Correlation between morphology and radiation resistance of polypropylene materials

点击翻译按钮获取中文摘要

Polypropylene solid materials in medical use are subjected to radiation sterilization, which causes oxidative degradation of their mechanical properties. In this research, the influence of morphology on the radiation degradation of polypropylene materials was investigated. The results are summarized as follows:(1) The crystal structures, as verified by means of X-ray diffraction measurement, and the spherulitic size in the isotactic polypropylene films are strongly affected by the conditions of compression moulding on the hot press. Rapid cooling of the polypropylene melts produces smectic modification of crystallines and small sized spherulites, while slow cooling leads to well grown spherulites consisting of monoclinic crystallines.(2) Upon -irradiation, the elongation at break of polypropylene films decreases in a sigmoidal form as a function of radiation dose. The dose leading to 50 % residual elongation, which is defined as a critical dose, is a good measure of the radiation resis … More tance of polypropylene materials.(3) The radiation resistance of polypropylene films, as measured by the critical dose, increases as the content of smectic crystallines in the film increases.(4) The polypropylene films with smaller yield stress before irradiation show higher radiation resistance. The critical dose of homopolymer films is greater than that of copolymer films, when compared at the same size of spherulites contained.(5) For the films containing spherulites with 10 um mean diameter, the yield stress before irradiation decreases rapidly as the mean spherulitic diameter becomes smaller. The films containing spherulites with more than 10 um breaks down before reaching a yield point, and the corresponding tensile strength decreases with the increase in mean diameter of spherulites.(6) The weight swelling ratio of polypropylene films at room temperature, which is evaluated by immersion of the films in p-xylene at 25 C, increases rapidly with the decrease in mean diameter of spherulites.(7) For the films containing smaller sized spherulites, the yield stress before irradiation increases and thus the radiation resistance increases as the weight swelling ratio at room temperature becomes grater. Less