Effects of nanoparticulate silver on the corrosion protection performance of polyurethane coatings on mild steel in sodium chloride solution

•Nanosilver was introduced in different types of polyurethane coatings.•Corrosion protection properties of the coatings on mild steel were studied by EIS.•Nanosilver in waterborne coating resulted in corrosion protection reduction.•Nanosilver in high solid coating had no significant effect on coating resistance.•Dual behavior of nanosilver in the coatings was examined by SEM and IR spectroscopy. Waterborne polyurethane (WPU) and high solid polyurethane (HPU) coatings containing nanoparticulate silver were coated on mild steel and compared to the corresponding coatings without nanoparticulate silver in NaCl solution using electrochemical impedance spectroscopy (EIS). The EIS results showed WPU coating degradation in the presence of nanoparticulate silver, while inclusion of nanoparticulate silver in HPU coating revealed no significant effect on the coating resistance. The WPU and HPU coatings morphology was investigated by SEM cross-section, which showed loss of WPU coating integrity in the presence of nanoparticulate silver, while no significant effect was observed for the HPU coating. The dual behavior of nanoparticulate silver in WPU and HPU coatings was connected to their different chemical structures confirmed by FTIR spectroscopy.