脱木质素处理对速生杨木和杉木细胞壁层结构影响

Effect of delignification on cell wall structure of fast-growing poplar and Chinese fir

木材吸湿性对于其自身性质和加工利用有重要意义,而吸湿机理尚未完全明晰。本研究旨在探究木材孔隙结构对于吸湿性的影响。以杨木和杉木为研究对象,采用亚氯酸钠溶液不同程度脱除木质素,分析了脱木质素对于孔径分布、微观结构、基团变化、结晶度等的影响,并用Hailwood-Horrobin模型进行了拟合分析与数理表征,进而研究了木材吸湿性及其变化机理。结果表明:脱木质素处理提高了杨木材和杉木材的吸湿平衡含水率,显著降低了吸湿滞后;脱木质素处理后多分子层吸附能力的提升幅度大于单分子层的,脱木质素处理后杨木材多分子层水的吸附能力强于杉木,特别是相对湿度70%~85%时最明显。脱木质素处理主要将微纤丝间隙和细胞角隅及胞间层等位置的木质素脱出,改变了细胞壁中木质素的分布规律,显著增加了2~30 nm间的介孔和1000~21000 nm间大孔的数量,杉木材各个孔径变化范围和孔容增量均大于杨木材。然而,脱木质素材的吸湿性并没有细胞壁中介孔量的变化明显;脱木质素处理没有改变杨木材和杉木材纤维素Ⅱ型结晶结构,但提高了两者的结晶度;红外光谱分析表明,半纤维素和纤维素等主要吸湿物质相对含量增大。因此,脱木质素处理后吸湿性的变化主要是由细胞壁的化学基团、微纳孔隙、结晶度等物理化学性能协同影响造成的。

The hygroscopicity is important for wood properties and processing,and the mechanism of hygroscopic pro-perties is not yet fully understood.This study was aimed at investigating the effects of wood pore structure on wood hygroscopicity.Poplar(Populus sp.)and Chinese fir(Cunninghamia lanceolata)were partly delignified using sodium chlorite solution,and the effects of delignification on pore size distribution,microstructure,chemical groups,and crystallinity were analyzed.Then the Hailwood-Horrobin model was used for fitting analysis and numerical characterization,and finally the wood hygroscopicity were investigated.The results showed that the delignification treatment improved the hygroscopicity of poplar wood and Chinese fir,and significantly reduced the sorption hysteresis.The enhancements of polylayer water adsorption of the poplar wood and Chinese fir wood by delignification were greater than that of monolayer water adsorption,and the polylayer water adsorption of the poplar wood was stronger than that of the Chinese fir wood after delignification,especially for poplar wood at 70%-85% relative humidity.The delignification treatment mainly removed the lignin of the space between microfibers,cell corners and compound middle lamella of poplar and Chinese fir,changed the distribution pattern of lignin in the cell walls,and significantly increased the number of mesopores between 2 and 30 nm,and macropores between 1000 and 21000 nm on the basis of the original micropores of the control wood.The range of variation in pore size distribution and pore volume increment of Chinese fir was greater than that of poplar,and the hygroscopicity of delignified wood was not as pronounced as the volume change of mesopore in the cell walls.The delignification treatment did not change the Type II crystalline structure of poplar and Chinese fir but increased the crystallinity.The Fourier infrared spectra showed an increase in the relative content of major hygroscopic substances such as hemicellulose and cellulose.Therefore,the changes in hygroscopicity are mainly caused by the synergistic effects of the chemical groups of the cell walls,pore structure,crystallinity and other physicochemical properties of poplar and Chinese fir before and after the delignification treatment.