Nanocellulose E-Book
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- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Fachliteratur
- Sprache: Englisch
Comprehensively introduces readers to the production, modifications, and applications of nanocellulose
This book gives a thorough introduction to the structure, properties, surface modification, theory, mechanism of composites, and functional materials derived from nanocellulose. It also provides in-depth descriptions of plastics, composites, and functional nanomaterials specifically derived from cellulose nanocrystals, cellulose nanofibrils, and bacterial cellulose. It includes the most recent progress in developing a conceptual framework of nanocellulose, as well as its numerous applications in the design and manufacture of nanocomposites and functional nanomaterials. The book also looks at the relationship between structure and properties.
Featuring contributions from many noted experts in the field, Nanocellulose: From Fundamentals to Advanced Materials examines the current status of nanocomposites based on nanocelluloses. It covers surface modification of nanocellulose in the nanocomposites development; reinforcing mechanism of cellulose nanocrystals in nanocomposites; and advanced materials based on self-organization of cellulose nanocrystals. The book studies the role of cellulose nanofibrils in nanocomposites, as well as a potential application based on colloidal properties of cellulose nanocrystals. It also offers strategies to explore biomedical applications of nanocellulose.
- Provides comprehensive knowledge on the topic of nanocellulose, including the preparation, structure, properties, surface modification and strategy
- Covers new reports on the application of nanocellulose
- Summarizes three kinds of nanocellulose (cellulose nanocrystals, cellulose nanofibrils, and bacterial cellulose) and their production, modification, and applications
Nanocellulose: From Fundamentals to Advanced Materials is a useful resource for specialist researchers of chemistry, materials, and nanotechnology science, as well as for researchers and students of the subject.
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Veröffentlichungsjahr: 2019
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Table of Contents
Cover
Preface
Acknowledgments
1 Introduction to Nanocellulose
1.1 Introduction
1.2 Preparation of Nanocellulose
1.3 Surface Modification of Nanocellulose
1.4 Nanocellulose‐Based Materials and Applications
1.5 Conclusions and Prospects
References
2 Structure and Properties of Cellulose Nanocrystals
2.1 Introduction
2.2 Extraction of Cellulose Nanocrystals
2.3 Structures and Properties of Cellulose Nanocrystals
References
3 Structure and Properties of Cellulose Nanofibrils
3.1 Production of CNF
3.2 Features and Properties
3.3 Conclusion
References
4 Synthesis, Structure, and Properties of Bacterial Cellulose
4.1 Introduction
4.2 Biogenesis of Bacterial Cellulose
4.3 Structure and Exciting Features of Bacterial Cellulose
4.4 Production of Bacterial Cellulose: Synthesis Approaches
4.5 Additives to Enhance BC Production
4.6 Strategies Toward Low‐Cost BC Production
4.7 Conclusions and Future Prospects
Acknowledgment
References
5 Surface Chemistry of Nanocellulose
5.1 Brief Introduction to Nanocellulose Family
5.2 Surface Modification of Nanocellulose
5.3 Advanced Functional Modifications
References
6 Current Status of Nanocellulose‐Based Nanocomposites
6.1 Introduction
6.2 Cellulose Nanocrystal‐Filled Nanocomposites
6.3 Fibrillated Cellulose‐Filled Nanocomposites
6.4 Conclusion and Prospect
References
7 Reinforcing Mechanism of Cellulose Nanocrystals in Nanocomposites
7.1 Percolation Approach
7.2 Interfacial Behaviors Between Cellulose Nanocrystals and Matrix
7.3 Conclusions
References
8 Role of Cellulose Nanofibrils in Polymer Nanocomposites
8.1 Introduction
8.2 Characteristics of Cellulose Nanofibrils
8.3 Mechanical Properties of CNF Polymer Nanocomposites
8.4 Effects of Extrusion on Mechanical Properties of PE/CNF Nanocomposites
8.5 Effect of Fiber Size and Lignin Presence
8.6 Multifunctionality: Optical and Barrier Properties of CNF Nanocomposites
8.7 Outlooks in CNF Nanocomposites
References
9 Advanced Materials Based on Self‐assembly of Cellulose Nanocrystals
9.1 Self‐assembly Structure of CNCs
9.2 Self‐assembly Methods and Materials
9.3 Structural Adjustment of CNC Self‐assembly
9.4 Modifying Surface Chemical Structure of CNC
9.5 Properties of CNC Self‐assembly
9.6 Potential Applications
References
10 Potential Application Based on Colloidal Properties of Cellulose Nanocrystals
10.1 Colloidal Properties of CNC and Applications in Functional Materials
10.2 Nanocellulose for Paper and Packaging
10.3 Nanocellulose for Wood Coatings
References
11 Strategies to Explore Biomedical Application of Nanocellulose
11.1 Introduction
11.2 Research on Biological Toxicity of Nanocellulose
11.3 Application of Nanocellulose for Immobilization and Recognition of Biological Macromolecules
11.4 Application of Nanocellulose for Cell Imaging
11.5 Application of Nanocellulose for Cell Scaffolds
11.6 Application of Nanocellulose in Tissue Engineering
11.7 Application of Nanocellulose in Drug Carrier and Delivery
11.8 Application of Nanocellulose as Biomedical Materials
11.9 Summary
References
12 Application of Nanocellulose in Energy Materials and Devices
12.1 Introduction
12.2 Nanocellulose for Lithium Ion Batteries (LIBs)
12.3 Nanocellulose for Supercapacitors
12.4 Nanocellulose for Other Energy Devices
12.5 Conclusion and Outlook
References
13 Exploration of Other High‐Value Applications of Nanocellulose
13.1 Fire Resistant Materials
13.2 Thermal Insulation Materials
13.3 The Templated Materials
References
Index
End User License Agreement
List of Tables
Chapter 2
Table 2.1 The fundamental properties of CNCs from various sources obtained by di...
Table 2.2 Thermal properties of nanocrystals from different sources.
Table 2.3 Contact angles for water and total surface energy of CNCs derived from...
Chapter 3
Table 3.1 Cellulose nanofibrils derived from different sources.
Chapter 4
Table 4.1 Illustration of the
G. hansenii
PJK enzymes in the cell‐free extract inv...
Table 4.2 Production of BC in static and agitation cultures with a variety of BC...
Chapter 5
Table 5.1 Reactive conditions of adsorption of anionic, cationic, and nonionic s...
Table 5.2 Reactive conditions of sulfonation and sulfur contents for the prepare...
Table 5.3 Reactive conditions and grafting efficiency for the preparation of pol...
Table 5.4 Reactive conditions and grafting efficiency (GE %) for the surface gra...
Table 5.5 Reactive conditions and properties of various grafted polymeric chains...
Table 5.6 Reactive conditions and grafted molecules on the basis of the end hemi...
Table 5.7 Reactive conditions and optical spectrum of the fluorescent molecule m...
Chapter 6
Table 6.1 The nanocomposite processing methods and the CNC modification methods ...
Table 6.2 Effect of the CNC filler on rubber‐based nanocomposites.
Table 6.3 Mechanical properties and processing strategies of CNF‐filled composit...
Table 6.4 Recent research on CNF‐reinforced starch nanocomposites using differen...
