Water-based & eco-friendly & high-efficiency 3,4,5-Trihydroxybenzoic acid ester as a novel rust conversion agent and its polymer composites for enhanced surface anticorrosion

Abstract A novel water-based rust conversion agent (abbreviated as “TE-GAE”) was firstly synthesized using gallic acid (3,4,5-Trihydroxybenzoic acid, abbreviated as “GA”) and triethanolamine (abbreviated as “TE”) by esterification reaction. A new type of rust conversion coating (abbreviated as “TE-GAE coating”) containing the TE-GAE and additives was also prepared. The structural feature of rust conversion agent TE-GAE was characterized using Fourier transform infrared spectrum (FT-IR). The effect of the synthetic water-based TE-GAE coating on original rust layer were investigated by X-ray diffractometer (XRD) and Scanning electron microscope (SEM). Compared with traditional rust conversion coatings that apply tannic acid and phosphoric acid as rust converters, the as-synthesized integrated TE-GAE coating firstly revolutionized the application method of the anti-corrosion coatings, combined the traditional “primer” and “topcoat” into one, and improved engineering efficiency while ensuring protective effect. Additionally, the adhesion test indicated that the integrated TE-GAE coating presented remarkably strong film adhesion between the coating and steel substrate. Meanwhile, the neutral salt spray test and weather-resistant test showed significant corrosion resistance. Furthermore, a corrosion resistance mechanism including the combined effect of the rust conversion, barrier and corrosion inhibition for the integrated TE-GAE coating was tentatively proposed, which indicating that the rust converter chelates with Fe2+/Fe3+ to form a dense chelating film, extend the penetration path of corrosive medium and delay the occurrence of corrosion process. Thus, such a “green” and “efficient” integrated rust conversion coating is promising for protecting steel from corrosion, which is critical for the sustainable development of functional coating materials.