2 h to raise the surface area of cellulosic fibers and to make it more susceptible to hydrolysis. B. Hydrolyzing the fibers with hydrochloric acid (HCl) solution for 1 h at 60e80 C to solubilize the hemicelluloses. C. Treating the fibers with 2 wt% NaOH solution for 2 h at 60e80 C would disrupt the lignin structure and would also break down the linkages between carbohydrate and lignin.

6.3.3 Ionic liquids Ionic liquids are organic salts having the temperature below 100 C [70]. They have very interesting and valuable properties such as nonflammability, thermal and chemical stability, and infinitely low vapor pressure [71,72]. ILs have been extensively used to dissolve cellulosic materials [73,74]. Li et al. [75] coupled pretreatment by 1-butyl-3-methylimidazolium chloride as ILs with High Pressure Homogenizer (HPH) for the first time to isolate NFC from sugarcane bagasse. The ILs dissolved cellulose and easily passed through homogenizer without clogging. Afterwards, cellulose was precipitated by adding water and was regenerated by freeze drying. They found that solubilization of cellulose was affected by reaction temperature, power of microwave, and weight ratio of cellulose to ILs.

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6.4 Isolation of nanofibrillated cellulose NFC can be extracted by various methods. In this section, the processes for producing NFC, their advantages and disadvantages, as well as some important issues regarding these methods are described.

6.4.1 Homogenization Homogenization is one of the mechanical processes which can be used for the production of NFC. In this process, a high pressure homogenizer is used and cellulose suspension passes through a small nozzle with high pressure [1]. Besides, effective parameters in diminishing the size of the fibers to nanoscale include high shear and impact forces along with high pressure and velocity on fluid to generate shear on the stream [33]. Pressure, different passing times through the machine, concentration of suspension, and temperature are the most important parameters which affect the properties of obtained nanofibers [1]. In 1983, Herrick and Turbak applied this method for the first time to isolate NFC from wood fiber [76,77]. It is a very simple process without the need for organic solvents [78] but clogging is one of the most important issues related to application of this instrument due to its small orifice. To overcome this problem, various pretreatments like refining, cryocrushing [79], and milling [80] are used by the researchers to reduce the size of the fibers. High energy consumption is another main drawback of this process. In this regard, researchers suggest some pretreatments including enzyme [61,65,81], alkaline [45,67], and ionic liquids [75] to decrease the amount of energy for production of CNF. Fig. 6.4 shows the morphology of NFC with various treatments. The diameter of wheat straw after alkaline treatment was 9 mm and after mechanical isolation it reached 30e40 nm (Fig. 6.4(a)) [67]. Fig. 6.4(b) displays long and distinct NFC with diameter around 5 nm after enzyme treatment (size of original fibers was 10 mm) [66]. Circular-shape nanoparticle with a diameter in the range of 10e20 nm was produced from ionic liquid treatment of sugarcane bagasse, as presented in Fig. 6.4(c) [75].

FIGURE 6.4 TEM image of nanocellulose from (a) alkaline-treated wheat straw [67], (b) enzyme-treated soft wood pulp [66] and (c) ionic liquid-treated sugarcane bagasse [75].

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The final application of NFC produced through homogenization process is a critical issue. Due to the hydrophilic nature of cellulose nanofibers, their incorporation and dispersion with common polymers, which are hydrophobic, are very difficult [49]. Low interfacial adhesion between these two parts in the composite leads to reduction in the mechanical and other properties of the final product. To overcome this challenge, a wide variety of modifications like carboxymethylation [82], 2,2,6,6-tetramethylpiperdine-1-oxyl (TEMPO) oxidation [83,84], acetylation [4,85], and silylation [86,87] have been suggested by the researchers.

6.4.2 Grinding Ultrafine friction grinding is another technique which is used for the production of NFC. For such treatment, super mass collider grinders (Masuko Sangyo Co. Ltd., Japan) are commonly used. Taniguchi and Okamura [88] described the production of NFC by passing 5e10 wt% natural fiber suspensions from different sources through a grinder 10 times and obtained NFC with a diameter in the range of 20e90 nm. During such a process, the cellulose slurry is passed between static and rotating grinding stones (disks). The distance between these disks can be adjusted which enables avoiding the problem of clogging. The grinding process is very close to double-disk refining. However, the main difference is the possibility of a lower gap between the disks when using grinders. To increase the fibrillation efficiency, [89] reported the use of reducing the gap between the grinding stones to 100 mm from the zero position of motion. The motion zero position is the contact position between two stones before cellulose loading and the “negative” gap is set after cellulose loading [90].

6.4.3 Ultrasonication High intensity ultrasonication is considered as a mechanical method for producing NFC with hydrodynamic forces [91]. In this process, ultrasonic waves create strong mechanical stress due to cavitations and therefore cause disaggregation of cellulosic fiber to nanofibers [92]. To isolate CNF by ultrasonication, several attempts have been done from various cellulose sources such as microcrystalline cellulose, regenerated and pure cellulose fibers [91], kraft pulp [93], flax, wood, wheat straw and bamboo [94], para rubberwood sawdust [95], poplar wood powders [16], etc. In ultrasonic process, the efficiency of defibrillation depends on power, concentration, temperature, size of fibers, and time [96]. Besides, researchers have used combination of ultrasonic and other methods to increase fibrillation of nanoscale cellulose. Furthermore, [96] reported that combination of ultrasonic and homogenization boosts uniformity and fibrillation of cellulose nanofiber in comparison to ultrasonic solely. In addition, [97] concluded that

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TEMPO-oxidized fibers treatment with ultrasonic probe is more efficient for nanocellulose production compared to mechanical blender, ultrasonic probe, and ultrasonic bath.

6.4.4 Electrospinning A versatile and simple process called electrospinning was patented by Formhal in 1930 and used for formation of nanofibers from various sources, such as cellulosic fibers, by electrical force [98]. An electrospinning instrument includes high voltage supply, syringe to carry polymer solution, and a target to collect nanofibers [99] (Fig. 6.5). In this process, nanofibers form from polymer solution between two electrodes with opposite polarity where one electrode is connected to syringe and the other one to collector [101]. A conical-shape droplet known as taylor cone is held at capillary tip due to surface tension at a critical voltage [102,103]. When electric force, which is created at the surface of polymer solution, conquers surface tension of solution, electrically charged jet emerges and electrospinning occurs [104,105]. When the jet moves in whipping motion between needle and collector, the solvent of polymer solution evaporates and the dry nanofiber in the form of nonwoven mat forms on the collector [106]. In this process, the parameters can be categorized into solution parameters (surface tension, concentration, viscosity, and conductivity), processing conditions (voltage, distance from needle to collector, type of collector, flow rate), and ambient conditions (humidity, pressure, and temperature) [107,108]. The morphology and size of resultant nanofibers can be changed depending on interaction of all these factors.

Spinneret

Syringe pump

Rotating drum

High voltage power supply FIGURE 6.5 Schematic of electrospinning apparatus [100].

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In electrospinning process, first a polymer solution should be prepared. However, processing of cellulose via electrospinning is a big challenge because of its limited solubility in common solvents, as well as its tendency for agglomeration [109].

6.4.5 Cryocrushing Another method for production of NFC was proposed by [110] and is called cryocrushing. In this method, cellulose is frozen using liquid nitrogen and further crushed by applying high shear forces. Under mechanical impact, ice crystals exert pressure on the cell walls, causing them to break and release cell wall fragments. Dufresne et al. [110] showed that NFC can be produced from hydrated and cryocrushed raw sugar beet pulp which was further passed through a Manton-Gaulin homogenizer at 500 bar for 2 h.

6.4.6 Steam explosion Steam explosion is a type of thermo-mechanical process. At high pressure, steam penetrates into cellulose fiber through diffusion and when the pressure suddenly releases, creates shear force, hydrolyses the glycosidic and hydrogen bonds, and leads to formation of nanofibers [111]. Mason introduced the steam explosion method to defibrillate wood to fiber for board production in 1927 [112]. In this process, pressure, temperature, and time of being of the material in autoclave are the effective parameters. This process can be used solely or in combination with other processes. For instance, cellulose nanofibers from banana at 20 lb pressure, 110e120 C, for 1 h [17] and from pineapple at 20 lb pressure [113] produced just using steam explosion. TEM and AFM images of Fig. 6.6 confirm individualization of NFC from cell wall using steam explosion process. Only little association happened

FIGURE 6.6 NFC from pineapple leaf (a) TEM (b) AFM [113].

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between adjacent NFC. The author estimated the aspect ratio of 50 through TEM and diameter of around 5e60 nm through AFM for NFC..

6.4.7 Ball milling Ball milling is another technique which was reported very recently for the production of NFC. In this method, a cellulose suspension is placed in a hollow cylindrical container, partially filled with balls (e.g., ceramic, zirconia, or metal). While the container rotates, cellulose is disintegrated by the high energy collision between the balls. Zhang et al. [114] studied the process of NFC production from once-dried bleached softwood kraft pulp suspension at a solid concentration of 1 wt% using ball milling. They showed the influence of the process conditions such as the ball size and ball-to-cellulose weight ratio on the morphology of the produced NFC. An average diameter of 100 nm was reported for the disintegrated fibers. The control of the processing parameters was necessary to prevent cellulose decrystallization and to produce cellulose nanofibers rather than short particles.

6.5 Drying of nanofibrillated cellulose As nanocellulose is hydrophilic and tends to agglomerate, their drying process is one of the most important challenges related to their application. Two main reasons are to maintain nano-size of material for application and to reduce transportation cost of nanocellulose in aqueous form [115]. Besides, during drying of nanofibrillated cellulose, hydrogen bonds can be generated and lead to irreversible agglomeration known as hornification due to the hydrophilic nature of cellulose materials [82,116]. Thus, the size of nanocellulosic materials as well as their unique characteristics can be changed. A wide variety of drying methods have been employed and compared together by researchers to overcome this drawback. Table 6.2 displays various drying process steps. Abe et al. [52] applied undried fibers to produce NFC and to reduce their agglomeration. The particular feature of crystallization at temperatures lower than the freezing temperature of water is increasing the rate of freezing and thus preventing from aggregation [118]. Flow rate of suspension and temperature of hot air are some of key factors in this context [117]. In addition, parameters such as concentration, feed rate of liquid, and gas flow rate have effect on this process [115].

6.6 Modifications of nanofibrillated cellulose Modification of NFC has gained a significant interest from the scientific community. It is considered to improve the hydrophilic nature of cellulose in

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TABLE 6.2 Various nanofibrillated cellulose drying processes steps Freeze drying (FD) l l

Frozen suspension in very low temperature (around 65 C) Transfer suspension to freeze dryer for lyophilization [21]

Supercritical drying (SCD) l l l

l

Dehydration of suspension with nonaqueous media like ethanol Replacement of nonaqueous with liquid CO2 Pressurizing and heating of liquid CO2 and cellulose mixture to the supercritical conditions Elimination of liquid CO2 by decompression to the atmosphere [115]

Atomization drying (AD) l l l

Spraying suspension Passing material through a nozzle Drying by hot air flow [117]

Spray drying (SD) l l l l l l

Preconcentration of initial liquid to appropriate viscosity Pumping liquid through atomizer Dehydration process in stream of hot gas Powder separation Cooking Packaging [115]

polar and nonpolar environments, as well as to increase compatibility with a wider variety of matrices [1]. Different reactions have been performed to modify the surface properties of cellulose [119,120], including corona or plasma discharges [121], surface derivatization [122], graft copolymerization [123], or application of surfactant [124,125]. Some approaches aiming to hydrophobize nanocellulosic materials are briefly discussed in this section.

6.6.1 Acetylation Kim et al. [126] reported that cellulose was partially acetylated to modify its physical properties while preserving the microfibrillar morphology [53]. Transparency and hygroscopicity of cellulose/acrylic resin composite materials were improved and reduced by acetylation, respectively, though the composites exhibited an optimum degree of substitution and were reduced in properties with excessive acetylation [127]. A study by [128] claimed that acetylation

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(a)

(b)

(c)

(d)

FIGURE 6.7 SEM micrographs of unmodified EFB composite (a) severe degradation of unmodified EFB (b) acetylated EFB composite (c) and slight degradation of acetylated EFB composite (d) [129].

improved the thermal degradation resistance of cellulosic fibers. The effect of biological exposure (Fig. 6.7) upon the properties of acetylated and surfacetreated plant fiberebased polyester composites was studied by [129], and it was found that acetylation exhibited superior bioresistance followed by silane, as well as cast resin and glass fiber composites, in soil tests up to 12 months exposure. In other research of [130], modified fibers were shown to have a smoother surface compared to the unmodified ones, which was believed to be a factor in improving the fiberematrix adhesion.

6.6.2 Silylation Silane-based surface modification is a popular way to change the surface of fibers from hydrophilic to hydrophobic. Isopropyl dimethylchlorosilane is used by [131] for surface silylation of cellulose microfibrils resulting from the homogenization of parenchymal cell walls. They found that microfibrils

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retained their morphology under mild silylation conditions and could be dispersed in a nonflocculating manner into organic solvents. Andresen et al. [86] reported that hydrophobizing of MFC via partial surface silylation using the same silylation agent resulted in partial solubilization of MFC and loss of nanostructure when silylation conditions were too harsh. Films prepared from the modified cellulose by solution casting showed a very high water contact angle (117e146 degrees). It is probable that in addition to decreased surface energy, higher surface roughness as a result of modification could contribute to increased hydrophobicity. Moreover, study by [132] found that hydrophobized MFC could be used for stabilization of water-in-oil type emulsions. Fig. 6.8 compares the morphology of MFC samples silylated with four and six equivalents of chlorodimethyl isopropylsilane per glucose unit.

(a)

(b)

(c)

(d)

FIGURE 6.8 TEM of MFC silylated with six equivalents (a); four equivalents (b) of CDMIPS per cellulose glucose unit; severely decomposed microfibril bundle (c); and compact aggregates of degraded microfibrils and fiber fragments (d) [86].

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O NH

HO

O OH

OH O

O HO

O

NH

n O O

O

NCO R

O O HO

NH O OH

O O

NH

O

R O

O HO

O

R

HO

O

NH

n O

NH O OH

R COOH

O O

O HO

O

NH

n O

FIGURE 6.9 Chemical reactions that occur in the alternative chemical modifications of chitin whiskers with phenyl isocyanate, alkenyl succinic anhydride, and 3-isopropenyl-R, R’-dimethylbenzyl isocyanate [135].

6.6.3 Application of coupling agents By applying three different coupling agents, the adhesion between microfibrils and epoxy resin polymer matrix is successfully enhanced. These are 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and a titanate coupling agent, Lica 38. Surface modification changes the character of NFC from hydrophilic to hydrophobic while the crystalline structure of the cellulose microfibrils remains intact. Among the tested coupling agents, Lica 38 gave the most hydrophobic surface probably due to the lower polarity of the titanate modifier alkyl chain. Unlike silane coupling, titanate coupling is thought to occur via alcoholysis, surface chelation, or coordination exchange. The monoalkoxy- and neoalkoxy-type titanium-derived coupling agents react with the hydroxyl groups present on the surface of the substrate to form a monomolecular layer [133,134]. Nair et al. [135] used phenyl isocyanates and alkenyl succinic anhydride to improve the quality of the interface between natural rubber and chitin whiskers in presence of 3-isopropenyl-R, R’-dimethylbenzyl isocyanate. The expected chemical reactions that occur in the alternative chemical modifications are seen in Fig. 6.9.

6.6.4 Grafting Three methods have been reported for the modification of Nanofibrillated cellulose (NFC) by heterogeneous reactions in both water and organic solvents to produce cellulose nanofibers with a surface layer of moderate hydrophobicity [51]. Epoxy functionality was applied onto the NFC surface by oxidation with cerium (IV) followed by grafting with glycidyl methacrylate. Reactive epoxy groups served as a starting point for further functionalization with ligands,

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which typically unreacted with the surface hydroxyls present in native NFC. The major advantage of this technique is the use of organic solvents, and laborious solvent exchange procedures can be avoided as the reaction is conducted in aqueous media. In the same research conducted by these authors, grafting of hexamethylene diisocyanate followed by reaction with amines yield a far more hydrophobic NFC surface. Succinic and maleic acid groups can be introduced directly onto the NFC surface as a monolayer by a reaction between the corresponding anhydrides and the surface hydroxyl groups of the NFC. Also, n-octadecyl isocyanate (C18H37NCO) has been applied as the grafting agent to improve NFC compatibility with polycaprolactone [136].

6.7 Applications of nanofibrillated cellulose 6.7.1 General applications NFC can be used as reinforcement in nanocomposites that are multiphase products in which at least one phase has a dimension of 1e100 nm [137]. Properties of nanocomposites depend on the nature of polymer matrix, interaction between matrix and nanoparticles, and structure of large interphase elements [138]. Recently, many researches have been employed to study the use of cellulosic fibers as a filler or reinforcement phase instead of synthetic fibers to keep our environment safe [139] and due to their biodegradability, lower weight, renewability, lower cost, higher stiffness, and strength [140e142]. Nowadays, NFC has been extensively used to produce nanocomposites with phenolic resin [143,144], styrene butyl acrylate [58], amylopectin [63,64], polyurethane [145], melamine formaldehyde [62], etc. Again, cellulose nanopaper (Fig. 6.10) is an attractive product in nanotechnology due to the opportunity to tailor porosity, high toughness, and renewability of its resource. It can be defined as a network constructed by high aspect ratio (beyond 100) intertwined nanofibrils and random surface nanofibril orientation [53] that exhibits high strength, transparency, foldability, and low thermal expansion coefficient [147].

FIGURE 6.10 Visual appearances of the transparent papers with NFC contents of 100% (a), 50% (b), and 0% (c), respectively [146].

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NFCs are the perfect candidates for substrates used for continuous roll-toroll processing for the production of electronic devices and could replace the expensive conventional batch processing of glass. They show good heat-transfer characteristics in comparison to glass and are also transparent due to the densely packed structure and small space between fibers to avoid light scattering [25]. Many applications such as transparent films for food packaging, coating technologies, electronic devices, or using it for its excellent barrier properties are being studied by many researchers. Oxygen barrier plays a key role in food packaging, and it was found that NFC contributed to the impermeability of films when they were prepared at a sufficient thickness [24,148e150]. The use of NFC in printing applications has recently become the subject of increasing study. Researchers used NFC as a coating agent to improve the print quality of synthetic fiber sheets and found that NFC improved the quality of print and the ink density [151e154]. The ability of nanocellulose to form strong transparent films and porous dense aerogels is currently attracting attention in new domains such as electronics and medicine.

6.7.2 Applications in automobile industry The automobile industry has a never ending need to develop stronger lightweight vehicles and an important part of this is to develop injection molded components that are lighter than those available today and preferably recyclable. NFC has the potential to be used to manufacture reinforced injection molded composites having significantly improved mechanical properties [155]. Besides, the industry has a demand for lightweight transparent materials with good thermal stability as well. NFC can be used as reinforcement in transparent composites due to the size of the fibrils and crystals [156]. Again, the automobile industry needs to develop high performance structural materials at the lowest possible weight. Today, it is possible to spin

Hemp fiber

Non-woven mat

Finished door

Pre-finished door

FIGURE 6.11 Automobile components based on polymer composites reinforced with lignocellulosic fibers [156].

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continuous strong and stiff fibers directly from NFC suspensions that could be used as a biodegrade alternative to today’s woven reinforcement fabrics [156]. Fig. 6.11 illustrates a modern automobile together with several of its components made of polymer matrix composites reinforced with lignocellulosic fibers.

6.8 Conclusion This chapter focuses on the production process of NFC and its challenges, the opportunities for modification in the process, and scope of application of NFC. Main drawbacks are related to an efficient NFC isolation process from the natural resources. Homogenous dispersion of NFC in polymer matrix is a key issue to apply it in nanocomposites. Surface modifications can be considered as a solution for this problem. Two categories of surface modification, that is, making the surface more hydrophobic and introduction of ionic groups on the surface of fibers direct to increase the mechanical properties of NFCreinforced composites. NFC can be used in medical devices, nanopaper, construction materials, automobiles, sports equipment, electronics, pharmaceuticals, cosmetics, packaging, and so on. Though it has many advantages, its production is not economic due to heavy energy consumption. However, different pretreatments could reduce the energy consumption. Eventually, more research should be done focusing efficient NFC production methods, pretreatments, modifications, and drying.

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Part III

Nanomaterials and additive manufacturing composites

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Chapter 7

Nanocomposites with nanofibers and fillers from renewable resources N. Saba, M. Jawaid, M. Asim Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Serdang, Malaysia

Chapter Outline 7.1 7.2 7.3 7.4

Introduction Nanomaterials Renewable nanomaterials Advantages over micro-sized particles 7.4.1 Nanoclays 7.4.2 Nanocellulose 7.5 Applications of renewable materials 7.6 Polymer composites 7.7 Polymer nanocomposites

145 146 147 148 148 149 154 154 157

7.7.1 Characterization and applications of nanocomposites 7.8 Renewable nanomaterialebased polymer nanocomposites 7.9 Applications of nano fillers or nanofibers reinforced polymer nanocomposites 7.10 Conclusions Acknowledgment References

157 158

161 162 162 163

7.1 Introduction Nanoscience and nanotechnology advent the introduction of exciting research areas by exploiting renewable nanomaterials as reinforcements in order to advance materials with innovative properties that cannot be met by the conventional materials. Interestingly, nanoscience is a convergence of chemistry, physics, biology, and materials science that deals with the manipulation and characterization of matter on length scales between the molecular and the micron-size [1,2]. In nanotechnology, various types of nano-sized filler materials such as nanoclays, metallic nanoparticles, carbon nanomaterials, and nanocellulose have been exploited to improve physical, mechanical, flame and gas barrier properties of polymers [3]. Development of nanocomposites is one of Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00007-0 Copyright © 2019 Elsevier Ltd. All rights reserved.

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the emerging areas of materials research. Nanocomposites are regarded as extraordinary materials of high potential, required for the new generation [4]. Nanocellulose is classified as a nontoxic nano-based cellulosic material [5], completely biodegradable and without adverse effects on health or the environment. These benefits contribute to facilitating the use of cellulose nanofibers or nanofibrillated cellulose (CNFs) and cellulose nanocrystals (CNCs) to eliminate safety concerns commonly encountered for mineral and carbon nanofillers [6]. The nanocellulose can be isolated into filament-like CNFs or rod-like or elongated rice-like CNCs, previously known as whiskers, from lignocellulosic plant biomass and from some marine animals. CNFs are usually produced via mechanical shearing methods like ultrasonication, homogenization, grinding, microfluidization, or milling in combination with enzymatic and/or chemical pretreatments [7]. CNCs could be extracted from purified cellulose fibers after a complete dissolution of the noncrystalline fractions by chemical hydrolysis, while the CNFs are produced by high pressure and/or shearing forces of mechanical fibrillation after pretreatment [8].

7.2 Nanomaterials The growing global safe ecological concern, environmental rules/regulations, high rate of depletion of fossil fuels, climate changes, as well as reduced variability in feedstock costs relative to petroleum-derived building blocks have driven the interest for the search of new green materials that are compatible with the environment [9]. Nanomaterials are defined as the materials with the microstructure having at least one dimension in nanometer range. These nanomaterials, also referred as nanofillers, nanoparticles, nanofibers, nanoscale building blocks, or nanoreinforcements, have at least one dimension in nanometer scale and possess high aspect ratio [10]. The particles like polyhedral oligomeric silsesquioxane (POSS), silica (SiO2), carbon black, titanium dioxide (TiO2), calcium carbonate (CaCO3), nanoclay, nanocellulose, and carbon-based nanofillers are the most important and well-established nanosized fillers used for modifying the properties of polymer and polymer-based composites [11,12]. Nanomaterials displayed better reinforcement for the nanocomposite production and are generally incorporated on a weight basis, usually lesser than 5% [13]. The nanofillers can be one-dimensional (layered minerals such as clay), twodimensional (like carbon nanotubes, nanowires, nanofibers, cellulose whiskers, etc.), or three-dimensional (spherical particles include silica nanoparticles, nanowhiskers, etc.) [14]. Nanofillers possess appeal of miniaturization and impart enhanced mechanical, electronic, magnetic, optical, and chemical properties to a level that cannot be achieved by conventional materials [15]. A variety of ways have been reported to synthesize nano-level materials such as plasma arcing, chemical vapor deposition, electro deposition, solegel synthesis, acid hydrolysis, ultrasonication, and high-intensity ball milling [16].

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7.3 Renewable nanomaterials The renewable nanomaterials are green, biodegradable, and renewable in nature and are solely derived from natural sources like agricultural, forests, municipal wastes, and biomass. They possess similar and comparable unique properties to that of nano metal oxides and carbon-based nanomaterials like graphite, graphene, and carbon nanotubes. Currently, nanocellulose, oil palm nanofiller, coir nanofiller, jute nanofiller, and nanoclay are receiving higher attention from both academicians and industrialists to minimize the usage of toxic, nonrenewable, and costly nanoparticles or fillers. SEM images of oil palm nanofiller obtained by cryogenizing and high-energy ball milling technique [11], CNFs from microfibrillated cellulose [17], and short, stable cotton fibers by a chemo-mechanical process [18] are shown in Fig. 7.1. TEM images of nanocellulose from spinifex grass (T. pungens) obtained via acid hydrolysis [7] and jute nanofibers from steam explosion process [19] are shown in Fig. 7.2.

FIGURE 7.1 SEM of oil palm nano filler [11], Cellulose nanofibers from microfibrillated cellulose [17] and Cellulose nanofibers from short stable cotton fibers by a chemo-mechanical process [18].

FIGURE 7.2 TEM images of nanocellulose from spinifex grass (T. pungens) obtained via acid hydrolysis [7] and jute nanofibers from by steam explosion process [19].

148 PART | III Nanomaterials and additive manufacturing composites

 Abundantly available  Low weight  Biodegradable  Waste biomass

Increased profit

Reduced cost

 Renewable

 Relatively cheaper  Satisfactory mechanical and physical properties FIGURE 7.3 Advantages of renewable nano fillers/fibers.

7.4 Advantages over micro-sized particles Nanoparticles have proportionally larger surface area than their micro-scale counterparts, which favors the fillerematrix interactions and the performance of the resulting composite materials [20]. Nanofibers compared to microfibers also possess lowered width and high aspect ratio which add unique dimensions to optical, mechanical, electrical, and other characteristics for the development of new promising advanced materials from the application viewpoint. Some of the most important benefits realized by using renewable nanomaterials relative to microfibers are illustrated in Fig. 7.3.

7.4.1 Nanoclays Clay is a naturally occurring mineral composed primarily of fine grained minerals [21]. Fig. 7.4 shows the most typical structure of clay mineral [22].

Al,Mg OH O Si

Tetrahedral Octahedral

d001

Tetrahedral Gallery height

Exchangeable cation nH2O

FIGURE 7.4 General structure of clay mineral [22].

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149

Nowadays, clays (layered silicates) are found to be one of the ideal nanoreinforcements for polymers, because of its high intercalation chemistry, high aspect ratio, ease of availability, and low cost [14]. Nanoclays are the general term for the naturally occurring layered mineral clay silicate nanoparticles having phyllosilicate or sheet structure with a thickness of about 1 nm and surfaces about 50e150 nm in one dimension and high aspect ratio [23]. Depending on the morphology of nanoparticles and chemical composition, nanoclays are organized into various classes such as illite, halloysite, bentonite, kaolinite, montmorillonite, hectorite, and chlorite [22]. Organically modified nanoclays or organoclays are formed when nanoclay products are typically modified with ammonium salts [21]. The clay surface modification renders them organophilic, to make them compatible with hydrophobic organic polymers [24]. Research study illustrates that the usual content of lamellar nanoclay and organo-modified montmorillonite is in the range of 5e10 wt% due to their high aspect ratio (more than 1000), high surface area (more than 750 m2/g), and higher modulus values (176 GPa) [25]. Organoclays are one of the attractive and promising hybrid organic/inorganic nanomaterials generally used for polymers and polymer-based composite modification.

7.4.2 Nanocellulose Nanocellulose has attracted interest due to its unique features such as biodegradability, biocompatibility, renewability, abundance, high modulus, mechanical strength, high specific surface area, light weight, and low density for its use in nanocomposite materials [26]. Nanocellulose can be isolated by several mechanical methods such as high-pressure homogenization, grinding, ultrasonication, or high-speed blending [27]; chemical methods including sulfuric acid, hydrochloric acid, or TEMPO (2,2,6,6-tetramethylpiperidine-Loxyl) oxidation [28]; enzyme-assisted hydrolysis, as well as a combination of any two. Researchers claimed that nanocellulose materials obtained by the chemical methods usually by acid hydrolysis are relatively uniform in size with high crystallinity [29,30]. CNFs and CNCs are the two promising classifications of nanocellulose. CNFs are the renewable materials that have the potential to serve as a platform for the next generation of green nanomaterials [31]. The CNFs, also referred to as nanofibrillated cellulose (NFC) and microfibrillated cellulose (MFCs), represent natural nano-scale fiber, made purely from cellulose molecules. The simplest representation of CNFs is presented in Fig. 7.5 [32]. A series of processes are necessary to isolate CNFs. There are many ways to extract CNFs, all of which lead to different types of fibrillar material with characteristics that will depend on the raw material (cellulose), pretreatment, and disintegration process [33]. The defibrillation of nanofibrillated cellulose generally needs intensive mechanical treatments such as high-intensity ultrasonication, high pressure homogenization, cryocrushing,

150 PART | III Nanomaterials and additive manufacturing composites

Nanofiber bundles Macrofibril

Nanofiber Cellulose fiber

FIGURE 7.5 Typical CNFs from cellulosic fiber [32].

microfluidization, grinding, and combinations of two or three [34]. Recently, cotton CNFs isolated by chemical purification and pretreatment by a highspeed blender combined with high-pressure homogenization possess high crystallinity and thermal stability [35], presented in Fig. 7.6. There have been several researches about the extraction of CNFs from cellulosic sources, such as kenaf, hemp, cotton, bamboo, wood pulp, flax, oil palm biomass, and rice straw [34]. Moreover, removal of the amorphous region allows access to highly crystalline, rod-like CNCs [36]. CNCs are most usually isolated via acid hydrolysis, enzymatic treatment, hydrothermal treatment, ultrasonication, and mechanical methods, or combinations thereof [7]. Most widely used techniques to isolate nanocellulose from different sources with different shapes are listed in Table 7.1.

Nanofibrillation

Cotton

Nanofibers

FIGURE 7.6 Cotton CNFs from cotton fibers by pretreatment followed by nano-fibrillation [35].

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TABLE 7.1 Reported study on the isolation of nano fillers from natural sources and its shapes Renewable nanomaterials

Nature and shape

Preparation method

References

Jute nanofibers

Spherical and elliptical shape

High-energy ball milling

[37]

Coir nanofiller

Spherical

Grinding

[38]

Oil palm ash nanofiller

Spongy and porous

Grinder/Refiner machine

[39]

Bamboo stem (BS), oil palm empty fruit bunches (OPEFB), and coconut shells

Circular with much fewer and irregular micropores

Pyrolysis

[40]

Rice husk nanosilica

Particulate nature and spherical shape

Precipitation with a weak organic acid followed by calcination

[41]

Nano fly ash

Rough and irregular shape

High-energy planetary ball milling

[16]

Bamboo cellulose nanofibers

Long cellulose nanofibrils

Chemical pretreatmentcombined with high-intensity ultrasonication followed by freeze-drying

[42]

Oil palm nanofiller

Porous and spherical

Cryogenizer and highenergy ball milling

[11]

Sesbania Javanica cellulose nanofibers

Long cellulose nanofibrils

Centrifuge

[43]

Kenaf cellulose nanocrystals

Rod or needlelike shape

Acid hydrolysis of cellulose

[44]

Noninvasive grass Miscanthus Giganteus cellulose nanocrystals

Ribbon or rodlike shape

Acid hydrolysis of bleached pulp followed by TEMPO oxidation

[45]

Bamboo pulp residue cellulose nanowhiskers

Rod shape

Acid hydrolysis of the bamboo pulp

[46]

Banana cellulose nanofibers

Long nanofibrils

Steam explosion

[9]

Soybean nanofibers

Web-like structure

Combined chemical and mechanical treatments

[47]

Paper mulberry pulp cellulose nanowhiskers

Needle or rodlike shape

Acid hydrolysis of mulberry pulp cellulose fibers

[26]

Continued

152 PART | III Nanomaterials and additive manufacturing composites

TABLE 7.1 Reported study on the isolation of nano fillers from natural sources and its shapesdcont’d Renewable nanomaterials

Nature and shape

Preparation method

References

Surface-modified polyethyleneimine (PEI) cellulose nanofibers

Web-like with rough surface

Mechanically extracted from filter paper

[48]

Banana peel cellulose nanofibers

Long and entangled cellulosic filaments

Alkaline treatment followed by enzymatic treatment with xylanase

[33]

Cellulose nanofibrils from bleached eucalyptus pulp (Eucalyptus globulus)

Long and thin individual fibrils

TEMPO-mediated oxidation

[6]

Electrospun nanocellulose from cellulose acetate polymer solution

Long nanofibrils

Electrospinning

[49]

Cellulose nanofibrils from corn husks and oat hulls

Long nanofibrils

2,2,6,6tetramethylpiperidinyl1-oxyl (TEMPO)mediated oxidation followed high-pressure homogenizer

[50]

Cellulose nanocrystals from microcrystalline cellulose powder

Needle-like structure

Acid hydrolysis

[51]

Nanocellulose from spinifex grass (Triodia pungens)

Needle shaped

Acid hydrolysis

[7]

Nanocellulose fibers from jute fibers

Web structures

Steam explosion process

[19]

Cellulose nanocrystals isolated from cotton linter pulp fiber/ agar film

Rod shape

Acid hydrolysis and neutralization with NaOH

[30]

CNFs from pineapple leaf fibers

Well interconnected web-like structure

Steam coupled acid treatment

[52]

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TABLE 7.1 Reported study on the isolation of nano fillers from natural sources and its shapesdcont’d Renewable nanomaterials

Nature and shape

Preparation method

References

Montmorillonite/ Cellulose nanowhiskers [MMT/CNW(SO4)]

Rod shaped

Acid hydrolysis

[53]

Cellulose nanowhiskers from microcrystalline cellulose

Rod shaped

Acid hydrolysis

[54]

Cellulose nanofibers from short stable cotton fibers

Complex webshaped

Chemomechanical process

[18]

Cellulose nanocrystals extracted from Posidonia oceanica waste Poly(lactic acid) (PLA)

Needle shaped

Chemical treatment, followed by sulfuric acid hydrolysis

[55]

Cellulose nanocrystals from commercial microcrystalline cellulose/PLA

Ribbon-like particles

Acid hydrolysis

[56]

Cellulose nanocrystals from sugarcane bagasse (SCB)/Poly(vinyl alcohol)

1D needle

Sulfuric acid hydrolysis

[57]

Cellulose nanocrystals from microcrystalline cellulose/high oleic sunflower oil thermosets

Rod-like nanocrystals

Sulfuric acid hydrolysis

[58]

Cellulose nanocrystals from Luffa cylindrica fibers/polycaprolactone

Rod shape

Acid hydrolysis

[59]

Cellulose nanofibers

Web network fibrils

e

[17]

Oxidized cellulose nanocrystals from the bleached rice straw pulp

Rod shape

Acid hydrolysis

[60]

Nanocellulose

Rod-like whiskers

Sulfuric acid hydrolysis of commercial microcrystalline cellulose

[61]

Continued

154 PART | III Nanomaterials and additive manufacturing composites

TABLE 7.1 Reported study on the isolation of nano fillers from natural sources and its shapesdcont’d Renewable nanomaterials

Nature and shape

Cellulose nanocrystals

Preparation method

References

Rod shape

Acid hydrolysis of microcrystalline cellulose

[62]

Cellulose nanofibers

Long nanofibrils

e

[20]

Rice straw nanofibrillated cellulose

Smooth and web-like structure

High-shear homogenizer at 10,000 rpm using oxidized pulp suspensions of 2%

[63]

Nanocrystalline cellulose from OPEFB fibers

Rod structure with some agglomerated network

Sulfuric acid hydrolysis process

[64]

7.5 Applications of renewable materials CNFs also offer promising application in broad fields of polymer-based nanocomposites, strength additives for paper, packaging with enhanced barrier properties, drug delivery, adsorbents for water treatment, functional membranes, foams, and coating additives [6]. CNCs possess better stiffness, strength, and optical properties and hence show extensive applications such as coatings, pharmaceuticals, reinforced plastics, textiles, energy storage, sound insulators, acoustic membranes, recyclable oil absorbents, paper applications, packaging, security papers, air filtration, and gas barriers [65]. The development of CNCs for future important reinforcements in composite materials is desirable because of the wide availability of cellulose sources, potential mitigation of other inorganic reinforcing agents, and biodegradability of cellulose materials [36]. Table 7.2 highlights the biodiverse applications of renewable nanomaterials in different industrial sectors.