Chapter 7
Table 7.1 Geometrical characteristics of some cellulose nanocrystals: average le...
Table 7.2 Parameters used for plotting Figure 7.5.
Table 7.3 Rubbery tensile storage modulus estimated at 0 °C (
E'
) and high te...
Chapter 8
Table 8.1 Bending properties of CNF‐based thermoset resin nanocomposites.
Chapter 10
Table 10.1 Water vapor permeability (WVP) and contact angle (CA) of CMC and CMC/...
Chapter 11
Table 11.1 Toxicological evaluations of nanocellulose.
Table 11.2 Surface immobilization of enzyme or protein on nanocellulose.
Table 11.3 Drug carrier systems based on nanocellulose.
Table 11.4 Some of the types of antimicrobial materials.
Chapter 13
Table 13.1 ORT (cm
3
/mm/m
2
/d/atm) of NFC and 50 N/50 M clay nanopaper under 0%, 5...
Table 13.2 Flammability data from vertical flammability test of CNF and CNF/MTM ...
Table 13.3 Starting compositions and properties of typical aerogels obtained in ...
Table 13.4 Characteristics of the cobalt ferrite‐based nanocomposites with diffe...
Table 13.5 Properties of the cellulose and magnetic composite aerogels.
Table 13.6 Comparison among different aerogel preparation methods.
List of Illustrations
Chapter 1
Figure 1.1 Schematic illustration for the preparation of cellulose nan...
Figure 1.2 TEM micrograph of cotton linter‐derivate CNC obtained throug...
Figure 1.3 Preparation of cellulose nanofibers from different raw mater...
Figure 1.4 Preparation of bacterial cellulose.
Figure 1.5 Schematic illustration for surface chemical modification of ...
Chapter 2
Figure 2.1 TEM images of cellulose nanocrystals derived from cotton li...
Figure 2.2 Acid hydrolysis mechanism (a) and esterification (b) of cell...
Figure 2.3 TEM images of cellulose nanocrystals extracted by (a) HCl; (...
Figure 2.4 Schematic representation of the HBr hydrolysis preparation o...
Figure 2.5 TEM images of phosphoric acid hydrolyzed cotton as a functio...
Figure 2.6 TEM images of nanocellulose treated by (a) Co(II)‐, (b) Ni(I...
Figure 2.7 TEM micrographs of (a) Mn(II)‐ and (b) Cr(III)‐hydrolyzed na...
Figure 2.8 Simplified oxidation scheme.
Figure 2.9 TGA curves of CNCs and neutralized CNCs: (a) the thermal sta...
Figure 2.12 (a) Chiral nematic texture of the anisotropic phase of a CN...
Figure 2.10 Schematic representation of rod‐like CNCs orientation in bo...
Figure 2.11 Polarized optical micrographs of CNC colloids at concentrat...
Figure 2.13 Polarized optical micrographs of birefringent gel phases in...
Figure 2.17 Inverted sample tubes containing 0.5, 1.0, 2.0, and 3.0 wt%...
Figure 2.14 Aqueous 0.53% (w/v) suspensions of CNCs observed between cr...
Figure 2.15 Polarized optical micrographs of the silylated CN suspensio...
Figure 2.16 Viscosity as a function of shear rate for CNC suspensions o...
Chapter 3
Figure 3.1 A schematic model of the nanostructure of cellulose nanofib...
Figure 3.2 High‐pressure homogenizer(a), microfluidizer (b), and grinde...
Figure 3.3 Scanning electron micrographs of (a) the original pulp; the ...
Figure 3.4 (a) Schematic illustration of the production process for chl...
Figure 3.5 The dual water jet aqueous counter collision (ACC) system. ...
Figure 3.6 Twin‐screw mini extruder used for the disintegration of fibe...
Figure 3.7 CNF in different forms (suspension, powder, aerogel, hydroge...
Figure 3.8 (A) Sedimentation test for 0.2 wt% water suspensions of neve...
Figure 3.9 (a) Pictures of the different samples obtained for each samp...
Figure 3.10 (a) CNF nanopaper and (b) the traditional cellulose paper p...
Figure 3.11 The oxygen permeabilities of the AU cellulose films [84]. ...
Figure 3.12 (a) Preparation of DC cellulose hydrogels. (i) Chemical cro...
Figure 3.13 Electrochemical properties of the mCel‐membrane‐based MSC. ...
Chapter 4
Figure 4.1 Illustration of formation of cellulose chains in microbial ...
Figure 4.2 Schematic representation of bio‐cellulose production by the ...
Figure 4.3 Cellulose synthesis in
A. xylinum
. AxCESA, with 8 to 10 puta...
Figure 4.4 Various bioreactors designed for enhanced production and pro...
Figure 4.5 Effect of different additives on BC production. Figure modif...
Figure 4.6 Cost‐effective production of BC from various waste sources i...
Chapter 5
Figure 5.1 Transmission electron micrographs from a dilute suspension ...
Figure 5.2 Transmission electron micrographs from a dilute suspension o...
Figure 5.3 Scanning electron micrographs of a bacterial cellulose pelli...
Figure 5.4 Three approaches of the sulfonation modification on nanocell...
Figure 5.5 Scheme of the TEMPO‐mediated oxidation mechanism of cellulos...
Figure 5.6 Transesterification modification of nanocellulose.
Figure 5.7 Two commonly used approaches for the silylation of nanocellu...
Figure 5.8 Scheme for the silylation of nanocellulose with vinyltrimeth...
Figure 5.9 Different methods of introducing PEG/PEO chains on the surfa...
Figure 5.10 Schematic illustration of the grafting of PEO onto the CNC ...
Figure 5.11 Three‐step routine for the PCL‐grafting on the surface of C...
Figure 5.12 Chemical routes of surface grafting of PCL (a), PLA (b), an...
Figure 5.13 Common synthetic routes of grafting polyolefin chains on CN...
Figure 5.14 Synthetic routes of grafting polyolefin chains on CNCs with...
Figure 5.15 Three traditional end modification approaches on the hemiac...
Figure 5.16 Common synthetic routes of topochemically functionalizing n...
Figure 5.17 Reaction pathways of attaching FITC (a) and pyrene (b) moie...
Figure 5.18 Two reactive routines of the self‐cross‐linking between the...
Chapter 6
Figure 6.1 Pictures of the extruded films: unfilled polyethylene (LDPE)...
Chapter 7
Figure 7.1 Logarithm of the normalized storage shear modulus (log
G
′
T
/
Figure 7.2 Schematic representation of a “quasi isotropic”composite. ...
Figure 7.3 Logarithm of the shear modulus, taken at 325 K, as a functio...
Figure 7.4 Schematic representation of the series–parallel model. R and...
Figure 7.5 Logarithm of the relative storage tensile modulus measured a...
Figure 7.6 Storage tensile modulus
E'
and loss angle tangent, tan
δ
...
Figure 7.7 Comparison of between predicted data and experimental storag...
Figure 7.8 Schematic representation of the proposed mechanism for the e...
Figure 7.9 Representative DMA traces for (a) neat EO‐EPI, EO‐EPI/PVA bl...
Figure 7.10 Experimental data (symbols) and values predicted by a perco...
