Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties and Applications 3527349308, 9783527349302

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Natural and Synthetic Fiber Reinforced Composites

Natural and Synthetic Fiber Reinforced Composites Synthesis, Properties, and Applications

Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin

Editors Dr. Sanjay M. Rangappa

King Mongkut’s University of Technology North Bangkok Department of Materials and Production Engineering 1518 Pracharaj 1 Wongsawang Road, Bangsue 10800 Bangkok Thailand Prof. Dipen Kumar Rajak

Sandip Institute of Technology and Research Department of Mechanical Engineering Mahiravani 422213 Nashik India

All books published by WILEY-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate. Library of Congress Card No.: applied for British Library Cataloguing-in-Publication Data

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The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at .

Prof. Suchart Siengchin

King Mongkut’s University of Technology North Bangkok Department of Materials and Production Engineering 1518 Pracharat 1 Wongsawang Road, Bangsue 10800 Bangkok Thailand Cover Image: © MirageC/Getty Images

© 2022 WILEY-VCH GmbH, Boschstr. 12, 69469 Weinheim, Germany All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law. Print ISBN: 978-3-527-34930-2 ePDF ISBN: 978-3-527-83298-9 ePub ISBN: 978-3-527-83300-9 oBook ISBN: 978-3-527-83299-6 Typesetting

Straive, Chennai, India

Printed on acid-free paper 10 9 8 7 6 5 4 3 2 1

Editors are honored to dedicate this book to their family members and friends.

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Contents Preface xvii About the Editors xix 1

1.1 1.2 1.3 1.3.1 1.3.2 1.3.3 1.3.4 1.3.5 1.3.6 1.3.7 1.3.8 1.4 1.5 1.6 1.7

2

2.1 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5

Introduction to Glass Fiber-Based Composites and Structures 1 Jay Prakash Srivastava and Pankaj Kumar Introduction 1 Applications 2 Classification of GFRC 5 A-Type 5 C-Type 6 D-Type 6 E-Type 7 R-, S-, and T-Type 7 S2-Type 7 M-Type 7 Z-Type 7 Classifications Based on Form 8 Structure 9 Mechanical Properties 10 Conclusion 13 References 13 Synthesis of Cotton Fiber and Its Structure 17 Pankaj Kumar, Cherala Sai Ram, Jay P. Srivastava, Arun K. Behura, and Ashwini Kumar Introduction 17 Cotton Fiber Classification 17 Classification of the Cotton Fiber Based on the Strength 18 Classification of the Cotton Fiber Based on Fiber Length Uniformity 18 Classifications of the Cotton Based on Fiber Fineness 18 Classifications of the Cotton Based on Fiber Color 18 Classifications of the Cotton Based on Trash 18

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2.2.6 2.2.7 2.2.8 2.3 2.4 2.5 2.6 2.7 2.7.1 2.7.2 2.7.3 2.7.4 2.8 2.8.1 2.8.2 2.9 2.10 2.11 2.12 2.13 2.14

Classifications of the Cotton Based on Leaf Grade 18 Classifications of the Cotton Based on Extraneous Materials 19 Classifications of the Cotton Based on Module Averaging 19 Surface Modification of Cotton Fibers 21 Solvents for Cotton 21 Chemical Treatment of Cotton Fiber 22 Chemical Composition 23 Structural Properties of Cotton 25 Constitution and Molecular Weight Distributions 25 Cotton Fiber Structure 25 Microscopic View of Cotton Fiber 26 Physical Properties of Cotton Fiber 26 Characterization Methods of Cotton Fiber 27 Measurement of Density 27 Measurement of Diameter 27 X-Ray Diffraction (XRD) Analysis 28 Fourier Transformation by Infrared Spectroscopy (FTIR) Analysis 29 Thermogravimetric Analysis (TGA) 29 Investigation of Scanning Electron Microscope 30 Investigation of Transmission Electron Microscope 31 Conclusions 32 References 32

3

Fundamentals of Carbon-Fiber-Reinforced Composite and Structures 37 Rupita Ghosh, Subhadip Das, Sarada P. Mallick, and Rajan Introduction 37 Classification of Carbon Fibers 38 Synthesis of Carbon Fiber 38 Surface Treatment of Carbon Fibers 40 Carbon-Fiber-Reinforced with Polymer Matrix Composites 41 Manufacturing of the Polymer Composites Reinforced with Carbon Fibers 42 Hand Lay-up and Spray-up Process 42 Molding 43 Filament Winding 43 Pultrusion 44 Injection Molding 44 Reinforcement of Carbon Fibers and Properties of CFRP Composites 44 Carbon-Fiber-Reinforced Ceramic Matrix Composites 46 Structure of Carbon-Fiber-Reinforced CMCs 47 Synthesis and Properties of Carbon-Fiber-Reinforced CMCs 48 Hot Pressing 48 Spark Plasma Sintering (SPS) 48 Infiltration Methods 49

3.1 3.2 3.3 3.4 3.5 3.5.1 3.5.1.1 3.5.1.2 3.5.1.3 3.5.1.4 3.5.1.5 3.5.2 3.6 3.6.1 3.6.2 3.6.2.1 3.6.2.2 3.6.2.3

Contents

3.6.2.4 3.6.2.5 3.6.2.6 3.6.2.7 3.7 3.7.1 3.7.2 3.7.2.1 3.7.2.2 3.7.2.3 3.8

4

4.1 4.2 4.2.1 4.2.1.1 4.2.1.2 4.2.1.3 4.2.1.4 4.2.1.5 4.2.2 4.2.2.1 4.2.2.2 4.2.2.3 4.2.2.4 4.2.2.5 4.2.2.6 4.3 4.4

5

5.1 5.2 5.2.1 5.2.2 5.2.3

Slurry Infiltration Process 50 Reactive Melt Infiltration 51 Polymer Infiltration and Pyrolysis 52 Sol–Gel Infiltration Process 52 Carbon-Fiber-Reinforced Carbon Matrix Composites 53 Structure of Carbon–Carbon Composites 53 Synthesis of Carbon–Carbon Composites 53 Thermosetting Resin-Based Carbon–Carbon Composite and Properties 54 Thermoplastic Pitch-Based Carbon–Carbon Composite and Properties 56 Chemical Vapor Deposition (CVD) and Properties 57 Conclusion 59 References 59 Introduction to Semisynthetic and Synthetic Fiber Based Composites 67 Vishal N. Sulakhe Introduction 67 Classifications 69 Semisynthetic Fibers 69 Rayon 69 Modal Fiber 69 Bamboo Rayon 70 Seacell Fiber 70 Acetate Fibers 70 Synthetic Fibers 71 Glass Fibers 71 Carbon Fiber 72 Graphene Fiber 73 Basalt Fiber 73 Kevlar 73 Nylon and Terylene 74 Challenges 74 Conclusions 75 References 75 Tribological Properties of Natural Fiber-Reinforced Polymer Composites 81 A. Muthuraja and Dipen Kumar Rajak Introduction 81 Chemical Treatment–Alkaline Treatment 83 Alkaline Treatment (Mercerization) 83 Silane Coupling Agents (Silanization) 83 Mechanical Properties of Synthetic and Natural Fibers 83

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5.3 5.4 5.5

Tribological Behavior of Chemically Treated Composites 84 Tribological Behavior of Hybrid Composites 87 Conclusion 89 References 89

6

Nonstructural Applications of Synthetic Fibers Composites 93 Ashish Gupta, Pankaj Kumar, Mandeep Singh, Hema Garg, Anisha Chaudhary, and Sanjay R. Dhakate Introduction 93 Nonstructural Applications of SFRCs 94 Energy Sector 95 Batteries 95 Supercapacitors 96 Fuel Cells 97 Thermal Energy Storage (TES) Technology 99 Thermoelectric Energy Eneration 99 Mechanical Industry 101 Tribological Applications 101 Civil Engineering 102 Electronic Sector 102 Light Emitting Diode (LED) Devices 103 Field-Effect Transistors (FET) 104 Sensors 104 EMI Shielding 106 Medical Sector 107 Drug Delivery 107 Protein/Gene Therapy 108 Conclusions and Future Challenges 108 References 109

6.1 6.2 6.2.1 6.2.1.1 6.2.1.2 6.2.1.3 6.2.1.4 6.2.1.5 6.2.2 6.2.2.1 6.2.2.2 6.2.3 6.2.3.1 6.2.3.2 6.2.3.3 6.2.3.4 6.2.4 6.2.4.1 6.2.4.2 6.3

7

7.1 7.2 7.2.1 7.2.2 7.2.3 7.2.4 7.2.5 7.3

Structural Evolution, Mechanical Features, and Future Possibilities of Fiber, Textile, and Nano-cementitious Materials 117 Prashant Rawat, Sai Liu, and Deju Zhu History of Fiber and Textile Reinforced Concrete 117 Components of Cementitious Materials 119 Matrix Materials 119 Reinforcements 121 Short Discontinuous Fibers 121 Textiles/Woven 123 Advanced Nanoparticles 126 Mechanical Performance of Reinforced Concrete 127

Contents

7.3.1 7.3.2 7.3.3 7.4

Mechanical Behavior of SF Reinforced Concrete 128 Mechanical Behavior of Textile Reinforced Concrete 128 Mechanical Behavior of Nanoparticles Reinforced Concrete 129 Outlook and Future of Reinforced Concrete 130 References 131

8

Physical and Chemical Properties of Cotton Fiber-Based Composites 137 Pankaj Kumar, Cherala Sai Ram, Jay P. Srivastava, Ashwini Kumar, and Arun K. Behura Fabrication Process for Cotton Fiber-Reinforced Composite 137 Mechanical Properties of Cotton Fiber-Reinforced Composites 138 Tensile Strength 138 Buckle Power 139 Compressive Strength 140 Impact Strength 141 Hardness 142 Thermogravimetric Analysis (TGA) 142 Water Absorption Test 143 Microscopic Morphology 144 Fourier Transformation by Infrared Spectroscopy (FTIR) Analysis 145 Investigation of Transmission Electron Microscope 146 Life Cycle and Environmental Assessment of Cotton Fibers Reinforced Composites 147 The Durability of Cotton Fiber-Reinforced Composites 148 Conclusions 148 References 148

8.1 8.2 8.2.1 8.2.2 8.2.3 8.2.4 8.2.5 8.2.6 8.2.7 8.2.8 8.2.9 8.2.10 8.3 8.4 8.5

9

9.1 9.2 9.2.1 9.2.2 9.3 9.3.1 9.3.2 9.3.3 9.3.4 9.3.5 9.4

Properties of Carbon Nanotubes (CNT) 155 Vijay K. Singh, Puneet Kumar, Sunil K. Yadav, Chandrasekhar Saran, and Kaki V. Rao Introduction 155 Carbon Nanotubes Family 156 Single-Walled Carbon Nanotube (SWCNT) 156 Multiwalled Carbon Nanotube (MWCNT) 157 Properties of CNTs 157 Mechanical Properties 157 Thermal Properties 157 Electrical Properties 158 Electronic Properties 159 Field-Emission Properties 159 Conclusion 160 Acknowledgment 160 References 161

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10.1 10.2 10.2.1 10.2.2 10.2.3 10.2.4 10.3 10.3.1 10.3.2 10.4

11

11.1 11.2 11.2.1 11.2.2 11.2.3 11.2.3.1 11.2.3.2 11.3 11.3.1 11.3.2 11.3.3 11.3.4 11.3.5 11.3.6 11.4 11.4.1 11.4.2

12 12.1 12.2 12.2.1 12.2.2 12.2.3

Mechanical and Thermal Properties of Sisal Fiber-Based Composites 163 Vivek Mishra, Alok Agrawal, Saurabh Chandraker, and Abhishek Sharma Introduction 163 Mechanical Properties of Sisal Fiber-Reinforced Composites 166 Tensile Properties 167 Flexural Properties 168 Impact Properties 171 Hardness 173 Thermal Behavior of Sisal Fiber-Reinforced Polymer Composites 175 Thermal Stability 175 Glass Transition Temperature 179 Conclusion 181 References 182 Mechanical, Electrical, Magnetic, and Smart Properties of Synthetic Fiber Composites 187 Hema Garg, Jayashree Mohanty, Abhishek K. Pathak, Ashish Gupta, Satish Teotia, and Bipin Kumar Introduction 187 Mechanical Properties of FRP 188 Tensile Properties 189 Flexural Properties 190 Interlaminar Properties 191 ILSS and IFSS 192 Interlaminar Fracture Toughness 193 Influential Parameters on Mechanical Properties of FRP 194 Influence of Fiber Types 194 Influence of Matrix 195 Effect of Nanofillers 195 Electrical Properties 198 Magnetic and Electromagnetic Properties 200 Electromagnetic Properties: EMI Shielding 201 Smart Properties 201 Shape Memory Composites 202 Self-Healing Composites 203 References 204 Thermal Properties of Natural Based Fibers Composites 211 Ashwini Kumar, Arun K. Behura, Dipen K. Rajak, and Pankaj Kumar Introduction 211 Natural Fibers 214 Natural Plant Fibers 215 Resins 217 Fillers 217

Contents

12.3 12.3.1 12.3.2 12.3.3 12.4 12.5 12.5.1 12.5.2 12.6 12.7 12.8

Thermo-gravimetric Investigation 218 Isothermic and Non-isothermic Thermo-gravimetric Investigation 219 Equation of Coats–Redfern 220 Equation of Horowitz–Metzger 220 Choice of Substance Based on TGI 220 Common Fibril-Strengthened Compounds 221 Thermosetting Compounds 221 Laminate Agrochemical Compounds 223 Common Fiber-Strengthened Bio Agrochemical Compounds 224 Blend of Nano Compounds 228 Conclusion and Summary 229 References 230

13

Thermic and Mechanical Valuables of Synthetic Based Fibers Blend Compounds 241 Arun K. Behura, Ashwini Kumar, Dipen K. Rajak, and Pankaj Kumar Introduction 241 Synthetic Fibers 242 Carbon Fibrils 242 Glass Fibrils 243 Blend Fibril-Based Agrochemical Compounds 244 Synthetic Reinforced Hybrid Composites 245 Implementations of Polymerized Fibril Agrochemical Hybrid Compounds 245 Thermal Characteristics of Blend Polymerized Fibril Strengthened Compounds 246 Thermal Properties of Glassy Carbon (Woven) 248 Thermal Properties of Kevlar 249 Thermal Properties of Carbon Fibrils 249 Thermal Properties of Basalt Fibers Reinforced Composites 250 Mechanical and Physical Characteristics of Blend Fiber Compounds 250 Epoxy Based-Hybrid Composites 250 Polyester Based Hybrid Composites 252 (C2 H4 )n Basis of Blend Compounds 252 Thermo-Cool Basis of Blend Compounds 253 Conclusions and Summary 253 References 254

13.1 13.2 13.2.1 13.2.2 13.3 13.3.1 13.3.2 13.4 13.4.1 13.4.2 13.4.3 13.4.4 13.5 13.5.1 13.5.2 13.5.3 13.5.4 13.6

14

14.1 14.1.1

Advancement of Natural Fiber-Based Polymer Composites 261 Sivaramakrishnan Natesan, Biswajit Parida, Nithya Natesan, Muthuraja Ayyankalai, Waleed Alhazmi, and Anil K. Deepati Introduction of Synthetic Fiber 261 Fiber-Reinforced Plastic (FRP) Composites 262

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14.2 14.2.1 14.2.1.1 14.2.1.2 14.2.1.3 14.2.1.4 14.2.2 14.2.2.1 14.2.2.2 14.2.2.3 14.2.2.4 14.2.2.5 14.2.2.6 14.2.2.7 14.2.3 14.3 14.3.1 14.3.2 14.3.3 14.3.3.1 14.3.3.2 14.3.3.3 14.3.4 14.3.4.1 14.3.4.2 14.3.4.3 14.4 14.4.1 14.4.1.1 14.4.1.2 14.4.1.3 14.4.2 14.4.2.1 14.4.2.2 14.4.2.3 14.4.2.4 14.4.3 14.5 14.5.1 14.5.2 14.5.3 14.5.4 14.5.5 14.6

Classification of Natural Fibers 262 Plant Fibers 263 Seed Fibers 263 Leaf Fibers 264 Bast Fibers 264 Stalk Fibers 265 Animal Fibers 266 Wool 266 Mohair 266 Cashmere 266 Alpaca Hair 266 Angora Hair 267 Silk Fiber 267 Avian Fiber 267 Mineral Fibers 267 Synthesis and Production of Natural Fibers 267 Extraction of Fibers 267 Extraction and Processing of Plant-Based Fiber 268 Extraction and Processing of Animal Fiber 268 Animal Wool and Hair Fiber Processing 269 Silk Fiber Processing 269 Feather and Avian Fiber 269 Extraction and Processing of Mineral Fiber 269 Asbestos 269 Ceramic Fiber 270 Metal Fiber 270 Treatment and Enhancement of Natural Fiber 270 Physical Treatment 271 Mechanical Treatment 271 Solvent Extraction 272 Electric Discharge 272 Chemical Treatment 273 Alkaline Treatment (Mercerization) 274 Acetone Treatment 274 Peroxide (Benzoylation) Treatment 275 Silane Coupling Agents (Silanization) 275 Biological Treatment 275 Fabrication of Techniques of NFRC 275 Hand Lay-up Technique 276 Vacuum Infusion Molding 276 Spray Lay-up Technique 276 Pultrusion 277 Resin Transfer Molding (RTM) 277 Mechanical Performance of Natural Fiber Reinforced Polymer Composites (NFRP) 277

Contents

14.6.1 14.7 14.7.1 14.8 14.8.1 14.8.2 14.8.3 14.9 14.9.1 14.9.2 14.9.3 14.10 14.10.1 14.10.2 14.10.3 14.10.4 14.10.5 14.10.6 14.11

15

15.1 15.1.1 15.1.2 15.2 15.3 15.4 15.4.1 15.4.2 15.4.3 15.4.4 15.5 15.6 15.7 15.8 15.9 15.10 15.11

Influence of Chemical Treatment 277 Effect of Hybridization 279 Fiber Percentage (%) 279 Effect of Hybridization and Its Application of Nanofiber 281 Effect of Hybridization of Nanofibers Over Mechanical and Tribological Fibers 281 Nano-based Fibers 284 Synthesis of Nanofiber by Using the Electro-spinning Process 285 Preparation and Characterization of Nanofibers 285 Polyacrylonitrile (PAN) Fibers 285 Alumina Fibers 286 BaTiO3 Nanofiber 287 Applications of Electrospun Nanofibers 287 Nanofibers in Air Filtration 287 Nanofiber in Water Filtration 288 Recycled PET (RPET) Nanofibers for Water Filtration 289 Energy Conversion and Storage Device 290 Nanofibers in Solar Cells 290 Nanofiber-Based Li–S and LiO2 Batteries 290 Conclusions 291 References 292 Recent Advancements in the Natural Fiber-Reinforced Polymer Composites 301 Satish Teotia, Anisha Chaudhary, Ashish Gupta, and Hema Garg Introduction 301 Natural Fibers 301 Natural Fiber-Reinforced Composites 303 Natural Fiber-Reinforced Polymer Composites (NFRCs) 304 Advancement in Natural Fiber-Reinforced Composites 305 Mechanical Properties of NFRCs 306 Fiber Treatment and Modification 307 Chemical Treatment 307 Coupling Agent 309 Fiber Hybridization 310 Reinforcement with Nanocellulosic Fillers 312 Flame Retardant Properties of the NFRCs 312 Water Absorption Characteristics of the NFRCs 313 Advancement of Conventional Manufacturing Processes 314 3D Printing in NFRCs 316 Natural Fiber-Reinforced Polymer Composites Application 317 Summary and Prospects 319 Acknowledgments 320 References 320 Index 329

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Preface Fiber Reinforced Polymer (FRP) composites offer several exclusive properties and are preferred for wide use in automotive, aerospace, marine, construction, and co-industrial applications. They are made-up from a combination of polymers such as epoxy, phenol-formaldehyde, and vinyl-ester and are reinforced with a variation of fibers such as matrix carbon, glass, and aramid. When composites are combined with reinforcement supplements, the use of natural compounds containing synthetic fibers and synthetics containing natural fiber materials in a mixture or as individual constituents are mandatory to obtain superior properties of the resulting composites. In modern era, FRP has become a very important alternative material for structural components such as reinforcement bars and pre-stressing owing to their outstanding properties such as high tensile strength, corrosion resistance, no magnetism, and light weight. Moreover, FRP has an excellent linear elastic response to stress up to failure and relatively low shear resistance, also fire resistance is very low even at elevated temperatures. FRP composites have great potential in the market because they can constitute a wide variety of integrated materials that meet the requirements for high-precision applications. Designers and engineers can easily modify the chemical and physical properties of FRP composite materials by selecting certain types of fillers, additives, and core materials. However, only few books have been published in the area of FRP composites. Therefore, we believe the book “Natural and Synthetic Fiber Reinforced Composites” will be beneficial for scientists, engineers, academic staff, and students working in the area of natural and synthesis reinforced polymers, and composites. The book consists of 15 chapters. Chapter 1 summarizes the insights into glass fiber-based composites. Chapter 2 mainly focuses on presenting findings on the synthesis of cotton fiber and its structure. It includes the basics of cotton fibers in terms of their origin, their classifications, major steps of cotton production and cultivation, surface modification of cotton fibers, and solvents for cotton. Chapter 3 reviews the generalized structure, synthesis procedures, and properties with a special emphasis on the change of properties with a change in synthesis conditions. Chapter 4 emphasizes the introduction, classification, functionality, and applications of semi-synthetic and synthetic fiber composites. Chapter 5 discusses the role of tribological behavior of natural fiber reinforced composites and helps to understand the effectiveness of treatment and hybridization for influencing the

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Preface

factors friction and wear. Chapter 6 is dedicated to the current state-of-the-art of synthetic fibers composites and their non-structural applications such as energy storage, thermoelectrics, chemical sensing, tribology, EMI shielding, drug delivery, etc. Chapter 7 analyzes the evolution of reinforced cementitious materials and their future possibilities as advanced building materials. Chapter 8 focuses on the fabrication of cotton fiber reinforced composites. Chapter 9 deals with the extraordinary mechanical, thermal, electrical, electronic, and field emission properties of carbon nanotubes (CNTs) that have been attracting the attention of engineers and researchers for last three decades. Chapter 10’s main emphasis is on the mechanical and thermal behavior of composites and their applications in various fields. A review of the research on sisal fibers in a polymer matrix is a main part of this chapter. Chapter 11 highlights the properties of FRP with the aim to target the influence of various reinforcement fibers, polymer matrices, and fillers on the individual properties. Chapter 12 gives an overview of the thermal behavior of natural based fibers composites, a topic that is further elaborated in Chapter 13. Chapters 14 and 15 give an overview of the recent advances in naturla fiber based polymer composites. They cover the current research efforts carried out in the area of NFRCs development, major approaches, and revolutions in enhancing their performance. Different fibers pre-treatment and modification techniques are also discussed along with their effect on characteristics of natural fibers, polymer composites reinforced with natural fibers and their recent development, challenges, and opportunities in the area of NFRCs. Dr. Dipen Kumar Rajak, India Dr. Sanjay M. Rangappa, Thailand Prof. Dr.-Ing. habil. Suchart Siengchin, Thailand

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About the Editors Dr. Dipen K. Rajak, Assistant Professor, Department of Mechanical Engineering, Sandip Institute of Technology & Research Centre (SITRC), Nashik-422213, Maharashtra, India. Dr. Dipen K. Rajak, in the midst of a healthy and intellectual upbringing, obtained his Diploma in Technology-Manufacturing Engineering from University Polytechnic, BIT, Mesra, Ranchi in 2008. Subsequently, he graduated (BTech) in Mechanical Engineering from Ramgovind Institute of Technology, Koderma/Vinoba Bhave University, Hazaribag in 2012. Besides having strong technical expertise and analytical skills, he acquired his doctorate degree (PhD) from the Indian Institute of Technology (ISM), Dhanbad in 2017. The academic achievements are manifested in his original research contributions through over 70 papers published in refereed international journals, including 8 Indian Patents, 2 Designs, 8 book chapters, and 2 books. He has received numerous awards such as the “Young Scientist Awards” 2019, Kasetsart University, Bangkok, Thailand, the “Young Scientist on Research Excellence and Academic Awards” 2019, Mumbai and the “Excellence in Research Awards” 2018 Delhi, India, the “Outstanding Reviewer Award” from Elsevier journals in 2016, and an “International Travel Grant” and a “Best Session Paper Award” in International Conferences 2015 in Thailand. Dr. Rajak is associated with foreign and national universities and is an editorial board member and reviewer of refereed international journals. Dr. Rajak is currently working as Assistant Professor in the Department of Mechanical Engineering at Sandip Institute of Technology & Research Centre, Nashik. He also serves as a Nashik-Branch President for International Engineering and Technology Institute, Hong Kong, and his recent work consists of the development of aluminum foams for different applications where low density and high specific energy absorption is required in automobile, aerospace, and thermal management sectors, include fiber reinforcement materials, and metal matrix composites. Google Scholar: https://scholar.google.co.in/citations?user=vw44NJkAAAAJ& hl=en. Dr. Sanjay M. Rangappa, Senior Research Scientist, Natural Composites Research Group Lab, King Mongkut’s University of Technology North Bangkok, 1518 Pracharaj 1, Wongsawang Road, Bangsue, Bangkok 10800, Thailand.

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About the Editors

Dr. Sanjay M. Rangappa is currently working as Senior Research Scientist and also an Advisor within the office of the President for University Promotion and Development toward International goals at King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand. He has received the BE (Mechanical Engineering) in the year 2010, MTech (Computational Analysis in Mechanical Sciences) in the year 2013, PhD (Faculty of Mechanical Engineering Science) from Visvesvaraya Technological University, Belagavi, India in the year 2017, and Post Doctorate from King Mongkut’s University of Technology North Bangkok, Thailand, in the year 2019. He is a Life Member of the Indian Society for Technical Education (ISTE) and an Associate Member of the Institute of Engineers (India). He acts as a Board Member of various international journals in the fields of materials science and composites. He is a reviewer for more than 85 international Journals (for Nature, Elsevier, Springer, Sage, Taylor & Francis, Wiley, American Society for Testing and Materials, American Society of Agricultural and Biological Engineers, IOP, Hindawi, NC State University USA, ASM International, Emerald Group, Bentham Science Publishers, Universiti Putra, Malaysia), also a reviewer for book proposals, and international conferences. He has published more than 125 articles in high quality international peer-reviewed journals, 5 editorial corners, 35 book chapters, 1 book, 15 books as an Editor, and also presented research papers at national/international conferences. In addition, he has filed one Thailand Patent and three Indian patents. His current research areas include natural fiber composites, polymer composites, and advanced material technology. He is a recipient of the DAAD Academic exchange–PPP Programme (Project-related Personnel Exchange) between Thailand and Germany to the Institute of Composite Materials, University of Kaiserslautern, Germany. He has received a Top Peer Reviewer 2019 award, Global Peer Review Awards, Powered by Publons, Web of Science Group. The KMUTNB selected him for the “Outstanding Young Researcher Award 2020.” He has been recognized by Stanford University’s list of the world’s Top 2% of the most cited scientists in single year citation impact 2019. Google Scholar: https://scholar.google.com/citations?user=al91CasAAAAJ& hl=en. Prof. Dr.-Ing. habil. Suchart Siengchin, President of King Mongkut’s University of Technology North Bangkok. Department of Materials and Production Engineering (MPE), The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, 1518 Pracharaj 1, Wongsawang Road, Bangsue, Bangkok 10800, Thailand. Prof. Dr.-Ing. habil. Suchart Siengchin is the President of King Mongkut’s University of Technology North Bangkok. He has received his Dipl.-Ing. in Mechanical Engineering from University of Applied Sciences Giessen/Friedberg, Hessen, Germany in 1999, MSc in Polymer Technology from University of Applied Sciences Aalen, Baden-Wuerttemberg, Germany in 2002, MSc in Material Science at the Erlangen-Nürnberg University, Bayern, Germany in 2004, Doctor of Philosophy in Engineering (Dr.-Ing.) from Institute for Composite Materials, University of Kaiserslautern, Rheinland-Pfalz, Germany in 2008, and Postdoctoral Research from Kaiserslautern University and School of Materials Engineering, Purdue University, USA. In 2016, he received the habilitation at the Technical University

About the Editors

of Chemnitz, Sachsen, Germany. He worked as a Lecturer for the Production and Material Engineering Department at The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), KMUTNB. He has been a full Professor at KMUTNB and became the President of KMUTNB. He won the Outstanding Researcher Award in 2010, 2012, and 2013 at KMUTNB. His research interests in Polymer Processing and Composite Material. He is Editor-in-Chief of the KMUTNB International Journal of Applied Science and Technology and the author of more than 250 peer-reviewed Journal Articles. He has participated in presentations in more than 39 International and National Conferences with respect to Materials Science and Engineering topics. He has recognized and ranked among the world’s top 2% scientists listed by prestigious Stanford University. Google Scholar: https://scholar.google.com/citations?user=BNZEC7cAAAAJ& hl=en.

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1 Introduction to Glass Fiber-Based Composites and Structures Jay Prakash Srivastava and Pankaj Kumar SR University, Department of Mechanical Engineering, Center for Materials and Manufacturing, Ananthasagar, Hasanparthy, Warangal Urban 506371, Telangana, India

1.1 Introduction Composites are formed by the association of fillers, reinforcing fibers along with compactable matrix materials, and other components [1]. The origin of the matrix can be metallic, polymeric, or ceramic. This furnishes composites their surface appearance, form, resilience, and environmental tolerance. Most of the structural strain is borne by the fibrous reinforcement, giving macroscopic rigidity and strength [2]. Superior mechanical and physical properties can be given by a composite material because it incorporates the most desirable properties of its constituents while removing their least desirable properties [3, 4]. Glass Fiber-Reinforced Composite (GFRC) is a thermoset plastic resin that is reinforced with glass fibers [5]. Weight, dimensional stability, and heat resistance are given by fiber. Additives provide color, decide the surface finish, and influence many other characteristics, such as wear and flame retardancy. Complex chemical action requires manipulating glass fiber reinforced polymer (GFRP) composites [6]. Factors, including the form, quantity, and composition of the resins and orientation of reinforcements, determine the final properties [7]. Lightweight, high strength, corrosion endurance, dimensional steadiness, component consolidation and tooling minimizations, low moisture absorption, high dielectric strength, minimal finishing required, low moderate tooling cost, and design versatility are the benefits and characteristics of GFRC [8]. Rene Ferchault de Reaumur invented glass fiber. At the completion of the eighteenth century, large-scale glass fiber manufacturing began. It continued as a forgotten composite material until 1935, and it gained prominence only after fiberglass was turned into yarn. Fiberglass composite first finds its application in the aircraft industry. Since then, it has been expanded in various profit-making applications. Although glass has the best characteristics, it lacks reusability and bio-degradability. Therefore, researchers [9–12] are working at an approach that encourages both reusability and bio-degradability. Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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1 Introduction to Glass Fiber-Based Composites and Structures

Glass fibers are one of the most adaptable industrial and domestic materials in the current scenario [13]. They are readily available in abundance to meet their demand. Silica is the main ingredient of almost all glass fibers [14]. They demonstrate properties viz hardness, clearness, chemical resistance, constancy, and inertness, as well as fiber properties such as strength, flexibility, and stiffness, which are desirable. Glass fibers are used in the manufacturing of structural composites, printed circuit boards, and a wide variety of special-purpose items. One of the most prevalent fibers used in the reinforced polymer industry is fiberglass or glass fiber. Fiberglass is extremely flexible and can be converted into sheets. For the manufacturing of fiberglass, it is melted and pushed in diameter through superfine holes [15]. The created glass threads can be knitted into thin sheets or condensed into bloated materials that can be utilized in soundproofing and isolation. GFRC is used in the manufacturing of a variety of products, such as cars, aircraft, pressure vessels, defense equipment, and consumer goods, etc. Fiberglass is more versatile than carbon fiber and less costly. It has the peculiarity of being sturdier as compared to numerous metals as well. These are lightweight and have good malleability [16]. For all the right reasons, GFRC has acquired the marketplace. Earlier, the higher cost of polymers is found to be one of the reasons for its limited use in industrial application. However, the addition of fillers strengthened the GFRP properties and eventually decreased preparation and overall costs also. GFRC has a wide variety of applications in the aerospace, marine/shipping, construction, chemical, automobile, consumer commodities, and piping industries, etc. Laminated GFRC materials are used because of good corrosive resistance, better impact loading and damage tolerance, high specific strength, and rigidity. In Section 1.2, the application of GFRC is discussed in detail.

1.2 Applications GFRCs are a favored material because of their enormous properties including electrical protection, strength, and toughness. Glass fiber fortified saps are utilized generally in the structure and development industry. They are utilized as a layer and/or cover for other underlying materials as well as a divider board; window outlines, reservoirs/containers, washroom utilities, lines, and channels are basic models. Boat frames, since the mid-1960s, have principally been made of GFRC. The utilization of GFRC in the consumer functionalities (reservoirs, pipelines, and pressure vessels) is genuinely standard. All three modes of transport, i.e. railways, roadways, and air transportation are another huge client of GFRC. As referenced earlier, fiberglass is quite possibly the most ordinarily utilized material in almost all engineering applications. Probably the most unmistakable uses of fiberglass are as follows: 1. The material utilized in the airplane and aeronautic trade must be steady and lightweight. S-glass possesses superior strength and modulus, making it a favored sort of fiberglass in the industrial sector. Also, S-glass likewise has better overlay solidarity to weight proportion, high weariness life, and good maintenance life at elevated temperatures.

1.2 Applications

25.51% 29.63%

5.84% 5.18%

4.97%

4.43%

Legend Structural parts Luggage bins and storage racks

Figure 1.1

Flooring, closets, cargo liners, and seating

39.02%

Others

Global fiber-glass for aerospace industry market by application.

GFRC has been broadly utilized in avionics and aviation component as it better suits the applications [17]. Commonplace GFRC applications are structural parts, luggage bins and storage racks flooring, closets, cargo liners, and seating as shown in Figure 1.1. It is additionally broadly utilized in ground-dealing with hardware. It is commonly used to make protective layers in aero vehicles, flight deck shields, floorings, and armchairs of airplane. S-glass has more prominent mechanical properties as well as nonconductive. By offering lower radar warm profiles, it supports better stealth technology that gives these composites sharp edges for aviation equipment. 2. GFRC offers good dimensional constancy that makes it a perfect choice to be utilized in development. Decreased weight, low combustibility, sway obstruction, and high strength are altogether the properties that any development material ought to have, and GFRC is all that it requires to be. It is utilized in the development of both inside and outside parts of the business, private, and modern developments, going from washroom apparatuses to pool wall to lookout windows of mechanical structures to sun-based warming components. 3. GFRC is broadly used in various consumer commodities. These are utilized in the fabrication of furniture structures, decorative items, sports and gym equipment, etc. It is used as an essential material in consumer products because of its expanded flexibility, lower mass with superior strength, sturdiness, simple formability, great surface, and protection from corrosion and wear. It likewise discovers great purpose in the manufacture of home and furniture appliances viz rooftop sheets, bathroom accessories, racks, coffee tables, etc. 4. GFRC is also utilized for many applications where corrosion-resistant materials are required. For longer work-life in hostile and chemical process industries, GFRCs with proper additives are used for approximately 95% of corrosionresistant equipment [18]. These materials possess good resistance to wear and corrosion. The above properties make it an ideal material for making equipment such as underground petrol tank, sewage systems, dam gates, drainage and chemical pipes, water and waste treatment areas, cooling towers, pollution

3

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1 Introduction to Glass Fiber-Based Composites and Structures

5.

6.

7.

8.

9.

control equipment, tanks and vessels, pipe, ducting, hoods, fans, scrubbers, stacks, grating, and specialty fabrications. Good electrical insulation property and stable mechanical behavior at elevated temperature make the GFRC an appropriate choice of material for its application in electrical appliances [14]. GFRCs have been extensively used in circuit board making, computer parts and accessories, transformers, mobile phones, switchgear, structural covers, and electrical components. Good toughness and the better strength to weight ratio of GFRC give significant reason for its overwhelming acceptance in the marine and shipping industry. It has a better ability to be formed into different shapes with ease. These properties are undeniably fit for boat development. In spite of the fact that there were issues with water retention, the cutting-edge gums are stronger and they are utilized to simplify the sort of boats. Truth be told, GFRC is a lightweight material contrasted with different structural materials [19]. Low density with higher strength of GFRC has made it a favored development material choice in the automobile sector also. Various underlying components of a vehicle are made with fiberglass, like the strap in a belted-inclination tire. GFRC is likewise used to make rail line fishplates. It has assumed control over the automobile industry in abundance. It has supplanted traditional structure materials. It will keep on improving its quality with consistent enhancements and further turns of events. It has effectively fulfilled the necessities of the designing field partly, and it keeps on facilitating fulfill the prerequisites of different businesses. It has been widely utilized for car body-parts such as boards, seat, cover-plates, entryway boards, door, bumpers, engine cover, guards, and various vehicle accessories cover, etc. Good wear resistance, low porosity, and nonstaining ability of GFRCs make them suitable for medical equipment applications. Because of their transparency, GFRCs are used for making X-ray beds. Nowadays, GFRCs are commonly used in pressure application, as shown in Figure 1.2. With proper design consideration and analysis, it works safely for up to 1200 psi. For high temperature and military application also, it is applicable with the proper combination of reinforcement material and resins. Figure 1.2 High-pressure containers prepared of thermosetting resin and glass fiber reinforcement. Source: Reproduced from Rajak et al. [3].

1.3 Classification of GFRC

Composites are mostly suitable for the design of aircraft components such as wind turbine blades, pipelines, automobile structures, partitioning, seating, and marine construction. The character of composite is determined by the nature of reinforcement used, fiber orientation, method of molding, and operating conditions. In order to allow stress transfer, the mechanical behavior of a GFRC is essentially subjected to the mechanical characteristics of the fiber, chemical constancy, strength of the matrix, and the interfacial connection between the fiber and matrix. The shape of the component is provided by the matrix used. Reinforcements are man-made at the beginning, both by different physical techniques and by chemical synthesis. They are mass-produced and delivered to various factories for composite manufacturing because of the wide use of reinforcements. In course of production, glass fibers are utilized in various forms, such as long fibers, short fibers, and woven mats among various classes of artificial fibers. Glasses are easily available with lower cost and better properties making them a superior choice over other options. Centered on a particular application, glass fibers are of various kinds. Symbols like A-glass symbolizes alkali glass, C-glass embodies good chemical resistance, E-glass possesses properties suitable for an electrical application, S-glass is graded and nominated for structural purposes. In Section 1.3, classification of glass fiber is presented.

1.3 Classification of GFRC Glass-fibers can be utilized in numerous varieties to suit explicit applications. Various types of glass-fiber have differing constituents that bring about a particular quality of each kind. The essential ingredient of different types of glass-fiber is the equivalent except for a couple of crude constituents. The amounts of all crude elements in each sort of glass-fiber are unique, subsequently providing each type with a novel arrangement of properties, as depicted in Figure 1.3. The fundamental crude elements that are utilized in the assembling of glass-fiber incorporate silica, soda ash, and limestone. Other constituents contain borax, magnesite, calcined alumina, feldspar, kaolin clay, etc. Silica sand contributes to glass formation and soda ash along with limestone brings down the melting point. Different fixings add to the enhancement of various properties. For instance, borax enhances the ability to resist chemical attack [5]. As discussed earlier, there are numerous sorts of fiberglass relying on the forming elements. The significant sorts of fiberglass, depicted in Figure 1.2, are as follows.

1.3.1

A-Type

Alkali glass (soda-lime glass), abbreviated as A-type glass is the most common variety of glass fiber available. About 90% of the overall glass production comprises alkali glass. It is one of the very widely used glass type that is used in making window panes, glass jars, bottles for beverages, and food items. Tempered alkali glass is utilized in the making of baking utensils. This type of glass is quite hard, extremely

5

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1 Introduction to Glass Fiber-Based Composites and Structures

1

A-glass

High durability, strength, and electric resistivity

2

C-glass

Higher corrosion resistance

3

D-glass

Low–dielectric constant

4

E-glass

Higher strength and electrical resistivity

5

AR-glass

Alkali resistance

6

R-glass

Higher strength and acid corrosion resistance

7

S-glass

Higher tensile strength

8

S2-glass

High strength, modulus, and stability

Figure 1.3

Categorization and related properties of different glass fiber composites.

workable, chemically stable, and relatively cheaper. It can be recycled n number of times. The main ingredients for the formation of A-glass consist of soda (Na2 CO3 ), lime, silica (Si2 O3 ), dolomite, alumina (Al2 O3 ). Sodium chloride (NaCl) and sodium sulfate (Na2 SO4 ) are considered to be the fining agents, which are also used in the production of soda-lime glass.

1.3.2

C-Type

Compound glass also termed as C-glass demonstrates the most superior safeguard from chemical attack. The occurrence of a large amount of calcium borosilicate provides structural stability against corrosive surroundings. This type of glass is utilized in the external coating of covers as surface tissue for lines and tanks, which hold water and synthetic compounds.

1.3.3

D-Type

The existence of boron-trioxide in D-glass gives it recognition for its low dielectric constant. This characteristic makes it suitable for its application in optical cables. D-glass fiber-reinforced composite possesses a very low coefficient of thermal expansion making it appropriate for electrical devices and cookware.

1.3 Classification of GFRC

1.3.4

E-Type

This type of glass is an alkali glass normally termed electrical glass. It is a highperformance GFRP having lightweight used in marine, aerospace, and other industrial application. The constituent elements used in the production of E-type glass fiber composite are silica (SiO2 ), calcium oxide (CaO), alumina (Al2 O3 ), magnesium oxide (MgO), sodium oxide (Na2 O), boron trioxide (B2 O3 ), and potassium oxide (K2 O). The significant characteristics that make E-glass a popular type of fiberglass are better strength, economical, higher stiffness, heat resistant, low density, fire-resistant, better endurance to chemicals, comparatively inert to wetness, better electrical isolation, and ability to uphold structural integrity in diverse circumstances.

1.3.5

R-, S-, and T-Type

These are trademarks for a similar kind of GFRP. They acquire prominent modulus and rigidity when contrasted with E-type GFRP. Their acidic strength and wetting properties are likewise better. These characteristics are attained by reducing the fiber filament radius. This variety of glass-fiber is created and aimed at aerospace and defense application.

1.3.6

S2-Type

This type of glass has more content of silica as related to other forms of glass fiber. Because of that, it has improved characteristics, superior weight performance, elevated compressive strength, high-thermal endurance, and advanced impact resistance. Most importantly, S2-type GFRPs are economical having 85% more tensile strength than conventional fiberglass. It has improved toughness and impact capabilities, together with better damage tolerance and composite durability.

1.3.7

M-Type

This type of glass fiber possesses additional flexibility due to the presence of beryllium.

1.3.8

Z-Type

It is relatively transparent and utilized in several industries, involving the construction industry and 3D printing. This type of glass fiber is superior in mechanical strength, UV resistant, salt, alkali, acid, wear, temperature, and scratch resistance. It is perhaps the strongest as well as dependable kind of glass fiber. For the above-described glass fibers, their constituent percentage is presented in Figure 1.4. Various mechanical as well as physical properties for example tensile

7

8

1 Introduction to Glass Fiber-Based Composites and Structures Fe2O3 K2O Na2O MgO CaO B2O3 TiO2 Al2O3 SiO2 0

10

20

30

SiO2

Al2O3

TiO2

Basalt

52

17.2

1

EGR-glass

61

13

R-glass

60

24

D-glass

74

A-glass

67.5

3.5

S-glass

65

25

C-glass

64.6

4.1

E-glass

55

14

Figure 1.4 Table 1.1

B2O3

40

50

60

80

CaO

MgO

Na2O

K2 O

Fe2O3

8.6

5.2

5

1

5

22

3

9

6

0.5

22.5 1.5

70

6.5

4.5

0.5

0.1

1.5

2

13.5

3

10

0.2

5

13.4

3.3

9.6

0.5

7

22

1

0.5

0.3

Constituent percentage for different type of glass fiber. Physical and mechanical properties of glass fiber.

Young’s modulus (GPa)

Elongation (%)

Coefficient of thermal expansion (10−7 /∘ C)

Poisson’s ratio

Refractive index

0.2

1.558

Fiber

Density (g cm−3 )

Tensile strength (GPa)

E-glass

2.58

3.445

72.3

4.8

54

C-glass

2.52

3.310

68.9

4.8

63

S2-glass

2.46

4.890

86.9

5.7

16

A-glass

2.44

3.310

68.9

4.8

73

1.538

D-glass

2.11–2.14

2.415

51.7

4.6

25

1.465

R-glass

2.54

4.135

85.5

4.8

33

1.546

ECR-glass

2.72

3.445

80.3

4.8

59

1.579

AR glass

2.70

3.241

73.1

4.4

65

1.562

1.533 0.22

1.521

Source: Sathishkumar et al. [8].

strength, Young’s modulus of elasticity, coefficient of thermal expansion, refractive index, density, and Poisson’s ratio of glass fibers are given in Table 1.1.

1.4 Classifications Based on Form Glass fibers are primarily considered as reinforcement for polyester, phenolic resins, and epoxy. They are economical as well as available in a variety of arrangements. The assembly of distinctive fibers is termed as a continuous strand. The collection of similar strands comprises the roving form. A length of about 5–50 mm strands encompasses chopped fibers. Woven fabric, nonwoven mats, chopped strand mats,

1.5 Structure

Figure 1.5 600 grams per square meter (GSM) fiberglass woven roving mat. Source: Modified from Anon [21].

veil mats, and tow are some of the available forms of fiberglass [20]. Maximum properties are achieved when glass fiber is in form of tow or roving. In this type, fiberglass is delivered in the form of reels, which can be unrolled and cut as necessary or taken into filament winders. The fibers of fiberglass must remain under tension to maintain their mechanical properties. A randomly looped continuous strand of fiber in a thin pile arrangement forms the veil mats. They are not suitable for structural applications. The woven fabrics are relatively stronger, shown in Figure 1.5, as they are sewed together and are bundled into yarn [22]. Fibers of length of 3–4 in. are randomly arranged in chopped strand mats [23]. This type of glass fiber is cheaper and hence the most commonly used glass fiber as well. However, the length of fiber is shorter, making it less strong as compared to others.

1.5 Structure Silica-based-inorganic glasses are amorphous and hence identical to organic glass polymers. They are devoid of any crystalline material-characteristic long-range order. At 1800 ∘ C, pure, crystalline silica melts. However, with the addition of certain metal oxides, the bonding of silicon oxide can be broken down. This can cause the lowering of glass transition temperature and hence the formation of a series of amorphous glasses. In Figure 1.6, 2D arrangement of silica is presented. Silicon is covalently bonded with an oxygen atom in each polyhedron. Figure 1.6b shows the modification in structure when Na2 O is added. Sodium ions are connected to the atoms of oxygen; however, they are not specifically joining the network. The addition of other kinds of metal oxide helps to modify the structure of the network and the bonding and, subsequently, the properties. Remember that this contributes to the isotropic properties in the three-dimensional network structure of glass. Young’s modulus of elasticity and coefficient of thermal expansion of the glass fiber remain uniform along the longitudinal and transverse axis.

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1 Introduction to Glass Fiber-Based Composites and Structures

O2–

Na+ Si4+

(a)

(b)

Figure 1.6 Amorphous glass structure: (a) a 2D illustration of silica glass arrangement and (b) a reformed arrangement with Na2 O added to (a). Source: Chawla [24].

1.6 Mechanical Properties Singh et al. [25] studied mechanical and tribological characteristics of 20 wt% short glass fiber reinforced with 80 wt% poly-oxy-methylene (POM) and 20 wt% poly-tetra-fluoro-ethylene (PTFE) blend. Sixty-three percent (i.e. from 46.5 to 75.36 N mm−2 ) increase in tensile strength of the POM/PTFE blend reinforced with 20 wt% short glass fiber was reported. Vijay and Srikantappa [26] from their experimental study found superior mechanical and wear behavior of MoS2 filled glass-epoxy composites as compared to unfilled composite. Mechanical properties of different forms of glass fiber with resins and volume fraction are listed in Table 1.2. Shanti and Satyadevi [47] developed a glass fiber reinforced (GFR) composite with graphite as a filler and showed that these types of composites exhibit more mechanical and thermomechanical strengths compared to the composite without a filler. Kunishima et al. [48] investigated the tribological behavior of GFRP-polyamide 66 composite in contact with carbon steel under high contact pressure, sliding, and grease-lubricated conditions. They found sliding causes peeling off of the fibers and scratches on polyamide also [49]. Although a multitude of glass fiber forms exists, the most important types, resins, curing agent, testing standards their mechanical strength properties are listed in Table 1.2. Rajamahendran et al. [19] experimentally analyzed the mechanical and tribological behavior including sliding wear E-glass fiber-reinforced interpenetrating polymer networks (IPN) composites using a pin-on-disk apparatus. They found a massive increase in wear resistance with the addition of 5% alumina filler into the matrix material. Ravi et al. [50] experimentally investigated using a pin-on-disk wear tester to study the sliding wear behavior of the friction stir welded polyamide 66 including and excluding the glass fiber reinforcement. Vijaya Kumar et al. [51] numerically and experimentally studied about the mechanical properties of bamboo–GFR hybrid composite by changing the lamina orders. They opined that the lamina with order G/B/G/G (45% E-glass fiber, 15% bamboo fiber, and 40% epoxy resin) composite specimen offers more mechanical strength as compared to other lamina orders.

Table 1.2

Mechanical properties of GFRCs available in literature.

Testing standard

Tensile strength (MPa)

Tensile modulus (MPa)

Elongation at break (%)

Flexural strength (MPa)

Impact strength

Interlaminar shear strength (MPa)

44.7

References

Type of glass fiber

Resin

Vf

Woven mat

Polyester

0.25 ASTM D412 (T)

1.601

80.5

20.0

—

41.850 (J)

Woven mat

Polyester with 3% oligomeric siloxane

0.37 ASTM D-3039 (T), ASTM D 790 (F), ASTM D 2344 (S)

395.8

18 000

3.9

399.4

—

Woven mat

Polyester

0.33 ASTM D 638-97 (T), 2810 E6 (T)

249

6 240

—

—

—

—

Woven mat

Polyester

—

189.0

—

—

—

—

—

[17]

Chopped strand

Polyamide66 0.30 GB/T 16,421-1996 — (PA66)/poly(T) GB/T phenylene sulfide 16,419-1996 (F), (PPS) blend GB/T 16,420-1996 (I)

124

—

159

98.2 (kJ m−2 ) —

[30]

Woven mat (0∘ /90∘ )

Poly-phenylene sulphide (PPS) blend

0.42 PS25C-0118 (T)

200

—

—

—

10 (J)

—

[31]

Woven mat (non-symmetric)

Polyester

—

362F (BS, 1997) (T)

220

7 000

0.055

—

—

27

[32]

Woven

Polyurethanes

0.49 ASTM D3039 (T), ASTM D790M (F), ASTM D2344 (S)

278

18 654

—

444

—

—

[33]

Chopped strand mat

Polyester

0.60 ASTM D638 (T)

250

325

0.022

—

—

30

[34]

Woven mat

Polyester (acid resistant resin)

—

—

—

—

—

—

—

[35]

ASTM D 2344 (S)

[27] [28]

[29]

(continued)

Table 1.2

(Continued)

Testing standard

Tensile strength (MPa)

Elongation Flexural Tensile strength Impact modulus at break (MPa) strength (%) (MPa)

Interlaminar shear strength (MPa) References

3 000

Type of glass fiber Resin

Vf

Chopped strand mat

Polyester ruin

0.015 ASTM E 399 (T)

—

Chopped strand + vertical roving

Polyester

—

ASTM D 3039 (T), ASTM D 5379 (I)

Virgin fiber

Polyester

—

Glass

—

16.5

—

—

[36]

103.4719 —

—

—

37.926 (J)

—

[37]

ASTM D256 (T), ASTM D2240 (I)

64.4

7 200

1.8

—

645.1 (J m−1 )

—

[38]

Polyester 0.40 (3 wt% Na-MMT)

ASTM-D638 (T), ASTM-D790 F, ASTM-D256 (I)

130.03

—

—

206.15

153.50 (kJ m−2 ) —

[39]

Chopped strand

Epoxy (5.1 Vf fly ash)

3.98

ASTM standard

—

—

—

—

0.0176 J mm−2

18.2

[40]

Woven (biaxial stitch)

Epoxy

0.57

ASTM D 2355 (S)

—

—

—

—

—

—

[41]

Randomly oriented

Epoxy (10 wt% SiC)

0.5

ASTM D 3039-76 (T), ASTM D 256 (I)

179.4

6 700

—

297.82

1.840 (J)

18.99

[42]

Woven

Epoxy (0.5 wt% MWCNTs)

0.73

ASTM D 2344 (S)

—

—

—

—

—

41.46

[43]

Unidirectional

Epoxy

0.55

ASTM D 3039 (T)

784.98

—

0.032

—

—

—

[44]

Woven

Epoxy (6 wt% joc) 0.60

ASTM D 3039 (T)

311

18 610

3.8

—

—

—

[45]

—

355

43 700

1.65

—

—

—

[46]

Woven + (35 wt% Epoxy short borosilicate)

—

T, tensile test; F, flexural test; I, impact test; S, shear test; joc, Jatropha oil cake; Na-MMT, sodium montmorillonite; MWCNT, multiwalled carbon nanotube. Source: Modified from Sathishkumar et al. [8].

References

1.7 Conclusion The demand for lighter, stronger, and economical glass-fiber-based composite materials requires constant and incremental research. In order to bring in as best possible details of GFR composites, types based on composition, different forms, and orientations are presented. Their use in industrial, domestic, aerospace, construction, and chemical corrosive environment is also discussed. Proper selection of glass fiber, reinforcement, and resins are critical as they are the key element to produce Glass Fibers-Based Composites at around 70–75% by weight and approximately 50–60% in size. The necessity to improve the quality of GFR composites with a different combination of fillers and chemical compositions is an intriguing area of research. Advances in glass fiber formulation acknowledge for strengths in parity with carbon fibers and equivalently significant for mass manufacturing by the efficient process. It is expected that this chapter will provide the fundamental knowledge about GFR composites to educationists and investigators willing to work in this area.

References 1 Zweben, C.H. (2005). Composites: overview. In: Encyclopedia of Condensed Matter Physics (eds. F. Bassani, G.L. Liedl and P. Wyder), 192–208. Elsevier Academic Press. 2 Madhusudhan, T., Senthilkumar, M., and Athith, D. (2016). Mechanical characteristics and tribological behaviour study on natural-glass fiber reinforced polymer hybrid composites: a review. International Research Journal of Engineering and Technology (IRJET) 03 (04): 2243–2246. 3 Rajak, D.K., Pagar, D.D., Menezes, P.L., and Linul, E. (2019). Fiber-reinforced polymer composites: manufacturing, properties, and applications. Polymers 11, 11 (10): 1667. https://doi.org/10.3390/polym11101667. 4 Stickel, J.M. and Nagarajan, M. (2012). Glass fiber-reinforced composites: from formulation to application. International Journal of Applied Glass Science 3: 122–136. 5 Foruzanmehr, M., Elkoun, S., Fam, A., and Robert, M. (2016). Degradation characteristics of new bio-resin based-fiber-reinforced polymers for external rehabilitation of structures. Journal of Composite Materials 50: 1227–1239. 6 Li, E.Z., Guo, W.L., Wang, H.D. et al. (2013). Research on tribological behavior of PEEK and glass fiber reinforced PEEK composite. Physics Procedia 50: 453–460. 7 Jyotikalita, J. and Kumar Singh, K. (2018). Tribological properties of different synthetic fiber reinforced polymer matrix composites: a review. IOP Conference Series: Materials Science and Engineering 455: 012134. https://doi.org/10.1088/ 1757-899X/455/1/012134. 8 Sathishkumar, T.P., Satheeshkumar, S., and Naveen, J. (2014). Glass fiberreinforced polymer composites: a review. Journal of Reinforced Plastics and Composites 33: 1258–1275.

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9 Correia, J.R., Almeida, N.M., and Figueira, J.R. (2011). Recycling of FRP composites: reusing fine GFRP waste in concrete mixtures. Journal of Cleaner Production 19: 1745–1753. 10 Kumar, S., Joshi, A., and Gangil, B. (2013). Physico-mechanical and tribological properties of glass fiber based epoxy hybrid natural composite. In: Proc. of Int. Conf. on Emerging Trends in Engineering and Technology (ed. Association of Computer Electronics and Electrical Engineers), 1–6. 11 Rovero, L., Galassi, S., and Misseri, G. (2020). Experimental and analytical investigation of bond behavior in glass fiber-reinforced composites based on gypsum and cement matrices. Composites Part B: Engineering 194: 108051. 12 Gehlen, G.S., Neis, P.D., de Barros, L.Y. et al. (2020). Tribological behavior of glass/sisal fiber reinforced polyester composites. Polymer Composites 41: 112–120. 13 Martynova, E. and Cebulla, H. (2018). Chapter 7 - Glass fibers. In: The Textile Institute Book Series, Inorganic and Composite Fibers (eds. B. Mahltig and Y. Kyosev), 131–163. Woodhead Publishing. 14 Yasufuku, S. (1994). Application of glass fiber-reinforced plastics to electrical and electronic apparatus in Japan. IEEE Electrical Insulation Magazine 10: 8–15. 15 Cevahir, A. (2017). 5 - Glass fibers. In: Woodhead Publishing Series in Composites Science and Engineering, Fiber Technology for Fiber-Reinforced Composites (eds. M.Ö. Seydibeyo˘glu, A.K. Mohanty and M. Misra), 99–121. Woodhead Publishing. 16 Adekomaya, O. and Adama, K. (2017). Glass-fibre reinforced composites: the effect of fibre loading and orientation on tensile and impact strength. Nigerian Journal of Technology 36: 782–787. 17 Rama Krishna, K.B.S.S., Nagaraju, B., Raja Roy, M., and Ashok Kumar, B.B. (2016). Studies on tribological properties of SiC and fly ash reinforced glass fiber epoxy composites by Taguchi method. International Journal of Mechanical Engineering and Technology 7: 199–208. 18 Karpe Ganesh, G. and Dhamejani, C.L. (2016). Investigation of tribological behavior of PEEK with carbon filled composites under harsh operating condition. International Journal of Advance Research and Innovative Ideas in Education 2 (1): 271–279. 19 Rajamahendran, S., Suresh, G., Srinivasan, T. et al. (2021). An analysis on mechanical and sliding wear behavior of E-glass fiber reinforced IPN composites. Materials Today: Proceedings 45 (Part 2): 1388–1392. https://doi.org/10.1016/j .matpr.2020.07.072. 20 Awan, G.H., Ali, L., Ghauri, M. et al. (2010). Effect of various forms of glass fiber reinforcements on tensile properties of polyester matrix composite. Journal of Faculty of Engineering and Technology 16: 33–39. 21 Anon. https://www.fortunefibreglass.com/fiber-glass-woven-roving-mats.html. 22 Negawo, T.A., Polat, Y., Akgul, Y. et al. (2021). Mechanical and dynamic mechanical thermal properties of ensete fiber/woven glass fiber fabric hybrid composites. Composite Structures 259: 113221. https://doi.org/10.1016/j .compstruct.2020.113221.

References

23 Yousif, B.F. and El-Tayeb, N.S.M. (2008). Wear and friction characteristics of CGRP composite under wet contact condition using two different test techniques. Wear 265: 856–864. 24 Chawla, K.K. (2012). Composite Materials: Science and Engineering. Germany: Springer Berlin Heidelberg. 25 Singh, S., Bhardwaj, S.K., and Taneja, P.K. (2014). Evaluation of mechanical and tribological properties of composite materials. Journal of Civil Engineering and Environmental Technology 1: 80–84. 26 Vijay, B.R. and Srikantappa, A.S. (2019). Physico-mechanical and tribological properties of glass fiber based epoxy composites. International Journal of Mechanical Engineering and Robotics Research 8: 929–934. 27 Aramide, F.O., Atanda, P.O., and Olorunniwo, O.E. (2013). Mechanical properties of a polyester fibre glass composite. International Journal of Composite Materials 2: 147–151. 28 Erden, S., Sever, K., Seki, Y., and Sarikanat, M. (2010). Enhancement of the mechanical properties of glass/polyester composites via matrix modification glass/polyester composite siloxane matrix modification. Fibers and Polymers 11: 732–737. 29 Al-alkawi, H.J., Al-fattal, D.S., and Ali, A.H. (2012). Fatigue behavior of woven glass fiber reinforced polyester under variable temperature. Elixir Mechanical Engineering 53: 12045–12050. 30 Chen, Z., Liu, X., Lü, R., and Li, T. (2006). Mechanical and tribological properties of PA66/PPS blend. III. Reinforced with GF. Journal of Applied Polymer Science 102: 523–529. 31 Yuanjian, T. and Isaac, D.H. (2008). Combined impact and fatigue of glass fiber reinforced composites. Composites Part B: Engineering 39: 505–512. 32 Faizal, M.A., Beng, Y.K., and Dalimin, M.N. (2008). Tensile property of hand lay-up plain-weave E-glass/polyester composite: curing pressure and ply arrangement effect. Borneo Science 23: 27–34. ´ S., Javni, I., and Petrovic, ´ Z.S. (2005). Thermal and mechanical properties 33 Husic, of glass reinforced soy-based polyurethane composites. Composites Science and Technology 65: 19–25. 34 Leonard, L.W.H., Wong, K.J., Low, K.O., and Yousif, B.F. (2009). Fracture behaviour of glass fibre-reinforced polyester composite. Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 223: 83–89. ´ S., Bajˇceta, B., Vitkovic, ´ D. et al. (2009). The interlaminar strength of the 35 Putic, glass fiber polyester composite. Chemical Industry and Chemical Engineering Quarterly 15: 45–48. 36 Avci, A., Arikan, H., and Akdemir, A. (2004). Fracture behavior of glass fiber reinforced polymer composite. Cement and Concrete Research 34: 429–434. 37 Alam, S., Habib, F., Irfan, M. et al. (2010). Effect of orientation of glass fiber on mechanical properties of GRP composites. Journal of the Chemical Society of Pakistan 32: 265–269.

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1 Introduction to Glass Fiber-Based Composites and Structures

38 Araújo, E.M., Araújo, K.D., Pereira, O.D. et al. (2006). Fiberglass wastes/polyester resin composites: mechanical properties and water sorption. Polimeros 16: 332–335. 39 Mohbe, M., Singh, P.P., and Jain, S.K. (2012). Mechanical characterization of Na-MMT glass fiber reinforced polyester resin composite. International Journal of Emerging Technology and Advanced Engineering 2 (12): 702–707. 40 Gupta, N., Brar, B.S., and Woldesenbet, E. (2001). Effect of filler addition on the compressive and impact properties of glass fibre reinforced epoxy. Bulletin of Materials Science 24: 219–223. 41 Yang, B., Kozey, V., Adanur, S., and Kumar, S. (2000). Bending, compression, and shear behavior of woven glass fiber-epoxy composites. Composites Part B: Engineering 31: 715–721. 42 Patnaik, A., Satapathy, A., and Biswas, S. (2010). Investigations on three-body abrasive wear and mechanical properties of particulate filled glass epoxy composites. Malaysian Polymer Journal 5: 37–48. 43 Liu, Y., Yang, J.P., Xiao, H.M. et al. (2012). Role of matrix modification on interlaminar shear strength of glass fibre/epoxy composites. Composites Part B: Engineering 43: 95–98. 44 Torabizadeh, M.A. (2013). Tensile, compressive and shear properties of unidirectional glass/epoxy composites subjected to mechanical loading and low temperature services. Indian Journal of Engineering and Materials Science 20: 299–309. 45 Mohan, N., Kumar, R.A., Rajesh, K. et al. (2019). Investigation on sliding wear behaviour of UHMWPE filled basalt epoxy composites. AIP Conference Proceedings 2057 https://doi.org/10.1063/1.5085619. 46 Godara, A. and Raabe, D. (2007). Influence of fiber orientation on global mechanical behavior and mesoscale strain localization in a short glass-fiberreinforced epoxy polymer composite during tensile deformation investigated using digital image correlation. Composites Science and Technology 67: 2417–2427. 47 Shanti, Y. and Satyadevi, A. (2021). Effect of wood and graphite fillers on the glass fiber reinforced composite. Materials Letters 284: 128971. 48 Kunishima, T., Nagai, Y., Kurokawa, T. et al. (2020). Tribological behavior of glass fiber reinforced-PA66 in contact with carbon steel under high contact pressure, sliding and grease lubricated conditions. Wear 456–457: 203383. 49 Kunishima, T., Nagai, Y., Nagai, S. et al. (2020). Effects of glass fiber properties and polymer molecular mass on the mechanical and tribological properties of a polyamide-66-based composite in contact with carbon steel under grease lubrication. Wear 462–463 https://doi.org/10.1016/j.wear.2020.203500. 50 Ravi, N., Shanmugam, M., Bheemappa, S., and Gowripalan, N. (2020). Influence of reinforcement on tribological properties of friction stir welded glass fiber reinforced polyamide 66. Journal of Manufacturing Processes 58: 1052–1063. 51 Vijaya Kumar, K., Arul Marcel Moshi, A., and Selwin Rajadurai, J. (2021). Mechanical property analysis on bamboo-glass fiber reinforced hybrid composite structures under different lamina orders. Materials Today: Proceedings 45 (Part 2): 1620–1625.

17

2 Synthesis of Cotton Fiber and Its Structure Pankaj Kumar 1 , Cherala Sai Ram 1 , Jay P. Srivastava 2 , Arun K. Behura 3 , and Ashwini Kumar 4,5 1 SR University, Department of Mechanical Engineering, Center for Materials and Manufacturing, Ananthasagar, Hasanparthy, Warangal Urban 506371, India 2 SR Engineering College, Department of Mechanical Engineering, Ananthasagar, Hasanparthy, Warangal Urban 506371, India 3 VIT, School of Mechanical Engineering, Vellore 632014, Tamilnadu India 4 Shree Guru Gobind Singh Tricentenary University, Department of Mechanical Engineering, Faculty of Engineering & Technology, Gurugram 122505, HR India 5 Praxis Value, Senior Technical Consultant (Research), Banglore 560068, Karnataka India

2.1 Introduction Cotton is a very soft natural fiber surrounded by fibers known as a cotton ball. Cotton and cotton balls can contain about 5 lakh of cotton fibers. The biological source of the cotton is epidermal trichomes (hairs) of seeds of Gossypium herbaceum and other species. The family name of the cotton fiber is Malvaceae, and the main constitutes of raw cotton include 90% cellulose, 7–8% moisture wax, fat, purified cotton, or absorbent cotton: entirely cellulose, 6–7% moisture [1, 2]. The climate conditions required for growing cotton fiber plants include 100 cm rainfall and 25 ∘ C temperature (Figure 2.1). Warm climate and black soil are necessary for growing cotton [3, 4]. The general heights of the cotton plants are 1–2 m. In India, cotton is usually grown in the months of March–November [5].

2.2 Cotton Fiber Classification Cotton fiber is classified according to the length of the fiber, fiber strength, fiber length uniformity, fiber fineness, fiber color, trash, leaf grade, extraneous materials, module averaging, etc. [6, 7]. Classification of the cotton based on the length: ● ● ● ● ● ●

Short staple length: 3/18′′ to 15/16′′ Medium staple length: 1′′ to 1–1/8′′ Long staple length: 1–3/6′′ to 2–1/2′′ Diameter of the cotton fiber is: 11–22 μm Fiber length to breadth ratio: 600 : 1 to about 350 : 1 Cross-section of the cottonseed is kidney-shaped fiber.

Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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2 Synthesis of Cotton Fiber and Its Structure

Figure 2.1 Fully developed cotton along with a plant in the field.

2.2.1

Classification of the Cotton Fiber Based on the Strength

Fiber strength is measured in terms of grams per tex that is defined as the enforcement in grams necessary to crack the bunch of fibrils per tex. Tex can be defined as the weight of fiber in grams of 1000 m of fibril [8].

2.2.2 Classification of the Cotton Fiber Based on Fiber Length Uniformity The length uniformity strength affects the yarn strength and fineness. The higher the length uniformity strength, the lesser will be the variance in the fiber length, which results in a better quality of the yarn [9].

2.2.3

Classifications of the Cotton Based on Fiber Fineness

The fineness of the cotton fiber is measured in terms of micronaire. It can be measured by evaluating the air permeability of the fixed amount of the fiber placed in a constant volume [10]. It varies from fine to coarse. The measurements of micronaire are affected by various environmental factors that include ambient temperature, moisture, light, nutrient contents, etc. Moreover, it is also affects the performance and quality of the manufactured item using cotton fiber.

2.2.4

Classifications of the Cotton Based on Fiber Color

Almost all types of cotton produce are white or near white. Due to continuous exposure to light and adverse ambient conditions, the cotton fiber loses its brightness and becomes pale yellow color [11].

2.2.5

Classifications of the Cotton Based on Trash

The presence of fragments of leaves, grass, sand, and dust is known as trash in the cotton fiber [12]. Smaller fragments of this trash are highly undesirable due to the difficulty in removal of small-sized particles as compared to large-sized particles.

2.2.6

Classifications of the Cotton Based on Leaf Grade

The presence of the leaf contents in the cotton fiber is measured in terms of leaf grade. Seven leaf grade standards are starting from leaf grade “1” to “7.” It is

2.2 Cotton Fiber Classification

measured by a trash meter. Leaf grade is affected by the presence of fragments remaining in the cotton, harvesting condition, and procedure [13].

2.2.7

Classifications of the Cotton Based on Extraneous Materials

The presence of a substance other than leaf or fiber is known as extraneous matter. It includes grass, bark, seed cover, dust, oil, and fragments of plastics [14].

2.2.8

Classifications of the Cotton Based on Module Averaging

Module averaging is a procedure for making high-volume instrument measurements of cotton length, strength, length uniformity, and degree of cotton fineness [15]. Some of the commercially grown cotton species are as follows [16, 17]: i. Gossypium hirsutum: This type of cotton is called upland cotton, this cotton is originated in Mexico, the Caribbean, southern Florida, and Central America. Ninety percent of the world is producing this type of cotton. ii. Barbadense plant: This kind of cotton is called additional-span-principal fawn. It is native to the regions such as tropical southern America. Around the world, 8% of this cotton production can be seen. iii. Gossypium arboretum: This type of cotton is native to the regions such as India and Pakistan. Production of this cotton around the world is less than 2%. iv. Gossypium herbaceum: This can be called Levant cotton; this type of cotton is originated in the Arabian Peninsula and southern Africa. The major steps which are involved cotton production and cultivation are as follows: i. ii. iii. iv. v. vi. vii. viii. ix. x.

Harvesting and grafting Ginning and bailing Opening and picking Carding Combing Silvering Drawing Roving Spinning and weaving Dyeing and finishing

i. Harvesting: It is the process of growing cotton crops from the beginning of the seed to plant grown. Cotton is grown at a temperature of 60 ∘ C, with fertile soil and well-drained soil [18]. After harvesting the cotton, it is compressed and sent to gins. Figure 2.2 represents the growing cotton crop in Telangana, India. ii. Ginning: It is the process of separating the seeds from the cotton yarn with help of a cotton engine, which is also called the cotton gin. iii. Bailing: Bailing is the process of packing the compressed cotton after ginning and tying with help of metallic bands or some kind of wires. iv. Combing: Usually, cotton is combined when it is used for quality fabric.

19

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2 Synthesis of Cotton Fiber and Its Structure

Figure 2.2 Growing cotton plants in Telangana, India.

v. Silvering: Silver is a length of a bunch of cotton fibril that is commonly utilized to revolve the thread. vi. Drawing: The drawing process is also called drafting. vii. Roving: It is a long and narrow bundle of fiber. viii. Spinning: In the spinning process, cotton fibers are buckled jointly to generate a thread. ix. Weaving: It is the process of textile production where the fabric or cloth can be obtained. Weaving is the process of interlacing the two separate sets of threads perpendicular to the textile. x. Dyeing: It is the most commonly utilized process for imparting color to cotton. It can be called piece dyeing and yarn dyeing. xi. Finishing: In this process, the woven fabric is scoured, bleached, and distributed. The life cycle of cotton grown in Telangana, India is presented in Figure 2.3. Figure 2.3 Various developmental stages of cotton ball in Telangana, India.

2.4 Solvents for Cotton

2.3 Surface Modification of Cotton Fibers Cotton surface modification is focused on elevated tint fatigue for atomic tints and germicide tasks [19, 20]. For the application of hydrophobic surface needs, cotton should be modified using plasma technology [21]. For industrial applications, cotton should be modified by using magnetic and magnetic core-shell mesoporous silica nanoparticles. Cotton should be modified with sericin for medical textile applications [22, 23]. For industrial technical application, superhydrophobic cotton textile with robust composition and flame retardancy was used. Figure 2.4 presents surface modification of the cotton fiber including smoothing, removal of wax, application of the sol–gel method, and polymer coating [24, 25].

2.4 Solvents for Cotton Cotton is a natural cellulose material. It is only soluble in complex solvents systems. Several solvents, such as cupriethylene diamine (CUEN) hydroxide, depending on the formation of metal ion complex with cellulose. Cotton can be dissolved in a 70% solution of sulfuric acid and this process is named carbonization. Solvents are chemical compounds that usually exist in the liquid state at room temperature. Even some gases will also act as solvents when it is required. Some of the familiar samples of toxins are H2 O, methanol, ethanol, butanol, carbon disulfide, ether, dichloromethane, n-propanal, and so on [26, 27]. The limited amounts of cellulose can be dissolved in the sodium chloride solution. Cellulose can be dissolved in some solvents such as n-methyl morpholine. Solvent plays an important role in the breaking of strong hydrogen bonds between the raw cotton fiber. Many researchers [28] presented the process for the splitting of the strong hydrogen bond between the molecules of the cotton fiber by using microwave-assisted deep eutectic solvent pretreatment followed by deep ultrasonication. Figure 2.5 presents various fibers and solvents used for pretreatment and deep ultrasonication of cotton fiber.

Untreated cotton fabric

O2 plasma

HMDSO

N2 plasma

HMDSO

O2 plasma-treated cotton

CA = 151°

N2 plasma-treated cotton

CA = 148.6°

Figure 2.4 Surface modification technique to enrich hydrophilic nature of the cotton fiber. Source: Reproduced from Yang et al. [24]. Licenced under CC BY 4.0.

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2 Synthesis of Cotton Fiber and Its Structure

Dripping Acetone

Immersion Ethanol

Acetone

Ethanol

Cotton (a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Polyester

Figure 2.5 Different fibers and solvents used for the treatment. (a) Acetone dye on cotton, applied through dripping; (b) Ethanol dye on cotton applied through dripping; (c) Acetone dye on cotton applied through immersion; (d) Ethanol dye on cotton applied through immersion; (e) Acetone dye on polyester applied through dripping; (f) Ethanol dye on polyester applied through dripping; (g) Acetone dye on polyester applied through immersion; (h) Ethanol dye on polyester applied through immersion. Source: Reproduced from Vega Gutierrez et al. [28] under open access license.

2.5 Chemical Treatment of Cotton Fiber During the fabrication of composites, the coupling between the reinforcement and matrix is challenging due to the different chemical structures of the cotton fiber and the matrix materials. Therefore, to improve bonding between the reinforcement and the matrix, chemical treatment of the fiber is performed using various chemical treatment processes. Different chemical treatments are used to reduce the hydrophilic nature of the cotton fiber [22]. The most commonly used chemicals for the cotton fiber are as follows: (i) Sodium hydroxide (NaOH): It is the most widely used chemical for cotton fiber treatment. This is the better economical and micro-level treatment for the removal of hemicellulose and other fatty ingredients. The chemical treatments are followed by fiber chemical neutralization, cleaning using deionized water, and removal of water from the fiber. NaOH treatment can be performed either at a constant concentration of NaOH or variable concentrations [29]. (ii) Acetic acid (CH3 COOH): Treatment of cotton fiber with CH3 COOH results in a better quality of the cotton fiber surface due to removal of the hemicellulose and other impurities. This can be performed at different concentrations with a constant period and temperature [23]. (iii) Silane solution (SiH4 ): It is an inorganic compound that is used and prepared according to the weight of the cotton fiber. That is because the nature of the chemical treatment is through the reactions between the silane and the oxide functions (–OH or –COOH) on the surface of particles. This silane solution treatment results in easy removal of different minerals from

2.6 Chemical Composition

NH2

Composite with CF Increased tensile strength Faster biodegradation in compost Silane coupling Increased tensile strength No effect on biodegradation

3-Aminopropyltrimethoxysilane Si

HO

OH

O

+

CH2OH O OH OH

OH O

O CH2OH

Cotton fiber (CF)

Figure 2.6

(iv)

(v)

(vi)

(vii)

(viii)

PBS/CF composite

O

HO

O O n

O

O n

Poly(butylene succinate) (PBS)

Silane solution treatment process for cotton fiber. Source: Calabia et al. [30].

the cotton fiber surface. Figure 2.6 indicates a schematic representation of the silane treatment process on the cotton fiber surface [30]. Benzoyl peroxide (BPO): In this chemical treatment process, the fiber is immersed in the solution and dried in the air medium. In this process, 10% (w/v) of the BPO solution is used for better treatment of the cotton fiber [31]. Cellulose powder ((C6 H10 O5 )n ): In this method for cotton fiber treatment, the mechanical and hydrophilic characteristics of the fiber are enriched very significantly [25]. Polymer coatings: In this treatment technique, the cotton fiber is immersed in the prepared solution for 30 minutes resulting in the replacement of the hydroxyl group with the carboxylic acid from a functional group of itaconic acid [32]. Bleaching (NaClO): This is one of the most economical chemical treatment processes for cotton fiber. Bleached fiber results in enriched hydrophilic nature on the fiber surface by removing hydrophobic impurities present in the cotton fiber [33]. Corrosion and stearic acid (C18 H36 O2 ) treatment: The hydrophilic nature of the cotton fiber is increased by this treatment process. In this process, the contact angle of the fiber surface approximately reach up to 138∘ when fiber is immersed in the solution of 1% (w/v) stearic acid in ethyl alcohol [21].

2.6 Chemical Composition The non-fructose enzymatic of fawn comprise of amino acid, clinker, wax position 3% dextrose and 0.8% biological vinegary, and other enzymatic composites, which build up 3-position 1% [34]. The chemical treatments (Table 2.1) and chemical composition of the cotton fiber are presented in Table 2.2.

23

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2 Synthesis of Cotton Fiber and Its Structure

Table 2.1

Different chemical treatments and their influence on the cotton fiber.

Chemical treatments

Effect of the treatment

References

Sodium hydroxide (NaOH)

It is the better economical and micro-level treatment for removal of hemicellulose and other fatty ingredients

[29]

Acetic acid (CH3 COOH)

Better quality of the cotton fiber surface due to removal of the hemicellulose and other impurities

[23]

Silane solution (SiH4 )

Easy removal of different minerals from the cotton fiber surface

[30]

Benzoyl peroxide (BPO)

It is used to remove mild to acne strain from the fiber surface

[31]

Cellulose powder ((C6 H10 O5 )n )

Mechanical and hydrophilic characteristics of the fiber are enriched very significantly

[25]

Polymer coatings

This coating results in the replacement of the hydroxyl group with the carboxylic acid from a functional group of itaconic acid

[32]

Bleaching (NaClO)

Enriched hydrophilic nature on the fiber surface by removing hydrophobic impurities present on the cotton fiber

[33]

Corrosion and stearic acid (C18 H36 O2 )

The contact angle of the fiber surface was approximately reached up to 138∘ when fiber immersed in the solution of 1% (w/v) stearic acid in ethyl alcohol

[21]

Table 2.2

Enzymatic structure of fawn.

Component

Amount (dry basis %)

Main location

Primary wall (%)

Cellulose

94

Secondary wall

48

Protein

1.3

Lumen

12

Pectine substance

0.9

Primary wall

12

Oil fat and Wax

0.6

Cuticle

Ash

1.2

Malic, citric, other organic acids

0.8

Total sugar Pigment

7 3

Lumen

14

0.3

Primary wall

—

Trace

Primary wall

—

Other Source: Based on Amiri [34].

