The Guggenheim-Anderson-de Boer (GAB) three-parameter sorption equation has been used to interpret the adsorption and desorption isotherms of water vapour measured for 21 important cultural heritage wood species used in the past for panel paintings and woodcarving. The equation is capable of describing the full shape of the isotherms and yields meaningful physical parameters, especially the monolayer capacity from which the water accessible specific surface area can be obtained. It is demonstrated that average sorption isotherms can be derived using the GAB equation for the sorption data available for sets of specimens and that moisture properties of various wood specimens or chemically modified wood can be more easily compared.
Analyse der Wasseraufnahme von Holz mit der Guggenheim-Anderson-de Boer-GleichungZusammenfassung Anhand der dreiparametrigen Guggenheim-Anderson-de Boer-Sorptionsgleichung (GAB) wurden die Adsorptions-und Desorptionsisothermen von 21 kulturell wichtigen Holzarten bestimmt, die in früheren Zeiten für Tafelmalereien und Holzschnitzereien verwendet wurden. Mit dieser Gleichung kann die vollständige Form der Isothermen dargestellt werden. Sie liefert aussagekräftige physikalische Parameter, insbesondere die Monoschichtkapazität, aus der die für das Wasser zugängliche spezifische Oberfläche bestimmt werden kann. Es wird gezeigt, dass anhand der GAB-Gleichung aus den verfügbaren Sorptionsdaten für
The finite element method was used to model the moisture movement and strain in the wood supports of panel paintings, in response to changing climate conditions – temperature and relative humidity (RH). The material properties of lime wood (Tilia sp.), determined experimentally, were used in the modelling. Critical amplitudes of cyclic sinusoidal RH fluctuations generating strain of 0.002 in the most responsive tangential direction of the unrestrained, single wood panel, which the pictorial layer was assumed to endure without damage, were derived for the mid‐RH region as a function of cycle duration, panel thickness and diffusion configuration. Panels do not respond significantly to diurnal fluctuations or shorter. The panels respond more and more significantly when the duration of the fluctuations increases until the panel fully responds to each cycle. These fluctuation periods are 14 and 90 days at 20 °C for a panel thickness of 10 and 40 mm, respectively, with two faces of a panel diffusively opened. Sinusoidal RH variations bringing about wood’s full response have the critical amplitude of ±6% RH, that is strain of 0.002 endangering the pictorial layer is produced at such amplitude in the tangential direction of the unrestrained panel.
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