Effects of various types of cellulose nanofibers on the physical properties of the CNF-based films

Cellulose-based films using three different types of cellulose nanofibers (CNFs), carboxymethylated CNF (CNFCM), enzyme-treated CNF (CNFENZ), TEMPO-oxidized CNF (CNFTEMPO), and sodium carboxymethyl cellulose (CMC) were prepared using a solution casting method, and their film properties were characterized to test the effect of CNF types. FE-SEM image showed the densely packed fibers in the film with different fiber shapes depending on the CNF types, while the AFM image showed the roughness of the films. The CNFTEMPO film was as transparent as the CMC film, while the other CNF films were translucent. The CNF films also showed different crystalline structures depending on the CNF types, so the film properties were greatly influenced by the cellulose crystallinity index (CI). The CNFENZ film with the highest CI showed higher thermal stability and water vapor barrier properties than the other films. Also, the water vapor permeability of CNF films was significantly lower than the CMC film. The carboxylate and carboxymethyl groups in the CNFTEMPO and CNFCM films increased the tensile strength, which was about two times higher than that of the CNFENZ and CMC films. The CNF film properties depended on the CNF type and were comparable or superior to the CMC film.