Thermal aging behavior and lifetime prediction of industrial elastomeric compounds based on styrene–butadiene rubber

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Abstract
This work describes the thermal aging behavior of three industrial elastomeric compounds based on styrene–butadiene rubber (SBR) reinforced with carbon black. Samples were exposed to thermo‐oxidative aging at temperatures ranging from 70 to 120°C for durations between 14 and 365 days. The tensile and hardness tests were performed on the samples to determine changes in their mechanical properties. Upon aging, hardness and 100% modulus increased, while elongation at break decreased for all three samples. The results showed a significant decrease in elongation at break and an increase in hardness and modulus with prolonged aging time and higher temperatures. For instance, the elongation at break of the three types of samples decreased by approximately 50% in less than 90 days at 70°C, whereas at 120°C, this same level of degradation occurred in less than 2 days. These significant changes were correlated with increased brittleness and reduced flexibility of SBR composites. Swelling tests confirmed an increase in crosslink density due to aging. Laser scanning confocal microscopy revealed surface roughness and defects, attributed to oxidation, crosslinking, and the evaporation of low molecular weight components. Lifetime prediction methods, including the Arrhenius equation and time–temperature superposition (TTS), were applied to estimate the service life of the materials. The Ahagon plot was utilized to understand the aging mechanisms, revealing a transition from crosslinking‐dominated degradation to chain scission processes at higher temperatures and longer aging times. Highlights: Thermal aging makes SBR compounds more brittle and less flexible over time. The hardness and stiffness of SBR compounds increase with aging temperature and time. Aging increases crosslink density, confirmed by swelling tests. Increased surface roughness and defects due to oxidation and crosslinking. The aging mechanism shifts from crosslinking to chain scission at higher temperatures.
Funding Information
  • Natural Sciences and Engineering Research Council of Canada

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