Mechanical and corrosion protection properties of polymer–clay nanocomposite coatings for mild steel in marine environment

Abstract

Polymer–clay nanocomposites (PCNs) are potentially interesting as anti-corrosion surface pretreatment layers because of their outstanding barrier characteristics. Corrosion behavior of steel coated with epoxy–indole-modified clay nanocomposite films was studied. The electrochemical behavior of films containing polymer–clay nanocomposites was analyzed by potentiodynamic polarization techniques, electrochemical impedance spectroscopy (EIS), and scanning electrochemical microscopy (SECM) measurements in 3.5% NaCl solution. Microstructural characterization and surface analysis of substrates and coatings were performed by FE-SEM/EDX techniques. Results from electrochemical measurements reveal good long-term corrosion protection of steel provided by polymer–indole-modified clay coating. This polymer–clay coating yields a highly ordered multilayered brick and mortar structure, where polymer provides a physical barrier for the diffusion of corrosive agents/corrosion products within the coating. The results of the study show that the incorporation of nanoclay has a significant effect on the mechanical behavior of composites. Mechanical properties of the coatings were found to be improved in the presence of modified nanoparticle. The adhesion strength was found to have increased (8.10 MPa) up to 2 wt.% and decreased in its value to 7.56 MPa for 3 wt.% of nanoclay reinforcement, which made the composite to become more brittle. The optimum loading of clay in the epoxy–fclay composites was attained at 2 wt.%, where the improvement in hardness and properties was seen.