The correlation between the morphology and radiation resistance of polypropylene solid materials

Abstract The influence of morphology on the radiation-induced oxidative degradation of polypropylene solid materials has been studied. γ-Irradiation in air caused oxidation of polypropylene films to produce hydroperoxide and carbonyl groups, thus giving rise to a remarkable decrease in elongation at break (γ B ) in the tensile test. Although the radiation-induced degradation of the mechanical properties was attributable to oxidation, it was not always determined by the extent of oxidation. The critical dose ( D C ), which was defined by the irradiation dose leading to 50% residual elongation, increased as the yield stress (σ Y ) before irradiation decreased: both quantities varied significantly depending upon the polymer processing conditions. The σ Y before irradiation increased with increase in the mean diameter of spherulites, up to ca 10 μm, which were formed in the polypropylene films. Films with spherulite diameter larger than ca 10 μm were broken before reaching their yield points and the corresponding tensile strength (σ B ) decreased with increasing spherulite diameter. A universal curve was obtained such that σ Y before irradiation decreases with increase in weight-swelling ratio ( S W ) measured by immersion in p -xylene at room temperature. The radiation resistance of polypropylene materials, as measured by the D C value, became greater as spherulite size decreased and S W at room temperature increased.