【作者】 张晓峰；

【导师】 顾继友； 蔡英春；

【作者基本信息】 东北林业大学 ， 木材科学与技术， 2010， 博士

【摘要】 在现代木材加工工业生产中,由于对胶粘剂的依赖性在不断增强,所以胶接质量越来越成为影响木制品质量的一个重要因素。对于胶接质量的研究,很多学者做了大量工作。但是,对于木材干燥质量对胶接质量影响的研究却是空白。不同干燥基准和不同热湿处理条件下,木材会有不同干燥质量。木材干燥质量指标主要包括以下内容：1)最终含水率；2)锯材厚度上的含水率偏差；3)残余应力指标；4)可见干燥缺陷等。因为不同干燥质量对木材表面的性质如润湿性、表面张力、表面自由能、活性基团的数量与性质等,都会产生一定影响。因而会直接影响胶接界面的性质。本论文主要探索了在不同的干燥质量条件下,木材干燥质量和表面性质的变化,从微观的角度分析这些变化对胶接界面产生的影响,从宏观的角度建立胶接界面的情况与胶接力学强度的关系。从而说明干燥质量对胶接力学强度的影响,结合数学分析方法进而提出改善胶接界面性能的理论依据,以此来优化木材的干燥工艺和干燥过程的控制,使干燥质量能够满足胶接设计的要求。本论文的主要研究结论如下：1、木材的含水率厚度上含水率偏差：厚度上含水率偏差,随着存储时间的延长,呈现出波动变化的趋势。对于最终含水率较高(含水率高于当地平衡含水率时)的木材,其含水率偏差较大,随着存储时间的延长,呈现下降的趋势。在这个过程中,芯层含水率下降的速度为3.1%/天比表层含水率下降的平均速度1.47%/天快1.63%/天,这样就会使芯层表层含水率迅速接近而使含水率偏差迅速减小；最终含水率较低的木材,其含水率偏差较小。随着存储时间的延长,呈现上升的趋势。在这个过程中,芯层的含水率上升的速度为0.85%/天,比表层含水率上升的平均速度0.60%/天快0.25%/天,这样就会使芯层表层含水率拉开距离使含水率偏差逐渐加大；前者厚度上含水率偏差在3-4天内降到最小值；后者在3-4天上升到最大值；5-6天后,两者厚度上的含水率偏差都趋于稳定。木材表层含水率：高含水率的木材,木材表层的含水率,随着存储时间的延长,呈现下降的趋势。低含水率的木材,木材表层含水率,随着存储时间的延长,呈现上升的趋势。最后都趋向于存储环境下的平衡含水率。到了5天后趋向稳定。当木材含水率远远低于使用环境下的平衡含水率时,木材的吸湿性明显降低,随着存储时间的延长,不能吸湿到应有的与平衡含水率接近的程度。厚度上含水率偏差波动大约在1%左右的范围内；木材表层的含水率,随着存储时间的延长,总体呈现上升的趋势。2、木材干燥后应力在干燥结束后,随着存储时间的延续,木材应力总的变化趋势是在增大。通常来说呈现波动变化的趋势：1-2天应力在逐渐增大,第3天有所下降,4-5天继续增大,6天以后趋于平稳。这与木材的含水率的变化有着密切的关系。含水率变化,应力也相应变化；含水率稳定时,应力也趋向稳定。3、胶接强度(常态压缩剪切强度)木材的剪切强度与木材胶接时含水率关系极密切,与木材胶接时的应力也有一定的关系。应力增加时剪切强度下降。应力基本一致时,厚度上含水率偏差成为影响剪切强度的主要因素。当木材厚度上含水率偏差增加时,剪切强度减小。在含水率相同的条件下,厚度上的偏差越小,剪切强度越大；厚度上含水率偏差变化的速率对剪切强度的影响是：在速率方向相同的条件下,剪切强度有着相同的变化规律,并且,速率大的其剪切强度变化滞后于速率小的剪切强度的变化。含水率、含水率偏差和应力在剪切强度上起了主要作用。4、木材表面润湿性木材干燥后,其接触角随着存储时间的延长都会增大。接触角的余弦值会随着储存时间的延长而减小-木材的表面润湿性降低。木材表面润湿性受木材表层含水率变化的影响较大：表层的含水率变化剧烈。润湿性下降得就快；表层的含水率变化的平缓,润湿性下降的就缓慢。高含水率木材表面润湿性好于低含水率木材。在含水率相同条件下：采用较高温度干燥的木材,木材表面润湿性低于采用相对低温干燥的木材。5、木材表面自由能木材表面自由能随着存储时间的延长呈现降低趋势。这与木材含水率变化有关有关：高含水率木材的表面自由能要高于低含水率木材的表面自由能。6、木材表面活性基团木材表面活性基团,随着储存时间的延长有如下的变化：Cls的百分含量呈现出波动变化的规律,通常来说是先减小然后再增加然后再减小；氧的含量变化呈现一定的规律性,氧的含量从35%逐渐降低到27%,而后又增加到30%。最后趋于稳定。Nls的百分含量比较少,呈现逐增加的渐波动变化。7、胶接界面Cls,Ols和Nls原子百分含量变化比较明显,与木材的界面相比较：Cls的量相对减少了；Nls的含量显著增加了；Ols的含量减少了。说明胶粘剂与木材发生了反应。更多还原

