Deformation Behavior of Isotactic Polypropylene Spherulite during Hot Drawing Investigated by Simultaneous Microbeam SAXS-WAXS and POM Measurement

Abstract

The process of rearranging lamella crystal structures in isotactic polypropylene (iPP) and butene randomly copolymerized iPP (bPP) spherulites during hot drawing was investigated by in-situ microbeam small-angle X-ray scattering (SAXS)−wide-angle X-ray scattering (WAXS)−polarized optical microscopy (POM) simultaneous measurements. We subjected a fixed position in an upper quadrant of a spherulite, which is stretched in the horizontal direction, to microbeam X-ray irradiation, and observed local structural changes, such as those in ordered crystal size and orientation, and a lamella stacking structure. We successfully obtained the structural information on parent and daughter lamellae in various orientations. In iPP, the long period of perpendicular parent lamellae increased, and then the disordering of crystal packing structures along the a-axis started. When necking started, the long periods of parent and daughter lamellae drastically started to decrease with the alignment of the c-axis in the stretching direction. The ease of crystal fragmentation and c-axis alignment strongly depended on the type of lamella, indicating the order of stress concentration during drawing. In bPP, it was found that the alignments of all the lamellae occur almost simultaneously and that parent and daughter lamellae independently rotate until necking.