Influences of polypropylene grafted to SiO₂ nanoparticles on the crystallization behavior and mechanical properties of polypropylene/SiO₂ nanocomposites

Influences of polypropylene (PP) grafted to SiO₂ nanoparticles (7 nm) were studied on the crystallization behavior and the mechanical properties of PP/SiO₂ nanocomposites. PP for the matrix and grafting was synthesized in order to have an identical primary structure, aiming at their co-crystallization and resulting reinforcement of filler-matrix interfaces. The grafted PP chains improved the dispersion of SiO₂, and notably accelerated nucleation in crystallization. It was plausible that the grafted chains whose one chain end was pinned to SiO₂ became nuclei of the crystallization (co-crystallization between the matrix and grafted chains), thus directly bridging between the matrix and SiO₂ nanoparticles. The Young’s modulus and tensile strength were most improved by the grafted PP chains at low filler contents such as 2.3 wt%, whose origin was attributed to effective load transfer to SiO₂ through the co-crystallization-mediated bridging.