0.9

—

—

2.7 Structural Properties of Cotton

2.7 Structural Properties of Cotton 2.7.1

Constitution and Molecular Weight Distributions

Cellulose is the pure form of cotton, which contains 90% of cotton. All herbs comprise of fructose but in different percentages. 40–50% of the cellulose is present in the wood, both coniferous and deciduous. Normal plants contain less cellulose. Cellulose in the cotton plants can be seen as highly crystalline, oriented, and fibrillar, and in the highest structural order. After bleaching and scouring, cotton contains 99% of cellulose. The molecular weight of the cellulose is 162.1406 g mol−1 . The formula of cellulose is (C6 H10 O5 )n . Many researchers [35–37] performed an investigation to study molecular weight distribution of polymer fiber and reported that at the early developmental stages of the fiber, the fiber has broader peak distribution as presented in Figure 2.7.

2.7.2

Cotton Fiber Structure

Cotton is a long-chain polymer in which the repeating unit is known as cellobiose that is made of two glucose units. The –OH and hydroxymethyl groups (CH2 OH) are the most important groups present in the polymer. It has a degree of polymerization of approximately 5000. The chemical structure of the cellulose is presented in Figure 2.8 [38]. The microscopic view of the fawn fiber is presented in Figure 2.9. It reveals different parts of the cotton fiber such as cuticle, primary wall, secondary wall, and lumen [39]. i. Cuticle. The cuticle is the outermost wax-coated layer. It is a glassy, H2 O-impervious layer that preserves the fibers from chemical and other degrading agents. ii. Primary wall. The main barrior is the narrow cell barrior below the cuticle. The primary wall consists of fibrils of cellulose spiral at 70 ∘ C.

Cellulose content (%)

100 80 60 40 20 0 0

10

20

30

40

50

60

dpa (days post anthesis)

Figure 2.7 Molecular weight distribution of cotton fiber at different stages of development. Source: Cabrales and Abidi [35]. Licenced under CC BY 4.0.

25

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2 Synthesis of Cotton Fiber and Its Structure

Figure 2.8 Chemical structure of cellulose acetate. Source: Aldalbahi et al. [38]. Licenced under CC BY 4.0.

Winding or transition layer

Lumen

Purified primary wall

Secondary wall

Figure 2.9 Microstructure of cotton fiber modified. Source: Modified and reproduced Kozlowski and Mackiewicz-Talarczyk [39].

iii. Peripheral barrior. The peripheral barrior is concentric layers of fructose below the primary wall. Fibril spiral at about 20∘ to 30∘ to the fiber axis. iv. Lumen. Lumen is the central hollow region running along the fiber length, filled with cell sap during the growth period.

2.7.3

Microscopic View of Cotton Fiber

Different microscopic view of the cotton fiber includes a cross-sectional and longitudinal structure. The cross-section image of the cotton fiber reveals its kidney-shaped structure, whereas the longitudinal structure appears as a single elongated cell that is flatly twisted like a ribbon. Figure 2.10 reveals microscopic views of the raw cotton fiber, (a) cross-sectional and (b) longitudinal structure [40, 41].

2.7.4

Physical Properties of Cotton Fiber

Hydroscopic nature: Due to the presence of the OH group, cotton fiber is more absorbent as water molecules attached by these OH groups allocate the static charge in the fiber. Particular stress of fawn fiber: Tenacity is the ratio of failure consignment to the linear density of fiber. Tenacity = Fat break load ∕linear density(tex)

2.8 Characterization Methods of Cotton Fiber

(a)

(b)

(c)

Figure 2.10 SEM images of cotton fiber at different developmental stages, (a) 21 dpa (days postanthesis); (b) 27 dpa; and (c) 56 dpa. Source: Reproduced from Cabrales et al. [40] under open access license.

The cotton fiber has long polymer chains and they get straight then wet due to the position of polymers and increase in the hydrogen bond numbers. All these properties provide good strength in the cotton fiber. Elasticity: Cotton fiber is elastic due to the presence of a crystalline polymer system and due to its elastic nature, the cotton fiber has wrinkles and crease formation properties.

2.8 Characterization Methods of Cotton Fiber 2.8.1

Measurement of Density

The density of the fiber is measured in terms of the linear mass density of the fiber [42]. Researcher [43] presented a measurement of the linear mass density of the cotton fiber using the CottonscanTM instrument. In this technique, the average fiber fineness is measured considering 95% of the confidence level. Figure 2.11 represents the correlation between fiber bundle tenacity and linear density measurement.

2.8.2

Measurement of Diameter

In general, the diameter of the cotton fiber is measured using the digital micrometer having a precision of 0.0001 mm [44]. The diameter of the measured cotton fiber varies from 11 to 22 μm. Cotton fiber fineness is measured by air flow methods. It is measured using a micronaire instrument that measures the flow of air through porous cotton fiber. The measured value is represented in terms of tmic . Fiber fineness =

Weight of the fiber Length of the fiber

27

2 Synthesis of Cotton Fiber and Its Structure

Figure 2.11 Correlation between fiber bundle tenacity and linear density measurement. Source: Liu et al. [43].

25 24 Tenacity (g/tex)

28

R2 = 0.16

23 22 21 20 19 0.11

0.13

0.15

0.17

0.19

0.21

Linear density (tex)

Table 2.3 Different types of fiber fineness and their ratings. Fiber type

Rating

Very fine fiber

Below 3

Fine

Between 3 and 3.9

Average fine

Between 4 and 4.9

Source: Based on Delhom et al. [44].

where the weight of the fiber is measured in grams and the length of the fiber is measured in inches. Table 2.3 represents the rating of the fiber fineness for different types of fiber fineness

2.9 X-Ray Diffraction (XRD) Analysis It is an analytical technique for the identification of the crystal structure and chemical composition of metallic and polymer materials. It is a rapid and nondestructive analytical technique in which material surface is allowed to scan through radiographic dispersion. The outcomes of this process are evaluated in terms of the 2𝜃 degree angle in the range of 10–50∘ . Figure 2.12 represents the X-ray diffraction (XRD) pattern of cotton fiber at three different values of DPAs. Researchers [45] performed XRD analysis of cotton fiber and reported that at 20, 34, and 60 DPAs, the XRD pattern was normalized and smooth.

2.11 Thermogravimetric Analysis (TGA)

Intensity (a.u.)

(002)

(101) (040) (004) (a)

(200)

(105)

(201)

(b) (c)

20

30

40

50

60

70

2θ (°)

Figure 2.12 XRD pattern of cotton fiber at three different values of DPAs. Source: Zhang et al. [45]. Licenced under CC BY 4.0.

2.10 Fourier Transformation by Infrared Spectroscopy (FTIR) Analysis This is a nondestructive, qualitative, and quantitative analysis of both metallic and non-metallic materials. In this technique, infrared spectra are obtained to study the quantum of light that can be absorbed by the cotton fiber sample at the narrow range of the frequency typically between 400 and 4000 cm−1 . Figure 2.13 shows spectra obtained from Fourier transformation by infrared spectroscopy (FTIR) between 500 and 4000 of wavenumber. From Figure 2.13, it can be concluded that the spectrum of cotton fiber indicates peaks at 1132 and 3400 cm−1 [46, 47].

2.11 Thermogravimetric Analysis (TGA) In this technique, the weight of the sample is measured with the variation of temperature. As the weight of the cotton fiber changes, the thermal performance changes accordingly. The thermal analyzer is used to measure the thermogravimetric analysis (TGA) of the cotton fiber. In this technique, the nitrogen gas is passed through the cotton fiber at a flow rate of 20 ml min−1 . Many researchers [48, 49] investigated the effects of TGA on the maturity and fineness of the cotton fiber and reported that on increasing the measuring temperature, a very significant change in the weight of cotton fiber measured, as presented in Figure 2.14.

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2 Synthesis of Cotton Fiber and Its Structure

dpa

(g) (f) (e) (d) (c) (b) (a)

3000

2000

1000 –1

Wavenumbers (cm )

Figure 2.13 Spectra obtained from FTIR between 500 and 4000 of wavenumber. Source: Modified from Liu and Kim [46]. 100

101.30 °C 90.03% 0.79%/°C

60

1.5

1.0 40

Deriv. weight (%/°C)

2.0 343.90 °C 46.29% 1.476%/°C

80 Weight (%)

30

0.5

20

0 0

100

200

300

400

500

600

Temperature (°C)

Figure 2.14 Thermogravimetric analysis on the maturity and fineness of the cotton fiber. Source: Teklu et al. [48]. Licenced under CC BY 4.0.

2.12 Investigation of Scanning Electron Microscope Investigation of the scanning electron microscope cotton fiber is performed to investigate the structure form of the fiber such as straightness, twisting, or ribbon-like surface. Figure 2.15 reveals an SEM image of the raw cotton fiber, (a) cross-sectional and (b) longitudinal structure. Whereas [50] presented the SEM analysis of the cotton fiber treated with corona discharge at different temperatures and reported that on increasing the corona discharge temperature, fineness of the fiber may be lost due

2.13 Investigation of Transmission Electron Microscope

(a)

(b)

(c)

(d)

Figure 2.15 SEM analysis of the cotton fiber, (a) neat fiber, (b) treated with 0.5% w/v silver, (c) cotton fibers treated with 4% w/v silver, and (d) cotton fibers treated with 0.5% w/v silver. Source: Reproduced from Paladini et al. [50] under open access license.

to melting of the fiber. Figure 2.15 shows SEM images of the cotton fiber before and after fiber treatment.

2.13 Investigation of Transmission Electron Microscope This investigation of transmission electron microscope is utilized to estimate the length or diameter of the cotton fiber [51–53]. It is one of the most significant characterization instruments to observe microstructure [54–57]. The microstructure

Figure 2.16 TEM image of the cotton nano-fiber captured at different magnifications. (a) Cotton fiber cut along its fiber axis. The scale bar corresponds to 500 nm. (b) Magnification of the area delimited by the white square in (a). Source: Reproduced from Schelling et al. [51] under open access license.

31

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2 Synthesis of Cotton Fiber and Its Structure

of the length or diameter of the individual nano-fiber is measured with the help of ImageJ software. Figure 2.16 shows a TEM image of the cotton nano-fiber captured at different magnifications. In this technique, a sample is prepared very carefully starting with the boiling of the fiber in the NaOH solution for three hours followed by treatment with HCl solution and washing in deionized water.

2.14 Conclusions Synthesis, testing, and characterization of cellulose fiber is an important aspect of biodegradable fiber. This chapter is mainly focused on presenting findings on the synthesis of cotton fiber and its structure. It includes different findings such as methods of surface modification of cotton fibers and solvents for cotton fiber surface modifications. From various chemical treatment methods of cotton fiber, it is highlighted that different treatment methods result in less tendency toward the hydrophilic nature of the fiber surface. Whereas, from the report of the structural properties of cotton fiber, different parts of the cotton fiber such as cuticle, primary wall, secondary wall, and lumen can be observed in microscopic view. Physical properties of cotton fiber are reported by studying various macro and microscopic structures of the cotton fiber. From this study, it is revealed that due to its elastic nature the cotton fiber has wrinkles and crease formation properties. Moreover, different characterization methods of cotton fiber include measurement of density, measurement of diameter, fiber fineness, investigation of radiographic dispersion, investigation of FTIR, investigation of transmission electron microscope, investigation of thermogravimetric, investigation of scanning electron microscope. These testing and characterization techniques were performed to investigate the feasibility of the cotton fiber in different industrial applications.

References 1 Smole, M.S., Hribernik, S., Kureˇciˇc, M. et al. (2019). Surface Properties of Non-conventional Cellulose Fibres. Springer International Publishing. 2 Chand, N. and Fahim, M. (2020). Tribology of Natural Fiber Polymer Composites. Woodhead Publishing. 3 Gormus, O. and Yucel, C. (2002). Different planting date and potassium fertility effects on cotton yield and fiber properties in the Cukurova region, Turkey. Field Crops Research 78 (2–3): 141–149. 4 Pettigrew, W.T. (2008). The effect of higher temperatures on cotton lint yield production and fiber quality. Crop Science 48 (1): 278–285. 5 Jiang, Y., Li, C., and Paterson, A.H. (2016). High throughput phenotyping of cotton plant height using depth images under field conditions. Computers and Electronics in Agriculture 130: 57–68. 6 Park, Y.H., Alabady, M.S., Ulloa, M. et al. (2005). Genetic mapping of new cotton fiber loci using EST-derived microsatellites in an interspecific recombinant inbred line cotton population. Molecular Genetics and Genomics 274 (4): 428–441.

References

7 Haigler, C.H., Betancur, L., Stiff, M.R., and Tuttle, J.R. (2012). Cotton fiber: a powerful single-cell model for cell wall and cellulose research. Frontiers in Plant Science 3: 104. 8 Islam, M.S., Fang, D.D., Thyssen, G.N. et al. (2016). Comparative fiber property and transcriptome analyses reveal key genes potentially related to high fiber strength in cotton (Gossypium hirsutum L.) line MD52ne. BMC Plant Biology 16 (1): 1–19. 9 Krifa, M. (2006). Fiber length distribution in cotton processing: dominant features and interaction effects. Textile Research Journal 76 (5): 426–435. 10 Graupner, N., Endres, H.J., and Müssig, J. (2008). Influence of fiber fineness, fiber maturity, and nep content on the properties of natural fiber reinforced cotton-epoxy composites. Journal of Natural Fibers 5 (4): 289–315. 11 Gonçalves, M.I.S., Vilar, W.T., Medeiros, E.P., and Pontes, M.J.C. (2015). A novel strategy for the classification of naturally colored cotton fibers based on digital imaging and pattern recognition techniques. Analytical Methods 7 (14): 5869–5875. 12 Siddaiah, M., Lieberman, M.A., Hughs, S.E., and Prasad, N.R. (1999). A soft computing approach to classification of trash in ginned cotton. In: Proceedings of the Eighth International Fuzzy Systems Association World Congress, vol. 1, 151–155. IEEE. 13 Kazama, E.H., Ferreira, F.M., da Silva, R.P. et al. (2015). Multivariate analysis of fiber characteristics of dense cotton in different harvest systems. Australian Journal of Crop Science 9 (11): 1075–1081. 14 Whitelock, D.P., Ed Hughs, S., and Armijo, C.B. (2017). Classifying cotton bark and grass extraneous matter using image analysis. Textile Research Journal 87 (8): 891–901. 15 Hassan, T., Jamshaid, H., Mishra, R. et al. (2020). Acoustic, mechanical and thermal properties of green composites reinforced with natural fibers waste. Polymers 12 (3): 654. 16 Azhar, M.T., Amin, I., Anjum, Z.I. et al. (2010). Both malvaceous and nonmalvaceous betasatellites are associated with two wild cotton species grown under field conditions in Pakistan. Virus Genes 41 (3): 417–424. 17 Khadi, B.M., Santhy, V., and Yadav, M.S. (2010). Cotton: an introduction. In: Cotton (ed. U.B. Zehr), 1–14. Berlin, Heidelberg: Springer. 18 Shaw, R.H. (1988). Climate requirement. Corn and Corn Improvement 18: 609–638. 19 Bashar, M.M. and Khan, M.A. (2013). An overview on surface modification of cotton fiber for apparel use. Journal of Polymers and the Environment 21 (1): 181–190. 20 Haji, A. and Naebe, M. (2020). Cleaner dyeing of textiles using plasma treatment and natural dyes: a review. Journal of Cleaner Production 265: 121866. 21 Shu, W., Zhaojun, T., Zengfu, J. et al. (2015). Preparation and characterization of hydrophobic cotton fibre for water/oil separation by electroless plating combined with chemical corrosion. International Journal of Environmental Research and Public Health 2 (10): 144–150.

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22 Fei, Z., Liu, B., Zhu, M. et al. (2018). Antibacterial finishing of cotton fabrics based on thiol-maleimide click chemistry. Cellulose 25 (5): 3179–3188. 23 Reddy, K.O., Maheswari, C.U., Dhlamini, M.S. et al. (2018). Extraction and characterization of cellulose single fibers from native African Napier grass. Carbohydrate Polymers 188: 85–91. 24 Yang, J., Pu, Y., Miao, D., and Ning, X. (2018). Fabrication of durably superhydrophobic cotton fabrics by atmospheric pressure plasma treatment with a siloxane precursor. Polymers 10 (4): 460. 25 Billah, S.M.R. (2019). Textile coatings. Functional Polymers 10: 825–882. 26 Zhang, S., Wang, W.C., Li, F.X., and Yu, J.Y. (2013). Swelling and dissolution of cellulose in NaOH aqueous solvent systems. Cellulose Chemistry and Technology 47 (9–10): 671–679. 27 Shown, I. and Murthy, C.N. (2009). Grafting of cotton fiber by water-soluble cyclodextrin-based polymer. Journal of Applied Polymer Science 111 (4): 2056–2061. 28 Vega Gutierrez, S.M., He, Y., Cao, Y. et al. (2019). Feasibility and surface evaluation of the pigment from Scytalidium cuboideum for inkjet printing on textiles. Coatings 9 (4): 266. 29 Silverstein, R.A., Chen, Y., Sharma-Shivappa, R.R. et al. (2007). A comparison of chemical pretreatment methods for improving saccharification of cotton stalks. Bioresource Technology 98 (16): 3000–3011. 30 Calabia, B.P., Ninomiya, F., Yagi, H. et al. (2013). Biodegradable poly(butylene succinate) composites reinforced by cotton fiber with silane coupling agent. Polymers 5 (1): 128–141. 31 Kahraman, E. and Güngör, S. (2016). Polymeric micellar nanocarriers of benzoyl peroxide as potential follicular targeting approach for acne treatment. Colloids and Surfaces B: Biointerfaces 146: 692–699. 32 Zahid, M., Heredia-Guerrero, J.A., Athanassiou, A., and Bayer, I.S. (2017). Robust water repellent treatment for woven cotton fabrics with eco-friendly polymers. Chemical Engineering Journal 319: 321–332. 33 Abdel-Halim, E.S. (2012). Simple and economic bleaching process for cotton fabric. Carbohydrate Polymers 88 (4): 1233–1238. 34 Amiri, A. (2017). Characterization, long-term behavior evaluation and thermomechanical properties of untreated and treated flax fiber-reinforced composites. PhD dissertation. North Dakota State University. 35 Cabrales, L. and Abidi, N. (2019). Kinetics of cellulose deposition in developing cotton fibers studied by thermogravimetric analysis. Fibers 7 (9): 78. 36 Timpa, J.D. (1991). Application of universal calibration in gel permeation chromatography for molecular weight determinations of plant cell wall polymers: cotton fiber. Journal of Agricultural and Food Chemistry 39 (2): 270–275. 37 Tokumoto, H., Wakabayashi, K., Kamisaka, S., and Hoson, T. (2002). Changes in the sugar composition and molecular mass distribution of matrix polysaccharides during cotton fiber development. Plant and Cell Physiology 43 (4): 411–418.

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38 Aldalbahi, A., El-Naggar, M.E., El-Newehy, M.H. et al. (2021). Effects of technical textiles and synthetic nanofibers on environmental pollution. Polymers 13 (1): 155. 39 Kozlowski, R.M. and Mackiewicz-Talarczyk, M. (eds.) (2020). Handbook of Natural Fibres: Volume 1: Types, Properties and Factors Affecting Breeding and Cultivation. Woodhead Publishing. 40 Cabrales, L., Abidi, N., and Manciu, F. (2014). Characterization of developing cotton fibers by confocal Raman microscopy. Fibers 2 (4): 285–294. 41 Mahjoub, W., Harzallah, O., Jean-Yves, D. et al. (2017). Cotton fiber tensile properties. In: Cotton Fibers Characteristics, Uses and Performance (eds. S. Gordon and N. Abidi), 115–134. 42 Gordon, S.G., Naylor, G.R.S., and Brims, M. (2012). Cottonscope: a new instrument for maturity and fineness measurements. (A) Instrument design. In: Proceedings of the 31st International Cotton Conference (ed. G.R.S. Naylor), 133–142. 43 Liu, Y., Thibodeaux, D., and Rodgers, J. (2014). Preliminary study of linear density, tenacity, and crystallinity of cotton fibers. Fibers 2 (3): 211–220. 44 Delhom, C.D., Kelly, B., and Martin, V. (2018). Physical properties of cotton fiber and their measurement. In: Cotton Fiber: Physics, Chemistry and Biology (ed. D. Fang), 41–73. Cham: Springer. 45 Zhang, G., Wang, D., Yan, J. et al. (2019). Study on the photocatalytic and antibacterial properties of TiO2 nanoparticles-coated cotton fabrics. Materials 12 (12): 2010. 46 Liu, Y. and Kim, H.J. (2017). Fourier transform infrared spectroscopy (FT-IR) and simple algorithm analysis for rapid and non-destructive assessment of developmental cotton fibers. Sensors 17 (7): 1469. 47 Liu, Y., Thibodeaux, D., Gamble, G. et al. (2012). Comparative investigation of Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) in the determination of cotton fiber crystallinity. Applied Spectroscopy 66 (8): 983–986. 48 Teklu, T., Gebremedhin, T.K., Tesfay, A.H. et al. (2020). Polyaniline deposition on the surface of cotton fibers: structural studies, swelling behavior, and water absorption properties. Advances in Materials Science and Engineering 2020: 1650364. 49 Abidi, N., Hequet, E., and Ethridge, D. (2007). Thermogravimetric analysis of cotton fibers: relationships with maturity and fineness. Journal of Applied Polymer Science 103 (6): 3476–3482. 50 Paladini, F., Di Franco, C., Panico, A. et al. (2016). In vitro assessment of the antibacterial potential of silver nano-coatings on cotton gauzes for prevention of wound infections. Materials 9 (6): 411. 51 Schelling, M., Kim, M., Otal, E., and Hinestroza, J. (2018). Decoration of cotton fibers with a water-stable metal–organic framework (UiO-66) for the decomposition and enhanced adsorption of micropollutants in water. Bioengineering 5 (1): 14.

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52 de Morais Teixeira, E., Corrêa, A.C., Manzoli, A. et al. (2010). Cellulose nanofibers from white and naturally colored cotton fibers. Cellulose 17 (3): 595–606. 53 El-Nahhal, I.M., Zourab, S.M., Kodeh, F.S. et al. (2012). Nanostructured copper oxide-cotton fibers: synthesis, characterization, and applications. International Nano Letters 2 (1): 14. 54 Hussain, M., Gupta, P., Kumar, P., and Das, A.K. (2020). Selective laser melting of single track on Ti–6Al–4V powder: experimentation and finite element analysis. Arabian Journal for Science and Engineering 45 (2): 1173–1180. 55 Kumar, P., Srivastava, J.P., and Kaleem, M. (2020). Investigation on effects of graphite particle on the mechanical properties of stir cast AA6061-Gr MMCs. Materials Today: Proceedings 39: 403–407. 56 Saikiran, M. and Ravali, G. (2019). Comparative study of vegetable based and conventional cutting fluids in machining of copper alloys. Materials Today: Proceedings 19: 611–614. 57 Singh, P.K., Kumar, P., and Das, A.K. (2019). Unconventional physical methods for synthesis of metal and non-metal nanoparticles: a review. Proceedings of the National Academy of Sciences, India Section A: Physical Sciences 89 (2): 199–221.

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3 Fundamentals of Carbon-Fiber-Reinforced Composite and Structures Rupita Ghosh 1 , Subhadip Das 2 , Sarada P. Mallick 1 , and Rajan 2 1 Koneru Lakshmaiah Education Foundation, Department of Biotechnology, Green Fields, Vaddeswaram, Guntur, 522502, Andhra Pradesh, India 2 Chaudhary Ranbir Singh University, Department of Chemistry, Jind, 126102, Haryana, India

3.1 Introduction Composites are unique and superior material which possesses two or more dissimilar constituents. The uniqueness of the composites originates from their structure which consists of dual constituents, a backbone material, and filler fibers which augments the characteristics of the material, e.g. fiber-reinforced polymer (FRP) composites [1] in which the matrix is a polymer and is loaded with carbon fibers. The composite constituents are synergistic to each other in that the fibers are protected by the polymer matrix from any external influence (environmental) and also distribute the load between the fibers. The fibers, in turn, provides the requisite strength to reinforce the matrix which makes the composite crack resistant and free from fractures. The properties of the composite are a direct consequence of its structure which can be classified on the basis of phase and matrix material. The phases of the composite can be classified as given in Table 3.1. The pictorial representation of the phases is shown in Figure 3.1. On the other hand, the composites can also be sorted based on the materials of a matrix as given in Table 3.2 [3–6]. Another class of composites in which both the reinforced fiber and matrix material are made from carbon and its allotropes are the carbon-fiber-reinforced carbon composite (CFRCC). Some of the examples of CFRCC include polyacrylonitrile (PAN), pitch, or cellulose carbon fiber, etc., which combine with Term Matrix1 material which can include C60 , graphite resulting in a material with improved shear properties and low density compared to its lone constituents. The resultant product is in the form of a woven mesh of carbon fiber which is generally classified as carbon–carbon composite [7, 8]. 1 Term matrix material correspond to the main phase/constituent of material. Additional phase is distributed in the backbone or coated on it. Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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3 Fundamentals of Carbon-Fiber-Reinforced Composite and Structures

Table 3.1

Phases of composite and its definition.

Phase

Definition

Continuous phase

It is the material constituent that forms the bulk of the composite. Also known as matrix phase, it may be in the form of metal, ceramic, or polymer

Dispersed phase

It is the constituent that complements the continuous phase as the internal structure. Also known as reinforcement, it may be fibers, particles, flakes, whiskers, etc.

Inter phase

It is the interlayer between bulk matrix and bulk fiber or a zone across which matrix and reinforcing phase interact, the interaction may be of chemical, physical, or mechanical nature

Continuous phase (matrix) Dispersed phase (reinforcement) interphase

Figure 3.1 General structure of composite with the depiction of all of its phases. Source: Daniel et al. [2].

3.2 Classification of Carbon Fibers Carbon fibers are categorized into different groups depending upon the precursor used for the synthesis of fiber, as well as fiber’s strength and the final temperature of heat treatment, as given in Table 3.3.

3.3 Synthesis of Carbon Fiber Majority of the carbon fibers are made up of the PAN process and the remaining are extracted from rayon or petroleum pitch. So, the carbon fiber can be either PAN- or pitch-based. The raw material for PAN-based fiber can be polyacrylonitrile, rayon, or pitch [9]. A typical reaction pathway for the synthesis of PAN-based carbon fiber is shown in Figure 3.2. PAN is the most common precursor used to synthesize carbon fiber. It is generally prepared from acrylonitrile and its comonomers methyl methacrylate, methacrylic acid, etc., by polymerization. The precursor is further heated under low temperature (220–270 ∘ C) by passing of hot air. The hot air performs dual functions, the first one is to supply oxygen for combustion and the next one is to remove the exhaust

3.3 Synthesis of Carbon Fiber

Table 3.2

Composite categorization on the basis of matrix material.

Composite

Definition

Examples

Polymer matrix composite

The material consists of a polymer (resin) matrix in combination with fiber used as a reinforcement material

Polyester, polypropylene, cellulose, etc.

Metal matrix composite

The material in which metals and alloys are incorporated with various reinforcing phases

Silicon carbide fibers in aluminum, graphite fibers in aluminum

Ceramic matrix composite

Consists of the ceramic fiber embedded in a ceramic matrix. In these composites, both the matrix and fiber consist of a suitable ceramic material

Calcium alumina silicate (CAS), lithium alumina silicate (LAS)

Bulk metallic glass composite

These are ceramic reinforcement or ductile metal reinforcement used to strengthen, toughen the glass-forming matrix

Zr48 Cu47.5 Al8 Co0.5 , an example of Zn–Cu–Al–Co glass system

Sources: Based on Hays et al. [3]; Hofmann [4]; Hofmann et al. [5], and Wang et al. [6].

Table 3.3

Categorization of carbon fibers based on given criteria.

Precursor

Strength

Temperature of heat treatment

PAN

Ultrahigh modulus

High (temperature ≥ 2000 ∘ C)

Pitch

High modulus

Mesophase pitch

Intermediate modulus

Intermediate (temperature = 1500–2000 ∘ C) Low (temperature ≤ 1500 ∘ C)

Isotropic pitch

Low modulus based and high tensile strength

Rayon

Super high tensile strength

Gas phase

components and the heat evolved. However, to completely remove the exhaust gas components, it is passed through a heated platinum metal which adsorbs the remaining exhaust gases. The oxidized PAN fiber is then passed through a low-temperature furnace (950–1000 ∘ C) under inert atmosphere to remove the tar and gases formed in the process. The fiber is then subjected to a high temperature run in the furnace under inert atmosphere to increase the modulus and to remove surface defects in the fiber. The carbon fiber can also be made from rayon-based precursor through a series of processes. The precursor is first subjected to pyrolysis either in the absence of air or in the presence of air. In the presence of air, flame retardants must be added

39

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3 Fundamentals of Carbon-Fiber-Reinforced Composite and Structures Heat C

C

C N

N

C N

C N

C

C N

N

C

C N

N

C

C N

N

C

C N

N

C N

C N

N

Polyacrylonitrile Excess of heat ~900 to 1200 °C

N

N

N

N

N

N

N

N

N

N

N

N

PAN-based carbon-fiber

Figure 3.2 Synthesis of carbon fiber by using spun PAN polymer filaments. Reaction occurs by carbonization (removal of H-atom) and graphitization (removal of N-atom) in excess of heat.

which makes the process more economical. In absence of oxygen, slow pyrolysis has to be undertaken with a controlled increase of temperature to sweep out the evolved gases and tars. It is further subjected to carbonization under inert atmosphere with both low- and high-temperature stages to remove the evolved gases. It is also passed through a hot stretching stage which improves the modulus of the fiber. The pitch-based precursor can also be used for industrial-scale synthesis of carbon fiber. In this process, the precursor is first subjected to oxidation to convert into a thermosetting material. The temperature of oxidation will depend on the oxidizing agent and the final product. The pitch-based precursor can also be enrolled under another stabilization step where the system is first oxidized and then subjected to solvent extraction which removes the necessary impurities. Then it is passed through a carbonization step where it is heated up to ∼1000 ∘ C in the chemically inactive environment to remove the evolved gases after which it is passed through a graphitization step at about ∼2500–3000 ∘ C in inert atmosphere where the fibers are turned into a graphite-like structure [9].

3.4 Surface Treatment of Carbon Fibers Surface treatment methods such as wet methods and dry methods are in use since 1960s and 1970s. Several other surface treatment methods include treatment with plasma, oxidation at anode, mild fluorination, and coating of metal. The components involved in wet method surface treatment are oxidizing agents such as nitric acid and chromic acid in which the fibers are immersed for performing electrochemical oxidation and is regarded as the frequently used surface treatment methods for

3.5 Carbon-Fiber-Reinforced with Polymer Matrix Composites

carbon fibers. The other method, i.e. the dry method involves oxidation in oxygen or air. The method gives rise to a functional group on surfaces of carbon fiber, which is one of the appropriate and potent methods for the same [10, 11]. The modification in the physicochemical properties of carbon fibers ensures proper adhesion of reinforcement on the matrix. Intimate contact is required for the proper adhesion of the fibers to the matrices. In other words, the contact must fulfill an equilibrium intermolecular distance among the matrix and the fibers [12, 13]. A large interfacial area is required between the fiber and the matrix for an effective Vander Waal’s bonding between the two. On account of free energy considerations, the energy of the fiber at the surface is more than that of the liquid polymer based on the explanation of London dispersive forces which approves complete wetting of the fibers in the liquid medium. Commercial carbon fibers without any treatment possess an interfacial surface tension of about 40 mJ m−2 . Also, because of their manufacturing from the processes of carbonization or graphitization requiring exceptionally high temperatures of around (±700–1500 ∘ C) and (±2500 ∘ C), respectively, these commercial untreated carbon fibers are extremely hydrophobic [14].

3.5 Carbon-Fiber-Reinforced with Polymer Matrix Composites In the past few years, carbon fibers have turned out to be one of the most significant reinforcing materials. Their characteristics include resistance to temperature along with high strength and high modulus [15, 16]. Scientists have put a lot of effort in enhancing and examining their performance particularly that of the composite systems with carbon fibers. Despite these advantages and efforts, it is reported that the interfacial strength among the carbon fiber and the matrix in a composite system determines the mechanical properties of the composites, to some extent [17]. The bonding present in between the matrix and carbon fibers comprises weak and intermolecular interactions, such as hydrogen bonds and van der Waals forces [18, 19]. These connections play a crucial role in refining the resulting mechanical properties. Moreover, the interfacial adherence between the matrix and carbon fibers is essential for improving the strength and reliability of the composite polymers created from these materials [20, 21]. Various aerospace, marine, and recreational application make use of carbon-fiberbased polymeric composites, for example, carbon fibers along with epoxy resins and carbon fibers along with PEEK systems [22–24]. Certain selected composites rely on the application. The cross-linking of epoxy resins can be carried out with a good deal of different anhydrides, amines, and acids [25]. It validates itself to be the most flexible in this respect along with having the characteristic of reacting with numerous other polymeric substances. The characteristics of such composites, notwithstanding are regulated not just by the characteristics of individual segments, yet in addition by the interface between the fibers and the resins of the matrix [26]. It achieves efficient reinforcement of

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3 Fundamentals of Carbon-Fiber-Reinforced Composite and Structures

Protruding structure

Descending area Concave

h d CFRP

Small energy impact

Big energy impact Protruding structure

Figure 3.3

General impact characteristics for carbon-fiber-reinforced polymer structures.

composite materials by only achieving adequate transfer of stress between the fibers and the resins of the matrix. This can be acknowledged by physical and secondary interactions between the two. Epoxy resins try not to bond emphatically to untreated carbon fibers. To conquer this, pretreatments, typically oxidative, of fiber surfaces have been built up that extraordinarily improve the fiber/matrix adhesion [27]. As the name suggests, carbon-fiber-reinforced polymer (CFRP) is composed of two parts: a matrix and a reinforcement. Carbon fibers are reinforced in a polymeric matrix which acts as the support to hold the fibers together. The characteristic assembly of CFRP is shown in Figure 3.3.

3.5.1 Manufacturing of the Polymer Composites Reinforced with Carbon Fibers Polymer composites reinforced with carbon fibers are such types of composite materials in which the fiber phase is constituted by carbon fibers. Carbon fibers consist of elemental carbon and essentially belong to a group of fibrous materials. In the manufacturing of composite structural systems, there are several production methods. Items have many variants and procedures that are proprietary, such as hand lay-up, spray-up, molding, filament winding, pultrusion, injection molding, etc. Among them, we are discussing four essential techniques of production in Sections 3.5.1.1–3.5.1.5. 3.5.1.1 Hand Lay-up and Spray-up Process

The hand lay-up method is the most usual and extensively common procedure as compared to various open mold composite manufacturing processes. First, it involves the placement of fiber preforms in a mold. For easy extraction, an antiadhesive coat layer is implemented on the mold. After that, the resin is applied to the reinforcement material. It can be either poured or applied using a brush. For

3.5 Carbon-Fiber-Reinforced with Polymer Matrix Composites

Liquid resin pot Fiber spool Release gel coat

Spray gun

Resin Chopped fibers Roller

Mold

Figure 3.4

Schematic showing spray-up process.

enhancing the interaction between the matrix material and the reinforcement, usage of a roller is required to nudge the resin into the fabrics. Therefore, the process of hand lay-up incorporates the construction of mats of the fibers by hand or machines that are securely and permanently held together by the resin. This approach allows a wide variety of layers of various fiber orientations to be constructed up to the desired thickness of the sheet and the form of the components. A technique similar to the hand lay-up method is the spray-up method [28, 29]. It involves the spraying of both chopped fibers and the resin onto the mold (Figure 3.4). It is faster than the hand lay-up method. Nguyen et al. suggested that the lay-up method being used for the prominent temperature behavior of CFRP [30]. 3.5.1.2 Molding

Molding is one of the foremost common strategies of molding plastic resins. The method is also identified as vacuum bag molding as it includes the resources, for example, polyvinyl alcohol and polyethylene nylon to enclose and seal the portion from the air present outside. The hand lay-up method is also used various times for assisting the vacuum bag molding method in making the laminate. For ensuring a good amount of fibers infusion into the matrix, laminate is then positioned in the middle of the mold and the vacuum bag. A vacuum pump is used to withdraw the air present among the mold and the vacuum bag [31, 32]. Meanwhile, the atmospheric pressure is applied for compressing the part. Molding is a substrate strip with separate cross-sections used to mask gaps between materials or for decorative purposes. Ketabchi et al. proposed the development of natural-fiber-reinforced polymer composites by the molding method [33]. The process of vacuum bag molding is shown in Figure 3.5. 3.5.1.3 Filament Winding

To create circular or polygonal forms, the filament winding process can be streamlined to wrap resin-wetted fibers around a mandrel. The process starts with the

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3 Fundamentals of Carbon-Fiber-Reinforced Composite and Structures To vacuum pump

To vacuum pump Vacuum bagging film

Composite laminate

Breather fabric Perforated film Tool release material

Coated mold

Figure 3.5

Representation showing vacuum bag molding process.

carbon fibers passing through a roller loaded with resins and the resultant impregnated fibers are wound around a mandrel. The impregnated yarns move around the mandrel by lateral movement and several such movements are necessary for achieving a desired thickness of the yarn/fiber. After attaining the desired thickness, the impregnated fibers are cured using a heated mandrel and an external heater. It is further heated in an oven for the desired time and then removed from the mandrel which yields a demolded hollow structure. 3.5.1.4 Pultrusion

The method of pultrusion involves ceaseless pulling of the uninterrupted strands of fiber rovings and mats by a resin bath. The fibers are stretched and further amalgamated in a hot die. Within the die, the elevated temperature cures the composite matrix into a steady structural cross-sectional form. Being an uninterrupted process, the method is very useful for fabricating composites having constant cross-section and longer lengths. The production process is automatic and is a cost-effective technique [34, 35]. Correia et al. proposed behavioral changes of polymer reinforced with hybrid fiber pultruded short columns [36]. 3.5.1.5 Injection Molding

The method has the advantages of being highly precise and having the ability to fabricate the composite parts in less cycle times. The injection molding process involves a hopper through which the feeding of fiber pellets is performed [37]. They are then transported further with the help of a screw into a heated barrel. The screw then removes the melted material in the barrel into the mold through the nozzle. Here, the material gets cooled and takes the desired shape. The application of this method involves thermoplastic encapsulations of electronic products preferred in medicine industries as reported by Rajak et al. [38].

3.5.2 Reinforcement of Carbon Fibers and Properties of CFRP Composites Fibers exist as a significant component of polymer composites. A considerable amount of effort has been put into determining the effect of fibers in terms of their types, architecture, fraction of volume, and orientation. Nearly 30–70% volume of the polymer composites is occupied by the fiber [39, 40]. Fibers are such that they can be cleaved, embroidered, woven, and stitched. For effective handling, improvement in the bond and binders is ensured for which they are usually treated with sizing such as starch, gelatin, oil, or wax. Aramid, glass and carbon are some of

3.5 Carbon-Fiber-Reinforced with Polymer Matrix Composites

the familiar types of fibers used for structural applications in advanced composites. Though carbon fibers among them are very high-priced, they also own the highest specific physicochemical properties [41, 42]. Carbon fibers are reinforced on the polymer matrix and hence called carbon-fiber-reinforced polymer (CFRP). Two forms of reinforcing may be done, namely, continuous or discontinuous carbon fibers having a diameter of around 7 μm, which are being routinely woven into a cloth. Although they are very high-priced, still carbon fibers are known for having high excessive mechanical properties with regards to strength and elastic modulus [43, 44]. Following properties make carbon fibers highly suitable for reinforcing polymer matrix: (a) (b) (c) (d) (e) (f) (g)

Having elastic modulus more than that of steel Good amount of tensile strength reaching up to 7 GPa Less density, approximately 1800 kg m−3 Being chemically inert Thermally stable in the absence of O2 Being thermally conductive which assists in certain fatigue properties Being creep resistive

The alignment of fiber in the polymeric matrix determines the performances of carbon fibers-based polymeric composites [45, 46]. The performance of discontinuous carbon fiber-based composites is known to be determined by this key factor only. Apart from improving the mechanical performance, the preferential orientation of carbon fiber also helps in processing the requirement of low molding pressure. Formation of void occurs in the polymeric matrix on account of imperfection during the fabrication of composites. This is an indication of weakness resulting in depletion of strength. Other reasons for weakness are large-size crystallite and surface pits which are formed at the time of composite fabrication [47]. Although several problems associated with carbon fibers-based composites have been reported, its properties have concealed all such defaults. Following properties of carbon fibers-based polymer composites have bestowed its application: (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)

It weighs less and has a low density Have high strength like that of steel and stiffness like that of titanium Resistant to creep Longer wear and tear life Resistance to abrasion and very low coefficient of friction With the change in orientation of carbon fiber, polymer’s toughness and damage can be managed Sufficient resistance to chemical Sufficient resistance to corrosion Very high resistance to vibration Good dimensional stability Sufficient thermal conductivity High electromagnetic interference (EMI) shielding Low resistance to electricity

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Epoxy resin

4th layer

Carbon fiber, 245 g m–2 twill

3rd layer 2nd layer 1st layer Mold release

Polyester gel-coat Piece of glass in order to flatten the sample

Figure 3.6

Carbon-fiber-reinforced polymer sample.

Retaining the correct fiber orientations and stacking order in CFRPs during production is essential for reaching the required mechanical properties of a component. To increase the durability and hardness of fibers, thermosetting polymers based on functional groups such as epoxy, polyester, phenolic, and polyimide resins and thermoplastics based on polypropylene, and polymethyl methacrylate have been generally considered. Generally, CFRP mixtures use thermosetting resins such as epoxy, polyester, or vinyl ester. Figure 3.6 shows the pictorial representation of CFRP with epoxy resin and polyester gel coat [48].

3.6 Carbon-Fiber-Reinforced Ceramic Matrix Composites Ceramic materials have strong bonding interactions and thus possess outstanding properties such as high mechanical strength and hardness, inertness and increased thermal, corrosion, wear upholding properties. However, owing to their high hardness they are extremely brittle resulting in poor fracture toughness and easy crack propagation. To strengthen these ceramics nowadays composites are manufactured using a ceramic matrix that contains various reinforcing phases to develop ceramic matrix composites (CMCs). The carbon fibers have properties that have attracted much attention due to their density and coefficient of thermal expansion being on the lower side, high tensile modulus, mechanical strength, and thermal conductivity, which is often reinforced within a matrix made up of resin, metal, or ceramic to form a composite with excellent structural properties [49, 50]. The addition of carbon fiber in the CMCs has the potential to enhance mechanical performance in comparison with the single-phase ceramic. Therefore, on their introduction in the matrix, the composites exhibit attractive physicomechanical characteristics for their high strength and hardness and strong fracture toughness.

3.6 Carbon-Fiber-Reinforced Ceramic Matrix Composites

Ceramic matrix

Long carbon fibers

Figure 3.7

Short carbon fibers

Long and short carbon-fiber-reinforced within a ceramic matrix.

Carbon fibers can withstand high temperatures; therefore, these fibers can be used in high-temperature thermostructural applications. Moreover, they are cheap compared to ceramic fibers and can sustain their mechanical properties even at a very high temperature of 2000 ∘ C [51, 52]. The brittle nature and poor fracture toughness of the ceramics can also be modified by introducing these carbon fibers as the reinforcing phase. The carbon fibers in the CMCs acts as a soft and weakly bonded interface that can be cleavaged easily promoting the toughening mechanism which results in the progressive failure of the cracks in the ceramics instead of brittle fracture [53–55]. Thus, the fracture energy is found to be dissipated through various mechanisms which include interfacial debonding or breakage, crack deflection, and fiber bridging. This part focuses on the CMCs reinforced with carbon fibers. The CMCs reinforced with carbon fibers are generally manufactured to fabricate structural ceramics with enhanced mechanical, thermal, magnetic, and electrical properties. This section further focuses on their structure, various synthesis methods, and properties.

3.6.1

Structure of Carbon-Fiber-Reinforced CMCs

CMCs can be classified based on the matrix type and the reinforcement phase. The ceramic matrix can be an oxide such as alumina (Al2 O3 ), zirconia (ZrO2 ); carbides such as zirconium carbide (ZrC), silicon carbide (SiC), boron carbide; nitrides such as silicon nitride (Si3 N4 ). The carbon fiber includes carbon nanotubes (CNT), carbon nanofibers (CNF), and carbon short fibers (Csf ). The carbon fiber reinforcement can be continuous (long) fibers or discontinuous (short) fibers or whiskers (Figure 3.7). Discontinuous or short-fiber CMCs are generally manufactured by traditional ceramic processes. Continuous or long-fiber CMCs are reinforced either by long monofilament or multifilament fibers. CMCs have different carbon fiber orientations in the matrix, which can be unidirectional, bidirectional, multidirectional, random, or fabrics. Again the fibers can be woven or nonwoven. The fibers are converted into a porous preform in which ceramic matrices are incorporated by different techniques. The preform can be biaxial or triaxial weaved, multiaxial multilayered knitted, 3D cylindrical, braided or orthogonal, angle interlock construction, etc.

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3.6.2

Synthesis and Properties of Carbon-Fiber-Reinforced CMCs

Carbon-fiber-reinforced CMCs can be manufactured by different routes based on the type of raw material and reinforcing phase being used. These routes include solid phase, gas phase, liquid phase, and sol–gel process. The CMCs with discontinuous carbon-reinforced phase (particulate or short fiber) can be manufactured by conventional processing. The steps include powder synthesis; composite powder mixture preparation by the process of mixing or milling; shape forming by pressing and different casting processes followed by subsequent sintering at high temperatures. However, CMC with continuous carbon fiber reinforcement is rarely manufactured through traditional sintering because the fibers may get damaged mechanically and also there is a chance of getting degraded at a higher sintering temperature due to chemical reactivity between the matrix and the fibers. The sintering phenomenon also results in increasing porosity and restricting densification in the fiber-reinforced composites because of the constant shrinkage of the matrix from the reinforcing fibers. Therefore, different techniques have been used to densify CMCs reinforced with continuous carbon fibers. 3.6.2.1 Hot Pressing

The solid phase routes for the production of CMCs include hot pressing and spark plasma sintering (SPS). Hot pressing is the common method used for manufacturing short carbon-fiber-reinforced CMCs. The process is mostly done at thermodynamic variables such as pressure in the span of 20–40 MPa; the temperature is between 1300 and 2000 ∘ C (Figure 3.8). In some cases, slip casting and injection molding processes are also performed, followed by pressureless sintering. A process of hot pressing was performed to synthesize zirconium diboride (ZrB2 ) – 20 vol% SiC CMC containing 20 vol% 2 mm short carbon fiber as the reinforcing phase. The process was accomplished by mixing the constituent powders in a ball mill in ethanol medium using ZrO2 balls for 10 hours. The solvent was removed to minimize the segregation of constituents by sedimentation during drying. The dried powder mixture was then pressed under a high temperature of 2000 ∘ C in a boron nitride-coated graphite mold for one hour in an inert atmosphere under a uniaxial load of 30 MPa. The fracture toughness of the composites increased with the inclusion of the Csf compared to only ZrB2 –SiC composite. However, the flexural strength decreased as a result of the formation of the graphitization transition layer in between the fiber and the matrix [56]. The dense BaSi2 Al2 O8 and Ba0.75 Sr0.25 Si2 Al2 O8 glass–CMCs with different volume fractions of Csf (20–40 vol%) reinforcement were also fabricated by hot pressing technique [57]. 3.6.2.2 Spark Plasma Sintering (SPS)

SPS is another solid phase route for manufacturing CMCs reinforced with small carbon fiber or CNT, where the ceramic matrix is sintered to its full density at a very fast rate. Hot pressing and SPS processes are alike, but in SPS heating is done by electrodes present on the upper and lower part of the graphite punch. Spark discharges are applied in voids present in between particles by a direct current

3.6 Carbon-Fiber-Reinforced Ceramic Matrix Composites

30 MPa

Heating coil Graphite die Thermocouple 2000 °C

Ceramic matrix composites

Pressure

Figure 3.8

Schematic design of the hot pressing.

pulse generator which activates the particle surface, thereby generating a self-heat treatment phenomenon [58]. A sintering temperature in the range of 1000–1800 ∘ C and pressure in the range of 40–60 MPa, followed by cooling is required in the process of SPS (Figure 3.9). For example, a CMC having Al2 O3 matrix with 3 vol% reinforcement of multi-walled carbon nanotubes (MWCNTs) was fabricated through the SPS process under a constant pressure of 40 MPa at different sintering temperatures. Allow the composite material to cool naturally to room temperature. The microstructural observation showed a strong bond between the CNTs and alumina matrix leading to an increase in fracture toughness and microhardness [60]. Another ultra-high temperature CMC containing matrix ZrB2 and SiC in the volume ratio of 4 : 1 core inforced with zirconium carbide and carbon fiber was prepared by the SPS route. ZrC and carbon fiber ratio was maintained at a constant ratio of 2 : 1. The CMC was sintered at 1800 ∘ C for five minutes at 30 MPa under vacuum pressure. It was observed that an appropriate amount of ZrC and carbon fiber incorporation increased the flexural strength of the composite, the fracture mode also changed from transgranular to intergranular mode. However, increasing carbon fiber addition (above 2.5 vol%) decreases the density and fracture toughness due to agglomeration of fibers in certain areas [61]. A composite matrix made up of mullite-titanium borate (TiB2 ) reinforced with CNTs achieved nearly full density when prepared through SPS. The process was undertaken at 1350 ∘ C initially at a pressure of 10 MPa followed by 30 MPa. The composite showed increased flexural strength, fracture toughness, and Vickers hardness compared to the mullite matrix composite reinforced with either TiB2 or CNT [62]. The process of SPS was combined with high-temperature sintering to manufacture SiC-carbon fiber CMC without any sintering aids. The mixing up of the constituents in a shaker mill for 10 minutes in ethanol medium was done before sintering at 50 MPa to obtain random carbon fibers distribution. The sintering was done at temperatures of 1900 and 2200 ∘ C [63]. 3.6.2.3 Infiltration Methods

CMCs strengthened with continuous or long fibers are fabricated commonly by the process of infiltration. The infiltration methods involve the formation of the ceramic

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Pressure

Upper electrode

Thermocouple Upper punch DC pulse generator

Die

Ceramic matrix composites

Lower punch Vacuum chamber Lower electrode

Pressure

Figure 3.9 et al. [59].

Schematic design of spark plasma sintering. Source: Adapted from Saheb

matrix from a fluid (gas or liquid) precursor infiltration into the woven or nonwoven carbon fiber preform structure. The gas-phase pathway includes the chemical vapor infiltration (CVI) process. The liquid phase path includes molten ceramic infiltration, slurry infiltration process (SIP), reactive melt infiltration (RMI), polymer infiltration and pyrolysis (PIP), and sol–gel infiltration process. CVI involves deposition of the ceramic matrix into the voids of the fiber preform through chemical vapor reaction to densify the CMCs [64]. The CVI process has various advantages of modifying the microstructure of the CMCs by tailoring fiber–matrix interface. However, the process is quite complex and costly which requires a long densification time and the matrix may still have substantial porosity. Infiltration of molten ceramic process is one of the liquid phase routes which is carried out by infiltrating molten ceramic matrix into a fiber preform [65]. Because the melting temperature of ceramics is high; therefore, this high temperature may lead to a chemical reaction in between the matrix and the fiber preform. Moreover, due to the low viscosity of molten ceramics, CMCs fabricated by this process may have high porosity. 3.6.2.4 Slurry Infiltration Process

SIP is a process of manufacturing carbon-fiber-reinforced CMCs in which carbon fiber spool is passed by a filament winding method through a ceramic slurry. The slurry impregnated fiber is then winded onto a drum followed by drying. The fiber is stacked according to the desired shape. Finally, the CMC is consolidated by

3.6 Carbon-Fiber-Reinforced Ceramic Matrix Composites

Slurry impregnated fiber drum

Carbon fiber spool Ceramic slurry

Hot pressing

Figure 3.10

Drying

Stack of slurry impregnated carbon fiber

Schematic design of slurry infiltration process. Source: Chawla [66].

the process of hot pressing in a graphite die at an elevated sintering temperature (Figure 3.10). For example, in a study, three different types of CMCs were prepared by the method of SIP followed by hot pressing. The CMCs were reinforced with continuously aligned carbon fibers. The matrices used were made from a slurry of SiC, Si3 N4 -Sialon, and Si3 N4 [67]. To lower the porosity in the CMCs, a novel modified SIP method followed by hot pressing was used to manufacture carbon-fiber-reinforced silica (SiO2 ) matrix composites. In this method, the fiber preform instead of impregnating in the slurry and winding continuously, the process followed injecting of the SiO2 slurry through the pores of the fiber preform. The fibers were also coated layer by layer with the slurry during the weaving process. The process was then followed by a vacuum assistant slurry transfer molding (VASTM) method. In this method, infiltration of the slurry into the voids of the fiber preform was carried out in a vacuum to fabricate a densified CMC with low porosity. The impregnated preform was subsequently sintered and hot-pressed to form a dense CMC. The flexural strength of the resultant CMC was found to increase double that of pure SiO2 [68]. 3.6.2.5 Reactive Melt Infiltration

The RMI technique for fabricating CMCs involves ceramic matrix formation by a chemical reaction between a liquid molten metal infiltrated into the voids of the carbon-matrix-reinforced fiber preform. Liquid silicon infiltration (LSI) is one type of RMI technique that is mainly used to fabricate SiC matrix composites involving molten silicon (Si) melt infiltration at a temperature above its melting point 1414 ∘ C into a carbon matrix containing fiber preform [69]. The infiltration process is carried out as a result of capillary action. The liquid Si then reacts with the carbon matrix of the impregnated fiber preform to form fiber-reinforced SiC CMC. RMI process has also been used for infiltration of liquid aluminum (Al) into a fiber preform to form an alumina–aluminum (Al2 O3 –Al) matrix [70]. ZrC matrix composite reinforced with carbon fiber was also manufactured by RMI process where molten Zr reacted with

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carbon to form ZrC matrix composite [71]. RMI is a low-cost, fast method of manufacturing CMC with very little porosity, high thermal conductivity, and electrical conductivity. 3.6.2.6 Polymer Infiltration and Pyrolysis

PIP is one of the preferred techniques used to fabricate CMCs with complex structures. The process involves infiltration of a preceramic polymer into a fiber preform followed by its subsequent high-temperature pyrolysis into its constituent ceramic matrix by the process of curing and chemical reaction [72]. One of the major problems involved during the process of pyrolysis is the shrinkage and densification of the ceramic matrix resulting in the formation of macro or micropores in the CMCs [73]. In a process involving pyrolysis of polycarbosilane (PCS) to SiC matrix, significant volume shrinkage and densification from 1.1 to 2.7 g cm−3 was noticed [74, 75]. To overcome the porosity issue, multiple cycles of infiltration and pyrolysis should be repeated to reduce porosity [76]. To overcome the shrinkage issue, polymer precursors are sometimes mixed with some inert or active fillers before fiber impregnation. The inactive fillers being inert does not undergo any volume shrinkage and the active fillers react to form some carbide or nitride by-products at high temperatures [77]. For example, SiC is the most common inert filler used to reduce porosity and enhance mechanical properties in PIP-derived CMCs [78]. The oxidation resistance of some CMCs fabricated by the PIP process has found to be increased by the introduction of different active fillers into the matrix such as boron [79, 80] and ZrC [81]. 3.6.2.7 Sol–Gel Infiltration Process

Sol–gel infiltration process involves soaking of carbon fiber preform into a colloidal suspension of ceramic sol which subsequently transforms into a solid gel at a high temperature. The gel is then transformed into a ceramic matrix at a much lower temperature thereby reducing the chance of damage to the reinforcing fiber. The sols are mainly prepared from an organometallic compound such as alkoxides which undergoes gel transformation at a high temperature by the process of polycondensation or hydrolysis. For example, alumina-CNT CMC was prepared from alumina gel by the process of hydrolysis of aluminum alkoxides [82]. The composite showed increased microhardness and fracture toughness due to the incorporation of the CNTs. The advantage of this process is that sols have low viscosity which enables better penetration into the preform voids and also the low processing temperature application reduces chances of damage to the reinforcing fiber. To avoid the volume shrinkage from gel to ceramic matrix formation, the infiltration-drying step is repeated multiple times to achieve the desired density. Carbon-fiber-reinforced silicon matrix composite was also fabricated by sol–gel infiltration method by copolymerization of tetraethyl orthosilicate (TEOS) with furfuryl alcohol. No reaction between the composite matrix and the carbon fiber was observed; moreover, the composite showed good bonding between the fiber and the matrix with non-catastrophic failure [83].

3.7 Carbon-Fiber-Reinforced Carbon Matrix Composites

3.7 Carbon-Fiber-Reinforced Carbon Matrix Composites Carbon–carbon composite material is a kind of synthetic pure carbon fiber composed of carbon fiber and a reinforcing matrix. The first report of the synthesis of carbon–carbon composites came in the late 1950s which was used as an ablative material in those times. The research on the carbon–carbon material started with the program of Boeing X20 Dyna-sore under the responsibility of the U.S. Air force. The program was not successful and it was discarded before the first prototype came into reality [84]. It again reemerged in 1958 but was not elaborately investigated, it started with the space shuttle program in the late 1960s which was a NASA research project related to the space shuttle program [84]. The need of the hour for carbon-fiber-reinforced carbon structure material was originated shortly after World War 2, for manufacturing the bodyline of military aircraft in United States, although these composites were used for manufacturing the German rocket fins during this period. Again, in the 1970s era, carbon–carbon structures were widely developed for their use in rocket nozzles and LCA frame. The modern century use of CFRCC because its high mechanical strength is widespread including brake discs, automobile parts, space vehicles, etc. The current developments in the field of CFRCC need a strong backup from the basic fundamentals. The present book chapter; therefore, emphasizes the need for understanding the basics of CFRCC including its structure, synthesis, and properties.

3.7.1

Structure of Carbon–Carbon Composites

Carbon–carbon composites are woven mesh of carbon fiber. The structure of carbon–carbon composite is based on mainly two components, i.e. carbon fiber and matrix. The carbon fiber consists of thin interlocking layers of atoms of carbon arranged in the pattern which resembles graphene sheets (hexagonal) as shown in Figure 3.11. The dimension of the fiber is around 5–10 μm which is much smaller as compared to human hair. The hexagonal sheets are tightly packed to each other and these carbon-fibers are usually combined with the reinforcing material termed as matrix which imparts strength to the overall matrix. Matrix is a monolithic and homogeneous material in which the fiber material is embedded. The matrix may be composed of fullerenes (C60 ), graphite, or other suitable materials which provide the basis with carbon fiber to form the composite [8]. A representative arrangement of a composite matrix reinforced with fibers is given below in Figure 3.12.

3.7.2

Synthesis of Carbon–Carbon Composites

The process starts with the synthesis of carbon-fibers which proceeds to the fabrication of carbon–carbon composites. Carbon–carbon composites can be manufactured in several ways from fibers. These are:

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Figure 3.11 Representative structure of carbon fiber having hexagonal lattice of carbon atoms forming sheets of graphite.

Carbon fiber + reinforced matrix

Composite

Matrix material

Fiber material

Figure 3.12 Representative structure of a composite material consisting of fiber sandwiched in matrix material in a regular uniform arrangement. Source: Adapted from Bavan and Kumar [85].

7.2.1 Thermosetting resin-based carbon–carbon composite. 7.2.2 Thermoplastic resin-based carbon–carbon composite. 7.2.3 Chemical vapor deposition (CVD). The properties of the carbon–carbon composites obtained from a particular synthesis procedure will be added along with the synthesis procedure to ensure the given synthesis conditions based classification. 3.7.2.1

Thermosetting Resin-Based Carbon–Carbon Composite and Properties

The substrate (impregnated resin) for the pyrolysis process which is conducted at a temperature of around 350–800 ∘ C can be prepared in a lot of ways. The ways can be defined as follows: (i) The resin which is to be infiltrated into the fiber preform is dissolved in a suitable solvent along with a catalyst/curing agent. The curing agent assists in the curation of the resin in the resin-fiber preform complex (Species A). (ii) The curing is performed with the help of prepreg which is an impregnated system of resin and carbon fiber. The prepreg is in a partially cured state which

3.7 Carbon-Fiber-Reinforced Carbon Matrix Composites

Species A

Species B

Species C

Pyrolysis 2–4 times

Resin impregnation

Graphitization

Figure 3.13 Flow diagram for the formation of carbon–carbon composites from thermosetting polymer. Source: Balasubramanian [86]. The details of species A, B, and C are already given.

is further cured again. Finally, the prepregs are oriented in a definite array by cutting it to a particular size (Species B). (iii) The resin is loaded into the continuous fiber preform, but before the resin is cured, it is threaded into filaments and woven in several patterns by a process known as filament winding (Species C). Pyrolysis is then conducted on the species A, B, and C under inert atmosphere during which the gases such as H2 O, H2 , CO,CH4 , and CO2 are released. The pyrolyzed species is passed through the graphitization process at a temperature of about 1000 ∘ C. In the graphitization step, the associated nanopores in the composites get closed due to the heat treatment. The cycle comprising of resin impregnation and pyrolysis which is the densification step is repeated several times to make the sample denser in line with the requirements. A flow diagram in Figure 3.13 shows the formation of carbon–carbon composites from thermosetting polymer precursors. [86, 87]. Carbon–carbon composites can be prepared by the addition of external agents which also increases the mechanical strength if proper conditions are given for pyrolysis/curing. In this regard, Ko et al. [88] prepared carbon–carbon composites from resin and carbon black, the thermosetting resin and the fiber preform from PAN were mixed and the composites were cured, hot-pressed, and pyrolyzed at suitable temperature conditions to prepare the carbon–carbon composite. The addition of carbon black increased the mechanical attributes due to effective interaction between the matrix and carbon black. The interaction promoted the formation of the ordered structure of carbon around the carbon black which reduced the formation of pores. Another instance of synthesis of carbon–carbon composites was conducted with the addition of external agents, but it led to a reduction of the mechanical strength for

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the material. This was demonstrated by Ravikumar et al. [89] when a composite was prepared with different concentrations of graphitic fillers/dopant. The graphitic fillers were mixed with the thermosetting phenolic resin and mixed with the carbon fiber preform. To ensure a continuous fiber carbon–carbon composite, the sheets of the preform were laid in molds along with the resin and stacked up, so that all the molds are in the same direction. The mold is then hot-pressed/cured and carbonized at a range of temperatures ∼600–1200 ∘ C. The rigidity of the composite was found to depend on the bonding strength (interfacial) between the fiber and the backbone matrix and was found to be independent of the dopant loading. The strongness of the carbonized samples was found to be lower than the cured samples due to the degradation of phenolic resin at the given temperature and weakening of the between the fiber and the matrix. 3.7.2.2

Thermoplastic Pitch-Based Carbon–Carbon Composite and Properties

The precursors of the carbon fiber preform are the pitches that are extracted from coal tar, petroleum, natural asphalt, etc. Pitch can be termed as the mixture of hundreds and thousands of aromatic hydrocarbons, containing structures that are made up of three to eight-membered rings possessing an alkyl side group. Initially, the carbon fiber preforms infiltrate into thermoplastic-based molten pitch form, further, the pitch-loaded preform is passed through two subsequent steps: pyrolysis (carbonization) and graphitization. The carbonization is done in a nonreactive atmosphere at about ∼500–800 ∘ C and the graphitization is executed at a condition of ∼1000–2700 ∘ C temperature. The subsequent step converts the organic compound into graphitized coke. The densification of the sample takes place during the pyrolysis steps when the molten pitch infiltrates into the preform. The densification step is repeated several times under normal atmospheric pressure/reduced pressure so that the final composite becomes considerably denser in alignment with the requirements. [86]. Synthesis of carbon–carbon composites from thermoplastic pitch-based composites is shown in Figure 3.14. Carbon–carbon composites can be prepared from thermoplastic polymer polyetherimide and in order to increase the mechanical strength, the composites impregnated with silicon [90]. For the said composites, the carbon preform was obtained commercially and was loaded with the thermoplastic polymer polyetherimide at a given pressure. Before the loading, the carbon fibers were pretreated in a nonreactive environment at a given temperature to remove the epoxy coating and after loading, hot pressing was executed at given thermodynamic conditions. Subsequent pyrolysis was done in an inert atmosphere with a controlled heating rate followed by graphitization separately in an inert atmosphere of nitrogen and argon at different temperatures under high pressure. The silicon impregnation was done afterward in a vacuum at a suitable temperature and pressure. The carbonization temperature variation showed an advantage of the tensile strength variation exhibiting the maximum at a temperature of around 2000 ∘ C exhibiting a decrease further with the increase in temperature. This was affixed to the decreased strongness of the carbon fibers which can be attributed to the decrease in covalent cross-links between the graphene planes. The decrease in covalent links occurred

3.7 Carbon-Fiber-Reinforced Carbon Matrix Composites

Figure 3.14 Flow diagram for the formation of carbon–carbon composites from thermoplastic polymer. Source: Balasubramanian [86].

Fiber preform

Pyrolysis with or without pressure 550–800 °C Repeat 1–4 times

Molten pitch impregnation

Carbonization 1000–1500 °C

Heat treatment 2200–2750 °C

as the carbon fibers became ordered as the temperature was increased. In another study, carbon–carbon composites were again prepared from both polyetherimide and polyetheretherketone which was obtained commercially [91]. The carbon fiber was pretreated in a nonreactive environment at predecided conditions for removing the epoxy coating. The carbon fiber was then loaded with the given polymers polyetherimide and polyetheretherketone. The system was also subjected to hot-pressing at given thermodynamic conditions of temperature and pressure. Afterward, it was subjected to pyrolysis under a nitrogen atmosphere followed by graphitization in a vacuum. The silicon loading was done after graphitization in an inert atmosphere at a given temperature and duration. The synthesis procedure was the same as in [88] except for the graphitization process being done in a vacuum. The system was studied at various pretreatment temperatures to elucidate the impact on its mechanical properties. The mechanical strength measured by interlaminar shear strength and four-point bending tests was found to decrease with increasing pretreatment temperatures for both the polyetherimide and polyetheretherketone matrix. The reason was ascribed to the formation of disturbances in the fabrics which was due to the removal of functional groups containing oxygen by desorption as the temperature was increased. 3.7.2.3

Chemical Vapor Deposition (CVD) and Properties

Carbon–carbon composites can also be prepared directly by the CVD process which is defined as the process of gas-phase deposition of pyrolytic carbon on a substrate. CVD [92] is a process where a hydrocarbon gas is passed over the substrate (generally carbon fiber pretreated) under experimental conditions and the hydrocarbon

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Flow of gaseous reactant

Figure 3.15 Steps involved in chemical vapor deposition for preparation of carbon–carbon composites. Source: Adapted from [85].

Diffusion of gaseous reactant through laminar boundary layers

Adsorption of gaseous reactant on the substrate

Vapor-phase pyrolysis

Desorption and diffusion of gaseous products

gas reacts with the substrate by its decomposition leading to nucleation and growth of the required product on the substrate. The basic steps involved in CVD can be broken into steps that can be generalized for various techniques involved in CVD are given in Figure 3.15. Zhang et al. [93] synthesized two types of one-dimensional carbon–carbon composites possessing a higher thermal and electrical conductivity by CVD techniques by a process known as chemical vapor infiltration (CVI). CVI refers to the densification process occurring in the fiber preform. One of the types was prepared by impregnation of the precursor with phenolic resin followed by subsequent heat treatment, carbonization, graphitization followed by the CVI densification process. The impregnation and heat treatment process was repeated several times before proceeding with the carbonization and graphitization step. Another type was prepared without loading the phenolic resin by direct CVI densification. Both the products prepared by the two processes were subjected to a second CVI treatment by closing the pore on the surface of the products. However, the secondary CVI treatment, in fact, decreased the axial electrical resistivities compared to the samples subjected to graphitization for both the synthesis procedures. This is attributed to the decrease

References

in the concentration of the pyrolytic carbon around the carbon fibers. Additionally, the carbon–carbon composite produced by the CVI process only had higher axial thermal diffusivity and conductivity compared to the sample produced by graphitization and the CVI route. This was due to the bonding strength between fiber and matrix which was greater in the CVI processed sample due to the higher relative proportion of fiber and matrix in the sample. In another study, the synthesis was conducted using impregnation of the phenolic resin in the carbon fiber followed by high-temperature treatment and densification by CVI technique [94]. The impregnation of the phenolic resin in the carbon fiber was conducted by heating it to a suitable temperature and then the impregnated carbon fiber was molded using compression molding. The mold was then carbonized at a high temperature in an inert atmosphere after which the densification was carried out using methane as the gas precursor under the argon atmosphere. It was found that the density increased with an increase in the processing temperature used in the CVI route. The increase in density also leads to an increase in flexural strength. The flexural strength of the composites also depended on the processing time in the CVI technique [95]. It was observed that there was an increase in flexural strength with processing time because of the reduction of porosity and surface cracks. However, after a certain duration, it was observed that due to the development of the surface cracks, the flexural modulus showed a decreasing trend.

3.8 Conclusion The story of carbon-fiber-reinforced composite materials starts with the synthesis of carbon fibers and ends with their properties. The origin of carbon fibers can be varied based on PAN, rayon, or pitch. Generally, most of the carbon fibers are PAN-based because of the efficiency of the end material in terms of performance, cost, etc. The carbon fibers can then be surface treated and then be reinforced into the suitable material which gives us either the polymer, ceramic, or carbon-based composites. Different conditions and processes are employed for the synthesis of composites which varies the properties depending upon the end-user requirements. Nevertheless, carbon-fiber-reinforced composite materials offer improved rigidness, strength, and resilience as compared to other composites as compared to its counterparts based on metal and alloys. The fibers are responsible for carrying out the burden, the matrix distributes the burden evenly between the fibers and also ensures the fibers from any external damage. Finally, but not the end, the future of the carbon-fiber-reinforced composites will be heavily dependent upon the way the innovator molds the composites for their wide usage.

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36 Correia, M., Nunes, F., Correia, J., and Silvestre, N. (2013). Buckling behavior and failure of hybrid fiber-reinforced polymer pultruded short columns. Journal of Composites for Construction 17 (4): 463–475. 37 He, L., Lu, G., Chen, D. et al. (2017). Three-dimensional smoothed particle hydrodynamics simulation for injection molding flow of short fiber-reinforced polymer composites. Modelling and Simulation in Materials Science and Engineering 25 (5): 055007. 38 Rajak, D.K., Pagar, D.D., Menezes, P.L., and Linul, E. (2019). Fiber-reinforced polymer composites: manufacturing, properties, and applications. Polymers 11 (10): 1667. 39 Pickering, K.L., Efendy, M.A., and Le, T.M. (2016). A review of recent developments in natural fibre composites and their mechanical performance. Composites Part A: Applied Science and Manufacturing 83: 98–112. 40 Chakraborty, S. (2020). Behavior of Glass/Carbon Fiber Hybrid Composites Under Impact Loading for Aerospace Applications. North Carolina Agricultural and Technical State University. 41 Chen, S., Li, X., Zhou, Y. et al. (2020). Systematic investigation of the physicochemical properties of eco-friendly biobased anionic-nonionic surfactants for enhanced oil recovery. Journal of Molecular Liquids 323: 114628. 42 Fayomi, O., Okwilagwe, O., Agboola, O. et al. (2020). Assessment of composite materials in advance application: a mini overview. Materials Today: Proceedings 38: 2402–2405. 43 Tang, J., Swolfs, Y., Longana, M.L. et al. (2019). Hybrid composites of aligned discontinuous carbon fibers and self-reinforced polypropylene under tensile loading. Composites Part A: Applied Science and Manufacturing 123: 97–107. 44 Shi, C.-s., Zhang, J.-w., and Li, G.-j. (2000). Continuous plating equipment and Cu electroplating of discontinuous carbon fiber. Materials Protection 10. 45 Zhao, Z., Teng, K., Li, N. et al. (2017). Mechanical, thermal and interfacial performances of carbon fiber reinforced composites flavored by carbon nanotube in matrix/interface. Composite Structures 159: 761–772. 46 Sharma, S. and Lakkad, S. (2011). Effect of CNTs growth on carbon fibers on the tensile strength of CNTs grown carbon fiber-reinforced polymer matrix composites. Composites Part A: Applied Science and Manufacturing 42 (1): 8–15. 47 Poveda, R.L. and Gupta, N. (2016). Carbon Nanofiber Reinforced Polymer Composites. Springer. 48 Chong, A.Y.B., Salski, B., Theodorakeas, P., et al. eds. (2014). Inspection of carbon-fiber-reinforced polymer composites using radio frequency inductive sensors and ultrasonic techniques. 6th International Symposium on NDT in Aerospace, Madrid, Spain (12–14 November 2014). 49 Krenkel, W. (2005). Carbon fibre reinforced silicon carbide composites (C/SiC, C/C–SiC). In: Handbook of Ceramic Composites (ed. N.P. Bansal), 117–148. Boston, MA: Springer. 50 Chung, D.D. (2017). Carbon fibers, nanofibers, and nanotubes. Carbon Composites 2: 12–47.

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4 Introduction to Semisynthetic and Synthetic Fiber Based Composites Vishal N. Sulakhe Sandip Institute of Technology and Research Centre, Department of Mechanical Engineering, Nashik 422213, Maharashtra, India

4.1 Introduction Natural fibers are produced from plants, creatures, and topographical processes [1]. These fibers are utilized as a segment of composite materials, where the route of filaments impacts the properties. Ramie, flax, rice husk, cotton, sisal, kenaf, hemp, jute, and coir are examples of the various natural fibers [2]. Table 4.1 depicts the basic properties of frequently used fibers. Semisynthetic fibers are produced using traditional crude materials with usually happening long-chain polymer structure. They are just altered and incompletely corrupted by compound cycles [7]. Most semisynthetic fibers are cellulose recovered filaments, the soonest of which is rayon, otherwise called gooey. Cellulose filaments are recovered from regular cellulose: Rayon, for the most part, comes from the wood pulp model that frequently comes from beech trees. Bamboo gooey comes from bamboo grass and seacell comes from ocean growth. Figure 4.1 shows the classification of semisynthetic fibers. Synthetic fibers are chemically produced, and they comprise continuous fiber filaments (like silk). This human-made fiber is prepared through a chemical process and further classified as organic and inorganic based on the substance used [11]. Figure 4.2 shows the classification of synthetic fibers. Manufactured fibers of polyester are made by joining monomers into polymers through an interaction called polymerization. Synthetic fabrics have various characteristics, some of which are not feasible with standard filaments. For instance, a synthetic fiber is made waterproof for external security or versatile for swimwear. Synthetic compounds are added to make it milder, without wrinkle, stain-safe, or even fire-safe in the textile industry. A manufactured texture, when amplified, seems as if synthetic plastic fabrics are spun together. Generally, fiber robustness and solidness are significantly higher than the lattice material, which convert them into a heap behavior component in the composite construction [12, 14–17].

Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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Table 4.1

Basic properties of frequently used fibers [3–6].

Fiber

Density (g cm−3 )

Tensile strength (MPa)

Young’s modulus (GPa)

Applications

Aramid

1.4

3000–3150

63–67

Aerospace and military

E-glass

2.5

2000–3500

70

Electrical and thermal

S-glass

2.5

4570

86

Automobile

Cotton

1.5–1.6

287–597

5.5–12.6

Textile

Coir

1.2

175–220

4–6

Construction, civil

Kenaf

0.6–1.5

223–1191

11–60

Packaging

Bamboo

1.2–1.5

500–575

27–40

Paper, textile

Flax

1.4–1.5

345–1500

27.6–80

Paper industry

Ramie

1.5

220–938

44–128

Clothing

Oil palm

0.7–1.6

50–400

0.6–9

Mattress, cushion

Hemp

1.48

550–900

70

Textile, insulation

Jute

1.3–1.46

393–800

10–30

Carpets, curtains

Sisal

1.33–1.5

400–700

09–38

Clothing, footwear

Source: Based on Refs. [3–6].

Glass

Carbon

Basalt

Kevlar

Figure 4.1 Classification of semisynthetic fibers. Source: Reproduced from Refs. [3] under open access license.

4.2 Classifications

4.2 Classifications 4.2.1

Semisynthetic Fibers

Semisynthetic fibers are prepared with natural raw fiber through a synthetic interaction. So primarily, the natural fiber is collected, separated, and afterward remade. This process is generally finished with cellulose. Cellulose is a primary part, plentiful in plants. The cellulose is extricated from the plant, made solvent, and afterward spun into fiber. The following classification explains various human-made semisynthetic fibers. 4.2.1.1 Rayon

Rayon fiber is produced using recovered cellulosic fiber. Wood pulp or cotton liners are crude materials. An illustration of a semisynthetic fiber is rayon, otherwise called “gooey,” which was initially evolved after the formulation of a few unenterprising strategies for creating counterfeit silk. Cellulose got from wood with an antacid and carbon disulfide delivers a thick substance semi-synthesized fiber [18]. Unadulterated cellulose is extricated and recycled under precise circumstances to form fibers. The decontaminated cellulose is treated with synthetic substances to get a thick, gooey nectar-shaded spinning solution [8]. It is then constrained through a spinneret’s openings into a suitable medium so that the liquid streaming consistently through the spinneret openings hardens into filament strands. Primarily three types of rayons are available, namely, viscose, cuprammonium, and high-wet-modulus rayon. Different chemicals are utilized for acquiring the above mentioned rayons [19]. Mostly cellulose in the recovered structure and length is called a long fiber. Strength: It shifts from reasonable to magnificent, relying on the cycle of production. It loses its strength when it gets wet. The absorption of these fibers is more excellent than standard cellulose fibers; therefore, rayon has application in the material industry for making clothes. Rayon fiber is used for making tire strings, mats, and dressings [20]. Perpetual rayon filaments (Cordenka) were utilized to reinforce polyhydroxy butyrate (PHB) nanocomposites holding 2.5 wt% nano fibrillated cellulose (NFC) to make advanced green composites [20]. Indeed, synthetic fibers are bound to hold microbes and assimilate natural poisons. Studies have additionally revealed that even plastics tried to be without bisphenol A (BPA-Industrial chemical) discharge endocrine disruptors (like BPA) when presented to ordinary regular wear [21]. 4.2.1.2 Modal Fiber

Semisynthetic modal fiber is produced using beech tree mash and polymerization for the reinforced material. The beech tree is an antiquated, very safe, and profound establishing plant. Beechwood is a crude material for modal fiber. Beechwood remained a mother of the jungle since the dawn of time. An average beechwood woodland is home to around 7000 creatures and is a significant crude material supplier. With around 250 notable fields of utilization, beechwood is the most adaptable sort of wood around. Beech trees are extraordinary. Modal fiber is viewed as

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an extravagance material for wearing and is regularly used to mix with different textures to give a top-of-the-line feel with its daintiness and sheer quality. It has gotten exceptionally mainstream among eco-cognizant style originators due to its soft, stretchable, eco-friendly, and water-absorbent nature [22]. It is broadly used in the textile industry to produce garments, nightgown, and family unit things, similar to bed sheets and towels [23]. Modal rayon, a plant-based material, has some degree of more reliability and versatility than the ordinary structure. Adding strength, modal is frequently blended with various strands such as cotton and spandex. Modal is appreciated and viewed as a rich material known for its sensitive feel and enormous cost, more exorbitant than either cotton or silk [23]. 4.2.1.3 Bamboo Rayon

Initially produced using the mash of bamboo grass, bamboo texture has grabbed the eye of architects. A portion of the advantages of utilizing bamboo texture is contrasted with different sorts of fabric. Generally, in Asia, bamboo was utilized for the hand-made creation of paper. The bamboo mash is presently fit for making bamboo fiber, which is utilized to make yarn and texture because of current assembling. The bamboo texture is a characteristic material produced using the bamboo grass mash, and the bamboo fiber is then made by pulping the bamboo grass until it isolates into dainty strings of fiber spun and colored for meshing into cloth [24]. Bamboo Viscose (bamboo rayon) otherwise called recovered bamboo, is a recovered cellulose fiber that has been available for materials such as clothing and home goods [25]. Items from recovered bamboo are appropriate for a broad scope of end-users, for example, towels, shower robes, careful garments, bedding, food bundling, and even cleanliness items, for example, sterile cushions, careful veils, swathes, and sleeping pads [26]. 4.2.1.4 Seacell Fiber

The thought behind seacell is quite primary: regular, unadulterated, and successful dynamic fixings from the ocean that should give us and our skin a treat. Biological, naturally mindful, and henceforth state-of-the-art, seacell brings nature’s positive accomplishments back to men [27]. On this ground, characteristic substances are utilized to build up the seacell fiber, which is useful, skin defensive, and developed, advanced and ensure wellbeing. It lays the foundation for items that innovative individuals with requests and quality mindfulness expect. The seacell fiber is ground from common kelp and becomes not more than a micron granule; at that point, it adds its powder into wood-cellulose [28]. In a medical application, silver-loaded cellulosic fiber is prepared from seacell fiber, which carries fungal and bacterial prevention properties [29]. 4.2.1.5 Acetate Fibers

Acetate fiber derivation strands are one of the leading kinds of semisynthetic fibers. The fiber framing substance is cellulose acetate fiber derivation, in which, in any event, 92% of the hydroxyl bunches are acetylated. This fiber is called triacetate or triacetate cellulose [30]. Auxiliary acetate fiber derivation contains just around 76%

4.2 Classifications

acetylated cellulose gatherings. The diacetate fiber is commonly known as acetate fiber derivation, while the triacetate cellulose is called triacetate. Cellulose acetic acid derivation filaments can be de-acetylated by sodium hydroxide saponification under controlled conditions [31]. The item is a genuine recovered cellulose fiber. This innovation was created by Celanese, who called the fiber “Fortisan.” The filament’s conventional name is rayon. It has remarkable strength and low extension and finds numerous mechanical uses where these two properties are required [32].

