Cellulose Nanocrystals

Wiley Series in

Renewable Resources

Series EditorChristian V. Stevens—Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium

Titles in the SeriesWood Modification—Chemical, Thermal and Other ProcessesCallum A. S. Hill

Renewables—Based Technology—Sustainability AssessmentJo Dewulf and Herman Van Langenhove

Introduction to Chemicals from BiomassJames H. Clark and Fabien E. I. Deswarte

BiofuelsWim Soetaert and Erick Vandamme

Handbook of Natural ColorantsThomas Bechtold and Rita Mussak

Surfactants from Renewable ResourcesMikael Kjellin and Ingegard Johansson

Industrial Application of Natural Fibres—Structure, Properties and Technical ApplicationsJorg Mussig

Thermochemical Processing of Biomass—Conversion into Fuels, Chemicals and PowerRobert C. Brown

Biorefinery Co‐Products: Phytochemicals, Primary Metabolites and Value‐Added Biomass ProcessingChantal Bergeron, Danielle Julie Carrier, and Shri Ramaswamy

Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and ChemicalsCharles E. Wyman

Bio‐Based Plastics: Materials and ApplicationsStephan Kabasci

Introduction to Wood and Natural Fiber CompositesDouglas Stokke, Qinglin Wu, and Guangping Han

Cellulosic Energy Cropping SystemsDouglas L. Karlen

Introduction to Chemicals from Biomass, Second EditionJames Clark and Fabien Deswarte

Lignin and Lignans as Renewable Raw Materials: Chemistry, Technology and ApplicationsFrancisco G. Calvo‐Flores, Jose A. Dobado, Joaquin Isac‐Garcia, and Francisco J. Martin‐Martinez

Sustainability Assessment of Renewables‐Based Products: Methods and Case StudiesJo Dewulf, Steven De Meester, and Rodrigo Alvarenga

Forthcoming TitlesBiorefinery of Inorganics: Recovering Mineral Nutrients from Biomass and Organic WasteErik Meers and Gerard Velthof

Bio‐Based SolventsFrancois Jerome and Rafael Luque

Fuels, Chemicals and Materials from the Oceans and Aquatic SourcesFrancesca M. Kerton and Ning Yan

Nanoporous Catalysts for Biomass ConversionFeng‐Shou Xiao

Cellulose NanocrystalsProperties, Production,

and Applications

WADooD Y. HAMADCellulosic Biomaterials, FPInnovations, Vancouver, Canada

Department of Chemistry, University of British Columbia, Vancouver, Canada

This edition first published 2017© 2017 John Wiley & Sons Ltd

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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–dc23LC 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

Series Preface xiii

Foreword xv

Prologue xviii

1 New Frontiers for Material Development and the Challenge of Nanotechnology 11.1 Perspectives on Nanotechnology 11.2 Societal Ramifications of Nanotechnology 31.3 Bio‐inspired Material Development: The Case for Cellulose

Nanocrystals 51.4 A Glance at Bio‐inspired Hierarchical Materials 91.5 Concluding Thoughts 13Notes 13

2 Assembly and Structure in Native Cellulosic Fibers 162.1 Physical and Chemical Characteristics of the Cellulose Molecule 16

2.1.1 The Origin of Cellulose 162.1.2 The Chemistry of Cellulose 182.1.3 The Physics of Cellulose 20

2.2 Morphology and Structure of Native Cellulosic Fibers 222.3 Physical and Mechanical Properties of Native Cellulosic Fibers 25

2.3.1 Anisotropy of the Fiber Cell Wall 252.3.2 Mechanical Properties of Cellulosic Fibers 29

Notes 32

3 Hydrolytic Extraction of Cellulose Nanocrystals 333.1 Introduction 333.2 The Liberation of CNCs Using Acid Hydrolysis 35

Contents

x Contents

3.3 Reaction Kinetics of CNC Extraction 383.3.1 Effects of H

2SO

4 Hydrolysis Conditions and 

Sulfation on CNC Yield of Extraction 383.3.2 H

2SO

4 Hydrolysis Reproducibility and 

Yield Optimization 463.3.3 Commentary on Hydrochloric Acid‐Hydrolyzed CNCs 483.3.4 CNC Stability and Post H

2SO

4‐Hydrolysis Aging 49

3.4 Processing Considerations for Sustainable and Economical Manufacture of CNCs 50

3.5 Micro/Nano Cellulosics Other Than CNCs 533.5.1 Microfibrillated Cellulose 533.5.2 Microcrystalline Cellulose 573.5.3 Bacterial Cellulose 60

