聚合物基功能纳米复合材料的制备及导电导热与电磁屏蔽性能的研究

发布时间：2018-05-27 09:34

本文选题：石墨烯气凝胶 + 聚合物复合材料　；参考：《北京化工大学》2017年博士论文

【摘要】：聚合物因其具有耐腐蚀、质轻、优良力学以及易加工等特性,在人们的生产与生活中的应用愈发广泛。近年来随着能源、电子等领域的迅猛发展,人们对具有导电和导热等功能特性的聚合物材料需求越来越大。然而除少数聚合物本身具有导电性外,多数聚合物是电与热的绝缘体,聚合物本身已经不能满足多功能性的需求,开发具有导电导热和电磁屏蔽等功能性的聚合物复合材料是摆在科研工作者面前的重要课题。通过填充功能性纳米填料制备聚合物功能复合材料具有成本低、开发周期短、易于推广等优点,在国内外受到广泛关注。功能纳米填料不仅能够为聚合物提供多功能特性,还对聚合物具有一定的增强作用,然而单纯加入这些纳米填料通常需要很高的填充量,不利于复合材料的加工成型,同时多数纳米填料具有刚性,会大大降低复合材料的韧性。因此,如何在获得高导电导热性能的同时,通过特定内部结构形成填料网络、减小填料用量,同时改善复合材料的力学性能,是我们亟待解决的难题。基于以上分析,本论文分别以热固性环氧树脂(epoxy)和热塑性聚丙烯(PP)为基体,以各向异性三维石墨烯气凝胶(AGAs)、碳纳米管(CNTs)、碳酸钙(CaC03)、氮化硼(BN)、石墨烯纳米片(GNPs)和石墨化碳纤维(GCFs)为填料,制备了一些具有特定内部结构的复合材料,在表征材料力学性能的同时,系统研究了不同填料及填料结构状态对聚合物复合材料导电、电磁屏蔽或者导热性能的影响。本论文的主要内容包括以下四个部分:1.环氧树脂/各向异性三维石墨烯气凝胶复合材料电磁屏蔽性能的研究。在聚合物/石墨烯复合材料体系的研究中,石墨烯片的分散和空间分布状况是决定其性能至关重要的因素。本研究中采用定向冷冻和冷冻干燥的方法制备了具有高度取向网络结构的取向结构石墨烯气凝胶(AGA),AGA在轴向(冷冻方向)和径向(垂直于轴向)两个方向上具有不同的微观结构和性能特征。1300 ℃高温热处理能够提高石墨烯的品质,基于热处理取向石墨烯气凝胶(TAGA)和热处理各向同性石墨烯气凝胶(TGA)制备的环氧树脂复合材料,其导电和电磁屏蔽性能显著提高。epoxy/TAGA复合材料具有各向异性的力学和电学性能,且在极低的TAGA含量下就具有优异的电磁屏蔽效能。其中,TGA含量0.8wt%的环氧树脂复合材料电磁屏蔽效能为27 dB,而TAGA含量0.8 wt%的环氧树脂复合材料在径向方向上测得电磁屏蔽效能高达32 dB,轴向方向上为25 dB。在TAGA含量仅为0.2 wt%时,环氧树脂复合材料的径向方向屏蔽效能就达到25 dB,能够满足高于20 dB的实际应用需求。2.环氧树脂/热处理各向异性三维石墨烯气凝胶复合材料的导电及导热性能研究。利用三维网络结构作为骨架,制备导热复合材料近年来受到学者们的广泛关注。本研究采用定向冷冻干燥的方法制备了 AGAs,通过热处理获得TAGAs并以此为导热网络结合真空浸渍的方法构筑环氧树脂复合材料,研究了材料在石墨烯片取向方向(轴向方向)和垂直于轴向方向(径向方向)上的导电导热及力学性能。AGA与TAGA具有高度取向的结构,因此制得的环氧树脂复合材料具有各向异性的结构和性能。通过对不同质量分数(0.5、0.8、1.2、1.5 wt%)在不同热处理温度(1000、1600、2200、2800 ℃)下的电导率和热导率进行分析探讨,发现提高填料的填充量以及石墨烯的热处理温度均对材料的导电导热性能有促进作用。在2800 ℃热处理温度下,含量1.5 wt%的各向异性复合材料在轴向方向上分别具有1054 S·-1和6.57 W·m-1·K-1的超高电导率及热导率。此外,定向冷冻速率越高,TAGA具有越小的泡孔孔径,小孔径有利于复合材料的导热和力学性能,但对电导率影响不大。本研究中所制得的epoxy/TAGA复合材料具有杰出的导电导热性能,具有巨大的实际应用价值。3.聚丙烯/碳纳米管/碳酸钙复合材料的导电与韧性性能研究。本研究采用熔融共混的方法制备了 PP/CNT/CaC03复合材料,研究了其电学和力学性能。CNTs的引入赋予PP导电性,但它对材料的韧性破坏很大,因此向复合材料中加入第三组分CaC03纳米颗粒来制备三相复合材料。CaCO3纳米颗粒的加入在提高PP/CNT复合材料冲击强度和杨氏模量的同时,还起到了体积排除的作用,提高了导电率、降低了逾渗阈值。加入30 wt%的CaCO3后,材料电导率提高,导电逾渗阈值由导电填料含量6.2 wt%降低到5.6 wt%,PP/9 wt% CNT复合材料的冲击强度由16.0 KJ·m-2提高到24.4 KJ·m-2。为了增强无机填料和聚合物间的界面性能,本文还使用了一种特殊的铝酸酯偶联剂对纳米CaC03颗粒进行表面处理,它对于材料的导电及冲击性能有积极影响。加入相对CaC03含量5 wt%的偶联剂后,三相复合材料导电逾渗阈值进一步降为3.6 wt%,冲击强度提高到33.1 KJ·m-2。以上结果表明CaC03纳米颗粒具有提高PP/CNT两相复合材料韧性和导电性的双重作用,具有导电性与韧性的PP纳米复合材料有希望应用于更广泛的领域中。4.聚丙烯/氮化硼/石墨烯纳米片(石墨化碳纤维)复合材料的导热性能研究。三相导热复合材料是以PP为基体,采用熔融复合的方法与BN和其他两种碳系填料加工制备而成。通过比较BN与氮化铝(AlN)、碳化硅(SiC)填充PP复合材料在导热和力学性能的差异后,选择BN作为一种导热填料,GNPs或GCFs作为第二种导热填料。在填料总含量保持60wt%不变情况下,改变GNPs或GCFs的含量(1-5wt%),发现增加碳系填料含量能有效提高复合材料导热性能,其中GNPs表现更突出。此外,钛酸酯偶联剂起到了促进填料分散、降低界面热阻和提高热稳定性等作用,有利于复合材料的导热性能。总填料量为60 wt%,偶联剂处理的GNPs或GCFs含量为5 wt%时,三相复合材料热导率分别为1.55 W·m-1·K-1和1.36 W·m-1·K-1,分别比不含碳系填料的PP/60 wt%BN热导率(0.73 W·m-1·K-1)高 86 %和 112 %,并高于 PP/80 wt%BN 热导率(1.35 W·m-1·K-1)。碳系填料的加入,在不影响复合材料弯曲模量的同时,对弯曲强度有一定改善。以上结果表明,碳系填料的引入可减少了导热填料用量、降低了材料加工难度,并在一定程度上改善了复合材料力学性能。
[Abstract]:Polymers have become more and more widely used in the production and life of people because of their corrosion resistance, light quality, good mechanics and easy processing. In recent years, with the rapid development of energy and electronics, the demand for polymer materials with electrical and thermal conductivity is becoming more and more important. In addition, most polymers are electrical and thermal insulators. Polymer itself can not meet the needs of multifunction. It is an important task for researchers to develop polymer composites with conductive and conductive heat and electromagnetic shielding. The polymer functional composites are prepared by filling functional nano fillers. It has the advantages of low cost, short development cycle, easy to spread and so on. It is widely concerned at home and abroad. Functional nano fillers can not only provide multi-functional properties for polymers, but also have a certain enhancement to polymers. However, the addition of these nanoscale filler is usually very high, which is not conducive to the processing of composite materials. Most nanometers are rigid and will greatly reduce the