Effect of Low Molecular Weight Part of LDPE on DC Conductivity of XLPE

Crosslinked polyethylene (XLPE) is commonly used as high voltage direct current (HVDC) cable insulation material, which is obtained by crosslinking low-density polyethylene (LDPE). Its electrical and mechanical properties will be influenced by LDPE. In addition, the electric field distribution within DC cable insulation depends on the material's conductivity. Therefore, this paper focuses on the relationship between XLPE conductivity and the low-molecular-weight part of LDPE. Though controlling the extraction temperature, the low-molecular-weight part was removed to different extents, which can be supported by the decreasing trends of methyl, carbonyl, and vinyl. The research on the change in material structure showed that with the removal of the low-molecular-weight part, the crosslinking degree of XLPE slightly increased, the crystallinity of LDPE increased while that of XLPE remained essentially unchanged, mainly due to the inhibition of crosslinking on crystallization. Analysis of conductivity revealed that the removal of the low molecular weight part led to a decrease in DC conductivity and an increase in activation energy. This can be attribute to the reduced carrier concentration and enhanced crosslinking network. Based on the relationship between the low-molecular-weight part and XLPE conductivity, this paper provides a perspective on the control of base resin for the development of XLPE.