Studies on Retention Behavior of Filler and Pigment in Sheets at the Wet End by Aluminum Sulfate Addition

Abstract

The effects of addition levels of aluminum sulfate to paper stock on retentions of TiO2 filler or red pigment (α-Fe2O3) in handsheets were investigated. The addition levels of aluminum sulfate to the blank and TiO2 filler-or red pigment-containing pulp slurries were set to 0-3% based on dry weight of the pulp, and retention ratios of Ti, Fe and Al originating from the filler, red pigment and aluminum sulfated added, respectively, were determined for the handsheets by inductively-coupled plasma emission spectrometry. Retention ratios of both TiO2 filler and red pigment in sheets increased with aluminum sulfate added ; aluminum sulfate behaves as a retention aid for both these filler and pigment. However, retention mechanism and distribution of the additives in the sheets were different between the TiO2 filler- and red pigment-containing handsheets. The amounts of Al retained in sheets, zeta-potentials of pulp fibers in the slurries and SEM images of the handsheet surfaces were studies for fines-containing and fines-free pulps in terms of the addition level of aluminum sulfate. The zeta-potential of the original TiO2 filler was -41mV, which was close to the pulp fiber used. However, the red pigment had a zeta-potential of -1.1mV, and the zeta-potential distribution indicated that each red pigment particle had both positive and negative surface charge sites. This difference in zeta potential between the TiO2 filler and red pigment caused the different retention behavior, retention mechanism and distribution of these additives in the sheets. The obtained results show that fines fraction in beaten pulp plays a significant role in filler and pigment retentions in sheets at the wet-end.