Sandwich compression of wood: effect of superheated steam treatment on sandwich compression fixation and its mechanisms

摘要

The permanent fixation is essential for the full industrialization of sandwich-compressed wood. In this study, sandwich-compressed wood was modified with superheated steam for compression fixation. Effects of superheated steam pressure on set-recovery were investigated. Changes in microstructure, chemical structure and cellulose crystalline structure of the compressed wood were analyzed, to clarify the reason and mechanism for sandwich compression fixation under superheated steam treatment. It was found that set-recovery of central-compressed wood was higher than that of surface-compressed wood. Effects of superheated steam treatment on set-recovery were statistically significant (P 0.05). Higher superheated steam pressure contributed to lower set-recovery, but the extent of the impact of superheated steam pressure depended on the pressure levels and the reasons causing the set-recovery (exposure to high humidity, immersion in water or boiling in water). The decreased set-recovery was related to micro-cracks in the cell wall, degradation of hemicelluloses, loss of the C=O linked to the aromatic skeleton in lignin and increase in crystallinity. This research demonstrated that superheated steam treatment is effective in permanently fixing the compression of sandwich-compressed wood.