Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering 352782457X, 9783527824571

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Hybrid Fiber Composites

Hybrid Fiber Composites Materials, Manufacturing, Process Engineering

Edited by Anish Khan Sanjay Mavinkere Rangappa Mohammad Jawaid Suchart Siengchin Abdullah M. Asiri

Editors Dr. Anish Khan

King Abdulaziz University Chemistry Department P.O. Box 80203 21589 Jeddah Saudi Arabia

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.

Dr. Sanjay Mavinkere Rangappa

King Mongkut’s Univ. of Technology Department of Mechanical & Process Engineering 1518 Pracharaj 1 Wongsawang Road Bangsue 10800 Bangkok Thailand

Library of Congress Card No.:

applied for British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

Dr. Mohammad Jawaid

Bibliographic information published by the Deutsche Nationalbibliothek

Universiti Putra Malaysia Inst. of Tropical Forestry Serdang 43400 Selangor Malaysia

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

Prof. Suchart Siengchin

© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany

King Mongkut’s University of Technonogy Dpt. of Materials & Production Engin. 1518 Pracharat 1 Road, Bangsue 10800 Bangkok Thailand Prof. Abdullah M. Asiri

King Abdulaziz University Chemistry Department P.O. Box 80203 21589 Jeddah Saudi Arabia

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: 978-3-527-34672-1 ePDF ISBN: 978-3-527-82456-4 ePub ISBN: 978-3-527-82458-8 oBook ISBN: 978-3-527-82457-1 Typesetting SPi Global, Chennai, India Printing and Binding

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

Editors are honored to dedicate this book to their parents.

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Contents About the Editors xix 1

Natural and Synthetic Fibers for Hybrid Composites 1 Brijesh Gangil, Lalit Ranakoti, Shashikant Verma, Tej Singh, and Sandeep Kumar

1.1 1.2 1.3 1.4 1.4.1 1.4.2 1.4.3 1.4.4 1.4.5 1.5 1.5.1 1.6

Introduction 1 Natural Fibers 2 Microstructure of Natural Fibers 3 Natural Fiber-Reinforced Polymer Composites 3 Synthetic Fibers 7 Glass Fibers 8 Carbon Fibers 8 Kevlar or Aramid Fibers 9 Comparison Between Natural and Synthetic Fibers 9 Hybrid Fiber-Based Polymer Composites 10 Applications 11 Conclusion 12 References 13

2

Effect of Process Engineering on the Performance of Hybrid Fiber Composites 17 Madhu Puttegowda, Yashas Gowda Thyavihalli Girijappa, Sanjay Mavinkere Rangappa, Jyotishkumar Parameswaranpillai, and Suchart Siengchin

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.7.1 2.7.2 2.7.3 2.7.4 2.7.5

Introduction 17 Fibers 18 Polymers 20 Hybrid Polymer Composites 21 Fiber Extraction Methods 22 Fiber Treatments 22 Processing Methods of Hybrid Composites Pultrusion 24 Hand Lay-up/Wet Lay-up 25 Vacuum Bagging 25 Filament Winding 26 Resin Transfer Molding 27

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2.7.6 2.7.7 2.8 2.8.1 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2.8.7 2.9

Compression Molding 27 Injection Molding 28 Application of Each Hybrid Polymer Composite Processing Methods 29 Pultrusion 29 Hand Lay-up 29 Vacuum Bagging 31 Filament Winding 31 Resin Transfer Molding 31 Compression Molding 31 Injection Molding 32 Conclusion 32 References 32

3

Mechanical and Physical Test of Hybrid Fiber Composites 41 Mohit Hemath, Arul Mozhi Selvan Varadhappan, Hemath Kumar Govindarajulu, Sanjay Mavinkere Rangappa, Suchart Siengchin, and Harinandan Kumar

3.1 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.2.7

Introduction 41 Materials and Methods 44 Materials 44 Extraction of Sugarcane Nanocellulose Fiber (SNCF) 44 Synthesis of Al–SiC Nanoparticles 44 Fabrication of SNCF/Al–SiC Vinyl Ester Nanocomposites 44 Design of Experiments (DOE) 45 Development of Experimental Models and Optimization 45 Characterization on SNCF/Al–SiC Vinyl Ester Hybrid Nanocomposites 46 FTIR Spectra and XRD Curves 46 Physical Properties 47 Mechanical Properties 47 Viscoelastic Properties 48 Morphological Properties 48 Results and Discussion 48 Optimization 48 Maximization 52 FTIR and XRD Curves 54 Mechanical Properties 55 Flexural Properties 55 Morphological Properties 57 Compression Properties 58 Tensile Properties 58 Viscoelastic Properties 58 Storage Modulus 58 Loss Modulus 60 Damping Factor 60

3.2.7.1 3.2.7.2 3.2.7.3 3.2.7.4 3.2.7.5 3.3 3.3.1 3.3.2 3.3.3 3.3.4 3.3.4.1 3.3.4.2 3.3.4.3 3.3.4.4 3.3.5 3.3.5.1 3.3.5.2 3.3.5.3

Contents

3.3.5.4 3.3.6 3.3.7 3.3.8 3.4

Glass Transition Temperature 60 Impact Strength 61 Vickers Hardness 62 Physical Properties 62 Conclusion 63 References 63

4

Experimental Investigations in the Drilling of Hybrid Fiber Composites 69 Sathish Kumar Palaniappan, Samir Kumar Pal, Rajasekar Rathanasamy, Gobinath Velu Kaliyannan, and Moganapriya Chinnasamy

4.1 4.2 4.3 4.4 4.5 4.5.1 4.5.2 4.5.3 4.5.4 4.5.5 4.6

Introduction 69 Characteristics of Drilling 70 Hybrid Fiber Composites 70 Machining Limitation on Hybrid Fiber Composite Drilling 71 Investigation of Hybrid Fiber Composites Drilling 71 Condition for Hybrid Composites Drill 72 Factors Affecting Drilling 72 Drilling of GF-Reinforced Hybrid Composites 73 Survey on NF-Reinforced Hybrid Composites Drilling 75 Drilling of CF Reinforced Hybrid Composites 77 Conclusion 79 References 79

5

Fracture Analysis on Silk and Glass Fiber-Reinforced Hybrid Composites 87 Gangaplara Basavarajappa Manjunatha and Kurki Nagaraja Bharath

5.1 5.2 5.2.1 5.2.2 5.2.3 5.3 5.3.1 5.3.2

Introduction 87 Materials and Methods 88 Materials and Specimen Preparation 88 Compact Tension Shear (CTS) Test 90 Single-Edge Notched Bend (SENB) 90 Results and Discussion 92 Compact Tension Shear (CTS) Test 92 Mode I, Mode II, and Mixed Mode Fracture Toughness for Different Loading Angle 93 Single-Edge Notched Bend (SENB) 93 Fracture Toughness of SENB Test 95 Conclusion 96 References 96

5.3.3 5.3.4 5.4

6

Failure Mechanisms of Fiber Composites 99 C˘at˘alin Iulian Pruncu and Maria-Luminita Scutaru

6.1 6.2 6.3

Introduction 99 Industrial Benefits and Applications 100 Materials for Reinforcing 104

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6.3.1 6.3.2 6.3.3 6.4 6.4.1 6.4.2 6.4.3 6.4.4 6.4.5 6.5 6.6 6.6.1 6.6.1.1 6.7 6.8 6.9

Composites Reinforced with Continuous Fibers 104 Composites Reinforced with Discontinuous Fibers 105 Composites Reinforced with Fillers 106 Resin Type 106 Epoxy Resins 106 Formaldehyde Resins 107 Polyurethane Resins 107 Polyester Resins 108 Silicone Resins 108 Interfacial of Composite Structure 109 Micromechanics 110 Mechanical Properties 110 Coefficients of Thermal Expansion and Heat Transfer Properties 111 Short Overview of Specific Failure Modes 112 Future Perspective 113 Conclusions 114 References 114

7

Ballistic Behavior of Fiber Composites 117 Ignacio Rubio, Josué Aranda Ruiz, Marcos Rodriguez Millan, José Antonio Loya, and Marta María Moure

7.1 7.2 7.2.1 7.2.2 7.2.3 7.2.3.1 7.2.3.2 7.2.3.3 7.3 7.4

Introduction 117 High-Velocity Impact Test 119 Material 119 Experimental Setup 119 Analysis and Results 121 Ballistic Curves 121 Failure Modes 123 Back-Face Displacement 123 Computational Methods 124 Conclusions 126 References 127

8

Mechanical Behavior of Synthetic/Natural Fibers in Hybrid Composites 129 Navasingh Rajesh Jesudoss Hynes, Ramakrishnan Sankaranarayanan, Jegadeesaperumal Senthil Kumar, Sanjay Mavinkere Rangappa, and Suchart Siengchin

8.1 8.2

Introduction 129 Impact Strength of Natural Fiber (Flax), Synthetic Fiber (Carbon), and Hybrid (Carbon/Flax) Composites 130 Kenaf/Aramid (Epoxy) Hybrid Composites with Different Fiber Orientation 132 Impact Strength of Carbon/Flax (Epoxy) Hybrid Composites with Different Fiber Orientation 134

8.3 8.4

Contents

8.5 8.6 8.6.1 8.6.2 8.6.3 8.7

Comparison of Absorbed Impact Energy of Different Hybrid Composites 135 Comparison of Strength of Natural Fiber (Ramie), Synthetic Fiber (Glass), and Hybrid (Ramie/Glass) Composites 137 Tensile Strength of Natural Fiber (Ramie), Synthetic Fiber (Glass), and Hybrid (Ramie/Glass) Composites 138 Flexural Strength of Natural Fiber (Ramie), Synthetic Fiber (Glass), and Hybrid (Ramie/Glass) Composites 139 Impact Strength of Natural Fiber (Ramie), Synthetic Fiber (Glass), and Hybrid (Ramie/Glass) Composites 140 Summary and Outlook 141 References 143

9

Bast Fiber-Based Polymer Composites 147 Sandeep Kumar, Brijesh Gangil, Krishan Kant Singh Mer, Manoj Kumar Gupta, and Vinay Kumar Patel

9.1 9.1.1 9.2 9.2.1 9.2.2 9.2.3 9.2.4 9.2.5 9.3

Introduction 147 Bast Fiber as Reinforcing Material 149 Polymer Composites Reinforced with Bast Fibers 149 Polymer Composites Reinforced with Flax Fibers 150 Polymer Composites Reinforced with Grewia Optiva Fiber 152 Polymer Composites Reinforced with Hemp Fiber 155 Polymer Composites Reinforced with Nettle Fiber 156 Polymer Composites Reinforced with Jute Fiber 158 Applications of Polymer Composites Reinforced with Bast Fibers 160 Conclusion 161 References 161

9.4

10

Flame-Retardant Balsa Wood/GFRP Sandwich Composites, Mechanical Evaluation, and Comparisons with Other Sandwich Composites 169 Subin Shaji George, Vivek Arjuna, Venkata Prudhvi Pallapolu, and Padmanabhan Krishnan

10.1 10.2 10.2.1 10.2.2 10.2.3 10.2.4 10.2.5 10.3 10.3.1 10.3.2 10.3.3 10.3.4

Introduction 169 Literature Survey 171 Sandwich Composite Structure and Properties 171 Knowledge Gained from the Literature Review 172 Gaps Identified from Literature Survey 172 Objective of the Project 173 Motivation 173 Methodology and Experimental Work 173 Hand Lay-up Procedure 173 Vacuum Bagging 174 Testing and Evaluations 175 Technical Specification 177

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10.3.5 10.3.6 10.3.7 10.4 10.4.1 10.4.1.1 10.4.1.2 10.4.1.3 10.4.1.4 10.4.2 10.4.2.1 10.4.2.2 10.4.2.3 10.4.2.4 10.4.2.5 10.4.2.6 10.4.2.7 10.4.2.8 10.4.2.9 10.4.3 10.5 10.6

Design Approach Details 177 Codes and Standards 178 Fabrication Methodology 178 Results and Discussion 179 Compression Testing 179 Flatwise Transverse Grain Test 179 Edgewise Transverse Grain Compression 180 Edgewise Longitudinal Grain Compression 182 Discussion and Comment (Compression Test) 183 Three-Point Bending Test (Flexural Test) 183 Experimental Results for Three-Point Bending Test of Balsa Wood 184 Experimental Results for Three-Point Bending Test of Composite of Skin-to-Core Ratio 1 : 1 184 Experimental Results for Three-Point Bending Test of Composite of Skin-to-Core Ratio 2 : 1 184 Experimental Result for Three-Point Bending Test of Composite of Skin-to-Core Ratio 3 : 1 187 Experimental Results for Three-Point Bending Test of Composite of Skin-to-Core Ratio 4 : 1 187 Experimental Results for Three-Point Bending Test of Composite of Skin-to-Core Ratio 5 : 1 188 Mean, Minimum, and Maximum Mechanical Properties of Sandwich Composites 188 Mechanical Properties of Sandwich Composite for Different Core Materials 189 Discussion and Comments (Flexural Testing/Three-Point Bending Test) 189 Types and Modes of Failure During the Test on Sandwich Composites 190 Conclusions 192 Scope for Future Work 193 Acknowledgment 193 List of Symbols and Abbreviations 193 References 193

11

Biocomposites Reinforced with Animal and Regenerated Fibers 197 Manickam Ramesh, Chinnaiyan Deepa, Sanjay Mavinkere Rangappa, and Suchart Siengchin

11.1 11.2 11.2.1 11.2.2 11.2.3 11.3 11.3.1

Introduction 197 Animal Fibers 198 Silk 199 Wool 200 Chicken Feather 201 Regenerated Fibers 202 Lyocell 205

Contents

11.3.2 11.3.3 11.4 11.5 11.6

Viscose 206 Regenerated Keratin Fibers 207 Industrial Applications 207 Summary and Discussion 207 Conclusions and Scope for Future Research References 208

12

Effect of Glass and Banana Fiber Mat Orientation and Number Layers on Mechanical Properties of Hybrid Composites 217 T.P. Sathishkumar, S. Ramakrishnan, and P. Navaneethakrishnan

12.1 12.2 12.3 12.4 12.5 12.5.1

Introduction 217 Materials 220 Preparation of Composites 221 Characterization 222 Results and Discussion 224 Effect of Number and Orientation of Layers on Tensile Properties 224 Effect of Number and Orientation of Layers on Flexural Properties 225 Effect of Number and Orientation of Layers on Impact Properties 228 Conclusion 229 References 230

12.5.2 12.5.3 12.6

208

13

Characterization of Mechanical and Tribological Properties of Vinyl Ester-Based Hybrid Green Composites 233 B. Suresha, R. Hemanth, and P.A. Udaya Kumar

13.1 13.2 13.2.1 13.2.2 13.2.2.1 13.2.2.2 13.2.3 13.2.4 13.3 13.3.1 13.3.1.1 13.3.1.2 13.3.1.3 13.3.1.4 13.3.2 13.3.3 13.4 13.5

Introduction 233 Materials and Methods 237 Matrix 237 Reinforcements 238 Coir Fiber and Coconut Shell Powder 238 Aramid Fiber 239 Chemical Treatment 239 Fabrication of Vinyl Ester-Based Hybrid Composites 239 Characterization 240 Physicomechanical Characterizations 240 Hardness 240 Tensile Testing 241 Flexural Testing 241 Impact Testing 242 Wear Testing 242 Fractography Analysis Using Scanning Electron Microscope 243 Surface Treatment of Reinforcements 244 Results and Discussion 245

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13.5.1 13.5.2 13.5.2.1 13.5.3 13.5.3.1 13.5.4 13.5.4.1 13.5.5 13.5.5.1 13.5.5.2 13.5.5.3 13.6

Hardness of Vinyl Ester and Their Hybrid Composites 245 Tensile Properties of Vinyl Ester and Their Hybrid Composites 246 Fractography Analysis 247 Flexural Properties of Vinyl Ester and Their Hybrid Composites 248 Fractography Analysis 248 Impact Strength of Vinyl Ester and Their Hybrid Composites 249 Fractography Analysis 250 Tribology of Vinyl Ester Hybrid Composites 251 Effect of Fiber and Filler on Coefficient of Friction 252 Effects of Sliding Distance and Applied Load on Specific Wear Rate 254 Worn Surface Morphology 256 Conclusions 260 References 260

14

Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic Rock-Derived Natural Wool-Reinforced Epoxy and Cashew Nut Shell Liquid-Based Composites 265 Nikunj Viramgama, Anmol Garg, Kevin Thomas, and Padmanabhan Krishnan

14.1 14.1.1 14.1.2 14.1.3 14.1.4 14.1.5 14.1.6 14.2 14.2.1 14.3 14.3.1 14.3.2 14.3.3 14.3.4 14.3.4.1 14.3.4.2 14.3.5 14.3.5.1 14.3.5.2 14.3.5.3 14.3.6

Introduction 265 Natural Fibers as a Substitute for Synthetic Fibers 265 Biocomposites 265 Rockwool Fibers 266 Composites with Rockwool Fiber as Reinforcement 266 Resin or Matrix Materials 267 Gaps in the Literature Review 267 Methodology and Approach 267 Fabrication and Experimentation 268 Results and Discussion 270 Energy-Dispersive X-ray Spectroscopy (EDS of Rockwool) 270 Thermogravimetric Analysis (TGA of Rockwool) 272 Differential Scanning Calorimetry of Rockwool 272 Volume Fraction of Fabricated Composite 273 Volume Fraction of Rockwool for Epoxy-Based Composite 273 Volume Fraction of Rockwool Fiber for CNSL Composite 274 Epoxy-Based Composite Tests and Analyses 274 Tensile Test 274 Compression Test 280 Flexure Test 284 Scanning Electron Microscopy (SEM) Analysis of Epoxy-Based Composites 289 Rockwool/CNSL Composite Test Results 294 Tensile Test Results 294 Compression Test Results 297 Flexure Test Results 299

14.3.7 14.3.7.1 14.3.7.2 14.3.7.3

Contents

14.3.8 14.3.9

Scanning Electron Microscopy (SEM) Analysis of the CNSL-Based Composite 301 Further Scope of Research 304 Acknowledgments 305 References 305

15

Hydrogel Scaffold-Based Fiber Composites for Engineering Applications 307 Ikram Ahmad, Josè Heriberto Oliveira do Nascimento, Sobia Tabassum, Amna Mumtaz, Sadia Khalid, and Awais Ahmad

15.1 15.1.1 15.1.2 15.1.3 15.1.3.1 15.1.3.2 15.1.3.3 15.1.4 15.1.4.1 15.1.4.2 15.1.4.3 15.1.4.4 15.1.5 15.1.5.1 15.1.5.2 15.1.5.3 15.1.5.4 15.1.5.5 15.2

Introduction 307 Hydrogels 307 Hydrogels as Compared to Gels 308 Classification of Hydrogels 308 Hydrogel Origin 308 Hydrogel Durability 308 Hydrogel Response to Environmental Stimuli 309 Methods of Preparation of Hydrogels 309 Free Radical Polymerization 309 Irradiation Cross-linking of Hydrogel Polymeric Precursors 310 Chemical Cross-linking of Hydrogel Polymeric Precursors 310 Physical Cross-linking of Hydrogel Polymeric Precursors 310 Scaffold 311 Biocompatibility 312 Biodegradability 312 Mechanical Properties 312 Structure 312 Nature 313 Potential Applications of Hydrogels as Scaffold in Biomedical Application 313 Hydrogel and Tissue Engineering 314 Hydrogels as Carriers for Cell Transplantation 314 Hydrogels as a Barrier Against Rest Enosis 314 Hydrogels as Drug Depots 315 Design Criteria for Hydrogel Scaffolds in Tissue Engineering 315 Biodegradation 316 Biocompatibility 316 Pore Size and Porosity Extent 317 Mechanical Characteristics 317 Surface Characteristics 317 Vascularization 318 Hydrogel Scaffold: A Main Tool for Tissue Engineering 318 Fabrication of Hydrogel Scaffolds for Tissue Engineering 318 Emulsification 318 Lyophilization 319 Emulsification Lyophilization 320 Solvent Casting Leaching 320

15.2.1 15.2.2 15.2.3 15.2.4 15.3 15.3.1 15.3.2 15.3.3 15.3.4 15.3.5 15.3.6 15.4 15.4.1 15.4.1.1 15.4.2 15.4.2.1 15.4.2.2

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15.4.2.3 15.4.2.4 15.4.2.5 15.4.2.6 15.4.2.7 15.4.2.8 15.5 15.6 15.6.1 15.6.2 15.6.3 15.7 15.7.1 15.7.2 15.7.3 15.7.4 15.7.5 15.8 15.8.1 15.8.1.1 15.8.1.2 15.8.1.3 15.8.1.4 15.8.1.5 15.8.1.6 15.8.1.7 15.8.1.8 15.8.1.9 15.9

Gas Foaming Leaching 320 Photolithography 321 Electrospinning 321 Microfluidics 322 Micromolding 322 Three-Dimensional Organ/Tissue Printing 323 Hydrogel Scaffolds for Cardiac Tissue Engineering 324 Hydrogel Scaffold Fabrication for Skin Regeneration 326 Molding Scaffolds 326 Nanofiber Fabrication Scaffolds 326 Three-Dimensional (3D) Printing 327 Osteochondral Tissue Regeneration 327 Single-Layer Gelatinous Scaffolds 327 Multilayer Gelatinous Scaffolds 328 Gel/Fiber Scaffolds 329 Fabrication of Gradient Hydrogels 330 Fabrication of Gradient Hydrogel/Fiber Composites 331 Biopolymer-Based Hydrogel Systems 332 Polysaccharide Hydrogels as Scaffolds 332 Chondroitin Sulfate 332 Hyaluronic Acid 333 Chitosan 334 Cellulose Derivatives 335 Alginate 336 Collagen 337 Gelatin 337 Elastin 339 Fibroin 339 Summary 340 References 340

16

Experimental Analysis of Styrene, Particle Size, and Fiber Content in the Mechanical Properties of Sisal Fiber Powder Composites 351 Kátia Melo, Thiago Santos, Caroliny Santos, Rubens Fonseca, Nestor Dantas, and Marcos Aquino

16.1 16.2 16.3 16.4

Introduction 351 Materials and Methods 352 Results and Discussion 353 Conclusions 364 Acknowledgments 364 References 365

Contents

17

Influence of Fiber Content in the Water Absorption and Mechanical Properties of Sisal Fiber Powder Composites 369 Kátia Melo, Thiago Santos, Caroliny Santos, Rubens Fonseca, Nestor Dantas, and Marcos Aquino

17.1 17.2 17.2.1 17.2.2 17.3 17.4

Introduction 369 Materials and Methods 370 Mechanical Test 370 Water Absorption 370 Results and Discussion 371 Conclusions 376 Acknowledgments 377 References 377

18

Recent Advances of Hybrid Fiber Composites for Various Applications 381 Praveen Kumar Alagesan

18.1 18.2 18.3 18.4 18.5

Introduction 381 What Is a Hybrid Composite? 384 Hybrid Biocomposites 386 Hybrid Nanobiocomposites 388 Potential Applications of Hybrid Composites in Various Applications 389 Aerospace Applications 389 Automotive Applications 391 Ballistic Applications 394 Impact Loading Applications 395 Challenges, Prospects, and Future Trends 397 Conclusions 398 Acknowledgments 398 References 398

18.5.1 18.5.2 18.5.3 18.5.4 18.6 18.7

Index 405

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About the Editors Dr. Anish Khan, Assistant Professor, Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia, Email: [email protected]. Dr. Anish Khan received his PhD from Aligarh Muslim University, India, from 2010. He has research experience of working in the field of synthetic polymers and organic–inorganic electrically conducting nanocomposites. He received complete postdoctoral from the School of Chemical Sciences, Universiti Sains Malaysia (USM), in electroanalytical chemistry in 2010–2011. He has research and teaching experience and has published more than 100 research papers in referred international journals. He has attended more than 20 international conferences/workshops and published three books, 6 books are in progress, and 12 book chapters. He has completed around 20 research projects. He is also the managerial editor of Chemical and Environmental Research (CER) Journal, Member of American Nano Society. His field of specialization is polymer nanocomposite/cation-exchanger/chemical sensor/microbiosensor/nanotechnology, application of nanomaterials in electroanalytical chemistry, material chemistry, ion-exchange chromatography, and electroanalytical chemistry, dealing with the synthesis, characterization (using different analytical techniques), and derivatization of inorganic ion exchanger by the incorporation of electrically conducting polymers; preparation and characterization of hybrid nanocomposite materials, and their applications; polymeric inorganic cation – exchange materials, electrically conducting polymeric, materials, composite material use as sensors, green chemistry by remediation of pollution, heavy metal ion selective membrane electrode, and biosensor on neurotransmitter. Dr. Sanjay M.R., Research Scientist, Department of Mechanical and Process Engineering, King Mongkut’s University of Technology North Bangkok, 1518 Pracharaj 1, Wongsawang Road, Bangsue, Bangkok 10800, Thailand, Email: [email protected]. Dr. Sanjay Mavinkere Rangappa received his BE (mechanical engineering) from Visvesvaraya Technological University, Belagavi, India, in the year 2010, MTech (computational analysis in mechanical sciences) from VTU Extension Centre, GEC, Hassan, in the year 2013, PhD (faculty of mechanical engineering science) from Visvesvaraya Technological University, Belagavi, India, in the year 2017, and Postdoctorate from King Mongkut’s University of Technology

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About the Editors

North Bangkok, Thailand, in the year 2019. He is a life member of Indian Society for Technical Education (ISTE) and associate member of Institute of Engineers (India). He has reviewed more than 40 international journals and international conferences (for Elsevier, Springer, Sage, Taylor & Francis, Wiley). In addition, he has published more than 70 articles in high-quality international peer-reviewed journals, 13 book chapters, 1 book, 11 books as editor, and also presented research papers at national/international conferences. His current research areas include natural fiber composites, polymer composites, and advanced material technology. He is a recipient of DAAD Academic exchange-PPP Programme (Project-related Personnel Exchange) between Thailand and Germany to Institute of Composite Materials, University of Kaiserslautern, Germany. He has received a Top Peer Reviewer 2019 award and Global Peer Review Awards, Powdered by Publons, Web of Science Group. Dr. Mohammad Jawaid, Fellow Researcher (Associate Professor), at Biocomposite Technology Laboratory, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Serdang, Selangor, Malaysia, and also a Visiting Professor at the Department of Chemical Engineering, College of Engineering, King Saud University, Riyadh, Saudi Arabia since June 2013, Email: [email protected]. Dr. Mohammad Jawaid received his PhD from Universiti Sains Malaysia, Malaysia. He has more than 10 years of experience in teaching, research, and industries. He is also a visiting scholar to TEMAG Labs, Department of Textile Engineering, Istanbul Technical University, Istanbul, Turkey. He previously worked as a visiting lecturer at the Faculty of Chemical Engineering, Universiti Teknologi Malaysia (UTM) and also worked as an expatriate lecturer under UNDP project with the Ministry of Education of Ethiopia at Adama University, Ethiopia. His area of research interests includes hybrid reinforced/filled polymer composites, advance materials: graphene/nanoclay/fire-retardant, lignocellulosic reinforced/filled polymer composites, modification and treatment of lignocellulosic fibers and solid wood, nanocomposites and nanocellulose fibers, and polymer blends. So far, he has published 11 books, 22 book chapters, more than 160 international journal papers, and five published review papers under top 25 hot articles in Science Direct during 2014–2016. He is also the deputy editor-in-chief of Malaysian Polymer Journal and Guest Editor for Current Organic Synthesis and Current Analytical Chemistry. He has reviewed several high-impact ISI journals (44 Journals). 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, Email: [email protected]. Prof. Dr.-Ing. habil. Suchart Siengchin received his Dipl.-Ing. in mechanical engineering from the University of Applied Sciences Giessen/Friedberg, Hessen, Germany in 1999; MSc in polymer technology from the University of Applied Sciences Aalen, Baden-Wuerttemberg, Germany in 2002; MSc in materials science at the Erlangen-Nürnberg University, Bayern, Germany in 2004,

About the Editors

Doctor of Philosophy in Engineering (Dr.-Ing.) from the 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 Chemnitz University in Sachen, Germany. He worked as a lecturer for Production and Material Engineering Department at The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), KMUTNB. He has been a full-time 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 include polymer processing and composite material. He is the editor-in-chief of KMUTNB International Journal of Applied Science and Technology and has authored 150+ peer-reviewed journal articles. He has participated with presentations in more than 39 international and national conferences with respect to materials science and engineering topics. Prof. Dr. Abdullah Mohammed Asiri, Director of the Center of Excellence for Advanced Materials Research (CEAMR), Chair, Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia, Email: [email protected]; [email protected]. Prof. Dr. Abdullah Mohammed Ahmed Asiri received his PhD (1995) from the University of Walls College of Cardiff, UK, on tribochromic compounds and their applications. He is currently the chairman of the Department of Chemistry, King Abdulaziz University, and also the director of the Center of Excellence for Advanced Materials Research, the director of Education Affair Unit–Deanship of Community services, the member of advisory committee for advancing materials (National Technology Plan, King Abdul Aziz City of Science and Technology, Riyadh, Saudi Arabia). His research interests include color chemistry, synthesis of novel photochromic and thermochromic systems, synthesis of novel colorants and coloration of textiles and plastics, molecular modeling, applications of organic materials into optics such as OEDS, high-performance organic dyes and pigments, new applications of organic photochromic compounds in new novelty, organic synthesis of heterocyclic compounds as precursor for dyes, synthesis of polymers functionalized with organic dyes, preparation of some coating formulations for different applications, photodynamic thereby using organic dyes and pigments virtual labs and experimental simulations. He is the member of editorial board of Journal of Saudi Chemical Society, Journal of King Abdul Aziz University, Pigment and Resin Technology Journal, Organic Chemistry Insights, Libertas Academica, Recent Patents on Materials Science, and Bentham Science Publishers Ltd. Besides that, he has professional membership of International and National Society and Professional bodies.

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1 Natural and Synthetic Fibers for Hybrid Composites Brijesh Gangil 1 , Lalit Ranakoti 2 , Shashikant Verma 3 , Tej Singh 4 , and Sandeep Kumar 1 1

H.N.B. Garhwal University, Department of Mechanical Engineering, Srinagar, Garhwal, India NIT, Department of Mechanical Engineering, Uttarakhand, India 3 Bundelkhand University, Jhansi, Department of Mechanical Engineering, Jhansi, India 4 Eötvös Loránd University, Savaria Institute of Technology, Szombathely, Hungary 2

1.1 Introduction Emerging research concerns mainly with the environmental and economic issues related to the design of new materials for future industries. For the past few decades, various industrial sectors are trying to replace the synthetic fibers with natural fibers as reinforcements in polymer composites. Composite materials have been providing a major amount of research and industrial work for an age because of their favorable and outstanding properties. Moreover, they can be produced and processed with low investment [1]. The composite material is a combination of fiber/filler and matrix (polymer). The combination of fiber and matrix can be arranged by using the hybrid (one or two fibers) with the base polymer matrix. The main purpose of using fibers is to provide strength to the composite. Factors that influence the properties of fibers are length, orientation, shape, and materials [2]. Based on the polymer used for the manufacturing, fibers can be selected either naturally or synthetically. Fibers that are generally obtained from plant, animal, or cultivated are called natural fibers such as jute, ramie, sisal, hemp, coir, grewia optiva, silk, bamboo, etc. On the other hand, fibers that are manufactured through various man-made processes are called synthetic fibers such as carbon, Kevlar, glass, etc. Both natural and synthetic fibers have their own merits and demerits with respect to the polymer used for the fabrication of the composite. As compared to synthetic fibers, natural fibers are environment friendly, renewable, cheap, nonhazardous, nonabrasive, and easily available, but the cons of using natural fibers is their low mechanical properties as compared to synthetic fibers [3]. Another major drawback of natural fibers is their affection toward water because of the presence of cellulose. This hydrophilic nature leads to poor interfacial bonding between the fiber and matrix. On the other hand, synthetic fibers, being hydrophobic materials, form a good bonding with the polymers. Sometimes, fibers are applied in hybrid form to take the advantage of both Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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1 Natural and Synthetic Fibers for Hybrid Composites

natural and synthetic fibers, which is generally called hybridization in composite. This hybridization brings out various attractive properties of both natural and synthetic fibers, which resulted in superior mechanical and tribological properties of the final composite [4, 5]. However, this is not the sole cause of the variation in the properties of the composite. Fiber type, fiber size, percentage of fiber, polymer used, processing techniques, and chemical treatment are the vital factors that can be employed to achieve promising results in the composite properties. The present discussion is therefore relied on the various natural and synthetic fibers available, their effect on the composite, chemical alteration of natural fibers, and the applications of natural and synthetic fibers. The discussion also includes the inclusion of hybridization in composite structure and their effects.

1.2 Natural Fibers The suitability of synthetic fibers in polymer composites is losing hold because of their higher price, nonbiodegradability, and problems of dumping off. These problems can be easily resolved with the exploitation of natural fibers in the field of polymer composites, but a compromise is made among the physical and mechanical properties obtained. Natural fibers, as the name suggests, are a particular substance that exist naturally and are not man-made. Being renewable, natural fibers are assumed as a good substitute for traditional materials. Because of their higher aspect ratio and high strength, natural fibers are gaining greater attention in the automotive sectors for structural applications [6]. In addition, natural fibers are also gaining interest in the field of textile, medical implantation, building structures, aviation, etc. New plant fibers are being investigated by researchers seeking their interest in developing lightweight, renewable, economical, and socially benefited for replacing traditional materials. It has been found that composites are produced by using natural fibers that hold good electrical resistance, better mechanical properties, Animal Silk

Natural fiber

Mineral

Tussah

Hair/wool

Mulberry/spider

Asbestos Cellulose/lignocellulose

Bast Jute Ramie Flax Kenaf Roselle Mesta Hemp

Leaf Sisal Banana Henequen Agave Palf Abaca

Lamb Goat Angora Horse feather

Seed

Fruit

Wood

Stalk

Loofah Milk weed Kapok Cotton

Oil palm Coil

Hard Wood Soft Wood

Rice Wheat Barley Maize Oat Rye

Figure 1.1 Classification of natural fibers [12, 13].

Grass Bamboo Bagasse Corn Sabai Rape Esparto Cancry

1.4 Natural Fiber-Reinforced Polymer Composites

decent thermal and acoustic insulating properties, and higher resistance to fracture in some cases [7–9]. Fibers can be transformed into various forms, such as rovings, mats, fabrics, and yarns, and then used as reinforcements in composite materials. [10, 11]. Natural fibers are available in three forms: vegetables/plants, animals, and minerals (e.g. asbestos), as shown in Figure 1.1 [12, 13]. The physical and mechanical properties of natural fibers are not as attractive as those of synthetic fibers. However, if we compare these properties, it can be well stated that synthetic fibers can be replaced for some but not all areas of the polymer composites. These areas can be interiors of automobile, dashboard, rooftops, tiles, etc., where the load bearing requirement is low. Some common natural fibers and synthetic fibers and their properties are listed in Table 1.1.

1.3 Microstructure of Natural Fibers Natural fibers consist of a complex structure having amorphous lignin as the reinforced material and/or hemicelluloses as the matrix. Natural fibers generally have cellulose, lignin, hemicelluloses, pectin, water-soluble compounds, and wax constituents beside cotton. Lignin, hemicellulose, and pectin jointly function as matrix and adhesive to hold the cellulosic frame structure of natural fibers [14]. The properties of cellulose, lignin, hemicellulose, and pectin are discussed in Table 1.2 [15] (Table 1.3).

1.4 Natural Fiber-Reinforced Polymer Composites Composites are the combination of two or more constituents having different phases, and phases can clearly be observed macroscopically by naked eyes. Composites have two main parts: one is matrix and another is reinforcement. Matrix has constant properties throughout the section and is ductile in nature. Therefore, another phase is added in the matrix to enhance the property in the desired direction is known as reinforcement. Matrix provides the support and texture and reinforcement provides strength for matrix. According to the materials used, matrix is of three types, namely, polymers, metal matrix, and ceramic metal composites. Polymers are the best option to be used in various industries because they show convenience in processing, increased productivity, and reduced cost [3]. A natural fiber-reinforced polymer (NFRP) is a composite material that consists of a polymer matrix embedded with high-strength fibers, such as jute, cotton silk hemp wool, etc. Upcoming biopolymers entail special processing settings for the enhancement of specific properties. PLA (polylactic acid), PHAs (polyhydroxyalkanoates), PHB (polyhydroxybutyrate), PBS (polybutylene succinate), TPSs (thermoplastic starches), and PEF (polyethylene furanoate) are common trending biopolymers in the composite field. Among all the biopolymers, PLA is found to be more economic and available [16]. The properties of the composites not only depend on the percentage, orientation, and shape of fiber but also majorly depend on the interfacial/surface bonding

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Table 1.1 Properties of natural fibers in relation to those of synthetic fibers [51–53].

Fiber

Density (g/cm3 )

Length (mm)

Diameter (𝛍m)

Failure strain (%)

Tensile strength (MPa)

Young’s modulus (GPa)

Specific tensile strength (MPa/(g cm3 ))

Specific Young’s modulus (GPa/(g cm3 ))

29–85

Ramie

1.5

900–1200

25–50

2.0–3.8

400–938

44–128

270–620

Silk

1.3

Continuous

10–13

15–60

100–1500

5–25

100–1500

4–20

Cotton

1.5–1.6

10–60

11–22

3.0–10

287–800

5.5–13

190–530

3.7–8.4

Pineapple leaf fiber

1.07

3–9

100–280

2.2

120–130

4.405

112.15–121.5

0.68–2.04

Flax

1.5

5–900

12–16

1.2–2.2

345–1830

27–80

230–1220

18–53

Hemp

1.4–1.5

5–55

16–50

1.6

550–1110

58–70

370–740

39–47

Jute

1.3–1.5

1.5–120

17–20

1.5–1.8

393–800

10–55

300–610

7.1–39

Harakeke

1.3

4–5

6–30

4.2–5.8

440–990

14–33

338–761

11–25

Sisal

1.33–1.5

900–1000

200–400

2.0–2.5

507–855

9.4–28

362–610

6.7–20

Alfa

1.4

350

—

15

300–900

18–25

214–643

13–18

Coir

1.15–1.46

20–150

10–460

15–30

131–200

4–6

110–180

3.3–5

Oil palm

0.7–1.55

248

50–500

3–4

200–250

3.20

129–357

2.06–4.57

Abaca

1.5

1800–3700

40

1.0–7.0

100–900

6–32

70–600

4–21.3

Bagasse

1.25

1.2

15

1.1

170–290

17–28

136–232

13.6–22.4

Bamboo

0.6–1.1

1–5

14–27

1–3

450–800

5–25

409–1333

4.54–42

Banana

0.91

2.5–13

80–250

1.4–2.9

53.7

3–15

59.01

3–16

Curaua

1.3–1.5

150–1500

40–320

3.7–4.3

500–1150

63.7

333.33–885

7.87–9.08

Date palm

0.9–1.2

20–250

100–1000

2.5–5.4

393–773

13–26.5

327.5–858.89

10.83–29.44 —

Isora

1.39

6–14

10–20

5, 6

550

—

395.68

Kenaf

0.6–1.5

3000

20–80

1, 2

400–800

12

266.67–1333.33

8–20

Piassava

1.40

134–143

400–2400

5–10

138.5

—

98.9

—

E glass

2.5

Continuous

0.55–0.77

2.5

2000–3000

70

800–1400

29

Carbon

1.65–1.75

Continuous

5–10

1.7

3790

—

2165–2400

—

Kevlar-49

1.467

Continuous

12

2.8

2900–3620

151.7

1977–2468

103.4

Table 1.2 Properties of natural fibers. Cellulose

Hemicellulose

Lignin

Pectin

1. Linear glucose polymer consisting of β-1,4 linked glucose units 2. Produces stable hydrophobic polymers with high tensile strength

1. Branched polymers containing sugar and carbon of varied chemical structure

1. Amorphous, cross-linked polymer network 2. Works as chemical adhesive within and between fibers

1. Complex polysaccharides with chains consisting of glucuronic acid polymers and residue of rhamnose. 2. Calcium ions improve surface integrity in pectin rich area

CH

CH HO

OH

O O

O

O

OH OH

HO

CH

O

CH

OH

n

O

O

O

OH

OH

OH

OH O

O

CH

HO

CH

O

n

OH

HO

O

O

OH

OH O O

OH

O

O O

O

HO OH

HO O

OH

O

O HO O Activete V

Source: From Westman et al. 2010 [15].

OH n

O

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1 Natural and Synthetic Fibers for Hybrid Composites

Table 1.3 Chemical composition of natural plant fibers.

Fiber

Cellulose (wt%)

Hemicellulose (wt%)

Lignin (wt%)

Wax (wt%)

Pectin (wt%)

Cotton

82.7

5.7

—

0.6

—

Ramie

68.6–76.2

131–16.7

0.6–0.7

0.3

1.9

Bagasse

55.2

16.8

25.3

—

—

Henequen

77.6

4–8

13.1

—

—

Bamboo

26–43

30

21–31

—

—

Flax

71

18.6–20.6

2.2

1.5

2.3

Kenaf

72

20.3

9

—

—

Jute

61–71

14–20

12–13

0.5

0.4

Hemp

68

15

10

0.8

0.9

Ramie

68.6–76.2

13–16

0.6–0.7

0.3

0.3

Pine apple leaf fiber (PALF)

70–82

—

5–12

—

—

Abaca

56–63

20–25

7–9

3

12, 13

Sisal

65

12

9.9

2

10

Coir

32–43

0.15–0.25

40–50

—

3, 4

Oil palm

65

—

29

—

—

Pineapple

81

—

12.7

—

—

Curaua

73.6

9.9

7.5

—

—

Wheat straw

38–45

15–31

12–20

—

—

Rice husk

35–45

19–25

20

14–17

—

Rice straw

41–57

23

8–19

8–28

—

Banana

81.80

—

15

—

—

Date palm

40.21

12.8

32.2

5.08

—

Kapok

64

23

13

—

—

Areca

—

35–64.8

13–24.8

—

—

between the fiber and the matrix. Subsequently, better interfacial bonding leads to greater bonding between the fiber and the matrix. Thus, surface treatment of fiber is considered as a vital process in the field of composites. Chemical treatment has now become one among the most important areas in today’s research. A large amount of literature available has targeted the studies on the treatment of fibers to improve the bonding between fiber and matrix [17]. It was reported in the study that treatment of fibers with alkali solution (20% NaOH solution) leads to reduction in moisture absorption to 20%, provided the fiber is further treated with 5% acrylic solution [18]. Literature also suggested that reinforcement of fiber should be limited to a certain amount beyond that limit and no changes have been observed. Properties such as tensile strength, young modulus, flexural strength, and impact strength are found to be enhanced with the reinforcement of fiber. Alongside, natural fillers are also available in the

1.4 Natural Fiber-Reinforced Polymer Composites

market, which not only enhance the mechanical properties but also make the composite economical viable. Fillers have the ability to improve properties such as toughness and fatigue. With regard to fillers, natural fillers obtained from processing of oak wood enhanced strain in failure for a wood filler polypropylene composite but reduce the strength and stiffness as compared to a virgin polymer produced in a six-step filter process [19]. Variation of percentage of fiber indeed is a vital factor in the properties of a composite. The presence of cellulose and hemicellulose in the natural filler provides better adhesive property upon treatment with NaOH. This may be attributed to the porosity created at the surface of the fiber because of the addition of bamboo fillers to the epoxy–fiber composite. Carada et al. [20] investigated the heat treatment of kenaf fiber. It was performed for an hour at different temperatures ranging from 140 to 200 ∘ C with the difference of 20 ∘ C. Results obtained in the study suggested that adequate tensile strength was obtained at 140∘ , and no improvement is observed beyond it [20]. The fiber in mat form also improves the mechanical property of the polymer composite. Hemp fiber in the form of mat after treatment resulted in enhanced mechanical property of the hemp–polyester composite [21]. Alkali treatment of bamboo fiber leads to enhancement of interfacial bonding of fiber and matrix [22]. One of the treatments called biological treatment of fiber resulted in the improvement of tensile strength of the composite and reduces the degradation of sample [23]. 1.4.1

Synthetic Fibers

Synthetic fibers are the man-made fibers that do not originate naturally. Products of petroleum are the main source of synthetic fibers. Synthetic fibers have better properties than natural fibers. Different chemicals having their own property are mainly used to produce the synthetic fibers. Nylon, acrylics, polyesters, polyurethanes, etc., are the synthetic fibers produced from chemical products [24]. These fibers possess high mechanical property, durability, and stability and have long-lasting life span. There are various types of synthetic fibers in which mainly three types of synthetic fibers are used in the composite industry at a large scale: Kevlar (aramid), glass fiber, and carbon (Figure 1.2).

(a)

(b)

(c)

Figure 1.2 Images of synthetic fibers: (a) glass fiber, (b) Kevlar fiber, and (c) carbon fiber.

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1 Natural and Synthetic Fibers for Hybrid Composites

Table 1.4 Different types of glass fibers and physical and mechanical properties.

Glass fiber type

Silicon dioxides (SiO2 ) (%)

Density (g/cm3 )

Tensile strength (MPa)

Modulus (GPa)

Elongation at break (%)

A-type

63–72

2.44

3300

72

4.8

C-type

64–68

2.56

3300

69

4.8

D-type

72–75

2.11

2500

55

4.5

E-type

52–56

2.54

3448

72

4.7 5.1

R-type

56–60

2.52

4400

86

S-type

64–66

2.53

4600

89

5.2

ECR-type

54–62

2.72

3400

80

4.3

AR-type

55–75

2.7

1700

72

2.3

Source: From Saba and Jawaid 2017 [24].

1.4.2

Glass Fibers

Highly attractive physical and mechanical properties of glass fibers, ease of manufacturing, and their comparable low cost to carbon fibers make it a highly preferable material in high-performance composite applications. Glass fibers are composed of oxides of silica. Glass fibers have outstanding mechanical properties, such as less fragility, extreme strength, less stiffness, and lightweight. Glass fiber-reinforcing polymers consist of a large family of different forms of glass fibers such as longitudinal, chopped strand fiber, woven mat, and chopped strand mat used to increase the mechanical and tribological properties of polymer composites [25]. Study has been carried out to investigate the suitability of glass fibers with the polymer such as rubber. It is possible to obtain high initial aspect ratio with fibers of glass, but fragility causes fibers to break during processing. Some physical and mechanical properties of glass fibers are listed below (Table 1.4). 1.4.3

Carbon Fibers

It is one of the strongest fibers known and has wide applications in highperformance applications. Because of its outstanding mechanical and thermal properties such as high stiffness, high thermal conductivity, high tensile strength, high elastic modulus, low weight, high temperature tolerance, high chemical resistance, and low weight, they are mainly used in the aerospace industry. Carbon fibers are manufactured from rayon, petroleum pitch, and polyacrylonitrile (PAN) [26]. There are three types of fore runners commonly used such as PAN forerunner, rayon forerunner, and pitch forerunner. Fifty percent of fiber mass of commercial carbon fibers are mainly generated by PAN forerunner. Short carbon fibers are extensively used because of their appealing properties such as ease of fabrication, high stiffness, relatively low cost, and strength to weight ratio [27] (Table 1.5).

1.4 Natural Fiber-Reinforced Polymer Composites

Table 1.5 Properties of carbon fibers. Precursor Property

PAN

Pitch

Rayon

Density (g/cm3 )

1.77–1.96

2.0–2.2

1.7

Tensile strength (MPa)

1925–6200

2275–4060

2070–2760

Tensile modulus (GPa)

230–595

170–980

415–550

Elongation (%)

0.4–1.2

0.25–0.7

—

Thermal conductivity (W/m K)

20–80

400–1100

—

Fiber diameter (μm)

5–8

10–11

6.5

Table 1.6 Typical properties of Kevlar fibers.

Kevlar grade

Density (g/cm3 )

Diameter (𝛍m)

Tensile strength (MPa)

Tensile modulus (GPa)

Elongation (%)

Kevlar 29

1.44

12

2760

62

3.4

Kevlar 49

1.44

12

3620

124

2.8

Property (unit)

1.4.4

Kevlar or Aramid Fibers

Kevlar fibers or aromatic polyamide threads (aramid) are produced by using para-phenylenediamine and terephthaloyl chloride [28]. Because of the molecular orientation, these fibers have high strength and excellent thermal conductivity as compared to glass and carbon fibers [29]. The manufacturing process and the equipment used in the manufacturing of Kevlar fibers are very costly, so Kevlar fibers are generally high in cost [29]. Kevlar fibers have abundant properties such as good resistance to abrasion, nonconductivity, high degradation temperature, good fabric integrity, good resistance to organic solvent, no melting point, and low flammability [30]. There are three types of Kevlar fibers in existence: Kevlar, Kevlar 49, and Kevlar 29 (Table 1.6). In order to increase the mechanical properties and improve the interfacial interaction, some modifications were adopted, such as direct hydrolysis, planetary ball milling, and hydrolysis treatment of ball mill [31]. Various kevlar fiber (KF) treatment methods are as follows (Table 1.7). 1.4.5

Comparison Between Natural and Synthetic Fibers

The selection of natural fibers depends on the availability in local level and after that is seeking to property requirements. It is seen that the mechanical properties of natural fibers are moderate as compared to those of synthetic fibers; similarly, in opposite manner, the thermal and moisture sensitivity of natural fibers is higher than that of the synthetic fibers. Natural fibers exhibit superior mechanical properties such as flexibility, stiffness, and modulus compared to glass fibers. In

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1 Natural and Synthetic Fibers for Hybrid Composites

Table 1.7 Nomenclature used for Kevlar fibers without and with various surface treatments [31, 54]. Fiber

Kevlar

Surface modification techniques

Untreated Hydrolyzation Ball milling technic Ball milling + hydrolyzation Ball milling + phosphoric acid Ball milling + phosphoric acid + hydrolyzation

Table 1.8 The basic comparison between natural and synthetic fibers. Properties

Natural fibers

Synthetic fibers

Density

Low

Twice that of natural fibers

Cost

Low

High, compared to natural fiber (NF)

Renewability

Yes

No

Recyclability

Yes

No

Energy consumption

Low

High

Distribution

Wide

Wide

CO2 neutral

Yes

No

Abrasion to machines

No

Yes

Health risk when inhaled

No

Yes

Disposal

Biodegradable

Not biodegradable

an environmental point of view, the major factor of selection of natural fibers to the synthetic fibers is that recyclability of natural fibers is better than the synthetic fibers. Some basic comparison between natural and synthetic fibers is shown in Table 1.8 [32].

1.5 Hybrid Fiber-Based Polymer Composites Hybridization is a technique in which two or more than two fibers are employed to a single-base matrix. The term hybridization sometimes also refers to the implementation of fillers in the fiber polymer composite [33]. Hybridization is not new to the researchers; in fact, it has been in practice for centuries. Properties such as physical, mechanical, and thermal get influenced in a positive manner because of the hybridization. This is attributed to the increase in the fiber–fiber and fiber–matrix adhesion. To reduce the overall cost of manufacturing, natural fibers are added to synthetic fiber polymer composites but compromising with the strength of the composite. It has been found that the hybridization has

1.5 Hybrid Fiber-Based Polymer Composites

been in the top most priorities of various researchers. Hybrid composites are now being formed in various forms. These are core shell type, sandwich type, laminated type, two-by-two type, intimately type, etc. Mechanical, thermal, and dynamic properties increase substantially for oil palm–epoxy-based composite because of the enhancement in the adhesive bonding of fiber and matrix. Addition of natural fibers in glass fiber-reinforced polymer composites leads to enhancement of impact tensile and flexural strength [34]. It has been noticed that hybridization of jute and oil palm fiber resulted in higher tensile strength, provided that the weightage of jute fiber should be higher [35]. The majority of work in the field of hybridization has been stick to hybridization of natural and synthetic fibers. In this regard, sisal, a natural fiber, can be hybridized with glass fibers, which results in the enhancement of tensile and flexural modulus. Hybridization does not always work for every aspect of the composite taken into consideration. It can be stated that enhancement of one property sometimes leads to reduction of another and vice versa. Similar results have been reported for sisal–glass/polypropylene hybridization. It has been reported that tensile and flexural strength increases but negotiating with the properties such as tensile and flexural modulus. Moreover, thermal and water resistance behavior also improves for sisal–glass polymer composites [36]. Hemp, which is a plant fiber, is also finding its place in hybridization because of its influential properties. In the hybrid composites, layering sequence plays an important role in deciding the mechanical properties of the formed composites. From previous research, it is concluded that hybrid laminates with two extremes synthetic fibers plies on both sides has the optimum amalgamation with a good balance between the properties and the cost. It has also been found that glass fibers, when hybridized with hemp fiber, lead to improvement in mechanical and physical properties and reduction in the overall cost of composites [37]. Similar to hemp, flax fiber well known from the centuries can also be hybridized with synthetic fibers [38]. Hybrid composites of flax and glass fiber lead to significance improvement in the tensile strength of the composite. Jute is a natural fiber available in very large amount, which is also applied in the hybridization with glass leading to better tensile and flexural strength of the composite. Hybridization also plays a very critical role in the enhancement of properties for green composites [39]. Thus, green composites of bamboo–cellulosic fiber-based PLA composite are found to have better resistance for fracture toughness [40]. 1.5.1

Applications

Applications of synthetic fiber polymer composites can be seen as gradual increasing phenomena. It is the need of the hour that requires replacement of synthetic fibers with the natural fibers for various applications because of the favorable properties of natural fibers [41, 42]. However, because of certain drawbacks, the natural fibers cannot be used solely; hence, the time requires the combined advantages of both fibers (natural and synthetic) in a single component. This gives rise to the development of hybrid composites; the various applications of hybrid natural fiber composites are as follows:

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1 Natural and Synthetic Fibers for Hybrid Composites

Parts of automobile such as door panels, instrument panels, armrests, headrests, and seat shells and parcel shells are now being fabricated by hybrid fiber composites [43]. In the recent development, the under-floor protection chamber in a passenger car for the safety purpose has been successfully designed and developed by the banana fiber polymer composite [44]. Similarly, mirrors, visor of a two-wheeler, billion seat cover, indicator cover, cover L-side, and name plate are also being manufactured with the use of natural sisal fiber polymer composites [45]. Cost-effective components can also be easily manufactured with the use of hybridization technique [46]. One such application can be seen in the application of bumper of automobile, which is manufactured by the hybridization of kenaf and glass fibers [47]. In the water bodies such as small boats and ships, composites based on glass–sugar palm fiber finds hell of a lot of applications [48]. Natural fiber and synthetic fiber-based composites have proved their potential to be a good material for the structural applications. Jute fiber-based hybrid composites with concrete as a matrix are being developed for the application of structural composites [49]. These applications comprise building panels, roofing sheets, door frames, door shutters, transport, packaging, geo textiles, chipboards, absorbent cotton, storage device, furniture, transportation, household accessories, and biodegradable shopping bag. Coir-based polymers and ceramic composites are also used in building panels, flush door shutters, roofing sheets, storage tank, packing material, helmets and postboxes, mirror casing, paper weights, projector cover, voltage stabilizer cover, a filling material for the seat upholstery, brushes and brooms, ropes and yarns for nets, bags, and mats, as well as padding for mattresses and seat cushions. Thermally sound materials that require fire resistance properties can also be fabricated with the help of natural fiber polymer composites. This is due to the fact that natural fibers have porous microstructures that provide fire-resistant properties [50].

1.6 Conclusion Advancement in material research has been pushed ahead further by the development in composite materials. Diversion of research from monolithic materials to polymeric composites has been successfully achieved by natural and synthetic polymeric composites. High-strength materials can now be easily designed and manufactured by the use of composite materials. Synthetic fiber-reinforced composites are somehow shown to be a better alternative for metal materials as compared to natural fiber-reinforced composites, but sustainability issues make the natural fiber more impressive. Chemical modification of natural fiber helps in enhancement of strength of natural fiber and interfacial bonding between the fiber and the matrix. Fabrication technique is also an important issue that should also be taken in the consideration. Research should be excelled in the field of hybridization to achieve better and sustainable composites.

References

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2 Effect of Process Engineering on the Performance of Hybrid Fiber Composites Madhu Puttegowda 1 , Yashas Gowda Thyavihalli Girijappa 2 , Sanjay Mavinkere Rangappa 2 , Jyotishkumar Parameswaranpillai 2 , and Suchart Siengchin 2 1 Visvesvaraya Technological University, Malnad College of Engineering, Department of Mechanical Engineering, Salagame Road, Hassan – Belagavi, 573202, Karnataka, India 2 King Mongkut’s University of Technology North Bangkok, The Sirindhorn International Thai–German Graduate School of Engineering, Department of Mechanical and Process Engineering, 1518 Pracharat 1 Road, Wongsawang, Bangsue, Bangkok 10800, Thailand

2.1 Introduction The ever-growing human awareness toward the exhaustion of the fossil fuels and environment depletion has garnered for the development of novel eco-friendly materials to be used in various fields of engineering for developing new products [1]. The need for clean and healthy environment has forced the humans for the utilization of more green materials for the production of high-performance engineering products from easily and cheaply available natural resources [2]. Therefore, in recent times, engineers, technologists, and scientists have focused their attention toward developing high-performance products with excellent biodegradable properties based on the fibrous materials or fiber-reinforced composites, which would help in obtaining sustainable economic growth and as well as finding a solution for rising environmental problems around the globe [3, 4]. The use of composites gives a unique exploration of mechanical and thermal properties in a single material; otherwise, it could not be achievable by any other conventional material. Recently, more natural fibers are being used as reinforcing materials in polymer composites mainly because of the renewability and biodegradability of the natural fibers. These lignocellulosic materials are the world’s most abundantly available source with its annual production reaching beyond 200 billion tonnes [2, 5]. The natural fibers are attractive because of their lightweight, cost-effective processing, eco-friendly behavior, and unique physical and mechanical characteristics. They are available in various forms such as cellulose fibers (bast fibers, leaf fibers, seed fibers, fruit fibers, grass fibers, stalk fibers, and wood fibers), animal fibers (silk, wool, and hair), and mineral fibers (asbestos). Nowadays, natural fibers find their application in aerospace and automotive industries and also used in the fabrication of biocomposite components such as boards, paper, and structural components in construction industries [6–9]. The polymer composites comprise a polymer reinforced with Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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fiber. The reason for their popularity lies in their low cost, easy processing, high strength-to-weight ratio, good corrosion and chemical resistance, and simple manufacturing methods [10, 11]. The polymer-based composites reinforced with woven, braided, or roving forms of fibers provide excellent physical, mechanical, and thermal properties. The polymers provide flexibility by reinforcing with both natural fibers and synthetic fibers that include glass, carbon, Kevlar, and aramid fibers [12–14]. The natural fiber-reinforced polymer composites have been now vastly utilized because of their good mechanical characteristics, availability in abundance, and biodegradable characteristics, while the synthetic fiber-reinforced polymer composites are not biodegradable. The natural fiber-reinforced polymer composites have got some disadvantages such as poor interfacial adhesion between hydrophobic polymer matrix and hydrophilic fibers, low strength, and moisture absorption [15–17]. To overcome these limitations and to reduce the hydrophilic behavior of the natural fibers, they are surface treated with several chemical reagents to improve the adhesive bonding characteristics between fiber and matrix [18]. A chemical treatment help in minimizing the hydrophilic nature of the fibers, modifies fiber structure, removes the undesirable fiber constituents, and separates individual fibers from bundle, thus improving the mechanical strength of the fibers. Such fibers employed in hybrid polymeric composites will perform better characteristics [19]. Several fabrication techniques have been developed to develop hybrid fiber reinforced polymer composites, and factors such as raw material properties, economics involved during the processing, and shape and size of the composite to be produced, etc., have to be considered while selecting a particular fabrication method [20–22]. Benefits such as lightweight, low cost, larger availability, and environmental friendly characteristics of these hybrid natural fiber-reinforced polymeric composites has made industries such as aerospace, automotive, marine, sports, electrical and electronics, and construction sectors to utilize these materials to manufacture their products [15]. This chapter gives insights into natural and synthetic fibers, polymers, natural fiber extraction and processing, and processing of composites and also discusses some of the applications of natural fiber-reinforced polymer composites.

