Comparison of cure,mechanical, electric properties of EPDM filled with Sm2O3 treated by different coupling agents

Composites based on ethylene–propylene–diene rubber (EPDM) were prepared. EPDM was reinforced with 100 phr Sm₂O₃ treated with coupling agents: stearic acid (SA), isopropyl tri(dioctylphosphate) titanate (NDZ102), bis-[-3-(triethoxysilyl)propyl]tetrasulfide (KH845-4), and N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane (SG-Si602), respectively. Cure, mechanical and electrical properties of the composites were investigated. It was found that carboxyl in coupling agents could retard EPDM cure while amino groups, PO bonds and S atoms could accelerate EPDM cure. Amino groups enhanced composite mechanical properties by forming additional rigid C–C linkages, whilst S atoms boosted composite mechanical properties by generating flexible S–C linkages. PO bonds might be subject to cleavage during vulcanization and form flexible P–C linkage. Thus, composites with NDZ102 and KH845-4 treated filler exhibited better mechanical properties than that with SG-Si602 treated filler. In addition, treatment of filler could reduce composite electrical properties due to interfacial improvement.