Effect of Different Accelerator Systems on the Processing, Mechanical, Dynamic, and Network Properties of Natural Rubber Vulcanizates

In this work, the efficiency of various primary and secondary accelerators on natural rubber (NR) vulcanizates was compared. Twelve formulations were prepared with six accelerators in a conventional sulfur system. The effects on rheological, mechanical, dynamic mechanical, abrasion, and set properties were evaluated. Chemical probe treatments were used to study crosslink types, and their influence on crosslink density was also examined. The data, including crosslink density and distribution types for various curatives, were correlated with mechanical and aging properties. Accelerators showed synergistic effects, producing either higher or lower physical properties than expected. The CBS+TMTD system exhibited the fastest cure rate index (CRI = 34.6 min −1 ), more than double that of CBS+DPG (13.4 min −1 ) TMTD‐based systems achieved a modulus of 11.5 MPa and a cure rate index (CRI) of 34.6 min −1 . TMTD‐based binary systems achieved the highest modulus at 300% elongation (≈11.5 MPa), compared to 8.1 MPa for MBTS+ZBEC. CBS‐based vulcanizates showed the best retention of properties after aging, with only ~8% reduction in tensile strength compared to ~17% for TBBS+ZBEC. Results also indicated that less polar accelerators formed crosslinks with longer sulfur chains, that is, more polysulfidic in nature, while accelerators with higher polarity produced networks with shorter sulfur crosslinks.