Effect of supercritical CO2 treatment and kiln drying on collapse in Eucalyptus nitens wood
Bernard S. W. Dawson, Hamish Pearson, Mark O. Kimberley, Bruce Davy, Alan Dickson
Abstract
Abstract Collapse-prone timbers such as species of Eucalyptus are poorly utilised due to low conversion rates that necessitate long pre-drying times. A supercritical CO 2 lumen water expulsion pre-treatment prior to kiln drying is proposed to bypass lengthy pre-drying. After drying (air, kiln or oven drying), shrinkage, collapse, washboard depression and checking of Eucalyptus nitens were determined using image analysis of 0.8 mm thick wafers and 5 mm thick biscuits. Lumen water expulsion-kiln drying reduced collapse by 75% and washboard depression by 71%, compared to drying from green. As water is removed from the water conductive tissue (vessels, rays, and fibre-tracheids) by lumen water expulsion, the water column is broken throughout the specimen, thereby disrupting the development of meniscus-induced water tension as subsequent drying occurs. Remaining water is proposed to reside in the non-water-conductive fibre tissue. If the process can be applied on large scale to Eucalyptus nitens , there is the opportunity for higher conversion rates to increase the commercial viability of solid wood products.