Fixation of compressive deformation in wood by pre-steaming

Wood block specimens pre-steamed at 120–220 °C for 5–20 min were compressed in the radial direction. The recovery of set decreased with increasing pre-steaming temperature and time. The reduction of set recovery correlated with the amount of weight loss in steaming irrespective of pre-steaming temperature and time. The weight loss for the highest level of fixation of compressive deformation was about 7.5% that was obtained by pre-steaming at 210–220 °C for 10 min. Moreover, the set recovery of the pre-steamed specimen decreased as pressing temperature and time increased. The compressibility of wood block increased with increasing pre-steaming temperature and time. Large transverse compression and stress relaxation tests showed that Young’s modulus and yield stresses were reduced while the stress relaxation magnitude was increased by more severe pre-steaming condition. Scanning electron micrographs showed some cell structure destruction at large deformations in specimens steamed at above 180 °C. This suggests that the wood becomes brittle due to steaming. Creep test data indicate that fluidity decreased with increasing steaming time and temperature. Pre-steam fixation of compressive deformation is due to degradation of the microfibril framework, as well as the viscous flow of the matrix components resulting from the scission of their cross-linked network.