Engineering hybrid crosslink networks in nitrile butadiene rubber via polymeric plasticizer-assisted thermoradiation vulcanization

The effect of a polymeric plasticizer on crosslinking behavior and performance of nitrile butadiene rubber (NBR, SKN-40) was evaluated under thermal, radiation, and thermoradiation vulcanization. Under thermoradiation curing (250 kGy +150°C) at low sulfur content (0.2 phr), the polymeric plasticizer produces a markedly higher effective crosslink density than non-plasticized systems, demonstrating a synergistic interaction between sulfur-mediated and radiation-induced crosslinking. FTIR analysis shows enhanced consumption of butadiene unsaturation (∼965–970 cm −1 ) without alteration of nitrile groups, indicating selective network formation. EPR spectroscopy reveals rapid recombination of radiation-induced macroradicals, with stabilization of weak carbon-centered radicals (g = 2.0031, ΔH = 0.44 mT) within 48 h, confirming suppression of post-irradiation chain scission. As a result, polymeric plasticizer-assisted thermoradiation vulcanizates exhibit the highest intrinsic viscosity (∼3.0 dL g −1 ), tensile stress at 300% elongation (M300) (∼10 MPa), and tear resistance (∼27 MPa). Thermogravimetric analysis demonstrates delayed thermal degradation (T 5 % ≈ 390°C, T 10 % ≈ 420°C) and increased char residue (∼48%), consistent with the formation of a compact hybrid network combining thermally stable carbon–carbon crosslinks with short sulfur bridges.