polydiallyldimethylammonium chloride (poly-DADMAC) and polyaluminum chloride (PAC) contain chloride. Polyvinyl Amine (PVam) and fixatives e.g. Al 3+ ions mainly come from inorganic fixatives.ĭifferent dry-strength additives e.g. Sodium hydroxide used for control-ling the pH of the stock is the main source for Na + ions, while calcium carbonate used as filler or coating pigment is the main source of Ca 2+ and CO 3 2- -ions. The main sources of the other metal ions (Na +, Ca 2+, and Al 3+) and anions (Cl –, SO 4 2-, and CO 3 2-) studied in this paper are different chemical additives, fillers, and coating pigments used in the papermaking process. In addition, fillers and coating pigments used in paper making, especially kaolin, can contain relatively large amounts of iron. Because the chelation and washing are usually incomplete, the metal ions can be carried with the pulp to the circulation waters of a paper machine. The removal can be carried out by acidifying the pulp to pH levels of 2 to 3 or by treating the pulp with a chelating agent.Īcidification and the chelating agent release the metal ions from the fibers, but they still have to be washed out of the system in a washer ahead of the bleaching stage. Because iron and manganese decompose peroxide, it is important to remove them before a peroxide bleaching stage. Iron and manganese are typical disturbing metal ions in peroxide bleaching processes of mechanical pulps (Lindholm 1999 Johns 1996 Kappel and Sbaschnigg 1991 Colodetto et al. 1988). The white water of a paper machine contains relatively large amounts of various ions that can decrease the brightness of the produced paper.ĭifferent ions can be carried into the water flows of a paper machine with pulps, fresh water, fillers, and chemical additives or they can be dissolved from the process equipment. Therefore, it is important to be able to produce mechanical pulps with high brightness in an ecofriendly and cost-effective way (Enberg et al. 2009 Ohlsson and Federer 2002 Luoma et al. 2004). Box 44, FI02271, Espoo, Finland *Corresponding brightness demands for improved newsprint and for many magazine paper grades have been raised in recent years. Box 16300 FI-00076 Aalto, Espoo, Finland b: Kemira Oyj, Luoteisrinne 2 P.O. Keywords: Brightness reduction Fines Thermomechanical pulp Mechanical pulp Wet end Water circulation Cation AnionĬontact information: a: Aalto University, School of Chemical Technology, Dept. Manganese, sodium, sulfate, or carbonate ions did not affect the optical properties.īrightness Reduction of Mechanical Pulp in the Wet End of a Paper Machine: The Effect of Different Ions in the Circulation Water Aluminum ions increased the brightness of the fines fraction by increasing the light scattering. Calcium chloride is used very commonly as a model chemical for calcium ions in laboratory tests, but the use of it is not recommended, if the darkening phenomena are studied, because chloride ions decrease the brightness. The increased light absorption dominated and the brightness decreased. Calcium ions increased both the light absorption and light scattering of the fines fraction. Also, chloride ions decreased the brightness by increasing the light absorption of the fines and fiber fraction. It is very important to keep the iron content of the pulp and white water as low as possible because even low contents of iron have a negative effect on the brightness of produced paper. Ferrous ions darkened the fines and fiber fraction by increasing the light absorption. Selected chemicals were dissolved in the circulation water to study the effect of different cations and anions. 8(3), 4117-4133.ĭarkening of the fines and fiber fraction of peroxide-bleached thermo-mechanical pulp (TMP) was studied on a laboratory scale using a device that simulates the short circulation of a paper machine. 'Brightness reduction of mechanical pulp in the wet end of a paper machine: The effect of different ions in the circulation water,' BioRes.

Mgs 5 lower brightness