Cellulose Fibre Reinforced Composites: Interface Engineering, Processing and Performance 0323901255, 9780323901253

Table of contents :
Cover
Cellulose Fibre Reinforced Composites
Contributors
Copyright
Preface
Acknowledgments
Cellulose fiber-reinforced composites-History of evolution, chemistry, and structure
Introduction
Cellulose fiber-reinforced composites-History of evolution
Chemistry
Glucose monomer
Glucose biopolymerization
Cellulose structure
Chemical and solubility properties of cellulose
Sources of cellulose
Separation of cellulose
Purification of cellulose
Cellulose polymorphism
Chemical modification of cellulose
Preparation of nanocellulose
Structures
Cellulose reinforcement in polylactic acid and polybutylene succinate
Melt flow index of the composite
SEM analysis of composite foams
FTIR spectroscopy
XRD analysis
Mechanical properties
Cellulose reinforcement in natural bamboo-composite
FTIR analysis
SEM analysis
Mechanical properties
Cellulose fibers reinforcement in ethylene-nonbornene copolymer composite
FTIR analysis
Mechanical properties
Optical characterization
Acknowledgment
References
Bamboo cellulose: Structure, properties, and applications
Introduction
Bamboo cellulose extraction process
Bamboo cellulose production by wet spinning
Kraft pulping
Bamboo nanocellulose by mechanochemical process
Bamboo cellulose extraction by acid hydrolysis (99% sulfuric acid)
Hydrothermal extraction
Standard alkali extraction
Ambient condition extraction
Two-stage extraction
Bamboo cellulose using HNO3/KClO3 method
Bamboo-derived cellulose nanofiber (CNF) by ultrasonication
Anatomy of bamboo
Physical structure of bamboo
Chemical structure of bamboo fiber
Properties of bamboo cellulose
Durability
Elasticity
Antimicrobial resistance
Biodegradability
Breathable and cool
Hardness
Impact resistance
Absorption characteristics
Thermal property
Air permeability
Water vapor permeability
Tenacity
UV protectivity
Applications of bamboo cellulose
Composite reinforcement
Textile application
Cellulosic nanofiber preparation
Medical applications
Food and food packaging
Furniture and interior
Sports industry
Construction
Bioenergy production
Paper industry
Conclusion
References
Electrospun cellulose nanofiber composites
Introduction
Electrospinning technique and its applicability
Cellulose, its properties, and applications
Cellulosic composites
Electrospun cellulosic composite nanofibers
Applications of electrospun cellulosic composite nanofibers
Conclusion
References
Chemical modification of cellulose fiber surface
Introduction
Cellulose fibers
Classification of natural fibers
Fiber surface modification
Physical treatments
Chemical treatments
Alkaline treatment
Silane treatment
Acetylation treatment
Benzoylation treatment
Summary
References
Physical modification of cellulose fiber surfaces
Introduction and present scenario
Cellulose fibers: Source, structure and constituents
Physical modification of cellulose fibers
Plasma treatment
Corona treatment
Dielectric barrier treatment
Atmospheric pressure glow discharge
Atmospheric pressure plasma jet
Ultrasound and ultraviolet treatments
Ozone treatment
Effect of physical modification toward performance and functionality of thermal fiber composites
Conclusions
References
Interface engineering-matrix modification in cellulose fiber composites
Introduction
Effect of chemical treatment on cellulose fiber-reinforced composites
Conclusion
References
Characterization of fiber surface treatment by Fourier transform infrared (FTIR) and Raman spectroscopy
Introduction
Significance of the FTIR and RS in fiber characterization
FTIR spectroscopy (FTIR)
Raman spectroscopy
Comparing FTIR and Raman spectra
Analysis of fiber surface modification
Conclusions
References
Evaluation of the effect of processing and surface treatment on the interfacial adhesion in cell
Introduction
Effect of surface treatment on the mechanical properties of cellulose fiber-reinforced composites
Conclusion
References
Manufacturing aspects of cellulose fiber-reinforced composites
Introduction
Effect of processing variables on the quality of thermoset-based cellulosic fiber-reinforced composites
Composite manufacturing with thermoplastic matrices
Twin screw extrusion and injection molding
Advanced 3D-printing manufacturing techniques
Conclusions
References
Further reading
Compression and injection molding techniques
Introduction
Compression molding technique
CMT for thermosetting polymer composites
CMT for thermoplastic polymer composites
Injection molding technique
IMT for thermosetting polymer composites
IMT for thermoplastic polymer composites
CMT vs IMT
Mechanical properties
Wood fiber-reinforced polypropylene composites
Sugarcane bagasse fiber-reinforced polypropylene composites
Jute fiber-reinforced poly lactic acid composites
Sisal fiber-reinforced poly lactic acid composites
Kenaf fiber (KF)-reinforced poly lactic acid composites
Agave fiber-reinforced poly lactic acid composites
Conclusions
References
Thermomechanical characterization of cellulose fiber composites
Introduction
Classification of cellulosic fibers
Chemical composition of cellulose fibers
Cellulose
Hemicellulose
Lignin
Based on properties of fiber
Microfibril angle
Crystallinity
Fiber density
Properties
Morphology
Mechanical properties
Chemical property
Thermal property
Tribological behavior
Modification of fiber
Physical modification
Steam explosion method
Heat treatment
Chemical modifications
Alkali treatment
Silane coupling agent
Applications of cellulose fiber composites
Merits and demerits of cellulose fibers over synthetic fibers
Merits
Demerits
Conclusion
References
Evaluation of moisture uptake behavior in cellulose fiber
Introduction
Moisture uptake by cellulose fibers in cellulose-based composites
Moisture uptake mechanism and its effects
Influence of moisture uptake on cellulose fiber properties
Restoration processes for moisture uptake behavior of cellulose fibers
Conclusion
References
Effect of zinc oxide filler on compressive and impact properties of jute fiber fabric-reinforced epoxy composites
Introduction
Materials
Preparation of composites
Compressive properties
Impact properties
Results and discussion
Compressive properties
Impact properties
Conclusions
References
Predication of impact strength reduction and service life of 45-degree laminate jute fiber fabric in epoxy c
Introduction
Materials
Jute fiber mat
Preparation of composites
Artificial aging of composites
Impact properties
Results and discussion
Weight variation
Impact properties
Diffusion coefficient and activation energy
Arrhenius plots for service life prediction of the JEC
Conclusion
References
Extraction and characterization of cellulosic fibers from the stem of papaya tree (Carica papaya L.)
Introduction
A worldwide clamor for vegetable fiber
Natural and vegetable fibers
Experimental
Extraction of papaya stem fiber and fiber extraction yield
Characterization of papaya stem fiber
Results and discussions
Conclusions
Acknowledgments
References
Cellulose-based composite materials for dye wastewater treatment
Introduction
Application of dyes and its impact
Cellulose
Cellulose-based composites for dye removal
Cellulose-ZnO-based composite for dye removal
Cellulose-activated carbon-based composite
Cellulose-graphene oxide-based composite
Cellulose-chitosan-based composite
Conclusion
References
Cellulose fiber-reinforced polymer composites as packaging materials
Introduction
Packaging
Categories of packaging
Packaging polymer properties
Barrier properties
Oxygen transmission rate (OTR)
Water vapor transmission (WVTR)
Mechanical properties
Thermal properties
Packaging materials
Bio-based packaging materials
Bioplastic packaging applications
Classification of bio-based food packaging materials
Cellulosic fiber
Cellulosic fiber composition
Cellulosic fiber properties
Cellulosic fiber production
Cellulosic fiber treatment
Physical treatment
Chemical treatment
Cellulosic fiber-based polymeric composites
Cellulosic fiber-based biocomposites in packaging
Cellulosic fiber-based biopolymeric composites properties
Structural properties
Mechanical properties
Aging properties
Advantages and disadvantages of cellulosic fibers in packaging
Cellulosic fiber-based biodegradable polymer composite film in packaging
Conclusion
References
Bionanocomposites reinforced with cellulose fibers and agro-industrial wastes
Introduction
Mechanical properties
Natural rubber-based composites
Polyvinyl alcohol (PVA) matrix-based composites
Epoxy resin matrix-based composites
High-density polyethylene (HDPE)-based composites
Poly butylene succinate (PBS)-based composites
Starch-based composites
Polyethylene oxide (PEO)-based composites
Polyacrylamide (PAM)-based composites
Polystyrene (PS)-based composites
Poly(lactic acid)-based composites
Thermal properties
Natural rubber-based composites
Epoxy-based composites
Polyvinyl alcohol-based composites
Poly ethylene-co-vinyl acetate (EVA)-based composites
Poly(3-hydroxybutyrate) (PHB)-based composites
Polypropylene-based composites
Polyurethane-based composites
Xylan-based composites
Poly(ethylene glycol)-based composites
Starch-based composites
Fabrication processes
Using tea waste
Preparation of tea waste
Fabrication of silica nanoparticles
Synthesis of bionanocomposite
Using waste jackfruit peels
Preparation of plant material
Pectin isolation from jackfruit peel
Partial isolation of pectin from the cell wall material
Synthesis of bionanocomposites
Using waste turmeric spent
Isolation of dietary fiber (DF) from turmeric residue
Turmeric nanofiber preparation
Synthesis of bionanocomposites
Using spent hens
Microwave-assisted lipid extraction
Synthesis of monomer and polymer
In situ dispersion of nanoclay and synthesis of nanocomposite
Synthesis of bionanocomposite
Using waste sunflower stalk
Extraction of cellulose nanocrystals
Extraction of cellulose nanofibrils
Synthesis of bionanocomposites
Physical properties and tribology of different bionanocomposite reinforced by agro-industrial wastes
Sugar palm fiber
Sisal
Coir
Ramie fiber
Hemp
Flax
Kenaf (bast)
Sugarcane bagasse
Wheat straw fiber
Soy hull fiber
Banana fiber
Coconut sheath
Acknowledgment
References
Effects of machining on the acoustic and mechanical properties of jute and luffa biocomposites
Introduction
Materials and methods
Results and discussion
Conclusion
Acknowledgments
References
Jute and luffa fibers: Physical, acoustical, and mechanical properties
Introduction
Background information
Materials and methods
Physical, acoustical, and mechanical properties
Internal structures of jute and luffa fiber samples
Diameter and length
Density
Youngs modulus
Sound absorption coefficient
Transmission loss
Discussion and concluding remarks
Acknowledgments
References
Prediction of the sound absorption performance of porous samples including cellulose fiber-based structures
Introduction
Calculation of sound absorption coefficients
Mathematical models for the prediction of acoustic properties
Simple empirical models: Delany-Bazley model and its modified versions
Rigid-frame models
Johnson-Champoux-Allard model
Johnson-Champoux-Allard-Lafarge model
Deformable-frame model: Biot-Allard model
Estimation of the parameters needed in the mathematical models
Parameters for the air outside the sample
Parameters for the porous sample
Analyses and results
First test case
Second test case
Third test case
Discussion
Summary of the parameters used in the mathematical models
Regression constants used in the empirical models
Evaluation of viscous, thermal, and inertial effects
Evaluation of the elastic and damping properties of the frame of porous sample
Estimation of the frame resonance frequency
Conclusion
References
Index

Citation preview

Cellulose Fibre Reinforced Composites

Woodhead Publishing Series in Composites Science and Engineering

Cellulose Fibre Reinforced Composites Interface Engineering, Processing and Performance Edited by

Asst. Prof. R. ArunRamnath Assistant Professor, Department of Mechanical Engineering, PSG College of Technology, Coimbatore, India

Assoc. Prof. Dr. Mavinkere Rangappa Sanjay Senior Research Scientist & Associate Professor, Natural Composites Research Group Lab, Department of Materials and Production Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok (KMTUNB), Bangkok, Thailand

Prof. Dr.-Ing. habil. Suchart Siengchin President of King Mongkut’s University of Technology North Bangkok, Thailand 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

Assoc. Prof. Dr. Vincenzo Fiore Associate Professor, Department of Engineering, University of Palermo, Italy

An imprint of Elsevier

Contributors

Nafis Abir BGMEA University of Fashion & Technology (BUFT), Dhaka, Bangladesh Nisar Ali Key Laboratory for Palygorskite Science and Applied Technology of Jiangsu Province, National & Local Joint Engineering Research Center for Deep Utilization Technology of Rock-salt Resource, Faculty of Chemical Engineering, Huaiyin Institute of Technology, Huaian, China Salete Alves Textile Engineering Graduate Program (PPGET), Federal University of Rio Grande do Norte, Natal, RN, Brazil Marcos Aquino Textile Engineering Graduate Program (PPGET), Federal University of Rio Grande do Norte, Natal, RN, Brazil M. Aravindh Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India R. ArunRamnath Department of Mechanical Engineering, PSG College of Technology, Coimbatore, India B. Aakash Balaji Department of Mechanical Engineering, PSG Institute of Technology and Applied Research, Coimbatore, Tamil Nadu, India Muhammad Bilal Institute of Chemical Technology and Engineering, Faculty of Chemical Technology, Poznan University of Technology, Poznan, Poland Muthukumar Chandrasekar School of Aeronautical Sciences, Hindustan Institute of Technology & Science, Padur, Kelambakkam, Chennai, Tamil Nadu, India Swati Chaturvedi Department of Mechanical Engineering, University of Petroleum and Energy Studies, Dehradun, Uttarakhand, India Vaibhav Chaudhary Department of Mechanical Engineering, University of Petroleum and Energy Studies, Dehradun, Uttarakhand, India S. Dharani Kumar Centre for Machining and Material Testing, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India

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Contributors

V. Gautham Department of Mechanical Engineering, PSG College of Technology, Coimbatore, India Garip Genc Mechatronics Engineering Department, Marmara University, Istanbul, Turkey S. Gokulkumar Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India V. Hariharan Department of Mechanical Engineering, Kongu Engineering College, Erode, Tamil Nadu, India Abdellaoui Hind Mohammed 6 Polytechnic University (UM6P), Supramolecular Nanomaterial Group (SNG), Benguerir, Morocco Md. Arafat Hossain Department of Consumer and Design Sciences (CADS), Auburn University, Auburn, AL, United States Mohammad Irfan Iqbal BGMEA University of Fashion & Technology (BUFT), Dhaka, Bangladesh Naman Jain Department of Mechanical Engineering, ABES Engineering College, Ghaziabad, India Sangilimuthukumar Jeyaguru Department of Automobile Engineering, Kalasalingam Academy of Research and Education, Krishnankoil, Tamil Nadu, India Aditya Kataria Department of Mechanical Engineering, University of Petroleum and Energy Studies, Dehradun, Uttarakhand, India Adnan Khan Institute of Chemical Sciences, University of Peshawar, Peshawar, Khyber Pakhtunkhwa, Pakistan Ayub Nabi Khan BGMEA University of Fashion & Technology (BUFT), Dhaka, Bangladesh Hasan Koruk Mechanical Engineering Department, MEF University, Istanbul, Turkey Senthilkumar Krishnasamy Department of Mechanical Engineering, Kalasalingam Academy of Research and Education, Krishnankoil, Tamil Nadu, India Sumeet Malik Institute of Chemical Sciences, University of Peshawar, Peshawar, Khyber Pakhtunkhwa, Pakistan

Contributors

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J. Maniraj Department of Mechanical Engineering, KIT—Kalaignarkarunanidhi Institute of Technology, Coimbatore, Tamil Nadu, India T.L.D. Mansadevi Department of Aeronautical Engineering, Sri Ramakrishna Engineering College, Coimbatore, Tamil Nadu, India K.C. Nagaraja Department of Mechanical Engineering, Acharya Institute of Technology, Bengaluru, Karnataka, India L. Prabhu Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India R. Ranga Raj Department of Aeronautical Engineering, Sri Ramakrishna Engineering College, Coimbatore, Tamil Nadu, India G. Rajeshkumar Department of Mechanical Engineering, PSG Institute of Technology and Applied Research, Coimbatore, Tamil Nadu, India; Department of Mechanical Engineering, PSG Institute of Technology and Applied Research, Coimbatore, India Lakshminarayanan Rajeshkumar Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India Karthikeyan Ramalingam Department of Automobile Engineering, Kalasalingam Academy of Research and Education, Krishnankoil, Tamil Nadu, India M. Ramesh Department of Mechanical Engineering, KIT—Kalaignarkarunanidhi Institute of Technology, Coimbatore, Tamil Nadu, India Mohammad Mamunur Rashid BGMEA University of Fashion & Technology (BUFT), Dhaka, Bangladesh Kashif Rasool Qatar Environment and Energy Research Institute (QEERI), Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar Mavinkere Rangappa Sanjay Department of Materials and Production Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS); Natural Composites Research Group Lab, Academic Enhancement Department, King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand Caroliny Santos Textile Engineering Graduate Program (PPGET), Federal University of Rio Grande do Norte, Natal, RN, Brazil

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Contributors

Thiago Santos Textile Engineering Graduate Program (PPGET), Federal University of Rio Grande do Norte, Natal, RN, Brazil Carlo Santulli School of Science and Technology, Geology Division (SST), University of Camerino, Camerino, Italy Nasmi Herlina Sari Department of Mechanical Engineering, Faculty of Engineering, University of Mataram, Mataram, West Nusa Tenggara, Indonesia Subramani Satheeshkumar Department of Mechanical Engineering, Kongu Engineering College, Perundurai, Tamil Nadu, India S. Sathish Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India Thottyeapalayam Palanisamy Sathishkumar Department of Mechanical Engineering, Kongu Engineering College, Perundurai, Tamil Nadu, India Krishnasamy Senthilkumar Department of Materials and Production Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand S. Arvindh Seshadri Department of Mechanical Engineering, PSG Institute of Technology and Applied Research, Coimbatore, Tamil Nadu, India Abu Bakr Siddique BGMEA University of Fashion & Technology (BUFT), Dhaka, Bangladesh Suchart Siengchin Department of Materials and Production Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS); Natural Composites Research Group Lab, Academic Enhancement Department, King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand R. Supriya Department of Aeronautical Engineering, Sri Ramakrishna Engineering College, Coimbatore, Tamil Nadu, India Thirugnanasambandan Theivasanthi International Research Centre, Kalasalingam Academy of Research and Education, Krishnankoil, Tamil Nadu, India Senthil Muthu Kumar Thiagamani Department of Automobile Engineering, Kalasalingam Academy of Research and Education, Krishnankoil, Tamil Nadu, India

Contributors

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Akarsh Verma Department of Mechanical Engineering, University of Petroleum and Energy Studies, Dehradun, Uttarakhand, India; Brigham Young University, Provo, UT, United States Huseyin Yuce Mechatronics Engineering Department, Marmara University, Istanbul, Turkey

Woodhead Publishing is an imprint of Elsevier 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, OX5 1GB, United Kingdom Copyright © 2023 Elsevier Ltd. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. ISBN: 978-0-323-90125-3 (print) ISBN: 978-0-323-90126-0 (online) For information on all Woodhead publications visit our website at https://www.elsevier.com/books-and-journals

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Preface

Cellulose fiber reinforced composites are lightweight materials that are used for many advanced applications such as automotive, construction and building, and aerospace and practical applications such as household appliances. However, in many of these applications, the cellulose fiber reinforced composites are subjected to dynamic conditions such as impact load, friction, wear, and tear. Researchers and scientists have established that the incorporation of filler materials has significantly improved the thermomechanical, electrical, and other physical properties of the cellulose fiber reinforced composites. Thus, to withstand the external forces during operation, micro- and nanofillers, including both natural and synthetic fibers such as carbon nanotubes, carbon black, graphene, nanoclay, nanosilica, plant fibers, glass fibers, carbon fibers, carbon mats, and plant fiber mats, were incorporated as filler material with the polymer-reinforced composites. Additionally, fibers are modified chemically and physically to enhance the interfacial bonding and other mechanical properties. Moreover, many fillers provide additional functionality to these cellulose-reinforced composites. For example, when carbon-based fillers such as carbon nanotubes, carbon nanofibers, and graphene are used with polymers, it enhances the conductivity of the polymers. Similarly, magnetic particles are incorporated into polymers to provide shape memory properties. Recent research studies across the globe indicate that cellulose fiber reinforced composites are preferred for developing structures for automobile, aerospace, and marine applications due to its lightweight and eco-friendly nature that support sustainable and cleaner production. Significant progress has been made in the area of cellulose fiber reinforced composite structures since the beginning of this century. This led to a surge in the number of papers, patents, and review studies published on this topic. Therefore, we believe this is the right time for this important book on Cellulose Fiber Reinforced Composites: Interface Engineering, Processing, and Performance. Several eminent scholars have contributed chapters in this book. We hope that scientists, academic staff, faculty members, researchers, and students working in the area of cellulose fiber reinforced composite structures will find this book to be very informative. The book comprises 21 chapters that shed light on cellulose fiber reinforced composites. Chapter 1 titled “Cellulose fiber reinforced composites: History of evolution, chemistry, and structure” focuses on the synthesis of the cellulose fibers, the extraction methods from biological resources, and its properties, and highlights the chemical structure of fibers extracted from plants. The authors emphasize the significance of fibers derived from plants, its evolution over the years, and its suitability as a reinforcing material along with polymer matrix for the development of lightweight structures. Chapter 2 titled “Bamboo cellulose: Structure, properties, and applications” discusses the chemical structure, physical and mechanical properties, and suitability

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Preface

of bamboo cellulose as an alternative in composites for commercial and other structural applications. Chapter 3 titled “Robust electrospun cellulose nanofiber composites” describes the processing techniques and manufacturing of electrospun cellulose nanofiber composites for biomedical and packaging applications. Chapter 4 titled “Chemical modification of cellulose fiber surfaces” reviews the different chemical treatment techniques that exist and provides information on the modification of the surface properties of the cellulose fibers and the enhancement in the properties. Chapter 5 titled “Physical modification of cellulose fiber surfaces” provides holistic information on the different physical treatment techniques for surface modification of fiber surfaces and the enhancement in properties. Chapter 6 titled “Interface engineering-matrix modification in cellulose fiber composites” discusses the phenomenon of interface engineering and provides information on current matrix modification techniques. Chapter 7 titled “Characterization of fiber surface treatment by Fourier transform infrared (FTIR) and Raman spectroscopy” highlights the importance of characterization of cellulose fibers and evaluates the properties of cellulose fibers for its application as a reinforcement in composites. Chapter 8 titled “Evaluation of the effect of processing and surface treatment on the interfacial adhesion in cellulose fiber composites” provides an overview of the effect of processing of the surfacetreated cellulose fiber composites and its recent developments. The efficiency and usability of such composites can be improved by introducing additional functionalities. Chapters 9 and 10 titled “Manufacturing aspects of cellulose fiber reinforced composites” and “Compression and injection molding techniques,” respectively, discuss the different manufacturing techniques for the production of cellulose fiber reinforced composites. Different processing methods such as hand lay-up, spray-up, vacuum bagging, vacuum infusion, filament winding, resin transfer molding, and prepreg used for the manufacture of polymer components are highlighted. Chapter 11 titled “Thermomechanical characterization of cellulose fiber composites” investigates the thermal characteristics and mechanical properties of cellulose fibers for thermal stability to exhibit the required strength, stiffness, and stability in the composites. Chapter 12 titled “Evaluation of moisture uptake behavior in cellulose fiber” summarizes the research investigations performed on the estimation and analysis of the moisture absorption characteristics of the cellulose fiber and its influence on the performance of the composites. Chapter 13 titled “Effect of zinc oxide filler on compressive and impact properties of jute fiber fabric reinforced epoxy composites” provides an insight on the research studies performed on incorporation of zinc oxides as filler material and its influence on the mechanical properties of the hybrid polymer composites. Chapter 14 titled “Predication of impact strength reduction and service life of 45-degree laminate jute fiber fabric in epoxy composites” discusses the impact strength reduction and the service life of hybrid polymer composites. Chapter 15 titled “Extraction and characterization of cellulosic fibers from the stem of papaya tree (Carica papaya L.)” summarizes the research investigations performed on the extraction of cellulosic fibers from the stem of the papaya tree and evaluates the mechanical, physical, chemical, thermal, morphological, and crystalline properties of the fibers. Chapter 16 titled “Cellulose-based composite materials for dye wastewater treatment” elaborates wastewater treatment for surface modification of cellulose fibers.

Preface

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Chapter 17 titled “Cellulose fiber reinforced composites as packaging materials” discusses the scope for the application of cellulose fiber composite materials in the food and packaging industries. Chapter 18 titled “Bionanocomposites reinforced with cellulose fibers and agro-industrial wastes” explores the utilization of agro-wastes as bioconstituents with nanomaterials for manufacturing cellulose fiber composites that could help in the reduction of greenhouse gas emissions. Chapter 19 titled “Effects of machining on the acoustic and mechanical properties of jute and luffa biocomposites” summarizes the research investigations performed on machining of biocomposites and its influence on the mechanical and sound absorption properties. Chapter 20 titled “Jute and luffa fibers: Physical, acoustical, and mechanical properties” provides additional information on the mechanical, physical, and sound absorption properties of hybrid biofiber-reinforced composites. The last chapter titled “Prediction of the sound absorption performance of porous samples including cellulose fiber-based structures” highlights the importance of sound absorption properties and investigates the performance and impact of porous samples in cellulose fiber composites. The editors are thankful to the authors for their contributions and the Elsevier editorial team for their support and guidance. Editors Asst. Prof. R. ArunRamnath Assoc. Prof. Dr. Mavinkere Rangappa Sanjay Prof. Dr.-Ing. habil. Suchart Siengchin Assoc. Prof. Dr. Vincenzo Fiore

Acknowledgments

This research was funded by the National Science, Research and Innovation Fund (NSRF) and King Mongkut’s University of Technology North Bangkok with contract no. KMUTNB-FF-66-01.

Cellulose fiber-reinforced composites—History of evolution, chemistry, and structure

1

Aditya Katariaa, Swati Chaturvedia, Vaibhav Chaudharya, Akarsh Vermaa,b, Naman Jainc, Mavinkere Rangappa Sanjayd, and Suchart Siengchind a Department of Mechanical Engineering, University of Petroleum and Energy Studies, Dehradun, Uttarakhand, India, bBrigham Young University, Provo, UT, United States, c Department of Mechanical Engineering, ABES Engineering College, Ghaziabad, India, d Department of Materials and Production Engineering, The Sirindhorn International Thai–German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand

1.1

Introduction

The increment in natural consciousness and local area interest, the new natural guidelines, and unjustifiable utilization of petroleum impelled thinking about the employment of the materials that are harmless to the ecosystem. Natural cellulose fiber is thought about one of the harmless to the ecosystem materials, which have great properties contrasted with synthetic or engineered fiber (May-Pat, Valadez-Gonza´lez, & Herrera-Franco, 2013). Through the latest survey of 2010, it is found that the world-wide natural cellulose fiber-reinforced composites industry sector reached 2.1 billion dollars. By analyzing it and the current scenario where the use of natural & biodegradable fiber is increasing, we can assume that production and the usage of natural cellulose-reinforced composites industries is estimated to grow by 15%–20% worldwide (Uddin, Abro, Purdue, & Vaidya, 2013). Cellulose fibers are fibers made with ethers or esters of cellulose, which can be attained from the bark, wood, or leaves of plants, or other plant-based material. In addition to cellulose, the fibers may also comprise of hemicellulose and lignin, with varying percentages of these components fluctuating the mechanical properties of the fibers. Cellulose was found in 1838 by a French physicist named Anselme Payen, who segregated it from plant stock and chose its engineered formula (TheFreeDictionary.com, n.d.). Cellulose was used to convey the essential viable thermoplastic polymer, celluloid, in Hyatt Manufacturing Company in 1870. Manufacture of rayon (“fake silk”) from cellulose commenced during the 1890s, and cellophane was composed in 1912. In 1893, Arthur D. Little made one more cellulosic thing, acidic corrosive determination, and made it into a film. The primary business material usages for acidic corrosive inference in fiber structure were made by the Celanese Company in the early 1920s. A scientist named Hermann Staudinger took the polymer development of cellulose in 1920. The compound was initially misleadingly linked short of the use of Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00012-4 Copyright © 2023 Elsevier Ltd. All rights reserved.

2

Cellulose Fibre Reinforced Composites

any naturally decided proteins in 1992, by Kobayashi and Shoda (Gilbert & Kadla, 1998). It is defined as the fibers that are not synthetic or manmade but are sourced from plants or animals. The use of natural cellulose fiber from various resources, renewable and nonrenewable like bamboo, sugarcane bagasse, hemp, flax, jute, and so on to make composite materials have gained quiet a lot of consideration in the latter decades, so far. The plants that yield or give us the cellulose fiber are classified in various categories and that can be seen in Fig. 1.1.

1.2

Cellulose fiber-reinforced composites—History of evolution

Composite materials are being used for centuries. The composite term from the beginning was utilized in 1500 BC. Early Mesopotamian and Egyptian designers and craftsmen made robust and tough constructions by means of a mix of straw and mud. Since then, after 25 BC, 10 books on Architecture described the strong development and portrayed several sorts of lime and mortars. From the bygone era outline, engineers, producers, craftsman, and creators were endeavored to advance the use of composite materials in a particular field in a more refined way. In 1200 AD, Mongols arranged the essential composite bows which were crafted up of a mix of bamboo, wood, horns, cow’s tendons, and silk invigorated by ordinary pine sap which was by and large staggering and utmost definite weapons until the 14th century. From here on out, from 1870 to 1890, the headway of the composite material started to vary due to the engineered distress. In the modern period, the progression of the composites materials was not underway until scientists were focused on the improvement of plastics.

Fig. 1.1 Classification of different types of natural cellulose fiber.

Cellulose fiber-reinforced composites

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During the 1900s, plastics materials like vinyl, phenolic, polystyrene, and polyester were completed and advanced. In 1907, the foremost plastics like Bakelite were developed with produced fragments. These newly designed materials were given favored execution over various composites materials. Regardless, for essential applications, plastic alone couldn’t invigorate adequate and unyielding nature. In this way, for the enhancement of the strength and toughness of the plan, it was given sincere and notable help. In 1935, Owens Corning at first revealed the primary glass fiber. The improvement of tars was on track from the 1930s, taking everything into account which procedures/techniques are used in the composites business today. The blend of a plastic polymer and fiberglass made a remarkable development. Unsaturated polyester tars were authorized in 1936. Other better tar structures were beginning to see use from 1938 (Keya et al., 2019; May-Pat et al., 2013; Mohammed, Ansari, Pua, Jawaid, & Islam, 2015; Uddin, 2013). Currently, people have started to depend upon composite materials and they do start to employ composite materials at different points. Natural cellulose fiber composite materials are eco-obliging, strong, lightweight, endless, unassuming, ecological, and viable. Natural cellulose fibers have incredible assets separating them from designed/synthetic fiber (Keya et al., 2019). Lately, basic fibers consumed as an elective help in polymer composites which have obtained thought amid various inspectors and experts because of their benefits over standard fabricated materials (Taj, Munawar, & Khan, 2007). These typical strands link jute, hemp, kenaf, coir, banana, bamboo, sugarcane, and various others (Faruk, Bledzki, Fink, & Sain, 2012), which give extraordinary mechanical properties that appeared differently with man-made strands and their cost are realistic, they are environmental and supportable, declining energy use, not as much of prosperity peril and doesn’t increase wear on the equipment, not detrimental to the skin (Nguong, Lee, & Sujan, 2013). Hence, it can be utilized as a developed material because of its thermosetting and thermoplastic behavior. Thermosetting pitches like unsaturated polyester sap, polyester, epoxy, polyurethane, and phenolic are normally used for collecting composites material gives superiority in various applications. They give adequate mechanical properties and their expense is reasonable. Taking into account their incredible properties like high strength, small thickness, also, natural advantages over customary composites, regular fibers are standing apart enough to be seen among academicians, subject matter experts, and understudies and besides in industry. Because of their nondisease causing and biodegradable, the use of cellulose fiber-reinforced composites is growing step by step and quite rapidly. Natural cellulose fiber-reinforced composites are a very cost-effective material which is the reason of its use in different sectors such as aerospace, automobile, building, packaging and construction sectors, railway coach interiors, and storage devices and also acts as a replacement of high-cost glass fiber (Akil et al., 2011; Zini & Scandola, 2011). Braga and Magalhaes (2015) considered the mechanical and thermal properties of polyester hybrid composites (e.g., jute also, glass fiber) and thought about and dissected their properties (e.g., flexural, thermal, thickness, and effect properties). He clarified that jute fiber-based composites exhibited a preferred/better conformation over glass fiber. Thwe and Liao (2000) contemplated the mechanical properties of

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bamboo fiber and built up the base composite, the impact of bamboo fiber length, fiber content, bamboo to glass fiber proportion and demonstrate the mechanical properties of bamboo glass fiber-reinforced plastics. Okubo, Fujii, and Yamamoto (2004) grown new composite material utilizing bamboo fiber and polypropylene and examined the mechanical conduct of those composites. Balaji, Karthikeyan, and Sundar (2014–2015) examined the use and eventual fate of normal strands and biocomposite material and talked about their uses that can be utilized in creation of modern items because of its eco-friendly nature, minimal effort, effectively accessible conduct. Normal fiber and biocomposites are utilized to make family furniture, fencing, flooring, athletic gear, lightweight auto parts.

1.3

Chemistry

1.3.1 Glucose monomer Cellulose is formed from a monomer called glucose. This formation takes place through condensation polymerization or can take place through biological catalysts: the enzymes through step-growth mechanisms (Shanks, 2014). Cellulose has monomer of which are very complex. Chiral carbons groups are arranged in a ring of six, which leads to a very precise stereochemistry. Monomers which have primary covalent bond needs to be developed to understand the complex nature of cellulose. This understanding also helps us in analyzing the role played by stereochemistry and interaction within and outside the molecule. Apart from four chiral, due to the linkages which are present in the chain and cyclic nature, a fifth chiral carbon arises. As a result, conformation is maintained. Cellulose is made up of repeating units of alpha 1–4 linkages between D-glucose units. Glucose is a sugar consisting of six carbons. Sixteen configurations arise due to the presence of chiral carbon (2,3,4,5). These configurations consist of both diastereoisomers and enantiomers. Glucose has a pyronase form that arises when 5-hydroxy is combined with aldehyde. As a result, the formation of six-member cyclic hemiacetal will take. There is no planarity in the cycle structure. However, in the case of glucose, the cycle structure is planar. A total of 32 diastereoisomers and enantiomers are formed due to the presence of a new chiral center in the hemiacetal hydroxyl on carbon 1. This type of conformation is called betaglucopyranoside and is found with cellulose. Bent link is formed in starch due to the alpha-glucopyranoside which is the opposite conformation. Chirality in carbon 1 is the main reason for the difference between cellulose and starch. The stability of alpha-anomer is two times more than the stability beta-anomer. However, alphahydroxy is less stable. This is due to the anomeric effect. The anomeric effect takes place with the help of dipole’s interaction by the electrons that are no bonded which are present on the adjacent hemiacetal-ring oxygen that is aligned with the hemiacetal hydroxy Group. The close packaging and crystal formation is ensured by the planar structure of cellulose. Loose coils formation takes place because of the bent conformation of starch. These crystallize with a complex molecule. In glucopyranoside structure, each carbon consists of hydrogen and pendant hydroxy. The hydrogen

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atoms are small and are less crowded that’s why they are directed out of the cyclic plane. Groups that are present out of the plane are known as axial. On the other hand, groups that are present inside the plane are called equatorial. Cellulose consists of hydroxyl groups that behave similarly to alcohol functional groups. These hydroxyl groups react with strong bases like sodium hydroxide to form salt. The concentration of salt formed is very less because the hydroxyl groups are acidic only to a limited extent. Swelling, dyeing, and partial dissolving are done by taking advantage of the acidic behavior of hydroxyls present in cellulose. Aldehyde and carboxylic acid are formed by the oxidation of glucose at the C6 hydroxyl. Aldehydes are oxidized at carbon 1 which is in the open-chain structure to form glycolic acid. Glutamic acid is formed by the oxidation of C1 and C6 in open-chain form.

1.3.2 Glucose biopolymerization Cellulose is formed by the biopolymerization of glucose. As a result, a regular polymer is created in which inversion of glucose which is adjacent takes place, without any change in stereochemistry. Two glucose units are present in the repeating unit of the cellulose chain. Glucose units are linked with chains of cellulose by polymerization leading to the formation of cellulose I crystal morphology. Glucose, cellobiose, and short glucans are formed by the enzymatic hydrolysis of cellulose. Complete hydrolysis leads to the formation of glucose. Multistep synthetic process is required for cellulose microfibrils. Assembly from the synthesizing sites is required for the microfibrils to be assembled from cellulose chains. This is a spontaneous process. Typically formation of crystalline cellulose type 1 takes place from biosynthesis, whole sometimes crystalline cellulose type 2 can also be formed. Synthesis of cellulose takes some place within the membrane of enzyme complexes. A complex network of microfibrils is formed through the synthesis mechanism. Polymerization of beta (1–4)-glucopyranose is done by cellulose synthase from uracil diphosphateglucose (Guerriero, Fugelstad, & Bulone, 2010). The morphology, width of cellulose fibril deposition and extracellular chain assembly are controlled by the arrangement of cellulose synthase units (Ross, Mayer, & Benziman, 1991).

1.3.3 Cellulose structure Cellulose has 300–1000 glucose units in each molecule and biopolymerization takes place with a high degree of polymerization. Thus, the molar mass varies from 540,000 to 1,800,000 g/mol. Therefore, it has a high molar mass and can form hydrogen bonds. The proximity of hydroxyl groups and alignment of hydroxyl groups and monomer units is determined by the orientation of hydroxyl groups within each glucose unit. Due to the regularity and symmetry of individual chains, the formation of assemblies of cellulose chains takes place which is confined to a fixed conformation by intramolecular bonding. Cellulose I crystals are less stable thermodynamically. However, it is found in abundance (Fidale, Ruiz, Heinze, & Seoud, 2008). Cellulose type II crystals were not found in abundance in plants. Ironic liquids and other components are used for determining the transition of crystal structure as a function of permeation (Cheng et al., 2011).

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1.3.4 Chemical and solubility properties of cellulose Acetal groups which link the cellulose monomers are resistant to alkali. Shorter chain length and glucose are formed when hydrolysis of cellulose takes place by hydrochloric A day sulfuric acid. In amorphous and crystallites which are less perfect and small, the rate of hydrolysis is more. Selective hydrolysis uses differential hydrolysis for the preparation of nanofibers and nanocrystals. Cellulose is oxidized by alkali when oxidizing agents are present. C6 hydroxyl is the site for oxidation, resulting in the formation of carboxylic acid. Thermogravimetry is used for studying thermal degradation. Degradation steps were revealed due to the presence of pectin, hemicellulose, and cellulose when thermal degradation of hemp was investigated. When noncellulose substances were treated with sodium hydroxide, TGA derivative peaks decreased. On the other hand, the onset temperature decreased when treated with sodium hydroxide (Rachini, Le Troedec, Peyratout, & Smith, 2009). During the development of cotton fiber, to study the structural changes, TGA was used. There were differences noted in the primary and secondary cell walls (Abidi, Cabrales, & Hequet, 2010). Differential scanning calorimetry was utilized to sisal degradation. Nitrogen and air were used to examine raw and defatted fibers and their chemical constituents. Degradation of raw sisal took place at a higher temperature than cellulose. The reason behind this was the lignin content of the sisal (Martin, Martins, da Silva, & Mattoso, 2010). In liquid such as water (which are organic), swelling of cellulose takes place. Sixteen aprotic solvents were used to study swelling in native and microcrystalline cotton. There are various factors on which the swelling depends such as—basicity, polarizability, molar volume, and nature of chain whether they are parallel or nonparallel (Fidale et al., 2008). In liquids and solutions, which have hydrogen bonding, cellulose is soluble. Lower critical solution temperature (LCST) phenomena are observed in cellulose. The swelling of cellulose is caused by sodium hydroxide and crystal II is formed from crystal I by mercerization process upon heating. Adding urea to sodium hydroxide increased the solubility because of the increase in hydrogen bonding. Effective solvents when lithium chloride is added for cellulose are N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and dimethylsulfoxide (DMSO), which are dipolar aprotic in nature. NMMO 9 (N-methylmorpholine-N-oxide) exists in solid form at room temperature, that’s why solutions are made at a higher temperature. It is used to dissolve cellulose and purification. It is nonvolatile in nature and can precipitate cellulose, after dilution with water. It can then recycle after the evaporation of water from the NMMO filtrate. Cellulose fibers are regenerated under the names Lyocell, Tencel, from NMMO solutions, by injecting them into a precipitation bath.

1.3.5 Sources of cellulose The cell wall and structural component of plants consist of cellulose. Fabrics of the fungi cell walls, insects, mollusks, and the exoskeleton of crawfishes are made up of polysaccharides and chitin. Cellulose, lignin, pectin, and hemicellulose constitute the composite of the plant cell wall which provide rigidity and strength and helps in preventing

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swelling of the cell. Wood is the main source of cellulose. About 30%–40% of cellulose is present in wood and the composition also depends on the species of wood.

1.3.6 Separation of cellulose Many other plant components along with cellulose fibers co-exist which are necessary for the functioning of the plant but they play no role in mechanical properties and performance. Adhesion of fibers with a polymer matrix causes these components to detract. These components can lose their color when comes in contact with heat or sunlight. Retting is a selective natural purification step in which the plant material is left in contact with stagnant water. It helps in further purification as the original plant material gets degraded. Decortication is a process where materials of plants are physically beaten; this is done by passing them through rollers. Since they are flexible and stronger than the rest of the plant; therefore, these fibers resist mechanical rupture. Physical disruption of fibers takes place with the steam explosion. Heating the fibers under pressure increases the temperature of water above atmospheric boiling temperature. Water boils because of the sudden release of pressure. Physical disruption is caused because of the force of the boiling water. Due to the properties such as strength, crystal structure, and limited water uptake as compared to the rest of the material, no significant damage takes place in these fibers. The formation of 5hydroxymethylfurfural is a sign of cellulose degradation ( Jacquet et al., 2011).

1.3.7 Purification of cellulose Organic solvent extraction with acetone or ethanol, to remove waxes is generally the first step in the purification of cellulose. The absorptivity of water in fibers increases after alkali extraction. After that, extraction of alkali is used for dissolving lignin and pectins. Phenolic groups are present in lignins and carboxyl groups are present in pectins and hemicellulose (Shanks, 2014). During alkali treatment, swelling of cellulose takes place. Chemical procedures such as acid hydrolysis, chlorination, alkaline extraction are used for the purification of cellulose (Astley & Donald, 2001; Mora´n, Alvarez, Cyras, & Va´zquez, 2008). In amorphous regions, the rate of acid hydrolysis is more. As a result, the cellulose which is left after a major portion of cellulose is pure. For bleaching the product of cellulose, oxidative alkaline extraction is used. This treatment produces carboxyl groups that are soluble in the alkali of sodium hypochlorite and chlorite. When enzyme pectinase is used, a milder and selective form of hydrolysis is used. Aspergillus aculeatus is used for preparing pectinase. Pectin which is the component of the cell wall hydrolyses pectinase. In the pH buffer, a pectinase solution is used to incubate raw cellulose.

1.3.8 Cellulose polymorphism Depending on the source and treatment, crystalline cellulose can take several morphologies. Cellulose type I is known as native cellulose. It is mostly found in cell walls and other plant structures. On the other hand, cellulose type II is known as textile

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cellulose. It is mostly obtained by a process called mercerization in which strong alkalis are heated. Cellulose III and cellulose IV are mostly found in combination with types I and II. Cellulose I has unit cell lattice parameters of a ¼ 0.835 nm; b ¼ 1.03 nm; c ¼ 0.79 nm and crystallizes in monoclinic form. Crystal size from equatorial reflection and apparent crystal length from meridional reflections were obtained when diffraction peak widths were analyzed. To characterize crystal dimensions and shape, small-angle X-ray scattering was used. To measure the cellulose fibril structure, SAXS (small-angle X-ray scattering) was performed on flax fibers. Hydration level was responsible for microfibril misalignment. Repeat distance of about 0.6–0.7 was found in crystalline and noncrystalline. In dry and wet states, structures of fibers differed (Vorawongsagul, Pratumpong, & Pechyen, 2021). SAXS (small-angle X-ray scattering) and WAXS were used to measure fiber symmetry of collagen and cellulose. Fibers exhibit cylindrical rotational symmetry, thus WAXS can be used to determine the oriental angle.

1.3.9 Chemical modification of cellulose Solubility is imparted by alkyl cellulose such as methyl and ethyl cellulose by varying their amount used for substitution. Methylcellulose is soluble in water and can behave as a rheological agent when the degree of substitution is low. Methylcellulose becomes soluble in organic solvents with higher substitutions. Transient Rheological and Isotropic liquid crystalline solution behavior is noticed when ethyl cellulose solutions are placed in m-cresol. The free hydroxyl group can be reduced by using and the combinations that can be formed from these derivatives.

1.3.10 Preparation of nanocellulose There are various structures of cellulose example—MCC, bacterial cellulose, CNF, CNC where dimensions are small and internal structure is maintained. When purified cellulose is hydrolyzed by partial and selective method, formation of each form takes place. After mixing aqueous mineral acid with cellulose, suspension formation takes place which is diluted. Amorphous and semicrystal are hydrolyzed first, thus having the most perfect crystal structures.

1.4

Structures

1.4.1 Cellulose reinforcement in polylactic acid and polybutylene succinate This study was aimed at making cellulose fiber-reinforced PLA/PBS with the help of a twin-screw extruder along with injection molding (Vorawongsagul et al., 2021). Its mechanical properties of the structures were investigated and reported.

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1.4.1.1 Melt flow index of the composite The index melt flow is used to quantify the viscosity of the melt which shows that a lower melt flow rate is linked to higher melt viscosity. The addition of cellulose fibers in the PLA/PBS blend led to a growth in the melt flow index and subsequently, a reduction in the viscosity of PLA/PBS/CF with respect to pure PLA or PBS. In a low-frequency range, a substantial increase in the intricate viscosity of composites occurred. Because the fibers were oriented in the flow direction, all composites exhibited shear thinning. At a phr value of 15 for the loading of CF, the highest filling effect was obtained. Bhatia, Gupta, Bhattacharya, and Choi (2007) reported that lesser content of cellulose fibers in the PLA/PBS matrix had established itself due to higher viscosity of the melt in the entire array of the shear rates present. The value of the melt flow index diminished when the amount of CF taken was escalated from a value of 5 phr to 15 phr, but also increased the probability of distribution of fiber in the matrix. Hence, the ideal value is kept at 15 phr for the appendage of CF in PLA/PBS. Meant for the production of foam, foam injection molding through chemical foaming is used. The chemical foaming agent can be added in two ways, first through the hopper of the injection molding machine along with the polymer pellets, and second when plasticization of the polymer is ongoing in the barrel. The foaming agent dissolves throughout the procedure. During foam extrusion, the spin of the screw pushes out the melt forwards and exits out of the extruder die. In foam injection molding, the screw revolves and simultaneously moves rearward because of the gathering of a pool made up of a gas-polymer mix by the screw’s end. The extreme pressure and temperature in the unit where plasticization occurs, deliver a supercritical condition of the foaming agent during the chemical foaming procedure. To attain a high degree of solubility, CO2 is used as a chemical foaming agent and utilized in an overcritical state. Since a fluid has a low viscosity, high diffusion properties, and low surface tension, providing it brilliant solubility in the polymer (Mathew, Oksman, & Sain, 2005; Yu et al., 2015).

1.4.1.2 SEM analysis of composite foams SEM analysis is done to find the shape and size of the cellulose fibers and their compatibility with the polymer matrix. The standard thickness of the CF was around 16.19  0.33 μm. Vorawongsagul et al. (Astley & Donald, 2001) reported that the cell wall structures of PLA/PBS and PLA/PBS-CF foams show closed-cell walls due to sodium bicarbonate decomposing into carbon dioxide gas that facilitates sealed cells on biofoam structures. Melt-based foam construction machineries were combined with other means to increase porosity. To generate pores, various methods like foaming of gas and phase separation methods were used. The composite foam consisting of CF was larger than PLA/PBS foam by 5 phr. When the content of CF was improved, the quantity of cells and uniformity of distribution of cells also increased. Cellulose fibers were helpful in the improvement of the properties of gas barriers. The polymer’s viscosity decides the bubble growth bubbling shape (Ma et al., 2012). The best foam was with a CF content of 15 phr, i.e., PLA/PBS-CF15

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as it was the most uniform in terms of shape and cell size. The number of closed cells was also increased when the PLA/PBS foam was dipped in hot water for 75°C for 30 min. Increasing the temperature expands the material and increases the diffusivity. Sodium bicarbonate has two states, one exists at 80°C, which leaves solid sodium bicarbonate, and second at 120–150°C, which leaves solid sodium oxide (Sadik, Pillon, Carrot, & Ruiz, 2018).

1.4.1.3 FTIR spectroscopy The adsorption peaks of PLA foam were observed at 3299 cm1 for C-H vibrations and at 1749 cm1 for CO] vibrations. In PBS foam, dOH vibrations was observed at 3300 cm1, CO] vibrations at 1712 cm1, COd vibrations at 1155 cm1, and C-H vibrations at 2919 cm1 (Cai, Lv, & Feng, 2013). The peak of CF was observed at 3333 cm1 for dOH vibrations, at 2897 cm1 for C-H vibrations, and 1031 cm1 for COd vibrations. No new peaks were observed in the PLA/PBS-CF composite.

1.4.1.4 XRD analysis The diffraction peaks of PBS foam were observed, recorded as (020) at 2θ ¼ 19.5° and (110) at 2θ ¼ 22.5° of a crystalline of monoclinic nature (Wang et al., 2013). For PLA foam, a broad peak was observed, which can be attributed to a small level of matrix crystallinity due to quick cooling rates when the foam underwent extrusion and injection molding. The fibers exhibited strong peaks at 2θ ¼ 15.8° and 22.6° with index to (200) and (002) (Mathew et al., 2005; Zhao et al., 2007). PLA/PBS blends don’t show any strong peaks in the XRD pattern. The XRD of PLA/PBS-CF composite foams exhibiting a peak at 2θ ¼ 16.6° and 22.6° as the most protuberant and telling of CF crystallinity. As CF matter is increased to 15 phr, a stable increment in the concentration of the peak at 2θ ¼ 16.6° and 22.6° is detected, which were not projecting at low reinforcement content. Hence, it was observed that 15 phr of fibers has a higher-level crystallinity of the matrix than when CF is not added, which can also explain the lower tensile modulus of the PLA/PBS when compared with PLA/ PBS-CF.

1.4.1.5 Mechanical properties The accumulation of cellulose fibers to the PLA/PBA foam increased its mechanical properties both when it was immersed in hot water, and when it was not submerged in hot water. When the CF content was increased from 0 to 15 phr, an increase in tensile strength from 36.51 MPa at 0 phr to 42.30 MPa at 15 phr was observed. The Young’s modulus also increased from 1146.57 MPa at 0 phr to 1393 MPa at 15 phr. This exhibits that an increase in the CF content will proportionally increase the modulus value (Mulinari & Da Silva, 2008). For the complete values, refer to Table 6 in the reference (Vorawongsagul et al., 2021). Due to the addition of CF fibers, the rigidity of the composite increased, which resulted in the decrease of elongation percentage upon addition of stress (Mulinari, Voorwald, Cioffi, & da Silva, 2017). Conversely, an increase in the elongation was observed upon growing the CF content. Upon

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immersion in boiling water, the tensile strength of the composite foams with CF was reduced because the superior the closed-cell of composite foams, the lower the density.

1.4.2 Cellulose reinforcement in natural bamboo-composite This study was aimed at removing cellulose fibers from bamboo stalks and using them as reinforcement for an epoxy composite (Kalali, Hu, Wang, Song, & Xing, 2019). The mechanical properties of the composite include ultimate tensile strength, specific tensile strength, modulus, and impact strength. Characteristic analyses like SEM and FTIR were also reported. These tests were then compared with other materials like normal epoxy, TRIPLEX, and Al alloy 2000 to benchmark the composite prepared.

1.4.2.1 FTIR analysis The lignin present in the bamboo was first removed, and then FTIR was done to confirm its removal. To do so, the analysis was done on both natural bamboo and the lignin removed bamboo. Natural bamboo exhibited many characteristic lignin bands along with bands at 1735 cm1 for carbonyl vibrations (Sa´nchez, Aperador, & Capote, 2018), 1602, 1510, 1421, and 1327 cm1 for aromatic skeletal (Zhang et al., 2017, 2018), 1460 cm1 C-H vibrations due to dOCH3 (Nishida, Tanaka, Miki, Ito, & Kanayama, 2017), and at 1167 cm1 due to carbonyl vibration (Zhang et al., 2017). When this analysis was done on the de-lignified bamboo, the lignin bands were missing, exhibiting the successful removal of lignin from the bamboo stalks. A reduction in the density between bulk bamboo and de-lignified bamboo also verified the same fact. Delignified bamboo had a bulk of 0.26 g/cm3, while the loose bamboo had a bulk of 0.60 g/cm3.

1.4.2.2 SEM analysis SEM images of the natural bamboo in the upright direction to growth displayed a porous structure made up of fiber bundles, parenchyma cells, and vessels, while the same images in the growth direction showed the fibers bound by lignin. Removal of lignin led to a honeycomb structure. Additionally, the microstructure along well-aligned fibers along the growth direction was well-maintained during the chemical treatment procedure to remove lignin. Epoxy resin was then permeated into the de-lignified bamboo microstructures under the assistance of vacuum. The analysis also showed that each and every one the gaps and channels were entirely occupied with the epoxy resin. The distinction between the original bamboo cell walls and the epoxy resin is clear, signifying that the crude bamboo microstructures were also well conserved after the epoxy penetration procedure. In the direction of growth, due to the presence of epoxy resin, the surface of the fiber packs had become coarser and the fibers were associated to each other, which were expected to form a sturdy bond between the infiltrated epoxy resins and bamboo cellulose fibers.

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1.4.2.3 Mechanical properties The removal of lignin and penetration of epoxy caused in the epoxy permeated bamboo-composite helped in meaningfully improving the strength. The ultimate tensile strength of natural bamboo was 68.55 MPa. In comparison to crude bamboo, the ultimate tensile strength of the lignin removed bamboo was reduced to 36.64 MPa, due to the fact that the lignin served as a supporting binder in the cellulose fibers was uninvolved. On the other hand, the epoxy-filled bamboo-composite showed an ultimate tensile strength of 162.12 MPa, twice the values for crude bamboo. The ultimate tensile strength for the epoxy infiltrated bamboo composite is more appreciable than the previously reported values, such as 28.1 MPa for small bamboo fiber-reinforced epoxy composite (Yu, Huang, & Yu, 2014), 32.05 MPa for bamboo epoxy composite (Khan, Yousif, & Islam, 2017), 79.11–99.62 MPa for bamboo-epoxy composites preserved with different silanes (Kushwaha & Kumar, 2010), 89 MPa for bamboo fibers/biobased epoxy modified by means of starch nanocrystal and 88 MPa silica fume which is silanized (Gauvin, Richard, & Robert, 2018), and 80.24–133.39 MPa for bamboo stripped fiber-reinforced epoxy composites (Costa, Monteiro, & Loiola, 2011). Also, the lightness of the bamboo fibers lead to high specific strength of the epoxy infiltrated bamboo composite with a value of 145 MPa cm3/g, which was much extreme than an epoxy matrix at about 72 MPa cm3/g (Yang, Wu, Guan, Shao, & Ritchie, 2017) and became comparable to the light-weight TRIPLEX steels which exhibited a value of 157 MPa cm3/g and aluminum alloy which was around 167 MPa cm3/g (Dursun & Soutis, 2014; Frommeyer & Br€ ux, 2006). Moreover, the epoxy infiltrated bamboo-composite displayed an improvement of 63% in its modulus, when associated with natural or crude bamboo. As reported by Ritchie (2011), explaining the struggles between strength and toughness in materials is an ongoing and challenging task, since these tend to be reciprocally exclusive. The composite also had a sophisticated strain at 3.5% when compared to the natural bamboo which was at 1.6%. Additionally, for the characterization of the ductility of the samples, the Izod impact test was conducted. The epoxy infiltrated bamboo-composite showed a better ductility toughness of 67.14 kJ/m2 than the natural bamboo which was at 49.33 kJ/m2. For the tables comparing epoxy infiltrated bamboo composite with other sources, refer to Tables 1 and 2 in reference (Kalali et al., 2019).

1.4.3 Cellulose fibers reinforcement in ethylene-nonbornene copolymer composite This study was aimed at making ethylene-norbornene copolymer composites occupied with cellulose fibers and montmorillonite (MMT) (Cichosz, Masek, & Wolski, 2019). The composite was formed and aged to understand any differences that may occur due to it. Furthermore, their structure was investigated to find out their mechanical and optical properties. Additionally, characterization techniques like FTIR have been done. The cellulose fibers were altered with vinyl trimethoxy silane (VTMS) and maleic anhydride (MA) before their surface was made compatible with the polymer matrix improvement using hydrophobization. The employment of natural fibers like cellulose is being sought

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after and investigated in resins (Manfredi, Rodrı´guez, Wladyka-Przybylak, & Va´zquez, 2006), thermoplastic (Ruseckaite & Jimenez, 2003), elastomeric materials (Vieira, Nunes, & Visconti, 1996), and in polymer films (Bastos et al., 2016). Natural fibers are currently being used in packaging, automotive, furniture industry, and building constructions (Bachtiar, Sapuan, & Hamdan, 2008).

1.4.3.1 FTIR analysis An in-depth and accurate analysis of the chemical modifications of treated fibers has been done (Cichosz, Masek, Wolski, & Zaborski, 2019). The analysis exhibited two peaks at 2915 cm1 and another at 2847 cm1 which were accredited to the C-H vibrations and CH2 groups in the ethylene-norbornene copolymer (Kazayawoko, Balatinecz, & Woodhams, 1997). A band at 1463 cm1 is related to an additional C-H bending of CH2 (Misra, 1993), another at 718 cm1 was correlated to CH2 rocking mode. Adsorption bands corresponding to cellulose fibers were found at 1400–800 cm1 (Pandey, 1999). Materials that were treated with cellulose fibers showed bands at concentrations at 1245 cm1 for CH3 and 1158 cm1 for COd (Colom, Carrasco, Pages, & Canavate, 2003; Faix, 1991). This proves that the existence of variations in the composite structure was instigated due to the modification of cellulose fibers’ presence. The deficiency of dCH3 and C-O groups provides an intensity surge of other absorption bands that are detected. The usage of VTMS led to the upsurge of absorption band at 1058 cm1 for C-O vibrations (Ołdak, Kaczmarek, Buffeteau, & Sourisseau, 2005). Interestingly, an alteration with MA does not provide any new bands or peaks. These variations in the peak can also be associated with the construction of ]CdOdC] bonds (Yang, Zhang, Endo, & Hirotsu, 2003), which may be due to the possibility of cellulose fibers creating new bonds between themselves. After the aging process, called thermo-oxidizing aging is done; the results of FTIR were again analyzed. For cellulose, the intensity decreases between 1300 and 1100cm1 due to the drop in the quantity of C-O and dOH entities (Gulmine, Janissek, Heise, & Akcelrud, 2002). An upsurge of intensity is seen at 1100– 1000cm1 which exhibits the existence of COdOdCO bonds (Fan, Dai, & Huang, 2012) which are in connection with the recombination of CdO bonds inside the composite structure. Another absorption band at 819 cm1 is present for vibrations of C]O and CdOdC groups which were created after the aging procedure was complete. In the case of composites with altered cellulose spectra offered it may be observed that the quantity of CdO, C]O, C]C, and COOH has increased at around 1300–1000 cm1 (Barry, Kamdem, Riedl, & Kaliaguine, 1989; Blackwell, Vasko, & Koenig, 1970) and 830–800 cm1 regions (Santos, Gonzalez, & Gonzalez, 1998). Grafting VTMS and MA with hydroxyl groups on the cellulose surface, changes in the structure of alkyl chains are observed that are bonded to the cellulose fibers, which in turn decreased the signal from dOH entities. This results in a minor modification in the 1700–1500 cm1 region that can be easily observed. This proves the existence of C]C and C]O bonds in the model after aging is done (Hinterstoisser & Salmen, 1999). For the complete table of wave numbers refer to Table 2 of reference (Cichosz, Masek, & Wolski, 2019).

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1.4.3.2 Mechanical properties As reported, tensile properties of composites can be remarkably improved by the addition of fibers to a polymer matrix due to the fact that fibers have better and higher strength and values of stiffness (Holbery & Houston, 2006; Malkapuram, Kumar, & Negi, 2009), but when left unprocessed and natural additives supplemented, composites exhibit inferior tensile strength (Bledzki, Reihmane, & Gassan, 1998) and meagre compatibility with polymer matrix. Here, mechanical properties were analyzed for the determination of standards of the tensile strength (TS) and elongation at breaking (Eb) that is done before and after the aging process, as investigating it was a crucial step for the characterization of composites. Upon investigating the data that were gathered, it was found that mechanical properties changed after the aging process depending upon the orientation of the fibers and were stronger when cellulose or MMT was combined. This proved the point that a controlled aging process was theoretically possible with simple additives like cellulose fibers. The tensile strength before aging was 40  3 MPa and after aging was 37  2 MPa. The percentage of elongation before aging of the composite was at 450  30% and after aging, the percentage was at around 440  30%. This proved that the degradation process was not intensive, just as the FTIR analysis proved.

1.4.3.3 Optical characterization Optical properties like the stability of color throughout the aging of the material were inspected to further understand the impact of the aforementioned process. It provides data about the intensity of the various processes performed as the yellowing or browning of samples is a common occurrence which is connected with the aging and can be the evidence of the creation of carbonyl groups in the matrix. The optical properties of analyzed composites tell that they were affected by the temperatures during the processes. The highest values of color changes were observed for composites occupied with MMT. However, samples made with cellulose and MAtreated natural fibers and MMT mixed with cellulose exhibited color variation at around the same level. Alternatively, VTMS treated with cellulose fibers was the least affected sample due to the aging process, also being the only material changing its optical properties fewer than pure ethylene-norbornene copolymer. On the same page, chroma values associated with saturation were offered. Similarly, this constraint was the most altering and changing in the case of composites treated with MMT. Conversely, changes of chroma values were lowest in the case of the pure ethylenenorbornene copolymer, and the samples present with unchanged or VTMS-treated cellulose, validating its color stability. Saturation was recorded to be the highest in the case of samples treated with MMT and MA natural fibers. It was also observed that VTMS-treated cellulose showed hue angle values wavering between 90° and 100°. This means the color or shade of the samples was similar to yellow. Alternatively, MMT, MA-treated cellulose and cellulose mixed with MMT had angle of hue shifting among 70° and 80° which made their color or shade nearer to orange. Nonetheless, the values of hue angles weren’t varying meaningfully after aging producing virtually no

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alteration in the shade of the composites. In addition, the authors have a vast experience in the field of nanomaterials and biocomposites (Arpitha, Verma, Sanjay, & Siengchin, 2021; Bharath et al., 2020; Bisht, Verma, Chauhan, & Singh, 2021; Chaudhary, Sharma, & Verma, 2022a, 2022b; Chaurasia, Verma, Parashar, & Mulik, 2019; Deji, Verma, Choudhary, & Sharma, 2021; Deji, Verma, Kaur, Choudhary, & Sharma, 2022; Jain, Verma, & Singh, 2019; Kataria, Verma, Sanjay, & Siengchin, 2022; Rastogi, Verma, & Singh, 2020; Singh, Jain, Verma, Singh, & Chauhan, 2020; Singla, Verma, & Parashar, 2018; Verma et al., 2021; Verma, Baurai, Sanjay, & Siengchin, 2020; Verma, Budiyal, Sanjay, & Siengchin, 2019; Verma, Gaur, & Singh, 2017; Verma, Jain, Kalpana, Siengchin, & Jawaid, 2020; Verma, Jain, Parashar, et al., 2020a, 2020b; Verma, Jain, Rastogi, et al., 2020; Verma, Joshi, Gaur, & Singh, 2018; Verma, Kumar, & Parashar, 2019; Verma, Negi, & Singh, 2018a, 2018b; Verma, Negi, & Singh, 2019; Verma & Parashar, 2017; Verma & Parashar, 2018a; Verma & Parashar, 2018b; Verma & Parashar, 2018c; Verma & Parashar, 2020; Verma, Parashar, Jain, et al., 2020; Verma, Parashar, Singh, et al., 2020; Verma, Parashar, & Packirisamy, 2018a, 2018b; Verma, Parashar, & Packirisamy, 2019a, 2019b; Verma & Singh, 2016; Verma & Singh, 2019; Verma, Singh, & Arif, 2016; Verma, Singh, Singh, & Jain, 2019; Verma, Singh, Verma, & Sharma, 2016; Verma, Zhang, & Van Duin, 2021).

Acknowledgment Monetary and academic support from the University of Petroleum and Energy Studies, Dehradun, India (SEED Grant program) is highly appreciable.

Conflicts of interest There are no conflicts of interest to declare by the authors.

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Yang, L., Zhang, F., Endo, T., & Hirotsu, T. (2003). Microstructure of maleic anhydride grafted polyethylene by high-resolution solution-state NMR and FTIR spectroscopy. Macromolecules, 36(13), 4709–4718. Yu, Y., Huang, X., & Yu, W. (2014). A novel process to improve yield and mechanical performance of bamboo fiber-reinforced composite via mechanical treatments. Composites Part B: Engineering, 56, 48–53. Yu, P., Mi, H. Y., Huang, A., Geng, L. H., Chen, B. Y., Kuang, T. R., et al. (2015). Effect of poly (butylenes succinate) on poly (lactic acid) foaming behavior: Formation of open cell structure. Industrial & Engineering Chemistry Research, 54(23), 6199–6207. Zhang, Y., Hou, Q., Xu, W., Qin, M., Fu, Y., Wang, Z., et al. (2017). Revealing the structure of bamboo lignin obtained by formic acid delignification at different pressure levels. Industrial Crops and Products, 108, 864–871. Zhang, Y., Qin, M., Xu, W., Fu, Y., Wang, Z., Li, Z., et al. (2018). Structural changes of bamboo-derived lignin in an integrated process of autohydrolysis and formic acid inducing rapid delignification. Industrial Crops and Products, 115, 194–201. Zhao, H., Kwak, J. H., Zhang, Z. C., Brown, H. M., Arey, B. W., & Holladay, J. E. (2007). Studying cellulose fiber structure by SEM, XRD, NMR and acid hydrolysis. Carbohydrate Polymers, 68(2), 235–241. Zini, E., & Scandola, M. (2011). Green composites: An overview. Polymer Composites, 32(12), 1905–1915.

Bamboo cellulose: Structure, properties, and applications

2

Mohammad Mamunur Rashida, Nafis Abira, Md. Arafat Hossainb, Mohammad Irfan Iqbala, and Abu Bakr Siddiquea a BGMEA University of Fashion & Technology (BUFT), Dhaka, Bangladesh, bDepartment of Consumer and Design Sciences (CADS), Auburn University, Auburn, AL, United States

2.1

Introduction

In recent years, because of environmental concerns, the depletion of fossil resources, climate change. Bamboo fiber and its reinforced composite (Liu, Song, Anderson, Chang, & Hua, 2012), and the nonbiodegradable nature of the synthetic fiber (Huang & Young, 2019), there is a growing interest in replacing synthetic fibers in polymeric composites with natural plant fibers such as jute, coir, flax, hemp, bamboo, and sisal (Akil et al., 2011; Baley, Lan, Bourmaud, & Le Duigou, 2018). Natural plant fibers have been considered an alternative to synthetic fibers because they are lightweight, renewable, low cost, low energy requirements, abundant availability, high strength, elasticity modulus, strong thermal insulation, mechanically durable, sustainable, and biodegradability. Natural plant fibers provide economic, functional, and environmental advantages as substitutes for standard synthetic fibers such as aramid and glass fibers. They are gaining favor in automobile, aerospace, and structural building applications (Sanjay et al., 2018). Bamboo fiber has received particular attention among many natural fibers due to its low density, high stiffness, high strength, and rapid growth, making it abundant. As a plant, bamboo plays an immense role in carbon sequestration due to its rhizome root system (Gu et al., 2019), preventing soil erosion and reinforcements in embankments (Ben-zhi, Mao-yi, Jin-zhong, Xiao-sheng, & Zheng-cai, 2005). As a material, bamboo finds many applications in various industries, including building, automotive, electronics, and aerospace (Kaur, Pant, & Kaushik, 2019). Bamboo is considered the most functionally gradient composite material available in the market. It is found that the 1 mm2 region at the outside perimeter of a piece of bamboo includes around eight fibers, and the inner periphery contains two fibers (Ray, Mondal, Das, & Ramachandrarao, 2005). Cellulose is the main constituting element of bamboo fiber. Bamboo consists of cellulose, hemicellulose, and lignin ratio 2:1:1 (Zhang et al., 2019). It contains relatively higher cellulose than other woody cellulose, as shown in Table 2.1 ( Jawaid & Abdul Khalil, 2011). Though natural cellulose offers many advantages over other materials, it has various shortcomings, such as excessive water absorption, low strength, and poor thermal stability (Rasheed, Jawaid, Parveez, Zuriyati, & Khan, 2020). These limits can be using bamboo cellulose since it possesses high thermal stability and strength Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00007-0 Copyright © 2023 Elsevier Ltd. All rights reserved.

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Cellulose Fibre Reinforced Composites

Table 2.1 Chemical composition amount of different lignocellulosic fiber. Fiber

Cellulose

Hemicellulose

Lignin

Extractives

Ashes

Water soluble

Jute Flax Ramie Sisal Hemp Kenaf Coir Bamboo

64.4 64.1 68.6 65.8 74.4 53.4 32–43 73.83

12.0 16.7 13.1 120 17.9 33.9 0.1–0.25 12.49

11.8 2.0 0.6 9.9 3.7 21.2 40–45 10.15

0.7 1.5–3.3 1.9–2.2 0.8–0.0.11 0.9–1.7 – – 3.16

– – – – – 4.0 – –

1.1 3.9 5.5 1.2 – – – –

Reprinted with permission from Jawaid, M. & Abdul Khalil, H. P. S., (2011). Cellulosic/synthetic fiber reinforced polymer hybrid composites: A review. Carbohydrate Polymers, 86(1), 1–18. Elsevier.

(Rasheed, Jawaid, Karim, & Abdullah, 2020). Bamboo cellulose is widely applied in textile industries, drug delivery, wound healing, antibacterial activity, UV-protective clothing, and thermal regulation (Prakash, 2020; Singla et al., 2017). It cannot be obtained directly from the bamboo culm and requires several treatments before being produced. Bamboo cellulose can be extracted from leaf also (Fan et al., 2018). Typically, cellulose extracted from bamboo is in nanocrystal form. Bamboo cellulose is extracted in different forms, such as microcrystalline cellulose (MCC), cellulose nanocrystal (CNC), cellulose nanofiber (CNF). The main goal of this chapter is to review the bamboo cellulose extraction process, structures, properties, and applications.

2.1.1 Bamboo cellulose extraction process 2.1.1.1 Bamboo cellulose production by wet spinning Bamboo cellulose can be chemically (hydrolysis alkalization with multi-phase bleaching) processed by the wet spinning technique. This production process contains many steps, as described below (Chand, Shukla, & Sharma, 2008). Step 1: Preparation: Bamboo leaves and soft inner piths are collected from the bamboo culm. After that, they are crushed to facilitate the subsequent processes. Step 2: Steeping: Crushed bamboo particles are soaked in 15%–20% alkali solution. This soaking is continued for 1–3 h at the temperature range from 20°C to 25°C. This process turns the bamboo cellulose into alkali cellulose. Step 3: Pressing: Excess alkali solution is removed by pressing. Step 4: Shredding: A grinder or shredding machine is used to shred the obtained alkali cellulose into smaller particles. Therefore, the surface area increases as well as eases further steps. Step 5: Aging: Shredded alkali cellulose must be dried and kept in standard ambient condition for 24 h. During this time, alkali cellulose comes in contact with

Bamboo cellulose: Structure, properties, and applications

25

atmospheric oxygen. It promotes the degradation of polymer chains. A shorter polymer chain length is required to maintain the proper viscosity of the spinning solution. Step 6: Sulfurization: In the sulfurization stage, carbon disulfide is added to bamboo alkali cellulose. The obtained material is sulfurized by this process and turns into gel form. Step 7: Xanthation: The carbon disulfide from the sulfurized gel is evaporated by decompression. Cellulose sodium xanthate is formed after this process. Step 8: Dissolving: A diluted sodium hydroxide solution is added to the cellulose sodium xanthogenate to dissolve it to produce a viscous solution containing approximately 5% sodium hydroxide and 7%–15% bamboo fiber cellulose. Step 9: Spinning: The viscous bamboo solution is forced through a spinneret nozzle as the spinneret is submerged into a dilute Sulfuric acid solution. When the viscous bamboo cellulose solution comes into contact with dilute sulfuric acid, it solidifies and converts into bamboo yarn. The described production method for regenerated bamboo fiber is similar to that of viscose rayon fiber, also known as bamboo viscose.

2.1.1.2 Kraft pulping Microcrystalline cellulose can be isolated from bamboo fibers. The process starts with alkali treatment. After that, hypochlorite bleaching by NaOCl was performed at 70– 80°C. At last, acid hydrolysis was done by 2.5 moL/L of HCl. A temperature of 85°C was maintained during the acid hydrolysis process. During the early stages, the pulp shows brown color. This color tends to be whiter after each step due to the removal of hemicellulose, lignin, and other impurities and becomes pure white after the final stage (Rasheed, Jawaid, Karim, & Abdullah, 2020).

