Polymer degradation under ionizing radiation: The role of ozone

Abstract

Gamma‐radiation degradation of poly(butadiene‐co‐styene) [SBR rubber] and poly(butadiene‐co‐acrylonitrile) [Buna‐n rubber] in the presence of air has been investigated. Using a recently‐developed modulus profiling techniques, it is shown that the degradation of these materials is very heterogenous through the sample thickness. There is a broad, paraboloidally‐shaped modulus profile through the sample interior, together with a dramatic change in modulus in the surface regions. Mechanistic investigations lead to the conclusion that the radiation‐inducted degradatoin of these materials results from two different process: (1) the standard free radical‐mediated radiation chemistry, which gives rise to oxidation involving O₂ dissolved in the polymer and which leads to heterogenous oxidation due to oxygen diffusion effects; and (2) ozone chemistry in the surface regions of the samples, which results from attack by O₃ generated by the action of the ionizing radiation on the air atmosphere surrounding the samples. It appears that the intense role which this ozone mechanism can play in radiation‐induced oxidative degradation of polymers has not been widely appreciated. This study provides evidence that the simultaneous action of ozone and ionizing radiation can in fact be strongly synergistic in their effect on organic materials