Highly dispersed polypyrrole nanotubes enhance the corrosion resistance of polyurethane coatings

Corrosion is a major challenge across various industries, leading to significant economic losses and safety hazards. This study synthesized polypyrrole nanotubes (PPy-NTs) using methyl orange (MO) as a template and polyvinylpyrrolidone (PVP) as a dispersant. The PPy-NTs exhibited excellent dispersion stability (zeta potential of 34 mV) and high electrical conductivity (28.5 S/cm). Waterborne polyurethane (WPU)-based coatings with varying PPy-NT concentrations (0 %, 0.5 %, 1.0 %, and 2.0 %) were evaluated for corrosion resistance in a 3.5 wt% NaCl solution over immersion periods of 1, 7, 14, and 28 days. Electrochemical impedance spectroscopy (EIS) showed that the 1.0 % PPy-NT coating provided the best corrosion protection, with an initial impedance about 30 times higher than the pure WPU coating. After 28 days, its impedance remained over 200 times higher than that of the pure WPU coating. Polarization tests confirmed the 1.0 % PPy-NT coating had improved corrosion resistance, with a lower corrosion current density (49.4 nA/cm²) and higher corrosion potential (-0.13 V) compared to the pure WPU coating (636 nA/cm², −0.58 V). Salt spray testing showed the 1.0 % PPy-NT coating had superior corrosion resistance. These results demonstrate the enhancement of WPU coatings with PPy-NTs, showing potential for long-term corrosion protection.