Effects of Cobalt-60 Gamma Radiation on Poly (vinyl alcohol) : II. Effects of Gamma Radiation on Water-Swollen Poly (vinyl alcohol) Films

Abstract

Poly (vinyl alcohol) films swollen in water or swollen with adsorbed water vapor were irradiated with the dose up to 3.2×10⁷ γ in the presence of air. In these cases, gel formation occurred over a definite radiation dose. The active ends produced by main-chain fractures are assumed to be more capable of attacking other molecules at any point and joining to them, owing to the more mobile character of chains in the swollen films. On the assumption that the energy indirectly absorbed by the polymer depends on the water content in the swollen film, and that the free radicals produced from the water molecules do not directly contribute to the formation of linkage, theoretical calculation was performed for the case where the molecules are fractured by radiation and only a certain proportion e of the ends thus formed results in endinking and the remainder are stabilized and result in degradation. The experimental values of the radiation dose at gel point, the sol fraction, the average mole weight and the degree of swelling were compared with the theoretical relations. Assuning that the energy absorbed by the swollen film may entirely contribute to the polymer, we estimated the value of e at about 0.4 in the case of film swollen in water at 30°C.