Investigation on electrical trees propagation characteristic in polyethylene based on etching method

Abstract

To investigate characteristics of the electrical trees propagation in PE, the low-density polyethylene (LDPE) samples with electrical trees were cut into slices using ultramicrotome, then the slices are etched by potassium permanganate solution. Finally, the crystalline structure and propagation path of electrical trees were observed by polarized light microscopy (PLM). The observation results show that there is a crystalline dense region in the center of LDPE spherocrystal structure, and the crystallization around this region shows obvious radial morphology. Under the electrical field, most branches of the electrical tree grow along the boundary between spherocrystal and spherocrystal or spherocrystal and amorphous region due to their structure differences in LDPE. Electrical tree will insert the inside of the spherocrystal and then grow to the spherocrystal center along the interphase between lamellar crystals when local electrical field is higher or electrical field is subjected for long-term. And the color of electrical tree path is darker. When the electric tree branches inside the small spherocrystal grow to a certain extent, they will cross the spherocrystal grow again along the spherocrystal boundary. Most branches of the electrical tree present a form that they are bypasses the spherocrystal and grow along the boundary between spherocrystals, so the propagation shapes of electrical treeing associate with the spherocrystal morphology and exhibit the fractal characteristic of multi inflection point.