The effect of chemical changes on the wood-moisture relationships in thermally-modified wood

IRG/WP 09-40473

M M González-Peña, M D C Hale

Small specimens of three wood species were thermally modified following twenty schedules in the 190-245°C temperature range for treatment times between 0.3 and 16 h. Five wood-moisture relations were subsequently determined, namely: anti-swelling efficiency (ASE), movement, hygroscopicity (adsorption and desorption), transversal swelling (radial and tangential directions), and equilibrium moisture content. The chemical composition of thermally modified wood (TMW) was also determined; an analysis of the relationship between chemical changes and moisture-related properties was next undertaken. Most wood-moisture properties were found to be strongly correlated with changes in each chemical constituent in TMW. Regardless of the species, the weakest correlation between moisture parameters and chemical changes was with the cellulose fraction, while the strongest correlation was usually with the hemicellulose component. This reflects the involvement of all chemical constituents towards the reduction of hygroscopicity -with the consequent reduction in swelling and movement. The evaporation of wood components, particularly hemicelluloses, was found not to be the only reason for the reduction of hygroscopicity; the hygroscopicity of all individual constituents also decreased with the treatment. This effect was verified for isolated lignin samples by dynamic vapour sorption measurements.

Keywords: anisotropy; chemical composition; dimensional stability; heat-treatment; sorption

Conference: 09-05-24/28 Beijing, China

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