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Licensed Unlicensed Requires Authentication Published by De Gruyter August 14, 2013

Modeling the influence of thermal modification on the electrical conductivity of wood

  • Christian Brischke EMAIL logo , Kathrin A. Sachse and Christian R. Welzbacher
From the journal Holzforschung


A model has been developed aiming at the description of the effect of thermal modification on the electrical conductivity of wood. The intention was to calculate the moisture content (MC) of thermally modified timber (TMT) through the parameters electrical resistance R, wood temperature T, and CIE L*a*b* color data, which are known to correlate well with the intensity of a heat treatment. Samples of Norway spruce (Picea abies Karst.) and beech (Fagus sylvatica L.) samples were thermally modified in laboratory scale at 11 different heat treatment intensities and the resistance characteristics of the samples were determined. Within the hygroscopic range, a linear relationship between the resistance characteristics and the mass loss (ML) through the heat treatment was established. Based on this, a model was developed to calculate MC from R, T, and ML. To validate this model, color values of 15 different TMTs from industrial production were determined for estimation of their ML and fed into the model. MC of the 15 arbitrarily heat-treated TMTs was calculated with an accuracy of ±3.5% within the hygroscopic range. The material-specific resistance characteristics based on experimental data led to an accuracy of ±2.5%.

Corresponding author: Christian Brischke, Faculty of Architecture and Landscape Sciences, Institute of Vocational Sciences in the Building Trade, Herrenhäuser Str. 8, D-30419 Hannover, Germany, e-mail:


Akyildiz, M.H., Ates, S. (2008) Effect of heat treatment on equilibrium moisture content (EMC) of some wood species in Turkey. Res. J. Agric. Biol. Sci. 4:660–665.Search in Google Scholar

Altgen, M., Welzbacher, C.R., Humar, M., Willems, W., Militz, H. (2012) Bestimmung der Behandlungsqualität von Thermoholz mithilfe von Schnellverfahren. Teil 1: Elektronenspin-Resonanz-Spektroskopie. Holztechnologie 53:44–49.Search in Google Scholar

Bekhta, P., Niemz, P. (2003) Effect of high temperature on the change in color, dimensional stability and mechanical properties of spruce. Holzforschung 57:539–546.10.1515/HF.2003.080Search in Google Scholar

Brischke, C., Welzbacher, C.R., Brandt, K., Rapp, A.O. (2007) Quality control of thermally modified timber: interrelationship between heat treatment intensities and CIE L*a*b* color data on homogenized wood samples. Holzforschung 61:19–22.10.1515/HF.2007.004Search in Google Scholar

Brischke, C., Rapp, A.O., Bayerbach, R. (2008) Measurement system for long-term moisture recording with internal conductively glued electrodes. Build. Environ. 43:1566–1574.Search in Google Scholar

Brown, J. H., Davidson, R. W., Skaar, C. (1963) Mechanism of electrical conduction in wood. For. Prod. J. 13:455–459.Search in Google Scholar

Burmester, A. Formbeständigkeit von Holz gegenüber Feuchtigkeit – Grundlagen und Vergütungsverfahren. BAM-Bericht Nr. 4, Bundesanstalt für Materialforschung, Berlin, 1970.Search in Google Scholar

Burmester, A. (1981) Dimensional stabilisation of wood. Document No. IRG/WP 3171, International Research Group on Wood Preservation, Sarajevo, Yugoslavia.Search in Google Scholar

CEN (2007) CEN/TS 15679: Thermally modified timber – definitions and characteristics. European Committee for Standardisation, Brussels, Belgium.Search in Google Scholar

Davidson, R.W. (1958) The effect of temperature on the electrical resistance of wood. For. Prod. J. 8:160–164.Search in Google Scholar

Du, Q.P. Einfluss holzartenspezifischer Eigenschaften auf die elektrische Leitfähigkeit wichtiger Handelshölzer. Doctoral thesis. University Hamburg, Department Biology, Hamburg, 1991.Search in Google Scholar

Du, Q.P., Geissen, A., Noack, D. (1991) The effect of temperature on the electrical resistance of wood. Holz Roh- Werkst. 49:305–311.10.1007/BF02663796Search in Google Scholar

Forsén, H., Tarvainen, V. (2000) Accuracy and functionality of hand held wood moisture meters. VTT Publications 420. VTT Technical Research Centre of Finland, Espoo.Search in Google Scholar

Fredriksson, M. Methods for determination of moisture conditions in wood exposed to high moisture levels. Licentiate thesis. Lund University, Division of Building Materials, Lund, 2010.Search in Google Scholar