4.2.2

Synthetic Fibers

Synthetic fibers are human-made fibers prepared from the chemical synthesis of small molecules of polymers. Synthetic fibers are the result of scientist’s extensive research to improve the properties of plant and animal fibers. Various synthetic fibers and reinforced composites available out of glass, carbon, graphene, basalt, and acetate fiber are summarized below. 4.2.2.1 Glass Fibers

Glass fibers are framed from dissolution and produced in different arrangements by changing the measure of crude materials like sand for silica, earth for alumina, calcite for calcium oxide, and colemanite for boron oxide. In this way, various sorts of glass fibers show various exhibitions like antacid obstruction or high mechanical properties utilizing different silica or different sources [2]. Glass fiber items are arranged by the kind of composite at which they are used. Also, cleaved strands, direct draw rovings, gathered rovings, and mats are the main items utilized in the infusion shaping, fiber winding, pultrusion, sheet trim, and hand layup cycles to frame glass fiber-strengthened composites [33]. Assurance of the glass fibers from breakage or deterioration is a significant issue either during the assembling of glass fiber or during composite creation. Applying estimated specialists to the glass fiber during the assembling of strands causes grease of the glass fibers, notwithstanding the friction-based electricity collection, the fibers bond, and the attachment between fibers and the polymer framework of the composites [34]. During assembling of composites, an interphase layer is framed, at which interpenetration of the measuring to the lattice or dissemination of the network polymer is estimated. The resultant interphase layer can either increase or reduce the composite thinking exhibition about amicability between measuring and network polymers. Similarity among measuring and framework polymer improves high mechanical properties and on the opposite side, inconsistent estimating results in low mechanical properties. A decrease in vehicle heaviness is the primary motive to save energy in the transportation business from an energy perspective. In such a manner, the development of lightweight vehicles with about half heaviness validates the significance of the glass fiber-strengthened composites. This way, development in glass fiber creation is something that occurred. Figure 4.2 shows the classification of various types of fiberglass. Alkali and chemical types of glass are highly resistant to chemicals impact. E-glass observes a good insulator, whereas S-glass has stable mechanical properties [35].

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Chemical glass (C)

Electrical glass (E)

Alkali glass (A)

Fiber glass types Alkali electrical glass (AE)

Structural glass (S) Alkali chemical glass (AC)

Figure 4.2

Classification of glass fibers. Source: Based on Ref. [35].

Fiberglass comes in different structures to suit different applications, the significant ones being fiberglass tape, cloth material, and rope. Fiberglass has excellent mechanical strength, low thermal conductivity, and is an excellent electrical insulator. In terms of dimensional stability, it has a low coefficient of linear expansion. This fiberglass has a compatibility to combine with many synthetic resins for forming the composites [36]. Materials with high-temperature protection give a successful thermal boundary to modern gaskets. Since fiberglass is reliable, safe, and offers high thermal protection, it is one of the generally favored materials in modern gaskets. It gives superior protection and helps secure the apparatus, rationing the energy, and guarantee the wellbeing of expert labor forces. It explains why fiberglass is broadly utilized in enterprises. Fiberglass used in various industries such as beverage, aerospace, defense, automotive, marine, pulp, paper industry, food processing, metals, and mining industries. 4.2.2.2 Carbon Fiber

Carbon fibers (CF) are produced using a cycle that is partly a mechanical and chemical process [3]. It starts with drawing long fibers and afterward heat them at an exceptionally high temperature without permitting oxygen to keep the strands from consuming [13]. At this point, carbonization happens when the molecules within the strands vibrate savagely, ousting the non-carbon particles of a large portion. This process makes a fiber out of long, firmly bolted chains of carbon particles with a couple of remaining non-carbon molecules. A run-of-the-mill successions used to shape carbon strands from polyacrylonitrile includes turning, settling, carbonizing, treating the surface, and measuring. Carbon fiber made from

4.2 Classifications

carbon iotas reinforced composed to shape a long chain. These fibers are incredibly hardened, reliable, and lightweight, utilized in numerous cycles to make brilliant structure materials [37]. Albeit a portion of different kinds of synthetic fibers like basalt, aramid, polyacrylonitrile (PAN-F), polyethylene terephthalate (PET-F), or polypropylene filament (PP-F) are a few favorable circumstances. They are utilized explicitly in thermoplastic short fiber reinforcement polymers (SFRP); also utilized for explicit applications where their ideal properties are material [38]. Carbon fiber-reinforced polymer (CFRP) composites bear various uses in the aviation, automobile, and sports industry along with various other industries [3, 39]. 4.2.2.3 Graphene Fiber

Graphene fiber (GF) has a functional reputation; subsequently, it coordinates unreasonable properties of individual graphene sheets into significant, naturally visible outfits with typical fiber characteristics. It has mechanical versatility for materials while keeping up the great inclinations over customary carbon strands, negligible exertion, lightweight, and straight forwardness of functionalization of a post-synthetic path for numerous applications [40]. Graphene fiber is another kind of elite carbonaceous fiber, which reflects high elasticity with upgraded electrical conductivity at the time contrasted with carbon fiber. A few improved graphene fiber properties show their probability in an assortment of uses, such as lightweight conductive links and cables, supercapacitors, actuators, micro-sized motors, and sun-oriented cell materials, and so on [41, 42]. The sub-atomic element reenactment of polymer composites with graphene fortifications indicates increments in shear modulus (27.6%), Young’s modulus (150%), and hardness (35%). Besides, a decrease in the coefficient of friction (35%) and scraped area rate (48%) was accomplished [43]. 4.2.2.4 Basalt Fiber

The Soviet Union has investigated the creation of strands from basalt during the virus battle and local business examination and creation. The Soviets investigated basalt as a wellspring of fiber for safe airborne materials. The cost of producing strands from aramid, E-glass, and S-glass is much lesser than the basalt. Researchers are working to reduce the cost of fiber produced using basalt [44]. Basalt fiber (BF) is a general novice to fiber-reinforced polymers (FRPs), underlying composites. GF has improved strength qualities, and dissimilar to furthermost glass fibers, it is exceptionally impervious to acidic, essential, and salt assault creation. It is a decent contender for reliable scaffold and shoreline structures [45, 46]. Basalt fiber (BF) has many mechanical and physical properties superior to fiberglass. Furthermore, BF is fundamentally less expensive in comparison with carbon strands. Their temperature impact has been analyzed on the basalt fiber-reinforced polymer (BFRP) composite; it has been observed that an increase in static strength and fatigue life at a particular and most prominent pressing factor was noted with a fall in temperatures [47]. 4.2.2.5 Kevlar

Kevlar is a warmth safe para-aramid fiber with a molecular construction of many interchain and chain bonds that make kevlar unimaginably strong. Most famous for

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its utilization in ballistic body armor, kevlar has numerous applications due to its high rigidity to weight proportion [48]. Kevlar 149, the most grounded fiber, generally translucent in design, has an option in specific pieces of airplane construction [49]. The driving edge of the kevlar wing is less disposed to break in a flying creature than a wing made of carbon or glass fiber. Hybridization of kevlar filaments (KFs) with carbon or glass fibers improves kevlar fiber-reinforced composites’ thermal properties. KFRCs produce better effect strength in a severe level of elastic properties, yet because they are not invariant with direction nature, they have little pressure strength contrasted with their glass and carbon fiber partners [50]. 4.2.2.6 Nylon and Terylene

Nylons are condensation copolymers, outlined with reacting di-useful identical parts monomers of amine and carboxylic destructive; amides are molded at each monomer two terminations in an association analogous to polypeptide biopolymers [51]. Nylons are created using the reaction of a dicarboxylic destructive with a diamine. These are linear polymers, with support, notwithstanding after adding three amino acids at any rate than possible to introduce nylon branches after the buildup of dicarboxylic acids with polyamines [52]. Nylon is observed as high strength fiber in comparison with natural fiber. Nylons are extensively used to prepare fishing nets, ropes, and parachute cables. In the textile industry for texture modification, nylon plays a crucial role, whereas crinkled nylon fibers are used to manufacture elastic hosiery. Nylon is comprehensively used as plastic for making machine parts blended with downy for the strength explanation [53]. Terylene has broadly been utilized in the material industry to make sarees, garments, and dress material. Terylene has been produced by a cycle of polymerizing ethylene glycol and terephthalic corrosive [54]. Terylene has additionally mixed with standard fiber such as cotton and fleece to make more assortments of garments. Terylene is a solid fiber and observed to lose strength in wet conditions. This fiber is versatile and has the property of opposing wrinkles. It sets into long-lasting if exposed to the right temperature for an hour of manufacturing [55]. Terylene is effortlessly washed and dries rapidly. Terylene is principally utilized in making plastic jugs and clothing. Terylene fiber is utilized as polyester tricot weave style pieces of clothing fabric. It is also used to make a nonwoven, needle-punched cover, particularly for presentation [56].

4.3 Challenges A significant challenge is reducing the cost of fiber-reinforced composites with an advanced process, also the advanced lab facility and equipment. The creation of synthetic fibers exceptionally affects the climate. The creation of fibers utilizes a lot of energy and non-inexhaustible assets. It likewise has many side effects and assembling waste. Further, dressing made with manufactured fiber sheds tiny bits of plastic all through their item life. Moreover, when manufactured apparel is discarded, it remains in landfills for many years while siphoning toxins. In terms of individual wellbeing, synthetic fibers

References

are not our best option. However, some advancements are required in the fiber properties. Thus, the fiber blending process should be initiated smoothly to overcome the new challenges in the field. In the fiber blend, two different fibers combine to form a new fiber with unique properties.

4.4 Conclusions This semisynthetic and synthetic fiber becomes high-performance fibers after the reinforcement and is used in various fields. These fibers are the backbone of the newly developed composite material industry. Fiber composites have a better strength-to-weight ratio and are unique because they enable technology for present and future high technology products. These reinforced fiber composites have long-term importance for the economy and manufacturing industry. This study summarizes the semisynthetic and synthetic fiber classification, functionality, and applications. Along with the researcher’s contribution in all aspects of fiber-reinforced composites, research and development has been presented.

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8 Franciszczak, P., Merijs-Meri, R., Kalninš, ¸ K. et al. (2017). Short-fibre hybrid polypropylene composites reinforced with PET and Rayon fibres – effects of SSP and interphase tailoring. Composite Structures 181: 121–137. https://doi.org/10 .1016/j.compstruct.2017.08.075. 9 Seacell® fiber – the Hall collection. https://thehallcollection.co.za/seacell-fiber/ (accessed 13 February 2021). 10 Seacell Fiber Top/1oz – Laughing Lamb Fibers. https://www.laughinglambfibers .com/products/seacell-fiber-top-undyed-natural-spinning-fiber-roving-1oz (accessed 13 February 2021). 11 Sathishkumar, T. P., J. and Naveen, and S. Satheeshkumar (2014). Hybrid fiber reinforced polymer composites – a review. Journal of Reinforced Plastics and Composites 33 (5): 454–471. https://journals.sagepub.com/doi/abs/10.1177/ 0731684413516393. 12 Abdellaoui, H., Raji, M., Essabir, H. et al. (2019). 6 – Mechanical behavior of carbon/natural fiber-based hybrid composites. In: Mechanical and Physical Testing of Biocomposites, Fibre-Reinforced Composites and Hybrid Composites (eds. M. Jawaid, M. Thariq and N. Saba), 103–122. Woodhead Publishing. 13 Bhatt, P. and Goe, A. (2017). Carbon fibres: production, properties and potential use. Material Science Research India 14 (1): 52–57. 14 Rahman, R. and Putra, S.Z.F.S. (2019). 5 – Tensile properties of natural and synthetic fiber-reinforced polymer composites. In: Mechanical and Physical Testing of Biocomposites, Fibre-Reinforced Composites and Hybrid Composites (eds. M. Jawaid, M. Thariq and N. Saba), 81–102. Woodhead Publishing. 15 Jawaid, M., Thariq, M., and Saba, N. (2018). Mechanical and Physical Testing of Biocomposites, Fibre-Reinforced Composites and Hybrid Composites. Woodhead Publishing. 16 Rajak, D.K., Pagar, D.D., Kumar, R., and Pruncu, C.I. (2019). Recent progress of reinforcement materials: a comprehensive overview of composite materials. Journal of Materials Research and Technology 8 (6): 6354–6374. https://doi.org/10 .1016/j.jmrt.2019.09.068. 17 Ghalia, M.A. and Abdelrasoul, A. (2019). 7 – Compressive and fracture toughness of natural and synthetic fiber-reinforced polymer. In: Mechanical and Physical Testing of Biocomposites, Fibre-Reinforced Composites and Hybrid Composites (eds. M. Jawaid, M. Thariq and N. Saba), 123–140. Woodhead Publishing. 18 Semi-synthetic fiber. Patternmaking and Tailoring Wiki. https://tailor.fandom .com/wiki/Semi-synthetic_fiber (accessed 13 February 2021). 19 Kauffman, George B. (1993). Rayon: the first semi-synthetic fiber product. Journal of Chemical Education 70 (11): 887. https://pubs.acs.org/doi/pdf/10 .1021/ed070p887. 20 Bax, B. and Müssig, J. (2008). Impact and tensile properties of PLA/Cordenka and PLA/flax composites. Composites Science and Technology 68 (7): 1601–1607. https://doi.org/10.1016/j.compscitech.2008.01.004. 21 Woodings, C.R. (1995). The development of advanced cellulosic fibres. International Journal of Biological Macromolecules 17 (6): 305–309. https://doi.org/10 .1016/0141-8130(96)81836-8.

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5 Tribological Properties of Natural Fiber-Reinforced Polymer Composites A. Muthuraja 1 and Dipen Kumar Rajak 2 1

Sandip University, Department of Mechanical Engineering, Nashik 422213, India Sandip Institute of Technology and Research Centre, Department of Mechanical Engineering, Nashik 422213, India 2

5.1 Introduction At the beginning of the twentieth century, the dominance of natural fibers almost came to an end in many industries, as polymer-based products were born to be superior and occupied in many commercial products starting from home to space applications. Then, domination of polymer-based products increased in the automotive, manufacturing, aerospace, and transport sectors. Despite numerous attractive characteristics of polymer-based products such as mechanical, thermal, and tribological superiority, they are nonbiodegradable in nature, which cause more ecological problems [1]. Due to the evil nature of polymer-based products, the environmental burden has been enormously escalating day-by-day. In the light of the problems of synthetic polymer fiber, searching for alternatives is highly essential and therefore natural fibers were found as a promising alternative material for the synthetic fibers [2, 3]. The reverse trend has arrived that the natural fibers (Figure 5.1) are getting considerable attention by many researchers for the last two decades, as natural fibers have some attractive qualities such as biodegradability, sustainability, lightweight, and low cost, etc. However, there are few problems with natural fibers such as inadequate resistance to water and thermal, notably limited tensile and impact strength, insufficient interfacial adhesion, incompatible matrix, and durability, etc. Among these problems, the compatibility of fiber and matrix system is the foremost sensitive factor in composite manufacturing. The hydrophilic natural fibers and hydrophobic matrix are incompatible with each other and this effect significantly weakens the adhesiveness of the fiber-matrix system (F-M system) and diminishes the reinforcing efficiency of the fiber [4]. The adhesiveness is the major factor for the considerable interfacial bonding which increases mechanical and tribological characteristics of the natural fiber-based composites. Therefore, it is critical to enhance the interfacial bond

Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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Natural fibers

Plant fiber Seed type Cotton Coir etc. Bast type Flax Hemp Jute Kenaf etc.

Leaf type Sisal Banana Abaca Palf etc.

Animal fiber

Silk type Mulberry Tussah etc.

Wool/hair type Lamb wool Goat hair Horse hair etc.

Mineral fiber

Asbestos Glass etc.

Stalk type Rice Maize Wheat etc. Grass and reed type Bamboo Bagasse Esparto etc.

Figure 5.1

Classification of natural fibers.

between fiber and matrix (F-M) system. The chemical treatment helps in enhancing adhesiveness between F-M systems by modifying the surface of natural fiber and enhancing durability and resistance to wear of the composite. An adequate number of research works have been published on surface treatment techniques such as alkalization, acetylation, benzoylation, electric discharge, permanganate, peroxide, silane, and cyanoethylation by many researchers for the last two decades [5, 6]. Among these surface treatments, alkalization and silane have been chosen for this review article to enhance tribological characteristics of natural fiber-based composites. The next method of enhancing mechanical and tribological properties is hybridization. Hybridization is a process in which polymer composites are being made by merging two or more fibers in it. This fiber combination can be natural–synthetic, natural–natural, and micro–nano for making hybrid composites. The hybridization of polymer composites can also be a better solution for enhancing both mechanical and tribological properties than that of non-hybrid composites [7]. Hybridization can be done through bio-based, thermoplastic, or thermoset plastics with various volume fractions and different orientations of fibers in hybrid composites. Thus, this review work is inclined toward the significant effect of surface treatment and hybridization on tribological properties. The objective of this work is to

5.2 Chemical Treatment–Alkaline Treatment

understand the treatment and hybridization and critically review the influence of these two methods on tribological properties of natural fiber-based composites.

5.2 Chemical Treatment–Alkaline Treatment 5.2.1

Alkaline Treatment (Mercerization)

Alkaline or mercerization treatment is the process of immersing the fiber into an aqueous alkaline solution with water. The importance of this treatment is to enhance interlocking mechanically between fiber and matrix and also disrupting the hydrogen bonding in the network structure for increasing the surface roughness of the fibers [8]. NaOH is a common technique of alkaline treatment used for fiber chemical treatment [9]. A considerable amount of lignin, wax, and oils covers the external surface of the fiber cell wall via alkaline treatment. The alkali groups (OH) are usually broken down and react with molecules of water to move out from the fiber structure. The remaining molecules then form fiber-cell-O-Na groups and provide hydrophobic behavior to the fiber [10]. This NaOH treatment increases the surface roughness of the fiber, which is responsible for better mechanical interlocking.

5.2.2

Silane Coupling Agents (Silanization)

The area between an inorganic substrate and an organic substrate acts as a bonding or bridging agent to improve the adhesion between the two dissimilar composite materials, while silane coupling agents are present in the interphase region [11]. Some of the traditional reinforcing fibers and mechanical properties of natural fibers are depicted in Table 5.1.

5.2.3

Mechanical Properties of Synthetic and Natural Fibers

Tribometer or tribotester (Figure 5.2) is a device, which is utilized to obtain tribological properties such as friction force that develops between surfaces in a relative motion and wear of composites for the product development and the research purpose. These devices measure wear qualitatively. Moreover, an infrared thermal sensor is utilized during wear test and the effect of load, speed, time, and distance on the interface of a developed specimen and counter material is monitored by temperature measurement using an infrared thermal sensor (IR-Camera). Figure 5.3 operates by closing the pin/ball against a rotating disk and applying on the pin/ball a normal load. Contact can occur on the disk’s flat surface or on the circumference of the disk. In reciprocating tribometers, presented in Figure 5.3, the pin/ball moves along the horizontal stroke following a linear trajectory coupled with a flat surface. The parameters to set such as frequency, time, normal load, stroke, lubricant type, and temperature, if any, provide both the measurement of the kinetic friction coefficient and the possibility to investigate the specimen’s wear phenomena.

83

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5 Tribological Properties of Natural Fiber-Reinforced Polymer Composites

Table 5.1 [12–15].

Mechanical properties of natural fibers and traditional reinforcing fibers

Fiber type

Density (g cm−3 )

Dimension/ elongation (%)

Tensile strength (MPa)

Young’s modulus (GPa)

Abaca

1.5

3–10

400

18.6

Bagasse

1.25

—

290

17

Bamboo

0.6–1.10

—

140–230

27–40

Banana

1.35

30

500

12

Coconut

1.2

—

140–225

3–5

Cotton

1.5–1.6

7.0–8.0

287–597

5.5–12.6

Flax

1.38

2.7–3.2

700–1000

27.6

Hemp

1.35

3

530–1110

70

Jute

1.3–1.49

1.5–1.8

393–800

13–26.5

Kenaf

1.2

1.6

745–930

53

Sisal

1.5

2.0–2.50

460–855

9.4–22

E-glass

2.5

2.5

2000–3000

70.0

S-glass

2.5

2.8

4570

86.0

Aramid

1.45

3.30–3.70

2700–4500

130

Source: Based on Refs. [12–15].

5.3 Tribological Behavior of Chemically Treated Composites Yousif et al. performed the surface enhancement study on the carbon-fiber-reinforced polymers (CFRPs) composite to understand the significant effects of chemical treatment on the tribological properties [16]. From experimental investigation, tribological properties of the composites were obtained using a pin-on-disk (POD) tribometer (Figure 5.2). The abrasive paper of SiC grit sheet was utilized to polish the counterface surface and the composite samples before every test. An infrared thermometer was utilized to monitor the online interface temperature. The experimental results of treated CFRP revealed that superior adhesion enhanced the wear resistance of the CFRP. Inadequate adhesive bonding between the coir fiber and polyester matrix leads to the existence of debonding gap around the fiber (Figure 5.4). It was also observed that untreated CFRP composites also exhibited a higher wear rate due to the debonding between coir fiber and the matrix and micro crack attributed to the more material loss. CFRP composites with alkaline treatment have superior wear resistance than that of bleached treated and untreated CFRP composites. However, bleached CFRP composites have no significant difference with the friction coefficient of untreated CFRP composites. The surface modification on coir fibers by bleached or alkaline treatment, individually exhibits good

5.3 Tribological Behavior of Chemically Treated Composites

Normal load

Infrared thermometer

Load cell

Friction indicator

Specimen

Speed controller

Counterface Motor

Figure 5.2

Pin-on-disc tribometer machine [16]. Applied load Applied load Sample

Counterface Rotating disk

Rotating direction Sliding directions

Sample Holder

Contact area

(a)

Contact area

(b)

Figure 5.3 (a) Pin-on-disk configuration and (b) reciprocating ball-on-flat configuration. Source: Based on Yousif et al. [16].

interfacial adhesion. It was also observed that the high adhesion bonding between the matrix and the coir fiber assists in protecting the rubbing surface from worn. Tribological properties of hemp, glass, and carbon fiber composites were addressed and the tribological wear tests were carried out at a constant peripheral speed of 210 mm s−1 with varying applied load of 10, 20, 50, and 70 N [17]. It was obtained that the hemp type fiber showed superior wear resistance with a volume loss of 10% in 700 seconds than that of 90% in glass and 56–57% in carbon fibers composites. When there was a loss of volume with applied load, hemp fiber showed better results in the highest load condition than the other two. However, the friction coefficient of carbon fiber composites showed 28% and 51% less than hemp and glass fibers, respectively. The wear rate increases with rpm for all the composites and hemp fiber is satisfied with superior wear resistance rather than friction coefficient (Figure 5.5).

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5 Tribological Properties of Natural Fiber-Reinforced Polymer Composites

0106 10 KV

X200 100 μm WD24

(a)

0108 10 KV

X120 100 μm WD24

(b)

Figure 5.4 SEM micrographs of worn-out surface (a) untreated and (b) treated. Source: Yousif et al. [16]. 100

Wear depth/thickness (%)

86

H type G type C type

80

60

40

20

0

0

200

400 Time (s)

600

800

Figure 5.5 Wear depth (%) versus the sliding time (s) for unimpregnated fabric type. Source: Fazio et al. [17].

From this investigation, it was observed that the hemp composites showed a significant performance under higher load conditions of 50 and 70 N, during a prolonged time, and due to the absence of brittle behavior of the natural fibers. The alkali treatment and its effect on the mechanical strength of the jute fiber composite were studied [11]. The experimental study showed that the composite with alkali-treated fiber had better mechanical strength than the untreated one. The reason may be that treated fiber seems rough, which improved the adhesive behavior of the fiber surface (Figure 5.6a,b). Scanning electron microscope (SEM) image for untreated jute fibers revealed that some trapped foreign particles were present, whereas after the treatment, the surface impurities were disappeared and made them rough. The weight loss of silane treated poly lactic acid (PLA) with jute fiber sample is shown better than other treated and nontreated samples (Figure 5.6c).

5.4 Tribological Behavior of Hybrid Composites PLA/untreated JF PLA/silane 1 treated JF PLA/silane 2 treated JF PLA/alkali treated JF

0.06 Weight loss (g)

0.05 0.04 0.03 0.02 0.01 0 0 10 kV

(a)

X5,000

5 μm 0002

08/MAR/07

10 kV

(b)

X5,000

5 μm 0001

08/MAR/07

(c)

20

40

60

80 100 120 140 160 180 200

Sliding distance (m)

Figure 5.6 (a) Micrograph of untreated single kenaf fiber, (b) micrograph of treated single kenaf fiber, (c) weight loss for untreated and several treated composites [11, 18]. Source: Omrani et al. [18].

The effect of a chemical treatment such as alkali and silane was investigated on the mechanical and bond strength between fiber-matrix of kenaf and pineapple leaf fibers [19]. It was shown that chemical treatments enhanced the tensile properties of fibers by removing lignin and hemicelluloses. It was identified that silane treated pineapple leaf fiber (PALF) and Kensaf Fiber (KF) reduces their hydrophilic characteristics. Therefore, water absorption was reduced significantly. The natural fibers (grewia optiva fibers (GOF), nettle fibers (NF), and sisal fibers (SF)) with 20% weight fraction reinforced PLA composites were fabricated by hot pressing with a film stacking technique (Figure 5.7), followed by tribological behavior that was investigated under dry contact at different operating parameters of applied load in the range of 10–30 N, sliding speed (1–3 m s−1 ), and sliding distance (1000–3000 m) [20]. The experimental results showed that the addition of natural fiber into PLA matrix significantly improved the wear behavior of the neat polymer. There was a 10–44% reduction in friction coefficient and a 70% reduction in specific wear rate of developed natural fiber PLA composites as compared to neat PLA. It was obtained that variation of applied normal load much more influences the wear behavior of the developed composites as compared to that of the sliding speed variation.

5.4 Tribological Behavior of Hybrid Composites The flax/kenaf/glass/carbon fiber-reinforced composites were developed using dry hand-layout to understand the mechanical properties of natural fiber for hybridization [21]. Additionally, tribological properties of composites were also investigated. Experimental results revealed that the synthetic fibers offered high impact strength and greater hardness due to their superior bonding strength. The natural fiber of kenaf and flax fiber has 76.6% lesser hardness than carbon fiber, due to inadequate interfacial bonding between the natural fiber and epoxy matrix. However, kenaf has shown 10% and 25% less specific wear rate under a load of 25.5 N, a sliding distance of 1.26 km, and speed of 125 rpm, than that of carbon and glass fiber composites, respectively (Figure 5.8). Low wear rate with the soft surface of natural fiber made it suitable for an abrasive environment and it was also observed that the flexural extension of natural fiber was superior. Therefore, withstanding sudden transverse load by natural fiber was higher than the synthetic fiber.

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5 Tribological Properties of Natural Fiber-Reinforced Polymer Composites

Upper mold plate Teflon sheet PLA film Fiber mat

Hot compression

Teflon sheet Lower mold plate Mold assembly

Laminated green composite

Figure 5.7 Graphical view of film stacking method for composite laminate fabrication. Source: Based on Bajpai et al. [20]. 23

Specific wear rate Hardness

22

70 60

21

50

20 40 19 30

18

20

17 16

Hardness (BHN)

Specific wear rate (×10–3 mm3/N m)

88

Glass

Carbon

Flax

Kenaf

10

Classification

Figure 5.8 Specific wear rate and hardness of different composites. Source: Based on Khandai et al. [21].

The solvent casting method was utilized to prepare biodegradable and electrically conductive polyvinyl alcohol (PVA) based jute fiber hybrid composites [22]. From the result, it was obtained that 20 wt% jute reinforcement with PVA + 2.5 wt% multi-walled carbon nanotube (MWCNT) and 17.5 wt% multi-layer graphene (MLG), enhancing to the highest electrical conductivity of 3.64 × 10−4 S m−1 . However, jute decreased the electromagnetic interference (EMI) shielding. The wear resistance was increased of PVA/MLG/jute fiber (JF) hybrid composites with jute content up to 10 wt% in composites and then showed a decline after 10 wt%.

References

Increasing jute content improved the storage modulus and hardness of PVA/MLG with 10 wt% of jute in nanocomposites and revealed the superior shore hardness of about 70. Shore D hardness value of all the composites was obtained in the range of 60–70. In addition to it, the jute content with more count disrupted the network and separated the graphene sheets from the hybrid composites.

5.5 Conclusion From the critical review on tribological behavior of natural fiber-reinforced polymer composites, the following conclusions have been arrived: ●

●

●

The chemical treatment most significantly affects the mechanical properties than tribological properties. The alkaline treatment significantly enhances the tribological properties of natural fiber-based composites as compared to various chemical treatments. Hybridization process significantly enhances the impact strength and tribological properties of natural fiber composites.

References 1 Harish, S., Michael, D.P., Bensely, A. et al. (2009). Mechanical property evaluation of natural fiber coir composite. Materials Characterization 60 (1): 44–49. https://doi.org/10.1016/j.matchar.2008.07.001. 2 Abilash, N. and Sivapragash, M. (2016). Optimizing the delamination failure in bamboo fiber reinforced polyester composite. Journal of King Saud University, Engineering Sciences 28: 92–102. https://doi.org/10.1016/j.jksues.2013.09.004. 3 Burgueñoa, R., Quagliata, M.J., Mohanty, A.K. et al. (2005). Hybrid biofiber-based composites for structural cellular plates. Composites Part A: Applied Science and Manufacturing 36 (5): 581–593. 4 Hong, C.K., Hwang, I., Kim, N. et al. (2008). Mechanical properties of silanized jute-polypropylene composites. Journal of Industrial and Engineering Chemistry 14: 1471–1476. https://doi.org/10.1016/j.jiec.2007.07.002. 5 Aziz, S.H. and Ansell, M.P. (2010). The effect of alkalization and fiber alignment on the mechanical thermal properties of kenaf and hemp bast fiber composites: part 2 – cashew nut shell liquid matrix. Composites Science and Technology 64: 1231–1238. https://doi.org/10.1016/j.compscitech.2003.10.002. 6 Yu, T., Ren, J., Li, S. et al. (2010). Effect of fiber surface-treatments on the properties of poly(lactic acid)/ramie composites. Composites Part A: Applied Science and Manufacturing 41: 499–505. https://doi.org/10.1016/j.compositesa.2009.12 .006. 7 Swolfs, Y., Gorbatikh, L., and Verpoest, I. (2014). Fibre hybridisation in polymer composites: a review. Composites Part A: Applied Science and Manufacturing 67: 181–200. https://doi.org/10.1016/j.compositesa.2014.08.027.

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8 Deo, C.R. (2010). Preparation and characterization of polymer matrix composite using natural fiber Lantana-Camara. Thesis. National Institute of Technology Rourkela – 769 008, India. 9 Chikouche, M.D.L., Merrouche, A., Azizi, A. et al. (2015). Influence of alkali treatment on the mechanical properties of new cane fibre/polyester composites. Journal of Reinforced Plastics and Composites 34 (16): 1329–1339. https://doi.org/ 10.1177/0731684415591093. 10 Mukhopadhyay, S. and Fangueiro, R. (2009). Physical modification of natural fibers and thermoplastic films for composites – a review. Journal of Thermoplastic Composite Materials 22 (22): 135–162. 11 Liu, L., Yu, J., Cheng, L., and Qu, W. (2009). Mechanical properties of poly(butylene succinate) (PBS) biocomposites reinforced with surface modified jute fibre. Composites Part A: Applied Science and Manufacturing 40 (5): 669–674. https://doi.org/10.1016/j.compositesa.2009.03.002. 12 Xess, P.A. (2012). Erosion wear behaviour of Bamboo fiber based hybrid composites. Master’s thesis. Department of Mechanical Engineering, National Institute of Technology, Rourkela, India, May 2012. pp. 39. 13 Alves, C., Ferrao, P.M.C., Silva, A.J. et al. (2010). Eco-design of automotive components making use of natural jute fiber composites. Journal of Cleaner Production 18 (4): 313–327. https://doi.org/10.1016/j.jclepro.2009.10.022. 14 Ramnath, B.V., Kokan, S.J., Raja, R.N. et al. (2013). Evaluation of mechanical properties of abaca–jute–glass fiber reinforced epoxy composite. Materials and Design 51: 357–366. https://doi.org/10.1016/j.matdes.2013.03.102. 15 Djafari Petroudy, S.R. (2017). Physical and mechanical properties of natural fibers. In: Advanced High Strength Natural Fibre Composites in Construction (ed. M.F.F. Fu), 59–83. http://dx.doi.org/10.1016/B978-0-08-100411-1.00003-0. 16 Yousif, B., Ong, L., Low, K.O., and Jye, W.K. (2009). The effect of treatment on tribo-performance of CFRP composites. Recent Patents on Materials Science 2: 67–74. https://doi.org/10.2174/1874465610902010067. 17 Fazio, D., Luca, B., and Durante, M. (2020). Tribological behaviour of hemp, glass and carbon fibre composites. Biotribology 21: 100113. https://doi.org/10 .1016/j.biotri.2019.100113. 18 Omrani, E., Menezes, P.L., and Rohatgi, P.K. (2016). 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 19: 717–736. https://doi.org/10.1016/j.jestch.2015.10.007. 19 Asim, M., Jawaid, M., Abdan, K., and Ridzwan Ishak, M. (2016). Effect of alkali and silane treatments on mechanical and fibre-matrix bond strength of kenaf and pineapple leaf fibres. Journal of Bionic Engineering 13 (3): 426–435. https:// doi.org/10.1016/S1672-6529(16)60315-3. 20 Bajpai, P.K., Singh, I., and Madaan, J. (2012). Frictional and adhesive wear performance of natural fibre reinforced polypropylene composites. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 227 (4): 385–392.

References

21 Khandai, S., Nayak, R.k., Kumar, A. et al. (2019). Assessment of mechanical and tribological properties of flax/kenaf/glass/carbon fiber reinforced polymer composites. Materials Today: Proceedings 18 (7): 3835–3841. https://doi.org/10.1016/j .matpr.2019.07.322. 22 Joseph, J., Prithvi Raj, M., Manoj, K. et al. (2020). Sustainable conducting polymer composites: study of mechanical and tribological properties of natural fiber reinforced PVA composites with carbon nanofillers. Polymer-Plastics Technology and Materials 59 (10): 1088–1099. https://doi.org/10.1080/25740881.2020.1719144.

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6 Nonstructural Applications of Synthetic Fibers Composites Ashish Gupta 1,* , Pankaj Kumar 2,* , Mandeep Singh 1 , Hema Garg 3 , Anisha Chaudhary 4 , and Sanjay R. Dhakate 1 1 CSIR-National Physical Laboratory, Advanced Carbon Products and Metrology, Dr. K. S. Krishnan Marg, New Delhi 110012, India 2 General Biologicals Corporation, Research and Development Department, Innovation First Road, Hsinchu 300092, Taiwan 3 Indian Institute of Technology Delhi, School of Interdisciplinary Research, Hauz Khas, New Delhi 110016, India 4 University of Delhi, Department of Physics and Astrophysics, North Campus, New Delhi 110007, India

6.1 Introduction Fibers are cylindrical, long-length structures with diameters in micron to nano range [1]. These can be classified on the basis of their origin as natural and synthetic fibers. Synthetic fibers, also known as man-made fibers or polymeric fibers, are those that can be synthesized in a laboratory or an industry either from a natural source or synthetic polymer. Figure 6.1 shows the general classification of synthetic fibers on the basis of their core components and nature [2]. Synthetic fibers are better than natural fibers due to the liberty for physical or chemical enhancement in their structure, and such change also results in a change in their physicomechanical and physicochemical properties. Also, the separation and purification of natural fibers take much effort. Therefore, synthetic fibers (SFs) can be inexpensive as compared to natural fibers in pure form. The main drawback of synthetic polymer-based fibers is that they are mostly nonbiodegradable, but this does not limit its application in most of the cases. Synthetic fiber-reinforced composites (SFRCs) are one of the latest and most significant materials that have diminished the dependency on metals for a number of applications. Also, the main advantages of SFRCs are their lightweight, tailorable structure and properties, higher mechanical strength (bending, tensile, and interlaminar strength) by weight, ease of molding, less reactivity, etc. SFRCs are high-performance composites generally meant for structural applications which required high performance in mechanical properties such as fatigue, stiffness,

* Authors contributed equally. Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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Synthetic fibers

Organic

Natural polymer based

Lignin Alginate Acetate Rubber

Figure 6.1

In-organic

Synthetic polymer based

Polyester Polypropylene Polyamide Polyethylene Vinyl Aramid Kevlar

Carbon Glass Metal Ceramic

Types and classification of synthetic fibers. Source: Based on Ghori et al. [2].

creep, fracture toughness, dynamic, and static strength [3]. These properties help in building structural composites for applications in automobiles, aviation, and the construction sector. Carbon fibers and aramid fibers are some of the best synthetic fibers providing excellent strength to the structure. Commercially, 90% of carbon fibers are obtained from poly acrylonitrile (PAN) polymer and utilized in preparing structural composites. However, many other applications depend on other properties of fibers rather than structural. These applications are termed nonstructural applications. The examples include but are not limited to electrochemical energy storage, tribology, field-effect transistors (FETs), electromagnetic interference (EMI) shielding, electrical wiring or board, light-emitting diodes (LEDs), fire retardancy, thermal energy storage (TES), water purification, conductive and corrosion resistance coatings, etc. The properties individually or in combination required for such applications include chemical resistance, conductivity, ease of functionalization and modification on the surface of synthetic fiber, magnetic properties contribute to the nonstructural application of the SFRCs and lay down to its non-conventional applications. In further Section 6.2 of the chapter, we will discuss the nonstructural applications of these SFRCs in detail with the most recent research work reported in the literature for these kinds of applications.

6.2 Nonstructural Applications of SFRCs Depending upon the type of industry involved, the nonstructural applications of these SFRCs have been divided into various sections such as electronic industry, energy storage and generator sector, biomedical, the medical industry, as well as civil engineering sector. The energy sector is further divided into sub-sections energy storage, energy conversion, and energy generator describing batteries,

6.2 Nonstructural Applications of SFRCs

Table 6.1

Nonstructural applications of SFRCs.

Energy sector

Energy storage: such as lithium batteries and supercapacitors Energy conversion: such as fuel cells and thermal energy

Mechanical sector

e.g. civil engineering, tribology, marine applications

Electronic sector

e.g. LEDs, FETs, photovoltaics, logic EMI shielding, lightning strike Electrochemical sensor, optical sensor, wearable textile

Medical sector

e.g. drug delivery, gene therapy, etc.

supercapacitors (SCs), fuel cells, and thermoelectric devices. Table 6.1 summarizes the nonstructural applications of SFRCs on the basis of the industrial sector.

6.2.1

Energy Sector

The energy sector is a fast-growing and futuristic sector that deals with energy storage and energy conversion needs of small devices to the transportation sector. The energy storage devices include rechargeable batteries such as lithium-ion and sodium ion batteries, supercapacitors, TES devices, etc. Both the batteries and supercapacitors deal with the storage of energy via electrochemical reaction, while thermal storage devices store energy from waste heat employing phase change materials (PCMs). Energy conversion devices include fuel cells and thermoelectric devices. Fuel cells utilized hydrogen as a fuel to convert it into energy and water, while thermoelectric devices convert waste heat into electrical energy. SFRCs play an important role in building devices as support materials as well as main constituents based on their properties. The application of SFRCs in these devices is discussed in Sections 6.2.1, 6.2.2, 6.2.3, and 6.2.4. 6.2.1.1 Batteries

Graphite is the commercially used anode material in batteries. However, its theoretical specific capacity in batteries is low, i.e. 370 mAh g−1 . In search of improvement in electrochemical performance of batteries, carbon fiber and its composites as anode have found to play an important role due to its advanced morphology, good conductivity, and ability to form a membrane which excludes the use of both binder and conductive filler, improving flexibility and free-standing nature [4–10]. In a study by Yuan et al. [4], CuO-CF composites were prepared and tested for their electrochemical performance as anode material in lithium ion batteries (LIBs). At first, chopped carbon fibers (CFs) (1 mm length) were oxidized in (NH4 )2 S2 O8 followed by treatment with NaOH solution. The distilled water (DI)-washed CFs were sensitized (SnCl2 /HCl), activated (AgNO3 /NH4 OH), and dipped in a copper plating solution until no bubbles were produced. The final CuO-CF composites were obtained after sintering in N2 at 800 ∘ C and in the air at 400 ∘ C. The CuO-CF fibers composite showed an excellent capacity of 598 mAh g−1 as compared to bare

95

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6 Nonstructural Applications of Synthetic Fibers Composites

CuO nanowires, i.e. 434.9 mAh g−1 with higher capacity retention. Also, the results show that CuO-CF-based composites are better in performance than other reported CuO/carbon materials. Glass fiber (GF) based composites have low electrical conductivity; however, they are being used as an electrolyte membrane in both lithium and sodium-ion batteries [11–15]. Gao et al. prepared glass fiber/gel-polymer composite using poly(vinylidene fluoride-co-hexafluoro propylene) (PVDF-HFP). Glass fibers paper enhanced the mechanical strength of electrolyte, and its highly porous structure acts as a microchannel, which is advantageous in device application. Aramid fiber composites also found their application in batteries as separators [16]. Mechanical failure or thermal shock is the main cause of battery failure, mainly due to changes in electrolytes that are flammable and highly reactive. So there is a need for a separator that can hold electrolytes, mechanically and thermally stable, and provide a channel for ion movement. Patel et al. utilized high mechanical and thermal stability properties of aramid fibers. They fabricated aramid nanofibers from bulk fibers using vacuum-assisted self-assembly. Also, aramid-based fibers are flame resistant, which helps to sustain it on the flame while other separators get melts or decompose in contact with flame [17, 18]. 6.2.1.2 Supercapacitors

Supercapacitor (SCs) is another type of electrochemical energy storage device that has energy density lower than batteries but higher power density. Fiber-based composites are now being also tested as electrodes for supercapacitor applications. In most cases, carbon fiber paper or cloth-based composites have been utilized in supercapacitor performance [19, 20] due to their good electrical conductivity. Almeida et al. [21] utilized CF interconnected three-dimensional structure (CF felt) as a substrate to deposit graphene oxide sheets, followed by potentiostat reduction at −1.25 V for 15 minutes against Ag/AgCl electrode to form reduced graphene oxide (rGO)/CF binary composite. The composite shows linear capacitive performance due to electric double layer formation. Further, the composite was coated with polyaniline (PANI), a conducting polymer, which not only increases conductivity but also generates pseudo capacitance along with double-layer capacitance, increasing the overall specific capacitance. Shang et al. have demonstrated that composite CF cloth impregnated with WS2 platelets shows higher capacitance than bulk WS2 . The graphene-like structure of WS2 was confirmed using scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis dispersed uniformly over the surface of each carbon fiber. The WS2 /carbon fiber cloth (CFC) composite shows a specific capacitance of 399 F g−1 for 1 A g−1 discharge current density. The high electrochemical properties and performance is attributed to the good conductivity of CF cloth and also the intimate interaction between individual CF and WS2 sheet [22]. However, carbon fibers are somewhat costly; to lower down the cost, Wang et al. utilized glass fiber-based paper instead of carbon fiber as substrate. To increase the conductivity of PANI, a conductive polymer, was coated on the glass fiber surface through chemical oxidative polymerization. They prepared glass fiber paper/PANI composite by surface functionalization of glass fiber paper with (3-aminopropyl)triethoxysilane, which makes a connection of PANI with

6.2 Nonstructural Applications of SFRCs

glass fibers. This shows a conductivity of 2.78 S cm−1 with a good capacitance value of 391.3 F g−1 . However, in the case of rapid oxidative polymerization (within one minute), the amino-functionalized glass fiber PANI composite shows low conductivity of 1.8 S cm−1 but a higher capacitance value of 490.6 F g−1 . Electrospinning-based composite fibers are also nowadays popular in energy storage research due to their higher surface area as compared to microfibers, flexible sheet type nature, and easy modification process [23–28]. In view of utilizing all these advantages, Lu et al. [28], synthesized composite core-shell type fibers having poly(acrylic acid) (PAA) embedded with MnO2 nanoparticles as the core and polypyrrole (PPy) polymer as the shell. Electrospun PAA/manganese acetate fibers were surface-functionalized using FeCl3 to make them water-insoluble followed by surface coating with manganese acetate. KMnO4 creates MnO2 particles on the surface of fibers by oxidation followed by coating PPy solution on nanofibers. These nanofibers show a specific capacitance of 564 F g−1 at a 10 mV s−1 scan rate. Nowadays, fiber SCs are also a new fashion in energy storage [29]. In a simple approach, two fibers separated by a separator (filled with gel-type electrolyte) are twisted by twinning or twisting [30] and used as a supercapacitor. At first, Bae et al. [31] demonstrated the poly methyl methacrylate (PMMA) fiber and Kevlar fiber twisted fiber SC. The twisted fiber was gold-coated to collect current, and PVA/ H2 SO4 gel electrolyte was utilized. However, the composite fiber electrodes have shown only moderate capacitance of 2.4 mF cm−2 ; however, the study motivated further work on fiber supercapacitors. Zhou et al. [32] also demonstrated the fabrication of carbon nanotube (CNT)-PPy fiber by twisting their film. The specific capacitances of both film and fiber were tested, and it was observed that in the case of twisted fiber, the specific capacitance is (331.4 F g−1 ) much higher as compared to film, i.e. 139.2 F g−1 . Also, the fiber electrode shows high stability during charge–discharge for 10 000 cycles. Such practice also increases the interface area, enhancing electrochemical performance. These fibers SCs are reported to produce the same electrochemical performance even when bending to any shape or angle. In a work, Chen et al. [33] developed an electrochromic fiber shape supercapacitor. They wrapped the aligned CNT-PANI film on an elastic rubber fiber, followed by coating with PVA/H3PO4 gel electrolyte. Both positive and negative electrode show different colors such as light yellow, blue, and green at different working voltages. Also, a capacitance of 255 F g−1 with a power density of 12.75 Wh kg−1 has been achieved with this fiber supercapacitor. 6.2.1.3 Fuel Cells

Polymer electrolyte membrane-based fuel cells (PEM fuel cells) are new generation devices that can generate high power densities for mobility applications. Fuel cells have promising applications in transportation to reduce environmental pollution as well as crude oil dependency. Bipolar plate (BP) is one of the key components of the PEM-based fuel cell stake (Figure 6.2). BP in fuel cells provides an electrically conducting path to electrons between two cells. They also distribute reactant gases and act as a barrier for these gases, remove waste heat generated in the process, and also provide stack structural integrity providing strength. For making fuel cells

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6 Nonstructural Applications of Synthetic Fibers Composites

Current collector

Figure 6.2 stack.

Bipolar plates in a fuel cell

Bipolar plate Catalyst Electrolyte Catalyst Bipolar plate Flow channels Current collector

lighter and more efficient, BPs should have good electrical and thermal conductivity along with suitable strength in terms of specific stiffness. Fiber composites based on thermoplastic polymers such as polypropylene (PP), PVDF, polyethylene, fluoropolymers have been used very little [34] due to their low chemical and thermal stability in comparison to carbon or glass fibers and thermosetting resins. Carbon fiber-epoxy composites can provide all three much-needed properties. In this direction, Hwang et al. [35] designed and prepared carbon fiber-epoxy-based composites as BPs using the compression molding technique. To get good conductivity and high modulus, unidirectional pitch-based carbon fibers in the form of prepreg were selected, and three layers of this prepreg were stacked in a selected manner (0/90/0). They hot-pressed this prepreg with the help of designed flow channels on top and bottom side. This fiber composite BPs shows lightweight (1.82 × 103 kg m−3 ) and high in-plane electrical conductivity 300 S cm−1 (three times above the planned value). Also, the thermal conductivity achieved as 85 W m−1 K−1 and the gas permeability as 1.4 × 10−6 cm3 cm−2 s−1 for air at pressure 0.3 MPa was acceptable but lower than the required value of 2 × 10−8 m3 m−2 s−1 for BPs application. Recently, Choi et al. [36] fabricated woven CF-resin reinforced BP with excellent performance. These plates have a thickness of only 300 μm and show 6.9 times reduced weight as compared to commercial plates of graphite. The gas diffusion layer is another area in fuel cells where chopped carbon fiber-based composite papers are in high demand [37, 38]. In a study by Kaushal et al. [39], micron-size graphite particles were introduced in carbon fiber phenolic resin composite to increase the overall conductivity and power density of gas diffusion layer (GDL). However, its hydrophobicity was not found suitable for controlling the water flooding in the GDL. Therefore, to overcome this problem, in another study, Kaushal et al. [40] introduced multi walled carbon nanotubes (MWCNTs) in CF paper composite. The composite was fabricated by two methods first by direct growth of MWCNTs over carbon fiber-resin composite using chemical vapor deposition (CVD), and the second one by mixing MWCNTs with phenolic resin. This results in an enhancement in power density as 594 from 361 mW cm−2 , which is also higher than graphite particles based carbon fiber composite (563 mW cm−2 ).

6.2 Nonstructural Applications of SFRCs

6.2.1.4 Thermal Energy Storage (TES) Technology

TES is a technology toward more efficient use of thermal energy. Generally, PCMs are employed in the TES, which temporally store heat and deliver in the form of energy. Organic PCMs materials such as paraffin have high specific phase change enthalpy; however, in the molten state, leakage of thermal energy restricts their use [41]. If a carbon-based material or metal is used as a stabilizing agent, it is also possible to increase the thermal conductivity of the system. The process is known as shape stabilization. Such composites can also be used in temperature-regulated water storage systems, smart garments [42, 43], and electronic device coolants as supplementary in the structural component. However, it is also necessary to choose a stabilizing fiber compatible and non-reactive with PCMs. Fredi et al. [44] developed epoxy and short carbon fiber reinforced multifunctional composites containing MWCNTs and PCMs, which can act as TES and release systems. The composite shows super retention of thermal energy even after 50 cycles and good melting enthalpy of 47 J cm−3 . Interlaminar shear strength decreases with PCMs addition, which confirms the presence of PCMs in the interlaminar region despite in-between CF tow. Similarly, polyamide/glass fiber composites containing paraffinic wax were prepared in another work by Fredi et al. [45]. Glass fiber-based PCMs composites shown low melting enthalpy of 17.1 J g−1 . Electrospun poly urethane (PU) fibers are also used in stabilizing PCMs such as quaternary fatty acid eutectics (stearic acid, capric acid, myristic acid, lauric acid, palmitic acid) for their application in TES [46]. These composite nanofibers on the coating with silver particles using sputtering show an immense increase in thermal storage and melting enthalpy (ΔH m = 118.7 J g−1 ). Fluorescent PCM (organic lanthanides) encapsulated with PU using electrospinning to form composite fibers were investigated by Xi et al. [47]. These bifunctional composite fibers exhibit both TES and luminescent properties. The composite fibers show melting enthalpy, i.e. ΔH m = 128.15 J g−1 . In the case of hybrid fibers including PMMA with PU, both luminescent and TES properties got improved, and phase change temperature also decreased down from 18–55 to 28–48 ∘ C. Centrifugation spinning is a faster technique to spun polymer fibers composites encapsulating with functional PCM materials, which also provide leakage protection along with improving shape stabilization. Recently, polyacrylonitrile/polyethylene glycol (PAN/PEG)-based hybrid polymer nanofibers exhibiting good TES properties have been fabricated using centrifugation spinning. The latent heat of the PAN/PEG/SiC fibers having 4.0 wt% SiC was 69.91 J g−1 , while with increasing SiC content as 6, 8, and 10 wt%. Latent heat ranged from 45.61 to 61.02 J g−1 . 6.2.1.5 Thermoelectric Energy Eneration

Thermoelectric or thermal energy harvesting is one of the major areas of research to get an energy generation source. It works by converting waste heat to electric energy via temperature difference and heat flow. They generate voltage by utilizing the Seebeck effect [48], which in turn generates current to produce power and load. Present research in thermoelectric materials is based on ZT value, i.e. figure of merit [49]. The device consists of two main components – heat sink and heat source – that

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Seeback effect Cold –

+

––

–

+

+

+

– – – –

+ + +

– – –

+ + +

– – – – n-type – –

+ + + p-type + +

–

+

– – –

+

Hot

+

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Hot

Electron flow

Figure 6.3 Schematic of thermoelectric generator with electrons (−) and holes (+) as charge carrier.

release and absorbs the heat produced resp., Afterward, p-type and n-type materials are used, which transfer heat from the source to the heat sink. Figure 6.3 shows the schematics of a basic thermoelectric generator producing the Seebeck effect. In a work by Sung et al., CNT-glass fiber-epoxy composites and CF-epoxy composites were prepared and tested for their thermoelectric application. The CF/epoxy composite has shown better electrical and thermal properties and shows p-type behavior in the Seebeck coefficient. The CNT/GF/epoxy composite delivers characteristics related to n-type thermoelectric. A closed-loop device prepared shows the generation of current in both in-plane and through-plane directions showcasing its application as a thermoelectric material. A higher current was produced while using a device having n and p-type materials in in-plane direction as compared to the through plane direction. However, the ZT value obtained much lower than the commercial required value. Recently, in a study by Karalis et al. [50], glass fibers tow (10 cm) were coated with n-type (single walled carbon nanotube [SWCNT]/sodium dodecylbenzene sulfonate [SDBS]/polyethylimine) and p-type (SWCNT/SDBS) thermoelectric material. The combination shows good electrical conductivity and high Seebeck coefficients. CF reinforced cement composites have also grabbed the attention of researchers worldwide because research has shown that CF cement composites have a good Seebeck effect [51–53]. Wei et al. demonstrated that cement-based composites have various

6.2 Nonstructural Applications of SFRCs

cons, such as microcracks, porosity, and brittleness, which affect both conductivity (negative) and Seebeck effect (positive). They prepared cement CF composites with expanded graphite (EG) shows a ZT value of 2.22 × 10−7 which increases up to a porosity value of approximately 10% and further decreases. Liu et al. introduced Bi2 Te3 thermoelectric material in CF/cement composite, which enhanced electrical conductivity due to quantum tunneling, and improved the Seebeck effect. The increase in thermoelectric properties is observed as almost 10 times that of the bare cement CF composites. Such an increase is attributed to the increase in carrier reflow due to the increased amount of Bi2 Te3 . Nanofiber composites are also being utilized for thermoelectric applications because nanomaterial can increase ZT value by phonon scattering at grain boundaries and their interface. In a recent work, Ryu et al. prepared nanofiber from PAN/N,N dimethyl formamide (DMF) and PVP/sodium cobalt oxide (NaCo2 O4 ) precursor solutions using dual-mode electrospinning. The nanofibers were converted into CNF/NaCo2 O4 composite nanofiber webby successive heat treatments at 600–900 ∘ C. The composite nanofibers (with 45% NaCo2 O4 and heat treatment temperature 700 ∘ C) show a high ZT value ∼0.01 and power factor 5.79 μW m−1 K−2 . The high performance was obtained due to a good combination of thermal conductivity, electrical conductivity, and morphology of composite nanofibers.

6.2.2

Mechanical Industry

6.2.2.1 Tribological Applications

Tribology refers to the study of the property of a material related to lubrication, wear, and friction [54, 55]. Wear can be of three types, i.e. adhesive type, abrasion, and fatigue type. It is reported that as compared to a single material such as fiber, composites are better tribological materials [56]. It is because composite brings several advantages such as high fatigue strength, resistance to corrosion and surface modification, etc. [57]. However, synthetic fiber reinforcement increases the overall tribological properties, only up to a certain limit. Also, in a composite material, fiber volume fraction plays an important role in defining the final characteristics and application [58]. In a work reported by Schon et al., the fiber volume fraction of carbon fibers in epoxy is found to be between 3% and 9% for optimum wear resistance properties. This may be because higher fiber concentration results in poor bonding between resin and fiber due to the higher surface area of fiber references [59] glass fiber [60, 61]. However, having the advantage of low cost, glass fibers possess environmental issues, so researchers are trying to replace them with natural fibers. Recently, a hybrid of natural/synthetic fibers, specifically jute/glass composite, has been demonstrated for tribology applications [62]. As compared to pure jute fibers, hybrid jute glass composite shows a higher coefficient of friction, specific wear, and abrasive nature, and so it is considered as more suitable for friction pad application. However, it is reported in investigations by Suresha et al. [63] and Rezzoug et al. [64] that CF/epoxy composites have higher wear resistance than glass fiber/epoxy composites due to higher modulus, reduced coefficient of

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friction, and strength of CFs. Rezzoug et al. also demonstrated that the tribological property of CF/epoxy composite could be further improved to a higher extent by adding a small amount of metallic filler layer such as copper-stainless steel [64]. 6.2.2.2 Civil Engineering

Although civil engineering is mainly the structural application, there are various nonstructural aspects in civil engineering where synthetic fibers can also be used, such as rigid roadways, partitions, retaining and cladding walls, canal lining, and embankments. Since the beginning of the twentieth century, synthetic fibers have also been used in the application of raw materials for concrete [65]. These fibers are being utilized to enhance the shatter resistance, impact, abrasion, and control on cracking of concrete due to drying and plastic shrinkage along with mechanical strength [66]. Also, the fiber in mesh form prevents thawing and loss of moisture from concrete. The main synthetic fibers being used are metallic (steel), polymer (PP, olefins, and polyvinyl, etc.), glass, carbon, and nylon. However, it is reported that a single type of fiber reinforcement cannot provide optimum properties, so a combination of fibers should be optimized [67]. Waste fibers have been proven as nonstructural components in civil engineering [68]. Several industries produce huge waste fibers such as steel fibers (tire industry), polyethylene terephthalate (PET) fibers (plastic bottle industry), etc. The use of these fibers in concrete can help in increasing mechanical properties, decreasing cost, and solid waste management. There are several reports on the use of waste fiber composites [66, 68–70]. However, more work is needed in this direction. As concrete is brittle and not perfect, it may carry micro-cracks that are present before applying loads or can originate through plastic settlement, excess water, or shear or strain levied external manacles. Polymeric synthetic fibers can prevent micro-cracks propagation and protect them from further harsh environmental conditions such as corrosion [71]. Sivakumar [67] found that non-metallic synthetic fibers such as glass, polyester, and PP have more ability to bridge small micro-cracks as compared to steel fibers alone. Ahmed and Jia [72] have shown the application of hybrid fiber composite using short-length glass fiber and PP fibers in limiting micro-crack and increasing air permeability across the concrete. The results demonstrate that a mechanical property also increases with fiber content. Also, glass fiber incorporation improves the impermeability of concrete. Similarly, the synergistic effect of GF and PP was studied on recycled aggregated concrete performance and durability [73]. They reported that different fractions of fibers impart different synergistic property and the durability of composite concrete depends on the chemical bonding between cement and fibers, which occurs via the hydration process.

6.2.3

Electronic Sector

Composite polymers are one of the promising targets for the development of flexible electronics. Since the twentieth century, glass fiber/epoxy-based SFRCs have been used as structural substrates in printed circuit boards (PCBs). They support the integrated circuits, transistors, and resistors at all digital technologies. The components

6.2 Nonstructural Applications of SFRCs

on the glass fiberboard are connected electrically through conductive pathways (Cu or Al) via etching or printing on their surfaces. These composites were also utilized as an insulating material for high voltage energy cabin apparatuses, cables, and cable coated materials to transfer the electrical energy. With an advancement in deposition techniques for Micro and nanofibers structures, the composite nanofibers in electronic devices show great potential in meeting the most of increasing demands for higher integration density, faster operating speed, and lower power consumption due to their well-focused carrier transport channel. In this section, we will be focusing preliminarily on the electronics application of synthetic nanofibers composite. The composite structure of fibers has been demonstrated to enhance the functional properties of polymer fibers. The enhancement in electrical conductivity of composite fibers has been demonstrated in both the cases either prepared using direct co-deposition or by post-deposition treatment of fibers. 6.2.3.1 Light Emitting Diode (LED) Devices

Composite fibers have received considerable interest in the optical industry due to their controlled light scattering and reflecting ability. Control on the diameter of fibers and the blended ratio of composite material allows the linear correlation with its optical properties. In one of the earliest attempts in using composite fibers for LED applications, Madhugiri et al. [74] have demonstrated the modification of optoelectronics characteristics of poly{2-methoxy-5-(2′ -ethyl-hexyloxy)-1, 4-phenylenevinylene} (MEH-PPV) fibers by preparing the blended composite with Santa Barbara Amorphous-15 (SBA-15) (three layers stack of poly(ethylene oxide), poly(propylene oxide), and poly(ethylene oxide)). The composite fibers show the blue shift in the emission spectrum while excitation at the same wavelength as the MEH-PPV. The emission of composite fibers can be fine-tuned by introducing the various organic functional group at the SBA-15 side chain. The phenyl silane containing SBA-15 was blended with MEH-PPV, which results in a further blue shift in the emission spectrum. Moran-Mirabal et al. [75] demonstrated ruthenium(II) tris(bipyridine)/polyethylene oxide nanofibers prepared using electrospinning with dimension range from 150 nm to 5 μm. The fibers that were spun over the interdigitated electrodes have a gap of ∼500 nm. The composite nanofibers show light emission detectable with the naked eye at 4 and 3.2 V with a charged-coupled device (CCD) camera. The presented composite fiber allows integration with microfluidics application as a light source as well as a nanoscopic light emission source to excite multiple fluorescent tags. Yang et al. [76] have explained another example of standalone fiber as a LED device where ionic Transition Metal complex (iTMC)-based electroluminescent fibers were fabricated using co-electrospinning. The coaxial core–shell fiber structure fabricated using metal as core material and a composite of (Ru(bpy)3 )2+ ((PF6 )− )2 and poly(ethyl oxide) (PEO) as a shell structure act as an electroluminescent layer (Figure 6.4). Electroluminescence from the prepared OLED (Organic Light Emitting Diode) structure can be detected using a CCD camera at a voltage of 4.2 V and can be seen by naked eyes at 5.6 V in N2 environment. In a study, Vohra et al. [77] described the conjugated fibers obtained with a blend of poly(9,9-dioctyl fluorenyl-2,7-diyl)-alt-(1,4-benzothiadiazole) and PEO. The fibers

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Figure 6.4 Schematic structure of co-axially spun composite fibers with electroluminescence.

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ine

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Anode

V Cathode

are demonstrated to be applied in OLEDs with a brightness of 2300 cdm−2 at 6 V. The report also highlights the comparative importance of post-deposition treatment of blended fiber for filling the gap for improved performance. The annealing of composite fibers leads to structure modification, poly(9,9-dioctyl fluorenyl-2,7-diyl)alt-(1,4-benzothiadiazole) (F8BT)/PEO ration increasing by reducing PEO content, improved chemical resistance due to crystallization, and higher electroluminescence yield. 6.2.3.2 Field-Effect Transistors (FET)

The semiconductor fibers have gained a lot of interest due to their supercharge transport characteristics. Various metal oxides such as In2 O3 , SnO2 based composite nanofibers have been applied to field-effect device applications [78, 79]. In a similar example, Lin et al. [80] have fabricated the poly(3-hexylthiophene) P3HT/ graphene composite fibers as the nanoscale channel for organic FETs applications. P3HT/graphene was electrospun using chlorobenzene and deposited over ODTS (octadecyltrichlorosilane) treated dielectric layer. The 1D structure of fibers could limit the graphene aggregation and promote carrier transport to produce high carrier mobility. The motilities of composite nanofibers-based FET were found to be higher as 0.09 cm2 V−1 s−1 for pristine P3HT to 1.82 cm2 V−1 s−1 for 25.4% graphene loading with P3HT while maintaining the On/Off switching (as high as at least 104 ). Graphene is well known for its higher charge transport characteristics, but the carrier mobility in fibrous morphology was found to be greater than one magnitude order if compared to the thin composite film due to the one-dimensional charge confinement in fibers. 6.2.3.3 Sensors

In electrochemistry, the composite nanofiber plays a significant role due to its enhanced catalytic activity and attractive high surface area. Carbon nanofibers (CNF) have been researched extensively for electrochemical sensing applications. However, pure fibers lack sufficient sensing performance. To improve the sensing performance, various examples of composite fibers have been studied for superior electrochemical sensing. In one of the latest examples, Hu et al. [81] have prepared the SnO2 doped CNF using electrospinning method and applied

6.2 Nonstructural Applications of SFRCs

it to demonstrate the simultaneous detection of acetaminophen (APAP) and p-hydroxyacetophenone (p-HAP). The composite sensor was found to detect APAP in the linear range 0.50–700 μM with detection limit 0.086 μM and p-HAP in the linear range 0.20–50 μM with detection limit 0.033 μM. In another example, Balasubramanian et al. [82] have prepared the CNF-β-cyclodextrin (β-CD) composite using ultrasonic mixing. The CNF-β-CD-based sensor exhibits high stability, good selectivity with a dynamic range of 0.004–308 μM, and a detection limit of 1.8 nM. Wang et al. [83] have done extensive work on studying the composite nanofibers for electrochemical sensor application in immune-sensor as well as DNA sensor. In their recent work, they have developed an electrochemical immune-sensor using composite nanofiber based on MWCNT-PA6-PTH (Multiwall Carbon Nanotube doped Nylon-6 spun with PolyThionine) for sensitive detection of tumor suppressor Protein 53 with as low as 1 pg ml−1 . In another study, carboxylated MWCNTs doped polyamide (PA6) were spun with PPy to synthesize composite nanofibers. The composite 1D structure demonstrated tumor mutation P53 gene with a detection limit as low as 50 fM. Similarly, polythionine composite with MWCNT-PA6 was prepared using electrospinning and applied to detect KRAS gene mutation for colorectal cancer patients. In an extensive study, Bishop-Haynes and Gouma [84] described the use of conductive polymer PANI blended with carrier presenting polyvinyl pyrrolidone (PVP) hybrid structures for nitrogen dioxide detection at 25 ∘ C. Leucoemeraldine-based PANI is a suitable sensing material, while PVP act as a steric stabilizer for PANI and avoids agglomeration and microtubules formation. The present nanocomposite was electrospun on an alumina substrate. The gold contacts were made using a DC voltage power supply on electrospun nanofibers. The sensor was tested at 40% relative humidity (RH), where the minimum detection limit of the sensor is estimated at approximately 1 ppm for nitrogen dioxide. Sadek et al. [85] have developed a layered surface acoustic wave (SAW) sensor utilizing polyaniline embedded In2 O3 nanofiber composite for sensing different gases at room temperature. The SAW sensor was fabricated by drop-casting the nanocomposite onto a layered ZnO/64∘ YX LiNbO3 based SAW transducer. The nanocomposite was synthesized by chemical oxidation polymerization of aniline having finely In2 O3 . The detection limits of the sensor for nitrogen dioxide, carbon monoxide, and hydrogen were 510 ppb, 60 ppm, and 0.06%, respectively. The response times were 30, 24, and 30 seconds, and the recovery times were 65, 36, and 40 seconds for nitrogen dioxide, carbon monoxide, and hydrogen, respectively. Wearable sensor is one of the integrating parts of future intelligent textiles and requires the flexible sensor structure to collect the electronic information from the body. Composite fibers are one of the ideal platforms to integrate the flexible electronics on textile for sensing and monitoring the body signals. One of the latest examples in this area demonstrated by Gao et al. [86], where they fabricated the composite fibers of PEDOT:PSS/PVA/EG (PEDOT – poly(3,4-ethylenedioxythiophene), PSS – poly(styrene sulfonate), PVA – polyvinyl alcohol, EG – ethylene glycol) was using the wet-spinning method. The conductive fiber shows the stable resistance of 0.6 ± 0.2 MΩ under along with 0–20% elongation. Further, the concept is evidenced

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by knitting the fabric using composite fiber and demonstrated to sense the respiration and activities of body parts, such as fingers, neck, and elbow area. 6.2.3.4 EMI Shielding

EMI shielding is the application that deals with the reflection or absorption of electromagnetic radiations to shield a particular product against electromagnetic radiation penetration. Metal-based composites are mainly based on the reflection phenomenon, while carbon-based composites cause an absorption effect. Continuous CFs are being used in body frames of airplanes as conductive 1D filled to provide strength and regulate lightning strikes [87] and acoustic shock waves. Continuous CFs have good electrical conductivity and high strength. Due to high conductivity properties, their composite has found applications in EMI shielding. Recently, researchers are working toward the development of ultra-thin, flexible, and lightweight EMI shielding materials. Xing et al. [88] recently fabricated ultra-thin carbon-fabric/Ag/PU having an electromagnetic interference shielding effectiveness (EMI-SE) 102.9 dB and conductivity 11 986.8 S cm−1 at a sample thickness of 0.183 mm. It is demonstrated that these thin films can be rolled, bent, and folded easily and are flexible enough to regain their shape in unstressed form. The good electrical property of CF results from the electrons migrating and hopping between the graphite layers of CF. However, their cost is very high, but in the case of nonstructural applications, instead of continuous CFs, short-length fibers (chopped fibers) can be used. The use of these fibers not only cut the overall cost but also provide conductivity. However, in chopped carbon fibers, a problem of uniform dispersion is the main concern. Small CF, fabricated in the form of CF paper using a simple vacuum filtration method, overcomes the problem of dispersion and connectivity. Presently, a number of materials are being investigated in EMI-shielding, such as woven and non-woven fabrics [89, 90]. Duan et al. [91] prepared a CF fabric/polyurethane lightweight composite by hot compression method. This composite demonstrated a shielding effectiveness (SE) value of 73 dB (thickness 1.5 mm) and excellent tensile strength of 160 MPa. Also, SE/density/thickness is calculated as 383 dB cm2 g−1 , which is reported as the highest among other similar materials. Balaraju et al. [92] fabricated a carbon fiber reinforced polymer (CFRP) composite through electroless nickel coatings. This composite showed shielding effectiveness of 37 dB. Similarly, to extensively enhance EMI-SE of CF cloth, Lee et al. deposited copper on the surface of CF cloth [93]. Vapor-grown CFs are known to have higher conductivity than polymer-based CFs but comparable to carbon nanotubes due to their high structural crystallinity. As compared to making CFRP conducting by coating with copper [93] or nickel metal [94], vapor-grown carbon fibers can be used and can be further coated with conducting polymers such as PPy or PANI [95] to increase conductivity. Such practice leads to a high EMI SE total of 51 dB in X-band for 2 mm CF/PANI-dodecylbenzene sulfonic acid (DBSA)/divinylbenzene (DVB) sample [95]. However, the low conductivity of carbon fibers is not sufficient and sometimes requires a metallic mesh on the top surface to deploy such radiations. Stainless

6.2 Nonstructural Applications of SFRCs

steel fibers (SSF) have high conductivity, good strength, and sufficient magnetic permeability [96, 97]. In a study by Shajari et al. [98], SSF/PP/CNT-based composites have been utilized as EMI shielding material. They demonstrated that SSF/PP/CNT composites show SE/mm of 23.5 dB for the sample with 15.6 wt% (SSF + CNT) of loading, which is higher as compared to CF/CNT/PP composite (SE/mm = 16 dB) with filler loading (CF + CNT) of 30 wt%.

6.2.4

Medical Sector

6.2.4.1 Drug Delivery

Drug delivery is a sensitive area for use of synthetic fibers as it directly deals with human health. For drug delivery applications, only biocompatible, biodegradable polymer-based fibers can be used, such as polylactic acid (PLA), polycaprolactone (PCL), polylactic-co-glycolic acid (PLGA), PVA, etc. [99, 100]. The nature of polymeric fibers to be used for drug delivery is also determined by the route of administration and site of action of the drug. The degradation rate of the carrier polymer is one of the important characteristics to modulate the release kinetics of the drug [101]. The degradation rate of the specific polymer may depend on its characteristic properties such as melting point temperature, molecular weight, surface roughness, wettability, and crystallinity. The composite fibers allow the balance of properties to achieve the desired carrier for optimized drug release. Lv et al. [102] have demonstrated the targeted drug delivery of anticancer drug Daunorubicin with Fe3 O4 /PLA composite nanofibers. The drug attachment with composite fibers helps in facilitating the uptake of anticancer drug daunorubicin (DNR) into the targeted tumor cells as well as inhibiting the drug-resistant effect of drug-cultured cells. The mechanism of nanocomposite role in enhanced drug uptake efficiency is also discussed, where a negative charge of PLA carboxyl group allows the self-assembly of positively charged Daunorubicin. Also, Fe3 O4 nanoparticles possess a lipid shell layer of tetraheptylammonium which may help them inlay into the bilayer phospholipids membrane. In a similar example, Amna et al. [103] showed that the encapsulation of camptothecin (CPT) in Fe2 O3 /PLGA composite fiber improves the structural integrity by moderating the drug release and hence increases the anti-tumor activity of the drug. The composite nanofibers demonstrate the prolonged release of the drug for more than 96 hours as evaluated in in vitro C2C12 cells. The pristine PLGA did not exhibit noteworthy cytotoxicity, which was confirmed from cytotoxicity results. However, contrariwise, the CPT/Fe2 O3 fiber composite inhibited C2C12 cells significantly. In the promising field of precise transdermal drug therapy, Yun et al. [104] have studied the electro responsive transdermal drug release using PVA/PAA/MWCNT composite fibers. They demonstrated that the drug release kinetics could be controlled using electric voltage application that alters the ionization and ultimately swelling of the composite fibers. The precise control of transdermal drug delivery enhanced using composite fibers and found reproducible to be applied in future transdermal drug therapy.

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6.2.4.2 Protein/Gene Therapy

Composite fibers have been extensively demonstrated as a promising gene delivery carrier in tissue engineering and regenerative medicine. In one of the earliest works by Luu et al. [105], the scaffold of PLA-poly(glycolic acid) (PGA) composite fibers was prepared with plasmid and transfected to study the release kinetics in the MC2T3E1 osteoblastic cell line. The composite ratio of PLA-PGA optimized for desired characteristics of scaffold sustaining more than 20 hours, with more than 80% release of plasmid from the scaffold, and exhibit a tensile modulus of ∼35 MPa. In another example, Rujitanaroj et al. [106] fabricated composite fibers of polycaprolactone and ethyl ethylene phosphate (PCLEEP) and demonstrated their application for siRNA (small-interfering RNA) delivery for regenerative therapy. As tissue regeneration usually requires prolonged time, fiber-based delivery provides the long sustainable carrier for siRNA therapy. The composite fiber delivers the siRNA with enhanced sustained-release ∼89.3–97.2% by day 49 as compared to PCL release only 3%. Zhang et al. [107] have fabricated multifunctional composite fibers using PANI, blended poly(L-lactic acid-co-3-caprolactone) and silk fibroin for nerve growth. The fiber’s diameter, Young’s modulus, and conductivity are properties tunable by varying the PANI concentration in the composite. The composite fibers loaded with nerve growth factor (NGF) and studied for controlled release for nerve cell regeneration. The scaffold was demonstrated with mouse Schwann cells and Pheochromocytoma cells (PC12) show a high growth rate in an oriented manner and PC12 neurites outgrowth.

6.3 Conclusions and Future Challenges SFRCs are in great demand in nonstructural applications too. They are being used mainly in the energy sector for storage, conversion, and generation of energy. Batteries and supercapacitors require good conductivity and high surface area for energy storage, and SFRCs make it possible with ease of tailorable surface structure and encapsulation with conductive additives. Also, their lightweight and free-standing nature help in a step forward to flexible wearable devices. With the involvement of spinning techniques such as electrospinning, force spinning, and centrifugal spinning, in situ fiber composites can be prepared easily with moderate properties and surface enhancement in one step. Carbon fibers and conducting polymer-based fibers are the main reinforcement in applications where conductivity is the main concern, while other polymer fiber-based composites have been utilized in biomedical applications. Also, carbon fiber composites are highly thermally stable and have good thermal conductivity, so they find their use in thermal energy applications. However, other polymer fibers have low thermal stability and low fire-resistant properties, which make fire safety an important concern during their applications in offshore oil and gas platforms. Also, the nonstructural applications required good porosity, high surface area, and the use of functional additives. All these property enhancements reduce the mechanical strength of composite materials.

References

In arc furnaces, nonstructural SFRCs are being used, which are based on thermal insulation. However, these must provide sufficient mechanical strength for handling during repair and installment. Similarly, SFRCs have shown a high improvement in electromagnetic properties but show the same problem of decreased strength on tailoring these properties. Therefore, there is a strong desire for the development of fibers with improved structural characteristics. For this, scientific knowledge is required, and the factors affecting the fiber structure and properties need to be understood, such as fiber synthesis rate, physical and chemical processes involved. For a good fiber composite, it is also important to study the chemical nature of the surface so as to ensure the bonding and integrity of the composite to make better compatibility. Also, lack of biodegradability is one of its biggest challenges which resist its use in some medical and biomedical applications. Electrospun-based composite nanofibers have paved the way to use them in applications such as drug delivery due to their ability to make fibers from biodegradable synthetic and natural polymers, such as PLGA, poly (L-lactic acid) (PLLA), PCL, lignin, etc. However, there is a strong need to combine the properties of natural and synthetic polymers to obtain optimum performance in different applications.

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7 Structural Evolution, Mechanical Features, and Future Possibilities of Fiber, Textile, and Nano-cementitious Materials Prashant Rawat 1 , Sai Liu 2 , and Deju Zhu 3 1 Indian Institute of Technology Madras, Department of Aerospace Engineering, Tamil Nadu, Chennai 600036, India 2 Shandong University of Science and Technology, College of Civil Engineering and Architecture, Qingdao 266590, China 3 Hunan University, College of Civil Engineering, Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, Changsha 410082, China

7.1

History of Fiber and Textile Reinforced Concrete

The principal inventor of reinforced concrete Joseph Monier received his first patent on reinforced concrete in 1867. His design of metal wire/rod reinforced concrete gained significant attention. Later, a patent for a modified design for columns and girders (reinforced with iron rods in a grid pattern) was granted to Joseph Monier in 1877 [1, 2]. Finally, the uniform mixing of iron fibers in the cement matrix was attained and patented by H. Alfsen in 1918. This French patent reported that uniformly distributed small iron fibers (with rough surfaces) could improve the tensile strength in concrete. In general, the development phase of reinforced concrete can be divided into two groups. First, before the 1900s early development stage (where several non-scientific patents were registered) and second, after the 1900s when the focus of investigators worked on developing high strength concrete with enhanced mechanical properties. A brief history with major milestones in the development of fiber/textiles concrete is shown in Figure 7.1. The breakthrough developments on high-performance fibers or textile concrete started after the 1960s [5–7], although it is not easy to predict the first application of textile reinforced concrete (TRC). The use of Cem-FIL glass fiber with the combination of cement matrix was done by an English glass company in 1966 [8]. It is also predicted that possibly in 1982, the first patent (Patent no: DD 210102) on textile-reinforced material was granted for transportation safety. Later, more patents (Patent no: DD 253,442 and DD 275,008) were registered for meshed metallic reinforcements [9]. Alternatively, the development in manufacturing technologies resulted in the fabrication of high-quality fiber-based polymeric textiles (made of AR-glass, carbon, etc.) [10]. These reinforcement materials were used in several shapes and designs, for example, rods, plates, bars, ropes, and textiles. Initial Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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2013: Carbon fiber bundle based reinforced concrete materials [US8367569B2]

Initial creation of textilereinforced concrete (TRC) began in the 1980s [First Patent was granted in 1982]

2015: Roof structure consisting of four large precast TRC shells (photo: bauko 2, RWTH Aachen University) [Thin-walled shell structures made of textile-reinforced concrete Part I: Structural design and construction]

1997: Fabric reinforced concrete walls patent [US5649398A]

1996: the first Dresden textile reinforced concrete boats in 1996

1966: Use of continuous glass fiber with cement matrix

In 1911, G.M. Graham (US) suggested the use of steel fibers (short cut steel wires) in addition to conventional reinforcement to increase the strength and stability of reinforced concrete

1992: Patent registered for wrapping the concretes columns with composite reinforcement layers [US5218810A]

Use of sheet U.S. Patent Office, 1969, 1970, 1972 (smooth straight steel fibers produced by cutting wire or sheet metal became more widley available)

Concept of adding “annuli” fibers by H. Etheridge was proposed in 1933

1953 et al. [4]

J.C.Seailles in France suggested to use metal scraps and chips in concretes to improve the strength French patent in 1918 for uniformly mixed iron fibers in cement matrix [3]

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Figure 7.1 materials.

