Solid-phase preparation and characterization of Chitosan

Chitosan was prepared with stressing method by blending chitin and solid alkali in a single-screw extruder at given temperature and characterized by potentiometric titration, gel permeation chromatography (GPC), infrared spectrum (IR) and carbon-13 magnetic resonance sperctroscopy (¹³C NMR). Chitosan with a deacetylation degree (DD) of 76.1% was obtained at a mass ratio 0.2:1:1 for H₂O/chitin/NaOH at 160°C for 12 min. Compared to conventional solution method(usually 1: 10 for chitin/NaOH), the alkali assumption greatly decreased. Molecular weight of chitosan obtained by solid-phase method (S3,M _w 1.54×10⁵) was lower than that obtained by suspension method (Y2,M _w 3.34 ×10⁵). During deacetylation, molecular weight decreased with high reaction temperature and long reaction time but remained same at different initial ratios of NaOH/chitin. It might be concluded that degradation of chitosan was caused by breakout of the main chain of the oxidized chitosan catalyzed by alkali during the deactylation. IR and¹³C NMR showed that structures of chitosans prepared by solid-phase method were not changed. Foundation item: Supported by the National Natural Science Foundation of China (29977014) Biography: Gao Le-ping (1977), male, Master, research direction: renewable sources and chemobiology.