2.1.1.3 Bamboo nanocellulose by mechanochemical process Mechanochemistry is the molecular combination of mechanical and chemical phenomena, including phase change, size reduction, and polymer degradation with the effects of compression and friction and cavitation-related phenomena (Zhang, Liang, & Lu, 2007). Mechanical energy is transmitted from balls to a target substance during the mechanical process, which causes specific chemical reactions. Compared to other approaches, mechanochemistry consumes less power and is more environmentally friendly, allowing for determining total kinetic and thermodynamic parameters in the degradation process (Lear et al., 2007). Bamboo cellulose nanocrystals (BCNC) can also be manufactured from the bamboo pulp in various ways. According to the mechanochemical approach, bamboo pulp is cut into pieces at first and then processed by a Fiber Standard Dissociation device at 2000 rpm to convert the bamboo pulp into cellulose pulp. This step needs 30 min to perform. After that, cellulose pulp and phosphoric acid are added to a ZrO2 mil pot. The pot contains ZrO2 balls and PTFE, coated stirring device in it. The mixture is kept in a water bath of 40–60°C and then stirred at 400 rpm, which continues for 1.5–3.5 h. After this stirring, a transparent cellulose solution is obtained. The addition of distilled water to this solution

26

Cellulose Fibre Reinforced Composites

separates cellulose from the gelatinous precipitates. This cellulose is neutralized and treated in an ultrasonic reactor to obtain cellulose nanocrystals (Lu et al., 2015).

2.1.1.4 Bamboo cellulose extraction by acid hydrolysis (99% sulfuric acid) Bamboo fiber is oven-dried and then treated by NaOH aqueous solution. After 90 min treatment at 170°C fatty acid, lignin, and other impurities are removed. This process also swells the amorphous cellulose so that sulfuric acid can penetrate the bamboo pulp. After that, a separate bleaching step is required to remove the lignin and hemicellulose. Bamboo pulp is poured into 40% sodium hypochlorite solution at above 70°C. After stirring at 700 rpm for 30 min, washing is done. If lignin remains in the cellulose pulp, it is again alkali-treated. The pretreated bamboo pulp is treated with sulfuric acid at 45°C for 45 min to obtain nanocrystal cellulose. Then the pulp is kept in an ultrasonic bath for stirring at 20 KHz. This stirring makes the suspension dark yellow. This color is the indication of adequate hydrolysis. At this point, deionized water is added to the suspension to stop the hydrolysis reaction. After that, the suspension is kept still for several hours. After settling down, when the suspension is layered, the dense bottom layer is washed with deionized water several times. Each time the liquid upper layer on the sediment is removed, new deionized water is added until the pH remains constant. The remaining material is then oven-dried at 55°C and powdered to get nanocrystal cellulose (Rasheed, Jawaid, Karim, & Abdullah, 2020).

2.1.1.5 Hydrothermal extraction In the hydrothermal cellulose extraction process, bamboo slivers are first pretreated in benzene alcohol solvents. This mixture is kept for 48 h at room temperature. The mixture is then treated for 3 h in a water bath at 60°C. The remaining material is then washed and cleaned by distilled water and dried at room temperature. Hemicellulose is removed when this processed bamboo is boiled in 180 mL distilled water under high pressure for three hours, maintaining a temperature at 170°C. After removing the hemicellulose, the remaining bamboo is washed, filtrated, and dried. This bamboo is kept in a chamber with acetic acid, distilled water, and NaClO2 for 5 h at a 75°C water bath to remove the lignin. After that, final washing, filtering, and drying are done to get hydrothermally extracted cellulose (Lin, Huang, & Yu, 2021).

2.1.1.6 Standard alkali extraction Bamboo cellulose can also be extracted by the alkali extraction method to extract cellulose. Bamboo slivers are processed in a benzene ethanol mixture and then treated with 65 mL of distilled water. This step is done in a water bath where 75°C temperature is maintained. The obtained bamboo is treated with acetic acid and sodium chlorite gradually until the bamboo becomes white through removing lignin. After that, the remaining material is washed and oven-dried at 103
2°C. The obtained bamboo is processed by alkali solution in a water bath at 25°C. This treatment is continued for

Bamboo cellulose: Structure, properties, and applications

27

45 min to remove the hemicellulose. After several filtration and washing with distilled water, the alkali extracted cellulose is obtained (Lin et al., 2021).

2.1.1.7 Ambient condition extraction This method can extract bamboo cellulose in ambient conditions, but it is timeconsuming. The bamboo slivers are processed with sodium chloride in distilled water to remove lignin. Acetic acid is gradually mixed into the mixture to maintain pH 4.0. After that, the mixture is stirred by magnetite (300 rpm) for around two months in ambient conditions. After filtration and drying, the obtained bamboo is treated in an alkali solution for 72 h in magnetite to remove the hemicellulose. After filtration and washing with distilled water, the residue is freeze-dried. This extracted cellulose is known as ambient condition extraction cellulose (Lin et al., 2021).

2.1.1.8 Two-stage extraction At first, bamboo slivers are mixed with diluted slightly acidic (pH 4.5) sodium chlorite solution and treated in an 80°C water bath. The sodium hypochlorite solution is changed after every 6 h. This phenomenon continues until the bamboo turns white. This process removes the lignin of bamboo. After filtering and drying with distilled water, the lignin-free bamboo is treated in sodium hydroxide solution in an 80°C water bath. This alkali solution has to be changed every 6 h until the color of the remaining bamboo turns pale yellow. After washing and freeze-drying, two-stage extraction cellulose is obtained (Lin et al., 2021).

2.1.1.9 Bamboo cellulose using HNO3/KClO3 method The dry bamboo fiber (BF) quantity compared to dry raw bamboo strips was around 45%. Further acid hydrolysis was carried out to create nano-sized bamboo cellulosic crystals (BCCs). The resultant bamboo fiber (approximately 40 g) was combined with sulfuric acid (392 g, 50%). The slurry was aggressively agitated for 48 h before being rinsed by dialysis in distilled water for 72 h. A 10% suspension of bamboo cellulose crystals was made and preserved for future testing and analysis, as was a 0.1% suspension after further dilution (Liu, Zhong, Chang, Li, & Wu, 2010).

2.1.1.10 Bamboo-derived cellulose nanofiber (CNF) by ultrasonication Two grams of the bamboo were dewaxed in a Soxhlet apparatus (SE-Series, Vinci Technologies, France) for 6 h with a 2:1 (v/v) combination of benzene/ethanol. Then, lignocellulosic compounds in the samples were extracted using a sodium chlorite (NaClO2) solution at 75°C for an hour, and the process was repeated five times until the sample turned white. Next, the sample was treated with 2 wt% potassium hydroxide (KOH) at 90°C for 2 h to remove the remaining hemicelluloses, starch, and pectin. Then, a 0.5 wt% bamboo cellulose dispersion was created by changing the dispersion concentration with distilled water. The bamboo cellulose dispersion was then placed

28

Cellulose Fibre Reinforced Composites

in an ultrasonic generator machine for 1 h for sonication to get disintegrated cellulose nanofibrils. The ultrasonication was carried out in an ice/water cooling bath system to reduce the unwanted temperature increase during the high-intensity sonication operation (Kwak, Lee, Lee, & Jin, 2018).

2.1.2 Anatomy of bamboo 2.1.2.1 Physical structure of bamboo Fig. 2.1 shows the main parts of a bamboo stem (Lorenzo, Mimendi, Godina, & Li, 2020). Bamboo plants can reach a height of 30 m (98 ft.) and a width of 25–30 cm (10– 12 in.) in diameter. The main parts of a bamboo stem are the cavity, diaphragm, node, branch, internode, and wall. An internode or culm is a hollow cylindrical part that connects two nodes. The bamboo culm can be 10–25 cm (4–10 in.) long. The exodermis is the outer side (green region) of the bamboo stem made up of dense vascular bundles, and the endodermis is the inner part (yellowish area) of the stem that comprises a few vascular bundles. The main cellulosic portion exists between the exodermis and the endodermis (Rocky & Thompson, 2018). Bamboo is a natural composite material since it is mainly made up of vascular bundles (sclerenchyma, metaxylem vessels, sieve tubes with partner cells) embedded in a ligneous matrix (parenchyma) see in Fig. 2.2 (Azadeh, Ghavami, & Garcı´a, 2021). Fig. 2.1 Major parts of bamboo stem. Reprinted with permission from Lorenzo, R., Mimendi, L., Godina, M. & Li, H., (2020). Digital analysis of the geometric variability of Guadua, Moso and Oldhamii bamboo. Construction and Building Materials, 236, 117535, Elsevier.

Bamboo cellulose: Structure, properties, and applications

29

Fig. 2.2 Cross-section of bamboo. (A) Bamboo culm cross section, (B) bamboo segment, (C) bamboo cross section components, (D) porosity of parenchyma. Reprinted with permission from Azadeh, A., Ghavami, K. & Garcı´a, J. J., (2021). The influence of heat on mechanical properties of Dendrocalamus giganteus bamboo. Journal of Building Engineering, 43, 102613. Elsevier.

Bamboo culm possesses 50% parenchyma tissues, 40% fibers, and 10% conducting tissue (vessels, sieve tubes with companion cells) with some variation according to species (Hu, Huang, Fei, Yao, & Zhao, 2017). The parenchyma cells, which have polygonal geometry, form the base of the stem cross-section. It comprises thin cell walls filled with live protoplasm containing water and molecules (Mannan, Paul Knox, & Basu, 2017). The sclerenchyma cells are long hollow tubes aligned in the stem direction. Sclerenchyma cells have thick cell walls surrounding holes (lumen) with a polygonal or circular cross-section. The cell wall thickness in the sclerenchyma cells varies radially in the cross-section (Dixon & Gibson, 2014). The fibers are present around the vascular bundles as sclerenchyma sheaths (fiber sheaths; fiber cap). Bamboo fibers are thin, long, tapering, and frequently forked at the ends. They run longitudinally through the culm Investigations have revealed that the fiber walls are composed of many alternating thin and thick layers at the microscopical level (Parameswaran & Liese, 1980; Wai, Nanko, & Murakami, 1985). Each layer consists of cellulose microfibrils oriented at varying angles to the fiber axis and surrounded by a hemicellulose and lignin matrix (Wegst, Bai, Saiz, Tomsia, & Ritchie, 2015). The microstructure of single bamboo fiber is shown in Fig. 2.3. The figure represents a multilayer wall with concentric circles. The layer consists of a thick cell wall, small lumen, and a small microfibril angle. The fiber length significantly varies within the species. According to the species, individual fiber length can vary from 1 to 4 mm. The thickness of bamboo fibers varies from 10 to 30 μm (Yu, Wang, Lu, Tian, & Lin, 2014). The parenchyma and sclerenchyma cells are made up of cellulose fibers embedded in a noncellulosic matrix of hemicellulose and lignin. Cellulose fibrils are helically wrapped in the cell wall material, with an average microfibril angle (MFA) to the cell axis denoted by θ (Suzuki & Itoh, 2001). Fig. 2.3 also describes the structure of a fiber’s multilamellar possesses secondary cell wall (Zakikhani, Zahari, Sultan, & Majid, 2014; Zou, Jin, Lu, & Li, 2009). Beginning with the middle lamella, the main cell wall, and a transition layer S0, the microfibril angles alternate from near to 0° in the thick lamella and 90° in the thin ones see in Fig. 2.3 E(Zakikhani et al., 2014). The principal component of the lamella is cellulose, which is formed by assembling glucose molecules into microfibrils with either rectangular or hexagonal

30

Cellulose Fibre Reinforced Composites

Fig. 2.3 (A)–(D) Representation of cellulose in the bamboo cell wall, and (E) MFA. Reprinted with permission from Zou, L., Jin, H., Lu, W. Y. & Li, X., (2009). Nanoscale structural and mechanical characterization of the cell wall of bamboo fibers. Materials Science and Engineering C, 29(4), 1375–1379. Elsevier.

cross-sections and a diameter of 3–5 nm (Youssefian & Rahbar, 2015). The cellulose microfibrillar angle (MFA) was found to be roughly 9° in one research, regardless of radial and longitudinal position inside the culm. In contrast, in another study, the MFA was found to be 10° for the middle and outermost parts, and 44° for the interior region of bamboo (Dixon & Gibson, 2014). As previously stated, the structure and density of the vascular bundles’ gradient variation from the inner edge to the outer zone see in Fig. 2.4 (Kanzawa, Aoyagi, & Nakano, 2011). It depicts the distributions of fiber bundles at the inner edge, mid-thickness, and periphery. Bundles are denser at the outer parts. The fiber structure varies between sheaths and the inner edge to the periphery. The aspect ratio of the fibers is 70–150 (Mannan et al., 2017).

2.1.2.2 Chemical structure of bamboo fiber Bamboo is a lignocellulosic fiber derived from the bamboo culm. The orientation of the cellulose chain was in two distinct crystalline and amorphous cellulose regions. Highly ordered (crystalline) areas form when the hydrogen bonds between the hydroxyl groups form in order. If random hydrogen bonds occur, disordered (amorphous) regions arise. Bamboo is a composite material that is naturally composed of lignin and cellulose. It is made up of comparatively long and aligned cellulose fibers that provide reinforcement and are embedded in a lignin matrix (Rusch, Wastowski, de Lira, Moreira, & de Moraes Lu´cio, 2021). The main chemical elements of bamboo fibers are cellulose, hemicellulose, and lignin, which account for more than 90% of the total mass. Fig. 2.5 represents the chemical structure and orientation of bamboo fiber forming constituents (Menon & Rao, 2012). The rest include soluble polysaccharides,

Bamboo cellulose: Structure, properties, and applications

31

Fig. 2.4 Gradient density of bamboo fiber in the bamboo culm and changes of shape inner to outer layer. (A) Cross-section of moso bamboo, (B) schematic shape change of vascular bundle. Reprinted with permission from Kanzawa, E., Aoyagi, S. & Nakano, T., (2011). Vascular bundle shape in cross-section and relaxation properties of Moso bamboo (Phyllostachys pubescens). Materials Science and Engineering C, 31(5), 1050–1054. Elsevier.

waxes, resins, tannins, proteins, and ashes (Chaowana, 2013). The volumetric percentage of cellulose, hemicellulose and lignin is 73.83%, 12.49%, and 10.50%, respectively (Youssefian & Rahbar, 2015). Cellulose biopolymer comprises a long linear chain with a high molecular weight and a well-organized fibrous network composed of anhydro-D-glucose units (C6H10O5)n connected by β-1,4 glycosidic linkages (Fig. 2.5). The glucose rings have a high polymerization degree, and the molecule is insoluble in alkali and aqueous conditions, allowing the creation of compact fibers (Yan, Kasal, & Huang, 2016). The bamboo culms consist of 60%–70% holocellulose (cellulose + hemicellulose) and lignin 20%–30%. This composition varies based on the species, growing environment, bamboo maturity, and stem part (Mohamad Ibrahim, Zakaria, Sipaut, Sulaiman, & Hashim, 2011). The α -cellulose content of bamboo is 40%–50%, equivalent to the reported α-cellulose contents of softwoods (40%–52%) and hardwoods (38%–56%), making bamboo an excellent raw material for the pulp and paper industry (Nayak & Mishra, 2016). Since increasing cellulose content and aspect ratio increase stiffness in the nanocomposite, ductile polymer matrices tend to become brittle and hard (Abdul Khalil et al., 2015)]. The chemical composition of different bamboo species is shown in Table 2.2. Cellulose molecules link with other polymers to produce microfibrils, which are high stress-resistant linear structures with a diameter of around 10–20nm, and these overlapping layers construct the cell wall (Yan et al., 2016). The amount of cellulose decreases with the increasing age of bamboo (Abdul Khalil et al., 2012).

Fig. 2.5 Chemical structure of bamboo. Reprinted with permission from Menon, V. & Rao, M., (2012). Trends in bioconversion of lignocellulose: Biofuels, platform chemicals & biorefinery concept. Progress in Energy and Combustion Science, 38(4), 522–550. Elsevier.

Bamboo cellulose: Structure, properties, and applications

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Table 2.2 Chemical composition of different bamboo species.

Species Bambusa blumeana Bambusa vulgaris Gigantochloa brang Gigantochloa levis Gigantochloa scortechinii Gigantochloa wrayi Phyllostachy pubescens

Cellulose + hemicellulose (holocellulose) (%)

α-Cellulose (%)

Lignin (%)

Ashes (%)

65.7–72.6

40.3–45.1

20.5–22.7

–

67.8–69.6

37.9–43.2

22.7–23.9

1.8–2.1

79.94

51.58

24.83

1.25

85.08

33.80

26.50

1.30

74.62

46.87

24.9–27.9

1.1–1.4

84.53

37.66

30.04

0.88

71.40

47.00

22.8

1.5

References Liese and Tang (2015) Liese and Tang (2015) Wahab et al. (2013) Wahab et al. (2013) Wahab et al. (2013) Wahab et al. (2013) Oliveira, Cunha, Reyes, Gacitu´a, and Petit-Breuilh (2016)

Hemicelluloses are heterogeneous types of polysaccharides that, unlike cellulose, typically contain side chain groups (Scheller & Ulvskov, 2010). The branched polymers contain five-carbon sugars (pentoses) such as xylose or six-carbon sugars (hexoses) other than glucose. They are amorphous and create the matrix with the ligninembedded cellulose (Wahab et al., 2013). Hemicellulose can absorb water easily due to its low molecular weight, irregular chain arrangement, and low crystallinity. These features of hemicellulose reduce time and energy consumption during cellulose pulp refining (Wan, Wang, & Xiao, 2010). Glucomannans and xylans are the two main types of hemicelluloses. In bamboo, xylan is a relatively short polymer with a low degree of polymerization 200. More than 90% of the hemicelluloses in bamboo are xylan (Nayak & Mishra, 2016). Bamboo hemicellulose has been described as xylan and characterized as a β-(1 ! 4)-linked-xylopyranosyl backbone with Larabinofuranose and 4-O-methyl-D-glucuronic acid as single side chains (4-Omethy1-D-glucuronic-arabino-xylan). This chain is organized irregularly (Anwar, Gulfraz, & Irshad, 2019; Youssefian & Rahbar, 2015). The ratio of uronic acid/arabinose/xylose is 1:3:32. Hemicellulose molecules can form various chemical bonds with lignin, although most evidence points to ether and ester bonds. Jeffries suggested structures forester and ether bonds for lignin/uronic acid and lignin/arabinoxylan groups, respectively (Youssefian & Rahbar, 2015). These linkage models are

34

Cellulose Fibre Reinforced Composites

employed to link lignin and hemicellulose in the cross-linked LCC network. Covalent bonding in the cell wall structure is coordinated by hemicellulose and phenolic acids (Abdul Khalil et al., 2012). Lignin is another component of bamboo fiber. In plants, lignin and cellulose give structural support (Abdul Khalil et al., 2012). It makes the bamboo fiber stiffer and yellow (Muhammad, Rahman, Hamdan, & Sanaullah, 2019). Lignin is a naturally occurring phenolic macromolecule found mainly in the secondary cell wall of plants. It is composed of three major phenylpropanoid subunits: p-hydroxyphenyl (H-type), guaiacyl (G-type), and syringyl (S-type) (Malherbe & Cloete, 2002). It is dissolved by different chemical treatments to produce wood pulps, leaving the cellulose and hemicelluloses in fibrous form. Because of their lower molecular weight, higher solubility, and ease of hydrolysis, some hemicelluloses are lost throughout the process (Wahab et al., 2013). Table 2.3 shows the chemical elements of several bamboo species, including the average concentrations of carbon (C), hydrogen (H), nitrogen (N), and oxygen (O),

Table 2.3 Elemental composition of different bamboo species and other cellulosic fibers. Biomass

C

H

N

O

H/C

O/C

References

Bambusa vulgaris

46.80

6.38

0.22

46.60

0.14

0.99

Dendrocalamus latiflorus Phyllostachys pubescens Phyllostachys makinoi Rice husk

46.10

6.20

0.09

46.62

0.13

1.01

47.02

5.88

0.09

44.19

0.13

0.94

Rousset, Aguiar, Labbe, and Commandre (2011) Lin, Chang, Ko, and Wang (2016) Lin et al. (2016)

44.95

6.20

0.06

42.57

0.14

0.95

Lin et al. (2016)

48.36

5.13

0.72

32.79

0.11

0.68

Timber wood

47.72

5.54

0.89

44.85

0.11

0.93

Wood

45.68

6.30

0.30

47.42

0.14

1.04

Coir pith

44.03

4.70

0.70

43.44

0.11

0.99

Tsai, Lee, and Chang (2007) Della Rocca, Cerrella, Bonelli, and Cukierman (1999) Fagbemi, Khezami, and Capart (2001) Neves, Thunman, Matos, Tarelho, and Go´mez-Barea (2011)

Bamboo cellulose: Structure, properties, and applications

35

as well as the H/C and O/C ratios (Rusch et al., 2021). It is found that the H/C ratios are closet one each other (from 0.11 to 0.14), suggesting bamboo fibers are significantly carbonized. The overall average of O/C ratios was 0.96, indicating that the carbon and oxygen percentages are almost equal and that the surface has a higher hydrophobicity (Chun, Sheng, Chiou, & Xing, 2004). The nitrogen content of different bamboo species ranges from 0.06 to 0.22, lower than other fibers presented in Table 2.3. Low nitrogen content is vital for environmental protection since NOx formation during material combustion causes adverse effects on the environment (Rusch et al., 2021).

2.1.3 Properties of bamboo cellulose 2.1.3.1 Durability Bamboo cellulose fabrics possess a more pilling resistance than cotton. Socks with plain and rib structures were manufactured with different fibers. In the presence of lycra, bamboo cellulose fabric showed better pilling resistance than cotton fabric (Arafa Badr, 2018). The effect of bamboo cellulose incorporation in the earth soil matrix is also investigated. It is found that the inclusion of 5% bamboo cellulose pulp in the earth soil matrix increases the specific energy and fracture toughness up to 275% and 31%. Flexural strength and wear resistance was also found to be higher (Stanislas et al., 2021). Surface-modified bamboo cellulose provides more durability. PLA matrix was reinforced with bamboo cellulose after modification. Increased strength of 28.6% and young’s modulus of 34.6% were found with alkali pretreatment. In bamboo cellulose-epoxy composite tensile strength and elongation at break were found best with silane coupling agent with 71% and 53% (Lu et al., 2014).

2.1.3.2 Elasticity The aqueous counter collision method investigated the elastic modulus of different cellulose nanofibers. Bamboo cellulose nanofibers showed a slightly higher elastic modulus of 95.3
16.8 GPa than cotton cellulose nanofiber (91.7
29.4) GPa (Zhai, Kim, Kim, Kang, & Kim, 2018). Bamboo cellulose crystals (BCC) increase the stiffness of a composite also. Mechanical properties of BCC-reinforced starch composite were investigated, and it was observed that after inclusion of 0%–8% BCC, Young’s modulus increased from 20.4 to 210.3 MPa (Liu et al., 2010). However, the inclusion of surface-modified bamboo cellulose positively influences the elongation of a composite. Lu et al. developed a PLA biocomposite reinforced with surfacemodified bamboo cellulose and found 61% increased elongation after treating with silane coupling agents compared to untreated samples (Lu et al., 2014).

2.1.3.3 Antimicrobial resistance Bamboo has antibacterial, antifungal, and antistatic properties that are naturally present. Bamboo possesses a unique antibacterial and bacteriostatic bioagent known as “Bamboo Kun” which links strongly with bamboo cellulose molecules during the

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normal process of bamboo fiber development. This characteristic is also kept in bamboo textiles. Bamboo textiles become healthier, germ-free, and odor-free as a result (Prakash, 2020). The bamboo cellulose can resist the growth of bacteria naturally (Muhammad et al., 2019). This capability comes due to chlorophyll, sodium copper chlorophyllin, which are natural antibiotics. Bamboo fabric can resist up to 71% colonization of bacteria in 24 h (Liu et al., 2012). This resistive action was found active even after 50 washes. Its effectiveness is tested by Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) and found to be more effective against E. coli (Kathirvel & Ramachandran, 2014). Bamboo cellulose resists the colonization of both Grampositive (S. aureus) and Gram-negative (E. coli) bacteria (Arafa Badr, 2018). The inclusion of Cu nanoparticles in bamboo cellulose composites can increase the antimicrobial property and the resistance to wash. Teli et al. found the antimicrobial resistance of Cu nanoparticle reinforced bamboo composites durable up to 50 times of washing (Teli & Sheikh, 2014).

2.1.3.4 Biodegradability As regenerated cellulose fiber, bamboo was created entirely from bamboo using a high-tech procedure. It generates natural and environmentally friendly fiber without any chemical additives. It is completely biodegradable in soil by microorganisms and sunlight as a natural cellulose fiber. The breakdown process does not pollute the environment. Bamboo fiber has been dubbed “the natural, ecological, and eco-friendly new-type textile material of the twenty-first century (Prakash, 2020).” Bamboo-poly lactic acid (PLA) composites are eco-friendly because they are biodegradable and help protect the environment from pollution (Nurul Fazita et al., 2016).

2.1.3.5 Breathable and cool Bamboo fiber allows human skin to breathe freely. The unique breathability and coolness of bamboo fiber are noteworthy. The bamboo fiber offers excellent moisture absorption and ventilation since the cross-section is loaded with numerous micro gaps and micro holes (Karthikeyan, Nalakilli, Shanmugasundaram, & Prakash, 2017). Bamboo fiber clothing has an unparalleled microstructure that allows it to collect and evaporate human sweat in a fraction of a second. In the hot summer, such clothing, like breathing, make people feel exceedingly cool and comfortable. Even in the heat of summer, it never sticks to the skin. According to reputable testing results, bamboo fiber clothing is 1–2 degrees cooler than regular clothing in hot summer. Air cooling clothing constructed of bamboo fiber has been crowned (Prakash, 2020).

2.1.3.6 Hardness The polygonal cellulose nanograins provide a considerable amount of hardness to any final structure of bamboo cellulose (Imadi, Mahmood, & Kazi, 2014). The Rockwell hardness tester examines the hardness test of bamboo-epoxy and other hybridized composites. It is observed that the inclusion of jute or coir fiber along with bamboo can boost the hardness further (Bansal, Ramachandran, & Raichurkar, 2017).

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2.1.3.7 Impact resistance The impact behavior of a composite improves with the addition of bamboo cellulosic fibers. Impact resistance of bamboo cellulose-reinforced epoxy composite is investigated by a pendulum impact tester after surface modification with a silane coupling agent and NaOH. It is observed that surface modification slightly decreases the impact resistance of the composite samples, and the highest result was found at 30% cellulose content (Lu et al., 2014). Impact strength of 0%–16% bamboo cellulose-reinforced cementitious composite is tested by the drop weight method. It is found that with up to 12% bamboo cellulose addition, the impact resistance increases with the addition of fiber content (Xie, Zhou, & Yan, 2019). There is no significant changes not appeared in impact strength of composite prepared with and without node (Iqbal, Al Mizan, & Nabi Khan, 2020).

2.1.3.8 Absorption characteristics The kinetics of moisture absorption in bamboo is matched Fick’s hypothesis (Kushwaha & Kumar, 2010). Moisture absorption of bamboo cellulose fiber is found at 13%, which is higher than cotton, lyocell, viscose rayon, modal, and soybean fibers (Erdumlu & Ozipek, 2008). Bamboo fiber acts as a moisture reservoir, allowing moisture to permeate into interfacial areas and reduce shear strength (Chen, Miao, & Ding, 2009). The moisture absorption of bamboo epoxy composite is 41%, and when benzoylation is applied, the moisture absorption drops to 16% (Kushwaha & Kumar, 2010).

2.1.3.9 Thermal property The thermal conductivity and resistance of bamboo cellulose are reported to be lower than conventional cotton fiber (Majumdar, Mukhopadhyay, & Yadav, 2010). Bamboo cellulose fiber is more thermally stable than conventional viscose fiber. During thermogravimetric analysis at 200°C, bamboo cellulose fiber shows 7.706% mass loss with a residue of 7.9% after 500°C, while viscose fiber experiences 8.153% mass loss at 200°C with a residue left of 7.685% (Xu, Lu, & Tang, 2007). Bamboo cellulose nanowhisker filler in PLA composite hinders macromolecular mobility and thus increases the glass transition, cold crystallization, and melting temperature (Qian, Zhang, Yao, & Sheng, 2018). The thermal stability of microcrystalline cellulose (MCC) synthesized from bamboo is better than commercially available MCC (Rasheed, Jawaid, Karim, & Abdullah, 2020).

2.1.3.10 Air permeability The air permeability of bamboo fibers is higher than cotton fiber. The yarn prepared from bamboo fibers has been shown to have less hairiness than cotton. This lower hairiness is also a contributing factor to high air permeability (Majumdar et al., 2010).

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2.1.3.11 Water vapor permeability Water vapor permeability of bamboo fiber-based fabric is higher than cotton fabric. This is because of lower fabric weight per unit area, thickness, and hairiness than cotton fabric while all of the parameters for production same (Majumdar et al., 2010).

2.1.3.12 Tenacity The tenacity of bamboo cellulose yarn is 22–25 cN/tex in dry conditions, but lower tenacity is found at 13–17 cN/tex in wet conditions. A 100% bamboo cellulose yarn of 14.85 tex linear density with 350 twist multiplier shows a tenacity of 11.66 cN/tex (Erdumlu & Ozipek, 2008). The mechanical characteristics of cellulose-reinforced polylactic acid (PLA) composites are improved by the chemical treatment of bamboo cellulose nanofibers ( Lu et al., 2014).

2.1.3.13 UV protectivity With the gradual degradation of the ozone layer, the ultraviolet ray is now a significant threat to human health. The resistance of apparel to UV rays comes from two phenomena, UV scattering and UV absorption. Researchers have proved the UV absorption property of bamboo. It is revealed that the lignin present in the bamboo, which is a lignocellulosic fiber, can absorb the UV rays (Afrin, Tsuzuki, & Wang, 2012). But the conventional regenerated bamboo viscose manufacturing processes remove the lignin, making it unable to absorb UV. Therefore, researchers have also developed novel approaches to manufacture regenerated bamboo using a microwave, ultrasonication, and enzyme with minimum lignin removal (Afrin, Kanwar, Wang, & Tsuzuki, 2014).

2.1.4 Applications of bamboo cellulose 2.1.4.1 Composite reinforcement Bamboo cellulose crystal is used to reinforce plasticized starch. The tensile strength and Young’s modulus were 12.3 and 210 MPa, respectively (Liu et al., 2010). Many researchers modified bamboo cellulose fibers with NaOH, ethanol, and some silane coupling agents applied them as reinforcement in both epoxy-based composites and showed high tensile strength (Lu et al., 2013). MCC has the potential to use as a reinforcement element to produce green composite (Rasheed, Jawaid, Karim, & Abdullah, 2020). Bamboo cellulose surface was modified with alkali and applied to prepare cellulose/poly (l-lactic acid) composites. The impact of various treatments on the mechanical characteristics of cellulose/poly (l-lactic acid) composites was studied. The results demonstrated that the alkali soaking provided the composites with the highest strength and Young’s modulus increased by 28.6% and 34.6%, respectively, than untreated samples (Lu et al., 2014). The bamboo cellulose has been extracted as microcrystalline cellulose by the kraft pulping process. The prepared MCC showed 82.6% crystallinity. It is suggested that extracted bamboo cellulose can be used as a reinforcing element to produce a green composite (Rasheed, Jawaid, Karim, & Abdullah, 2020).

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2.1.4.2 Textile application The high moisture adsorption capacity, softness, and brightness property of bamboo cellulose make it suitable to use in textile. Regenerated bamboo fiber has great potential in the textile application. It contains a very low amount of noncellulosic content than other cellulosic fibers, and this gives an immense advantage to be used as a textile fiber. This fiber has an excellent luster, and researchers have found it suitable for spinning, knitting, or weaving. In the modern textile industry, bamboo fiber is used in socks, underwear, t-shirts, bathrobes, towels, sleepwear, bed sheets (Yueping et al., 2010). Bamboo cellulose is used in bamboo intimate apparel, bamboo nonwoven fabric (made by pure bamboo pulp), bamboo sanitary materials (bandage, mask, surgical clothes, nurses wear, and so on), bamboo decorating, bamboo bathroom series, etc. (Prakash, 2020). The regenerated bamboo cellulose-based fabric has been used in UV-protective clothing (Mamnicka & Czajkowski, 2012).

2.1.4.3 Cellulosic nanofiber preparation Generally, cellulosic fibers are not suitable for nanofiber production through the electrospinning technique due to the lack of proper solvent to make cellulose solutions. Cai et al. proposed a method in which bamboo cellulose is converted into cellulose acetate first, which can be used to produce cellulosic nanomaterial, also known as nano cellulose (Cai et al., 2018).

2.1.4.4 Medical applications Diabetes, a highly prevalent chronic disease, leads to a higher risk of delayed wound healing and has become a serious issue in the public health care system. Nanocomposite (NCs) hydrogels prepared from bamboo cellulose nanocrystals impregnated with silver nanoparticles serve as effective dressing materials for healing wounds in the streptozotocin-induced diabetic mice model. The developed NCs hydrogel resulted in accelerated diabetic wound healing within a time span of 18 days, compared to various control groups that took a long time to heal. NCs hasten the healing process by reducing inflammation along with 23 early proliferation, collagen formation, and epithelialization by regulating the expression of certain proinflammatory cytokines and growth factors responsible for delaying diabetic wound healing. In a nutshell, these NCs have immense potential to be used as ideal wound dressing materials for efficient and faster healing in diabetic patients (Singla et al., 2017). Bamboo cellulose-based nanocomposite can be used as an anticancer scaffold for wound healing and skin cancer treatment (Rao, Jeyapal, & Rajiv, 2014). It has been found that bamboo-derived cellulose nanofibrils (B-CNFs)-reinforced sericin composite can be used as a drug delivery carrier and wound dressing material (Kwak et al., 2018). Bamboo cellulose have potential application in antifertility (Vanithakumari, Manonayagi, Padma, & Malini, 1989), anti-inflammatory and antiulcer activities (Muniappan & Sundararaj, 2003), antitumor activity (Seki, Kida, & Maeda, 2010), etc.

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2.1.4.5 Food and food packaging Bamboo shoots and shoot fibers are used as food. Bamboo shoots and fibers are often used in Asian stir-fry dishes and pickled condiments. Phyllostachys is the essential genus for producing edible shoots. Bamboo tea, bamboo wine, bamboo vinegar, and charcoal-coated dried fruits are just a few foods made from bamboo fiber. Bamboo fibers are also employed in manufacturing food packaging materials such as cellophane. The nutritional value of bamboo reveals that the total carbohydrate content of bamboo leaves declines throughout the growing season remains steady for some time, then increases throughout the winter. In contrast to carbohydrates, crude protein content increases throughout the growing season and decreases during the cold season. Because of the high content of fiber and proteins, it is an excellent feedstock source. The bamboo can be used as winter feed by goats and other animals. Bamboo also minimizes the risk of gastrointestinal parasites in farm animals (Imadi et al., 2014). A simple blending was used to prepare a green nanocomposite of chitin and bamboo cellulose nanofiber (BCNF). The nanocomposite offers good thermal stability, biodegradability (degrade within 7 days), and mechanical properties that make it promising for food packaging material (Hai, Choi, Zhai, Panicker, & Kim, 2020). Poly (lactic acid) (PLA) has been widely used as a packaging material. Low thermal stability and brittleness limit the use of PLA as packaging material such as garbage bags, food containers, food packaging, and agricultural films. To overcome this limitation, PLA combined with bamboo nanocellulose to use the facility of high thermal stability and enhanced toughness of composite (Qian, Sheng, Yu, Xu, & Fontanillo Lopez, 2018). There is some other bamboo cellulose-based composite that has been used as food packaging material, such as poly (3-hydroxybutyrate) (PHB)/bamboo cellulose nanocrystal (Dhar, Bhardwaj, Kumar, & Katiyar, 2015), microcrystalline bamboo cellulose-based seaweed (Hasan et al., 2019), and B-CNF (bamboo-derived cellulose) fabricated sericin films (Kwak et al., 2018).

2.1.4.6 Furniture and interior Bamboo-propylene composite can be a choice for furniture & interior decoration purposes. Researchers have blended bamboo flours made from matured bamboo culms with polypropylene and developed a composite with better tensile and flexural properties. Furniture like the chair, decks, window frames, door panels, etc., can easily be made by this composite. Chauhan et al. have also designed a portable toilet made from this bamboo-reinforced polypropylene composite (Chauhan, Aggarwal, Venkatesh, & Abhilash, 2018).

2.1.4.7 Sports industry Bamboo fiber-reinforced composites can be used in making various sports goods like polo balls, baseball, surfing board, etc. due to their lightweight, durability, and better mechanical property (Subie, Mouritz, & Troynikov, 2009).

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2.1.4.8 Construction Bamboo fibers can reinforce concrete due to their lightweight, better hardness, and excellent mechanical property. Many researchers have proved the suitability of bamboo as a reinforcing element to concrete composite manufacturing (Imadi et al., 2014; Iqbal, Kabir, Rakib, Rashid, & Sikdar, 2018).

2.1.4.9 Bioenergy production Biofuels from bamboo fibers can be a substitution for fossil fuels. Bamboo is almost nonfood biomass, and it is also a renewable lignocellulosic material. Research has shown that bamboo fibers contain desirable fuel characteristics. However, commercial production of bamboo biofuel requires a secured and steady supply which is a great challenge. But it can be converted into solid, liquid as well as gaseous fuel (Imadi et al., 2014).

2.1.4.10 Paper industry Bamboo fibers are one of the ideal materials for paper manufacture due to their pulping ability and pulp strength. Bamboo pulping is suitable due to its form, chemical content, and structure. The paper produced from bamboo pulp reduces pressure on wood demand, less pollution, and environmental protection. Bamboo fiber pulp can be used to manufacture newspaper, bond paper, toilet tissue, cardboard, cement sacks, and coffee filters in the paper industry (Imadi et al., 2014).

2.1.5 Conclusion This chapter summarizes the extraction process, properties, structure, and application of bamboo cellulose. Compared to other cellulosic or lignocellulose fibers, bamboo cellulose fiber holds its distinction due to some of its exceptional characteristics. Various extraction processes from natural bamboo culm have ensured its vast and diverse range of applications. Specifically, the UV absorption and antimicrobial characteristics have provided a nobility compared to cotton or viscose (which are mainly used as natural and regenerated apparel fibers). Besides its textile application, researchers have also proven the usability of bamboo cellulose in composite reinforcement, medical sector, packaging, construction, even sports. Bamboo cellulose is a potential source of value-added products from low-cost raw materials. The world market for bamboo products is growing every year, and demands are increasing to fulfill more novel and diversified needs. Researchers are trying to develop genetically engineered bamboo plants that may meet humankind’s future needs.

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Singla, R., Soni, S., Patial, V., Kulurkar, P. M., Kumari, A., Mahesh, S., et al. (2017). In vivo diabetic wound healing potential of nanobiocomposites containing bamboo cellulose nanocrystals impregnated with silver nanoparticles. International Journal of Biological Macromolecules, 105, 45–55. https://doi.org/10.1016/j.ijbiomac.2017.06.109. Stanislas, T. T., Komadja, G. C., Ngasoh, O. F., Obianyo, I. I., Tendo, J. F., Onwualu, P. A., et al. (2021). Performance and durability of cellulose pulp-reinforced extruded earth-based composites. Arabian Journal for Science and Engineering, 46(11), 11153–11164. https://doi. org/10.1007/s13369-021-05698-1. Subie, A., Mouritz, A., & Troynikov, O. (2009). Sustainable design and environmental impact of materials in sports products. Leisure/Loisir, 2(3–4), 67–79. https://doi.org/10.1080/ 19346182.2009.9648504. Suzuki, K., & Itoh, T. (2001). The changes in cell wall architecture during lignification of bamboo, Phyllostachys aurea Carr. Trees, 15(3), 137–147. https://doi.org/10.1007/ s004680000084. Teli, M. D., & Sheikh, J. (2014). Bamboo rayon-copper nanoparticle composites as durable antibacterial textile materials. Composite Interfaces, 21(2), 161–171. https://doi.org/ 10.1080/15685543.2013.855528. Tsai, W., Lee, M., & Chang, Y. (2007). Fast pyrolysis of rice husk: Product yields and compositions. Bioresource Technology, 98(1), 22–28. https://doi.org/10.1016/j. biortech.2005.12.005. Vanithakumari, G., Manonayagi, S., Padma, S., & Malini, T. (1989). Antifertility effect of Bambusa arundinacea shoot extracts in male rats. Journal of Ethnopharmacology, 25 (2), 173–180. https://doi.org/10.1016/0378-8741(89)90019-6. Wahab, R., Mustafa, M. T., Salam, M. A., Sudin, M., Samsi, H. W., & Rasat, M. S. M. (2013). Chemical composition of four cultivated tropical bamboo in genus Gigantochloa. Journal of Agricultural Science, 5(8). https://doi.org/10.5539/jas.v5n8p66. Wai, N. N., Nanko, H., & Murakami, K. (1985). A morphological study on the behavior of bamboo pulp fibers in the beating process. Wood Science and Technology, 19(3), 211– 222. https://doi.org/10.1007/BF00392050. Wan, J. Q., Wang, Y., & Xiao, Q. (2010). Effects of hemicellulose removal on cellulose fiber structure and recycling characteristics of eucalyptus pulp. Bioresource Technology, 101 (12), 4577–4583. https://doi.org/10.1016/j.biortech.2010.01.026. Wegst, U. G. K., Bai, H., Saiz, E., Tomsia, A. P., & Ritchie, R. O. (2015). Bioinspired structural materials. Nature Materials, 14(1), 23–36. https://doi.org/10.1038/nmat4089. Xie, X., Zhou, Z., & Yan, Y. (2019). Flexural properties and impact behaviour analysis of bamboo cellulosic fibers filled cement based composites. Construction and Building Materials, 220, 403–414. https://doi.org/10.1016/j.conbuildmat.2019.06.029. Xu, Y., Lu, Z., & Tang, R. (2007). Structure and thermal properties of bamboo viscose, Tencel and conventional viscose fiber. Journal of Thermal Analysis and Calorimetry, 89(1), 197– 201. https://doi.org/10.1007/s10973-005-7539-1. Yan, L., Kasal, B., & Huang, L. (2016). A review of recent research on the use of cellulosic fibres, their fibre fabric reinforced cementitious, geo-polymer and polymer composites in civil engineering. Composites Part B: Engineering, 92, 94–132. https://doi.org/ 10.1016/j.compositesb.2016.02.002. Youssefian, S., & Rahbar, N. (2015). Molecular origin of strength and stiffness in bamboo fibrils. Scientific Reports, 5. https://doi.org/10.1038/srep11116. Yu, Y., Wang, H., Lu, F., Tian, G., & Lin, J. (2014). Bamboo fibers for composite applications: A mechanical and morphological investigation. Journal of Materials Science, 49(6), 2559–2566. https://doi.org/10.1007/s10853-013-7951-z.

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Yueping, W., Ge, W., Haitao, C., Genlin, T., Zheng, L., Feng, X. Q., et al. (2010). Structures of bamboo fiber for textiles. Textile Research Journal, 80(4), 334–343. https://doi.org/ 10.1177/0040517509337633. Zakikhani, P., Zahari, R., Sultan, M. T. H., & Majid, D. L. (2014). Extraction and preparation of bamboo fibre-reinforced composites. Materials and Design, 63, 820–828. https://doi.org/ 10.1016/j.matdes.2014.06.058. Zhai, L., Kim, H. C., Kim, J. W., Kang, J., & Kim, J. (2018). Elastic moduli of cellulose nanofibers isolated from various cellulose resources by using aqueous counter collision. Cellulose, 25(7), 4261–4268. https://doi.org/10.1007/s10570-018-1836-x. Zhang, K., Li, H., Xiao, L. P., Wang, B., Sun, R. C., & Song, G. (2019). Sequential utilization of bamboo biomass through reductive catalytic fractionation of lignin. Bioresource Technology, 285. https://doi.org/10.1016/j.biortech.2019.121335. Zhang, W., Liang, M., & Lu, C. (2007). Morphological and structural development of hardwood cellulose during mechanochemical pretreatment in solid state through pan-milling. Cellulose, 14(5), 447–456. https://doi.org/10.1007/s10570-007-9135-y. Zou, L., Jin, H., Lu, W. Y., & Li, X. (2009). Nanoscale structural and mechanical characterization of the cell wall of bamboo fibers. Materials Science and Engineering C, 29(4), 1375–1379. https://doi.org/10.1016/j.msec.2008.11.007.

Electrospun cellulose nanofiber composites

3

Adnan Khana, Sumeet Malika, Nisar Alib, and Muhammad Bilalc a Institute of Chemical Sciences, University of Peshawar, Peshawar, Khyber Pakhtunkhwa, Pakistan, bKey Laboratory for Palygorskite Science and Applied Technology of Jiangsu Province, National & Local Joint Engineering Research Center for Deep Utilization Technology of Rock-salt Resource, Faculty of Chemical Engineering, Huaiyin Institute of Technology, Huaian, China, cInstitute of Chemical Technology and Engineering, Faculty of Chemical Technology, Poznan University of Technology, Poznan, Poland

3.1

Introduction

The everyday increase in the population worldwide and the associated rise in pollution have reverted the researchers’ attention toward exploring naturally occurring substances (Akshaykumar et al., 2021; Ali et al., 2018b; Khan et al., 2021a). The naturally occurring materials cover a broad horizon of materials used in different fields as per demand. The materials like chitosan, chitin, rice husk, bagasse, cellulose, glycogen, etc., are some of the many naturally occurring substances that have been used by researchers in different fields (Choi et al., 2021; Khan et al., 2021b; Shah, Ud Din, Khan, & Shah, 2018). Among other naturally occurring substances, cellulose is a polysaccharide with a great abundance. The useful properties associated with cellulose, like its biodegradability, biocompatibility, sustainability, low prices, less energy consumption, etc., have grabbed the attention of researchers (Ali et al., 2021; Wang et al., 2021; ZabihiSahebi et al., 2019) (Fig. 3.1). The cellulose and its composites are being used in a number of fields with efficient and profitable output. Another important area of interest when it comes to research is the development of micron- and nano-sized materials/particles (Abdalkarim et al., 2018; Wsoo et al., 2021; Yang et al., 2021b). These minute-sized particles, specifically nanoparticles, have many advantages due to their large surface-to-volume ratios. Hence, modern-day research dramatically relies on the concepts of nanotechnology for developing useful products. Considering the advancement of research brought about by nanotechnology, the cellulose-based nanoparticles are also being synthesized due to their preparation feasibility and efficiency in the results (Aboamera, Mohamed, Salama, Osman, & Khattab, 2018; Mehdi et al., 2021; Nawaz, Khan, Ali, Ali, & Bilal, 2020). The reported literature shows that incorporating more than one material in the form, a composite further enhances the material’s properties. Apart from other useful characteristics, the cellulosic materials have the ability to incorporate with other polymeric or nonpolymeric materials to form composites that are eventually utilized in different fields (Ali, Bilal, Khan, Ali, & Iqbal, 2020c; de Souza, Kringel, Dias, & da Rosa Zavareze, 2021). Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00013-6 Copyright © 2023 Elsevier Ltd. All rights reserved.

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Cellulose Fibre Reinforced Composites

Biodegr adability Less energy consum ption

Biocomp atibility Properties of Electro spun cellulose composite nanofibers

Large surface area

Sustaina bility Low prices

Fig. 3.1 Some of the useful properties of electrospun cellulose composite nanofibers.

The fabrication of cellulosic nanofibers has been explored many times, and varieties of methods are available for this purpose, including drawing, phase separation, template, self-assembly, electrospinning, etc. Each of the mentioned processes has some disadvantages, like no control over the diameter and orientation of the fiber, use of limited polymer, etc. (Ali, Naz, Shah, Khan, & Nawaz, 2020i; Czapka, Winkler, Maliszewska, & Kacprzyk, 2021). The base alternate for these problems is the electrospinning process, which has many advantages like holding over the obtained fiber’s structural properties (size and dimensions), porosity, alignment, etc. Hence, the electrospun cellulose composite nanofibers are being synthesized greatly as they have applications in many fields like tissue engineering, as sensors, filtration materials, wastewater decontamination, etc. (Ali et al., 2020e; Brandes, Brouillette, & Chabot, 2021). Keeping into consideration the advantages of electrospun cellulose composite nanofibers, many researchers have explored their synthetical pathways, properties, applicability, etc. The presented chapter covers the important aspects related to the electrospun cellulose composite nanofibers (Khan et al., 2020; Yadav & Patel, 2021).

3.2

Electrospinning technique and its applicability

Electrospinning is one of the mostly utilized fabrication processes with many advantages like simplicity and versatility. The electrospinning process produces nano- or micron-sized particles obtained from a solution/melt through electrostatic interaction (Ali et al., 2020a; Deeraj, Jayan, Saritha, & Joseph, 2021). A general design of the electrospinning process proceeds as the electric forces are involved in the spinning of the solution rather than the mechanical spinning as in the conventional fiber spinning process (Fig. 3.2). While carrying out the electrospinning process, a solution of

Electrospun cellulose nanofiber composites

51

Fig. 3.2 Electrospinning technique of electrospun cellulose nanofiber.

polymer present at the end of the capillary tube and held there by the surface tension is provided with an external electric field. The applied electric field induces a charge on the surface of the polymer solution (Ali et al., 2020b; Haider et al., 2021; Khan, Badshah, & Airoldi, 2015a). A mutual repulsion takes place, which generates a force opposite to the surface tension. With the increase in the intensity of the electric charge, the solution at the capillary end becomes elongated, owning the shape of a cone called the Taylor cone. Once a point is reached where the repulsive electric forces overtake the surface tension forces, the tip of the Taylor cone ejaculates a charged jet of solution (Ali et al., 2020d; Xing, Shao, Du, Tao, & Qi, 2021). The electric field controls the trajectory of the jet produced due to the charge present. The jet moves through the air, thereby evaporating the solvent present in it. Once the solvent is evaporated, the lagging behind a jet is a charged polymer fiber that reaches the metal collector and gets attached to it. The electrospinning apparatus thus consists of three major parts, a metal collector, an injector, preferably a syringe carrying the polymer solution, and a high voltaic electric source (Aziz et al., 2020; Zhuang, Zhu, & Wang, 2021). The process of electrospinning is affected by various operating parameters like air velocity, temperature, conductivity, viscosity, surface tension, etc. Once all the stated parameters are optimized, a goodquality nanofiber is obtained (Guo et al., 2021; Sartaj et al., 2020). The nanofibers obtained from this procedure are very small in size and have high surface-to-volume ratios and a high-length-to-diameter ratio. The nanofibers obtained from the electrospinning sources have been used in many fields, including nanocomposites, artificial blood vessels, wound dressing materials, etc. (Ali et al., 2020f; Khan, Wahid, Ali, Badshah, & Airoldi, 2015b; Ko, Lee, Rezk, Park, & Kim, 2021).

3.3

Cellulose, its properties, and applications

Cellulose is well known for its abundant presence as a natural polysaccharide. One of the most important sources of cellulose is the plant cell wall, while other living species like fungi, algae, bacteria also contain it. The main function of cellulose is to maintain the cell wall structure (Ali et al., 2020h; Jatoi, Kim, & Ni, 2019; Lee et al., 2021). The

52

Cellulose Fibre Reinforced Composites

structural properties of the cellulose are confined to having a tough, fibrous, and water-insoluble nature. Cellulose is the center of attention for many researchers and research processes and is considered the best alternative to fossil-based fuel polymers due to its biocompatibility, biodegradability, and renewability (Ali et al., 2020j; Alven, Buyana, Feketshane, & Aderibigbe, 2021). The structural analysis of cellulose shows that it consists of units of β-1,4-linked glucopyranose assembled into a linear homopolymer with a high molecular weight. Each monomer unit of the structure lies at 180° to each other. Cellulose can also be termed as 1,4- β D-glucan. The repeating units/monomers of the cellulose are composed of a glucose dimer called cellobiose, while the number of repeating units per molecule is termed as half of the degree of polymerization (DP) (Ali et al., 2020g; Khan, Khalil, Khan, Saeed, & Ali, 2016; Madhukiran et al., 2021). The cellulose obtained from different sources has a different degree of polymerization. The cellulose obtained from wood contains 10,000 glucose units, while the cellulose obtained from cotton contains 15,000 units of glucose. The properties of cellulose, like its chirality, hydrophilicity, biodegradability, etc., are associated with the three hydroxyl groups present on the glucopyranose groups (Adamu, Gao, Jhatial, & Kumelachew, 2021; Ali, Ahmad, Khan, Khan, Bilal, et al., 2020a; Salama, Mohamed, Aboamera, Osman, & Khattab, 2018) (Fig. 3.3). The reactivity of these hydroxyl groups initiates the above-stated properties. While the hydrogen bond formation ability of the hydroxyl groups initiates some other useful properties like cohesive nature, crystalline and amorphous fractions, microfibrillated structure, etc. Based on the unique properties and structure of cellulose, it has been used in many applications. The most commonly employed fields of cellulose include pharmaceutical applications, nanobiosorbents, biosensors, etc. (Khan, Shah, Mehmood, Ali, & Khan, 2019b; Tamahkar, Bakhshpour, & Denizli, 2019; Xu et al., 2021).

Fig. 3.3 Bioactive electrospun nano fibrous for wound dressings (Adamu et al., 2021).

Electrospun cellulose nanofiber composites

3.4

53

Cellulosic composites

The composites are a frequently used form of materials that have taken the research to another pace due to their useful properties. The composites can be identified as materials consisting of more than one constituent (two or even more) engineered together (Ali et al., 2019; Maharjan et al., 2021; Park et al., 2019). The combined constituents of the composites have the useful properties of both materials present. One of the constituents is scientifically termed as the matrix, while the other one is called the reinforcement material. The matrix is the major portion of the composite material, while the reinforcement is added to the composite to enhance its properties (Keshvardoostchokami et al., 2021; Khan et al., 2019a). Employing the beneficial aspects of the composites, there has been an increased interest in the designing and deployment of cellulose-based nanocomposites in various fields, produced preferably through the electrospinning technique (Haghdoost, Bahrami, Barzin, & Ghaee, 2021; Khan, Khalil, & Khan, 2019c; Wahid et al., 2017). The cellulose-based nanocomposites with a variety of materials have been reported to dates like cellulose modification with polyaniline and polypyrrole, cellulose modification with poly(3,4ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and poly(allylamine) (PAH), polyethene glycol (PEG), etc. (Ali et al., 2018a; Dobosz, Kuo-Leblanc, Bowden, & Schiffman, 2021; Khan et al., 2017). While designing cellulose-based nanocomposites, the material properties need to be considered like physical, mechanical, and chemical properties of the natural fibers (Fig. 3.4). The factors affecting the properties of the plant fiber’s locations, the climatic and weather conditions, soil features, etc. While fiber processing also affects the properties of the natural fibers like bleaching, spinning, scotching, retting, etc. (Liang, Wang, & Tao, 2021; Saeed et al., 2018; Sohni et al., 2018).

Membrane

Nanofibers

Nanofiber-enhanced Ultrafiltration Membranes Unveiling the structure-property-chemistry relationships Nanofiber diameter Hydrophilic

Crosslinked

O

MWC

Feed solution

Hyd

rop h

obic

Noncrosslinked

100 µm

Fig. 3.4 Ultrafiltration membrane with robust hydrophilic nanofibers (Dobosz et al., 2021).

54

3.5

Cellulose Fibre Reinforced Composites

Electrospun cellulosic composite nanofibers

The electrospun cellulosic composite nanofibers have been utilized in different fields with great efficiency. The commonly used solvents for the dissolution of the cellulose include ionic liquids, LiCl/DMAc, NMMO/H2O, etc. A variety of literature is available for cellulosic composite nanofibers prepared through the electrospinning technique. Aboamera, Mohamed, Salama, Osman, and Khattab (2019) prepared cellulose acetate composite nanofibers combined with graphene oxide through the electrospinning technique. The mechanical properties of the obtained composite nanofibers were studied by varying graphene oxide percentages. The results showed that increasing graphene oxide content also improves the tensile strength and Young’s modulus of the composite nanofibers. Ni, Cheng, Huan, Wang, and Han (2019) also prepared electrospun cellulose nanocrystals/poly(methyl methacrylate) composite nanofibers. The obtained electrospun nanofibers were then analyzed to study the relative humidity effect on the prepared electrospun nanofibers. The analysis showed that the hydrogen bonding between the poly (methyl methacrylate) and the cellulose nanocrystals enhanced the thermal property of the obtained composite nanofibers. While the other properties like the tensile strength and the young’s modulus were also improved. Tan et al. (2020) also prepared composite nanofibers by incorporating cellulose acetate butyrate and hydrophilic polyethylene glycol through the electrospinning technique. The tensile strength of the nanofibers was increased two times as compared to pristine cellulose acetate butyrate. The reinforcement of polyethylene glycol also caused a decrease in hydrophobicity based on contact angle analysis. The cell attachment of the nanofibers was also increased as compared to the pristine counterparts. Lu, Wang, Li, Qiu, and Wei (2017) also prepared electrospun water-soluble zein/ethylcellulose composite nanofibers. The prepared nanofibers were used for studying the drug release properties using Indomethacin as the target drug. The obtained product had improved mechanical properties as compared to its pristine counterparts. The analysis of the electrospun nanofibers showed a sustained drug release profile through Fickian diffusion (Fig. 3.5).

Fig. 3.5 Construction of composite nanofiber from electrospun cellulose acetate butyrate/ polyethylene glycol (CAB/PEG) (Tan et al., 2020).

Electrospun cellulose nanofiber composites

3.6

55

Applications of electrospun cellulosic composite nanofibers

The applicability of electrospun cellulosic composite nanofibers has greatly increased in the past few decades. The interest has been drawn toward the utilization of natural polymers instead of commercial ones due to their easy availability and relative abundance. Among many available natural polymers, cellulose has been given prime importance due to its useful properties, like mechanical properties due to the presence of hydrogen bonds. Incorporating the electrospinning technique further enhances the properties of the nanofibers due to the long and continuous fibers obtained as a result. The electrospun nanofibers are being utilized in a variety of fields like catalysis, filtration, textiles, pharmaceutical, mechanical, electrical applications etc. (Khalil, Fouad, Elsarnagawy, & Almajhdi, 2013; Sahay et al., 2012) (Table 3.1).

Table 3.1 Electrospun cellulosic composite nanofibers and their applications. Nanofiber composite

Technique

Application

Reference

Carboxymethyl cellulose (CMC)-based electrospun composite nanofiber mats Electrospun polyacrylonitrile/ cellulose nanocrystal (PAN-CNC) nanofibers Cellulose nanocrystals incorporated with poly(caprolactone) (PCL) Electro spun cellulose acetate nanofibers

Electrospinning

Food packaging

Hashmi et al. (2021)

Electrospinning

Adsorption

Electrospinning

Wound regeneration

Awad, Mamaghani, Boluk, and Hashisho (2021) Hivechi et al. (2021)

Electrospinning

ZIF@electrospun cellulose nanofiber derived N-doped metallic cobalt embedded carbon nanofiber composite Cellulose acetate/silk fibroin/Au-Ag hybrid composite nanofiber PCL/Gelatin electrospun nanofibrous scaffold

Electrospinning

Mechanical properties analysis Super capacitance electrode

Cellulose nanocrystal (CNC)-polyamide 6 (PA6) composite nanofiber

Ji et al. (2021)

Wu et al. (2021)

Electrospinning

Biocidal activity

Arumugam et al. (2021)

Electrospinning

Tissue engineering

Electrospinning

Adsorption

Goudarzi, Behzad, GhasemiMobarakeh, and Kharaziha (2021) BuyukadaKesici et al. (2021) Continued

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Cellulose Fibre Reinforced Composites

Table 3.1 Continued Nanofiber composite

Technique

Application

Reference

Sambong oil-loaded electrospun cellulose acetate nanofibers Electrospun chitosanpolyethylene oxide/ TEMPO-oxidized cellulose (CS-PEO/TOC) bio-based composite Polyacrylonitrile/ cellulose acetate (PAN/ CA) composite nanofiber membranes Electrospun cellulose nanofibers (ECNFs)

Electrospinning

In vitro biocompatibility

Ullah et al. (2021)

Electrospinning

Adsorption

Bates, Loranger, Mathew, and Chabot (2021)

Electrospinning

Yang, Liang, and Jia (2021a)

Electrospinning

High performance lithium-ion batteries Adsorption

Cellulose nanofiber membrane Polyacrylonitrile (PAN)/cellulose composite Cellulose nanocrystalsbased composite

Electrospinning

Enzyme carriers

Electrospinning

Lithium-ion battery

Electrospinning

Textile materials

Cellulose nanofibers previously loaded with hydroxyapatite (HAp)

Electrospinning

Tissue engineering

3.7

Petroudy, Kahagh, and Vatankhah (2021) Zeng, Shi, Feng, and Wang (2021) Dong, Li, Wang, Jiang, and Ma (2021) Ge, Yin, Yan, Hong, and Jiao (2021) Sofi et al. (2021)

Conclusion

Lately, the attention of researchers has diverted toward the use of natural materials which are abundantly available, cheap, nontoxic, and easy to handle to be used in different research fields. This concept has taken into consideration the usage of cellulose fibers for deployment in different fields. Electrospinning technique stands out among other techniques for the designing of cellulose-based nanofibers. Hence, electrospun cellulose composite nanofibers have been used greatly for different fields. The chapter covers the properties and applications of electrospun cellulose composite nanofibers.

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G. Rajeshkumara, K.C. Nagarajab, and V. Hariharanc a Department of Mechanical Engineering, PSG Institute of Technology and Applied Research, Coimbatore, Tamil Nadu, India, bDepartment of Mechanical Engineering, Acharya Institute of Technology, Bengaluru, Karnataka, India, cDepartment of Mechanical Engineering, Kongu Engineering College, Erode, Tamil Nadu, India

4.1

Introduction

Natural fibers are widely employed in different forms like strands, rope, and reinforcing phases in biodegradable composites and are found in applications such as domestic appliances, sports goods, automobile parts, aerospace components, building/construction materials due to their easy availability, biodegradability, low density, reusability, and acceptable physical and mechanical characteristics (Mohanty, Khan, & Hinrichsen, 2000). Natural fiber-incorporated polymer composites, on the other hand, are more prone to water absorption and have poor compatibility between fiber surface and matrix (Mohanty, Wibowo, Misra, & Drzal, 2004). The fiber surface modification plays a significant role in improving the bonding between composite elements (Mukesh & Godara, 2019). Generally, the surface modification could be done through alkali solution and silane coupling agent treatment to improve bonding strength at the interface (Rong, Zhang, Liu, Yang, & Zeng, 2001; Sinha & Rout, 2009). The popularity of natural fiber in composites is increasing where glass fibers are being traditionally used. The mechanical and chemical properties are influenced by cellulose content, which will vary from fiber to fiber. These fibers have quite complicated cell structures and chemical compositions. The chemical treatment can help to increase the performance of the natural fibers (Komuraiah, Kumar, & Prasad, 2014). Natural fibers were discovered to be a viable alternative to man-made fibers such as glass, aramid, carbon, etc., which were previously employed as reinforcements for panels, dashboards, seatbacks, and other interior automotive components. The mechanical qualities of synthetic fiber-reinforced composites made them popular. Moreover, these synthetic fibers are abrasive and difficult to machine (Ragoubi, Bienaim
e, Molina, George, & Merlin, 2010). Hence, there will be a lot of scopes to fabricate and characterize the natural fiber-reinforced biopolymers to use as a replacement for synthetic fiber composites.

Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00001-X Copyright © 2023 Elsevier Ltd. All rights reserved.

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4.2

Cellulose Fibre Reinforced Composites

Cellulose fibers

Cellulose is the biopolymer abundantly available on the planet earth. It represents 40%–60% of the wood mass and this can be isolated from plants in the form of fibers of 20–40 μm thickness upon pulping. These fibers are made of ethers/esters of the cellulose obtained from wood, plant leaves, bark, and other materials related to plants. Cellulose is the essential component of every fiber extracted from plants. In composites, cellulose, lignin, pectin, waxes, hemicelluloses, and water-soluble compounds make up a single natural fiber (Mohanty, Misra, & Drzal, 2001). In addition, they have a small amount of sugar and starch proteins. The chemical composition and physical qualities of these fibers determine their performance (Rajeshkumar, Seshadri, et al., 2021). The mechanical characteristics of microfibrils are determined by their orientation to the cell axis. Cheap density, low cost, nontoxic nature, plentiful availability, biodegradability, high toughness, and strong specific strength qualities are some of the benefits of natural fibers (Rajeshkumar, 2021; Rajeshkumar, Devnani, et al., 2021; Rajeshkumar, Sanjay, Siengchin, & Hariharan, 2021). Natural fibers have several disadvantages, including considerable differences in mechanical qualities, wettability, flammability, water absorption, and swelling properties. These fluctuations will cause fractures, material flaws, and failure (Cantero, Arbelaiz, Llano-Ponte, & Mondragon, 2003; Fernandes, Mano, & Reis, 2013).

4.3

Classification of natural fibers

The basic types of natural fibers (animal and plant fibers) are shown in Fig. 4.1. Animal fibers include materials such as wool and silk. The natural fibers such as seed, fruit, root, stem, and grass are kept under the umbrella of plant fibers. When compared to synthetic fibers, these fibers have a numerous benefits, including low weight, recyclability, biodegradability, and no skin discomfort or itching (Garkhail, Heijenrath, & Peijs, 2000; Hornsby, Hinrichsen, & Tarverdi, 1997; Oksman, Wallstr€om, Berglund, & Filho, 2002). On the other hand, a few disadvantages are also present in using natural fibers such as water uptake, nonuniform dimensions, and lesser thermal stability. Hand lay-up, press molding, pultrusion, resin transfer, extrusion, and injection moldings are all appropriate manufacturing techniques for natural fiber-added composites (Bledzki, Reihmane, & Gassan, 1996; Dittenber & Gangarao, 2012; Oksman, 2000; Natural Fibers

Animal Fibers

Wool

Silk

Plant Fibers

Seed/Fruit

Fig. 4.1 Classifications of natural fiber.

Stack

Root/Stem

Grass

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Kalia, Kaith, & Kaur, 2009). Studies have been made on biodegradable and degradable matrix materials, which can be used along with natural fibers. Some of the matrices available are polycaprolactone (PCL), modified cellulose, polylactic acid (PLA), modified cellulose, acetic acid, and polyester amide (Oksman & Selin, 2004; Riedel & Nickel, 1999; Williams & Wool, 2000).

4.4

Fiber surface modification

The strong fiber–matrix interfacial connection is essential for the composites to have good mechanical characteristics. This is at the optimum level in polymer composites, which provide better mechanical properties. Natural fibers’ fundamental drawback is that they are hydrophilic, which reduces their mechanical capabilities owing to poor adherence at the contact region. Because the hydrophilic nature of natural fiber leads to high water absorption in turn reduces their utility in many applications. The existence of a waxy component on the natural fiber’s surface aids in the reduction of fiber–matrix bonding and surface wetness. With most resins, the presence of free water decreases the capacity to create appropriate adhesive properties. The presence of significant moisture content leads the natural fiber to expand, causing a plasticizing impact that results in dimension instability and a reduction in mechanical characteristics (Mohanty et al., 2001). Resins cannot permeate the fiber unless the cell wall is expanded during the production process. As a result, natural fibers undergo a variety of treatments. Chemical modification is one such treatment. The methods like dewaxing, bleaching, acetylation, peroxide treatment, treatment with different agents, sizing with polymeric isocyanates, etc. have shown improvement in fiber–matrix adhesion of natural fibers (Herrmann, Nickel, & Riedel, 1998; Physics & Publishers, 2000).

4.4.1 Physical treatments The various physical treatments are heat, laser, argon, and plasm. The physical treatment will only influence the surface conditions of natural fibers and will have no impact on their chemical makeup (Bledzki, Mamun, Lucka-Gabor, & Gutowski, 2008). Compared to chemical treatment, physical treatments are found to be advantageous, because of the enhanced physical and mechanical characteristics of physically treated cellulose fibers. Physical treatments, on the other hand, are more expensive than chemical ones (Komuraiah et al., 2014). Therefore, the researchers prefer chemical treatments to physical treatments.

4.4.2 Chemical treatments The different chemicals used in surface treatments are silane, alkali, TiO2, grafting and oligomeric siloxane which changes the chemical composition, morphology, and surface topology of natural fibers. Chemical treatments of natural fiber are essential to (i) remove noncellulosic compounds from natural fibers, (ii) improve the compatibility of the elements, (iii) enhance the surface roughness of fibers, and (iv) enhance the

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thermal stability of natural fibers (Amiri, Ulven, & Huo, 2015; Asumani, Reid, & Paskaramoorthy, 2012; Dayo et al., 2017; Komuraiah et al., 2014). Chemical therapies have several advantages over physical treatments, including a lower cost and simplicity of use. As a result, it is crucial to investigate the impact of various chemical treatments on the characteristics of fibers.

4.4.2.1 Alkaline treatment Alkaline treatment is the most often utilized method of surface modification on natural fibers. It is also known as mercerization, which eliminates undesirable surface contaminants, lignin, pectin, and hemicelluloses and enhances the fibers’ surface roughness (Ramakrishnan, Krishnamurthy, Rajeshkumar, & Asim, 2021). This treatment also removes the wax, oils, and lignin content present on the outer surface of the cell membrane (Valadez-Gonzalez, Cervantes-Uc, Olayo, & Herrera-Franco, 1999). This can be achieved by adding sodium hydroxide (NaOH) to the fiber, which facilitates the ionization of the alcoholic body by hydroxyl (Mohanty et al., 2001). The following reaction takes place during the alkali treatment. Fiber
OH + NaOH ! Fiber
O
Na + H2 O During treatment, the natural fibers are dipped in NaOH solution for a specific period and then washed with water. The jute (Ray, Sarkar, Rana, & Bose, 2001), sisal (Mishra, Misra, Tripathy, Nayak, & Mohanty, 2001), and flax fibers ( Joseph, Thomas, & Pavithran, 1996) were treated with NaOH solution and observed two major effects on the fibers: (i) it enhances the surface roughness leads to better mechanical interlocking and (ii) it exposes more cellulose to the fiber surface (Li, Tabil, & Panigrahi, 2007; Zannen, Ghali, Halimi, & Hssen, 2014).

4.4.2.2 Silane treatment Silane coupling agents can successfully remove the cellulose hydroxyl groups on the fiber surface. Hydroxyl alcohol produces silanes when exposed to moisture. These silanes then react with the hydroxyl groups on the fiber’s surface, forming covalent bonds. Therefore, with the application of silane, the hydrocarbon chain reduces fiber crimping by creating a cross-linked basic structure, because the fiber matrix is connected by covalent bonds. The following shows the reaction of the silane treatment (Agrawal, Saxena, Sharma, Thomas, & Sreekala, 2000). CH2 CHSiðOHÞ3 + Fiber
OH ! CH2 CHSiðOHÞ2 O
Fiber + H2 O Numerous research have employed silane treatment to modify cellulose fiber surface and determined that the silane-coupling agent is also effective at modifying the cellulose fiber–polymer matrix interface and increasing its strength (Debnath, Wunder, McCool, & Baran, 2003; Kim, Sham, & Wu, 2001; Mohd Ishak, Ariffin, & Senawi, 2001).

Chemical modification of cellulose fiber surface

67

4.4.2.3 Acetylation treatment Acetylation surface modification is described as a reaction of an organic compound with acetyl ion CH3 COO–. This treatment is also named as acetylation of natural fibers. When acetic anhydride reacts with lignocellulosic materials, acetic anhydride reacts inside the hydroxyl cellulose. The following is the reaction that occurs during the acetylation process. Fiber
OH + CH3 COOCOCH3 ! Fiber
OCOCH3 + CH3 COOH Studies have shown that treating sisal fiber with acetylation improves fiber–matrix adhesion. The method begins with alkali treatment and ends with acetylation. Mishra et al. (2003) explored sisal fiber acetylation. The dewaxed sisal fiber was soaked in 5% and 10% of NaOH solutions for 1 h at 30 °C; the alkali-treated fiber was soaked in glacial acetic acid at 30 °C for 1 h; decanted and placed in a drop of concentrated H2 SO4 soak in acetic anhydride for 5 min. The surface of the treated sisal fiber is said to become highly rough and void-filled, allowing for improved mechanical interaction with the polystyrene matrix.

4.4.2.4 Benzoylation treatment The transformation in benzoyl chloride and organic synthesis is a decent example of benzoylation, which is used for fiber treatment. This treatment reduces fibers’ water absorption and improves the interface between composite elements (Mukesh & Godara, 2019). The following is the reaction of chemical modification that occur during benzoylation treatment. Fiber
OH + NaOH ! Fiber
ONa + H2 O Joseph et al. (1996) and Manikandan Nair, Thomas, and Groeninckx (2001) use a solution of NaOH and benzoyl chloride to treat sisal fibers’ surfaces. The thermal stability of treated fiber-incorporated composite material is higher than that of untreated fiberadded samples, according to the findings. In another work, benzoylation was employed to enhance the interfacial interaction between flax fiber and polyethylene matrix. It was discovered that the interfacial bonding at the fiber–matrix interface was greatly improved (He et al., 2011). The comparison between different properties of untreated and various chemically treated fibers was presented in Table 4.1. It was observed that the treatments improved the properties of fiber irrespective of the chemicals used.

4.5

Summary

The surface treatment techniques available for natural fibers are reviewed in this chapter. The chemical modification techniques are simple and economic when compared to physical modification methods. The chemical treatment removes undesirable

Table 4.1 Properties of raw and surface modified fibers. Physical properties

Chemical properties

Mechanical properties

Jute

Untreated

1.4

17–20

61–72

13.6–20

11.8– 13

393–800

13–55

2.2–2.6

Alkali

1.275

25

62.60

12.65

13.40

536  259

14.89

1.63  0.43

Untreated

1.45

200–400

45–71.5

13.6–21

12–26

468–700

9–22

3–7

Alkali Silane Untreated Alkali

1.4245 1.3336 1.48 1.160

114  2 117  3 66 –

2.9 16.6 14–22.4 12.28–22.4

7.9 12.0 3.7–13 3.7–5.7

323 298 550–900 1073.72

5.8  2.9 13.9  4.4 70 58.14

6.1  1.8 2.0  0.5 1.6 2.40

Untreated Alkali

1.25 1.02

576 501

89.2 71.4 57–77 70.2– 76.12 61.13 66.57

12.56 –

19.91 30.10

350 190

7.5 5.5

– 2.6%

Benzoyl chloride

1.36

376

67.22

9.07

17.83

400

8

–

Phoenix sp.

