Functionalized Soybean Oil as a Sustainable Processing Oil for Enhanced Performance of Silica-Reinforced NR/EPDM Blends

This study addresses the growing demand for sustainable alternatives to petroleum-based processing oils by investigating the use of soybean oil (SO) and functionalized soybean oil (FSO), the latter modified with bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT), in silica-reinforced natural rubber (NR)/ethylene-propylene-diene monomer (EPDM) blends. Naphthenic oil (NO), a conventional petroleum-derived processing oil, served as the reference. All blends containing oil exhibited improved processability over the oil-free blend, indicated by reduced viscosity. Both SO and FSO improved the thermal stability and aging resistance of the blends. The FSO-containing blend showed enhanced filler–rubber interactions, as evidenced by increased bound rubber content, attributed to silane functionalities bonding with the silica surface and possible reactions between the FSO moiety and rubber chains during vulcanization. Consequently, the FSO-based blend exhibited improved elasticity (lower tan δ) and superior mechanical properties, including a 17% increase in tensile strength and 8% increase in elongation at break, compared to the NO-based blend. Additionally, the use of FSO enables a reduction in the required amount of TESPT coupling agent, thereby enhancing the sustainability profile of the formulation. Overall, the findings highlight FSO as a viable and eco-friendly alternative to petroleum-based processing oils in silica-reinforced NR/EPDM blends, offering improved performance and environmental benefits.