Enhanced conductivity composites for aircraft applications: carbon nanotube inclusion both in epoxy matrix and in carbonized electrospun nanofibers

The potential of carbonized electrospun nanofiber mats to render epoxy resin composites for aircraft applications electrically and thermally more conductive was investigated. The effect of carbon nanotube inclusion both inside the carbon nanofiber and in the epoxy resin matrix material was studied, in order to reveal any synergistic effects of multilevel presence of nanosized reinforcements on the conductivity and mechanical properties. The carbon nanotube inclusion into the carbonized nanofibers increased the electrical conductivity of the samples by 20–50% and the thermal conductivity by approximately three times leading to a higher value than that of the conventional composites. The preparation of layered composites with a conductive upper layer containing nonwoven carbon nanofabric and a load bearing lower layer with conventional unidirectional carbon fiber reinforcement can offer a cost‐effective and weight‐saving solution for the replacement of metal meshes in structural aircraft composites. Copyright © 2014 John Wiley & Sons, Ltd.     

The effect of MWNTs on the microstructure of resin carbon and thermal conductivity of C/C composites

Multi-walled nanotubes were added into furan resin. Unidirectional carbon/carbon preforms were densified with the nanotube-doped furan resin by impregnation–carbonization cycle. The effects of Multi-walled nanotubes on the microstructure of resin carbon and thermal conductivity of carbon/carbon composites were investigated. The results show that Multi-walled nanotubes can induce the ordered arrangement of planar carbon microlites in resin carbon during high-temperature treatment and enhance the graphitization degree of resin carbon. Small amount of Multi-walled nanotubes in resin carbon can enhance the thermal conductivity of C/C composites evidently, especially the thermal conductivity vertical to the direction of fiber axis, due to the improvement of microstructure of resin carbon. Excess Multi-walled nanotubes in resin are disadvantageous to the enhancement of thermal conductivity instead, because they are difficult to disperse and easy to agglomerate, resulting thermal resistances in carbon matrix.     

Enhanced thermal conductivity of rheologically percolated carbon nanofiber reinforced polypropylene composites

Three different types of carbon nanofibers (CNF) were incorporated in the same polypropylene (PP) matrix by twin‐screw extrusion. The rheological and thermal properties were investigated. The rheological characterization of CNFs/PP composites as function of their volume fraction shows different microstructures: percolated and non‐percolated behaviors of their CNF's networks. In this work, the laser flash technique is employed in the experimental determination of the thermal diffusivity and conductivity of composites at room temperature. The ultimate aim is to correlate microstructure described by rheological analysis with final thermal properties. The results show that thermal diffusivity and conductivity are clearly higher for rheologically percolated composites suggesting that above certain critical content of nanofibers thermal transport is mainly controlled by percolated structures caused by interconnected CNFs' networks. Finally, thermal conductivity results are described by means of percolation theory from which an intrinsic thermal conductivity for the CNFs' network of approximately 6.5 W/m K, i.e. close to three times lower than some values reported in literature for SWCNTs' networks, was calculated. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of aspect ratio of vertically aligned copper nanowires in the presence of cellulose nanofibers on the thermal conductivity of epoxy composites

The composites comprising vertically aligned network of copper nanowires (CuNWs) in the presence of cellulose nanofibers were fabricated by using the freeze‐templating method and the effect of aspect ratio (A/R) of CuNWs on the thermal conductivity of epoxy composites was investigated. The thermal conductivity of epoxy composites increased to 0.79 W m^?1 K^?1 at 1.12 vol% of high A/R CuNWs loading, corresponding to the thermal conductivity enhancement of 365% as compared to the pure epoxy. The thermal conductivity of vertically aligned higher A/R CuNWs/epoxy, which is 38.5% and 51.9% higher than those of the lower A/R CuNWs and the randomly aligned CuNWs, respectively. The application of the epoxy composites in heat dissipation was demonstrated by the temperature changes of composites on a hot plate with the increase of heating time. These results indicate that the thermally conductive composites in this study could be applied for thermal dissipating materials in electronic devices.     

