The water vapour sorption properties of Sitka spruce determined using a dynamic vapour sorption apparatus |
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| Authors: | Callum A S Hill Andrew J Norton Gary Newman |
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| Institution: | (1) Centre for Timber Engineering, Joint Research Institute for Civil Engineering, School of Engineering and the Built Environment, Edinburgh Napier University, Edinburgh, UK;(2) Renuables Ltd., Llanllechid, Gwynedd, UK;(3) Plant Fibre Technology Ltd., Bangor, Gwynedd, UK |
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| Abstract: | The water vapour sorption properties of Sitka spruce (Picea abies) have been investigated over a range of temperatures (14.2–43.8°C) using a dynamic vapour sorption apparatus. The sorption
kinetics behaviour was evaluated using the parallel exponential kinetics model which has been found to give very accurate
fits to the data in studies of foodstuffs or plant fibres, but has not been previously applied to sorption studies with wood.
Both the adsorption and desorption kinetics curve can be deconvoluted into a fast and slow exponential process. Under conditions
of adsorption, the fast process appears to be associated with the formation of monolayer water (determined using the Hailwood
Horrobin model) up to a relative humidity of 20%. Under desorption, there is no clear differentiation between fast and slow
processes. The area bounded by the sorption hysteresis loop reduced as the temperature at which the isotherm was measured
increased, due to movement of the desorption curve only, with the adsorption curve remaining the same at all temperatures.
This behaviour is consistent with sorption processes taking place on nanoporous glassy solids below the glass transition temperature.
The heat of wetting was determined from the temperature dependence of the desorption isotherms by using the Clausius–Clapeyron
equation, yielding results that are consistent with literature values. However, doubts are raised in this paper as to the
applicability of using the Clausius–Clapeyron equation for analyses of this type. |
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