Nature and kinetics of paramagnetic defects in chitosan induced by beta-irradiation of chitosan

Abstract

A set of chitosan samples irradiated by electrons with various doses was studied using the EPR method. Two kinds of paramagnetic defects, PC1 and PC2, initiated by this irradiation due to the breakage of bonds in positions C5 and C1 of the chitosan structure, are revealed in the “amorphous” and “crystalline” samples of chitosan. The structure of defects, their spectroscopic parameters, and the kinetics of accumulation/decay have been established for the first time. It is found that the EPR spectrum of the “crystalline” samples consists of 10 almost equidistant lines of the super-hyperfine (SHF) structure with the splitting between them A = 7.4 G for the PC1 center, and a single wide line with a markedly different g-value, attributed to the PC2 one. Both these lines are also present in powder “amorphous” samples, but the SHF structure of the PC1 centers in them is not registered because of the broadening of the individual SHF components. Kinetics of defect accumulation with increasing dose D of the irradiation, and their gradual disappearance during prolonged storage of samples in air, were discovered and studied. Kinetic equations were solved, and the D-dependence and decay times were found from the comparison of theoretical results with the experimental ones. It has been shown that the concentration of shallow and deep traps for electrons affects the rate of the decay process. The recovery process is much slower in the samples having a more perfect crystalline structure.