Cellulose nanocrystals : properties, production, and applications 9781118675601, 1118675606, 9781119968160, 111996816X

Table of contents :
Content: Series Preface xiii Foreword xv Prologue xviii 1 New Frontiers for Material Development and the Challenge of Nanotechnology 1 1.1 Perspectives on Nanotechnology 1 1.2 Societal Ramifications of Nanotechnology 3 1.3 Bio?]inspired Material Development: The Case for Cellulose Nanocrystals 5 1.4 A Glance at Bio?]inspired Hierarchical Materials 9 1.5 Concluding Thoughts 13 Notes 13 2 Assembly and Structure in Native Cellulosic Fibers 16 2.1 Physical and Chemical Characteristics of the Cellulose Molecule 16 2.1.1 The Origin of Cellulose 16 2.1.2 The Chemistry of Cellulose 18 2.1.3 The Physics of Cellulose 20 2.2 Morphology and Structure of Native Cellulosic Fibers 22 2.3 Physical and Mechanical Properties of Native Cellulosic Fibers 25 2.3.1 Anisotropy of the Fiber Cell Wall 25 2.3.2 Mechanical Properties of Cellulosic Fibers 29 Notes 32 3 Hydrolytic Extraction of Cellulose Nanocrystals 33 3.1 Introduction 33 3.2 The Liberation of CNCs Using Acid Hydrolysis 35 3.3 Reaction Kinetics of CNC Extraction 38 3.3.1 Effects of H2SO4 Hydrolysis Conditions and Sulfation on CNC Yield of Extraction 38 3.3.2 H2SO4 Hydrolysis Reproducibility and Yield Optimization 46 3.3.3 Commentary on Hydrochloric Acid?]Hydrolyzed CNCs 48 3.3.4 CNC Stability and Post H2SO4?]Hydrolysis Aging 49 3.4 Processing Considerations for Sustainable and Economical Manufacture of CNCs 50 3.5 Micro/Nano Cellulosics Other Than CNCs 53 3.5.1 Microfibrillated Cellulose 53 3.5.2 Microcrystalline Cellulose 57 3.5.3 Bacterial Cellulose 60 Notes 62 4 Properties of Cellulose Nanocrystals 65 4.1 Morphological Characteristics of CNCs 65 4.2 Structural Organization of CNCs 68 4.3 Solid?]State Characteristics of CNCs 74 4.3.1 X?]Ray Diffractometric Analysis of CNCs 76 4.3.2 CNCs Phase Structure Based on SS?]NMR 81 4.3.3 Concluding Remarks 87 4.4 CNCs Chiral Nematic Phase Properties 87 4.4.1 Ionic Strength Effect on Chiral Phase Separation 88 4.4.2 Temperature Effect on Chiral Phase Separation 91 4.4.3 Suspension Concentration Effect on Chiral Phase Separation 92 4.4.4 Magnetic Field Effect on Chiral Phase Separation 94 4.4.5 Sonication Effect on Physicochemical Properties 94 4.5 Shear Rheology of CNC Aqueous Suspensions 95 4.5.1 Basic Rheological Behavior of CNC Aqueous Suspensions 95 4.5.2 Sonication Effects on the Microstructure and Rheological Properties of CNCs Suspensions 98 4.5.3 Concentration Effects on the Microstructure and Rheological Properties of CNC Suspensions 100 4.5.4 Temperature Effects on the Microstructure and Rheological Properties of CNC Suspensions 106 4.5.5 CNCs Surface Charge Effects on the Microstructure and Rheological Properties of CNC Suspensions 112 4.5.6 Ionic Strength Effects on the Microstructure and Rheological Properties of CNC Suspensions 118 4.5.7 Aging and Yielding Characteristics of CNC Suspensions 123 4.5.8 Concluding Remarks 128 4.6 Thermal Stability of CNCs 129 Notes 134 5 Applications of Cellulose Nanocrystals 138 5.1 Prelude 138 5.2 The Reinforcing Potential of CNCs in Polymer Nanocomposites 140 5.2.1 Basic Concepts in Composites 140 5.2.2 Generic Methods for Surface Functionalization 142 5.2.3 Why CNCs for Reinforcement? 147 5.2.4 Performance of CNCs in Compatible Polymer Systems 150 5.2.5 Nanocomposites Prepared by Postpolymerization Compounding of CNCs and Thermoplastic Polymers 154 5.2.6 Controlling Nanocomposite Crystallinity and Plasticity via In Situ Polymerization Methodologies in the Presence of CNCs 165 5.2.7 CNCs in Thermosetting Polymers: Tailoring Cross?]Linking Density and Toughness 172 5.2.8 Comments on Modeling the Mechanical Response of CNC?]Reinforced Nanocomposites 177 5.2.9 Conclusions and Critical Insights 181 5.3 CNC?]Stabilized Emulsions, Gels, and Hydrogels 184 5.3.1 Pickering Emulsions 184 5.3.2 High Internal Phase Emulsions 187 5.3.3 pH?]Responsive Gels and Flocculants 189 5.3.4 Hydrogels 190 5.4 Controlled Self?]Assembly of Functional Cellulosic Materials 194 5.4.1 Flexible CNC Films with Tunable Optical Properties 194 5.4.2 Mesoporous Photonic Cellulose Films 197 5.5 Toward Bio?]inspired Photonic and Electronic Materials 202 5.5.1 Mesoporous Photonic Materials from Cellulose Nanomaterial Liquid Crystal Templates 202 5.5.2 Actuators and Sensors 217 5.5.3 Sustainable Electronics Based on CNCs 225 5.5.4 Conclusions and Outlook 232 5.6 CNCs in Biomedicine and Pharmaceuticals 233 5.7 Environmental, Health, and Safety Considerations of CNCs 235 5.8 Perspectives and Challenges 238 Notes 239 Epilogue The Never?]Ending Evolution of Scientific Insights 248 Bibliography 252 Subject Index 288

