Nanocellulose Polymer Nanocomposites

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Nanocellulose Polymer Nanocomposites

Edited by

Vijay Kumar Th akur

Fundamentals and Applications

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10 9 8 7 6 5 4 3 2 1

To my parents and teachers who helped me become what I am today

Vijay Kumar Th akur

vii

Contents

Preface xvii

Part 1: SYNTHESIS AND CHARACTERIZATION OF NANOCELLULOSE-BASED POLYMER NANOCOMPOSITES

1 Nanocellulose-Based Polymer Nanocomposites: An Introduction 3

Manju Kumari Th akur, Vijay Kumar Th akur and Raghavan Prasanth1.1 Introduction 31.2 Nanocellulose: Source, Structure, Synthesis

and Applications 51.3 Conclusions 12References 13

2 Bacterial Cellulose-Based Nanocomposites: Roadmap for Innovative Materials 17

Ana R. P. Figueiredo, Carla Vilela, Carlos Pascoal Neto, Armando J. D. Silvestre

and Carmen S. R. Freire2.1 Introduction 172.2 Bacterial Cellulose Production, Properties and Applications 18

2.2.1 Bacterial Cellulose Production 182.2.2 Bacterial Cellulose Properties and Applications 25

2.3 Bacterial Cellulose-Based Polymer Nanocomposites 282.3.1 BC/Natural Polymers Nanocomposites 282.3.2 BC/Water-Soluble Synthetic Polymer Nanocomposites 352.3.3 BC/ Th ermoplastic (and Th ermosetting) Nanocomposites 362.3.4 BC-Based Electroconductive Polymer Nanocomposites 41

2.4 Bacterial Cellulose-Based Hybrid Nanocomposite Materials 412.4.1 Bacterial Cellulose Hybrids with Silver Nanoparticles (BC/Ag NPs) 422.4.2 Bacterial Cellulose Hybrids with Miscellaneous

Metallic Nanoparticles 442.4.3 Bacterial Cellulose Hybrids with Silica Nanoparticles (BC/SiO

2 NPs) 45

2.4.4 Bacterial Cellulose Hybrids with Titanium Oxide Nanoparticles (BC/TiO

2 NPs) 47

2.4.5 Bacterial Cellulose Hybrids with Iron Oxides (BC/FexO

y NPs) 48

2.4.6 Bacterial Cellulose Hybrids with Hydroxyapatite (BC/HAp NPs) 50

viii Contents

2.4.7 Bacterial Cellulose Hybrids with Carbon Allotropes 512.4.8 Miscellaneous Bacterial Cellulose Hybrids 532.4.9 Final Remarks and Future Perspectives 54

2.5 Acknowledgements 55References 55

3 Polyurethanes Reinforced with Cellulose 65

María L. Auad, Mirna A. Mosiewicki and Norma E. Marcovich3.1 Introduction 653.2. Conventional Polyurethanes Reinforced with Nanocellulose Fibers 673.3. Waterborne Polyurethanes Reinforced with Nanocellulose Fibers 763.4. Biobased Polyurethanes Reinforced with Nanocellulose Fibers 78

3.4.1 Biobased Composites Obtained by Using Organic Solvents 783.4.2 Biobased Composites Obtained by Using Water as a Solvent 83

3.5 Conclusions and Final Remarks 84References 85

4 Bacterial Cellulose and Its Use in Renewable Composites 89

Dianne R. Ruka, George P. Simon and Katherine M. Dean4.1 Introduction 894.2 Cellulose Properties and Production 91

4.2.1 Introduction to Cellulose 914.2.2 Bacterial Cellulose 92

4.3 Tailor-Designing Bacterial Cellulose 1054.3.1 Modifying the Properties of Bacterial Cellulose 1054.3.2 In-Situ Modifi cations 1064.3.3 Post Modifi cations 108

4.4 Bacterial Cellulose Composites 1144.4.1 Introduction 1144.4.2 Renewable Matrix Polymers 1154.4.3 Bacterial Cellulose Composites 115

4.5 Biodegradability 1214.6 Conclusions 123References 123

5 Nanocellulose-Reinforced Polymer Matrix Composites Fabricated by

In-Situ Polymerization Technique 131

Dipa Ray and Sunanda Sain5.1 Introduction 1315.2 Cellulose as Filler in Polymer Matrix Composites 132

5.2.1 Source 1325.2.2 Structure 1335.2.3 Properties 1335.2.4 Cellulose Nanofi llers 1335.2.5 Extraction of Cellulose Nanofi llers 134

Contents ix

5.2.6 Advantages and Disadvantages of Cellulose Nanofi llers 1365.2.7 Surface Modifi cation of Cellulose Nanofi llers 137

5.3 Cellulose Nanocomposites 1385.4 In-Situ Polymerized Cellulose Nanocomposites 1385.5 Novel Materials with Wide Application Potential 140

5.5.1 Bone Defect Repair and Bone Tissue Engineering 1405.5.2 Electrically Active Paper 1425.5.3 Nanostructured Porous Materials for Drug Delivery or as

Bioactive Compounds 1465.5.4 Surface Coating Applications 1485.5.5 Biobased Green Nanocomposites 152

