基于扫描热显微技术的木材微观导热和胶合界面及热解特性研究

发布时间：2018-03-18 11:17

本文选题：木材　切入点：热扫描显微镜　出处：《南京林业大学》2016年博士论文　论文类型：学位论文

【摘要】：导热特性是材料最重要的物理性质之一。木材是典型的多孔材料,宏观尺度测定的木材导热特性是木材结构中固、液、气三相共同作用的结果。随着木材微纳加工及重组技术研发工作的开展,获得微尺度下木材中固相物质的导热特性具有重要意义,同时微尺度分析木材中固相物质的导热特性对木材宏观尺度下导热特性的理解也具有重要作用。另一方面材料导热特性由材料的结构与性质所决定,材料的结构与性质发生变化将引起材料导热特性的变化,由此分析材料的导热特性也是研究材料结构与性质的重要途径。扫描热显微镜技术(SThM)是微尺度研究材料导热特性的有效手段。本论文主要通过使用SThM研究木质基材料的微观导热物性,从微观导热特性的角度分析木质基材料的微观结构特征。主要研究内容包括如下方面:第一部分重点研究木材细胞壁的微观导热特性。同时基于木质材料微观导热特性的研究,分析木质材料的微观组成与结构的特性,重点从热物性的角度解释细胞壁不同壁层的结构特征。第二部分使用SThM技术从导热特性角度研究胶粘剂树脂和木材胶合界面的结构特征,基于在微观尺度木材与胶粘剂树脂导热特性的差异,分析了树脂在木材细胞壁和细胞腔中的渗透作用,为木质复合材料结合特性的研究建立新的技术途径。第三部分结合光谱分析技术、X射线衍射技术、纳米压痕等技术尝试将SThM技术引入到木材热解的研究工作中,重点研究热解后木材细胞壁的化学组成、微观构造及物性的转变,分析热解过程木材化学、物理及微观构造特性转变的相互关联性。通过本研究开拓了木质材料微观导热特性的研究途径,开发了基于导热特性分析的木质材料微观组成与结构的研究方法。本文获得的主要研究结果归纳如下:(1)使用SThM研究橡木纤维细胞壁在横切面导热特性的结果表明,细胞壁S2层的导热能力要明显高于胞间层(CML)和角隅(CC);显微拉曼技术研究结果显示S2层的纤维素含量较高;X射线衍射研究获得纤维素在S2层中以约11°的纤丝角近似平行于细胞轴向分布排列的结论。在S2层中热量顺纤维纹路方向传递;而CML和CC中木质素含量高,且CML和CC的化学成分中呈杂乱分布排列,没有规则的纹路方向,因此此区域相比较S2层导热能力要低。使用SThM在木材径向解剖面对细胞壁进行扫描成像,结果显示从径向对细胞壁施加热量后细胞壁的不同区域(S2、CC和CML)没有表现出导热能力的差异。造成上述结果的机理是木材细胞壁径向施加热量后热量在S2层的传递垂直于木材的微纤丝方向,即热量沿木材横纹方向传递;同时CC,CML区域化学成分排列成无序状态,因此从径向施加热量后,细胞壁不同区域表现出的导热能力近似一致。本部分可得出结论,造成木材细胞壁不同区域导热特性的差异主要是由于不同区域组成成分的空间排列特征造成。木材导热在宏观尺度表现出典型的各向异性,本部分SThM实验研究表明细胞壁由于其自身构造特征,在微尺度其导热特性也表现出了各向异性的特点。(2)使用SThM研究木质复合材料胶合界面结构特征,从微观导热特性角度分析木材细胞壁与添加纳米纤维素的酚醛树脂的结合特征。研究结果表明酚醛树脂在微尺度下表现出的导热能力要明显低于木材细胞壁。纳米纤维素纤丝、纳米纤维素晶体添加到酚醛树脂胶中对微尺度下胶粘剂的导热物性没有造成影响。由于胶粘剂与细胞壁导热特性的差异,从胶粘剂过渡到木材细胞壁有一个明显的SThM探针电流值由小到大的过渡区间,此区间包含了胶合界面区域中的胶粘剂与木材基质相互影响的区域和两相物质直接接触结合的界面区。通过SThM扫描图像分析确定了过渡区间的长度,添加了纳米纤维素晶体的酚醛树脂与细胞壁的区间长度为1.92±0.32μm,而添加纳米纤维素纤丝的酚醛树脂与细胞壁的区间长度为1.76±0.277μm,其中胶粘剂与木材基质直接接触的界面区长度分别为0.73±0.144μm和0.7±0.092μm。SThM的测试结果显示在胶合界面附近的木材细胞腔中发现了胶粘剂的不连续渗透,即胶粘剂在个别细胞腔中充分充填。而根据探针电流分析结果显示,细胞腔中的胶粘剂与胶合区的纯胶粘剂的导热物性有差异,原因是充填到细胞腔中的胶粘剂与细胞腔中原有的充填物进行了混合,充填物在胶粘剂中的掺杂造成了细胞腔中胶粘剂的成分与性质有别于纯胶粘剂。(3)使用SThM研究热解过程中木材细胞壁结构转变特性,SThM研究结果表明随着热解温度的提高,木材细胞壁的壁层结构直到300℃都能观测到,而在325℃的热解后,细胞壁横切面反应出细胞壁壁层结构已经消失,整个细胞壁结构成均一化。SThM图像识别细胞壁不同壁层,主要是基于壁层的导热物性差异。造成不同壁层热物性差异主要原因又是在S2层中热量顺纹传递,而CML区域结构排列无序导致导热能力不及S2层。经325℃热解后,细胞壁的微纤丝定向排列结构特征已经消失,即热量在S2层中已无顺纹传递的条件。红外光谱研究表明,热解温度达到325℃后木材细胞壁的化学成分中纤维素和半纤维素已经基本热裂解。拉曼光谱同样表明325℃木材细胞壁各区域的化学成分结构已呈现均一化。元素分析也证实热解温度由300℃上升到325℃后,木材中的元素含量发生重大变化。X射线衍射表明热解温度到325℃时反应细胞壁微纤丝定向排列的衍射峰已经消失。使用纳米压痕技术对细胞壁的微观力学性能进行测试,结果表明达到热解温度300℃时木材细胞壁的弹性模量发生重大变化。本部分研究表明在木材热解过程中细胞壁物理性质、微观构造和化学成分转变具有很强的相关性,SThM技术可以有效的应用到木质材料微观物性与结构转变的研究工作中。
[Abstract]:Thermal conductivity is one of the most important physical properties of materials. Wood is a typical porous material, wood thermal properties determination of macro scale is wood structure solid, liquid, gas phase interaction results. With wood micro nano processing and recombinant technology research and development work, it is of great significance to thermal conductivity of solid materials in micro scale wood in the meanwhile, the micro scale analysis also plays an important role in the thermal conductivity of solid wood material to understand thermal characteristics of wood macro scale. On the other hand, the material thermal properties are determined by the structure and properties of materials, structure and properties of materials change will lead to changes in thermal properties of materials, which is an important way to heat analysis properties of materials is also on the material structure and properties. Scanning thermal microscope technology (SThM) is an effective means to study the characteristics of micro thermal conductivity materials. This theory This paper mainly through the micro thermal properties using SThM of wood based materials, analysis of microstructure characteristics of wood based materials from the micro