Improving quality of seasoned Tasmanian eucalypt timbers

The initial purpose of this thesis was to optimise kiln predrying times, without increasing the levels of drying degrade, for 25mm thick regrowth Eucalyptus obliqua using KilnSched scheduling program. The first trial conducted involved the daily measurement of moisture gradients to accurately determine the accuracy of KilnSched from measured behaviour. This trial was conducted over three weeks under mild conditions (20°C DBT, 19°C WBT). After this period of drying 100% of the backsawn boards dried showed signs of collapse and 90% of the quartersawn boards were collapsed. Surface checking severity was also unsatisfactory. It was evident that the timber was dried above the collapse threshold temperature. A subsequent trial was conducted to determine the collapse threshold temperature of the timber. The results of the trial showed that half of the boards tested collapsed at a collapse threshold temperature of 10°C. As a result of this discovery, the research aim was changed to reducing the severity of collapse, surface checking and internal checking degrade of regrowth E. obliqua, by pretreating the timber whilst in its green state prior to drying. Three pretreatment regimes were trialed. The regimes included two chemical pretreatments involving common table salt (sodium chloride) and a physical regime involving presoaking green logs in heated water. Sodium chloride was chosen due to its low cost and availability. The salt regimes consisted of both soaking green boards in a saturated salt solution, and packing green boards with a layer of salt between each row and wrapping in moist hessian. The salt regimes were conducted over nine weeks. The presoaked regime logs were soaked at 45°C over three days. Control boards were used to compare the pretreatments with untreated timber cut from the same stock. Following the pretreatment regimes, the control and pretreated boards were randomly racked and kiln predried following a typical drying schedule used by the Tasmanian timber industry for this species of timber. Upon completion of predrying, the boards were reconditioned and then final dried (following typical industry schedules) before they were investigated for levels of degrade.