This critical review provides a processing-structure-property perspective on recent advances in cellulose nanoparticles and composites produced from them. It summarizes cellulose nanoparticles in terms of particle morphology, crystal structure, and properties. Also described are the self-assembly and rheological properties of cellulose nanoparticle suspensions. The methodology of composite processing and resulting properties are fully covered, with an emphasis on neat and high fraction cellulose composites. Additionally, advances in predictive modeling from molecular dynamic simulations of crystalline cellulose to the continuum modeling of composites made with such particles are reviewed (392 references).

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Cellulose nanomaterials review: structure, properties and nanocomposites

Background Since at least 400 C.E., when the Mayans first used layered clays to make dyes, people have been harnessing the properties of layered materials. This gradually developed into scientific research, leading to the elucidation of the laminar structure of layered materials, detailed understanding of their properties, and eventually experiments to exfoliate or delaminate them into individual, atomically thin nanosheets. This culminated in the discovery of graphene, resulting in a new explosion of interest in two-dimensional materials. Layered materials consist of two-dimensional platelets weakly stacked to form three-dimensional structures. The archetypal example is graphite, which consists of stacked graphene monolayers. However, there are many others: from MoS 2 and layered clays to more exotic examples such as MoO 3 , GaTe, and Bi 2 Se 3 . These materials display a wide range of electronic, optical, mechanical, and electrochemical properties. Over the past decade, a number of methods have been developed to exfoliate layered materials in order to produce monolayer nanosheets. Such exfoliation creates extremely high-aspect-ratio nanosheets with enormous surface area, which are ideal for applications that require surface activity. More importantly, however, the two-dimensional confinement of electrons upon exfoliation leads to unprecedented optical and electrical properties. Liquid exfoliation of layered crystals allows the production of suspensions of two-dimensional nanosheets, which can be formed into a range of structures. (A) MoS 2 powder. (B) WS 2 dispersed in surfactant solution. (C) An exfoliated MoS 2 nanosheet. (D) A hybrid material consisting of WS 2 nanosheets embedded in a network of carbon nanotubes. Advances An important advance has been the discovery that layered crystals can be exfoliated in liquids. There are a number of methods to do this that involve oxidation, ion intercalation/exchange, or surface passivation by solvents. However, all result in liquid dispersions containing large quantities of nanosheets. This brings considerable advantages: Liquid exfoliation allows the formation of thin films and composites, is potentially scaleable, and may facilitate processing by using standard technologies such as reel-to-reel manufacturing. Although much work has focused on liquid exfoliation of graphene, such processes have also been demonstrated for a host of other materials, including MoS 2 and related structures, layered oxides, and clays. The resultant liquid dispersions have been formed into films, hybrids, and composites for a range of applications. Outlook There is little doubt that the main advances are in the future. Multifunctional composites based on metal and polymer matrices will be developed that will result in enhanced mechanical, electrical, and barrier properties. Applications in energy generation and storage will abound, with layered materials appearing as electrodes or active elements in devices such as displays, solar cells, and batteries. Particularly important will be the use of MoS 2 for water splitting and metal oxides as hydrogen evolution catalysts. In addition, two-dimensional materials will find important roles in printed electronics as dielectrics, optoelectronic devices, and transistors. To achieve this, much needs to be done. Production rates need to be increased dramatically, the degree of exfoliation improved, and methods to control nanosheet properties developed. The range of layered materials that can be exfoliated must be expanded, even as methods for chemical modification must be developed. Success in these areas will lead to a family of materials that will dominate nanomaterials science in the 21st century.

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Liquid Exfoliation of Layered Materials

Biocomposites reinforced with natural fibers: 2000–2010

Due to their abundance, high strength and stiffness, low weight and biodegradability, nano-scale cellulose fiber materials (e.g., microfibrillated cellulose and bacterial cellulose) serve as promising candidates for bio-nanocomposite production. Such new high-value materials are the subject of continuing research and are commercially interesting in terms of new products from the pulp and paper industry and the agricultural sector. Cellulose nanofibers can be extracted from various plant sources and, although the mechanical separation of plant fibers into smaller elementary constituents has typically required high energy input, chemical and/or enzymatic fiber pre-treatments have been developed to overcome this problem. A challenge associated with using nanocellulose in composites is the lack of compatibility with hydrophobic polymers and various chemical modification methods have been explored in order to address this hurdle. This review summarizes progress in nanocellulose preparation with a particular focus on microfibrillated cellulose and also discusses recent developments in bio-nanocomposite fabrication based on nanocellulose.

