Thermal conductivity models for carbon/liquid crystal polymer composites

Thermally conductive resins are needed for bipolar plates in fuel cells. Currently, the materials used for these bipolar plates often contain a single type of graphite in a thermosetting resin. In this study, varying amounts of four different types of polyacrylonitrile carbon fillers (Ketjenblack carbon black, Thermocarb synthetic graphite, Fortafil 243 carbon fiber, and Panex 30 carbon fiber) were added to a thermoplastic matrix (Vectra A950RX Liquid Crystal Polymer), with the resulting resins tested for through‐plane and in‐plane thermal conductivity. There are two unique contributions of this work. The first contribution is the use of the Nielsen model for the through‐plane thermal conductivity as a function of the single filler volume fraction. The model fits the data for all composites well. The second contribution is the development of a new, accurate, empirical model to predict the in‐plane thermal conductivity for all resins containing synthetic graphite or carbon fiber. Both of these models will form the basis for the development of new thermal conductivity models for composites with multiple fillers for fuel cell bipolar plate applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Thermal conductivity of carbon fiber/liquid crystal polymer composites

Thermally conductive resins are needed for bipolar plates in fuel cells. Currently, the materials used for these bipolar plates often contain a single type of graphite in a thermosetting resin. In this study, varying amounts of two different types of polyacrylonitrile based carbon fibers, Fortafil 243 and Panex 30, were added to a thermoplastic matrix (Vectra A950RX Liquid Crystal Polymer). The resulting single filler composites were tested for thermal conductivity and a simple exponential thermal conductivity model was developed for the square root of the product of the in‐plane and through‐plane thermal conductivity . The experiments showed that the through‐plane thermal conductivity was similar for composites up to 40 vol % fiber. However, at higher loadings, the Panex 30 samples exhibited higher thermal conductivity. The experiments also showed that the in‐plane thermal conductivity of composites containing Panex 30 was higher than those containing Fortafil 243 for all volume fractions studied. Finally, the model agreed very well with experimental data covering a large range of filler volume fraction (from 0 to 55 vol % for both single filler systems). The model can be used with existing through‐plane thermal conductivity models to predict in‐plane thermal conductivity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5456–5462, 2006     

Preparation and properties of polystyrene/SiCw/SiCp thermal conductivity composites

The silicon carbide whisker (SiCw) and silicon carbide particle (SiCp) were employed to prepare polystyrene/silicon carbide whisker/silicon carbide particle (PS/SiCw/SiCp) thermal conductivity composites, and the titanate coupling reagent of NDZ‐105 was introduced to functionalize the surface of fillers. The thermal conductive coefficient λ improved from 0.18 W/mK for native PS to 1.29 W/mK for the composites with 40% volume fraction of SiCw/SiCp (volume fraction, 3 : 1) hybrid fillers. Both the thermal decomposition temperature and dielectric constant of the composites increased with the addition of SiCw/SiCp hybrid fillers. At the same addition of SiCw/SiCp hybrid fillers, the surface modification of hybrid fillers by NDZ‐105 could improve the thermal conductivity and the mechanical properties of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of thermal conductivity and heat transfer on crystallization,structure, and morphology of polypropylene containing different fillers

The crystallization behavior, structure, and morphology developed was investigated for polypropylene containing different fillers such as silica, calcium carbonate, talc, mica, graphite, etc. by using compression‐molded samples prepared at several cooling rates. It was observed that the crystallinity obtained for any given composition depended on the thermal conductivity of the filler and the PP composite containing it as well as the cooling rate to which it was subjected. These composites exhibited skin‐core type of morphology and the skin layer thickness was found to depend not only on the cooling rate but also on the type of filler, its thermal conductivity, etc. These various experimental findings were discussed in light of the phenomenological model described in our earlier work, which correlates thermal conductivity and degree of crystallinity for various compositions of PP containing additives. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 615–623, 2004     

Electrical conductivity model evaluation of carbon fiber filled liquid crystal polymer composites

