STRUCTURE AND FUNCTION OF CHITOSAN .3. CRYSTALLINITY OF PARTIALLY N-ACETYLATED CHITOSANS

In order to search for a chitosan with low crystallinity, partially N- deacetylated chitins (PDC) and partially N-acetylated chitosans (PAC) with a low degree of N-acetylation (DAc) were examined by X-ray powder diffraction measurements. Three PDC samples, having less than 30% DAc and prepared by solid-state deacetylation, gave X-rav powder patterns showing the presence of alpha-chitin, a hydrated crystal of chitosan, or their mixture, respectively. When these PDC samples were treated w ith an acid-alkali, however, reduced crystallinity was observed. By an nealing in water at 160 or 200-degrees-C, the latter PDC having DAc le ss than approx. 22% gave powder patterns indicating the presence of an anhydrous crystal which may spoil the chitosan's functionality. In co ntrast, PAC prepared by N-acetylating pure chitosan (DAc = 0%) in a sw ollen state, which can be expected to have random copolymers in the ch ain, was always less crystallized than PDC, this crystallinity dependi ng on the molecular weight. In the case of high-molecular-weight PAC s amples, whose DAc was in the range of 5-21%, the effect of high molecu lar weight on reducing crystallinity was larger than that of the degre e of N-acetylation.