Preparation of CaCO₃nanoparticle/pulp fiber composites using ultrafine bubbles

Abstract In this study, CaCO₃nanoparticle/pulp fiber composites were prepared by formation of ultrafine bubbles of CO₂gas in aqueous Ca(OH)₂solution containing beaten or unbeaten pulp fibers. Scanning electron microscopy images of the fiber/CaCO₃composites showed that primary CaCO₃nanoparticles with average diameters of 50–80 nm densely formed on the pulp fiber surfaces. The average sizes and morphologies of the precipitated CaCO₃nanoparticles can be controlled by controlling the CO₂flow rate into the pulp slurry. From dynamic drainage analysis of the CaCO₃/pulp slurries with high shear force, retention of the CaCO₃nanoparticles on the pulp fiber mats was ∼10 % higher for the slurry formed by the ultrafine bubble method than for that formed by mixing precipitated CaCO₃and pulp fiber. Therefore, precipitated CaCO₃nanoparticles stably formed on the pulp fiber surfaces in the slurry by the ultrafine bubble method. Compared with reference handsheets, handsheets prepared with the CaCO₃nanoparticle/pulp fiber composites had higher CaCO₃contents and had consequently higher specific surface areas and surface smoothness values. In contrast, the tensile strength and elongation at break decreased because the sheet density decreased with increasing CaCO₃content in the handsheets.