【作者】 江赛华；

【导师】 胡源； 卢兆明； 桂宙；

【作者基本信息】 中国科学技术大学 ， 安全科学与工程， 2014， 博士

【摘要】 聚甲基丙烯酸甲酯(PMMA),俗称“有机玻璃”,是一种典型的透明聚合物材料。它应用广泛却极易燃烧且耐热性差。本论文在综述PMMA阻燃方法的基础上,发现目前最为常用的物理添加阻燃剂方法在阻燃PMMA时往往会牺牲材料本身的热性能和透明性；而另一种常见方法——化学引入普通反应型阻燃剂法,虽能协调阻燃性与透明性间的矛盾,却易造成材料热性能的降低。因此,制备兼具阻燃、耐热、透明等性能的PMMA既是材料本身应用的客观要求,同时也是目前材料设计制备环节所面临的一大挑战。硅烷交联技术能有效改善材料热性能,同时对材料透明性影响较小；纳米复合技术能实现高效阻燃,且对材料其它性能影响小。基于以上考虑,本论文—方面从分子设计角度出发制备含磷、氮、硅等阻燃元素的反应型阻燃剂,通过硅烷交联技术将其引入PMMA中,并进一步研究该类阻燃剂对PMMA的阻燃及热性能的影响机理；另一方面,从纳米复合材料设计入手,将具有催化作用的层状磷酸铝和耐高温的二维石墨烯材料用于PMMA基纳米复合材料的制备,并研究这两类二维纳米粒子对PMMA热降解机理及燃烧性能的影响,探讨其中存在的阻燃耐热机理。为了建立更为高效的阻燃体系,我们还将硅烷交联和纳米复合技术相结合,选取效果最佳的反应型阻燃剂和纳米粒子,共同引入PMMA中,制备出新型含磷氮硅PMMA基纳米复合材料,且细致研究纳米粒子和反应型阻燃剂在阻燃PMMA时存在的协同效应。主要研究工作如下：1.以二氯化磷酸苯酉旨(PDCP)和亚磷酸二甲酯(DMPP)为磷源,二乙胺、3-氨基丙基三乙氧基甲硅烷(APTES)为硅、氮源,丙烯酸羟乙酯(HEA)为“双键源”,通过两步取代反应或Kabachnik-Fields反应成功合成了三种含磷反应型阻燃剂——(丙烯酸羟乙酯基氨丙基)三乙氧硅基-苯基磷酸酯(SNP)、(四甲基(3)-三乙氧硅基氨丙基)二磷酸酯(TMSAP)和丙烯酸羟乙基-苯氧基-二乙基磷酰胺(APEEA);并制备出各自低聚物。结果显示三种低聚物不仅起始热降解温度(T01)和PMMA相近,且燃烧热释放速率低、热释放容量低、高温成炭效果好。以上表明三种阻燃剂均适用于PMMA阻燃。其中TMSAP低聚物成炭效果最好,因此具备最低燃烧性能。2.以APEEA和甲基丙烯酸甲酯(MMA)为原料,通过自由基本体共聚法成功制备线型含磷、氮PMMA基共聚物。热重分析仪、微型燃烧量热仪及极限氧指数结果显示共聚物具有较好的热稳定性和阻燃性,这归功于共聚物中含磷部分在材料燃烧过程中促进PMMA基体生成炭层。炭层能隔热隔氧进而延缓聚合物基体发生进一步燃烧或降解。但是,APEEA的引入也使得共聚物硬度和玻璃化转变温度发生了明显下降,这和线型共聚物分子链柔性及自由体积的增加不无关系。3.通过硅烷交联技术(溶胶凝胶法)分别将SNP和TMSAP引入PMMA中,得到两类新型含磷、氮、硅PMMA基有机无机杂化材料。两类杂化材料均表现为显著改善的热性能、硬度及较高透明度；这是由于杂化材料内部经硅烷的水解缩合过程形成了交联网络结构和氧化硅纳米粒子；纳米粒子结合交联作用能增强聚合物分子链间相互作用从而提高材料热与力学性能；此外,纳米粒子的良好分散性使得材料透明度受影响较小。两类杂化材料均表现为显著改善的阻燃性能,这是由杂化材料内部含磷单元的“催化成炭效应”及“磷-硅阻燃协同效应”引起的。对比APEEA与SNP,TMSAP在PMMA阻燃方面具有更好的阻燃效率,因为TMSAP具备更高的磷含量以及催化成炭效率。4.基于纳米复合技术的优点,通过溶剂热法一步合成有机改性层状磷酸铝(DDA-LAP),并利用原位聚合法制备PMMA/DDA-LAP纳米复合材料;DDA-LAP在PMMA基体中成功实现插层且分散良好。以丙烯酸羟乙酯、氯化亚砜、氧化石墨为原料成功实现氧化石墨的一步还原改性,制备出表面接枝双键的功能化石墨烯(FGN)；通过乳液技术对FGN进行表面包覆处理,制备PMMA/FGN复合材料；包覆处理有效抑制了FGN片层在PMMA中团聚堆叠,改善其分散性。结果显示少量层状磷酸铝(≤5.0wt%)和FGN (≤1.0wt%)便能显著提高了PMMA的热性能及力学性能；力学性能的增强主要来源于无机片层自身优异力学性能和无机片层与基体间强的相互作用(如PMMA/DDA-LAP中以氢键、范德华力为主,PMMA/FGN中以共价键为主)；热性能的提高除了相互作用因素外还受益于无机片层的“物理阻隔效应”。阻燃性能方面,DDA-LAP效果明显优于FGN,这是由于LAP具备“片层阻隔”及“催化成炭”双重效应,而石墨烯不仅没有催化成炭效应且自身高热导率不利于材料阻燃。此外,DDA-LAP对PMMA透明度影响较小,这是由于DDA-LAP本身颜色浅且在PMMA中分散较好的缘故。5.通过溶胶凝胶法成功将TMSAP和DDA-LAP一起引入PMMA基体中,制备新型含磷、氮、硅PMMA基有机无机杂化纳米复合材料。复合材料在保持较高透明性的同时,硬度、玻璃化转变温度、热稳定性等都得了显著改善,这是由于材料内部不仅具备均匀分散的层状磷酸铝片层,且形成了稳固的交联网络,二者相互结合导致上述性能的改善。DDA-LAP与TMSAP混合物对比等量TMSAP阻燃效果更明显,主要表现在极限氧指数的提升和热释放速率的进一步下降；由此说明二者在提高PMMA材料的阻燃性能方面存在着协同效应；机理分析表明磷酸铝的片层阻隔效应、催化基体生成石墨碳作用及TMSAP的催化成炭作用对于材料阻燃性能的提高均有帮助。此外,等量LAP比TMSAP催化成炭作用高。更多还原

【Abstract】 As a typical transparent amorphous polymer, polymethyl methacrylate (PMMA) has been widely used in building construction, plastic optical fibers and optical lenses because of its excellent characteristics including high strength, good flexibility, weather resistance, and dimension stability. However, the poor thermal stability and flammability limits its further application. Consequently, improving the thermal properties and flame retardancy of PMMA has been attracting increasing attention. To avoid environmental pollution, there is a trend toward using halogen-free flame retardants (FRs) in PMMA resins. Phosphorus-, nitrogen-, or silicon-containing compounds as promising "green" flame retardants are mostly used to replace halogenated compounds in polymers.In this dissertation, different reactive FRs containing phosphorus, nitrogen and/or silicon (APEEA, SNP and TMSAP) were synthesized by the way of molecular design and well characterized. The non-halogenated FRs were added into PMMA matrix by chemical incorporation including copolymerization or/and silane cross-linking method to improve the flame retardancy, thermal property and mechanical property. By comparison, TMSAP exhibits the best flame-retardant