A Comparative Study on <scp>CO</scp> ₂ Permeability in <scp>NBR</scp> and <scp>HNBR</scp> Rubbers: The Effects of Material Properties, Moisture, Pressure, and Thickness

ABSTRACT This study compares the CO 2 permeability of nitrile butadiene rubber (NBR) and hydrogenated nitrile butadiene rubber (HNBR) to support seal material selection for carbon capture, utilization, and storage (CCUS) applications. CO 2 permeability coefficients were measured via the differential pressure method at 1–4 MPa and with sample thicknesses of 3–4 mm, complemented by molecular dynamics simulations. Results reveal that HNBR exhibits significantly higher CO 2 permeability than NBR, attributed to enhanced molecular chain flexibility and greater free volume induced by hydrogenation. For both elastomers, permeability rises with increasing pressure, showing a step increase at 1–2 MPa. Increasing thickness from 3 to 4 mm markedly reduces the permeation rate. Although intrinsic permeability is theoretically thickness‐independent, experimentally determined apparent permeability decreases with rising thickness, indicating non‐ideal Fickian diffusion possibly caused by non‐equilibrium effects and microdefects in thicker specimens. Water immersion further elevates permeability, with a more pronounced effect in HNBR due to swelling and plasticization. These findings demonstrate that HNBR's molecular structure yields higher CO 2 permeability, and pressure, thickness, and moisture are key influencing factors. For CCUS seal design, these parameters must be integrated to ensure long‐term stability and safety, with thickness regarded as an engineering variable for barrier performance optimization rather than an intrinsic material property modifier.