Figure 7.11 DSC thermograms for 15% filled tunicin whiskers/sorbitol‐pl...
Figure 7.12 Wide‐angle X‐ray diffraction patterns for 75% RH conditione...
Figure 7.13 Typical stress–strain curves for (a) modCNC/PVAc nanocompos...
Figure 7.14 Schematic illustration on the reinforcing mechanisms for (a...
Figure 7.15 Mechanical properties of CNC/CMC and mCNC/CMC films: (a) Ty...
Figure 7.16 (a) For PHBV and different nanocrystals (CN, CNeF, and CNeC...
Figure 7.17 Tensile strength, Young's modulus, and elongation at break ...
Figure 7.18 Grafting reaction of DDSA on CNC surface.
Figure 7.19 Storage moduli for PU and DDSA‐CNC‐PU nanocomposites at dif...
Figure 7.20 (a) The gel‐like appearance of 3 w/v% DDSA‐CNCs suspension ...
Figure 7.21 Sketch of the synthesis of the CNC‐
g
‐polymers as initiated ...
Figure 7.22 Dynamic storage modulus versus frequency as recorded for (●...
Figure 7.23 Synthetic route of the PEG‐PCL‐CNC nanocomposite network. ...
Figure 7.24 The storage modulus and tan
δ
of PEG‐PCL‐CNC nanocompo...
Figure 7.25 TGA thermograms for pure MPEG‐NH2, PEO5M; pristine CN, graf...
Figure 7.26 Storage modulus at
T
g + 10 °C (389 K) and fitted curves for...
Figure 7.27 A scheme of the mCNC/PBD composites with structures at two ...
Figure 7.28 The tensile mechanical properties for cross‐linked mCNC/PBD...
Figure 7.29 Illustration of the structure for the NR/m‐CNCs nanocomposi...
Figure 7.30 Tensile stress–strain curves of pure NR, NR/CNCs, and NR/m‐...
Figure 7.31 Chemical structures of 4‐oxo‐4‐(prop‐2‐yn‐1‐yloxy) butanoic...
Figure 7.32 Mechanical properties of the GP2/ACNC nanocomposites involv...
Figure 7.33 Schematic representation of the cross‐linked hydrogels.
Figure 7.34 (a) Dynamic rheological observations of the gelatin gels. (...
Figure 7.35 Schematic representation of chemically cross‐linked CNC aer...
Figure 7.36 Compressive stress–strain curves of aerogels prepared from ...
Figure 7.37 Schematic representation of injectable hydrogels reinforced...
Figure 7.38 Dynamic storage modulus (
G
′) and loss modulus (
G
″) of injec...
Figure 7.39 Schematic representation of cross‐linked nanocomposites. ...
Figure 7.40 Schematic illustration of the acetal cross‐linking of PVA w...
Figure 7.41 Mechanical properties of CNC‐reinforced PVA films: (a) tens...
Figure 7.42 Illustration of IPDI/CNC reaction with the secondary NCO gr...
Figure 7.43 Tensile strength and work of fracture for um‐ and m‐CNC com...
Figure 7.44 DSC thermograms of WBPU1.05 and WBPU1.2 and their nanocompo...
Figure 7.45 Thermal properties of WBPU1.05 (solid lines) and WBPU1.2 (d...
Chapter 8
Figure 8.1 Typical morphologies of (a) cellulose nanofibrils, CNFs, an...
Figure 8.2 Relative Young's modulus (a) and tensile strength (b) for th...
Figure 8.3 Relative Young's modulus of PLA and other biodegradable ther...
Figure 8.4 Relative tensile strength of PLA and other biodegradable the...
Figure 8.5 Relative tensile strength for polyolefins‐based nanocomposit...
Figure 8.6 Relative Young's modulus and tensile strength of water‐solub...
Figure 8.7 Young modulus (a) and tensile strength (b) as a function of ...
Figure 8.8 Morphologies of the PE/CNF (10 wt%) nanocomposite before and...
Figure 8.9 Optical properties of PE/CNF nanocomposites before and after...
Figure 8.10 Schematic of melt extrusion effect on PE/CNF nanocomposites...
Figure 8.11 Effect of fiber size (CNF vs. CF) and composition (CNF vs. ...
Figure 8.12 Morphology of PE/LCNF samples (a) and (b) 5 wt% LCNF, (c) a...
Figure 8.13 Morphology of PE/CF samples. (a) Pure CF, (b) 5 wt% CF, (c)...
Figure 8.14 Comparison between the optical properties of PE/CNF and PE/...
Figure 8.15 A comparison between
oxygen transmission rate
(
OTR
) of CNF,...
Chapter 9
Figure 9.1 (a) Schematic of cholesteric liquid crystals of CNCs. (b)
P
...
Figure 9.2 Schematic of cellulose nanocrystalline/polyethylene glycol c...
Figure 9.3 Schematic of (a) cellulose nanocrystalline/glycerol composit...
Figure 9.4 (a) POM image of a PAAm (poly acrylamide) nanocomposite prep...
Figure 9.5 The drying process of the casting method to prepare CNC bulk...
Figure 9.6 (a) The CNC‐film casting setup of the casting method to prep...
Figure 9.7 Optical image of a multilayer film of PAH/cellulose prepared...
Figure 9.8 Schematic for the preparation process of (a) CNC iridescent ...
Figure 9.9 Schematic of the EISA method with CNC as the template to pre...
Figure 9.10 Relationships between (a) the
P
and salt concentration, (b)...
Figure 9.11 (a) Relationship between the intensity of the electric fiel...
Figure 9.12 Helix orientation of CNC in cholesteric liquid crystalline ...
Figure 9.13 Schematic of the mesoporous cholesteric phenol–formaldehyde...
Figure 9.14 SEM images of PAAm nanocomposites with (a) 10 wt% CNC and (...
Figure 9.15 (a) Optical images, (b) side SEM images, and (c) POM images...
Figure 9.16 Reflective spectra of CNC and CNC/silica composite films [...
Figure 9.17 Schematic for preparing cholesteric mesoporous titania from...
Figure 9.18 The AFM image of CNC vertical‐assembly film prepared by the...
Figure 9.19 Schematic for isolation of rod‐like CNC from trees and the ...
Figure 9.20 Schematic for oxidation of C6 primary hydroxyl of CNC by TE...
Figure 9.21 (a) Optical images of dispersion of (left) PEO‐grafted CNC ...
Figure 9.22 Stress–strain curves of CNC/DMAPS composites with CNC:DMAPS...
Figure 9.23 (a) SEM images and (b) schematics of CNC iridescent films t...
Figure 9.24 Stress–strain curves of (a) CNC/PEG and (b) CNC/PVA composi...
Figure 9.25 CNC films cast from the suspensions sonicated for (a) 0, (b...
Figure 9.26 Circular dichroism spectra of the CNC films prepared by cov...
Figure 9.27 Relationship between the intensity of the electric field an...
Figure 9.28 (a) Optical images of CNC/GO film prepared by adding (I) GO...
Figure 9.29 Schematic for the self‐assembly of CNC/AgNW composites with...
Figure 9.30 Optical images of silica films prepared with different cont...
Figure 9.31 Optical images of an iridescent film of the PAAm/CNC nanoco...
