SILYLATION OF CELLULOSE NANOFIBRILS AT VARIOUS pH CONDITIONS OF AQUEOUS SYSTEMS

摘要

Various chemical modifications are done to widen the application of cellulose nanofibirils (CNF) with good performance and convertability. Hydrophobization has been done to overcome the drawbacks originated from numerous hydroxyl groups on the surface of CNF. Silylation that substitutes hydroxyl groups with silyl groups has been used as one of the useful hydrophobization of CNF. Silylation by a sol-gel method allows to minimize use of organic solvents. While several studies examined the CNF aerogel silylated by methyltrimethoxysilane (MTMS) in aqueous system, few studies dealt with characteristics of silylated CNF films and the silylated suspension under various pH conditions. Therefore, we investigated the properties of CNF films silylated under different pH conditions. Pre-hydrolyzed MTMS was added to CNF suspension, where the pH was adjusted at acidic, neutral and alkaline conditions. CNF films were prepared by casting and vacuum filtration of the modified CNF suspension. Hydrophobicity of the films was analyzed by water contact angle measurement. Scanning electron microscope (SEM), Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses were carried out to investigate the characteristics of the silylated CNF films. The CNF films silylated at acidic and mild alkaline conditions showed the highest water contact angles, which was about 120°. In the case of the silyated CNF in alkaline conditions, the films had hydrophobic surfaces but contained particles of self-condensated poylsiloxane structure which can deteriorate hydrophobicity. Therefore, it is suggested that the desirable pH condition would be acidic condition or mild alkaline conditions.