Chain dynamics evolution of ethylene-propylene-diene monomer in response to hot humid and salt fog environment

This work is dedicated to the mechanism underlying the influence of the harsh environment that may cause accelerated aging (high temperature, humidity, and salt spray) on the static and dynamics characteristics of ethylene-propylene-diene monomer (EPDM) copolymer. A molecular dynamics simulation was employed to provide an insight into the effects of the hot humid and salt fog environment on the micro and macroscopic properties. First, evidence shows that the T_g obtained by fitting mean square displacement does not rely on the selection of the equilibrium time. Second, radial distribution function, chain configuration, and nonbonding interaction were analyzed and it is inferred that the ambient humidity and temperature show a significant synergy on the EPDM system, which is attributed to the aggregation state transition and diffusion behavior of partial water at high temperatures. Finally, water and salt were considered as two factors to explore the influence on the T_g and the mobility of the molecular chain. It is concluded that the existence of water molecules significantly affects the chain dynamic behavior of EPDM, while salt is not regarded as an influencing factor. In general, our simulated work provides some insights and guidance for the durability of EPDM when used in harsh environments.