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Measurement and modeling of the in-plane permeability of oriented strand-based wood composites Zhang, Chao


The objective of this research is to investigate the effects of panel density and air flow direction on the in-plane permeability of oriented strand-based wood composites. In-plane permeability is a key factor governing the energy consumption and pressing time during manufacture. The result is expected to provide information which could potentially reduce the pressing time. The thick, oriented strand boards of five densities were made of aspen (Populus tremuloides), and pressed in the laboratory. The production procedure yielded a uniform vertical density profile and good strand orientation. The specimens were sealed in a specially designed specimen holder and connected to a permeability measurement apparatus. The permeability values in parallel, perpendicular, and 45° to the strand orientation were obtained. The results showed that permeability values decreased rapidly as the density increased. The permeability was highest in the parallel-to-strand direction, and lowest in the perpendicular-to-strand direction. The permeability value in 45° direction was between the values of parallel- and perpendicular-to-strand directions. A polynomial equation was fitted to the results and an R² was between 0.93 8 and 0.993. To examine the void structure changes during the densification, microscopic techniques were employed. Microscopic slides for each density level were prepared with a typical method widely used for petrography, and then investigated with a fluorescence microscope. The compression of inter-strand and intra-strand voids, including the failure of cell walls, was observed. The compression of cell structures was found and a high variability between regions was observed to occur within one specimen. A model for the permeability in the direction parallel to strand orientation was developed based on the microscopic and macroscopic geometry measurements. The vessel element was considered as the main path for intra-strand fluid transportation and its size development with compression was determined by the microscopic analysis. Permeability was then calculated by the sum of flows occurring intra-strand voids added with the effect of inter-strand voids. The model predictions closely matched the experimental data for densities between 450 and 700 kg/m³.

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