Effect of iPP molecular weight on its confinement within mesoporous SBA-15 silica in extruded iPP-SBA-15 nanocomposites

Different nanocomposites based on two isotactic polypropylenes (iPP) and mesoporous SBA-15 silica have been attained by melt extrusion as an attempt to understand the influence of average molecular weight in the rheological behavior, morphological and crystalline features and in the final properties (thermal stability and mechanical response) as well as in the capability of incorporating iPP chains within the nanometric SBA-15 pores. Closeness to rheological percolation and a significant increase of viscosity are observed as SBA-15 content is raised, this effect being more evident for the materials prepared from the iPP with the lowest molecular weight. These composites also shift their maximum degradation to lower values under inert atmosphere but keep rather unchanged decomposition behavior in oxidant conditions. No considerable changes are found with molecular weight in their morphological characteristics, nor in the type of iPP polymorph developed. The confinement of iPP chains in the SBA-15 channels, implied by a small endotherm in the DSC melting curves, is definitely ascertained by real-time variable-temperature Small Angle X-ray Scattering measurements with synchrotron radiation, suggesting, additionally, that somewhat thicker crystallites are developed within the mesostructure in the materials prepared from the iPP with inferior molecular weight. Moreover, the SBA-15 mesoporous particles exert a reinforcing role in all cases and reduce the deformation capacity of the ultimate materials as their content is increased.