Pulse radiolysis study on aqueous solution of polysaccharide derivatives. Carboxymethyl cellulose, carboxymethyl chitin/chitosan

Irradiated polysaccharides generally become degraded, but some kinds of polysaccharide derivatives, for example carboxymethyl cellulose and carboxymethyl chitin/chitosan (Figure) etc, become crosslinked and form hydrogels in the case of concentrated aqueous solution. By irradiating a polymer solution, polymer radicals are produced by the reaction of polymer chains with some radicals of water decompositions, such as OH radical and hydrated electron etc, and then the crosslinking takes place by the reaction of the polymer radicals with each other. To study the early process of hydrogelation of polysaccharide derivatives by ionizing irradiation, we evaluated the reactivity of OH radical and hydrated electron with polymer chains by pulse radiolysis technique. The rate constants were calculated from the absorbance at 720 nm (absorption peak of hydrated electron) and at 472 nm (absorption peak of (SCN)2.- : competitor of OH radical). By measuring absorbance at around 300 nm for about 1 hour, we confirmed the steady absorbance in the case of carboxymethyl chitosan solution and the slow decay of absorbance in the case of carboxymethyl cellulose. We assumed that some long-lived polymer radicals are produced after irradiation and diminish by some reactions. To study the change of the absorption spectrum after irradiation, we measured the spectrum of these polymer solutions with ultraviolet-visible spectroscopy, and observed the decay of the absorption spectrum. (authors)