Cellulose nanocrystals as stabilizers for waterborne fluorescent non-isocyanate polyurethane latexes

Abstract

Non-isocyanate polyurethanes (NIPUs) exhibit significantly greater sustainability than conventional polyurethanes (PUs) by adhering to key principles of green chemistry, particularly the elimination of toxic chemicals. In this study, waterborne non-isocyanate polyurethane (WNIPU) latexes, exclusively stabilized by cellulose nanocrystals (CNCs) and partially derived from renewable resources, were synthesized for the first time via suspension polymerization. A polyaddition reaction between a siloxane diamine and 1,6-hexanediol bis(cyclic carbonate) occurred within the monomer-in-water Pickering emulsion droplets effectively stabilized with CNCs. The concentration of the CNCs was optimized for the Pickering emulsion. The CNCs acted as nanoparticle surfactants on the surface of the WNIPU latex particles, as confirmed using rhodamine B-labelled CNCs and confocal laser scanning microscopy. Spherical-shaped monomer droplets and WNIPU latex particles with a median size of 10 μm were achieved. The effect of the cyclic carbonate-to-amine molar ratio on the amine monomer conversion, molecular weight, and thermal properties of the WNIPU was investigated. The obtained WNIPU suspensions exhibited fluorescence under UV irradiation at 365 nm owing to the clustering of carbamates. Combining the fluorescence properties with low glass transition temperatures, these latexes open various potential applications as functional coatings.