2.2 Fibers Fiber is a substance that is obtained in the nature or man-made material, which is longer in size than its width. As mentioned above, the natural fibers are obtained from plants, animals, and minerals. These fibers are utilized to manufacture various products that are useful in daily life [23, 24]. Natural fiberreinforced polymer composites are one such materials used in a variety of applications over the synthetic fibers because of their better properties such as renewability, low density, high specific strength, low cost, low energy for processing, and biodegradability. Synthetic fibers are man-made fibers obtained from coal, petroleum, and natural gas. These include materials such as nylon, modacrylic, olefin, acrylic, polyester, carbon, glass, aramid, basalt, etc. The composite materials produced using synthetic fibers are extensively used in

2.2 Fibers

various applications such as automobile, aerospace, construction, and sporting industries. Synthetic fiber-reinforced composites are widely known for its low cost with good mechanical properties [25, 26]. Rapid developments and advancement in technology along with the competition in the global markets have raised demands on the major resources, availability of raw materials, and its sustainability. The natural fibers have gained importance mainly because of its renewability and biodegradability; hence, they are the major alternative for synthetic fibers. They are mainly extracted from different plants and animals in nature. As stated above, the plant fibers are classified as bast fibers, leaf fibers, seed fibers, core fibers, and grass and reed fibers [27]. Some of the important plant fibers are discussed briefly as follows. Hemp is one of the bast fibers that belong to the family of Cannabaceae. It was first found in Asia around 10 000 years ago. The fibers are removed from the bast by using the retting process. The extracted fibers measure about 2500 mm in length and can be bundled to required size. The main content of hemp fibers is cellulose (62–67%), hemicellulose (8–15%), lignin (4%), and pectin (1%). Hemp is used for making rope, textiles, clothing, paper, biofuel, etc. [28]. Ramie belongs to the family of Urticaceae. The ancient Egyptians used ramie cloths for wrapping mummies. Ramie is a nonbranching, fast-growing plant that grows up to 1–2 m height. Ramie is a bast fiber, which is strongest and longest of the natural bast fibers. Ramie is used for making sewing threads, fishing nets, and clothing [29, 30]. Sisal (Agave sisalana) belongs to the family of Asparagaceae. It belongs to the leaf fibers and is native to Central America. The size of the plant varies up to 3 ft in height and the leaves grow in the lance shape out from stalk, which is dark green in color and each leaf is 2 ft long and 4–7 in. wider. In an average, 25 leaves are produced per year from the sisal plant. The fibers are extracted by crushing and brushing by rotating wheel with the blunt knives; this process is known as decortication. The main constituents of the sisal fibers are cellulose (65.8%), hemicellulose (12%), lignin (9.9%), and wax (0.3%). These fibers are used in making mats, handicrafts, ropes, carpets, twins, and as reinforcements in polymer composites [31, 32]. Pineapple (Ananas comosus) belongs to the Bromeliaceae family. The pineapple leaves (PALF) are the waste products of cultivation of the pineapple. Therefore, it is abundantly available. The size of these leaves is about 6 cm wide, and each plant has a cluster of 20–25 leaves. Fibers are extracted from the PALF by retting process. The main constituents of PALF are cellulose (70–82%), lignin (5–12%), and ash (1.1%). The various applications of PALF are in automobiles, textile, mats, construction, etc. The treated and surface-modified fibers are used for making conveyor belt cord, airbag, advanced composites, etc. [33, 34]. The natural fibers are also obtained from the animals in the form of silk, wool, hair, and feathers. The major share of animal fibers is from domestic sheep. Natural silks are usually obtained from silk worms that belong to the family of Bombycidae and known by the scientific name Bombyx mori mainly found in China, India, Korea, and Japan. The annual production of silk is highest in China with 146 000 metric tonnes and the second highest in India with 28 708 metric tonnes. The process of extraction of silk comprises harvesting of cocoons, thread extraction, dyeing, spinning, and weaving. The silk usually consists of two types of proteins, namely, fibroin, and sericin [35].

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Synthetic fibers are made from petrochemicals. These fibers are extensively used in every field of fibers and industrial applications, which account to half of fiber usage. Synthetic fibers are commonly manufactured by melt-spinning process. Nowadays, synthetic fibers are commonly used as reinforcements in composite materials. The important synthetic fibers are glass fibers, carbon fibers, Kevlar fibers, etc. Glass fibers are one of the most widely used reinforcements in polymer composites because of their high strength, stiffness, flexibility, chemical resistance, and superior insulating characteristics [36–38]. Carbon fibers are the most important synthetic fibers commonly used as reinforcements in polymer composites. Carbon fibers are available in mat form, fibers, and filaments. They have high specific modulus and strength. They are widely used in automotive, aerospace, and nuclear engineering [39]. Kevlar fibers are known for their uniqueness among all synthetic fibers. The stiffness of Kevlar is more because of the extra benzene ring in its polymer chain. Kevlar fibers have good tensile strength and modulus and lower elongation than other synthetic fibers. Kevlar fibers are used in industrial and military applications because of their exceptional mechanical properties [40].

2.3 Polymers Polymers are macromolecules made up of monomers. The monomers are the smallest repeating unit in polymers. The monomers combine together to form polymers by the process called polymerization. Polymers are used in every field and one cannot imagine life without them. Some of the important applications of polymers are in paints; adhesives; elastomers; aerospace applications; packing industries; surgical sutures; contact lens; medical supplies; electrical components; contact lenses; house wares such as cups, plates, bottles, pipes, body panels, windows, doors, flooring adhesives, roofing sealant, building panels, boat hulls, passengers, and naval vessels; gas masks; boats; television; mobile phones; digital camera; rechargeable batteries; watches; instrument panels; engine; tires; flooring adhesives; roofing sealant; building panels; etc. [41–44]. Polymers are of two types, i.e. natural polymers and synthetic polymers. Natural polymers are usually found in nature in the form of proteins (carbohydrates, lipids, amino acids, and nucleic acids), silk, wool, starch, cellulose, etc. Natural polymers are mainly found in human bodies as well as in plants. Starch is composed by several monomers made of glucose. Starch is mainly found in food that contains carbohydrates such as potatoes and cereal grains. A variety of other natural polymers exist in nature such as shellac, amber, cotton, and natural rubber [45]. Some of these polymers are commercially valuable, which are synthesized by chemical modifications. Natural rubber is extracted from rubber tree in the form of the latex, which is in form of sticky gel and is collected in vessels, and the process is known as tapping. The extracted rubber/latex is made up of isoprene units. The latex is either processed to latex concentrate by centrifugation (manufacturing of dipped goods) or coagulated using formic acid. The coagulated rubber is further processed to high-grade block rubbers (for example, SVR 3L or SVR CV)

2.4 Hybrid Polymer Composites

or used to produce Ribbed Smoke Sheet grades. For advanced applications, the natural rubber is often vulcanized using sulfur to improve the cross-link density and thermomechanical properties. The main advantage of natural rubber is its elasticity, resilience, and water proof behavior. Therefore, it is extensively used in many industrial applications [46, 47]. Synthetic polymers are referred as man-made polymers. They are mainly classified into thermoplastics and thermosetting polymers. Thermoplastics can be remolded into a number of times by the application of heat. Examples of thermoplastics are polypropylene (PP), polystyrene (PS), low-density polyethylene (LDPE), high-density polyethylene (HDPE), etc.; PP and polyethylene (PE) are crystalline polymers, while PS is amorphous. LDPE is widely used in packing industries, while HDPE and ultra-HDPE are used for making gas and water pipelines, insulating wires, etc. [48]. On the other hand, one cannot change the shape of the thermosetting polymer by the application of heat once it is completely cross-linked [49, 50]. Once the system is cross-linked, it has a three-dimensional network structure. Examples for thermosetting polymers are epoxy resin, phenol formaldehyde, amide, polyether, polyesters, etc. Both thermoplastic and thermosetting polymers are used as matrix for developing natural and synthetic fiber-reinforced composites [51].

2.4 Hybrid Polymer Composites The polymer composites made up two or more different reinforcements called hybrid composites. Different combinations of fibers, fillers, or mats/fabrics can be used to develop hybrid composites. The reinforced fibers can be synthetic or natural. Researchers are working on to formulate the best combinations of fibers to prepare composites for different applications [46, 52–54]. The drawback of natural fibers is that it is susceptible to absorb moisture and the thermomechanical properties are inferior to synthetic fibers. The moisture absorption of natural fibers may affect the performance of the composites especially in outdoor applications. This drawback can be overcome with the hybridization of the natural fibers with synthetic fibers. The hybridization of natural fibers with synthetic fibers enhances the strength, stiffness, and resistance to moisture of the composites. In other words, the drawbacks of natural fiber can be complemented with synthetic fibers. Thus, the performance of the composites could be enhanced with proper selection of matrix and reinforcements. The other advantages of hybridization include cost reduction, more greener, and good thermomechanical properties [55]. For example, the incorporation of glass fiber with jute and sisal reinforced polyester composites enhanced the mechanical and reduced water absorption properties of the materials [56]. Similar studies have been reported in the literature [57–59]. The hybridization of woven flax with carbon fiber and also jute with carbon fiber reported that the increase in carbon content would increase the tensile property of the composites, and also suggestions were made to replace jute with more carbon fibers to obtain a stronger material [60, 61].

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Researchers are currently focusing on natural–natural fiber-reinforced hybrid composites as an alternative to synthetic fibers, such as carbon and glass fiber hybrid composites. The effect of an oil palm nanofiller in kenaf/epoxy composites was studied. Three percent of oil palm nanofiller considerably improved the mechanical properties of the epoxy composites [62]. In an interesting work, it is reported that the hybridization of sisal/banana fiber in polyester composites increased the mechanical properties as compared with composites with individual fibers [63]. The synthetic/synthetic hybrid composites are also developed for some structural applications, which facilitate the structure weight reduction [64]. Glass fiber is cheaper than other synthetic fibers such as carbon, Kevlar, etc.; therefore, combinations of glass fiber with carbon, Kevlar, etc., will be more economic without any loss in thermomechanical properties [58].

2.5 Fiber Extraction Methods Most of the plant fibers are extracted either manually or mechanically by retting, decortication, or by the combination of both the processes. This section provides the general information of these two methods. Retting is one of the most important methods utilized for the removal of cellular tissues, wax, and pectin in plant fibers. Traditionally, retting can be carried out through various methods such as mechanical retting, physical retting, chemical retting, and biological retting. Mechanical retting produce fibers by making use of a decorticator; this process is quick but fiber quality is poor [65–67]. Physical retting is used to obtain clean and high-quality fibers. Physical retting method is categorized as ultrasonic retting (UR), enzyme retting (ER), and stem explosion retting (SER). The SER method results in obtaining high fineness fibers that are comparable with cotton fibers, while in UR technique, ultrasound is used for the separation of the fibers, and the fibers obtained are nontextile in grade. The ER method is used to produce long and undamaged fibers with excellent strength. Chemical retting method involves the extraction of fibers by chemical reagents. The chemicals used are chlorinated lime, sodium hydroxide, sulfuric acid, and potassium hydroxide. This process is fast and the fibers have good consistent properties. Biological retting method is subdivided into dew retting and water retting process. Dew retting process is also called as field retting process and is carried out in the areas where there is scarcity of water. In this method, the harvested plants are spread in the field, and it undergoes degradation in the presence of sunlight, moisture, bacteria, etc. This is a slow process and may take 12–24 days for the retting process. In water retting method, the plants are dipped in the pond or tank water and essentially require large quantity of water, making the procedure expensive as compared to dew retting process. Water retting method provides finer and higher quality fibers and is a more preferred method [1, 68–72].

2.6 Fiber Treatments The mechanical performance of any fiber composites mainly depends on the compatibility of fiber–matrix interaction. Plant fibers have poor adhesion with

2.6 Fiber Treatments

polymers and high moisture absorption. To enhance the interfacial interaction between the fiber and polymers and to reduce the water absorption behavior, the fibers are surface treated with different chemical reagents. These treatments would reduce the hydrophilic characteristics of fibers and improve their interfacial bonding with matrix material, thereby improving the mechanical strength of the polymer composites. Many researchers have carried out investigations on different chemical treatments such as alkaline treatment, stearic acid, potassium permanganate, acetylation, mercerization, silane treatment, fungal treatment, plasma treatment, benzoylation, etc. [29, 73–78]. Asim et al. [79] treated pineapple leaf and kenaf fibers with alkali, silane, and a combination of these two solutions to understand their effects in terms of compatibility and mechanical properties. The results showed that the silane-treated pineapple leaf fibers and kenaf fibers possess good interfacial shear strength and tensile properties as compared to raw, alkali, and alkali–saline-treated fibers. Weyenberg et al. [80] carried out alkaline treatment on flax–epoxy composites and found that the chemical treatment yielded a significant increase in tensile strength, tensile modulus, bending strength, and stiffness with the removal of pectin from the treated fibers. Mishra et al. [81] reported that the 5% alkali-treated sisal fiber-reinforced polyester/glass fiber hybrid composite tends to exhibit good tensile properties compared to 10% alkali-treated hybrid composites. This decrease in 10% treated composites is mainly attributed because of the high concentration of alkali treatment, which has weakened the fiber by excess delignification. Ismail et al. [82] reported on the mechanical properties of raw and alkali-treated kenaf fiber-filled natural rubber composites. The better interfacial bonding along with good mechanical properties was achieved through treated fibers. Valadez-Gonzalez et al. [83] treated henequen fibers with silane and alkali treatment. It was reported that a better interfacial bonding between fiber and matrix is observed in silane-modified fibers than alkali-treated fibers. Nair et al. [84] investigated on various chemically treated sisal fiber-reinforced PS composites. The T g and thermal stability of the treated fiber composites are found to be better as compared to those of raw fiber composites. Sreekala et al. [85] studied the water sorption properties in oil palm fiber-reinforced phenol formaldehyde hybrid composites and oil palm fiber/glass fiber-reinforced phenol formaldehyde hybrid composites. The authors observed an increase in water absorption with fiber content; however, incorporation of glass fiber reduced the water absorption. Sawpan et al. [86] reported untreated and various chemically treated (alkali, acetic anhydride, maleic anhydride, and silane) hemp fiber-reinforced polylactide composites to study on the interfacial shear strength of the composites. Improved interfacial shear strength was observed in all the treatment except maleic anhydride-treated composites, showing the inadequate bonding of polylactide matrix with maleic anhydride-treated fibers. Mishra et al. [87] reported that the water absorption behavior in hemp, sisal, and banana fiber-reinforced novolac composites reduced with maleic anhydride treatment. Also, the impact strength, flexural modulus, Young’s modulus, and hardness of the plant fiber/novolac resin composites were increased with maleic anhydride treatment.

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2.7 Processing Methods of Hybrid Composites The science of converting the raw materials into products of desired shape is called processing. Because hybrid composites are the material systems composed of two or more different materials, the processing methods used for the manufacturing of these composites are extremely important. The most important criteria to be considered while selecting a particular production method are size, shape, desirable properties of the composites, speed of the production, and manufacturing cost involved in the processing [88]. Numerous different processing techniques for the development of hybrid natural fiber-reinforced polymer (thermosets/thermoplastic) composites are now available and are illustrated in Figure 2.1. The following Section 2.7 discusses some of the processing techniques utilized in the development of hybrid composites. 2.7.1

Pultrusion

Pultrusion is an economical method that combines the process of pulling and extruding while performing high-volume manufacturing. In other words, the fibers or fabrics are pulled through the resin bath, and then it is passed through a shape former, cured, and cut into required length. The mechanism of operation is similar to the extrusion process except that a work material instead of being rammed inside a die, it will be pulled through the die in pultrusion process. This method is used for processing thermosetting polymers such as epoxy and unsaturated polyesters. This process creates constant cross sections with continuous lengths and the final shape of the products obtained will be of circular, rectangular, square, H, or I shape. The main advantage of this process is that it is a completely automated process that enables in obtaining high-volume Method

Thermoset

Thermoplastic

composites

composites

Pultrusion

Injection molding

Filament winding

Blow molding

Injection molding

Thermoforming

Hand lay-up

Compression molding

Resin transfer molding Autoclave process

Figure 2.1 Some of the processing methods used for the manufacturing of hybrid composites. Source: From Mazumdar 2001 [88].

2.7 Processing Methods of Hybrid Composites

T Fiber

Let-off

Resin-saturated fiber

Resin bath

Shape performer

z

Pultrusion die

y

Puller

Cut-off

Product

Curing

Figure 2.2 Schematic of pultrusion process. Source: Acquah et al. 2006 [93]. Reproduced with permission of Elsevier.

composite parts. The production speeds are in the range of 2–10 ft/min, and this method generally uses cheaper fibers and resins, thus helping in the production of low-cost consumer products. The major limitations of this process are that this method is limited for producing only constant cross sections and cannot be used for producing complex-tapered shapes. Also, high tolerance products are difficult to be developed by this method [22, 88–92]. Figure 2.2 shows a schematic of pultrusion process. 2.7.2

Hand Lay-up/Wet Lay-up

Hand lay-up process is one of the most main methods utilized for various composite applications. In this method, before the actual fabrication begins, the molds are sprayed with releasing agents for the easy handling of the composites. The reinforcements are then placed on the top of the mold before being impregnating the fibers with resins with suitable rollers. Further, another layer of reinforcement and resin will be applied until the desired thickness is achieved. The user is allowed to optimize the different sequential stacking of the fiber and reinforcements as per the requirement, showing the higher flexibility of the method. Both thermosetting and thermoplastic polymers such as polyurethane, vinylester, epoxy, etc., can be processed by this method. Some of the advantages of this process include low capital investment, versatility in processing any fiber with any orientation, and low-cost raw material utilization. The major limitations include specialized labor requirement, styrene emission is more in hand lay-up, and maintaining cleanliness may be a problem [1, 69, 88]. Figure 2.3 illustrates hand lay-up process. 2.7.3

Vacuum Bagging

Vacuum bagging technique is one of the pre-preg molding method while the other being autoclave molding process. The major difference between these two methods lies in the method employed in the curing of the matrix. Vacuum bagging is a process that involves the utilization of a vacuum bag for providing compaction pressure to consolidate the ply of laminates. This process is the extended

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Woven reinforcement

Gel coat

Resin

Figure 2.3 An illustration of hand lay-up technique. Source: Raji et al. 2019 [94]. Reproduced with permission of Elsevier.

Vacuum bag

Insulation

Composite and release plies

Rigid heated tool

Sealant

Breather plies

Figure 2.4 Vacuum bagging set up for fabricating composite materials. Source: Mallon and Óbrádaigh 2000 [97]. Reproduced with permission of Elsevier.

version of wet lay-up or hand lay-up process and is also known as vacuum bag molding. Initially, the prepreg materials are mounted on horizontal mold before sealing them in a vacuum bag. After proper sealing, the air is drawn out from the vacuum bag by using a vacuum pump to create vacuum atmosphere in order to cure the matrix material. Polymers such as phenolics, epoxies, and polyimides are processed using this method. The advantages of this method are its flexibility in manufacturing simple to complex products, higher fiber volume fractions (60%) can be obtained, low tooling cost, and strong and stiff part fabrication. The demerits of the process are expensive and not suitable for higher volume production applications [1, 87, 95, 96]. Figure 2.4 depicts one of the vacuum bagging techniques used for fabricating hybrid polymer composite panels. 2.7.4

Filament Winding

Filament winding is an open molding process generally used to produce circularshaped components. The mold used in filament winding process is usually

2.7 Processing Methods of Hybrid Composites Continuous fiber strands

Separator combs

Nip rollers

Carriage guide

Bath resin

Creel Rotating mandrel

Figure 2.5 Filament winding process. Source: Henriquez and Mertiny 2018 [99]. Reproduced with permission of Elsevier.

a rotating mandrel. In operation, the natural fibers are first passed through the resin bath and then the impregnated fibers are winded over the rotating mandrel. The process is widely used in producing the components such as oxygen tanks, fuel tanks, spherical pressure vessels, helicopter blades, and automotive drive shafts. Three winding patterns, namely, helical, hoop, and polar forms, can be achieved through this process. The advantages are the production of high-performance composites at low cost and complete automation can be achieved, resulting in the production of high-volume hybrid composite parts. The limitations of the process are need for mandrel, nonuniform fiber distribution, and poor finish [87, 90, 98]. Figure 2.5 depicts a simple filament winding process. 2.7.5

Resin Transfer Molding

Resin transfer molding (RTM) or liquid transfer molding process is widely used in the manufacturing of structural parts of aircrafts and automobiles. During the process, first either long or woven fibers will be precisely cut with the help of a scissors or knives. The cut fibers called as performs will be placed inside a match mold comprising of two halves. Then, by using some dispensing equipment, a mixture of polymer and additives will be injected inside the mold with the help of single or double ports. Finally, resins will be allowed to cure and composites will be removed from the mold. Resins such as polyester, vinylester, phenolics, and epoxies are generally processed in this process. RTM process has got several advantages such as low investment cost because of its minimized tooling cost and operating expenses, high dimensional tolerance parts can be easily produced, higher fiber volume fractions (65%) can be obtained, near-net shape parts with low material wastage can be achieved, and process can be completely automated with high production rates [21, 88, 98, 100]. Figure 2.6 shows the schematic of RTM process. 2.7.6

Compression Molding

Compression molding is a very popular composite manufacturing technique employed for both thermoset and thermoplastic polymeric composites. This process is most preferably utilized in the fabrication of automotive components

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2 Effect of Process Engineering on the Performance of Hybrid Fiber Composites Press to hold tool together Mold tool

Optional vacuum assistance

Resin injected under pressure

Mold tool Dry reinforcement preform

Figure 2.6 Various steps involved in RTM process. Source: Mouritz 2012 [101]. Reproduced with permission of Elsevier. Mold: heated and cooled

Mold plunger Guide pins

Molding compounds

Figure 2.7 Compression molding method. Source: Wang et al. 2019 [104]. Reproduced with permission of Elsevier.

Mold cavity Mold open

because of its high-volume production capability. The two different molding techniques used in this method are cold and hot type. The hot process utilizes the combined application of pressure and temperature to perform the operation, while the cold type uses only pressure to carry out the action. The curing in the hot process is done by the application of heat and heat transfer, and the curing in the cold process is carried out in a room temperature. In order to obtain homogeneous distribution of composite materials during the process, this process makes use of an internal mixer and a twin-screw extruder. This process offers some merits such as production of high-quality products and high-volume production rates with less mold cycle time. The limitations are high capital initial investment cost because of expensive equipment and mold and low production rates [88, 102, 103]. Figure 2.7 shows a simple illustration of compression molding. 2.7.7

Injection Molding

Injection molding is a process that is widely used in the processing of thermoplastics into many usable forms, and nowadays, it has also been employed for processing some thermoset polymers. It finds its applications in areas such as automotive sector, consumer fields, and recreational fields. The fibers in this process are generally made small or should be converted into powder form, while the resins have to be in the form of small pellets. The mixture of matrix particles

2.8 Application of Each Hybrid Polymer Composite Processing Methods

Hopper Heating zone Nozzle

Rotating screw

Mold

Figure 2.8 Schematic diagram of injection molding process. Source: Wang et al. 2019 [104]. Reproduced with permission of Elsevier.

and short or powdered fiber reinforcements are consistently mixed in a screw extruder. The mixed particles are then passed into a heating chamber through a hopper, where the heated particles are then injected into a desired shape of a mold at high pressure to obtain the composite product. The typical process time for the entire process is about 30–60 seconds, and the process is capable of producing high-quantity three-dimensional structural components [105, 106]. Figure 2.8 illustrates a simple injection molding process.

2.8 Application of Each Hybrid Polymer Composite Processing Methods The concept of hybrid polymer composites was developed to overcome the limitations such as poor thermal stability, moisture absorption, and deprived surface quality of natural fiber composites by adding additional natural or synthetic fibers [88]. Nowadays, polymer composites have found commercial success in various sectors such as in aircraft and aerospace, automotive, construction and building, marine, household, and sports industries to name a few [15]. This section discusses the applications of some important hybrid polymer composite processing methods. 2.8.1

Pultrusion

Pultrusion is a process widely used in fabricating solid and hollow structures with uniform cross sections. This process finds its application in automotive and various infrastructural sectors and is usually used in applications such as producing tubes, beams, channels, handrails, flooring systems, grating devices, ladders, electrical enclosures, light poles, walkways, and bridges [107]. Figure 2.9 shows an example of a product produced by a pultrusion process. It is train interiors pultruded components. Figure 2.10 illustrates some typical pultruded shapes. 2.8.2

Hand Lay-up

Hand lay-up process because of its low capital investment is widely used in developing prototype parts, and both simple and complex shapes can be produced by

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Figure 2.9 Train interiors with pultruded components.

Figure 2.10 Some typical pultruded shapes. Source: Narayan 2018 [108]. Reproduced with permission of Elsevier.

2.8 Application of Each Hybrid Polymer Composite Processing Methods

using this method. Some of the useful products manufactured using this method include airframe components, turbine blades, car, boat and truck body parts, chairs, bath wares, tanks, ducts decks, swimming pools, boat hulls, and architectural moldings [109]. 2.8.3

Vacuum Bagging

Vacuum bagging method is widely used in developing prototypes of various parts in aerospace industries. The parts such as radomes, wing structures, yacht structures, and some sporting goods are fabricated by means of this technique [87]. 2.8.4

Filament Winding

The combination of filament winding process and computer aided design (CAD) systems has nowadays resulted in the production of many complex geometries, which were earlier difficult to be produced. The products such as pressure vessels, rocket motor casings, tubular structures, telescopic poles, rollers and bushings, fishing rods, chemical storage tanks, various tool handles, rocket launch tubes, fuselages, bicycle frames, golf shafts, hockey stick, baseball bats, bottles, and connecting rods are manufactured using filament winding technique [110]. Figure 2.11 shows the joining of space frame structure using the filament winding. 2.8.5

Resin Transfer Molding

RTM process is widely used for developing small- to big-sized structures in medium volume applications. It finds its application in aerospace, automotive, consumer, and sports goods industries. Some of the structures made utilizing this method are spars, bulkheads, stiffeners and spacer blocks of aircrafts, automotive panels, doors, helmets, windmill blades, bicycle frames, hockey sticks, and sports car bodies [112]. 2.8.6

Compression Molding

Compression molding process is used for molding both thermoplastic and thermosetting polymers and finds its increased use in automotive applications. This process is used to produce some utility products such as military drop boxes, Figure 2.11 Unit for joining space frame structures by filament winding. Source: Fleischer et al. 2018 [111]. Reproduced with permission of Elsevier.

T-joint Rotor Stator Fiber Impregnation unit

Tightening unit

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Figure 2.12 Compression molded graphite–polymer composite bipolar plates. Source: Chen et al. 2010 [114]. Reproduced with permission of Elsevier.

radiator supports, door stopper, tray, table top, heavy truck sleeper cabs, plastic rubber bands, designs of cap and jar cover, showers and bath tubs, outdoor lamps, and street light canopying [113]. Figure 2.12 shows compression-molded graphite–polymer composite bipolar plates. 2.8.7

Injection Molding

Injection molding technique is utilized for high volume applications. Some of the components manufactured by this technique include cups, buckets, toys, automotive parts, electrical plug fuses, small power tools, mobile case, etc. [87]. This process is being utilized widely in producing electronics applications. Some other examples include NEC Corporation, making a mobile case, and Xiaomi used this technique to develop thin-walled casing for their Mi2A mobile device [115, 116].

2.9 Conclusion From this chapter, it can be concluded that the natural fiber-based hybrid polymer composites can successfully replace synthetic fiber reinforced polymer composites in different engineering applications by providing excellent material properties. The properties of bio-based composites can be improved by treating fibers with various chemical agents and provide excellent mechanical interfacial adhesion behavior with different thermoset and thermoplastic polymers. The hybrid polymeric composites are processed and manufactured using different fabrication methods and can produce various products belonging to aerospace, automotive, sports, marine, defense, construction, and electronic sectors.

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bundwerkstoffe: Werkstoffe, Verarbeitung, Anwendung. Carl Hanser Verlag GmbH & Co. KG. Zhu, J., Chandrashekhara, K., Flanigan, V., and Kapila, S. (2004). Manufacturing and mechanical properties of soy-based composites using pultrusion. Composites Part A Applied Science and Manufacturing 35 (1): 95–101. Acquah, C., Datskov, I., Mawardi, A. et al. (2006). Optimization under uncertainty of a composite fabrication process using a deterministic one-stage approach. Computers and Chemical Engineering 30 (6–7): 947–960. Raji, M., Abdellaoui, H., Essabir, H. et al. (2019). Prediction of the cyclic durability of woven-hybrid composites. In: Durability and Life Prediction in Biocomposites, Fibre-Reinforced Composites and Hybrid Composites (eds. M. Jawaid, M. Thariq and N. Saba), 27–62. Woodhead Publishing. Mayer, R.M. and The Design Council (1993). Design with Reinforced Plastics: A Guide for Engineers and Designers. Netherlands: Springer. Sapuan, S.M. and Yusoff, N.B. (2015). The relationship between manufacturing and design for manufacturing in product development of natural fibre composites. In: Manufacturing of Natural Fibre Reinforced Polymer Composites (eds. M.S. Salit, M. Jawaid, N.B. Yusoff and M.E. Hoque), 1–15. Cham: Springer. Mallon, P.J. and Óbrádaigh, C.M. (2000). Compliant mold techniques for thermoplastic composites. In: Comprehensive Composite Materials (eds. A. Kelly and C. Zweben), 873–913. Elsevier. Balasubramanian, K., Sultan, M.T., and Rajeswari, N. (2018). Manufacturing techniques of composites for aerospace applications. In: Sustainable Composites for Aerospace Applications (eds. M. Jawaid and M. Thariq), 55–67. Woodhead Publishing. Henriquez, R.G. and Mertiny, P. (2018). 3.21 filament winding applications. In: Comprehensive Composite Materials II (eds. P.W.R. Beaumont and C.H. Zweben), 556–577. Elsevier. Rouison, D., Sain, M., and Couturier, M. (2004). Resin transfer molding of natural fiber reinforced composites: cure simulation. Composites Science and Technology 64 (5): 629–644. Mouritz, A.P. (2012). Introduction to Aerospace Materials. Elsevier. Wirawan, R., Sapuan, S.M., Yunus, R., and Abdan, K. (2011). Properties of sugarcane bagasse/poly(vinyl chloride) composites after various treatments. Journal of Composite Materials 45 (16): 1667–1674. Hull, J.L. (2006). Compression and transfer molding. In: Handbook of Plastic Processes (ed. C.A. Harper), 455–473. Wiley. Wang, M., Guo, L., and Sun, H. (2019). Manufacture of biomaterials. In: Encyclopedia of Biomedical Engineering (ed. R. Narayan), 116–134. Elsevier. Holbery, J. and Houston, D. (2006). Natural-fiber-reinforced polymer composites in automotive applications. JOM Journal of the Minerals Metals and Materials Society 58 (11): 80–86. Rouison, D., Sain, M., and Couturier, M. (2003). Resin-transfer molding of natural fiber–reinforced plastic. I. Kinetic study of an unsaturated polyester

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107 108 109

110 111 112 113

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resin containing an inhibitor and various promoters. Journal of Applied Polymer Science 89 (9): 2553–2561. Schwartz, M. (2005). New Materials, Processes, and Methods Technology. CRC Press. Narayan, R. (2018). Encyclopedia of Biomedical Engineering. Elsevier. Fong, T.C., Saba, N., Liew, C.K. et al. (2015). Yarn flax fibres for polymer-coated sutures and hand layup polymer composite laminates. In: Manufacturing of Natural Fibre Reinforced Polymer Composites (eds. M.S. Salit, M. Jawaid, N.B. Yusoff and M.E. Hoque), 155–175. Cham: Springer. Munro, M. (1988). Review of manufacturing of fiber composite components by filament winding. Polymer Composites 9 (5): 352–359. Fleischer, J., Teti, R., Lanza, G. et al. (2018). Composite materials parts manufacturing. CIRP Annals 67 (2): 603–626. Fisher, K. (1997). Resin flow control is the key to RTM success. High-Performance Composites (USA) 5 (1): 34–38. Hasan, M., Hoque, M.E., Mir, S.S. et al. (2015). Manufacturing of coir fiber-reinforced polymer composites by hot compression technique. In: Manufacturing of Natural Fibre Reinforced Polymer Composites (eds. M.S. Salit, M. Jawaid, N.B. Yusoff and M.E. Hoque), 309–330. Cham: Springer. Chen, W., Liu, Y., and Xin, Q. (2010). Evaluation of a compression molded composite bipolar plate for direct methanol fuel cell. International Journal of Hydrogen Energy 35 (8): 3783–3788. Azaman, M.D., Sapuan, S.M., Sulaiman, S. et al. (2015). Processability of wood fibre-filled thermoplastic composite thin-walled parts using injection moulding. In: Manufacturing of Natural Fibre Reinforced Polymer Composites (eds. M.S. Salit, M. Jawaid, N.B. Yusoff and M.E. Hoque), 351–367. Cham: Springer. Zini, E. and Scandola, M. (2011). Green composites: an overview. Polymer Composites 32 (12): 1905–1915.

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3 Mechanical and Physical Test of Hybrid Fiber Composites Mohit Hemath 1 , Arul Mozhi Selvan Varadhappan 2 , Hemath Kumar Govindarajulu 3 , Sanjay Mavinkere Rangappa 1 , Suchart Siengchin 1 , and Harinandan Kumar 4 1 King Mongkut’s University of Technology, North Bangkok, The Sirindhorn International Thai-German Graduate School of Engineering, Natural Composite Research Group, Department of Mechanical and Process Engineering, 1518, Pracharat 1, Wongsawang Road, Bangsue, Bangkok 10800, Thailand 2 National Institute of Technology, Department of Mechanical Engineering, Tiruchirappalli 620015, India 3 Madanapalle Institute of Technology and Science, Department of Mechanical Engineering, Chittoor, Angallu, Andhra Pradesh 517325, India 4 University of Petroleum and Energy Studies, Department of Petroleum and Earth Science, Dehradun, Uttarakhand 248007, India

3.1 Introduction Sugarcane bagasse is the primary agro-industrial waste of sugarcane industry, and its main constituent is cellulose. This type of bagasse is mainly used to generate electricity in mills, and in some countries, it is utilized for ethanol production [1, 2]. Sugarcane bagasse mainly consists of 45% cellulose, 24% lignin, and 26% of hemicellulose content with other small constituents such as extractives and ash [3]. The cellulose nanofibers are segregated by various techniques such as grinding, 2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO)-mediated oxidation, cryocrushing, enzyme-assisted process, and sulfuric acid hydrolysis [4]. It is also observed that cellulose nanofibers can be extracted from high-shear mechanical treatment process and combined chemical or enzymatic pretreatments [5, 6]. The cellulose nanofibers have a rod, needle, or spherical shape with higher crystallinity index (56.78%), 7.5 GPa of tensile strength, 10 GPa of bending strength, and 150 GPa of Young’s modulus, require lower energy during fabrication, and are biodegradable in nature. From these attractive properties, the addition of nanocellulose crystals as reinforcements in polymer composites has shown interest [7–9]. The cellulose has the facial influence of hydroxyl functional (–OH) groups, which supports the production of hydrogen bonds within the polymer matrix and applied as a reinforcement to the polymer [10]. Chemical surface modification has been summarized as an adequate method for improving the cellulose nanocrystal surface [11]. Morelli et al. fabricated isocyanate-modified and unmodified cellulose nanocrystal-reinforced poly(butylene adipate-co-terephthalate) nanocomposites, and it was found Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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3 Mechanical and Physical Test of Hybrid Fiber Composites

that isocyanate decreased the hydrophilicity of nanocrystals, which leads to an increase in the mechanical properties of nanocomposites such as elastic modulus and yield stress up to 120% and 40%, respectively. A similar result is also observed in modified cellulose nanocrystal reinforced in polylactic acid, poly(3-hydroxybutyrate), and polylactide-co-glycolide [12, 13]. There are different types of surface modification techniques, such as gamma irradiation; corona, plasma, alkaline, acetylation; benzoylation; peroxide, silane, maleated coupling; enzyme, sodium chlorite, acrylation, and acrylonitrile grafting; isocyanate, fatty acid, stearic acid, silylation; esterification or etherification; and fungal, permanganate, and triazine treatment for the extraction of cellulose fibers, and among them, alkaline, silylation, and esterification or etherification process were utilized generally [14, 15]. To form an ester and carboxylic functional groups on the surface of nanofiber, the cellulose nanofibers were treated with a step esterification process [16, 17]. Ferreira et al. extracted cellulose nanofibers from sugarcane bagasse using sulfuric acid and found that nanofibers showed a significant aspect ratio (l/d) and higher crystallinity index of 35% and 56%, respectively. The surface modification using acid reduces the nanocrystal dimensions (length and width from 413 to 242 nm and from 10 to 6.8 nm, respectively) because of the elimination of amorphous region from the crystalline structure, which also modifies hydrophilic affinity and electrostatic repulsion [10]. These types of surface modifications affect the environment vigorously by means of air pollution, skin problems, etc., during the extraction process. Recently, nanoparticle-reinforced polymer composites have shown interest in the enhancement of mechanical and thermal properties of the final materials. A wide range of nanoparticles such as carbon oxide dots (zero-dimensional), carbon nanotubes (one-dimensional), rigid nanoparticles (spherical), metal dichalcogenides (two-dimensional), graphene, and nanoclays and their effect on the fabricated composites have been investigated. The mechanical properties of polymer composites fabricated from these nanoparticles ranged the tensile strength (4.3–97.4 MPa), flexural strength (FS) (75–119 MPa), elongation at break (2.6–5.3%), Young’s modulus (1.55–3.8 GPa), yield strength (48–91 MPa), toughness (2.8–460 J/m3 ), pullout strength (20–22.5 kgf/cm2 ), and fracture toughness (0.52–1.58 MPa m1/2 ), whereas the glass transition and decomposition temperature varies from 243 to 525 ∘ C and 138 to 600 ∘ C, respectively [18–26]. In previous literature, the carbon nanotubes and graphene have been selected as possible reinforcement materials to polymers because of lower density (1206.7–1244.7 kg/m3 ), higher aspect ratio (length to width ratio as 32), extraordinary strength (97.4 MPa as flexural strength), and stiffness (1.58 MPa m1/2 ) [19, 20, 22, 27]. The dispersion of these types of nanoparticles can be attained from functionalization process using an oxidizing agent, but it is a very costly (US$15–20 per 20 g of carbon nanotubes or graphene), complicated, and time-consuming (24–56 hours) process. Also, the toxicity level of these types of materials is comparably higher than that of other nanoparticles such as silica, silicon carbide, boron carbide, aluminum silicon carbide, aluminum titanium oxide, titania, etc. These types of nanoparticles are readily available and easy to disperse in polymer matrices because of the lower aspect ratio (15) and stronger van der Waals force within the polymer matrix [28–30]. Among these ceramic, metal

3.1 Introduction

oxide, and metal-based nanoparticles, nano-Al–SiC have been selected as the reinforcement material to polymer because of lightweight (2760–2980 kg/m3 ), higher strength (200–800 MPa), higher thermal conductivity (170–180 W/mK), lower thermal expansion (10 × 10−6 to 15 × 10−6 ), improved wear resistance (0.84–0.39 m3 /m), and damping capabilities [31, 32]. Al–SiC nanoparticles are manufactured by reinforcing SiC nanoparticles in the matrix via powder metallurgy, disintegrated melt deposition, spray deposition, high-intensity ultrasonic stirring, and sol–gel synthesis [33, 34]. The homogeneous dispersion of nanoparticles in the polymer matrix can be achieved from mechanical, shear mixing, acoustic cavitation, and ultrasonication process [35–37]. Goyat and Ghosh manufactured epoxy-TiO2 nanocomposites using ultrasonic assisted dual-mixing process [37]. The result shows a very active dispersion of 10 wt% of TiO2 nanoparticles in the epoxy matrix and enhances the glass transition temperature (from 63.5 to 97.75 ∘ C), Young’s modulus (from 0.75 to 0.87 GPa), and tensile strength (from 31.25 to 45 MPa) of the TiO2 epoxy nanocomposites. The tensile fracture surfaces showed various toughening mechanisms such as void growth, particle pulls out, crack bridging, deflection, and plastic deformation in the matrix [37, 38]. Xiao et al. investigated mechanical characteristics of the epoxy nanocomposites reinforced with hybrid nanoparticles such as SiO2 (silica) and multiwalled carbon nanotubes (MWCNTs). It is observed that there is an increment in mechanical properties such as tensile strength, flexural strength, and Young’s modulus up to 71.62, 95.79, and 3108.45 MPa, respectively, with the reduction in stress concentration and absorption of more energy [39]. In general, an epoxy polymer shows a wide range of molecular structures and consists of two oxirane classes as an epoxide functional group in the polymeric network [40]. An epoxy polymer is primarily applied in modern industries, ranging from microelectronic materials, adhesives, owing to excellent thermal, mechanical properties, and better adhesion to specific substrates with minimum shrinkage during the curing process [41]. The cured epoxy polymers also acquire poor crack resistance and inbuilt brittle fracture nature, which reduce the mechanical characteristics [5]. Presently, the reinforcement of lower nanocellulose fiber concentration in the vinyl ester polymer is gaining interest in the manufacturing of high-performance engineering materials with higher mechanical and thermal properties. The nanocellulose fibers are renewable, environmentally friendly, and readily extractable from richly available biomass for a wide range of industrial applications. From the literature survey, it is observed that very limited investigation has been performed on sugarcane nanocellulose fiber (SNCF) and inorganic nanoparticle-reinforced vinyl ester nanocomposites. Hence, the present investigation is aimed to optimize the concentration of chemically treated nanocellulose fibers, Al–SiC nanoparticles, and sonication time to improve the mechanical, viscoelastic, and physical properties of vinyl ester nanocomposites. The success of this research findings offers promising environmentally friendly hybrid nanocomposites, which can distract the utilization of expensive and toxic nanoparticles such as graphene oxide, metal oxides, and carbon nanotubes.

43

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3 Mechanical and Physical Test of Hybrid Fiber Composites

3.2 Materials and Methods 3.2.1

Materials

A vinyl ester adhesive contains four components, (i) vinyl ester resin, (ii) promoter, (iii) accelerator, and (iv) catalyst supplied from Sakthi Fiber Glass, Chennai, India, as the matrix materials. Aluminum (Al) particles with an average diameter of about 15 μm were procured from Ganapathy Colours, Chennai, India. The raw silicon carbide (SiC) particles were supplied by Carborundum Universal, Kochi, India. The diameter of SiC was 150 μm, and its length ranges from 2 to 3 μm. Both Al and SiC are utilized as reinforcement materials to the vinyl ester polymer. 3.2.2

Extraction of Sugarcane Nanocellulose Fiber (SNCF)

The waste sugarcane bagasse was collected from various juice shops and sugarcane mills near southern India. The bagasse was washed using fresh tap water to remove dirt and dust particles and then dried in sunlight for 48 hours. After drying in sunlight, the raw bagasse sample was separated, denoted as SRS (sugarcane raw sample). Then, the raw sugarcane bagasse was immersed in salt solution (prepared with NaCl and fresh tap water in 1 : 10 ratio) for two days under atmospheric pressure and temperature (32 ± 2 ∘ C), considered as salt solution treatment (SST). Finally, the bagasse was treated with 0.1 N NaOH solution for four hours at 100 ∘ C, and modified fibers were denoted as SAT (combined salt solution and alkaline treatment). SRS, SST, and SAT were milled separately using an industrial grinder. The fine nanocellulose particles were obtained from 70 nm (average size) of the sieve. 3.2.3

Synthesis of Al–SiC Nanoparticles

Mechanical alloying was performed in a horizontal type of high-energy ball mill. The silica gel of 3 wt% was poured into the mixture during the ball milling process to avoid severe cold welding. The steel balls with different diameters (8, 10, 12, 15, 18, and 20 mm) and balls to powder a weight ratio of 10 : 1 were employed. The speed of milling was chosen as 200 ± 5 rpm. The ball milling time was fixed to be three hours, with an interval period of 20 minutes for every one hour, in order to prevent from over-heating. After the milling, Al–SiC nanoparticles were separated from 55 nm of nanosieve and applied as a reinforcement to the vinyl ester polymer. 3.2.4

Fabrication of SNCF/Al–SiC Vinyl Ester Nanocomposites

Firstly, an ultrasonicator machine (UP400ST, Hielscher) was applied to disperse SNCF and Al–SiC nanoparticles in the vinyl ester polymer. Vinyl ester resin, promoter, accelerator, SNCF, and Al–SiC nanoparticles were weighed carefully and mixed together in 1000 ml of cylindrical flask. During the process of ultrasonication, the cylindrical flask was submerged in an ice bath to prevent

3.2 Materials and Methods

from overheating on SNCF and Al–SiC surface. After the completion of the ultrasonication process, the catalyst was mixed with modified polymer using mechanical stirrer for 30 minutes. The mixture was poured in mold dimensions 260 × 130 × 5 mm and then shifted to the vacuum chamber for 30 minutes to reduce the entrapped air and voids. The fabricated SNCF/Al–SiC vinyl ester hybrid nanocomposites were post-cured at 60 ± 2 ∘ C for four hours to remove the internal moisture content. 3.2.5

Design of Experiments (DOE)

Design of experiments (DOE) is the systematic and controlled experimental design for the collection and examination of the enormous quantity of data to achieve an extensive evaluation of the parameters. It simplifies statistical research on the effect of various input factors on the response. A general response surface methodology (RSM) design, which is also considered as the central composite design, was investigated in this present investigation using Design Expert 9.0 Statistical software. From the basic composite design, three independent parameters, the concentration of SNCF, Al–SiC, and sonication time, were examined at five coded levels (−2, −1, 0, +1, and +2) to establish the experimental design as shown in Table 3.1. The experiment has 20 runs with a mean of three replicates for each series, also given in Table 3.2 (obtained from Figure 3.1). The sequence of experiments was randomized to reduce the impacts of independent factors. 3.2.6

Development of Experimental Models and Optimization

The response surface regression was applied to create complex mathematical quadratic equations for flexural strength of SNCF/Al–SiC vinyl ester hybrid nanocomposites on independent parameters and their interactions on output responses. Each experimental model was analyzed using analysis of variance (ANOVA) under the confidence level of 95%. The experimental design model was obtained from the least-square method as shown in Eq. (3.1) Z = a0 +

3 ∑

ai Y i +

i=1

3 ∑

aii Yi2 +

i=1

3 2 ∑ ∑

aij Yi Yj + 𝜀

(3.1)

i=1 j>1

where Z is the response output (flexural strength); a0 is a constant; 𝜀 is the error residual; terms ai , aii , and aij are linear, quadratic, and interaction coefficient, Table 3.1 Parameters in central composite design. Levels used Variables

−2

−1

0

1

2

18.41

SNCF (wt%)

1.59

5

10

15

Al–SiC (wt%)

1.59

5

10

15

18.41

Sonication time (min)

39.55

60

90

120

140.45

45

46

3 Mechanical and Physical Test of Hybrid Fiber Composites

Table 3.2 Central composite experimental design. Flexural strength (MPa)

Run

SNCF (wt%)

Al–SiC (wt%)

Sonication time (min)

SST

SAT

SRS

1

5

15

120

86.76

93.69

79.82

2

15

5

120

84.16

90.89

77.42

3

10

10

90

88.52

95.61

81.44

4

10

10

90

88.52

95.61

81.44

5

5

5

60

85.42

92.25

78.58

6

15

15

60

89.86

97.04

82.67

7

5

5

120

88.06

95.11

81.02

8

15

5

60

84.16

90.89

77.42

9

5

15

60

81.63

88.16

75.10

10

15

15

120

85.87

92.75

79.00

11

10

10

140.45

86.90

93.86

79.96

12

1.59

10

90

82.86

89.48

76.22

13

10

10

90

88.52

95.61

81.44

14

10

10

90

88.52

95.61

81.44

15

10

10

39.55

84.47

91.22

77.71

16

10

1.59

90

87.16

94.13

80.18

17

10

18.41

90

85.17

91.98

78.35

18

10

10

90

88.52

95.61

81.44

19

18.41

10

90

87.59

94.60

80.58

20

10

10

90

88.52

95.61

81.44

respectively; and Y i and Y j are dimensionless coded-independent parameters. Equation (3.2) was used to change the independent parameters of the regression model into dimensionless coded parameters: y − y0 (3.2) Yi = i Δyi where yi and Y i are the actual and coded values of the independent parameters, respectively; y0 is the actual quantity of the independent parameter at the center, and Δyi is the step change quantity of both high and low ranges of yi . 3.2.7 Characterization on SNCF/Al–SiC Vinyl Ester Hybrid Nanocomposites 3.2.7.1

FTIR Spectra and XRD Curves

Fourier transform Infra-red spectroscopy (FTIR) spectra of neat polymer and SNCF-reinforced vinyl ester composites were examined using Perkin Elmer Spectrum 2, FTIR spectrometer, USA. The spectrum was recorded in a potassium bromide (KBr) matrix in transmission mode under the wavenumber ranges between

3.2 Materials and Methods

100 Stress (MPa)

Stress (MPa)

100 80 60 40 20 0 (a)

0

1

2 3 Strain (%)

4

80 60 40 20 0

5

0

1

2 3 Strain (%)

(b)

4

5

Stress (MPa)

100 80 60 40 20 0

0

1

(c)

4

2 3 Strain (%)

5

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Figure 3.1 Flexural stress–strain graphs of SNCF/Al–SiC vinyl ester hybrid nanocomposites (a) SRS, (b) SST, and (c) SAT.

4000 and 400 cm−1 with 1 cm−1 resolution. X-ray diffraction (XRD) for SNCF and SNCF vinyl ester nanocomposites was conducted in a Rigaku Ultima IV X-ray diffractometer with 40 kV voltage and diffraction angle between 5∘ and 80∘ with the step size of 0.05∘ [20]. 3.2.7.2

Physical Properties

The density of SNCF/Al–SiC vinyl ester hybrid nanocomposite was measured from the density gradient method according to the ASTM D 1505-10 standard. In porosity measurements, the nanocomposite specimens were sectioned into 0.01 × 0.01 m dimension and placed on the cylindrical base using Araldite glue. The samples were polished from Struer RotoPol 22 machine, and the laminate surface was examined with a DP70 camera system, Olympus, and Image Analyzer software. The water absorption test was performed for nanocomposite samples of rectangular dimensions of 39 × 10 × 5 mm according to ASTM D 570 by soaking in distilled water for 90 days. After the soaking process, additional water from the specimen surface scrubbed from soft cloth, and the final mass of specimen was recorded with an Instron weighing instrument of accuracy 0.001. 3.2.7.3

Mechanical Properties

The compression, flexural, and tensile properties of vinyl ester nanocomposite samples were analyzed in Tinius Olsen, Universal Testing Machine (H-50 kN capacity). Compression test was performed to investigate the compression performance of vinyl ester hybrid nanocomposite samples with a size

47

48

3 Mechanical and Physical Test of Hybrid Fiber Composites

of 15 × 10 × 5 mm according to the ASTM D 695-15 standard. The compression measurement was conducted at 1 mm/min. The three-point bend (flexural) test was performed according to ASTM D 790-15, in which the bending speed is 1 mm/min. The tensile test was conducted at a crosshead speed of 1 mm/min according to the ASTM D 3039/D 3039M-17 standard, and modulus of elasticity (tensile modulus) was measured using an electronic extensometer. The impact test was carried out using an Izod Impact Tester that contains a 10.4 N m hammer with 20 J of energy and samples of 62.5 × 12.5 × 5 mm, as per the ASTM D 256 standard. A notch is produced at the center of the sample, and a hammer pendulum is dropped to affect the notch and break the sample. The maximum energy absorbed by the vinyl ester hybrid nanocomposite sample is noted. For each testing condition, 10 samples were fabricated, and tests were performed in room temperature (28 ± 3 ∘ C) with a relative humidity of 60 ± 2%. The Vickers hardness was measured with a load of 1.96 N applied for 10 seconds by a Wilson Wolpert Superficial hardness tester. Five indents were created on each surface by keeping an appropriate distance from sample edges and indentation marks to verify the consistency of data. The Vickers hardness of vinyl ester hybrid nanocomposites was estimated from diagonal of the Vickers imprint and indentation load. 3.2.7.4

Viscoelastic Properties

The dynamic mechanical analysis was carried out in dynamic mechanical analysis (DMA) Q800 with 1 Hz frequency. The test was performed in flexural (three-point bend) test mode, at temperature ranges between 30 and 250 ∘ C with a heating rate of 3 ∘ C/min. The dimensions of the specimen were 50 × 10 × 5 mm3 , and at least, five samples of each combination were tested to verify the data reproducibility. From DMA, various viscoelastic properties such as storage modulus, loss modulus, damping factor, and glass transition temperature were estimated using the ASTM D 4065-01 standard. 3.2.7.5

Morphological Properties

The SNCF and Al–SiC-reinforced vinyl ester hybrid nanocomposites were sputtered with gold ion for 10 seconds in a sputter coating machine to convert the material as a conducting medium. The flexural fracture of vinyl ester hybrid nanocomposites was measured from field emission (FE)-scanning electron microscope (SEM), Hitachi, Europe, with an accelerating voltage of 15 kV and an operating distance of less than 5 mm. The microstructure and dispersion of nanoparticles in SNCF/Al–SiC vinyl ester hybrid nanocomposites were examined from a transmission electron microscope (JEOL-EM, 2200FS), which executes at 200 kV accelerating voltage.

3.3 Results and Discussion 3.3.1

Optimization

Flexural strength has been chosen for experimental design to determine the optimal sonication time and SNCF content because it can withstand at bending forces

3.3 Results and Discussion

perpendicular to the longitudinal axis, which contains both compression and tensile stress. Flexural deformation initially occurs at the outer surface of the sample, and the material is deflected until a rupture occurs in the outer surface of the nanofibers. The nanofibers located in the sample surface significantly respond to the applied load. Flexural strength can predict both resistance and durability of the composite material when compared with other measurements such as tensile, compression, impact strength, and Rockwell hardness. ANOVA results of flexural strength (FS) of SNCF (SST, SAT, or SRS)/Al–SiC vinyl ester hybrid nanocomposites are shown in Table 3.3. The SNCF, Al–SiC nanoparticles and sonication time were significant with a selected p-value of 0.05 under the confidence level of 95%. From Table 3.3, it can also be found that the squares of SNCF, Al–SiC, and sonication time were efficient with the probability of 95%. It can be observed that the interaction between SNCF × Al–SiC and SNCF × sonication time was only a dynamic interaction with probability about 95%. The lack-of-fit p-values were 0.221, 0.228, and 0.331 for SST, SAT, and SRS vinyl ester hybrid nanocomposites, respectively, which signified that the model fitted the data satisfactorily. Hence, the generated fitted model shows that the central composite design is an excellent choice for selecting an experimental design and result analysis. FSSRS = 78.31 + 0.66 × A − 0.066 × B + 0.51 × C + 1.38 × AB − 1.30 × AC − 0.17 × BC − 0.99 × A2 − 0.70 × B2 − 0.85 × C2

(3.3)

FSSST = 85.12 + 0.71 × A − 0.072 × B + 0.56 × C + 1.50 × AB − 1.41 × AC − 0.18 × BC − 1.08 × A2 − 0.76 × B2 − 0.92 × C2

(3.4)

FSSAT = 91.93 + 0.77 × A − 0.078 × B + 0.60 × C + 1.62 × AB − 1.53 × AC − 0.19 × BC − 1.16 × A2 − 0.82 × B2 − 0.99 × C2

(3.5)

It can be examined that the coefficients of Eqs. (3.3)–(3.5) for SST, SAT, and SRS fiber vinyl ester hybrid nanocomposites, respectively, show that SNCF has the highest impact, followed by sonication time and Al–SiC nanoparticles. Figure 3.2a,b displays the actual versus predicted and normal probability distribution graphs of flexural strength for three different SNCF/Al–SiC vinyl ester hybrid nanocomposites, respectively. These types of curves resolve whether specific distribution fits gathered data and permits compared to distinct specimen distributions. When the distribution fits the data, both predicted and actual values are found nearly to the straight line. From these curves, it can also be seen that the independent factors of predicted flexural strength values are good. While comparing with actual values, there is a satisfactory correlation within flexural strength and SNCF, Al–SiC content, and sonication time. The impact of linear terms on response signified that the flexural strength of SRS, SST, and SAT improved up to 78.31, 85.12, and 91.93 MPa, respectively, by incrementing in SNCF (0–10 wt%), Al–SiC (0–10 wt%), and sonication time (39.55–90 minutes). While the flexural strength decreased by 13.67%, 12.42%, and 11.25% for SRS, SST, and SAT vinyl ester nanocomposites with the increase in SNCF (11–15 wt%) and Al–SiC (11–15 wt%), it can be noticed that the flexural strength value showed little improvement (5.56%) by increasing the sonication time from 100 to 140.45 minutes.

49

Table 3.3 ANOVA results for flexural strength. SST Source

SS

df

MS

Block

SAT F

P

SS

df

MS

SRS F

P

SS

df

MS

F

P

23.29

2

11.65

27.11

2

13.55

19.73

2

9.86

Model

66.11

9

7.35

9.61

0.002

77.26

9

8.58

9.6

0.002

56.05

9

6.23

9.59

0.002

A

4.18

1

4.18

5.47

0.047

4.89

1

4.89

5.46

0.047

3.52

1

3.52

5.42

0.048

B

0.077

1

0.077

0.101

0.758

0.089

1

0.089

0.099

0.760

0.062

1

0.062

0.096

0.763

C

6.7

1

6.7

8.77

0.018

7.85

1

7.85

8.78

0.018

5.69

1

5.69

8.76

0.018

AB

19.53

1

19.53

25.56

0.001

22.85

1

22.85

25.55

0.001

16.57

1

16.57

25.5

0.001

AC

17.26

1

17.26

22.59

0.001

20.12

1

20.12

22.5

0.001

14.65

1

14.65

22.55

0.001

BC

0.280

1

0.280

0.366

0.561

0.329

1

0.329

0.367

0.561

0.239

1

0.239

0.368

0.560

A2

7.9

1

7.9

10.34

0.012

9.23

1

9.23

10.32

0.012

6.7

1

6.7

10.32

0.012

B2

7.97

1

7.97

10.43

0.012

9.32

1

9.32

10.42

0.012

6.75

1

6.75

10.39

0.012

C2

5.15

1

5.15

6.74

0.031

6.02

1

6.02

6.73

0.031

4.34

1

4.34

6.68

0.032

Residual

6.11

8

0.764

7.15

8

0.894

5.2

8

0.649

Lack of fit

6.11

4

1.53

7.15

4

1.79

5.2

4

1.3

Pure error

0

4

0

0

4

0

0

4

0

Correlation total

95.52

19

111.52

19

80.98

19

Remarks

Significant

78

76

74 79.4883 72 72

74

78

76

1

80

–2.00

–1.00

0.00

1.00

2.00

(a1)

(b1)

86 84 82 80 86.4004

80

84

82

86

95 90 80 70 50 30 20 10 5 86.4004 78.4908

1

88

–3.00

–2.00

–1.00

0.00

1.00

2.00

3.00

Actual flexural strength (MPa)

Externally studentized residuals

(a2)

(b2)

94 92 90 88 86 93.3124 84 86

88

90

92

4.00

99 95 90 80 70 50 30 20 10 5 1

93.3124 84.7701

84.7701 84

4.00

99

78.4908 78

3.00

Externally studentized residuals

78

–3.00

94

Actual flexural strength (MPa)

–2.00

–1.00

0.00

1.00

2.00

3.00

4.00

Externally studentized residuals

(a3) (a)

79.4883 72.2116 –3.00

Normal probability (%)

Predicted flexural strength (MPa)

95 90 80 70 50 30 20 10 5

Actual flexural strength (MPa)

88

Predicted flexural strength (MPa)

99

72.2116

Normal probability (%)

Predicted flexural strength (MPa)

80

Normal probability (%)

3.3 Results and Discussion

(b3) (b)

Figure 3.2 Flexural strength of SNCF/Al–SiC vinyl ester hybrid nanocomposites: (a) Predicted versus actual (a1) SRS, (a2) SST, and (a3) SAT; and (b) normal probability distribution plot (b1) SRS, (b2) SST, and (b3) SAT.

