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Strategies to reduce heat-induced darkening for enhanced bleachability of mechanical pulps
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. SCA R and D Centre AB, SE-851 21 Sundsvall, Sweden. (FSCN)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. AkzoNobel Pulp and Performance Chemicals, SE-445 80 Bohus, Sweden. (FSCN)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. (FSCN)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.ORCID iD: 0000-0002-5543-2041
2014 (English)In: Appita journal, ISSN 1038-6807, Vol. 67, no 1, p. 50-57Article in journal (Refereed) Published
Abstract [en]

Under mechanical pulping conditions, elevated temperature initiates reactions in the wood constituents resulting in the formation of coloured structures. In an attempt to reduce the formation of colour, a number of additives have been examined to assess their ability to inhibit heat-induced darkening of a Norway spruce (Picea abies) stone groundwood (SGW) pulp. SGW pulp was used as a model pulp with the purpose of imitating a thermomechanical pulp (IMP). The heat-treated SGW pulp, both with and without additives present, was subsequently bleached with 4.5% hydrogen peroxide at high pulp consistency and with varying alkali charges in order to examine the hydrogen peroxide bleachability of such pulps. Heat treatment at 170 °C resulted in a loss of brightness of about 4% ISO after heating for 60 seconds. The reduction in brightness could only partly be regained through high consistency hydrogen peroxide bleaching; the SGW pulp displayed a brightness of 83.7% ISO whereas the heat-treated SGW pulp reached a brightness of 80.4% ISO. Heat treatment with a low addition rate (1 %) of alkaline hydrogen peroxide, sodium bisulfite or sodium sulfite, with a subsequent hydrogen peroxide bleaching stage, resulted in an improved bleached brightness of about 81.6% ISO, i.e. the loss of brightness due to heat was still approximately 2% ISO. Sodium borohydride (1 %) did not suppress the thermal darkening but improved the bleached brightness by approximately 2% ISO compared to the heat-treated SGW pulp and resulted in a brightness of 82.6% ISO. Addition of a chelating agent (DTPA, 0.11 and 0.45%) and the radical scavengers phthalic hydrazide (1 %) and 1 -hexanol (1 %) suppressed the heat-induced darkening somewhat but did not improve the hydrogen peroxide bleachability to any noticeable extent. Addition of citric acid (0.6%) did not suppress the thermal darkening and resulted in impaired bleachability.

Place, publisher, year, edition, pages
2014. Vol. 67, no 1, p. 50-57
Keywords [en]
Bleaching, Brightness, Hydrogen peroxide, Light absorption, Light scattering, Mechanical pulps, Temperature
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-20980ISI: 000342037800014Scopus ID: 2-s2.0-84901988527OAI: oai:DiVA.org:miun-20980DiVA, id: diva2:684732
Available from: 2014-01-08 Created: 2014-01-08 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Improved hydrogene peroxide bleaching of mechanical pulps through fundamental understanding of the influence of heat, iron, fines and chemical treatment on chromophore content
Open this publication in new window or tab >>Improved hydrogene peroxide bleaching of mechanical pulps through fundamental understanding of the influence of heat, iron, fines and chemical treatment on chromophore content
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2013. p. 76
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 170
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-20982 (URN)978-91-87557-16-3 (ISBN)
Supervisors
Available from: 2014-01-08 Created: 2014-01-08 Last updated: 2014-01-08Bibliographically approved

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Karlsson, AnettePaulsson, MagnusEngstrand, PerHedenström, Erik

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