Abstract
This paper reviews studies on dissolution, derivatization, and nanomaterial processing of chitin using an ionic liquid as useful media. Because chitin is the second most abundant polysaccharide on the earth after cellulose, there is major interest in conversion of native chitin resources into various useful materials after proper dissolution in suitable solvents. For the derivatization and nanomaterial processing of chitin, the author has been focusing on ionic liquids because which have been found to be used as good solvents for cellulose in a past decade. The author found that an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), dissolved chitin in concentrations up to 4.8 wt% and mixtures of the higher amounts of chitin with AMIMBr gave ion gels. Acetylation, the simplest derivatization, of chitin using acetic anhydride was achieved in the AMIMBr solvent under mild conditions. Furthermore, the chitin nanofibers were fabricated by regeneration technique from the chitin ion gel with AMIMBr using methanol. Moreover, filtration of the chitin nanofiber dispersion with methanol was carried out to give a chitin nanofiber film. The chitin nanofiber-poly(vinyl alcohol) composite film was also prepared from the ion gel by co-regeneration method.
Highlights
Ionic liquids are low-melting-point molten salts, defined as that form liquids at room temperature or even at temperatures lower than the boiling point of water
For the derivatization and nanomaterial processing of chitin, the author has been focusing on ionic liquids because which have been found to be used as good solvents for cellulose in a past decade
Because the author found that allyl-3-methylimidazolium bromide (AMIMBr) dissolved chitin in the concentrations up to 4.8 wt% by heating and further the chitin ion gels were obtained from the mixture of the higher amounts of chitin with AMIMBr, acetylation of chitin using acetic anhydride was performed in the AMIMBr solvent to give the acetylated chitins with the high degree of substitution (DS) values
Summary
Ionic liquids are low-melting-point molten salts, defined as that form liquids at room temperature or even at temperatures lower than the boiling point of water. Only the limited investigations have been reported regarding the dissolution of chitin with ionic liquids including the author’s study, in which the author found that an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), dissolved or swelled chitin to form weak gel-like materials (ion gels) (Figure 2) [20,21]. The preparation of self-assembled fibrillar nanostructures, so-called nanofibers, is one of the most useful methods to practically utilize polymeric functional materials from native chitin sources [31,32,33]. On the basis of the above backgrounds and viewpoints, this paper reviews the studies on the dissolution, acetylation, and nanofibrillation using AMIMBr. The series of the studies provide new approaches for material processing from native chitin sources
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