【Abstract】 Due to the increasing dependency extent of the modern wood industry on the wood adhesives, the bonding quality has become one of the most important factors showing great influence on the final quality of wood products. Although numerous researchers have paid more attention to the bonding properties of wood products, the study associated with the interrelationship between timber drying quality and bonding quality still remains a research vacancy now.As results of the different drying schedules and also different conditioning parameters, the final dried timbers will show particular drying quality. The wood drying quality characters include the following ones,1. The final MC; 2. The MC gradients along the wood thickness direction; 3. The drying stress; 4. The visual drying defects. Different drying quality will have characteristic influences over the actual properties of material surface, namely, wet ability, surface tension, surface energy, the numbers and properties of activated atoms. These physical and chemical changes will, in turn, have the direct influences on the properties of bonding interface.Based on the specified wood drying quality, this paper mainly aimed to investigate the influences of the timber drying quality and the surface changes of wood materials on bonding interface in the microscopic level, trying to establish the inter-relationship between the bonding interface properties and the bonding mechanical strength in the macroscopic level. According to the theoretical analysis and research results of the experimental practices, the influence of drying quality on the bonding mechanical properties will be well documented. The theoretical backgrounds for the improvement of bonding interface qualities were put forward by making use of the mathematical analysis method. In consequence of these works, the drying technology and drying process control strategy can be optimized accordingly, so that the resulting drying quality can be applicable to the bonding design process.The main research results are as follows:1. Moisture content (MC) of woodThe MC tolerance on the wood thickness:it shows the undulation change with the storage time. For the higher MC wood (the MC is higher than that of the local Equilibrium Moisture Content), the MC tolerance is higher too, with the storage time pass on, it shows to become lower trend. In this progress, the core MC degressive speed is 3.1 percent per day, it is faster than that of the surface one 1.47 percent per day. This will bring about the core MC and the surface MC come together faster and let the MC tolerance become minished quickly. For the lower MC wood, the MC tolerance is lower too, with the storage time pass on; it shows to become higher trend. In this progress, the core MC increased speed is 0.85 percent per day, it is faster than that of the surface one 0.60 percent per day. This will bring about the core MC and the surface MC bigger distance and let the MC tolerance become big quickly. The MC tolerance decreased to the lowest volume in 3 to 4 days for the higher MC lumber; on the contrary, the MC tolerance increased to the highest volume in 3 to 4 days for the lower MC lumber. Both of them, the MC tolerance become to the stable in 5 to 6 days.For the MC on the wood surface, the higher MC become to lower with the storage time pass on; on the contrary, for the lower MC on wood surface, it will become higher. After 5 days, both of them will be stable. The research showed the best MC of wood bonding is 9-10%.2 Wood drying stressThe trend of the wood stress will become higher after completed drying, this is fluctuated change:it has the close relationship to the changing of the MC.MC changes and the stress changes accordingly. The MC is stable and the stress is stable too. When the wood drying schedule’s highest temperature is 90℃,the MC tolerance is around 1%, the drying stress is in the smallest condition. It will be increased when the wood dried at higher temperature as well as the big MC tolerance.3 Bonding strength (compressive and shear)The wood bonding strength has the close relationship to the MC as well as the wood drying stress. If the stress higher, the bonding strength will be lower. The MC tolerance will become main factor to the bonding strength when the stress is similare.The bonding strength will be the highest when the N1s content around 3% and O1s 23-24% on the bonding interface. The wood drying schedule temperature is 90℃accordingly.4 Wet ability on the wood surfaceThe cosine contact angle will become lower and lower with the wood storage time pass on, in another words, the wood surface wet ability is decreased. The wet ability will be affected by the wood surface MC changing, the more MC changes on the wood surface, the more decreased to the wet ability, on the contrary, the small MC changes on the wood surface, the even changes to the wet ability. The higher MC wood wet ability is better than that of the lower MC one.Undered the same MC condition, The wood, which dried in the higher temperature,the wet ability will be lower than that of the one which dried in the lower temperature. The wet ability will be in the best when the MC is 8-10% and the dried temperature is around 90℃. When the MC is less than 7%, no mater how lower temperature used to dry the wood, the wet ability could not has a higher volume.5 Wood surface free energyThe wood surface free energy will become lower and lower with the storage time pass on. It has the close relationship with the MC changing:the higher MC wood surface free energy is better than that of the lower one. The wood surface free energy will be in the highest volume under the 8-9% MC as well as the dried temperature is 90℃. There is lower free energy volume if the wood MC is less than 6%.6 Wood surface active functional groupWith the storage time pass on, the wood surface active functional group will be changed as below:C1s changed in fluctuate way, normally it is decreased at first then increased; O1s content volume is changed from 35% to 27% then increased to 30%.The Nls content is small on the wood surface. The wood drying temperature will give a great effect to the C1s volume on the wood surface:C1s volume will be less when the dried final temperature is lower than that of it dried under the higher final temperature. O1s on the wood surface will be in highest volume when the MC is around 10%, the dried final temperature is 90℃. When the MC is less than 6%, there is no big change of the O1s on the wood surface with the different dried temperature.7 Bonding interface active functional groupCompared with the wood surface,C1s, O1s and N1s atom volume are changed obviously on the bonding interface, C1s is decreased; Nls is increased more; O1s is decreased. This indicated that there are some chemical changes between the wood and the adhesive surface. C1s volume is in the best condition under the 9-10% MC and the dried final temperature is 90℃. The dried temperature give less affect to O1s volume on the bonding interface, the wood surface MC gives a big effect to O1s.更多还原