Hemicellulose (%)

Lignin (%)

Elongation (%)

Treatment type

Hemp

Cellulose (%)

Tensile modulus (GPa)

Fiber

Sisal

Diameter (μm)

Tensile strength (MPa)

Density (g/cm3)

References Khalid et al. (2021) and Benyamina, Mokaddem, Doumi, Belkheir, and Elkeurti (2021) Gopinath, Kumar, and Elayaperumal (2014) and Liu and Dai (2007) Rajeshkumar et al. (2021) and Ku, Wang, Pattarachaiyakoop, and Trada (2011) Zhu, Hao, and Zhang (2018) Zhu, Mo, and Hao (2019) Li, Tabil, and Panigrahi (2007) Hashim et al. (2017) Rajeshkumar et al. (2021) Rajeshkumar, Hariharan, and Scalici (2016) Rajeshkumar et al. (2021)

Chemical modification of cellulose fiber surface

69

components and roughens the fiber surface, which enhances the mechanical performance of composites by mechanical interlocking mechanisms. The alkali treatment is majorly used by researchers to improve the performance of cellulose fibers and their composites. Other suitable eco-friendly chemicals may also be utilized in the near future to alter the surface of natural fibers. This will pave the way for future advancements in the field of natural fiber-based composites.

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R. ArunRamnatha, V. Gauthama, Mavinkere Rangappa Sanjayb, and Suchart Siengchinb a Department of Mechanical Engineering, PSG College of Technology, Coimbatore, India, b Natural Composites Research Group Lab, Academic Enhancement Department, King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand

5.1

Introduction and present scenario

Natural fibers in composites have slowly replaced manmade synthetic fibers in several engineering applications and industrial products over the decades. Natural fiber–reinforced polymer composites have gained prominence over these years due to its lightweight, cost, ease in availability and other biodegradable characteristics. Natural fibers derived from hemp, jute, Kenaf, sisal, flax, coir, cotton, and ramie have proved as an ideal replacement to the synthetic fiber material like glass and carbon fibers due to its lower density, recyclability and minimum hazardous effects toward to the environment (Madhu et al., 2019a, 2019b; Pec¸as, Carvalho, Salman, & Leite, 2018; Pickering, Efendy, & Le, 2016). Mechanical properties such as strength, stiffness and stability of natural fiber–reinforced polymer composites are equivalent and good enough relative to that of synthetic fiber–reinforced composites. The most critical advantages and limitations of the natural fiber composites relative to that of manmade synthetic fiber composites are shown in Table 5.1 (Vinod, Sanjay, Suchart, & Jyotishkumar, 2020). Natural fiber–reinforced composites are mainly classified based on its origin, climate, geography, derived resources like plants, animals, and other minerals (Balaji & Nagarajan, 2017; Ganapathy, Sathiskumar, Senthamaraikannan, Saravanakumar, & Khan, 2019; Kumar et al., 2020; Siva, Valarmathi, Palanikumar, & Samrot, 2020; Vinod et al., 2021). Natural fiber composites derived from plant resources contains cellulose as the primary constituents whereas the natural fiber–reinforced composites produced or manufactured from animal fibers contains protein as the key constituents. The major constituents present in plant fibers are cellulose, hemicellulose, lignin, pectin, and waxes. Composite materials derived from animal fibers are widely found in most sophisticated applications (Gurukarthik Babu, Prince Winston, Senthamarai Kannan, Saravanakumar, & Sanjay, 2019; Kathirselvam, Kumaravel, Arthanarieswaran, & Saravanakumar, 2019; Maheshwaran, Hyness, Senthamaraikannan, Saravanakumar, & Sanjay, 2018). The time and cost involved in processing of animal fiber–based composite materials are quite higher than that of plant fiber–based composites. Several down-to-earth applications of human activities and the industrial needs are met with products manufactured from plant Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00016-1 Copyright © 2023 Elsevier Ltd. All rights reserved.

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Table 5.1 Summary of advantages and limitations of natural fiber composites over synthetic fiber composites. Advantages

Limitations

Cost effective Light weight Renewable Biodegradable Nontoxic and environment friendly Good sound insulation and acoustic properties Minimal energy consumption

Higher moisture absorption Minimum processing temperature Lesser thermal resistance Minimum impact strength Limited durability Lesser reliability in structural applications with limited mechanical properties Lesser microbial resistance

fiber–based composite materials without any trade-off among them in terms of strength, stiffness and stability and other thermal characteristics. Despite with all these unique characteristics and value additions natural fiber–reinforced polymer composites has its own limitations due to its poor compatibility characteristics. Limited interfacial strength and debonding among fiber interface and matrix regions eliminates the application of natural fiber composite materials in several structural applications. The debonding mechanism across the fiber-matrix is shown in Fig. 5.1. Moisture absorption induces a crack at the interface regions followed with leaching of fiber surfaces and finally leads toward debonding across the fiber and matrix regions. The contradictory behavior of hydrophilic plant fibers and hydrophobic polymer matrices tends to reduce its effect as an ideal reinforcing agent with limited interfacial strength and bonding across fiber-matrix interfaces. Interfacial adhesion among fibers and matrix has a significant influence in the mechanical properties of natural fiber–reinforced polymer composites. Stress transfer between fibers and matrix occurs across the interface; thereby optimum reinforcement is needed to achieve good interfacial bonding and limit the crack propagation. The hydroxyl (–OH) groups which exhibit polar behavior in the natural fibers increase the moisture uptake content in the CFRCs. The other significant drawback concerned is the limited thermal properties of natural fibers. For better compatibility between fiber and matrix, wettability could be considered as a precursor to bonding. Fiber wettability limits the endurance and performance of CFRCs resulting in reduced mechanical properties. The issues such as fiber wettability and lesser interfacial adhesion are resolved to a certain extent by suitable physical and chemical modification techniques. Physical and chemical treatment of cellulose reduces the moisture content and enhances the compatibility between fiber and matrix. Engineering the interface among the cellulose fibers and polymer matrix enhances the properties of composites and results in maximum performance. Physical treatments namely corona, ultraviolet (UV), plasma,

Physical modification of cellulose fiber surfaces

(a)

Fibre swells after moisture absorption

75

(b)

Capillary mechanism – water molecules flow along fibre-matrix interface

Matrix microcrack around swollen fibres

Water diffusion through bulk matrix

(c)

(d)

Water soluble substances leach from fibres Ultimate fibre-matrix debonding

Fig. 5.1 Sequence of debonding mechanism across fiber-matrix interface region. Reproduced from Alomayri, T., Assaedi, H., Shaikh, F. U. A., & Low, I. M. (2014). Effect of water absorption on the mechanical properties of cotton fabric-reinforced geopolymer composites. Journal of Asian Ceramic Societies, 2(3), 223–230, with permission from Elsevier, License Number: 4898180897831.

fiber beating and ozone techniques alters the surface properties of cellulose fibers. Prime objective of these physical modification techniques is that it increases the interfacial adhesion between natural fiber and matrix; alter the fiber structural properties without any changes in chemical properties (Sanjay et al., 2019). Chemical modification of fibers includes different techniques such as alkaline treatment, silane treatment, acetylation treatment, benzoylation treatment, permanganate treatment and peroxide treatment, treatment by maleated coupling agents, sodium chlorite treatment, isocyanate treatment, stearic acid treatment, oleoyl chloride treatment, triazine treatment, and fungal treatment. This chapter specifically discusses in detail the most widely used different physical techniques for the modification of the fiber surfaces. In the earlier decade, many research investigations are carried out to analyze the influence of physical modification techniques toward the performance and properties of natural fiber–reinforced composites. This chapter contribution toward the book edition on cellulose fiber–reinforced composites mainly focuses on the major physical treatment methods namely plasma, corona, ozone, and laser and UV irradiation methods and discusses the effect of fiber surface modification and its impact toward the mechanical and thermal characteristics.

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5.2

Cellulose Fibre Reinforced Composites

Cellulose fibers: Source, structure and constituents

Cellulose fibers are mainly derived from two forms of resources that exist in environment such as plants and minerals. The constituents and properties of the fibers derived from nature are dependent on several parameters namely its origin, geographic conditions, nature of weather condition, location, methods of cultivation and processing. Cellulose fibers processed from plants are applied as reinforcements for polymer matrices and other industrial products (Yashas Gowda et al., 2018). Predominantly cellulose fibers obtained from plants are mainly discussed in detail and its extraction methods, chemical constituents and the physical analysis is discussed. Fig. 5.2 demonstrates the cellulose fiber structure and its microstructure comprising three critical components. Cellulose fibers obtained from plants and minerals are categorized into eight different types: bast fibers derived from skin and bast around the plant stem, leaf fibers collected from plant leaves, grass fibers produced from grasses, seed fibers collected from seeds, root fibers, fruit fibers, core fibers from plant stalks and wood pulp fibers. Cellulose fibers are further divided as primary and secondary fibers based on its consumption. Fibers are termed primary since they are cultivated only for the main purpose of fiber whereas cellulose fibers termed as secondary are obtained as byproduct or secondary source of consumption from plants beyond its consumption such as banana, pineapple, palm, coconut, etc. Bast fibers include jute, hemp, kenaf, banana, ramie, rattan, flax, soybean, and vine. Leaf fibers are abaca, pineapple, sisal, and banana. Grass fibers consist of rice, wheat, corn, barley, and bamboo

Fig. 5.2 Cellulose fiber structure. Reproduced from Abiola, O. S., Kupolati, W. K., Sadiku, E. R., & Ndambuki, J. M. (2014). Utilisation of natural fibre as modifier in bituminous mixes: A review. Construction and Building Materials, 54, 305–312, with permission from Elsevier, License Number: 4898190549215.

Secondary wall S3

Secondary wall S2 Microfibril angle Cellulose crystalline microfibrils Secondary wall S1

Cellulose amorphous microfibrils (consists of lignin and hemicelluloses)

Primary wall

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(Cheung, Ho, Lau, Cardona, & Hui, 2009; Westman, Fifield, Simmons, Laddha, & Kafentzis, 2010; Yu, Wang, Lu, Tian, & Lin, 2014). Seed fibers include coir, cotton, and kapok. Borassus, banana, coir, and tamarind are some of the available fruit fibers. Corn and wheat stalks are the core fibers collected from stalks of plants. Fibers from wood are teakwood and rosewood. Luffa, cassava, and swede are the common root fibers. Plant fibers are in-built of key components such as cellulose, lignin, hemicellulose, pectin, and wax. Mechanical characteristics, physical, chemical properties and microstructural behavior of plant fibers are influenced by parameters: geography and climatic condition, extraction mode and processing techniques. Existing species of cellulose fibers are well-explored and wide range of research studies have been performed across the globe for development of greener, sustainable, and eco-friendly products. However, cultivation of similar species of natural resources leads to imbalance in the ecological system and depletion of available species. From the year 2015 onward, researchers and scientists have identified wide range of new breed of cellulose fibers derived from plants and minerals, which were an efficient reinforcement for polymer matrices in development of biocomposites (Azwa, Yousif, Manalo, & Karunasena, 2013; Hemath, Mavinkere Rangappa, Kushvaha, Dhakal, & Siengchin, 2020; Mittal, Saini, & Sinha, 2016). These newer breeds of cellulose fibers derived from plant resources are developed as sustainable and eco-friendly composite products, which are commercialized in several industrial and other household appliances. Fibers derived from plant resources comprise cellulose, hemicellulose, wax, lignin, starch, pectin, and some inorganics. Quantities of these chemical constituents in plant fibers are determined in weight percent by prior chemical analysis. The percentage amount of these constituents varies with regard to different types of fibers and its natural characteristics. Cellulose is a moisture absorbent and exhibits hydrophilic behavior in plant fibers. Cellulose the major component is semicrystalline whereas hemicellulose, which is partially soluble in water, is an amorphous polysaccharide. Lignin exhibits hydrophobic behavior and enhances the stiffness as a cementing agent (Ali et al., 2018). Strength and stability of fibers in bio composites is highly influenced by these chemical constituents. Structure of cellulose, hemicellulose and lignin is presented in Fig. 5.3. Chemical constituents of cellulose fibers are analyzed by different methods and existing standards. TAPPI standards such as T 222 and T 203 were applied for estimation of lignin and α-cellulose content in fibers (Bledzki & Gassan, 1999). Cellulose content is determined by calorific method with apparatus Sartorius, MA45. Electronic moisture analyzer SHIMADZU, MOC120H reveals the information on moisture content present in the fiber. Wax content can be determined by Conrad method. ASTM standard E1755-01 and its testing procedure aids in determination of ash content after dry oxidation. The quantities of chemical constituents in plant fibers are varied largely by suitable surface treatment techniques (Ravi, Dubey, Shome, Guha, & Anil Kumar, 2018). Research investigations on fiber modification reveal an information that reduced amorphous components and with higher quantities of cellulose, content leads to enhanced mechanical strength of cellulose fiber–reinforced composites. Cellulose fiber–reinforced composites with

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O

HO O

O HO

OCH3

OH

OH

O O H2C

O

OH

OH

C

OH

CH2 n OCH3 O

(a)

(c) H H

O

H

H

H

CH3 C O

O

O O

O H

H

H

O

H

H HO

OH H

H

OH

(b) Fig. 5.3 Chemical structure—(A) cellulose, (B) hemicellulose, and (C) lignin. Reproduced from Abiola, O. S., Kupolati, W. K., Sadiku, E. R., & Ndambuki, J. M. (2014). Utilisation of natural fibre as modifier in bituminous mixes: A review. Construction and Building Materials, 54, 305–312, with permission from Elsevier, License Number: 4898190366904.

its remarkable properties and functionality perform well, when cellulose fibers reinforced are modified by suitable physical and chemical treatments. Chemical constituents of newer varieties of cellulose fibers identified from different plant species and other existing fibers is presented in Table 5.2 (Gholampour & Ozbakkaloglu, 2020; Pickering, 2008; Woigk et al., 2016). Physical characteristics of cellulose fibers comprises fiber diameter, density and are determined by suitable experimentation techniques. Fiber diameter can be determined by optical microscope Zeiss, Olympus BX43 and by scanning electron microscope (SEM) images (Misra, Pandey, & Mohanty, 2015; Sanjay et al., 2018). In textile industries, fiber diameters are measured by standards SN/T 2672-2010, a procedure for testing textile materials fitness. Density of plant fibers are determined by pycnometer experimentation. ASTM standard 3800M based on Archimedes principle is employed in estimation of density. Physical characteristics of newly identified plant fibers are listed in Table 5.3 (Abdul Khalil et al., 2014; Jawaid & Abdul Khalil, 2011).

Table 5.2 Chemical and crystalline properties of different cellulose fibers. Chemical constituents S. no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Plant fibers Tridax procumbens Acacia nilotica L. tree Pithecellobium dulce Elettaria cardamomum stem Albizia amara bark Epipremnum aureum stem Eleusine indica grass Cortaderia selloana grass Sansevieria ehrengergii Saharan aloe vera Leucas aspera stem Cardiospermum halicababum Parthenium hysterophorous Banyan tree aerial root Citrullus lanatus climbers Thespesia populnea Jute Hemp Sisal

Crystalline properties

α-cellulose (wt%)

Hemicellulose (wt%)

Lignin (wt%)

Moisture (wt%)

Crystalline index (%)

Crystal size (nm)

32 56.46 75.15 63.12

6.8 14.14 10.23 13.7

3 8.33 12.14 16.5

11.2 – 6.24 10.93

34.46 44.82 49.2 36.84

25.04 3.21 14 5.82

64.54 66.34

14.32 13.42

15.61 14.01

9.34 7.41

63.78 49.33

15 15.46

61.3 53.7

14.7 14.43

11.2 10.32

5.6 7.6

45 22

21.99 21.01

80

11.25

7.8

10.55

52.77

–

60.2 50.7 59.82

14.2 13.2 16.75

13.7 9.7 9.3

7.6 11.3 1.9

56.5 20.2 32.21

5.72 6.7 2977

51.5

9.7

14.3

8.6

40.68

16.28

67.32

13.46

15.62

10.21

72.47

6.28

53.7

12.5

10.1

14

33.33

21.52

70.27 61 70.2 65

12.64 13.6 17.9 12

16.34 12 3.7 9.9

10.83 12.6 10.8 11

48.17 71.4 87.8 –

– 29.25 4.5 –

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Table 5.3 Physical properties of different cellulose fibers. S.no.

Plant fibers

Density (g/cm3)

Diameter (microns)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Tridax procumbens Acacia nilotica L. tree Pithecellobium dulce Elettaria cardamomum stem Albizia amara bark Phaseolus vulgaris Areva javanica Azadirachta indica bark Furcraea foetida Epipremnum aureum stem Eleusine indica grass Cortaderia selloana grass Sansevieria ehrengergii Saharan aloe vera Leucas aspera stem Cardiospermum halicababum Parthenium hysterophorous Banyan tree aerial root Kigelia africana fruit fiber Citrullus lanatus climbers Thespesia populnea

1.16 1.165 0.865 1.47 1.043 0.852 1.4005 0.740 0.778 0.654 1.143 1.261 1.410 1.325 1.118 1.141 1.251 1.23 1.316 1.227 1.412

233.1 – 144.3 217.38 – 53.56 70 40–250 12.8 – 315.4 372.6 – 91.15 335.01 315.4 381.67 0.14 629 210 256

5.3

Physical modification of cellulose fibers

Physical techniques employed in processing cellulose fibers are used to separate bundles of cellulose fibers to fine form of threads and alter the fiber structure’s surface structure to optimize their application to compositions. Some physical methods of functionalizing cellulose fibers are plasma treatment, ultrasound and ultraviolet treatments and ozone treatment.

5.3.1 Plasma treatment Plasma treatment is the widely applied physical techniques in the industry today. These techniques are highly efficient in modification of cellulose fibers resulting in enhanced performance and functionality. In the discussion toward this plasma treatment, the four main forms of atmospheric plasma techniques such as corona treatment, dielectric barrier discharge technology (DBD), and glow discharge (APGD) and atmospheric pressure plasma jet (APPJ) techniques is discussed in detail.

5.3.1.1 Corona treatment The corona treatment is the highly effective treatment with regard to inducing surface oxidation over a wide range of materials. Superior compatibility between hydrophilic cellulose fibers and hydrophobic matrix is obtained only based on the repeated

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Fig. 5.4 Corona treatment photography. Reproduced from Ferreira, D. P., Cruz, J., & Fangueiro, R. (2018). Surface modification of natural fibers in polymer composites. In Green composites for automotive applications (pp. 3–41). Elsevier, with permission, License Number: 4925761106964.

attempts of surface modification of the cellulose fibers. The working principle of corona treatment is by means of high-frequency discharge over the electrodes and further embedded with a grounded metal roll. The experimental set up for corona treatment is shown in Fig. 5.4. Such high-frequency discharges over the electrodes induces ionization effect in the surrounding atmosphere, resulting in plasma (ionized air) and blue color emission, as shown in Fig. 5.4. In the gap between the electrodes, the sample or substrate is loaded with high-speed electrons. These electrons have enough energy to disrupt the molecular bonds on most of the substrate surfaces. The oxidants, such as ozone, atomic oxygen, and oxygen-free radicals, present in a corona discharge induces surface oxidation of the materials. When combined with free radicals on the material surface, these oxidants forms oxidizing groups such as hydroxyl, carboxyl, carbonyl, or ester groups. The presence of such polar groups over the material exhibits an enhanced surface energy, resulting in excellent wettability and adhesive bonding among cellulose fibers and polymer matrix. The corona treatment is highly effective treatment in textile industries and it is considered as pretreatment in processing textile fibers. The treatment could be employed in elimination of impurities over the material surface and improve compatibility and adhesive bonding with the matrix. The limiting factor associated with the corona treatment is its limited penetration depth over the fiber surfaces indicating that it can only be successful in modification of surfaces of short fibers. Corona treatment of fibers is not effective in application of yarns or woven fabrics since it cannot penetrate deeply over the surfaces resulting in limited effects over the fabrics and other textile fibers. Nonetheless, the corona treatment has numerous benefits over conventional plasma treatments as well as other surface modification methods. First, there are no criteria for certain conditions to be met during modification (except for the low-temperature plasma therapy, which employs vacuum chambers). Second, a low-cost technique

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uses little energy. Finally, the method can be applied on a wide scale and directly to a significant amount of material, which is critical for industrial production.

5.3.1.2 Dielectric barrier treatment The plasma dielectric-barrier discharge (DBD) technique is similar to that of corona treatment. However, the discharges in the corona treatment are among the bare metal electrodes without any dielectric. The DBD plasma experimental set up comprises two flat parallel metal electrodes, one of which is covered by a dielectric layer that gathers the transferred charge on its surface and distributes it across the entire electrode area as shown in Fig. 5.5. Ideal dielectric materials employed as a dielectric barriers are either glass or silica glass, ceramics and polymer layers or thin enamel. When an alternating voltage ranging from low frequency AC to 100 kHz is applied to the electrodes, breakdown processes in the gas gap begin, and transient micro discharges with durations of nanoseconds are formed and spread throughout the dielectric surface. This type of discharge is widely recognized for the surface treatment for the synthesis of ozone. In terms of surface treatment, dielectric barrier discharges create high-energy electrons (due to collisions during discharge) that can efficiently form radicals and electronically excited particles. The DBD can initiate several reaction pathways that result in the formation of reactive intermediates, therefore promoting the surface activation of the materials. This technique is frequently used in treatment of textile fibers, polymers, plastic foils, metal surfaces, surface sterilization, film deposition, component removal from flue gases, and greenhouse gas conversion. The major limiting factor concerned with DBD is that the discharge is not fully consistent and only lasts for a short duration of time.

High voltage electrode

High voltage Discharge gap AC generator

Dielectric barrier Ground electrode

Dielectric barrier

Discharge gap

High voltage electrode

Ground electrode

Fig. 5.5 A generic dielectric barrier discharge apparatus. Reproduced from Ferreira, D. P., Cruz, J., & Fangueiro, R. (2018). Surface modification of natural fibers in polymer composites. In Green composites for automotive applications (pp. 3–41). Elsevier, with permission, License Number: 5118171077624.

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5.3.1.3 Atmospheric pressure glow discharge Compared to the DBD approach, atmospheric pressure glow discharge (APGD) is highly suited for more homogeneous way of treatment of cellulose fiber surfaces. Glow discharge is a uniform, homogeneous, and stable approach of discharge that is typically created by means of inert gases lime helium, argon, and nitrogen. The schematic illustration of atmospheric pressure glow discharge (APGD) technique is presented in Fig. 5.6. With regard to relation with the dielectric barrier discharge technique, APGD technique is employed by application of relatively modest voltages across symmetrical conductive electrodes at a higher range of frequencies (MHz). Plasma is uniform across the electrodes and produces one current pulse for every half cycle. The APGD plasma has high electron energy and higher concentrations of excited and charged particles at lower range of gas temperatures. This treatment is employed for a wide range of applications, including surface modification, etching, thin-film deposition, ozone production, organic compound degradation, sterilization, disinfection, biological and chemical decontamination, removal of surface impurities and biowaste treatment.

5.3.1.4 Atmospheric pressure plasma jet Atmospheric pressure plasma jet (APPJ) technique comprises the experimental set up arranged with two tubular metal electrodes separated by a gap through which a discharge current namely a plasma jet flows over the surface. The schematic illustration of the experimental set up of APPJ is shown in Fig. 5.7. A quartz cylindrical tube

Fig. 5.6 Scheme for comparison of air pressure glow discharge (APGD) with dielectric barrier discharge (DBD). Reproduced from Ferreira, D. P., Cruz, J., & Fangueiro, R. (2018). Surface modification of natural fibers in polymer composites. In Green composites for automotive applications (pp. 3–41). Elsevier, with permission, License Number: 5118171318099.

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Cellulose Fibre Reinforced Composites

Fig. 5.7 Schematic view of one of the possible experimental set-ups of APPJ. Reproduced from Maqsood, H. S., Bashir, U., Wiener, J., Puchalski, M., Sztajnowski, S., & Militky, J. (2017). Ozone treatment of jute fibers. Cellulose, 24 (3), 1543–1553, with permission, License Number: 5118171500101.

circulates helium and other inert gases through the electrodes at the both the ends. Several factors, such as the wave pulse, pulse frequency, and gas flow rate are adjusted to produce plasma. The plasma is sent directly into the sample in the open end of the quartz cylindrical tube. An APPJ can offer local therapy by containing a high density of charged particles, reactive oxygen, and nitrogen gases. Since, the plasma plume (bright area) can extend for many centimeters from the APPJ opening. Resulting in short-lived entities like atomic oxygen which participate in reactions with the target. Furthermore, due to the high gas velocity, the plasma components may be penetrated into small cavities, allowing for an extremely accurate treatment. The APPJ technique is highly preferred in applications such as surface modification of cellulose fibers, biological material sterilization, and biomedical applications such as dermatological, dentistry, ozone production, and heat-sensitive material treatment.

5.3.2 Ultrasound and ultraviolet treatments Ultrasound is described as a very high frequency sound exceeding 20 kHz. Ultrasound therapies are not as often utilized as the previously mentioned plasma treatments. Nevertheless, they are efficient in removing various chemicals and contaminants from surfaces even when no surfactants are used in the rinsing bath. This phenomenon might be linked to acoustic cavitation, also known as the process of bubble production and collapse, which is responsible for the majority of ultrasound’s physical and chemical effects, observed in solid and liquid or liquid-liquid systems. The effects of ultrasonic treatment on cellulosic fibers, such as cotton reveal that that the ultrasonic treatment can alter the crystalline morphology of cotton and the subsequent mechanical and chemical properties of these fibers.

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UV light is a kind of electromagnetic radiation having wavelengths ranging from 10 to 400 nm, which triggers chemical interactions with various organic compounds, resulting in more complex effects than simple heating. UV light is a possible energy source, which induces photochemical reactions in cellulose fiber molecular structures, and highly influences the mechanical properties. UV radiation proves to be a clean and cost-effective approach in modification of cellulose fiber surfaces and it is widely preferred due to its low cost of experimental set up and ease of operation.

5.3.3 Ozone treatment The ozone generator is generally kept at a constant range of 50% power capacity. The oxygen concentrator, which had a variable output oxygen flow rate, was utilized as an oxygen supplier to the ozone generator. The research studies on jute fiber wastes were experimentally studied with the aid of ozone treatment. The jute waste substrate fibers were immersed in a humid ozonized environment for a prolonged period. The mass flow rate of ozone was determined to be 4.5 mg/L. The oxygen concentrator’s output concentrated oxygen flow rate was set to 5.0 L/min, and this oxygen was supplied to the ozone generator. This treatment was carried out in a humid environment since a humid atmosphere is more efficient for the interaction of ozone gases with lignocellulosic fiber material. Since the oxygen delivered by the concentrator and the ozone produced by the ozone generator in the series are both dry, a humidification method was created for administering ozone to jute samples. For every single hour, the jute samples were removed from the container and tested. The ozone-treated fibers were immediately immersed in a nonionic surfactant solution for 1 h for the removal of the remaining ozone over the fiber surfaces. This solution included 1 g/L of nonionic surfactant in distilled water. Further, the surface treated fibers were rinsed with distilled water and then dried in an oven (at 105°C) for 3 h. This method of surface treatment eliminates the impurities present over the fiber surfaces and displays higher compatibility with the hydrophobic matrix.

5.4

Effect of physical modification toward performance and functionality of thermal fiber composites

Organic fibers have smooth surfaces and minimal surface energy, resulting in poor adhesion to the matrix (Seki & Sever, 2009). These fibers often lack chemical functional groups that would allow covalent bonds to form at the fiber-matrix interface. The most frequent treatments alter the fibers by removing the superficial layer, altering the topology, and modifying the chemical composition of the surface. Plasma treatment enhances fiber-matrix adhesion mostly by creating a new polymer layer capable of forming strong covalent connections between the fiber and the matrix, and occasionally by roughening the surface of fibers to increase mechanical interlocks between them. Gibeop et al. (2013) discussed the major ways for improving the

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mechanical characteristics of composite materials by surface treatment of cellulose fibers. These cellulose fibers when subjected to plasma treatment, its mechanical characteristics, performance and functionality are enhanced. Tensile strength, Young’s modulus, and flexural strength of plasma polymerized jute fiber composites were higher by an order of 28%, 17%, and 20%, respectively. Furthermore, plasma polymerization results in a greater (>20%) improvement in flexural strength than untreated fiber composites. SEM images reveal that the plasma treated cellulose fiber composites exhibits an increased interfacial adhesion between jute fiber and poly lactic acid. Sarikanat et al. (2016) examined the flax fibers that were treated by employing argon and air atmospheric pressure plasma treatments to enhance the mechanical characteristics of flax fiber-reinforced unsaturated polyester composites. Tensile strength, flexural strength values of flax fiber-reinforced polyester composites improved by up to 34% and 31%. However, mechanical characteristics of argon plasma-treated flax fiber-reinforced polyester composites are enhanced by up to 200 W in relation to the argon plasma power. Ramachandran et al. (2022) investigated on Agave fiber powder (AFP) that was coated by plasma polymerization by spraying ethylene gas to create composites based on low-density polyethylene (LDPE). Water dispersion testing indicated that the treated composites displayed a behavior that altered from hydrophilic to hydrophobic behavior, which was also supported by water contact angle experiments. The inclusion of treated and untreated AFP (200 mesh) at 20 wt% increases the composites Young’s modulus by up to 60% and 32%, respectively, in comparison to the clean matrix. In addition, the inclusion of treated and untreated AFP increased the crystallinity of LDPE. Scalici, Fiore, and Valenza (2016) employed Fourier transform infrared spectroscopy and thermogravimetric analysis to evaluate the effect of plasma treatment on the functional groups and thermal behavior of cellulose fibers. The mechanical characteristics of these composites get enhanced significantly following plasma treatment, indicating that plasma treatment improves fiber-matrix adhesion. SEM micrographs indicates that the interfacial bonding among the polymer resin and the plasma treated cellulose fibers are higher and highly efficient than untreated counterparts. Cellulose fibers have proved to be a good alternative to glass fibers as reinforcing material in polymer composites by Woigk et al. (2016) and it can be attributed to the equivalent specific strength and stiffness. As a result, composites including plasma-treated cellulose fibers and engineering polymers, with a high fiber volume content have a significant potential to be developed and utilized as an ecologically sustainable alternative material for synthetic composites for a wide range of applications. Plasma treated coir fibers with either air or oxygen as a gaseous medium proved to be highly efficient as it eliminates the maximum content of lignin constituents over the surface of the coir fibers as investigated by de Farias et al. (2017). It is observed that the plasma treated coir fibers displayed an tensile strength which is higher by up to 300%, while elastic modulus increased by roughly a factor of 20 than its untreated coir fibers. Rao, Bao, Wang, Fan, and Feo (2018) demonstrated plasma technique for functionalization of both carbonized and noncarbonized bamboo surfaces. The plasma treatment with oxygen as working fluid induces efficient surface oxidization oxygen-containing groups are formed over the fiber surfaces, resulting in a substantial alteration in the

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87

microstructure of the bamboo surface layer. Experimental results convey that there is a considerable increase in the wettability and interface bonding of the bamboo surface as well as the physical and mechanical characteristics of bamboo composites. Modulus of Rupture (MOR) of 170 MPa was obtained from tests, which indicates there is a 47% rise in values than the untreated bamboo composites. Fazeli, Florez, and Sima˜o (2019) applied X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy techniques with regard to predict the characteristics of plasma treated fibers. Cellulose fiber composites reinforced with thermoplastic matrix (TPS) were manufactured by high friction and hot compression techniques. Tensile test results and SEM images of the fractured surfaces reveal that the adhesion between the treated cellulose fibers and the TPS matrix has improved significantly. Thermogravimetric results reveal a significant breakdown at temperatures ranging from 250°C to 350°C. XRD analysis revealed that the crystallinity of composites increased significantly when compared to TPS. Macedo et al. (2020) studied the dynamic mechanical and thermal studies of plasma-treated fiber composites and the results revealed an increase in storage moduli. When compared to the pure polymer, it also demonstrated an increase in glass transition temperature. Thus, cold plasma is shown to be a feasible nonpolluting option for activating cellulosic fibers and enhancing the fiber/matrix interfaces. Ragoubi, Bienaim
e, Molina, George, and Merlin (2010) investigated the mechanical characteristics of CFRCs produced from various combinations of untreated and corona-treated cellulose fibers and polypropylene matrix. Corona treated cellulosic fibers reinforced with polypropylene matrix displays a larger improvement in composite characteristics, with a 30% increase in Young’s modulus. The etching effect caused by corona discharge treatment (CDT) as observed through microscopic images is primarily responsible for the enhanced mechanical strength and stiffness embedded with higher interfacial adhesion among the compounds. Bahramian, Atai, and NaimiJamal (2015) investigated the effects of corona and silane surface treatment in terms of mechanical characteristics of ultra-high molecular weight polyethylene (UHMWPE) fiber reinforced composites (FRCs). Fibers corona treated for 5 s had greater surface nanotoughness. In the FRCs, specimens corona treated for a duration of 5 s had greater mechanical characteristics such as flexural modulus, flexural strength, and fracture toughness and microscopic images reveals a superior resin-fiber interfacial bonding over the surfaces. Mesquita et al. (2017) investigated plant fibers pretreated chemically with NaOH and further with corona discharge prior to be used as a reinforcing element in unsaturated polyester-based fiber composites. The corona discharge treatment enhanced the composites impact and tensile strength with a limited ability toward water absorption. Surface activation enhanced the interfacial adhesion between fibers and the polyester matrix. Corona treatment depolymerizes the lignocellulosic material thereby enhances the adhesive bonding with the polyester matrix. The effects of spray duration, nanoclay content, and corona discharge on oxygen transmission rate (OTR), water vapor transmission rate (WVTR), base weight, thickness, and tensile strength of coated sheets were studied by Mirmehdi, Hein, de Luca Saranto´poulos, Dias, and Tonoli (2018). Corona discharge enhanced the wettability of paper surfaces thereby resulting in better adhesion between paper and hybrid

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composite. Increase in spray time proportionately increases the tensile strength as well as barrier characteristics such as OTR and WVTR. The presence of more nanoclay in coated paper enhanced its barrier characteristics with a limited tensile strength. Tensile strength and morphological characteristics showed that the substrate and hybrid composite were effectively adhered together. Adekomaya and Majozi (2019) evaluated cellulose fiber surface treatment as a potential approach to enhance cellulose fiber compatibility with the matrix in order to develop more sustainable composite materials. The benefits of cellulose fibers over synthetic fibers drew attention to biobased fibers, which have a positive impact on the environment and biodiversity. Oudrhiri Hassani et al. (2020) conducted research on Green Composites made of lignocellulosic fibers, which are low-cost sustainable materials. They offer a greener alternative to using glass fibers as reinforcement in engineering composites. To enhance the interfacial contact with the matrix, lignocellulosic fibers were surface modified, where Aloe Vera fibers are treated with corona discharge. Mechanical tests on treated fibers also revealed a reduction in elastic modulus and ultimate tensile strength. Abdullah-Al-Kafi, Abedin, Beg, Pickering, and Khan (2006) conducted research on the characteristics of jute and glass fiber–reinforced hybrid composites and treated these fibers with exposure to UV light of varying intensities. Compared to untreated jute-and-glass–based hybrid composites, UV pretreated jute, and glass fibers (1:3) at optimal intensities exhibits the enhanced mechanical characteristics and higher values of impact strength. Torres-Giner, Montanes, Fenollar, Garcı´a-Sanoguera, and Balart (2016) examined the use of vegetable oils as new plasticizers for polyvinyl chloride, which has gained prominence over these years in polymer sector owing to its inherent sustainability. The effectiveness of a new vinyl plastisol/wood flour composite based on epoxidized linseed oil was investigated. The impact of UV light on the surface of wood flour was investigated in order to enhance its interfacial adhesion with vinyl plastisol. To analyze the composites fracture and estimate the dispersion of wood flour in the vinyl matrix, stereomicroscopy and scanning electron microscopy techniques were applied. From the surface appearance and mechanical findings, optimum materials for vinyl plastisol composites with high amounts of wood flour with the higher size particles that had previously been exposed to UV for 4 min were detected. The resulting renewable vinyl plastisol composites have a lot of potential as an engineering material for wood substitution in construction applications. Mahzan, Fitri, and Zaleha (2017) evaluated the influence of UV radiation on mechanical characteristics, as well as the effect of chemical treatment on cellulose fiber. The effect of UV light on deterioration rate is affected by the parameters and its effect of wavelength, intensity, and exposure period. Stanciu, Bucur, V^alcea, Savin, and Sturm (2018) employed dynamic mechanical analysis to investigate the changes in the elastodynamical properties of composites comprising small waste oak particles and a polyester resin that had been subjected to photo-degradation by UV radiation and thermal degradations caused by temperature variations ranging from 30°C to 120°C. After being exposed to UV radiation, the damping capacity of the particle-reinforced specimens rose marginally, regardless of the applied frequency of loading. Furthermore, increasing particle size in the composite resulted in a decrease in glass transition temperature. On the surface of the specimens, UV light caused structural morphological instability at the

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nanometric scale. Nguyen, Hao, and Wang (2018) investigated the performance of high-density polyethylene/wood-flour composites with a basalt fiber (BF)–reinforced shell. The performance of these composites was evaluated after they were exposed to UV weathering for 2000 h. The composite shells containing BF and UV326 had the least discoloration and surface fractures. The spectra indicated that the oxidation of these composites increased with exposure time, as measured by the carbonyl group concentration on the surface. The combination of BF and UV326 shows a synergistic impact on the photo oxidation of wood-plastic composite shell layers with an enhanced performance and functionality. From the research studies performed by Ching et al. (2018), the UV resistance of polymer composites is frequently enhanced by the dispersion of nanoparticles, UVAs, and UV stabilizers in the polymer matrix. The incorporation of nanoparticles or graphene into the polymer matrix has improved the UV-resistant characteristics of organic polymer coatings. Long-term UV radiation exposure degrades the main matrix characteristics and results in color defects in polymer composite materials. Polymer composites, which have improved thermal and UV-resistant characteristics, are now ideally suited for UV-resistant and hightemperature applications due to their low cost, light weight, high strength, and ease of processing when compared to the conventional metal matrix–based composites. Hedenberg and Gatenholm (1996) examined the impact of ozone gas treatment on the adhesion of low-density polyethylene (LDPE) and cellulose fibers. The ozone treatment of LDPE resulted in a substantial increase in interfacial shear strength, as assessed by the single fiber fragmentation test, but the ozone treatment of cellulose fiber had no effect on adhesion. To further understand the adhesion process, comprehensive surface characterization was carried out. Several carbonyl compounds and hydro peroxides were produced during the ozone treatment. Due to the oxidation, the surface energy of the polar components is increased for the ozone-treated materials. Extraction of LDPE laminated with a regenerated cellulose sheet revealed that significant bonding occurs during the lamination technique between the ozone-treated LDPE and cellulose. Jabbar, Militky´, Wiener, and Karahan (2016) investigated the mechanical and dynamic mechanical characteristics of woven jute fabric–reinforced green epoxy composites as a function of jute fiber modified by enzyme treatment, CO2 pulsed infrared laser, and ozone treatments. The treatments improved the flexural and impact characteristics. A one-way analysis of variance was employed in evaluation of the mechanical characteristics of composites, and the findings revealed substantial differences. The findings of dynamic mechanical study indicated that treated composites have a greater storage modulus across a wider temperature range. A positive shift in the loss modulus and tangent delta peaks of treated composites was seen at higher temperatures. Olewnik-Kruszkowska, Nowaczyk, and Kadac (2016) addressed the variables that influence the characteristics of polymers and polymer-based composites when treated by ozone techniques. The changes in structural and thermal characteristics of the materials were observed for an exposure toward ozone for a period ranging from 1 to 4 months. The data show that addition of the filler material fastens the ozone-induced deterioration. The inclusion of montmorillonite, on the other hand, has no effect on the mechanism of the degrading process. The microstructure pictures of polylactide and polylactide-based composites

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following ozone treatment show that introducing unmodified nanofiller into the system reduces the changes in surface shape. Maqsood et al. (2017) conducted research on the oxidation of cellulosic materials. In a humid atmosphere, ozone gas was utilized to cure waste jute fibers over various time periods. The results indicated that fiber tensile strength consistently decreases with treatment time and surface functional groups change correspondingly. Changes in crystallinity were also found following ozone treatment. The fiber bundles were physically separated into brittle single fibers. Nishata, Sulong, Yuliana, and Sahrim (2017) addressed alkali, acid, and ultraviolet-ozonolysis (UV/O3) treatment of RH surfaces. Extrusion method as employed in fabrication of composites. The study is performed for treated and untreated RH comprising 30 wt% content of RH fibers and the results are compared. Flexural strengths of untreated RH, alkali-treated RH, acid-treated RH, and UV/O3treated RH composites are 27.97, 31.25, 30.22, and 30.87 MPa, respectively. Flexural strength of composites filled with UV/O3 treated RH is closer in agreement to alkali treatment. As a result, UV/O3 treatment may be utilized as an alternate technique to change the RH surface in order to enhance adhesion between the hydrophilic fiber and the hydrophobic polymer matrix.

5.5

Conclusions

Within this study the cellulose fibers—source, structure and constituents, physical modification techniques and effect of physical modification toward performance and functionality of cellulose fiber composites have been investigated. The following conclusions were made from the study of physical modification of cellulose fiber surfaces. Cellulose fibers have a great deal of promise for usage as continuous reinforcing fibers in thermoplastic matrix composites (George, Sreekala, & Thomas, 2001). The use of high-performance engineering polymers as well as plasma-based fiber surface treatments, may improve mechanical characteristics further making cellulose fiber–reinforced composites an alternative and ecologically acceptable option. Based on the existing published research, it is possible to conclude that corona treatment only altered the surface architecture of cellulose fibers, with no conclusive evidence to demonstrate the retention of fiber components after treatment. Corona treatment has the unintended consequence of imposing interlocking on the fiber, which might result in poor mechanical boding. More research is needed to explore the impact of long-term bonding, as stated. Another unresolved issue in most published research is the ability of corona treatment to raise the surface energy of the fiber, thereby affecting the compatibility between the reinforcing fiber and matrix. This finding is also subjective in many literary works. Polymer composites with combined strength and heat resistance/UV sustainability have been utilized in aerospace, electrical engineering, and outdoor applications. Because of its high strength, low weight, and heat resistance, carbon fiber composites are frequently used in aerospace applications. Thermally resistant polymer composites are used in the insulation systems of medium and high-power electrical equipment.

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The addition of nanoparticles or graphene to the polymer matrix enhanced the UVresistant characteristics of organic polymer coatings. Fiber-reinforced polymers are highly desirable in architectural applications because of their UV resistance. The impact of ozone treatment on cellulosic fiber waste was studied. The physical and chemical characteristics of jute fibers decrease dramatically after a given time due to a shift in functional groups present in fiber shape. Ozone destroys lignin while mildly solubilizing the hemicellulose fraction. Furthermore, it enhances the degree of crystallinity and crystallite size, therefore enhancing fiber shape. As a result, ozone gas provides an alternate and ecologically acceptable technique for cellulose oxidation. Along with wastewater treatment, ozone gas might be utilized for lignocellulosic fiber oxidation, allowing us to tap into its enormous potential in sectors as diverse as textile manufacturing, medical, and the creation of micro/nanocellulose. This study concludes that ozone treatment is a very good and environmentally friendly replacement for chemical oxidation of cellulose, particularly jute.

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Madhu, P., Sanjay, M. R., Senthamaraikannan, P., Pradeep, S., Saravanakumar, S. S., & Yogesha, B. (2019b). A review on synthesis and characterization of commercially available natural fibers: Part-I. Journal of Natural Fibers, 16(8), 1132–1144. Maheshwaran, M. V., Hyness, N. R. J., Senthamaraikannan, P., Saravanakumar, S. S., & Sanjay, M. R. (2018). Characterization of natural cellulosic fiber from Epipremnum aureum stem. Journal of Natural Fibers, 15(6), 789–798. Mahzan, S., Fitri, M., & Zaleha, M. (2017). UV radiation effect towards mechanical properties of natural fibre reinforced composite material: A review. In Vol. 166. IOP Conference Series: Materials Science and EngineeringInstitute of Physics Publishing. Maqsood, H. S., Bashir, U., Wiener, J., Puchalski, M., Sztajnowski, S., & Militky, J. (2017). Ozone treatment of jute fibers. Cellulose, 24(3), 1543–1553. Mesquita, R. G. D. A., C
esar, A. A. D. S., Mendes, R. F., Mendes, L. M., Marconcini, J. M., Glenn, G., et al. (2017). Polyester composites reinforced with corona-treated fibers from pine, eucalyptus and sugarcane bagasse. Journal of Polymers and the Environment, 25(3), 800–811. Mirmehdi, S., Hein, P. R. G., de Luca Saranto´poulos, C. I. G., Dias, M. V., & Tonoli, G. H. D. (2018). Cellulose nanofibrils/nanoclay hybrid composite as a paper coating: Effects of spray time, nanoclay content and corona discharge on barrier and mechanical properties of the coated papers. Food Packaging and Shelf Life, 15, 87–94. Misra, M., Pandey, J., & Mohanty, A. (Eds.). (2015). Biocomposites: Design and mechanical performance Elsevier. Mittal, V., Saini, R., & Sinha, S. (2016). Natural fiber-mediated epoxy composites – A review. Composites Part B: Engineering, 99, 425–435. Nguyen, V. D., Hao, J., & Wang, W. (2018). Ultraviolet weathering performance of highdensity polyethylene/wood-flour composites with a basalt-fiber-included shell. Polymers, 10(8), 831. Nishata, R. R. R., Sulong, A. B., Yuliana, N. Y., & Sahrim, A. (2017). Effect of surface modified rice husk (RH) on the flexural properties of recycled HDPE/RH composite. Advances in Materials and Processing Technologies, 3(4), 482–489. Olewnik-Kruszkowska, E., Nowaczyk, J., & Kadac, K. (2016). Effect of ozone exposure on thermal and structural properties of polylactide based composites. Polymer Testing, 56, 299–307. Oudrhiri Hassani, F., Merbahi, N., Oushabi, A., Elfadili, M. H., Kammouni, A., & Oueldna, N. (2020). Effects of corona discharge treatment on surface and mechanical properties of Aloe Vera fibers. Materials Today: Proceedings, 24, 46–51 (Elsevier Ltd). Pec¸as, P., Carvalho, H., Salman, H., & Leite, M. (2018). Natural fibre composites and their applications: A review. Journal of Composites Science, 2(4), 66. Pickering, K. L. (2008). In K. L. Pickering (Ed.), Woodhead publishing series in composites science and engineering. Properties and performance of natural-fibre composites Woodhead Publishing. Pickering, K., Efendy, M. G. A., & Le, T. M. (2016). A review of recent developments in natural fibre composites and their mechanical performance. Composites Part A: Applied Science and Manufacturing, 83, 98–112. Ragoubi, M., Bienaim
e, D., Molina, S., George, B., & Merlin, A. (2010). Impact of corona treated hemp fibres onto mechanical properties of polypropylene composites made thereof. Industrial Crops and Products, 31(2), 344–349. Ramachandran, A., Mavinkere Rangappa, S., Kushvaha, V., Khan, A., Seingchin, S., & Dhakal, H.N. (2022). Modification of fibers and matrices in natural fiber reinforced polymer composites: A comprehensive review. Macromolecular Rapid Communication.

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Rao, J., Bao, L., Wang, B., Fan, M., & Feo, L. (2018). Plasma surface modification and bonding enhancement for bamboo composites. Composites Part B: Engineering, 138, 157–167. Ravi, M., Dubey, R. R., Shome, A., Guha, S., & Anil Kumar, C. (2018). Effect of surface treatment on natural fibers composite. IOP Conference Series: Materials Science and Engineering, 376, 012053. Sanjay, M. R., Madhu, P., Jawaid, M., Senthamaraikannan, P., Senthil, S., & Pradeep, S. (2018). Characterization and properties of natural fiber polymer composites: A comprehensive review. Journal of Cleaner Production, 172, 566–581. Sanjay, M. R., Siengchin, S., Parameswaranpillai, J., Jawaid, M., Pruncu, C. I., & Khan, A. (2019). A comprehensive review of techniques for natural fibers as reinforcement in composites: Preparation, processing and characterization. Carbohydrate Polymers, 207, 108–121. Sarikanat, M., Seki, Y., Sever, K., Bozaci, E., Demir, A., & Ozdogan, E. (2016). The effect of argon and air plasma treatment of flax fiber on mechanical properties of reinforced polyester composite. Journal of Industrial Textiles, 45(6), 1252–1267. Scalici, T., Fiore, V., & Valenza, A. (2016). Effect of plasma treatment on the properties of Arundo donax L. leaf fibres and its bio-based epoxy composites: A preliminary study. Composites Part B: Engineering, 94, 167–175. Seki, Y., & Sever, K. (2009). The influence of oxygen plasma treatment of jute fibres on mechanical properties of jute fibre reinforced thermoplastic composites. In 5th international advanced technologies symposium (IATS’09). Siva, R., Valarmathi, T. N., Palanikumar, K., & Samrot, A. V. (2020). Study on a novel natural cellulosic fiber from Kigelia Africana fruit: Characterization and analysis. Carbohydrate Polymers, 244, 116494. Stanciu, M. D., Bucur, V., V^alcea, C. S., Savin, A., & Sturm, R. (2018). Oak particles size effects on viscous-elastic properties of wood polyester resin composite submitted to ultraviolet radiation. Wood Science and Technology, 52(2), 365–382. Torres-Giner, S., Montanes, N., Fenollar, O., Garcı´a-Sanoguera, D., & Balart, R. (2016). Development and optimization of renewable vinyl plastisol/wood flour composites exposed to ultraviolet radiation. Materials and Design, 108, 648–658. Vinod, A., Sanjay, M. R., Suchart, S., & Jyotishkumar, P. (2020). Renewable and sustainable biobased materials: An assessment on biofibers, biofilms, biopolymers and biocomposites. Journal of Cleaner Production, 258, 120978. Vinod, A., Vijay, R., Singaravelu, D. L., Sanjay, M. R., Siengchin, S., Yagnaraj, Y., et al. (2021). Extraction and characterization of natural fiber from stem of Cardiospermum Halicababum. Journal of Natural Fibers, 18(6), 898–908. Westman, M. P., Fifield, L. S., Simmons, K. L., Laddha, S., & Kafentzis, T. A. (2010). Natural fiber composites: A review. Richland, WA, United States: Pacific Northwest Laboratory. Woigk, W., Rion, J., Hegemann, D., Fuentes, C., Van Vuure, A. W., Masania, K., et al. (2016). Mechanical properties of tough plasma treated flax fibre thermoplastic composites. In ECCM 2016 – proceeding of the 17th European conference on composite materialsMAI Carbon Cluster Management GmbH. Yashas Gowda, T. G., Sanjay, M. R., Subrahmanya Bhat, K., Madhu, P., Senthamaraikannan, P., & Yogesha, B. (2018). Polymer matrix-natural fiber composites: An overview. Cogent Engineering, 5(1), 1446667. Yu, Y., Wang, H., Lu, F., Tian, G., & Lin, J. (2014). Bamboo fibers for composite applications: A mechanical and morphological investigation. Journal of Materials Science, 49(6), 2559–2566.

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S. Sathisha, M. Aravindha, S. Gokulkumara, S. Dharani Kumarb, L. Prabhua, and R. Ranga Rajc a Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India, bCentre for Machining and Material Testing, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India, cDepartment of Aeronautical Engineering, Sri Ramakrishna Engineering College, Coimbatore, Tamil Nadu, India

6.1

Introduction

Synthetic fiber-reinforced composites have several disadvantages such as high density, nondegradable and also lead to other major issues like a diminishment of fossil fuels and waste management (Sanjay et al., 2018). Drawbacks of synthetic fibers have been driven scientists and researchers to discover alternative reinforcement with ecofriendly characteristics in directive to reduce or replace the use of synthetic fiber. Moreover, the world is in necessity of more eco-friendly products in commercial applications (Sanjay et al., 2019). Therefore, researchers around the world are focusing on developing new and innovative materials that would reduce environmental pollution (Vijay et al., 2019). They investigated the research in the use of composites which is developed by reinforcing the raw natural fibers in polymer matrices in recent periods. They found that reinforcing the natural fiber in polymer matrices is one of the possible alternatives for replacing environmentally harmful synthetic materials and helps to control the environmental pollution problems (Girijappa, Gowda, Rangappa, Parameswaranpillai, & Siengchin, 2019). Tufan, Akbas, and Aslan (2016) conducted a study to determine whether synthetic fibers such as aramids, boron, glass as well as carbon fibers could be effectively used as a means to recycle them. They highlighted the potential risk to the environment made by these fibers that become a major concern in terms of disposal from industries that use textile fabrics and rubber. This owes eco-friendly and low cost along with satisfying the requirements by the users. In addition, the natural fibers are very low cost, have better and strong mechanical properties, and have low energy consumption while manufacturing (La Mantia & Morreale, 2011). The need for environment-friendly materials resulted in the extraction of several natural fibers which are found to be used as potential reinforcement material. Several kinds of literature reported on the extraction and pretreatment of the mechanical properties of the natural fibers. There are Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00011-2 Copyright © 2023 Elsevier Ltd. All rights reserved.

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several extraction methods adopted for the extraction of fiber from plants. One of the most widely used methods of extraction is retting. Retting is the process by which the collected natural substances are placed in water over a period of days for the primary walls of the plants to get softened. The physical and mechanical properties of natural fibers may differ based on several parameters like the condition of the soil in which the plants are grown, temperature and crop production. The selection of fiber plays a vital part in deriving the specific composite properties based on the application. The natural fiber properties are also induced by the location of the plant (Dittenber & GangaRao, 2012). Several researchers worked on different natural fibers extracted from different sources such as flax, hemp, kenaf, snake grass, banana, jute, sisal, coir, bamboo, etc. The natural fibrils constitute cellulose, hemicellulose and lignin in varying percentages. In addition, the natural fibers do have other substances like pectin, wax, and other water-soluble compositions. The cellulose is enclosed in the soft lignin, while the hemicellulose forms the ancillary layer of the fiber material (Sathish, Prabhu, et al., 2021). The tensile properties are enhanced in the bottom part of the tree fiber due to their chemical composition particularly cellulose, hemicellulose, and lignin. Moisture absorption of the natural composite is increased when increasing the fiber content because of its improved cellulose amount (George, Sreekala, & Thomas, 2001). The natural fibers extracted from plant sources offer numerous benefits such as low density, better mechanical and thermal characteristics and also the fibers can be extracted by simple processing techniques (Prabhu et al., 2021; Sathish, Karthi, et al., 2021). Out of the natural fibers extracted from different sources plant-based fibers are finding a prominent replacement for artificial fibrils in polymer matrix owing to the strength and stiffness nature of the lignocellulose fibers. The natural fibers have a high amount of hydrophilic properties which leads to poor adhesion properties between the hydrophilic fiber and hydrophobic matrix (Vijay et al., 2019). Hydrophilic means having a strong affinity for moisture. The major disadvantage of natural fiber is poor adhesion between fiber and matrix, presence of cellulose content, moisture absorption, voids at interface between fiber and matrix that resulting dimensional inaccuracy and thus affect the mechanical properties (Gowda et al., 2018; Karthi et al., 2020; Manimaran, Senthamaraikannan, Murugananthan, & Sanjay, 2018). The reinforced materials are used as natural plant fibers because of their low cost, easy availability, biodegradability, renewable and good strength, and also it is a better alternate for artificial fibers. The biodegradability of natural fibers is associated with physical, chemical, mechanical, and thermal and moisture conditions which have increased its scope for use in numerous applications ( Jawaid & Abdul Khalil, 2011). The cellulose-based natural fibers (e.g., flax, hemp, kenaf, jute, and ramie) are good in mechanical properties and are used as reinforced materials for various applications. Generally, the natural plant fiber properties mostly depend on chemical composition and formation and are also related to fiber variety as well as growing conditions, the fiber extraction process, harvesting sessions and chemical treatment methods (Pickering, Efendy, & Le, 2016). Ishak, Sapuan, Leman, Rahman, and Anwar (2012) studied the tensile properties of sugar palm fiber obtained from a different height of the palm plant. The tensile properties are enhanced in the bottom part of the tree fiber due to their chemical composition particularly cellulose, hemicellulose, and lignin. This incompatibility can be

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overcome by means of three methods; using a coupling agent between the fibers and the polymers, enhancing the natural fiber properties prior to fabricating the composites, and carefully selecting the proper method for the composite production (Madhu et al., 2020). Pretreatments are used to remove noncellulosic elements such as lignin, hemicelluloses, pectin, oil, waxes, and fats of natural fiber to enhance their adhesion with a polymer matrix (Karthi, Kumaresan, Rajeshkumar, Gokulkumar, & Sathish, 2021; Prabhu et al., 2020; Sathish, Kumaresan, Prabhu, & Vigneshkumar, 2017). Natural fiber surface modification is obtained by following chemical treatments. These chemical treatments are namely alkalization (mercerization), acetylation, cyanoethylation, silanization, isocyanates treatment, benzoylation, esterification, graft copolymerization, and etherification. The chemical treatment creates a bond between the fiber and matrix, which allows them to react to each other at the interface (Jagadeesh, Puttegowda, Mavinkere Rangappa, & Siengchin, 2021). From the literature studies, the alkaline treatment effectively modified the surface of the fiber, and thereby an improvement of mechanical properties. Analyzing and governing the fiber/ matrix interactions and their impact on mechanical properties of the composites were addressed in this chapter. The effect of various chemical treatments used to enhance the fiber/matrix at the interphase is also described in this chapter. The significance of the alkaline treatment (5% NaOH) on natural fiber surface to enhance the fiber/matrix interactions is discussed.

6.2

Effect of chemical treatment on cellulose fiber-reinforced composites

The structure and chemical composition of fibers depends upon the climatic conditions, degradation process, and the life of fibers. Water is the primary constituent of all the fibers. Though there are some other sugar-based polymers, like cellulose and hemicelluloses, along with the little number of extractives in fibers like protein, starch, inorganics, etc. These chemical constituents are widely spread along the cell walls of the fibers; present in primary and secondary wall layers. Different plants have different chemical compositions, which further vary for different parts of the plant cells (Bharath et al., 2020). Fig. 6.1 shows the chemical constitution of cellulosic fiber. Natural fibers contain a highly polarized hydroxyl group, which makes them hydrophilic in nature and it reduces their compatibility with hydrophobic Cellulose

Hemicellulose

Lignin

Fig. 6.1 Constitution of cellulosic fiber.

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thermoplastics. Due to improper wetting of natural fibers with polymer matrix, the interfacial bond in NFRCs becomes weak, thus leading to poor mechanical properties (Gassan, 2012). The external surface of natural fibers is of great significance meanwhile reactive functional groups present at their surface are likely to interact with the polymer matrix to form hydrogen or covalent bonds that could considerably improve the fiber/matrix interactions at the interphase. The mechanical properties of NFRCs are extremely dependent on the fiber and matrix interactions which produce composites with better strength and stiffness but increase their brittleness, low toughness, and sensitivity to impact. Fig. 6.2 shows fiber/matrix interphase in a composite laminate. The fiber-polymer interaction can be improved by subjecting natural fibers to chemical treatment and using compatibilizers (Verma et al., 2020). In an attempt to improve fiber-matrix adhesion in NFRCs, the natural fibers are first pretreated to remove impurities from their surface, improve their surface roughness, and reduce their moisture absorption behavior (Sumrith, Techawinyutham, Sanjay, Dangtungee, & Siengchin, 2020). The interfacial strength of the NFRC has mostly impacted their mechanical properties and the role of fiber/matrix interaction on their structural integrity is now commonly accepted. Strengthening the quality of the fiber/matrix interface could be achieved by adopting appropriate chemical treatments and coupling agents that would promote fiber interlocking to the polymer matrix without abating fiber properties. Fig. 6.3 presents different types of natural fiber surface treatments. Alfa fibers were kept under the various fiber surface treatments involving acetylating and it confirmed that the treatment enhanced the resistance of fiber to moisture (Bessadok, Roudesli, Marais, Follain, & Lebrun, 2009). Flexural, impact, and tensile properties improved in treated fiber polyester composites (Nam, Ogihara, Tung, & Kobayashi, 2011). Joseph, Thomas, and Pavithran (1996) studied the benzoyl chloride treatment on sisal fiber and found higher thermal stability compared to raw fiber

Bulk matrix

Mechanical Chemical, Thermal environment

Modified matrix

Interphase zone Coupling agent Physico-chemical reactivity Bulk fibre

Fig. 6.2 Fiber/matrix interphase in a composite laminate.

Topography

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Fig. 6.3 Classification of natural fiber surface treatments.

composites. The treatment removes the hemicellulose and fatty substance in fiber surfaces for better mechanical and thermal properties. Li et al. (Li, Hu, & Yu, 2008) analyzed the strength of the properties of the mechanical behavior of various composite materials. The authors found that the bonding relationship between natural fibers and polymer fibers was good for manufacturing the materials for industrial needs. The oxidation behavior of both materials was analyzed by improving the strong bond between them in order to improve the behavior of the natural fibers to industrial standards. Shanmugam, Thiruchitrambalam, and Thirumurugan (2015) concluded that the dry sliding wear behavior of palmyra palm leaf fiber polyester composite by Pin on disk apparatus. The coefficient of friction and wear loss value was reduced in alkaline treated fibers when compared with untreated. The alkaline treatment is one of the effective pretreatments of natural fibers when used to reinforce with polymer matrices. This pretreatment gives a positive effect on the mechanical properties of composites. Marcovich and Villar (2003) has investigated the effect of NaOH, and Maleic anhydride treated wood flour composite on flexural, compressive strength, and dynamic mechanical behavior. It is found that there is no improvement in the mechanical properties when treated with NaOH. However, maleic anhydride-treated wood flour composites improve the dispersion of filler and also enhance the mechanical properties of the composite. Table 6.1 presents the effect of chemical treatment on various natural fibers.

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Cellulose Fibre Reinforced Composites

Table 6.1 Effect of chemical treatment on natural fibers. Type of chemical treatment

Effects

Alkaline treatment

Better fiber characteristics

Alkaline treatment

3

Sisal, hemp, and jute Bagasse, alfa, and coir Prosopis juliflora

4

Napier grass fiber

Alkaline treatment

5

Coir fiber

Alkaline treatment

6

Sansevieria leaves

Alkaline treatment

7

Jute fiber

5% alkali treatment

8

EFB fiber

2% NaOH treatment

9

Hildegardia fiber

Alkaline treatment

10

Alfa fiber

Alkaline treatment

11

Borassus fiber

5% NaOH treatment

12

Luffa fiber

Alkaline treatment

13

Coir and palm fiber

14

PALF

Treatment with salt of benzene diazonium Isocyanate, peroxide, and silane treatment

15 16

Bamboo mat Raw borassus fiber

Silane treatment 5% NaOH treatment

17

Kenaf fiber

7% NaOH treatment

Improved fiber characteristics Enhanced thermal, physical and chemical characteristics Improved physical, chemical, thermal and mechanical characteristics No significant change in tensile strength Improved mechanical and thermal properties Minimum changes in characteristics Improved fiber characteristics Improved thermal, physical, mechanical, and chemical properties Improved mechanical properties Enhancement in tensile property Change in fiber structure reduced the amorphous component Improved mechanical properties Improvised interfacial bonding between fiber and matrix Reduced tensile property Improved mechanical property Better mechanical properties

Sl. no.

Fibers used

1 2

5% NaOH treatment

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Table 6.1 Continued Type of chemical treatment

Sl. no.

Fibers used

18

Roystonea regia fiber

5% NaOH treatment

19

Woven bamboo mat

20

Continuous Agave fiber

Benzoyl chloride, preimpregnation, and maleic anhydride treatment 5% NaOH treatment

21

Sisal fiber

Alkaline treatment

22

Palm leaf fiber

Benzoyl treatment

23

Kenaf fiber

Alkaline treatment

24

Alfa fiber

Alkaline treatment

25

Kenaf fiber

6% NaOH treatment

26

Tamarind fiber

27

Coconut fiber

Silane and alkaline treatment Alkaline treatment

28

Avicel, alfa pulps, and pine fibers

30

Kenaf fiber

31

Coir fiber

Methacryloxy propyl trimethoxy (MPS), mercaptopurine trimethoxy (MRPS), and hexadecyltrimethoxysilanes (HDS) treatments Alkaline treatment

Ethylene dimethylacrylate treatment

Effects Improved physical, electrical and nonconductor properties Reduced water absorption and improved mechanical property Reduced water absorption and improved mechanical property Improved impact, tensile and compressive properties Improved thermal and mechanical property and reduced water absorption characteristics Reduction in mechanical properties with increase in NaOH concentration Increased mechanical and thermal properties Increased flexural properties Improved mechanical properties Improved mechanical properties Improvement in mechanical properties

Removes impurities and improved mechanical properties Enhanced physicomechanical properties Continued

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Cellulose Fibre Reinforced Composites

Table 6.1 Continued Type of chemical treatment

Sl. no.

Fibers used

32

Flax, kenaf, abaca, and sisal fibers

3% NaOH treatment

33 34

Americana fiber Coir fiber

Alkaline treatment Alkaline treatment

35 36

Sisal fiber Flax fiber

37

Short henequen fiber

Alkaline treatment Melamine formaldehyde Alkaline treatment and silane treatment

38

Fique fiber

39 40

Hildegardia populifolia fiber Curaua fiber

41

Hemp fiber

Alkaline treatment

42

Jute fiber

Alkaline treatment

43

Short hemp fiber

5% NaOH treatment

44

Banana fiber

Alkaline treatment

45

Bagasse fiber

Acetyl treatment

46

Flax fiber

Maleic anhydride, acetic anhydride, silane, and styrene treatments

Alkalization, formaldehyde, glycidyl methacrylate, and isocyanate treatment Alkaline treatment Alkaline treatment

Effects Excess treatment of natural fibers could have a negative effect Improved tensile property Increase in mechanical property Improved tensile property Increases the compressive strength Increase in tensile strength Increase in flexural strength Enhancement in mechanical properties

Improved mechanical properties Increase in fracture strain and other mechanical properties Improved flexural properties Improvement in strength and stiffness Improvements in tensile strength, Young’s modulus, fiber separation, crystallinity index, lignin reduction and thermal stability Increased tensile strength and modulus Dissolved the hemicellulose Reduction of water uptake and improved mechanical properties

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Table 6.1 Continued Type of chemical treatment

Sl. no.

Fibers used

47 48

Roselle and sisal fiber Palm and coir fiber

49

Sisal fiber

Benzene diazonium salt treatment Admicellar treatment

50

Jute fiber

Alkaline treatment

10% NaOH treatment

Effects Improved tensile and flexural strength Increases compatibility Increases tensile, flexural properties, impact strength and hardness Improved tensile and flexural properties

Albano (Ichazo, Albano, Gonza´lez, Perera, & Candal, 2001) has studied the tensile, impact strength, and morphology of wood flour-reinforced polypropylene (PP) and sisal-reinforced polypropylene. They have studied the addition of a coupling agent and chemical treatment with NaOH for wood fillers and sisal fiber. They have observed that Young’s modulus of the wood flour composites is 41.89% higher than that of sisal-reinforced polypropylene composites. From the results, they have concluded that the tensile and impact strength of the treated composites have produced better results than the untreated composites, due to better bonding between filler and matrix. Sri Aprilia et al. (2018) has experimented with tensile, flexural, and morphology of the carbonized jatropha seed shell reinforced vinyl ester composites. They have studied the environmental durability of the composite by soaking them in 5% NaOH, 5% HCL solution, and distilled water for 12 months. After that, the weight gain and mechanical properties of the composites are evaluated. The study has revealed that the tensile and flexural strength is maximum for the composites treated with the alkaline solution. From the morphological study, it is understood that the original luster is lost after soaking in three different environments. Fig. 6.4 shows the alkaline treatment procedure. Alkali (NaOH) treatment is an important technique for improving the mechanical and physical properties of cellulose-based fiber composites (Gomes, Gomes, & Von Zuben, 2009). The NaOH-treated coconut fibers confirmed the enhanced mechanical properties and were capable of removal of the hemicellulose, wax, and oil content effectively (Brı´gida, Calado, Gonc¸alves, & Coelho, 2010). Improvement is found in the interfacial bonding between the fiber and matrix due to the chemical treatments of fibers which reduce the hydrophilicity, fiber surface cleanness, reduce the moisture absorption process, and improve the surface roughness (Edeerozey, Akil, Azhar, & Ariffin, 2007). Arthanarieswaran, Kumaravel, and Saravanakumar (2015) investigated the tensile, flexural, impact, and thermal properties of composites by reinforcing Acacia leucophloea fiber into an epoxy resin. The treated 5% NaOH and untreated fiber composites are prepared by hand layup technique by varying fiber content from 5 to 25 wt%. The 20 wt%-treated fiber loading composites exhibited better mechanical

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Cellulose Fibre Reinforced Composites

Collection of Raw Fibers

Flax Fiber

Bamboo Fiber

Flax Seed

Bamboo plant

Water Treatment of Fibers

Fibers are initially washed with the normal running water in-order to remove dirt in it

Chemical Pre-treatment of Fibers

Fiber– OH- + Na+OH-

Preparation of NaOH Solution

Fiber – O – Na+ + H2O

Fibers Soaked in NaOH Solutions

Heat Treatment for drying of water in fiber layers

After & Before Chemical Treatment

Before Chemical Treatment

After Chemical Treatment

Fig. 6.4 Alkaline treatment procedure.

