Post-curing Effects on Sulfur Network Stability and Thermo-oxidative Aging Resistance of Vulcanized Natural Rubber

The long-term durability of natural rubber (NR) in demanding applications depends critically on the stability and evolution of its sulfur crosslinked network, as thermo-oxidative aging alters both the polymer backbone and the crosslink structure. Post-curing treatments—often referred to as maturation—can reshape the sulfur network architecture and, in turn, influence resistance to degradation. While some studies have considered how the topology of the initial sulfur crosslink network affects aging, the specific effects of maturation remain underexplored. To address this gap, this study examines the impact of maturation on the aging behavior of NR vulcanizates cured to t’95 at 180 °C. The evolution of the elastically active chain (EAC) density and mechanical properties was tracked using equilibrium swelling experiments and tensile testing under both thermal and thermo-oxidative conditions.Findings show that post-curing enhances crosslink density, reduces network defects, and delays the onset of oxidative degradation. In contrast, unmatured samples exhibit an initial crosslinking phase, driven by residual curatives and oxygen, followed by accelerated degradation. Ultimately, both systems converge to similar EAC densities, underscoring the overriding influence of oxidative degradation on long-term material performance.