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ABSTRACT
The aim of this paper was to determine the moisture desorption isotherms and certain thermodynamic properties of Eucalyptus gomphocephala wood using the static gravimetric method at five temperatures: 40°C, 50°C, 60°C, 70°C and 80°C, and relative humidity ranging from 5% to 90%. A “thermodynamic” equation was selected to describe the desorption isotherms under controlled conditions. Desorption isotherms were a “type II” sigmoid. The Clausius–Clapeyron relationship was applied to determine the isosteric heat of desorption. Results showed that for equilibrium moisture content less than 6%, the differential enthalpy and entropy decreased with increasing moisture content according to an exponential law from 26 to 0.5 kJ/mol and from 44 to 0.16 J/(mol K), respectively. The difference in isokinetic and harmonic temperature confirmed the enthalpy-entropy compensation theory of desorption reaction. The negative value of Gibbs free energy (−208.2 kJ/mol) indicated the spontaneous wood-water desorption reaction. Spreading pressure decreased with increasing temperature from 1 J/m² at 40°C to 0.16 J/m² at 80°C and increased with increasing water activity with the rate of 0.014% J/m² per relative humidity.
Disclosure statement
No potential conflict of interest was reported by the author(s).