原位合成纳米SiO2增强阴离子聚酯型上浆剂及其对碳纤维复合材料层间剪切强度的影响

采用溶胶-凝胶法, 在侧链带有羧基的线性不饱和聚酯中加入正硅酸乙酯(TEOS), 使TEOS在酸性条件下发生水解反应, 原位合成纳米SiO₂增强阴离子型聚酯乳液(SEAPE). 利用傅里叶变换红外光谱(FTIR)仪、 激光粒度分析仪和冷冻扫描电子显微镜(Cryo-SEM)对SEAPE进行分析与表征. 将SEAPE与聚乙二醇单油酸酯润滑剂、 非离子型表面活性剂FC-4430及抗氧剂1010进行复配, 原位制备纳米SiO₂增强阴离子型聚酯乳液上浆剂(SEAPEs), 用扫描电子显微镜(SEM)、 视频动态接触角测量仪、 X射线能谱(EDS)仪和纤维强力仪对SEAPEs上浆后碳纤维的表面形貌、 表面能、 碳纤维(CF)表面元素及碳纤维增强不饱和聚酯(UPR)复合材料(CF/UPR)的层间剪切强度(ILSS)进行测试与表征. 结果表明, 当TEOS添加质量分数为5%时, SEAPEs上浆后的碳纤维有效增强了其与UPR的结合强度, CF/UPR复合材料的ILSS达到40.03 MPa, 与市售环氧树脂型上浆剂上浆后碳纤维增强UPR复合材料相比, ILSS提高90.1%. SEAPEs中原位生成的纳米SiO₂分散均匀, 乳液储存稳定, 上浆后SiO₂均匀吸附在碳纤维表面, 增加碳纤维表面能, 改善碳纤维与树脂间的浸润性, 可有效提高碳纤维增强不饱和聚酯树脂复合材料的ILSS.     

Comparative analyses of the electrical properties and dispersion level of VGCNF and MWCNT: Epoxy composites

The electrical properties and dispersion of vapor‐grown carbon nanofibers (VGCNF) and multiwalled carbon nanotubes (MWCNT)—epoxy resin composites are studied and compared. A blender was used to disperse the nanofillers within the matrix, producing samples with concentrations of 0.1, 0.5, and 1.0 wt % for both nanofillers, besides the neat sample. The dispersion of the nanofillers was qualitatively analyzed using scanning electron microscopy, transmission optical microscopy, and grayscale analysis. The electrical conductivity and the dielectric constant were evaluated. The percolation threshold of MWCNT epoxy composites is lower than 0.1 wt % while for VGCNF lies between 0.1 and 0.5 wt %. The difference on the dispersion ability of the two nanofillers is due to their intrinsic characteristics. Celzard's theory is suitable to calculate the percolation threshold bounds for the VGCNF composites but not for the MWCNT composites, indicating that intrinsic characteristics of the nanofillers beyond the aspect ratio are determinant for the MWCNT composites electrical conductivity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Morphology,thermal stability,and flammability of polymer matrix composites coated with hybrid nanopapers

In this study, a hybrid nanopaper consisting of carbon nanofiber (CNF) and polyhedral oligomeric silsequioxane (POSS) or cloisite Na⁺ clay, has been fabricated through the papermaking process. The hybrid nanopaper was then coated on the surface of glass fiber (GF) reinforced polymer matrix composites through resin transfer molding (RTM) process. The morphologies of the hybrid nanopaper and resulting nanocomposites were characterized with scanning electron microscopy (SEM). It can be seen that the nanopaper had a porous structure with highly entangled carbon nanofibers and the polyester resin completely penetrated the nanopaper throughout the thickness. The thermal decomposition behavior of the hybrid nanopapers and nanocomposites was studied with the real‐time thermogravimetric analysis/ flourier transform infrared spectrometry (TGA/FTIR). The test results indicate that the addition of pristine nanoclay increased the thermal stability of the nanopaper, whereas the POSS particles decreased the thermal stability of the nanopaper. The fire retardant performance of composite laminates coated with the hybrid nanopaper was evaluated with cone calorimeter tests using a radiated heat flux of 50 kW/m². The cone calorimeter test results indicate that the peak heat release rate (PHRR) decreased dramatically in composite laminates coated with the CNF‐clay nanopaper. However, the PHRRs of the CNF‐POSS nanopaper coated composite laminates increased. The formation of compact char materials was observed on the surface of the residues of the CNF‐clay nanopaper after cone calorimeter test. The flame retardant mechanisms of the hybrid nanopaper in the composite laminates are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

