Explore the Applicability of Nitrile Butadiene Rubber With Different Cyanide Content in Supercritical <scp> CO ₂ </scp> Environment

ABSTRACT To address premature failure of packer rubber seals in supercritical CO 2 injection wells, this study systematically investigated the effect of acrylonitrile (ACN) content (18%–40%) on the CO 2 resistance of nitrile rubber (NBR). Two material systems were evaluated: unfilled NBR and NBR/carbon black N550 (N550) composites with 50 phr carbon black. Performance under CO 2 conditions (100°C, 10 MPa, 72 h) was assessed through compression set, mass and volume changes, mechanical and tribological properties, and microstructural analysis, elucidating ACN‐dependent structure–property relationships. For unfilled NBR, DN3350 with moderate ACN exhibited balanced tensile strength (1.9 MPa) and elongation (160%), achieving the lowest compression set (46.0%). In NBR/N550 composites, high‐polarity DN4050/N550 (40% ACN) formed a dense filler–matrix network, enhancing anti‐swelling behavior (volume change rate: 0.734%), maintaining superior mechanical performance (tensile strength: 23.6 MPa; elongation: 198%) and low coefficient of friction (0.72). FTIR and microscopic analyses confirmed that higher ACN strengthens intermolecular forces and filler compatibility, suppressing CO 2 ‐induced microcracking and degradation. These findings provide a theoretical foundation for designing high‐performance packer seals, highlighting DN4050/N550 as the optimal material for supercritical CO 2 environments.