Anticorrosive waterborne epoxy (EP)coatings based on sodium tripolyphosphate-pillared layered double hydroxides (STPP-LDHs)

Waterborne epoxy (EP)coatings were modified by incorporating sodium tripolyphosphate pillared layered double hydroxides (STPP-LDHs)to improve their anticorrosion ability for steel structures. The structural and morphological properties of STPP-LDHs in reference to LDHs were studied comprehensively using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA)and scanning electron microscopy (SEM), showing the successful intercalation of tripolyphosphate ions within the interlayers of LDHs. The corrosion resistance of the EP surface coatings on the mild carbon steel was assessed by the electrochemical impedance spectroscopy (EIS)and salt spray test, showing the improved anticorrosion performance of the STPP-LDHs modified EP coatings compared to neat EP and LDHs modified EP coating. The results obtained under the controlled corrosive environment (with NaCl solutions)showed that the specimen coated with EP containing 1.0 wt.% STPP-LDHs exhibited the optimum anticorrosion performance among other specimens studied. In addition, STPP-LDHs(1.0%)-EP showed the highest impedance value of EP composite coating of 6.019 × 10⁸ Ω∙cm², surpassing the state-of-the-art composite EP coatings.