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Limitations of the efficiency of fluorescent whitening agents in uncoated paper
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (DPC)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. (DPC)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.ORCID iD: 0000-0002-0529-1009
Univ Eastern Finland, Dept Math & Phys, FI-80101 Joensuu, Finland.
2011 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 3, p. 319-328Article in journal (Refereed) Published
Abstract [en]

The fluorescence efficiency of one fluorescent whitening agent (FWA) inuncoated and unfilled paper was characterised at different FWA concentrations. An extendedKubelka-Munk model proposed earlier by several authors was applied to quantify the effect onCIE whiteness of absorption of the FWA in the visible spectrum . At high FWA concentration,chemical interactions slightly modify the emission spectrum of the FWA, and the quantumefficiency depends on the FWA concentration. This effect has however a negligible effect onthe CIE whiteness for FWA concentrations used in practice. The overlap of the absorption andemission bands of the FWA is shown to be the main cause of greening (a shift of thechromaticity towards green) and saturation of the fluorescence effect. With increasing FWAconcentration, the positive effect of fluorescence is neutralised by the reduction of thereflectance factor in the violet-blue region of the spectrum induced by a significant absorptionof the FWA in that region.

Place, publisher, year, edition, pages
2011. Vol. 26, no 3, p. 319-328
Keywords [en]
Fluorescence, paper, fluorescence whitening agents, greening, whiteness
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:miun:diva-12142DOI: 10.3183/NPPRJ-2011-26-03-p319-328ISI: 000294524200010Scopus ID: 2-s2.0-80052349477OAI: oai:DiVA.org:miun-12142DiVA, id: diva2:357562
Projects
PaperOptAvailable from: 2010-10-18 Created: 2010-10-18 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Whiteness and Fluorescence in Paper: Perception and Optical Modelling
Open this publication in new window or tab >>Whiteness and Fluorescence in Paper: Perception and Optical Modelling
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is about modelling and predicting the perceived whiteness of plain paper from the paper composition, including fluorescent whitening agents. This includes psycho-physical modelling of perceived whiteness from measurable light reflectance properties, and physical modelling of light scattering and fluorescence from the paper composition.

Existing models are first tested and improvements are suggested and evaluated. The standardised and widely used CIE whiteness equation is first tested on commercial office papers with visual evaluations by different panels of observers, and improved models are validated. Simultaneous contrast effects, known to affect the appearance of coloured surfaces depending on the surrounding colour, are shown to significantly affect the perceived whiteness. A colour appearance model including simultaneous contrast effects  (CIECAM02-m2), earlier tested on coloured surfaces, is successfully applied to perceived whiteness. A recently proposed extension of the Kubelka-Munk light scattering model including fluorescence for turbid media of finite thickness is successfully tested for the first time on real papers.

It is shown that the linear CIE whiteness equation fails to predict the perceived whiteness of highly white papers with distinct bluish tint. This equation is applicable only in a defined region of the colour space, a condition that is shown to be not fulfilled by many commercial office papers, although they appear white to most observers. The proposed non-linear whiteness equations give to these papers a whiteness value that correlates with their perceived whiteness, while application of the CIE whiteness equation outside its region of validity overestimates perceived whiteness.

It is shown that the quantum efficiency of two different fluorescent whitening agents (FWA) in plain paper is rather constant with FWA type, FWA concentration, filler content, and fibre type. Hence, the fluorescence efficiency is essentially dependent only on the ability of the FWA to absorb light in its absorption band.  Increased FWA concentration leads accordingly to increased whiteness. However, since FWA absorbs light in the violet-blue region of the electromagnetic spectrum, the reflectance factor decreases in that region with increasing FWA amount. This violet-blue absorption tends to give a greener shade to the paper and explains most of the observed greening and whiteness saturation at larger FWA concentrations. A red-ward shift of the quantum efficiency is observed with increasing FWA concentration, but this is shown to have a negligible effect on the whiteness value.