5.6 Eff ect of In-Situ Polymerization on Biodegradation Behavior of Cellulose Nanocomposites 154

5.7 Future of Cellulose Nanocomposites 157References 159

6 Multifunctional Ternary Polymeric Nanocomposites Based on  Cellulosic

Nanoreinforcements 163

D. Puglia, E. Fortunati, C. Santulli and J. M. Kenny6.1 Introduction 1636.2 Cellulosic Reinforcements (CR) 166

6.2.1 Microfi brillated Cellulose (MFC) 1676.2.2 Nanocrystalline Cellulose (NCC) 1686.2.3 Bacterial Cellulose (BC) 170

6.3 Interaction of CNR with Diff erent Nanoreinforcements 1716.3.1 CNR and Metallic Nanoparticles 1726.3.2 CNR and Ceramic Nanoparticles 1756.3.3 CNR and Carbon-Based Nanoparticles 1766.3.4 CNR and Biological Nanoreinforcements 177

6.4 Ternary Polymeric Systems Based on CNR 1796.4.1 Th ermoplastic Matrices and CNR-Based Systems 1806.4.2 Th ermosetting Matrices and CNR-Based Systems 186

6.5 Conclusions 190Acknowledgments 191References 191

7 Eff ect of Fiber Length on Th ermal and Mechanical Properties of

Polypropylene Nanobiocomposites Reinforced with Kenaf Fiber

and Nanoclay 199

Na Sim and Seong Ok Han7.1 Introduction 1997.2 Experimental 200

7.2.1 Materials 2007.2.2 Fabrication of Nanobiocomposites 2017.2.3 Analysis 201

x Contents

7.3 Results and Discussion 2027.3.1 Th ermal Properties (TGA) 2027.3.2 Th ermomechanical Properties (TMA) 2037.3.3 Dynamic Mechanical Analysis (DMA) 2057.3.4 Tensile Properties 2067.3.5 Flexural Properties 2077.3.6 Impact Properties 2087.3.7 SEM and EDX Observation 209

7.4 Conclusions 211References 211

8 Cellulose-Based Liquid Crystalline Composite Systems 215

J. P. Borges, J. P. Canejo, S. N. Fernandes and M. H. Godinho8.1 Introduction 2158.2 Liquid Crystalline Phases of Cellulose and Its Derivatives 216

8.2.1 All-Cellulosic-Based Biomimetic Composite Systems 2198.2.2 Liquid Crystalline Electrospun Fibers 227

8.3 Conclusion 232Acknowledgements 232References 232

9 Recent Advances in Nanocomposites Based on Biodegradable Polymers

and Nanocellulose 237

J. I. Morán, L. N. Ludueña and V. A. Alvarez9.1 Introduction 237

9.1.1 Bioplastics Classifi cation and Current Status 2389.1.2 Nanocellulose for Bionanocomposites 239

9.2 Cellulose Bionanocomposites Incorporation of Cellulose Nanofi bers into Biodegradable Polymers: General Eff ect on the Properties 2439.2.1 Bioplastics-Based Nanocellulosic Composites 2449.2.2 Treatment of CNW: Improvement of Cellulose Nanofi bers/

Biodegradable Matrix Compatibility 2489.2.3 Processing of Cellulose-Based Bionanocomposites 248

9.3 Future Perspectives and Concluding Remarks 249References 250

Part 2: PROCESSING AND APPLICATIONS NANOCELLULOSE-BASED POLYMER NANOCOMPOSITES

10 Cellulose Nano/Microfi bers-Reinforced Polymer Composites: Processing

Aspects 257

K. Priya Dasan and A. Sonia10.1 Introduction 25710.2 Th e Role of Isolation Methods on Composite Properties 260

Contents xi

10.3 Pretreatment of Fibers and Its Role in Composite Performance 26210.4 Diff erent Processing Methodologies in Cellulose Nanocomposites

and Th eir Eff ect on Final Properties 26410.5 Conclusion 268

References 268

11 Nanocellulose-Based Polymer Nanocomposite: Isolation, Characterization

and Applications 273

H. P. S. Abdul Khalil, Y. Davoudpour, N. A. Sri Aprilia, Asniza Mustapha, Md.

Nazrul Islam and Rudi Dungani11.1 Introduction 27411.2 Cellulose and Nanocellulose 27411.3 Isolation of Nanocellulose 276

11.3.2 Ultrasonication 27811.3.3 Electrospinning 27911.3.4 Acid Hydrolysis 28111.3.5 Steam Explosion 283

11.4 Characterization of Nanocellulose 28311.4.1 Physical Properties 28311.4.3 Th ermal Properties 28611.4.4 Morphological Properties 288

11.5 Drying of Nanocellulose 28911.6 Modifi cations of Nanocellulose 290

11.6.1 Acetylation 29111.6.2 Silylation 29111.6.3 Application of Coupling Agents 29211.6.4 Graft ing 293

11.7 Nanocellulose-Based Polymer Nanocomposites 29511.7.1 Th ermoplastic Polymer-Nanocellulose Nanocomposites 29611.7.2 Th ermoset Polymer-Nanocellulose Nanocomposites 29811.7.3 Application of Nanocomposites Based on Nanocellulose 301

11.8 Conclusion 302Acknowledgement 303References 303

12 Electrospinning of Cellulose: Process and Applications 311

Raghavan Prasanth, Shubha Nageswaran, Vijay Kumar Th akur and

Jou-Hyeon Ahn12.1 Cellulosic Fibers 31112.2 Crystalline Structure of Electrospun Cellulose 31212.3 Applications of Cellulose 31312.4 Electrospinning 313

12.4.1 Processing – Fundamental Aspects 31612.5 Electrospinning of Cellulose 317

xii Contents

12.6 Solvents for Electrospinning of Cellulose 31812.6.1 Room Temperature Ionic Liquids 32012.6.2 N-methyl morpholine-N-oxide 32512.6.3 Lithium Chloride/N,N-Dimethylacetamide 329

