Effect of high energy electron radiation on MIPB-impregnated polypropylene film

The effect of impregnating capacitor-grade polypropylene film with an aromatic hydrocarbon fluid is examined with a view towards assessing the response under radiation of the relevant properties of the film. Monoisopropyl biphenyl (MIPB)-impregnated polypropylene film was exposed in air to 1-MeV electrons at different dose rates and the post-radiation effects on the electrical, mechanical, morphological, and chemical properties were evaluated. The results obtained indicate that the oil-impregnated films remain relatively stable even at the highest dose of 10⁸ rads. This is in contrast to the results reported by the authors (ibid., vol.NS-34, no.6, p.1822-6, 1987) for dry polypropylene films which underwent degradation due to chain scission and oxidation. In the present instance, it is believed that impregnation of the film has inhibited the diffusion of oxygen and consequently favored crosslinking. The chemical characterizations as well as the changes in some of the measured properties of the film are seen to corroborate this belief