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Modifying kraft pulping to produce a softwood pulp requiring less energy in tissue paper production
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. (FORIC)
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Modification of softwood kraft pulp by the addition of either polysulfide (PS) or sodium borohydride (NaBH4) has been shown to increase the pulp yield due to a higher retention of glucomannan.  The pulps with higher yield gave a paper with higher tensile index than reference pulp, especially at lower degrees of refining. The higher yield pulps also showed a greater porosity of the fibre wall, indicating an increase in the swelling potential of the fibres. This can lead to increased fibre flexibility and increased joint strength between the fibres and to the higher handsheet tensile index. However, the swelling increase associated with the higher hemicellulose content could also make dewatering more challenging because of the higher water retention of the pulp. The results of this study show however that the positive influence of the increase in yield (fewer fibres and a more open sheet structure) dominates over the negative influence of the higher hemicellulose content on the dewatering properties, especially at lower refining energy levels. Studies simulating full-scale tissue machine dewatering conditions showed that pulps with a higher yield and a higher hemicellulose content had a higher tensile index at the same dryness. Moreover, the same dryness level was achieved in a shorter dwell-time. A given tensile index was also achieved with less refining energy.

Increasing the yield and hemicellulose content by the addition of either an oxidizing or a reducing agent in the softwood kraft pulping process thus has a potential for giving high quality fibres for tissue paper production with less refining energy and lower drying energy costs.

 

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University , 2018. , p. 40
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 137
Keywords [en]
Modifying kraft pulp, tissue dewatering, polysulfide, sodium borohydride, tensile index, hemicellulose
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:miun:diva-32833ISBN: 978-91-88527-42-4 (print)OAI: oai:DiVA.org:miun-32833DiVA, id: diva2:1182008
Presentation
2018-03-22, M102, Holmgatan 10, Sundsvall, 10:00 (English)
Opponent
Supervisors
Funder
Knowledge Foundation
Note

Vid tidpunkten för framläggningen av avhandlingen var följande delarbeten opublicerade: delarbete 2 inskickat.

At the time of the defence the following papers were unpublished: paper 2 submitted.

Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2018-02-12Bibliographically approved
List of papers
1. The effect of increased pulp yield using additives in the softwood kraft cook on the physical properties of low-grammage handsheets
Open this publication in new window or tab >>The effect of increased pulp yield using additives in the softwood kraft cook on the physical properties of low-grammage handsheets
Show others...
2017 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 3, p. 317-323Article in journal (Refereed) Published
Abstract [en]

The effect of increasing the pulp yield by the addition of sodium borohydride (NaBH4) or polysulfide (PS) in softwood kraft cooking, i.e. enhancing the retention of glucomannan, on the physical properties of low-grammage handsheets was studied. In addition to the yield improvement, an increase in tensile index was observed, especially at lower degrees of beating. These higher yield pulps showed an increase in pore volume, indicating an increased degree of swelling of the fibres. Presumably, the increased flexibility of the fibres affects the bonding strength and leads to the higher tensile index observed.

National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-31895 (URN)10.3183/NPPRJ-2017-32-03-p317-323 (DOI)000411768200001 ()
Available from: 2017-10-18 Created: 2017-10-18 Last updated: 2018-09-19Bibliographically approved
2. Dewatering properties of low grammage handsheets softwood kraft pulps modified to minimize the need for refining
Open this publication in new window or tab >>Dewatering properties of low grammage handsheets softwood kraft pulps modified to minimize the need for refining
2018 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 3, p. 397-403Article in journal (Refereed) Published
Abstract [en]

Previous paper (Rahman et al. 2017) showed that the yield of softwood kraft pulp increased by the addition of either polysulfide or sodium borohydride because of higher hemicellulose retention. An increase in hemicellulose content can make dewatering more difficult as WRV of the pulp increases, but instead, an overall increase in pulp yield could improve dewatering as a sheet of a certain weight will contain fewer fibres, giving a more open sheet structure. It was therefore of interest to measure the dewatering properties of low grammage handsheets (20 g/m2) under conditions mimicking the tissue paper machine dewatering processes, and sheet strength properties, WRV, °SR and fibre dimensions were also studied. The results showed that the positive influence of overall yield increase dominated over the negative influence of an increase in hemicellulose content on the dewatering properties, particularly at lower refining energy levels. Moreover, higher yield and higher hemicellulose content pulps had a higher tensile index at the same dryness. A given tensile index was achieved with less refining energy. The results indicate that increased yield and hemicellulose content by modification of the kraft pulping process will result in a pulp with a potential to improve tissue paper quality.

Keywords
dwell time, hemicellulose, refining, solid content, suction box dewatering, tensile index, thermoporosimetry, water retention value
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-32836 (URN)10.1515/npprj-2018-3037 (DOI)2-s2.0-85052642839 (Scopus ID)
Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2018-10-03Bibliographically approved

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Rahman, Hafizur

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