WATER TREEING IN CHEMICALLY CROSSLINKED POLYETHYLENE

The water tree resistance of chemically crosslinked polyethylene (XLPE) and of low density polyethylene (LDPE) were compared in order to elucidate whether the crosslinking itself influences or not the water tree propagation in polymer insulation. For this purpose, water trees were grown in compression molded disks, obtained from pellets of either thermoplastic (LDPE) or chemically crosslinkable polyethylene provided by Borealis. Two types of pellets of crosslinkable polyethylene were evaluated: one containing only peroxide (XLPE1) and another having, besides peroxide, a tree retarding additive system (TRXLPE). The results obtained indicate that there is no significant difference between the average of water tree lengths in XLPE1 (286 µm) and those in LDPE (269 µm). This is in agreement with the result of a previous study in which water treeing in irradiation crosslinked samples was analysed. On the other hand, the water tree lengths in TRXLPE (122 µm) are much smaller than in LDPE and XLPE1.