The effect of gamma radiation on the properties of polypropylene blends with styrene—butadiene—styrene copolymers

摘要

The effects of gamma radiation on polypropylene, styrene—butadiene—styrene copolymers and their blends were studied. Colorimetry determinations, melt flow index measurements, FTIR and DSC analysis were carried out to characterize the products. Electron spin resonance was also used to study the generation and decay of free radicals in all the blends at different radiation doses and to establish the kinetics of the processes involved. A pronounced decrease in the weight-average molecular weight of PP took place as a consequence of an intense degradation (chain scission). Blends containing low amounts of SBS displayed an increase in their MFI values when irradiated, due to the scission of PP chains. However, blends with higher amounts of SBS showed a decrease in their flow. Such behaviour is attributed to crosslinking reactions that take place in the butadiene units in the SBS. These studies lead us to infer a competition between chain scission in PP and crosslinking associated with the SBS as degradation mechanisms. The presence of SBS beyond 30 wt.% decreases the PP sensitivity to radiation effects, which results in a lower decrease in the melting temperature and enthalpy of the PP at higher SBS contents.