Novel healing coatings based on natural-derived polyurethane modified with tannins for corrosion protection of AA2024-T3

Polyurethane coatings derived from crambe and castor oil formulated with different proportions of additives were modified with tannin and applied on AA2024-T3 coupons. The coatings were characterized by water uptake and attenuated total reflectance Fourier transform infrared spectroscopy (FTIR-ATR). The thickness of the coatings was determined by scanning electron microscopy (SEM) and adhesion was evaluated by the ASTM D3359 standard. The barrier properties and corrosion protection ability were assessed by open circuit potential (Eocp) and electrochemical impedance spectroscopy (EIS). The self-healing ability of the coatings was studied by localized impedance spectroscopy (LEIS) and by the scanning vibrating electrode technique coupled with the scanning ion -selective electrode technique (SVET/SIET). The measurements demonstrate that tannin-modified coatings provide effective corrosion protection due to polymer healing and the results give important highlights concerning the mechanism of corrosion inhibition.