7.6 Polymer composites The term of composite materials was first used during the 1960s. Composite materials have been used by the people of earlier civilizations since many centuries. One of finest examples includes the preparation of bricks for building construction using straw and mud [96]. Composite materials

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TABLE 7.2 Biodiverse applications of renewable nanomaterials in different areas Renewable nanomaterials

References

Biomedical engineering, flexible optoelectronics, tissue regeneration, films, foams, nanocomposites, screen-printing, functional membranes for water cleaning, vehicle bio-bumper, ionic liquid supercapacitors, solar cells, energy storage devices, treatment of municipal wastewater, hydrogels with poly(vinyl alcohol)

Nanocellulose

[66e74]

Antibacterial agents, biophotonics, thinfilm electrode, antibacterial cotton garment, controlling pesticide, removal of oil from water, epoxy anticorrosive coatings

MMT and OMMT nanoclay

[75e82]

Hydrogen storage medium, solid-state lithiumesulfur batteries, flame retardants for polylactide, packaging and nano containers, prodrug for pharmacological applications, flame retardant for nylon 6

Halloysite nanoclay

[83e88]

Removal of Phosphorus in Water and Wastewater, Solid Catalyst in Heterogeneous Electro-Fenton System

Allophane nanoclay

[89,90]

Active food packaging, Heterogeneous Photocatalysts for Dyes Degradation

Modified kaolinite nanoclay

[91,92]

Flame retardant for epoxy

Oil palm nano and coir nanofiller

[11,38]

Advanced Lightweight Structural Applications including, Aircrafts, Buildings, Bridges, Boats, Reservoirs, Pressure Vessels, and Railway Tracks

Oil palm nanofiller

[12,93]

Biomedical Applications, Scaffolds Tissue Engineering, Cardiovascular Implants, Repair of Articular Cartilage, Vascular Grafts, Urethral Catheters, Mammary Prostheses, Penile Prostheses, Adhesion Barriers, and Artificial Skin

Pineapple leaf cellulose nanofiber

[52]

Waterborne Polyvinylacetate (PVA) Adhesive Paper, Board, Textile, Ceramics, and Foils

Cellulose nanofibrils from bleached Eucalyptus pulp (Eucalyptus globulus)

[6]

Industrial applications

Continued

156 PART | III Nanomaterials and additive manufacturing composites

TABLE 7.2 Biodiverse applications of renewable nanomaterials in different areasdcont’d Renewable nanomaterials

Industrial applications

References

Innovative and Promising High Performance Anode Materials for Future Application in Rechargeable Lithium Ion Batteries (LIBs) and sodium Ion Batteries (SIBs)

Biomass carbon materials derived from ramie fibers and corncobs

[94]

Promising Route to Design Advanced Anodes for Sodium Ion Batteries with Excellent Electrochemical Performance

Hierarchical porous carbon from peanut skin from Shandong region of China

[95]

composed of at least two constituents of different phases, in order to achieve combined properties that cannot be met by a single-phase material. Polymer composites have one phase as a polymer or matrix, and binder as the second phase, including reinforcing fibers or nanoparticles in a matrix to improve dimensional and thermal stability, stiffness, toughness, and tensile strengths. Most general scheme for the fabrication of composites is represented in Fig. 7.7. Moreover, composites can be classified into three subclasses, including particles, fibers, and structural-based composites, shown in (Fig. 7.8) http://textilelearner.blogspot.my/2012/09/glass-fiber-composites-properties-of. html. The development of polymer composite materials displays keen interest as they are light weight, flexible, tougher, and are usually fabricated on large size into intricately shaped components for industrial applications by combining large varieties of reinforcements and polymers [10,97]. Polymer composites

Composites

Particles

Large particle

Fibers

Dispersion strengthen

Continuous (aligned)

Structural

Discontinuous (short)

Aligned

Laminates

Randomly oriented

FIGURE 7.7 Classification of polymer composites.

Sandwich

Nanocomposites with nanofibers and fillers Chapter | 7

Polymer/ matrix

Reinforcements

Fibers Thermoplatics • Polypropylene • Polystyrene • Polyurethane • Polyethylene

Thermosets • Epoxy • Polyester • Vinyl ester • Phenolic

• Glass • kevlar • Carbon • Natural fibers

157

Composites

Nano fillers • Carbon-nanotubes • Graphite • Nanoclay • Metal oxides • Nanocellulose

FIGURE 7.8 Scheme of the polymer composites (http://textilelearner.blogspot.my/2012/09/ glass-fiber-composites-properties-of.html).

are able to meet diverse design requirements with significant weight savings, as well as high strength to weight ratio.

7.7 Polymer nanocomposites Polymer nanocomposites are composites in which at least one of the phases shows dimensions in the nanometer range (1 nm ¼ 109 m). They are reported to be the materials of the 21st century in the view of possessing design uniqueness and property combinations that are not found in conventional composites [12]. Nanocomposite materials signify as the most encouraging and promising family of material science to overcome limitations of microcomposites and monolithics, while posing preparation challenges related to the control of elemental composition and stoichiometry in the nanocluster phase. The structure of nanocomposites usually consists of the matrix material containing the nano-sized reinforcement components in the form of particles, whiskers, fibers, and nanotubes. Polymer nanocomposites can be fabricated and processed in ways similar to that of conventional polymer composites, which make them particularly attractive from a manufacturing point of view. Nanocomposites exhibit light weight, good dimensional stability, enhanced heat and flame resistance, as well as barrier properties with far less loading of nanoparticles than conventional composite counterparts [14].

7.7.1 Characterization and applications of nanocomposites Different instruments have been employed for the characterization of nanocomposites, including atomic force microscopy (AFM), scanning tunneling microscopy (STM), Fourier transformed infrared spectroscopy (FTIR), X-ray

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photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), scanning and transmission electron microscopy (SEM/TEM). Simultaneous small angle X-ray scattering (SAXS) and X-ray diffractometer (XRD) studies have also been used for quantitative characterization of nanostructures and crystallite structures in some nanocomposites. In addition, theoretical calculations/simulations have been worked out to predict strength properties, including stress/strain curves [98]. Nanocomposite research embraces applications in wide spectra due to their unique characteristic of enhancing the mechanical and barrier properties such as electronics and computing, construction, cosmetics, data storage, communications, aerospace, sporting materials, health-medicine, energy, environmental, transportation, national defense, and many other composite-based industry applications [4].

7.8 Renewable nanomaterialebased polymer nanocomposites Green chemistry coupled with nanotechnology brings a new platform based on environmental and technological concerns to develop renewable and sustainable end products [99]. A wide variety of polymer matrixes, including both thermosets and thermoplastics from natural or organic sources, are being reported to form nanocomposites with modified and improved properties, due to appealing intrinsic and exceptional unique properties of dispersed renewable nanomaterials like nanocellulose and nanoclays. Currently, among CNCs and CNFs, CNCs received considerable attention and emerged as green nanoreinforcements for a variety of organic polymers to fabricate advanced and high-performance nanocomposites, due to their exceptional properties conferred by their high rigidity, stiffness, crystallinity, mechanical strength, and optical properties, besides their exciting surface chemistry [100]. CNCs’ incorporation improved the mechanical properties and the reinforcing capacity of composites for diverse industrial applications [101,102]. The reinforcement capability of nanoclay is due to its high modulus, high strength, and high aspect ratio. Interestingly, MMT and organoclays are widely used for dispersion in polymers due to high aspect ratio and large interface of the polymer-nanoclay interaction in the polymer composites [103]. The structure of nanoclays or its dispersion in resins is of various types and can be characterized as phase-separated, intercalated, or exfoliated as displayed in Fig. 7.9 [104]. Literature reviewed that depending on the manufacturing process (such as homogenization methods, centrifugation, solution intercalation, melt intercalation, melt blending, etc.) and polymer/nanofiller bonding (involving the insertion or dispersion of clay materials into a polymer matrix), the layered silicates get dispersed into the polymer matrix resulting in intercalation and/or exfoliation nanocomposites [105]. However, the best performances of

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159

+ Layered-MMT

Microcomposite

Polymer

Intercalation

Exfoliation

FIGURE 7.9 Dispersion mechanism of nanoclay in resin [104].

advanced nanocomposites are generally achieved with the exfoliated structures. The nanoclay-reinforced polymer composites display vast potential applications in a variety of areas such as electronics, sensors, information storage, catalysis, and structural components [106,107]. Rate of cure, reaction time, enthalpy, activation energy, viscoelastic properties, and cross-linking density influence the nanoclay-reinforced nanocomposites [108]. Some of the most recent and exclusive research on natural nanofillers or nanofibersreinforced thermoset, thermoplastic, and elastomer polymer composites and their applications are listed in Table 7.3.

TABLE 7.3 Reported study on renewable nanomaterials based polymer nanocomposites Nanocellulose/ nanofibers/nano fillers

Extractions

References

Epoxy

MMT nanoclay

e

[108]

Epoxidized soybean oil

Cloisite 30B nanoclay

Modified MMT

[109]

Poly(vinyl alcohol)

Nanocellulose from commercial microcrystalline cellulose

Sulfuric acid hydrolysis

[61]

Poly(lactic acid)

Montmorillonite/ cellulose nanowhiskers [MMT/CNW (SO4)]

Acid hydrolysis

[53]

Polymers Thermosets

Thermoplastics

Continued

160 PART | III Nanomaterials and additive manufacturing composites

TABLE 7.3 Reported study on renewable nanomaterials based polymer nanocompositesdcont’d

Polymers

Nanocellulose/ nanofibers/nano fillers

Extractions

References

Poly(lactic acid)

Cellulose nanocrystals

Acid hydrolysis of microcrystalline cellulose powder

[51]

Poly(lactic acid)

Cellulose nanocrystals

Acid hydrolysis from commercial microcrystalline cellulose

[56]

Poly(lactic acid)

Cellulose nanocrystals

Sulfuric acid hydrolysis

[110]

Whey protein isolate

Oat husk nanocellulose

Acid hydrolysis

[111]

Poly(vinyl alcohol)

Barley straw and husk cellulose nanocrystals

Revalorization

[112]

Poly(lactic acid)

Cellulose nanocrystals

Sulfuric acid hydrolysis

[110]

Castor oil and cornbased flexible polyurethane foam

Cellulose nanocrystals

Acid hydrolysis

[62]

Poly(3-hydroxybutyrate)

Organoclay CloisiteÒ 30B

Modified MMT

[113]

Poly(lactic acid)

Cellulose nanofibers from softwood

e

[20]

Poly(lactic acid)

Cellulose nanofibers

e

[17]

Waterborne polyurethane

Cellulose nanowhiskers from microcrystalline cellulose

Acid hydrolysis

[54]

Poly(lactic acid)/Poly(3hydroxybutyric acid-co3-hydroxyvaleric acid)

Cellulose nanocrystal from OPEFB fibers

Sulfuric acid hydrolysis process

[64]

Nanocellulose from Jute fibers

Steam explosion

[19]

Elastomers Natural rubber

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7.9 Applications of nano fillers or nanofibers reinforced polymer nanocomposites CNCs from sugarcane bagasse obtained by sulfuric acid hydrolysis reinforced in polyvinyl alcohol/carboxymethyl cellulose (PVA/CMC) blend, fabricated PVA/CMC-CNCs bio-nanocomposite films. Films possess high stiffness and strength required for eco-friendly food packaging applications with superior properties [114]. In another study, oil palm nanofiller developed by cryogenizer and high-energy ball milling are incorporated in the epoxy polymer which acts as a promising alternative to steel, iron metals, iron/cobalt and iron/ copper/nickel alloys. They show extensive diverse structural applications as they possess a high degree of dimensional stability with temperature variations [93]. Alternatively, incorporation of oil palm nanofiller in kenaf/epoxy composites possess enhanced dynamic and thermal properties and indicate a high possibility in advanced lightweight structural applications where renewable resource and high performance are required, such as aircrafts, buildings, bridges, boats, reservoirs, and pressure vessels [12]. CNFs polyethyleneimine (PEI) surface-modified reinforced epoxy nanocomposites show promising applications in automotive, construction, and electronic devices, as well as in engineering devices, and circuit board manufacturing [48]. ZnS/Bacterial cellulose/epoxy nanocomposites possess good flexibility and optical and mechanical properties for potential applications in the flexible optoelectronic materials [115]. In other research findings, MMT nanoclay/Tetraglycidyl epoxies nanocomposites offered advanced applications and deliver improved performance and longevity than the materials currently used in automotive, electronics, and advanced aerospace application [116]. Researchers incorporated nanofibrillated cellulose and CNCs from the rachis of date palm tree in natural rubber (NR) [117]. Developed NR/cellulose green nanocomposite films show high potential to be used for electrical applications and are suggested as a promising candidate for battery separators [117]. In other work, CNFs from pineapple leaf fibers are reinforced in polyurethane to fabricate nanocellulose/polyurethane nanocomposites [52]. They showed exclusive and versatile biomedical applications due to their high cross-linking, uncomplicated chemical structure, and nontoxic nature, including nonlatex condoms, breathable wound dressing, surgical gloves, surgical gowns or drapes, medical bags, organ retrieval bags, and medical disposables [52]. Key factors of nanocomposites governing their applicability in automotive sectors involve excellent superior mechanical, thermo-mechanical, optical, thermal, and electrical properties [118,119]. Nanomaterials such as nanoclays and cellulose nanofiber/crystal products also extend their impact in automotive industries owing to outstanding performance that allows cost reduction, weight reduction, improved engine efficiency (fuel saving), reduction in CO2 emissions, superior performance (greater safety, increased comfort, and better driveability), and product improvement. Remarkably, the automotive industries

162 PART | III Nanomaterials and additive manufacturing composites

exclusively get benefitted from polymer nanocomposites worldwide owing to several applications such as rear bumpers, antifog coatings for headlight and windshield, higher scratch-resistant car coatings, weather resistant coatings, paints, lubrication, ultra-reflecting layer for automobile mirror and improved gloss [120]. Other applications include engines and powertrain, suspension and braking systems, exhaust systems and catalytic converters, under-bonnet parts, exterior frames/body parts, tires, electric and electronic equipment [121e125].

7.10 Conclusions Green chemistry coupled with nanotechnology and the development of renewable materials because of the environmental and technological concerns. Recent decades marked the utilization of renewable nanomaterials as promising reinforcements in polymer composites derived from natural sources of plant or animal in academic and industrial fields as they possess high aspect ratio and high surface area. Renewable nanomaterials show several advantages over traditional materials, such as glass, carbon nanotubes, carbon black, silica, metal oxides, talc, and mica, that include biodegradability, abundance, low density, high specific strength, enhanced energy recovery, nontoxicity, and low production costs. Nanoclays, nanocellulose, jute, oil palm, and coir nanofiller received increased interest as reinforcing agents in polymer composites. Incorporation of renewable nanomaterials greatly enhance the physical, mechanical, chemical, thermal, dielectric, electrical, flame, and barrier properties of several polymer matrices including epoxy, polypropylene, polyethylene, polyimide, polystyrene, poly(methyl methacrylate), natural rubber, and polylactic acid. Nanomaterialreinforced polymer nanocomposites show wide applications from packaging to construction and medical and high-performance engineered materials due to their renewability and excellent mechanical properties. This chapter delivers valuable literature information on the reported research findings for the extraction of nanomaterials from different cellulosic biomass, wastes, and organic residues, their properties, their diverse promising applications, and an insight into polymer nanocomposites to extend their modern commercial and advanced applications.

Acknowledgment The authors acknowledge Universiti Putra Malaysia, Malaysia, for supporting this study through Putra grant-9441501.

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Chapter 8

3D printing technologies and composite materials for structural applications Rajkumar Velu1, Felix Raspall1, Sarat Singamneni2 1 Singapore University of Technology and Design, Singapore; 2Auckland University of Technology, Auckland, New Zealand

Chapter Outline 8.1 Introduction 8.2 3D printing technologies 8.3 Composites and its properties for fabrications 8.3.1 Challenges for 3D printing material properties

171 174 177 179

8.4 3D printing of composite materials 8.4.1 3D printing of green composite materials 8.5 Conclusion and future directions References

183 189 190 190

8.1 Introduction Composites represent the current trend in material research, combining different “pure” materials to accomplish a new one compound with properties that exceed those of its components. Composites exist in nature: a piece of wood is a composite, with long fibers of celluloseda complex form of starchdheld together with lignin. Whereas cellulose provides the strength, the comparatively weaker lignin keeps the fibers in place [1]. The early manmade composite was fabricated by combining natural materials such as wood or bamboo with pine resin to form bows; some examples are recorded from as early as 1200 AD [2]. In the 1800s, advances in chemistry led to the development of polymer composite materials, using polymerization methods to form synthetic resins like celluloid, melamine, and bakelite [3]. During the 1900s, various synthetic polymers such as vinyl and polystyrene were developed [4]. The rapid development and use of composite materials began in the 1940s, propelling the search for appropriate candidate composite materials. Such research begins with military vehicles, airplanes, helicopters, and Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00008-2 Copyright © 2019 Elsevier Ltd. All rights reserved.

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rockets, which require high strength and lightweight materials [5,6]. While metal-based materials present good mechanical properties, they are comparatively heavier. Instead, lightweight parts can be produced using polymer materials; however, they lack in mechanical properties when long-term durability is required. This encouraged scientific and industrial research efforts to increase the mechanical properties of polymers. As a result, high-strength materials like glass fibers were developed for high strength applications. Until the 2000s, combinations of various fibers, polymers, and metals were tested to form candidate materials toward appropriate applications [7e9]. However, the environmental challenges of composite materials became evident as sustainability awareness intensified. Reuse and recycling composites are not trivial at the different stages, leading to waste of material cost and pollution. To overcome these issues, research on “Green Composites” begins to identify the alternative materials that can reduce the environmental impacts [10]. The processing methods also contribute significantly to the environmental impact of composites like creating waste, smoke, and high thermal emissions. The traditional manufacturing of polymers, metals, and ceramics into sheets, rods, and other forms is essentially done either by extrusion or casting. The extrusion method is simpler and inexpensive, but it presents limitations on the possible geometry of parts and is prone to scratches [11]. Though the extrusion process is based on liquid polymer, the material is pressed by means of roller to form sheets while cooling. The casting method is typically stronger than extrusion and used for various applications [12]. Apart from these, it is also critical to highlight the major metal casting processes that have been employed mainly for automotive application; these examples include sand casting, lost wax casting, permanent mold casting, and centrifugal casting [13e16]. The above casting methods have a long cycle time; metal flow is slower as flow depends on gravity to fill the mold; in addition to that a thicker mold is required for these techniques [17,18]. To overcome these issues, die casting has been introduced. Though time saving is achieved, the limitation faced is material waste [19]. After casting, the parts are subjected to subtractive process for end use, for example, to make an aluminium part, a block is placed into CAD system and the excess material is removed, which leads to 60% e70% of material to be sent to scrap. To achieve accurate functional parts, the processing methods are quite varied and modified. However, inadequacies are experienced based on material and process limitations. Industries often suffer based on processing methods and enormous material wastes [20]. Also, high process costs needed for high skilled workforces, excessive processing times, and unavoidable internal stresses are among the significant bottlenecks. Long cycle and dwell times lead to change in material properties of end use products. Eventually, these processes mainly depend on individual skills and pose serious limitations toward achieving consistent results and complex forms [21]. Consequently, the manufacturing industries are searching for alternative manufacturing methods with novel materials and the recent

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scientific research is focused on additive manufacturing for processing of wide range of materials [22]. Three-dimensional (3D) printing is an additive manufacturing and solid freeform fabrication method used to fabricate high complex geometries without molds or tools. It involves a layer-by-layer fabrication process based on 3D computer-aided design (CAD) data [23]. 3D printing is highly flexible and can be cost-effective for low and mid-scale manufacturing. Interest in this technology from manufacturing scientific research community has rapidly grown in recent years. Applications of 3D printing extend to concept modeling, functional prototyping, and digital manufacturing stages [24]. In concept modeling, the designers or engineers can translate their ideas into physical form within abbreviated time, whereas the functional prototyping reveals the structure and performance before committing to mass production [25]. For the past decade, 3D printing has been the valuable platform for the industries as a rapid prototyping tool. Although the involvement of 3D printing technology in the final production of functional parts is still in its infancy, industry survey shows that for most industries around 10% of the manufactured parts can be more efficiently produced through 3D printing. Continued reduction in cost and increase in quality [26e28] evidences that this technology may soon overcome its current bottlenecks and achieve mainstream implementation, a scenario that would revolutionize the economy [29]. The implementation of 3D printing has already produced key transformations in manufacturing, as highlighted in Fig. 8.1. True rapid prototyping

Low volume production Rapid design iteraton

True rapid prototyping

Mass customization

3D printing changes in manufacturing industries

Product innovation

Virtual inventory

Long tail of parts

FIGURE 8.1 3D printing changes in worldwide manufacturing.

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is achieved when the fabrication of prototype models is completed within a few days, in-house or outsourced to specialized companies that can ship parts through global distribution companies. This enables rapid design iterations, expedites the release of products to market, and therefore benefits companies’ competitiveness [30]. Car manufacturer Ford, for example, has benefitted from the implementation of rapid design iterations using 3D printing. The traditional way to develop and test an engine, however, takes more than 6 months and costs hundreds of thousands of dollars. But, when they started using 3D printing technology, numerous versions of engine prototypes are tested simultaneously, each costing only four to five thousand dollars [31]. In addition, 3D printing is transforming industrial production through low-volume production by eliminating tool and mold costs, mass-customization by allowing each product to be completely customized [32], and virtual inventory, by replacing the stock of physical parts with digital files that can be printed on demand as needed [33]. Long tail represents the large set of products that consumers buy at very low volumes. With the rapid advancement of 3D printing, it is possible and economical to produce products at a low volume. In other words, 3D printing can make the long tail much longer and reduce distribution costs in the process. Finally, 3D printing technologies are promoting a renaissance in product innovation, whereas companies move from the redesign of existing products to the creation of new products that can take full advantage of 3D printing’s greater design freedom and flexible productions [34]. The effect of the changes above promoted by 3D printing in the manufacturing sector can ultimately reduce its environmental impact [35]. The objective of this chapter is to introduce the fundamentals of 3D printing, its classifications, its applications in composite components, and its relevance to the development of green composites.

8.2 3D printing technologies 3D printing builds prototypes and final functional parts through the addition, layer by layer, of raw materials in the form of liquid, powder, or sheets. The process starts with a CAD model of a part, which can be an original design or reverse-engineered from a 3D scan. Then, the model is converted into a compatible digital file describing the three-dimensional object geometry, typically a stereolithography file (STL). A slicer software will read the geometry and generate the machine code file that contains the information that the 3D printer will follow layer by layer to fabricate the designed part. This program generates G-code to perform insert support and prepare a model for printing [36]. There are several types of 3D printing technology and selecting the most suitable process for an application could be a challenging task. The wide range of 3D printing technologies and materials are used for different applications. Each processing technique has variations in dimensional

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accuracy, surface finish, and postprocessing requirements. The distinct types of 3D printing processes and the processing techniques are shown in Table 8.1. The above classified 3D printing technologies have taken wide range of materials for processing. Vat polymerization is a resin-based process whereby photopolymer resins are cured by UV light. It has an elevated level of accuracy and good finish, and also requires support structures and postcuring of the product before structural applications. The layer thickness of the process

TABLE 8.1 Classification of 3D printing/additive manufacturing technology Sl No

Processing techniques

1

Vat photopolymerization

Classification of 3D printing

Processing method

Stereolithography (SLA)

Cured with laser

Digital Light Processing (DLP)

Cured with projector

Continuous Digital Light Processing (CDLP)

Cured with LED and oxygen

2

Material extrusion

Fusion Deposition Modelling (FDM)

3

Material jetting

Material Jetting (MJ)

Cured with UV light

Nanoparticle Jetting (NPJ)

Cured with heat

Drop on Demand (DOD)

Milled to form

4

Binder jetting

Binder Jetting (BJ)

Joined with bonding agent

5

Powder bed fusion

Multi-Jet Fusion (MJF)

Fused with agent and energy

Selective laser sintering (SLS)

Fused with laser

Direct Metal Laser Sintering (DMLS)/Selective Laser Melting (SLM)

Fused with laser

Electron Beam Melting (EBM)

Fused with electron beam

Laser Engineering Net Shape (LENS)

Fused with laser

Electron Beam Additive Manufacturing (EBAM)

Fused with electron beam

Laminated Object Manufacturing (LOM)

Adhesives are used for bonding

6

7

Direct energy deposition

Sheet lamination

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varies from 0.025e0.5 mm. However, only limited materials can be used as photo resins. The materials used are UV-curable photopolymer resins and Visijet range resins (3D system) [37e39]. Material extrusion process is a widely used and inexpensive method. A nozzle deposits material by extrusion on the cross-sectional area in accordance with the object slice. The following layers are added on top of previous layers. Dimensional accuracy, low speed, and support material removal are the notable shortcomings in this method. A wide range of materials are compatible with this process, including acrylonitrile butadiene styrene (ABS), polyamide (PA). acrylonitrile styrene acrylate (ASA), polyetherimide (PEI), polylactic acid (PLA), polyphenylsulfone (PPSF), polyethylene terephthalate (PET), polypropylene (PP), high-density polyethylene (HDPE), polymethylmethacrylate (PMMA), polycarbonate (PC), polystyrene (PS), and thermoplastic polyurethane (TPU) [40,41]. Material jetting process provides high accuracy and comparatively low wastage. It requires supporting structure and is suitable for polymers and waxes. This technology is similar to 2D printing ink jet printer. Material is jetted onto the build platform surface in droplets using either thermal or piezoelectric methods. When in contact with the air, the droplets solidify and make the first layer. Further layers are built to generate the structural parts. The polymers used in this process are PP, HDPE, PMMA, PC, PS, ABS, and high impact polystyrene (HIPS) [42e44]. Binder jetting process overcomes some of the material limitations for the aforesaid processes, as it can process a wide range of materials including metals, polymers, and ceramics. This process is typically faster than the process mentioned above. In binder jetting, materials are used in the form of powder, which is spread and compacted as a thin layer over the build platform using a roller. The print head deposits the binder adhesive on top of the powder based on the target geometry requirement. Further, the build platform moves down by the model and another layer of powder is spread for processing. The unbound powder serves as supporting material for the object and can be saved and reused after the printing is completed and depowdered. However, this process is not suitable for many structural parts as the mechanical properties of the binder limit those of the final part. In addition, postprocessing can be more time-consuming. Materials like metal (stainless steel), PC, polyamide (PA), ABS, and ceramics (glass) are suitable candidate materials [45e47]. Powder bed fusion is a very promising and inexpensive technology suitable for both visual models and functional parts. It opens an exhaustive wide range of material options. Similar to binder jetting, the materials are presented in a powder form and layered on a bed. A laser is then used to selectively fuse the powder on the layer, and the process repeats until the entire model is created. The surface finish is dependent on powder grain size and its speed is relatively slow. Several powder-based materials can be used in this process, including

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metals and polymers such as PA, alumide, carbonmide, stainless steel, titanium, aluminium, and cobalt chrome, among others. Powder bed fusion is among the most promising 3D printing technologies in current research scenario [48e51]. Within the existing 3D printing technologies, the widest range of materials belongs to polymers such as thermoplastic and thermoset polymers. 3D printing has already entered the aerospace industries, automotive sectors, industrial design, architecture, and the medical field. However, most 3D printed products are currently used as prototypes rather than real-time functional products due to limitations in mechanical properties. Consequently, to enhance the mechanical performance and functionality such as strength and loadbearing capacity, 3D printing of composite materials has been identified as an area of opportunity. Several 3D printing methods are presently compatible with fiber reinforcement in the form of short fibers within polymer powders and filaments. As previously mentioned, composite research is steering toward green composites and 3D printing technology is starting to follow the trend. Natural resins combined with plant and other natural fibers can be processed using additive manufacturing method. For example, a recent development at Oak Ridge National Laboratory uses 10% bamboo fiber with biopolymer resin in 3D printed parts. This material is used for molds, prototypes, appliances, and furniture. This requires the use of filler materials of suitable attributes, which add further material and process challenges, discussed in the next section.

8.3 Composites and its properties for fabrications As mentioned, while polymers and metals are the main material group in 3D printing applications, composites are rapidly gaining attention for structural applications. Fig. 8.2 is a graphical visualization of the need, essential components, and target outcomes of the endeavors around polymer-based composite material development for 3D printing applications. Polymers can adopt different structural forms, including linear, cross-linked, and interconnected polymer networks [52], but their modulus of elasticity and deformation resistance properties are typically low. Therefore, metals, ceramics, natural and synthetic fibers are often used as fillers to enhance the mechanical, thermal, surface morphology, dielectric, and/or bioconductive attributes based on the target application [53]. Commercial manufacturing of polymers and its composites in sheet, rod, and other forms is usually done either by extrusion or casting. The extrusion method involves pushing the liquid polymer by means of a roller or die and pressing them into sheets, rods, or other sections while cooling. Domestic decoration items, artistic pieces, and kitchenware are often artifacts produced by this method [54]. Casting is done by pressing liquid

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Reinforcement material (particle, fiber and nanoshapes)

Polymer

• • • • • •

Less weight Low cost Ease of processing Availability Suitable for any complex shapes Environment friendly

Polycaprolactone (PCL) Polyethylene (PE) Polyurethane (PU) Polytetrafluoroetheylene(PTFE) Polyacetal (PA) Polyethyleneterephthalate (PET) Silicone rubber (SR) Polysufone (PS) Polyetheretherketone (PEEK) Polyglycolic acid (PGA) Poly-lactic acid (PLA) Polymethyl methacrylate (PMMA) Polydioxanone (PDS) Polyacetal (PA) Polypropylene (PP) Polycarbonate (PC) Polyvinyl chloride (PVC)

• •

Enhance the mechanical properties Improves the functionality

Composite material for 3D printing

•

High mechanical strength

•

High thermal conductivity Reduced coefficient of thermal expansion Improve in dielectric permittivity Controlled porosity Controlled local composition of particle Improved heat transfer Potential biocompatibility

• Aluminium Copper nano powder Titanium nano powder Silicon carbide

• • •

Tantalum Stainless steel Co-Cr NiTi(shape memory alloy) Ti alloys Alumina Titania Zirconia Bioglass Carbon Hydroxyapatite Tricalcium phosphate Calcium carbonate Kaolin Mica Wollastonite Silica Graphite PET based fibers PVA based fibers Aramidic Synthetic polymers

• •

Gold,

FIGURE 8.2 The polymer-based composite realm.

polymers between parts of a closed mold, often made of glass, and subjecting it to a thermal cycle. Beyond casting and extrusion, the following methods are used: l

l

l

l

Chemical welding involves the fusion of parts using solvents like chlorinated hydrocarbons, methylene chloride, and carbon tetrachloride. Emulsion polymerization, solution polymerization, and bulk polymerization are used to produce flat sheets, elongated rod and tubular forms, and molding powders of polymers [55]. Injection molding is commonly used to form shapes based on thermoplastics [56]. Micro-injection molding is the development stage of injection molding, which is used for the direct production of microparts [57].

