Moisture transfer and drying stress of eucalyptus wood during supercritical CO2 (ScCO2) dewatering and ScCO2 combined oven drying

Abstract

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 °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.