The effect of fibre properties, fines content and surfactant addition on dewatering, wet and dry web properties

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.