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l

l

l

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Compression molding involves the placement of polymers on a heated metal mold, and as heating softens the material, it is forced to conform to the shape of the mold as the mold closes [58]. Thermoforming comprises the heating of a plastic sheet, which is subsequently heated and stretched into mold cavity by applying pressure or vacuum. The process can also be assisted with mechanical loading [59]. Hot embossing and thermal nanoimprinting are used in combination to fabricate polymer microchannel arrays and ascertained to result in fluid flow behavior like the master stamps [60].

The following discussion describes the wide application of polymer-based composites and their divergent processing methods. However, material combinations and manufacturing processes present several limitations and shortcomings. For example, processing methods often suffer from delamination, embedded contaminants, stringiness, warping, the appearance of welding lines, and enormous material waste. Further, high process costs, need for skilled workforces, excessive processing times, and unavoidable internal stresses constitute significant bottlenecks. At a material level, long cycle and dwell times often also lead to polymer degradation. Table 8.2 details the specific drawbacks of each processing method. Polymerization techniques used for biomedical applications are restricted due to both extrinsic and intrinsic factors [61].

8.3.1 Challenges for 3D printing material properties Conventional manufacturing process routes seriously limit the freedom to fabricate parts of complex shapes economically, especially when small batches are required. Biomedical industry is a clear example of an application that is constrained by conventional manufacturing, because it requires reproduction of very complex shapes customized for each patient. Alternative methods, including reverse engineering and rapid prototyping, have attained much attention [62,63], and the developments occurring in the layered processing methods gradually evolved as additive manufacturing. The success of 3D printing technology in any form of material structures such as filament, powder, or resin heavily depends on the processing technique [64]. Therefore, selecting the suitable form of material by the processing parameters plays a crucial role in accomplishing the target properties [65]. In the case of composite materials, it is critical to determine the interface between the matrix and reinforcement, as the strength of the composite improves when the interface is strong enough to avoid debonding and fiber pullout takes place. Other parameters to be considered are shape, size, orientation, and distribution of the reinforcement with the matrix. Microstructure analysis of the material is a suitable method of performing [66,67]. For example, Fig. 8.3 shows PMMA powder particle measurements to assess the size and uniformity of the particle

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TABLE 8.2 Conventional fabrication methods, applications and limitations Conventional fabrication method Injection Molding

Compression Molding Process

Applications

Limitations

Automotive parts (instrument panel, interior bezels, shifter knobs and assemblies, keyless entry housings, back lighting controls and buttons, pads and cushions, door handle components, sunroof components and assemblies, DVD housings)

Delamination

Commercial signs, solar panels, bath housing, and shower doors

Enormous material waste

Embedded contaminates Stringiness Weld line Warping

High Labor cost High skill level required for larger part tools Slower processing time High part cost

Thermoforming

Hot Embossing

Automotive parts (dashboard assemblies, interior door panels, interior panelling, seating parts, engine bay panelling, exterior body panels, bumpers, air ducts) Eye lenses, binoculars and fiber optics for light piping

Material waste

Watch, clock and radio faces, motorcycle helmet visors

Difficulty in building up pressure

Higher process cost The mold defines only one side of the part Causes internal stresses

Long cycle time Extended dwell time results in polymer degradation Synthesis and Polymerization

Biomedical applications like bone cement for orthopedic and dentistry. Paints and artistic paint surfaces

Difficulties in speed and time of mixing, mixing methods, composition of monomers and powders

for selective laser sintering (SLS) process. The recommended particle size for selective laser sintering process is 50e70 mm [68]. However, the microstructure properties are in indirect proportion to the law of mixture and the volume fraction of the composites has a significant role in determining the properties of the 3D structures. In some cases, composite materials require a uniform

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5.0 kV 18.3 mm × 600 SE(M)

181

50.0 µm

FIGURE 8.3 Scanning electron image of PMMA powder.

distribution of the reinforcement, though it can be difficult to achieve. In addition to physical properties, chemical properties are also a key factor to consider in 3D printing. For example, thermoplastics are suitable for SLS and fusion deposition modeling (FDM) [69]. On the other hand, thermoset plastics are suitable for material jetting and stereolithography (SLA) [70]. Metals are printed using selective laser melting [71] and binder jetting process. Ceramics such as sand and clay can be processed using binder jetting process [72]. The nature of the material flow together with the thermal and physical characteristics will eventually control the quality of the processing as shown in Fig. 8.4. As noteworthy, with respect to advanced 3D printing technology, SLS and SLM thermal radiation emitted in the form of electromagnetic waves play a significant role in controlling the thermal fields. All materials emit and receive thermal radiation at rates primarily dependent on the temperature. The radiation properties of the materials such as emissivity, absorptivity,

Material selection

Material properties

Radiation properties

Thermal and physical properties

Emissivity

Thermal conductivity

Absorptivity

Specific heat

Reflectivity Transmissivity

Density

FIGURE 8.4 Material and thermal properties compound to influence the sintering attributes.

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transmissivity, and reflectivity will come into play influencing the effective heat transfer as the thermal responses of the material are compounded [73,74]. Thermal conductivity (k) is a physical property of a material and is a measure of the rate at which heat is transferred through a body. Thermal energy is conducted in polymeric materials by the vibration and molecular motion of the polymer chains and is understood to be anisotropic [75]. The reason being that the heat transferring along the primary backbone bond encounters less scattering than that transmitted from chain to chain along the secondary bonds. Consequently, an increase in the degree of polymerization and the existence of extensive cross-links can allow higher thermal conductivity [76]. Amorphous polymers have low thermal conductivities compared to other polymers due to the loosely packed structure minimizing the points at which the polymer chains contact one another. As the temperature of the polymer increases, the atoms gain thermal energy and vibrate. The vibration of each atom is then transferred to the surrounding atoms. Considering the noteworthy influence on the final mechanical properties, density achieved through 3D printing process is often important together with the evaluation of the influences of constituent factors. One of the methods employed in increasing the density of fabricated parts is by increasing the density of raw material, prior to 3D printing processing. Though 3D printing process is a quick process fabricated from design to end use product, especially which has complicated features, would be challenging for predicting mechanical performance [77]. Researchers and manufacturers have established the standardized methods to determine material properties from 3D printing processing rather than the mechanical properties of a design. Despite typical geometrical variables related to deposition, geometry of materials is significant for critical manufacturing. The main focused studies are raster angle, air gap, filament width, layer height, and build orientation to major part axis (x, y, and z direction). Correspondingly the direct proportional interacting factors are filament length, temperature gradients, and nozzle velocity to gain mechanical properties for FDM processing method [78]. Similarly, powder bed fusion processing concerns thermal gradients and void space in the part. When the laser penetrates deeply with high power, the layer height increases, and this layer acts as thermal insulator for lower powder layer and prevents heat transfer, which will result in improper coalescence between the layers [79]. In case of material jetting, the uniform cross-linking between the successive layers are achieved based on thermal annealing and the kinetics of photopolymerization of the fabricated part [46]. Apart from appropriate material properties, mixing the two materials to form composites is basic key factor for processing into 3D printing technique. There are various methods of mixing the polymers with fillers such as polymer dissolution process, extrusion, and particle mixing methods and do not require any further treatment prior to 3D printing. Materials system employed are introduced in the discussions, attempting to identify the material property relationships for 3D

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printing process. The critical observations for various composite materials involved in 3D printing process for structural applications are discussed in the next section, eventually, converging on green composite materials for future pollution-free 3D printing components.

8.4 3D printing of composite materials In recent years, there has been a tremendous attention directed toward compatible composite materials which are appropriate for 3D printing techniques. As mentioned above, the polymer-based composite materials are reinforced in terms of particles, fibers, or nanomaterials as shown in Fig. 8.5. Initially particle reinforcements are used to improve the properties of polymer matrix. The part fabricated from particle-filled polymers has excellent mechanical properties and high accuracy. Typical applications of these materials 3D printing composites (FDM, SLS, SLA, SLM, and binder jetting)

Particle reinforced

Fiber reinforced

Enhanced mechanical properties like storage modulus, thermal conductivity, tensile modulus, and compressive modulus.

Enormous increase in mechanical properties from 140% to 335%

Reduced elongation at break and coefficient of thermal expansion

For example: AI & ZrB2/ABS, AI & AI2O3/nylon-6, CaTiO3/ polypropylene, diamond/acrylic, glass bead/polyamide

Mostly used composites for structural applications, which require light weight.

Nanostructure reinforced Enhanced mechanical properties like tensile modulus and compressive modulus Reduced elongation at break and coefficient of thermal expansion The unique feature is increased electrical conductivity and thermal stability

For example: For example: Short glass fiber/ABS Short carbon fiber/ABS Short carbon fiber/silican carbide yarn/PP Continuous carbon fiber/nylon

CNF/nylon, CNF/ABS, Graphite/polystyrene, metal nano powder/polymers

FIGURE 8.5 3D printing composite materials and their properties.

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are automotive part housings and thermally stressed parts. Ebubekir et al. [80] studied the effects of microparticle reinforcement with polymer matrix 3D printed parts using FDM process. In this study, aluminium (Al) and zirconium diboride (ZrB2) particles were used as microreinforcements in ABS matrix. The authors explored the effects of mechanical and thermal properties of the 3D printed parts. The observation revealed that strain increased around 82.5% in the tensile test. In yet another study, 30% (weight to volume) of microdiamond particles are mixed with acrylic resins to fabricate heat sink using SLA techniques [81]. Based on this composite material heat transfer rates are improved, when the sink is heated at higher temperatures. Similarly, other particles like barium titanate (BaTiO3), copper, and iron particles embedded in polymers like ABS solve the problems of distortion of final FDM printed parts by the reduction in coefficient of thermal expansion [82,83]. Other commercial particles reinforced powder-based materials available in the market suits only for selective laser sintering process as follows. Glassfilled nylon powder is characterized by excellent stiffness in combination with good elongation at break. Still better parts are obtained by using glass bead-filled nylon powder for use in deep drawing dies and within the engine area of cars. Glass bead-filled nylon provides greater rigidity and is perfect when prototyping rigid parts intended for production in advanced engineered thermoplastics. Adding the filler (glass beads and not fiber) to nylon predominantly increases the stiffness, but not the strength of the part [84]. Alumide is a material made by EOS GmbH, consisting of metallic gray aluminium-filled polyamide-12 powder, which is characterized by its high stiffness, excellent dimensional accuracy, metallic appearance, and good postprocessing possibilities. The surfaces of alumide parts can be refined very easily by grinding, polishing, or coating. The machining of alumide lasersintered parts is simplified through the cut breaking effect of the aluminium filling. A typical application for alumide is the manufacture of stiff parts for applications in automotive manufacture, for tool inserts for injecting molding in small production runs, for illustrative models, for education and jig manufacture, among other aspects [85,86]. Windform is a commercial name introduced by EOS. This is a light gray composite polyamide-based material with added aluminium and glass, with improved heat deflection temperature and superior stiffness, excellent surface finish, wear resistance, and first-rate detail reproduction. It offers an attractive, gleaming, metallic look appreciable in many applications, such as in wind tunnel design and functional applications. Moreover, it absorbs slightly less liquid and is particularly suitable for applications which require a superior surface finish [87]. New grades of nylon powders (i.e., duraform PA12, fine polyamide, PA2200) even yield a resolution and surface roughness close to those of PC, making PA also suited for casting silicone rubber and epoxy molds [88]. Other polymer-based materials available commercially are acrylic styrene for investment casting and an elastomer for rubber-like applications. Sic/

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Polyamide composite has been developed for use with SLS. It consists of two materials, polyamide and silicon carbide filler, as rigid particles. The polyamide powder is therefore used as a binder because of its low melting point. Simple and complex shapes are easily produced with this material by using optimized parameters. Sic/Polyamide composite can be infused with metal by using an infiltration process to produce both metal matrix and ceramic matrix composites, such as by infiltrating aluminium matrices into SiC in a nitrogen atmosphere at 750e850 C, where the polymer was thermally removed [89]. Copper polyamide (CuPA) is a metaleplastic composite of a copper powder and polyamide blend introduced by DTM in May 1998 for use in the SLS process. CuPA is produced to create tooling for short production runs of equivalent plastic parts with conformal cooling, good thermal conductivity, heat resistance, and durability. CuPA can be built into mold tool inserts in the SLS machine in the same way as other PA materials (e.g., PA2200) [90]. In addition, the advantages of using CuPA are numerous, significant, and suitable for injection molded inserts for several hundred parts (100e400 parts) from common plastics such as PE, PP, polystyrene, ABS, PC/ABS. Moreover, the surface of parts made of CuPA can be easy to machine and finish. In contrast, one of the drawbacks of CuPA is that it is costly. Tontowi and Childs [91] measured density of commercially supplied powders, known as duraform (nylon-12 and protoform [glass-filled nylon-11]) and studied the effect of varying bed temperature on the density of sintered parts produced by the SLS process. They developed a simulation model for density prediction based on the experimental results. The results show that at a powder bed temperature of 182 C, an entirely solid density, 970 kg/m3, can be obtained at a default energy density of 0.0284 J/mm2. By reducing powder bed temperature to 178 C, at the same energy density, the final density of the sintered part decreases by about 4%. In yet another paper, Childs and Tontowi [92] measured density of glass filled nylon-11 and simulated the effect of varying bed temperature on the density of sintered parts. The simulation is based on a continuum view of heat conduction in the powder bed. While this approach worked well with nylon-12 system, they observed poor correlation between experimental and analytical predictions with nylon 11 system. They speculated (based on experimental observations of sintered microstructure) that the continuum view of heat conduction is inadequate, and that consideration must be given to differential absorption of laser radiation in the glass and polymer fractions of the powder. A final application of the simulation suggests that the ambient temperature of the powder bed must be held to within 4 C of its set value to maintain process accuracy. Mozzoli et al. [93] developed and characterized a new aluminium-filled polyamide powder for application in SLS from a rheological point of view. They reported that the new material allowed SLS manufacturing of models with considerably high dimensional accuracy, strength, and resistance to

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mechanical stresses. Moreover, the aluminium-filled polyamide material promised a smoother surface, better finishing properties, excellent accuracy, and high stiffness in the direct manufacturing of metallic looking plastic parts. Pei-kang et al. [94] evaluated laser sintering of polymer-coated molybdenum powder and presented a numerical model of the temperature field based on laser heating properties, parameters of powder thermal physics, and the laser sintering process. They used finite element method to simulate the temperature field during laser sintering and verified the results with experimental results on laser sintering temperature field using an infrared camera and thermocouple measurements. Wang et al. [95] studied the SLS of a blended powder of PA12 and organically modified rectorite (OREC). The effects of OREC on the sintering parameters and mechanical properties of the sintered samples were investigated. Compared with pure PA12, the results showed that the laser power needed for sintering greatly decreased and the mechanical properties of the sintered samples were considerably improved with the addition of OREC (0e5 weight%). Moreover, they concluded from the XRD and SEM results that PA12 intercalated rectorite and PA12/ORCE nanocomposites were formed. Experimental investigations into the production of particulate silicon carbide (SiC) polyamide matrix composites using the selective laser sintering process have been conducted by Gill et al. [89]. SiC grit was blended with duraform polyamide to produce a powder blend at a composition of 50% by weight of grit to polyamide. A full factorial experimental approach was applied to examine the effects and interactions of key fabrication parameters, regarding the tensile strength and porosity of the composite SLS produced samples. Their investigation revealed that the optimum energy density for producing samples of maximum strength was independent of the initial powder blend composition. Currently, additive manufacturing finds applications in aerospace, automotive, and biomedical fields to produce end use parts directly from CAD files and enhancing the material options and postprocessing properties will bring significant benefits to these applications. Evidently, most material systems currently in use for SLS are highly proprietary in nature and are usually very expensive. On the other hand, the basic mechanism and mechanics of material consolidation in SLS suggest the suitability of the process for a variety of other polymeric materials. In particular, it is important to evaluate the possibility of processing polymer-based composites using SLS. The fiber reinforcements on polymer matrix enhance the properties of the composite materials. There are two types of fiber reinforcements: continuous fiber and short or small fiber reinforcements. The most commonly used fibers are glass fibers and carbon fibers to improve the mechanical properties of the polymer composite materials in 3D printing technology. These fiber-based composites are nowadays mostly processed in fused deposition modeling processing technique. The composite filaments are fabricated by mixing the

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polymer pellets and fibers in a blender and then processed in the extruder. The extrusion process could be the homogeneous distribution of fibers among polymer matrix. The main parameters considered are fiber orientation and void fraction of composites to fabricate the final composite parts. The other potential fiber materials expanded are Kevlar, metal wires, and medical suture materials. Structural engineers from automotive applications use carbon fiber for rapid prototyping to make tooling and molds, as well as first article pieces. Dongmin et al. [96] developed the numerical approach for modeling the 3D printing process fiber-reinforced polymer composites by FDM process. Halil et al. [97] investigated short carbon fiber (0.2e0.4 mm)ereinforced ABS with FDM process, the mixtures of 10, 20, 30, and 40 wt% carbon fibers were prepared with ABS by means of plasticorder prep mixer. The properties of printed FDM samples are compared with compression molded samples. The results reveal that the mechanical properties of the 3D printed parts are increased with high fiber orientation in the printing directions compared to compression molded parts. Relatively high porosity is observed in 3D printed composite parts when compared with compression molded parts. This is because the polymers can float within the melting pool area and their particles form bonds with each other without any other particle disturbance. However, when the fibers are added with the polymer material, they are wrapped with polymer material while fusing and that results in a 3D printed composite of high porosity. Short fibers mixing with polymer matrix has limitations like improper physical bonding between the short fibers and lack of structured orientation and continuity against stress and strain forces. To overcome these issues, continuous fibers have been developed which have better resistance force against tension and large bending strains, when there is optimum orientation due to the proper alignment of fibers [69]. The continuous fiber-reinforced composites processes are prepreg or autoclave and resin transfer molding (RTM) [98]. Significantly the mechanical properties of the continuous fibers are increased by maintaining the fibers’ continuity which will be the primary load carrying part in composites. There are quite few researchers working in the field of 3D printing of continuous fiber-reinforced composites for structural applications and mainly focused on aerospace and automobile parts [99]. Whereas to achieve the regulations for environmental protection and safety standards, the fiber-reinforced materials is a developing field which reduces the weight of the automobiles, and has the capability of absorbing the shock energy. Other benefits to automotive applications are: l l l

Suitable for unique conditions within alternative fuels power-train Fiber-reinforced casing withstand harsh environment Other thermal management systems which have thermal stability with new developing alternative fuels

Namiki et al. [100] investigated 3D printed continuous fiber-reinforced composite using PLA as base polymer matrix and carbon fibers are used as

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reinforcement materials based on FDM techniques. The result revealed that there is enormous improvement in the tensile stiffness and strength. However, there are notable pores and gaps identified between the filaments, which are suppressed with the increase in tensile properties. Peng Zhuo et al. [101] investigated the desktop FDM processed printing of continuous carbon fiberereinforced nylon filaments and continuous glass fiberereinforced nylon filaments from Markforged have been used, which are preimpregnated with prepreg materials. The result proves that the flexural strength and the modulus of the 3D printed continuous fiber reinforced composites have higher value compared to neat polymers, though the materials are prepared by conventional process like prepreg/autoclave for 3D printing. Evidently, materials that are used to fabricate polymer-based composites with 3D printing parts are of high strength and thermal stability. However, when specific material characteristics are targeted, for example, flame retardancy, specific polymers need to be developed such as polymer nanocomposites. It has become essential and interesting to investigate how these nanopolymer composites respond to 3D printing processing techniques. Goodridge et al. [102] presented initial research into the laser sintering of reinforced polyamides with carbon nanofibers (CNF) whereas, mixing the microfibers with the polymer powders to form a smooth layer is quite challenging. They investigated the effects of CNF addition to the processing parameters on the mechanical properties of laser sintered parts and demonstrated that CNF can increase the strength of a base polyamide 12 polymer prepared using the melt-mixing technique. After the characterization of the polymer nanocomposite parts and dynamic mechanical testing, they inferred that the nanofibers were well-dispersed within the polymer matrix and increased the storage modulus compared to the base material. It was noted that improvements are required in the production process of the nanocomposite powders to be able to effectively use them for laser sintering. Jiaming Bai et al. [103] investigated laser sintering of polyamide12 (PA12) and carbon nanotube (CNT)-reinforced PA12-CNT nanocomposites, and observed the powder morphology and CNT dispersion of the PA12-CNT and also identified the effects of the thermal properties. The tensile modulus and the tensile strength of PA12-CNT were improved by 45% and 7%, respectively, together with improvement in the thermal conductivity. M.S.Wahab et al. [104] described the fabrication and characterization of polymer nanocomposite (PNC) materials for use in the SLS process. PNC materials are of great interest generally because of their excellent physical properties and offer excellent potential in rapid manufacturing of structural polymeric parts. They used three different nanoadditive materials: cerium oxide IV, yttrium stabilized zirconia, and layered hectorite clay. These materials have been used to reinforce PA6 polymer using solution blending and spray drying to create powder with particle sizes in the range of 5e40 mm. They reported improved mechanical properties with laser sintered PNC materials compared to those of the unfilled polymers.

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8.4.1 3D printing of green composite materials The adverse effects that waste plastics are having on the environment are becoming increasingly apparent. Therefore, recent research agenda is to develop environment friendly materials, the so-called green materials, for many structural applications, also targeting the automotive industries which have enormous manufacturing possibilities worldwide. In this section are discussed techniques and material properties achieved via the 3D printing and some of the matrices are derived from conventional synthetic resources. The fabrication of environment friendly polymer-based composites is a challenging task for the materials engineer nowadays. Recent research identified the natural organic fillers, which are renewable sources and biodegradable materials. However, some materials have processability and reduction in the ductility; these limitations can be overcome by adding adhesion promoters and additives or by modifying the filler chemically to enhance its properties. In general, natural fibers like wood fibers, vegetable fibers, animal fibers, and mineral fibers have been used excessively in composite structures [105e107]. When it comes to processing techniques, 3D printing is identified as a legend in manufacturing areas. Some notable researchers investigated green composite materials for 3D printing process. Chin et al. [108] investigated the 3D printed samples of composite materials containing polylactide and Camellia oleifera fruit hull powder (COFHP). They evaluated the mechanical and structural properties for medical applications, and the results showed the biocompatibility of the materials to be suitable for medical applications. David and Kim [109] developed the harakeke and hemp-based filament with PP matrix and processed using 3D printing technologies. The author claims that the tensile strength and Young’s modulus is increased up to 77% and 275%, respectively when compared to glass fiberereinforced materials. Montalvo et al. [110] developed and studied the 3D printing of sugar cane bagasse filler on varying compositions with polymer matrix like PE, PP, ABS, and PLA. Although the composite is only acting as filler rather than as reinforcement, chemical treatments in the fiber and the inclusion of other additives can improve the mechanical properties. Natural fibers and other sustainable fillers are an alternative which bring enormous potential to replace mineral-inorganic materials in automotive applications. These green composites are placing some interesting structural applications using conventional processing techniques. From then as soon as the market for these composites increases based on 3D printing process, improvement of the quality will be achieved. However, current scientific studies in developing the materials focus on identifying the suitable biomaterial matrix with optimization of processing parameters for industrial applications.

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8.5 Conclusion and future directions Recent development in manufacturing demonstrates that this era belongs to 3D printing technology. Currently, synthetic polymers and fibers are almost the only focus, with highly associated environmental impacts. The need for composites of more sustainable outlook is emerging. Still, there are many barriers to overcome to incorporate natural printable materials into 3D printing. Automotive and aerospace components come in complex designs and/or organic forms, and thus their prototyping is becoming costly and timeconsuming. As such, 3D printing techniques involve metal parts gradually replaced with polymer composites to reduce the weight in automobile and aerospace applications. Also, the engine parts made up of polymer-based composites have shown to increase the fuel efficiency in recent studies. 3D printing is also a noteworthy technique to fabricate functionally graded polymer composites based on particle reinforcement, fiber reinforcement, and nanostructures. The composite materials can be customized by delivering various volume fractions. As a result, the mechanical properties can be optimized to the specific requirements of the application. Thermal stability is another significant advantage that comes handy with 3D printing composites, if polymer composites have a wide range of material choice that can withstand elevated temperatures when developed for automobile or aerospace applications. Researchers in the 3D printing area must put efforts and focus on natural materials and processes that are compatible with a greener environment. There are little research initiatives on green composite materials for 3D printing technologies at this moment. Green polymer composites with natural fillers represent a magnificent view for future research, aiming to reduce the use of petroleum-based nonrenewable sources. Based on these requirements, recent and future research targets on selecting the most suitable biodegradable matrix and optimizing the processing parameters. Through rigorous research, the costs of natural composites will decline, quality will increase, markets will expand, and ultimately, the environmental impact will soften.

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Chapter 9

Biocomposites: present trends and challenges for the future Malladi Nagalakshmaiah1, Sadaf Afrin2, Rajini Priya Malladi1, Saı¨d Elkoun1, Mathieu Robert1, Mohd Ayub Ansari3, Anna Svedberg4, Zoheb Karim4 1

Center for Innovation in Technological Ecodesign (CITE), University of Sherbrooke, QC, Canada; 2Department of Chemistry, Faculty of Science, Aligarh Muslim University, Aligarh, India; 3 Department of Chemistry, Bipin Bihari College, Jhansi, India; 4MoRe Research O¨rnsko¨ldsvik AB, O¨rnsko¨ldsvik, Sweden

Chapter Outline 9.1 Introduction 9.2 Reinforcement phase 9.3 Polymer matrices 9.3.1 Renewable source 9.3.2 Mixed source 9.3.3 Fossil fuelebased source 9.4 Bio-composites processing and properties 9.4.1 Processing techniques 9.4.2 Improved properties 9.5 Bionanocomposites

197 199 201 201 202 202 202 202 202 203

9.5.1 Lignin-based bionanocomposites 9.5.2 Hemicellulose-based bionanocomposites 9.5.3 Nanocellulose-based bionanocomposites 9.6 Challenges 9.6.1 Challenges at industrial scale 9.7 Conclusion References

206 206 207 208 209 210 211

9.1 Introduction In the modern world, dependency on petroleum-based polymers has extensively increased over the years. Synthetic polymers like polyethylene (PE), polypropylene (PP), nylon, polyester (PS), polytetrafluoroethylene (PTFE), and epoxy (commonly known as plastic) are derived from petroleum hydrocarbons [1]. These polymers are an incredibly versatile group of compoundsdso versatile, in fact, they can be found in all sorts of unexpected places. Society uses synthetic polymers because many of them have highly desirable properties, such as strength, flexibility, resistivity, chemical inertness, Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00009-4 Copyright © 2019 Elsevier Ltd. All rights reserved.

197

198 PART | III Nanomaterials and additive manufacturing composites

and so forth [2e4]. Currently, Kevlar has many applications, ranging from bicycle tires and racing sails to body armor because of its high tensile strength. It is also used to make modern drumheads that withstand high impact. When used as a woven material, it is suitable for mooring lines and other underwater applications [5]. On the other side, various serious problems are discussed regarding the utilization of synthetic polymers [5,6]. Many synthetic polymers’ most desirable feature is their chemical inertness and their resistance to various kinds of chemical/biological degradation. This same property, however, also means they last a long time once they are thrown away. For example, scientists estimate that a single plastic bag could take as much as 500 years to break down [7]. In the past, major interest has been in the use of synthetic polymers for the production of composites. The use of these polymers, however, presents great challenges [6,8]. These include a shortage of the organic compounds due to declining oil and gas resources and increasing oil and gas prices. Other effects include environmental concerns for their degradation or incineration and global warming, uneconomical costs, and cross-contaminations in their recycling, and consumer toxicity risks [5,9,10]. These concerns gave birth to the quest for materials that can overcome these challenges and maintain the required properties for the various applications. Therefore, in order to reduce the dependency on petroleum-based polymers (synthetic polymers), scientists are working toward the development of the polymer composites based on better performance and low cost. However, these polymer composites are often reinforced with glass fibers, carbon nanotubes, clays, silica, and graphite [2]. These fillers are entirely nondegradable, inorganic, and sometime petrol-derived. Thus, engineers and researchers are still struggling with the production of biocomposites, where both phases (reinforced polymer and matrix) are derived from natural sources, renewable, and completely biodegradable. Some studies show that the reinforced polymer with biofibers or natural fibers has a direct effect on the improvement of product properties [1,3]. Biopolymers reinforced with degradable polymer phase are called “biocomposites/green composites” [1]. Green composites are widely researched because of the need for innovations in the development of materials from biodegradable polymers, preservation of fossil-based raw materials, and reduction in the volume of carbon dioxide released into the atmosphere. Application of agricultural resources (wastes and products) for the production of green materials is one of the reasons why green composites have attracted tremendous research interest. The use of these biocomposites is expected to improve manufacturing speed and recycling with enhanced environmental compatibility. The importance of the green composites in various industries has been increased, especially in the automobile industry. This can be attributed to their mechanical, electronic, thermal isolation, flame retardance, and wear resistance properties. Importantly, due to environmental issues, new regulations from governments are also a major concern [11,12].

Biocomposites: present trends and challenges for the future Chapter | 9

199

In this chapter, a detailed study is summarized related to the processing and properties of biocomposites/green composites, understanding of processability and improved properties using various types of natural or manmade degradable polymers and matrixes for the production of biocomposites. Furthermore, bionanocomposites have also been discussed using the advantage of “nanosize” properties (high aspect ratio and surface area but nm diameter range). Researchers are still struggling for the upscaling of these “centimeter”-sized (lab-based) products, therefore, specific focus has been given for summarizing some concrete evidence related to the production of biocomposites at pilot/ industrial scale. Nanocellulose is taken as example and production of various nanocellulose-reinforced films/membranes/papers is summarized. Thereafter, challenges in future regarding the production and utilization are further discussed.

9.2 Reinforcement phase Green reinforcement materials are also called as biofibers or biofillers or natural fibers. Principally, green reinforcement materials are derived from plant and animal-based biomass, and they are classified based on their origin as shown in Fig. 9.1. However, before using in composite, these natural fibers Green-reinforced phase

Animal-derived

Wood

Soft Araucaria Hoop pine Cedar, etc.

Silk

Hard

Spider Tasar Mussel, etc.

Pine Redwood Ash Birch, etc.

Wool Angara Cashmere Mohair Qiviut, etc.

Nonwood/agricultural biomass

Stem Flax Hemp Jute Kenaf Ramie, etc.

Leaf Abaca Banana Sisal Cantala, etc.

Grass Bagasse Bamboo, etc.

Seed Cotton Kapok, etc.

Root Broom root

FIGURE 9.1 Classification of natural fibers from renewable sources. Adapted from Ashori A. Woodeplastic composites as promising green-composites for automotive industries! Bioresource Technology 2008;99:4661e7 with some modifications. Copyright Elsevier, 2008.

200 PART | III Nanomaterials and additive manufacturing composites

have to be separated or purified from other constituents (lignin, hemicelluloses, wax, and proteins) present in the respective sources. The main objective to use natural fibers as reinforcement phase in composites is to improve the mechanical properties and production of lightweight materials [13,14]. The diameter, density, and mechanical properties of the different natural fibers used in diverse polymer composites are reported in Table 9.1 and compared with nonrenewable filler (glass fiber). Replacing the glass fibers with natural fibers is an added benefit for the automobile industry due to their low density and high fiber diameter, which can increase the tensile strength using low filler content and producing lightweight materials. Essentially, it leads to the low consumption of fuel and is valid for high mileage. Moreover, the biodegradability, renewability, nontoxicity, and abundance in nature made natural fibers to be ideal for the composites for future utilization in automotive industry.

TABLE 9.1 Physical and mechanical properties of the different natural fibers used in composites Source

Density (g/cm3)

Diameter (mm)

E-Modulus (GPa)

Strength (MPa)

References

Flax

1.5

40e600

27e39

345e1500

[9,15]

Hemp

1.47

25e250

38e70

550e900

[9,15]

cotton

1.5e1.6

22e68

5e12.5

287e800

[8,12]

jute

1.3e1.4

25e250

13e26.5

393e773

[9,15]

kenaf

1.5e1.6

2.6e4

40e53

350e930

[5,7]

ramie

1.5e1.6

0.049

61.4e128

400e938

[5,7]

sisal

1.45

50e200

9.4e22

468e700

[5,7]

coir

1.2

0.25e0.4

4e6

175

[6,16]

softwood

1.5

e

40

1000

[7,17]

wool

1.4

0.25

e

e

[18]

aramide

1.4

0.02e1

63e67

3000 e3150

[19]

abaca

1.5

10e30

31.3e33.6

430e813

[12]

milkweed floss

0.9

0.2e0.5

2.3

2.3

[13]

silk

1.34

0.03e0.05

e

e

[14]

e-glass

2.5

15e25

70e73

2000 e3500

[7,15]

Biocomposites: present trends and challenges for the future Chapter | 9

201

9.3 Polymer matrices In a broader terminology, green polymeric matrices, also called “bioplastics” are derived from 100% renewable or fossil fuelebased materials, which are either degradable or compostable by the microorganisms [20]. However, all biodegradable polymers may not be generated from renewable sources and can be also from fossil fuelebased plastics, for example, polycaprolactone (PCL). Recently, conventional polymers (like PE, PP) were also prepared by using monomers generated from renewable sources [21]. Green matrices are classified into three categories based on their derived sources, that is, (1) renewable source, (2) mixed source, and (3) fossil fuelebased source; the matrices as shown in Fig. 9.2.

9.3.1 Renewable source This segment is completely generated with renewable sources like plants or animals. This section comprises some biopolymers from plant sources (cellulose, lignin, and starch), animal sources (chitin, proteins), poly(lactic) acid (PLA), hydroxyalkanoates (PHA), poly-3-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV), and polyhydroxyhexanoate (PHH). Emerging technology in this segment is synthesis of polyethylene (PE), polypropylene (PP) and nylon by using the monomers generated from natural sources [21]. However, PP, PE and polytri(methylene terephthalate) (PTT) are not biodegradable though they are generated from bio-based materials. Green polymer Matrices

Renewable sources

Mixed sources

Poly(lactic acid)

Polyesters

Polyhydroxyalkanoates

Thermosets

Cellulose-based

Fossil fuel-based

Aliphatic polyesters Aliphatic/aromatic polyesters Poly(vinylalcohol)

Starch-based

Protein-based plastic

FIGURE 9.2 Classification of green polymeric matrices based on sources. Figure was adapted from Reddy MM, Vivekanandhan S, Misra M, Bhatia SK, Mohanty AK. Biobased plastics and bionanocomposites: current status and future opportunities. Progress in Polymer Science 2013;38:1653e89 with major modifications. Copyright Elsevier, 2013.

