Effect of hot-air aging on properties of EPDM/SmBO3/EAA and EPDM/ATO/EAA composites

Ethylene-propylene-diene monomer (EPDM) rubber/samarium borate (SmBO3)/ethylene acrylic acid (EAA) and EPDM/sb in Sb-doped SnO2 (antimony tin oxide)/EAA composites are aged at 150°C for different intervals. It is found that alkaline SmBO3 can lower the oxidation rate of EPDM composites by scavenging acids formed during aging. The grown acrylic acid content lowers the pH level of EPDM composites and then elevates the oxidation rate. For EPDM/filler control, the chain scission dominates in the early stage of aging, while cross-linking takes the main effect in the latter stage of aging. Moreover, the poly (circular acid anhydride) formed by carboxylic acid in EAA during curing decomposes and influences the overall chemical cross-link points. The lowest crystallinity of EAA in EPDM/filler/EAA composites appears at the 10th day of aging and is attributed to the varied cross-link density. The changing trend of tensile strength is well consistent with that of swelling ratios, and electric properties are correlated with increased polar groups and crystallinity.