The objectives of this study were to characterize OSB panel permeability in comparison with plywood and low density fiberboard; to determine the effect of panel characteristics on the speed of moisture movement through the thickness of the OSB panels; to create a finite element model of the permeability of OSB; to suggest improvements of the OSB panel structure in function of permeability.
The introduction of current report presents extracts of the theory of moisture transfer in wood materials and introduces the concept of water potential and the instantaneous profile method as adapted to OSB to be used for the determination of the diffusion coefficient (D).
The experimental part is divided into three stages. In the first stage the permeance of the OSB panels, plywood and low density fiberboard is compared according to the dry cup method. The experiments showed that the low-density fiberboard panels’ permeance is more than twice as high as compared with the permeance of the OSB panel; the Western Red Cedar has an approximately equal permeance with the OSB panel, which is in turn higher as compared with the permeance of the Aspen plywood. The Aspen plywood produced with parallel plies shows approximately 30 % higher permeance as compared to the regular plywood.
In the second stage, the effects of density, strand geometry and orientation level, panel density and moisture content on the permeance and on the diffusion coefficient are determined. The experiment is organized based on an experimental design. For the permeability (permeance and diffusion coefficient), the lower the strand thickness, the lower the permeability; the lower the level of strand orientation, the higher the permeability; the larger the strand width and length (surface area), the lower the permeability, the higher the permeability.
During the third stage, the dynamics of moisture movement in the panel is modeled with a finite element model based on an unsteady-state moisture transfer equation and the results from simulations are compared to experimental results in order to validate the model. Ten cases of adsorption and two cases of desorption are considered. Seven of the cases are duplicated with experimental results to serve for validation of the model. The closeness of the experimental and simulation results allow concluding the validity of the finite element model, which can be used to optimize the OSB panel structure by selecting practical layer characteristics leading to desired moisture permeability.