Citation preview

Cellulose Nanocrystals

Wiley Series in Renewable Resources Series Editor Christian V. Stevens—Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium

Titles in the Series Wood Modification—Chemical, Thermal and Other Processes Callum A. S. Hill Renewables—Based Technology—Sustainability Assessment Jo Dewulf and Herman Van Langenhove Introduction to Chemicals from Biomass James H. Clark and Fabien E. I. Deswarte Biofuels Wim Soetaert and Erick Vandamme Handbook of Natural Colorants Thomas Bechtold and Rita Mussak Surfactants from Renewable Resources Mikael Kjellin and Ingegard Johansson Industrial Application of Natural Fibres—Structure, Properties and Technical Applications Jorg Mussig Thermochemical Processing of Biomass—Conversion into Fuels, Chemicals and Power Robert C. Brown Biorefinery Co‐Products: Phytochemicals, Primary Metabolites and Value‐Added Biomass Processing Chantal Bergeron, Danielle Julie Carrier, and Shri Ramaswamy Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals Charles E. Wyman Bio‐Based Plastics: Materials and Applications Stephan Kabasci Introduction to Wood and Natural Fiber Composites Douglas Stokke, Qinglin Wu, and Guangping Han Cellulosic Energy Cropping Systems Douglas L. Karlen Introduction to Chemicals from Biomass, Second Edition James Clark and Fabien Deswarte

Lignin and Lignans as Renewable Raw Materials: Chemistry, Technology and Applications Francisco G. Calvo‐Flores, Jose A. Dobado, Joaquin Isac‐Garcia, and Francisco J. Martin‐Martinez Sustainability Assessment of Renewables‐Based Products: Methods and Case Studies Jo Dewulf, Steven De Meester, and Rodrigo Alvarenga

Forthcoming Titles Biorefinery of Inorganics: Recovering Mineral Nutrients from Biomass and Organic Waste Erik Meers and Gerard Velthof Bio‐Based Solvents Francois Jerome and Rafael Luque Fuels, Chemicals and Materials from the Oceans and Aquatic Sources Francesca M. Kerton and Ning Yan Nanoporous Catalysts for Biomass Conversion Feng‐Shou Xiao

Cellulose Nanocrystals Properties, Production, and Applications Wadood Y. Hamad Cellulosic Biomaterials, FPInnovations, Vancouver, Canada Department of Chemistry, University of British Columbia, Vancouver, Canada

This edition first published 2017 © 2017 John Wiley & Sons Ltd Registered Office John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com. The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or ­otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best e­ fforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of ­merchantability or fitness for a particular purpose. It is sold on the understanding that the publisher is not engaged in rendering professional services and neither the publisher nor the author shall be liable for damages arising herefrom. If professional advice or other expert assistance is required, the services of a competent professional should be sought. The advice and strategies contained herein may not be suitable for every situation. In view of ­ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of experimental reagents, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each chemical, piece of equipment, reagent, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. The fact that an organization or Website is referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the ­organization or Website may provide or recommendations it may make. Further, readers should be aware that Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read. No warranty may be created or extended by any promotional statements for this work. Neither the publisher nor the author shall be liable for any damages arising herefrom. Library of Congress Cataloging‐in‐Publication Data Names: Hamad, Wadood. Title: Cellulose nanocrystals : properties, production, and applications / Wadood Y. Hamad. Description: Chichester, West Sussex : John Wiley & Sons, Inc., 2017. | Includes bibliographical references and index. Identifiers: LCCN 2016036141| ISBN 9781119968160 (cloth) | ISBN 9781118675700 (epub) Subjects: LCSH: Cellulose–Chemistry. | Cellulose nanocrystals. | Nanocrystals. Classification: LCC TP248.65.C45 H36 2017 | DDC 661/.802–dc23 LC record available at https://lccn.loc.gov/2016036141 A catalogue record for this book is available from the British Library. Set in 10/12pt Times by SPi Global, Pondicherry, India

10 9 8 7 6 5 4 3 2 1

For Dima, Reemo, and Seby—lovingly inspiring, par excellence

Contents Series Preface

xiii

Forewordxv Prologuexviii 1 New Frontiers for Material Development and the Challenge of Nanotechnology1 1.1  Perspectives on Nanotechnology 1 1.2  Societal Ramifications of Nanotechnology 3 1.3  Bio‐inspired Material Development: The Case for Cellulose Nanocrystals5 1.4  A Glance at Bio‐inspired Hierarchical Materials 9 1.5  Concluding Thoughts 13 Notes13 2 Assembly and Structure in Native Cellulosic Fibers 16 2.1  Physical and Chemical Characteristics of the Cellulose Molecule 16 2.1.1  The Origin of Cellulose 16 2.1.2  The Chemistry of Cellulose 18 2.1.3  The Physics of Cellulose 20 2.2  Morphology and Structure of Native Cellulosic Fibers 22 2.3  Physical and Mechanical Properties of Native Cellulosic Fibers 25 2.3.1  Anisotropy of the Fiber Cell Wall 25 2.3.2  Mechanical Properties of Cellulosic Fibers 29 Notes32 3 Hydrolytic Extraction of Cellulose Nanocrystals 3.1 Introduction 3.2  The Liberation of CNCs Using Acid Hydrolysis