Microfibrillated cellulose and new nanocomposite materials: a review

This paper provides an overview of recent progress made in the area of cellulose nanofibre-based nanocomposites. An introduction into the methods used to isolate cellulose nanofibres (nanowhiskers, nanofibrils) is given, with details of their structure. Following this, the article is split into sections dealing with processing and characterisation of cellulose nanocomposites and new developments in the area, with particular emphasis on applications. The types of cellulose nanofibres covered are those extracted from plants by acid hydrolysis (nanowhiskers), mechanical treatment and those that occur naturally (tunicate nanowhiskers) or under culturing conditions (bacterial cellulose nanofibrils). Research highlighted in the article are the use of cellulose nanowhiskers for shape memory nanocomposites, analysis of the interfacial properties of cellulose nanowhisker and nanofibril-based composites using Raman spectroscopy, switchable interfaces that mimic sea cucumbers, polymerisation from the surface of cellulose nanowhiskers by atom transfer radical polymerisation and ring opening polymerisation, and methods to analyse the dispersion of nanowhiskers. The applications and new advances covered in this review are the use of cellulose nanofibres to reinforce adhesives, to make optically transparent paper for electronic displays, to create DNA-hybrid materials, to generate hierarchical composites and for use in foams, aerogels and starch nanocomposites and the use of all-cellulose nanocomposites for enhanced coupling between matrix and fibre. A comprehensive coverage of the literature is given and some suggestions on where the field is likely to advance in the future are discussed.

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Review: current international research into cellulose nanofibres and nanocomposites

Preface About the Editor List of Contributors PART I 1 Introductory Overview (David Plackett) 11 Introduction 12 Worldwide Markets for Films and Coatings 13 Sustainability 14 Bio-Derived Polymers 15 Other Topics References 2 Production, Chemistry and Degradation of Starch-Based Polymers (Analia Vazquez, Maria Laura Foresti and Viviana Cyras) 21 Introduction 22 Gelatinization 23 Effect of Gelatinization Process and Plasticizer on Starch Properties 24 Retrogradation 25 Production of Starch Polymer Blends 26 Biodegradation of Starch-Based Polymers 27 Concluding Remarks 28 Acknowledgement References 3 Production, Chemistry and Properties of Polylactides (Anders Sodergard and Saara Inkinen) 31 Introduction 32 Production of Polylactides 33 Polylactide Chemistry 34 Properties of Polylactides 35 Concluding Remarks References 4 Production, Chemistry and Properties of Polyhydroxyalkanoates (Eric Pollet and Luc Averous) 41 Introduction 42 Polyhydroxyalkanoate Synthesis 43 Properties of Polyhydroxyalkanoates 44 Polyhydroxyalkanoate Degradation 45 PHA-Based Multiphase Materials 46 Production and Commercial Products References 5 Chitosan for Film and Coating Applications (Patricia Fernandez-Saiz and Jose M Lagaron) 51 Introduction 52 Physical and Chemical Characterization of Chitosan 53 Properties and Applications of Chitosan 54 Processing of Chitosan 55 Concluding Remarks References 6 Production, Chemistry and Properties of Proteins (Mikael Gallstedt, Mikael S Hedenqvist and Hasan Ture) 61 Introduction 62 Plant-Based Proteins 63 Animal-Based Proteins 64 Solution Casting of Proteins an Overview 65 Dry Forming of Protein Films 66 Concluding Remarks References 7 Synthesis, Chemistry and Properties of Hemicelluloses (Ann-Christine Albertsson, Ulrica Edlund and Indra K Varma) 71 Introduction 72 Structure 73 Sources 74 Extraction Methodology 75 Modifications 76 Applications 77 Concluding Remarks References 8 Production, Chemistry and Properties of Cellulose-Based Materials (Mohamed Naceur Belgacem and Alessandro Gandini) 81 Introduction 82 Pristine Cellulose as a Source of New Materials 83 Novel Cellulose Solvents 84 Cellulose-Based Composites and Superficial Fiber Modification 85 Cellulose Coupled with Nanoparticles 86 Electronic Applications 87 Biomedical Applications 88 Cellulose Derivatives 89 Concluding Remarks References 9 Furan Monomers and their Polymers: Synthesis, Properties and Applications (Alessandro Gandini) 91 Introduction 92 Precursors and Monomers 93 Polymers 94 Biodegradability of Furan Polymers 95 Concluding Remarks References PART II 10 Food Packaging Applications of Biopolymer-Based Films (N Gontard, H Angellier-Coussy, P Chalier, E Gastaldi, V Guillard, C Guillaume and S Peyron) 101 Introduction 102 Food Packaging Material Specifications 103 Examples of Biopolymer Applications for Food Packaging Materials 104 Research Directions and Perspectives 105 Concluding Remarks References 11 Biopolymers for Edible Films and Coatings in Food Applications (Idoya Ferandez-Pan and Juan Ignacio Mate Caballero) 111 Introduction 112 Materials for Edible Films and Coatings 113 Edible Films and Coatings for Food Applications 114 Concluding Remarks References 12 Biopolymer Coatings for Paper and Paperboard (Christian Aulin and Tom Lindstrom) 121 Introduction 122 Biopolymer Films and Coatings 123 Bio-Nanocomposite Films and Coatings 124 Concluding Remarks 125 Acknowledgement References 13 Agronomic Potential of Biopolymer Films (Lluis Martin-Closas and Ana M Pelacho) 131 Introduction 132 The Potential Role of Biodegradable Materials in Agricultural Films 133 Presently Available Biopolymers and Biocomposites 134 Past and Current International Projects on Biodegradable Agricultural Films 135 Present Applications of Biopolymer Films in Agriculture 136 Potential Uses: Current Limitations and Future Applications 137 Concluding Remarks 138 Acknowledgements References 14 Functionalized Biopolymer Films and Coatings for Advanced Applications (David Plackett and Vimal Katiyar) 141 Introduction 142 Optoelectronics 143 Sensors 144 Miscellaneous Applications 145 Concluding Remarks References 15 Summary and Future Perspectives (David Plackett) 151 Introduction 152 Bioplastics 153 Bio-Thermoset Resins 154 Nanocomposites Based on Inorganic Nanofillers 155 Nanocomposites Based on Cellulose Nanofillers 156 Concluding Remarks References Index

