摘要
热处理是一种改善木材尺寸稳定性的重要方法,同时会引起木材多尺度结构变化,进而影响热处理材的微宏观力学性能。本文从纳米、微米、毫米三个尺度总结了热处理对木材结构单元及力学性能的影响。在纳米尺度,热处理过程中木材半纤维素大量降解导致其作为界面偶联剂的基质特性被破坏;纤维素的羟基与半纤维素降解产生的有机酸发生酯化反应,其分子间氢键以及与半纤维素连接的氢键大量断裂,引起分子链断裂,削弱了半纤维素与纤维素之间的结合强度;多糖解聚引起木质素相对含量变化,木质素自缩聚反应以及与多糖降解产物发生的交联反应是热处理后细胞壁基质力学性能发生变化的重要因素。在微米尺度,热处理木材细胞壁胞间层出现裂缝,各细胞间产生分离,微纤丝的定向排列规律性下降、倾角增大,沿微纤丝长度方向断裂,进而引起细胞壁力学强度明显下降。在毫米尺度,早晚材的横切面上由方形、圆形变成椭圆形,其中早材开裂较多;径切面上管胞和导管的胞壁变形开裂,随着热处理程度增加,胞壁出现垂直轴向断裂、纹孔破坏、木射线开裂等现象,射线薄壁细胞被大量破坏,进而引起木材的载荷承载能力下降。本文可以为深入研究热处理对木材各尺度结构及力学性能的影响机制提供参考。
Heat treatment is an important method to improve the dimensional stability of wood.At the same time,it will cause changes in the multi-scale structure of wood,and then affect the micro and macro mechanical properties of heat-treated wood.In this paper,the effects of heat treatment on multiscale structures and mechanical properties of wood were summarized from three scales of nanometer,micron,and millimeter.At the nanoscale,the degradation of wood hemicellulose during heat treatment resulted in the destruction of matrix properties as an interfacial coupling agent.The hydroxyl groups of cellulose were esterified with the organic acid produced by the degradation of hemicelluloses,and the intermolecular hydrogen bond and the hydrogen bond connected with hemicelluloses were broken in large numbers,which caused the break of mole-cular chain and weakened the bond strength between hemicelluloses and cellulose.The relative content of lignin changes due to polysaccharide depolymerization,and the self-polycondensation of lignin and the cross-linking reaction with polysaccharide degradation products were important factors for the mechanical properties of the cell wall matrix after heat treatment.At the micron scale,cracks appeared in the intercellular layer of the cell wall of heat-treated wood,and there was a separation between cells.The directional arrangement of the microfibril decreased regularly,the inclination increased,and the mechanical strength of the cell wall broke along the length direction of the microfibril.At the millimeter scale,the early wood and late wood changed from square and round to oval on the transverse section of heat-treated wood,and the early wood cracked more.The cell wall of tracheids and vessels was deformed and cracked on the diameter section.With the increase of heat treatment,the cell wall appeared to vertical axial fracture,pits damage,wood ray cracking,and other phenomena,and a large number of ray parenchyma cells were destroyed,which led to the decrease of the load carrying capacity of wo
作者
王旭洁
雒翠梅
母军
漆楚生
WANG Xujie;LUO Cuimei;MU Jun;QI Chusheng(Key Laboratory of Wood Material Science and Application,Beijing Forestry University,Beijing 100083,China;Beijing Key Laboratory of Wood Science and Engineering,College of Materials Science and Technology,Beijing Forestry University,Beijing 100083,China)
出处
《材料导报》
EI
CAS
CSCD
北大核心
2024年第18期277-284,共8页
Materials Reports
基金
国家自然科学基金(31971589,31870536)。
关键词
木材
热处理
多尺度结构
力学性能
wood
heat treatment
multiscale structure
mechanical property
