Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

The electrical conductivity and electromagnetic interference shielding of injection molded multi-walled carbon nanotube/polystyrene composites

Multi-walled carbon nanotube (MWCNT)/polystyrene (PS) composites were injection molded into a mold equipped with three different cavities. A high alignment of MWCNTs in PS was achieved by applying high shear force to the melt. The effects of gate and runner designs and processing conditions, i.e., mold temperature, melt temperature, injection/holding pressure and injection velocity, on the volume resistivity of the composites were investigated in both the thickness and in-flow directions. The experiments showed that volume resistivity could be varied up to 7 orders of magnitude by changing the processing conditions in the injection molded samples. The electromagnetic interference shielding effectiveness (EMI SE) of the molded composites was studied by considering the alignment of the MWCNTs. The EMI SE decreased with an increase in the alignment of the injection-molded MWCNTs in the PS matrix. This study shows that mold designs and processing conditions significantly influence the electrical conductivity and shielding behavior of injection molded CNT-filled composites.     

功能化碳纳米管/环氧树脂多孔复合材料制备及电磁屏蔽性能

以马来酸酐（MA）为功能性单体,通过自由基反应制备了马来酸酐功能化的多壁碳纳米管（MA-MWCNT）;以MA-MWCNT、环氧树脂、蓖麻油酸改性的四乙烯五胺固化剂、釉粉、水为原料,通过悬浮乳液聚合法制备了功能化碳纳米管/环氧树脂多孔复合材料。采用拉曼光谱、X射线衍射、红外光谱、X射线光电子能谱对功能化的碳纳米管进行了表征和测试。采用扫描电镜（SEM）、表面电阻测量仪、矢量网络分析仪对复合材料的表面形貌、电导率和电磁屏蔽性能进行了测试。结果表明：马来酸酐功能化单体的引入能够很好地改善碳纳米管的分散性能及材料的电磁屏蔽性能;随着碳纳米管含量的增多,复合材料的电导率增大,电磁屏蔽效能峰值增大,材料的电磁屏蔽性能增强;加入功能化的碳纳米管比加入未功能化碳纳米管的电磁屏蔽性能高,多孔复合材料比无孔复合材料的电磁屏蔽性能高。当加入功能化的碳纳米管的量为3%时,制备得到的多孔材料电磁屏蔽性能最佳,其电磁屏蔽性能峰值达到31.1dB。     

Morphological,electrical and electromagnetic interference shielding characterization of vapor grown carbon nanofiber/polystyrene nanocomposites

The influence of melt mixing conditions on the level of dispersion and the aspect ratio of vapor grown carbon nanofibers (VGCNFs) in a polystyrene (PS) matrix was studied. Final electrical and electromagnetic shielding capabilities in the 0.05–1.5 GHz frequency range are reported and discussed in the light of the composites' microstructure. The morphological study was based on analyzing scanning electron microscopy and optical microscopy micrographs and measuring the VGCNF length as a function of shear mixing conditions. The influence of mixing conditions on the microstructure was also indirectly studied by analyzing the dynamic mechanical behavior of the composites via rheology. Degradation of the VGCNF aspect ratio was found to be a function of the mixing energy. VGCNFs lost one‐third of their aspect ratio under gentle (low shear stress and mixing energy) mixing conditions. After VGCNFs had lost 40% of their aspect ratio, they had more resistance to breakage with increase in mixing energy. The dispersion of the VGCNFs was remarkably enhanced with increase in mixing energy. The percentage of area taken up by big agglomerates in the micrographs decreased from 14.1% to 5.5% when the mixing energy was increased from 100 J mL^?1 to 453 J mL^?1. The electrical and electromagnetic shielding properties of the 7.5 vol% VGCNF/PS composites were not affected by changing the processing energy because the enhancement of VGCNF dispersion with increasing mixing energy was accompanied by a loss in nanofiber aspect ratio. © 2012 Society of Chemical Industry     

Analysis of electrical,dielectric, and electromagnetic interference shielding behavior of graphite filled high density polyethylene composites

Conducting polymer composites were prepared by hot compression molding of high‐density polyethylene (HDPE) prelocalized with graphite (Gr). The variation of room temperature electrical conductivity, dielectric constant, and Shore‐D hardness as a function of graphite content were studied below and above percolation threshold. The percolation threshold at which insulator‐conductor transition takes place is estimated to be 0.029 volume fraction of graphite. The observed increase in dielectric constant with addition of graphite also found to be percolative in nature. Above percolation threshold, the dielectric constant is found to decrease sharply with increase in frequency. Electromagnetic shielding effectiveness of HDPE/Gr composites was evaluated in the X‐band frequency range. The composites were found to possess both positive and negative temperature coefficient of resistance. Reproducibility of electrical resistivity with temperature was observed only below the processing temperature. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Effect of conducting fillers on the microstructure and electrical conductivity of thermoplastic polymer composites

