Comparative effects of epoxy and acrylonitrile functional groups on the properties of carbon black–filled natural rubber/ether-based urethane rubber blends

This study systematically investigates carbon black–filled natural rubber (NR) and ether-based urethane rubber (UR) blends with emphasis on blend ratio optimization and compatibilizer selection. The work was conducted in two stages: (i) evaluation of NR/UR blend ratios and (ii) assessment of different compatibilizers, including epoxidized natural rubber with 25 and 50 mol% epoxide content (ENR25 and ENR50) and acrylonitrile–butadiene rubber (NBR), at a defined NR/UR ratio of 90/10. Increasing UR content from 0 to 40 phr led to a reduction in tensile strength, accompanied by a 15–35 % decrease in torque difference, reflecting diminished crosslink density and reduced strain-induced crystallization of NR. Incorporation of ENR significantly improved processability, reducing Mooney viscosity by up to ~18 % compared with the uncompatibilized blend. ENR25 provided the most balanced performance, slightly increasing tensile strength, markedly improving tear resistance (~25 %), reducing abrasion loss (~10 %), and maintaining comparable cure characteristics. In contrast, ENR50 caused a dilution effect, leading to inferior mechanical performance, while NBR resulted in prolonged optimum cure time, suggesting limited co-vulcanization. Dynamic mechanical analysis confirmed the superiority of ENR25 through a reduced Payne effect and lower tan δ at 60 ◦C (~7 %), corresponding to improved filler dispersion and reduced rolling resistance. X-ray photoelectron spectroscopy (XPS) analysis further verified enhanced interfacial interactions between NR and UR phases. Overall, the NR/UR (90/10) blend compatibilized with ENR25 is a promising formulation for applications requiring balanced processability, durability, and energy efficiency.