Abstract
Wood veneer 700×700 mm2 specimens made with aspen (Populus tremuloides) and hybrid poplar clone 15303 (Populus maximowiczii × Populus balsamifera) were densified using heat, steam, and pressure. Temperatures of 140, 160, 180, 200, and 220°C were applied at a maximum steam pressure of 550 kPa and maximum press hydraulic pressure ranging from 4.5 to 9.0 MPa. After densification, the oven-dry density increased significantly, veneers darkened, and lathe checks that were present on veneers before densification were conglutinated and veneer surface roughness decreased. Densified veneers showed markedly reduced hygroscopicity: the higher the densification temperature, the lower the wood hygroscopicity. The Brinell hardness of densified veneer was about two to three times that of control for both aspen and hybrid poplar. Tensile and bending strength also increased significantly after densification. However, the mechanical properties of densified veneers decreased slightly with increased densification temperature. The modulus of elasticity in tension and bending increased after densification, especially at high temperatures. A very high compression set recovery was found for veneers densified at low temperatures. Recovery decreased dramatically when densification temperature exceeded 180°C. Almost no recovery was found for veneers densified at 220°C.
Zusammenfassung
Furnierprüfkörper (700 mm×700 mm) aus Espenholz (Populus tremuloides) und dem Hybridpappelklon 15303 (Populus maximowiczii × Populus balsamifera) wurden mittels Hitze, Dampf und Druck verdichtet. Die Temperaturen betrugen 140, 160, 180, 200 und 220 °C bei einem maximalen Dampfdruck von 550 kPa und einem maximalen Hydraulikdruck von 4,5 bis 9,0 MPa. Nach der Verdichtung war die Darrdichte signifikant angestiegen, die Furniere waren nachgedunkelt, vor der Verdichtung vorhandene Schälrisse waren verklebt und die Rauhigkeit der Furniere nahm ab. Die verdichteten Furniere wiesen eine merklich verringerte Hygroskopizität auf: diese war umso geringer, je höher die Verdichtungstemperatur war. Die Brinell Härte der verdichteten Furniere war sowohl bei Espe als auch bei Hybridpappel um das zwei- bis dreifache höher als die der Kontrollproben. Die Zug- und Biegefestigkeit der verdichteten Furniere ist ebenfalls signifikant angestiegen. Jedoch nahmen die mechanischen Eigenschaften der verdichteten Furniere mit zunehmender Verdichtungstemperatur leicht ab. Der Biege- und Zug-Elastizitätsmodul erhöhte sich nach der Verdichtung, insbesondere bei hohen Temperaturen. Furniere, die bei niedrigen Temperaturen verdichtet wurden, wiesen eine sehr hohe Rückverformung auf. Diese ging bei Temperaturen über 180 °C drastisch zurück. Bei 220 °C verdichtete Furniere wiesen keine Rückverformung auf.
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Acknowledgements
The authors wish to thank the Fonds québécois de recherche sur la nature et les technologies (FQRNT), FPInnovations and Réseau Ligniculture Québec for funding of this project. We also thank Temlam Inc. for providing aspen veneers and Réseau Ligniculture Québec and Ministère des Ressources naturelles du Québec for providing hybrid poplar veneers.
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Fang, CH., Mariotti, N., Cloutier, A. et al. Densification of wood veneers by compression combined with heat and steam. Eur. J. Wood Prod. 70, 155–163 (2012). https://doi.org/10.1007/s00107-011-0524-4
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DOI: https://doi.org/10.1007/s00107-011-0524-4