Crystallization of Isotactic Polypropylene under Shear Flow Observed in a Wide Spatial Scale

Abstract

We studied crystallization process of isotactic polypropylene (iPP) under shear flow as a function of shear rate using time-resolved wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), depolarized light scattering (DPLS), and polarized optical microscopy (POM) to elucidate the formation mechanism of the so-called shish-kebab structure in a wide spatial scale from 0.1 nm to several tens of μm. In the time-resolved DPLS, SAXS, and WAXS measurements we observed the formation processes of the shish-like structure, the kebab structure, and the crystalline lattice (mostly in the kebab), respectively, and found that there were critical shear rates for the anisotropic structure formation in the DPLS, SAXS, and WAXS measurements. The values are very close each other, suggesting the anisotropic structure formations in both of the shish and the kebab are dominated by a common origin. Furthermore, comparing the onset times of intensities in DPLS, SAXS, and WAXS, we found that the onset of DPLS intensity is the most accelerated by the shear among the three. On the basis of the observations, we propose a possible mechanism for the shish-kebab structure.