【作者】 唐晓淑；

【导师】 赵广杰；

【作者基本信息】 北京林业大学 ， 木材科学与技术， 2004， 博士

【摘要】 为了从分子水平上弄清楚压缩木材在热处理变形固定过程中的“架桥结合反应”和“分子链切断反应”两种截然不同的观点，选择压缩密化材热处理永久固定过程中的最佳热处理路径，为开发杉木压缩密化加工新技术、新工艺奠定理论基础和提供技术参数，本研究首先以温度(T)和时间(t)为坐标建立了杉木压缩密化材热处理过程中等回复率的T-t平面，并对T-t平面上的一些具有相同回复效果的不同热处理路径进行了等效性验证。然后以回复率RS=10％情况为例，对这些通过不同路径得到的相同回复效果的热处理材进行了动态粘弹性测定。明确各个压缩处理材的力学性能的同时，也在各路径之间进行了比较。通过对回复率为10％的不同热处理材，以及在180oC下不同回复率压密化材的木粉进行X射线衍射和红外吸收光谱的测定，讨论了各处理条件下处理材的结晶度变化以及木材内部化学成分的变化。为了明确压缩木材在热处理过程中究竟哪一阶段发生了分子切断反应或者架桥结合反应，同时也为了从根本上解释各路径间的物性差异，作者首次将高分子粘弹理论中的Tobolsky不连续应力松弛测定理论应用在压缩密化材永久固定机理的研究上，并设计、制造出国际第一台力传感器式木材化学应力松弛测定仪。通过分析杉木压缩木材在不同温度下的连续不连续应力松弛曲线，计算表观活化能，考察了木材内部不同阶段的切断、架桥反应，分离所发生的物理、化学应力松弛。最后为了验证松弛机构是否具有普遍性，对非压缩密化材是否也适用，又对绝干木材在不同温度领域下的应力松弛曲线进行了分析，考察了其各个热处理阶段的内部反应变化。 本研究的主要结果归纳如下： (1) 对压缩密化材进行热处理固定时，T-t平面上的低回复率领域(RS≤10％)完全可以通过不同热处理路径达到，各路径等效性较好。在各个路径中木材内部都同时产生了分子链的切断反应和分子间架桥反应，后者对各路径的等效性起了积极作用。对于较高回复率的等效路径，温度的影响不能忽略，具体路径必须经过一定的修正才能得到理想的结果。 (2) 径向压缩密化处理本身，并没有引起杨氏模量所反映出的材性劣化，但直接参与压缩密化处理的弦切面表面附近的损伤相对比较大。中文摘要(3)(4)(5)(6)(7)在热处理过程中，压缩密化材的结晶度在初期呈增大趋势，然后随着热处理时问的延长而逐渐减少。热处理使木材内部发生了半纤维素和木素的热分解，同时也引起纤维素的结晶形态发生了变化。在180吧下的热处理中，木素的热分解非常活跃，另外还存在着吸着水的散失现象。而纤维素并没有发生明显的化学反应。在具有10%回复率的不同热处理路径中，木材内部都发生了半纤维素，木素的热分解反应以及吸着水的“物理性脱水”现象，但内部发生的主化学反应类型并不相同。热处理固定效果和效率，除了与温度域有关，降温、升温的处理，以及升降温的速度一也对其有影响。杉木压缩密化材在不同温度下热处理过程中，其连续应力松弛行为可以用高分子粘弹理论中的3种Maxwell一Wieehert模型来模拟。即，180℃一220oC、160℃、120一140℃三个温度领域下的应力松弛曲线可分别用:两个Maxwell单元并联组合模型A:两个Maxwell单元同一个理想弹簧并联组合模型B;一个Maxw。U单元同一个理想弹簧并联组合模型C来表现。通过对不连续应力松弛曲线的分析，首次明确了木材达到永久固定过程中(160℃一220℃领域内)在木材内部先后发生的5个松弛过程。即，(l)非晶区域中纤维素、半纤维素分子链之问产生滑移引起的物理松弛I;(2) matrix分子被软化，分子运动引起的物理松弛H;(3) matrix分子内，非晶区中半纤维素分子与纤维素分子问形成氢键结合的物理松弛111;(4)基于半纤维素，少量木素的热分解，由分子切断反应引起的化学应力松弛I;(5)基于半纤维素，木素的进一步热分解，在有分子氧或无分子氧的参与下形成半缩醛、醚键等架桥构造的化学应力松弛H。5个松弛过程对应的表观活化能依次为74.7，43.8，56.5，96.8，83.5kJ/mol。热处理固定过程中，化学应力松弛阶段所对应的木材内部分子反应机理:木材分子在热处理达到一定阶段后，分子内的某些碳原子吸收能量被激发形成自由基，引发一系列的级联反应。首先发生的是，有分子氧参一与和无分子氧参与下的链切断反应。伴随着热处理的进一步推进，自由基的进一步反应将会造成新的架桥结构的形成。其中无氧条件下可能发生侧链烷烃交联而形成支链，在有氧分子参与的情况下，反应进一步进行形成一些架桥结合，诸如半缩醛、醚键等等。另外，反应过程中形成的次级自由基同时又能引发新一轮的架桥和切断中文摘要 反应。(8)本研究以RS=10%，180℃一200℃之间的复合热处理路径为例，讨论了复合路 径中木材内部的反应变化。当处理材处于稳定的温度环境中时，木材内部应力 随着时间的推移而逐渐松弛，但是当温度变化时，应力在短时间内迅速随之变 化。温度升高，内部应力增加;温度降低，内部应力随之迅速减少。(9)木材在180OC条件下热处理时，内部的分子切断反应占绝对优势，不连续曲线更多还原

