真空热处理人工林落叶松木材吸湿性变化机理研究

热处理是一种环境友好型的木材改性方法,可提高木材的耐腐性和尺寸稳定性。研究以落叶松木材为试验材料,在处理温度200℃的条件下,对其进行了不同时间的真空热处理。利用动态水蒸气吸附(DVS)对热处理前后木材吸湿性的变化进行了表征,通过傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)和X射线衍射(XRD)分析了热处理前后木材化学组分和结构变化,通过化学变化分析阐明了热处理木材吸湿性变化的作用机制。结果表明:真空热处理落叶松木材的平衡含水率降低,热处理木材的平衡含水率随热处理时间的延长呈逐渐下降的趋势。结合红外光谱和光电子能谱发现,热处理后木材纤维素和半纤维素等化学成分发生降解,木质素发生交联缩合反应,使得吸湿性基团含量减少,碳元素与氧元素含量发生变化,氧碳比降低,从C原子的结合形式来看,热处理材的C1含量增加,C2和C3含量降低,这些化学变化使得热处理材的吸湿性降低。此外,真空热处理未破坏木材的结晶结构,木材的相对结晶度随真空热处理时间的延长而增大,结晶度的增大减少了纤维素分子链上吸水性基团的数量,从而降低了木材的吸湿性。

Study on Mechanism of Moisture Absorption Change of Larch Plantation under Vacuum Heat Treatment

Heat treatment is an environmentally friendly method which can improve the decay resistance and dimensional stability of wood.In this study,in order to investigate the effects of thermo-vacuum treatment on dynamic water vapour sorption and chemical properties of larch wood,wood samples were treated at 200 ℃ in a vacuum oven for different durations.The changes of wood hygroscopicity before and after heat treatment were characterized by dynamic water vapour sorption.Fourier transform in-frared spectroscopy (FTIR),X-ray photoelectron spectroscopic (XPS)and X-ray diffraction were used to characterize the chan-ges in the chemical composition.The results showed that the equilibrium moisture content of wood decreased as the treatment time increased.FTIR and XPS found that the chemical composition of wood such as cellulose and hemicellulose degraded after heat treatment and the crosslinking condensation reaction of lignin occurred resulting in the decrease of the content of hygroscopic group.During heat treatment,the contents of carbon and oxygen changed and O/C ratio decreased.Besides,changes were also identified from the detailed C(1s )spectra.The C1 content of heat treated wood increased,and the C2 and C3 contents de-creased.These chemical changes reduced the hygroscopicity of the heat treated wood.The relative crystallinity of wood increased with the increase of heat treatment time.The increase of the crystallinity decreased the number of water-absorbing groups on the cellulose chain,which decreased the hygroscopicity of wood.