33 33 35

x  Contents

3.3  Reaction Kinetics of CNC Extraction 38 3.3.1  Effects of H2SO4 Hydrolysis Conditions and  Sulfation on CNC Yield of Extraction 38 3.3.2 H2SO4 Hydrolysis Reproducibility and  Yield Optimization 46 3.3.3  Commentary on Hydrochloric Acid‐Hydrolyzed CNCs 48 3.3.4  CNC Stability and Post H2SO4‐Hydrolysis Aging 49 3.4  Processing Considerations for Sustainable and Economical Manufacture of CNCs 50 3.5  Micro/Nano Cellulosics Other Than CNCs 53 3.5.1  Microfibrillated Cellulose 53 3.5.2  Microcrystalline Cellulose 57 3.5.3  Bacterial Cellulose 60 Notes62 4 Properties of Cellulose Nanocrystals 4.1  Morphological Characteristics of CNCs 4.2  Structural Organization of CNCs 4.3  Solid‐State Characteristics of CNCs 4.3.1  X‐Ray Diffractometric Analysis of CNCs 4.3.2  CNCs Phase Structure Based on SS‐NMR 4.3.3  Concluding Remarks 4.4  CNCs Chiral Nematic Phase Properties 4.4.1  Ionic Strength Effect on Chiral Phase Separation 4.4.2  Temperature Effect on Chiral Phase Separation 4.4.3  Suspension Concentration Effect on Chiral Phase Separation 4.4.4  Magnetic Field Effect on Chiral Phase Separation 4.4.5  Sonication Effect on Physicochemical Properties 4.5  Shear Rheology of CNC Aqueous Suspensions 4.5.1  Basic Rheological Behavior of CNC Aqueous Suspensions 4.5.2  Sonication Effects on the Microstructure and Rheological Properties of CNCs Suspensions 4.5.3  Concentration Effects on the Microstructure and Rheological Properties of CNC Suspensions 4.5.4  Temperature Effects on the Microstructure and Rheological Properties of CNC Suspensions 4.5.5  CNCs Surface Charge Effects on the Microstructure and Rheological Properties of CNC Suspensions 4.5.6  Ionic Strength Effects on the Microstructure and Rheological Properties of CNC Suspensions

65 65 68 74 76 81 87 87 88 91 92 94 94 95 95 98 100 106 112 118

Contents   xi

4.5.7  Aging and Yielding Characteristics of CNC Suspensions123 4.5.8  Concluding Remarks 128 4.6  Thermal Stability of CNCs 129 Notes134 5 Applications of Cellulose Nanocrystals 138 5.1 Prelude 138 5.2  The Reinforcing Potential of CNCs in Polymer Nanocomposites140 5.2.1  Basic Concepts in Composites 140 5.2.2  Generic Methods for Surface Functionalization 142 5.2.3  Why CNCs for Reinforcement? 147 5.2.4  Performance of CNCs in Compatible Polymer Systems 150 5.2.5  Nanocomposites Prepared by Postpolymerization Compounding of CNCs and Thermoplastic Polymers 154 5.2.6  Controlling Nanocomposite Crystallinity and Plasticity via In Situ Polymerization Methodologies in the Presence of CNCs 165 5.2.7  CNCs in Thermosetting Polymers: Tailoring Cross‐Linking Density and Toughness 172 5.2.8  Comments on Modeling the Mechanical Response of CNC‐Reinforced Nanocomposites 177 5.2.9  Conclusions and Critical Insights 181 5.3  CNC‐Stabilized Emulsions, Gels, and Hydrogels 184 5.3.1  Pickering Emulsions 184 5.3.2  High Internal Phase Emulsions 187 5.3.3  pH‐Responsive Gels and Flocculants 189 5.3.4 Hydrogels 190 5.4  Controlled Self‐Assembly of Functional Cellulosic Materials 194 5.4.1  Flexible CNC Films with Tunable Optical Properties 194 5.4.2  Mesoporous Photonic Cellulose Films 197 5.5  Toward Bio‐inspired Photonic and Electronic Materials 202 5.5.1  Mesoporous Photonic Materials from Cellulose 202 Nanomaterial Liquid Crystal Templates 5.5.2  Actuators and Sensors 217 5.5.3  Sustainable Electronics Based on CNCs 225 5.5.4  Conclusions and Outlook 232 5.6  CNCs in Biomedicine and Pharmaceuticals 233 5.7  Environmental, Health, and Safety Considerations of CNCs 235 5.8  Perspectives and Challenges 238 Notes239

