Deformation-induced morphology evolution during uniaxial stretching of isotactic polypropylene: effect of temperature

The effects of draw temperature on the deformation-induced morphology evolution of isotactic polypropylene in terms of crystal orientation, degree of crystallinity, crystal size in the direction normal to chain axis, long spacing, and the deformation behavior at the crystal lattice and lamellae scale were investigated using differential scanning calorimetry, two-dimensional wide-angle X-ray diffraction, and small-angle X-ray scattering, respectively. The results revealed that the thermal behaviors are associated with the deformation-induced morphology evolution, and the morphology evolution is strongly temperature dependent. At low strain, crystal fragmentation takes place at all the draw temperature range studied; at high strain, after crystal fragmentation the draw temperature shows different effects on the morphology evolution: at low temperature (25 A degrees C), fragmentation of the crystal blocks continues; at medium temperatures (80 and 110 A degrees C), the broken crystal blocks remain stable and the unfolded chains and disentangled chains in amorphous region crystallize into crystal blocks with crystal size almost identical to that of the original broken ones; at high temperatures (130 and 140 A degrees C), not only the unfolded chains and disentangled chains in amorphous region crystallize into crystal blocks, but also these small broken crystal blocks melt and recrystallize and the new crystal blocks formed possess larger crystal size than those of the original broken ones.