A comparative study on the effect of carbon fillers on electrical and thermal conductivity of a cyanate ester resin

Carbon fillers including multi-walled carbon nanotubes (MWCNTs), carbon black (CB) and graphite were introduced in a cyanate ester (CE) resin, respectively. The effects of the fillers on the electrical and thermal conductivity of the resin were measured and analyzed based on the microscopic observations. MWCNTs, CB and graphite exhibited percolation threshold at 0.1 wt%, 0.5 wt% and 10 wt%, respectively. The maximal electrical conductivity of the composites was 1.08 S/cm, 9.94 × 10⁻³ S/cm and 1.70 × 10⁻⁵ S/cm. MWCNTs showed the best enhancement on the electrical conductivity. The thermal behavior of the composites was analyzed by calorimetry method. Incorporation of MWCNTs, CB and graphite increased the thermal conductivity of CE resin by 90%, 15% and 92%, respectively. Theoretical models were introduced to correlate the thermal conductivity of the CE/MWCNTs composite. The interfacial thermal resistance between CE resin and MWCNTs was 8 × 10⁻⁸ m²K/W and the straightness ratio was 0.2. The MWCNTs were seriously entangled and agglomerated. Simulation results revealed that thermal conductivity of the CE/MWCNTs composites can be substantially elevated by increasing the straightness ratio and/or filler content of MWCNTs.     

Synthesis,characterization, biocompatibility,thermal and mechanical performances of sawdust reinforced composite

The work outlines the synthesis of a new and easy technique to develop sustainable composites of sawdusts reinforced polyester resin composites. For shaping a new approach we have found very rare approach for developing composites with sawdusts of Mahagoni wood (Swietenia mahagoni) reinforced polyester resin composites in open literatures. Due to this gap, a plan made to develop untreated and treated sawdusts (very common in Bangladesh and many other countries of the world) reinforced strong and durable composites with unsaturated polyester resins along with their biodegradability, thermal and mechnical properties where the material properties were revealed and corelations were elaborated in the subsequent sections. Specifically, the tensile strengths of virgin resin (VR), untreated sawdust reinforced composite (UTSDC) and 4% caustic soda treated sawdust reinforced composite (4TSDC) are 10.77, 15.83 and 21.64 N/mm², respectively. That means the observed reinforcement property for UTSDC and 4TSDC increased ~47% and 101%, respectively. Moreover, the binding phenomena were explained with the own schamatic presentation. The composite phenomena was explained sequentially by using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, etc. Between the developed composites 4TSDC was strong (25% as compared from tensile strength) and durable (8% as observed in biodegradability results) than the UTSDC of unsaturated polyester resin. The pattern of water uptake follows usual Fickian diffusion behavior. The observed properties of the developed convincible composites indicate that they can be considered for indoor to outdoor applications especially for using the fence, roof, furniture items like chair, table, park benches, etc.     

Thermally conductive cyanate ester nanocomposites filled with graphene nanosheets and multiwalled carbon nanotubes