12.7 Cellulose Composite Fibers 33312.8 Conclusions 336Abbreviations 336Symbols 336References 337

13 Eff ect of Kenaf Cellulose Whiskers on Cellulose Acetate Butyrate

Nanocomposites Properties 341

Lukmanul Hakim Zaini, M. T. Paridah, M. Jawaid, Alothman

Y. Othman and A. H. Juliana13.1 Introduction 34113.2 Experimental 342

13.2.1 Materials 34213.2.2 Whisker Isolation 34313.2.3 Nanocomposite Preparation 343

13.3 Characterization 34413.3.1 Fourier Transform Infrared Spectroscopy (FTIR) 34413.3.2 Th ermogravimetric Analysis (TGA) 34413.3.3 Diff erential Scanning Calorimetry (DSC) 34413.3.4 Dynamic Mechanical Properties (DMA) 344

13.4 Result and Discussion 34513.4.1 Fourier Transform Infrared Spectroscopy (FTIR) 34513.4.2 Th ermogravimetric Analysis 34613.4.3 Diff erential Scanning Calorimetry Analysis 34713.4.4 Dynamic Mechanical Analysis 350

13.5 Conclusions 352Acknowledgements 353References 353

14 Processes in Cellulose Derivative Structures 355

Mihaela Dorina Onofrei, Adina Maria Dobos and Silvia Ioan14.1 Introduction 355

14.1.1 Liquid Crystalline Polymers 35714.1.2 Liquid Crystal Dispersed in a Polymer Matrix 35914.1.3 Techniques for Obtaining Liquid Crystals

Dispersed into a Polymeric Matrix 36014.1.4 Some Methods to Characterize the

Liquid Crystal State 36014.1.5 Liquid Crystal State of Cellulose and Cellulose

Derivatives in Solution 36414.1.6 Cellulose Derivatives/Polymers Systems 373

14.2 Conclusions 383References 384

Contents xiii

15 Cellulose Nanocrystals: Nanostrength for Industrial and Biomedical

Applications 393

Anuj Kumar andYuvraj Singh Negi15.1 Introduction 39315.2 Cellulose and Its Sources 39415.3 Nanocellulose 39615.4 Cellulose Nanocrystals 398

15.4.1 Extraction of CNCs 39915.4.2 Overview of CNCs Production by Acid Hydrolysis 40115.4.3 Characterization Methods 40415.4.4 Properties and Behavior of CNCs 405

15.5 Aqueous Suspension and Drying of CNCs 40815.6 Functionalization of CNCs 410

15.6.1 Oxidation 41015.6.2 Polymer Graft ing 41115.6.3 Cationic Functionalization 41215.6.4 Acetylation 41215.6.5 Silylation 413

15.7 Processing of CNCs for Biocomposites 41415.7.1 Solution Casting 41415.7.2 Melt Compounding 41415.7.3 Partial Dissolution 41515.7.4 Electrospinning 41515.7.5 Layer-by-Layer Assembly 415

15.8 Applications of CNCs-Reinforced Biocomposites 41615.8.1 Industrial Applications 41615.8.2 Photocatalytic Materials 41615.8.3 Printed Electronics Applications 41715.8.4 Lithium-Ion Batteries (LIBs) 41715.8.5 Other Studies 419

15.9 Biomedical Applications 42115.9.1 Drug Delivery Systems 42115.9.2 Tissue Engineering 42215.9.3 Hydrogels 42515.9.4 Bioimaging 42615.9.5 pH-Sensing Materials 427

15.10 Conclusion 427Acknowledgements 428References 428

16 Medical Applications of Cellulose and Its Derivatives: Present and Future 437

Karthika Ammini Sindhu, Raghavan Prasanth

and Vijay Kumar Th akur16.1 Historical Overview 43816.2 Use of Cellulose for Treatment of Renal Failure 439

16.2.1 Types of Dialyzers 44116.2.2 Performance of Hollow-Fiber Dialyzers 443

xiv Contents

16.3 Types of Membranes 44416.3.1 Unmodifi ed Cellulosic Membrane 44516.3.2 Modifi ed Cellulosic Membrane 44516.3.3 Synthetic Membranes 446

16.4 Use of Cellulose for Wound Dressing 44716.5 Cotton as Wound Dressing Material 44816.6 Biosynthesis, Structure and Properties of MC 45016.7 MC as a Wound Healing System 45116.8 Microbial Cellulose/Ag Nanocomposite 45616.9 Nanocomposites of Microbial Cellulose and Chitosan 45816.10 Commercialization of Microbial Cellulose 46116.11 Use of Cellulose as Implant Material 46216.12 Dental Applications 470Conclusions 471Abbreviations 472Symbols 472References 473

17 Bacterial Cellulose and Its Multifunctional Composites: Synthesis

and Properties 479

V. Th iruvengadam and Satish Vitta17.1 Introduction 479

17.1.1 Synthesis Mechanism of Bacterial Cellulose 48017.1.2 Production Methods for Bacterial Cellulose 48217.1.3 Properties of Bacterial Cellulose 483