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9.3.2 Mixed source Generated from both renewable and fossil fuelebased monomers are mixed source bioplastics. For example, poly tri(methylene terephthalate) (PTT), is produced from the monomers of terephthalic acid and 1,3-propanediol originated from fossil fuel and renewable based materials, respectively. Some bio thermosets like bio-epoxy resins also come under this category.

9.3.3 Fossil fuelebased source These green polymers are generated completely from fossil fuelebased sources, but they are biodegradable. The nature of the functional groups present on the polymers will allow them to degrade by the bacteria at certain conditions [21]. The partially bio-derived polymers, for example bio-based PP and PTT are not biodegradable. Nevertheless, the PCL and poly(butylene adipate-co-terephthalate) (PBAT) fully derived from fossil fuels are biodegradable.

9.4 Bio-composites processing and properties 9.4.1 Processing techniques Exclusively same techniques based on existing techniques for conventional processing of plastics or composite materials are designed to manufacture/ fabricate biocomposites. These include open mold (hand lay-up and spray-up) and closed mold techniques such as pultrusion, extrusion, direct long-fiber thermoplastic (D-LFT), vacuum infusion, injection molding, filament winding, resin transfer molding, compression molding, and sheet mold compounding [22]. The processing conditions and appropriate processing methods have substantial effect on the parameters such as dispersion, aspect ratio, orientation, and moderate temperatures (below 200
C) that govern the mechanical properties of the developed biocomposites [23]. Fiber drying before processing is crucial as the presence of moisture on the fiber surface acts as a debonding agent at the fiberematrix interface. Additionally, evaporation of water during the reaction generates voids within the matrix. Both the aspects lead to a significant decrease in the mechanical properties of biocomposites [24]. However, manufacturers believe that the major challenge to fabricate biocomposites basically involves the contest to procure the biopolymers from natural resources as matrices.

9.4.2 Improved properties The impact of reinforced biopolymers has been discussed in literature in various articles, but many research results showed the dominant effect on mechanical properties. In a study, cassava starchebased biocomposites

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incorporated fibers from Brazilian green coconuts. The tensile properties of cassava starch improved with both the incorporation of fibers and thermal treatment. Water uptake, swelling, and moisture absorption of TPS showed decrease with the incorporation of fibers, which is due to better interfacial bonding between the matrix and fibers, as well as the hindrance to absorption caused by the fibers [25]. Furthermore, earlier research on thermoplastic starch-based composites focused on the use of plasticized starch as matrix for green composites. De Carvalho et al. [26] first reported the use of thermoplastic starch for the production of composites by melt intercalation in twin screw extruder. The study recorded a significant increase in the tensile strength from 5 to 7.5 MPa for the composite. The modulus of elasticity increased from 120 to 290 MPa while the tensile strain at break decreased from 30% to 14%. Pandey and Singh [27] varied the sequence of addition of plasticizers to determine the effect of plasticizers on the mechanical and structural properties of resulting composites. The modulus of composites increased significantly for all compositions relative to the unfilled matrix, irrespective of the method of preparation. Guan and Hanna [28] modified the starch with acetate and produced biocomposites with cellulose fibers. Results of X-ray diffraction showed losses in the crystallinity of starch and cellulose. Composite films were made from the aqueous dispersions of starch with microcrystalline cellulose. Young’s modulus of composites reinforced with 5, 10, and 15 wt% which were irradiated for 30 min improved by 72.41%, 42.5%, and 32%, respectively, when compared to control Kumar and Singh [29]. Green composites have been successfully produced from cellulose acetate (CA), triethyl citrate (TEC) plasticizer and organically modified clay via melt compounding [30]. The cellulosic plastic with 80 wt% pure cellulose acetate and 20 wt% triethyl citrate plasticizer was used as the polymer matrix for composite production. Cellulosic plasticebased composites containing 5 and 10 wt% organoclay have better exfoliated and intercalated structure than those of 15 wt% organoclay. Tensile strength and modulus of cellulosic plastic reinforced with 10 wt% organoclay improved by 75% and 180%, respectively. Thermal stability of the cellulosic plastic also increased. Improved mechanical properties as discussed in the literature for produced biocomposites and processing techniques are shown in Table 9.2.

9.5 Bionanocomposites Production of green bionanocomposites is in boom nowadays. Utilization of filler or reinforced materials at “nanoscale” is offering important competitive advantages in the field of automotive industry, not only because of their renewability, biocompatibility, sustainability, and carbon-neutral nature, but also because of their low density, high aspect ratio, high tensile strength, and reactive surfaces [39,40]. Physical and thermal properties of composites reinforced with nanoparticle filler are superior to those filled with micron-sized

Composites

Elongation to Break (%)

Tensile Strength (MPa)

Young Modulus (GPa)

Processing

References

Starch þ 30% jute

2  0.2

26.3  0.55

2.5  0.23

Thermoplastic injection molding

[31]

PLA þ 30% ramie

4.8  0.2

66.8  1.7

n.s

Hot pressing sheet molding

[32]

PLA þ 30% jute

1.8  0

81.9  2.9

9.6  0.36

Thermoplastic injection molding

[33]

PTP þ 25% hemp

n.s

_62  2

7.2  0.3

Compression molding

[34]

PHBV þ 30% jute

0.8  0

35.2  1.3

7  0.26

Thermoplastic injection molding

[35]

PLLA þ 30% flax

2.3  0.2

98  12

9.5  0.5

Film stacking compression molding

[36]

PHB þ 30% flax

7  1.5

40  2.5

4.7  0.3

Film stacking compression molding

PLA þ 30% flax

1  0.2

53  3.1

8.3  0.6

PP þ 30% flax

2.7  1.5

29.1  4.2

PP þ 30% jute

1.4  0.1

PP þ 30% fiberglass

3.01  0.22

[36] a

Twin-screw extruder þ compression molding

[37]

5  0.4

Twin-screw extruder þ compression molding

a

[37]

47.9  2.7

5.8  0.47

Thermoplastic injection molding

[33]

82.8  4.0

4.62  0.11

Compression molding

[38]

a, long-fiber composites; n.s, not studied. Adopted form Oksman K, Bismark A, editors. Handbook of green materials: processing technologies, properties and applications, vol. 4. World Scientific Publication; 2014, copyright Elsevier, 2013.

204 PART | III Nanomaterials and additive manufacturing composites

TABLE 9.2 Mechanical properties of several green composites

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particle of the same filler [8]. Moreover, some exclusive properties, which traditional microparticles cannot attain, make nanocomposites be prominent and draw attention. It has been reported [41,42] that additions of nanoparticles to base polymers confer improved properties that make them usable in automotive, construction, and medical areas. Properties which have been shown to improve substantially are mechanical properties (e.g., strength, elastic modulus, and dimensional stability), thermomechanical properties, and permeability (e.g., gases, water, and hydrocarbons). Others are thermal stability and heat distortion temperature, flame retardancy and smoke emissions, chemical resistance, surface appearance, physical weight, and electrical conductivity [43e45]. Fabrication, characterization, and properties for various bionanocomposites have already been discussed in literature. Highly reputed review articles [46e49], book chapters [1,50e53], and other documents are easily available for readers. Cellulose, hemicellulose, and lignin, the most common natural polymers from plants, are always one of the research emphases in eco-friendly polymer science and nanotechnology [43,44]. Materials and nanocomposites based on cellulose, hemicellulose, chitosan, and natural fibers have attracted the interest of the scientists during the recent years, resulting in eco-friendly natural polymerebased composites with combination of outstanding properties (Fig. 9.3). Wood-derived nanocomposites have received great attention due to their outstanding properties: renewable origin, low cost, facile processability, high specific strength, lower density than inorganic-reinforced composites, energy saving, and recycling possibility [1,54e57].

Cellulose Microfibril Hemicellulose Hemicellulose

Cellulose

Lignin

Lignin

FIGURE 9.3 Arrangement of cellulose, hemicelluloses, and lignin within plant cell wall.

206 PART | III Nanomaterials and additive manufacturing composites

9.5.1 Lignin-based bionanocomposites In recent years, eco-friendly nanocomposite films based on biopolymers have been used for membrane productions [58]. Cellulose and lignins are two potential natural materials that can prepare nanocomposite films with considerable properties [59]. Neva´rez et al. [60] prepared biopolymer-based nanocomposite films using cellulose triacetate (CTA) as polymer matrix and lignin as filler [60]. Using the same vapor-induced phase separation method, Neva´rez et al. prepared another nanocomposite film from propionated lignin and CTA [60]. The kind of CTA-lignin nanocomposite has impact on film performances; while propionation of lignin was higher, the wettability and fluxes of nanocomposites were lower. Chitosan, another abundant polysaccharide with good biocompatibility, biodegradability, and multiple functionalities, has been widely studied in many fields such as water treatment, biosensors, and tissue engineering [61]. Chen and coworkers [62] prepared biodegradable composite films based on lignin and chitosan with various compositions via a casting/solvent evaporation method. Soy protein can be made into plastics, possessing good biodegradability but poor flexibility [63,64], so three-dimensional structural lignin can be used as a plasticizer to improve the stability of soy protein plastics, meanwhile maintaining high tensile strength. Poly(lactic acid) (PLA) is a thermoplastic, high-strength, high-modulus aliphatic polymer derived from corn or potato starch, tapioca roots, beet, sugarcane, lactose, and other renewable resources [65]. PLA is considered to be the most promising biodegradable material because of its excellent biodegradability and biocompatibility [63]. Chung et al. fabricated lignin-PLA composites using a solvent-free method with catalyst [66].

9.5.2 Hemicellulose-based bionanocomposites The preparation of these nanocomposites has aimed at studying the interactions of the components or at improving the functional properties such as tensile strength or water vapor barrier properties of hemicellulose-based films. Recently, nanocomposites were prepared from aspen glucuronoxylan and bacterial cellulose (BC) produced by Acetobacter xylinum [67]. A pronounced decrease in modulus was observed for the film from pure aspen glucuronoxylan at about 85% RH. The presence of BC had an impact on the softening behavior, resulting in a less steep decline of the modulus curve. In another study, chitosan incorporated into a quaternized hemicellulose/MMT matrix was introduced to produce nanocomposite films with significantly enhanced mechanical properties. The fabricated film had higher optical transparency, good thermal behavior, lower oxygen permeability, and water vapor permeability. Thus, these films offer great potential application in the field of packaging material [68]. Furthermore, Xylan-rich hemicellulose (XH) films

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are produced and efforts have been made to prepare XH films with improved mechanical properties. This work described an effective approach to produce nanocomposite films with enhanced mechanical properties by incorporation of cellulose nanofibers into XH. The nanocomposite films had improved thermal stability. XH film with 25% plasticizer (sorbitol-based dry XH weight) showed poor mechanical properties, whereas incorporation of cellulose nanofibers (2% e20%, based on total dry weight) into the film resulted in enhanced mechanical properties due to the high aspect ratio and mechanical strength of cellulose nanofibers and strong interaction between nanofibers and XH matrix. This effective method makes it possible to improve hemicellulose-based biomaterials to better quality [69].

9.5.3 Nanocellulose-based bionanocomposites During the past two decades micro/nanocellulose-reinforced composites have been the subject of intensive research and a number of review papers have appeared covering this work [1,53e58,69]. Nanocellulose either in cellulose nanocrystals (CNC) or nanofibrillated cellulose (NFC) forms will result in varying reinforcement of bionanocomposites. Also, different types of nanocellulose can be used in various forms of reinforcement, including distributed reinforcements, planar reinforcements, or continuous networked structures. A wide variety of polymer matrixes, including both thermosets and thermoplastics, is being reported to form bionanocomposites with modified and improved properties, due to the appealing intrinsic and exceptional, unique properties of dispersed nanocellulose. Starch, PLA, poly(hydroxyalkanoate), soy protein, regenerated cellulose, cellulose acetate butyrate, chitosan, and silk fibroin as natural matrices, and poly(butylene adipate) (PBA), poly(oxyethylene), PP, poly(ε-caprolactone), (PCL)-based waterborne polyurethane, poly(vinyl chloride), poly(vinyl alcohol) (PVOH) as synthetic polymers [70] have been perfectly modified by incorporating nanocellulose. Moreover, segmented polyurethanes [71] and thermoset epoxies have successfully been modified by adding nanocellulose. Basically, four processing techniques, namely, melt compounding, solution casting, partial dissolution, and electrospinning have been used to fabricate nanocellulose-reinforced polymer nanocomposites or bionanocomposites [72]. Currently, among CNCs and CNFs, CNCs have received great attention and have emerged as green nanoreinforcements for a variety of organic polymers to fabricate advanced and high-performance nanocomposites due to the exceptional properties conferred by their high rigidity, stiffness, crystallinity, mechanical strength, and optical properties, as well as their exciting surface chemistry [73]. Incorporation of CNCs has improved the mechanical properties and reinforcing capacity of composites for diverse industrial applications [74,75].

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9.6 Challenges The greatest challenge in the making of nanocomposites over the past decade has been the compatibility of the hydrophobic (water repelling) polymer matrix and hydrophilic (water absorbing) fibers which result in nonuniform dispersion of fibers within the matrix and poor mechanical properties [7,76]. To improve the affinity and adhesion between fibers and thermoplastic matrices in composite production, additives such as chemical coupling agents or compatibilizers (maleated polyethylene [MAPE], carboxylated polyethylene [CAPE], titaniumderived mixture [TDM], maleic anhydride polypropylene [MAPP], corono discharge); calendaring; stretching; thermo treatment; reaction with methanolmelamine, isocyanates, triazine, silane, and mercerization of the matrix have been employed [77e79] with no significant results. A better understanding of the molecular structure and interfacial interaction between the matrix and the fibers and the relationship between the structure and property would be a major breakthrough in this area of research. Another challenge of interest is the quest for true green polymers with good mechanical properties to be used as matrix material. Biopolymers such as starch have poor water resistance, inferior tensile properties, and are highly brittle due to their large particle size which necessitate the use of plasticizers such as glycerol in the presence of heat and pressure [80]. No significant result has been recorded apart from ductility imparted by the plasticizers. Moreover, it is noted that the use of plasticizers in starch leads to the presence of residual sugar in the matrix which impairs its adhesion properties to natural fillers [81]. On the other hand PLA has unique properties such as high mechanical strength, low toxicity, and good barrier properties [9]. However, PLA composites are limited in applications due to their low glass transition temperature, weak thermal stability, low ductility and toughness, and low modulus above the glass transition temperature [82]. Generally, modifiers have been used to improve stiffness at elevated temperatures, reduce cost, and increase the degradation rate. PLA is the most promising of all the biopolymers currently in use and require much attention. Other biopolymer sources such as cellulose, gelatin, chitosan and plant-based oils are more scarce sources and involve a more tedious and costly production process. In nanotechnology, it is necessary to separate filler particles into the right shape and layer structure. To achieve maximum properties, these particles need to be very thin (1 nm) and very wide (500 nm). Achieving this is an enormous task and requires sophisticated machines such as high pressure homogenizers and inline dispersers. Although recent technology has made this possible, it has been observed that efforts to attain nanosize particles produce a result of wide size ranges, which gives rise to inconsistencies [83,84]. In addition, particle orientation has effect on the tensile properties of nanocomposite materials. It is difficult to take the orientation of nanosize fibers into consideration, but in macromechanics it has been observed that the orientation

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of the fibers have an overriding effect on the mechanical properties of the composite material. How to achieve proper orientation of particles in the matrix is already being investigated.

9.6.1 Challenges at industrial scale Michael Ricks, Director Engineering Projects, GKN Driveline, Germany, said, the lack of mass production/automation techniques influence the price, but still beyond the efforts in this area the price for composite parts is limiting the applications. According to Prof. Mikael Skrifvars, University of Bora˚s, Sweden, mass production of composites is a key area which must be developed, as then the costs will be reduced, and many new applications can be found, where the benefits with composites are useful. This means development of new processing techniques, and especially development of thermoplastic composites, especially liquid resin-free system. Dr. Douglas Ashby, technical engineer, Maskell Productions, New Zealand, further discussed and agreed with all the comments above but knows from his past experience that it is price of the raw materials that is holding us back in a number of key markets. Some efforts for the production of nanocellulose-based composites at pilot/ industrial scale have been made. There are several different routes for the manufacturing of nanocellulose-based films/papers. The choice of the production process will influence the final properties of the films as discussed previously. Very few reports are available for the production of nanocellulosebased film at pilot scale setup. Innventia are currently working together with several industrial companies to identify and implement technologies for prepilot production of nanocellulose-based films. The development of the test bed that allows a flexible manufacturing and evolution of different types of nanocellulose-based films would be a crucial step toward commercialization. Recently, the research carried out at VTT Technical Research Centre of Finland relates to the whole production chain of nanocellulose from the selection of raw materials to the development of the production process and modification of nanocellulose material according to the needs of various applications. VTT and Aalto University have developed a pilot-scale method to manufacture nanofibrillated cellulose film. The method enables industrial scale roll-to-roll production of the film, which is suitable for specific packaging applications, or can be used in several added value applications of printed electronics and diagnostics. The nanocellulose films are translucent, showing no shrinkage or defects. The high smoothness of the surface provides excellent printing quality, and the densely packed structure results in a material with outstanding oxygen barrier properties. Based on their properties, the potential applications for these films are numerous, being high performance packaging, flexible displays, and printable electronics or low-cost diagnostics. Recently our group produced nanocellulose-based paper using traditional paper-making approach. Currently, we are running a project funded by Kempe

210 PART | III Nanomaterials and additive manufacturing composites

foundation which deals with upscaling of nanocellulose-based nanopaper and nanofoams using Experimental Paper Machine (XPM). A well-known “nanopaper approach” could be tried for the continuous production of nanopaper or nanofoam for packing applications or several other value added products [85]. Thanks to the flexibility of XPM, hybrid, coated and layer-bylayer assembly of nanocellulose with other support materials is also possible. The bottleneck of upscaling is dewatering of nanocellulose, which could be solved by the addition of coagulants, change in wire mesh, surface modification of nanocellulose, and drying could be done in continuous mode or in a controlled manner by using a range of existing techniques (dynamic sheet former, coating in continuous mode, online layered structure formation using XPM, etc.). Nevertheless, various industries are using bio-based fibers for the production of biocomposites that could be used in automobile industry. Interior parts (various panels, shelves, trim parts, brake shoes, etc.) and exterior parts (wheel compartment cover, transmission cover, etc.) of a car have been made and used currently by various car manufacturing companies like Audi, BMW, Ford, Volvo, and Mercedes.

9.7 Conclusion In this chapter, an effort has been made to explain the overview of biocomposites with respect to their fundamental and application point of view. Furthermore, a concise summary of the major material properties attributed to green composites has been discussed. This includes good, specific but variable mechanical properties and good environmental credentials (renewable biodegradable, low embodied energy, nontoxicity). As work continues to improve the attributes of green composites, particular care must be taken to ensure the inherent green characteristics of these materials are not underlined. Various applications of bio/green composites have been discussed in various articles (as discussed in this chapter), but this chapter is specifically focused on the possible constructive and challenges for the production and utilization of green composites in automobile industry. For example, using cellulose-based materials as reinforcement in thermoplastic composites is a novel application of nature-derived materials, and it has numerous advantages for the environment, such as reducing CO2 emissions in the atmosphere during their cycle of production, processing, and use. However, incorporating green reinforcement materials in thermoplastic polymers also has challenges including: (1) the issue of compatibility between hydrophilic cellulose and hydrophobic polymers, (2) moisture sensitivity because of its hydrophilic nature, (3) uniform dispersion and extreme agglomeration, and (4) low thermal stability, limiting its applications in thermoplastics with high melting points. These challenges may be the reason for the limited application of cellulose composites in automotive applications compared to glass fiberebased composites.

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Although the information presented in this chapter does not delve into the details of green composite material science, it is anticipated to allow engineers and designers to have a better grasp of the most appropriate approach for the production of green composites for automobile applications. Hopefully, this will lead to the increased demand for green composites and sustainably improved material systems.

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Part IV

Life cycle assessment and risk analysis

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Chapter 10

Risk-sensitive life cycle assessment of green composites for automotive applications U. Go¨tze1, P. Pec¸as2, H.M. Salman2, J. Kaufmann3, A. Schmidt1 1 Chair of Management Accounting and Control, Chemnitz University of Technology, Chemnitz, Germany; 2IDMEC, Instituto Superior Te´cnico, Universidade de Lisboa, Lisbon, Portugal; 3 Institute of Lightweight Structures, Department of Textile Technologies, Chemnitz University of Technology, Chemnitz, Germany

Chapter Outline 10.1 Introduction 10.2 Green composites and their LCA: a review 10.2.1 Green composites based on natural fibers 10.2.2 Advantages and disadvantages of natural fiber-based composites 10.2.3 LCA of Green Composites 10.3 Modeling risks of LCA and their management 10.3.1 Modeling risks

219 221 221

225 228 233 233

10.3.2 Management of modeling risks 10.4 Real-world risks of green composites and their management 10.4.1 Real-world risks of green composites 10.4.2 Management of real-world risks 10.5 Example from the Automotive Industry 10.6 Conclusion References

236

239 239 241 243 246 247

10.1 Introduction Against the background of an increasing awareness of environment and environmentally friendly materials in the automotive and other industries, green composites are gaining significantly in importance. Compared to conventional materials, they promise lower environmental impacts and thereby a Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00010-0 Copyright © 2019 Elsevier Ltd. All rights reserved.

219

220 PART | IV Life cycle assessment and risk analysis

contribution to an ecologically sustainable production and usage of goods. To evaluate whether such a promise will or might be fulfilled, in principle the established instrument for calculating of environmental impactsdlife cycle assessment (LCA)dcan be used [1]. Riskdoften understood as a danger of a loss or another adversity [2,3] or “the danger of making a wrong decision that leads to failing the targets set” [4], p. 261,dis an ubiquitous phenomena threatening the success or even the existence of companies and other institutions. Therefore, they are well advised or even obligated to establish a risk management for successfully handling the existing risks. On the one hand, LCA can be regarded as an instrument of risk management because it is usable to evaluate and to interpret the environmental burdens caused by companies’ (or other institutions’) resources (such as green composites), processes, and products as a possible source of risk. On the other hand, LCA itself is inevitably concerned with different types of risk sources implying the danger of calculating results which do not exactly reflect the environmental burdens of the object under evaluation and might lead to wrong considerations and decisions. One type of risk is the “modeling risk” to generate a wrong or inappropriate picture of reality not showing the true environmental impact of an object. Such a danger results from parameter uncertainty (because, e.g., of missing or wrong data), model uncertainty (due to simplifications in LCA models and resulting loss of information), and decision (rule) uncertainty (caused by arbitrary choices in a model) [5] (further uncertainties are defined, e.g., by Rosenbaum et al.) [6]. Specifically for green composites existing knowledge is still limited, input data are not available or show a high degree of uncertainty and/or variability, so this danger is considerably relevant for an LCA of green composites as well. One important source of modeling risks is another type of risk, the “real-world risk”: This risk is constituted by the variability of the agricultural and industrial production processes as well as the usage and end-of-life processes depending on the environment, time, technologies, etc., including effects of catastrophes, accidents, damages, etc. This variability is inherent in the environment as well as the involved companies and other actors (the “real world”) and cannot be reduced by LCA but only better characterized by additional research and measurements [1,5,7,8]. This type of risk is strongly relevant in the context of green composites and the complex processes related with them as well. Against this background, a risk-sensitive LCA should be conducted in order to analyze and control modeling as well as real-world risks and thus contribute to enhancing the significance of LCA results and improve the quality of decisions based on LCA results. Among others, this combination of LCA with (other) risk analysis (instruments) [9] is reflected in ISO 14040:2006 [10] which recommends uncertainty analyses. Some elaborated concepts for such risk-sensitive LCA exist (see Section 10.3), but are not specified for green composites until now.

Risk-sensitive life cycle assessment of green composites Chapter | 10

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This motivates the chapter. It firstly intends to give an overview of green composites based on natural fibers, their advantages and disadvantages, and existing LCA studies referring to them in order to bundle the existing knowledge about the environmental burdens caused by them (Section 10.2). Then, uncertainties causing modeling risks and approaches to handle them by means of risk management are described (Section 10.3). Afterwards, realworld risks in the context of green composites are structured and corresponding risk management measures are proposed (Section 10.4). In the following, an example from the automotive industry is introduced for demonstrating the approaches (Section 10.5).

10.2 Green composites and their LCA: a review 10.2.1 Green composites based on natural fibers Polymer-based composites based on non-renewable resources (especially petrol) have been intensively used since some decades and their use is continuously growing. These composites have numerous considerable advantages; however, their reuse and recycling are extremely difficult. The common practices are the direct disposal in landfill or the incineration which involves high costs as well as technical challenges and cause environmental impacts. Furthermore, conventional plastic production requires a remarkable consumption of petroleum-based resources, which are non-renewable resources and cause damage to environment and human health. The increasing awareness about these environmental impacts is causing a major paradigm shift from conventional materials, technologies, and products to more environmentally friendly materials, technologies, and products. This trend is leading to the development of other types of composites that are able to replace traditional polymer-based composites and at the same time have lower environmental impacts. Since a lot of them are based on renewable resources, these are often called “bio”, “eco”, or “green composites” [11e13]. For the sake of simplicity, in this chapter the term green composites will be used. Since composite material is made of two constituents: matrix and reinforcement (fibers), green composites can appear in two ways: Either both constituents are materials obtained from renewable resources such as plants and animals (“completely green composites”) or one of the constituents, either matrix or reinforcement, is not obtained from renewable resources (“partially green composites”). This study focuses the particular case of green composites that use natural fibers, that is, composites with the reinforcement obtained from renewable resources. Fig. 10.1 shows the general scheme of green composites’ life cycle which is the base for any LCA. The first life cycle phase includes as a first step the extraction of crude oil or the crop production depending on if bio-based natural resources or synthetic fibers or bio-based matrix and fibers are to be

222 PART | IV Life cycle assessment and risk analysis

Raw material extraction Crop production

Composite production

Material production Natural fiber extraction and processing

Biofuels production

Use

Composite part production

End of life

Recycling incineration landfill

Use

Polymer matrix

Biopolymer production

Crude oil production

Polymer production

FIGURE 10.1 Life cycle of a natural fibersereinforced composite part. Adapted from Joshi SV, Drzal LT, Mohanty AK, Arora S. Are natural fiber composites environmentally superior to glass fiber reinforced composites? Composites Part A: Applied Science and Manufacturing 2003; A(35):371e376, Kim S, Dale BE, Drzal LT, Misra M. Life cycle assessment of kenaf fiber reinforced biocomposite. Journal of Biobased Materials and Bioenergy 2008;2(1):85e93.

obtained. There is also the possibility of obtaining fibers from animals, like silk or wool (not included in the life cycle of Fig. 10.1)da classification of the several types of natural fibers and their origin is presented in Fig. 10.2. Both types of raw materials are then processed to obtain polymers for the matrix. Similar chemical syntheses are used despite the different origins of the raw materialsdthe isolation of the monomer and the production of a stable and interbonded mixture of monomers (polymer). The natural fibers are obtained in general by chemically removing organic components of the natural material (resin, sap, grease, etc.) followed by mechanical and/or chemical processes of isolating fibers. The fibers are then spun to make long fibers, yarns, or woven (crimped and noncrimped) and knitted fabrics to obtain a textile structure. The specific characteristics of natural fibers demand usually a chemical surface treatment to reduce water absorption level and eliminate residues of organic materials and living organisms. These processes of generating matrix and

Animals

Natural Fibers

Silk

Wool

Feathers

Bast

Flax

Hemp

Leaf

Sisal

Banana

Fruit

Cotton

Coir

Grass

Bamboo

Straw

Corn

Kenaf

Plants Indiangrass

Switchgrass

Rice

Wood Pulp

FIGURE 10.2 Classification of natural fibers. Adopted by Joshi et al. [13].

Jute

Risk-sensitive life cycle assessment of green composites Chapter | 10

223

fibers are assigned to the material production life cycle phase in Fig. 10.1. The distinction of which processes are part of the first and the second life cycle phases may be difficult, so it might not be possible to distinguish these two phases. In the next life cycle phase the composite is produced by joining matrix and reinforcement fibers in a unique materialdwith no particular distinctions between partially and fully green composites. The material is then used in a product until the product ends its life. Concerning the end-of-life phase, the recycling of composite materials is not an easy task and degrades the properties of its constituents, so incineration is also a common end-of-life alternative for these materials. Furthermore, some of these composites end in landfill although this is not a recommended practice. Summarizing, despite the different origins of their constituents the natural fibers based green composites follow a life cycle that is similar to that of the traditional composites. In general, natural fibers exhibit lower density than glass fibers, lower Young’s modulus than carbon fibers, and higher moisture absorption than those synthetic fibers (Table 10.1). There are numerous possible combinations of natural fibers and polymers (natural and synthetic) that allow the current use of composite materials based on them in the automotive industry, construction, fabrics, packaging, toys, consumer goods, furniture, electronics, sports, etc. [15,20,21]. The selection of the proper combination for a specific application is a complex task, so a methodology enabling a designer to select the appropriate combination of fiber and matrix has been proposed by Koronis et al. [22] with a specific example for automotive applications. According to Directive 2000/53/EC, the European Community requests its member states to reuse and recover at least 95% of all end-of-life (EOL) vehicles by 2015. As a result of this, the application of natural fiber composites is significantly increasing in the automobile sector with an annual growth rate of above 20% [15]. In the particular case of automotive industry, the rapid growth of application of composites based on natural fibers was predicted since 2007 [15,20,23]. From that time, a significant interest has been shown for fibers like kenaf [23,24], hemp [25,26], flax [27,28], jute [29], ramie [22,24], and curaua´ [15] to produce composites for automotive applications. Concerning the properties of natural fibers, the density of the several types of natural fibers ranges between 1 and 1.5 g/cm3 without significant differences among them (only bamboo has a lower density). Nevertheless, these fibers are a natural product meaning that the density (and other properties) of batches harvested in different regions, different areas in the same region, or even different months in the same locality and region might show large differences among the batches of the same type of natural fiberdthis may even be larger than the differences between different types of fibers. Furthermore, the properties are influenced by weather conditions, by nutrients used in farming, by the seeds, and even by the stocking and processing conditions after harvesting [15,30]. In addition, there are no international standards or

Fibers

Density (g/cm3)

Elongation at break (%)

Fracture stress (MPa)

Young’s modulus (GPa)

Moisture absorption (%)

References

E-glass

2.5e2.55

2.5e3.0

e

70e73

0

[17,18]

Carbon (standard)

1.4

1.4e1.8

e

230e240

e

[14]

Cotton

1.5

7.0e8.0

287e597

5.5e12.6

8e25

[14,16]

Bamboo

0.8

2.5e3.7

391e1000

48e89

e

[16,19]

Soft wood

1.5

e

1000

40

e

[16]

Flax

1.4e1.5

2.7e3.2

345e1500

10e80

7

[16e18]

Hemp

1.48

1.6

270e900

20e70

8

[16e18]

Jute

1.3e1.46

1.5e1.8

393e800

10e30

12

[16e18]

Ramie

1.5

3.6e3.8

400e938

44e128

12e17

[16e18]

Sisal

1.2e1.5

2.0e2.5

511e700

3.0e9.8

11

[16e18]

Coir

1.15e1.25

15e40

e

4e6

10

[17,18]

Curaua´

1.4

3.7e4.3

e

11.8

e

[15,17]

224 PART | IV Life cycle assessment and risk analysis

TABLE 10.1 Properties of E-glass, carbon, and some of the common natural fibers [14,15,16,17,18,19]

Risk-sensitive life cycle assessment of green composites Chapter | 10

225

commercial requirements that frame or create limits of acceptance for the properties of each type of fiber and reduce their variability. This is reflected by the values presented in Table 10.1 which were collected from several references (denoted by the e in some cases very wide e range of values for each fiber type and the absence of values for several types of fibers). This is a considerable source of modeling as well as real-world risks.

