Investigation on thermal-mechanical degradation, rheological and mechanical properties of polypropylene-ethylene/silica composites

Abstract

The thermal-mechanical degradation resulting from heated two roll mill of silica filled polypropylene-ethylene (PPE) composites was investigated. The influence of processing temperature and silica loading was studied and focused on rheological and mechanical properties of the PPE/silica composite. Thermal-mechanical degradation was found to occur in neat PPE and PPE/Si composites. The degradation mechanism in neat PPE was chains scission and produced more cis and trans alkene. FTIR identified that the degradation level became greater when processing temperature for PPE copolymer increased, especially at 170 °C.Thermal-mechanical degradation exhibited higher melt flow index as molecular weight decreased due to chains scission. Chains scission is also the reason to decline tensile properties of PPE copolymer. The influence of silica loading on thermal-mechanical degradation of PPE/Si composites was determined by the FTIR spectra analysis. The oxidization was found to occur and a tertiary alcohol spectrum was detected by FTIR. The result was confirmed with TGA testing. The higher silica content, the more thermal-mechanical degradation was. The tensile fracture morphology showed that silica at above 10 wt% content tended to aggregate and agglomerate. Therefore, excess silica caused more internal stress during compounding and increased the thermal-mechanical degradation. In fact, tertiary alcohol was only present in PPE/Si composite.