Morphology of syndiotactic polypropylene/alumina nanocomposites

The effect of the addition of 50 nm spherical alumina nanoparticles with hydrophilic or hydrophobic surfaces on the morphology of syndiotactic polypropylene (sPP) was investigated. The filler content in the nanocomposites was 3 wt%. Polarized Optical Microscopy and Small Angle Light Scattering (SALS) studies showed that sPP and the nanocomposites form hedrites. The addition of alumina nanoparticles significantly increased the number of hedrites. A higher number of nucleation sites in the nanocomposites promote a higher crystallization rate, and thus hedritic growth was stopped at the early stage of crystallization. Quantitative evaluations by SALS analysis show that the object size is decreased by not only the crystallization conditions but also the presence of Al2O3 nanoparticles. A small amount of Al2O3 nanoparticles did not noticeably affect the crystallinity of sPP, but increased the melting point. Transmission Electron Microscopy images showed that the lamellar thickness did not change significantly with the incorporation of nanoparticles. The lamella thickness, however, depends on cooling rates. X-ray diffraction characterization indicated that the sPP and the nanocomposites were crystallized in disordered “form I”. The incorporation of alumina nanoparticles had a small effect on the crystal structure of syndiotactic polypropylene.