【作者】 蔡小霞；

【导师】 吴国章；

【作者基本信息】 华东理工大学 ， 材料科学与工程， 2011， 博士

【摘要】 有机-无机复合微球的应用已经渗透到生活的每个角落,从涂料、纸张、化妆品等大宗产品到微波吸收、电泳显示、蛋白质分离、靶向给药、生物酶固定、生化反应等具有极高附加值的特种功能器件。迄今为止,聚合物基纳米复合微球大多采用乳液聚合技术,存在反应时间长、纳米粒子分散困难、包埋率低和包含量少、微球的力学强度、耐磨、耐温性能亟待提高等问题。本论文巧妙地利用纳米粒子在两相高分子熔体反应共混过程中的定向分散特性,首次通过反应挤出等可大规模连续生产的低成本技术,成功地制备了多种结构和形态可控的有机-无机复合微球。全文以聚苯乙烯(PS),尼龙6(PA6)为模型聚合物,经不同表面修饰的二氧化硅(SiO2),二氧化钛(TiO2)和四氧化三铁(Fe3O4)为纳米粒子,系统地研究了反应挤出法制备聚合物基纳米复合微球的基本原理、加工工艺、微结构调控及其应用技术。首先研究了各种纳米粒子在PS/PA6共混物以及在反应增容体系中的选择性分散行为。结果表明,亲水性SiO2纳米粒子选择性分散在PA6相内,与SiO2粒径无关；而表面主要为-CH3基团的疏水性SiO2纳米粒子则分散在PS/PA6两相的界面处。TiO2纳米粒子一般分散在PA6相中,即使在共混过程中TiO2纳米粒子先分散在PS相内再与PA6进行共混,TiO2纳米粒子也会由PS相向PA6相迁移,最终分散在PS/PA6界面或PA6相内。对于PS/PA6/Fe3O4体系,表面未处理和表面经末端含-NH2的硅烷偶联剂处理的Fe3O4纳米粒子在PS/PA6中定向分散在PA6相内,而对于表面经高级脂肪酸处理的Fe3O4纳米粒子则大多分散在PS/PA6的界面处。这些结果都表明纳米粒子的表面与聚合物分子的相互作用力(即热焓的作用)对选择性分散起主导作用。为了进一步调控PA6的相形态和粒径,我们在Fe3O4纳米粒子填充PS/PA6体系中添加了末端接枝马来酸酐的聚苯乙烯(FPS)进行反应共混,结果发现无论哪种Fe3O4纳米粒子均大量被拖出至PS相内。研究表明FPS和Fe3O4表面基团的反应与FPS和PA6分子链之间的反应存在竞争关系,而且前者占优,只有当FPS与PA6反应完全后再加入Fe3O4纳米粒子才能使Fe3O4纳米粒子选择性分散在PA6相内。其次重点研究了TiO2纳米粒子定向分散对PS/PA6共混体系相反转行为及微结构演变的影响。当加入少量TiO2纳米粒子且选择性分散在PA6相内时,PS/PA6共混体系出现了由共连续结构转变成海岛结构的反常现象；随着TiO2含量继续增加,由于PA6/TiO2复合相与PS相的含量比不断上升,共混体系又从海岛结构转变为共连续结构,但是相尺寸变大。采用光学显微镜实时跟踪了PS/PA6/TiO2体系在热处理过程中的微结构演变规律,发现热处理促使共连续结构向海岛结构转变。这些实验结果与CB、SiO2等分散体系的演变规律完全不同。我们还发现,在低TiO2含量区,PA6液滴的凝聚过程符合Lifshitz-Slyozov-Wagner (LSW)机理,而TiO2含量较高时,凝聚速率大幅度减小。进一步研究表明,与CB在聚合物熔体中形成三维网络的凝聚形式不同,TiO2在聚合物熔体中倾向于形成团簇状聚集体。这种凝聚特征诱导了TiO2偏聚的PA6相形态发生根本的转变,即添加TiO2或热处理可以促使PA6相形成海岛结构,并且PA6分散相粒径随着TiO2含量的增加而增大。在上述研究成果的基础上,我们进一步考察了PA6组分含量、PA6与PS的粘度比、相容剂含量以及通过热处理使PA6相球形化过程对PA6基纳米复合微球粒径及粒径分布的影响。结果表明,降低PA6粘度有助于减小复合微球粒径,添加少量的反应性相容剂FPS不仅可以大幅度减小复合微球的平均粒径,而且可以将PS/PA6共混物的相反转点提高到50/50,粒径分布变窄,球形度更好。利用纳米粒子表面修饰和加工工艺优化,获得了两种微结构迥异的窄分布复合微球：一种微结构是纳米粒子均匀分散在复合微球中,另一种是纳米粒子偏聚在微球内表面。值得一提的是,我们获得了平均粒径为1.4μm,磁含量高达56wt%,饱和磁化强度达42.3emu/g的PA6/Fe3O4磁性复合微球。最后,我们利用反应挤出技术制备的PA6/Fe3O4磁性复合微球,初步研究了该微球在蛋白质分离方面的应用技术。为了高效率吸附牛血清白蛋白,采用PA6/Fe304微球与丙烯酸共聚以提高磁性微球表面的羧基活性基团。结果表明,微球表面的羧基含量可达1.0m mol/g,对牛血清白蛋白的最大吸附效率达215mg/g。这个数值明显高于文献报道,由此可见本实验获得的磁性复合微球在生物分离方面具有很大的应用潜力。更多还原

