【作者】 郑净植；

【导师】 解孝林； 周兴平；

【作者基本信息】 华中科技大学 ， 高分子化学与物理， 2010， 博士

【摘要】 超细二氧化硅(包括微、纳米二氧化硅)由于其良好的光学透明性、生物相容性、物理与化学稳定性及可裁剪的表面性质等优点而被广泛应用。聚丙烯(PP)是用途广泛的通用塑料,与二氧化硅(SiO2)复合可提高其加工、力学、热稳定等性能,有望实现聚丙烯的工程化。如何实现SiO2在聚丙烯基体中的均匀分散及提高两相的界面相容性是制备聚丙烯/SiO2复合材料的关键。本论文分别采用改性SiO2和二氧化硅聚合物复合微球为填料,通过熔融共混和注塑成型的方法制备了PP/微、纳米SiO2复合材料,系统研究了SiO2在PP基体中的分散及复合材料的结构与性能。具体研究内容及主要结果如下：(1)采用马来酸酐接枝氢化苯乙烯/乙烯-丁烯/苯乙烯嵌段共聚物(MA-SEBS)作增容剂,通过熔融共混和注塑成型的方法制备了PP/SiO2纳米复合材料。研究了MA-SEBS对复合材料的分散状态、力学性能、结晶形态及结晶及熔融行为的影响。结果表明MA-SEBS起到了界面相容剂的作用,降低了纳米SiO2的团聚,改善了其在PP基体中的分散,显著提高了复合材料的冲击强度；MA-SEBS使SiO2在PP结晶过程中能更好地起到异相成核作用,提高了复合材料中PP相的结晶温度,使PP形成尺寸更小、结构更完整的球晶。(2)将甲基丙烯酸甲酯(MMA)和丙烯酸丁酯(BA)通过原位乳液共聚合的方法对纳米SiO2进行接枝改性;将改性SiO2与PP复合制备了PP/纳米SiO2复合材料。研究了接枝改性对SiO2表面性质、SiO2在PP基体中的分散、PP/SiO2复合材料力学性能和结晶、熔融行为的影响。结果表明聚甲基丙烯酸甲酯(PMMA)和聚丙烯酸丁酯(PBA)成功地接枝到了纳米SiO2表面,且可通过改变共聚单体的种类和配比调控SiO2表面接枝聚合物的溶度参数和模量；由于接枝在纳米SiO2表面的PMMA加强了SiO2的亲油性和异相成核能力,增强了纳米SiO2在PP基体中的分散性和界面粘合、降低了复合材料中PP的球晶尺寸,从而导致杨氏模量和韧性同时提高；与PP相容性更好的PBA对纳米SiO2的接枝改性进一步改善了SiO2粒子在PP中的分散和界面的粘结,使PP/SiO2复合材料的韧性进一步提高,但使复合材料的模量下降；相比PMMA或PBA的改性,用共聚物P (MMA-co-BA)对纳米SiO2粒子进行接枝改性能使PP/SiO2复合材料呈现出均衡的强度和韧性。(3)利用溶胶-凝胶法和原位乳液聚合法,制备了以SiO2为核、P(MMA-co-BA)共聚物为壳的复合微球,将复合微球与PP熔融共混、注塑成型制备了均匀分散的PP/SiO2复合材料。研究了SiO2聚合物复合微球的粒径大小及其壳层厚度的影响因素,复合微球对PP/SiO2复合材料的分散、力学性能、结晶、熔融及非等温结晶动力学行为的影响。结果表明通过改变SiO2胶体微球的粒径、MMA和BA的用量可以调控核-壳复合微球的粒径和壳层厚度；由于复合微球壳层的高分子链有效地阻止了无机粒子间的直接接触从而改善了SiO2粒子在PP基体的分散,同时壳层高分子链与基体间良好的相容性增强了PP与SiO2的界面粘结强度,有效地提高了PP/SiO2复合材料的冲击强度；SiO2复合粒子的粒径及壳层厚度对复合材料的力学性能有显著的影响,当复合粒子壳层厚度为15nm时,在不降低复合材料拉伸强度的情况下,使复合材料的冲击强度提高到纯PP的两倍；粒子脱粘、塑性银纹扩张和基体剪切屈服吸收冲击破坏产生的能量是造成复合材料韧性提高的原因；均匀分散的SiO2复合粒子对PP能够起到很好的结晶成核作用、提高复合材料中PP相的结晶温度；并通过Mo法准确地描述了PP/SiO2复合材料的非等温结晶动力学行为。更多还原

