Effect of Wood Extractives on the Equilibrium Moisture Content of Six Sudanese Hardwood Species

Abstract

The objective of this investigation was to study the effect of
extractive content on the wood sorption isotherms of six Sudanese hardwood
species i.e. Acacia nilotica, A.senegal, Anogeissus leiocarpus, Boswellia
papyrifera, Ailanthus excelsa and Calotropis procera growing in North and
South Kordofan States. For each species, wood samples were collected from
six trees, from which specimens were prepared. The effect of extractives on
equilibrium moisture content was studied by comparing the equilibrium
moisture content of hot water extracted and unextracted wood. Experimental
equilibrium moisture content values for extracted and unextracted specimens
were obtained at different levels of relative humidity. These specimens were
placed in a closed desiccator, which contained saturated salt solution or
different concentrations of sulphuric acid to maintain relative humidity and
then kept in an oven at the specified temperature (60 ○
C) until equilibrium
moisture content was obtained. Desorption and adsorption isotherms of the
six wood species exhibited sigmoid curves. The results showed direct
relationship between equilibrium moisture content and relative humidity that
could be well explained by third-order polynomial functions. The effect of
extraction was significant at few relative humidity values in some species;
unextracted wood had higher equilibrium moisture content than extracted
wood.