Vegetable tannins are natural, non-toxic, water-soluble polyphenols present in the roots, branches, leaves, flowers, fruits, and seeds of various trees. Tannins can remove rust and inhibit corrosion. Because the high solubility of tannins in water may impair their use as an anticorrosion pigment, a reduction in solubility is necessary. In this work, two tannin-based anticorrosive pigments were synthetized by the reaction of black wattle tannin with zinc and magnesium salts to form zinc tannate and magnesium tannate, respectively. Pigment synthesis was verified by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). Epoxy coatings containing both tannates were formulated and their corrosion performance was evaluated using electrochemical impedance spectroscopy (EIS) and salt spray tests. Corrosion tests showed that zinc tannate was an excellent anticorrosive pigment in neutral saline media making it an environmentally friendly option for anticorrosive coatings.
Volume 121, August 2018, Pages 23–29