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.

中文翻译：

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木材夹层压缩：过热蒸汽处理对夹层压缩固定的影响及其机制

永久固定对于夹心压缩木材的全面工业化至关重要。在这项研究中，夹心压缩木材用过热蒸汽进行了改性以进行压缩固定。研究了过热蒸汽压力对凝固恢复的影响。分析了压缩木材的微观结构、化学结构和纤维素晶体结构的变化，阐明了过热蒸汽处理下夹层压缩固定的原因和机制。结果表明，中央压缩木材的凝固恢复率高于表面压缩木材。过热蒸汽处理对凝固恢复的影响具有统计学意义（P < 0.05）。较高的过热蒸汽压力有助于降低凝固回收率，但过热蒸汽压力的影响程度取决于压力水平和引起凝固恢复的原因（暴露于高湿度、浸入水中或在水中沸腾）。凝固恢复的降低与细胞壁的微裂纹、半纤维素的降解、与木质素中芳香骨架相连的 C=O 的损失和结晶度的增加有关。这项研究表明，过热蒸汽处理可有效地永久固定夹层压缩木材的压缩。