8 - Surface derivatization and grafting on self-assembled chitin nanofibers for modification, functionalization, and application

Abstract

In this chapter, the research endeavors regarding surface derivatization and grafting on self-assembled chitin nanofibers (ChNFs), which have been prepared by regeneration from ion gels with an ionic liquid, are overviewed. Although chitin is identified to be poorly in solubility and processability, leading to mostly an unutilized biomass resource, some ionic liquids have been found to dissolve and swell chitin. The author reported that an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), dissolved chitin in concentrations up to 4.8wt% and formed ion gels in higher contents of chitin. Accordingly, studies on efficient derivatization of chitin, that is, acylation, through the dissolution and gelation with AMIMBr have been investigated. Interestingly, the self-assembling process to fabricate ChNFs was achieved by regeneration from the chitin ion gel with AMIMBr using methanol, which formed a film by subjecting the resulting dispersion to filtration. Surface-acylation on the self-assembled ChNF film was attempted to modify its property as more flexible by constructing semi-crystalline fashion. Anionic groups were also introduced by the surface-acylation approach on the self-assembled ChNF film. The anionic ChNFs were used as stabilizer for Pickering emulsion polymerization of styrene to produce ChNF-polystyrene composite particles, which were converted into hollow particles by solubilizing out inner polystyrene. ChNF-graft-synthetic polymer composite films were successfully prepared by the surface-initiated ring-opening graft polymerization technique using cyclic monomers. The abovementioned surface-acylation technique in the AMIMBr solvent was extended to the synthesis of chitin macroinitiators from ChNFs for atom transfer radical polymerization (ATRP). Surface-initiated graft ATRP of vinyl monomers was then carried out to give ChNF-graft-synthetic polymer films.