Flow-induced crystallization precursor structure in high molecular weight isotactic polypropylene (HMW-iPP)/low molecular weight linear low density polyethylene (LMW-LLDPE) binary blends

The formation of initial crystallization precursor induced by flow was investigated by synchrotron-based wide- and small-angle X-ray scattering techniques (WAXS/SAXS), using polymer blends consisting of high molecular weight isotactic polypropylene (HMW-iPP) and low molecular weight linear low density polyethylene (LMW-LLDPE) as model systems. LMW-LLDPE, the dominant component, served as the amorphous matrix. Crystallization behavior of the blends with three different HMW-iPP concentrations, i.e., 3, 6 and 9 wt%, were examined at temperatures higher than the blends' cloud points, in a time-resolved manner. It was found that the formation of a flow-induced precursor of crystallization was strongly influenced by the concentration of HMW-iPP in the blends. The blend with low HMW-iPP content (3 wt%) was not able to form a shear-induced crystalline structure. As the concentration of HMW-iPP increased, crystallization kinetics, crystallinity, and lamellar orientation were greatly enhanced.