Effects of Pre-Freezing Prior to Drying upon Some Physical and Mechanical Properties of Eucalyptus Urophylla × Eucalyptus Grandis Wood

Abstract

To investigate the effect of pre-freezing treatment on the shrinkage properties and discoloration of Eucalyptus urophylla × Eucalyptus grandis wood, E. urophylla × E. grandis wood samples were treated by pre-freezing at -20 and -40 °C for 72 h and then dried to reach equilibrium moisture content at 12% and 8%, respectively. Color changes were measured by colorimeter and evaluated by diffuse reflectance visible (DRV) spectrometry; mechanical properties were also tested. The results showed that the shrinkage of Eucalyptus wood samples decreased after being pre-frozen, and the overall color change ΔE* increased by 6.11 when the treatment temperature changed from minus 20 to -40 °C. Absorption (ΔK/S) spectra in the range of 450 to 740 nm of the treatment samples exhibited flat-lined, which suggests that the color of wood stabilizes after being pre-frozen and dried. The tensile, compression and bending strengths decreased 4.74, 6.05, 1.18 after pre-freezing treatment at -40 °C, respectively. Pre-freezing treatment at -20 °C is better than that at -40 °C for improving the drying properties of E. urophylla × E. grandis wood.