Summary This paper reports on the synthesis and characterization (electrical, mechanical, thermal and dynamic mechanical) of electrically conducting polymer composites based on thermoplastic matrices (low density polyethylene (LDPE) and polypropylene (PP)) and two conducting fillers: iron particles (Fe) and carbon black (CB). The addition of Fe allows the easy incorporation of higher amounts of CB. Results suggest that the electrical and mechanical properties of these materials are improved by the presence of both fillers being necessary the addition of CB to achieve interesting values of conductivity. On the other hand, the crystalline structure of the polymer matrix is gradually reduced with the incorporation of both fillers but Fe by itself does not affect the geometry of growing crystals.     

Reflection and absorption contributions to the electromagnetic interference shielding of single-walled carbon nanotube/polyurethane composites

The electromagnetic interference (EMI) shielding of well dispersed single-walled carbon nanotube (SWCNT)/polyurethane composites was studied and the results show that they can be used as effective and lightweight shielding materials. The EMI shielding of the composite shows a reflection-dominant mechanism, while a shift from reflection to absorption was observed with increased SWCNT loading and frequency. This is explained using EMI shielding theory and the intrinsic properties of the components.     

Electrical conductivity and EMI shielding effectiveness of polyurethane foam–conductive filler composites

The morphological, electrical, and thermal properties of polyurethane foam (PUF)/single conductive filler composites and PUF/hybrid conductive filler composites were investigated. For the PUF/single conductive filler composites, the PUF/nickel‐coated carbon fiber (NCCF) composite showed higher electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) than did the PUF/multiwall carbon nanotube (MWCNT) and PUF/graphite composites; therefore, NCCF is the most effective filler among those tested in this study. For the PUF/hybrid conductive fillers PUF/NCCF (3.0 php)/MWCNT (3.0 php) composites, the values of electrical conductivity and EMI SE were determined to be 0.171 S/cm and 24.7 dB (decibel), respectively, which were the highest among the fillers investigated in this study. NCCF and MWCNT were the most effective primary and secondary fillers, and they had a synergistic effect on the electrical conductivity and EMI SE of the PUF/NCCF/MWCNT composites. From the results of thermal conductivity and cell size of the PUF/conductive filler composites, it is suggested that a reduction in cell size lowers the thermal conductivity of the PUF/conductive filler composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44373.     

Mild functionalization of carbon nanotubes filled epoxy composites: Effect on electromagnetic interferences shielding effectiveness

The effect of nitric acid mild functionalized multiwalled carbon nanotubes (MWCNTs) on electromagnetic interference (EMI) shielding effectiveness (SE) of epoxy composites was examined. MWCNTs were oxidized by concentrated nitric acid under reflux conditions, with different reaction times. The dispersion of MWCNTs after functionalization was improved due to the presence of oxygen functional groups on the nanotubes surface. Functionalization at 2 h exhibits the highest EMI SE and electrical conductivity of MWCNTs filled epoxy composites. However, EMI shielding performance of MWCNTs filled epoxy composite declined when the functionalization reaction time was prolonged. This was due to extensive damage on the MWCNT structure, as verified by a Raman spectroscope. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42557.     

Thermal conductivity,electrical resistivity,mechanical, and rheological properties of thermoplastic composites filled with boron nitride and carbon fiber

Hybrid composites consisting of boron nitride (BN) platelets and carbon fibers (CF) in a polybutylene terephthalate (PBT) matrix were melt‐compounded, and their thermal and electrical conductivity, tensile, and rheological properties were investigated. While it does not lead to an enhancement in thermal conductivity with respect to PBT/BN composites, the results indicate that a combination of BN and CF in PBT can significantly reduce electrical conductivity of the composites compared to that of PBT/CF composites. The relative low thermal conductivity of the hybrid composites is attributed to CF breakage that occurred during the extrusion and alignment of CF in melt flow direction, which is normal to the heat flow encountered during the thermal conductivity tests induced by injection molding. The hybrid composites were, however, found to have better tensile properties and processibility than PBT/BN composites at the same total filler content. POLYM. COMPOS., 26:66–73, 2005. © 2004 Society of Plastics Engineers     

Effect of surface treatment on electrical conductivity of carbon black filled conductive polymer composites

Two different types of surface modifiers, 3‐aminopropyltriethoxysilane and formamide, were applied to carbon black (CB) particles to lower electrical resistivity of polymer composites prepared by treated CB. Two different matrices, low‐density polyethylene and nylon 6, were chosen to compound with surface modified CB. Surface energy of CB was increased by adding amine or amide functional groups during surface treatment of CB. According to electron spectroscopy for chemical analysis (ESCA), chemical modification in surface chemistry of CB was obtained with the chemicals used for the treatment due to the nitrogen atoms in their structures, which may act as dopant atom. As a result of this, electrical resistivity of composites prepared by treated CB decreased. In addition, there was not any significant change in tensile strength and tensile modulus of the composites with the surface treatment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Electrical conductivity and electromagnetic interference shielding effectiveness of nano-structured carbon assisted poly(methyl methacrylate) nanocomposites

