Development of schedule to steaming prior to drying and its effects on Eucalyptus grandis × E. urophylla wood

To investigate the influence of moisture content (MC) and steaming temperature on defects developing during steaming prior to kiln drying, mass loss, heat transfer, microstructures, extractives, and chemical transformation of Eucalyptus grandis × E. urophylla specimens (with moisture content of 120, 70, 60, 50, 40, 30, 20%) were observed in this study. Specimens of each experimental moisture content were steamed at 80, 100, and 120 °C for 4 h after pre-heating at atmospheric pressure, respectively. Results revealed that it was most beneficial to conduct steaming at 100 °C when the moisture content was approximately 50% after air drying when stagewise heating-up and continuous steaming schedule were adopted. Under this condition, there was a notable decrease in defects including edge bends, surface splits, and inner splits. Steaming was also a drying period characterized by various extents of mass loss. Changes in microstructures and extractive contents proved the increasing permeability of steamed wood. Deacetylation and crosslinking reactions happened in the hemicellulose of the sample materials, which contributed to the loss of hemicellulose after treatment.