Sol-gel preparation and mechanical properties of machinable cellulose/silica and polyvinylpyrrolidone/silica composites

Acetylcellulose (AC)/silica and polyvinylpyrrolidone (PVP)/silica composites were prepared by the sol-gel method from Si(OCH3)(4)-AC-HNO3-H2O-tetrahydrofuran-CH3OC2H4OH and Si(OCH3)(4)-PVP-(CH3COOH or NH3)-H2O-CH3OH-CH3OC2H4OH solutions. AC/silica composites were composed of micrometer-sized particles rich in silica and a matrix rich in AC, while PVP/silica composites were single-phase on the SEM length scale. The AC/silica composites exhibited elastic-plastic behavior, and had excellent machinability without chipping on cutting with an electric saw while the PVP/silica composites showed less plasticity and machinability. Young's modulus and bending strength were increased by post-drying, 1.8-2.8 GPa and 49-88 MPa, respectively, for the AC/silica composites, and 1.0-3.9 GPa and 17-79 MPa, respectively, for the PVP/silica composites.