Fabrication of nanostructured and microstructured chitin materials through gelation with suitable dispersion media

Abstract

Recent developments in the fabrication of nano- and microstructured chitin materials are reviewed, specifically focusing on approaches through gelation with suitable dispersion media. Although chitin is one of the most abundant natural polysaccharides, it is under-used as a result of its poor solubility and difficulties in processing. The dissolution of chitin in different solvent systems, including ionic liquids, has been investigated for the production of various materials. For example, the ionic liquid 1-allyl-3-methylimidazolium bromide dissolved chitin at concentrations up to 5% w/w and formed ion gels at higher concentrations of chitin. A highly concentrated solution of CaBr₂·2H₂O/methanol also induced the gelation of chitin. As one of the most efficient methods of production of nanomaterials from chitin, self-assembled nanofibers have been fabricated by regeneration from solutions or gels of chitin with the appropriate solvents and dispersion media using a bottom-up approach. For example, a chitin ion gel with 1-allyl-3-methylimidazolium bromide was regenerated using methanol to produce a chitin nanofiber dispersion, which was then used to construct a film with a highly entangled nanofiber morphology by filtration. Physical and chemical approaches have been investigated for the fabrication of composite materials of self-assembled chitin nanofibers with other polymeric components. Poly(vinyl alcohol) and carboxymethyl cellulose were made compatible with chitin nanofibers by co-regeneration and electrostatic interaction procedures, respectively. Surface-initiated graft polymerization of some monomers from chitin nanofiber films with the appropriate initiating groups have been conducted using the latter approach to obtain composite films covalently linked to graft chains on the nanofibers. Regeneration from gels with CaBr₂·2H₂O/methanol resulted in the efficient production of microporous materials.