Corrosion performance of chemically synthesized poly(aniline-co-o-toluidine) copolymer coating on mild steel

A soluble copolymer from aniline and o-toluidine [poly(aniline-co-o-toluidine)] was synthesized by chemical oxidative copolymerization using ammonium persulphate as an oxidant in hydrochloride aqueous medium. The resultant copolymer was characterized by Fourier Transform Infrared (FTIR) spectroscopy and chemically deposited on mild steel specimens using N-methyl-2-pyrrolidone (NMP) as solvent via solution evaporation method. The anticorrosive properties of copolymer coating was investigated in major corrosive environments, such as 0.1 M HCl, 5% NaCl solution, artificial seawater, distilled water and open atmosphere by conducting various corrosion tests which include: immersion test, open circuit potential (OCP) measurements, potentiodynamic polarization measurements and atmospheric exposure test. The corrosion performance of copolymer coating was also compared separately with polyaniline (PANi) and poly(o-toluidine) (POT) homopolymer coatings. The surface morphologies of polymer coatings were evaluated using scanning electron microscopy (SEM). The synthesized copolymer exhibited excellent protection against mild steel corrosion; the protection efficiency being in the range of 78–94% after 30 days of immersion. The corrosion performance of copolymer in 5% NaCl and artificial seawater was comparable, which was only marginally better than in 0.1 M HCl. In general, the performance of copolymer coating was found to be better than that of homopolymer coatings.