Study on thermal cycling ageing resistance of performances of polypropylene/elastomer/boron nitride nanocomposites for high voltage direct current cable insulation

The influences of thermal cycling ageing on structures and insulation performances of polypropylene (PP)/elastomer/boron nitride (BN) nanocomposites are investigated. The Melt blending method was used to prepare the nanocomposites, in which propylene-based elastomer (PBE) or ethylene-octene copolymer elastomer (EOC) was contained for comparison. Then, the samples were treated using a thermal cycling process with a temperature range from −30 to 150°C, and the number of thermal cycles was set from 0 to 15. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry and X-ray diffraction measurements were taken to facilitate the comprehension of structural changes. Additionally, measurements were taken to assess the trap distribution and direct current (DC) breakdown strength of the samples. The obtained results revealed that following thermal cycling ageing, the morphology and crystallinity of PP/PBE/BN remained almost unchanged. In contrast, PP/EOC/BN exhibited substantial microstructural damage accompanied by a significant reduction in crystallinity. As the number of thermal cycles increased, the trap level and DC breakdown strength of PP/PBE/BN were maintained at high levels, while those of PP/EOC/BN initially remained stable but then experienced a sharp decline. It is suggested that the addition of BN nanoparticles enhances the thermal cycling ageing resistance of the PP/PBE blend, whereas it weakens this resistance of the PP/EOC blend.