Study on Controlling the Surface Structure and Properties of a Cellulose Nanocrystal Film Modified Using Alkoxysilanes in Green Solvents

Film and sheet products made from naturally derived materials that exhibit high-performance surface functions are important as regards the environment. This study aimed to control the surface structure of a cellulose nanocrystal (CNC) film modified using methyltriethoxysilane and tetraethoxysilane coprecursors with environmentally friendly solvents (water and ethanol) during a spin-coating process. The surface-modified CNC film on the glass substrate was evaluated by microstructure analyses (Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM)) and water contact angle (hydrophobicity) measurements. Through FT-IR, NMR, and XPS, it was confirmed that the silane compounds were chemically bonded to the surface of the CNC. The AFM images suggested that the local surface structure of the silylation-modified CNC film was formed along with the rod-like shape of the CNC. The water contact angle was approximately 90°, owing to the silylation of the hydroxy group and increased surface roughness of the CNC layer enabled by the sol–gel reaction