17.2 Magnetic Composites 48517.3 Composites with Catalytic Activity 48917.4 Electrically Conducting Composites 492

17.4.1 Conducting Polymer-Based Composites 49317.4.2 Carbon Nanomaterials-Based Composites 495

17.5 Composites as Fuel Cell Components, Electrodes and Membrane 496

17.6 Optically Transparent and Mechanically Flexible Composites 49917.7 Summary and Outlook 502References 502

Index 507

xv

Preface

Th e increasing environmental awareness has resulted in a renewed interest in polymer nano-composites that are procured from biorenewable polymers such as nanocellulose. Th ese polymer nanocomposites off er higher thermal and mechanical properties, transport barrier, thermal resistivity and fl ame retardance in comparison with the conventional biocompos-ites. Nanocomposite describes a two-phase material where one of the phases has at least one dimension in nanometre range (1–100 nm). Th ey diff er from conventional composites by the exceptionally high surface to volume ratio of the reinforcing phase and/or its exceptionally high aspect ratio. Th e reinforcing material can be made up of particles (e.g. minerals), sheets (e.g. exfoliated clay stacks) or fi bers (e.g. carbon nanotubes, electrospun fi bers or cellu-lose nanofi bers). Large reinforcement surface area means that a relatively small amount of nanoscale reinforcement can have an observable eff ect on the macroscale properties of the composites. Th e ability to control the material features at the nanoscale and evaluation of their infl uence on the micro and macroscopic properties provides a new aspect to the devel-opment of nanocomposite systems. Th ere has been enormous interest in the commercial-ization of nanocomposites for a variety of applications, and a number of these applications are already found in the market. Nanocomposites are currently used in a number of fi elds and new applications are continuously sought aft er.

In line with the development of nanotechnology and recent concern about environmen-tal issues, more attention is being paid to utilizing bio-based nano-materials. In this regard, nanocellulose has gained much more interest because of the promising characteristics such as biodegradable nature, renewability and lower price. Nanocellulose-based materials are showing signifi cant interest as potential nanofi llers for nanocomposites due to their nano-scale dimension (very high surface area-to-volume ratio), high aspect ratio and impres-sive mechanical properties (or nano-strength) imparting to desired nanocomposites. Advantages in the use of nanosize cellulosic materials are related not only to these proper-ties, in fact, its dimensions, in the nanometer scale, open a wide range of possible properties to be discovered. Nanosize cellulosic materials can be isolated from a variety of cellulosic resources, including plants, animals (tunicates), bacteria, algae, and in principle could be extracted from almost any cellulosic material by using diff erent procedures. Remarkable achievements have been witnessed in green technology of cellulose nanomaterials in the field of materials science including the development of bio- nanocomposites. Th e growing interest in green product and unsurpassed physical and chemical properties of nanocel-lulose has resulted in increased academic and industrial interests towards development of cellulose nanocomposites. However, there are still some issues to be overcome and main challenges in the fi eld are related to an effi cient separation of nanosize cellulosic materials from the natural resources. Th e non-compatible nature of nanocellulose with most of the polymers is also a crucial issue for its application in nanocomposites. In addition, the

xvi Preface

drying process of nanocellulose for application in polymer composite is another challenge. Last but not least is that we need to fi nd a process for obtaining higher yields in nanocel-lulose isolation. All these challenges and drawbacks have become the strong driving forces for discovering more effi cient processes and technologies to produce nanocelluloses for application in nanocomposites, and for inventing new applications as well.

Th is book is aimed to provide a detailed knowledge on the issues mentioned above. It also provides a comprehensive overview on the synthesis and applications of nanocellulose-based nanocomposites materials. Th is book discusses extensive developments for the next generation research in the fi eld of nanocellulose-based nanocomposites. Th e book contains seventeen chapters and each chapter addresses some specifi c issues related to nanocellulose and also demonstrates the real potentialities of these materials in diff erent domains.

Th e principal credit of this goes to the authors of the chapters for summarizing the sci-ence and tech nology in the exciting area of nanocellulose. I would also like to thank Martin Scrivener of Scrivener Publishing along with Dr. Srikanth Pilla (Series Editor) for their invaluable help in the organisation of the editing process.

Finally, I would like to thank my parents and wife Manju for their continuous encourage-ment and support.

Vijay Kumar Th akur, Ph.D. Washington State University, U.S.A.

August 30, 2014

Part 1

SYNTHESIS AND CHARACTERIZATION

OF NANOCELLULOSE-BASED POLYMER

NANOCOMPOSITES

3

Vijay Kumar Th akur, Nanocellulose Polymer Nanocomposites, (3–16) 2015 © Scrivener Publishing LLC

*Corresponding author: shandilyamn@gmail.com

1

Nanocellulose-Based Polymer Nanocomposites: An Introduction

Manju Kumari Th akur *,1 , Vijay Kumar Th akur 2 and Raghavan Prasanth 3

1 Division of Chemistry, Govt. Degree College Sarkaghat, Himachal Pradesh University, Summer

Hill, Shimla, India

2 School of Mechanical and Materials Engineering, Washington State

University, Washington, U.S.A.

3 Department of Mechanical Engineering and Materials Science, Rice University, Houston, Texas,

U.S.A.

Abstract Rising environmental awareness and the high demand for alternatives to non-renewable petro-

leum resources has led to extensive research focused on the concept of biomass-based biore-

newable materials. Natural cellulosic polymers are such materials of prime choice for diff erent

applications due to their inherent advantages which include the fact that they are easily available,

environmentally-friendly and have lower health risks; and also that they are economical, bio-

degradable, easily processed, have acceptable specifi c properties and have excellent insulating/

noise absorption properties to name a few. Th ese cellulosic materials in nano form, i.e., as nano-

cellulose, are rapidly emerging as one of the most promising future materials with outstand-

ing physical, chemical, mechanical and thermal properties for multifunctional applications in

diff erent fi elds. Keeping in mind the promising characteristics of nanocellulosic materials, the

present chapter gives an overview of the recent progress in the structure and applications of

nanocellulose procured from diff erent resources.

