Castor oil‐based polyurethane coatings reinforced with biomass‐derived activated carbon: Experimental and <scp>DFT</scp> insights

Abstract The environmental concerns associated with petroleum‐derived polyurethanes necessitate the development of sustainable coating materials. In this study, a bio‐based polyurethane (CPU) coating was synthesized using castor oil as the polyol reinforced with Bhimal fiber‐derived activated carbon (BFAC) at 1, 2, and 5 wt.% loadings. Structural and thermal characterization (FTIR, XRD, TGA, and DSC) confirmed successful urethane formation, enhanced structural order, and improved thermal stability upon BFAC incorporation. Density functional theory calculations, including geometry optimization, intrinsic reaction coordinate analysis, and Gibbs free energy profiling, demonstrated the thermodynamic feasibility of urethane bond formation with an activation barrier of 36.1 kcal/mol, supported by simulated FTIR and HOMO–LUMO analysis. Electrochemical impedance spectroscopy and Tafel polarization revealed markedly improved corrosion resistance, with the 5 wt.% BFAC‐CPU coating exhibiting the highest charge transfer resistance and lowest corrosion current density in 3.5 wt.% NaCl. These results highlight BFAC‐reinforced CPU as an effective, environmentally benign corrosion‐protective coating.