Physicochemical characterization of thermally treated chitosans and chitosans obtained by alkaline deacetylation

Abstract

The thermal depolymerization of chitosan and alkaline deacetylation of chitin were characterized by measurement of viscosity, gel permeation chromatography (GPC), potentiometric titration (PT), and proton nuclear magnetic resonance spectroscopy (H 1 NMR). The depolymerization rates (DR) measured by kinematic viscosity (KV), apparent viscosity (AV), and GPC (Mw) until 4 h of treatment were DR KV = 21.9, DR AV = 25.5, and D R M w = 23.3 % h - 1 and for 5 to 10 h of treatment they decreased slowly to produce of D R KV = 0.545, D R AV = 0.248, and DR Mw = 1.11 % h - 1. The mole fraction of N-acetylglucosamine residues F A of chitosans was not modified after 10 h of thermal treatment at 100°C. The initial F A values of chitosan without any treatment were F APT = 0.21 and F A HNMR 1 = 0.22 and of chitosan treated for 10 h were F APT = 0.27 and F A HNMR 1 = 0.22. The variables used to characterize the depolymerization process showed a good correlation. Six hours of thermal treatment as sufficient to obtain chitosans with a molar mass 90% smaller than that of the control chitosan without treatment.