Hence, Al–SiC has direct influence while sonication time has a reverse impact on flexural strength and most of modifying response existed to sonication time as observed in predicted versus actual value graph (Figure 3.2). The main principle to enhance flexural strength is the transfer of load from polymer matrix to nanoparticles, causes certain loads to be borne by particles, and therefore flexural strength would be enhanced. The higher quantity of SNCF can bring a more flexural load. Also, it is clarified from results that the effect of sonication time on vinyl ester resin enhances the interaction within the SNCF and polymer matrix. Better adhesion within the matrix and nanoparticles can abolish debonding mutually and enhance the efficiency of stress transfer. Moreover, increase of Al–SiC nanoparticles from 0 to 10 wt% initially enhanced this response by 12.36%, 14.07%, and 15.58% for SRS, SST, and SAT vinyl ester nanocomposites, respectively, whereas further increment up to 15 wt% resulted in a decrease of flexural strength by 11.57%, 10.64%, and 9.86% for all three vinyl

51

52

3 Mechanical and Physical Test of Hybrid Fiber Composites

ester nanocomposites (SRS, SST, and SAT), respectively. The enhancement in flexural strength at lower Al–SiC nanoparticles can be assigned to higher contact surface area and adhesion within an vinyl ester resin, as well as the uniform dispersion of SNCF and Al–SiC nanoparticles in the matrix, which tends to efficient transfer of load from polymer matrix to nanofillers [42–44]. Furthermore, the addition of Al–SiC nanoparticles could not enhance the flexural strength. This reason could be described by the accumulation of nanoparticles because of weaker van der Waals forces within Al–SiC nanoparticles, which restricts the efficient transfer of load [42, 44–46]. This principle is due to the potential of Al–SiC to improve the properties of nanocomposites under lower proportion because of the higher contact surface area between vinyl ester and Al–SiC nanoparticles. The significant interaction of AB (SNCF and Al–SiC) and AC (SNCF and sonication time) was considered to anticipate the three-dimensional (3D) response surface curves of flexural strength with independent factors for three different types of vinyl ester hybrid nanocomposites (SST, SAT, and SRS), which are shown in Figure 3.3a–f. In all conditions, the influence of SNCF on the flexural strength is highly significant at higher sonication time (up to 140.45 minutes) so that the actual improvement in flexural strength from 0 to 15 wt% was observed for SNCF content. It can be ascribed to the reason that the ultrasonication process disperses nanofiller within the polymer matrix and improve matrix/nanoparticle interface adhesion. Finally, the significant interaction between SNCF × ultrasonication is observed in Figure 3.3b,d,f. It also determines that the maximum flexural strength can be attained at a higher content of SNCF, a lower concentration of Al–SiC nanoparticles, and a higher sonication time. 3.3.2

Maximization

Response targets are simultaneously maximized, and response function is modified into single desirability function (d), varies between 0 and 1. In this present investigation, larger better has been selected and shown in Eq. (3.6). ⎧ ⎪0 ) ( ⎪ y−L r d=⎨ ⎪ T −L ⎪1 ⎩

yT

where y is the response output, L is the lower limit of response, T is the target of the response, and r is super index and also termed as the weight factor [47]. The ideal condition of single desirability (d) for every response is unity. In this condition, the desirability of composites is also 1. The desirability function in this work can be estimated from Eq. (3.7). √ (3.7) D = 3 d1 (flexural strength (x)) where D defines the desirability of composites, x is a vector of designed factor (actual coded units), and d1 is the single desirability function corresponds to the

82 80 78 76 74 15

13

11

B: Al–SiC (wt%)

9

7

5 5

7

9

11

13

15

A: SNCF (wt%) 75.0984

Flexural strength (MPa)

(a) 88 86 84 82 80 15

13

11

B: Al–SiC (wt%)

9

7

5 5

7

9

11

13

15

A: SNCF (wt%) 81.*6296

82 80 78 76 74 120 110

100

90

80

C: Sonication time (min) 82.6696

70

60 5

7

9

11

13

15

A: SNCF (wt%)

90 88 86 84 82 80 120 110

100

90

80

C: Sonication time (min) 89.856

70

60 5

7

9

11

13

15

A: SNCF (wt%)

(d) Flexural strength (MPa)

(c) Flexural strength (MPa)

84

(b)

90

98 96 94 92 90 88 15

13

11

B: Al–SiC (wt%)

9

7

5

5

7

9

11

13

15

A: SNCF (wt%) 88.1608

(e)

Flexural strength (MPa)

84

Flexural strength (MPa)

Flexural strength (MPa)

3.3 Results and Discussion

98 96 94 92 90 88 120 110

100

90

80

C: Sonication time (min)

70

60 5

7

9

11

13

15

A: SNCF (wt%)

97.0424

(f)

Figure 3.3 3D surface graph of flexural strength of SNCF/Al–SiC vinyl ester hybrid nanocomposites (a) SRS-AB, (b) SRS-AC, (c) SST-AB, (d) SST-AC, (e) SAT-AB, and (f ) SAT-AC.

response (flexural strength). The unique desirability functions of each response output and desirability functions of composites estimated from Design Expert 9.0 statistical analysis software by selecting the weight factor as 0.5. The optimum condition of the vinyl ester hybrid nanocomposites was found to be SNCF, Al–SiC and sonication time as 5 wt%, 5 wt%, and 120 minutes. respectively under the desirability of 0.924. Furthermore, the levels of factors at the optimized condition, RSM, experimental design, and desirability functions depict desirable flexural strength as shown in Table 3.4. Therefore, results signify that the desirability of composites (0.924) is close to 1. It signifies that settings are suitable to obtain satisfactory results for response output. Furthermore, the single desirability settings are highly effective for maximizing the flexural strength of vinyl ester hybrid nanocomposites. After the optimization process, a confirmation experiment was conducted under

53

54

3 Mechanical and Physical Test of Hybrid Fiber Composites

Table 3.4 Results of confirmation experiment for optimal case. Optimal values SNCF: 5 wt% Al–SiC: 5 wt% Sonication time: 120 min

Optimal variables Prediction SST

Desirability

0.924

Flexural strength (MPa)

89.25

SAT

SRS

96.39

82.11

Confirmation experiment Flexural strength (MPa)

91.25 ± 1.25% 99.21 ± 1.36% 84.75 ± 1.55%

optimum conditions for three different types of vinyl ester hybrid nanocomposites. The flexural strength achieved from confirmation experiments is nearly correlated with optimized data obtained from RSM as shown in Table 3.4. 3.3.3

FTIR and XRD Curves

Figure 3.4a shows the FTIR spectra for both pure vinyl ester and SNCF/Al–SiC vinyl ester hybrid nanocomposites. The FTIR spectra of neat vinyl ester resin show the appearance of characteristic peaks such as bending –CH3 and –CH2 symmetrical and asymmetrical, Ar–C=C–H stretching, and vinyl ester –CH2 –(O–CH–) ring stretching vibrations [48, 49]. The pure vinyl ester resin FTIR spectra occur in specific peaks of wavelength bands 1550–1635 cm−1 ascribed to N–H bending and C–H oxirane ring, indicating the aromatic behavior of vinyl ester polymer. The various peaks at 1615, 1505, 1025, 1350, and 908 cm−1 relates to stretching aromatic rings (C=C), aromatic ring (C–C), stretching of ether (C–O–C), stretching of aldehyde (C–O), and oxirane ring stretching (C–O) functional groups, respectively [50]. Similar FTIR spectra are also observed for cured vinyl ester resin, which is described from the literature [51, 52]. However, characteristic stretching of vinyl ester resin at various bands 830–815 cm−1 and 1325–1250 cm−1 are not observed in all three SNCF/Al–SiC vinyl ester hybrid nanocomposites, which signify the complete curing. The appearance of carbonyl functional groups is around 1720 cm−1 from vinyl ester resin, and no wavelength is found in vinyl ester hybrid nanocomposites, which states the functionalization of SNCF and Al–SiC nanofillers [38, 53]. The broad wavelength around 3450–3550 cm−1 relates to the hydroxyl group of vibration mode, formed during the curing of vinyl ester nanocomposites, which is also supported by other investigators [38, 53]. The peak corresponding to C=O stretching (1720–1740 cm−1 ) is not found in SST and SAT vinyl ester nanocomposites, which indicates the elimination of lignin, hemicellulose, and pectin contents from the nanocellulose under salt solution and combined treatment process. The FTIR spectra also reveal that there are no unreacted aliphatic polyamine peaks, which explains the introduction of higher content of nanofillers in the polymer matrix. This also provides a potential hindrance to cross-linking density of polymers owing from the smaller aspect

3.3 Results and Discussion

100 90 85 Pure resin

80

SST

75

SAT

70

Transmittance (%)

95

65

SRS 3890 3390 2890 2390 1890 1390

60 390

890

Wavenumber (cm–1)

(a)

Intensity (a.u.)

7000 6000

Pure resin

5000

SST

4000

SAT

3000

SRS

2000 1000 0 0

(b)

10

20 30 40 50 60 Diffraction angle (2θ)(°)

70

80

Figure 3.4 SNCF/Al–SiC vinyl ester hybrid nanocomposites (a) FTIR and (b) XRD curves.

ratio [38, 54]. Furthermore, the examination of the peak about 1620 cm−1 because of the presence of carboxylic content in functional groups at the surface of nanocellulose also existed in all SNCF/Al–SiC vinyl ester nanocomposites, which confirms that loading of SNCF and Al–SiC nanoparticles in the vinyl ester matrix is efficient. Figure 3.4b displays the XRD curves of vinyl ester nanocomposites combined with SNCF (SST or SAT or SRS) and Al–SiC nanoparticles. In the condition of pure vinyl ester resin, curves show a wide peak at 20.5∘ , signifying its amorphous nature. From XRD analysis, all SNCF/Al–SiC vinyl ester hybrid nanocomposites followed a similar trend. After the incorporation of SNCF and Al–SiC nanoparticles in the vinyl ester matrix also shows the same peaks but the increase in intensity occurred [55]. The intensity of wide peak of pure vinyl ester resin goes on reducing, which signifies addition of both SNCF (SST or SAT or SRS) and Al–SiC nanoparticles in the vinyl ester polymer, which shows no structural modification but the production of a new phase of the material. 3.3.4 3.3.4.1

Mechanical Properties Flexural Properties

The flexural stress–strain graph and flexural properties of optimized SST, SAT, and SRS vinyl ester nanocomposites are shown in Figure 3.5a,b, respectively. It displays the impact of fiber surface modification on the properties of materials

55

3 Mechanical and Physical Test of Hybrid Fiber Composites

80 60 40 20 0 0

1 Pure resin

2 Strain (%) SST

3

120.00 100.00 80.00 60.00 40.00 20.00 0.00

Pure resin

4

SAT

SST

SAT

6 5 4 3 2 1 0

Type of composite material

SRS

(a)

SRS

Flexural modulus (GPa)

100 Flexural strength (MPa)

Stress (MPa)

120

(b)

Flexural strength

Flexural modulus

80 60 40 20 0 0

1 Pure resin

2 Strain (%)

3

SST

SAT

140.00 120.00 100.00 80.00 60.00 40.00 20.00 0.00

6 4 2 0 Pure resin

4 SRS

(c)

8

(d)

Compression modulus (GPa)

100

Compression strength (MPa)

Stress (MPa)

120

SRS

SST

SAT

Type of composite material Compression strength Compression modulus

Tensile strength (MPa)

40 30 20 10 0 0

1 Pure resin

(e)

2 3 Strain (%) SST

4 SAT

140.00 120.00 100.00 80.00 60.00 40.00 20.00 0.00

6 5 4 3 2 1 0

Tensile modulus (GPa)

50 Stress (MPa)

56

Pure SRS SST SAT resin Type of composite material

5 SRS

(f)

Tensile strength

Tensile modulus

Figure 3.5 SNCF/Al–SiC vinyl ester hybrid nanocomposites: (a) stress–strain flexural, (b) flexural properties, (c) stress–strain compression, (d) compression properties, (e) stress–strain tensile, and (f ) tensile properties.

obtained from the three-point bend test. This also reveals that addition of SNCF (SST or SAT or SRS) and Al–SiC nanoparticles in the vinyl ester polymer under optimum condition has enhanced the overall flexural properties by 2.97, 3.25, and 2.65 times as compared with pure vinyl ester resin. The effect of SNCF, Al–SiC, and ultrasonication in the improvement of mechanical characteristics for SST, SAT, and SRS vinyl ester nanocomposites were examined from SEM analysis displayed in Figure 3.6. From the SEM analysis, the compatibility and dispersion of both nanofillers within the matrix could be exhibited. From Figure 3.6a(1) depicts the SST vinyl ester composites, which have certain cavities remaining after the SNCF particles are pulled from the polymer matrix. From these cavities, a weaker interfacial bonding within the polymer and nanofillers is found. Hence, both SNCF and Al–SiC could not offer effective transfer of load from the matrix because of agglomeration of both nanofillers (SNCF and Al–SiC). It is also well established that cellulose fibers are hydrophilic in nature, which produces complexities in attaining proper homogenization within the polymeric networks [56]. Both Al–SiC and SNCF particles were

3.3 Results and Discussion

(1)

(2)

10 μm

(3)

10 μm

10 μm

(a) SNCF (1)

(2)

20 nm (b)

(3)

20 nm

20 nm

Al–SiC

Figure 3.6 SNCF/Al–SiC vinyl ester hybrid nanocomposites: (a) fracture (1) SST, (2) SAT, and (3) SRS; and (b) microstructure (1) SST, (2) SAT, and (3) SRS.

mixed and agglomerated, which is also shown in Figure 3.6a(2). In this optimum condition, all the three vinyl ester nanocomposites have certain lower cavities. This reason is attributed to good adhesion, observed at the interface, which is already described in the flexural properties of composites and corresponds to sonication time, which disperses both the nanoparticles in the polymer matrix and leads to stronger bonding (Figure 3.6a(2)). Figure 3.6a(3) displays the fracture surface of the vinyl ester polymer reinforced with SRS fibers and Al–SiC nanoparticles. Probably, the Al–SiC nanoparticles were dispersed homogeneously and employed in the vinyl ester polymer matrix. There is no segregation observed from both nanoparticles in the polymer and a better interaction within the matrix concluded from the image. Finally, it can be examined that addition of Al–SiC nanoparticles restricts separation of SNCF from the polymer matrix. Similar results also were recorded by many researchers [57–59]. 3.3.4.2

Morphological Properties

Transmission electron microscope (TEM) is applied to study the surface morphology of nanofillers in the polymer matrix that controls the characteristics of the nanocomposites [60, 61]. Figure 3.6b illustrates the TEM images of SST, SAT, and SRS vinyl ester hybrid nanocomposites, respectively. The dispersion of SST nanocellulose and Al–SiC nanoparticles in the vinyl ester nanocomposites is uniform, as shown in Figure 3.6b(1). Figure 3.6b(2) showed the perfect and uniform dispersion of SNCF and Al–SiC nanoparticles within the vinyl ester polymer. Noticeably, the uniformly dispersed nanocelluloses and Al–SiC nanoparticles present the larger contact surface area and strong interfacial bonding, which

57

58

3 Mechanical and Physical Test of Hybrid Fiber Composites

enhance the interfacial interaction and flexural strength and modulus of the vinyl ester nanocomposite. During the reinforcement of SRS nanocellulose with vinyl ester hybrid nanocomposites, it mainly consists of dirt particles, poor dispersion, particle agglomeration, and weaker interfacial bonding within the matrix, which leads to the reduction in mechanical properties (Figure 3.6b(3)). 3.3.4.3

Compression Properties

Figure 3.5c,d displays the compression stress–strain curves and compression properties of sugarcane nanocelluloses (SST, SAT, or SRS) and Al–SiC nanoparticle-reinforced vinyl ester hybrid nanocomposites, respectively. All the vinyl ester nanocomposite graphs examined that both SST and SAT laminates exhibited a similar stiffness behavior when compared with SRS. The SRS vinyl ester nanocomposite sample failed more vigorously and noticed a dissimilar failure manner because of the presence of hemicellulose, lignin content, and agglomeration of higher nanoparticles, which leads to propagation of microcracks on the surface [55]. The overall compression properties of vinyl ester hybrid nanocomposites fabricated from SST and SAT improved by 7.57% and 19.02%, respectively, as compared with SRS vinyl ester nanocomposites. 3.3.4.4

Tensile Properties

Figure 3.5e,f illustrates the tensile stress–strain graphs and tensile properties (tensile strength and modulus) of SNCF (SST or SAT or SRS)/Al–SiC-reinforced vinyl ester polymer nanocomposites, respectively. The tensile properties such as strength and modulus of vinyl ester hybrid nanocomposites reinforced with SNCF and Al–SiC under the optimized condition. The fabricated vinyl ester nanocomposites became tougher and stiffer than neat vinyl ester polymer because of the hard nature of SNCF and Al–SiC nanofillers. From Figure 3.5f, a remarkable increase in the tensile strength and modulus of the vinyl ester nanocomposites is observed when compared with the pure vinyl ester polymer. The reason may be due to the homogeneous dispersion of both nanoparticles (SNCF and Al–SiC) and higher interaction between the SNCF/Al–SiC/matrix [53]. This interaction effect possesses higher transfer of longitudinal load within the nanofiller and polymer matrix. In all SNCF (SAT)/Al–SiC vinyl ester hybrid nanocomposites, the reinforcement influenced by SNCF, Al–SiC, and sonication time is assignable to the production of the rigid polymeric network composed of hydrogen bonding. A similar trend was also observed for tensile modulus of the SRS and SST vinyl ester nanocomposites. Finally, the SST and SAT vinyl ester hybrid nanocomposites improved the overall tensile properties by 5.89% and 16%, respectively, as compared with SRS. 3.3.5 3.3.5.1

Viscoelastic Properties Storage Modulus

The DMA was applied to measure storage modulus, loss modulus, damping factor, and glass transition temperature. Figure 3.7a displays the deviation of storage modulus as a temperature function for both pure resin and optimum vinyl ester hybrid nanocomposites (SST, SAT, or SRS).

Pure resin SST SAT SRS

0

50

100

150

200

Sample temperature (°C)

tan δ

(a)

5 4 3 2 1 0

Loss modulus (MPa)

Storage modulus (GPa)

3.3 Results and Discussion

(c)

1 0.8 0.6 0.4 0.2 0

250 200 150 100 50 0

(b)

Pure resin SST SAT SRS

0

50

100

150

200

Sample temperature (°C) Pure resin SST SAT SRS

0

100

200

300

Sample temperature (°C)

Figure 3.7 Viscoelastic properties of SNCF/Al–SiC vinyl ester hybrid nanocomposites (a) storage modulus, (b) loss modulus, and (c) damping factor.

From the plot, it is observed that vinyl ester composites exhibit lower storage modulus because of the lesser degree of stiffness provided by the vinyl ester polymer [56]. This reason may be assigned to higher stiffness nature of both SNCF and Al–SiC nanoparticles, which effectively restricted the motion of polymer networks because of the effect of uniform dispersion of particles within the matrix. Among these three types, the SAT vinyl ester nanocomposites have larger storage modulus when compared with SST and SRS vinyl ester nanocomposites, which are exhibited in Figure 3.7a. Simultaneous improvement of storage modulus is assigned to uniform dispersion, with the effect of alkali-treated fibers in vinyl ester hybrid nanocomposites. It may ultimately enhance the hydrogen bonding between SNCFs, Al–SiC, and polar regions of vinyl ester polymer [56]. However, in SRS vinyl ester hybrid nanocomposites, accumulation of both nanoparticles and formation of higher voids in the polymeric chain with the molecular movement are observed, which tends to the reduction in storage modulus and glass transition temperature by 11.75% and 7.25%, respectively, when compared with SST and SAT vinyl ester nanocomposites. A similar curve was obtained by other researchers with the incorporation of maximum loading of Al2 O3 nanoparticles to the vinyl ester resin, improving storage modulus [57]. The vinyl ester resin modified with MWCNTs and Al2 O3 nanoparticles in poly(styrene-b-butadiene-b-styrene) copolymer also exhibited a similar trend [62]. As an outcome, all the fabricated vinyl ester hybrid nanocomposites finally loses its efficiency as the structural materials and their compounds become more transferable. The examined curves are slightly comparable and are in better agreement with another research investigation, but in the rubbery portion, there is a little modification in the modulus. The synergic improvement in the storage modulus of SST and SAT vinyl ester nanocomposites is due to the optimum concentration of SNCF and Al–SiC, which uniformly dispersed and tended to better interaction between the resin and both nanofillers (SNCF

59

60

3 Mechanical and Physical Test of Hybrid Fiber Composites

and Al–SiC), whereas SRS vinyl ester nanocomposites indicate lower storage modulus, signifying weaker interfacial bonding within the polymer and particles, because of the presence of dirt particles. 3.3.5.2

Loss Modulus

Loss modulus is considered as a viscous output of components and could be determined as loss of energy at deformation and assigned with an internal friction. The DMA plots of loss modulus with the function of temperature and SNCF (SST or SAT or SRS) and Al–SiC-reinforced vinyl ester nanocomposites and pure vinyl ester polymer under 1 Hz frequency are displayed in Figure 3.7b. From the loss modulus curve, it is evident that loss modulus also shows a similar curve to storage modulus. From Figure 3.7b, it is also observed that the peak height of loss modulus of vinyl ester resin is comparably lower and the addition of SST or SAT or SRS fibers in vinyl ester has improved loss modulus value. Remarkably, higher loss modulus and peak height were examined for SAT fibers, highlighting uniform dispersion of nanoparticles, and there is no agglomeration of both SNCF and Al–SiC nanoparticles in the vinyl ester matrix. Similar curves and agreements were also noticed by other investigators [63, 64]. 3.3.5.3

Damping Factor

The damping factor also specifies viscoelastic characteristics of the system, and the height of the peak is correlated with energy dissipation of nanoparticles/polymer matrix [65, 66]. The damping factor (tan 𝛿) of pure vinyl ester resin and SNCF/Al–SiC vinyl ester hybrid nanocomposites versus temperature is plotted in Figure 3.7c. It is apparent that pure vinyl ester polymer has a higher peak value of 0.79, which indicates the larger molecular mobility. However, SNCF (SST or SAT or SRS)/Al–SiC-reinforced vinyl ester nanocomposites display lower damping factor because of the addition of both nanofillers, which increases the viscoelastic properties of the matrix. The decrement in peaks intensity also recommends slowing down of energy with the addition of both SNCF and Al–SiC nanofillers [67]. This effect also signifies that the loss modulus is affected more by the incorporation of both SNCF and Al–SiC when compared with pure vinyl ester [63]. The SRS vinyl ester hybrid nanocomposites exhibit slightly lower damping factor when compared with pure vinyl ester composites, signifying excellent dispersion within the matrix and efficiently inhibiting the polymeric chain movements. The similar outcomes were also recorded with the reinforcement of amino-functionalized MWCNTs and Al2 O3 nanoparticles [68]. 3.3.5.4

Glass Transition Temperature

The glass transition temperature of the SST, SAT, and SRS vinyl ester hybrid nanocomposites is observed from the peak of damping factor [69]. The glass transition temperatures of pure vinyl ester, SST, SAT, and SRS vinyl ester hybrid nanocomposites are 60.05(±1.78%) ∘ C, 140(±2.67%) ∘ C, 151(±1.17%) ∘ C, and 138(±3.16%) ∘ C, respectively. It is proved that vinyl ester has comparably a low value of glass transition temperature than other vinyl ester hybrid nanocomposites. The lower value of pure vinyl ester resin is assigned to a specific, movable, and flexible vinyl ester polymeric network. Hence, the values of vinyl ester

3.3 Results and Discussion

nanocomposites are comparable with other recorded research investigation [63]. The addition of SNCF/Al–SiC nanoparticles to the vinyl ester polymer acts as an obstruction and enhances the heterogeneity of the cross-linked shape. The heterogeneity can be increased by minimizing the voids and restricts the mobility within SNCF/Al–SiC nanocomposites. The noticeable restriction in the movement of the polymeric network completely enhanced the glass transition temperature of vinyl ester hybrid nanocomposites. The achieved results are also verified with other investigators [66, 70]. 3.3.6

Impact Strength

The impact test was conducted for SNCF (SST or SAT or SRS)/Al–SiC vinyl ester nanocomposites and is shown in Figure 3.8. These SST, SAT, and SRS vinyl ester nanocomposites showed more considerable impact strength, which is 4.4, 4.8, and 4.14 times higher than the pure vinyl ester polymer. These results were predicted, when the impact strength is influenced by particle matrix adhesion and usually powerful interfacial adverse influence on impact characteristics. The fracture is mainly ascribed to the production of microcracks in the matrix, followed by failure in fiber. The energy absorbed during impact corresponds to pulling out of the fiber [62]. Generally, the formation of crack takes place in the polymer, which is less resistant than cellulose fibers. From front crack, the bridging fibers freely expanded along the faces of cracks. While comparing with Hook’s law, energy absorbed may be possible at the tip of the crack. Both nanofillers expand along the length of debonding, where expansion is prevented from friction, which depletes extra thermal energy. This effect attributed to the development of shear frictional loads applied during sliding motion. The affluence of SNCF and Al–SiC dispersion in vinyl ester composites and large surface area possible for sliding in specific 2.00

120 100

1.60 1.40

80

1.20 1.00

60

0.80 40

0.60 0.40

20

Vickers hardness (kgf/mm2)

Impact strength (kJ/m2)

1.80

0.20 0.00

Pure resin

SRS SST Type of composite material Impact strength

SAT

0

Vickers hardness

Figure 3.8 Impact strength and Vickers hardness of SNCF/Al–SiC vinyl ester hybrid nanocomposites.

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directions, which is noticed as dynamic energy dissipation [64]. Finally, the SAT vinyl ester nanocomposite had better impact strength when compared with the other two types that improved by 9.09% and 15.86%, respectively. 3.3.7

Vickers Hardness

Vickers hardness of vinyl ester hybrid nanocomposites reinforced with SNCF/ Al–SiC nanoparticles primarily depends on the distribution of particles in the polymer matrix [41, 71]. All vinyl ester nanocomposites have shown enhancement in hardness as compared with the neat vinyl ester polymer. This reason may be assigned to the uniform dispersion of both nanofillers in the matrix and stronger interface adhesion within the matrix and nanofillers (SNCF and Al–SiC) [69, 70]. The Vickers hardness of SST and SAT vinyl ester nanocomposites enhanced by 6.49% and 14.71%, respectively, as compared with SRS nanocomposites (Figure 3.8). 3.3.8

Physical Properties

The density of SNCF/Al–SiC vinyl ester hybrid nanocomposites is shown in Figure 3.9a after the confirmation experiment. It is observed that the density of 2500

Density (kg/m3)

2000 1500 1000 500 0

SRSA

SSTA

SATA

120.00

6

100.00

5

80.00

4

60.00

3

40.00

2

20.00

1

0.00 (b)

Pure resin

Pure resin

SRS

SST

SAT

Water absorption (%)

(a)

Porosity (%)

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0

Type of composite material

Figure 3.9 Physical properties of SNCF/Al–SiC vinyl ester hybrid nanocomposites: (a) density in kg/m3 and (b) porosity and water absorption in %.

References

all the three types of nanocomposites is comparably higher than pure vinyl ester polymer. This may be attributed to a higher density of Al–SiC nanoparticles, which is greater than pure polymer. However, SAT fiber vinyl ester nanocomposites are comparatively lower than the other two types, SST and SRS, by 6.83% and 10.49%, respectively. The reason states that the alkali-treated fiber has lower density with the effect of depolymerization in cellulose fiber. Porosity is one of the essential factors of SST, SAT, and SRS vinyl ester hybrid nanocomposites. However, in the optimized condition, the porosity of SAT vinyl ester hybrid nanocomposites has lower porosity content (Figure 3.9b) than other two types because of the removal of hemicellulose and lignin content from alkaline treatment. The improper impregnation of fibers and agglomeration of Al–SiC nanoparticles were observed in SRS and SST vinyl ester nanocomposites. From the confirmation experiment, both SST and SAT vinyl ester hybrid nanocomposites also have lower water absorption capacity (Figure 3.9b) as compared with SRS because of lower concentration of hemicellulose, lignin, and stronger interfacial bonding within the SNCF/Al–SiC nanoparticles/vinyl ester matrix as observed from the FTIR and XRD analysis.

3.4 Conclusion In the present investigation, chemically treated nanocellulose fiber and Al–SiC nanoparticles are applied as reinforcements to the vinyl ester polymer. The statistical experimental design was performed using RSM under three independent factors: SNCF (2.93–17.07 wt%), Al–SiC (2.93–17.07 wt%), and sonication time (39.55–140.45 min). ANOVA results exhibit that SNCF, Al–SiC, and sonication time have a potential effect on the mechanical properties of vinyl ester nanocomposites. The mechanical properties of SNCF/Al–SiC vinyl ester nanocomposites were optimized and validated with the confirmation experiment to verify the efficiency of the developed polynomial model. The viscoelastic and mechanical properties of SST and SAT vinyl ester nanocomposites are higher when compared with SRS sample. This effect may be attributed to homogeneous dispersion and strong interfacial bonding between both nanofillers (SNCF and Al–SiC nanoparticles) and polymer matrix, which is also clearly observed from SEM and TEM micrographs. Overall, it is concluded that SAT-vinyl ester nanocomposites offer improved mechanical, viscoelastic, and physical properties than neat polymer.

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4 Experimental Investigations in the Drilling of Hybrid Fiber Composites Sathish Kumar Palaniappan 1 , Samir Kumar Pal 1 , Rajasekar Rathanasamy 2 , Gobinath Velu Kaliyannan 2 , and Moganapriya Chinnasamy 2 1 Indian Institute of Technology Kharagpur, Department of Mining Engineering, Kharagpur, West Bengal 721302, India 2 Kongu Engineering College, Department of Mechanical Engineering, Erode, Tamil Nadu 638060, India

4.1 Introduction Drilling is the mainly used postproduction machining process in industry [1, 2]. Because of the inhomogeneous behavior of the materials, anisotropy in nature, numerous scientists have reported many distinct issues encountered in drilling fiber composites to date [2–7]. The main issues are extreme wear in tool and workpiece or quality concern. Among the multiple issues associated with work materials, delamination in drilling fiber composites has been acknowledged by most scientists as one of the main issues, as it rigorously impacts the quality of the hole. It is considered to be a behavior or phenomenon of failure dominated by resin or matrix [8]. Pushout delamination mainly occurred in the base area of workpiece or on hole exit is found to be significant or severe. In general, the thrust obtained or the feed power in the fiber composite drill is observed by nearly all literature researchers as the foremost accountable aspect for delamination. The drilling feed rate used directly affects or controls the thrust force. So far, a number of scientists have created many empirical and analytical models in anticipating the thrust energy for initiating pushout delamination [3, 4, 8–10] in this respect. Hocheng and Dharan’s work [9] initiated this type of mathematical modeling for critical driving force and pushout delamination back in 1990, a fact frequently cited and utilized by several other scholars in subsequent research. The general applications of fiber-reinforced composites has emerged over years and extended in aerospace and military sectors, which result in more costeffective processes. Because of less weight compared to metallic alloys, hybrid fiber composites suggest outstanding and extremely personalized mechanical properties. The components developed using hybrid fiber composites are basically for mechanical assemblies, so obviously drilling plays a major role in the production process of such components and during last stages in order to fix the same. Normally, metallic plates react in a related approach beneath machining loads because of isotropic behavior in nature, but composite plates have localized Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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responses, which lead to defects in internal structure, i.e. delamination due to anisotropic conditions. Delamination is a critical aspect of drilling composites leading to failure, which is not detectable visually and is in need of special inspection process.

4.2 Characteristics of Drilling Hybrid fiber composite drilling is one of the main cutting procedures and a costeffective way to remove large quantities of materials into the cavity. Compared to composite materials and principal functions in contraction components, holes in composites must be made to rive the primary load transport system. The end of the boiler moves through the center composites when it reaches the hole during drilling [11]. The affinity of components to shift away because of stress in machining forces is the main effect in drilling of composite materials. There was little damage such as delamination, edge tearing, to create excellent surface properties of the generated holes and fiber/matrix pullout [12]. There are different techniques for boiling troughs in composite materials, but conventional boiling methods are well developed and often used for the production of troughs [13]. In terms of the form of the hole and decreasing the damage caused by the primary force produced during machining. A research has been conducted by [13], which experimentally and numerically determines the impact of machining factors on tangential strength and torque. The damage caused by tangential force and torque had been perceived to increase significantly as feed rates have increased, but it decreases with the increase of spindle speed.

4.3 Hybrid Fiber Composites As a structural material in different sectors such as the marine, sports, automotive, naval, transportation, aerospace, and aeronautical industries, the importance of hybrid fiber composites has grown [14, 15]. Their elevated weight and rigidity ratio make structural materials desirable. Because of their synergistic effect called the hybrid effect [14], the use of hybrid composites can enhance the achievable fiber reinforcement characteristics. This effect gives the reinforcement fiber the most desirable properties and enhances cost efficiency. For the manufacture of laminates, intraply GSM 200 hybrids containing 70% carbon and 30% glass interwoven had been used together. In such hybrid carbon fibers, the density is reduced and the combination of rigidity and tensile strength contributes to lower costs of glass fiber [16, 17]. The combined impact provides outstanding mechanical characteristics and reduces a designer-specific cost. Despite the fact that the technical properties of hybrid fiber-reinforced composites have been enhanced, processing in such materials is complex and challenging. This is due to heterogeneity, delamination of the surface, fiber pulp, burning, surface ruggedness, failure of the fiber matrix, propagation of the laminar cracks, and breach of fiber [14, 18, 19]. These faults lead to bad assembly tolerance and part refusal.

4.5 Investigation of Hybrid Fiber Composites Drilling

4.4 Machining Limitation on Hybrid Fiber Composite Drilling Hybrid fiber composite drilling causes various damaging conditions such as semicut edges, delamination, fibers, fiber pullouts, and so on. This consequential feature leads to reduced dimensional limits, minimizing composite solidity, and long-term performance deterioration applications [20]. The impact on tangential strength and machining abilities of synthetic fiber composites was determined by processing factors such as speed of the spindle, rate of the feed, and diameter of the tool [21]. The processing parameters such as performance of induced damage, surface quality, and strength of the load carrying have been shown to increase the delamination when the rate of feed and the diameter of the boiler increase. The delamination feature increases during higher thrust force at an elevated rate of feed, and the drill temperature decreases bearing strength, which mainly affects the quality of the resin and the high-temperature-generated region. Processing factors were described through delamination, machine thrust strength, torque, and machined hole surface feature [22]. The obtained results showed that the character of force created in machining generally depended on the tools used. The geometry of drilling instrument for strengthened fiber laminates was assessed in [23]. A case-based assessment of various geometries of the boiling edges and feed rate for the components was evaluated while cutting. The analysis has shown that slow feed rates appear to be appropriate for boiling on the plate because they minimize the pump strength in the axis direction and the risk of induced damage from boiling. Twist and special exercises have not caused any significant change. The superiority of hole surface and consequences were excessively dispersed toward permitting suitable outcomes. Lastly, the unique exercise could be an alternative exercise.

4.5 Investigation of Hybrid Fiber Composites Drilling During drilling, delamination happened at device passage or apparatus exit mostly identified with push power produced on it. The power obtained for a given workpiece and material blend primarily relies on the geometry of drill and working environment. The majority of the research ponders on drilling of crossover fiber-reinforced composites, examining the push power and torque created during the procedure. Additionally, numerous scientists recommended that it is conceivable to acquire increasingly expounded insights about the heap dissemination during drilling with a variety in power examination during apparatus passage. This will be useful for choosing the fitting drills and working conditions for drilling half and half fiber-strengthened composites, ideal displaying of delamination imperfection, cutting power improvement models, geometry of drills, and enhancement of procedure plan. It was discovered during the cutting study conducted on synthetic fiber polymer fabrics that debonding of fiber while cutting is not regular, resulting in product life reduction. At the

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entrance of the drill, the elevated spindle speed, sluggish feed rate, and extremely tiny edge angle decrease the delamination problem. The experiment on a nonwoven composite plate showed that compared to the woven arrangements, the fiber density/concentration was high. The tool fracture happened while working at a greater intensity of rate of feed. Nearly all instruments have been screened for catastrophic failure at the greater pace of feed outcomes. For all combinations, the drilled surface diameter was found lesser [24]. An examination into the drilling properties of glass:jute:sisal fiber-reinforced hybrid composites was performed. Natural fibers were integrated onto synthetic fibers, by utilizing the polymer resin matrix, partly eco-friendly hybrid composites were created. Composite drilling is performed on autofeed drilling equipment, and simultaneously quasi-static strength standards are recorded during drilling and torque. Using scanning electron microscopy, the caused damage was assessed by the profile projector and the drilled surfaces are noted. They suggested from the experimental analysis that lower rate of feed and moderate velocities of spindle were more suitable on behalf of machining hybrid fiber composites as they subsequently decreased the damage caused by drilling [25]. 4.5.1

Condition for Hybrid Composites Drill

Business fiber-reinforced composite materials have clear highlights that drive their assembling conduct. The procedures occupied with drilling composite materials in this manner contrast explicitly during homogeneous resource drilling, for example, metals. Working with viable composites during the drilling procedure has acknowledged countless parameters that can affect the working variables and the harm to the substance. The damage specifically connected with composite drill mostly explores delamination processes because of the primary and most critical reason for segment refusal as an outcome of which the utilization of composite covers for basic applications is confined. Further, drilling-stimulated failures include delaminations such as peeling-up and pushing-out, error in circularity, and the likelihood of occurring small cracks. When drilling on fiber-reinforced composites, delamination provoked by drilling was triggered through wear of drilling tool. The experimental findings indicate that with increasing wear, the critical thrust force is enhanced, which in turn improves the delamination. For reduced feed rate, drilling delamination of worn twist drill is extremely small in contrast to sharp drills and the obtained findings are contracted with industrial results [26]. 4.5.2

Factors Affecting Drilling

The parameters of the info technique, for example, cutting parameters, apparatus geometries, device types, and device parts, demonstrate the effect on the push power, torque, wear of the instrument, delamination, surface unpleasantness, and so forth. It is along these lines basic to choose the right procedure parameters so as to acquire the most noteworthy yield in the drilling technique, for example, the most elevated opening feature, addresses negligible mischief to machined parts and surfaces.

4.5 Investigation of Hybrid Fiber Composites Drilling

4.5.3

Drilling of GF-Reinforced Hybrid Composites

Specifically, drilling on GF-reinforced hybrid composites was examined by different researchers wherever the impact on drilling parameters, for example, device wear, surface unpleasantness, delamination, and cutting powers, was talked about by an enormous number of studies. Mohan et al. [27] investigated GF-reinforced hybrid composite drilling execution. The exploration focused was fundamentally superficially honesty built up inside the GF composite-penetrated opening. Bored surface was assessed on three influencing parameters. Machining was performed at various axle speeds between 90 and 445 rpm with rate of feed as 0.5 mm/rev. Outcome of analysis finishes up the cozy connection between the thickness of the example and the penetrated surface quality. The surface unpleasantness made by drilling a glass fiber incorporated polymer was investigated by Dhiraj Kumar et al. [28]. Drilling was performed with various diverse geometries of drill. Machining of carbide on various drill aspects demonstrated a more grounded surface unpleasantness than other drill pieces, where 0.384–2.227 μm of surface harshness was estimated. Prabhu et al. [29] found GF-reinforced hybrid composites and nano-crossover dirt and CG-reinforced composite machining proficiency. The examination was performed with three separate boring apparatus each of 6 mm breadth (carbide bend drill D5407060, HSS contort drill BS-328, and HSS end plant). Three diverse shaft speeds of 600, 852, and 1260 rpm and 0.045, 0.1 mm/rev rate of feed had been set to the desired test circumstance. By enhancing the machining constraints like 0.1 mm/rev as the rate of feed and 852 rpm as the speed of axle, the perfect working circumstance creating negligible delamination was found. Delamination was less for the carbide instrument when working at a more noteworthy feed rate. Moreover, apparatus wear is likewise brought about by the nearness of nanodirt in the CG-reinforced composite. A crossbreed composite was made utilizing glass fiber for support utilizing two regular strands (sisal and jute). Half and half composite drilling highlights were assessed for various working parameters such as rate of feed, speed of cutting, and instrument breadth. Push power ends up more prominently when the feed rate is expanded and the drill width shifts, where the push power was at crest at the most extreme feed rate, which further lowers the torque speed of the axle. The composite got more delamination just at a greater feed [25]. The machining proficiency of glass fiber-inserted composites was unveiled in the activity performed by El-Sonbaty et al. [30]. Superficially unpleasantness, torque, and push power of the machined composite were found to impact drill size, feed, cutting speed, and fiber content. It was found from the result of the machining execution that the cutting velocity has an unfriendly response to the intensity of the push. Besides rate of feed, speed of axle had negligible outcome on top surface of the composites become unpleasantness, and further ascent in the cutting rate has upgraded the harshness of the surface. Krishnaraj [31] examined the GF-reinforced hybrid composites drilled with drill of Zhirov-point, bend, and multifaceted. To look at their consequence on push, surface harshness, and delamination, factors such as shaft speed and feed rate influenced the drilling. Multifacet drill demonstrated less delamination than

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different drills, which additionally produced superb unpleasantness superficially. Contrasted and other instrument Zhirov dab bored openings at diminished push and demonstrated negligible wear of the instrument. Adam Khan and Senthil Kumar [32] utilized two particular alumina clay instruments to make the glass fiber a strengthened polyester composite. Machining operation was completed by variable velocity and relentless feed rate of the axle. SiC hair-strengthened alumina trimming contraption demonstrated a base device wear compared to TiC/TiN mixed instrument. Verma et al. [33] led the test utilizing obscured advancement strategy to locate the ideal state of drilling on GF-reinforced hybrid composites. Extraction pace of materials and the surface harshness made during machining were assessed under various cutting conditions. Murthy et al. [34] investigated machining on GF-reinforced hybrid composites to decide push quality and torque carbide drilling based on the effect of several machining factors. Based on the investigation structure (design of experiments [DOE]) outcome, it was discovered that the speed of the axle importantly affected the intensity of the push and the torque of the drilling was essentially influenced via drill parameters. Davim and Reis [35] analyzed those factors for analysis of composite drill hurt made of carbon fiber with epoxy upgradation. Utilizing Taguchi explore and on the analysis of variance (ANOVA) assessment, the info parameters were assessed. Mohd Ariffin et al. [36] checked the outcome of drilling hurt in GF-reinforced hybrid composites utilized by Boeing Corporation on flying machine. For machining, two diverse boring tools were utilized. Ali et al. [37] analyzed the machining consequence by drilling and processing on woven overlaid GF-reinforced hybrid composite material. ANOVA assessed the two slicing process parameters to estimate the importance of composite drill and process. Uysal et al. noticed the abatement in apparatus wear when drilling a glass fiber polymer by elevating the feed rate [38]. Ramesh et al. [39] looked into the drilling productivity of noncovered GF-reinforced hybrid composites. Covered solidified carbide drill was utilized in different procedure parameters to penetrate the composite. Taguchi’s strategy and ANOVA procedure assessed the impact of feed rate and machining speed to decide their significance on the factor of push quality, torque, and mischief. With 88.52% and 92.83%, the feed rate fundamentally impacts both the push and torque. Moreover, the cutting velocity on both the push and torque demonstrated an unfavorable response. The effects of axle speed and feed were unimportant in the case of dent feature at the entrance of workpiece’s. Khashaba et al. [40] experimented and examined the machining parameters of epoxy-reinforced woven glass fiber composite. Expanded feed and drill distance across expanded the delamination because the expanded push diminishes the undeformed size of the chip. The penetrated material’s surface unpleasantness improves as the speed of cutting rises. Khashaba and coworkers [22] further unlimited his activity during assessing the contact of prewear of drill on drilling factors with a similar material handling under different exploratory circumstances. Drill prewear has prominently affected the pushed power demonstrating unfavorable consequences for delaminations and harshness of the surface. Dhawan et al. [41] performed spiral drilling system on composite with particular overlays. The example was bored by four sorts of drill point geometries at three unmistakable feed input and speed of the axle. Moreover,

4.5 Investigation of Hybrid Fiber Composites Drilling

discoveries of test were stood out from the result of the procedure of the artificial neural networks (ANNs). Capello [42] explored the importance of rate of feed mainly on delamination result while drilling glass fiber polymer and low feed rates were seen with negligible delamination. Davim and Mata [43] proposed the utilization of polycrystalline precious stone (PCD) and solidified carbide cutting devices for drilling on GF-reinforced hybrid composites. Drilling discoveries demonstrated the PCD slicing instrument’s improved effectiveness with respect to the carbide apparatus. Researchers discovered to facilitate feed rate as a very impacting parameter for cutting on surface harshness, whereas factual and exploratory outcomes depend on cutting pressure. Bhatnagar et al. [44] and Singh and Bhatnagar [45] investigated drilling hurt on a cover with glass fiber support. These investigations reason that the drilling powers were not firmly identified with the mischief brought about by an illustrative point drill. Eight features and Jo-drills were found to be increasingly appropriate for composite drilling, in which decreased torque and push power were indicated from the results. Kishore et al. [46] directed examinations on composites made of GF to look at the corresponding machining parameters affecting the machined composite’s staying elasticity. Constraints such as geometry, speed of axle, and rate of feed were respected on 4 mm distance across drills made of carbide, which were utilized for drill applications. However, 750 rpm machining speed and 15 mm/min as feed pace are the ideal drilling circumstances for more prominent lingering quality. The result likewise says that drill geometry decision is basic to limiting drill hurt. 4.5.4

Survey on NF-Reinforced Hybrid Composites Drilling

Because of the biodegradable property, straightforward accessibility, and upgraded technical qualities, the advancement in characteristic fiber-fortified composites (NFRCs) has been in prominent range over a time of quite a long while. Number of study chips away at NFRCs focused on the mechanical attributes of regular fiber composites and their machining conduct. Babu et al. [47] demonstrated that common fiber composites have been fortified as compelling composites for basic applications. It was not frequently easy to machine these items, so the solidified carbide end factory shaper was utilized in this exploration to penetrate the composite. The examination further contrasts the consequences of the test and similar activities on GF-reinforced composites. The discoveries of machining show the effectiveness of normal composites that is superior to composites from GF-reinforced composites. They additionally extended their business to examine drilling consequence of hemp fiber-reinforced composites [48]. Therefore, as to deliver low delamination and more prominent rigidity, the cutting parameters were assessed utilizing improvement procedures. Higher effect on delamination appeared on the parameter examination feed rate and cutting speed. Naveen et al. [49] analyzed composites through support of sandwich strands, hemp, and glass to decide their conduct in cutting machines. At an independent volume extent, filaments were reinforced by 10, 20, and 30 wt%. On machining, hurt at raised feed rate was found to be more noteworthy. It was additionally seen that during the handling

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of more prominent feed strands, the cutting was uneven. Velumani et al. [50] directed examinations on half and half composites reinforced by sisal fiber in addition to glass fiber to investigate drill effectiveness utilizing several network procedures. Jayabal and Natarajan [51] considered polyester composites fortified by coir fiber to comprehend their assembling conduct. The 6 mm drill breadth and 600 rpm as cutting pace demonstrated negligible impact resting on wear of instrument, torque, and push power when upgrading parameters to discover ideal machining condition. Therefore, to assess their machining highlights, Jayabal and Natarajan [52] further produced half-breed composites with coir and glass fortification on network composed of polyester. A relapse model was made to account the limitation of wear of instrument, power, and torque. On test study, the dominating impact of feed rate was watched. Durão et al. [53] directed a relative report on drilling highlights of glass and sisal fiber-fortified composites toughened with epoxy. The authors secured from the exploratory position that, because of the conspicuous effect in trial factors, geometry of instrument and material, delamination occurs at a more prominent push. Sridharan and Muthukrishnan [54] broke down composite polyester bolstered by untreated and soluble base-treated jute filaments. To assess their drilling highlights, the made composites were penetrated. Test discoveries demonstrated a diminishing in treatment fiber delamination, yet the results of ANOVA demonstrate that negligible effect on delamination occurred because of treatment of fiber. Moreover, the delamination of the two composites improved when the rate of feed was expanded. Yallew et al. [55] led a review of drill on network of polypropylene implanted in woven jute fiber. The consequences of the machining parameters were analyzed for push quality and torque. It was clear from the results that the push power shifted altogether with the drill geometry. Moreover, it has likewise been seen that the ascent in drill breadth builds certainty. The perception of the delamination aspect shows that the composite has additional delamination pushout compared to delamination strip-up because of push intensity. Bajpai and Singh performed drilling on the sisal fiber-fortified polypropylene network with the bend drilling and trepanning instrument made of HSS device material [56]. The authors surveyed green composite especially on push, torque, and drilling harm for the drilling response. Results found that the whole three factors prominently affected machining. Drill geometry, specifically, greatly affected drilling powers and mischief to drilling. Jute strands were utilized as the material for support in an epoxy composite, and they were explored for drilling. The examination demonstrates the hugeness of setting the best drilling circumstance for composite machining. Drill size assumed an unmistakable job in the shirking of delamination factor in exploratory results [57]. Abilash and Sivapragash [58] watched composites upgraded by delamination on bamboo fiber drilling. Improved surface quality gaps were practiced by utilizing lower penetrates and low feed rate to limit delamination. Vinayagamoorthy et al. [59] analyzed the drilling injury and unpleasantness surface of machining sandwich composites. The composite of the sandwich has fortifying of glass, vetiver, and jute in vinyl ester network. By diminishing drilling hurt, common fiber reinforcing improved drilling proficiency.

4.5 Investigation of Hybrid Fiber Composites Drilling

4.5.5

Drilling of CF Reinforced Hybrid Composites

Complex materials made up of carbon fiber-incorporated hybrid composites were utilized in diverse basic usage because of low thickness, higher quality, elevated inflexibility, magnificent strength, brilliant weariness, creep, wear, protection from erosion, low contact coefficient, and astounding dimensional security. The materials are normally machined for resilience alteration purposes and fitting and joining surfaces are produced [60]. For their drilling proficiency, numerous researchers investigated the carbon fiber-incorporated hybrid composites. Through his work, Jia et al. [61] built up the carbon fiber-incorporated hybrid composites machining component focused basically on the system including material expulsion and drilling harm. Hocheng and Tsao [62] looked into the drill effectiveness of carbon fiber-strengthened composite material with a measurement of 10 mm each. The ultrasonic C scan procedure was used to survey the delamination formed during machining operation. Trial discoveries were differentiated toward the beginning of delamination with the hypothetical projections of basic push power. Because of the move in the geometry of the boring tool, each bore demonstrated a variety in the push power. With no delamination, the center drill was worked at a more noteworthy feed rate than other boring tools, where curve drill was at decreased feed rate. It was found to be the base at diminished pushed power for all tried boring tool delamination. By contrasting the exploratory results and the diagnostic model, Lachaud et al. [63] investigated the drill harm carbon/epoxy-incorporated composites. Eneyew and Ramulu did a drilling review on carbon fiber/plastic-incorporated composites [64]. Li et al. [65] screened a modified composite with multiwalled carbon nanotubes (MWCNTs) through drilling. During manufacturing, the composite was recuperated by smaller scale waves to diminish delamination and warmth hurt. The aftereffect of the analysis was contrasted and the composite was strengthened by thermally restored MWCNT. The solidified carbide instrument with 6 mm width, 30× helix edge, 140× point edge, and 0.3 mm etch edge was utilized for drilling. Delamination was altogether decreased and the microwave cooled composite’s interlaminar break durability expanded by more than 66% contrasted with warmth relieved composites. There was additionally a further decrease in drilling temperature to 23 ∘ C. To look at the delamination incited by drilling, Seif et al. [66] led an exploration of polymers made of carbon epoxy. Similarly, delamination on composites was assessed via utilizing shadow-based and further laser-based imaging strategy. Shyha et al. [67] utilized a drill with a width of 1.5 mm created from solidified carbide of differing geometry to bore the carbon fiber cover. The instrument’s life and trust depended intensely on the sort of drill and further torque was impacted by cutting rate and feed. As inward splits, break in lattice, strands, and grid run, the bored gap has most extreme harm. Phadnis et al. [68] examined the importance of push vitality and torque machining factors on carbon fiber-incorporated hybrid composites. Both tentatively and numerically, drilling was completed utilizing limited component (field emission [FE]) model in which the trouble of the drill–workpiece interface was assessed inferable from cinematics. Consequences of the test and model have been found to be significant on the results of machining. At the point when the

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feed rate increments in push power, torque, and delamination damage have been watched, steady reduction is additionally found the other way while expanding the cutting speed. Examination of the FE model expresses that it is conceivable to perform compelling carbon fiber incorporated hybrid composites drilling at decreased feed and more prominent cutting pace. Feito et al. inquired about the impact of drill geometry on carbon fiber-incorporated hybrid composite machining [69]. In a new instrument, push power has no effect on point edge sway; however; at a critical stage, if the instrument wears, it makes them mean. At the point when the point edge rises, variety in delamination was found at both the passage and leave focuses. Wear, point edge, and feed rate from the ANOVA examination result are the parameters that show significance on push while diminishing speed had a unimportant effect. Studies completed on carbon fiber-incorporated hybrid composites drilling by Merino-Pérez et al. [70] found that the composite lattice material demonstrates the most elevated effect for raised torque, raised push, and temperatures during machining. Iliescu et al. [71] surveyed drill factors for the drilling of woven carbon fiber-incorporated hybrid composites (feed rate and device wear). The secured and uncoated activities were utilized to bore. Feed and device wear were found to be unmistakable in affecting the pushed power from the machining result evaluation. Contrasted with the push power, the torque demonstrated insignificant wear sway. Mayuet et al. prepared customary drilling made up of carbide drill reinforced with woven carbon fiber-incorporated hybrid composites [72]. Delamination accomplished the most extreme at the passage and drill end where rate of cutting and feed gets diminished. Karpat et al. [73] investigated that broad texture overlays the carbon fiber-incorporated hybrid composites. Trials were performed among variable geometries of uncoated carbide drills and precious stone-covered carbide drills. On the effect of the feed, most extreme drilling harm was noted compared to speed of cutting. Karnik et al. [74] decided delamination factor in carbon fiber-incorporated hybrid composites, thinking about working parameters such as point edge, feed, and speed. The discoveries demonstrated that the harm to the delamination can be diminished at inferior feed along with point edges. Moreover, delamination on point edge, speed of axle, and feed rate vary and impressively prejudiced by them. The drill highlights of polyetheretherketone (PEEK) composites were given by Mata et al. [75]. Absolutely, response surface methodology (RSM) numerical method was intended toward considering the impact of machining on cutting weight and power. The discoveries of the machining demonstrated the diminished push, an incentive as the network ends up relaxed during the drilling procedure. Besides, in contrast with the PEEK composite, the machining yield of the reinforced PEEK was poor. Schorník et al. [76] and Feito et al. [77] examined carbon fiber-incorporated hybrid composites’ drilling cutting factors and their corresponding importance. Various researchers tended to further study the effect of a few drilling parameters on preparing carbon fiber-incorporated hybrid composites to decide composites’ machinability for diverse applications in mechanical field [78–81].

References

4.6 Conclusion A literature review on experimental investigation of drilling hybrid fiber composites has been submitted. For the composite-style material, the performance of boiling processes was equally investigated for glass, natural, and carbon fiber-reinforced hybrid composites. Based on the literature review, several noteworthy observations have been summed up, which helps to process composite boxing. The traditional drilling process of composites is discovered more convenient and well established in comparison to the other unconventional boiling process in boiling of composites. During composite materials’ machining, the speed of spindle, rate of feed, and geometry of box were originated to have nearly all influences. The level of impact differs however with the proportion and type of strengthening. The parameters are different. New drilling instruments need to be developed, but cemented carbide drills are used mostly in the traditional drilling method. Although several trials have examined the outcome of cutting factors on composite material delamination through boiling operations, only a few have shown how the geometrical feature of hole is exaggerated. During machining at controlled feed rate and speed, quality of the hole can be improved. Given the damage caused by the delamination on composite drilling, feed rate and box geometry of drill parameters were important. The decrease of threshold strength on the drilled holes indicates improved surface quality. Rate of feed, size, and thickness of boil are the major factors that affect boiling polymers’ thrust force. Compared to feed rates, it has been noted from many study projects that increased feed increases thrust strength more prominently in influencing the thrust force. Drilling in optimal boiling conditions can progress the surface irregularity of drilled composites. In the event of irregularity of the surface, the feed rate, geometry of drills, and sampling material is important for improving the surface quality of the hole. Fiber strengthening in polymer composite gives conflict to drilling operation; however, this leads to principal cause for growth in trust and delamination factor. In order to diminish the development delamination harm and driving force strength, hybrid composite materials with strengthening such as glass, natural, and carbon fibers must be present and investigated with respect to the type and quantity of the reinforcement.

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61 Jia, Z., Fu, R., Niu, B. et al. (2016). Novel drill structure for damage reduction

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in drilling CFRP composites. International Journal of Machine Tools and Manufacture 110: 55–65. Hocheng, H. and Tsao, C.C. (2006). Effects of special drill bits on drillinginduced delamination of composite materials. International Journal of Machine Tools and Manufacture 46: 1403–1416. Lachaud, F., Piquet, R., Collombet, F. et al. (2011). Drilling of composite structures. Composite Structures 52: 511–516. Eneyew, E.D. and Ramulu, M. (2014). Experimental study of surface quality and damage when drilling unidirectional CFRP composites. Journal of Materials Research and Technology 3: 354–362. Li, N., Li, Y., Zhou, J. et al. (2015). Drilling delamination and thermal damage of carbon nanotubes/carbon fiber reinforced epoxy composites processed by micro wave curing. International Journal of Machine Tools and Manufacture 97: 11–17. Seif, M.A., Khashaba, U.A., and Oviedo, R. (2007). Measuring delamination in carbon/epoxy composites using a shadow moire laser based imaging technique. Composite Structures 79: 113–118. Shyha, I.S., Aspinwall, D.K., Soo, S. et al. (2009). Drill geometry and operating effects when cutting small diameter holes in CFRP. International Journal of Machine Tools and Manufacture 49: 1008–1014. Phadnis, V.A., Makhdum, F., Roy, A. et al. (2013). Drilling in carbon/epoxy composites: experimental investigations and finite element implementation. Composites Part A Applied Science and Manufacturing 47: 41–51. Feito, N., Díaz-Álvarez, J., Díaz-Álvarez, A. et al. (2014). Experimental analysis of the influence of drill point angle and wear on the drilling of woven CFRPs. Materials 7: 4258–4271. Merino-Pérez, J.L., Royer, R., Merson, E. et al. (2016). Influence of workpiece constituents and cutting speed on the cutting forces developed in the conventional drilling of CFRP composites. Composite Structures 140: 621–629. Iliescu, D., Gehin, D., Gutierrez, M. et al. (2010). Modeling and tool wear in drilling of CFRP. International Journal of Machine Tools and Manufacture 50: 204–213. Mayuet, P., Gallo, A., Portal, A. et al. (2013). Damaged area based study of the break-IN and break-OUT defects in the dry drilling of carbon fiber reinforced plastics (CFRP). Procedia Engineering 63: 743–751. Karpat, Y., Deger, B., and Bahtiyar, O. (2012). Drilling thick fabric woven CFRP laminates with double point angle drills. Journal of Materials Processing Technology 212: 2117–2127. Karnik, S.R., Gaitonde, V.N., Rubio, J.C. et al. (2008). Delamination analysis in high speed drilling of carbon fiber reinforced plastics (CFRP) using artificial neural network model. Materials & Design 29: 1768–1776. Mata, F., Gaitonde, V.N., Karnik, S.R. et al. (2009). Influence of cutting conditions on machinability aspects of PEEK, PEEK CF 30 and PEEK GF 30 composites using PCD tools. Journal of Materials Processing Technology 209: 1980–1987.

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76 Schorník, V., Daˇ na, M., and Zetková, I. (2015). The influence of the cutting

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conditions on the machined surface quality when the CFRP is machined. Procedia Engineering 100: 1270–1276. Feito, N., Diaz-Álvarez, J., López-Puente, J. et al. (2016). Numerical analysis of the influence of tool wear and special cutting geometry when drilling woven CFRPs. Composite Structures 138: 285–294. Krishnaraj, V., Prabukarthi, A., Ramanathan, A. et al. (2012). Optimization of machining parameters at high speed drilling of carbon fiber reinforced plastic (CFRP) laminates. Composites Part B Engineering 43: 1791–1799. Li, M.J., Soo, S.L., Aspinwall, D.K. et al. (2014). Influence of layup configuration and feed rate on surface integrity when drilling carbon fibre reinforced plastic (CFRP) composites. Procedia CIRP 13: 399–404. Heisel, U. and Pfeifroth, T. (2012). Influence of point angle on drill hole quality and machining forces when drilling CFRP. Procedia CIRP 1: 471–476. Henerichs, M., Voß, R., Kuster, F., and Wegener, K. (2015). Machining of carbon fiber reinforced plastics: influence of tool geometry and fiber orientation on the machining forces. CIRP Journal of Manufacturing Science and Technology 9: 136–145.

