A Green, Facile, and Scalable Method for Fabricating High-Strength, Water-Resistant CNF/SA Composite Films

Cellulose nanofiber (CNF) film has been widely studied in recent years because of its high strength, high light transmittance, degradability, and low thermal expansion coefficient. However, challenges like shrinkage, long dehydration times, and poor water resistance limit its large-scale application. Herein, we report a facile and environmentally friendly method to prepare CNF/sodium alginate (SA) composite films. By adding a certain amount of SA in the CNF film and regulating the moisture in the film, the gap between CNF was filled and the dimensional stability of the film was improved. Meanwhile, the cross-linking property of SA significantly reduced the water absorption rate of the composite film, endowing the composite film with high strength (dry strength 125 MPa), high water resistance (wet strength 33 MPa), and high light transmittance (85–90%). Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD) analyses confirmed the microstructure and interaction mechanism of CNF and SA in composite films. This method is not only simple to operate without using toxic or harmful reagents but also effective to inhibit the deformation during the drying process of CNF, which is expected to provide a feasible basis for the commercial application of CNF film.