【作者】 闫丽；

【导师】 曹金珍；

【作者基本信息】 北京林业大学 ， 木材科学与技术， 2010， 博士

【摘要】 随着世界木材资源的日益紧缺,低质速生材的开发利用愈来愈受到重视。对木材进行压缩是一种行之有效的木材改性的方法,它不仅可以提高其物理力学性能,又保持了木材原有的优良特性,然而压缩木的变形容易发生回复使压缩木产品的应用受到很大的限制。本文从不同温度条件下甘油处理材的应力松弛、化学成分变化、细胞壁成分构造等方面探究了甘油预处理固定木材压缩变形的机理并将其应用于青杨(Populus cathayana Rehd.)的压缩变形固定,探索了一种环保、有效地固定木材压缩变形的方法,通过试验得出主要工艺参数,并检测了压缩木的物理力学性能、颜色变化、耐腐性能及耐老化性能。本研究的主要结论归纳如下：(1)甘油预处理压缩木的变形固定机理为：甘油进入木材无定形区后通过氢键结合吸附在木材无定形区的羟基上,使木材润胀、分子间容易发生滑移。在热压的过程中,木材的无定形区分子发生流动,半纤维素、木质素及少量的纤维素发生热解,分子链被切断,使蓄积在木材内的压缩应力得到松弛；木材组分热解生成的短链分子之间、短链分子与原来分子之间产生交联,无定形区分子发生序化重排,木材的相对结晶度提高,木材的压缩变形得到固定。(2)甘油预处理可加速木材的应力松弛,通过计算甘油处理材应力松弛过程的表观活化能(△E)发现,在25～180℃范围内,甘油处理材压缩应力松弛分为两个阶段,第一阶段25～100℃表观活化能(△E1)为8.24 kJ/mol,第二阶段120～180℃表观活化能(△E2)为81.38 kJ/mol。第一阶段对应着木材分子间滑移,氢键断裂引起的松弛,第二阶段对应着木材半纤维素及木质素分子链断裂所引起的松弛。(3)甘油处理可加剧热处理过程中木材主要化学成分的降解。甘油预处理木材140℃时部分纤维素开始降解；120℃时半纤维素开始降解,并且160℃时开始剧烈降解；120℃木质素开始降解,并且160℃开始剧烈降解。FT-IR谱图分析说明甘油处理材在高温条件下,半纤维素出现脱羧现象,分子链断裂；部分小分子的木质素的苯环发生断裂。(4)建立了不同温度条件下甘油处理材细胞壁成分构造模型。甘油仅能进入纤维素的非结晶区,对木材产生“结晶区间”润胀。甘油处理可以加快热处理材相对结晶度的提高,140℃以上甘油处理材结晶区宽度开始升高,200℃甘油处理材结晶区宽度降低。甘油分子进入木材无定形区后与水分子相似,通过氢键结合吸附在木材无定形区的羟基上的。甘油处理材E′的温度谱中观察到常温及120℃甘油处理材分子的“交联化”现象,甘油处理材tgδ的温度谱图中可观察到无定形区侧链吸附的甘油分子的运动引起的松弛过程及两个由木材分子链断裂生成的短分子链及短分子链发生交联或序化重排后形成的长分子链的微布朗运动引起的松弛过程。(5)甘油预处理压缩木同热水预处理压缩木相比压缩变形回复率明显降低,表面硬度提高,压缩后木材颜色明显加深,耐腐性能提高,老化后木材颜色的稳定性较好。甘油预处理杨木压缩木的主要工艺参数为：50%甘油水溶液预处理,热压温度160℃,保压60 min(抗弯强度较高)；热压温度180℃,保压30 min(表面硬度较高)。更多还原

【Abstract】 The development and utilization of fast-growing wood became more important with the decreasing wood resources. Wood compression is an effective modification method of wood because it can not only improve the physical and mechanical performance but also can maintain the superior characteristics of wood. However, the utilization of compressed wood has been greatly restricted because of the recovery of compression deformation.In this study, the mechanism of compressive deformation fixation of wood pretreated by glycerin was investigated by stress relaxation, change on structre of cell wall components and chemical compositions at different temperatures. The mechanism was applied to fix compressed deformation of Poplar (Populus cathayana Rehd.). Thus, an environment-friendly and effective method to fix compressive deformation of wood was explored; the process variables were determined by experiments and the physical and mechanical properties, color change, decay resistance and anti-weathering properties of compressed wood were also examined. The main results of this research are as follows:(1)The mechanism of deformation fixation for compressed wood pretreated by glycerin is summarized as follows:Glycerin was adsorbed to hydroxyl groups through hydrogen bonding in amorphous region after pretreatment so the wood was in swollen state and the molecules were easy to slip. The matrix of wood began to flow, the hemicellulose, lignin and a small amount ofβ-cellulose were degraded and the molecular chains were cut so the recovery force of wood was relaxed; the cross-linking was formed between short-chain molecules from wood component degradation or between short-chain molecules and the original molecules, the crystallinity of wood increased, matrix rearranged so that the deformation of compressed wood was fixed.(2) The effect of temperature on the stress relaxation of wood was apparent, and the stress relaxation accelerated by the increase of tempereature and glycerin pretreatment. The stress relaxation during 25-180℃can be divided into two phases acorrding to the apparent activation energy{ΔE). TheΔE1 of PhaseⅠequals 8.24 KJ/mol andΔE2 of PhaseⅡequals 81.38 KJ/mol. PhaseⅠwas the relaxtion caused by the breakage of hydrogen bonding and PhaseⅡwas the relaxation caused by the breakage of hemicellulose and lignin molecular chains.(3) The degradation of wood components was accelerated by glycerin treatment. For glecerin-treated wood (GTW), a part of cellulose began to degrade at 140℃; Hemicellulose bagin to degrade at 120℃and degrade violently at 160℃; Lignin begin to degrade at 120℃and degrade violently at 160℃. FT-IR results showed that the molecular chains of hemicelluloses were broken by decarboxylic reaction and the benzene rings of lignin with small molecular weight were broken in GTW at high temperature.(4) The structural model of cell wall components of wood treated by glycerin was built. Glycerol can only enter the non-crystalline region of cellulose and swell wood between crystalline regions. The crystallinity of wood was improved by heat treatment and was acceletated by glycerin pretreatment at above 140℃, and decreased above 200℃. Glycerol was adsorbed on hydroxyl groups in amorphous region of wood by hydrogen bonding after entering into the amorphous region, which was similar to water molecules. The phenomenon of molecular "cross-linking" of glycerol treated wood at room temperature and 120℃was observed in E’temperature spectra. The relaxation process of glycerol molecule adsorbed to the side chains in amorphous region of glycerol treated wood can be observed in tgδtemperature spectra. Two relaxation processes due to the micro-Brownian motion of the short molecular chains formed by degradation and the new molecular chains formed by crossing-linking and rearrangement can also be observed in tg8 temperature spectra.(5) The recovery ratio of compressed wood pretreated by glycerin (CWPG) is significantly lower than the compressed wood pretreated by hot water (CWPW) and the surface hardness, decay resistance, stability of color after weathering of CWPG were higer than CWPW. The color of CWPG was darker than CWPW. The main process parameters of compressed wood pretreated by glycerin are: pretreat by 50% glycerin solution, compressed at 160℃for 60 min (with optimized MOR) or compressed at 180℃for 30 min (with optimized surface hardness).更多还原