Using a non-covalent modification to prepare a high electromagnetic interference shielding performance graphene nanosheet/water-borne polyurethane composite

We prepared flexible, lightweight, and high electromagnetic interference (EMI) shielding performance graphene nanosheet (GNS)/water-borne polyurethane (WPU) composites. WPU, with sulfonate functional groups, was used as the polymer matrix. By adsorbing the cationic surfactant (stearyl trimethyl ammonium chloride) on the surface of the GNSs (S-GNSs), restacking and aggregation of the GNSs have been efficiently suppressed, which also attracted sulfonate groups from the WPU matrix. Because of the favorable interfacial interactions arising from electrostatic attraction, the S-GNS exhibited good compatibility with the WPU matrix. Such a homogeneous dispersion contributed to the construction of an electrical conductive network. The S-GNS/WPU composite exhibited a low electrical conductivity percolation threshold and an outstanding enhanced electrical conductivity of approximately 5.1 S/m. A high EMI shielding effectiveness of approximately 32 dB was obtained by the WPU composites with contents of 5 vol.% (approximately 7.7 wt.%) S-GNSs.     

Enhancement in electrical conductive property of polypyrrole‐coated cotton fabrics using cationic surfactant

Recently, great efforts have been made to gain highly conductive fabrics for smart textiles and flexible electromagnetic shielding materials. Different from the conventional chemical synthesis method, fibrillar polypyrrole was synthesized on the cotton fabrics via a simple chemical polymerization process with micelles of cationic surfactant (cetyltrimethylammonium bromide, CTAB) as soft template. The modified cotton fabric exhibited excellent electrical conductivity and electromagnetic interference shielding effectiveness due to the formation of fibrillar polypyrrole on the fiber surface. Electrical conductivity of fabric surface were studied by four‐probe resistivity system. The highly conductive fabric with surface conductivity of 5.8 S cm^?1 could be obtained by changing cationic surfactant concentration. The electromagnetic interference shielding effectiveness (EMI SE) of the modified fabrics was evaluated by the vector network analyzer instrument. Compared with the sample without using surfactant, the EMI SE value of PPy‐coated cotton fabrics increased by 28% after using 0.03 M CTAB as soft template. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43601.     

Flexible electromagnetic interference shields made of silver flakes,carbon nanotubes and nitrile butadiene rubber

The recent advances in portable and flexible electronic devices demand integration of flexibility into future electromagnetic interference shielding materials. Here we synthesized flexible adhesive shields made of microscale silver flakes (Ag flakes), multi-walled carbon nanotubes decorated with nanoscale silver particles (nAg-MWNTs), and nitrile butadiene rubber (NBR). The addition of nAg-MWNTs into the Ag flake–NBR mixture significantly enhanced both conductivity and shielding effectiveness. Long nanotubes electrically linked microscale Ag flakes embedded in the NBR matrix, and nanoscale silver particles further improved the contact interface. There was a logarithmic relationship between the conductivity and shielding effectiveness. The dominant mechanism of electromagnetic interference shielding was reflection. The achieved maximum shielding effectiveness was about ∼75 dB at 1 GHz. The flexible adhesive shield printed on a polyimide film was wrapped around a cylindrical rod with a radius of 4 mm. The shielding effectiveness decreased about 20% after 100 wrapping cycles. The conductivity and shielding effectiveness could be adjusted by changing the Ag flake concentration. There was an excellent agreement between the theoretically predicted shielding effectiveness and the experimental data.     

