Role of Talc With High Aspect Ratio in Shear‐Induced Crystallization and Viscosity Enhancement of Isotactic Polypropylene

In the present study, the impact of talc on shear‐induced crystallization and viscosity increase in isotactic polypropylene (PP) is investigated using two types of talc comprising particles of a similar average size with different shapes: one is a conventional talc and the other has a high aspect ratio. After exposure to shear flow, PP crystallization is slightly enhanced by the addition of the conventional talc. This is known as flow‐induced crystallization. In contrast, the talc with the high aspect ratio greatly promotes PP crystallization, resulting in a high degree of orientation of the PP chains. The excess localized stress of PP between talc particles, which is known as lubrication hydrodynamic force, is responsible for the prompt formation of extended‐chain crystals. This force also increases the shear stress at high pressure by jamming effect, which may induce poor flowability during injection molding.