Moisture desorption isotherms and thermodynamic properties of two dense tropical woods: Tali (Erythrophleum suaveolens Brenan) and Bilinga (Nauclea diderrichii Merr)

The aim of this study was to determine moisture desorption isotherms and some thermodynamic properties of two dense tropical woods from Cameroon: Tali (Erythrophleum suaveolens) and Bilinga (Nauclea diderrichii), which are classified as medium-heavy (Bilinga) and heavy (Tali) woods with high economic values. Equilibrium moisture contents (EMC) were determined using the static gravimetric method at three temperatures (30 ?, 40 ?, 60 ?) and relative humidities (RH) between 5.5 and 83.6%. For thermodynamic properties, Gibbs free energy (GFE), net isosteric heat (q(st,n)) and differential entropy (& UDelta;S) were determined using Clausius Clapeyron and Avramidis equations. To interpret hygroscopic behavior and thermodynamic properties, anatomical and chemical structures were analyzed using microscopic images and infrared (IR) spectroscopy respectively. EMC decreased from 19.39 to 1.99% for Bilinga and from 11.17 to 0.51% for Tali as temperature increased. GAB model best described desorption isotherms data. Desorption isotherms recorded type II sigmoids. Anatomical analysis revealed that Tali and Bilinga had porosities of 40.52 and 50.32%, 3-6 and 6-12 vessels/mm(2), 400-700 mu m and 700-1000 mu m rays respectively. Specific Surface Areas (SSA) decreased from 155.602 to 57.115 m(2)/g for Tali and 287.692 to 175.688 m(2)/g for Bilinga. This result supports the isotherms measurement in terms of hygroscopic capacity of woods. Positive thermodynamic properties revealed that desorption was non-spontaneous and the difference between harmonic mean and isokinetic temperatures confirms an enthalpy-entropy compensation theory. q(st,n) is higher for Tali implying it is less hygroscopic and requires more energy than Bilinga.

Automated summary

The aim of this study was to determine the moisture desorption isotherms and thermodynamic properties of Tali and Bilinga woods from Cameroon. The equilibrium moisture contents decreased with increasing temperature. The GAB model best described the desorption isotherms data. Anatomical and chemical analysis revealed the structure and properties of the woods. The positive thermodynamic properties indicated that desorption was non-spontaneous and that Tali required more energy than Bilinga.