Schlüsselwörter
(Englisch)
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Wood modification; Thermo-Hygro-Mechanical processing; neutron imaging; in-situ treatment; equilibrium moisture content; thermo-sorptive aging
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Forschungsprogramme
(Englisch)
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COST-Action FP0904 - Thermo-Hydro-Mechanical Wood Behaviour and Processing
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Kurzbeschreibung
(Englisch)
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Changes occurring during thermo-hygro-mechanical treatment of wood will be determined in-situ by means of neutron imaging. For this purpose a neutron transparent testing chamber allowing high temperature/high pressure treatment will be designed and constructed.
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Weitere Hinweise und Angaben
(Englisch)
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Full name of research-institution/enterprise: Paul Scherrer Institut / PSI Neutron Imaging and Activation Group ASQ Division WBBA/112
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Partner und Internationale Organisationen
(Englisch)
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AT, CH, DE, DK, EL, FI, FR, HR, HU, IE, IT, NL, NO, PL, PT, RO, SE, SI, UK
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Abstract
(Englisch)
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Wood is a natural building material whose properties rely to great extent on its moisture content (MC), which is subdued to changes of the ambient climate due to the hygroscopic behaviour of the material. It is commonly known that high temperature heat treatments reduce the hygroscopicity of wood. However, the mechanism and level of this phenomenon are not well-understood or -quantified, mainly due to experimental difficulties and equipment constraints. In contrast to other approaches, the presented project studies the changes of the MC during the actual modification process (in-situ study) using neutron imaging (NI). This method offers for such experiments a unique opportunity: it is a non-invasive testing method with on the one hand a high sensitivity for hydrogen and thus water and on the other hand a high transparency for some metals such as Aluminium. Both properties are necessary preconditions for the in-situ investigations of MC changes of wood in high temperature / pressure environments. Furthermore the method allows for the determination of dimensional changes of the samples during the high temperature / pressure treatment. For the tests, a neutron transparent pressurised measuring chamber allowing high temperature (Tmax.: 180°C) and pressure (up to 10 bar) treatment was designed and built in collaboration with the ZAG engineering company, Oeschgen (AG). This setup was used to monitor the moisture content and dimensional changes of wood samples during the hydro-thermal modification treatment. Small specimens of European beech (Fagus sylvatica) and Norway spruce (Picea abies) wood were subjected to different thermal modification cycles (temperature range: 70°C - 150°C; relative humidity (RH): 0% - 100%). It could be demonstrated that with the method of neutron imaging and the corresponding evaluation software, the change of moisture content and the dimensional changes of wood during heat treatment could be measured and quantified. It was shown that MC and RH during the thermal treatment highly influence the wood modification process (hygroscopicity, colour change etc.). Therefore, neutron imaging with the possibility of in-situ MC and space measurements opens the door for further important investigations within the field of thermal wood modification. Thereby, one important aspect may be the dimensional and moisture changes near the fibre saturation point which highly influence the treatment results. Additionally, the sorption behaviour at 20°C after heat treatment was investigated where a clear decrease of the sorption isotherms with increasing treatment temperature was found (for desorption of spruce only above a treatment temperature of 90°C). Scanning electron microscopic analyses did not show unambiguous results, which is due to lack of available specimens. Also, colour measurements were carried out before and after the treatment. Thereby, the dry heated specimens show clearly lower colour change than the specimens heated with saturated steam. First results of the tests were presented on the 6th European conference on wood modification held on 16-18 September 2012 in Ljubljana, Slovenia and were published as a scientific paper in its proceedings (Sonderegger et al. 2012). The final results were presented on the 3rd Annual Action Conference of the COST Action FP0904 held on 9-11 April 2013 in Iasi, Romania and submitted for publication in the scientific journal 'Holzforschung'.
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Datenbankreferenzen
(Englisch)
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Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C11.0053
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