Effect of hot-water extractives on water sorption and dimensional changes of black locust wood

The hygroscopicity and the dimensional changes of black locust heartwood were investigated in relation to the progressive removal of hot-water extractives. Extraction in the original specimen form removed only part of the total 8.434 % hot-water extractives, 3.601 % in first extraction and 4.642 % in second extraction. As a result, the adsorption and desorption behaviour of black locust wood was little affected by the extraction and only a small increase was observed in dimensional changes at every RH from 0 % to 97 %. The mean hysteresis coefficient was also little affected by extraction and increased from 0.75 at the unextracted stage to 0.77 at the second extraction. The initial dimensional change 3.76 % of unextracted black locust wood corresponding to RH changes between 43 % and 80 % increased after the first and second extraction to the respective values of 3.96 % and 3.97 %. Extraction had no effect on the significant, very strong linear relationships between swelling or shrinkage and equilibrium moisture content (EMC).