Highly thermal conductivity silicon nitride/carbon fibres/bismaleimide composites

Hybrid fillers of silicon nitride/carbon fibres (Si₃N₄/CFs) are performed to improve the thermal conductivities, mechanical and thermal resistance properties of the bismaleimide (BMI) composites. The thermally conductive coefficient of the Si₃N₄/CFs/BMI composites is improved to 1.68 W/mK with 50 wt% modified Si₃N₄ fillers. The flexural strength and interlaminar shear strength of the composites are optimal with 10 wt% modified Si₃N₄ fillers. The thermal resistance properties of the Si₃N₄/CFs/BMI composites are also improved with the addition of Si₃N₄ fillers. Surface modification of Si₃N₄ fillers exhibits positive effects on the thermal conductivities and mechanical properties of the Si₃N₄/CFs/BMI composites. POLYM. COMPOS., 37:468–471, 2016. © 2014 Society of Plastics Engineers     

氧化石墨烯的制备及其掺杂的炭/炭复合材料导热性能研究

设定两种不同配比强酸氧化剂,以鳞片石墨为原料,采用Hummers法,制备了氧化石墨烯,再经过高温炭化得到热处理氧化石墨烯。并分别以中间相沥青为基体炭前驱体,炭纤维为增强相,氧化石墨烯及其热处理物为热疏导功能体,制备出掺杂氧化石墨烯的炭/炭复合材料。TEM、SEM等表征表明,选用强酸氧化剂组合配比用量较少的制备出的氧化石墨烯,其形貌整体上要优于用量较多的,具有独特的褶皱结构;相比于氧化石墨烯,掺杂其热处理物的复合材料界面覆盖均匀平滑且结合更优良,且其导热系数可达到60 W.m-1.K-1,是无掺杂的纯复合材料两倍多,导热系数得到了较大幅度提高。     

Nielsen thermal conductivity model for single filler carbon/polypropylene composites

In this study, three different carbon fillers (Thermocarb TC‐300 synthetic graphite, Ketjenblack EC‐600 JD carbon black, and Hyperion Catalysis International's FIBRIL? carbon nanotubes) were added to a polypropylene matrix to produce single filler composites with filler concentrations of up to 80 wt % synthetic graphite (61.6 vol %), 15 wt % carbon black (8.1 vol %), and 15 wt % carbon nanotubes (7.4 vol %). The through‐plane thermal conductivity for each formulation was measured. For the synthetic graphite, carbon black, and carbon nanotubes composites, the Nielsen model was applied to the experimental through‐plane thermal conductivity data. The Nielsen Model presented in this work showed very good agreement with experimental data. The model parameters were similar to those used in the literature for these fillers in other polymers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermophysical properties of carbon/carbon composites and physical mechanism of thermal expansion and thermal conductivity

Five different carbon/carbon composites (C/C) have been prepared and their thermophysical properties studied. These were three needled carbon felts impregnated with pyrocarbons (PyC) of different microstructures, chopped fibers/resin carbon + PyC, and carbon cloth/PyC. The results show that the X-Y direction thermal expansion coefficient (CTE) is negative in the range 0-100 °C with values ranging from −0.29 to −0.85 × 10⁻⁶/K. In the range 0-900 °C, their CTE is also very low, and the CTE vs. T curves have almost the same slope. In the same temperature range composites prepared using chopped fibers show the smallest CTE values and those using the felts show the highest. The microstructure of the PyC has no obvious effect on the CTE for composites with the same preform architecture. Their expansion is mainly caused by atomic vibration, pore shrinkage and volatilization of water. However, the PyC structure has a large effect on thermal conductivity (TC) with rough laminar PyC giving the highest value and isotropic PyC giving the lowest. All five composites have a high TC, and values in the X-Y direction (25.6-174 W/m K) are much larger than in the Z direction (3.5-50 W/m K). Heat transmission in these composites is by phonon interaction and is related to the preform and PyC structures.     

Dispersion and thermal conductivity of carbon nanotube composites

A mechanical method was used to shorten carbon nanotubes (CNTs) for improving dispersion without reducing their thermal conductivity. Single walled carbon nanotubes (SWCNTs) were mechanically cut to produce short and open-ended fullerene pipes. These shortened SWCNTs were then used in polymer composites. Both atomic force microscopy and scanning electron microscopy characterizations suggested that nanotube shortening significantly improved CNT dispersion. Thermal conductivity of composites containing short CNTs were found to be much better than those containing pristine CNTs.     

