Preparation of Vegetable Oil-based Isocyanate-Free Urethane Coating and Study of Their Mechanical and AntiCorrosion Properties

In this study, synthesize of the non-isocyanate-based polyhydroxy urethane from linseed oil and the effect of increasing the carbonation conversion percentage on the resulted polyurethane coating properties were studied. For this purpose, double bonds of the linseed oil were converted to the epoxy rings at the first step, and then these epoxy rings were turned into the carbonate rings with carbonation reaction with different percentages (۴۵%, ۷۵% and ۱۰۰%), which will break these rings and form urethane bond by reacting with amine hardeners. The Fourier-transform infrared spectroscopy (FTIR) was used to characterize the samples )In the epoxidation step, the ۱۶۸۹ cm-۱ peak, which corresponds to the carbonate double bonds in linseed oil, became smaller, and the ۸۲۳ cm-۱ peak, which corresponds to the epoxy rings, formed, and then in the second stage, ۸۲۳ cm-۱ become smaller and  the formation of the peak of ۱۸۰۰ cm-۱ represent the carbonate ring formed instead of epoxy rings). Differential scanning calorimetry (DSC) was used to assesses the curing conditions. After that, the optimal curing temperature and time were determined (suitable time for curing is ۲ hours for preheating at ۱۰۰°C and then ۲ hours to complete the cure process at ۱۸۰°C), and finally, the physical, mechanical and anti-corrosion properties of samples were compared through Pull-off, Crosscut, hardness, impact, bending and Electrochemical Impedance Spectroscopy (EIS) tests. The results of the characterization tests confirmed the epoxidation of linseed oil and carbonation of the epoxidized linseed oil. Also, coating properties showed improvement of adhesion and hardness and reduction of flexibility by increasing the carbonation conversion and increasing of the anti-corrosion properties first and then decreasing it by increasing the percentage of carbonation. After ۲ weeks immersion in corrosive electrolyte, sample with ۷۵% of carbonation revealed anti-corrosion resistance equal to ۵.۳۸×۱۰۶ ohm.cm۲ while solvent-base polyurethane indicated ۱.۰۳×۱۰۷ ohm.cm۲. Finally, polyurethane resine synthesized from ۷۵% carbonated linseed oil represents the optimum properties for coating application.