RATE OF SWELLING OF VACUUM-IMPREGNATED WOOD

The swelling rate of wood wafers vacuum-impregnated with water and oth er swelling agents was measured by a videotaping technique. After an i nitial period of inhibited swelling, the rate of swelling could be des cribed quantitatively by a simple membrane Fickian diffusion model for solvent penetration into the wood cell walls. Diffuse porous aspen sw elled more slowly than red pine as a result of differences in initial distribution of solution in the wood tissue. In red pine, swelling rat e increased with increasing degree of saturation of the wood void spac e, while in aspen the swelling rate was not related to solution absorp tion. Wood relative density did not affect swelling rate significantly over the range of densities tested. Increased solution temperature ha d the expected effect of increased swelling rate. The estimated activa tion energy for bound water diffusion inducing swelling depended on th e direction of swelling and the treating solution and ranged from 26.4 to 41.6 kJ/mole. Treatment with 8% monoammonium phosphate (MAP) resul ted in slower swelling rates compared to water and 10% polyethylene gl ycol (PEG) treated wafers under most conditions. The organic swelling solvents dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) initial ly swelled wood much more slowly than water.