Breakthrough events during the evolution of fiber/textile cement-based

engineering approaches majorly investigated the mechanical performance of short fiber embedded in Portland cement composites. The fundamental properties like strength and toughness were investigated with various types of fiber, geometry, aspect ratio, and diameter to understand the failure mechanisms in fiber-reinforced composites (FRCs) [11]. In the late 1900s, several projects concluded that knitted reinforced fabrics could provide excellent strengths in different parts of a building, especially thin-walled structures [9, 12]. The primary studies related to continuous woven reinforced concrete were limited in European countries (Germany, England) [8, 13, 14], Israel [15, 16], and the United States [17, 18]. However, over time, application possibilities in building industries gained significant recognition, and the research on TRC started in China, Brazil, and other countries as well. In recent days, research communities are focused on developing fabrication methods for textile reinforced composites with minimum defects. In this series, the application of advanced nanoparticles such as nano-silica [19], graphene [20, 21], and carbon nanotubes (CNTs) [22, 23] is increasing day by day. The fundamental feature of using these nanoparticles is related to the reduction of nanoscale voids (or deformities) and improving the interfacial strength between the textile reinforcement and/or

7.2 Components of Cementitious Materials

cementitious matrix. As a result, the flexural, tensile, bonding performance of TRCs improves, and the possibilities to use these materials as building components increase. The fabrication parameters, constituents, and testing parameters have changed the entire scenario of building materials. Therefore, a critical analysis of constituents is required to identify the progress of TRCs as advanced materials in construction engineering. This comparative study is also helpful in identifying future possibilities.

7.2

Components of Cementitious Materials

Cementitious materials can be divided in three categories (i) cement paste (cement + water), (ii) mortar (cement paste + sand), and (iii) concrete (mortar + stone). Reinforced cement concrete (RCC) is a combination of aggregates (gravel, small-sized stones), fine sand, cement, water, and some other materials. The aggregated particles are known as reinforcement, and cement binds all components together; it is known as the matrix. The FRCs are slightly different from RCC; as in FRC, the reinforcement materials are fibrous (with short or long lengths), which provides strength to the cementitious component. The short fibers can be distributed evenly or randomly in the cement matrix containing fine sand, water, and other constituents. Similarly, the continuous textile-based cement composites (TRC) have woven or textile as the main load-bearing constituent. Therefore, various reinforcements with the cement-based matrix are two major constituents of reinforced concrete or mortars. Figure 7.2 represents the general overview of different constituents of reinforced cement-based composites.

7.2.1

Matrix Materials

Cement is a prime binder material. Currently, the use of Portland cement is widespread at the commercial level. The manufacturing of Portland cement is done

Cement, water, fly ash, silica fume, ground slag, clay, etc., admixtures (superplasticizers, accelerators retarders, air passing agents), viscosity agents

Conventional iron/steel rebars and/or FRP tendons made of carbon, glass and aramid fibers

Other materials: recycled waste, umwanted materials, organics, voids or micropores salts etc.

Matrix

Reinforcement

Aggregates: coarse (gravel), fine or normal or sea sand

Reinforced cement-based composites

Figure 7.2

Components of reinforced cement-based materials.

Discontinuous fibers: Carbon, steel, glass, basalt fibers and/or Microscale nanmaterials such as, carbon nanotubes, graphene etc. nanoparticles

Continuous: long unidirectional fiber sheet, woven/textile materials (AR-glass, carbon, basalt etc.)

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Cement powder

(a)

Ettringite

(b) Hydration product

Portlandite (c)

Figure 7.3

Hydration product (d)

(a–d) Cement hydration stages. Source: Paul et al. [24].

by fusing calcium-bearing materials with aluminum-bearing materials. As per ASTM standard C-150, depending upon the properties, and features eight types of Portland cement are available. When water is mixed with cement, “Hydration products” are produced. The major hydration products are Calcium silicate hydrate (C–S–H), Calcium hydroxide or Portlandite (Ca(OH)2 ), AFm (also known as monosulfate or C3 A⋅CaSO4 ⋅12H2 O), and AFt (also known as ettringite or [Ca3 Al(OH)6 ⋅12H2 O]2 ⋅2H2 O]). This hydration reaction is shown in Figure 7.3a–d. Pozzolan (or superplasticizers) is secondary binder material, which reacts with the chemicals released after cement and water react. The primary function of pozzolan materials is to fill the capillary channels present in the cement paste. As a result, a more densify structure with chemical resistive properties is attained. Fly ash is a pozzolan material, which reduces the amount of water used, improves the setting time. Silica fumes have almost 100 times smaller particle size than that of Portland particle size is another useful and highly reactive pozzolan material. The function of silica fumes is to improve particle-packing, and ultimately it improves the density of concrete. Additionally, it helps in improving the compression strength and, most importantly, improving the bonding between aggregates, reinforcements and hydration products. Aggregates are granular materials, which are mixed to reduce the cost of the cementitious materials. River stone, crushed stones, sand, gravel, etc. are the example of aggregates. Aggregates occupy approximately 75% of concrete’s volume and improve the strength, density, durability, and thermal resistive properties in concrete. In the present time, the use of aggregates from industrial waste has also increased [25, 26].

7.2 Components of Cementitious Materials

7.2.2

Reinforcements

Reinforcing agents make a strong bond with the cement matrix and provide resistance to crack formation and propagation under loading situations. There are various types of reinforcement materials available, from well-organized meshed textiles to short linear needle-like filaments. The mixing method of these reinforcements varies depending upon their shape and form. However, the distribution of reinforcements in the cement matrix is one of the major challenges. Uniformly distributed reinforcements are capable of distributing applied stresses throughout the members. As a result, it improves the mechanical performance of cementitious composites. Depending upon the size of reinforcements, two major categories are in existence which can be classified as macroscopic and microscopic fillers. Generally, the structures (or geometries) which can be visualized by naked eyes come in the type of macroscopic reinforcements. In contrast, the microscopic fillings appear like powder forms from eyes, although they carry a complicated and organized molecular structure. The typical examples of macroscopic and microscopic fillers are steel fibers, short carbon, glass, basalt fibers, textiles and CNTs, and graphene nanosheets, respectively. In the 1960s, when proper investigation on fiber-reinforced cement structures was initiated, a discussion on reinforcement importance started in the research community [27]. This discussion is continuing for textile reinforcements and hybrid fillers in the cement-based matrix.

7.2.3

Short Discontinuous Fibers

When short fibers are embedded in the cement matrix, there are multiple geometrical (or structural) features related to the shape and size of fibers. The profile, shape, aspect ratio, and fiber alignment (in the matrix) are the most critical parameters to consider avoiding any unexpected failure. With the development in time, multiple forms of short metallic fibers are available from smooth needle-like structure to end modified (cone-shaped, hooked, or spaded) or profile (twisted, crimped) modified fillers. Figure 7.4a represents different types of metallic fillers that are commonly used in cementitious materials. When fibers are embedded in cement paste or mortars as reinforcement, their mechanical response is directly dependent on the applied load. However, three different phenomena, strengthening, toughening, and crack hindrance, may take place. Under tensile, flexural, or bending load at the point of the stress-concentrated region, a microcrack generates in the cement matrix. If proper reinforcement is present in the system, it distributes the stress, resists the crack growth, and provides strength to the component. Nevertheless, a continuous rise in implemented load fractures the tested samples. After the interfacial bond between the fiber and cement matrix is broken, the sample is failed, and short fiber is pulled out at one end while another end is attached to the matrix. Therefore, it is clear that well-oriented (aligned) short or long fibers offer better mechanical loading characteristics as compared to randomly aligned fibers, as shown in Figure 7.5a,b.

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Smooth straight wire shaped fiber Flat foil shaped

(b)

AR-glass yarn

End-modified coned shape Warp Hooked shape

Crimped shape

(a)

Weft

5 mm

Mechanically deformed (twisted) Basalt textile

(c)

Figure 7.4 (a) Representation of various shapes in metallic fibers, (b) single yarn made of AR-glass filaments, and (c) basalt textile which is woven in specific arrangements using basalt yarns. Sources: Based on Liu et al. [28] and Du et al. [29]. Micro-crack growth Macro-crack growth

 C

fct

B Bridging and branching

A

w

FRC

D D

Concrete

E

E

(a)

Randomly oriented short fibers

Elongation, l

(c) Macro-crack

E

D

C

B

A

w

Traction free

(b)

Aligned short fibers

MacroMicrocrack Bridging and growth cracking branching Aggregate bridging

Bridging stress

(d)

Figure 7.5 Fracture phenomena under tensile loading in cement matrix composites reinforced with (a) randomly, (b) aligned short fibers, (c) crack opening behavior in normal concrete, and (d) crack behavior in fiber-reinforced concrete. Sources: Based on Paul et al. [24] and Dopko [30].

Depending upon the number of fibers, the strain capacity of the sample is improved; it is a result of the toughening effect, which occurs due to the presence of reinforcements. The estimation of the increased amount of energy can be measured by the area under the load-deformation (or stress–strain curve). Once the matrix is completely failed, the load is taken by the short fibers (oriented in the direction of loading). These fibers resist the applied load and are failed by shearing phenomena.

7.2 Components of Cementitious Materials

Figure 7.5c,d differentiates the crack opening behavior in concrete without and with fiber reinforcements, respectively. It is visible that the presence of short fibers in the system improves load capacity (see Figure 7.5c) with increased elongation. Moreover, the attached fibers cause a bridging effect even after the complete failure of the cement matrix (Figure 7.5d). Apart from intrinsic fiber properties (such as fiber strength, elasticity, and ductility) and orientation, the mechanical performance of short or long fiber reinforced cement-based composites is highly dependent on the interfacial bonding between fibers and cement matrix. Therefore, the most suitable fiber as reinforcement has to be undergone multiple criteria, which may affect the interfacial behavior in short fiber reinforced concrete (SFRC). The optimum fiber volume fraction, condition of reinforcement (i.e. single or multiple fibers), fiber shape, form (separate filaments or fiber bundles), and surface (smooth, rough, or coated) are the other parameters, which provide improvement in the mechanical behavior of SFRC.

7.2.4

Textiles/Woven

Textiles are made of carbon, glass, basalt, etc., and filaments that form continuous yarn are the basic unit for textile (see Figure 7.4b,c). Furthermore, yarns are woven’s basic elements in particular patterns (2D and 3D) depending upon requirements. The continuous fiber-based cement-based composites were developed between the 1980s and 1990s [9]. Interestingly, these investigations were highly inspired by the fabrication techniques used in polymeric composites laminates such as extrusion, pultrusion, filament windings, etc. [17]. To prepare thin sheet concrete, woven meshed structures were used [31, 32]. Studies performed in the past 20 years proved that textile reinforced cement composites are suitable for masonry structures as well as pre-fabricated structural elements [33, 34]. When open meshed configurations or meshed woven are used as reinforcements, their mechanical performance is positively affected by the woven patterns and strength properties. Textiles are formed by the fiber roving method, and therefore, fibers are arranged in two or more directions which show “mechanical interlocking.” Figure 7.6a–e represents several roving patterns made of different materials for TRC. Liu et al. [28] compared the pullout behavior of single yarn and textile in mortar under various strain rates. This comparative analysis proved that the mechanical interlocking has an advantage (for providing anchorage effect) over single yarn reinforcement (Figure 7.4b) to provide better and stable resistance to the applied load. Notably, plain 2D textiles are more suitable for tensile, flexural and cyclic loading conditions. Spacer fabrics or 3D textiles (Figure 7.6f) are used to further improve the mechanical performance of TRC composites, especially for impact loadings. The uneven distribution of yarns or the presence of waviness must be resolved during the fabrication [35, 36]. Additionally, uneven filament gaps may create stress-concentrated zones and can be responsible for unexpected failure. These drawbacks can be significantly reduced by the mechanical stretching of the textile during the fabrication process [37]. To minimize the defects at the textile surface,

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(a)

(b)

(c) Warp knitting yarns 90° yarns

Spacer yarns Z

0° yarns

X Y Spacer yarns II

Spacer yarns I

(d)

(e)

(f)

Figure 7.6 Textile reinforcement materials (a) carbon fiber woven, (b) glass fiber woven, (c) basalt fiber woven, (d) polyphenylenebenzobisoxazole (PBO) fiber woven, (e) steel fiber textile. Source: Koutas et al. [12], and (f) 3D spacer yarn used in textile cement-based composites.

the resin coating is preferred before using it as reinforcement. It improves the interfacial bonding between the cement matrix and textile yarn, resulting in better stress-distribution properties [38]. Textile volume fraction (TVF) is another parameter, which significantly affects the mechanical performance of textile composites [39, 40]. This factor improves the stress-distribution capacity and number of anchorage (yarn junction points) [28], which significantly improves the mechanical resistance of TRCs. Figure 7.7 illustrates the concept of textile pre-tensioning for multi-layered cement composites, which is used at a commercial level to enhance the quality of TRCs [41]. Therefore, similar to short-fiber reinforcements, multiple modifications (during the fabrication) are required to take care to maximize the mechanical features of TRC. Textile pre-stressing [41], increasing the number of textile layers, surface coating, and hybrid mixing (i.e. the embedding of short fibers in the matrix) are the most common methods opted for enhancing mechanical properties. The fracture modes in textile cement-based composites follow a step-by-step failure which can be seen on load curves as well [42]. This series of failures in TRCs depends on the presence of microlevel flaws in brittle solids (like cement matrix) and at the interface region of matrix and reinforcement (see Figure 7.8a). Moreover, microscale defects present in the filaments of textile yarns [44] are also responsible for failure due to stress-concentration zones. Figure 7.8b highlights three different failure stages under normal loading condition (I) initially, the loading performance of TRC (tensile, flexural, pullout, and impact) shows an elastic elongation until the cracking of cement matrix, (II) once first crack [39] is

7.2 Components of Cementitious Materials Sliding end with rollers to avoid frictional force

Fixed end with cylinders for textiles anchorage

Textile alignment in metallic mold

(i)

(iv)

(iii)

(a) (ii)

Basalt textile with steel bars to provide uniform gap between two textile layers

Pre-tensioning

(b)

Figure 7.7 Schematic illustration of the (a) pre-tensioning setup displaying (i) the end with rollers which can slide to minimize the friction during (ii) pre-tensioning of the textiles, (iii) tightened textile in the metallic mold, and (iv) fixed end of the pre-tensioning setup; (b) stack-up of metallic bars to control the uniformity in spacings between textile layers. Source: Liu et al. [41].

Voids (flaws) in cement matrix

Textile yarn

(a)

Non-uniform interfacial region between cement matrix and textile reinforcement Basalt textile reinforcement Zone I Uncracked concrete

Loading direction

Zone II

(I)

(II) Textile failure

Cement cracking Stress (MPa)

Matrix cracking

Multiple cracking

Zone III Postcracking

Textile Single crack Strain %

(b)

(III)

(c)

Figure 7.8 (a, b) Schematic representation of flaws in the cement matrix and at the interfacial region which lead to failure in TRCs (I) TRC under tensile loading, (II) failure (matrix cracking) of cement matrix, and (III) ultimate failure of TRCs with failure in textile reinforcement, and (c) typical stress–strain curve of a TRC composite under tensile loading showing there distinguished failure zones. Source: Tysmans et al. [43].

generated, considerable fluctuations are observed on load curves which indicate the matrix failure at several points, and (III) after the cement matrix is completely failed, load is taken by textiles and when failure of textile occurs, a sudden load drop is observed. A typical stress–strain curve of TRC under tensile loading is shown in Figure 7.8c, which indicates three diverse stages of failure with three zones on the load curve.

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7.2.5

Advanced Nanoparticles

Architecture designs with overhang (or expanded) structures, complicated shapes, and structures exposed to extreme environmental conditions are highly susceptible to catastrophic failure [45]. A catastrophic failure (complete collapse of the component) is caused when small-sized micro-cracks (which are rarely visible) adjoin to create matrix failure. Developments in nanotechnologies have impacted researchers working in almost every sector. Therefore, the use of nanofillers nano-Fe2 O3 , graphene oxide (GO), nano-TiO2 , CNTs, and nano-SiO2 have gained explicit attention to improve the cement matrix bridging capacity [46–48]. As a result, the durability of the concrete structure can be enhanced at the microscopic level, even for extreme environmental conditions [49]. However, as per the authors’ best knowledge, Colston et al. [50] performed the first studies on cement-based materials modified with nanoparticles (Spheriglass, zeolites, magnetic, and protein). This study proved that the use of nanoparticles in cementitious materials improves the microstructure, and porosity as well. Generally, the particle size of nanomaterials is considered in the range of 1–100 nm. The application of nanoparticles in cement paste or composite is similar to polymeric composites, electronic devices, and biomedical equipment. Meanwhile, it improves the material’s performance as compared to the reference structure. Due to the higher surface-area-to-volume ratio, nanoparticles offer incomparable bonding at the microscopic scale; as a result, better bonding performance is achieved [51–53]. Notably, the interfacial region of nanoparticles is a critical section, which is majorly affected by the chemical nature (or bonding) of two adjacent constituents. In the absence of an appropriate dispersion state of the nanoparticles, the aggregation takes place, which causes a negative effect on the resultant properties of composites [54]. Especially in the case of mixing nanoparticles in cement composites, the amount of water used is increased to attain proper wetting [52]. Nevertheless, the addition of nanoparticles in cement-based materials has a significant influence on microstructural, physical, and mechanical properties [24]. Factors such as pore size and microscopic structure, shrinkage of the cement matrix, and water absorption capacity are critical to consider, as nanoparticle reinforcements affect structures at the microstructure level. As discussed, calcium hydroxide in crystal form (Ca(OH)2 ) and calcium silicate hydrate in the amorphous form (C–S–H) are the main products of cement clinker and water. In total, (Ca(OH)2 ) and (C–S–H) contain more than 60% of hydration products. Moreover, the setting and hydration state of Portland cement is primarily controlled by the physical properties of calcium silicate hydrate (C–S–H) [24, 49]. The mixing of nanoparticles (such as nano-TiO2 and nano-SiO2 ) in cementitious materials causes early hydration and enhances the production of C–S–H gel [55, 56]. As a result, the cement matrix is densified, and it ultimately improves the aggregates/cement interfacial transition zone (ITZ). Recent studies suggested that with the use of very fine additives, the void content in cementitious materials is reduced [57]. This method is also helpful for reducing the amount of water due to the reduced water capillarity effect, as shown in

7.3 Mechanical Performance of Reinforced Concrete Water

C-S-H phases

Aggregate

Ettringite

Water

Aggregate

Ettringite

C-S-H phases

Hydration

Cement

Cement

Hydration

Capillary pore

(a)

Silica fume/fly ash

Portlandite

(b)

Traditional concrete

Portlandite

HPC concrete Nano materials

Aggregate

C-S-H phases Ettringite

Nano-particles/fibers

(c)

Nanoengineered UHPC concrete

Conventional concrete (2000)

Portlandite

(d)

Durability

Cement

Sand Cement

Performance

Admixture Aggregate

Hydration

Strength

Water

High Nanoperformance engineered concrete (2010) concrete (2020)

Possibilities of producing green composites

Figure 7.9 (a–c) Pore filling effects with the use of fine to nanoscale components (such as fly ash, silica fumes, and nano-particles or nano-fibers) and (d) development of high strength green concrete with nanoengineering technology. Source: Singh et al. [58].

Figure 7.9a–c [58]. Notably, the reaction mechanism with different materials such as CNTs, nano-silica particles may vary significantly. These chemical reaction mechanisms have a direct influence on hydration, compactness, and strength properties of cementitious composites. Therefore, it is critical and one of the essential features to consider before the selection of micro-scale constituents. Nevertheless, most of the available nanomaterials have a positive effect on the mechanical characteristics of cement materials [59–61]. Figure 7.9d shows the increasing application of green composites embedded with nanomaterials.

7.3

Mechanical Performance of Reinforced Concrete

It has been shown that wide-ranging reinforcing materials result in different mechanical properties by providing micro-to-macroscopic level alterations. Each reinforcement can be mixed in the cementitious matrix with and without modifications. For short fibers, improvements are mainly associated with shape and size; for textile-embedded concrete, modifications are related to pre-tensioning, coating. In contrast, nanoscale reinforcements can be used in functionalized or oxidized forms for better mechanical properties. Moreover, the use of a single or hybrid type of reinforcement is another vital aspect to consider, which drastically modifies the mechanical performance. Most cementitious materials are used under compression loading, and the compressive strength of these materials is relatively much higher than the tensile strength. Other common application of cementitious concrete deals with bending, flexural, and creep loading situations. Based on the failure mechanisms, each reinforcement has advantages as well as some limitations depending upon load type. For example, discontinuous SFRC does not offer significant elongation under

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tensile loading as compared to textile reinforcements. However, the deformations offered by SF reinforcements are sufficient under flexural or bending loading. At the same time, nanoparticle reinforcements reduce the void contents. Therefore, the stress transfer is higher under any type of loading. However, improper mixing causes agglomerations, which reduces mechanical strength. In this section, a comprehensive investigation of previous studies is summarized with different types of reinforcements. This comparative analysis will help in arbitrating the improvements made with time. Also, future predictions can be made based on comparative studies.

7.3.1

Mechanical Behavior of SF Reinforced Concrete

Initially, steel fibers were embedded in cementitious materials, and their performance was enhanced using high elastic synthetic fibers for reinforcements. Interestingly, it has been proved that the use of steel fibers in high-performance concrete improves compressive strength. The use of 2% steel fibers (as reinforcement) is a critical limit for best mechanical properties [62]. Above this reinforcement value, the mechanical properties are likely to reduce because of higher porosity issues. Additionally, various studies have suggested that the aspect ratio [63] of fibers has a remarkable effect on mechanical properties as compared to other fiber factors. Nevertheless, a better anchorage effect is offered by hooked shape steel fibers under tensile loading [64]. The improvement in tensile and flexural strength by adding steel SF (up to the critical limit) is relatively greater than that of enhancement in compressive strength. The modulus of elasticity and toughness of concrete is remarkably improved with hybrid reinforcement (i.e. the combination of steel and synthetic fibers) than that of discrete use of fibers. In addition, hybrid reinforcement has a positive effect on the compactness of concrete, which shows better shrinkage resistance and proper curing with the use of combined use of metallic and synthetic fibers together [65, 66]. Long-term loading or creep behavior of cement-based materials showed that the aspect ratio of fibers is the most critical factor behind better creep resistance [67]. Therefore, the need and importance of long and continuous fiber are observable. Additionally, a high aspect ratio (or continuous fibers) can provide much better properties in cementitious materials.

7.3.2

Mechanical Behavior of Textile Reinforced Concrete

Textile composites are a relatively new class of materials and still in the developing phase. Textile embedded concrete offers a balanced stress transfer mechanism under mechanical loadings as compared to non-weaved (or continuous yarns) reinforcements [28]. The geometry of textiles can easily control the anchorage behavior in cementitious materials with textile reinforcement [16]. Most importantly, the use of 3D-spacer fabrics allows the fabrication of thin, highly compressible composites. However, it has proved their significance over SF reinforced composites in terms of higher ductile behavior under tensile loading. Comparative studies have shown that the strain rate of load implementation influences the stiffness of textile reinforced mortars (TRM) composites. Meanwhile, the textile-embedded composites offer toughness variations under load implementation; it is a result of uniformly distributed stress [68, 69].

7.3 Mechanical Performance of Reinforced Concrete

Therefore, TRM reduces any catastrophic failures in thin concrete. It is also helpful to design complicated shapes with better mechanical features. As already discussed, textile reinforcements offer a unique failure (or ductile) phenomenon when subjected to tensile, pullout, or flexural loadings. Therefore, the tensile, bending, and flexural loading of TRCs result in a much stable failure phenomenon; it is better than that of SF reinforced concrete. Another advantage is the availability of various woven patterns in fabrics, which directly impact on strength features by providing better anchorage bonding [12]. Undoubtedly, the comparative results suggested that the textile reinforcement is better from the perspective of practical application as thin laminates or roofs [70]. These structures are also highly suitable for extreme environmental and unfavorable situations. Moreover, as compared to conventional analysis, the calculation of mechanical behavior of TRCs at higher strain rates, temperatures, and the acidic medium is enormously going on in the present time [39]. The major drawback of textile concrete is related to the microstructural features as non-uniform interfacial surfaces, improper impregnation, void content in matrix, and filament gaps between the textile yarns [19]. It may result in yarn slippage or partial rapture of external filaments (at the interface), which is catastrophic (sudden load drop) in nature. Debonding is another common failure caused by stress concentrated regions (especially at bending or twisting sections) which propagate and capable of causing ultimate failure in the TRM component. Similar to SF reinforcement, the increase in TVF improves the mechanical performance up to a critical value. Above this critical volume fraction, improper impregnation causes a reduction in performance [41]. Nevertheless, methods such as pre-tensioning, coating, and mixing of short fiber in the cement matrix have a positive influence, which has already discussed.

7.3.3

Mechanical Behavior of Nanoparticles Reinforced Concrete

The major purpose of nanoparticles can be subdivided as a filler agent that reduces the growth of microsize pores, densifies the matrix, and enhances the mechanical feature. From the perspective of an increase in mechanical strength, several breakthrough investigations have been performed in the past 10 years. Among them, most studies have focused on investigating the enhancement in mechanical properties by embedding different nanoparticles (see Figure 7.10) in cement paste. As a result, the maximum improvements in cement pastes and mortars for tensile strength are 102% (with nano-clay), 50% (with CNTs), for flexural strength 41.3% (with GO), 40% (with CNTs) and for compressive strengths 16.4% (with GO), 26% (with nano-Fe2 O3 ), 20% (with SiO2 ), 33% (with nano-TiO2 ), 87% (with nano-clay), 16% (with CNTs), and 26% (with zeolite) [72–79]. The influence of nanoparticle mixing in the cement-based composite’s microstructure is positively affected by the chemical interactions between the constituents. Therefore, the product strength varies with the type of nanoparticle. As a result, the studies related to the mechanical performance of cementitious materials embedded with nanoparticles are very complex. Moreover, the mixing of nanoparticles influences the curing behavior, amount of water used, shrinkage phenomenon, and porosity of cement composite. These all factors need to analyze carefully to define

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Nano-Fe2O3 and Nano-SiO2

Graphene oxide (GO)

Nano-Al2O3 and Nano-TiO2

Zeolites Nanomaterials in cement matrix Nano-fly ash

Nano-clays

Carbon based nanofibers

Carbon nanotubes

Figure 7.10 Advanced nanoparticles used in cement-based composites for improved mechanical performance Based on [24, 71].

IRC 1.2kV 2.5mm ×50.0k SE(M) 6/4/2004

(a)

1.00 m

IRC 1.2kV 3.7mm ×80.0k SE(M) 5/20/2008

500 nm

(b)

Figure 7.11 (a) Crack bridging by single-wall carbon nanotube bundle and (b) pullout of SWCNTs after fracture at ordinary Portland cement surface. Source: Raki et al. [80].

to strengthening mechanism. Usually, it is believed that the mixing of nanoparticles in the cement matrix improves the bridging effect (or bonding strength). This increased bond strength results in higher mechanical properties. The bridging effect and pullout (of CNT) are shown in Figure 7.11a,b. Figure 7.11 proves the importance of nanoscale reinforcement in resisting microcracks, which ultimately improves the first failure strength in cementitious materials.

7.4

Outlook and Future of Reinforced Concrete

Cementitious materials have already proved themselves as the backbone of building industries. However, their journey as thin light-weighted, and ultra-strong materials has just started. Research studies on high-performance fiber-reinforced cement-based materials have explored almost all features related to its use as an

References

advanced building component. The studies on textile-reinforced concrete started two-to-three decades ago and still in the developping research phase. Therefore, the implementation of TRC as a common construction material has not been done yet. Remarkably, the performance of TRC as an alternative material for extreme environmental conditions has astonished the research community. It has proved an effective alternative to reinforced concrete in rusting, corrosion, or highly reactive environments. The major drawbacks of TRC materials are related to interfacial behavior between the cement matrix and textile reinforcement. There are approaches that attempt to minimize or resolve the limitations of TRC composites. The addition of advanced nanomaterials (with extraordinary strength) in cement mortar may be the most suitable option. However, only a few studies have reported the characteristics of cement mortars with nanomaterials. Whereas, sufficient researches are available with cement paste which has already proved that mixing of nanoparticles significantly alters the microstructural structure and enhances the mechanical performance. Therefore, in the present time research community seems more focused on maximizing the performance of cementitious materials by modifying the structure at nano-to-macro scale. These types of cement-based materials can show high deformation capacity with reduced brittleness and can be very useful in extreme environmental situations. From the perspective of durability, these composites are chemically nonactive. Another challenge is associated with the availability of nanomaterials (such as CNTs and GO) in colossal amounts and unattainability of standard mixing methods. However, in the past few years, some advanced synthesis methods have been proven that economic mass production of nanoparticles (such as thermal catalytic chemical vapor deposition, arc-discharge method) is possible. Similarly, mixing techniques such as sonication, the addition of supporting agents has shown that uniform dispersion of nanomaterials can be achieved. These techniques are in the developping stage and can be developed to implement at a commercial scale. At present time, several challenges yet to be solved, but the research in this area is on the right path and committed to providing high-quality building materials for normal-to-extreme service conditions.

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39 Liu, S. et al. (2019). Low velocity impact behavior of AR-glass textile reinforced mortar under varying range of loading and temperatures. Construction and Building Materials 228: 116773. 40 Liu, S. et al. (2018). Impact response of basalt textile reinforced concrete subjected to different velocities and temperatures. Construction and Building Materials 175: 381–391. 41 Liu, S. et al. (2020). Experimental study and analytical modeling on tensile performance of basalt textile reinforced concrete. Construction and Building Materials 267: 120972. 42 Li, H. et al. (2020). Flexural performance of basalt textile-reinforced concrete with pretension and short fibers. Journal of Materials in Civil Engineering 32 (3): 04020004. 43 Tysmans, T. et al. (2009). Structural analysis of small span textile reinforced concrete shells with double curvature. Composites Science and Technology 69 (11–12): 1790–1796. 44 Xu, X. et al. (2019). Tensile mechanical properties of basalt fiber reinforced polymer tendons at low to intermediate strain rates. Composites Part B: Engineering 177: 107442. 45 De Larrard, F. (1999). Concrete Mixture Proportioning: A Scientific Approach. CRC Press. 46 Qing, Y. et al. (2007). Influence of nano-SiO2 addition on properties of hardened cement paste as compared with silica fume. Construction and Building Materials 21 (3): 539–545. 47 Senff, L. et al. (2013). Formulation of mortars with nano-SiO2 and nano-TiO2 for degradation of pollutants in buildings. Composites Part B: Engineering 44 (1): 40–47. 48 Oltulu, M. and Sahin, ¸ R. (2013). Effect of nano-SiO2 , nano-Al2 O3 and nano-Fe2 O3 powders on compressive strengths and capillary water absorption of cement mortar containing fly ash: a comparative study. Energy and Buildings 58: 292–301. 49 Reches, Y. (2018). Nanoparticles as concrete additives: review and perspectives. Construction and Building Materials 175: 483–495. 50 Colston, S. et al. (2000). Functional micro-concrete: the incorporation of zeolites and inorganic nano-particles into cement micro-structures. Journal of Materials Science Letters 19 (12): 1085–1088. 51 Rawat, P. et al. (2019). Optimizing weight percentage of MWCNTs for enhancing LVI resistance of quasi-isotropic symmetric laminate of carbon woven fabric/epoxy embedded with MWCNTs. Experimental Techniques 43 (6): 719–728. 52 Aggarwal, P., Singh, R.P., and Aggarwal, Y. (2015). Use of nano-silica in cement based materials: a review. Cogent Engineering 2 (1): 1078018. 53 Makar, J., Margeson, J., and Luh, J. (2005). Carbon Nanotube/Cement Composites-Early Results and Potential Applications. NRC Publications Archive Archives des publications du CNRC.

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70 Bournas, D.A. et al. (2007). Textile-reinforced mortar versus fiber-reinforced polymer confinement in reinforced concrete columns. ACI Structural Journal 104 (6): 740. 71 Mendes, T., Hotza, D., and Repette, W. (2015). Nanoparticles in cement based materials: a review. Reviews on Advanced Materials Science 40 (1): 89–96. 72 Long, W.-J. et al. (2017). Dynamic mechanical properties and microstructure of graphene oxide nanosheets reinforced cement composites. Nanomaterials 7 (12): 407. 73 Li, H. et al. (2004). Microstructure of cement mortar with nano-particles. Composites Part B: Engineering 35 (2): 185–189. 74 Zhang, R. et al. (2015). Influences of nano-TiO2 on the properties of cement-based materials: hydration and drying shrinkage. Construction and Building Materials 81: 35–41. 75 Al-Rifaie, W.N. and Ahmed, W.K. (2016). Effect of nanomaterials in cement mortar characteristics. Journal of Engineering Science and Technology 11 (9): 1321–1332. 76 Xu, S., Liu, J., and Li, Q. (2015). Mechanical properties and microstructure of multi-walled carbon nanotube-reinforced cement paste. Construction and Building Materials 76: 16–23. 77 Xu, S., Gao, L., and Jin, W. (2009). Production and mechanical properties of aligned multi-walled carbon nanotubes-M140 composites. Science in China Series E: Technological Sciences 52 (7): 2119–2127. 78 Alrekabi, S. et al. (2017). Effect of high-intensity sonication on the dispersion of carbon-based nanofilaments in cementitious composites, and its impact on mechanical performance. Materials and Design 136: 223–237. 79 Ahmadi, B. and Shekarchi, M. (2010). Use of natural zeolite as a supplementary cementitious material. Cement and Concrete Composites 32 (2): 134–141. 80 Raki, L. et al. (2010). Cement and concrete nanoscience and nanotechnology. Materials 3 (2): 918–942.

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8 Physical and Chemical Properties of Cotton Fiber-Based Composites Pankaj Kumar 1 , Cherala Sai Ram 1 , Jay P. Srivastava 2 , Ashwini Kumar 3,4 , and Arun K. Behura 5 1 SR University, Department of Mechanical Engineering, Center for Materials and Manufacturing, Ananthasagar, Hasanparthy Warangal Urban, Warangal 506371, India 2 SR Engineering College, Department of Mechanical Engineering, Ananthasagar, Hasanparthy Warangal Urban, Warangal 506371, India 3 Shree Guru Gobind Singh Tricentenary University, Department of Mechanical Engineering, Faculty of Engineering & Technology, Gurugram 122505, Delhi, India 4 Praxis Value, Senior Technical Consultant (Research), Banglore 560068, Karnataka India 5 VIT, School of Mechanical Engineering, Vellore 632014, Tamilnadu India

8.1 Fabrication Process for Cotton Fiber-Reinforced Composite The cotton fiber bundles are cut as per the required dimensions to fabricate the cotton fiber-reinforced composite. Three plies of the cotton fiber mats are placed in between with epoxy for target fiber content by adding the required mass of epoxy to a known mass of the fiber mat [1, 2]. The fiber, epoxy resin, and hardener were measured in the required proportions followed by mixing of epoxy and hardener. Epoxy and hardener were mixed in required proportions by weight ratios and the mixture was mechanically stirred for 10–15 minutes [3, 4]. To avoid the formation of bubbles, the prepared mixture was degasified for 8–10 minutes. Fabrication of the composite laminates starts with the application of the releasing film solution on the mold. Subsequently, the cotton fiber mat was placed over the releasing film and uniform rolling was carried out. These processes can be repeated for three layers of the fiber mat and epoxy resin. Researchers in [5–7] presented the fabrication of cotton fiber composites using a woven mat of the fiber, as represented in Figure 8.1. For the fabrication of fawn fibril-based composite laminates, the cotton can be reinforced in the form of fabrics or woven mats from the cotton rove or yarn. Roving is the process of making a long and narrow bundle of fibers. The roving of fibers is produced during the processing of raw cotton. Most composites have strong stiff fibers in a matrix that is weaker and less stiff. After harvesting cotton, cotton is ginned with engines and prepared for yarn spinning. Yarn is a twisted fiber thread used in knitting or weaving. Selecting the proper yarn can help in enhancing Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

8 Physical and Chemical Properties of Cotton Fiber-Based Composites

co

nu

th

ga wa rca ste ne

Co

Fiber reinforcement

Hand layup fabrication

us

Su

138

k

Cotton fly

Green epoxy

Metalic mold

Sample under compression at 100 bar and 80 °C

Cotton Sugarcane Coconut composite composite composite

Figure 8.1 Cotton fiber along with other waste materials and fabrication of its composites. Source: Hassan et al. [7].

the mechanical characteristics of the compound material. Enhancement in the elastic power can be noticed in the cotton composites compared to normal cotton. As compared to cotton/cotton laminates, 14.58% of tensile strength increase can be observed in cotton composites [8, 9]. The flexural strength of cotton composites increases by 23.3% compared to cotton/laminates [10, 11].

8.2 Mechanical Properties of Cotton Fiber-Reinforced Composites Testing and characterization of the fabricated composites have to be conducted at room temperature and according to the ASTM standards [12]. The mechanical testing includes tensile test, flexural test, compression test, Shore D hardness test along with water absorption test, and SEM analysis of the fabricated laminates [13–16].

8.2.1

Tensile Strength

The tensile test of the cotton fiber laminates is performed according to the ASTM D3039 standard [17–21]. The tensile strength can be measured on Universal Testing Machine (Zwick/Roell Z010 10 kN), as shown in Figure 8.2a–d. Before knowing the tensile strength of the composite materials, one has to be aware of the fiber strength of the natural fiber composite. The fibril power of the common fibril-based compounds is measured in two ways: (i) bundle strength (ASTM standard D1445) and (ii) single fiber strength (ASTM standard D3822) [22–24]. Sharma et al. [25] performed tensile testing of the cotton fibril-strengthened compounds and described that the tensile power of the laminates was in decreasing order. The maximum tensile strength of the sample was due to excellent adhesion between different matrices of the composites, which results in better wettability and firm bonding. Poor adhesion between the linen fiber and epoxy resin results in lower tensile strength. Figure 8.2a–d shows different specimens for tensile test and specimens under tensile loading. The stress–strain diagram of composites reinforced with cotton fabrics is depicted in Figure 8.3a,b. The tensile test was carried out using the load of 50 kN and the tensile properties of the fabricated specimen were measured according to the ASTM D3039 [26, 27].

8.2 Mechanical Properties of Cotton Fiber-Reinforced Composites

Polymer-matrix composite PP-50% + cotton fiber-50%

Polymer-matrix composite PP-100%

(a)

(b) Polymer-matrix composite PVC-50% + cotton fiber-50%

Polymer-matrix composite PVC-10%

(c)

(d)

Figure 8.2 (a–d) Tensile test specimen and specimen under tensile loading. Source: Hassan et al. [7]. 1.0

1800 VB-CF

1600

0.6 0.4 CF VB-CF NPA-CF DC-CF

0.2

DC-CF

1200 1000 800 600 400 200

0.0

0 0

(a)

NPA-CF

1400 ΔR/R0 (%)

Stress (MPa)

0.8

20

40

60

80 100 120 140 160 180 Strain (%)

0 (b)

10

20

30

40

50

Strain (%)

Figure 8.3 (a, b) Stress–strain diagram of composites reinforced with cotton fabrics. Source: Based on De Baere et al. [26].

8.2.2

Buckle Power

The ultimate buckle power properties of the phenolic compounds reinforced with cotton fabrics are measured and presented in Figure 8.4a,b [28–30]. It shows better flexural strength due to the higher load transferring capability along with the combined effects of the present higher quantity of cotton fabrics and epoxy matrix. In addition to this, the higher flexural strength of the composite is due to excellent adhesion between the different matrices of the composites, which results in better

139

8 Physical and Chemical Properties of Cotton Fiber-Based Composites

Flexural strength (KN/mm2)

4

3

2

1

0 (a)

Composites Sample-II

Sample-I Stress (KN/mm2)

140

Sample-III

Sample-IV

4 3.5 3 2.5 2 1.5 1 0.5 0 0

0.2

0.6

0.4

(b)

0.8

1

Strain (%) Flexural strength (KN/mm2) Sample-I 2

Flexural strength (KN/mm ) Sample-III

Flexural strength (KN/mm2) Sample-II Flexural strength (KN/mm2) Sample-IV

Figure 8.4 (a, b) Flexural behavior of phenolic composites reinforced with cotton fabrics. Source: Based on Refs. [28–30].

wettability and firm bonding. The poor interfacial adhesion between the cotton fabrics and epoxy resin results in lower flexural strength [31, 32].

8.2.3

Compressive Strength

The compressive strength depends on the quality of the adhesive bonding between the fiber and matrix [33–35]. Non-uniform and excess use of the epoxy resin leads to improper wettability and firm bonding. This results in lower compressive strength of the fabricated laminates. The compressive strength of all the fabricated samples is presented in Figure 8.5a. Figure 8.5b shows stress–strain diagram of the compressive strength. Sample-(a) has better compressive strength due to higher load transferring capability along with combined effects of the present higher quantity of cotton fiber and epoxy matrix. Therefore, from these different fabricated laminates, sample-(a) has the highest compressive strength and can withstand a higher load as compared to other samples.

8.2 Mechanical Properties of Cotton Fiber-Reinforced Composites

Stress (kN mm–2)

Ultimate compressive strength (kN mm–2)

76 74 72 70 68 66 64

80 70 60 50 40 30 20 10 0 0

62 Composites Sample-I

Sample-II

0.2

0.4 Strain (%)

0.6

0.8

–2

Sample-III

Compressive strength (kN mm ) Sample-I Compressive strength (kN mm–2) Sample-III Compressive strength (kN mm–2) Sample-II Compressive strength (kN mm–2) Sample-IV

Sample-IV

(a)

(b)

Figure 8.5 (a) Compressive strength behavior of cotton fiber composites and (b) compressive stress–strain curves of cotton fiber composites.

8.2.4

Impact Strength

Impact strength is measured from the impact test analysis in which the impact resistance capability of a particular material is measured in terms of shock-absorbing capacity at high speed [36–39]. From these test results, the applications area of the materials can be explored, such as various body parts either interior or exterior in the automobile sector, aircraft industry, and buildings. The low-velocity impact test includes Izod, Charpy impact, and drop weight impact test, whereas the ballistic impact test comes under the high-velocity impact test. Tserki et al. [40] performed impact test using Izod impact measurement process according to ASTM D256 and reported that due to the increase in the matrix contents, the impact strength of the prepared laminates decreases as presented in Figure 8.6. 10

Sugarcane Coconut Cotton

Impact strength (kJ m–2)

09 08 07 06 05 04 03 9

10

11

12

13

14

15

16

17

18

19

20

Fiber volume fraction (%)

Figure 8.6 Influence of fiber contents on the impact strength. Source: Hassan et al. [7]. Licensed under CC BY 4.0.

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8 Physical and Chemical Properties of Cotton Fiber-Based Composites

Ta¸sdem𝚤r et al. [41] carried out impact measurement and noted that on enhancing the length of the fibril, the impact power increases, whereas on increasing the fiber contents, the impact strength of the composite laminates decreases. However, the toughness of the fabricated cotton fabric-reinforced composites was measured using the Izod impact test techniques [25]. However, Rukmini et al. [35] conducted a multiaxial impact test analysis on the polypropylene composite laminates fabricated using cotton fabric as a reinforcement and reported that the total absorption energy reduces very significantly on reinforcing the cotton fabric. Moreover, the impact test investigation was completed to analyze the influence of the cotton fiber on the strength of the composite laminates fabricated using cotton fiber-reinforced geopolymer [42].

8.2.5

Hardness

The hardness of the fawn fibril compound laminates is measured using various hardness tester. For the softer materials, Shore D hardness tests are being performed to measure the hardness. It is a gauge-type shore hardness tester with a range of 0–100 shore and an accuracy of 1 shore for hardness measurement. The Shore D hardness should be measured at five different areas of the same specimen and the average values of all the samples should be considered. Before performing the hardness measurement, the sample under test is polished thoroughly with a fine polisher such as diamond paste of 10-μm grade for better results. Alomayri and Low [42] presented hardness measurement of various samples. Measurement of the hardness of the composite laminate was conducted to study the influence of the different percentages of the fiber contents [42]. The authors found that on enhancing the fibril contentment, the rigidity of the laminates increases up to 0.5 wt%, and then the hardness of laminates decreases. This is due to the distribution of the uniformly applied load on the fiber surface and thus hinders the penetration of the test load. Moreover, many researchers [43–45] performed an investigation on the effects of the length of the cotton fiber on the hardness of the composite and found that on enhancing the length of the fibril, the hardness of the composite decreases, whereas Koçak et al. [46] measured the Shore D rigidity of the hybrid-reinforced compounds accompanied by cotton and silk fiber according to ASTM D 2240-2004. From this investigation, Shore D hardness of the fabricated hybrid composite laminates increases on increasing the fiber contents. However, Achukwu et al. [47] measured the hardness of the hybrid composites fabricated using cotton and polyester. Measurement of the hardness was performed using Rockwell hardness tester and reported that the hardness of the polyester resin increased very significantly upon reinforcing with cotton fabric in polyester resin.

8.2.6

Thermogravimetric Analysis (TGA)

Thermogravimetric analysis of composites is used to quantify the amount of mass percentage of fiber and matrix materials [48, 49]. In this technique, the weight of

8.2 Mechanical Properties of Cotton Fiber-Reinforced Composites

101 100 99 98

Weight (%)

97 96 95 94 93 Coconut Cotton Sugarcane Pure green epoxy

92 91 90 0

50

100

150

200

250

300

Temperature (°C)

Figure 8.7 Effects of temperature on TGA analysis of cotton fiber. Source: Hassan et al. [7]. Licence under Creative Commons Attribution CC BY 4.0.

the sample is measured with the variation of temperature. As the weight of the cotton fiber changes, the thermal performance changes accordingly. The thermal analyzer is used to measure the thermogravimetric analysis (TGA) of the cotton fiber. In this technique, the nitrogen gas is passed through the cotton fiber at a flow rate of 20 ml min−1 . Abidi et al. [50, 51] investigated the effects of TGA on the maturity and fineness of the cotton fiber and reported that on increasing the measuring temperature, a very significant change in the weight of cotton fiber measured as presented in Figure 8.7.

8.2.7

Water Absorption Test

The study of water absorption behavior for the cotton fiber-reinforced composites was carried out using distilled water and according to the ASTM570 standard [52, 53]. The following equation is used to determine the percentage of water absorbed in the prepared composites as such Wt =

W2 − W1 W1

where W t is the percentage of water absorption, W 1 is the original weight, and W 2 is the final weight of the composites before and after the test. First, all the samples were weighed separately, and then, they were immersed in the distilled water for 90 hours. Next, all the samples were removed from the water, and all the water droplets wiped from the samples. Researchers [39, 54, 55]

143

144

8 Physical and Chemical Properties of Cotton Fiber-Based Composites Fiber swells after moisture absorption

Capillary mechanism– water molecules flow along fiber-matrix interface

Matrix microcrack around swollen fibers

(a)

(b)

Water diffusion through bulk matrix

Water soluble substances leach from fibers Ultimate fiber-matrix debonding

(c)

(d)

Figure 8.8 Water absorption behavior of cotton fiber-reinforced geopolymer composites. (a) Fiber swell after moisture absorption, (b) flow of water molecules along fiber matrix interface, (c) leaching of water soluble substance from fiber, and (d) debonding of fiber matrix. Source: Alomayri et al. [39].

investigated the water absorption deportment of the fawn fiber-strengthened increases on increasing the fiber contents as cotton fiber is hydrophilic. Due to this, various mechanical characteristics such as fracture firmness, hardness, flexural power, and flexibility decrease significantly. Figure 8.8 shows the H2 O immersion behavior of cotton fiber-strengthened inorganic polymer compounds. Figure 8.8 shows the effects of water penetration such as swelling, the formation of micro-cracks, and debonding of fibers.

8.2.8

Microscopic Morphology

The scanning electron microscope (SEM) analysis of the fawn fibril-strengthened compound is performed to investigate the structure form of the fiber such as straightness, twisting, or ribbon-like surface. Figure 8.9 reveals an SEM image of the raw cotton fiber (a) cross-sectional and (b) longitudinal structure, whereas Alomayri et al. [56] presented the SEM analysis of the fawn fibril cared with rosary dispense at different temperatures and reported that on increasing the corona discharge temperature, fineness of the fiber may be lost due to melting of the fiber may take place. Figure 8.9 shows SEM images of the cotton fiber treated with corona discharge at different temperatures. From the SEM, the fracture surface of the cotton fiber-reinforced geopolymer composite reveals that the void formation takes at higher temperatures due to

Fiber pullout

8.2 Mechanical Properties of Cotton Fiber-Reinforced Composites

(b) Magnified cracked area

Magnified shear failure

(a)

Magnified shear failure (c)

(d)

Figure 8.9 Depicts different mode of failure of polypropylene/cotton fiber and poly(vinyl chloride)/cotton fiber composites. (a, c) Shear failure and (b, d) fiber pull-out. Source: Alomayri et al. [56]. Under open access license.

the burning of the cotton fiber [56]. The author has presented that the survival of the cotton fiber takes place when heated between 200 and 600 ∘ C. Whereas Zeng et al. [57] carried out the investigation on the tensile fracture of the laminates and reported that the fiber pull out can be seen from the microscopic Figure 8.9. However, the tribological behavior of the fabricated cotton fiber composite laminates in various wear modes reveals that the damage occurs to both cotton fiber and polyester due to sliding wear as presented in Figure 8.10 [58].

8.2.9

Fourier Transformation by Infrared Spectroscopy (FTIR) Analysis

This is a non-destructive, qualitative, and quantitative analysis of both metallic and non-metallic materials. In this technique, infrared spectra are obtained to study the quantum of light that can be absorbed by the cotton fiber sample at a narrow range of frequency typically between 400 and 4000 cm−1 . Figure 8.11 shows spectra obtained from Fourier transformation by infrared spectroscopy (FTIR) between 500 and 4000 of wavenumber. From Figure 8.11, it can be concluded that the spectrum of cotton fiber indicates peaks at 1032 and 3330 cm−1 [59]. Chemical characterization of the cotton fiber-based composites performed and reported that the different peaks of the absorption band of the cotton fiber were

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8 Physical and Chemical Properties of Cotton Fiber-Based Composites

Adhesive failure

Adhesive layer Cohesive failure

Cohesive failure

Filer FCR700 Cohesive failure

Adhesive bonded material S235J0 Adhesive failure

(a)

(b)

(c)

Figure 8.10 SEM image of the worn-out surface of the reinforced cotton fiber composite. (a) Adhesive failure, (b) cohesive failure, and (c) both adhesive and cohesive failure. Source: Wang et al. [58].

(d) Intensity

146

(c) (b)

(a)

3500

3000

2500

2000

1500

1000

Wavenumbers (cm–1)

Figure 8.11

FTIR spectra of cotton fiber. Source: Based on Portella et al. [59].

observed in the range of 3400–3200, 3080–2900, 1390–1449, 1115–1080, and 1100–950 cm−1 , for the different functional groups present in the composite [44].

8.2.10 Investigation of Transmission Electron Microscope This investigation of the transmission electron microscope is utilized to estimate the length or diameter of the cotton fiber [44]. The length or diameter of the individual nano-fiber is measured with the help of ImageJ software. Figure 8.12a,b shows the TEM image of the nitrogen-doped cotton fiber captured at different magnifications.

8.3 Life Cycle and Environmental Assessment of Cotton Fibers Reinforced Composites

(a)

(b)

Figure 8.12 (a, b) TEM image of the cotton fiber at different magnifications. Source: Prachayawarakorn et al. [44].

In this technique, the sample is prepared very carefully starting with the boiling of the fiber in the NaOH solution for three hours followed by treatment with HCl solution and washing in de-ionized water.

8.3 Life Cycle and Environmental Assessment of Cotton Fibers Reinforced Composites The goal of the life cycle assessment is to study the environmental impact of the cotton fiber composites. In this assessment, the durability and recycling of the composites are accomplished. Different stages of the life cycle assessment include raw materials extraction, manufacturing, distribution, applications, and end life, as shown in Figure 8.13. Many researchers investigated the environmental effects of both fiber and resin [60–63]. They reported that the resin has more impact on the environment as compared to the reinforcement fiber. Raw materials cotton fiber

Seeds Bursting of cotton balls and cotton is collected

Colour change of flower(pinkred)

Plant

End of life

Applications

Flower

Fabrication of the composites

Packaging and transportation

Figure 8.13 Various developmental stages cotton flower and life cycle of cotton fiber-reinforced composites.

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8 Physical and Chemical Properties of Cotton Fiber-Based Composites

8.4 The Durability of Cotton Fiber-Reinforced Composites The durability of the fawn fibril-strengthened compounds is evaluated in terms of the service life of the composites. Various environmental aspects such as moisture absorption ability and ultraviolet radiation are also considered [64, 65]. Composites fabricated from the cotton fiber as reinforcement are considered more durable offer higher strength to weight ratio, stiffness, flexural strength, along with excellent corrosion resistance property. Cotton composites are used in the thermic-acoustic without heat transfer, like no heat transfer substances are mostly based on the components of the cotton fiber up to 80% by weight. Cotton is more durable than silk fabric and at the same timeless durable compare to wool. Cotton fabric is relatively prone to pilling, rips, and tears.

8.5 Conclusions In this chapter, the authors presented an insight into the physical and chemical characteristics of the fawn fibril-strengthened compounds. It showed different methods of fabrication of the cotton fibril-reinforced compounds and challenges occurred during fabrication. It also described the somatic characteristics of the cotton fibril composites such as tensile power. Many literatures reported that the tensile power of the compounds was in decreasing order. The flexural strength of the laminates was also seen in the decreasing trend during the measurement. From the measurement of compression strength, decreasing order of measured values has been observed. Shore D hardness tests were performed and a decreasing trend of shore D hardness has been measured. From the water absorption test, it concludes that the water absorption behavior of the cotton fiber-reinforced increases on increasing the fiber contents as cotton fiber is hydrophilic. From the SEM analysis of the fractured sample of the tensile test, the fiber can be seen in the form of a bundle and wetted uniformly by the epoxy resins. Moreover, spectra obtained from FTIR between 500 and 4000 of wavenumber, and can be concluded that the spectrum of cotton fiber indicates peaks at 1032 and 3330 cm−1 . Life cycle and environment assessment of the cotton fiber composites show that the resin has more impact on the environment as compared to the reinforcement fiber.

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9 Properties of Carbon Nanotubes (CNT) Vijay K. Singh 1 , Puneet Kumar 2 , Sunil K. Yadav 1 , Chandrasekhar Saran 3 , and Kaki V. Rao 4 1 National Project Implementation Unit (NPIU) under Ministry of Education, Govt of India, MMMUT, Gorakhpur 273010, Uttar Pradesh, India 2 Karunya Institute of Technology and Sciences (Deemed to be University), Department of Aerospace Engineering, Siruvani Main Road, Karunya Nagar, Coimbatore 641114, Tamilnadu, India 3 Government College of Engineering, Department of Mechanical Engineering, Kalahandi 766002, Odisha, India 4 Vignan’s Foundation for Science, Technology & Research (Deemed to be University), Department of Mechanical Engineering, Guntur-Tenali Road, Vadlamudi 522213, Andhra Pradesh, India

9.1 Introduction There is a group of emerging technologies, known as nanotechnology, where the size of the structural matter is limited to the nanometer scale for producing novel materials and devices with useful and unique properties. In 1991, Japanese scientist Sumio Iijima first observed the nested structures (similar to Russian doll) of concentric tubes of carbon during the two-carbon-electrode electric discharge experiment. Thenceforth, carbon nanotubes (CNTs) are among the profound members of existing nanoscale materials and have attracted a large community of scientists and researchers in contrast to boron nitride and molybdenum nanotubes. Carbon is the key element of this technology, which forms its compounds almost everywhere, such as in human body, food items plants, atmosphere, and fuels. Carbon is the only element with allotropes of zero dimension (carbon amorphous) to three dimensions (diamond). Three main allotropic forms of carbon are amorphous carbon, diamond, and graphite. Diamond is a poor conductor of electricity, whereas graphite is a good electrical conductor, due to the difference in the hybridization of the carbon atoms. There is an sp3 hybridization in diamond, whereas graphite (Figure 9.1) has sp2 hybridization in which three electrons form covalent bonds with the three carbon atoms and the fourth is weakly bonded (Figure 9.2). All the electron transport in graphite layer–graphene sheet occurs due to this (fourth) weakly bonded electron. The different shapes, such as tubes, wires, and balls, prepared from carbon atoms control most of the current nanotechnology research. Tubes made of carbon

Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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Figure 9.1 Graphite structure. Source: Based on Qian et al. [1].

 bond

 bond

Figure 9.2

Hexagonal bonding in graphene sheet. Source: Qian et al. [1].

atoms can be CNTs, buckytubes, and nanowires. CNTs can be defined as the rolled graphene sheet with outstanding mechanical properties such as highest stiffness, strength, and electronic properties. The extraordinary properties of CNTs are extremely high tensile strength, high modulus, flexibility, lightweight, and thermal conductivity.

9.2 Carbon Nanotubes Family 9.2.1

Single-Walled Carbon Nanotube (SWCNT)

It may be considered as a seamless cylinder that is obtained after rolling a 2D hexagonal lattice of carbon (i.e. graphene). It has a highly symmetrical structure in the form of a hollow cylindrical tube made of graphene sheet with an equivalent covalent bond. The typical diameter of single-walled carbon nanotube (SWCNT) varies from 1 to 2 nm.

9.3 Properties of CNTs

9.2.2

Multiwalled Carbon Nanotube (MWCNT)

Multiwalled carbon nanotubes (MWCNTs) are coaxially nested cylinders of SWCNTs with the interlayer spacing and diameter in the range of 0.34–0.39 and 10–100 nm, respectively.

9.3 Properties of CNTs The nanostructures of carbon exhibit various important unexpected properties (mechanical, thermal, and electrical) and therefore have found many technological and industrial applications. These mechanical, thermal, and electrical properties are interrelated with each other and depend on the bonding of the carbon network [2]. Some important properties of SWCNTs/MWCNTs are discussed in Sections 9.3.1–9.3.5.

9.3.1

Mechanical Properties

The presence of high strength (very stiff and strong) C—C bond of sp2 hybridization in graphene sheet is the main reason behind CNT’s exceptional physical and mechanical properties. All the outstanding properties of the graphene sheet along the tube axis are obtained due to the perfect alignment of the graphite planes along the fiber axis of the nanotube. According to the theoretical study of the researchers, CNTs are stiffer and strongest material than any materials investigated to date. MWCNTs explicitly showed 100 times better specific tensile strength than steel specimens while the stiffness of graphene lattice is equal to that of the diamond. Young’s modulus of SWCNT and MWCNT is in the order of 3.0 and 1.7–2.4 TPa, respectively [3]. The mechanical properties of CNTs are measured experimentally using many techniques such as atomic force microscopy, high resolution scanning electron microscopy, and transmission electron microscopy. Nanotube attached to the silicon/silicon nitride cantilever acts as a force sensor and its deflection is tracked in two ways either by the laser signal from the cantilever to the photodiode in atomic force microscope (AFM) or by imaging the movement of the cantilever in scanning electron microscope (SEM). The average young’s modulus of CNT has been determined by using AFM technique and small-deformation theory (d = FL3 /aEI).

9.3.2

Thermal Properties

The product of the density of occupied phonon modes at a particular temperature, group velocity of modes, mean free path (elastic and inelastic), lattice specific heat (Cp ), and intrinsic/extrinsic phonon scattering process measure the thermal conductivity of CNTs. The dependency of CNTs’ thermal conductivity on temperature has been examined by Barber et al. with the help of molecular dynamics simulation [4]. The highest value of thermal conductivity of a pristine (10,10) nanotube was found to be approximately 6000 W/m K at room temperature, as shown in Figure 9.3. Theoretical as well

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9 Properties of Carbon Nanotubes (CNT)

4  104

 (W/m K)

3  104

2  104

1  104

0  104

0

100

200

300

400

T (K)

Figure 9.3 Thermal conductivity with respect to temperature for a (10,10) CNT. Source: Berber et al. [4]. Figure 9.4 The thermal conductance of an individual MWCNT (d = 14 nm). Source: Kim et al. [5].

10–7

10–8 3000  (T) (W/m K)

Thermal conductance (W/K)

158

10–9

2000 1000 0 100

200

300

T(K)

10

100 Tepmerature (K)

as experimental approaches have been utilized to determine the thermal conductivity of CNTs. A surprising thermal conductivity for a single nanotube was noted at about 3000 W/m K at 47 ∘ C and measured by attaching MWCNT with microfabricated devices, as shown in Figure 9.4.

9.3.3

Electrical Properties

The use of CNTs for the next-generation device applications such as sensing elements, transistors, field emission devices due to their unique electrical properties are under consideration of many researchers and industries. Though it is difficult

9.3 Properties of CNTs

to obtain the I–V characteristic of ideal CNT but the various studies on band structures indicate the dependency of electrical characteristics on the structural parameters (diameter and chirality). One of the most wonderful properties of SWCNT is to behave as metallic and semiconducting in the function of its helicity. This property will explore nano-electronic device applications. Dispersion relations of electrons must be studied to understand the electrical properties where there are many energy levels possible correspond to a single momentum and there may not be any energy available to some momentum. The behavior of material as an insulator, semiconductor, or conductor depends on the properties of band structure (collection of all possible energies and momentum). A wide variety of behavior for SWCNT has been studied by Balents and Fisher [6]. Where metallic behavior was predicted with “armchair” (n,0) tubes and insulating with “zigzag” (n,0).

9.3.4

Electronic Properties

The diameter and chirality of nanotube are the important parameters to predict the band structure and the CNTs’ electronic properties. There are various studies [7–12] available on strong band structure and energy of perfect CNT, which show dependence on these factors. As CNTs are formed into the cylindric structure by rolling a graphene sheet, they must be studied extensively to explore their band structures and electronics characteristics. There is a hexagonal arrangement/two-dimensional array of carbon atoms in graphene where each atom of carbon (sp2 hybridized) is bonded with three-neighboring carbon atoms. The unique electronic properties of graphene can be obtained by the electron cloud on both sides of the graphene plane created by the unhybridized electron (pz ). By considering the tight-binding approximation [10] for graphene sheet the 2D energy dispersion relation can be derived. There are six points in the Brillouin zone where the lower valence band and upper conduction band meet with each other, these points are known as K points. More interestingly, graphene is found as a zero-band gap semiconductor. The wavefunction of graphene in company with the periodic boundary condition determines the band structure of CNTs. The detailed studies on band structures have shown the metallic and semiconducting nature is governed by the tube chirality. The electronic properties of CNTs is widely interrelated with its’ tube chirality.

9.3.5

Field-Emission Properties

Field emission is the process of tunneling electrons from the surface of a solid matter under the application of voltage or electrostatic field. CNTs field emission was first observed by Walt A. de Heer and his group. The influence of applied electric field on the energy barrier (electrons) through a metallic surface has been studied in the Fowler–Nordheim model for field electron emission [13]. The potential barrier takes a triangular shape with decreasing slope when a negative amplitude potential is applied and becomes horizontal in the absence of an electric field to the solid. Generally, local electric field (E) amplitude governs the slope of the potential barrier. The local electric field will be higher by a factor 𝛾 (field amplification factor)

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9 Properties of Carbon Nanotubes (CNT)

Metal Surface Vacuum F = 0 V/nm e–

EF

D(E

F)

D(E) – (a)

+ V

(b)

F = 2 V/nm

Figure 9.5 (a) Experimental setup for field emission. (b) Field emission model Fowler–Nordheim approach. Source: Oostrom [14].

times than the macroscopic field V/do , where V is the applied voltage between the two parallel electrodes at a distance do . The field at the emitter surface is presented mathematically as 𝛾E = 𝛾V/do , where the field amplification factor (𝛾) completely depends on the emitter’s geometrical shape. The peak of the field emission is affected by the work function (Φ) and exactly occurs at the Fermi level, as shown in Figure 9.5 [14, 15]. The field emission theory more precisely explains that the emitted charge varies with respect to electric field and work-function. The astounding properties of CNTs, such as high length to diameter ratio, little curvature radius at its end, high elastic strength, chemical morphology, make them a favorable candidate for field emission.

9.4 Conclusion CNTs have been manifested as a wealth of outstanding characteristics and structural phenomena. Some of them have already been explored by researchers and scientists, whereas others are still challenging. There is no doubt that CNTs have shown amazing structural and materialistic properties, but being a new material in nanotechnology, nanotubes product commercialization could not gain a foothold in the structural and condensed-matter market. The challenges like high production cost and sophisticated characterization and testing of CNT will keep them an exciting area of research for many years to come.

Acknowledgment The authors are very grateful to the National Project Implementation Unit (NPIU) under Ministry of Education (MoE), Govt. of India and MMMUT- Gorakhpur for all the support provided in this sanctioned project (CRS ID-1-5755587331) under the Collaborative research scheme of AICTE.

References

References 1 Qian, D., Wagner, G.J., Liu, W.K. et al. (2002). Mechanics of carbon nanotubes. Applied Mechanics Reviews 55 (6): 495–532. 2 Kar, K.K. (2011). Carbon Nanotubes: Synthesis, Characterization and Applications. Research Publishing. 3 Lourie, O. and Wagner, H.D. (1998). Transmission electron microscopy observations of fracture of single-wall carbon nanotubes under axial tension. Applied Physics Letters 73 (24): 3527–3529. 4 Berber, S., Kwon, Y.K., and Tománek, D. (2000). Unusually high thermal conductivity of carbon nanotubes. Physical Review Letters 84 (20): 4613–4616. 5 Kim, P., Shi, L., Majumdar, A., and McEuen, P.L. (2001). Thermal transport measurements of individual multiwalled nanotubes. Physical Review Letters 87 (21): 215502-1–215502-4. 6 Balents, L. and Fisher, M.P.A. (1997). Correlation effects in carbon nanotubes. Physical Review B: Condensed Matter 55 (18): R11973–R11976. 7 Fischer, J.E. and Johnson, A.T. (1999). Electronic properties of carbon nanotubes. Current Opinion in Solid State and Materials Science 4 (1): 28–33. 8 Cao, J.X., Yan, X.H., Ding, J.W. et al. (2002). Electronic properties of single-walled carbon nanotubes. Journal of the Physical Society of Japan 71 (5): 1339–1345. 9 Kharlamova, M.V. (2016). Advances in tailoring the electronic properties of single-walled carbon nanotubes. Progress in Materials Science 77: 125–211. 10 Liu, Y.N., Lu, J., Zhu, H. et al. (2017). Derivative and electronic properties of zigzag carbon nanotubes. Wuli Xuebao/Acta Physica Sinica 66 (9): 093601. 11 Mohammad Nejad, S., Srivastava, R., Bellussi, F.M. et al. (2021). Nanoscale thermal properties of carbon nanotubes/epoxy composites by atomistic simulations. International Journal of Thermal Sciences 159: 106588. 12 Kour, R., Arya, S., Young, S.-J. et al. (2020). Review – Recent advances in carbon nanomaterials as electrochemical biosensors. Journal of the Electrochemical Society 167 (3): 037555. 13 Riyajuddin, S., Kumar, S., Soni, K. et al. (2019). Study of field emission properties of pure graphene-CNT heterostructures connected via seamless interface. Nanotechnology 30 (38): 385702. 14 van Oostrom, A.G.J. (1966). Validity of the Fowler-Nordheim model for field electron emission. Philips Research Reports 1: 1–100. 15 Cutler, P.H. (1993). Theory of electron emission in high fields from atomically sharp emitters: validity of the Fowler–Nordheim equation. Journal of Vacuum Science and Technology B 11 (2): 387.

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10 Mechanical and Thermal Properties of Sisal Fiber-Based Composites Vivek Mishra 1 , Alok Agrawal 2 , Saurabh Chandraker 3 , and Abhishek Sharma 4 1 Indore Institute of Science and Technology, Department of Mechanical Engineering, Rau – Pithampur Road, Indore, Madhya Pradesh 453331, India 2 Sagar Institute of Research and Technology Excellence, Department of Mechanical Engineering, Bhopal, Madhya Pradesh 462041, India 3 National Institute of Technology Surathkal, Department of Mechanical Engineering, Mangalore, Karnataka 575025, India 4 Manipal University Jaipur, Department of Mechanical Engineering, Jaipur, Rajasthan 303007, India

10.1 Introduction Composite materials earlier found their application mainly in civil engineering for construction purposes. However, recently, composites are extending the horizon in almost all branches of engineering and science. Generally, composites are material that has a combination of two or more distinct constituents. Distinct phases mean chemically dissimilar interphases. Among the two components, one should be a continuous phase which is often present in greater quantity in the composite, though it is not always true. This phase is called a matrix. The other constituents are known as the reinforcing phase. In general, the reinforcement is sturdier and stiffer than the matrix, although there are some exceptions. The area of contact between the two distinct phases is called an interface. The constituents forming the composite should be chemically nonreactive. Classification of composites can be done in two different categories. The first classification is based on matrix materials, which can be metal matrix, ceramic matrix, and polymer matrix composites. The polymer can be thermoset and thermoplastics. The main difference between thermoplastic and thermoset arises from the makeover process from the prepolymer to the final polymer. The second classification of composites is related to reinforcement, which comprises particulate composites, fiber composites, whiskers composites, flakes composites, and laminar composites. The matrix used in the preparation of composite has to fulfill different functions. Its primary function is to arrange the fibers properly by holding them as they align in the particular direction for which they is designed. The other important work of the matrix is to isolate the discontinuous phase from one another. With this, the main aim is to make them behave as separate entities. Matrix also protects the reinforcing material from mechanical damage. Reinforcement plays an important role in the Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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composite as it fulfills the requirement. Generally, fibers improve the mechanical properties, whereas filler improves the intrinsic behavior of the composites. Fiber-reinforced polymer composites comprise fibers of high strength and modulus implanted within the polymeric matrix body. In this combination, both the fiber and matrix do not lose their physical and chemical identities. Rather, the combination produces the properties which are impossible to attain by the individual phase. Fiber-reinforced polymer composites have a wide variety of industrial and commercial applications. The structural applications of such composites are in the aircraft, for which weight reduction is critical. In space, this category of composites has various applications ranging from heavy to light. In heavy application, it includes applications in space shuttles, payload bay door, pressure vessels, and remote manipulator arm. In lightweight applications, it consists of support structures for smaller components. Applications in the automotive industry include body components, chassis components, and engines. The optimum design of sports equipment mainly concerns on avoidance of injury. Another important concern of sports equipment is to make it userfriendly with enhanced performance. Here, material characteristics are of importance. The different characteristics of importance are mainly related to mechanical behavior such as ductility, strength, fatigue, toughness, modulus (damping). The other noticeable characteristics are density and cost of the material. To fulfill the requirements, a combination of materials is selected. The materials may be from any category depending upon the requirement of the properties. Fiber-reinforced composites are very useful in medical applications as well. For the last 40 years, the use of fiber-reinforced composite in medical application is ongoing whereas, for 25 years, such composites are established in the dental field. They are also used in making lightweight glass–Kevlar/epoxy face masks. The material is mainly used for epileptic patients. One of the applications of graphite–glass/epoxy composites are the artificial portable lungs to provide mobile flexibility to the patient [1]. Fibers used in polymeric material fall under two broad categories: synthetic fibers and natural fibers. Synthetic fibers are those which are man-made whereas natural fibers are extracted from various natural resources. The fiber-reinforced polymeric composites are normally prepared using synthetic fibers. Synthetic fibers deliver additional advantages as they provide resistance to corrosion, good resistance to wear, they are aesthetic, are stable temperature-dependent, and also provide excellent environmental stability. Apart from being advantageous, these fibers have some drawbacks. The shortcomings are high cost, comparatively high density, difficult in recycling, and nonbiodegradable. For the growth and betterment of the community, scientists started working on environmentally friendly materials. Because of this, natural fibers have evolved as one of the best environmentally friendly materials. Also, they consume low energy during processing, have very low density, greater modulus to weight ratio, higher acoustic damping with low cost, and are available easily. Fibers as reinforcement can also be classified based on their length. Matrix reinforced with long fiber is known as continuous fiber-reinforced composites and the composites reinforced with short fibers are known as discontinuous fiber-reinforced composites. Aspect ratio differentiates these two types of fibers.

10.1 Introduction

While calculating the aspect ratio the length of fiber will be in numerator and diameter of the fiber will be in the denominator. If the aspect ratio is less than 100, the fibers are under the category of short fibers, and if the aspect ratio is any value greater than 100, they are called long fibers. Long fiber is used as unidirectional or bidirectional fiber and can effectively take the load. Also, they are anisotropic and show different behavior in different loading conditions. Against that, short fibers are much more versatile. It is mainly because of their isotropic behavior. They can be fabricated using extrusion techniques with thermoplastics. Also, they behave isotropically due to their random distribution in the matrix body. Thus, both the categories of fibers have their specific advantages and different drawbacks as well. Natural fibers are commonly categorized based on the source from which they are available as a plant, animal, or minerals. Cellulose is the major structural constituent of all kinds of plant fibers, whereas protein is the constituent of animal fiber. The use of mineral fibers is in decline because of its hazardous nature. Among plant and animal fibers, plant fibers are more suitable to be used as reinforcement as they fulfill the structural requirement of composites and also can be artificially grown and harvested according to the need. Matrix is a critical part of natural fiber-reinforced composites. For this, the polymer matrix is most suitable because of its very low density and low-temperature processing, so that plant fiber does undergo any thermal damage. Polymers have a high toughness value which prevents the fiber from mechanical damage and nicely distribute the load. Both categories of polymers are used in combination with plant fibers to develop composite material. Thermoset has an advantage over thermoplastic in terms of resistance to temperature, dimensional stability, flexibility in design, and cost-effectiveness. Epoxy, vinyl ester, and polyester are the often used thermosetting plastics. All thermosets require at least one more component to cure them. In polyester and vinyl ester it is called accelerator whereas, for epoxy, it is called hardener. Sisal fibers are well-established natural fibers extracted from the sisal plant. The sisal plant is botanically known as Agave sisalana. Sisal plant are found all over the globe. Though the more favorable condition for its growth is a tropical region and subtropical region and thus, they are mostly found in these areas. Again, Tanzania and Brazil are the two main sisal producing countries. Generally, the sisal plants are not systematically cultivated. Soil rich in different minerals helps the fast development of the sisal plant. The annual production of sisal fiber is around 45 Lakhs tons altogether. In India, there are four types available: Sisalana, Vergross, Istle, and Natale. Depending on the type of plant, the yields of fiber are different. The quantity of fiber obtained from Sisalana is maximum. The other three types yield relatively less amount of fiber. The average life of the sisal plant is 7–10 years. In its complete life span, it produces around 250 leaves. A single leaf of the sisal plant can produce up to 1000 fiber bundles. Each leaf of sisal fiber is a typical combination of 4% fibers, 0.75% cuticle, 8% is of dry matter, and the remaining 87.25% is of moisture. Fibers can be taken out from the sisal leaf when its age is around two years. The weight of each leaf is around 600 g. Leaf of sisal fiber can be ripe when the length of the leaves reaches the approximate length of 80–100 cm [2].

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A single leaf of the sisal plant has three different types of fibers: mechanical fiber, ribbon fiber, and xylem fiber. They are classified based on the portion of a leaf from which they are riped. Mechanical fiber is commercially useful fiber among the three types. They are taken out from the edge of the leaf. Ribbon fiber is obtained from the median line of leaf and is obtained quite easily during processing. They are also superior in strength compared to mechanical fiber due to the presence of conducting tissue structure. They are the longest fiber among the three and can reach a length of around 1.2 m. Xylem fibers are of the irregular shape obtained from the opposite of ribbon fibers. They have broken up as they had a cell of thin wall which lost during extraction and have no commercial application [3]. Its chemical composition includes 78.8% cellulose, 8% lignin, 10% hemicellulose, 2% wax, and 1% ash. All the values are in percentages of weight. The most used method for extracting sisal fiber is microbiological retting, hand-scraping, or by using rasped or machine [4]. Sisal fibers are widely used natural fiber and has the second-largest consumption across the world only after cotton. It has high strength with good durability. It also has a good percentage elongation before the break and not deteriorates effortlessly in salty water. These fibers are smooth and straight with a high degree of inflexibility. Their growth does not require pesticides or chemical fertilizers as they grow naturally in an environment. Also, they do not cause environmental degradation. There exist certain drawbacks of sisal fiber and one of them is an affinity toward moisture. With this, frequent expansion and contraction of material occur. Such behavior gives rise to the possibility of microbial attack. From long ago, sisal fibers were used traditionally in almost every part but mainly in villages. Sisal fiber is the leading material used in the manufacturing of ropes and general cordages. Sisal fiber found applications mainly because of its properties discussed earlier. Also, the cost of sisal fiber is low, almost one-tenth of the price of glass fiber. Even low-grade sisal fibers also have some applications. If they have high cellulose and hemicellulose content, they are potential material for industries-produced papers. If the grade is a little better than low-grade fiber and is used mainly in the cordage industry for making ropes, baler and binder and this found application in the marine sector. It is used for such an application because it has excellent resistance to saltwater. It has a potential agriculture sector as well. Finally, the high-grade fiber obtained undergone proper surface treatment where they transformed into precious yarns which find application in carpet manufacturing. Apart from conventional usage, sisal fibers as reinforcement in the polymeric matrix are in use. The same is discussed here with reference to mechanical and thermal behavior. It helps the scientific community to get a benchmark and fundamental basis to perform further work in a similar area.

10.2 Mechanical Properties of Sisal Fiber-Reinforced Composites Composite materials are used to produce various valuable products that can found different applications in construction, aerospace, environmentally sustainable systems, and ground transportation. For that, newly developed composite material

10.2 Mechanical Properties of Sisal Fiber-Reinforced Composites

should undergo physical and mechanical testing before recommended for such applications. Hence, for the use of the material for structural applications, it needs to undergo a wide range of loading tests. Hardness, tensile strength, flexural strength, and impact strength are the different mechanical properties that need to evaluated [5]. Several investigations conducted on natural fiber-reinforced composites exhibited that their mechanical properties are governed by factors such as the aspect ratio of the fiber, content or loading of fibers, fiber orientation, fiber–matrix adhesion, etc.

