Enhancement of thermo-oxidative stability in natural rubber via strain-induced network reorganization

Abstract

Rubber materials are frequently degraded by environmental factors such as light, heat and oxygen during service. Conventional protective approaches, however, often involve adding antioxidants during processing, which not only causes significant environmental pollution but also limits the applicability of rubber products in the biomedical field. Therefore, developing robust aging mitigation strategies constitutes a critical imperative to ensure material longevity. This study proposes a feasible and effective strategy: inducing network rearrangement in rubber through pre-stretching to achieve a more stable crosslinked structure, thereby enhancing its thermo-oxidative stability. During vulcanization, polysulfide and disulfide bonds are formed in the crosslinking network of rubber. Pre-stretching preferentially broke weaker bonds, inducing the conversion of polysulfide bonds to disulfide bonds during the stretching process. This strain-induced network rearrangement enhanced the rigidity and stability of rubber. At elevated temperatures, this mechanism became more pronounced. Pre-stretching triggered rapid conversion of polysulfide to disulfide bonds during the initial stages of thermo-oxidative aging. Given the higher bond energy and stability of disulfide bonds under thermal-oxidative conditions, the aging resistance of rubber is significantly improved. Both atomic force microscopy tests and mechanical tests demonstrated that stretching induced dynamic transformation of sulfur bonds in the crosslinking network, leading to significant changes in spatial heterogeneity under thermo-oxidative conditions. As a result, the thermo-oxidative resistance of natural rubber was enhanced, with the retention of tensile strength increasing from 58.6 % to 81.1 % after 24 h of thermo-oxidative aging. This study not only provided important guidance for the general design of thermo-oxidation-resistant elastomers but also advanced the understanding of rubber network evolution mechanisms under thermo-mechanical coupling conditions.