Optimum Refining of Thermomechanical Pulp by Means of Primary Pulp Fractionation, 2007 International Mechanical Pulping Conference

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The pulp used in this work was sampled after the first TMP refining stage of a Canadian newsprint mill. This pulp was fractionated with a pressure screen in two or more fractions of long fibres and fine fibres. We refined the fractions at high consistency in one or two stages or at low consistency. We recombined there fined fractions together to recreate the initial pulp. The initial pulp, itself refined at high consistency as in a typical TMP process, has been compared with there combined pulps. It appears that refining consistency has strong effect on the quality of there combined pulp and that it is possible to optimize the quality by this kind of treatment. This optimization is closely related with the fractionation efficiency. The best fractionation process is a pressure screen cascade using baskets with very small apertures. This process is very efficient in separating fibres by length but also able to separate fibres on the basis of wall thickness, leading to fractions of long fibres enriched in late wood and fractions of short fibres enriched of early wood.