VERTICAL COMPRESSION RATE PROFILE AND DIMENSIONAL STABILITY OF SURFACE-DENSIFIED PLANTATION POPLAR WOOD
Xinwu xu, Zhengjie Tang
Hot-pressing densification is nowadays widely applied to modify plantation wood. In this study, plantation poplar wood lumbers, 300 mm by 50 mm by 10 mm, respectively, in longitudinal, tangential, and radial directions, were surface-densified at 125 oC for 2, 3, and 5 minutes, with or without water addition on the surface of lumbers. The pressure was 1 MPa. The vertical compression rate profile (VCRP) in thickness direction of densified specimens was acquired through an X-ray densitometer combined with a mathematical model. In addition, the time-related springback rate (S) of densified specimens was recorded. It was shown that all specimens were compressed by 9.38 to 14.10% on average in the thickness direction, and CR values decreased from surface to core of specimens, resulting in U-shaped VCRP curves. The surface layers had the maximum CRs of 33.45 to 37.24%, while 21 to 53% of the whole thickness at core position showed no significant residual compression (CRs lower than 1%). After conditioning at room temperature and 65% relative humidity for 240 hours, all the specimens were shown to be dimensionally stable with S values under 2%. Water addition on the specimen surface helps densify the surface layers and stabilize the densified wood. The acquired data and results were thought to be helpful for the precisely control of wood loss in a densification process.