Waterborne isocyanate-free polyurethane epoxy hybrid coatings synthesized from sustainable fatty acid diamine†
The coatings industry is increasingly aware of the need to protect the environment and is constantly striving to ensure the safety of the industry and the health of consumers, which creates demand for environmentally friendly non-isocyanate polyurethanes (NIPU). In this study, the waterborne NIPU epoxy hybrid coatings were prepared from waterborne amine-terminated NIPU and waterborne epoxy chain extender. The waterborne amine-terminated NIPU were derived from diglycerol dicarbonate, 3,3′-diamino-N-methyldipropylamine, and fatty acid diamine (FDA). The waterborne epoxy chain extender was synthesized from diethanolamine and trimethylolpropane triglycidyl ether. The Fourier transform infrared spectroscopy and nuclear magnetic resonance were applied to confirm the chemical structure of synthesized materials. The effect of the soft/hard segment on waterborne NIPU epoxy hybrid coatings was studied by differential scanning calorimetry, thermogravimetric analysis, and tensile tests. Two glass transition temperatures were found in the samples with the largest amount of FDA while only one glass transition temperature was found on the other two samples. The thermal stability was enhanced by incorporating a higher amount of FDA. Finally, Young's modulus and tensile strength decreased with an increasing amount of soft segment and elongation-at-break was increased as expected. In general, this work explored the method for preparing waterborne non-isocyanate polyurethane epoxy hybrid coatings, which could reveal similar soft/hard segment performance with conventional isocyanate-based waterborne polyurethane.