Revisiting the sulfur vulcanisation of rubber

Sulfenamide accelerators in combination with zinc oxide activator are used extensively in the sulfur cure systems of a wide range of industrial rubber articles. However, the excessive use of these chemicals has raised major concerns regarding their adverse effect on marine life and human health as well as the environment. Zinc oxide was functionalised with a sulfenamide accelerator in an organic solvent to provide a convenient single material to use as an additive. The effect of the additive on the cure properties of natural rubber was then measured. The aim was to minimize the use of these two chemicals in the cure system and enhance the efficiency of the sulfur vulcanisation of the rubber. Functionalising zinc oxide with the accelerator reduced the excessive use of these chemicals in the cure system. When the cure properties were compared with those of a sulfur cure-based natural rubber compound used to make tyres, the optimum cure time was noticeably shorter and the rate of cure significantly faster despite reducing the use of these two curatives by almost 77 %. All the indications are that the cure efficiency improves considerably when the chemicals in the cure system are reduced.