Pressure-Modulated Interfacial Crystallization Behavior and Morphology in XLPE Homogeneous Interfaces

Cross-linked polyethylene (XLPE) factory joints are critical components in submarine cable systems. This study proposes a pressure-regulated crystallization strategy to optimize the interfacial micromorphology and crystalline integrity of asynchronously molded homogeneous interfaces. Multiscale characterization reveals that these interfaces initially contain microporous defects (0.5–5 μm) and lower crystallinity than bulk insulation, causing significant performance degradation. Elevating molding pressure to 3.0 MPa under a fusion temperature of 125 °C and a cross-linking temperature of 175 °C enhances molecular chain entanglement and lamellar thickness, effectively reducing free volume and suppressing micropores. This significantly boosts both the electrical and mechanical properties. Conversely, excessive pressure (3.0–6.0 MPa) imposes steric hindrances that inhibit crystal growth and reintroduce structural defects; while mechanical properties remain stable, electrical performance declines significantly. This research elucidates a nonmonotonic correlation between interface crystallization and molding pressure. By identifying 3.0 MPa as the optimal condition, this work provides a theoretical foundation and technical guidance for manufacturing higher-voltage factory joints with superior operational stability.