Vulcanization of an Ethylene Propylene Diene Rubber

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Abstract
This study concerns the sulfur vulcanization of EPT with dithiocarbamate accelerators. The reactions undergone by the accelerators are equivalent to those found during natural rubber or SBR vulcanization; TMTM and TMTD are almost completely converted to ZDMC. During vulcanization about 50% of the double bonds are saturated, and approximately one crosslink is formed for each two double bonds initially present. Equilibrium swelling measurements before and after mercaptan cleavage were used to determine the concentration of all crosslinks and that of monosulfide ones as functions of vulcanization conditions. Vulcanization kinetic were followed by Monsanto rheometer measurements. The process takes place in two stages: an initial fast reaction representing vulcanization by the primary accelerator, followed by a slower first order reaction due to acceleration by ZDMC. Accelerator, sulfur, and zinc oxide concentrations have little effect on the rate constants which, however, are nearly proportional to polymer unsaturation. The rate constants approximately double with each temperature rise of 10° C.

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