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5 Fracture Analysis on Silk and Glass Fiber-Reinforced Hybrid Composites Gangaplara Basavarajappa Manjunatha 1 and Kurki Nagaraja Bharath 1,2 1 Visvesvaraya Technological University, GM Institute of Technology, Department of Mechanical Engineering, PB Road, Davanagere 577 006, India 2 Washington State University, Composite Materials and Engineering Centre, Pullman, WA 99164, USA

5.1 Introduction In recent decades, fiber-reinforced polymer composites are getting much attention in structural applications. A hybrid composite is the combination of two or more fibers, in which one type of fiber compensates the lack of properties of the other. The purpose of hybridization is to create a new material that will hold the advantages of its constituents, but not their disadvantages. Because of the fact that a flaw-free material is particularly difficult to be formed and cracks may be created during service, understanding the crack resistance capability is thus necessary. Good toughness and crack stopping ability are mainly important. It has been stated that toughness of a brittle thermosetting polymer such as polyester and epoxy can be improved through natural fiber reinforcement [1, 2]. Fracture mechanics deals with the initiation and propagation of cracks over a solid body. Because of its anisotropy, the nature of crack initiation and propagation in fiber-reinforced plastic (FRP) composites is slightly different as related to conventional isotropic materials [3]. The existence of delamination is a major problem in composite structure to use in high-performance applications. Delamination is the separation of composite layers due to interlaminar shear stresses in-service condition. The initiation and growth of a delamination are directly related to the interlaminar fracture toughness of the composite [4]. The majority of studies on fracture toughness are performed for mode I loading. However, there are situations where the cracks are not normal to maximum principal stress direction. Furthermore, at the microscale level, depending on microstructural details, deviations in crack direction may occur even under mode I loading. Macroscopic crack deflection occurs because of asymmetry in stresses near the crack tip, resulting from multiaxial far field loading or from nonuniformity in mechanical properties near the crack tip. Because mixed mode loading tests are not standardized, several specimens have been developed. The compact tension shear (CTS) geometry is widely used to study mixed mode I/II loading. It is a rectangular specimen with crack and three holes for fixing on each side. This geometry was used to study fracture toughness of materials [5]. Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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The fracture behaviors of materials with short cracks have been evaluated in studies on different composites. Bending failures with short cracks are enormously inconsistent based on descriptions in the current study. However, several materials are fabricated, but cracks are not entirely preventable. The presence of cracks leads to growing and finally fractures of materials take place. Also, a brittle fracture in the material causes catastrophic failures, which may cause serious disasters [6]. Beams are widely used in automobile parts and machine components. Some of their applications contain connecting rod of internal combustion (IC) engine, shafts, axles, and gears. Most of them practice various load condition in their service life, which may initiate a crack and cause crack growth [7]. The goal here is to describe the development and preliminary test results of a single-edge notched bend (SENB) that allows for the determination of mode I (opening) and mixed mode (opening and shearing) fracture properties of polymer composites [8]. The main objective of this work is to show the hybrid benefits in terms of fracture toughness properties by addition of glass fiber with woven silk fiber reinforcement in order to decrease the cost of the hybrid composite system for the structural applications such as aerospace, military, and space settles, etc., by increasing its properties. CTS and SENB composite specimens were prepared as per the ASTM standard in different compositions. Very limited results were found during a literature review of failure analysis with fiber-reinforced composite. This is followed by description of the test procedure and the consistent experimental results. Finally, fracture resulted from a new type of mixed mode specimen are presented.

5.2 Materials and Methods 5.2.1

Materials and Specimen Preparation

Hybrid composite laminates were produced using different fibers such as glass and silk as reinforcements and epoxy matrix as the matrix material. All fibers were supplied by a local third-party supplier. Epoxy resin was supplied by Yuje Enterprises, Malleshwaram, Bangalore. Epoxy resin L12 cured with hardener K6 in the ratio of 10 : 1 was used as a matrix. Hybrid fiber-reinforced polymer composites were fabricated by hand layup technique in hydraulic hot press machine [9, 10]. Silk, commonly branded in the textile industry for its luster and mechanical properties, is produced by cultured silkworms. Silks are produced by members of the class Arachnida (over 30 000 species of spiders) and by several worms of the order Lepidoptera, which includes mites, butterflies, and moths [11]. Glass fiber has a white color and is available as a dry fiber fabric. An E glass of good strength and electrical resistance is used [9]. Unidirectional types of fabrics are used with an alkali (NaOH) treatment. The compositions for testing material and their designations are shown in Tables 5.1 and 5.2. The process of fabrication of laminated board is shown in Figure 5.1.

5.2 Materials and Methods

Table 5.1 Designation for different loading angles of materials for CTS test. Composition Serial numbers

Glass fiber

Silk

Epoxy resin

1

45

15

40

Loading angle (∘ )

Designation

0

J1

2

30

J2

3

60

J3

Table 5.2 Designation for different compositions of materials for SENB test. Composition

Serial numbers

Glass fiber

Silk fiber

Epoxy resin

Designation

1

45

15

40

S1

2

40

20

40

S2

3

50

10

40

S3

(a)

(b)

(c)

(d)

Figure 5.1 Fabrication of laminated composite: (a) cutting jute fabric, (b) mixing of resin with hardener, (c) application of resin through jute layers, and (d) hydraulic hot press machine.

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5.2.2

Compact Tension Shear (CTS) Test

The mode I, mode II, and mixed mode fracture tests were conducted on CTS specimen. The details of the specimen configuration and special fixtures are shown in Figure 5.2. The fixing of the fixture was changed during testing for mode I and mixed mode fracture tests [12]. The specimens were obtained in the in-plane loading. The initial notch depth was 45 mm and the width was 0.25 mm, as shown in Figure 5.3. The experiments were conducted in universal testing machine (UTM). The experimental setup for CTS test is shown in Figure 5.4. The critical stress intensity factor (K IC ) value was calculated from load by equations that have been established on the basis of elastic stress analysis on specimens of the type described in the ASTM D6671 standard [13]. 5.2.3

Single-Edge Notched Bend (SENB)

SENB specimen was prepared based on the ASTM D5045 standard, and the specimen has to be precracked [14]. The standard specimen configuration of the specimen is shown in Figure 5.5. The experiments were conducted in a computerized UTM. The experimental setup of SENB test is shown in Figure 5.6. The specimen was placed in between the two jaws of the testing machine. The precracked specimen was loaded at the center of the specimen with a suitable loading device. Fixture 176.9 5 holes, ∅ 10.5 thro

10.0 59.7

R100

36.0 16.2 27.0 25.3 27.8

5.0

62.5 27.0

20.0

27.0

18.0

60 34.0

168.6 62.0 7.5 13.5 122.0 3 holes, ∅ 15 thro 73.0

28.0

Note: All dimensions are in mm

Figure 5.2 CTS specimen loading fixture [12].

Material : MS Qty.: 2 nos.

5.2 Materials and Methods

Figure 5.3 Standard specimen configuration.

14 54

148 45

18

27

27

18

90

(a)

(b)

(c)

Figure 5.4 Experimental setup for CTS test. (a) 0∘ loading angle, (b) 30∘ loading angle, and (c) 60∘ loading angle.

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5 Fracture Analysis on Silk and Glass Fiber-Reinforced Hybrid Composites

Figure 5.5 Standard specimen configuration.

a

W

4W

B

Figure 5.6 Experimental setup of SENB specimen.

5.3 Results and Discussion Experiments were conducted to describe the fracture toughness in different configurations of the specimen. The tested results are discussed in the following section. 5.3.1

Compact Tension Shear (CTS) Test

The load–deflection curves of hybrid composites for different loading angles are shown in Figure 5.7. It can be seen that the load-carrying capacity of J2 (65 kN) and J3 (68 kN) is greater than that of J1 (45 kN). It means that the strength of Load versus deflection for different loading angles 80 Load (kN)

92

60 J1

40

J2

20 0

J3 0

200

400

600 800 Deflection (mm)

1000

1200

Figure 5.7 Load–deflection comparison of composites for different loading angles.

5.3 Results and Discussion

hybrid composite is high for J2 and J3 loading angle compared to that of J1. It is observed that the J1 material with mode I loading angle can withstand less load because the loading angle is exactly normal to the crack propagation. In-plane loading from mode I to mode II and mixed mode loading on J2 and J3 materials withstand more loads [15]. 5.3.2 Mode I, Mode II, and Mixed Mode Fracture Toughness for Different Loading Angle In this section, results from the fracture tests of CTS specimen are presented for different loading angles as shown in Figure 5.8. The fracture toughness (K IC and K IIC ) is estimated by using geometrical factors or nondimensional stress intensity factors [12]. It is observed that K IC , K IIC , and K eff are maximum for the J3 material as compared to J1 and J2 materials. Fracture toughness increases from 0∘ to 60∘ because the inclined load against crack propagation intern increases crack resistance [16]. It is also observed that the mode I fracture toughness occurs for all the loading angles because crack begins to fracture at the notch tip, as the crack propagates in a path parallel to the notch direction [17]. 5.3.3

Single-Edge Notched Bend (SENB)

Fracture toughness (MPa m1/2)

Experiments were conducted to describe the fracture toughness in configuration of the specimen. The SENB test was conducted for different specimen compositions. Experimental results of failure load for different compositions were recorded as shown in Figures 5.9–5.11. Result shows that the S3 composition gives a maximum load of 1849.67 N with 9.2 displacements as compared to S1 and S2 compositions. Load-withstanding capacity increases with the increase of the percentage of composition of glass fiber in S3 composition [9]. S1 composition shows a minimum load of 1572.78 N with 6.59 mm displacement. This is in agreement with the fact that the increase in the percentage of fiber content with the polymer increases the mechanical properties of the composite material. This is because of the combined effect of fiber stiffness and good interfacial bonding between the fiber and the matrix with increased bending load of the hybrid composite [17]. 4 3.5

3.225

3.355

3 2.5 2 1.5

1.335 1.335

0

KI 0.927

1 0.5

1.575 1.652 0.5

Keff

0 J1

J2 Loading angles (°)

KII

J3

Figure 5.8 Fracture toughness versus different loading angles.

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1730.1 1557.1 1384.0 1211.0

Load (N)

1038.0 865.0 692.0 519.0 346.0 173.0 0.0 0.0

1.0

2.0

3.0 4.0 5.0 6.0 Displacement (mm)

Bending load (N)

1572.78

Max displacement (mm)

6.59

7.0

8.0

9.0

10.0

8.8

9.9

11.0

Figure 5.9 Load–displacement comparison for S1 composition.

2014.0 1812.6 1611.2 1409.8 1208.4 Load (N)

94

1007.0 805.6 604.2 402.8 201.4 0.0 0.0

1.1

2.2

6.6 3.3 4.4 5.5 Displacement (mm)

Bending load (N)

1830.86

Max displacement (mm)

7.48

7.7

Figure 5.10 Load–displacement comparison for S2 composition.

5.3 Results and Discussion

2034.6 1831.2 1627.7 1424.2

Load (N)

1220.8 1017.3 813.9 610.4 406.9 203.5 0.0 0.0

1.0

2.0

6.0 3.0 4.0 5.0 Displacement (mm)

Bending load (N)

1849.67

Max displacement (mm)

9.2

7.0

8.0

9.0

10.0

Figure 5.11 Load–displacement comparison for S3 composition.

5.3.4

Fracture Toughness of SENB Test

Figure 5.12 Fracture toughness versus composition of SENB test.

Fracture toughness (MPa m1/2)

Figure 5.12 shows the fracture toughness data glass/silk-reinforced epoxy hybrid composites. The fracture toughness was observed to improve significantly with the increase in the addition of the reinforcement [18]. S3 composition shows the maximum fracture toughness of 331.5 MPa m1/2 as compared to S1 and S2. It can be evidently observed that the increased toughness of the hybrid polymer composite due to the addition of fiber gives an increase in the measured interlaminar fracture toughness, although the steady-state propagation fracture toughness of the hybrid composite laminates is far greater than the toughness of the corresponding polymer composite. This is due to fiber debonding, fiber bridging, and pullout present in the composites [19]. 340

328.09

330

331.5

320 310 300 290

281.48

280 270 260 250

S1

S2 Composition

S3

95

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5 Fracture Analysis on Silk and Glass Fiber-Reinforced Hybrid Composites

5.4 Conclusion In this study, experimental analyses were performed using CTS specimen under different mixed mode I/II loading and SENB specimens under different compositions. Experimental results for the new specimen under different loading cases and different compositions were also presented. Compact Tension Shear Test (CTS): 1. The material J3 (68 kN) with 60∘ loading angle withstands more load as compared to J1 (45 kN) and J2 (65 kN) at loading conditions 0∘ and 30∘ , respectively. 2. The material J3 has mode I fracture toughness (K IC = 3.325 MPa m1/2 ) and mode II fracture toughness (K IIC = 0.927 MPa m1/2 ). 3. The material J3 has a high effective fracture toughness of about 3.355 MPa m1/2 as compared to J1 and J3. 4. The values of toughness of the glass/silk fiber-reinforced hybrid composites, compared to polymer composites, were enhanced by additional fiber-based toughening mechanisms, i.e. fiber bridging, fiber debonding, and fiber pullout. Single-Edge Notched Bend (SENB): 1. The material S3 composition (1849.67 N) withstands more load as compared to S1 (15722.78 N) and S2 (1830.86 N) compositions, respectively. 2. The material S3 has the highest fracture toughness of 331.5 MPa m1/2 as compared to S1 and S2. 3. Geometry seems to offer acceptable results, and investigations into the fracture characteristics of hybrid composite will continue. The key aspect will be the experimental results to improve a fundamental understanding of the fracture mechanisms. This is particularly true for the mixed mode testing.

References 1 Wong, K.J., Zahi, S., Low, K.O., and Lim, C.C. (2010). Fracture characterisa-

tion of short bamboo fibre reinforced polyester composites. Materials and Design 31: 4147–4154. 2 Harikrishnan, K.R., Deviprasad Varma, P.R., and Shivakumar, E. (2015). Mode I fracture toughness of jute/glass fibre hybrid composite – an experimental and numerical study. International Journal of Engineering Trends and Technology 8: 307–310. 3 Rakshit, D. and Chakraborty, S. (2015). Determination of fracture parameters of FRP composites: a combined experimental and numerical investigation. Journal of Composite Materials 49: 231–241. 4 Bensadoun, F., Verpoest, I., and Van Vuure, A.W. (2015). Interlaminar fracture toughness of flax-epoxy composites. Journal of Reinforced Plastics and Composites 36: 1–16.

References

5 Antunes, F.V., Branco, R., Ferreira, J.A.M., and Borrego, L.P. (2019). Stress

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9

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13

14

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17

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intensity factor solutions for CTS mixed mode specimen. Frattura ed Integrità Strutturale 48: 676–692. Manjunath, G.B., Bharath, K.N., and Ganesh, D.B. ANOVA and response surface methodology for the optimization of fracture toughness parameters on jute fabric-epoxy composites using SENB specimens. Materials Today 4: 11285–11291. Sandhan, S.A. and Kadlag, V.L. (2015). Crack propagation analysis of single edge notch beam. International Journal of Computer Science Trends and Technology 5: 162–173. Wagoner, M.P., Buttlar, W.G., and Paulino, G.H. (2005). Development of a single-edge notched beam test for the study of asphalt concrete. Fracture 217: 1–13. Sathishkumar, T.P., Satheeshkumar, S., and Naveen, J. (2014). Glass fiberreinforced polymer composites – a review. Journal of Reinforced Plastics and Composites 33: 1258–1275. Shivakumar, G., Kudari, P.S., and Prabhuswamy, S.K. (2011). Fracture toughness of glass carbon (0/90)S fiber reinforced polymer composite – an experimental and numerical study. Journal of Minerals and Materials Characterization and Engineering 10: 671–682. Li, G., Li, Y., and Chen, G. (2015). Silk-based biomaterials in biomedical textiles and fiber-based implants. Advanced Healthcare Materials 48: 1134–1151. Shiva Kumar Gouda, P.S., Kodancha, K.G., and Siddaramaiah (2013). Experimental and numerical investigations on fracture behavior of high silica glass/satin textile fiber reinforced hybrid polymer composites. Advanced Materials Letter 11: 827–835. Bian, L.-C. and Kim, K.S. (2004). The minimum plastic zone radius criterion for crack initiation direction applied to surface cracks and through-cracks under mixed mode loading. International Journal of Fatigue 26: 1169–1178. Manjunatha, G.B. and Bharath, K.N. (2018). Investigating the contribution of geometrical parameters and immersion time on fracture toughness of jute fabric composites using statistical techniques. Frattura ed Integrità Strutturale 46: 14–24. Jamali, J., Mohammadzaheri, M., and Sharifi, P. (2016). Polymers and Polymer Composites Mixed Mode Fracture Testing, vol. 16, 73–77. IEEE. Demir, O. and Iric, S. (2016). Investigation of mixed mode – I/II fracture problems – part 1: computational and experimental analyses. Frattura ed Integrità Strutturale 35: 330–339. Bharath, K.N., Pasha, M., and Nizamuddin, B.A. (2015). Characterization of natural fiber (sheep wool)-reinforced polymer-matrix composites at different operating conditions. Journal of Industrial Textiles 45: 1–22. Shivaraja, H.B. and Praveen Kumar, B.S. (2012). Experimental determination and analysis of fracture toughness of MMC. International Journal of Science and Research 3: 87–892. Declan, C., Kinloch, A.J., Ivankovic, A., and Sprenger, S. (2016). Mechanical and fracture performance of carbon fibre reinforced composites with nanoparticle modified matrices. Procedia Structural Integrity 2: 96–103.

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6 Failure Mechanisms of Fiber Composites C˘at˘alin Iulian Pruncu 1,2 and Maria-Luminita Scutaru 3 1 Imperial College London, Department of Mechanical Engineering, Exhibition Road, London SW7 2AZ, UK 2 University of Birmingham, Edgbaston, School of Engineering, Department of Mechanical Engineering, Birmingham B15 2TT, UK 3 Transilvania University of Brasov, Department of Mechanical Engineering, B-dul Eroilor, 29, Bra¸sov 500036, Romania

6.1 Introduction The past decades indicate high usage of natural fibers in polymeric composites because of factors such as natural availability, cost economy, low density compared to synthetic fibers, easy processing, and biodegradability [1]. High-performance composites reinforced with carbon/glass fibers reveal great strength and stiffness, which make them attractive for lightweight applications such as spacecraft, aerostructures, motorsports, and recreational equipment [2]. At present, in the industrialized world, there is pressure from public opinion to reduce activities that can degrade the environment, such as mining or metallurgy activities. It also seeks ways to save the energy as much as possible for production processes because these manufacturing processes have the biggest impact on the environment. In addition, the consumption claimed by freight or passenger transport activities should be reduced as much as possible, and there are numerous research programs that pursue such objectives. These pressures offer enormous opportunities to use the high performance of composite materials because they are stiffer, lighter, more durable, easier to manufacture, and larger than classic materials. They also require less energy than required to be manufactured (e.g. in metallurgy) and can be recycled. Some of these composite materials can be cast in the shape of parts that are desired and can be easily processed. By using these materials, it is possible to produce lighter, smaller, more efficient, and more comfortable cars and devices. When analyzing the indicators that determine the amount of materials needed for domestic consumption in developed countries, it is noted that, although the amount of these consumptions is constantly increasing, the quantities of materials per capita are decreasing. This is mainly because of the replacement of traditional, lighter, more resistant, economical, and recyclable materials. The market trends within the development of these materials show more demand, leading to lower prices of end components. After 50 years of economic Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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development without a destructive conflict, industrialized countries are beginning to see a tendency to maintain stationary industrial consumption and the only component that is developed is household consumption. This will allow a strong penetration of unconventional materials in this area. Although these materials are better, lighter, and cheaper, the large widespread use is still low for individual economic reasons. For example, a manufacturer who has invested in a manufacturing line will not change the line until it is depreciated, which, depending on the industry, can take many years. As the benefits of composites are detectable in the long run, the inertia of using them will have the same order of magnitude over time. For all states, there are some strategic reasons for using composite materials: • Because natural wealth is concentrated in a small number of states, any disruption of economic links with them can lead to supply problems. There is also the danger of monopolistic actions undertaken by these states in order to increase profits. The alternative offered by composite materials may prove decisive in these circumstances. There are two important factors limiting the growth of the sale of any material: (a) Producers’ demand for better performance with less material; (b) Minimizing losses by using appropriate materials. Composite materials meet these requirements, which is why their market is believed to grow soon very fast.

6.2 Industrial Benefits and Applications The different types of composite materials used in the formed product produces for large-scale components some specific qualitative differences. However, the composites have a number of special properties, making their use an advantage for the manufacturer. The research has led to an identification of the main advantages of these materials: Low volumetric mass relative compared to metals; Increased fracture strength; Extremely low expansion coefficient compared to metals; High durability in operation; High capacity for vibration damping; High security in operation (breaking of a fiber does not constitute a breaking point for the piece); • Low-energy consumption in manufacturing and simpler technological processes; • Very high resistance, depending on the type of composite, to the action of the processes caused by the atmospheric agents; • Chemical stability and high resistance to high temperatures. • • • • • •

Of course, a composite material will have some of these benefits, and its choice for an application will be based on the requirements imposed by the design theme.

6.2 Industrial Benefits and Applications Metals Fe, Al, Ni, Cu, Pb, etc. Dense, brittle, strong Co/WC tools Polymers (CH2)n, (CONHH(CH2)6)n Easy to manufacturing, elastic, low density

Kevlar/Al Arall

Ceramic C, Al2O3, SiC, B4C Dense, brittle, strong

Epoxy/carbon Rubber GRP

Rubber Elastomers with extension

Al/SiO2 Glass Inorganic, polymeric, metalic

Polystiren

Figure 6.1 Picture of different possibilities of combining materials to obtain composites. Source: Adapted from Scutaru et al. 2013 [3].

Figure 6.1 shows different combinations of materials that will result in different types of composites. Because of the very different components used and the various methods of production, the classification of these materials is very challenging. The classification can be done by matrix material, type of reinforcement materials, types of phase combinations, application domains, mechanical, physical, or chemical properties, manufacturing methods, etc. In the following, a general classification will be presented [4]. Thus, in general, the following eight large groups can be distinguished: • Macromolecular products modified by block copolymerization, which are polymer blends; • Whiskers or fiber-reinforced products; • Fiber-reinforced metal products, cladding, gas intercourse, etc.; • The materials entering the composite structure are: – Plastic products; – Synthetic, glass, carbon, boron, wood, metal, cellulose fibers; – Metals such as Ni, Co, Al, Cr, Ti, W, Ta, Zr, Mo, etc.; – Cellulose (paper) and wood in the form of plywood, agglomerated slabs. From a manufacturing point of view, we distinguish the following types of composites: • Laminated: – Plastics; – Cushioned; • With fibers: – Reinforced materials

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6 Failure Mechanisms of Fiber Composites

• Honeycomb type: – Made of metal; – Nonmetallic; – Expanded plastic, with hexagonal shaped hollows in a circle between 1.5 and 3.5 mm in diameter. They can have a compressive strength of 350–400 MPa, a density of 20–130 kg/m3 and rigidity 10 times higher than steel; metal–metal oxide systems; • Layered (bimetallic, sandwich type [5]); • Foam type. The main properties studied for these materials were primarily mechanical properties but also physical, technical, chemical, electrical, magnetic, optical, esthetic, and machinability properties. Depending on these properties and in relation to the field of use, the extraction and processing as well as the equipment processes, the measuring equipment and the related control and the qualification of the personnel involved in the design and realization of the material can be separately established. Below are some of the main areas of use of composite materials. Aerospace is currently one of the main beneficiaries of these materials because of the extreme requirements that the materials used must meet. Here, pure carbon, boron, and silicon fibers are used or as epoxy resin matrix reinforcement materials. It is generally used for aircraft structures and spacecraft in the form of composite materials with ceramic or metal matrix. Figure 6.2 depicts the specific location of using hybrid composites in an airplane. Composites made of Ni- and Co-based alloy matrix reinforced with carbide and metal oxides (CTa, CNi, CZr, and Al2 O3 ) are used for vital components that operate in high-temperature turbojet engines and rockets.

Toughened graphite

Graphite

Hybrid

Fiber glass

Figure 6.2 Use of different types of composite materials to build an airplane. Source: Adapted from Scutaru et al. 2013 [3].

6.2 Industrial Benefits and Applications

Foam-type composites, called “syntactic,” have a very low density (400 kg/m3 ) and their future use in the aerospace industry. Composites made of polyester resin, reinforced with glass fibers, carbon fibers, and aramid fibers, especially for sporty craft and light vessels, are used in shipping (see example in Figure 6.3), as they have high rigidity and low weight. The use of these materials has made it possible to increase speed and reduce fuel consumption. Vehicle construction currently uses many components, composite materials, because of the advantages created by low weight, high corrosion resistance, and oxidation. Details of such use are depicted in Figure 6.4. In the electronics field, electrotechnics are increasingly the requirement for the composite materials, especially those containing special plastics, polyamide resins, polycarbonates, polyphenylene sulfide, polyphenylene oxide, silicones, polybutylene terephthalate, etc. In telecommunications, composites are used to insulate high- and low-voltage cables as well as to build cable and antenna suspension structures. Medicine is increasingly using composite materials, both in physicians’ intervention inventory and prosthetics. A good example is the dental implant. Their

Figure 6.3 The outer shell of the yacht is composed of composites. Source: Adapted from Scutaru et al. 2013 [3].

Figure 6.4 The bonnet of the car is made of composite carbon fiber-reinforced composites. Source: Adapted from Scutaru et al. 2013 [3].

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6 Failure Mechanisms of Fiber Composites

Figure 6.5 The distribution of reinforcement particles of materials used in dental techniques.

composite configuration can look as is replicated in Figure 6.5. Polymers for transplants, prostheses, and cardiac implants were created; blood coagulation substances (polyurethanes, silicone rubber, dacron, expanded Teflon, special polyethylene, fluoropolymers, etc.) have also been manufactured. Orthopedics use polysulfuric and glass–aramid–polypropylene glass and epoxy glass composites with good biological adaptability properties. Household consumption was also seen to massively use composite materials in countless applications. However, the problems imposed by the use and manufacture of composite materials are numerous. The difficulty arises from the prediction of the properties of a novel material. There is a need for the determination of some methods and materials to overcome the disadvantages that they pose. There is a wide variety of materials used, with a large variation of characteristic properties and a multitude of combinations involving various mechanical, physical, and chemical effects. Therefore, a number of problems that need to be addressed, in different ways, require a considerable effort. In the following chapters, the main types of matrix and reinforcement materials that may form a composite will be presented and some details of the challenge that these combinations raise are offered.

6.3 Materials for Reinforcing 6.3.1

Composites Reinforced with Continuous Fibers

The introduction of glass fiber in the 1930s and the development of polyester resins soon allowed the emergence of new era in materials engineering through the manufacture of composites in a wide variety of shapes and properties [6–12]. The resistance properties of a composite are generally determined by the reinforcing fibers (see an example in Figure 6.6). These can lead to the development of fibers made of materials with very good properties such as boron, carbon, aramid, and other organic fibers, which are convenient and easy to obtain. After establishing and developing the manufacturing technology of such materials, a wide applicability was identified where the needed of high temperature use or high loads is necessary as most researchers turned their focus on the metal

6.3 Materials for Reinforcing

105

matrix composites (MMCs), ceramic matrix composites (CMCs), and intermetal matrix matrix (BMI). The reinforcing materials for these composites must possess not only high-strength properties but also excellent chemical properties or thermomechanical stability because they have been used up to temperatures of about 1500 ∘ C. Figure 6.6 shows an electron microscope image of parallel cylindrical fibers of a very long length. Below are some types of fibers and whiskers widely used in composite fabrication. Table 6.1 presents the characteristics of several fiber types used to produce high-performance composite materials. 6.3.2

Composites Reinforced with Discontinuous Fibers

Gibson et al. [13] used analytical and experimental efforts to determine the effects of fiber aspect ratio, fiber spacing, and viscoelastic properties of constituent Figure 6.6 Cylindrical fibers incorporated in the matrix. Source: Adapted from Scutaru et al. 2013 [3].

50um

Table 6.1 Characteristics of different fibers used to produce high-performance composite materials.

Material

Diameter (𝛍m)

Glass

Tensile strength R (MPa)

The modulus of elasticity E (MPa)

Density 𝝆 (kg/m3 )

Resistivity R/d

Specific module E/d

4000–6000

87 000

2.500

2 × 1012

3.5 × 1013

Graphite fibers Graphite HT

8

2600

250 000

1.750

1.5

14.2

Graphite

8

2000

360 000

1.920

1

18.7

Boron

100–140–200

3200

420 000

2.600–2.700

1.2

15.8

Borsic

100–140

3000

420 000

2.600–2.700

1.1

15.8

Boron/BC

100–140

3800

420 000

2.600–2.700

1.4

15.8

SiC

100

1500–3000

490 000

3.300

—

14.8

Kevlar 49

12

2700

130 000

1.450

1.9

9

Kevlar 29

12

2700

60 000

1.440

1.9

4.2

Refractory fibers

Organic fibers

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6 Failure Mechanisms of Fiber Composites

materials on the damping and stiffness of aligned discontinuous fiberreinforced polymer matrix composites. Highly aligned discontinuous fiber composites can indicate mechanical properties comparable to those of unidirectional continuous fiber composites [14]. Some study shows the possibility to use the discontinuous fiber-reinforced thermoplastic composites within random-in-plane fiber orientation [15]. The research indicates that inclusion of preimpregnated fibers above the critical aspect ratio yields major advancements [16]. 6.3.3

Composites Reinforced with Fillers

For the high ranking among composite materials, they could offer the highstrength and high-modulus organic fibers and fibrous materials based on them. Without the filler materials, it would be impossible to design the essential load-bearing elements of various structures such as ropes, radioengineering equipment, tires, and reinforced plastic materials [17]. Therefore, the addition of fillers will drastically enhance the mechanical properties of polymer matrix composites [18]. For examples in the biocomposite, the bionanofillers in hybrid polymer composites permit the enhancement of the tensile strength, flexural strength, and hardness [19].

6.4 Resin Type 6.4.1

Epoxy Resins

These resins form the most widespread group in practice, and they are called conventional resins. The defining characteristics of epoxy resins are the viscosity at 25 ∘ C, which varies between 600 and 14 000 cP and the melting point, which varies between 70 and 150 ∘ C. These resins can be obtained by reacting epichlorohydrin with a glycol such as bisphenol A. The reactions between these compounds are shown below: CH3 C

HO

OH

+ 2H2C

CH

CH2

Cl

O

CH3

NaOH Cl

CH2

CH

CH2

O

R

O

CH2

CH

CH2

Cl NaCl

OH

OH

H2C

CH

CH2

O

R

O

CH2

CH

O

HO R

CH2

2HO

R

OH

CH

CH2 O

R

OH

O

O

CH2

CH OH

CH2

O

R

O CH2

OH

6.4 Resin Type

These reactions occur in alkaline media at temperatures below 120 ∘ C. The average degree of polymerization obtained is 20%. If this degree increases, then the viscosity increases, and the solubility decreases. 6.4.2

Formaldehyde Resins

They are obtained by reactions of formaldehyde and phenols. These reactions take place in the presence of basic or acidic catalysts and represent a substitution process. Condensations will depend on their own reaction mechanisms and are derived from the pH of the catalyst and the molar ratio of the two reactants. The resins obtained in a basic medium with a pH greater than eight and with a ratio of formic/phenolic aldehyde of 1.5–3 are called resolute and they are a complex mixture of mono, di, and trimethylolphenols. The formation of methylene and methylene ether bridges (reticulation) is accompanied by internuclear bonds. Condensation in a basic medium will result in derivatives with good stability. If the formaldehyde, aldehyde, and phenols are placed in an acidic environment, we can observe in the phenols the increase of electronic density at the ortho and para positions, favoring the electrophilic attack of the ion + CH2 –OH: OH

OH CH2OH + H+

CH2+ + H2O

OH

OH

OH

CH+OH2

OH

OH

CH2+ +

CH2

+

H2+

CH2

OH

This is followed by the reactions: OH

OH

OH

OH

(–) +

Or

+CH

2

OH

+ H+

Or

(–) CH2OH

The reaction is continued in the presence of catalysts, sulfuric, hydrochloric, and oxalic acid with the formation of methylene bridges and the resin obtained is novacol. 6.4.3

Polyurethane Resins

It is a large class of polymers with many practical applications. These resins are characterized by the high content of urethane-type linkages in the molecule, independent of the structure of the other parts of the chain. The properties of polyurethanes can be modified by choosing the primary substances. The flexibility of the chains, the number of cross-links, and the character of intermolecular actions can be modified, and hence various materials such as synthetic fibers, rigid elastomers, plastics, etc., can be obtained.

107

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6 Failure Mechanisms of Fiber Composites

The polyurethane forming reaction is a synthesis reaction that is carried out by the interaction of diols with diisocyanates, catalyzed reaction of metal salts, bases, or organometallic compounds: n OCN

R NH

–[ CO

n HO

NCO R

NH

CO

R′ O

OH R′

O ]n

In the reaction, an isocyanate-based complex is first formed, which reacts with the diol to give the urethane function. For the synthesis of polyurethanes, it is preferred to polymerize in solution at temperatures above 225 ∘ C to start dissociating them. 6.4.4

Polyester Resins

The reaction leading to the formation of polyesters is carried out at 150–200 ∘ C, in the presence or absence of catalysts, by directly condensing diols with dicarboxylic acids: n HO H[

O

R R

OH + O

CO

n HOOC R

R′

COOR

CO ] n OH + (2n–1) H2O

Nonsaturated polycarboxylic acids (maleic acid and fumaric acid), saturated fatty acids, glycols (ethylene glycol, diethylene glycol, propylene glycol, and butylene glycol), monomers such as methyl styrene and methyl methacrylate, stabilizers or inhibitors such as hydroquinone, quaternary ammonium salts, and hydrazines, catalysts (organic peroxides), accelerators (naphthenates of cobalt, lead, and zinc). There is a particularly large number of polyester resins among which • • • • •

fiber reinforcing resins; resins for translucent plates; thermally resistant resins; chemically resistant resins; resins used in electrotechnical engineering.

Unsaturated polyester resins are highly flammable materials, with flame retardance reducing flammability. If the styrene content of the resin increases, a better water resistance is obtained. 6.4.5

Silicone Resins

Silicones are substances of the structural formula R𝛼 [SiO(4−𝛼)/2 ]4.4n , where 𝛼 has a value between 0 and 4. If 𝛼 = 0, the formula reduces to (SiO)n , which corresponds to an organic polymer. The polymers with the organic base chain are obtained from monomers with substituents that also contain the Si atom. Silicone polymers are characterized by thermal stability, dielectric properties, hydrophobic properties being used in the manufacturing of electrically insulating materials, stectoplasts, and, in general, high-temperature materials. Glass fiber-reinforced silicone resins are recommended where temperature conditions (250–500 ∘ C) and exposure to oxidation are required.

6.5 Interfacial of Composite Structure

6.5 Interfacial of Composite Structure In this section, we will present the importance of the effects occurring at the two-phase separation surface. The region separating two components can generate discontinuities surfaces. In practice, the region of separation is actually a volume, the passage does not occur suddenly, but there is a continuous transition. The importance of studying interface effects has two major reasons: (i) The interface occupies a large area inside the composite (ii) Generally, the enhancer and matrix will form a system that is not in a thermodynamic equilibrium. The interface can be defined as a boundary between two phases between which there are discontinuities regarding certain descriptive parameters of the materials. Among the most important parameters that are of interest are the modulus of elasticity, the thermodynamic parameters as the chemical potential, and the coefficient of thermal expansion, respectively. Discontinuities in chemical potential will cause chemical reactions that will lead to a diffusion area or the formation of a chemical compound at the interface. The discontinuity coefficient of thermal expansion will cause the interface to be in equilibrium only at the temperature at which the composite and the hardener were put together. At other temperatures, that could generate a normal use. There will be a voltage field that requires the formation of the composite around the interface. This addition can produce the stress that occurs in the normal use of the material and causes the composite strength to decrease generally. In the following, we present the reason why the interface becomes important especially in the case of very low diameter reinforcement materials. For example, a cubic meter of composite consists of continuous fibers of diameter d, aligned with one face of the cube. If the number of fibers is N and the cube’s side is a, then the percentage volume of fiber in the composite is: Fiber volume N𝜋d2 a N𝜋d2 = = Total volume 4a3 4a2 and the interface area is: v̂ f =

S = N𝜋da Making the relationship between the two relationships to become: v̂ f

d = 2 S a and if we consider the percentage of fiber v̂ f that represents 25% of the total and the cube considered as sideways have a = 1 then result: v̂ f

1 = (m2 ) d 4d From this relationship, we can state that for a given percentage of fiber, the surface of the interface varies inversely with the diameter of the fibers. If a similar calculation is made for a spherical particle-reinforced composite, the specimen will have 1 m3 in which the N spheres of diameter d will be found. S=

109

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6 Failure Mechanisms of Fiber Composites

In this case, we can write: Particle volume N𝜋d3 = Total volume 6a3 and the interface area: v̂ f =

S = N𝜋d2 Under the same conditions as in the previous case, it follows: 6̂vf a3

1.5 2 = (m ) d d If we compare with the case of particle-reinforced composites, the interface area is inversely proportional to the diameter of the spherical particles and in addition, in this case, the area is larger than the continuous fiber composites. If, for example, the fiber diameter is 10 μm, an interface area of 100 000 m2 , it results in 1 m3 of a continuous fiber composite and 150 000 m2 in 1 m3 of spherical particle composite. It follows that if there are phenomena or chemical reactions at the two-component separation surface. Because of the very large size of the interface, they will be able to significantly influence the behavior of the composite. S=

6.6 Micromechanics The properties of the composite materials depend on the properties of the constituent parts, their distribution, and the quality of fiber bonding. Micromechanics will determine the properties of the composites by considering the properties of the fibers and the matrix. Micromechanical analysis has been widely used to know the properties of polymeric composites. 6.6.1

Mechanical Properties

The use of mechanical models for composite materials was aimed at estimating the strength and hardness of polymeric composites. In order to obtain these estimates, a number of results from the theory of elasticity were used. Elastic constants were determined using simple equations. The longitudinal and transverse elastic moduli were determined with the relations: EL = Ef v̂ f + Em v̂ m and v̂ f v̂ 1 = + m ET Ef Em where Ef , Em are the elastic moduli of the fibers and the matrix, v̂ f , v̂ m are the percentage volumes of the fiber and the matrix, and EL , ET are the longitudinal and transverse elastic moduli, respectively. The indices (L) represent the longitudinal direction and (T) the transverse direction, the two directions defining the coordinate system for the material.

6.6 Micromechanics

The Poisson coefficient and the transverse elastic modulus are given by 𝜈xy = v̂ m vm + v̂ f vf and Gxy =

G m Gf Gf v̂ m + Gm v̂ f

where 𝜈 f , 𝜈 m = The Poisson coefficients corresponding to the fiber and the matrix Gf , Gm = Transverse elasticity modulus for the fiber and the matrix, respectively 𝜈 xy

= Poisson’s coefficient in the plane L–T

Gxy

= Transverse elastic modulus corresponding to the plane L–T

An important development is the Halpin–Tsai equations, which is developed by an interpolation process that allows an approximate representation of the results of more sophisticated studies. The results obtained from the Halpin–Tsai equations are quite accurate for fibers with a fractional volume of less than 0.8. These equations are given by: 1 + 𝜉𝜂 v̂ f P = Pm 1 − 𝜂 v̂ f where Pf

𝜂

=

Pm Pf Pm

−1 +𝜉

P = The property of the composite (E2 , G12 , or 𝜈 23 ) Pf = Fiber property (Ef , Gf , or 𝜈 f ) Pm = Matrix property (Em , Gm , or 𝜈 m ) 𝜉

= Measure of fiber curing, which depends on the fiber geometry, packaging, and loading conditions. For circular fibers, it has been proposed that 𝜉 = 2

6.6.1.1

Coefficients of Thermal Expansion and Heat Transfer Properties

The coefficients of thermal expansion of unidirectional composites can be obtained by the following equations proposed by Schapery [20]: 𝛼f Ef v̂ f + 𝛼m Em v̂ m 𝛼L = EL 𝛼T = 𝛼f v̂ f + (1 + 𝜈m )𝛼m v̂ m where 𝛼 f , 𝛼 m = Coefficients of thermal expansion for the fiber or matrix Longitudinal thermal conductivity can be calculated using the rule of the mixture KL = v̂ f Kf + v̂ m Km where K f , K m are the thermal conductivities of the fiber and the matrix.

111

112

6 Failure Mechanisms of Fiber Composites

The transversal thermal conductivity is given by the Halpin–Tsai equation: 1 + 𝜉𝜂 v̂ f KT = Km 1 − 𝜂 v̂ f where Kf

𝜂=

Km Kf Km

−1 +𝜉

√ a′ 3 log b′ ′ ′ where a , b represent the width and thickness of the fiber, respectively. For circular fibers, a′ /b′ = 1. log 𝜉 =

6.7 Short Overview of Specific Failure Modes The fracture and failure process starts with the void nucleation, followed by growth, matrix debonding, delamination, and fiber breakage [21]. The fracture energy of a model carbon fiber/glass fiber/epoxy resin hybrid composite system can be evaluated as a function of the carbon fiber/glass fiber ratio. There, the fiber-debonded lengths and fiber pullout lengths for the carbon and glass fibers can accurately be measured using a projection microscope technique. It was noticed that the post-debond friction energy provides a major contribution to the fracture energy of the glass fibers. Further, the post-debond sliding mechanism is primarily responsible for the nonlinear behavior of the work of fracture of the hybrid composite [22]. A three-dimensional progressive failure model based on the chain of bundles able to represent the stiffness loss in unidirectional composite materials loaded in the fiber direction was proposed by [23]. See details of model depicted in Figure 6.7. It was noted that the hybridization of selective ply interfaces could affect the location and severity of the failure mechanisms. Details of these mechanisms are depicted in Figure 6.8. A positive hybrid effect was detected when a segregated hybrid was used in which one layer of carbon fiber was sandwiched between two layers of Kevlar. Further, the hybrids with a higher degree of hybridization may show a negative hybrid effect [25]. The state of the art shows that the effect of changing temperature greatly affects the macroscopic fracture mode, microscopic failure behavior, and rupture morphology of the composite along with its mechanical properties [26]. The stiffness of the composites may decrease substantially with increasing temperatures, which increases the absorbed energy and peak deflection causing extensive damage to the specimens [27]. The initial failure strength or strain at the failure of low elongation layers, unidirectional hybrid laminates, and [±𝜃/90]s nonhybrid laminates can be analyzed by applying the statistical approach based on the weakest link model [28].

6.8 Future Perspective

Start PFM simulation Input data: r, E, Em, G, Gm, τ, rm, νf, νf1, νf2, a, b, L, l, (Δu)t, fiber positions, strength distribution, SCF model, post-processing and stiffening options Starting displacement: u1 = 0, u1 = min

u σPA

EPA

L t=t+1

New step t: update u, ε0 No

Yes

Reached end?

Apply Dp,q = 1 to all new broken (p,q) elements Yes

Update kp,q, kp, K, F, εp, Ωp Any Dp,q = 1?

No

Yes in Calculate Lp,q , Dp,q, SCFp,q Update kp,q, kp, K, F, εp, Ωp Calculate σp,q u Any σp,q > σp,q ?

No Output data: σ0, ε0, ρb other Reached end?

No

Yes Stop PFM simulation

Figure 6.7 Progressive failure model flowchart. PFM, progressive failure mode; SCF, stress concentration factors. Source: Guerrero et al. 2018 [23]. Reproduced with permission of Elsevier.

The various failure modes in glass, carbon, and their hybrid composite laminates in epoxy resin under uniaxial tensile loading were examined with acoustic emission (AE) monitoring [29].

6.8 Future Perspective Hybrid composites comprising both brittle and ductile continuous reinforcing fibers exhibit complex failure behavior. To theoretically predict this behavior up to complete failure, a novel analytical approach was introduced. If we consider the fracture mechanics approach, it will be a good opportunity to design better hybrid composites because the fracture zone of influence can be interpreted as the bonding failure between the fibers and the resin. Therefore, it can be concluded that the bigger the failed boundary layer surface, the higher is the ultimate

113

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6 Failure Mechanisms of Fiber Composites

0°/90° delamination

0°/90° delamination

45°/–45° delamination

45°/–45° delamination

(a)

45°/90° delamination

(b)

45°/90° delamination

0°/90° delamination

45°/–45° delamination

45°/–45° delamination

0°/90° delamination

45°/90° delamination 5 mm

(c)

(d)

Figure 6.8 Typical X-ray radiographs of (a) HTS (0/90/45/45)2S, (b) HTS_IMS_A (0/90/45/45)2S, (c) TS_IMS_O (0/90/45/45)2S, and (d) IMS (0/90/45/45)2S compact compression configurations. Source: Tsampas et al. 2015 [24]. Reproduced with permission of Elsevier.

failure strain of the hybrid composite with a given fiber volume fraction. Consequently, it can be postulated that the lower the fiber resin adhesion, the higher is the elongation at break [30]. The potential of use of biodegradable material to form novel hybrid composite will help to overcome nowadays challenges and to offer ecological solutions. The combination of rubber wastes and bagasse fibers appears to offer an appealing alternative for the development of new environmentally friendly structural materials for low-carbon impact engineering applications [31].

6.9 Conclusions The failure of hybrid composite (i.e. laminates or other types) demonstrates that the complexity degradation process is quite vast. For example, the laminates reinforced with unidirectional carbon fibers are characterized by a brittle fracture in the composite layer, while the destruction of the metal layer is caused by the release of energy accumulated in the fibers [32]. Despite the enormous research and its progress maturity of hybrid composite in design, manufacturing, and applications, there are plenty of needs to overcome the requirement to meet the strict requirements of industry 4.0.

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20 Schapery, R.A. (1968). Thermal expansion coefficients of composite materials

based on energy principles. Journal of Composite Materials 2: 380–404. 21 Pruncu, C.I. (2012). A short review of recent research on mechanics of frac-

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hybrid carbon and glass fibre composites. Journal of Materials Science 13 (10): 2197–2204. Guerrero, J.M., Mayugo, J.A., Costa, J., and Turon, A. (2018). A 3D Progressive Failure Model for predicting pseudo-ductility in hybrid unidirectional composite materials under fibre tensile loading. Composites Part A Applied Science and Manufacturing 107: 579–591. Tsampas, S.A., Greenhalgh, E.S., Ankersen, J., and Curtis, P.T. (2015). Compressive failure of hybrid multidirectional fibre-reinforced composites. Composites Part A Applied Science and Manufacturing 71: 40–58. Marom, G., Drukker, E., Weinberg, A., and Banbaji, J. (1986). Impact behaviour of carbon/Kevlar hybrid composites. Composites 17 (2): 150–153. Schmitt-Thomas, K.G., Yang, Z.-G., and Malke, R. (1998). Failure behavior and performance analysis of hybrid-fiber reinforced PAEK composites at high temperature. Composites Science and Technology 58 (9): 1509–1518. Ridzuan, M.J.M., Abdul Majid, M.S., Khasri, A. et al. (2019). Effect of moisture exposure and elevated temperatures on impact response of Pennisetum purpureum/glass-reinforced epoxy (PGRE) hybrid composites. Composites Part B Engineering 160: 84–93. Fukunaga, H., Chou, T.-W., Schulte, K., and Peters, P.W.M. (1984). Probabilistic initial failure strength of hybrid and non-hybrid laminates. Journal of Materials Science 19 (11): 3546–3553. Chelliah, S.K., Kannivel, S.K., and Vellayaraj, A. (2019). Characterization of failure mechanism in glass, carbon and their hybrid composite laminates in epoxy resin by acoustic emission monitoring. Nondestructive Testing and Evaluation 34 (3): 254–266. Rehra, J., Hannemann, B., Schmeer, S. et al. (2019). Approach for an analytical description of the failure evolution of continuous steel and carbon fiber hybrid composites. Advanced Engineering Materials 21 (6): 1800565. Moni Ribeiro Filho, S.L., Oliveira, P.R., Panzera, T.H., and Scarpa, F. (2019). Impact of hybrid composites based on rubber tyres particles and sugarcane bagasse fibres. Composites Part B Engineering 159: 157–164. Ostapiuk, M., Bienia´s, J., Surowska, B. et al. (2014). Experimental investigation on the influence of fibers orientation on the failure of carbon hybrid laminates. Aircraft Engineering and Aerospace Technology 86 (4): 307–311.

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7 Ballistic Behavior of Fiber Composites Ignacio Rubio 1 , Josué Aranda Ruiz 2 , Marcos Rodriguez Millan 1 , José Antonio Loya 2 , and Marta María Moure 3 1 University Carlos III of Madrid, Department of Mechanical Engineering, Avda. de la Universidad 30, Leganés, Madrid 28911, Spain 2 University Carlos III of Madrid, Department of Continuum Mechanics and Structural Analysis, Avda. de la Universidad 30, Leganés, Madrid 28911, Spain 3 University Carlos III of Madrid, Department of Bioengineering and Aerospace Engineering, Avda. de la Universidad 30, Leganés, Madrid 28911, Spain

7.1 Introduction The emergence of fiber composite materials implied a great revolution in the industry because of its low weight, high specific strength, and high stiffness compared to other materials such as metals. Nowadays, the use of these types of materials has a wide extent in sectors such as aerospace industry, automotive industry, or defense. Within the different types of loads to which a structure may be subjected, impact is one of the most important factors and is relevant by its effect. Impact loads are continuously present in the industry, and according to the impact velocity and the projectile mass, they can be classified in low- or high-velocity impacts. For example, a typical low-velocity impact event is usually given when tools are dropped on composite structures during maintenance operations, or when little hits are produced in the structure. This type of impacts are critical because, although external damage is not easily appreciable by visual inspection, internal damages can be produced, weakening the structure and therefore decreasing the stiffness of the material. On the other hand, high-impact events are commonly produced, i.e. during take-off or landing when fragments impact on aircrafts at high velocities, or, for example, in defense sector when small masses impact at high speed against the armor or personal body shields. In the literature, there are some discrepancies to establish the thresholds between low-velocity and high-velocity regime. Cantwell and Morton [1] determined that the maximum value to consider low-velocity impacts is 10 m/s because it is the order of magnitude of velocities typically used in this type of test. However, Abrate [2] increases that limit to 100 m/s. On the contrary, other authors did not differentiate those regimes based on the impact velocities but taking into account induced damage. Liu and Malvern [3] and Joshi and Sun [4] associate high-velocity impact events to the perforation of the target Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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because of the fiber breakage, while delamination and matrix cracking are failure mechanisms typically associated with low-velocity regime. Other researchers [1] consider high-impact velocity when the damage induced to the target is localized in a small area around the impact zone and low-impact velocity when the contact time between the impactor and the target is high because of the wave propagation inside the material. Because of the anisotropy and heterogeneity of composite materials, different failure mechanisms can appear, such as matrix cracking, fiber breakage, or delamination among others. These failure modes can appear individually or simultaneously under impact events, either at high- or low-velocity impact, being each type of failure mechanism more predominant according to the speed regime. Matrix cracking is usually the first failure mode that appears and is one of the most important failure mechanisms because although it does not produce the total breakage of the laminate, it degrades their mechanical properties and induces other failure modes as delamination [5]. The crack is initiated in defects of the interface fiber-matrix which grows and join producing an intralaminar crack transverse to the ply thickness and parallel to the fiber orientation. For this reason, this failure mode is difficult to be observed visually. Delamination is also a critical failure mechanism in laminated fiber-reinforced polymer matrix composites and is one of the key factors differentiating their behavior from that of metallic structures. It is caused by high interlaminar stresses in conjunction with the typically very low through-thickness strength. The phenomenon arises because fibers lying in the plane of a laminate do not provide reinforcement through the thickness, and so the composite relies on the relatively weak matrix to carry loads in that direction. This is compounded by the fact that matrix resins are typically quite brittle [6]. Schoeppner and Abrate [5] mint the concept of significant damage, defined like a damage that is not detectable by visual inspection. On the other hand, when talking about impact analysis, fiber breakage normally occurs as a consequence of the other failure mechanisms. It is produced as a result of cracks propagation and high flexural stress on the back side of the impact area. This is the previous step before the total failure of the laminate, and after this, the penetration and perforation of the impactor occurs. As it was mentioned before, one of the most exposed sectors against impact loads is defense. The use of personal protections has increased in the past decades because of the recent rise in terrorism, civil, and international conflicts because it enables to minimize the morbidity and mortality resulting from ballistic injuries. For all these reasons, it is important to know how fiber composite materials behave under different impact loading conditions in order to optimize the performance of the structure during service life. Continuum efforts are being made to further reduce the shield and helmet weight, actually made of composites, without diminishing the ballistic strength. This chapter focuses on the analysis of ballistic behavior of fiber composites, concretely based on aramid fibers as these are the most used fibers in defense sector for personal body armor development. Failure and damage modes induced to target, through which energy absorption is produced, are analyzed.

7.2 High-Velocity Impact Test

7.2 High-Velocity Impact Test As mentioned above, ballistic impact is a high-impact velocity collision in which a small mass is launched against a target. According to the characteristics of the projectile and the target, penetration or perforation of the target can be produced. At the time of impact, if the kinetic energy of the projectile is lower than the one the material is able to absorb, it may happen that the projectile bounces or penetrates trough the target and becomes embedded in it. Moreover, when impact energy is higher than the energy absorption capacity of the material, the projectile perforates the target with a residual velocity (V r ). On the other hand, when the projectile completely perforates the target, but has zero residual velocity, that impact velocity is denoted as ballistic limit (V bal ). Abrate [7] and Kumar [8] define the ballistic limit as the minimum impact velocity at which complete penetration occurs. Another important concept related to ballistic terminology is V 50 , which defines the impact velocity at which 50% of the projectiles completely penetrate the target while the other 50% do not. The ballistic design should not be limited only to the condition of penetration; back-face displacement (BFD) is also an important concept to analyze. Even if the projectile does not perforate the target, the elements that are in direct contact with the rear part of the impact area receive an amount of energy as a consequence of the displacement because of the absorption energy from the impact. This can produce damage in adjacent elements of the target. 7.2.1

Material

The material used in this study consists of Kevlar fiber-reinforced polymer composites (KFRPC) made of aramid fibers with plain wave-woven configuration, which are embedded in polyvinyl butyral (PVB) phenolic resin. The fiber volume within the composite is approximately 82%. Two different nominal thicknesses were used in order to analyze its influence on ballistic behavior. Specimens of 7.4 mm thickness (denoted as “thick” plates), which are typically used in personal body armors, such as helmets or shields, and specimens of 3.7 mm thickness (denoted as “thin” plates) were selected. In ballistics, specimens are usually denoted by the areal density, being in this study 8.8 and 4.4 kg/m2 for thick and thin plates, respectively (see Figure 7.1). The plates were molded using manual stacking and thermoforming manufacturing process. In this way, low-resin content is achieved in the composite. 7.2.2

Experimental Setup

Impact tests were conducted using a pneumatic 7.62 mm caliber gas gun barrel to impulse the projectiles. The working fluid responsible for the projectile impulse is stored in a pressure tank. By opening a valve, gas is delivered through cannon for firing. This valve must have a fast response in order to deliver a uniform pressure. The actuation of the valve is carried out electrically by means of a control panel, in which the necessary pressure is selected to reach the required velocity and the

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pareal = 8.8 and 4.4 kg/m2 Plain wave woven aramid/PVB Resin volume ≅ 18%

Figure 7.1 Composite material used in experimental test. High-speed camera Highlight focus

Projectile

Gas chamber

Pneumatic launch system

Target plate Control panel

Fastening system

Figure 7.2 Complete experimental setup.

shot is carried out. Also, it is necessary to generate a calibration curve based on experience, which reflects the impact velocity (velocity measured at the exit of the cannon) as a function of the pressure delivered by the valve. The gas employed for shooting was argon with CO2 for low pressures and Helium for higher pressures. The projectiles used in this work are 0.22 fragment simulating projectile (FSP) of 1.1 g of mass and 7.5 mm diameter spherical steel projectiles of 1.7 g mass. Projectiles were not mounted directly on the gun; to ensure a good seal and a uniform distribution of pressure in the projectile, a sabot was used. Perforation tests were performed with impact velocities in the range of 350 m/s < V i < 800 m/s. It should be noted that, for all the tests performed, the projectiles did not present plastic strains, damage, or erosion after the impact. This simplifies the analysis because all the impact energy is considered kinetic energy. These projectiles pretend to simulate shrapnel originated in an explosion or shot of high caliber. The fastening system on which the specimens was placed is perpendicular to the projectile path. Specimens were clamped in their perimeter with no sliding effects observed during tests (see Figure 7.2). A Photron FastCam SA-Z digital high-speed camera placed perpendicular to the specimens was used to measure both the impact velocity of the projectile (V i )

7.2 High-Velocity Impact Test

and the residual velocity (V r ) when it perforates the target. The selected frame rate (28 000 frames per second, fps) and the resolution 1024 × 744 pixels were chosen based on earlier tests, allowing a proper focus on the images. In addition, recording with high-speed cameras requires high-intensity illumination. The use of high-speed cameras allows to observe in great detail the sequence of the impact being able to measure the velocities at the same time. Laser sensors are often used to measure velocities. 7.2.3

Analysis and Results

In this section, the analysis of the results is presented. Different impact tests have been carried out for both thicknesses and both projectiles, in order to analyze their influence on the ballistic behavior and failure modes. 7.2.3.1

Ballistic Curves

A comparison in terms of experimental ballistic curves (residual velocity versus impact velocity, V r –V i ) for both thicknesses considered is presented in Figure 7.3. Regarding FSP, the ballistic limit for thin plates is 437 m/s while 696 m/s for thick plates. On the other hand, taking into account steel spheres, the ballistic limit for thin plates and thick plates is 376 and 608 m/s, respectively. It can be observed that for the same thickness but different projectiles, the obtained ballistic limit differs. The shape of the projectile (curved for spheres and sheared for FSP) and its mass have a great influence on the ballistic limit. On the other hand, considering the same kind of projectile, if thickness increases 100%, the ballistic limit does not increase proportionally, something that happens in both types of projectiles. Emphasizing Figure 7.3, it can be observed how all ballistic curves present three clearly differentiated regions. The first region is the nonperforation zone, in which all velocities are below the ballistic limit and therefore, there are not residual velocites. The second region is a critical zone, where the material presents a complex behavior. A sudden change in curve slope can be fostered by huge variations on the residual velocities related to small changes on impact velocities. It is difficult to experimentally determine the behavior in the critical zone because of the great variability of results that occurs in this narrow range of impact velocities, where the material behaves unpredictably. Among the factors that hinder the correct characterization of this critical zone, it can be mentioned that the impossibility of repetition of the exact point of impact and the possible misalignments suffered by the projectile during its trajectory, which means that (in the case of the FSP-type projectile) the impact does not occur completely perpendicular to the fabric. Finally, above this critical zone, the curve grows asymptotically toward residual velocities equal to the impact velocities. Typically, experimental results of ballistic curves could be fitted via the expression proposed by Recht and Ipson [9] as follows: Vr = (Vik − Vblk )1∕k

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ϕ 7.5 mm sphere 1.7 g

500

Residual velocity (m/s)

400

Vi = Vr

100 × 100 mm2

300

200

Critical velocity

100 Thick exp. Thick exp.

0

300

400

(a)

400

700 500 600 Impact velocity (m/s)

800

900

FSP cal. 0.22 1.1 g

500

Residual velocity (m/s)

122

100 × 100 mm2 Vi = Vr

300

200 Critical velocity 100 Thick exp. Thick exp.

0 (b)

300

400

700 500 600 Impact velocity (m/s)

800

900

Figure 7.3 Residual velocity versus impact velocity comparison for different thicknesses and projectiles: (a) spherical steel projectile and (b) FSP projectile.

where V r , V i , and V bl are residual velocities resulting from fitting expression, impact velocity, and ballistic limit, respectively. Also, k is a parameter that depends on the material and projectile shape. For the results analyzed, it has been obtained a value of k = 2.34 and k = 2.62 for thick plates when they are impacted with FSP and spherical projectile, respectively. In the case of

7.2 High-Velocity Impact Test

Fiber’s shear and compressive failure

Delamination

Boundary conditions

Fiber’s tensile failure

Figure 7.4 Different failure modes appearing on impact sequence.

thin plates, values of k = 2.45 and k = 2.50 were found for FSP and spherical projectiles, respectively. 7.2.3.2

Failure Modes

To analyze the different failure mechanisms associated with the ballistic impact during the perforation event, the cross-sectional area of each penetrated plates has been considered and analyzed. Depending on the predominant failure mechanism, the impact event can be divided into different stages. The primary failure mechanism is driven by shear plugging and compression because of the projectile impact on the target surface. As the projectile penetrates, bulge formation on the back face is formed, and delamination is generated between the different layers along the thickness. Finally, the projectile exits through the back face because of the tensile breakage of the rear fibers. Figure 7.4 shows the different failure mechanisms observed during impact event. 7.2.3.3

Back-Face Displacement

The maximum BFD during the impact process is obtained by means of the high-speed camera records. It can be observed that BFD increases with impact velocity up to near the ballistic limit for both projectiles, see Figure 7.5. This is because most of the kinetic energy of the projectiles is transferred to the plate and reflected by means of the failure mechanisms (principally delamination). The maximum BFD occurs at ballistic limit because for this impact velocity, the maximum energy absorption without perforation occurs. However, for impact velocities above the ballistic limit, most of the kinetic energy is associated with more localized failure mechanisms (i.e. compression or shear plugging) and BFD

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Maximum back-face displacement

35 30 Back-face displacement (mm)

124

Sphere exp. FSP exp.

pa = 8.86 kg/m2

25 20 15 10 5 0 400

450

500

550 600 650 700 Impact velocity (m/s)

750

800

850

Figure 7.5 Back-face displacement on thick plates for both FSP and sphere projectiles.

decreases to a constant value. This behavior has also been observed in other materials subjected to similar impact tests [10, 11].

7.3 Computational Methods Understanding the behavior of a material subjected to impact loads is a complex issue because of the influence of many parameters such as the impact velocity, material properties of the projectile and target, boundary conditions, interactions, etc. The resources needed to carry out the experimental tests to study the behavior against impact are not easily accessible, in spite of consuming a great amount of time and reporting a high economic cost. For these reasons, predictive computational tools, based on the finite element method, are commonly used to perform a simulation of experimental tests. This numerical analysis allows to define all the variables involved in the test, such as the geometry of the projectile and the target, its properties, as well as the boundary conditions. The process of contrasting numerical and experimental results is called validation, and it is very important in determining whether the results predicted by the developed numerical model can be regarded as good. In this section, a comparison between experimental and numerical results is presented. The model has been developed in the finite element commercial code Abaqus/Explicit in order to show the potential of the numerical simulation tools in modeling impact problems. The behavior of the material has been implemented by a VUMAT user subroutine.

