Phosphorylated chitin as a chemically modified polymer for ecofriendly corrosion inhibition of copper in aqueous chloride environment

Heterocyclic organic molecules containing oxygen, nitrogen or sulfur are generally used as inhibitors for corrosion protection of copper. These compounds form protective films by adsorption onto the metal surface. Nevertheless, most such inhibitors are biologically toxic, hence there is a need for development of ecofriendly inhibitors. Chitin is a nontoxic biological polymer that is known to be enzymatically biodegradable. In the present study chitin was chemically modified to phosphorylated chitin (PCT) to make it soluble in aqueous medium and increase its complexing ability with metal ions. The ability of this modified polymer to inhibit corrosion of copper in aqueous NaCl and the nature of the inhibition process were investigated by gravimetric analysis, electrochemical impedance spectroscopy, and polarization measurements. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) analysis were used to examine the surface morphology and analyze the chemical composition of the film formed on the metal surface. Maximum efficiency of 92 % was achieved by addition of 200 ppm PCT as inhibitor to an aqueous corrosive environment containing 200 ppm chloride at 30 +/- 0.1 A degrees C. SEM studies revealed that the smoothness of sample surface was retained on PCT addition to the aggressive medium. EDX and XPS studies on the surface film revealed the presence of PCT. A plausible mechanism for the inhibition by PCT is suggested.