Synergistic Enhancement for Hydrogenated Nitrile Rubber Resistance to Supercritical <scp> CO ₂ </scp> Refrigerant via Modified Carbon Black and Flake Fillers

ABSTRACT Supercritical CO 2 is a preferred refrigerant due to its low global warming potential (GWP = 1), high latent heat of vaporization and excellent thermodynamic efficiency. However, its application poses severe challenges to the high‐temperature/high‐pressure resistance and cycling stability of rubber sealing materials. Herein, the effects of modified carbon black (CB) plus glass flake (GF) and graphene (GE) on the resistance to thermal aging and supercritical CO 2 of hydrogenated nitrile rubber (HNBR) were studied. Modified CB combined with GF/GE significantly enhanced HNBR's resistance to aging in supercritical CO 2 , with an optimal 10 phr GF/10 phr GE formulation achieving peak performance. After 72 h of thermal aging at 180°C, the tensile strength retention was measured at 89.6% (20.7 MPa), while after 72 h of immersion in supercritical CO 2 at 165°C and 17 MPa, the tensile strength retention was recorded at 77.5% (17.9 MPa). Furthermore, the residual strength after additional cyclic aging remained at 10.2 MPa. Microscopic morphology confirms that there are no small voids on the modified HNBR surface caused by the escape of CO 2 . These findings enable HNBR's reliable sealing in supercritical CO 2 refrigeration and accelerate its industrial‐scale adoption as a refrigerant.