The effect of the addition of polypropylene grafted SiO2 nanoparticle on the crystallization behavior of isotactic polypropylene

The crystallization behavior of isotactic polypropylene (iPP)/silica particle (SiO2, 26 nm) nanocomposite has been investigated. In addition to the non surface-modified SiO2, iPP grafted SiO2 was synthesized and adopted to this study with an aim to understand the role of grafted polymer chain on the crystallization process. The crystallization rate of non surface-modified iPP/SiO2 composite stays constant up to 1 vol%. It suggests the very weak nucleation ability of nano-sized silica particle. While large acceleration effect was observed for iPP-grafted SiO2/iPP composite. The spherulite density increased with increasing SiO2 contents, and more interestingly, the spherulite growth rate also increased. This finding leads to the conclusion that the grafted iPP chain has a plasticizing effect that reduces the chain entanglements at the interface. Further increase in SiO2 contents, the crystallization rate, the spherulite density, and the spherulite growth rate showed the steep decreases at higher SiO2 content range regardless of the surface modifications of SiO2. It was attributed to the confinement of matrix chain since the inter-particle distance of adjacent SiO2 approaches to the end-to-end distance of matrix chain, which a large molecular motion is restricted. Moreover, the average size of SiO2 aggregation in iPP matrix was successfully evaluated by analyzing the contents dependence of the growth rate, assuming that the inter-particle distance with zero growth rate coincided with end-to-end distance of matrix iPP chain.