Figure 9.32 (a) Schematic of the self‐assembly of CNC/Au nanoparticle m...
Figure 9.33 (a) Contact angle test image for the hydrogel prepared by M...
Figure 9.34 (a) Evolution of the mass loss of the iridescent pigment wi...
Figure 9.35 (a) Schematic of the proposed correspondence between CNC as...
Chapter 10
Figure 10.1 Schematic illustration of the organization of the isotropi...
Figure 10.2 (a) Schematic of the chiral nematic liquid‐crystalline text...
Figure 10.3 Proposed correspondence between CNC rigid rod assembly orie...
Figure 10.4 CNC films formed by heating a Na‐CNC suspension in a Petri ...
Figure 10.5 Tuning the iridescence of CNC chiral nematic films with a v...
Figure 10.6 FE‐SEM images of a fracture surface across an iridescent CN...
Figure 10.7 Formation of chiral nematic structure in nanocomposite hydr...
Figure 10.8 (a) FE‐SEM images of the fracture surfaces of polymer compo...
Figure 10.9 Self‐assembly of tailored mixtures of EGUPyX polymers modif...
Figure 10.10 Preparation of cholesteric, crustacean‐mimetic CNC/PVA nan...
Figure 10.11 Nanocellulose combined with paper or film for food packagi...
Figure 10.12 The release mechanism between the CHX, the cyclodextrins, ...
Figure 10.13 UV–vis spectra of thin films for different CNF/chitosan. ...
Figure 10.14 Schematic representation of the colloidal behavior upon mi...
Figure 10.15 Wet tensile properties for base‐treated and not base‐treat...
Figure 10.16 Cyclic tensile tests of the base‐treated CNF/chitosan 80/2...
Figure 10.17 WVTR of Nanopaper coated with fillers.
Figure 10.18 Water adsorption vs. lignin content for MFC films, origina...
Figure 10.19 Initial contact angle vs. lignin content for film samples ...
Figure 10.20 Frequency and dissipation changes upon LbL build‐up of all...
Figure 10.21 Effect of capping layer on normalized force versus separat...
Figure 10.22 Inhibitory zones of
S. Typhimurium
growth on a bacterial p...
Figure 10.23 Arithmetic mean roughness (
R
a
) and 85° gloss level of be...
Figure 10.24 Wear resistance of oiled wood surfaces containing 1 wt% CN...
Figure 10.25 MOE and tensile strength for pure coating (a) and nanocomp...
Chapter 11
Figure 11.1 Bright field (left) and fluorescence (right) images of
Daph
...
Figure 11.2 (A) Process for synthesis of CNC/Fe
3
O
4
NP/AuNP/papain and a ...
Figure 11.3 (a) Representative confocal microscopic images showing inte...
Figure 11.4 (A) Fluorescence images of hMSCs cultured on the TCPs, RGO ...
Figure 11.5 (a) Cryo‐TEM image of vitrified NFC hydrogel. The scale bar...
Figure 11.6 (A) Typical tensile stress–strain curves of electrospun MPL...
Figure 11.7 Procedure of the operation of full‐thickness skin injury mo...
Figure 11.8 FE‐SEM images of (a) BC, (b) BC‐PVP, (c) 5‐PVP‐HAp‐BC, and ...
Figure 11.9 (a) BC tubes with different sizes and shapes for applicatio...
Figure 11.10 Postulated molecular interactions between OCNC and fibrin ...
Figure 11.11 (a) Comparison between pig meniscus (left) and BC hydrogel...
Figure 11.12 (A) SEM images of bamboo pulp fibers before (a) and after ...
Figure 11.13 Optical images of inhibition zones of BC/SA and BC/SA–AgSD...
Figure 11.14 (A) Schematic illustration of the grafting of cellulose na...
Chapter 12
Figure 12.1 Schematic showing the preparation of nanocellulose/MWCNT e...
Figure 12.2 (a) A schematic to illustrate the nanoporous structural evo...
Figure 12.3 Schematic showing the preparation of self‐standing binder‐f...
Figure 12.4 (a) Functionalized CNCs and capacitive materials for 3D lig...
Figure 12.5 (a) Schematic showing the preparation of electrodes with ca...
Figure 12.6 (a) Schematic representation of fuel cells with nanocellulo...
Figure 12.7 (a) Schematic structure and an image of an NFC‐based TENG. ...
Chapter 13
Figure 13.1 Thermal decomposition of melamine and related products. ...
Figure 13.2 Sketch of the procedure adopted for the production of clay ...
Figure 13.3 Schematic representation of clay nanopaper preparation and ...
Figure 13.4 (a) Temperature measurement set‐up for cone calorimetry; (b...
Figure 13.5 SEM micrographs of microtome cut cross sections and XRD spe...
Figure 13.6 TG and dTG plots of CNF and CNF/MTM nanocomposites in nitro...
Figure 13.7 TG and dTG plots of CNF and CNF/clay nanocomposites in air....
Figure 13.8 Residues collected after vertical flammability test of CNF/...
Figure 13.9 Nanotechnology and its application in high‐performance ther...
Figure 13.10 SEM images of PMSQ–CNF composite aerogels and pure PMSQ ae...
Figure 13.11 Microstructure of freeze‐cast nanocomposite foams. (a) SEM...
Figure 13.12 Thermal transport properties of anisotropic nanocomposite ...
Figure 13.13 Schematic illustration of CNF and CNC production from fibe...
Figure 13.14 Scheme of main steps needed to prepare NCC from lignocellu...
Figure 13.15 Morphologies and dimensions of inorganic nanoparticle‐temp...
Figure 13.16 SEM images of the surface morphology of ZnO/BC composites ...
Figure 13.17 Nanocomposite preparation by a template approach. Schemati...
Figure 13.18 Synthesis of elastic aerogel magnets and stiff magnetic na...
Figure 13.19 Magnetic aerogels at different loadings of cobalt ferrite ...
Figure 13.20 Particle size histograms from electron micrographs. Estima...
Figure 13.21 Tunability of the mechanical properties and large‐strain m...
Figure 13.22 Water release and deformability. (a–d) Magnetic aerogel (d...
Figure 13.23 SEM (a) and TEM (b) images of cellulose xerogel after bein...
Figure 13.24 SEM images of the composite aerogels; (a–d) were for RCF‐0...
Figure 13.25 TEM images of the composite aerogels; (a–d) were for RCF‐0...
Figure 13.26 XRD of cellulose and magnetic composite aerogels.
Figure 13.27 Hysteresis cycles of the composite aerogels at 298 K; the ...
Figure 13.28 Compression stress–strain curves of cellulose and composit...
Figure 13.29 FE‐SEM images of freeze‐dried BC (a) and different represe...
Figure 13.30 (a) Schematic representation of the preparation processes....
Figure 13.31 SEM (a–f) and TEM (g–i) of ALD coated aerogels. The number...
Figure 13.32 Scanning electron microscopy micrographs of ZnO coated aer...
Figure 13.33 Effect of calcination on ZnO‐coated aerogels demonstrated ...
Figure 13.34 SEM micrographs of Al
2
O
3
(on left) and TiO
2
(on right) coa...
Figure 13.35 Films cast from a crushed hollow TiO
2
nanotube dispersion ...
