Synthesis of novel plant oil-based isocyanate-free urethane coatings and study of their anti-corrosion properties

Abstract

In this study, a bio-resource resin was synthesized via epoxidation and carbonation of linseed oil (LO) in acidic conditions, and then in the presence of tetra ‐ n ‐ butyl ammonium bromide (TBAB) and under purging of CO2 gas, respectively. The synthesized resins were characterized using FTIR spectroscopy, NMR analysis, and titration method. The resins were cured with diethylenetriamine to form non-isocyanate polyhydroxy-urethane networks. Rheometry analysis and DSC were utilized for determining the proper time and temperature of the curing process. The physical and mechanical properties of the mild steel coated samples were evaluated using various techniques. Finally, the corrosion resistance of the coated samples was assessed via Electrochemical Impedance Spectroscopy (EIS) and the results were compared with commercial polyurethane-based coated samples.The characterization tests confirmed the formation of epoxy and cyclo-carbonate groups as a result of the epoxidation process and carbonation reaction of LO, respectively. The various tests showed the appreciation of the mechanical properties of the coating samples with different carbonation weight percentages. The results revealed the improvement of adhesion and hardness properties and reduction of the flexibility of the coating samples with increasing the conversion % of carbonation. As the carbonation content increases, more hydroxyl groups were formed in the final polyhydroxy-urethane structure due to the reaction of the cyclo-carbonate with the amine, resulting in increased adhesion strength and mechanical properties of the polymer. EIS study revealed increasing of the anti-corrosion properties first and then decreasing it by increasing the percentage of carbonation. The 75% carbonated sample revealed the best corrosion performance, which was comparable with PU-based coated samples.