Comparative study of epoxy and urethane primers for optimized interfacial adhesion of nitrile–butadiene rubber

Nitrile–butadiene rubber (NBR) is essential in diverse industries due to its oil resistance, yet its low surface reactivity hinders robust bonding with dissimilar materials. This study investigates the synergistic effects of sandblasting and epoxy/urethane-based primers on the interfacial adhesion of NBR. Sandblasting was employed to enhance mechanical interlocking by introducing micro-scale roughness. Surface energy variations were quantitatively analyzed using the Owens–Wendt–Rabel–Kaelble (OWRK) model. Results indicated that while epoxy primers increased the polar component, urethane primers significantly enhanced the dispersive component. In lap shear tests, the urethane-primed specimens exhibited higher average shear strength than the epoxy-primed specimens, consistent with the surface energy analysis results. This improvement is attributed to the high dispersive affinity of the urethane primer, which ensures superior thermodynamic compatibility with the nonpolar NBR backbone. This research demonstrates that aligning primer chemistry with substrate characteristics is vital for optimizing adhesion, and provides practical guidelines for high-performance industrial bonding processes.