Surface properties of cross-linked polyethylene

This study reports on the loss of hydrophobicity of cross-linked polyethylene (XLPE) insulation. Specimens of steam cured XLPE cut from a nominal 28 kV_rms cable were immersed in saline solutions of varying conductivities from 5 to 10⁵ μS/cm over a wide range of temperatures from 0 to 98°C. Specimens of XLPE were also left in air over the same temperature range. The hydrophobicity of the surface was determined by measuring the contact angle of a sessile drop of water. The contact angle decreased with increasing conductivity and increasing temperature of the saline solution. The time of immersion in the saline solution was extended up to 3,000 h until the reduced contact angle saturated at all the temperatures and all conductivities. The saturated values of the reduced contact angles and the time they took to reach it, depended on the temperature and the conductivity of the saline solution. In addition, the changes in the weight due to the uptake of water and the surface roughness of the XLPE specimens were determined during immersion. It will be shown that the decrease in the contact angle is related to the increased weight of the specimens and increased surface roughness