Characterization and corrosion protection properties of epoxy powder coatings containing nanoclays

Two types of nanoclays, montmorillonite nanoflakes and halloysite nanotubes, at various concentrations were tested as nanofillers in epoxy powder coatings applied on an aluminum foil and a steel panel. The produced coatings were separated from the aluminum foil, enabling determination of peel strength, and mechanical properties and water permeability were determined for the obtained free films. Coated steel panels were characterized in terms of microstructure and corrosion protection properties in 0.5 M NaCI solution. The results showed that nanoclays may be used to improve both mechanical and corrosion protection properties of the epoxy coating. Addition of flake-like montmorillonite nanoparticles introduced a homogeneous coating structure, with the nanoparticles being fully embedded in the epoxy matrix, and improved the moduli values and water barrier properties of the epoxy coating at all studied amounts, evidently due to a favorable aspect ratio and orientation of the nanoparticles. Dispersion of montmorillonite nanoparticles in the epoxy matrix and the resulting interfacial strength were the best at the lowest nanoparticle amounts, 0.5 and 1.0 wt.%, giving slightly improved tensile strength, ductility and corrosion protection properties. As far as electrochemical behavior is concerned, particularly dielectric constant of the epoxy coating was decreased by montmorillonite additions. Halloysite nanotube additions in the epoxy matrix yielded coatings where the nanotubes were relatively randomly oriented and which introduced occasionally even greater improvement in mechanical properties, particularly elongation at break, than montmorillonite additions, due to good dispersion. However, the barrier and corrosion protection properties were clearly compromised, probably as a result of less favorable aspect ratio and relatively random orientation of the nanotubes. (C) 2013 Elsevier B.V. All rights reserved.