Synthetic aspects and characterization of polypropylene-silica nanocomposites prepared via solid-state modification and sol-gel reactions

A new route is developed by combining solid-state modification (SSM) by grafting vinyl triethoxysilane (VTES) with a sol-gel method to prepare PP/silica nanocomposites with varying degree of adhesion between filler and matrix. VTES was grafted via SSM in porous PP particles. Bulk polymerization under similar experimental conditions as in SSM resulted in homopolymerization of VTES. However, SEC and NMR experiments showed that VTES was grafted as a single monomeric unit in the amorphous phase of PP with the possibility of VTES-polymer grafting during SSM. Silica-like nano-particles were synthesized in-situ by the sol-gel method. Magic-angle spinning (MAS) 29Si NMR spectra showed that the chemical building blocks of the silica-like clusters are of Q3 and Q4 type. MAS 29Si NMR and FT-IR spectroscopy showed that the grafted VTES becomes part of the in-situ formed silica particles. No decrease in molecular weight of PP was observed, indicating that chain scission is marginal compared to melt modification. The morphology of the nanocomposites as observed by ATR-FTIR microscopy showed a uniform dispersion of grafted VTES as well as in-situ formed silica. TEM and SEM demonstrated that the in-situ formed silica particles are nearly spherical and have sizes in the range of 50-100 nm.