toughness of composite materials. Therefore, it is a difficult problem to solve the problem that how to form a packing network through a specific internal structure, reduce the amount of filler and improve the mechanical properties of the composite at the same time, while obtaining high conductivity and thermal conductivity, it is a difficult problem to resolve. A number of composite materials with specific internal structures were prepared by using epoxy and PP as the matrix, with anisotropic three-dimensional graphene aerogels (AGAs), carbon nanotubes (CNTs), calcium carbonate (CaC03), boron nitride (BN), graphene nanoscale (GNPs) and graphene carbon fiber (GCFs) as fillers. At the same time, the effects of different packing and packing structure on the conductive, electromagnetic shielding or thermal conductivity of polymer composites are systematically studied. The main contents of this paper include the following four parts: Study on the electromagnetic shielding properties of 1. epoxy resin / anisotropic three-dimensional graphene aerogel composite. In the study of the material system, the dispersive and spatial distribution of graphene sheets is a crucial factor determining its performance. In this study, oriented structure graphene aerogels (AGA) with highly oriented network structure were prepared by directional freezing and freeze drying, and two sides of AGA in axial direction (freezing direction) and radial (perpendicular to axial). The high temperature heat treatment at.1300 C can improve the quality of graphene, based on the thermal treatment oriented graphene aerogels (TAGA) and the thermally treated isotropic graphene aerogels (TGA), the conductive and electromagnetically shielding properties of the composites are significantly improved for the.Epoxy/TAGA composite. With anisotropic mechanical and electrical properties and excellent electromagnetic shielding effectiveness under extremely low TAGA content, the electromagnetic shielding effectiveness of the epoxy resin composite with TGA content 0.8wt% is 27 dB, while the epoxy resin composite with TAGA content of 0.8 wt% can measure the electromagnetic shielding effectiveness of up to 32 dB in the radial direction, in the axial direction. When the content of TAGA is only 0.2 wt%, the shielding effectiveness of the epoxy resin composite material in the radial direction is 25 dB, which can meet the practical application requirements of the epoxy resin / heat treatment anisotropic three-dimensional graphene aerogel composite material higher than 20 dB. The conductive and thermal properties of the anisotropic three-dimensional graphene aerogel composite material are studied. The three-dimensional network structure is used as the skeleton to prepare the guide. Thermal composites have been widely concerned by scholars in recent years. In this study, AGAs was prepared by the method of directional freeze drying. TAGAs was obtained by heat treatment and used as a heat conduction network to construct epoxy resin composite with vacuum impregnation. The orientation direction (axial direction) and perpendicular to axial square of the material were studied. The conductivities and mechanical properties of.AGA and TAGA in the direction of (radial direction) have a highly oriented structure, so the prepared epoxy resin composite has anisotropic structure and properties. The conductivity and thermal conductivity of different mass fraction (0.5,0.8,1.2,1.5 wt%) at different heat treatment temperatures (1000160022002800 degrees C) are divided. It is found that the filling amount of the filler and the heat treatment temperature of graphene can promote the conductive and thermal conductivity of the material. Under the heat treatment temperature of 2800 C, the anisotropic composites with 1.5 wt% content have the ultra high conductivity and thermal conductivity of 1054 S. -1 and 6.57 W. M-1. K-1 respectively in