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Influence of Pre-heating on Brown Discoloration whenDrying Oak Heartwood
Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
2005 (English)In: Proceedings of the 9th InternationalIUFRO Wood Drying Conference, 2005, p. 127-130Conference paper, Published paper (Refereed)
Abstract [en]

General loss of lightness and brown discoloration of oak heartwood are major problems to the European woodindustry. In this investigation has the effect of pre-heating timber to 100°C prior to conventional kiln drying at 15, 35and 50°C been studied. Pre-heating significantly reduced the level of local brown discolouring streaks and spots aswell as slightly increasing the general lightness. Drying temperature has a major impact on the development of localbrown discoloration as higher temperature cause more discoloration. The thermal effect on general lightness is lessdistinct and a turning point seams to exist in the 40-50°C range above which the lightness is distinctly reduced.

Place, publisher, year, edition, pages
2005. p. 127-130
National Category
Other Materials Engineering
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
URN: urn:nbn:se:lnu:diva-29007OAI: oai:DiVA.org:lnu-29007DiVA, id: diva2:650927
Conference
9th International IUFRO Wood Drying Conference, Nanjing, China, August 21–26.
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. p. 78
Series
Linnaeus University Dissertations ; 148/2013
Keywords
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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CiteExportLink to record
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Citation style
  • apa
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