INFLUENCE OF CURING SYSTEMS ON THE PROPERTIES OF BROMOBUTYL RUBBER .3. EFFECT OF DIFFERENT TYPES OF CURING SYSTEMS ON THE CURE CHARACTERISTICS, PHYSICAL-PROPERTIES AND THERMOOXIDATIVE DEGRADATION CHARACTERISTICS

The effect of various curing systems on the properties of bromobutyl rubber vulcanizates was studied. Various curatives, e.g. conventional sulphur, efficient vulcanization (EV), semi-EV, maleimide/promoter (both mercaptobenzothiazyl disulphide and dicumyl peroxide used as promoter), resin (resin concentrations between 2 and 25 parts per hundred resin (phr)) and metal oxide systems were employed. Curing characteristics, physical properties and thermo-oxidative degradation characteristics were evaluated. Crosslink density (before and after ageing for various periods of time) was assessed by swelling measurements in cyclohexane. The results indicate that scorch safety of resin-cured systems is higher than that of metal oxide, sulphur, semi-EV and EV systems. Vulcanization with dimaleimide provides a very safe processing stock and a very high final state of cure. The strength properties before ageing are comparable among the various curing systems. Significant differences in heat resistance characteristics among the various cure systems are observed. Conventional sulphur cure, semi-EV and EV systems offer poor heat resistance characteristics at high temperature (150-degrees-C). However, phenolic resins in conjunction with zinc oxide, and bismaleimide/promoter systems, give excellent heat resistance characteristics. It is also observed that increase in phenolic resin concentration in the vulcanizate imparts better heat ageing behaviour.