The influence of single-walled carbon nanotube structure on the electromagnetic interference shielding efficiency of its epoxy composites

Three types of single-walled carbon nanotube (SWCNT) homogeneous epoxy composites with different SWCNT loadings (0.01-15%) have been evaluated for electromagnetic interference (EMI) shielding effectiveness (SE) in the X-band range (8.2-12.4 GHz). The effect of the SWCNT structure including both the SWCNT aspect ratio and wall integrity, on the EMI SE have been studied and are found to correlate well with the conductivity and percolation results for these composites. The composites show very low conductivity thresholds (e.g. 0.062%). A 20-30 dB EMI SE has been obtained in the X-band range for 15% SWCNT loading, indicating that the composites can be used as effective lightweight EMI shielding materials. Furthermore, their EMI performance to radio frequencies is found to correspond well with their permittivity data.     

Fabrication and characterization of NBR/MWCNT composites by latex technology

To develop a rubber composite with excellent electrical properties, a sort of synthetic rubber, acrylonitrile butadiene rubber (NBR) with CN dipoles as matrix, multi‐walled carbon nanotubes (MWCNTs) as filler, was synthesized. NBR composites reinforced with 0.5, 1.5, 3, 10, and 20 phr MWCNT contents were fabricated by latex technology. The electrical conductivity, dielectric characteristics, and electromagnetic interference (EMI) shielding effectiveness at room temperature of NBR/MWCNT composites were investigated. MWCNTs were found well dispersed into NBR matrix even for 20 phr content by FESEM observation. The electrical conductivity increased with an increment of MWCNT content. The dielectric constant was over 10⁴ at 10³ Hz frequency for 10 and 20 phr MWCNTs‐reinforced NBR composites. It was attributed to the increased electrons and interface polarization. The improved conductivity and dielectric permittivity resulted in an enhanced EMI shielding effectiveness. The EMI shielding effectiveness reached 26 dB at 16.7 GHz frequency for NBR/20 phr MWCNT composite with 1.0 mm thickness. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Strong and Flexible Carbon Fiber Fabric Reinforced Thermoplastic Polyurethane Composites for High‐Performance EMI Shielding Applications

Electromagnetic shielding materials play a significant role in solving the increasing environmental problem of electromagnetic pollutions. The commonly used metal‐based electromagnetic materials suffer from high density, poor corrosion resistance, and high processing cost. Polymer composites exhibit unique combined properties of lightweight, good shock absorption, and corrosion resistance. In this study, a novel high angle sensitive composite is fabricated by combining carbon fiber (CF) fabric with thermoplastic polyurethane elastomer (TPU). The effect of stacking angle of CF fabric on EMI shielding performance of composite is studied. When the stacking angle of CF fabric changed, the electromagnetic interference (EMI) shielding effectiveness (SE) of CF fabric/TPU composite can reach a maximum of 73 dB, and the tensile strength can reach 168 MPa. In addition, the composite has anisotropic conductivity, which is conductive along the plane direction and nonconductive along the thickness direction. Moreover, the CF fabric/TPU composite manifests exceptional EMI‐SE/density/thickness value of 383 dB cm² g^?1, which is higher than most of current EMI shielding composites reported in literature. In summary, CF fabric/TPU composite is an excellent EMI shielding material that is lightweight, highly flexible, and mechanically robust, which can be applied to the field of aerospace and some intelligent electronic devices.     

Effect of oxyfluorination on electromagnetic interference shielding of polypyrrole-coated multi-walled carbon nanotubes

The polypyrrole-coated multi-walled carbon nanotubes (MWCNTs) were prepared by in situ chemical oxidative polymerization of pyrrole on the surface of MWCNTs for the novel electromagnetic interference (EMI) shielding materials. The oxyfluorination treatment on MWCNTs introduced the hydrophilic functional groups resulting in well distribution and higher interfacial affinity between polypyrrole (PPy) and MWCNTs. The PPy phases formed on MWCNTs were observed by SEM. The thickness of PPy on the surface of MWCNTs decreased as increasing the hydrophilic groups on MWCNTs by the oxyfluorination treatment. The PPy-coated MWCNT composites showed the remarkable increases in permittivity, permeability, and EMI shielding efficiency (SE). The EMI SE of PPy-coated MWCNTs increased up about 28.6 dB mainly based on the absorption mechanism.     