7.3 Computational Methods

ϕ 7.5 mm sphere 1.7 g

500

Residual velocity (m/s)

400

Vi = Vr

100 × 100 mm2

300

200

Thick exp. Thick num. Thin exp. Thin num.

100

0 300

400

(a)

Residual velocity (m/s)

800

900

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500

400

500 600 700 Impact velocity (m/s)

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300

200

Thick exp. Thick num. Thin exp. Thin num.

100

0 300 (b)

400

500 600 700 Impact velocity (m/s)

800

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Figure 7.6 Residual velocity versus impact velocity comparison between experiments and numerical simulations for (a) spherical steel projectile and (b) FSP projectile.

With the numerical model, the ballistic curve for any impact velocity, and for each projectile and thickness, can be obtained. In Figure 7.6, the comparison between numerical and experimental results is presented, showing faithful correlation between them. On the other hand, the numerical model can accurately reproduce the failure modes that occur along impact event. Figure 7.7 illustrates in a qualitative way

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Figure 7.7 Failure mechanisms produced during ballistic impact test within the finite element model.

Impact sequence

Fiber’s punch and shear

Fiber tensile failure Delamination

that all the failure mechanisms also observed experimentally during the impact process of the spherical projectile against the aramid plate. Attending to the previous results, both the ballistic curves for each projectile and areal densities, and the qualitative representation of failure modes, reproduce the experimental results in a good way. Therefore, the numerical model can be considered validated in the range of the impact velocities analyzed.

7.4 Conclusions Composite materials are subjected, during their service life, to different loading statuses, impact being one of the most critical, both at high and low velocities. This type of impact can be produced by different causes, such as at low velocities, the hit of a tool on the structure, damaging it internally without appreciating any visual defect. On the other hand, high-velocity impacts represent a very critical field in the design of structures. These last can be produced in the aeronautical industry when a small mass impacts the fuselage during flight, take-off or landing of an airplane, or in defense sector, during armed conflicts or terrorist attacks. This chapter focuses on the study of the ballistic response of composite materials (specifically aramid fiber, which is a widely used material in the design and manufacture of personal protections) at high-impact velocities. In order to analyze the ballistic impact behavior of this type of structures, experimental tests have been carried out, consisting of the launching of spherical or FSP-type projectiles by means of a gas gun, in order to observe differences in the behavior of the material. After the analysis of the tests, it has been observed that the projectile with the highest mass propitiates has a lower ballistic limit because of the greater impact energy transferred to the material, generating a greater damage. It has also been noted that several failure mechanisms appear sequentially in the aramid specimens, that is: firstly, the shear plugging and compression are produced because of projectile impact; subsequently, delamination

References

between the different layers along the thickness appears, and finally complete perforation occurs because of tensile breakage of the last layers of the material. At the same time, another important parameter analyzed is the BFD. The evolution of this BFD with the impact velocity is similar for both projectiles, growing up to the velocity of the ballistic limit, where it is maximum, because this point sets the maximum energy that the material is capable of absorbing. Moreover, it was found that delamination is one of the mechanisms that absorb more energy during impact. Finally, a finite element model has been presented, calibrated, and validated as a predictive tool, capable of reliably reproducing the behavior of the composite material against ballistic impact. It has been seen that the model faithfully reproduces both the ballistic curves and the failure modes. It must be highlighted that the validated simulation models are a great alternative because of the time and economic saving for the accomplishment of experimental tests.

References 1 Cantwell, W.J. and Morton, J. (1989). Comparison of the low and high veloc-

ity impact response of CFRP. Composites 20 (6): 545–551. 2 Abrate, S. (1991). Impact on laminated composite materials. Applied

Mechanics Reviews 44 (4): 155–190. 3 Liu, D. and Malvern, L.E. (1987). Matrix cracking in impacted glass/epoxy

plates. Journal of Composite Materials 21 (7): 594–609. 4 Joshi, S.P. and Sun, C.T. (1985). Impact induced fracture in a laminated

composite. Journal of Composite Materials 19 (1): 51–66. 5 Schoeppner, G.A. and Abrate, S. (2000). Delamination threshold loads for low

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velocity impact on composite laminates. Composites Part A Applied Science and Manufacturing 31 (9): 903–915. Wisnom, M.R. (2012). The role of delamination in failure of fibre-reinforced composites. Philosophical Transactions of the Royal Society of London, Series A: Mathematical, Physical and Engineering Sciences 370: 1850–1870. Abrate, S. (ed.) (2011). Impact Engineering of Composite Structures, vol. 526. Springer Science & Business Media. Kumar, S., Gupta, D.S., Singh, I., and Sharma, A. (2010). Behavior of Kevlar/epoxy composite plates under ballistic impact. Journal of Reinforced Plastics and Composites 29 (13): 2048–2064. Recht, R.F. and Ipson, T.W. (1963). Ballistic perforation dynamics. Journal of Applied Mechanics 30 (3): 384–390. Rodríguez-Millán, M., Vaz-Romero, A., Rusinek, A. et al. (2014). Experimental study on the perforation process of 5754-H111 and 6082-T6 aluminium plates subjected to normal impact by conical, hemispherical and blunt projectiles. Experimental Mechanics 54: 729–742. Rodriguez-Millan, M., Garcia-Gonzalez, D., Rusinek, A. et al. (2018). Perforation mechanics of 2024 aluminium protective plates subjected to impact by different nose shapes of projectiles. Thin Walled Structures 123: 1–10.

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8 Mechanical Behavior of Synthetic/Natural Fibers in Hybrid Composites Navasingh Rajesh Jesudoss Hynes 1 , Ramakrishnan Sankaranarayanan 1 , Jegadeesaperumal Senthil Kumar 2 , Sanjay Mavinkere Rangappa 3 , and Suchart Siengchin 3 1 Anna University, Mepco Schlenk Engineering College (Autonomous), Department of Mechanical Engineering, Sivakasi 626005, Tamil Nadu, India 2 Anna University, Mepco Schlenk Engineering College (Autonomous), Department of Electronics & Communication Engineering, Sivakasi 626005, Tamil Nadu, India 3 King Mongkut’s University of Technology, North Bangkok, The Sirindhorn International Thai – German Graduate School of Engineering (TGGS), Department of Mechanical and Process Engineering, 1518 Pracharat 1, Wongsawang Road, Bangsue, Bangkok 10800, Thailand

8.1 Introduction Composite materials receive excellent properties both mechanically and thermally through reinforcements, especially fiber-based reinforcements [1]. For example, synthetic fibers (nylon, carbon, polyamide, aramid, acrylic, etc.) have been used for a long time to enhance the properties of a composite materials [2–4]. These fibers also enhance the morphology and the structure of the composite that are very important in modern applications. However, composite manufacturing industries are facing two major challenges related to fibers in the form of environmental concerns and downward trend of the availability of petroleum products. Synthetic fibers are creating disturbances on environment during the service and afterlife also. The manufacturing of these fibers is also becoming a matter of concern because of the depletion rate of supply of the petroleum from mother earth. These problems enforce manufacturers to find feasible alternative sources for fiber production. The alternative search for fibers is solved by the adaptation of natural fibers of different nature. Natural fibers have been scientifically proven for their multiple advantages. The presence of natural fibers at large scale is the boosting factor for choosing these eco-friendly fibers. The curtailment of weight of the composite is possible through reinforcing the natural fibers of lightweight nature, as most of the natural fibers are lightweight. The cost-effective manufacturing of natural fibers supports the industry financially. The sustainability of these green fibers is well proven. Apart from all, these fibers are easily biodegraded once the service is over as reinforcements inside the composite. These eco- and industry-friendly properties take these fibers to multiple applications. All these qualities and properties made Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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industries to consider the natural fibers in their composite material products [5–8]. Raw materials for manufacturing natural fibers can be derived from various plants, naturally available minerals, extracts of animals, etc. Application-oriented limitations are there for the incorporation of these green fibers in composites. A typical example is the structural field. Moreover, the environment around these fibers deteriorates their qualities and properties [9, 10]. Highly humid condition makes these fibers to biodegrade. The same can be applicable for a high-temperature environment. The variations in the mechanical properties of fiber-distributed structure, poor stability in dimensions, insufficient impact load carrying capacity, etc., are other limiting factors associated with these fibers. All these constraints make synthetic fibers superior than natural fibers as far as the functional performance is concerned [11–13]. However, the complete replacement of natural fibers with synthetic fibers is not advisable as it carries the problem to its initial stage again. Balanced inclusion of both fibers is the appropriate way of handling the issue. Incorporation of both natural and synthetic fibers within a composite enhances the performance of the composite through the inclusion of beneficial aspects of two distinct fibers. This incorporation converts a normal composite into a “hybrid composite,” and the respective process can be termed as “hybridization.” One of the enhancements is the impact performance of the hybrid composite [9, 10, 14, 15]. The current chapter handles such hybrid composites where the mechanical behavior of a combination of synthetic and natural fibers is discussed in detail.

8.2 Impact Strength of Natural Fiber (Flax), Synthetic Fiber (Carbon), and Hybrid (Carbon/Flax) Composites The real potential of hybrid composites can be exhibited through effective comparison of their properties with different composites made of different fiber materials. Here, the analogy is done between hybrid, natural, and synthetic fiber composites. The hybrid composite that is taken for comparison was manufactured through hybridization of woven (W) carbon fibers and unidirectional (UD) flax fibers in epoxy matrix medium [8]. The other two composites that are going to be compared with hybrid composites are synthetic (UD) [16] and natural fiber (UD) composites [17] and are made up of carbon and flax fibers, respectively, in the same epoxy matrix medium. Typical orientation of unidirectional carbon and flax fibers within a hybrid composite structure is shown as a cross-sectional view in Figure 8.1. Flax fibers are chosen to represent natural fibers for their ample qualities. These green fibers are very much compactible for hybridization with synthetic fibers. Few examples are carbon, glass, and aramid. The mechanical properties of these fibers are giving confidence for implementing them in different applications as expressed by Mahboob et al. [18]. Damping properties are exclusive specialty of flax fibers as researched by Safri et al. [14], which are also inexpensive and environment-friendly. Mueller and Krobjilowski reveal that it secures the highest position among natural fibers in terms of impact strength [16, 17, 19]. However,

8.2 Impact Strength of Natural Fiber, Synthetic Fiber, and Hybrid Composites

(a)

(b)

Figure 8.1 Cross-sectional view of orientation of unidirectional carbon (a) and flax (b) fibers within a hybrid composite structure. Source: Dhakal et al. 2013 [12]. Reproduced with permission of Wiley.

the impact strength of these fibers is comparatively low with synthetic fibers. For example, the impact strength of the composite made of flax fibers (natural) possesses the least values of 33.8 kJ/m2 [17]. It indicates the inefficiency of flax fibers in absorbing the quantum of energy before the occurrence of fracture in comparison to the composite made of carbon fibers (synthetic) that possesses the impact strength of 315 kJ/m2 [16]. Huge progress in impact strength can be observed when flax fibers were replaced with carbon fibers in the same epoxy matrix medium. This improvement can be taken further when the combination of carbon (W) and flax (UD) fibers is accommodated with a composite of epoxy matrix. The resultant impact strength was registered with 380.94 kJ/m2 [8], the highest among three distinct composites as represented in Figure 8.2. This analogy proves that the impact strength is a positive output from the hybrid composite in comparison to natural fiber and synthetic fiber composites. In addition, the partial replacement of carbon fibers with flax fibers is not deteriorating the impact strength of the composite. Consequently, the purpose of adding natural fibers is met without compromising the impact resistance of the composite. The major difference is associated with the fiber direction of carbon fibers. Hybrid composite consists of woven carbon fibers, whereas unidirectional fiber construction is in synthetic composite. 400 Impact strength (kJ/m2)

350

380.94

300

315

250 200 150 100 50 33.8

0 Carbon/flax (epoxy) Fiber direction – W/UD

Carbon (epoxy) Fiber direction – UD

Flax (epoxy) Fiber direction – UD

Fiber (matrix)

Figure 8.2 Impact strength of hybrid, synthetic, and natural fiber composites.

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8.3 Kenaf/Aramid (Epoxy) Hybrid Composites with Different Fiber Orientation Hybrid composites are increasing their presence through various applications. The basic research studies accepted their capability, and further analysis on these composites can increase their application spectrum. Here, the influence of fiber orientation on the performance of the hybrid composites in terms of impact strength is analyzed. The combination of kenaf (natural) and aramid (synthetic) fibers is considered for the analogy where epoxy is common matrix medium in hybrid composites. Kenaf fibers as reinforcements are chosen for the analysis, as these can be effective alternatives for the synthetic fibers for partial replacement in composites. Akil et al. [20] analyzed the specific modulus of distinct fiber materials and respective data show the specialty of kenaf fibers over other compared fibers. The specific modulus of these fibers is excellent as shown in Figure 8.3. Several research works confirmed the utilization of kenaf fibers along with synthetic materials as part of hybridization with glass [21–24], carbon [25], and polyethylene terephthalate [26] for producing hybrid composites. In line to these synthetic fibers, aramid is also a potential synthetic fiber applied in hybrid composites. This heat resisting and strong fiber has been preferred widely in defense and aerospace applications. Para-aramid is a commercial form of aramid fiber that is well known as Kevlar fiber. These fibers possess properties such as thermal stability, modulus, toughness, and additional tenacity, which are uniquely combined together as reviewed by Jassal and Ghosh [27]. Kenaf–Kevlar combination of hybrid composites has been widely applied in defense sector [28–30]. To infer the importance of fiber orientation, Yahaya et al. [31] made two hybrid composites with woven (Figure 8.4) and unidirectional kenaf fibers, respectively. The woven aramid fibers were employed to represent the synthetic fibers in both hybrid composites. 60 Specific modulus (E-modulus/density)

132

50 40 30 20 10 0 Kenaf

Hemp

E-glass

Flax

Sisal

Coir

Figure 8.3 Specific modulus (E-modulus/density) of distinct fiber materials. Source: Adapted from Akil et al. 2011 [20].

8.3 Kenaf/Aramid (Epoxy) Hybrid Composites with Different Fiber Orientation

Figure 8.4 Representation of woven kenaf fibers. Source: Palani Kumar et al. 2013 [32]. Reproduced with permission of Springer Nature.

The orientation of natural fibers (kenaf ) only varied to study the influence on the impact strength of hybrid composites. Woven kenaf fiber-employed hybrid composite shows higher impact strength (51.41 kJ/m2 ) [31] than hybrid composites with unidirectional kenaf fibers (41.24 kJ/m2 ) [31] as shown graphically in Figure 8.5. Woven structure performs superior than unidirectional fiber

Impact strength (kJ/m2)

60 50

51.41

40 41.24 30 20 10 0 Kenaf/aramid (epoxy) Fiber direction – W/W

Kenaf/aramid (epoxy) Fiber direction – UD/W Fiber (matrix)

Figure 8.5 Impact strength of kenaf/aramid (epoxy) hybrid composites with different fiber orientations.

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orientation through absorbing a higher amount of energy before fracture failure of hybrid composite.

8.4 Impact Strength of Carbon/Flax (Epoxy) Hybrid Composites with Different Fiber Orientation Carbon fibers are excellent reinforcing agents for manufacturing composites for advanced applications. These crystal-aligned fibers are known for their excellent properties. Specific tensile strength of carbon fibers exhibits their superiority. These carbon atom-bonded fibers show high resistance against wear. High modulus is an added advantage for these fibers. All these qualities have been well recognized by aerospace industries, automotive sectors, sporting industries, etc. [33–40]. On the other hand, flax fibers or technical fibers also preferred for different applications for their positives. These bundled natural fibers could be easy to handle and low-density nature aids for utilization as reviewed by Ramesh [41]. Bos et al. reveal that flax fibers are one among the strongest fibers present in the plant fiber categories [42]. Saheb and Jog reviewed the properties of flax fiber and explained that the density of these fibers is inferior to glass fibers. However, flax fiber’s strength could be competent with glass fibers [43]. Al-Hajaj et al. [8] took carbon fibers (synthetic fibers) and flax fibers (natural fibers) for hybridization to produce hybrid composite. The point of focus for the analysis is the influence of orientation of flax fibers on the impact strength of the hybrid composite. One combination of hybrid composite was made with woven carbon fibers and unidirectional flax fibers in epoxy matrix medium. Another combination was with woven carbon fibers and cross ply (CP) flax fibers in epoxy matrix medium. Typical orientation of cross ply flax fibers within a hybrid composite structure is shown as a cross-sectional view in Figure 8.6. The resultant impact strength of these two different combinations reveals the importance of the placement of the flax fibers in hybrid composites. Cross ply flax Figure 8.6 Cross-sectional view of orientation of cross ply flax fibers within a hybrid composite structure. Source: Dhakal et al. 2013 [12]. Reproduced with permission of Elsevier.

8.5 Comparison of Absorbed Impact Energy of Different Hybrid Composites

Impact strength (kJ/m2)

600 500

507.15

400 380.94 300 200 100 0 Carbon/flax (epoxy) Fiber direction – W/UD

Carbon/flax (epoxy) Fiber direction – W/CP

Fiber (matrix)

Figure 8.7 Impact strength of carbon/flax (epoxy) hybrid composites with different fiber orientations.

fiber-employed hybrid composite shows higher impact strength (507.15 kJ/m2 ) [31] than hybrid composites with unidirectional flax fibers (380.94 kJ/m2 ) [31] as shown graphically in Figure 8.7. Here, flax fibers with cross ply orientation possess more impact strength than flax fibers with unidirectional orientation.

8.5 Comparison of Absorbed Impact Energy of Different Hybrid Composites Hybrid composites with carbon and flax fiber combination are known for their extraordinary mechanical performance because of carbon fiber content and excellent dynamic properties because of flax fiber content as evaluated by Assarar et al. [44]. Carbon fibers play a significant role compared to flax fibers within a hybrid composite in taking load at a tensile-loaded condition [16]. In other side, flax fibers hold the highest impact strength in comparison with other contemporary natural fibers [16, 17, 19]. One of three hybrid composites taken for comparison is carbon–flax hybrid composite in epoxy matrix medium for analyzing the absorbed impact energy. Here, carbon as well as flax fibers are placed in multiple directions (MD). The second combination is basalt–carbon hybrid composite in the same epoxy matrix medium. Here, basalt and carbon fibers are placed in woven condition in the matrix. A type of alumina silicate material forms the base for basalt fibers that are found in filament form normally as researched by Wang et al. [45]. Heat-related properties are exclusive of these fibers, as high-temperature environment could not disturb their nature. Moreover, a wide range of temperatures for these fibers is provided for working in different temperature conditions. Basalt fibers are toxic free in nature, nonpolluting, and noncombustible [46–48]. The abundance of basalt material is adding commercial advantage to these fibers. Typical basalt fibers are represented in Figure 8.8.

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8 Mechanical Behavior of Synthetic/Natural Fibers in Hybrid Composites

Figure 8.8 Representation of basalt fibers. Source: Wang et al. 2019 [49]. Reproduced with permission of Elsevier.

30 Absorbed impact energy (J)

136

25

26.68 24.26

20

21.84

15 10 5 0 Carbon/flax (epoxy) Basalt/Carbon (epoxy) Basalt/flax (vinyl ester) Fiber direction – MD/MD Fiber direction – W/W Fiber direction – UD/CP Fiber (matrix)

Figure 8.9 Comparison of absorbed impact energy of different hybrid composites.

Basalt fiber-reinforced epoxy matrix composite has shown superior mechanical properties than glass fiber reinforcement as revealed by Kim et al. [50]. The third combination is basalt–flax hybrid composite in the vinyl ester matrix medium. Here, basalt and flax fibers were given unidirectional and cross ply orientation, respectively, within the vinyl ester matrix. All the three combinations of hybrid composite are brought under impact test, out of which, the carbon/flax (epoxy) hybrid composite absorbed the highest impact energy (26.68 J) [51] followed by basalt/flax (vinyl ester) hybrid composite with an absorbed impact energy of 24.26 J [52]. Basalt/carbon (epoxy) hybrid composite registers the least absorption of impact energy (21.84 J) [53] among compared hybrid composites as shown in Figure 8.9.

8.6 Comparison of Strength of Natural Fiber, Synthetic Fiber, and Hybrid Composites

8.6 Comparison of Strength of Natural Fiber (Ramie), Synthetic Fiber (Glass), and Hybrid (Ramie/Glass) Composites Ramie fibers are upcoming materials to represent the natural fibers. These fibers have the potential to play the effective role as reinforcements in composites. The successful implementation of ramie fibers in thermoset as well as thermoplastics is the best example to take forward these fibers for wide applications. Typical ramie fibers are represented in Figure 8.10. These eco-friendly fibers share similarity with other natural fibers as far as easy availability is concerned. Persistence (tenacity) is one of the exclusive properties of ramie fibers. These inputs project ramie fiber material as an excellent contender for high load applications including tensile load. The extension of fibers during breaking in wet and dry conditions exhibits the uniqueness of this natural material. Ramie fibers have been well recognized in spite of limited research studies on these green fibers as disclosed by Giridharan [54]. Paiva Junior et al. [55] researched and revealed that these fibers are very much compactible to resin matrix composites. It is evidently proved by Hendra [56] that strength in terms of impact, tensile, and flexural is improved with the increased presence of ramie fibers. Huge research space is present to involve ramie fiber for producing hybrid composite either with synthetic or natural fibers as stated by Jawaid and Abdul Khalil [57]. Typically, Giridharan [54] has experimented ramie fibers as reinforcements along with E-glass fibers in epoxy matrix to produce hybrid composites with natural and synthetic fiber combination and also compared the hybrid composite with composites made with ramie and E-glass fibers in the same epoxy matrix medium. Typical E-glass fibers are represented in Figure 8.11. To evaluate mechanical properties, Giridharan [54] has produced and compared three combinations of composites. One of the combination comprises of 20 wt% fraction of ramie fibers in epoxy matrix medium, whereas 20 wt% fraction of E-glass fibers is another combination. Ramie and E-glass fibers put together Figure 8.10 Representation of ramie fibers. Source: Giridharan 2019 [54]. Reproduced with permission of Elsevier.

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Figure 8.11 Representation of E-glass fibers. Source: Giridharan 2019 [54]. Reproduced with permission of Elsevier.

with 20 wt% fraction forms the third combination (hybrid composite). Here, the common platform is epoxy matrix medium. Similarly, another set of hybrid composites have been produced by Giridharan [54] with 30 wt% (10% ramie fibers and 20% E-glass fibers) fraction of fibers for comparison. Giridharan [54] suggested that these different combinations of composites under distinct testing conditions and respective behaviors of these composites have been discussed as follows. 8.6.1 Tensile Strength of Natural Fiber (Ramie), Synthetic Fiber (Glass), and Hybrid (Ramie/Glass) Composites All combinations of composites with 20 and 30 wt% fraction were tested for tensile strength evaluation. The respective tensile test results are represented in Figure 8.12. The tensile strength performance of these composites reveals individual abilities of ramie and E-glass fibers and also both fibers put together. Hybrid (ramie/glass) composite shows the highest performance in bearing tensile load followed by glass fiber-reinforced composite. Ramie fiber-reinforced composite registers with least performance. Consequently, the results infer that natural fibers (ramie) can be an effective and efficient player when used along synthetic fibers (E-glass). The trend is similar in both 20 and 30 wt% fraction of fiber reinforcements. In 20 wt% fraction of fibers, hybrid composite exhibits 1.44% more tensile strength than composite with glass fiber reinforcements. However, this percentage increases considerably when compared to composite with ramie fiber reinforcements. 69.9% is the enhancement in tensile strength when ramie and glass fibers are hybridized compared to ramie fibers alone as reinforcements. In 30 wt% fraction of fibers, hybrid composite exhibits 2.45% more tensile strength than composite with glass fiber reinforcements. However, the percentage increases considerably when compared to composite with ramie fiber reinforcements. 64.7% is the enhancement in tensile strength when ramie and glass fibers are hybridized compared to ramie fibers alone as reinforcements. Among all combinations, hybrid composite with 30 wt% (10% ramie fibers and 20% E-glass fibers) fraction of fibers registers the highest tensile strength [54].

8.6 Comparison of Strength of Natural Fiber, Synthetic Fiber, and Hybrid Composites

100 90 Tensile strength (MPa)

80 70 60 50 40 30 20 10 0 30% 20% 30% 30% 20% 20% hybrid glass glass hybrid ramie ramie fiber fiber fiber fiber fiber fiber (epoxy) (epoxy) (epoxy) (epoxy) (epoxy) (epoxy) composite composite composite composite composite composite

Figure 8.12 Tensile strength of natural fiber (ramie), synthetic fiber (glass), and hybrid (ramie/glass) composites at 20 and 30 wt% fraction of fiber presence in composites. Source: Giridharan 2019 [54]. Reproduced with permission of Elsevier.

Further inference can be made with reference to the inclusion of additional 10 wt% fraction of fibers in all combinations as this additional inclusion of fibers has increased the tensile strength (Figure 8.12). 8.6.2 Flexural Strength of Natural Fiber (Ramie), Synthetic Fiber (Glass), and Hybrid (Ramie/Glass) Composites A similar combination of composites as discussed above with 20 and 30 wt% fraction was tested for flexural strength evaluation. The respective flexural test results are represented in Figure 8.13. Trend of flexural strength performance resembles with tensile strength performance. Hybrid composite outperforms here also in comparison to composites made with natural (ramie) and synthetic (glass) fiber reinforcements. On the other hand, the composite made with synthetic (glass) fiber reinforcements registers higher flexural strength than composites made with natural (ramie) fiber reinforcements. These results also ensure that ramie fibers have to be applied along glass fibers to achieve higher flexural strength. The trend is similar in 20 and 30 wt% fraction of fiber reinforcements. In 20 wt% fraction of fibers, hybrid composite exhibits 7.6% more flexural strength than composite with glass fiber reinforcements. However, the percentage increases considerably when compared to composite with ramie fiber reinforcements. 25.7% is the enhancement in flexural strength when ramie and glass fibers are hybridized compared to ramie fibers alone as reinforcements. In 30 wt% fraction of fibers, hybrid composite exhibits 5.8% more flexural strength than composite with glass fiber reinforcements. However, the percentage increases considerably

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80 70 60 Flexural stress (MPa)

140

50 40 30 20 10 0 30% 30% 20% 20% 30% 20% hybrid glass glass hybrid ramie ramie fiber fiber fiber fiber fiber fiber (epoxy) (epoxy) (epoxy) (epoxy) (epoxy) (epoxy) composite composite composite composite composite composite

Figure 8.13 Flexural strength of natural fiber (ramie), synthetic fiber (glass), and hybrid (ramie/glass) composites at 20 and 30 wt% fraction of fiber presence in composites. Source: Giridharan 2019 [54]. Reproduced with permission of Elsevier.

when compared to composite with ramie fiber reinforcements. 22.5% is the enhancement in flexural strength when ramie and glass fibers are hybridized compared to ramie fibers alone as reinforcements. Among all combination, hybrid composite with 30 wt% (10% ramie fibers and 20% E-glass fibers) fraction of fibers registers the highest flexural strength [54]. Further inference can be made with reference to the inclusion of additional 10 wt% fraction of fibers in all combinations as this additional inclusion of fibers has increased the flexural strength (Figure 8.13). 8.6.3 Impact Strength of Natural Fiber (Ramie), Synthetic Fiber (Glass), and Hybrid (Ramie/Glass) Composites Natural fiber (ramie), synthetic fiber (glass), and hybrid (ramie/glass) composites have also been tested for observing impact strength with 20 and 30 wt% fraction by Giridharan [54]. The respective impact test results are represented in Figure 8.14. Trend of impact strength performance resembles with tensile and flexural strength performance. Hybrid composite also outperforms here in comparison to composites made with natural (ramie) and synthetic (glass) fiber reinforcements. On the other hand, composite made with synthetic (glass) fiber reinforcements registers higher impact strength than composites made with natural (ramie) fiber reinforcements. These results also ensure that ramie fibers have to be applied along glass fibers to achieve higher impact strength. The trend is similar in 20 and 30 wt% fraction of fiber reinforcements. A maximum of 89.5% more impact strength is observed in hybrid composite with

8.7 Summary and Outlook

200 180

Impact strength (J/m2)

160 140 120 100 80 60 40 20 0 30% 30% 30% 20% 20% 20% hybrid hybrid ramie glass glass ramie fiber fiber fiber fiber fiber fiber (epoxy) (epoxy) (epoxy) (epoxy) (epoxy) (epoxy) composite composite composite composite composite composite

Figure 8.14 Impact strength of natural fiber (ramie), synthetic fiber (glass), and hybrid (ramie/glass) composites at 20 and 30 wt% fraction of fiber presence in composites. Source: Giridharan 2019 [54]. Reproduced with permission of Elsevier.

30 wt% (10% ramie fibers and 20% E-glass fibers) fraction of fibers than composite with ramie fiber reinforcements. For the same hybrid composite, the impact strength is 4.9% more than composite with glass fiber reinforcements [54]. The performance of ramie fibers can be enhanced when synthetic fibers (E-glass) and are combined with these green fibers. The phenomenon called hybridization simultaneously boosts the mechanical properties and reduces the cost involved in manufacturing these hybrid composites. Hybridization partly converts these composite materials eco-friendly because of the addition of green fibers (ramie). The hybrid structure also becomes light in weight. Agriculture industries are utilizing the advantages of ramie fibers as reinforcements in hybrid composites. Potential research space is available in ramie fiber-based composite materials for the enhancement of impact strength as well as hardness. Electrical and thermal based treatment can also be tried for improving mechanical properties.

8.7 Summary and Outlook Hybrid composites with natural and synthetic fiber combination could be the positive step toward building green composites. The inclusion of natural fibers brings their own advantages within hybrid composites. Overall weight of hybrid composite could be reduced through adding these green fibers. Environmental concerns could be addressed at large scale through adapting natural fibers. The sustainability is also out of doubt region for these eco-friendly fibers. On the other side, synthetic fibers are contributing considerably in the enhancement

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of mechanical properties of hybrid composites. These fibers also enhance the morphology and structure of the composite that are very important in modern applications. The depleting trend of the availability of raw materials for producing synthetic fibers and ecological disturbances made by these fibers are ended with searches on alternative fibers to replace synthetic fibers either partially or completely. Natural fibers are the most preferable alternates. The present book chapter handles typical natural and synthetic fibers and their mechanical behavior as fiber reinforcements in hybrid composites. Flax (natural) fibers secure the highest position among natural fibers in terms of impact strength. However, the impact strength of these fibers is comparatively low with synthetic fibers. For example, composite made of flax fibers (natural) possesses the least impact strength of 33.8 kJ/m2 [17], whereas composite made of carbon fibers (synthetic) possesses the impact strength of 315 kJ/m2 [16]. Therefore, synthetic fibers outperform natural fibers in bearing impact load. However, hybrid (flax/carbon) composites register the highest impact load bearing capacity of 380.94 kJ/m2 [8] in comparison to composites made of flax and carbon fibers separately. Consequently, the purpose of adding natural fibers is met without compromising the impact resistance of the composite. The respective results encourage researchers to focus further on hybrid composites. The orientation of natural fibers within a hybrid composite also influences the mechanical properties of the respective composites. Woven kenaf fiber-employed hybrid composite shows higher impact strength (51.41 kJ/m2 ) [31] than hybrid composites with unidirectional kenaf fibers (41.24 kJ/m2 ) [31]. Woven structure performs superior than unidirectional fiber orientation through absorbing a higher amount of energy before fracture failure of hybrid composite. Similarly, cross ply flax fiber-employed hybrid composite shows higher impact strength (507.15 kJ/m2 ) [31] than hybrid composites with unidirectional flax fibers (380.94 kJ/m2 ) [31]. Here, flax fibers with cross ply orientation possess more impact strength than flax fibers with unidirectional orientation. Different hybrid composites with distinct fiber combination and orientation are responding differently under impact test. Carbon (MD)/flax (MD) (epoxy) hybrid composite absorbed the highest impact energy (26.68 J) [51] followed by basalt (UD)/flax (CP) (vinyl ester) hybrid composite with an absorbed impact energy of 24.26 J [52]. Basalt (W)/carbon (W) (epoxy) hybrid composite registered the least absorption of impact energy (21.84 J) [53]. Even though woven fibers are reinforced here, carbon/flax (epoxy) hybrid composite with multidirectional fibers are absorbing more impact energy. Therefore, the selection of combination of natural and synthetic fibers for producing hybrid composite also plays a vital role for boosting the impact strength. Ramie/E-glass (epoxy) hybrid composites have the capability of bearing higher tensile, flexural, and impact load than composite made of ramie (epoxy) and E-glass (epoxy) fibers individually. The trend is similar in both 20 and 30 wt% fraction of fiber reinforcements. Further inference can be made with reference to the inclusion of additional 10 wt% (20–30) fraction of fibers in all combinations, as this additional inclusion of fibers has increased the tensile, flexural, and impact

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sive properties of flax fibres for natural fibre reinforced composites. Journal of Materials Science 37: 1683–1692. Saheb, D.N. and Jog, J.P. (1999). Natural fibre polymer composites: a review. Advances in Polymer Technology 18: 351–633. Assarar, M., Zouari, W., Sabhi, H. et al. (2015). Evaluation of the damping of hybrid carbon–flax reinforced composites. Composite Structures 132: 148–154. Wang, M.C., Zhang, Z.G., Li, Y.B. et al. (2008). Chemical durability and mechanical properties of alkali-proof basalt fibre and its reinforced epoxy composites. Journal of Reinforced Plastics and Composites 27: 393–407. Yang, Z.M., Liu, J.X., Feng, X.Y. et al. (2018). Investigation on mechanical properties and failure mechanisms of basalt fibre reinforced aluminum matrix composites under different loading conditions. Journal of Composite Materials 52: 1907–1914. Fiore, V., Scalici, T., Bella, G.D., and Valenza, A. (2015). A review on basalt fibre and its composites. Composites Part B Engineering 74: 74–94. Xing, D., Xi, X.-Y., and Ma, P.-C. (2019). Factors governing the tensile strength of basalt fibre. Composites Part A Applied Science and Manufacturing 119: 127–133. Wang, D., Ju, Y., Shen, H., and Xu, L. (2019). Mechanical properties of high performance concrete reinforced with basalt fiber and polypropylene fiber. Construction and Building Materials 197: 464–473. Kim, Y.H., Yang, D.H., Yoon, S.W. et al. (2011). A study on the mechanical properties comparison for the composites application of basalt fibres with GFRP. Advanced Science Letters 4: 1633–1637. Sarasini, F., Tirillo, J., D’Altilia, S., and Valente, T. (2016). Damage tolerance of carbon/flax hybrid composites subjected to low velocity impact. Composites Part B Engineering 91: 144–153. Zivkovic, I., Fragassa, C., Pavlovic, A., and Brugo, T. (2017). Influence of moisture absorption on the impact properties of flax, basalt and hybrid flax/basalt fiber reinforced green composites. Composites Part B Engineering 111: 148–164. Sarasini, F., Tirillo, J., and Ferrante, L. (2014). Drop-weight impact behaviour of woven hybrid basalt–carbon/epoxy composites. Composites Part B Engineering 59: 204–220. Giridharan, R. (2019). Preparation and property evaluation of glass/ramie fibers reinforced epoxy hybrid composites. Composites Part B Engineering 167: 342–345. Paiva Junior, C.Z., De Carvalho, L.H., Fonseca, V.M. et al. (2004). Analysis of the tensile strength of polyester/hybrid ramie–cotton fabric composites. Polymer Testing 23: 131–135. Hendra (2017). A study on cotton–ramie fabric reinforced composites. International Journal of Materials Sciences 12: 117–125. Jawaid, M. and Abdul Khalil, H.P.S. (2011). Cellulosic/synthetic fibre reinforced polymer hybrid composites: a review. Carbohydrate Polymers 86: 1–18.

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9 Bast Fiber-Based Polymer Composites Sandeep Kumar 1 , Brijesh Gangil 1 , Krishan Kant Singh Mer 2 , Manoj Kumar Gupta 1 , and Vinay Kumar Patel 2 1 S.O.E.T., H.N.B. Garhwal University, Department of Mechanical Engineering, Srinagar 246174, Uttarakhand, India 2 Govind Ballabh Pant Institute of Engineering & Technology, Department of Mechanical Engineering, Pauri Garhwal, Ghurdauri 246194, Uttarakhand, India

9.1 Introduction Natural fiber often referred to as plant fibers plays an important role in our day-to-day life. The synthetic fibers are strongly replaced by various plant fibers such as bamboo and wood; have been extensively used in the construction of fibers obtained from jute, coir, banana, and sisal, etc.; and have been found particularly in aerospace and automotive [1], packaging [2–4], and building industries [5–7]. Plant fibers are classified as bast fibers (jute, nettle, hemp, and ramie), leaf fibers (sisal, abaca, and pineapple), seed fibers (kapok and cotton), grass (rice, wheat, and corn), and reed. Among the different plant fibers, bast fibers (outer cell of plant stem) are of utmost interest in applications striving for lightweight and high strength. The bast plant is determined by three layers: the first layer is very thin and known as the epidermis layer; the second layer of the fiber is surrounded by the phloem; and the last layer is the core, as shown in Figure 9.1. The advantages of bast fibers are as follows: high tensile strength, low specific gravity, high strength-to-weight ratio, and high fiber productivity rates. The major benefits of bast fibers over conventional reinforcement materials such as glass, carbon, Kevlar, and talc, etc., are less expensive, good thermal properties, and carbon dioxide sequestration [8–10]. This makes the bast fibers one of the important plant fibers that could be used as reinforcing agents in the thermoset/thermoplastic polymers. Other advantages of bast fibers are abundant availability in nature, easy recycling, and production of nontoxic fumes. The general, family, and scientific names of commonly used bast fibers are shown in Table 9.1. In the past decades, bast fiber composites with polymer (thermoset/ thermoplastic) matrices have been applied to produce automotive nonstructural components such as dash board, speaker shelf, spare tire holder, seat backs, and Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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Top of plant Skin layer Immature fiber Core Middle of plant Epidermis Bast Bottom of plant

Immature fiber Core

Epidermis Bast Immature fiber Core

Figure 9.1 The structure of bast fiber plant. Table 9.1 Bast fibers, general name, family name, and scientific names. General name

Family name

Scientific name

Flax

Linaceae

Linum usitatissimum

Hemp

Cannabaceae

Cannabis sativa

Bhimaal or Bihul

Tiliaceae

Grewia optiva

Nettle

Urticaceae

Urtica dioica

Jute

Tiliaceae

Corchorus capsularis

Kenaf

Malvaceae

Hibiscus cannabinus

door panel [11]. Despite the numerous benefits of bast fibers, these fibers have some drawbacks such as degradation during processing, unsuitability with a few polymeric resins, and high water uptake capacity makes them incompatible for composite applications [12]. These properties of bast fiber-based composites can be easily improved by hybridization of such fibers with synthetic/natural fiber and chemical modification of surface of bast fibers [13, 14].

9.2 Polymer Composites Reinforced with Bast Fibers Decortication Post decortication cleaning

Single fiber Fiber bundle

Struc tu

es sin

g

C co hem m ic po a si l tio ns

e

Chemical retting

M ex ech tra an cti ica on l

ulos

Pr oc

Hem icell

e ulos Cell

tin

nin Lig

Pe c

res

Dew retting R ex etti tra ng ct io n

Water retting

Insulation Bast fiber

Applications

sp

ec t

Composites

ur e

tre

nd

s

En vir on

m

en

ta

Geotextile

Enzymatic retting

Fu t

Figure 9.2 Characterization of bast fibers.

9.1.1

Bast Fiber as Reinforcing Material

Recently, there is a growing interest in the utilization of bast fibers as reinforcements in composite manufacturing industries because they are environmentally friendly and less expensive as compared to synthetic fibers [15]. The characterization of bast fibers is illustrated in Figure 9.2. The attractive features of the bast fibers such as jute, flax, hemp, and nettle because of their high specific strength and lightweight attracted various scientists toward the utilization of these fibers as an alternative source for synthetic fibers in composite material preparation [16, 17]. In the past few years, mankind used synthetic fibers as reinforcements for thermoset/thermoplastic composites; however, it has some drawbacks such as health hazards and nonrenewability [18]. To reduce the effect on the environment, fully natural and seminatural composite materials are being prepared with a combination of bast fibers and biodegradable polymers.

9.2 Polymer Composites Reinforced with Bast Fibers The demand of product made by bast fiber-reinforced composites is increasing day by day. Bast fibers are among the natural fibers now finding use in thermoplastic polymer composites for packaging, automotive and furniture industries, and residential house construction. In this context, bast fibers such as flax, hemp, grewia optiva, jute, and nettle as reinforced elements in composites are discussed in detail as follows.

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9 Bast Fiber-Based Polymer Composites

9.2.1

Polymer Composites Reinforced with Flax Fibers

Flax is one of the most extensively used bast fibers, and generally, flax plant ranges in length up to 90 cm, which possesses strong fibers with 12–16 μm diameter [19]. The main constituent of flax fibers are cellulose (60–81%), hemicelluloses (14–19%), lignin (2–3%), and pectin (0.9%). The rapid manufacturing technique for fabrication of woven flax/propylene composites was developed by Derbali et al. [20] and observed that for making V-shaped parts, the composites were fabricated in less than 200 seconds, which is less than the thermal-compression cycle time (140 minutes). Ameur et al. [21] fabricated thermoset composites reinforced with flax and carbon fibers, and these composites attained higher tensile fatigue strength than neat epoxy composites. In addition to that, earlier studies reported that flax fiber is found to have a good potential as reinforcement in thermoset resin [22]. Because of 10 wt% short flax fibers, the fatigue strength of polylactide-based composite increases, whereas thermoplastic starch filled with short flax fibers showed lower fatigue strength than neat polymer [23]. Prasad et al. [24] designed the flax fiber-reinforced epoxy composites with different volume fractions of fibers. They revealed that the fabricated composite with 42% flax volume fraction exhibited optimum tensile strength, and finest range of properties can be obtained by postcuring. The alkali treatment of short flax fiber has improved the mechanical and thermal properties of poly lactic acid (PLA) eco-composites when compared to neat PLA composites [25]. The mechanical properties such as impact strength and flexural strength of vinyl ester-flax fiber-reinforced composites increase and obtained good flexural strength between 109 and 165 MPa compared to neat vinyl ester composites (40 MPa). Finally, it is concluded that flax fiber can be a good natural reinforcing agent for composite production and also that flax fiber can be used in fiber/silver form for composite material applications [26]. Xia et al. [27] focused that fiber–matrix adhesion plays a key role in the development of high-performance PLA/flax composites. The surface of flax fiber is modified by the chemical treatments such as maleic acid grafting, alkali, and silane treatment. They observed that tensile modulus, impact strength, and elongation-at-break of PLA/flax composites were higher than those of pure PLA. The toughness of PLA/treated fiber composites was higher than that of PLA/untreated fiber composites because of the improvement in the adhesion between the fiber flax and matrix. Also, the crystallization ability of PLA can be improved by the addition of flax fibers, and the more fiber weight percentage (2.5–12.5 wt%) gives more effective improvement [28]. Ramnath et al. [29] found that jute–flax-reinforced hybrid glass epoxy composites exhibited superior tensile strength (56.88 N/mm2 ) and flexural strength (134.05 N/mm2 ) as compared to mono-jute fiber-reinforced composites (tensile strength 56.88 N/mm2 ), whereas the jute fiber composites performed better in percentage elongation and impact loading. The effect of orientation of flax–glass fiber hybrid composites with 0∘ and 90∘ was performed by Ramesh and Sudharsan [30] who found out that the 0∘ fiber orientation can hold the optimum mechanical properties (tensile strength of 82.71 MPa, flexural strength of 134.99 MPa, and impact strength of 4 kJ/m2 ). The polypropylene composite reinforced with short flax

9.2 Polymer Composites Reinforced with Bast Fibers

fiber was discussed by Notta-Cuvier et al. [31] and revealed that the behavior of composites strongly depends on the weight fraction of fibers. The mechanical characteristics of fiber-reinforced composites generally depend on the adhesion of the constituents, which can be characterized by interfacial shear strength (IFSS). The modifying agent maleic anhydride-grafted polypropylene leads to increase the IFSS of composites by 50% and the apparent IFSS was found to decrease with increasing fiber volume percent [32]. Chaudhary et al. [33] focused on tribomechanical and dynamic behavior of jute/flax/hemp reinforce composites with references to different combinations of hybridization (jute/epoxy, jute/hemp/epoxy, hemp/epoxy, jute/hemp/flax/epoxy, flax/epoxy, and neat epoxy). According to their findings, wear resistance property of all developed composites were increased. The effects of speed and normal loads on coefficient of frication are nominal and negligible. Jute/hemp fiber-reinforced composites have superior tribological property, among all the fabricated composites. Aslan et al. [34] prepared the flax/polyethylene terephthalate composites by means of filament winding techniques, followed by compression molding with low and high consolidation pressure, and with variable fiber weight percent. The result showed that the maximum stiffness attained at high pressure composites is 40 GPa. Habibi et al. [35] prepared the combination of short fiber and unidirectional flax fiber polymer composites by paper making process. The study showed that the presence of short fibers in the composite resulted in a slight reduction of about 10% of the longitudinal tensile modulus and strength. However, the transverse tensile properties are almost twice, and the compressive strength in the yarn direction was more influenced by the presence of short fibers and was reduced by 30% compared to a decrease of 10% in the case of tensile loading. Here again, the transverse modulus was slightly enhanced, even if no effect was observed on the transverse compressive strength. Moreover, ±45∘ sort flax fiber laminates give a positive impact on tensile, shear, and compressive properties [36]. The frame of wooden house can be manufactured by hemp–flax composites because these composites have low apparent density, low thermal conductivity, and low strength properties as compared to conventional building materials [37]. Zhang et al. [38] studied the properties of flax fiber-reinforced wood flour/high density polyethylene composites. From the experimental observations, the flexural strength and modulus were increased by 14.6% and 51.4%, respectively, with 9 wt% flax fiber content. However, the toughness and creep resistance were remarkably improved without changing the plastic content in wood plastic composites. Tayfun et al. [39] characterized the properties of surface-modified flax fiber (alkali, permanganate, peroxide, and silanization) thermoplastic polyurethane composites. They conducted tensile test, modulus of elasticity, water absorption behavior, melt flow properties, and morphology of composites. They revealed that treated composites exhibited superior mechanical properties, but silane-treated flax fiber-reinforced composites attained a higher tensile strength (19.1 MPa) and lowest water absorption. Also, the flax fiber-based polymer composites have potential to reduce the noise pollution and can be used as an alternate for commercially available glass fiber mat [40]. Moudood et al. [41] studied the influence of moisture on the mechanical properties of

151

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9 Bast Fiber-Based Polymer Composites

epoxy/flax composites by applying the different relative humidity (RH). The authors observed that the moisture in the fiber with different RHs reduced the flexural modulus and stiffness but increase the tensile strength (287.96 MPa at 50% RH). Huner [42] investigated the effect of chemical treatment on mechanical properties of flax–reinforced epoxy composites. For this purpose, the authors used acetic anhydride, sodium hydroxide, and silane. They revealed that particularly sodium hydroxide treated flax fiber improved the adhesion between fiber and matrix and also improved the mechanical properties of the epoxy matrix composites. Recently, researchers investigated that the flax fiber-based composites have the potential to reduce the noise pollution, the noise reduction coefficient increased from an average value of 0.095–0.11 for unidirectional flax/epoxy composite to 0.10 for cross-ply flax/epoxy system [43]. 9.2.2

Polymer Composites Reinforced with Grewia Optiva Fiber

Grewia optiva (Tiliaceae) is obtained from the stalk of plant that is 9–12 m high and contains 58–75% cellulose. The local name of grewia optiva is Bhimaal or Bihul, and the extraction process of fibers from grewia optiva is summarized in Figure 9.3 [14]. The influence of size of grewia optiva fiber on the mechanical and thermal properties of urea formaldehyde-based composites has been studied. The particle fiber-reinforced composites exhibited superior tensile and compressive behavior as compared to long- and short-fiber reinforcement [44]. Bajpai et al. [45] prepared the natural fiber PLA composites reinforced with grewia optiva, sisal, and nettle. The study showed that the incorporation of natural fiber increases the wear-resistant properties as compared to neat PLA.

(a)

(b)

(c)

(g) (d)

(e)

(f)

Figure 9.3 (a) Grewia optiva plant, (b) preparation of khall, (c) retting process in khall, (d) separation of bark, (e) fiber extraction, (f ) sun drying of extracted fiber, and (g) bidirectional mat of grewia optiva fiber.

9.2 Polymer Composites Reinforced with Bast Fibers

Specific wear rate and friction coefficient are detected to be reduced by 70% and 10–44%, respectively, as compared to neat PLA. The influence of 31.5 wt% of grewia optiva in polymer matrix has been focused by Gupta et al. [46] and observed that the tensile strength and compressive strength of fabricated composites is much higher than flax and palmyra reinforced composites. Kumar et al. [14] studied the influence of rice husk/wheat straw on the mechanical properties of grewia optiva fiber-reinforced hybrid composites. They observed that the rice husk and wheat straw content in composite give superior impact energy, hardness, and wear properties in comparison to mononatural fiber specimens. Upreti et al. [47] investigated the mechanical properties of grewia optiva fiber-reinforced polymer composites with reference to effect of fiber content. According to their findings, tensile strength (46.11 MPa), compressive strength (127.69 MPa), and flexural strength (93.022 MPa) show a maximum value at 5 wt%. Kumar et al. [9] focused on a review of different chemical treatment methods and its effect on mechanical properties of grewia optiva fiber-reinforced polymer composites and conclude that enhancement of properties is possible by graft copolymerization, mercerization, benzoylation, and silane method. An investigation on holes making in bast fiber-reinforced composites was done by Bajpai et al. [48]. They observed that the superior drill point geometry and feed rate are significant parameters of grewia optiva composite laminates for generating damage-free holes. The combined effect of nettle and grewia optiva on mechanical properties of thermoset and thermoplastic composites have been investigated by Singhal et al. [49] and the following results are obtained (Figures 9.4 and 9.5). For fiber-reinforced composites, higher tensile strength (epoxy/grewia optiva), higher flexural strength and impact energy (PLA/grewia optiva), and elongation at break (PP/nettle) were obtained. 70 200 60

160

50

120

40 30

80 20 40

Tensile strength (MPa)

Flexural strength (MPa)

Flexural strength (MPa) Tensile strength (MPa)

10

0

0 A

B

C

D E F G Laminate composites

H

l

Figure 9.4 The variations of flexural strength versus laminate composites (A: neat PLA, B: PLA/NF, C: PLA/GF, D: neat PP, E: PP/NF, F: PP/GF, G: neat epoxy, H: epoxy/NF, and I: epoxy/GF, where PLA – polylactic acid, GF – grewia optiva fiber, NF – nettle fiber). Source: Singhal et al. 2016 [49]. Reproduced with permission of Taylor & Francis.

153

9 Bast Fiber-Based Polymer Composites 10 Elongation at break (%) Impact energy (kJ/m2)

40

8 30 6 20 4 10

Impact energy (kJ/m2)

Elongation at break (%)

154

2

0

0 A

B

C

E F G D Laminate composites

H

I

Figure 9.5 The variations of elongation at break versus laminate composites (A: neat PLA, B: PLA/NF, C: PLA/GF, D: neat PP, E: PP/NF, F: PP/GF, G: neat epoxy, H: epoxy/NF, and I: epoxy/GF, where PLA – polylactic acid, GF – grewia optiva fiber, NF – nettle fiber). Source: Singhal et al. 2016 [49]. Reproduced with permission of Taylor & Francis.

Thakur et al. [50] evaluated the effect of graft copolymerization on mechanical properties of grewia optiva fiber-reinforced composites. After applying the treatment, the tensile strength result showed that the fabricated composite strength was improved. Singha et al. [51] prepared the thermoset composite reinforced with grewia optiva fiber (raw and surface modified). The optimization of fiber weight percentage has been done in terms of tensile, flexural, and compressive strength. These optimized specimens were characterized by scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA), and differential scanning calorimetric (DSC) techniques. They revealed that benzoylation-treated fiber composites have highest mechanical strength followed by AN grafted, silanted, mercerization, and AAc-grafted particle fiber. Also, the treated fiber shows better dielectric properties than raw fibers. The crystallinity of the raw fibers increased after mercerization but decreased slightly after the APS treatment. The thermal stability of both alkali and APS-treated fibers has been found to be higher than that of raw fiber [52]. In particular, Thakur et al. [53] evaluated the effect of fiber weight amount (i.e. 10%, 20%, 30%, and 40%) on the mechanical and thermal performance of Grewia optiva short fiber (i.e. 3 mm) reinforced phenol-formaldehyde composites, manufactured by compression molding, showing that the best tensile, flexural, and compressive properties were achieved at fiber content of 30%. An identical result was achieved by reinforcing phenol-formaldehyde resin matrix with 200 μm G. optiva particles [44]. The physicochemical and flammable properties of raw fiber-reinforced unsaturated polyester composites increased considerable after the surface modification of fiber [54]. Kumar et al. [55] fabricated the epoxy composites reinforced with different proportions of grewia optiva and bauhinia vahlii fiber. The mechanical properties

9.2 Polymer Composites Reinforced with Bast Fibers

such as tensile strength, flexural strength, and impact energy were evaluated. Furthermore, wear behavior according to Taguchi optimization technique was applied on fabricated samples and evaluated mechanical properties such as tensile strength, flexural strength, hardness, and impact energy were found to increase with increasing fiber content and remained higher for hybrid grewia optiva and bauhinia vahlii fiber reinforcement. The optimum mechanical properties for all combination were attained at 6 wt% hybrid fiber loadings. 9.2.3

Polymer Composites Reinforced with Hemp Fiber

Hemp (Cannabis sativa) is one of the most common bast fibers, which is used as reinforcing agent in fiber-reinforced polymer composites [56]. Hemp is used in the various applications in the world such as textile, food, bio fuel, textile, construction, etc. The physical, chemical, and mechanical strength of raw hemp fiber is shown in Table 9.2. Investigation on mechanical properties jute/flax/hemp-reinforced composites and the interface between fiber and matrix was examined [33]. The combination jute/epoxy, hemp/epoxy, flax/epoxy, and jute/hemp/flax epoxy was prepared and revealed that jute/hemp/epoxy hybrid composites exhibited higher flexural strength (86.6 MPa). According to the findings, jute/hemp/flax fiber-reinforced composites have potential for structural applications. The diameter of hemp fiber also affects the mechanical and water absorption properties of composites [57]. The mechanical properties of polybenzoxazine composites have been enhanced by the addition of 30 vol% hemp fiber loading of 20 mesh size and the result indicated an increase of 43%, 91%, 168%, 73%, Table 9.2 The chemical and physicomechanical properties of hemp fiber. Chemical constituents (wt%)

Value

Cellulose

55–90

Hemicellulose

15–22.4

Lignin

4–13

Pectin

0.8–1.6

Moisture

9–12

Ash

0.8

Physical and mechanical properties Density (g/cm3 )

1.4–1.6

Tensile property (MPa)

310–1235

Specific tensile strength (MPa)

210–510

Elastic modulus (GPa)

20–70

Specific Young’s modulus (GPa)

20–41

Failure strain (%)

0.9–4.2

Diameter (μm)

17–24

Aspect ratio (l/d)

549

155

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9 Bast Fiber-Based Polymer Composites

and 137% in flexural strength, tensile strength, impact strength, flexural modulus, and tensile modulus, respectively. The increasing hemp fiber weight percentage up to 40% in polyurethane composites increases the flexural strength to 193.24%. Additionally, the flexural strength was further increased (274.3%) by the optimum hemp fiber length of 15 mm [58]. Gupta and Rao [59] evaluated the water absorption and mechanical properties of hemp/sisal fibers to assess their potential for use as reinforcement in epoxy composites. In this study, they found that the 40 wt% of sisal/hemp fiber composites exhibited higher value of flexural (approximately 82 MPa) and compressive strength. Inbakumar and Ramesh [60] studied the effects of volume fraction of hemp fiber and egg shell on mechanical and tribological properties of epoxy composites. The specimens were prepared by hand lay-up techniques with different weight percents of hemp fiber (30%, 40%, and 50%) and egg shell filler (0.25%, 0.50%, and 1.0%). The resulting composites containing 50 wt% hemp and 0.5 wt% egg shell showed the highest tensile and flexural strength. In other hybridization, 40 wt% of sisal/hemp fiber-reinforced polymer composites attained a maximum flexural strength (82 MPa), whereas maximum hardness (76.3 hardness number) achieved at 50 wt% fiber loadings [59]. The tensile property of polypropylene composite is increased about 2.6 times by the incorporation of less than 50 wt% of hemp fiber [61]. Sullins et al. [62] focused on the effect of chemical treatment on the mechanical behavior of hemp fiber-reinforced polypropylene composites. The mechanical properties are evaluated with different combinations of material treatment(s) such as 5 wt% maleic anhydride grafted polypropylene, 5% sodium hydroxide treated hemp fiber, 10% sodium hydroxide treated hemp fiber, 5% sodium hydroxide, and 5 wt% maleic anhydride grafted polypropylene. 15 and 30 wt% hemp fiber loadings are used in the composites with these material treatments. It is found that the chemical treatment of material in composites exhibited superior mechanical properties as compared to the composites without any treatment. In addition, the composites with 5 wt% maleic anhydride grafted polypropylene incorporation shows the best mechanical properties. The silane treatment of woven hemp fiber was used to improve the mechanical properties of composites [63], and hemp fiber-reinforced polyurethane composites may provide a promising solution for building insulation [64]. 9.2.4

Polymer Composites Reinforced with Nettle Fiber

Nettle fiber belongs to temperate region bast fiber category. The uses of Nettle plant are as follows: leaves are used as vegetables and medicines (headache, swollen joint, and fever), and the extracted fiber is used for making ropes, thread, and other items. Various applications of nettle plant are shown in Table 9.3. The fiber extracted from nettle plant by water retting process, the stems are kept under water tank for two to three weeks by which the pectinous substances that bind fiber, and other plant tissues start degraded by microorganisms. After retting process, fibers were subjected for drying by exposing under sunlight for three hours. The mechanical properties of nettle fiber-reinforced polyester composites were decreased with the increased diameter of fiber and due to high content of cellulose, hemicellulose, and lignin that result

9.2 Polymer Composites Reinforced with Bast Fibers

Table 9.3 Application of nettle fiber plant. Application field

Use

Textile

Tissues and fabrics, ropes and fishing nets, silky fabric, biocomposites, paper and cloth, paper, natural dye (for yams, eggs, etc.)

Cosmetic

In tea, nettle seeds stimulate hair growth and reduce hair loss. It is used in commercial shampoo and has the same effects

Food/drink

Salad, pier, decocted tea, soups, and is an excellent source of vitamin C, Mg, Fe, Ca, and numerous trace elements

Forage crop

Cattle, poultry, horses, and pigs for enhancing yolk yellowness

in better mechanical, thermal stability, and biodegradable properties of the fiber-reinforced composites, respectively [65]. Lila et al. [66] investigated the mechanical and thermal properties of sisal/ hemp/nettle fiber-reinforced polymer composites. In these studies, the author evaluated the maximum values approximately (tensile strength 37 MPa and flexural strength 70 MPa) of nettle fiber-reinforced epoxy composites. In addition, increase of 159%, 163%, and 143% in flexural strength is observed for sisal, nettle, and hemp fiber-reinforced composites, respectively. The maximum voids attained in pure epoxy composites and minimum voids occur in nettle fiber epoxy composites. The 70 wt% cotton/30 wt% nettle can be significantly used in towel production industries, and the hydrophilicity property of the towel was not affected negatively by the addition of nettle fiber [67]. In another investigation, Yallew et al. [68] focused on the mechanical properties of nettle/cotton fiber reinforced in polyethylene composites. They prepared 0, 15, 20, and 25 wt% of nettle/cotton fiber in composites and revealed that the 20 wt% hybrid fiber composites give optimum mechanical properties of the polyethylene composites (Figure 9.6). The tensile strength of nettle fiber-reinforced polypropylene 22 Tensile strength (MPa) Flexural strength (MPa)

20

20

18

18

16

16

14

14

12

12

10 0

20 10 Cotton/nettle fiber (wt%)

Flexural strength (MPa)

Tensile strength (MPa)

22

10 30

Figure 9.6 The variation of tensile and flexural strength versus cotton/nettle fiber (wt%). Source: Yallew et al. 2016 [68]. Reproduced with permission of Taylor & Francis.

