Abstract:

Polypropylene random copolymer （PP?R）/nano?SiO₂ composites were prepared through a melt blending method， and their mechanical properties， crystallization thermodynamics， crystalline morphology and micromorphology were characterized using an electronic universal tensile testing machine， differential scanning calorimeter， polarizing microscope and scanning electron microscope. The results indicated that the addition of nano?SiO₂ resulted in an increase in the crystallization temperature of PP?R from 93 to 105.6 °C and in the melting temperature from 141.6 to 142.8 °C. The nano?SiO₂ plays a role of heterogeneous nucleation in improving the crystallization rate of PP?R and refining its crystal grain. The composites containing 2 wt% nano?SiO₂ achieved a maximum value in impact strength at -15 °C. This result was more than 2 times higher than that of pure PP?R. On the other hand， the composites containing 1 wt% nano?SiO₂ achieved a maximum value in impact strength at 23 °C， which is nearly 2 times higher than that of pure PP?R. Moreover， the bending strength， tensile strength and elongation at break of the composites were improved as well.

Key words: polypropylene random copolymer, nano silica, composite material, mechanical property, crystallization performance