Gellerich, A., Bollmus, S., Militz, H., Krause, A. (2012) Influence of moisture conditions on the colonisation of modified wood by sapstaining fungi during outside weathering. In: Proceedings of the 6th European Conference on Wood Modification, Ljubljana, Slovenia, 17–18 September 2012. Eds. Jones, D., Militz, H., Petrič, M., Pohleven, F., Humar M., Pavlič, M. pp. 127–135.Search in Google Scholar

Hearle, J.W.S. (1953) The electrical resistance of textile materials. IV. Theory. J. Text. Inst. Trans. 44:177–198.Search in Google Scholar

Hofmann, T., Rétfalvi, T., Albert, L., Niemz, P. (2008) Investigation of the chemical changes in the structure of wood thermally modified within a nitrogen atmosphere autoclave. Wood Res. 53:85–98.Search in Google Scholar

Holleboom, B., Homan, W. (1998) The effect of wood preservatives on the relation between the electric resistance and moisture content in Scots pine (Pinus sylvestris L.) sapwood. Document No. IRG/WP 98-20142, International Research Group on Wood Protection, Maastricht, The Netherlands.Search in Google Scholar

James, W.L. (1968) Effect of temperature on readings of electric moisture meters. For. Prod. J. 18:23–31.Search in Google Scholar

Jones, D. (2012) Life since the European Thematic Network on Wood Modification: the first 10 years. In: Proceedings of the 6th European Conference on Wood Modification, Ljubljana, Slovenia, 17–18 September 2012. Eds. Jones, D., Militz, H., Petrič, M., Pohleven, F., Humar M., Pavlič, M. pp. 29–36.Search in Google Scholar

Krackler, V., Ammann, S., Camathias, U., Niemz, P. (2011) Untersuchungen zum Feuchteverhalten und zur Porosität von thermisch modifiziertem Holz. Bauphysik 33:374–381.10.1002/bapi.201110799Search in Google Scholar

Lin, R.T. (1967) Review of the electrical properties of wood and cellulose. For. Prod. J. 17:54–60.Search in Google Scholar

Metsä-Kortelainen, S., Antikainen, T., Viitaniemi, P. (2006) The water absorption of sapwood and heartwood of Scots pine and Norway spruce heat-treated at 170° C, 190° C, 210° C and 230° C. Eur. J. Wood Wood Prod. 64:192–197.10.1007/s00107-005-0063-ySearch in Google Scholar

Meyer, L., Brischke, C., Lampen, S.C. (2012) Electric moisture content measurements in the field to examine the performance of wood based materials. In: Proceedings of the 8th Meeting of the Northern-European Network for Wood Science & Engineering (WSE), September 13–14, 2012, Kaunas, Lithuania. Eds. Baltrušaitis, A., Ukvalbergiene, K. pp. 115–121.Search in Google Scholar

Militz, H. (2008) Processes and properties of thermally modified wood manufactured in Europe. Development of commercial wood preservatives: efficacy, environmental, and health issues. American Chemical Society, Washington, DC, 655.10.1021/bk-2008-0982.ch022Search in Google Scholar

Olek, W., Majka, J., Czajkowski, Ł;. (2013) Sorption isotherms of thermally modified wood. Holzforschung 67:193–191.10.1515/hf-2011-0260Search in Google Scholar

Paul, W. Thermische Modifizierung von Spanmaterial und Holzwerkstoffplatten zur Verbesserung ausgewählter Eigenschaften. Doctoral thesis. University Hamburg, Faculty for Mathematics, Informatics and Natural Sciences, Hamburg, 2006.Search in Google Scholar

Schnabel, T., Zimmer, B., Petutschnigg, A.J., Schonberger, S. (2007) An approach to classify thermally modified hardwoods by color. For. Prod. J. 57:105.Search in Google Scholar

Schneider, A. (1966) Der Einfluss von Wärmebehandlungen im Temperaturbereich bis 200°C und von Wasserlagerung bis 100°C auf den spektralen Remissionsgrad verschiedener Hölzer. Holz Roh- Werkst 24:542–547.10.1007/BF02610359Search in Google Scholar

Schneider, A. (1971) Untersuchungen über den Einfluss von Wärmebehandlung im Temperaturbereich von 100 bis 200°C auf Elastizitätsmodul, Druckfestigkeit und Bruchschlagarbeit von Kiefern- Splint- und Buchenholz. Holz Roh- Werkst 29:431–440.10.1007/BF02625823Search in Google Scholar

Schneider, A. (1973) Zur Konvektionstrocknung von Schnittholz bei extrem hohen Temperaturen. Zweite Mitteilung: Trocknungsschäden, Sorptions-, Farb- und Festigkeitsänderungen von Kiefern- Splint- und Buchenholz bei Trocknungstemperaturen von 110 bis 180°C. Holz Roh- Werkst 31:200–206.Search in Google Scholar

