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Removal of extractives from the pulp furnish is of great importance for the improvement of paper machine efficiency and also for reducing the energy consumption during the thermomechanical pulp refining process. Extractives can exist in many different forms in the process water; as colloidal particles, dissolved or attached to fines and fibres. It is therefore important to know in which form they exist in order to fully understand their behaviour. In this paper, we report on an evaluation of the removal of extractives released from chips of different raw materials pre-treated in an Impressafiner, in pilot and in mill scale. In pilot trial the raw materials used were loblolly pine and white spruce and in the mil scale trial the raw material used was norway spruce. The colloidal stability of extractives present in the pressate water from the Impressafiner and their flocculation behaviour by cationic polymers (CPAM and Poly-DADMAC) under different conditions was also investigated. Calculations of mass balances around an Impressafiner showed that it was possible to remove up to 40% of extractives before the refining process. The reduction in total extractives content was mainly due to released resin acids while fatty acids, triglycerides, steryl esters and sterols to a large extent remained in the wood chips after pre-treatment. The removal of extractives from pine was four times higher than from spruce chips. The results can be explained in terms of the extractive composition in the raw material and the morphological differences in the wood structure.

Mass balance of lipophilic extractives around impressafiner in mill and pilot scale