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.     

Study on the structure and properties of conductive silicone rubber filled with nickel‐coated graphite

In this study, the conductive silicone rubber composites filled with nickel‐coated graphite (NCG) have been prepared, and their morphology structure, electrical conductivity, electromagnetic interference shielding efficiency (EMI SE), and mechanical properties have been investigated with reference to the NCG filler loading. The mechanical strength of NCG particle was poor that it can be easily ground into smaller particle during the mixing process if the shear force during mixing is large enough. The electrical conductivity of the composites existed an obvious threshold value with the variation of the loading amount of the conductive filler. EMI SE of the composites increases with the decrease of the volume electrical resistivity. The Payne effect can be used to characterize the intensity of the three‐dimensional conductive network structure in silicone rubber matrix, and the difference of storage modulus in the low and high shear strain has good linear correlation with the electrical conductivity. So, the electrical conductivity and EMI SE can be estimated by means of the difference of storage modulus obtained from rubber process analysis test. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Microwave absorbing rubber composites containing carbon black and aluminum powder

Natural rubber (NR), epoxidized natural rubber (ENR), and chlorosulfonated polyethylene (CSM) composites filled with conductive carbon black and aluminum powder have been prepared by using a two‐roll mill. An electromagnetic interference shielding effectiveness of those rubber composites was carried out in the frequency range of 8–12GHz (X‐band microwave). The increase of filler loading enhanced shielding effectiveness of the rubber composites. Conductive carbon black was more effective in shielding than aluminum powder. Binary filler‐filled rubber composites showed higher shielding effectiveness than that of single filler‐filled rubber composites. It has been observed that the shielding effectiveness of these rubber composites could be ranked in the following order: ENR ≥ CSM > NR, whereas the mechanical properties of the rubber composites were in the order of CSM > ENR > NR. The correlation between shielding effectiveness and electrical conductivity as well as mechanical properties of the rubber composites are also discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

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     

导电炭黑/杜仲胶复合材料电磁屏蔽性能的研究

采用机械共混法制备了导电炭黑/杜仲胶复合材料,研究炭黑用量对复合材料电性能和电磁屏蔽性能的影响。结果表明：随着炭黑用量的增加,复合材料的导电率增大,当炭黑用量为25份时,导电率达到3.3S/cm,导电率遵循导电逾渗规律;复合材料的Payne效应越来越大,有利于形成稳定的导电网络;复合材料的拉伸强度逐渐增大后略微降低,断裂伸长率先增加后逐渐下降。复合材料的屏蔽效能增大,当炭黑用量为20份时,屏蔽效能最高能达到33.2dB,可以满足一般工业或者商业用电子设备的要求。     

Investigation of the electric conductivity and the electromagnetic interference shielding efficiency of SWCNTs/GNS/PAni nanocomposites

This work demonstrates the fabrications and characterizations of polyaniline (PAni) composites containing single-walled carbon nanotubes (SWCNTs), graphite nanosheets (GNS), or hybrid fillers (SWCNTs/GNS). The characterization of microstructure, examination of fracture surface morphologies, and measurement of electric conductivity and electromagnetic interference shielding efficiency (EMI SE) were performed. It was found that both the electric conductivity and the EMI SE increase with filler loading, and the nanocomposites filled with 1.0 wt.% SWCNTs/GNS possessed the highest electric conductivity of 16.2 S/cm and total EMI SE of 27.0 dB. The experimental results also show that absorption is the primary mechanism of EMI SE for all of the loadings and fillers.     

