Abstract
Supercritical CO2 (ScCO2) is a drying medium with excellent solubility and mass transfer efficiency. Supercritical CO2 drying (SCD) can remove the water of wood rapidly and prevent a change of microstructure caused by capillary tension in the drying process. In this study, Eucalyptus urophylla × E. grandis specimens with lengths of 50 and 100 mm were dried with ScCO2. Conventional kiln drying (CKD) and oven-drying (OD) were used as control. After 1 h, the drying rate, shrinkage, moisture distribution, drying stress were measured to explore the influence of drying methods and specimen length for drying characteristics during the early drying stage. The results showed that compared with CKD and OD, water removal was the fastest under SCD, and the drying rate was nine times of CKD and one time of OD. The shrinkage of SCD was the lowest among the three drying methods. Moisture distribution of SCD and OD was uneven. The drying stress of SCD was relatively high, the drying stress index of it was almost five times of CKD and three times of OD. Regardless of the drying method, shorter specimens had a shorter drying period but greater drying defects than the long specimens.
Highlights
With the rapid development of China’s forest product industry, the demand for wood resources is increasing
We proposed a hypothesis that Supercritical CO2 drying (SCD) can benefit wood drying quality regardless of different specimen length by comparing conventional kiln drying (CKD) and OD
Moisture distribution, drying stress index and shrinkage rate to explore the influence of drying methods and specimen length on the Eucalyptus urophylla × E. grandis wood during the stage of initial drying, to provide a reference for improving the drying quality and expanding the solid wood utilization of eucalyptus
Summary
With the rapid development of China’s forest product industry, the demand for wood resources is increasing. China’s limited natural forest resources cannot meet the demand of the forest product industry, and the imbalance of supply and demand leads to China’s wood resources depending on imports [1]. Planted forests have a fast growth rate and high survival rate, and their development and planting can bring abundant wood resources to China’s forest production industry [2]. Eucalyptus is one of the main tree species in China’s planted forests, with high yield, short rotation cutting cycle, multiple varieties, hard texture, and beautiful patterns. Eucalyptus is an important raw material for the production of wood-based panels, wood floors, and wooden furniture [3]. The key technology to reduce the drying defects mentioned above is to develop suitable drying methods
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