Polypyrrole nanocapsules bearing quaternized alkyl pyridine in a green self-healing coating for corrosion protection of zinc

Abstract

The corrosion rate of coated zinc in a 3.5 wt. % NaCl electrolyte solution was studied. Epoxy resin coatings loaded with polypyrrole/dodecyl benzene sulfonate/quaternized alkyl pyridine and polypyrrole/dodecyl benzene sulfonate nanocapsules were compared to a non-loaded resin coating. Nanocapsule-loaded coatings exhibited improved self-healing corrosion inhibitory properties. Nanocapsules were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). Atomic force microscopy (AFM), FESEM and EDX maps analysis confirmed the uniform dispersion of polymer nanocapsules in epoxy resin coatings. Self-healing properties were characterized by swelling ratio, electrochemical impedance spectroscopy, tafel polarization, open circuit potential (OCP), FESEM, and optical microscopic imaging. The results over a 50-day time interval confirmed the stable self-healing behavior with the corrosion protection of 99.87 % in the scratched coating, containing polypyrrole/dodecyl benzene sulfonate/quaternized alkyl pyridine nanocapsule. The controlled release of quaternized alkyl pyridine was monitored by fluorescence emission spectroscopy and fluorescence microscopic imaging. A potentially synergistic effect in corrosion protection and self-healing is expected to have happened by polypyrrole inhibitory properties, the formation of Zn(DBS)2 complex, and the physical adsorption of quaternized alkyl pyridine on the metal surface.