【作者】 秦志永；

【导师】 李建章； 张世锋；

【作者基本信息】 北京林业大学 ， 木材科学与技术， 2014， 博士

【摘要】 木材胶接主要是木材与胶粘剂表界面之间发生的物理化学变化,表明在木材和胶粘剂的表界面上存在某种基本能量,决定胶接现象的本质。木材及胶粘剂本身的表界面特性对木材的物理化学性能有很大影响,因此,研究木材和胶粘剂的表界面特性对于探索木材胶接理论具有十分重要的意义。本文以常用速生杨木和酚醛树脂(PF树脂)为主要原材料,以接触角测量仪为主要仪器,采用座滴法测定了液体在木材表面的相对平衡接触角,计算了表面自由能,分析了四种计算方程在木质材料表面自由能计算上产生的差异；研究了不同加工工艺对木材表面自由能及PF树脂在木材表面的润湿性的影响；利用接触角测量仪、X射线光电子能谱(XPS)、傅里叶红外光谱(FTIR)、核磁共振(13CCP/MAS NMR)等测试方法研究了PF树脂在液体、固体状态下的各项表面物理化学性质及结构；探讨了表面自由能、润湿性和胶合强度之间的关系,研究了不同热压温度条件下,PF树脂在木材中的固化性能。得出主要结论如下：(1)采用4种不同的方法测定并获得相对平衡接触角,计算出6种不同木质材料的表面自由能。结果表明,速生杨渗透性最好,木材的表面自由能大于木质复合材料(纤维板和木塑复合材料)；木材表面自由能的非极性分量大于极性分量,碱性分量大于酸性分量。(2)4种不同方程计算得到的木塑复合材料表面自由能存在较大差异。木塑复合材料表面自由能不仅依赖于材料本身的化学组成、物理结构等,还受到不同计算方法和接触角测量过程中使用液体的种类和数量的影响。(3)不同加工工艺木材表面的润湿性不同。旋切木材试样的接触角大于刨切和锯切试样,旋切木材的表面自由能小于刨切和锯切表面自由能；与表面结构形态相比,木材表面粗糙度对润湿的影响不明显,旋切松面的润湿性要好于紧面。(4)新加工木材与陈放木材表面润湿性不同。水在新加工木材接触角随砂光目数的增加而减小,新加工木材表面比陈放木材表面更易被水润湿。陈放木材接触角随表面粗糙度的降低而增大。新加工木材非极性分量和极性分量随砂光目数的增大而增加,陈放木材表面自由能随砂光目数的增大而降低,但非极性分量却增加。选用的四种润湿模型可用来准确描述胶粘剂的润湿过程,相关系数的R2值均高于0.90,其中M-D模型为0.99。单板松紧面表面的润湿性和渗透性随温度的升高变化差异不大,可以在生产中忽略。在20℃时,芯材表面润湿性和渗透性要好于单板松紧面,但是随着温度的增加,差异减小。(5)摩尔比对PF树脂的表面特性影响较大。摩尔比为1.75以上时,PF树脂液体表面张力变化很小,非极性分量占主导地位,当摩尔比为2.5时,表面张力和非极性分量最大,而极性分量最小,PF树脂表面张力越小,润湿性越好。PF树脂表面总表面自由能和极性分量随着摩尔比的降低,呈现先增大后减小的趋势,与树脂表面的-OH关系密切。不同摩尔比固化后,峰值差距不大,只有苯环骨架-CH振动吸收峰,随着摩尔比的降低,峰值强度逐渐增加,这主要是苯酚含量逐渐增加的原因。(6)表面粗糙度对新加工木材和陈放木材的胶合强度影响不同。木材的胶合强度随着由Zisman方程计算得出的表面自由能与胶合强度之间的增加而不断降低。对于新加工木材,胶合强度随着表面自由能增大而减小,当极性分量增加时胶合强度也降低,这种规律非线性相关。陈放木材的胶合强度随着表面能增加而降低。对于S-D方程,新加工木材随着渗透性的增加,胶合强度增加,但对于陈放木材而言,相关性不明显,利用M-D模型得到的关系和S-D方程基本一致,利用Santoni模型计算出的渗透速率(K值)和胶合强度之间的关系也不明显。(7)热压过程中,芯层温度随着时间的增加而不断增加,在热压温度(上下压板的温度)增加时,胶合板芯层的升温速率逐渐增加,平均胶合强度随着时间的增加而不断增加,最终到达一个相对平衡值。FTIR说明树脂结构中羟甲基发生了聚合反应,相对数量减少。13CCP/MAS NMR分析表明亚甲基桥键碳原子与未反应的羟甲基碳原子的比值随着加热固化时间的增长而增加,说明固化程度的增加,胶合强度也增加。更多还原

