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Modification of domestic timbers by impregnation using supercritical carbon dioxide

A comparison
: Jelen, E.; Ghosh, S.C.

Englund, F. ; SP Technical Research Institute of Sweden, Stockholm:
Fourth European Conference on Wood Modification 2009. Proceedings : Norra Latin City Conference Centre, Stockholm, Sweden 27 - 29th April 2009
Stockholm: SP Technical Research Institute of Sweden, 2009
ISBN: 978-91-86319-36-6
ISBN: 91-86319-36-1
European Conference on Wood Modification (ECWM) <4, 2009, Stockholm>
Conference Paper
Fraunhofer UMSICHT Oberhausen ()
wood modification; impregnation; supercritical carbon dioxide (scCO2); silicon compound; Holzmodifizierung; Imprägnierung; überkritisches Kohlendioxid; Siliziumverbindung

Domestic timbers are often not suited for construction trade applications because of low dimensional stability, low durability or low mechanical strength and are squeezed out of the market by tropical lumbers or other materials (such as plastics or metals). Therefore it is of considerable interest to improve their characteristic properties in order to open new potential markets. One possibility to accomplish this aim is the impregnation of wood with silicon containing substances such as silane based nanosols or silicones. During this process, the silicon compounds are deposited in the lumina and the cell walls causing a change of wood properties. In many important domestic wood species, particularly in spruce wood, conventional procedures using water or organic solvents achieve only superficial penetration with depths of only a few millimetres. Thus a solvent is needed, which enables the complete penetration of the wood without damaging its structure. It was previously shown, that supercritical impregnation with saline and silicone compounds resulted in reduced water uptake and complete penetration of the specimens. Thus, the objective of the investigations described here is to verify the suitability of supercritical carbon dioxide (scCO2) as solvent for the impregnation process and to study the achieved improvement of wood properties. In comparison to the classical vacuum-pressure impregnation the supercritical infiltration shows the same load (weight percentage gain), but in shorter time and with less amount of chemicals used in the treatment process. Another advantage of supercritical impregnation is that no additional drying after the process is needed.