Figure 13.36 X‐ray diffraction profile of a TiO
2
nanotube film deposite...
Figure 13.37 Optical microscope image (a, crossed polars) of a CNC film...
Figure 13.38 Schematic illustration of the CNC‐templating of inorganic ...
Guide
Cover
Table of Contents
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Nanocellulose
From Fundamentals to Advanced Materials
Edited by Jin Huang, Alain Dufresne, and Ning Lin
Copyright
Editors
Prof. Jin Huang
Southwest University
School of Chemistry and Chemical Engineering, and Chongqing Key Laboratory of Soft‐Matter Material Chemistry and Function Manufacturing
Tiansheng Road 2
Beibei District
400715 Chongqing
China
Prof. Alain Dufresne
Grenoble INP‐Pagora
International School of...Lab. Génie des
461 rue de la Papeterie
38402 Saint Martin d'Hères cedex
France
Dr. Ning Lin
Wuhan University of Technology
School of Chemistry, Chemical Engineering and Life Sciences
122 Luoshi Road
430070 Wuhan
China
Cover Image: © imaginima/iStock/Getty Images Plus
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Preface
Recently, nanocellulose has been considered as a promising and ideal candidate for the development of high‐performance functional composite materials. Nanocellulose is a kind of biomass nanomaterial that is constructed by cellulose and can be extracted from most plants, some animals, and microorganisms. Its hydroxyl group‐rich surface makes nanocellulose hydrophilic and easily modifiable. Meanwhile, as a polysaccharide‐based material, nanocellulose has proved to be nontoxic, biocompatible, renewable, and degradable. Thus, nanocellulose‐based nontoxic drug carriers, wound coverage and contrast agents have been reported and have shown a great potential application in clinical medical care. On the other hand, as nanocellulose contains a large amount of cellulose crystalline regions, its mechanical strength is extremely high. In addition, because of the capability of nanocellulose to form networks cross‐linked by hydrogen bonds in the suspension/matrix, it has also been widely used as a green reinforcing agent in polymer materials to prepare high‐performance materials.
Nanocellulose mainly consists of three kinds of nanomaterials – cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and bacterial nanocellulose (BC). CNC is the pure nano‐sized cellulose monocrystal, and occurs as rod‐like nanoparticle with a highly hydrophilic surface. CNF and BC are nanofibers containing both crystalline and amorphous regions. These three nanomaterials can form networks in liquid medium or matrix via hydrogen bonds or chain entanglements. However, the main problem with these nanomaterials is to keep the balance between the compatibility with the matrix ensuring their dispersibility and the capability to form hydrogen‐bonded network providing high mechanical stiffness. Appropriate surface modification of the nanomaterial would allow the development of stiff materials with interesting functions. On the other hand, CNC itself also has special self‐assembling behavior. The CNCs can form cholesteric liquid crystal phase in aqueous suspensions, and thus can be used to make some interesting optical‐tuning materials and so on. For the abovementioned interesting properties, nanocellulose has drawn much attention and has been given more importance in the development of advanced materials.
Nanocellulose has been profoundly studied and widely applied in the development of high‐performance and functional materials. In this book, Nanocellulose: From Fundamentals to Advanced Materials, we have tried to provide a full overview of the structure and preparation of nanocellulose and its applications.
We first introduce the structure and strategies for the extraction of CNC, CNF, and BC, including physical and chemical approaches. Then, as a fundamental step for the preparation of nanocellulose‐based composites, a variety of approaches for the surface modification of nanocellulose are exposed. The following chapters focus on the current status of nanocellulose‐based nanocomposites and the mechanisms involved in their reinforcing capability; we discuss the applications of these high‐performance nanocomposites. The application of the colloidal characteristics and self‐assembling behavior of CNC for the development of functional nanomaterials is highlighted for their huge potential to make promising optical materials, and so on. Finally, in the last three chapters, the use of nanocellulose for biomedical applications, energy materials and devices, and other high‐value use is introduced.
October 6, 2018
Jin Huang
Lanhua Building, Southwest University
Acknowledgments
We are thankful for the contribution of all writers of this book, especially the chief editors Jin Huang, Alain Dufresne, and Ning Lin, who did a lot of work to ensure the high quality of this book. The first and corresponding authors of every chapter, i.e. Xiaozhou Ma, Chunyu Chang, Peter R. Chang, Pei Huang, Min Wu, Muhammad Wajid Ullah, Guang Yang, Ge Zhu, Yuhuan Wang, Yaoyao Chen, Thiago Henrique Silveira Maia, Alessandra de Almeida Lucas, Lin Gan, Shiyu Fu, Yanjie Zhang, Gang Chen, Zhiqiang Fang, Ruitao Cha, and Xingyu Jiang (according to the order of the chapters), and all the other coauthors have also provided their input in different areas to successfully complete this book. We also thank Muhammad Wajid Ullah for his great proofreading work during the preparation of this book.
Lastly, we thank the grant of the National Natural Science Foundation of China (51373131, 51873164, 51603171, 31570569, 51733009, 21574050, 31700508, 21774039, and 21875050), and the Talent Project of Southwest University (SWU115034).
1Introduction to Nanocellulose
Jin Huang1, Xiaozhou Ma1, Guang Yang2 and Dufresne Alain3
1Southwest University, Chongqing Key Laboratory of Soft‐Matter Material Chemistry and Function Manufacturing, School of Chemistry and Chemical Engineering, Tiansheng Road 2, Chongqing, 400715, China
2Huazhong University of Science and Technology, College of Life Science and Technology, Luoyu Road 1037, Wuhan, 430074, China
3University Grenoble Alpes, CNRS, LGP2, Grenoble INP, 38000 Grenoble, France
1.1 Introduction
Cellulose is the most abundant polymer on earth produced by plants, microorganisms, and cell‐free systems. Chemically, it is composed of repeated β‐D‐glucose monomers linked together through β‐(1,4) glycoside linkage. The morphology of natural cellulose is usually fibrous with intermittent crystalline and amorphous sections [1]. Separation of fibers results in nanoscale cellulose substances known as nanocellulose, which exists in different morphologies such as cellulose nanocrystals (CNCs) or cellulose nanowhiskers (CNWs) as another name, and cellulose nanofibers (CNFs) (Figure 1.1). Compared to the plant cellulose containing lignin and hemicelluloses, microbial cellulose, termed as bacterial nanocellulose (BNC) and cell‐free cellulose, represents the purest form of cellulose. Nanocellulose exhibits distinctive structural and physicochemical, mechanical, and biological characteristics, including reticulate fibrous three‐dimensional web‐shaped structure, high crystallinity, good mechanical strength, biocompatibility, biodegradability, optical transparency, high specific surface area, polyfunctionality, hydrophilicity, and moldability into 3D structures [2–4]. As a sustainable material, nanocellulose could be extracted from the disintegration of plant and animal cellulose [5], synthesized by different microbial strains [6], and cell‐free systems [7]. As a tunable material, nanocellulose both alone and in composite form with other materials is immensely used in various fields such as wound dressing, textiles and clothing, food, cosmetics, regenerative medicines, tissue engineering, energy, optoelectronics, bioprinting, environmental remediation, and so on [ 28–13].