In this work, dodecylamine‐modified graphene nanosheets (DA‐GNSs) and γ‐aminopropyl‐triethoxysilane‐treated multiwalled carbon nanotubes (f‐MWCNTs) are employed to prepare cyanate ester (CE) thermally conductive composites. By adding 5 wt% DA‐GNSs or f‐MWCNTs to the CE resin, the thermal conductivities of the composites became 3.2 and 2.5 times that of the CE resin, respectively. To further improve the thermal conductivity, a mixture of the two fillers was utilized. A remarkable synergetic effect between the DA‐GNSs and f‐MWCNTs on improving the thermal conductivity of CE resin composites was demonstrated. The composite containing 3 wt% hybrid filler exhibited a 185% increase in thermal conductivity compared with pure CE resin, whereas composites with individual DA‐GNSs and f‐MWCNTs exhibited increases of 158 and 108%, respectively. Moreover, the composite with hybrid filler retained high electrical resistivity. Scanning electron microscopy images of the composite morphologies showed that the modified graphene nanosheets (GNSs) and multiwalled carbon nanotubes (MWCNTs) were uniformly dispersed in the CE matrix, and a number of junction points among MWCNTs and between MWCNTs and GNSs formed in the composites with hybrid fillers. Generally, we can conclude that these composites filled with hybrid fillers may be promising materials of further improving the thermal conductivity of CE composites. Copyright © 2014 John Wiley & Sons, Ltd.     

Green synthesis of polymer nanofibers and their composites as flame‐retardant materials for polymer nanocomposites

Polyaniline nanofibers and their composites with carbon nanotubes were developed as an effective flame‐retardant material using a facile green method. Polyaniline nanofibers were used as a smart flame‐retardant for acrylonitrile–butadiene–styrene polymer. The polyaniline nanofibers were dispersed in polymer matrix forming well‐dispersed polymer nanocomposites. Effect of polyaniline nanofiber mass ratio on the polymer nanocomposite properties was studied. Polyaniline nanofiber composites with carbon nanotubes were also dispersed in polymer matrix. The thermal stability and flammability properties of the polymer nanocomposites were investigated. The rate of burning of polymer nanocomposites achieved 82.5% reduction (7.32 mm/min) compared with virgin polymer (42.5 mm/min). The reduction in peak heat release rate and total heat release of the polymer nanocomposites containing nanofibers achieved 74 and 34%, respectively. Interestingly, the average mass loss rate was significantly reduced by 58% and the emission of carbon monoxide and carbon dioxide gases were suppressed by 20 and 47%, respectively. The effect of polyaniline nanofibers composites on the flammability of polymer nanocomposites was also studied. Polyaniline nanofibers and their composites were characterized using Fourier transform infrared spectroscopy and transmission and scanning electron microscopy. The dispersion of polyaniline nanofibers in polymer nanocomposites was characterized using transmission electron microscopy. The different polymer nanocomposites were characterized using thermogravimetric analysis, UL94 flame chamber, and cone calorimeter tests. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of treatment on the thermal conductivity and thermal diffusivity of oil‐palm‐fiber‐reinforced phenolformaldehyde composites

The thermal conductivity and thermal diffusivity of oil‐palm‐fiber‐reinforced untreated (Sample 1) and differently treated composites were measured with the transient plane source technique at room temperature and under normal pressure. All the composites were 40% oil‐palm fiber by weight. The fibers were treated with alkali (Composite 2), silane (Composite 3), and acetic acid (Composite 4) and reinforced in a phenolformaldehyde matrix. The thermal conductivity and thermal diffusivity of the composites increased after treatment to different extents. The thermal conductivity of the treated fibers as well as of the untreated fibers was calculated theoretically. The model results show that the thermal conductivity of the untreated fiber was smaller than the thermal conductivity of the treated fibers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 916–921, 2000     

Electrical Conductivity,Oil Absorption and Electric Heating of Carbon Black-modified Carbon Nanofibers

Carbon-black-modified carbon nanofibers were prepared by electrospinning, and the effects of the carbon black content and processing temperature on the physical and chemical properties of the resulting composites were investigated. The results showed that the conductivity of carbon-black-modified nanofibers increased with the carbon black content. The addition of carbon black in a 20% mass ratio increased the conductivity of the composite(0.75 S/cm) by 230% compared with the undoped nanofiber(2.47 S/cm), while the adulteration with 5% CB allowed the preservation of the mechanical properties of the composites. The fabricated carbon-black/carbon-nanocomposite fibers exhibited excellent oil absorption and electrothermal conversion performance. Furthermore, the conductivity and oil absorption capacity increased with increasing carbonization temperature. With a carbonization temperature of 1000℃(5% carbon black), the voltage was 31 V, the current was 0.66 A, and the surface temperature of the composite reached 234.1℃. The overall enhancement in physical properties upon the addition of even low amounts of carbon black makes these composites advantageous for future industrial applications.     

