Abstract
<jats:p>This study examines the effect of adipic acid concentration on the physicomechanical and chemical properties of nitrile–butadiene rubber (NBR) and ethylene–propylene–diene monomer (EPDM) blends reinforced with carbon black. Four composite formulations were prepared with a fixed NBR/EPDM ratio of 70/30 phr, identical amounts of reinforcing fillers, activators, accelerators, and curing agents, while varying adipic acid contents at 0.0, 0.5, 1.0, and 3.0 phr. Mixing was performed on a laboratory two-roll mill, followed by vulcanization under optimized time–temperature conditions. Adipic acid was incorporated as a potential co-curing agent and compatibilizer to improve phase interaction between the polar NBR and non-polar EPDM phases. The influence of adipic acid on vulcanization characteristics, tensile strength, elongation at break, modulus, hardness, crosslink density, and thermal–oxidative aging resistance was systematically evaluated. The results showed that increasing adipic acid content modified the curing kinetics and improved interfacial adhesion, leading to notable enhancements in certain mechanical and aging resistance properties, particularly at moderate concentrations. However, excessive adipic acid levels resulted in a decline in performance due to overplasticization effects. These findings contribute to the optimization of hybrid elastomer formulations for automotive, sealing, and other industrial applications where enhanced durability and environmental resistance are required.</jats:p>