Figure 1.1 Schematic illustration for the preparation of cellulose nanofibers and cellulose nanocrystals using the wood resource.
Nanocellulose exhibits superior structural characteristics than microcrystalline cellulose (MCC), and possesses high mechanical strength and can be facilely surface‐modified via different strategies. For example, the longitudinal modulus of CNC extracted from tunicate can reach as high as 151 GPa, while the Young's modulus of CNF varies between 58 and 180 GPa and its tensile strength can reach up to 22 GPa according to the type of raw material and the preparation method [14, 15]. Nanocellulose contains greater number of hydroxyl (OH) groups, which make it highly hydrophilic and can be modified via different chemical and physical strategies [16]. Thus, considering its high biocompatibility, high mechanical strength, renewability, and low cost, nanocellulose has received immense consideration as an ideal nanostructure to make new high‐value nanomaterials.
1.2 Preparation of Nanocellulose
Depending on the type of nanocellulose and its source, different strategies are employed for its production. For example, destructuring strategies involving high‐pressure homogenization, grinding, and chemical or enzymatic treatments, are used for the isolation of nanocrystalline cellulose (NCC). In contrast, BNC is naturally produced by different microorganisms. The following section briefly overviews different preparation methods of nanocellulose (see Chapters and 4 for details).
1.2.1 Cellulose Nanocrystals
Cellulose nanocrystals (CNCs) are the mostly commonly used nanocellulose, which are mainly produced through hydrolysis of the amorphous section of cellulose fibers [17]. This process consists of two steps: the pretreatment of the raw material followed by its hydrolysis into CNCs. The raw material contains different impurities in the form of esters, wax, hemicelluloses, and lignin, which are removed by treating with alkaline (NaOH) solution or applying a bleaching method before hydrolysis. Thereafter, the purified raw material is heat‐treated in the acidic environment for around 45 min in general or longer time up to several hours to hydrolyze the amorphous section of cellulose fibers. The obtained suspension is then centrifuged and dialyzed to achieve the purified CNCs. The CNCs produced through this strategy commonly show a rod‐like morphology when observed under transmission electron microscopy (TEM) (Figure 1.2). The diameter and length of CNCs obtained through acid hydrolysis vary depending on raw material type, acid type, and hydrolysis temperature and time. For example, CNCs with diameter of 10–30 nm and length 200–300 nm were obtained through acid hydrolysis of cotton fibers at 65 °C using H2SO4. In contrast, CNCs with the length more than 1 μm were obtained from ascidian under the same experimental conditions [18, 19]. Similarly, CNCs with length 100–200 nm and diameter 10 nm were obtained through acid hydrolysis using HCl under the analogous experimental conditions [20]. Besides acid hydrolysis, other reactants including oxidants such as tetramethyl‐piperidin‐1‐oxyl (TEMPO) or ammonium persulfate (APS), and some bio‐enzymes, are also used for the production of CNCs. For instance, TEMPO, NaBr, and NaClO could be together used to directly produce TEMPO‐oxidized CNC (TOCNC) from cellulose fibers [21]. During the preparation process, the reaction is carried out in an alkaline environment by constantly adding NaOH solution to the reaction mixture until a constant pH is kept. The TOCNC in the mixture could be purified by centrifugation and dialysis. Similarly, Satyamurthy et al. used the cellulolytic fungus to hydrolyze MCC. The yield of this strategy could be as high as 20%; however, its high cost strongly limits its large‐scale application [22].
Figure 1.2 TEM micrograph of cotton linter‐derivate CNC obtained through acid hydrolysis (scale bar = 200 nm).
1.2.2 Cellulose Nanofibers
Compared to CNCs, the preparation of cellulose nanofibers (CNFs) is much simpler as it does not require severe chemical cleavage in the molecular structure of the cellulose chain. Generally, CNFs are prepared by the physical separation of cellulose fibers, such as grinding, homogenization, and ultrasonication [23–26]. Besides the strategies of mechanical peeling and dissection, CNFs can also be prepared by chemical methods. For example, oxidation of wood raw material by TEMPO under gentle stirring results in fine individual CNFs [27]. Sometimes, both mechanical and chemical strategies could be employed together to produce individual CNFs. For example, carboxymethylation and high‐pressure homogenization can be applied simultaneously to prepare uniformly distributed CNFs [28]. For the preparation of CNFs, the most commonly used raw materials are wood, however, cotton fibers, tunicate, and other raw materials are also attempted to be used. Depending on the type of raw materials, the diameter of CNFs usually varies from 2 to 50 nm [29] (Figure 1.3). CNF usually has a high aspect ratio, which makes it an ideal positive ingredient for the enhancement of polymer materials (see Chapter and 8 for details).
Figure 1.3 Preparation of cellulose nanofibers from different raw materials.
Source: Chen et al. 2018 [29]. Reproduced with permission of RSC.
1.2.3 Bacterial Nanocellulose
Bacterial nanocellulose (BNC) is naturally produced by several bacterial genera including Acetobacter, Rhizobium, Agrobacterium, Aerobacter, Achromobacter, Azotobacter, Salmonella, Escherichia, and Sarcina[30] and cell‐free systems [7]. It is produced in the form of a hydrogel at the air–medium interface. During the synthesis, β‐1,4‐glucan chains are produced in the interior of the bacterial cell, which is then excreted across the cell membrane as protofibrils that crystallize to form ribbon‐shaped microfibrils followed by formation of pellicle [31] (Figure 1.4). The structural characteristics such as diameter (20–100 nm), arrangement of fibers, and physico‐mechanical properties of BNC strictly depend on the microbial strain type, the synthesis method (cell and cell‐free systems), and the culture conditions including carbon and nitrogen source [33, 34]. BNC has been largely used for various biomedical applications such as tissue engineering, regenerative medicines, enzyme immobilization, drug delivery, and 3D printing biomaterials [2, 35–37]. However, the large‐scale applications of BNC are hampered by its high production cost [38]. Different strategies have been developed for high‐yield and cost‐effective production of BNC with superior structural and physico‐mechanical features. These include the advanced fermentation approaches, genetic engineering strategies, and strain improvement for high‐yield BNC production, and use of different industrial wastes such as fruit juices, sugarcane molasses and agricultural wastes for low‐cost production [39–43] (see Chapter 4 for details).
Figure 1.4 Preparation of bacterial cellulose.
Source: Lai et al. 2013 [32]. Reproduced with permission of Springer Nature.
1.3 Surface Modification of Nanocellulose
The hydroxyl groups present on the surface of nanocellulose make it highly hydrophilic and favorable for surface chemical modification or physical interaction [16]. The chemical and physical properties of nanocellulose can be easily controlled by different strategies (see Chapter 5 for details), and some chemical methods are summarized in Figure 1.5[44]. In order to guarantee the quality and efficiency of surface modification of nanocellulose, the uniform dispersibility of nanocellulose in the suspension medium is the principle factor to reactive conjugation and physical attachment of the nanocellulose surface. Especially when using an organic solvent as the suspension medium, due to the hydrophilicity of the nanocellulose surface, the solvent replacement from aqueous medium to organic solvent is employed as an effective way while the intensified dispersion techniques, such as ultrasonication, high‐speed shear and so on, are essential to homogenize the nanocellulose suspension.
