Abstract
Abstract Chemithermomechanical pulp (CTMP) is often used in central layers of multiply paperboards due to its high bulk and strength. Such a CTMP should consist of well-separated undamaged fibres with sufficient bonding capacity. The basic objective of this work is to optimize process conditions in low-consistency (LC) refining, i. e. to select or ultimately develop new optimal LC refiner filling patterns, in order to produce fibrillar fines and improve the separation of fibres from each other while preserving the natural fibre morphology as much as possible. Furthermore, the aim is to evaluate if this type of work can be done at laboratory-scale or if it is necessary to run trials in pilot- or mill-scale in order to get relevant answers. First stage CTMP made from Norway spruce (Picea abies) was LC refined in mill-, pilot- and laboratory-scale trials and with different filling patterns. The results show that an LR1 laboratory refiner can favourably be used instead of larger refiners in order to characterize CTMP with regard to tensile index and z-strength versus bulk. A fine filling pattern resulted in CTMP with higher tensile index, z-strength and energy efficiency at maintained bulk compared to a standard filling pattern.
Highlights
Chemithermomechanical pulp (CTMP) is often used in central layers, as a mixture together with broke and softwood kraft pulp, of multiply paperboards due to its high bulk and strength
The results show that an LR1 laboratory refiner can favourably be used instead of larger refiners in order to characterize CTMP with regard to tensile index and z-strength versus bulk
A fine filling pattern resulted in CTMP with higher tensile index, z-strength and energy efficiency at maintained bulk compared to a standard filling pattern
Summary
Chemithermomechanical pulp (CTMP) is often used in central layers, as a mixture together with broke and softwood kraft pulp, of multiply paperboards due to its high bulk and strength. The present study is based on results from the LC refining technology area and its objective is to produce fibrillar fines, improve fibre surface area and improve separation of fibres from one another while preserving the fibre stiffness as much as possible. This would be achieved by gentle mechanical treatment, i. The impact of possible improvements in the three technology areas is modelled in a fourth parallel synergetic project both with regard to process modifications and with regard to material properties as strength and bulk These models are validated by means of mill scale trials
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