Combined effect of pH level and surface treatment of Sm2O3, SmBO3 and ATO particles on cure, mechanical and electric properties of EPDM composites

The aim of this study is to investigate the effect of pH level and surface treatment of samarium oxide (Sm2O3), samarium borate (SmBO3) and Sb-doped SnO2 (ATO) particles on properties of peroxide-cured ethylene-propylene-diene rubber (EPDM) composites. The bis-(-3-(triethoxysilyl)propyl)tetra-sulfide (KH845-4) treated particles were added to EPDM at various filler contents. The pH values of particles, and cure, mechanical and electric properties of the EPDM composites were evaluated. It was found that alkaline SmBO3 particles would accelerate cure by producing more radicals from dicumyl peroxide (DCP), but acidic ATO particles would retard vulcanization because of making DCP generate less radicals, and neutral Sm2O3 particles did not affect the cure process. Moreover, sulfuric linkages from KH845-4 on the filler surface would provide sulfuric radicals to form S-C linkages. Therefore, composites with SmBO3 exhibited excellent mechanical properties. Additionally, polar fillers could reduce electrical properties of composites due to increased composite polarity.