Abstract
AbstractThe dynamic vapour sorption behaviour of two Malaysian hardwoods, acacia (Acacia mangiumWild) and sesendok (Endospermum malaccenseBentexMüll. Arg.) was studied over a narrow temperature range (20–40°C). The rate of sorption or desorption of water into or out of the wood cell wall was considered to be limited by the viscoelastic behaviour of the material and the sorption kinetics was accordingly analysed in terms of a canonical series of Kelvin-Voigt elements. A two series and three series model have been applied to the kinetic data and the results are compared. Characteristic times and moisture contents were obtained from the models. The Arrhenius equation was used in conjunction with the reciprocals of the characteristic times to calculate the activation energy and activation entropy of sorption, and the Gibbs free energy of activation for the sorption process was also determined. This is the first time that entropy of activation and Gibbs free energy of activation for sorption processes with wood have been reported. Interpretation of these data invokes a model describing the polymeric relaxation processes occurring within the cell wall during adsorption or desorption. A possible link between sorption kinetics, polymeric relaxation processes, and sorption hysteresis is discussed.
Highlights
The scientific discussion concerning the interrelation of wood with moisture has a long tradition, but it is still frequently a topic in the context of thermal modification (Pfriem et al 2010), chemical modification (Dieste et al 2008), damaged wood (Todoruk and Hartley 2011), or wood drying (Herritsch and Nijdam 2009), just to mention a few
One purpose of this paper is to examine the consequences of introducing additional K-V elements to the rheological model describing water vapour sorption kinetics
By analysing data of water vapour sorption according to the parallel exponential kinetics (PEK) model, it has been possible to obtain values for the activation energy, entropy, and Gibbs free energy of sorption throughout the hygroscopic range
Summary
The scientific discussion concerning the interrelation of wood with moisture has a long tradition, but it is still frequently a topic in the context of thermal modification (Pfriem et al 2010), chemical modification (Dieste et al 2008), damaged wood (Todoruk and Hartley 2011), or wood drying (Herritsch and Nijdam 2009), just to mention a few. The literature abounds with studies on sorption isotherms (e.g., Venkateswaram 1970; Simpson 1980) and there have been many reports on the sorption kinetic behaviour of wood, the practical determination of truly accurate kinetic curves requires skilled experimental work. These sorption kinetics studies invariably interpret the data in terms of a Fickian model (e.g., Droin et al 1988; Wadso 1994a,b; Houska and Koc 2000; Time 2002; Krabbenhoft and Damkilde 2004; Shi 2007; Salin 2010). Our research group has been studying the sorption kinetics properties of cellulose, plant fibres and Bereitgestellt von | SUB Göttingen Angemeldet | 134.76.162.17
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