Preparation Of Ionic Liquid Assisted Graphene Composites And Its Microcellular Foaming Performance

The graphene has drawn wide attention in different areas due to its excellent physical and chemical properties,one of them is the application in microcellular foaming materials, not only to the heterogeneous nucleation effect in the preparation process of microcellular foaming materials, the optimization of cell size and structure, but also to give materials with excellent electrical conductivity, dielectric and electromagnetic shielding function, graphene has important application prospect. In this field, the dispersion of graphene plays an important role, which determines the efficiency of heterogeneous nucleation, and influences the formation of the conductive network. However, graphene in many polymers are easy to form aggregates, the oxidation, grafting modification can improve the dispersion, but will affect its electrical properties. Therefore, how to realize the uniform dispersion in polymers under the condition of maintaining the electrical properties of graphene has become an important research direction in this field. Based on this, this paper used ion-π and π-π interaction between the imidazolium salts of ionic liquids and graphene to modify the graphene, promoting the dispersion of graphene layers in the polymer matrix,and used the dear carbon dioxide property of ionic liquids to realize the enrichment of supercritical carbon dioxide on the surface of graphene, increased the heterogeneous nucleation efficiency and improved the cell structure. In the course of preparing microcellular foam materials, it was an important method to reduce the cell size increase,the cell density and improve the microporous structure and properties of materials through adding inorganic nanoparticles as heterogeneous nucleate agents. According to different dimensions, there are different types of heterogeneous nucleation agents, among them, the graphene as a kind of nanoparticles, has been applied in different foaming materials. However, the inorganic nanoparticles nucleation efficiency is affected by the size, morphology, surface properties of inorganic nanoparticles and the interaction between the inorganic nanoparticles and the polymer matrix,as a result of the graphene itself is easy to agglomerate, improving the dispersion of graphene in the polymer matrix to improve its heterogeneous nucleation efficiency has become an important research direction in this field.This paper first used the method which grind the graphene and the ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate([BMIM][PF6]) to achieve non-covalent modification. Then with the aid of melt blending and extrusion of the modified graphene and the polystyrene(PS) and polymethyl methacrylate(PMMA),we got graphene-ionic liquids/polystyrene(PS/G-ILs) composites and graphene-ionic liquids/polymethyl methacrylate(PMMA/G-ILs), the morphology and structure characterization of SEM and TEM on the composites showed that the dispersion of graphene was improved under the assisting of ionic liquids. Then the composites were foamed by supercritical CO2,through comparing the foaming behaviors of PS and PMMA composites, we found that the ionic liquids and the graphene layers had influences on the structure of foaming composite materials. Usually, the ionic liquids play the role of plasticizer in the polymer matrix, leading to foam longer pore radius and lower pore density, while the graphene plays the role of heterogeneous nucleation and the bubble size is decreased,the cell density is increased. AS ionic liquids have different compatibility in different polymers that foaming behavior of the polymer and the dispersion of graphene are affected,leading to the microcellular foaming behavior of PS and PMMA composites are different. The ionic liquids have the poor compatibility with polystyrene,just have a little effect on polystyrene foaming,but can effectively disperse graphene, heterogeneous nucleation effect of graphene leads to polystyrene composites foam small size, high cell density pores. While ionic liquids have good compatibility with PMMA, though the graphene dispersion can reduce the bubble size, when the content of ionic liquids in composites is high, there will still be a large cell size and low cell density. Therefore, in the composite system of PMMA, the formed cell size first decreases then increases and then decreases with the increase of ionic liquids ratios.In addition, in order to prepare aligned with microporous structure and graphene layers composite foaming materials, the paper also conducted the research on the foaming behavior of composite materials under confined condition with the methods of quick pressure relief forming and rapid heating forming. By fixing the confined space and applying force to achieve the bubble growth orientation, the effects of foaming temperature, saturation pressure and limited space on the bubble structure were systematically studied. Research showed that: in the limited space forming, we can get microcellular foaming materials with part oriented structure, when space was smaller, the bubble orientation was more obvious, but the oriented pore structure were mostly found in the edge. Use the rapid heating with the aid of force forming method can promote the formation of pore structure, at the same time, it can form the oriented pore structure. TEM characterization of the graphene layers showed that the graphene layers were oriented along the direction of cell growth,indicating that this method in the preparation of both orientation hole and the graphene layers composite foam materials has certain advantages and application prospects.