In the present work

structure changes during stretching of isotactic polypropylene (

i

PP) and

i

PP/silicon dioxide (SiO

2

) composites have been investigated systematically. The α-form crystal structure of both

i

PP and

i

PP/SiO

2

composites is destroyed and transforms into the mesophase as the samples are stretched at a low temperature (35℃)

while stretching at high temperatures (90℃ and 120℃) 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

i

PP

however

the orientation of

i

PP/SiO

2

composites is greatly changed by the tensile temperature. In the case of micron-sized SiO

2

particles (average particle diameter

d

>

1 μm)

the orientation of the composites is lower than that of pure

i

PP at all stretching temperatures. The above results suggest that the stretching temperature and the SiO

2

particle size have great influence on the structure variation and orientation behavior of

i

PP/SiO

2

composites.