Expanded graphite/polydimethylsiloxane composites with high thermal conductivity

Expanded graphite (EG)/polydimethylsiloxane (PDMS) composites with high thermal conductivity and high flexibility are prepared in this work. EG derived from natural graphite flake is infiltrated in PDMS prepolymer solution and then hot pressed in a steel mould at 80 °C for 2 h. Optical microscope and scanning electron microscope investigation reveals the interpenetrating network structures in the EG/PDMS composites. When mass fraction of EG increases to 10.0 wt %, the thermal conductivity of EG/PDMS reaches to 4.70 W/m K which should be attributed to the conductive path of graphite platelets. Meanwhile, the composites have excellent flexibility (the compressive modulus is 0.68 Mpa) because of its continuous PDMS network. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44843.     

Anisotropic thermal conductivity of polypropylene composites filled with carbon fibers and multiwall carbon nanotubes

Polypropylene‐based composites filled with carbon fibers and multiwall carbon nanotubes were produced by coagulation precipitation technique. Composite articles were produced by conventional injection molding technique. It was shown that the addition of carbon nanotubes (10% of total amount of carbon fibers) results in significantly increased anisotropic thermal conductivity of the composite due to formation of thermal conductive bridges between carbon fibers, which are oriented during molding. The addition of CNTs has a significant effect with more than a 50–70% increase of both the axial and transverse thermal conductivity of the composite. Produced composites were used for injection molding of polymeric radiators for LED lamps, showing sufficient heat dissipation efficiency allowing using them for industrial application in the field. POLYM. COMPOS., 36:1951–1957, 2015. © 2014 Society of Plastics Engineer     

Multilayered ultrahigh molecular weight polyethylene/natural graphite/boron nitride composites with enhanced thermal conductivity and electrical insulation by hot compression

A scalable strategy to fabricate thermally conductive but electrically insulating polymer composites was urgently required in various applications including heat exchangers and electronic packages. In this work, multilayered ultrahigh molecular weight polyethylene (UHMWPE)/natural graphite (NG)/boron nitride (BN) composites were prepared by hot compressing the UHMWPE/NG layers and UHMWPE/BN layers alternately. Taking advantage of the internal properties of NG and BN fillers, the UHMWPE/NG layers played a decisive role in enhancing thermal conductivity (TC), while the UHMWPE/BN layers effectively blocked the electrically conductive pathways without affecting the thermal conductive pathways. The in-plane TC, electrical insulation, and heat spreading ability of multilayered UHMWPE/NG/BN composites increased with the increasing layer numbers. At the total fillers loading of 40 wt%, the in-plane TC of multilayered UHMWPE/NG/BN composites with nine layers was markedly improved to 6.319 Wm⁻¹ K⁻¹, outperforming UHMWPE/BN (4.735 Wm⁻¹ K⁻¹) and pure UHMWPE (0.305 Wm⁻¹ K⁻¹) by 33.45% and 1971.80%, respectively. Meanwhile, the UHMWPE/NG/BN composites still maintained an excellent electrically insulating property (volume resistance~5.40×10¹⁴ Ω cm ; breakdown voltage~1.52 kV/mm). Moreover, the multilayered UHMWPE/NG/BN composites also exhibited surpassing heat dissipation capability and mechanical properties. Our results provided an effective method to fabricate highly thermal conductive and electrical insulating composites.     

Enhanced thermoelectric power factor and low thermal conductivity in one-dimensional Te/Ag2Te composites

We reports the synthesis and characterization of Te/Ag₂Te nanorod composites with various Ag₂Te contents. The composite samples were prepared by mixing Te and Ag₂Te nanorods synthesized by polyvinylpyrrolidone (PVP)-assisted solution-phase mixing. The thermoelectric properties of the prepared composites vary according to the Ag₂Te content. Furthermore, the samples exhibit an enhancement in electrical conductivity and a reduction in the Seebeck coefficient with increasing Ag₂Te content. The maximum power factor (350.71 µV/K at room temperature) is observed for the sample containing 30% Ag₂Te. The samples were assembled as 1D nanostructures, which led to a decrease in thermal conductivity owing to the strong phonon scattering effect. The maximum thermoelectric figure of merit (ZT) at room temperature, 0.34 was obtained for the sample with 30% Ag₂Te content. This value is 480% larger than that obtained for the pristine Te nanorod samples.     

Properties of nanoporous carbon material with one-dimensional conductivity

The nanoporous carbon material (PCM) prepared from petroleum coke or organic compounds that simulate the structure of coke can possess both one-dimensional and three-dimensional conductivity, which is described by the Mott law. It is proposed to consider these materials as two different PCMs with different conductivity, which has an effect on the properties of catalysts, for example, in the cathodes of solid polymer fuel cells and in the production of an anode material and the nanoparticles of 3d metals (iron, cobalt, and nickel), when PCMs are used as the supports of catalysts (or substrates).     

