Surface Modification of Cellulose Nanocrystals

Eyley S, Thielemans W (2014) Surface modification of cellulose nanocrystals. Nanoscale... 

Study of the incorporation of cellulose nanocrystals in a polyurethane elastomer shows the modification produced in the properties of the resulting material [154]. In this context, the surface hydroxyl groups on cellulose are reacted to produce modified cellulose crystals. The study reveals a strong dependence of materials properties on the cellulose content, a peculiar behavior appearing below the percolation threshold. 

Dufresne et al. [153] noted that surface adsorption of potyojq ethylene chains on the surface nanocrystals can improve dispersibility and thermal stability of nanocrystals during the melt processing of polyethylene based nanocomposites. The chemical modification of cellulose is a most effective approach to avoid irreversible agglomeration during drying, and enhance the adhesion between nanocellulose and nonpolar matrices [132]. Dufresne et al. [98] showed also, that chemical and physical compatibilization imparted by poly(ethylene glycol) and polyoxyethylene layers promoted the interfacial interaction between cellulosic nanoparticles and polystyrene. 

This chapter focuses on the use of nanotechnology in the development of cellulose and chitin nanoctystals and their novel biomedical applications. It consists of four main sections. The first section is a brief introduction. The second section focuses on cellulose nanocrystals (CNCs) and their preparation procedure, physical properties, and surface modifications. Cationic modification of CNCs is also presented to produce positively charged CNCs. Various bioapplications of CNCs in bionanocomposites, drug delivery, and biosensors are discussed as well. The third section focuses on chitin nanoctystals (CHNCs). Except for a short introduction on chitin and its structure, the methods of isolation and characterization of chitin are discussed and the surface modifications and properties of CHNCs are summarized. The applications of CHNCs as reinforcing fillers in nanocomposites and several biomedical applications are discussed. The fourth section is a summary and perspective highlighting the future directions on the application of these natural nanoctystals in various key industries related to biomedicine. 

Excluding the use of an aqueous polymer dispersion, or latex, an alternative way to process nonpolar polymer nanocomposites reinforced with cellulose nanocrystals consists of their dispersion in an adequate (with regard to matrix) organic medium. Coating with a surfactant or a surface chemical modification of the nanoparticles can be considered. The global objective is to reduce their surface energy in order to improve their dispersibUity/compatibility with nonpolar media. 

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