Notes 62

4 Properties of Cellulose Nanocrystals 654.1 Morphological Characteristics of CNCs 654.2 Structural Organization of CNCs 684.3 Solid‐State Characteristics of CNCs 74

4.3.1 X‐Ray Diffractometric Analysis of CNCs 764.3.2 CNCs Phase Structure Based on SS‐NMR 814.3.3 Concluding Remarks 87

4.4 CNCs Chiral Nematic Phase Properties 874.4.1 Ionic Strength Effect on Chiral Phase Separation 884.4.2 Temperature Effect on Chiral Phase Separation 914.4.3 Suspension Concentration Effect on Chiral

Phase Separation 924.4.4 Magnetic Field Effect on Chiral Phase Separation 944.4.5 Sonication Effect on Physicochemical Properties 94

4.5 Shear Rheology of CNC Aqueous Suspensions 954.5.1 Basic Rheological Behavior of CNC

Aqueous Suspensions 954.5.2 Sonication Effects on the Microstructure and

Rheological Properties of CNCs Suspensions 984.5.3 Concentration Effects on the Microstructure and

Rheological Properties of CNC Suspensions 1004.5.4 Temperature Effects on the Microstructure and

Rheological Properties of CNC Suspensions 1064.5.5 CNCs Surface Charge Effects on the Microstructure and

Rheological Properties of CNC Suspensions 1124.5.6 Ionic Strength Effects on the Microstructure and

Rheological Properties of CNC Suspensions 118

Contents xi

4.5.7 Aging and Yielding Characteristics of CNC Suspensions 123

4.5.8 Concluding Remarks 1284.6 Thermal Stability of CNCs 129Notes 134

5 Applications of Cellulose Nanocrystals 1385.1 Prelude 1385.2 The Reinforcing Potential of CNCs in Polymer

Nanocomposites 1405.2.1 Basic Concepts in Composites 1405.2.2 Generic Methods for Surface Functionalization 1425.2.3 Why CNCs for Reinforcement? 1475.2.4 Performance of CNCs in Compatible Polymer Systems 1505.2.5 Nanocomposites Prepared by Postpolymerization

Compounding of CNCs and Thermoplastic Polymers 1545.2.6 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 1815.3 CNC‐Stabilized Emulsions, Gels, and Hydrogels 184

5.3.1 Pickering Emulsions 1845.3.2 High Internal Phase Emulsions 1875.3.3 pH‐Responsive Gels and Flocculants 1895.3.4 Hydrogels 190

5.4 Controlled Self‐Assembly of Functional Cellulosic Materials 1945.4.1 Flexible CNC Films with Tunable Optical Properties 1945.4.2 Mesoporous Photonic Cellulose Films 197

5.5 Toward Bio‐inspired Photonic and Electronic Materials 2025.5.1 Mesoporous Photonic Materials from Cellulose

Nanomaterial Liquid Crystal Templates 2025.5.2 Actuators and Sensors 2175.5.3 Sustainable Electronics Based on CNCs 2255.5.4 Conclusions and Outlook 232

5.6 CNCs in Biomedicine and Pharmaceuticals 2335.7 Environmental, Health, and Safety Considerations of CNCs 2355.8 Perspectives and Challenges 238Notes 239

xii Contents

Epilogue—The Never‐Ending Evolution of Scientific Insights 248

Bibliography 252

Subject Index 288

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, pharma-ceutical, 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 alterna-tives 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

Series Preface

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 renewa-bles 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. StevensFaculty of Bioscience Engineering

Ghent University, BelgiumSeries Editor “Renewable Resources”

June 2005

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 characteriza-tion of the nanocrystals, and the assessment of their potential application in indus-trial products and processes. It is a timely publication because cellulose nanocrystals are a key member of the family of cellulosic nanomaterials which are rapidly mov-ing 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 addi-tion, 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 inter-national 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

Foreword

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 nanoma-terials 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 character-istics, 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, cosmet-ics, 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 provid-ing the base of technical information required for assessing the potential value of new products or processes based on cellulose nanocrystals. Innovation in nano-technology 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 charac-terisation 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 suggested, in many ways establishes it as a model for presenting the characteriza-tion 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, PhDVice President—Research (1993–1997),

