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 stren gth of blends of linear and branched polyethylenes were investigated. A ran ge of blend systems were considered, in which both the molecular mass of th e linear polymer and the comonomer in the branched component were varied. A ll the blends contained 10% linear polyethylene and 90% branched polymer an d, in each system, three crystallization procedures were employed to modify the morphology. Isothermal crystallization at 124 degrees C generally resu lted in compact linear inclusions within a branched matrix; isothermal crys tallization at 115 degrees C produced a space-filling network of open, sphe rulitic structures; and quenching gave a banded spherulitic morphology. In these systems, the electrical strength, as measured by ramp testing, was de pendent on the morphology of the material but was not influenced per se by significant changes in the molecular composition of the blend. The effect o f crosslinking was also examined; the inclusion of a network did not, in it self, affect the breakdown strength or the morphology. (C) 2000 John Wiley & Sons, Inc.