The effects of metal oxides on thermal stabilization of EPDM insulation compounds

The efficiency of two metal oxides, red lead and zinc oxide, and their binary mixture as thermal stabilizers in an ethylene-propylene-diene-monomer (EPDM)-based compound for high-voltage insulating cable has been investigated. Mechanical characteristics were monitored during long term aging up to the point of obtaining both 50% retention of tensile strength and elongation at break. It was possible to identify the best metal oxide combination for improved compound thermal stability. Tinned copper conductor insulated wires, not aged, were submitted to an electrical moisture absorption test at 90°C in accordance with AEIC CS 6-79. The electrical behavior of the tested compounds was compared on the basis of the loss tangent and permittivity results. By analyzing the electrical and thermal behavior it was possible to establish the best metal oxides composition for an EPDM-based compound