Anticorrosive effect of green sulfonated PANI-Zn with epoxy for the corrosion protection of aluminum alloy 6061-T651

Abstract

The synergistic effect of epoxy resin and PANI-metal composites in anti-corrosion coatings is well known. However, the conventional chemical synthesis of PANI and its composites generates environmentally hazardous waste on an industrial scale. Given this, the study proposes synthesis of PANI-Zn composites by a “green” method to protect the AA6061-T651 alloy against corrosion. For the synthesis, hydrogen peroxide and sulphuric acid were used to promote polymerization and doping. PANI-Zn were characterized by FTIR, UV–Vis, XPS, XRF, ICP-OES and SEM. To prepare the coatings, 10 mg of composites were dissolved in 500 μL of ethanol/NMP solution (1:1) and mixed with 500 mg of epoxy resin and 250 mg of hardener. These were applied to AA6061-T651 alloys by the drop-casting method and allowed to stand at room temperature for 7 days, followed by heating at 70 °C for 1 h. After curing, the coatings were subjected to morphological (SEM and AFM), adhesion tests and electrochemical (EIS and linear polarization) characterizations. FTIR and UV–Vis spectra confirmed the structure of PANI in the materials. They also show that the composites are sulfonated and partially oxidized. XPS analysis demonstrated that the composites are in the protoemeraldine state (0 < y < 1; y ≠ 0.5) and that the presence of Zn in the synthesis influences the oxidation and doping state of the PANI. Furthermore, the XPS spectrum showed a weak ZnO signal only in PZn4, probably due to the amount of Zn used in the synthesis. However, XRF and ICP-OES confirmed the presence and content of zinc oxide in samples. Indeed, the anticorrosion performance of the composites varied according to their composition. The E-PZn2 (Epoxy-PANI-2 % Zn) was the best-performing coated electrode due to the morphology and distribution of the composites in the epoxy resin as well as good adhesion. This resulted in a better barrier effect against the penetration of corrosive ions, as well as providing anodic and cathodic protection by PANI, hydrogen sulfate ions, and ZnO.