【作者】 江京辉；

【导师】 吕建雄；

【作者基本信息】 中国林业科学研究院 ， 木材科学与技术， 2013， 博士

【摘要】 高温热处理优点是提高木材尺寸稳定性和耐久性能，但是也会导致木材力学强度降低、重量减轻以及木材颜色变化等。如何平衡热处理木材尺寸稳定性的提高与力学强度下降、重量损失以及颜色变化的关系；根据热处理材木制品（如地热地板用热处理材）最终要求来选择和优化热处理工艺，是木材高温热处理研究和加工企业急需解决的问题。因此，掌握热处理材性质变化规律与性质间相互关系，应用多种分析手段揭示热处理材尺寸稳定性与力学强度变化机理，对高温热处理加工工艺和推动木材热处理生产企业进步，具有重要的现实意义和理论意义。本文以柞木（Quercus mongolica）木材为研究对象，传热介质为过热水蒸汽，考察了热处理温度、时间、氧气浓度和窑内压力4个因子对热处理材性质影响规律以及室内抗白蚁性能，应用运筹学中非线性回归模型优化热处理材用于地热地板的高温热处理工艺，并结合利用扫描电镜、气相色谱、X-射线衍射仪与纳米压痕等技术手段揭示热处理材尺寸稳定性与力学强度变化机理。本文主要结论如下：1)建立了热处理温度、氧气浓度和热处理窑内过热水蒸汽压力等3个因子与热处理材抗弯弹性模量（MOE）、抗弯强度（MOR）、径向抗膨胀系数（Anti-swelling efficiency inradial direction: ASE-R）、宽度方向耐湿尺寸稳定性（Anti-humidity efficiency in width:AHE）、平衡含水率（EMC）和颜色变化（△E*）等6项性质的相互关系。其中：温度与MOE呈三次多项式关系，与MOR、ASE-R、AHE、EMC和△E*为线性关系；氧气浓度与以上6项性质呈二次三项式关系；窑内蒸汽压力和时间与上述6项性质呈线性关系。2)根据影响因子与热处理材性质的相互关系，建立了6项热处理性质与4个因子的非线性回归函数，根据木质地热地板标准要求以及4个影响因子的界定，通过运筹学中的非线性规划求解，获得优化热处理工艺：在常压下进行热处理，处理温度195℃、氧气浓度8.0%和处理时间1h，相对应求解得到的热处理材MOE、MOR、ASE-R、AHE、EMC和△E*分别为17.79GPa、80.02MPa、18.19%、0.28%、7%和16.06，与实际试验结果相近。在满足标准对AHE和EMC要求外，使处理材MOE和MOR最大，同时△E*较小。3)对柞木热处理而言，当温度小于180℃时，氧气浓度不能超过10%，当温度大于220℃，氧气浓度不能超过8%。4)与常压热处理相比，加压过热水蒸汽在热处理温度160℃和180℃时，对进一步提高尺寸稳定性有显著性影响，而在热处理温度220℃时，对进一步提高尺寸稳定性影响较小；随着处理窑中压力的增加，MOE、MOR和硬度逐渐下降。5)对于热处理材分层颜色与密度而言，在热处理温度160℃（180℃）与2h时，第1层的△E*与其它4层的差异不显著；而在热处理温度200℃和220℃下，第1层的△E*与其它4层的差异显著；但其它4层的△E*之间差异不显著；△E*从第1层（最外层）至第5层（中心层）逐渐降低，然而分层气干密度刚好相反。热处理材△E*与EMC、ASE-R呈二次三项式相关，与MOR呈线性关系，而与弦面硬度、径面硬度和MOE不相关。热处理材△E*预测EMC、ASE-R以及MOR较为准确。6)在室内抗白蚁试验中，热处理柞木木材被蛀等级为4级，为不耐抗白蚁蛀蚀。7)热处理柞木木材尺寸稳定性提高的原因：其一，热处理温度180℃木材半纤维素降解生成的各种糖类总量最多，可能主要是五碳糖，当热处理温度继续升高，纤维素生成少量的六碳糖类。由于木材降解，降低木材吸湿性。其二，由于纤维素非结晶区的降解，使处理材相对结晶度增加；加压热处理在密闭环境下，热处理过程中木材产生甲酸、乙酸和糖类等物质，使热处理环境为酸性，处理材的相对结晶度进一步提高。由于相对结晶度的提高，降低木材吸湿性。8)热处理柞木木材力学强度变化的原因：其一，晚材导管等细胞由圆形或方形经高温热处理后变为椭圆形；同时热处理材相对结晶度的增加，使得热处理温度200℃和2h的热处理材MOE较对照材的有所增加。其二，当增加热处理温度、时间延长或窑体蒸汽压力，处理后早材导管附近崩塌严重，甚至开裂，以及木材化学成分热降解，使MOR、MOE和顺纹抗压强度下降。其三，随着热处理温度升高，处理材细胞壁的纵向弹性模量呈先增加后降低趋势，与无疵小试样木材端面硬度变化趋势相同；热处理材细胞壁端面硬度大于对照材的；使热处理材表面硬度也大于对照材的。更多还原