Some cell structures disrupted as NaOH dissolves lignin in cell walls but still significant amount of intact cell wall structure

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properties. In thermogravimetric analysis, the residual mass of raw fiber composite was superior to the treated composite. The degradation temperature of raw fiber composite was relatively lower compared to treated fiber composite. In common, the mechanical properties of the most natural plant-based fiber composites increased with increasing the quantity of fiber into the polymer matrix. The fiber length, fiber orientation, and fiber loading on the mechanical properties of short sisal fiber-reinforced polypropylene composites were examined by Joseph, Joseph, and Thomas (1999). Preet Singh, Dhawan, Singh, and Jangid (2017) conducted an investigation on banana, jute, and sisal fibers-reinforced composites as a function of chemical treatment. The considerable improvement in tensile, flexural, and impact strength was observed with a suitable selection of surface treatment methods. Idicula, Joseph, and Thomas (2010) showed that the natural fibers-reinforced composites exhibited better adhesion with fiber and matrix, which gives the fibers better damping. Elkhaoulani, Arrakhiz, Benmoussa, Bouhfid, and Qaiss (2013) treated Moroccan hemp using an alkaline solution in an attempt to remove wax and noncellulose matters from the fiber. They used styrene and epoxy resin as matrices to create a binary composite material. A coupling agent maleic anhydride was used in order to make a ternary composite. Comparison of its mechanical properties revealed that the binary composite containing 25 wt% of hemp gained Young’s modulus of 50%. However, the ternary composite containing just 20 wt% of hemp showed Young’s modulus of 74%. Its tensile strength curve was noted to show stable results after adding the anhydride as the coupling agent. Kumar Sinha, Narang, and Bhattacharya (2017) produced bidirectional abaca fiber reinforcement and epoxy resin matrix composite material using the hand layup method. The 5 wt% of abaca fibers was treated using NaOH solution in an attempt to increase its wettability in an epoxy resin matrix. They tried to characterize the composite material that had varying stacking sequences such as single, double, triple, and five layers. From the study, it was deduced that the addition of five layers of abaca fiber resulted in improving the tensile strength. The impact of fiber orientation on tensile and impact strength of 5% NaOH-treated sisal/epoxy composites were investigated by Kumaresan, Sathish, and Karthi (2015). Composites with different orientations of sisal fiber such as 0°/90°, 90°, and 45° were produced by using compression molding techniques. The results showed that the orientation 90° displayed the maximum mechanical properties compared to the other two. Huda et al. (Huda, Drzal, Mohanty, & Misra, 2008) conducted a study and revealed that treatment of kenaf fibers using poly lactic acid (PLA) resulted in enhancing the properties of the fibers and also improving the surface bonding with epoxy resin. This increased the mechanical properties of the resulting composite. Sreenivasan, Ravindran, Manikandan, and Narayanasamy (2012) investigated the influence of various chemical treatments such as alkali, benzoyl peroxide, potassium permanganate, and stearic acid on mechanical properties of composite was examined. The results reported that potassium permanganate increased in tensile strength, modulus, and flexural strength, modulus by 87.3%, 11.9%, 79.9%, 37.5%, and 147.7%, respectively, among treated composites. Alkaline-treated fibers increased the tensile strength, flexural strength, tensile modulus, and flexural modulus by 8.7%, 22.3%, 0.3%, and 1.1% respectively. Stearic acidtreated fibers were increased by 11.2%, 63.1%, 0.1%, and 25%, respectively. Benzoyl

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Cellulose Fibre Reinforced Composites

peroxide-treated fibers were increased by 13.8%, 51.9%, 0.7%, and 23.8%, respectively. Arrakhiz et al. (2012) used alkali-treated, crushed fiber nonoven mats to prepare coir fiber polyethylene composite by using heated two roll mixing followed by hot press mold method. Chemically treated with NaOH, silane, and dodecane bromide treatment of coir/polyethylene composite were examined. The results indicated that silane-treated composite with 20% fiber weight content had an increase in tensile strength by 16% among treated composites. Moreover, dodecane bromide treatment had a better tensile modulus by 24% among treated composite. Sreekala, Kumaran, Joseph, Jacob, and Thomas (2000) investigated the influence of chemical treatments such as mercerization, acrylonitrile grafting, acrylation, latex coating, permanganate treatment, acetylation, silanization, and peroxide on chopped strands oil palm fiber phenol-formaldehyde-reinforced composite that was manufacturing using closed and hot press molding method. Among treated fibers, latex coating on fiber was observed higher impact resistance but decreased in tensile strength, modulus, flexural strength, and modulus by 64.9%, 52.2%, 67.3%, and 77%. Similarly, tensile strength, modulus, flexural strength, and modulus of acetylation of oil palm/phenol formaldehyde decreased by 48.6%, 52.2%, 67.3%, and 77%, respectively. Furthermore, tensile strength, tensile modulus, flexural strength, and flexural modulus of silanized oil palm was decreased by 59.5%, 39.1%, 53.1%, and 60.7%, respectively. Similarly, acrylation of oil palm of tensile strength, modulus, flexural strength, and modulus was decreased by 51.4%, 47.8%, 40.8%, and 41%, respectively. Similarly, acrylonitrile grafting of oil palm of tensile strength, modulus, flexural strength, and modulus was decreased by 29.7%, 30.4%, 6.1%, and 18%, respectively. Furthermore, permanganate treatment shows enhanced tensile strength, modulus, flexural strength, and modulus by 8.1%, 4.3%, 12.2%, and 23%, respectively. Similarly, peroxide treatment on resin increased flexural strength by 10.2%. Mouhoubi, Bourahli, Osmani, and Abdeslam (2016) reported the SEM images of alfa fiber with alkali treatment (5% NaOH) at different time intervals (2, 4, 6, and 24 h). Fig. 6.5 represents the alfa fiber. It shows the fiber treated with 5% NaOH at 2 h. During this time period, the waxy substances in the fiber were removed, and the fiber resulted in low moisture absorption, removal of extractives, and increase in crystallinity and stiffness. Ray, Sarkar, Rana, and Bose (2001) subjected the chopped strands of jute fibers to alkaline treatment with 5% NaOH solution for 0, 2, 4, 6, and 8 h at 30°C and studied their flexural properties. Flexural strength, flexural modulus, and lamina shear strength of alkaline-treated jute/vinyl ester composites were increased by 35%, 23%, and 19%, respectively, at 4-h treatment. They concluded that the tenacity of the fiber increased by 46% after 6 and 8 h treatment and breaking strain was reduced by 23% after 8-h treatment. Salim et al. (2020) studied the water absorption and accelerated weathering behavior of kenaf fiber-reinforced polyester composites. The composite was fabricated by impregnation and compression molding technique using nonwoven kenaf fiber. Accelerated weathering behavior was studied by involving the composite into UV irradiation and two reactions were observed such as postcrosslinking and photo-oxidation process. Postcrosslinking occurred at an earlier stage, and photo-oxidation has occurred after exposure. Further, the authors pointed out the postcrosslinking enhanced the flexural and thermal properties of the

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107

Fig. 6.5 NaOH treated alfa fiber at different time interval (A) raw fiber, (B) 2 h, (C) 4 h, (D) 6 h, and (E) 24 h.

composite, whereas the photo-oxidation did not show any improvement. SEM analysis showed that the degradation was observed due to the photo-oxidation process by observing voids on the composite surface. The water absorption study revealed that all the composites were followed the Fickian behavior. Wet samples significantly lost the flexural strength; however, 79% of flexural strength was regained after drying the samples. The authors concluded that the alkali-treated kenaf fiber-reinforced composite showed an improvement in the mechanical properties even after the durability test. Wu et al. (2020) developed the zinc oxide-blended kenaf fiber composite and evaluated the properties for automotive applications. Composite was fabricated using vacuum-assisted resin transfer molding technique. Results showed that including the 12.4% zinc oxide nanoparticles improved the tensile strength by 38%, flexural strength by 121%, and wear resistance by 76%. Authors pointed out that the fabricated composite using 12.4% zinc oxide and kenaf fiber-reinforced composite consumed less energy (9%) and reduced the environmental burden (33%) compared to the ordinary glass fiber molding compound applicable in automobiles. Further, the authors concluded that the water resistance behavior of the composite was significantly improved after adding 12.4% zinc oxide with the kenaf fiber composite. Dashtizadeh, Khalina, Cardona, and Lee (2019) studied the mechanical properties of short kenaf/cardanol green resin composite. Composite was fabricated by hand layup and compression molding technique and the fiber content was varied as 0, 30, 40, 50, and 60 wt%. The results showed that the tensile strength and impact strength of the composite with 50 wt% kenaf fiber was increased by 92% and 43%,

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Cellulose Fibre Reinforced Composites

respectively, compared to that of cardanol resin. This study confirmed that the kenaf fiber had the potential to transfer high load due to the strong adhesion between the resin and kenaf fiber. However, the flexural strength of the composite was observed as decreasing after fiber loading due to the stress concentration at the end of the composite and the processing temperature was found to be influenced by the flexural strength of the composite. Nimanpure et al. (2019) investigated the mechanical, thermal, and electrical properties of sisal/kenaf/polyester hybrid composite. The weight percentage of reinforcement was varied from 10 to 40 in the polyester resin. They observed that the tensile strength of the hybrid composite was improved by 24% and 18%, flexural strength was improved by 30% and 36%, and the impact strength was increased by 196.3% and 196% for the same amount of fiber loading (40 wt%) compared to that of sisal and kenaf fiber composites. Thermal analysis showed that the thermal stability of the composite was higher than the thermal stability of sisal and kenaf fiber composites. The authors concluded that the developed hybrid composite was a suitable material to replace synthetic and natural fiber composite. Anand, Rajesh, Senthil Kumar, and Saran Raj (2018) studied the performance of treated jute/kenaf/epoxy composites. Surface treatment removed the pectin, cellulose, and hemicelluloses from the surface of the composite. Treated fiber showed better bonding between the resin due to the rougher surface and increase of the effective surface area of the fiber. The authors concluded that the hybrid composite of stacking sequence kenaf-jute-jute-kenaf exhibited superior mechanical properties compared to untreated fiber composites. Majid, Jamal, and Manan (2018) studied the impact performance of kenaf/glass/epoxy hybrid composite. Composite was fabricated by vacuum-assisted resin method and the impact test was performed at three different types of energy levels 3, 6, and 9 J. The results showed that the impact peak and displacement level were increased as the energy levels increased. The authors concluded that severe damage of hybrid composite was observed at 3 J energy level and the fracture failure mode followed the circular and bi-axial cracking mechanism. Hashim et al. (2017) investigated the influence of alkali treatment on the physical properties of the kenaf fiber. The kenaf fiber was involved in various alkali treatments. The concentration of alkali solution was maintained as 2%, 6%, and 10%, immersion time was maintained as 30, 240, and 480 min, and the immersion temperature was maintained as 27, 60, and 100-degree centigrade. The authors reported that the diameter of the kenaf fiber showed a decrement value when increasing the alkalization parameter value compared to the untreated kenaf fiber. Husin et al. (2017) studied the flexural properties of treated and untreated kenaf/PP composites. The authors studied the effect of 10 and 20 wt% treated and untreated kenaf fiber on the flexural properties of polypropylene composites. Further, the fibers were treated with 5% and 10% sodium hydroxide (NaOH) solution. Composite was fabricated by melt blending and injection molding technique. The results showed that the 20 wt% treated kenaf fiber showed better flexural strength. SEM analysis showed that 5% NaOH treatment on 20 wt% kenaf fiber polypropylene composite displayed better adhesion between the kenaf fiber and PP matrix. The authors concluded that the composite containing 20 wt% treated kenaf fiber by 5% NaOH solution displayed the maximum flexural strength of 30.25 MPa. Ariawan, Mohd Ishak, Salim, Mat Taib, and Ahmad Thirmizir

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(2017) studied the interfacial strength of NaOH treated kenaf/polyester composites by resin transfer molding. Kenaf fiber was treated with 6% NaOH solution for 1–5 h to improve the interfacial bonding. The authors reported that the atomic force microscopy showed an increase in the contact area of kenaf fiber and polyester. The results showed that 3 h of alkali-treated kenaf fiber displayed better interfacial characteristics. Xia, Shi, Wu, and Cai (2016) attempted to enhance the property of the composite reinforced with kenaf fiber and impregnated with aluminum hydroxide. Composite was fabricated using vacuum-assisted resin transfer molding. Kenaf fiber was involved in alkali treatment. They observed that the tensile strength of the kenaf fiber was observed as 810 MPa and the tensile modulus was observed as 13.5 GPa. Results showed that the inclusion of 2.2% aluminum hydroxide improved the modulus of elasticity, modulus of rupture, tensile modulus, and tensile strength of a composite by 67%, 56%, 33%, and 36%, respectively, compared to that of composite made with untreated fiber. The water absorption study showed that the aluminum hydroxide impregnation reduced the water absorption of composite from 20% to 6%. The authors concluded that the fabricated composite could be a better alternative choice to replace the glass fiber composites in automotive applications. Akhtar et al. (2016) investigated the NaOH treatment and fiber loading on the physical properties of kenaf/PP composites. Composites of treated and untreated kenaf fiber were prepared with the injection molding technique. Fiber loading was varied from 10 to 50 wt% in the composites. They noticed that the alkali treatment of kenaf fiber displayed enhancement in physical, mechanical, and morphological properties of the composites. Tensile strength and flexural strength depended on the fiber loading and fiber treatment process. Composite fabricated with polypropylene and 40 wt% kenaf fiber showed better mechanical properties. However, the composite with 50 wt% kenaf fiber showed a decrement in mechanical properties due to the improper mixing of the fiber and matrix. Further, it was observed that the burning of composite happened when the fiber loading exceeded 50 wt%. The authors concluded that the fabricated composites could be used in automotive applications, sports and construction applications. Krishna and Kanny (2016) studied the effect of surface treatment of kenaf fiber using the green approach and the epoxy reinforced composites. Kenaf fiber was treated with two amino acids such as glutamic acid (acid) and lysine (base). TGA study showed that treated fiber composite exhibited more mass loss than the untreated composites. The tensile study showed that enhancement in the mechanical properties of treated fiber composite was observed than the untreated fiber composite. The dynamic mechanical analysis resulted that the storage modulus, loss modulus, and tan δ of the treated fiber composite showed improvement compared to untreated fiber composite. The authors concluded that the lysine treatment showed better results than the glutamic treatment.

6.3

Conclusion

Natural fiber and thermoset/thermoplastic matrix communications at the interphase is one very significant property that is of great concern to all polymer scientists involved in polymer composites. The interactions between natural fiber and matrix are mainly

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Cellulose Fibre Reinforced Composites

directed by the chemical coupling reagent and pretreatment process. The alkaline treatment method was effectively removed noncellulosic elements from the natural fibers resulting in higher mechanical properties due to strong adhesion between fiber and matrix. Sodium hydroxide reagent (NaOH) was also effectively removed weakly bonded intercellular components and increased fiber surface roughness.

References Akhtar, M. N., Sulong, A. B., Radzi, M. K. F., Ismail, N. F., Raza, M. R., Muhamad, N., et al. (2016). Influence of alkaline treatment and fiber loading on the physical and mechanical properties of kenaf/polypropylene composites for variety of applications. Progress in Natural Science: Materials International, 26(6), 657–664. https://doi.org/10.1016/j. pnsc.2016.12.004. Anand, P., Rajesh, D., Senthil Kumar, M., & Saran Raj, I. (2018). Investigations on the performances of treated jute/Kenaf hybrid natural fiber reinforced epoxy composite. Journal of Polymer Research, 25(4). https://doi.org/10.1007/s10965-018-1494-6. Ariawan, D., Mohd Ishak, Z. A., Salim, M. S., Mat Taib, R., & Ahmad Thirmizir, M. Z. (2017). Wettability and interfacial characterization of alkaline treated kenaf fiber-unsaturated polyester composites fabricated by resin transfer molding. Polymer Composites, 38(3), 507–515. https://doi.org/10.1002/pc.23609. Arrakhiz, F. Z., El Achaby, M., Kakou, A. C., Vaudreuil, S., Benmoussa, K., Bouhfid, R., et al. (2012). Mechanical properties of high density polyethylene reinforced with chemically modified coir fibers: Impact of chemical treatments. Materials and Design, 37, 379– 383. https://doi.org/10.1016/j.matdes.2012.01.020. Arthanarieswaran, V. P., Kumaravel, A., & Saravanakumar, S. S. (2015). Characterization of new natural cellulosic fiber from Acacia leucophloea Bark. International Journal of Polymer Analysis and Characterization, 20(4), 367–376. https://doi.org/10.1080/ 1023666X.2015.1018737. Bessadok, A., Roudesli, S., Marais, S., Follain, N., & Lebrun, L. (2009). Alfa fibres for unsaturated polyester composites reinforcement: Effects of chemical treatments on mechanical and permeation properties. Composites Part A: Applied Science and Manufacturing, 40(2), 184–195. https://doi.org/10.1016/j.compositesa.2008.10.018. Bharath, K. N., Madhu, P., Gowda, T. G. Y., Sanjay, M. R., Kushvaha, V., & Siengchin, S. (2020). Alkaline effect on characterization of discarded waste of Moringa oleifera fiber as a potential eco-friendly reinforcement for biocomposites. Journal of Polymers and the Environment, 28(11), 2823–2836. https://doi.org/10.1007/s10924-020-01818-4. Brı´gida, A. I. S., Calado, V. M. A., Gonc¸alves, L. R. B., & Coelho, M. A. Z. (2010). Effect of chemical treatments on properties of green coconut fiber. Carbohydrate Polymers, 79(4), 832–838. https://doi.org/10.1016/j.carbpol.2009.10.005. Dashtizadeh, Z., Khalina, A., Cardona, F., & Lee, C. H. (2019). Mechanical characteristics of green composites of short kenaf bast fiber reinforced in cardanol. Advances in Materials Science and Engineering. Dittenber, D. B., & GangaRao, H. V. S. (2012). Critical review of recent publications on use of natural composites in infrastructure. Composites Part A: Applied Science and Manufacturing, 43(8), 1419–1429. https://doi.org/10.1016/j.compositesa.2011.11.019. Edeerozey, A. M. M., Akil, H. M., Azhar, A. B., & Ariffin, M. I. Z. (2007). Chemical modification of kenaf fibers. Materials Letters, 61(10), 2023–2025. https://doi.org/10.1016/j. matlet.2006.08.006.

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Prabhu, L., Krishnaraj, V., Sathish, S., Gokulkumar, S., Karthi, N., Rajeshkumar, L., et al. (2021). A review on natural fiber reinforced hybrid composites: Chemical treatments, manufacturing methods and potential applications. Materials Today: Proceedings, 45, 8080–8085. Elsevier Ltd https://doi.org/10.1016/j.matpr.2021.01.280. Prabhu, L., Krishnaraj, V., Sathish, S., Gokulkumar, S., Sanjay, M. R., & Siengchin, S. (2020). Mechanical and acoustic properties of alkali-treated Sansevieria ehrenbergii/Camellia sinensis fiber–reinforced hybrid epoxy composites: Incorporation of glass fiber hybridization. Applied Composite Materials, 27(6), 915–933. https://doi.org/10.1007/s10443-020-09840-4. Preet Singh, J. I., Dhawan, V., Singh, S., & Jangid, K. (2017). Study of effect of surface treatment on mechanical properties of natural fiber reinforced composites. Materials Today: Proceedings, 4(2), 2793–2799. https://doi.org/10.1016/j.matpr.2017.02.158. Ray, D., Sarkar, B. K., Rana, A. K., & Bose, N. R. (2001). Effect of alkali treated jute fibres on composite properties. Bulletin of Materials Science, 24(2), 129–135. https://doi.org/ 10.1007/BF02710089. Salim, M. S., Ariawan, D., Ahmad Rasyid, M. F., Mat Taib, R., Ahmad Thirmizir, M. Z., & Mohd Ishak, Z. A. (2020). Accelerated weathering and water absorption behavior of kenaf fiber reinforced acrylic based polyester composites. Frontiers in Materials, 7. https://doi. org/10.3389/fmats.2020.00026. Sanjay, M. R., Madhu, P., Jawaid, M., Senthamaraikannan, P., Senthil, S., & Pradeep, S. (2018). Characterization and properties of natural fiber polymer composites: A comprehensive review. Journal of Cleaner Production, 172, 566–581. https://doi.org/10.1016/j. jclepro.2017.10.101. Sanjay, M. R., Siengchin, S., Parameswaranpillai, J., Jawaid, M., Pruncu, C. I., & Khan, A. (2019). A comprehensive review of techniques for natural fibers as reinforcement in composites: Preparation, processing and characterization. Carbohydrate Polymers, 207, 108–121. https://doi.org/10.1016/j.carbpol.2018.11.083. Sathish, S., Karthi, N., Prabhu, L., Gokulkumar, S., Balaji, D., Vigneshkumar, N., et al. (2021). A review of natural fiber composites: Extraction methods, chemical treatments and applications. Materials Today: Proceedings, 45, 8017–8023. Elsevier Ltd https:// doi.org/10.1016/j.matpr.2020.12.1105. Sathish, S., Kumaresan, K., Prabhu, L., & Vigneshkumar, N. (2017). Experimental investigation on volume fraction of mechanical and physical properties of flax and bamboo fibers reinforced hybrid epoxy composites. Polymers and Polymer Composites, 25(3), 229– 236. https://doi.org/10.1177/096739111702500309. Sathish, S., Prabhu, L., Gokulkumar, S., Karthi, N., Balaji, D., & Vigneshkumar, N. (2021). Extraction, treatment and applications of natural fibers for bio-composites—A critical review. International Polymer Processing, 36(2), 114–130. https://doi.org/10.1515/ipp2020-4004. Shanmugam, D., Thiruchitrambalam, M., & Thirumurugan, R. (2015). Wear behavior of Palmyra palm leaf stalk fiber (PPLSF) reinforced polyester composites. Composite Interfaces, 23(2), 89–103. https://doi.org/10.1080/09276440.2016.1102558. Sreekala, M. S., Kumaran, M. G., Joseph, S., Jacob, M., & Thomas, S. (2000). Oil palm fibre reinforced phenol formaldehyde composites: Influence of fibre surface modifications on the mechanical performance. Applied Composite Materials, 7(5–6), 295–329. https:// doi.org/10.1023/A:1026534006291. Sreenivasan, V. S., Ravindran, D., Manikandan, V., & Narayanasamy, R. (2012). Influence of fibre treatments on mechanical properties of short Sansevieria cylindrica/polyester composites. Materials and Design, 37, 111–121. https://doi.org/10.1016/j.matdes.2012. 01.004.

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Characterization of fiber surface treatment by Fourier transform infrared (FTIR) and Raman spectroscopy

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Karthikeyan Ramalingama, Senthil Muthu Kumar Thiagamania, Thirugnanasambandan Theivasanthib, Muthukumar Chandrasekarc, Carlo Santullid, Krishnasamy Senthilkumare, and Suchart Siengchine a Department of Automobile Engineering, Kalasalingam Academy of Research and Education, Krishnankoil, Tamil Nadu, India, bInternational Research Centre, Kalasalingam Academy of Research and Education, Krishnankoil, Tamil Nadu, India, cSchool of Aeronautical Sciences, Hindustan Institute of Technology & Science, Padur, Kelambakkam, Chennai, Tamil Nadu, India, dSchool of Science and Technology, Geology Division (SST), University of Camerino, Camerino, Italy, eDepartment of Materials and Production Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand

7.1

Introduction

Owing to the serious concerns over the environmental pollution, the use of petroleumbased synthetic fibers has been replaced by naturally available lignocellulosic fibers (Thiagamani et al., 2019). The use of natural fibers not only reduces the dependence on the synthetic fibers but also provides economic benefits for the consumers (Chandrasekar et al., 2019). The natural fibers are significantly used in composites owing to their less weight, abundantly available, and cheap cost. On the other hand, their functional properties cannot be matched with that of their synthetic counterpart. This may be due to their hygroscopic nature, poor wettability, and thermal stability (Krishnasamy, Thiagamani, et al., 2019). In order to overcome these issues, the fibers can be chemically modified by treatment methods. The chemical treatment techniques can reduce the hydrophilic nature of the fibers and also roughens the fiber surface by the removal of hemicellulose components. This could lead to better interfacial bonding between the fiber and polymer matrix and thereby resulting in enhanced performance (Krishnasamy, Muthukumar, et al., 2019). The natural fibers consist of lignocellulosic structures, waxy substances, and microfibrillar cellulose. The interaction of these components with the polymers is to be analyzed to get improved mechanical properties. The interaction can be understood from the characterization of the fiber by different techniques.

Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00020-3 Copyright © 2023 Elsevier Ltd. All rights reserved.

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Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy (RS) are the commonly used methods to analyze the constituents of a material based on the principle of spectroscopy. In RS, incident light from the laser of wavelength from 229 to 1064 nm is allowed to irradiate the cellulosic fiber surface and the nonelastic scattering of light from the constituents on the surface is obtained as the spectra. The Raman bands (cm 1) reflected from the molecular structure of the hemicellulose, cellulose, lignin, pectin, and moisture enable to determine the compositional changes due to the fiber treatment. In case of the FTIR, the fiber is irradiated with infrared light and certain frequencies are absorbed by the constituents which are reflected in the FTIR spectra as wavenumber (cm 1). There are three modes of operation in this method: (1) Attenuated Total Reflectance (ATR), (2) use of diamond anvil cell with spectrometer, and (3) KBr disk for large specimens with constituents in the powdered form. ATR method involves scanning of the fiber surface without damaging the fiber surface and is limited to the fiber surface, whereas the diamond anvil cell with spectrometer and KBr disk are through the transmission methods where the molecular structural changes in the entire fiber thickness can be measured. However, fiber analysis with diamond anvil cell is a destructive technique in contrast to the ATR method (Kavkler & Demsar, 2012). This chapter deals with the influence of FTIR and RS techniques in the fiber characterization of natural fibers as a result of the chemical modification process.

7.2

Significance of the FTIR and RS in fiber characterization

7.2.1 FTIR spectroscopy (FTIR) FTIR spectroscopy is used to find the chemical composition of many commercial products such as plastics, paints, rubbers, coatings, and adhesives. The molecular vibrations corresponding to the functional groups can be explained based on the quantum mechanics. The frequency of a molecular vibration can be increased by illuminating the material by light energy resulting in the excitation of the bond. FTIR is a nondestructive method that is able to identify the functional groups in materials by the changes in molecular structure. In FTIR, mid-infrared light of wavenumber from 4000 to 400 cm 1 is used to quantify the materials. When the sample is illuminated by infrared light, the sample absorbs some amount of light energy and the remaining amount of energy is transmitted. The FTIR instrument consists of an interferometer that is able to modulate the infrared light. The FTIR spectrum is plotted using wave number verses the intensity of transmitted or reflected light. The spectrum exhibits a peak whenever the molecular dipole moment changes for a particular vibration. Finally, the raw data are converted into the spectrum by the method of Fourier transform.

7.2.2 Raman spectroscopy RS is used to find the vibrational modes of molecules and is now a days mostly employed in the identification of carbon nanomaterials and two-dimensional materials. RS helps to probe the chemical composition of materials without destroying

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the samples. It is more specific to the identification of materials even if they have the same atoms in various arrangements. Raman spectra are recorded using a microscope fitted with a laser of 532 nm and 600 g/mm grating. The polarized laser light is used to get the enhanced signal of the cellulose chains in natural fibers. The power on the sample is 1 mW and the samples are exposed with laser light for 600 s. The calibration of Raman scattering detector is performed by mica plate and to analyze the data, curve fitting is performed. 1610 cm 1 band is assigned for the epoxy resin. A Raman spectrum is plotted using wavelength shift verses intensity of light. In Raman analysis, the sample is excited using the argon-ion laser (514.5 nm) and diode laser (782 nm). The Raman spectra are analyzed from 4000 to 10 cm 1 so that Raman active normal modes of vibration of organic molecules can be found. RS is a nondestructive method and there is no need for sample preparation. In RS, the polarizability of the molecule decreases, whenever there is an increase in electron density, bond strength and decrease in the bond length. FTIR-active molecules show changes in dipole moment, whereas Raman-active molecules show changes in polarizability. Samples with water content do not produce interference in Raman and can be analyzed more effectively. The FT Raman technique is not highly sensitive to hydrogen bonds since the absorption band in the region of 3000–3500 cm 1 has less intensity. The absorption band at 1625 cm 1 which is responsible for the bending motions of water molecules is not present in Raman spectrum. The performance of a composite depends only on the bonding between the filler and the matrix.

7.3

Comparing FTIR and Raman spectra

FTIR spectra are obtained by the variations in the electric dipole moment of the molecule, whereas RS deals with the electric polarizability of the molecule. The samples are illuminated with laser light to obtain the absorption bands. FTIR and RS are complementary in such a way that FTIR bands are related to polar functional groups, whereas Raman bands are related to nonpolar functional groups. The distinct spectroscopic bands are observed in RS to identify the interaction between the matrix and the filler in any composite. An absorption band at 895 cm 1 appears for the matrix and 1095 cm 1 band is for the micromechanical deformation of the fibers. The external strain applied to a natural fiber-reinforced composite causes shift in the position of Raman peaks. The shift is due to the deformation of the reinforcing fiber. The Raman peak at 1095 cm 1 appears to broaden in addition to the shift. This broadening is found to be asymmetric due to a nonuniform distribution of stress in the composite. The stress is transferred from the matrix to the natural fiber. But there is no such asymmetric broadening in the 895 cm 1 peak (Pullawan, Wilkinson, & Eichhorn, 2010). Adebajo, Frost, Kloprogge, and Kokot (2006) investigated the influence of acetylation treatment on the cotton fiber through FTIR and RS as shown in Fig. 7.1A and B. According to them, the changes in composition of the cotton fiber due to the treatment were visible from the distinctive spectra obtained from RS and FTIR at certain frequencies. The intensity band obtained in RS was relatively lower in magnitude than

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0.3

(a)

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0.25 0.2 0.15 Raw

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1234 1369

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Fig. 7.1 Cotton fiber (A) FTIR spectra and (B) Raman spectra (Adebajo et al., 2006) (figure reused with permission). From Adebajo, M. O., Frost, R. L., Kloprogge, J. T., & Kokot, S. (2006). Raman spectroscopic investigation of acetylation of raw cotton. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 64, 448–453.

the absorbance obtained from the FTIR spectra. The RS peak at 1735 cm 1 is attributed to ester bond formed between the acetyl group and hydroxyl group of the fiber. Peak at 1460, 835, and 655 cm 1 correspond to the CH3 symmetric deformation, H3C–C stretching, and O–C O in-plane deformation representing the presence of acetyl functional groups.

7.4

Analysis of fiber surface modification

Cellulose nanofibrils are reinforced with gelatin to achieve enhanced mechanical properties. The interface engineering between gelatin and cellulose nanofibrils are analyzed using FTIR-ATR technique. The FTIR spectrum of the neat gelatin film

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shows peaks at 1649, 1552, and 1242 cm 1 that are assigned to amide-I (C¼O stretching), amide-II (N–H bending), and amide-III (C–N and N–H stretching) of the protein backbone structure, respectively. N–H stretching vibration and C–H stretching vibration appeared at 3306 and 2936 cm 1. The crosslinking of cellulose nanofibrils with gelatin films causes the shift of these peaks to lower wave numbers. The chemical crosslinking is formed through Michael addition or Schiff base reactions and intermolecular hydrogen bonding. The interfacial adhesion of fillers in the matrix is due to multiple interfacial interactions such as covalent bonding, hydrogen bonding, and catechol-metal ion chelation (Li, Jin, Chen, & Li, 2019). The chemical modification on flax yarn is analyzed using FTIR spectra. The FTIR spectrum of untreated flax yarn shows the peaks at 1103, 1060, 1429, 896, and 1731 cm 1 that are associated with glycosidic stretching, C–OH stretching, CH2 bending, out of phase ring stretching, and carbonyl groups, respectively. Chemical treatments like mercerization and alkalization of natural fiber decrease the intensity of the peaks in FTIR spectra. Since hemicellulose is removed in the treated fiber, the peak corresponding to carbonyl groups disappears. The alkalization reduces the polar nature of flax yarn as evidenced from the reduced peak intensity of the peak at 1641 cm 1. When flax yarn is treated with 3-aminopropyltriethoxysilane, a new peak appears at 1558 cm 1 that belongs to the amine group. The intensity of the peak at 1029 cm 1 corresponding to Si–O–Si and Si–O–C peak increases because of silylation. Acetylation of flax yarns exhibits a peak at 1731 cm 1 for acetyl group and the reduction in the intensity of the peaks at 3342 and 1635 cm 1 corresponding to –OH group and absorbed water is observed. Acetylation reduces the hydrophilicity of natural fibers (Rajan, Joseph, Skrifvars, & Jarvela, 2012). The FT-Raman spectra of curaua´, jute, and sisal fibers possess the absorption bands at 3300 cm 1, 2950 cm 1 for O–H stretching and C–H stretching and peaks in the range of 1800–400 cm 1. This is because of a high cellulose content in these fibers. But Raman spectra of coconut fibers show different profiles due to their low cellulose and high lignin content. The band at 1600 cm 1 is assigned for C]C of aromatics and aliphatic for sisal fiber confirming its low lignin content (Ferreira, Trindade, Frollini, & Kawano, 2004). The natural fibers are treated with silanes and maleic anhydride grafted polypropylene (MAPP). The silane treatment decreases the hydrophilicity of natural fibers, whereas MAPP treatment introduces new bonds in the composite as revealed from FTIR spectrum. There occur more challenges in the compatibility between the polymer matrix and natural fibers because the former is hydrophobic while the latter is hydrophilic in nature. This leads to a poor ability of transfer of stress from the matrix to natural fiber. Surface modification of natural fibers helps to enhance the interface between the matrix and the filler. FTIR analysis is performed to identify the chemical composition of the fillers, matrices, and new bond formation due to the addition of coupling agents. The decrease in hydrophilicity of natural fibers is confirmed by analyzing the band at 3400 cm 1 and the band at 2990 cm 1 corresponding to OH groups on cellulose and characteristic peak of cellulose, respectively. The ratio of the intensity of these two bands decreases as hydrophilicity of natural fibers decreases. The FTIR spectrum of MAPP-treated natural fibers shows new bands that are assigned to carbonyl groups (Shao, He, & Ma, 2016).

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Starch-modified natural rubber is added as a coupling agent to Sorghum fibersnatural rubber composite. An enhancement in the molecular interaction is noticed in FTIR spectrum (Figs. 7.2 and 7.3) from the peak intensity of the functional groups. The peak at 1663 cm 1 is corresponding to carbon double bond for cis-1,4 polyisoprene of natural rubber. The sorghum fibers exhibit the peaks at 1730 and 1040 cm 1 that are responsible for ketone/aldehyde C]O stretch and CdO bond of amorphous cellulose. The FTIR spectrum of the composite after crosslinking possesses CH2 and CH3 peaks at wavenumber range of 2830–2970 cm 1 with more absorbance values and shows a shift toward lower wavenumber. Thus, changes are observed both in the peak intensity and position of the peak. This confirms the molecular interactions between functional groups of the matrix and the filler during the curing process. The interaction between the protein molecules in natural rubber and the carbonyl groups of sorghum fibers is clearly understood from the peak at 1539 cm 1 (Chalid, Husnil, Puspitasari, & Cifriadi, 2020).

1663 cm-1 C=C Blank 1040 cm-1 C–O 1730 cm-1 C=O

Absorbance (a.u.)

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2830-2970 cm-1 CH2 and CH3

1376 cm-1 (δ asym. CH3)

1539 cm-1 (C–N stretching, N–H bending)

Crosslinked NR composite

3800

3300

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1300

800

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Fig. 7.2 FTIR spectra of Sorghum fibers-natural rubber composites (Open Access content, no permission required).

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Fig. 7.3 Split wave number in the FTIR spectra of Sorghum fibers-natural rubber composites (Open Access content, no permission required).

The interface between the natural fiber and polymer can be enhanced by the alkaline treatment of fibers. When rice straw is subjected to alkaline treatment, the intensity of the absorption band at 3334.92 cm 1 assigned for the hydroxyl groups is reduced and the peak at 1741.72 cm 1 disappears. This is because uranic acid which is a constituent of hemicellulose xylan is removed by alkaline treatment of rice straw. The changes in the chemical composition of natural fibers affect relative motion between the rice straw and the matrix ( Jayamani et al., 2016). The sample preparation for FTIR analysis is made by milling the jute fibers in a ceramic pestle, sieved and mixed with KBr. The sample is then pressed to make a film suitable for FTIR testing. The physical and chemical treatments of natural fibers cause changes in the fiber molecular structure that can be visualized in the FTIR spectrum. FTIR spectrum is not only helpful for understanding the interface between the matrix and the filler in a composite but also can be used to determine the crystallinity index. Crystallinity index of a polymer defines the alignment of chains that can be found in XRD, FTIR and Raman analyses. The crystallinity index of jute fiber is calculated by the ratio of the intensities of 1429 and 893 cm 1 peaks in the FTIR spectrum and is found to be 1.01 for jute fiber. The crystallinity index calculated from FTIR gives the information about the organized structure and facility to decompose in natural

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fibers. A low value of crystallinity index makes jute fiber easier to decompose. The water molecules and alcohols present in cellulose, hemicellulose, lignin, and carboxylic acids of natural fiber are identified from the 3400 cm 1 peaks. All the natural fibers have the absorption band at 2900 cm 1 corresponding to the CH2 and CH3 stretching. The bands with wave number ranging from 1370 to 1235 cm 1 are assigned to CH3 bending and C–H stretching of lignin. The absorption bands from 1150 to 1030 cm 1 are associated to C–O–C, O–H, and C–O stretching of celluloses and hemicellulose. A high O–H stretching band at 3400 cm 1 results in water desorption as well as hemicellulose and lignin decomposition. The reactivity of cellulose, hemicellulose, and lignin in jute fiber can be observed by the 2900 cm 1 peak (da Silva et al., 2016). FTIR and Raman analyses give the information about the molecular interactions in natural fiber composites in polyester/Alfa, wool/thermo-binder fibers. The surface of Alfa fiber is modified chemically using wool and PET-PE fibers. The hydrogen bonding between water molecules in Alfa fibers and wool fibers decreases the hydrophilic nature of Alfa fibers. This is confirmed from the amplification of ν-OH vibration intensity at 3329 and 3282 cm 1 and its shift to lower frequencies such as 3326 and 3276 cm 1. The hydrophobic nature is given to the composite from the PET which is shown by the appearance of the molecular vibration at 1710 cm 1. Secondary bonding is formed between the Alfa fibers and the polyester matrix resulting in enhanced compatibility. A high-volume fraction of thermo-binder is explained from vibrations attributed to aromatic ring stretch and σC–O vibration at 1507 and 1410 cm 1, respectively. The out-of-plane σ-OH vibration of Alfa fibers at 660 cm 1 shows a high intensity due to the vibrations of wool fibers or PET-PE fibers. The vibrations corresponding to lignin at 322, 368, 426, and 506 cm 1 is lowered resulting in less hydrophilic nature of Alfa fibers (Triki et al., 2016). Man-made cellulose fibers (MMCFs) are prepared from cellulose solutions via wet or dry-jet wet spinning and added as fillers in epoxy composites. The changes in cellulose chains by mechanical deformation of the composites can be observed by RS. The deformation mechanisms in natural fiber can be demonstrated by the corresponding shift in the absorption band of Raman spectrum. A decrease in the shift of the 1095 cm 1 band (CdOdC bond) is shown for the corresponding increase in fiber loading. The shift of the Raman band confirms the stress transfer through the interface showing a very good fiber-matrix interaction (Bulota et al., 2021). Alfa fibers are modified with wool and thermo-binder fibers to get more compatibility in polyester matrix. Wool and thermo-binder fibers offer adsorption wettability, interdiffusion, and chemical bonding to Alfa fibers. An intimate contact is obtained in the composite with adhesion as a three-dimensional volume process (Omri et al., 2013). The changes in composition of the constituents such as cellulose, hemicellulose, lignin, and pectin in the natural fiber due to fiber treatment with chemical, physical, and biological method can be determined from the FTIR spectra. The characteristics peaks in the FTIR spectra can be associated with the constituents of the natural fiber. According to Fernandes, Mano, and Reis (2013), the characteristics peaks corresponding to lignin (1610 cm 1) displayed lower intensity for the sisal fiber treated with 5 wt% sodium hydroxide (NaOH) for 2 h at room temperature while the carbonyl band between 1660 and 1760 cm 1 completely vanished from the FTIR

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spectra indicating the changes in composition of the fiber due to the NaOH treatment. They also indicated that treated fiber showed reduced hydroxyl groups as the hydroxyl groups in the natural fiber reacted with NaOH. In their research, Senthilkumar et al. indicated that pineapple leaf fiber (PALF) treated with 1 N aqueous solution of NaOH and potassium hydroxide (KOH) for 1 h led to the removal of hemicellulose, lignin, and pectin in the fiber as could be noted from the absence of corresponding characteristic peaks shown in Table 7.1 (Senthilkumar et al., 2019).

Table 7.1 Characteristics peaks of untreated, NaOH-treated and KOH-treated PALF (Senthilkumar et al., 2019) (table re-used with permission). Vibration

Source

Peaks in the FTIR spectra (cm21)

–

–

Untreated

– C–OH out-of-plane bending COC, CCO, and CCH deformation – C–O–C asymmetrical stretching C]O and G ring stretching –CH2 rocking vibration In-the-plane CH bending HCH and OCH in-plane bending C]C aromatic symmetrical stretching C]O stretching – – – C–H symmetrical stretching –CH2 stretching

– Cellulose

OH stretching

518 667

NaOHtreated 422 –

KOHtreated 420 –

Cellulose

896

896

894

– Cellulose

1107 1159

– –

– –

Lignin

1251

–

–

Cellulose Cellulose Cellulose

1321 1379 1429

1327 1373 1425

– 1367 –

Lignin

1508

1508

Pectin and waxes – – – Cellulose and hemicellulose Cellulose and hemicellulose Cellulose and hemicellulose

1739 2144 2337 2364 2893 2941

– – – 2358 2841 and 2883 2945

1504 and 1539 – 2133 – 2360 2887

3332 3591 3743 3836

– – 3799 3900

2941 – – – 3840 and 3871

From Senthilkumar, K., Rajini, N., Saba, N., Chandrasekar, M., Jawaid, M., & Siengchin, S. (2019). Effect of alkali treatment on mechanical and morphological properties of pineapple leaf fibre/polyester composites. Journal of Polymers and the Environment, 1–11.

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Disappearance of the characteristic peaks 1737 and 1248 cm 1 in the FTIR spectra for the pineapple leaf fiber (PALF) due to treatment with the aqueous solution containing 1 M calcium hydroxide (Ca(OH)2) for 1 h were reported in a study (Krishnasamy, Muthukumar, et al., 2019). These characteristic peaks correspond to the hemicellulose and lignin in the natural fiber (Thiagamani, Nagarajan, Jawaid, Anumakonda, & Siengchin, 2017). Diminishing of characteristic peaks related to hemicellulose and lignin due to the Ca(OH)2 were reported for PALF, piassava fibers (Santos et al., 2018), and bagasse fibers (Anggono, Sugondo, Henrico, & Purwaningsih, 2015). The peak at 1736 and 1436 cm 1 which represents the hemicellulose and lignin in the PALF and kenaf was not visible in the FTIR spectra of the fiber treated with 2 wt% aqueous silane solution for 3 h. In addition to the compositional changes, silane-treated fibers displayed characteristic peak at 889 cm 1 in the FTIR spectra which corresponds to the silanol functional group. The presence of silanol groups on the fiber surface was believed to be responsible for improved interaction of the fiber with polymer matrix (Asim, Jawaid, Abdan, & Ishak, 2017). Tserki et al. investigated the influence of acetic anhydride and propionic anhydride on the flax, hemp, and wood fiber. They reported that treated fibers had increased absorbance in the region between 1735 and 1737 cm 1 and 1162–1229 cm 1. The treated fibers were also found to have new characteristic peak at 1740 cm 1 due to the formation ester bonds between the acetyl and propionic functional group with the hydroxyl group of the fiber (Tserki, Zafeiropoulos, Simon, & Panayiotou, 2005). According to Kabir, Wang, Lau, Cardona, and Aravinthan (2012) hemp fiber treatment with alkali, acetylation, and silane led to the removal of lignin and hemicellulose, respectively. The removal of lignin was visible from the shift in the characteristic peak from 1249 to 1252 cm 1 and 1253 cm 1 and 1256 cm 1 for the silane, acetylated, and alkali-treated fibers. Removal of the hemicellulose in the alkali-treated fiber was evident from the disappearance of band at 1737 cm 1 corresponding to hemicellulose, while the characteristic peak remains unchanged due to silane treatment and a slight shift to 1726 cm 1 for the acetylated fiber indicating partial removal of the hemicellulose. In their study, Sari, Thomas, Spatenka, Ghanam, and Jenikova (2019) indicated that plasma-treated coir fiber showed increased absorbance compared to the untreated fibers. On the other hand, characteristic peaks at 1741 and 1168 cm 1 corresponding to the oxygen functional groups or polar groups of the plasma were observed in the FTIR spectra. In addition to the changes in fiber composition due to the treatment, FTIR can also be useful in determining the photo-degradation and hydrolysis induced by the weathering of natural fibers. Senthilkumar et al. (2021) showed that characteristic peaks corresponding to cellulose (–OH stretching) between 3300 and 3750 cm 1 tend to coalesce for the hemp/sisal hybrid composite subjected to accelerated weathering. The absorbance at characteristic peaks corresponding to hemicellulose, lignin, and pectin were found to be decreased for the specimens exposed to accelerated weathering under the UV irradiation and water spray as shown in Fig. 7.4. Kumar et al. (2019) obtained FTIR spectra for the poly-propylene carbonate packaging films containing coconut shell filler at concentrations ranging from 5 to 25 wt% in the increasing intervals of 5. Their results indicate that as the CSP filler concentration

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HSSH(after weathering) HSHS (after weathering)

% Transmittance

HSSH(unweathered)

HSHS(unweathered)

4000

3500

3000 1500 Wavenumber (cm-1)

1000

Fig. 7.4 FTIR spectra of the hemp/sisal composite before and after weathering (Senthilkumar et al., 2021) (figure re-used with permission). From Senthilkumar, K., Ungtrakul, T., Chandrasekar, M., Senthil Muthu Kumar, T., Rajini, N., Siengchin, S., et al. (2021). Performance of sisal/hemp bio-based epoxy composites under accelerated weathering. Journal of Polymers and the Environment, 29, 624–636. doi:10.1007/ s10924-020-01904-7.

increased, the absorbance at characteristic peaks 1740, 1224, 1064, 973, and 783 cm 1 declined in magnitude indicating the increased presence of the CSP filler on the polymer film surface.

7.5

Conclusions

FTIR works based on the mechanism of absorbance of IR by the constituents of the cellulosic fiber at certain wavenumber or frequencies, while the RS displays the reflected laser light at certain wavenumber or frequencies from the constituents of the fiber. Both the FTIR spectra and RS can be suitable for identifying the composition changes in the cellulosic fiber subjected to surface modification with various fiber treatment methods. However, the intensity of the fiber from the RS is relatively lower than the absorbance obtained from the FTIR spectra. Thus, certain functional groups belonging to the chemical treatment may not be identified from the RS method. The composition changes in the treated fibers can be observed in the form of intensity changes in the certain frequencies as well as disappearance and diminishing of characteristic peaks corresponding to the constituents of the fiber.

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In addition to the compositional changes within the fiber surface due to the treatment, FTIR and RS also provide evidence on the functional groups of the chemicals such as acetyl groups, propionic groups, silanol group which forms bond with the hydroxyl group of the cellulosic fiber as well as with the polymer matrix.

References Adebajo, M. O., Frost, R. L., Kloprogge, J. T., & Kokot, S. (2006). Raman spectroscopic investigation of acetylation of raw cotton. Spectrochimica Acta, Part A: Molecular and Biomolecular Spectroscopy, 64, 448–453. Anggono, J., Sugondo, S., Henrico, S., & Purwaningsih, H. (2015). Effect of alkali treatment using calcium hydroxide and the fiber length on the strength of sugarcane bagasse fibers-polypropylene composites. In Applied mechanics and materials (pp. 106–110). Trans Tech Publications. Asim, M., Jawaid, M., Abdan, K., & Ishak, M. R. (2017). Effect of pineapple leaf fibre and kenaf fibre treatment on mechanical performance of phenolic hybrid composites. Fibers and Polymers, 18, 940–947. Bulota, M., Sriubaite, S., Michud, A., Nieminen, K., Hughes, M., Sixta, H., et al. (2021). The fiber-matrix interface in Ioncell cellulose fiber composites and its implications for the mechanical performance. Journal of Applied Polymer Science, 138, 50306. Chalid, M., Husnil, Y. A., Puspitasari, S., & Cifriadi, A. (2020). Experimental and modelling study of the effect of adding starch-modified natural rubber hybrid to the vulcanization of sorghum fibers-filled natural rubber. Polymers (Basel), 12, 3017. Chandrasekar, M., Shahroze, R. M., Ishak, M. R., Saba, N., Jawaid, M., Senthilkumar, K., et al. (2019). Flax and sugar palm reinforced epoxy composites: Effect of hybridization on physical, mechanical, morphological and dynamic mechanical properties. Materials Research Express, 6, 105331. https://doi.org/10.1088/2053-1591/ab382c. da Silva, I. L. A., Bevitori, A. B., Rohen, L. A., Muylaert Margem, F., de Oliveira Braga, F., & Monteiro, S. N. (2016). Characterization by Fourier transform infrared (FTIR) analysis for natural jute fiber. In Materials science forum (pp. 283–287). Trans Tech Publications. Fernandes, E. M., Mano, J. F., & Reis, R. L. (2013). Hybrid cork–polymer composites containing sisal fibre: Morphology, effect of the fibre treatment on the mechanical properties and tensile failure prediction. Composite Structures, 105, 153–162. Ferreira, L. C., Trindade, W. G., Frollini, E., & Kawano, Y. (2004). Raman and infrared spectra of natural fibers. In Fifth Int. Symp. Nat. Polym. Compos. (ISNaPol 2004) Proceedings. Sao Pedro, Bras (pp. 12–15). Jayamani, E., Hamdan, S., Bin Bakri, M. K., Kok Heng, S., Rahman, M. R., & Kakar, A. (2016). Analysis of natural fiber polymer composites: Effects of alkaline treatment on sound absorption. Journal of Reinforced Plastics and Composites, 35, 703–711. Kabir, M. M., Wang, H., Lau, K. T., Cardona, F., & Aravinthan, T. (2012). Mechanical properties of chemically-treated hemp fibre reinforced sandwich composites. Composites. Part B, Engineering, 43, 159–169. Kavkler, K., & Demsar, A. (2012). Application of FTIR and Raman spectroscopy to qualitative analysis of structural changes in cellulosic fibres. Tekstilec, 55, 19–31. Krishnasamy, S., Muthukumar, C., Nagarajan, R., Thiagamani, S. M. K., Saba, N., Jawaid, M., et al. (2019). Effect of fibre loading and Ca(OH)2 treatment on thermal, mechanical, and physical properties of pineapple leaf fibre/polyester reinforced composites. Materials Research Express, 6, 085545. https://doi.org/10.1088/2053-1591/ab2702.

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Krishnasamy, S., Thiagamani, S. M. K., Muthukumar, C., Tengsuthiwat, J., Nagarajan, R., Siengchin, S., et al. (2019). Effects of stacking sequences on static, dynamic mechanical and thermal properties of completely biodegradable green epoxy hybrid composites. Materials Research Express, 6, 105351. https://doi.org/10.1088/2053-1591/ab3ec7. Kumar, T. S. M., Senthilkumar, K., Chandrasekar, M., Rajini, N., Siengchin, S., & Rajulu, A. V. (2019). Characterization, thermal and dynamic mechanical properties of poly(propylene carbonate) lignocellulosic Cocos nucifera shell particulate biocomposites. Materials Research Express, 6. https://doi.org/10.1088/2053-1591/ab2f08. Li, K., Jin, S., Chen, H., & Li, J. (2019). Bioinspired interface engineering of gelatin/cellulose nanofibrils nanocomposites with high mechanical performance and antibacterial properties for active packaging. Composites. Part B, Engineering, 171, 222–234. Omri, M. A., Triki, A., Guicha, M., Ben Hassen, M., Arous, M., Ahmed El Hamzaoui, H., et al. (2013). Effect of wool and thermo-binder fibers on adhesion of alfa fibers in polyester composite. Journal of Applied Physics, 114, 224105. Pullawan, T., Wilkinson, A. N., & Eichhorn, S. J. (2010). Discrimination of matrix–fibre interactions in all-cellulose nanocomposites. Composites Science and Technology, 70, 2325–2330. Rajan, R., Joseph, K., Skrifvars, M., & Jarvela, P. (2012). Evaluating the influence of chemical modification on flax yarn. In ECCM15–15th Eur. Conf. Compos. Mater. Venice, Italy, June (pp. 24–28). Santos, E. B. C., Moreno, C. G., Barros, J. J. P., de Moura, D. A., de Fim, F. C., Ries, A., et al. (2018). Effect of alkaline and hot water treatments on the structure and morphology of piassava fibers. Materials Research, 21. Sari, P. S., Thomas, S., Spatenka, P., Ghanam, Z., & Jenikova, Z. (2019). Effect of plasma modification of polyethylene on natural fibre composites prepared via rotational moulding. Composites. Part B, Engineering, 177, 107344. Senthilkumar, K., Rajini, N., Saba, N., Chandrasekar, M., Jawaid, M., & Siengchin, S. (2019). Effect of alkali treatment on mechanical and morphological properties of pineapple leaf fibre/polyester composites. Journal of Polymers and the Environment, 27, 1–11. Senthilkumar, K., Ungtrakul, T., Chandrasekar, M., Kumar, T. S. M., Rajini, N., Siengchin, S., et al. (2021). Performance of sisal/hemp bio-based epoxy composites under accelerated weathering. Journal of Polymers and the Environment, 29, 624–636. https://doi.org/ 10.1007/s10924-020-01904-7. Shao, X., He, L., & Ma, L. (2016). Water absorption and FTIR Analysis of three type natural fiber reinforced composites. In 2015 2nd Int. Forum Electr. Eng. Autom. (IFEEA 2015) (pp. 269–272). Atlantis Press. Thiagamani, S. M. K., Nagarajan, R., Jawaid, M., Anumakonda, V., & Siengchin, S. (2017). Utilization of chemically treated municipal solid waste (spent coffee bean powder) as reinforcement in cellulose matrix for packaging applications. Waste Management, 69, 445– 454. https://doi.org/10.1016/j.wasman.2017.07.035. Thiagamani, S. M. K., Rajini, N., Alavudeen, A., Siengchin, S., Rajulu, A. V., & Ayrilmis, N. (2019). Development and analysis of completely biodegradable cellulose/banana peel powder composite films. Journal of Natural Fibers, 1–10. https://doi.org/10.1080/ 15440478.2019.1612811. Triki, A., Dittmer, J., Ben Hassen, M., Arous, M., Bulou, A., & Gargouri, M. (2016). Spectroscopy analyses of hybrid unsaturated polyester composite reinforced by Alfa, wool, and thermo-binder fibres. Polymer Science, Series A, 58, 255–264. Tserki, V., Zafeiropoulos, N. E., Simon, F., & Panayiotou, C. (2005). A study of the effect of acetylation and propionylation surface treatments on natural fibres. Composites. Part A, Applied Science and Manufacturing, 36, 1110–1118.

Evaluation of the effect of processing and surface treatment on the interfacial adhesion in cellulose fiber composites

8

S. Sathisha, M. Aravindha, S. Dharani Kumarb, S. Gokulkumara, L. Prabhua, R. Ranga Rajc, T.L.D. Mansadevic, and R. Supriyac a Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India, bCentre for Machining and Material Testing, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India, cDepartment of Aeronautical Engineering, Sri Ramakrishna Engineering College, Coimbatore, Tamil Nadu, India

8.1

Introduction

The world’s environmental concern has made the shift from the application of synthetic fibers to the application of natural fibers as reinforcements in polymers. As the replacement of synthetic fiber polymer composites, natural fibers play a vital role (Girijappa, Mavinkere Rangappa, Parameswaranpillai, & Siengchin, 2019; Sanjay et al., 2019; Sathish, Prabhu, et al., 2021). When compared to glass fiber, natural fibers are available at minimum cost and have a reduction in density. Even though the strength of the natural fiber is not as much as that of the glass fiber, specific properties were comparable. The environment gets polluted due to the use of synthetic fiber in composite material, because of its nonbiodegradable property and energy consumption. Natural fibers were eco-friendly and they competed with glass fibers (Gowda et al., 2018; Jawaid & Abdul Khalil, 2011). They possess potential advantages such as thermal recycling, low raw material price, weight saving, and the ecological advantages of renewable resources. Due to this, from the last decade, natural fibers were used as a substitute for synthetic fibers. Natural fibers have been developed under of rigorous environment in which natural fibers have high strength and toughness ( Jagadeesh, Puttegowda, Mavinkere Rangappa, & Siengchin, 2021; Karthi, Kumaresan, Rajeshkumar, Gokulkumar, & Sathish, 2021; Prabhu et al., 2020). Application for the natural fiber composites is in the fields of building industry, automotive industry, consumer, and sports goods. Biomedical products and lightweight structures are made by mixing the polymer with natural fibers (Bharath et al., 2020). These composites can easily be employed to substitute conventional materials. Usage of natural Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00008-2 Copyright © 2023 Elsevier Ltd. All rights reserved.

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fiber will reduce energy consumption by 60% lower than synthetic fiber manufacturing. It reduces environmental impact like global warming which is necessary and it will help to improve the economy of the country through the cultivation of fiber plants, and energy saving when compared with synthetic fibers is the motivational factor for promoting natural fiber composite (Karthi et al., 2020; Sanjay et al., 2018). It also has equal responsibility in reducing the impacts on the environment such as global warming caused due to the consumption of petroleum products, which are nonrenewable resources. To make advanced composites, the availability of the traditional glass and carbon fibers is limited, whereas the natural fibers are abundant in nature. It takes a very short period to grow natural fiber and it is a renewable resource (Vijay et al., 2019). Composites reinforced with natural fiber have been developed by considering profit from policy attained by a number of governments to support the development of technical applications to use renewable resources. Natural fibers like bamboo, jute, kenaf, flax, pineapple, hemp, sisal, and coir-reinforced composites based on thermoset/thermoplastic polymer have been in use in producing many automotive and household components (Madhu et al., 2020; Manimaran, Senthamaraikannan, Murugananthan, & Sanjay, 2018; Sathish, Kumaresan, Prabhu, & Vigneshkumar, 2017). Cost-effectiveness and weight reduction are the main factors that are considered for employing natural fiber composites in this industry (Kumaresan, Sathish, & Karthi, 2015). The factors like the chemical composition of fiber, age of the plant, nature of the plant, the environment of the plant growth, extraction method, and fiber chemical treatment make considerable impacts on the properties of the natural fibers and also affect the mechanical properties of the natural fibers (Prabhu et al., 2021; Sathish, Karthi, et al., 2021; Vijay et al., 2019). Fig. 8.1 shows various factors influencing NFRCs. Natural fibers are extracted as long fibers or short fibers. Long fibers are combined with matrices like polyester, polypropylene, phenolic, or epoxy and short fibers are combined with the above matrices using production methods like uniformly distributed and randomly oriented to make products with good mechanical properties ( Joseph, Thomas, & Pavithran, 1996; Rakesh et al., 2021). There are different kinds of natural fibers (African teff, areca, abaca, banana, bamboo, coir, jute, sisal, ramie, pineapple, kenaf, hemp, flax, snake grass, etc.) that are produced in bulk and used in the production of products of various applications. Natural fibers are obtained from different parts of a plant such as the stalks, canes, grasses, reeds, leaf, bast, seed, fruit hairs, husk, and stem (Kumar et al., 2020; Rangaraj et al., 2022). The structural integrity of the composite material may be increased by the fibrous material content. Nonwood fibers are classified as stalk fibers, bast or stem fibers, leaf fibers, seed fibers, and fruit fibers. Most useful industrial fibers are taken from the bast (jute, kenaf, hemp, and flax). The phloem of the plants that surround the stem enables fibers with high stiffness to preserve stability. Improvements must be made for making the natural fibers to be competent with the synthetic fibers in the market involving composite materials (Rajeshkumar et al., 2021). The crucial factor for fiber-reinforced composite is the adhesion between the members of the fibers and the matrix. The structure and

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131

Fig. 8.1 Factors influencing NFRC.

behavior of the fiber/matrix interface have the foremost role in the mechanical performance of the fiber-reinforced composites (Sumrith, Techawinyutham, Sanjay, Dangtungee, & Siengchin, 2020). In fiber-based thermoplastic system, the surface of the matrix, the surface of the fiber face and the phase between the fiber and the matrix are together known as the interface. Some assumptions have been made about the characteristics of the interface for the mathematical investigation of stress transmitted from the fiber to the matrix as given follow: (i) the matrix and the fibers act as classic materials, (ii) the interfacial connection is infinitesimally weak, (iii) the bond between the fiber and the resin is perfect, and (iv) the fibers are organized in a regular or repeating array. For good adhesion, the material must be strong because the stress is equally transferred among the load-carrying fibers. Water absorption, mechanical and thermal properties of the composites are affected by the adhesion between the fibers and matrix. Effective load transfer ensured a strong fiber-matrix bond. The fiber surface was made rough by removing the surface impurities by different surface treatments of the fibers. The adhesion between the members of fiber and matrix was improved by better mechanical interlocking of the fiber with resin caused by the creation of a rough surface (Yorseng, Mavinkere Rangappa, Parameswaranpillai, & Siengchin, 2020). This chapter represents various surface treatments done to enhance the properties of the fibers, enrichment in physical and mechanical properties of the composites in contrast with untreated fiber-reinforced polymer composites. Therefore, we summarized the major finding on different types of chemical treatments.

132

8.2

Cellulose Fibre Reinforced Composites

Effect of surface treatment on the mechanical properties of cellulose fiber-reinforced composites

Faruk, Bledzki, Fink, and Sain (2012) discussed the existence of several methods to modify the properties of the fibers used in the composite. They revealed that factors like coupling agents, fiber types and moisture content had a remarkable influence on the properties of the composites. They concluded the research article by discussing recent developments and future trends of composites made of biodegradable materials. Kalia, Thakur, Celli, Kiechel, and Schauer (2013) stated that the factors like good interfacial bonding and relationship between the water particles and hydroxyl segments of the fiber were found to be hydrophilic and there existed a weak similarity between the plant fiber and the hydrophobic polymer lattices because of the hydrophilic natures of the plant fibers. Due to this, for the purpose of enhancing the interfacial bonding strength, it was necessary to change the fiber surface. In order to develop the fiber and composite properties, treatments like isocyanate treatment, benzoylation, mercerization and acetylation were carried out. The impact of the surface alteration on the stimulated polymer composites and properties of the plant fiber was studied by exploring different techniques for surface alteration. Ibrahim, Dufresne, ElZawawy, and Agblevor (2010) extracted banana fibers and banana microfibrils from waste banana plants and treated them with steam explosion and alkaline pulping. The treated fibers and microfibrils were chemically modified with an MA coupling agent and reinforced into an HDPE matrix to obtain composites. The composites prepared were checked for thermal (crystallinity) and mechanical properties (tensile strength, Young’s modulus) the results were compared with those noticed for unmodified banana fibers/HDPE composites. The 20% MA-treated banana fiber/HDPE composite exhibited higher tensile strength. The steam exploded banana fiber-reinforced composite exhibited a higher degree of crystallinity, which resulted in a higher modulus of the composite. Asasutjarit, Charoenvai, Hirunlabh, and Khedari (2009) reported that the coir fiber can be used as reinforcement in the composites. In the coir-based green composites, the modification of the surface and the chemical combination of the coir fibers were studied. Composites were prepared by the reinforcing coir fiber which was treated under varying pretreated conditions. As a result of surface modification and chemical composition modifications, it was found that for the coir fiber based green composites, the mechanical properties like rupture modulus and internal bonding were found to have increased. As observed from the scanning electron microscopy investigations, the fiber-matrix adhesion improved by surface modifications. Girisha, Sanjeevamurthy, and Srinivas (2012) analyzed chemically treated materials that were used for improving the mechanical behavior. These materials were extracted from the fruit of tamarind and these were used for different applications. The authors proved that fibers with the treating process have more advantages than the fibers without the treating process. The authors have improved the volume fraction of fiber by hybridization of different fibers with various proportions. The authors found that the mechanical strength was improved by combining different fibers with proper ratios. Orue et al. (2016) reported the effect of poly (lactic acid)-based composites of tensile

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133

properties with different chemical treatments on sisal fiber. The treatment process of sisal fiber was done at various chemicals at varying times. The NaOH pretreatment and silane chemical treatment were carried out on the sisal fibers. The final results hence proved that the tensile properties increased because of the surface treatment on sisal fiber when compared with untreated fiber. Zafeiropoulos, Dijon, and Baillie (2007) studied the problem of interfacial bonding and surface treatment was induced though it has a negative impact on the economy. During the application of the surface treatment of natural fibers, it was prone to degradation or to the alteration of structures. The focus of the study was a change in flax fiber tensile strength because of two surface treatments. The study declared that the bulk and surface properties of the fiber were altered by treatment. Different mode of failure was shown by the acetylated fiber when compared to others and it was revealed from the SEM analysis. Danyadi, Gulyas, and Pukanszky (2004) investigated the effect of using different fiber/matrix treatments on homogeneity, interfacial adhesion, water absorption and processability of wood flour/PP composite. The study used treatments like maleated polypropylene (MAPP), benzoylation and two different surfactants (stearic acid and cellulose palmitate). The study concludes that maleated polymer only helps in improving the interfacial adhesion between reinforcement and matrix and does not have any sizable impact on the properties investigated. Benzoylation of fibers does not improve any of the properties of the composite. However, the use of surfactants shows improvement in the processability and homogeneity of the composite. Table 8.1 presents the effects of various chemical treatments on the physical and mechanical properties of NFRCs. Goulart, Oliveira, Teixeira, Mil
eo, and Mulinari (2011) studied the reinforced palm fibers using a coupling agent of 5% weight in the polypropylene (PP) matrix. On the basis of mechanical behavior, evaluation was carried out to study the effects of the presence of the coupling agent on the surface of the palm fibers for reinforcing with PP composites. It was revealed from the results that the flexural modulus and the flexural strength of the composite improved with the addition of the coupling agents when compared to the same properties of the pure polymer. Kord, Hemmasi, and Ghasemi (2011) investigated the effect of using MA compatibilizer on the tensile and flexural properties of wood flour/PP composite. The sawdust flour was incorporated in the PP matrix with equal proportions for varying content of MA in the coupling agent (0%, 1%, and 2%). The presence of MA in composite helped in improving the mechanical properties to a significant extent. Corrales et al. (2007) studied the jute strands reinforced starch-based composites obtained by injection molding and evaluated the degree of adhesion at the fiber-matrix interface and its influence on the mechanical properties. Identification of the mechanical properties of the composites was done by alkali (NaOH) treatment of jute strands. The stiffness and the strength of starch composites reinforced with jute strands were found to have improved as a result of alkali treatment. The results showed the increase in flexural strength and tensile strength with the modified jute strands by the way of mechanical anchoring and the hydrogen bonds formation in fiber/matrix interface and the low compatibility factor. The development of the surface of the jute strand by the treatment of alkali was examined in terms of adhesion compatibility and extension at the interface between the fiber

Table 8.1 Effects of various chemical treatments on physical and mechanical properties of NFRCs. S. no.

Fibers used

Type of chemical treatment

Effects

1

Sisal/oil palm (length 10 and 6 mm)

Alkaline (0.5%, 1%, 2%, 4%, and 10%)

2

Sisal

Acetylation

3 4

Flax Sisal

Esterification Alkaline

5

Sisal

Alkaline (0.25%, 0.5%, 1.0%, 2.0%, 5.0%, 10% w/w) & 1.0%, 2.0%, or 3.0% w/w N-isopropyl acrylamide aqueous solution

(1) Reduction in diameter and weight of the fiber due to removal of lignin. (2) 4% treated fibers possessed better tensile strength (1) It reduced the moisture content from 11% to 5.45%. (2) The tensile strength of acetylated sisal fiber was reduced from 445 to 320 MPa caused by the loss of the hemicellulose in the fiber during acetylation Excellent thermal stability Improved interfacial adhesion between fiber and matrix (1) The best performance of sisal polyester composites are likely to be produced when sisal fibers are treated with 2.0% isopropyl acrylamide aqueous solution. (2) Revealed higher tensile strength and lower moisture absorption but also, best results in pull-out tests with polyester matrix

6

Jute

Alkaline (10%)

7

Alfa pulps and pine fibers

8

Date palm

Three silane coupling agents, namely methacryloxypropyltrimethoxy (MPS), mercaptoproyltrimethoxy (MRPS), and hexadecyltrimethoxy-silanes (HDS) were added Alkaline treatment with different concentration and acid treatment with various concentrations

9

Agave americana fiber

Alkaline

10

Coir

Alkaline, bleaching, and vinyl grafting

Improved the mechanical properties of the composites due to strong fiber/matrix interlocking at the interface The composite materials treated with MPS and MRPS showed good mechanical properties when compared to HDS The results showed that the chemical treatment to the fibers enhanced the fiber mechanical properties of the date palm fiber (1) It was noticed that the alkaline treatment reduced the hemicellulose, lignin, and wax content of the fibers. (2) The treated fibers have more tensile strength than the raw fibers. (3) Optimum alkali treatment was found to be 5% NaOH (1) The mechanical properties of composites like tensile, flexural and impact strength increased as a result of surface modification. (2) Bleached (65°C) coir-polyester composites showed better flexural strength (61.6 MPa) Continued

Table 8.1 Continued S. no.

Fibers used

Type of chemical treatment

Effects

11

Sisal

Alkaline

12

Short henequen fiber

NaOH & silane

13

Fique fiber

Alkaline, formaldehyde, glycidyl methacrylate and isocyanate

14

Hildegardiapopulifolia fiber

Alkaline

15

Curaua fiber

Alkaline

Improved mechanical properties of the fiber (1) The tensile strength of alkali treated henequen fiber was found to have improved. (2) The silane treatment produced a considerable increase in flexural strength while the flexural modulus also remains relatively unaffected The mechanical properties of these treated fiber composites were higher than those of the untreated composites due to the enhancement of the fiber-matrix adhesion at the interface (1) The microscopic investigation of the brittle-fractured composite samples revealed enhanced bonding between the matrix and the fibers. (2) Improved mechanical properties (1) Tensile test results showed that alkaline treated fiber composites increased in fracture strain two to three times more than untreated fiber composites. (2) The results proved that appropriate alkaline treatment is an influencing factor for improving the mechanical properties of cellulose-based fiber composites

16 17

Hemp fiber Jute fiber

Alkaline Alkaline

18

Short hemp fiber

Alkaline (5% NaOH)

19

Banana fiber

Alkaline

20

Bagasse fiber

Acetylation and acetone

21

Flax fiber

Maleic anhydride, acetic anhydride, silane, and styrene

Improved the flexural properties The alkaline treatment leads to the increase of strength and stiffness of the jute strand/starch composites 5% NaOH treatment to the fibers led to the improvements in tensile strength, Young’s modulus, fiber separation, crystallinity index, lignin reduction, and thermal stability The results indicated that at 0.3 volume fraction, tensile strength and modulus of alkali treated fiber reinforced soy protein composites increased to 82% and 96.3%, respectively, when compared to soy protein film without fiber (1) It has been shown that acetylated treated fiber composites improved the tensile strength. (2) Acetone treatment increased the tensile property of the fiber by dissolution of hemicellulose, thus creating a superior bonding with the matrix (1) It was found that the acetic anhydride and particularly silane treatments reduced the overall water uptake of flax fibers. (2) It was confirmed that tensile modulus, breaking strength, and breaking strain depend on the type of chemical treatment used Continued

Table 8.1 Continued S. no.

Fibers used

Type of chemical treatment

Effects

22

Roselle and sisal fiber

10% NaOH

23

Palm and coir fiber

Benzene diazonium salt

24

Sisal fiber

Admi cellar treatment

25 26

Rice husk fiber Alfa fiber

Mercerization and acetylation Alkaline (1%, 5%, and 10%)

27

Alfa fiber

Alkaline(1%, 5%, and 10% NaOH)

The tensile strength was found improved by 22.4% in 6 h treatment whereas the flexural strength was found to have improved by 22.2% in 4 h treatment It was found that treated fiberreinforced composites yielded better mechanical properties when compared to the raw composites The tensile, flexural and impact strength of the composite were found to increased due to treatment Compatibility was improved The flexural strength and flexural modulus were found improved for 5% NaOH treated fibers and decreased beyond that Fibers treated with 10% NaOH over a period of 24 h led to the improvement of flexural strength and modulus of about 60% and 62%, respectively. However, 5% treated Alfa fibers showed better properties

28

Betel fiber

Alkaline

29

Coconut fiber

Alkaline

30

Luffa and groundnut fiber

Alkaline (2% NaOH)

They found that 6% NaOH treatment improved the wear resistance of composites than the untreated one A decrease in fatigue life of composites when applying greater tension, due to interfacial bonding Removed greasy substances

140

Cellulose Fibre Reinforced Composites

and the matrix. Yilmaz (2013) found out the result of corn husk fiber extraction and alkalization method was used to remove the surface impurities. The corn husk fiber was investigated by various physical, mechanical, and thermal characteristics. The infrared spectroscopy measurements were used to learn chemical structures of fibers and chemical concentration reduce the linear density and extracted fiber moisture. Cantero, Arbelaiz, Llano-Ponte, and Mondragon (2003) investigated the effect of fiber chemical treatments on the mechanical properties (tensile and flexural strengths) of flax fibers (natural flax and flax pulp) reinforced PP composites. Three types of treatments, viz. maleic anhydride-polypropylene copolymer (MAPP), maleic anhydride (MA), and vinyl trimethoxysilane (VTMO), were carried out on flax fibers. The mechanical properties of MAPP-treated composites were found to be the highest, while the other fiber treatments (MA, VTMO) did not affect the mechanical properties of the composites when compared with untreated flax/PP composite. Ayswarya, Vidya Francis, Renju, and Thachil (2012) investigated the effect of adding a compatibilizer on the mechanical properties (tensile) and thermal stability of rice husk ash (RHA)-reinforced HDPE composite. The study reveals that RHA does not improve the properties of HDPE polymer significantly when mixed directly with the polymer. However, the use of compatibilizer in RHA/HDPE composite improves the tensile strength, elongation at break and thermal stability as compared to those observed for virgin HDPE. Paul, Joseph, Mathew, Pothen, and Thomas (2010) prepared polypropylene composites reinforced with short banana fiber. To enhance the interfacial bonding, the banana fiber surfaces were chemically modified. By using the solvatochromic technique, the investigation was done on the chemically modified banana fiber and their polarity parameters were studied. After the chemical treatment, the polarity of the banana fiber decreased. The adhesion between the fiber and the matrix was polarity-dependent. As the tensile property and the flexural property enhanced, the relations between the fiber and the matrix were also found to have improved. Joseph, Tol^edo Filho, James, Thomas, and de Carvalho (1999) studied the benzoyl chloride treatment on sisal fiber and found higher thermal stability compared to raw fiber composites. The treatment removes the hemicellulose and fatty substance in fiber surfaces for better mechanical and thermal properties. Akhtar et al. (2016) studied the influence of alkaline treatment on the mechanical and physical properties of kenaf/polypropylene composites. Herrera-Franco and ValadezGonza´lez (2005) studied the effect of short fibers and matrices made of polyethylene on mechanical properties. The shear strength exhibited along the interface between the fibers and matrix showed the many defects had been reduced. This was attributed to the degree at which the fiber and matrix had adhered with each other. With an increase in the bond strength between fibers and matrix, the defects changed from failure at the interface to fiber pull-out. Reddy, Mohana Reddy, Mohan Reddy, and Reddy (2020) fabricated the Cordia-Dichotoma fiber-based composite and studied the mechanical, thermal, and morphological properties of the prepared composites. The authors treated the Cordia-Dichotoma fiber with NaOH to improve the adhesion strength of the composite. Epoxy resin was used to make the composite. The tensile and flexural tests showed the maximum strength of 64 and 348 MPa, respectively, when including 20 wt% fibers with epoxy. The thermal study reported that the composite displayed

Evaluation of the effect of processing and surface treatment

141

15% residual weight at 850°C and was thermally stable up to 256°C while adding 20 wt% fibers. Neto et al. (2018) investigated the influence of surface treatment of fibers on the thermal stability of composites. The authors performed alkalized and mixed, i.e., alkalized and silanized treatment on the jute, ramie, sisal, and curaua´ natural fibers. Results showed that the chemical treatment improved the thermal stability of the composites. SEM report showed that a rough surface was formed on the fiber surface when alkali-treated and a thin layer was formed on the surface when mixed treatment was performed. The authors concluded that the chemical treatment displayed a positive response for sisal and ramie fiber composite and showed a negative response for jute and curaua fiber. Abhemanyu et al. (2019) characterized the natural fiber-reinforced composite. The authors used epoxy as a matrix and agricultural waste as reinforcements. The composite containing 27% banana fiber and 9% jute fiber showed the maximum tensile strength of 30 MPa. The composite containing 21.5% coconut sheath and 15.5% jute displayed the maximum compressive strength of 34 MPa. The authors concluded that the tensile strength of the different composites was improved with the increase of banana fiber content and the hardness value was not shown any significant changes for all the fabricated composites. Fiore, Sanfilippo, and Calabrese (2019) investigated the influence of sodium bicarbonate on the aging resistance of the natural fiber-reinforced composite in the marine environment. The fiber was treated with 10 wt% sodium bicarbonate solution and the composite was fabricated with a vacuum infusion technique. Two types of composite namely flax/epoxy and jute/epoxy was fabricated for the study. The results showed that the flax/epoxy composite displayed better adhesion compared to untreated flax/epoxy composite and showed superior flexural properties. However, the sodium bicarbonate treatment of jute/epoxy composite showed a worsening effect on the durability of the composite. Sepe, Bollino, Boccarusso, and Caputo (2018) studied the influence of chemical treatment on the mechanical properties of hemp fiberreinforced composites. The fiber was involved in alkali treatment and silane treatment. The authors reported that the silane-treated woven hemp fiber showed better bonding with the epoxy and the mechanical properties such as flexural and tensile strengths were improved. However, the composite was not shown much high value. Chaudhary, Bajpai, and Maheshwari (2018) performed an investigation on the wear and dynamic mechanical properties of hemp/jute/flax-reinforced composites and its hybrid composites. The experimental results showed that the wear behavior of natural fiber-reinforced composites showed improved results compared to a neat epoxy matrix. The jute/epoxy composite displayed the highest coefficient of friction, frictional force, and wear rate among the developed composites. Dynamic mechanical analysis showed that the dynamic behavior, i.e., damping capacity, storage modulus, and loss modulus was depended on the types of fiber and the combination of hybrid fibers. Further, the incorporation of natural fiber into the epoxy matrix reduced the brittle nature of the composites. Lila, Singh, Pabla, and Singh (2018) studied the influence of environment conditioning on the NFRC. The authors fabricated jute/epoxy composite and examined it in four types of environments such as water, 5% NaOH, petrol, and vegetable oil. The composite laminate was immersed for 3 months and the mechanical test, i.e., tensile and flexural was performed after exposing every month.

