Application of Nelson's Sorption Isotherm to Wood Composites and Overlays'

Equilibrium moisture content (EMC) as a function of relative humidity (RH) was measured in oriented strandboard. particleboard, medium-density fiberboard, hardboard, high pressure laminates, and solid wood. The measurements were made in both adsorption and desorption at 2 9 2 . The EMCRH data were fit to Nelson's sorption isotherm. It was found that Nelson's model can be used to describe the experimental data from different composite materials. The parameters that define the sorption isotherm varied with material type and sorption mode. Determination of the model parameters for various products allows the use of the model as a tool for predicting moisture change in woodbased products under varying environmental conditions. K r y ~ ~ o n l . ~ : Adsorption, desorption. model, moisture, panel products The relationships between equilibrium moisture content (EMC), relative humidity (RH), and temperature are of considerable practical interest for wood composite materials (Suchsland 1972). These relationships, known as sorption isotherms, greatly affect the strength and dimensional stability of different products during service. Their determination is required for analyzing moisture-related problems such as warping of a furniture panel and shrinkage and swelling of a structural composite (Burch et al. 1992; Wu and Suchsland 1996). Nelson (1983) developed a model based on Gibbs free energy to describe the sorption behavior of cellulosic materials. The model is of the form