Morphology of Injection-Molded Isotactic Polypropylene/Silica Composites Prepared via <i>in-Situ</i> Sol−Gel Technology

Abstract

We report on the semicrystalline morphology of injection-molded isotactic polypropylene (iPP)/silica composites prepared via in situ sol−gel technology using hyperbranched polyethoxysiloxane as a silica precursor. The microstructural analysis has been carried out with a combination of small- and wide-angle X-ray scattering and 1 H solid-state NMR spectroscopy. The in situ formed silica particles significantly alter the semicrystalline morphology of iPP by improving orientation of the “mother” crystals in the sample core simultaneously with an increase of the “daughter” crystal fraction. Moreover the particles induce formation of thicker crystalline domains and growth of β-crystals in the sample core. The observed morphological modifications can be accounted for by a 2-fold effect of the silica particles, i.e., their action as a nucleating agent of the β-phase, on the one hand, and as a lubrificant reducing the polymer melt viscosity, on the other. Proton spin-diffusion experiment using a double-quantum filter was found suitable for the measurement of the chain mobility gradient in the interface region. The results obtained indicate enhanced polymer chain mobility in the amorphous region in the presence of the silica particles. Finally, the morphology and chain dynamics of the iPP/silica composites are correlated to mechanical properties of the injection-molded samples.