Supercritical carbon dioxide treatment: Effect on permeability of Douglas-fir heartwood

The effect of supercritical fluid treatment on superficial gas permeability of Douglas-fir was investigated by using carbon dioxide either alone or amended with methanol. Permeability increased in a majority of samples, although nearly one-third of the specimens declined in permeability. Improvements in permeability appeared to be unrelated to variations in temperature, pressure, or the presence of a cosolvent, suggesting that the conditions were uniformly suitable for extractive solubilization. Decreased permeability may reflect redeposition of solubilized extractives to positions where they again diminish permeability as conditions drop out of the critical range, a possibility that will be studied further.