10.2.2 Advantages and disadvantages of natural fiber-based composites Green composites are usually appraised to be environmentally friendly [12,13,15,20,21,27,31e35] but there exist some issues and concerns affecting the ecological advantageousness compared to conventional composites. One of these concerns is the chemical stability of these composites, which most of the times require special pre- and postmanufacturing treatments [36,37]. Other problems include lower and variable strength, lack of interfacial adhesion, lower durability and highly variable quality in general, etc. [15,17,36]. However the use of adhesion promoters, additives, or chemical modification can help in overcoming such limitations [11]. Summarizing, several advantages and disadvantages of green composites as documented in literaturedand largely resulting from the properties of natural fibers described in Section 10.2.1dare presented in Table 10.2. As can be seen in Table 10.2, authors recurrently mention lower environmental impact as an advantage of natural fiber composites. This advantage is several times concretized by lower emissions, lower fuel consumption achieved by lower weight, biodegradability, recyclability, compostability, and lower use of energy, among others. Consequently, some authors also state that these advantages create conditions for a potential of lower costs of the fibers. Regarding natural fibers’ disadvantages, the most referred one is the increasing of local eutrophication because of fertilizers used. This is the origin of the other two most frequently mentioned general disadvantages: higher ecological footprint in terms of land use and negative impacts on ecosystem quality. From this brief analysis of literature it is possible to identify some contradictory statements and findings about natural fiber performance. Additionally, in some of the publications most of these advantages and disadvantages are listed as granted information and not as a result of the study, for instance in [14,16,17,23,34,43]. In addition, each particular case is based on specific conditions of farming and disposal practices, land occupation, water consumption, processing, transport facilities, weather conditions, soil, fertilizers, and other resources used like electricity and fueldwhich are usually not fully describeddaffecting the overall fiber performance and the study results. Moreover, no information is usually available about these factors creating significant doubts about the reliability, accuracy, and comparability of the studies [43]. Finally, methodological differences will affect the results of

226 PART | IV Life cycle assessment and risk analysis

TABLE 10.2 Advantages and disadvantages of natural fiberebased composites Advantages of green composites

References

Lower environmental impact

[12,13,15,17,23,31,32,35,36]

Lower cumulative energy demand and energy consumption

[12,13,20,31,33,38]

Lower costs

[13,17,21,24,32,36,38]

Reduced dependence on NRE resources

[13,17,23,27,34,36]

Recyclability

[12,17,20,27,39]

Improved fuel efficiency due to light weight

[12,13,15,38]

End-of-life biodegradability

[13,15,36]

Higher fiber content for equivalent performance

[13,15,32]

Compostable

[12,27]

Enhanced energy recovery

[13,15]

Social benefits such as schools, medical and transport facilities

[15,40]

Soil quality improvement

[20]

Non abrasive

[36]

Nontoxic

[17,36]

Job creation in underdeveloped regions

[15]

Disadvantages of green composites

References

Increased local eutrophication because of fertilizers use

[12,13,15,25,32,41,42]

Higher ecological footprint in terms of land use

[12,20,21,34]

Negative impacts on ecosystem quality

[12,15,21]

Acidification

[23,42]

Maximum processing temperature

[15,17,36]

Lack of production and availability

[15]

Unregistered workers

[15]

Heavier than conventional composites for equivalent strength

[27]

Lower strength

[15,17]

Photochemical smog formation (kenaf fiber)

[23]

Risk-sensitive life cycle assessment of green composites Chapter | 10

227

TABLE 10.2 Advantages and disadvantages of natural fiberebased compositesdcont’d Disadvantages of green composites

References

Eco-toxicity (water, soil)

[27]

Lack of interfacial adhesion

[36]

Higher water and wood consumption

[38]

Highly variable quality

[15,17]

Lower durability, poor fire resistance, and moisture absorption

[15,17]

Price can fluctuate by harvest results or agricultural politics

[17]

studies. So, there is a latent threat of promoting or inhibiting the use of a specific type of natural fibers or of natural fibers in general without consistent or highly significant arguments. Nevertheless, most of the studies show the potential of natural fibers, especially for lightweight design based on the lower density of natural fibers (around 1.5 against 2.5 g/cm3 for glass) along with their good mechanical properties [13,20,33]. For example, one study demonstrates that the production of flax fibers as reinforcing component results in lower environmental impacts than production of glass fibers [27]: static applications of polylactid acid (PLA)/ flax green composites and PLA/flax/balsa biosandwich exhibit several environmental advantages compared to those of e-glass/polyester composites and sandwich counterparts [27]. Moreover, these fully green composites can be recycled or composted provided that matrix resin is biodegradable [12,27,35]. Most of the disadvantages can also be understood as a source of real-world risks. Especially for natural fibers as decisive parts of green composites, for example, Zah et al. [15] presented social, environmental, and economic risks of Caraua´ fiberebased composites which include using unregistered workers during production of crops, high environmental impact of monocultures, and risk of variability both in availability and crop production which could be caused by economic, weather, or political issues. The use of fertilizers in natural fibers cultivation produces higher nitrate and phosphate emissions, which increases the level of eutrophication in local environment. So, the improvement in overall environmental impact comes at the expense of deterioration in local environment and water quality. Additionally, the environmental superiority of green composites may disappear if these composites have significantly lower operating life compared to their conventional counterparts [13]. Moreover, higher water consumption during production and

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extraction of natural fibers may lead towards water shortage problems in areas with water scarcity [38], however, this is not the case for all types of natural fibers. Additionally, Colwill et al. [44] predicted the risk that all crop and grazing land, and cleared forest land would not be sufficient to meet the rising demand for food, liquid fuels, and plastics assuming that all fuels and plastics are derived from agricultural products due to depletion of fossil resources by 2050 in a high consumption and low productivity scenario. Summarizing, Le Duigou et al. [35] stated that the origin of natural fibers from natural resources does not necessarily mean that they have lower environmental impact than synthetic materials. This implies the need for a significant LCA to evaluate and demonstrate whether there is ecologically advantageousness or not.

10.2.3 LCA of Green Composites The World Commission on Environment and Development [45] defined sustainable development as “Meeting the needs of the present without compromising the ability of future generations to meet their own needs.” Life Cycle Assessment (LCA) is an environmental assessment method which, according to the international standard “Environmental Management-Life Cycle Assessment-Principles and Frameworks” (ISO 14040:2006(E) (2006)), considers the entire life cycle of a product from raw material extraction and acquisition, through product production, to its use and end of life. This standard suggests a protocol with four main steps to apply the LCA method. The first step deals with Definition of Goal and Scope, as it happens in many assessment standards. The following step of Life Cycle Inventory Analysis (LCI) implies identifying, analyzing, and recording the relevant inputs/outputs (flows) and their quantities. The subsequent Life Cycle Impact Assessment (LCIA) aims at evaluating the magnitude and significance of potential environmental impacts of a product/system throughout its whole life cycle. Finally, Interpretation is the phase of LCA in which the findings of either the inventory analysis or the impact assessment, or both, are evaluated in relation to the defined goal and scope to reach conclusions and recommendations. So, an LCA includes (1) collecting information about the inputs and outputs related with the life cycle of processes/products (life cycle inventory), (2) the use of databases of datasets like Ecoinvent to estimate the emissions caused and resources consumed, and (3) translating them to environmental impact factors (using impact assessment methodologies) such as the contribution to climate change, smog creation, eutrophication, acidification, and human and ecosystem toxicity [15,20,21] (denominated as midpoint assessment). A comprehensive LCA requires the consideration of at least eight Environmental Impact Classification Factors (EICF) as outlined in ISO/TR 14047/ 2003 which are listed in the caption of Table 10.3. These impact factors can be aggregated into a single eco-indicator by using the ReCiPe endpoint method

TABLE 10.3 Environmental impact classification factors and life cycle analyses

A q T P

C E D

E P

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Duflou et al. [12]

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Joshi et al. [13]

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Kim et al. [23]

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La Rosa et al. [20]

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Zah et al. [15]

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Korol et al. [21]

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Duigou et al. [27]

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Duigou et al. [35]

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Akhshik et al. [38]

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Yates et al. [43]

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Life cycle phases

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Life Cycle Phases: 1. Raw material extraction/Material Production; 2. Composite/Part Production; 3. Use; 4. EOL. Environmental impact classification factors (EICF): AP, acidification potential; AqTP, aquatic toxicity potential; CED, cumulative energy demand; EP, eutrophication potential; FAETP, freshwater aquatic ecotoxicity potential; GWP, global warming potential; HTP, human toxicity potential; LO, land occupation, MAETP, marine aquatic ecotoxicity potential; NRADP, nonrenewable/abiotic resource depletion potential; ODP, ozone depletion potential; POCP, photochemical oxidants creation potential; TETP, terrestrial ecotoxicity potential.

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Environmental impact classification factors (EICF)

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which allows the assessment concerning three damage categories: human health, ecosystem quality, and resources (by normalizing, weighting, and adding the results for the calculation of a single score in points) [21]. The details of specific material and energy flows, emissions, and manufacturing processes vary depending on the specific application. However, material flows, energy use, emissions, and environmental impacts over all these stages need to be modeled, inventoried, and analyzed for a comprehensive LCA [13]. The way LCA is being used to assess natural fiber-based composites’ environmental performance is presented in Table 10.3. For identification of relevant studies, a literature search was conducted using the keywords LCA, life cycle assessment, biocomposites, bio-composites, bio composites, green composites, green-composites, natural fiber composites, and natural fiber based composites in automotive applications. Most of the studies found and presented in the following table are based on automotive applications except the one by Korol et al. [21]. In five of the studies the data was used from Ecoinvent databases [13,20,21,35,38]. In the other studies, different sources of information were used. For example, Zah et al. [15] used several data sources. The data for the materials (e-glass fiber and polypropylene) and for the production process was derived from the publications of Althaus et al. [46] and Kellenberger et al. [47]. The data for the three different cases considered by Zah et al. [15], a hypothetical light weight car (LIRECAR), a Golf Car, and an advanced light weight car (HYPERCAR), was obtained from Schmidt et al. [48], Spielmann et al. [30], and Lovins et al. [49], respectively. The study by Zah et al. [15] also used information about fuel consumption from [48] for the LIRECAR and from [49] for HYPERCAR. In the work of Kim et al. [23], data on fertilizers, agrochemicals, and fuel consumption for crop production at county and state level in the United States was obtained from several references [50e52]. For the evaluation of environmental burdens associated with glass fibers and polypropylene (PP), Kim et al. [23] used the data from literature [53,54], Ecoinvent database [55], and TEAM LCA software by Ecobilan. Process information on the injection molding process was obtained from literature [56]. Life cycle inventory information on other chemicals (fertilizers, agrochemicals, sodium hydroxide, etc.) and energy carriers (diesel, electricity, natural gas, etc.) was obtained from [57] and commercial LCA databases [55,56]. Akhshik et al. [38] used US EPA TRACI 2.1 method for modeling the impacts of engine beauty covers. Those authors collected all primary life cycle inventory data by collaboration with mining industries, parts manufacturers, material suppliers, landfills, and researchers. Primary and secondary data categories were selected based on impacts as indicated by TRACI. Landfill data was collected from the European generic database and confirmed by using Canadian sources. All other secondary data came from OpenLCA (GreenDelta GmbH, Germany 2014), SimaPro (PRe´Consultants, The Netherlands 2015), Gabi (Think step, Germany 2015), GREET (Argonnenational lab, 2015), and

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NREL [58] databases. Wherever no data was available for North America, European data was used for the calculations. In terms of methodologies used, Joshi et al. [13], Duigou et al. [27,35], Corbiere-Nicollier et al. [33], and Zah et al. [15] calculated the environmental impact factors based upon CML methodology. Akhshik et al. [38] used EPA’s TRACI 2.1 LCIA. Wo¨tzel et al. [32] and Corbiere-Nicollier et al. [33] applied Eco-indicator 95 methodology. During the survey, it was observed that most of the studies on LCA did not consider full eight EICF as outlined in ISO/TR 14047/2003dthis outcome was confirmed by Yates et al. [43]. Only three studies analyzed fulfill this requirement [15,20,21]. Usually the authors selected specific environmental impact factors such as HTP, AP, EP, GWP, etc., for their studies. Most of the papers analyzed global warming potential, acidification potential, and eutrophication potential because there are significant differences in these impact factors when a comparison is made for natural fiber composites and conventional composites. Regarding life cycle phases, most of these LCA studies performed a complete cradle to grave analysis comprising raw material production, composite or part production, use phase, and EOL scenarios [12,13,15,20,23,35]. Korol et al. [21] and Akhshik et al. [38] also performed cradle to grave analysis but they did not evaluate the use phase. However, they pointed out that there will be fuel savings and hence emission reductions during the use phase because of the light weight of green composites compared to their counterparts. There are reservations about waste management process in the EOL stage of LCA studies due to lack of data on the extent of biodegradation of different biopolymers in different environments. This data is important in determining the suitability for disposal route as well as the emissions generated and energy recovered for different biopolymers [43]. As an example, the study by Duigou et al. [41] was limited to cradle to gate approach because of lack of data about waste treatment. Concerning the results, a few studies support that green composites have an overall lower environmental impact than conventional ones. Duflou et al. [12] studied a long list of green composite fibers, matrices, and combinations regarding cumulative energy demand, greenhouse gas emissions, and ecopoints and concluded that the materials and the combination processes (to obtain composites) are valid alternatives with a reduced overall impact compared to traditional composite fibers, matrices, and processes. In addition, Le Duigou et al. [35] concluded that flax fibre/PP green composite is 6% lighter than glass fiber/PP composites and generates 10%e20% lower environmental impacts. Other studies support the same performance for green composites but identify some environmental aspects where their impact is higher. For example, Akhshik et al. [38] stated that cellulose/carbon fiber-reinforced polypropylene composites cause lower environmental impact than glass fiber-reinforced polyamide in the production of an engine beauty cover, despite the latter performs better regarding water and wood

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consumption; La Rosa et al. [20] concluded that natural fiber-based green composites have lower environmental impact, lower energy consumption, and lower impact at the end of life due to recycling, despite they are heavier for an equivalent strength that would cause a lower performance if the use phase involves transport applications. Le Duigou et al. [27] concluded in the same way about high mass of green composites, also confirming the lower environmental impact of green composites, in this case flax mat/PLLA-based sandwich bio-composites was compared with conventional glass/polyester and balsa sandwich composite. Furthermore, Zah et al. [15] evaluated the prospective environmental, economic and social impacts of using curaua´ fiber in automobile application and concluded that though curaua´ fibers can promote regional development, they have to be lighter than glass fiber-based composites to achieve significant environmental benefits. Another study in the same direction was presented by Kim et al. [23] who concluded that kenaf fiberereinforced green bio-composite with glass fiber-reinforced composite for automobile parts can reduce nonrenewable energy consumption by 23% e24% and greenhouse gas emissions by 6%e16%. However, the kenaf fiberereinforced composite produces more local environmental impacts such as photochemical smog formation, acidification, and eutrophication than the glass fiber-reinforced one because of nutrient losses to the environment during biomass production. Other studies point out that not all the green composites have a lower environmental impact than traditional composites. Korol et al. [21] studied the production of a pallet, and concluded that cotton fibers and glass fiber-based composites have higher environmental impact when compared with jute fibers and kenaf fibers composites (with a matrix of polypropylene). This situation can be caused by the industrial cultivation of cotton on a large scale. The lowest environmental impact was observed in the use of kenaf and jute fibers. In summary, the studies revealed that green composites have the capacity to bring numerous advantages for several industries such as automotive, construction, packaging and fabrics, etc. but there are also still many challenges associated with their use which should be addressed for successful application of these composites. The review also shows that the use of natural fibers offers several risks such as variability in their properties due to weather and farming conditions, due to susceptibility to damage in hot or wet environments, and to water shortage issues in water scarce areas, among others. These results were mainly obtained by calculating the environmental impact using a suitable methodology such as ReCiPe endpoint method (eco-indicator, that aggregates several types of impact in a single score). Regarding life cycle phases, most of the studies performed a complete cradle to grave LCA considering raw material production, composite/part manufacturing, use, and EOL phases. However it is important to clarify that especially the considered EICF vary significantly among different studies (due to different assumptions, data availability and quality, farming techniques, etc.) implying the results

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might not be comparable or might not give the true and complete picture. The results of LCA of the published works analyzed show that in some cases especially in the mobility sector they are environmentally benign and they have lower costs, mainly because they allow weight reduction and hence save fuel during use phase. Furthermore, they offer energy recovery during the EOL phase and are biodegradable. However, they also cause local eutrophication and land damage due to monoculture. Although the referred ISO standard has standardized LCA up to a certain extent, these guidelines leave a broad range of opportunities to create and apply an evaluation model in an LCA study. This is reflected by the studies described above with their consideration of different types of natural fibers, environmental impact classification factors, methods of LCA, life cycle phases, and data bases. As a consequence, the comparison of results from different studies is hindered. Even if different studies are considered as comparable, there is the need for a careful interpretation of results for a number of reasons including methodological differences such as functional unit, allocation method, impact assessment methodology, and inventory data used [43]. Although the concept of the LCA is simple, the analysis is rather complex mainly because of the difficulty in establishing the correct system boundaries, obtaining accurate data, and interpreting the results correctly [59]. So, for LCA in general as well as the specific LCA of green composites there is an implicit risk related with the way all the referred steps and definitions are performed and decided. This is specific part of the modeling risks discussed in the following.

10.3 Modeling risks of LCA and their management 10.3.1 Modeling risks The literature review in Section 10.2 has not only described the main characteristics of natural fibers, green composites, and LCA studies about them, but has also shown that a couple of risks are accompanying all of them possibly leading to wrong evaluations and decisions of a company or industry about the use of green composites. They raise the need for the conscious consideration of modeling as well as real-world risks in LCA studies, or in other terms, a “risk-sensitive LCA” as it is suggested in this paper. In this section, modeling risks are focused. Modeling risks primarily result from uncertainties. In literature, several classifications of uncertainties in LCA exist [1,5,6,60]. Referring to Huijbregts [1], Steinmann et al. [5] distinguish three types of uncertainties: “(1) uncertainty due to lack of knowledge of the “true” value of a model parameter (parameter uncertainty), (2) uncertainty caused by arbitrary choices in a model (decision rule uncertainty), and (3) uncertainty caused by the loss of information resulting from the simplification of reality via models (model

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uncertainty)” [5], p. 1147 (see also [61,62]). Parameter uncertainty is caused by “Empirical inaccuracy (imprecise measurement), unrepresentative data (incomplete or outdated measurements), and lack of data (no measurements)” [1], p. 274. In a wider sense, uncertainty in this context is also given when model parameters are used for which more than one value is available due to the variability of real facts [6,60,62]. Decision rule or simply decision uncertainty [62] occurs if there is no general agreement about the decision rules, for example, regarding the selection of the functional unit and allocation procedure for multi-output processes or the weighting of damage categories [1,61]. Decisions have to be made based on individual knowledge, assumptions, preferences, and risk attitude. Again in a wider sense, uncertainties in making conclusions, recommendations in the interpretation phase, etc. (“interpretation uncertainties”) may arise and cause decision uncertainties and corresponding risks as well. Model uncertainty arises from simplifications of reality by LCA models by using surrogate data (e.g., “using wind speed at the nearest airport as a proxy for wind speed at the facility site” [8], pp. 2e4), excluding variables, aggregating circumstances into a few, broad categories (such as damage categories), approximations (e.g., assuming linear relations between environmental impacts and emitted pollutants, neglecting temporal and spatial variabilities), and incorporating model elements which are items of disagreement of experts (e.g., because they can be interpreted differently, based on individual experiences and biases) [1,5,61,62]. It has already been mentioned in the introduction that some modeling risks result from real-world risks and especially from the variability of the life cycles of green composites. Several types of variability are found in literature, referring to differences in location (spatial), time (temporal), processes/technologies producing the same output (technological), and individuals (interindividual) [1,5,62]. Variability reflects “real-world differences among alternative life cycles of equivalent products” [5], p. 1147, is inherent in the environment [7] as well as in the involved companies and other actors anddin contrast to the aforementioned types of uncertaintydmay not be reduced by additional research and measurements [5,7,63], only better characterized [8]. Variability is an important source of uncertainty. Its effects on modeling risks are similar, as stated by Haimes: Like parameter, model, and decision uncertainty, stochastic variabilities “affect one’s ability to determine or state the true value of a quantity of concern” [62], p. 266, and approaches for dealing with uncertainty and variability coincide to a large extent [60]. The hereaddressed uncertainties can arise in each of the interrelated steps of the LCA procedure according to ISO 14040. However, there are some focuses as Fig. 10.3 shows. Decision-makers are faced by parameter uncertainty, model uncertainty, decision uncertainty, as well as variabilities especially in the evaluation steps (LCI and LCIA). The steps of goal and scope definition and interpretation are primarily affected by decision uncertainty.

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Types of uncertainties

Steps of LCA (according to ISO 14040) Decision about, e.g., - intended application, audience, and reasons of the study - product system, functional unit, system boundary, reference flows, impact categories, and methodology of impact assessment (e.g., CML, EI99, ReCiPe 2016)

– Decision uncertainty

Life cycle inventory analysis (LCI)

Data collection, e.g., – inputs (energy, raw materials, auxiliary, other physical inputs) – outputs (products, co-products, waste, emissions, discharges to water and soil) for each unit process (type and quantity) Data calculation, e.g., relating data to reference flows Allocation of flows and releases

– Parameter uncertainty – Model uncertainty – Decision uncertainty

Life cycle impact assessment (LCIA)

Selection of impact categories, category indicators, and characterization models Assignment of LCI results (classification) Calculation of category indicator (quantitative) results (midpoints, endpoints) (characterization) Normalization (grouping, weighting), e.g., determination of EI99

Interpretation

Conclusions, explanation of limitations, recommendations to decision-makers Considering results of LCI and LClA, referring to the defined goal and scope

Goal and scope definition

– (Variability)

– – – –

Parameter uncertainty Model uncertainty Decision uncertainty (Variability)

– Decision uncertainty

FIGURE 10.3 Steps of life cycle assessment according to ISO 14040 and types of uncertainties causing modeling risks. Adapted from Huijbregts MAJ. Application of uncertainty and variability in LCA. Part I: a general framework for the analysis of uncertainty and variability in life cycle assessment. International Journal of Life Cycle Assessment 1998;3(5). ISO. ISO 14040Environmental management e life cycle assessment e principles and framework. International Organization for Standardization; 2006.

Fig. 10.3 provides an overview of types of uncertainties that are relevant in the different steps of LCA. Additionally, different modeling risks can be distinguished according to the several life cycle phases of green composites (see Fig. 10.1) and the different processes in these phases as well as the different objects under consideration: fibers, green composites and their constituents (interface, matrix, and reinforcement), the components and products manufactured by using them, as well as emissions, waste, and recyclates (see also Section 10.4.1). Especially for green composites, an important source of risk is the data provided by the established LCA tools/databases. The probable incorrectness and incompleteness of these data result in a parameter uncertainty. Such an uncertainty is directly passed through the LCA process and might affect the results of LCA considerably. Not all relevant fibers are included (e.g., Ramie) and the influence of the origin and agricultural process etc.dor: the variabilitydare only partly regarded in the state-of-art-tools. Especially due to the inherent variability, the limited number of existing published studies, and the free space of performing LCA studies about green composites, modeling risks tend to be considerably high. This is especially true if LCA is conducted in the early phases of the life cycle (e.g., during the

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design process). Thus, it seems to be necessary or at least meaningful to consider the analysis and management of these risks.

10.3.2 Management of modeling risks For handling the uncertainties which cause modeling risks in LCA, several approaches and methods can be used. In literature on LCA, the distinction of the following main lines has been proposed [60,64]: l

l

l

l

scientific approach: doing more research for improving measurements and collection of more accurate data, social/constructive approach: involving stakeholders and expert judgment to analyze and reduce uncertainties by discussing and finding a consensus, for example, on appropriateness of impact category indicators, legal approach: relying on standards such as ISO by recognizing decrees as the truth, statistical approach: using methods from statistics such as Monte Carlo simulation or fuzzy set theory, “to determine confidence intervals and other indicators of robustness” [60].

According to Heijungs and Huijbregts [60], the first three approaches aim at reducing uncertainty while the fourth approach strives for incorporating uncertainties into planning. In the context of LCA, authors suggest a broad range of instruments available for incorporating and reducing uncertainties, not necessarily related to only one of these approaches. Furthermore, instruments can address several uncertainties [1,63]. For example, in LCIA according to the scientific approach and the social/constructive approach expert judgment can contribute to acquire more accurate data (reducing parameter uncertainty) and to select appropriate impact category indicators (reducing decision uncertainties), respectively [1]. Furthermore, sensitivity and scenario analyses are suitable to incorporate parameter uncertainty and variabilities as well as model uncertainty and decision uncertainties into LCA [1,63]. Concepts and methods that are useful for managing modeling risks can be found in another domain: economic risk management (theory). There, a generic risk management process comprising the steps of l l

l l l

setting risk-related targets, analyzing risks (consisting of the identification of risks, analysis of causeeffect relationships, and assessment of risks), searching measures for handling specific risks, assessing and selecting such measures, and realizing and controlling the measures

is suggested [2]. Referring to modeling risks, the first step implies the necessity to determine the accepted degree of modeling risk or the required

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degree of confidence in the results [8]dpossibly together with the available time and costs for modeling. In the second step, modeling risks may be identified according to the different steps of the LCA procedure and types of uncertainties (see Fig. 10.3) as well as the life cycle phases, processes, and relevant objects. The cause-effect relationships are mainly depending on the procedure of LCA and the applied methodsdthey determine which rules and data are used to calculate (intermediate) results and, thereby, the relationships between the different types of uncertainties and the corresponding modeling risks. The assessment of modeling risks refers to their effects on the results of LCA and their deviation from the “true” results. It can especially be supported by sensitivity analysis. Measures for handling risks are often distinguished in two types: those referring to the sources/causes of risks which are intended to reduce the probability of their entrance and those referring to the (negative) effects and trying to reduce them. Considering modeling risks, especially the first type of measures is relevant, such as the improvement of data/information, the postponement of evaluation, and the inclusion of different scenarios. The assessment and selection of the measures are typically based on a comparison of their positive (reduction of modeling risks) and negative (additional time needed and cost) effects [2]. The improvement of the available information/data is also focused in LCA literature [63]. EPA exemplarily suggests the following strategies for improving data quality [8]: l l l

l l l l l

collection of new data, implementation of an unbiased sample design, application of more direct measurement methods and/or definition of a more appropriate target population, model-based estimation of missing values, use of surrogate data, use of default assumptions, narrowing of the assessment scope, and data collection from expert surveys.

In general, a profound knowledge management could help to handle the challenge of data quality. Furthermore, for the different steps of risk management a variety of different methods can be applied (for an overview see [2,3,62,65]). As a means of data uncertainty (risk) identification and assessment as well as the assessment of measures, data quality indicators for LCI data can be applied [60]. As partly already mentioned, for the managing of modeling risks, scenario analysis, probabilistic simulation (Monte Carlo method), and sensitivity analysisdwhich are all established in the economic context as welldseem to be especially relevant (as means of the statistical approach) [60,64]. The two latter ones are explicitly suggested by LCA in ISO 14040 [10].

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For scenario analysis the consideration of a couple of interrelated factors as well as different future developments (scenarios) is characteristic. This method is already included in the ReCiPe 2016 method for LCA [66,67]: Three different scenarios with different sets of assumptions for evaluating different environmental burdens can be applieddthe individualist, hierarchist, and egalitarian. Thus, some decision and parameter uncertainties can be taken into account. Probabilistic simulation (or the Monte Carlo method) comprises the estimation of probability distributions for the relevant uncertain parameters. Usually by simulation and based on a model reflecting the relationship between the parameters and the target figure(s), from these input data probability distributions of the target figure(s) outcome(s)dhere environmental burdensdare derived. This method bears the potential to generate a quite realistic picture of the “real world” and its uncertainties. However, it requires considerable efforts for data collection and modeling (which needs support by adequate IT tools) and the results may be difficult to interpret [4,5,7,68]. Sensitivity analysis aims to investigate the relationships between the various data and the target values of a model calculation. The following questions are addressed by sensitivity analysis [4]: l

l

How does the target value change with given variations of an input measure or of several input measures? (type A analysis) Which critical values must an input measure, or a combination of several input measures, achieve to reach a given target value? (type B analysis)

The execution of a sensitivity analysis is based on the construction of a model or even model systemdhere this is the model system build up in the LCA procedure under the assumption of certainty. For LCA, especially type A analysis seems to be relevant. This can be conducted in two different ways: By starting with the original data and changing it by gradual increments, or by using different possible input values (e.g., one minimum, one mean, and one maximum value), each in a separate calculation (a procedure which is similar to scenario analysis). Besides the selection of one of these approaches, it has to be determined which types of uncertainties and which concrete parameters (taking parameter and modeling uncertainties and variabilities into account) or decision rules should be subject to sensitivity analysis. Furthermore, for parameters as well as decision rules the concrete way of variation (number and spread of different values) has to be arranged. After these preliminary steps, the LCA calculation procedure is conducted repeatedly, in each “run” with varied value of (only) one parameter or one modified decision rule (a variation of more than one parameter or decision rule is possible as well but generates results which are difficult to interpret). The results show how the LCA result varies in dependence of the values of the single parameters or decision rules. On the one hand, this allows to compare the effects of the uncertain parameters or decision rules and to identify those with the strongest influence (thereby

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contributing to risk identification). On the other hand, the variety of the LCA results and thereby the existing risk is disclosed (as a contribution to risk analysis). This provides a basis for identifying, evaluating, and selecting measures for handling of modeling risks as well.

10.4 Real-world risks of green composites and their management 10.4.1 Real-world risks of green composites Due to the complex network of activities and actors being involved in the manufacturing, use, and EOL activities of green composites and their elements, the corresponding possible risks are quite manifold. Thus, a structuring of these risks seems to be helpful as a means for their identification and handling. Fig. 10.4 shows a suggestion for such a structuring of the real-world risks of green composites referring to the dimensions of life cycle phases (including the processes ongoing in these life cycle phases), objects, and type of environmental impacts. Typical points of environmental impacts are the effect on climate change or global warming as well as the effect on smog creation, acidification, aquatic and terrestrial eutrophication and toxicity. These different types of environmental impacts are affected by a huge amount of objects which change their

Type of environmental impact (...)

Objects • Fibers • Interface • Matrix • Green Composites • Components • Product • Waste • Emissions • Recyclates • ...

Components Life cycle phases (incl. processes)

Example of an impact element Climate change

Composite/part production FIGURE 10.4 Structuring of real-world risks of green composites. Adapted from DIN. DIN EN 60300-3-3: Zuverla¨ssigkeitsmanagement e Teil 33: Anwendungsleitfaden Lebenszykluskosten:2014.

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impact level according to their current life cycle phase like raw material extraction/material production, composite/part production, use and EOL as explained in Section 10.2.3. Concerning green composites and plantable components like natural fibers, these life cycle phases have to be complemented with the phases of the growth. The key objects for a real-world risk analysis for green composites are the fibers, the fibers interface, and the matrix. By using these main semi-finished products, different components of green composites and final products are buildable with different amounts of waste, emissions, and recyclates. Real-world risks of using green composites mainly result from the Raw material extraction/Material Production phase of fibers such as flax. The main risks occur during the growth phase of the fibers with the process steps: tillage, fertilizer, drilling, weed control, plant growth, desiccation, harvest rippling, retting, decortication, hackling, carding, and spinning [70]. These mainly natural growing (production) steps which are taking place outside a classical production surrounding are running with a lots of coincidental weather parameters like amount of rain, humidity, sunshine duration, and temperature [71]. The year-dependent combination of these parameters during the growing (production) process and differences between locations leads to an alternate product quality from season to season or from one growth location to another one. This fact is one of the most important drivers for (technological) variability of green composites and has a huge impact on composite/part production phase. As shown in Table 10.1, a wide range of each of the mechanical properties is significant for natural fibers, especially for flax. For minimizing this effect, a mixing of raw materials from several regions and production years, aiming to achieve a stable average stiffness and strength values, mainly in serial production environment must be achieved. This is sometimes a recommendable practice to reduce the high variation of mechanical properties, but there is no guarantee of the aimed stability of properties. Compared to classical composites made out of chemical fibers, there are, consequently, considerable differences having a not negligible effect on the design process of parts made out of green composites. One effect of the mechanical properties uncertainty is reflected in dimensioning of components. So, the engineer has to calculate with the lowest available strength and stiffness values for being sure the product with natural fibers will not fail under the assumed boundary conditions. Hence, green compositesebased products tend to be oversized, too heavy, or too stiff [72]. Further risks are caused by different weather conditions during the growth season leading to a seasonal variability of availability and in worst-case scenarios to crop failures. If there is a year with disadvantageous growing conditions, the harvest of the raw materials is less and as a consequence prices for fiber-materials are higher. Besides, considerable risks also exist in the Composite/Part Production Phase. One important type of such risk has its origin in the material production phase. Up to now there are hardly available certifications like ISO 9001 for the

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growing process of natural fibers. These certificates start mostly at the further technical processing after the flax fiber has finished its growth phase. With the beginning of the harvesting a classical parameter-driven, human-influenced process starts, for which certificates like ISO 9001 are available. The lack of normed processes in the important growth phase in combination with coincidental weather parameters within this phase leads to a process risk, since the range of the parameters of the mechanical properties of the fibers is very wide. Additionally, there are a lot of new upcoming processes and technologies which shall improve the stability of the processing as well as the quality of the semi-finished products. Therefore, there is also a huge variability referring to processes and technologies causing real-world risks. In the Use Phase, one important technical risk is the flammability of natural fibers. Apart from mechanical properties, the flammability characteristics can restrict the field of application. Studies about composites made of polypropylene (PP) and natural fibers revealed that the thermal decomposition of these materials is different to PP alone. Containing flax fibers with more than 30% fiber content, the ignition starts much earlier while the process of combustion is running at a lower level of heat release rates and mass loss rate than pure PP [73]. Flammability is an important point, not only in architecture. In the course of electromobility with lithium-ion-battery systems the fire protection of passenger compartment becomes increasingly important. Based on the high electrical power, these batteries are a dangerous fire source. But there is the ability to treat green composites with fire retardants like special fiber coatings or non-flammable binders or resins to widen the range of applications. In the End-of-Life (EOL) Phase, recyclability is an important point and critical risk of products made by green composites. Some studies run by the German automobilist BMW Group showed that the recycling of plastics reinforced by natural fibers is not useful. The required amount of energy makes the processes too expensive and environmentally unfriendly with the result that only an energetic process like burning the material for energy production is a meaningful recycling of green composites [74].

