Amine cured double Schiff base epoxy as efficient anticorrosive coating materials for protection of mild steel in 3.5% NaCl medium

A double Schiff base epoxy (DSBE) molecule comprising of 1-phenoxybenzene unit, double azomethine functionalities, two benzene moieties and two terminal epoxy groups (i.e., glycidylether) has been successfully synthesized with an aim of serving as an alternative for the commercially available bisphenol based epoxies. The structure of the synthesized molecule has been affirmed by sophisticated analytical instrumentations such as FT-1R, matrix-assisted laser desorption ionization (MALDI) mass spectrometry and H-1-NMR spectroscopy. Diethylenetriamine (DETA), triethylenetetramine (TETA) i.e., aliphatic and p-phenylenediamine (PPD) i.e., aromatic curing agents have been used to cure DSBE. The amine cured DSBE viz., DSBE + DETA, DSBE + TETA and DSBE + PPD have been further analysed by FT-IR spectroscopy and differential scanning calorimetry. The curing mechanism of epoxy with aliphatic and aromatic amine has also been discussed. The thermal stability of DSBE and amine cured DSBE has been confirmed by thermogravimetry analysis (TGA). The solution of stoichiometric quantity of amines and DSBE in tetrahydrofuran has been applied as coating materials on the surfaces of mild steels. In order to establish the corrosion resistance properties of amine cured DSBE coated substrates, the potentiodynamic polarization technique and electrochemical impedance spectroscopy have been performed in 3.5% NaCl medium which transparently exhibited the superior corrosion inhibition efficacy of DSBE + PPD coated surface showing highest polarization resistance and the lowest rate of corrosion than that of DSBE + DETA and DSBE + TETA. Additionally, the morphological and topographical analysis of the coated substrates have been performed by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) to reveal the uniformity as well as soaring smoothness in the surfaces of coating. The hydrophobicity of the developed coating has also been analysed by contact angle measurements. (C) 2019 Published by Elsevier B.V.