Tailoring toughness of injection molded bar of polypropylene random copolymer through processing melt temperature

In this study, a facile route to realize the superior toughness of injection molded polypropylene random copolymer (PPR) is reported. The toughness of PPR is increased about twofold when the processing melt temperature increases from 180 to 250 °C. Systematic and detailed structural characterizations have been carried out to establish the structure–property relationships by using polarized light microscopy, scanning electron microscopy, infrared microscopy and dynamic mechanical analysis. It is found that increasing the melt temperature is beneficial for the coalescence of rubbery domains and enhanced molecular mobility which are mainly responsible for the improvement in toughness. Other factors, such as molecular orientation, crystallinity and so on, seem to have little effect. The vital role of enhanced molecular mobility in improving toughness is further demonstrated by the annealing of injection molded samples at elevated temperature, i.e. 110 °C.