10.4.2 Management of real-world risks The management of real-world risks arising from the usage of green composites can principally follow the risk management process outlined in Section 10.3.2. In the first step, real-world risks-related targets have to be formulated. On the one hand, this includes the willingness to accept and the preference to avoid or limit risks of a specific type to a specific degree. On the other hand, the ecological targets and the corresponding effects might be weighted against the economic consequences of risks as well as the measures of managing them. For the identification of risks in the second step, the structuring described in Section 10.4.1 seems to be useful. Furthermore, expert interviews or other

242 PART | IV Life cycle assessment and risk analysis

typical methods of risk identification such as checklists, inspections, inputoutput analysis, FTA (Fault Tree Analysis), FMEA (Failure Mode and Effects-Analysis), etc., can be applied. The analysis of cause-effect relationships should try to reveal the sources of the risks and their different effects along their way to specific threats of environmental burdensdit can be supported by input-output analysis, FTA, FMEA, and system analysis. The final assessment of the risks should consider their probability and the impact caused by themdthey both determine their relevance and the necessity of counteracting. Besides portfolio methods, especially scenario analysis, Monte Carlo method, and sensitivity analysis can be used for this. The application of the three last mentioned methods implies the repeated conduction of LCA. It has to be “modeled” how the risk (source) changes the input data of LCA and then the results of LCA have to be recalculated. The effect of the risk is reflected by the deviation between the initial and the new results (assumed that the risk has not been included in the initial calculation). Afterwards, adequate measures for systematically influencing the identified relevant risks have to be found. The appropriateness of measures largely depends on the risk source and its effects. In the context of ecological risks, primarily measures for reducing the probability of the entrance of such risks (and their sources) seem to be useful. They can comprise collecting more and better data for decreasing uncertainty, reducing variability by more standardization of fibers, composites, components, and products and their properties, as well as the life cycleewide processes concerned with them, avoiding failures by better quality management along the supply chain, and improving the process technologies, for example, toward a “stable” processing of fibers and green composites with a specific range of properties (this might also be understood as a measure to handle the risk caused by the variability of such properties). The assessing and systematical selection of risk measures is a challenging task. In general, the positive effects (reduction of entrance probability and/or effects) and the negative effects (additional environmental burdens, costs) have to be compared. Besides the normal difficulties of conducting an LCA (reflected by the modeling risks addressed in Section 10.3), on the one hand this evaluation and decision-making is characterized by an exceptional amount of uncertainty: The entrance of a risk is always uncertain. Furthermore, effects of a risk as well as the effects of counteracting measures are typically uncertain as well. A simple way to generate a result that can be easily interpreted is the use of the expected values of all data and results. On the other hand, at this point economic consequences are typically relevant as well. Risk measures will cause costs, however, they might also reduce not only the (expected) environmental effects but also generate (expected) positive economic effects (since the entrance of risks in some cases will also induce negative economic effects). Thus, the evaluation and decision-making have to consider both target dimensions (by stating target preferences, formulating a budget for risk measures, using multi-criteria decision methods, etc. [2]).

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10.5 Example from the Automotive Industry The example selected to illustrate the LCA related risks refers to a golf buggy bonnet. This is a very simple example but it illustrates the risks and risk-causing uncertainties in a very descriptive way. A buggy bonnet is usually made of composite material, obtained by the wet lay-up process of glass fiber embedded in epoxy resin. There is a published study, from (amongst others) one of the authors of this chapter, where this component is analyzed for several composite materials, namely for several kinds of fibers (glass fibers, carbon fibers, ramie, and jute) as to understand the influence of using natural fibers in this kind of products regarding their economic and environment performance [75]. The scope of the LCA study was the comparison of the environmental impact of the bonnet composite alternatives. A cradle to grave approach including life cycle phases from raw material acquisition (that includes raw material extraction, production, and transport) to bonnet end-of-life was considered. During the building-up of the LCI some decisions were taken involving considerable uncertainties. The first one was related to the design specificationsdthe required bonnet dimensions for each alternative had to be estimated and determined. The requirements were to support a uniform load pressure of 800 N applied over a circular area of radius 200 mm (simulating an average man’s weight at the center of the bonnet). Finite elements analysis was used having mechanical properties of the fibers and resin as inputs (Table 10.4). In this task, the authors of the study were confronted with a wide range of mechanical properties of the natural fibers, ramie, and jute in this case. The values selected within those ranges to apply the finite elements analysis were based on literature and own considerations but introduced uncertainty in the final mass, thickness, and displacement calculation mainly for these two alternatives. Another source of uncertainty was the input of the type of transport and origin of the fibers. The type of transport selected was the most common one for these type of fibers, truck within Europe and cargo ship between continents. The natural fibers origin locations are very different, that is, ramie is produced in China, India, Indonesia, and Brazil. The region producing most quantities of a fiber was selected as the original location of that kind of fiber (Table 10.4). Furthermore, still in the LCI stage, a few decisions have been taken for sake of comparability regarding the bonnet manufacturing process. The resin-transfer molding (RTM) process was considered since it allows a good surface finishing. A plain woven fabric of each fiber type is required to realize RTM. This kind of fabric is commercially available for glass and carbon fibers; nevertheless for jute and ramie there are only a few suppliers with very different specifications. So, the study authors had to decide which concrete fabric to consider using the available limited information. Another source of uncertainty was related with the decision of how to include the use phase. There was no published information about the average distance

Glass fiber

Carbon T300

Ramie

Jute

Unsaturated polyester

(Fiber) Properties 3

Density (kg/m )

2600

1760

1530

1400

1200

Young’s modulus (GPa)

69

230

65

31

2.8

Tensile strength (MPa)

2750

3530

800

500

65

Design specifications of alternatives (resin þ fiber) Weight (kg)

2.2

1.55

1.94

2.12

Fiber volume (%)

21.0

19.9

35.7

39.0

Thickness (mm)

4.4

3.3

4.4

4.95

Displacement (mm)

22.62

21.59

15.99

15.84

Germany

China

China

Location Origin of material

Portugal

Bonnet production

Portugal

Portugal

Adapted from Carvalho H, Raposo A, Ribeiro I, Pec¸as P, Silva A, Henriques E. Influence of the use of natural fibers in composite materials assessed on a life cycle perspective. In Thakur VK, Thakur MK, Kessler MR, editors. Handbook of composites from renewable materials. Scrivener Publishing LLC;2017. p. 377e398.

244 PART | IV Life cycle assessment and risk analysis

TABLE 10.4 Properties considered for the alternative fibers (and resin) and resulting design specifications for each bonnet composite alternative (identified by the type of fiber used) after finite element analysis. Information regarding fibers’ origin is also included

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covered per year (and even per life) of a golf buggy. This distance was estimated by a few visits to golf yards organizations, by interviewing experts and buggy maintenance records analysis. Again, using the same covered distance for every alternative was considered a robust study decision, but a sensitivity analysis to this parameter had to be carried out to understand its effectdit was found that this parameter does not have a significant influence for comparison purposes. Besides the uncertainty related with average covered distance per year, there was also another uncertainty related with fuel consumption. A direct relation between the vehicle weight and the fuel consumption was assumed to be a good way to handle the lack of data. So, for the LCI phase modeling risks were related with parameters, modeling, and decision uncertainty. Variability was also relevant since the fibers’ mechanical properties are not steady from batch to batch as mentioned before. For the LCIA stage, the uncertainties involved in the study were mainly related with the data sets and methods used. It was decided to use the ReCiPe database and the midpoint and endpoint analyses with hierarchist quantification because relevant interdependencies among the several impact groups were assumed to exist. The existent data sets of ReCiPe were processed using SimaPro software. Yet, no dataset was available for ramie fiber. So, it was decided to base the ramie environmental impact analysis on the jute processes, changing a few aspects like eliminating harvesting and postprocessing phases that ramie does not require and adapt cropping time (information available in the referred publications). This was considered the most reliable way to do the intended comparison, but caused additional uncertainty of the results. Therefore, the LCIA modeling risks are primarily caused by decision uncertainties as regards the quantifications methods selected and parameter uncertainty as regards the build-up of the ramie fiber structure inside SimaPro based on jute fiber. The interpretation stage was a challenge regarding the results analysis (Table 10.5). The carbon fiber alternative was the one with the best score mainly because of its performance in the use phasedlighter bonnet, meaning less fuel consumed (the use phase causes around 60% of the life cycle environmental impact). For the other life cycle phases, the differences between alternatives are only considerable for material acquisition, where ramie has the best score and carbon fiber the worst, but this phase accounts only for 15% e20% of the life cycle impact. Applying sensitivity analysis to the use phase, varying the covered distance per year, it was possible to observe that if the covered distance per year is lower than 50% of the distance considered (300 km per year were considered as baseline), the ramie fiber alternative causes lower environmental impact than the carbon fiber alternative. In fact, depending on the golf yard size and level of use, this distance varies significantly having a significant influence on the results. To deal with the modeling risks present in this phase, the sensitivity analysis was used as countermeasure.

246 PART | IV Life cycle assessment and risk analysis

TABLE 10.5 Environmental impact results (hierarchist endpoint, ReCiPe Method) for 600 units/year of the four bonnet composite alternatives (Identified by the type of fiber used) Glass fiber

Carbon T300

Ramie

Raw material þ Material production þ Transport

1.08

1.26

0.81

0.86

Manufacturing phase

0.75

0.70

0.73

0.74

Disposal scrap

0.004

0.002

0.0041

0.005

Use phase

4.75

3.35

4.19

4.58

End of life

0.07

0.04

0.06

0.07

Total

6.67

5.37

5.80

6.27

Human health

16.9%

22.3%

18.2%

18.1%

Ecosystems

12.2%

12.4%

13.4%

13.3%

Resources

70.9%

65.3%

68.4%

69.6%

Jute

Life cycle phases

Damage categories

Adopted by Carvalho et al. [76].

Summarizing, it is obvious that a couple of modeling risks (caused by parameters, modeling, and decision uncertainties) as well as real-world risks (caused by variabilities) do exist. A couple of modeling-related decisions under uncertainty and corresponding assumptions had to be made to allow the research work to be carried out. Due to restricted time and resources, only an intense data collection and some sensitivity analyses were performed (e.g., for the distance covered) in order to handle the risks caused by these uncertainties. A deeper analysis is subject of future work.

10.6 Conclusion Green composites are a promising alternative showing high potential for an environmental-friendly and sustainable usage in products such as automobiles. However, to enable well-informed decisions about their design, to reveal and prove their advantages, and to justify their usage, a significant LCA should be performed. This is a considerable challenge due to the manifold real-world risks of green composites as well as modeling risks coupled with a risksensitive LCA of them. Against this background, the paper characterizes natural fibers as well as green composites, and gives a survey on the existing

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LCA studies on green composites. Furthermore, relevant modeling risks and the underlying uncertainties, as well as real-world risks, are structured and described, and risk management approaches for handling them are suggested. A case from automotive industry is used for demonstration. Besides these results, the work on the topic revealed a strong need for further work concerning: l

l

l

l

LCA studies on green composites: The existing studies (see Section 10.2.3) present only a small “patchwork” image of the environmental burdens of different types of green composites. Modeling risks and their management: Amongst others, the knowledge and databases of green composites and their environmental burdens should be improved in terms of quantity (completeness) as well as quality (accuracy, reliability, transparency, etc.). Real-world risks and their management: One major concern is the improvement and standardization of life cycle-wide processes, which should go along with a (far-reaching) standardization of the properties of fibers, composites, and the resulting products. Integration of ecological and economic analyses: Integrated ecological and economic studies (combining LCA with life cycle costing), are necessary or at least favorable at two levels: on the one hand, for the evaluation of design and process alternatives for green compositesdthe choice between green and other composites as well as different types of green composites should consider both target dimensions [76]. On the other hand, for the selection of measures of risk managementdthe measures intended to reduce modeling and real-world risks will typically cause additional costs and thereby reduce profit so that both target dimensions are concerned.

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Chapter 11

Ramie and jute as natural fibers in a composite partda life cycle engineering comparison with an aluminum part P. Pec¸as1, I. Ribeiro1, H. Carvalho1, A. Silva2, H.M. Salman1, E. Henriques1 1 IDMEC, Instituto Superior Te´cnico, Universidade de Lisboa, Lisbon, Portugal; 2Singapore University of Technology and Design, Engineering Product Development Pillar, Singapore

Chapter Outline 11.1 Introduction 11.1.1 The need to be greener 11.1.2 Motivation and contribution 11.2 Background 11.2.1 Natural fibers and green composites 11.2.2 Industrial applications of natural fibers 11.2.3 Life cycle analysis and case studies from literature 11.3 Bonnet case study 11.3.1 Means and methods 11.3.2 Materials and assumptions 11.3.3 Requirements and FEM analysis

254 254 254 255 255 260

262 267 268 268 270

11.4 Life cycle studies of different alternatives 11.4.1 Raw material and transport 11.4.1.1 Environmental impact of ramie 11.4.2 Manufacturing phase 11.4.3 Use phase 11.4.4 End-of-life phase 11.4.5 Overall environmental impact and costs during whole life cycle 11.5 Life cycle engineering and CLUBE analysis 11.5.1 CLUBE analysis 11.6 Conclusions and outlook References

Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00011-2 Copyright © 2019 Elsevier Ltd. All rights reserved.

271 272

272 274 274 275

275 276 277 279 280

253

254 PART | IV Life cycle assessment and risk analysis

11.1 Introduction 11.1.1 The need to be greener The human life style in the 21st century is heavily dependent upon petroleumbased products ranging from clothes, food, and houses to electronic gadgets and transportation vehicles such as cars, buses, and airplanes. This dependency has been increasing continuously after the commercial production of petroleum during the middle of 20th century, which is leading toward the inevitable issues of resource depletion, waste generation, and environmental degradation. Plastic waste is continuously growing, and waste disposal and recycling are simply not enough to manage this tremendous amount of waste [1]. These increasing issues of global waste generation and environmental degradation, along with the increasing awareness in the society and stringent environmental regulations, are forcing the industries and academic research institutions to explore and discover new materials and technologies which are socially, economically, and environmentally more sustainable or greener compared to the conventional materials and technologies. Now, the industries need to consider the environmental impacts of their products at all stages of their lives spanning from material extraction to the end of life (EOL) of the products. Therefore, to find greener alternatives to conventional materials and technologies, the industries and research institutions are turning toward nature, and remarkable examples of such materials are natural fibers and biopolymers which make it possible to produce fully green composites that could play a positive role in this new paradigm shift of manufacturing eco-friendly products [2]. There were many authors who qualitatively pointed out the benefits of using natural fiberebased composites in several applications without performing any quantitative analyses [3e9]. However, as a result of the literature review it was observed that no work was found on ramie, evaluating its environmental impacts during all of its life cycle phases. Additionally, there was also no document found in literature on life cycle cost (LCC) analysis of bio, green, or natural fiberebased composites. Furthermore, no integrated analysis was found on LCC and life cycle analysis (LCA) of ramie fiber and its composites. These are the major gaps in the field of green composites, and it could be interesting as well as challenging to work on these research gaps. Therefore, a case study is presented in Section 11.3 in which the bonnet of a buggy was produced with ramie along with four other alternatives and a cradle-to-grave LCA was performed on the bonnet component covering raw material, transport, manufacturing, use, and EOL phases.

11.1.2 Motivation and contribution The aim of the study is to analyze the environmental and economic impacts of using natural fibers in fiber-reinforced compositeebased products from a life cycle perspective. Two commercially available natural fibers, jute and ramie,

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are compared with other common synthetic fibers, carbon fibers, and glassfibers. In addition, a noncomposite component alternative, aluminum bonnet obtained by stamping, was included in the study for the sake of understanding the comparative position of the natural fiber composites. Wide comparison boundaries were used to analyze the life cycle phases comprehensively covering material production, component manufacturing, use, and end-of-life phases. The transportation impact was also considered because the several fibers and other materials are produced in several regions of the planet. The economic and environmental impacts assessment is done for each life cycle phase and for the total life cycle using golf’s car bonnet as a case study. This component is usually manufactured using resin transfer molding (RTM) process to produce a composite material composed of glass-fibers embedded in epoxy resin. So, the same manufacturing process, and resin type, was considered for the other fiber alternative components under study. The baseline for the study was the glass-fiber composite component regarding its mechanical behavior, namely the required supporting load and maximum allowed deformation. Using finite elements analysis, the required number of layers and thickness were derived. This result is used as input to calculate the material and other resources consumed and disposed, as well as the required process time and transport load. The Life Cycle Engineering (LCE) approach was used to allow an integrated performance analysis [10,11]. The functional or technical performance equivalence is assured by the calculation of the required dimensions for each alternative derived from the finite element analysis. The economic and environmental analyses were done dividing the total life cycle in the upstream phases (material and component manufacturing phases) and in the downstream phases (use and EOL phases). In fact, the stakeholders involved in the upstream phases are different from the one in the downstream phases, meaning that analyzing separately these two moments of life cycle impact allows for a more informed comparison and decision-making process when selecting a material. An LCE realm approach published by [12] was used to develop a CLUBE model for the best alternative mapping. The outcome of the study aims to contribute new knowledge regarding the potential use of natural fibers and to identify aspects requiring further research, as well as further industrial development.

11.2 Background 11.2.1 Natural fibers and green composites Nature is abundant with many different types of natural fibers obtained from plants, animals, and minerals such as hemp, flax, sisal, ramie, jute, bamboo, coir, and many others as presented in Fig. 11.1.

Animal

Plant

Mineral

Wool/hair

Silk

Seed

Fruit

Bast or stem

Leaf or hard

Wood

Stalk /husk/hull

Cane/grass/ reed fibers

Asbestos

Lamb's wool

Tussah silk

Cotton

Coir

Flax

Pineapple

Yellow birch

Wheat , rice & rye husk

Bamboo

Wollastonite

Goat hair

Mulberry Silk

Kapok

Coconut

Hemp

Abaca

Eucalyptus

Olive , almond & areca husk

Bagasse

Fibrous brucites

Angora wool

Coarse Silk

Milkweed

Oil palm

Jute

Henequen

Pine

Barley

Esparto

Ramie

Sisal

Spruce

Oat

Sabei

Yak

Kenaf

Agave

Maize

Phragmites

Horse hair

Nettle

Banana

Palm kernel shell

Communis

Camel hair

Kudzu

Bromelia

Hazelnut shell

Wildcane

Rabbit hair

Okra

Cocos

Sunflower hull

Rattan

Curaua

Soy hull

Cashmere

Akon

Sponge gourd

FIGURE 11.1 Classification of natural fibers [3,6,13,14].

256 PART | IV Life cycle assessment and risk analysis

Natural Fibers

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Taking advantage of the potential benefits of the natural fibers, there are many industrial sectors such as construction, packaging, automotive, fabrics, toys, electronics, sports, biomedical applications, and furniture which are using natural fibers, and this trend will grow significantly in the coming years [5,15]. In this section an overview of the characteristics and performance of natural fibersebased green composites is presented with a special attention to its applications in the automotive industry. Natural fibers offer a wide range of benefits in terms of cost, environment, mechanical, and chemical characteristics. The mechanical properties of some of the most common natural fibers are presented in Table 11.3 and advantages and disadvantages in Tables 11.1e11.2, respectively.

TABLE 11.1 Advantages of natural fibers Advantages

References

Lower environmental impact

[3,15e25]

Lower emissions

[2,5,7,15,18,19,21e26]

Lower weight

[2,3,5,7,8,18,20,22,24,27e31]

Lower CED and energy consumption

[2,15e18,22,24,26]

Lower cost

[2,3,7,8,19,24,27,29]

Reduced dependence on NRER

[3,8,18,21,23,28,30,32]

Recyclability

[3,7,8,15,17,21,27,29,33]

EOL biodegradability

[3,5,8,28,29,31]

TABLE 11.2 Disadvantages or limitations of natural fibers Disadvantages

References

High variability in quality

[2,4,6e8,27]

Increased local eutrophication

[17,18,21,25,34,35]

Moisture absorption

[2,5,7,8,31]

Limited processing temperature

[27,30]

Poor fire resistance

[2,7]

Inferior mechanical properties

[2,3,27,28,31]

Lack of interfacial adhesion

[2,7,30]

Higher ecological footprint in terms of land use

[15,17,23]

Fibers

Density (g/cm3)

Elongation at break (%)

Fracture stress (MPa)

Young’s modulus (GPa)

Moisture absorption (%)

References

E-glass

2.5e2.55

2.5.3.0

e

70e73

0

[27,36]

Carbon

1.4

1.4e1.8

e

230e240

e

[37]

Cotton

1.5

7.0e8.0

287e597

5.5e12.6

8e25

[37]

Bamboo

0.8

2.5e3.7

391e1000

48e89

e

[5]

Soft wood

0.3e0.59

e

45.5e111.7

3.6e14.3

e

[6]

Flax

1.4e1.5

2.7e3.2

345e1500

10e80

7

[36]

Hemp

1.48

1.6

270e900

20e70

8

[36]

Jute

1.3e1.46

1.5e1.8

393e800

10e30

12

[36]

Ramie

1.5

3.6e3.8

400e938

44e128

12e17

[36]

Sisal

1.2e1.5

2.0e2.5

511e700

3.0e9.8

11

[36]

Coir

1.15e1.25

15e40

e

4e6

10

[36]

Curaua´

1.4

3.7e4.3

e

11.8

e

[25,27]

258 PART | IV Life cycle assessment and risk analysis

TABLE 11.3 Comparison of mechanical properties of common natural fibers with E-glass and carbon fiber

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However, the use of natural fibers in industrial applications is not without issues. The technical and social issues of natural fibers in the particular case of the automotive industry in South America were discussed by Lea˜o, Sartor, and Caraschi (2006). Many disadvantages or limitations of natural fibers are listed in the following table from literature. Natural fiberebased biocomposites, like the conventional composites, consist of two distinct constituents: a reinforcing fiber and a matrix polymer, which when combined together result in a new material with completely different mechanical and chemical properties than the parent individual components. However, the properties of this “new” composite material strongly depend upon the properties of natural fiber or conventional fiber and polymer matrix which were used to produce the composite material. Thus, careful selection of the reinforcing fibers and matrix polymers is crucial in obtaining a composite with the desired properties for a specific application. Additionally, the behavior of green composites can be controlled by changing the factors that control its properties, such as fiber architecture, fiber and matrix interface, fiber angle, etc. [38]. A method has been proposed by Koronis, Silva, and Fontul (2013) [38a], with a specific example for automotive applications that enable a designer to select the appropriate combination of fiber and matrix. In addition, the same authors pointed to ramie as one of the most promising natural fibers currently in the market, and in another study also investigated environmental stability of ramie fiber (Koronis, Silva, & Soares Dias, 2015). In the literature, natural fiberebased composites are discussed with many different names such as natural fiberereinforced composites, biocomposites, green composites (partially or fully green), bio-based composites, etc. However, in this chapter, the terms biocomposites or green composites will be used alternatively. Natural fiberereinforced composites are obtained by incorporating natural fiber reinforcements from fibers such as kenaf, flax, hemp, ramie, jute, coir, or cotton into a polymer matrix obtained from renewable or nonrenewable resources. If both of the constituents of the composites are obtained from renewable resources, then they are termed as full green composites. In the case when one of the constituents, that is, either reinforcement or the matrix is not obtained from a renewable resource then they are referred to as partially green composites as shown in Fig. 11.2. In terms of production, generally, natural fiberereinforced composite production technologies are similar to those of glass fiberereinforced composites [1]. However, during processing, the natural fibers should not be exposed to high temperature for long durations to avoid destruction of the fibers. The various technologies that could be used for manufacturing these composites include injection molding, thermoforming, compression molding, extrusion, RTM, and sheet molding [1]. Particularly, compression molding is used for the production of extensive, lightweight, and high class interior parts in medium and luxury cars for its cost-effectiveness, suitability for light construction, good crash resistance, and deformation properties. Ford Motor

260 PART | IV Life cycle assessment and risk analysis

Biocomposite Partially green Fully green Either reinforcement or matrix is obtained from a nonrenewable resource and vice versa. Example: flax and PP

Reinforcement and matrix are obtained from renewable resources. Example: flax and PLA

FIGURE 11.2 Green and partially green composites. Adapted from Witayakran S, Smitthipong W, Wangpradid R, Chollakup R, Clouston PL. Natural fiber composites: review of recent automotive trends. In Reference module in materials science and materials engineering. 2017. http:// doi.org/10.1016/B978-0-12-803581-8.04180-1.

Company is exploring the feasibility of sheet molding compounding (SMC) as a potential procedure for manufacturing natural fiberereinforced auto parts [4]. Daimler Chrysler developed express processing methodology for production of flax fiberereinforced polypropylene (PP) composites for interior auto parts [4].

11.2.2 Industrial applications of natural fibers The use of natural fibers is not new in the automotive industry. Henry Ford, in 1908, used hemp fiber in Ford Model-T, to line the side panels which resulted in improvement of impact strength, and the side panel was 10 times stronger than steel panels [2]. But after exploration and production of petroleum, the petroleum-based synthetic fibers obtained more attention because of lower prices and better mechanical characteristics. According to the statistics from [39], the total world production of plastics was 322 million tonnes in 2015 with 58 million tonnes produced in Europe (Fig. 11.3). Moreover, in 2015, the total demand of plastics in Europe was 49 million tonnes with a highest share in packaging sector, followed by the building and construction, automotive, electronics, and agriculture. Additionally, 70% of this demand was concentrated in six European countries with highest demand in Germany followed by Italy, France, Spain, UK, and Poland; China was the largest producer of plastics in the world in 2015 [39]. Despite this scenario, the more stringent environmental regulations in Europe compared to the rest of the world, may represent a window of opportunity for growing application of natural fibers in automotive, packaging, and building and construction sectors in Europe. For instance, in the 2000/53/EC directive, the European community requests member countries to reuse and recover at least 95% of all of EOL vehicles by 2015 [7], which could be possible by the use of biodegradable and compostable natural fiberebased composites. As a result of this directive, stringent

Ramie and jute as natural fibers in a composite part Chapter | 11

261

39.90 22.40

19.70

er s

g

th O

ag ck Pa

tru ns &

co

Au

in

n ct

iv ot to

m

tro ec el l&

g

ca

Bu

ild

in

tri ec El

io

e

cs ni

re tu ul ric Ag

8.90

5.80

3.30

FIGURE 11.3 Plastics demand in Europe by sectors in percentages with total demand of 49 million tonnes in 2015. Adapted from data available in PlasticsEurope. Plastics - the facts; 2016. Retrieved from http://www.plasticseurope.org/documents/document/20161014113313-plastics_the_ facts_2016_final_version.pdf.

environmental regulations, and growing social awareness about this topic, the application of natural fiberereinforced composites is increasing tremendously in the automobile sector with an annual growth rate of above 20% [25]. Several major reports and journal papers have been published about natural fibers and biocomposites. Of these, the report from the UK Knowledge Transfer Network initiative on Materials [25a] and the review papers on natural fiber composites from Fuqua et al. [6] and Thakur et al. [6a] stand as important literature for anyone interested in this topic. Environmental friendliness does not come without a cost, however. The very same characteristics that make green composites very appealing are the same that make them biodegradable; and as much as this may seem interesting, it brings some issues and concerns to the equation when designing with these materials. One of these concerns is the environmental stability of these composites, which most of the times requires special pre- and postmanufacturing treatments. A more recent and comprehensive review of the state-of-the-art in biocomposites was presented by Gurunathan, Mohanty, and Nayak (2015) [6b]. Automotive industry is one of the industrial sectors taking advantage of the use of natural fibers from a very long time; nevertheless, only in the last 10 years its share has been increasing significantly. Natural fibers are a promising way of achieving weight reduction in cars and nearly 75% of fuel consumption is directly related with the vehicle weight [4]. Several automotive components are being manufactured using natural fibers as presented in Table 11.4 [24,40,41].

262 PART | IV Life cycle assessment and risk analysis

TABLE 11.4 Application of natural fiberebased composites in automotive industry. References

Natural fibers used

Parts produced

[24]

Hemp fiber

Interior side panel

[20]

Flax fiber

Under-engine panels

[25]

Curaua fiber

e

[40]

Hemp fiber

Casing component of bus front headliner

[15]

Hemp fiber

Interior side door panel

[32]

Kenaf fiber

e

[21]

Flax fiber

Panels

[17]

Flax, hemp, and jute fibers

Car interior and side door

[19]

Cotton, jute, and kenaf fibers

Plastic pallet

[26]

e

Car engine beauty cover

[22]

Hemp fiber

Auto insulation panel

[16]

China reed fiber

Transport pallets

[41]

Sugarcane bagasse

Internal car panels

[42]

Cotton fiber

Automotive panels

[43]

Ramie and kenaf fibers

A composite part for automotive headliner

The following chart shows the share of different types of natural fibers being used in automotive industry in Europe with largest share of wood fiber followed by cotton, flax, kenaf, and other fibers, mainly jute, coir, sisal, and abaca fibers. The total volume of fibers used in automotive industry was 80,000 tonnes in 2012 [1].

11.2.3 Life cycle analysis and case studies from literature It has been claimed by many authors in the literature that natural fiberebased biocomposites are more environment friendly than their conventional counterparts [15,16,18,20,22,24]. Nevertheless it is essential to examine in detail and accurately the environmental performance of such materials as only the fact that they are obtained from natural resources does not essentially mean that they have lower environmental impact than existing materials. Life cycle

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37% 24% 19% 8% 5% Wood

Cotton

Flax

Kenaf

Hemp

7%

Others

FIGURE 11.4 Natural fibers in EU automotive industry. Adapted from Witayakran S, Smitthipong W, Wangpradid R, Chollakup R, Clouston PL. Natural fiber composites: review of recent automotive trends. In Reference Module in materials Science and materials engineering. 2017. http://doi.org/10.1016/B978-0-12-803581-8.04180-1.

analysis (LCA) is the most recommended tool for this comprehensive and life cycle base analysis [19]. Accordingly, this subsection is dedicated to discuss the several studies published involving the application of LCA to assess the performance of natural fibers. LCA is an environmental assessment method which considers the entire life cycle of a product from raw material extraction and acquisition, manufacturing, and use phase to end of life of products. It involves collecting information about the inputs and outputs of all life cycle phases, such as emissions, waste, and resources consumed by the processes and product (life cycle inventory). After this inventory, the physical quantities of resources consumed are translated to environmental impact factors such climate change potential, eutrophication potential, acidification potential, and human and ecosystem toxicity using different assessment methodologies [15,19,20]. These impact factors could be aggregated into a single eco-score by using any method such as ReCiPe Endpoint which allows the assessment of three damage assessment categories: human health, ecosystem quality, and resources and then adding them to obtain a single score in points per functional unit [27]. The details about material and energy flows, emissions, and manufacturing processes could vary depending upon the specific application which should be modeled over all the stages of a product for a comprehensive LCA [18]. LCA has been standardized up to a certain extent by the International Organization for Standardization (ISO) although these guidelines can be interpreted and selected individually by the LCA user/developer depending upon a specific product or system. As a result, the comparison of results from different studies may not be possible because of methodological differences such as functional unit definition, allocation method, impact assessment methodology, and inventory data used [44]. Although the concept of the LCA

264 PART | IV Life cycle assessment and risk analysis

is simple, the analysis is rather complex mainly because of the difficulty in establishing the correct system boundaries, obtaining accurate data, and interpreting the results correctly [45]. There are many different types of impact factors for LCA studies such as Acidification Potential (AP), Aquatic Toxicity Potential (AqTP), Cumulative Energy Demand (CED), Eutrophication Potential (EP), Freshwater Aquatic Ecotoxicity Potential (FAETP), Global Warming Potential (GWP), Human Toxicity Potential (HTP), Land Occupation (LO), Marine Aquatic Ecotoxicity Potential (MAETP), Nonrenewable/Abiotic Resource Depletion Potential (NRADP), Ozone Depletion Potential (ODP), Photochemical Oxidants Creation Potential (POCP), Terrestrial Ecotoxicity Potential (TETP). However, for a comprehensive LCA a minimum of eight Environmental Impact Classification Factors (EICF) should be considered as outlined in ISO/TR 14047/ 2003, namely AP, AqTP, HTP, EP, GWP, NRADP, ODP, and POCP. A key issue in LCA is a well-defined goal and scope with clear allocation of the inputs and outputs because the waste streams from one industry could be used as raw materials for other industries; for instance, the waste streams of agricultural systems could be used a raw material for many other industries such as paper production, power generation, natural fiber production, etc. [45]. Life cycle of fully green composites is shown in Fig. 11.5. Initially the crop is produced and natural fibers and biopolymers are obtained from the crops which are then used to make green composites. These green composites are

Fully green composites from natural fibers and biopolymers or bioplastic

Crop production

Biopolymer production

Natural fiber extraction

Biocomposite production

Part manufacturing Part use End of life (EOL) FIGURE 11.5 Life cycle of fully green composites. Adapted from Mohanty, AK, Manjusri Misra, LTD. Natural fibers, biopolymers, and biocomposites. (L. T. D. Mohanty AK, Misra M, Ed.). Taylor & Francis Group; 2005.