双隔离结构聚乙烯/石墨烯导热复合材料的研究

采用聚二烯丙基二甲基氯化铵改性石墨烯纳米片、聚苯乙烯磺酸钠改性聚乙烯颗粒,通过静电诱导自组装和热压成型工艺制备了具有蜂窝状石墨烯框架的聚乙烯复合材料(N?PE?HD/P?GNPs).利用红外光谱仪、扫描电子显微镜、导热系数测试仪、电子拉力试验机对复合材料的改性状态、微观形貌、导热性能和力学性能等进行分析表征.结果表明,...     

Electrical conductivity of carbon fibers/ABS resin composites mixed with carbon blacks

In this article, the electrical conductivity of composites with different ratios of carbon fiber (CF) content to carbon black (CB) content was studied. The CF content is the main factor to determine the resistivity of the composites filled with CF and CB. The conduction mechanism for this kind of composite is discussed. From comparison of the resistivity of the composites filled with CF and CB with that of the composites filled with CF only, it is shown that using CB as a substitute for part of the CF in CF-filled composites can decrease the production cost, but hardly change the conductivity. The optimum substitution amount is 5% when CF content is beyond 10% in the composites. © 1996 John Wiley & Sons, Inc.     

Improved thermal conductivity of epoxy composites using a hybrid multi-walled carbon nanotube/micro-SiC filler

By adding 6 wt% multi-walled carbon nanotubes (MWCNTs) or 71.7 wt% micro-SiC to an epoxy resin the thermal conductivities of the composites reached maxima that were respectively 2.9 and 20.7 times that of the epoxy alone. To further improve the thermal conductivity a method that partially replaces microfiller with nanofiller was used, and a thermal conductivity, 24.3 times that of the epoxy, was obtained with 5 wt% MWCNTs + 55 wt% micro-SiC.     

Improved thermal conductivity and mechanical properties of SiC/SiC composites using pitch-based carbon fibers

Pitch-based carbon fibers were assembled in horizontal and thickness directions of SiC/SiC composites to form three-dimensional heat conduction networks. The effects of heat conduction networks on microstructures, mechanics, and thermal conductivities were investigated. The results revealed the benefit of introducing heat conduction networks in the densification of composites. The maximum bending strength and interlaminar shear strength of the modified composites reached 568.67 MPa and 68.48 MPa, respectively. These values were equivalent to 18.6% and 69.4% increase compared to those of composites without channels. However, channels in thickness direction destroyed the continuity of fibers and matrix, creating numerous defects. As the volume fraction of heat conduction channels rose, the pinning strengthening effect of channels and influence of defects competed with each other to result in first enhanced mechanical properties followed by a decline. The in-plane thermal conductivity was found anisotropic with a maximum value reaching 86.20 W/(m·K) after introducing pitch-based carbon unidirectional tapes. The thermal conductivity in thickness direction increased with volume fraction of pitch-based carbon fibers and reached 19.13 W/(m·K) at 3.87 vol% pitch-based carbon fibers in the thickness direction. This value was 90.75% higher than that of composites without channels.     

Morphology,thermal expansion,and electrical conductivity of multiwalled carbon nanotube/epoxy composites

Multiwalled carbon nanotube/epoxy composites loaded with up to 0.5 wt % multiwalled carbon nanotubes were prepared and characterized. Infrared microscopy, scanning electron microscopy, thermogravimetry, differential scanning calorimetry, thermomechanical analysis, and electrical conductivity measurements of the composites were performed. Infrared microscopy and scanning electron microscopy images showed that the debundled nanotubes were well dispersed. The thermal expansion coefficients, before and after the glass transition, remained approximately constant with the addition of nanotubes, whereas the electrical conductivity at room temperature increased approximately 5 orders of magnitude. This result was attributed to the thermal expansion coefficients of the intertube gap on the carbon nanotube bundles, which were in the same range as that of the epoxy resin. Therefore, nanocomposites capable of electrostatic dissipation can be processed as neat epoxy materials with respect to the volume changes with temperature. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and electrical conductivity of graphene/ultrahigh molecular weight polyethylene composites with a segregated structure

Graphene-coated ultrahigh molecular weight polyethylene (UHMWPE) powders were prepared by a two-step process. The first step is to coat UHMWPE polymers with graphene oxide (GO) sheets. The second step is to reduce GO on the powders to graphene. The two-step process can effectively prevent the aggregation of graphene during reduction. The resultant graphene/UHMWPE mixtures were hot pressed at 200 °C to obtain the composites with a segregated structure. The composites exhibit high electrical conductivity at a very low percolation threshold (0.028 vol.%). Our method provides a new route for preparing electrical conductive graphene/polymer composites with low percolation threshold.     

聚合物基导热复合材料的研究进展

阐述了聚合物基导热复合材料的导热机制。综述了国内外导热胶粘剂、导热橡胶和导热塑料等研究进展。介绍了提高复合材料导热性能的途径,并在此基础上,展望了聚合物基导热复合材料的应用前景和未来的发展方向。