On the Mechanism of GCC Filler Particle Retention During Dewatering - New Techniques and Initial Findings, 2000 Papermakers Conference Proceedings

Daniel Solberg, Dr. Lars Wågberg--The main objective of this present investigation was to clarify the mechanism of ground calcium carbonate (GCC) retention during dewatering through a thick pad of pulp fibers. It has earlier been claimed that mechanical filtration of aggregated filler particles during dewatering and the deposition of filler particles onto the fiber surface prior to dewatering, are the main filler retention mechanisms. In the present study, the effect of filtration was studied by examining the filler particle size distribution before and after filtration of a filler suspension through a thick pad of pulp fibers. Changes in the wet-web pore size distribution in beds with and without filler were measured by liquid porosimetry. The filler distribution through the bed was obtained from SEM micrographs. The results indicate that deposition on fibers is the dominant process for the retention of commercial GCC particles with a mean particle size of 0,6 and 0,8 µm. Only a marginal fraction of these particles are retained by filtration even though the experimental conditions (laminar flow and a very high grammage) were chosen to favour such process. These results are valid for well-dispersed, non-flocculated GCC particles.