离子液体辅助分散石墨烯制备聚合物复合材料及其微孔发泡性能研究

发布时间：2018-08-12 14:09

【摘要】：石墨烯(graphene)由于其优异的物理和化学性能,在不同领域都引起了广泛的关注,在微孔发泡材料中的应用便是其中之一,石墨烯不仅在微孔发泡材料制备过程起到异相成核作用、优化泡孔尺寸和结构,同时还赋予材料优异的导电、介电以及电磁屏蔽功能,具有重要的应用前景。在这一领域,石墨烯在聚合物基体中的分散起着重要作用,既决定异相成核效率,又影响导电网络的形成。然而,石墨烯在许多聚合物中均易形成团聚体,对其进行氧化处理、接枝改性能够提高其分散性,但会影响其电学性能。因此,如何保持石墨烯电学性能的情况下实现其在聚合物中的均匀分散成为该领域的重要研究方向。基于此,本论文利用离子液体中咪唑盐与石墨烯的离子-π和π-π相互作用对石墨烯进行改性,促进石墨烯片层在聚合物基体中的分散,并利用离子液体的亲二氧化碳性质实现超临界二氧化碳在石墨烯表面富集,提高异相成核效率,改善泡孔结构。在制备微孔发泡材料过程中,通过添加无机纳米粒子作为异相成核剂,是一种降低泡孔尺寸、提高泡孔密度、改善材料微孔结构及性能的重要方法。根据不同尺寸级别,出现了不同类型的异相成核剂材料,其中石墨烯作为纳米粒子,在不同发泡材料中得到了应用。但是,无机纳米粒子的异相成核效率受到无机纳米粒子的尺寸、形貌、表面特性以及其与聚合物之间的相互作用的影响,而石墨烯本身容易团聚,因此提高石墨烯在聚合物基体中的分散性,提高其异相成核效率已成为该领域的重要研究方向。本论文首先将离子液体1-丁基-3-甲基咪唑六氟磷酸[bmim][pf6]与石墨烯共混研磨实现非共价键改性,改性后的石墨烯分别与聚苯乙烯(ps)和聚甲基丙烯酸甲酯(pmma)熔融共混挤出得到石墨烯-离子液体/聚苯乙烯(ps/g-ils)复合材料和石墨烯-离子液体/聚甲基丙烯酸甲酯(pmma/g-ils)复合材料,通过sem及tem对复合材料形貌结构表征表明石墨烯在离子液体的辅助下在聚合物中的分散性均得到了改善。进而对复合材料进行了超临界co2微孔发泡。通过对ps和pmma复合体系发泡行为进行比较,我们发现,离子液体和石墨烯片层均对复合材料发泡材料的结构有所影响。通常,离子液体在聚合物基体中起到增塑剂作用,导致发泡材料泡孔变大,泡孔密度变低,而石墨烯起到异相成核作用,会使泡孔尺寸变小,泡孔密度增大。离子液体与不同聚合物基体相容性不同,从而对聚合物的发泡行为以及石墨烯的分散存在影响,进一步导致ps和pmma两种复合材料体系的微孔发泡行为存在很大不同。离子液体与聚苯乙烯相容性差,单独对聚苯乙烯的发泡影响小,但能有效地分散石墨烯,石墨烯的异相成核作用导致聚苯乙烯复合材料的泡孔尺寸小,泡孔密度高。而离子液体与pmma相容性较好,虽然分散的石墨烯能够降低泡孔尺寸,但当离子液体含量高时,复合材料仍会出现较大的泡孔尺寸和较低的泡孔密度。因此,PMMA复合发泡材料随着离子液体比例的增大,其泡孔尺寸先变小后变大再变小。此外,为了制备具有取向微孔结构以及石墨烯片层的复合发泡材料,论文还对复合材料在受限条件下的发泡行为进行了研究,分别采用了快速泄压和快速升温两种发泡方式实现微孔发泡,通过固定受限空间以及施加外力实现泡孔生长取向,系统考察了发泡温度、饱和压力、受限空间大小等对泡孔结构的影响。研究表明:在受限空间内发泡能够得到具有部分取向结构的微孔发泡材料,空间越小,泡孔取向越明显,但取向的泡孔结构多在边缘处。采用快速升温发泡同时施加外力的方法能够促进泡孔结构的形成,同时生成取向的泡孔结构,TEM表明石墨烯片层会沿泡孔生长方向发生取向,说明这种方法在制备同时具有取向孔及石墨烯片层的复合发泡材料上具有一定的优势和应用前景。
[Abstract]:Graphene has attracted extensive attention in various fields due to its excellent physical and chemical properties. The application of graphene in microporous foaming materials is one of them. Graphene not only plays a heterogeneous nucleation role in the preparation of microporous foaming materials, optimizes the size and structure of the foam, but also gives materials excellent conductivity and dielectric properties. In this field, the dispersion of graphene in polymer matrix plays an important role, which determines the heterogeneous nucleation efficiency and affects the formation of conductive network. However, graphene is easy to form aggregates in many polymers, which can be oxidized and modified by grafting. Therefore, how to realize the uniform dispersion of graphene in polymer under the condition of keeping the electrical properties of graphene becomes an important research direction in this field. Based on this, this paper uses the ion-pi and pi-pi interaction of imidazole salt and graphene in ionic liquids to modify graphene and promote graphene. Dispersion of lamellae in polymer matrix, enrichment of supercritical carbon dioxide on graphene surface by ionic liquids, enhancement of heterogeneous nucleation efficiency and improvement of cell structure are realized. In the process of preparing microporous foaming materials, inorganic nanoparticles are added as heterogeneous nucleating agents, which can reduce cell size and improve cell structure. Different types of heterogeneous