MgO as a cure modifier for reducing the conventional rubber vulcanization temperature at water's boiling point with improved vulcanization kinetics

In this investigation, MgO was employed as a secondary cure activator to decrease the rubber curing temperature. To study the curing kinetics at various temperatures, the moving die rheometer (MDR) measurement technique was utilized, and Coran kinetic models of accelerated sulfur vulcanization were adopted. Results from the curing studies revealed that the inclusion of MgO, along with ZnO as the primary cure activator in the traditional vulcanization system, substantially reduced the optimal curing time. The diminished scorch safety time indicated that MgO accelerated the decomposition of accelerator and sulfur, leading to the rapid formation of zinc-based active sulfurating compounds. These compounds contributed to an improved vulcanization rate with lower activation energies. Even when used as the sole cure activator, MgO exhibited higher activation energies for crosslinking but achieved a reduced optimum cure time due to the accelerated decomposition of curatives, resulting in swift formation of final cross-links. A small quantity of 1 phr (per hundred grams of rubber) MgO in the conventional vulcanization system effectively lowered the vulcanization temperature to the boiling point of water, accompanied by an increased vulcanization rate and reduced activation energies of vulcanization reactions. This low-temperature vulcanization approach opens possibilities for critical structures previously challenging to vulcanize through simple molding processes, ushering in a new era in rubber vulcanization.