Electrically conductive resins may have applications as fuel cell bipolar plates. The current trend in this technology is a thermosetting polymer as the matrix containing high concentrations of various types of fillers. These fillers are carbon based and electrically conductive powders, particles, or fibers. In this study, we utilized two composite formulations of polyacrylonitrile fibers (Fortafil 243 and Panex 30) in a liquid crystal polymer (Vectra A950RX) with increasing concentrations. Electrical conductivity tests were performed and modified Mamunya and additive models were applied to the experimental data. These models fit the entire range of data for each composite tested. Four alternate models were also produced: linear, quadratic, exponential, and geometric, with a restricted range of electrical conductivity data greater than 10^?2 S/cm. The exponential and the geometric resulted in the best fits over this restricted data range. These particular models may allow researchers to extrapolate beyond the maximum filler concentrations studied here. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Mechanical and thermal properties of polypropylene/modified basalt fabric composites

Basalt fabric (BF) was first treated with silane coupling agent KH550, modified basalt fabric (MBF) was obtained. Then MBF were molded with polypropylene (PP) matrix, and polypropylene/modified basalt fabrics (PP/MBF) composites were obtained. The influence of concentration and treating time of KH550 on MBF were characterized by hydrophilicity and lipophilicity. The tensile strength and morphology of basalt fabric were tested by single filament strength tester and scanning electron microscopy. The mechanical properties of composites were measured with electronic universal testing machine and impact testing machine, and the thermal properties were tested by thermogravimetric analysis and dynamic mechanical analysis. The results showed that the lipophilicity of MBF is improved significantly by KH550 while the tensile is nearly damaged. The mechanical properties of composites are larger than that of pure PP, among which the impact property was improved the most, showing 194.12% enhancement. The thermal stability and dynamic viscoelasticity were better than pure PP; furthermore, the concentration of KH550 virtually had no effect on the thermal stability. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42504.     

Mechanical and thermal properties of polypropylene/sugarcane Bagasse composites

To determine the possibility of using sugarcane bagasse (SCB) waste as reinforcing filler in the thermoplastic polymer matrix, SCB‐reinforced polypropylene (PP) composites were prepared. The PP and SCB composites were prepared by the extrusion of PP resin with 5, 10, 15, and 20 wt % of SCB filler in a corotating twin screw extruder. The extruded strands were cut into pellets and injection molded to make test specimens. These specimens were tested for physicomechanical properties such as tensile, flexural, Izod, and Charpy impact strengths, density, water absorption, and thermal characteristics, namely, heat deflection temperature (HDT), melt flow index, and thermogravimetric analysis. It was found that the flexural strength increased from 23.66 to 26.84 MPa, Izod impact strength increased from 10.499 to 13.23 Kg cm/cm, Charpy impact strength increased from 10.096 to 13.98 Kg cm/cm, and HDT increased from 45.5 to 66.5°C, with increase in filler loading from 5 to 20% in the PP matrix. However, the tensile strength and elongation decreased from 32.22 to 27.21 MPa and 164.4 to 11.20% respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3827–3832, 2007     

Effect of filler surface treatment on mechanical properties and thermal properties of single and hybrid filler–filled PP composites

The influence of two types of surface treatments (aminosilane and Lica‐12) on the mechanical and thermal properties of polypropylene (PP) filled with single and hybrid filler (silica and mica) was studied. An improvement in tensile properties and impact strength was found for both treatments compared to those of untreated composites. However, the filler with silane coupling agent showed better improvement compared to the filler with Lica‐12 coupling agent. This was due to better adhesion between filler and matrix. Thermal analysis indicates that surface treatments increased the nucleating ability of filler, but decreased the coefficient of thermal expansion of PP composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

Bamboo fiber reinforced polypropylene composites and their mechanical,thermal, and morphological properties

Short bamboo fiber reinforced polypropylene composites were prepared by incorporation of various loadings of chemically modified bamboo fibers. Maleic anhydride grafted polypropylene (MA‐g‐PP) was used as compatibilizer to improve fiber–matrix adhesion. The effects of bamboo fiber loading and modification of the resin on the physical, mechanical, thermal, and morphological properties of the bamboo reinforced modified PP composites were studied. Scanning electron microscopy studies of the composites were carried out on the interface and fractured surfaces. Thermogravimetric analysis and IR spectroscopy were also carried out. At 50% volume fraction of the extracted bamboo fiber in the composites, considerable increase in mechanical properties like impact, flexural, tensile, and thermal behavior like heat deflection temperature were observed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Effective thermal conductivity behavior of filled vulcanized perfluoromethyl vinyl ether rubber

