THERMAL AGEING EFFECTS ON THE PROPERTIES OF ETHYLENE-PROPYLENE-DIENE MONOMER (EPDM)

In this paper, we present the dielectric and mechanical behaviour under thermal ageing of Ethylene Propylene Diene Monomer (EPDM), used in medium and high voltage cables. Dielectric and mechanical tests were carried out under continuous thermal ageing going up to 5000 hours on samples at four ageing temperatures varying from 80 degrees C to 140 degrees C. Every 500 hours approximately, we measure the transverse resistivity, the dielectric constant, the dielectric losses factor and the dielectric strength. The mechanical properties, elongation at break and tensile strength, were measured before and after ageing. The physical properties were also studied. They relate to the loss of mass as well as to the colour change of the sample. The results revealed that the thermal ageing affects considerably the material properties at important ageing temperatures. In fact, a significant degradation of the mechanical and physical properties of the studied material was obtained at the temperature of 140 degrees C. This degradation is due to the chain scissions, which cause a reduction in the average molecular mass and cross-linking rate on one hand, and to a plasticizer loss on the other hand. In fact, the process of chain scission increases the chain mobility.