Keywords: Nanocellulose, natural fi bers, structure, processing and applications

1.1 Introduction

Polymer-based materials derived from both natural and petrochemical resources are currently being extensively used in a wide range of products and in numerous appli-cations [1-3] . Th ese polymers have superseded the use of other materials such as metals, glasses and ceramics in a number of fi elds [4-6] . Compared to their natural counterparts, synthetic polymers have been widely used in a vast number of applica-tions such as fi lms, fl exible plastic bags, composites and rigid containers to name a few [7-9] . Properties such as light weight, strength, chemical inertness and inexpensive

4 Nanocellulose Polymer Nanocomposites

production make them a favorable candidate for most present day applications [10-12] . However some of their other properties also cause considerable environmental prob-lems, with their high molecular weight, chemical stability and relatively low surface area-to-volume ratio making them resistant to degradation by microbial attack, and causing them to persist in the environment long aft er disposal [5, 13, 14] . In addition, these polymers are produced by oil-based technology, which raises a number of per-tinent issues related to increasing oil prices and dwindling resources, so the impetus to replace these polymers with renewable materials is increasing [15-17] . In order to conserve resources and avoid adding increased carbon emissions, materials must be developed that consume less energy and use raw materials that are derived from renew-able resources [18] .

Indeed, rising environmental awareness around the world has resulted in a renewed interest in materials procured from biorenewable resources [19, 20] . One of the com-mon practices to prepare new environmentally-friendly materials is the incorporation of a least one component that is derived from renewable resources [21, 22] . Green mate-rials have attracted great attention and interest in the development of biodegradable or natural polymer-derived green composites, while minimizing the generation of pollution [23] . Natural polymers, or biopolymers, are polymers that are produced from renewable resources [24, 25] . Th ey may be produced by biological systems such as plants or animals, or be chemically synthesized from biological materials [26] . It is also desirable to make use of natural materials which do not, for example, compete with the food chain [27, 28] . A biodegradable polymer can be defi ned as a material in which degradation results from the action of microorganisms such as bacteria, fungi and algae [29, 30] . Th erefore the use of biopolymers to replace synthetic polymers is attractive due to their obvious environmental advantages of being sustainable, renewable and biodegradable, being broken down into carbon dioxide and water when exposed to microbial fl ora [16, 31, 32] . In this advance-ment, the development of high-performance polymer biocomposite materials made from natural resources has been increasing worldwide due to environmentaland sustainability issues [9, 27, 33] . Th e use of renewable materials such as natural cellulose (most abun-dant biopolymer) is becoming impellent because of the great demand for alternatives to non-renewable petroleum materials and good reinforcing material due to its availability, low cost, low density, nontoxicity, low abrasiveness, biocompatibility and biodegradability [28, 34, 35] . Biocomposites consisting of the polymer matrix and natural cellulose fi bers are environmentally-friendly materials which can replace glass fi ber-reinforced polymer composites, and are currently used in a wide range of fi elds such as the automotive and construction industries, electronic components, sports and leisure, etc. [36, 37] .

Recently, the research on biobased nanocomposites which are reinforced with both natural fi bers and nanofi llers is actively proceeding in order to off er higher thermal and mechanical properties, transport barrier, thermal resistivity and fl ame retardance in comparison with the conventional biocomposites [20, 38] . Nanocomposite describes a two-phase material where one of the phases has at least one dimension in nanometer range (1–100 nm) [39] . Th ey diff er from conventional composites by the exception-ally high surface-to-volume ratio of the reinforcing phase and/or its exceptionally high aspect ratio. Th e reinforcing material can be made up of particles (e.g., minerals), sheets (e.g., exfoliated clay stacks) or fi bers (e.g., carbon nanotubes, electrospun fi bers or cel-lulose nanofi bers) [40] . Large reinforcement surface area means that a relatively small

Nanocellulose-Based Polymer Nanocomposites: An Introduction 5

amount of nanoscale reinforcement can have an observable eff ect on the macroscale properties of the composites. Th e ability to control the material features at the nanoscale and evaluation of their infl uence on the micro- and macroscopic properties provides a new aspect to the development of nanocomposite systems. Th ere has been enormous interest in the commercialization of nanocomposites for a variety of applications, and a number of these applications are already found in the market [41] . Nanocomposites are currently used in a number of fi elds and new applications are continuously sought aft er.

