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Colour changes in birch and beech during kilndrying
Linköping University.
2001 (English)In: Proceedings of the 7th International IUFRO Wood DryingConference, 2001, 300-305 p.Conference paper, Published paper (Refereed)
Abstract [en]

The aim of this study was to investigate the colour responses of Silver Birch (Betula pendula Roth.) and Beech(Fagus sylvatica L.) during conventional kiln-drying at industrial used conditions. The response of dryingtemperature, relative humidity, initial moisture content and board thickness on wood colour was investigated in two24 factorial designed experiments. The method was used to investigate and rank the effects of the variables and allpossible combinations of the variables with a minimum of tests. A total number of 224 clear green sapwood samplesdivided in to 32 groups were kiln-dried below 20% in a climate chamber, followed by room climate drying toapproximately 8%. Colour measurements were conducted on dry planed samples using a photoelectric colorimeterand results were expressed in the CIE L* (lightness) C* (chroma) h (hue) colour space. A comparison was also madewith 32 samples dried in room climate from green to 8%, differences were calculated and expressed as CIE (ΔE*ab)effects. The factorial experiments used high and low level for investigating the variables: temperature (60/30C),relative humidity (82/62%), initial moisture content (green/30%) and wood thickness (16/10 mm).Experimental results showed that drying temperature is the most important factor for the colour responses in theinvestigated intervals for both birch and beech. The second most important factor, for both species, was thickness ofthe wood. Relative humidity was found to be the third most important factor. Both species reacted in a similar way toincreasing temperature, thicker dimensions and high relative humidity. The wood colour became darker, moresaturated and redder compared to the reference material. The colour response effects were larger on birch comparedto beech.

Place, publisher, year, edition, pages
2001. 300-305 p.
National Category
Other Materials Engineering
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
URN: urn:nbn:se:lnu:diva-29003OAI: oai:DiVA.org:lnu-29003DiVA: diva2:650913
Conference
7th International IUFRO Wood Drying Conference, Tsukuba, Japan, July 9–13
Available from: 2013-09-24 Created: 2013-09-24 Last updated: 2013-10-08Bibliographically approved
In thesis
1. Colour Response in Drying of Nordic Hardwoods
Open this publication in new window or tab >>Colour Response in Drying of Nordic Hardwoods
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Colour and appearance of hardwood are of great importance for the interiorand furniture industry. The widespread use of transparent surface treatmentand a fashion that prescribe light colour on many species, means that deviationfrom the ideal have considerable impact on the industrial operations. Kilndrying is generally regarded as the process that has the greatest impact on thecolour of Nordic hardwood species. The lack of satisfactory explanation modelsfor many types of discoloration, however, complicates the control of the dryingprocess.This thesis is an attempt to increase the knowledge of which factors thatcontrol the appearance of some commonly found discolorations associated withdrying of beech, birch and oak. The main focus is on convection drying but alsothe influence of timber storage, pre-steaming and press drying has beeninvestigated for individual species. The studies have been conducted ascomparative studies based on design of experiments in which the colour wasdetermined using a colorimeter.Results show that reddish and dark discoloration of beech and birch duringconvective drying is mainly dependent on the temperature and time of exposurewhen the local moisture content exceeds the fibre saturation point. Theconversion of naturally occurring substances in birch into coloured compoundsis not due to active precursors created at high moisture content levels duringthe subsequent drying at low moisture content levels. Interior grey stain inbeech is caused by slow initial drying at low temperatures. Log storage in coldwinter and spring climate does not cause discoloration in beech. Birch becomeslighter when press-dried at high temperatures, resulting in a colour comparableto that of traditionally kiln dried wood. Steaming of oak before kiln dryingreduce the presence of brown discoloration, a general darkening of the woodoccurs at temperatures above 50°C.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2013. 78 p.
Series
Linnaeus University Dissertations, 148/2013
Keyword
beech, Betula pendula, birch, CIELAB, discolouration, drying, Fagus sylvatica, log storage, oak, press drying, wood colour, Quercus robur
National Category
Other Materials Engineering
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-29011 (URN)978-91-87427-52-7 (ISBN)
Public defence
2013-10-18, M1088, Linnéuniversitetet, Växjö, 10:00 (English)
Opponent
Supervisors
Available from: 2013-10-08 Created: 2013-09-24 Last updated: 2016-08-22Bibliographically approved

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Stenudd, Stefan

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  • apa
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