Supercritical fluids (SCF) offer an attractive alternative to conventional treatment processes for delivering material into wood, but there are many unanswered questions concerning the technology. One major concern is the potential for the development of excessive pressure gradients in the wood that might exceed the material properties and lead to crushing or other pressure-induced damage. Previous studies suggest that the pressure gradients in solid wood of some species exceed the material properties of the wood, resulting in collapse or splitting, but there is little data on these processes in composites. The rates of pressure change were studied in oriented strand board (OSB) during SCF treatment with carbon dioxide. In general, pressure equilibrated far more rapidly in OSB than in solid wood. The presence of gaps and voids in the composite apparently permit more rapid equilibration of pressure, thereby avoiding the problems found with less permeable solid woods. Further studies are underway to incorporate the pressure development data into a model to predict solubility of biocides in the composite during treatment.

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