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 degrees, owing to the silylation of the hydroxy group and increased surface roughness of the CNC layer enabled by the sol-gel reaction.