【作者】 赵殊；

【导师】 顾继友； 方桂珍；

【作者基本信息】 东北林业大学 ， 生物材料工程， 2010， 博士

【摘要】 聚氨酯胶黏剂(PU)是适用于多种基材及不同材质间粘接且性能优异的胶黏剂,用于木制品加工业替代传统的三醛胶具有重要的经济和社会效益。但是PU价格昂贵,目前我国将其用于木材加工业还很有限,研究PU对木材的胶接机理,对于PU的设计开发、降低成本具有重要意义。研究PU对木材胶接机理遇到的主要困难是：木材多孔且组成复杂,PU又有极其活泼的异氰酸酯官能团(-NCO),使各种粘接作用不能分离；没有准确测定胶接强度的测试技术。本文创新性地巧妙地设计制备各种模型物模拟木材和PU以分解胶黏剂对木材的不同胶接作用,创新性地使用反相气相色谱(IGC)技术研究界面吸附作用机理,用扫描电镜(SEM)、X-射线衍射(XRD)、X光电子能谱(XPS)结合胶接强度测试深入研究了胶接的机械互锁机理和界面扩散机理,用交叉极化魔角旋转核磁共振(15N、13C CP/MAS NMR)、红外光谱(FTIR)表征了苯基异氰酸酯与(含水)纤维素反应产物的结构,并研究了胶接的化学键作用机理。用木材中的主要组分且化学结构明确的纤维素模拟木材,用不能交联且活性唯一的单官能团的苯基异氰酸酯(PI)模拟PU，研究PU对木材胶接的化学键作用机理。用15N和13C交叉极化魔角旋转核磁共振(15N、13C CP/MAS NMR)和傅里叶变换红外光谱(FTIR)表征了98%15N标记的PI与(含水)微晶纤维素反应产物的结构,并且详细研究了纤维素湿含量、反应温度、反应时间、反应物配比等条件对反应的影响。研究发现PI能与绝干纤维素反应生成(二)脲基甲酸酯和氨基甲酸酯,但是与含水纤维素反应时在低温(<130℃)短时间(<4 h)PI主要与水反应生成脲和二脲为主,而在高温长时间主要得到脲和氨基甲酸酯,证明了PU对木材胶接存在化学键作用。但是,一般木材含水率8%-12%、胶合热压温度120℃、热压时间3 min,则聚氨酯与木材反应形成的化学键很少。用IGC技术测定了水曲柳、杨木、桦木、-NCO含量不同的固化PU和固化酚醛胶(PF)的表面色散自由能及表面酸碱性,研究PU对木材粘接的吸附作用机理。结果表明这几种木材属于高表面能且表面酸性占优势的两性材料,而固化的PU和PF都是表面碱性占优势的两性材料,PU的表面色散自由能随-NCO含量增加变化很大。测得水曲柳、杨木和固化PU的表面自由能及其色散分量和酸碱分量,表明色散分量大于酸碱分量,测出水曲柳/PU、杨木/PU界面的粘附功,粘附功的色散分量是酸碱分量的5-6倍。证明了PU对木材粘接存在吸附作用,色散吸附作用远大于酸碱吸附作用。应用SEM和XPS技术分别观察了木材胶合板断面的形貌,研究胶接的机械互锁作用机理。选择不与PU发生化学键作用和酸碱作用的聚乙烯(PE)制备表面光滑、表面打磨、内部气室、孔隙连通的各种PE板模拟木材,用PU粘接成PE胶合板,测试其剪切强度。SEM观察到桦木胶合板胶接断面胶黏剂沿木材表面的空隙流经木材导管、导管壁上的纹孔以及梯状穿孔进入木材内部,在胶接断面的胶面看到从木材的梯度穿孔中拔出的胶钉,揭示了在木材胶接面一定厚度形成了胶黏剂在木材中的“半互穿网络”；PE胶合板的剪切强度随PE板粗糙度增加、孔径增大、孔隙率加大而提高。这些实验结果证明了胶黏剂粘接木材的机械互锁作用机理。在不存在化学作用和吸附的酸碱作用,扩散作用加色散作用比机械互锁作用对胶接强度贡献更大。用PU/纤维素膜模型物以消除界面机械互锁作用,研究了粘接的界面扩散机理。SEM观察固化的PU/纤维素膜界面形貌,140℃固化的试件界面模糊,100℃固化的试件界面清晰,证明高温固化界面发生了扩散作用。而纤维素膜/PF界面见有裂缝,证明PU比PF对纤维素的扩散作用更强。用SEM的电子能谱分析仪,测出140℃固化纤维素膜/PU试件的PU在纤维素膜中的扩散厚度为300 nm。XRD测试出纤维素膜的结晶度很低表明PU在纤维素膜的无定形区扩散,揭示PU在木材中穿越无定形区扩散。用没有-NCO的PU粘附纤维素膜并固化,然后浸入溶剂中溶解再淋洗掉表面胶层,XPS测得膜表面N含量随着固化温度的升高和时间的延长而增加,甚至高于PU本体的N含量。证明了在固化过程中PU分子链的扩散作用且固化的PU逐渐发生了相分离。通过纤维素膜胶接件的强度测试数据和胶接件断裂模式分析,表明温度提高有利于分子链段扩散,-NCO含量高导致过度交联不利于PU的微观相分离从而使胶接强度下降,固化温度和PU中软硬段的比例是影响扩散的重要因素,扩散作用是影响胶接强度的主要作用。本文通过创新地设计制备模型物、创新性地运用先进的测试技术、巧妙地设计实验、深入系统地进行理论研究,得出创新性的研究成果。揭示了聚氨酯胶黏剂粘接木材存在化学键机理、吸附机理、机械互锁机理和扩散机理,各种作用对胶接强度的贡献有如下顺序：扩散作用>吸附作用(色散作用>酸碱作用)>机械互锁作用>化学键作用。更多还原

【Abstract】 Polyurethane (PU) is a high-performance adhesive which can be applied to bond a variety of materials and different substrate materials. The application of PU in woodwork industry to replace three traditional aldehyde adhesives archives remarkable economic and social benefits. However, its application to furniture industry is restricted in our country by its high cost. It is considerably valuable for researching the adhesion mechanism of PU for wood and developing advanced and low cost PU. The primary difficulty lying in research of the adhesion mechanism of PU to wood are as the follows:first, none of adhesion reactions can be separated because the woods are porous and complex in component, and PU has the reactive functional group-NCO; second, there are no accurate test technology for adhesion strength. In this paper, a novel method of modeling wood and PU by decomposing and substituting the wood by components which have pre-defined similar characteristics was developed and hence