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Light-induced yellowing of mechanical and chemimechanical pulp sheets: influence of wood raw material, process and ageing method
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
2007 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 1, 117-123 p.Article in journal (Refereed) Published
Abstract [en]

The light-induced brightness reversion of different types of unbleached and bleached high-yield pulps was studied under both accelerated and long-term ambient light-induced ageing conditions. It was found that accelerated ageing conditions that mimic indoor daylight exposures overestimate the yellowing tendencies of hardwood high-yield pulps (especially aspen pulps) compared to long-term ambient aging with no indirect sunlight present. It was, however, possible to predict the yellowing characteristics of softwood high-yield pulps. The lignin content of the pulps was found to be strongly correlated with the degree of photo-yellowing in the case of long-term ambient light-induced ageing. The presence of small amounts of birch chemithermomechanical pulp (CTMP) in a fine paper furnish resulted in extensive light-induced discoloration. The extent of photo-yellowing was found to be nearly linearly related to the amount of birch CTMP in the paper.

Place, publisher, year, edition, pages
2007. Vol. 22, no 1, 117-123 p.
Keyword [en]
High-yield pulp, Softwood, Hardwood, Light-induced, Ageing, Light sources, Lignin, Pulping processes
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-426DOI: 10.3183/NPPRJ-2007-22-01-p117-123ISI: 000248528700017Scopus ID: 2-s2.0-34247205393Local ID: 4076OAI: oai:DiVA.org:miun-426DiVA: diva2:2056
Note

Erratum: Light-induced yellowing of mecanical and chemimecanical pulp sheets - Influence of wood raw material, process and aging method (Nordic Pulp and Paper Research Journal (2007) 22:1 (122)) Page 275

ScopusID: 2-s2.0-34547245485

Available from: 2008-11-13 Created: 2008-11-13 Last updated: 2016-10-05Bibliographically approved
In thesis
1. Inhibition of light-induced colour reversion of wood-containing papers by means of coating
Open this publication in new window or tab >>Inhibition of light-induced colour reversion of wood-containing papers by means of coating
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main purpose of this thesis was to find ways to maintain a low level of light‐induceddiscolouration at an increased addition of mechanical and chemimechanical pulps in coated highqualityfine paper and magazine paper grades. Current technology allows the production of highyieldpulps such as thermomechanical and chemimechanical pulps with properties suitable formanufacturing high‐quality paper or paperboard with a low basis weight. Coating of woodcontainingpaper will probably be necessary for photo‐stability reasons if lignin‐containing pulps areto be used as the main fibre furnish in long‐life and high‐value products.In order to find the most suitable pulp for this purpose, light‐induced discolouration of a variety ofpaper samples from unbleached and bleached softwood and hardwood pulps was studied under bothaccelerated and long‐term ambient light‐induced ageing conditions. Hardwood high‐yield pulps,especially aspen pulps, were proven to be more photo‐stable compared to softwood pulps. Hardwoodpulps should therefore be the first choice for applications where a high permanence is desirable.Evaluating ageing characteristics using the CIELAB colour system showed that accelerated ageingconditions tend to mainly increase the b* value and decrease the L* value (i.e. yellow the pulp),whereas long‐term ambient ageing also increases the a* value, which makes the pulp more reddish.A new method for studying the influence of the UV‐screening properties of coating layers on abase paper was developed, and used to investigate the effect of pigment, pigment size distribution,binder and UV‐absorbing additives. The coat weight and pigment type were found to be the mostimportant factors for reducing the transmittance of UV‐radiation. Coating colours containing kaolinpigments had a lower UV‐transmittance than calcium carbonate pigments. Of the calcium carbonates,precipitated calcium carbonates were better than ground calcium carbonates and the difference wasgreater at higher coat weights. The particle size distribution should preferable be narrow. When thebest pigment (bleached kaolin) and the best binder (styrene butadiene latex) were combined withtitanium dioxide, the UV‐transmittance could be reduced by about 90% at a coat weight of ~10 g/m2.At a coat weight close to 20 g/m2, the transmittance was close to zero. This shows that it is possible tomore or less fully protect a double coated base paper from harmful UV‐radiation, when the coatinglayer has an optimum composition for that purpose. A prerequisite to reach so far is that the coatinglayer has an even coat weight.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2008
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 44
Keyword
High-yield pulp, CTMP, birch, light-induced, ageing, photo-stabilising, lignin, coating, pigment, kaolin, calcium carbonate, titanium dioxide, binder, FWA
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-95 (URN)978-91-85317-84-4 (ISBN)
Public defence
2008-01-25, O102, Mittuniversitetet, Sundsvall, 10:00 (English)
Opponent
Supervisors
Available from: 2008-02-14 Created: 2008-02-14 Last updated: 2013-12-18Bibliographically approved
2. The Photostabilising Effect of Coating Layers on CTMP‐based Papers
Open this publication in new window or tab >>The Photostabilising Effect of Coating Layers on CTMP‐based Papers
2006 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2006
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 13
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-9104 (URN)
Presentation
(English)
Available from: 2009-06-08 Created: 2009-06-08 Last updated: 2009-07-13Bibliographically approved

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