Influence of Soda and Kraft lignin in polyurethane coatings for the corrosion protection of mild steel in 3.5 % NaCl solution

Abstract

This study highlights the potential of coconut shell biomass waste-derived lignins (CSL) as corrosion inhibitors to reinforce the coating properties of polyurethane. The utilization of CSL involves a green approach to prepare eco-friendly metallic coatings. Herein, lignin was extracted via Kraft and Soda pulping processes. The present findings indicated that the percentage yield of Soda lignin (SL) (26.43 ± 0.75 %) was significantly higher than that of Kraft lignin (KL) (8.52 ± 0.39 %). Electrochemical impedance spectroscopy and potentiodynamic polarization corrosion monitoring techniques were used to evaluate the anticorrosive performance of modified polyurethane coatings on mild steel exposed to 3.5 % NaCl solution. In this study, doping concentration of 5 wt% KL and SL into polyurethane attained the optimum anticorrosion performance. The surface conditions of uncoated and coated mild steel substrates were investigated through scanning electron microscopy/energy dispersive X-ray (EDX) analysis, salt spray and adhesion tests. EDX analysis demonstrated that polyurethane added with 5 wt% doping concentration of SL contained the highest content of Fe (86.05 wt%) compared to 5 wt% KL which contained 79.64 wt% of Fe, whereas neat polyurethane coating contained 75.43 wt% of Fe. Hence, enhanced corrosion protection of polyurethane through the addition of CSL, particularly SL, possesses a viable and an effective green approach to utilize coconut shell biomass waste for the application as a potential corrosion inhibitor in organic coatings.