Feasibility of supercritical carbon dioxide as a carrier solvent for preservative treatment of wood-based composites

Supercritical carbon dioxide (SC-CO2) was tested for its potential as a carrier solvent for preservative treatment of solid wood and wood-based composites. A preliminary trial showed that the treatability of solid wood varied with its original permeability and that the SC-CO2 treatment was not promising for refractory timber species such a Larix leptolepis Gordon. In contrast, 3-iodo-2-propynyl butylcarbamate (IPBC)/SC-CO2 treatment resulted in enhanced decay resistance without any detrimental physical or cosmetic damage in all structural-use wood-based composites tested: medium density fiberboard, hardwood plywood, softwood plywood, particleboard, and oriented strand board (OSB). Further trials under various treatment conditions [25degreesC/7.85 MPa (80 kgf/cm(2)), 35degreesC/7.85 MPa, 45degreesC/7.85 MPa, 35degreesC/11.77 MPa (120 kgf/cm(2)), and 45degreesC/11.77 MPa] indicated that although small changes in the weight and thickness of the treated materials were noted the strength properties were not adversely affected, except for a few cases of softwood plywood and oriented strand board. The results of this study clearly indicated that the treatment condition allowed SC-CO2 to transport IPBC into wood-based composites, and the optimum treatment condition seemed to vary with the type of wood-based composite.