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 (Δτcom) 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 Δτcom, 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 Δτcom among the fillers. Lastly, wollastonite filler provided higher Δτcom 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.

Effect of zinc oxide nanoparticle size on the dielectric properties of polypropylene‐based nanocomposites

“…The number of cavities increased with the increment in stress. When the smaller size ZnO particles were more uniformly stressed, the larger size ZnO particles were more likely to act as a microcrack initiation point in the matrix, leading to fractures in the material 21,22 . Moreover, the uniformity degree of nanoparticle dispersion in the matrix may become a key factor affecting the mechanical properties of the material.…”

“…When the smaller size ZnO particles were more uniformly stressed, the larger size ZnO particles were more likely to act as a microcrack initiation point in the matrix, leading to fractures in the material. 21,22 Moreover, the uniformity degree of nanoparticle dispersion in the matrix may become a key factor affecting the mechanical properties of the material. As shown in Figure 7, the elongation at the break of both nanocomposites decreased with the increasing nanoparticle content.…”

Effect of silicon dioxide and organized montmorillonite on the crystalline morphology and dielectric properties of polypropylene‐based composites

“…In general, the mechanical properties of micron composites are worse than those of nano-composites because the larger particles are more likely to cause stress concentration and debonding at the particle-matrix interface during deformation. [26][27][28] When particle sizes are comparable, particles with higher aspect ratios are significantly less tough than particles with higher symmetry. [29] When stress is applied, the nanoparticles are subjected to stress concentration, which leads to debonding and cavitation at the nanoparticle and substrate interface, consuming abundant energy and thus producing a toughening effect.…”