【Abstract】 The applications of organic-inorganic composite microspheres are pervaded in every field, which include bulk products, such as coating, paper, cosmetic, and high value added devices with special function, for example, microwave absorber, electrophoretic display, protein separation, targeting drug delivery, enzyme immobilization and biochemical reaction etc. Up to now, most of the polymer-based nanocomposite microspheres were prepared by various emulsion polymerization. These approaches are limited by many disadvantages, for instance, long preparing period, difficulty in nanoparticle dispersion, low encapsulation efficiency and nanoparticle content, and limitation in mechanical strength, wear resistance and heat resistance. To tackle these problems, based on the selective location of nanoparticles in one domain of immiscible melted polymer blends, we proposed a novel method to low-costly prepare size-controlable composite microspheres by reactive extrusion. In this work, various nanoparticles with different surface treatment, such as silica (SiO2), titanium dioxide (TiO2) and tetroxide (Fe3O4) nanoparticles, were mixing with the polystyrene (PS) and polyamide 6 (PA6) model blends to prepare PA6-based nanocomposite microspheres. The basic principle, processing technology, micro-morpology tailoring as well as application of reactive blending for fabricating polymer-based nanocomposite mocrospheres were systemically investigated.Firstly, the selective location of various nanoparticles in the PS/PA6 blends or in the reactively compatibilized PS/PA6 blends was studied. The results showed that the hydrophilic SiC>2 with-OH groups was preferentially distributed in the PA6 doamin having nothing with the size of nanoparticle, while, the hydrophobic SiO2 with-CH3 groups was selectively located at the interface of PS/PA6. For TiO2 filled PS/PA6 blends, when PS and TiO2 were blended first and then mixed with PS in the second step, the TiO2 was transferred itself from PS to the preferential PA6 phase and accumulated at the blend interface and in PA6. For PS/PA6/Fe3O4 blends, both the as-produced Fe3O4 and Fe3O4 with surface treated by a NH2-end silane coupling agent were selectively located in PA6 domain, while, the Fe3O4 with stearic acid surface-treatment was distributed at the interface. The results implied that the heterogeneous distribution of nanoparticles in immiscible polymer blends depends on the interaction between the nanoparticle and polymer chains (i.e. enthalpic interactions). In order to regulate the morphology and size of PA6 phase, a terminal maleic anhydride functionalized polystyrenes (FPS) was introduced to PS/PA6/Fe3O4 blends for reactive blending. It was found that a large part of Fe3O4 particles was pulled out from the PA6 phase or the interface to PS domain. The results showed that becaused the reaction of FPS with the surface ligands of particle is more competitive than that of FPS with PA6 chain, only when Fe3O4 is added after a complete reaction of FPS with PA6 could the Fe3O4 be preferentially dispersed into the PA6 domains.Secondly, the effect of selective dispersion of TiO2 in PA6 domian on the phase inversion and morphology evolution of PS/PA6 blend was researched. By adding a small amount of TiO2, the morphology of the PS/PA6 blend abnormally transformed from a co-continuous into a matrix-droplet structure. With further increases in nanoparticle loading, the increase of the content of PA6/TiO2in PS/PA6/TiO2 composite indued the transformation of PA6 phase from the dispersed phase to the continuous one, however, the PA6 domain becomes larger. Morphology evolution of PS/PA6/TiO2 blend during the static annealing process was real-time traced by optical microscopy. These experimental results are different from those in carbon black-filled or silica-filled immiscible polymer blends as reported previously. It was found that by adding a small amount of TiO2, the coarsening of PA6 domain is in accord with the Lifshitz-Slyozov-Wagner (LSW) mechanism, which is the same as the immiscible polymer blend. However, at higher TiO2 loads, the coarsening rate is sharply decreased. Further experiments revealed that unlike carbon black self-agglomeration to form 3D network structure, TiO2 nanoparticles appears to self-coagulation to form separated crowding of clusters in the PA6 phase, which induces PA6 phase to transformate from co-continuity to a matrix-droplet structure by adding low content TiO2 or by annealing process, and thus turns out a larger PA6 domain size at a higher TiO2 loading.Furthermore, the influences of the content of PA6, the viscosity ratio of PA6 and PS, the content of compatibilizer and annealing process glomerating PA6 domain on the diameter and size distribution of PA6-based microspheres were investigated. The results showed that a lower PA6 viscosity is favourable to decrease the size of PA6-based microspheres. By adding a small amount of FPS for reactive extrusion, it not only can sharply decrease the diameter of microspheres as well as the size distribution of microspheres, but also increase the phase inversion for PS/PA6 blend to 50/50. By modifying the surface of nanoparticles and optimizing the processing conditions, two kinds of uniform microspheres with different structure were fabricated. One owns structure in which nanoparticles are distributed evenly throughout PA6 microspheres, the other has structure in which nanoparticles were selectively located at the interior interface of PA6 microspheres. It should be mentioned particularly that PA6/Fe3O4 microspheres were prepared with number-average diameter of 1.4μm and very high Fe3O4 content. It’s saturation magnetization is about 42.3 emu/g.Finally, the protein immobilization utilizing the reactively extruded PA6/Fe3O4 composite magnetic microsphere was preliminarily investigated. Carboxyl functional group, bonded with PA6/Fe3O4 microsphere by copolymerization of acrylic acid with PA6 chain was used as a ligand for protein adsorption. The results showed that the surface concentration of carboxylic acid of the functionalized microsphere can be add up to 1.0 m mol/g, and the adsorption capacity of BSA reaches 215mg/g microspheres which is much higher than the reported value, showing its potential for application in bioseparation and biomedical fields.更多还原