Transverse Permeability of OSB. Part II. Modeling the Effects of Density and Core Fines Content

Authors

  • Hamid R. Fakhri
  • Kate E. Semple
  • Gregory D. Smith

Keywords:

Wood composites, OSB, transverse permeability, fines content, core density, modeling, rule of mixtures

Abstract

In this work a simple rule of mixtures model to characterize the permeability of an OSB composite as a function of fines contents and density is presented. Strands and fines in the core of the board are considered to lie between two extremes, either stacked in a series configuration (series model) or side by side in a parallel configuration (parallel model), with the permeability of the composite, Ksystem, being a function of relative permeabilities of the series and parallel models. Equations for the permeability of these two configurations, Kparallel and Kseries, are developed as functions of the known permeability of 100% strands, Ks, and 100% fines, Kf, and the mass fraction of fines, Mf. Data on the permeability of the core of OSB compressed to three density classes and made with 0 and 100% fines content are used to determine the permeability of the parallel and series models, respectively. The series coefficient, α, which represents the contribution from the series model, is determined using least squares fits to the permeability data for different target densities and 25%, 50%, and 75% fines contents. α was fairly consistent, ranging from 0.47 to 0.49 for these fines contents. Kparallel increases linearly with increasing fines content and Kseries increases exponentially, in accord with the actual data. The data for the low and medium target density boards were well described by the Ksystem predictions, whereas the model underestimates the permeability of boards containing 75% or 100% fines and compressed to high target density. The model was most sensitive to changes in Mf, Kf, and Ks, with other parameters, α and density ratio (ρs/ρf), having smaller effects. The proposed model is general and could be applied to other composites of mixed particle sizes such as particleboard.

References

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Published

2007-06-05

Issue

Number 3 / July 2006

Section

Research Contributions

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