Waterborne coatings often delaminate and settle during long-term storage, requiring the addition of thickeners. The effects of nanofibrillated cellulose (NFC) and the commonly used thickener, hydroxyethyl cellulose (HEC), on the storage stability of waterborne coatings were compared in this study. The morphology of NFC was characterized using infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The rotational viscosity and rheological properties of the waterborne coatings with NFC and HEC were tested. Stationary settling experiments were also conducted at different temperatures to compare the difference of NFC and HEC on improving the storage stability of the waterborne coatings. The results showed that the waterborne coating with NFC exhibited pseudoplastic fluid characteristics; a small addition of NFC can achieve the same improvement effect on the storage stability of waterborne coatings as HEC. Further, the improvement effect of NFC was not affected by temperature. The waterborne coating with NFC still exhibited good storage stability at high temperatures, which was significantly superior to that of HEC. Therefore, NFC is a feasible agent for improving the prolonged storage stability and warming-induced delamination of waterborne coatings.

To improve the performance of polyurethane films, small amounts of cellulose nanofibrils (CNF) were physically blended with a waterborne polyurethane (WPU) emulsion, and then CNF/WPU composite films were prepared by cast-coating and drying. The particle size of the emulsions and the chemical structure, micromorphology, thermal stability, mechanical properties, and water resistance of the composite films were characterized using a Malvern laser particle size analyzer, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), an electronic strength machine, water contact angle analysis (WCA), and water absorption tests, respectively. The results showed that at a low CNF content of 0.3 wt%, the particle size of the WPU emulsion and chemical structure of the film did not change significantly. In addition, the tensile strength of the composite film increased by up to 108% compared to the neat WPU film, and the thermal stability and water resistance were slightly improved. The addition of CNF greatly enhanced the tensile strength while maintaining the other original properties of the WPU film, which may greatly improve the service life and tear resistance of commercial coatings in the future.