Assembly of well-aligned multiwalled carbon nanotubes in confined polyacrylonitrile environments: electrospun composite nanofiber sheets

Highly oriented, large area continuous composite nanofiber sheets made from surface-oxidized multiwalled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were successfully developed using electrospinning. The preferred orientation of surface-oxidized MWNTs along the fiber axis was determined with transmission electron microscopy and electron diffraction. The surface morphology and height profile of the composite nanofibers were also investigated using an atomic force microscope in tapping mode. For the first time, it was observed that the orientation of the carbon nanotubes within the nanofibers was much higher than that of the PAN polymer crystal matrix as detected by two-dimensional wide-angle X-ray diffraction experiments. This suggests that not only surface tension and jet elongation but also the slow relaxation of the carbon nanotubes in the nanofibers are determining factors in the orientation of carbon nanotubes. The extensive fine absorption structure detected via UV/vis spectroscopy indicated that charge-transfer complexes formed between the surface-oxidized nanotubes and negatively charged (-CN[triple bond]N:) functional groups in PAN during electrospinning, leading to a strong interfacial bonding between the nanotubes and surrounding polymer chains. As a result of the highly anisotropic orientation and the formation of complexes, the composite nanofiber sheets possessed enhanced electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and dimensional stability. The electrical conductivity of the PAN/MWNT composite nanofibers containing 20 wt % nanotubes was enhanced to approximately 1 S/cm. The tensile modulus values of the compressed composite nanofiber sheets were improved significantly to 10.9 and 14.5 GPa along the fiber winding direction at the MWNT loading of 10 and 20 wt %, respectively. The thermal deformation temperature increased with increased MWNT loading. The thermal expansion coefficient of the composite nanofiber sheets was also reduced by more than an order of magnitude to 13 x 10(-6)/ degrees C along the axis of aligned nanofibers containing 20 wt % MWNTs.     

Synergetic effect of thermal conductivity and flame retardancy of cyanate ester composites containing DOPO and BN with great dielectric properties

DOPO and boron nitride (BN) fillers with different particle sizes and several loadings were employed to improve the properties of cyanate ester (CE) resin. The effects of BN content and particle size on the thermal conductivity of the BN‐DOPO/CE ternary composites were discussed. The influence of enhancing the thermal conductivity of the ternary composites on their flame retardancy was studied. The consequences showed that increasing the thermal conductivity of BN‐DOPO/CE composites had an active impact on their flame retardancy. Approving flame retardancy of the ternary composites was certified by the high limiting oxygen index (LOI), UL‐94 rating of V‐0, and low heat release rate (HRR) and total heat release (THR). For instance, in contrast with pure CE matrix, peak of HRR (pk‐HRR), average of HRR (av‐HRR), THR, and average of effective heat of combustion (av‐EHC) of CEP/BN_{0.5 μm}/10 composite were decreased by 51.7%, 33.8%, 18.7%, and 18.9%, respectively. Thermal gravimetry analysis (TGA) showed that the addition of BN fillers improves the thermal stability of the composites. Moreover, the ternary composites possess good dielectric properties. Their dielectric constants (ε) are less than 3, and dielectric loss tangent (tgδ) values are lower than neat CE resin.     

