Nanofibrillated Bacterial Cellulose Surface Modified with Methyltrimethoxysilane for Fiber-Reinforced Composites

Surface modification of nanofibrillated bacterial cellulose (NFBC) with methyltrimethoxysilane was performed in water to hydrophobize its surface. A series of cellulose samples with different degrees of molar substitution of methyltrimethoxysilane was prepared by changing the NFBC:methyltrimethoxysilane ratio in the preparation. Detailed structural characterization of these samples, including their degrees of molar substitution and crystallinity, was conducted by X-ray diffraction, Fourier-transform infrared spectroscopy, and solid-state NMR spectroscopy, and their molecular dynamics were studied by solid NMR relaxation measurements. Furthermore, the effects of degrees of molar substitution on their dispersibility in organic solvents and fiber morphology were evaluated. These analyses revealed that the solid-state relaxation behaviors of the cellulose and polysiloxane domains formed on the NFBC surface strongly correlate with their dispersibility in chloroform. The optimal degree of molar substitution for NFBC was found to be 0.66. The surface-modified NFBC with the degree of molar substitution of 0.66 showed the almost equivalent molecular mobility as NFBC and could be uniformly dispersed in chloroform. Therefore, it was revealed that the solid-state NMR could provide extremely valuable information on the mobility and surface chemical property of the surface-modified NFBC. In addition, the surface-modified NFBC could be an excellent filler for fiber-reinforced nanocomposite resins.