xii  Contents

Epilogue—The Never‐Ending Evolution of Scientific Insights

248

Bibliography252 Subject Index

288

Series Preface Renewable resources, their use, and modification are involved in a multitude of important processes with a major influence on our everyday lives. Applications can be found in the energy sector, paints and coatings, and the chemical, pharmaceutical, and textile industry, to name but a few. The area interconnects several scientific disciplines (agriculture, biochemistry, chemistry, technology, environmental sciences, forestry, etc.), which makes it very difficult to have an expert view on the complicated interaction. Therefore, the idea to create a series of scientific books that will focus on specific topics ­concerning renewable resources has been very opportune and can help to clarify some of the underlying connections in this area. In a very fast‐changing world, trends are not only characteristic for fashion and political standpoints; science is also not free from hypes and buzzwords. The use of renewable resources is again more important nowadays; however, it is not part of a hype or a fashion. As the lively discussions among scientists continue about how many years we will still be able to use fossil fuels—opinions ranging from 50 to 500 years—they do agree that the reserve is limited and that it is essential not only to search for new energy carriers but also for new material sources. In this respect, renewable resources are a crucial area in the search for alternatives for fossil‐based raw materials and energy. In the field of energy supply, ­biomass and renewable‐based resources will be part of the solution alongside other alternatives such as solar energy, wind energy, hydraulic power, hydrogen technology, and nuclear energy. In the field of material sciences, the impact of renewable resources will probably be even bigger. Integral utilization of crops and the use of waste streams in certain industries will grow in importance, leading to a more sustainable way of producing materials. Although our society was much more (almost exclusively) based on renewable resources centuries ago, this disappeared in the Western world in the nineteenth century. Now it is time to focus again on this field of research. However, it should

xiv   Series Preface

not mean a “retour à la nature,” but it should be a multidisciplinary effort on a highly technological level to perform research toward new opportunities, to develop new crops and products from renewable resources. This will be essential to guarantee a level of comfort for a growing number of people living on our planet. It is “the” challenge for the coming generations of scientists to develop more sustainable ways to create prosperity and to fight poverty and hunger in the world. A global approach is certainly favored. This challenge can only be dealt with if scientists are attracted to this area and are recognized for their efforts in this interdisciplinary field. It is, therefore, also essential that consumers recognize the fate of renewable resources in a number of products. Furthermore, scientists do need to communicate and discuss the relevance of their work. The use and modification of renewable resources may not follow the path of the genetic engineering concept in view of consumer acceptance in Europe. Related to this aspect, the series will certainly help to increase the visibility of the importance of renewable resources. Being convinced of the value of the renewables approach for the industrial world, as well as for developing countries, I was myself delighted to collaborate on this series of books focusing on different aspects of renewable resources. I hope that readers become aware of the complexity, the interaction and interconnections, and the challenges of this field and that they will help to communicate on the importance of renewable resources. I certainly want to thank the people of Wiley’s Chichester office, especially David Hughes, Jenny Cossham, and Lyn Roberts, in seeing the need for such a series of books on renewable resources, for initiating and supporting it, and for helping to carry the project to the end. Last, but not least, I want to thank my family, especially my wife Hilde and children Paulien and Pieter‐Jan, for their patience and for giving me the time to work on the series when other activities seemed to be more inviting. Christian V. Stevens Faculty of Bioscience Engineering Ghent University, Belgium Series Editor “Renewable Resources” June 2005

Foreword This monograph tells the compelling story of the importance of cellulose nanocrystals as a material with many and diverse industrial applications, and hence a very significant potential market value. It lays out in profound depth the unique physical and chemical characteristics that underlie this importance and provides the understanding to assess the potential of specific, new opportunities. The monograph is an important and timely publication. It presents the state of technical knowledge and understanding about cellulose, the production process to extract cellulose nanocrystals from natural sources of cellulose, the characterization of the nanocrystals, and the assessment of their potential application in industrial products and processes. It is a timely publication because cellulose nanocrystals are a key member of the family of cellulosic nanomaterials which are rapidly moving from a focus of scientific research toward commercial production and their introduction into commercial applications. It is timely because world interest in cellulosic nanomaterials has grown ­significantly over the past few years, and we are now able to confidently predict the size range of the global economic value of their production and application, which is vast. Because of this potential economic value, industrial enterprises in a number of countries are focusing on developing their capacity to participate in this activity both in terms of the production and use of these nanomaterials. In moving forward, these firms need access to the best information available on these materials and international trade will depend on a consistent ability to specify and certify the materials produced for the full spectrum of application areas. In addition, this trade and other factors will lead to the need for coherent international science‐based standards and regulations related to the production and use of these materials: a requirement that is already recognized at both the national and international levels within, for example, the ISO Technical Committees. The world of nanotechnology has been a focus of interest for both governments and private sector organizations for well over a decade now. In its early days, the world perspective focused on the potential importance of nanoparticles, such as

xvi  Foreword

nano‐silver and nano‐gold, and on areas related to carbon nanomaterials, most importantly single‐walled carbon nanotubes, which were seen to have immense potential as structural materials as well as important elements of other so‐called high technology domains such as nano‐electronics. The contribution of nanomaterials to the global economy has grown considerably over the intervening decade and is now estimated to have an annual value of many hundreds of millions of dollars. However, the future potential of these early materials seems to have been overestimated, and we are now beginning to see new areas coming into play as future major contributors. Among these nanomaterials which offer important new potential are graphene and other two‐dimensional materials as well as those derived from supramolecular assembly. Surprising to many, the availability of cellulosic nanomaterials is seen as part of this major family of potentially important new materials with applications in a very broad range of industries. Apart from their physical and chemical characteristics, this family of materials has two other important attributes. First, they are based on natural, renewable materials and can be derived from many cellulose sources including trees and other fibrous cellulose plants such as flax and cotton that already have a substantial industrial base for their collection and processing. Second, their base material, cellulose, is also a product that has widely dispersed applications from paper and rayon through to cellulose additives in food, cosmetics, and so on. It is widely used and is recognized to have very little or no inherent human toxicity. The monograph is also important because it presents a new approach in providing the base of technical information required for assessing the potential value of new products or processes based on cellulose nanocrystals. Innovation in nanotechnology offers a vast spectrum of potential applications which each need to be assessed for their potential as well as their market value. The challenge faced by innovators is the assessment of possible new innovations in a world market, a process that needs the base of technical information in a form that facilitates such assessment. The monograph, focused on cellulose nanocrystals, provides such an in‐depth and detailed information base and can be seen as a model for the characterisation of nanomaterials with a broad spectrum of potential applications. The monograph takes us through the full spectrum of technical information that is the base upon which the potential of cellulose nanocrystals is built. It goes from perspectives on the importance and value of nanotechnology, the nanostructure and self‐assembly in cellulosics, the hydrolytic extraction of cellulose nanocrystals, and the morphological characteristics of cellulose nanocrystals to finally the ­applications of this material. In bringing this information forward, Dr. Hamad takes us systematically into a much greater detailed depth than other treatments of  cellulosic nanomaterials. This is critical since, in doing so, he provides the basic  information for others to assess the potential of cellulose nanocrystals in ­applications of interest.

