【作者】 方露；

【导师】 王正；

【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， 2014， 博士

【摘要】 胶合板由于加工简单、性能优异，得到了世界各国的重视和前所未有的发展，其产品已广泛应用于各个领域。然而，当前胶合板生产所用的胶黏剂仍以脲醛树脂、酚醛树脂、三聚氰胺-甲醛树脂并称的“三醛胶”为主，“三醛胶”及其制品使用时存在甲醛污染环境、危害身心健康等问题。因此，亟待开发无甲醛胶黏剂以解决现有含醛胶合板对我国人居环境的污染问题，这种胶合板品种的问世必将带来巨大的社会效益和经济效益。本论文以无甲醛的高密度聚乙烯（High density polyethylene, HDPE）薄膜作为木材胶黏剂，采用改进的人造板生产工艺，与杨木单板复合制备HDPE薄膜/杨木单板复合胶合板（木塑复合胶合板），评价了HDPE薄膜的黏结能力，探讨了改性方法及工艺因子对木塑复合胶合板物理力学性能及其胶接界面结构的影响机制，并评价了木塑复合胶合板的耐湿循环能力。论文的主要结论如下：（1）采用响应面试验考察了热压温度（140、155、170oC）、热压时间（0.4、0.8、1.2min/mm）和HDPE层数（1、3、5层）3个因素对木塑复合胶合板胶合强度的影响。结果表明：热压温度、热压时间和HDPE层数以及热压温度和热压时间的交互效应对胶合强度都有显著影响。当热压温度为152oC，热压时间为1.1min/mm，薄膜用量为4~5层（等价施胶量为264.92g/m2）时，胶合强度（“热水浸泡”处理）达到最大值1.68MPa，远超过GB/T9846.3-2004中II类胶合板的使用要求。（2）采用动态力学分析（DMA）及扫描电镜（SEM）等方法分别测定木塑复合胶合板与脲醛树脂/杨木单板复合胶合板（UF树脂胶合板）的性能，评价了HDPE薄膜替代UF树脂胶黏剂的可行性。结果表明：HDPE薄膜与UF树脂在热压过程中都可以流动进入杨木单板的多孔性结构中，与单板形成机械啮合结构，HDPE薄膜具有与UF树脂可比的黏结能力；HDPE薄膜的耐水性能更加优异，浸泡168h后木塑复合胶合板的吸水率（WA）与吸收厚度膨胀率（TS）分别为85.75%和7.65%，分别比UF树脂胶合板低18.8%和4.9%。HDPE的熔融特性对木塑复合胶合板的动态热力学性能有很大影响，当测试温度达到130oC时，木塑复合胶合板中的胶层逐渐软化并滑移，胶接结构失效，表现为储能模量E’值急剧降低和损耗角正切tan值急剧增加。（3）利用红外光谱（FTIR）、X射线光电子能谱（XPS）、接触角（CA）、动态水蒸气吸附仪（DVS）和SEM等方法评价了高温加热（130、160、180、200oC）和乙烯基三甲氧基硅烷A-171（1、2、5%）喷淋处理对杨木单板表面性能的影响。结果表明：高温处理后半纤维素不同程度的降解，以及硅烷处理后单板表面憎水性涂层的沉积及Si-O-C共价键的形成，降低了单板表面的极性，与HDPE薄膜的相容性提高。当单板经200oC高温或2%硅烷A-171处理后，表面的水接触角分别由42o增加到122o和114o，平衡含水率分别由15.36%降低到13.3%和14.71%。高温处理后单板变脆，表面出现了明显的断裂现象；硅烷溶液喷淋处理后，单板表面因覆盖了硅烷涂层而变得光滑。（4）高温加热和硅烷偶联剂喷淋处理均能提高木塑复合胶合板的胶合强度和耐水性能及木材/塑料的界面黏结力。当单板经200oC高温或2%硅烷A-171处理后，胶合强度（“煮-干-煮”处理）分别达到1.24MPa和1.8MPa，比未处理材分别增加51%和128%；24h吸水率从65.81%分别降至49.33%和52.97%。但高温处理会降低胶合板的抗弯性能，200oC处理后MOR和MOE值分别降低了41%和32%。表面预处理后，胶接界面层的刚性提高，木塑复合胶合板储能模量E’值增加，损耗角正切tan max降低。DMA结果显示：未处理胶合板的E’值终保留率为4.48%，tan max为0.234；经200oC高温或2%硅烷A-171处理后，E’值的终保留率分别增至27.42%和30.48%，tan max分别降至0.211和0.115。SEM结果表明：杨木单板在硅烷偶联剂A-171和引发剂过氧化二异丙苯（DCP）的共同作用下，与HDPE大分子发生了有效的化学反应，形成能有效提高杨木单板-HDPE薄膜界面黏结力的胶接结构。这种优良的胶接结构促进了胶接性能的提高，木塑复合胶合板的木破率保持在90%以上。（5）以硅烷A-171和引发剂DCP为改性剂，制备高性能HDPE薄膜/杨木单板复合胶合板，研究了热压温度、HDPE层数、A-171和DCP添加量对木材/塑料界面结构及其性能的影响机制。当热压温度从140oC升高到160oC时，胶合强度（“煮-干-煮”处理）、MOR和MOE的值分别由1.27MPa、63.9MPa和5970MPa增加到1.89MPa、72.2MPa和6710MPa，但热压温度继续增加，胶合强度和抗弯性能均呈现降低趋势；胶接界面层的耐高温破坏能力随着热压温度增加逐渐增强：当热压温度从140oC增至170oC时，胶合板130oC的E’保留率由62.31%提高到92.01%，到达tan max的温度点从141oC延后至200oC。引发剂是促进硅烷改性单板与HDPE薄膜形成良好胶接结构的重要因子：当DCP的添加量从0增至0.15%时，胶合强度、MOR和MOE值分别达到2.07MPa、77.2MPa和6822MPa，130oC时的E’保留率提高到88.34%，到达tan max的温度点延至194oC；当硅烷A-171用量为2%，HDPE的用量为1层时，增容效果最好，界面黏结力最大，胶合强度达到1.89MPa，130oC时的E’保留率为85.58%，180oC到达tan max；当HDPE用量为4层时，耐水性能最强，24h吸水率和吸水厚度膨胀率分别为48.86%和3.40%。（6）利用SEM和DMA研究了木塑复合胶合板及其胶接界面结构的耐湿循环能力。SEM结果显示：经3次湿-冷冻-热循环处理后，木材-塑料胶接结构中同时存在内聚破坏和界面破坏。在未处理和高温处理材的胶接界面结构中，可观察到明显的裂缝及脱落的HDPE碎片；而硅烷改性胶接界面结构中仅存在少量的裂纹，破坏程度减弱。胶接界面结构的破坏引起了木塑复合胶合板胶合强度和抗弯性能不同程度的降低，未处理、200oC高温处理和2%硅烷处理材胶合强度的保留率分别为57%、72%和84%；抗弯性能的保留率均在80%以上。DMA结果表明：湿循环处理后，木塑复合胶合板的耐高温破坏能力降低，当环境温度达到200oC，未处理和200oC高温处理材的胶接界面结构完全破坏，木材单板与塑料薄膜两相完全分离；而硅烷改性的胶接界面结构并未破坏，单板与HDPE薄膜两相仍保持紧密胶合状态。更多还原

【Abstract】 Plywood has long been studied in the world and widely used in various applicationsbecause of their high performance and simple technology. However, adhesives mainly used forplywood are largely formaldehyde-based materials, such as phenol-formaldehyde resins,urea-formaldehyde resins and melamine-formaldehyde resins. The emission of formaldehydein the production and use of plywood poses a great hazard to human health and our livingenvironment. As a result, there is an urgent need for developing formaldehyde-free woodadhesives, which will bring great economic and environmental value for our society.In order to evaluate the bonding ability of plastic films, high density polyethylene (HDPE)films were selected as formaldehyde-free wood adhesive to manufacture HDPE film/poplarveneer plywood (wood-plastic