Preparation of CaCO3 nanoparticle/pulp fiber composites using ultrafine bubbles

In this study, CaCO3 nanoparticle/pulp fiber composites were prepared by formation of ultrafine bubbles of CO2 gas in aqueous Ca(OH)2 solution containing beaten or unbeaten pulp fibers. Scanning electron microscopy images of the fiber/CaCO3 composites showed that primary CaCO3 nanoparticles with average diameters of 50–80 nm densely formed on the pulp fiber surfaces. The average sizes and morphologies of the precipitated CaCO3 nanoparticles can be controlled by controlling the CO2 flow rate into the pulp slurry. From dynamic drainage analysis of the CaCO3/pulp slurries with high shear force, retention of the CaCO3 nanoparticles on the pulp fiber mats was ∼10 % higher for the slurry formed by the ultrafine bubble method than for that formed by mixing precipitated CaCO3 and pulp fiber. Therefore, precipitated CaCO3 nanoparticles stably formed on the pulp fiber surfaces in the slurry by the ultrafine bubble method. Compared with reference handsheets, handsheets prepared with the CaCO3 nanoparticle/pulp fiber composites had higher CaCO3 contents 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 CaCO3 content in the handsheets.