【Abstract】 High Temperature Heat Treatment (HTHT) on wood is one of the most well-establishedtechnologies to reduce hygroscopicity, increase dimensional stability and bio-durability ofwood. While the mechanical strength and oven density of wood are generally reduced, andcolor difference (△E*) increases during this process. It’s an urgent issue for relatedresearching academies and wood processing enterprises to seek a good balance among thosecontradictory effects induced by HTHT through selection and optimization of related processin accordance with the end-users’ demand on properties of Heat Treatment Wood (HTW).Therefore it’s of critically practical and theoretical importance for upgrading HTHT technologyand promoting the development of related wood processing enterprises to master the HTW’sproperties changing patterns and relationship amongst various properties, and to explore themechanism on dimensional stability and mechanical strength of HTW through application ofdifferent analysis tools and approaches.The paper studies the effect of such parameters as temperature, time, oxygenconcentration and steam pressure on the wood properties and in-laboratory termite resistanceproperty of Oak (Quercus mongolica) samples treated in an environment of superheated steam.A non-linear regressive model is established to optimize the processing technology for HTWapplied in flooring for ground with heating system. Apart from this, various testing approaches,including Scanning Electron Microscopy, Gas Chromatography, X-ray Diffraction andNano-indentation are adopted to explore the mechanism of change in dimensional stability andmechanical strength of HTW.The key conclusions are drawn as follows:1) The relationships between the parameters (including temperature, oxygen concentrationand steam pressure inner kiln) and the properties of THW (including the Modulus ofElasticity (MOE), Modulus of Rupture (MOR), Anti-Swelling Efficiency in Radialdirection (ASE-R), Anti-Humidity Efficiency in width (AHE), Equilibrium MoistureContent (EMC) and color difference (△E*)) are established. An cubic polynomial relationship exists between temperature and MOE, a linear one between temperature andMOR, ASE-R, AHE, EMC and△E*, a quadratic polynomial for oxygen concentration andthese six properties mentioned above, and a linear for steam pressure inner kiln and heattreatment time with these six properties.2) Six regression equations (temperature, oxygen concentration, steam pressure and time asfunctions of MOE, MOR, ASE-R, AHE, EMC and△E*) are developed for the estimationand a nonlinear programming model is derived with operation research theory to obtain themost desirable HTW properties under heat flooring constraints. The results indicate that amaximum MOR of80.02MPa for the HTW can be obtained when heat treated at atemperature of195℃, oxygen concentration of8%, steam pressure of0.1MPa for1h.Under these production conditions, MOE, ASE-R, AHE, EMC and△E*are17.79GPa,18.19%,0.28%,7%and16.06respectively, which meet the requirements of the standards.3) In the practice, when the heat treatment temperature was less than180℃, oxygenconcentration was not over10%. While the temperature was higher than200℃, theoxygen concentration was less than8%.4) Compared with HTW treated at atmospheric pressure, the heat treatment temperature ofless than180℃has a significant impact on improving the dimensional stability of HTW atsteam pressure of kiln, where the heat treatment temperature of larger than200℃has aslight impact on dimension stability of HTW at steam pressure of kiln. However, with anincrease in steam pressure of kiln, the MOE, MOR and surface hardness decrease.5) When the heat treatment temperature was less than180℃for2h, no significant differencein△E*between the first layer and other four layers was found. When the temperature washigher than200℃, there was a significant difference in△E*between the first layer andother four layers. However, there was no significant difference in△E*among the otherfour layers. The△E*value become gradually small from first to fifth layer, but the airdensity was gradually large. The linear relationship between△E*and MOR and thepolynomial relationships of△E*with EMC and ASE-R were obtained, but there was norelationship between△E*and hardness in tangential, hardness in radial and MOE. Therefore, the EMC, ASE-R and MOR can be estimated by△E*.6) In terms of termite (Coptotermes formosanus Shiraki) resistance of HTW in laboratory, thevisual rating of the heat treated Oak was No.4grade, the HTW did not resist termite.7) The reasons why the dimension stability of HTW was improved are as follows: Firstly,when treated at temperature of180℃, the hemicellulose was decomposed into varioussugars. The content of sugar reached maximum level at temperature160~220℃, mainlyE-carbon sugar. As the temperature increased to220℃, the cellulose would bedecomposed into hexose. The hygroscopicity was reduced due to decomposing. Secondly,the crystallinity of HTW increased as a result of decomposition of non-crystalline regionof cellulose. HTW in steam pressure could produce formic acid, acetic acid and sugars,which created an acid environment within kiln, the HTW would be further decomposed, sothe crystallinity was higher than the HTW in atmospheric pressure. The hygroscopicitywas reduced due to an increase in crystallinity.8) The reasons why the mechanical strength of HTW was changed are as follows: Firstly, theHTW could be intensified because the vessel shape of late wood converted from round orrectangular to oval after HTHT, and the crystallinity of HTW was increased, so the MOEof HTW treated at200℃for2h was higher than un-treated wood. Secondly, with anincrease in the heat treatment temperature, time and steam pressure, predominant collapseor even cracks of the early wood vessels were observed in HTW, and so the MOR, MOEand Compressive strength parallel to grain were reduced. Thirdly, as the heat treatmenttemperature increased, the longitudinal elastic modulus of HTW cell increased, and thenreduced, which followed the same changing patterns with cross-section hardness of smallclear wood. The longitudinal and cross-section hardness of HTW cell were larger thanun-treated wood.更多还原