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

Nanocelluloses, including nanocrystalline cellulose, nanofibrillated cellulose and bacterial cellulose nanofibers, have become fascinating building blocks for the design of new biomaterials. Derived from the must abundant and renewable biopolymer, they are drawing a tremendous level of attention, which certainly will continue to grow in the future driven by the sustainability trend. This growing interest is related to their unsurpassed quintessential physical and chemical properties. Yet, owing to their hydrophilic nature, their utilization is restricted to applications involving hydrophilic or polar media, which limits their exploitation. With the presence of a large number of chemical functionalities within their structure, these building blocks provide a unique platform for significant surface modification through various chemistries. These chemical modifications are prerequisite, sometimes unavoidable, to adapt the interfacial properties of nanocellulose substrates or adjust their hydrophilic–hydrophobic balance. Therefore, various chemistries have been developed aiming to surface-modify these nano-sized substrates in order to confer to them specific properties, extending therefore their use to highly sophisticated applications. This review collocates current knowledge in the research and development of nanocelluloses and emphasizes more particularly on the chemical modification routes developed so far for their functionalization.

Key advances in the chemical modification of nanocelluloses

Bull. Chem. Soc. Jpn. への投稿のすすめ

Starch Nanoparticles: A Review

Because of their wide abundance, their renewable and environmentally benign nature, and their outstanding mechanical properties, a great deal of attention has been paid recently to cellulosic nanofibrillar structures as components in nanocomposites. A first major challenge has been to find efficient ways to liberate cellulosic fibrils from different source materials, including wood, agricultural residues, or bacterial cellulose. A second major challenge has involved the lack of compatibility of cellulosic surfaces with a variety of plastic materials. The water-swellable nature of cellulose, especially in its non-crystalline regions, also can be a concern in various composite materials. This review of recent work shows that considerable progress has been achieved in addressing these issues and that there is potential to use cellulosic nano-components in a wide range of high-tech applications.

Cellulosic nanocomposites: a review

Polycaprolactone (PCL) is an important polymer due to its mechanical properties, miscibility with a large range of other polymers and biodegradability. Two main pathways to produce polycaprolactone have been described in the literature: the polycondensation of a hydroxycarboxylic acid: 6-hydroxyhexanoic acid, and the ring-opening polymerisation (ROP) of a lactone: e-caprolactone (e-CL). This critical review summarises the different conditions which have been described to synthesise PCL, and gives a broad overview of the different catalytic systems that were used (enzymatic, organic and metal catalyst systems). A surprising variety of catalytic systems have been studied, touching on virtually every section of the periodic table. A detailed list of reaction conditions and catalysts/initiators is given and reaction mechanisms are presented where known. Emphasis is put on the ROP pathway due to its prevalence in the literature and the superior polymer that is obtained. In addition, ineffective systems that have been tried to catalyse the production of PCL are included in the electronic supplementary information for completeness (141 references).

/pdf/synthesis-of-polycaprolactone-a-review-vlm9rxg878.pdf

Synthesis of polycaprolactone: a review

Over the past 10 years, the grafting of polymers from the surface of cellulose nanocrystals (CNCs) has gained substantial interest in both academia and industry due to the rapidly growing number of potential applications of surface-modified CNCs, which range from building blocks in nanocomposites and responsive nanomaterials to antimicrobial agents. CNCs are rod-like nanoparticles that can be isolated from renewable biosources and which exhibit high crystallinity, tunable aspect ratio, high stiffness, and strength. Upon drying, the abundance of surface hydroxyl groups often leads to a degree of irreversible aggregation, as a result of strong hydrogen bonding. Moreover, their relatively hydrophilic character renders CNCs incompatible with hydrophobic media, e.g., nonpolar solvents and polyolefin matrices. By grafting macromolecules from their surface, CNCs can be imparted with surface characteristics and other physicochemical properties that are reminiscent of the grafted polymer. This has allowed the desi...

Grafting Polymers from Cellulose Nanocrystals: Synthesis, Properties, and Applications

Polymer grafting onto starch nanocrystals.

In our group, we work on the surface modification of cellulose nanocrystals. During this work, we have encountered reproducibility issues when the same reactions were performed on nanocrystals from different hydrolysis batches, indicating a variable surface composition. Given the inherent purity of the nanoparticles themselves, this issue was believed to be due to the presence of adsorbed species at the surface of the nanocrystals blocking reactive sites. To investigate this in detail, nanocrystals from several batches were extracted with different solvents. The effect of these extractions on the surface composition of the nanowhiskers was investigated, followed by its effect on the Surface-Initiated Ring-Opening Polymerization (SI-ROP) of e-caprolactone. The extracted impurities were analysed by NMR (1H and 13C) and MS, showing a variety of adsorbed species which can be removed by solvent extraction. A Soxhlet extraction using ethanol before the reaction was shown to be the most effective in removing adsorbed low molecular weight organic compounds produced during the hydrolysis, resulting in improved reproducibility between reactions using nanocrystals from different batches, as confirmed by FTIR, elemental analysis and XPS. Extraction with ethanol should thus be performed before all reaction as these adsorbed species can be expected to interfere with all surface modification reactions.

Marianne Labet

Papers

Synthesis of polycaprolactone: a review

Grafting Polymers from Cellulose Nanocrystals: Synthesis, Properties, and Applications

Polymer grafting onto starch nanocrystals.

Improving the reproducibility of chemical reactions on the surface of cellulose nanocrystals: ROP of ε-caprolactone as a case study

Citric acid as a benign alternative to metal catalysts for the production of cellulose-grafted-polycaprolactone copolymers