angle thermal properties. The main contents include the following aspects: the first focuses on the micro thermal properties of wood cell wall. At the same time, based on micro thermal properties of wood materials, microstructure and properties analysis the structure of wood materials, mainly to explain the structure characteristics of different wall layer of the cell wall from the thermal point of view. The second part is the use of SThM technology from the thermal properties of adhesive resin and wood bonding interface of structural features, differences in micro scale wood and adhesive resin thermal characteristics based on the analysis of the penetration of resin in wood cell cell wall and cavity, for wood composite materials combining with the characteristics of the establishment of a new approach to the third part of the combination of spectral analysis. Technology, X ray diffraction technology, nano indentation technology to introducing SThM technology to the research work of wood pyrolysis, chemical composition of wood cell wall of pyrolysis, change the microstructure of transitivity analysis, the pyrolysis process of wood chemistry, relationship of the change of physical properties and microstructure of micro thermal conductivity approaches. Wood materials development through the study on the development of the characteristic analysis method for thermal conductivity of wood materials based on micro composition and structure. The main results obtained in this paper are summarized as follows: (1) SThM of oak fiber cell wall in cross section shows that thermal conductivity of the thermal conductivity of cell wall layer was higher than that of S2 the cell layer (CML) and corner (CC); micro Raman spectroscopy study showed higher cellulose content in S2 layer; X ray diffraction of cellulose in the S2 layer to about 11 degrees The microfibril angle approximately parallel to the axial distribution of cells arranged. Conclusion in the S2 layer along the fiber texture direction of heat transfer; while CML and CC in high lignin content, and chemical composition of CML and CC in a random arrangement, ridge orientation with no rules, so this area compared to the S2 layer to low thermal conductivity. The use of SThM in the wood cell wall face radial anatomy imaging, results from different regions of the cell wall of radial cell wall after applying heat (S2, CC and CML) showed no difference in conductivity. The mechanism of causing these results is the wood cell wall heat transfer in heat applied radial microfibril the direction perpendicular to the wood of the S2 layer, the heat transfer along the wood grain direction; at the same time CC, CML regional chemical components are arranged in a disordered state, so the heat is applied from the radial, approximate conductivity of cell wall in different regions show Consistent. This part can be concluded, caused by differences in thermal properties of wood cell wall in different regions is mainly due to the different components of the spatial arrangement of regional characteristics. By wood heat conduction exhibit anisotropy typical on the macro scale, experimental study of this part of SThM showed that the cell wall due to its structural characteristics, its thermal properties in micro scale show the anisotropic characteristics. (2) using the characteristics of SThM research of wood composite bonding interface structure, from the perspective of micro thermal characteristic analysis of wood cell wall and adding nano cellulose phenolic resin bonding characteristics. The research results show that the thermal conductivity showed phenolic resin under