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.