The results are directly applicable to industrial applications for better instrumental measurement of whiteness and thereby optimising the use of FWA with the goal to improve the perceived whiteness. In addition, a modular Monte Carlo simulation tool, Open PaperOpt, is developed to allow future spatial- and angle-resolved particle level light scattering simulation.

 

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2010. p. 94
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 47
Keywords
Paper Whiteness, Fluorescence Whitening Agents, Kubelka-Munk, light scattering, paper industry applications, Colour Appearance Models, CIECAM02, Monte Carlo
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:miun:diva-12143 (URN)978-91-86073-97-8 (ISBN)
Presentation
2010-11-09, O111, Mid Sweden University, Sundsvall, 20:30 (English)
Opponent
Supervisors
Projects
PaperOpt
Available from: 2010-10-19 Created: 2010-10-18 Last updated: 2010-10-19Bibliographically approved
2. Whiteness and Fluorescence in Layered Paper and Board: Perception and Optical Modelling
Open this publication in new window or tab >>Whiteness and Fluorescence in Layered Paper and Board: Perception and Optical Modelling
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is about modelling and predicting the perceived whiteness of plain paper from the paper composition, including fluorescent whitening agents. This involves psychophysical modelling of perceived whiteness from measurable light reflectance properties, and physical modelling of light scattering and fluorescence from the paper composition.

Existing models are first tested and improvements are suggested and evaluated. A colour appearance model including simultaneous contrast effects (CIECAM02-m2), earlier tested on coloured surfaces, is successfully applied to perceived whiteness. An extension of the Kubelka-Munk light scattering model including fluorescence for turbid media of finite thickness is successfully tested for the first time on real papers. It is extended to layered constructions with different layer optical properties and modified to enable parameter estimation with conventional d/0° spectrophotometers used in the paper industry. Lateral light scattering is studied to enable simulating the spatially resolved radiance factor from layered constructions, and angle-resolved radiance factor simulations are performed to study angular variation of whiteness.

It is shown that the linear CIE whiteness equation fails to predict the perceived whiteness of highly white papers with distinct bluish tint. This equation is applicable only in a defined region of the colour space, a condition that is shown to be not fulfilled by many commercial office papers, although they appear white to most observers. The proposed non-linear whiteness equations give to these papers a whiteness value that correlates with their perceived whiteness, while application of the CIE whiteness equation outside its region of validity overestimates perceived whiteness.

It is shown that the fluorescence efficiency of FWA is essentially dependent only on the ability of the FWA to absorb light in its absorption band. Increased FWA concentration leads accordingly to increased whiteness. However, since FWA absorbs light in the violet-blue region of the electromagnetic spectrum, the reflectance factor decreases in that region with increasing FWA amount. This violet-blue absorption tends to give a greener shade to the paper and explains most of the observed greening and whiteness saturation at larger FWA concentrations. A red-ward shift of the quantum efficiency is observed with increasing FWA concentration, but this is shown to have a negligible effect on the whiteness value. The results are directly applicable to industrial applications for better instrumental measurement of whiteness and thereby optimising the use of FWA with the goal to improve the perceived whiteness.

Place, publisher, year, edition, pages
Sundsvall: annat förlag, 2012. p. 158
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 138
Keywords
Whiteness, Perception, Colour Appearance Modelling, Paper Optics, Light Scattering, Fluorescence, Lateral Light Scattering, White-Top Mottle, Kubelka-Munk, Radiative Transfer
National Category
Paper, Pulp and Fiber Technology Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:miun:diva-17782 (URN)978-91-87103-50-6 (ISBN)
Public defence
2013-01-23, Sal 0111, Mittuniversitetet, Holmgatan 10, Sundsvall, 10:31 (English)
Opponent
Supervisors
Projects
PaperOpt
Funder
The Knowledge FoundationVinnova
Available from: 2012-12-20 Created: 2012-12-17 Last updated: 2012-12-20Bibliographically approved

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Gustafsson Coppel, LudovicAndersson, MattiasEdström, Per

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