the axial direction. The higher the freezing rate, the smaller the pore size of the TAGA, the small aperture is beneficial to the thermal conductivity and mechanical properties of the composite, but it has little effect on the conductivity. The epoxy/TAGA composites obtained in this study have excellent conductive and conductive properties, and have great practical application value of.3. polypropylene / carbon nanotubes / calcium carbonate composites. The study of electrical and toughness properties. PP/CNT/CaC03 composites were prepared by melt blending. The electrical and mechanical properties of.CNTs were introduced to PP electrical conductivity, but the toughness of the materials was greatly destroyed. Therefore, third components of CaC03 nanometers were added to the composite materials to prepare the three phase composite.CaCO3 nanoscale. When adding the impact strength and Young's modulus of the PP/CNT composites, the particles also play the role of volume exclusion, increase the conductivity and reduce the percolation threshold. After adding CaCO3 of 30 wt%, the conductivity of the material is increased and the percolation threshold of the conductive filler is reduced from 6.2 wt% to 5.6 wt%, and the impact strength of the PP/9 wt% CNT composite material. From 16 KJ. M-2 to 24.4 KJ. M-2. to enhance the interfacial properties between inorganic fillers and polymers, a special aluminate coupling agent is used to surface treatment of nano CaC03 particles. It has a positive effect on the conductive and impact properties of the materials. After adding a coupling agent with a relative CaC03 content of 5 wt%, a three-phase composite material is added. The conductive percolation threshold is further reduced to 3.6 wt%, and the impact strength is increased to 33.1 KJ. M-2.. The results show that CaC03 nanoparticles have double effects on improving the toughness and conductivity of PP/CNT two phase composites. The PP nanocomposites with conductivity and toughness are expected to be applied to.4. polypropylene / boron nitride / graphene in a wider field. Study on the thermal conductivity of nanocomposite (graphene carbon fiber) composite material. The three-phase thermal conductive composite is made of PP as the matrix and fused with BN and other two kinds of carbon fillers. By comparing the thermal and mechanical properties of BN with aluminum nitride (AlN) and silicon carbide (SiC) filled PP composites, the choice of BN is chosen. For a kind of thermal conductive filler, GNPs or GCFs as second kinds of thermal conductive filler. The content of GNPs or GCFs is changed when the total content of the filler remains unchanged (1-5wt%). It is found that increasing the content of the carbon system filler can effectively improve the thermal conductivity of the composite, and the GNPs performance is more prominent. In addition, the titanate coupling agent plays a role in promoting the dispersing of the filler and reducing the boundary. The thermal conductivity of the composites is beneficial to the thermal conductivity of the composite. The total filler amount is 60 wt% and the GNPs or GCFs content of the coupling agent is 5 wt%, the thermal conductivity of the three-phase composite is 1.55 W. M-1 K-1 and 1.36 W. M-1. K-1 respectively, which is 86% and 1 higher than the PP/60 wt%BN thermal conductivity (0.73). 12%, and higher than the PP/80 wt%BN thermal conductivity (1.35 W. M-1. K-1). The addition of carbon fillers, without affecting the flexural modulus of the composite, has a certain improvement in bending strength. The above results show that the introduction of carbon fillers can reduce the amount of thermal conductive filler, reduce the difficulty of the material addition, and improve the composite force to a certain extent. Learning performance.
【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB332

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