nucleating agent materials have emerged according to different size levels. Graphene, as a nanoparticle, has been used in different foaming materials. However, the heterogeneous nucleation efficiency of inorganic nanoparticles is affected by the size and morphology of inorganic nanoparticles. Graphene is easy to agglomerate due to its surface properties and interaction with polymers. Therefore, improving the dispersion and heterogeneous nucleation efficiency of graphene in polymer matrix has become an important research direction in this field. Graphene-ionic liquid / polystyrene (ps / g-ils) composites and graphene-ionic liquid / polymethyl methacrylate (pmma / g-ils) composites were prepared by melt blending and extrusion of modified graphene with polystyrene (ps) and polymethyl methacrylate (pmma / g-ils), respectively. The morphological and structural characterization of the composites showed that the dispersibility of graphene in the polymer was improved with the assistance of ionic liquids. The supercritical carbon dioxide microporous foaming was carried out on the composites. In general, ionic liquids act as plasticizers in polymer matrix, resulting in larger foam pores and lower cell density, while graphene acts as heterogeneous nucleation, resulting in smaller cell size and higher cell density. In order to improve the dispersion of graphene, the microporous foaming behavior of PS and PMMA composites is very different. ionic liquids have poor compatibility with polystyrene and have little effect on the foaming of polystyrene, but they can disperse graphene effectively. The heterogeneous nucleation of graphene results in polystyrene composites. Although dispersed graphene can reduce the cell size, when the content of ionic liquids is high, the composite still has larger cell size and lower cell density. Therefore, with the increase of the proportion of ionic liquids, the foam size of PMMA composite foaming materials increases. In addition, in order to prepare composite foaming materials with oriented microporous structure and graphene lamellae, the foaming behavior of the composites under confined conditions was studied. Two foaming methods, rapid pressure relief and rapid temperature rise, were adopted to realize microporous foaming, and the confined space was fixed. The effects of foaming temperature, saturation pressure and confined space size on the structure of the foam were investigated systematically. The results showed that microporous foams with partially oriented structure could be obtained in confined space. The smaller the space, the more obvious the orientation of the foam was, but the oriented structure of the foam was mostly at the edge. TEM indicates that the graphene lamellae will be oriented along the direction of the bubble growth, which indicates that this method has certain advantages and applications in the preparation of composite foam materials with both oriented pores and graphene lamellae. Prospects.
【学位授予单位】：浙江工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB332

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