Biopolymers : new materials for sustainable films and coatings

Poly(L-lactic acid) (PLA) films are in use for various types of food packaging; however, a wider range of applications would be possible if the barrier properties of these films could be improved. To make such improvements, combinations of PLA with two nanofillers, laurate-intercalated Mg-Al layered double hydroxide (LDH-C12) and a cationic organomodified montmorillonite (MMT) clay (Cloisite® 30B), were investigated. The dispersion of these fillers in PLA by melt processing was explored using two methods, either by mixing the nanofillers with PLA granulate immediately before extrusion or by preparation and subsequent dilution of PLA-nanofiller masterbatches. After melt processing of these materials, PLA molecular weight, thermal stability, film transparency, morphology, and permeability characteristics were determined. Direct addition of LDH-C12 drastically reduced the PLA molecular weight. Although this reduction in molecular weight was still very significant, it was less when a PLA/LDH-C12 masterbatch was processed. In contrast, there was no significant reduction in PLA molecular weight when processing with Cloisite® 30B. However, film transparency was compromised when either LDH or MMT nanofillers were used. Evidence from DSC analyses showed a significant increase in heat of fusion when LDH-C12 was dispersed in PLA compared with Cloisite® 30B, likely indicating a difference in nucleating properties. Complementary optical purity analyses suggested that racemization as a result of processing could influence the PLA crystallinity as determined by DSC in certain cases. A reduction in thermal stability when incorporating LDH-C12 could be a direct result of PLA molecular weight reduction. XRD and TEM analyses showed that both Cloisite® 30B- and LDH-C12-based PLA composites yielded exfoliated and intercalated morphologies, but nanofiller agglomeration was also seen when LDH-C12 was used. PLA/Cloisite® 30B nanocomposite films exhibited significant enhancement in oxygen and water vapor barrier properties, but no such improvement was found in PLA/LDH-C12 nanocomposite films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Melt processing of poly(L-lactic acid) in the presence of organomodified anionic or cationic clays

Modification of jute fibers with polystyrene via atom transfer radical polymerization.

Extraction and chemical characterization of rye arabinoxylan and the effect of β-glucan on the mechanical and barrier properties of cast arabinoxylan films

Conifer fibers were used to reinforce polypropylene (PP). To improve the compatibility between the conifer fibers and the PP matrix, the fibers were either grafted with maleated PP (MAPP), treated by adding MAPP, or mixed with ethylene/propylene/diene terpolymer (EPDM). The treatments resulted in improved processing, as well as improvements in the thermal and mechanical properties of the resultant composites compared with the composites filled with untreated conifer fibers. Moreover, MAPP grafting and MAPP treating displayed more obvious benefits than EPDM treating in terms of thermal properties, processing flowability, and tensile strength improvements. EPDM treating also produced more significant benefits than either MAPP grafting or MAPP treating in terms of impact strength and tensile elongation improvements. These improvements were attributed to surface coating of the fibers when EPDM was used. In addition, the effect of the concentration of the conifer fibers on the properties of the composites and the difference between MAPP grafting and MAPP treating were evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2833–2841, 2001

David Plackett

Papers

Biopolymers : new materials for sustainable films and coatings

Melt processing of poly(L-lactic acid) in the presence of organomodified anionic or cationic clays

Modification of jute fibers with polystyrene via atom transfer radical polymerization.

Extraction and chemical characterization of rye arabinoxylan and the effect of β-glucan on the mechanical and barrier properties of cast arabinoxylan films

Conifer fibers as reinforcing materials for polypropylene-based composites