Improvement of Corrosion Resistance and Solid Content of Zinc Phosphate Pigmented Alkyd Coating by Methacrylated Cardanol

Abstract

Two cardanol (CO) derivatives, methacrylated cardanol (MACO) and triethoxysilane functionalized cardanol (TSCO) were investigated as the reactive diluents for a zinc phosphate pigmented alkyd coating. It was found that 5 wt% of MACO or TSCO can reduce the dosage of xylene by ∼ 3 wt% while maintaining the viscosity of the alkyd coating system. TSCO presented a negative influence on the drying time and the pull-off adhesion strength of the alkyd coating; however, the addition of 15 wt% MACO decreased the drying time from 12 h to 8 h and increased the pull-off adhesion strength from ∼ 1.73 to ∼ 2.10 MPa, comparing with the neat alkyd coating (without MACO and TSCO). As evidenced by the salt spray test, the addition of TSCO did not show an enhancement of corrosion resistance for the alkyd coating; however, the alkyd coating containing 15 wt% MACO (labelled as M-15) presented superior corrosion resistance to other coating systems. M-15 and the neat alkyd coating were further characterized by electrochemical impedance spectroscopy (EIS). The results of EIS further demonstrated that the corrosion resistance of M-15 is much better than the neat alkyd coating in the 3.5 wt% NaCl solution immersion. Importantly, M-15 can provide an excellent protection of the steel in the corrosive immersion condition for at least 123 days. The improvement of the overall performance was attributed to the homo-polymerization of the methacrylate moiety in MACO. Taken these results together, MACO is an efficient chemical for formulating high solid alkyd coatings with outstanding corrosion resistance.