Vulcanization of saturated ethylene-propylene rubber with tetramethylthiuramdisulphide in the presence of dicumyl peroxide

Abstract

THE curing of saturated hydrocarbon polymers (polyethylene, ethylene-propylene rubber, etc.) is most frequently effected by using a combination of dicumyl peroxide (PDC) and sulphur with small amounts of tetramethylthiuramdisulphide (TMTD) and zinc oxide [1] added to activate the process. We know that spontaneous reactions between TMTD and saturated polymers take place only at temperatures above 200 ° [2], and so under peroxide vulcanization conditions (140-160 °) one would rather expect the curing efficiency to be reduced through blocking by TMTD or by products of the thermal conversion of polymeric radicals emerging in the reaction with PDC. A study of the curing of ethylene-propylene rubber (EPR) by TMTD in the presence of dicumyl peroxide should also be of interest from the point of view of elucidating the mechanism of the action of this accelerator. The total available experimental data show that the vulcanization of unsaturated rubbers in the presence of TMTD gives rise to a complex chain of reactions of thermal breakdown of TMTD and of interaction of the breakdown products with one another and with the rubber. Most authors are inclined to take the view that the curing reaction involving TMTD is mainly of a radical nature [3-5]. However, according to the suggestions recently advanced in [6] ionic reactions have a considerable role in thiuram vulcanization processes. The processes involved in the curing of a saturated polymer in the presence of TMTD and PDC are much simpler in view of the absence of any spontaneous reactions ~,f the TMTD and the conversion products of TMTD with the rubber. Their addition to EPR becomes possible only after the saturated polymer molecules have been activated as a result of their reactions with the peroxide. These reactions are of a radical nature [7], and in the case to be considered here we may expect to find mainly radical reactions of TMTD. The aim of this investigation was to study features of the peroxide vulcanization of EPR with TMTD and zinc oxide.