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Inhibition of light-induced colour reversion of wood-containing papers by means of coating
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (FSCN – Fibre Science and Communication Network)
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
Keywords [en]
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: urn:nbn:se:miun:diva-95ISBN: 978-91-85317-84-4 (print)OAI: oai:DiVA.org:miun-95DiVA, id: diva2:2061
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
List of papers
1. Light-induced yellowing of mechanical and chemimechanical pulp sheets: influence of wood raw material, process and ageing method
Open this publication in new window or tab >>Light-induced yellowing of mechanical and chemimechanical pulp sheets: influence of wood raw material, process and ageing method
2007 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 1, p. 117-123Article 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.

Keywords
High-yield pulp, Softwood, Hardwood, Light-induced, Ageing, Light sources, Lignin, Pulping processes
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-426 (URN)10.3183/NPPRJ-2007-22-01-p117-123 (DOI)000248528700017 ()2-s2.0-34247205393 (Scopus ID)4076 (Local ID)4076 (Archive number)4076 (OAI)
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: 2017-12-13Bibliographically approved
2. Discolouration of mechanical and chemimechanical pulps: influence of wood raw material, process and ageing method
Open this publication in new window or tab >>Discolouration of mechanical and chemimechanical pulps: influence of wood raw material, process and ageing method
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 1, p. 14-18Article in journal (Refereed) Published
Abstract [en]

The change in colour of a wide range of unbleached and bleached high-yield pulps was assessed using the CIELAB colour system. The influence of ageing method, pulping process and wood raw material is discussed.

National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-427 (URN)10.3183/NPPRJ-2008-23-01-p014-018 (DOI)000255491400002 ()2-s2.0-50949095750 (Scopus ID)5162 (Local ID)5162 (Archive number)5162 (OAI)
Available from: 2008-11-13 Created: 2008-11-13 Last updated: 2017-12-13Bibliographically approved
3. A novel method of studying the ability of coating layer to retard the photo-yellowing of the base paper
Open this publication in new window or tab >>A novel method of studying the ability of coating layer to retard the photo-yellowing of the base paper
Show others...
2007 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 3, p. 343-349Article in journal (Refereed) Published
Abstract [en]

A method was developed which made it possible to study the reflectance/transmittance of thin coating layers and to link this to the inhibition of the light-induced yellowing. The ability of a coating layer to retard the photo-yellowing of a hydrogen-peroxide-bleached birch chemithermomechanical pulp (CTMP) is exemplified using this method. It is shown that the repeatability of the model system is excellent, even for coat weights below 10 g/m2. Furthermore, the transmittance in the UV-region is strongly correlated with the coating layers ability to protect the birch CTMP against photo-yellowing.

Keywords
High-yield pulp, CTMP, Birch, Coating, Pigments, Titanium dioxide, Light-induced, Ageing, Kaolin, Calcium carbonate, Optical brightening agent
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-428 (URN)10.3183/NPPRJ-2007-22-03-p343-349 (DOI)000250025000009 ()2-s2.0-34948901794 (Scopus ID)4077 (Local ID)4077 (Archive number)4077 (OAI)
Available from: 2008-11-13 Created: 2008-11-13 Last updated: 2017-12-13Bibliographically approved
4. Inhibition of light-induced brightness reversion of high-yield pulps: the UV-screening properties of coating layers containing kaolin or calcium carbonate pigments
Open this publication in new window or tab >>Inhibition of light-induced brightness reversion of high-yield pulps: the UV-screening properties of coating layers containing kaolin or calcium carbonate pigments
2007 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 3, p. 350-355Article in journal (Refereed) Published
Abstract [en]

A newly developed method making it possible to study the reflectance/transmittance of thin coating layers and to link this to the inhibition of the light-induced yellowing, was used to describe the photo-stabilising properties of different types of commercial kaolin and calcium carbonate pigments. A base paper produced from a hydrogen-peroxide-bleached birch chemithermomechanical pulp (CTMP) was used throughout the study.The transmittance of the coating layers in the UV-region (300-385 nm) was found to be very low (below 1.0% at coat weights < 5g/m2) for all of the tested pigments, it strongly depends on the coat weight especially for coat weights below 10 g/m2. The kaolin pigments examined were found to be better in inhibiting the brightness reversion compared to the calcium carbonate pigments, even though the differences between the pigment types were only a few brightness units. The coating layer was, however, able to conceal some of the colour formed through the light-induce brightness reversion. For example, a coating layer consisting of kaolin pigments (coat weight of 15.6 g/m2) could conceal about 30% of the discoloration of the CTMP base paper.

Keywords
High-yield pulp, CTMP, Birch, Coating, Pigments, Kaolin, Calcium carbonate, Light-induced, Ageing
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-429 (URN)10.3183/NPPRJ-2007-22-03-p350-355 (DOI)000250025000010 ()2-s2.0-34948836656 (Scopus ID)4078 (Local ID)4078 (Archive number)4078 (OAI)
Available from: 2008-11-13 Created: 2008-11-13 Last updated: 2017-12-13Bibliographically approved
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