Defibering of paper in a dry content of fifty percent and higher

摘要

Cutting down on water consumption could be possible in papermaking by processing fibers in a high dry content. In earlier studies, however, dry defibering of paper has been found to detrimentally affect the papermaking potential of pulp. The aim of this research was to find the reasons for this and to study possibilities of avoiding a loss of papermaking potential. Defibering was studied using a disk refiner and a hammer mill. The disk refiner experiments were done with thermomechanical pulp (TMP) based newspaper. The hammer mill experiments were done with chemithermomechanical pulp (CTMP), chemical softwood and a mix of chemical softwood and hardwood kraft. Various operating parameters and conditions were tested. The pulp and fiber properties were compared with wet slushed reference samples by evaluating their bonding ability, the internal strength of the fiber, the strength properties of the paper, and the fiber morphology. In the disk refiner trials the properties of the defibered material varied considerably. In the best experiments the properties were near those of the reference. The defibering results depended on the fiber material, disk geometry, moisture content and use of steam. The pulp properties were best preserved when moisturized paper was defibered in a steam atmosphere using a coarse disk pattern. Poor pulp properties seemed to be due to fiber cutting. Changes in the fiber level seemed to be minor, and there were no changes in the internal strength of the fibers. The hammer mill seemed to be more suitable for chemical pulp defibering. The properties of the pulp were comparable to wet slushed pulp, both before and after beating. The loss of papermaking potential of long-fibred spruce CTMP was considerable and could not be recovered with beating. The defibering results could only be fine-tuned with the operating conditions.