Effect of elastomer on crystalline transition and deformation behavior of isotactic polypropylene

The structural evolution during uniaxial tensile deformation of isotactic polypropylene (iPP) and its blend with olefin block copolymer (OBC) was comparatively investigated by in-situ synchrotron X-ray scattering. Small angle X-ray scattering showed that cavitation in iPP/OBC blend took place at a smaller strain than that in neat iPP. The reorientation of the cavities in iPP/OBC occurred at a lower strain than that in iPP as well. Wide angle X-ray scattering was applied to study the crystal-mesophase transition and the orientation process. Compared to the sharp transition in neat iPP, the mesophase formation and orientation in iPP/OBC blend proceeded gradually. The mesophase content and degree of orientation of iPP matrix in iPP/OBC blend were much lower than that in neat iPP within the investigated strain range. By the combination of scattering results and morphological observations, a deformation mechanism based on strain distribution and fracture mechanics was proposed.