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Frontpage | Column | News Archive | Forchem.com |
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Control of birch extractives with new ForExt rosin soaps in kraft pulping  Extractives are compounds that protect trees against degradation, micro-organisms andinsects; some also serve as an energy source. They are nature-derived chemical compounds with a variety of structures and they give the tree its characteristic color, smell and taste. The biggest problems caused by extractives in pulp and paper manufacturing are deposits in screening and paper machines, the blocking of wires, and dirt specks in pulp and paper. A major part of extractives is comprised of rosin acids, fatty acids and neutral compounds. Rosin and fatty acids form water-soluble soaps in kraft pulping. Neutral compounds are insoluble in water and they cause most of the problems related to extractives in pulp and paper mills. Birch has more neutral compounds than coniferous trees and it does not contain any rosin acids. The soaps of rosin and fatty acids are both water absorbent and water repellent. In water solutions they form small spherical particles called micelles, where the water absorbent ends are oriented towards water and the water repellent parts are oriented to the core. These micelles can take up neutral components to their core, since the neutrals are attracted to the water repellent parts of the soaps. This is referred to as solubilisation and it increases the removal of neutral components from pulp. A high amount of rosin and fatty acids in comparison to neutrals is an advantage in kraft pulping. If the ratio between soaps (of rosin and fatty acids) and neutrals is too small, it can result in decreased solubilisation and poorer removal of neutral compounds. In birch this ratio is too small and it presents problems to the removal of neutral compounds. Pine, which has fewer problems with extractives, has a much higher ratio. When tree species with a high amount of neutrals like birch and aspen are used, the removal of neutral compounds through solubilisation is quite low if no free rosin and fatty acids are added to the pulping. Rosin soap contains only rosin and fatty acids so it can be used to increase the amount of soaps thus providing a better ratio between soaps and neutrals. This makes it possible to obtain a better removal of neutral compounds through solubilisation. Micelles that are formed from both rosin and fatty acids have a particularly high capacity to solubilise neutral compounds. Birch has no rosin acids, which diminishes the amount of solubilisation. More rosin acids are needed, and can be added as rosin soap since rosin soap contains more rosin acids than fatty acids. Rosin acids are also more easily washed away from pulp than fatty acids. For these reasons Forchem’s ForExt 35/90 rosin soap is very suitable for controlling birch extractives in pulp mills. ForExt 35/90 contains 90 % of rosin acids and only 10 % of fatty acids and it can be used to improve the ratios of extractives so that a better solubilisation is achieved. Using ForExt 35/90 improves pulp quality for paper making purposes. Tuula Lehtimaa Research Scientist Laboratory of Forest Products Chemistry Helsinki University of Technology |
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