10.2.1 Tensile Properties The most widespread and utmost studied mechanical test for composite materials is a uniaxial tensile test. The acceptance of uniaxial tension as a test method is mainly due to ease of processing and investigation of the results. The tensile test seems to be simple though the fact is different. It has problems associated with it. The problem is mainly because of the structure formed by the composites together with properties generated by the end product. The main difficulty of conducting a satisfactory tensile test usually increases as the orthotropic nature of these materials increases, i.e. the ratio of axial strength to the transverse strength increases [6]. Several researchers [7–14] conducted tensile tests to know the behavior of polymeric composites with sisal fiber as reinforcement. Gupta and Srivastava [7] used a combination of sisal fiber and epoxy matrix for the fabrication of composites. They evaluated different mechanical properties of the developed material. Composites are fabricated with 0, 15, 20, 25, and 30 wt% fiber loading for the study. In their study, they observed that the tensile strength and tensile modulus of the fabricated samples are superior to neat epoxy and this improvement is function of fiber loading. It means composite with 30 wt% of sisal fiber delivers maximum tensile strength and modulus. The increment in the properties with fiber content is the result of strong adhesion arises between the continuous and discontinuous phase. Due to such strong bonding, stress transfer is uniform from the epoxy to the sisal fiber, and the same results in an improvement in tensile properties. Authors [8] worked on the tensile behavior of epoxy reinforced with sisal fiber-reinforced in the form of unidirectional fiber in one set and in the form of mat in another set. Fabrication of composites is performed with 15, 20, 25, 30 wt% unidirectional fiber and 30 wt% mats through the hand lay-up technique. Unidirectional sisal fiber composites having 30 wt% exhibited maximum strength and modulus among all the prepared composites. The 30 wt% sisal mat reinforced epoxy have shown inferior tensile properties against unidirectional sisal fiber of 30 wt% when reinforced in epoxy composites. They explained the behavior as a result of improper adhesion between the sisal and epoxy when it is in the form of mat. Li et al. [9] studied the consequence of surface modification on sisal fiberreinforced polylactide (PLA) composites. Sisal fibers surface was modified using MPS-g-PLA (polylactide-graft-γ-methacryloxypropyltrimethoxysilane)/PLAco-PGMA (polylactide-co-glycidyl methacrylate) as a coupling agent. Authors reported that tensile strengths of MPS-g-PLA-treated and PLA-co-PGMA-treated

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sisal fiber-reinforced composites were improved by 5.35% and 6.77% respectively, in comparison to the untreated one. The modification of the fibers yields better compatibility and good wettability between fiber and matrix. Because of this, effective stress allocation from the continuous to the discontinuous phase took place. Ragunath et al. [10] reported the tensile behavior after combining glass fiber with sisal fiber as a reinforcing agent in epoxy composites. Improvement in tensile properties for hybrid composites is reported in comparison to when only sisal fiber is reinforced epoxy composites. Again, the investigated properties of the hybrid composites exhibit approximately equivalent tensile strength as that of glass fiber-reinforced epoxy composites. Alemayehu et al. [11] carried out an experimental study of sisal fiber-reinforced composites for light vehicle body applications with unsaturated polyester resin. Sisal fibers with fiber orientations of 0∘ and 45∘ and 0∘ and 90∘ were reinforced with unsaturated polyester resin to prepare samples through the open molding method. After performing the tensile test on different sets of composites, they found that composites fabricated with 0∘ and 90∘ orientation along with treated sisal fiber exhibit better tensile properties as compared to the composites fabricated with 0∘ and 45∘ orientation of fibers. Bernard et al. [12] reported fiber content effect on tensile behavior of sisal fiber reinforcement with IPN (Interpenetrating Polymer Networks) resins. Five composites samples having fiber content 10, 20, 30, 40, and 50 wt% of sisal fibers were prepared to study the effect of fiber content. They found that the property under investigation increases as the loading of fiber increases. The authors also compared the experimental results with finite element analysis results and reported that both the results are in good correlation. On a similar note, Samouh et al. [13] worked on the tensile properties of sisal fiber with polylactic acid resin. Composites with 0, 5, 10, and 15 wt% sisal fiber fabricated through the injection molding technique are part of their investigation. Similar to the result obtained by other researchers, they also reported that the tensile properties of the composites are the function of fiber loading. Maximum tensile strength is obtained for a combination of polylactic acid with 15 wt% sisal fiber. Bichang’a et al. [14] studied the consequence of alkali treatment on the sisal fiber-reinforced epoxy composites. They used sisal fiber as woven fabric. From the analysis, they found that surface modification of the fabric resulted in improved tensile properties. Again, an excellent interface between the fabric and matrix is the reason for such an improved result. Surface modification of fibers removes the cementing material like lignin and increases their surface area. With this increased surface area, matrix material adhesion with fabric improved.

10.2.2 Flexural Properties The flexural test consists of bending of the beam, supported at two ends and load is applied at the center. The load required to bend the beam to a certain degree is a measure of flexural strength. The same applies to rigid as well as semirigid materials,

10.2 Mechanical Properties of Sisal Fiber-Reinforced Composites

laminated fiber composites, and resins. The flexural test also gives a rough idea about the interfacial strength through which matrix and fiber bind them together. Nagamadhu et al. [15] analyzed the effect of composition and loading direction on flexural properties. They used the combination of sisal fabric and polyvinyl alcohol for developing green composites. Two woven fabric with different Gram Square Meter (GSM) is selected for composite fabrication. Composites with 0%, 20%, 40%, and 60% fabric content are under investigation. Composites are manufactured using a vacuum-assisted pressure compression method. Authors reported that wt% of sisal fabric reinforcement increased the flexural properties of the composites. Similar behavior is obtained for both sets of composites, though the samples prepared with the weft direction delivered better properties in comparison to the samples prepared in the warp direction. Such behavior is obtained because yarn count and percentage of crimp associated with weft direction are more than that for warp direction. Sun and Wu [16] evaluated the effect of sol–gel modification. They used a combination of sisal fiber and polypropylene in their work. They kept the loading of fiber as 20 wt%. They fabricated the samples with untreated fibers as well as treated fibers. They performed the flexural test on the developed materials. From the results obtained they concluded that composites with modified fiber possess better flexural strength and flexural modulus against composites prepared with untreated sisal fiber. The improvement reported is 3.61% and 16.02% for strength and modulus, respectively. Vishnuvardhan et al. [17] worked on sisal fiber-reinforced epoxy composites and studied the effect of fiber content on flexural strength. The composites are fabricated over a wide range of fiber content. The selected content of fibers is 15 wt% (S15), 20 wt% (S20), and 25 wt% (S25). The flexural strength of the specimens increased as the loading of fiber increased. Maximum flexural strength is obtained when the fiber content is 25 wt%. Sahu and Srivastava [18] analyzed flexural properties of short sisal fiber-reinforced epoxy composites. They studied the effect of fiber length on the flexural properties of the composites. In their work, they kept the content of fiber constant to 30 wt% and varies the length of the fiber. The fabricated samples were represented as E, S5, S10, S15, and S20 for epoxy, 5 mm fiber length, 10 mm fiber length, 15 mm fiber length, and 20 mm fiber length, respectively. From the results, it can be seen that flexural strength and modulus of neat epoxy is 99.76 MPa, 4.61 GPa, respectively. The flexural strength of samples S5, S10, and S15 were comparatively lesser than the pure epoxy sample. It is because short fiber might act as a defect at the macroscopic level. The optimum values obtained are 115.86 MPa, 5.84 GPa respectively, for S20 composites samples. Srisuwan et al. [19] observed the effect of two different treatments, i.e. alkali and silane on flexural properties of woven sisal fabric reinforced natural rubber-modified epoxy resin composites. Woven fabrics were alkali treatment with 2 wt% NaOH solution and silane treatment of woven fabrics was done using 3-glycidoxypropyltrimethoxysilane over alkalized fabrics. The composites were prepared through hand lay-up technique using 3, 5, and 7 wt% of treated woven sisal fabric as reinforcing material and grafted

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Table 10.1

Sets of blend and fabricated composites [19].

Composition

A-sisal fiber (wt%)

S-sisal fiber (wt%)

GDNR (g)

Neat epoxy resin

—

—

—

GDNR/epoxy blend

—

—

1.5

Sample with 3 wt% A-sisal

3

—

1.5

Sample with 5 wt% A-sisal

5

—

1.5

Sample with 7 wt% A-sisal

7

—

1.5

Sample with 3 wt% S-sisal

3

3

1.5

Sample with 5 wt% S-sisal

5

5

1.5

Sample with 7 wt% S-sisal

7

7

1.5

Source: Srisuwan et al. [19].

Figure 10.1 Flexural modulus of (a) neat epoxy resin, (b) GDNR/epoxy blend, (c) sample with 3 wt% A-sisal, (d) sample with 5 wt% A-sisal, (e) sample with 7 wt% A-sisal, (f) sample with 3 wt% S-sisal, (g) sample with 5 wt% S-sisal, and (h) sample with 7 wt% S-sisal. Source: Srisuwan et al. [19].

Flexural modulus (GPa)

4 3.5 3 2.5 2 1.5 1 0.5 0 (a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Type of polymers

depolymerized natural rubber (GDNR)/epoxy resin blend as matrix material. The various combinations of prepared composites are given in Table 10.1. The experimental result of the flexural test is presented in Figures 10.1 and 10.2. The flexural modulus of all the composite specimens under investigation was better than the GDNR/epoxy blend and increased with fiber weight percentage. The flexural modulus further improved on using silanized sisal fiber for composites. Further, all the composites exhibited inferior flexural strength than the virgin epoxy and their Flexural strength (GPa)

170

100 80 60 40 20 0 (a)

(b)

(c)

(d)

(e)

(f)

Type of polymers

(g)

(h)

Figure 10.2 Flexural strength of (a) neat epoxy resin, (b) GDNR/epoxy blend, (c) sample with 3 wt% A-sisal, (d) sample with 5 wt% A-sisal, (e) sample with 7 wt% A-sisal, (f) sample with 3 wt% S-sisal, (g) sample with 5 wt% S-sisal, and (h) sample with 7 wt% S-sisal. Source: Srisuwan et al. [19].

10.2 Mechanical Properties of Sisal Fiber-Reinforced Composites

blend. Despite that, silanized sisal fiber-reinforced composites exhibited enhanced flexural strength in comparison to alkalized sisal fiber-reinforced composites. The adhesion at the interface plays a critical role in it. The result indicates that silanized fiber-reinforced composites could have better interfacial adhesion properties than the alkali-treated sisal fiber-reinforced composites.

10.2.3 Impact Properties Impact strength is explained as the amount of energy absorbed when a load is applied suddenly over the material. There are various methods to determine the impact energy absorbed by fiber-reinforced composites under the application of load. Some of them are Charpy, Izod, split Hopkinson, drop weight, ballistic impact, and explosive. The results can be in any form such as damage accumulation, fracture energy, or number of falls to attain a given stress level or damage. The outcome depends on numerous factors such as strain rate, specimen size, test setup, and the nature of the measuring device [20]. Prasad et al. [21] inspected the impact properties of sisal fiber/polyester composites. In this study, both untreated sisal fiber and sisal fiber treated with 5% NaOH as reinforcement is selected. Cobalt naphthenate and methyl ethyl ketone peroxide were used as curing agents and catalysts respectively . The composite sample was prepared with 10 mm long fiber in the volume fraction of 10%, 15%, 20%, 25%, and 30%. The thicknesses was varied from 2 to 6 mm at the interval of 1 mm. The impact strength as the function treatment of fiber and the volume fraction of fiber is presented in Figures 10.3 and 10.4. There is an enhancement in the impact strength as the thickness (2, 4, 5, and 6 mm) of the composite and fiber volume fraction increases. The highest impact strength of the fabricated composites is for the fiber volume fraction of 30%. The authors reported that the 5% NaOH treated sisal fiber-reinforced composites exhibited less strength than the untreated sisal fiber-reinforced composites. It is very important to choose the ideal NaOH concentration and the duration of treatment for effective treatment of natural fibers such as sisal or any other. Srisuwan and Chumsamrong [22] studied the effects of type of weave and fiber content on the suddenly applied load. The combination under investigation is sisal fiber-reinforced epoxy composites. Three types of weaves are plain weave, basket weave, and right-hand twill weave. Each one is taken for composites preparation in the present work. Untreated sisal fiber and alkali-treated sisal fibers in a weight ratio of 3, 5, and 10 wt% were used for reinforcement in composites. The impact strength of all the prepared composites was lower than the pure epoxy. It is because of poor interfacial adhesion between the fiber and matrix. The space available in between the fiber and matrix behaves as a stress concentrator. It results in large differences in impact values of epoxy and the composites. The impact strength increases with an increase in fiber content in the composites. The composites having plain weave fiber reinforcement, particularly in case 3 and 5 wt% fiber content exhibited higher impact strength than composites having other types of fibers as reinforcement. Such behavior is obtained because maximum fabric stability is obtained by plain weave

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10 Mechanical and Thermal Properties of Sisal Fiber-Based Composites

Untreated sisal fiber polyester composite 4 3.5

Impact strength (N m)

3

2 mm thick specimen 3 mm thick specimen 4 mm thick specimen 5 mm thick specimen 6 mm thick specimen

2.5 2 1.5 1 0.5 0 10

12

14

16

18

20

22

24

26

28

30

Fiber volume fraction (%)

Figure 10.3 et al. [21].

Impact strength of the composites with untreated fibers. Source: Prasad Treated sisal fiber polyester composite

2 1.8 1.6 Impact strength (N m)

172

2 mm thick specimen 3 mm thick specimen 4 mm thick specimen 5 mm thick specimen 6 mm thick specimen

1.4 1.2 1 0.8 0.6 0.4 0.2 10

12

14

16

18

20

22

24

26

28

30

Fiber volume fraction (%)

Figure 10.4 et al. [21].

Impact strength of the composites with treated fibers. Source: Prasad

10.2 Mechanical Properties of Sisal Fiber-Reinforced Composites

and hence this results in good strength. The weave type has no significant effect on impact strength at 10 wt% fiber content. Results also showed that fiber treatment has not much influence on impact properties. Zhong et al. [23] studied the impact behavior of alkali-treated short sisal fiber-reinforced composites. The self-synthesized urea-formaldehyde resin is a matrix material. The fabrication of composites with different fiber content (30, 40, 50, 60, and 70 wt%) through the compression molding technique route is done. The impact strength increases with an increase in fiber content from 30 to 50 wt%. But with a further increase in fiber content, the impact strength decreases. The impact properties of composites are governed by various factors which include matrix fracture, fiber pullout, and fiber-matrix debonding. The higher impact strength of 50 wt% composites may be due to proper bonding between the continuous and discontinuous phases. As the fibers are present to a sufficient extent, they successfully transfer the stress from one part of the system to another part. Also, the spaces between the two different phases and concentration of stress increase rapidly as the content of fiber increases. With this stress concentration is generated to act as the crack initiation points when the impact load is acted upon it. As a result, minimum strength is obtained in composites with 60 wt% sisal fiber content.

10.2.4 Hardness Hardness is defined as the resistance of the material against local surface deformation. An indenter is placed over the material surface and then pressed into the surface. The size of the depression formed in the material surface is measured to obtain material hardness. Some of the methods for determining the hardness of the material are the Vickers hardness test, Rockwell hardness test, Brinell hardness test, Shore D hardness test, and Barcol hardness test. Out of these, the Barcol hardness test is not used much among the scientific community [20]. Webo et al. [20] studied the effect of fiber content and fiber treatment on hardness. They used sisal fiber-reinforced epoxy composites in the investigation. They found, initially, the hardness value of composites increases up to 10 wt% fiber content, then hardness reduces a little bit at 15 wt% fiber content. After 15 wt% fiber content, the hardness value of composites increases up to 50 wt%. The reduction in hardness value after 10 wt% of fiber content may be due to insufficient wettability between matrix and fibers. The hardness of material increases from 15 to 50 wt%. It is because of the even distribution of the fibers within the matrix that results in increased stiffness. The composite fabricated with treated sisal fiber exhibited better hardness than the composite fabricated with untreated one. Karthikeyan et al. [24] examined the hardness of short sisal fiber-reinforced silicone composites. They prepared both untreated and silane treated with 0, 5, 10, 15, and 20 wt% of fiber loading. The hardness was determined using a Shore A type durometer. The incorporation of fiber in the matrix makes composites harder and stiffer and thus the hardness increases with an increase in fiber content. The hardness of silane-treated composites with 20 wt% fiber was 10% more than untreated sisal fiber-reinforced silicone composites. The reported improvement may be due

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10 Mechanical and Thermal Properties of Sisal Fiber-Based Composites

73

Hardness (shore D)

72.5 72 71.5 71

Untreated fiber 0.025%v/v MMA 0.050%v/v MMA 0.075%v/v MMA 0.100%v/v MMA

70.5 70 0

10

20

30

40

50

Amount of fiber (%v/v)

Figure 10.5 Effect of fiber treatment and fiber content on the hardness of the composite keeping fiber length constant. Source: Sangthong et al. [25].

to better interfacial adhesion and improved compatibility between fiber and matrix and enhanced network structures within the cross-linked system. Sangthong et al. [25] investigated the effect of unsaturated polyester composite reinforced with micellar-treated sisal fibers. Hardness of specimens was measured against the change in fiber content (0, 10, 20, 30, and 40%v/v), change in methylmethacrylate (MMA) concentration for fiber treatment (0.025%, 0.05%, 0.075%, and 0.1% by volume), and change in fiber length (10, 20, 30, and 40 mm). Figure 10.5 represents the hardness of the sisal fiber-reinforced unsaturated polyester composites. Hardness value increased with increasing fiber loading as well as MMA concentration. Figure 10.6 shows the variation in hardness property concerning fiber length and MMA concentration. They reported that hardness increase within fiber length and MMA concentration. 73

Hardness (shore D)

174

72.5 72 71.5

Untreated fiber 0.025%v/v MMA 0.050%v/v MMA 0.075%v/v MMA 0.100%v/v MMA

71 70.5 0

10

20

30

40

50

Fiber length (mm)

Figure 10.6 Effect of fiber treatment and fiber length on the hardness of the composite keeping fiber content constant. Source: Sangthong et al. [25].

10.3 Thermal Behavior of Sisal Fiber-Reinforced Polymer Composites

10.3 Thermal Behavior of Sisal Fiber-Reinforced Polymer Composites Sisal fiber has ample potential to be used as reinforcement in polymeric resin as it improves the various mechanical properties appreciably. However, like other natural fibers, sisal fiber also has compromising thermal properties. Hence, evaluation of the thermal behavior of such composite is mandatory and has become common practice for the last one decade. The thermal properties of interest among the scientific community for any natural fiber reinforced polymer composites are thermal stability and glass transition temperature. Polymer composites prepared using sisal fiber were also studied mainly for these thermal properties. In this section, a detailed discussion of the same is given.

10.3.1 Thermal Stability The thermal stability of natural fiber and its composites with polymer as matrix material were generally determined using a thermogravimetric analyzer (TGA). The TGA is a measure of loss of weight of the material as the temperature increases. For performing TGA analysis, the nitrogen atmosphere is a must. The analysis is performed generally between the temperature range of 30 and 700/800 ∘ C and is further depends upon the type of fiber incorporated. The heating range in almost every case is between 10 and 20 ∘ C per minute. During TGA, the parameters registered start with initial degradation temperature followed by major degradation temperature. With further increase in temperature, the final degradation temperature of the material reaches and at the end, it gives the amount of char formed. From this, the material with a higher degradation temperature is more thermally stable [26]. Martin et al. [27] performed a detailed thermal analysis of sisal fiber. They first performed a thermogravimetric analysis of the sisal fiber followed by differential scanning calorimetry (DSC) of sisal fiber. The thermogravimetric and first derivative thermogravimetric curve obtained in their work is shown in Figure 10.7. From the curve (Curve i), it is clear that initial weight loss took place in a temperature range of 32–221 ∘ C accounted for 2.9% of the total weight. This loss is mainly the loss of moisture present within the fiber. Degradation of sisal fiber starts once the temperature reaches 222 ∘ C. With further increase in temperature, degradation of sisal fiber occurs very rapidly till the temperature reaches 415 ∘ C. From the graph, it can be seen that 72% is the total weight loss. This weight loss took place between the temperature of 221 and 415 ∘ C. When the temperature increases beyond 415 ∘ C, the degradation rate reduces with weight loss of 5.4% is registered for a temperature range of 416 ∘ C to a maximum of 520 ∘ C. The degradation rate goes down due to the slow char degradation rate. Finally, they reported that the char yield of sisal fiber is 19.7%. This took place at 520 ∘ C. The reported char formed because of the condensation of lignin content of the sisal fiber and the generation of aromatic compounds in the nitrogen atmosphere. In Figure 10.7, from the derivative thermogravimetric (DTG) curve (Curve ii), it can be seen that there are two distinct peaks at 310 and 377 ∘ C. Figure 10.7 shows the two-step degradation of fiber. The first peak represents

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10 Mechanical and Thermal Properties of Sisal Fiber-Based Composites

ii

100

0.0

80 –0.5 60 DTG

Mass (%)

176

–1.0

40 i 20

–1.5 0 100

200

300

400

500

Temperature (°C)

Figure 10.7 TGA curve (i) and DTG curve (ii) of raw sisal fiber under nitrogen atmosphere. Source: Martin et al. [27].

slow degradation. Here, hemicellulose degradation occurs between the temperature range of 220 and 328 ∘ C with a weight loss of 17.7%. The second peak represents the fast degradation of cellulose between 328 and 416 ∘ C. Bakare et al. [28] studied the thermal stability of raw sisal fiber along with rubber seed oil polyurethane resin (RSOPU) and their composites using TGA. The curve obtained in their analysis is shown in Figure 10.8. TGA curve shows that raw sisal fiber experiences significant weight loss at three distinct temperature regions at different intervals of time. The first loss of weight took place near 100 ∘ C. It is because of the release of moisture present within the fiber. The next two weight loss took place between 250 and 480 ∘ C, respectively. It is due to the decomposition of cellulose, lignin, and hemicellulose. RSOPU and its composites with sisal fiber have no such weight loss till 200 ∘ C. They compared the degradation of sisal fiber, RSOPU and composite at 400 ∘ C and observed that sisal fiber degraded by 66%, RSOPU by 50% and their composite is by 64%. Results show that the thermal stability of composite is in between the RSOPU matrix and sisal fiber. Hence, they concluded that the inclusion of sisal fiber reduces the thermal stability of the matrix. Munde et al. [29] recently evaluated the thermal stability of raw sisal fiberreinforced in the polypropylene matrix. They found that up to 200 ∘ C, polypropylene did not show any weight loss whereas its composites registered weight loss of 4%. But, when the temperature increases to 400 ∘ C, the reverse trend is obtained. Here polypropylene shows a weight loss of 99.59% and its composite had 78.08% weight loss. It has been seen from this analysis that the inclusion of sisal fiber in the polypropylene matrix enhances the thermal stability of composites above 200 ∘ C. Similar behavior of thermal stability for polypropylene/sisal fiber composites was

10.3 Thermal Behavior of Sisal Fiber-Reinforced Polymer Composites

100

a

80

Weigth (%)

c

60

b 40

20

0 0

100

200

300

400

500

600

700

Temperature (°C)

Figure 10.8 TGA curve of (a) sisal fiber, (b) rubber seed oil-based polyurethane matrix, and (c) sisal reinforced rubber seed oil-based polyurethane composite. Source: Bakare et al. [28].

reported earlier by Jeencham et al. [30], as shown in Figure 10.9. They found that reinforcement of sisal fiber enhances the thermal stability of composite but the addition of any of the flame retardants, i.e. ammonium polyphosphate (APP), Mg(OH)2 , Zb improves the thermal stability of polypropylene (PP)/sisal fiber composite further. The increase in thermal stability is because of the formation of 100 100

80

95 90 85

Weight (%)

80

60

75 70 300 320 340 360 380 400 420 440

40 20

PP PP/30sisal PP/30sisal/40APP PP/30sisal/40Mg PP/30sisal/40zb PP/30sisal/30APP/10Mg PP/30sisal/30APP/10zb

0 100

200

300

400

500

600

700

Temperature (°C)

Figure 10.9 TGA curve showing the effect of flame retardant on the thermal stability of polypropylene composites. Source: Jeencham et al. [30].

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10 Mechanical and Thermal Properties of Sisal Fiber-Based Composites

magnesium phosphate and zinc pyrophosphate. It induces physical/thermal barrier protecting over the substrate. Paluvai et al. [31] modified the surface of sisal fiber using alkali treatment and alkali-silane treatment. They compared the thermal decomposition temperature of raw sisal fiber, alkali-treated sisal, and alkali-silane treated sisal fiber. They found that treated fiber shows high thermal decomposition temperature against untreated sisal fiber. Among the two differently treated fibers, alkali-silane treatment provides ´ maximum thermal stability to the sisal fiber. On a similar note, Głowinska et al. [32] compared the thermal stability of raw sisal fiber and silane-modified sisal fiber. They found that modification of sisal fiber surface using silane enhances thermal stability. Later, composites were prepared with treated and untreated fibers. The matrix used is polyurethane. They found similarities in the thermal stability of both sets of composites. From this analysis, it was observed that modification of sisal fiber using silane is not an effective method for improving the thermal stability of its composites. Sun and Mingming [16] modified the surface of sisal fiber using silane and tetraethylorthosilicate (TEOS). They also use TEOS alone for surface modification. With this, they prepared three sets of composites (untreated, TEOS treated, silane-TEOS treated fiber) using polypropylene as a base matrix and compared their thermal stability. The TGA curve (Figure 10.10) obtained in their analysis shows that modification of sisal fiber with TEOS increases thermal stability. Further, when fibers are treated with a combination of chemicals, the thermal stability of the composites is increased appreciably. Gupta et al. [33] used different chemicals for modifying the surface of sisal fiber and reinforced those fibers in recycled polypropylene and evaluated the thermal stability of composites. The chemicals used are sodium hydroxide, acetic anhydride, silane, strontium titanate, glycidyl methacrylate, acetic acid, and O-hydroxybenzene diazonium chloride. Later, they fabricated different sets of composites using sisal

100

Weight ratio (%)

178

80 60 40 Untreated Combination TEOS

20 0 0

100

200

300

400

500

600

Temperature (°C)

Figure 10.10 TGA curve of polypropylene-based untreated and treated sisal fiber composites. Source: Sun and Mingming [16].

10.3 Thermal Behavior of Sisal Fiber-Reinforced Polymer Composites

Table 10.2

Thermogravimetric analysis of samples under investigation [33]. Initial degradation temperature (∘ C)

Final degradation temperature (∘ C)

Recycled polypropylene (RPP)

356

460

RPP/SF (70/30)

234.20

412.5

Sample

RPP/Si-SF/MA-g-PP (65/30/5)

362.13

472.6

RPP/GMA-SF/MA-g-PP (65/30/5)

363.67

494.3

RPP/OBDC-SF/MA-g-PP (65/30/5)

379.44

512.8

Source: Gupta et al. [33]. Licensed under CC BY 3.0.

fiber treated with the chemical. Further, they compare the thermal stability of the composites. The result obtained in their study is shown in Table 10.2. It is clear that virgin polypropylene possesses an initial degradation temperature of 356 ∘ C and a final degradation temperature of 460 ∘ C. When 30 wt% sisal fiber is incorporated, both this temperature reduces. It shows that the inclusion of sisal fiber decreases the thermal stability of polypropylene composites. When treated fibers have opted as reinforcement, the thermal stability of the composites increases. Sodium hydroxide (NaOH)-treated fiber enhances the thermal stability of composites. But the thermal stability of composite is lower than that of neat polypropylene. On the other hand, silane-treated fiber delivers better thermal stability as compared to virgin polypropylene. Glycidyl methacrylate treated fiber shows an increase in thermal stability compared to silane treated. Maximum thermal stability is with sisal fiber treated with O-hydroxybenzene diazonium chloride where final degradation temperature reached 512.8 ∘ C. Improvement in thermal stability is due to increased compatibility between the modified sisal fiber and the polymer matrix.

10.3.2 Glass Transition Temperature Generally, the glass transition temperature is evaluated by DSC analysis. In DSC analysis, a sample of around 20 mg is enough. It is kept on an aluminum pan for testing. The test took place under a nitrogen atmosphere. The rate of heating varies from 10–20 ∘ C/min. The range of temperature for polymeric composites is around 30–600 ∘ C. Generally, DSC is performed in a controlled environment. When the material is heated over a wide range of temperature, the endothermic and exothermic process occurs, and the main function of DSC to measure the heat flow during this process. During this analysis, different peaks are visible in the temperature/heat flow curve. These are exothermic and endothermic peaks. Its magnitude and location provide the thermal phase transformation of the material under observation. Heat is absorbed during the endothermic process and gives information such as melting, phase transition, evaporation, and dehydration. Heat is evolved during the exothermic process and gives information about crystallization, oxidation, combustion, and decomposition [34]. The transition that took

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10 Mechanical and Thermal Properties of Sisal Fiber-Based Composites

Exo

Raw sisal

Figure 10.11 DCS curve of raw sisal fiber and its constituents. Source: Martin et al. [27].

Heat flow

Defatted sisal

Cellulose

Enod

180

Hemicellulose

Lignin

0

100

200

300

400

500

600

Temperature (°C)

place during the endothermic process gives information regarding glass transition temperature and the ultimate decomposition temperature [26]. Figure 10.11 shows the DSC curve of raw sisal fiber presented by Martin et al. [27]. From the curve, they observed three peaks that correspond to the major constituents of sisal fiber, i.e. cellulose, hemicellulose, and lignin. The first peak is called the endothermic peak took place near 75 ∘ C and is associated with the release of moisture from the sisal fiber. Later, the exothermic peak is visible in the curve starting at temperature 234 ∘ C and reach its maximum value at 297 ∘ C. This peak is associated with the degradation of hemicellulose. The same is observed in the isolated curve of hemicellulose. The built-up of the second endothermic peak is visible at 330 ∘ C. It reaches the maximum at 365 ∘ C. It is associated with the degradation of cellulose and can be confirmed in the isolated curve of cellulose. Finally, the second exothermic peak of weak nature is starting at 387 ∘ C and reaches a maximum of 415 ∘ C and it shows the degradation of lignin. Gupta et al. [33] also performed a DSC analysis of the samples and evaluated glass transition temperature (T g ), crystalline temperature (T c ), and melting temperature (T m ). Table 10.3 shows the results of their work. It has been seen from the obtained data that glass transition temperature decreases with the addition of raw sisal fiber in recycled polypropylene. Again with treated fiber, glass transition temperature increases. Maximum glass transition temperature obtained is for sisal fiber treated with glycidyl methacrylate. Also melting temperature and crystalline temperature of polypropylene are not much affected with the inclusion of sisal fiber in raw form as well as in treated form.

10.4 Conclusion

Table 10.3

DSC analysis of samples under investigation [33].

Sample

T g (∘ C)

T m (∘ C)

T c (∘ C)

Recycled polypropylene (RPP)

−12.18

167.86

128.18

RPP/SF (70/30)

−14.23

165.83

127.42

RPP/Si-SF/MA-g-PP (65/30/5)

−3.91

166.32

128.87

RPP/GMA-SF/MA-g-PP (65/30/5)

−3.36

165.54

128.29

RPP/OBDC-SF/MA-g-PP (65/30/5)

−4.48

166.49

128.44

Source: Gupta et al. [33]. Licensed under CC BY 3.0.

Hence, Ye et al. [35] modified the surface of sisal by low-polymerization degree PLA after alkali treatment for preparing one set composite. Two sets are prepared with raw sisal fiber and alkali-treated sisal fiber. The matrix used in their investigation is the PLA matrix. The DCS curve indicated that the glass transition temperature of neat PLA is 62 ∘ C. It increases to 64.5 ∘ C when untreated sisal fiber is in the PLA matrix. Alkali treatment of sisal fiber reduces the glass transition temperature to 61.6 ∘ C. Combine treatment improves the value of the glass transition temperature to 62.6 ∘ C. It is better than that from neat polymer and alkali-treated fiber but still lower than untreated sisal fiber. Hence, from their work, it is said that surface modification of sisal fiber does not give increased glass transition temperature. On the contrary, Johari et al. [36] prepared cellulose microfibrils using sisal fiber with PLA matrix for studying the effect of surface modification (alkali and silane treatment) on glass transition temperature. They found that the inclusion of cellulose microfibrils does not have any effect on improving the glass transition temperature of the composites. But the inclusion of treated fibers enhances the glass transition temperature irrespective of the type of treatment used in their investigation. Apart from the glass transition temperature, the presence of fibers improves the melting temperature. In more recent work, Verma et al. [37] found that incorporation of sisal fiber to soy protein-polymer matrix increases the glass transition temperature of the composite system. They evaluated the effect of coating over sisal fiber on glass transition temperature. The value of glass transition temperature at different content of sisal fiber along with the effect of coating on sisal fiber is reported. It is clearly observed that the maximum glass transition temperature is 5 wt% of sisal fiber. Again, irrespective of fiber content, sisal fiber coated with chitosan gives a higher glass transition temperature.

10.4 Conclusion Fiber extracted from sisal plant has a high potential to be used as reinforcing material in a polymeric resin. The reasons for this are many. Few of them are high specific strength and modulus, lightweight, low cost, no health risk, renewability, and easy

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availability. Sisal fiber application is increasing day by day because of its outstanding performance. Apart from the traditional application of sisal fiber-reinforced composites, numerous applications such as aerospace, automobiles, packaging, constructions, buildings, railways, and sports are also there. The use of sisal fibers in the plastic industry provides a renewable material. It also helps in the economic development of rural areas. Due to the extraordinary properties and better chemical composition, sisal fiber is a superior substitute for synthetic fibers. Mechanical and thermal properties of sisal fiber composites are dependent on fiber content, fiber length, stacking sequence, and orientation. Further, different surface treatment processes help a lot in the improvement of different mechanical and thermal properties of sisal fiber-reinforced with different polymer matrices.

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11 Mechanical, Electrical, Magnetic, and Smart Properties of Synthetic Fiber Composites Hema Garg 1 , Jayashree Mohanty 1 , Abhishek K. Pathak 2 , Ashish Gupta 3 , Satish Teotia 4 , and Bipin Kumar 5 1

Indian Institute of Technology, Delhi, School of Interdisciplinary Research, New Delhi 110016, India The University of Tokyo, Department of Aeronautics and Astronautics, Bunkyo-Ku, Tokyo 113-8656, Japan 3 CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012, India 4 NIMS University Rajasthan, NIET, Department of Physics, Jaipur 303121, Rajasthan, India 5 Indian Institute of Technology, Department of Textile and Fibre Engineering, New Delhi 110016, India 2

11.1 Introduction Synthetic fibers have become a topic of great interest for researchers due to their ability to overcome major shortcomings of natural fiber’s low mechanical and thermal properties. Synthetic fibers are produced by chemical synthesis through man-made manufacturing processes, and their counterpart natural fibers are derived from natural resources. Synthetic fiber is manufactured from petroleum products by the extrusion process, such as melt spinning from spinnerets. The process involved in producing these fibers is polymerization, which involves combining monomers to form a polymer’s long chain. An essential step in their preparation involves aligning fiber in the parallel direction, allowing enhanced orientation, crystallization, and high strength to volume ratio. This has been of interest for a considerable period, ranging from the early eighteenth century. Synthetic fibers such as glass, carbon, and aramid fiber have proven to be high-performance fibers whose properties could be tailored to fit in different applications such as textiles, defense, automotive, aerospace, etc. Considerable advances in research and technology have led to its remarkable presence in the commercial market, with over 50% synthetic fiber usage in composite industries. The high performance of these fibers is due to their superior mechanical and thermal properties. The property of a material is a direct function of its chemical structure. Aramid/Kevlar (KF) is an organic fiber with tensile strength reported as 3620 MPa, possessing high crystallinity from intermolecular hydrogen bond association between carbonyl and NH with additional strength conferred by adjacent aromatic stacking interactions. Carbon fiber (CF) is also an organic fiber that consists

Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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11 Mechanical, Electrical, Magnetic, and Smart Properties of Synthetic Fiber Composites

Advantages of FRP

Tailorable properties stiffness and toughness electrical/thermal conductivities thermal expansion

Corrosion resistance

Figure 11.1

Resistance to creep at high temperature

Lighter weight

Multifunctional/smart properties

The advantages of synthetic fiber reinforced polymer.

of a carbon backbone where carbon atoms are packed in crystal and aligned in the fiber direction, imparting high stiffness, and tensile strength, low weight, high chemical resistance, high-temperature tolerance, and low thermal expansion. In contrast, glass fiber (GF) is an inorganic fiber, which consists majority of its silica (50%) with different mineral oxides. It is employed in applications where low cost, low stiffness, and robust material are required. Fiber-reinforced polymer (FRP) matrix composites can be thermosetting or thermoplastic, and reinforcement in FRP forms the crucial part of providing high mechanical strength, proper stiffness to weight ratio, resistance to fatigue, specific modulus, good corrosion resistance properties, and acts as the load-bearing component. The advantages of the FRPs are depicted in Figure 11.1. Synthesis of high modulus fibers has replaced steel in many structural applications owing to their high strength to weight ratio [1, 2]. The key factors affecting synthetic fiber composite properties include the type of fiber/filler, geometry, content, distribution, orientation, and the type of matrix involved. In this chapter, the mechanical, electrical, and magnetic properties of synthetic FRP composites are reviewed, targeting the influence of various reinforcement fiber, polymer matrix, and fillers on the individual property.

11.2 Mechanical Properties of FRP Mechanical performance is of prime importance in various structural applications and designing body parts of several aircraft and automobiles. The major mechanical properties of FRP include tensile, flexural, interlaminar shear strength (ILSS)/interfacial shear strength (IFSS), and fracture toughness. The mechanical behavior of a composite structure relies on many factors such as fiber volume, fiber orientation, fiber/polymer modulus, and fiber/polymer interface.

11.2 Mechanical Properties of FRP

11.2.1 Tensile Properties The tensile properties of FRP are measured using the universal testing machine following ASTM D3039 [3]. The crucial terms associated with tensile testing are tensile strength, strain at break, and modulus of elasticity. Tensile strength refers to the maximum stress a material sustains before its failure and is expressed in MPa. Tensile modulus measures the stiffness, described as the ratio of tensile stress to strain. The factors influencing the tensile properties include material type, Poisson’s ratio, layup sequence, specimen conditioning, testing environment, void content, and fiber volume fraction. P (11.1) Ftu = max A where F tu is the ultimate tensile strength, Pmax is the maximum load at failure, and A is the area of cross-section. The tensile strength and modulus of fiber are generally high as compared to the polymer matrix. The polymer exhibits a higher elongation at break. The amalgamation of two constituents results in FRP whose tensile properties fall between the two, as shown in Figure 11.2 [4]. This effect is observed by Meshram et al. where nylon fiber mat is reinforced in the epoxy matrix by hand layup method, and mechanical properties are reported [5]. The mechanical behavior showed that the neat epoxy behaved as a flexible material, whereas in the case of nylon reinforced epoxy, the elongation decreased but the tensile strength increased. The fiber reinforcement improves the matrix’s tensile strength, whereas the rigid nature of the fibers decreased the elongation at break. Various factors contribute to the tensile properties of a composite. In GF, the tensile strength of the fiber and its composite deteriorated after surface treatment and 1000 900 FRP

Tensile stress (MPa)

800

Fiber

700 600 500 400 300 200

Polymer

100 0 0

1

2

3

4

5

Strain (mm/mm)

Figure 11.2

Tensile stress versus strain curve for fiber, polymer, and FRP.

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11 Mechanical, Electrical, Magnetic, and Smart Properties of Synthetic Fiber Composites

increased interfacial adhesion. This is due to the brittleness induced after chemical treatment such as silanization, acid, or alkali action. While interface adhesion is vital in stress transfer between fiber and matrix during the flexural test, it negatively impacts the tensile properties [6]. The influence of environmental aging and fiber type on polymeric nanocomposite’s mechanical properties has been studied using carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) based on polyetherimide (PEI) matrix [7]. The tensile strength behavior and the matrix nature of the CFRP and GFRP reinforced composites were analyzed for a period of 200 months. A higher tensile strength of more than 600 MPa was observed for CFRP composite and nearly 400 MPa for GFRP composites initially, with the continuous decline observed for GFRP composites with time. However, the tensile strength of CFRP composites declined up to 13% and remained constant throughout the testing period. The higher the matrix loss, the faster the aging will be, and there will be a negative influence on the mechanical properties. ILSS variations with time were less in the case of CFRP composites, which is why the CFRP composites have higher tensile strength as compared to GFRP composites. Poisson’s ratio is a critical factor in tensile measurement and quantifies the deformation in the perpendicular direction to the loading. A perfect linear and elastic material has a Poisson’s ratio of 0–0.5. The out-of-plane tensile properties are drastically affected by Poisson’s ratio in FRP. A study conducted by Hara et al. [8] revealed that in unidirectional CFRP, the larger deformation of the composite sample was observed in the side surfaces of the direction perpendicular to the fibers. In 0∘ orientation, no such deformation was observed. A larger Poisson ratio causes shrinkage in the 90∘ direction to the loading.

11.2.2 Flexural Properties Flexural properties determine the flexural strength and stiffness in FRP using three-point bending (Figure 11.3a) or four-point bending test (Figure 11.3b) methods prescribed in ASTM D7264 [9]. It is a fundamental measurement for engineers and designers to accurately know the maximum stress a specific structure would take before its collapse/failure when subjected to bending loads. Also known as modulus of rupture, it takes into account both tensile and compressive stresses. Under flexural loading, the upper surface of the composite experiences compressive force while the lower part is under tensile stress. Thus, the flexural strength in three- and four-point bending is given by 3PL (11.2) 2bd2 3PL (11.3) 𝜎(4 point) = 4bd2 where P is the load at a given point, L is the span length, b is the width, and d is the thickness of the test sample. Monteserin et al. designed polyamide fibers of two types (PA6 Ultramid and Badamid) by electrospinning and interleaved them with CF plies, which they integrated into the interlaminar region and external layers of antistatic 𝜎(3 point) =

11.2 Mechanical Properties of FRP

P/2

P/2

L/2

P/2

d

d

b P/2

L/2

L/2

L/4

L

(a)

b

L/4

P/2

P/2

P/2

L

(b)

Figure 11.3 The flexural testing of FRP composite sample in (a) three-point bending and (b) four-point bending.

polypropylene (PP). Infusion molding processes were carried for the process of lamination. The laminates were then pushed into an epoxy matrix for resin impregnation through the whole laminate, followed by curing. The mechanical properties obtained in these cases were excellent, particularly the flexural properties. Stress at failure increased from 19.7% to 42.4% for composites modified by PA6 Ultramid to PA6 Badamid, respectively [10]. This is due to the highly crystalline Badamid and formation of three-veil structures, which hampered the crack propagation growth and delayed failure. The role of interface plays a primary role in determining the interactions between the matrix and fiber. Aramid fibers have a very poor adhesion property with polymer matrices, which indirectly hampers the flexural and shear strength, load transfer to fiber–matrix, and may cause interfibrillar fibrillation. Tarantili and Andreopoulos treated aramid fibers by using methacryloyl chloride due to possible chemical grafting of methacrylic groups on the surface of the fibers on hydrolysis of amide bonds [11]. The chloride-treated aramid fibers were reinforced in the epoxy matrix, and an excellent mechanical interlocking is observed from the morphological evidence. The tensile properties were found to decrease, resulting from etching, whereas the flexural properties have improved, particularly at a low volume fraction of fibers. The enhanced mechanical performance is due to the surface roughening that has improved the fiber and matrix’s interfacial properties.

11.2.3 Interlaminar Properties Delamination is one of the primary causes of the failure of FRP [12]. Thus, identifying interlaminar properties becomes a significant research objective. Interlaminar/Interfacial properties are governed by the nature of the interface between fiber and polymer, which relies on the type of fiber, polymer, and nanofillers. The high-performance synthetic fibers, although possess high strength, however, have smooth surfaces. According to their carbonization temperature, different CF grades are available in the market, such as T300, T700, and T800. Thus, they contain varying amounts of carbon, nitrogen, oxygen content, and functional groups such as carboxylic, hydroxyl, etc. Comparatively, Kevlar and GF exhibit a smooth surface

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leading to poor adhesion with the polymer in the FRP fabrication process. Thus, such fibers require physical or chemical pretreatment to acquire a rough surface before the fabrication step. Modification of fiber surface can be done through plasma treatment, γ-ray irradiation, ultrasonic treatment, chemical grafting, and etching to improve the fiber and matrix’s interfacial properties. However, the methods employed are costly, and the reaction conditions are difficult to be maintained. Besides, the fiber properties deteriorate due to the harsh surface treatment condition. Therefore, Zeng et al. improved the interfacial adhesion of aramid fibers with epoxy matrix by using fiber surface treatment with poly(dopamine) (PDA) and graphene oxide (GO) at ambient conditions [13]. The PDA was self-polymerized onto the surface of aramid fibers where the carboxyl, amine, and catechol groups interact with the fibers to improve the physical properties, and GO is grafted to PDA fibers to increase the mechanical properties between the matrix and the fibers. The IFSS improved by 210%, and the fiber tensile strength increased by 24% compared to unmodified aramid fiber. The surface grafting of PDA-GO onto the epoxy matrix increases the surface reactivity and polarity, besides covering all the untreated fiber flaws. The method modified the fiber surface without any etching or damaging the bulk properties of the matrix. In this section, ILSS, IFSS, and interlaminar fracture modes (I and II) are discussed in detail. 11.2.3.1 ILSS and IFSS

ILSS/short beam strength evaluates the fiber–matrix interaction at the laminate level. Figure 11.4 shows the schematics of the method of short-beam testing. It is described as the mode II transverse shear loading to assess the quality of the interface. The test where the matrix fails before an interfacial fracture is rendered inappropriately. Thus, fiber volume has to be optimum, which allows fiber–fiber rubbing and results in an adhesive fracture as opposed to cohesive fracture at the fiber–matrix interface. While IFSS plays a significant role in describing the load transfer efficiency between the individual fiber and polymer. A good interface ensures stress reduction and improves the threshold of damage initiation, fracture toughness, and overall mechanical performance. The ILSS and IFSS are given by Eqs. (11.4) and (11.5). ILSS = 0 ⋅ 75 × 𝜏(IFSS) =

P bd

P 𝜋Df Le

(11.4) (11.5)

where P is the maximum load at break, b is the width, d is the thickness of the sample, Df is the fiber diameter, and Le is the embedded length. Godara et al. [14] studied the GF/epoxy interfacial bonding with and without modification with CNT. They prepared four types of composites: virgin glass fiber in epoxy (VGF/epoxy), CNT sized glass fiber in epoxy (SGF/epoxy), VGF in CNT dispersed epoxy (VGF/CNT-epoxy), and CNT SGF in CNT-epoxy (SGF/CNT-epoxy). The result indicated that the most effective interface is between CNT sized GF and

11.2 Mechanical Properties of FRP

3

3 2

1

Fibers

Compression

Compression Shear failure (delamination)

Tension

Figure 11.4 planes). Table 11.1

Tensile failure (complete failure)

Tension

Short beam shear testing of FRP composites (1, 2, 3 represent the direction of

Interfacial properties of GF/epoxy and modified systems.

Sr. no.

Sample

IFSS (MPa)

% Increase

1.

VGF/epoxy

57

2.

VGF/CNT-epoxy

75

32

3.

SGF/CNT-epoxy

84

48

4.

SGF/epoxy

109

92

Source: Data from Godara et al. [14].

epoxy (Table 11.1). This is due to the formation of a new tough interface formed by the dissolution of CNT in epoxy. Although SGF/CNT-epoxy has improved IFSS from VGF/epoxy, CNT’s percolation threshold restricts IFSS. This results in the agglomeration and acts as stress-concentrated defect sites in the composites. 11.2.3.2 Interlaminar Fracture Toughness

Interlaminar fracture toughness is tested using double cantilever beam (DCB) specimens in accordance with ASTM D5528-13 [15]. The fracture mode I represent delamination in which two open faces, formed after delamination, move away from each other. Mode II fracture toughness (GIIc ) is determined by using an end notched flexure (ENF) specimen as per ASTM D7905 tested under mode II shear loading [16]. They are quantified by Mode I/Mode II interlaminar fracture toughness (GIC /GIIC ), given by strain energy release rate defined by loss of energy in increasing the delamination length a. −1 dU × (11.6) b da where dU is the differential increase in strain energy, da is the differential increase in the delamination length, and b is the specimen width. GIC ∕GIIC =

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The delamination of laminated composites has been explored by numerous researchers [17, 18]. Bascom et al. [19] reported the delamination studies of glass and graphite fiber/epoxy DCB samples where they concluded that strain energy release rate can be increased by the addition of either the elastomeric hardeners to the epoxy or replacing epoxy with a thermoplastic matrix. Gill et al. [20] explored the impact of the ratio of fiber volume on the mode I and II fracture toughness of the woven CFRP. The mode I and II fracture toughness were found to be directly proportional to the ratio of fiber volume. Also, the fracture toughness of mode II was dependent on the delamination surface friction. Various researchers compared the fiber orientation effect on fracture toughness and concluded that woven CFRP exhibit more fracture toughness than unidirectional CFRP. Therefore, woven GF and CF composites have attracted a lot of research attention [21–24]. Wood et al. investigated the fiber bridging impact on the interlaminar fracture toughness of the woven CFRP using ENF specimens both numerically and experimentally. Mishra et al. [25] studied the influence of Glycidyl isobutyl polyhedral oligosilsesquioxane (POSS) on mechanical properties of CFRP (3K weave and novolac epoxy system). A 70% increase in fracture toughness is observed in POSS reinforced epoxy composite compared to the base matrix. The adhesion between the fiber and resin has increased in the presence of POSS, which was clear with the rise in storage modulus by 13%.

11.3 Influential Parameters on Mechanical Properties of FRP 11.3.1 Influence of Fiber Types The type of fiber reinforcement, its surface properties, and the mechanical performance of virgin fiber directly affect the mechanical properties of FRP. Badawy and Khashaba compared the properties of composite prepared with two fibers: Kevlar (KFRP) and glass fiber (GFRP). It was found that KFRP exhibited a 101.6% improvement in tensile strength due to more toughness of Kevlar fiber [26]. Ek¸sı and Genel [27] also fabricated composites with woven and unidirectional GF, CF, and aramid, and studied the effect of fiber orientation and fiber type. The tensile strength of CFRP was higher than GFRP composites. 0∘ oriented unidirectional fibers are higher than 90∘ oriented unidirectional CFRP. Woven aramid-reinforced epoxy composite exhibited 1.5 times higher tensile strength than woven GF reinforced epoxy composite. This is due to the high elastic modulus of woven aramid-reinforced composite over glass reinforced composite. Pathak et al. [28] fabricated composites by reinforcing carbon nanofibers (CNF) and graphitized graphene (GG) in a polypropylene matrix. CNF exhibited increased flexural strength at 45 wt% as compared to 60 wt% GG. The enhancement is attributed to aligned networks of CNF, whereas aggregation was observed in GG. The concept of hybridization is under buzz, for it expands the flexibility of FRP where the drawbacks of one fiber are overcome by the other. For this reason, natural and synthetic fiber-based hybrid composites are researched extensively.

11.3 Influential Parameters on Mechanical Properties of FRP

Velmurugan and Manikandan reported the influence of palmyra and GF on the mechanical properties of rooflite resin [29]. Composites were prepared by varying the size and content of fillers using dispersion and sandwiched core-skin type. The dispersion technique involves simple dispersion of fillers in the matrix, and in the sandwich model, the palmyra fibers are reinforced in the GF mat and then dipped in the resin. The elongation at break, tensile strength, tensile modulus, flexural strength, and impact strength increases with GF’s content for the sandwiched palmyra fiber than the dispersed. Composites containing 55 wt% GF with 50 mm length attained maximum mechanical properties. The large contact area in the dispersed phase between the glass and palmyra fibers is accountable for the low strength. In contrast, a positive effect is observed for the sandwich core-skin type. Glass reinforced natural hybrid composites and natural fiber composites using abaca and jute fibers variegated together to achieve suitable mechanical strength epoxy resin [30]. The tensile strength, strain at failure, and flexural properties were highest for hybrid glass-reinforced composite than abaca and jute, which is as per the rule of hybrid mixtures and the directional delamination behavior fibers on orientation. The delamination behavior was minimum for the hybrid composite than abaca or jute composites because of fewer voids and uniform load application. The crack propagates swiftly through natural fibers rather than glass fibers, with very little stress transfer from matrix to the fibers.

11.3.2 Influence of Matrix Khandker et al. designed weft knitted fabric based on the concept of “one unity composite,” where the matrix and fibers are based on the same material [31]. These will avoid the mismatch that occurs in conventional matrices consisting of different matrix and fiber materials. To analyze the effect of adhesion with similar and dissimilar matrices, an aramid-reinforced polyamide matrix and an aramid-reinforced epoxy matrix were prepared by employing hand-layup and hot compression molding. The normalized tensile strength of aramid/nylon was comparatively less than aramid/epoxy composites (in the wales direction) and vice versa (in the course direction). The tensile properties of the aramid/nylon composite are comparable to aramid/epoxy in course direction. The high tensile strength of aramid/nylon composites in the course direction was explained from the morphological analysis. Less debonding is observed in aramid/nylon resulting in a higher interfacial bonding among the fibers and the matrix. Masaki et al. [32] compared delamination performance of CFRP in epoxy and thermoplastic polyether ether ketone (PEEK) resin. The fracture toughness data indicates higher toughness of CF/PEEK as compared to CF/epoxy. The fracture surface observed in static and fatigue fracture implies ductile and drawing of resin in CF/PEEK, whereas the brittle fracture is observed in CF/epoxy composites. Toughened laminates with PEEK showed resistance to fatigue crack growth and lower crack growth rates.

11.3.3 Effect of Nanofillers The polymer exhibits a lower modulus than the synthetic fiber/fabric and therefore carries load partially leading to matrix crack. Ultimately, FRP failure occurs due

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(a)

(b) Filler

Polymer

(c)

V

Fiber–matrix interphase

(d)

Figure 11.5 Strategies to enhance interlaminar and interfacial properties (a) nanofiller growth on the fiber, (b) coating filler solution on fabric, (c) dispersion of filler in polymer, and (d) aligning filler in the fiber–matrix interphase.

to the brittle matrix, debonding at the fiber/matrix interface, and fiber fracture. Thus, it is essential to reinforce the interface with toughening agents to attain strong interfacial adhesion. A range of nanofillers such as multi-walled carbon nanotube (MWCNT), GO, graphene nanoplatelets (GNPs), silver nanoparticles (Ag NPs) is incorporated in FRP, which provide a bridging effect between the fiber and resin. Several strategies have been employed to achieve an ideal interface: (i) in situ synthesis of nanofillers on the fiber surface (Figure 11.5a) [33–36], (ii) coating on the fiber surface (Figure 11.5b) [37], (iii) aligning nanofillers in the interface using electric/magnetic field (Figure 11.5c) [38, 39], and (iv) dispersing nanofillers in the polymer (Figure 11.5d) [40, 41]. The low interlaminar fracture toughness of CFRP is a taboo for FRP. A second phase modifier is essential to bridge the gaps between the resin, fibers, and the filler. Size, type of fillers, and the amount the dispersion level have a tremendous influence on the overall matrix’s mechanical properties. Carbon-based nanofillers are a widespread choice for researchers due to their large specific surface area, aspect ratio with good electrical and thermal properties. Quan et al. [42] reinforced thermoplastic veils with GNPs and MWCNTs to prepare carbon fiber reinforced epoxy (CFRE). The interaction between the epoxy and the CF and the fracture toughness of the epoxy improved. The GNP and MWCNT act as a toughening agent for the composite matrix, and the interlaminar thermoplastic veils improve the fracture toughness. The effect of spray time and CNT volume incorporated into woven CF reinforced epoxy matrix by electrospray deposition technique was investigated by Muhammad et al. [43] The CF-CNT epoxy has 21% higher tensile

11.3 Influential Parameters on Mechanical Properties of FRP

strength (641 MPa) than CF-epoxy. CF is nonpolar and inert, which results in weaker adhesion between the matrix and the fiber. Deposition of CNT increases the area between the CNT-epoxy and decreases the area between the epoxy and CF. Besides, tensile modulus, ILSS, and thermal conductivity are increased by 37%, 25%, and 35%, respectively, attributed to the 3D network structure that improves the load and heat dissipation capability. The types of CNTs- single-walled carbon nanotube (SWCNT), double-walled carbon nanotube (DWCNT), and multi-walled carbon nanotube (MWCNT) also affect the interaction with the epoxy and, ultimately, mechanical properties of nanocomposites [44]. SWCNTs have a higher aspect ratio and a larger specific area responsible for more strength, but larger amounts in epoxy lead to agglomeration. Due to the presence of internal layers in DWCNTs, the specific surface area decreases significantly. Thus, in DWCNT and MWCNT, only the outermost layer contributes toward the interfacial adhesion in composites. However, low dispersion of GNP, CNT is still a challenge due to high cohesive force among filler surfaces, which forms entangled structures creating nano defects. These forces could be overcome by various treatments such as ball milling, sonication, and chemical functionalization [44, 45]. GO and its functionalized forms (GO-COOH and GO-NH2 ) have been explored for decades and have proven to be a vital filler in overcoming dispersion issues. GO’s popularity is owed to its high interfacial adhesion with the epoxy, confirmed by density functional theory (DFT) modeling and experimentally [45]. These interactions are due to many functional groups such as hydroxy, carboxyl, epoxide on the GO surface and its wrinkled morphology [46]. Apart from organic fillers, inorganic fillers too are explored. Muralidhara et al. reinforced barium nitride (BN) filler in the epoxy matrix [47]. The CF reinforcement and the BN filler enhanced all the mechanical properties except the epoxy matrix’s impact resistance. The damping capacity, thermal stability, and wear resistance were significantly enhanced for matrix containing BN-1%. At BN-1%, the voids in the CF/epoxy, which cause debonding, are filled, thus enabling higher tensile strength. Xu and coworkers prepared CFRE reinforced clay nanocomposites based on tetraglycidyl-4,4′ diamino diphenylmethane and cured them with diamino-diphenyl sulfone resin [48]. The interlaminar fracture toughness increased by 53% and 85% at 2 and 4 phr nanoclay content. However, flexural strength increased to 2 phr nanoclay content but eventually decreased with a further increase in clay content. Based on scanning electron microscopy (SEM’s) morphological evidence, the matrix without nano clay was smooth, whereas the one with the nanoclay content was rough and made good intact of the fibers with the resin. The protrusions from the fiber surface are accountable for the enhanced fracture toughness in the matrix. Bio-based fillers such as char, lignin, and agricultural waste are in buzz in recent research topics. The introduction of such bio-fillers along with synthetic fibers has significantly participated in improving the mechanical and electrical properties. Matykiewicz [49] introduced biochar as a modifier in CF reinforced epoxy matrix. The storage modulus, flexural strength (275–323 MPa), and tensile properties show a marked rise in their bio-char content values. Tensile properties were best for

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V

V

–I

+I

Substrate (a)

Two-probe method

Figure 11.6 methods.

–I

+I

Substrate (b)

Four-probe method

The electric properties measurement using (a) two-probe and (b) four-probe

biochar (10%), attributed to reinforcing CF, weave, and structure in the epoxy matrix. Besides, thermal stability is also improved with the bio-char content in the fiber-reinforced composite.

11.3.4 Electrical Properties The through-thickness electrical conductivity is measured using impedance spectroscopy, with two probes or four-point probe technique using resistivity meter, as shown in Figure 11.6a,b, respectively. Initially, the surface of the composite is polished until the fibers are exposed. Conductive copper tape is used to establish a link between the sample and the clamp of the instrument. The resistance of the sample is measured in the set range of frequency (100 000–0.1 Hz). Hence, the electrical conductivity is given by L (11.7) 𝜎= AR where 𝜎 is the electrical conductivity, L is the length of the sample in a testing (cm), A is the area of cross-section (cm2 ), and R is the electrical resistance (Ω). The electrical conductivity of composites is an essential aspect of providing lightning current pathways to protect composite airframes in aerospace and aeronautical applications. This is also beneficial in electromagnetic interference (EMI) shielding and microwave absorber material in radar-absorbing applications. In man-made fibers, CF is intrinsically conductive, whereas GF and aramid are insulators. Therefore, their composites are also intrinsically insulated but made conductive by including conducting fillers in an insulating matrix, conducting a matrix, coating the composite surface with a conductive material, and interleaving conductive material laminate [50]. Conventional methods such as metal coatings like aluminum, copper, and nickel are feasible methods to obtain electrical conduction in composites [51, 52]. However, the direct coating is subject to peel off from the substrate. Thus, an interlayer

11.3 Influential Parameters on Mechanical Properties of FRP

of metal is plasma-sprayed before coating. Therefore, to realize significant improvement, various groups incorporated several fillers to establish a new conductive pathway in enhancing the existing electrical conductivities of CF. Qin et al. [53] coated GNP solution on CF when fabricating CFRP and showed a 165% increase in through-thickness conductivity. High percolation of GNPs in fiber resulted in generating a continuous end-to-end conducting network. This is beneficial in structural applications where the dissipation of static electricity is required. Wang et al. [36] reported the growth of spherical and dendritic shape Ag NPs on CF’s surface because of improving electrical conductivities. The spherical Ag NPs loaded CF showed superior electrical conductivity due to the even distribution and formation of interconnected percolation networks on the CF surface than the dendritic Ag loaded CF. CNT is the most sought-after filler to achieve high conductivity in composites. Jelmy et al. optimized hybrid MWCNT/PANI filler content (0.5 wt%) in GF/epoxy composite. A high aspect ratio of MWCNT and its high interaction with amine groups of polyaniline (PANI) provide a continuous pathway for electric conduction [50]. Kumar et al. explored MWCNT in the form of bucky paper and interleaved epoxy impregnated MWCNT bucky paper between the CFRP laminates to enhance through-thickness conductivity [54]. The composites showed 697% and 643% improvement in in-plane and through-thickness conductivity, which worked efficiently against simulated lightning strike tests of 40 kA intensity but deteriorated mechanical performance. The improved conductivity reduced the pyrolysis phenomenon and epoxy evaporation, which is the primary reason for the catastrophic failure of composites upon light strike. Chen et al. reported CNT/CF epoxy composites, where CNT films were prepared by chemical vapour deposition (CVD) technique [55]. The electrical measurements were carried for axially aligned fibers based on the results obtained from the surface resistivity. The surface resistance decreases from 10 MΩ (pure epoxy/CF) to 11.7 ± 0.6 Ω/sq when only two-layer CNT plies were employed and showed an almost 350% decrease in the case of transverse direction. Stacking further reduces the resistivity, and bidirectional stacking causes a considerable increase in conductivity in the transverse direction and a small decrease (10%) in the axial direction. The macroscale architecture of the CNT films, where long and continuous strands allow higher CNT loading (without comprising mechanical integrity) and maintain good connectivity that enhances the electrical conductivity. Apart from in-plane properties, out-of-plane properties are essential to determine both the fiber–matrix interface’s mechanical integrity and electrical properties. Yao et al. reported that on integrating the CNT on CF’s surface by CVD technique, the ILSS and IFSS increased by 30.73% and 32.29% [56]. The dielectric loss is minimized (visible in CFRE). In contrast, the dielectric permittivity is increased with CNT loading that has improved the interfacial polarization and prevents the current leakage, which occurred conventionally in the matrix. Epoxy is a widely explored polymer in FRP composites due to its high strength and stiffness, good thermal and thermo-mechanical stability. However, it suffers from a significant drawback of low electrical properties. In this quest,

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various researchers resort to conducting polymers such as polyaniline (PANI), poly(3,4-ethylene dioxythiophene) (PEDOT), polyphenylene sulfide (PPS), polythiophenes, poly(p-phenylene vinylene) (PPV) with or without dopants [57]. PANI offers a unique combination of good electrochemical response, synthesis flexibility with cost-effectiveness, and environmental stability.

11.3.5 Magnetic and Electromagnetic Properties The magnetic properties of composite samples are assessed by a vibratory magnetometer. The magnetic field is applied in an in-plane (0∘ ) and through-thickness (90∘ ) direction to measure the coercivity and saturation magnetization (SM). Magnetization is the density of dipoles in magnetic material and numerically equals the magnetic moment of a volume unit. Coercivity/magnetic hardness is the field intensity required to reduce the magnetization of a fully magnetized material to zero. It thus measures the resistance of a material to change its magnetization. Figure 11.7 shows the magnetization curve of typical magnetic material. The magnetization in FRP is achieved either through the modification on the surface of the fiber or tailoring the polymer with magnetic fillers. Virgin fibers are either diamagnetic or nonmagnetic. Therefore, fibers are coated with a magnetic

Induced magnetic field

B Saturation

Remanence retentivity

Coercivity

Applied magnetic field

–H

H

Saturation

–B

Figure 11.7

Magnetization curve of typical magnetic material.

11.4 Smart Properties

material such as iron oxide, nickel, or composite coatings like Ni/Fe3 O4 to acquire magnetic properties in composites [58, 59]. The magnetic behavior of composite directly relies on filler’s magnetic quality, weight percentage, and geometric parameters. Yakovenko et al. [60] reinforced the epoxy resin with aligned magnetic barium ferrite (BaM) filler in graphene/epoxy and MWNT/epoxy hybrid composites. The coercivity of the composite, as determined using a vibratory magnetometer, was found to be four times more than BaM powder. The aligned filler resulted in anisotropic magnetization relative to the alignment axis. In contrast, Guo et al. [61] coated Fe/Ni alloy on the CF surface by electroplating. Fe/Ni-CFs displayed soft magnetic performance (SM = 25.5 emu g−1 ). Also, Fe/N-CF composite with epoxy resin prepared by hot-compression molding was homogeneous. Tugirumubano infused a layer of FeSi during the layup of CFRP prepreg to form sandwich structure and reported superior through-thickness SM of 149.71 A m2 kg−1 . The thick layer of magnetic particles uniformly distributed imparted high magnetization [62]. Such properties are useful in electromagnetic actuation for biomimicking natural creature’s snapping motion, such as venus flytrap and building origami structures [63].

11.3.6 Electromagnetic Properties: EMI Shielding Recently, there is a surge in the search for lightweight EMI shielding materials. This is primarily due to the excessive use of wireless communication devices and high-frequency circuits, which cause EMI pollution. These materials are capable of absorbing microwave frequency and thus shield the potential EMI signal. To achieve this, the composite is filled with a filler that serves the dual purpose of high conductivity and dielectric, magnetic properties. The conventional materials include metals and their ferrites, which suffer from the limitation of high densities, causing surface reflections. Nanostructured metal oxides have attracted great interest. α-MnO2 forms a unique tunnel structure due to its crystallographic arrangement. The octahedral close-packed structure can link in different ways to significantly reduce reflection loss (RL) intensity. Hazarika grew nano MnO2 structure on woven Kevlar fabric and achieved an RL of −36.5 dB and 207% absorbed impact energy [64]. The carbon-based fillers such as graphene, CNT, carbon black, graphite, carbon foam, CF exhibit high conductivity and are employed as useful EMI shielding materials due to their high surface area and aspect ratio [60]. In addition to fillers, conductive coatings are also useful in EMI shielding. Das et al. [65] used PANI doped with divinylbenzene to impart EMI shielding property in GFRP and CFRP. Shielding effectiveness reached 17 and 45 dB for GFRP and CFRP, respectively.

11.4 Smart Properties Smart properties refer to the reversible change in physical/chemical properties such as color, optics, shape, and porosity in response to a suitable stimulus such as light, temperature, electricity, magnetic field, etc. These smart features include sensing,

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Healing agent

(a)

Repair Stimuli Recovery force (b)

Figure 11.8 Smart composite fabrication using (a) encapsulation of healing agent in hollow fibers and (b) shape memory assisted self-healing (SMASH) behavior of polymer matrix.

self-healing, self-actuating, self-diagnostic, and shape-changing capabilities, as shown in Figure 11.8 [66]. Among all these, shape-changing materials are in full bloom, for they exhibit the behavior to remember their original shape and return after deformation under the action of a stimulus [67]. The current research and industrial focus are directed to shape memory alloy (SMA) and shape memory polymers (SMPs). The SMPs exhibit advantages such as low cost, low density, a broad range of tailorable transition temperature, high elastic deformation capability, and biodegradability making them dominant over SMA [68–71]. These materials can actuate and alter the system characteristics and response behavior in a controlled fashion. Numerous applications involving smart technology to the physical system are taking over markets, from textiles, automotive, civil, aircraft, and biomedical applications [72]. But this robust scenario sets back with some barriers, mainly because of their low actuation capabilities, lack of actuation control strategies, and reliable database. Therefore, integrated systems are of utmost importance for the current smart systems [73].

11.4.1 Shape Memory Composites Shape memory FRP combines SMP matrix and reinforcement (particles, fibers, platelets, or tubes). SMPs are active materials that can fix from a permanent shape to a temporary shape and regain the original when exposed to suitable stimuli. A combination of a smart polymer matrix and synthetic fiber reinforcement can overcome the drawbacks of the polymer matrix – like the low recovery stress (3 ± 2 MPa) that draws a major set-back during constraint conditions [74]. Incorporating

11.4 Smart Properties

fillers, particularly synthetic fibers, is widely preferred for their wide aspect ratio, contributing to mechanical, electric, and magnetic properties and adds more novel functionalities. Wang et al. prepared a trans-polyisoprene (TPI) based SMP composite with CF-based reinforcement [75]. At 4%, 6%, and 8% CF content, the composite is less coarse; hence ductile mode of fracture is observed. At 10%, 12%, and 14%, the tensile specimen is much coarser, and eventually, the crack size is larger due to aggregation. The maximum fracture stress observed is for the specimen containing 8% CF content. The tensile strength and fracture stress rely on CF dispersibility in the matrix and its mass fraction. The specimen with 8% CF content has the lowest residual strain, and shape recovery more significant than 90% is reported. Recent studies are entirely related to real-time applications. One such study carried by Gong et al. reported epoxy with CF felt as the reinforcement for morphing wings [76]. The prepared corrugated sheet has variable stiffness in response to the temperature. The stiffness obtained is 1.04 ± 0.06 and 0.15 ± 0.03 N mm−1 in the transverse and linear direction based on the force-displacement results. The transverse tensile stiffness is 6.9 times that of T g , indicating an excellent variable stiffness property of the reinforced composite. The shape recovery behavior of aramid-fiber reinforced epoxy composites is reported by Jing et al. for deployable structures [77]. The shape memory fold deploys experiments. The fixed strain of flat and curved tape of the reinforced composite is 99.8% and 99.6%, respectively, as obtained from the finite element modeling. The study showed that the recovery force is due to the modulus of the tape stored in the temporary shape (during shape fixity). The viscosity associated with the reversible phase is the source of resistance during recovery.

11.4.2 Self-Healing Composites Self-healing is a material’s ability to recover from any sort of repair or damage without any human or external intervention. Such material property is very useful in composite structure for marine, aerospace, military, and construction applications, where human reachability is hampered. Self-healing composites involve a combination of fibrous fillers in self-healing polymer or the use of smart fibers [78]. Many novel materials such as polymers, elastomers are designed using strategies such as microencapsulation of the healing agent, reversible physical/chemical crosslinking as the mechanism of self-healing. Hayes et al. reported the self-healing efficiency of diglycidyl ether of Bisphenol A with a healing agent polybisphenol-A-epichlorohydrin in GFRP [79]. A healing efficiency of 43–50% is obtained, and the area of delamination decreases with an increase in GF content in the matrix. Amidated CF is reinforced into the dendritic oligomers, and the self-healing mechanism is based on hydrogen bonding [80]. The elongation at break of Amidated CF (7%) decreased from 450% (Amidated CF 3%) to 103% (Amidated CF 7%). Amidated CF has a self-healing efficiency of 50% and 100% in 20 and 60 minutes respectively. With the rise in temperature, healing efficiency increased,

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almost 100% at 40∘ , which is because the free hydrogen requires time for rebonding; and at high temperature, the free energy of the bond’s increases making it suitable for the recombination.

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12 Thermal Properties of Natural Based Fibers Composites Ashwini Kumar 1 , Arun K. Behura 2 , Dipen K. Rajak 3 , and Pankaj Kumar 4 1 Shree Guru Gobind Singh Tricentenary University, Department of Mechanical Engineering, Faculty of Engineering & Technology, Gurugram 122505, HR, India 2 VIT, School of Mechanical Engineering, Vellore 632014, Tamilnadu, India 3 Sandip Institute of Technology and Research Centre, Department of Mechanical Engineering, Nashik 422213, Maharashtra, India 4 SR University, Department of Mechanical Engineering, Center for Materials and Manufacturing, Warangal, India

12.1 Introduction A compound is a basic substance, which comprises of at least two joined ingredients that are consolidated at a perceptible quantity and are condensed in one another. One ingredient is known as the strengthening stage and the other one that is implanted is known as a lattice. The fortifying stage substances might be given as fibers, particles, or drops. The lattice stage substances are ceaseless. Compound’s substances are ordered into metal matrix composites (MMCs), polymer matrix composites (PMCs), and ceramic matrix composites (CMCs). At the point when the agrochemical gum is utilized as a lattice substance, it is known as an agrochemical grid compound. Agrochemical compounds are having characteristics such as small thickness, great electrical and thermic encasing, and ease. MMCs and PMCs are ordinarily utilized in a better way. The agrochemical grid compounds comprising of agrochemical (e.g. superglue, inelegant) are strengthened through fibers. The alloy grid compounds have an alloy lattice. Alloys are chiefly strengthened to increment or diminishing the characteristics. In the agrochemical network compounds, the glass is utilized maximum in fiber due to its elevated quality, ease, elevated substance obstruction, and simple accessibility. Enthusiasm for natural fibers has expanded worldwide due to their minimal effort, low thickness, hardness, great thermic and mechanical impedance [1], and due to its ecological agreeableness [2]. Vegetable fibers have replaced non-regular fibers which have a ton of points of interest that can be legitimized by natural adjustments. On the occasion, alfa [3], hemp [4], kenaf [5], coir [6], oil palm [7, 8], or sisal fibers [9] have mechanical characteristics, which can legitimize its employments in numerous implementations. Yet, additionally, it represents a few disadvantages as a Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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result of their low pliancy [10]. In any case, this can be evaded by going along with accompanied characteristic or engineered agrochemicals to capitulate thin compound substances accompanied by the necessary mechanical characteristics. To exploit the whole advantages of compounds determined from common fibers, it is important to accomplish a decent bond between the fibers and the agrochemical network. Naturally, fibers are hydrophilic while the network is hydrophobic, consequently making a bond issue between both. Accordingly, the objective of support may not be achieved if the fibers cannot make joins with the grid [11]. To this end, numerous investigations completed pointed toward improving the union among fibers and networks [12, 13]. The utilization of compound treatment impacts the fiber network bond and uncovered amazing interfacial grip characteristics of the fiber and the grid [11]. This quickens the mechanical utilization of this fibers everywhere on the globe. Also, build them appropriately relevant for a car factory, development, aviation, bundling, etc. [13, 14]. A great deal of work is never really a bit of leeway of the broad reach in the characteristics of normal fibers. Furthermore, to accomplish mechanical [15, 16]and thermic characteristics [17], these examinations are centered on shifting the fiber ingredient [6], utilization of the synthetic care, and the decision of the agrochemical lattice [18–20]. For example, it is discovered that a few mechanical characteristics as Young’s modulus expanded inconceivably accompanied by expanding fiber stacking [13]. This tends to be likewise citing a few instances of inconstancy of compound medicines utilized in the writing, like polyethylene imine (PEI) a fiber care, to enhance mechanical characteristics of compound [19], the EDTA corrosive ethylene–diamine–tetraacetic a fiber care, which affected the pressure crack of the composites [19]. Numerous other significant investigations were unquestionably catalyzed to common fibers, e.g. Doum, to create mechanical utilizations of fibers. The Doum fibers are customarily utilized in building canvas, mash, paper, ropes, and lately for protection and carpets [20–22], these have been chosen in this investigation as support in LDPE not just because of their great quality and resistivity [21], but in addition to a specific situation of valorizing a bountiful yet unexploited fibers in Morocco. Albeit, natural fibers are additionally described as biodegradable, recyclable, as well as, lignocellulosic strands; notwithstanding, recent examinations have recognized them as the best option in contrast to trustworthy financial aspects and furthermore, normal security [23]. Lignocellulosic fibers have numerous inalienable focal points such as smooth in identity, less vitality utilization, elevated aspect proportion, less thickness, less price, and ecological when contrasted with engineered fibers [24–26]. Although the manufactured strengthened polymer composites have higher mechanical properties in contrast with the characteristic fiber, they have a significant impediment of being a natural toxin and non-biodegradable material [27]. The developmental use of composites depends on the outfit investigation of elevated explicit solidarity heaviness and explicit solidness heaviness proportions of compound [28]. Aside from this explicit characteristic, for example, mechanical, somatic, thermic, and electric characteristics [29], another basic perspective required to be engaged is a biological-clock assessment of the items. Additionally, the ecological worries of its creation are expected to lessen the negative effect. This is additionally

12.1 Introduction

value contemplating, which the world has preceded toward sustainable and recycled substances [23, 30]. The normal fibers and thermosetting lattice are utilized immensely in vehicle areas for different small and weighty implementations, for example, entryway boards, seat backs, main events, bundle plate, dashboards, inside parts, etc. [31–33]. The market concentrates on worldwide normal fiber composite materials delivered by Lucintel [34] that assessed the market development at a compound annual growth rate of 8% from 2015 to 2020. There are a few huge business sectors, such as the EU and another significant car producer, which offer need to the biological basis strengthened composites for worldwide supportability. The car enterprises have perplexing and exact structures with more than 40 000 little and large pieces of almost 1000 different materials; furthermore, 10 000 materials. Out of all substances, 75% establishes alloys, 17% of substances are pliants, and the remaining are rubbers and materials. Industrially, compound substances are successful in semi-structural implementations and later, non-basic (makeup) motivations; be that as it may, the physical furthermore, thermal soundness are the significant requirements [30]. Further, the use of biomaterials is limited because of its heterogeneous qualities against the homogeneous and extremely exact manufactured fibers [35]. These biomarkers can be adjusted through compound care and get consistency associate holding of fibers and grid, which will eventually enhance the thermic opposition and mechanical characteristics of compounds. Despite plane alteration increments (the preparing price), it enhances the nature of compounds, which lessens the prudent intensity of the normal fiber compounds [36]. Notwithstanding, the decision of characteristic fibers is yet the theme of broad examination on every side of the globe. Throughout the removal of agrochemicals, few fundamental characteristics are concentrated through analysts and producers on thermosetting, what’s more, fused practices, restoring temperature, and dissolving temperature. Celibate agrochemicals as a rule have solitary and explicit kind of compound shape, thus comparable essential properties have been found. In any case, common strands are altogether different from one another regarding constituent animal types; even comparable fibers have various creations because of geology and atmosphere. In this manner, every fiber is needed to be read for this characteristic just as its conduct directly utilized as a strengthened substance. Common fibers comprise of numerous small compound structures that influence their associate holding accompanied by agrochemicals. Thermic characteristics of common fiber-strengthened compounds are a significant oblige in its implementation. At elevated temperatures, the fiber segments, similar to lactose, polyose, and phenolic start corrupting and the significant characteristics of composite exchange. The reasonableness of characteristic fibers accompanied by agrochemicals furthermore, elevated temperature dependability has been read for a few many years, however, the strength of characteristic fiber with various kinds of polymers, two distinctive natural fibers strengthened agrochemical compounds or characteristic fiber strengthened mixed accompanied by two distinct agrochemicals are expected to arrange data by relative examinations. This examination helps scientists’ selected strengthened substances and networks for the need of thermic dependability. A whole report is expected to comprehend the thermic impacts on characteristic

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fibers and their composites. Until now, no investigations have given an account of the thermo-gravimetric investigation of natural fibers and their compounds. This chapter is roused to arrange all past examination take a shot at the impact of temperature furthermore, its impact on fiber weight reduction and its qualities.

