Evaluation of furnishes for tissue manufacturing; suction box dewatering and paper testing

Water removal on a tissue machine becomes progressively more difficult and expensive in each successive zone. A good way to reduce cost can therefore be to improve the dewatering prior to evaporative drying. This can be done by selecting proper raw materials and optimizing the treatment of the fibres in the furnish. In this work, four pulps beaten to different levels were studied in vacuum dewatering trials. Mixing of the pulps, common in tissue manufacturing, was also performed. To simulate the suction boxes on a tissue machine, bench-scale laboratory equipment was used. Conditions typically used on a tissue machine regarding dwell times and vacuum levels were chosen. Paper properties relevant for tissue, like wet strength and absorption were measured on non-creped papers. To obtain information about the fibre properties, fibre characterization and microscope studies were also conducted. Vacuum dewatering in tissue manufacturing is shown to be affected by the choice of pulp which can be explained by structural differences in the networks caused by variations in fibre properties. Beating has a strong negative impact on the solids contents reached, which is believed to be an effect of both internal and external fibrillation. These results, together with additional data from mixing and paper testing, give a better understanding of how the furnish should be prepared to reduce energy use in the process and still fulfil consumer requirements on properties.