Speed of paper machines is often limited by the drainage rate of the furnish and the mechanical properties of the wet web, i.e. the tension and relaxation properties. In this study, the effects of alteration of fibre properties and fines content by gentle and harsh refining on dewatering as well as on wet and dry web properties were determined. Both types of refining or addition of fines prolonged the dewatering time but also improved the mechanical properties. Harsh refining with much fibre cutting resulted in longer dewatering time, lower dry content after wet pressing and higher density of dry sheets than gentle refining with much external/internal fibrillation of fibres. Removal of fines shortened the dewatering time but decreased the wet web and dry tensile strength, and the residual tension compared to pulps containing fines. The fibre properties contributed more to the residual tension, while the fines content was more important for the wet web tensile strength. Addition of a non-ionic surfactant shortened the dewatering time of refined pulp without deteriorating the mechanical properties. By tailoring the refining and addition of surfactants, the mechanical properties of the wet web could be improved without prolonging the dewatering time.

No abstract

The aim of this work was to improve the dewatering characteristics of thermo-mechanical pulp (TMP) through enzymatic treatment without any significant reduction of the quality of the end product. The cellulose and hemicellulose content of TMP was altered by means of enzymatic treatments using different purified cellulases and hemicellulases as well as commercial enzyme preparations, in order to clarify the target carbohydrate components affecting the dewatering of TMP. The effects of enzymatic treatments on the properties of the pulp as well as its forming, pressing and drying were studied by lab scale measurements. An increased dewatering rate of TMP was observed in initial drainage, wet pressing and drying laboratory experiments, as a result of various enzymatic treatments. Interestingly, both cellulose and galactoglucomannan components in TMP were found to affect the dewatering properties of the pulp, and a greatest improvement in dewatering could be obtained with a combined treatment with an endoglucanase type of cellulase and mannanase.