Corrosion protection of benzoxazine and cardanol-doped polyaniline coatings

In this work a corrosion protection material formed by commercial benzoxazine and polyaniline (PAni) for coatings applications was developed. PAni doped with a natural phenolic compound, cardanol, was used in the coating preparation, and conventional hydrochloric acid-doped PAni was also used for comparative purposes. Cardanol is a reddish-brown liquid obtained from the by-product of cashew nut processing. The presence of the aliphatic group and the hydroxyl of the cardanol, as well as the amine groups of the PAni, can enhance the corrosion barrier of a benzoxazine coatings. The anticorrosive properties of the coatings were evaluated by electrochemical impedance spectroscopy in 3.5% NaCl solution for a total period of 168 h. The coatings of benzoxazine filled with PAni showed better anticorrosion performance and adhesion strength on carbon steel substrate when compared to pristine benzoxazine and PAni doped with 3 wt% cardanol exhibits the best performances. This last result can be explained by both the presence of PAni and the better PAni dispersion within benzoxazine when doped with cardanol. In addition, the incorporation of cardanol-doped PAni in the benzoxazine reduced the cure temperature of the benzoxazine.