Enhanced dielectric performance of polypropylene for hvdc cable insulation via 4‑allyloxybenzil grafting for multiscale structural modulation

Abstract

Impact Polypropylene Copolymer (IPC) is a promising candidate for HVDC cable insulation, yet the lack of rigorous, quantitative structure-property correlations limits its performance optimization. In this study, a functional monomer, 4-Allyloxybenzil (AOB), containing benzene rings, carbonyl groups, and ether bonds, was synthesized and grafted onto IPC via an aqueous suspension method to enhance its dielectric properties. Distinct from traditional cross-scale analyses, this work establishes direct quantitative correlations within specific scales before integrating them into a comprehensive model. At the micro-scale, Density Functional Theory (DFT) and Kelvin Probe Force Microscopy (KPFM) revealed that the specific molecular structure of AOB introduces deep electron (HOMO) and hole (LUMO) traps. This modification significantly prolonged the surface potential decay time from 3.9 s to 9.2 s, effectively suppressing carrier injection and mobility. At the meso-scale, AOB acted as a nucleating agent, refining spherulites and increasing crystalline density. Finite element simulations based on the Voronoi algorithm demonstrated that this morphological evolution reduced the dielectric mismatch between crystalline and amorphous phases, thereby decreasing the interfacial electric field distortion from 43% to 21%. Consequently, at the macro-scale, the synergistic effect of micro-scale trap capture and meso-scale field homogenization resulted in an 85% reduction in space charge accumulation, a one-order-of-magnitude decrease in conductivity, and a 30% increase in DC breakdown strength. This study provides a multi-scale, quantitative theoretical basis for the rational design of advanced cable insulation materials.