Direct Correlation Between Charge Evolution and Crystalline Structure in Isotactic Polypropylene

Adding nucleating agents (NAs) is one of the most efficient ways to obtain improved mechanical, optical, and thermal properties of isotactic polypropylene (iPP). While it is well-appreciated that electrical property is critically affected by the crystalline modification, the roles between them remain unclear. Here, we address this issue by incorporating commercial alpha-NA and beta-NA into iPP, both of which exhibit strong nucleation ability, e.g., reducing the crystal size from 45.3 mu m (Pure-iPP) to 2.5 mu m (alpha-iPP) and 7.6 mu m (beta-iPP), respectively. A well-dispersed beta-iPP system obtains a comprehensive improvement of electrical properties, including dielectric breakdown strengths, space charge suppression, and internal field distortion under a high external field (-100 kV/mm) at 30 degrees C due to newly-generated deep charge trapping sites. This crystalline modification strategy is attractive for future development of many engineering insulating polymers.