Radiation crosslinking of polysaccharide derivatives

Nagasawa, Naotsugu; Wasikiewicz, J. M.; Yagi, Toshiaki; Mitomo, Hiroshi*; Yoshii, Fumio; Tamada, Masao

In the past few decades a great interest has been focused on the research of naturally occurring polymers, so called polysaccharides. Their main advantages are occurrence in large amounts in nature, as well as their biodegradability. The chemically modified, water-soluble polysaccharide derivatives such as carboxymethylcellulose (CMC), carboxymethylstarch (CMS), carboxymethylchitin (CMCT) and carboxymethylchitosan (CMCS) have been widely used in many industrial applications such as food and medicine fields. The effect of ionizing radiation on aqueous solution of these polysaccharides leads to their degradations. However, the -rays and the electron beam induced the intermolecular crosslinking in the paste-like conditions, i.e., concentration of 10-60%. When the concentration of these polymers was 20%, the gel fractions of CMC, CMS, CMCT and CMCS were 38, 54, 8, 0% at a dose of 20 kGy, respectively while that of CMCS was 40% at high dose of 100 kGy. The obtained biodegradable hydrogels swelled significantly up to about 500 times of dried gel in aqueous media. Radiation parameters of irradiation, such as yields of degradation and crosslinking and the gelation dose, were evaluated by sol-gel analysis on the basis of Charlesby-Rosiak equation. From comparison of the results, we concluded that the structure of functional groups as hydroxyl, carboxymethyl, amino and N-acetylamino groups and molecular weight of polymers are the most important factors for radiation crosslinking of polysaccharide derivatives. If the material has the branched chain structure with carboxymethyl group and high molecular weight, it was crosslinked easily by radiation. The great advantage of these hydrogels is that they might be biodegraded after utilization. The biodegradable hydrogel polymers, synthesized by radiation crosslinking were applied as pressure dispersion materials in the bedsore-prevention mat and water-adsorbent materials for the composting of the livestock excreta.