National Research Council of Canada (NRC)Director General (2003–2005),

NanoQuébecConvenor 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 micro-crystalline cellulose—discovered by the Canadian-American chemist Orlando A. Battista more than six decades ago—with applications in food, paints and pharma-ceuticals. 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 fea-ture 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 nanocrys-tals could be preserved in the solid state, offer significant promise for developing a new generation of sustainable photonics and optoelectronics. While basic knowl-edge pertaining to the hydrolytic extraction of cellulose nanocrystals is decades-old, 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 nanosci-ence 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-responsi-ble 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 extrac-tion is a critical processing step. Chapter 3 systematically deals with the mechanics of hydrolytic extraction of these nanocrystals, whereas Chapter 4 extensively pre-sents 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 col-leagues at FPInnovations, CelluForce Inc. and UBC, and to my post-docs, gradu-ate 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 profes-sional 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. HamadVancouver, Canada

November 2016

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

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 nanotech-nology 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 constitu-ents 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

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 technol-ogy 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 renuncia-tion 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 con-verge, 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 abil-ity 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 conven-tional 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 produc-tion. 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 tech-nological wave seen for at least 500 years—a technological platform, whose potential for social change and/or disruption may surpass that of electricity, com-puting, 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 pri-mary 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 insti-tuted, 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 biona-notechnology 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 sub-jectivity, in the sense of agency, is thus a social, common, decentered, and transpersonal subject—an intersubjective subject. In contrast, the subject of con-scious 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 commercial race to put nanotech products into the market place. Against the backdrop of increas-ing research into, and development of, nanomaterials and nanotechnology, risk assessment models and toxicology studies have to be committed to by governmen-tal, academic, industrial, and commercial outfits. For  research and development (R&D) workers and the public at large, health, safety, and environmental considera-tions 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 exter-nal 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 socioeco-nomic, 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 [C

6H

10O

5]

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, cellu-lose 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 depend-ence (Dri et al. 2013). Based on ab initio density functional theory with semiem-pirical 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 fib-ers 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 nanocrys-tals (CNCs),13 of excellent physical attributes approaching those of perfect crys-tals. 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 prod-ucts. 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 materi-als with long‐range chirality.15

CNCs are not dispersible in many organic solvents but can form colloidal sus-pensions 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 suspen-sions than those obtained from hydrochloric acid hydrolysis, because the former produces negatively charged crystallites through the sulfate esters introduced dur-ing 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).

Tabl

e 1.

1 Ty

pica

l phy

sica

l pro

pert

ies

of d

iffer

ent f

orm

s of

 cel

lulo

sic

mic

ro/n

ano

mat

eria

ls a

nd s

truc

ture

s ob

tain

ed u

sing

dis

tinct

ly d

iffer

ent

proc

essi

ng—

mec

hani

cal,

chem

ical

, and

/or

enzy

mat

ic—

of th

e sa

me

raw

mat

eria

l, so

ftwoo

d kr

aft p

ulp

fiber

s.

Mor

phol

ogy

Dia

met

er (n

m)

Asp

ect R

atio

(L

engt

h/W

idth

)M

odul

us (G

Pa)

Spec

ific

Surf

ace

Are

a (m

2 /g)

CN

FsN

etw

ork

15–1

,000

a15

–100

b10

–13c /2

9–36

d~

7e /29–

202f

MC

CPa

rtic

ulat

e1,

000–

100,

000g

<5h

5–9i /~

25j

~1–

20k

CN

Cs

Spin

dlel

5–20

m~

20–1

00m

143–

150n

400o

Softw

ood

kraf

t pul

pH

ollo

w tu

be1,

500,

000p

~50

p20

p~

4p

a Mea

sure

d on

indi

vidu

al fi

brils

(Tur

bak

et a

l. 19

83; C

hakr

abor

ty e

t al.

2005

; Hen

riks

son

et a

l. 20

07).

b Mea

sure

d on

indi

vidu

al fi

brils

(Cha

krab

orty

et a

l. 20

05; H

enri

ksso

n et

al.

2007

, 200

8).

c Mea

sure

d on

she

ets

of C

NFs

usi

ng te

nsile

test

ing

(Hen

riks

son

et a

l. 20

08).

d Mea

sure

d on

indi

vidu

al fi

brils

(Tan

pich

ai e

t al.

2012

a).

e BET

ana

lysi

s on

lyop

hiliz

ed C

NF

or m

icro

fibri

llate

d ce

llulo

se (M

FC) (

Lu e

t al.

