Influence of Thermal Ageing on Surface Degradation of Ethylene-Propylene-Diene Elastomer

Evolution of the surface characteristics of EPDM elastomer was studied as a function of thermal ageing at 80°C and 120°C in air for up to 100 days. 

The components of the surface free energy (SFE) were determined from contact angle measurements of five liquids using acid–base regression and Fowke´s theories. SFE increased with ageing duration. For ageing at 80°C, SFE increased exponentially with time and stabilized after 60 days. Ageing at 120°C promoted a steep enhancement of SFE within the first 5 days followed by a slow long-term linear increase. Rate parameters of the SFE evolution were analyzed using Dakin´s kinetic model. Analysis of the surface composition using X-ray photoemission spectroscopy evidenced an enhancement of the oxygen content with increasing the ageing time. The increase of the polar component of the SFE was attributed to the presence of these oxygen functional groups. This tendency was more pronounced for ageing at 80°C