On the morphology of metallocene polyethylene for cable applications

The crystallization behaviour of polyethylene produced with metallocene catalysts (metallocene polyethylene, MPE) was examined in its cross-linked form. Large spherulitic structures were observed very easily in these polyethylene compounds of very low density. Such a microstructure was absent in a cross-linked low density polyethylene (LDPE) produced with free radical polymerization technology. When MPE and LDPE were melt blended and cross-linked, the morphology depended on the blend ratio and annealing conditions. The spherulitic structure disappeared at 50/50 blend ratio and when annealing took place above 90°C. Although the cross-linked blends of MPE and LDPE may exhibit resistance to the growth of water trees under laboratory tests on moulded dishes, their performance under full-size cable tests deserve more attention and scrutiny. The crystallization behaviour of these MPE´s can be expected to complicate the aging process under accelerated conditions with a strong thermal gradient