Boosting mechanical and aging resistance performances of filled-rubber with MgO and ZnO co-cure activators in diverse vulcanization systems

Over the decades, ZnO has been the primary cure activator in the sulfur vulcanization of rubber, but due to its environmental impact on aquatic ecosystems, its use in rubber formulation must be reconsidered. This study explores the effects of MgO, known for its low toxicity, as a cure activator, either alone or in combination with ZnO, in carbon black-filled various vulcanization systems such as efficient, semi-efficient, and conventional vulcanization (EV, SEV, and CV). Curing, mechanical, and aging resistance properties were thoroughly examined. Curing studies indicate that incorporating MgO into binary cure activator systems significantly accelerates vulcanization. In the SEV vulcanization system, ZnO/MgO binary cure activators, with a 1:2 ratio totaling 3 phr (per hundred grams of rubber), exhibit a comparable tensile modulus at 100% elongation, along with higher tensile strength, elongation at break, and improved aging resistance compared to conventional ZnO as a sole cure activator. Notably, in ZnO-free compounds, MgO as a single cure activator demonstrates superior tensile strength, elongation at break, and excellent aging resistance. In conclusion, this study suggests that the usage of ZnO can be optimized in rubber vulcanization by considering the desired mechanical properties along with improved aging resistance performances.