Moisture Transfer and Drying Stress of Eucalyptus Wood during Supercritical CO2 (ScCO2) Dewatering and ScCO2 Combined Oven Drying

Supercritical CO2 (ScCO2) dewatering is a lumen water expulsion process, in which CO2 is cycled between atmospheric pressure and supercritical phase and results in a fast expulsion of free water. In this study, specimens of 100 mm length Eucalyptus exserta F.V. Muell. wood were dewatered using ScCO2, then the dewatered and un-dewatered wood were dried in oven at 100 degrees C to investigate moisture transfer and drying stress. The ScCO2 dewatering was very fast. When the moisture content (MC) was over 40%, the MC distribution and gradient after dewatering and oven drying were different. The oven drying MC showed a ring contour distribution, but the ScCO2 showed a higher MC in one side and a lower MC in the opposite; the oven drying MC gradient was great in the middle and small in the end part of wood, but the ScCO2 MC gradient was small and roughly consistent. The oven drying moisture migration rates along the fiber and transverse directions were similar; however, the ScCO2 migration rate was faster in the transverse directions. The MC distributions of the dewatered and un-dewatered wood after oven drying were similar at 30% MC. The ScCO2 dewatering reduced wood residual stress, and it affected the stress development in the subsequent oven drying.

Automated summary

This study investigated the moisture transfer and drying stress of wood specimens dried using supercritical CO2 (ScCO2) dewatering. The results showed that ScCO2 dewatering was fast and had an impact on the moisture distribution and gradient in the wood. The residual stress in the wood was reduced after ScCO2 dewatering.