【作者】 林兰英；

【导师】 傅峰；

【作者基本信息】 中国林业科学研究院 ， 木基复合材料科学与工程， 2008， 博士

【摘要】 木材无机质功能性复合化制备的复合材料,具有阻燃和耐腐和天然无毒等优良性能,且产品价格低廉而日益受到人们的关注,但由于其力学性能除硬度和耐磨性得到提高以外,冲击韧性、抗弯强度、抗弯弹性模量都有不同程度的降低。为此,本文以人工林杨树木材为研究对象,在总结国内外该领域的研究进展和先进研究方法的基础上,在不削弱木材多孔性结构的前提下,以强化细胞壁为主要目标开展了硅溶胶强化杨木复合材的制备与性能研究,为赋予人工林杨树木材高强度、高性能,拓宽其应用范围提供技术支持,为人工林木材高效利用开辟新的途径,具有重要的科学意义和实用价值。本文以人工林杨树木材为研究对象,硅溶胶作为浸渍处理液,采用真空加压复合工艺路线开展强化低密度杨树木材的制备及其结构和性能的研究。论文的主要研究结论如下:(1)相同工艺参数下,液压浸渍工艺制备的复合木材其各项性能明显优于气压浸渍工艺制备复合木材的性能。就增重率而言,卸压之前的抽真空处理可以有效地增加复合材的增重率,卸压之后的真空处理对增重率的影响不明显,但可以除去处理材表面多余的浸渍液,使复合木材表面清洁又不致减少复合木材的增重率。(2)满细胞法浸渍硅溶胶可以最大程度地提高木材的增重率、抗弯弹性模量、抗弯强度。研究表明,复合木材的抗弯弹性模量与增重率存在线性关系,而复合木材的抗弯强度与硅溶胶进入木材内部的位置和深度有关,简单的物理填充不改变复合木材的抗弯强度。(3)硅溶胶浸渍处理的杨树木材,其抗弯强度的平均值为87.70 MPa,抗弯弹性模量的平均值为12.41 GPa,端面、弦面和径面的硬度分别提高了34.62%,49.15%和53.45%,顺纹抗压强度没有得到改善,基本保持不变或略有下降。浸渍硅溶胶处理后,木材在三个方向上都有不同程度的膨胀,弦向、径向和纵向尺寸分别增加了1.64%、0.55%和0.80%。延长前真空时间可以有效提高增重率和复合木材的力学性能,但对于木材的尺寸稳定性有不利的影响。因此,在保证复合木材力学性能达标的前提下要缩短前真空时间。对于杨树这样的软质木材,最优的浸渍工艺参数是:前真空时间20 min,浸渍压力1 MPa,浸渍时间30 min,后真空时间20 min。(4)硅溶胶浸渍处理不会影响木材的胶合性能。复合木材的胶合强度和木破率与未处理材差异不大,都达到了JAS标准。热重分析表明,复合木材较未处理材的热稳定性得到了改善,使得复合木材有一定的阻燃性能;并且随着增重率的增加,燃烧后残余物的重量随之增加,阻燃性能也随之提高。硅溶胶浸渍处理复合木材在弦向、径向和纵向的尺寸稳定性都得到了改善,且其尺寸稳定性的提高与增重率有关,改善的程度基本在25%至35%之间。润湿性研究指出,硅溶胶浸渍处理制备的复合木材产生了显著的接触角增大作用,表现出良好的表面疏水性能。(5)通过光学显微镜和扫描电镜观察,复合木材中存在块状聚集的二氧化硅,其分布情况是:横切面>径切面>弦切面;且径切面和弦切面均有SiO2薄层与细胞壁组织紧密相联,基本保持了木材的多孔性结构。荧光显微镜观察结果表明,在横切面上,二氧化硅主要以物理填充为主;在径切面和弦切面上,细胞壁物质不同程度地与二氧化硅发生了化学键合。(6)X射线能谱仪检测指出,硅元素在木材中的分布是不均匀的,主要分布在导管、木纤维、木射线和胞间层中。在浸渍过程中硅溶胶可以通过物理渗透方式进入木材内部的空隙。研究发现,木纤维和射线细胞的细胞壁上均有较高含量的硅,这是因为木纤维和射线的细胞腔相对小,在真空加压过程中,硅溶胶更容易进入细胞腔相对小的木材组织。杨树木材富含大量的纹孔,纹孔是实现浸渍处理液横向渗透的主要途径,因此,纹孔的硅含量较高。纤维细胞壁上有大量的纹孔,硅溶胶可以进入纤维中,导致木材纤维细胞壁上的硅浓度也较高。(7)XRD衍射峰的位置没有改变,说明硅溶胶复合木材的晶胞参数没有改变。红外光谱分析表明硅溶胶聚合后的二氧化硅与木材的骨架物质发生了作用;通过对素材和复合材的光谱图的对比,其主要特征峰没有明显变化,只有复合材中的Si-O-Si反对称伸缩振动峰向高频方向移动,Si-O-Si的弯曲振动也有小的位移,这主要是与氢键的形成有关。更多还原

