Changes in Physical Properties of Yellow Birch Below and Above the Fiber Saturation Point
Keywords:Equilibrium moisture content, desorption, wood strength, compliance coefficient, shrinkage
AbstractTwo experimental techniques were used to perform moisture sorption tests at 25°C on specimens of yellow birch sapwood. The first used saturated salt solutions (from 33% to 90% relative humidity), and the second used the pressure membrane method (above 96% relative humidity). These sorption tests were combined with dimensional measurements and perpendicular-to-the-grain tangential compression tests. Results showed that at equilibrium moisture content, radial, tangential, and volumetric shrinkage, as well as changes in transverse strength, occur above the fiber saturation point. This behavior can be explained by the effect of hysteresis at saturation on wood properties. This hysteresis indicates that loss of bound water takes place in the presence of liquid water, which contradicts the concept of FSP. The initial equilibrium moisture content at which bound water is removed from yellow birch was about 41%.
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