12.2 Natural Fibers Natural fibers are created through herbs, nature, and geographical processes. These can be used as a segment of compound substances, where the regulation of fibers affects the characteristics. Common fibers can also be entangled into linens to build a wrapper. The recent evidence of individuals using fibers is the disclosure of dupe and shaded fennel fibers established in an earliest black out the Republic of Georgia, which move backward to 36 000 BP [37, 38]. Natural fibers can be utilized for cutting extremity implementations, for example, compound segments for motors. Contrasted with composites reinforced with glass fibers, composites with characteristic fibers have points of interest, for example, lower thickness, better thermal protection, and diminished skin disturbance. Further, unlike glass fibers, characteristic fibers can be detached through invisible entities when they are not, at this point being used. Natural fibers are acceptable transpiration swabs and can be established in a variety of planes. Fawn fibers generated utilizing the fawn herb, for the occurrence; generate consistencies, which are small in mass, fine in a plane that can be built in various shapes and tones. Outfits built of natural fibers, for example, the fawn is commonly favored over attire built of synthetic fibers through discrete existing in balmy and adhesive climates. Natural fibers, such as jute, coir, sisal, bamboo, etc., are sustainable, modest, biodegradable, and climate neighborly materials. Fibrils from herbs, for example, banana, ramie, jute, sisal, pineapple, hemp, bamboo, cotton, etc., just as timber and nuts of fennel are utilized as the support in agrochemical framework compounds. Its accessibility, less thickness, and cost just as good mechanical characteristics, build them alluring fortification to carbon, glass, and supplementary synthetic fibers. Although glass fibers have high explicit quality, their fields of utilization are extremely restricted due to their innate greater expense of creation. Natural fibers, for example, sisal jute fibers are supplanting the carbon and glass fibers because of its simple accessibility and price. Table 12.1 shows some significant farming harvests and their individual synthetic structures. At the point when the temperature is applied, it brings about an assortment of somatic and substance exchanges, which eventually decide the characteristic. The common fibers, such as H2 O, sisal, Roselle, reed, and hyacinth contrast, are in their disintegration temperature. To assess the conduct of thermal corruption, the temperature range was inspected somewhere in the range of 290–490 ∘ C [41]. The introductory mass reduction was noted in the temperature span somewhere in the span of 50 and 100 ∘ C because of the dissipation of H2 O particles. Additionally, the mass reduction was established in the temperature scope of 200–350 ∘ C because of the debasement of hemicelluloses, however thermic humiliation of phenolics and hemicellulose were in the temperature scope of

12.2 Natural Fibers

Table 12.1

Chemical characteristics of fructose-based common fibrils.

Fibrils

Dextrose

Phenolics

Polyose

Jelly

Cinders

Moisture content

Wax

Fennel

71

2.2

18.6–20.6

2.3

—

8–12

1.5–3.3

Kenaf

31–72

15–19

21.5–23

—

2–5

—

—

Jute

45–71.5

12–26

13.6–21

0.2

0.5–2

12.5–13.7

0.5

Hemp

57–77

3.7–13

14–22.4

0.9

0.8

6.2–12

0.8

Ramie

68.6–91

0.6–0.7

5–16.7

1.9

—

7.5–17

0.3

Cissus quadrangularis

77.17

10.45

11.02

—

—

7.3

0.14

Bang

55–62

8–10

14–16

—

5–10

—

Hemp

46–77

8–12

11–25

10

Rugs

76.9

12.9

5–9

—

—

10–22

2

—

—

Source: Adapted from Indran and Raj [39]; Asim et al. [40].

300–450 and 200–300 ∘ C, separately. Because of polyose and phenolics, around 60% of the thermic deterioration of common fibers happened in the temperature scope of 230 and 350 ∘ C [42]. The underlying disintegration of the segments may clarify the less thermic security [41]; notwithstanding, rust decay, portrayed through quick mass reduction at elevated temperatures, is additional steady accompanied by thermic dependability [43]. A point-by-point depiction of thermal debasement of different natural fibers at various temperatures has been represented in Table 12.2. The thermo-gravimetric conduct of natural fibers straight forwardly relies upon their compound constituents. Comparable characteristic fibers, such as sisal, jute, fawn, and wood, have comparable DTG/TG bends and thermal deterioration design. The main phase clarifies the dissipation of dampness pacify at less temperature, the subsequent phase is the deterioration of polyose at forum temperature and the last phase shows the decay of phenolics and cellulose at elevated temperature. At times, the main phase does not show up because of extremely low dampness substance or least weight reduction and displays the second stage as the main stage [44, 45]. A few scientists [46, 47] have examined the vanishing of dampness substance to 200 ∘ C as starting mass reduction that relates to a greatest mass reduction of 10%. The second phase of corruption represents the deprivation of mass of over 70% of starting load at a temperature of around 500 ∘ C. The third phase speaks to the furthest limit of thermic debasement and ensures, which all the segments of common fibers are thermic corrupted at a temperature approximately 800 ∘ C and the last staying weight arrives at 20% of the underlying load as debris and single contentment.

12.2.1 Natural Plant Fibers The cells of plants are encircled by an inflexible cell divider, and this is the primary trademark recognizing them from stalls in creatures. Within certain kinds of stalls,

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Table 12.2

DTG Information of solid fuel specimens. Stage-I

Stage-II

Fibers

Peak temperature (∘ C)

Range of temperature (∘ C)

Fructose

339

301–362

Phenolics Amande shell

0 299

T Peak (∘ C)

0

Range of temperature (∘ C)

0

0

549

451–602

251–392

479

401–722

Briquette

343

260–400

509

410–550

Brick nugget hull

312

225–350

627

425–634

Joe nugget hull

319

220–360

502

440–634

Bud

289

250–340

454

400–550

Frond of pineapple

344

250–380

496

420–570

Corn hull

334

260–360

450

400–540

Holy clover

301

230–330

456

390–522

Jungle trimming

334

260–370

538

400–760

Prickle

345

240–400

473

420–550

Wheat straw

312

260–360

543

420–650

Source: Data from Álvarez et al. [44].

the stall dividers are expanded to have prevalent mechanical characteristics that give the necessary basic execution of the plants. The components of these supposed fibers change between various plants; however, their general shape is regularly extended accompanied by the extents in the span of 1–35 mm and distances across in the reach 15–30 mm. Within the viewpoint of compound support, this is smarter to assemble the fibers through its spans. 1. Small fibers (1–5 mm), starting normally from timber and non-wood condiments and regularly utilized for building compounds accompanied by in-surface isotropous characteristics, that is, compounds accompanied by a vague (irregular) fiber direction. 2. Long fibers (5–50 mm), starting normally from non-wood yearly plants breeds (e.g. fennel, jute, hemp) and ordinarily utilized for building compounds accompanied by anisotropic characteristics, that is, compounds accompanied by a particular fiber direction. Additionally, regular plant fiber comprises of the following: (i) Seed hairs – These are strands gathered from seeds or seed cases such as cotton, kapok, coir, and poplar seed. The most significant seed fiber is cotton that has properties that license them to be spun into string or stuffing. (ii) Bast fibers – These fibers are obtained from the bark of cotyledons, which incorporate herbaceous plants, bushes, and trees (hardwood, softwood, and reused wood); (iii) Leaf fibers – These fibers are obtained from the vascular packs of long leaves of certain monocotyledons. Leaf fibers are otherwise called “hard” strands since they are more lignified than bast fibers; (iv) Grass fibers – These are

12.2 Natural Fibers

Natural fibers (plants)

Non-wood

Seed fruits Cotton Linter Coir Milkweed Kapok

Figure 12.1

Bast Flax Hemp Ramie Kenaf

Wood

Leaf Pineapple Abaca Henequen Sisal

Stalk Wheat Rice Kenaf (core) Barley Corn Rye Oat Maize

Grass

Soft wood and Hard wood

Bamboo Bagasse Esparto Phragmites Sabei Communis Reed

Graph for natural plant fiber classification.

another gathering of monocotyledonous strands, where the whole stem along with the leaves are pulped and utilized in papermaking. Such pulps are made of fibers along with other cell components [48] (Figure 12.1).

12.2.2 Resins The resins/tars, which are used in fiber strengthened compounds, can furthermore be suggested as “agrochemical.” All agrochemicals display a significant regular characteristic in which they are building out of lengthy chain-like atoms incorporating many basic restating components. Artificial agrochemicals are for the better segment known as “phony saps” or fundamentally “pitches.” Agrochemicals can be arranged in two types, that is, “laminate” and “thermoset,” as indicated by the effect of thermal on its characteristics. There are three sorts of pitches utilized in the compound substance factory, for example, Superglue paste, inelegant gum, and bootleg ester resins.

12.2.3 Fillers Lining substances are the dormant substances that are utilized in common fiber strengthened compounds. For adjusting the compound and somatic characteristics of the grid agrochemicals to diminish substance expenses enhance process ability and enhance item execution. Lining shapes the expansion solidarity to the mechanical and thermic characteristics of the compound substance. Within this lining, silicon carbide is one of the linings accessible. The SIC, when utilized as support, will build the characteristics such as Young’s modulus, extreme elasticity, rigidity, hardness of the composite materials. Within another investigation, the thermic conduct of jute fiber studied for antacid jute fibers, and extraordinary pinnacles of respective fibers were watched [49]. The not-cared fibers uncovered two pinnacles: the main 300 ∘ C and the second pinnacle that was noted at 365 ∘ C demonstrated the thermic

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debasement of cellulosic contentment. Thus, fructose accords the significant bit of common fiber, the subsequent pinnacles assume an incredible part in weight misfortune. The wide top in all the reach speaks to the presence of lignin [49]. In salt-treated fiber, in contrast to untreated fiber, just one pinnacle showed up at less temperature contrasted with the second pinnacle of not-cared fiber. The first top didn’t show up in treated fibers because of halfway evacuation of phenolics and polyose. The additional corruption of the complex model of phenolics and polyose was uncovered, yet at the less temperature of the second pinnacle when analyzed to not-cared fibers [50]. The thermic characteristics of the ocotea fiber were explored, what’s more, the underlying weight reduction of 5% was seen at 221 ∘ C, what’s more, in the second thermic debasement, and a significant mass reduction at 379 ∘ C was accomplished accompanied by a 64% decrease in weight [51]. Moreover, the deliberate outstanding build-up of all-out weight was just 14% and was established at approximately 990 ∘ C. The thermic characteristics of the ocotea fibers uncovered the manageability of temperature up to 221 ∘ C that can be used effectively the place at the greatest temperature is under 221 ∘ C. A few jobs revealed that common fibers were consolidated in agrochemicals as support and contemplated the primary phases of mass reduction because of support and impact on the thermic soundness of compounds. By the use of TGA, the thermic corruption measure of compounds can be examined and the acquired boundaries to decide the level of corruption of substances [52]. Yao et al. [42] contemplated the corruption temperature of various common fibers for near investigation. The thermic characteristics influence the analysis of common fiber-strengthened compounds fundamentally. Contingent upon the temperature, the compounds extend or agreement, making breaks in the compounds, which inevitably hold wetness. The common fibers grasp up dampness by capillary activity, seeding thickness expanding in compounds [53]. Fructose-strengthened polythene composites were utilized by the blight cycle that enhanced the combined holding of fructose and grid and positively affected thermal debasement [54]. Another trial on non-cared and silane-cared sisal fibers was completed and debasement temperature and weight misfortune were determined [55]. The weight reduction of 5%, 10%, and 0.5% was noted at 83, 255, and 360 ∘ C, respectively, for non-cared fiber; and for saline-cared fiber, the weight reduction was noted at 100, 278, and 365 ∘ C, in the expressed request. The polyose of sisal fibers was thermally debased at 297 ∘ C and lactose contentment was corrupted as uncovered in the second phase at 365 ∘ C.

12.3 Thermo-gravimetric Investigation Thermo-gravimetric investigation is a quality strategy to analyze the general thermic security of characteristic fibers. Within these techniques, the thermic debasement of common fiber composites accompanied by expanding the temperature is concentrated alongside the mathematical computation of value corruption. At the point when the temperature builds, the heaviness of the fiber drops gradually, and at the purpose of glass progress mass reduction pointedly atop a tight reach lastly

12.3 Thermo-gravimetric Investigation

turns around to nullify inclines as the impetus is depleted. The debasement cycle in the thermo-gravimetric investigation can be introduced in the bend that is subject to the motor boundaries of the cineration, for example, recurrence component, response request, and enactment vitality. The worth of the bend relies on different factors, such as test mass, test shape, air, stream charge, rate of heating, and the numerical care implemented. The result of differential thermal analysis speaks to the response of temperature accompanied by the example and the response rate per minute is demonstrated through the diversion or pinnacle. Within a solitary part try, if the temperature of response shifts, the top differs regarding temperature just as the vitality of enactment. The distinction in top temperature decides the enactment vitality for the responses accompanied by various response sequences [56]. Within the thermic debasement, the thermo-gravimetric investigation and subordinate thermo-gravimetric bends decide the mass reduction and recognize the decay of substance at a specific temperature separately [54].

12.3.1 Isothermic and Non-isothermic Thermo-gravimetric Investigation Thermo-gravimetric investigation is called for the thermic corruption of substance accompanied with regard to time and temperature and for deciding the last build-up to break down the thermic soundness. Within the isothermic procedure, the temperature in the heater is steady and debasement or then again disintegration of weight is estimated accompanied by time. Within the non-isothermic procedure, the rate of heating is steady and mass reduction is estimated as for temperature and time, and weight versus temperature or weight refrains time bend is created. Isothermic and non-isothermic procedures contrast in the suspicion of characteristics and cycle of information assortments. These distinctions in information, because of its particular technique, give extraordinary data. The isothermal active examination anticipated the thermal decay of polyose, fructose, xylan, and phenolics [57]. The non-isothermal strategy is utilized for the pyrolysis tests that assist to contemplate the connection of weight misfortune stanzas time. The technique likewise assists with deciding the actuation energy which gives various outcomes. Nevertheless, the isothermal cycle of thermal corruption is utilized for plotting a regular log of response amount in opposition to the reverse of temperature. Within these mapped decrease techniques, the motor boundaries are acquired from the incline and capture of the coming about the direct condition. The information of non-isothermic analysis is likewise utilized to plot a condition in a direct way, where the linear edge speaks to the initiation vitality and response request. Isothermal what’s more, non-isothermal techniques need distinctive information to study the active boundaries [58]. Rather than a blunder, sole rate of heating techniques or non-isothermic strategy is extremely mainstream for dissecting the strong phase energy. There are different approaches to examine the sole rate of heating strategies such as MacCallum–Tanner condition, Madhusudana–Krishnan–Ninan condition, Van Krevelen technique, Coats–Redfern technique, Horowitz–Metzger condition, etc. [59].

219

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12.3.2 Equation of Coats–Redfern Equation (12.1) of Coats–Redfern condition has a few impediments in the count of initiation vitality and pre-enormously factor, which is impossible and absent of pre-presumption of the response structure. This is suggested, which you accept the underlying estimation of the response request is “n” and locate the right estimation of the dynamic boundaries till the finest linear strand is gotten, or the mistake is not exactly the resistance esteem [60]. )( ] [( [ )] g(𝛼) 2RT E AR 1− − (12.1) = ln ln 2 𝛽E E RT T Since 2RT ≪ 1 in the temperature span generally utilized, the expression )] [( ) (E 2RT 1 − in Eq. (12.1) is reasonably steady. Subsequently, the slant of ln AR 𝛽E E [ ] g(𝛼) 1 the plot of ln T 2 versus − RT will be equivalent to E, and the estimation of the pre-exponential element can be determined through likening the capture of the . These response structures can be sourced from diverse condition equivalent to AR 𝛽E active boundaries accompanied by similar test information. The subsequent bend for the significant information from each expected structure represents the measure of initiation vitality.

12.3.3 Equation of Horowitz–Metzger ) ( ARTs2 E E𝜃 − ln(g𝛼) = + 𝛽E RTs RTs2

(12.2)

Actuation energy esteems can be determined from the graph of ln(g𝛼) against 𝜃, E which incline will be equivalent to RT . The significant burden of this strategy is its s reliance on top temperature, T S , which worth relies upon the heating rate and test weight [60].

12.4 Choice of Substance Based on TGI While getting ready the latest substances, the decision of crude substances, creation method, and eventual outcomes are similarly significant. For hard core use, the material ought to be precisely solid and thermal steady too, because hotness from mechanical vitality can decrease the stacking limit. Within these cases, TGI assists with knowing the thermic characteristics of the substance and assists with understanding the reasonableness of the material. TGI assists a lot when auxiliary accuracy is needed in items. After the examination of TGI, it has been concluded that many machine parts are fundamentally steady. It tends to be guaranteed that at which temperature the substance will exchange their stage. A few explore dependent on hibiscus fiber and a frond of pineapple fiber-strengthened agrochemical compounds have been executed on the thermic characteristics and discovered the T g .

12.5 Common Fibril-Strengthened Compounds

An exploration in light of hibiscus fibril and a frond of pineapple fibril-strengthened high-thickness polyethylene [61] was contemplated and analyzed with hibiscus fibril and a frond of pineapple fibril-strengthened lignin compounds [62].

12.5 Common Fibril-Strengthened Compounds 12.5.1 Thermosetting Compounds Numerous scientists have considered different regular fiber-reinforced-based compounds and portrayed their characteristics. Out of every one of these portrayals, the thermic characteristics of fiber-strengthened thermosetting agrochemical compounds are one of the basic highlights, broken down by utilizing thermo-gravimetric examination. The thermic conduct of crude strands of phormium and their reinforcement compounds was investigated by the TGI strategy [63]. The underlying weight misfortune in crude fibers of phormium was noted 8% in the middle of 37 and 130 ∘ C because of dampness contentment exist in the fiber center. Fiber thermic debasement started among 200 and 305 ∘ C, demonstrating that thermic debasement was brought about through discontinuity of fructose glucoside links and depolymerization of polyose and gelatin [64, 65]. The most elevated thermic debasement of common strands was noted at 305–370 ∘ C because of the corruption of fructose contentment. The corruption temperature of phenolics has a broad reach in the middle of 200 and 900 ∘ C because of the multiplex fragrant model of phenolics accompanied by different splits [64–66]. The bend of DTG of phormium-strengthened compounds was gained at 347 ∘ C that is the most noteworthy out of all characteristic fibers and lattice compound. The thermic debasement temperature of common fibers and network are 337 and 347 ∘ C, separately. Another investigation related to the jute fiber-strengthened vinyl ester compounds, which showed a thermic degradation of compounds happens in two stages [50]. The principal corruption footstep showed the disintegration of characteristic fibers at 368 ∘ C; notwithstanding, the subsequent debasement footstep spoke to the decay of lattice. The thermic debasement of compounds was learned at different rates of heating and established modest variety. The thermic solidness was enhanced accompanied by expanding the thermal rate. The relative investigation of lingering measure of grid, fiber, and compounds uncovered, which the remaining measure of compounds is in the middle of that of the grid and fibers. Thermic characteristics of cared and uncared coconut scabbard fiber-strengthened superglue compounds were examined [67]. The underlying weight misfortunes were expected to the disappearing of negatively charged anion gatherings and additional thermic corruption because of corruption of polyose at 100, 105, 230, and 300 ∘ C separately. The last thermic corruption was exposed to the corruption of fructose and superglue at the temperature of 300–400 ∘ C. The lingering sum of cared compounds was not as much as that of the uncared compounds since roast capitulates rely upon the accessibility of phenolics in the strands. This showed that care of characteristic fibers halfway eliminated phenolics and provoked the scorch

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contentment to be not as much as that of the uncared compound [67]. A near investigation of thermic characteristics of jute and bamboo compounds was done and mass reduction at different temperatures was estimated by TGI bends [68]. Introductory mass reduction close to 100 ∘ C is because of the negatively charged anion bunch existence in bamboo and jute fibers. The two composites were debased thermally in the temperature scope of 240–260 ∘ C. The precise thermic debasement of jute compound was noted at 255 ∘ C; be that as it may, the bamboo compounds were debased thermally at 246 ∘ C. An examination dependent on chaplet date fiber superglue compound at different fiber delivering was done to investigate the thermic characteristics by TGI investigation [69]. The underlying misfortune in the scope of 60–100 ∘ C means that the existence of negatively charged ions bunches in superglue compound. Additionally, this was seen that the existence of H2 O particle in the cell divider model or null area and the H2 O retention at the fiber–lattice associate holding [70] demonstrate the limiting mechanical quality of regular fiber compounds [71]. Additionally, the fiber stacking of 40% superglue compound and half superglue compound displays the thermic corruption at 300 and 317 ∘ C respectively. In any case, the remaining level of unadulterated superglue, 40% superglue compound, and half superglue compound were 9.59%, 12.52%, and 19.82%, respectively. The remaining sums were expanded accompanied by increasing the fibers in compounds; however, 61% fiber stacking diminished the remaining sum because the grid was smaller and could not carry the strands appropriately. The thermic characteristics of superglue compounds uncovered that its characteristics are essential because of the heating decay of polyose, phenolics, gelatin, and the nucleotide connection of fructose of characteristic fibers [72]. Thermic conduct of lignin sap, uncared and saline-cared PALF and hibiscus compounds at different fiber consignments were examined [73]. Hibiscus and PALF composites uncovered that mass reduction under 101 ∘ C compares to the accessibility of negative charged ions bunch in all characteristic fiber-reinforced composites [45, 74]. An unadulterated grid didn’t represent the mass reduction in the beginning and a solitary phase thermic debasement was noted at 421.73 ∘ C accompanied by 33.16% mass misfortune. The thermic debasement of the framework relies upon the dihydroxy lignin methane elements accessible in the lignin bunches [75]. Uncared PALF and hibiscus compounds demonstrated the principal phase of heating corruption at 283–304 ∘ C, nonetheless, cared PALF and hibiscus compounds uncovered the introductory phase of corruption at 294.14 and 306.41 ∘ C, respectively. The underlying thermic humiliation was started because of the presence of a few integrals in common fibers, for example, glucoside connections of fructose, gelatin hemicellulose what’s more, and lignin [76]; nonetheless, thermal depolymerization of polyose and separation of the glucoside’s connection of fructose of treated compounds enhanced the thermic security [77]. The temperatures of conclusive thermic debasement of PALF-strengthened compounds and hibiscus-strengthened compounds were noticed somewhere in the range of 388.7 and 422 ∘ C and 408.58 and 447.99 ∘ C, individually, as a result of the thermal debasement of α-cellulose and depolymerization of the framework [54, 55].

12.5 Common Fibril-Strengthened Compounds

12.5.2 Laminate Agrochemical Compounds Few jobs gave an account of the manufacturing cycle of natural fiber-strengthened thermoplastic composites, what’s more, their properties, for example, somatic, mechanical, thermic, electrical potential, and flak retardancy. Of the apparent multitude of characteristics, thermic characteristics are one of the better significance for the temperature resistance of compounds. The needle of Pineapple fibers and belladonna seed hull-strengthened PP half-breed compounds were learned at different fiber feelings accompanied by equivalent fiber proportion in half-breed compounds [78]. The TGI bend of the half-breed compound of all-fiber feelings uncovered that negatively charged ions bunch origin introductory mass reduction under 101 ∘ C. Mixture compounds accompanied by 6% and 14% fiber stacking uncovered that their thermic debasement happens approximately 226–359 ∘ C also, 224–375 ∘ C, individually, though 11% fiber stacking mixture compound displayed, which its decay is near 251–411 ∘ C. Within another investigation, the fennel compounds copolymerized accompanied by grind MAPP of kind A were concentrated by DTG and TGI and it worked out that the thermic debasement was three-phase. The principal phase of thermic debasement is expected to the existence of H2 O particles, the subsequent debasement is expected to polyose and fructose, and the last phase is due to the existence of phenolics [79]. The DTG bends didn’t represent any roasting top at 501 ∘ C. Notwithstanding, the compounds indicated two particular tops in the scope of 369.5–374.98 ∘ C also, 433.4–482 ∘ C that demonstrated the pace of thermic degradation of fennel and PP, individually [80]. Other investigations on hibiscus-strengthened thermosetting polyurethane (TPU) composites indicated thermic characteristics by TGI bends [81]. The underlying mass reduction was noted at approximately 9.6% in the temperature scope of 32–154 ∘ C, which indicated elevated dampness contentment in hibiscus fibers. Additionally, weight misfortune was noted at 195–331 ∘ C because of the corruption of polyose and fructose and finally, corruption was noted because of phenolics contentment at 306–387 ∘ C. The thermic debasement of unadulterated TPU appeared a broad scope of temperature from 251 to 538 ∘ C. The DTG pinnacle of TPU debasement at 364 ∘ C was because of the polymerization of the prepolymer–isocyanide connection. When the temperature is gained, the isocyanide is dissipated and dense once more into fumes, yet the pre-polymer is the equivalent and disintegrated at elevated temperatures [82]. This is likewise seen, which expanding the fiber stacking in TPU diminished the thermic strength more than those of unadulterated TPU. Thermic debasement of characteristic fiber-strengthened TPU compounds uncovered drying out at an introductory temperature and indicated heating separate of glucoside connection through trans-methylation and division of C–C and C–O links at fewer temperatures. Thermic debasement at elevated temperature was credited to the scent, including drying out responses [81]. The thermic characteristics of unadulterated LDPE and characteristic fiber-strengthened LDPE compounds were examined by utilizing TGI [83]. The underlying weight misfortune in the middle of 101 and 151 ∘ C indicated, which fibers have dampness contentment. Expansion of strengthened substances decreased the thermic security also, the gingerbread

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fibers and LDPE framework demonstrated elevated shear quality and frictional powers which forestalled the breaking of LDPE bonds, which enhanced mechanical characteristics [84]. The thermic characteristics of pine strands, PP grid, and pine fiber-strengthened PP compounds were breaking down through the TG method [85]. The pine strands demonstrated thermic degradation at two temperatures: the underlying thermic debasement was noted in the scope of 221–281 ∘ C because of the debasement of polyose; be that as it may, the second phase of thermal debasement was uncovered in the scope of 281–301 ∘ C because of debasement of phenolics and fructose [86]. In the wake of the fuse of pinus cone fiber in PP, the debasement temperature diminished from 356 ∘ C for slick PP to 322 ∘ C for a 26 wt% pinus cone-strengthened PP. DTG delineated, which is suitable for influenced the thermic soundness when contrasted with fiber/PP compounds without suitability. Thermic characteristics of curaua fiber-strengthened elevated-thickness polyethene composites were concentrated within the sight of two distinctive integrating operators [87]. The TGI consequences of unadulterated HDPE demonstrated less steadiness than the composites. Different composites consisting of integrating operators of PE-g-MA demonstrated the smallest thermic strength. Notwithstanding, accompanied by another integrating operator, (poly(ethylene-co-vinyl acetate)), this was better steady. The most un-thermic strength was disclosed because of superior bond holding in the middle of the corrosive gatherings of the hydrazide anhydride and the negative OH bunches on the fiber planes. The superior connection may advance debasement measures [87]. The thermic humiliation of uncared and cared HDPE/jute compounds was considered [88]. The total deterioration of unadulterated HDPE was seen at 431–516 ∘ C. For the 31% fiber stacking of jute-strengthened HDPE, the underlying deterioration was somewhere in the range of 304.7 and 382 ∘ C because of parchedness furthermore, thermic division of glucoside connection through transglycosylation furthermore, breakage linkage of C—C and C—O bonding. The second thermic corruption was seen in the middle of 453 furthermore, 531.7 ∘ C because of scent. Another scientist also discovered a similar pattern for PALF-strengthened HDPE compounds [89]. The cared compound was disintegrated at 365 ∘ C because of heat discontinuity and division of C—C and C—O bonding. The significant corruption was identified in the middle of the scope of 478.5 and 597.78 ∘ C which was nearly equivalent to that of the uncared HDPE/jute compound and its scorch buildup was less than the roast buildup of uncared compounds [88].

12.6 Common Fiber-Strengthened Bio Agrochemical Compounds The yearly utilization of agrochemicals is expanding accompanied by the pace of 6% and is assessed to be over 301 million tons [90]. Generally, the agrochemicals utilized in the mechanical creation of ductile are removed from chemical assets. The use of chemical-based agrochemicals in ductile assembling is nearly 8% of the worldwide gas and oil utilization [91]. These durable engineered agrochemicals

12.6 Common Fiber-Strengthened Bio Agrochemical Compounds

represent a noteworthy danger to the climate and manageable turn of events. A few activities have been taken to create inventive innovations from inexhaustible feed stocks to bio-polymeric materials’ handling. Some inexhaustible feed stocks such as regular oils, polysaccharides (starch and sugars), wood (lignocellulose) what’s more, proteins are extensively used to separate monomers [92, 93]. Among the sustainable feed stocks, fatty substance oils separated from soybeans are effectively accessible, of moderately minimal effort, and have synthetic usefulness, just as 109 million metric huge amounts of edamame were collected in the country United States in the year 2014 [94, 95]. The thermic characteristics of PLA/jute compounds were examined and mass reduction at different temperatures was watched [96]. Jute fibers at first lose their mass close to 101 ∘ C because of H2 O particles’ existence in the stall divider. The second and third thermic corruptions were noted at 281 and 361 ∘ C, separately, because of the decay of less atomic load of polyose, phenolics, and fructose [97]. For PLA/jute compounds, sole-phase thermic debasement has likewise been noted at 347 ∘ C. The thermal solidness of the compound is lesser than that of unadulterated PLA that might be because of the jute strands. Antacid, Arrhenius acid also, decolor medicines of jute fiber decreased the thermic soundness of the compounds when contrasted with that of uncared jute PLA/fiber compounds. In any case, silane care of jute fiber-strengthened compounds enhanced the thermic properties because of the disposal of handily hydrolyzed substances which ordinarily corrupt underneath the debasement temperature of polyose, phenolics, and fructose [96, 98]. An examination of sisal/elastic nut solvent-free Bakelite compounds demonstrated thermic corruption at three unmistakable temperatures [99]. The underlying mass reduction was beneath 101 ∘ C because of the dissipation of dampness contentment. The second and third phases of thermic debasement were because of fructose, phenolics, and polyose at 251 and 481 ∘ C, individually [100]. Three-phase corruption was noted for the thermic corruption of RSOPU. The elastomer holding of Teflon was corrupted somewhere in the range of 218 and 337 ∘ C [101]. Nonetheless, the last phase of thermic debasement was in the middle of 451 and 501 ∘ C because of the corruption of elastic nut oil fraction [99]. The thermic characteristics of hibiscus and rice hull strengthened PLA were researched through TGI and this was established that the underlying temperature has a place with dampness dissipation [102]. Fiber stacking was considered and it was uncovered that the expansion of normal fiber diminishes the temperature of thermic corruption of compounds [103]. The most noteworthy mass reduction of rice hull and hibiscus was noted in the middle of 231 and 361 ∘ C relating to the corruption of the carbohydrate materials of polyose, fructose, and phenolics. Other examination on TGI investigations of silane-cared furthermore, uncared sisal fibers strengthened bio-PU compounds noted thermic disintegration and discovered comparative weight corruption bend for both uncared and cared fibers [104]. Notwithstanding, silane-cared compounds were demonstrated superior thermic strength because of superior interlinking holding [55]. An examination dependent on the corn-and rice dextrose-based bioplastics for bundling implementations was finished utilizing TGI and distinguished three phases of corruption: the main temperature span was somewhere in the range of 100 and 200 ∘ C and showed little weight reduction because of dampness dissipation;

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the subsequent stage demonstrated significant dissipation somewhere in the range of 251 and 301 ∘ C that was because of the disintegration of pectin and galactose, and the three phase indicated just scorch contentment [105]. The thermic properties of bamboo fiber-strengthened cashew nutshell fluid bio-composites were examined through TGI and this was discovered, which the primary phase of debasement was in the temperature span somewhere in the range of 250 and 380 ∘ C because of deterioration of gelatin, hemicellulose, and cellulose [106]. The subsequent stage of thermal corruption uncovered the debasement of agrochemicals connections in the scope of 401–451 ∘ C. Antacid-adjusted fiber strengthened compounds enhanced the greatest corruption temperature in the DTG bend from 401 to 422 ∘ C [106]. Thermal corruption of the polymer demonstrated a wide scope of disintegration from 250 to 450 ∘ C that was because of a few synthetic disintegrations, for example, CO, CO2 , CH4 , phenols furthermore, and cresols [107]. The thermal steadiness of regular fiber-strengthened CNSL composites was researched and there was no mass reduction beneath 101 ∘ C that was because of the aquaphobic creation of CSNL [108]. The cared compounds indicated mass reduction under 101 ∘ C also, cared compound accompanied by the elevated grouping of potassium hydroxide indicated elevated mass weight reduction under 101 ∘ C because basic treatment uncovered the hydroxyl gatherings of the fiber thus expanded their communication with water [109]. The DTG bends plainly uncovered the main pinnacle which was because of vanishing of dampness and the second pinnacle which was expected to the corruption of essential constituents of natural fibers [110] furthermore, corruption of frail chain of the lattice [108]. Thermal corruption of regular fibers strengthened CSNL compounds noted 11% mass reduction at 244.0 ∘ C because of the corruption of regular fibers [111]. The last thermal deterioration of compounds was at 946 ∘ C. The thermic corruption phases demonstrated that carbohydrate substance affects the thermic security of CSNL compounds. The care of regular strands accompanied by copper-containing enzymes is very much examined as oxygenase catalyst. This has a double property; this source extreme fermentation or dehydrogenation phenolics composite by unbound extreme response [112, 113]. The thermal soundness of laccase-cared and uncared fibers was seen at two temperatures: First, it begins at 301 ∘ C because of shapeless fructose, and afterward, the translucent fructose debases at an elevated temperature approximately 351 ∘ C [114]. This was additionally established that cared fibers enhance the thermic soundness. A similar investigation of cared and uncared fibers indicated which cared fibers increment the thermic soundness from 450 to 492 ∘ C. Thermic characteristics were enhanced in cared strands in view of its elevated limpid record. This was seen that cared fibers enhance the thermic dependability accompanied by expanding the limpid of the fiber [76]. Uncared and cared sisal-strengthened compounds appeared a fast reduction in temperature somewhere in the range of 340 and 360 ∘ C, which is basically because of corruption of materials [115]. The sisal strengthened PLA compounds demonstrated less thermic dependability than unadulterated PLA that might be because of the thermic debasement of fibers throughout the assembling measure. Another explanation that possibly antacid care, taken out the lignin and harmed the fructose model. A less limpid list of cared compounds could be another

12.6 Common Fiber-Strengthened Bio Agrochemical Compounds

explanation also. Moreover, the weight level of the buildup of three substances varied from the farther. The uncared compound had the maximum buildups while the perfect PLA had the minimum. This showed that sisal PLA/fiber compounds had an elevated thermal opposition than flawless PLA on account of sisal fibers as support and thermal opposition of uncared sisal that was superior to those of cared sisal [115]. An investigation on thermic characteristics of unadulterated PLA and bio-composites accompanied by various bamboo scorch filling indicated a sole-phase decay measure [116]. Unadulterated PLA uncovered higher thermal dependability than BC composites because unadulterated PLA needs the elevated temperature to crack the molecular string. Through the expansion of bamboo scorch to PLA, the atomic versatility was expanded and few other atomic strings were disintegrated also, crystallization was created because of plasticization what’s more, heterogeneous nucleation, which brought about diminishing of thermal corruption at less temperature. The other investigation [117] demonstrated with a diminished beginning temperature and an expansion afterward, that showing an enhancement of crystallization while moving thermal debasement to elevated temperatures. The thermic characteristics of mixed agrochemical of polyhydroxybutyrate and poly(hydroxybutyrate-co-hydroxyvalerate) were researched through the TGI method furthermore, there was no mass reduction under 101 ∘ C because of the non-attendance of negatively charged ions bunches [118]. The thermic corruption of unadulterated PHB demonstrated a 6% mass reduction at 243 ∘ C; notwithstanding, the thermal corruption of P(HB-HV) was seen at 248 ∘ C. Afterward the expansion of normal fibers to PHB and P(HB-HV), the thermic strength was enhanced through 11 ∘ C. Regular fiber strengthened PHB compounds showed thermic corruption at 291 ∘ C and normal fiber-strengthened P(HB-HV) composites demonstrated thermic corruption at 271 ∘ C. The elevated fiber proportion upgraded the lingering sum because of the presence of remains. An investigation of Bhardwaj et al. [119] established that expansion of fructose doesn’t deliver exchanges in the thermic solidness of P(HB-HV), however, this can expand the measure of definite buildup. A concentrate on blanched paper delicate timber (BKSW)-strengthened PLA bio-composites by TGI indicated the primary thermic corruption at 251 ∘ C [120] that was because of the decay of polyose and fructose [121]. The thermal debasement of unadulterated PLA began from the temperature 301–402 ∘ C. An expansion of characteristic strands to PLA decreased the thermic dependability because of fructose. A similar investigation of PLA/hibiscus and rice PLA/hull crossover compounds was executed to analyze their thermic conduct [102]. Shibata et al. [122] established that polyoses disintegrate first, followed through fructose and phenolics. After 361 ∘ C, the mass reduction is due to the deterioration of non-carbohydrate substances. The thermic debasement of unadulterated PLA was at 324 ∘ C; afterward the consolidation of hibiscus and rice hull the temperature of debasement reduced to 322 and 306 ∘ C, separately. Hibiscus-strengthened PLA compound demonstrated 76% mass reduction at 358 ∘ C when rise hull/PLA compound debased at 341 ∘ C. Within all situations, the rise hull compound indicated low thermic soundness than the hibiscus compound that might be expected to the synthetic synthesis of the two characteristic fibers [102].

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12.7 Blend of Nano Compounds Within the creation and handling, the nano compounds are extremely like the customary agrochemical compounds and the simpler method of creation builds the nano compound additional appealing [123]. Nano compounds are additionally noticeable of the traditional compounds because of their floaty, great volume strength, improved thermal and fire obstruction, just as boundary characteristics accompanied by within limits smaller stacking of nanoparticles [124]. DTG bends of Ag micro particles lining PLA composites represented that expansion of Ag micro particles up to 0.99% affected the thermal soundness inconsequential. The thermal corruption temperature of 5% microcrystalline cellulose (5MCC)/PLA moved to bring down the temperature, and further expansion of 1% of Ag diminished the temperature of thermic corruption around 25 ∘ C [112]. TGI characteristics of all pinus timber zeolite/flour crossover compounds were respectably steady up to a temperature over 201 ∘ C that is elevated than the measured temperatures for the two-screw dismiss and infusion shaping. The principal thermic deterioration was near 231 ∘ C and the subsequent pinnacles were approximately 421 ∘ C. The last buildup of the catalyst-consisting compounds was lesser than those of timber flour compounds [125]. Thermic characteristics of hibiscus/atomic nanocrystals/PP/ MAPP nanocomposites uncovered the impact of atomic nanocrystals on the thermic strength of PP compound [126]. GNP stacking of three phr demonstrated the most noteworthy thermic strength because of elevated GNP perspective proportion and constant circulation that gave hindrance insurance and thwarted evolvement of vaporous atoms throughout thermic deterioration. Consistently scattered GNP impeded the gracefully of O2 by the development of sheets of single on nanoparticles’ plane accordingly enhancing thermic soundness. The composites displayed sole-step debasement top in the scope of 474–491 ∘ C. The temperature of thermic debasement and scorch contentment expanded accompanied by expanding incorporation of GNP. Scientists researched the uncared and cared bamboo/PLA compounds and contrasted them and PLA/nanoclay/bamboo mixture compounds [127]. The introductory and last thermic debasement temperatures of uncared bamboo composites were 285 and 373 ∘ C, individually. TGI bend of cared bamboo compounds uncovered barely elevated starting and last thermic corruption temperatures of 287 ∘ C also, 3737 ∘ C because of silane care on fiber [128]. Nanoclay was scattered equivalent and gone about as a gas obstruction in the type of an unpredictable result [129]. Thermic characteristics of uncared and cared bamboo cellulose nano-whiskers PLA compounds exchanged from 101 to 151 ∘ C because of parchedness of H2 O particles [130]. The uncared compounds uncovered an elevated rate of heat transfer inside compounds because of the helpless similarity of PLA and uncared BCNW [131] that builds the thermal dependability moderately higher contrasted with treated composites. Silane care accompanied by 5 wt% enhanced the associate characteristics, which interfaces with sub-atomic bonds of PLA firmly that need elevated vitality to separate into substance and somatic connections [132]. Abundance measure of silane began self-buildup response accompanied by PLA and BCNW particle [133–137] and diminished thermic security. After including

12.8 Conclusion and Summary

nanoparticle (6 wt%) thermic characteristics enhanced the system of nanoparticle in compounds, a defensive boundary of vaporized at very high-temperature catalyst coatings on the rest of the agrochemical [138] is shaped through agonizing way for unpredictable items by which evaporation may be deferred [139]. Thermal security of fructose nanoparticles (graphene/PLA nano compounds) demonstrated a huge weight misfortune (>95 wt%) somewhere in the range of 280 and 380 ∘ C because of polymer spine debasement [140, 141]. Rainmaking specialists give a diverse seeding at raised temperatures when the main thrust for homogeneous nucleation is powerless when softener enhances the liquefaction at fewer temperatures and permitting the bond versatility.

12.8 Conclusion and Summary The thermic conduct of normal fibers consists of a connection accompanied by its synthetic components, for example, cellulose, polyose, and phenolics. Introductory mass reduction in normal fibers in the middle of the temperature 51 and 101 ∘ C is related accompanied by the vanishing of negatively charged ions bunches from the fiber surface. Thermic corruption of phenolics and fructose was noted somewhere in the range of 301 and 45 ∘ C when polyoses existing an undefined substance corrupted in the temperature scope of 201–30 ∘ C. Around 61% of the thermic disintegration of maximum normal strands happened inside a temperature range somewhere in the range of 231 and 351 ∘ C. Post temperature 451 ∘ C, the buildup could be relegated as a roast or another item from disintegration responses. Plane adjusted common fibers uncovered lower weight misfortune in the introductory phase, demonstrating, which the care incompletely builds the fibers fairly liposome in the creature. The underlying mass reduction is because of the dissipation of dampness from the fiber plane, thus the agrochemical network commitment, assuming any, ought to be generally little. For commonsense use, be that as it may, the temperature identified with the beginning of thermal debasement can be reviewed as the compound thermic security limitation. The normal fiber-strengthened compounds uncovered mass reduction under 101 ∘ C and demonstrated, which dampness was retained throughout the assembling cycle of composite. At elevated temperatures, common fiber-strengthened composites demonstrated preferred thermal strength over natural fibers lone. The cared fibers additionally enhanced the thermic characteristics because of superior associate holding among fibers and network. Superior fiber–framework structure envelopes the fibers completely and ensures the fibers through dodging straight touch accompanied by temperature, in any case, treated fiber-reinforced composites generally appeared lower leftover sum because of the incomplete gully of phenolics throughout treatment measure. Thermic debasement is additional subject to the idea of agrochemicals; thusly, thermosetting are profoundly additional steady than polymers. The thermic corruption of crossover compounds was influenced by various kinds of fibers because of the assortment in compound constituents. The nanocomposites demonstrated superior thermic strength because of the small lining that goes about as thermic safe substances.

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The enhancement of thermic soundness in regular fiber-strengthened polymer composites has incredible worry in cutting-edge substances. There are numerous jobs, which are accounted for aloft in different conditions that can assist in the determinations of materials for a particular reason. In any case, the characteristic fiber-strengthened agrochemical compounds are being explored to propel its thermic safe characteristics through utilizing micro particles, flak blockings, and normally thermic resistant lignocellulose fibers.

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13 Thermic and Mechanical Valuables of Synthetic Based Fibers Blend Compounds Arun K. Behura 1 , Ashwini Kumar 2 , Dipen K. Rajak 3 , and Pankaj Kumar 4 1

School of Mechanical Engineering, Vellore Institute of Technology, Vellore, 632014, Tamilnadu, India Shree Guru Gobind Singh Tricentenary University, Department of Mechanical Engineering, Faculty of Engineering & Technology, Gurugram 122505, HR, India 3 Sandip Institute of Technology and Research Centre, Department of Mechanical Engineering, Nashik 422213, Maharashtra, India 4 SR University, Department of Mechanical Engineering, Center for Materials and Manufacturing, Warangal, India 2

13.1 Introduction Developing exploration concerns chiefly with the ecological and monetary issues identified with the plan of latest substances for subsequent businesses. Over a few years, different mechanical areas are attempting to supplant the polymerized fibril accompanied by characteristic fibers as fortifications in polymer compounds. Compound substances have been giving a significant measure of exploration and mechanical effort for the duration due to their ideal and remarkable goods. Besides, every substance can be created and handled accompanied by small speculation [1]. The compound substance is a mix of fibril/filler and grid (agrochemical). The blend of fibril and grid can be orchestrated by utilizing the hybrid (a couple of fibers) with the base polymer framework. The principal reason for utilizing fibrils is to give solidarity to the compound. Elements, which impact the characteristics of fibrils, are span, direction, appearance, and substances [2]. In view of the agrochemical utilized for the assembling, fibrils can be chosen either by naturally or artificially. Fibrils, which are large and got from herb, creature or developed are called common fibrils, for example, bamboo, hemp, jute, sisal, coir, silk, ramie, grewia optiva, and so on. Then again, fibrils, which are fabricated by different artificial cycles, are known as polymerized fibrils, for example, glass, kevlar, carbon, etc. Both common and polymerized fibrils have self-benefits and bad marks as for the polymer utilized for the creation of the compound. When contrasted with polymerized fibrils, common fibrils are climate cordial, inexhaustible, modest, nonhazardous, nonabrasive, and effectively accessible, however, the cons of utilizing common fibrils are their small mechanical characteristics as thought-about to polymerized fibrils [3]. Another significant disadvantage of common fibrils is their friendship toward H2 O on account of the existence of carbohydrates. Then again, natural Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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fibrils, being hydrophobic substances, structure a decent holding accompanied by the polymers. Once in a while, fibers are applied in crossover structure to exploit both regular and polymerized fibrils that is by and large known as blending in the compound. This blending leads out different appealing characteristics of both common and polymerized fibrils that brought about prevalent tribological and mechanical characteristics of the last compound [4, 5]. Although, this isn’t the only reason for the variety in the characteristics of the compound. Fibril type, fibril size, level of fibril, the polymer utilized, preparing procedures, and synthetic care are the indispensable variables that can be utilized to accomplish encouraging outcomes in the compound characteristics. The target of this chapter is to introduce a survey on ongoing examinations identified with mechanical and thermic characteristics of synthetic/synthetic based blend fiber-reinforced agrochemical composite. Mechanical properties, for example, flexural quality, elasticity, flexural modulus, pliable modulus, and effect quality of crossover/blend compound are considered.

13.2 Synthetic Fibers Synthetic fibers are the fibers made by people through substance union, rather than regular fibers that are legitimately gotten from living life forms. There are aftereffects of broad examination by researchers to refine normally happening creature and plant fibers. When all is done, polymerized fibrils are made through expelling fibril-framing substances by spinnerets, shaping a fibril. These fibrils are known as polymerized or fake fibrils. Polymerized fibrils are made through a cycle called synthetization that includes consolidating monomers to build extensive trammels or agrochemicals. Generally, two kinds of polymerization are available: direct polymerization and cross-connected polymerization. As such we can say that polymerized fibrils are artificial fibrils, which don’t start normally. Results of oil are the primary wellspring of polymerized fibrils. Polymerized fibrils have preferable characteristics over common fibrils. Various synthetic compounds having their self-property are essentially utilized to create the polymerized fibrils. Polyurethanes, acrylics, nylon, polyesters, and so forth, are the polymerized fibrils created from substance items [6]. These fibrils have inflated mechanical characteristics, strength, and soundness and have durable existence expectancy. There are different kinds of polymerized fibrils in which chiefly three sorts of polymerized fibrils are utilized in the compound business at an enormous scale: Figure 13.1 (a) Carbon, (b) Kevlar (aramid), and (c) glass fibril.

13.2.1 Carbon Fibrils Carbon fibrils are delivered through utilizing terephthaloyl chloride and para-phenylenediamine [7]. Due to the atomic direction, these fibrils have inflated quality and amazing thermic conductivity when contrasted with carbon fibers and glass [8]. The fabricating measure and the gear utilized in the assembling of carbon fibrils are exorbitant, so they are commonly inflated in price [8]. Carbon fibrils have bountiful characteristics, which have great protection from the

13.2 Synthetic Fibers

(a)

(b)

(c)

Figure 13.1 Part of polymerized fibrils: (a) glass fibril, (b) kevlar fibril, and (c) carbon fibril. Source: Saba and Jawaid [6]. Table 13.1

Classical characteristics of carbon fibrils.

Carbon fibrils grade

Diameter (𝛍m)

Density (g cm−3 )

Tensile modulus (GPa)

Tensile strength (MPa)

Elongation (%)

Carbon fibrils 29

13

1.46

63

2761

3.43

Carbon fibrils 49

13

1.46

125

3622

2.867

Table 13.2 Terminology utilized for carbon fibrils with and without different surface cares. Fiber

Surface modification techniques [10, 11]

Carbon fibrils

Unprocessed Carbon cycle Globule grinding technique Globule grinding + carbon cycle Ball milling + phosphoric acid Globule grinding + phosphoric acid + carbon cycle

scraped spot, nonconductivity, and high corruption temperature, and great texture respectability, great protection from natural dissolvable, no softening position, and little combustibility [9]. Table 13.1 represents the two kinds of carbon fibrils: Carbon fibril 49, and Carbon fibril 29. To expand the mechanical characteristics and enhance the interfacial communication, a few adjustments were embraced, for example, direct hydrolysis, planetary ball processing, and carbon cycle care of ball factory [10]. Table 13.2 shows the different carbon fibrils care strategies.

13.2.2 Glass Fibrils Profoundly appealing mechanical and physical characteristics of glass fibrils, simplicity of fabricating, and their tantamount minimal effort to carbon fibrils build it a

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profoundly best substance in superior compound implementations. Glass fibrils are made out of oxides of silica. Glass fibrils have remarkable mechanical characteristics, for example, less delicacy, outrageous quality, less firmness, and insubstantiality. Glass fibril-fortifying polymers comprise of an enormous group of various types of glass fibrils, for example, lengthwise, hacked coast fibril, twist tangle, and cleaved coast tangle utilized to build the tribological and mechanical characteristics of agrochemical compounds [6, 12–14]. Analysis has been done to explore the appropriateness of glass fibrils accompanied by the agrochemical, for example, elastic. This is conceivable to acquire inflated introductory perspective proportion accompanied by fibrils of glass; however, delicacy makes fibrils smash in the course of handling.

13.3 Blend Fibril-Based Agrochemical Compounds The blend is a strategy wherein at least two or more fibrils are utilized to a solitary base network. The word blend at times additionally alludes to the execution of stuffs in the fibril agrochemical compounds [15]. Blend is old to the analysts; indeed, this has been practically speaking for quite a long time. Properties for example, mechanical, physical, and thermic obtain impacted in a constructive way on account of the crossbreeding. It is ascribed to the expansion in the fibril–fibril furthermore, fibril–framework grip. To diminish the general expense of assembling, common fibrils are introduced to polymerized fibril agrochemical compounds, however, trading off is accompanied by the quality of the compound. This has been discovered that crossbreeding has been in the highest needs of different specialists. Crossover compounds are presently being shaped in different structures. These compounds are sandwich type, center shell type, covered sort, in pair’s type, personally type, and so forth. The dynamic, mechanical, and thermic characteristics increment considerably for oil palm–epoxy-like compound in light of the upgrade in the glue holding of fibril and lattice. Expansion of common fibrils in glass fibril-reinforced agrochemical compounds prompts upgrade of effect tractable and flexural quality [16]. This has been seen that crossbreeding of jute and oil palm fibril came about in inflated elasticity, given that the heaviness of jute fibril ought to be inflated [17]. Most of the effort in the area of crossbreeding has been at stake to crossbreeding of regular and polymerized fibrils. In such a manner, sisal, a characteristic fibril, can be crossbreeding accompanied by the glass fibrils that brings about the upgrade of ductile also, flexural modulus. Crossbreeding doesn’t generally effort for each part of the compound mulled over. It may be expressed very well that improvement of one characteristic once in a while prompts decrease of another and the other way around. Comparative outcomes have been accounted for sisal–glass/polypropylene crossbreeding. It has been accounted for elastic and flexural quality increments, however, haggling with the properties, for example, elastic and flexural modulus. Also, thermic and H2 O opposition conduct likewise enhances for sisal–glass agrochemical compounds [18]. The name of a plant fibril is Hemp, which is likewise discovering its position in crossbreeding, as a result of its persuasive characteristics. In the crossover compounds,

13.3 Blend Fibril-Based Agrochemical Compounds

stacking succession plays a significant role in choosing the mechanical characteristics of the framed compounds. It is reasoned from past examination that hybrid covers accompanied by two limits polymerized fibrils utilized on the two edges have the ideal mixture accompanied by a decent equilibrium in between the characteristics and the expense. This has additionally been discovered that glass fibrils, when blended accompanied by hemp fibril, tend to progress in physical and mechanical characteristics and decrease in the general expense of compounds [19]. As compare to hemp, flax fibril – notable from the hundreds of years – can likewise be blended accompanied by polymerized fibrils [20]. Blend compounds of glass and flax fibril tend to impart important enhancement in the rigidity of the compound. The name of one fibril is Jute which characteristic accessible in extremely huge sum, which is likewise implemented in the crossbreeding accompanied by the glass, prompting superior pliable and flexural quality of the compound. Hybridization additionally assumes an exceptionally basic part in the upgrade of characteristics for green compounds [21]. Hence, green compounds of bamboo–cellulosic fibril-like PLA compounds are developed to have superior obstruction for break sturdiness [22].

13.3.1 Synthetic Reinforced Hybrid Composites Numerous analysts have announced concentrated the impact of extra polymerized fibril stacking on mechanical characteristics of synthetic fibril strengthened agrochemical compound. They didn’t locate a noteworthy enhancement in the mechanical characteristics of crossover compounds. Within this part, polymerized fibril is fused accompanied by synthetic fibril reinforced polymer compound. The mechanical characteristics of carbon/glass fibril concentrate on strengthening epoxy compound introduced by Atiqah et al. [23]. The crossover carbon/glass strengthened epoxy compound does not represent enhanced mechanical characteristics when contrasted accompanied by those of various compounds. Concentrate on hybrid T77S and E-glass carbon fibril strengthened epoxy compound revealed by Naik et al. [24]. The compound is set up by hand lay-up strategy and their flexural characteristic is concentrated by utilizing a three position twisting test according to ASTM D790-07. They detailed on the premise of test, crossbreeding of these two fibrils didn’t represent enhancement in flexural quality yet reenactment represents the beneficial outcome of crossbreeding. Isa et al. [25–27] considered the impact of the expansion of carbon nanotube on flexural characteristics of carbon epoxy compound. Flexural quality and modulus are developed to enhance by utilizing carbon nanotube as an extra support.

13.3.2 Implementations of Polymerized Fibril Agrochemical Hybrid Compounds Uses of polymerized fibril agrochemical compounds can be viewed as slow expanding wonders. This is the requirement of great importance, which needs supplanting of polymerized fibril accompanied by the common fibrils for different implementations on account of the great characteristics of regular fibrils [28–34]. Be

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that as it may, on account of specific downsides, the natural fibers can’t be utilized exclusively; henceforth, the time requires the joined favorable circumstances of both fibers (common and engineered) in a solitary part. This offers to ascend to the turn of events of hybrid composites; the different uses of mixture characteristic fiber composites are as per the following: Parts of car, for example, entryway boards, instrument boards, armrests, headrests, and package shells are currently being created through crossover fibril compounds [35]. Within the ongoing turn of events, the basement security cabin in a traveler vehicle for the well-being reason has been effectively planned and created through the banana fibril agrochemical compound [36]. Likewise, reflectors, shade of a bike, billion seat spread, marker spread, spread nameplate, and L-side are additionally being produced accompanied by the utilization of normal sisal fibril agrochemical compounds [37]. Financially, savvy segments can likewise be handily produced accompanied by the utilization of crossbreeding strategy [38]. Among them, one such implementation can be noticed in the use of guard of car that is fabricated by the crossbreeding of kenaf and glass fibrils [39]. Within the H2 O frameworks, for example, little vessels and boats, composites dependent on glass–sugar palm fibril discover whale of a great deal of uses [40]. Common fibers and manufactured fibril-based compounds have demonstrated self-capability to be a decent substance for the basic implementations. Jute fibril-based mixture compounds accompanied by tactile as a network are being produced for the use of basic compounds [41]. These implementations involve building boards, material sheets, entryway outlines, entryway shades, transport, bundling, geomaterials, chipboards, permeable cotton, stockpiling gadget, furniture, transportation, family adornments, and biodegradable shopping pack. Coir-based agrochemicals furthermore, fired compounds are likewise utilized in making boards, mantle entryway shades, material sheets, stockpiling tank, pressing material, protective caps and postboxes, reflect packaging, paper loads, projector spread, spread of the stabilizer voltage, a packing substance for the seat filling, brooms and brushes, cables and filaments for networks, packs, what’s more, mats, just as cushioning for sleeping pads and seat pads. Solid substances, which need thermally imperviousness to fire characteristics can likewise be created and accompanied by the assist of common fibers agrochemical compounds. Thus, because of this, common fibrils have permeable microstructures that give heat-proof characteristics [42].

13.4 Thermal Characteristics of Blend Polymerized Fibril Strengthened Compounds Thermal investigation of materials is fundamental to enterprises that are creating or then again/and utilizing inorganic and natural synthetic substances, drugs, nourishments, oil, polymers, polymeric composites, to make reference to yet a less. This is one of the principal parts of material science, where the physical what’s more, substance characteristics of the substances are researched, as capacities of time and temperature [43, 44]. Thermic explanatory strategies have been in presence from the past eighteenth era. The primary thermic logical estimation was built through

13.4 Thermal Characteristics of Blend Polymerized Fibril Strengthened Compounds

Le Chatelier in 1887, due to putting a temperature measurement instrument in a dirt example and warming it in a heater. At that point, the heating plots were visualized and written on a photographic plate utilizing a mirror galvanometer [45]. Within the year 1899, a critical enhancement was built through Roberts-Austen accompanied by the presentation of two differential thermistors associated in resistance, to quantify the temperature distinction between the example and a latent recommendation [46]. Until the creation of thermo-gravimetric estimations in 1915, the mass distinction was estimated as it was by back gauging [47]. The advancement of the heating by differential scanning calorimetry (DSC) and the force remunerated, DSC was seen in nineteenth-century [48, 49]. Besides, later on, the energetic mechanical estimations came into truth accompanied by diverse alternative repetitions. The cutting-edge improvements in the thermic investigation strategies and their incredible utilization in substance portrayal could be ascribed to the endeavors of the researchers and the development of productive PC equipment and programming frameworks. A more extensive expository methodology is needed to comprehend the thermal conduct of the substances. These days, the thermic investigation strategies can give data to latest substance turn of events and determination measure advancement, designing plan, and the forecast of end-user execution. They can likewise be utilized to examine substances for uniformity in opposition to details and to investigate preparing issues [50]. As of now, a wide scope of demonstrated thermal investigation procedures, for example, differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), DSC, thermo-mechanical analysis (TMA), and dynamic mechanical examination (DMA) have been utilized. These explanatory strategies are very helpful in the investigation of the auxiliary interchanges (softening/crystallization, volatilization, crosslinking, glass progress, and stage advances in the strong and fluid conditions), mechanical characteristics (flexible conduct, damping), thermic characteristics (development/contraction, explicit heating limit, softening/liquefaction temperature, amount of development and synthetic responses disintegration and thermic strength in various vaporous conditions, synthetic responses in arrangements or fluid stage, responses with the cleanse gas and lack of hydration) [51, 52]. Besides, polymers and polymeric composites are utilized in an assortment of utilizations, for example, gadgets, biomedical, energy, food bundling, development, and assembling enterprises for quite a few years. Be that as it may, on account of the inborn underneath thermic potential and strength of this polymeric substances, its broad scope of utilization is limited, particularly where brilliant heating dissemination and less thermic development is fundamentally needed [53]. Besides, contrasts in the auxiliary angles, synthetic creation and additional preparing boundaries affected the practical characteristics of the fibril strengthened agrochemical compounds [54, 55]. This is likewise indispensable to analyze the thermic characteristics of fibrils in the plan of compounds. Besides, this is basic to guarantee that the fibrils utilized in the agrochemical compounds that can sustain the heat needed at the time of preparing and hold their attributes afterward uncovered to thermal. It will be valuable in deciding the thermo-mechanical what’s more, thermo-dielectric attributes of the fibril [56]. Common fibrils are viewed as potential raw materials for the enormous creation of sustainable compound shapes [57]. Be that as it may, their

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indigent somatic characteristics, for example, fragile shape, underneath mechanical characteristics, substandard common characteristics and less dissolve consistency restrict its adequacy in numerous implementations. Henceforth, so as to conquer these problems, it is unavoidable to comprehend its thermic and rheological qualities [58, 59]. The helpless thermic characteristics of the fibrils can likewise restrict its implementations, anyway detailing of compounds could grasp various implementations [60, 61]. The piece of the fibrils can likewise impact its thermic characteristics [62]. This was accounted for that the substance care of fibrils can enhance the thermic characteristics through eliminating its lignocellulosic parts [63, 64]. Consequently, potential procedures to conquer other a few disadvantages have been executed to create different new substances for the dynamic modern requirements. Within the ongoing years, broad explores are attempted for the upgrade of thermic characteristics of compound substances. The consideration of carbon, metallic also, earthenware-based stuffers has enhanced the characteristics of the resulting hybrid compounds [65]. The thermic and mechanical exhibitions of a substance assume a noteworthy function in deciding their last implementation. To enhance substance characteristics, thermic examination is a fundamental investigation of the new substance advancement [66]. In the upcoming sub-segments thermal properties of various synthetic hybrid composites have been talked about.

13.4.1 Thermal Properties of Glassy Carbon (Woven) Glass-like carbon, frequently called polished carbon or glassy carbon, is a nongraphitizing or non-graphitizable carbon, which consolidates shiny and clay properties with those of graphite. The most significant properties are high-temperature opposition, hardness (7 Mohs), low thickness, low electrical obstruction, low erosion, low thermal obstruction, extraordinary protection from compound assault, and impermeability to gases and fluids. Lustrous carbon is generally utilized as a cathode material in electrochemistry, for high-temperature pots, and as a part of some prosthetic gadgets. It tends to be created in various shapes, sizes, and segments. The mechanical characteristics of the agrochemical-based blend compound and established that the stacking succession has an additional effect on the outcomes acquired [67]. The pliable characteristics and break conduct of the blend poles for differing arrangement and discovered, which managing the revoked were extremely troublesome and elasticity and modulus increments accompanied by expanding with an increment of carbon fibril [68]. The flexural characteristics of glass and carbon fibril rein-constrained epoxy mixture compounds were considered to utilize FEA and it was established that there is 20–30% less flexural quality and prototypes fizzled accompanied by shear [69]. Glass fibrils have lower shear modulus, Poisson’s proportion, and Young’s modulus where as carbon fibril that is exorbitant has superb mechanical characteristics. The direction of the fibrils assumes a crucial job and the hybrid compound are utilized to accomplish wanted mechanical characteristics [70]. FEA was utilized to acquire flexural quality and disappointment happens because of shear disappointments, the flexural quality is 20–30% less contrasted with other disappointment manners [71].

13.4 Thermal Characteristics of Blend Polymerized Fibril Strengthened Compounds

From the above writing study, this was discovered that however, there were additional jobs for blend compound, very little job had been moved on for CSM microwave glass fibril and one-way carbon fibril. The expense of the two fibrils was relatively modest and, in this way, a couple of years back, an exertion was built to examine and investigate on thermic and mechanical characteristics of the discrete fibril compound and epoxy-based crossover compound [72]. To break down, assess and analyze the thermic and mechanical characteristics of epoxy-based compounds accompanied by various fibril fortifications an examination was completed. The creation of glass fibril, carbon fibril, and hybrid compounds was one through hand lay-up method. Elastic examine, three-point twist examine, inter-laminar shear examine, and compression examine were done on the composite covers according to the ASTM Standards to get mechanical characteristics, for example, rigidity, cross over quality, top burden, compressive quality. Thermal properties, for example, Transition of Glass temperature, dissolving and deterioration tops were explored through TGA; DSC was done to contemplate the decay conduct of the compounds. The thermic characteristics and the conduct of the compounds were estimated utilizing twain TGA and DSC. The method incorporated relieving the covers utilizing a SDT Q600 Differential Scanning calorimeter from TA tools. The cycle was conveyed through sloping of about 4 mg of test from room temperature to 600, 900, and 1000 ∘ C for carbon fiber, glass fiber, and crossover compounds individually. The warming rate was 20 ∘ C min−1 . All DSC what’s more, TGA examine utilized aluminum Pots and air is the trying air. All the thermo-grams revealed for DSC where skyward pinnacles that are exothermal. Within the Thermo-Gravimetric investigation, the somatic characteristics and substance characteristics are documented and examined as an element of expanding time and temperature. This examination was done to consider the thermic strength of the compounds. The adjustments in the bunch of the examples were contemplated on the point of the examples that were exposed to inclining inclusion of heat. It additionally assisted in the examination of unpredictable items, vaporous items lost during the response in composites.

13.4.2 Thermal Properties of Kevlar Kevlar keeps up its quality and versatility downward to coldish temperatures (−196 ∘ C); actually, it is marginally more grounded at moderate temperatures. At elevated temperatures, the rigidity is promptly decreased through around 10–20%, and then succeeding after certain hours, the quality logically diminishes additionally. For instance, suffering 160 ∘ C (320 ∘ F) for 500 hours diminishes quality through approximately 10%, and suffering 260 ∘ C (500 ∘ F) for 70 hours lessens quality through approximately 50%.

13.4.3 Thermal Properties of Carbon Fibrils The charcoal percentage of carbon fibrils are fibrils around 5–10 μm in measurement and built commonly from carbon molecules. The charcoal percentage of carbon fibrils has a little central position incorporating giant solidness, elevated elasticity,

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little mass, soaring synthetic opposition, elevated temperature flexibility, and small heat supplement. These characteristics have built carbon fibril especially mainstream in paragliding, constructional designing, defense and auto-sports, besides additional competitiveness, sports. Notwithstanding, they are quite expensive at the time of contradiction and comparable fibers, for example, glass fibers or fictile fibers. The carbon can turn out to be additionally upgraded, as soaring modulus, or elevated quality carbon, through warm care measures. The charcoal percentage of carbon heated in the scope of 1500–2000 ∘ C shows the most noteworthy rigidity (5650 MPa, or 802 000 psi), when carbon fibril warmed from 2500 to 3000 ∘ C displays a soaring modulus of versatility (531 GPa, or 70 700 000 psi).

13.4.4 Thermal Properties of Basalt Fibers Reinforced Composites The impact of basalt fiber on the thermal properties of PBS composites has been illustrated. The thermal redirection temperature of the composite increments from 82 to 114 ∘ C (expanding by 40% and near the liquefying temperature) and the Vicat mellowing temperature increments from 96 to 109.1 ∘ C with expanding fiber-mass extent.

13.5 Mechanical and Physical Characteristics of Blend Fiber Compounds Within the blend compound, the mechanical and physical characteristics are represented through the fiber contentment, fiber span, fiber direction, and plan of discrete fibers, reach out of blending of the fibers and the associate bond in the middle of the fiber and lattice [73–75]. A large portion of the examination on regular fiber crossover composite includes investigation of mechanical characteristics as a component of fiber span, fiber stacking, degree of intermixing of fibers, fiber to framework holding and game plan of both the fibers, the impact of different compound medicines of fibers, and utilization of coupling operators.

13.5.1 Epoxy Based-Hybrid Composites Water ingestion, dimensional strength, and thickness are the physical characteristics of palm oil. EFB compound enhanced accompanied by blending of palm oil, EFB compounds accompanied by jute fibers, and furthermore examined compound opposition, null content, and mechanical characteristics of palm oil EFB/jute blend compounds were focused by many researchers and investigators [76–78]. The impact of fiber pack stacking and alteration of biomass fiber plane in jute/biomass hybrid fiber strengthened epoxy compound have been considered. This reasoned that fiber plane change enhanced fiber/network association and altogether expanded mechanical characteristics of hybrid compounds [79]. It additionally gives intriguing discovery of thermo-mechanical characteristics and assessment of fiber/network collaborations. Hariharan and Khalil [67, 80] contemplated the

13.5 Mechanical and Physical Characteristics of Blend Fiber Compounds

pliable and effect conduct of the palm oil EFB-glass fibers strengthened epoxy pitch. The blending of the palm oil fibers accompanied by glass fibers expanded the elasticity, the Young’s modulus, and additionally the extension at snap of the hybrid compounds. The effect quality of the mixture compound expanded accompanied by the expansion of glass fibers. An obstructive hybrid impact was watched for the tractable quality and Young’s modulus while a constructive mixture impact was watched for the lengthening at snap of the mixture compounds. Mechanical and H2 O ingestion characteristics of jute/glass fiber strengthened the epoxy compounds and were contemplated [81]. Results demonstrate that mixture compounds have halfway mechanical characteristics than that of jute and glass compounds. Within this examination, they likewise attempt to discover the impact of H2 O assimilation in various compound conditions and bubbling H2 O. This has seen that hybrid compounds represent enhancement in H2 O retention conduct contrasted with jute composite and glass compound. Stacking rate conduct of jute/glass hybrid strengthened epoxy compounds analyzed and revealed in this investigation [82]. This represents that stacking rate inhumanity of hybrid compounds in the feeling of worry at capitulate, relocation at capitulate, also, inter-laminar shear quality [83] values at elevated stacking rate were gotten. Specialists examined the mechanical support acquired through the presentation of glass fibers in cellulosic fibers (silk texture) and strengthened epoxy compounds [84]. It saw that a generally modest quantity of glass texture to the silk texture strengthened the epoxy network and improved the mechanical characteristics of the subsequent hybrid compounds. Blend of silk fibers accompanied by glass fiber additionally expanded weight division of support and H2 O take-up of hybrid compounds was discovered to be not as much as that of un-hybridized composites. Hardness, sway quality, grinding coefficient, and substance opposition of sisal/glass hybrid compounds accompanied by and without salt medicines were examined [85]. Hybrid composites show ideally enhanced mechanical characteristics at 2 cm fiber span contrasted with 1 and 3 cm fiber spans. Synthetic obstruction was likewise essentially enhanced for all compound aside from sodium carbonates furthermore, phenyl methane. Associate pressure move in replica hybrid composite has been explored. Sm3+ doped glass fiber and an elevated-modulus recovered glycogen fiber were implanted in nearness to one another in a superglue gum network free weight molded model composite [86]. This investigation offers another methodology for subsequent micromechanical of the synapses inside hybrid compound substances, specifically the point at glycogenic fibers that are utilized to supplant glass fibers. Specialists explore impact of salt care and propenoate of jute fibers on tractable, convolution, voltaic quality, and volume impedance of jute/glass bisphenol-C basis blended superglue carbolic acid tar compounds [87]. Comparative investigation on mechanical characteristics of sisal/glass (cared furthermore, uncared) hybrid compounds strengthened in mixed superglue what’s more, formaldehyde of bisphenol-C were completed [88]. The convolution, compacting characteristics of bamboo/glass fibril strengthened superglue crossover compounds were considered [89]. Results demonstrate that soluble base treated bamboo fibers hybrid composites represent superior characteristics contrasted with crude bamboo fibers compounds. Point of

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this examination is to research the admixture of glass fibers accompanied by regular fibers for implementation in the channeling business [90].

13.5.2 Polyester Based Hybrid Composites As of late, sway conduct of palm glass/oil crossover compounds have been considered and discovered that sway quality is enhanced accompanied by expanding number of glass fiber coating and augmentation in fiber span [91]. The hybrid effect of palm glass/oil EFB fibril on the ductile, flexible and sway characteristics of the (C10 H8 O4 )n compounds was researched accompanied by extending bundle of two, one is palm oil EFB and other is glass fibrils [92]. The mechanical characteristics of EFB/glass hybrid (C10 H8 O4 )n compound are discovered to be a lot elevated than that of EFB/(C10 H8 O4 )n compounds. Each one of these upgrades in the hybrid compound characteristics are for the maximum segment due to the elevated standard and modulus calculation of glass fibril compared accompanied by EFB fibrils. Another specialist likewise examined somatic and mechanical characteristics of palm/glass oil fiber strengthened (C10 H8 O4 )n compounds identified with EFB fiber example span and fiber stacking [93]. EFB fiber example span demonstrated no essentialness impact on the flexible quality and thickness of compounds, however, more limited EFB fiber represents elevated H2 O assimilation and proportional exchange contrasted with extended EFB fiber. Flexible quality and thickness decline accompanied by expanding EFB fiber, however the expansion of 40–70% volume part of EFB increments flexible quality of (C10 H8 O4 )n sap by 350%.

13.5.3 (C2 H4 )n Basis of Blend Compounds A strain was built to assess the malleable characteristics of personally blended small sisal/glass mixture fiber strengthened low density polyethylene (LDPE) as an element of fiber span and different plane substance adjustments on the fiber just as the lattice [94]. This is seen that the fiber disintegrates at the time of preparing of the compound, and it is extra on account of glass fiber because of its fragile category than those of sisal fiber. The outcomes obviously show that the tractable characteristics of personally blended sisal/glass hybrid compounds are exceptionally reliant on the span of sisal fiber. Medicines accompanied by various synthetic compounds enhanced the elastic characteristics of crossover compounds. Out of the different synthetic alterations, compounds consisting C14 H10 O4 cared fibers represent the most noteworthy rigidity and modulus. Price/execution proportion investigation represents that C2 H3 O is more productive than different medicines utilized within this investigation. Compounds built accompanied by cotton and flax-containing business textures and reused elevated-thickness polyethylene (HDPE) were assessed for somatic and mechanical characteristics [95]. Fuse of flax and cotton fibers are reused into HDPE compound that expanded the compounds H2 O ingestion and growing conduct. Textures were dealt accompanied by C4 H2 O3 , SiH4 , chemical, or including C4 H2 O3 united (C2 H4 )n (MAA-PE; MDEX 102-1, ExxelorVA 1840) to advance collaborations among agrochemical and fibers. Within the special case of the SiH4 care, the cared lykra texture rigidity esteems diminished as for untreated textures.

13.6 Conclusions and Summary

13.5.4 Thermo-Cool Basis of Blend Compounds Contemplated the impact of fibril matter, fibril stacking, and crossover impact on the mechanical characteristics, for example, rigidity, youthful modulus, stretching at snap and flexible characteristics of the banana/glass crossover fibril strengthened thermo-cool compound [96] has been studied. The impact of alliance change on the mechanical characteristics of the mixture compound was explored, substance adjustment, for example, salt, C7 H5 ClO, and polystyrene maleic anhydrites care enhanced the malleable characteristics of the compounds. Alteration came about in improved fibril scattering in the compound, decreased hydrophobic of banana fibril and enhanced fiber/network similarity by mechanical securing, somatic, and substance holding.

13.6 Conclusions and Summary This chapter has fundamentally, widely, and exhaustively tended to the warm properties of normal fiber-based half-breed composites. In view of the warm properties described from DSC, TMA, TGA, and DMA procedures, the accompanying ends are starved. The fibril pieces represent in a few half-breed composites affected the weight reduction of the compounds. The roast buildup accessibility was exposed to the warm electric resistance of separate filaments in half-breed compounds. Fibril plane medicines and the expansion of joining operators were likewise assisted with improving the warm properties. Nonetheless, the treated fiber cross breed composites showed lower burn buildup and elevated weight drops, on the time contrasted accompanied by the crude fibril cross breed compounds. The thermosetting and thermoplastic-basis cross breed compounds showed a comparative pattern in warm qualities, as seen from the TGA procedure. DMA characteristics of artificially cared fibril half breed compounds were enhanced by giving great fibril-lattice associate holding and upgrading dispersal of vitality inside the compounds. Also, these characteristics could be upgraded through the expansion of stuffing such as Ag2 O, Fe2 O3 , Mg(OH)2 , MgO, and nanoclay. The outcomes acquired from TMA are pertinent to substances utilized in the stains and colors, pliant and trampolines, compound substances, earthenware production, glass, movies, strands, and glue layers. Likewise, TMA was reasonable for contemplating the substance elements, for example, (i) impacts of neckless gatherings, (ii) cross linkage, (iii) tactility and, (iv) atomic concentration that have the essential impact on the glass change temperature and development of the agrochemical. The significant uses of DSC incorporate, however, are not restricted to, drug grasslands, nutriment innovation, biochemical, agrochemical, inanimate what’s more, natural science. DSC can be utilized to decide: (i) glass progress pyrexia, (ii) warm limit seize the glass progress, (iii) liquefying and liquefaction pyrexias, (iv) warm of combination, (v) warmth of responses, (vi) virtue of the example, (vii) estimating the warmth limit, (viii) thermosetting portrayal, and (ix) estimating the fluid precious stone progress.

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58 Ilyas, R.A., Sapuan, S.M., Ishak, M.R., and Zainudin, E.S. (2018). Development and characterization of sugar palm nanocrystalline cellulose reinforced sugar palm starch bio-nanocomposites. Carbohydrate Polymers 202: 186–202. 59 Ilyas, R.A., Sapuan, S.M., Ishak, M.R., and Zainudin, E.S. (2019). Sugar palm nano fibrillated cellulose (Arenga pinnata (Wurmb.) Merr): effect of cycles on their yield, physic-chemical, morphological and thermal behavior. International Journal of Biological Macromolecules 123: 379–388. 60 Bledzki, A.K. and Gassan, J. (1999). Composites reinforced with cellulose based fibres. 24: 221–274. https://doi.org/10.1016/S0079-6700(98)00018-5. 61 Mishra, S., Mohanty, A.K., Drzal, L.T. et al. (2004). A review on pineapple leaf fibers, sisal fibers and their bio-composites. Macromolecular Materials and Engineering 289 (11): 955–974. 62 Ilyas, R.A., Sapuan, S.M., Ishak, M.R., and Zainudin, E.S. (2017). Effect of delignification on the physical, thermal, chemical, and structural properties of sugar palm fibre. BioResources 12 (4): 8734–8754. 63 Ilyas, R.A., Sapuan, S.M., and Ishak, M.R. (2019). Isolation and characterization of nanocrystalline cellulose from sugar palm fibres (Arenga pinnata). Carbohydrate Polymers 181: 1038–1051. 64 Ilyas, R.A., Sapuan, S.M., Ibrahim, R. et al. (2019). Sugar palm (Arenga pinnata (Wurmb.) Merr) cellulosic fibre hierarchy: a comprehensive approach from macro to nano scale. Journal of Materials Research and Technology 8 (3): 2753–2766. 65 Burger, N., Laachachi, A., Ferriol, M. et al. (2016). Review of thermal conductivity in composites: mechanisms, parameters and theory. Progress in Polymer Science 61: 1–28. 66 Costa, C.S.M.F., Fonseca, A.C., Serra, A.C., and Coelho, J.F.J. (2016). Dynamic mechanical thermal analysis of polymer composites reinforced with natural fibers. Polymer Reviews 56 (2): 362–383. 67 Hariharan, A.B.A. and Abdul Khalil, H.P.S. (2005). Lignocellulose-based hybrid bilayer laminate composite: Part I – Studies on tensile and impact behavior of oil palm fiber-glass fiber-reinforced epoxy resin. Journal of Composite Materials 39 (8): 663–684. 10.1177%2F0021998305047267. 68 Angrizani, C.C. and Drummond, M.L. (2010). Influence of the stacking sequence on the mechanical properties of glass/sisal hybrid composites. Journal of Reinforced Plastics and Composites 29: 179–190. 69 Jesthi, D.K., Mandal, P., Rout, A.K., and Nayak, R.K. (2018). Enhancement of mechanical and specific wear properties of glass/carbon fiber reinforced polymer hybrid composite. Procedia Manufacturing 20: 536–554. 70 Naito, K. and Oguma, H. (2017). Tensile properties of novel carbon/glass hybrid thermoplastic composite rods. Composite Structures 161: 23–31. 71 Dong, C. (2016). Uncertainties in flexural strength of carbon/glass fibre reinforced hybrid epoxy composites. Composites Part B: Engineering 98: 176–181. 72 Ambigai, R. and Prabhu, S. (2018). Analysis on mechanical and thermal properties of glasscarbon/epoxy based hybrid composites. IOP Conf. Ser.: Mater. Sci. Eng. 402: 012136. https://doi.org/10.1088/1757-899X/402/1/012136.

