On the effects of morphology and molecular composition on the electrical strength of polyethylene blends

The effects of morphology and molecular composition on the electrical strength of blends of linear and branched polyethylenes were investigated. A range of blend systems were considered, in which both the molecular mass of the linear polymer and the comonomer in the branched component were varied. All the blends contained 10% linear polyethylene and 90% branched polymer and, in each system, three crystallization procedures were employed to modify the morphology. Isothermal crystallization at 124 °C generally resulted in compact linear inclusions within a branched matrix; isothermal crystallization at 115 °C produced a space-filling network of open, spherulitic structures; and quenching gave a banded spherulitic morphology. In these systems, the electrical strength, as measured by ramp testing, was dependent on the morphology of the material but was not influenced per se by significant changes in the molecular composition of the blend. The effect of crosslinking was also examined; the inclusion of a network did not, in itself, affect the breakdown strength or the morphology.