Dewatering characteristics of Juglans mandshurica wood using supercritical carbon dioxide: A comparison with conventional drying

Supercritical carbon dioxide dewatering (SCD) offers significant potential for wood treatment due to its unique physical-chemical properties. SCD has the advantage of avoiding drying defects caused by capillary tension during the removal of free water in conventional kiln drying (CKD). In this study, 150 mm-long specimens of Juglans mandshurica wood underwent both SCD and CKD treatments, allowing for comparison of various dewatering characteristics such as dewatering rate, moisture distribution, deformation, and drying stresses. The findings revealed that the optimal dewatering time was 25 min. SCD proved highly effective, especially during the high moisture content (MC) phase, demonstrating a dewatering rate up to 5.6 times faster than CKD. SCD achieved a more even dewatering process across the wood, with a maximum MC difference of 4.52% between the core and surface zones. In contrast, CKD exhibited an MC difference 8.3 times larger than SCD. Furthermore, in the longitudinal direction, CKD displayed lower MC at the wood's end locations compared to SCD. Additionally, wood showed shrinkage following CKD but swelling after SCD treatment. Interestingly, both SCD and CKD treatments resulted in nearly identical drying stresses.