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73 Munikenche Gowda, T., Naidu, A.C.B., and Chhaya, R. (1999). Some mechanical properties of untreated jute fabric-reinforced polyester composites. Composites Part A: Applied Science and Manufacturing 30 (3): 277–284. 74 Sreekala, M.S., George, J., Kumaran, M.G., and Thomas, S. (2002). The mechanical performance of hybrid phenol-formaldehyde-based composites reinforced with glass and oil palm fibres. Composites Science and Technology 62 (3): 339–353. 75 Sreekala, M.S., Thomas, S., and Groeninckx, G. (2005). Dynamic mechanical properties of oil palm fiber/phenol formaldehyde and oil palm fiber/glass hybrid phenol formaldehyde composites. Polymer Composites 26 (3): 388–400. 76 Jawaid, M., Abdul Khalil, H.P.S., and Abu Bakar, A. (2010). Mechanical performance of oil palm empty fruit bunches/jute fibres reinforced epoxy hybrid composites. Materials Science and Engineering A 527 (29–30): 7944–7949. 77 Jawaid, M., Abdul Khalil, H.P.S., Noorunnisa Khanam, P., and Abu Bakar, A. (2011). Hybrid composites made from oil palm empty fruit bunches/jute fibres: water absorption, thickness swelling and density behaviours. Journal of Polymers and the Environment 19 (1): 106–109. 78 Jawaid, M., Khalil, H.P.S.A., Bakar, A.A., and Khanam, P.N. (2011). Chemical resistance, void content and tensile properties of oil palm/jute fibre reinforced polymer hybrid composites. Materials and Design 32 (2): 1014–1019. 79 Saw, S.K. and Datta, C. (2009). Thermo mechanical properties of jute/bagasse hybrid fibre reinforced epoxy thermoset composites. BioResources 4 (4): 1455–1476. 80 Hariharan, Bakar, A.A., and Abdul Khalil, H.P.S. (2004). Influence of oil palm fibre loading on the mechanical and physical properties of glass fibre reinforced epoxy bi-layer hybrid laminated composite. In: Lignocellulose: materials for the future from the tropics. Proceedings of 3rd USM-JIRCAS Joint International Symposium, Penang, Malaysia, 9–11 March 2004., JIRCAS Working Report 2004 No.39 (eds. R. Tanaka and L.H. Cheng), 230–233. 81 Koradiya, S.B., Patel, J.P., and Parsania, P.H. (2010). The preparation and physicochemical study of glass, jute and hybrid glass–jute bisphenol-C-based epoxy resin composites. Polymer – Plastics Technology and Engineering 49 (14): 1445–1449. 82 Srivastav, A.K., Behera, M.K., and Ray, B.C. (2007). Loading rate sensitivity of jute/glass hybrid reinforced epoxy composites: effect of surface modifications. Journal of Reinforced Plastics and Composites 26 (9): 851–860. 83 Gatenholm, P., Bertilsson, H., and Mathiasson, A. (1993). Effect of chemical composition of interphase on dispersion of cellulose fibers in polymers. I. PVC-coated cellulose in polystyrene. Journal of Applied Polymer Science 49 (2): 197–208. 84 Priya, S.P. and Rai, S.K. (2006). Mechanical performance of biofiber/glass reinforced epoxy hybrid composites. Journal of Industrial Textiles 35 (3): 217–226.

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85 Ashok Kumar, M., Ramachandra Reddy, G., Siva Bharathi, Y. et al. (2010). Frictional coefficient, hardness, impact strength, and chemical resistance of reinforced sisal–glass fiber epoxy hybrid composites. Journal of Composite Materials 44 (26): 3195–3202. 86 Kong, K., Hejda, M., Young, R.J., and Eichhorn, S.J. (2009). Deformation micromechanics of a model cellulose/glass fibre hybrid composite. Composites Science and Technology 69 (13): 2218–2224. 87 Patel, V.A., Vasoya, P.J., Bhuva, B.D., and Parsania, P.H. (2008). Preparation and physicochemical study of hybrid glass–jute (treated and untreated) bisphenol-C-based mixed epoxy phenolic resin composites. Polymer – Plastics Technology and Engineering 47 (8): 842–846. 88 Patel, V.A. and Parsania, P.H. (2010). Preparation and physico-chemical study of glass–sisal (treated–untreated) hybrid composites of bisphenol-C based mixed epoxy-phenolic resins. Journal of Reinforced Plastics and Composites 29 (1): 52–59. 89 Raghavendra Rao, H., Varada Rajulu, A., Ramachandra Reddy, G., and Hemachandra Reddy, K. (2010). Flexural and compressive properties of bamboo and glass fiber-reinforced epoxy hybrid composites. Journal of Reinforced Plastics and Composites 29 (10): 1446–1450. 90 Cicala, G., Cristaldi, G., Recca, G. et al. (2009). Properties and performances of various hybrid glass/natural fibre composites for curved pipes. Materials and Design 30 (7): 2538–2542. 91 Wong, K.J., Nirmal, U., and Lim, B.K. (2010). Impact behavior of short and continuous fiber-reinforced polyester composites. Journal of Reinforced Plastics and Composites 29 (23): 3463–3474. 92 Abdul Khalil, H.P.S., Hanida, S., Kang, C.W., and Nik Fuaad, N.A. (2007). Agro-hybrid composite: the effects on mechanical and physical properties of oil palm fiber (EFB)/glass hybrid reinforced polyester composites. Journal of Reinforced Plastics and Composites 26 (2): 203–218. 93 Karina, M., Onggo, H., Dawam Abdullah, A.H., and Syampurwadi, A. (2008). Effect of oil palm empty fruit bunch fiber on the physical and mechanical properties of fiber glass reinforced polyester resin. Journal of Biological Sciences 8 (1): 101–106. 94 Kalaprasad, G., Francis, B., Thomas, S. et al. (2004). Effect of fibre length and chemical modifications on the tensile properties of intimately mixed short sisal/glass hybrid fibre reinforced low density polyethylene composites. Polymer International 53 (11): 1624–1638. 95 Foulk, J.A., Chao, W.Y., Akin, D.E. et al. (2006). Analysis of flax and cotton fiber fabric blends and recycled polyethylene composites. Journal of Polymers and the Environment 14 (1): 15–25. 96 Haneefa, A., Bindu, P., Aravind, I., and Thomas, S. (2008). Studies on tensile and flexural properties of short banana/glass hybrid fiber reinforced polystyrene composites. Journal of Composite Materials 42 (15): 1471–1489.

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14 Advancement of Natural Fiber-Based Polymer Composites Sivaramakrishnan Natesan 1 , Biswajit Parida 2 , Nithya Natesan 3 , Muthuraja Ayyankalai 4 , Waleed Alhazmi 5 , and Anil K. Deepati 5 1

Saveetha Engineering College, Department of Mechanical Engineering, Chennai, Tamilnadu 602105, India Skill Development & Technical Education Department, Govt. Polytechnic Kendrapara, Department of Mechanical Engineering Odisha 754289, India 3 SRM Valliammai Engineering College, Department of Mechanical Engineering, Chennai, Tamilnadu 603203, India 4 Sandip University, Department of Mechanical Engineering, Nashik 4220025, India 5 Jazan University, CAIT, Department of Mechanical Engineering Technology, Jizan, Baysh PO Box 275 Kingdom of Saudi Arabia 2

14.1 Introduction of Synthetic Fiber Enhancement of material properties of fibers has been the focus in the research area over more than 50 years. Synthetic fibers are produced by a chemical synthesis process using petroleum chemicals named petrochemicals. Synthetic fibers exhibit superior characteristics in terms of strength, elasticity, lightweight, washability, softness, cost-effectiveness, and they are also having some special characteristics such as shear resistance, elastic property after applying the crease, resistance to humidity, and high sheen property. The synthetic fibers are categorized as organic and inorganic synthetic fibers. The organic fibers are further classified into rayon, nylon, polyester, polyacrylics, polyamide, and polyolefins. Figure 14.1a–c show the organic synthetic fibers of rayon, nylon, polyester, white polyacrylic, black polyacrylic, multicolor polyacrylic, white polyamide, and polyolefin fibers, respectively. The inorganic fibers are further classified into glass fibers, carbon fibers, boron fibers, and silica carbide fibers. The global price of synthetic fiber in the year 2019 was worth US$ 147.16 billion. It is expected to reach US$ 175.06 billion by 2023 with a 5% of rate of annual return. Count Hilaire demonstrated [2] the formation of spun fiber from cellulose nitrate by means of the hydrolysis process in the beginning of 1880. In 1930, Carothers and Julian Hill did some key experiments on the condensation of polymers, which turned into the formation of higher melting aliphatic polyamides. Synthetic polymers were analyzed for the formation of fibers till 1938. Synthetic fibers are not natural are also called “man-made fibers.”

Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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(a)

(b)

(c)

Figure 14.1 The view of various fibers; (a) glass, (b) Kevlar, and (c) carbon. Source: Saba and Jawaid [1].

14.1.1 Fiber-Reinforced Plastic (FRP) Composites The manufacturing methods, properties, and applications of fiber-reinforced plastic (FRP) have been presented in Ref. [3]. The properties of FRP can be varied with the various parameters such as continuous (long) fiber reinforcement on the matrix, discontinuous (short) fiber reinforcement on the matrix, and orientation of the fiber. More than two different fibers have been reinforced in the matrix in order to produce the hybrid composites. Natural fibers can undergo chemical treatment for the improvement of impact toughness and fatigue strength. Natural fiber-reinforced plastic composite has a vital role in the modern-day manufacturing systems for various applications and with eco-friendly nature. The natural fibers are available plenty and obtained from an animal, vegetable, or cellulose-based mineral source. The most commonly used FRP composites are glass fiber-reinforced polymer (GFRP) composites and carbon fiber-reinforced polymer (CFRP) composites. The method of preparation and material characterization of GFRP have been presented in Ref. [4]. The authors have also illustrated the mechanical, tribological, thermal, water absorption, and vibrational properties of various GFRP composites. A silicon rubber-made mold has been used for the preparation of woven-mat glass fiber (GF) unsaturated reinforced polyester by means of compression. The hand layup method was utilized to fabricate the woven-mat E/GF polyester composites. The results revealed that the tensile strength, bonding strength, and impact strength are increased after reinforcing the glass fiber in the matrix. The applications of CFRP in civil engineering have been investigated in many research articles, as CFRP exhibits well in high specific strength and stiffness and it can be able to withstand the fatigue load than any other composites [5].

14.2 Classification of Natural Fibers There are many sources such as plants, animals, and minerals from which natural fibers can come [6]. In this section, the various aspects of the formation of natural fibers and the sources of generation have been discussed. This can be covered by classifying these types of fibers in detail. These fibers can be any raw material,

14.2 Classification of Natural Fibers

such as hair, which are directly obtainable from an animal, plant, or any mineral source [7]. Further, they can be converted to fabrics or similar types of materials. According to their origin, natural fibers can be categorized into three major categories, i.e. plant-based/vegetable/cellulose-based, animal-based, or protein-based and the important one is mineral-based [8]. The plant-based fiber has a long narrow cell and its types are coir, cotton, and kapok. These are originated on the inner walls of the fruit as the hairs borne on the seeds. The inner bast tissues of the stems of some plants produce fibers such as jute, flax, ramie, and hemp. These tissues are made up of overlapping cells. Leaves of the plants give abaca, henequen, and sisal types of fibers, which represent their fibro-vascular system. The straws of wheat, rice, barley, bamboo, and straw are also the fibers from the stalks of plants known as stalk fiber [9]. The animal fibers generally comprise various proteins of collagen, fibroin, and keratin. These fibers are taken from animal hair such as sheep, goats, and horses. The glands of insects secrete silk fibers while they are preparing cocoons. The fibers from the feathers of the birds are known as avian fiber.

14.2.1 Plant Fibers 14.2.1.1 Seed Fibers

The fiber that is collected from the seeds of the plant is known as seed fiber. Cotton Perhaps it is the most universally used natural fiber across the globe. In every nation, it is virtually consumed by the people and produced in more than dozens of countries. The wide variety of these fiber applications is on apparels and has its uniqueness in benefits for the user. It can be used for a longer duration with a reduced washing frequency as cotton does not retain odors. These are durable and tough enough to last for years. It is one of the most skin-friendly fibers used for clothes and has a very rare history of irritation for the skin. The ability to absorb or drawing off liquid by capillary action provides higher breathability compared to other materials, which helps in moving moisture and heat away from our body. Coir The highest concentrations of lignin make the vegetable fibers such as coir stronger (Figure 14.2). In the meanwhile, due to less flexibility, these are not suitable for dyeing. These are extracted from the outer shell of coconuts and are short and coarse. We can easily mark out these fibers in mattresses, ropes, cushioning of automobile seats, etc. Coir has lower tensile strength than Abaca but has good resistance to marine water and contagious action. Kapok Kapok is an example of fiber originating from the hairs borne on the seeds or inner walls of the fruit (Figure 14.2). It is a light-brown-color silky fiber, which contains the void of 80–90% of overall volume along with abundant hollow micro tubes. It has been received much attention in latest research work. It can also be used in soundproof and heat resistance materials.

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Hemp

Kenaf

Silk

OPEFB

Abaca

Coir

Figure 14.2 Jawaid [1].

Flax

PALF

Jute

Sisal

Ramie

Kapok

Natural fibers as reinforcement in thermosets polymer. Source: Saba and

14.2.1.2 Leaf Fibers

The fiber that is collected from the leaf cells of the plant is known as leaf fiber. Abaca It is famous for its higher mechanical strength and having a lignin content of more than 15% (Figure 14.2). It also has good resistance to marine water applications with better buoyancy where the fiber length may go up to 3 m. As a leaf fiber, it forms the leaf support part and comprises lean cells. It is emerging as a promising energy-saving replacement for glass fibers in automobile applications. Sisal This fiber is stretchable and strong, but moisture absorbance capacity is significantly less. Due to its hardness and coarser property, it is unsuitable for textiles or fabrics. The appearance varies from lustrous to creamy white. It resists marine water (saltwater applications) deterioration and accepts a wide range of dyes. These are used to make cars and furniture replacing glass fibers in composite materials (Figure 14.2). 14.2.1.3 Bast Fibers

The fiber that is collected from the outer layer of the plant’s stem cell is known as bast fiber. Flax It has a crystalline structure but also is a cellulose polymer such as cotton. This

crystalline structure makes the flax fibers stiffer and stronger to handle. It is known

14.2 Classification of Natural Fibers

to be nature’s most potent vegetable fiber. The length and diameter range of flax fibers may be up to 90 cm and 12–16 microns, respectively (Figure 14.2). Jute Due to its length, softness, and shiny appearance, it is otherwise known as

golden fiber. The diameter may range from 17 to 20 microns, whereas length may vary between 1 and 4 m. It falls second in the list after cotton in terms of production quantity and another strongest vegetable fiber from nature. It has high thermal insulation behavior due to which the thermal conductivity gets low. The strong threads made from these fibers make them useful worldwide (Figure 14.2). Hemp It is the oldest cultivated fiber plant, first originated in Southeast Asia then spread to other regions. These fibers contain about 70% cellulose and around 8–10% lignin. These are durable and strong and the diameter may range from 16 to 50 microns. The length of these fibers is also substantial. Hemp is good in dyeing and blocks harmful ultraviolet (UV) lights. It has natural antibacterial properties and conducts heat. The property of growing quickly without agrochemicals made using these fibers in agro textiles, automobile panels (Figure 14.2). Kenaf It is a lightweight and eco-friendly fiber. It has high tensile strength as com-

pared to synthetic fiber. This fiber has emerged as an essential plant cultivated in different countries and has been regarded as an industrial crop. It has great potential for replacing synthetic fiber such as glass fiber (Figure 14.2). Ramie These are mainly produced in East Asian countries and made for summer (Figure 14.2). It is a lustrous, white-colored silky fiber with a similar absorbing capacity and density as flax but having a coarser size of approximately 25–30 microns. It is an easy dyeing fiber with low elasticity. The strand length of these fibers may range up to 190 cm with as long as 40 cm length of individual cells. It is lightweight and facilitates ventilation. 14.2.1.4 Stalk Fibers

The fiber that is collected from the stalks of the plants is known as stalk fiber. Wheat It is the bran, the outer part of the wheat grain. Wheat fiber is an off-white dietary fiber. Rice The outer husk of the rice contains fiber, which is very helpful to provide

energy along with the rice for the whole day. Barley This contains soluble fiber. This helps in controlling blood sugar levels and reduces cholesterol by dissolving in water.

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Bamboo These are regenerated from bamboo plants and come under cellulosic

fiber. The strength level can be comparable to conventional glass fibers. The presence of various micro-gaps in these fibers makes them softer and also increases the moisture absorption capability. Alps bamboo fibers are elastic, eco-friendly, and biodegradable. Straw Three significant types of straw comes from crops such as rice, wheat, and

corn. It is produced about 1.2 tons per acre from wheat alone. The primary applications of these fibers are animal fodder and bedding. These are also burnt to prevent soil-borne diseases. However, these fibers have a waxy covering on the surface. Alkali materials are difficult to penetrate due to their unique morphological structure. The obtained fiber bundles were considerably coarser than cotton.

14.2.2 Animal Fibers Animal fibers are mainly protein-based fibers except for silk and they can be derived from animal hair. 14.2.2.1 Wool

It is easiest to spin due to its natural crimpiness and scale types of pattern. These fibers are elastic and durable and provide better insulation. The fiber diameter may vary from 40 to 16 microns from coarser hairy wool to superfine merino wool, respectively. Its exceptional properties and limited supply made it one of the world’s premier textile fibers. 14.2.2.2 Mohair

These are lightweight, insulating fibers having thinner surface scales like wool. The significance of the name is because of a characteristic luster due to the reflection of light. It is smooth to touch but has significantly higher tensile strength than merino wool. 14.2.2.3 Cashmere

It is one of the expensive and rare fibers, which has small air spaces between itself. This makes it warm with minimum weight, while the cuticle cells present on the fiber surface result in its smoothness and luster. The best quality fiber’s diameter is just 14 microns, which is not more than 19 microns. 14.2.2.4 Alpaca Hair

These are lustrous, dense, and silky fibers used to make high-end luxurious fabrics, particularly outdoor sporting clothes. It provides excellent insulation with lighter weight and is stronger than the wool from the sheep. The diameter of the threads ranges from 20 to 70 microns with partial hollowness and may be available up to 22 natural colors.

14.3 Synthesis and Production of Natural Fibers

14.2.2.5 Angora Hair

It is one of the silkiest animal fibers with hollowness under the wool class (Figure 14.2). The diameter range is 14–16 microns with silky white color. Due to the presence of cuticle scales, it is exceptionally soft to touch. 14.2.2.6 Silk Fiber

These are secreted from glands of animals’ mouths (insects). This occurs during the preparation of cocoons. This continuous thread filament has a tensile strength of the order of 500–1500 m in length with a diameters range of 10–13 microns. The natural shine of these fibers comes from their triangular structure (in woven silk), which acts as a prism. And when the light refracts, it gives shine. These fibers can be dyed easily and have properties such as low conductivity and sound absorbency. It remains the queen of fabrics. 14.2.2.7 Avian Fiber

These are the fibers taken from the feathers of the birds.

14.2.3 Mineral Fibers These are inorganic and nonmetallic fibers. Asbestos comes under naturally occurred fiber, whereas synthetic fibers such as slag wool or rock wool can be produced by blowing air or steam through molten rock or slag. Fibrox is another widely used mineral fiber because of its better thermal and acoustic insulation. But the mineral fibers are made of tiny fibers that, when inhaled, can settle inside the lungs and irritate the tissues in the respiratory tract.

14.3 Synthesis and Production of Natural Fibers Synthesizing of bio-based natural fibers for composite material application begins with extraction from the source, then preparation to process the fibers. The extraction process of the fiber from various sources is different. It includes ginning/retting, barking, decortication, degumming [10]. After extracting the fiber, the fiber preparation stage is carried out. This stage includes cleaning, hackling, carding, refining, sorting, and chemical modifications followed by the fiber processing stage. In this stage, the fibers pass by spinning, weaving, and finishing through different techniques [11].

14.3.1 Extraction of Fibers Production of natural fiber-based polymer composite starts with extraction of the fiber from its origin. For instance, plant fiber (from plant and vegetable), animal fiber (from animal wool, hair, and feather), and mineral fiber (from minerals). Extraction of natural fibers needs particular precaution since the fibers sustain all the load in the composite material. Overall fiber quality directly affects the strength of the composite material.

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14.3.2 Extraction and Processing of Plant-Based Fiber In the plant fiber extraction process, the two main procedures are done. These are fiber separation/extraction and refinement/preparation process. These processes are different for different plant types. For most plant types, most of the technical fiber separation from its bark, woody tissue, or fleshy part is done using a mechanical processing technique. It is related to the demolition of the bark, plant stem, and distinctive plant parts by crushing, squeezing, decortication, peeling, rubbing, or breaking. This mechanical process is suitable for mass production. The fiber obtained by this technique is lower in quality since it induces fiber damage and wears [12]. Then the extracted fiber follows the fiber preparation stage. In fiber preparation, cleaning, hackling, carding, and refining, extrusion, chemical/physical treatments are carried out. First, fiber was extracted with different types of the fiber extraction process and then fiber is prepared. The fiber is processed with spinning, weaving, dyeing, printing, or finishing processes [13, 14]. The technical stages of fiber extraction with mechanical processes, which are suitable for long fiber are as follows: ● ● ● ●

Breaking machine or softener Scotching Conditioning Sorting fibers according to fiber type and quality [14].

The extraction of fibers from plants is put through stem, seed, bast, core, and leaf. The extraction of the fiber can be passed through in three stages: The initial stage is decortication. In the decortication stage, the bark is detached manually or by using a machine. Then, the cortex is abraded to get rid of the outer layer which is called bark, fleshy layer, some of the gums, and pectin. The bark or waxy layer is removed and breaks into an entry passage for the retting processes. Then, the cortex is water-washed and dried up followed by a degumming procedure [12]. Factors to be considered during the mechanical processing of fiber extraction are as follows: ● ● ● ●

Suitable workspace for separating various fibers. Feeler rolls size and shape Forces of working elements on the fibers Roller speeds and other operating factors

The effect of moisture is crucial in fiber production since it directly affects the fiber quality [14–16].

14.3.3 Extraction and Processing of Animal Fiber Animal fiber, such as wool, silk, human hair, cashmere, feathers, is sourced from animal or hairy mammals.

14.3 Synthesis and Production of Natural Fibers

14.3.3.1 Animal Wool and Hair Fiber Processing

Fibers found from animal sources are passed through different stages such as shearing, washing, spinning. For instance, animal hair is a protein-based filament that grows on its body [17]. It starts with shearing from the source animal. The significant methods to procure wool from the sheep are trimming or shearing, cleaning, sorting, carding and spinning, weaving, and finishing. 14.3.3.2 Silk Fiber Processing

The silk fiber is acquired from the larvae of various silkworms specifically some species of Bombyx mori, cocoons. Silk processing mainly involves two steps, sericulture and silk filature operations [18]. Sericulture is an important step in silk processing, which focuses on silkworm rearing for the production of cocoons. The major activity of sericulture is to cultivate the plants that help as a feed to the silkworms formed as cocoons at a later stage. Cocoons are the basic fundamental material for the preparation of silk fiber. The essential primary-raw silk filaments are rolled around the silkworm and followed by the filature process. Reeling silk fiber from the cocoon is called silk filature process. Silk filature involves sorting the cocoons based on their size, texture, color, and shape. In the later stage, the extracted silk fibers are immersed in hot and cold water to get softened. Then after passing through several processes, such as the tram, crepe, organize. It is followed by the silk fabric finishing step. This involves calendaring, creeping, and singeing processes. In this process, the silk fabric improved its appearance, durability, and becomes smooth [19]. 14.3.3.3 Feather and Avian Fiber

Feathers are found in the epidermal layer of the skin in birds and some vertebrate animals as the external covering/plumage on the birds. Processing of these feathers starts with the removal of the feather quill inner and parting the feather at the center. Cleaning of feathers is the main task to process further the feathers [19].

14.3.4 Extraction and Processing of Mineral Fiber 14.3.4.1 Asbestos

Asbestos is naturally available in the environment as a rocky ore. Asbestos is a naturally existing mineral-based fiber [20]. Magnetic sensors are the instruments used to detect the availability of the ore in various places around the world. Mining, milling, and several processes are used to use in composite material applications. Asbestos processing includes flaky fiber separation from its ore by the operations called branch drilling, open-pit mining, etc. With the help of a crushing machine, mining and milling operations are performed and the open-pit mining is a surface/exterior mining technique of asbestos ore. Asbestos fibers are collected in a vacuum chamber to avoid free-flowing to the environment due to air. Then separating the fibers according to their length with the rock circuit followed by compressing and packaging is performed [19].

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14.3.4.2 Ceramic Fiber

Ceramic fibers are the predecessor fiber materials obtained while processing the tungsten wires. Ceramic fiber applications in composite material manufacturing are well known for decades. Composite materials made of these fibers endure high temperatures, corrosion resistance, and possess high mechanical properties. Alumina fiber-based composite material named Nextel 610 is an example. Using the mullite matrix, a classic lamination procedure is adapted to fabricate composites of polymer matrix [20–22]. Other types of ceramic fibers include aluminum oxide (Al2 O3 ), ceramic glass fiber, silicon carbide (SiC), and boron carbide (b4 C). 14.3.4.3 Metal Fiber

Various metal fibers are used for manufacturing composite materials, which include aluminum, molybdenum, magnesium, tungsten, and copper. These metal fibers are produced from recycled alloys, which possess good heat resistance and other mechanical properties [23, 24].

14.4 Treatment and Enhancement of Natural Fiber Apart from the essential features of natural-based fiber, it also has downsides such as absorption of moisture, minimal fire resistance, comparatively reduced mechanical properties, inferior durability and quality under loads, and difficulties during the manufacturing process [25]. The significant challenges in natural fiber composite are inferior sticking among fiber and matrix and low compatibility issues among the hydrophobic matrix and the hydrophilic fiber, causing a bulge in fiber within the matrix. To improve these weaknesses of natural fiber, it passes through several surface treatments. These fiber surface treatments may include physical and chemical treatment techniques to attain some of the objectives mentioned below [26–28]: ●

● ● ● ● ●

To remove surface impurities and undesirable fiber constituents (such as oils, waxes, pectin) To roughen the fiber surface topography To remove the variations in the fiber surface chemistry Chemical modification of the surface of the cellulose fiber Individual fiber bifurcation among fiber bundles Reduction in the fiber hydrophobicity

There are three treatment techniques, physical, chemical, and biological [29]. Physical treatments adapt to enhance the modulus, strength, and elongation characteristics of the fibers. In contrast, chemiluminescence procedures are accustomed to boost the durability and interfacial features of the fiber–matrix combination [30]. This natural fiber surface treatment provides better mechanical strength, adhesion, and hydrophobicity characteristics. Natural fiber sourced from animals is protein-based material such as keratinous fibers (wool and hair). Many studies suggest removing this lipid layer that involves

14.4 Treatment and Enhancement of Natural Fiber

altering surface properties since it exposes a proteinaceous surface to various reactive chemical moieties. The surface treatment of proteinaceous fibers includes both physical and chemical treatment techniques: physical such as plasma, UV/ozone (UVO) and chemical such as bleaching, acylation, chlorination, and other treatments. Some enzymatic treatments are also utilized to denticulate, enhance the surface properties [29].

14.4.1 Physical Treatment In the physical treatment of both cellulose and protein-based fiber, the fiber surface is etched or roughened to enhance the fiber exterior area and facilitate mechanical interlocking during fiber–matrix bonding [20]. These treatments enhance the fiber–matrix interaction bond without altering the composition of the fiber surface. This method is used to segregate natural fiber envelopes into separate fibers to avoiding fiber overlying [30]. Based on the treatment techniques, physical treatments of cellulose-based plant fiber are classified into (i) mechanical treatment, (ii) solvent extraction, and (iii) electric discharge (ED) treatment. Figure 14.3 shows the classification of various fiber treatment techniques. 14.4.1.1 Mechanical Treatment

Mechanical treatment is the surface enhancement of the fiber by using stretching, calendaring, and rolling techniques. In the mechanical stretching process, the fiber possesses a maximum tensile strength and reduced fiber rigidity and density. Due to that, better load distribution in the composite exists. However, it can also trigger Natural fiber modification

Physical treatment

Chemical treatment

Biological treatment

Mechanical (stretching, calendaring, rolling)

Alkali

Retting

Solvent extraction

Coupling agent

Fungal treatment

Electric discharge (corona, plasma, thermal, UV)

Enzymes

Bleaching

Figure 14.3

Natural fiber modification technique.

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extra elongation and shrinkage on the fiber responsible for fiber pre-failure [30, 31]. In the mechanical calendaring process, by using the roller, the fibers are converted into an extended sheet, which can be fitted into the designed mold. The fibers are susceptible to get damaged while calendaring process. The rolling and the swaging processes are used to yield the fiber bundle into individual filaments. The rolling operation enhances the dispersibility and adhesion of fibers with polymeric matrices [32]. In this process, the fibers become plasticized, the fiber surface and its structural properties are enhanced physically to mechanical interlocking. It is a conventional fiber treatment technique that minimizes the fiber damage and enhances the fiber–matrix surface interaction. 14.4.1.2 Solvent Extraction

Mechanical fractionation is one of the solvent extraction techniques, which helps to remove soluble impurities from the fibers. It uses a blend of water and organic solvents such as acetone, carbon tetrachloride, benzene, petroleum ether, methanol, etc. to extricate soluble contaminants from the fiber. Nevertheless, the solvent treatment is not commonly used since the fiber experiences and contaminates the ecosystem water during discharging [30]. High fiber cellulose content is extracted in this process. 14.4.1.3 Electric Discharge

Electric discharge (ED) treatment is a suitable treatment method to improve the fiber’s hydrophilicity during fiber–matrix bonding through roughening the fiber surface. It has a lower impact on the environment than the solvent extraction treatment technique. Thermal treatment, plasma treatment, and corona treatment are the common listed techniques in electric-discharge treatment. Thermal treatment of fiber is the most common ED technique to vary the fiber physical characteristics by heating at the temperature range of 100–200 ∘ C for some duration [33]. Plasma treatment is an effective and stable treatment method of electrical discharge treatment. It modifies the outer surface layers of the fiber by changing the surface morphology by sputtering effect and producing roughen contact area, which is the reason for mechanical interlocking of matrix and the fiber. However, the fiber is exposed to degradation, which is the cause of lower strength [30–34]. The roles of plasma treatment are as follows: ● ● ● ●

Cleaning the fiber surface Etching the fiber surface that leads to a rougher surface Cross-linking/branching the fibers that facilitates mechanical interlocking Modification of surface ionic properties with the introduction of free radicals [29, 30].

Types of established electric discharge treatment methods intended for the treatment of fiber are (i) plasma treatment, (ii) corona treatment, and (iii) ultraviolet treatment.

14.4 Treatment and Enhancement of Natural Fiber

Plasma Treatment Plasma treatment is a clean, dry, and environmentally green phys-

ical technique. This treatment employs a plasma gas electrical discharge to modify surfaces by cleaning and etching the fiber’s surface. It is the process of electrical discharge methods replacing the surface polymer functional group of the fibers with different atoms from ions in the plasma. Plasma treatment is held with radiation of UV at a high level to the fiber. Exposing the fiber surface to energetic species breaks the polymer surface, which creates free radicals [29, 35–37]. The plasma treatment technique alters the layers of the external surface of the plant fiber. However, the plasma-treated fibers show significantly minimal strength owing to the fiber degradation during treatment. It is a facile and environmentally green process to modify the fiber’s surface without changing the bulk properties [38, 39]. Fiber surface ablation, a subsequent decrease in the tenacity, and weakening of the exterior portion of the material can occur due to the increase of discharge energy during plasma and corona treatment. The plasma-treated fiber immediately processed using the resin infusion under flexible tooling (RIFT) manufacturing method to avoid contamination of the treated fiber [33]. For animal-based fibers, both plasma and corona treatments oxidize protein-based fibers surface. Corona Treatment Corona treatment method uses an electric current to treat or change cellulose fiber energy [30]. This method makes the fiber surface rough so that the fiber adhesion to the polymer is significantly improved. Although the process is low energy consuming and low cost, it is not widely used because of the process complexities and difficulties. In corona fiber treatment, the fiber surface polarity is improved and due to that fiber wettability is improved. However, because of etching and surface ablation, fiber tenacity is possibly reduced. Plasma means the product of an electromagnetic field with ionized gas, which contain ions, electron, and neutral particles [33, 40, 41]. Ultraviolet Treatment Ultraviolet (UV) rays are applied for the exterior treatment of natural fibers, which consist of shorter wavelengths compared to visible light that confines 10–400 nm. This process is clean and widely applicable since UV sources are adequately economical, flexible to operate, handle, and establish the setup. UV treatment altered the fibers’ polarity due to improved wettability [33, 42, 43]. Generally, physical treatment of the fibers is carried out exhaustively to separate the individual filaments from their bundles to modifying the surface roughness and to remove contaminates and foreign substances settled on the fiber.

14.4.2 Chemical Treatment Most of the chemical treatments of fiber are done by impregnating the fiber under chemical solutions. A third material is introduced as a compatibilizer or coupling agent for a matrix to fiber bond. Chemical treatments are used to intensify the durability, adherence properties of the fiber–matrix by altering the chemical properties of the external surface of the fiber [29, 30]. Chemical treatment of animal-based fibers,

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shrinkage, felting, and diffusion barriers are the most unwanted features of wool and other protein-based fibers. Chemical treatment of plant fiber is used to reform and enhance the surface structure of the fiber using a chemical such as hydroxyl (OH) group to adjust its constituents by introducing a new element. Using chemical reagents such as alkali, enzymes, bleaching, and others are used in these treatment techniques [26]. 14.4.2.1 Alkaline Treatment (Mercerization)

Mercerization is the practice of plunging the fiber into an aqueous alkaline solution with water. The importance of this treatment is used to disrupt the hydrogen bonding in the network, which increases the fiber skin roughness, thereby improved the interlocking phenomenon of fiber and matrix takes place [44]. Sodium Hydroxide (NaOH) NaOH is a common technique used for fiber chemical treatment [45–50]. The alkaline treatment eliminates some quantity of wax, lignin, and oils that cover the skin of the fiber [33]. In alkaline treatments, especially NaOH’s use to alter the surface of the fiber in the composite has been reported by many studies [37–39]. NaOH plays a critical role in removing hemicellulose, and artificial impurities utilizing alkaline cleavage and pectin are also removed in this solution. It results in exposed cellulose of the fiber to the possible reaction in the sites. This aqueous sodium hydroxide (NaOH) treatment of natural fibers endorses the hydroxyl group’s ionization to the alkoxide from the fiber surface [51]. Many scholars report that fibers, which are immersed in 5% NaOH and cleaned with distilled water, are used to remove amorphous compounds and increased the crystallinity index of cellulose fiber. They recorded that due to increasing crystallinity the tensile property of the fiber also increases and is better than the untreated one. NaOH alkali treatment has been a simple and economically viable tool to modify fibers’ surface chemistry. The consequences and results of alkali treatment on the mechanical performance of the jute-based composite were reported [39]. The study showed that composite with alkali-treated fiber exhibits superior mechanical strength than the untreated one. The reason may be that treated fiber seems rough, which improves the adhesive characteristics. Most studies focused on protein fibers such as feather, hair, wool, and silk have a low resistance to alkalis [44].

14.4.2.2 Acetone Treatment

Acetone is an organic solvent that dissolves the nonorganic components of fiber-like lignin, cellulolignin, and others. This acetone treatment was conducted by dipping the fibers in acetone at 90 ∘ C for about 60–80 minutes, followed by cleaning with pressurized water followed by drying at room temperature [44, 52, 53]. The concept of acetone treatment is coating the OH group of the fiber with hydrophobic molecules of an acetyl group responsible for fiber hydrophilic characteristics. The acetylation of the OH group in cellulose is represented in the equation below.

14.5 Fabrication of Techniques of NFRC

14.4.2.3 Peroxide (Benzoylation) Treatment

Benzene carbonyl chloride is the most usually used chemical in benzoylation treatment. It also includes C7 H5 CIO, which is responsible for the hydrophilic nature of the treated fiber and improves fiber–matrix adhesion. After submerging the fiber into benzoyl solution and washed through water, the fiber is then immersed in ethanol for 60 minutes to eliminate the benzoyl chloride. Usually followed by NaOH treatment, this alkali pretreatment is used to activate cellulose-OH groups for benzoylations [54]. 14.4.2.4 Silane Coupling Agents (Silanization)

Silane coupling agents present in the interphase region, the area between an inorganic substrate and an organic substrate represent as a bonding agent to enhance the bonding phenomenon over two nonidentical composite materials [54, 55].

14.4.3 Biological Treatment Biological treatment is the use of naturally existing microorganisms to modify the surface structure of the fiber. Bacterial and fungal are the common microorganism to be used in this technique. These types of treatment are performed in an aqueous environment and cheap but need a long processing time and are water-polluting. The two most known biological treatments are retting and fungal treatment [56]. In the retting process, the fiber is separated from fiber bundles and woody core, and epidermis with controlled degradation. Bacteria and fungi liberate enzymes are used to degrade pectin and hemicelluloses. This process provides the separation of the fiber from the bast, the woody core, and leaves, and then it provides soft and clean fiber. In this process, high-quality fiber may be produced. However, it is highly reliant on environmental conditions and the judgment ability of the worker [29]. The fungal treatment enhances the surface roughness of the fiber, which is helpful for mechanical interlocking with the matrix. However, it has a biological impact on the environment [57–59]. Many treatment techniques are listed in different studies, including TDI treatment, esterification, isocyanate treatment, and silane. But the above listed are the frequently used methods for the fiber treatment used in composites manufacturing.

14.5 Fabrication of Techniques of NFRC The physical and chemical features of NFRC may differ from subject to the fiber type, fiber orientation, composition, fiber treatment, and matrix. Polymer matrix, environmental effects, and the fabrication/processing techniques are implemented [60]. A significant amount of research findings were reported to assess the influence of the above aspects on the properties of natural fiber-reinforced composites [61–67]. The manufacturing techniques of NFRP composites are shown in Figure 14.4. Some of the primary and familiar fabrication methods for fiber-based composites are hand lay-up, vacuum infusion molding, pultrusion, spray lay-up, resin transfer molding (RTM), and filament winding [68].

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Short/discontinuous fibers

Continuous fibers

Open mold

Close mold

Hand layup

Filament winding

Compression

Pultrusion process

Automated tape winding

Other Tube rolling

RTM

Open mold Spray method

Close mold Compression molding

Other Centrifugal casting

Transfer molding Injection molding

Figure 14.4

Fabrication methods of NFRPC.

14.5.1 Hand Lay-up Technique It is an old and comparatively easy technique [69]. The fabrication of composite material by this method includes the standard steps. Initially, the mold surface must be treated by release anti-adhesive gel to get rid of polymer sticking to the mold bottom and side surfaces [70]. Appropriate fiber layers to be added to the mold, followed by the resin layers to be spread over the fibers using a brush. Proper care must be taken while adding and spreading the resin to get a homogeneous surface [62, 71]. Keep a thin plastic sheet over each layer and apply some pressure using a roller, it helps to remove any air bubbles and spread of resin in the entire area over the fibers. And the same procedure must be followed until acquiring the desired thickness of the material. Keep the mold at room temperature to get cured for about 24–36 hours, and finally, the composite must be removed from the mold [72, 73].

14.5.2 Vacuum Infusion Molding The vacuum infusion molding method for processing NFRPC is developed and patented by Marco in 1950. This method possesses good potential in designing and fabricating the composites materials economically. This technique is a straightforward molding process where the resin is driven by the vacuum into mold similar to the RTM process. This method is usually applied for fabric-based composite materials. The fabric-based natural fibers are cut into the size and shape of the mold, placed over the die layer by layer. The mold with multilayered fibers is then vacuum-bagged [74]. The resin is dried and fused to the fabric with the help of a vacuum. The final composite laminate is slowly removed from the mold [75, 76].

14.5.3 Spray Lay-up Technique The spray lay-up technique is very similar to hand lay-up. Nevertheless, it uses an electric gun to spray resin and chopped fibers on a mold. Instantaneously, a simple hand-operated roller is used to remove any trapped air inlay and fuse the fibers into the resin [77–79].

14.6 Mechanical Performance of Natural Fiber Reinforced Polymer Composites (NFRP)

14.5.4 Pultrusion Pultrusion is a continuous composite fabrication process that involves the coiling of fibers that are driven through the resin chamber. Finally, these fibers are passed through the preheater to get the desired shape and followed by the final curing. Toward the end, with the help of a cutting saw, the final product of the composite material has to be bisected to the desired shape and size. The products by the pultrusion process come under mass production and this process is not economical for batch production [80, 81].

14.5.5 Resin Transfer Molding (RTM) The RTM can be described as a fast injection molding process. A mat of weave fibers or fabric is positioned on the lower die, the top die closes the fiber mat and the resin is sent over the fibrous mat then cooled to get the finished product. Controlling the pressure and temperature of the resin is crucial in this process. This process is considered the fastest of all composite fabrication techniques. The surface finish and the final product quality obtained by RTM are quite accurate. RTM is widely applicable in making the automobile, sanitary tubes and tubs, aircraft parts, etc. [82, 83].

14.6 Mechanical Performance of Natural Fiber Reinforced Polymer Composites (NFRP) The natural fiber composite has significant properties, which depend on physical and mechanical properties, interfacial adhesion, surface defects, orientation, and volume fraction. Among all, the mechanical behavior of natural fiber-reinforced polymeric composites is mostly influenced by interfacial bonding between the fibers and matrix. Interfacial adhesion bonding occurs when two different materials are blended, combined, or mixed. These combinations may create a better dispersion of materials into the matrices. The mechanical properties of various natural and synthetic fibers were discussed in the available literature [77–80].

14.6.1 Influence of Chemical Treatment The ability of the material to resist the deformation under the load before fracture is said to be flexural strength. It is also known as bending strength or transverse rupture strength. Flexural properties signify the materials’ flexibility, and it indicates the nature of materials such as brittle or high hardened materials [81]. The specimens were prepared as per the ASTM D790 standards for evaluating flexural strength under bending tests. The flexural strength of composites increases with bonding strength between fibers and matrix [82]. The failure of bonding of the F–M system leads to the pull out of fibers from composites during loading. The fiber–matrix interface, therefore, plays an essential part in the strength of materials. In this light of view, the understanding of the bonding mechanism of fiber and matrix systems

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needed to be reviewed. The bonding can be improved by providing sufficient adhesiveness in the F–M interface. The adhesion behavior of almost all the natural fibers is generally inadequate with polymeric matrix (epoxy, polypropylene [PP], etc.). The hydrophilic behavior of natural fiber encourages increasing moisture absorption, which results in the formation of voids at the interface of the F–M system. Therefore, understanding methods to enhance the adhesion behavior between fibers–matrix (F–M) interface is essential to carry out the research. The factors which are influencing the flexural strength of F–M systems can be interfacial adhesion and fiber wettability. Wetting is liquids’ ability to spread with a minimum contact angle less than 90∘ on solid surfaces (or liquid). Wettability is considerable to upgrade the mechanical strength of the natural fiber-reinforced polymer composites. These factors can be modified through surface treatment. The surface treatment enhances the mechanical properties of fibers through the upgrading of shear strength between fibers–matrix system. Fiber wettability refers to the reflection of surface free energy, which comprises polar and dispersive components. Surface free energy can be analyzed using the Wilhelmy method (dynamic contact angle analysis). The wettability analysis of fiber on interfacial bonding of fiber-reinforced pultruded poly phthalazinone ether sulfone ketone [PPESK] composite has been investigated [83]. There was no treatment done, rather the drying process was carried out. It was concluded that aramid fiber obtained greater surface polarity than glass fiber in composites. The aramid fiber increased surface free energy of 38.9 mN/m and 10–50% greater than CFRP and GFRP composites. It was attributed to the lesser contact angle between fiber–matrix system. The higher the surface energy the higher the wettability, and it reduces interfacial failure. Scanning electron microscopy (SEM) analysis revealed that interfacial failure was in glass fiber composite and matrix failure was in both aramid and CFRP composites. The flexural strength of aramid and CFRP was therefore about 15% and 5% greater than GFRP, respectively. This result of glass fiber is attributed to more moisture absorption and more damage to interfacial adhesion than others. An experimental investigation was carried out on an alkaline treatment of flax-resin system on mechanical properties and creep response [84]. The result revealed that alkaline treated flax/VE composites gained 70% greater interlaminar shear strength than the untreated ones. Acrylic resin with vinyl ester in composites increased interlaminar bonding strength by 30% of untreated. Tensile strength was increased by 11% for alkaline treated flax-acrylic resin-vinyl ester composites. This can be attributed to enhancing the crystallinity and structure of the cellulose after treatment. Nevertheless, the tensile modulus of treated flax fiber reduced, attributed to the breakdown of flax fiber. But, flexural properties were not much increased in the case of treated composites. It was revealed that the flexural strength of the treated one was about 5% greater than the untreated one. The tensile and flexural modulus of fiber was shown to decline after treatment. This reduction of modulus is attributed to the structural modification of flax fiber. The addition of 1% of acrylic resin was successful in delaying creep and extended creep response. From the above results and discussion, it was understood that alkaline treatment and adding acrylic resin to the resin influences mechanical properties and creep response.

14.7 Effect of Hybridization

The significant effects of chemical treatments were reported on the surface energy and mechanical properties of composites [85]. The natural flax and flax pulp fibers were used, and polypropylene was used as a matrix. The surface energy of long flax fibers and irregular pulps was calculated using the dynamic contact angle method and capillary rise method, respectively. The result revealed that maleic anhydride-polypropylene copolymer (MAPP) enhanced surface energy and mechanical properties. Natural flax fiber gained greater stiffness than composites containing flax pulp. 10 wt% MAPP treated fibers in composites have shown superior flexural and tensile strength as treatment enhances wettability and interfacial adhesion increases. Therefore, no evidence of a significant effect on modulus was observed by treatment. This result indicated that treatment not significantly influences tensile and flexural modulus, instead influences those strengths. Two similar matrices of bisphenol an epoxy resin 618 and bisphenol-F epoxy resin NPEF-164X were procured and utilized for improving wettability and interfacial bonding in between carbon fibers (CF)/epoxy composites using a modified epoxy emulsifier [86]. In this experimental investigation, the Young–Laplace equation was used to obtain a contact-angle of the prepared epoxy sizing droplets and the fiber. Composite with modified epoxy resin was shown a narrow particle size distribution, which indicates that a modified epoxy emulsifier has a superior emulsifying effect on F-type matrix than A-type matrix in composite. The result revealed that the interfacial bonding between fiber and resin matrix was enhanced due to sizing, which upgraded the fiber wettability and formed a strong bond with the matrix.

14.7 Effect of Hybridization Hybridization is the process of merging synthetic fibers with one or more natural fibers. It enhances the overall properties of composites. Hybrid natural fiber polymer composites can be developed with the required qualities of expected properties in a very cost-effective way, which is very complicated to do with composites that contain only one type of fiber/filler dispersed in the matrix. The hybridization of fiber led to better mechanical properties of flexural, tensile, and impact strengths of composites. Therefore, the mechanisms and their impact on properties need to be understood. The various factors, such as volume fraction, orientation, etc. play an essential role in enhancing mechanical properties via hybridization. To understand the factors and their effect, many available research works have been reviewed as follows.

14.7.1 Fiber Percentage (%) The hybrid flax laminates of composites with low carbon fiber volume fractions reinforced epoxy matrix were fabricated [87]. The result shown was a brittle failure of carbon and flax laminates. Microscopical studies indicated superior interfacial shear strength due to good wetting between flax fibers and carbon fibers in the hybrid composites. The pores in natural fibers are attributed to a blend of low-viscosity

279

0°

±22.5°

±45°

±67.5°

90°

Ultimate tensile strength (MPa)

14 Advancement of Natural Fiber-Based Polymer Composites

Tensile direction

280

160 120 80 40 0

(a)

(b)

0°

22.5°

45°

67.5°

90°

PP

Figure 14.5 (a) Schematic of different fiber orientation of CLY and (b) fiber orientation of composites on ultimate tensile strength. Source: Cordin et al. [89].

epoxy resin into the fiber wall pores. However, fiber pull-out at a minimal level was observed. With 8 vol% of carbon, strength and stiffness increase to 50% and more and enhance specific strength up to 30%, which is higher than composites with aluminum. With an additional 6 vol% of carbon content, stiffness of composite increases 2.3 times greater than composites with the flax-epoxy system. The experiments were carried out on polypropylene–lyocell composites to evaluate the effect of fiber orientation on mechanical behavior [88]. The composites of the reinforcing cellulose type lyocell fibers (CLY) were prepared with five different orientation with the angle to the long axis of 0∘ , ±22.5∘ , ±45∘ , and ±67.5∘ , and 90∘ fiber orientation were selected (Figure 14.5a). The different orientation has been taken for experimental analysis as shown in Figure 14.5b. The highest ultimate tensile strength was obtained for the composite with all CLY fibers oriented in parallel to the direction (Figure 14.5b). Therefore, it was concluded that stiffness of composites with an angle above 45∘ was observed low in value. The result has also shown that interfacial shear strength between the fiber–matrix system was not adequate. The effect of alkali and silane on bonding and mechanical strength between fiber–matrix system of kenaf and pineapple leaf fibers was reported [90]. It was shown that treatments enhanced the properties of fibers by removing lignin and hemicelluloses and got cemented with cellulose. It was identified from Fourier transform infrared (FTIR) spectra that the silane treated pine apple leave fiber (PALF) and Kenaf fiber (KF) reduce their hydrophilic characteristics. Therefore, water absorption is reduced significantly. The flax fibers were considered as a reinforcement to produce biodegradable composites using a film stacking technique and hot-press [91] method. The variable factors of flax and silane addition, hot-press temperature, and hot-press time were selected for experimental investigation. The experimental results showed that flexural strength and its modulus increase then decrease with increasing of 30–50% of flax fiber in developed composites. The sugar palm fibers with reinforced phenolic composites were fabricated and their mechanical properties were investigated [92]. The result revealed that compressive, impact, and flexural strengths were increased with increasing sugar palm fiber percentage up to 30 vol% of sugar and phenolic composites. Figure 14.6a has shown the flexural strength on various orientation fibers. It was shown that sisal with 90∘ was 371.33 MPa was 65% higher than that of banana fibers with 90∘ . Figure 14.6b has shown the tensile strength on various orientations of sisal and banana fibers.

(a)

Sisal 90

Banana 90

Sisal 0.90.0

Banana 0.90.0

(b)

0.0

0

0.9 an a Ba n

0

a9

Si sa

l9

0

96.375

an

126.67

100

32.5 20

16

Ba n

200

56.5

.90 .0

300

60 50 40 30 20 10 0

l0

320.625

Si sa

371.33

(MPa)

400

Tensile strength

Flexural strength (MPa)

14.8 Effect of Hybridization and Its Application of Nanofiber

Orientation of fibers

Figure 14.6 (a) Fiber orientation of different composites on flexural strength and (b) fiber orientation of different composites on tensile strength. Source: Sinha et al. [6].

It was observed that sisal with 90∘ has 65% higher tensile strength than that of banana fibers with 90∘ . Thus, the influence of chemical treatment and fiber-fraction, orientation on mechanical properties has been reviewed. From the review of the mentioned contents, it was concluded that alkaline chemical treatment was observed as a superior method and it increases the mechanical performance of fiber composites. The increase of fiber orientation, possibly reducing stiffness as compared with different orientations (Table 14.1).

14.8 Effect of Hybridization and Its Application of Nanofiber This chapter illustrates the constructive effects on hybridization of nanofibers, synthesis of nanofibers, and their latest applications.

14.8.1 Effect of Hybridization of Nanofibers Over Mechanical and Tribological Fibers The hybridization mechanism improves the mechanical, tribological properties of fibers in general and also in biomedical and structural applications. The recent applications of hybridization are wear behavior, ballistic performance, green composite materials, and the development of hybrid micro/nanocomposites. A novel and scalable process method to manufacture hybrid micro/nanocomposites has been presented in Shariatnia et al. [99]. The author investigated the properties of hybridization of cellulose nanocrystal (CNC), pristine carbon nanotubes (CNTs) along with CFRPs without any addition of surfactants for chemical functionalization. During the process of manufacturing, CNC, fCNT, and CNC-pCNT were dissolved in water and these dissolvent have been used as coating suspensions. Experiments had been conducted to measure the flexural properties, interlaminar properties of CF hybrid material coated with different weight percentages of fCNT, CNC, and CNC-pCNT. The obtained results show that the strength has been increased 5% with the increase of 0.2–0.4 wt% of fCNT. The strength has been decreased to 4% with the coating of fCNT lesser than 0.2 wt%. The intense

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Table 14.1

Impact of fiber orientation on properties.

Matrix

Fiber reinforcement

Fabrication

References

Epoxy

Carbon flax fiber

Platen press process The addition of two flax layers outside to a carbon laminate improves damping behavior by decreasing its bending modulus The specific damping of the [C/F/C/C/F/C] laminate was found to be increased by 15% as compared with non-hybrid carbon laminate

[93, 94]

Epoxy

Jute/hemp/flax fiber

Hand-layup preparation technique Flax fiber with a maximum shore-D hardness of 98 was achieved and it was greater than that of H/E and J/E

[95]

F/E showed a superior tensile strength of 46.2 MPa than that of H/E and J/E Poor adhesion was observed in cases of natural fibers with epoxy. This may be due to inadequate adhesion Epoxy

Flax/linen/ bamboo fiber

Vacuum bagged method

[96]

Alkali treated F/E increased 21.9% of tensile strength and 16% of flexural strength as compared to untreated The density of F/E is reduced by about 17% after the treatment The influence of treatment on tensile strength of F/E is greater than flexural strength, as microscopical analysis showed less fiber pullout

Polypropylene/ poly L-lactic acid

Flax fiber

Twin-screw extruder Compared PP/flax and PLA/flax PLA/flax is 50% stronger than PP/flax

[89, 97, 98]

The addition of plasticizer does not improve the properties rather degrade the mechanical and impact properties The thermal properties of PLA are superior to flax fibers than PP/flax

functionalizing process can damage the sidewalls of CNT, which leads to the weakening of bonding and thus results in the reduction of strength. The flexural strength has been increased to 8% for 0.4fCNT-CFRP with the IS coating. The results revealed that the tensile strength has been increased to 8% for 0.2fCNT-CFRP with the IS coating. The interlaminar shear strength has been increased up to 12% for CF coated with 0.2CNC–0.2pCNT when compared to uncoated CF. The effect of hybrid dispersion at interlaminar space of flax with carbon fibers at lower volume

14.8 Effect of Hybridization and Its Application of Nanofiber

Table 14.2

Weight proposition of hybrid dispersion of flax and carbon laminates. Flax

Carbon

Laminates

wt%

No of layers

Position

Alignment

wt%

No of layers

F1

100

1

N/A

N/A

0

0

FC1

19.2

1+1

One near the midplane

Symmetric

80.8

3

FC2

32.4

2+2

One near the midplane

Symmetric

67.6

3

FC3

32.4

1+1

One near the midplane

Symmetric

67.6

3

FC4

32.4

1+1

One away from the midplane

Symmetric

67.6

1

FC5

32.4

1

Extreme end from the midplane

Symmetric

67.6

1

C2

0

0

N/A

N/A

100

1

fractions level has been investigated and illustrated in Kureemun et al. [100]. Five different hybrid laminates such as FC1–FC5 were manufactured with different dispersion of piles of flax with carbon piles along with plain flax and carbon flax laminates. The weight proposition of hybrid dispersion of laminates is shown in Table 14.2. The author limited the experimental study to only under tensile load. The results have shown that the average tensile strength is increased by 72% for FC1 when compared to non-hybrid laminate. The tensile strength has been increased to 144% for FC2–FC5 laminates when compared to non-hybrid laminates. The main reason for this increment in tensile strength is that the hybridization of carbon fibers neutralizes the nonlinear behavior of the resulting composites. The effect of hybridization of 4 wt% of nanoparticles of SiO2 integrated with 0.5 wt% of Multiwalled nano carbon tubes (MWNCTs) in order to study the mechanical properties of basalt fiber-reinforced (BFR) epoxy composite [101]. The experiment analysis has shown a 27.7–29% of increase in tensile strength for SiO2 /2-bromo-3,3,3-trifluoropropene (BTP)/BFR composites. The main reason behind this is the filling of SiO2 into BFR/Epoxy nanocomposites, which strengthen the hybrid composite. The comparison of strength characteristics between hybrid fiber-reinforced polymer (HFRP) and nano hybrid fiber-reinforced polymer (nHFRP) was presented in Szmigiera et al. [102]. The experimental results of tensile strength values for basalt fiber-reinforced polymer (BFRP), HFRP, and nHFRP are 1103.3, 1277.92, and 1223.48 MPa, respectively. It has been observed that HFRP has greater tensile strength. The modulus of elasticity for HFRP has been increased to 16%, which shows that the HFRP is good in ductility. The experimental results have shown better characteristics for HFRP than nHFRP mainly because of the nonhomogeneous scattering of nanosilica particles in the matrix. The hybridization of silk and Kevlar to improve the mechanical properties have been examined and presented in Lili et al. [103]. The hybrid Kevlar and silk materials undergo a proper hydrothermal treatment process, which can form hybrid films. This hybrid film carries a large number of β-sheets of silk which results in a maximum value of stress and modulus of elasticity than regenerated silk fibroin (SF) films. It has been observed that Kevlar acts as a key reinforcing element and it has

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good compatibility characteristics with fibroin (SF) films. An extensive review on the effect of hybridization and mechanical properties of hybrid composites are presented in Swolfs et al. [104]. The authors have classified the reviews based on hybrid effect, disadvantages of existing models and future development, improvement of mechanical properties by hybridization, and recent trends in fiber hybridization. The authors have formulated three different hypotheses based on following: (i) residual stresses, (ii) damage, and (iii) concentrations of dynamic stress. It has been observed that these hypotheses were applied on one-direction hybrid composites either in the intra-yarn or interlaminar configuration. It has been reported that the modulus of tensile at intra-layer in the core of unidirectional carbon fiber/carbon fiber hybrid shows a greater value than at interlayer of one-direction carbon fiber/carbon fiber hybrid. The flexural strength of hybrid carbon fiber mainly depends on the layer direction. The linear stress at the neutral layer is zero and it will increase in the direction away from the neutral axis. A material characterization on microstructural evaluation on hybridization of nano-B4 C with extruded magnesium (MG) composites/Ti particulate has been carried out and presented in Sankaranarayanan et al. [105]. The elemental particles of B4 C and MG/Ti have been blended for one hour with the addition of 0.3 wt% of stearic acid. The blended particles were put up in a ball milling machine to prepare the mixture of hybrid particulate with different fractions of B4 C. The fractions of B4 C with Mg and Ti materials are listed as follows: (i) Mg-5.6Ti (without B4 C), (ii) Mg-(5.6Ti þ 0.5B4 C)BM, (iii) Mg-(5.6Ti þ 1.5B4 C)BM, and (iv) Mg-(5.6Ti þ 2.5B4 C)BM. The authors have examined the results of the hybrid particulate in following various aspects: (i) X-ray diffraction, (ii) characteristics of microstructure, (iii) grain characteristics, (iv) crystallographic structure, and (v) strength. The new Mg-materials were tested under various loading conditions such as indentation, tensile, and compressive loads to study the mechanical properties. It had been noticed in the indentation test that the hardness values are increasing with the increase in hybridized Ti particles. And, it is also noticed that the hardness property was found superior with the inclusion of nano B4 C after the addition of Ti particles. Mg-(5.6Ti þ 2.5B4 C)BM material exhibits the highest microhardness, ultimate strength values among other fractions of Mg/Ti with B4 C hybrid materials. Mg-(5.6Ti þ 1.5B4 C)BM material shows the highest ductility value among other fractions of Mg/Ti with B4 C hybrid materials.

14.8.2 Nano-based Fibers Nanofibers are polymer filaments with a diameter range of 50–10 000 nm. Polymer nanofibers are good in high porosity with appreciable molding characteristics under mechanical load, high in flexibility when compared to microfibers. It has a large value of the ratio of surface area to the volume. Various methods exist to manufacture the nanofibers. One of the most popular methods is the electro-spinning process. Electrospun nanofibers are used in various applications such as membranes in separation processes such as air filtration, liquid filtration, protective textiles, sensors, advanced composites, photovoltaic cells, scaffolds in tissue engineering, and drug delivery.

14.9 Preparation and Characterization of Nanofibers

14.8.3 Synthesis of Nanofiber by Using the Electro-spinning Process In the year 1600, William gilbert observed the electrostatic attraction of the liquid. Christian Friedrich Schönbein had recognized the possibilities of a new compound of cellulose with the nitro groups in the year 1845. In the year 1887, Charles Vernon Boys heated a quartz rod to the point of melting for experimental analysis of a torsional balance system which results in the formation of the thin fiber. The electro-spinning process was discovered and patented by John Francis Cooley in the year 1900. Electro-spinning process involves the preparation of a suitable polymer solution with the compatible solution in the presence of electrostatic forces to form a thin finite filament. During the electro-spinning process, the electro field forces acting on the solution of polymer are melt to form the electrospun jet. The solidification of fiber is attained by evaporating the solvents. Cooley had also developed an experimental setup to manufacture the nanofibers. The electro-spinning process improves the separation of volatile components from the mixed substances of composite fluids in the presence of a high voltage electrical supply. This process also aids the directional cell growth, which leads to the alignment of fibers. The electro-spinning set up [106] consists of a needle (as an anode), pump (injection type) with a syringe, high voltage power supply, and the collector plate (as a cathode). An electric field is generated between the collector plate and needle due to the supplied high voltage source to the system. The electrostatic force by the field acing on the liquid droplet to form the shape of the Taylor cone. The distortion led to an electrically charged jet ejection, which moves toward the collector plate in the form of thin wires in nanoscale. The expression of critical voltage for the electro-spinning process is given in Eq. (14.1). ( ) 2l 3 h2 2 0.117𝜋𝜎R (14.1) Vcr = 4 2 ln − R 2 l where V cr is critical voltage, h is the distance between ground and capillary, l is capillary height, R is capillary radius, and 𝜎 is the surface tension of the liquid. When a polymer solution is supplied with an electric field (V) under the capillary action, a positive charge will be inducted on the liquid surface due to its surface tension. When V > V cr , a miniscule jet of the positive-charged solution has been exploded from the needle tip of the cone surface. This positive-charged solution will be attracted by the nearest cathode charged particles of opposite polarity or electrical ground through a viscous medium. Table 14.3 shows the various combinations of polymer solutions with solvents. The polymer solution has been chosen based on its viscosity, molar conductivity, surface tension, and molecular weight. The solvent has been chosen based on its boiling point and volatility.

14.9 Preparation and Characterization of Nanofibers 14.9.1 Polyacrylonitrile (PAN) Fibers Polyacrylonitrile (PAN) solution has been mixed with dimethylformamide solvent for the preparation of electro-spinning process. Three different solutions

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Table 14.3

Various combination of polymer solutions with solvents [107].

Sl no.

Polymers

Suitable solvents

1

Polyvinyl alcohol (PVA)

Water

2

Polyvinyl acetate (PVAc)

Acetone, water

3

Polyethylene oxide (PEO)

Water, chloroform, isopropyl alcohol

4

Polyvinyl chloride (PVC)

Tetrahydrofuran (THF), dimethylformamide (DMF)

5

Polyurethane (PU)

DMF

6

Polycarbonates(PC)

DMF, THF

7

Polyvinyl pyrrolidone (PVP)

Water, ethyl alcohol, isopropanol, dichloromethane

8

Cellulose acetate

Acetone

9

Polyacrylonitrile (PAN)

DMF

10

Polystyrene (PS)

DMF, diethyl formamide (DEF), toluene

11

Polyether amide (PEA)

Hexafluoro 2-propanol

12

Polyethylene terephthalate

Dichloromethane + trifluoro acetic acid

13

Polyaniline

Chloroform

14

Polyamides (PA)

Phenol, dimethyl acetamide

15

Polysulfone

N,N-Dimethylformamide

16

Nylon 6

1,1,1,3,3,3-Hexafluoro 2-proponal (HFIP)

17

Polycaprolactone

Acetone

18

Polymethyl methacrylate (PMMA)

Toluene + DMF, THF, acetone, chloroform

19

Polyethylene terephthalate (PET)

Dichloromethane + trifluoro acetic acid

20

Collagen

Hexafluoro-2-proponol

Source: Adapted from Subbiah et al. [107].

of 8%, 12%, and 16% of DMF with PAN were prepared for the synthesis of PAN nanofibers. The homogeneity and viscosity of the solution have been maintained by applying the constant stirring work for two hours. A 9 kVdc power source is supplied and the nanofibers were collected on the cathode collector plate. The needle and the collector plate were separated at a gap of 7 cm. SEM analysis has been used for the characterization of nanofibers. It has been noticed that the fiber diameters were in the range of 100–900 nm. It has been observed that the maximum amount of fibers, around 55%, is in the sizes of 290 ± 25 nm [108].

14.9.2 Alumina Fibers Alumina fibers were manufactured from poly vinyl alcohol (PVA) solution with aluminum acetate solvent. The needle and the collector plate were separated at a gap

14.10 Applications of Electrospun Nanofibers

of 10 cm. The flow rate of the solution has been controlled at 1.3 ml/l and the power supply has been increased from 17 to 19 kVdc . The nanofibers are subjected to a thermal load in the range of 900–1300 ∘ C to remove the organic compounds, which results in the formation of pure alumina nanofibers. The sintering process can be used for the further reduction in the diameter of the nanofiber [108].

14.9.3 BaTiO3 Nanofiber Polyvinyl pyrrolidone (PVP) solution with barium acetate and titanium isopropoxide solvents has been used for the production of barium titanate (BaTiO3 ) nanofibers. A 9 kVdc power source is supplied within the distance of 7 cm to the tip (TCD) of 7 cm. The decomposition of organic compounds of the fiber was analyzed by using a thermo gravimetric process with the presence of thermal load from room temperature to 800 ∘ C. The diameter distribution of BaTiO3 nanofiber shows that the fiber diameters are of 50–400 nm. It has also been observed that the maximum amount of fibers is distributed, which are in the size of 250 nm [107]. The BaTiO3 nanofiber is calcined for further reduction in the size of diameter. The thermal load (>800 ∘ C) on the BaTiO3 nanofiber changes the structure to coarse and brittle. It has been seen that the diameter is greatly reduced to 220 nm from 250 nm with the increase in the amount of fibers present. This is due to the high temperature around 700 ∘ C decomposes the organics which leads to weight loss [108].

14.10 Applications of Electrospun Nanofibers 14.10.1 Nanofibers in Air Filtration Nanofibers are intensively used in air filtration mainly because of their large ratio value of surface and volume. The aerosol filtration method has been used and the performances of nanofiber on the filtration have been analyzed. Generally, activated carbon has been used to remove high toxic compounds in the chemicals by means of adsorption. High-efficiency particulate air (HEPA) filters were used to filter the particles such as short dirt fiber and other rubbles from the air. Filtration theory depicts that the skidded flow particles of air should be diminished completely to achieve high efficient performance on filtration. The nanofibrous layer has been coated over the conventional air filter, which aids the control of the slip flow of the air particles [109]. ISO fine dust test is commonly conducted for the purification of air particles entering into the engine. ISO fine dust test has been conducted on both of the substrates for the analysis of filter performance. Both of the substrates were loaded with the same pressure drop for the test. It has been observed in the sample of cellulose substrate with coated nanofiber that a large number of submicron particles were captured over the surface when compared with the sample of cellulose substrate alone. Table 14.4 shows the comparison of engine filter performance on a 992G wheel loader cab. It can be seen that the reduction of dust was greatly achieved with the influence of nanofiber coating over the cellulose substrate.

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Table 14.4

Comparison of filter performance on a 992G wheel loader cab [109].

Type of filter

Dust in exit (mg/m3 )

Dust in inlet (mg/m3 )

Minimization of dust (%)

Cellulose – submicron

0.031

0.01

68

Cellulose – respirable

0.441

0.06

86

Cellulose with nanofiber – submicron

0.037

0.003

92

Cellulose with nanofiber – respirable

0.361

0.025

93

Source: Data from Graham et al. [109].

14.10.2 Nanofiber in Water Filtration [110] A polyethersulfone (PES) nanofiber has been used as a membrane in the liquid filtration process. Polyethylene terephthalate (PET) has been added over PES as nonwoven in order to enhance the flexural properties of the membrane. The polymer solutions were prepared with PES of 20 wt% with DMF. A 20 kVdc power supply is given for the electro-spinning process. The water flux characterization of PES/PET membrane has been analyzed. It has been noticed that the water flux measurement shows a high initial flux. The porosity of the membrane has been deformed due to the increase of feed pressure, which leads to a decrease in the water flux [111]. The heat treatment process was carried out on few samples of PES/PET membrane in a heated oven at a temperature of 190 ∘ C for the time duration of six hours and then the samples were cooled down gradually. The chosen temperature was well below the boiling point temperature of DMF (i.e. 150 ∘ C) and greater than the glass transition temperature of PES (i.e. 225 ∘ C). Experiments were conducted to analyze the filtration performances of PES/PET membrane by using a retention test. The experiments were carried out for the measurement of pure water flux for four different varieties of PES/PET, such as (i) Thermal treated, one layered membrane, (ii) Nonthermal treated, one layered membrane, (iii) Thermal treated, multilayered (max of five layers) membrane, (iv) Nonthermal treated, multilayered (max of five layers) membrane. The water fluxes were measured with the primary feed rate of 60 l/h m2 . It has been observed that the measured fluxes are constant for both heat-treated and untreated, single-layered PES/PET membranes. The measured fluxes, for both heat-treated and untreated multilayered PES/PET membrane, were decreased with the increase in time. It has also been noticed that the pressure at the surface of membrane was 820 mbar at the beginning of the experiment and the surface pressure of membrane had been reached to 1300 mbar after one day of filtration. The pressure differences across the membrane were increased for the case of the multilayered membrane, which aids the development of compressive and shear forces that can deform the surfaces of the membrane. These deformed surfaces can decrease the effective porosity, which results in better particle suspensions. Size distribution of d90 has been considered for the measurement of retention performances. When the average pore size of the membrane is very close to the size of

14.10 Applications of Electrospun Nanofibers

d90 and also exceed the size of 1 μm, the membrane can absorb the particles of a size that varied from 1100 to 600 nm for the first hour of filtration and it becomes constant up to till the end of the filtration. It clearly indicated that the bigger particles were suspended and also it was not blocking the porous medium of the membrane. It has also been noticed that a similar phenomenon occurs when the particles of size are closest to d90 and also well below the size of 1 μm, the particles that were suspended are in the size of 560–200 nm after the first one hour of filtration. It has been concluded that a significant amount of smaller particles was suspended during the filtration process.

14.10.3 Recycled PET (RPET) Nanofibers for Water Filtration Recycled polyethylene terephthalate (RPET) bottles were used for the microfiltration of water [111]. PET nanofiber membranes were produced by an electrospun process with fibers of size lesser than the average size of c. 100 nm. Latex beads of sizes that are ranging from 30 to 2000 nm were used for the measurement of the efficiency of filtration. Quaternary ammonium and biocide were added functionally with the membrane to attenuate the biofouling. Quaternary ammonium has been synthesized with 5.5 g of Lupasol was liquefied in 70 ml tert-butanol. The mixture has been heated up to 80 ∘ C and added with 21 g of potassium carbonate and 53 ml of bromohexane. The potassium carbonate was removed by filtration after 24 hours of reaction. 15 ml of iodomethane has been added to the resultant mixture and it is stirred and heated up to 60 ∘ C for another 24 hours. It is expected that the polymer can be washed away with hexane. Nuclear magnetic resonance analysis was conducted to analyze the peaks of the compounds present. The results have shown that the peaks were dominant for terminal methyl, interior CH2 groups, b-CH2 groups, a-CH2 groups, and methylammonium. The discarded PET bottles were collected from the recycling industry. The labels of the PET bottle were removed and cut into small pieces. The small pieces of PET bottles were cleaned with water and ethanol and dried latter. The PET shreds were dissolved in the HFIP (hexafluoro-2-propanol) and stirred at room temperature in order to prepare 5–10 wt% solutions. The thickness and surface densities are 18.2 ± 8.4 μm and 25.1 ± 11.6 g/m2 , respectively, for the RPET mats of 5–10 wt% solutions. The vacuum filtration test was conducted by passing an aqueous solution of latex fluorescent beads of 3 g of 200 ppm with a pressure of 7.3 psi. The filtration process has been made for the size of 2 μm, 1 μm, and 500 nm latex beads for 5 wt% solution, 7.5 wt% solution, and 10 wt% solution, respectively. It has been noticed that the bead sizes are greater than the porous size for the 5 wt% solution RPET mat. It has also been observed that the bead sizes are smaller than the porous size for both 7.5 and 10 wt% solution RPET mat, respectively. However, the results have shown that the 2 μm of the size of beads were trapped fair enough due to the anisotropic fiber layers. It has been observed that very few 500 nm beads were captured by the multilayers of mat 5 wt% solution. It has also been seen that the 500 nm beads were not captured well for 7.5 wt% solution and 10 wt% solution. The efficiency of filtration of 500 nm latex beads for all the three different solutions is

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insignificant mainly because of its lacking ability to remove the particles and it is not suitable for ultrafiltration. However, the analysis shows that the efficiency of filtration of recycled PET nanofibers with the size of lesser than c. 100 nm is greatly achieved and the mat can be used as a prefilter in a wastewater treatment system.

14.10.4 Energy Conversion and Storage Device Nanofibers are more advantageous in energy harvesting, energy conversion, and energy than conventional materials [112, 113].

14.10.5 Nanofibers in Solar Cells The solar cell can be able to generate electricity from the direct contact of light rays in the presence of photosensitizing dye [112]. A dye-sensitized solar cell (DSSC) is consists of three items such as photoanode, electrode, and electrolyte. A photoanode is made of transparent glass coated with a porous semiconductor film. The adsorption of photosensitizing dye takes place on this semiconductor film. The photons were absorbed by the photosensitizer and then moves into the conducting band of the semiconductor. The photoelectrons are further transferred to the counter electrode with the help of an external circuit. The charge carrying capacity and overall energy conversions may severely be affected by the maximum light adsorption. Electrospun metal oxide nanofiber can be coated as a thin film with the photoanode to improve the energy conversions. A counter electrode is a major component of DSSC for omitting and receiving the electrons. The catalytic movement may affect the performances of the counter electrode due to the internal series resistance. Integrated carbonaceous materials have been used as an alternative counter electrode to overcome the drawbacks of platinum. The integrated carbonaceous materials are graphite, mesoporous carbon (C), CNTs, and carbon nanofibers (CNF). The power conversion efficiency is mainly based on nonvolatile liquid electrolytes. The effect of leakage and volatilization of electrolytes results in deprived stability of DSSC. Poly vinylidenefluoride-co-hexafluoropropylene (PVDF-HFP) nanofiber has been used for better stability and ionic conductivity at room temperature.

14.10.6 Nanofiber-Based Li–S and LiO2 Batteries Sulfur has been used in energy storage devices mainly because of its high specific energy [113]. It has been analyzed that the performances of Li–S battery got degraded due to dissolutions of its intermediate i.e. (Li2 Sx , 3 ≤ x ≤ 8). The porous carbon nanofiber (PCNF) with sulfur as a nanocomposite (PCNF/S) has been used as an alternative solution for the intermediate dissolutions. The PCNF/S nanocomposite is a cathode that has high electrical conductivity and high surface area. The sulfur has dispersed and lost mobility in the porous structure of CNF, which can attenuate the polysulfide shuttle phenomenon. This leads to improving the reversible capacity and discharge capacity of PCNF/S nanocomposite. The comparative analysis of performances of nanofiber-based Li–S batteries are shown in Table 14.5.

14.11 Conclusions

Table 14.5

Comparative analysis of performances of nanofiber-based Li–S batteries. Initial discharge capacity (mAh/g)

Sl no

Nano composite

1

PCNF/S

1155

0.02

2

Carbon/sulfur

845

0.25

3

OMCF/S

690

0.3

Table 14.6

Discharge rate (C)

Comparative analysis of performances of nanofiber-based LiO2 batteries. Initial discharge capacity (mAh/g)

Sl no.

Nano composite

Stability cycles

1

1D Co3 O4 NFs

10 500

80

2

1D porous La0.5 Sr0.5 CoO2.91

7 205

85

Li2 O2 components have been decomposed in the evolution of oxygen reactions. The electrode O2 is porous and can be available in triple-phase form, which is more important for the architecture for the migration of electrons. 1D Co3 O4 nanofiber that had obtained by electrospinning has been used to enhance the performance of LiO2 batteries. The Co3 O4 nanofiber in the form of a sphere is entrenched in the TiO2 fiber mesh. TiO2 fiber mesh acts as a support in terms of blocking the Co3 O4 layer that prevents the detachment from the current collector. TiO2 fiber mesh also provides structural strength and cycling ability. The comparative analysis of performances of nanofiber-based LiO2 batteries is shown in Table 14.6.

14.11 Conclusions This section provides the conclusions of the comprehensive review of the advancement of natural fiber-based polymer composites. The following observations have been made from the review: ●

●

●

Natural fibers are used for numerous applications due to their superior characteristics such as biodegradable, lightweight, and adequate load-bearing capacity. The research on the utilization of natural fibers is prominent for the automotive industry, space, and defense sector. There are few drawbacks of synthetic fibers such as they are nonbiodegradable and nonrecyclable. Few natural fibers were identified in order to overcome the drawbacks of synthetic fibers such as flax, abaca, hemp, and sisal. It has been identified that both chemical treatment and hybridization process are enhancing the mechanical properties of flax such as tensile strength, flexural strength, and impact strength. However, the chemical treatment shows better performance than the hybridization process due to the presence of bonding strength.

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●

●

The effect of hybrid dispersion at inter-laminar space of flax with carbon fibers at lower volume fractions level has been investigated and illustrated. Five different hybrid laminates such as FC1–FC5 were manufactured with different dispersion of piles of flax with carbon piles along with plain flax and carbon flax laminates. The cellulose coated with the nanofibers is showing the greater performance of filtration of air particles. The pressure at the surface of the membrane was increased from 820 mbar at the beginning of the experiment conducted to 1300 mbar after 24 hours of filtration. The pressure differences across the membrane were increased for the case of multilayered membrane, which aids the increase of high compressive and shear forces. These high compressive and shear forces are capable to deform the surfaces of the membrane. These deformed surfaces can decrease the effective porosity, which results in better particle suspensions. The PCNF/S nanocomposite is a cathode that has high electrical conductivity and high surface area. The sulfur has dispersed and lost mobility in the porous structure of CNF, which can attenuate the polysulfide shuttle phenomenon. This leads to improving the reversible capacity and discharge capacity of PCNF/S nanocomposite. PCNF/S has a high initial discharge capacity of 1115 mAh/g.

