Effect of curing agent on mechanical and chemical properties of EPDM in an acidic environment

Ethylene-propylene-diene terpolymer (EPDM) is a widely used sealing material in many industrial applications. These gaskets are subjected to mechanical compressive load and may expose to acidic environments during operation. Therefore, these gaskets' mechanical and chemical properties can be changed over time, so it is crucial to assess the gasket performance in such conditions. One of the key parameters that define the properties of an elastomeric gasket is the vulcanization system. In this paper, the mechanical and chemical properties of peroxide cure EPDM with various amounts of curing agent in an accelerated durability test (ADT) acidic solution (۱۲.۵ ppm H۲SO۴ + ۱.۸ ppm HF) was investigated. Polymer Electrolyte Membrane (PEM) fuel cell stack requires elastomeric gaskets and seals in each cell to prevent leaking the reactant gases from their respective regions, which are of great significance for both sealing and electrochemical performance of fuel cells during the long-term operation. These gaskets are subjected to mechanical compressive load and may expose to acidic environments during operation. Therefore, the mechanical and chemical properties of these gaskets can be changed over time, so it is crucial to assess the gasket performance in such conditions [۱,۲]. Ethylene-propylene-diene terpolymer (EPDM) is a widely used sealing material in many industrial applications such as sealing and gaskets. In this paper, the mechanical and chemical properties of peroxide cure EPDM with various amount of curing agent in an accelerated durability test acidic solution was investigated [۳,۴].EPDM (KEP۲۷۰) was purchased from KUMHO polychem (Seoul, South Korea). Dicumyl peroxide (DCP, purity > ۹۸ %) was utilized as a curing agent and was supplied by Sinopharm Chemical Reagent Co., Ltd. (Beijing, China). The three compounds contained ۲ (EP۲), ۳ (EP۳), and ۴ (EP۴) phr DCP with ۲۰ phr carbon black, respectively. The samples were exposed to ADT solution at ۸۰ C for ۴۰۰ hours and the change in mechanical and chemical properties of the samples, such as hardness and compression set were investigated.The cure characteristics and swelling ratio are presented in Table۱. Hardness and compression set results for each sample before and after the degradation test is depicted in Fig ۱ and Fig ۲. As we can see from these figures, EP۴ has the highest hardness and the lowest compression set. It is evident that increasing the amount of DCP will lead to an increase in crosslink density (CLD). Higher CLD results in more rigidity so that hardness will increase. In addition, as CLD increases, the number of crosslinks responsible for strain recovery as the load is removed is higher; therefore, the compression set will decrease. After the aging process, the hardness of the samples is almost intact, indicating that the surface of the samples didn’t change after the aging. On the other hand, the compression set of all the samples increased, but in the case of EP۳, the compression set increased slightly. This can be due to the degradation of the elastomer molecular chains, such as chain scission or breakage of the crosslink bonds, which deteriorates the mechanical properties. The EP۳ sample exhibit superior performance compared to the other two, so it will be more suitable for fuel cell gasket application.