【Abstract】 Wood bonding is physical and chemical interacttion between the wood and adhesive, which indicate that energy was exsited in the surface or interface that determined the intrinsic quality of adhesive phenomenol. The effect of property of wood and adhesive on the bonding strength were remarkable, so it was important to investigate the surface and interface properties of wood and adhesive. The fast growing wood and phenonlic formaldhyde adhesive as the mainly materials to investigated:(1) measured the relative equilibrium contact angle by the sessile drop method using the contact angle intsructment (OCA20), and the surface free energy were calculated; the differences of four calculated methods used to calculated the surface free energy were compared.(2) The influence of different machined process on the wettability of wood were determined.(3) The surface properties of liquid and solid PF adhesives were investigated by using the OCA20, X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), nuclear magnetic resonance (13CCP/MAS NMR).(4) The relationships betweeen the surface free energy, wettability and bonding strength were studied, and the curing properties were also investigated during the hot process. And the conclusions were followed(1) Four different methods were used to obtain the relative equilibriun contact angle, and also the obtained contact angles were used to calculated the surface free energy, the result indicated that the penetration of fast-growing poplar wood was better than that of the other wood materials, and also the surface free energy of wood samples were higher than that of the wood material, the disperse compent of wood surface was higher than the polar component and base component was higher than that of acid component.(2) The surface free energy of wood plastic composites (WPCs) calculated by four methods were significant different. The surface free energy of WPCs were not only depends on the chemical components or physical structure but also on the different calculated methods, species of reference liquids and the amount of reference liquids.(3) The wettability of different processing the wood surface is different. The contact of water on the rotary wood samples were higher than that of planed and sawn wood samples, and the surface free energy of the rotary wood samples was lower. The effect of surface roughness on contact angle was insignificant compared with surface structure morphology. (4) The fresh wood surface was more easily wetted by water than was the aged wood sample. The contact angles increased as the surface roughness decreased. The disperse and polar components of fresh wood both increased as the grit number increased. For aged wood, the surface free energy decreased as the grit number increased, but the disperse component increased. The effect of roughness on the acid-base components, acid component, and base component (calculated using the vOCG method) were unremarkable. The surface free energy of wood samples (obtained using the liquid parameters given by Volpe and Siboni) can effectively balance the relationship between the acid and base components. All coefficient of determination R-squared values were over90%, and the value of the Modified model was99%. The models can be used to accurately describe the adhesive wetting process.(5) The molar ratio had a great impact on the surface properties of phenolic resin. When the molar ratio was above1.75, the change of PF liquid surface tension were small, the dispersion component took hold; when the molar ratio was2.5, the surface tension and the dispersive component maximized, polar component minimized, the smaller the surface tension of a phenolic resin, the better the wettability. Total surface free energy and polar component of PF resin showed a decreasing trend after the first increase with the decrease of the molar ratio, closely related to-OH in resin surface. The cured resin with the different molar ratio, the change of FTIR peak was not obvious, only a benzene ring skeleton-CH vibration absorption peak. With the lower molar ratio, the peak intensity increased gradually, mainly due to the increasing phenol content.(6) The effects of surface roughness on bonding strength of fresh wood and aged wood were different. According to the S-D equation, the bonding strength of fresh wood enhanced with increasing permeability; but for aged wood, the correlation was not obvious, the relationship when using the M-D model were basically the same as using S-D equation. The relationship between K value and the bonding strength with Santoni model to calculate was also not distinct.(7) Core temperature increased over time and when the hot pressing temperature(i.e, temperatures of upper and down pressing plates) rised, plywood core heating rate was gradually increased, the average bond strength enhanced over time, and eventually reached a relative equilibrium value. FTIR suggested that polymerization reaction hydroxymethyl in resin structure, reducing the relative quantity.13CCP/MAS NMR analysis showed that the ratio of methylene bridge bond carbon atoms and unreacted hydroxyl methyl carbon atoms increased with heating curing time, indicated the increase of cure degree, but also enhancement the bonding strength.更多还原