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New Zealand Journal of Forestry (2019) 64(3): 8–12
©New Zealand Institute of Forestry

Feature article
A review of Scion research using supercritical carbon dioxide

Bernard Dawson

Senior Scientist, Scion, Rotorua. Email:
*Corresponding author.

Abstract: Scion has researched the application of supercritical CO2 to remove water from timber. For CO2 to become a supercritical fluid, a pressure of 7.4 MPa and a temperature of 31°C is required. Timber species that have been treated include a range of New Zealand softwoods and hardwoods, with radiata pine being most widely studied. Supercritical CO2 offers advantages of being less energy intensive than thermal drying, it leaves no residue as the fluid reverts to gas below 7.4 MPa, and it can penetrate wet timber as a consequence of high pressure. Supercritical CO2 can be used to remove water in radiata pine down to about 40% cycling from gas to supercritical fluid multiple times. At this moisture content chemicals or fluids can be added to radiata pine without water (sap) in the cell lumens to improve or add properties such as stiffness or decay resistance. For difficult-to-dry collapse-prone hardwoods, such as eucalypts, dewatering prevents timber collapse and has the potential to increase conversion rates from green timber into product. Following the supercritical CO2 dewatering process, a kiln drying schedule will be required to achieve a moisture content of 10-14% in the timber. However, the effect of the supercritical CO2 dewatering process is retained and collapse will not occur on kiln drying.
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