Synergistic activities of binary accelerators in presence of magnesium oxide as a cure activator in the vulcanization of natural rubber

We describe the synergistic activities of binary vulcanizing accelerators in presence of magnesium oxide as cure activator in the vulcanization of natural rubber. Thiuram type tetramethyl thiuram disulfide (TMTD) and thiocarbamate type zinc dimethyl dithiocarbamate (ZDMC) accelerators in combination with dibenzothiazyl disulfide (MBTS) were investigated for the vulcanization of rubber. The cure, mechanical, and thermal properties of rubber vulcanizates were studied with magnesium oxide-based cure activator. Notable synergism in the delta torque, cross-link density, and mechanical properties was found when using binary accelerators with magnesium oxide. The zinc-containing thiocarbamate accelerator, ZDMC, showed better synergistic activity in presence of magnesium oxide than the non-zinc-based thiuram accelerator, TMTD. To find out the possibility of making a zinc-oxide-free natural rubber compound, a control compound was prepared with 5 phr of zinc oxide as a cure activator with the best evaluated binary accelerators system with magnesium oxide (3:6 millimolar ratio of ZDMC to MBTS). We also compared the curing and mechanical properties of carbon black-reinforced rubber with zinc oxide and magnesium oxide separately with this binary accelerators system. The results indicated that a completely zinc-oxide-free natural rubber compound was possible with comparable values in the mechanical properties, thermal properties and a higher rate of vulcanization.