Foreword   xvii

This approach sets the monograph apart from other work and, as already s­ uggested, in many ways establishes it as a model for presenting the characterization of nanomaterials and, more generally, nanotechnology. Nanotechnology is an enabling technology. It is showing progressively more and more potential across the application of enhanced technological knowledge through most, if not all, industrial sectors and into areas of sociological potential. Much of what is written about nanotechnology and its potentially unique contributions provides examples to bolster that perspective. This approach raises the interest in nanotechnology across all of the key communities in innovation from the scientific community, the industrialists, government policy, and public awareness. This positioning of ­nanotechnology is critical. However, from the perspective of innovators who are focused on specific ­potential applications, it is significantly lacking in that it does not provide the core, detailed information that would allow them to assess the potential value of individual applications. The monograph sets out to do precisely that for cellulose nanocrystals, and it will be an essential handbook as we go from early potential applications through the subsequent generations of greater technology‐added value. Chapter 5 of the monograph presents a focused approach to this. It not only draws out the key characteristics that underlie potential applications in a very broad spectrum of domains and are provided in the earlier chapters, but it also builds on this base knowledge and explains how the assessment of the potential of the characteristics can be broken down for specific cases. Clive Willis, PhD Vice President—Research (1993–1997), National Research Council of Canada (NRC) Director General (2003–2005), NanoQuébec Convenor for Group 1, Terminology and Nomenclature, ISO Technical Committee 229 on Nanotechnology

Prologue Cellulose, the most abundant biopolymer on Earth, has had decades of rigorous research leading to successful and remarkable developments. Paper, exceptionally important for humankind, for well over a millennium, both in the development of tangible goods and in intangible realms such as communication and knowledge, is a well-known example. Another widely used cellulosic material has been microcrystalline cellulose—discovered by the Canadian-American chemist Orlando A. Battista more than six decades ago—with applications in food, paints and pharmaceuticals. All cellulosic materials to date have, however, merely served as a passive substrate or filler for the functional component(s) in a variety of applications. Considering the bioavailability and societal relevance of cellulose, turning this renewable resource into an active material is a vital step towards sustainability. Cellulose nanocrystals (CNC) are obtained from the controlled acid hydrolysis of biomass such as plants, fungi, bacteria, and marine animals. They are arguably the first sustainable nanomaterial, derived from renewable resources, with the potential to advancing active materials and structures. Cellulose nanocrystals are charged nanoparticles capable of self-assembly, and possess unique optical and electromagnetic properties originating from their ability to form chiral nematic organization under the influence of the Earth’s magnet. The liquid crystalline feature of these nanocrystals above a critical concentration in aqueous suspensions— first unravelled by the Canadian scientist Robert H. Marchessault in the 1950s—and the subsequent realization that the chiral nematic organization of these nanocrystals could be preserved in the solid state, offer significant promise for developing a new generation of sustainable photonics and optoelectronics. While basic knowledge pertaining to the hydrolytic extraction of cellulose nanocrystals is decadesold, CNC-inspired conceptual development and design of new functional and active materials and structures with potential applications in bio-sensing, optics, functional membranes, chiral separation and tissue engineering—to name a few— could only become possible as a result of the multidisciplinary approach nanoscience and nanotechnology have successfully managed to bring together.