efficiency. Considering the advantage of nanocomposite technique, two layered nanoaddtives comprising layed aluminophosphate (LAP) and graphene was firstly organic-modified and then dispersed into PMMA. Compared to heat-conductive graphene, the addition of small amounts of non-conductive LAP nanolayers better improve the flame retardancy and thermal stability. To achieve higher flame-retardant efficiency, chemical incorporation method and nanocomposite technique are combined. The research work of this dissertation is composed of the following parts:1. Three phosphorus-, nitrogen-and/or silicon-containing reactive flame retardants, noted as APEEA, SNP and TMSAP, were synthesized and well characterized using FTIR,’H NMR,31P NMR and29Si NMR. The APEEA and SNP were synthesized by the esterification of phenyl dichlorophosphate (PDCP) with hydroxyethyl acrylate (HEA), and followed by the reaction with diethylamine (APEEA) or3-aminopropyltriethoxysilane (APTES). The TMSAP was synthesized by a Kabachnik-Fields reaction. The oligomers of these three compounds were prepared by homopolymerization and/or silane cross-linking. The thermal stability and flammability of the oligomers were evaluated by TGA and MCC. The TGA results showed that the char residues of Olig-APEEA, Olig-SNP and Olig-TMSAP were18.6%,34.6%and63.5%, respectively. The HRC of the three oligomers are304J/K-g,93J/K-g and75J/K-g respectively. Both the TGA and MCC results showed the three monomers had high char formation and low flammability.2. The phosphorus-and nitrogen-containing flame retardant, APEEA, was copolymerized with MMA monomers to prepare a novel linear PMMA-based copolymer. The morphology and structure of the copolymers were characterized using FTIR. The copolymers exhibit relatively high transparency and significant improvements to the thermal stability and fire retardancy when compared to PMMA. However, the mechanical properties and glass transition temperature (Tg) are reduced remarkably. From the mechanism analysis, the char formation of copolymers caused by APEEA during degradation plays a key role in the flame retardancy enhancement. The increased molecular flexibility and copolymer free volume is responsible for the deterioration of mechanical properties and Tg.3. Two novel reactive flame retardants (SNP and TMSAP) containing phosphorus, nitrogen, and silicon were incorporated into PMMA matrix through copolymerization and the sol-gel method to produce PMMA based organic-inorganic hybrids. The29Si MAS NMR results for the hybrid materials suggested the formation of cross-linked networks in the hybrids. A morphological study showed that the inorganic particles were well distributed in the PMMA matrix. The hybrids retained a high transparency and exhibited a significant improvement in glass transition temperature, thermal stability, hardness, and flame retardancy upon the incorporation of flame retardants into the PMMA matrix. The network structure, homogeneous distribution, and char formation during degradation were proposed as three key reasons for the improved properties.4. PMMA/DDA-LAP intercalated nanocomposites are prepared by in situ bulk polymerization of MMA. The intercalated structure is characterized by XRD and TME. With the intercalation of DDA-LAP in PMMA matrix, the Tg obtained from DSC are increased. From UV-vis, TGA and MCC results, the nanocomposites obtained keep relatively high transparency in optical property and have a significant improvement in mechanical properties, thermal stability and flame retardancy. The mechanism for the properties enhancement is