Salicylaldehyde azine-functionalized polybenzoxazine: Synthesis, characterization, and its nanocomposites as coatings for inhibiting the mild steel corrosion

Abstract

In this work, we have successfully designed a new simple salicylaldehyde azine-functionalized benzoxazine (Azine-BZ−CH3) monomer via Mannich condensation reaction of 1,2-bis(2,4-dihydroxybenzylidene)hydrazine and paraformaldehyde with p-toluidine. FT-IR and NMR spectroscopy were carried to confirm the chemical structure of Azine-BZ−CH3. Based on DSC analyses, our BZ monomer showed the lowest maximum exothermic peak (237 °C) compared with 3-phenyl-3,4-dihydro-2H-benzooxazine monomer (263 °C), which ascribed to the basic characteristics of phenolic groups (OH) and the presence of the azine group in the benzoxazine monomer. Furthermore, the anticorrosion behavior of mild steel electrodes coated by Azine-BZ−CH3, poly(Azine-BZ−CH3), poly(Azine-BZ−CH3)/nanoclay and poly(Azine-BZ−CH3)/ E-SBO (epoxidized soybean) and E-bpc (epoxy resin of bisphenol-C) exposed to 1.0 M H2SO4 aqueous solution is studied by the potentiodynamic polarization. The results show decrease in both anodic and cathodic slopes of Tafel plots of the used inhibitors than a mild steel bar exposed to acidic media to indicate that these inhibitors act as mixed type inhibitors. Moreover, these inhibitors can be used as hybrid inhibitors where the anode and cathode slope of their Tafel curves used were lower than those of mild steel exposed to acidic media. In addition, the mild steel coated by epoxy E-SBO with poly(Azine-BZ−CH3)/nanoclay has more efficient corrosion protection (99.63%) than other used inhibitors. SEM images also confirmed that the protective layer of that inhibitor on the mild steel surface retards the corrosion when the electrodes are exposed to acidic media.