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Sheet properties of high yield pulps related to different pressing and drying conditions - part I
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. (FSCN – Fibre Science and Communication Network)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Responsible organisation
2005 (English)In: International Mechanical Pulping Conference: IMPC 2005, Oslo, Norway, 7-9 June 2005, Oslo: Pappersindustriens tekniske forening , 2005, 344-348 p.Conference paper, (Other academic)
Abstract [en]

The objective of this investigation was to evaluate how physical properties of laboratory sheets, made from different thermomechanical and chemithermomechanical pulps, depend on the pressure and temperature levels during pressing and drying. Sheet were formed from long fibre fractions, defined as the pulp retained on a 50 mesh wire in a Britt Dynamic Drainage Jar, and pressed and dried according to a number of different pressure and temperature settings. The results showed that there were large differences in the sheet properties depending on what type of method that were used for pressing and drying. High freeness pulps were more sensitive to the type of method used for pressing and drying than low freeness pulps. The results indicate that the difference in sheet properties between ISO and Rapid Köthen sheets might be explained by the fact that ISO sheets are only wet pressed, the fibres are then allowed to spring back when pressure is released whereas the fibres in Rapid Köthen sheets are locked in their positions as the sheets are pressed and dried till over dry.

Place, publisher, year, edition, pages
Oslo: Pappersindustriens tekniske forening , 2005. 344-348 p.
Keyword [en]
Mechanical pulps, pressing, drying
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-3823Local ID: 4487OAI: oai:DiVA.org:miun-3823DiVA: diva2:28855
Available from: 2008-09-30 Created: 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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