Structure and physicochemical properties of nitrogenated derivatives of cellulose

Nitrogenated derivatives of cellulose, and namely chitin and chitosan, are of commercial interest because of their antibacterial activity, biocompatibility, biodegradability and sorption ability. Structure and some physicochemical properties of these derivatives have been studied by methods of wide-angle X-ray scattering (WAXS), microcalorimetry and sorption. To determine the crystallinity degree of the samples, 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 0.57. After ball-grinding for a short time, the decrease in the crystallinity degree was observed, whereas the prolonged grinding resulted in complete amorphization of the samples. The wetting enthalpy and sorption ability of the samples were inversely proportional to degree of crystallinity. Reduction of the crystallinity degree of the samples promoted increasing of the wetting enthalpy and water sorption. This evidences that mechanism of interaction between the nitrogenated polysaccharides and water is absorption of the water molecules into amorphous domains of the hydrophilic polymers. The crystallinity degree values calculated from results of water vapor sorption and wetting enthalpy were close to the crystallinity degree of the samples obtained by the WAXS method.