Post-irradiation degradation of polypropylene

We present the mechanical changes (elongation at break, tensile strength, modulus of elasticity) and electrical changes (volume and surface resistivity, tg, , breakdown voltage) ofisotactic polypropylene (PP) due to -radiation. Ageing of PP was achieved in air by using a¹³⁷Cs -source with 400 Ci activity; the dose rate was of 8·10⁴ rad/h, and the integrated doses ranged from 2 to 160 Mrad. Severe deterioration of mechanical properties was observed. The changes of electrical properties were not as significant as those of mechanical characteristics. These variations are caused by the increase in density of crosslinking chain-scission and by oxidative processes. The rate of extent of degradations has been evaluated by the growth of the hyydroxy and carbonylbands in the IR spectrum By using FTIR mapping, we have also investigated the degradation of PP which had been irradiated in air 15 years ago. We determined the contour lines of FTIR absorption bands of carbonyl groups at different regions of the cross-section of an irradiated sample. Dust particles of irradiated brittle PP were also studied. The FTIR showed that the carbonyl band is broad, indicating a mixtures of many different functional groups (ester, acid, ketone, lactones). We determined also the gel content at different irradiation doses.