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utilized in different products aiming to obtain an environmental friendly product. Good environmental performance of these products is expected because the green composites are biodegradable and compostable which at the EOL of the product again become part of soil or ecosystem without producing any significant impacts on the environment in comparison to conventional plastic-based products [14]. The products made from natural fibers can be incinerated or composted after their end of life and hence they do not result in net addition of CO2 emissions into the atmosphere because of the fact that the plants from which natural fibers were obtained normally absorb atmospheric CO2 during their production phase. Therefore, the amount of CO2 released into the atmosphere during burning process is negligible in comparison to the amount of CO2 absorbed by the plant during its production phase resulting in a very favorable carbon balance [46]. Further on, some of the results of LCA studies are presented here from literature review. The environmental impacts analysis of sugarcane bagasseereinforced PP showed that in addition to similar mechanical performance, natural fiberereinforced composites have superior environmental performance in automotive applications. It also reported that the economic utilization of natural fiber composites also holds a great opportunity for social and economic progress in developing countries [41]. Similar behavior was also observed for chemically treated hemp fiber composite [47] and for flax fiberereinforced epoxy rotor blade in comparison to other alternatives of carbon fiberereinforced epoxy rotor blade and glass-fiberereinforced epoxy rotor blade [48]. Additionally, in another LCA case study, three alternatives of acoustic components produced by the Brazilian automotive sector: dual-layer polyurethane panel, recycled textile absorption-barrier-absorption panel, and recycled textile dual-layer (DL) panel were compared considering production, use, and EOL phases [42]. Two EOL scenarios were analyzed: landfill and incineration with energy recovery. For the LCA model, some LCI datasets from Ecoinvent database were adjusted to the Brazilian context. LCA results show that, within the entire life cycle, the DL-cotton option is overall the best alternative from an environmental perspective [42]. Likewise [19] performed an LCA study using a pallet produced from composites based on PP and glass fiber (GF) and biocomposites based on cotton, jute, and kenaf fibers. They concluded that the lowest environmental impact was observed in the case of kenaf and jute fibers. For similar function as of conventional component manufactured by PP and GF, a 30% w/w flax fiber/PP composite is 6% lighter than 30% GF/PP composites and generates 10%e20% lower environmental burdens [20]. The micromechanical analysis, material index selection, and LCA showed that fiber content, Young’s modulus, and aspect ratio have to be maximized to achieve a decrease in environmental footprint of flax/PP biocomposites [20]. In another study, the same authors found that the biocomposites appear to be an attractive alternative to conventional GF/polyester composites. They allow

266 PART | IV Life cycle assessment and risk analysis

reductions in the majority of the environmental impact indicators, such as global warming (
70%), photochemical oxidation (
60%), and human toxicity (
80%). Nevertheless they cause higher local impacts in terms of eutrophication (þ50%) and fresh water toxicity (þ20%) [21]. An LCA study by [32] compared the environmental performance of kenaf fiberereinforced biocomposite (polyhydroxybutyrate/kenaf fiber) to that of GF reinforced composite (PP/GF) for automobile parts. The system boundary in the analysis covered the entire life cycle of kenaf fiberereinforced biocomposite from cradle to grave. Two waste management scenarios, landfill and composting, were considered in the analysis to determine the environmental effects in these two scenarios. The results showed that using kenaf fibere reinforced biocomposite could reduce nonrenewable energy consumption by 23%e24% and greenhouse gas emissions by 6%e16%. However, the kenaf fiberereinforced biocomposite product system produced more local environmental impacts such as photochemical smog formation, acidification, and eutrophication than the GF-reinforced composite product system because of nutrient losses to the environment during biomass production. They observed that only greenhouse gas emissions associated with the kenaf fiberereinforced biocomposite product system are significantly affected by the waste management scenarios [32]. Furthermore, LCAs for two designs of an insulation component in a Ford car: one component made of polymer reinforced by GF, and the other one reinforced by hemp fibers indicated that the natural fibere based component showed less energy demand and lower greenhouse gas (GHG) emissions [22]. Moreover, the life cycle energy consumption and emissions were measured and compared for a 3 wt% GF composite part (3 kg), a 30 wt% cellulose-fiber composite part (2.65 kg), and 40 wt% kenaf fiber composite part (2.79 kg) for seven vehicles ranging from cars, crossovers, and sport utility vehicles [49]. In this study, it was found that the cellulose-based component on average allowed a reduction in life cycle energy by 9.4% and GHG emissions by 18.5% while the kenaf-based composite part reduced energy by 6.1% and GHG by 10.6% compared to the GF composite part. The study results indicate that vehicles with higher fuel consumptions should be targeted for lightweight components in order to achieve higher life cycle energy and GHG emission savings because the use phase dominates over the life cycle of the component [49]. A cradle-to-grave LCA of poly-3-hydroxybutyrateebased composites was performed and compared to commodity petrochemical polymers using a cathode ray tube monitor housing (conventionally produced from high-impact polystyrene) and the internal panels of an average car (conventionally produced from GF/PP). The environmental impact was evaluated on the basis of nonrenewable energy use and global warming potential over a 100-year time horizon. Sugarcane bagasse and nano-scale organophilic montmorillonite were used as PHB fillers. The results obtained show that despite the unsatisfying mechanical properties of PHB composites, depending on the type of filler and

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on the product, it is possible to reach lower environmental impacts than by the use of conventional petrochemical polymers. Sugar cane bagasseebased composites seem to be environmentally superior to clay-based ones [50]. In another study, a bus body component produced by sheet molding compounding from natural fiber (hemp fiber), and a vegetable-based thermoset resin was compared with conventionally produced component made of GF-reinforced polyester. The LCA of these components, considering the production, use, and disposal phases, showed that the natural fiberebased component had significantly lower environment impacts in comparison to the conventional component [40]. The economic and social advantages of applying curaua´ fiber composites in car parts were identified by [25]. They found that besides costing 50% less than GF, the use of curaua´ fibers can promote regional development in the Amazon region and in order to realize significant environmental benefits, the curaua´-based composites would have to be lighter than their GF-based counterparts. The new hybrid materials for engine cover based on cellulose fiber not only perform better in terms of emissions during car operation because of the fuel savings resulting from weight reduction, but that their production and end of life is also environmentally benign [26]. A cost analysis of the two types of engine covers showed that the new hybrid materials are a good substitute for current materials because their manufacture costs are half of that of current materials [26]. In a review study [18], it was proposed that natural fiberereinforced composites are likely to be environmentally superior to GF-reinforced composites in most applications for the following reasons: (1) natural fiber production results in lower environmental impacts compared to GF production (2) natural fiberereinforced composites have higher fiber content for equivalent performance, which reduces the amount of more polluting base polymers (3) lower weight of natural fiberereinforced composites improves fuel efficiency and reduces emissions during the use phase of the component, especially in auto applications and (4) EOL incineration of natural fibers results in energy and carbon credits. They concluded two important remarks in their study. First, the fertilizer use in natural fiber cultivation results in higher nitrate and phosphate emissions, which can contribute to increased eutrophication in local water bodies. Second, the environmental superiority of natural fibere reinforced composites may vanish as their components have significantly lower operating life compared to GF-reinforced components. According to those authors, the future of natural fiberereinforced composites appears to be bright because they are cheaper, lighter, and environmentally superior to GFreinforced composites in general [18].

11.3 Bonnet case study The case study consists in evaluating the use of different materials for a buggy bonnet as shown in Fig. 11.6 based on functional, environmental, and

268 PART | IV Life cycle assessment and risk analysis

FIGURE 11.6 Buggy model with zoom up of bonnet.

economic performances. The materials evaluated comprised of different fiberbased composites and an aluminum alloy. Two of the composites included in this study are made of natural fibers, ramie and jute. Other studies performed similar analyses but comprised different composite configurations and assumptions [18a,b].

11.3.1 Means and methods Initially a 3D model of the bonnet was constructed with a CAD software using the dimensions from [51] and then imported to the ABAQUS 6.14 software to perform numerical analysis. The inputs for FEA are the mechanical properties of the alternatives such as Young’s modulus, Poisson’s ratio, shear modulus, etc., and outputs obtained are the technical performance parameters of the component such as maximum deformation, number of layers, and weight of the component, etc. Other than the technical analysis, life cycle cost (LCC) and LCA are also performed covering the whole life cycle of the component from raw material extraction, transport, manufacturing, and use to the end of life of the product. These analyses are then combined using the life cycle engineering approach and mapped using the CLUBE method [12], which shows the best alternatives for different sets of weights given to each dimension of analysis.

11.3.2 Materials and assumptions The materials considered for this study are GF (baseline material), carbon fiber T300 (CF T300), ramie, jute, and aluminum alloy, and most relevant properties of these alternatives along with resin properties are presented in Table 11.5. The production volume considered is 600 bonnets per year. Regarding the manufacturing processes, the process considered was the production by Resin Transfer Molding (RTM), except for the aluminum bonnet where the process considered was blanking.

Ramie and jute as natural fibers in a composite part Chapter | 11

269

Ramie,jute,CF,GF,aluminum Bonnet case study

Alternative materials

3D model

Input Mechanical properties of material alternatives

Finite element analysis

Transport Raw material

Manufacturing Life cycle Phases

End of life

LCA

LCC

Technical analysis

Use

Maximum deformation, number of layers, weight of component

LCE CLUBE analysis

Results

FIGURE 11.7 Graphical representation of methods and processes used in the case study.

TABLE 11.5 Properties of different alternatives and resin Alternatives Properties

GF

CF T300

Ramie

Jute

Al

Resin

Fiber volume [%]

21

19.9

35.7

39

e

e

Fiber mass [%]

36.5

26.8

41.4

42.7

e

e

Grammage [g/m ]

300

193

300

300

e

e

Young’s modulus [GPa]

69

230

65

31.31

74

2.8

Poisson ratio

0.25

0.2

0.3

0.38

0.33

0.4

Density [kg/m ]

2600

1760

1530

1400

2750

1.200

Filament diameter [mm]

20

7

65.3

17.5

e

e

Lamina thickness [mm]

0.55

0.55

0.55

0.55

e

e

Tensile strength [MPa]

2750

3530

800

500

e

65

2

3

For materials comparison some assumptions were considered. It was assumed that the factor of safety must be higher than one for all alternatives to avoid failure in comparison to the baseline scenario. Also, the same ply thickness is considered for all alternatives. The structural analyses for the several materials must present the same deformation or lower than that obtained with the baseline material. For some material alternatives, the model may require more or less layers than the baseline material model, in order to satisfy the last assumption, that is, number of layers. Since no unidirectional

270 PART | IV Life cycle assessment and risk analysis

fabrics are available commercially for natural fibers like ramie and jute, a balanced plain weave was used in this case study. Moreover, the fiber volume depends upon the manufacturing process and the fiber reinforced form. Different type of composites cannot have same fiber volume due to variability in density. If the fiber volume is constant the models will have different volumes. To establish a fair comparison, the composite must have the same dimensions so the lamina thickness will be equal in all cases which lead to the assumption of similar fiber volume or grammage. Based on the market offer, similar fiber volume assumption is applied for the bonnet component. In other words, for the same lamina thickness, a fiber with lower density needs to have a lower grammage in order to match similar fiber volume and if the grammage is constant, the fiber volume is higher.

11.3.3 Requirements and FEM analysis As a requirement, the bonnet component has to be able to support a specific load during its product life. Therefore, the model is analyzed under stress conditions. For production of the bonnet by RTM, the fiber volume goes up to 50%e60%; however, this study considers a fiber volume of 40%, since it is not a high performance part. For the mechanical behavior analysis, a uniform load pressure of 800 N was applied over a circular area of radius 200 mm, simulating a medium man’s weight at the center of the bonnet. The interaction between the bonnet and the main enclosure of vehicle is assumed as two embedded areas placed symmetrically from the center of the bonnet, simulating both joints, and a support base line around the bonnet as depicted in Fig. 11.8.

1

1

3

2

1-Embedded joints (Ui = Roti = 0, i = x,y,z); 2-Pressure area; 3-Support line(Uz = 0) FIGURE 11.8 Buggy bonnet, FEA boundary conditions.

271

Ramie and jute as natural fibers in a composite part Chapter | 11

TABLE 11.6 Composite and Al part properties Alternatives/properties

GF

CF T00

Ramie

Jute

Al

Thickness

4.40

3.30

4.40

4.95

3.40

No. of layers

8

6

8

9

e

Max. deformation

22.62

21.59

15.99

15.84

5.18

FoS

1.15

1.50

1.29

1.01

1.04

Model weight

2.20

1.55

1.94

2.12

3.13

E1 ¼ E2

10.104

25.793

14.612

9.124

e

G12 ¼ G13 ¼ G23 [GPa]

1.254

1.246

1.52

1.551

e

V12

0.128

0.049

0.106

0.187

e

X ¼ Y [MPa]

628.85

755.852

327.02

234.481

e

T [MPa]

21.4

21.4

21.4

21.4

e

The original bonnet model was composed of e-glass continuous filament mat, with 23% fiber volume and 4 mm thickness [52]. The stark performance between composites and aluminum is a common discussion nowadays. So, a bonnet composed of aluminum alloy is simulated, according VM criterion, to compare with other materials. The number of layers has a direct outcome on the model deformation, fewer layers lead to higher maximum deformation. As presented in Table 11.6, the worst solution in the weight and thickness context is the aluminum alloy solution. The carbon fiber composite solution suppresses considerably the competition in the weight and thickness categories. A similar e-glass deformation is obtained but it has slightly lower fiber volume content. Among the natural fibers, jute is no match for the ramie. From a synthetic versus natural fibers perspective, carbon fiber was followed by ramie fiber. The alternative models present lower deformation values than that of the baseline material. The worst solution in the weight context is the GF solution. The CF T300 solution surpasses considerably the competition in the weight and thickness categories. The deformation is neglected for comparison purposes, since the solutions have a lower value than the e-glass composite and the study is done under assumption of elastic material behavior up to fracture.

11.4 Life cycle studies of different alternatives In this section, LCC and LCA studies of all the alternatives are presented. LCC and LCA are multistep procedures that can be applied at a product or a process level, based on the system boundaries and the functional unit. The functional unit stands for the quantity of the inventory being assigned. Moreover, LCA is

272 PART | IV Life cycle assessment and risk analysis

an environmental assessment method which considers the entire life cycle of a product from raw material extraction to EOL. It attempts to quantify the potential environmental impact of a product or process in terms of several environmental impact factors using midpoints or endpoints analyses. However, the present work only considers the endpoints indicators, which follow a hierarchical perspective and are expressed in points (pts) units. On the other hand, LCC stands for the costs incurred during the life cycle of a product or process. These analyses attempt to minimize the impacts and expenditures which may occur during the whole life cycle of a product or process. In this study, LCA and LCC give the overall environmental impacts and costs of all the alternatives during the entire life cycle from raw material extraction, transport, manufacturing, and use phase to the EOL of the bonnet component.

11.4.1 Raw material and transport For the bonnet production, the materials are obtained from different places around the world. The natural fibers are transported from China by freighter transoceanic; the carbon fiber T300 (CF T300) from Germany by road, the aluminum alloy from France, and the rest of the material is national including GF and resin, Quires 406 PA. For the carbon fiber, only transport by road is considered, since the city does not have an international port. The world freight rates depend on volume, weight, and commodity value of the cargo. The cost of materials takes into account the volume of production of 600 parts/year for the bonnet component. The eco-score in pts for each alternative is calculated according to the tkm unit, where, tkm ¼ weight in tonnes  distance in km. The costs and environmental impacts during the raw material production and transport phase are presented in Table 11.7. The quantities disclosed are for one component.

11.4.1.1 Environmental impact of ramie In order to determine the life cycle impact assessment of the natural fibers using the SimaPro software, some adaptations needed to be made. The software libraries do not contain any available indicator for the ramie fiber. Thus, to solve the problem the ramie fiber needs to adopt the indicator value of other natural fiber and then model it by adding any difference to it. The available possibilities are jute or kenaf. These two fibers are analyzed in some categories to assure the best approximation to ramie, based on the production and chemical and physical properties. Like ramie, these two belong to the group of bast fiber crops; jute and kenaf have the same production [ton/ha]; jute has similar fiber density and chemical composition (similar morphology). That said ramie will use jute’s indicator value. The SimaPro jute’s indicator includes the cultivation and processing to yarn. The difference on manures and

Material

Location

Distance [km]

Tran-sport costs

Transport impact

Raw material cost

Raw material impact

GF

Lisbon, PT

e

e

e

18.92

1.08

CF T300

Geesthacht, DE

2640 (road)

0.498

0.068

50.08

1.20

Ramie

Shanghai, CN

23,724 (sea)

0.376

0.031

13.44

0.78

Jute

Guangdong, CN

22,430 (sea)

0.305

0.033

18.48

0.84

Aluminum alloy

Saint Herblain, FR

1.506 (Road)

0.805

0.310

e

5.19

1.315 (Sea)

0.510

0.007

Ramie and jute as natural fibers in a composite part Chapter | 11

TABLE 11.7 Costs (V/part) and environmental impacts (pts) of raw material production and transport per part

273

274 PART | IV Life cycle assessment and risk analysis

fertilizers between jute and ramie plants is neglected, because it depends on a vast number of variables, such as the location, the composition of soil, and the number of crops harvested annually. So the only difference to be taken into account is the fiber processing, where in ramie case there is the impact of the alkali solution of the degumming process.

11.4.2 Manufacturing phase The blanking process is the most suitable process to manufacture the component from aluminum alloy and resin transfer molding (RTM) to manufacture the component in composite materials. Based on a process-based cost model the costs of these processes were computed considering the different materials. In parallel, the resources required for each manufacturing process were translated also into environmental impacts. The costs and environmental impacts of the manufacturing phase are presented in Table 11.8. Results show very similar results for the alternatives produced by RTM, the blanking process for producing the aluminum component being the most costeffective one.

11.4.3 Use phase The use phase is responsible for most of the environmental impact due to the consumption of fuel during the life of a vehicle [53]. The weight of the buggy influences the fuel consumption directly. The expected use phase life is based on [54], in which it is claimed that the annual mileage for a petrol vehicle is 5284 km and the average life of a Portuguese passenger vehicle is about 18 years. The buggy weighs about 600 kg with a fuel consumption of 10 L ¼ 100 km [52] and the fuel consumption was allocated to the weight of the component. At the time of the study, petrol price and density were 1.534 V/L and 0.72 kg/L, respectively. An interest of 10% per year was taken into account based on time value of money. As presented in Table 11.9, the aluminum alternative causes highest environmental impact, whereas CF T300 causes lowest environmental impact during the use phase.

TABLE 11.8 Costs (V/part) and environmental impacts [pts] per part during manufacturing Alternatives GF

CF T300

Ramie

Jute

Al

Costs (V/part)

8.32

7.74

8.09

8.23

10.78

Impacts [pts]

1.84

1.97

1.55

1.63

5.15

275

Ramie and jute as natural fibers in a composite part Chapter | 11

TABLE 11.9 Total cost and environmental impacts during use phase GF

CF T300

Ramie

Jute

Al

Fuel consumption [kg]

25.11

17.69

22.14

24.20

35.72

Costs [V]

24.65

17.36

21.73

23.75

35.06

4.76

3.35

4.20

4.59

6.77

Impacts [pts]

11.4.4 End-of-life phase EOL refers to the stage when a certain product reaches the end of its product life cycle. Waste processes, such as recycle or reuse processes, have negative environmental indicators. The energy and materials obtained through the process are claimed as environmental profit. In other words, the environmental effects for the production of the material are deducted. Often the deduction is higher than the environmental impact of the process, which gives rise to negative figures [55]. However, the EOL scenario of recycling was only considered for the aluminum component, as the most likely scenario for composites is landfill or incineration [55a]. The EOL scenario for composites considered in this study was incineration. The results of environmental impacts and costs during the EOL are given in Table 11.10.

11.4.5 Overall environmental impact and costs during whole life cycle The overall costs and environmental impacts during all of the life cycle phases considered in this study are summarized in Fig. 11.9 and 11.10. Results show that the use phase is the one with most environmental impacts. Therefore, the alternatives with better performance in this phase, related to the weight of the components, are the ones with a better LCA result. The aluminium component is clearly the worst choice environmentally in all phases except in the EOL, given its recyclability. However, this is not enough to compensate its poor performance in the upstream phases. In terms of LCC, the raw material acquisition and use phase are the most important ones. In fact, the EOL and

TABLE 11.10 Costs (V/part) and environmental impact during EOL phase GF

CF T300

Ramie

Jute

Al

Costs [V/part]

0.40

0.30

0.35

0.38


4.38

Impacts [pts]

0.07

0.05

0.06

0.07


0.30

276 PART | IV Life cycle assessment and risk analysis 80

Life cycle costs (€/part)

70 60 50 40 30 20 10 0 GF

–10

Carbon T300

Ramie

Jute

AL

Transport

Raw material

Manufacturing phase

Disposal scrap

Use phase

End of life

FIGURE 11.9 Overall comparison of life cycle costs of all alternatives.

18 Life cycle environmental impacts (points/part)

16 14 12 10 8 6 4 2 0 –2

GF

Raw material

Carbon T300 Transport

Ramie Manufacturing

Jute Use

Aluminum End of life

FIGURE 11.10 Overall comparison of environmental impact during whole life cycle of all alternatives.

transport phases are negligible in both LCA and LCC analyses. The worst economic option is the carbon fiber component, and the best one the ramie component. This is mainly due to their raw material costs.

11.5 Life cycle engineering and CLUBE analysis Life cycle engineering is a life cycle methodology that intends three dimensions in paralleld cost, environmental impacts, and technical performance. It takes into account the entire life cycle of the product from raw material acquisition and manufacturing to use and the EOL. In this case study the technical performance is equivalent between the alternatives. The different material characteristics are reflected in the different thickness of the components, leading to different weight of the components, which was already

Ramie and jute as natural fibers in a composite part Chapter | 11

277

TABLE 11.11 Results of LCC for the bonnet part Alternatives

LCC (V)

LCA [pts]

E-Glass

52.28

7.75

CF T300

75.96

6.64

Ramie

44.01

6.62

Jute

51.19

7.15

Aluminum alloy

52.949

17.13

translated into costs and environmental impacts. The overall LCC and LCA results represent the two life cycle dimensions of this analysis and are presented in Table 11.11. The main differences occur between the metal and composite alternatives, with the aluminum component as a good economic choice but a poor environmental one, mainly due to its weight. Among the composites, the best alternative in terms of LCC is the ramie component and the worst the carbon fiber one. These two alternatives are in terms of LCA the best ones. The results are in the next section mapped to a CLUBE analysis tool to clearly visualize the alternatives in the different dimensions and upstream versus downstream life cycle phases.

11.5.1 CLUBE analysis The CLUBE mapping model intends to compare design alternatives addressing two aspects subject to controversy when dealing with dual outputs. First, the question of integrated costs and environmental impact (EI) performance supported by the different entities involved in the whole life cycle in different timeframes, namely the upstream designers and producers and the downstream stakeholders involved in the use and EoL phases. Second, the separation between costs and environmental impacts that forces the decision-maker to choose a design alternative based on two dimensional criteria, often with an opposite performance evolution. The first step to map and compare the alternatives is the normalization of the costs and EI of each life cycle phase. The normalized values are then aggregated in production-related (upstream phases) and user-related (downstream phases) values. For each design alternative (A1, ., Ak), the normalized production-related costs (nCP), the normalized user-related costs (nCU), the normalized production-related (nEP) and normalized user-related (nEU) environmental impacts are computed as shown in Tables 11.12e11.13. The method is detailed in [12].

278 PART | IV Life cycle assessment and risk analysis

TABLE 11.12 Aggregated LCC and EI in (V/Bonnet) and (Points/Bonnet) results for the producer and user GF

CF T300

Ramie

Jute

Al

CP

27.21

58.32

21.91

27.04

22.95

CU

25.07

17.64

22.11

24.16

30.68

EP

2.92

3.24

2.36

2.49

10.66

EU

4.83

3.40

4.26

4.65

6.47

TABLE 11.13 Normalized values of production and user-related costs and EIs GF

CF T300

Ramie

Jute

Al

nCP

0.81

0.38

1

0.81

0.95

nCU

0.70

1

0.80

0.73

0.57

nEP

0.81

0.73

1

0.95

0.22

nEU

0.70

1

0.80

0.73

0.53

ScoreK ¼ nCPk þ a$nCUk þ b$ðnEPk þ a$nEUk Þ The above equation is applied on alternatives as shown herein. ScoreAl ¼ 0:95 þ a:0:57 þ b:ð0:22 þ a:0:53Þ Scorejute ¼ 0:81 þ a$0:73 þ b$ð0:95 þ a$0:73Þ Scoreramie ¼ 1 þ a$0:80 þ b$ð1 þ a$0:80Þ ScoreCF ¼ 0:38 þ a$1 þ b$ð0:73 þ a$1Þ ScoreGF ¼ 0:81 þ a$0:70 þ b$ð0:81 þ a$0:70Þ where a and b represent the importance given to the costs of downstream phases and the importance given to the environmental impacts, respectively. Both are relative to the production-related costs, which are fully supported by the producer(s) (importance of 100%). This approach assumes that the cost of upstream life cycle phases (production cost) is fully important for any stakeholder involved. So, in the (a, b) space the domains of the “best alternatives” can be mapped depending upon the relative importance given to production or user-related phases.

β - influence of environmental impact

Ramie and jute as natural fibers in a composite part Chapter | 11

279

3 2.5 2 Ramie

CF T300

1.5 1 0.5 0 0

0.5

1 1.5 2 2.5 α - influence of downstream phases

3

FIGURE 11.11 Clube analysis of the alternative materials.

The graphical representation of CLUBE model is presented in Fig. 11.11 and it clearly shows the potential of ramie for this particular application. The carbon fiber component is only the best choice if a very high importance is given to the downstream phases, which are related to its slightly lower weight. The other alternatives do not show as potential best choices for any set of weights. This is a result only valid for this particular case, as a different product with a different use scenario could alter completely the material’s performance.

11.6 Conclusions and outlook This paper is in line with the need for the development of products considering their sustainability, which has fostered the development of new technologies and materials. The design process of a product needs to take into account not only its cost, but also its environmental impacts throughout the product life cycle. In this study is shown how the design of a product influences its life cycle performance, being crucial to develop in parallel environmental and cost LCA. The case study chosen was a component of a buggy, where different materials were evaluated. An aluminum alloy was compared with different types of fiber composites, namely two natural fibers, a glass-fiber and a carbon fiber. In order to maintain the same technical performance of the component, an FE analysis was performed to assess the design requirements in each material, namely the number of layers and thickness of the components in each material. This led to different weights, with significant impacts in the life cycle performance of the component. The results were mapped to a CLUBE diagram, showing the best options for different sets of importance given to the environmental versus cost dimensions and to the upstream versus downstream phases. The results of the study show that ramie fiberebased component

280 PART | IV Life cycle assessment and risk analysis

performed better than other alternatives in terms of environmental and economic performance. The carbon fiber alternative performs better in the use phase due to its slightly lower weight, which is a result of the better mechanical characteristics of this material. Although these results are only valid for this particular application, this chapter illustrated how the engineering design can incorporate LCA to support decisions in product development and foster more sustainable products.

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Zah R, Hischier R, Lea˜o AL, Braun I. Curaua fibers in the automobile industry - a sustainability assessment. Journal of Cleaner Production 2007;15(11e12):1032e40. https:// doi.org/10.1016/j.jclepro.2006.05.036. Knowledge Transfer Network. Materials KTN, Netcomposites. UK: Technology Overview Biocomposites; 2014. Retrieved from https://netcomposites.com/media/1211/biocompositesguide.pdf (accessed 2018/Oct/07). Akhshik M, Panthapulakkal S, Tjong J, Sain M. Life cycle assessment and cost analysis of hybrid fiber-reinforced engine beauty cover in comparison with glass fiber-reinforced counterpart. Environmental Impact Assessment Review 2017;65:111e7. https://doi.org/ 10.1016/j.eiar.2017.04.005. W. D Brouwer (Rik). Natural fiber composites in structural components: alternative applications for sisal?. Rome: The Food and Agriculture Organization (FAO), The United Nations; 2000 (http://www.fao.org). Retrieved from: http://www.fao.org/docrep/004/ Y1873E/y1873e0a.htm#fn30. Goda K, Cao Y. Research and development of fully green composites reinforced with natural fibers. Journal of Solid Mechanics and Materials Engineering 2007;1(9):1073e84. https://doi.org/10.1299/jmmp.1.1073. Jiying F, Elias N, James B, Alain De Larminat JN. New structural bio composites for car applications. Barcelona: Society of Plastics Engineers-EUROTEC 2011 Conference; 2011. Kalia S, Kaith BS, Kaur I. Pretreatments of natural fibers and their application as reinforcing material in polymer composites-a review. Polymer Engineering & Science 2009;49(7):1253e72. https://doi.org/10.1002/pen.21328. Ton Peijs. Natural fiber based composites. Materials Technology: Advanced Performance Materials 2000. https://doi.org/10.1080/10667857.2000.11752892. Kim S, Dale BE, Drzal LT, Misra M. Life cycle assessment of kenaf fiber reinforced biocomposite. Journal of Biobased Materials and Bioenergy 2008;2(1):85e93. https:// doi.org/10.1166/jbmb.2008.207. Mohanty AK, Drzal LT, Misra M. Engineered natural fiber reinforced polypropylene composites: influence of surface modifications and novel powder impregnation processing. Journal of Adhesion Science and Technology 2002;16(8):999e1015. https://doi.org/ 10.1163/156856102760146129. Antoine Le D, Peter Davies CB. Environmental impact analysis of the production of flax fFibers to be used as composite material reinforcement. Journal of Biobased Materials and Bioenergy 2011;5(1):153e65. https://doi.org/10.1166/jbmb.2011.1116. Essel R. Meta-analysis of life cycle assessments for bio-based polymers (PLA and PHA). In: Cologne, Germany: 5th international congress on bio-based plastics and composites; 2012. Mohanty AK, Misra M, Hinrichsen G. Biofibers, biodegradable polymers and biocomposites: an overview. Macromolecular Materials and Engineering 2000. https:// doi.org/10.1002/(SICI)1439e2054(20000301)276:13.0.CO;2-W. Elisa Zini MS. Green composites: an overview. Journal of Polymer Composites, Society of Plastics Engineers 2011. https://doi.org/10.1002/pc.21224. Fowler PA, Hughes JM, Elias RM. Biocomposites: technology, environmental credentials and market forces. Journal of the Science of Food and Agriculture 2006. https://doi.org/ 10.1002/jsfa.2558. Koronis G, Silva A, Fontul M. Green composites: A review of adequate materials for automotive applications. Composites Part B: Engineering 2013;44e1:120e7. https:// doi.org/10.1016/j.compositesb.2012.07.004.

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Chapter 12

Recycling processes and issues in natural fiber-reinforced polymer composites Sibele Piedade Cestari, Daniela de Franc¸a da Silva Freitas, Dayana Coval Rodrigues, Luis Claudio Mendes Instituto de Macromole´culas Professora Eloisa Mano (IMA), Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil

Chapter Outline 12.1 Introduction 12.2 Polymers recycling 12.3 Polymer composites/ nanocomposites 12.3.1 Natural fiber-reinforced polymer composites

285 286 287 288

12.3.2 Green automotive composites 12.4 Recycling and natural fiberreinforced composites in the automotive industry 12.5 Conclusion References

295

295 296 297

12.1 Introduction Humanity is making use of natural resources as if there is no tomorrow. But the impossibility of having an endless growth over a finite planet is becoming more and more present in our daily lives [1,2]. In the past two centuries, mankind has treated the environment as an unlimited self-healing system. However, from time to time nature reminds us that this is not possible; at least, not within the current laws of physics. The current development of society was achieved through the cumulative search for new technical and scientific knowledge. And the contemporary economic system is strongly based on consumerism. Governmental and private actions must be taken to increase social awareness about reducing, reusing, and recycling of the Earth’s resources. It is not enough just to use renewablesource feedstock, in order to have an “environmentally friendly” material.

Green Composites for Automotive Applications. https://doi.org/10.1016/B978-0-08-102177-4.00012-4 Copyright © 2019 Elsevier Ltd. All rights reserved.

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Any agricultural raw material is attached to a heavy ecological footprint, demanding good soil, clean water, and fertilizers. Considering that polymers are disseminated in our daily lives, the removal of waste plastics from the environment must be encouraged. This should be the most important attitude for the preservation of life on Earth, and to ensure the survival of generations to come. And we can find some efforts in this direction by the automotive industry. Authors like Baillie [3] state that the automobiles industry, in the year 2000, was estimated to hold the largest market share of composite materials.

12.2 Polymers recycling Polymersdplastics and rubbersdentered our lives in the middle of the last century. They have grown in importance, and nowadays it is impossible to dissociate them from human activities. Their chemical diversity and applications as commodity materials has led to the increase of the disposal of polymeric waste. Only a small percentage of postconsumer thermoplastic polymers is sent to the recycling process. The vast majority of these discarded materials is incinerated (to produce energy) or disposed in landfills. These methods of disposal demand a high social and environmental cost, due to the release of toxic and greenhouse gases that may harm human health, wildlife, and marine species. The presence of metals in polymers formulation increases the risk of contamination and pollution. To avoid the social and environmental impacts of these materials, an emerging consciousness about polymer recyclability must be proposed [3,4]. The simplest and cleanest procedure of polymer recycling is the primary mechanical process. It is applied to clean, factory-floor discarded pieces (injection molding branches and scraps) of thermoplastic polymers, and requires initially the disintegration of the original piece (milling, grinding, or shredding) and then extrusion, in order to prepare the material to be used again. This recycled polymer usually shows nearly the same properties, and can be added to virgin polymers to obtain new products. The secondary mechanical process is quite complex, and depends on the availability of thermoplastic waste. The collection, transportation, separation, cleaning, grinding, and storing steps are needed before the reprocessing of polymers. Some chain scissions may occur in the polymer during the reintegration, depending on its chemical structure. Heat, presence of water, or chemical agents released on degradation can lead to the decrease of the molar mass, affecting mainly the mechanical performance. Some protective agentsdstabilizing and antioxidants additivesdare used to compensate possible chain degradation during the recycling process of postconsumed polymers [5]. Another option of polymer recycling is called tertiary recyclingdalso known as chemical recycling. The aim of this process is to recover monomers through chemical depolymerization of the polymeric chains. The recovered materials are potential raw materials for the polymer and fuel industries.

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According to Ignatyev [5], the recovery assisted by enzymatic reactions can be considered as tertiary recycling. The last kind of polymer recovering is named quaternary recyclingdor energetic recoverydand is basically the incineration of the polymeric waste. The concept of this process is to transform the energy constricted in polymer into other forms of energy (heat, electricity), and also reduce the volume of plastic waste. It is suitable for heterogeneous polymeric waste, and to polymers impregnated with toxic, contagious, and hazardous chemicals [5].

12.3 Polymer composites/nanocomposites From the earliest records of its use, natural fiber-reinforced composites, or NFRC, acted as more efficient, less dense, and more easily moldable substitutes for the industry. Parts of airplanes and automobiles were precursors in the use of this kind of material. Metallic materials have been gradually replaced by polymer composites, owing to their attractive characteristics in terms of processability, high strength, temperature resistance, and ease of molding into different design forms [3]. Generally speaking, polymer composites/nanocomposites were developed in order to improve the properties of neat polymers. They belong to a class of heterogeneous, two-phase or multiphase materials. At least one of the phases is discontinuous dstructural component, supplying the load resistance and the other one is continuousd matrix componentdresponsible for the load transferring. In general, the constituents do not dissolve in each other; they keep their individual characteristics. The resulting material is a combination of the properties of both parent materials. The interfacial region plays an important role in the performance of the composite. The structural component may have dimensions of micro- or macrosize. High resistance and rigidity, together with low deformation, are required. Due to these characteristics, the structural element is mainly constituted by fibersdrandom or with a varied level of organization. The most commonly used fibers are organicdcarbon fiber or aromatic polyamidedor inorganic dglass, metallic, and ceramic. Powder materials, like silica and carbon black, are also applied as reinforcing filler. For nanocomposites, the structural component has at least one of its three dimensions in nanometric size. These components can be fillersdphilosilicates or layered double hydroxides, powdersdinorganic oxidesdor yet graphene, carbon nanotubes, among others. Some thermoplastic and thermoset polymers are used as matrices components, and can perform different roles in the nanocomposite, such as maintaining the fibers’ orientation and spacing, protecting the fibers against surface damages, and transmitting the shear load through the fiber layers. In order to improve the final properties, both composites and nanocomposites need a good interaction between structural and matrix components. There are many ways to achieve this improvement. The interfacial region between polymer/filler can be enhanced by the addition of compatibilizing agent or through the chemical modification of the filler surface [6e15].

