Retarded recovery of remaining growth stress in Agathis wood specimen caused by drying and subsequent re-swelling treatments

A wood block often changes its original dimension when it is kept in hot water. This is because the locked-in component of the growth stress is released by hygrothermal softening of the cell wall matrix. However, it is still unknown whether or not heating is a necessary requirement for the release of the visco-elastic locked-in component of the growth stress (GS). To solve this question, Agathis green specimen was treated by drying and re-swelling at room temperature, followed by boiling at 120 °C and 0.2 MPa. Then dimensions of green, re-swollen, and boiled specimens were measured at room temperature. Based on the obtained data, it was discussed whether the drying and subsequent re-swelling treatments release the visco-elastic locked-in component of the GS in green wood. The following conclusions were obtained. Locked-in component is released in part by the drying and subsequent re-swelling treatments without heating. After repeating the drying and subsequent re-swelling treatments, viscoelastic components are gradually released; however, rapid or complete release is made by boiling in hot water.