Phosphorous-based epoxy resin composition as an effective anticorrosive coating for steel

Abstract

Epoxy resin (ER) is an attractive material for metal protection against corrosion; it can form a strongly adhered film onto a metal surface through its multi coordination sites. In this study, an epoxy resin-based formulation was designed, prepared, and applied onto steel surface with and without a pigment. The anticorrosive formulation (ER–MDA–ZP) was prepared from the ER and the hardener 4,4′-methylene dianiline (MDA) in the presence of the anticorrosive pigment zinc phosphate (ZP). A second standard formulation (ER–MDA) was prepared without ZP. The epoxy and the hardener react to form a 3D cross-linked polymeric network with multicoordination sites (hydroxyl and amino groups) for metals. The characterization of the epoxy resin was performed using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H and 31P NMR). Both samples exhibited excellent thermal properties as they subjected to thermal analysis using differential scanning calorimetry. The ER–MDA–ZP formulation showed a higher glass transition temperature (Tg) than ER–MDA. The coated steel specimens were immersed for 1 h in a 3 wt% NaCl solution and their anticorrosive properties were monitored by electrochemical impedance spectroscopy (EIS). The total resistance (Rt) values obtained by the EIS method for the ER–MDA and ER–MDA–ZP formulations were 21,383 Ω cm2 and 55,143 Ω cm2, respectively. The coated steel samples after the acid treatment were subjected to aging by exposing them to a UV light for 2000 h. The aging caused the Rt values to drop to 1621 Ω cm2 and 7264 Ω cm2, respectively. The results indicate the formation of a highly stable film of ER–MDA–ZP formulation on the steel surface that withstands an accelerated corrosive environment of 2000 h exposure to UV light and 1 h of immersion in a 3 wt% NaCl.