Abstrait

Crystallinity and Hydrophility of Chitin and Chitosan

Michael Ioelovich

The structure of initial and ground samples of chitin and chitosan have been studied using a wide-angle X-ray scattering (WAXS) and sorption of water vapor. To determine the crystallinity degree, an improved WAXS method was used based on the calculation of the relationship between integrated intensities of X-ray diffraction from crystalline and amorphous domains. The calculations revealed that the actual degree of crystallinity of initial chitin was 0.72, and of initial chitosan sample was 0.57. After ball-grinding in a short time, the decrease of the crystallinity degree was observed, whereas the prolonged grinding resulted in complete amorphization of the samples. Sorption of water vapor for chitin, containing hydrophobic acetyl groups was lower than for chitosan, containing hydrophilic groups. The sorption ability of the samples was inversely proportional to their degree of crystallinity. Reduction of the crystallinity degree promoted to the increase in sorption ability of the samples. This evidences that sorption mechanism of water vapor is absorption of the water molecules into amorphous domains of the hydrophilic polymers. The crystallinity degree calculated from results of water vapors sorption was close to the crystallinity degree of the samples obtained by the WAXS method.