different adhesion reactions were decoupled. Inverse gas chromatography (IGC) was used to research the mechanism of interfacial adsorption in originality and scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), combined with the test of the mechanics performance were applied in the research of the adhesion mechanism of mechanical anchoring and interfacial diffusion in depth, respectively. Products structures of phenly isocyanate reacting with cellulose were also characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and the mechanism of chemical bonding were investigated.The chemical mechanism of PU boning wood was studied by modeling wood by cellulose, which is the main composition in wood and has a thorough defined chemical structure, and by modeling PU using phenyl isocyanate (PI), which is a compound with mono functional group, so that PI cannot cure crosslinking and the -NCO reactivity is unique. The product structures of 98% 15N-labelled PI reacting with microcrystalline cellulose with different moisture contents were characterized by applying 15N and 13C CP/MAS NMR and FTIR. The effects of moisture content of woods, reaction temperature and time etc. on reaction were studied in detail. It was found that PI reacts with anhydrous cellulose and produces (bi)allophanate, and urethane, however, PI reacts with water predominantly as using hydrous cellulose and results in urea and biuret. At lower temperature (<130℃) and short time (<4 h) PI reacts mostly with water, while the urea and urethane are main products at high temperature and long time. The chemical bonding exists between wood and PU, but the chemical bonds is less for the PU bonding wood with the moisture content mostly within 8%-12%.The adsorption mechanism of PU bonding woods was studied by means of IGC in order to determine the surface dispersive free energy, surface acidity and basicity of the fraxinus manshurica, birch, poplar and cured phenol formaldehyde adhesives (PF) and cured PU at various-NCO content. The results indicate that these three kinds of woods have high surface energy and are acidity dominant amphiprotic materials, whereas cured PU and PF were basicity dominant amphiprotic materials, and the surface dispersive free energy of PU varied largely due to a increasing content of -NCO. The surface free energy of the fraxinus manshurica, poplar and cured PU was determined, and it was found that the dispersive component was larger than the acidic-basic components. Test of the interface adhesive works of fraxinus manshurica/PU and poplar/PU revealed the dispersive component of their adhesive works was 5-6 times larger than the acidic-basic components. The results demonstrated the existence of adsorptive interactions of PU boning wood and dispersive reactions of adsorptive were far more than acidic-basic interactions.The mechanical anchoring mechanism of adhesion were studied by observing the cross section morphology of plywood using SEM, and by combing with the test of adhesion strength of PU bonding PE boards made by polyethene (PE) boards, which were prepared