micro scale was significantly lower than that of wood cell wall. Nano fiber, nano crystalline cellulose added to the thermal properties of micro scale adhesive phenolic resin without impact. The adhesive The difference of thermal conductivity and cell wall properties of the agent, the adhesive transition to the wood cell wall has an obvious transition interval SThM probe current value increases, the interval contains the interface region and two-phase material adhesive and wood matrix bonding interface in the area of mutual influence in direct contact with the transition interval length is determined. Through SThM image analysis, add the interval length and cell wall phenolic resin nano crystalline cellulose was 1.92 + 0.32 m, interval length and cell wall phenolic resin and nano cellulose fibrils was 1.76 + 0.277 m, of which the length of the interfacial area directly contact adhesive and wood matrix were 0.73 + 0.144 m and 0.7 + 0.092 m.SThM test results show that the adhesive is not found in the continuous penetration of the wood cell cavity near the interface bonding, the adhesive in the individual cells in the cavity filling According to the current probe points filling. Analysis results show that the thermal properties of adhesive and bonding area of cells in the cavity of pure adhesive has the difference, reason is filling the original adhesive and cell cavity filling into cells in the cavity were mixed, filling in the adhesive and the doping caused the composition and properties of adhesives in the cell cavity is different from the pure adhesive. (3) the wood cell wall structure using SThM on the pyrolysis process of transition, SThM results show that with increasing pyrolysis temperature, wood cell wall lining structure until 300 degrees can be observed, while in the pyrolysis of 325 DEG C, the reaction cross section of the cell wall a cell wall layer structure has disappeared, the cell wall structure into a normalized.SThM image recognition of different cell wall layers, is the main difference between thermal wall layer. Based on differences in wall thermal properties is the main reason In the S2 layer heat transfer along the grain, and the CML regional structure disorder lead to heat capacity is less than the S2 layer. By 325 DEG C after pyrolysis, microfibril orientation of cell wall structure characteristics have disappeared, the heat in the S2 layer has no grain transfer conditions. FTIR analysis showed that the chemical composition of cellulose pyrolysis temperature up to 325 DEG C after the wood cell wall and hemicellulose pyrolysis has been basically. Raman spectroscopy also shows that the chemical composition of wood cell wall structure 325 degrees each area has been normalized. Elemental analysis also confirmed that the pyrolysis temperature increased from 300 to 325 DEG C., element content in wood changed.X X-ray diffraction show that the diffraction peaks of the pyrolysis temperature to 325 DEG C when the reaction cell wall of microfibril orientation has disappeared. The micro mechanical properties of the cell wall using nanoindentation test results show that the pyrolysis temperature reached 3 The elastic modulus of wood cell wall at 00 C with significant changes. This part of the study showed that in the pyrolysis process of wood cell wall in physical properties, microstructure and chemical composition change has a strong correlation, SThM technology can be applied to study changes in the micro material of wood material and structure effective.

【学位授予单位】：南京林业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S781

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