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74 Plummer, C.J.G., Bourban, P.E., and Manson, J.A.E. (2001). Polymer matrix composites: matrices and processing. Journal of Encyclopedia of Materials: Science and Technology, 7388–7396. https://doi.org/10.1016/ B978-0-12-803581-8.02386-9 75 Spasojevic, P.M. (2019). Thermal and rheological properties of unsaturated polyester resins-based composites. In: Unsaturated Polyester Resins Fundamentals, Design, Fabrication, and Applications, 367–406. Elsevier. 76 Hashim, N., Majid, D.L.A., Baitab, D.M. et al. (2019). Tensile properties of woven intra-ply carbon/kevlar reinforced epoxy hybrid composite at sub-ambient temperature. In: Reference Module in Materials Science and Materials Engineering. https://doi.org/10.1016/B978-0-12-803581-8.11567-X. 77 Perna, A.S., Viscusi, A., Astarita, A. et al. (2019). Manufacturing of a metal matrix composite coating on a polymer matrix composite through cold gas dynamic spray technique. Journal of Materials Engineering and Performance 28: 3211–3219. 78 Komal, U.K., Lila, M.K., Chaitanya, S., and Singh, I. (2019). Fabrication of short fiber reinforced polymer composites. In: Reinforced Polymer Composites: Processing, Characterization and Post Life Cycle Assessment. https://doi.org/10 .1002/9783527820979.ch2. 79 Rajak, D.K., Pagar, D.D., Menezes, P.L., and Linul, E. (2019). Fiber-reinforced polymer composites: manufacturing, properties, and applications. Polymers 11: 1667. https://doi.org/10.3390/polym11101667. 80 SME (2020). Composite materials and manufacturing by society of mechanical engineering. https://www.sme.org/technologies/manufacturing-topics/ composite-materials-anufacturing/ (accessed 22 December 2020). 81 Bhatt, A.T., Gohil, P.P., and Chaudhary, V. (2018). Primary manufacturing processes for fiber reinforced composites: history, development & future research trends. IOP Conference Series: Materials Science and Engineering 330: 012107. 82 Dai, D. and Fan, M. (2014). Wood fibres as reinforcements in natural fibre composites: structure, properties, processing and applications. In: Natural Fibre Composites, 3–65. Woodhead Publishing. ISBN: 9780857095244. https://doi.org/ 10.1533/9780857099228.1.3. 83 Devaraju, S. and Alagar, M. (2019). Unsaturated polyester – macrocomposites. In: Unsaturated Polyester Resins, 43–66. Elsevier. ISBN: 9780128161296. https:// doi.org/10.1016/B978-0-12-816129-6.00002-8. 84 Xess, P.A. (2012). Erosion wear behaviour of bamboo fiber based hybrid composites. Master’s thesis, Department of Mechanical Engineering, National Institute of Technology, Rourkela, India, May 2012. p. 39. 85 Alves, C., Ferrão, P.M.C., Silva, A.J. et al. (2010). Eco-design of automotive components making use of natural jute fiber composites. Journal of Cleaner Production 18 (4): 313–327. https://doi.org/10.1016/j.jclepro.2009.10.022. 86 El-Shekeil, Y., Sapuan, S., Abdan, K., and Zainudin, E.S. (2012). Influence of fiber content on the mechanical and thermal properties of kenaf fiber reinforced thermoplastic polyurethane composites. Materials and Design 40: 299–303.

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87 Benkhelladi, A., Laouici, H., and Bouchoucha, A. (2020). Tensile and flexural properties of polymer composites reinforced by flax, jute and sisal fibers. International Journal of Advanced Manufacturing Technology 108: 895–916. 88 Chen, P., Lu, C., Yu, Q. et al. (2006). Influence of fiber wettability on the interfacial adhesion of continuous fiber-reinforced PPSESK composite. Journal of Applied Polymer Science 2006 (102): 2544–2551. 89 Cordin, M., Bechtold, T., and Pham, T. (2018). Effect of fibre orientation on the mechanical properties of polypropylene–lyocell composites. Cellulose 25: 7197–7210. https://doi.org/10.1007/s10570-018-2079-6. 90 Amiri, A., Ulven, C.A., and Huo, S. (2012). Effect of chemical treatment of flax fiber and resin manipulation on service life of their composites using time-temperature superposition. Polymers 7: 1965–1978. 91 Cantero, G., Arbelaiz, A., Llano-Ponte, R., and Mondragon, I. (2003). Effects of fiber treatment on wettability and mechanical behavior of flax/polypropylene composites. Composites Science and Technology 63: 247–1254. 92 Akash, S., Avinash, S.S., and Ramachandra, M. (2018). A study on mechanical properties of silk fiber reinforced epoxy resin bio-composite with SiC as filler addition. Materials Today: Proceedings 5(1), 3: 3219–3228. 93 Zhang, D., Tan, K.H., Dasari, A., and Weng, Y. (2020). Effect of natural fibers on thermal spalling resistance of ultra-high performance concrete. Cement and Concrete Composites 109: 103512. 94 Assarar, M., Zouari, W., Sabhi, H. et al. (2015). Evaluation of the damping of hybrid carbon–flax reinforced composites. Composite Structures 132: 148–154. 95 Liu, F., Shi, Z., and Dong, Y. (2018). Improved wettability and interfacial adhesion in carbon fiber/epoxy composites via an aqueous epoxy sizing agent. Composites Part A: Applied Science and Manufacturing 112: 337–345. 96 Kureemun, U., Ravandi, M., Tran, L.Q.N. et al. (2018). Effects of hybridization and hybrid fiber dispersion on the mechanical properties of woven flax-carbon epoxy at low carbon fiber volume fractions. Composites Part B: Engineering 134: 28–38. 97 Yuan, Y., Guo, M., and Wang, Y. (2011). Flax fibers as reinforcement in poly(lactic acid) biodegradable composites. In: Intelligent Computing and Information Science. ICICIS 2011. Communications in Computer and Information Science, vol. 134 (ed. R. Chen), 547–553. Berlin, Heidelberg: Springer. https:// doi.org/10.1007/978-3-642-18129-0_85. 98 Oksmana, K., Skrifvarsb, M., and Selinc, J.F. (2003). Natural fibers as reinforcement in polylactic acid (PLA) composites. Composites Science and Technology 63: 1317–1324. 99 Shariatnia, S., Kumar, A.V., Kaynan, O., and Asadi, A. (2020). Hybrid cellulose nanocrystal-bonded carbon nanotubes/carbon fiber polymer composites for structural applications. ACS Applied Nano Materials 3: 5421–5436. 100 Kureemun, U., Ravandi, M., Tran, L.Q.N. et al. (2018). Effects of hybridization and hybrid fibre dispersion on the mechanical properties of woven flax-carbon epoxy at low carbon fibre volume fractions. Composites Part B: Engineering 134: 28–38.

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101 Demirci, I., Ahmet, A., and Demirci, M.T. (2020). Investigation of nano-hybridization effects on low velocity impact behaviors of basalt fiber reinforced composites. Journal of Composite Materials: 55(3) 1–14. 102 Szmigiera, E.D., Protchenko, K., Urbanski, M., and Garbacz, A. (2019). Mechanical properties of hybrid FRP bars and nano-hybrid bar. Archives of Civil Engineering LXV: 97–109. 103 Lv, L., Han, X., Zong, L. et al. (2017). Biomimetic hybridization of kevlar into silk fibroin: nanofibrous strategy for improved mechanic properties of flexible composites and filtration membranes. ACS Nano 11: 8178–8184. 104 Swolfs, Y., Gorbatikh, L., and Verpoest, I. (2014). Fibre hybridisation in polymer composites: a review. Composites Part A: Applied Science and Manufacturing 67: 181–200. 105 Sankaranarayanan, S., Sabat, R.K., Jayalakshmi, S. et al. (2014). Microstructural evolution and mechanical properties of Mg composites containing nano-B4 C hybridized micro-Ti particulates. Materials Chemistry and Physics 143: 1178–1190. 106 Zabar, N. and Al-Hazeem, A. (2018). Novel nanomaterials – synthesis and applications. In: , 191–210. IntechOpen Publications. http://dx.doi.org/10.5772/ intechopen.72060. 107 Subbaiah, T., Bhat, G.S., Rock, R.W. et al. (2004). Electrospinning fibers. Journal of Applied Polymer Science 96: 557–569. 108 Panda, P.K. and Sahoo, B. (2013). Synthesis and applications of electrospun nanofibers – a review. In: Nanotechnology, Fundamental and Its Application, vol. 1 (eds. N.K. Navani, S. Sinha and J.N. Govil), 399–416. Studiun Press LLC. 109 Graham, K., Ouyang, M., Raether, T., et al. (2002). Polymeric nanofibers in air filtration applications. Fifteenth Annual Technical Conference & Expo of the American Filtration & Separations Society (1–17 April 2002), Texas, 1–17. 110 Homaeigohara, S.S., Buhra, K., and Ebertb, K. (2010). Polyethersulfone electrospun nanofibrous composite membrane for liquid filtration. Journal of Membrane Science 365: 68–77. 111 Zander, N.E., Gillan, M., and Sweetser, D. (2016). Recycled PET nanofibers for water filtration applications. Materials 9 (247): 1–10. 112 Shi, X., Zhou, W., Ma, D. et al. (2015). Electrospinning of nanofibers and their applications for energy devices. Journal of Nanomaterials 16 (1): 1–20. 113 Sun, G., Sun, L., Xie, H., and Liu, J. (2016). Electrospinning of nanofibers for energy applications. Nanomaterials 6 (129): 1–30. https://doi.org/10.3390/ nano6070129.

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15 Recent Advancements in the Natural Fiber-Reinforced Polymer Composites Satish Teotia 1 , Anisha Chaudhary 2 , Ashish Gupta 3 , and Hema Garg 4 1

NIMS University Rajasthan, NIET, Department of Physics, Shobha Nagar, Jaipur 303121, Rajasthan, India University of Delhi, Department of Physics and Astrophysics, University Enclave, North Campus, New Delhi 110007, India 3 CSIR-National Physical Laboratory, Advanced Materials and Devices Metrology Division, Advanced Carbon Products and Metrology Section, Dr. K.S. Krishnan Marg, Pusa Road, New Delhi 110012, India 4 Indian Institute of Technology, School of Interdisciplinary Research, Hauz khas, New Delhi 110016, India 2

15.1 Introduction The wide global interest and awareness toward green, eco-friendly natural materials have gathered the research interest on the development and commercialization of natural fibers and their products for various applications instead of using petroleum-based nondegradable materials. Also, according to the environmental safety guidelines, use of oil in an impractical manner increases the attention toward eco-friendly materials. Natural fibers are ecologically harmonious materials that possess excellent properties and potential to replace the engineered or synthetic fibers. Besides, demand for low energy utilization and low ecological effects open the doors for the development and advancement of natural fiber-reinforced polymer composites (NFRCs) and their utilization in numerous areas.

15.1.1 Natural Fibers Natural fibers, obviously, are fibers of natural origin and are not artificial or synthetic, although their sourced origin may vary from plants to animals or minerals. Mineral fibers such as asbestos, ceramic, and metal strands are not biodegradable and are energy demanding. Animal fibers comprise generally of protein such as silk, hair, wool, fur, feathers, etc. Plant fibers are made basically of cellulose, lignin, and hemicellulose, which provide them remarkable properties. Generally, they are recognized as lignocellulosic fibers. Employment of natural fibers such as jute, bamboo, flax, and sisal from renewable and nonrenewable resources to create composite materials has picked up significant consideration in the most recent years [1–3]. The most broadly utilized plant fibers with the end goal of composite polymers are hemp, kenaf, jute, ramie, and flax, etc. Figure 15.1 shows the classification of fibers Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

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Fibers

Natural fibers

Plant fibers

Synthetic fibers–glass fibers, aramid fibers, carbon fibers Animal fibers

Bast fibers–flax, hemp, jute, kenaf, ramie

Slik fibers–silk from silkworm

Leaf fibers–sisal, abaca, and palm

Avian fibers–fibers from bird’s feather

Seed fibers–cotton, coir, kapok

Animal hair–sheep’s wool, goat hair

Figure 15.1

Classification of fibers into different categories with their examples.

into different groups with their examples. The chemical structure or composition in natural fibers (even for a similar type of fibers) may vary and depends on the developing condition and test techniques used in any event. Cellulose, the main constituent in most natural fibers, is a polysaccharide which is semicrystalline. It is comprised of D-glucopyranose units connected with each other by β-(1-4)-glucoside bonds. Generally, cellulose is a characteristic natural polymer and own high strength with solidness per unit weight. Additionally, it mounts a long fiber-like cell structure, which is a basic constituent in all parts of plants such as stem, leaf, and seed [4]. However, when cellulose-based natural fibers are used as reinforcements in hydrophobic matrices, hydrophilicity in natural fibers (because of huge availability of hydroxyl group in the structure of cellulose) prompts weak interface and low level of protection from moisture absorption. Cellulose fibrils contain hemicellulose firmly bound through hydrogen bonds. The polymer hemicellulose is amorphous and possesses a lower subatomic weight as compared to cellulose. Furthermore, hemicellulose contains numerous hydroxyl and acetyl groups in its open cell structure, thus is hygroscopic and easily soluble in water [5, 6]. On the other hand, lignin is an exceptionally perplexing, amorphous, and mainly sweet-smelling polymer consisting of phenylpropane units, yet it possesses less moisture absorption ability. The composition and physical properties influence the choice of cellulosic filters for various applications. Traditionally, natural fibers such as coir, pineapple, and banana leaves are used for textiles and polymer-based composites while wheat, rice straw, and corn stalks for pulp and paper making. The jute plant, local to Southeast Asia (India and Bangladesh), is accountable for up to 90% of overall production. Additionally, it is used in the development of floor covering backing, rope, handbags, and sack fabric (burlap). The most widely recognized and economical natural fibers with their chemical composition are discussed in Table 15.1.

15.1 Introduction

Table 15.1

Chemical composition of some widely utilized natural fibers [7–10].

Fibers

Cellulose (%)

Hemicellulose (%)

Lignin (%)

Pectin (%)

Wax (%)

Bagasse

25–45

16.8

15–25

—

—

Bamboo

26–43

30

5–31

—

10

Jute

71

14

13

0.2

2

Hemp

70

22

6

0.8

1.2

Kenaf

45–57

8–13

21.5

0.6

0.8

Cotton

95

2

1

0.6

0.4

Ramie

68–76

13–15

1

1.9

6

Abaca

56–63

15–17

7–9

0.5

3

Banana

64

20

5

3–5

—

Sisal

73

14

11

—

2

Flax

70–73

18–20

2

1.8

2–2.2

Coir

31–42

10–20

40–46

3–4

4

Pineapple

81

4–6

12.8

—

1–2

Curaua

73.6

9.9

7.5

—

—

Source: Adapted from Refs. [7–10].

15.1.2 Natural Fiber-Reinforced Composites The term composites used for materials comprise of at least two or more constituents separated by dissimilar interface and having properties that are impressively not the same as those of any of the constituents. There are two phases in a composite, one is the continuous phase called a matrix, which is typically not so much hard but rather more bendable and forms the bulk part of the composite. The other one is discontinuous phase called a dispersed phase, which is uniformly dispersed in the matrix and generally harder in comparison to the continuous phase. Reinforcement is the other term most commonly employed for the dispersed phase. The main purpose of reinforcement is to improve the general mechanical properties of the matrix in a composite. Composite can be ordered into three categories according to the kind of matrix materials utilized, one is metal matrix composites, the second one is ceramic matrix composites, and the last one is polymer matrix composites [11–13]. All types of composite materials are appropriate for various applications. However, polymer is the most normally utilized matrix material in composite, especially for automobile applications. Two factors are important for their popularity. One, they have low strength and stiffness compared with ceramic and metal-based matrix but these inadequacies are overwhelmed by strengthening different materials with polymers. Second, the handling of polymer matrix composite does not need the application of high pressure in addition to high temperature during the fabrication process. Consequently, polymer matrix-based composites are growing quickly and before long getting famous for primary applications. The physical properties of some popular natural fibers are listed in Table 15.2.

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Table 15.2

Properties of some commonly used natural fibers [14–23].

Fibers

Diameter (𝛍m)

Density (g cm−3 )

Tensile strength (MPa)

Tensile modulus (GPa)

% Elongation

Bagasse

—

1.2

20–290

19–27

1.1

Bamboo

88–125

0.91–1.26

503

35.91

1.4

Jute

25–250

1.3–1.48

393–800

0.13–26.5

1.16–1.80

Hemp

25–600

1.48

550–900

70

1.6–4.0

Kenaf

—

1.25–1.40

284–930

21–60

1.16

Cotton

—

1.51

400

12

0.3–10

Ramie

20–280

1.3–1.5

400–938

61.4–128

3.6–3.8

Abaca

1030

1.5

430–813

31–33

2.9–10

Banana

100–250

1.35

529–914

27–32

2.6–5.9

Sisal

—

1.3–1.4

390–450

12–41

2.3–2.5

Flax

25

1.4

800–1500

60–80

1.2–1.6

Coir

150–250

1.15–1.25

131–220

4–6

15–40

Crystalline cellulose

—

1.6

7500–7700

110–220

—

Lyocell

—

1.4

553

23

11

—, not reported. Source: Adapted from Refs. [14–23].

15.2 Natural Fiber-Reinforced Polymer Composites (NFRCs) NFRCs are advanced composites, which comprise natural fibers as reinforcement material dispersed uniformly in a polymer matrix. As a result of high strength and modulus, natural fibers act as a load-bearing part in the composite while the role of the matrix is to transfer load between the fibers. The properties of the final composite are enormously affected by the properties of the matrix, fibers, and its interface. NFRCs have played a major role in various applications for a long time due to their high strength and modulus [24]. Additionally, these composite materials possess low density, low cost, recyclability, biodegradability, high strength, and design flexibility, which make them appealing materials for advanced applications [25–28]. The fundamental advantages of NFRCs are: ● ● ●

●

●

Low production cost and easy accessibility. High strength and stiffness than glass fibers due to their low density. Low energy consumption and renewable energy source as CO2 is utilized and oxygen is released back into the environment. Low wages countries acknowledge natural fibers since the item can be produced and delivered at low cost with low investment. Healthier working conditions and minimal health hazards.

15.3 Advancement in Natural Fiber-Reinforced Composites ●

●

Reusability, whereas issues are faced with glasses during processing in combustion furnaces. Thermal insulators.

Among different normal strands, jute is considered as one of the most possible support for polymer composites because of its numerous preferences, for example, its simple accessibility, cost-effective production, and acceptable mechanical properties. Mechanical characteristics of composite material are affected by numerous factors, for example, fiber content [29], orientation [30], types [31], length [32], and so on. Commonly, polymers utilized as matrix materials in the composite can be grouped into two categories, thermoplastics and thermosets. As the name suggests, thermoplastics can be softened and reshaped multiple times on the application of heat. Some examples of thermoplastics are polypropylenes (PP), nylons, acrylics, and so forth [33, 34]. On the other hand, thermosets go through a restoring cycle called curing; during the fabrication process and postcuring, they become rigid and further unable to be reshaped. Some commonly used thermosets include phenolics and epoxies. Epoxy is widely used as a matrix material because it is a good adhesive, which can have an excellent ability to hold different materials. Besides this, it has effective mechanical strength, electrically insulating nature, and good chemical resistance, etc. [35]. Despite several advantages and favorable properties, a few downsides exist in the fabrication and acknowledgment of common natural fibers when used as a support in composites to improve their performance. A major problem that exists between the natural fibers and polymer matrices is their poor compatibility as natural fibers are hydrophilic whereas most polymer matrices are hydrophobic. Natural fibers comprise cellulose, hemicelluloses, pectin, etc., which are prone to moisture absorption. These hindrances produce a poor interface, influencing the fibers–matrix bond [2]. Hence, adhesion between the strengthening natural fibers and the polymer matrix significantly affects the stress transfer. In other words, the adhesion between the interfaces controls the load-bearing ability and subsequently affects the properties of the composite. Hence, natural fiber structure modifications or new composite preparation methods are need to be utilized for advanced NFPC applications. In general, these changes are commonly related to the modification through chemical functional groups that certainly modify the structures of natural fiber and increase its resistance to moisture. Therefore, fiber modifications lead to superb compatibility between the two phases and in turn enhance the overall performance of the composite.

15.3 Advancement in Natural Fiber-Reinforced Composites In general, the most commonly used polymer matrix in natural fiber composites shows the highest tensile strength (20–140 MPa) and modulus (1–10 GPa) [36–39].

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These values are very low for commercial usage. In a composite, these low mechanical properties are mainly associated with characteristics of the natural fibers, such as the heterogeneous nature of fibers bring about variation in the quality of the fibers; hydrophilic characteristics of fibers affect the binding to the hydrophobic polymer matrix, and difficulty in the transformation to yarns and textures compared to synthetic or glass fibers. Additionally, low thermal stability and sensitivity to moisture absorption yet again worsen the mechanical properties. Therefore, various strategies have been investigated to overcome these drawbacks, which include fiber treatment and modification, fiber hybridization and structure configuration, reinforcement through nanocellulose, engineering process advancement, and 3D printing, etc.

15.4 Mechanical Properties of NFRCs In a composite, mechanical properties mainly depend on surface interaction along with fiber–matrix adhesion. Generally, fiber–matrix adhesion affects the development of an interface and is important for maintaining load-bearing capacity, as pressure moves at the surface or interface requires a proper adhesion between the fibers and matrix [9, 40]. This strong fiber–matrix adhesion can strongly be influenced by several characteristics of the reinforcing fibers, such as length, orientation, volume fraction, aspect ratio, moisture absorption, impurities, and fiber–matrix adhesion. These are some important parameters that are crucial for enhancing the mechanical performance of the NFRCs [41–44]. In order to obtain strong interfacial adhesion between fibers and matrix in a composite mechanical interlocking, chemical bonding, and physical adhesion play an important role. Mechanical interlocking is acknowledged with surface roughness characteristics and can have the two impacts: either increase or decrease in bonding among fibers and matrix. Hence, if the matrix can infiltrate into the defects or irregularities of the surface of the fibers, it will be locked mechanically to the surface and increase the absolute contact area between the polymer and the fibers. Then again, if the matrix is unable to fill the irregularities, the contact region between the matrix and the fibers will be decreased and it will consequently decrease the fiber–matrix adhesion to a greater extent. The extent of fiber orientation on the green strength is reported by Geethamma et al. [45]. It is found that composite having 0∘ fiber orientation angle shows the highest mechanical properties. In addition, the load-bearing capacity is higher in the case where there is a parallel alignment of fibers to the direction of applied force. The reason being associated with the least fibers end defects and continuity of fiber length throughout the direction of the applied load. Luo and Netravali [46] explored the impact of fiber loading over elastic and flexural behavior in pineapple fiber-reinforced composite. It is discovered that both elastic and flexural strengths of the composite are enhanced with an increment in fiber content along the longitudinal direction while strength reduces in the transverse direction with the increase in

15.4 Mechanical Properties of NFRCs

fiber content. Schneider and Karmaker [47] revealed that PP composites arranged from jute fibers exhibit higher mechanical properties over kenaf fibers. Furthermore, it is found that better mechanical properties than pure matrix can be observed in conditions where PLA (polylactic-acid) matrix was reinforced with jute fibers. An improvement of about 75% in the elasticity of PLA was obtained. On the other hand, replacing jute fibers with flax fibers indicated a negative effect on strength and decreases the elasticity of the composites. Similarly, composites of PP are reinforced with hemp, kenaf, and cotton fibers to improve their mechanical properties [30]. On incorporation of jute in polyester-based composites, the greatest improvement of about 121% is obtained in comparison to as such polyester. It is additionally realized that stiffness and stress transfer increase with the fiber content in composites, which gives a superior loss modulus and a superior storage modulus [29]. Ismail et al. examined the variation in mechanical properties with fiber size and content of oil palm wood flour (OPWF) and observed that with increased fiber content, mechanical properties such as percentage elongation, tear strength, elastic modulus, and hardness are achieved [48]. Furthermore, it is observed that with even low OPWF loading, higher elasticity and tear strength are recognized in composites [35]. Additionally, the nonlinear mechanical behavior of natural fibers as a result of elastic shear force largely affects the fracture behavior of composites.

15.4.1 Fiber Treatment and Modification To tackle the challenges of incompatibility and poor bonding of natural fibers in a matrix, some fiber treatment techniques are adopted to modify the chemical or physical properties of the fibers to increase wettability and uniform dispersion in the matrix. The general methods utilized for fiber treatment can be categorized into two sections: 1. Surface or chemical treatment 2. Surface coating modified with coupling agents

15.4.2 Chemical Treatment The various chemical treatments used for fiber modification include alkali [49], acrylation [50], benzoylation [51], silane [52], permanganate [53], acrylonitrile and acetylation grafting [54], peroxide [55], stearic acid [56], isocyanate [57], triazine [58], and fungal [59]. Although the above-mentioned chemical treatments are highly accessible, most commonly alkali treatment (mercerization) is utilized to fibrillate and purify fibers before composite fabrication to partially remove oil, wax, pectin, hemicellulose, and lignin [60–62]. Alkali treatment shows four positive impacts in enhancing the NFRC’s mechanical properties. (i) High cellulose content with high crystallinity offering higher fiber strength and stiffness; (ii) Improved surface roughness characteristics to increase fibers and matrix mechanical interlocking; (iii) A greater

307

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15 Recent Advancements in the Natural Fiber-Reinforced Polymer Composites

number of available bonding/reaction sites due to the increased surface exposure of fibers, and (iv) good wettability and compatibility as a result of increased surface energy. Mild alkali treatment has little or no effect on fiber texture but can remove the fiber impurities efficiently. Although the higher alkaline treatment removes the lignin, it can damage the fibers [63, 64]. A study uncovered the various used chemical treatments methods and their effect on the mechanical properties of the hemp fiber and lime-based composite materials using ethylenediaminetetraacetic acid (EDTA), NaOH, polyethyleneimine (PEI), CaCl2 , and Ca(OH)2 [65]. This study shows that 6% NaOH treatment has a direct cleansing effect on fiber surface through removing amorphous constituents and improving crystallinity index of fiber bundles. Similarly, the effect on the interfacial properties of natural fibers on controlled surface treatment is investigated by May-Pat et al. and reported that stress transfer region or interphases and properties of constituents largely affect the fracture behavior of the composite along with other mechanical properties [1]. Venkateshwaran et al. investigated the effect on mechanical properties of composite made of banana and epoxy by varying concentrations (0.5–20%) of alkali (NaOH) treatments [66]. The outcomes suggested that compared to untreated fibers, alkali-treated fiber surface brings about improved mechanical properties. Also, composites reinforced with 1% NaOH treated fibers result in superior effects. On the other hand, a higher concentration of alkali possibly causes damage to the fiber surface, prompting a decline of mechanical properties. The hybrid composite of sisal-oil palm fibers and natural rubber is investigated by John et al. [67]. The work was concentrated on variation in mechanical properties and characteristics with the different chemical treatment and it was found that torque values increase with chemical treatment, which results in better crosslinking and hence better mechanical properties. Furthermore, Merlini et al. studied the surface roughness characteristics of banana fiber composite after chemical treatment [68]. It was observed that chemical treatment increases the surface roughness characteristics of banana fibers, which correspondingly builds a better fiber–matrix adhesion, and ultimately improves the mechanical characteristics of the composite. Islam et al. investigated the bonding characteristics of the hemp fiber composites with chemical treatment and found that chemical treatment increases the fracture resistance of the composite by improving the fiber–matrix adhesion [69]. Mylsamy and Rajendran studied agave fibers after chemical treatment and their composites [70]. They discovered that alkali treatment disintegrated hemicellulose and thus fiber aspect ratio increases which in turn improved the fiber–matrix adhesion and ultimately improves the mechanical strength of the composite. Bledzki et al. examined the PP composites reinforced with abaca fibers and reported that chemical treatment improves tensile strength and flexural strength of the composites [71]. The improved surface area after chemical modification and improved fiber–matrix adhesion are the main factors responsible for this enhancement. They have likewise revealed that the variation in fiber fibrillation and fiber diameter additionally impacts the strength of the fiber composite. Different chemical treatment and modification techniques with their advantages are discussed in Table 15.3.

15.4 Mechanical Properties of NFRCs

Table 15.3 The different chemical treatment techniques and their impact on the characteristic of natural fibers. Type of chemical treatment

Type of fibers

Advantages

Alkaline treatment

Jute, flax

Increase the surface roughness by eliminating amorphous content from the fibers which improves the bonding

Acrylation, acrylonitrile grafting

Jute

Improved fiber–matrix compatibility and load-bearing ability

Acetylation treatment

Flax

Increase the surface topography and fiber uniformity, and lower fiber hydrophilicity

Bleaching

Flax, cotton

Improved thermal stability and tensile strength of fibers

Benzoylation treatment

Sisal

Increased fiber–matrix adhesion, mechanical strength, and thermal stability

Fungal treatment

Flax

Reduce noncellulosic fiber content and produce roughness of fiber surface, ecofriendly method

Graft copolymerization

Wood, flax

Improve the thermo-mechanical properties

Isocyanate treatment

Flax

Modifies fiber surface, increases thermal stability and mechanical performance

Maleated coupling agents

Coir, wood

Improved fiber–matrix bonding and fiber impregnation within the matrix

Permanganate treatment

Coconut

Increased fiber–matrix chemical interaction and bonding

Peroxide treatment

Sisal

Improved fiber–matrix adhesion and mechanical strength

Polymer coating

Wood

Reduces fiber–matrix incompatibility

Silane treatment

Flax, hemp

Increased fiber–matrix physicochemical properties

15.4.3 Coupling Agent To increase the interfacial bonding between the fibers and matrix, coupling agents such as maleic anhydride (MA)-grafted copolymer and silane agent are widely employed [72–74]. The function of MA-grafted copolymers (anhydride part) is to decrease the formation of hydrogen bonds through the esterification of hydroxyl groups in natural fibers. While the other portion of the copolymer reduces the incompatibility between the fibers and matrix by entanglement with the polymer matrix having comparable polarities. Recent studies suggest that the nucleation cycle, as well as crystallization energy, is also affected by the coupling agents [75]. Commonly used coupling agents include silane that improves the fiber–matrix

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interfacial bonding [76–78]. Silane agent modify the fiber surface through following actions [79]: (i) Silane hydrolysis in presence of water to free reactive silanol group; (ii) Silanol self-condensation by controlling pH; (iii) Hydrogen bonding between the reactive silanol group and the hydroxyl group of the fibers; (iv) Covalent bond formation (—Si—O—C—) on heating between silanol and hydroxyl group. A study was conducted on flax/PLA composites and focused on the elements of various silane treatment conditions including organosilane concentration, temperature, and drenching time [80]. It is found that optimum organosilane treatment conditions containing trimethoxysilane (5–10 wt%) treated flax fibers at 70 ∘ C, bringing about 20–25% better yield stress compared to as such fibers (without treated). Similarly, PP/hemp composites treated with γ-methacryloxypropyltrimethoxysilane show better hemp fiber disintegration and consequently the more prominent progression in the tensile modulus compared to other silane agents such as γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, etc. [81]. The more efficient γ-methacryloxypropyltrimethoxysilane impact was ascribed as steadier adsorption with better collaboration to the surface of hemp fibers, low lubrication, and self-condensation. Further, interfacial topology analysis is used to study fiber–matrix bonding in a single fiber composite. In the case of single sisal fibers/PP composite, it was observed that variation in interfacial crystalline morphologies closely influenced the interfacial shear strength [82]. For example, as compared to the amorphous structure transcrystalline superstructure indicated 95% better interfacial shear strength. In a similar study, Srisuwan et al. examined the epoxy composites containing chemically treated sisal fibers as reinforcement with 2% of NaOH and silane. It is found that the silane component enhanced the fiber–matrix adhesion and increases the flexural properties of the composite [83]. Different chemical methods with reaction mechanisms are shown in Figure 15.2.

15.4.4 Fiber Hybridization Fiber hybridization is a method to overcome the weaknesses of one specific fiber and improving the overall performance of the NFRCs [92, 93]. Hybridization strategies give flexibility in fiber choice in order to design composite materials with specific properties as per the industry-based application requirements. Fiber hybridization is achieved through hybridization of natural fibers with other natural fibers or engineered fibers having superior properties, for example, higher mechanical strength, nontoxicity, fire-resistant, better chemical and thermal stability, moisture resistance, etc. Fiber hybridization is normally carried out either by means of intermixing of various types of fibers before their incorporation into the matrix or interlaminating layers of various fibers [94]. However, hybrid composites consist of natural and synthetic fibers can essentially show better mechanical properties compared to individual composites of either type. Performance evaluation in hybrid composites is controlled by several parameters, for example, fiber content, the hybrid ratio of each fiber, fiber direction in the matrix [95, 96], stacking sequences [97, 98], and inherent properties of the fibers. A study shows that tensile strength and failure strain in the case of flax fiber-reinforced composite improved to 0.9% in the case of a hybrid

15.4 Mechanical Properties of NFRCs Mercerization O–Na+ + H2O

OH + NaOH

O

O Esterification

R

+

OH

O

O

R

O

R

+ RCOOH

C CH3

Where R is CH2

Silane treatment CH2CHSi(OC2H5)3

CH2CHSi(OH)3 + 3C2H5OH CH2CHSi(OH)3 + Fiber – OH CH2CHSi(OH)2O – fiber + H2O O

O

Acetylation

C O CH3 + CH3COOH

H3C C

OH +

O H3C C O

Etherification Cell Cell

OH + NaOH –

+

O Na + Cl

Cell R

O–Na+ + H2O

Cell

R + NaCl

O

O

O

Benzoylation O–Na+ + Cl

O

C

C

+ NaCl

Peroxide treatment RO + Cellulose

H

R

OH + Cellulose

Isocyanate treatment R

N

C

O + HO

R

H

O

N

C

O

Figure 15.2 Different chemical treatment methods to modify natural fibers. Source: Adapted from Refs. [84–91].

composite of flax fiber hybridized with glass fibers [99]. Furthermore, superior interlaminar shear strength is obtained in the case of hybrid composite while individual fiber-reinforced (natural or glass fibers) composites remain inferior compared to hybrid composite. The twisted yarn-like structures in flax fibers with highly rough surface result in significantly high interlaminar fracture toughness due to better interconnection and network structure existed between the interfaces. Thus, the main advantage of hybridization is that it can overcome the drawbacks of the individual fibers and improve the overall performance of the hybrid composite. For instance, a study conducted by Yusoff et al. shows that the stacking layers of different fibers such as kenaf/bamboo/coir into the PLA-based hybrid composite result in wide variation in its mechanical properties [100]. The outcomes suggest that the excellent mechanical performance shown by the hybrid composite relies on the fibers placed in the external layers having high strength and high modulus. Additionally, proper matrix impregnation of inner layers of the fibers is the crucial component for hybridization configuration. Recently, a research work published on the fiber aspect ratios discovered that before the expulsion cycle, the aspect ratio of the fibers can be utilized straightforwardly to forecast the mechanical performance

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of the composite because after the extrusion process, variation in aspect ratio was unable to impart a major variation in tensile modulus.

15.5 Reinforcement with Nanocellulosic Fillers Nanocellulosic fillers have currently become very attractive reinforcement material as they possess high surface area, high aspect ratio, high strength, and stiffness. Some of the popular used nanocellulosic fillers include cellulose nanofibrils (CNFs), electrospun cellulose nanofibrils (ECNFs), cellulose nanocrystals (CNCs), and bacterial cellulose, etc. [101–104]. Like other filler materials, nanocellulosic fillers (micro or nano-size) give an enormous area to connect or hold the matrix and subsequently help in better adhesion between the interfaces, improve load-bearing capacity, and at last result in the excellent mechanical performance of the composite [105]. Although, the problem of uniform dispersion within the matrix and incompatibility of nanocellulosic fibers with polymer matrix affect the composite fabricating process, the incorporation of nanometric fillers could solve these problems to some extent and help in providing superior mechanical properties at low reinforcement concentration. Further, different strategies such as utilization of silane agents or alkenyl succinic anhydride for surface modification nanocellulose can overcome nanofibers agglomeration and improve their uniform dispersion within the matrix, which bring out enhance interfacial bonding [106–108]. Moreover, the mechanical performance of composite also depends on the high aspect ratio of nanocellulose. Further, a study conducted on nanocomposites of polyurethane reinforced with CNF and CNC shows that on comparing the mechanical and thermal performance of both the composite, CNFs with high aspect ratio favor in obtaining better properties in contrast to CNCs [109]. Similarly, Benhamou et al. additionally reported the fact that the presence of hemicellulose and lignin in CNFs brought about good fiber–polymer compatibility. Furthermore, Graupner et al. demonstrated lyocell fibers doped with lignin in PLA, maleic anhydride grafted polypropylene (MAPP), and PP matrix provide better interfacial bonding and shear strength due to (i) low viscosity of PLA matrix on addition of lignin; (ii) enhanced surface area on exfoliation of lignin for better interfacial bonding; and (iii) better chemical interactions through van der Waals force between the fibers and matrix [110].

15.6 Flame Retardant Properties of the NFRCs In the process of natural fiber composite fabrication, fire retardancy has become an important aspect while taking proper security measures [111]. During the burning of a composite in flame, following five different processes take place: a) heating, b) decomposition, c) ignition, d) combustion and e) propagation.

15.7 Water Absorption Characteristics of the NFRCs

On the burning of a composite generally two types of byproduct generated; either cellulose content or lignin content. It is observed that higher cellulose content favors flammability while more lignin content imparts more possibility of char formation [112]. Some fibers such as flax fibers and silica provide thermal resistance to fire [113]. However, for advanced applications, improvement in fire retardancy becomes important. For this purpose, different types of barriers are developed to resist the flammability of the composite. These barriers are called fire barriers that act as a shield to be applied on phenolics, glass mats, silicone, ceramics, etc. for protection against fire. Further, extremely encouraging fire-resistant methods utilized in arrangement of intumescent discovered that coating and additive materials used are expanded on heating and form a circular charred surface. This charred external surface protects the internal components and parts against the heat flux. Generally, the blend of char forming cellulose and polymers is the most notable flame retardants utilized in wide applications [114]. Furthermore, a technique for decreasing combustion in NFRCs is mainly based on increasing both charring ability and thermal stability of the polymer, which bring about better fire resistance, reduce noticeable smoke, and limit the generation of by-products as a result of combustion [115]. Fire-resistant coating is another strategy that can act as a shield and therefore improve the fire-resistant ability of the materials. The fire-resistant coating is carried out during the final finishing stage or impregnation. The most commonly utilized flame retardants based on the metal hydroxide include aluminum hydroxide [Al(OH3 )] and magnesium hydroxide [Mg(OH)2 ], which are deliberately added to polymers [116, 117]. Moreover, it is reported that the flame retardancy increases on incorporation of expandable graphite and ammonium polyphosphate in flax fiber-reinforced PP composite. Additionally, it is indicated that the heat release rate decreases to 35 from 167 kW m−2 when a combination of flax fibers (30 wt%) and expandable graphite (25 wt%) are used [118]. The intumescent flame retardant used for PLA composite called spirocyclic pentaerythritol bisphosphorate disphosphoryl melamine (SPDPM) is reported by Zhan et al. [119]. SPDPM results in char formation that function as fire-resistant, improves antidripping performance and flame retardancy of PLA on 25 wt% loading. Fire retardancy is definitely not something simple to be granted but it is just conceivable on stacking of optimum loading of inorganic filler.

15.7 Water Absorption Characteristics of the NFRCs Natural fibers are used widely to reinforce polymers because they are environment friendly, green, and easily accessible; however, sensitivity to moisture becomes the principal shortcoming in the utilization of natural fibers for commercial applications [120, 121]. Moisture absorption affects the fiber–matrix interfacial adhesion between the polymer matrix and thus reinforcing fibers strongly influence the mechanical

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Natural fibers– reinforced composite Water diffusion through fibers–matrix interphas Fibers swelling after moisture absorption

Dissolution of water soluble contents Water soluble content leach from fibers Fibers–matrix debonding Effect of water absorption on fibers–matrix bonding

Figure 15.3 bonding.

Schematic representation of moisture absorption effect on fiber–matrix

properties of polymeric composites. As already discussed (Table 15.1), there are several hydroxyl groups carrying components in the natural fibers, for example, cellulose, hemicellulose, lignin, and pectin. However, the most commonly used polymer matrices show considerable hydrophobicity irrespective of the natural fibers, which are hydrophilic due to the presence of the hydroxyl group. Consequently, there exist significant difficulties in maintaining compatibility between the matrix and fibers that probably could weaken the fiber–matrix interface region [122]. When such composites come in contact with water/moisture, water gets absorbed through the outer layers and diffuses progressively into the main part, i.e. the bulk part of the matrix. Therefore, when composite absorb moisture from the surrounding environment, this will result in swelling of the fibers and considerable decline in their strength and also compressed other structures in their proximity. Other effects such as distortion, buckling, microbial inhabitation chances greatly worsening the mechanical characteristics of composite materials [123]. A mechanism of moisture uptake and its effect on fiber–matrix bonding is presented in Figure 15.3.

15.8 Advancement of Conventional Manufacturing Processes The most widely used processes for fabricating NFRCs include compression molding, injection molding, sheet stacking, resin transfer molding, and extrusion,

15.8 Advancement of Conventional Manufacturing Processes

etc. During the fabrication of composite, the process parameters, for example, processing time, temperature, weight, and pressure are the key factors in determining the final properties of NFRCs. Some of the reported works demonstrated the variation in processing parameters and their effect on the mechanical performance of the composites, for example, wood flour/PP [124], flax/PLA [125], bamboo/epoxy [126], and kenaf/HDPE (high density polyethylene) [127]. These reported works show that proper impregnation of fibers within the matrix followed by their uniform dispersion in the matrix affects the mechanical properties of the composite. Secondly, proper impregnation of natural fibers within the polymer matrix and rheological properties both are significantly affected by the variation in processing temperature and pressure while compression holding time has a little effect. Lastly, the degradation of natural fibers due to the thermo-chemical reaction should be of major concern in order to avoid the reduction in the mechanical strength of the composite. Furthermore, the adopted processing technique for NFRC fabrication depends mostly on the type of application, and sometimes the performance of the composite is compromised to maintain other parameters. For example, the injection molding process is used instead of extrusion–injection separate molding process to reduce fibers wear and tear during the processing of sisal reinforced PLA composite, and their pellets were straightforwardly fed into the machine, which exhibited better ability in keeping up fiber lengths [128]. Though, the mechanical properties such as tensile and flexural strength of the composite are compromised and less values are obtained compared to those of extrusion–injection molding process. The successful uniform dispersion of fibers within the polymer matrix remains the important factor for obtaining NFRCs with excellent performance. A work reported on Cordenka cellulose-reinforced polyamide polymer composite fabricated by twin-screw extrusion process shows that both physical morphology of the fibers and mechanical performance of the composite are slightly affected by the screw configuration and temperature used in the extrusion process while considerably higher impact on the fiber length distribution [129]. Similarly, a study on kenaf/PP composites found that appropriate fiber dispersion regardless of fiber length brought about better mechanical properties during the process of extrusion injection [130]. Another study suggested that short fibers reinforcement by jute fibers show better wetting of PLA on the pull-out fibers of the fractured surface in comparison to long length fiber-reinforcement. Recently, it is reported that injection-molded hemp/PP composites have longer fibers toward sideways or typically toward the last point at the injected inlet while short fibers close to the entrance of the mold [131]. Further, on varying the different molding conditions, the deviation of about 30% in fiber content can be obtained. Thus, the mechanical performance of such composites largely gets affected by the homogenous distribution of fibers and suggested the possible challenges of using a particular technique for fabricating composite [132]. To tackle such challenges of uniform dispersion and fiber length orientation within the polymer matrix generally, a process of solid-state shear pulverization is the best option [133, 134].

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15.9 3D Printing in NFRCs In recent years, 3D printing also called additive manufacturing has been emerged as an advanced technology to overcome the limitations of conventional manufacturing technologies specially used in commercial applications. 3D printing has numerous advantages over conventional composite making processes such as easy and fast processing, broad variation for composites geometry, better control over content and orientation of reinforcement fibers, better thermal stability of natural fibers, and low wear and tear of expansive molds and tools [135, 136]. The most commonly used 3D printing technique is fused deposition modeling (FDM) as it is compatible to the most widely used polymers such as polycarbonate, polylactide, acrylonitrile butadiene styrene, and polyphenylsulfones, etc. The homogeneous composite dispersion in the FDM process is allowed to force through the feeding roller with a hot nozzle. Then on a printing platform, melted composite dispersion is layer by layer deposited according to a computerized programmed process. These layers get fused with each other on solidification after cooling. Recently, composite of PLA with micro and nanocellulose fabricated by 3D printing technique is reported in which micro-cellulose incorporated PLA composite filament with 3D printing has been developed first through solvent casting technique and then by the twin-screw extrusion process [137, 138]. However, there are more chances of formation of bubbles due to micro-cellulose incorporation and also micro-cellulose/PLA filament is more susceptible to moisture uptake. But if the extrusion parameters are perfectly optimized, these problems can be solved easily. Tekinalp et al. reported CNF reinforced PLA composite fabricated by 3D printing technology and compared the 3D printed composites with composite fabricated by the conventional compression molding process on the basis of their mechanical properties [139]. It is observed that 3D printed composite containing CNF content of 30 wt% exhibited superior mechanical properties (elastic and storage modulus) than the composite made from the conventional technique. The higher crystallinity of the 3D printed composite as a result of maintaining temperature for an extended period during the printing process results in a higher modulus. Additionally, fiber orientation in the printing direction favors better fiber–matrix adhesion. Hinchcliffe et al. reported a combination process for obtaining composite with excellent properties using both 3D printing and fiber prestressing [140]. In this work, firstly, PLA composite without using pretension was produced and then using fixed pretension strands of fibers (jute or flax) were fixed at the predefined position with the help of anchors on the ducts. It is found that the better mechanical performance of the composite is shown by reducing the amount of material that passes through the ducts. Also, an improvement in tensile strength and tensile modulus is observed if flax fibers were prestressed before threaded through a duct in contrast to the composite without duct. Through 3D printing technology, it is possible to make the composite structure sense the changes in environmental conditions (e.g. humidity, temperature, pressure) with the help of its hygroscopic property. Furthermore, 3D printing technology enables the user to control the degree and direction of twisting during a fabrication process. Correa et al. reported the fabrication of self-transformable acrylonitrile butadiene styrene-based

15.10 Natural Fiber-Reinforced Polymer Composites Application

composites reinforced with wood fibers or nylon fibers [141]. It is observed that composite started twisting after exposure to moisture but in a controlled manner as programmed according to the climatic conditions. Interestingly, the twisting actuation behavior observed was reversed back even after more than 30 cycles with no obvious deformities or changes in the twisting range.

15.10 Natural Fiber-Reinforced Polymer Composites Application Over few decades, the use of NFRCs in numerous engineering fields is rising very fast as a result of their low density, fairly high mechanical strength, cost-effective production, corrosion resistance property, biocompatibility and biodegradability, good surface finishing, and most importantly their renewable source. NFRCs reinforced with various types of natural fibers such as long flax fibers, short wood fibers, cotton, jute, bamboo, and abaca fibers have gotten an extraordinary significance for numerous applications including automotive manufacturing of structural component [142–146]. NFRCs have become integral parts in sports, automotive vehicle component manufacturing, electronic and communication industries, etc. The utilization of bio-based materials for manufacturing vehicle parts was made in the 1930s by Ford Motor Company and these early efforts encourage the initiation of NFRCs application in the automotive industry till today [147, 148]. For instance, the A2 mid-range car launched by Audi in 2000 consist of flax and sisal fiber-strengthened polyurethane composite-based entryway trim panels. Similarly, first time Mercedes-Benz used flax fiber-reinforced polyester composite to manufacturing enclosures for typical outside parts. Further, Porsche broadcast its first race car in 2019 using a whole outer body made from composite reinforced with hemp and flax fibers (718 Cayman GT4 Clubsport race car). Governments of many developed countries over past many years are continuously supporting the uses of NFRCs for the automotive sector because these are considered as “green” composites obtained from natural fibers. Thus, these composites are progressively and broadly utilized in vehicle parts by makers and providers (Table 15.4). Generally, over few decades, all big companies or manufacturers are utilizing these green composites in different applications. For example, Mercedes-Benz has been using natural fiber-reinforced composites in segments of different models [149]. For instance, for 20 components of A-class natural fibers wood, banana, and flax are utilized, for 21 components of B-class wood, coconut, and honeycomb are used while for more than 27 components of C-class honeycomb, charcoal coke, sisal, are used, for 44 components of E-class jute, flax, hemp, sisal, and olive coke are used while for 27 components of S-class wood, banana, and flax are utilized. Usually, NFRCs are utilized for inside car parts on account of their moisture sensitivity and generally moderate mechanical strength. Numerous internal nonstructural components, for example, indoor boards, dashboard, floor mats, bundle racks, capacity containers, seatback, etc. can incorporate NFRCs. Some of the companies

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Table 15.4 Natural fiber-reinforced composite application in automobile companies [24, 149–154]. Natural fibers

Producer

Model

Applications

Flax, sisal

Audi

A2, A3, A4, A4 Avant, A6, A8, Roadstar, Coupe

Side and back door panel, boot liner, seatback, hat rack, spare tire lining

Flax, sisal, cotton, bast, wood

BMW

Series 3, 5, and 7

Boot liner, door panel, seatback, bumper, molded footwell liners, noise insulation panels, headliner panels

Vegetable, wood

Citroen

C5

Boot liner, interior door panel

Flax

Chevrolet Impala

—

Trim panel

Bamboo

Fiat

Punto, Brava, Marea, Alfa Romeo 146, 156, 159

Panels of door

Hemp, kenaf, wheat straw

Ford

Mondeo CD 162, Focus

Floor trays, door inserts, door panels, B-pillar, and boot-liner

Hemp, kenaf, flax

General Motor

—

Seat backs, inner door panels, cargo area floors

Hemp, kenaf, sisal

Lotus

Eco Elise (July 2008)

Body panels, spoiler, seats, and interior carpets

Hemp, kenaf, sisal, banana, abaca, wood, flax, cotton, coconut, natural rubber

Mercedes Benz

C, S, E, and A classes

Door panels, glove box, instrument panel support, insulation, molding rod/apertures, seat backrest panel, trunk panel, and seat surface/backrest

Hemp, flax, bamboo, cotton

Mitsubishi

—

Cargo area floor, door panels, and instrumental panel

Kenaf, sweat potato, sugarcane

Toyota

Raum, Brevis, Harrier, Celsior

Floor mats, spare tire cover, door panels, and seat backs

Flax, sisal

Volkswogan

Golf, Passat

Door panels, seat backs, boot-lid finish panels, boot liners

Hemp, flax, jute, wood, sisal

Volvo

V70, C70, XC60

Seat padding, floor mat, cargo floor tray, power ribs

Source: Adapted from Refs. [24, 149–154].

15.11 Summary and Prospects

are using natural fiber-reinforced composite in the manufacturing of automobile parts, which are listed in Table 15.4. Although NFRCs have achieved tremendous popularity in the automotive sector but also gaining possibilities in other sectors such as construction, sports, cosmetics, roof tiles, roof frames, partition boards, false ceilings, spacecraft, office furniture, and machinery, etc. Mostly, natural fiber-based composites are preferred in interior civil applications due to their low cost and processing friendliness [155]. Further, it is believed that green buildings are ecologically mindful and more appropriate to work and resides. Moreover, bio-composites are gaining interest in recent years as green materials for various applications in the building and construction industries. It can be used as structural bio-composites, which incorporate scaffolds just as roof frames and in bridge structures. Also, it is feasible for nonstructural applications such as ceiling panels, doors, window frames, wallboards, etc. [156]. The natural fiber-based composites are gaining popularity in building and construction industries due to lightweight, low cost, easy availability, decomposability, and biocompatibility [157–159]. They can be used in ceiling panels, roofing, and decorative walling for the building of low-cost houses [160].

15.11 Summary and Prospects In recent years, tremendous growth and development is seen in the field of NFRCs. Natural fibers possess excellent inherent characteristics such as biodegradability, biocompatibility, low density, renewability, and suitable mechanical properties that make them excellent materials for wider commercial utilization, especially in the automotive sector. Additionally, environmental awareness becomes a major driving force in gaining natural fibers broad utilization for various applications as reinforcement materials. However, some of the fiber characteristics such as weak interfacial bonding, low thermal stability, susceptibility to moisture, and incompatible with hydrophobic matrix have become the major challenges during the fabrication of NFRCs. Therefore, different fiber treatment and modification techniques are used, which can improve the fiber–matrix adhesion and increase their mechanical performance. Additionally, consistent quality of fibers is a significant component for stable NFRCs performance. Exploration of the fundamental knowledge about the microstructure characteristics of the interphase further aids in improving the uniform dispersion of fibers within the matrix, better fiber–matrix bonding, which consequently improves the mechanical performance of NFRCs. Furthermore, incompatibility between the hydrophilic fibers and hydrophobic polymer matrix can be reduced by adopting different chemical pretreatment methods or surface modification using coupling agents; however, the adhesion between the fibers and matrix impart major effect in obtaining excellent thermo-mechanical performance. Besides these, aligned fibers, hybridization of different fibers in a single composite, and developments in fabrication techniques can generously help in improving the performance of NFRCs. Especially, nanocellulosic fillers have arisen with excellent mechanical strength and could assume a vital part as new strengthening materials for polymer composites. Additionally, the use of 3D printing in the complex structural design and development of NFRCs with advanced actuation performance can

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change and potentially extend the utilization of NFRC applications in the coming years. Moreover, in the present market, NFRCs with tremendous future scopes are expanding very fast and their use, especially in cars, structural designing, construction, and building materials, is very encouraging. Thus, it can be believed that natural fibers will replace synthetic fibers in the coming future and become one of the sustainable and renewable resources in the composite field for numerous applications.

Acknowledgments Author, Anisha Chaudhary expresses her thanks to DST for providing SERBNational Postdoctoral Fellowship (file no. PDF/2017/002601). Author, Ashish Gupta would like to thank the Council of Scientific and Industrial Research (CSIR), India for financial assistance under the Research Associate Fellowship scheme.

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Index a A-type glass 5 abaca fiber 264, 308 acetaminophen (APAP) 105 acetate fiber 71 acetic acid (CH3 COOH) 22 acetone treatment 274 acrylics 242, 305 acrylonitrile butadiene styrene 316 additional-span-principal fawn 19 advanced nano-particles 126 Agave sisalana 165 aggregates 120 agrochemical compounds 211 air filtration 287 alkali glass 5 alkali-silane treated sisal fiber 178 alkali-treated short sisal fiber-reinforced composites 171, 173, 178 alkaline treatment 274 alkaline/mercerization treatment 83 alpaca hair 266 alumina (Al2 O3 ) 6, 47 alumina fibers 286 aluminum oxide (Al2 O3 ) 270 amino functionalized glass fiber PANI composite 97 amorphous glasses 9 (3-aminopropyl) triethoxysilane 96 angora hair 267 animal fiber(s) 266 animal wool and hair fiber processing 269

animal wool and hair fiber processing 269 antacid 225 antacid adjusted fiber strengthened compounds 226 aramid 73 aramid fibers 94 aramid-fiber reinforced epoxy composites 203 aramid-reinforced epoxy matrix 195 aramid-reinforced polyamide matrix 195 Aramid/Kevlar (KF) 187 Arrhenius acid 225 asbestos 269 aspect ratio 164 avian fiber 263, 267

b bacterial cellulose 312 bailing 19 Bakelite compounds 225 bamboo 266, 315 bamboo fiber 10 bamboo fiber-strengthened cashew nutshell fluid bio-composites 226 bamboo rayon 70 Bamboo Viscose 70 banana fibril agrochemical compound 246 Barbadense plant 19 Barcol hardness test 173 barium nitride (BN) filler 197 barley 265

Natural and Synthetic Fiber Reinforced Composites: Synthesis, Properties, and Applications, First Edition. Edited by Sanjay M. Rangappa, Dipen Kumar Rajak, and Suchart Siengchin. © 2022 WILEY-VCH GmbH. Published 2022 by WILEY-VCH GmbH.

330

Index

basalt 73 basalt fiber (BF) 74, 216, 264 basalt fiber reinforced polymer (BFRP) composite 74, 250 basalt fiber reinforced (BFR) epoxy composite 283 BaTiO3 nanofibers 287 batteries 95–96 beechwood 70 bending strength 277 benzoyl peroxide (BPO) 23 Bi2 Te3 thermoelectric material 101 bio-based fillers 197 bio-based materials 317 bipolar plate (BP) 97 Bisphenol 279 Bisphenol A 203 Bisphenol-F epoxy resin NPEF-164X 279 blanched paper delicate timber (BKSW)-strengthened PLA bio-composites 227 bleaching (NaClO) 23 blend fiber compounds (C2 H4 )n basis of blend compounds 252 epoxy based-hybrid composites 250–252 polyester based hybrid composites 252 thermo-cool basis of 253 blend fibril-based agrochemical compounds polymerized fibril agrochemical compounds 245–246 synthetic reinforced hybrid composites 245 blend polymerized fibril strengthened compounds basalt fiber reinforced composites 250 carbon fibrils 249–250 glassy carbon (woven) 248–249 Kevlar 249 bombyx mori 269 boron carbide (b4 C) 47, 270 Brinell hardness test 173

buckle power 139 bundle strength 138

c C3 A CaSO4 12H2 O 120 C-glass 6 Ca(OH)2 308 CaCl2 308 calcium hydroxide 120 calcium silicate hydrate (C-S-H) 120 camptothecin (CPT) 107 carbon fiber(s) (CF) 73, 94, 187 classification of 38 reinforced carbon matrix composites 53 reinforced ceramic matrix composites 46 reinforced with polymer matrix composites 41 surface treatment methods 40 synthesis of 38 carbon fiber composites 85 carbon fiber-epoxy composites 98, 100 carbon fiber fabric/polyurethane lightweight composite 106 carbon fiber reinforced carbon composite (CFRCC) 37 carbon fiber reinforced carbon matrix composites chemical vapor deposition and properties 57–59 structure of 53 thermoplastic pitch 56–57 thermosetting resin 54–56 carbon fiber reinforced cement composites 100 carbon fiber reinforced ceramic matrix composites hot-pressing 48 infiltration methods 49–50 polymer infiltration and pyrolysis 52 reactive melt infiltration technique 51–52 slurry infiltration process 50–51 sol gel infiltration process 52

Index

spark plasma sintering 48–49 structure of 47 carbon fiber reinforced polymer (CFRP) 73, 190, 278 carbon fiber reinforced with polymer matrix composites filament winding 43–44 hand lay-up and spray-up process 42–43 injection molding 44 molding 43 properties 44 pultrusion 44 carbon fiber reinforced polymer (CFRP) composites 262 carbon fiber paper/cloth-based composites 96 carbon fibrils 242, 249 carbon/glass fibril strengthened epoxy compound 245 carbon nano fibers (CNF) 104, 194, 290 carbon nanotubes (CNTs) 118, 126, 290 electrical properties 158–159 electronic properties 159 field emission properties 159–160 mechanical properties 157 multiwalled 157 single walled 156 thermal properties 157–158 carbon nanotubes-Glass Fiber-epoxy composites 100 cashmere 266 celibate agrochemicals 213 cellulose 165, 301, 305 cellulose based natural fibers 302 cellulose fibrils 302 cellulose microfibrils 181 cellulose nanocrystals (CNCs) 312 cellulose nanofibrils (CNFs) 312 cellulose powder ((C6H10O5)n) 23 Cem-FIL glass fiber 117 cement carbon fiber composites 101 cementitious materials 119 advanced nano-particles 126–127 components of 119–127

matrix materials 119–120 reinforcements 121 short discontinuous fibers 121–123 textiles/woven 123–125 ceramic fibers 270 ceramic glass fiber 270 ceramic matrix 163 ceramic matrix composites (CMCs) 46, 211 (C2 H4 )n basis of blend compounds 252 chemical vapor deposition (CVD) and properties 57 chemical vapor infiltration (CVI) process 50, 58 chemical-based agrochemicals 224 chloride treated aramid fibers 191 (C10 H8 O4 )n compounds 252 chopped sarbon fibers 95 civil engineering 102 CNF-β-cyclodextrin (β-CD) composite 105 CNT-PANI film 97 CNT/GF/epoxy composite 100 coasts–Redfern equation 220 coaxial core-shell fiber structure 103 cobalt naphthenate 171 cocoons 269 coercivity/magnetic hardness 200 coir 263 coir reinforced polyester (CFRP) composite 84 common fiber-strengthened bio agrochemical compounds 224 composite(s) categorization on the basis of matrix material 39 general structure of 38 phases of 38 composite nanofibers 103 compressive strength 140 continuous fiber-based cement-based composites 123 continuous fiber reinforced composites 164

331

332

Index

continuous woven reinforced concrete 118 cordenka 70 cordenka cellulose reinforced polyamide polymer composite 315 corn-and rice dextrose-based bioplastics 225 corona treatment method 273 corrosion and stearic acid (C18 H36 O2 ) treatment 23 cotton 17, 263 cotton ball 17 cotton composites 138 cotton fiber chemical composition 23 chemical treatment 22–23 classification based on fiber length uniformity 18 classification based on the strength 18 classifications based on extraneous materials 19 classifications based on fiber color 18 classifications based on fiber fineness 18 classifications based on leaf grade 18–19 classifications based on module averaging 19–20 classifications based on trash 18 constitution and molecular weight distributions 25 Fourier transformation by infrared spectroscopy analysis 29 measurement of density 27 measurement of diameter 27–28 microscopic view 26 physical properties 26–27 production and cultivation 19 scanning electron microscope 30–31 solvents 21 structure 25–26 surface modification 21 thermogravimetric analysis 29–30

transmission electron microscope 31–32 X-ray diffraction analysis 28–29 cotton fiber-reinforced composites buckle power 139–140 compressive strength 140–141 durability 148 fabrication process 137–138 Fourier transformation by infrared spectroscopy analysis 145–146 hardness 142 impact strength 141–142 life cycle and environmental assessment 147 microscopic morphology 144–145 tensile strength 138–139 thermogravimetric analysis 142–143 transmission electron microscope 146–147 water absorption test 143–144 coupling agent 309 CuO-CF composites 95 Cuprammonium 69 curaua fiber-strengthened elevated-thickness polyethene composites 224

d Daunorubicin 107 1D Co3 O4 nanofiber 291 delamination 191, 194 D-glass 6 D-glucopyranose units 302 DI-washed CFs 95 differential scanning calorimetry (DSC) 179 diglycidyl ether 203 dimethyl formide solvent 285 distinct phases 163 dolomite 6 double walled CNT (DWCNT) 197 Doum fibers 212 drawing process 20 drug delivery 107 durable engineered agrochemicals 224

Index

dyeing 20 dynamic contact angle analysis 278

e EFB/glass hybrids (C10 H8 O4 )n compound 252 E-glass carbon fibril strengthened epoxy compound 245 E-glass fiber 10 electric discharge (ED) treatment 272 electro spinning process 285 electro spun metal oxide nanofiber 290 electro-spun nanofibers 284 electrochromic fiber shape supercapacitor 97 electrospinning based composite fibers 97 electrospun cellulose nanofibrils (ECNFs) 312 electrospun PAA/manganese acetate fibers 97 electrospun PU fibers 99 EMI shielding 106, 201 end notched flexure (ENF) 193 energy conversion and storage device 290 energy storage devices 95 epoxy 165, 305, 315 epoxy based-hybrid composites 250 epoxy resin 10 epoxy resin 618 279 ethylenediaminetetraacetic acid (EDTA) 308 E-type glass 7 ettringite 120

f fawn fibers 214 fawn fibril-based composite laminates 137 feathers and avian fiber 269 Fe3 O4 /PLA (poly lactic acid) composite nanofibers 107 fiber(s) 93 fiber and textile reinforced concretes 117

fiberglass 2 fiber-matrix adhesion 306 fiber-matrix (F-M) interface 278 fiber-matrix (F-M system) 81 fibers hybridization 310 fiber percentage 279 fiber-reinforced polymer composites 164 fiber-reinforced polymer matrix composites (FRP) 74 composites 37 electrical properties 198–200 EMI shielding 201 flexural properties 190–191 interlaminar properties 191–194 magnetic and electromagnetic properties 200–201 matrix influence 195 nanofillers effect 195–198 self-healing composites 203 shape memory composites 202 tensile properties 189–190 type of fiber reinforcement 194–195 fiber-reinforced PPSEK composite 278 fiber reinforced plastic (FRP) composites 262 fiber stacking 225 fiber-strengthened thermosetting agrochemical compounds 221 fiber surface ablation 273 fibrils 241 field-effect transistors (FET) 104 filament winding 43 fillers 217 finishing 20 flax fibers 265 flax/PLA composites 310, 315 flax/kenaf/glass/carbon fiber reinforced composites 87 flexural properties 190 fluorescent phase change material 99 fluoropolymers 98 fly ash 120 Fourier transformation by infrared spectroscopy (FTIR) analysis 29, 145

333

334

Index

frequently used fibers 67 fructose 219 fructose-based common fibrils 215 fuel cells 97 fused deposition modeling (FDM) 316

g γ-methacryloxypropyltrimethoxysilane 310 γ-aminopropyltriethoxysilane 310 γ-methacryloxypropyltrimethoxysilane 310 GDNR/epoxy resin blend 170 GF/epoxy interfacial bonding 192 ginning 19 glass fiber(s) (GF) 2, 71, 96, 85, 188 glass fiber fortified saps 2 glass fiber paper/polyaniline composite 96 glass fiber reinforced composite (GFRC) applications 2 bio-degradability 1 classification of 5 classifications based on form 8 defined 1 mechanical properties 10 reusability 1 structure 9 glass fiber reinforced polymer (GFRP) 190 composites 262, 278 glass fiber/gel-polymer composite 96 glass fibril(s) 243 glass fibril-fortifying polymers 244 glassy carbon (woven) 248 glycidyl methacrylate treated fiber 179 golden fiber 265 gooey 69 Gossypium arboretum 19 Gossypium herbaceum 19 Gossypium hirsutum 19 Gram Square Meter (GSM) 169 graphene 118 graphene fiber (GF) 73 graphene nanoplatelet (GNP) 196, 199

graphene oxide (GO) 126, 192, 197 graphite 95, 290 graphite structure 156 graphite–glass/epoxy composite 164 graphitized graphene (GG) 194 grass fibers 216 “green” composites 317 Grewia optiva fibers (GOF) 87

h hand lay-up sans spray-up process 42 hand lay-up technique 276 hardness 142 harvesting 19 hemicellulose 301, 302, 305 hemp 244 hemp fiber 85, 265 hexagonal bonding in graphene sheet 156 hibiscus-strengthened PLA compound 227 hibiscus-strengthened thermosetting polyurethane (TPU) composites 223 hibiscus/atomic nanocrystals/PP/MAPP nanocomposites 228 high efficiency particulate air (HEPA) filter 287 high-performance synthetic fibers 191 high-wet-modulus rayon 69 hot-pressing 48 Horowitz–Metzger equation 220 hybridization 82, 194, 279 hybrids T77S 245

i impact strength 141 In2 O3 nanofiber composite 104, 105 infiltration methods 49 infusion molding processes 191 injection molding 44 inorganic fibers 261 interface phase 163 interfacial shear strength (IFSS) 192 interlaminar fracture toughness 193

Index

interlaminar properties 191 interlaminar shear strength (ILSS) 192 interpenetrating polymer networks (IPN) resins 168 ionic Transition Metal complex( iTMC) based electroluminescent fibers 103 isothermic and non-isothermic thermo-gravimetric investigation 219

j jute fibers

225, 265, 307

k Kapok 263 Kenaf and Pineapple Leaf Fibers 280 kenaf fiber 265 kenaf/HDPE 315 Kevlar 74, 249 knitted reinforced fabrics 118

l laccase-cared and uncared fibers 226 laminate agrochemical compounds 223 laminated GFRC materials 2 lattice 211 layered ZnO/64o YX LiNbO3 based SAW transducer 105 leaf fibers 216, 264 leucoemeraldine-based PANI 105 Levant cotton 19 Li-S and LiO2 batteries 290 light emitting diode (LED) devices 103 lightweight glass–Kevlar/epoxy face masks 164 lignin 301 lignocellulosic fibers 212 lime 6 liquid silicon infiltration (LSI) 51 long fiber(s) 70, 216 lustrous carbon 248 lyocell fibers 312

m magnetization 200 MA-grafted copolymers 309 maleic anhydride (MA)–grafted copolymer 309 maleic anhydride-polypropylene copolymer (MAPP) 279 man-made fibers 93, 261 matrix 303 matrix materials 119 matrix phase 163 mechanical fiber 166 mechanical interlocking 306 mercerization 274 mesoporous carbon (C) 290 metal fibers 270 metal matrix 163 metal matrix composites (MMCs) 211 methyl ethyl ketone peroxide 171 methylmethacrylate (MMA) 174 micellar-treated sisal fibers 174 micro/nano composites 281 mineral fibers 165, 267, 301 asbestos 269 ceramic fibers 270 metal fibers 270 mineral fibers 165 MnO2 nanoparticles 97 modal fiber 70 modal rayon 70 mode I/mode II interlaminar fracture toughness (GIC /GIIC ) 193 mohair 266 molding 43 molten ceramic infiltration 50 monosulfate 120 M-type glass fiber 7 multiwall carbon nanotube doped nylon-6 spun with polythionine (MWNT-PA6-PTH) 105 multiwalled carbon nanotube (MWCNT) 49, 157, 196, 197 multi walled nano carbon tubes (MWNCTs) 283

335

336

Index

n nano fibrillated cellulose (NFC) 70 nano-B4 C 284 nanocellulosic fillers 312 nanoclay 228 nanocompounds 228 nanofiber air filtration 287 alumina fibers 286 BaTiO3 nanofibers 287 electro spinning process 285 hybridization effect 281 Li-S and LiO2 batteries 290 polyacrylonitrilefibers 285 recycled PET nanofibers 289 solar cells 290 water filtration 288 nanofiber composites 101 nanofillers effect 196 nanofillers nano-Fe2 O3 126 nano-particles reinforced concrete 129 nano-silica 118 nano-SiO2 126 nano-TiO2 126 nanotechnology 155 NaOH 308 natural fiber(s) 67, 93, 164, 301 bast fiber 264–265 biological treatment 275 blend of nanocompounds 228–229 chemical treatment 273–275 choice of substance based on TGI 220–221 Coasts–Redfern equation 220 common fiber-strengthened bio agrochemical compounds 224–227 electric discharge treatment 272–273 extraction and processing of plant-based fiber 268 extraction of 267 farming harvests 214 fawn fibers 214 fiber percentage 279 fillers 217–218

fructose-based common fibrils 215 Horowitz–Metzger equation 220 isothermic and non-isothermic thermo-gravimetric investigation 219 laminate agrochemical compounds 223–224 leaf fibers 264 mass reduction 214 mechanical treatment 271 phenolics 215 plant fiber 215–217, 263–264 polyose 215 resins/tars 217 solvent extraction 272 stalk fiber 265–266 thermosetting compounds 221–222 ultraviolet treatment 273 natural fiber reinforced polymer composites (NFRP) 43, 275, 304 advancement in 305–306 alkaline/mercerization treatment 83 applications 317–319 chemical treatment 277, 307–309 classification of natural fibers 81 conventional manufacturing processes 314–315 coupling agent 309–310 fibers treatment and modification 307 fibers hybridization 310–312 flame retardant properties 312–313 mechanical properties, of synthetic and natural fibers 83 nanocellulosic fillers 312 silane coupling agents 83 3D printing 316–317 tribological behavior, of chemically treated composites 84–87 tribological behavior, of hybrid composites 87–89 water absorption characteristics 313–314 natural fibers reinforced composites 303 natural fibrils 242 nettle fibers (NF) 87

Index

nitrides 47 non-metallic synthetic fibers 102 novolac epoxy system 194 nylon(s) 74, 242, 261, 305

o Oil Palm Wood Flour (OPWF) 307 oil palm–epoxy-like compound 244 one unity composite 195 organic fibers 261 organic lanthanides 99 organic PCMs 99 oxidized PAN fiber 39

p PA6 Badamid 190 palm oil EFB/jute blend compounds 250 palm/glass oil fiber strengthened (C10 H8 O4 )n compounds 252 PAN/PEG/SiC fibers 38, 99 para-phenylenediamine 242 PA6 Ultramid 190 pectin 305 peroxide (benzoylation) treatment 275 perpetual rayon filaments 70 phase change materials (PCM) 95, 99 phenolics 215, 219 phenyl silane containing SBA-15 103 phenylpropane units 302 P3HT/graphene 104 p-hydroxyacetophenone (p-HAP) 105 pin-on-disk (POD) tribometer 84 pine fiber-strengthened PP compound 224 pine strands 224 pitch 56 pitch-based precursor 40 PLA/jute compounds 225 PLA/nanoclay/ bamboo mixture compounds 228 plant fiber 215, 263, 301 plasma treatment 273 Poisson’s ratio 190 polished carbon 248 polyacrylic(s) 261

poly (acrylic acid) (PAA) 97 polyacrylonitrile (PAN) fibers 73, 285 polyacrylonitrile/PEG (PAN/PEG) based hybrid polymer nanofibers 99 polyamide 190, 261 polyamide/glass fiber composites 99 polyaniline (PANI) 105, 200 polycaprolactone (PCL) 107 polycaprolactone and ethyl ethylene phosphate (PCLEEP) 108 polycarbonate 316 poly (9,9-dioctyl fluorenyl-2,7-diyl)-alt(1,4-benzothiadiazole) 103 poly(dopamine) (PDA) 192 polyester(s) 67, 165, 242, 261 polyester based hybrid composites 252 polyetheretherketone 57 polyetherimide 57 polyetherimide (PEI) 190 polyethylene 98 poly (ethylene-co-vinyl acetate) 224 polyethylene imine (PEI) 212, 308 polyethylene nylon 43 poly(ethylene oxide) 103 poly(3,4-ethylene dioxythiophene) (PEDOT) 200 poly ethylene terephlate (PET) 288 polyethylene terephthalate (PET-F) 73 poly(ethyl oxide) (PEO) 103 polyether sulfone (PES) nanofiber 288 polyhydroxybutyrate 227 polyhydroxy butyrate (PHB) nano-composites 70 poly(3-hexylthiophene) P3HT/graphene composite fibers 104 poly (hydroxybutyrate-cohydroxyvalerate) 227 polylactic acid (PLA) 107, 307 poly lactic-co-glycolic acid (PLGA) 107 polylactic acid resin 168 polylactide 316 polymer-based CFs 106 polymer-based products 81 polymer coatings 23

337

338

Index

polymer electrolyte membrane based fuel cells (PEM fuel cell) 97 polymer hemi-cellulose 302 polymeric fibers 93 polymeric synthetic fibers 102 polymer infiltration and pyrolysis (PIP) 50, 52 polymer matrix composites (PMCs) 163, 211 polymer nanofibers 284 polymerization 67 polymerized fibril agrochemical compounds 245 polymerized/fake fibrils 242 polyolefins 261 polyose 215, 219 polyphenylene sulfide (PPS) 200 polyphenylsulfones 316 poly(p-phenylene vinylene) (PPV) 200 polypropylene 98, 305 polypropylene composites 308 polypropylene filament (PP-F) 73 polypropylene–lyocell composites 280 poly(propylene oxide) 103 polypyrrole (PPy) polymer 97 polythionine composite 105 polythiophenes 200 polyurethanes 242 polyvinyl alcohol (PVA) 43, 107 poly (vinylidene fluoride co-hexafluoro propylene) (PVDF-HFP) 96, 98 polyvinyl pyrrolidone (PVP) solution 287 polyvinyl pyrrolidone(PVP) hybrid structures 105 poly{2-methoxy-5-(2′ -ethyl-hexyloxy)1,4-phenylenevinylene}(MEHPPV) fibers 103 porous carbon nano fiber (PCNF) 290 Portland cement 119 Portlandite (Ca(OH)2 ) 120 pozzolan 120 PP grid 224 PP/hemp composites 310 protein/gene therapy 108 pultrusion 44, 277

PVA/H3 PO4 gel electrolyte

97

q quaternary fatty acid eutectics

99

r ramie fiber 265 raw sisal fiber 178 rayon 69, 261 reactive melt infiltration (RMI) 50, 51 recycled PET (RPET) nanofibers 289 reeling silk fiber 269 reinforced concrete nano-particles 129–130 outlook and future of 130–131 steel fiber 128 textile 128–129 reinforcements 121 resin transfer molding process (RTM) 276, 277 resins/tars 217 rGO/CF binary composite 96 ribbon fiber 166 rice 265 Rockwell hardness test 173 roving 20, 137 R-,S-, and T-type glass 7 rubber seed oil polyurethane resin (RSOPU) 176 (Ru(bpy)3 )2+ (PF6 )− )2 103 ruthenium(II) tris(bipyridine)/ polyethylene oxide nanofibers 103

s saturation magnetization (SM) 200 scanning electron microscope 30 Seacell fiber 71 Seebeck effect 100 seed fiber 263 seed hairs 216 self-healing composites 203 self-synthesized urea-formaldehyde resin 173 semi-synthetic fibers 67, 69 sensors 104

Index

sericulture 269 shape memory composites 202 shape stabilization 99 Shore D hardness test 142, 173 short discontinuous fibers 121 short fiber reinforcement polymers (SFRP) 73 short sisal fiber reinforced epoxy composites 169 silane agent 309 silane coupling agents 83, 275 silane hydrolysis 310 silane solution (SiH4 ) 22 silane-cared compounds 225 silanol self-condensation 310 silica (Si2 O3 ) 2, 6 silica-based-inorganic glasses 9 silicon carbide (SiC) 47, 270 silicon nitride (Si3 N4 ) 47 silk fiber 267, 269 silk fibroin (SF) films 283 silver nanoparticles (Ag nps) 196 silvering 20 single fiber strength 138 single walled carbon nanotube (SWCNT) 156, 197 SiO2 /BTP/BFR composites 283 sisal fibers (SF) 87, 165, 264 advantages 166 flexural properties 168–171 glass transition temperature 179–181 hardness 173–174 impact properties 171–173 tensile properties 167–168 thermal stability 175–179 types of 166 slurry infiltration process (SIP) 50 Sm3+ doped glass fiber 251 small fibers 216 SnO2 based composite nanofibers 104 SnO2 doped CNF 104 soda (Na2 CO3 ) 6 soda-lime glass 5 sodium chloride (NaCl) 6 sodium hydroxide (NaOH) 22, 179, 274 sodium sulfate (Na2 So4 ) 6

sol gel infiltration process 50, 52 solar cells 290 sole-phase thermic debasement 225 solvent(s) 21 solvent casting method 88 soy protein-polymer matrix 181 spark plasma sintering (SPS) 48 spinning process 20 spirocyclic pentaerythritol bisphosphorate disphosphoryl melamine (SPDPM) 313 spray lay-up technique 276 SSF/Polypropylene(PP)/CNT-based composites 107 stainless steel fibers (SSF) 107 stalk fiber 263, 265 steel fiber reinforced concrete 128 straw 266 strengthening stage 211 S2-type glass 7 sugar palm fibers 280 supercapacitors (SCs) 96 sweet-smelling polymers 302 synthetic fabrics 67 synthetic fiber(s) 67, 71, 93, 164, 187, 261 carbon fibrils 242 glass fibrils 243 polymerized fibrils 242 synthetic fiber reinforced composites (SFRC) 93 advantages of 93 batteries 95–96 civil engineering 102 drug delivery 107 EMI shielding 106–107 field-effect transistors 104 light emitting diode devices 103–104 mechanical industry 101–102 nonstructural applications of 95 protein/gene therapy 108 sensors 104–106 thermal energy storage technology 99 thermoelectric or thermal energy harvesting 99–101 supercapacitors 96–97

339

340

Index

synthetic fiber reinforced composites (SFRC) (contd.) fuel cells 97–98 synthetic plastic fabrics 67 synthetic reinforced hybrid composites 245 synthetization 242

t tensile strength 189 terephthaloyl chloride 242 terylene 75 tetraethylorthosilicate (TEOS) 178 textile pre-stressing 124 textile reinforced concrete 117, 128 textile volume fraction (TVF) 124 textiles/woven 123 thermal energy storage(TES) technology 99 thermoelectric or thermal energy harvesting 99 thermogravimetric analyser (TGA) 29, 142, 175 thermoplastic pitch 56 thermosetting compounds 221 thermosetting resin 54 3D printing 316 3D-spacer fabrics 128 3K weave 194 trans-polyisoprene (TPI) based shape memory polymer composite 203 transmission electron microscope 31, 146 transverse rupture strength 277 tribological behavior of chemically treated composites 84–87 of hybrid composites 87–89 tribometer/tribotester 83 trimethoxysilane 310

u unadulterated cellulose 69 unidirectional pitch-based carbon fibers 98

unsaturated polyester composite 174 untreated sisal fiber 171 upland cotton 19

v vacuum bag molding 43 vacuum infusion molding 276 vapor-grown CFs 106 vegetable fibers 211 Vickers hardness test 173 vinyl ester 165 virgin fibers 200 viscose 69

w waste fibers 102 water absorption test 143 water filtration 288 wearable sensor 105 weaving 20 weft knitted fabric 195 wettability 278 wheat 265 Wilhelmy method 278 wood flour/PP 315 wool 266 woven CF-resin reinforced BP 98 woven fabrics 169 woven-mat E/GF polyester composites 262 WS2 /CFC composite 96

x X-ray diffraction (XRD) analysis 28 xylan 219 xylem fiber 166

y yarn 1, 137

z Z–type glass fiber 7 zirconia (ZrO2 ) 47 zirconium carbide (ZrC) 47

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