Nanostructured carbon-based polymeric nanocomposites are gaining research interest because of their cost-effectiveness, lightweight, and robust electromagnetic interference (EMI) shielding performance. Till now, it is a great challenge to design and fabricate highly scalable, cost-effective nanocomposites with superior EMI shielding performance. Herein, highly scalable EMI shielding material with tunable absorbing behaviors comprising of low-budget ketjen black (K-CB) reinforced poly(methyl methacrylate) (PMMA) nanocomposites have been prepared using simple solvent assisted solution mixing technique followed by hot compression technique. The morphological investigation revealed the homogeneous distribution of K-CB and strong interfacial interaction in PMMA matrix, which validated the strong reinforcement and other intriguing properties of the nanocomposites. The PMMA nanocomposites showed a low percolation threshold (2.79 wt%) and excellent electrical conductivity due to the formation of 3D conductive network like architecture within the polymer matrix. Specifically, the 10 wt% K-CB nanocomposite possessed a superior EMI shielding performance of about 28 dB for X-band frequency range. Further, a huge change in EMI shielding performance of PMMA nanocomposites is observed with varying thickness. The brand new K-CB decorated PMMA nanocomposites are expected to open the door for next-generation cost-effective EMI shielding materials for academic and industrial applications.     

Enhanced impact resistance and electromagnetic interference shielding of carbon nanotubes films composites

High reliability and high-performance electromagnetic interference (EMI) shielding polymeric composite was fabricated by introducing carbon nanotube films (CNT_f) into an epoxy (EP) matrix as mechanical and EMI shielding reinforcement simultaneously. According to the computed tomography (CT) detection recorded by a high-speed camera, CNT_f exhibited excellent mechanical behavior and good energy absorption. While being introduced into laminated EP composite, the CNT_f enhanced both the mechanical performance and EMI shielding performance. The damage mechanism of CNT_f/EP was studied by CT detection of the impact process, indicating that the CNT_f absorbed the impact energy by improving the delamination resistance. Additionally, the multilayered CNT_f can trap and attenuate the entered electromagnetic microwaves by repeated adsorption, reflection, and scattering in the composite, resulting in excellent EMI shielding performance. Consequently, the energy absorption and the total shielding effectiveness of the CNT_f/EP reached to 4.58 × 10⁻³ J and 52.31 dB, respectively. Therefore, we demonstrated that the CNT_f was an ideal functional reinforcement for mechanically strong and high-performance EMI shielding polymeric composites and the CNT_f reinforced EP composite is promising in practical EMI-shielding applications.     

Electrical conductivity and electromagnetic interference shielding effectiveness of carbon black/sisal fiber/polyamide/polypropylene composites

The effects of hybrid fillers on the electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) of polyamide 6 (PA6)/polypropylene (PP) immiscible polymer blends were investigated. Carbon black (CB) and steam exploded sisal fiber (SF) were used as fillers. CB was coated on the surface of SF, and this was exploded by water steam to form carbon black modified sisal fiber (CBMSF). CB/SF/PA6/PP composites were prepared by melt compounding, and its electromagnetic SE was tested in low‐frequency and high‐frequency ranges. We observed that SF greatly contributed to the effective decrease in the percolation threshold of CB in the PA6/PP matrix and adsorbed carbon particles to form a conductive network. Furthermore, an appropriate CB/SF ratio was important for achieving the best shielding performance. The results indicate that CBMSF was suitable for use as electronic conductive fillers and the CB/SF/PA6/PP composites could be used for the purpose of EMI shielding. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42801.     

The effect of thermal stresses on the EMI (electromagnetic interference) shielding of conductive plastics

The electrical properties of a number of filled and coated plastics were examined after subjecting the materials to rigorous thermal cycling between −20 and 80°C. Filled compounds that obtained their conductivity through the addition of carbon based conductive fillers maintained their conductivity throughout the thermal cycling. Compositions which contained metal fillers were able to maintain their conductivity only when a high temperature thermally stable polymer was used as the polymer matrix. Plaques coated by a zinc arc spray or with acrylic paints containing graphite, silver, and nickel particles were unaffected by thermal cycling. Plaques coated with an acrylic paint containing copper particles lost most of their conductivity during the changes in sample temperature.     