In line with the  development of nanotechnology and recent concern about envi-ronmental issues, more attention has been paid to the utilization of biobased nano-materials. In this regard, nanocellulose has gained much more interest because of its promising characteristics such as biodegradable nature, renewability and lower price [19] . Nanocellulose-based materials are gaining signifi cant interest as potential nano-fi llers for nanocomposites due to their nanoscale dimension (very high surface area-to-volume ratio), high aspect ratio and impressive mechanical properties (or nanostrength), which are imparted to the desired nanocomposites [42] . Th e advantages for the use of nanosize cellulosic materials are not only related to these properties; in fact, its dimensions, in the nanometer scale, open a wide range of possible properties yet to be discovered. Nanosize cellulosic materials can be isolated from a variety of cellulosic resources, including plants, animals (tunicates), bacteria  and algae, and in principle could be extracted from almost any cellulosic material by using diff erent procedures. Remarkable achievements have been witnessed in the  green technology of cellulose nanomaterials in the  fi eld of materials science, including the development of bio-nanocomposites. Th e growing interest in green product and unsurpassed physical and chemical properties of nanocellulose have resulted in increased academic and indus-trial interest towards the  development of cellulose nanocomposites. However, there are still some issues to be overcome and the main challenges in the fi eld are related to an effi cient separation of nanosize cellulosic materials from the natural resources [43] . Th e incompatible nature of nanocellulose with most polymers is also a crucial issue for its application in nanocomposites. In addition, the drying process of nanocellulose for application in polymer composite is another challenge. Th e last but not least point is related to fi nding a process for obtaining a higher yield in nanocellulose isolation. All these challenges and drawbacks have become the strong driving force for discovering more effi cient processes and technologies to produce nanocelluloses for application in nanocomposites, and for inventing new applications as well [15] . Chapters 2–9 of this book discuss in detail the synthesis and characterization of diff erent types of nanocellu-lose-based polymer composites, while Chapters 10–17 discuss in detail the processing and multifunctional applications of cellulose-based polymer nanocomposites.

1.2 Nanocellulose: Source, Structure, Synthesis and Applications

Human society has used natural cellulose-based materials for thousands of years, both knowingly  and unknowingly [44] . All the industries around the world are looking for materials that can be easily procured from renewable and sustainable resources. However, although cellulose-based materials off er a number of advantages, for advanced

6 Nanocellulose Polymer Nanocomposites

applications some of the imperative properties such as functionality, uniformity and durability are not achieved using traditional cellulosic materials. Fortunately, the use of cellulose in nanoform can solve these issues. By suitable extraction of cellulose from diff erent biorenewable resources at the nanoscale, next generation of multifunc-tional polymer nanocomposites can be obtained by employing a new cellulose-based “building block” known as nanocellulose. Nanocellulose off ers a number of advantages such as high aspect ratio, low density (1.6 g cm −3 ), and a reactive surface of –OH side groups compared to the parental cellulose, and these functional groups also facilitate the attachment of desired functional groups onto these nanocellulose surface to achieve diff erent surface properties. Nanocellulose can be obtained in diff erent forms depend-ing upon the source material and the intended applications. Chapters 2–9 of this book discuss in detail the diff erent types of nanocellulosic materials. Natural cellulosic fi bers are one of the most promising resources for the synthesis of nanocellulose. Natural cel-lulosic fi bers can be divided into diff erent types ( Figure 1.1 ) [45] .

 It has been reported that cellulose fi brils (micro/nano size) or cellulose whiskers can be easily procured from cotton fi bers as well as cellulose fi lter papers [46] . Nanocellulose can be obtained from diff erent resources such as wood, plants, tunicates, algae and bac-teria. Figure 1.2 shows the structure of cellulose. Cellulose is a non-branched linear polysaccharide molecule that is comprised of two anhydroglucose rings (C

6 H

10 O

5 ) n; n

= 10000 to 15000, where n depends upon the source of cellulose. Th ese rings are linked together through the β 1–4 glucosidic bond [44] .

Cellulose is one of the most abundant natural polymers on earth and provides strength/stability to the plant cell walls [45] . Th e properties and economics of fi ber production for various applications are infl uenced by the amount of cellulose in a fi ber. In natural cellulosic fi bers, stiff semicrystalline cellulose microfi brils have been found to be embedded in a pliable amorphous matrix ( Figure 1.3 ) [45] .

Nanocellulose can be obtained through diff erent processes [47] . Th e length of these nanocellulosic materials depends upon the resource from which they are obtained [52] . For example, in the nanocellulose obtained from tunicates and green algae, crystallites

CottonKapok

Seed

Fruit

Coconut

Coir

Hard Wood Soft Wood

Fibers (More than

thousands of varieties)Wood Stalk

SisalManilaCurauaBananaPalm

Leaf Blast

Cellulosic

Fibers

Bamboo, Wheat, Grass

Corn, Rice

FlaxHempJuteKenafRamieRattan

Figure 1.1 Classifi cation of cellulosic fi bers. Reprinted with permission from [45]. Copyright 2010 Wiley.

Nanocellulose-Based Polymer Nanocomposites: An Introduction 7

have lengths in the range of a few micrometers, while those obtained from wood and cotton have lengths of the order of a few hundred nanometers. Th ese nanocellulose are referred  to by diff erent names such as microcrystalline cellulose (MCC), nano-crystalline cellulose (NCCs), nanowhiskers, bacterial cellulose, etc., depending upon their specifi c characteristics and synthesis procedures [48] . Chapters 2 and 5 of this book are solely focused on the bacterial cellulose-based polymer nanocomposites. Bacterial cellulose (BC) is generally biosynthesized by numerous bacteria as a 3D net-work of nano- and micro-fi brils. It has received greater attention during the last few years because of its unique features such as crystallinity, high purity, water-holding

O

O

O

OH

OH

CH2OH

Figure 1.2 Schematic structure for carbon atoms in an anhydroglucose unit of cellulose.

Middlelarnella

(a)

(b)

(c)

Primarywall

Plasmamembrane

Secondary wall

Rosette

Secondarywall (S3)

Soluble protein

Hemicellulose

Secondarywall (S2)

Secondarywall (S1)

Primarywall

Primary wall

Lignin

Cellulose

Hemicellulose

Protein

Middle larnella

Middlelarnella

Plasmamembrane

Figure 1.3 Plant plasma membrane and cell wall structure: a) Cell wall containing cellulose microfi brils,

hemicellulose, pectin, lignin and soluble proteins; b) Cellulose synthase enzymes are in the form of

rosette complexes, which fl oat in the plasma membrane; c) Lignifi cation occurs in the S1, S2 and S3

layers of the cell wall. Reprinted with permission from [45, 52]. Copyright 2010 Wiley and 2008 Nature.