142

Cellulose Fibre Reinforced Composites

The authors concluded that the alkaline treatment showed better mechanical properties in petrol and vegetable oil environments. Singh, Dhawan, Singh, and Jangid (2017) investigated the influence of chemical treatment on the tensile, flexural, and impact strength of NFRCs. The authors used banana, jute, and sisal natural fibers and epoxy resin to fabricate the composites by a compression molding technique. Tensile, flexural, and impact test was carried out on the treated and untreated composite and the results were compared. The results showed that the surface treatment enhanced the tensile, flexural strength and decreased the impact strength of the composites. Further, the jute/epoxy composite displayed the maximum tensile strength among the developed all other composites. Manikandan et al. (2017) analyzed the tensile and flexural strength of jute/polyester composite. The fiber was involved in chemical treatment prior to composite fabrication. Alkali treatment of fiber was done using 5% NaOH solution for 3, 5, and 7 h time duration at room temperature. The authors used two types of polyester resin as recycled and virgin. They observed that the tensile and flexural strengths of the composites improved after fiber treatment and the composite fabricated with recycled polyester displayed a higher strength than the virgin polyester. Espinach et al. (2017) studied the tensile strength of polyoxymethylene composites. The fiber was treated with a eucalyptus bleaching process. The authors reported that the composite with bleached fiber showed high tensile strength compared to the composite with unbleached fiber. The high tensile strength in bleached fiber composite was due to the interface mechanism of the composite. Sullins, Pillay, Komus, and Ning (2017) fabricated the hemp/polypropylene composite and investigated the influence of surface treatment on the physical properties of the composite. The surface treatment involves the various concentrations of NaOH solutions and maleic anhydride-grafted polypropylene (MAPP) inclusion in the composite. The authors concluded that the composite with fiber treatment showed better tensile strength compared to untreated fiber composite and the composite treated with 5 wt % MAPP displayed the maximum tensile strength compared to all other concentrations. Rajesh, Pitchaimani, and Rajini (2016) analyzed the free vibrational characteristics of sisal and banana fiber-reinforced hybrid composite beams. The fibers were treated with sodium hydroxide and the hybridization effect was studied. The authors observed that the fiber treatment and hybridization enhanced the vibrational characteristics of the composite due to the better adhesion between hydrophilic fiber and hydrophobic matrix. Cai, Takagi, Nakagaito, Li, and Waterhouse (2016) studied the influence of NaOH reagent on the mechanical properties of the abaca/epoxy composites. The authors performed the alkali treatment of fiber by varying the NaOH concentration from 5 to 15 wt% and studied the changes in mechanical properties of the abaca/epoxy composite. The results showed that the abaca/epoxy composite displayed better mechanical properties while abaca fiber was treated with 5 wt% NaOH than the untreated fiber composite. Further, the authors concluded that the stronger alkali treatment showed a negative effect on the stiffness of the fiber and the mechanical properties of the composite. Prasad, Agarwal, and Sinha (2016) fabricated the banana/ LDPE composite and investigated the influence of surface treatment of fiber and compatibilizer inclusion on the properties of the composites. Composite was fabricated using compression molding technique by varying the fiber loading from 10 to 30 wt% in the step of 5. The authors concluded that the LDPE/banana composite with

Evaluation of the effect of processing and surface treatment

143

25 wt% fiber loading showed the optimum performance in biodegradation and mechanical behavior. Further, the alkali, acrylic acid treatment of fiber and compatibilizer showed enhanced mechanical properties. Manral and Bajpai (2020) analyzed the influence of surface treatment of kenaf fiber on the properties of kenaf/ epoxy composites. The authors treated the kenaf fiber with sodium acetate by varying the chemical concentrations as 10%, 15%, and 20% and investigated the thermal and chemical properties of the kenaf fiber-based composites. They concluded that the chemical and thermal stability of the composite was improved owing to the removal of hemicellulose, lignin, and waxy elements from the kenaf fiber when treated with 20% sodium acetate for 48 h. Further, the authors pointed out that the chemical treatment of kenaf fiber enhanced the crystalline phase by removing the amorphous phase of the fiber. Ramesh, Prasad, and Narayana (2019) investigated the mechanical and morphological behavior of kenaf fiber/MMT/PLA composites fabricated by a screw extruder. Kenaf fiber was treated with 6% NaOH solution and 30 wt% treated kenaf fiber was added in the composite whereas the MMT filler was varied as 1%, 2%, and 3%. The authors concluded that 30 wt% treated kenaf fiber/1% MMT/PLA composite showed superior mechanical properties than other composites and the SEM analysis revealed that the MMT inclusion improved the load transfer capacity and microstructure of the composite. Nematollahi, Karevan, Fallah, and Farzin (2020) investigated the mechanical, thermal, and morphological properties of extruding and injection molded kenaf/polypropylene (PP) composite. Kenaf fiber was treated with NaOH solution and the maleic anhydride polypropylene (MAPP) coupling agent was used in the composite fabrication process. The treated kenaf fiber content was varied from 10 to 40 wt% in the composite. The authors found that the tensile and flexural strength of the composite was improved by 100% and 120% compared to pure PP. However, the impact strength of the composite was decreased by 18%. The thermal study showed that the melting temperature, crystallinity, and crystalline temperature were increased due to the inclusion of kenaf fiber.

8.3

Conclusion

Increasing environmental awareness has encouraged the studies of new eco-friendly materials to replace the existing products based on petroleum fuels. Scientific researchers have done their research toward eco-composite materials to analyze environmental problems and cleaner processes for future generations. In recent years, composite materials with natural fibers are predominantly used in sound damping in the automotive industry. In addition to that, natural fibers have renewable properties and biodegradable characteristics as donate to the high performance like low cost, superior mechanical properties, toughness, and compactness. This gives superior technical performance and environmental advantages. The physical and mechanical properties of various cellulosic fibers-reinforced composites were improved upon modification of fiber surfaces, while fiber swelling effect and water absorption rate were decreased by various chemical treatments like alkaline, silane, acetylation, permanganate, peroxide, benzolylation, acrylonitrile grafting, maleic anhydride grafted, acrylation, and isocyanate.

144

Cellulose Fibre Reinforced Composites

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Kumaresan, M., Sathish, S., & Karthi, N. (2015). Effect of fiber orientation on mechanical properties of sisal fiber reinforced epoxy composites. Journal of Applied Science and Engineering, 18(3), 289–294. https://doi.org/10.6180/jase.2015.18.3.09. Lila, M. K., Singh, B., Pabla, B. S., & Singh, I. (2018). Effect of environmental conditioning on natural fiber reinforced epoxy composites. Materials Today: Proceedings, 5(9), 17006– 17011. Elsevier Ltd https://doi.org/10.1016/j.matpr.2018.04.105. Madhu, P., Sanjay, M. R., Senthamaraikannan, P., Pradeep, S., Siengchin, S., Jawaid, M., et al. (2020). Effect of various chemical treatments of Prosopis juliflora fibers as composite reinforcement: Physicochemical, thermal, mechanical, and morphological properties. Journal of Natural Fibers, 17(6), 833–844. https://doi.org/10.1080/15440478.2018.1534191. Manikandan, N., Morshed, M. N., Karthik, R., Azad, A., Deb, S., Rumi, H., et al. (2017). Improvement of mechanical properties of natural fiber reinforced jute/polyester epoxy composite through meticulous alkali treatment. American Journal of Current Organic Chemistry, 3, 9–18. Manimaran, P., Senthamaraikannan, P., Murugananthan, K., & Sanjay, M. R. (2018). Physicochemical properties of new cellulosic fibers from Azadirachta indica plant. Journal of Natural Fibers, 15(1), 29–38. https://doi.org/10.1080/15440478.2017.1302388. Manral, A., & Bajpai, P. K. (2020). Static and dynamic mechanical analysis of geometrically different kenaf/PLA green composite laminates. Polymer Composites, 41(2), 691– 706. https://doi.org/10.1002/pc.25399. Nematollahi, M., Karevan, M., Fallah, M., & Farzin, M. (2020). Experimental and numerical study of the critical length of short kenaf fiber reinforced polypropylene composites. Fibers and Polymers, 21(4), 821–828. https://doi.org/10.1007/s12221-020-9600-x. Neto, J., Lima, R. A. A., Cavalcanti, D. K. K., Souza, J., Aguiar, R., & Banea, M. (2018). Effect of chemical treatment on the thermal properties of hybrid natural fiber-reinforced composites. Journal of Applied Polymer Science, 136. Orue, A., Jauregi, A., Unsuain, U., Labidi, J., Eceiza, A., & Arbelaiz, A. (2016). The effect of alkaline and silane treatments on mechanical properties and breakage of sisal fibers and poly(lactic acid)/sisal fiber composites. Composites Part A: Applied Science and Manufacturing, 84, 186–195. https://doi.org/10.1016/j.compositesa.2016.01.021. Paul, S. A., Joseph, K., Mathew, G. D. G., Pothen, L. A., & Thomas, S. (2010). Influence of polarity parameters on the mechanical properties of composites from polypropylene fiber and short banana fiber. Composites Part A: Applied Science and Manufacturing, 41(10), 1380–1387. https://doi.org/10.1016/j.compositesa.2010.04.015. Prabhu, L., Krishnaraj, V., Sathish, S., Gokulkumar, S., Karthi, N., Rajeshkumar, L., et al. (2021). A review on natural fiber reinforced hybrid composites: Chemical treatments, manufacturing methods and potential applications. Materials Today: Proceedings, 45, 8080–8085. Elsevier Ltd https://doi.org/10.1016/j.matpr.2021.01.280. Prabhu, L., Krishnaraj, V., Sathish, S., Gokulkumar, S., Sanjay, M. R., & Siengchin, S. (2020). Mechanical and acoustic properties of alkali-treated Sansevieria ehrenbergii/Camellia sinensis fiber–reinforced hybrid epoxy composites: Incorporation of glass fiber hybridization. Applied Composite Materials, 27(6), 915–933. https://doi.org/10.1007/s10443-02009840-4. Prasad, N., Agarwal, V. K., & Sinha, S. (2016). Banana fiber reinforced low-density polyethylene composites: Effect of chemical treatment and compatibilizer addition. Iranian Polymer Journal, 25(3), 229–241. https://doi.org/10.1007/s13726-016-0416-x. Rajesh, M., Pitchaimani, J., & Rajini, N. (2016). Free vibration characteristics of banana/sisal natural fibers reinforced hybrid polymer composite beam. Procedia Engineering, 144, 1055–1059. Elsevier Ltd https://doi.org/10.1016/j.proeng.2016.05.056.

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Rajeshkumar, G., Arvindh Seshadri, S., Devnani, G. L., Sanjay, M. R., Siengchin, S., Prakash Maran, J., et al. (2021). Environment friendly, renewable and sustainable poly lactic acid (PLA) based natural fiber reinforced composites—A comprehensive review. Journal of Cleaner Production, 310, 127483. https://doi.org/10.1016/j.jclepro.2021.127483. Rakesh, K. M., Srinidhi, R., Gokulkumar, S., Nithin, K. S., Madhavarao, S., Sathish, S., et al. (2021). Experimental study on the sound absorption properties of finger millet straw, darbha, and ripe bulrush fibers. Advances in Materials Science and Engineering, 2021, 1–12. https://doi.org/10.1155/2021/7382044. Ramesh, P., Prasad, B. D., & Narayana, K. L. (2019). Morphological and mechanical properties of treated kenaf fiber/MMT clay reinforced PLA hybrid biocomposites. AIP Conference Proceedings, 2057. AIP Publishing LLC. Rangaraj, R., Sathish, S., Mansadevi, T. L. D., Supriya, R., Surakasi, R., Aravindh, M., et al. (2022). Investigation of weight fraction and alkaline treatment on Catechu Linnaeus/Hibiscus cannabinus/Sansevieria Ehrenbergii plant fibers-reinforced epoxy hybrid composites. Advances in Materials Science and Engineering, 2022, 1–9. https://doi.org/10.1155/2022/ 4940531. Reddy, B. M., Mohana Reddy, Y. V., Mohan Reddy, B. C., & Reddy, R. M. (2020). Mechanical, morphological, and thermogravimetric analysis of alkali-treated Cordia-Dichotoma natural fiber composites. Journal of Natural Fibers, 17(5), 759–768. https://doi.org/10.1080/ 15440478.2018.1534183. Sanjay, M. R., Madhu, P., Jawaid, M., Senthamaraikannan, P., Senthil, S., & Pradeep, S. (2018). Characterization and properties of natural fiber polymer composites: A comprehensive review. Journal of Cleaner Production, 172, 566–581. https://doi.org/10.1016/j. jclepro.2017.10.101. Sanjay, M. R., Siengchin, S., Parameswaranpillai, J., Jawaid, M., Pruncu, C. I., & Khan, A. (2019). A comprehensive review of techniques for natural fibers as reinforcement in composites: Preparation, processing and characterization. Carbohydrate Polymers, 207, 108–121. https://doi.org/10.1016/j.carbpol.2018.11.083. Sathish, S., Karthi, N., Prabhu, L., Gokulkumar, S., Balaji, D., Vigneshkumar, N., et al. (2021). A review of natural fiber composites: Extraction methods, chemical treatments and applications. Materials Today: Proceedings, 45, 8017–8023. Elsevier Ltd https:// doi.org/10.1016/j.matpr.2020.12.1105. Sathish, S., Kumaresan, K., Prabhu, L., & Vigneshkumar, N. (2017). Experimental investigation on volume fraction of mechanical and physical properties of flax and bamboo fibers reinforced hybrid epoxy composites. Polymers and Polymer Composites, 25(3), 229– 236. https://doi.org/10.1177/096739111702500309. Sathish, S., Prabhu, L., Gokulkumar, S., Karthi, N., Balaji, D., & Vigneshkumar, N. (2021). Extraction, treatment and applications of natural fibers for bio-composites—A critical review. International Polymer Processing, 36(2), 114–130. https://doi.org/10.1515/ipp2020-4004. Sepe, R., Bollino, F., Boccarusso, L., & Caputo, F. (2018). Influence of chemical treatments on mechanical properties of hemp fiber reinforced composites. Composites Part B: Engineering, 133, 210–217. https://doi.org/10.1016/j.compositesb.2017.09.030. Singh, J. I. P., Dhawan, V., Singh, S., & Jangid, K. (2017). Study of effect of surface treatment on mechanical properties of natural fiber reinforced composites. Materials Today: Proceedings, 4, 2793–2799. Sullins, T., Pillay, S., Komus, A., & Ning, H. (2017). Hemp fiber reinforced polypropylene composites: The effects of material treatments. Composites Part B: Engineering, 114, 15–22. https://doi.org/10.1016/j.compositesb.2017.02.001.

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Sumrith, N., Techawinyutham, L., Sanjay, M. R., Dangtungee, R., & Siengchin, S. (2020). Characterization of alkaline and silane treated fibers of ‘water hyacinth plants’ and reinforcement of ‘water hyacinth fibers’ with bioepoxy to develop fully biobased sustainable ecofriendly composites. Journal of Polymers and the Environment, 28(10), 2749– 2760. https://doi.org/10.1007/s10924-020-01810-y. Vijay, R., Lenin Singaravelu, D., Vinod, A., Sanjay, M. R., Siengchin, S., Jawaid, M., et al. (2019). Characterization of raw and alkali treated new natural cellulosic fibers from Tridax procumbens. International Journal of Biological Macromolecules, 125, 99–108. https:// doi.org/10.1016/j.ijbiomac.2018.12.056. Yilmaz, N. D. (2013). Effect of chemical extraction parameters on corn husk fibres characteristics. Indian Journal of Fibre and Textile Research, 38(1), 29–34. http://nopr.niscair.res. in/bitstream/123456789/16374/1/IJFTR%2038%281%29%2029-34.pdf. Yorseng, K., Mavinkere Rangappa, S., Parameswaranpillai, J., & Siengchin, S. (2020). Influence of accelerated weathering on the mechanical, fracture morphology, thermal stability, contact angle, and water absorption properties of natural fiber fabric-based epoxy hybrid composites. Polymers, 12(10), 2254. https://doi.org/10.3390/polym12102254. Zafeiropoulos, N. E., Dijon, G. G., & Baillie, C. A. (2007). A study of the effect of surface treatments on the tensile strength of flax fibres: Part I. Application of Gaussian statistics. Composites Part A: Applied Science and Manufacturing, 38(2), 621–628. https://doi.org/ 10.1016/j.compositesa.2006.02.004.

Manufacturing aspects of cellulose fiber-reinforced composites

9

Sangilimuthukumar Jeyagurua, Senthil Muthu Kumar Thiagamania, Senthilkumar Krishnasamyb, Muthukumar Chandrasekarc, Nasmi Herlina Sarid, Mavinkere Rangappa Sanjaye, and Suchart Siengchine a Department of Automobile Engineering, Kalasalingam Academy of Research and Education, Krishnankoil, Tamil Nadu, India, bDepartment of Mechanical Engineering, Kalasalingam Academy of Research and Education, Krishnankoil, Tamil Nadu, India, cSchool of Aeronautical Sciences, Hindustan Institute of Technology & Science, Padur, Kelambakkam, Chennai, Tamil Nadu, India, dDepartment of Mechanical Engineering, Faculty of Engineering, University of Mataram, Mataram, West Nusa Tenggara, Indonesia, e Department of Materials and Production Engineering, The Sirindhorn International ThaiGerman Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand

9.1

Introduction

Nowadays reinforcements and types of biodegradable sources of natural fibers are most commonly used to replace better properties of petroleum-based materials and synthetic fibers (Senthil Muthu Kumar et al., 2018; Thiagamani, Krishnasamy, & Siengchin, 2019). Natural fibers classified based on their origins are from plants, animals, or minerals. Plant fibers are mainly formed by lignocellulosic compounds such as cellulose, hemicellulose, lignin, etc., while the animal fibers were mostly composed of proteins like collagen and keratin. Flax, hemp, jute, sisal, banana, and kenaf fibers are considered as most promising sustainable fibers due to their abundance availability and reinforcing agents that could also yield good functional properties (Thiagamani et al., 2019). Natural fibers are reinforced with both thermoplastic and thermosetting matrices. Selection of matrices generally depends on the materials, which commonly defines the environmental characteristics and decide overall service temperature of the components (Arpitha & Yogesha, 2017). Natural fiber composites are nowadays most frequently used in industries such as the automotive, aerospace, home appliances, construction, and many more (Chandrasekar et al., 2019; Krishnasamy et al., 2019). The prime motive in using natural fiber-based composites in these industries is mainly due to their significant weight reduction, better specific strength, stiffness, aerodynamic, and acoustic emission. Components with limited loading such as dash boards, bumpers, standby tire holders, etc. are made of long fiber composites. The use of natural fiber composites in the automotive market has seen an increasing trend in the past decade (Friedrich & Almajid, 2013).

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Natural fiber composites are made from both thermoset and thermoplastic polymeric materials where the thermoset composites cannot be recycled as they undergo the process of thermoset resin while they maintain good rigidity, thermal stability, and dimensional stability. Some of the thermosetting resins are vinyl ester, polyamideimide, silicone, polyamide, epoxy, polyester, and polyurethane (Lotfi, Li, Dao, & Prusty, 2019). On the other hand, the thermoplastic composites possess better toughness and impact strength than the thermosets. Further, they can be easily reformed and recycled. The major drawback of the thermoplastics is that it is difficult to penetrate the reinforcing fibers as they are in solid state. Few examples of thermoplastic polymers are poly(butylene terephthalate), polyethylene, polyvinyl chloride, acrylonitrile butadiene styrene, poly propylene, polystyrene, polycarbonate, etc. (V€ais€anen, Das, & Tomppo, 2017). Fabrication of composites plays a crucial role in the properties, life, and the economics of the ensuing component. The selection of material and processes plays a vital role in this regard. Furthermore, the development of new process, the selection, and the usage of the fundamental science in the manufacturing process had increased the manufacturing technologies. To increase the growth of composite materials in different industries, the coupling of the composite material is important in manufacturing and arranging process to enhance the composite manufacturing with lower production cost (Advani & Hsiao, 2012). This chapter deals about the manufacturing of composite materials and their growth trends. Benefits of manufacturing methods, effects of processing variables, and factors affecting the process of manufacturing in natural fiber composites are discussed in detail. Use of advanced 3D-printing techniques in manufacturing of natural fiber composites is also explained.

9.2

Effect of processing variables on the quality of thermoset-based cellulosic fiber-reinforced composites

Generally, the properties of cellulose fiber-reinforced composites are influenced by many factors: (i) type of fiber, (ii) type of polymers, (iii) additives, and (iv) manufacturing technique. Sometimes, the composites perform differently due to the fiber structure variations, though the composites are made by using similar fiber with different matrices used. Besides, the performance of the composites is reduced due to: i. Fiber damage. ii. Poor interfacial bonding between the fiber and matrix. iii. Degradation of fiber and matrix (Krishnasamy et al., 2019; Rojo, Alonso, Oliet, Del SazOrozco, & Rodriguez, 2015; Rojo, Oliet, Alonso, Del Saz-Orozco, & Rodriguez, 2014).

In this section, the quality of thermoset-based cellulosic fiber-reinforced composites is discussed based on different properties, whereby different manufacturing techniques involve to fabricate the composites: (i) compression molding, (ii) hot pressing, and (iii) resin transfer molding. Many researchers reported that the manufacturing

Manufacturing aspects of cellulose fiber-reinforced composites

151

technique would significantly influence the composite properties and their interfacial bonding characteristics (Ku, Wang, Pattarachaiyakoop, & Trada, 2011; Liu, Drzal, Mohanty, & Misra, 2007). Furthermore, the properties of the composites could be changed by varying the processing conditions: (i) operating temperature, (ii) speed, (iii) pressure, etc. Sreekumar, Joseph, Unnikrishnan, and Thomas (2007) compared the mechanical properties of sisal fiber/polyester matrix composites using compression molding and resin transfer molding techniques. The mechanical properties of the composites were improved in both techniques by increasing the fiber content. However, the void content and water absorption of compression-molded composites were higher than the resin transfer molding technique. It was ascribed to the increased fiber pull-outs and poor fiber-matrix bonding of compression-molded composites. In another work, Srinivasa et al. (2011) characterized the physical, bending, and impact properties of areca fiber-reinforced polymer matrix composites using three different polymers such as (i) formaldehyde, (ii) melamine urea-formaldehyde, and (iii) epoxy resins. The composites were fabricated by using compressing molding technique. Furthermore, the performance of these composites was improved by following the two approaches. (i) The fibers were subjected to alkali treatment with potassium hydroxide and (ii) Composites fabricated by increasing the fiber loading (50 wt% and 60 wt%).

Result analysis revealed that the treated areca fiber-reinforced composites exhibited a better performance in bending and impact properties than the untreated fiber composites. The improved mechanical properties were attributed to the (i) enhanced adhesion and (ii) improved polar interactions between the fiber and matrix interfaces. Furthermore, the area fiber composites were found to strengthen bending and impact properties by increasing the fiber loading from 50 wt% to 60 wt%. The obtained results proved that the fiber surface modification could be the possible way of improving the properties of cellulose fiber-reinforced composites. These composites can play a promising role in fabricating lightweight materials used in different applications such as aerospace, automobile, furniture industries, and construction and building, etc. In another work, Chandrasekar et al. (2020) studied the sisal/polyester matrix composites under different temperatures such as 60°C, 70°C, 80°C, 90°C, and 100°C. The sisal/polyester composites improved in mechanical and vibration properties considerably by increasing the working temperatures. Bennet, Rajini, Siva, Jappes, and Amico (2015) investigated the effect of molding temperatures (30°C and 60°C) on the mechanical and vibration damping properties of Sansevieria cylindrica fiber/polyester matrix, coconut sheath/polyester matrix, and their hybrid composites. The compression molding technique was used to fabricate the composites at different temperatures. From their findings, the mechanical and vibration behavior improved (i) by increasing the working temperature from 30°C to 60°C and (ii) varying the fiber layering sequences of Sansevieria cylindrica and coconut sheath fibers in hybrid composites. In nonhybrid fiber composites, the Sansevieria cylindrica/polyester composites were outperformed the coconut sheath/polyester matrix composites.

152

Cellulose Fibre Reinforced Composites

The hot-pressing approach would be easy to fabricate simple flat samples. Because two hot plates are only required to compress fiber and matrix, and followed by heat is applied. However, manufacturing thick samples using the hot press is not easy because the viscosity and temperature are hard to control during fabrication. Based on the results from the various researchers (Khondker, Ishiaku, Nakai, & Hamada, 2005; Ku et al., 2011; Liu, Yu, Cheng, & Qu, 2009), the matrix’s viscosity should be low to penetrate thoroughly into the fibers and high enough to prevent spurting out. Thus, the mechanical performance and interfacial bonding between the fiber and matrix would increase. Ashrafi, Vaziri, and Nayeb-Hashemi (2011) studied the roles of composition and processing parameters on the mechanical behavior of wood plastic-reinforced composites (WPC). The WPC fabricated using African blackwood powder, and phenolic was used as a matrix in the composite materials. The compositions were heated for 196°C under 35 MPa; the temperature and pressure were maintained for 30 min during fabrication, followed by cooling. When the filler was increased by over 70%, cracks were noticed in the composite samples. It was ascribed to (i) lack of fluidity and (ii) formation of gases in the composite samples. Based on the results obtained, 60% of wood-filled composites performed better static mechanical properties. Table 9.1 gives some of the works reported on the hot compression molding technique. Table 9.1 Reported works of natural fiber-reinforced composites fabricated by using hot compression molding technique. Reinforcement

Matrix

Temperature

Pressure

References

Jute

Polyester

135°C

0.2 MPa

Kenaf

Vinyl ester

135°C

8 MPa

Kenaf

Polyester

140°C

2.5 MPa

Sisal, hemp

Bioepoxy

100°C

275 bars

Date palm filler

Epoxy

110°C

–

Oil palm empty fruit bunch, jute

Epoxy

105°C

275 bars

Ashrafi et al. (2011) Westman, Fifield, Simmons, Laddha, and Kafentzis (2010) Ibrahim, Hadithon, and Abdan (2010) Krishnasamy, Thiagamani, Muthukumar, et al. (2019) Alothman et al. (2020) Jawaid, Khalil, Bakar, Hassan, and Dungani (2013)

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153

Table 9.1 Continued Reinforcement

Matrix

Temperature

Pressure

References

Saccaharum cilliare

Resorcinol formaldehyde Unsaturated polyester

50°C

4 MPa

185°C

2 MPa

Phenolic formaldehyde Epoxy

160°C

30 Ton

105°C

–

Singha and Thakur (2010) Sawpan, Pickering, and Fernyhough (2012) Asim et al. (2015) Jawaid, Saba, Alothman, Khalil, and Mariatti (2017)

Hemp fiber

Pineapple leaf fiber Oil palm empty fruit bunch, jute

The resin transfer molding (RTM) technique is economically best and helps to produce a high-volume composite. Many researchers have studied the composites using natural fiber and renewable polymer as matrix materials (Ferland, Guittard, & Trochu, 1996; Ikegawa, Hamada, & Maekawa, 1996; Warrior, Turner, Robitaille, & Rudd, 2003; Williams & Wool, 2000). In the RTM technique, the composite quality depends on many factors: (i) matrix injection pressure, (ii) mold temperature, (iii) fiber permeability, (iv) matrix viscosity, (v) gate locations, etc. Paglicawan et al. (2014) made an effort to produce biocomposites using abaca fabric/unsaturated polyester matrix using a vacuum-assisted resin transfer molding technique. The mechanical properties were analyzed by varying plasma exposure time. The result analysis reported that the composites fabricated with 10–20 s of plasma treatment exhibited better mechanical characteristics than the more extended plasma-treated composites. In another study, Pothan, Mai, Thomas, and Li (2008) analyzed the tensile and flexural behavior of woven sisal/polyester matrix composites using plain, twill, and matt weaving architectures. Furthermore, the performance of the composites was compared by varying (i) matrix viscosity, (ii) pressure, (iii) fiber weaving type, and (iv) chemical treatment. Among the processing factors, the fiber weaving architecture and chemical treatment played a significant role in influencing the composite properties.

9.3

Composite manufacturing with thermoplastic matrices

9.3.1 Twin screw extrusion and injection molding The twin-screw extruder machine consists of two co-penetrating and self-cleaning identical screws mounted adjacent to each other in a fixed barrel. It provides as a good mixing of the fiber and resin and contains a melt compounding technology which

154

Cellulose Fibre Reinforced Composites

melts the resin and blends it with the fiber. The fiber-resin blend can be obtained in a short span of time (Ashter, 2013). Extrusion is a simple and effective process for PLA, cellulose-based polymers, and thermoplastic polymer-based composites (Lotfi et al., 2019). Oksman, Mathew, La˚ngstr€ om, Nystr€ om, and Joseph (2009) used flax, jute, sisal, and banana fiber roving as reinforcement to produce long fiber thermoplastic composite using Twin screw extrusion and compression molding process. According to their observations, sisal fiber remained longest without any damage after fabrication, while the flax fibers broke into elementary fiber bundles and the fiber length shortened after fabrication. Thus, sisal/PP composites with longest fiber length after fabrication exhibited fiber pull-out which led to superior impact strength while flax/ PP composites had superior stiffness due to the fiber breakage into elementary bundles. Uniform fiber dispersion was obtained for the composites fabricated using this technique. However, the processing conditions can affect the fiber dispersion characteristics. Gunning, Geever, Killion, Lyons, and Higginbotham (2014) investigated the influence of screw configuration, mixing zone length of the compounding and processing temperature on the mechanical properties of the hemp-, lyocell-, and jute-based PLA composites manufactured by twin screw extrusion injection molding. More fiber length was retained for the composites when the mixing zone length was reduced which in turn led to superior tensile properties of the investigated composites. On the other hand, lower processing temperature resulted in better mechanical properties than the composites subjected to higher processing temperature. The reason for decline in mechanical properties at elevated temperature is the aggravated degradation of natural fibers which tends to weaken the natural fiber leading to inferior properties. In case of the torque applied for different screw configurations, optimal properties were observed for 200 rpm. Feldmann, Heim, and Zarges (2016) fabricated manmade cellulose cordenka type glass fiber/polyamide 10.10 composite using twin screw extrusion injection molding with screw containing kneading disk and mixing zone post the fiber feeding zone (referred to as extrusion injection molding), while the other configuration doesn’t have mixing zones post the fiber feeding zone (referred to as direct injection molding). According to them, the change in screw configuration and processing temperature had minimal influence on the mechanical properties of the composites at 20 and 30 wt% of fibers. However, significant differences were observed in fiber dispersion and fiber distribution length as evident from their microstructural images. Santos, Spinace, Fermoselli, and De Paoli (2007) fabricated short fiber and long fiber-based curaua/polyamide-6 composites with twin screw extrusion process followed by injection molding. According to them, composites with long fiber had superior tensile strength and Young’s modulus than the composites with short fibers. Microstructural images indicated damage to the long fibers as evident from the shortening of fiber length for the composites with long fibers. Higher shear rate produced in the mixing zone of the twin screw extruder is believed to have shortened the fiber length during the processing of long fiber. They also reported that drying the short fibers in dessicator prior to twin screw extrusion or their use in the raw form did not affect the tensile, flexural and impact properties of the composite.

Manufacturing aspects of cellulose fiber-reinforced composites

155

Fig. 9.1 Injection molding process (Rajak, Pagar, Menezes, & Linul, 2019).

Hydraulic Mechanism

Hopper

Mold Heater

Screw

Motor

Short and long sisal fiber with PLA matrix was fabricated using the direct injection molding (D-I-M) and extrusion injection molding (E-I-M) by Chaitanya and Singh (Chaitanya & Singh, 2017). Their results indicate that E-I-M was suitable for short fiber-based composites, while the D-I-M was found to be suitable for both the short fibers and long fibers. The main limitation of E-I-M with long fibers is the fiber damage which leads to shortening of fiber length and makes them less effective in carrying load and lowers its load carrying capability. They also reported that uniform dispersion of fiber regardless of the technique or fiber length was obtained. Haque, Hasan, Islam, and Ali (2009) investigated the influence of fiber loading on the palm and coir based PP composites with weight % varying between 5% and 35%. The fibers and resin were mixed using the single screw extrusion process and the composites were fabricated by the injection molding process. Coir fiber/PP composites had better mechanical properties than the palm/PP composites. Tensile strength and stiffness increased with the fiber loading up to 35 wt%, while the flexural strength and impact strength declined after 30 wt% (Fig. 9.1). D-I-M, E-I-M, and extrusion compression molding (E-C-M) were utilized for fabricating banana fiber/PLA composites. Their results indicate superior impact properties for D-I-M-manufactured composites, while E-I-M-manufactured composites exhibited higher tensile and flexural strength than the D-I-M and E-I-M. The reason for variation in thermal and mechanical properties between the investigated processes was attributed to the fiber distribution, fiber orientation, and attrition of fibers. Fiber length retention was better for D-I-M composites which helped the composites to undergo fiber-pull out during impact, an essential characteristic for superior impact resistance (Komal, Lila, & Singh, 2020). Table 9.2 shows the application, advantages and limitations of the most commonly used manufacturing techniques for thermoset and thermoplastic-based composites.

9.4

Advanced 3D-printing manufacturing techniques

Advanced 3D printing has been widely explored over the last few decades due to its potential in the design of complex materials and structures. Among the numerous 3Dprinting methods, fused filament fabrication (FFF) is one of the most useful methods

Table 9.2 Applications, advantages, and limitations of various manufacturing techniques. Process name

Applications

Advantages

Limitations

References

Hand lay up

Structural application in automobile parts, marine structure, Wind-turbine blades

Process cost is less, less time consuming Thick parts can be made

Bhatt, Gohil, and Chaudhary (2018); Rajak et al. (2019)

Auto Clave

Aerospace industry

Compression molding

Automobile panels, aero plane parts, Truck parts

Resin transfer molding

Air craft parts, Automobile components, cabinets

High quality Uniform and glossy surface finishing Superior mechanical properties Good surface finish, High quality, Less investment cost Large rapid manufacturing, highperformance parts

Lower fiber volume fraction Voids, resin starvation, microcracks and other structural defects Inferior mechanical properties Process is slow Expensive Part size limited to medium size and small parts, thus requires joining of parts Higher waste, Complex parts can’t be made with the mold

VARTM

Rail carriage and bridge sections Offshore utility scale Wind turbine blades

Complex parts can be easily made Low-cost tooling

Production cost and time are slightly high It requires special tooling and individual curing for each part. Only one smooth surface is possible Thin parts

Halley (2012); Nagavally (2017)

Bhatt et al. (2018); Saba, Paridah, Jawaid, Abdan, and Ibrahim (2015) Bhatt et al. (2018); Kalia et al. (2011)

Bhatt et al. (2018); Nagavally (2017); Rajak et al. (2019)

Twin screw extrusion

Plastic, food, and pharmaceutical sectors.

Injection molding

Automobile sectors, construction, food and pharmaceutical sectors.

Continuous production process Better control of process parameters High level of process flexibility Fast production and highly efficient Low labor costs

High capital and maintenance costs, Greater constrains on the operating ranges

Arao, Fujiura, Itani, and Tanaka (2015); Hyv€arinen, Jabeen, and K€arki (2020)

High tooling costs and long set up lead times High investment

Bledzki, Faruk, and Mamun (2008); Chaitanya and Singh (2017)

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in the manufacture of polymer composites. In this method, the thermoplastic resin is deposited layer-by-layer deposition with the help of a heated nozzle onto the platform. The major pros of this method are that it reduces the cost, design-manufacturing cycle, and the wastage. Further, it also possesses the capability to build intricate geometries and modify the microstructure and properties (Le Duigou, Correa, Ueda, Matsuzaki, & Castro, 2020). Even though, the use of FFF technique in developing natural fiberreinforced composites has improved the mechanical performance of the ensuing 3Dprinted components; there is a requirement for major research to aid the 3D-printed components to encounter the structural loads for different applications. The major hindrances for 3D-printed composites are the characteristic defects induced during the extrusion process such as the porosity, produced by poor interfacial bonding between the fibers and the matrix (Le Duigou & Castro, 2017; Parandoush & Lin, 2017). The major factors that influence the printability of the composites are the orientation, geometry, and composition. Hence, it is significant to differentiate the characteristics of the materials and the properties of the printed part. Furthermore, it is also to be noted that the printing and slicing parameters such as the infill percentage, printing pattern, raster angle, printing height, printing orientation, bed temperature, and printing speed play a vital role in the performance of 3D-printed components manufactured using FFF (Fernandez-Vicente, Calle, Ferrandiz, & Conejero, 2016). From literatures, it is evident that the 3D-printed natural fiber composites exhibited lower tensile properties when compared to their traditionally manufactured counterparts (Filgueira et al., 2017). Le Duigou, Castro, Bevan, and Martin (2016) reported a reduction of about 44% in the stiffness and 30% reduction in strength when compared to compression-molded wood/PLA/PHA composites. Similarly, another researcher reported that 3D-printed ABS/coconut fiber composites exhibited a stiffness and strength which was 50% less that the injection-molded counterparts (Sˇafka et al., 2016). Another researcher established that 3D-printed composites consisting of thermomechanical pulp and biopolyethylene exhibited reduced performance than their injection-molded counterparts with the same fiber content. It was found that there was a decrease of about 40% in modulus and 45% in strength, respectively. This substantial reduction was due to the microstructure of the 3D-printed components with poor adhesion between the printed layers resulting in a substantial increase in the porosity content (Tarres et al., 2018). Normally, the natural fiber-reinforced biocomposites manufactured by FFF produce modest mechanical properties that prevent them from being used in semi-structural applications. Hence, more research is required to overcome the shortfall identified in both processing methods and material formulation in this technique.

9.5

Conclusions

There has been a mounting increase in the development of cellulosic fiber-based composites; thanks to the increasing environmental consciousness and stringent norms on reducing the carbon pollution. The practical usage of these materials in various fields such as the automotive and aerospace industries showed that they have become a

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significant aspect in designing light weight structures. It is well established that the performance of the composite materials is highly governed by the type of fiber and matrix used and the manufacturing process involved. However, there exists an uncertainty on the selection of the manufacturing techniques that are appropriate for fabricating these composites. This chapter reports an inclusive review on elementary principles for the manufacture of composite materials and their influence on the performance of the components. Predictions about future manufacturing techniques such as the 3D-printing techniques were also reported.

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Komal, U. K., Lila, M. K., & Singh, I. (2020). PLA/banana fiber based sustainable biocomposites: A manufacturing perspective. Composites. Part B, Engineering, 180, 107535. https://doi.org/10.1016/j.compositesb.2019.107535. Krishnasamy, S., Thiagamani, S. M. K., Muthu Kumar, C., Nagarajan, R., Shahroze, R. M., Siengchin, S., et al. (2019). Recent advances in thermal properties of hybrid cellulosic fiber reinforced polymer composites. International Journal of Biological Macromolecules, 141, 1–13. https://doi.org/10.1016/j.ijbiomac.2019.08.231. Krishnasamy, S., Thiagamani, S. M. K., Muthukumar, C., Tengsuthiwat, J., Nagarajan, R., Siengchin, S., et al. (2019). Effects of stacking sequences on static, dynamic mechanical and thermal properties of completely biodegradable green epoxy hybrid composites. Materials Research Express, 6, 105351. https://doi.org/10.1088/2053-1591/ ab3ec7. Ku, H., Wang, H., Pattarachaiyakoop, N., & Trada, M. (2011). A review on the tensile properties of natural fiber reinforced polymer composites. Composites. Part B, Engineering, 42, 856–873. https://doi.org/10.1016/j.compositesb.2011.01.010. Le Duigou, A., & Castro, M. (2017). Hygromorph BioComposites: Effect of fibre content and interfacial strength on the actuation performances. Industrial Crops and Products, 99, 142–149. https://doi.org/10.1016/j.indcrop.2017.02.004. Le Duigou, A., Castro, M., Bevan, R., & Martin, N. (2016). 3D printing of wood fibre biocomposites: From mechanical to actuation functionality. Materials and Design, 96, 106–114. https://doi.org/10.1016/j.matdes.2016.02.018. Le Duigou, A., Correa, D., Ueda, M., Matsuzaki, R., & Castro, M. (2020). A review of 3D and 4D printing of natural fibre biocomposites. Materials and Design, 194, 108911. https://doi. org/10.1016/j.matdes.2020.108911. Liu, L., Yu, J., Cheng, L., & Qu, W. (2009). Mechanical properties of poly (butylene succinate) (PBS) biocomposites reinforced with surface modified jute fibre. Composites. Part A, Applied Science and Manufacturing, 40, 669–674. https://doi.org/10.1016/j.compositesa. 2009.03.002. Liu, W., Drzal, L. T., Mohanty, A. K., & Misra, M. (2007). Influence of processing methods and fiber length on physical properties of kenaf fiber reinforced soy based biocomposites. Composites. Part B, Engineering, 38, 352–359. https://doi.org/10.1016/j.compositesb. 2006.05.003. Lotfi, A., Li, H., Dao, D. V., & Prusty, G. (2019). Natural fiber–reinforced composites: A review on material, manufacturing, and machinability. Journal of Thermoplastic Composite Materials, 34. 0892705719844546. Nagavally, R. R. (2017). Composite materials-history, types, fabrication techniques, advantages, and applications. International Journal of Mechanical and Production Engineering, 5, 82–87. Oksman, K., Mathew, A. P., La˚ngstr€om, R., Nystr€om, B., & Joseph, K. (2009). The influence of fibre microstructure on fibre breakage and mechanical properties of natural fibre reinforced polypropylene. Composites Science and Technology, 69, 1847–1853. https:// doi.org/10.1016/j.compscitech.2009.03.020. Paglicawan, M. A., Kim, B. S., Basilia, B. A., Emolaga, C. S., Marasigan, D. D., & Maglalang, P. E. C. (2014). Plasma-treated abaca fabric/unsaturated polyester composite fabricated by vacuum-assisted resin transfer molding. International Journal of Precision Engineering and Manufacturing-Green Technology, 1, 241–246. https://doi.org/10.1007/s40684-0140030-3. Parandoush, P., & Lin, D. (2017). A review on additive manufacturing of polymerfiber composites. Composite Structures, 182, 36–53. https://doi.org/10.1016/j.compstruct. 2017.08.088.

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Pothan, L. A., Mai, Y. W., Thomas, S., & Li, R. K. Y. (2008). Tensile and flexural behavior of sisal fabric/polyester textile composites prepared by resin transfer molding technique. Journal of Reinforced Plastics and Composites, 27, 1847–1866. https://doi.org/10.1177/ 0731684408090342. Rajak, D. K., Pagar, D. D., Menezes, P. L., & Linul, E. (2019). Fiber-reinforced polymer composites: Manufacturing, properties, and applications. Polymers, 11, 1667. https://doi.org/ 10.3390/polym11101667. Rojo, E., Alonso, M. V., Oliet, M., Del Saz-Orozco, B., & Rodriguez, F. (2015). Effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites. Composites. Part B, Engineering, 68, 185–192. https://doi.org/10.1016/j.compositesb. 2014.08.047. Rojo, E., Oliet, M., Alonso, M. V., Del Saz-Orozco, B., & Rodriguez, F. (2014). Mechanical and interfacial properties of phenolic composites reinforced with treated cellulose fibers. Polymer Engineering and Science, 54, 2228–2238. https://doi.org/10.1002/pen.23772. Saba, N., Paridah, M. T., Jawaid, M., Abdan, K., & Ibrahim, N. A. (2015). Manufacturing and processing of kenaf fibre-reinforced epoxy composites via different methods. In Manufacturing of natural fibre reinforced polymer composites (pp. 101–124). Springer. Sˇafka, J., Ackermann, M., Bobek, J., Seidl, M., Habr, J., & Be˘ha´lek, L. (2016). Use of composite materials for FDM 3D print technology. In Materials science forum (pp. 174–181). Trans Tech Publications Ltd. Santos, P. A., Spinace, M. A. S., Fermoselli, K. K. G., & De Paoli, M.-A. (2007). Polyamide6/vegetal fiber composite prepared by extrusion and injection molding. Composites. Part A, Applied Science and Manufacturing, 38, 2404–2411. https://doi.org/10.1016/j. compositesa.2007.08.011. Sawpan, M. A., Pickering, K. L., & Fernyhough, A. (2012). Flexural properties of hemp fibre reinforced polylactide and unsaturated polyester composites. Composites. Part A, Applied Science and Manufacturing, 43, 519–526. https://doi.org/10.1016/j.compositesa.2011.11.021. Senthil Muthu Kumar, T., Rajini, N., Obi Reddy, K., Varada-Rajulu, A., Siengchin, S., & Ayrilmis, N. (2018). All-cellulose composite films with cellulose matrix and Napier grass cellulose fibril fillers. International Journal of Biological Macromolecules. https://doi.org/ 10.1016/j.ijbiomac.2018.01.167. Singha, A. S., & Thakur, V. K. (2010). Mechanical, morphological, and thermal characterization of compression-molded polymer biocomposites. International Journal of Polymer Analysis and Characterization, 15, 87–97. https://doi.org/10.1080/10236660903474506. Sreekumar, P. A., Joseph, K., Unnikrishnan, G., & Thomas, S. (2007). A comparative study on mechanical properties of sisal-leaf fibre-reinforced polyester composites prepared by resin transfer and compression moulding techniques. Composites Science and Technology, 67, 453–461. https://doi.org/10.1016/j.compscitech.2006.08.025. Srinivasa, C. V., Arifulla, A., Goutham, N., Santhosh, T., Jaeethendra, H. J., Ravikumar, R. B., et al. (2011). Static bending and impact behaviour of areca fibers composites. Materials and Design, 32, 2469–2475. https://doi.org/10.1016/j.matdes.2010.11.020. Tarres, Q., Melbø, J. K., Delgado-Aguilar, M., Espinach, F. X., Mutje, P., & Chinga-Carrasco, G. (2018). Bio-polyethylene reinforced with thermomechanical pulp fibers: Mechanical and micromechanical characterization and its application in 3D-printing by fused deposition modelling. Composites. Part B, Engineering, 153, 70–77. https://doi.org/10.1016/j. compositesb.2018.07.009. Thiagamani, S. M. K., Krishnasamy, S., Muthukumar, C., Tengsuthiwat, J., Nagarajan, R., Siengchin, S., et al. (2019). Investigation into mechanical, absorption and swelling behaviour of hemp/sisal fibre reinforced bioepoxy hybrid composites: Effects of stacking

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sequences. International Journal of Biological Macromolecules, 140, 637–646. https://doi. org/10.1016/j.ijbiomac.2019.08.166. Thiagamani, S. M. K., Krishnasamy, S., & Siengchin, S. (2019). Challenges of biodegradable polymers: An environmental perspective. Applied Science and Engineering Progress, 12, 149. V€ais€anen, T., Das, O., & Tomppo, L. (2017). A review on new bio-based constituents for natural fiber-polymer composites. Journal of Cleaner Production, 149, 582–596. https://doi.org/ 10.1016/j.jclepro.2017.02.132. Warrior, N. A., Turner, T. A., Robitaille, F., & Rudd, C. D. (2003). Effect of resin properties and processing parameters on crash energy absorbing composite structures made by RTM. Composites. Part A, Applied Science and Manufacturing, 34, 543–550. https://doi.org/ 10.1016/S1359-835X(03)00057-5. Westman, M. P., Fifield, L. S., Simmons, K. L., Laddha, S., & Kafentzis, T. A. (2010). Natural fiber composites: A review. U.S. Department of Energy. Williams, G. I., & Wool, R. P. (2000). Composites from natural fibers and soy oil resins. Applied Composite Materials, 7, 421–432. https://doi.org/10.1023/A:1026583404899.

Further reading Antony, S., Cherouat, A., & Montay, G. (2020). Fabrication and characterization of hemp fibre based 3D printed honeycomb Sandwich structure by FDM process. Applied Composite Materials, 27, 1–19. Kariz, M., Sernek, M., Obucina, M., & Kuzman, M. K. (2018). Effect of wood content in FDM filament on properties of 3D printed parts. Materials Today Communications, 14, 135–140. https://doi.org/10.1016/j.mtcomm.2017.12.016. Krishnasamy, S., Muthukumar, C., Nagarajan, R., Thiagamani, S. M. K., Saba, N., Jawaid, M., et al. (2019). Effect of fibre loading and Ca(OH)2 treatment on thermal, mechanical, and physical properties of pineapple leaf fibre/polyester reinforced composites. Materials Research Express, 6, 085545. https://doi.org/10.1088/2053-1591/ab2702. Le Duigou, A., Barbe, A., Guillou, E., & Castro, M. (2019). 3D printing of continuous flax fibre reinforced biocomposites for structural applications. Materials and Design, 180, 107884. https://doi.org/10.1016/j.matdes.2019.107884. Long, H., Wu, Z., Dong, Q., Shen, Y., Zhou, W., Luo, Y., et al. (2019). Mechanical and thermal properties of bamboo fiber reinforced polypropylene/polylactic acid composites for 3D printing. Polymer Engineering and Science, 59, E247–E260. https://doi.org/10.1002/ pen.25043. Matsuzaki, R., Ueda, M., Namiki, M., Jeong, T.-K., Asahara, H., Horiguchi, K., et al. (2016). Three-dimensional printing of continuous-fiber composites by in-nozzle impregnation. Scientific Reports, 6, 23058. Stoof, D., Pickering, K., & Zhang, Y. (2017). Fused deposition modelling of natural fibre/polylactic acid composites. Journal of Composites Science, 1, 8. https://doi.org/10.3390/ jcs1010008. Torrado, A. R., Shemelya, C. M., English, J. D., Lin, Y., Wicker, R. B., & Roberson, D. A. (2015). Characterizing the effect of additives to ABS on the mechanical property anisotropy of specimens fabricated by material extrusion 3D printing. Additive Manufacturing, 6, 16–29. https://doi.org/10.1016/j.addma.2015.02.001.

Compression and injection molding techniques

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G. Rajeshkumar, B. Aakash Balaji, and S. Arvindh Seshadri Department of Mechanical Engineering, PSG Institute of Technology and Applied Research, Coimbatore, Tamil Nadu, India

10.1

Introduction

Compression molding technique (CMT) and injection molding technique (IMT) are two of the most flexible composites manufacturing processes, each with its own set of capabilities for creating composites in a variety of forms and sizes. The majority of composite parts are huge components manufactured in lesser numbers, the primary exemption being injection-molded composite parts reinforced with short fibers. IMT involves a significant capital investment in equipment and tools, making it economically viable only for large-scale mass manufacturing. Additionally, it enables quick processing into complicated geometries, albeit at the cost of fiber length preservation. Big injection-molded structures often have poorer impact strength and stiffness than compression-molded structures owing to short fiber length and low fiber loading. Yet, the rapid manufacturing periods and minimal finishing processes required for IMT result in significant cost savings throughout manufacturing. By weight, IMT accounts for 32% of all polymeric materials treated (Turng, 2001). Transportation, consumer items, voltaic equipment, and civil applications are the primary industries seeing development. IMT has emerged as one of the most crucial processes for processing short or long glass fiber-reinforced thermoplastics. More sustainable and recyclable fillers will be developed in the future. These include “eco” fillers like recycled paper, “lignocellulosic” fiber, and “high cellulose” fiber. In the meantime, a new foaming process that produces parts with no sink marks, low warpage, and a high-quality surface has been developed, as has injection molding (IM) of long fiber-reinforced thermoplastics with good creep resistance and impact performance, as well as IM of conductive thermoplastics. These processes also include the IM of ultra-thin composite parts at high speeds with effective EMI shielding (Liu, 2012). Natural fibers such as Phoenix sp., cotton, flax, pineapple, date palm, sisal, banana, coir, jute, bagasse, Palmyra palm, ramie, and kenaf are some good alternatives used with different biocomposites (Nagarjun, Kanchana, & Rajesh Kumar, 2020; Rajeshkumar, Hariharan, et al., 2021; Sumesh, Kavimani, Rajeshkumar, Indran, & Saikrishnan, 2021; Vigneshwaran & Rajeshkumar, 2018). CMT, on the other hand, is a highly prolific and cost-effective method of creating composite products. CMT has been utilized for thermoset powders and rubber compounds since the early 20th century. This technology has grown significantly in Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00018-5 Copyright © 2023 Elsevier Ltd. All rights reserved.

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popularity in appliance and automotive applications since the early 1950s, owing to the invention of sheet molding compounds (Park & Lee, 2012). For instance, the first implementation of glass fiber matrix composites in the vehicle sector was the 1953 GM Corvette’s front panel (Davis, Allen, & Gramann, 2003). CMT is well suited to high volume applications such as those found in the automobile sector. It is critical to increase yield ratio and reduce cycle time in order for this production process to be economical. Good material selection and process design could conceivably enhance process performance and product quality. Process modeling, in particular, may be beneficial for reducing product development time by predicting resin flow and curing. CMT and IMT procedures are widely used to manufacture composites with short fiber reinforcement (SFRC). Fiber breaking occurs during the production of injection molded SFRC (Lee, Seop, & Lee, 2001; von Turkovich & Erwin, 1983). Fiber breaking occurs consequently due to interface between polymer and fiber, fiber-to-fiber contact, and fiber contact with processing equipment’s surfaces. As a result of augmented fiber–fiber interaction and fiber–equipment wall contact as fiber content rises (von Turkovich & Erwin, 1983), fiber length reduces with rising fiber content, and this drop in fiber length diminishes the efficiency of fiber reinforcement (Fu, Lauke, M€ader, Yue, & Hu, 2000). However, using compression-molded SFRC, fiber damage during processing may be reduced, allowing considerably longer fiber. As a result, considerable improvements in mechanical qualities may be gained by increasing the starting fiber length compared to injection-molded components. Nevertheless, the consistency of compression-molded components is critical. CMT’s primary processing factors are ram speed, molding pressure, and mold temperature (Lee, 2006). Numerous advances have been made to increase productivity in IMT and CMT molding. Dielectric heating is an appealing alternative for thermoset molding firms looking to boost their output quickly and inexpensively. Thermoset powder is preheated using dielectric heating. Preheating powder reduces the time required for compression, and warmed material flows more freely through the mold. Product quality is typically improved, and another profit may be gained via greater production (Duranik, Ruzbarsky, & Stopper, 2013). Today’s technology allow for the prediction of fiber orientation using molding simulation software (Davis, Theriault, & Osswald, 1997; Osswald, Sun, & Tseng, 1996). This same software may also be utilized to optimize molding settings in order to buildup orientation of fiber and hence the part’s strength. Analysis of mold filling is crucial to assure adequate part filling and eliminate knit lines, but also to calculate fiber orientation to do anisotropic structural analysis. When the results of fiber orientation and mold filling are integrated with structural analysis, the molding process can be altered to adapt fiber orientation to reinforce critical structural portions of the component. Additionally, the position of ribs and thicker portions may be improved to lower the part’s weight, cost, and performance (Davis, Paul, Gramann, & Rios, 2002). Natural fiber-based composites are widely used in automotive sliding panels, interiors, machine tools, bushings, and the textile industry (Rajeshkumar, Arvindh Seshadri, et al., 2021; Rajeshkumar, 2021). Additionally, there has been a sustained effort and endeavor in recent years to combine natural fibers into high-temperature engineering thermoplastics, primarily by lowering the resin’s melting point or

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increasing the heat resistance of natural fibers. The second technique seems to be more promising in case of improving total composite performance, as it does not impact the matrix resin’s inherent qualities. The IMT technique is generally confined to the manufacturing of objects with short to intermediate length fibers, the lengths of which are determined by the compounding process pellets. CMT, on the other hand, is a more adaptable method that may be employed with any kind of fiber; however, the forming process takes longer than IMT. As a result, it’s understandable that the industry created injection–CMT technology lately in order to capitalize on the advantages of both molding techniques (Leong, Thitithanasarn, Yamada, & Hamada, 2013). For the very first time, different properties of various alternatives to nonbiodegradable materials like purple bauhinia and Phoenix sp. fibers are investigated, which shows the developments in study of biocomposites (Rajeshkumar, Devnani, et al., 2021; Rajeshkumar, Hariharan, et al., 2021). Furthermore, due to their improved mechanical properties, nano-clay incorporated natural fiber composites have emerged as one of the most promising materials for a variety of applications (Rajeshkumar, Seshadri, et al., 2021).

10.2

Compression molding technique

The CMT procedure is divided into four stages. Precharge preparation and placement: Molding material is put in the heated mold (e.g., sheet molding compound sheets) (Komal, Lila, & Singh, 2020). This substance is referred to as the precharge. The proportions of the precharge are chosen to cover 50% of mold surface area, and precharge weight is determined prior to placement in the mold. The precharge location in the mold is critical for component quality as it impacts void content, fiber orientation, and knit line formation. Mold closure: Once the precharge material is inserted in the mold, the upper mold rapidly descends to meet the precharge material’s top surface. The top mold then continues to descend gently (often at a rate of 5–10 mm/s) to compress the precharge. As the mold is closed, the precharge material flows into the mold cavity, causing escape of air via the mold’s shear edges or air vents. The speeds with which the mold closes and the temperature at which it closes are critical elements affecting the process’s performance and product quality. Curing: The mound is sealed and the molding pressure is maintained for a period of time after the precharge material has been entirely filled into the mold cavity. The resin cures, and the portion is cemented during this time. Curing time is dependent on the formulation of the resin mixture, the thickness of the component, and the mold temperature. Component release: Once the resin has dried and the part has set, ejector pins are used to extract the part from the mold. After cooling, the components are taken outside of the mold. The process cycle time is typically between 1 and 3 min, depending on the component thickness. The material temperature is maintained between 130 and 160 °C throughout the process, with a comparatively low molding pressure of around 10 MPa (Park & Lee, 2012). The fabrication process for laminated composites using CMT is depicted in Fig. 10.1 (Song et al., 2018).

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Compression direction Compression surface Bulk charge

Compression direction

Compression direction

Compression surface Bulk charge

Cavity Bulk charge placement in mold

Final part

Cavity Ongoing compression molding process

Sample ready after demold

Fig. 10.1 Compression molding setup. From Song, Y., Gandhi, U., Sekito, T., Vaidya, U.K., Vallury, S., Yang, A., & Osswald, T. (2018). CAE method for compression molding of carbon fiber-reinforced thermoplastic composite using bulk materials. Composites Part A: Applied Science and Manufacturing, 114, 388–397. https://doi.org/10.1016/j.compositesa.2018.09.002 (reused with permission from Elsevier, License number: 5210620128271).

10.2.1 CMT for thermosetting polymer composites A molding compound is an intermediate semi-cured composite material used for thermoset polymers. Bulk and sheet molding compounds are two thermosetting-based molding compounds that are commonly utilized. For thermosetting polymers, matrices utilized in this technique include phenolic, vinyl ester, and epoxy resin. When opposed to thermoplastic resins, thermoset resins have reduced toughness. Thermoset material must be warmed prior to CMT, which increases cycle time (Asim et al., 2017; Park & Lee, 2012).

10.2.2 CMT for thermoplastic polymer composites A glass mat thermoplastic is commonly used as a molding compound for thermoplastic polymers. Composite ingredients are combined in a mixer and twin-screw extruder for homogenous distribution in laboratory-scale CMT. For thermoplastic polymers, matrices utilized in this method include polypropylene, polyamide, and polyether ether ketone (PEEK) (Asim et al., 2017). When opposed to thermoset resins, thermoplastic resins have more toughness. Because thermoplastics need not require chemical reactions, they can be preheated outside before being put into the mold for component formation, eliminating the need for heating inside the mold. As a result, when compared to thermosetting polymers, the cycle time can be significantly reduced (Park & Lee, 2012).

10.3

Injection molding technique

Glass fiber-reinforced composites IMT may generate products with extraordinary physical and mechanical properties that are close to net shape. The procedure is typically carried out using a reciprocating single-screw extrusion machine. The mechanism in the machine transports melts and pressurizes granular fiber-filled polymeric materials. The compound melts within the barrel due to conduction of heat through the walls of the barrel and heat dissipation within the sheared polymer melt. During the

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plasticization process, melt gathers in front of the screw, which is driven back against an adjustable internal pressure until the desired shot size (melt volume) is achieved. Following that, the screw advances to drive the polymer melt via a runner system and into the mold’s comparatively cold empty chamber. The melt in front of the screw is retained under pressure to compensate for any shrinkage produced by the melt cooling within the cavity, forcing additional materials into the void. When the material introduced through the gate freezes, no more material can be introduced through the gate, and the product continues to cool without shrinkage compensation. Water runs via channels to maintain the mold cavity walls at a temperature between ambient and the glass transition temperature (for amorphous polymers) or melt temperature of the polymeric materials (for semi-crystalline polymers). When the product has attained a suitably hard state, which occurs when every area of the component has cooled below the polymer’s melt temperature or glass transition, the mold is opened and the result is ejected. Fig. 10.2 depicts the schematic of machine setup and machine with hopper dryer used for injection molding process.

Fig. 10.2 Injection molding setup: (A) schematic on injection molding machine setup and (B) injection molding machine with hopper dryer. From Leong, Y. W., Thitithanasarn, S., Yamada, K., & Hamada, H. (2013). Compression and injection molding techniques for natural fiber composites. In: Natural fibre composites: Materials, processes and applications (pp. 216–232). Elsevier Inc. https://doi.org/10.1533/ 9780857099228.2.216 (reused with permission from Elsevier, License number: 5210670173299).

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Cellulose Fibre Reinforced Composites

IMT is a cyclical process. The time it takes for the melted plastic to cool determines the cycle time, which can range from 10 to 100 s. IMT allows for close tolerances on small complicated pieces. Typically, very little postproduction work is necessary because the pieces have a relatively polished appearance upon ejection. To reduce waste, every scrap can be reground and repurposed. Furthermore, IMT allows for complete automation (Liu, 2012).

10.3.1 IMT for thermosetting polymer composites For granular thermosetting compounds, a small amount of transferred heat is required to help in the fluxing of the molding material within the injection barrel. Typically, a fluid jacket is utilized for thermosets (Singh, Chen, & Jones, 1998). In the case of thermosets, the melt front tends to accelerate during the filling process. The front acceleration can be ascribed to a reduction in melt viscosity caused by conduction and heat of reaction heating of the polymer (Kamal & Ryan, 1980). Thermosetting materials require extra heating after injection into the mold to accomplish complete cure and solidification. Additionally, a breath facility is necessary to allow volatiles to escape during phenolic compound terminal curing. To attain the same degree of reinforcing efficiency as thermoplastics, it is necessary to increase fiber length retention to improve mechanical properties. The pseudoplastic response of the polymer melt has a significant effect on fiber orientation in thermoset composites, and the issue is exacerbated further by the effect of cure level on the resin’s rheology. The thermoset screw’s flight depth remains consistent throughout its length. The screw length is also much shorter in thermoset composites than in thermoplastic composites. Because the mold temperature is tuned to the higher cure temperature in thermosets, a slow injection speed accelerates cure and increases viscosity, resulting in visible fiber alignment in the skin areas.

10.3.2 IMT for thermoplastic polymer composites Due to the lack of a requirement for externally provided significant temperature gradients along the barrel, a system of temperature-controlled band heaters is used to aid the fluxing of molding material inside the injection barrel for thermoplastics. Typically, thermoplastics demonstrate a monotonic decline in the rate of advancement of the melt front throughout the filling stage. This is because the viscosity of the polymer increases as it cools and the pressure gradients decrease as more polymers enter the cavity. After injection into the mold, thermoplastics must be chilled until the molding hardens. Unlike thermosets, this material does not require a final curing step. In thermoplastics, fiber length retention is higher, which increases mechanical properties. There is universal agreement that the pseudoplastic response of the polymer melt significantly affects the orientation of the fibers in thermoplastic composites. There are three distinct flight zones for thermoplastic screws: compression, melting, and metering, each with a different flight depth. Screw length is also substantially longer for thermoplastic composites than it is for thermosets. A low shear rate combined with a slow injection speed results in poor skin alignment in thermoplastics.

Compression and injection molding techniques

10.4

171

CMT vs IMT

When compared to CMT, the IMT has better tensile and flexural qualities. Furthermore, the impact resistance of the IMT outperforms that of the CMT (Bledzki & Faruk, 2004). The IMT process is generally confined to the manufacture of parts with short to intermediate length fibers, and these lengths are determined by the pellet lengths created during the compounding process. On the other hand, CMT is a more adaptable technique that can be utilized for all types of fibers, albeit the forming process requires longer cycle durations as compared to IMT. Large composite panels incorporating either chopped fiber strands or continuous fibers can be Natural fiber composites manufactured utilizing the CMT technique, and the molded object will likely require postmolding treatment. IMTs are often more complicated in shape and have very strict dimensional tolerances (Leong et al., 2013). In the injectionmolded groups, increasing fiber concentration resulted in improvements in all mechanical properties assessed, but increasing fiber length resulted in increases only in modulus of elasticity and longitudinal strength. The concentration of fibers in the compression molded groups had a significant impact on the modulus of elasticity and impact strength of the materials. The CMT is a very effective way of creating natural fiber composite materials. As a result of the high molding temperature and pressure associated with the IMT method, natural fibers are not as effective. It is possible to maintain the mechanical properties of natural fibers while employing relatively modest molding pressure and temperature in the CMT process (Park & Lee, 2012).

10.5

Mechanical properties

10.5.1 Wood fiber-reinforced polypropylene composites It has been shown that injection-molded composites outperform compression-molded composites in tensile strength at 50% wood fiber content, the IMT demonstrated stronger flexural strength, with a 60% improvement in flexural strength when compared to the CMT method. The IMT test revealed better flexural strength at a wood fiber content of 50%, with a trend toward the CMT test at this concentration. In this study, it was discovered that the Charpy impact strength of compression-molded hardwood fiber composites is larger than the strength of injection-molded composites. The maximum Charpy impact strength for hard-wood–fiber–PP composites during the CMT process was improved by the addition of a compatibilizer to the composites, according to the findings. In the IMT process, impact resistance is increased, while CMT results in the initiation of damage. With the inclusion of a compatibilizer, however, the impact resistance of hard-wood– fiber–PP composites performs admirably throughout the CMT process, with minimal initial damage. As a result, when compared to CMT, the IMT approach demonstrated superior tensile and flexural characteristics, with tensile and flexural strengths increasing by about 155% and 60%, respectively. For hard-wood–fiber–PP (PP) composites, the maximum Charpy impact strength in CMT has been increased by around 70%. In comparison to CMT, IMT has a greater impact resistance (Bledzki & Faruk, 2004).

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Cellulose Fibre Reinforced Composites

10.5.2 Sugarcane bagasse fiber-reinforced polypropylene composites Compression-molded composites had homogeneous fiber distribution in the matrix. The plate distribution, however, was not uniform. The superior and inferior plate fibers were bigger and shorter. The top-down push allows the shorter fibers to easily enter the melted polymer. Blisters were identified in both the composite and the polypropylene plate. The content of reinforcement has little effect on the tensile and flexural moduli fluctuation. The inclusion of fibers can enhance modulus since their Young’s modulus is greater than the thermoplastic modulus. A big increase requires a good interfacial connection between the fiber and the matrix (Luz & Gonc¸alves, 2002). The flexural and tensile strengths showed a poor fiber–matrix connection. The lower elongation at break (tensile test) of the composite compared to polypropylene is most likely owing to flaws in the material after the fibers were incorporated. Blisters are empty spaces caused by mold air infiltration, causing the specimen to burst. This revealed that CMT is not suitable for thermoplastic composite production. In terms of elongation (tensile testing), the composites produced had a shorter elongation than the polypropylene used in the IMT method. There are two possible hypotheses: (a) failed fibers may generate a fracture and (b) the fibers slide in relation to the matrix. Elongated materials display ductile fracture, whereas failure spots in samples exhibit brittle fracture (Sawyer & Grubb, 1996). In the case of sugarcane bagasse, vacuum injection is the best molding process since it produces products with uniform fiber dispersion and no blisters. The tensile and flexural tests indicated that the samples developed lacked in both the strengths. Blisters and/or fiber nonhomogeneity are material imperfections that directly interfere with mechanical properties and prohibit the development of a high-resistance material. In general, the interfacial contact between elements was not adequate in the composites. The inclusion of fibers, on the other hand, increased the flexural modulus, resulting in stiffer composites.

10.5.3 Jute fiber-reinforced poly lactic acid composites The CMT process revealed that the reinforcing jute fibers in the PLA matrix improved mechanical characteristics. Tensile strength, flexural strength, and hardness all raise linearly with increasing fiber volume fraction until 30% fiber volume fraction is reached, at which point they rapidly fall. The greatest tensile strength was 64.133 MPa at a curing temperature of 160 °C as shown in Table 10.1. SEM study of samples demonstrates that brittle failure occurs in jute/PLA composites and that interfacial interaction between the composite elements decreases as the curing temperature increases from 160 to 180 °C. The reduction in interfacial bonding might be a result of fibers thermally degrading at elevated temperatures. Hydrophilic jute fiber–PLA composites as the fiber content rises, the amount of water absorbed increases proportionately. The generated composite with a 50% fiber volume fraction showed maximum water absorption of 20.7% at 160 °C curing

Table 10.1 Mechanical properties of composites fabricated using CMT and IMT. Manufacturing technique

Tensile strength (MPa)

Tensile modulus (GPa)

Elongation in %

Flexural strength (MPa)

Flexural modulus (GPa)

Impact strength

20 28 47 55

– – 2.2 1.5

– – 2.3 2.3

40 50 72 70.1

3 3.5 3.8 3.2

8.5 (mJ/mm2) 9 (mJ/mm2) – –

Fiber

Matrix

Hard wood

Polypropylene

Agave

Polylactic acid

CMT IMT CMT IMT

Sugarcane bagasse

Polypropylene

CMT

18.7

1

1.81

19.2

0.22

–

Kenaf

Polypropylene

IMT CMT

20 33

1 1.25

2.42 –

23 39

0.28 –

– –

Sisal

Polylactic acid

IMT CMT

24.7 75

2.35 3

– 6.2

45.6 100

2.37 6.1

– 9 (kJ/m2)

Jute

Polylactic acid

IMT CMT

55 64.1

7.1 3.39

– –

92 97.7

8.1 7.36

39 (J/m) –

Flax

Polypropylene

IMT CMT IMT

58 23 45

4.7 1 5.3

– 17.8 –

92 45 –

4.2 1.5 –

14 (kJ/m2) – 1.88 (kJ/m2)

Sisal

Polypropylene

CMT

18

0.8

–

45

1.7

–

IMT

26

1.95

9

43

3.15

45 (J/m)

CMT

–

–

–

42

9

39 (J/m)

IMT

74

4.7

–

115

7.2

12 (kJ/m2)

Kenaf

Polylactic acid

References Bledzki and Faruk (2004) Bledzki and Faruk (2004) Cisneros-Lo´pez et al. (2018) Perez-Fonseca, RobledoOrtı´z, Gonza´lez-Nu´n˜ez, and Rodrigue (2016) Luz, Gonc¸alves, and Del’Arco (2007) Luz et al. (2007) Asumani, Reid, and Paskaramoorthy (2012) Akhtar et al. (2016) Liang, Wu, Liu, and Wu (2021) Chaitanya and Singh (2017) Singh, Singh, and Dhawan (2020) Jiang, Yu, and Li (2018) Soleimani et al. (2008) Barkoula, Garkhail, and Peijs (2010) Oladele and Agbabiaka (2015) Munde, Ingle, and Siva (2019) Huda, Drzal, Mohanty, and Misra (2008) Anuar, Zuraida, Kovacs, and Tabi (2012)

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temperature. It demonstrates unequivocally that biocomposites are the future of commercial materials due to their environmental friendliness. Since many cracks formed during the tensile failure, the PLA matrix clearly displays brittle failure. Interfacial bonding is a critical factor affecting the mechanical strength of composites. Curing temperature is also critical in determining the fiber’s interfacial adherence to the matrix. When the curing temperature is increased, it has been observed that the interfacial connection between the fibers and matrix degrades, resulting in a decrease in the tensile strength of the jute/PLA composites. Tensile tests reveal that jute/PLA composites are fragile. It was revealed that the matrix fails first, followed by fiber failure and fiber pull-out in terms of fracture mechanics. The Young’s modulus of jute/PLA composites increased with increasing fiber volume percent up to 30% and then decreased with increasing fiber loading. In contrast to various fiber loadings and curing temperature ranges, a maximum Young’s modulus of 3.39 GPa for a 30% fiber volume fraction at 160 °C was recorded. Additionally, the results indicate that as fiber volume percentage increases, flexural strength increases linearly and reach a maximum of 97.741 MPa. The higher flexural strength of plain PLA was determined to be 65.531 MPa at 160 °C. The outcomes demonstrate explicitly that reinforcing fibers in the matrix improves flexural strength. Jute fibers’ flexural modulus was shown to rise with reinforcement. The greatest flexural modulus was 7.36 GPa at 30% volume of fiber and 160 °C curing temperature. Flexural strength is mostly dictated by the reinforcing %, the kind of fiber surface treatment, and the processing methods used to manufacture these green composites. The findings demonstrated that for jute fiber-reinforced polylactic acid composites, mechanical parameters such as tensile strength, flexural strength, and flexural modulus were all superior in tested specimens when compression molded versus injection molded (Singh et al., 2020; Jiang et al., 2018).

10.5.4 Sisal fiber-reinforced poly lactic acid composites These biocomposites are manufactured and compared independently using extrusion IMT E-IM and extrusion CMT E-CM processes. The long sisal fiber-reinforced PLA composites used in the study were formed from premixes created by the extrusion process of continuous long sisal fibers and PLA. These continuous long fibers could substantially aid in the composite material’s ability to sustain load. Sisal fibers are clearly hydrophilic, whereas the polylactic acid molecules are hydrophobic. Because of the low compatibility between sisal fibers and PLA, it is simple for defects, such as voids, to emerge in the composite’s interfacial layer, which has a significant impact on interfacial strength. Because of the shearing action of the open mill during the blending process, the sisal fiber retention length in short sisal fiber composites (SSFCs) was further reduced. As a result, when the composite material was stretched, the stress on the matrix was not properly shifted to the fiber. Furthermore, stress concentration was most likely caused by the presence of additional fiber ends in SSFCs, which worsened cracks in the composite material.

