Bisbenzylidene cyclopentanone and cyclohexanone-functionalized polybenzoxazine nanocomposites: Synthesis, characterization, and use for corrosion protection on mild steel

Abstract

In this study, we synthesized and investigated bisbenzylidene cyclopentanone and cyclohexanone-functionalized polybenzoxazine nanocomposites as anti-corrosion coatings. The chemical structures of CP-BZ and CH-BZ were confirmed using Fourier transform infrared (FTIR) spectroscopy and 1H and 13C nuclear magnetic resonance spectroscopy. Differential scanning calorimetry (DSC) revealed that the thermal polymerization temperature of the uncured CH-BZ (198 °C) was significantly lower than that of the monomer 3-phenyl-3,4-dihydro-2H-benzoxazine (263 °C). We used DSC and FTIR spectroscopy to study the curing behavior of these monomers. The degradation temperature of poly(CH-BZ) (326 °C) was higher than that poly(CP-BZ) (249 °C), based on thermogravimetric analysis. We used solution dispersion and thermal ring-opening polymerization to prepare a new class of bisbenzylidene-based polybenzoxazine (PBZ; CP-BZ or CH-BZ) composites with epoxidized soybean oil (E-SBO; 10 or 20 wt%) and E-SBO/bentonite (nanoclay; 3 or 5 wt%) for use as corrosion-protection coatings for mild steel (MS). We employed salt-spray and electrochemical measurements to investigate the influence of the epoxy and nanoclay contents, respectively, on the corrosion-resistance of these coatings. A 20 wt% epoxy content in the PBZ/E-SBO coatings provided corrosion-resistance superior to those of pure PBZs. Furthermore, the addition of 20 wt% E-SBO and 3 wt% of nanoclay decreased the corrosion rate by one order of magnitude (2.653 × 10−3 mm year–1) when compared with that of pure poly(CH-BZ) (1.292 × 10-2 mm year–1) and two orders of magnitude when compared with blank(MS) (1.094 × 10-1 mm year–1) with protection efficiency (98.16 %), revealing markedly increased barrier properties of the composite coatings towards corrosive species. Thus, these materials function as excellent corrosion-resistance coatings for MS.