Chitin and chitosan nanofibers: preparation and chemical modifications

Abstract

Chitin nanofibers are prepared from the exoskeletons of crabs and prawns, squid pens and mushrooms by a simple mechanical treatment after a series of purification steps. The nanofibers have fine nanofiber networks with a uniform width of approximately 10 nm. The method used for chitin-nanofiber isolation is also successfully applied to the cell walls of mushrooms. Commercial chitin and chitosan powders are also easily converted into nanofibers by mechanical treatment, since these powders consist of nanofiber aggregates. Grinders and high-pressure waterjet systems are effective for disintegrating chitin into nanofibers. Acidic conditions are the key factor to facilitate mechanical fibrillation. Surface modification is an effective way to change the surface property and to endow nanofiber surface with other properties. Several modifications to the chitin NF surface are achieved, including acetylation, deacetylation, phthaloylation, naphthaloylation, maleylation, chlorination, TEMPO-mediated oxidation, and graft polymerization. Those derivatives and their properties are characterized.

Figure 1

Chemical structures of cellulose, chitin, and chitosan.

Figure 2

Schematic presentation of the exoskeleton structure of crab shell.

Figure 3

SEM images of chitin nanofibers from crab shell after grinder treatment.

Figure 4

SEM image of chitosan nanofibers after high pressure waterjet treatment.

Scheme 1

Acetylation of chitin nanofibers.

Scheme 2

Partial deacetylation for chitin nanowhiskers.

Scheme 3

Phthaloylation, maleylation, and naphthaloylation of chitin nanofibers.

Scheme 4

Preparation of surface N-halamine chitin nanofibers.

Scheme 5

TEMPO-mediated oxidation for chitin nanocrystals.

Scheme 6

Graft co-polymerization of acrylic acid onto chitin nanofibers.