【作者】 晏泓；

【导师】 许并社；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2009， 博士

【摘要】 氢氧化镁作为添加型无机阻燃剂,具有热稳定性好、无毒、抑烟、高效促基材成炭的作用,且在不产生腐蚀性气体的同时还具有中和燃烧过程中产生的酸性和腐蚀性气体功能,作为一种环境友好型的绿色阻燃剂具有很好的市场前景。然而,氢氧化镁在高分子材料中的分散性和相容性较差,往往导致阻燃材料力学性能下降。因此,如何增加氢氧化镁与聚合物之间的相容性、减少其使用量成为亟待解决的问题。本文针对这些问题,采用以下方法对氢氧化镁进行了制备和改性。采用反向化学沉淀法、利用聚乙二醇(PEG1000)作为软模板在室温下制备了一维纳米Mg(OH)2粒子。获得针状形貌氢氧化镁的最佳PEG含量为4%,此时的氢氧化镁晶型完整,形貌规整而且分散性好,高分子型分散剂PEG1000的使用能够有效地控制氢氧化镁晶体的生长取向,并推测和探讨了此一维材料的形成机理。首次以水/环己烷/Triton X-100/正己醇四元油包水微乳液体系中的微乳液滴作为纳米微反应器,向增溶有镁离子的微乳液区通入氨气作为沉淀剂,制备了纳米氢氧化镁粒子。这些空间受限的纳米微反应器可用来控制氢氧化镁纳米粒子的成核、生长和结晶。调整水和表面活性剂的摩尔比(ω0)可以有效地控制微乳胶束的大小,从而达到控制纳米粒子粒径的目的,纳米粒子的平均粒径随ω0的增大而增大。微乳液法获得的纳米氢氧化镁粒子在有机相中的分散性和相容性都较化学沉淀法有了较大改善。通过在水热溶液中加入阳离子表面活性剂十六烷基三甲基溴化铵(CTAB),实现了在较低的水热温度下获得高分散片状超细氢氧化镁。用此法得到的超细氢氧化镁的平均粒径为400nm,厚度为60nm,最佳工艺条件为150℃,pH为8, Mg2+/CTAB摩尔比为80的条件下水热6h。令人关注的是:CTAB的加入可以明显地促进氢氧化镁在水热条件下的溶解-沉淀过程,在较低水热温度下,生成形貌规整、粒径分布窄、结晶性好的超细氢氧化镁粒子。并探讨了CTAB在水热过程中对产物氢氧化镁形貌的影响机理。通过对纳米氢氧化镁粒子进行油酸(OA)表面改性,然后在其表面接枝大分子聚甲基丙烯酸甲酯(PMMA)得到了疏水纳米氢氧化镁粒子。首先,通过油酸对氢氧化镁进行表面修饰,在其表面引入双键烯烃基团,利用分散聚合法在修饰过的氢氧化镁表面接枝上有机大分子PMMA。接枝改性后的氢氧化镁粒子分散性得到较大的提高,在有机相中的分散稳定性和相容性得到了很大的提高。在此基础上,为了从根本上解决氢氧化镁的分散及阻燃效率问题,研究了一步法原位合成PMMA/Mg(OH)2/MMT纳米复合材料的合成工艺及阻燃性能,借助蒙脱土(MMT)来提高氢氧化镁的阻燃效率。首次将微乳液法和分散聚合法相结合,利用微乳液法制备纳米氢氧化镁,并在同一体系中利用分散聚合法原位一步合成了PMMA/Mg(OH)2/MMT三相纳米复合材料。氢氧化镁纳米粒子蒙脱土纳米片层在基体材料中呈单分散状态,有效地解决了纳米粒子在高聚物基体中的团聚问题,基本保证了复合材料的透明性;复合材料阻燃性能也得到了很大提高,其热释放速率(HRR)和热释放速率峰值(PHRR)均明显降低,并在文中对阻燃机理进行了详细讨论。更多还原

【Abstract】 Magnesium hydroxide, one of inorganic additive flame retardants, is a kind of promising green flame retardant and has attracted much attention because of its good thermal stability, nontoxicity, fume suppression, char-forming promotion, and no formation of acid and corrosive gas product during burning process. However, its poor dispersibility in and compatibility with polymer matrices would decrease the mechanical properties of the filled polymer. In this paper, therefore, the preparation and surface modification of ultrafine and nanometer magnesium hydroxide were investigated aiming at the problems above-mentioned.Magnesium hydroxide nanoneedles and nanorods were synthesized by reverse precipitation in the presence of polyethylene glycol (PEG1000) at ambient temperature. The experimental results showed that the growth of magnesium hydroxide crystals and dispersivity of nanoparticles were greatly influenced by polymer dispersant. The mechanism of the formation of magnesium hydroxide nanorods and nanoneedles was also proposed.Well-dispersed magnesium hydroxide nanoplatelets were first synthesized by simple water-in-oil (w/o) microemulsion process, blowing gaseous ammonia (NH3) into the microemulsion zones solubilized by magnesium chloride solution (MgCl2). The typical quaternary microemulsions of Triton X-100/cyclohexane/n-hexanol/water were used as space-confining microreactors for the nucleation, growth and crystallization of magnesium hydroxide nanoparticles. The mole ratio of water to surfactant (ω0) played an important role in the sizes of micelles and nanoparticles, increasing with the increase ofω0. The compatibility and dispersibility of nanoparticles obtained from reverse micelles were improved in organic phase.The high-dispersed lamellar ultrafine magnesium hydroxide was obtained at relatively low hydrothermal temperature in the presence of cationic surfactant, cetyl trimethyl ammonium bromide (CTAB). The procedure described in this study is attractive since proper amount of CTAB could promote the dissolution and precipitation of magnesium hydroxide in hydrothermal system, resulting in the well-defined morphology, narrow size distribution and good crystallinity of ultrafine particles. The method led to the production of particles with mean size of 400 nm and a diameter of 60 nm. The optimal conditions of preparation were hydrothermal treatment at 150°C for 6 h at pH 11 with Mg2+/CTAB molar ratio of 80. The influence mechanism of CTAB on morphology of magnesium hydroxide was discussed.Hydrophobic magnesium hydroxide nanoparticles were obtained by means of grafting poly(methyl methacrylate) (PMMA) onto the surface of nanoparticles after oleic acid (OA) modification. The functional double bonds were firstly introduced on the surface of nanoparticles by OA modification, followed by dispersion polymerization on the particles surface in ethanol solution to graft PMMA on the surface of modified magnesium hydroxide. The results showed that the organic macromolecule PMMA could be successfully grafted on the surface of OA-modified magnesium hydroxide nanoparticles, with the dispersibility and the compatibility of nanoparticles greatly improved in organic phase.In order to solve the problems of dispersibility and flame retardant efficiency of magnesium hydroxide, the in-situ synthetic technique and flame retardant propertie of PMMA/Mg(OH)2/MMT were further researched on the basis of the synthesis and modification of magnesium hydroxide, employing montmorillonite (MMT) to improve the flame efficiency of magnesium hydroxide. The microemulsions and dispersion polymerization were first combined together to synthesize ternary nanocomposite. The magnesium hydroxide nanoparticles and layers of MMT were monodispersed in the PMMA matrix, basically ensuring the transparence of nanocomposite. And the flame retardant efficiency was greatly improved, with the obviouse decrease of heat release rate (HRR) and peak of heat release rate (PHRR). The flame retardant mechanism was discussed in detail.更多还原