Deformation investigation on iPP/SiO2 composites: Influence of stretching temperature and particle size on morphology evolution and crystalline structure of thin films

In the present work, structure changes during stretching of isotactic polypropylene (iPP) and iPP/silicon dioxide (SiO₂) composites have been investigated systematically. The α-form crystal structure of both iPP and iPP/SiO₂ composites is destroyed and transforms into the mesophase as the samples are stretched at a low temperature (35°C), while stretching at high temperatures (90°C and 120°C) can restrain the appearance of defects and keep the perfection of crystal structure. FTIR results reveal that the stretching temperatures show no obvious difference of the effect on the orientation of pure iPP, however, the orientation of iPP/SiO₂ composites is greatly changed by the tensile temperature. In the case of micron-sized SiO₂ particles (average particle diameter d > 1 μm), the orientation of the composites is lower than that of pure iPP at all stretching temperatures. The above results suggest that the stretching temperature and the SiO₂ particle size have great influence on the structure variation and orientation behavior of iPP/SiO₂ composites.