Figure 1.5 Schematic illustration for surface chemical modification of CNCs by various methods including sulfonation (a), oxidation (b), nucleophilic substitution (c), etherification (d), esterification (e), carbamation (f), and silylation (g).
1.3.1 Esterification
The most common strategy used to modify nanocellulose is by esterification, which offers a high substitution ratio of OH groups on nanocellulose surface [45–47]. According to the chemical structure of cellulose, there are three OH groups on each glucoside unit, which are C2‐OH, C3‐OH, and C6‐OH. In general, the order of activity of these OH groups is C6‐OH > C3‐OH > C2‐OH (Figure 1.5). During the chemical reaction, only one moiety for C3‐OH and C2‐OH might be modified due to the steric hindrance effect of nanoscale CNC surface. Another advantage of this esterification method is that the reaction conditions are mild; thus, a high substitution ratio can be achieved without compromising the crystalline structure of nanocellulose [48–50]. Researchers have successfully used this method to make hydrophobic nanocellulose, which can be easily used to enhance the mechanical properties of hydrophobic polymer matrix. In addition, when using ethylenediaminetetraacetic dianhydride (EDTAD) to decorate carboxyl groups onto the CNC surface, high carboxylation degree of the CNC surface was achieved. Furthermore, in comparison with the TEMPO-oxided CNC with an equivalent carboxylation degree, the surface integrality of EDTAD-esterified CNC was kept [51].
1.3.2 Oxidation
Oxidation is the most commonly used method for making carboxylated nanocellulose because the C6‐OH on nanocellulose surface can be easily oxidized into a carboxyl group. This oxidation reaction usually takes place in the presence of TEMPO [ 27, 32, 52]. Additionally, TEMPO can selectively oxidize C6‐OH to a carboxyl group in the presence of NaClO and NaBr under alkaline environment. However, high TEMPO concentration and long oxidation time may break the chemical bonds between glucoside units, and thus compromise the crystalline structure and surface integrality of nanocellulose [21]. It was also reported that such phenomenon could be used in making carboxylated CNC directly from the cellulose‐containing raw materials. Another oxidant that can be used in nanocellulose oxidation is APS. However, due to its high oxidation potential, APS seriously damages the crystalline structure of cellulose; thus the morphology of the CNC produced is obviously shorter and thinner than the one produced through traditional acid hydrolysis [53]. By using oxidation strategy, aldehyde groups can also be formed onto the nanocellulose surface. Usually, sodium periodate (NaIO4) is used to oxidize the 2,3‐diol structure of the glucoside, and thus can make two aldehyde groups, which can be widely used in Schiff base reaction‐based further modification [54]. Besides, a study has also reported that some of the glucoside units on CNC innately present aldehyde groups, and thus the amino‐ or diamine‐containing fluorescent molecules could be directly conjugated on the CNC surface without any additional pretreatment [55].
1.3.3 Etherification
Etherification is a highly efficient modification method for cellulose, which usually uses an epoxylated molecule as the modification agent together with organic solvent‐containing heating system [56–58]. The efficiency of this process is largely compromised by the polymerization; nevertheless, it offers a high substitution ratio. As well‐known, the epoxy group reacts with the OH group of the nanocellulose surface and forms ether bonds and an OH at its β position. The OH group formed further reacts with the epoxy groups; hence, polymerization takes place on the nanocellulose surface. This issue can be partially resolved by controlling the reaction conditions; however, polymerization cannot be completely avoided.
1.3.4 Amidation
As most biomolecules possess amine groups, amidation is considered as a mild and efficient way to modify the nanocellulose surface with these biomolecules. The amidation reaction can take place both in organic solvents (e.g. dimethylformamide, abbreviated as DMF) and aqueous solutions to conjugate two molecules that have carboxyl groups and amine groups, respectively. Since nanocellulose generally has no carboxyl groups or amine groups on its surface, the carboxyl groups or amine groups should be decorated on the nanocellulose surface before the amidation, for example using TEMPO oxidation. In the aqueous reaction system, the carboxylated nanocellulose is thereafter reacted with N‐hydroxylsuccinimide (NHS), which can improve the reactivity of carboxyl groups on nanocellulose surface with the amide groups. The final step of amidation modification is to mix the NHS‐activated carboxylated nanocellulose with the amide‐containing molecules. The amine groups of the molecules can directly react with NHS‐activated carboxylated nanocellulose, and conjugate the molecules onto the nanocellulose surface with the linkage of amide bonds [59, 60]. However, if organic solvent (e.g. DMF) is used instead of aqueous medium, the amine‐containing molecules can be directly conjugated onto the carboxylated surface of nanocellulose.
1.3.5 Other Chemical Methods
Other chemical methods, such as nucleophilic substitution, carbamation and so on, have also been reported to modify the nanocellulose surface, especially in making hydrophobic nanocellulose for nanocomposite enhancement or fluorescent nanocellulose for biomedical applications [62, 61]. In addition, long chain molecules and polymers have been attempted to be grafted on the nanocellulose surface. In this case, the “graft onto” strategy has been employed via the abovementioned chemical methods to covalently linked long chains on the nanocellulose surface, but is obviously subject to the steric hindrance of nanoscale surface; meanwhile, the “graft from” strategy could produce higher grafting density and longer polymer chains using various polymerization methods, which are initiated by hydroxyl groups and newly formed corresponding functional groups on the nanocellulose surface (see Chapter 5 for details). All these methods mentioned above generally require organic solvents and heating condition during the reaction. As a result, such chemical modification methods are quite suitable to hydrophobic surface modification of nanocellulose; however, these methods are limited for the modification of many hydrophilic molecules on the nanocellulose surface due to the mismatching of solvent in the reaction system.
1.3.6 Physical Interaction
Physical interaction is another way to modify the nanocellulose surface; however, the physical interactions are commonly relatively weaker than the covalent bonds. Generally, physical interactions include hydrogen bonding, electrostatic interaction, hydrophilic/hydrophobic interaction, and π–π stacking. The rich OH groups on nanocellulose surface can directly interact with the electron‐rich groups containing oxygen or nitrogen atom, other hydroxyl groups, and carboxyl groups to form hydrogen bonds. The hydrogen bonding potential of nanocellulose might improve the association with the pre‐designated modifiers; and then the hydrophobized nanocellulose after physical modification has been frequently used to enhance its dispersibility in nonpolar polymer matrix of composites. For example, a simple method that can improve the dispersion of nanocellulose in nonpolar matrix is to introduce surfactants or amphiphilic polymers containing both polar and nonpolar moieties, which can interact with both hydrophilic nanocellulose surface in physical pre‐modification stage and the nonpolar matrix in material compounding process, and can act as a bridge to improve the compatibility between nanocellulose and the matrix [63, 64]. Also, the carboxylated surface enables nanocellulose to strongly interact with the molecules containing positive charges (e.g. ammonium‐containing molecules). Such interaction can also be used in the surface modification of nanocellulose and thus allows compounding with nonpolar polymers or hydrogels to produce nanocellulose‐based composites with excellent properties. The surface modification strategy based on physical interaction of nanocellulose with other substances offers several advantages, including the protection of nanocellulose crystalline structure, facile and cost‐effective preparation process, and so on. However, it is also noteworthy that the physical interaction between the components in most cases is not as strong as covalent bonds, and the integrity preservation of nanocellulose and modifiers in applications is a key issue (see Chapter 5 and 6 for details).
