Effects of surface coupling agents on the mechanical properties of polypropylene/silica composites

Abstract

We examined the effects of interfacial interactions on the crystallization behavior and properties of polypropylene (PP) composites containing unmodified silica, hexamethyldisilazane (HMDS)-modified silica, and aminopropyltriethoxysilane (APTES)-modified silica. Through Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC), and Density Functional Theory (DFT) calculations and mechanical testing, we demonstrated that surface functional groups strongly affect polymer–filler interactions. HMDS-modified silica generated broad damping factor (tan δ) peaks, indicating the presence of weak, heterogeneous interfaces that decrease both the crystallization rate and mechanical performance. In contrast, APTES-modified silica produced moderately strong and flexible interfaces owing to the presence of amino groups and the formation of a polysiloxane layer, enhancing nucleation, accelerating crystallization, and improving mechanical properties. Comparisons with unmodified silica revealed that both strength and spatial uniformity of the interfacial interactions determine the crystallization pathway and the overall composite performance. In this study, we examined the effects of interfacial interactions on the crystallization behavior and properties of PP composites containing unmodified silica, hexamethyldisilazane (HMDS)-modified silica, and aminopropyltriethoxysilane (APTES)-modified silica. Through DMA, DSC, and DFT calculations, and mechanical testing, we demonstrated that surface functional groups strongly influence polymer–filler interactions.