to surface glazed, surface rough, inner air chamber or porosity connected. PE was selected to simulate wood due to its not any chemical reactions and acidic-basic interactions with PU. The adhesive in wood vessels, pits and scalariform perforations at the bonding cross section of birch plyboard, and the bonding nails at adhesive side was observed by SEM, which reveals the forming of semi-interpenetrating polymer networks of adhesive in wood within a definite thickness from the wood bonding side. The shear strength of plywood increases with the increasing of the surface roughness, the aperture and the porosity. The result demonstrates the mechanical anchoring mechanism of adhesion existing in bonding of adhesives to wood. The summation of dispersive and diffusion interactions contribute to bonding strength more than the mechanical anchoring reactions in existing not any the chemical interactions and the acidic-basic interactions.The diffusion mechanism of PU bonding wood was investigated in detail using the model of PU/cellulose film, which eliminates the interface mechanical anchoring reactions. The interface morphology of cured PU/cellulose film was observed by SEM. A blurring interface of the test piece cured at 140℃and a clear-cut interface of it cured at 100℃were observed. Whereas an interfacial crack of a PF/cellulose film was found, suggest the PU possessing a grater diffusion interactions to cellulose film than that of PF. A diffusion thickness of 300 nm of PU in PU/cellulose film cured at 140℃was determined by an electron spectrometer with SEM. The crystallinity index of cellulose film was very low caculated by XRD testing, that shows the PU diffusion by amorphous fraction of wood. It was tested by XPS that the surface N content of cellulose film cured conglutinating PU without-NCO, and then immerged solvent and then eluviated the surface adhesive layer, which revealed an increase with the increasing of cured temperature and time even exceed the N content of the PU bulk. All of these proved the diffusion of PU molecule chain segments and phases separation accrued gradually with curing of PU/cellulose film. The analysis of the data of strength test and the breach mode of cellulose film bonding test specimen showed that elevation of the cured temperature was propitious to the diffusion of molecule segments, and high-NCO content lead to an excessive crosslinking against the phases separation of PU, thus reduced the bonding strength. The curing temperature and the ratio of polyethylene glycol in PU are important factors for diffusion. The results show that the interface diffusion is the main interactions effecting adhesion strength.These researches, in a detailed and systematical way, shows that the chemical bonding, adsorption, mechanical anchoring and diffusion mechanism exist in the adhesion of PU to wood; and the contribution of these various interactions to adhesion are ranked as following: diffusion interactions> adsorption (dispersion> acidic-basic) interactions> mechanical anchoring interactions> chemical bonding interactions.更多还原