Prologue   xix

This monograph aims to tell this story in detail, and begins with a vision for applying nanoscience and nanotechnology towards sustainable, socially-responsible material development (Chapter 1). Chapter 2 offers basic insights into the assembly and structure of cellulosic fibers—an abundant and economic source for these nanocrystals. However, cellulose only exists in combination with other chemicals and polymers in plants or marine animals; consequently, efficient extraction is a critical processing step. Chapter 3 systematically deals with the mechanics of hydrolytic extraction of these nanocrystals, whereas Chapter 4 extensively presents the morphological, solid-state, photonic, rheological and thermal properties of cellulose nanocrystals. We conclude with a fairly comprehensive exposé of the underlying science governing the development, and characterization, of improved as well as novel CNC-based material and structure platforms—spanning polymer composites, gels, bio-inspired photonic materials, CNC-templated sensors and actuators, flexible electronics and applications in biomedicine and pharmaceuticals (Chapter 5). The final chapter also offers a critique of the environmental, health and safety considerations of cellulose nanocrystals. Writing a monograph on a fast-evolving topic is a challenging, but rewarding, task. It is hoped the reader will find Cellulose Nanocrystals: Properties, Production and Applications valuable, current and comprehensive. I am indebted to Dr Clive Willis, who kindly wrote the Foreword and offered critical commentary on an earlier version of this monograph. His support for cellulose nanocrystals R&D over the years has been exemplary and refreshing. I extend my gratitude to colleagues at FPInnovations, CelluForce Inc. and UBC, and to my post-docs, graduate and undergraduate students for their critical engagement and dialogue throughout the years. This project would not have seen the light of day without continued, remarkable support and encouragement by Mrs. Sarah Higginbotham, Commissioning Editor at Wiley. My sincere thanks also go to the editorial staff at Wiley, Sarah Keegan, Kelvin Matthews, Rebecca Ralf, Karthika Sridharan and Emma Strickland, whose tireless dedication to ensuring an efficient and professional production of this monograph is second to none. Last, but not least, I am grateful to Professor Christian V. Stevens for suggesting this monograph to be part of the Wiley Series in Renewable Resources, and to the anonymous reviewers who offered insightful commentary on earlier drafts. Wadood Y. Hamad Vancouver, Canada November 2016

1 New Frontiers for Material Development and the Challenge of Nanotechnology 1.1  Perspectives on Nanotechnology Richard Feynman, the late prominent physicist and Nobel laureate, was perhaps the first to articulate, in a classic lecture delivered more than half a century ago,1 There’s Plenty of Room at the Bottom, a revolutionary vision of a powerful and general nanotechnology, based on nanomachines that are built with atom‐by‐atom control, promising great opportunities and, if abused, great dangers. The term “nanotechnology”2 as applied to the Feynman vision was (re)introduced in the mid‐1980s by K. Eric Drexler, author of Engines of Creation: The Coming Era of Nanotechnology. Many, vastly broadened definitions of nanotechnology ensued; the Feynman vision was muddied over the years to come and, at times, reduced to a rhetorical buzzword by many practitioners and laypersons alike. A great debate took place, at the turn of the twenty‐first century,3 between the Nobel laureate Richard Smalley and Drexler over the meaning, possibilities, and challenges of nanotechnology. Drexler stated his grand, but straightforward, vision of nanotechnology in Engines of Creation: Since the matter is discrete, we will, at some ­juncture, be able to consistently and reliably control the position of its constituents and build structures atom by atom. This led to Drexler’s pronouncement that “nanoassemblers” could build things step by step and ultimately self‐replicate— much like macroscopic assembly lines.4 Nanotechnology, notably over the past decade, began to slowly creep into ­popular culture and was somewhat influenced by Drexler’s view, which effectively

Cellulose Nanocrystals: Properties, Production, and Applications, First Edition. Wadood Y. Hamad. © 2017 John Wiley & Sons Ltd. Published 2017 by John Wiley & Sons Ltd.

2   Cellulose Nanocrystals

morphed into the realm of science fiction. Understandably, however, scientists always viewed self‐replicating nanorobots with suspicious eyes and were rather uneasy with the extrapolations that followed. Dorian, the British novelist Will Self’s modern reworking of Oscar Wilde’s classic, The Picture of Dorian Gray, is but one example of the unsavory interpretations of nanotechnology. In one scene, set in a dingy industrial building on the outskirts of Los Angeles, we find Dorian Gray and his friends looking across rows of Dewar flasks, in which the heads and bodies of the dead are kept frozen, waiting for the day when medical science has advanced far enough to cure their ailments. Although one of Dorian’s friends doubts that technology will ever be able to repair the damage caused when the body parts are thawed out, another friend—Fergus the Ferret—is more optimistic. • Course they will, the Ferret yawned; Dorian says they’ll do it with nannywhatsit, little robot thingies—isn’t that it, Dorian? • Nanotechnology, Fergus—you’re quite right; they’ll have tiny hyperintelligent robots working in concert to repair our damaged bodies.

Richard Smalley’s Scientific American article in 2001 came as a powerful renunciation of nanotechnology as science fiction. Smalley introduced the “fat fingers” and “sticky fingers” argument to demonstrate how it is physically impossible to control chemical reactions atom by atom and build molecular assemblers as Drexler had envisaged. Smalley clearly stated, on more than one occasion, that nanorobots would never see the light of day, and should not be a concern for aspiring young scientists, who should instead carefully and diligently address the palpable ­complexities, risks, and challenges of the real world. Smalley’s cardinal message served to assure scientists and laypersons that nanotechnology should not be ­perceived as a science fiction enterprise and, thus, aligned most of the pure and applied science community behind him.5 Perhaps, the briefest and deepest message would be to take inspiration from nature—with its overarching simplicity, yet ­dialectical complexity, at various levels. Nanoscience, where physics, chemistry, biology, and materials science converge, deals with the manipulation and characterization of matter at molecular to micron scale. Nanotechnology is the emerging engineering discipline that applies nanoscience to create products. Because of their size, nanomaterials have the ability to impart novel and/or significantly improved physical, chemical, biological, and electronic properties. While the chemistry and physics of simple atoms and molecules is fairly well understood, predictable, and no longer considered overly complex, serious attempts to bridge across the length scales from nano to macro remain a major challenge and will occupy researchers and scientists for years ahead. It is apposite to note, however, that many successes that are currently attributed to nanotechnology are in fact the result of years of research into conventional fields like materials or colloids sciences. The material challenges in nanotechnology may be subdivided into two groups: basic or fundamental and applied or application‐related. Process–structure–­ property relations need to be developed in order to enable manufacturing and

