Structural deformation behavior of isotactic polypropylene with different molecular characteristics during hot drawing process

Structural evolution in hot drawing process of isotactic polypropylene (iPP) films with different molecular weight distribution (MWD) and isotacticity (IT) was investigated by in situ time-resolved measurements of synchrotron-sourced wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). Any significant difference was not recognized among different molecular characteristics as for the changes in the WAXD patterns, indicating that the deformation behavior viewed at the crystal lattice scale was almost the same among these samples. On the other hand, the deformation behavior of lamellar stacking structure was found to be significantly dependent on the molecular characteristics of the sample used. For iPP sample with narrower MWD and higher IT, only the lamellar stacking structure with c-axis crystallites oriented along the drawing direction was detected at the deformation stage after necking, but the oriented fibrillar structure was observed in addition to the lamellar stacking structure for the iPP sample with broader MWD and IT distribution. The structural deformation models were presented for both the samples with different molecular characteristics, and these models were reasonably related with the difference in the stress-strain curve.