BENEFITS OF FRACTIONATION DURING PULPING IN DEINKING, 2010 TAPPI PEERS Conference

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Balancing pulping operations to achieve sufficient defibering, good ink detachment and minimal ink fragmentation during pulping is sometimes considered a complex issue. The aim of this work was to study whether ink detachment could be improved by fractionating the pulp slurry after a very short pulping time and by continuing the pulping of the fiber fraction obtained including the undefibered material. The laboratory pulping procedure used in this study included variable pulping periods for old newsprint (ONP) in neutral conditions with a subsequent fractionation by intensive washing and continued pulping of the undefibered fiber fraction. Ink detachment was assessed by measuring the residual ink concentration from sheets prepared from hyperwashed pulps after each pulping stage. The results were compared to samples obtained by pulping ONP without single or multiple intermediate fractionation stages. The results show that significant improvement in ink detachment can be achieved by fractionating pulp after a very short pulping time and by continued pulping of the fiber fraction. Usage of multiple fractionation stages in between pulping provided the highest ink detachment efficiency and the best quality of stock in terms of attached residual ink content.