Highly protective performance of water-based epoxy coating loaded with self-doped nanopolyaniline synthesized under supercritical CO2 condition

•Synthesized flake SPAni using Sc-CO2 was used to prepare water-based epoxy coating.•SPAni particle size in hardener and film were in range of 2–4 and 60nm, respectively.•Stable thin oxide layer was formed on metal surface by exposing to corrosive media.•SPAni increases significantly the epoxy coating performance in corrosive media. In this study corrosion properties of water-based epoxy coating on carbon steel (CS) are improved by adding self-doped nano-polyaniline (SPAni) synthesized under supercritical carbon dioxide (ScCO2) condition. The modified ScCO2-synthesized SPAni using water-based polyamidoamine hardener results in formation of the water-based SPAni composite (Sc-WB). To obtain the water-based polyaniline epoxy coating (SP-WBE), the Sc-WB was mixed with epoxy resin in stoichiometric ratio. Applying SP-WBE on CS substrate resulted in high improvement in corrosion properties compared to the similar coating without SPAni. Formation of oxide layers and adhesion properties of SP-WBE at corrosive medium were evaluated using scanning electron microscope (SEM). The transmission electron microscope (TEM) was used to observe the distribution and particles size of nanopolyaniline in the final dried film. The anti-corrosion performance of water-based epoxy coating (blank sample) and SP-WBE coating on CS substrates were studied using salt spray standard test according to ASTM B-117, electrochemical impedance spectroscopy (EIS) and adhesion tests. EIS studies, after 1800hrs of exposure to corrosive solutions, result in charge transfer resistance of 1.816E9Ω and 8.64E7Ω for SP-WBE and blank samples, respectively.