Study of high melt strength polypropylene (HMS-PP) under thermal ageing

Abstract

The irradiation of PP to obtain HMS-PP allows introducing energy into the material to generate favorable changes, when used in adequate doses. On the other hand, the stability to ageing of HMS-PP obtained by radiation process have not been evaluated until yet. In this study HMS-PP was obtained by the irradiation in atmosphere of acetylene as crosslinker agent. It was employed doses of 12.5 kGy and 20 kGy of gamma radiation. Thermal treatment was used as a post irradiation in order to permit the annihilation of the remaining radicals. The thermal stability of the HMS-PP was evaluated in stove at temperature of 90 °C, in presence of air at different periods of time. Physical and Mechanical properties were monitored during the ageing by the techniques of Tensile Mechanical Test, Thermogravimetry (TGA), Differential Calorimetry (DSC), Scanning Electronic Microscopy (SEM) and Optical Microscopy (MO). Oxidative degradation on the network of HMS-PP, formed in the radiation process of PP, was revealed by the analytical results showing the susceptibility of HMS-PP to thermal oxidative degradation. Yellowing of the samples surface, loss of mechanical property of tension strength, oxidative products of degradation among other evidences were observed. In thermo-oxidative conditions, the formation of the oxidation products essentially involves a hydrogen abstraction by the peroxy radicals, leading to hydroperoxides as primary products, chemical degradation in the immediate crack tips.