Modifying the molecular weight of chitosan

Abstract

Chitosan is a biodegradable, biocompatible, nontoxic, environmentally friendly raw material and applied to many fields, such as agriculture, food/nutrition, biomedicine, biochemistry, cosmetics, textiles, materials science, wastewater treatment, etc. Various raw materials such as shrimp and crab shells, squid pens, and different manufacturing methods have been used to prepare commercial chitosan products with different molecular weight (MW), degree of deacetylation (DDA), and high polydispersity index (PDI). MW, PDI, DDA, and distribution of acetyl groups are important intrinsic factors of chitosan, which can affect its physicochemical properties and bioactivity. Modifying the MW and PDI to suit the application is crucial and key to tackling targets. In this chapter the methods for modifying the MW and PDI of chitosan will focus on mechanical degradation methods (shearing, ultrasonication, and microfluidization), fractionation (or regeneration), and supercritical carbon dioxide methods.