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composites was greatly influenced by the environment conditions and maximum reduction was observed in river water and sunlight conditions, whereas minimum reduction was observed in soil condition [45]. Fischer et al. [69] investigated the properties of nettle fiber composites and PLA resin. In these studies, the authors determined the approximate maximum values (Young’s modulus 5500 MPa and tensile strength 58 MPa) with the increase of fiber content 30 wt%. These properties were higher than those of PLA composite (Young’s modulus 3400 MPa and tensile strength 52 MPa). They suggested at the end that nettle fiber can be a good reinforcement material for better performance in biodegradable composite material world. The 50/50 nettle/kapok blended structure shows higher soil sorption capacity than polypropylene-based nonwoven [70]. 9.2.5

Polymer Composites Reinforced with Jute Fiber

Jute belongs to tropical region bast fiber and the scientific name is Corchorus capsularis. Jute plant takes three month to grow to a height of 12–15 m height. The inner and outer stem of jute fiber is separated by retting process, and the outer part of stem gets individualized to form fibers [71]. Polymer composites reinforced with jute fibers have a wide range of applications in automotive industries, constructions, toys, indoor furniture, etc., as a replacement of hazardous plastic and plastic reinforced composites [72]. Oil palm bunch (OPB)/jute fiber-based composites were fabricated by hand-lay-up technique. The mechanical properties such as tensile strength and flexural strength of composites were recorded and revealed that jute/OPB/jute (treated) hybrid composites exhibited higher flexural strength (55.9 MPa), whereas OPB/jute/OPB (treated) attained higher impact strength (90.4 J/m2 ) [73]. The tensile and bending strength of polyethylene terephthalate polymer can be enhanced by the addition of jute fiber [74]. Jute/betel nut fiber-based composites with different weight percentages (10 : 5%, 10 : 10%, and 10 : 15%) were developed by hot press molding techniques and then characterized. Different mechanical properties such as bending and tensile strengths of these composites were evaluated and observed that fabricated composites showing best properties, and 10 wt% jute fiber composites attained higher tensile strength (27 MPa) and flexural strength (51 MPa) [75]. The investigation on mechanical properties of polyester matrix nanocomposites reinforced with treated and untreated jute mat was done by Ganesan et al. [76]. In addition, the effects of nanoclay/egg shell filler on mechanical properties of jute fiber-reinforced composites are also discussed. The superior mechanical properties were obtained in the combination of treated jute fiber/nanoclay 1.5 wt% and egg shell 1.5 wt% as shown in Figures 9.7–9.9. The flexural and tensile strength of low-density polyethylene was successfully enhanced by the jute fiber reinforcement. Further, the strength was enhanced by chemical treatment of jute fiber by 2-hydroxyl ethyl methacrylate. The result shows that the tensile and flexural properties were 33% and 50% improved by the addition of treated jute fiber in low-density polyethylene composites [77]. In other investigations, tensile strength, flexural strength, impact, and hardness of NaOH treated jute/sisal reinforce composites by 20%, 25%, 27.27%, and 5%,

Figure 9.7 The variations of tensile strength versus fabricate composites (A: neat unsaturated polyester, B: egg shell powder(3 wt%) + unsaturated polyester, C: nanoclay (3 wt%) + unsaturated polyester, and D: egg shell powder (1.5 wt%) + nanoclay (1.5 wt%) + unsaturated polyester). Source: Ganesan et al. 2018 [76]. Reproduced with permission of Taylor & Francis.

Tensile strength (MPa)

9.2 Polymer Composites Reinforced with Bast Fibers

NaOH-treated jute mat Untreated jute mat

30

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0 A

50

NaOH-treated jute mat Unteated jute mat

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0 A

B C Fabricated composites

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Impact strength (MPa)

Figure 9.9 The variations of impact strength versus fabricated composites (A: neat unsaturated polyester, B: egg shell powder (3 wt%) + unsaturated polyester, C: nanoclay (3 wt%) + unsaturated polyester, and D: egg shell powder (1.5 wt%) + nanoclay (1.5 wt%) + unsaturated polyester). Source: Ganesan et al. 2018 [76]. Reproduced with permission of Taylor & Francis.

D

40 Flexural strength (MPa)

Figure 9.8 The variations of flexural strength versus fabricated composites (A: neat unsaturated polyester, B: egg shell powder (3 wt%) + unsaturated polyester, C: nanoclay (3 wt%) + unsaturated polyester, and D: egg shell powder (1.5 wt%) + nanoclay (1.5 wt%) + unsaturated polyester). Source: Ganesan et al. 2018 [76]. Reproduced with permission of Taylor & Francis.

B C Fabricated composites

NaOH-treated jute mat Untreated jute mat

2.8 2.6 2.4

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2.0 A

C B Fabricated composites

D

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9 Bast Fiber-Based Polymer Composites

respectively, as compared to untreated fiber-reinforced composites [78]. Khan et al. [79] developed the melamine matrix composites with different weight proportions of jute fiber (16–35 wt%) by hot press at 120 ∘ C for 10 minutes. The optimum values of tensile, bending, and impact strengths were found to be 44 MPa, 112 MPa, and 13 kJ/m2 . By the addition of 50 wt% jute in glass polyvinylchloride composites, the impact, bending, and tensile strengths were found to be increases by 37.5%, 47%, and 44% [80]. The influence of surface modification of woven jute fabric on the mechanical properties of fiber-reinforced laminates was investigated by Karabulut et al. [81]. The surface modification has been done by 5%, 10%, and 15% NaOH solution for 15 days at room temperature. The results showed that the surface-modified jut fiber-reinforced composites exhibited better result in tensile, compressive, and shear property. Vinod et al. [82] focused on the effect of calotropis gigantea stem powder in jute fiber-based epoxy composites. They revealed that the higher wt% of calotropis gigantea filler-based jute fiber composites exhibited superior tensile, hardness, compression, and impact properties.

9.3 Applications of Polymer Composites Reinforced with Bast Fibers Bast fibers and its polymer-based composites have a lot of applications. Bast fibers are being used in manufacturing of ropes, baskets, carpets, and packing materials, whereas jute fiber-reinforced polymer composites are being used in decorative materials (wall and roof decoration), sports (leg guards and helmets), temporary outdoor applications (low-cost housing for defense), and transportation (car interior parts and panel separating the passenger and engine compartment). The general applications of bast fiber-reinforced polymer composites are automobiles, infrastructure, furniture, and dais–deck assembly [83]. Huang et al. [84] established that the production of flax–fiber reinforced polypropylene composites suitable for vibroacoustic environment, and the result supported that the flax composites have noise mitigation solution for marine and aircraft industries. As for the good sound absorption properties at the higher frequency range, these composites could be used as stealth aircraft to reduce the in radio-frequency spectrum. The flax fiber-reinforced composites may be used for making cover lid for siphon-type solar panel accumulator tank and water accumulator tank and are depicted in Figure 9.10 [85]. In addition, the surfboard was manufactured by flax epoxy composites, but some manufacturing difficulties were faced [86]. For example, the flax fibers have low wettability as compared to glass fiber; for this reason, a thick coating of epoxy is used in lamination process. Because of this extra resin, the weight of surfboard is 1 kg, which is 25% heavier than reference model. Bast fiber composites are mostly being used for interior part of motor vehicles such as dashboards, seat cushions, backrests, door panel, etc., whereas these composites have limitation for exterior parts [87].

References

(a)

(b)

Figure 9.10 (a) Cover lid for siphon-type solar panel accumulator tank and (b) water accumulator tank fabricated by using flax biaxial fabric. Source: Goutianos et al. 2006 [85]. Reproduced with permission of Springer Nature.

9.4 Conclusion In this chapter, the physicomechanical properties of different bast fibers (flax, hemp, nettle, grewia optiva, and jute) reinforced composites such as tensile strength, flexural strength, and impact strength and the influence of surface modification to improve the interfacial bonding between fiber and matrix resulting to enhance the physical properties of bast fiber-reinforced polymer composites were reviewed. Various types of chemical treatments were used by different researchers to enhance the mechanical properties of composite, and positive results of chemical treatments were found to increase the mechanical properties. Hence, it can be concluded that bast fiber may be considered as one of the better alternate of synthetic fibers in the existing composite world owing to their biodegradability, high specific strength, low cost, eco-friendliness, and abundantly available in nature. The uses of indigenous raw material in polymer industries not only provide a biodegradable resource but also provide a chance of employment in rural areas and encouragement of plantation and vegetation throughout.

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10 Flame-Retardant Balsa Wood/GFRP Sandwich Composites, Mechanical Evaluation, and Comparisons with Other Sandwich Composites Subin Shaji George 1 , Vivek Arjuna 1 , Venkata Prudhvi Pallapolu 1 , and Padmanabhan Krishnan 1 1 VIT University, Department of Manufacturing Engineering, School of Mechanical Engineering, Katpadi-Thiruvalam Road, Vellore 632104, India

10.1 Introduction A structural sandwich composite is a hybrid form of a laminated composite composed of a combination of different materials that are bonded to each other to utilize the properties of each separate component to the structural advantage of the whole assembly. Typically, a sandwich composite consists of three main parts: two thin, stiff, and strong faces separated by a thick, light, and weaker core. The design principle of a sandwich composite is based on an I-beam, which also has an efficient structural shape because of the sizeable material placed on the flanges situated farthest from the center of bending or neutral axis to take axial loads. Only enough material is left in the connecting web to make the flanges act in coherence and to resist shear and buckling loads. In a sandwich composite, the faces take the place of the flanges and the core takes the place of the web. The difference is that the core of a sandwich is of a different material from the faces and it is spread out as a continuous support for the faces rather than concentrated in narrow web. The faces act together to form an efficient stress couple or resisting moment counteracting the external bending moment. The core resists shear and stabilizes the faces against buckling or wrinkling. The bond between the faces and the core must be strong enough to resist the shear and tensile stresses set up between them. The adhesive that bonds the faces to the core is of critical importance. For a marginal weight increase due to the foam or honeycomb, the moment of inertia (second moment of area) increases the manifold and improves flexural rigidity. Types of balsa wood core used in this investigation are as follows: 1. Regular Balsa: Here, the grains are oriented along the length of the sheet in the regular balsa. 2. End Grain Balsa: The grains are maintained along the thickness in the case of the end grain balsa. End grain balsa and regular balsa were used in this study as a core material for the glass fabric/epoxy skin sandwich composite [1]. Figures 10.1 and 10.2 illustrate the types of balsa woods used in sandwich composite constructions. Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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Core grain orientation X-axis Balsa type used

Y-axis

Z-axis

Regular Radial

End grain Tangential

Parallel

Loading with respect to grain

Figure 10.1 Types of balsa wood and grain orientations. Z Tangential to grain

X

Parallel to grain

End-grain balsa wood

Y

Regular balsa wood

Figure 10.2 End grain balsa and grain orientations.

Tensile and compressive stresses in a sandwich composite are carried by the two skins. Continuously reinforced materials will often constitute a layered or laminated structure. The woven and continuous fiber styles are typically available in various forms, being preimpregnated with a given matrix (resin) as a dry, unidirectional tape of various widths, plain weave, and harness satins that are braided and stitched. Common fibers used for reinforcement include glass fibers, carbon fibers, and high-strength polymers, for example, aramid. The matrix systems that are commonly used are thermoset systems and to a lesser extent thermoplastic systems. The matrix used here is a liquid, low-viscosity, bisphenol-A-based epoxy resin modified with reactive diluents. It has excellent mechanical properties and chemical resistance and very good processing properties, and it is cured with polyamines, polyamidoamines, or their products for solvent-free coatings, flooring screeds, etc. A hardener is a substance or mixture added to a plastic composition to take part in and promote or control the curing action, also a substance added to control the degree of hardness of the cured film. AD 140 hardener is generally used in reactive adhesives, castings, and heat-resistant mortars. Alumina powder with LR-grade purity and an average particle size of 365 μm was used here as a filler in the epoxy matrix for improving the flame retardancy

10.2 Literature Survey

of the composite. The epoxy resin with the filler was coated onto the balsa wood to increase its limiting oxygen index and improve its flame retardancy.

10.2 Literature Survey 10.2.1

Sandwich Composite Structure and Properties

Sandwich composites based on balsa wood have been investigated to a lesser extent and from different available publishers and the following surveys were made: Investigators [2] performed a study to focus on low-velocity impact response of new sandwich composite plates comprising E-glass/epoxy composite laminate face sheets and core made from two different materials, end grain and regular balsa wood, and conducted a thorough damage analysis to understand the role of failure modes on composite strength. Compression after impact test was conducted to correlate the impact damage with the residual strength. It was concluded that the sandwich structures with end grain core are able to withstand higher impact loads compared with regular balsa core because the higher stiffness of end grain core and end grain sandwich composite retained higher residual strength. However, sandwich panels with regular balsa core offer higher energy absorption than end grain core sandwich composite structures because of a higher displacement under impact load, providing for more area under the load–displacement curve. Another investigation [3] deals with the fabrication and use of sandwich composites for aerospace applications. Nallagula Sandeep [4] performed a detailed study on the mechanical properties of balsa wood core sandwich composite with glass fiber polyester facings and with glass phenolic facings. They conducted the bending and compression tests in the elevated temperatures and compared the data of mechanical properties with composites at room temperature. They made a conclusion that the values of balsa wood core sandwich composite with glass phenolic facings do not vary by a large difference. The statistical analysis proved that there is a significant difference between the tests done at room and elevated temperature. The glass transition temperature for glass phenolic is around 220 ∘ C. Glass phenolic with good resin curing may have a glass transition temperature around 350 ∘ C. However, the material properties such as the modulus of elasticity decrease after the glass transition temperature because above this point, a noncrystalline phenolic exhibits the properties of a rubbery solid or a viscous liquid. Further, cooling results in the transformation of phenolic into a hard, brittle, glass-like material that now has increased stiffness and behaves in a highly elastic manner. In this case, there was a difference in the mean failure load for tests done at room and elevated temperature. It was observed that the failure load at elevated temperature was lower than the failure load at room temperature, which means for glass phenolic, the modulus of elasticity decreases with the increase in temperature, and then, it suddenly rises at a point and continues to increase until glass transition temperature is reached and then decreases rapidly. G. Rayjade and G.S. Rao [5] carried out a detailed study on various failure modes of

171

172

10 Flame-Retardant Balsa Wood/GFRP

sandwich composites and how they are generated and how they propagate. The objective of the paper was to provide a review of various aspects of sandwich structures. The paper is also helpful for understanding the failure modes and analytical aspects of the three-point bend test. In aircraft, sandwich construction will be increasingly used particularly for large aircraft, such as the global range transport. Many countries are using sandwich composite constructions for their navies’ ship hulls. However, one of the largest uses may be for bridge constructions. Meisam Shir Mohammadi and John A. Nairn [1] performed a detail study on the comparison of the fracture toughness of a laminated veneer lumber (LVL) made from balsa to the toughness of conventional butcher block balsa material. When using a good lamination adhesive, an LVL balsa core material has enhanced toughness compared to solid balsa and the LVL balsa also has enhanced fiber bridging effects. Padmanabhan and coworkers have carried out considerable work on the design optimization of foam sandwich composites for strength and stiffness [6, 7]. The optimization studies involved compression, shear and flexural testing, and property evaluation. Design optimization studies on sandwich composites with balsa core for strength and stiffness are limited and hence led to this investigation that resulted in a book chapter. 10.2.2

Knowledge Gained from the Literature Review

Balsa wood core sandwich composite core is highly anisotropic in nature and it was also known that if the force is made to act in the direction parallel to the grains, the strength is three to four times more than if the force is applied perpendicular to the direction of the grains. Sandwich structures with end grain core are able to withstand higher impact loads compared with regular balsa core because the higher stiffness of end grain core and end grain sandwich composite retained higher residual strength. However, sandwich panels with regular balsa core offer higher energy absorption than end grain core sandwich composite structures for reasons mentioned above. When using a good lamination adhesive, an LVL balsa core material has enhanced toughness compared to solid balsa and the LVL balsa also has enhanced fiber bridging effects. If the flame retardancy of the balsa wood core can be increased without hampering the mechanical properties of the same, it can be used as a more economical and stronger alternative for making airplane body structures. Hence, in this investigation, the flame retardancy of epoxy resins and that of balsa wood are significantly improved with powder alumina additions. 10.2.3

Gaps Identified from Literature Survey

The effect of temperature on coated balsa wood core, and how its properties deteriorate upon reaching close to ignition temperatures, was shown in the publications, but none of the publications showed anything about the ways to increase the ignition temperature without deteriorating the mechanical properties. It is intended to work on this problem by coating the material with the mixtures of epoxy resins and alumina powder, which will act as a fire-proofing agent. Alumina

10.3 Methodology and Experimental Work

dispersoids are also known to stiffen and strengthen the epoxy resin in addition to the fabric reinforcements. 10.2.4

Objective of the Project

The main objective of this project is to test the mechanical strength of the regular and end grain balsa wood core through the compression and flexure tests after coating the balsa wood with alumina-mixed epoxy resin. This coating is to be done in order to reduce the inflammability of the balsa wood and make it much more useful as an alternative material that is economical, stronger, and stiffer than some polymeric foams. 10.2.5

Motivation

The motivation was to fabricate sandwich composites using coated balsa wood as a core and increase the strength of the wood by reinforcing it with a glass fiber/epoxy matrix of different skin-to-core weight ratios and to increase the flame retardancy of the composite using a weight ratio of Al2 O3 , which will help to increase its ability to withstand the temperature. All these enhance the interest to achieve the results that will help to improve the quality of aerobodies.

10.3 Methodology and Experimental Work 10.3.1

Hand Lay-up Procedure

Based on the weight and volume fraction calculations for the composite, required amounts of glass fabric and resin mixture are considered. The glass fabric to be cut and used has a maximum overhang of 20 mm on each side. This is done to use the fabric optimally, reduce wastage, and avoid the volume fraction errors in the panel fabricated as much as possible. The resin and hardener considered are to be taken precisely in order to avoid different designs than that assigned. The following is the order of the material stacked and applied to the mold: i. The base plate is taken according to the size of the composite required. The mold/plate/board is to be cleaned such that it is devoid of chemicals/protrusions. The breather cloth is placed above the board/plate. ii. A nylon peel/ply release film is laid over the breather fabric and a release agent is sprayed. The release agent used was silicone mold release spray. This is a wax or nonbinding polymer that is first coated onto the mold. This allows the finished cured part to easily pop out and release from the mold. iii. A coat of resin is applied and spread over the peel ply and a layer of a specific fabric is placed over the spread. The layer is flattened to the shape of the mold with a roller by applying sufficient pressure. The rolling helps to infuse a certain amount of resin mix into the fabric layer from beneath it and places it firmly over the mold. A volume fraction of 0.35 glass fiber was maintained.

173

174

10 Flame-Retardant Balsa Wood/GFRP

(a)

(b)

Figure 10.3 Sandwich composite samples (a) before and (b) after fabrication process.

iv. The epoxy GY257 and the hardener Aradur 140 are used for lamination; two measures of resin and one measure of hardener are used by volume. However, in order to increase the flame retardancy, aluminum oxide powder (Al2 O3 ) of 365 μm size is mixed in 10% of the total resin mixture by weight. Resin is again applied and spread over the layer. The second layer of fabric is placed over the first and rolled. This process is repeated for all the layers to be stacked. The final layer may be coated with the resin as well. Another nylon release film, sprayed with the release agent, is placed over the final layer and rolled with the roller. See Figure 10.3 for the details of vacuum-bagged sandwich composites. 10.3.2

Vacuum Bagging

The typical vacuum bag molding process is shown in Figure 10.4 [6, 7]. The stacked composite layers from the wet lay-up are placed in a vacuum bag and sealed on three sides. A vacuum connector valve is inserted through the bag with a dam at its base. Finally, the fourth side is sealed and a vacuum hose is connected to the connector valve. The vacuum through valve is opened and the

Figure 10.4 A photograph of the vacuum bagging technique.

10.3 Methodology and Experimental Work

vacuum pump is switched on. The pump may be run for about half hour. It must be ensured that the vacuum through valve is closed before the vacuum pump is turned off. The lay-up is left to cure at room temperature for 24–48 hours. The reader is directed to Figure 10.4 for the details of vacuum bagging technique. 10.3.3

Testing and Evaluations

The various tests performed to determine the properties of balsa and sandwich composites are as follows: i. The edgewise and flatwise compression test [8], and ii. The flexure test – three-point bending [9, 10]. The machine used for testing was a servohydraulic testing machine (Model: INSTRON 8801). Figures 10.5 and 10.6 depict the compression and flexure test fixtures, respectively. The compression testing options are 50 mm (2.0 in.) diameter fatigue rated compression platens, static capacity of 200 kN, and dynamic capacity of 100 kN. Figure 10.5 INSTRON universal testing machine compression fixture setup.

Figure 10.6 Flexural three-point bend test fixture on INSTRON UTM.

175

176

10 Flame-Retardant Balsa Wood/GFRP

During the compression testing, lateral, transverse, and flatwise testing was done on the coated balsa wood sample, and for each of the sample, the graphs were plotted until a steady load value was obtained. The maximum load value was calculated and the results were then used to find the maximum compression load. The flexure testing options are fatigue-rated three-point bend fixture and a dynamic capacity of 100 kN with 25 mm (1.0 in.) diameter rollers. During the flexure testing of the samples, a span length of 16 : 1 was set, the sample was placed just between the rollers, and the data were fed into the computer, which included the length, width, thickness, and the specimen number. After this, the test was carried out, the graph was plotted for each specimen, and the results were saved, and their maximum load was determined during this testing. The testing was done until a steady graph was obtained. The tests were done following the respective ASTM standards. Observations made during testing must be noted, and preferably snapshots of the same are to be taken for documentation. Evaluations of the various properties from the test results are to be done in the observation notebooks that are prepared after a soft copy is generated. The shear stresses, generally, vary parabolically through the thickness of the face and the core. The maximum normal stresses are related to the bending moment “M” and the distance from the neutral axis “y,” and the maximum shear stresses are related to the shear force. If the faces are thinner and stiffer than the core, then the axial stresses can be treated as linear through the thickness of the face sheet and the core. The various properties of the sandwich composites that can be evaluated in flexure test are as follows: Flexure Test: From flexure testing, the maximum load obtained at the failure of the specimen is denoted as W in the following equations [11, 12]. Flexural rigidity, D =[(Es × b × t 3 )∕6] + Es (2 × b × t) [(d + t)∕2]2 + (Ec × b × c3 )∕12 (N∕mm2 ) Bending stiffness, K = D∕L3 (N∕mm) Bending moment, M = (W × L)∕4 (N∕mm) Bending stress, 𝜎b = (M × h)∕(b × t × d2 ) (MPa) Maximum shear stress in core,Tc = {(Q∕D) [(Es × t × d)∕2 + (Ec (c2 ∕4 − y2 )]} (MPa), where Q = W ∕2 Normal stress, 𝜎x =M × h∕2 × I (MPa), where I is the moment of inertia of sandwich core I = b (h3 − c3 )∕12 (mm4 ) Shear deflection, 𝛿shear (mm) ∶ 𝛿shear = [(W Lc )∕(4bd2 Gc )], where G = E∕2 (v + 1)

10.3 Methodology and Experimental Work

Table 10.1 Dimension and density of balsa wood samples. Length (cm)

Breadth (cm)

Height (cm)

Volume (cm3 )

Mass (g)

Density (g/cm3 )

1

39.9

10.2

1

406.98

43.18

0.1061

2

40.1

10.2

1

409.02

45.35

0.1109

3

40.0

10.2

1

408

45.54

0.1116

4

40.0

10.2

1

408

32.19

0.0789

5

40.1

10.2

1

409.02

34.83

0.0852

6

40.0

10.2

1

408

32.58

0.0799

Batch

Table 10.2 Dimensions of samples for compression testing. Length, L (mm)

Breadth, W (mm)

Height, T (mm)

Flatwise (force perpendicular to the direction of fiber)

40

20

10

Edgewise transverse (force perpendicular to the direction of fiber)

40

20

10

Edgewise longitudinal (force along the direction of fiber)

40

20

10

Test sample

10.3.4

Technical Specification

Firstly, the Balsa wood core sandwich composite samples were cut and then weighed, and their respective densities were determined and given in Table 10.1. Six samples of balsa wood of various skin-to-core weight ratios were tested with vernier calipers and their thicknesses were determined. Now, the width for sample preparations for testing was taken as 2T and the span length was taken as 16 : 1. Three samples were cut along with one reduced size sample. For three batches of balsa, for which the thickness was 1200 °C @ 20 °C/min N2 Purge = 100 ml/min

Operator: TGA Operator Instrument: SDT Q600 V20.9 Build 20

100.2

100 R 99.8

Weight (%)

272

Highly volatile 0.2% matter

V

Medium volatile matter 0.41%

H

99.6 S 99.4

99.2

99.0

98.8

Residue: 98.89% (12.89 mg)

0

100

200 X 300

400

500

600

700

800 Y 900

Temperature (°C)

1000 1100 1200 Universal V4.5A TA Instruments

Figure 14.6 TGA scan of Rockwool sample. X, temperature taken in the center of the first mass loss plateau; Y, temperature corresponding to the mass loss plateau used for switching atmospheres; S, mass measured at temperature Y (mg); V, highly volatile matter content (%); R, mass measured at temperature X (mg).

14.3.2

Thermogravimetric Analysis (TGA of Rockwool)

At room temperature, the sample weighed 13.0350 mg, and on reaching 1200 ∘ C, the sample weighed 12.89 mg. About 98.89% of the residue still remained in the crucible. Thus, it can be concluded that the material is thermally stable. Highly volatile matter obtained from the compositional analysis was just 0.2%. This indicates that the sample consists of only 0.2% or lesser amount of moisture by weight. Most of the natural fibers exhibit a high moisture absorption characteristic or they are severely hydrophilic. Of the total of 0.2% highly volatile matter, some portion of it could be chemicals used while manufacturing the Rockwool LRB mattress. The resin for bonding also acts as a plasticizer, as pointed out by M. Zihlif and G. Ragosta [10]. The material seemed to be quite stable up to 869 ∘ C as the depletion rate was not high, as can be seen from the plot. However, as soon as it reached the next phase, the depletion rate increased drastically. Figures 14.4–14.6 throw some information on the EDS composition and TGA analysis aspects of Rockwool samples. The compositional EDS analysis and TGA results are illustrated in Tables 14.1–14.4. 14.3.3

Differential Scanning Calorimetry of Rockwool

1. The midpoint temperature (T mg ) obtained from the analysis of the DSC plot is regarded as the glass transition temperature. Thus, the glass transition temperature obtained was around 252 ∘ C.

14.3 Results and Discussion

Table 14.3 Rockwool sample details of TGA scan. Density (kg/m3 )

150

Weight (mg)

13.0350

Method

Ramp

Heating rate (∘ C/min)

20

N2 purge (ml/min)

100

Instrument

SDT Q600 V2.0.9 Build 20

Table 14.4 Analysis from the thermogravimetric results.

Components

Start temperature (∘ C)

Rate (∘ C/min)

High volatile

Ambient

20

Medium volatile

268

20

Combustible

869

20

Ash

—

20

Final temperature (∘ C)

Weight (mg)

Gas

wt%

268 (X)

N2

0.2

2.607

869 (Y )

N2

0.41

5.344 35

—

Air

—

—

—

Air

—

—

2. An endothermic peak was followed by the glass transition phase. This is evident from the nature of DSC plot obtained, which is concave shaped, signifying the absorption of heat. 3. The endothermic peak wherein the sample weight does not decrease rapidly over a span of the peak can be regarded as the melting peak. In the temperature range of 750–900 ∘ C, the weight loss rate was low. Thus, it can be concluded that this concave-shaped peak obtained in the DSC plot was the endothermic melting peak. The shape of the peak obtained, as can be seen from the DSC plots, was broad and asymmetric, which signifies the presence of impurities leading to such nature of peak. 4. The exothermic peak (exo up) was followed by the endothermic peak phase. This is evident from the nature of DSC plot obtained, which is convex shaped, signifying the release of heat. 5. The exothermic peak wherein the sample weight decreases rapidly over the span of the peak can be regarded as a decomposition peak. For example, exothermic decomposition peak was obtained in the range of 900–1000 ∘ C. Also, from the compositional analysis performed in the TGA results, it can be seen that in the range of 900–1000 ∘ C, the residues are the combustible matter. They undergo combustion, thereby leading to an exothermic nature of the DSC plot. Figure 14.7 clearly illustrates these aspects. 14.3.4 14.3.4.1

Volume Fraction of Fabricated Composite Volume Fraction of Rockwool for Epoxy-Based Composite

Higher amount of matrix was infused in the composite with 100 kg/m3 Rockwool as reinforcement than in the composite with 150 kg/m3 Rockwool as reinforcement. This was due to the fact that Rockwool with higher density will

273

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic Sample: Rockwool density 150 Size: 13.0350 mg Method: Ramp Comment: RT --> 1200 °C @ 20 °C/min N2 Purge = 100 ml/min

Operator: TGA Operator Instrument: SDT Q600 V20.9 Build 20

1.0

Teig Tmg 0.5

Heat flow (W/g)

274

Tml

Tefg

0.0

–0.5

–1.0

Tm –1.5

0

200

Exo up

400

600

800

Temperature (°C)

1000

1200

Universal V4.5A TA Instruments

Figure 14.7 The DSC results of Rockwool sample. T eig , extrapolated onset temperature, 192 ∘ C; T mg , midpoint temperature, 252 ∘ C; T efg , extrapolated end temperature, 319 ∘ C; T m , endothermic melting peak, 854 ∘ C; T m1 , exothermic decomposition peak, 948 ∘ C. The glass transition temperature obtained is 252 ∘ C.

have lesser and smaller pores in the given dimension. This results in higher resistance in the flow path of the matrix through Rockwool laminate and thereby reducing the matrix content. Thus, as the density of the reinforcement increases, the volume fraction of the composite also tends to increase, if the rest of the parameters are unchanged in the RIM process. Tables 14.5 and 14.6 provide information on the volume fraction evaluation. 14.3.4.2

Volume Fraction of Rockwool Fiber for CNSL Composite

The volume fraction of 100 kg/m3 Rockwool CNSL composite was estimated as 0.08 and that of the 150 kg/m3 density Rockwool CNSL composite was estimated as 0.16. Thus, the effect of density on CNSL-based composites was similar to that of epoxy-based composites, as can be seen in the following sections (Tables 14.7 and 14.8). 14.3.5 14.3.5.1

Epoxy-Based Composite Tests and Analyses Tensile Test

The specimens were prepared and tested as per ASTM D3039/D3039M-14 on Instron 8801 Universal Testing Machine [17].

14.3 Results and Discussion

Table 14.5 Density 100 kg/m3 /Epoxy composite. Sr. No.

Particulars

Units

Quantity

1

Volume of epoxy GY257 used

ml

400

2

Volume of hardener AD140 used

ml

200

3

Volume of acetone used (volatiles)

ml

100

4

Total volume of matrix in composite

ml

600

5

Weight of the Rockwool slab before fabrication

g

75.0

6

Weight of Rockwool unused

g

30.0

7

Weight of Rockwool in the composite

g

45.0

8

Density of Rockwool fiber

g/cc

2.4

9

Volume of Rockwool in the composite

ml

31.5

10

Total volume of the composite

ml

631.5

11

Fiber volume fraction of the prepared composite

%

5

Table 14.6 Rockwool 150 kg/cu.m/Epoxy composite. Reno

Particulars

Units

Quantity

1

Volume of epoxy GY257 used

ml

450

2

Volume of hardener AD140 used

ml

225

3

Volume of acetone used

ml

113

4

Total volume of matrix in composite

ml

675

5

Weight of the Rockwool slab before fabrication

g

161.0

6

Weight of Rockwool unused

g

12.4

7

Weight of Rockwool in the composite

g

148.6

8

Density of Rockwool fiber

g/cc

2.4

9

Volume of Rockwool in the composite

ml

67

10

Total volume of the composite

ml

742

11

Fiber volume fraction of the prepared composite

%

9

• To avoid the premature failure of the specimen, tabs made of corrugated cardboard were used to damp the effect of the compressive force induced from clamping. • The dimensions of the tabs used were 25 mm × 25 mm, and the overall length of the specimen was chosen to be 300 mm. Thus, a gage length of 250 mm was obtained. The width of the specimen was taken as 25 mm. Adhesive was used to bond the tabs to the sample at the two ends. A standard head displacement rate of 2 mm/min was set. • Failure Mode Analysis: A three-part failure mode code, wherein the first code is for failure type, the second code is for failure area, and the third code is for failure location, was used to describe and analyze the failure modes, as shown in Figure 14.8.

275

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14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

Table 14.7 Density 100 kg/m3 /CNSL composite. Sr. No.

Particulars

Units

Quantity

1

Volume of CNSL used

ml

150

2

Volume of toluene used

ml

800

3

Volume of formaldehyde used

ml

160

4

Total volume of matrix in composite

ml

310

5

Weight of the Rockwool slab before fabrication

g

70.0

6

Weight of Rockwool unused

g

12.0

7

Weight of Rockwool in the composite

g

58.0

8

Density of Rockwool fiber

g/cc

2.4

9

Volume of Rockwool in the composite

ml

29.00

10

Total volume of the composite

ml

339.00

11

Volume fraction of the prepared composite

%

8.6

Units

Quantity

Table 14.8 Rockwool 150 kg/cu.m/ CNSL composite. Sr. No.

Particulars

1

Volume of CNSL used

ml

150

2

Volume of toluene used

ml

800

3

Volume of formaldehyde used

ml

140

4

Total volume of matrix in composite

ml

290

5

Weight of the Rockwool slab before fabrication

g

104.0

6

Weight of Rockwool unused

g

0

7

Weight of Rockwool in the composite

g

104.0

8

Density of Rockwool fiber

g/cc

2.4

9

Volume of Rockwool in the composite

ml

58.33

10

Total volume of the composite

ml

348.33

11

Volume fraction of the prepared composite

%

16.74

• The most prominent mode of failure for the above-mentioned specimens was lateral, gage, and top as the failure type, failure area, and failure location, respectively. • Catastrophic fracture with no sign of warning was observed for the above-mentioned samples. • The crack propagation observed was rapid without any significant plastic deformation. These are the signs of brittle fracture of the material. Also, as can be seen from the stress–strain curve, the fracture is purely brittle as the breaking point corresponds to the ultimate tensile strength point for most of the samples. Figure 14.9 provides information about the failure modes of the epoxy-based composites.

Sample No.

1

2

LGT 72 mm from top

LGM 115 mm from top

Density 150 kg/m3 3

4

5

LGT 79 mm from top

LGT 72 mm from top

Fractured sample images

Failure mode code Failure location

LGT 71 mm from top

Figure 14.8 Tensile fracture samples of Rockwool/epoxy composite (density 150 kg/m3 ).

Sample No.

1

2

LGM 145 mm from top

GAT 54 mm from top

Density 100 kg/m3 3

4

5

LGM 118 mm from top

LGT 43 mm from top

Fractured sample images

Failure mode code Failure location

LGT 65 mm from top

Figure 14.9 Tensile fracture samples of Rockwool/epoxy composite (density 100 kg/m3 ).

14.3 Results and Discussion

Table 14.9 Tensile test operating conditions. Rate (mm/min)

2.000 00

Humidity (%)

60

Temperature (∘ C)

25

Table 14.10 The tensile test results of the Rockwool/epoxy samples.

Sr. No.

Particulars

Units

Density 100 (kg/m3 )

Density 150 (kg/m3 )

1

Maximum load

N

860.590

673.586

2

UTS

MPa

4.960

3.849

3

Breaking load

N

859.430

621.110

4

Breaking strength

MPa

4.911

3.549

5

Modulus of toughness

kJ/m3

22.190

21.505

6

Elongation at UTS

mm

2.039

1.572

7

Elongation at breaking point

mm

2.042

1.67

8

Elongation at maximum load

%

0.81

0.6

9

Elongation at breaking load

%

0.817

0.66

10

Modulus of elasticity

MPa

714.65

841.658

11

Average stiffness

N/mm

427.74

452.14

The test results are given in Tables 14.9–14.11. • The above differences can be attributed to the difference in the volume fraction of the fabricated composites. Owing to the lower matrix content in the 150 kg/m3 Rockwool as compared to the 100 kg/m3 Rockwool, weak interfacial bonding may be developed. Because of this, the matrix may not be able to transfer and distribute the load effectively among the reinforcements and thereby resulting in lower load bearing capacity, UTS, and breaking strength as compared to the composite with 150 kg/m3 Rockwool as reinforcement. Tables 14.9–14.11 give the operating conditions and average tensile test result values. • It can be inferred that the elongation between the UTS and breaking point was very less as it is a brittle fracture. Also, the % elongation is minute, which indicates high stiffness. • The drastic fall in the load–displacement plot graph after the UTS represents the breaking of the specimen or rupture point. The following straight horizontal path is due to the fact that the specimen is already into two pieces, and thus, the plot shows only the extension without any load or stress. This part of the curve needs to be discarded, and thus, the end of this straight plot should not be recorded as the breaking point.

279

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14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

Table 14.11 Proof yield stress and yield strain of the tensile samples.

Sr. No.

Proof or offset yield strain (mm/mm)

Proof or offset yield stress (MPa)

Sample details

1

0.004 7

1.763 07

Density 150 Sample No. 1

2

0.009 42

6.499 29

Density 150 Sample No. 2

3

0.009 63

5.144 12

Density 100 Sample No. 4

14.3.5.2

Compression Test

• The specimens were prepared and tested as per ASTM D3410/D3310M-03 on Instron 8801 Universal Testing Machine [17]. • The dimension of the specimen used was 14 mm × 10 mm × 3 mm. The anvil height was 14 mm, width was 10 mm, and thickness was 3 mm. Because the dimension of the specimen was small, bending stress might be induced in the specimen apart from compressive stress, and the results thus obtained will not be solely representative of the compressive strength of the specimen. To avoid this, a compression die was used to hold the specimen, as in Figure 14.10. The slot in the compression die was 3 mm in thickness and 4 mm in height. A standard displacement rate of 2 mm/min was set. • Failure Mode Analysis: Compression test specimen three-part failure identification codes and overall specimen failure schematics as specified in the standards were used to describe and analyze the failure modes. The first code is for failure type, the second code is for failure area, and the third code is for failure location, as described above. • The most prominent mode of failure for the above specimens was splitting, gage, and middle as the failure type, failure area, and failure location, respectively. • The crack initiation was by the mode of splitting in most of the cases. The crack initiation and propagation with the reduction in the specimen height on compressive loading is demonstrated (see Figures 14.10 and 14.11 for failure modes). • In some cases, multiple modes of failure were observed as in the case Density 100 Sample No. 4, Density 150 Sample No. 2, and Density 150 Sample No. 4. The sample demonstrated below is Density 150 Sample No. 2; failure mode M(SET)AB. 1. The crack is initiated by splitting, as can be seen in Figure 14.12. 2. As this crack propagates, the specimen starts to buckle. It undergoes elastic microbuckling. 3. The microbuckling in the shear mode gives rise to compressive forces that are not coaxial. This finally induces shear failure in the specimen at the end, as shown in Figure 14.13. • The signs of fracture were easily evident before the failure. Thus, the material does not show a brittle nature in the compression loading as in the case of tension loading. Figures 14.12–14.14 schematically show the fracture and failure modes of the epoxy composite in compression.

Sample No.

1

2

SGM

M(SET)AB

Density 100 kg/m3 3

4

5

M(ET)GM

SGV

4

5

M(ET)GM

SGM

Fractured sample images

Failure mode code

Sample No.

1

2

SGM

SAB

SGM

Density 150 kg/m3 3

Fractured sample images

Failure mode code

Figure 14.10 Compression test fracture modes of Rockwool/epoxy samples.

SAB

282

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

1

3 Density 150 kg/m Sample No. 1 – Crack initiation and propagation 2

4

5

7

8

3

6

Figure 14.11 Compression test fixture and fracture modes of Rockwool/epoxy samples. Figure 14.12 Antiphase microbuckling of fibers in compressions.

14.3 Results and Discussion

Figure 14.13 In-phase and out-of-phase microbuckling of fibers in compression.

Fibers

Matrix

(a)

(b)

(c)

Figure 14.14 In plane–in-phase microbuckling of fibers in compression. (a) Compression test in progress. (b) Sample after testing. (c) In-plane microbuckling.

Test Results: • The differences can be attributed to the difference in the volume fraction of the fabricated composites. Owing to higher Rockwool content and lesser matrix content in the case of composite with 150 kg/m3 Rockwool as reinforcement, the compressive strength of the specimen is increased as the reinforcement is in the form of wool, which is only likely to crimp rather than fail under the compressive load. On the other hand, higher content of matrix in the 100 kg/m3 density Rockwool composite specimen makes it prone to compressive loading owing to the brittle nature of the matrix (see Tables 14.12 and 14.13). • The average compressive strength of the composite with 100 kg/m3 Rockwool as reinforcement was obtained to be 3.69 times its average ultimate tensile strength, and the average compressive strength of the composite with 150 kg/m3 Rockwool as reinforcement was obtained to be 12.53 times its average ultimate tensile strength. This indicates that the composite in much stronger and effective in compression mode than the tension mode. • Also, the average strain developed at its maximum load for the composite with 100 kg/m3 Rockwool as reinforcement in the compression mode was 27.49 times the average strain developed in the tension mode. The average strain

283

284

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

Table 14.12 Compressive test operating conditions. Rate (mm/min)

2.000 00

Humidity (%)

60

Temperature (∘ C)

26

Width (mm)

10.000 00

Thickness (mm)

3.000 00

Anvil height (mm)

14.000 00

Table 14.13 Compressive test results of the Rockwool/epoxy composite. Density 100 (kg/m3 )

Density 150 (kg/m3 )

Sr. No.

Particulars

Units

1

Maximum load

N

549.764

1447.5

2

Compressive strength

MPa

18.326

48.25

3

Modulus of toughness

kJ/m3

1353.58

4239.86

4

Compression at maximum load

mm

3.11

3.46

5

Compression at maximum load

%

22.26

24.76

developed at its maximum load for the composite with 150 kg/m3 Rockwool as reinforcement in the compression mode was 41.28 times the average strain developed in the tension mode. This indicates that the material is more brittle in tension mode than in compression mode. • A rapid increase in the stress in the graph after the flat land represents that the specimen is bent over to almost right angle from the fracture point and now the 10 mm × 10 mm face is taking the load rather than the initial 10 mm × 3 mm face. Thus, no reading should be recorded beyond the horizontal flat landing of the load–displacement plot. 14.3.5.3

Flexure Test

• The specimens were prepared and tested as per ASTM D7264/D7264M-15 on Instron 8801 Universal Testing Machine [18]. • The three-point bending test was performed with central loading on a simply supported beam. Standard head displacement rate of 2 mm/min was used. • Span-to-depth ratio for the sample used was 16 : 1. The dimensions of the sample were 162 mm × 13 mm × 7 mm. The span length was 112 mm, the width was 13 mm, and the thickness was 7 mm. The excess length of the specimen at the end was kept 20% of the span at each end to prevent the rolling down of specimen from the supports under bending. The average thickness of the specimen was obtained and the span length was calculated using 16 : 1 span-to-depth ratio as span length (l) = 7 × 16 = 112 mm. • Failure Mode Analysis: A three-part failure mode code was adopted wherein the first code was for failure type, the second code was for failure area, and the third code was for failure location (Figure 14.15).

Sample No.

1

2

TAM

TAM

Density 100 kg/m3 3

4

5

TAM

TAM

Fractured sample images

Failure mode code

Figure 14.15 Fracture and failure modes of the flexurally tested D100 samples.

TAM

286

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

• The most prominent mode of failure for the above specimens was tension, at loading nose and middle as the failure type, failure area, and failure location. • Because the failure type is tension, it can be inferred that the tensile strength of the specimen is less than that of the compressive strength. This can also be seen in the tensile test and compressive test results (see Figure 14.22). • The failure location was observed at the midspan because the flexural stress is maximum at the center of the span or at the loading point in the case of three-point bending. • Because the tensile strength is low, the crack initiates on the tensile surface and later propagates in direction opposite to that of the loading direction to the surface under compressive stress. This was common for both types of specimens. Figure 14.16 provides information about the fracture and failure modes of the D150 specimens. • Sudden fracture with no sign of warning was observed for the above samples, as shown in Figure 14.17. The crack propagation observed was rapid without any significant plastic deformation. These are the signs of brittle fracture of the material. Also, as can be seen from the stress–strain curve, the fracture is purely brittle as the breaking point corresponds to the maximum load point for most of the samples. Test Results: • Toe Compensation: There may be a toe region in the stress–strain curve or load–displacement curve, as shown in Figure 14.18. It is due to the initial seating of the specimen or take-up of slack and alignment. Toe compensation is needed in such cases, wherein a corrected zero point is established on the strain or deflection axis. This was obtained as shown in Figure 14.18: • The linear portion of the flexural stress-strain curve is chosen as shown in Figure 14.18. • Function INDEX (LINEST(stress range, strain range),1) and INDEX (LINEST(stress range, strain range),2) was used in Excel, which gives the slope (m or E) and Y intercept (c) in the liner trend line Y = mX + c. • X intercept is obtained as X = −c/m. This is nothing but the amount of compensation to be made or a corrected zero point. With reference to this corrected point, the corrected values of extension and strain are obtained. The flexural strength of the 100 kg/m3 Rockwool composite was 3.61 times the tensile strength and 0.97 times the compressive strength. The flexural strength of the 150 kg/m3 Rockwool composite was 8.54 times the tensile strength and 0.68 times the compressive strength. Thus, the compressive strength of the epoxy-based Rockwool composites was highest, followed by the flexural and compressive strength. The vibrational characteristics for the first two modes were obtained for the Rockwool epoxy-based composite for which the specimen dimension was 200 mm × 30 mm × 7 mm as length, width, and thickness (see Figure 14.19). First, two natural frequencies and damping factors were noted down from the experiment. From the damping factors obtained, it can be concluded that

Sample No.

1

2

TAM

TAM

Density 150 kg/m3 3

4

5

TAM

TAM

Fractured sample images

Failure mode code

Figure 14.16 Fracture and failure modes of the flexurally tested D150 samples.

TAM

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

Figure 14.17 Three-point bend setup and fracture of a Rockwool/epoxy sample. 50 Flexure stress (MPa)

288

Y = 2179.9X – 20.06

40 30 20 10 0 0.00

Compensation

0.01

0.02

0.03

0.04

Flexure strain (mm/mm)

Figure 14.18 A typical load–displacement plot with toe compensation in flexure.

Figure 14.19 The frequency response function (FRF) curve of the Rockwool/epoxy composite.

14.3 Results and Discussion

Table 14.14 Flexural test operating conditions. Rate (mm/min)

2.000 00

Humidity (%)

60

Temperature (∘ C)

26

Table 14.15 Flexural properties of D100 and D150 samples. Density 100 (kg/m3 )

Density 150 (kg/m3 )

Sr. No.

Particulars

Units

1

Maximum load

N

68.0025

124.7500

2

Flexure strength

MPa

17.9352

32.9010

3

Flexure extension at maximum load

mm

6.6077

6.2710

4

Flexure strain at maximum load

mm/mm

0.0221

0.0210

5

Max flexural extension

mm

10.6899

7.1988

6

Max flexural strain

mm/mm

0.0358

0.0241

7

Flexural modulus of elasticity

MPa

956.7100

1598.6729

8

Modulus of toughness

kJ/m3

318.315

420.554

Table 14.16 Vibrational analysis of the Rockwool/epoxy composite. Natural frequency (Hz) Modes

Density 100 (kg/m3 )

Density 150 (kg/m3 )

Damping factor Density 100 (kg/m3 )

Density 150 (kg/m3 )

First mode

34.789

55.484

0.085 937

0.066 271

Second mode

230.13

346.48

0.067 85

0.050 149

the material can be used in vibration, isolation, and damping applications (Tables 14.14–14.16). 14.3.6 Scanning Electron Microscopy (SEM) Analysis of Epoxy-Based Composites • Fracture surfaces of tensile, compression composite specimens were examined by Oxford Instruments SEM. • Prior to examination, the surfaces were coated with a thin layer of a gold–palladium alloy in order to improve conductivity and prevent charging. Figure 14.20 shows the steps formed in the matrix. The loading direction was in the Z axis (coming out of the sheet). This justifies the brittle nature of the failure of the matrix in tension mode. This indicates the absorption of energy by local deformation. The direction of the increasing height and thickness of the steps

289

290

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

River line steps

10 µm

EHT = 10.00 kV WD = 8.5 mm

Signal A = SE1 Mag = 2.50 K X

Date:5 Apr 2016 Time:11:09:15

Figure 14.20 Step formation in the epoxy matrix indicating brittle failure.

represents the direction of crack propagation. As described above, the step size and thickness increase downward. Thus, it can be concluded that the direction of the crack propagation is downward. Figure 14.21 shows a fracture cross section of the fiber in the tension mode. The loading direction was in the Z axis (coming out of the sheet). This induced the shearing force in the fiber as per the orientation of the fiber with respect to the loading direction. The shear marks are evident from the cross section of the fiber at the end. This indicates the crack initiation at the other end of the fiber, propagation toward the end with shear marks, which again is in line with the loading direction. Figure 14.22 shows multiple river line steps/river line fracture. This again signifies the brittle failure of the matrix under the tension mode. However, as can be seen from the figure, there were signs of debonding of the fiber with the matrix. This shows the relative nature of adhesion of the resin to the Rockwool compared to other fibers. Thus, a relatively good adhesion along with brittle matrix failure justifies the lower tensile strength of the composite. Figure 14.23 illustrates the curing of the resin droplet over the fiber. The angle at the drop end made with the fiber is known as the contact angle and the length of contact of cured resin drop with the fiber is called drop length. The contact angle signifies the compatibility of the resin with the fiber. The lesser the contact angle, the more compatible it is with the fiber. As can be seen from the SEM image, the contact angle is acute, which indicates that the resin selected is quite compatible with the fiber. This justifies the selection of Rockwool epoxy combination for composite fabrication. Figure 14.24 shows the compressed, crumbled, and failed debris of the matrix after compression. Here, the failure mode of matrix was not by means of river

14.3 Results and Discussion

Shear marks

2 µm

EHT = 10.00 kV WD = 8.0 mm

Signal A = SE1 Mag = 5.00 K X

Date:5 Apr 2016 Time:11:11:52

Figure 14.21 Fracture cross section of Rockwool fiber in tension.

20 µm

EHT = 5.00 kV WD = 11.5 mm

Signal A = SE1 Mag = 1.00 K X

Date:5 Apr 2016 Time:12:45:15

Figure 14.22 River pattern fracture of matrix due to tension. The figure shows fibre pull out in the marked boxes.

steps as in the case of tension mode, this gives the composite a lesser brittle nature in compression mode. Figure 14.25 shows the bridging of the Rockwool fiber across the crack produced in the matrix part. This signifies that the matrix predominantly fails in the case of compression mode and the Rockwool fiber tries to prevent it from cracking as far as possible by the means of bridging.

291

292

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

10 µm

EHT = 10.00 kV WD = 12.0 mm

Signal A = SE1 Mag = 2.00 K X

Date:5 Apr 2016 Time:10:22:10

Figure 14.23 A low contact angle denoting good adhesion of epoxy matrix with Rockwool.

20 µm

EHT = 10.00 kV WD = 16.5 mm

Signal A = SE1 Mag = 2.00 K X

Date:5 Apr 2016 Time:10:32:06

Figure 14.24 Compressive fracture feature of the epoxy resin composite.

Figure 14.26 shows the cross section of the Rockwool fiber of density 100 kg/m3 . As can be seen from the image, the end of the Rockwool fiber is quiet planar without any marks. Figure 14.27 shows multiple rive line steps/river line fracture. This signifies the brittle failure of the matrix under flexure mode. These river patterns were expected because under flexure loading, the crack initiation was on the tensile surface and the failure was catastrophic as seen under the tensile loading, which also has these patterns. The same case was seen in the flexure specimens of Density 150.

14.3 Results and Discussion

20 µm

EHT = 10.00 kV WD = 16.0 mm

Signal A = SE1 Mag = 500 X

Date:5 Apr 2016 Time:10:35:53

Figure 14.25 Fiber bridging due to shear in compressive testing.

10 µm

EHT = 10.00 kV WD = 12.5 mm

Signal A = SE1 Mag = 3.00 K X

Date:5 Apr 2016 Time:11:50:54

Figure 14.26 Planar fracture feature of the fiber cross section in compression.

Figures 14.28 and 14.29 show the random orientation of the Rockwool fiber of densities 100 and 150 kg/m3 . The pores (or the open space) seen in these fibers were more in D100 as compared to the Rockwool fiber of density 150 kg/m3 . The pore size and density govern the flow of resin through the Rockwool. More space offers less resistance to the resin flow. The 150 kg/m3 Rockwool composite exhibited higher volume fraction as compared to that of the 100 kg/m3 Rockwool composite.

293

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14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

30 µm

EHT = 10.00 kV WD = 14.5 mm

Signal A = SE1 Mag = 800 X

Date:27 Apr 2016 Time:12:49:08

Figure 14.27 Flexure specimen density 100 showing multiple river patterns.

100 µm

EHT = 10.00 kV WD = 14.5 mm

Signal A = SE1 Mag = 300 X

Date:5 Apr 2016 Time:11:37:28

Figure 14.28 Rockwool density 100 kg/m3 .

14.3.7 14.3.7.1

Rockwool/CNSL Composite Test Results Tensile Test Results

• The specimens were prepared and tested in the same manner as in the case of the epoxy-based composites. The average thickness of the specimen was obtained and the cross-sectional area was calculated using A = w × h = 25 × 3 = 75 mm2 . • Failure Mode Analysis: • The most prominent mode of failure for the above specimens was lateral, gage, and midspan as the failure type, failure area, and failure location were identified, respectively (see Figure 14.30).

14.3 Results and Discussion

100 µm

EHT = 10.00 kV WD = 14.5 mm

Signal A = SE1 Mag = 300 X

Date:5 Apr 2016 Time:12:11:01

Figure 14.29 Rockwool density 150 kg/m3 .

1

Sample No.

Density 100 kg/m 2

3

3

4

5

M(AO)GM

M(LO)GT

M(LO)GT

Fractured sample images

Failure mode code

M(LO)GM

M(LO)GM

Density 100 kg/m3 Sample No.

1

2

3

4

5

M(LO)AB

M(LO)GB

M(LO)GM

M(LO)GM

Fractured sample images

Failure mode code

M(LO)GM

Figure 14.30 Tensile failure modes of the Rockwool/CNSL matrix composite.

• Brittle fracture of the specimens with the tensile load justifies the lateral type of failure in the above samples. The other type of failure mentioned in the code is the shear. Most of the specimens experienced this mode of failure. The shear mode of failure in the tensile specimen is shown in the figure.

295

296

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

Figure 14.31 Tensile fracture of a CNSL/Rockwool composite showing a mixed mode of fracture.

Table 14.17 Tensile test results of the CNSL/Rockwool composite.

Sr. No.

Particulars

Units

Density 100 (kg/m3 )

Density 150 (kg/m3 )

1

Maximum load

N

28.861

16.424

2

UTS

MPa

0.385

0.219

3

Breaking load

N

16.253

7.659

4

Breaking strength

MPa

0.217

0.102

5

Modulus of toughness

kJ/m3

2.868

0.480

6

Elongation at UTS

mm

3.442

2.364

7

Elongation at breaking point

mm

4.358

2.666

8

Elongation at maximum load

%

1.377

0.945

9

Elongation at breaking load

%

1.743

1.066

10

Modulus of elasticity

MPa

28.618

21.950

11

Average stiffness

N/mm

8.436

6.847

• As can be seen from the figure, the crack initiates on the outer surface and then propagates through the thickness diagonally to the opposite surface, thereby breaking the specimen into two pieces (see Figure 14.31). The test results are given in Tables 14.9 and 14.17. The tensile modulus of elasticity and the modulus of toughness for CNSL composites were obtained in the same way as in the case of epoxy composites. • Similar inferences can be drawn from the above test as in the case of the tensile test on the epoxy-based composites. • The UTS of the 100 kg/m3 Rockwool epoxy composites was obtained to be 29.81 times the UTS of 100 kg/m3 Rockwool CNSL composites and the UTS

14.3 Results and Discussion

of the 150 kg/m3 Rockwool epoxy composites was obtained to be 41.01 times the UTS of 150 kg/m3 Rockwool CNSL composites. • The drastic fall in the graph after the UTS represents the breaking of the specimen or rupture point. The following straight horizontal path is due to the fact that the specimen is already into two pieces, and thus, the plot shows only the extension without any load or stress. This part of the curve needs to be discarded, and thus, the end of this straight plot should not be recorded as the breaking point. 14.3.7.2

Compression Test Results

• The specimens were prepared and tested in the same manner as in the case of the epoxy-based composites. The average thickness of the specimen was obtained and the cross-sectional area was calculated using A = w × h = 3 × 10 = 30 mm2 . A failure mode analysis conducted is as follows: • Most prominent mode of failure for the above specimens was splitting, followed by Euler microbuckling, “Gage and Middle” as the failure type, failure area, and failure location, respectively (see Figure 14.32). • The multiple mode of failure was seen M(SE), as shown in Figure 14.33: 1. Splitting 2. Elastic microbucklingconsisted of shear mode and out-of-phase mode, as shown in Figure 14.34. 3. The fracture finally induces shear failure in the specimen because of in-plane microbuckling in the shear mode at the end, as shown in Figure 14.35. Other failure modes, such as the in-phase and out-of-phase microbuckling, were also observed, as shown in Figures 14.34 and 14.35. The test results are given in Tables 14.12 and 14.18.

Density 100 Kg/m3 and 150 Kg/m3

Fractured sample images

Failure mode code

M(SE)GM

Figure 14.32 Fracture and failure mode in compression.

297

298

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

(a)

(b)

Figure 14.33 Fiber splitting in compression. (a) A schematic of fibre splitting. (b) Sample after compressive test. Fibers

Matrix

(a)

(b)

Figure 14.34 In-plane–in-phase and out-of-phase microbuckling. (a) As given already. (b) Compressive micro-buckling.

(a)

(b)

Figure 14.35 In-plane shear mode failure through microbuckling of fibers in compression. (a) As given. (b) In-plane micro-buckling of fibres.

14.3 Results and Discussion

Table 14.18 Compressive properties. Density 150 kg/m3

Sr. No.

Particulars

Units

Density 100 kg/m3

1

Maximum load

N

42.348

13.761

2

Compressive strength

MPa

1.412

0.459

3

Modulus of toughness

kJ/m3

41.115 051 09

22.809 318 39

4

Compression at maximum load

mm

1.010

2.416

5

Compression at maximum load

%

7.211

17.256

6

Stiffness

N/mm

52.453

8.047

The differences in the compressive results can be attributed to the difference in the volume fraction of the fabricated composites, as shown in Tables 14.12 and 14.18, and the mode of failure, as can be seen from the SEM images ahead. • This is just opposite to the case of epoxy-based composite wherein the higher volume fraction gave higher compressive strength. The higher matrix content in the epoxy-based composites made it more prone to the compressive load, thereby reducing its strength. This is may be due to the fact that the epoxy hardener matrix was more brittle and stiffer as compared to that of the CNSL matrix. • The compressive strength of the 100 kg/m3 Rockwool epoxy composites was obtained to be 12.9 times the compressive strength of 100 kg/m3 Rockwool CNSL composites and the compressive strength of the 150 kg/m3 Rockwool epoxy composites was obtained to be 105.18 times the compressive strength of 150 kg/m3 Rockwool CNSL composites. The reader may refer to Tables 14.12 and 14.13 for the comparisons. • The compressive strength of the 100 kg/m3 Rockwool CNSL composites was obtained to be 3.66 times the tensile strength and the compressive strength of the 150 kg/m3 Rockwool CNSL composites was obtained to be 2.09 times the tensile strength. This indicates that the composite is much stronger and effective in compression mode than in the tension mode because of the presence of Rockwool ceramic wool as the reinforcement. Ceramics are normally better with compression than in tension. 14.3.7.3

Flexure Test Results

• The instruction in the flexure test for CNSL-based Rockwool reinforced composite are the same as mentioned in the epoxy-based composites. The span-todepth ratio for the sample used was 16 : 1. The dimension of the sample was 86 mm × 13 mm × 3.5 mm. The span length was 56 mm, width was 13 mm, and thickness was 3.5 mm. The average thickness of the specimen was obtained, and the span length was calculated using 16 : 1 span-to-depth ratio as span length (l) = 3.5 × 16 = 56 mm.

299

300

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

(a)

(b)

Figure 14.36 Flexural test procedure for CNSL/Rockwool composite. (a) Set up before flexure test. (b) Sample after flexure test. Table 14.19 Flexural properties of CNSL/Rockwool composites.

Sr. No.