【Abstract】 Wood inorganic functional composite in their excellent fire-retardant, decay resistance, natural drug-free and low prices, has attracted increasing attention. However, except hardness and abrasion resistance, its mechanical properties, such as toughness, modulus of rupture (MOR), modulus of elasticity (MOE), have decreased in some degrees. Summing up the research progress and advanced research methods at home and abroad in this field, on the premise of no weakened porous structure of poplar wood, this study aimed to strengthen the cell wall to prepare wood-inorganic composite,which will make the plantation wood have high intensity and high performance, and will provide technical supports for widening the application field of plantations, also will open up new avenues for the efficient use of plantations. It will be of important scientific significance and practical value. In this paper, plantation of poplar wood is selected for study; silica sol as impregnating solution. Poplar-solica sol composite was prepared through vacuum-pressive process. The main research results are as follows:(1)Under the same process parameters, the properties of the composite wood prepared by the liquid pressure impregnating process are better than those of prepared by air pressure impregnation process. As for the weight percentage gain (WPG), the vacuum treatment before the un-pressure can effectively increase WPG of wood composite and vacuum treatment after un-pressure does not have obvious effect on WPG. However, the latter can effectively remove excess impregnating solution on wood surface and does not reduce WPG of wood composite.(2)Full-cell pressure method can maximize WPG, MOE and MOR of wood composite. The research also showed that there was a certain linear relationship between the MOE and WPG of wood composite, however, MOR of wood composite was related to the location and depth of the silica sol impregnated inside wood. The simple physical filling will not change MOR of wood composite.(3)The average value of MOR of poplar wood impregnated with silica sol was 87.70 MPa, the average value of MOE was 12.41 GPa, the hardness of the end surface, flat surface and edge surface increased by 34.62%, 49.15% and 53.45% respectively, but the compressive strength parallel to grain was nearly changed or declined slightly. After being impregnated with silica sol, polar wood had some expansion along three different directions. Dimension in tangential, radial and longitudinal direction increased by 1.64%, 0.55% and 0.80%, respectively. Although the extension of vacuum time before impregnating can effectively increase WPG and mechanical properties of wood composite, it had a strong negative impact on the stability of wood size. So, the vacuum time before impregnating should be shortened in order that the mechanical properties of wood composite can reach to the standards. The optimal impregnating process parameters for poplar wood, such a soft wood, were as follows: the vacuum time before impregnating was 20 min, impregnating pressure was 1 MPa, impregnating time was 30min and the vacuum time after impregnating was 20 min.(4)Bonding properties will not be affected after wood impregnated with silica sol. The bonding strength and wood failure was up to the JAS standards and was similar to that of untreated wood. Thermal analysis result showed that thermal stability of wood composite had improved, which made wood composite have a certain fire-retardant property. And with the increasing of WPG, the remnants weight was increased and burning and fire-retardant property was also improved. By impregnating silica sol into wood, the dimension stability of wood in tangential, radial and longitudinal direction had been improved. And the dimension stability was related to WPG, and the improvement degree was from 25% to 35%. The study of wettability indicated that the contact angle of the wood increased significantly by impregnating with silica sol, and the wood composite showed good surface hydrophobic performance.(5)By the optical microscope and scan electron microscopy, there was mass silica accumulated in wood composite, and the distribution is: cross section > radial section > tangential section. Thin layer of SiO2 was found to be closely linked to the cell walls in radial section and tangential section, and the porous structure of wood was basically kept. The results from fluorescent microscope showed that SiO2 in cross section existed as physical filling; and that in radial and tangential section SiO2 had a chemical bond with cell wall in different levels.(6)The distribution of silicon elements in timber was uneven detected by X-ray spectrometer. Silicon was mainly distributed in tracheid, wood fiber, wood ray and intercellular layers. In the process of impregnation, silica sol penetrated into the wood gap through physical infiltration. It was found that more silicon appeared in the cell wall of wood fibers and wood rays. Because the cell chambers of the wood fibers and ray cells were relatively small, during the vacuum and pressure process, the silica sol can easily soak into wood organization. Poplar wood has a large number of pits, which is the major channel to realize transverse infiltration. Therefore, the pits had high content of silicon. Cell wall of wood fibers has a large number of pits, so that silica sol can easily be impregnated into the wood fiber.(7)Unchanged XRD diffraction peak position indicated that the lattice parameters of wood composite has not changed. IR spectrum analysis showed that SiO2 gained from silica sol polymerization interacted with wood frame materials. According to composite spectrum and untreated wood spectrum, it was found that the main characteristic peak has not changed significantly, but just the Si-O-Si antisymmetric stretching vibration peak of composite moved to the high-frequency direction, and the Si-O-Si bending vibration peak also had small displacement, this’s mainly related with the formation of hydrogen bonds.更多还原