Cationic water dispersion of bio-sourced cross-linked polyurethane

Abstract

A series of cross-linkable waterborne polyurethanes (WPUs) from a bio-sourced diol was synthesized through the acetone process. WPUs have attracted much interest for coating and adhesive applications as they have low levels of emission of volatile organic compounds. Cross-linking of an obtained polyurethane (PU) film should improve its mechanical properties and water and solvent resistance. In this study, N-methyldiethanolamine, the emulsifier, was used as short hydrophilic diol to obtain a cationic dispersion after quaternization with acetic acid. The cross-linker synthesized in this study, N-4-vinylbenzyl-diethanolamine, also contains a tertiary amine, which can improve dispersion in addition to the mechanical properties. Finally, a telechelic diol (Priplast 1900) obtained by polyesterification of a dimer fatty acid was used as a long hydrophobic diol. Stable PU water dispersions (40 wt%) were obtained through the acetone process with various diisocyanates (dicyclohexylmethane 4,4′-diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate) and characterized by dynamic light scattering. After complete evaporation of water, films were obtained from these dispersions. Then, the films were cross-linked by solar irradiation. Network formation was confirmed using a swelling test in acetone and tetrahydrofuran. Comparison of films after and before irradiation demonstrated that irradiation improves not only solvent and water resistance, but also the mechanical properties of each film.