1.4 Nanocellulose‐Based Materials and Applications
Based on the chemical and physical properties of nanocellulose and its surface modification strategies related with various methods, varieties of nanocellulose‐based composite materials have been developed and widely applied in electronic and energy devices, biomedical diagnosis and treatment, and other high‐value fields. Nanocellulose generally possesses high mechanical properties; and, for example, the longitudinal modulus of CNC extracted from tunicate can reach as high as about 151 GPa, which is equivalent to that of steel as about 200 GPa. Such high mechanical strength with highly reactive surface, renewability and degradability, makes nanocellulose an ideal sustainable candidate for material enhancement. Similarly, when cellulose raw material is hydrolyzed into CNC, the resultant suspension can perform some interesting optical properties. The as‐prepared CNC in the suspension can form a chiral nematic liquid crystal phase. The pitch and twist angle of this liquid crystal structure strongly depend upon the cellulose resources and the concentration of CNC in suspension, and also are affected by some environmental conditions, such as salt concentration, temperature, pH and so on. Furthermore, this kind of chiral nematic CNC arrangement could be transplated into the solid‐state materials, and even the matrix exhibit stimuli‐response characteristics and contribute to produce thermo‐, pH‐, and other stimuli‐sensitive composite materials (see Chapter 9 for details). In addition, without any material as matrix, the CNC could arrange vertically to the suspension plane by a facile evaporation-induced method, and produce the film-form materials with a structural color of monochromatic light as specifically limited in the ultraviolet region, which is attributed to scattering enhancement of uniaxial periodical CNC arrays. It is worthy of note that this assembly strategy removes the usual chirality and iridescence of the traditional optical materials derived from the free assembly of CNC mentioned above, and prevents the iridescence-based information from being misread and shows an application potential as information-hiding and anti-counterfeiting materials [65]. The following section overviews various preparation strategies, performances and potential applications of nanocellulose‐based materials (detailed in Chapter of this book).
Firstly, the major issue associated with the fabrication of nanocellulose‐based composite material is the compatibility and dispersion of the nanofiller in the matrix. Generally, the nanocellulose reinforcer is blended with the hydrophobic polymer matrix, such as polypropylene (PP) or poly(butylene succinate) (PBS). However, its hydrophilic nature makes it hard to uniformly disperse into the hydrophobic material, thus seriously affecting the performance of as‐prepared composite material. As described earlier, the hydrophobic moieties can be conjugated to the nanocellulose surface to turn the particles or fibers hydrophobic together with polarity matching. An effective way is to conjugate the acetyl groups onto the nanocellulose surface via different chemical reactions. A study has shown that modifying the acetyl groups onto CNC surface via esterification of acetic anhydride improved the dispersibility of CNC in organic solvents as a blending medium, which ultimately enhanced the performance of the composite material [49, 66]. On the other hand, various processing technologies and compatibilizers (via in situ chemical reactions or physical interaction) can also be used to improve the compatibility of nanocellulose with nonpolar and hydrophobic matrix [ 50, 67]. For example, CNFs can be blended into polypropylene and polyethylene by twin‐screw extrusion with maleic anhydride as compatibilizer. Maleic anhydride forms hydrogen bonds or esterifies the hydroxyl groups of CNF during the blending process and thus can adjust the hydrophobicity and polarity of the nanocellulose surface; it facilitates the uniform dispersion of CNF in the matrix. The results showed that the Young's modulus of polyolefin‐based composites was improved about six times after blending with 50 wt% CNF. The situation becomes more complex when BNC is used to blend with nonpolar substances [68]. As BNC is synthesized by microorganisms in the culture medium, the achieved BNC usually presents in gel state, [69] while all the fibers are entangled with each other and hard to be separated. Thus, blending BNC with nonpolar polymers requires surface pre‐modification towards BNC as that of CNF (see Chapter and 8 for details). In contrast, it is relatively easier to enhance the polar polymers such as poly(lactic acid) (PLA) using nanocellulose as filler due to its innate polarity nature mainly ascribed to surface OH groups. The nanocellulose or modified nanocellulose has been directly blended with various types of matrix by different processing technologies, and showed excellent dispersion, mainly attributed to the matching surface characteristics of nanocellulose.
Another important application of nanocellulose in material field is the unique self‐assembling behavior of CNCs. The CNCs self‐assemble into cholesteric liquid crystal under higher concentration in aqueous media and demonstrate interesting optical phenomenon [70], which is utilized in the preparation of optical materials and devices (see Chapter 9 for details). According to previous report [71], the morphology of the films made by the CNC self‐assembly is intimately related to the ionic strength and evaporation speedof the system. The ionic strength in CNC suspension affects the pitch of the liquid crystal structure formed by CNC, while the evaporation speed also exerts some effect on the integrity and pitch of the CNC film. High ionic strength and fast evaporation are unfavorable to the pitch of ordered structure and make a disordered CNC film, while low ionic strength and slow evaporation make the CNC film more uniform with good optical properties. It is believed that the ions in the system and evaporation speed affect the formation of hydrogen bonds and the electrostatic interaction between the CNCs [71]. Based on these basic principles, the composite materials, which inherited optical properties of CNC assembly, can be prepared. For example, by in situ polymerization of the suspension containing monomers and 3% CNCs, the ordered spacial arrangement of CNC could be kept in the newly formed polymer matrix, and the as‐prepared composite inherited the optical properties of the CNC-based liquid crystal structure [72]. Furthermore, the CNC also enhanced the mechanical strength of the polymer materials [72]. In another work, the CNC with a higher loading‐level was used to prepare tough composite film with high mechanical strength. The mass fraction of CNC in the composite material could reach 50–90%, while the mechanical strength of the composite material could be as high as about 12 GPa [73]. Currently, various kinds of monomers, such as organosilica monomer of tetramethoxysilane, have been attempted to fabricate the supporting matrix of chiral nematic‐arranged CNCs [74]. Moreover, the silicon oxide‐based mesoporous chiral materials were derived by removing the chiral nematic phase of CNC, which inherited the unique optical properties [74], and further acted as a removable hard‐template to produce the mesoporous titanium oxide‐based replica films as the candidates of energy and sensor materials [75]. In addition, one more facile method has been carried out to controllably prepare the chiral plasmonic films via simple mixing and subsequent evaporation of the gold rod and CNC suspension, and showed a potential of the scalable and cost‐effective manufacturing [76]. (see Chapter 9 for details).
Nanocellulose‐based materials and composites possess high biocompatibility, improved mechanical properties, good degradability, and special optical properties. These materials and composites have found potential applications in various fields. For example, fluorescent cellulose nanocrystal (fCNC) can be used in in vivo bioimaging. Studies have shown that the Alexa Fluor 633‐decorated fCNC can be injected into living mice, where the fluorescence can be held in the body for more than seven days and the fCNC can be selectively enriched at the limb bones of mice; furthermore, these fCNCs can also be potentially used as a biocompatible luminous reporter of bone disease [55]
