真空热处理日本落叶松木材化学性质的变化

Chemical property changes of vacuum heat-treated Larix kaempferi wood

为了揭示真空热处理对日本落叶松Larix kaempferi木材的作用机制,以日本落叶松木材为研究对象,分别在160,180,200,220和240℃的条件下对木材进行真空-常压热处理4h.采用X射线衍射法研究了热处理对木材结晶性能的影响;利用傅里叶红外光谱、固体核磁共振和电子自旋共振分析了木材在热处理过程中化学基团和表面自由基的变化.结果表明：经真空度为0.05-0.09MPa联合常压热处理后,木材纤维素结晶度的变化趋势为先增大,后减小,再增大.未处理材结晶度为36.21%,热处理温度为160,180,200,220和240℃时,木材的结晶度分别为43.56%,46.26%,32.09%,32.66%和37.97%.随着热处理温度的升高,木材中羰基官能团减少,热处理过程中木材半纤维素发生降解脱除乙酰基,酚型木素结构单元增多,醚化木质素结构单元减少.热处理前后木材表面自由基类型未发生改变,随着热处理温度的升高,木材表面自由基的数量增加.真空热处理对半纤维素与木质素产生了不同程度的影响,对纤维素的影响相对较小,通过对不同热处理条件下日本落叶松木材化学性质的分析,进一步阐释了真空热处理对木材的作用机制。

To understand how vacuum heat treatment affects larch wood, Lari% kaempferi wood specimens were heat treated in a vacuum at a degree of 0.05-0.09 MPa and under an atmospherie pressure with 160, 180, 200, 220, and 240℃ for 4 h. X-ray diffraction （XRD） was used to study the effect of heat treatment on crystallization properties of wood with three replications, the significant differences were analyzed using one-way ANOYA at=0.01 level. The changes of chemical groups and surface free radicals were studied by Fourier transform infrared spectroscopy （FTIR）, nuclear magnetic resonance （NMR）, and electron spin-resonance spectroscopy （ESR）. After heat treatment, wood samples were ground into powder and passed through a 100-mesh screen, but not a 120-mesh screen for XRD and ESR; passed through a 200-mesh screen for FTIR and NMR, Results obtained after heat treatments showed that the change of cellulose crystallinity increased first, then decreased, and finally increased; the crystallinity of untreated wood was 36.21%, and percent crystallinity of wood for corresponding temperatures was 43.56% at 160℃, 46.26% at 180℃, 32.09% at 200℃, 32.66% at 220℃, and 37.97% at 240℃. There was a significant difference about the crystallinity at 0.01 level （P=2.9E-17）. FTIR showed that with an increase of temperature, carbonyl groups and lignin composition were degraded. The solid NMR spectrum showed that during heat treatment hemicellulose degraded and acetyl groups were removed, the intensities of the phenolic lignin unit of treated samples were higher, and the intensities of the etherified lignin unit of treated samples were lower. ESR showed that the radical type was not changed before or after heat treatment. With an increase in heat treatment temperature, the intensities of free radicals changed. As a conse-quence, vacuum heat treatment resulted in the degradation of hemicellulose and lignin. Thus, through analysis of the chemical properties of wood with different heat treatments, the effect of vacuum heat treatment on wood was further explained. [Ch, 3 fig. 2 tab. 23 ref.]