Solute diffusion into cell walls in solution-impregnated wood under conditioning process I: effect of relative humidity on solute diffusivity

Abstract

This study focused on solute diffusing into cell walls in solution-impregnated wood under conditioning. The purpose of this paper was to clarify the effect of relative humidity (RH) of the conditioning on solute diffusivity in the impregnated wood. Water evaporation, swelling, and shrinkage of wood samples impregnated with an aqueous solution of polyethylene glycol (PEG) polymer were examined under conditioning at an RH of 11, 32, 55, or 80 % followed by drying under vacuum. Dried samples were observed using a micro-focus X-ray computed tomography instrument. The total amount of PEG polymer diffusing into cell walls during conditioning increased with RH. Theoretical interpretation indicated that this was caused by an increase in polymer (solute) diffusivity as the amount of water (solvent) in samples increased. Temporal variability of the evaporation rate of water and of the swelling rate of the sample also were examined. Solute diffusivity, which was similar at each RH at the beginning of conditioning, decreased during conditioning; this decrease was greater at lower RH values due to a higher evaporation rate.