【作者】 丁严艳；

【导师】 胡源； 桂宙；

【作者基本信息】 中国科学技术大学 ， 安全技术及工程， 2008， 博士

【摘要】 聚合物/氢氧化合物纳米复合材料将无机材料的刚性、尺寸形貌和热稳定性与聚合物的韧性、可加工性和介电性等结合在一起,因表现出优异的力学性能、热稳定性、气体阻隔性等而受到广泛关注,已成为材料科学研究的前沿。本文在大量文献调研的基础上,综述了一维和二维形貌无机化合物基纳米复合材料的最新研究进展。在具体的研究工作中,作者以合成的一维（锌基纳米带,氢氧化镧纳米线）和二维（层状双氢氧化物）氢氧化合物为主体材料,在对材料进行适当的处理之后,分别采用单体插层—原位聚合,协效-熔融共混,溶剂共混等方法制备了几种典型的聚合物/氢氧化合物纳米复合材料,并对材料的结构进行了表征,研究了材料的结构与性能特别是氢氧化合物的组成尺度形貌与其热稳定性和燃烧性能的关系。对所制备的纳米复合材料进行了结构分析,燃烧分析（热重和锥形量热分析）和机理分析（热解动力学分析）等发现,在聚合物/氢氧化合物纳米复合材料的燃烧降解过程中,既有层状纳米无机物的气体阻隔作用,一维纳米无机物的促进成炭和交联网络作用也有因降解控制步骤的改变而引起的活化能增大的能量阻隔作用机理。归纳起来,本文由以下四个部分组成:第一,首先优化了含镁铁的双氢氧化物的制备条件,并以所制备的LDH和MMA单体为起始物通过原位聚合法制备了低含量高热稳定性的层离型纳米复合材料。并对无机元素组分和层状形貌对聚合物基体的热稳定化作用机理进行了分析,以及通过动力学分析方法研究了纳米复合材料的降解机理。实验结果表明有机改性的MgFe-LDH可以显著的提高复合材料的热稳定性,其作用原因一方面由于纳米级均匀分散的无机物片层的阻隔作用,另一方面由于层板上的结构基元铁离子发挥了捕获自由基的作用。再通过纳米复合材料热解动力学分析有理由判断,纳米复合材料中的稳定化作用不仅与片层的物理阻隔作用有关,也应当与热解反应活化能变化即能量阻隔有关。第二,通过共沉淀法和离子交换法合成了三种不同元素组成的双氢氧化物,采用熔融共混方法制备了LDH和MH对EVA协效的纳米复合材料体系,三种体系在5%LDH含量下均形成了层离型复合结构。详细研究了MH/MgAl-LDH,MH/ZnAl-LDH和MH/MgFe-LDH三种协效体系对EVA的力学性能和阻燃性能的影响。动态力学分析的结果表明LDH的片层促进了MH在聚合物基体中的分散使得聚合物分子链段运动增强,纳米复合材料的玻璃化转变也呈现了相似的变化。利用锥形量热仪对此纳米复合材料进行燃烧性能测试,三种纳米复合材料的热释放速率及主要燃烧参数相对于EVA/MH组成的比较样是显著降低的,其中MH与MgAl-LDH具有最佳阻燃协效作用。对材料的燃烧残余物的形貌分析表明,含LDH的阻燃EVA纳米复合材料在燃烧过程中能形成致密而连续的保护层,有效阻隔了材料在燃烧过程中气体挥发物的扩散和与燃烧环境间能量的交换,提高燃烧残留量,降低了材料的火灾危险性。第三,在温和的实验条件下合成了一维形貌的多组分无机纳米带。通过一系列表征证实了该纳米带有着长程有序的结构,其纯度高、产量大、尺度均匀、表面洁净。对煅烧后的产物也进行了研究。这种新型的一维无机纳米带是碱性的,表面含有大量活性基团,易于和聚合物中的官能团发生相互作用,比如聚丙烯酸酯类,聚碳酸酯以及含有羧基团的其他聚合物体系,从而组成新型的聚合物/锌基纳米带复合材料。以锌基纳米带为起始物通过溶液共混法制备了PVA基纳米复合材料。实验结果证实了未经过修饰的无机纳米带与聚合物基体有良好的相容性,无机相含量为11.8%的纳米复合材料仍具有90%以上的可见光透过率,并且锌基纳米带在PVA的降解过程中起到了促进成炭的作用。通过对复合材料炭渣的形貌分析,能够进一步验证纳米带促进成炭的机理。以锌基纳米带和MMA单体为起始物采用原位聚合法成功制备了PMMA基纳米复合材料。实验结果表明因聚合物和纳米带之间的有效作用力可以使得纳米带均匀的分散于聚合物基体中,并且使得含量小于1wt%的纳米复合材料的热稳定性获得了显著的提高。这可能是因为一维纳米带的表面组成使得其与单体在开始形成了氢键作用,经过聚合反应后无机相和有机相之间形成纵横交错,相互贯穿的类似交联结构,从而大大限制了聚合物链段的运动,同时也表现出了玻璃化温度的提高和丙酮萃取实验的结果。第四,这部分以水热法合成了尺度均匀的一维氢氧化镧纳米线,并以其为起始物通过原位聚合法制备PMMA/La（OH）₃纳米复合材料。研究了一维形貌的稀土化合物对于PMMA材料热性能的影响。并通过热重分析结合热解动力学分析,评价PMMA/La（OH）₃纳米复合材料的热降解机理,初步推断La（OH）₃对PMMA降解过程的能量阻隔作用。更多还原