New Frontiers for Material Development and the Challenge of Nanotechnology   3

end‐use performance predictions. The applied—or application‐related—challenge will focus on how to scale up laboratory materials into industrial‐scale production. As such, there are intricate interrelationships between fabrication, materials design, implementation, and functionality that are critical to any rigorous research and development activity in nanomaterials and nanotechnology. Improving the properties of many materials by controlling their nanoscale structure would entail a developmental process.6 The challenge ahead will, however, be to move beyond materials that have been redesigned at the nanoscale to actual nanoscale devices of a specific functionality, as in devices that can sense the environment, process information, or convert energy from one form to another. Examples of ongoing research cover nanoscale sensors to detect environmental contaminants or ­biochemicals.7 Nanotechnology will inevitably impact established processing/ manufacturing industries, as well as inspire new ones.

1.2  Societal Ramifications of Nanotechnology The potential convergence of technologies enabled by nanoscience may be regarded as the unleashing of the widest, deepest, and most significant new technological wave seen for at least 500 years—a technological platform, whose potential for social change and/or disruption may surpass that of electricity, computing, or genetic engineering. Technology discloses our mode of dealing with nature and the immediate process of production by which humankind sustains life. Technology also critically lays bare the mode of foundation of (modern) human social relations and of the mental conceptions that ensue.8 Suis generis, science has a critical social role to play and is necessarily required to have public accountability—since the public, via state organizations, is the primary funder of scientific research in academia and research institutes.9 Scientists have, for instance, been endeavoring to mimic nature and heed important lessons from biological life that has been optimized by billions of years of evolution. Cell biology, for instance, makes extensive use of the principles of self‐assembly and molecular shape change. These principles exploit the special physics of the nanoworld, namely, the ubiquitous Brownian motion and strong surface forces. Thus, a new developmental process—termed bionanotechnology—may be instituted, which makes use of biological design paradigms and soft materials—for example, proteins, polysaccharides, and so on. In essence, bionanotechnology involves the stripping down and then partially reassembling a very complex and only partially understood system to obtain something else with a new ­functionality. For instance, the self‐assembly properties of DNA can be used to create quite complicated nanoscale structures and devices. As we learn more about how bionanotechnology works, we can use some of the design methods of biology to ­synthesize materials, that is, biomimetic nanotechnology. When applied to human social life, materialism—philosophically speaking— can explain social consciousness as the outcome of social being, and allow us to comprehend the world not as a complex of ready‐made things, but as a complex

4   Cellulose Nanocrystals

of processes, in which dialectic relations define nothing as absolute, final, or sacred. This reveals the transitory character of everything and in everything, that is, innate stochasticity or randomness. To live, therefore, is to shape each other in this diverse, decentered but common activity from which we—human beings— cannot separate ourselves any more than we can remove ourselves from our nerves, muscles, bones, and internal organs. Conscious thought is only one part of this activity; it emerges within the context of subpersonal cognition. Instead of interpreting the raw data of a world outside of our thought, it draws from and depends on the subpersonal, which provides it all it can ever know. Human subjectivity, in the sense of agency, is thus a social, common, decentered, and transpersonal subject—an intersubjective subject. In contrast, the subject of conscious experience is an individual and apparently isolated subject. The confusion of these two is commonplace in the modern (industrial) world, but it is a deeply and, arguably, dangerously misleading error. It leads to the specious isolation of the individual and to the alienated reappearance of the thought of the body as the omniscient and demanding social world. There may be a gap—or misconception—between what technology promises and what it actually delivers, which has been further complicated by the c­ ommercial race to put nanotech products into the market place. Against the backdrop of increasing research into, and development of, nanomaterials and n­ anotechnology, risk assessment models and toxicology studies have to be ­committed to by governmental, academic, industrial, and commercial outfits. For  research and development (R&D) workers and the public at large, health, safety, and environmental considerations are understandably paramount.10 Regulations controlling the introduction of new materials into the workplace and the environment are—rightly—much stricter now than in the past, and we should appreciate that the properties of materials depend on their physical manifestation as well as their chemical content. But we do not have to assume that all nanoscale materials are inherently dangerous. Imposing a blanket ban would be absurd and unenforceable, simply because we have enough experience of many forms of nanoparticles to know they are safe. Milk, for example, is full of nanoscale casein particles. Moreover, patenting technology necessarily becomes an exercise in power, and history has shown that technological waves, at least initially, destabilize the lives of especially the poor and vulnerable, and do not necessarily trickle down. More than a century and a quarter after Edison invented the light bulb, a quarter of the world’s population (roughly 1.75 billion) still does not have access to electricity. Such technological gaps exacerbate the existing inequalities of power. Besides, the fear of loss of control is a (legitimate) primal fear about any technology. The prospect, for instance, of cheap powerful computing enabled by nanotechnology, when combined with mass storage and automated image processing, could be considered a totalitarian’s dream and libertarian’s nightmare. The success of any new technology critically depends on public acceptance: the (potential) benefits must clearly outweigh the (potential) risks. Thus, to overcome

New Frontiers for Material Development and the Challenge of Nanotechnology   5

misconceptions on the perceived meaning of these purportedly powerful and useful technological advances, practitioners in the field—academic, government, and ­private—need to lead a concerted effort to become transparent and educative. Public opinion is based on trust, and, in this respect, it depends on scientists and managers reporting accurate and reliable data, free from the interference of external pressure. Science and technology have offered humans significant progress over time, while they certainly caused significant death and misery to untold ­numbers too. However, it would be defeatist to approach the subject with cynicism and distrust. What is needed is a strong dose of public education and involvement at the strategic level, while it would be unrealistic, as well as counterproductive, to expect lay involvement in the research decision‐making process. The socioeconomic, environmental, and political implications of science and technology ­configure (or preconfigure) many societal applications, and as such, the question of  democratic accountability necessarily figures in this discussion—a hugely ­complex area worthy of elaborate, and separate, analysis.