investigated. The strong interfacial interaction between the aluminophosphate layers and the PMMA chains, the homogeneously distribution and the graphitized char formation during heating are three key roles for the properties improvement.Graphene is a kind of very promising filler for polymer composites, but its irreversible aggregation when introduced into polymers is a challenge for property enhancements and limits its industrial application. To address this, we report one-step covalent functionalization and simultaneous reduction of graphite oxide (GO) with hydroxyethyl acrylate (HEA), resulting in a functionalized graphene with double bonds. The functionalized graphene obtained, noted as FGN, is successfully incorporated into polymethyl meth-acrylate (PMMA) matrix by latex technology and melt blending. Latex technology is used for the pretreatment of FGN through emulsion copolymerization between methyl methacrylate (MMA) monomers and FGN double bonds. After pretreatment of FGN, covalent attachment of PMMA particles to the edges of FGN sheets can effectively prevent their agglomeration and markedly improve their dispersion in the polymer matrix. Since these PMMA particles act as good compatibilizers in the interface between FGN and PMMA matrix during the melt mixing process, the PMMA/FGN composites obtained exhibit exfoliated morphology and very good dispersion, as evinced by the results from X-ray diffraction (XRD) and transmission electron microscopy (TEM). When even a small amount of FGN (<1.0wt%) is incorporated, the thermal properties and mechanical properties of PMMA/FGN composites are enhanced significantly. The Tg increases from103.8to110.5℃, while the tensile strength increases by31.0%(1.0wt%FGN addition). Moreover, the storage modulus of PMMA/FGN composites increases by27%(1.0wt%FGN addition) at room temperature. These enhancements are attributed to the strong chemical interaction between the FGN sheets and PMMA and the good distribution of FGN sheets in the PMMA matrix. However, due to the high heat conductivity of FGN sheets, the flammability of composites is a little decreased, which suggest that the graphene sheets do not exhibits good flame-retardant effect on PMMA resin.5. To further improve the flame-retardant efficiency,15%DDA-LAP/TMSAP mixture with different DDA-LAP contents was incorporated into PMMA matrix by sol-gel method to prepare a novel PMMA based composite (poly (MMA-co-MSMA)/TMSAP/DDA-LAP). XRD and TEM results showed that the LAP nanolayers were intercalative or/and exfoliated in the composites, exhibiting high dispersion degree. The29Si MAS NMR results for the composites suggested the formation of cross-linked networks. From hardness test, DSC, TGA, LOI, UV-vis and MCC results, the composites obtained possess enhanced hardness, glass transition temperature, thermal stability and flame retardancy, and keep high transparency. The degradation process of composites was studied by RTIR. Raman and SEM were used to study the components and structure of char residue. Possible mechanisms for the performance enhancements of composites are proposed. Moreover, it may be observed that much more PHRR reduction and LOI increment were observed in the composites with the addition of15%DDA-LAP/TMSAP than those with the addition of15%TMSAP, suggesting that a synergistic effect occurs between DDA-LAP and TMSAP in enhancing flame retardancy of PMMA. The physical barrier effect of LAP nanolayers combining with the graphitized char catalyzed by DDA-LAP and TMSAP during combustion plays key roles in the significantly enhanced flame retardancy.更多还原