Influence of Fluorine Content and Carbon Black Loadings on Fluoroelastomers for CO₂ Pipeline Transport

Fluoroelastomers (FKMs) are widely used in oilfield seals due to their chemical resistance and thermal stability, yet their performance under liquid carbon dioxide (LCO2) conditions remains insufficiently understood. This study investigates the performance of two FKMs, a copolymer (FKM1) and a terpolymer (FKM2), each formulated with carbon black (CB) loadings of 0, 25, and 37.5 wt %, under exposure to liquid CO₂ at 23 ± 2 °C and 58 ± 2 bar, which are representative of typical CO₂ pipeline transport conditions. The compounds were characterized through in-situ swelling measurements and, before and after exposure, using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile testing, and compression set (CS). Morphological evaluation was conducted using scanning electron microscopy (SEM) on cryogenically fractured samples. The results show that FKM2, which contains higher fluorine content and estimated cross-linking density, exhibits lower swelling during and after decompression, improved dimensional recovery, and more stable mechanical performance following CO₂ exposure compared to FKM1. The addition of CB reduces CO₂-induced rapid gas decompression (RGD) effects and increases tensile strength and stiffness, while reducing elastic recovery at higher filler loadings. Wide-angle X-ray scattering (WAXS) shows negligible changes in polymer structure following exposure to LCO2 in both FKM types. Overall, this study highlights that factors such as cross-link density, fluorine content, and carbon black loading are important when selecting fluorinated elastomers for CO₂ transport applications.