Increasing the melt viscosity of post-consumer recycled polypropylene via E-Beam techniques

Polypropylene from post-consumer waste (PCR-PP) was melt-mixed with a di- and trifunctional molecule and treated with E-Beam radiation, to increase its viscosity and melt strength by long-chain branching and partial crosslinking. After adding diallyl- or triallylisocyanurate to polypropylene by melt compounding, the compounds were subjected to e-beam irradiation with doses between 10 and 60 kGy. Two types of polypropylene recyclates were investigated, both differing in the content of polyethylene. The samples were investigated with respect to the formation of microgels (gel content), rheological behaviour, melt flow rate and their mechanical properties. It was found that low irradiation doses in the range from 10 to 30 kGy reduce the melt flow rate significantly, and increase the tensile properties of PCR-PP while the gel content stays low. The results are discussed with respect to the amount of polyethylene impurities, and the processing behaviour of polypropylene, aiming at technically feasible recycling strategies for polyolefin recyclates.