Multiphase Topology of Impact Polypropylene Copolymers and Its Effects on Electrical and Mechanical Performance for Recyclable HVDC Cable Insulation

Impact polypropylene copolymers (ICPs) are promising thermoplastics for recyclable high-voltage direct-current (HVDC) cable insulation, yet the links among molecular sequence, crystalline framework, multiphase topology, and charge transport remain unclear. A homopolymer-matrix (HICP), a random-copolymer-matrix (RICP), and a commercial high-phase-continuity (CICP) ICP were compared across molecular, crystalline, morphological, rheological, electrical, and mechanical scales. Relative to HICP, matrix randomization in RICP raised the soluble fraction at ≤35 °C from 18.92 to 27.21 wt%, lowered crystallinity from 51.1% to 32.1%, and reduced the effective crystalline-layer contribution from 7.84 to 4.05 nm. Concurrently, the characteristic trap depth increased from 0.92 to 1.05 eV, the maximum local space-charge density decreased from 65.5 to approximately 28.4 C m−3, and the characteristic DC breakdown strength rose from 226.2 to 310.8 kV mm−1, while the tensile modulus fell from 1000 to 612 MPa. CICP combined the lowest modulus (89.4 MPa, without fracture at the 630% instrument limit) with the lowest space-charge density (below 12.5 C m−3) and the highest breakdown strength (384.4 kV mm−1). Matrix-sequence regulation and multiphase topology thus provide a structural route to reconcile flexibility with high-field stability in recyclable PP cable insulation.