Gamma irradiation effect on isotactic poly(propylene) studied by microhardness and positron annihilation lifetime methods

The commercial isotactec PP, pristine and after 60Co γ-irradiation in air, has been studied using microhardness and Positron annihilation methods. It was found that at irradiation dose Dγ = 100 kGy a clear inverse effect in iPP response to γ-radiation took place. The degree of crystallinity Xc, melting temperature Tm, as well the Vickers and total microhardnesses, all sharply change the trend of their variation at the same dose Dγ = 100 kGy. The observed behavior was explained by the different response of iPP to γ-radiation. At low doses the prevalent effect of γ-radiation is chain scission phenomena, while for higher doses the main effect are chain branching and/or crosslinking. The complicated dependence of the relative o-Ps intensity on degree of crystallinity was ascribed to the supposition that γ-irradiation of PP with doses up to 100 kGy influences mainly the lamella surface. The explanation of changes is based on the idea of pushing the irradiation defects out of the crystalline areas into the intermediate layers that leads to improvement of both lamellae and their fold surface perfectness. (author)