Effect of talc content on the degradation of re-extruded polypropylene/talc composites

We have investigated the influence of talc on the rheological, chemical, thermal and mechanical properties of polypropylene (PP)/talc composites (talc content was 0 wt.%, 10 wt.% and 20 wt.%) during multiple re-extrusions. In particular, the materials were extruded and re-extruded after a mechanical grinding of the extrudates for up to six times and then injected to make tensile sample. The main results show the reprocessing of the blends induced thermo-mechanical degradation by chain scission without significant oxidation. Re-extrusion induced a significant decrease of talc particles size and an increase of their aspect ratio. This mechanism caused an increase of rigidity whose intensity increased with the content of talc, and overcame the loss of rigidity due to the thermo-mechanical degradation of PP. The yield stress was stable for PP/talc 80/20 (20 wt.% talc) but increased for PP/talc 90/10 (10 wt.% talc) with the re-extrusion number, while that of neat PP increased for the first re-extrusion and then decreased for higher number of re-extrusions. Therefore, talc has a positive effect on the mechanical properties of PP/talc composites during re-extrusion.