WATER TREEING IN BINARY LINEAR POLYETHYLENE BLENDS - THE MECHANICAL ASPECT

Water treeing tests were performed on low density polyethylene (LDPE) and four different binary blends of sharp linear polyethylene (LPE) fr actions (M(w), = 2500 and 76000), which were either quenched in air fr om the melt or isothermally crystallized at 123 degrees C. Although th e morphology and initial mechanical properties of the materials tested were significantly different, the vented tree growth characteristics were similar for all of them. This is in disagreement with the electro mechanical models of water treeing, which correlate water tree growth with the fracture toughness of the material. Time to breakdown distrib utions were also similar for both LDPE and the binary LPE blends, whic h indicates that, regardless of the initial material morphology and th e actual structure of water trees, the length of water trees is one of the controlling factors in insulation failure. The visible light imag e of water trees in LPE blends did not disappear upon drying as it usu ally does in LDPE and crosslinked polyethylene insulation,