Characterization and anti-corrosion performance of eco-friendly mimosa tannin-waterborne epoxy paints

Purpose This study aims to investigate the corrosion inhibition efficacy of eco-friendly mimosa tannin on AA1050 aluminum substrates and evaluate its performance as a sustainable, nontoxic active pigment in waterborne epoxy paints. The research seeks a green alternative to traditional hazardous anticorrosive pigments. Design/methodology/approach The investigation was conducted in two sequential phases. In the first phase, the inhibition efficiency of mimosa tannin (0.5% w/v) was evaluated in 0.1 M NaCl solution using linear polarization resistance and potentiodynamic polarization, benchmarking its performance against a commercial anticorrosive pigment (modified zinc phosphate). In the second phase, the study transitioned to waterborne epoxy coatings. Two distinct formulations were evaluated: MIM1, where the tannin was incorporated as a solid pigment, and MIM2, where the tannin functioned as an aqueous-phase predissolved additive. The protective performance of these systems was compared against a commercial phosphate-pigmented epoxy control through electrochemical impedance spectroscopy and 150-day accelerated aging protocols in both humidity and salt spray chambers. Findings Electrochemical tests in 0.1 M NaCl solution confirmed mimosa tannin as a highly efficient mixed-type inhibitor (89% efficiency), significantly outperforming the commercial phosphate (73%). When integrated into coatings, the tannin incorporation method proved to be a decisive factor for performance. The MIM2 formulation, featuring the tannin predissolved in the aqueous phase, exhibited superior long-term barrier properties and robust substrate protection. In contrast, the epoxy paint containing commercial phosphate underwent significant degradation, characterized by widespread blistering and loss of adhesion after 150 days of salt spray exposure. Originality/value This research validates mimosa tannin as a high-performance, sustainable “green” inhibitor for waterborne coatings, demonstrating that its efficacy is highly dependent on the incorporation strategy. By using an aqueous-phase predissolution method, this study establishes a viable and superior pathway for replacing traditional anticorrosive pigments. These findings provide a scalable solution for the advanced protection of aluminum alloys, aligning industrial performance with environmental sustainability.