Compatibilization of EPDM/NBR Blends Using 1-Naphthol: Rheological, Morphological, and Sealing Performance Analysis

The development of high-performance rubber sealants requires elastomer blends with high strength, elasticity, and long-term chemical stability. In this study, ethylene–propylene–diene monomer (EPDM) and nitrile butadiene rubber (NBR) were compounded at a fixed 60/40 ratio. Standard additives such as carbon black (N330), zinc oxide (ZnO), stearic acid, and a sulfur-based curing system were incorporated. 1-Naphthol was introduced as a reactive compatibilizer in amounts of 0, 2, 4, 8, and 10 phr to improve interfacial adhesion between the non-polar EPDM and the polar NBR phases. Rheological analysis demonstrated that moderate concentrations of 1-naphthol (2–4 phr) increased the maximum torque (MH), complex viscosity, and elastic modulus, indicating enhanced crosslink density and stronger interphase interactions. Higher concentrations (≥8 phr) led to partial network disruption and phase separation. The blend containing 4 phr 1-naphthol exhibited the best mechanical performance, with a tensile strength of 14.6 MPa, elongation at break of 280%, and compression set of 22%. SEM micrographs confirmed the formation of a uniform and finely dispersed morphology at 2–4 phr, while excessive compatibilizer loading resulted in coarser domains. These improvements are attributed to hydrogen bonding and π–π stacking interactions between 1-naphthol and the polymer chains, which enhance interfacial compatibility and overall cohesion. Therefore, the optimum compatibilizer concentration for EPDM/NBR sealing materials lies within 2–4 phr, offering enhanced rheological, mechanical, and sealing performance suitable for automotive, oil and gas, and construction applications.