Rate of Swelling of Vacuum-Impregnated Wood
Keywords:Swelling, diffusion, bound water, monoammonium phosphate (MAP), polyethylene glycol (PEG-1000), red pine (<i>Pinus resinosa</i> Ait.), trembling aspen (<i>Populus tremuloides</i> Michx.), temperature, activation energy, dimethylsulfoxide (DMSO), dimethyl formamide (DMF)
AbstractThe swelling rate of wood wafers vacuum-impregnated with water and other swelling agents was measured by a videotaping technique. After an initial period of inhibited swelling, the rate of swelling could be described quantitatively by a simple membrane Fickian diffusion model for solvent penetration into the wood cell walls. Diffuse porous aspen swelled more slowly than red pine as a result of differences in initial distribution of solution in the wood tissue. In red pine, swelling rate increased with increasing degree of saturation of the wood void space, while in aspen the swelling rate was not related to solution absorption. Wood relative density did not affect swelling rate significantly over the range of densities tested. Increased solution temperature had the expected effect of increased swelling rate. The estimated activation energy for bound water diffusion inducing swelling depended on the direction of swelling and the treating solution and ranged from 26.4 to 41.6 kJ/mole. Treatment with 8% monoammonium phosphate (MAP) resulted in slower swelling rates compared to water and 10% polyethylene glycol (PEG) treated wafers under most conditions. The organic swelling solvents dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) initially swelled wood much more slowly than water.
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