The effective average distance that a solute must diffuse to penetrate the cell wall matrix following pressure treatment is estimated from the rate of swelling of wood, vacuum treated with water. It is assumed that the diffusion paths are similar for water and a solute such as a wood preservative component. Since bound water diffusion coefficients for water in wood have been estimated by others, the effective path lengths (Le) can be estimated. Effective average path lengths are estimated for red pine (Pinus resinosa), Southern yellow pine (Pinus sp), trembling aspen (Populus tremuloides) and soft maple (Acer rubra) sapwood and red oak (Quercus rubra) heartwood samples. The estimated path lengths are shortest for the softwoods, and longest for the ring porous oak. The results reflect the different patterns of cell penetration and different densities of the wood species.

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