plywood) by improved hot-pressing in this study. The effects ofsurface modifications and technological factors on the physical-mechanical properties andinterfacial adhesion of wood-plastic plywood, as well as the wet cycle resistance of plywoodwere studied. The main researches and results are summarized below:(1) Response surface methodology was used to optimize the processing technologyincluding pressing temperature (140、155、170oC), pressing time (0.4、0.8、1.2min/mm) andlayers of HDPE film (1、3、5). Results showed that shear strength of the plywood wassignificantly affected by pressing temperature, pressing time, layers of HDPE film as well asthe interaction effects between pressing temperature and pressing time. When plywood wasmanufactured under the pressing temperature of152oC, pressing time of1.1min/mm, HDPEfilms of4to5layers (264.92g/m2), shear strength (soaking in hot water) could reach themaximum value of1.68MPa, which totally met the requirement of type II plywood accordingto the National Standard of GB/T9846.3-2004.(2) In order to evaluate the feasibility of using HDPE film to replace UF resins as woodadhesives, performance of two kinds of plywood, made with HDPE film and UF resinsrespectively, were investigated by dynamic mechanical analysis (DMA) and scanning electronic microscope (SEM). Results showed that both HDPE film and UF resins canpenetrate into the porous structures of poplar veneer and form mechanical interlock duringhot-pressing, which endowed these two adhesives comparable bonding ability. HDPE film hasbetter water resistance than UF resins because of its hydrophobic character. Water absorption(WA) and thickness swelling (TS) values after soaking in water for168hours of the plywoodbonded with HDPE film were85.75%and7.65%, which was18.8%and4.9%lower thanthose with UF resins respectively. Dynamic mechanical properties of wood-plastic plywoodwere greatly affected by the melting behaviour of HDPE film. When experimental temperatureincreased to130oC, the bondline in the wood-plastic plywood began to melt and slip, and thebonding structure failed, indicating by the rapidly decreased E’ value and increased tan value.(3) Surface properties of poplar veneers either thermally modified in an oven at differenttemperatures (130,160,180,200oC) or chemically modified by vinyltrimethoxysilane (1,2,5%) were evaluated by Fourier transform infrared spectroscopy (FTIR), contact angle (CA),X-ray photoelectron spectroscopy (XPS), dynamic vapour sorption (DVS) and SEM. Theresults indicate that polarity of veneers lowered because of the hemicelluloses degradationafter thermal treatment, or the deposition of hydrophobic silane coating and the formation ofSi-O-C covalence after silane treatment, which improved the interfacial compatibility betweenpoplar veneer and HDPE film. The untreated veneer had lower contact angel (42o) and higherequilibrium moisture content (15.36%) compared with that thermally modified at200oC (122oand13.3%) or modified by2%silane A-171(114oand14.71%). The veneer became morebreakable and fragile after thermal-treatment, with obvious breakages on its surface. While theveneer surface became much smoother after silane-treatment, because of the deposition ofsilane coating.(4) Both thermal treatment and silane modification resulted in enhancement of shearstrength and water resistance of wood-plastic plywood as well as the interfacial adhesionbetween wood and plastic. When veneers were heated at200oC or spraying by2%silaneA-171, shear strength of wood-plastic plywood reached1.24MPa or1.80MPa (treated by‘boiling-dry-boling’ procedure),51%or128%higher than the untreated sample. It also caused 24-hour WA value decreased from65.81%to49.33%or52.97%respectively. However,bending strength were lowered due to thermal treatment. MOR and MOE values decrease by41%and32%respectively after veneers heated at200oC.The modified plywood exhibited higher E’ and lower tan maxvalues with respect tountreated sample, indicating much more rigid interface The eventual retention rate of E’increased from4.48%to27.42%after heated at200oC and to30.48%after treated by2%silane as shown by DMA results. Higher retention rate of E’ corresponded to the tan maxvalues,which decreased from0.234for untreated sample to0.211for thermal-treated and0.115forsilane-treated sample. SEM results showed that poplar veneer and HDPE film were closelyentangled by means of a chemical bond thanks to bifunctional structural silane A-171and theoxy radicals generated by dicumyl peroxide, which contributed to forming enhanced interlockand a stronger interface between the two phases. This kind of bonding structure in turnresulted in much higher shear strength and wood failure (almost above90%).(5) High performance HDPE film/Poplar veneer plywood were made using silane A-171and DCP as coupling agent. The effects of pressing temperature, HDPE layer, dosage of A-171and DCP on wood/plastic interface and its performance were studied. When pressingtemperature increased from140oC to160oC, shear strength (treated by ‘boiling-dry-boling’procedure), MOR and MOE value increased from1.27MPa,63.9MPa,5970MPa to1.89MPa,72.2MPa,6710MPa. However, higher pressing temperature would adversely affect theshear strength, MOR and MOE. Interfacial rigidity at higher temperature strengthened withincreased pressing temperatures. The The retention rate of E’ at130oC increased from62.31%to92.01%when pressing temperature rose from140oC to170oC. This trend also applied to thetemperature for tan max, which lagged from141oC to200oC. DCP dosage greatly affected thechemical reaction between silane-treated veneer and HDPE film. When the addition of DCPraised from0to0.15%, shear strength, MOR and MOE values of the plywood reached2.07MPa,77.2MPa and6822MPa respectively. Also the retention rate of E’ at130oC and thetemperature for tan maxincreased to88.34%and194oC respectively. Optimal interfacialcompatibility can be obtained when only1layer HDPE film was used, with shear strength of 1.89MPa, retention rate of E’ at130oC of85.58%and180oC for tan max.The plywood had thestrongest water resistance when4layer films were used as wood adhesives with24-hour WAand TS values of48.86%and3.40%respectively.(6) Properties of wood-plastic plywood and its bonding structure after bond durabilitytests were studied by DMA and SEM. Both cohesive and interfacial failure existed in thewood-plastic plywood after3cyclic water-freezing-dry heat experiments by SEM results.Obvious cracks along the interface and the fragments of HDPE were observed in bothuntreated and thermal-treated samples, while there were only a little bit of break forsilane-treated sample after the bond durability tests. Different kinds of failures of the bondingstructure led to the decrease in mechanical properties of wood-plastic plywood at differentlevels. The retention rate of shear strength for untreated, thermal-treated and silane-treatedafter3cyclic tests were57%,72%and84%respectively while the retention rate of MOR andMOE values were both higher than80%. Thermal stability of wood-plastic plywood alsoweakened after bond durability tests by DMA results. Plastic film was totally separated fromboth the untreated and thermal-treated poplar veneers when plywood were heated at up to200oC. However, HDPE film could still closely tethered with silane-treated veneer in thewhole stage and the bonding structure did not destruct.更多还原