Effect of wetting agent on drying characteristics of 4/4 sugar maple

The newly formed sapwood in trees is extremely permeable and, therefore, easy to dry. However, as sapwood becomes physiologically dead heartwood, extractives are deposited in the cell lumens and on the pit membranes and, in some species, tyloses are bonded in the vessels (4). These extractives and tyloses tend to block the flow of fluids in wood, thus slowing the drying rate of heartwood. One potential way to increase the permeability of heartwood and reduce drying time is pre-soaking green lumber in a wetting agent solution before kiln drying. Wetting agents, such as common detergents, can lower the surface tension of wood sap, and also may dissolve and remove the water-soluble extractives from the pit membranes. Chen and Simpson (2) found that soaking sugar maple and black walnut heartwood blocks (2"x2"x1") in a wetting agent for 1 week increased the subsequent drying rates in a controlled temperature and humidity chamber as moisture content was reduced to near and below the fiber saturation point (fsp). This paper describes the effect of a wetting agent (common liquid detergent) on drying characteristics of 4/4 sugar maple lumber in a steam-heated dry kiln.