Polymer‐nanofiber composites: Enhancing composite properties by nanofiber oxidation

Nanocomposites of styrene and vinyl phenol copolymers, which contain varying (10, 20, and 40 mol %) vinyl phenol content, were prepared with 1 wt % unoxidized, 1 wt % oxidized, and 5 wt % oxidized carbon nanofibers. Dynamic mechanical analysis and differential scanning calorimetry indicate that the composites prepared from oxidized nanofibers exhibit improved thermal and structural properties relative to those prepared from unoxidized nanofibers. The optimum enhancement in the mechanical and thermal properties was observed for the composite containing oxidized nanofibers and the 20% vinyl phenol copolymer. These results are in excellent agreement with our previous work on carbon nanotube–polymer composites and suggest that the presence of intermolecular interactions between the copolymer matrix and nanofibers are responsible for the observed property enhancement. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3053–3061, 2006     

Electrical conductivity of carbon fibres/polyester resin composites in the percolation threshold region

The electrical conductivity of composites of a polyester resin filled with short carbon fibres has been investigated with a special attention to the properties in the percolation threshold region. A very low percolation threshold (0.7-0.8 vol% of the filler) was confirmed. In contrast to S-shaped curves calculated according to the percolation theory of composites of globular particles, the experimental conductivity vs. fibre content dependence, after a steep increase in the percolation region, increased almost linearly. This atypical behaviour was explained by a different mechanism of formation of fibrous and globular conducting structures above the percolation threshold. An increase in scatter of conductivity values observed at percolation threshold as a consequence of great fluctuation of fibre arrangement manifested itself also in the conductivity-temperature dependences.     

The crosslinking of epoxy resins at interfaces. III. At a carbonized polyacrylonitrile surface

The crosslinking chemistry of an anhydride-cured epoxy resin, in the first 200–400 nm adjacent to a carbonized polyacrylonitrile (PAN) surface (a model for the surface of a carbon fiber), is significantly affected by the humidity history of that surface. Prior humid aging of the carbonized PAN surface increases the subsequent rate of consumption of anhydride curing agent, and decreases the yield of ester crosslinked products. The crosslinking chemistry of an amine-cured epoxy resin appears unchanged by the presence of the carbonized surface. Dynamic mechanical analysis (DMA) of unidirectional composites made from carbon fibers and the above epoxy resin matrices shows that the damping characteristics of composites made with an epoxy–anhydride matrix are sensitive to the preconditioning history of the carbon fibers, while composites made with an epoxy–amine matrix are unaffected by the preconditioning history of the fibers. Partial removal of the carbon fiber surface coating by dichloromethane extraction does not change the sensitivity of the composites to fiber preconditioning history. These results are rationalized on the basis of the effect moisture adsorbed by the carbonized PAN and by the carbon fiber has on the epoxy resin crosslinking processes.     

Electrospun fibers from poly(methyl methacrylate)/vapor grown carbon nanofibers

Electrospinning has been used to obtain poly(methyl methacrylate) (PMMA) microfibers and nanofibers and PMMA/vapor grown carbon nanofibers (VGCNFs or CNFs) composite fibers with micrometer and nanometer size diameters. Thermogravimetric analysis (TGA) indicated that addition of CNFs caused a decrease in the thermal stability of the composite fibers. Scanning electron microscopy (SEM) was used to confirm the micro‐ and nano‐ nature of the fibers and transmission electron microscopy (TEM) was utilized to confirm the presence of CNFs embedded within the polymer matrix and along the surface. Copyright © 2006 John Wiley & Sons, Ltd.     

Engineering thermal and mechanical properties of flexible fiber-reinforced aerogel composites

Flexible aerogel was successfully supported onto 4-layer-aligned glass fibers through impregnation, followed by drying at atmospheric pressure. The prepared nanocomposites can achieve a low thermal conductivity of 0.026?W/(m·K), which holds great promising for their use in thermal insulation applications. By choosing different designs of the four fiber layers, in the terms of LLLL, LTLL, LLTT, LTLT, LTTL and LTTT, the laminated structures of aerogel composites can be accordingly controlled. Further microstructure characterization of the composites revealed the homogeneous dispersion of nanoporous structure through the aerogel matrix, as well as highly-aligned fibers to reinforce the structure. Detailed investigation on the thermal and mechanical properties of the prepared fiber-aerogel composites showed that their performances were highly related to the laminated design of fiber layers. The introduction of fibers as the backbone of the aerogel and the suitable design of their laminated structure can greatly improve the mechanical properties of the aerogel composites while maintaining a low thermal conductivity.