Facile Formulation of New Innovative Eco-Friendly Hybrid Protective Coating for Mild Steel in Acidic Media

This research deals with the formulation, characterization, and evaluation of new anticorrosive protective coatings. The study objective is to protect mild carbon steel in acidic media by adherent nonporous polymeric coatings formulated from polystyrene and shrimp shells. Solid wastes of shrimp shells are dried into a fine powder and sonicated in toluene. The obtained suspension is refluxed with polystyrene. The hot-melt coatings are applied to the metal surface by the hot dipping technique. The shrimp shells improve the performance of polystyrene. These eco-friendly, low-cost anticorrosive coatings are formulated from solid waste (SW) of shrimp shells and polystyrene (PS) with no aiding additives. Intense vibrational bands in the infrared spectra and the high thermal stability of the coating samples confirm the compatibility of the coating constituents. The results of the evaluation of coating performance by electrochemical impedance spectroscopy and potentiodynamic polarization techniques show that the coating is protective for mild steel in the aggressive acidic media of 1.0 M HCl. The coating protects the metal surface without affecting the corrosion mechanism. Polarization curves show that the coating film retards both the anodic metal dissolution reaction and the cathodic hydrogen evolution reaction, acting as mixed-type inhibitors. The percent protection (%P) increases with the increasing weight percent (wt.%) of PS and the SW of shrimp shells. A %P up to 99% is achieved for the coating composition of 2.0 g/L PS + 0.02 g/L SW. The %P obtained by impedance and polarization measurements are in good agreement. The prepared multi-functional polymeric coating forms an adherent nonporous coating film on the metal surface. Impedance plots show that the coating samples are insulating dielectric coatings that electrically insulate the metal surface from the aggressive acidic media. The coating protects the metal surface by the adsorption mechanism. Shrimp shells fill the pores and increase the stiffness of the polymeric coating film of polystyrene. The obtained results in this study will be useful for all industrial sectors and academic research in the field of corrosion control of metals and alloys.