Applicability and Medium-Resistance Performance of Hydrogenated Nitrile Butadiene Rubber with Varying Nitrile Levels Composites with Carbon Black in Supercritical CO2

Abstract The structural deterioration and performance instability of hydrogenated nitrile butadiene rubber (HNBR) under supercritical CO2 (scCO2) conditions remain major challenges for carbon capture, utilization, and storage (CCUS) applications, despite its widespread use as a sealing material in CO2 injection wells. This study methodically examined the effects of hydrogenation degree and acrylonitrile (ACN) content on the structural development and service performance of commercial HNBR. The results demonstrate that the combined effects of ACN content and hydrogenation degree dictate the scCO2 resistance of HNBR. By increasing residual unsaturation, lower hydrogenation degrees enhance the efficacy of peroxide cross-linking, improving structural stability and compression set resistance. Conversely, higher ACN concentrations increase polymer polarity and stiffness while worsening chain scission and mechanical degradation induced by scCO2. By strengthening the cross-linked network and limiting CO2 transport, the addition of N550 carbon black greatly improves thermal stability and inhibits scCO2-induced deterioration. With outstanding mechanical property retention and dimensional stability, the 2020/N550 composite exhibits the greatest balanced performance with a moderate ACN content (∼36%) and a low hydrogenation degree (∼91%). These results provide practical recommendations and mechanistic insights for the logical design of HNBR sealing materials in scCO2-rich downhole environments.