Water plays an important role in degradation processes of wood and influences physical wood properties such as dimensional stability and mechanical behaviour. The interaction between water and wood has therefore been widely studied and this is commonly done by determining sorption isotherms. Sorption isotherms show the relation between the equilibrium moisture content and the ambient relative humidity (RH). The equilibrium moisture content is however not only dependent on the ambient climate, but also on the moisture history of the sample; the moisture content is higher if equilibrium is reached by desorption than if equilibrium is reached by absorption (Pidgeon and Maass 1930). This is called sorption hysteresis and is observed in most porous materials. It is thus important to consider the moisture history of the specimen when determining sorption isotherms. After the introduction of automated sorption balances (Williams 1995), it has become common to determine sorption isotherms by initially drying the sample and then measure the absorption isotherm up to a high RH, typically 95% RH, see e.g. (Hill et al. 2009; Ceylan et al. 2014; Himmel and Mai 2015). Thereafter, desorption is initiated from this high RH and the sample is dried in steps back to 0% RH again. This procedure of measurement does however not yield desorption isotherms, but scanning isotherms. In the present study, the consequences of this procedure of measurement on the obtained sorption isotherms and the evaluated sorption hysteresis are shown.
Keywords: moisture content, sorption isotherm, sorption hysteresis
Authors
Maria Fredriksson
Department of Building and Environmental Technology, Lund University, Lund
Emil Engelund Thybring
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