In-situ measurement of dimensional changes during supercritical fluid impregnation of white spruce lumber

Supercritical fluids can markedly enhance preservative treatment of wood, but the high pressures employed can lead to collapse. We investigated the effects of the rates of pressure application and release on displacement of white spruce lumber during supercritical impregnation with carbon dioxide. Displacement was greatest when pressure was rapidly increased at the start of the process. Conversely, rapid pressure release at the conclusion of the treatment process resulted in the lowest level of permanent displacement. The results suggest that wood displacement during supercritical fluid impregnation can be controlled by altering process variables for a given species.