【Abstract】 Ultrafine silica particles, including micro- and nanosized silica, have been employed in a variety of areas because of their optical transparency, electrical insulation, chemical and physical stabilities, biocompatibility and tunable surface properties. Polypropylene (PP) is an important general plastic and PP-silica composites have attracted more and more attention owing to their excellent processability, unique mechanical and thermal stability, etc. However, to enhance the dispersion of nano-fillers is a major challenge due to their strong tendency to agglomerate. In the dissertation, modified nano-silica and silica-polymer hybrid-particles were respectively compounded with polypropylene (PP) by melt mixing to prepare PP/SiO2 composites. The dispersion of SiO2 in PP, as well as structure and properties of PP/SiO2 composites were studied. The main contents and results were drawn as following:(1) Maleic anhydride grafted styrene-ethylene-butylene-styrene (MA-SEBS) was used as compatibilizer of PP/SiO2 nanocomposites. The effects of MA-SEBS on dispersion, mechanical properties, crystallization and melting properties were stedied. MA-SEBS enhances the dispersion of silica in PP and improves the interface adhesion between silica and PP matrix, which leads to improving the impact strength of composites.(2) Nano-sized silica particles were modified with methyl methacrylate (MMA) and butyl acrylate (BA) by in situ emulsion copolymerization. These modified nanoparticles were compounded with PP to prepare PP/SiO2 nanocomposites. The effects of modification on dispersion of SiO2 in PP, mechanical properties, crystallization were studied.PMMA and PBA are successfully grafted onto nano-SiO2. The solubility parameter and modulus of the copolymer covering on SiO2 surface are controlled by means of changing the copolymer composition. PMMA grafted on nano-silica enhances the dispersion of the nanoparticles in PP and interfacial adhesion between SiO2 and PP, decreases the size of PP spherulites in nanocomposites, which increase the Young’s modulus and toughness of PP/SiO2 nanocomposites. PBA grafted on nano-silica further improves the dispersion and the interfacial interaction, decreases the size of PP spherulites in PP/SiO2 nanocomposite, which leads to further toughening the PP/silica nanocomposite. Howerever, its low modulus decreases the modulus of the PP/silica nanocomposite. The nanocomposites containing PP and nano-silica particles modified with P(MMA-co-BA) have balanced stiffness and toughness due to the moderate modulus and solubility parameter of P(MMA-co-BA).(3) A series of core-shell silica hybrid-particles with nanometer P(MMA-co-BA) shells were fabricated by the sol-gel process and emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA), which were subsequently compounded with PP in the molten state to prepare homogeneously dispersed PP/SiO2 composites. The effects of silica hybrid-particles on dispersion of SiO2 in PP, mechanical properties and crystallization behave were studied.Upon changing the sizes of silica and the feed silica/co-monomer ratio, the sizes of silica hybrid-particles P(MMA-co-BA) and shell thickness on the silica core were controled. Owing to the existence of the nanometer P(MMA-co-BA) shells, the silica hybrid-particles were almost mono-dispersed in the PP matrix and improve the the interfacial interaction between PP and silica, which leads to improve the impact strength of composites. The sizes of silica hybrid-particles and shell thickness have great effects on mechanical properties.That is, when the polymer shell thickness was 15 nm, compared to pure PP, the impact toughness of the PP/silica composite was more than doubled with little degradation of tensile strength. The homogeneous debonding at the PP/silica interface, plastic void expansion and plastic matrix shearing during impact fracture greatly toughened the PP/silica composites. The incorporation of well-dispersed silica hybrid-particles acts as nucleating agents to increase the Tcp of PP phase in the PP/SiO2. The non-isothermal crystallization kinetics of PP/SiO2 composites is studied using Mo approach.更多还原