ABSTRACT
The EPDM elastomer (NORDEL IP 4770P from Dow Chemical Company) is composed of 70% ethylene, 24.5% propylene and 4.9% ENB. Mw = 191 300 g/mol, Mn = 93700 g/mol have been measured via Gel Permeation Chromatography (GPC). The cross-linking agent is dicumyl peroxide (Perkadox BC-FF from Akzo Nobel). EPDM is filled with 50 phr of ATH, which is a mineral filler. Two types of ATH (from Nabaltec facility) have been chosen for this study: nanometric (APYRAL 200 SM with a diameter of 400 nm) and micronic (APYRAL 40 CD with a 2 μm diameter). The basic structure forms stacked sheets of linked
1 INTRODUCTION
EPDM copolymers (Ethylene Propylene Diene Monomer) offer good resistance to ozone and weather, to oxidant reagents, strong thermal stability and effective electrical insulating property making them suitable for many industrial applications. EPDM are usually cross-linked via the addition of peroxide during the processing, leading to enhanced mechanical properties. The insulation sheaths of electrical cables in nuclear plants are mostly made of EPDM because of its remarkable resistance to chemical aging. Nevertheless, as they endure exposition to radiation while in use, EPDM eventually lose their electrical insulating property. The degradation of the mechanical properties has been proved to be an indication of the degradation of the electrical properties (Davenas 2002 and Rivaton 2006). Thus, the lifetime prediction of EPDM is based on its mechanical performance, more specifically the material elongation at break. Mineral fillers are commonly added to the EPDM formulation-such as ATH (Aluminium TriHydrates)—in order to reduce the costs as well as improving the mechanical properties and providing a fire retardancy functionality. The influence of fillers on the radiochemical degradation processes has been investigated (Planès 2010), revealing an accelerating effect of the fillers on the degradation
octahedrons of aluminium hydroxide. The hydroxides can be assimilated to crystal water. This filler is an anti-flame agent: during thermal degradation, it undergoes endothermic dehydration releasing water, which leads to formation of a surface layer of Al2O3. This layer acts as a shield to heat and mass transfer between the polymer and the flame.
