Dissolution, gelation, functionalization, and material preparation of chitin using ionic liquids

In this article, a review of the research endeavors concerning ionic liquids, that have been used as media for dissolution, gelation, functionalization, and material preparation of chitin, is presented. Although chitin has been identified to show difficulty in solubility and processability, leading to mostly an unutilized organic resource, some ionic liquids have been found to dissolve chitin in certain concentrations. For example, the author found that an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), dissolved chitin in concentrations up to 4.8 wt% and formed ion gels at higher contents of chitin. Cellulose/chitin binary ion gel and film were also obtained from the individually prepared polysaccharide solutions with ionic liquids. The binary ion gel was applied as a novel electrolyte for an electric double layer capacitor. Acetylation of chitin using acetic anhydride in AMIMBr gave chitin acetates with high degrees of substitution. The modification technique in the AMIMBr solvent was applied to the synthesis of a chitin macroinitiator for atom transfer radical polymerization (ATRP). Grafting of styrene by ATRP from the resulting macroinitiator was conducted to give chitin-graft-polystyrene. Self-assembled chitin nanofibers were fabricated in a methanol dispersion obtained by regeneration from the chitin ion gel with AMIMBr using methanol, which formed a film by subjecting the dispersion to filtration. Co-regeneration from the chitin ion gel coexisting poly(vinyl alcohol) (PVA) gave a self-assembled chitin nanofiber/PVA composite film. The self-assembled chitin nanofibers have also been used as a reinforcing agent for cellulose derivatives to produce composite films.