Effect of Surface Properties of Nanoparticles on the Crystallization Behavior of Polypropylene/Polypropylene-g-Silica Nanocomposites

In order to investigate the effect of surface properties of nanoparticles (NPs) on the crystallization behavior of nanocomposite, three kinds of silica (SiO2) NPs are dispersed in isotactic polypropylene (iPP) matrix by solution blending method. Specifically, the poor compatibility between inorganic bare SiO2 NPs and organic PP matrix triggers the formation of aggregates and induces the fractionated crystallization with two crystallization peaks at higher particle loading (Phi), i.e., main crystallization peak (MCP) and low temperature crystallization peak (LCP, always located at 124.0 degrees C). Once short PP chains (0.9 x 10(4) g mol(-1)) are grafted onto the surface of SiO2 NPs, the nanocomposites with all Phi only exhibit a single MCP which is attributed to the strong interfacial interaction. With the increase of grafting chain length (9 x 10(4) g mol(-1)), the more stretched conformation of grafting chains can provide numerous heterogeneous nucleation sites and significantly accelerate the crystallization rate of PP chains near the surface of SiO2 NPs, which lead to the formation of an extra high temperature crystallization peak (HCP, almost kept constant at 133.0 degrees C). The occurrence of various crystallization peaks implies that the surface properties of nanoparticles play a vital role in the nucleation ability of nanoparticles.