A novel superior corrosion resistance and spot-weldable polyimide-polyaniline composite coating for low alloy mild steel

Abstract

In this work, we synthesized conducting polyaniline emeraldine salt (PANI-ES), which was subsequently used for the in-situ synthesis of a semiconducting, spot-weldable polyamic acid–PANI-ES (PAA–PANI-ES) composite coating. The PAA–PANI-ES coating was applied to mild steel using an automatic bar coater, which, upon drying, formed a uniform polyimide–PANI-ES (PI–PANI-ES) coating with a thickness of approximately 10 ± 2 μm. The PI–PANI-ES-coated steel substrates were spot-weldable, whereas substrates coated with pure PI were not spot-weldable, due to its insulating nature. We achieved superior corrosion resistance on mild steel substrates (>500 h, 5 % red rust) using the PI–PANI-ES coating, compared to ∼120 h (5 % red rust) for the pure PI coating. Both pure PI and PI–PANI-ES coating systems exhibited excellent adhesion to the mild steel substrate and successfully passed the required forming tests. Additionally, both types of coatings showed strong adhesion to polyester-based powder paint. The incorporation of conducting PANI-ES powder into the PI matrix enhanced the corrosion resistance and AC conductivity of the coating system. Owing to its excellent corrosion resistance, flexibility/stretchability, spot-weldability, and post-paintability, this coating can be used in a wide range of ready-to-paint applications, including appliances and general engineering industries.