Long-term corrosion protection of mild steel by epoxy coating containing self-doped polyaniline nanofiber

•Self-doped sulfonated polyaniline (SPANI) with well-dispersion was polymerized by aniline and 2-aminobenzenesulfonic acid.•Long-term and environmental friendly SPANI/epoxy composite coating with remarkable anti-corrosion performance was prepared.•The corrosion product of beneath coating was identified by X-ray diffraction pattern and scanning electron microscope. Sulfonated polyaniline (SPANI) with good processability and well-dispersion in common organic solvent was synthesized via the copolymerization of 2-aminobenzenesulfonic acid and aniline and was identified by UV-vis, Raman, X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. SPANI/epoxy composite coatings on the steel substrate were prepared for the anti-corrosive investigations in 3.5wt% NaCl solution via electrochemical impedance spectroscopy and polarization curves. It turned out that composite coatings with SPANI exhibited excellent protective performance with high impedance modulus during the 120days immersion while blank epoxy coating has been invalid after 80days immersion. Finally, the passivation of steel substrate by SPANI containing composite coating was proved by the composition and morphology of the rust products beneath the coatings. It’s concluded that self-doped SPANI enhanced the anti-corrosive property of composite coatings via forming a metal oxide film composed of Fe2O3 and Fe3O4.