Mesoscale Heterophase Structural Design in Polypropylene: A Strategy for Dielectric Enhancement via Charge and Field Modulation

Polypropylene (PP)-based materials have attracted considerable interest as sustainable candidates for high-voltage cable insulation. Composed of crystal and amorphous phases, its macroscale dielectric properties are closely related to this mesoscale heterophase structure. However, due to the lack of testing methods capable of quantitatively characterizing the dielectric property differences between crystal and amorphous phases, theories on the insulation degradation of semicrystalline polymers lack effective data support. This study establishes an experimental approach leveraging the asymmetric thermal behavior of impact polypropylene copolymers, complemented by numerical simulations, to deconstruct and quantify the intrinsic dielectric parameters of both phases. Results showed that the amorphous phase, owing to its lower deep-trap density, exhibits markedly weaker suppression of charge migration than the crystal phase. This disparity leads to a one-order-of-magnitude increase in conductivity and induces severe electric field distortion (46%) at the crystal–amorphous interface, which is identified as the primary driver of insulation degradation. Building on these insights, we propose a synergistic modulation strategy targeting both crystal morphology and the crystal phase itself through the incorporation of α/β composite nucleating agents. This method substantially mitigates both the magnitude and the spatial extent of electric field distortion, thereby enhancing insulation stability. Overall, this work not only provides data and theoretical basis for understanding insulation degradation in semicrystalline polymers but also offers guidance for developing high-performance dielectrics.