Low-density polyethylene (LDPE), as an excellent dielectric insulating material, is widely used in electrical equipment insulation, whereas its low thermal conductivity limits its further development and application. Hexagonal boron nitride (h-BN) filler was introduced into LDPE to tailor the properties of LDPE to make it more suitable for high-voltage direct current (HVDC) cable insulation application. We employed melt blending to prepare h-BN/LDPE thermally conductive composite insulation materials with different contents. We focused on investigating the micromorphology and structure, thermal properties, and electrical properties of h-BN/LDPE composites, and explained the space charge characteristics. The scanning electron microscope (SEM) results indicate that the h-BN filler has good dispersibility in the LDPE at a low loading (less than 3 phr (3 g of micron h-BN particles filled in 100g of LDPE)), as well as no heterogeneous phase formation. The results of thermal conductivity analysis show that the introduction of h-BN filler can significantly improve the thermal conductivity of composites. The thermal conductivity of the composite samples with 10 phr h-BN particles is as high as 0.51 W/(m·K), which is 57% higher than that of pure LDPE. The electrical performance illustrates that h-BN filler doping can significantly inhibit space charge injection and reduce space charge accumulation in LDPE. The interface effect between h-BN and the substrate reduces the carrier mobility, thereby suppressing the injection of charges of the same polarity and increasing the direct-current (DC) breakdown strength. h-BN/LDPE composite doped with 3 phr h-BN particles has excellent space charge suppression effect and high DC breakdown strength, which is 14.3% higher than that of pure LDPE.

Low-density polyethylene (LDPE) has excellent dielectric properties and is extensively used in electrical equipment. Hexagonal boron nitride (h-BN) is similar to a graphite-layered structure, and alumina fiber (Al₂O₃) has high-temperature resistance and a strong performance. Herein, we prepared Al₂O₃-h-BN/LDPE nanocomposites by using LDPE as the matrix material and h-BN and Al₂O₃ as the fillers. The influence of different doping contents and the mass ratio of Al₂O₃ and h-BN (1:1) to LDPE on the electrical properties and thermal conductivity of the nanocomposites was examined. The results showed that the suppression effect on space charge was the most obvious and average. The charge density was the lowest and had the minimum decay rate when the doping content was 2%. The breakdown strength of the film reached the maximum value of 340.1 kV/mm, which was 12.3% higher than that of the pure LDPE (302.8 kV/mm). The thermal diffusivity of the composite sample was also higher than that of the single h-BN-doped sample when the content of h-BN and Al₂O₃ was 7%. The thermal conductivity was 59.3% higher than that of the pure LDPE sample and 20% higher than that of h-BN/LDPE.