Modification of hydrogenated nitrile rubber with N,N′‐bismaleimide‐4,4′‐diphenylmethane to improve its resistance to heat aging and reduce its compression set

Abstract This paper delves to improve the upper‐limit temperature of hydrogenated nitrile rubber (HNBR) through regulation of the vulcanization process, filler system and cross‐linking additive. The tensile test and scanning electron microscope images showed that the aging at 180°C significantly accelerated the deterioration in the property of HNBR compared with 150°C aging. The results showed that a higher dosage of bis(1‐(tert‐butylperoxy)‐1‐methylethyl)‐benzene curing agent reduced the compression set of HNBR without sacrificing its tensile strength. Carbon black N539‐filled HNBR exhibited high tensile strength, while carbon black N774‐filled HNBR showed high heat resistance and low compression set. When the HNBR sample was reinforced with 20 phr of N539 and 20 phr of N774 carbon black, it achieved low compression set, high tensile strength, and heat resistance simultaneously. Then, N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) was introduced into the HNBR composite as a cross‐linking assistant agent. The residual strength of BMI‐modified HNBR was 20.3 MPa (the retention rate of 92.3%), and its compression set was as low as 19.2% after aging at 180°C for 72 h. Even after aging the composite at 180°C for 168 h, its strength retention rate remained at 83.2% (18.3 MPa). The approach provided here increased the upper‐limit temperature range of HNBR to 180°C.