Thermomechanical degradation of polypropylene – polystyrene blends during extrusion‐based melt blending – A first survey of shear‐induced molecular architecture changes

Polymer blends made of plastic waste and manufactured by extrusion-based melt blending are of particular importance for mechanical recycling in the context of tailoring material properties for value-added applications. For both, property tailoring and for suppressing downcycling, it is inevitable to understand the thermomechanical degradation behavior of the blends, induced by melt-blending. In this investigation, the thermomechanical degradation of polypropylene (PP) - polystyrene (PS) blends are analyzed for different blend compositions based on cross-fractionation chromatography. This method allows for the first time to separate PP from PS with simultaneously analyzing the change in the molecular architecture distribution due to thermomechanical degradation. It is revealed that the melt-blending induced degradation effect is primarily occurring in PP, where besides a reduction of chain length, significant chain irregularities are generated. It is observed that PP degradation is increasing with a growing proportion of PS. These new findings offer the first insights into the thermomechanical degradation of PP/PS blends.