Abstract
The reinforcement of non-polar ethylene-propylene-diene rubber (EPDM) by the polar metal salts of methacrylic acid was achieved by directly mixing the salt into EPDM at a high level and curing with peroxide. Mechanical properties and crosslink density of the vulcanizates were investigated. Wide-angle X-ray diffraction (WAXD) and Fourier transform-infrared spectroscopy (FTIR) were employed to analyze the reactivity of zinc dimethacrylate (ZDMA) in EPDM compounds before and after vulcanization. It was observed that the commercial ZDMA or magnesium dimethacrylate (MDMA) can greatly improve the hardness and tensile strength of the EPDM vulcanizates, while retaining a high elongation at break. WAXD and FTIR revealed that ZDMA is a reactive filler in the EPDM matrix during peroxide curing. The crosslink density of the vulcanizates was determined by equilibrium swelling. Covalent crosslinks and ionic crosslinks were distinguished by an acidolysis treatment. Ionic crosslinks were greatly improved by increasing the amount of zinc dimethacrylate or dicumyl peroxide, and the relationship between mechanical properties and crosslink density indicates that the tensile strength of the vulcanizate was principally dependent on ionic crosslink density.