Synthesis and characterizations of air-cured polyurethane coatings from vegetable oils and itaconic acid

Abstract

Polyurethane (PU) coatings were prepared using polyesteramide polyols based on different types of vegetable oils and itaconic acid. Long chain fatty diethanolamides were synthesized using the amidation of linseed/castor/karanja oils and the desired hydroxyl group was introduced via esterification reaction with itaconic acid to yield polyesteramide polyols. Its structural elucidation was carried out using Fourier-transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR). The study of crosslinking these polyols with hexamethylene diisocyanate (HDI-trimer and HDI-biuret) shows that the isocyanate structure and functionality contribute to the final polyurethane coatings properties. Various optical, mechanical, and durability performance of the cured PU metal coating films were examined. The gel content method was used to compare the crosslink density of various PU films. The thermal properties of the PU coating, including stability and glass transition temperature (Tg), were assessed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The corrosion resistance of PU coatings was analyzed by employing electrochemical impedance spectroscopy (EIS). PU metal coatings display superior gloss, adhesion, and chemical resistance properties. Differences in fatty acid compositions of linseed/castor/karanja oils were found to influence the air curing and mechanical and corrosion resistance properties of PU metal coatings. The use of itaconic acid and vegetable oils in the synthesis of these polyols contributes to their bio based characteristics and permits replacing the currently used petroleum-based polyols.