Effect of Poly (aniline-co-o-toluidine) loaded on emulsion paints with different pigments on corrosion inhibition of mild steel

Abstract

Three groups of plastic emulsion paints were formulated using three different types of pigments. TiO2 was applied in the first group of paint (T-series) as a neutral pigment. Zn3(PO4)2 and Fe2O3 were added in the two other paint groups (Z-series and F-series, respectively) as anticorrosive pigments. Styrene/butyl acrylate latex was prepared by semicontinuous seeded emulsion polymerization and used as a binder in the paint formulations. Poly (ani-co-o-toluidine) (PAOT) was introduced to the painting series as an inhibitor in proportions of 0%, 1%, 2%, 3%, and 4%. PAOT inhibitor was prepared by oxidative emulsion polymerization with an equimolar amount of aniline and o-toluidine monomers. The binder and the inhibitor were tested for their particle size and chemical structure by DLS and FTIR analysis. The properties of the paint formulations were estimated physically, mechanically, and thermally. The protection efficiency of the paint coatings on steel was estimated against corrosion using an immersion test and electrochemical measurements. The DLS curves of the binder latex and the inhibitor showed a unimodal distribution of sizes 151 nm and 42 nm, respectively. However, a mix of the two emulsions exhibited a bimodal distribution of both sizes. The potentiodynamic polarization measurements showed a decrease in the corrosion current density of TiO2 coating paint from 26.4×10-7 A/cm2 to 12.3×10-7 A/cm2 in Fe2O3 coating paint. The least corrosion current density was obtained from Zn3(PO4)2 coating paint of 7.50×10-7 A/cm2. PAOT inhibitor enhanced the protection efficiency of the paint coatings with the optimum of 3%. Zn3(PO4)2 coating paint loaded with 3% PAOT inhibitor demonstrated the highest protection efficiency of 99.96%.