EFFECTS OF COBALT-60 GAMMA RADIATION ON POLY(VINYL ALCOHOL). III. EFFECTS OF GAMMA RADIATION ON WATER-SWOLLEN FILMS AND AQUEOUS SOLUTIONS

Studies were done on the effects of gamma irradiation both in air and in vacuo on aqueous solutions and waterswollen films of polyvinylalcohol (PVA). The radiationinduced changes were followed by the measurements of viscosity, sol fraction, and degree of swelling. For the water-swollen films, remarkable differences were observed between the irradiation in vacuo and in air, but for the aqueous solutions of higher concentrations there were little difference. For the irradiation of water-swollen films in air the indirect effect of water is quantitatively discussed. It was found by a calculation that only 69% of the energy absorbed by water was used for the main chain fracture and that the energy dissipated per main chain fracture was about 36 ev. When aqueous solutions were irradiated, viscosities were increased with dose and finally a gel was formed in a manner similar to that observed in the case of vsouum-irradiation of water- swollen films. The ratio of the number of fractares and crosslinked units, p/sub 0//q/sub 0/, was increased with the weight fraction of the polymer; the value of p/sub 0//q/sub 0/ was 0.27, 0.39, and 0.55 at the weight more » fraction of 0.10, 0.20, and 0.25 respectively. The results obtained by the irradiation of the solutions containing 0.1 wt fraction of polymer which had stood for some period before irradiation showed that the sol fraction was decreased with standing time. (auth) « less