<p>Achieving efficient filler–matrix interaction is critical for advancing high-performance rubber composites, particularly in multiphase elastomer blends where interfacial behavior governs mechanical durability and solvent resistance. In this study, ethylene–propylene–diene monomer/acrylonitrile–butadiene rubber (EPDM/NBR) composites were reinforced with pristine and ionic liquid (IL)-modified multi-walled carbon nanotubes (CNTs) to systematically evaluate the influence of surface chemistry on vulcanization, network development, mechanical performance, and swelling resistance. Rheological analysis revealed that CNT incorporation increased minimum torque, maximum torque, delta torque, and cure rate index, while reducing scorch and optimum cure times, indicating enhanced network formation and accelerated vulcanization. IL-modified CNT systems exhibited superior curing efficiency compared to pristine CNTs. Mechanical properties improved significantly up to an optimal loading of 5 phr. At this concentration, tensile strength increased by ~ 198%, stress at 100% elongation by ~ 74%, and tear strength by ~ 111% relative to the unfilled blend, while elongation-at-break and rebound resilience decreased due to restricted chain mobility. Swelling measurements demonstrated reduced solvent uptake and increased swelling-derived crosslink density, confirming enhanced network effectiveness. Abrasion resistance improved with filler loading, whereas compression set increased moderately, reflecting increased stiffness. FESEM observations supported improved filler dispersion in IL-modified systems, particularly at moderate loadings. Overall, the results establish that ionic liquid functionalization enables controlled reinforcement in heterogeneous elastomer blends, providing a robust strategy for designing durable and solvent-resistant EPDM/NBR composite materials.</p> Graphical abstract <p></p>