The thermal‐mechanical degradation of mineral‐filled polypropylene‐ethylene copolymer composites during extrusion process

Abstract This work proposes a new understanding of the side effect of mineral fillers in polymer compounding that caused different levels of thermo‐mechanical degradation (TMD) during extrusion. Three mineral fillers, silica (random shape), kaolin (platy), and wollastonite (needle‐like), were selected and compounded with the polypropylene‐ethylene copolymer (PPcoE) using a twin‐screw extruder. Their influences on the TMD of PPcoE were examined by checking the substances in the extrudates using Fourier transform infrared spectroscopy. The built‐up shear stress causing by mineral filler in PPcoE composite (Δτ_com) as the root of TMD was measured and estimated using capillary rheometer. In this study, TMD is classified as two levels: chain scission and oxidization. These fillers were found to accelerate the TMD mechanism and generate the oxidised products during extrusion. The silica filler caused the highest Δτ_com, the lowest tensile strength, and elongation at break of PPcoE composites. The kaolin filler gave the most potent accelerating effect on oxidization, resulted in the formation of tertiary alcohol, and the highest ester contents in PPcoE composites; although, its composite had the lowest Δτ_com among the fillers. Lastly, wollastonite filler provided higher Δτ_com than kaolin composite, the second‐highest formation of alkene products, yet better retention in elongation at break compared to the silica‐filled PPcoE composite. In general, the side effect of mineral filler on TMD was a larger particle size always comes with higher chain scission, simpler particle morphology gives a smoother built‐up shear stress and minimizes TMD, and filler having hydroxyl groups catalyzes the oxidization TMD.