| Fractionation of thermomechanical pulp in pressure screening: An experimental study on the classification of fibres with slotted screen plates | ||
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Although advances have been made in the design of slotted pressure screens, these alone may not be selective enough to fulfil the requirements placed on pulps intended for the production of high quality papers. Slotted pressure screens should probably be used together with hydrocyclones and perhaps holed pressure screens, because fibre classification is based on different mechanisms in these devices. Although these processes have already been examined, the field is still open for new systematic research. The fractionation ability of the processes in relation to certain fibre properties and their responses in terms of paper quality should be tested under standardised conditions. Among other things, the role of fibre flexibility in the separation mechanism needs further investigation. With a view to enhancing the capacity, efficiency and selectivity of fractionation, the optimum interconnections between the unit processes mentioned above and the proper operating conditions for them would be issues worth taking up in future research. In fact, the balancing of the process as a whole, i.e. pulping, fractionation and further mechanical or chemical treatment of the fractions, is in need of re-evaluation.
An interesting research topic could arise from the coarseness index determined by image analysis in the manner of the Kajaani FiberLab. This research provided promising but brief results regarding its potential for characterising fibre properties. It would be worth investigating the method more closely. Issues that would need to be considered would include:
the correlation between the coarseness index and the papermaking potential of mechanical pulps,
the response of the coarseness index to changes in raw material, defibration and refining conditions,
the suitability of the coarseness index for characterising mechanical pulps other than TMP, and also chemical pulps,
extensive clarification of the information contained in the distributions of the coarseness index and fibre length.