The effective thermal conductivity behavior of vulcanized perfluoromethyl vinyl ether (PMVE) rubber filled with various inorganic fillers was investigated and analyzed with thermal conductivity models. Experimental results showed that there was no significant improvement in the thermal conductivity of PMVE rubber if the intrinsic thermal conductivity of the fillers was greater than 100 times that of the rubber matrix, and this agreed with the prediction of Maxwell's equation. The thermal conductivity of PMVE rubber filled with larger size silicon carbide (SiC) particles was greater than that of PMVE filled with smaller size SiC because of the lower interfacial thermal resistance, and there existed a transition filler loading at about 60 vol %. It was also found that flocculent graphite was the most effective thermally conductive filler among the fillers studied. A modified form of Agari's equation with a parameter independent on the units used was proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

聚丙烯/碳纳米管复合材料的研究进展

聚丙烯（PP）作为通用型热塑性塑料,具有物理性能优异、成型加工简单、密度小以及原料来源丰富等优点,广泛应用于电器、汽车和包装等行业。但是PP具有韧性差、低温脆性突出、抗冲击性能不佳、介电常数低、制品尺寸稳定性差等诸多缺点。碳纳米管（CNT）不仅具有独特的管状结构,还具有优异的力学、导电、导热以及耐磨等性能。将CNT和PP进行复合并制备出具有导电、导热、耐磨等高性能复合材料具有广阔的应用前景。因此,本文重点综述PP和CNT复合材料的新进展,主要包括结晶行为、力学性能、电学性能、摩擦性能、导热性能以及其他性能。针对现阶段PP/CNT复合材料研究和开发过程中存在的问题提出意见和建议,并对PP/CNT复合材料的未来发展做出展望。     

Thermal conductivity improvement in electrically insulating silicone rubber composites by the construction of hybrid three-dimensional filler networks with boron nitride and carbon nanotubes

In this study, we constructed hybrid three-dimensional (3D) filler networks by simply incorporating a relatively low content of one-dimensional carbon nanotubes (CNTs; 0.0005–0.25 vol %) and a certain content of two-dimensional boron nitride (BN; 30 phr) in a silicone rubber (SIR) matrix. As indicated by transmission electron microscopy observation, flexible CNTs can serve as bridges to connect BN platelets in different layers to form hybrid 3D thermally conductive networks; this results in an increase in thermally conductive pathways, and the isolation between CNTs can prevent the formation of electrically conductive networks. Compared to the SIR–BN composite with the same BN content, the SIR–BN–CNT composites exhibited improved thermal conductivity, slightly increased volume resistivity, and comparable breakdown strength without a largely decreased flexibility. When 0.25 vol % CNTs were incorporated, the SIR–BN–CNT composite exhibited 75 and 25% higher thermal conductivities relative to the neat SIR and SIR–BN composite with 30 phr BN, respectively, and a thermal conductivity that was even comparable to SIR–BN composite with 40 phr BN. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46929.     

Effects of carbon fillers on the thermal conductivity of highly filled liquid‐crystal polymer based resins

The thermal conductivity of insulating polymers can be increased by the addition of conductive fillers. One potential market for these thermally conductive resins is for fuel cell bipolar plates. In this study, various amounts of three different carbon fillers (carbon black, synthetic graphite particles, and carbon fiber) were added to Vectra A950RX liquid crystal polymer. Because the resulting composites were anisotropic, they were tested for both through‐plane and in‐plane thermal conductivities. The effects of single fillers and combinations of the different fillers were studied via a factorial design. Each single filler caused a statistically significant increase in composite through‐plane and in‐plane thermal conductivities at the 95% confidence level, with synthetic graphite causing the largest increase. All of the composites containing combinations of the different fillers caused statistically significant increases in the composite through‐plane and in‐plane thermal conductivities. It is possible that thermally conductive pathways were formed that linked these carbon fillers, which resulted in increased composite thermal conductivity. Composites containing 70, 75, and 80 wt % synthetic graphite and the composite containing all three fillers (2.5 wt % carbon black, 65 wt % synthetic graphite, and 5 wt % carbon fiber) had in‐plane thermal conductivities of 20 W m^?1 K^?1 or higher, which is desirable for bipolar plates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of carbon fillers on tensile and flexural properties in polypropylene‐based resins