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When the composites were stretched, the resistance to deformation of the fiber and the PLA matrix differed. As a result of the decreased interface connection between the fiber and the matrix, there was a relative slip between the two phases, which was referred to as fiber pull-out. The interface bonding between the composite elements, as well as fiber orientation and dispersion, determine the load-sharing capacity of composites. When compared to pure PLA, the two composite materials’ notched impact strength was improved to varied degrees, and both showed a trend of increasing impact strength as fiber content rose. Fiber-reinforced composites engross the impact energy in three ways: matrix breaking, fiber breakage, and pull-out. PLA is a notch-sensitive polymer with low impact strength. When composites are subjected to impact stress, the fiber rupture or pull-out can release more energy, improving the impact strength of composite. The energy absorbed when fibers are dragged out of the matrix has been reported to be more than the energy absorbed when fibers break. Poor compatibility reduces the strength of the interface bonding between the elements. When impact loads are applied to composites, cracks are frequently produced in the weakest interfacial layer, which finally leads to fracture of material (Chaitanya & Singh, 2017; Liang et al., 2021).

10.5.5 Kenaf fiber (KF)-reinforced poly lactic acid composites When compressed, the mechanical and thermomechanical characteristics of kenaf/ PLA composites were much more significant than those of lean PLA. This is understood to be due to improved interfacial contact, which causes increased flexural stiffness. While adding kenaf fibers reduces the flexural strength of PLA composites, surface-treated kenaf fibers greatly enhance the modulus of PLA composites. The decreased flexural strength was most likely due to the kenaf fibers adhering poorly to the PLA. Due to the high flexural strength of PLA, it is not easy to improve the stability of PLA composites. Flexural strength of composites reinforced with kenaf fibers varies with fiber percentages, with flexural strength decreasing as fiber volume fraction increases. The best loading percentage of kenaf fiber in a biocomposite consisting of PLA resin and kenaf fiber was determined to be 37 volume%. Because improved fiber/matrix bonding, combined with weakened intercellular affinity in the case of unidirectional laminates, is required to increase impact strength due to ultimate cell stretching and uncoiling, improved PLA/kenaf interfacial adhesion does not continually improve impact performance. Compared to unreinforced PLA, the introduction of kenaf fiber at a low starting weight significantly reduced tensile strength and elongation at break. However, when the fiber content was raised to 20% by weight, the tensile strength increased to its maximum value. The low aspect ratio of kenaf fiber and its irregular cross-section have no influence on stress transmission from PLA to KF. The fiber content or volume percentage of the composite has a more substantial effect on stiffness than the fiber length and aspect ratio. Tensile strength and modulus enhancements in short-fiber composites are impacted by fiber amount, fiber aspect ratio, processing technique, and the excellent interaction between KF and the PLA matrix. This enhanced the passage of stress from matrix to fiber, resulting in a more significant reinforcing effect.

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Cellulose Fibre Reinforced Composites

Additionally, KF has slowed the crack’s propagation throughout the whole surface of the PLA matrix. Despite the minor reduction in strain, the inclusion of KF results in a less brittle fracture pattern. Additionally, it is critical to observe that the surface of the tensile fracture specimen is reasonably smooth and devoid of cavities. This demonstrates favorable processing conditions since there is no moisture absorption during the PLA–KF biocomposite manufacture. Flexural strength rises with increasing KF concentration and reaches a maximum value. The modulus of KF has a significant effect on the flexural modulus of PLA/KF biocomposites. When only physical contact between components is required to transfer stress, the stiffness is determined at extremely tiny pressures. Flexural modulus increases, typically with increasing KF concentration, while impact strength decreases. If no powder particles are used in the manufacture of the PLA–KF biocomposite, it is conceived that the impact strength would be increased due to the fibers’ being more uniform in size and homogeneous (Anuar et al., 2012; Huda et al., 2008).

10.5.6 Agave fiber-reinforced poly lactic acid composites In the case of compression-molded composites, when the fiber content exceeds a threshold fiber level which is 30 wt%, then the porosity of the compression-molded composites increases significantly. The results indicated that the tensile modulus of compression-molded composites containing up to 30% wood decreased with mounting wood content. This behavior was associated with the presence of voids and flaws within the composites as a result of phase incompatibility and manufacturing conditions. Due to inadequate fiber–matrix adhesion, tensile strength falls as fiber content increases (Cisneros-Lo´pez et al., 2018). The elongation at break for compression molding dropped from 3.5% (for polylactic acid) to roughly 2.1% (for biocomposites). The low elasticity of agave fibers contributes to the reduction in elongation at break. Statistically, compression-molded samples had less elongation at break. This is likely because compression-molded composites have more stiffness and strength because they have less porosity, which allows for better interfacial stress transfer, which leads to stiffer and more brittle materials. Low fiber content (10 wt%) flexural modulus remains statistically similar to pristine polylactic acid, ranging from 3738 MPa for polylactic acid to 3936 MPa in compression molded parts. Because of their decreased porosity and flaws, compression-molded composites have many superior flexural characteristics at larger fiber concentrations. Flexural strength dropped with fiber content around 61% for compression-molded (from 92 MPa for polylactic acid to 36 MPa) composites at 40 wt% fiber than the neat polylactic acid, similar to tensile strength (Cisneros-Lo´pez et al., 2018). The impact strength of compression-molded composites increased by 71% (from 28 for polylactic acid to 48 J/m) at 40 wt% agave fiber. According to the polylactic acid composites study, the impact strength is determined not only by the interfacial strength between the elements but also by fiber lengths, which increase the resistance to fiber pullouts. In reality, impact strength is proportional to the energy required for sample failure. As a result, for materials with weak adhesion (such as agave and polylactic acid), more energy may be expended during failure as a result of fiber pullout,

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especially as the fiber concentration grows; that is, more fibers must be pulled from the matrix. The hardness of the composite materials at low fiber content (20 wt% for compression molding) was statistically equivalent to that of neat polylactic acid. However, when the fiber content rose, the hardness of compression-molded composite materials increased by 5% (from 81 for polylactic acid to 85 Shore D at 30% fiber content). As per literature, fiber addition increases the hardness of the material through its reinforcing effect. This is because the fibers and matrix are crushed during the hardness testing process (pressed together). As a result, the contact may more efficiently transfer normal stress (pressure), hence increasing the material’s resistance to indentation. The storage modulus of polylactic acid biocomposites increased with fiber content and type in injection molding. These increases were facilitated by the fiber reinforcing and their good interaction with the polylactic acid matrix, which allowed for stress transmission inside the composite. The impact strength of polylactic acid (30 J/m) increases with the addition of agave fiber, reaching 35 J/m at 20% fiber content. The impact strength of agave bio composites improved as fiber concentration increased. This behavior is connected to fiber length. As long as no fibers fail, the composite impact strength may improve as a result of the greater mechanical energy released during failure (longer fiber pullout distance) and possible fiber–fiber contact (entanglements). Due to the high number of long fiber pullouts, impact strength is significantly boosted when longer fibers are put into the polylactic acid matrix. With fiber addition, the flexural strength of polylactic acid, which is 95 MPa, decreases. The impact strength is significantly increased when longer fibers are introduced into the polylactic acid matrix due to a large number of long fiber pullouts. With fiber addition, the flexural strength of polylactic acid, which is 95 MPa, tends to decrease (Perez-Fonseca et al., 2016). Tensile strength follows the same patterns as flexural strength. As the fiber content increased, the values decreased. In most cases, tensile strength declines as fiber content increases. This indicates that the fibers and matrix have constricted adhesion, resulting in poor interfacial stress transfer. For agave, the tensile strength of neat polylactic acid (60 MPa) was reduced to 53 MPa (30% fiber). A maximum value of 55 MPa was obtained for agave biocomposites with 20% fiber. The tensile modulus findings suggest that as the fiber content increased, so did the tensile modulus property. That is, agave biocomposites have a tensile strength of 1540 MPa, whereas neat polylactic acid has a tensile strength of 1242 MPa. Because cellulosic fibers have a higher modulus than polylactic acid, this increment was presumed.

10.6

Conclusions

Both IMT technique and CMT technique have their own advantages and disadvantages when it comes to manufacturing polymer composites. When compared to CMT, the IMT method exhibits superior tensile and flexural qualities. Additionally, the IMT method has superior impact resistance compared to the CMT procedure. And the IMT is often confined to the manufacture of components with short to intermediate

178

Cellulose Fibre Reinforced Composites

length fibers, the lengths of which are determined by the compounding process. CMT, on the other hand, is a more adaptable method that may be employed with any kind of fiber; however, the forming process takes longer than IMT. The IMT seems to be advantageous for manufacturing certain composite materials like sugarcane bagasse fiber-reinforced polypropylene, hardwood reinforced polypropylene, etc., whereas the CMT is observed to be better for manufacturing certain other composite materials like glass-reinforced polypropylene. But also, there are various other factors that influence the quality of composites like fiber length, fiber orientation, melt flow, mold temperature, melt temperature, curing time, and so on. So, the best suitable method for manufacturing a composite material should be based on all these factors as well. It is therefore reasonable that the industry has recently developed the injection–CMT technology in order to exploit the benefits from both molding processes.

References Akhtar, M. N., Sulong, A. B., Fadzly Radzi, M. K., Ismail, N. F., Raza, M. R., Muhamad, N., & Khan, M. A. (2016). Influence of alkaline treatment and fiber loading on the physical and mechanical properties of kenaf/polypropylene composites for variety of applications. Progress in Natural Science: Materials International, 26(6), 657–664. https://doi.org/ 10.1016/j.pnsc.2016.12.004. Anuar, H., Zuraida, A., Kovacs, J. G., & Tabi, T. (2012). Improvement of mechanical properties of injection-molded polylactic acid-kenaf fiber biocomposite. Journal of Thermoplastic Composite Materials, 25(2), 153–164. https://doi.org/10.1177/0892705711408984. Asim, M., Jawaid, M., Saba, N., Ramengmawii, Nasir, M., & Sultan, M. T. H. (2017). Processing of hybrid polymer composites—A review (pp. 1–22). Elsevier BV. https:// doi.org/10.1016/b978-0-08-100789-1.00001-0. Asumani, O. M. L., Reid, R. G., & Paskaramoorthy, R. (2012). The effects of alkali-silane treatment on the tensile and flexural properties of short fibre non-woven kenaf reinforced polypropylene composites. Composites Part A: Applied Science and Manufacturing, 43(9), 1431–1440. https://doi.org/10.1016/j.compositesa.2012.04.007. Barkoula, N. M., Garkhail, S. K., & Peijs, T. (2010). Effect of compounding and injection molding on the mechanical properties of flax fiber polypropylene composites. Journal of Reinforced Plastics and Composites, 29(9), 1366–1385. https://doi.org/10.1177/ 0731684409104465. Bledzki, A. K., & Faruk, O. (2004). Wood Fiber reinforced polypropylene composites: Compression and injection molding process. Polymer-Plastics Technology and Engineering, 43 (3), 871–888. https://doi.org/10.1081/PPT-120038068. Chaitanya, S., & Singh, I. (2017). Processing of PLA/sisal fiber biocomposites using direct- and extrusion-injection molding. Materials and Manufacturing Processes, 32(5), 468– 474. https://doi.org/10.1080/10426914.2016.1198034. Cisneros-Lo´pez, E. O., Perez-Fonseca, A. A., Gonza´lez-Garcı´a, Y., Ramı´rez-Arreola, D. E., Gonza´lez-Nu´n˜ez, R., Rodrigue, D., et al. (2018). Polylactic acid-agave fiber biocomposites produced by rotational molding: A comparative study with compression molding. Advances in Polymer Technology, 37(7), 2528–2540. https://doi.org/10.1002/adv.21928. Davis, B., Allen, P. J., & Gramann. (2003). Compression molding. Hanser Verlag.

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Thermomechanical characterization of cellulose fiber composites

11

M. Ramesha, J. Maniraja, and Lakshminarayanan Rajeshkumarb a Department of Mechanical Engineering, KIT—Kalaignarkarunanidhi Institute of Technology, Coimbatore, Tamil Nadu, India, bDepartment of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India

11.1

Introduction

Globally, production and consumption of plastics are accumulating the municipal waste. Ecological alarms are aggregating day to day and the request of swapping the harmful synthetic fibers with the biodegradable, renewable, and economical natural fibers is increased. Cellulose fibers are majorly aftermath of either agricultural background or from its processing or from the production of filtrates when agricultural yields are processed. Manufacturing industries are turning to increasingly sustainable, eco-friendly economic production with the rapid improvements in science and technology. The usage of wood products for the processing industries such as furniture making and building construction is increasing in the recent years. Vegetal fibers are very economical friendly due to their biodegradability and do not release any harmful gases or its residues (Ashori & Sheshmani, 2010; V€ais€anen, Das, & Tomppo, 2017). It requires very less power to manufacture compared to synthetic fiber like carbon, asbestos, and glass fiber. It ultimately leads to employability to the countryside people. The plant fibers are classified based on the parts of the plants and cellulose content of it namely bast fiber, seed fiber, leaf fiber, grass fiber, core fibers, and other kinds such as woods and roots (Petroudy, 2017) (Table 11.1). Matrix materials of cellulose fiber-reinforced composites can be classified into thermosets and thermoplastics, whereas the polymer is further classified as biodegradable and nonbiodegradable. When combined with nondegradable thermoplastics, its characteristics may not be biodegradable but their ability to be recycled would be higher when compared with thermosetting polymers. Thermosetting polymers are epoxy, urethane, vinyl ester, phenolic, polyester, polyimide, and polyurethane. Thermoplastics are polyethene, polypropylene, nylon, polycarbonate, polyvinyl chloride, polyether ether ketone (PEEK), and acrylonitrile butadiene styrene (ABS). Few of the notable biodegradable thermoplastic polymers are polylactic acid (PLA), polyhydroxy alkanoates (PHA), and polyglycolic acid (PGA), while the most commonly used thermosetting biodegradable polymer is polycaprolactone (PCL). There are various manufacturing processes of composite materials such as injection molding, filament winding, compression molding, resin transfer molding, pultrusion method, and spray up method. Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00014-8 Copyright © 2023 Elsevier Ltd. All rights reserved.

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Table 11.1 Types of fiber based on the part of plant (Abdel Hakim, Nassar, Emam, & Sulthan, 2011; Ramesh & Deepa, 2020; Saravana Kumar, Maivizhi Selvi, & Rajeshkumar, 2017). Types of fiber

Name of the plant

Bast Seed Leaf Grass and reed Core Wood

Jute, flax, ramie, hemp, kenaf, isora Cotton, coir, kapok, coconut, loofah, milk weed, kapok Sisal, pineapple, abaca, banana, palm, agave Rice, corn, wheat, bamboo Hemp, kenaf, jute Soft wood, hard wood

11.2

Classification of cellulosic fibers

Plant cells are being encompassed by rigid walls which are the main difference between plant and animal cells. Globally available fibers are classified majorly based on the origin. Based on the length of the fiber, it is classified as short fibers (1–5 mm) which has random orientation and long fibers (5–50 mm) which has specific fiber orientation (Putra et al., 2013). The foremost classification of fibers is plant fiber, animal fiber, and mineral fibers. The animal fiber consist of protein such as human hair, feather, and wool whereas in the case of plant fiber, it is classified based on seed fibers, bast fibers, leaf fibers, and grass fibers which is derived from the various types of plant like wood, jute, hemp, kenaf, sisal, coir, flax, bamboo, and fruit fibers (Table 11.2).

11.2.1 Chemical composition of cellulose fibers The major classification of plant fiber is primarily depends on the constituents like lignin, cellulose, hemicellulose, and various other minor constituents such as water decipherable organic components, pectin, waxes, and moisture content. Animal fiber like human hair is composed of carbon, oxygen, nitrogen, hydrogen, and sulfur. The moisture around the natural fiber completely depends upon volume fraction of void content, viscosity of the matrix, and humidity of temperature. The water absorption by the hydrophilic polymer and hydrophobic natural fiber is based on the mechanism of moisture diffusion such as water molecules diffused inside the polymer chain through the micro gap, water molecule capillary transportation within the gap, and the defects at the interfacial region of fiber and the matrix, water mobilization into the microcracks in the matrix which originated at the time of compound reaction (Berardi, Iannace, & di Gabriele, 2016; Ramesh & Kumar, 2020). The major composition of cellulosic fibers is presented in Table 11.3.

11.2.1.1 Cellulose Cellulose is made of thousands of glucose molecular units joined in long chains. It contains 44.4% carbon, 6.2% hydrogen, and 49.4% oxygen. It forms a slender rod like crystalline micro fibrils. Cellulose microfibrils of 10–50 nm diameters render better

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185

Table 11.2 List of cellulose fibers and their facts. S. no.

Fiber

Fact about the materials

References

Plant-based fibers 1.

Sugarcane

l

l

l

l

2.

Arenga pinnata

l

l

l

3.

Coir fiber

l

l

l

Saccharum officinarum is scientific name for sugarcane. Sugarcane plantation in about 1 ha generates a sugarcane waste of about 10 tons of and the sugarcane waste is termed as bagasse This sugarcane waste consisted of tiny and soft fibers This soft fiber has strength related problem but this can be compensated if it is combined with a material having high strength Tensile test shows diameter of this fiber range from 11 to 23 μm A. pinnata is a plant fiber that is abundantly available across the globe and it originates from palm sugar tree Its application spectrum is wide spread in structural and nonstructural elements like roof, rope, water filter and sound proof in recording studio It is good acoustical properties Cell structure of coir fiber is hollow in nature Such hollow structure of the fiber reduces the overall fiber density and makes the fiber potential to be used as thermal insulator This fiber readily replaces conventional glass and wool based fibers in sound proofing and noise reducing applications

Ismail, Ghazali, Mahzan, and Zaidi (2010) and Ramesh and Rajeshkumar (2018)

Ramesh, Balakrishnan, Dhanaprabhu, Ravanan, and Maniraj (2021)

Waifielate and Abiola (2008)

Continued

186

Cellulose Fibre Reinforced Composites

Table 11.2 Continued S. no.

Fiber

Fact about the materials

4.

Rice husk

l

l

l

References

Rice husk is derived out of a commonly cultivated paddy crop all around the globe It is characterized with good moisture resistance, noncombustible nature and keeps the rice grains out of fungal attack Rice husk waste hybridized with in polyurethane fiber forms a potential candidate for sound absorption in low frequency range

Ramesh, Kumar, Khan, and Asiri (2020)

Feathers are also considered as a significant waste, particularly from the chicken processing industry It is used for filling duvets, garments and upholstery Wool fibers are advantageous I terms of recyclability and renewable nature and they are derived out of sheep fleece by shearing its hair fibers Wool fibers are breathable, elastic, resistant towards flame and fire, resistant towards water and possess better capacity to store moisture content As the sheep wool fiber is porous in nature, it could be considered as a better alternative for mineral based fibers for sound proofing and thermal insulation applications Regenerated wool obtained from the processing of wool can be used in building related applications

Ashori (2013) and Ramesh and Deepa (2019)

Animal-based fibers 5.

Chicken feathers

l

l

6.

Sheep wool

l

l

l

l

Campas, Matos, Marques, and Valente (2017), Chen et al. (2010), and Ramesh, Deepa, Tamil Selvan, and Hemachandra Reddy (2020)

Thermomechanical characterization of cellulose fiber composites

187

Table 11.2 Continued S. no.

Fiber

Fact about the materials

References

Mineral fibers 7.

Chitosan

l

l

8.

Porous asphalt

l

l

Chitosan is a naturally derived polymeric material through industrial deacetylation of chitin from crustacean shells Meritorious features of the chitosan fibers are nontoxic, functional and antimicrobial properties, biocomposite and biodegradable use able in the area of biomaterials Porous asphalt is the one of the pavements

Corscadden, Biggs, and Stilesba (2014) and Ramesh, Rajeshkumar, and Bhuvaneshwari (2021)

Ballagh (1996)

It was used to slippery roads. It has a good acoustical energy so used to reduce the traffic noise and development of silent road surfaces

mechanical characteristics to the plant-based fibers with which they are used. The cellulose content in the fiber increases the strength and stiffness of the material.

11.2.1.2 Hemicellulose It is the matrix substance found in between the cellulose microfibrils.

11.2.1.3 Lignin It is a coating substance that solidifies the cell wall associated with the matrix substances. It is considered to be the main element which acts as an absorbing element for water in cell structure that also undergoes thermal disintegration at appropriate temperatures. It also helps in the biological degradation and flammability.

11.2.2 Based on properties of fiber 11.2.2.1 Microfibril angle Cellulose microfibrils oriented at an angle to the normal fiber is known as microfibrillar angle (MFA). MFA affects the fiber strength properties. Natural fiber with high cellulosic content and low MFA is very important for high fiber strength. The ductile

Table 11.3 Composition of cellulose fibers. Moisture content

Plant fiber

Cellulose (%)

Hemicellulose (%)

Lignin (%)

Wax

References

Sugarcane bagasse Sugarcane straw Banana fiber Sisal fiber Bamboo Coir Cotton Flax Hemp Jute Kenaf Oil palm Pineapple Ramie

43 40 63–64 65–70 26–43 32–41 96 71–74 71 72 44–56 66 81 68–76

28 30 19 12 30 11–21 3 19–21 23 13 7–14 – – 13–15

22 25 5 9.9 28 41–45 1–1.5 3 7 12 21.6 28.5 13 2

– – 10–11 10 – – – – – – – – 13.5

– – –

Mahmoodi et al. (2019) and Meyers (2007)

Coconut sheath

68

22

–

8.79

–

Abaca

56–63

20–25

7–9

–

–

Berardi et al. (2016) – 4.1 0.5 5.9 1.85 1.9 0.9 – – 6

Chen et al. (2010)

Ramesh, Rajeshkumar, and Bhuvaneshwari (2021) Ramesh, Ramnath, Khan, Khan, and Asiri (2020)

Thermomechanical characterization of cellulose fiber composites

189

nature of the fiber depends on the orientation of MFA. For spirally oriented MFA, the ductility is more and for parallel-oriented fiber, tensile strength of the fibers is more due to their rigidity and inflexibility. MFA is an important property in terms of strength and varies reversibly with the stiffness of the fiber. Nonlinear stress–strain behavior of the plant-based fibers was also governed by MFA. Elongation of the fibers and MFA were connected through few empirical relations by some of the earlier researchers (Kumar, 2000; Ramesh, Deepa, Kumar, Sanjay, & Siengchin, 2020).

11.2.2.2 Crystallinity Cellulose crystallinity and cellulose content are the two microstructural properties that affect the mechanical characteristics of natural plant-based fibers. Fibers with high content of cellulose and crystallinity are very desirable for reinforcement in structural applications. When the ratio between amorphous and crystalline regions increase, the flexibility and the rigidity of the cellulose fibers decrease and increase respectively. High strength is the outcome of increased fiber crystallinity and maximum water uptake and increasing elongation are the outcomes of fiber crystallinity decrease. Due to the high water absorption of amorphous region of the plant fibers, crystallinity directly governs the moisture absorption behavior of the fibers. The crystallite size affects the thermal degradation temperature of natural fibers (Bhoopathi, Ramesh, Naveen Kumar, Sanjay Balaji, & Sasikala, 2018; Manap, Putra Jaya, Nazri Borhan, Manap, & Ahmad, 2019).

11.2.2.3 Fiber density The lignocellulosic fibers have hollow and a cellular nature and perform well in acoustic and thermal insulators. Many of the natural plant-based fibers possess a density of 1600kg/m3 which is factually higher than that of density of water. Mechanical characteristics of the composites could be increased when the natural fibers are added to the polymeric matrix without altering their density. Density plays an important role in weight reduction. It is also stated that the specific mechanical characteristics of the plant-based natural fibers emerge comparable with that of glass fibers owing to the lesser density of the lignocellulosic fibers (Mohammed, Ansari, Pua, Jawaid, & Islam, 2015).

11.3

Properties

The properties of cellulose fiber composites depend on factors like mechanical composition, MFA, cell dimensions, physical, and chemical constituents. The performance level depends on orientation of fiber, strength, physical properties, interfacial adhesion property, volume fraction, and moisture absorption.

11.3.1 Morphology Microscopic technique renders real-time images of the targeted surface in magnified form disclosing the finer details of the surface under examination. Information from the microscopic examination reveals crystallography of the surface giving

190

Cellulose Fibre Reinforced Composites

information about the atomic arrangement upon the surface, morphology of the surface revealing the size and shape of the topographic surface features, and finally the composition of the surface. The fiber morphology is tested using instruments such as environmental scanning electron microscope like XL 30, Dutch Philip. Field emission scanning electron microscopy (FESEM) is a magnification technique capable of magnification ranging between 10
and 300,000
revealing the information about elements present and their topographical data on the surface through unlimited field depth virtually. FESEM is characterized with clear images which have lower electrostatic distortion and a spatial resolution of 1.5 nm when compared to scanning electron microscopy and the values are better by 3–6 times (Balaji, Ramesh, Kannan, et al., 2020; Fushan He, 2010).

11.3.2 Mechanical properties The mechanical behavior is tested to understand the force withstanding capacity of the material. The force may be tensile or compressive force. The stress and strain behavior of the sample can be identified. Universal testing machine (UTM) also termed as universal tester is a machine used for the testing of materials within a test frame and is normally used for tensile or compressive strength testing of the materials. The term “universal” in the name of the machine indicates its capability of testing both tensile and compressive strengths for practically each material, structure, and components (Reddy et al., 2021). Nanoindentation is the modern technique used for determining the mechanical properties of the material at micron and submicron level without any damages. This method can be done either longitudinal or transverse direction of the material. Properties like Young’s modulus, hardness, transverse modulus, and stiffness are identified. Few fibers such as corn stalks, coconut, and gypsum were even made into acoustic composite material. The compressive behavior and flexure characteristics of the few samples were fabricated and reshaped into 12
12 cm and 2.5
2.5
2 cm as per the ASTM standards by using UTM. It has been found that in a coconut fiber and gypsum composites, the amount of coir increases to increase compressive strength and gypsum is increased to enhance the flexural strength (Binici, Aksogan, & Demirhan, 2016). The mechanical behavior of the materials is identified using INSTRON 5543 UTM which contains a 5 kN load cell. The cross-head speed to be maintained in the machine is about 5 mm/min and materials are clamped at length of 140 mm, and compressive behavior is also identified in testing machine in which the 120 kN load cell has been equipped in it. The mechanical test results were analyzed through a stress–strain curve. These curves are representation of mechanical characteristics. The curve will be of elastic and plastic areas, elastic curve shows a deformation or elongation usually correlates with stress induced and those values are in line with the reversible strain which is elastic in nature. Plastic curves shown will be of nonlinear and irreversible. Once when materials are deformed in the plastic area,

Thermomechanical characterization of cellulose fiber composites

191

that cannot be reshaped or reformed to its original shape (Ramesh et al., 2020). The coconut fiber is an abundantly available renewable resource in the southern part of India especially in the Pollachi region near Western Ghats and it is known as carbon dioxide neutral material. Coconut fiber has less density and light weight (Prabhu, Krishnaraj, Gokulkumar, Sathish, & Ramesh, 2019). The flax fiber is considered as a flexural fiber due to its high flexural strength. The biocomposites impregnated with flax fiber has a better flexural strength and modulus are 2.352  0.47 MPa and 105  7.98 MPa, respectively (Mati-Baouche et al., 2014). The strength and elastic modulus of a waste corn husk treated with alkaline sodium hydroxide by changing the concentration showed twice the strength compared to other treatment. The tensile strength of an untreated corn waste fiber was 160.49  17.12 MPa. After the treatment strength was increased in the range between 230.90  41.85 MPa and 368.25  78.97 MPa, the modulus of elasticity of a raw fiber of untreated corn husk was 4.57  0.54 GPa. Even cotton fiber reinforced after treatment, the elasticity is increased to a range between 7.09  0.52 GPa and 15.87  1.87 GPa (Meyers, 2007). The flexural strength of the cotton fiber-reinforced composite is greater than that of sugarcane and coir fiber composites. This could be due to the fact that cotton fibers had more tenacity than sugarcane and coir fibers and the fact that the binding rigidity of cotton fibers directly governs the tensile modulus (Ramesh, 2018). The mechanical properties of the plant-based cellulose fibers are presented in Table 11.4.

11.3.3 Chemical property It is an important factor considered on processing of cellulose fiber composites for improving the fiber–matrix interfacial adhesion and bonding. Chemical treatment of these fibers reduces the presence of loose hydroxyl group and this in turn reduces the hydrophilicity of the fibers which also increases the mechanical characteristics. Different chemical treatments include silane, alkali, acrylation, benzoylation, strontium titanate, glycidyl methacrylate, maleated coupling agents, stearic acid, and isocyanate; sodium chloride improves the bonding at the interface between fibers and the matrix and the effective stress transfer between the fiber and matrix in the composites (Waifielate, 2008).

11.3.4 Thermal property Thermal stability is considered to be most significant of all properties which establish a blending between cellulose fibers or nanoparticles with conductive polymers which normally happens well above the glass transition temperature or melting point of the matrix material. The thermal property of the fiber such as degradation temperature and glass transition temperature are identified using various instruments like Pyrisil, Perkin Elmer, Mettler Toledo TGA/DSC with the temperature range around 25–800 °C heating rate at 10 °C/min with argon flow 30 mL/min. Phase transition evaluations such as melting temperature and glass transition temperature could be made

192

Cellulose Fibre Reinforced Composites

Table 11.4 Mechanical properties of the plant based cellulose fibers.

Fiber

Density (g/cm3)

Tensile strength (MPa)

Elastic modulus (GPa)

Specific modulus (GPa)

Banana Sisal

1.350 1.450

550 350

3.5 3.8

– –

Coconut Bamboo

1.375 1.52

88.63 571

4.4 27

– 18

Coir

1.15

100–200

6

5.2

Cotton

1.55

400–700

6–10

4–6.5

Flax Hemp

1.45 1.43

510–910 300–760

50–70 30–60

34–48 20–41

Jute Kenaf

1.34 1.30

20–55 22–60

14–39 –

Pineapple

1.44

200–460 300– 1200 414

60–82

42–57

Ramie Henequen

1.55 0.96

915 75

23 1281

15 –

References Fushan He (2010) Reddy et al. (2021) Binici et al. (2016) Ramesh, Deepa, Tamil Selvan, Rajeshkumar, et al. (2020) Prabhu et al. (2019) Mati-Baouche et al. (2014) Meyers (2007) Ramesh, Ramnath, Khan, Khan, and Asiri (2020) Balaji et al. (2020) Fushan He (2010) Corscadden et al. (2014) Ballagh (1996) Berardi et al. (2016)

not only by TGA but also by another method termed as differential scanning calorimetry (DSC). Meanwhile, changes in physiochemical behavior associated with thermal stability of the polymer matrix composite specimens could be assessed through methods like tan delta curve plotting, loss modulus, and storage modulus (Bhuvaneswari et al., 2021; Ramesh, Deepa, Arpitha, & Gopinath, 2019). Thermal characteristics of several of natural fiber composite specimens were determined through the measurement of thermal conductivity of the composite specimens at various locations at a temperature of 20 °C through hot wire method. The heating source in the measurement setup is of nickel alloy wire and the temperature measuring wire is made of 2 T type copper constantan thermocouples. Heating source induces the thermal pulses which propagate through the specimen, and the thermal conductivity of the specimen is calculated by tracking the above said thermal pulse (Ramesh, Bhoopathi, Deepa, & Sasikala, 2018). Thermal characteristics of plant-based natural fiber

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193

composites were found to be better when compared with the fiber boards made of sunflower fibers (k ¼ 0.89 W/mK) and other biodegradable thermal insulating boards such as palm fiber insulation board (k ¼ 0.15 W/mK) and hemp with concrete husk boards (k ¼ 0.21 W/mK). The values of cellulose fiber composite boards was also better than synthetic fiber glass boards whose thermal conductivity value was noted to be 0.035 W/mK (Asrofi, Sapuan, Ilyas, & Ramesh, 2020; Prabahakaran, Krishnaraj, Senthilkumar, & Zitoune, 2014). It was also stated by few other authors that the plant-based cellulose composite fiber boards had their thermal conductivity values slightly higher than the thermal conductivities of rock wool insulating boards (k ¼ 0.04 W/mK) and mineral wool insulating material (k ¼ 0.04 W/mK) (Sari, Wardana, Irawan, & Siswanto, 2016). In areca nut leaf fibers, thermal characteristics for the composites with fiber length of around 20 mm were measured at a temperature of 20 °C. It was noted from the results that the thermal degradation temperature was around 345 °C–350 °C which is mainly due to the porosity of the areca fiber composites (Ramesh, Maniraj, & Rajeshkumar, 2021). Few other experimenters determined the thermal insulation behavior of sheep wool fibers which is believed to have excellent thermal insulation characteristics. Coefficient of thermal conductivity of the sheep wool-based polymer composite material was measured with the aid of a QTM-500 model thermal conductivity apparatus as per ASTM C1113-90. It was noted that the value of thermal conductivity for sheep wool-based composites was around 0.1 W/mK which was lesser than the thermal conductivity of any plant-based natural fibers. Few other experiments for measuring the coefficient of thermal conductivity for the polymer composites prepared using waste corn stalks reinforced within epoxy resin were carried out. Results showcased that among all the specimens tested, lowest value of thermal conductivity was 0.075 W/mK and highest value of thermal conductivity was 0.1538 W/mK. From these results, it could be noted that plant-based cellulose fiber composites behaved better in terms of thermal conductivity (Vimal, Hari Hara Subramanian, Aswin, Logeswaran, & Ramesh, 2015). Thermal degradation behavior of wheat gluten composites with and twice equivalent amount of water mixed was assessed by DSC method using DSC822 mettle Toledo model apparatus by placing the specimen in the sealed pan with the heat supplied at the rate of 250 °C per minute. It was noted from the results that the melting enthalpy of wheat gluten without and with twice the quantity of water with respect to the plasticizer was 110 J/g and 1.3 KJ/g, respectively. DSC curves exhibited a melting peak for both the variants of wheat gluten composites at 150 °C. Few other experiments conducted with rock wool fibers as reinforcements in epoxy matrix to determine the thermal degradation temperature and thermal conductivity exhibited the melting peak for the composites at a temperature of 650 °C and a conductivity value of 0.043 W/mK. Few experimental trails were conducted on abaca-based polymer composites to determine the thermal behavior through DTA tests. From the DTA curves, it was noted that heat flow decreased continuously until the temperature of the specimen reached 554 °C and saturated at this point while the heat flow increased beyond this temperature value. Results showcased that the sample experienced the first peak in DTA curve at a temperature of 379 °C, while the area covered under the curve was 588 mJ with an equivalent energy of 58 J/g. After this point, energy value raised with the increase in heat

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Table 11.5 Thermal properties of cellulose fibers (Asrofi et al., 2020; Bhuvaneswari et al., 2021; Prabahakaran et al., 2014; Ramesh et al., 2018; Ramesh, Deepa, et al., 2019; Ramesh, Maniraj, and Rajeshkumar, 2021; Sari et al., 2016).

Fiber Hemp fiber Kenaf fiber Coco plant fiber Sheep wool Wood fiber Cork fiber Cellulosic fiber Flax fiber Glass wool fiber Rock wool fiber Expanded polyester resin

Thermal conductivity (W/mK)

Relative vapor flux resistance (μ)

Coefficient of sound absorption (α)

Reduction index of noise impact (ΔLw) in dB

0.44 0.0435 0.0428 0.0436 0.0649 0.0387 0.0369 0.0396 0.036 0.0448 0.0309

3 3 19 4 4 11 1 2 – – 99.9

0.59 (30 cm) 0.756 (5 cm) 0.419 0.375 (6 cm) 0.319 0.39 0.99 (6 cm) – 0.99 (5 cm) 0.89 (5 cm) 0.48

– – 22 19 20 18 21 – – – 31

Cost incurred for production (Euro/m2) 4.6 – – – 11.5 18.6 – 6.5 11.8 5.6 10.2

flow until the aforementioned temperature point. Table 11.5 lists the thermal, sound absorption, and cost of manufacturing of various plant-, animal-, and mineral-based cellulose fibers (Franco, 2007).

11.3.5 Tribological behavior Various parts of automotive such as gears, wheel, bush bearing, and other mechanical parts are needed to be tested for its tribological behavior. Since the tribological loading condition-based components are made by using the plant-based cellulose fiber-reinforced polymer composite. The major selection criteria are selection of materials and surface processing in as much as they affect wear and tear. The asbestos fiber being a prevailing friction behavior being widely used in the worldwide in brake coupling, brake pads and brake lining but there are numerous health hazards because of this usage. The materials used for brake lining material are of 0.3–0.7 friction coefficient as the materials friction coefficient should not change with the braking with respect to time (Ramesh, Palanikumar, & Hemachandra Reddy, 2014). Various countries such as American and European countries are regulating amendments for using antifriction material which are made up of hazardous ingredients that have negative impact on the environment (Chikhi, Boudjemaa, Boudenne, & Gherabli, 2013). Usage of cashew can reduce noise as well as friction coefficient due to the content increases which simultaneously increases the acoustic performance.

Thermomechanical characterization of cellulose fiber composites

11.4

195

Modification of fiber

Cellulose fibers necessitate various type of surface treatment in order to enhance various ranges of properties suitable for different end users. The fiber’s hydrophilic polar nature and nonpolymer matrix with polar hydrophobic nature combines to have an incompatible boundary which seems to be a major drawback that can be solved through physical and chemical modification techniques of plant-based cellulose fibers to a certain extent (Franco, 2007; Ramesh et al., 2014; Ramesh, Deepa, Tamil Selvan, Rajeshkumar, et al., 2020; Vimal et al., 2015).

11.4.1 Physical modification Sputtering method, corona discharge technique, steam explosion method, low temperature plasma treatment method, calendaring, stretching technique, and thermal treatment technique are few notable classifications of physical treatment methods used widely. Yet, this practice of physical treatment has been masked by various chemical treatment methods during the past decade due to various disadvantages of the physical treatment method (Binici et al., 2016; Mati-Baouche et al., 2014; Reddy et al., 2021).

11.4.1.1 Steam explosion method Steam explosion method is utilized for extracting cellulose nanofibrils by applying high pressure steaming followed by decompression. This method with 2% NaOH and steam penetrates into the microfibril bundles to remove the natural and artificial impurities. This method is used modifying the various cellulose fiber treated at different steam pressure of around 0.8 MPa for bamboo in order to preserve the fiber affinity toward water, and mechanical properties, dissolving ability of the fiber in the caustic solution decrease with increase in explosion pressure (Prabhu et al., 2019; Ramesh, Deepa, Tamil Selvan, Rajeshkumar, et al., 2020).

11.4.1.2 Heat treatment This type of treatment is majorly used to stabilize friction and wear characteristics by heating the composite specimens within a temperature of around 140 °C for a time period of 4 h. The major drawback of this treatment is that when the fiber is over heated, it may have an adverse on the end characteristics of the composites such as composite modulus, elongation, and fracture toughness (Prabhu et al., 2019).

11.4.2 Chemical modifications Chemical modification methods are the widely used current-day technique for performing surface modification of plant-based cellulose fibers. Few of the noteworthy chemical treatment methods are fiber impregnation, silane treatments, maleic

196

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anhydride modification, graft copolymerization, acidic and alkali treatment, cyanate treatment, and substitution reactions. These methods help majorly in enhancing the adhesion between fiber and matrix interfacial region by means of induction of functional groups upon the surface of the fibers (Ramesh et al., 2018).

11.4.2.1 Alkali treatment The fiber surface is modified by using the sodium hydroxide (NaOH) solution for higher friction coefficient around 25 °C for 12 h (Franco, 2007). This improves the surface roughness of the cellulose fiber and few microlevel impurities with lesser molecular weight like lignin, hemicellulose, and pectin were washed away by the treating agent while the crystalline microconstituent namely cellulose remains stable. Hence increase in content of cellulose enhances the thermal resistance and also gives better tribological characteristics to the composites (Ramesh, Gopinath, & Deepa, 2016).

11.4.2.2 Silane coupling agent Natural plant-based cellulose fibers are soaked with the KH550 silane, which acts as a coupling agent, and ethanol for a time period of 3 h. This treatment method improves the hydrophilicity of the interface between polymer and fiber by the formation of silicon bonds with oxygen atom and cellulose present in the fiber microstructure. It falls under the category of silane having amino substitution such as inorganophilic silone and organophilic silone. This compound undergoes reaction with the matrix material and transition compounds formed out of the reaction establishes the compatibility among the fiber and the matrix material. Silane-modified fiber showed reduced wear and increase in friction coefficient (Evon, Vandembossche, Pontalier, & Rigal, 2014).

11.5

Applications of cellulose fiber composites

The cellulose fiber composites have been widely used in automotive industry for different parts of the vehicle and especially used for the brake system where wear and friction play a major role. These composites find their applications in automotive interior parts as well as for exterior components such as parcel shelves, seat backs, truck lines, noise insulation panel, back door panels, and floor trays where the demand for these composites is more with respect to low-density components. To state with an example, BMW uses cellulose fiber composites in soundproofing the interior cabin, wool-based fiber-reinforced composites in car upholstery, and the composites in seat rests. The phenolic bamboo fibersreinforced composites are used for the braking system. Cellulose fiber composites are also used in civil applications for their susceptibility to environmental attack. Sisal and coir fiber-reinforced composites find its application in roofing application so that they act as potential substitutes for harmful asbestos. The applications are listed in Table 11.6.

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Table 11.6 List of synthetic fibers and its application along with its competing fiber (Raj, Fatima, and Tandon, 2020; Ramesh, Muthukrishnan, Khan, and Azam, 2019; Ramesh, Rajeshkumar, Balaji, and Bhuvaneswari, 2021). Synthetic fiber composites Glass fiber reinforced with polyester Woven synthetic fiber reinforced with polyester Asbestos and mineral fiber Polyester Asbestos

11.6

Competing cellulose fiber composites

Performance-based application

Sugarcane fiber reinforced polyester Seed oil palm fiber with polyester Sisal fiber reinforced in phenolic resin Oil palm fiber reinforced in polyester Rice straw and rice husk dust

Friction–Brake application Friction and wear performance Brake pad with better friction performance Wear rate Break pad

Merits and demerits of cellulose fibers over synthetic fibers

11.6.1 Merits The cellulose fibers are preferred for various benefits such as strength, toughness, corrosion resistance, wear resistance, and also reduce dermal and respiratory irritation. Biodegradability: This nature regulates and reduces the accumulation of fund pollution after the concern usage. They are also called as the eco-materials since it creates a healthy eco-system and environmentally friendly atmosphere. Availability: The raw materials are available abundantly. Renewable resources, low relative density, high specific strength (Ramesh, Kumar, Khan, & Asiri, 2020). Cost effective: Light weight been an advantageous when the composites been used for automobile by cost effective nature, increasing the fuel economy, reduction in the carbon dioxide emission and mitigation of the greenhouse gases emission (Abdel Hakim et al., 2011). Hybridization of cellulose fiber along with the synthetic fiber provides a moisture resistant and corrosion resistant. This method is considered to be the best method to improving the properties (V€ais€anen et al., 2017). Energy recovery  Reduced tool wear  To maintain the product consistency, minimizing the voids and internal structure stress and also reduces the manufacturing cost. Best alternatives for replacing synthetic fibers.

11.6.2 Demerits Cellulose fibers are not easily miscible or incompatible with the polymer have a poor wettability nature. Fiber–matrix interaction is the chief parameter to determine the reinforcing capability of the lignocellulosic fiber in hydrophobic polymeric matrix

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(V€ais€anen et al., 2017). It absorbs high quantity of water or moisture. Low-dimensional stability, inadequate toughness (Ramesh, Kumar, Khan, & Asiri, 2020). Low thermal stability, higher moisture absorption, poor resistance to microbial attack.

11.7

Conclusion

Cellulose fibers are renewable, biodegradable and eco-friendly fibers have good acoustical, mechanical, thermal characteristics have been reported. These fibers necessitate various types of surface treatment in order to enhance various ranges of properties suitable for different end users. The advantages of the cellulose fiber composites are biodegradable nature, economically efficient, light weight, and its durability. The demerits of these fibers are the wettability and moisture absorption. Researchers are improvising cellulose fiber properties through treatment and fabricating composite material through various fabrication processes.

References Abdel Hakim, A. A., Nassar, M., Emam, A., & Sulthan, M. (2011). Preparation and characterization of rigid polyurethane foam prepared from sugarcane bagasse polyol. Materials Chemistry and Physics, 129, 301–307. Ashori, A. (2013). Effects of nano particles on the mechanical properties of rice straw polypropylene composites. Journal of Composite Materials, 47, 149–154. Ashori, A., & Sheshmani, S. (2010). Hybrid composites made from recycled materials: Moisture absorption and thickness swelling behavior. Bioresource Technology, 101, 4717–4720. Asrofi, M., Sapuan, S. M., Ilyas, R. A., & Ramesh, M. (2020). Characteristic of composite bioplastics from tapioca starch and sugarcane bagasse fibre: Effect of time duration of ultrasonication (bath-type). Materials Today: Proceedings. https://doi.org/10.1016/j. matpr.2020.07.254. Balaji, D., Ramesh, M., Kannan, T., et al. (2020). Experimental investigation on mechanical properties of banana/snake grass fibre reinforced hybrid composites. Materials Today: Proceedings. https://doi.org/10.1016/j.matpr.2020.09.548. Ballagh, K. O. (1996). Acoustical properties of wool. Applied Acoustics, 48, 101–120. Berardi, U., Iannace, G., & di Gabriele, M. (2016). Characterization of sheep wool panels for room acoustic applications. Proceedings of Meetings on Acoustics, 28, 015001. Bhoopathi, R., Ramesh, M., Naveen Kumar, M., Sanjay Balaji, P., & Sasikala, G. (2018). Studies on mechanical strengths of hemp-glass fibre reinforced epoxy composites. IOP Conference Series: Materials Science and Engineering, 402(1), 012083. Bhuvaneswari, V., Priyadharshini, M., Deepa, C., Balaji, D., Rajeshkumar, L., & Ramesh, M. (2021). Deep learning for material synthesis and manufacturing systems: A review. Materials Today: Proceedings. https://doi.org/10.1016/j.matpr.2020.11.351. Binici, H., Aksogan, O., & Demirhan, C. (2016). Mechanical, thermal and aoucstical characterizations of an insulation composite made of bio-based materials. Sustainable Cities and Society, 20, 17–26. Campas, J., Matos, E., Marques, A., & Valente, L. M. P. (2017). Hydrolyzed feather meat as a partial fishmeal replacement in diet’s for European sea bass (Dicentrarc Hus Labrax) juveniles. Aquaculture, 476, 152–159.

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Chen, K., Liu, Q., Liao, G., Yang, Y., Ren, L., Yang, H., et al. (2010). The sound suppression characteristics of using feather of owl. Journal of Bionic Engineering, 9, 192–199. Chikhi, M., Boudjemaa, A., Boudenne, A., & Gherabli, A. (2013). Experimental investigation of new bio-composite with low cost for thermal insulation. Energy and Buildings, 66, 267–273. Corscadden, K. W., Biggs, J. N., & Stilesba, D. K. (2014). Sheep’s wool insulation: A sustainable alternative use for a renewable resource? Resources, Conservation and Recycling, 86, 9–15. Evon, P., Vandembossche, V., Pontalier, P. Y., & Rigal, L. (2014). New thermal insulation fibreboards fromboards from cake generated during bio refinery of sunflower whole plant in a twin screw extruder. Industrial Crops and Products, 52, 354–362. Franco, A. (2007). An apparatus, for routine measurements of thermal conductivity of materials for building application based on a transient hot-wire method. Applied Thermal Engineering, 27, 2495–2504. Fushan He, C. G. A. S. Y. (2010). Effect of bamboo fibre modification on tribological performance of brake composites. Advanced Materials Research, 150-151, 1801–1805. Ismail, L., Ghazali, M. I., Mahzan, S., & Zaidi, A. M. A. (2010). Sound absorption of Arenga pinnata natural fibre. World Academy of Science, Engineering and Technology, 43, 438–440. Kumar, M. N. V. R. (2000). A review of chitin and chitosan applications. Polymer, 46, 1–27. Mahmoodi, N. M., Taghizadeh, M., Taghizadeh, A., Abdi, J., Hayati, B., & Shekarchi, A. A. (2019). Bio-based magnetic metal-organic framework nanocomposite: Ultrasoundassisted synthesis and pollutant (heavy metal and dye) removal from aqueous media. Applied Surface Science, 480, 288–299. Manap, N., Putra Jaya, R., Nazri Borhan, M., Manap, N., & Ahmad, J. (2019). Acoustic absorption characteristics of porous aphalt containing shells. International Journal of Recent Technology and Engineering, 8, 327–331. Mati-Baouche, N., de Baynast, H., Lebert, A., Sun, S., Lopez-Mingo, C. J. S., Leclaire, P., et al. (2014). Mechanical, thermal and acoustical characterizations of an insulating bio-based composite made from sunflower stalks particles and chitosan. Industrial Crops and Products, 58, 244–250. Meyers, H. K. (2007). Applications of chitosan for improvement of quality and shelly life of foods: A review. Journal of Food Science, 72, 87–100. Mohammed, L., Ansari, M. N. M., Pua, G., Jawaid, M., & Islam, M. S. (2015). A review on natural fibre reinforced polymer composite and its applications. International Journal of Polymer Science. https://doi.org/10.1155/2015/243947. Petroudy, S. D. (2017). Physical and mechanical properties of natural fibres. In Advanced high strength natural fibre composites in construction Elsevier. Prabahakaran, S., Krishnaraj, V., Senthilkumar, M., & Zitoune, R. (2014). Sound and vibration damping properties of flax fibre reinforcement composites. Procedia Engineering, 97, 573–581. Prabhu, L., Krishnaraj, V., Gokulkumar, S., Sathish, S., & Ramesh, M. (2019). Mechanical, chemical and acoustical behavior of sisal–tea waste–glass fibre reinforced epoxy based hybrid polymer composites. Materials Today: Proceedings, 16, 653–660. Putra, A., Effendy, H., Mohd Farid, W., Ayob, M. R., Abdullah, Y., & Sajidin Py, M. (2013). Utilizing sugarcane wasted fibres as a sustainable acoustics absorber. Procedia Engineering, 53, 632–638. Raj, M., Fatima, S., & Tandon, N. (2020). A study of areca nut leaf sheath fibres as a green sound—Absorbing material. Applied Acoustics, 169, 107490. Ramesh, M. (2018). Hemp, jute, banana, kenaf, ramie, sisal fibres. In Handbook of properties of textile and technical fibres (pp. 301–325). Woodhead Publishing. Ramesh, M., Balakrishnan, P., Dhanaprabhu, S. S., Ravanan, A., & Maniraj, J. (2021). Enzymemodified electrodes for biofuel cells: A comprehensive review. Materials Today: Proceedings. https://doi.org/10.1016/j.matpr.2020.11.922.

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Ramesh, M., Bhoopathi, R., Deepa, C., & Sasikala, G. (2018). Experimental investigation on morphological, physical and shear properties of hybrid composite laminates reinforced with flax and carbon fibres. Journal of the Chinese Advanced Materials Society, 6, 640–654. Ramesh, M., & Deepa, C. (2019). Processing of green composites. In Green composites (pp. 47–72). Singapore: Springer. Ramesh, M., & Deepa, C. (2020). Properties of cellulose based bio-fibres reinforced polymer composites. In Biofibres and biopolymers for biocomposites (pp. 71–89). Cham: Springer. Ramesh, M., Deepa, C., Arpitha, G. R., & Gopinath, V. (2019). Effect of hybridization on properties of hemp-carbon fibre-reinforced hybrid polymer composites using experimental and finite element analysis. World Journal of Engineering, 16, 248–259. Ramesh, M., Deepa, C., Kumar, L. R., Sanjay, M. R., & Siengchin, S. (2020). Life-cycle and environmental impact assessments on processing of plant fibres and its bio-composites: A critical review. Journal of Industrial Textiles. https://doi.org/10.1177/1528083720924730. Ramesh, M., Deepa, C., Tamil Selvan, M., & Hemachandra Reddy, K. (2020). Effect of alkalization on characterization of ripe bulrush (Typha domingensis) grass fibre reinforced epoxy composites. Journal of Natural Fibres. https://doi.org/10.1080/15440478.2020. 1764443. Ramesh, M., Deepa, C., Tamil Selvan, M., Rajeshkumar, L., Balaji, D., & Bhuvaneswari, V. (2020). Mechanical and water absorption properties of Calotropis gigantea plant fibres reinforced polymer composites. Materials Today: Proceedings. https://doi.org/10.1016/j. matpr.2020.11.480. Ramesh, M., Gopinath, A., & Deepa, C. (2016). Machining characteristics of fibre reinforced polymer composites: A review. Indian Journal of Science and Technology, 9(42), 1–7. Ramesh, M., & Kumar, L. R. (2020). Bioadhesives. In R. Inamuddin, M. I. Boddula, Ahamed, & A. M. Asiri (Eds.), Green adhesives (pp. 145–167). John Wiley & Sons, Inc. Ramesh, M., Kumar, L. R., Khan, A., & Asiri, A. M. (2020). Self-healing polymer composites and its chemistry. In Self-healing composite materials (pp. 415–427). Elsevier. https://doi. org/10.1016/b978-0-12-817354-1.00022-3. Ramesh, M., Maniraj, J., & Rajeshkumar, L. (2021). Biocomposites for energy storage. In Biobased composites: Processing, characterization, properties, and applications (pp. 123–142). John Wiley & Sons, Inc. Ramesh, M., Muthukrishnan, M., Khan, A., & Azam, M. (2019). Metal-organic-frameworkquantum dots (QD@ MOF) composites. In 58. Metal-organic framework composites: Volume II (p. 49). Materials Research Foundation. Ramesh, M., Palanikumar, K., & Hemachandra Reddy, K. (2014). Impact behaviour analysis of sisal/jute and glass fibre reinforced hybrid composites. Advanced Materials Research, 984, 266–272. Ramesh, M., & Rajeshkumar, L. (2018). Wood flour filled thermoset composites. In 38. Thermoset composites: Preparation, properties and applications (pp. 33–65). Materials Research Foundations. https://doi.org/10.21741/9781945291876-2. Ramesh, M., Rajeshkumar, L., Balaji, D., & Bhuvaneswari, V. (2021). Green composite using agricultural waste reinforcement. In Green composites (pp. 21–34). Singapore: Springer. Ramesh, M., Rajeshkumar, L., & Bhuvaneshwari, V. (2021). Bamboo fibre reinforced composites. In M. Jawaid, S. Mavinkere Rangappa, & S. Siengchin (Eds.), Composites science and technology. Bamboo fibre composites (pp. 1–13). Singapore: Springer. https://doi.org/ 10.1007/978-981-15-8489-3_1. Ramesh, M., Ramnath, R. A., Khan, A., Khan, A. A. P., & Asiri, A. M. (2020). Electrically conductive self-healing materials: Preparation, properties, and applications. In Selfhealing composite materials (pp. 1–13). Woodhead Publishing.

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Reddy, K. H., Meenakshi Reddy, R., Ramesh, M., Mohana Krishnudu, D., Madhusudhan Reddy, B., & Raghavendra Rao, H. (2021). Impact of alkali treatment on characterization of tapsi (Sterculia urens) natural bark fibre reinforced polymer composites. Journal of Natural Fibres, 18, 378–389. Saravana Kumar, A., Maivizhi Selvi, P., & Rajeshkumar, L. (2017). Delamination in drilling of sisal/banana reinforced composites produced by hand lay-up process. Applied Mechanics and Materials, 867, 29–33. Sari, N. H., Wardana, I. N. G., Irawan, Y. S., & Siswanto, E. (2016). Physical and acoustical properties of corn husk fibre panels. Advances in Acoustical and Vibration. https://doi. org/10.1155/2016/5971814. V€ais€anen, T., Das, O., & Tomppo, L. (2017). A review on new bio-based constituents for natural fibre-polymer composites. Journal of Cleaner Production, 149, 582–596. Vimal, R., Hari Hara Subramanian, K., Aswin, C., Logeswaran, V., & Ramesh, M. (2015). Comparisonal study of succinylation and phthalicylation of jute fibres: Study of mechanical properties of modified fibre reinforced epoxy composites. Materials Today: Proceedings, 2, 2918–2927. Waifielate, A. A. (2008). Mechanical property evaluation of coconut fibre. Blekinge Institute of Technology. Master’s thesis. Waifielate, A. A., & Abiola, B. O. (2008). Mechanical property evaluation of coconut fibre. Master of Science thesis Karlskrona, Sweden: Blekinge Institute of Technology.

Evaluation of moisture uptake behavior in cellulose fiber

12

Adnan Khana, Sumeet Malika, Nisar Alib, Kashif Rasoolc, and Muhammad Bilald a Institute of Chemical Sciences, University of Peshawar, Peshawar, Khyber Pakhtunkhwa, Pakistan, bKey Laboratory for Palygorskite Science and Applied Technology of Jiangsu Province, National & Local Joint Engineering Research Center for Deep Utilization Technology of Rock-salt Resource, Faculty of Chemical Engineering, Huaiyin Institute of Technology, Huaian, China, cQatar Environment and Energy Research Institute (QEERI), Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar, dInstitute of Chemical Technology and Engineering, Faculty of Chemical Technology, Poznan University of Technology, Poznan, Poland

12.1

Introduction

In the older times, artificial fibers have greatly been used in the manufacture of fiberbased composites. These artificial fibers include carbon, aramid, and glass materials that had been reinforced with their counterparts like polymers (Kosi
nski, Brzyski, & Duliasz, 2020). Such fiber composites provided many practical applications in a variety of fields. Some of the common applications of these artificial fiber composite materials included electronics, automobiles, aerospace, aviation, helmet, marine, oil spacing, etc. (Aliotta, Gigante, Coltelli, Cinelli, & Lazzeri, 2019; Khan, Khan, Khan, et al., 2021). These applications of fiber composites are associated with their unique properties like their strength and stiffness, better environmental resistance, hydrophobicity leading to stronger bonding with the polymers (Khan, Khan, Ali, et al., 2021; Senff, Ascensa˜o, Ferreira, Seabra, & Labrincha, 2018). Along with the high exploitation of artificially made cellulosic fiber composites, some of the issues have also been faced. Such issues include the nonrenewability, nonbiodegradability, and non-eco-friendly nature of these cellulosic fibers (Ali et al., 2021; Iucolano, Liguori, Aprea, & Caputo, 2018). This nature of cellulose fibers causes toxicity leading to adverse effects on the environment. In recent times, attention has been given to such practices to minimize the environment-devastating effects. In this context, scientists are trying to utilize natural, biodegradable, and renewable sources in different fields (Hussainn et al., 2019; Yang et al., 2021). The rise in environmental safety concerns has encouraged the utilization of natural fibers reinforcing materials along with polymers obtaining composites. The replacement of artificial fibers with natural organic fillers has been quite helpful toward less-hazardous tools in various fields (Dinh Vu, Thi Tran, & Duy Nguyen, 2018; Nawaz, Khan, Ali, Ali, & Bilal, 2020). Among various natural materials used, cellulose has been utilized on massive scales until recently for the manufacture of fiber-based engineered composites in various Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00021-5 Copyright © 2023 Elsevier Ltd. All rights reserved.

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applications. The facts behind the enormous usage of cellulose-based composites in different fields include its abundant presence in nature, biodegradable nature, light weight, high specific strength and modulus, enhanced energy recovery, low cost, and density, etc. (Ali, Uddin, et al., 2020; Babar et al., 2018). Contemplating these useful properties of cellulose, a variety of cellulosic fiber-based composites has been reported to be used in multiple fields. Apart from their useful properties and great utilization, some of the properties associated with cellulose fibers tend to lower their utilization (Ali, Ahmad, et al., 2020; Siakeng, Jawaid, Asim, Saba, Sanjay, Siengchin, and Fouad, 2020). These properties include the imperfect bonding of cellulose fibers with that of the polymer. The condition arises due to the interaction of hydrophilic and polar natural fibers with that of the hydrophobic and nonpolar fibers. The hydrophilic and polar nature of cellulose fibers ultimately gives rise to low-moisture resistance (Ali, Bilal, et al., 2020; Yu & Yang, 2021). All these conditions tend to lower the ability of the cellulose fibers in various fields. To overcome these problems surface modifications of the cellulosic fiber-based composites are performed. The chemical modifications help in the removal of lignin, hemicelluloses, and other amorphous parts of the fibers which are mainly responsible for the moisture uptake (Cichosz & Masek, 2019; Khan et al., 2020). The presented chapter gives a brief analysis of the moisture uptake property of the cellulosic fibers.

12.2

Moisture uptake by cellulose fibers in cellulose-based composites

Generally, cellulose-reinforced polymer composites are very commonly used in various applications. Such composites incorporate the useful properties of both their counterparts, i.e., the polymer and the cellulosic reinforcement material (Ali, Khan, Malik, et al., 2020; Syafri et al., 2019). Although the cellulose counterpart enhances the applicability of the polymer-based composites, certain restrictions are also associated with it. The water uptake property possessed by the cellulose fibers tends to limit its applicability (Ali, Khan, Bilal, et al., 2020; Senthilkumar et al., 2018). Due to this property of cellulose-based composites, their applicability is restricted in outdoor environments or areas with higher moisture content. The cellulose-based composites, if exposed to highly moistened areas, or immersed in water, tend to absorb high volumes of moisture due to the presence of cellulose fibers (Ali, Khan, Nawaz, et al., 2020; Tayeb, Tajvidi, & Bousfield, 2020). The hydrophilic nature of the cellulose fibers is due to the presence of hydroxyl groups as well as other polar groups. The hydroxyl groups are the main constituents of the cellulose, hemicelluloses, and lignin and hold water molecules by hydrogen bonding (Aziz et al., 2020; Jain, Kamboj, Bera, Kang, & Singla, 2019). Once water molecules are absorbed by the cellulosic composites, they affect the interfacial bonding ultimately causing poor transfer of stress, which decreases the mechanical properties of the composite (Sa´nchez, Capote, & Carrillo, 2019; Sartaj et al., 2020). While the cellulose composition is mainly responsible for the moisture uptake behavior, different cellulose-based composites show varying degrees of moisture uptake due to varying compositions. The major

Evaluation of moisture uptake behavior in cellulose fiber

205

contributor of moisture uptake is the hemicelluloses followed by amorphous cellulose, lignin, and then crystalline cellulose (Ali, Naz, Shah, Khan, & Nawaz, 2020; Kathirselvam, Kumaravel, Arthanarieswaran, & Saravanakumar, 2019). Some additional factors also contribute to the moisture uptake property of the cellulose-based fibers. These include volume fraction of cellulose fibers, orientation, permeability, temperature, humidity, voids presence, reinforcement materials, surface area, degree of cross-linking, crystallinity, diffusivity, surface modifications, interfacial bonding, etc. (Ali, Bilal, Nazir, Khan, Ali, and Iqbal, 2020; Mrad, Alix, Migneault, Koubaa, & Perr
e, 2018). All these factors are equally responsible for the moisture uptake nature of the cellulose-based composites. A number of research papers are available on the analysis of moisture uptake by cellulose fibers, and it is usually studied and calculated through the following equation. Water absorptionð%Þ ¼

w2  w1 w1

(12.1)

where “w1” stands for weight before immersing into the water, “w2” stands for weight after being immersed in water taken in grams (Ali, Azeem, Khan, Khan, Kamal, & Asiri, 2020; Sahu & Gupta, 2020) (Fig. 12.1).

12.3

Moisture uptake mechanism and its effects

As discussed in detail, moisture uptake in a humid environment is a defined quality of cellulose fibers. This quality of cellulose fibers causes a great impact on the mechanical properties and the dimensional stability of cellulose-based composites (Ali, Bilal, Khan, Ali, and Iqbal, 2020; Foong, Hamzah, Abd Razak, Saidin, & Nayan, 2018). The

Fig. 12.1 Alkali treatment of extracted fiber from Thespesia populnea tree (Kathirselvam et al., 2019).

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Cellulose Fibre Reinforced Composites

mechanical properties of the cellulose-based composites are weakened by the water uptake. A deep analysis of the mechanism of the water absorption by the cellulose-based fibers shows that the cellulose fibers are swollen as they absorb water (Ali, Khan, Malik, et al., 2020; Smiechowicz, Niekraszewicz, Kulpinski, & Dzitko, 2018). The swollen cellulose fibers have reduced stiffness and enhanced shear stress at the interfaces, which may cause degradation of the fiber–matrix interface region. Eventually, the mechanical properties of the cellulose fiber are disturbed causing a change in the dimensional property of the composite (Ali et al., 2019; Habibi, Laperrie`re, & Hassanabadi, 2019). The diffusion of water molecules can take place by three types of mechanisms; either the water molecules diffuse into the microgaps present in the polymer chains or movement of water into the holes occur and defects through capillary action because of the poor wettability and penetration at the interfaces, or third, the water molecules transmit through microcracks of the polymer matrix causing swelling of the fibers (Basit et al., 2019; Khan, Ali, Bilal, Malik, Badshah, and Iqbal, 2019). Any of the discussed mechanisms could be followed for the moisture uptake by the cellulose fibers. As the water-soluble substances leach from the fiber’s surface, it causes a rise in the osmotic pressure resulting in debonding of matrix and fibers (Khan, Shah, Mehmood, Ali, & Khan, 2019; Xia, Zhang, Yu, Pei, & Luo, 2020). The diffusion model is the most commonly accepted model in studying the mechanism of water absorption by cellulose fibers. The scientists agreed that the diffusion of water molecules by the cellulose fibers follows Fick’s diffusion law. Until recently, some of the researchers have also proposed a Parallel Exponential Kinetics model analyzing the absorption and desorption curves (Gupta, Rodriguez-Hernandez, & CastroFresno, 2019; Khan, Khalil, & Khan, 2019). According to some scientists, the swelling of the material limits the diffusion process rather than the diffusion phenomenon. According to the double exponential model, the diffusion kinetics is divided into two first-order kinetics namely, slow first-order kinetics and rapid first-order kinetics. The discussion about this model has been presented by Hill and Xie (2011) and Ali, Kamal, et al. (2018) (Fig. 12.2). According to their findings, the PEK parameters of sorption have been discussed with reference to two Kelvin–Voigt elements arranged in series. The force constant of Kelvin–Voigt elements shows the equilibrium moisture content while the time content of the models represents the viscosity of the dashpot. The water molecules absorbed inside the cellulose fibers ultimately exert pressure on the inner side of the cell walls causing a dimensional change which equals the Kelvin–Voigt spring extension (Buson, Melo, Oliveira, Rangel, & Deus, 2018). The moisture content of the system at an infinite time is shown by the spring modulus. Some other researchers have also given other theories explaining the moisture uptake by the cellulose fibers like Langmuir theory explaining the diffusion kinetics, Park’s model, etc. (Enciso, Abenojar, Paz, & Martı´nez, 2018). The techniques mostly followed for the quantification and visualization of the moisture content of cellulose fibers include Infrared spectroscopy (IR), Raman spectroscopy, Nuclear Magnetic Resonance (NMR), DSC, etc.

Fig. 12.2 (A) Schematics for the construction of CM-CS and (B) diagram for the skin wound covered with CM-CS (Xia et al., 2020).

208

12.4

Cellulose Fibre Reinforced Composites

Influence of moisture uptake on cellulose fiber properties

The evaluation of the moisture uptake and the water content present in the cellulosic fibers is very important due to the fact that it greatly alters the physical and chemical properties of the fiber (Ali, Ismail, et al., 2018; Yu & Yang, 2021). When the hydrophilic cellulose fibers are exposed to water, they interact causing variations such as changes in the dimensions, alteration of the mechanical and chemical properties, etc. The water molecules either cause a plasticization effect upon interaction with cellulose fibers or an anti-plasticizing effect by forming stable hydrogen bonds (Manich et al., 2021; Sohni et al., 2018). The dimensional changes due to the water uptake are very common in composites based on cellulosic fibers. When the cellulose-based composites are exposed to a humid environment, they swell up producing internal stress in the structure (Shah, Ud Din, Khan, & Shah, 2018; Stalin et al., 2020). While on drying, the water present in the natural fibers is lost resulting in a shrinkage in the transverse direction. Hence, the dimensional changes are greatly influenced by the composition and the presence of cellulosic fibers (Saeed et al., 2018; Sekar, Suresh Kumar, Vigneshwaran, & Velmurugan, 2020). Another important effect of the moisture uptake is the alteration in the mechanical properties of the cellulose fibers. Multiple reports are present in the literature that explain the effect of moisture uptake on the cellulose fibers (Nazir et al., 2021). Generally, the Young’s modulus of the cellulose fibers increases with an increase in the moisture content (Fig. 12.3). In some of the cases, an opposite trend is also observed. But mostly a direct relation is found to occur between the Young’s modulus and the moisture content (Bharath et al., 2021). This property increases the stiffness of the cellulose fibers by rearranging

Fig. 12.3 Water absorption ability of the different samples under different aqueous environments (Stalin et al., 2020).

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209

the microfibrils and the molecules surrounding them that act as a matrix. The swelling of fibers causes the activation of this rearrangement (Khan et al., 2017; Siakeng et al., 2020). The decrease in the Young’s modulus after a certain threshold limit can be explained on the basis of the plasticization of the fibers. The formation of hydrogen bonds by replacing the bonds in the hemicellulose structure also contributes to flexibility and compliance (AL-Oqla, 2020; Khan, Badshah, & Airoldi, 2015). Another property is the tensile strength of the cellulose fibers that have taken up moisture content. The tensile strength also tends to increase up to a certain threshold limit or 60–70 of relative humidity, while above this value it decreases (Bachchan, Das, & Chaudhary, 2021; Khan, Wahid, Ali, Badshah, & Airoldi, 2015). The tensile strength reduction could be explained on the basis of the fact that higher water content ruptures the hydrogen bonding between the crystalline fraction of fiber and the amorphous matrix. An elongation of fiber is also observed with the uptake of the water, which acts as a plasticizer (Ganesan et al., 2021). A rotation of fibers is also observed with the increase in the moisture content. Some of the structural changes have also been observed with the uptake of the water by cellulose fibers. It has been observed that the amorphous phase of cellulosic fibers becomes crystalline in the presence of moisture. The degree of crystallinity also increases (Viscusi & Gorrasi, 2021). All the changes are observed and reported in the literature with the uptake of moisture by the cellulose fibers.

12.5

Restoration processes for moisture uptake behavior of cellulose fibers

A detailed study of the moisture uptake behavior of the cellulosic fibers has shown that it causes a change in the properties of the fibers. This change in the properties leads to the limited applicability of the cellulosic fibers in different fields. To overcome this problem, certain strategies have been employed to minimize the water absorption of cellulosic fibers (Phomrak & Phisalaphong, 2020). These techniques include the chemical treatment of the cellulosic fibers (Trache et al., 2020), using a compatibilizer (Fonseca, Waldman, & De Paoli, 2021), adding fillers (Fahim & Abu-El Magd, 2021), hybridization (Biyogo, Hespel, Humblot, Lebrun, & Estour, 2020), polymer coating (Wei et al., 2020), etc. All these methods have greatly been utilized by various researchers and have come as very useful. As discussed in detail, the cellulosic fibers contain hydroxyl and other polar groups in their framework, which leads to worse interfacial bonding between the hydrophobic polymer matrices and the cellulose fibers (Dan et al., 2020). This poor interfacial bonding leads to a high amount of water uptake. The chemical treatment of the composites containing cellulosic fibers helps to develop water-resistant capability hence becomes very helpful. The main sources of water absorption like lignin, hemicelluloses, and amorphous regions of the cellulose fibers are also lost during the chemical treatment leading to fewer water absorption chances (Samyn, 2020). One of the most commonly utilized chemical treatments is the alkali treatment also called mercerization. Sodium hydroxide is the commonly used alkali used in the chemical treatment of cellulosic fibers. The NaOH first

210

Cellulose Fibre Reinforced Composites

removes the OH groups present in the structure of cellulose fibers, followed by interaction with water molecules eventually removing them (Gorur, Larsson, & Wa˚gberg, 2020). It also develops a roughness on the surface and a protective covering thus reducing water absorption. Another commonly used chemical treatment method is the benzoylation treatment of the cellulose fibers. In this type of chemical treatment, benzoyl chloride is used which strengthens the interfacial bonding thus reducing the chances of water absorption (Orelma et al., 2020). The benzoyl group replaces the hydroxyl group in the cellulose fibers enhancing the hydrophobicity. Another common treatment is the silane treatment in which silane is used as a coupling agent. The silane treatment is carried out in three steps. First, hydrolysis occurs forming silanol from silane in the presence of water molecules (Dufresne, 2020). In the next step, condensation takes place where the silanol group attaches itself to the polymer matrix at one end and the hydroxyl group of cellulose fibers at the other end. Finally occurs the bonding step where the hydrocarbon chain resists the swelling process improving the fiber adhesion (Panaitescu, Nicolae, Gabor, & Trusca, 2020). Some maleated coupling agents like maleic anhydride have also been used in the treatment of cellulose fibers. Similarly, potassium permanganate, acetyl, sodium bicarbonate, etc. gave also been used over the years for the chemical treatment of cellulose fibers and have been found to possess excellent water repellent properties (Isogai, 2020). Other than chemical treatment, polymer coating has also been utilized for the treatment of cellulosic fibers. The polymer coating enhances the compatibility of the cellulose fibers with the polymer matrix. It also increases their hydrophobicity, stiffness, and strength (Yao et al., 2021). The polymer coating improves the interfacial bonding and also prevents moisture absorption. Another technique to control the moisture uptake by the cellulose fibers is the hybridization technique. It has been noticed that artificial fibers tend to be more water-resistant than natural ones. So artificial fibers like glass, etc., can be used along with natural fibers for better water-resistant properties (Omran et al., 2021) (Table 12.1).

12.6

Conclusion

The need to develop eco-friendly and biocompatible materials for utilization in different fields has led to the development of biocomposites based on natural materials. This quest has led scientists to use cellulose fibers as reinforcement materials in a variety of biocomposites. These biocomposites are being used in different fields due to their beneficial aspects like abundance, ecofriendly nature, etc. The limitation associated with the cellulose fiber-based materials is that they tend to absorb high content of moisture when exposed to a humid environment and as a result, they swell up. This moisture uptake capacity of cellulose fibers affects their mechanical properties, hence reducing their activity. This chapter covers the moisture analysis of cellulose fibers, their effects, and the means to minimize the uptake of water by the cellulose fibers.