1.3  Bio‐inspired Material Development: The Case for Cellulose Nanocrystals Cellulose is arguably the most abundant biopolymer available on our planet, and is derived from biomass, such as plants, fungi, bacteria, and marine animals. It is a polysaccharide, whose chemical formula is [C6H10O5]n, where n = 10,000–15,000 depending on the source material. Cellulose is believed to comprise a linear chain with hundreds to thousands of β‐1,4 linked d‐glucose units, whose repeat segment is normally taken to be a dimer of glucose called “cellobiose.” The structures of cellulose have been determined using synchrotron X‐ray and neutron diffraction studies assuming each cellulose chain has twofold symmetry about the glycosidic linkages (French and Johnson 2009; Nishiyama 2009). Parallel stacking of multiple cellulose chains within a single crystal is believed to be promoted by van der Waals and intermolecular hydrogen bonds (Nishiyama et al. 2008; Wada et al. 2008). Typically, individual cellulose molecules form larger units known as elementary fibrils or protofibrils, which are packed into larger units called “microfibrils” and assembled into the familiar cellulose fibers (Frey‐Wyssling 1954).11 Within an individual cellulose elementary fibril, cellulose molecular chains are hierarchically organized in crystalline and amorphous regions. The cellulose chains are firmly held—in the fibril’s crystalline region— by a hydrogen bond network formed between surface hydrogen and oxygen molecules, intra and intermolecularly. This hydrogen bond network is also ­ believed to be responsible for the anisotropy of the elastic properties of cellulose, where the Young’s modulus and Poisson’s ratio show crystallographic dependence (Dri et al. 2013). Based on ab initio density functional theory with semiempirical correction for van der Waals’ interactions, Dri et al. (2013) demonstrated that the largest Young’s modulus (206 GPa) was found to be aligned with the axis

6   Cellulose Nanocrystals

where covalent bonds dominated the mechanical response of the cellulose crystal; the next greatest value (98 GPa) for Young’s modulus was associated with the direction perpendicular to the cellulose chain axis, and the lowest value (19 GPa) was computed along the direction perpendicular to the previous two—where weak van der Waals’ interactions dominate the mechanical response.12 Cellulose‐based products with specific end‐use requirements have long been developed through a judicious selection of fiber properties, whereby cellulose fibers are processed for many different requirements, for example, super‐absorbent hygiene products, ultrasoft tissue products, or ultra‐lightweight‐coated paper. The competitiveness of lignocellulosic materials for the twenty‐first century, however, rests on associating product development with the concept of fiber engineering and selective design, by using new technical tools to manipulate and restructure these bio‐fibers (and their constituents) in order to add functionality. For instance, isolation of the crystallites can yield individual elements, the cellulose nanocrystals (CNCs),13 of excellent physical attributes approaching those of perfect crystals. Table 1.1 compares some key physical attributes of CNCs, microcrystalline cellulose (MCC), and cellulose nanofibrils (CNFs) in relation to the raw starting material, kraft softwood fibers. Both CNCs and MCCs are produced using acid hydrolysis; however, nuanced processing differences lead to very different products. Moreover, CNFs are nanoscaled structures produced primarily using mechanical energy, with a suitable combination of enzymatic and/or chemical treatment—essentially to reduce energy input.14 The large surface area, charged surfaces, high stiffness, and strength of CNCs provide them, for instance, with a strong potential as rheology modifiers, nucleating agents, or high‐performance reinforcement scaffolds in polymers, gels, and emulsions, and can impact a wide variety of industrial and consumer applications. But more critically, CNCs have unique chiral nematic structures that render them suitable for producing color without dye—or structural color—and for templating advanced inorganic materials with long‐range chirality.15 CNCs are not dispersible in many organic solvents but can form colloidal suspensions in water. The stability of these suspensions depends on the dimensions of the crystallites, size polydispersity, and surface charge. As we will show in later chapters, CNCs prepared by sulfuric acid hydrolysis can form more stable suspensions than those obtained from hydrochloric acid hydrolysis, because the former produces negatively charged crystallites through the sulfate esters introduced during hydrolysis (Araki et al. 1998). The surface sulfate ester content of CNCs can be quantified by conductometric titration against diluted sodium hydroxide or via elemental analysis (Abitbol et al. 2013). If the concentration is high enough, well‐ dispersed CNC suspensions have birefringent domains when observed through two crossed polarizers (Marchessault et al. 1959). CNCs can form a chiral nematic‐ ordered phase above a critical concentration (Revol et al. 1992), and the ability to form such a phase is dependent on the acid employed for the hydrolysis. CNCs hydrolyzed in sulfuric or phosphoric acid can easily form a chiral nematic phase, whereas those hydrolyzed using hydrochloric acid cannot (Revol et al. 1998).

Network Particulate Spindlel Hollow tube

15–1,000a 1,000–100,000g 5–20m 1,500,000p

Diameter (nm) 15–100b