Thermal and oxidative degradation of PE-EPDM blends vulcanized differently using sulfur accelerator systems

Abstract

Blends of low density polyethylene (PE) of density 915 kg m − 3 and ethylene propylene diene rubber (EPDM) of density 860 kg m − 3 were vulcanized using two different sulfur accelerator curative systems: (A) a conventional curative system based on a combination of TMTD, MBTS and S; and (B) a silane curative system based on a combination of TMTD, Si69 and S. For each curative system, torque rheometric and morphological studies indicated development of a co-continuous phase morphology (involving hard PE and soft EPDM phases) for 30 70 PE/EPDM blend composition, particularly under dynamic curing conditions. Thermal degradation studies employing DSC and TGA indicated that sulfur vulcanization made the PE/EPDM blends thermally more stable. Between the two curative systems used, the conventional curative system imparted somewhat higher stability to the blend vulcanizate. Dynamic curing rendered the vulcanizates slightly more thermally stable than static curing under comparable conditions. Thermal degradation of the blend vulcanizates took place much faster at a relatively low temperature in air than in nitrogen. Studies of air oven aging of the blend vulcanizates enabled prediction of their life time in insulated cable applications at different temperatures. The predicted life time of 30 70 PE/EPDM blend vulcanizates at 70 °C (343 K) ranges between 10 and 15 yr.