Composite zinc oxide as a sustainable cure activator for NR/BR tire sidewall compounds: comparative evaluation of vulcanization efficiency and durability

Abstract Zinc oxide (ZnO) is an essential cure activator in sulfur-vulcanized rubber compounds, yet its conventional use is increasingly questioned because zinc-containing tire additives and dissolved zinc released from tire-derived particles are regarded as substances of environmental concern. In this context, the development of alternative ZnO systems has gained importance for tire compounds that require both efficient vulcanization and durable in-service performance. In the present study, conventional white seal ZnO, active ZnO, and three composite ZnO materials are comparatively evaluated in NR/BR based tire sidewall formulations through a component-oriented test matrix including elemental analysis, Mooney viscosity, moving die rheometer (MDR) cure behavior, tensile properties before and after thermal aging, hardness, tear strength, specific gravity, rebound resilience, flexometer response, and fatigue performance. The results show that composite ZnO does not cause any meaningful deterioration in processability, curing characteristics, mechanical integrity, or dynamic durability relative to the reference systems. All formulations also exhibit a similar thermal-aging pattern, with decreasing tensile strength and elongation at break accompanied by increasing low-strain modulus and hardness. Composite ZnO emerges as a technically viable and more sustainable alternative cure activator for tire sidewall compounds.