Compressive stress-thermo oxidative ageing behaviour and mechanism of EPDM rubber gaskets for sealing resilience assessment

EPDM rubber gaskets, as a water-proof sealing material installed in the tunnel segment joints, were subjected to compressive stress-thermo oxidative ageing at different temperature and compressive stress levels. It was found that compared with thermo-oxidative ageing, compressive stress-thermo oxidative ageing of EPDM samples was more aggressive due to the destructive effect of compressive stress: the molecular structure was oxidized to form oxygenated species such as carbonyl groups, while high compressive stress level resulted in the degradation of EPDM with lower degradation activation energy (E-a), and the breakage of CB network structure and phase separation. Meanwhile, the crosslinking reaction dominated over the chain scission reaction especially at high temperature during the whole ageing process, leading to the increase of crosslinking density of EPDM samples. With increasing ageing temperature and compressive stress, the ageing degree of EPDM rubber was much severe, and compressive stress promoted the degradation of samples, resulting in the decrease of glass transition temperature (T-g) and increase of free volume at high stress levels, while thermo-oxidative ageing promoted the crosslinking reaction of samples, leading to the higher T-g and lower free volume at high ageing temperature. As a result, the surface of EPDM rubber became much rough and interfacial debonding occurred between CB and EPDM matrix, while the mechanical and durable sealing resilience performance were deteriorated during stress-thermal ageing.