Pronounced shear-induced crystallization of polypropylene by addition of immiscible amorphous polymers

The shear-induced crystallization of polypropylene (PP) in immiscible blends with low-molecular-weight amorphous polymers was studied during a cooling process. The glass transition temperatures T_g's of these amorphous polymers were slightly higher than the PP crystallization temperature. The amorphous polymer promoted the shear-induced crystallization of PP. Because of its low viscosity at high temperatures, droplets of the amorphous polymer were deformed under shear flow. As the temperature approached the T_g, the amorphous polymer became rigid prior to PP crystallization. Consequently, the actual strain rate of the PP increased, leading to a large Rouse–Weissenberg number and shear-induced crystallization. Interfacial tension with PP also played an important role in shear-induced crystallization when the crystallization occurred after the cessation of flow.