2008

).f D

eter

min

ed o

n C

NF

or M

FC s

uspe

nsio

ns b

y C

ongo

red

ads

orpt

ion

met

hod

(Spe

nce

et a

l. 20

10).

g Afte

r M

athe

w e

t al.

(200

5), L

uukk

onen

et a

l. (1

999)

, Bor

ges

et a

l. (2

004)

, and

Ard

izzo

ne e

t al.

(199

9).

h Afte

r B

orge

s et

al.

(200

4).

i Mea

sure

d on

com

pres

sed

bulk

MC

C (H

anco

ck e

t al.

2000

).j M

easu

red

on in

divi

dual

MC

C p

artic

les

by fo

llow

ing

the

shift

of t

he R

aman

‐sen

sitiv

e ba

nd(s

) with

incr

easi

ng a

pplie

d st

rain

(Eic

hhor

n an

d Yo

ung

2004

).k A

fter

Luuk

kone

n et

al.

(199

9).

l Geo

met

rica

lly,

CN

Cs

are

spin

dle‐

like—

tape

ring

at

both

end

s an

d re

lativ

ely

thic

ker

in t

he m

iddl

e. H

owev

er,

they

are

ofte

n ap

prox

imat

ed t

o be

rod

s or

, in

the

cas

e of

hi

gh‐a

spec

t rat

io tu

nica

te‐d

eriv

ed C

NC

s, a

s w

hisk

ers.

m A

fter A

zizi

Sam

ir e

t al.

(200

5a).

n Afte

r Št

urco

vá e

t al.

(200

5), I

wam

oto

et a

l. (2

009)

, and

Sak

urad

a an

d N

ukus

hina

(196

2).

o Unp

ublis

hed

resu

lts fr

om th

e au

thor

s’ la

bora

tory

bas

ed o

n SE

M e

valu

atio

n of

~10

00 s

ampl

es.

p Afte

r H

amad

(200

2).

CN

Cs,

cel

lulo

se n

anoc

ryst

als;

CN

Fs, c

ellu

lose

nan

ofib

rils

; and

MC

C, m

icro

crys

talli

ne c

ellu

lose

.

8 Cellulose Nanocrystals

CNCs uniquely share with many natural materials the ability to possess photonic properties. Evolutionary biology has plentiful examples of animals and plants depicting bright, iridescent color as a result of a physical phenomenon called, structural color, and not owing to the presence of pigments or dyes. Structural color is a supramolecular phenomenon that emanates from light scatter-ing from a material’s nanostructures in such a way that certain wavelengths get reflected and amplified through constructive interference. This is distinctly differ-ent from dyes, which achieve color from their molecules’ electrons. Unlike dyes or pigments, structural colors resist fading—which is an attractive proposition for potentially synthesizing materials for ink and paint applications possessing fade‐resistant structural colors.

Vignolini et al. (2012) have recently presented a striking example of multilayer‐based strong iridescent coloration in plants—in the fruit of Pollia condensata.16 They showed that the color was caused by Bragg reflection of helicoidally stacked cellulose microfibrils that form multilayers in the cell walls of the epicarp, and that the reflected color differed from cell to cell, as the layer thicknesses in the multi-layer stack varied, giving the fruit a striking pixelated or pointillist appearance (Figure 1.1). Their systematic study carefully revealed that the multilayers uniquely formed with both helicoidicities, and the reflected light from every epidermal cell was polarized circularly either to the left or to the right—a unique feature. Earlier publications have demonstrated that, for instance, Morpho butterflies (Zhu et al. 2009) and bird feathers (Noh et al. 2010) have evolved multilayer‐based photonic structures that are also able to generate colors using entirely distinct materials. Precious opal, a mineraloid,17 or a hydrated amorphous form of silica, is another example of naturally occurring materials exhibiting structural color. It is composed of silica spheres, roughly 150–300 nm in diameter, arranged in highly ordered fashion—in a hexagonal or cubic close‐packed lattice. While silica—like nanostructures in fish and butterfly scales, as well as bird feathers—is colorless,

Figure 1.1 Pollia condensata fruit, another natural material exhibiting structural color, that is, internal color produced via the interference and diffraction of light passing through innate, ordered nanostructures (right image) (Source: Courtesy of Dr. Silvia Vignolini, Cambridge University. Left photo credit to P. J. Rudall). (See insert for color representation of the figure.)