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Table 12.1 Modification of cellulose fibers via different treatment methods Cellulose fiber

Biocomposite

Hemp fiber

Reinforced polypropylene composite Coir/pineapple leaf fibers reinforced polylactic acid hybrid Fiber-reinforced polymer composites Poly(3hydroxybutyric-co3-hydroxyvaleric acid) (PHBV) biopolymer Sugar palm/glass fiber hybrid composites Areca fine fibers reinforced phenol formaldehyde composites

Leaf fibers

Natural fiber

Flax and hemp fibers

Sugar palm/glass fiber Areca fine fibers

Sugar palm fiber Natural fibers

Pineapple leaf fiber Palm fiber Cellulose nanofibrils

Cellulose Plantain fiber

Palm fiber

Fiber-reinforced polymer composites

Polymer/cement composites Microalgae reinforced with cellulose nanofibrils Cellulose polymer matrix Plantain fiber/epoxy biocomposite Palm fiber vinyl ester composites

Modification method

References

Alkali treatment

Han, Gong, Zhou, and Wu (2020)

Alkali treatment

Siakeng et al. (2020)

Mercerization

Verma and Goh (2021)

Alkali treatment

Fra˛cz, Janowski, and Ba˛k (2021)

Benzoylation

Safri, Sultan, and Shah (2020)

Benzoylation

Navaneethakrishnan, Chokkalingam, and Malarkodi (2021)

Benzoyl treatment

Silane treatment Silane treatment

Izwan, Sapuan, Zuhri, and Mohamed (2020) Vijay, Manoharan, Arjun, Vinod, and Singaravelu (2020) Najeeb et al. (2020) Gao et al. (2021)

Silane treatment

Oyekanmi et al. (2021)

Maleinization

Cichosz, Masek, and Rylski (2020) Imoisili and Jen (2020)

Silane treatment

Potassium permanganate treatment Acetylation

Senthilraja, Sarala, and Antony (2020) Continued

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Cellulose Fibre Reinforced Composites

Table 12.1 Continued Cellulose fiber

Biocomposite

Punica granatum fiber

Bio-epoxy composites

Wood cellulose fibers

Titanium dioxide functionalized wood cellulose fibers Kenaf/Aloe vera fiber-reinforced polylactic acid hybrid nano biocomposites

Kenaf/Aloe vera fiber

Modification method

References

Sodium bicarbonate treatment Paper fabrication

Zindani, Kumar, Maity, and Bhowmik (2021) Wang, Xie, Chen, Liu, and Yu (2020)

Fiber hybridization

Ramesh, Prasad, and Narayana (2020)

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Effect of zinc oxide filler on compressive and impact properties of jute fiber fabric-reinforced epoxy composites

13

Thottyeapalayam Palanisamy Sathishkumara, Subramani Satheeshkumara, and Lakshminarayanan Rajeshkumarb a Department of Mechanical Engineering, Kongu Engineering College, Perundurai, Tamil Nadu, India, bDepartment of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India

13.1

Introduction

Green materials have emerged lately due to the overwhelming ecological worries including reconcilability, the safety of the environment, and biodegradability (Ramesh, Palanikumar, & Hemachandra Reddy, 2013; Sanjay et al., 2018). Polymer composites play a significant role in overcoming that concern and specifically composites reinforced with natural biofibers are more environmentally friendlier than composites reinforced with synthetic fibers like glass and carbon fibers. Among many advantages offered by natural fiber-reinforced polymer biocomposites (NFRPBC), the notable advantages include deprived petroleum energy source dependency, enhanced energy recovery, higher biodegradability, and lesser greenhouse gas emissions (Ramesh, Deepa, Rajesh Kumar, Sanjay, & Siengchin, 2020; Saravana Kumar, Maivizhi Selvi, & Rajeshkumar, 2017; Wu, Xia, Cai, Shi, & Cheng, 2018). It is well known that the production industry of glass fiber depends on fossil fuels and requires a lot of energy-intensive processes, while the cultivation and processing of plants and plant-based biofibers purely depend on solar energy which is completely renewable (Bhuvaneswari et al., 2021; Chandekar, Chaudhari, & Waigaonkar, 2020; Gogna, Kumar, Kumar Sahoo, & Panda, 2019; Ramesh, RajeshKumar, & Bhuvaneshwari, 2021; Xia, Zhang, Shi, Cai, & Huang, 2016). This turns the NFRPBC to be in the upper hand when compared to synthetic fibers in aspects like lighter weight, lesser impacts over the environment, credit of the higher amount of carbon owing to incineration during the end-of-life, and enormous content of fibers (Gopalraj & K€arki, 2020; Ramesh, Rajeshkumar, Balaji, & Bhuvaneswari, 2021). Even for the production of electric vehicles, lightweight materials are highly preferred by the industries since the large weight of batteries are to be compensated (Kong, Park, & Lee, 2014). Hence, the Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00015-X Copyright © 2023 Elsevier Ltd. All rights reserved.

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replacement of glass fiber composites with NFRPBC can be a promising approach. Additionally, some metal dedicated applications like a liquid particle or multi asperity erosion are also replaced with NFRPBC owing to their higher reliability (Alagarraja, Vijaya Ramnath, Rajendra Prasad, Naveen, & Ramanan, 2021; Ramesh et al., 2021). Few of such applications are high-speed vehicles, sand slurry pipes in petroleum refineries, automobile windscreens, helicopter rotor blade parts, water and wind turbine components, aircraft engine parts operating in adverse environments like deserts, and impeller blades of pumps (Abdel-Halim, El-Rafie, & Kohler, 2007; Rubino, Nistico`, Tucci, & Carlone, 2020). Epoxy resin is the most prominently used matrix material for manufacturing natural fiber-reinforced polymer composites. It is a well-established fact that the strength and stiffness of the epoxy material can be enhanced by reinforcing it with fillers or fibers despite its inherent poor strength and stiffness. Applications of epoxy resin extend to the space industry and in superconductive technology owing to its meritorious characteristics (Lv et al., 2018; Ramesh et al., 2021; Ramesh, Rajeshkumar, & Balaji, 2021). Jute fiber is one of the naturally available fibers which is well known for its cheap cost and abundant availability. Due to the uniform cross-section of the jute fibers, their physical and mechanical characteristics remain consistent over many factors. Elongation of jute fibers is prevented by their high-length chain molecules when subjected to strength evaluating tests. These fibers are also considered to be on par with synthetic fibers due to their higher strength-to-weight ratio and lower weight. Secondary and tertiary structural elements in which synthetic fiber composites were predominantly used are being taken up by jute fiber epoxy composites due to the aforesaid reason (Ramakrishnan, Krishnamurthy, Rajeshkumar, & Asim, 2021; Vinod, Vijay, & Lenin Singaravelu, 2018). In spite of all the above advantages, natural fiber-reinforced polymer composites faces restricted use due to the natural fibers which are characterized by certain demerits such as lower inherent strength, high moisture absorption, and lesser modulus when compared with the synthetic fibers as such. Many researchers pointed out that in order to overcome the above disadvantages, a hybrid composite approach could be adopted. A hybrid composite is one that contains more than one reinforcement out of which one would be natural and the other synthetic or both as natural fiber reinforcements. Another promising approach in the hybrid formulation would be the use of organic or inorganic filler materials (Devarajan et al., 2021; Ramesh, Rajeshkumar, & Bhoopathi, 2021). Generally, filler materials are categorized as active, inactive, and semi-active types. It was said that the degree of reaction between the filler and polymer matrix purely depends on the interaction forces between them. The incorporation of fillers also governs few other properties of matrix materials like viscosity and crystallinity. Some other properties like stiffness and chemical resistance are also improved by the fillers while the electrical properties of the polymer matrix are reduced by filler additions. Fillers can be incorporated as micro-sized or nanosized particles where the size of the filler material can be reduced by using

Effect of zinc oxide filler on compressive and impact properties

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planetary or rotary ball mills. Usually, if a particle size less than or equal to 100 nm could be obtained, then it could be stated as nanosize (Ghosh, Naskar, & Chandra Das, 2020; Ramesh, Deepa, Rajeshkumar, Tamil Selvan, & Balaji, 2021). Various researches were carried out by trying out the filler materials like TiO2, ZnO, SiO2, Al2O3, ZrO2, etc., in hybrid polymer composites. The incorporation of inorganic filler materials into polymer matrices not only reduces the cost but also aids in the increase of various mechanical characteristics like toughness, dimensional stability, and rigidity. Many researchers stated that the utilization of inorganic ZnO as a nanofiller enhances the photostability of the composites when compared with the UV protective layer coated over nanocomposites. Alongside, ZnO fillers also enhance the mechanical, thermal, and other related properties of the polymer nanocomposites (Balaji et al., 2021; Ramesh et al., 2020). Viswanath et al. evaluated the strength of hybrid jute/glass fiber-reinforced epoxy composites filled with nanosized TiO2 and ZnO fillers and the ratio of fibers was maintained as 1:1 at all times. Composites were manufactured by hand lay-up technique. It was observed from the results that the compressive and impact properties of hybrid filled composites 60% and 71% higher respectively when compared with individual glass fiber composites. It was also found from the results that the mechanical properties of TiO2 filler e-glass composites were higher than its ZnO filler counterpart, while the mechanical properties of hybrid composites filled with ZnO outperformed the composites filled with TiO2 (Allamraju, 2018). Few other experimenters assessed the tensile and flexural modulus of composites filled with micro-sized and nanosized fly ash, TiO2, and Al2O3 with varying filler content in each case. It was stated that the properties increased with the increase in the content of filler (Ozsoy, Demirkol, Mimaroglu, Unal, & Demir, 2015). Some experimenters determined the impact and flexural strengths of glass fiber-reinforced composites filled with ZnO. It was found that at 3 wt% of ZnO, the mechanical properties were better. In another experiment where ZnO-filled polymethyl methacrylate (PMMA) was examined for surface roughness and flexural strength, it was found that 5 wt% of ZnO rendered higher flexural strength and lower surface roughness for PMMA composites (Gull et al., 2015; Hamad, Abdullah, & Mohamad, 2016). Devaraju et al. prepared nanosized ZrO2 and ZnO fillers through the sol-gel technique and used them as fillers in alkali-treated sisal fiber polymer composites. Three different configurations of composites were prepared using the hand lay-up method and the results portrayed that ZnO filled nanocomposites rendered better mechanical characteristics (Devaraju & Sivasamy, 2018). Singh et al. evaluated the erosive wear and mechanical behavior of ZnO and TiO2 filled bidirectional glass fibers reinforced vinyl ester composites. Filler concentrations were maintained as 10 wt% and 20 wt% while preparing the composites. It was observed from the results that the tensile strength of the composites decreased with an increase in filler content while other characteristics like compressive, impact, interlaminar strength, and hardness increased with an

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increase in filler content (Singh, Gupta, & Singh, 2018). This chapter comprehensively deals with jute fiber-reinforced polymer composite materials filled with ZnO filler. It also throws some light on the effect of ZnO filler on compressive and impact properties of jute fiber composites.

13.2

Materials

13.2.1 Preparation of composites The composite laminate was prepared by compression molding technique with hand layup method. The lamina of the jute mat was cut into a mold size of 240 mm length  200 mm width (Fig. 13.1). There are several steps used to fabricate the composites, Step 1: The epoxy and hardener were mixed 10:1 ratio on a plastic bow with help of a mechanical stirrer for 10 min, Step 2: Place four steel square plates of 10  10  7 mm2 for maintaining the uniform thickness of composites plate. Step 3: polyethylene thin sheet was gluten on inside surface of the mold, Step 4: using a brush, a layer of resin solution applied on mold surfaces, Step 5: jute mat lamina was tipped in epoxy solution and placed in the female die mold. Step 6: A steel roller was rolled over the jute mat lamina for distributing resin uniformly and remove the gas formation in the composites, Step 6: Repeated 4, 5, and 6 steps for making laminated composites using 5 layer of jute mat. Step 7: The mold was closed by placing the male die on the female die. Step 8: Then the mold was kept in a hydraulic press with the application of 45 bars pressure for 5 h. Step 9: Finally the casted laminated composite was taken out carefully from mold and then it was preheated in a hot air oven at 45°C for 1 h. Then, the jute mat reinforced laminated epoxy composites are ready for characterization. The thickness of laminated composites is 7 mm which can be used by most structural sheet manufacturers. The prepared laminated composite was maintained a constant fiber weight fraction (Wf) of 70% and the jute mats were orientated by 0° in the composites.

Fig. 13.1 Jute fiber yarn mat.

Effect of zinc oxide filler on compressive and impact properties

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13.2.2 Compressive properties The compressive test was performed according to ASTM D3041 with a cross-head speed of 2 mm/min. The size of the specimen is 110 mm in length, 12.7 mm in width, and 3 mm in thickness. The UTM (Model: DTRX-5 kN, Make: Deepak poly-Plast Pvt. Ltd) machine with a load cell of 25 kN was used for the experiment.

13.2.3 Impact properties The impact test was performed ASTM D 256 standards. The digital drop tower impact tester was used to conduct the IZOD test. The capacity of the tester was 25 J. Five samples were tested for all tests and the average values were taken for the discussion.

13.3

Results and discussion

13.3.1 Compressive properties Fig. 13.2 shows the compressive stress versus compressive strain curves of JFMs epoxy-laminated composites with single, double, and triple layers of JFMs and various weight concentrations of zinc oxide filler. The figure shows that the compressive strength of the composites increased progressively against the compressive strain rate. In comparison to single-layer, double-layer, and triple-layer unfilled JFMs-reinforced laminates, the double layer (DL) jute fiber woven mats laminated epoxy composite Single layer without Zinc oxide Double layer with 5% zinc oxide Double layer with 15% zinc oxide Double layer with 25% zinc oxide

30

Triple layer without zinc oxide Double layer with 10% zinc oxide Double layer with 20% zinc oxide Double layer with 30% zinc oxide

Compressive stress(MPa)

25 20 15 10 5 0

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Fig. 13.2 Compressive stress versus strain of jute fiber epoxy composites.

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obtained the maximum compressive strength of 19.51 MPa which is 3.54% higher than SL (18.82 MPa) and 22.91% higher than TL (15.04 MPa). It is 1.04 and 1.3 times higher than SL and TL composites. This is an optimal number of layers of laminate epoxy-reinforced composites in JFMs. The content of epoxy may be appropriate and improved adherence of the matrix to JFMs. Therefore, DL laminate epoxy composite showed optimum compressive strength tan SL and TL. Composites with TL show lower compressive stress than SL laminate epoxy composites due to low matrix content. The JFMs epoxy-laminated composites are made using an optimized double layer to provide different ZnO filler content. It’s clear that no significant improvement in the 5% addition of fillers. DL with 10%, 15%, 20%, 25%, and 30% of ZnO filler composites have 5.41% (20.62 MPa), 13.49% (22.55 MPa), 26.75% (26.63 MPa), 29.56% (27.70 MPa), and 17.21% (23.56 MPa) more than pure DL jute fiber-woven mat-reinforced epoxy-laminated composite. Here the pure DL JFMs reinforced epoxy laminate epoxy composite is equal to 25% Wf of ZnO filler added DL JFMs reinforced epoxy laminate epoxy composite due more filler content leads to less load carrying capacity and more filler agglomeration. By increasing the ZnO filler from 25% Wf, the compressive strength is getting reduced. The maximum compressive strength showed for composites containing 25% Wf of ZnO filler (Fig. 13.3). The percentage different between maximum compressive strength to other composites with filler content is 29.75%, 25.53%, 18.58%, 3.85%, and 14.92% higher than DL5% ZnO, DL10% ZnO, DL15% ZnO, DL20% ZnO, and DL30% ZnO, respectively. So, the double-layer JFMs-reinforced laminate epoxy composite with 25% ZnO filler is showing maximum compressive strength. In Fig. 13.3, the compressive strain rate of all composites is also varying according to the number of jute fiber mats and weight content of ZnO filler. The maximum percentage of strain rate occurred for composite with 20% ZnO filler is 2.22% which is higher than other composites. The compressive strain starts to decrease by increasing the weight content of ZnO fillers from 20%Wf. The compressive strain rate of DL5% ZnO, DL10%ZnO, DL15%ZnO, DL25%ZnO, and DL30%ZnO composites is 1.58%, 1.48%, 1.36%, 2%, 1.98%, 1.88%, 2.06%, and 2.1%, respectively. The compressive modulus (Fig. 13.3) was reduced with increasing the weight content of ZnO filler in DLJFMs reinforced epoxy laminate epoxy composites except for 25% wt of filler. The maximum flexural modulus of pure jute fiber composites is found for the DL composite of 13.18 GPa. The pure DL jute fiber epoxy composite is 26.19%, 20.97%, 9%, 8.99%, and 14.87% higher than DL5%ZnO, DL10%ZnO, DL15%ZnO, DL20%ZnO, and DL30%ZnO. According to the concentration of filler content, the maximum compressive modulus of 13.45 GPa was obtained for composites containing 25% Wf of ZnO filler. The percentage difference between DL25%ZnO composite and other filler composites is 27.64%, 22.52%, 10.78%, 10.78%, and 16.54% higher than DL5%ZnO, DL10%ZnO, DL15%ZnO, DL20%ZnO, and DL30%ZnO composites. However, the DL15%ZnO and DL20%ZnO composites showed equal modulus of compressive due to the lower weight content of ZnO filler. By mixing less than/more than 25% of ZnO filler concentration, (i.e. is above 25% Wf filler composites), the compressive modulus is getting decreased. DL25%ZnO composite is 1.96% higher than pure DL composite (Fig. 13.2).

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Fig. 13.3 Compressive properties of jute fiber epoxy composites.

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13.3.2 Impact properties Fig. 13.4 shows that the impact properties increased with increasing JFMs layers in epoxy-laminated composite. The composites having double-layer (DL) showed impact strength compared to SL and TL composites, at 30%Wf. Compared with SL, the DL JFMs-reinforced epoxy laminate composite showed the maximum impact strength of 8.12 kJ/m2 which is 33.6% higher than SL (1.6 kJ/m2) and 25.14% higher than TL (2.4 kJ/m2). The optimum number of jute fiber mat is found for DL JFMs-reinforced epoxy-laminated composite. It shows that the impact strength increased with increasing the ZnO filler content in composites. Compared to pure DL composite, all ZnO filler DL composites are higher impact strength. The impact strengths of ZnO filler DL composites are 4.02 kJ/m2 (DL5%ZnO), 4.85 kJ/m2 (DL10%ZnO), 4.82 kJ/m2 (DL15%ZnO), 7.29 kJ/m2 (DL20%ZnO), 8.12 kJ/m2 (DL25%ZnO), and 6.48 kJ/m2 (DL30%ZnO). The percentage improvement between the filler reinforced DL composites to pure DL composite are 20.10% (DL5%ZnO), 33.73% (DL10%ZnO), 33.73% (DL15%ZnO), 55.94% (DL20%ZnO), 60.43% (DL25%ZnO), and 50.45% (DL30%ZnO). The maximum impact strength is showed for composites with 25% Wf of ZnO filler due to that filler absorbed the highest impact load during the experiments. The DL25%ZnO composite have 50.47%, 40.28%, 40.28%, 10.19%, and 20.14% higher than DL5%ZnO, DL10% ZnO, DL15%ZnO, DL20%ZnO, and DL30%ZnO composites, respectively. Increasing the ZnO filler content in DL composites by more than 25% reduced the impact strength due to more filler in the composites, filler agglomeration and nonuniform distribution of ZnO filler in the JFMs mesh, and less matrix content leads to reduce the impact energy.

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Effect of zinc oxide filler on compressive and impact properties

13.4

227

Conclusions

The effect of varying the number of jute fiber mat and ZnO filler in epoxy composites was investigated using the hand layup method followed by a compression molding process. The compressive and impact properties were studied according to ASTM standards. The main conclusions are: The maximum compressive strength of 19.51 MPa was found for DL jute fiberreinforced epoxy composite without adding fillers due to the slow delamination that occurred between the two laminas. Incorporation of ZnO filler increased the compressive strength of 27.7 MPa was found for DL composite containing 25% Wf. The ZnO filler containing composites absorbed more compressive load and slowed the specimen fracture failure. The maximum impact strength of 3.21 kJ/m2 was obtained for DL jute fiberreinforced epoxy composite without adding fillers. In addition of the ZnO filler, the highest impact strength of 8.12 kJ/m2 was obtained for DL composite containing 25% Wf of filler. The composite with 20% of ZnO filler was showed an impact strength of 7.29 KJ/m2. The higher amount of fillers in the composite can absorb more impact load. The incorporation of ZnO filler in JFMs reinforced laminate epoxy composites was increasing the compressive and impact properties. The optimum level of ZnO filler is a 25% weight fraction. The ZnO filler can be mixed for preparing fiber woven matreinforced laminate polymer composites for improving the compressive and impact properties and it is used for various structural applications.

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Predication of impact strength reduction and service life of 45-degree laminate jute fiber fabric in epoxy composites

14

Thottyeapalayam Palanisamy Sathishkumar and Subramani Satheeshkumar Department of Mechanical Engineering, Kongu Engineering College, Perundurai, Tamil Nadu, India

14.1

Introduction

The development of natural fiber composites is attractive among researchers because of their properties of light-in-weight, biodegradable, recyclable, nontoxic, high specific strength to weight ratio, ease of manufacture, and the desired properties for the desired direction. These natural fibers are employed as a suitable reinforcing material to meet the mechanical requirements of engineering composites. Water absorption is a major obstacle in development because moisture circumstances deteriorate and reduce the mechanical characteristics of composites. The prospect of using natural fiber in outdoor applications necessitates extensive research and analysis of their mechanical behavior in a humid environment over a lengthy period of time. Several investigations show that the natural fiberreinforced polymer composite loses its mechanical properties progressively as water enters the material and that the loss is proportional to the amount of water absorbed. Hamdan et al. (2019) immersed the natural hybrid-reinforced polyester composites in the distilled water for 30 days. The tensile properties show that layering size has a significant impact than layering sequences. The type of fabric used on the top layer composite influences the flexural properties. The Charpy impact test indicates that there may be less variance in the value regardless of the layering sequence or layering size. The water absorption reduces the tensile strength by 12%–27% and tensile modulus by 15%–35%. Athijayamani, Thiruchitrambalam, Natarajan, and Pazhanivel (2009) immersed the rosella and sisal fibers hybrid polyester composite in distilled water at 5 days and the laminate was prepared with various fiber lengths and fiber loading. The tensile and flexural strength increased with increasing fiber length and fiber content. But the maximum impact strength (1.39 kJ/m2) was found at 20% fiber content with 150 mm fiber length. Dhakal, Zhang, and Richardson (2007) found the maximum tensile and flexural strength retention by 5-layer hemp fiber polyester composite immersed in de-ionized water at 888 h. Deo and Acharya (2010) immersed the Lantana camara fiber-reinforced epoxy composite in three

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different environmental conditions such as steam, saline water, and subzero temperature. The moisture absorption increased with increasing fiber content. Zivkovi, Fragassa, Pavlovi, and Brugo (2017) prepared hybrid and nonhybrid green vinyl ester composites with basalt and flax fiber. The hybrid composite found higher impact behaviors than the nonhybrid composite for both dry and salt-water aged conditions. The basalt fiber in composites showed higher moisture absorption and lower fiber/ matrix adhesion than flax fiber. Assarar, Scida, Mahia, Poilane, and Ayad (2011) concluded that the tensile stress of flax and glass–fiber composites was decreased with increasing aging time. Najafi and Kordkheili (2011) immersed wood fiber-reinforced polypropylene composite in distilled water, Caspian seawater and Persian gulf water for 7 and 30 days. The Persian gulf water-aged specimen exhibited lower flexural properties due to higher water absorption. Le Duigou, Bourmaud, Davies, and Baley (2014) found that the linear elastic area of dry Flax/PLA biocomposites exhibited the irreversible damage than the wet composites for the various aging period. The tensile strength and tensile modulus were decreased gradually while increasing the aging period. Chilali, Zouari, Assarar, Kebir, and Ayad (2018) found the durability of flax fiber-reinforced acrylic/epoxy composites in tap water for 30 days. The elastic and failure properties of both resins exhibited approximately a similar variation. The tensile strength and modulus of both composites decreased gradually to reach 42% and 58% of their initial value. Shubhra, Alam, and Beg (2011) found the environmental effect on tensile strength loss of silk fiber-reinforced gelatin film composites for 30 h. The composite specimen obtained a lower percentage of tensile strength loss of 15.2% than the pure gelatin matrix of 32.5%. Hadi Saidane, Scida, Assarar, Sabhi, and Ayad (2016) investigated the hybridization effect on tensile behavior of flax–glass fibers-reinforced epoxy composites with different stacking sequences and aged at 55°C for 38 days. The incorporation of glass fibers in flax fiber-laminated composites has reduced the mechanical degradation properties due to the hydrophobic nature. Ramamoorthy, Di, Adekunle, and Skrifvars (2012) prepared acrylated epoxidized soybean oil reinforced with nonwoven and woven jute, regenerated cellulose mat (Lyocell and viscose), and woven glass fiber. The incorporation of 34 wt% glass/lyocell fiber in woven jute composite improved the tensile and flexural and impact strength properties in both dry and water exposed conditions. The alkali treatment of lyocell fiber proved ineffective because it is failed to enhance mechanical and viscoelastic characteristics. Cheour, Assarar, Scida, Ayad, and Gong (2016) prepared flax fiber reinforced epoxy composites by press platen process with a different fiber length of 240, 260, and 280 mm and orientation of 0°, 90°, and 45°. The loss factor of 45° fiber orientation composite showed 74.3% and 24.7% higher than the 0° and 90° fiber orientations due to more fiber-matrix friction in 45° direction. Ridzuan, Abdul Majid, Azduwin, Zahri, and Gibson (2016) prepared Pennisetum purpureum/glass fiber-reinforced epoxy hybrid composites by the vacuum infusion method. The outer layers of the glass fiber mat and an inner layer of P. purpureum fiber laminate reduced the moisture absorption level. The synthetic fiber content in the composite is reducing the mechanical degradation of the hybrid fiber composite. Fiore et al. (2017) prepared bidirectional jute/unidirectional basalt fiber-reinforced epoxy hybrid laminates prepared with different stacking

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233

sequences of sandwich and intercalated configuration. The laminates were subjected to accelerated aging in a climatic chamber for periods of 14, 28, 56, and 84 days. The sandwich configuration of thick external basalt layers postpones the degradative effect of aging exposure on mechanical properties. Venkatesha, Saravanan, and Anand (2021) immersed the woven hybrid composites in saline and distilled water for a period up to 10 days. The woven bamboo/glass fiber-reinforced epoxy composite prepared with different fiber stacking sequences of 15°, 30°, 45°, and 60°. The maximum tensile and flexural strength reduction was found by 45° composite laminate in a saline water environment. Mishra, Deo, and Baskey (2021) found the tensile strength retention of kenaf/glass hybrid composite showed 87.22%. Habibi, Laperriere, and Hassanabadi (2018) concluded that the tensile modulus and stress decreased 68% and 61% at 75°C than dry composites due to increasing water absorption period and temperature of nonwoven flax fiber mat reinforced epoxy composite. However, the tensile strain rate was increased by 30%. Moudood et al. (2019) concluded the service life of flax/bioepoxy composite under different environmental conditions such as water immersion, high humidity, and freeze/thaw cycling. The water absorption profile for the samples immersed in water at room temperature was partially Fickian, and this sample was the most affected and degraded. Cuinat-Guerraz, Dumont, and Hubert (2016) have found that the moisture absorption of flax/polyurethane composites showed a lower value than bioepoxy/flax composite. The polyurethane/flax composite was superior to retaining their compressive strength and modulus due to plasticizing effect during the aging period. Cheour, Assarar, Scida, Ayad, and Gong (2020) found the stacking order of the flax and glass fiber layers influenced the diffusion coefficient and saturation mass uptake significantly. The most effective way to slow down mechanical degradation during aging was to use two outside glass layers two inside flax layers. Fiore, Sanfilippoa, and Calabreseb (2019) immersed the sodium bicarbonate solution treated flax and jute fibers-reinforced epoxy composite in a salt-fog spray environment for up to 60 days. Flax fibers epoxy matrix laminates to better retain their tensile strength of 65.1 MPa, flexural strength of 75.5 MPa for 60 days. Fiore, Scalici, Calabrese, Valenza, and Proverbio (2016) found that the flexural properties of Flax-basalt fiber hybrid composites showed better durability than flax composite under salt-fog environment conditions. Hristozov, Wroblewski, and Sadeghian (2016) immersed the unidirectional flax and glass fiber-reinforced vinyl ester composites in distilled water, salt water, and alkaline solution for various aging periods of 21, 42, 83, and 125 and temperatures of 20°C, 50°C, and 60°C. The lowest strength retention was found in alkaline solution for all temperature and aging periods. Fiore and Calabrese (2019) concluded the sodium bicarbonate treated flax/basalt epoxy hybrid composite improved the impact resistance. So this research clearly showed that the long-term mechanical performance of natural fiber-reinforced polymer composites was affected by fiber stacking sequence, fiber content, fiber length, type of fiber, aging period, and temperatures. The aging process was done in distilled water, saltwater, alkaline water, hot water, normal water, and sewage water. Most of the studies do not consider the fiber orientation effect of water absorption and temperature on the impact behavior of the composite. The present work aims to evaluate the impact strength retention and service life of

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45° orientation Jute Fiber Yarn Mat Reinforced Epoxy Composite laminates (JEC) under normal water at various aging and temperature.

14.2

Materials

14.2.1 Jute fiber mat The jute fiber yarn mat (Fig. 14.1) was purchased from Khandelwal Jutex Private Ltd., Kolkata, India which is made of 100% hard jute fiber for making carpet backing cloth. According to B
S 946:1952 standard, the twisting of jute fiber for yarn making was maintained as 2.5 turns/cm. The hand-weaving machine was used to prepare a jute yarn mat with 5 yarns/cm on the weft and Warf direction with a weight of 700 gpm. The size of the mat was 342 cm in width and 1000 cm in length with 1.1  0.2 mm thickness. The LY556 grade of epoxy resin and HY951 grade of hardener was used for making composite laminate.

14.2.2 Preparation of composites The composite was fabricated using the compression molding technique with the hand layup method. The woven jute fiber mat was cut into mold size of 240 mm length  200 mm width. Polyethylene thin sheet was placed top and bottom of the mold for easy removal of the composite plate after the curing process is done. The epoxy resin was mixed with a hardener in the ratio of 10:1 and stirred continuously for 3 min using mechanical starrier. The mixed epoxy resin was poured on the fiber surface into the mold. The resin was spread uniformly on the surface of the woven mat to remove the entrapped air with the help of a brush and roller. This procedure was continued until the necessary number of layers was attained. All the fabrics were arranged in the direction of 45°. Finally, the mold was kept in a hydraulic press under the pressure of 45 bars and left for curing at room temperature for 5 h. The cured composite was postcured in hot air woven at 45°C for 1 h. Then, the composite plate was cut into respective dimensions as required by the standard.

Fig. 14.1 Jute fiber yarn mat.

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235

14.2.3 Artificial aging of composites The artificial aging was tested was performed as referred to the ASTM D570-98. Normal water was used to immerse the composite samples at various temperatures of 20°C, 40°C, and 60°C for up to 40 days. The calculation of water absorption was obtained using the following equation (Assarar et al., 2011; Athijayamani et al., 2009; Chilali et al., 2018; Deo & Acharya, 2010; Dhakal et al., 2007; Hamdan et al., 2019; Le Duigou et al., 2014; Najafi & Kordkheili, 2011; Shubhra et al., 2011; Zivkovi et al., 2017). M ð% Þ ¼

Mt  Mo 100 Mo

(14.1)

From Eq. (14.1), Mt represents the mass of the wet sample (gram) at the aging time, t and M0 represent the mass of the dry sample (gram). The impact testing samples were immersed in water before impact testing. The apparent diffusion coefficient (D) for all samples was determined using the following Equation (Assarar et al., 2011; Deo & Acharya, 2010; Hamdan et al., 2019).
D¼π

h 4Mm

2 2
2
M2  M1 h h pffiffiffiffiffiffiffiffiffiffiffiffiffi 1+ + l n t2  t1

(14.2)

From Eq. (14.2), h represents the thickness of the specimen (mm), l represents the length of the composite specimen (mm), n represents the width of the composite specimen (mm), Mm represents the maximum moisture absorption (gram), M1 and M2 represent the moisture absorption (gram) at time t1 and t2 (sec). Using the Arrhenius relation calculate the activation energy (Ea) was determined by using the following equation. D ¼ Do exp



Ea RT

 (14.3)

From Eq. (14.3), D represents the apparent diffusion coefficient (mm2/s), D0 represents the constant coefficient, R represents the universal gas constant equivalent (8.3144 J/mol K), or Boltzmann constant (1.38065  1023) J/Kelvin, and T represent the temperature of aging (Kelvin). The activation energy of polymer composites is determined by the slope of the plot of In(D) versus the reciprocal of the aging temperature (1/T) multiplied by the Boltzmann constant. The service life of polymer composite materials was calculated using an Arrhenius plot and the known rate of change of mechanical behaviors under various environmental conditions.

14.2.4 Impact properties At two different states such as before water immersion and after water immersion, the impact test was carried out according to the ASTM D 256 standards. The IZOD impact

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test was carried out using a digital drop tower impact tester and the capacity of the tester was 25 J. Minimum five samples were tested for each sample and the mean values are reported.

14.3

Results and discussion

14.3.1 Weight variation The percentage of water absorption for all the samples is shown in Fig. 14.2. It shows that the water absorption depends on immersion time and environmental conditions. For all environmental conditions, the average weight gain of five samples was recorded. The figures show that the highest weight gain percentage happens at 60°C. The wax content around all-natural fibers functioned as a barrier against water penetration into the fibers. In Fig. 14.2, jute fibers absorbed very less water at a lower temperature (20°C) due to the existence of wax content in the fiber, which could prevent water penetration. The wax content did not melt at low temperatures so the fiber clogging was significantly reduced. At 10 days of aging, the JEC had attained their maximal weight growth. The water absorption increased with increasing immersion time at elevated temperatures (40°C and 60°C). Increasing the aging temperature progressively melts the wax in the fiber, allowing water to get into the fiber. The rate of melting was enhanced at higher temperatures, allowing for rapid water penetration. The fibers have clogged as a result of water absorption, reducing the physical connection between the fiber and the matrix. The percentage of weight gain of JEC at 20°C, 40°C, and 60°C was 8%, 9.39%, and 10.79% at 20 days of aging. The percentage of

12

Impact sample

Weight gain (%)

10 8 6 20°

4

40°

60°

2 0 0

10

20

30

40

Ageing period (Days) Fig. 14.2 Weight variation versus square root of time of 45° JEC in water at 20°C, 40°C and 60°C.

Predication of impact strength reduction and service life

237

weight gain was 8.35%, 9.95%, and 11.12% at 30 days of aging. The percentage of weight gains was 8.44%, 10.20%, and 11.30% at 40 days.

14.3.2 Impact properties Fig. 14.3 shows the results obtained from the IZOD impact testing of the composite samples at both dry and wet conditions. Most of the previous studies show that impact strength deteriorated when exposed to excessive moisture. Therefore, the results obtained from this study are coherent as previous work. The dry JEC had an impact strength of 7.16 J/m2. The plot shows that the impact strength gradually decreased with increasing aging period and temperature. The impact strength of JEC obtained after 10 days are 6.78, 6.92, and 6.92 J/m2 at 20°C, 40°C, and 60°C, respectively (Fig. 14.4). The percentage difference between dry and wet composites is 5.30%, 3.35%, and

8

20° 40° 60°

Impact strength (J/m2)

7 6 5 4 3 2 1 0 DRY

10 Days

20 Days

30 Days

40 Days

Ageing period (Days) Fig. 14.3 Impact properties of the 45° laminate JEC at 20°C, 40°C and 60°C.

100

Ageing period (Days) 20° 60°

40°

80 60 40 20 0 Wet-10 Days Wet-20 Days Wet-30 Days Wet-40 Days Ageing period (Days)

Var. Impact strength reduction (%)

Var. Impact strength retention (%)

120

Wet-10 Days Wet-20 Days Wet-30 Days Wet-40 Days 0 –5 –10 –15 –20 –25 –30 –35

20° 60°

40°

–40 –45

Fig. 14.4 Variable impact strength versus time period for the JEC in water at 20°C, 40°C and 60°C.

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3.35% at 20°C. The impact strength was gradually reduced with increasing the aging period due to a decrease of physical bonding between the fiber and matrix. The impact strength of JEC obtained after 20 days are 6.12, 6.21, and 6.32 J/m2 at 20°C, 40°C, and 60°C, respectively. The percentage difference between dry and wet composites is 14.53%, 13.27%, and 11.73% at 20°C, 40°C, and 60°C. The impact strength of JEC obtained after 30 days are 5.45, 5.35, and 5.12 J/m2 at 20°C, 40°C, and 60°C, respectively. The percentage difference between dry and wet composites is 23.88%, 25.28%, and 28.49% at 20°C, 40°C, and 60°C. The impact strength of JEC obtained after 40 days is 4.87, 4.62, and 4.75 J/m2 at 20°C, 40°C, and 60°C respectively. The percentage difference between dry and wet composites is 31.98%, 35.47%, and 33.66% at 20°C, 40°C, and 60°C. Fig. 14.4 shows the holding and reduction of impact strength of the JEC at different environmental conditions. The rate of holding and reduction of impact strength at 20°C was 94.63, 85.42, 76.07, and 66.15% and 5.37, 14.58, 23.93, and 33.85% at 10, 20, 30, and 40 days, respectively. The rate of holding and reduction of impact strength at 40°C was 96.58, 86.67, 74.67, and 63.22% and 3.42, 13.33, 25.33, and 36.78% at 10, 20, 30, and 40 days respectively. The rate of holding and reduction of impact strength at 60°C was 95.19, 88.21, 71.46, and 64.59% and 4.81, 11.79, 28.54, and 35.41% at 10, 20, 30, and 40 days, respectively. The continuous aging of JEC composites increased the loss of impact strength due to a higher rate of water inhalation by jute fiber.

14.3.3 Diffusion coefficient and activation energy The diffusion coefficient (D) of JEC at 20, 40, and 60°C are 3.994  107, 4.627  107, and 4.985  107 mm2/sec which is calculated by using Eq. (14.2). The value of D depended on the aging period and temperatures. The minimum value of D was found at 20°C. The rate of impact strength and composite degradation was enhanced at various time intervals by increasing temperature. For JEC composites, the percentage difference of diffusion coefficient between temperatures is 13.68% (20– 40°C), 7.18% (40–60°C), and 19.88% (20–60°C). the aging temperature (1/T) in Kelvin versus ln(D). Fig. 14.5 shows the aging temperature (1/T) in Kelvin versus ln(D). Eq. (14.3) is used to calculate the activation energy (Ea) of JEC. The activation energy (Ea) was found 34.32 J/sec. Fig. 14.6 illustrates the JEC coefficient of correlation and the maximum reliability (R2) was observed at 60°C. As a result, this activation energy was suitable to study the JEC’s behavior.

14.4

Arrhenius plots for service life prediction of the JEC

Arrhenius’s principle was used to analyze the degradation of composites measured from the accelerated aging tests and to correlate with the natural aging data. In order to account for the chemical degradation of JEC, which is temperature dependent, the Arrhenius principle was used to find the long-term impact strength performance. JEC

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Impact strength retention (%)

100 90 80

20°C R2 = 0.7385

70

40°C R2 = 0.6696

60

2 60°C R = 0.6796

50 40 30 20 10 0 0

0.5

1 Log T (days)

1.5

2

Fig. 14.5 Impact strength retention versus time period for different aging temperature of JEC.

R2=0.9551

60

Impact strength retention (%)

50

40

30

20

10 3.00

3.19

3.41

1years 2years 3 years 4 years 5 years 6 years 7 years 8 years 9 years 10 years 11 years 12 years 13 years 14 years 15 years 16 years 17 years 18 years 19 years 20 years

3

1/Temperature (10 /Kelven) Fig. 14.6 Arrhenius plot of impact strength retention (%) against the different temperature of JEC.

experimental impact strength retention curves are shown in Fig. 14.7. The coefficient of correlation (R2) of JEC was higher than or equal to 0.9551, indicating that the materials degraded more slowly and were utilized for a longer period of time. As a result, the long-term performance was significantly lower than that of CG composites. At 40°C, the R2 value for aged composites is observed to be greater.

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100

Impact strength retention (%)

90 80

20°C

60

40°C 60°C

70 50 40 30 20 10 0 0

10

20

30

40

50

60

70

80

90

100

Service life of the composites (Years)

Fig. 14.7 Arrhenius plot of impact strength retention (%) versus service life of JEC.

The Arrhenius plots of aged composites are presented in Fig. 14.7. A maximum of 20 years was chosen to draw the curves by adding 1 year. This graph shows that the service life of JECs was calculated by maximum impact strength retention. Fig. 14.7 shows the impact strength retention versus service for 100 years for three environmental conditions. This helps to know the impact strength pattern of JECs at any point in time. When the application’s lowest acceptable value is known, the value of impact strength retention for that application may be determined using the desired time period.

14.5

Conclusion

In this study, the impact strength of JECs was conducted under three environmental conditions and different time periods. The water absorption of the samples increased with the water immersion period. The maximum water gain was found at 30 days immersion laminate and following that the water gain was leveled. The wet JECs samples impact test results show that the impact strength decreased with increasing immersion period of immersion and varying with environmental conditions. Arrhenius’ principle was implemented to predict the long-term impact properties of composites. During the first 20 days of aging, the impact strength has gradually decreased. After 30 and 40 days of aging, it showed a higher reduction in impact strength. During these periods, the JECs observed more water and started debonding between the jute fiber and the matrix. The diffusion coefficient values increase steadily with an increase in aging temperature, reducing the impact strength of JECs. The diffusion coefficient result of high water diffusion was found at 60°C. The service life of the JECs will be extended to 3 years by setting the impact strength to 40%. As a result, the 45° laminate of JECs’ maximum service life is around 3–5 years.

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241

References Assarar, M., Scida, D., Mahia, E., Poilane, C., & Ayad, R. (2011). Influence of water aging on mechanical properties and damage events of two reinforced composite materials: Flax–fibers and glass–fibers. Materials and Design, 32, 788–795. Athijayamani, A., Thiruchitrambalam, M., Natarajan, U., & Pazhanivel, B. (2009). Effect of moisture absorption on the mechanical properties of randomly oriented natural fibers/polyester hybrid composite. Materials Science and Engineering, 517, 344–353. Cheour, K., Assarar, M., Scida, D., Ayad, R., & Gong, X.-L. (2016). Effect of water aging on the mechanical and damping properties of flax fibre reinforced composite materials. Composite Structures, 152, 259–266. Cheour, K., Assarar, M., Scida, D., Ayad, R., & Gong, X.-L. (2020). Long-term immersion in water of flax-glass fibre hybrid composites: Effect of stacking sequence on the mechanical and damping properties. Fibers and Polymers, 21(1), 162–169. Chilali, A., Zouari, W., Assarar, M., Kebir, H., & Ayad, R. (2018). Effect of water aging on the load-unload cyclic behaviour of flaxfibre-reinforced thermoplastic and thermosetting composites. Composite Structures, 183, 309–319. Cuinat-Guerraz, N., Dumont, M.-J., & Hubert, P. (2016). Environmental resistance of flax/biobased epoxy and flax/polyurethane composites manufactured by resin transfer molding. Composites Part A Applied Science and Manufacturing, 88, 140–147. Deo, C., & Acharya, S. K. (2010). Effect of moisture absorption on mechanical properties of chopped natural fiber reinforced epoxy composite. Journal of Reinforced Plastics and Composites, 29(16), 2513–2521. Dhakal, H. N., Zhang, Z. Y., & Richardson, M. O. W. (2007). Effect of water absorption on the mechanical properties of hemp fiber reinforced unsaturated polyester composites. Composites Science and Technology, 67, 1674–1683. Fiore, V., & Calabrese, L. (2019). Effect of stacking sequence and sodium bicarbonate treatment on quasi-static and dynamic mechanical properties of flax/jute epoxy-based composites. Materials, 12(9), 1–18. Fiore, V., Sanfilippoa, C., & Calabreseb, L. (2019). Influence of sodium bicarbonate treatment on the aging resistance of natural fiber reinforced polymer composites under marine environment. Polymer Testing, 80(106100), 1–9. Fiore, V., Scalici, T., Badagliacco, D., Enea, D., Alaimo, G., & Valenza, A. (2017). Aging resistance of bio-epoxy jute-basalt hybrid composites as novel multilayer structures for cladding. Composite Structures, 160, 1319–1328. Fiore, V., Scalici, T., Calabrese, L., Valenza, A., & Proverbio, E. (2016). Effect of external basalt layers on durability behaviors of flax reinforced composites. Composites Part B Engineering, 84, 258–265. Habibi, M., Laperriere, L., & Hassanabadi, H. M. (2018). Effect of moisture absorption and temperature on quasi-static and fatigue behavior of nonwoven flax epoxy composite. Composites Part B Engineering, 166, 31–40. Hadi Saidane, E., Scida, D., Assarar, M., Sabhi, H., & Ayad, R. (2016). Hybridization effect on diffusion kinetic and tensile mechanical behaviour of epoxy-based flax–glass composites. Composites Part A Applied Science and Manufacturing, 87, 153–160. Hamdan, M. H. M., Siregar, J. P., Cionita, T., Jaafar, J., Efriyohadi, A., Junid, R., et al. (2019). Water absorption behaviour on the mechanical properties of woven hybrid reinforced polyester composites. The International Journal of Advanced Manufacturing Technology, 104, 1075–1086.

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Hristozov, D., Wroblewski, L., & Sadeghian, P. (2016). Long-term tensile properties of natural fiber-reinforced polymer composites: Comparison of flax and glass fibers. Composites Part B Engineering, 95, 82–95. Le Duigou, A., Bourmaud, A., Davies, P., & Baley, C. (2014). Long term immersion in natural seawater of flax/PLA biocomposite. Ocean Engineering, 90, 140–148. Mishra, C., Deo, C. R., & Baskey, S. (2021). Influence of moisture absorption on mechanical properties of kenaf/glass reinforced polyester hybrid composite. Materials Today, 38(5), 2596–2600. Moudood, A., Rahman, A., Khanlou, H. M., Hall, W., Ochsner, A., & Francucci, G. (2019). Environmental effects on the durability and the mechanical performance of flax fiber/ bio-epoxy composites. Composites Part B Engineering, 171, 284–293. Najafi, S. K., & Kordkheili, H. Y. (2011). Effect of seawater on water absorption and flexural properties of wood-polypropylene composites. European Journal of Wood and Wood Products, 69, 553–556. Ramamoorthy, S. K., Di, Q., Adekunle, K., & Skrifvars, M. (2012). Effect of water absorption on mechanical properties of soybean oil thermosets reinforced with natural fibers. Journal of Reinforced Plastics and Composites, 31(18), 1191–1200. Ridzuan, M. J. M., Abdul Majid, M. S., Azduwin, K., Zahri, J. M., & Gibson, A. G. (2016). Moisture absorption and mechanical degradation of hybrid Pennisetum purpureum/ glass–epoxy composites. Composite Structures, 141, 110–116. Shubhra, Q. T. H., Alam, A. K. M. M., & Beg, M. D. H. (2011). Mechanical and degradation characteristics of natural silk fiber-reinforced gelatin composites. Materials Letters, 65, 333–336. Venkatesha, B. K., Saravanan, R., & Anand, B. K. (2021). Effect of moisture absorption on woven bamboo/glass fiber reinforced epoxy hybrid composites. Materials Today, 45(1), 216–221. Zivkovi, I., Fragassa, C., Pavlovi, A., & 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.

Extraction and characterization of cellulosic fibers from the stem of papaya tree (Carica papaya L.)

15

Caroliny Santos, Thiago Santos, Marcos Aquino, and Salete Alves Textile Engineering Graduate Program (PPGET), Federal University of Rio Grande do Norte, Natal, RN, Brazil

15.1

Introduction

Plastic particles less than 5 mm in length—also microplastic materials—are a threat to both human health and the environment. These nondegradable residues of synthetic petroleum-based polymers are inert to water, microorganisms and ultraviolet light action, what turns into hard to degrade itself in nature. Thus, reducing these plastics is quite essential to decreasing the resulting pollution, as reported elsewhere (Faris et al., 2014; Kyrikou & Briassoulis, 2007; Pirc, Vidmar, Mozer, & Krzˇan, 2016; Wu, Yang, & Criddle, 2017). A suitable way to achieve this reduction is the total or, at least, partial replacement of these synthetic structures by biodegradable materials, especially from nature. Vegetal fibers are readily available and usually exhibit the property of low density, which is key to creating lighter materials (Pradip & Ashok, 2015). A study showed that natural fibers could replace their synthetic counterparts in polymer composites (Begum & Islam, 2013; Dos Santos et al., 2019). Another research studied natural fibers as an alternative material for sound absorber to replace synthetic fibers (Fouladi et al., 2016). Moreover, in the field of geotextiles, natural fibers may replace synthetic fibers, since they can compete in both technical and economic aspects (Lea˜o et al., 2012). Natural fibers can be obtained from mineral, animal, and plant sources. Plant fibers, in turn, can be extracted from several parts, including the stem. These types of fibers can be extracted by using chemical methods and by microbiological retting. The latter method consists of separating the plant fiber from nonfibrous materials in an aqueous solution environment, in which dew or water are usable. In dew retting, plants are exposed in the field to the action of microorganisms in order to remove pectins, hemicelluloses, and other carbohydrates from the matrix, thus releasing the fibers. In the water process, plants are submerged in fresh water, which penetrates the central part of the stem, increasing moisture content and promoting the development of pectinolytic bacteria (Graceraj, Venkatachalam, Shankar, & Kumar, 2016; Hurren, Wang, Dennis, & Clarke, 2014; Sisti, Totaro, Vannini, & Celli, 2018). Microbiological retting can be used to extract natural fibers such as flax, banana and papaya stem (Graceraj et al., 2016; Hall, Booker, Siloto,

Cellulose Fibre Reinforced Composites. http://doi.org/10.1016/B978-0-323-90125-3.00010-0 Copyright © 2023 Elsevier Ltd. All rights reserved.

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Jhala, & Weselake, 2016; Kempe et al., 2015; Konczewicz, Zimniewska, & Valera, 2018). Of these, only papaya stem fiber shows a lack of in-depth investigation by scientific community. This plant is mainly cultivated for its highly nutritional fruit and medicinal benefits, and after the harvest or at the end of its productive cycle (3 to 5 years), the papaya stems are collected (Saravana Kumaar, Senthilkumar, Sornakumar, Saravanakumar, & Arthanariesewaran, 2017). The stems are also a cheap and easily accessible source of natural fiber, providing additional income for papaya growers. Thus, this current research aims to extract papaya stem fiber using microbiological retting, as performed by Li (2004) and Shahinur, Hasan, Ahsan, Saha, and Islam (2015) in other plant fibers, and to analyze the influence of fiber location on its properties. After extraction, the papaya stem fiber was characterized by its physical and mechanical properties, X-ray diffraction, and field emission gun scanning electron microscopy.

15.1.1 A worldwide clamor for vegetable fiber Vegetable fibers can be obtained from different parts of plants, such as seeds, fruits, leaves and bast. Fibers extracted from the bast and leaf tend to be harder and their properties normally allow for use in composite applications. Examples of bast fibers include hemp, jute, flax, ramie, kenaf, and banana. Leaf fibers include sisal and banana leaf fibers (Williams & Wool, 2000). Vegetable fibers contain cellulosic and noncellulosic materials such as hemicellulose, pectin and lignin. They are also formed as lignocellulosic or cellulosic fibers. Cellulose is a semicrystalline polysaccharide and is the reason natural fibers demonstrate hydrophilic behavior in addition to providing strength and stiffness. Hemicellulose is an amorphous branched polysaccharide of pentose and hexose sugars. This can be found in the plant cell wall and its molecular weight is lower than that of cellulose (Khan et al., 2022; Khan, Rangappa, Siengchin, & Asiri, 2020). Pectin is a class of polysaccharide that can be found in the plant cell wall and is responsible for intercellular union, along with cellulose and hemicellulose (Rajeshkumar et al., 2021; Santos, Santos, Manicoba, & Aquino, 2022). Holocellulose, on the other hand, contains mainly cellulose and hemicellulose and is the total polysaccharide of natural fibers ( Jaiswal, Devnani, Rajeshkumar, Sanjay, & Siengchin, 2022; Khan et al., 2022; Khan, Rangappa, Siengchin, et al., 2020). Lignin is an aromatic, nonlinear polymer that has chemically diverse bonds. It acts as a binder for cellulose fibers and adds strength and stiffness to cell walls (Khan, Rangappa, Siengchin, et al., 2020; Santos et al., 2022).

15.1.2 Natural and vegetable fibers The need for environmentally friendly materials is leading researchers around the world to work on the development of new materials that improve the environmental quality of products, which, in turn, is available in abundance and can be applied in engineering, such as natural fibers (Madhu, Praveenkumara, Sanjay, Siengchin, & Gorbatyuk, 2022; Melo et al., 2020a; Sanjay et al., 2016). Natural fiber is considered

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one of the environmentally friendly materials which have good properties (Elseify, Midani, El-Badawy, & Jawaid, 2021a; Thyavihalli Girijappa, Mavinkere Rangappa, Parameswaranpillai, & Siengchin, 2019). Due to their properties, they are applications almost in all branches of economy (as composite, biocomposites, pulp, and paper industry) and are an excellent raw material for manufacturing of so-called “green products” (de Melo et al., 2019; Kici
nska-Jakubowska, Bogacz, & Zimniewska, 2012; Santos, Santos, Moreira, Aquino, & Zillio, 2021). This created an interest in natural materials which could be used as reinforcements or fillers in the composites and are thus referred to as “natural fiber reinforced composites,” “ecocomposites,” or “biocomposites” ( Jaiswal et al., 2022; Potluri, 2019; Sanjay et al., 2019; Zı´lio et al., 2020). Thus, several researchers came up with ideas of reinforcing different natural fibers in polymers to produce eco-friendly composites for several applications. The use of natural fibers as reinforcements in composites has been growing since then and has replaced several synthetic fiber reinforced composites in many applications such as automotive, marine, aerospace, construction industries, etc. (Elseify, Midani, El-Badawy, & Jawaid, 2021b; Khan, Rangappa, Jawaid, Siengchin, & Asiri, 2020; Moreira et al., 2021; Ramamoorthy, Skrifvars, & Persson, 2015; Thakur, Thakur, & Kessler, 2017). Vegetable fibers are textile structures used as reinforcing elements in composite materials based on polymeric matrices mainly because of the multiple advantages associated with this natural renewable material exploited when it is desired to obtain a material with good degradability, lightness and resistance (Krishnasamy, Nagarajan, Thiagamani, & Siengchin, 2021; Abdelmouleh et al., 2004; Reddy, Kim, & Park, 2016). Vegetable fibers are textile structures exploited when it is desired to obtain a material with good degradability, lightness and resistance. However, not all fibers can be obtained easily, as the cotton and kapok which can be harvested from bolls. The vegetables fibers are found in the leaves and basts of plants, as for example, the pineapple fiber, sisal, flax and kenaf fiber ( Jawaid & Khan, 2021; Madhu et al., 2018, 2019). Due to the need to know more about it, many fiber extraction processes were created. Agave fiber can be cited as a fiber that promoted research because of the action of economy in its production (Khan, Rangappa, Siengchin, & Asiri, 2021; Belaadi et al., 2022; Melo et al., 2020b; Moreira et al., 2021). From the research realized about the extraction of fibers, many techniques were developed, such as extraction by rectification and by alkalis. The rectification technique (or retting) was used in research for Rita Kant and Preeti Alagh (Kant & Alagh, 2013) that extracted the fiber of leaf of Sansevieria trifasciata in a process that took between 7 and 8 weeks. Rao and Shaker, in a Vakka and Vernonia fiber extraction experiment, used retting also, in a process that took between 8 and 25 days of immersion of leave in water (Rao & Rao, 2007; Shaker et al., 2020). The review realized for Zakikhani (Zakikhani, Zahari, Sultan, & Majid, 2014), show that it is possible to extract vegetable fibers using alkali (NaOH), in a shorter time than that used in the retting (only 5 h). However, the use of chemicals agents pollutes the environment. Then, this work analyzed properties of papaya tree fibers (PTFs) using microbiological retting, as performed by Li and Beijing (2004) and Shahinur, Hasan, Ahsan, Saha, and Islam (2015) in other plant fibers, and to analyze the influence of fiber location on its properties.

246

15.2

Cellulose Fibre Reinforced Composites

Experimental

15.2.1 Extraction of papaya stem fiber and fiber extraction yield The papaya fiber extraction method used was similar to that proposed in the literature (Li & Beijing, 2004; Shahinur et al., 2015), which consists of cutting the stem into three 1.5 m-long parts denominated PF1, PF2 and PF3, as shown in Table 15.1 and Fig. 15.1. Next, the pulp and bark of the papaya tree (Carica papaya L.) stem were removed. The stems were then placed in water-containing receptacles under anaerobic conditions for 15 days. Table 15.1 Parts of stem fibers and sample code. Stem fiber

Sample code

Parts 1 of stem Parts 2 of stem Parts 3 of stem

PF1 PF2 PF3

Fig. 15.1 Stem division for papaya fiber extraction.

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At the end of this period, the stems were beaten and the fibers brushed for maximum debris removal. Finally, they were rinsed under running water and dried. The fiber extraction yield was also calculated from equation below (Eq. 15.1).   extracted fiber weight Fiber yield ð%Þ ¼  100 stem weight

(15.1)

15.2.2 Characterization of papaya stem fiber Papaya fiberdensity was determined using a pycnometer, according to ASTM D2320-98 (2017). Crystallinity was analyzed on a Shimadzu XRD-6000 X-ray diffractometer, with 2θ angles between 5 and 30 degrees, step size of 0.05 degree and scanning speed of 1.5 degrees per minute. The analysis used Cu radiation generated at 40 kV and 30 mA for 2 s. The crystallinity index (CI) was calculated by Gaussian deconvolution (Park, Baker, Himmel, Parilla, & Johnson, 2010). Rietveld refinement analyses (Ling et al., 2019) were conducted using Origin Pro software. Eq. (15.2), described by Hermans (Poletto, Pistor, & Zattera, 2013; Seki, Selli, Erdogan, Atag€ur, & Seydibeyoglu, 2022; Sena Neto et al., 2015; Wada & Okano, 2001) defines the crystallinity index.  CI ð%Þ ¼

 Sum of crystalline band areas  100 Total area under the diffractograms

(15.2)

A tensile test was carried out on the fibers, adapting ASTM D3822 (ASTM D3822/ D3822M-14, 2020), used to measure the tensile properties of natural and artificial textile fibers. The samples were broken in a tensile testing machine employing a predetermined length and breaking strain rate. The stress-strain curve and linear density were used to calculate tensile strength (MPa) and breaking strain (%). Both properties are widely used to establish processing and application limits, toughness indicating the durability of the materials produced from the fiber. During the test, a length of 65 mm between claws was adopted for the sample. The speed of the tensiometer is a function of the breaking strain. A breaking strain rate of 10 mm/min was used and tensile strength was calculated in MPa. The wettability test was performed according to the experimental models described by Duprat, Protie`re, Beebe, and Stone (2012), Hong, Minary-Jolandan, and Naraghi (2015), and Rebouillat, Letellier, and Steffenino (1999). According to Rebouillat et al. (1999), the wettability test provides useful information on the state of the fiber surface in contact with the liquid. When the contact angle is greater than 90 degrees, the sample is classified as hydrophobic with low surface energy, whereby fiber-liquid adhesion forces are higher than their cohesion counterparts (Lamour et al., 2010; Von Fraunhofer, 2012). Field emission gun scanning electron microscopy (FEG-SEM) was used to visualize the surface morphology of the papaya stem fiber when submitted to the retting process. The results made it possible to identify the characteristics of the fibers and visualize possible damage, relating them to the values obtained in the tensile tests. Optical microscopy (OM) was used to examine transverse and longitudinal sections of the papaya stem fiber samples.

248

15.3

Cellulose Fibre Reinforced Composites

Results and discussions

Papaya stem fiber was extracted using a simple water retting process. Foreign matter dissolved in water after 15 days. The washing and brushing process resulted in complete separation of fibers from the foreign matter. The papaya stem contains between 5.0% and 14.5% fiber, depending on the stem part, as shown in Fig. 15.1. According to the yield results, PF2 exhibits the highest fiber content (14.5%) in relation to the other regions (PF1 and PF3). Papaya fiber extraction is depicted in Fig. 15.2. The most significant fiber extraction result was for PF2 of the stem. This is due to plant ripening period, where there is a higher concentration of fibers. Region 3 has the fewest fibers, since it is the youngest part of the plant. Region 1, on the other hand, also has a low concentration because a large number of fibers are dead and were therefore not extracted due to their degradation in the biological extraction process (Fig. 15.3). Table 15.2 shows that the densities of the papaya stem fiber extracted by the biological method differed between 0.64 and 0.74 g/cm3. This fiber is slightly less dense than that reported by Kempe et al. (2015) and Saravana Kumaar et al. (2017). Compared with other stem fibers, their density is similar to that of bamboo fiber and less than that of flax and banana. This characteristic is useful in the field of composites, which is constantly in search of increasingly lightweight materials.

Fig. 15.2 Percentage of fiber extraction-biological process as a function of stem location.

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Fig. 15.3 Papaya stem fiber extracted. Table 15.2 Stem fiber densities. Stem fiber

Density (g/cm3)

PF1 PF2 PF3 Banana (Pereira et al., 2015) Bamboo (Pereira et al., 2015) Papaya stem fiber (Kempe et al., 2015; Saravana Kumaar et al., 2017)

0.74  0.09 0.66  0.04 0.64  0.01 1.5 0.6–1.1 0.84–0.94

Morphology of the papaya fiber surface was investigated by OM and FEG-SEM (Figs. 15.4–15.7, respectively). In order to determine fiber structure and morphological damage, it is essential to predict fiber interaction with the polymer matrix in composites (Sisti et al., 2016). Fig. 15.4 shows longitudinal (first column) and crosssectional views (second column) of a papaya fiber. Fig. 15.4A and B show significant irregularities on the surface of fibers from PF1 of the papaya tree stem. This is expected since these fibers bear the full weight of the papaya tree over time. However, this irregularity may also be related to impurities (nonfibrous material) and wax that did not break away from the fiber during extraction (Gonc¸alves et al., 2015; Ok Han & Choi, 2010). Fig. 15.4C and D show that the surface of PF2 fibers is more regular than that of its PF1 counterpart (Fig. 15.4E and F), because the former is located in the central region of the stem. In the case of PF3, the surface is uniform, similar to that exhibited by fiber 2. The cross-sections of papaya stem fibers, analyzed by optical microscopy, show a large number of pores. Thus, pores are a predominant feature in papaya stem fibers and are present in any region of the stem from which they are extracted. However, the geometry of the cross-sections differs, with pores tending to be circular in fibers extracted from

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Fig. 15.4 Longitudinal (first column) and cross-sectional view (second column) of fiber from different parts of the papaya stem: PF1 (A and B), PF2 (C and D), and PF3 (E and F).

PF1 of the papaya tree (Fig. 15.4B), and elliptical in the other fibers extracted (PF2 and 3) (Fig. 15.4D and F). More detailed morphological analysis was carried out by FEG-SEM, in order to determine the characteristics of each fiber surface and verify if they are similar to those of other natural fibers. The FEG-SEM images from each sample (PF1, PF2, and PF3) are displayed in Figs. 15.5–15.7. FEG-SEM images of all papaya fibers (Figs. 15.5–15.7) demonstrate the presence of longitudinally oriented cells parallel to each other. The intercellular space is filled by lignin and fatty substances, which act as a binder, maintaining the cells firmly in a fiber, as reported (Bismarck et al., 2001). However, morphological changes, due to cell organization, were observed for fibers extracted from different parts of the papaya stem. A large number of protrusions or patches embedded in the papaya fiber surface and irregular cell intervals were identified in PF1. Moreover, PF1 fiber contains small

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Fig. 15.5 Field emission gun scanning electron microscope images of papaya fibers extracted from PF1 of the stem.

Fig. 15.6 Field emission gun scanning electron microscope images of papaya fibers extracted from PF2 of the stem.

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Cellulose Fibre Reinforced Composites

Fig. 15.7 Field emission gun scanning electron microscope images of papaya fibers extracted from PF3 of the stem.

particles attached to the fiber surface (wax and fats), making it slightly rougher than in the other parts. The fibers are more uniform at the extremities of the root. PF3 fiber exhibits a more uniform surface, with closely packed rectangular cells along the fiber (Fig. 15.7) and more microholes available on the fiber surface (Gonc¸alves et al., 2015; Ok Han & Choi, 2010). PF2 fiber shows intermediate morphology, greater uniformity and more microholes than in PF1. On the other hand, cell organization in the fiber structure is not uniform in PF3. This good cell organization on the fiber surface may be due to the fact that this fiber is more susceptible to a biological attack than other parts (Arsyad, Wardana, Pratikto, & Irawan, 2015; Defoirdt et al., 2010). The crystallinity index (CI) was determined by X-ray diffraction and the XRD spectrum for extracted fibers is displayed in Fig. 15.8. All fibers (PF1, PF2, and PF3) showed peaks 1 and 4 in the 2θ ¼ 15 degrees and 2θ ¼ 22.5 degrees regions, indicating crystallographic planes 110 and 200, respectively. The highest peak at 2θ ¼ 22.5 degrees and lowest at 2θ ¼ 15 degrees demonstrate the diffraction patterns of cellulose Iβ. Peaks 2 and 3 represent the amorphous part of the graphs (French, 2014; Ling et al., 2019). The calculated crystallinity index (CI) for entire parts of papaya steam fibers is displayed in Table 15.3, as well as some similar fibers reported in the literature, such as flax, banana and bamboo. From this Table 15.3 it is noted that papaya stem fiber presented higher CI than the bamboo and banana fibers. The smaller CI for PF1 can be explained based on morphology showed in Fig. 15.5, once more impurities and less uniformity promote the reduction of crystallinity (Gonc¸alves et al., 2015). However, fibers extracted from PF3 showed a higher CI (63.1%), thus indicating higher content

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Fig. 15.8 XRD with deconvolution curves of the papaya stem fibers extracted using the biological process. Fiber from PF1 (A), PF2 (B), and PF3 (C).

Table 15.3 Index of crystallinity (CI) of stem fibers. Stem fibers

CI (%)

PF1 PF2 PF3 Papaya stem (Kempe et al., 2015) Flax (Pereira et al., 2015) Banana (Pereira et al., 2015) Bamboo (Pereira et al., 2015)

61.9 62.2 63.1 56.3 86.1 39 59.7

of cellulose when compared to other parts. An important finding is that the crystallinity index from fibers extracted according to methodology used in this work is higher than found by Saravana Kumaar (Saravana Kumaar et al., 2017) for the papaya tree fibers in their study (56.34%). As the cellulose crystallinity is one of the most important crystalline structure parameters. According to Poletto, the rigidity of cellulose fibers increases, and their flexibility decreases with increasing of crystallinity (Poletto, 2017).

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The performance of a composite material is broadly influenced by the nature of interface between the two phases involved. Thus, surface-wetting characterization of natural fibers is largely useful for predicting fiber-matrix compatibility in composites. One method to determine the amount of water absorbed by fiber is the measure of the contact angle, which was obtained for all the fibers extracted in this investigation (Table 15.4). According to the results described in Table 15.4, papaya stem fibers are hydrophilic in the 82–98 degrees range, as observed for bamboo fiber (Chen et al., 2013). On the other hand, sisal and banana fibers are weakly hydrophilic. This hydrophilic nature corroborates the CI results, since higher crystallinity levels are found if the amount of cellulose and hemicellulose in the fiber is elevated (Schellbach et al., 2016). The fluctuation in Wettability values for different parts of the papaya stem is due to the morphological heterogeneity of the fiber surface, as illustrated in Figs. 15.5–15.7. Fig. 15.8 shows the mechanical properties of papaya fiber analyzed for breaking strain (%) and tensile strength (MPa). Fig. 15.9A shows that the highest tensile strength values were obtained for PF2 fibers (10.8 MPa) and the lowest for their PF3 counterparts (2.8 MPa), a 74% Table 15.4 Wettability of the stem fibers. Stem fiber

Contact angle (degrees)

PF1 PF2 PF3 Bamboo (Chen et al., 2013) Banana (Schellbach, Monteiro, & Drelich, 2016) Sisal (Gan˜a´n, Cruz, Garbizu, Arbelaiz, & Mondragon, 2004)

97.7 82.3 98.0 87.7 45.3 41.0

Fig. 15.9 Analysis of the mechanical properties of papaya stem fibers (PF1, PF2 and PF3) by biological extraction: (A) tensile strength, (B) breaking strain.

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Table 15.5 Comparison between the breaking strain and tensile strength of the papaya stem fiber and other plant fibers extracted from the stem. Stem fiber

Breaking strain (%)

Papaya stem

1.40 (Kempe et al., 2015)–1.62 (Saravana Kumaar et al., 2017) 1.5–9 (Ramesh, Logesh, Manikandan, Kumar, & Pratap, 2017) 2–3.4 (Zhang et al., 2018) 0.5–2

Banana Bamboo Papaya stem (this chapter)

Tensile strength (MPa) 49.0–530 54 187–337 28–12.2

reduction in toughness. This result indicates that cleaner and better-divided fiber (more uniform) promotes a decrease in tensile strength. The low toughness of PF3 fiber is associated with more uniformity, more microholes, and fewer impurities, thereby decreasing fiber rigidity, evident in the FEG-SEM images of Fig. 15.6 (Behera, Hari, Bansal, & Singh, 1997; Spinac
e, Lambert, Fermoselli, & De Paoli, 2009). The tensile strength obtained in the present study differs from earlier investigators, such as Kempe et al. (2015) and Saravana Kumaar et al. (2017), who found values of 49 and 530 MPa, respectively. These different values may be associated with soil and climate conditions, as well as the type of species. Moreover, the method used to determine this property may be different. In this investigation was adopted ASTM D3822, Saravana Kumaar et al. (2017) used ASTM D3379-75, while Kempe et al. (2015) did not report the standard used. According to Lautenschl€ager (Lautenschl€ager, Kempe, Neinhuis, Wagenf€uhr, & Siwek, 2016), the strength and stiffness of papaya fiber are below the average values of natural fibers (Table 15.5). The influence of stem part on breaking strain is depicted in Fig. 15.9B. Breaking strain percentages decreased as a function of the stem region from which the fiber was extracted, meaning that fiber closer to the top of the plant exhibits a lower breaking strain percentage (0.5%). Thus, PF1 papaya fiber obtained the highest breaking strain value (2%) compared to the others (PF2 and PF3), while for banana fiber it was 1.5% to 9% and bamboo 2% to 3.4% (Table 15.5). These values may be associated with the morphology analyzed in Fig. 15.4, where particles attached to the fiber surface were identified (wax and fats). This suggests an increase in breaking strain performance (Deopura, Sinha, & Varma, 1977). The current investigation demonstrated that papaya fiber is widely suitable for applications as composites reinforcement, since its properties are similar to those of other vegetal fibers, such as banana, flax, kenaf and hemp, which have been properly employed in polymer composites over the years, as reported in Table 15.6.

Table 15.6 Comparison of the properties of papaya tree fibers with other natural fibers. Properties

PF1

PF2

PF3

Flax

Kenaf

Banana

Hemp

Tensile strength (MPa)

3.8–6.0

9.6–12

2.6–3.0

510–910 (Ali et al., 2015)

300–1200 (Ali et al., 2015)

300–760 (Ali et al., 2015)

Tenacity (cN/Tex)

7.8–12.8

23.3–30.7

8.4–10.2

44.4–95.3 (Kromer, 2009)

Elongation at break (%)

1.7–2.3

0.5–1.3

0.3–0.7

Young modulus (GPa)

0.2–0.3

0.9–2.0

0.4–0.9

1.6–2.5 (Baley, Le Duigou, Morvan, & Bourmaud, 2018) 50–70 (Ali et al., 2015)

25.1–28.9 (Ben Mlik, Jaoudi, Khoffi, Slah, & Durand, 2020) 2.7–6.9 ( Jawaid, Sapuan, & Alotman, 2017) 22–60 (Ali et al., 2015)

53.7 (Khan, Rangappa, Jawaid, et al., 2020) 42.8 (Ortega, Moro´n, Monzo´n, Badallo´, & Paz, 2016)

Specific modulus— E/p (GPa) Number of fiber count (Tex) Wettability (degrees)

0.3–0.4

1.3–3.2

1.4–0.6

34–48 (Ali et al., 2015)

17–46 (Ali et al., 2015)

12.9– 17.3

15.0–19.2

12.0–15.2

–

–

–

20–41 (Ali et al., 2015) –

97.7

82.3

98.0

91.0 (Cantero, Arbelaiz,

55.0 (Park et al., 2015)

45.3 (Schellbach et al., 2016)

58.0 (Pietak, Korte,

51.2–60 (Pennas et al., 2019)

2 (Latif et al., 2018)

1.6 (Shahria, 2019)

27–32 (Vidya Bharathi, Vinodhkumar, & Saravanan, 2021) 20–23.7

30–60 (Ali et al., 2015)

Llano-Ponte, & Mondragon, 2003) Crystallinity index (%)

61.9

62.2

63.1

86.1 (Pereira et al., 2015)

Fiber yield (%)

6.9–7.6

13.8–15.3

4.1–5.9

Fiber density (kg/m3)

650– 830

620–700

630–650

Prices of dry stem fiber ($/kg)

–

–

–

14.7–17.0 (Rashwan, Mousa, ElSabagh, & Barutc¸ular, 2016) 1400 (Atmakuri, Palevicius, Siddabathula, Vilkauskas, & Janusas, 2020) 0.6–0.8 (Tahir et al., 2011)

Bold values correspond to those obtained in this chapter.

