Characterization of Sorption Behavior of Oriented Strandboard Under Long-term Cyclic Humidity Exposure Condition
Keywords:
Adsorption, desorption, EMC, moisture, OSB, sorption models, structural panelsAbstract
Sorption measurements for oriented strandboard (OSB) were carried out under cyclic relative humidity (RH) conditions at 25°C. The measurements were made by placing test materials in a climate-controlled conditioning chamber until the specimens reached their steady-state equilibrium moisture content (EMC) at each given RH. The EMC-RH data were fit to Nelson's sorption model through nonlinear regression analysis. The model was subsequently used to develop procedures for predicting EMC distribution in a board with a vertical density gradient and for predicting mean EMC change of OSB under cyclic RH exposure conditions.
It was shown that Nelson's model can be used to describe the sorption data of OSBs manufactured under various processing conditions. The parameters that define the sorption isotherm varied with sorption mode (adsorption or desorption) and processing variables. In a board with a vertical density gradient, the lower density range (core) reached higher EMCs than the higher density range (face) at a given RH level. Thus, it would be more appropriate to use an EMC distribution across panel thickness rather than a mean panel MC when modeling linear expansion and thickness swelling characteristics of OSB. Under long-term cyclic exposure condition, OSB's sorption isotherms are reproducible and can be predicted accurately with the model.
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