Effects of carbon fiber modification with multiwall CNT on the electrical conductivity and EMI shielding effectiveness of polycarbonate/carbon fiber/CNT composites

The effect of carbon fiber (CF) modification with multiwall carbon nanotube (CNT) on the electrical, mechanical, and rheological properties of the polycarbonate (PC)/CF/CNT composite was investigated. The CF and multiwall CNT (MWCNT) were treated with sulfuric acid and nitric acid (3:1 wt %) mixture, to modify the CF with the CNT. For the PC with acid-treated CNT (a-CNT) modified acid-treated CF (a-CF) (PC/a-CF/a-CNT) composite, the electrical conductivity, and the electromagnetic interference shielding effectiveness (EMI SE) showed the highest values, compared with those of the PC/a-CF and PC/a-CF/CNT composites. The EMI SE of the PC/a-CF (10 wt %)/a-CNT (0.5 wt %) composite was found to be 26 (dB at the frequency of 10.0 GHz, and the EMI SE was increased by 91.2%, compared to that of the PC/a-CF composite at the same amount of total filler content. Among the composites studied in this work, the PC/a-CF/a-CNT composite also showed the highest values of relative permittivity (ε_r) and dielectric loss factor. The above results suggest that the CF modification with the a-CNT significantly affected the electrical conductivity and EMI SE of the composite, and the hybrid fillers of the a-CNT and a-CF resulted in good electrical pathways in the PC/a-CF/a-CNT composite. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47302.     

Effects of hybrid fillers on the electrical conductivity,EMI shielding effectiveness,and flame retardancy of PBT and PolyASA composites with carbon fiber and MWCNT

The effects of hybrid fillers of carbon fiber (CF) and multiwall carbon nanotube (MWCNT) on the electrical conductivity, electromagnetic interference shielding effectiveness (EMI SE), flame retardancy, and mechanical properties of poly(butylene terephthalate) (PBT)/poly(acrylonitrile-co-styrene-co-acrylate) (PolyASA) (70/30, wt %) with conductive filler composites were investigated. The CF was used as the main filler, and MWCNT was used as the secondary filler to investigate the hybrid filler effect. For the PBT/PolyASA/CF (8 vol %)/MWCNT (2 vol %) composite, a higher electrical conductivity (1.4 × 10⁰ S cm⁻¹) and EMI SE (33.7 dB) were observed than that of the composite prepared with the single filler of CF (10 vol %), which were 9.0 × 10⁻² S cm⁻¹ and 23.7 dB, respectively. This increase in the electrical properties might be due to the longer CF length and hybrid filler effect in the composites. From the results of aging test at 85 °C, 120 h, the electrical conductivity and EMI SE of the composites decreased slightly compared to that of the composite without aging. The results of electrical conductivity, EMI SE, and flame retardancy suggested that the composite with the hybrid fillers of CF and MWCNT showed a synergetic effect in the PBT/PolyASA/CF (8 vol %)/MWCNT (2 vol %) composite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48162.     

Fabrication and electromagnetic interference shielding effectiveness of carbon nanotube reinforced carbon fiber/pyrolytic carbon composites

Carbon nanotube reinforced carbon fiber/pyrolytic carbon composites were fabricated by precursor infiltration and pyrolysis method and their electromagnetic interference shielding effectiveness (EMI SE) was investigated over the frequency range of 8.2–12.4 GHz (X-band). Carbon nanotubes (CNTs) were in situ formed through catalyzing hydrocarbon gases evaporating out of phenolic resin with nano-scaled Ni particles. The content of CNTs increased with the increase of Ni loadings (0.00, 0.50, 0.75 and 1.25 wt.%) in phenolic resin. Thermal gravimetrical analysis results showed that the carbon yield of phenolic resin increased with the addition of Ni catalyst. With the formation of CNTs, the EMI SE increased from 28.3 to 75.2 dB in X-band. The composite containing 5.0 wt.% CNTs showed an SE higher than 70 dB in the whole X-band.     

Single‐walled carbon nanotube/poly(methyl methacrylate) composites for electromagnetic interference shielding

Single‐walled carbon nanotube (SWNT)/poly(methyl methacrylate) (PMMA) composites were prepared using coagulation method. The electrical conductivity and the electromagnetic interference (EMI) shielding of SWNT/PMMA composites over the X‐band (8–12 GHz) and the microwave (200–2000 MHz) frequency range have been investigated. The electrical conductivity of composites increases with SWNT loading by 13 orders of magnitude, from 10^?15 to 10^?2 Ω^?1 cm^?1 with a percolation threshold of about 3 wt% SWNTs. The effect of the sample thickness on the shielding effectiveness has been studied, and correlated to the electrical conductivity of composites. The data suggest that SWNT/PMMA composites containing higher SWNT loading (above 10 wt%) be useful for EMI shielding and those with lower SWNT loading be useful for electrostatic charge dissipation. The dominant shielding mechanism of SWNT/PMMA composites was also discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers