【作者】 范传杰；

【导师】 周晓东；

【作者基本信息】 华东理工大学 ， 化学工程， 2010， 博士

【摘要】 脲醛树脂(UF)微胶囊具有较好的力学性能、耐热性、阻隔性等优点,已经被广泛地应用于许多领域。近年来,随着微胶囊在复合材料自修复中的应用,使得合成可应用于树脂基复合材料微胶囊的研究意义更加突出。本文首先考察了脲醛树脂微胶囊的一步法合成机理,制备了具有较好强度和阻隔性能的微胶囊,然后探讨了微胶囊的加入对环氧树脂(EP)和聚氨酯(PU)阻尼性能的影响,主要包括以下内容：选用经过疏水处理、粒径分布窄的玻璃微珠作为制备微胶囊的囊芯,采用一步法工艺制备了脲醛树脂微胶囊。利用光学显微镜(OM)、扫描电子显微镜(SEM),考察了反应过程中的初始pH值、囊壁材料的浓度、乳化剂浓度以及搅拌速率等工艺参数对脲醛树脂微胶囊表面形貌的影响。结果表明：溶液终点的pH值对微胶囊的表面形貌有显著的影响,随着反应终点的pH值的升高微胶囊表面的粗糙度降低。通过调节乳化剂和壁材的浓度以及搅拌速率可以制备出表面形貌可控的脲醛树脂微胶囊。氯化铵对脲醛树脂微胶囊的形成有重要影响,在反应过程中加入适量氯化铵可以促进囊壁材料在芯材表面的沉积。以四氯乙烯为囊芯,采用一步法工艺制备了脲醛树脂微胶囊。考察了小分子、合成和天然高分子等6种表面活性剂对微胶囊的影响。通过正交试验研究了壁材浓度、初始pH值、升温速率和氯化钠浓度等工艺参数对微胶囊合成状态、阻隔性能的影响规律,并利用OM和SEM进行了表征。结果表明：表面活性剂的类型对微胶囊的合成状态有较大的影响。采用天然高分子阿拉伯胶(GA)为乳化剂可以制备出表面光滑透明、强度较好的微胶囊。正交试验结果表明：壁材的浓度对微胶囊的力学强度和壁材利用率有显著影响。适当降低升温速率和提高反应的初始pH值,有利于制备出球形度良好、粒径较小且分布窄的微胶囊。在反应过程中加入适量的氯化钠有助于提高微胶囊的阻隔性能。优化的工艺条件为：初始pH值3.5、壁材浓度3.6×10-2g／ml、升温速率0.5℃／min、NaCl浓度2.5×10-2g／ml。为了提高脲醛树脂微胶囊囊壁的阻隔性能,本文在制备脲醛树脂微胶囊的过程中,在囊壁内加入了具有较大径厚比的蒙脱土(MMT),并利用红外光谱(FTIR)、X射线衍射(XRD)、透射电镜(TEM)和SEM对微胶囊进行了表征。结果表明,MMT被成功地引入到了脲醛树脂微胶囊囊壁当中,且在囊壁内已经完全剥离,得到的是剥离型的MMT/UF复合囊壁微胶囊。微胶囊的芯材释放测试表明,片状MMT的引入能够显著降低芯材双环戊二烯(DCPD)向外界扩散的速率,从而提高了壁材的阻隔性能。制备了两种不同粘度芯材的脲醛树脂微胶囊,研究了微胶囊的加入对EP阻尼性能的影响,并利用SEM和动态力学热分析仪(DMA)进行了表征。研究表明：加入微胶囊的含量、粒径以及囊芯液体的粘度对EP的阻尼性能有显著的影响。在微胶囊含量为10vol%时,微胶囊／环氧复合材料在玻璃化温度(Tg)下的损耗因子(tanδ)达到最大。相同的含量下,随着加入微胶囊的粒径的增大、芯材液体粘度的提高,复合材料阻尼性能也不断提高。复合材料的频率谱测试表明,微胶囊的加入提高了EP在低频下的阻尼性能。同时,微胶囊的引入降低了EP的压缩强度且改变了EP压缩破坏的形式,在微胶囊／环氧复合材料的的压缩破坏过程中出现了应力-应变的平台区。制备了包含粘性液体的脲醛树脂微胶囊,并将其应用到PU体系中,探讨了PU的合成工艺和微胶囊的引入对PU动态力学性能的影响。研究表明：选择PU预聚体中-NCO的理论含量为6%,控制预聚体合成的温度为75-80℃,反应时间1h,可以制得室温下具有较好力学性能和阻尼性能的PU弹性体。微胶囊的引入使PU在Tg下的tanδ的峰值提高约28%—54%,且拓宽了PU的高阻尼温域。通过时-温叠加得到了复合材料在宽频范围的动态力学参数,结果表明：微胶囊的加入能够有效提高PU在1000Hz以内低频段范围内的tanδ,且在微胶囊含量为10vol%时最高。压缩测试表明复合材料中的微胶囊可以在较高的压力环境下保持完整的形态结构而不破裂,可以满足材料在水下压力环境下的使用要求。更多还原

【Abstract】 Urea-formaldehyde Microcapsules are widely used in many fields due to their excellent mechanical property, thermal stability and sealing property, etc. In recent years, with the application of microcapsules into self-healing materials, it makes the preparation of microcapsules that applied to polymeric matrix composites more prominent. In this work, the mechanism of urea-formaldehyde microcapsules prepared by one-step process was studied. Microcapsules with good strength and barrier property were prepared and then used to epoxy (EP) and polyurethane (PU) system. The addition of microcapsules on the damping properties of EP and PU were discussed. The main contents are listed as follows:A series of microcapsules were prepared by in-situ polymerization with poly (urea-formaldehyde) as the shell material and glass beads as the core material. Glass beads were chosen as the core material because their size distribution was narrow and their surface was easily changed to be hydrophobic. OM and SEM were used to investigate the respective effects of process parameters, such as initial pH value, concentration of wall material and surfactant, stirring rate etc, on the surface morphology of microcapsules. The results showed that the surface morphology of the microcapsules depends mainly on the final pH value and a high final pH value corresponded to a smooth-surface microcapsule. Controlled surface morphology of UF microcapsules can be prepared by adjusting the concentration of the emulsifier and wall material and the stirring rate. Addition of ammonium chloride was found to be very important in the process preparation of PUF microcapsules. The involvement of ammonium chloride can cause a drop in the pH value substantially during the course of reaction and enhance the deposition of the UF nanoparticles onto the surface of microcapsule.The effects of emulsifier on the physical properties of poly (urea-formaldehyde) (PUF) encapsulated tetrachroloethylene (TCE) microcapsules were investigated by anionic, synthetic and natural macromolecular emulsifier. The properties of microcapsules were investigated by optical-photographic microscope (OM) and scanning electron microscope (SEM). Experimental results showed that: GA is a favorable emulsifier for preparing smooth-surface and good-strength microcapsule. The orthogonal test indicated that the concentration of the shell material has a great effect on the microcapsules’mechanical strength. A Slow heating rate and high initial pH value can help to prepare microcapsules with high degree of sphericity, small size and narrow distribution. The addition of Sodium chloride during the reaction is favor to increase the sealing property of the capsules. The optimizing conditions are initial PH value 3.5, concentration of the shell material 3.6×10-2g/ml, heating rate 0.5℃/min and concentration of Sodium chloride 2.5×10-2 g/m.To improve the microcapsules’ barrier properties, layered silicates were dispersed in the wall of microcapsule. TEM, SEM, XRD and FTIR were used to investigate the physical property of microcapsules. The tests showed that, MMT is successively introduced to the wall of microcapsule and exfoliate completely. Compared with conventional microcapsules (CMs), nano-composite microcapsules (NCMs) have better barrier property. This can be attributed to nano-composite structure of the microcapsules, in which nano-sized montmorillonite dispersed in UF to decrease core material cross-over.A series of epoxy composites filled with microcapsule of different core materials were prepared in this work. Microstructure analysis as well as damping properties of microcapsule/ EP composites was made by SEM and DMTA. The results showed that the content and diameter as well as viscosity of the core material of the filled microcapsules have a significant effect on the damping properties of microcapsule/EP composite. The loss factor (tan8) of composite at Tg temperature reached to the maximum value under 10vol% content of microcapsule. The larger diameter and higher viscosity of the core material are, the damping property of the EP/microcapsule composite is better. The tan8-f cure showed that the composite has excellent low-frequency damping property. However, the involvement of the capsules decreases the compressive strength of EP and changes the damager forms of EP.PUF microcapsules with viscous liquid core were prepared and applied to PU system. The synthetic process and involvement of capsules on the dynamic mechanical property of PU were studied. The studies showed that choosing the theory content of-NCO in the PU pre-polymer as 6%, and controlling the reaction temperature as 75-80℃and time as 1h can synthesis the PU polymers with good mechanical and dumping properties. The addition of capsules improves the peak value of tanδof PU at Tg temperature by about 28%—54%, and widened the range of temperatures of tanδabove 0.7. The dynamic mechanical parameters of the composites in broadband were achieved through time-temperature superposition principle.The results indicated that the addition of capsules improves the tanδof PU over the low-frequency ranged from 0-1000Hz. Compression test showed that the microcapsules embedded in the PU can maintain intact structure and not rupture at a high pressure, which meet the material requirement of being used in underwater pressure environment.更多还原