Particulars

Units

Density 100 (kg/m3 )

Density 150 (kg/m3 )

1

Maximum load

N

13.313

10.978

2

Flexure strength

MPa

7.022

5.790

3

Flexure extension at maximum load

mm

9.721

7.439

4

Flexure strain at maximum load

mm/mm

0.0651

0.0498

7

Flexural modulus of elasticity

MPa

38.9530

6.4580

8

Modulus of toughness

kJ/m3

133.4365

52.8694

• Failure Mode Analysis: No signs of crack initiation were observed up to a flexural extension of 8 mm, and no further loading was possible because of the sample deformation reaching limits. Thus, the sample was unloaded after reaching this point, as shown in Figure 14.36. The test results are tabulated in Tables 14.14 and 14.19. Modulus of elasticity and modulus of toughness were obtained in the same way as discussed earlier. • The differences in the properties can be attributed to the difference in the volume fraction of the fabricated composites. In this case, the higher Rockwool content and the lesser CNSL content in the 150 kg/m3 Rockwool composites lead to lesser resistance to the bending behavior, thereby leading to lesser flexure rigidity and flexure strength as compared to the 100 kg/m3 Rockwool composites as seen in Tables 14.14 and 14.19. As the volume fraction is low in both the composites, the shear rigidity at a low span (16 : 1) appears to be matrix dominated. Hence, the flexural strength and modulus of elasticity are higher when the matrix content is more. • The flexural strength of the 100 kg/m3 Rockwool composite was 18.24 times the tensile strength and 4.97 times the compressive strength. The flexural strength of the 150 kg/m3 Rockwool composite was 26.44 times the tensile strength and 12.62 times the compressive strength. Thus, the flexure strength

14.3 Results and Discussion

of the CNSL-based Rockwool composites was highest, followed by their compressive and tensile strength. 14.3.8 Scanning Electron Microscopy (SEM) Analysis of the CNSL-Based Composite As can be seen from Figure 14.37, the contact angle of the Rockwool CNSL density 100 based composites was acute, which signifies the compatibility of the CNSL resin with the Rockwool fibers. It was also noticed that this angle was greater than the Rockwool epoxy composites. This indicates weaker bonding of CNSL with the fiber as compared to that of the epoxy, relatively. This justifies the lower tensile, compressive, and flexure strength of CNSL-based composites as compared to epoxy-based composites. Figure 14.38 shows the failure crack patterns in CNSL-compressed specimen of density 100. The direction of compressive loading was in the horizontal direction parallel to plane of image. This initiated splitting in the specimen widening in vertical direction, as shown in the figure. The onset of splitting also brought fiber separation, as shown in Figure 14.38. Figure 14.39 shows the microcrack developed by tensile load and shear load in tensile specimen density 100. Because the direction of loading was in the vertical direction parallel to the plane of image, it can be concluded that the leftmost crack was produced by tensile load. The two microcracks seen on the right are in the direction of the loading. Thus, these cracks were produced by shearing. This also justifies the failure type M(LO) mentioned in the failure mode analysis of tensile test for CNSL/Rockwool composite. As can be seen from Figure 14.40, there were signs of debonding of the fiber with the matrix.

200 µm

EHT = 10.00 kV WD = 12.0 mm

Signal A = SE1 Mag = 200 X

Date:27 Apr 2016 Time:11:38:40

Figure 14.37 Fiber matrix fracture of the CNSL/Rockwool composite in tension.

301

302

14 Thermomechanical Characterization of Vacuum Resin Infusion-Molded Ceramic

20 µm

EHT = 10.00 kV WD = 12.5 mm

Signal A = SE1 Mag = 500 X

Date:27 Apr 2016 Time:12:21:46

Figure 14.38 Crack patterns of the matrix fracture in compression.

20 µm

EHT = 5.00 kV WD = 17.0 mm

Signal A = SE1 Mag = 1.00 K X

Date:27 Apr 2016 Time:12:40:25

Figure 14.39 Cracking pattern due to tensile loading revealing fiber matrix adhesion.

Figure 14.40 indicates the adhesion of the CNSL resin to the Rockwool of 150 kg/m3 as compared to that of 100 kg/m3 Rockwool. Higher volume fraction of the composite with 150 kg/m3 Rockwool obviously produces more interfacial area, which governs the fracture mode. For transverse fiber debondings, it is observed that the matrix develops oblong features depending on the matrix ductility. The vibrational tests for the CNSL composites with an impulse hammer yielded lower natural frequencies than their epoxy counterparts. This is mainly attributed to their lower stiffness. Tables 14.20 and 14.21 provide the material cost analysis details of the two sets of raw materials required for (i) epoxy-based Rockwool composite and (ii)

14.3 Results and Discussion

100 µm

EHT = 10.00 kV WD = 12.5 mm

Signal A = SE1 Mag = 300 X

Date:27 Apr 2016 Time:11:48:24

Figure 14.40 Fiber pull-out regions of the CNSL matrix.

Table 14.20 Material cost analysis of epoxy-based composites. Cost analysis of a single laminate for Rockwool reinforced with epoxy resin Particulars

Cost

Quantity

Total (Rs.)

Cost of 400 mm × 150 mm fabricated composite (100 density) 140 per m2

0.12

16.8

Epoxy GY 257

0.694 per ml

400

277.6

Hardener AD 140

0.9072 per ml

200

181.44

Acetone

0.4095 per ml

100

40.95

Total

—

—

516.79

Rockwool 100 density

Cost of 400 mm × 150 mm fabricated composite (150 density) Rockwool 150 density

140 per m2

0.12

16.8

Epoxy GY 257

0.694 per ml

450

312.3

Hardener AD 140

0.9072 per ml

225

204.12

Acetone

0.4095 per ml

112.5

46.068 75

Total

—

—

579.288 75

CNSL-based Rockwool composite. The costs are as on March 2017 and could vary with time. It can be seen that the individual advantages and disadvantages are observed for the above-mentioned material costs. The vacuum resin infusion costs that include consumables for tooling, fixturing, and manufacture and the process energy calculations have to be added depending on the scale and size with suitable changes to material costs. Labor and finishing costs are to be counted in at the end.

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Table 14.21 Material cost analysis of CNSL-based composites. Cost analysis of a single laminate for Rockwool reinforced with CNSL resin Particulars

Cost

Quantity

Total (Rs.)

Cost of 400 mm × 150 mm fabricated composite (100 density) Rockwool 100 density

140 per m2

0.12

16.8

CNSL

0.019 per ml

150

2.85

Toluene

0.437 58 per ml

800

350.064

Formaldehyde

0.244 8 per ml

160

39.168

Total

—

—

408.882

Cost of 400 mm × 150 mm fabricated composite (150 density) Rockwool 150 density

140 per m2

0.12

16.8

CNSL

0.019 per ml

150

2.85

Toluene

0.437 58 per ml

800

350.064

Formaldehyde

0.2448 per ml

140

34.272

Total

—

—

403.986

The Rockwool-based composites can be successfully used in acoustic, thermal, and vibrational insulation applications. Although their mechanical properties are not structurally compliant for advanced applications, they can be used in hybridized architectures and constructions for thermomechanical, thermoacoustic, and vibration damping applications at higher temperatures than polymer fiber-reinforced composites with the same resins. It must be emphasized that the CNSL resin is not only cost effective as a bioderived resin but also an excellent candidate for hygrothermal stability, termite, and rodent resistance and dielectric strength. There are four major milestones that were achieved to successfully complete the fabrication along with testing. • Preparing a new gate and runner system for each run of the RIM. • Preparing the RIM setup such as sealing of vacuum bag, cutting of wool slab, etc. • Running the RIM setup. • Specimen preparation as per ASTM standards and testing with fracture characterization. 14.3.9

Further Scope of Research

The impact test for the composite can be conducted on sensitive instruments meant for plastics. Fade and recovery behavior of the Rockwool epoxy-based composites can be evaluated owing to its high compressive strength and thermal stability to confirm its application as braking pads. The design of the gates and runner system can be changed, and its effect on the flow rates of the matrix and volume fraction of the composites can be noted. The research can be extended

References

with different matrix materials, densities, and thicknesses of Rockwool to gain a deeper insight into the change in the thermal, chemical, and mechanical behavior of the material and thereby obtain the perfect choice of matrix material, reinforcement density, and thickness for the desired optimum properties as per the area of application. Their durability studies in actual environment would be a good idea.

Acknowledgments The authors are thankful to the VIT management and the Dean, SMEC, for all the support and encouragement.

References 1 Kandachar, P. (2013). Materials and social sustainability. Materials Experience:

Fundamentals of Materials and Design 91: 91–103. 2 USDA (2008). U.S. Bio-Based Products Market Potential and Projections

Through 2025. USDA. 3 Saravana Bavan, D. and Mohan Kumar, G.C. (2010). Potential use of nat-

4

5

6 7

8

9

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11

ural fibre composite materials in India. Journal of Reinforced Plastics and Composites 29 (24): 3600–3613. https://doi.org/10.1177/0731684410381151. Ganesan, C., Pal, Y., Babu, R.S., and Kalpit, K. (2013). Effect of various fibres on mechanical properties of bio-composite materials. International Journal of Engineering Research and Development 6 (2): 67–73. Satapathy, B.K. and Bijwe, J. (2005). Fade and recovery behaviour of non-asbestos organic (NAO) composite friction materials based on combinations of rock fibres and organic fibres. Journal of Reinforced Plastics and Composites 24 (6): 563–577. 2016. www.rockwoolindia.com/pdf/sw_industrial1.pdf (accessed 22nd February). Karamanos, A., Hadiarakou, S., and Papadopoulos, A.M. (2008). The impact of temperature and moisture on the thermal performance of rockwool. Energy and Buildings 40: 1402–1411. https://doi.org/10.1016/j.enbuild.2008.01.004. Danielle, D.T., Abigail, H., and Buick, D. (2015). An environmental impact comparison of external wall insulation types. Building and Environment 95: 182–189. https://doi.org/10.1016/j.buildenv. 2014.11.021. Poologanathan, K. and Mahendran, M. (2012). Thermal performance of composite panels under fire conditions using numerical studies: plasterboards, rockwool, glass fibre and cellulose insulations. Fire Technology 49: 329–356. https://doi.org/10.1007/s10694-012-0269-6. Zihlif, M. and Ragosta, G. (2003). A study on the physical properties of rock wool fibre–polystyrene composite. Journal of Thermoplastic Composite Materials 16: 273–283. https://doi.org/10.1177/089270503028508. Öztürk, B. (2010). Hybrid effect in the mechanical properties of jute/rockwool hybrid fibres reinforced phenol formaldehyde composites. Fibers and Polymers 11 (3): 464–473. https://doi.org/10.1007/s12221-010-0464-3.

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12 Cheng, A., Lin, W.T., and Huang, R. (2010). Application of rock wool waste in

13

14

15 16 17

18

19

cement-based composites. Materials and Design 32: 636–642. https://doi.org/ 10.1016/j.matdes.2010.08.014. Dinesh, B. and Sabnis, A.S. (2014). CNSL: an environment friendly alternative for the modern coating industry. Journal of Coating Technology and Research 11 (2): 169–183. Prabhakar, M.N., Rehman Shah, A.U., Chowdoji Rao, K., and Song, J.I. (2015). Mechanical and thermal properties of epoxy composites reinforced with waste peanut shell powder as a bio-filler. Fibers and Polymers 16 (5): 1119–1124. Saw, S.K., Sarkhel, G., and Choudhury, A. (2012). Polymer Composites 33: 1824. ASTM E1131-08. 2008. Standard test method for compositional analysis by thermogravimetry. West Conshohocken, PA: ASTM Publications. ASTM D3039/D3039M-14. 2014. Standard test method for tensile properties of polymer matrix composite materials. West Conshohocken, PA: ASTM Publications. ASTM D7264/D7264M-15. 2015. Standard test method for flexural properties of polymer matrix composite materials. West Conshohocken, PA: ASTM Publications. ASTM D6641/D6641M-14. 2014. Standard test method for compressive properties of polymer matrix composite materials using a combined loading compression (CLC) test fixture. West Conshohocken, PA: ASTM Publications.

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15 Hydrogel Scaffold-Based Fiber Composites for Engineering Applications Ikram Ahmad 1 , Josè Heriberto Oliveira do Nascimento 2 , Sobia Tabassum 3 , Amna Mumtaz 4 , Sadia Khalid 4 , and Awais Ahmad 4 1

University of Lahore, Department of Chemistry, 54590, Pakistan 2C2T – Center for Science and Textile Technology, Textile Engineering Department, School of Engineering, Campus Azurem, 3 International Islamic University, Department of Biological Sciences, Islamabad, Pakistan 4 Government College University Faisalabad, Department of Applied and Biochemistry, 38000, Pakistan 2

15.1 Introduction 15.1.1

Hydrogels

The hydrophilic polymers are cross-linked to form a 3D network of hydrogels surrounded by intermolecular and intramolecular covalent bonds with strong physical desirability, which are apprehended together [1]. The enormous quantity of biological fluid and water is taken up in hydrogel, equal to the numerous thousand %, and without disband they engorge willingly [2]. The hydrogels have elevated hydrophilicity because of the presence of hydrophilic moieties such as amino group, amide group, carboxyl group, and hydroxyl group; in the backbone of polymeric series, these groups are dispersed. In case of swelling, the hydrogels are tough and soft, resembling living tissues to a great extent. In addition, there are many hydrogels, such as chitosan-based hydrogels, in alginate demonstrating attractive biocompatibility [2]. Dates back, the exterior of hydrogel is further than 50 years, when Wichterle [3] urbanized and examine a hydrogel based on the poly(2-hydroxyethyl methacrylate) for the submission of drop a line to lens. Since then, in the past two decades, the investigation of hydrogels has been radically prolonged. In addition, to enclose a broad diversity of relevance, the use of hydrogels is comprehensive and relevantly compromising; other than they are not inadequate to, liberation of medicine, wound-healing, tissue engineering, and the substance that is ophthalmic [4]. When there is equilibrium happen among the osmotic driving-forces than hydrogel arrive at their balance swelling typically, in the hydrophilic hydrogel medium, it give confidence the entry of biological liquid and water, and within the hydrogel by the polymer slanders the cohesive forces are apply. On the hydrogel growth, these cohesive forces are opposite, and the degree of cohesive forces is dependent on the irritated connecting density of

Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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the hydrogel [5]. In common, if the polymer is more hydrophilic than the hydrogel, the quantity of the entire water is superior, which is engrossed through the hydrogel. Uniformly, for an exact hydrogel, the cross-linking amount is elevated, and the amount of gel bulge is decreased. In dehydrated form, the hydrogels are typically called xerogels, while the dehydrated absorbent of hydrogel consequential by means of this procedure of drying, for instance, freeze drying, or the removal of solvent are referred to as aerogels. 15.1.2

Hydrogels as Compared to Gels

In the polymer science, one of the main common misconceptions is employing the idea of gel as a replacement of hydrogel and vice versa. Gels are semisolid substances prepared through hydrophilic polymers comprising minute quantity of solid and large quantity of liquid. On the other hand, gels do not materialize on the liquor similar to, they come into view on the hard similar to. The series of hydrophilic polymer hydrogels are complete; nevertheless, the cuffs are cross-linked and they facilitate them to swell without melting, maintaining their 3D arrangement. Consequently, gels can be distinguished from hydrogels by a number of standard features, such as their intrinsic cross-linking [6]. Nevertheless, besides the power of the pure armed forces, the gels are able to reach the squat stage of the practical cross-linking; this type of the cross-linking is reversible and extremely weak. 15.1.3

Classification of Hydrogels

There are many categorizations that are useful for hydrogels, which are discussed in Sections 15.1.3.1–15.1.3.3. 15.1.3.1

Hydrogel Origin

According to their source, hydrogel canisters are classified into ordinary artificial and semisynthetic. Through the customary polymerization of the trigger monomer of vinyl and mainly of the artificial hydrogel is manufacture. The bulge balance worth of artificial hydrogel is conflicting extensively according to the cross-linking thickness and the hydrophilicity of the monomer. To obtain the response of the in situ cross-linking, a bifunctional monomer is supplemented typically. These common hydrogels are complete through the usual polymer that comprises poly-nucleotides, poly-peptides, and poly-saccharides. Initially, the diverse usual source is from these usual polymers. For example, from the mammals, collagen is obtained, whereas from shell-fish, exoskeletons from chitosan are obtained [7]. 15.1.3.2

Hydrogel Durability

The hydrogels be able to be both study for example that hydrogels that are bottom on the poly-acrylate or the hydrogels are biodegradable for example that hydrogel which is stand on the poly-saccharides, depending on the attribute of constancy in the physiological surroundings. Recently, on the fabrication and utilization of new hydrogels that are biodegradable, a considerable body of examiners has

15.1 Introduction

been observing carefully. Use of these new biodegradable hydrogels wrap a lot of area that comprise together nonbiomedical and biomedical applications [8]. The biodegradable polymer inside the medium of the hydrogel, which shapes the low molecular weight oligomer, undergoes the series scission. Then, the resulting oligomer is auxiliary purged and suffer the degradation. 15.1.3.3

Hydrogel Response to Environmental Stimuli

It is observer through the history decades that the huge advance in examine and in the training of the exclusive group hydrogels is name the smart hydrogels. With the conformist kind the similarity in the technique of arrangements and the method of description, the “smart hydrogel” can, nonetheless the customary alter exhibit in their performance of bulge, mechanical individuality or system arrangement in comeback of the a variety of ecological stimuli for example the hotness, ionic strength, light, pH, or electric field [9]. To the neat hydrogels these alter are happen, in the reply to any of these incentive of surroundings vanish typically winning taking absent of the incentive and as a result the unique condition of the hydrogels are restored in a reversible way [10]. 15.1.4

Methods of Preparation of Hydrogels

Hydrogels are equipped via a different technique depending on the intended arrangement or the relevance in demand. Several of these techniques are summed up and discussed in Sections 15.1.4.1–15.1.4.4. 15.1.4.1

Free Radical Polymerization

The conservative free radical polymerization is a method favorable for hydrogels that depend on the monomers, for example, amides, acrylates, and vinyl-lactams [11]. In the growth of that polymer, which is usual, and depending on the hydrogels, these monomers offer an appropriate functional group or they encompass functionalization with the radically polymerizable collection [12]. For example, to expand that hydrogel that is dependent on the chitosan, this technique has been performed [13]. By using this method, the hydrogel, which is ready, involves the classic polymerization step of the free radical, initiation, propagation, chain transfer, and termination. In the pace of initiation, a broad array of evident, ultraviolet (UV), thermal, and the redox initiator is run for the creation of radical. When the monomers are retort with these fundamental and the monomer are exchange them in to the vigorous form with the extra monomer and so on in the pace of propagation. As a consequence, the extended series of radicals undergo the step of termination both by the chain transfer and during the permutation of the radical shaped polymeric matrices. The technique of the training of the hydrogel both in the bulk polymerization or solution polymerization. Throughout the fusion of a huge amount of hydrogel, the solution polymerization is attractive, and in this case, the major typically used solvent is water. Nevertheless, the bulk polymerization is quicker and the solution polymerization is deliberate, and the bulk polymerization does not require the elimination of the solvent; in the numerous way, this case is overwhelming.

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15.1.4.2

Irradiation Cross-linking of Hydrogel Polymeric Precursors

The radiation method of ionization, particularly stipulation, is coupled with the method of simultaneous sterilization, and for the amalgamation of hydrogels, it is an extremely efficient technique. The ionization radiation, for example, the ray of electron, and the γ-rays to ionize the trouble-free molecules, sufficiently elevates power together in the air and in the water [7]. For the duration of the irradiation of a polymer solution, there are a lot of place which is hasty are engender next to the normal of polymer. The arrangement of the huge number of cross-links the mixture of these radicals are guided. The advancement in the arrangement of hydrogel should be executed through the exploitation of irradiation of the polymer both in the bulk polymerization and in the solution polymerization. On the other hand, for the irradiation of the solution of the polymer for the configuration of macroradical, less energy is needed. In addition, the competence of the fundamental in the solution is elevated, owing to the fact that the thickness of the response combination is abridged [14]. To the growth of hydrogel via apply the irradiation are tender numerous benefit over the additional technique of the training where, through the procedure of irradiation to instigate the rejoinder no catalyst or preservative are desirable. Also, the technique of irradiation is extremely effortless and the amount of the cross-linking is with no trouble proscribed via unreliable amount of irradiation [15]. Owing to that recompense, many biomedical applications, where a broad variety of hydrogels are used than those used in this technique, have been used for the growth of this extensive range of hydrogels, where even the infectivity, which is extremely the slightest, is attractive. For example, to prepare the acrylic acid hydrogels, it is used extremely professionally, and in the grinding of poly(ethylene glycol) (PEG)/carboxymethyl, which is based on the chitosan, and the hydrogels are of receptive pH [16]. On the other hand, the polymer that can degrade under the process of ionizing irradiation in this method is not optional for hydrogel training. 15.1.4.3

Chemical Cross-linking of Hydrogel Polymeric Precursors

The process of chemical irritable linking of hydrophilic polymer is the main technique of the grinding of hydrogel. Rendering to this method a bifunctional cross-linking instrument is added to that solution which is insipid of that hydrophilic polymer and to respond with that instrument whose usage in the cross-linking of the polymer obligates a functionality that is precise appropriate for this [17]. For the groundwork of hydrogel together with artificial hydrophilic polymer and normal hydrophilic polymer, this technique is identically valuable and appropriate. For example, the hydrogels that are found on the gelation and albumin were advanced through exhausting the di-aldehyde or formaldehyde as an agent of cross-linking. That hydrogel that obligate high gratified of water and these polymers are also found on the cross-linking of the functionalized PEG and the poly-peptide that cover lysine are industrialized through this technique [18]. 15.1.4.4

Physical Cross-linking of Hydrogel Polymeric Precursors

Over the corporeal communication, the cross-linking of polymer for the creation of hydrogel is one of the mutual methods. There are some connections that comprise in the physical cross-linking, for example, the poly-electrolyte

15.1 Introduction

complexation, H-bonding, and hydrophobic connotation; through expending this method, the hydrogels are equipped under the mild circumstances. Polyelectrolyte Complexation (Ionic Interactions) In this method, over the devel-

opment of developments of poly-electrolyte hydrogels are equipped, among back-bones of polymer and the duo of exciting place a link is shaped. The shaped electrolyte link is differing from its constancy, rendering to the scheme pH. There is an instance of hydrogels which is equipped through this process are those which is subsequent from the poly-electrolyte complexation of the carboxylate group of the Na-alginate with the amino-group dispersed beside with the restraint of chitosan [19]. Hydrogen Bonding H-bonding among the sequence of polymers can also con-

tribute to the creation of hydrogels, for example, in the evolving of hydrogel that is founded on gelatin [18]. A H-bond is shaped through the connotation of an electron underprovided atom of H and that the functional group that obligates extraordinary electronegativity. The hydrogels, which are industrialized through this method, are exaggerated through the numerous factor, for example, the attentiveness of polymer, molar ratio of the each polymer, type of the solvent, hotness of the solution, and the grade of the connotation among the functionality of the polymer. Hydrophobic Association For procurement, the hydrogel here is an additional

methodology over the hydrophobic collaboration. Polymer and copolymer, for example, the block copolymer and graft copolymer, typically form the distinct construction through the hydrophobic microdomain. These domain which is hydrophobic piece as a point of connected cross-linking in the intact construction of polymer, and they are enclosed through the water which is hydrophilic fascinating district. To grow that hydrogels which is grounded on the category of the graft copolymer and tranquil of the hydrophilic PHEMA (methylmethacrylate) as a support and the minor quantity of hydrophobic PMMA (poly(methylmethacrylate)) as a long division [20]. In common, the motorized typical of these polymer which is joint hydrophobically are deprived owing to the interfacial adhesion, which is also deprived. This method for the groundwork of hydrogel has certain benefits, for example, the low cost of the coordination. 15.1.5

Scaffold

In tissue engineering, scaffolds play a significant role. The straight development of the cells is the determination of the scaffold, which ever showed within the absorbent construction of the scaffold or it is traveling from the nearby material. The preponderance of the cell type of the mammalian is a chorage reliant on, sense if a substrate of adhesion is not delivered, it will expire. The scaffold matrices are hand-me-down to the distribution of adhesive cell with the extraordinary competence and filling to the precise situates. Consequently, for the cell addition, a suitable substrate s on condition that through the scaffold, for the cell proliferation, differentiated function, and relocation of cell [21] to license

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the nutrients conveyance, excess, and the influence of biological gesturing that is permit for the existence of cell. At a manageable degree, the matrix material should be biodegradable and estimated the rate of that tissue regroup which is usual and should aggravate a negligible resistant and/or the provocative answer in vivo [22]. The scaffolds of the tissue engineering are meant to be occupied by the cells, and they also communicate the physiochemical signals to safeguard the development of the tissue. The scaffold, which is an artificial polymer, may be hand-me-down for the distribution of the protein and the issue of development with or without cells nearby to improve the reparation of tissue and the recohort of the tissue [23] in an ideal tissue engineering scaffold, which should be achieved the subsequent necessities [24]. 15.1.5.1

Biocompatibility

The scaffold should own the biocompatibility and poisonousness outlines, which are satisfactory [16]. To achieve a precise request, biocompatibility is the capability of the scaffold deprived of provoking a damaging immune or inflammatory reaction [22]. If the scaffold is degradable and nonpoisonous, the new tissue, which is custom, is substituted ultimately, or if it is biologically active or harmless with the nearby tissues, the scaffold will assimilate. However, if the scaffold is physically inactive, through the rubbery pill, it may be summarized in the nastiest circumstance when the scaffold is poisonous, the refusal of the scaffold and death of the tissue, which happens nearby. 15.1.5.2

Biodegradability

The scaffold is physically biodegradable. Its crops of degradation should not be poisonous and should be effortlessly removed from the place of establishment through the body [13], for an additional operation removing the necessity to eliminate it [25]. The degradation rate of the scaffolds must be regulated to compete with the rate of flesh recohort so that it is totally discrete once the tissue is repaired [21]. 15.1.5.3

Mechanical Properties

The motorized possessions of the scaffold should compete with those of the tissue at the location of establishment, or the motorized possessions at least ought be to the protection cells from harmful ductile forces or the compressive forces without constraining the suitable biomechanical signals [26] or below the functional complaint they endure. Instantaneously afterward, the implantation of the negligible level is provided through the scaffold and the flat of the biomechanical function that should increasingly recover until the usual tissue purpose has been reinstated, at which opinion the concept should obligate completely combined with the crowd tissues nearby [22]. 15.1.5.4

Structure

It should obligate macroscopic and microscopic construction, which is reproducible with the advanced relation of the superficial capacity appropriate or for the supplement of cell and medication [21]. With interface devotion, proteins or cells ascribe to the superficial of scaffolds. The scaffold must provide the cell adhesion and the proliferation, enabling cell–cell contact and cell relocation

15.2 Potential Applications of Hydrogels as Scaffold in Biomedical Application

[22]. Aimed at the optimum interaction of the scaffold with the cubicles, the absorbent construction is allowed. Exactly the competence of the cells is regulated through the extent of aperture at which the cells kernel n to the scaffolds; from all-pervading the scaffold, the minor scope apertures avoid the cells, although the apertures of the bulkiness averted the accessory of the cells, owing to the part which is abridged and, consequently, the thickness of the ligand that is obtainable [22]. The scaffold should obligate an absorbency, which is satisfactory, the greatness of the absorbency also contain in this and the scope of the aperture is dispersed and its interconnectivity. It allows the development of the cell and vascularization and endorses the conveyance of the metabolite [21]. A scaffold that obligates interconnected system of aperture and a high gradation of absorbency better than 90% is ideal for the scaffold to assimilate and interrelate with that tissue which is crowd [27]. 15.1.5.5

Nature

Imitating the ECM, which is innate, the material that borders the cell is the endogenous material, and it allows to quandary the tissue and it also delivers the indication of cellular growth and morphogenesis [28]. The processability and the pliability are owned effortlessly through the scaffold into the desired form, rendering to the necessity. They should be accomplished of existence shaped into a creation, which is disinfected. LC announcement kinetics is clear as the medication quantity varies into the scaffold. The supreme loading capacity has the scaffold so the unceasingly free the medication for the lengthier period after supplement into the body. It is essential to discrete the medication homogeneously throughout the scaffold or in separate parts and necessarily evade a first consequence of brust. The announcement of medication from the scaffold is essential to measure to aloe the suitable medication amount to spread the cell over an assumed time period. BA is distinct as in what way the medication binds firmly the scaffold; to permit the announcement of medication, this BA is identical low, although this binding affinity would principal to the dose dumping, which ultimately harvests the result which is toxic. The constancy of that medication, which is incorporated at the physiological temperature with admiration to the biochemical, bodily, and the biological movement, is to be measured. The dimensional constancy is parties the chemical constancy is also gangs and the organic activity over the lengthy time-period [23].

15.2 Potential Applications of Hydrogels as Scaffold in Biomedical Application Hydrogen can be used in the box directly after its preparation (with or without cell connections) or after shaping of the scaffolds. The hydrogel spring source scaffolds are a large part of the scaffolds because of the ability to adjust their features to show natural buildings. The scaffolds of hydrogel have been used directly to provide basic foundations and features in the dress hats, whether the holidays are resting in or following the 3D hydrogel process. If you want

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to discard a cellular hydrogel suspended between the scaffolds, the formation of peptide floor or all of the scaffold hydrogels can increase the size of the attachment. For example, one of the most effective ways to preserve skin absorption is the combination of RGD (arginine–glycine–aspartic acid) of peptide to attach peptide. On strengthening these RGD sites, hydrogels sites show internal testing, development, development, and processing of processing products. These cells include endothelial cells (ECs), fibroblasts, cell molecular cells (SMCs), chondrocytes, and osteoblasts. 15.2.1

Hydrogel and Tissue Engineering

An important research point has recently been based on the use of hydrogels through many tissue applications. For example, hydrogels used as scaffolds to use extracellular calculations, to provide reliable reliability systems and reliability and indicators of behavior, to achieve and produce cells, make barriers and tools, serve as drug accessories, and encourage influential groups that promote the process of mutation. 15.2.2

Hydrogels as Carriers for Cell Transplantation

Hydrogels can gain some time in cellular production because of their ability to repair when releasing machines, oxygen, and products made to spread easily to their species. For example, midi-polymerized midi (ethylene glycol) diacrylate, PEG (diacrylate) has been included in hydrogels made for the Langerhans installation. In this study, the home page has been briefed in a polymerizable solution and a solution used to build microspheres based on the PEG integrating islands. The hydrogel microspheres of PEG produce the potential for maturity, but the production of nutrients in the intestinal cells is not limited. We have won the debris error of the skin of the skin-polymerized hydrogel microspheres and as a result, the company was put into timely water and hydrogel ingredients stored in the work wise [27] in another survey [28], energy consumption outside the metalloproteinase (MMP)-Placed hydrogel in the study of the PEG based as a co-encapsulation flood bioactive flood of small peptide of vascular and small, β thyme. The study showed that the β4 remoisten co-operation in the magazines three-indicate position is therefore due to the human nerve endothelial dependence (HUVEC), survival, migration, and equipment needed. In addition, the β4 therapist prepares HUVEC and controls the intestines as PEG-hydrogels. These PEG-hydrogels make these long-term MMP ideas activate as a normal regulatory control of the encapsulation of muscles of the normal bioactive revision of the muscle ischemic muscle. In a recent survey, the built gelatin methacrylate (GelMA) hydrogel technology techniques for testing are used for the production of microtissues produced by blood [29]. Cells were tested, extended, extended, delivered, and taken from recording when we move to small hydrogel microgels. 15.2.3

Hydrogels as a Barrier Against Rest Enosis

Hydrogels that can be used to manage postrecovery clinics after these connections and other industries will stimulate cellular mobility, migration, and

15.3 Design Criteria for Hydrogel Scaffolds in Tissue Engineering

mathematical differentiation and therefore cause decay. Spring is based on poly(ethylene glycol-co-lactic acid), for example, made of polymerization-based polymerization in intraperitoneal intermediate levels, where it can be prevented from fibrin and fibroblast files on the site [30, 31]. 15.2.4

Hydrogels as Drug Depots

One of the most common applications of hydrogels is to use as local house skills. This is called the hydrophilic environment of sensitive height, and the ability to manage and the chemical bulk reversed the easiest way to find bio-oxidation connections [32]. In addition, we are able to manage kinetic requests according to recommendations by managers operations, such as oxygen, and the amount allowed for biodegradation measurement hydrogels [33]. Images of photopolymerizable hydrogels even unify for drugs that result in the ability to follow and are common, and we expect when we create controls. In addition, the power of drug delivery to hydrogels can be used simultaneously with such prohibition cover works, as described above, in the medical field and the field of simultaneously preventing any service-activated service [33]. For example, the hydrogel-polymerized level of review was created with an intrusionitoneal tissue to plasminogen activator urokinase, experimental plasminogen activator, and ancrod [34]. These guidelines have shown a high decline in training adhesion compared to the use of injections or preventing intraperitoneal hydrogel only. In another instance, mono- and multilayer hydrogels are designed to measure the blood vessels through the polymerization image using the interfacial used for nerve [35].

15.3 Design Criteria for Hydrogel Scaffolds in Tissue Engineering Supplemental alcohol (ECM) is a biological feature that provides protection against watches and other important functions. Here, ECM is one of the most important guidelines for the scaffolds of the leather work. ECM is a 3D micromatrix component and hydrophilic with highly powerful ways: collagen and proteoglycan filaments. Collagen coils came as columns and drew to the locations we offer, providing the power and ability to find tracking items. The proteoglycan filament varies and is not made from protein and hyaluronic acid (HA). Besides internal hair, plasma fluid but small promising proteins, ECM reflects gel [36]. Engineering equipment must meet the successful achievement of making ECM memory and therefore effectively work and promote new production. These hydrogel particles, for example, should provide a 3D image for mobile growth. Effective clocks organize natural designs and allow for ideas and information not made in 2D books. Design projects should include both technological and work standards (such as biodegradation, porosity, and the best chemicals) and biodiversity (such as inequality and cell adherence), and how it appears to be a good vascularization. In addition, the records as reliable and commercial enterprise should be assessed on the hydrogel scaffolds for technical purposes.

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15.3.1

Biodegradation

The most important thing we do is scalar-form work running recommendations to preserve cellular phone and mobile life and hopefully scoop. In most cases, the scaffold life will occur when the decay disappears. Therefore, the measurement rate of the most important idea of hydrogels in technology. A lack of scaffold of custom culture has been identified by the scaffold cell system that has not been updated. For example, PEG and poly(ethylene glycol)-dimethacrylate (PEGDMA) are polop and then hang hydrogel logs . o . images to make sa . sepo . and cow chondrocytes a month of renewal isel . op . o . [37]. After the photopolymerization, cells within the scaffold may maintain their energy, even that disintegrated, but because of not paying biodegradability of reputable for PEG logs, the cell number decreases very much at the moment. In fact, the position creates the scope of decaying through poly-polymerization of midi(propylene fumigate-co-ethylene glycol) and artery endothelial cell vascular. The World of Talent Nature 2013: 38 titles of hydrogel sharp and fast growing. In addition, we found a cell to turn and emerge from the hydrogel scalorytically degradable logs, but they were clustered by hanging on the hydrogel logs. In addition, it shows that then stretching logs that hydrogel fluctuation, molecular increases in the area of the ECM over cells that are exposed to the hydrogel scales. Lai, however, biodegradation corruption case is necessary to absorb hydrogel blocks of acne work, certain technological features that do not require scaffold scales, such as petroleum or cartilage cleaning. In these different types, the immediate or appropriate boundaries of the model may be a good solution to remove the lost or damaged work. Generally, scaffolds that do not have hydrogels have been developed by combining jealousy and/or genres that can be inserted into the polymer fluid. In the case of decomposing stems hydrogel scales, the main feature and then extending the degradable logs, the damage occurs through the crumbling process, it is a dasiloju enzymatic that engages in the decomposition hydrofoils can also be made through papaya with applications. The ECA contains biodegradable, hyaluronic acid, laminin, fibronectin, and collagen [34]. 15.3.2

Biocompatibility

The definition and development of the biocompatibility level is the most important technical building built for products like it is always a time of healing and the mobile process of transformation, and even when injuries are scratches [37]. Children hydrogel in the competition world can be offered for possible swelling and connectivity, regardless of the fact that the tissue is close or connected with the use of vasculature. One of the biggest challenges of biocompatibility of the hydrogel resistant to the chemical and chemical colors that can be used in the polymerization of hydrogels or has emerged that this polypus is a hydrogel, even if it means to change not less than 100%. Elements such as monomers are not protected, the guardian, managers, flavors of fats, and emulsifiers used in hydrogel preparation can also be dangerous, when they go to the reproductive cell or tissue [38]. For example, healing has used the most popular photos that have been used to reduce cellular functionality even at the end of count. Thus, hydrogel estimates are made by technology that allows you to clean up to avoid harmful chemicals

15.3 Design Criteria for Hydrogel Scaffolds in Tissue Engineering

before you use them. This skill can be used by using a variety of techniques such as crushing. In some cases, the correction of scaffold hydrogel is challenging or cannot be repaired, as the purpose of hydrogel given to the local connection. This is because the changes required to make hydrogel connection are inserted into the body when you hunt the first polymer. Therefore, if you use such reliable guidelines, you should be careful to ensure that all parts are not safe and safe. 15.3.3

Pore Size and Porosity Extent

The hydrogel scaffolds designed for the use of laboratory should be unique only for open connections, living in a large scaffold volume area. In this list of high quality, connections will promote the cellular connections and helps revascularization of matrix [39]. It is not only that it is a huge amount of ore but also many other boundaries such as polished size, volume, volume shape, heart failure, and pneumonia are very important if compared to the scaffold hydrogel operating. For example, the clay connection is necessary to ensure that all cell lines between 200 mm supply blood provided for the transfer of material transfer and basic oil size that the most important parameters in the holes are a small component, has pore through the cell will occur, inhibiting the cellular phone recommendations, ECM, and local revascularization within scaffolding. The size of the head of the skin for the cleaning of the product, as well as high temperatures for various reasons, has been discussed in many recent books. For example, it has been shown that the maximum temperature of revascularization is 5 mm [40], 5–15 mm for staining the fibroblast [41], and 20 mm in the form of ingrowth hepatocytes, the adult [42] 20–125 mm elastic reversible [43], and 200–350 mm for osteoconduction. 15.3.4

Mechanical Characteristics

The performance of hydrogels as the scaffolds of the model work can have a significant impact on the stored cells or skin. It has been established that ECM on the isometric scale in the cell within the cell is given in the given section, which differs from this type and can be converted into symbols. In addition, the response to each cell in the changing of treatment and treatment methods may vary from mind to speech statement [44]. For this reason, the distribution of hydrogel may need to be done on parts of a particular device. For example, it has been reported that hydrogel energy can be used to control the difference in the availability of electrical water mesenchymal cells [45]. For example, it has been reported that changes to PEG high-resolution decisions have been made that changes egg growth and morphological behavior [46]. 15.3.5

Surface Characteristics

The scaffold hydrogel soils are the first to start contact with cell and bones. Therefore, the physical features of the scaffolds are the key components in the management and production of cellular production. Many cells used for transformation are reliable; the hydrogel scaffolds should be designed in such a way to preserve

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their attachment. For this reason, hydrogel is being hit in large areas and accessibly may have a number of cells needed to install or repair a product or parts of the body. The results of the hydrogel scaffolds can be developed in various ways with lighted products and verification items such as RGD peptide, development characteristics (such as BF GF, EGF), insulin, fibronectin, and collagen. This change can result in a hydrogel scaffold number, so cells may recognize the scaffold. Adhesive biomoieties can be harmonious, sufficient, or integrated hydrogel scaffolds [47]. Scaffold hydrogel toward increasing surface-cells attachment and controlled release of regulatory growth factors. 15.3.6

Vascularization

Vascularization is important in providing nutritious food-based products and eliminating low yielding products. Therefore, analyzing the new blood application (revascularization) is the key difference for most technical advice. However, talking about appropriate colors that allow and encourage new blood clots is a huge challenge. The fact that scales on logs should be in degrees of carbon dioxide, the most appropriate size and space changes make the muscles occur as tissue aging. For other technological applications, hydrogels have a vascularizable scorpolds. For example, alginate scaffolds based on hydrogel have been found to be very successful in in vivo saline [48]. In general, there are two ways to encourage the tail to limit the body screen shown in (number 7). In the first way, the feature-featured growth of the glands between the scales of hydrogel to cause muscles in this area in this area to flourish in the marketplace. The second method is to transfer the scaffold seed of hydrogel and endothelial cell (ECs). Using the first method, for example, gelatin, alginate, PEG, and hyaluronic acid-based hydrogels full vasculogenic development showed that the guarantee after the development of micro vessel is installed. One of the mechanisms that have been assessed in promoting the scalar-form auxiliary is based on the end of the members (EPCs) [49, 50]. However, exposure to the EPC and vascular area to deal with scaffolds where it is included is based on the negative effects of accumulation of the EPC and can take a long time (to date) to occur. In all, you cannot remove more than 100 μm from blood products, so as some types of cells within the hydrogel screwdriver: they can learn for trips to necrosis while waiting for a throw. In addition, although the EPC is generally endless because of the offset of outside the cell phone, they should carry their tension.

15.4 Hydrogel Scaffold: A Main Tool for Tissue Engineering 15.4.1 15.4.1.1

Fabrication of Hydrogel Scaffolds for Tissue Engineering Emulsification

Emulsification is performed in multiphase agitation to produce minor droplets of aqueous hydrogel precursors within a medium like organic solvent or in oil that is hydrophobic in nature. Hydrogel precursor size of the droplet can be controlled

15.4 Hydrogel Scaffold: A Main Tool for Tissue Engineering

by viscosity, mechanical agitation level, and by means of the surfactants, and it is used to control surface tension between phases and used for prevention of aggregation of hydroparticles as well. Different cross-linking mechanisms are used for the hydrogel precursor droplets to produce particles that include spherical micro or nanoparticles from a wide range of particles from synthetic or natural polymers that include polylactic-co-glycolic acid, polylactic acid, chitosan, agarose, collagen, and alginate. Cells are added into the aqueous phase that contain the precursor of hydrogel through this addition of gel particles of cell-laden could be fabricated. Encapsulation of embryonic stem cells can be carried out through emulsification as in vitro culture within hydrogel microparticles; through this technique, more controllable environment can be developed for differentiation [51]. Through emulsification process, gel particles can be used to develop easily as it is the main advantage of this technique. However, this technique has potential limitations; for example, in the case fabricated gel, the shape is limited to sphere only, regardless of its ability to control the wide cell size distribution of particle. 15.4.2

Lyophilization

Lyophilization is a freeze-drying technique mostly depending on the quick cooling of the samples, and thermodynamic instability can be produced inside it, leading to phase separation. This process under vacuum followed by sublimation of the solvent, pores, and voids is left behind through this technique. This technique produces hydrogel matrices that are porous in nature, as this approach has been extensively used in tissue engineering. Wu [52] reported that hydrogel scaffolds were based on collagen-chitosan preparation and assessment was cross-linked with glutaraldehyde used for engineering of adipose tissue. In vivo and in vitro characterization proved that the hydrogel scaffolds based on collagen-chitosan that developed and planted by the preadipocytes cells that were most biocompatible, and ability to induced vascularization to produce adipose tissue, another report demonstrated that hydrogel scaffolds of agarose, having channels, as linear porous channels and modified lyophilization method used and by this way these were fabricated. In this technique, first of all, one side pillar of agarose gel was exposed to the dry ice block and was engrossed within a liquid nitrogen pool. Ice crystals are formed as a result of uniaxial temperature gradient, concerned within the direction of that slope, whereas in the second step of lyophilization, sublimation of water, a network of highly linear porous channels were formed with dimension as appropriate for cell infiltration. For spinal card injury model, these scaffolds, agarose-based hydrogel scaffolds fabricated by using that procedure, were exposed hopefully for axonal regeneration [53]. Lately, an alternative technique was reported by Ricciardi for the growth of hydrogel scaffolds. Frequent freeze–thaw cycles were performed in this procedure to evade the incomplete phase separation that may occur throughout the initial freezing step as the lean phase polymer may form into the scaffold [54]. Freezing steps are repeated to allow additional phase separation of lean phase polymer in pores of matrix, polymer-lean phase formed that is more diluted more focused polymer-rich phase, therefore greater pores formation can be achieved. This technique demonstrates difficulty in precise turning pores

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because of its solubility for lyophilization for fabrication of porous scaffold as long processing time is needed as a result of poor mechanical characteristics. Moreover, lyophilization generally lead to formation of skin surface, as matrix breakdown at it surface air interface scaffold, resulting as during solvent evaporation the interfacial tension change occurred [55]. 15.4.2.1

Emulsification Lyophilization

In this method, polymeric emulsions are generally composed of dispersed aqueous phase or organic dispersion medium, vice versa. In dispersed phase, biodegradable polymer was dissolved, and then these are lyophilized in order to yield porous biodegradable scaffolds, with diverse interconnectivity and pore sizes. This procedure was used to produce scaffolds with porosity about 95% degree and pore size more than 200 mm [56]. 15.4.2.2

Solvent Casting Leaching

This is the simplest technique for the development of scaffolds, as porous scaffolds for nearly uniform pore size. In this technique, the practice includes molding of solution, i.e. organic polymer solution that contains salt particulates and cross-linker that is followed by the dissolution of the deceived salt and solvent evaporation that is involved in the deceived salt particulates in water. However, this approach has some shortcomings as some residual salt particulates remain in the scaffold. Thin film scaffolds can also only be produced by this technique. For the production of thin scaffold membranes having comparatively high porosity (up to 93%) and open cell morphology, this technique has been reported to be used, and membranes of porous scaffold were coated with different anatomical structures to develop 3D scaffold [57]. 15.4.2.3

Gas Foaming Leaching

In this technique, a gas foaming agent, effervescent salt, is used to produce the scaffold structure that is porous in nature. Gel, such as polymeric gel, having consistently discrete salt particles was cast in a suitable mold like ammonium bicarbonate that leads to involvement in hot water. Ammonia gases and carbon dioxide (CO2 ) evolution result in removal of ammonium bicarbonate ((NH4 )2 CO3 ) particles, hardening hydrogel lead, followed by the matrix, i.e. porous matrix with high interconnectivity. Scaffolds that are obtain from this process open cellular structure exposed to a macroporous structure with uniform pore size and size of the pores range from 100 to 200 mm [58]. Citric acid and acidic salt were added into water to further modify this procedure before submerging the gel mold [59]. Citric acid salt reacts with ammonium bicarbonate ((NH4 )2 CO3 ), which enables the evolution of gases, and macroporous scaffolds are produced having pore sizes of 200 mm and porosity more than 90%. Mechanical characteristics and porosity through this modified method can be controlled by degree of evolution of foaming gases through controlling the reaction rate between salts. By using the same fabrication practice, highly open porous microspheres and injectable scaffolds can be produced and pore size 250 mm [60] and injectable scaffolds with an average pore size about 30 mm were also established, which were permissible promising for seeding and cell penetration.

15.4 Hydrogel Scaffold: A Main Tool for Tissue Engineering

15.4.2.4

Photolithography

This technique is particularly developed for the nano and electronics. Recently, this technique has been used to produce diversity of biomedical applications of hydrogel scaffolds, for instance, microengineered scaffolds are produced through this technique. Different synthetic and natural photo-cross-linkable polymers are used in these techniques, and these cross-linkers undergo crosslinking to form hydrogels. This technique depends on the contact of a photo-cross-linkable polymer thin film and UV light as a mask. The photosensitive polymer reached by light, through this transparent area is masked and photochemical reactions, as these reactions crosslink the polymers. Recently, hydrogel matrices are developed through a similar technique just focusing and scanning of light. Photo-cross-linkable matrices, for instance, blue light, are used; for the safety of this technology, further advancement and enhancement were added specifically for the purpose of tissue engineering [49]. Laser scanning lithography is a comparable photolithography practice. In this procedure, laser light is used to cross-link the photosensitive hydrophilic polymers at precise sites [61]. 3D complex tissue scaffolds were constructed with the help of similar strategies, one layer at a time. Conjugate bioactive moieties with the aid of focused light and/or prefabricated hydrogel scaffolds were demonstrated [62]. With photoactive RGD peptide pattern, for instance, this method has been used within agarose-based hydrogel for the development of adhesive pathways; these pathways enabled to focus cell migration into the hydrogel, although this photolithography has significance as a fabrication procedure to produce hydrogel scaffolds. Some possible disadvantages have been reported, including the requirement for polymers such as photo-cross-linkable polymers and UV light destructive effects on function and cytotoxicity of human cell that is related to the use of photoinitiators. Furthermore, this technique is principally a 2D method, and the matrices are required for more assembly to produce 3D scaffolds. 15.4.2.5

Electrospinning

One of the most momentous fabrication practices are used to fabricate interconnected porous scaffolds, and these scaffolds are best practiced in tissue engineering purposes. In electrospinning practices, an external electric field is essential, and capillary tube end microfibers are extracted from charged polymer solution. High voltage is applied to charge the polymer and then strained as a thin jet filament directed toward the rotating collector or oppositely charged plate in accordance to the desired direction of fibers collected. The characteristics of fibers obtained include morphology, porosity, or diameter, which could be precise as adjusted processing parameters, for instance, conductivity, temperature, applied voltage, viscosity, and polymer solution [63]. Various types of hydrogel scaffolds are produced through this technique, for instance, the submicron (ultrafine), porous fibrous hydrogels, for instance, a combination of polyvinyl alcohol (PVA) polyacrylic acid and polyvinyl alcohol (PVA). Interfiber pores were interconnected in fabricated fibrous hydrogel scaffolds, a drawback to engineered tissue that permits migration and cell-to-cell interaction. Another report demonstrated that a salt-leaching method and electrospinning were combined to fabricate collagen–hyaluronic acid hydrogel nanofibers [64]. This

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report demonstrates that salt, NaCl (sodium chloride) salt, particles are used to persuade the porosity of interfiber. Different in vitro reports demonstrate that to fabricate collagen-hyaluronic acid; a hydrogel fiber that can assist proliferation, retention, or adhesion of the in vivo chondrocyte cells, morphology of like bovine. Another study demonstrates that the nano and micro nonwoven hydrogels constructed fibrinogen, silk, fibroin, and collagen fabricated with the aid of electrospinning for tissue engineering purposes [65]. The different types of cells can attribute and then proliferate and can differentiate within scaffolds including fibrous hydrogel scaffolds having potential for tissue engineering applications. However, for the development of hydrogel scaffolds by using electrospinning for tissue engineering, many drawbacks are still limited because this technique has limited control over pore size and prosperity, mechanical properties comparatively bad, and specifically incapability of this practice for fabrication of 3D hydrogel scaffolds [66]. 15.4.2.6

Microfluidics

A variety of hydrogel microstructures are produced through this technique single- or multiphase created that flows within microfluidic channels. Mostly, the polymeric hydrogel precursors and cells are subjected to flow through these microchannels that control the shape developed by the hydrogel [67]. Cell-loaded microgels are layered on each other to form complex 3D structures patterned with multiple cells types related to each other and tissue-like complexity can be recreated through this procedure. In a hydrophobic medium, a two-phase system is developed, which is composed of hydrophilic droplets used to develop hydrogel droplets and control physicochemical characteristics. To engineer unique hydrogel scaffolds, a combination of photolithography and microfluidics has been recently used [68]. In this report microengineered hydrogel scaffolds, microfluidic channels were used and by exposure of a stream of polymeric gel precursors and used to light that through a predesigned mask focused by microscope. The polymeric precursors were cross-linked as the fluid was exposed to light to produce microgels, and outlets of the microchannels are used to collect microgels that are produced. Through this combined fabrication approach, it was possible to control the shape of encapsulated cells in hydrogel scaffolds [69]. 15.4.2.7

Micromolding

An fabrication technique used to generate hydrogels enable to control the prosperity and shape, soft lithography developed in this and technique become predominantly attractive as soft lithography developed that enabled fabricate molds easily, as it is based on poly(dimethyl siloxane) obtain from silicon wafers that are prefabricated, through this controlled structures fluoro-based nanoscale, micromold particles developed [70]. In this practice, initially polymeric hydrogel including, micromolded hydrogel precursors are molded and on later gelled and variety of shapes, sizes. Morphologies are produced [71, 72]. Microengineered hydrogels are fabricated by using this technique from diverse polymers, for instance, hyaluronic acid [72], chitosan [71], and PEG. Controlled

15.4 Hydrogel Scaffold: A Main Tool for Tissue Engineering

features of microengineered hydrogels were unable to fabricate polymers such as alginates and fibrin as gelling agents are required, for instance, both divalent and polyvalent ions. To evade this limitation, an innovative procedure is functional including micromolding of alginate, and other gels are used as templates. In this process, by using hydrogel mold, polymeric gel precursor is primarily formed and then cross-linking agents are added to the mold to the cross-linked matrices for developing a new gel. Alginate microstructures, by means of this procedure, are used to fabricate the alginate microstructures having auspicious ability to encapsulate cells with precise structure. For the development of macroporous hydrogel interconnected 3D matrices, this technique is successful as structures of hydrogel were molded across a packed bed of polymeric drops that were later on dissolved [73]. With the assistance of a template that is dissolvable, gelatin-based, microfluidic channels of gels inside their structures were developed. 15.4.2.8

Three-Dimensional Organ/Tissue Printing

An innovative practice in tissue engineering is based on layered strand of cell-laden hydrogels or dropwise deposition [74]. This procedure is valuable to develop 3D scaffolds such as a rapid prototyping-derived technique in which internal morphology was predesigned and external shape is similar to certain cell settlement. By the rapid prototyping machine, a design aided by computer of the graft is explained into a layered predefined internal morphology and external shape cell-laden hydrogel constructed using either in vivo grafting or an in vitro model. Attained through using numerous productions of heads that comprising a or hydrogel or precise cell type through this heterogeneous constructed. In this technique, practice of hydrogel scaffolds is substantial as these scaffolds offer an assist matrix with an extremely hydrated microenvironment for embedded cells, where oxygen diffusion and nutrient can be adjusted. Generally, the main hydrogel necessities for this technique include the following: (a) Preservation of internal morphology and printed shape after the deposition (b) Noncytotoxicity (c) Mechanical characteristics and deliberating adequate stability for in vivo implantation and in vitro culture (d) Preserving function and cell viability (e) Easy to handle the printed scaffolds Additionally, hydrogel should preferably deliver the embedded cells having suitable physical stimuli and biochemicals that guide numerous cellular procedures such as differentiation, proliferation, and migration, and additionally, organ printing as an optimal use wild gelation is vital throughout piling of subsequent cell-laden hydrogel layers. Preferably, common hydrogels used to produce 3D tissue or organ printing comprise collagen alginates and pluronics [75]. However, mostly, these hydrogels showed some limitations including limited mechanical characteristics, absence of adhesive biomimetic arrangements, and variability in culture. In 3D practice, these gels are used in organ or tissue printing technique for the development of tubule-like structures laden having endothelial cells and various coculture systems designed [76, 77].

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15.5 Hydrogel Scaffolds for Cardiac Tissue Engineering A unified process is involved in both stem cells and cardiomyocytes that also supports matrices because of their softness, tissue-like characteristics, and viscoelastic nature and has been used to carry cells into infarcted cardiac muscle and supportive agents in cardiac tissue engineering. In the infarcted area, they not only maintain cells but also provide suggestions to support restore myocardial wall stress for cell function and survival. In cardiac tissue engineering practice, both synthetic and natural polymers are suitable. The most frequently used natural polymers for cardiac tissue engineering applications are gelatin sodium alginate, laminin, collagen chitosan, Matrigel, and hyaluronic acid (hyaluronan). The natural polymer structures are very similar to those of molecules present in biological organisms, when these are implanted the possibility of immune response reduced. Cardiac tissue engineering practice is used for the development of hydrogel matrices when synthetic polymers are used, including PEG, PLA (polylactide), PLGA (polylactide-co-glycolic acid copolymer), PCL (polycaprolactone), PAAm (polyacrylamide), and PU (polyurethane). Synthetic polymers are important over natural polymers because of the comfort of modifying their physiochemical characteristics that include modulus, degradation rate, and water affinity, which encounter the necessities of cardiac muscle tissue engineering practices. Possible cytotoxicity, however, is a major apprehension when the synthetic polymers are used. FDA proved that only PLGA (polylactide-co-glycolic acid copolymer), PLA, and PEG were used for clinical practices, but other polymers, for instance, PU and PAAm, were used due to nontoxic effect both in vivo and in vitro. For cardiac tissue engineering, several hydrogel matrices have been industrialized over the past decade. For example, Singelyn et al. [78] reported that porcine myocardium hydrogel is an injectable hydrogel that has generated to support the existence of cardiomyocytes and also the migration of both SMCs and ECs in vivo. Another in vivo report demonstrates that permeation of both SMCs and ECs into the hydrogel demonstrates that inside the hydrogel matrices, vascularization was improved. The report demonstrates that the findings of a study performed in vivo on a normal rat heart and by using a MI (myocardial infarction) heart model need to be verified. Another report showed that [79] resonating fibrin hydrogel tubes and neonatal cardiomyocytes colonized with them fixed adult rats’ femoral artery. Organ and tissue printing was done by using fiber deposition. EPCs in Matrigel/hematoxylin and eosin staining, scale bar 1/4 200 mm. Image was adapted from [80] a cardiac tissue in mature form after three weeks of implantation with a comparatively thick capillary network. Cardiac tissue thus formed verified all normal cardiac functions, includes both synchronous wandering with an external electric signal and contractility beneath electric stimulation. From the recent studies of Huang et al. [81], fibrin hydrogel was used to embed rat cardiomyocytes and they also proved that the contractility within normal pacing ability can be preserved more than two months. A hydrogel was

15.5 Hydrogel Scaffolds for Cardiac Tissue Engineering

Seft assembly 3D scaffold

Transplantation of graft

Computer assisted grafting

Figure 15.1 Schematic diagram of organ tissue printing for cardiac tissue engineering application.

produced by mouse, Matrigel, and ECM mimicking. To distribute the MSCs, a genetically modified human, Engelbreth–Holm–Swarm tumor has been used as a carrier to transport into the infarcted heart. This report showed that MSCs can survive under both apoptotic and ischemic environment and was suggestively improved. Matrigel was combined with the other natural polymers to advance the angiogenesis of cell and also proliferation in vivo. Giraud et al., for instance, revealed that heart function was enhanced by Matrigel/collagen when implanted into acute MI (myocardial infraction) rat hearts [82]. H9 C2 cardiomyoblasts and Matrigel/collagen hydrogel implanted in an acute rat MI (myocardial infraction) model engraftment rate was meaningfully increased [83]. More recent studies demonstrate that Matrigel was incorporated into fibrin hydrogel for encapsulation of cardiomyocytes. Cardiomyocytes encapsulated were able to maintain normal function for 10 days [84]. Synthetic polymer-based hydrogels were also investigated for cardiac tissue engineering. Wang [85] showed that hydrogels were based on PEG derivative, triblock copolymer (PEG–PCL–PEG), a mixture of cyclodextrin and bone marrow encapsulation, and MSCs and delivered it to a rabbit MI (myocardial infraction) site. Walker et al. demonstrated and implanted mesh-reinforced PHEMA and poly(ethylene terephthalate) (PET) hydrogel in canine epicardium. This report demonstrated the thickening or absence of any significant fibrosis 12 months after implantation. However, a suggestion, classification was detected on the gel after 9 and 12 months of implantation, biocompatibility was traced and established and PET/PHEMA was constructed for a long timeframe [86]. Organ tissue printing had been shown for cardiac tissue engineering in Figure 15.1.

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15.6 Hydrogel Scaffold Fabrication for Skin Regeneration With respect to skin cell signaling functions, four main types of scaffolds are considered [87]. It is a platform to assemble or capture signaling molecules for skin [88] to localize signaling molecules at precise positions in the cell occurring at this place [89]. To adapt the signaling pathway, it manages both positive and negative feedback signals of the cells. It preserves reliable activation of signaling molecules [90]. These functions are significant in 3D scaffold structures for culturing purpose because cells and other numerous signaling interactions depend on scaffolds. The structural design of scaffolds essentially matches thoroughly with the natural structure of both ECM and in vivo environment at a target skin site for effective tissue regeneration. 15.6.1

Molding Scaffolds

For any tissue culture, the requirement is that it must have 3D structure. Lithographic fabrication process is one of the best methods to produce this structure [91]. Extensively used technique for this purpose is Bio-MEMS (biological micro electromechanical systems), where scaffolds can be constructed either bottom to top or top to bottom with LBL (layer-by-layer technique). 3D molds were used to culture skin cells in microenvironment for an appropriate scaffold design. To imprisonment tissues or skin cells, a harmless process of cell culturing or tissue generation can be applied that would be biocompatible and 3D molds. 15.6.2

Nanofiber Fabrication Scaffolds

To regulate the diameter of fibers and fiber networked scaffolds, a suitable way is nanofibers (diameter < 100 nm) [92]. Nanofibers are biocompatible, and they facilitate to formulate skin scaffolds with their exclusive properties. Nanofibers associate with preceding bulk materials having reputable mechanical properties, weight ratio, and high surface area [92]. Truly, in the skin regeneration situation, nanofibers are the perfect materials for treatment, curing the burned or injured skin. Consequently, nanofibers are ideal materials for ECM just like scaffold fabrication [93]. As several fibers are required, for instance, collagens in the ECM, regulator of length, diameter, and bulkiness need to produce appropriate scaffolds to regenerate skin. Nanofiber-based scaffolds furthermore have excessive affinity for cell adhesion and scaffold matrices [93]. In 3D culturing arrangement by means of biological components and materials, cells could firmly adhere to scaffold matrices. In what way, 3D scaffolds system, nanofibers are fabricated? Electrospinning [94, 95] is a suitable scaffold fabrication practice for mass production. By applying appropriate electrical voltage, the nanofiber length and diameter can be regulated. Moreover, using modest and appropriate steps depending on the polymers being used, a diversity of cell types and diameter sizes could be shaped. This fabrication approach [94] tolerates brilliant mechanical properties and tensile strength, related to bulk materials that are comparable to

15.7 Osteochondral Tissue Regeneration

the bulkiness and also to nanofibers with porous structure regarding 3D scaffold applications [95]. Nanofibers characteristics regulation influential attention as impacting the progression and nanofibrous scaffolds used. 15.6.3

Three-Dimensional (3D) Printing

Photolithography technique is used to fabricate scaffolds with hydrogels. Furthermore, cultures are established in multicellular systems, in vitro, using a suitable and fast technique to replicate the scaffold [96]. It is significant to produce a scaffold that is based on the chemical of material matrix and factors of regenerative skin, as it is captivating into the interpretation of scaffold morphogenesis.

