Effects of Cobalt-60 Gamma Radiation on Poly (vinyl alcohol) : I. Effects of Gamma Radiation on Solid Poly (vinyl alcohol) Films

Abstract

Solid films of the fractionated and unfractionated poly (vinyl alcohol) were cobalt-60 gamma irradiated both in the presence and absence of oxygen. The methods used to study the change in properties of the irradiated samples include intrinsic viscosity, swelling, solubility and density measurements. The changes of structure and the mechanism of reaction by the gamma radiation were quantitatively discussed in connection with the change in the molecular weight distribution. In our experimental condition of up to 5×10⁷ γ radiation dose, neither gel formation nor any difference dependent on the condition whether in the presence or the absence of oxygen was found. From the results obtained, we conclude that in the solid film, poly (vinyl alcohol) is dominantly degraded by random main-chain fracture throughout the crystalline and amorphous regions, although a small amount of endlinking may occur in the amorphous regions. Assuming the random main-chain fracture, the probability of a given main-chain bond being fractuated was estimated and it was found that the rate of degradation was propotional to the number of bond which was not fractured. The energy dissipation per chain fracture calculated was 38.7 e.v.