8 Nanocellulose Polymer Nanocomposites

capacity, tensile strength and Young's modulus, which can be successfully exploited in the development of innovative nanostructured composite materials. Diff erent synthesis and characterization aspects of the bacterial cellulose are discussed in Chapters 2 and 4. Chapter 3 discusses the synthesis and chemistry of cellulose whiskers, nanofi bril-lated cellulose and the synthesis of nanocomposites using polyurethane as the polymer matrix. Chapter 4 comprehensively discusses the structure, properties and methods of characterization along with the growth conditions for bacterial cellulose. Diff erent modifi cation strategies to alter the properties of bacterial cellulose for certain specifi c applications are also discussed in this chapter. Th ese modifi cation strategies include both physical and chemical modifi cations. Chapter 6 focuses on the synthesis of mul-tifunctional ternary polymer nanocomposites using cellulosic nano-reinforcement with an emphasis on nanocrystalline cellulose (NCC), microfi brillated cellulose nano-fi bers (MFC) and bacterial cellulose (BC). Chapter 8 of the book comprehensively dis-cusses the nanocellulose-based liquid crystalline composite systems in detail. Th e main emphasis of this chapter is on nanocrystalline cellulose, microcrystalline cellulose, composites, fi lms and electrospun fi bers. Chapter 11 describes in detail the isolation of nanocellulose from numerous sources and its utilization for fabrication methods, its characterization, drying processes and modifi cation. Th e chapter also discusses the application of nanoscale cellulosic materials in polymer nanocomposites. Chapter 13 is focused on the cellulose whiskers procured from kenaf fi bers. Diff erent thermal and dynamic mechanical properties of the nanocomposites are also discussed in this chap-ter. Chapter 4 focuses on the processes in cellulose derivative structures. Th e main  steps that are generally involved in the preparation of cellulose nanocrystals and microfi bril-lated celluloses are shown in reference [49] .

Figure 1. 4 shows the transmission electron micrographs (TEM) of microcrystalline cellulose obtained from dilute suspensions of cotton, sugar beet pulp, and tunicin (the cellulose extracted from tunicate) whiskers  [48] .

Microcrystalline cellulose has been found to be insoluble in common solvents gen-erally used in the preparation of nanocomposites. Th e MCC has been found to form colloidal suspensions when suspended in water ( Figure 1. 5). Diff erent parameters of MCC such as dimensions of the dispersed particles, surface charge and their size poly-dispersity control the stability of these suspensions [48] .

Nanocrystalline cellulose (NCCs) are general referred  to as rigid rod-like crystals having a diameter in the range of 10–20 nm and lengths of a few hundred nanometers [47] . Figure 1. 6 depicts the location and extraction of nanocrystalline cellulose [50]

Figure 1. 7 shows the TEM images of some of the nanocrystalline cellulose obtained using sulfuric acid hydrolysis. Nanocellulose contains an abundance of hydroxyl groups susceptible to various chemical reactions. Th e nanocellulosic materials such as nanofi -bers are also processed to produce the micro/nanocrystal using several pretreatments. Some of the common treatments include the removal of the amorphous regions at the interface of microcrystalline domains in these fi bers by acid treatment [46] . For a num-ber of applications nanocellulose is modifi ed using diff erent techniques. Some of the commonly used techniques include carboxylation, esterifi cation, silylation, cationiza-tion, and polymer graft ing [47, 53] .

A summary of the diff erent chemical modifi cation techniques used to alter the sur-face characteristics of nanocellulose can be found in reference [47].

Nanocellulose-Based Polymer Nanocomposites: An Introduction 9

Th ere has been Intense ongoing research to avoid the complex surface functionaliza-tion techniques. One of the new techniques is to combine the synthesis and functional-ization of nanocellulose in a single step  (see reference [47] ).

Nanocellulose and its derivatives can be processed into diff erent forms. Bacterial celulose is one such important type of nanocellulose. It has been processed into nano-fi bers for diff erent applications. Figure 1.8 shows the diff erent applications of cellulose acetate nanofi bers [51] . Chapters 2 and 4 discuss the diff erent perspectives of bacterial cellulose-based materials and their diff erent applications. In these chapters the authors discuss in detail a vast collection of BC nanocomposites prepared using diff erent poly-mer matrices such as natural polymers and thermoplastic matrices. In addition to this,

(a)

(b)

(c)

Figure 1.4 Transmission electron micrograph from a dilute suspension of hydrolyzed (a) cotton,

(b) sugar beet pulp and (c) tunicin. Reprinted with permission from [48] . Copyright 2005 American

Chemical Society.

10 Nanocellulose Polymer Nanocomposites

the eff ect of inorganic nanophases are also addressed to demonstrate the real potentiali-ties of bacterial cellulose in the polymer nanocomposites. Chapter 2 also discusses in detail the bacterial cellulose-based hybrid nanocomposite materials. Chapter 3 sum-marizes the new trends in the use of nanocellulose (nanowhiskers and nanofi brillated cellulose) as reinforcement of diff erent types of polyurethane systems.

