Interfacial Curing Kinetics and Compatibilization Behavior of NR/HNBR/ENR Blends: Morphology, Viscoelasticity, and Network Structure

The development of high-performance elastomers that reconcile the conflicting requirements of cryogenic flexibility, oil resistance, and dynamic durability remains a formidable challenge. Here, we investigate interfacial compatibilization and vulcanization kinetics in natural rubber/hydrogenated nitrile butadiene rubber (NR/HNBR) blends using epoxidized natural rubber (ENR) as a compatibilizer. We demonstrate that the vulcanization kinetics and properties of these immiscible constituents are governed not only by thermodynamic compatibility but, more critically, by the kinetically driven migration of curatives (sulfur and accelerators) across the phase boundaries. Atomic force microscopy (AFM) and dynamic mechanical analysis (DMA) show that ENR refines the phase morphology and improves interfacial compatibility. Upon incorporating 8 phr ENR into an NR/HNBR (80/20) blend, the interfacial roughness (Rq) decreases from 379 to 282 nm, accompanied by a reduction in ΔTg from ∼49 °C to ∼42 °C. Rheological and kinetic analyses reveal a synergistic acceleration in binary NR/HNBR compounds, which is consistent with kinetically heterogeneous curing associated with curative redistribution during the early stages of vulcanization. In addition, ENR is inferred to influence curative partitioning at the NR/HNBR interphase and to attenuate kinetic heterogeneity, as suggested by the evolution of the Kamal-Sourour cure-rate profile from bimodal toward quasi-single-peak behavior.