Preparation of CaCO₃nanoparticle/pulp fiber composites using ultrafine bubbles

Abstract

<jats:title>Abstract</jats:title><jats:p>In this study, CaCO<jats:sub>3</jats:sub> nanoparticle/pulp fiber composites were prepared by formation of ultrafine bubbles of CO<jats:sub>2</jats:sub> gas in aqueous Ca(OH)<jats:sub>2</jats:sub> solution containing beaten or unbeaten pulp fibers. Scanning electron microscopy images of the fiber/CaCO<jats:sub>3</jats:sub> composites showed that primary CaCO<jats:sub>3</jats:sub> nanoparticles with average diameters of 50–80 nm densely formed on the pulp fiber surfaces. The average sizes and morphologies of the precipitated CaCO<jats:sub>3</jats:sub> nanoparticles can be controlled by controlling the CO<jats:sub>2</jats:sub> flow rate into the pulp slurry. From dynamic drainage analysis of the CaCO<jats:sub>3</jats:sub>/pulp slurries with high shear force, retention of the CaCO<jats:sub>3</jats:sub> 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 CaCO<jats:sub>3</jats:sub> and pulp fiber. Therefore, precipitated CaCO<jats:sub>3</jats:sub> nanoparticles stably formed on the pulp fiber surfaces in the slurry by the ultrafine bubble method. Compared with reference handsheets, handsheets prepared with the CaCO<jats:sub>3</jats:sub> nanoparticle/pulp fiber composites had higher CaCO<jats:sub>3</jats:sub> 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 CaCO<jats:sub>3</jats:sub> content in the handsheets.</jats:p>

Structural analysis of CaCO3 nanoparticle/pulp fiber composites by tube flow fractionation

“…The CO2 gas was prepared from commercial industrial-grade liquid CO2 and held in a pressure-resistant cylinder. The precipitated CaCO3 nanoparticle/HBKP composite was prepared from a 1 wt% HBKP/water slurry that contained Ca(OH)2 (1 wt%) by blowing CO2 gas with the ultrafine bubble method (Fuchise-Fukuoka et al 2020). The dry mass ratio of the precipitated CaCO3:HBKP was set to 57:43 in the composite.…”

“…The solid content of the composite slurry was diluted to 0.25% with water before being subjected to TFF. The CaCO3 nanoparticles were prepared by bubbling CO2 gas into a Ca(OH)2 solution without HBKP, and the CaCO3/HBKP mixture was prepared by mixing the precipitated CaCO3/water and the HBKP/water slurries (Fuchise-Fukuoka et al 2020). The dry mass ratio of the precipitated CaCO3:HBKP and the solid content of the mixture slurry were set equal to those of the CaCO3/HBKP composite slurry.…”

“…Each fraction was collected and filtered using filter paper to collect the HBKP long and short fibers and CaCO3 particles, and the dry mass of the solid components was determined by drying with the filter paper (Fuchise- Fukuoka et al 2020). Part of the fraction sample was observed via a field-emission-type SEM (JSM-6700; JEOL, Tokyo, Japan) at 5 kV after coating with osmium via an OPC60A osmium plasma coater (Filgen, Japan).…”

“…In previous papers, new procedures were developed to prepare precipitated CaCO3 nanoparticles or pulp-fiber composites using cavitation flow and ultrafine bubble methods to improve the adsorption stability of CaCO3 nanoparticles on pulp fiber surfaces (Fukuoka et al 2019;Fuchise-Fukuoka et al 2020). In this study, a precipitated CaCO3 nanoparticle or unbeaten pulp fiber slurry was separated into five fractions using TFF, and the interactions between the CaCO3 nanoparticles and long and short pulp fibers were studied from optical and SEM images, mass ratios, and the CaCO3 contents of the fractions.…”

“…An unbeaten hardwood bleached kraft pulp (HBKP) was used, and two CaCO3/HBKP slurries were used for TFF classification. One slurry was a CaCO3/HBKP composite slurry that was prepared by flowing CO2 gas into a HBKP slurry that contained Ca(OH)2 via the ultrafine bubble method (Fuchise- Fukuoka et al 2020). The other slurry was a CaCO3/HBKP mixture slurry that was prepared by mixing HBKP/water and precipitated CaCO3/water slurries that had been prepared separately.…”