Abstract
Thermal treatment in inert atmosphere is used to preserve wood without utilisation of toxic chemical agents. In addition, this process increases the dimensional stability of the wood matrix and results in attractive dark colour. On the other hand, it can deteriorate the mechanical strength and the flexibility of wood. For this reason, heat treatment parameters (such as maximum temperature, heating rate, the duration of the first plateau at constant temperature (100–120°C) and the second plateau at the maximum treatment temperature, humidity, final cool down rate) must be optimised in order to benefit from advantages of thermal treatment without deteriorating significantly the mechanical properties of wood. Correlation between wood properties and thermal treatment parameters depends not only on the wood species but also the environment (climate, soil) where the given species grow. This paper presents a study on thermal treatment of Canadian Jack pine (Pinus banksiana) using a medium size prototype furnace. The aim of this study was to optimize the set of parameters used during industrial treatments. The possibility of shortening the process time without causing any deterioration in wood quality was also investigated. The results show that increasing the maximum heat-treatment temperature increased the dimensional stability of Jack pine and darkened its colour. This parameter did not affect the modulus of elasticity but it decreased the modulus of rupture of Jack pine. A slight reduction in gas humidity during the initial warming up period permitted to shorten the drying period and at the same time increased the mechanical strength. This improvement helps save energy and increase productivity.
Zusammenfassung
Die Wärmebehandlung von Holz unter Schutzgasatmosphäre wird zur Verbesserung seiner Dauerhaftigkeit ohne Verwendung giftiger chemischer Mittel angewandt. Zusätzlich wird mit diesem Verfahren die Dimensionsstabilität der Holzmatrix verbessert und eine attraktive Dunkelverfärbung erzielt. Andererseits kann sich dieses Verfahren jedoch negativ auf die mechanische Festigkeit und die Steifigkeit des Holzes auswirken. Deshalb müssen die Wärmebehandlungsparameter (wie zum Beispiel Maximaltemperatur, Aufheizrate, Dauer der ersten Temperaturstufe bei 100–120°C und der zweiten Stufe bei der Maximaltemperatur, Feuchte, Abkühlrate) optimiert werden, um die Vorteile einer Wärmebehandlung nutzen zu können ohne dabei die mechanischen Eigenschaften von Holz signifikant zu verschlechtern. Der Einfluss der Wärmebehandlungsparameter auf die Holzeigenschaften hängt nicht nur von der Holzart ab, sondern auch von den Wuchsbedingungen (Klima, Boden). In dieser Studie wird eine Wärmebehandlung von kanadischem Jack Pine Holz (Pinus banksiana) in einer mittelgroßen Prototypanlage vorgestellt. Ziel dieser Untersuchung war es, die Parameter bei der industriellen Behandlung zu optimieren. Zusätzlich wurde die Möglichkeit untersucht, die Verfahrensdauer zu verkürzen ohne die Holzqualität zu verschlechtern. Die Ergebnisse zeigen, dass eine Erhöhung der maximalen Behandlungstemperatur zu einer Verbesserung der Dimensionsstabilität von Jack Pine Holz sowie zu einer dunkleren Verfärbung führte. Dies hatte keinen Einfluss auf den Elastizitätsmodul, reduzierte jedoch die Biegefestigkeit von Jack Pine Holz. Mit einer geringfügigen Reduktion der Gasfeuchte während der Aufheizphase konnte die Trocknungszeit verkürzt und gleichzeitig die mechanische Festigkeit verbessert werden. Diese Verbesserung hilft, Energie zu sparen und die Produktivität zu steigern.
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Acknowledgements
The authors would like to thank their industrial partner, the Group Ohlin Thermotech for supplying wood and use of their prototype furnace for the tests. They would also like to thank Canada Economic Development (CED), Ministère du développement économique, de l’Innovation et de l’exportation (MDEIE), Conférence régionale des élus, Saguenay-Lac-St-Jean (CRÉ), Forintek, University of Quebec at Chicoutimi (UQAC), Foundation of University of Quebec at Chicoutimi (FUQAC), as well as their technicians, Mr. Renald Delisle and Mr. Jacques Allaire for their support and contributions.
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Poncsak, S., Kocaefe, D. & Younsi, R. Improvement of the heat treatment of Jack pine (Pinus banksiana) using ThermoWood technology. Eur. J. Wood Prod. 69, 281–286 (2011). https://doi.org/10.1007/s00107-010-0426-x
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DOI: https://doi.org/10.1007/s00107-010-0426-x