The effect of polymer morphology on the performance of a corrosion inhibiting polypyrrole/aluminum flake composite pigment

Two different morphologies of polypyrrole (PPy) aluminum flake composites, namely spherical PPy/Al flake composites and wire PPy/Al flake composites, were synthesized by chemical oxidative polymerization. These composites were characterized by Fourier transform infrared spectroscopy (FT-IR), four point probe conductivity, conductive atomic force microscopy (C-AFM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). These composites were incorporated into an epoxy primer and coatings were applied on an aluminum alloy (AA 2024-T3) substrate. The coatings were exposed to salt spray according to ASTM B117 and prohesion conditions according to ASTM G85-A5. The corrosion resistance properties were monitored via electrochemical impedance spectroscopy (EIS). The current produced by corrosion reactions on the surface of the substrate was mapped using the scanning vibrating electrode technique (SVET). Galvanic coupling experiments were performed for measurement of galvanic current and mixed potential in controlled environment. It was observed that the morphology of PPy on the surface of aluminum flake has an effect on the conductivity and anticorrosion performance of the pigment. The wire PPy/Al flake composite coatings exhibited better anticorrosion performance than the spherical PPy/Al flake composite coatings and as received aluminum flake coatings. The enhancement in anticorrosion performance was attributed to the unique morphology and electrochemical activity of the PPy on the surface of aluminum flakes. It was also revealed that the wire PPy/Al flake composite coating was sacrificially protecting the AA 2024-T3 substrate in larger defects.