Fibre Property Distributions and Rheology as Indicators of Mill-Scale Pulp Refining Performance

Fibre properties significantly influence paper quality. This study investigates fibre property development along an industrial pulp production line, analysing morphological distributions and rheological behaviour to enhance refining performance indicators. Understanding these developments is critical for optimising resource efficiency and increasing industrial sustainability. Softwood thermomechanical pulp (TMP), from high-consistency (HC) and low-consistency (LC) refining, and bleached hardwood kraft pulp (BHKP) were examined. Fibre morphological properties were characterised using an optical fibre analyser, while suspension rheology was assessed using a pulp viscometer, supported by computational fluid dynamics (CFD) and discrete element method (DEM) simulations. Results demonstrate that fibre property distributions provide deeper insights into refining effects compared to average values alone. Systematic trends showed that HC-refined TMP from the first and second refining stage required significantly greater torque to break the fibrous network and fluidise the pulp compared to pulp that was also LC refined. This indicates that alterations in fibre properties, especially shortened fibre length resulting from different refining processes, govern fibre interactions in the three-dimensional network of the pulp suspensions and, therefore, their flow behaviour. In conclusion, combining morphological distribution analysis with specialised rheological measurements offers a robust tool for better understanding and monitoring mill-scale refining processes, enabling improved process optimisation in pulping and papermaking.