Study on DC breakdown strength and morphology in XLPE/Al(OH)3 nanocomposites

Studies have proved that the dielectric strength of high-voltage DC cable used crosslinked polyethylene (XLPE) can be enhanced by nanoparticle incorporation. However, studies on the morphology of XLPE based nanocomposites and its relation with the DC dielectric strength are relatively inadequate. In this paper, XLPE/Al(OH)
₃
nanocomposites with different nano-filler contents (0.1 wt%-3wt%) were prepared. The nanoparticles were surface-modified by silane coupling agent which has alkyl chain on one end, then it was melt blended to prepare nanocomposites. Thin film samples were obtained using hot-press method. In order to observe the internal morphology and its change depending on the nano-filler content, permanganic etching was conducted to treat the samples. Results showed that the number of spherulite increased and the spherulite size remarkably decreased with the increase of nanofiller content, while the DSC results showed a little change in crystallinity. With the increase of nano-Al(OH)
₃
content, DC breakdown strength increased firstly and then decreased at 20°C, 50 °C and 70 °C, while it showed a exactly opposite trend at 90 °C. As DC breakdown strength decreased dramatically with the increasing temperature for all samples, then a “crossover” happened at about 80 °C. The morphology affects the dielectric properties of nanocomposites significantly. It should be one of the important parameters that used to explain the improved insulation performance of nanodielectrics especially the DC breakdown strength.