Preparation, characterization, and swelling behavior of N-acetylated and deacetylated chitosans

By using three original grades of chitosan, six different chitosans of reacetylated as well as the higher deacetylated types were synthesized and characterized by different methods. The effect of molecular weight and degree of deacetylation (DD) on inherent viscosity, crystallinity and swelling were evaluated. The results of polymer solution viscosity have confirmed that acetylation and deacetylation reactions had no degradative effect on polymer structure; and variation in inherent viscosity probably was related to intramolecular and intermolecular hydrogen bondings. Also the results indicated that the degree of crystallinity of chitosan powder was mainly dependent on degree of deacetylation. In the case of high and medium molecular weights, with the increase in degree of deacetylation, the crystallinity was initially increased and then it was decreased. With low molecular weight, however, the percent of crystallinity was increased with increasing degree of deacetylation. In addition, the variation in swelling was also referred to molecular weight, crystallinity and the pH medium. Comparing the results of DD with three different methods confirmed that DD values were totally dependent on the type of analytical method, as it should be considered while reporting these values. (c) 2006 Elsevier Ltd. All rights reserved.