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Energy efficient high quality CTMP for paperboard
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (FSCN – Fibre Science and Communication Network)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
2008 (English)In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 34, no 2, 98-106 p.Article in journal (Refereed) Published
Abstract [en]

This paper discusses the relationship between bulk and internal bond strength in paper sheets and their dependency on fibre length, fibre flexibility and fibre surface properties. It also discusses an interesting process concept for manufacturing of energy efficient high quality CTMP for paperboard. Post-refining pilot trials of spruce HTCTMP with an initial freeness of 740 ml were carried out at Metso Paper R&D in Sundsvall, Sweden. Both gentle high consistency and severe low consistency post-refining were performed. High consistency post-refining, at high energy input, gave freeness levels below 70 ml and still preserved the fibre length. These fibres were characterised by a very high flexibility giving sheets with a tensile index as high as 64 kNm/kg. Long fibres can however cause formation problems on a board machine which in turn can lead to poor surface properties, hence shorter fibres are from that perspective desirable. The low consistency post-refining resulted in a rapid drop in freeness due to fibre cutting. This was achieved at an extremely low specific energy input, which probably preserved most of the original fibre stiffness. In spite of this low energy input it was possible to reach the same Z-strength at a given bulk, as for the high consistency post-refined pulp. This implied that high bulk at certain internal bond strength could be achieved with stiff fibres even though the content of long fibres was low. Energy efficient low consistency post-refining of spruce HTCTMP yields high quality pulp at a total energy input of ~800 kWh/admt and is an interesting process concept for production of pulps intended for paperboard.

Place, publisher, year, edition, pages
2008. Vol. 34, no 2, 98-106 p.
Keyword [en]
CTMP, board, LC refining, HC refining, Acoustic Emission
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-6354ISI: 000261815400004Scopus ID: 2-s2.0-56649086697Local ID: 4939OAI: oai:DiVA.org:miun-6354DiVA: diva2:31393
Available from: 2008-12-07 Created: 2008-12-07 Last updated: 2009-06-08Bibliographically approved
In thesis
1. The influence of fibre characteristics on bulk and strength properties of TMP and CTMP from spruce
Open this publication in new window or tab >>The influence of fibre characteristics on bulk and strength properties of TMP and CTMP from spruce
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is intended to contribute to an increased knowledge about the influence of fibre characteristics on bulk and strength properties of thermomechanical pulp (TMP) and chemithermomechanical pulp (CTMP) from spruce. It deals with laboratory sheet properties and how they are affected by the conditions during pressing and drying, e.g. pressure, temperature and what dryness level the sheets have once pressing and drying is terminated. Further on it deals with how sheet properties depend on fibre properties, such as fibre length, fibre flexibility and fibre surface characteristics. The thesis is part of a long term project with the goal of increasing bending stiffness of paperboard, hence bulk and internal bond strength properties are of main interest. Apart from standard methods (ISO, TAPPI and Rapid Köthen), sheets have been pressed and dried in a modified Rapid Köthen dryer which has the capacity to press the sheets at higher pressure compared to a standard Rapid Köthen dryer. The results illustrated that there are large differences in mechanical pulp sheet properties depending on how the sheets have been pressed and dried. The main factors contributing to the bulk and strength levels achieved are a combination of pressure, temperature and to what dryness level the sheets are pressed. Sheets made from stiff fibres sprung back more when only wet pressed, and appeared to be less sensitive to pressure than sheets made from flexible fibres. The situation was the other way around when sheets were pressed and dried until dry at high temperature; pulps with stiff fibres were affected more by temperature and pressure than pulps with flexible fibres. When looking at strength development with respect to what dryness level the sheets had been pressed at high temperature, the most interesting finding was that the increase in strength was not continuous, especially when looking at the Z-strength development for high freeness pulps and long fibre fractions. There was a distinct inflection of the strength-dryness curve when dryness reached a level of ~50% and the most important dryness interval for internal strength development was found between 50 and 80%. This result combined with the fact that most paper and board machines only press the sheet to ~50% dryness, before the sheet is fed into the drying section, show that much of the inherent strength potential of mechanical pulps is unexploited. There are commercial techniques for pressing to higher dryness levels available, such as Condebelt drying and press drying. These techniques have however only been implemented to a limited extent. Further research on pressing to higher dryness levels will in the future be continued at FSCN at Mid Sweden University. Pilot refining trials with HTCTMP from spruce showed that densification and strength development were achieved by two different mechanisms: by making fibres flexible with gentle high consistency refining (HC refining) or by reducing fibre length with intense low consistency refining (LC refining). It was found that a high bulk at a very high Z-strength was achieved with LC refining even though the fibre length was reduced and at extremely low energy input. The results showed that fibres with extremely high content of sulphonated lignin on surfaces with low degree of fibrillation bond well as long as the surfaces get into contact during pressing and drying. This can be achieved by either making fibres flexible or by reducing fibre length. LC post-refining of spruce HTCTMP was found to be a very interesting process concept for production of high quality pulps intended for paperboard at a very low total energy input of ~800 kWh/admt.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2007
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 23
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-9112 (URN)978-91-85317-52-3 (ISBN)
Presentation
(English)
Available from: 2009-06-08 Created: 2009-06-08 Last updated: 2009-07-13Bibliographically approved

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