Effect of structural evolution on the electrical properties of oriented polypropylene films

Adjustment of processing parameters in semi-crystalline polymers leads to diverse crystalline structures and electrical properties. In this work, oriented polypropylene (PP) films were fabricated using a scalable “melt extrusion–uniaxial stretching” method under varying extrusion temperatures and stretching rates. Higher stretching rates promoted the formation of well-aligned shish-kebab crystals, improving crystallinity and optimizing trap distribution, which, in turn, suppressed charge carrier transport and enhanced breakdown strength. The tightly packed “mother–daughter” lamellae further contributed to the improved insulation performance. While moderate processing temperatures enhanced crystalline orientation and charge transport, excessively high temperatures reduced crystallinity and deteriorated insulating properties. Under optimal conditions (210 °C, 700 mm/min), the films achieved a 15.7% increase in breakdown strength. These findings establish a clear relationship between processing conditions, crystalline structure, and electrical performance, offering guidance for designing next-generation high-performance PP dielectric films for capacitor applications.