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12.3.1 Natural fiber-reinforced polymer composites Since the middle of the last century, polymeric materials are disseminated in society. As commodities or as engineering and high-performance materials, the polymer industry keeps on growing, and is closely linked to several human actions. Since then, the importance of polymer composites has been increasing in many different industrial sectors. The aim of preparing a polymer composite is to improve the properties of the neat polymer, mainly through the addition of synthetic fibrous fillers. Despite improving the performance of polymers, synthetic fibers of organic (carbon and aromatic polyamide) and inorganic (glass, metallic or ceramic) origin still have a high production cost, and their disposal is a potential environmental problem. Natural fibers that originate from the vegetable, animal, and mineral kingdoms have been always intimately linked to human life. Fibers like cellulose, silk, and flax have been used to feed and dress mankind for centuries. Amongst them, the vegetable fibers have great commercial significance. In a general way, they show many specific propertiesdsuch as low density and cost, good thermal and acoustic insulating. They are considered green materials owing to their fully degradable/renewable aspect, and their combustion does not release toxic gases. Although cellulosic natural fibers have a wide diversitydsheaves of plants, hard fibers from leaf, seed fibers, and othersdtheir intrinsic morphologies lead to distinct mechanical and physical properties [3,4,16e19]. The use of natural fibers as filler in polymer-based composites was started aiming at cost reduction. Low costs, high production rates, nonabrasive, and low energy for processing are some of their desired features. They are available worldwide, and mainly due to their high resistance, rigidity, and low deformation aspects are able to replace glass and carbon fibers as polymer reinforcing fillers. Nowadays automotive and packaging industries are searching for natural materials, targeting their recyclability and/or biodegradability after life cycle completion [18]. It must be emphasized that, due to the diversity of vegetable sources, NFRPC can be unlimitedly produced. Besides their attractive physicochemical attributes as polymer fillers, natural fibers may help in the decrease of environmental damage [4]. The main advantage of using natural fibers in polymer composites is their renewability. Besides, characteristics like low density, bioinertia, bioactivity, chemical functionality, CO2 neutrality, low abrasion, high elastic modulus, and tensile strength play an important role in the final product. All of these features favor the importance of natural fibers as filler in polymeric composites for industrial applications. For instance, lightweight, high strength, and high modulus artifacts can be produced to replace metal, glass, and ceramic ones [18,20]. According to the application, either long or short natural fibers must be feasible to accept loads without pulling out of the polymeric matrix. Great reinforcement of composite properties is achieved by reduction of the interfacial region between polymer/natural fiber. This region can be improved by the addition of compatibilizing agent, or through the surface chemical modification of one or both (structural and matrix) components [21]. The silanization reaction

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of filler and polymer matrix is a procedure that has been carried out. Peroxides are also applied as modifier, to improve the interfacial tension in natural fiber composites. Lignin was tested as natural compatibilizing agent [22]. The outcome is the enhancement of all properties, especially the mechanical ones. NFRPC can be understood as a green material. In addition, natural or synthetic virgin/recyclable polymers can be used as matrix for embedding the natural fibers [23e27]. Upcycled material to produce masonry bricks was developed through the filling of high-density polyethylene with microfibers of sugarcane bagasse, at different proportions. There was no significant variation in the melting and crystallizing temperatures compared to those of neat polymer. And no relevant change was found in the average size of the polymeric crystals. The degree of crystallinity of the composites increased to all filler contents, leading to conclude that some transcrystallization has happened. There was an increase in the compressive moduli of the composites, ranging from 37% to 63%. The modulus at the crossover point and the complex viscosity also rose due to the fibers ratio [28] (Fig. 12.1; Tables 12.1 and 12.2) Aiming a potential application as building material, composites based on recycled high-density polyethylene (HDPE) and sugarcane bagasse were investigated. The polymer/filler ratio varied between 100/0 and 60/40. The optical microscopy revealed that triturated bagasse showed a reduced and heterogeneous fiber size. The composite with highest content of bagasse presented better absorption, and was able to anchor the paint with organic solvent base. The bagasse fibers somehow structured the amorphous region

FIGURE 12.1 Scanning electron microscopy photomicrographies of the composites 80e20 (unpublished).

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TABLE 12.1 Differential scanning calorimetry data of the composites. Material

Tm ( C)

DHm ( C)

Tc ( C)

Xc (%)

100e0

133

180

120

62

80e20

133

170

120

73

70e30

133

140

120

69

60e40

132

130

121

75

TABLE 12.2 Secant compressive modulus (Ecs) of the materials. Composite

Ecs (MPa)

100e0

5.39

80e20

7.87

70e30

7.36

60e40

8.80

amongst the crystallized lamellae of the polymeric matrix, as shown in the dynamic-mechanical and diffractometric analyses [29] (Figs. 12.2e12.5). Coffee dregs were incorporated to recycled high density polyethylene (HDPE-R), to prepare composites at the polymer-filler ratio of 100%e0%, 90%e10%, 80%e20%, 70%e30%, 60%e40%, 50%e50%, and 40%e60%. The composites degraded in two steps. The first one was in a temperature lower than that of the neat HDPE-R, but higher than the average processing temperature of the polymer. Thermal propertiesdmelting temperature and the degree of crystallinitydand the compressive moduli of the composites resulted similar to the neat HDPE-R ones. The composites showed interesting properties as a building material [30] (Fig. 12.6; Table 12.3). In another study, different types of COFD (integral, extracted, major size, and minor size) were added to high-density polyethylene (HDPE) in order to study the effects of particle size and soluble extraction over the properties of the HDPE. The results showed that the integral COFD has a performance similar to the minor size one, and superior to the extracted. The melting temperature and the degree of crystallinity of the composites resulted similar to the neat HDPE ones. In general, extraction and particle size of the COFD showed little influence in the behavior of the HDPE. The study suggested that COFD can be used as filler in polymeric composites [31] (Fig. 12.7; Table 12.4). Without any previous chemical treatment or compatibilizer, fibers of sugarcane bagasse were embedded in a continuous polymeric matrix, in order

Recycling processes and issues Chapter | 12

291

(A)

0.6 mm 0.6 mm

1.5 mm

1.5 mm

1.5 mm

1.5 mm

(B)

0.6 mm 0.6 mm

FIGURE 12.2 Optical microscopy images of the SCB fibers [29].

Paint

Paint

Interaction Fibers Normal surface

FIGURE 12.3

Sanded surface

Interaction between the paint film and the different surfaces of the composites [29].

100–0 80–20 70–30 60–40 SCB

0

10

20

30 2 theta

40

50

FIGURE 12.4 WAXD curves of the materials [29].

Amorphous material Crystalline material

Crystallysation center

SCB fibres

FIGURE 12.5 Model of the possible structuring of the amorphous phase between the crystallized lamellae of the rHDPE, furthered by the SCB fibers [29].

100

100–0 90–10 80–20 70–30 60–40 50–50 40–60

Weight(%)

80

60

COFD 40

20

0 100

200

300

400

500

600

Temperature(°C) FIGURE 12.6 Superposition of TGA curves of the composites [30].

700

Recycling processes and issues Chapter | 12

293

TABLE 12.3 Crystalline melting temperature (Tm), fusion nthalpy (DH), degree of crystallinity (Xc), percentage variation (D%) of DH and Xc of the composites [30]. Material

Tm ( C)

DH (J/g)

Tc ( C)

Xc

100e0

131

169

118

58%

90e10

132

150

118

57%

80e20

132

134

118

57%

70e30

132

117

117

57%

60e40

132

100

117

57%

50e50

132

97

116

66%

40e60

130

70

117

59%

(a)

20 kV

X100

100 µm

IMA

- UFRJ

(c) 20 kV

(b)

20 kV

X100

100 µm

IMA

- UFRJ

X100

100 µm

IMA

- UFRJ

(d) X100

100 µm

IMA

- UFRJ

20 kV

FIGURE 12.7 SEM of the composites HDPE/COFD-I (a), HDPE/COFD-E (b), HDPE/COFDMA (c), and HDPE/COFD-ME (d) magnified 100 times, the filler highlighted in red [31].

to assess its feasibility as an ink-absorbing material. There was an increase in the thermal stability and in the degree of crystallinity of the HDPE. The optical microscopy revealed that the cellulosic material was homogeneously embedded within the HDPE matrix. The best result of printability was achieved in the composite with the highest content of SCB, as well as the shortest drying time [32] (Fig. 12.8; Table 12.5).

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TABLE 12.4 Crystalline melting temperature (Tm) and degree of crystallinity (Xc) of the composites [31]. Material

Tm ( C)

DH (J/g)

Xc

HDPE-P

134

200

69%

HDPE-COFD-I

133

166

64%

HDPE-COFD-E

132

176

67%

HDPE-COFD-MA

133

155

59%

HDPE-COFD-ME

134

172

66%

FIGURE 12.8 Printing test of the 30e70 composite (unpublished).

TABLE 12.5 Tonset, Tfinal, and Tmax of the materials [32]. HDPE/SCB composite

Tonset ( C)

Tfinal ( C)

Tmax ( C)

Residue (%)

100/0

433

500

461

e

80/20

307/459

500

354/478

e

50/50

303/444

550

349/472

3

30/70

258/448

550

295/351/472

10

SCB

292

575

344/496

2

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295

The recycling of polymer-based composites shows additional problems. Most of the polymeric matrices are thermosetting embedded with high filler content. An alternative is to shred these materials, and use them as fillers in the fabrication of products that ordinary fillers (as calcium carbonate or silica) are usually added [3,33,34]. These products have the same, or even better, mechanical properties as the initial first-generation composite material. In addition, ground recyclate has lower specific gravity and contributes to weight reduction when compared to conventional fibers. Henshaw noted that the composite community considers the secondary recyclingdgranulation followed by injection or compression moldingdthe better option, because this process uses existing technology, and an extensive market already exists [35]. Studies have shown that, if the composites are ground to a small particle size of less than 20 mm, they prove to be very efficient fillers for high strength mortars, concretes, and even paint films [36].

12.3.2 Green automotive composites Even Henry Ford has suggested the use of green composite materials [3], and the subject is recurrent in literature. Yang and coworkers [37] studied the recycling of automotive shredder residues “ASR” (materials that contains 70% of mixed polymers) using solid-state shear milling in pelletized ASR, and obtaining ultrafine particles. According to the authors, they achieved a material with improved mechanical properties, and proposed a “simple, low cost, efficient and green” strategy to recycle this waste material. Suryanegara [38] developed a composite of poly(lactic acid)dPLAdand microfibrillated cellulose, aiming to create a material with resistance to high temperatures. The addition of 20% of microfibrillated cellulose has increased the tensile modulus of PLA in 42%, and the tensile strength in 14%. The dynamic-mechanic analysis showed a storage modulus of 1 GPa at 120 C. Mashkour [39] studied composites of polypropylene and wood flours modified with Fe3O4 nanoparticles, to create a magnetic wood-plastic compositeda functional engineering material for the automotive industry. The purpose was to prevent the interference and leakage of electromagnetic waves in automotive applications. The Fe3O4 nanoparticles were synthesized in situ in an aqueous solution of pretreated wood flours, and compounded with PP using maleated PP as compatibilizer. They achieved a 10% reduction in saturation magnetization of the composites, and an increase in the water absorption and thickness swelling. But the presence of the Fe3O4 nanoparticles has decreased the polymer/filler interaction, as well as the tensile and flexural properties.

12.4 Recycling and natural fiber-reinforced composites in the automotive industry In the year 2000, there was already a concern about the recyclability of the polymeric components of a car. Mano [40] studied discarded car bumpers,

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aiming to identify the composition of these components. She concluded that the bumpers were made of a blend of PP and HDPE, compatibilized with ethylene propylene diene methylene (EPDM). According to Al-Oqla and Sapuan [4], there is a lack of information in literature about how/why/when to use natural fibers in reinforced composites. There are plenty of articles studying all kinds of natural fibers. But authors are usually motivated by aspects like local availability, compatibilization approach, use of renewable resources, and biodegradation capability [18,22,41e45]. In an effort to reduce this lack of information, in 2009, Cheung, Ho [19] classified 29 kinds of natural fibers that could be used in the automotive industry. The fibers were assessed in terms of density, tensile properties, functionality, and bio (inertia/activity) properties. Automotive companies are used to working together with researchers, looking for new recycling alternatives for their polymeric automotive parts. There are studies reporting increased strength in epoxy-molding compounds, after the addition of short fibers obtained from ground composites as reinforcing filler [3].

12.5 Conclusion In general, the automotive industry is currently showing a strong concern about the recyclability of its parts, and about broadening the use of recycled materials in its production. The extensive use of polymeric and advanced composite materials in automobiles has led to the challenge of finding ways to recycle these heterogeneous and lasting waste materials. As stated by Winter, Mostert [46], “with the increasing use of composites and plastics in automobiles, even separating functional units such as bumpers and dashboards will result in the mixture of polymer materials. Recycling of advanced composite materials, including those used for bumpers and dashboards, poses a serious problem in the industry. These materials are famous for being lightweight and durable, and therefore difficult to recycle.” But these problems cannot prevent both industry and society from finding sustainable solutions to the automotive industry. Recycling issues are actually complex, involving different stages and sectorsdselection and development of materials, engineering challenges, knowledge limitations, and life cycle studies. And it is undeniable that the economic factor sovereignly rules the decision making, not only in the automotive industry but also inside the laboratory, where many ideas and/or materials are discarded for not being costeffective. Therefore, we must remember that many times in history something was considered economically unfeasible at a specific time, until the happening of a future scientific or technological breakthrough.

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298 PART | IV Life cycle assessment and risk analysis [17] [18] [19] [20]

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Recycling processes and issues Chapter | 12 [38]

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Index ‘Note: Page numbers followed by “f ” indicate figures and “t” indicate tables.’

A

B

Acetobacter xylinum, 31 Acetylation, 17e18, 18f, 123, 127e128, 128f Acrylated epoxidized soybean oil (AESO), 66 Acrylic acid (AESO), 66e68 Alkaline-acid, 121 Alkali treatment, 16, 16f Alumide, 184 Aluminium (Al), 183e184 Aluminium-filled polyamide material, 185e186 Ammonium polyphosphate (APP), 49e50 Amorphous polymers, 181e182 Anacardium occidentale, 71 Annual production volume (APV), 102 Atmospheric pressure glow discharge, 13e14, 14f Atmospheric pressure plasma jet (APPJ), 11, 14e15, 14f Atomic force microscopy (AFM), 157e158 Automotive interior parts advantages, 85 biocomposites, 82 biodegradable polymers, 82 case studies, 85e95 cellulosic fibers, 89e95, 91t materials, 85e95 poly(lactic acid) (PLA), 87e89, 88f polyhydroxyalkanoates (PHAs), 86e87, 87t cellulose fibrils, 83 chemical composition, 82 experimental studies, 90e95 green composites, 84e85 heat deflection temperature (HDT), 91 injection parameters, 94 microfibrils, 83 natural fibers, 82e84 structural applications, 85

Bacterial cellulose (BC), 31 coating, 30e31 Bacterial nanocellulose (BNC), 118 Ball milling, 126 Bamboo fibers, 25 Banana fibers, 25 Barium titanate, 183e184 Benzoylation, 18, 18f Binder jetting process, 176 Bio-based polyurethanes, 70e71 Biocomposites bionanocomposites, 203e207 cellulose, 199f characterization, 205 fabrication, 205 hemicelluloses, 199f, 206e207 lignin, 199f, 206 nanocellulose, 207 properties, 205 biopolymers, 198 challenges, 208e210 industrial scales, 209e210 nanopaper approach, 209e210 true green polymers, 208 flammability performance. See Flammability performance green composites, 198 mechanical properties, 200t nanocellulose, 199 petroleum-based polymers, 198 physical properties, 200t polymer matrices, 201e202, 201f fossil fuel, 202 mixed source, 202 renewable source, 201 processing techniques, 202 properties, 202e203 reinforcement phase, 199e200, 199f synthetic polymers, 197e198 Biofibers, 89

301

302 Index Biomass fibers, 119e121 alkaline-acid, 121 cellobiohydrolases, 119 endoglucanases, 119 enzyme, 119e120 ionic liquids (ILs), 121 Boehmeria nivea, 103e104 Boundary conditions (BC), 102e103 Brazilian Association of Automotive Components Manufacturers Reports, 102 Bulk fibers, 90

C CaCO3, 31e32 Carbon nanofibers (CNF), 188 Cashew nut shell liquid (CNSL), 71e73, 72f Casting method, 172e173 Castor oil resin composites, 69e70, 70f Cellobiohydrolases, 119 Cellulose, 31 architecture, 117e118 nanocellulose, 116e119 wood fiber cell wall, 117e118, 117f Cellulose nanocrystal (CNC), 118e119, 207 Cellulose nanofibers, 116, 145e146 Cellulose triacetate (CTA), 206 Cellulosic fibers, 3e4, 90 Ceric ammonium nitrate (CAN), 19 Chemical recycling, 286e287 Chemical welding, 178 Chitosan, 206 CLUBE analysis, 276e279 CNSL. See Cashew nut shell liquid (CNSL) Compound injection molding (CIM), 94, 94f Compression molding, 179, 259e260 Computer-aided design (CAD), 173 Cone calorimetry, 44e45 Conventional fabrication methods, 180t Copper polyamide (CuPA), 184e185 Corona treatment, 11e12, 12f Coupling agents, 130, 130f Cryocrushing, 125

D Decision uncertainty, 233e234 Dielectric barrier discharge technology (DBD), 11e13, 13f Differential scanning calorimetry (DSC), 157e158 Diglycidyl ether of bisphenol A (DGEBA), 75

3D printing technologies applications, 173 binder jetting process, 176 biomedical industry, 179e181 casting method, 172e173 challenges, 179e183 chemical welding, 178 classification, 175t composite materials, 183e189, 183f composites, 177e183 compression molding, 179 computer-aided design (CAD), 173 conventional fabrication methods, 180t cost, 173e174 definition, 174e177 emulsion polymerization, 178 future perspectives, 190 G-code, 174e175 green composite materials, 189 high impact polystyrene (HIPS), 176 high-strength materials, 171e172 injection molding, 178 long tail, 173e174 low-volume production, 173e174 mass-customization, 173e174 material extrusion process, 175e176 material jetting process, 176 metal-based materials, 171e172 micro-injection molding, 178 microstructure analysis, 179e181 polymer-based composite realm, 178f powder bed fusion, 176e177 processing methods, 172e173 product innovation, 173e174 properties for fabrications, 177e183 quality, 173e174 rapid design iterations, 173e174 selective laser sintering (SLS) process, 179e181 stereolithography file (STL), 174e175 synthetic polymers, 171e172 true rapid prototyping, 173e174 vat polymerization, 175e176 Drying process, 126, 127t

E Eco-Audit tool, 100e101 Eco-impact assessment annual production volume (APV), 102 Brazilian automobiles, 102 components elements, 105t disposal phase, 106t

Index Eco-Audit tool, 100e101 end of life, 104e106 glass-fiber baseline, 110f hood boundary conditions, 102e103 functional unit, 102e103 life cycle analysis (LCA), 100e101 manufacture, 104e106 manufacturing approaches, 103e104 materials, 101e106 mechanical properties, 104t methods, 101e106 natural fiber incorporation, 103e104 polylactic acid (PLA), 99e100 ramie-reinforced biocomposite, 108 unsaturated polyester (UP) matrix, 102 Electrospinning, 124e125, 124f Emulsion polymerization, 178 End-of-life phase, 104e106, 275, 275t Endoglucanases, 119 Enzymatic treatment, 29, 29f Enzyme, 119e120 EPICEROL technology, 75 Epichlorohydrin, 75 Epoxy functionality, 130e131 polyester matrices, 25 Ethylene propylene diene methylene (EPDM), 295e296 EU Landfill Directive 1999/31/EC, 62

F FEM analysis, 270e271 Fiber reinforcements, 186e187 Flame retardant (FR) chemicals, 44 Flammability performance case studies, 47e55 ammonium polyphosphate (APP), 49e50 biochar, 51e52 biocomposites, 47e54 biopolymers, 47e54 green flame retardants, 54e55, 56f peak heat release rate (PHRR), 48 polybutylene succinate (PBS), 55 polyvinyl alcohol (PVA), 55 cone calorimetry, 44e45 flame retardant (FR) chemicals, 44 limiting oxygen index (LOI), 45e46 Ohio State University heat release apparatus, 47

303

pyrolysis combustion flow calorimetry (PCFC), 45 REACH Act, 43 testing techniques, 44e47 underwriters laboratories 94 (UL94), 46e47 Flax fibers, 22e23 Food packaging, 132 Ford Model-T, 260e261 Fourier transformed infrared spectroscopy (FTIR), 157e158 Fourier transform infrared (FTIR) spectrometer, 44 Fungal treatment, 30, 30f Fusion deposition modeling (FDM), 179e181

G G-code, 174e175 Glass-fiber baseline, 110f Glass-filled nylon powder, 184 Glass-reinforced composites, 89 Gluconoacetobacter xylinus, 118 Glycerol, 68 Graft copolymerization, 19 Grafting, 130e131 Green composite materials, 189 Green epoxy composites, 75 Green house gas (GHG), 61e62 Green thermoset biocomposites challenges, 75e76 EU Landfill Directive 1999/31/EC, 62 European Union (EU), 62 examples, 63t Intergovernmental Panel on Climate Change’s (IPCC), 61e62 vegetable oil resins, 64e75 acrylated epoxidized soybean oil (AESO), 66 acrylic acid (AESO), 66e68 bio-based polyurethanes, 70e71 cashew nut shell liquid (CNSL), 71e73, 72f castor oil resin composites, 69e70, 70f cost-effective green technology, 64 green epoxy composites, 75 hexamethylenetetramine (HMTA), 72e73 linseed oil thermoset composites, 65 methacrylated eugenol (ME), 66 methacrylic acid (MESO), 66e68, 67f N-vinyl-2-pyrrolidone (NVP), 66

304 Index Green thermoset biocomposites (Continued ) selected CNSL-based composites, 73t soybean oil thermoset composites, 65e68, 66f wheat gluten matrix composites, 68e69 zein matrix composites, 73e75 Grinding, 123

H Heat deflection temperature (HDT), 91 Hemicelluloses, 199f, 206e207 Hemp fibers, 21, 23 Hexagon vertex, 93 Hexamethylenetetramine (HMTA), 72e73 High-density polyethylene (HDPE) composites, 21e22, 290 High impact polystyrene (HIPS), 176 High-strength materials, 171e172 Homogenization, 122e123, 122f Hydroxyl groups (OH), 19 HYPERCAR, 230e231

I INGEO 3251D biopolymer, 89 Injection molding, 178 Interfacial shear strength (IFSS), 23 Intergovernmental Panel on Climate Change’s (IPCC), 61e62 Ionic liquids (ILs), 121 ISOJET Resin Transfer Molding, 102

J Jute fiber, 20

K Kenaf fibers, 25

L Legal approach, 236 Life cycle analysis, 262e267, 264f Life Cycle Assessment (LCA) methodology crop production, 221e223 crude oil extraction, 221e223 environmental classification factors, 229t environmental impact results, 246t examples, 243e246 fiber matrix, 221 fiber reinforcement, 221 flax fibre/PP green composite, 231e232

glass-fiber/PP composites, 231e232 green composites, 228e233 HYPERCAR, 230e231 interpretation stage, 245 Life Cycle Inventory Analysis (LCI), 228e230 LIRECAR, 230e231 modeling risks, 233e236 decision uncertainty, 233e234 legal approach, 236 management, 236e239 model uncertainty, 233e234 parameter uncertainty, 233e234 probabilistic simulation, 238 scientific approach, 236 social/constructive approach, 236 statistical approach, 236 variability, 234 natural fibers, 221e225 advantages, 225e228, 226te227t disadvantages, 225e228, 226te227t properties, 224t non-renewable resources, 221 polymer-based composites, 221 real-world risks composite/part production phase, 240e241 end of life (EOL) Phase, 241 management, 241e242 material production phase, 240 raw material extraction, 240 structuring of, 239, 239f ReCiPe Endpoint method, 232e233 steps, 235f Lightweight transparent materials, 132 Lignin, 199f, 206 Lignocellulosic materials, 71 Limiting oxygen index (LOI), 45e46 Linseed oil thermoset composites, 65 LIRECAR, 230e231

M Maleated coupling treatment, 18e19, 19f Manufacturing phase, 274 Material extrusion process, 175e176 Metal-based materials, 171e172 Metallic materials, 287 Methacrylated eugenol (ME), 66 Methacrylic acid (MESO), 66e68, 67f Microfibrillated cellulose (MFCs), 149e150 Micro-injection molding, 178 Micro-sized particles, 148e150

Index advantages, 148e150 nanocellulose, 149e150, 150f nanoclays, 148e149, 148f Mimosa tanninehexamine biocomposites, 23 Modeling risks, 233e236 decision uncertainty, 233e234 legal approach, 236 management, 236e239 model uncertainty, 233e234 parameter uncertainty, 233e234 probabilistic simulation, 238 scientific approach, 236 social/constructive approach, 236 statistical approach, 236 variability, 234 Motivation, 254e255

N Nanocellulose, 207 bacterial nanocellulose (BNC), 118 cellulose, 116e119 cellulose nanocrystal (CNC), 118e119 Gluconoacetobacter xylinus, 118 nanofibrillated cellulose. See Nanofibrillated cellulose size, 118e119 structures, 118e119 types of, 118t Nanoclay-reinforced polymer composites, 158e159 Nanofibrillated cellulose (NFC), 119, 145e146, 149e150, 207 applications, 131e133 automobile industry, 132e133 oxygen barrier, 132 printing applications, 132 coupling agents, 130, 130f drying, 126, 127t general applications, 131e132 grafting, 130e131 hierarchical structure, 119, 120f isolation, 122e126 ball milling, 126 cryocrushing, 125 electrospinning, 124e125, 124f grinding, 123 homogenization, 122e123, 122f steam explosion, 125e126, 125f ultrasonication, 123e124 modifications, 126e131

305

acetylation, 127e128, 128f silylation, 128e129, 128f surface modification, 116 transmission electron microscopy (TEM), 119, 121f Nano fillers/nanofibers applications, 161e162 characterization, 157e158 isolation, 151te154t microfibrillated cellulose (MFCs), 149e150 micro-sized particles, 148e150 nanofibrillated cellulose (NFC), 149e150 nanomaterials, 146 polymer composites, 154e157 renewable materials applications, 154 renewable nanomaterials, 147, 158e159, 159f Nanomaterials, 146 Natural fiber polymer composites (NFPCs), 20e23 Natural fiber-reinforced polymer composites, 288e295, 289f, 290t Natural fibers advantages, 257t aerospace industries, 3e4 application, 262t assumptions, 268e270 automotive industry, 3e4 automotive manufacturers, 5t biological methods, 28e31 bacterial cellulose coating, 30e31 enzymatic treatment, 29, 29f fungal treatment, 30, 30f bonnet case studies, 267e271, 268f case studies, 262e267 cellulosic fibers, 3e4 chemical composition, 7t chemical methods, 15e20 acetylation, 17e18, 18f alkali treatment, 16, 16f benzoylation, 18, 18f graft copolymerization, 19 maleated coupling treatment, 18e19, 19f permanganate treatment, 19e20 silane treatment, 16e17, 17f civil engineering, 3e4 CLUBE analysis, 276e279 compression molding, 259e260 contribution, 254e255

306 Index Natural fibers (Continued ) dimensional stability, 6 disadvantages, 257t end-of-life phase, 275, 275t FEM analysis, 270e271 future trends, 32e33 green composites, 255e260, 256f greener, 254 incorporation, 103e104 industrial applications, 260e262 International Organization for Standardization (ISO), 263e264 life cycle analysis, 262e267, 264f life cycle cost (LCC) analysis, 254 Life Cycle Engineering (LCE) approach, 255 manufacturing phase, 274 materials, 268e270 means and methods, 268 mechanical properties, 258t medical field, 3e4 mineral fibers, 3e4 motivation, 254e255 nanoparticles deposition, 31e32 functionalization, 31e32 natural fiber polymer composites (NFPCs), 20e28 physical methods, 6e20 plasma treatment, 10e15, 10f ultrasound treatments, 15 ultraviolet treatments, 15 properties, 6, 8te9t protein fibers, 3e4 ramie, 272e274 raw material, 272e274 requirements, 270e271 resin transfer molding (RTM) process, 254e255 surface modification, 6e20 transport, 272e274 use phase, 274, 275t vegetable fibers, 4 Natural rubber (NR), 161e162 NFC. See Nanofibrillated cellulose (NFC) NFRPC, 289 Novamix, 29 Nuclear magnetic resonance (NMR), 157e158 N-vinyl-2-pyrrolidone (NVP), 66

O Ohio State University heat release apparatus, 47 Oil palm fiber epoxy composites, 27e28 Organically modified rectorite (OREC), 186 Oxygen barrier, 132

P Parameter uncertainty, 233e234 Permanganate treatment, 19e20 Pineapple leaves (PALF), 25 Plasma treatment atmospheric pressure glow discharge, 13e14, 14f atmospheric pressure plasma jet (APPJ), 14e15, 14f corona treatment, 11e12, 12f dielectric-barrier discharge (DBD) technique, 12e13, 13f NFPCs, 20e23 Plasma vacuum, 11 Poly(butylene adipate) (PBA), 207 Poly(lactic acid) (PLA), 27, 206 Poly(vinyl alcohol) (PVOH), 207 Polyamide12 (PA12), 188 Polyester composites, 22 Polyethyleneimine (PEI), 161e162 Polyhydroxybutyrate (PHB), 86e87 Polylactic acid (PLA), 20, 99e100 Polymer composites, 154e157, 287e295 classification, 156f Polymer matrices, 201e202, 201f Polymer nanocomposites, 287e295 atomic force microscopy (AFM), 157e158 differential scanning calorimetry (DSC), 157e158 Fourier transformed infrared spectroscopy (FTIR), 157e158 nanocomposite materials, 157 nano fillers/nanofibers. See Nano fillers/ nanofibers nuclear magnetic resonance (NMR), 157e158 renewable nanomaterial, 158e159, 159f scanning tunneling microscopy (STM), 157e158 small angle X-ray scattering (SAXS), 157e158 X-ray diffractometer (XRD), 157e158 X-ray photoelectron spectroscopy (XPS), 157e158

Index Polymers recycling, 286e287 Polypropylene (PP), 18e19, 21, 23 Polyurethane composites, 25 Polyvinyl alcohol (PVA), 69 Polyvinyl alcohol/carboxymethyl cellulose (PVA/CMC) blend, 161e162 Printing applications, 132 Probabilistic simulation, 238 Product innovation, 173e174 Pyrolysis combustion flow calorimetry (PCFC), 45

Q Quaternary recycling, 287

R Ramie, 108, 272e274 Raw material, 272e274 REACH Act, 43 Real-world risks composite/part production phase, 240e241 end of life (EOL) Phase, 241 management, 241e242 material production phase, 240 raw material extraction, 240 structuring of, 239, 239f Recycling processes green automotive composites, 295 humanity, 285 natural fiber-reinforced polymer composites, 288e295, 289f, 290t automotive industry, 295e296 polymer composites, 287e295 polymer nanocomposites, 287e295 polymers recycling, 286e287 Renewable materials applications, 154 polymer nanocomposites, 158e159, 159f Resin transfer molding (RTM) process, 187, 254e255 Ricinus communis, 69

S Scanning tunneling microscopy (STM), 157e158 Schizophyllum commune, 30

307

Selective laser sintering (SLS) process, 179e181 Self-healing system, 285 Sheet molding compounding (SMC), 259e260 Silane-based surface modification, 128e129 Silane treatment, 16e17, 17f Silanization reaction, 289 Silicon carbide (SiC) polyamide matrix, 186 Silylation, 123, 128e129, 128f Sisal fibers, 25 Small angle X-ray scattering (SAXS), 157e158 Social/constructive approach, 236 Solid-state shear milling, 295 Soybean oil thermoset composites, 65e68, 66f Statistical approach, 236 Steam explosion, 125e126, 125f Synthetic polymers, 171e172

T Tertiary recycling, 286e287 2,2,6,6-Tetramethylpiperdine-1-oxyl (TEMPO), 123 Thermal conductivity, 181e182 Time to ignition (TTI), 44e45 Total heat release (THR), 44e45

U Ultrasonication, 123e124 Uncertainty decision uncertainty, 233e234 model uncertainty, 233e234 parameter uncertainty, 233e234 types, 235, 235f Underwriters laboratories 94 (UL94), 46e47 Unsaturated fatty acids, 65 Unsaturated polyester (UP) matrix, 102 Use phases, 274, 275t

V Vat polymerization, 175e176 Vegetable oil resins, 64e75 acrylated epoxidized soybean oil (AESO), 66e68 bio-based polyurethanes, 70e71 cashew nut shell liquid (CNSL), 71e73, 72f

308 Index Vegetable oil resins (Continued ) castor oil resin composites, 69e70, 70f cost-effective green technology, 64 green epoxy composites, 75 hexamethylenetetramine (HMTA), 72e73 linseed oil thermoset composites, 65 methacrylated eugenol (ME), 66 methacrylic acid (MESO), 66e68, 67f N-vinyl-2-pyrrolidone (NVP), 66 selected CNSL-based composites, 73t soybean oil thermoset composites, 65e68, 66f wheat gluten matrix composites, 68e69 zein matrix composites, 73e75

W Wheat gluten matrix composites, 68e69

X XH films, 206e207 X-ray diffractometer (XRD), 157e158 X-ray photoelectron spectroscopy (XPS), 157e158

Z Zein matrix composites, 73e75 Zinc oxide (ZnO) nanoparticles, 32 Zirconium diboride, 183e184