A potential application for conductive resins is in bipolar plates for use in fuel cells. The addition of carbon filler can increase the electrical and thermal conductivities of the polymer matrix but will also have an effect on the tensile and flexural properties, important for bipolar plates. In this research, three different types of carbon (carbon black, synthetic graphite, and carbon nanotubes) were added to polypropylene and the effects of these single fillers on the flexural and tensile properties were measured. All three carbon fillers caused an increase in the tensile and flexural modulus of the composite. The ultimate tensile and flexural strengths decreased with the addition of carbon black and synthetic graphite, but increased for carbon nanotubes/polypropylene composites due to the difference in the aspect ratio of this filler compared to carbon black and synthetic graphite. Finally, it was found that the Nielsen model gave the best prediction of the tensile modulus for the polypropylene based composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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。     

Improving thermal conductivity and shear strength of carbon nanotubes/epoxy composites via thiol‐ene click reaction

This study investigates the effect of the thiol‐ene click reaction on thermal conductivity and shear strength of the epoxy composites reinforced by various silane‐functionalized hybrids of sulfhydryl‐grafted multi‐walled carbon nanotubes (SH‐MWCNTs) and vinyl‐grafted MWCNTs (CC‐MWCNTs). The results of Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermal gravimetric analysis (TGA), and transmission electron microscopy (TEM) show that the sulfhydryl groups and vinyl groups are successfully grafted onto the surface of MWCNTs, after treatment of MWCNT with triethoxyvinylsilane and 3‐mercaptopropyltrimethoxysilane, respectively. Scanning electron microscopy (SEM), HotDisk thermal constant analyzer (HotDisk), optical microscope, and differential scanning calorimetry (DSC) are used to characterize the resultant composites. It is demonstrated that the hybrid of 75 wt % SH‐MWCNTs and 25 wt % CC‐MWCNTs has better dispersion and stability in epoxy matrix, and shows a stronger synergistic effect in improving the thermal conductivity of epoxy composite via the thiol‐ene click reaction with 2,2′‐azobis(2‐methylpropionitrile) as thermal initiator. Furthermore, the tensile shear strength results of MWCNT/epoxy composites and the optical microscopy photographs of shear failure section indicate that the composite with the hybrid MWCNTs has higher shear strength than that with raw MWCNTs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44579.     

Preparation and characterization of polypropylene/serpentine composites

Composites of serpentine and polypropylene (PP) were prepared by twin‐screw extrusion. Serpentine was collected as rocks from the Ankara–Beynam region and ground into powder with an average particle size of about 3 μm for composite production. Both as‐received (rock) and powdered serpentine were characterized. A silane coupling agent (SCA), γ‐aminopropyl triethoxy silane, was used for the surface treatment of serpentine. Mechanical properties of the composites were measured in terms of impact strength, elastic modulus, stress at yield, stress at break, and percentage strain at break. The addition of serpentine was found to have a profound effect on the reinforcement of the PP matrix. Because of the stronger interactions at the interphase induced by SCA treatment, mechanical properties were improved further in comparison with the untreated composites. Similar thermal and morphological behaviors were recorded for the composites with and without surface treatment. Thermal studies showed an increase in both melting temperature and percentage crystallinity of the composites. Scanning electron microscopy analysis revealed that homogeneous distribution of filler was observed at low filler contents, but a certain extent of agglomeration was also seen at high filler loadings. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal and dielectric properties of the aluminum particle/epoxy resin composites

Microsized aluminum/epoxy resin composites were prepared, and the thermal and dielectric properties of the composites were investigated in terms of composition, aluminum particle sizes, frequency, and temperature. The results showed that the introduction of aluminum particles to the composites hardly influenced the thermal stability behavior, and decreased T_g of the epoxy resin; moreover, the size, concentration, and surface modification of aluminum particles had an effect on their thermal conductivity and dielectric properties. The dielectric permittivity increased smoothly with a rise of aluminum particle content, as well as with a decrease in frequency at high loading with aluminum particles. While the dissipation factor value increased slightly with an increase in frequency, it still remained at a low level. The dielectric permittivity and loss increased with temperature, owing to the segmental mobility of the polymer molecules. We found that the aluminum/epoxy composite containing 48 vol % aluminum‐particle content possessed a high thermal conductivity and a high dielectric permittivity, but a low loss factor, a low electric conductivity, and a higher breakdown voltage. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010