Supercritical fluid impregnation with biocides of wood using temperature reduction

Supercritical fluid (SCF) impregnation is a promising preservative treatment method, however, the development of SCF processes has been slowed by a limited understanding of the process. Developing a better understanding of the effects of various process parameters on treatment results would allow for a more rational development of SCF impregnation. We explored a new process that introduced biocide in a methanol solution and then reduced temperature to induce deposition.; Temperature induced deposition produced more reproducible retentions between batches and reduced biocide consumption in comparison with the saturation method. A close relationship was observed between biocide input (g) and retention up to 0.5 kg/m3 (Y = 0.0255x, R2 = 0.9535) using this method. Operating at higher temperature and pressure reduced treatment reproducibility.; Although temperature induced deposition required additional cooling times, it also produced higher retentions, an absence of clogging in lines, allowed for methanol recycling, and created the potential for recycling liquid CO ₂. One possible drawback was the presence of a liquid phase at the end of the process that might result in biocide movement from the interior to the surface in wood.; Different wood materials including ponderosa pine sapwood, plywood, and oriented strand board showed varying biocide treatability due to differences in structural composition and permeability of the various materials. Although liquid impregnation produced similar retentions in all three wood materials, the liquid treatment can cause detrimental effects on the mechanical and physical properties of wood composites.