Preparation and characterization of nanocellulose-reinforced water-soluble cellulose acetate films

A water-soluble cellulose acetate (CA) with a degree of acetyl substitution of 0.9 was dissolved in water and mixed with aqueous dispersions of reinforcing cellulose nanofibers (CNFs) at various mass ratios. CA/CNF composite films with CNF contents of 0 %–16 % were prepared by casting and drying the mixtures to improve the fundamental properties of the films. Aqueous dispersions of TEMPO-CNFs containing sodium carboxylate and protonated carboxy groups were separately prepared and used to produce CA composite films (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl radical). Highly transparent CA/TEMPO-CNF films with tensile strengths and Young's moduli more than twofold those of the 100 % CA film were obtained at a TEMPO-CNF content of 16 %. Transmission electron microscopy images of the film cross-sections showed that the TEMPO-CNFs were almost homogeneously and individually distributed in the CA/TEMPO-CNF-COOH composite films. The thermal expansion patterns of the 100 % CA films were characteristically wavy between 30 and 100 °C, and the thermal expansion ratios decreased as the TEMPO-CNF contents of the films increased. The obtained results indicate that CA/CNF mixtures can be used as water-based coatings and paints with favorable properties.