【Abstract】 To justify the conflicting options on the dominance of either "crosslinking" or "cleavage" in compressed wood fixation, a planum of medium recovery of compression set of Chinese fir wood was constructed with temperature (T) and time (f) as coordinates. This provides theories and technical parameters making selection of optimal heating pathway of compressed wood permanent fixation possible, and might eventually leading to the development of new technology on softwood compression. The equivalency of different pathways targeting same recovery level had also been evaluated based on this T-t planum. Furthermore, the dynamic viscoelastic behavior of fixed wood with equivalent recovery set (10%) from different pathways had also been investigated. Subsequently, the mechanics of different specimens was compared. Both X-ray diffraction and infrared absorption of compressed wood powder samples, which were fixed either by heating at different temperatures resulting 10% recovery, or incubated at 180 C for certain times with subsequent recovery levels had been measured. The changes of relative crystallinity, chemical components and internal structure of compressed Chinese fir wood under different heating pathways were discussed based on this spectrometric data. Here, Tobolsky’s approximation method of discrete relaxation of stress in macromolecular viscoelasticity was first introduced to interpret the fixation mechanism of compressed wood. The distribution time of molecular bond breakage and crosslinking in the fixation process was deduced thereafter. The mechanistic change between different fixation pathways was proposed. We designed a strength-sensor meter to measure the stress relaxation in wood. The compressed Chinese fir wood continuous and/or discrete relaxation curves of stress were retrieved under different temperatures with this machine. Their apparent activation energies were subsequently calculated to uncover both the timedistribution of cleavage and crosslinking and the physical and chemical relaxation of stress. Finally, the stress relaxation curves of oven-dry wood had been monitored under different temperatures. The internal change at different stages of the fixation process was deduced as well. The ubiquitous existence of this relaxation process was confirmed, even in untreated wood.The major achievements of this research are following:(1) In heat fixation of compressed wood, low recovery levels (RS is less thanlO%) on T-t plane can be obtained by numerous different pathways composed of different time and temperatures, which have a high equivalence of fixation effect. The Breakage and crosslinking of molecular bond happened in wood during fixation. Crosslinking seems to contribute more on the recovery equivalence. But on the equivalent pathways of higher recovery, the influence of temperature can not be overlooked. The actual routes must be somewhat modified to obtain an expected result.(2) The wood physical properties decreased solely by compression had not been observed. This was clearly revealed by Young’s modulus measurements. On the other hand, the wood layer close to the tangential surface of specimen was damaged more seriously.(3) Relative crystallinity increased at early stage of heating fixation, and then decreased more and more later on. Hemicelluloses and lignin decomposition was induced by the fixation process, Furthermore, cellulose crystal structures changed accordingly.(4) Lignin was degraded actively under 180 C. Adsorbed water evaporation after heating had also been found, but cellulose didn’t change obviously. In the fixation pathways of 10% recovery level, hemicelluloses and lignin decomposed actively, accompanied by the losing of physical adsorbed water. However, the dominant reactions in different pathways were different accordingly. The fixation effect and rate are correlated to temperature range, temperature dynamic, and the speed of the temperature change.(5) The continuous relaxation of stress in compressed Chinese fir wood fixed under different tempera更多还原