Skaar, C. Wood-water relations. Springer, Berlin, 1988.10.1007/978-3-642-73683-4Search in Google Scholar

Stamm, A.J. Wood and cellulose science. The Ronald Press Company, New York, 1964.Search in Google Scholar

Smith, W.B., Yeo, H.M., Stark, C., Morey, B., Tascioglu, C., Schneider, P., Herdman, D., Freeman, M. (2007) Use of moisture meters with treated wood. Document No. IRG/WP 07-40382, International Research Group on Wood Protection, Jackson Lake, USA.Search in Google Scholar

Tjeerdsma, B.F., Militz, H. (2006) Chemical analysis of heat-treated softwoods. Holz Roh- Werkst. 64:204–211.10.1007/s00107-005-0078-4Search in Google Scholar

Tjeerdsma, B.F., Boonstra, M., Pizzi, A., Tekely, P., Militz, H. (1998) Characterisation of thermally modified wood: molecular reasons for wood performance improvement. Eur. J. Wood Wood Prod. 56:149–153.10.1007/s001070050287Search in Google Scholar

Tjeerdsma, B.F., Stevens, M., Militz, H., Van Acker, J. (2002) Effect of process conditions on moisture content and decay resistance of hydro-thermally treated wood. Holzforsch. Holzverwert. 5:94–99.Search in Google Scholar

Vermaas, H.F. (1984) The influence of sample density on the D.C. resistance of wood. Holzforschung 38:109–132.10.1515/hfsg.1984.38.2.109Search in Google Scholar

Vernois, M. (2001) Heat treatment of wood in France – state of the art. Review on heat treatments of wood. In: Proceedings of the special seminar held in Antibes, France, 9 February 2001, Forestry and Forestry Products, France. COST Action E22, EUR 19885. Ed. Rapp, A.O. pp. 35–42.Search in Google Scholar

Walter, N. Farbänderung unterschiedlicher Holzarten unter Hitzeeinwirkung [Color response on various wood species on heat treatments]. Master thesis. Leibniz University Hannover, Faculty of Architecture and Landscape Sciences, Hannover, 2010.Search in Google Scholar

Wang, J.Y., Cooper, P.A. (2005) Effect of oil type, temperature and time on moisture properties of hot oil-treated wood. Eur. J. Wood Wood Prod. 63:417–422.10.1007/s00107-005-0033-4Search in Google Scholar

Weiland, J.J, Guyonnet R. (2003) Study of chemical modifications and fungi degradation of thermally modified wood using DRIFT spectroscopy. Holz Roh- Werkst. 61:216–220.10.1007/s00107-003-0364-ySearch in Google Scholar

Welzbacher, C.R. Verhalten von nach neuen thermischen Modifikationsverfahren behandelter Fichte und Kiefer unter besonderer Berücksichtigung der Dauerhaftigkeit gegenüber holzzerstörenden Mikroorganismen. Doctoral thesis. University Hamburg, Faculty for Mathematics, Informatics and Natural Sciences, Hamburg, 2007.Search in Google Scholar

Welzbacher, C.R., Scheiding, W. (2011) Implementation of a quality assurance system for thermally modified timber (TMT) by the Association of Central European TMT-Producers. Document No. IRG/WP 11-40558, International Research Group on Wood Protection, Queenstown, New Zealand.Search in Google Scholar

Welzbacher, C.R., Brischke, C., Rapp, A.O. (2007) Influence of treatment temperature and duration on selected biological, mechanical, physical, and optical properties of thermally modified timber (TMT). Wood Mater. Sci. Eng. 2:66–76.Search in Google Scholar

Welzbacher, C.R., Brischke, Maier, G. (2012) Influence of heat treatment intensity on the structural integrity of 14 timber species. Document No. IRG/WP 12-40586, International Research Group on Wood Protection, Kuala Lumpur, Malaysia.Search in Google Scholar

Wetzig, M., Niemz, P., Sieverts, T., Bergemann, H. (2012) Mechanische und physikalisiche Eigenschaften von mit dem Vakuumpresse-Trocknungsverfahren thermisch behandeltem. Holz. Bauphysik 34:1–10.10.1002/bapi.201200001Search in Google Scholar

Wikberg, H., Maunu, S.L. (2004) Characterisation of thermally modified hard- and softwoods by 13C CPMAS NMR. Carbohydr. Polym. 58:461–466.Search in Google Scholar

Received: 2013-3-15
Accepted: 2013-7-23
Published Online: 2013-08-14
Published in Print: 2014-02-01

©2014 by Walter de Gruyter Berlin Boston

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