15.7 Osteochondral Tissue Regeneration The field of osteochondral tissue renewal is actually difficult owing to the separate possessions and also curative possibility of osseous and the chondral stage. In the usual area of osteochondral, the composition, construction, and procedure diverge easily from bony to cartilaginous stage. Consequently, the homogeneous scaffold cannot content the difficulty of the medium of the osteochondral. In spirit, an ECM is collected from the fibrous protein lengthened in to a gelatinous background. A hydrogel scaffold owning incline in the combined stages would be of great interest to reproduce the preparation of the matter of the osteochondral border which is natural. However, there are identical imperfect investigations that adventure the hydrogel scaffold for the osteochondral refurbishment [97]. 15.7.1

Single-Layer Gelatinous Scaffolds

For the scaffold construction, hydrogels are the greatest attractive selection. Viscoelastic similarity to that innate tissue, transportation of the possessions, and the water bulge brand of the hydrogel are convincing for the determination of the regeneration [98]. Hydrogels for the tissue engineering of the osteochondral are hand-me-down in the form of coating, which is solitary and the multilayer with or without the reinforcing and pharmacological seasonings. The obligate had been loaded a constituent which is pharmacological into a jellylike scaffold to upsurge the option of the osteochondral [99]. In the in vivo and in vitro valuation, the scaffold is considered. Rendering to the in vitro examination, the feasibility of the cells and the presentation of the cell were acceptable in usual or the oxygen which is sensitive to philosophy media. The appropriate conduct of the cell in the sensitive oxygen site milieu subsatiated the cell that obligate a consequence of scaffold, which is defensive for the free fundamental. In the vivo it is respect that, the creation of the con-current creation of the neo tendon and the jaw bone which is under-laying in addition to note the depletion in the inflammatory reply. In the accumulation to the consequence of the anti-inflammatory, the site, which is sensitive, is incorporated e scaffolds and exposed a leisurely rate of squalor and the motorized forte is higher when likened to those locations which is not sensitive.

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In addition to the consequence of osteogenic in the sensitive site, MSCs relocation is persuaded through the larger forte and into the undernourished linage the difference. In the normal osteochondral tissue, the experiential incline is needed by the scaffold. A scientist industrialized a scaffold of hydrogel collagen which is willingly concerned with and also they cover SDF-1 to overhaul the wound of osteochondral and to the place which is imperfect to persuade the stem cell relocation [100]. The oriented networks are owning through the scaffold which is tubular in the in cooperation course perpendicular and straight was invented via the incline of temperature guided-thermal parting of induced-stage. The method that is hand-me-down in centrifugally persuaded manifestation of the collagen which is published and therefore the apertures which are concerned with are outward following the lyophilization. After finishing the mixing of the fibrin answer, the SDF-1 was joined with the scaffold and then placed in the hollow region of the tubular scaffold. In the current educations the homing easing improvement an uncommon courtesy and the scaffold which is ready did not disclose some slow changes or shade all finished the construction. Scientist industrialized the two gradient issues for the development of, for instance, rhBMP-2 (bone morphogenetic protein 2) and the expansion subject I similar to insulin rhIGF-I in the scaffold of hydrogel to the unswerving joining requirement of stem cells. The microcompass and the incline of the microholes are summarized in the issue of development [101]. In the gelatinous scaffold, by consuming the incline creator, all conventional rights were industrialized. The consequences validate that the differentiation of osteogenic and chondrogenic of the stalk cell is improved in the attendance of the incline of the development issue. The scaffold is copied partially to the development issue incline, which is obtained at the border of gristle to jawbone. Through the physiognomies of scaffold, no alteration along the width of the scaffold was observed. 15.7.2

Multilayer Gelatinous Scaffolds

When the construction, which is multimalleable, takes place, they differ progressively from the distinguishing of one tissue to the additional matter of boundary, for example, the connection of the cartilage to bone [102]. In tissue engineering, the incipite plan is to overhaul the imperfection of osteochondral were absorbed on the distinct cartilage that is combining cartilage and concept of jawbone starting in a solitary scaffold. The biological and physiochemical synthesis is exploited to follow the dissimilar stage of the tissue. Although the devotions of this type did not guarantee correctly, an extended period tissue integration, particularly uncertainly the degradation of the substantial and the development of the matter, do not happen at a similar degree or the matter that is overhaul is situated in a site of weight manner [103]. Certainly, owing to the delamination, these constructions were functionally impracticable, attentive of stress, and unable to recapitulate the interfacial region. The procedure of interface, which is hardened among the cartilage of anticular and the jaw, is critical to circumvent the vascular tissue and the skinny tissue invasion into the district of cartilaginous. The hardened cartilage is vital to integrate the hard tissue and the soft tissue and to allocate the motorized loads crossways their interface [104]. The area of osteochondral is the

15.7 Osteochondral Tissue Regeneration

border of tissue and exhibits an incessant shade from the flesh of soft cartilaginous to the jawbone beneath. The interface of matter exhibits the difference of the mild arrangement, cradle of cell, mechanics, influence of cell gesturing, etc., from the area of soft tissue to hard tissue. To diminish the attentiveness of pressure, this incline is inconvertible at the region of interfacial and the good drive will safeguard [105]. A scientist is industrialized hydrogel scaffold coating with the construction, arrangement, and mechanics similarly to the tissue of osteochondral, which is innate. The collagen, GAGs (glycosaminoglycans), is the relaxed of inanimate of the scaffold were custom-made in the comparable method to those of the command which is normal. It is encompassed that the coating of gristle encompass the type I and type II hyaluronic acid and collagen; a coating of hardened cartilage contains type I and the collagen contains type 2 hydroxyapatite; and the coating of bone contains the type of collagen I and hydroxyapatite [106]. The postponements of the dissimilar arrangement were freeze dehydrated and cross-linked with the carbon diamide finished a method of coating by coating. The difference of the substantial arrangement along the scaffold allows upsurge unceasingly in the compressive modulus from the portion of cartilaginous to that district which is skinny. The beneficial aptitude of the scaffold which is fashioned is inspected in the vivo and vitro in the together replicas of trifling animal and large animal and the outcome which is talented is reached. The scaffold coordinated automatically and compositionally with the area of innate osteochondral; nonetheless, the microorganized is required through it to the innate flesh. Lengthways the gristle which is innate to bone interface dissimilar cell inhabitants with the specific forms which is current. The construction of scaffold which is absorbent is actual significant issue for adaptable the presentation of the cell and the statement of the tissue [107]. In the absorbent construction, the incline is authoritative to arbitrate the manifold material creation and the interface of the flesh [108]. The scope of hole and the absorbency are the key issues to regulate the chondrogenic and osteogenic distinction [109]. The cells are otherwise dissimilar to the scope of hole and porosity. Furthermore, the interconnectivity of the aperture of the cartilaginous and the chapters of osseous are unlike the articular cartilage, which is nourished generally through the articular fluid, while the bone is nourished through the nutrients from the movement of blood. It is reference overhead that the examination, the construction of absorbent was virtually are individual of the scaffold penetration is unaffected continue lengthways the breadth of scaffold. A scientist equipped a scaffold of multicoating and corroborated its scientific accomplishment. The abovementioned scaffold contained type I of collagen and hydroxyapatite as a coating of bone, the type I of collagen and hyaluronic acid as a coating of inbetween; and I type of collagen, type 2 of collagen, and hyaluronic acid as the layer of cartilage [73]. The scaffold was implanted into the consensual osteochondral grazes enduring and was flourishing fully. It is assessed through the education that the scientific applicability of the scaffold did not measure its physical and motorized characteristics. 15.7.3

Gel/Fiber Scaffolds

The ECM, which is innate container, is apparent as a cell-loaded hydrogel interrupted through the mechanical fiber. The reinforce hydrogel is not only

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hypothetical to be threads but also a regulator for the obligatory of the cell and control the destiny of the cell. Consequently the scaffold which is contrived comprising the portions of rubbery and gelatinous and can be painstaking as a commission which is self-same fine of the ECM which is innate [110]. The amalgamation of the stages of the rubbery and gummy will suggest a reasonable chance to enhance the overall functionality of the cell, for example, the mechanical possessions, biomimetic feature, and cellular relocation [111]. Compacted composites alleviate pristine fiber and welfares of amalgamate and disadvantages of hydrogel. The hydrogels are welt automatically and the rubbery are dense physically. The scaffold of hydrogel or fibrous can overcome the confines. Nevertheless, in these constructions, there is an acceptable meeting of threads while the hydrogels are considered. Further it is the amount of method for the mixture of the hydrogel and fiber in the solitary scaffold. The report of this method is studied in the part away [112]. 15.7.4

Fabrication of Gradient Hydrogels

There are many methods for the fabrication of gradient hydrogels, such as bioprinting, microfluidics, photopolymerization, etc., and it has been inspected to grow the hydrogel in the arrangement, mechanics, and absorbency. The methods of the microfluids which are founded on the, answers of dissimilar forerunner with the variable rate of flow and they are inaugurated into the stations of the microfluidic, unceasingly poured and it is varied to brand that incline which is appropriate. In greatest of the suitcases, the gradient which is produced is steadied through the chemicals, infection, or light [113]. The incline which is microfluidic are manufacture the expedient deliberate which is fine defined-gradient. Nevertheless, there is certain outstanding anxiety with that incline. The measurement of incline is thin [114]. Also, the remaining monomer cross-linker and the inventors in the positions of microfluid strength hamper and the appeal which is connected to the bio. Recently, there is a novel method of the stations of microfluidic and has been planned to grow centimeter-long incline of hydrogel. A microchannel was prefilled with the background solution and then infused through a drop of the envisioned solution. In the stations, the last solution is continue and shaped a gradient attentiveness of that physical which is envisioned by the grouping of the device of vanishing persuaded retrograde flow and the molecular dispersal [115]. It is careful that the bioprinting is the most convincing plan to grow the incline of hydrogel; meanwhile, a justly unconventional bioprinter is intelligent to switch the spatial injection of the substantial and correspondingly to generate the ramps. For the condense development factor of the incline and for the adhesive ligand, bioprinting is frequently used [116]. The attentiveness of the incline of the biochemical signaling molecules allows the creation of flesh and the cohort of the flesh. These particles will switch the conduct of cell in the method of the attentiveness reliant on confidential the tissue interface and the tissue. There is dissimilar caring of the bioprinter, for instance, inkjet printer, laser printer, extrusion printer, and the stereolithographic copier are used to grow the classified constructs. However, the selection of the material is the main concern

15.7 Osteochondral Tissue Regeneration

for the bioprinting. There is a correct physical for the bioprinting and they would obligate an equilibrium bioactivity, mechanical strength, and printability. This is problematic to contemporary in the solitary physical. Furthermore, in most of the cases, the substantial of the bioprinting is equipped in the previously unpackaged printing whose construction of the hamper-gradient owing to the necessity to formulate various sovereign solutions [117]. To posture the incline topographies, photopolymerization is the additional imaginable manner. Rendering to this method a solution which is photopolymerizable is unprotected to a remedial light in the presence of the sliding photomask. The prepolymer of hydrogel is exposed to the sunlight in the classified manner through expending the cover of incline and creating the hydrogel by the characteristic of the incline. In the hydrogel procedure, this method is mostly communicated on the incline slightly than the chemistry of hydrogel [118]. The form of the incline and the resolution are arbitrated through the geometric arrangement and extent of the photomask, whereas the belongings of the local gel are regulated through the cross-linking compactness or the content of prepolymer. This procedure is comparatively humble and inextensive. 15.7.5

Fabrication of Gradient Hydrogel/Fiber Composites

To the finest of authors’ information on the groundwork of the gel with the possessions of the incline, there is no bang. To invent a gel incline and scaffold of fiber, there are two feasible methods. First, the gelatinous stage and the fibrous stage with the topographies of incline are unconnectedly invented and are mutual to the scaffold’s single compound. In this case, the appropriate unification is delivered through the compound and the portions of gummy with no harmful result on the incline and the construction of all part. Second, the creation of the incline and the connotation of the stage can happen alongside. Certain technique of the construction may allow this method for the incidence. The method of bioprinting is an outstanding method with the aptitude of that physical which is just credit on the predesigned model. Together with the stages, the fibrous stage and the gelatinous stage with the arrangement of prearranged can be shaped and joined into a scaffold, which is solitary through a bioprinter [119]. However, the assortment of the substantial is the main anxiety, and the restraint for the bioprinting and hence the designated biomaterial would be printable [117]. The double procedure of the electrospraying and electrospinning is one additional method that is conceivable to harmonize the development of incline and the unification of stage. The fiber of electrospun and the atom of the electrospray are congregated in the solitary gatherer and they left-hand in the aqueous medium to aloe the subdivision for puffiness and the development of the hydrogel. For the positive employment of this procedure, certain significant facts are measured. Initially, the circulating excellence and the portion of the constituent in the concluding compound are extremely dependent on the speed of the gatherer [120]. The speed of the gatherer must be adaptable to permit for the together fibrous and subdivision efficient settlement. Furthermore, the vanishing of flush of the answer of both polymeric and must tuned to evade the remaining solvent. Through the procedure of electrospraying and electrospinning, if the subdivision

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or the rubbery which is semiwatery are dropped on the period of assembling, or the flush which is outstanding in the both constituent might interrelate chemically and the damagingly touch composite-characteristics. It has renowned that the solvable threads in the water cannot be hand-me-down for this methodology as they are brilliant slightly or liquefy completely during the composted interaction to the aqueous media. Consequently, this method is appropriate to that strength which is inexplicable in water and damage its applicability for that which is solvable in water. An additional method similar to freeze drying is the technique that is well-known for the construction of scaffold in which the solvent is detached from the forerunner of the scaffold and the holes are left overdue. Aimed at the construction of the conservative scaffold, freeze drying is the technique accomplished at the fixed temperature, while through variable freezing temperature, the incline is shaped. With the appropriate enterprise of the mildew cold, it is likely to devise a malaise incline through the freezing solution. The freezing casts owning selective conductive and the cloister shares can persuade the cold incline. The solution in incline is covered with ice and causes the construction, which is classified after the subdivisions of ice being detached. Furthermore, the freezing casts with the manifold layers or the appropriate applicant to progress the incline examples.

15.8 Biopolymer-Based Hydrogel Systems 15.8.1 15.8.1.1

Polysaccharide Hydrogels as Scaffolds Chondroitin Sulfate

CS (chondroitin sulfate) is a GAG acting as substitute units of d-glucuronic acid and N-acetyl-d-galactosamine. It has outstanding biocharacteristics, including modulation and binding of some growth factors, and natural CS is eagerly soluble in water [121]. For CS, chemical cross-linking is compulsory for hydrogel application, both in vivo and in vitro. For cross-linking of CS, a diversity of approaches exists. In literature previously revealed biocompatible hydrogel films produced by Pieper et al., adipic dihydrazide, a derivative CS-ADH suspended hydrazide produced a gel functionality, macro and micromolecular cross-linker include, propiondialdehyde, PEG and PEG-dialdehyde [122]. The maximum regularly functional cross-linking reagents include mixture of EDC (carbodiimide), NHS (N-hydroxysuccinimide), and 3-dimethyl aminopropyl (1-ethyl-3). In prevalence of collagen, the cross-linking reaction has frequently been accomplished by other reagents containing amine, for instance, 1,12-diaminododecane. Nevertheless, EDC used in cross-linking resulted in a partial matrix collapse in aqueous media. CS as an alternative procedure was operated with thiol groups, with a disulfide-containing hydrazide, by EDC-mediated compression, leading to dithiothreitol reduction. In a succeeding step, improved CS thiol was cross-linked by using PEG diacrylate [123]. GMA (glycidyl methacrylate) was applied by Li et al. in practical aqueous medium for heterogeneous reaction, irrespective of possible side effects of GMA’s. Two reactions take place immediately including both irreversible slow opening of epoxide ring and

15.8 Biopolymer-Based Hydrogel Systems

quick transesterification [124]. CS-based hydrogels have found extensive formal application in tissue engineering field. Hydrogels consisting CS and gelatin were functional for antibacterial proteins as measured release systems. Gelatin gels cross-linked with CS and expressively amplified the protein loading capability of the gels extending the release time. Alternate procedure impersonatore natural cartilage, gelatin-based CS hyaluronan, tricopolymer scaffolds were designated. It was experimentally demonstrated that the occurrence of CS encouraged the emission of type II collagen and proteoglycan. Bilayer biomatrices of CS–gelatin hyaluronan have also been intentional for the treatment of wounds. The outcomes exposed that a perpetual attention with effectively discriminated epithelial tissue and histologically normal, collagen network and definite dermal–epidermal junction were present in the skin dermis. As a consequence, a positive effect on skin superfluous on the elevation of the wound healing process and also contribution in deeply skin defects regeneration of. Additionally, tricopolymer scaffold can be used to human nucleus pulposus regeneration. Moreover, for diverse therapeutic approaches, CS-based gelatin was equipped for both microcarriers and membranes. 15.8.1.2

Hyaluronic Acid

A nonsulfated GAG comprises of units that are glycosidically linked with alternating bonds β-1,3 and β-1,4 d, N-acetylglucosamine and d-glucuronic acid together [123]. In the extracellular matrix of cartilage, skin, and vitreous humor, hyaluronic acid (HA) has major components. Healona biomedical product based on hyaluronan was established in the 1970s for corneal transplantation (eye surgery), which was permitted by FDA [125]. Benzyl ester of HA (HYAFF), HA-based product, was accessible commercially. The product occurs with variable esterification level, and several research groups have previously informed their differences in biological response and in mechanical properties [126]; although, to cross-link chemically HA extensively functional approach was and still polymerization of methacrylate practical at research level [127]. HA combines with collagen to form semi-IPNs (semi-interpenetrating networks). Attachment of endothelial cell was previously comprehended within microfluidic channels directing at blood vessel establishment [127]. Additionally, the semi-IPNs were appropriate to permit encapsulation of chondrocyte fibroblast [78] and succeeding proliferation [128]. To advance scaffolds for a diversity of tissue engineering submissions, HA was composed of poly-l-lysine [129] and alginate and was applied for regeneration of nerve lately, and composite scaffolds were also equipped for corresponding chemical functionalities. Tan et al. described the advancement of a new class, which is more biocompatible and biodegradable, complex hydrogels consequently from chitosan, water-soluble, and then hyaluronic acid oxidized without adding a chemical cross-linking agent. The gelation was credited to the Schiff base reaction. The reaction comprises aldehyde groups of polysaccharide derivatives and amino derivatives that contains aldehyde-improved hyaluronic acid and N-succinyl-chitosan, and furthermore, that research group has also particularized an innovative approach to produce animated hyaluronic acid-g-poly(N-isopropylacrylamide), (AHA-g-PNIPAAm). AHA equipped by linking the adipic dihydrazide to

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the backbone of HA was attached to carboxylic-capped PNIPAAm-COOH (PNIPAAm) that fashioned through essential polymerization by using a motivator, i.e. 4,40-azobis (4-cyanovaleric acid). Horn et al. assorted with acrylate-functionalized PEG and HA thiol-modified hydrogels fashioned that are appropriate for repairing spinal cord by using Michael’s addition. Mechanical properties of material were inadequate in the above-mentioned strategy to repair cartilage in tissue engineering field when targeting hard tissue. Consequently, several research groups deliberated the opportunity to demonstrate composites of HA-based owning synthetic polymers, with poly(propylene fumarate) [84] and PLGA (polylactic-glycolic acid). As proteins, for instance, fibrin, collagen, fibroin, and gelatin, are frequently part of these mixtures, most of the training functional to comprehend chemical cross-linking is EDC. Furthermore, HA (hyaluronic acid) has been improved with moieties consequently galactose targeting or RGD peptide, correspondingly precise or amplified cell attachment for hepatocytes lately, HA-based scaffolds (i.e. MMP sensitive) have been established to fine-tune degradation of material for new tissue formation, a most needed approach. Usually, cross-linkers are designated to influence MMP-cleavable peptides and to impersonate the renovation features by cell-derived MMPs of natural extracellular matrices. Additionally, HA-based porous scaffolds, microbeads, and nanofiber, have previously been established preliminarily from GAGs by using phase separation and electrospinning correspondingly. To conclude, HA and stem cells together for tissue growth purposes play the role of an injectable material. 15.8.1.3

Chitosan

Chitosan is a partially deacetylated derivative of chitin-attained shrimp and crabs. It becomes a biocompatible cationic polymer when dissolved in water with pH 6.2. Basicity enhanced by neutralization of the amine groups results in gel-like precipitation of the hydrated polymer. Sensitivity can be prolonged to a pH reliant on thermoresponsive system, for instance, LCST-characterized system, by the addition of polyol salts through β-glycerophosphate (GP). Ambient temperature and neutral pH are requirements for these preparations. It was detected that stability and time of gelation at room temperature increase with declining deacetylation degree. Hydration of the chitosan chain encouraged the solubility at ambient temperature and range of pH 7, supported by the GP, and the assured water is partially permitted, persuading chain associations and succeeding gelation when heated at body temperature. In gelation mechanism, several associations are elaborated. Electrostatic attraction between the GP phosphate group and chitosan ammonium groups. Between chitosan chains, hydrogen bonds owed to the declined electrostatic repulsion after neutralization of the ammonium groups by GP hydrophobic interactions between chitosan. Chitosan microspheres have previously been equipped by addition of sodium tripolyphosphate solution dropwise in a chitosan solution [128]. Subsequently, the microspheres were transported into a mold (fungus), leading to sintering for the growth of chitosan matrices appropriate for bone tissue engineering proposals. To cultivate scaffolds with morphology of a having channel-like pore, Bagnaninchi et al. have previously designated for muscle tendon. Tissue

15.8 Biopolymer-Based Hydrogel Systems

engineering on the latent of freeze drying in the presence of scaffolds established was earlier confirmed [130]. However, elongated channels of matrices possessing could also show novelty for some extinct feasibility in nerve regeneration field. Crompton et al. have improved chitosan with poly-d-lysine by azidoaniline photocoupling reactions. The consequences showed that cortical survival of cell was enhanced for poly-d-lysine adjustments up to 0.1%. Neurite significance was overdue enticingly when this number exceeds. Crompton et al. have designated on the expansion of chitosan or polyglycolic acid nerve implants for regeneration of axon [131]. Supercritical fluid processes are the substitute procedures to cultivate porous scaffolds, also stereolithography. Bagnaninchi et al. [130] have advanced scaffolds (i.e. chitosan inverse opal scaffolds) because of their exclusive regular 3-D interconnectivity and invariable pore size. As a model, PCL microspheres were designated by fabrication of a close cubic packed lattice. To conclude, the PCL model was selectively dissolved for bone tissue engineering, and potential scaffolds were exposed to be functional. The gelatin and chitosan composite scaffolds were established by merging freeze drying and stereolithography for tissue engineering of liver [132]. Nanofibers and chitosan-based scaffolds have also previously been functional for regeneration of bones; moreover, such or part of synthetic polymers with mixtures include poly(butylene-succinate), poly(l-lactic acid), or ceramics including hydroxyapatite. Chitosan-based scaffold ingredients such as collagen are frequently used in ECM engineering, after directing skin tissue. Additionally, collagen and their derivatives, also synthetic polymers that include pluronics and PEG, have also previously been assorted with chitosan for tissue regeneration purpose. The incidence of GAGs, for instance, hyaluronic acid, CS, or dermatan sulfate as a cross-linking agent EDC was used frequently. The matrices established permit the succeeding proliferation and adhesion of hepatocytes and chondrocytes. Later, to precisely target hepatocytes, galactose moieties were committed to hyaluronic acid first acid by using ethylene diamine. She et al. also assessed complex scaffolds of chitosan and silk fibroin liver tissue engineering of liver. Moreover, growth factors comprising BMP-6, bFGF, BMP-2, and peptides, for instance, RGD, have previously been mixed with chitosan to upregulate the interactive properties of cell. For cross-linking of scaffolds, i.e. chitosan-based, use of glutaraldehyde is the frequently functional technique [133]. Further, to cross-link dextran, oxidization has also been previously designated. In distinction, irrevocably cross-linked photocurable chitosans, thiolated chitosans, have also been established. In this case, cross-linking takes place through air oxidation of the thiols by forming disulfide linkages [134]. 15.8.1.4

Cellulose Derivatives

In distinction with other biopolymers uttermost, several cellulose derivatives including HPMC (hydroxypropyl methylcellulose) and MC gelation succeeds when heated [135]. HPMC and MC having LCST values set between 75–90 and 40–50 ∘ C and. As both polymers have transition temperature above 37 ∘ C, To reduce the LCST values can be regulated by reduction in the hydroxypropyl level or by adding NaCl both physiochemical approaches have been functional [135]. The gelation is primarily stimulated by adding hydrophobic side groups

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interactions of the methoxy or intermolecular, for both HPMC and MC; subsequently, at low temperatures, the macromolecules are entirely hydrated. Slow dehydration occurs, when heated, as a result of improved viscosity. Polymer–polymer interactions are significant at adjacent transition temperature; as a consequence, polymer network is formed [136]. Van Vlierberghe et al. evaluated the application of these polymers in tissue engineering field [134]. Consequently, the result confirmed that it functions as a brain cell support. In addition, MC is a promising candidate material. The potential several outcomes of MC scaffolding in brain includes irregular defects and multiple-site injury treatments. Many research groups reported the bacterial cellulose in tissue engineering proposals, although enzymatically, cellulose of bacteria cannot be degraded in vivo. 2,3-Dialdehyde adapted bacterial cellulose is demonstrated by Li et al. by periodate oxidation. Van Vlierberghe et al. additionally improved, by hydrazine, to fabricate 2,3-dihydrazone for cellulose derivative [134], and cellulose and hydroxyapatite in combination illustrate that it has the potential to be useful in tissue engineering of bones [134]. Cellulose is frequently composed of polysaccharides, e.g. chitosan, proteins, for instance, gelatin, or both [137]. 15.8.1.5

Alginate

Alginate is a brown algae derivative of polysaccharide composed of R-l-guluronic acid and β--mannuronic acid units. Depending on the production process and source, the molecular weight of this derivative can fluctuate ranging from 10 to 1000 kDa, an ion tropical gel rapidly formed by adding an alginate, multivalent cation solution. That made it enormously motivating to be beneficial in biomedical field [138]. Cross-linking proportion would be shortened, and injection of a Ca2 þ cross-linked alginate hydrogel in vivo. Attractively, polyols have previously been used practically to lower the formation of hydrogel. It has been predicted that the polyols delay the instantaneous Ca2 þ complexation by alginate. Moreover, this preparation, comprising polyols to decrease rate of hydrogel development, has uniform filed understandable. Alginate has been demonstrated to be biocompatible, nonimmunogenic, and mucoadhesive [134]. Alginate is frequently administered as microcarriers for encapsulation of cells. Although these alginate do not own cell communicating properties, to overwhelmed this subject, numerous authors, by coupling growth factors, i.e. VEGF cell-interactive peptides, e.g. RGD to the backbone of alginate [134]. Moreover, semi-interpenetrating alginate-based polymer networks have been equipped retaining responsive behavior for stimuli. Van Vlierberghe et al. have established good permeable hydrogel having pH-sensitive and composed of polyvinylpyrrolidone and sodium acrylate (sodium alginate-g-poly) by polymerization of free radical solution by using N,N-methylene-bisacrylamide as the cross-linker and ammonium persulfate ((NH4 )2 S2 O8 ) as the initiator [134]. Zhao et al. equipped thermosensitive hydrogels by UV irradiation technology via copolymerization of poly(ethylene glycol)-co-poly(ε-caprolactone) with N-isopropyl acrylamide in situ in the presence of sodium alginate. Electroresponsive performance has been encouraged by assembly of poly(acrylic acid), as initiator ammonium persulfate ((NH4 )2 S2 O8 ) used to sodium alginate and as cross-linker N,N ′ -methylene-bis-acrylamide considered. In the case of bone

15.8 Biopolymer-Based Hydrogel Systems

tissue engineering, alginate is frequently associated with calcium phosphates [134, 139]. Moreover, to advance the cell-interactive properties, in alginate-based scaffolds, protein gelatin is also frequently involved, furthermore, to freeze drying, and stereolithography scaffolds have also been established, which include porous alginate-based scaffolds by piling consecutively gel layers of alginate for encapsulation of and multilayer films of poly-l-lysine-hyaluronic acid effective as bioactive molecules reservoirs [134]. 15.8.1.6

Collagen

In ECM, collagen is the main protein, and in numerous tissues, 12 types of proteins exist. The most existing types are types I, II, and III and are used for formulation of comparable structure fibrils. 2D reticulum is formed by collagen type IV and is a main constituent of the basal lamina. Generally, by using stereolithography approaches or freeze-drying procedures, porous collagen-based scaffolds are formed. Additionally, Kim et al. reported an cryogenic direct-plotting system for fabrication of 3D collagen matrices. Porous collagen scaffolds were mixed with calcium phosphates for the regeneration of bone tissue [140]. Previously, composite scaffolds are confirmed by numerous investigators for both synthetic polymers, for instance, poly(glycolic acid), poly(lactic acid), or poly(caprolactone) adapted GAGs including linkable photocross such as hyaluronic acid-formed semi-IPNs. Precise scaffold shapes included for regeneration of blood vessels and cylindrical tubes have also been established [141]. Boccafoschi et al. composed both vascular cells and collagen by a rotating cylinder. Additionally, collagen-based nanofibers have previously been established using electrospinning to microporous scaffolds [142]. Furthermore, for adipogenic stem cells, differentiation of collagen microbeads was also practical earlier. In utmost studies, as a cross-linking agent, carbodiimide, is functional [134]. Moreover, a dehydrothermal treatment, or natural cross-linkers, for instance, genipin, as aldehydes [154] have also been functional for cross-linking of collagen in the incidence of GAGs [143]. To advance additional, the collagen-based matrices for cell-interactive properties, growth factors, specific peptides, for instance, BMP-2 or both, have previously been combined. Duan et al. adapted octa amine, 2-polypropyleneimine dendrimer, in functional as a cross-linker in the incidence of EDC for collagen scaffolds. Furthermore, these dendrimers have been adapted with YIGSR peptides [134]. Lee et al. combined VEGF with bioprinted complex scaffolds retaining fibrin tissue engineering of neural tissue. Furthermore, a human-like collagen recombinant was established, which is functional for safety issues, for instance, risk related to BSE infection [134, 144]. 15.8.1.7

Gelatin

A biopolymer derivative of collagen by hydrolytic degradation gelatin is used in diversity of applications because of its exclusive efficiency, ranging from pharmaceutical over food-related and technical products to photographic. However, gelatin has also been regularly functional, as a material for biomedical applications. As gelatin must be cross-linked chemically to evade implication at body temperature, with sol–gel transition temperature about 30 ∘ C, as gelatin

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with diversity of side chains, a wide variety of chemical adjustment approaches, presenting cross-linkable groups, have been expected [145]. Excellency of potential reagents is restricted to water stability as gelatin dissolves only in water and number of alcohols. In numerous cases, bifunctional reagents, for instance, diisocyanates [146], genipin [134], glutaraldehyde, acyl azides, carbodiimides, and polyepoxy compounds, have been practical. When gelatin is mixed with sugars for instance, agarose resulting 1,1-carbonyldiimidazole can be a functional cross-linking agent [134]. Derivatization of gelatin ensues frequently by the amine groups of hydroxylysine and lysine [147]. The group of arginine and guanidinium is protonated below slightly basic environments, which eliminate this group by nucleophile reaction. The histidine imidazole group can respond, but formation of unstable products takes place in this reaction [148]. Methacrylamide-modified gelatin could be cross-linked by applying UV irradiation in the incidence of a photoinitiator [149]. Van Den Bulcke et al. adapted methacrylic anhydride for primary amines of gelatin with methacrylamide moieties. The following chemical cross-linking took place in the incidence of a UV-active photoinitiator Irgacure upon UV irradiation [134]. The hydrogels attained seem to be very auspicious for wound treatment applications. Vlierberghe et al. adapted methacrylamide and gelatin as the preliminary materials for the preparation of porous scaffolds and determination of tissue regeneration. The cell carriers based on gelatin were equipped by a cryogenic treatment, by a lyophilization method [134]. The hydrogels established were used for the growth and support for attachment of a large diversity of human cells including endothelial cells, fibroblasts, osteoblasts, epithelial cells, and glial cells. Additionally, by combining methacrylate-modified CS and methacrylamide-modified gelatin, porous scaffolds were established. Otherwise, redox initiators also permit having methacrylamide moieties of gelatin polymerization. Supplementary opportunity to attain cross-linked hydrogels chemically by high-energy irradiation that includes γ-rays and electron beam. The main outcomes of high-energy irradiation practices include solvent-free reaction and a reagent for immediate sterilization and cross-linking. The conclusion, by performing sterilization and cross-linking instantaneously, is predominantly motivating in opinion of future applications as the manufacturing development is extremely reduced. Hu et al. designated for enzymatic cross-linking of gelatin hydroxypropionic acid. Furthermore, by means of a new fiber spinning technique, the attained material was then processed into resonating fibers for overall applications in tissue engineering. Sakai et al. applied cross-linking on peroxidase facilitated combined with hydroxyl groups of phenolic, gelatin, by applying other approaches including stereolithography. In addition, electrospinning could also be treated. As gelatin is a derivative of collagen, it is frequently mixed with calcium phosphates, GAGs [134], or both when aiming the regeneration of specific tissues. Besides this, gelatin is also a part of complexes by synthetic polymers including PUs, PCL, and poly(l-lactic acid). Dubruel et al. applied a reactive copolymer fashioned on N-isopropyl acrylamide, thermosensitive polymer and accomplished chemical cross-linking [150]. The copolymer comprised acrylic acid units in the incidence of a water-soluble carbodiimide that designed amide bonds with the amino

15.8 Biopolymer-Based Hydrogel Systems

groups of gelatins. The conceivable reactivity of the system was fine-tuned to regulate the gelation process just by setting the temperature below or above the LCST [134]. Phase separation and freeze-drying procedures are frequently functional for purposes of tissue engineering to produce the porous gelatin-based scaffolds [134]. Some instances, demonstrating the possible gelatin-based materials, are briefly listed below. Basic growth factor for fibroblast, Co-release, and insulin-like growth factor I, insulin encouraged de novo adipose tissue formation, from microsphere-based styrenated gelatin. For cardiac tissue engineering applications, gelatin-involved poly(N-isopropyl acrylamide) has been used [134]. 15.8.1.8

Elastin

Elastic is formulated by the main part of elastin, consequently instinctively active tissues, including elastic cartilage, blood vessels, and tendon. A dermal substitute, for instance, matriderm, as commercially accessible, formed by collagen and elastin has previously been assessed and regularly designated in the literature [151] as its widespread covalent cross-linking has functional innate elastin as cell carriers for tissue engineering applications only by few research groups. Consequently, Cabello et al. have established use of another auspicious recombinant elastin; repetitive polypeptides are made up of pentapeptide sequences, for instance, VPGXG. Here, X could be natural amino acid except for proline [152]. Attractively, this elastin recombinant illustrates the LCST thermoresponsive behavior, and the polymer remains soluble, under the transition temperature, while above the critical temperature, the hydrophobic chains assembled themselves into a more well-ordered structure. For instance, a recombinant elastin, i.e. poly(VPAVG), approximating innate elastin to the highest degree, poly(VPAVG) formed micelles, overheads the transition temperature of this [134]. Then, the materials are very auspiciously applicable for drug delivery determinations [153]. A scientist has established porous scaffolds preliminary from hexamethylene di-isocyanate, and cross-linked R-elastin by using high-pressure carbon dioxide (CO2 ) by changing the pressure applied attained pore size was disposed [134]. Elastin has also been treated in the presence of either gelatin or collagen into nanofibers by using electrospinning. To attain continuous and homogeneous fibers, a small amount of PEO had been added. The fibers produced were cross-linked by using NHS or EDC [154]. Moreover, elastin-like polymers illustrate outstanding biocompatibility as they are similar to natural elastin and also products of degradation are innate amino acids [152, 155]. Peptide arrangements include growth factors, such as bFGF and RGD, for the improvement of interactive properties of cells, which have previously been mixed with elastin [134, 156]. 15.8.1.9

Fibroin

Fibroin is a natural protein produced by the silkworm, Bombyx mori. The primary structure of this primarily consists of serine, alanine, and glycine. The protein can be treated as nanofibers [157], powders [158], scaffolds, films, gels [159], and membranes [134], which tremendously reduces its applicability appropriately in a large diversity of applications such as drug delivery and biomaterial field. Mandrycky et al. have established, for ligament tissue

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engineering, gelatin-based hybrid porous scaffolds [117]. Moreover, complex scaffolds associated with proteins, for instance, fibroin and collagen [134], have also been mixed with GAGs that include fibroin aqueous solutions, hyaluronan. In addition, hyaluronic acid was freeze dried to stimulate absorbency and then hatched in methanol to persuade water insolubility of silk fibroin. The scaffolds that attained were appropriate to facilitating the cell adhesion of mesenchymal stem cells; moreover, freeze drying and leakage out of porogens could be applicable to reduce fibroin porous scaffolds [134].

15.9 Summary Scaffold-based hydrogels are very promising agents as fiber composites in tissue engineering applications. These hydrogel modifications and novel applications in the form of fiber composites have been studied in recent years. These scaffold hydrogels had been formulated from both natural and synthetic sources and applied to different biomedical applications, but scaffold fibers mostly led to tissue engineering, i.e. bone tissue, skin tissue, and vascular tissue engineering. These biocomposites had been fabricated with different processes that had been described, and these were used for health care. Fabrication had been done in 2D as well as in 3D form. As these scaffold-based hydrogel fiber composites have potential applications in biomedical field, the modern era of research should think about establishing a more hybrid and novel scaffold hydrogel that would solve issues related to biomedicine.

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nanoHA scaffold with potential for bone tissue engineering. In: Tissue Engineering. New Rochelle, NY: Mary Ann Liebert, Inc. Sena, L.A. et al. (2009). Synthesis and characterization of biocomposites with different hydroxyapatite–collagen ratios. Journal of Materials Science Materials in Medicine 20 (12): 2395. Ananta, M. et al. (2008). A poly(lactic acid-co-caprolactone)–collagen hybrid for tissue engineering applications. Tissue Engineering Part A 15 (7): 1667–1675. Lee, Y.-B. et al. (2010). Bio-printing of collagen and VEGF-releasing fibrin gel scaffolds for neural stem cell culture. Experimental Neurology 223 (2): 645–652. Damink, L.O. et al. (1995). Crosslinking of dermal sheep collagen using hexamethylene diisocyanate. Journal of Materials Science Materials in Medicine 6 (7): 429–434. Schuster, M. et al. (2009). Gelatin-based photopolymers for bone replacement materials. Journal of Polymer Science Part A: Polymer Chemistry 47 (24): 7078–7089. Skardal, A. et al. (2010). Photocrosslinkable hyaluronan–gelatin hydrogels for two-step bioprinting. Tissue Engineering Part A 16 (8): 2675–2685. Benton, J.A. et al. (2009). Photocrosslinking of gelatin macromers to synthesize porous hydrogels that promote valvular interstitial cell function. Tissue Engineering Part A 15 (11): 3221–3230. Dubruel, P. et al. (2007). Porous gelatin hydrogels: 2. In vitro cell interaction study. Biomacromolecules 8 (2): 338–344. Kolokythas, P. et al. (2008). Dermal substitute with the collagen–elastin matrix Matriderm in burn injuries: a comprehensive review. Handchirurgie, Mikrochirurgie, plastische Chirurgie: Organ der Deutschsprachigen Arbeitsgemeinschaft für Handchirurgie: Organ der Deutschsprachigen Arbeitsgemeinschaft für Mikrochirurgie der Peripheren Nerven und Gefässe: Organ der Vereinigung der Deutschen Plastischen Chirurgen 40 (6): 367–371. Machado, R. et al. (2012). Elastin-based nanoparticles for delivery of bone morphogenetic proteins. In: Nanoparticles in Biology and Medicine, 353–363. Springer. Martín, L. et al. (2009). Synthesis and characterization of macroporous thermosensitive hydrogels from recombinant elastin-like polymers. Biomacromolecules 10 (11): 3015–3022. Barbosa, J. et al. (2009). Multi-layered films containing a biomimetic stimuliresponsive recombinant protein. Nanoscale Research Letters 4 (10): 1247. Pervaiz, M. et al. (2019). Synthesis, spectral and antimicrobial studies of amino acid derivative Schiff base metal (Co, Mn, Cu, and Cd) complexes. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 206: 642–649. Costa, R.R. et al. (2009). Stimuli-responsive thin coatings using elastin-like polymers for biomedical applications. Advanced Functional Materials 19 (20): 3210–3218.

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351

16 Experimental Analysis of Styrene, Particle Size, and Fiber Content in the Mechanical Properties of Sisal Fiber Powder Composites Kátia Melo 1 , Thiago Santos 1 , Caroliny Santos 1 , Rubens Fonseca 1 , Nestor Dantas 2 , and Marcos Aquino 1 1 Federal University of Rio Grande do Norte, UFRN, CEP, Textile Engineering Laboratory, LABTEX, 59078-970, Rio Grande do Norte, RN, Brazil 2 Federal Institute of Rio Grande of Norte, IFRN, CEP, 59015-000, Rio Grande do Norte, RN, Brazil

16.1 Introduction Currently, with the expanding growth of aerospace, sports, automotive, and packaging needs, there is also a growing need for renewable and sustainable reinforced composites [1]. Thus, the sisal fiber powder is a residue generated by the spinning of strings and ropes, extensively produced in the tropical regions of Brazil [2, 3]. The sisal produces about 300 000 tonnes of fiber annually. However, the dust generated is used for animal feed or is discarded causing environmental pollution problems [3]. Therefore, research and development are underway to find new applications for the sisal fiber powder. Thus, reinforcements of polymeric composites represent a natural way to exploit the properties of sisal fiber powder. Therefore, the use of reinforcing particles in composites can act as barriers against the propagation of cracks because of their high rigidity, which delays the growth of cracks in hybrid composites and increases their mechanical properties. Therefore, to evaluate the mechanical properties, the methodology of statistical analysis is used, which is a very useful tool to validate the results of an experiment [4]. From this evaluation, it is possible to identify the correlation between the data to observe if the mathematical model explains the results obtained and also to show the probability of obtaining a result equal or farther from what was observed (level of significance) [5, 6]. The analysis of variance (ANOVA) analysis aims to verify if there is a difference between the data referring to the sample groups, indicating the possible errors and if there are factors that influence these results in a positive or negative way, allowing knowledge of the population from the sample [7, 8]. It is also possible to perceive if the presence of some chemical component is relevant to the mechanical performance and what percentage reveals its best performance from the interaction between components, aiding the response positively or negatively.

Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering, First Edition. Edited by Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin, and Abdullah M. Asiri. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

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16 Experimental Analysis of Styrene, Particle Size, and Fiber Content

Therefore, the present work investigates the influence of styrene, particle size, and fiber content on the mechanical properties of the natural fiber powder composite as a sustainable material with good mechanical performance through a factorial design in the software Design Expert. The mechanical properties of sisal fiber composite analyzed were stress, strain, specific Young’s modulus (MOE), and tenacity. They were evaluated by ANOVA, which includes the coefficient of determination R2 , F-value, and the probability of significance (𝜌-value), in addition to the 3D response surface methodology (RSM). In this way, it was possible to understand the effects of the interactions and the factors styrene, particle size, and fiber content on the studied properties.

16.2 Materials and Methods The residue of the sisal fiber was from the spinning process, was in the form of a bush (Figure 16.1a), and was initially cut and crushed in an industrial blender. Then, the material was subjected to the process of separating the particles through the granulometric sieve with 12 mesh (1680 μm), 16 mesh (1190 μm), and 20 mesh (841 μm), as shown in Figure 16.1b–d. From the powder obtained with different particle sizes (12 mesh, 16 mesh, and 20 mesh) was used the fiber contents of 2.50%, 3.75%, and 5.00%, as well as the condition of addition (or not) of 2% of styrene in the composite; when there is addition of styrene, the abbreviation (CE) is used, and when there is no addition of styrene, the abbreviation (SE) is used as shown in Table 16.1.

(a)

(b)

(c)

(d)

Figure 16.1 (a) Residue in bushes; and particles with (b) 12 mesh, (c) 16 mesh, and (d) 20 mesh. Table 16.1 Experimental variables and conditions. Factor

Fiber content (%)

Experimental condition

2.5 3.75 5

Styrene

CE SE

Particle size (mesh)

12 16 20

m

16.3 Results and Discussion

25

m

3 mm

250 mm

Figure 16.2 Scheme of the dimensions of the composite samples.

Samples with dimensions of 250 mm in length, 25 mm in width, and 3 mm in thickness were made in gypsum molds with a layer of carnauba wax to facilitate the demolding of the samples. In addition, each sample consisted of a percentage of fiber (2.50%, 3.75%, and 5.00%), for the particle sizes (12 mesh, 16 mesh, and 20 mesh), with the addition of styrene (CE) or without the addition of styrene (SE) (Figure 16.2). Tension tests were performed using the Tensolab 3000 dynamometer from MESDAN, according to the standard ASTM D3039 [9]. The samples were assayed at a rate of 10 mm/min and distance between claws of 125 mm. Then, the results were treated and inserted into the Software Design Expert 7, following each condition presented in Table 16.2. Subsequently, the results were analyzed using RSM and ANOVA, which are statistical techniques used to determine the degree of difference (or similarity) between two or more data groups. In this way, the value-𝜌 is determined (level of significance to evaluate the null hypothesis) [10, 11]. The null hypothesis (Ho), in turn, states if the population averages are all the same. Then, when a significance level of 0.05 is obtained, it indicates a 5% risk of concluding that the terms of the model are not significant. A value-𝜌 less than or equal to 0.05 implies that the factor significantly affects the response (rejection of Ho) [11–13]. Finally, the influence of the factors (fiber content, particle size, and styrene) on the response variables (Young’s modulus, stress, strain, and tenacity) was obtained, in which the results are presented in surface graphs of response and tables, which represent the means for each factor of the data studied (see Tables 16.1 and 16.2).

16.3 Results and Discussion Figure 16.3 shows the stress of the samples of polymeric composites reinforced with sisal fiber powder without styrene. In the curve presented in Figure 16.3a, it was observed that the fiber content factor exerts little influence when compared to the particle size factor. However, the condition indicating high voltage values is 2.5% of fiber content and 20 mesh of the particle size (0.65 MPa), and for any fiber content (2.5%, 3.75%, and 5%) with the particle size, 12 mesh were obtained the lowest values of tensile strength [14, 15]. Figure 16.3b shows the contour plot of the influence of the variables, fiber content, and particle size on the tensile property. The fiber content was slightly influential and showed constant behavior for all particle sizes. The stress increased significantly with the decrease in particle size (20 mesh). As the particle size decreases, it is necessary to reduce the fiber content [16, 17].

353

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16 Experimental Analysis of Styrene, Particle Size, and Fiber Content

Table 16.2 Factorial planning (23 ) of variables (factors).

1

Fiber content (%)

Styrene

Particle size (mesh)

−1

CE

−1

2

1

SE

−1

3

−1

CE

1

4

0

SE

0

5

0

SE

0

6

0

CE

0

7

−1

SE

1

8

−1

CE

1

9

−1

SE

1

10

0

CE

0

11

1

SE

1

12

0

CE

0

13

0

SE

0

14

1

CE

−1

15

0

CE

0

16

1

SE

1

17

0

SE

0

18

−1

SE

−1 −1

19

1

CE

20

1

CE

1

21

1

SE

−1

22

0

CE

0

23

0

SE

0

24

1

CE

1

25

−1

SE

−1

26

−1

CE

−1

Figure 16.4 shows the stress of the samples of polymeric composites reinforced with sisal fiber powder with styrene. The curve (saddle-shaped) indicates that there are two high values as shown in Figure 16.4a. Thus, it is observed that the fiber content factor and particle size exert a significant influence on the stress of the samples with styrene. However, the condition indicating high stress values is 2.5% of fiber content and 20 mesh of the particle size (0.59 MPa), and the condition exhibiting the lowest stress value for the fiber content and particle size factors were 5% and 20 mesh, respectively [14, 16]. Figure 16.4b shows the contour plot of the influence of variables, fiber content, and particle size on the stress property. The fiber content was influent and presented a similar behavior to the particle size [17]. Because of the saddle point, the stress graph begins to decrease and then increase when the fiber content and the particle size are 2.5% and 20 mesh

16.3 Results and Discussion

0.66

Stress (MPa)

0.605 0.55 0.495 0.44

20.00

5.00 4.38

18.00 16.00

3.75 3.13

14.00

Particle size (mesh)

Fiber content (%)

12.00 2.50

(a) 20.00 0.615

Particle size (mesh)

0.58 18.00 0.545

16.00 0.51

14.00

12.00 2.50

(b)

0.475

3.13

3.75

4.38

5.00

Fiber content (%)

Figure 16.3 Result of stress (a) response surface and (b) outline of the samples without styrene.

(0.59 MPa) and 5% and 12 mesh (0.53 MPa), respectively. The stress increased significantly with the decrease of the particle size (20 mesh) [17, 18]. Figure 16.5 shows the results of the strain of the samples of polymeric composites reinforced with sisal fiber powder without styrene. In the curve shown in Figure 16.5a its evident that the factors fiber content and particle size promotes a significant influence on the strain. However, the condition indicating high strain values (5.68%) was 2.5% fiber content and 12 mesh particle size, and only in conditions of 5% fiber content and 12 mesh particle size, less significant values of strain (4.56%) were obtained [19]. Figure 16.5b shows the contour plot of the influence of the variables, fiber content, and particle size on the strain property. Presenting a more significant behavior in strain property was obtained on fiber content in range of 2.5–3.75% and particle size of 12–18 mesh. In this way,

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16 Experimental Analysis of Styrene, Particle Size, and Fiber Content

0.6

Stress (MPa)

0.5575 0.515 0.4725 0.43

20.00

5.00 4.38

18.00 16.00

Particle size (mesh)

3.75 3.13

14.00 12.00 2.50

(a)

Fiber content (%)

20.00 0.563 333

Particle size (mesh)

356

18.00

0.456 667 0.536667 0.483 333 0.51

16.00

14.00 0.51 0.483 333 12.00 2.50

(b)

3.13

3.75

4.38

5.00

Fiber content (%)

Figure 16.4 Result of stress (a) response surface and (b) the contour of the samples with styrene.

the best strain result was obtained in the lowest fiber content (2.5%) and larger particle size (12 mesh) [20]. Figure 16.6 shows the strain of the samples of polymeric composites reinforced with sisal fiber powder with styrene. The curve (saddle-shaped) indicates that there are two high strain values, so the graph begins to increase and then decrease when the fiber content and the particle size exhibit specific values (Figure 16.6a,b) [21]. Thus, it is evident that the fiber content factor and particle size exert a significant influence on the stress of the styrene samples. Therefore, two conditions of fiber content and particle size were obtained such that the strain was significantly elevated 5% and 12 mesh and 2.5% and 20 mesh, respectively, both showing strain values of 5.6% and the condition exhibiting the lowest strain value (4.68) was 2.5% and 12 mesh [22].

16.3 Results and Discussion

5.7

Strain (%)

5.4 5.1 4.8 4.5

20.00

5.00 4.38

18.00 16.00

Particle size (mesh)

3.75 3.13

14.00

Fiber content (%)

12.00 2.50

(a)

20.00

Particle size (mesh)

18.00

4.93333

5.12

16.00

5.306 67 14.00

4.74667 5.493 33

12.00 2.50

(b)

3.13

3.75

4.38

5.00

Fiber content (%)

Figure 16.5 Result of strain (a) response surface and (b) outline of the samples without styrene.

Figure 16.7 shows the MOE of the samples of polymerics composites reinforced with sisal fiber powder without styrene. It is perceived in Figure 16.7a that the fiber content factor exerts little influence when compared to the particle size factor. However, high stress values are obtained under conditions of 2.5% fiber content and 20 mesh particle size (13.20 GPa), and for any fiber content (2.5%, 3.75%, and 5%) with particle size 12 mesh, the lowest values of rupture MOE were obtained [14, 23]. Figure 16.7b shows the contour plot of the influence of the variables, fiber content, and particle size on the property of strain. The fiber content showed little influence on all particle sizes. The deformation increased significantly with the decrease of the particle size (12 mesh, 16 mesh, and 20 mesh). As the particle size decreases, it is necessary to reduce the fiber content [16, 23, 24].

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16 Experimental Analysis of Styrene, Particle Size, and Fiber Content

5.61

Strain (%)

5.375 5.14 4.905 4.67

20.00

5.00 4.38

18.00 16.00

3.75 3.13

14.00

Particle size (mesh)

Fiber content (%)

12.00 2.50

(a) 20.00

4.98667 5.446 67 5.14

5.293 33

18.00

Particle size (mesh)

358

16.00 5.14 5.29333

14.00

4.986 67 5.44667

4.833 33

12.00 2.50

(b)

3.13

3.75

4.38

5.00

Fiber content (%)

Figure 16.6 Result of strain (a) response surface and (b) outline of the samples with styrene.

Figure 16.8 shows the MOE of the samples of polymeric composites reinforced with sisal fiber powder with styrene. It is perceived in Figure 16.8a that the fiber content exerts less influence as well as reduction of property with the increase of fiber volume present in the composite (2.5%, 3.75%, and 5%) when compared to particle size factor [23]. However, the condition that indicates better MOE values was 2.5% fiber content and 20 mesh particle size (10.60 GPa), and for fiber contents above 2.5% up to 5% with the particle size 12 mesh up to 16 mesh, the lowest values of rupture MOE were obtained [25–27]. As shown in Figure 16.8a,b, the MOE increased significantly with the decrease of particle size (12 mesh, 16 mesh, and 20 mesh). As the particle size decreases, it is necessary to reduce the fiber content to obtain better results [26, 28].

16.3 Results and Discussion

13.3

MOE (GPa)

11.9 10.5 9.1 7.7

20.00

5.00 4.38

18.00 16.00

3.75 3.13

14.00

Particle size (mesh)

Fiber content (%)

12.00 2.50

(a)

20.00 12.283 3 11.366 7

Particle size (mesh)

18.00

16.00

10.45

14.00

9.533 3 3 8.616 6 7

12.00 2.50

(b)

3.13

3.75

4.38

5.00

Fiber content (%)

Figure 16.7 Result of MOE (a) response surface and (b) outline of the samples without styrene.

Figure 16.9 shows the tenacity of samples of polymeric composites reinforced with sisal fiber powder without styrene. From Figure 16.9a, it is observed that the fiber content factor exerts less influence because the increase in fiber volume in the composite (2.5%, 3.75%, and 5%) reduces tenacity, while the particle size factor causes a significant increase of this property [25]. However, the condition indicating better tenacity values was 2.5% fiber content and 20 mesh particle size (1.73E−05), and for fiber contents above 2.9–5% with the particle size of 12 mesh up to 20 mesh, the lowest tenacity values were obtained [26, 27]. As shown in Figure 16.9a,b, tenacity increased significantly with the decrease of the particle size (12 mesh, 16 mesh, and 20 mesh). As the particle size decreases, it is necessary to reduce the fiber content to obtain better results [28, 29].

359

16 Experimental Analysis of Styrene, Particle Size, and Fiber Content

10.7

MOE (GPa)

10.2 9.7 9.2 8.7

20.00

5.00 18.00

4.38 16.00

(a)

Particle size (mesh)

3.75 14.00

3.13 12.00 2.50

Fiber content (%)

20.00

9.016 67

Particle size (mesh)

360

18.00

10.283 3

16.00

9.966 67

9.65

9.333 33

14.00

12.00 2.50

(b)

3.13

3.75

4.38

5.00

Fiber content (%)

Figure 16.8 Result of MOE (a) response surface and (b) outline of the samples with styrene.

Figure 16.10 shows the tenacity of samples of polymeric composites reinforced with sisal fiber powder with styrene. From Figure 16.10a, it is observed that the fiber content exerts less influence, but the results obtained were significant because the increase of fiber volume in the composite practically does not promote the change in the tenacity, while the particle size causes a significant increase of property [29, 30]. However, the condition indicating better values of tenacity (2.01E−05) was 2.5% (fiber content) and 20 mesh (particle size), and for the fiber contents above 2.5–5% with a particle size of 12–16 mesh and of 3.75–5% and 16–20 mesh, respectively, were obtained the lowest values of tenacity [31]. From Figure 16.10a,b, it can be observed that the tenacity significantly increased with the decrease of the particle size (20 mesh). As the

16.3 Results and Discussion

Tenacity (MJ/m3)

1.74E–005 1.58E–005 1.42E–005 1.26E–005 1.1E–005 20.00

5.00 18.00

4.38 16.00

Particle size (mesh)

3.75 3.13

14.00

Fiber content (%)

12.00 2.50

(a) 20.00

Particle size (mesh)

18.00

1.634E–005

1.53E–005

16.00 1.426E–005

1.322E–005

14.00

1.218E–005 12.00 2.50

(b)

3.13

3.75

4.38

5.00

Fiber content (%)

Figure 16.9 Result of tenacity (a) response surface and (b) outline of the samples without styrene.

particle size decreases, it is necessary to reduce the fiber content to obtain better and significant results [32, 33]. The statistical model of stress, strain, MOE, and tenacity can be validated when the residues are well distributed along the straight line and the value-𝜌 is greater than or equal to 0.05 (𝜌 ≥ 0.05). The value of “F” corresponds to how much the means of the groups of analyzed samples are different. Thus, the more the “F” is higher, the better it is because it means that the average squares of the model are superior to the residual average squares and the smaller is the error. The more the “F” is extreme, the more significant the value-𝜌 for the factors is (styrene, particle size, and fiber content) and interactions [10, 33]. In the factorial design studied for stress, strain, MOE, and tenacity, the values of “F” obtained were significant for practically all factors (A, B, and C) and

361

16 Experimental Analysis of Styrene, Particle Size, and Fiber Content

Tenacity (MJ/m3)

2.02E–005 1.8125E–005 1.605E–005 1.3975E–005 1.19E–005 20.00

5.00 18.00

4.38 16.00

Particle size (mesh)

3.75 3.13

14.00

Fiber content (%)

12.00 2.50

(a) 20.00 1.87358E–005 1.73767E–005

Particle size (mesh)

362

18.00

1.32992E–005

1.60175E–005

1.46583E–005

16.00

14.00 1.32992E–005 12.00 2.50

(b)

3.13

3.75

4.38

5.00

Fiber content (%)

Figure 16.10 Result of tenacity (a) response surface and (b) outline of the samples with styrene.

interactions (AC, BC, and ABC), as shown in Table 16.3, except for the interaction AB of stress (𝜌 = 0.5839) and BC (𝜌 = 0.1657) of the tenacity and also for the particle size (𝜌 = 0.5119) of the strain. This means that there is little difference between these groups of independent variables studied, which can be adequately expressed through a significant model [13, 33, 34]. Both interactions present the B factor evidencing the need to study different concentrations of styrene in the composite to obtain AB and BC significant interactions, obtaining value-𝜌 equal to or less than 0.05 (𝜌 ≥ 0.05). Thus, it can be understood that the factors studied as well as their interactions can significantly improve the stress, strain, and MOE properties, as well as the tenacity of sisal fiber powder reinforced composites. In this way, the results of ANOVA of Table 16.3 also present the statistical adjustment of the data of the studied mechanical properties, where the standard deviations of stress (0.01), strain (0.04), MOE (0.21), and tenacity (4.47E−07)

Table 16.3 ANOVA of results of stress, strain, MOE, and tenacity of the sample studied. Stress F value

Value – 𝝆 (Prob > F)

Strain F value

Value – 𝝆 (Prob > F)

MOE F value

Value – 𝝆 (Prob > F)

Tenacity F value

Value – 𝝆 (Prob > F)

Model

247.30