Physicochemical Characterization of Thermally Treated Chitosans and Chitosans Obtained by Alkaline Deacetylation

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). Thedepolymerization rates (DR) measured by kinematic viscosity (KV), apparent viscosity (AV), andGPC (Mw) until 4 h of treatment were DRKV = 21.9, DRAV = 25.5, and DRMw = 23.3% h(-1) and for 5 to 10 h of treatment they decreased slowly to produce of DRKV = 0.545, DRAV = 0.248, and DRMw = 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 degrees C. The initial F-A values of chitosan without any treatment were F-APT = 0.21 and F-A1HNMR = 0.22 and of chitosan treated for 10 h were F-APT = 0.27 and F-A1HNMR = 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.