Chapter 4 discusses in detail the bacterial cellulose-reinforced renewable polymer-matrix-based composites. Th e techniques used to prepare the nanocomposites include

Figure 1.5 Photograph of an aqueous suspension of tunicin whiskers observed between cross nicols,

showing the formation of birefringent domains. Reprinted with permission from [48] . Copyright 2005

American Chemical Society.

Cell wall

Plant cells

Layeres mesh of

microfibrils in

plant cell wall

Microfibrils structure

Crystalline cellulose

Cellulose molecule

Glucose Cellobiose

HOHO HO

HO OH

OH OH OH OH

OHOH

O

OO

O

OH O

O

HO

O

O

Single microbril

Hemicellulose

Paracrystalline

celluloseCrystalline cellulose

Figure 1.6 Location and extraction of nanocrystalline cellulose. Reprinted with permission from [50] .

Copyright 2012 John Wiley.

Nanocellulose-Based Polymer Nanocomposites: An Introduction 11

Figure 1.7 TEM micrographs of nanocrystals obtained by sulfuric acid hydrolysis of (a) cotton (b)

avicel and (c–e) tunicate cellulose. Th e insets of (a) and (b) provide higher resolution images of some

characteristic particles. Reprinted with permission from [47, 53] . Copyright 2010 John Wiley and 2008

American Chemical Society.

Before adsorption

of metal ion

(e.g., Cu2+)

After desorption

of Cu2+ using EDTA

Zone of inhibition

t = 0 h

t = 4 h

t = 24 h

SELF-CLEARING TEXTILE

THERMOADAPATABLE MATERIAL

PHOTOCHROMIC DEVICE APPLICATION

BIOSENSOR AND

ANTI-COUNTERFEITING MATERIAL

CROP PROTECTIONSTRATEGY

Irradiated for 40 s

Irradiated for 20 s

Without UV

irradiation

SEM image (pseudocoloured)

Mating of male and female

insects fail: protected crops

Pheromone loaded mat,

applied in crop field

Male and female

insects mate-

damaged crops

NUTRACEUTICALDELIVERY SYSTEM

CELL CULTURE ANDREGENERATIVE MEDICINE

BIOFUNCTIONALIZATION-ENZYME BIOREACTOR-DRUG DELIVEY

Electrospun mat

Ground

Collector

Needle

High voltage

supply

Syringe with polymer solution

Cellulose acetrate in suitable solvent

After desorption of Cu2+

BIOREMEDIATION

ANTIMICROBIAL MAT

Figure 1.8 Schematic representation of electrospinning cellulose acetate nanofi bers (at the center) and

myriad biotechnological applications. Reprinted with permission from [51]. Copyright 2013 Elsevier.

12 Nanocellulose Polymer Nanocomposites

impregnating bacterial cellulose, solution blending and casting, electrospinning and melt blending, in-situ composites, along with several other methods. Chapter 5 focuses solely on the preparation of nanocomposites using the in-situ synthesis technique. It also summarizes the applications of the  in-situ synthesized nanocomposites in bone defect repair and bone tissue engineering, electrically active paper, nanostructured porous materials for drug delivery or as bioactive compounds, surface coating appli-cations, and biobased green nanocomposites. Th e eff ect of in-situ polymerization on the biodegradation behavior of cellulose nanocomposites is also discussed in this chap-ter. Chapter 6 reviews selected approaches for the modulation of the fi nal properties of a polymeric nanocomposite containing cellulosic nano-reinforcement combined with a second fi ller of diff erent chemical nature. Diff erent properties of the synthesized nano-composites are analyzed and reported in this chapter, taking into account the required functionality of the device in the appropriate fi nal application. Th e eff ect of the incor-poration of other fi llers on the properties of nanocellulose-based nanocomposites is also discussed in detail. Chapter 9 reviews the recent advances in nanocomposites based on biodegradable polymers and nanocellulose. Diff erent kinds of biodegradable polymers were used as the matrix material in the preparation of cellulose-based nano-composites. Th e diff erent ways to obtain nanocellulose from several sources (micro-crystalline cellulose, natural fi bers and agro-wastes) have been reviewed in this chapter along with the recent advances in biodegradable polymers/cellulose nanocomposites for packaging applications. Chapter 10 describes the fundamental problems faced in the development of cellulose nanocomposite and the methods adopted to overcome them. Chapter 12 is solely focused on the electrospinning of cellulose. It discusses in detail the fundamental processing aspect and utilization of diff erent solvents for elec-trospinning of cellulose, along with the preparation of cellulose composites. Chapter 15 of the book comprehensively discusses cellulose nanocrystals and their biomedical applications. In this chapter, the extraction and characterization of cellulose nanocrys-tals are discussed along with their functionalization as well as industrial and biological applications. Chapter 16 also focuses on the biomedical applications of cellulose and its derivatives. Th e last chapter focuses on recent advances in the multifunctional nano-composites based on nanocellulose. In this chapter diff erent types of nanocomposites ranging from magnetic to electrically-conductive nanocomposites are discuses, with a particular emphasis on the structure and chemistry.

1.3 Conclusions

Among various biobased nanomaterials, nanocellulose is one of the most economical and environmentally-friendly biorenewable materials that can be easily procured from diff erent resources. Diff erent kinds of eco-friendly polymer nanocomposite materials with outstanding thermal, morphological and mechanical properties can be obtained using nanocellulose as potential reinforcement. Th e versatile applications of nanocel-lulose ranges from biomedical to high-performance structural nanocomposites. One of the biggest challenges in the use of nanocellulose is its large-scale production. To extensively use the nanocellulose for multifunctional applications, active research