【Abstract】 Polymer/hydroxide nanocomposites is a novel type of advanced composites, which has become the focus of research in recent years because of their demonstrated excellent mechanical,thermal and gas barrier properties compared with their conventional counterparts due to the combinations of the rigidity,dimensional and thermal stability of inorganic component with the toughness, processing and dielectric of polymer.The latest progress in the field of nanocomposites based on one-dimensional and two-dimensional inorganic was reviewed in this dissertation based on the recent literatures.In this thesis, several typical polymer/hydroxide nanocomposites were prepared and characterized by different approaches based on the synthesis and properly modification of hydroxides. Then, the relationships between structure and properties, especially thermal stability and flammability properties of the nanocomposites, using both thermogravimetric （TG） analysis and cone calorimetry experiment, were discussed in detail. The kinetics of the thermal and thermo-oxidative degradation of the nanocomposites were studied, which suggested that besides a charring barrier mechanism of carbonaceous char formation as an insulator to the heat and a mass transport barrier during the combustion of the nanocomposites, there is an active mechanism from the increase of the effective activation energy of the degradation acting as an effect of energy barrier of the process. In general, it was revealed that the influence of preparation on the structure of the nanocomposites resulted in differentia in thermal and flammability properties. It is very important that the preparation procedure should be optimized to obtain the polymer nanocomposites with comprehensive excellent properties.In summary, this dissertation is composed of four parts as follows:Firstly, layered double hydroxide with a high content of hydroxyl groups was prepared by ion-exchange method and organically modified with Dodecyl Sulfate Sodium（DS）. Poly（methylmethacrylate） （PMMA）/MgFe-LDH nanocomposites were prepared via in-situ polymerization method. Though the XRD and TEM, the PMMA/LDH nanocomposites were partially interacted and partially exfoliated. The participation of Fe³⁺ ion was found to play an important role in improvement of thermal stability of nanocomposites with small inorganic loading and well-dispersed inorganic components. The thermal degradation mechanism was discussed by microscopic kinetic analysis. This indicated that the naocomposites also possessed an action mechanism of the effect of a charring insulator barrier and the effect of an energy barrier in the combustion behavior of the nanocomposites.Secondly, the flammability and mechanics properties of three series of EVA/MH/LDH nanocomposites as well as the flame retardant synergistic effect between LDH and the conventional flame retardant additive MH were investigated by cone calorimetry and dynamic mechanics analysis.The results demonstrated that the heat release rate （HRR） of the nanocomposites, in particular, their peak HRR value, has a more obvious decrease than that of comparative sample. In addition to the effect of an insulator barrier as other inorganic compounds such as clay, LDH may promote the formation of the carbonaceous char due to the abundant hydroxyl groups between its interlayer. It means that the combustion properties of the nanocomposites were reduced, which may lessen the fire hazard of the materials in use.Thirdly, a novel multicomponent nanoribbon have been synthesized in our group by mixing zinc acetate and hydrazine solution at low temperature. The nanoribbon with abundant functional groups on the surface of ribbons have been prone to interact to groups of polymers.PVA/nanoribbon nanocomposites were prepared by solution blending. All nanocomposites as-prepared were characterized by XRD, TEM, SEM, TG and UV-VIS.All nanocomposites have retained favourable transparence, even the content is up to 11.8%.The char process have possible been promoted by zinc nanoribbons, which also were verified by analysis of char morphology.PMMA/nanoribbon nanocomposites were prepared by free radical polymerization. Experimental results showed that inorganic nanoribbons were uniformly distributed in and bonded to the PMMA host matrix without macroscopic organic-inorganic phase separation. It was found that the thermal stability and glass transition temperature （Tg） of the nanocomposite films increased effectively with increasing inorganic content at low content and remained above 1wt% inorganic content. These results suggest the network formation because of the strong interaction between the inorganic nanoribbons and the polymer matrix, which induces the mobility restriction of polymer chains. The characteristics of the 1-dimensional inorganic nanoribbons we used here may play a key role in the formation of the "cross-link" networks and in the decision of the lower content of inorganic nanoribbon additive.Fourthly, Lanthanide hydroxide nanowires were synthesized by hydrothermal method, a series of characterizations were used to study the structure,morphology and degradation details of nanowires. Poly（methylmethacrylate）/La（OH）₃ nanocomposites were prepared via in-situ polymerization method. Experimental results showed that inorganic nanowires were uniformly distributed in the PMMA host matrix without macroscopic organic-inorganic phase separation and the thermal stability of nanocomposites have remarkably improved. Microscopic kinetic analysis verified the effect of an energy barrier of nanowires in the polymer martix.更多还原