67.0 (Zaini, Jonoobi, Tahir, & Karimi, 2013) 5–6 (Tahir, Ahmed, Saifulazry, & Ahmed, 2011)

39 (Pereira et al., 2015)

1–2 (Chand & Fahim, 2021)

20–80 (Shahinur et al., 2015)

1350 (Atmakuri et al., 2020)

0.7–0.8 (Tahir et al., 2011)

0.4–0.8 (Mukhopadhyay, Fangueiro, Arpac¸, & Şent€ urk, 2008)

Tan, Downard, & Staiger, 2007) 79.9 (Pereira et al., 2015)

40.0 (Abbas, Aziz, Abdan, Nasir, & Norizan, 2022) 1480 (Atmakuri et al., 2020) 0.7–0.8 (Tahir et al., 2011)

258

15.4

Cellulose Fibre Reinforced Composites

Conclusions

This study investigated retting extraction and papaya stem characterization in order to determine the viability of its use as a natural fiber in the manufacture of composites and provide additional value to waste. The following conclusions can be drawn: l

l

l

l

Retting extraction is simple, inexpensive, and produces quality papaya fibers. The part of the stem from which the fiber is extracted influences cellulose I intensity and the crystallinity index. PF1 fiber, which is closest to the top of the plant, exhibited more impurities and nonuniformity in fiber structure, in addition to less cellulose and crystallinity. On the other hand, PF3 fiber showed a more uniform fiber surface, well organized cells and the highest crystallinity index. The wettability of papaya fiber, irrespective of stem region, displays good hydrophilicity, thereby increasing fiber-matrix adhesion. The lower density demonstrates that this fiber may be promising in the manufacture of lightweight materials. Based on these results, the papaya fiber studied here can be included in the list of natural fibers suitable to apply in green composites manufacturing, as well as for textiles technologies.

Acknowledgments This study was funded in part by the Coordination for the Improvement of Higher Education Personnel (Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de Nı´vel Superior—CAPES)— Funding Code 001.

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Cellulose-based composite materials for dye wastewater treatment

16

Mohammad Mamunur Rashid, Mohammad Irfan Iqbal, and Ayub Nabi Khan BGMEA University of Fashion & Technology (BUFT), Dhaka, Bangladesh

16.1

Introduction

Freshwater is an essential resource to sustain life on earth and a critical feedstock in most agricultural and industrial processes. With the increasing population, the demand for freshwater is increasing proportionally. However, freshwater supplies rapidly decrease due to rising pollution caused by human activities (Goodman, Bura, & Dichiara, 2018). Global water consumption has become eight times more than in the previous century (1900–2010). Water availability has become related to social, economic, environmental, and political factors (Wada et al., 2016). The release of wastewater from different industries to natural streams and rivers presents severe causes of prime water pollution (dos Santos et al., 2013). Textile industries are the leading contributors to water pollution, among other sectors. Textile industries discharge unfixed colors as effluents into water resources (Haque, Smith, & Wong, 2015). Dyes are molecules that provide color to a substrate and possess chromophores and auxochromes in the structure. The auxochromes act to enhance the color of the dye. The different wavelength of light absorbed by chromophores and auxochromes defines the different colors provided by the dyes (Bethi, Sonawane, Potoroko, Bhanvase, & Sonawane, 2017). Dyes are extensively consumed in textile, paint, pigment, leather, and many other sectors as coloring agents (Liu et al., 2011). Textile industries are the highest dye consumer sector than others and form a large amount of wastewater and generate a massive quantity of colored liquid waste (Katheresan, Kansedo, & Lau, 2018). Acid, direct, disperse, reactive, and vat dyes are a major class of dyes used in textile industries. But none of them are able to fully fix with the substrate, and details are provided in Table 16.1 (Kausar et al., 2018; Patel, 2018; Tan et al., 2015). The removal of color from discharged effluents is a great concern because these dyes are toxic, mutagenic, and nonbiodegradable (Uddin, Rahman, Rukanuzzaman, & Islam, 2017). Dye-containing effluents cause severe threats to humans, such as severe damage to the liver, kidneys, reproductive system, central nervous system, etc. (Adegoke & Bello, 2015). Therefore, must effectively remove colorants from drainage to ensure the safe discharge of processed liquid effluent into watercourses. Because of serious problems induced by freshwater pollution, there is a significant concern for an Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00005-7 Copyright © 2023 Elsevier Ltd. All rights reserved.

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Table 16.1 Details of different types of dyes used in textile industries. Dyes

Properties

Application

Acid

Water soluble, anionic Water soluble, cationic, release cationic color dye solution Water insoluble, nonionic Water soluble, anionic Water soluble, anionic. Extremely good wash fastness

Wool, nylon, silk, protein fiber Paper, poly acrylonitrile (PAN), modified polyesters, used in medicine as antiseptics Polyester, nylon, acrylic fibers Cotton, cellulosic fibers, paper, leather Cotton, cellulosic fibers

Basic

Disperse Direct Reactive

% Fixation

% Loss

80–95

20–5

97–98

3–2

85–97

15–3

70–95

30–5

50–90

50–10

effective and affordable wastewater treatment system and remediation of this critical problem. Techniques and materials for eliminating such dyes are being built to improve existing ones or find new options for enhancing water treatment efficiency. This chapter highlights current advances in using cellulose-based composites to treat dyes from wastewater. It contains a general introduction to cellulose and the various techniques to form cellulose-based materials for wastewater dye removal. The dye removal efficiencies of cellulose-based composites, beads, aerogel such as cellulose-ZnO, cellulose-activated carbon (AC), cellulose-graphene oxide, and cellulose-chitosan have been discussed.

16.1.1 Application of dyes and its impact The consumption of dyes in industries is continuously increasing to meet the demand of the consumers. The nonbiodegradable nature of these dyes causes severe environmental hazards by affecting evaporation rate, absorption, precipitation, and biological activities. The presence of dyes is responsible for the aesthetically unpleasant appearance of water; it impedes the oxygenation capacity and disturbs the aquatic environment (Shivaraju et al., 2017). Even in low concentrations, the discharged unfixed dyes generate a colored aquatic system that causes severe environmental hazards by reducing the transmission of sunlight into the colored water. Hence, the photosynthesis process is hampered, causing a disturbance in the food chain of aquatic life (Bharathi & Ramesh, 2013). The reduction of plant protein, chlorophylls, and carbohydrate is a strong indication of toxic effects in textile coloring effluent on plants (Bhatia,

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Sharma, Singh, & Kanwar, 2017). Dyes can induce certain adverse effects on health, such as diarrhea, pain, cyanosis, jaundice, quadriplegia, and necrosis of the tissue (Uddin et al., 2017). The exposure time and intensity of the dyes may have acute and chronic consequences on exposed species. Dyes can contribute to allergic dermatitis, itching of the skin, disease, mutation, etc. (Bharathi & Ramesh, 2013). Methylene blue is a harmful dye for fish and some aquatic organisms and sometimes may cause permanent injury to human beings (Shakoor & Nasar, 2016). Malachite green belongs to the dyes triphenylmethane group that has an adverse effect on the liver, reproductive system, and kidney function. It also induces chromosomal disruption and degradation of the respiratory enzymes (Srivastava, Sinha, & Roy, 2004). The toxic effects of azo dyes may be induced by the direct action of the agent itself or by the aryl amine derivatives produced during reduced azo bond biotransformation (Rajaguru et al., 1999). Azo reductases of intestinal micro-organisms can metabolize the azo dyes reaching the body by absorption to aromatic amines. If the dyes are nitro, the nitro reductases formed by the same microorganisms will metabolize them. Mammalian liver enzymes and other organs may also catalyze the reductive cleavage of the azo bond and the nitro reduction of the nitro group. In both instances, such compounds can damage DNA if N-hydroxylamine is produced (De Araga˜o Umbuzeiro, Freeman, Warren, Kummrow, & Claxton, 2005). Moreover, the dyes in wastewater often adds to the high demand for chemical oxidation and induces bad smell (Bhatia et al., 2017). It is a great concern to develop an effective and affordable wastewater treatment system and remediation to overcome the serious problems induced by freshwater pollution.

16.1.2 Cellulose Cellulose is the most available natural renewable polysaccharide on earth. Cellulose is the widely used organic polymer, contributing approximately 1.5  1012 tons of the total worldwide annual biomass supply, and is called an almost limitless source of raw material for increasing demand for environmentally friendly and biocompatible goods (Sessini, Haseeb, Boldizar, & Lo Re, 2021). Some unique properties of cellulose such as nontoxicity, reactivity, chemical stability, biocompatibility, and biodegradability, etc. influence to draw attention for applications in the production of many organic-inorganic composites (Klemm, Heublein, Fink, & Bohn, 2005). The environmental issues led material scientists to investigate cellulose as a green filler in the production of renewable composites that are environmentally sustainable (Das, Ray, Bandyopadhyay, & Sengupta, 2010). Cellulose is a linear homo-polysaccharide type polymer consisting of ringed glucose molecules as a monomer (Brinchi, Cotana, Fortunati, & Kenny, 2013). Fig. 16.1 shows the structure of cellulose (Heinze & Liebert, 2001). Cellulose shows a high degree of functionality due to many hydroxyl groups in cellulose macromolecules where each glucose unit possesses three highly reactive hydroxyl groups at positions 2, 3, and 6 (Czaja, Romanovicz, Brown, & malcolm., 2004). The cellulose molecule comprises three types of AGU: a reducing end containing a free hemiacetal or aldehyde at position C1, a nonreducing end with a free hydroxyl group at position C4, and

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Cellulose Fibre Reinforced Composites CH2

H2C

H2C

NH2+Cl–

O

N

CH2

NH2+Cl–

O

N

Electrostatic attraction

Hydrogen bonding

H OH

H H O

O HO

H H

H

O OH H

OH

H

SO3–

HO H

H O H OH

H

H H O

O HO

HO

H

H OH

OH

H

O OH H

H O H OH

Fig. 16.1 Structure of cellulose including numbering of C-atoms. Reprinted with the permission from Heinze, T. & Liebert, T., (2001). Unconventional methods in cellulose functionalization. Progress in Polymer Science (Oxford), 26(9), 1689–1762. Elsevier.

internal glucose joined at the positions C1 and C4. Each internal AGU contains three groups of hydroxyls (OH). The OH group in position C6 is a primary alcohol, and the OH groups in positions C2 and C3 are secondary alcohols. These OH groups are responsible for making cellulose chemically active. Hydroxyl (OH) group at C6 is highly reactive than other hydroxyl groups (Roy, Semsarilar, Guthrie, & Perrier, 2009). The glucose units found in cellobiose allow the substitution, oxidation, or deoxidation of hydroxyl groups, the substitution or oxidation of C6, the oxidation of C2 and C3, and the hydrolysis of glycosidic bonds (Yeh, Chen, Hsi, Ko, & Wang, 2014). The functionality (e.g., dye cleaning capacity) of cellulose can be enhanced by modification of surfaces of cellulose by incorporating several materials reported by several studies (El-Naggar et al., 2018). This chapter aims to highlight the potentiality of cellulose-based composite materials for dye wastewater cleaning.

16.2

Cellulose-based composites for dye removal

Natural and modified cellulose-based composites are used for dye removal.

16.2.1 Cellulose-ZnO-based composite for dye removal Zinc oxide (ZnO) is a metal oxide that has gained a lot of attention because of its numerous attractive features such as environmental friendliness, electrical properties, nontoxicity, and low manufacturing cost (Zhu et al., 2019). ZnO possesses excellent optoelectronic properties, high catalytic activity against chemical and biological species, and strong antibacterial properties against a wide variety of pathogens. Owing to these features, ZnO has been found in a wide range of functional applications such as optical devices, ultraviolet, gas sensors, photodetectors, ultraviolet laser diodes, solar cells, ion insertion batteries, and pharmaceutical industries. Recently, ZnO application

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in wastewater treatment to remove dyes has been widely researched (Lefatshe, Muiva, & Kebaabetswe, 2017). But the use of bare ZnO nanoparticles has some limitations. Zinc oxide nanoparticles (ZnO NPs) can easily aggregate due to their small size and high surface energy, limiting their range of applications. Therefore, one of the effective ways to well dispersion ZnO nanoparticle is to assemble ZnO nanoparticles into suitable templates to form composite materials (Tomczak, Gupta, Drummy, Rozenzhak, & Naik, 2009). The use of cellulose as the carrier with ZnO nanoparticles has become attractive because of these attempts to modify and functionalize cellulose and overcome the aggregation problem of ZnO nanoparticles (Yu, Chen, Wang, & Yao, 2015). ZnO/CNC nanocrystal hybrids with variable morphologies (nearly spherical, thin sheet, and flower-like forms) were successfully synthesized using a green one-step method utilizing bamboo CNC as templates (Guan et al., 2019). It was discovered that the low OH content at pH value (8.5) would stimulate the development of almost spherical shape hybrids with a diameter of around 60 nm. Due to the high amount of OH at high pH levels (10.5 and 11.0), sheet-like and flower-like hybrids were produced. Besides, both the sheet-like and flower-like hybrids exhibited high crystallinity and ZnO content, resulting in increased thermal stability. Spherical ZnO/CNC hybrids synthesized at pH 8.5 showed a smaller size and more carboxyl groups (poor crystallinity), resulting in greater dye absorption capability for methylene blue (MB) and malachite green (MG) dyes. The absorption capacity of MB and MG can reach up to 46.77 mg/g and 49.51 mg/g, respectively. At pH 8.5, ZnO/CNC showed dye removal efficiencies of 93.55% for methylene blue and 99.02% for malachite green, which is fast and higher. Electrostatic interaction between carboxyl groups COO ) and positive charge functional groups NH+4 was the major absorption mechanism for hybrid dye absorption. Thus, such hybrids with enhanced characteristics have a high potential for application as effective cationic dye adsorbents in industrial effluent. It is clearly revealed that the high adsorption of MB and MG on ZNC/ CNC composites depends on surface carboxyl group, ZnO nanoparticle size, surface morphology, and electrostatic attraction between adsorbent and adsorbate. The composite synthesized at pH 8.5 possesses more residual carboxyl group on the surface, providing more active sites and resulting in high dye removal efficiency. 2D ZnO nanosheets-regenerated cellulose (ZNSRC) composite thin films were prepared at different reaction times (11, 13, 15 h) with NaOH (50% wt.) aqueous solution using a two-step synthesis method at room temperature (Zhou et al., 2019). The ZNSRC synthesized by 13 h reaction time exhibit good dispersion and the highest photocatalytic activity, as 1.53  10 5 mol methyl orange was fully destroyed within 50 min using 1 g catalyst. The explanation for this is that when the reaction time for synthesize ZNSRC was 13 h, more irregular nanopores formed in the composite structure compare with ZNSRC-11 and 15 h, which is not only favors electron-hole separation or carrier movement but also improves selective adsorption and photodegradation of pollutants. The existence of nanopores can provide more oxygen vacancy for photocatalytic action and increase opportunities of ultraviolet light utilization. The case of ZNSRC at 15 h showed low content of ZnO nanosheets and the absence of ample nanopores. The ZNSRC at 11 h possess relatively high crystallinity

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and less number of nanopores than ZNSRC-13 h. It degraded methyl orange in 80 min that is higher than ZNSRC-13 h. Bacterial cellulose (BC) was successfully fabricated with ZnO-NPs by immersing BC pellicles in zinc nitrate solution followed by treatment with NaOH solution (Wahid et al., 2019). Positively charged Zn2+ easily adhered with the 3D network of BC. FE-SEM results of the bacterial cellulose/ZnO (BCZ) composites displayed a uniform distribution of ZnO-NPs on the surface of BC films and the particle size ranging from 70 to 100 nm. The nanocomposites degrade 91% of methyl orange under UV-irradiation within 2 h. Typically, photocatalytic degradation occurs on the surface of the photocatalyst. The absorption of light by ZnO-NPs produces photogenerated electron-hole pairs, which can either directly react with organic contaminants to degrade it or migrate to the surface of ZnO-NPs and react with water and oxygen absorbed on the surface of ZnO-NPs to generate more reactive species (free radicals like OH , HO2 , O2 ), which then degrade dye through further degradation. The ZnO-cellulose nanocomposites (ZCN) films were produced from the aqueous cellulose-NaOH/urea/ZnO solution using a biomimetic one-step approach and coagulation with ethylene glycol (Fu et al., 2017). The degradation efficiency of rhodamine B reached 99.3% within 50 min with UV radiation and showed only a slight reduction of 99.3%–93.3% after three cycles. This result indicates that ZCN films could be easily recovered and had good photocatalytic stability, which would significantly contribute to their industrial application in the removal of dyes from wastewater. The reason behind such excellent photocatalytic reactivity of the ZCN could be better dispersion of nanosize (90.6 nm) ZnO with higher specific surface area and porous network structure in the composites. The porous structure could be caused by liquid-liquid demixing during the coagulation process. In this study, in situ mineralization of ZnO occurs in the presence of cellulose, which increases the contact between dyes and reactive radicals and eventually results in excellent photocatalytic activity. The in situ mineralization was possible due to the porous structure of cellulose. A new approach combining electrospinning and solvothermal methods was used to develop a nano ZnO/cellulose (CNF) composite (Ye, Zhang, Liu, & Zhou, 2011). RhB was decomposed around 50% after 24 h of irradiation under visible light using a 500 W tungsten lamp as the light source. These hybrid nanofibrous mats may be easily separated from the reaction medium using forceps. The thermal stability of cellulose in the ZnO/cellulose structure helps attain recyclability.

16.2.2 Cellulose-activated carbon-based composite Activated carbon (AC) is the most commonly used adsorbent for wastewater treatment due to its large surface area, porosity, and variable pore size (Malik, 2003). The practical application of activated carbon is limited due to its high cost and low efficiency (Machado et al., 2011). The utilization of cellulose as the carrier can improve the adsorption capacity of AC/cellulose composite (Luo & Zhang, 2009). Magnetic cellulose/Fe3O4/activated carbon composites (m-Cell/Fe3O4/ACC) were synthesized using a co-precipitation technology (Zhu et al., 2011). The m-Cell/Fe3O4/

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ACCs were applied as adsorbents to remove Congo red (azo structured) dye from the aqueous solution. The influence of various factors on the adsorption efficiency of azo dye from aqueous solutions onto m-Cell/Fe3O4/ACCs, including initial dye concentration, adsorbent dosage, and pH were investigated. About 94% adsorption was obtained for the initial concentration of 10 mg/L within 15 h, while it was 52.8% for an initial concentration of 70 mg/L at the same contact time. It can be explained as the increased concentration of Congo red (CR) dye increases the repulsive forces between dye molecules, making it difficult to adsorb on the surface of m-Cell/Fe3O4/ ACC. The adsorbent dosage was varying from 0.2 to 3.0 g/L at a fixed initial concentration of dye solution. The dye removal efficiency was found to increase as the adsorbent dose increased. This is due to the fact that more active sites were available at the m-Cell/Fe3O4/ACC surface for adsorption with increased adsorbent dosage. The neutral pH of CR is 5 at 20 mg/L concentration. In this study, the pH was kept at 4–9.5. The dye removal efficiency decreased from 83.1% to 14.1% with the increase of pH from 4 to 9.5. CR is anionic dyes and easily adsorbed on the composite at acidic and neutral pH. With the increase of pH of dye solution, the composite surface becomes anionic and causing enhancement of repulsion between CR and adsorbent composite increase. As a result, the dye removal efficiency decreases at higher pH. A biocomposite of cellulose/activated carbon (ACC) was prepared via solution casting and applied in methylene blue dye solution to examine the adsorption behavior of the synthesized composite (Somsesta, Sricharoenchaikul, & Aht-Ong, 2020). Activated carbon and cellulose were obtained from sisal fibers. The significance of initial dye concentration (20–100 mg/L), contact time (0–24 h), pH (3 11), and temperature (35–80°C) on adsorption capacity of ACC film was reported. The transition of pH can change the surface charge of composite film, and hence the adsorption capacity also changes accordingly. At low pH (3.0), ACC showed a poor (50.4 mg/g) adsorption capacity while it was drastically improved (72.5 mg/g) at high basic pH (11). In an acidic environment, the positively charged surface of the adsorbent may produce a repulsive force between the cationic methylene blue and the positively charged surface of the ACC film. In contrast, in basic conditions, electrostatic attraction occurred in negatively charged ACC and positively charged MB. These interactions impacted the adsorption capacity of the adsorbent by facilitating or obstructing the adsorption process. The dye adsorption went up from 27.51 mg/g to 103.66 mg/g with the increase of the initial concentration of MB due to the enhanced possibility of contact between MB and adsorbent ACC. The dye adsorption rose from 60.48 to 69.65 mg/g when the temperature increased from 35°C to 60°C. It is well known that increasing the temperature may speed up the mobility of dye particles and improve the interaction between adsorbate and adsorption sites on the adsorbent’s surface by providing enough energy. Furthermore, at higher temperatures, a swelling effect of the adsorbent’s internal structure may allow dye molecules to pass through, resulting in increased methylene blue adsorption. However, at higher temperatures (70–80°C), desorption may occur during the adsorption phase due to the rapid mobility of dye molecules, resulting in a decrease in the ACC film’s adsorption capacity. A porous cellulose/activated carbon monolith composite was developed using thermally induced phase separation of cellulose acetate in the presence of AC to

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eliminate methylene blue (MB) and rhodamine B (RhB) dye from an aqueous solution (Bai, Xiong, Li, Shen, & Uyama, 2017). It was found that 62% RhB dyes and 100% MB were removed at an adsorbent dosage of 0.30 g, 200 mg/L dye concentration, and 7 pH. The surface area and pore volume of the composite are higher than cellulose monolith, which helps to adsorb dyes quickly into the mesoporous structure. The maximum adsorption capacities of composite for both dyes MB and RhB were 159 and 33.4 mg/g, respectively. It is noted that with the concentration of dosage above 0.30 g, the removal efficiency was becoming reduced due to abundant active sites repulsing each other. It was also found that with the increase of initial dye concentration, the dye adsorption capacity increased, which indicates more utilization of adsorbent active sites. A new nanostructured amino-functionalized magnetic bacterial cellulose/activated carbon (BC/AC) composite bio adsorbent (AMBCAC) was prepared for the removal of methyl orange (MO) from an aqueous solution (Huang, Zhan, Wen, Xu, & Luo, 2018). At optimal conditions, 83.36 mg/g of MO dyes were adsorbed onto the adsorbent. The results from the adsorption kinetics and isotherm studies indicate MO fits well with the pseudo-second-order kinetic model. The thermodynamics studies reveal that the adsorption process was spontaneous and endothermic. The adsorption behavior was studied under different pH. At lower pH, MO exists as quinoid form, while it reforms as the azo structure at higher pH. It indicates MO can exist as a basic and acidic form at different pH in the dye solution. At pH 3, maximum adsorption was obtained since the adsorbent (AMBCAC) had the highest positive surface charge, and MB had a maximum negative charge.

16.2.3 Cellulose-graphene oxide-based composite Graphene oxide (GO) is used as an attractive adsorbent due to its unique twodimensional structure ( Jariwala, Sangwan, Lauhon, Marks, & Hersam, 2013). GO aggregates in an aqueous solution and provide difficulties in the separation of pollutants from the aqueous phase that limit the use of GO as an adsorbent (Banerjee, Mukhopadhyay, & Das, 2019). Studies have shown that composites formation with polymers helps overcome the limitation of GO and offers a large surface area (Banerjee, Barman, Mukhopadhayay, & Das, 2017). Polymers with long branched chains, stable structure, and plenty of negatively charged functional groups can provide more excellent binding features than GO itself and hence modify GO surface its structure and functional groups in order to achieve higher adsorption capacity (Qi, Yang, Xu, He, & Men, 2017). The biopolymer cellulose has been reported to improve the structural and functional characteristics of graphene oxide because of its broad availability, low cost, biodegradability, huge surface area, and abundance of negative charge carrying functional groups (such as dOH and dCOOH) (Chen, Zhou, Zhang, You, & Xu, 2016). Cellulose/graphene oxide (CGO) fiber adsorbent was prepared by wet-spinning technique for the removal of MB and the effects of solution pH, temperature, and contact time on adsorption of MB onto the CGO fibers were investigated 7. The adsorption capacity was found to increase with increasing solution pH. As the pH rises, the carboxyl and hydroxyl groups of the CGO fibers deprotonate to produce COO and

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O groups, resulting in an electrostatic attraction between the negatively charged surface of the CGO fibers and the MB cations, increasing adsorption. The adsorption capacity was enhanced from 419 to 451.08 mg/g by raising the temperature from 278 K to 313 K, suggesting that the adsorption process was endothermic. It is apparent that the beginning of the adsorption process was faster due to many active adsorption sites. With the increase of time, the number of adsorption sites becomes less, and adsorption slows down until equilibrium. The obtained maximum adsorption capacity of MB onto the CGO fibers was 480.77 mg/g. Moreover, CGO fibers can be regenerated efficiently with a dilute solution of NaOH and maintain a high adsorption capacity after three cycles. GO-CNC (graphene oxide-cellulose nanocrystal) nanocomposite was prepared using an in situ process where cellulose was extracted from jute waste (Zaman et al., 2020). It was applied as an adsorbent to remove methylene blue (MB) dye. Around 98% dye removes after 135 min. Cationic MB attaches with the negatively charged functional groups of GO-CNC via electrostatic force. The adsorption capacity of the nanocomposite was found to be 334.19 mg/g under the optimal experimental circumstances indicated by the response surface technique, whereas the maximum adsorption capacity as measured by the Langmuir isotherm was 751.88 mg/g. Further investigation indicated that the process was directed by both the Langmuir and Freundlich isotherms and followed pseudo-second-order kinetics. The nanocomposite’s cost-effective production technique and excellent adsorption capability indicate its enormous potential for large-scale application in wastewater treatment. The adsorption effectiveness of GO-CNC was stable throughout the first seven cycles and gradually decreased during the final three cycles. During the past three cycles, the percent MB elimination was 85.22%, 84.14%, and 82.76%, respectively. This decrease in percent MB removal owing to regenerated GO-CNC as adsorbent might be attributed to acid-induced alterations on the GO-CNC surface or loss of adsorbent mass during each step of retrieval and regeneration. Graphene oxide (GO)/cellulose bead (GOCB) composite was prepared using a simple sol-gel method and applied in malachite green (MG) dye solution (Zhang et al., 2015). The prepared composite show over 96% dye removal efficiency with stability after 5 times reuse through a simple filtration method. Moreover, the adsorption behavior of this novel adsorbent is compatible with the Langmuir isotherm and the pseudosecond-order kinetic model. Notably, as the pH varied from 6.0 to 8.0, the electrostatic attraction between the adsorbent and the MG increased. But, when the pH was less than 6 or greater than 8, this occurred because part of the GOCB degrades in acidic environments and dissolves in alkaline situations. For GOCB, maximum adsorption was obtained at pH 7. The adsorption capacity of GOCB become decreases above 25°C temperature since, after that temperature, adsorptive forces become weaker.

16.2.4 Cellulose-chitosan-based composite Chitosan is a nitrogenous polymer derived from chitin deacetylation (Crini & Badot, 2008). Chitosan can adsorb negatively charged molecules or materials such as anionic dyes because of its numerous amino groups that may be protonated in an acidic aqueous solution (Kyzas, Lazaridis, & Kostoglou, 2014). However, chitosan has several

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drawbacks that restrict its application. These disadvantages include only being soluble in acidic solutions, having poor chemical resistance, low mechanical strength, and low surface area (Zhao, Xu, Lan, Wang, & Luo, 2013). Researchers have used many attempts to improve chitosan material adsorption performance. Cellulose-chitosan composites have become more popular materials because of their high surface area, chemical accessibility, ease of operation, and absence of internal diffusion (Suman, Kardam, Gera, & Jain, 2015). A new form of the composite film was developed using chitosan and dialdehyde microfibrillated cellulose nanofibrils to efficiently remove anionic dye (Congo red) (Zheng et al., 2018). Microcrystalline cellulose was homogenized under high pressure to produce microfibrillated cellulose with a three-dimensional network structure. The adsorption capacity was 152.5 mg/g at equilibrium with the removal of 99.95% in only 10 min. The Langmuir model was used to predict Congo red adsorption onto DAMFC/ chitosan composite. The pseudo-second-order model was better suited to represent Congo red adsorption onto DAMFC/chitosan composites. Hydrogen bonding and electrostatic attraction were the main forces behind Congo red adsorption. The electrostatic interaction is caused by the protonated amino groups of chitosan chains and the sulfonate groups on dye. Hydrogen bonds may be formed between Congo red amino groups and chitosan and DAMFC hydroxyl groups; and Congo red sulfonate groups and chitosan and DAMFC hydroxyl groups. An eco-friendly porous adsorbent of cellulose (CE)/chitosan (CS) aerogel was prepared via sol-gel and freeze-drying method to remove Congo red (CR) (Wang et al., 2018). The adsorption performance was investigated with respect to the dosage of chitosan, initial pH, temperature, adsorbent dosage, contact time, and initial dye concentration on adsorption capacities for CR. Batch adsorption experiments revealed that aerogel with a composite ratio of 1:3 and a dose of 2.5 g/L had the highest removal effectiveness to CR. The CE/CS aerogel showed increased CR adsorption capabilities throughout a pH range of 3–11, indicating that the aerogel was stable in both acidic and alkaline environments. The pseudo-second-order kinetics and the Langmuir isotherm model were well fitted to CR adsorption on the composite aerogel. The Langmuir isotherm model indicated that this material’s highest theoretical adsorption capacity for CR was 381.7 mg/g at pH 7.0 at 303 K for 24 h. Electrostatic and chemical interactions were involved in the adsorption process. A composite membrane of chitosan/cellulose was prepared via a freeze-drying process (Karim, Mathew, Grahn, Mouzon, & Oksman, 2014). In this process, chitosan was used as a matrix. The dye removal of cationic Victoria blue 2B, Methyl violet 2B, and Rhodamine 6G dyes were observed at 98%, 90%, and 78%, respectively. The impregnated CNC having required COO , and SO3 resulting in strong electrostatic interaction with positively charged dyes and provide high adsorption capacities. CNC has a negative zeta potential in the pH range of 3–12. Variation of pH can affect the surface charge of the adsorbent. The electrostatic interaction between positively charged dyes and the surface of the adsorbent (composite membrane) grew weaker as solution pH increased, potentially resulting in a drop in adsorption rate. The highest proportion of dyes removed from model wastewater is at pH 5.01, and the percentage falls as pH increases.

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A polymeric bead of chitosan/cellulose was used to extract a cationic dye (MB) and an anionic dye (CR) (Vega-Negron et al., 2018). The findings demonstrated that both dyes adsorbed on the polymeric beads separately and simultaneously. All of the adsorption results fit the Langmuir model, which indicated the development of a monolayer. For CR and MB simultaneous adsorption, the max values were 1.6 and 0.68 μmol/g, respectively. In individual experiments, the composite beads removed 58.2 and 99.9% of MB and CR, respectively. When the two dyes were mixed, around 72% CR dye was adsorbed firstly onto the surface of the beads, which assisted to enhance MB absorption (62%). Hydrogen bond, dipole–dipole interactions and electrostatic interactions between the functional groups of each polymer, chitosan or cellulose, and the equivalent functional groups in CR and MB dyes, should have facilitated the corresponding adsorption processes Fig. 16.2. The existence of functional groups of cellulose and chitosan on the polymeric composite surface enables the removal of both types of dyes simultaneously. The chemical structure of the adsorbent and the dyes can help us understand the affinity of MB and CR to polymeric beads. Chitosan is a biopolymer with many dOH and dNH2 groups. At pH 6.5, about 61.8% of the chitosan amino groups protonated (+charge), promoting electrostatic contact with the CR sulfonic groups ( charge) (anionic dye). Moreover, at 6.5 pH, around 91% of the CR amine groups are deprotonated, eliminating any electrostatic repulsion with chitosan. Furthermore, hydrogen bonding between the amine groups of the CR and the hydroxyl groups of chitosan and cellulose can enhance affinity. At pH 6.5, MB (cationic dye) has a (+) charge, facilitating ion-dipole interactions with chitosan and cellulose hydroxyl groups. Furthermore, at this pH, approximately 80% of the amine groups of the MB are deprotonated, permitting the formation of hydrogen bonds with the hydroxyl groups of the chitosan and cellulose. Synergism was used to improve MB absorption after the CR was adsorbed onto the beads. This might be due to electrostatic interactions between the negative charge of the CR adsorbed on the surface of the beads and the positive charge of the MB. A cellulose-chitosan hydrogel bead was developed by extruding and regenerating the blends from ionic liquid 1-ethyl-3 methylimidazolium acetate ([Emim]Ac) in ethanol (Li, Wang, & Li, 2016). According to batch adsorption tests, the bead showed a maximum adsorption capacity of 40 mg/g for Congo red (CR) dye removal from

Fig. 16.2 A schematic representation of the mechanisms of binding of the dyes with CNCs via (A) hydrogen bond formation and (B) electrostatic attraction. Reprinted with permission from Karim, Z., Mathew, A. P., Grahn, M., Mouzon, J. & Oksman, K., (2014). Nanoporous membranes with cellulose nanocrystals as functional entity in chitosan: Removal of dyes from water. Carbohydrate Polymers, 112, 668–676. Elsevier.

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aqueous solutions. The equilibrium of adsorption was obtained within 115 min with an 89.6% removal rate using the starting concentration of CR was 30 mg/L, and the adsorbent dose was 2.0 g/L. The Langmuir model described the adsorption isotherm data, and the experimental findings followed a pseudo-second-order rate model, showing that intraparticle diffusion dominated the adsorption process. The CR adsorption capacity was related to initial CR concentration, beads dosage, and the CR solution’s pH values. The removal percentage of CR dropped from 83.5% to 20.8% when the pH of the CR solution was raised from 4.0 to 9.5. Because CR molecules contain two sulfonic groups, they were easily ionized in an acidic environment and converted into a soluble anion. The CR anions can then be readily adsorbed to the positively charged surface of the adsorbent in an acidic or neutral environment.

16.3

Conclusion

This chapter reviews the influence of cellulose loading with different materials (ZnO, chitosan, GO, activated carbon) in dye wastewater treatment. These materials are loaded with different forms of cellulose such as CNC, CNF, cellulose bead, bacterial cellulose, magnetic cellulose, etc. This loading caused modifications in the original structures. These modifications stated that the dye cleaning performance of cellulose-based composites enhanced than sole condition. The dye removal efficiency of cellulose-based composites has elevated due to an increase in active sites due to modification and the inclusion of additional functional groups. The existence of functional groups on the composite surface facilitates electrostatic attractions between composites and ionic dye molecules. Furthermore, it is reported that the amount of adsorbent dosage, the dye solution pH, and initial concentration have a significant impact on controlling the dye cleaning efficiency, kinetics, and capacities of the adsorbent particles. Cellulose is the most suitable carrier for ZnO, chitosan, GO, and activated carbon, and cellulose-based composites are a tremendous bio-based resource for dye wastewater cleaning that is less expensive and efficient.

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initiative and its approaches. Geoscientific Model Development, 9(1), 175–222. https://doi. org/10.5194/gmd-9-175-2016. Wahid, F., Duan, Y. X., Hu, X. H., Chu, L. Q., Jia, S. R., Cui, J. D., et al. (2019). A facile construction of bacterial cellulose/ZnO nanocomposite films and their photocatalytic and antibacterial properties. International Journal of Biological Macromolecules, 132, 692– 700. https://doi.org/10.1016/j.ijbiomac.2019.03.240. Wang, Y., Wang, H., Peng, H., Wang, Z., Wu, J., & Liu, Z. (2018). Dye adsorption from aqueous solution by cellulose/chitosan composite: Equilibrium, kinetics, and thermodynamics. Fibers and Polymers, 19(2), 340–349. https://doi.org/10.1007/s12221-018-7520-9. Ye, S., Zhang, D., Liu, H., & Zhou, J. (2011). ZnO nanocrystallites/cellulose hybrid nanofibers fabricated by electrospinning and solvothermal techniques and their photocatalytic activity. Journal of Applied Polymer Science, 121(3), 1757–1764. https://doi.org/10.1002/ app.33822. Yeh, S. W., Chen, Y. L., Hsi, C. S., Ko, H. H., & Wang, M. C. (2014). Thermal behavior and phase transformation of TiO2 nanocrystallites prepared by a coprecipitation route. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 45(1), 261–268. https://doi.org/10.1007/s11661-013-1963-9. Yu, H. Y., Chen, G. Y., Wang, Y. B., & Yao, J. M. (2015). A facile one-pot route for preparing cellulose nanocrystal/zinc oxide nanohybrids with high antibacterial and photocatalytic activity. Cellulose, 22(1), 261–273. https://doi.org/10.1007/s10570-014-0491-0. Zaman, A., Orasugh, J. T., Banerjee, P., Dutta, S., Ali, M. S., Das, D., et al. (2020). Facile onepot in-situ synthesis of novel graphene oxide-cellulose nanocomposite for enhanced azo dye adsorption at optimized conditions. Carbohydrate Polymers, 246. https://doi.org/ 10.1016/j.carbpol.2020.116661. Zhang, X., Yu, H., Yang, H., Wan, Y., Hu, H., Zhai, Z., et al. (2015). Graphene oxide caged in cellulose microbeads for removal of malachite green dye from aqueous solution. Journal of Colloid and Interface Science, 437, 277–282. https://doi.org/10.1016/j.jcis.2014.09.048. Zhao, H., Xu, J., Lan, W., Wang, T., & Luo, G. (2013). Microfluidic production of porous chitosan/silica hybrid microspheres and its Cu(II) adsorption performance. Chemical Engineering Journal, 229, 82–89. https://doi.org/10.1016/j.cej.2013.05.093. Zheng, X., Li, X., Li, J., Wang, L., Jin, W., & liu, J., Pei, Y., & Tang, K. (2018). Efficient removal of anionic dye (Congo red) by dialdehyde microfibrillated cellulose/chitosan composite film with significantly improved stability in dye solution. International Journal of Biological Macromolecules, 107, 283–289. https://doi.org/10.1016/j.ijbiomac.2017.08.169. Zhou, X., Li, X., Gao, Y., Li, L. C., Huang, L., & Ye, J. (2019). Preparation and characterization of 2D ZnO nanosheets/regenerated cellulose photocatalytic composite thin films by a twostep synthesis method. Materials Letters, 234, 26–29. https://doi.org/10.1016/j. matlet.2018.09.070. Zhu, H. Y., Fu, Y. Q., Jiang, R., Jiang, J. H., Xiao, L., Zeng, G. M., et al. (2011). Adsorption removal of Congo red onto magnetic cellulose/Fe3O4/activated carbon composite: Equilibrium, kinetic and thermodynamic studies. Chemical Engineering Journal, 173(2), 494–502. https://doi.org/10.1016/j.cej.2011.08.020. Zhu, X. L., Xu, C. Y., Tang, J., Hua, Y. X., Zhang, Q. B., Liu, H., et al. (2019). Selective recovery of zinc from zinc oxide dust using choline chloride based deep eutectic solvents. Transactions of Nonferrous Metals Society of China (English Edition), 29(10), 2222–2228. https://doi.org/10.1016/S1003-6326(19)65128-9.

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Abdellaoui Hind Mohammed 6 Polytechnic University (UM6P), Supramolecular Nanomaterial Group (SNG), Benguerir, Morocco

17.1

Introduction

Packaging, as a material, is used to protect packaged products from all kinds of chemical, biological, and physical hazards (Majeed et al., 2013; Sonia, 2016). Besides wood, paper, glass, and metals, plastic is one of the materials frequently used in packaging thanks to its softness, transparency, and lightness. Conventional plastic is made from nonrenewable raw materials from petroleum resources. Synthetic plastics like polyethylene terephthalate (PET), polyethylene (PE), polystyrene (PS), polypropylene (PP), polyvinyl chloride (PVC), and polyamide (PA) are widely used in the manufacture of packaging films due to their low cost, abundant availability, and excellent mechanical and barrier properties (Majeed et al., 2013). The use of conventional plastics in packaging creates a variety of environmental problems such as CO2 production, generation and accumulation of nondegradable waste, etc. As for the application of conventional plastics in food packaging, they still suffer from certain problems linked to the inherent permeability to vapors and gases (oxygen, organic vapors, and carbon dioxide). For example, the presence of oxygen degrades starches whether through direct oxidation or other indirect action leading to browning of foods and rancid flavors (Duhovic, Peterson, & Jayaraman, 2008; Preda, Popa, Mihai, Şerba˘nescu, & Holban, 2019; Siracusa, Rocculi, Romani, & Rosa, 2008; Sonia, 2016). To tackle this problem, bioplastics, made from renewable resources, have pierced the packaging materials market. In the current era, there is an increasing demand for bioplastics due to the advantages gained over conventional plastics (Vieira, Da Silva, Dos Santos, & Beppu, 2011). The biopolymers or bio-based plastics, especially biodegradable plastics or polymers are receiving special attention as green materials for packaging applications. Biodegradable plastics are generally derived from renewable resources such as biomass and microorganisms or by synthetically bio-derived monomers (Abdul Khalil et al., 2017; Vieira et al., 2011). Biodegradable polymers extracted from biomass like polysaccharides, lipids, and proteins are basically used for edible films. Commercially, biodegradable polymers such as poly (lactic acid) (PLA), polycaprolactone (PCL), polyhydroxyalkanoates, poly (ethylene glycol), aliphatic polyesters (poly Cellulose Fibre Reinforced Composites. https://doi.org/10.1016/B978-0-323-90125-3.00002-1 Copyright © 2023 Elsevier Ltd. All rights reserved.

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(butylene succinate and poly (butylene succinate-co-butylene) adipate)), are available in the market (Tserki, Matzinos, Zafeiropoulos, & Panayiotou, 2006). The production of completely renewable plastic packaging is based on the use of reinforcing matrices and fillers from renewable origin (Satyanarayana, Arizaga, & Wypych, 2009). However, the use of biodegradable polymers in packaging applications can be restricted because of the poor physicochemical, mechanical, and barriers properties. Some research studies of polymeric materials have developed composite materials reinforced with cellulosic fibers for promising food packaging applications due to their sensitivity to microorganisms and their biodegradability with low cost (Johansson et al., 2012). Cellulosic fibers are one of the potential materials used as packaging materials in our daily life. In 2006, the Food and Agriculture Organization of the United Nations (FAO) declared 2009 to be the International Year of Cellulosic Fibers with the aim of raising consumer awareness and strengthening demand for cellulosic fiber products, especially in the packaging industry (Robertson, 2008). Besides, cellulosic fiberreinforced packaging materials have many advantages compared to synthetic packaging materials such as recyclability and stiffness/weight ratio. In research studies, they concluded that biodegradability and bio-based characteristics are very essential for short-lived, single-use, disposable, and consumer-grade packaging (Narayan, 2006). With current advances, several companies have initiated the production of recycled packaging materials such as Toray Plastics America which has developed LumiLid solvent-free polyester-based cover films (Stewart, 2008). There is abundantly a wide range of cellulosic fibers which can be applied as reinforcement of polymeric matrices and remain less expensive compared to synthetic fibers (Abdellaoui, Bensalah, Echaabi, Bouhfid, & Qaiss, 2015; Abdellaoui, Bouhfid, & Qaiss, 2017, 2018; Abdellaoui, Raji, Bouhfid, Qaiss, & Kacem, 2019). The use of cellulosic fibers enables the production of durable, easily recyclable consumer products as well as can be applied in sound insulation and thermostable applications with high thermal stability (Abdellaoui, Bouhfid, & Qaiss, 2017). However, these cellulosic fibers have poor resistance to water, poor interfacial interaction between the highly polar cellulosic fibers, and the hydrophobic polymeric matrix leading to a loss of the final properties of the composite produced. To tackle these issues, different techniques are used in order to improve the compatibility between the cellulosic fibers and the matrix by using, for example, coupling agents and/or surface modification techniques (i.e., mechanical, chemical, and/or physical treatment). Maleic anhydride graft copolymer and alkali treatment of cellulosic fiber are the techniques most used and confirmed in the literature in order to improve the interfacial fiber-matrix adhesion (Abdellaoui et al., 2018). This chapter emphasizes the crucial role of cellulosic fibers used as reinforcement of polymeric packaging materials. It is essentially a question of: -

Identify the different polymers and biopolymers used in packaging with a potential for reinforcing cellulosic fibers while promoting biodegradable polymers. Identify the different kind of polymeric packaging applications and the requested characteristics in order to keep the freshness, safety, etc. Determine and examine the various structural, mechanical, barrier, and other physical properties recommended for packaging applications.

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-

285

Review the biodegradable polymers reinforced with cellulosic fibers which are already commercialized or under development.

17.2

Packaging

Packaging is a process allowing the preparation of an item for preservation, storage, transport and also display. The choice of packaging materials depends on the requirements of the item and the packaging category. In general, the packaging essentially protects the article from chemical and physical alterations, provide convenience in transportation and handling, and encourage the consumer to purchase the product (Azapagic & Emsley, 2003; Majeed et al., 2013). The packaging sector represents almost 40% of the total work consumption of plastics, generating an abysmally high flow of waste. Polymeric materials such as polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polyamide (PA), and polystyrene (PS) are commonly used in the industry packaging due to their availability, relatively low cost, good tensile and tear strength, heat sealability, and good barrier against carbon dioxide, oxygen, aroma compound, and anhydride (Azapagic & Emsley, 2003). Due to environmental considerations, legislation has started to encourage the use of biodegradable polymers, but their cost remains potentially high. In perspective, biodegradable polymers reinforced with cellulosic fibers are a better alternative to offer environmentally friendly and economically profitable solutions for the packaging industry (Majeed et al., 2013). The interest of application of cellulosic fibers in packaging is mainly attributed to some advantages such as stiffness and strength, reduction in weight and costs by reducing the polymer content. Moreover, they provide a biodegradable aspect to the packaging material when combined with biodegradable polymers (Siracusa et al., 2008).

17.2.1 Categories of packaging Generally, the materials used in packaging are divided into three categories (Haugaard et al., 2000): l

l

l

Primary packaging: this is the type of material that comes into direct contact with the product and remains separate from the product. Secondary packaging: it is used for the physical protection of the product. Tertiary packaging: it is used to protect the product against weather conditions and mechanical damage during transport while respecting storage and handling requirements.

Cellulosic fibers find many applications in all the three categories of packaging. As for example in food trays and containers (primary packaging), in rigid packaging for nonfood consumer products such as pallets and electronics and light and tertiary composite containers and bulk foam reinforced with natural fibers (packaging secondary and tertiary). Another type of packaging which does not make it easy to incorporate cellulosic fibers is composed of edible coatings and films.

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17.2.2 Packaging polymer properties Polymeric products such as synthetic polymers (polyolefins) and natural polymers (lignin, humus, and natural rubber) must be biodegraded in a controlled manner following the mechanism of oxo-biodegradation (Arvanitoyannis, 1999). In general, antioxidants and stabilizers are added to synthetic polymers to protect it from oxidation during processing and to provide the required shelf life. In terms of properties, natural and synthetic polymers are extremely different. For instance, natural polymers are hydrophilic, water-swellable, and biodegradable which makes them less advisable for food packaging where water resistance is required, while the synthetic polymers (e.g., polyolefin) are hydrophobic, hydrocarbon, and resistant to biodegradation and hydrolysis which is a main attribute in plastic packaging, of which antioxidants are to be added to promote oxo-biodegradation (Siracusa et al., 2008). The use of longlasting synthetic and natural polymers in short-lived packaging applications is unwarranted in terms of cost and the environment. A better understanding of the properties required in packaging materials is needed (Siracusa et al., 2008).

17.2.2.1 Barrier properties The estimation of the shelf life of the packaging of a product is carried out essentially through the determination of the barrier properties of the polymer used according to the characteristics of the product and the final application envisaged. Generally, polymers are permeable to very small molecules such as water vapor, gases, liquids, and organic vapors. Oxygen and gas vapor remain the main permeates in packaging applications due to being able to pass through the wall of the plastic either from the external or internal medium, affecting the quality of the product and its shelf life (Siracusa et al., 2008). A description is made below on the most necessary barrier properties for plastic films intended for packaging.

Oxygen transmission rate (OTR) The oxygen barrier of a food packaging container is a very essential property for the preservation of a fresh product such as ready meals, salads, fruits, etc. The oxygen barrier property is determined by calculating the oxygen permeability coefficient (OPC) indicating the amount of oxygen penetrated into the packaging material per unit area and time [kg m m
2 s
1 Pa
1]. The use of a polymeric film in packaging with a low coefficient of oxygen permeability causes a drop in the oxygen pressure inside the container while reducing oxidation and increasing the shelf life of the product (Siracusa et al., 2008). Generally, synthetic polymers are one or more orders of magnitude above the biodegradable polymer. Considering the coefficient of permeability, the oxygen transmission rate (OTR) of unit cc m
2 s
1 is given. The correlation of OPC to OTR is expressed by the following equation (Siracusa et al., 2008): OPC ¼

OTR∗l ΔP

(17.1)

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where P is the difference between the partial pressure of oxygen across the film [Pa]: (Δ P ¼ P1
P2 ), where P1 is oxygen partial pression at the temperature test on the test side and P2 is the partial pression equal to zero on the detector side, l is the thickness of the film (m).

Water vapor transmission (WVTR) The study of the water vapor barrier properties is very essential in order to maintain and prolong the shelf life of the packaged product, the chemical or physical deterioration of which is linked to its equilibrium moisture content. The water vapor permeability coefficient (WVPC) is used to measure the vapor barrier by indicating the amount of penetrating water vapor per unit area and time [kg m m
2 s
1 Pa
1] in the packaging plastic. The vapor transmission rate, expressed in cc m
2 s
1 (or g m
2 day
1), is given with the coefficient of permeability. For the oxygen parameter, the coefficient of permeability (WVPC) is given as a function of the WVPT as expressed in Eq. (17.1).

17.2.2.2 Mechanical properties It is important to evaluate the mechanical performance of packaging used under different temperatures through tensile tests. Among these tests, we mention (Siracusa et al., 2008): Tensile tests (ASTM D882-02, Standard Test Method for Tensile Properties of Thin Plastic Sheeting) make it possible to determine the tensile strength (MPa), the Young’s modulus (GPA), and the percentage of elongation at yield (%) and at failure (%). Impact test (ASTM D1709-03, Standard Test Methods for Impact Resistance of Plastic Film by the Free-Falling Dart Method) determines the energy that causes the plastic to fail under the specific impact conditions. Compression test (ASTM D642, Standard Test method to determine the compressive strength of shipping containers, components and unit loads) is performed on thermoformed samples. Compressive strength is a function of design, shape, size, and material. Chemical Resistance Properties: It is a good idea to evaluate the performance of plastic stored with a common food packaging solution over time for containers with either weak or strong acid characteristics. The final mechanical properties of the polymer can be affected due to the interaction and the absorption between the chemical compounds and the polymer used (Auras, Harte, & Selke, 2004; Siracusa et al., 2008). The chemical resistance test measures tensile stress, Young’s modulus, and elongation at break for samples immersed in strong and weak acid solutions as a function of time and varying temperatures 18°C, 23°C, and 29°C. Acetic acid is used to prepare weak acid and hydrochloric acid for strong acid (Auras et al., 2004). The thickness of the packaging film: it is measured by a thickness gauge (ASTM D4166-99 (2004) e1, Standard Test Method for Measurement of Thickness of Nonmagnetic Materials by Means of a Digital Magnetic Intensity Instrument) or by a

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micrometer (ASTM D 374-99, Standard Test Methods for Thickness of Solid Electrical Insulator) (Auras et al., 2004). Polymer Degradation Rate Index: It is determined from changes in molecular weight of samples dissolved in an appropriate solvent using gel permeation chromatography (Siracusa et al., 2008).

17.2.2.3 Thermal properties Differential Scanning Calorimetry (DSC): it is used to determine the melting temperature (Tm), the glass transition temperature (Tg) and the crystallinity of the polymer (ASTM D3418, Standard Test Method for Transition Temperatures and Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning Calorimetry). The crystallinity is determined (ASTM D3417-97) according to the following equation (Siracusa et al., 2008): Xc ð%Þ ¼ 100∗ΔHc:ΔHm: ¼ ΔHcm

(17.2)

where Δ Hm is the endothermic enthalpy of fusion, △ Hc is the exothermic enthalpy of cold crystallization, and Δ Hcm is the endothermic heat of the crystalline polymer (Auras et al., 2004; Siracusa et al., 2008). Thermogravimetric Analysis (TGA): used to determine the decomposition temperature (ASTM E1131-03, Standard Test Method for Composition Analysis by Thermogravimetry). Measuring the pH of the surrounding sample is a factor in degradation of the hydrolytic polymer due to changes in hydrolysis rates due to change in pH. Chemical resistance is measured on samples immersed in strong acids (hydrochloric acid, pH 2) and weak acids (acetic acid, pH 6) for a period of 0, 1, 3, 5, and 7 days (Siracusa et al., 2008).

17.2.3 Packaging materials During the last century, chemicals derived from petroleum are used largely in packaging applications due to their physical and chemical properties such as resistance to water and waterborne microorganisms, lightness, and strength. At present, the environmental trend tends toward the replacement of products from nonrenewable sources by products derived mainly from natural and biodegradable origin (Majeed et al., 2013). Actually, plastics of petroleum origin play an essential role in food packaging with an annual production of almost 250 million tons of which 40% is destined for packaging (Majeed et al., 2013). The conventional plastic used until now presents a number of health and environmental problems unlike bioplastic plastics. The bioplastics market remains weak with a total market share of 5%–7%. Bioplastics have a bright future due to their renewable source like potato, vegetable oil, wheat, etc. with natural degradation in short time (Majeed et al., 2013).

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17.2.3.1 Bio-based packaging materials For more than two decades, the use of bioplastics has increased rapidly thanks to its advantages which outweigh conventional petroleum-based plastics. Nowadays, conventional plastics are starting to be replaced by bioplastics like polyhydroxylalkanoate, polylactic acid, polyethylene, etc. (Sonia, 2016). The three main categories of bioplastics are (Sonia, 2016): Bio-based: Bio-based products come from a renewable resource such as sugar cane, corn starch, hemp, etc. Bio-based, of agricultural origin, have less CO2 emissions than those of conventional plastic. Among the most well-known bio-based plastics, there are polyethylene terephthalate (PET), polyethylene (PE), and polyamide (PA). In terms of physical and chemical properties, bio-based polyethylene is similar to conventional polyethylene with identical applications. Bio-based PE is used for applications requiring a longer product life. Bio-based polyamide (PA), derived from vegetable oil derivatives, is produced from castor seeds and is not biodegradable in nature. PA is characterized by thermal and heat resistance, chemical resistance with superior dimensional stability, and low environmental impact. The PA remains a little expensive and intended for the automotive industry, the production of electric cables and packaging. Biodegradable: This type of plastic, which degrades automatically in nature thanks to biological microorganisms, is used for single-use packaging because it degrades depending on environmental conditions in a few days to a few months. Among these plastics are poly-butyrate adipate-terephthalate (PBAT), poly caprolactone (PCL), etc. Poly caprolactone is a biodegradable plastic derived from crude oil and is characterized by its good resistance to water, solvents, and oil. It is mainly applied for applications of short life. Table 17.1 illustrates some of biopolymers, their composition, and their properties, particularly the ones used in food packaging (Qasim et al., 2021). Bio-based and biodegradable: They are plastics that are both bio-based and biodegradable like polylactic acid (PLA), polyhydroxylalkanoate (PHA), etc. PLA is a biodegradable plastic derived from agricultural resources such as potatoes, sugar cane, and tapioca roots. It is fully degradable under compost conditions and is not water soluble in nature with a very low carbon footprint. Typically, 1 kg of conventional plastic produces 6 kg of CO2, and 1 kg of PLA only produces 1.8 kg of CO2. It is generally applied for long-life use (Sonia, 2016). Bioplastics are growing and expanding rapidly in the packaging industry. Among their advantages, there are: -

Abundant raw material: they come from a renewed agricultural source compared to conventional plastics from petroleum. Biodegradable: No need for recycling, they naturally degrade in the environment and therefore this reduces the problem of filling the earth with waste. Reduction of dependence on foreign oil: an agricultural raw material available, abundant, and less expensive. Nontoxic: bioplastics, derived from natural resources, do not contain toxins or harmful chemicals that release harmful gases during the degradation phase.

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Table 17.1 Composition and properties of some biodegradable polymers applied in food packaging applications (Qasim, Osman, & Al-Muhtaseb, 2021). Polysaccharide

Composition

Properties

Alginate Chitin

Mannuronic glucuronic acid N-Acetylglucosamine

Cellulose

Glucose

Chitosan

D-Glucosamine

Carrageenan Gellan gum

N-acetyl-D-glucosamine Galactose Glucose, Rhamnose, Glucuronic acid

Biodegradable, brittle, cross-link with calcium, high water permeability Nontoxic, transparent, biocompatible, biodegradable, antibacterial, and antifungal Transparent, biodegradable, sensitive to water, good mechanical properties Biodegradable, brittle, antifungal, and antibacterial, barrier to gases, nontoxic Ductile, fragile, biodegradable Lipid barrier, edible, biodegradable, excellent gas barrier, good tensile strength Biodegradable, transparent, high gas barrier, poor water resistance

FucoPol

Galactomannans

-

-

Fucise, galactose, glucose, acetate, succinate, pyruvate Galactose, Mannose

Pullulan

Maltotriose (three glucose)

Xanthan gum

Glucose, glucuronic acid, mannose, acetate, pyruvate

Biodegradable, edible, semi permeable barrier to gas Transparent, edible, biodegradable, heat sealable, barrier to oxygen, high water solubility, oil resistant, grease resistant Biodegradable, edible

Environmentally friendly: bioplastics are ecological with less carbon emissions during production and incineration. The use of bioplastics in packaging still presents challenges such as (Sonia, 2016): High cost: the cost of bioplastics is almost double that of conventional plastic due to the still small market. Therefore, there is always a tendency to use conventional plastics due to their low cost. Recyclability: all types of bioplastics are not recyclable because they cannot be mixed. If for example an amount of PLA is mixed with PET bioplastic in the recycling process, poor quality material will result.

17.2.3.2 Bioplastic packaging applications Bioplastic is used in many industrial applications, especially in packaging in different sectors such as food, bulk, cosmetic, automotive, textile, etc. (Sonia, 2016; Vieira et al., 2011):

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Food industry: The food industry is the main user of bioplastics for packaging food products in single-use sachets. After use, the bioplastic sachets are discarded and allow themselves to degrade naturally thanks to biological organisms in a few days to a few months unlike conventional plastics which do not degrade for up to 100 years with an accumulation of waste. Bioplastics are applied in the packaging of baked foods, candies, cookies, cold drinks, bottles, and vegetables and fruits due to their excellent oxygen barrier, high transparency, and good resistance to air perforation. Cosmetic industry: Due to its high transparency, bioplastic is widely applied in the cosmetic industry. Polyhydroxylalkanoate (PHA) is one of the examples of bioplastics used in cosmetics. Among the applications in the cosmetic industry are hand washing bottles, shampoo bottles, powder boxes, nail paint bottles, jewelry boxes, cream tubes, blanket boxes, lipstick, toothpaste tubes, perfume bottles, etc. Pharmaceutical industry: Bioplastic is found in the pharmaceutical industry through applications such as artificial bodies, various medical devices which dissolve in the human body without producing any harmful effect. Among the applications, there are bandages, stitches, pill bottles, serene tubes, tubes, gloves, artificial body parts, medical instruments, etc. Biodegradable bioplastics are the most widely used type for once-usable and reusable instruments. Automobile industry: Bio-based bioplastic is applied in different automotive parts due to their weight which is 5%–7% less than that of conventional plastic. Bulk industry: Bulk packaging is when a number of products are packed together. The use of bioplastic in bulk packaging concerns metal packaging such as steel drums and large boxes, rigid packaging such as plastic drums, large boxes; flexible packaging such as woven bags, shrink wrap, and stretch wrap films; and finally, wooden packaging like pallets and crates.

17.2.4 Classification of bio-based food packaging materials Bio-based plastics used in food packaging are classified according to their origin, chemical composition, method of preparation, applications, and economic importance. The most used polymers in food packaging are summarized in Table 17.2. Polymers such as polycaprolactone (PCL), polyester-amides, and polyglycolic acid are synthesized from petroleum raw materials and therefore are excluded from this classification. Currently, there is not really an industrial process allowing to produce plastics only from renewable resources (Auras et al., 2004). Bioplastics or natural polymers are inherently biodegradable due to the presence of a depolymerase enzyme capable of catalyzing the degradation of each polymerase enzyme of the polymer (Auras et al., 2004). Traditionally, bio-based packaging materials are classified according to their historical development in three generations, and the third generation of which is subdivided into three categories according to their origin and method of production (Majeed et al., 2013). First generation: This first generation of bio-based plastic is applied in shopping bags made from synthetic polymers such as low-density polyethylene (LDPE) loaded

Table 17.2 Most used conventional polymers and their properties and applications in food packaging (Arvanitoyannis, 1999; Marsh & Bugusu, 2007). Polymer Polystyrene (PS)

Polypropylene (PP)

Low-density polyethylene (LDPE) Polyvinyl chloride (PVC)

High-density polyethylene (HDPE) Polyethylene terephthalate (PET)

Recycling symbol

Properties

Applications

Hard and brittle material, lightweight, rigid with impact protection, and thermal insulation properties Denser, harder, resistant to heat and chemicals, transparent Flexible, tough, easy to seal, resistant to moisture

Egg cartons/trays, containers, lids, disposable plastic silverware, plates, cups, food trays, and bottles

Medium strong, stiff and transparent material, stable electrical properties resistant to grease, oil, and chemicals Strong, resistant to moisture and chemicals, stiff, and easy to process Low permeability to vapors and gases, resistant to oils, solvents, mineral, acids, and heat

Yogurt containers, microwavable packaging, margarine tubes Films applications: bread, frozen food bags, squeezable food bottles, lids Packaging films, bottles, and blister packs

Bottle for juice, milk and water, tube, cereal box liners, margarine tubes Bottles for carbonated drinks, trays, containers, blister packs

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with 15% starch and other pro-oxidant and auto-oxidant additives. These materials remain nonbiodegradable despite their disintegration or biofragmentation character. Second generation: This generation consists of a mixture of LDPE and gelatinized starch (40%–75%) with the addition of a hydrophilic copolymer such as ethylene acrylic acid, vinyl acetate, and polyvinyl alcohol (PVOH) acting as compatibility reagents. Generally, starch degradation can take between 40 days and the film can reach at least 2–3 years. Third generation: This generation consists entirely of bio-based plastics classified into three categories according to their origin and their mode of production: -

Category 1: Polymers extracted directly from biomass as agricultural and marine products including cellulose. Category 2: Polymers chemically synthesized from biomass monomers. Category 3: Polymers produced by natural organisms or genetically modified by a direct process.

Several types of packaging are used in drinks with different components and colors. Among the most widely used packaging for drinks, there is the polyethylene terephthalate bottle which provides protection against flavors, CO2, and the external environment (Risch, 2009). The carbonation of packaging is preserved by using additional layers or coatings (Risch, 2009). The packaging material of edible oils like olive oil has a great effect on the quality of olive oil which can be influenced by temperature and light and which plastic bottles are less suitable than that glass in terms of conservation of properties (Coutelieris & Kanavouras, 2006). Olive oil stored in plastic PE bottles can lose its original taste and properties when exposed to light. Also, the storage of olive oil in glass bottles must be carried out in colored glass bottles so as not to impact the properties of the oil (Coutelieris & Kanavouras, 2006). Good beverage packaging must meet certain criteria for microbial interference, changes in flavor and flavor or loss of carbon/carbon dioxide in soft drinks and oxidation of vitamins. Certain methods are used to prevent microbial growth such as the use of aseptic packaging, chemical treatment or heat treatment of the beverage before or after packaging (Petersen et al., 1999). As for oxidation, it can be avoided by using packaging with low permeability to oxygen (Petersen et al., 1999). The design of the bottle is also influenced by the perception and preference of the consumer who may demand a certain design, ecological aspect, taste, or price of the product (Carl, Birgitta, & Sandra, 2015). In a market study, consumers even prefer fiber-based juice packaging due to ease of folding and low weight (Carl et al., 2015). For milk packaging, consumers choose glass because of its better conservation quality of the contents, its transparency, but it remains heavy and fragile (Carl et al., 2015). Choosing the right packaging material requires certain requirements to keep the product fresh with easy storage means (Marina, Arantzazu, Ana, & Marı´a, 2015). To tackle to that, the packaging can be formed from a multilayer system with more than one type of material by exploiting the functions and qualities of each of them (Marina et al., 2015). Good packaging should provide a barrier to moisture and

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oxygen. For example, if oxygen is present in fruit juice, it can promote microbial growth, oxidative reactions, and generate changes in color and flavor (Marina et al., 2015). Active packaging capable of releasing and absorbing substances from the packaging or the environment is recommended to extend shelf life and maintain product properties (Marina et al., 2015). Multilayer packaging, produced by Tetrapack, consists of two layers of polyethylene from the inside to the outside, followed by a very thin layer of aluminum, one of cardboard, and another of PE on the outside (Duhovic et al., 2008). Cardboard provides strength and shape retention, aluminum protects against light and oxygen, and the outer layer keeps the outer surface dry (Duhovic et al., 2008). The aluminum layer can be replaced by a layer of PET silicon oxide in order to pass the packaging in microwaves. Cellulose films, produced by Innovia, have long shelf-life properties and good antigas properties (Duhovic et al., 2008). UBPack, a biodegradable packaging material, is suitable for both cosmetics and food due to its hydrophilic properties and temperature resistance (Nurul Fazita et al., 2016). Packaging products from Biosphere industries, such as PPM100 and PPM200, are rigid starch-based foams that can be cooked in the microwave, oven, and freezer as well as can be flavored and scented (Nurul Fazita et al., 2016). The PPM200 is used for cold drinks or food (soup, noodles, pasta, etc.) and drinks such as coffee. These two types PPM100 and PPM200 have the capacity to biodegrade to 98% in almost 28 days and to 100% in less than 40 days (Duhovic et al., 2008).

17.3

Cellulosic fiber

17.3.1 Cellulosic fiber composition Cellulosic fibers are bio-based materials, renewed, and abundant in nature (Abdellaoui et al., 2018; Preda et al., 2019). Cellulosic fibers are generally classified according to their origin as leaf, fruit, seed hairs, and bast fibers as illustrated in Fig. 17.1 (Abdellaoui et al., 2018). Cellulosic fibers can be extracted from various types of plants such as wood, bagasse, flax, cotton, hemp, jute, doum fruit, ramie, curaua, bamboo, kenaf, sisal, oil palm, jowar, wheat straw, etc. (Abdellaoui et al., 2018; Cao, Shibata, & Fukumoto, 2006; Premalal, Ismail, & Baharin, 2002). Bamboo fiber is one of the most widespread cellulosic fibers and is widely cultivated in Central America and Asia (Nurul Fazita et al., 2016; Preda et al., 2019). Cellulose fibers are mainly composed of cellulose, hemicellulose, and lignin which can exist in different quantities depending on the nature of the plant and the climatic conditions (Abdellaoui, Bouhfid, & Qaiss, 2016). Other constituents such as pectins, waxes, inorganic salts, and nitrogen also exist but in very low amounts (Abdellaoui et al., 2016). Cellulose, generally exists in the second wall of the fiber, is the major component and the one responsible for the mechanical characteristics of the fiber (Preda et al., 2019). Lignin, its main role is to transport liquids in the plant (Preda et al., 2019). The structure of cellulose is composed of long linear homopolysaccharide chains formed of β-D-glucopyranose binding units per

Cellulose fiber-reinforced polymer composites as packaging materials

Bast

Cellulosic fibres

295

Jute, flax, hemp, remie, kenaf, roselle, mesta

Leaf

Sisal, bananaa, abaca, PALF, henequen, agave, raphia

Seed

Kapok, cotton, loofah, milk

Fruit

Coir, oil

Wood

Soft, hard

Stalk

Rice, wheat, barley, maizee, oat, rye

Grass/reeds

Bamboo, bagasse,corn, sabaï, rape, esparto, canary

Fig. 17.1 Different cellulosic fiber resources.

(1–4)-glycosidic (Abdellaoui et al., 2018). Cellulose is characterized by high crystallinity and insolubility (Abdellaoui, 2019; Abdellaoui et al., 2018; Abdellaoui, Bensalah, et al., 2015; Abdellaoui, Raji, Essabir, Bouhfid, & El kacem Qaiss, A., 2019). The crystallinity of cellulose varies from 20% to 90% depending on the origin of the plant, this percentage of which is closely proportional to the resistance and rigidity of the fiber (Abdellaoui, 2019). Structurally, cellulose can be described by two types of nanostructures: nanofibrils and nanocrystals (Abdellaoui, Raji, Essabir, et al., 2019). The nanocrystals, also called microcrystalline cellulose, have 100–1000 nm in length and 4–25 nm in diameter (Abdellaoui, Raji, Essabir, et al., 2019). They are obtained by a bleaching and acid hydrolysis process (Abdellaoui, Raji, Essabir, et al., 2019). In addition to cellulose obtained from plants and wood, there is also a cellulose of bacterial origin obtained by acid acetic bacteria in synthetic and nonsynthetic media (Preda et al., 2019). Acetobacter xylinum is one of the aerobic cellulose-producing bacteria (Abdellaoui, 2019). Unlike cellulose obtained from wood and plants, bacterial cellulose contains neither lignin nor hemicellulose, which spares bleaching processes (Abdellaoui et al., 2018) so that it can be incorporated into polymeric materials (Abdellaoui et al., 2018). Mainly, cellulose from bacteria is composed of fibrils based on β-1 !4 glucan chains linked by intra- and interhydrogen bonds (Preda et al., 2019). Over time, cellulosic fibers are used in various applications. Traditionally, they are used in basic products such as codes, textiles, decorative objects, food trays, and packaging (Duhovic et al., 2008). With the development of new materials, they also find an application in the reinforcement of thermoplastic and thermosetting polymers as a replacement for glass fibers (Duhovic et al., 2008). The use of cellulosic fibers as

296

Cellulose Fibre Reinforced Composites

reinforcements for composite materials is of great advantage in terms of meeting certain requirements such as low density, environmental friendliness, low cost, and improved specific properties (Abdellaoui, 2019). The incorporation of cellulosic fibers in composite materials offers an environmentally friendly character due to the biodegradability of cellulosic fibers. However, the compatibility between the cellulosic fibers and the hydrophobic polymeric matrix risks to not being perfect because of the hydrophilicity of the fibers which necessarily require prior treatment.

17.3.2 Cellulosic fiber properties The mechanical properties of cellulosic fibers depend primarily on the percentage of cellulose in the fibers. As a result, the properties of composite materials reinforced with cellulosic fibers are endowed with properties that vary widely depending on the chemical composition of these fibers (Abdellaoui et al., 2018). The different mechanical and physical properties are presented in Table 17.1 (Preda et al., 2019). Lignin, composed of derivatives of phenylpropane, is an amorphous polymer allowing to regulate the transport of the liquid in the plant (Preda et al., 2019). Each cellulosic fiber exhibits different properties depending on the size, shape, thickness of cell walls, orientations, etc. (Preda et al., 2019) and which remain important for the choice of the specific fiber for certain applications. The rigid cellulose microfibrils are firmly fixed and ordered in a matrix of hemicellulose and lignin. Each fibril, also called crystallites, is made up of almost 100 glucan chains with long, thin structures almost 5 nm wide. The variability in chemical composition of cellulosic fibers is generally attributed to growing conditions such as soil characteristics, botanical origin, meteorological conditions, etc., contributing differently to the properties of the reinforced composites of these fibers (Preda et al., 2019). From Table 17.3, it appears that the Young’s modulus of cellulosic fiber is better than that of glass fiber as well as the elongation at break of sisal fibers, coconut fibers, pineapple leaf, and pissava is much better than that of glass fibers (Preda et al., 2019). In addition, natural fibers such as flax, hemp, kenaf, sisal, and jute provide better stiffness and resistance to polymeric composite materials.

17.3.3 Cellulosic fiber production The cellulosic fibers, which are hydrophilic in nature, undergo pretreatment before incorporating them into the polymeric composites (Abdellaoui et al., 2018). Cellulose is obtained from wood pulp or cotton linters while having the ability to dissolve in sodium hydroxide and carbon disulfide to form cellulose xanthate which will remelt in acidic solution to make cellophane films (Preda et al., 2019). Physical treatment such as explosion of ionized gas, steam or laser is one of the methods applied for the pretreatment of cellulosic fibers (Abdellaoui et al., 2018). The gas explosion treatment is based on a plasma treatment and the steam treatment is based on the application of high pressure and high temperature followed by a mechanical disturbance

Table 17.3 Physical, mechanical properties, and chemical composition of cellulosic fibers as compared to E-glass and wood fibers (Abdellaoui et al., 2016, 2018; Preda et al., 2019). Tensile strength (MPa)

Tensile modulus (GPa)

Elongation At break (%)

Cellulose (wt%)

Hemicellulose (wt%)

Lignin (wt%)

70–76

1.8–4.8

–

–

–

– – 10–34

2000– 3500 400–980 35 222–290

6.2–20 22 17–27.1

1–10 5.8 1.1

56–63 45.4 32–55.2

20–25 38.5 16.8

25–40 12–30

140–800 500

11–32 12

2.5–3.7 1.5–9

26–65 63–67.6

30 10–19

7–13 14.9 19– 25.3 5–31 5

100–450

131–175

4–13

–

36–43

41–45

20–150

10–460

95–230

2.8–6

15–51.4

32–43.8

0.15– 0.25 0.15–20

– 10–60 35

– 10–45 7–10

– 287–800 87–1150

– 5.5–12.6 11.8–96

– 3–10 1.3–4.9

26.1 82.7–90 70.7–73.6

45.9 5.7 9.9

1.4–1.5

5–900

12–600

27.6–103

1.3–3.3

62–72

Hemp Henequen

1.4–1.5 1.2

5–55 –

25–500 –

343– 2000 270–900 430–570

1–3.5 3.7–5.9

68–74.4 60–77.6

3.7–10 8–13.1

Isora

1.2–1.3

–

–

500–600

23.5–90 10.1– 16.3 –

18.6– 20.6 15–22.4 4–28

11.3