Effect of processing method on microstructure,electrical conductivity and electromagnetic wave interference (EMI) shielding performance of carbon nanofiber filled thermoplastic polyurethane composites

In this study, effect of processing method on microstructure formation and related electrical conductivity and electromagnetic interference shielding effectiveness of carbon nanofiber (CNF) filled thermoplastic polyurethane (TPU) composites, prepared via three different processing techniques; (i) melt compounding (MC) in a twin screw extruder, (ii) simple solution mixing (SM) on a magnetic stirrer, and (iii) solution mixing with sonication (SM-U) were investigated. It was found that the electrical conductivity values of samples decreased in the order of SM > SM-U > MC for a particular amount of CNF. The electromagnetic test results showed that the samples prepared with SM and SM-U methods yielded higher total shielding effectiveness (SE_T) values than those prepared with MC. SE_T values of samples including of 20 phr of CNF prepared with MC, SM-U and SM methods were varied in the range of 10–30 dB, 20–60 dB and 20–80 dB, respectively within a frequency range of 1–12 GHz.     

Highly ordered porous carbon/wax composites for effective electromagnetic attenuation and shielding

We have demonstrated a highly ordered porous carbon (HOPC) as an effective electromagnetic absorber. The unique porous structures allow HOPC to possess high surface area and establish effective three-dimensional (3D) conductive interconnections at very low filler loading, which is responsible for effective electrical loss in terms of dissipating the induced current in the corresponding wax composites. Owing to the 3D porous frame, the wax composites with 1 and 5 wt% HOPC have shown effective bandwidth ∼2 and ∼4.5 GHz, respectively, which is considerably competitive to the performance found in the carbon nanotube- (CNT) and graphene-based composites of much higher filler loadings. This concept based on porous absorbers demonstrates more advantages in the fabrication of lightweight microwave-absorbing materials. Furthermore, the composite with 20 wt% HOPC has exhibited highly effective electromagnetic shielding performance up to 50 dB, which competes well with what has already been achieved in the composites embedded with CNTs and graphene. The fundamental mechanism based on electrical conductivity and complex impedance suggests specific strategies in the achievement of high-performance composites for electromagnetic attenuation and shielding.     

高性能聚酰亚胺电磁屏蔽材料的研究进展

电磁信号之间的干扰和混乱已成为当今5G无线通信时代的首要挑战，研发有效、屏蔽高、低频电磁干扰的高性能电磁屏蔽材料已成为当前的研究热点。未来电磁屏蔽材料将朝着超薄、柔性化、轻质化、宽频高效吸收、耐高温、力学性能好等方向发展。聚酰亚胺（PI）因其具有质量轻、可柔化、机械性能好、热学稳定性好等特点，常被用作高性能电磁屏蔽复合材料的基体材料。该文介绍了PI电磁屏蔽材料的屏蔽机理，重点总结了其屏蔽性能的影响因素及研究进展，并阐述了高性能PI电磁屏蔽材料未来的发展趋势。     

Electromagnetic interference shielding effectiveness of ethylene vinyl acetate based conductive composites containing carbon fillers

Conductive polymeric based composites were derived from ethylene vinyl acetate rubber filled with Vulcan XC‐72, short carbon fiber (SCF), and their blends. The electromagnetic interference (EMI) shielding effectiveness (SE), return loss, and reflection coefficient were studied. The measurements of the SE of the composites were carried out in two different frequency ranges of 100–2000 MHz and 8–12 GHz (X band). It was observed that the SE of the composites was frequency dependent and it increased with increasing frequency. The increasing of filler loading also enhanced the SE of the composites. The 100% SCF filled composites showed a higher SE compared to that of the filler blend or purely carbon black filled composites. The correlation between the SE and bulk conductivity of various composites was also discussed. The compromise between EMI SE, electrical conductivity, and mechanical properties was obtained when the composites contained both types of filler like particulate carbon black and SCF. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1601–1608, 2001     

Electrical and Electromagnetic Interference (EMI) shielding properties of hexagonal boron nitride nanoparticles reinforced polyvinylidene fluoride nanocomposite films

The hexagonal boron nitride nanoparticles (h-BNNPs) reinforced flexible polyvinylidene fluoride (PVDF) nanocomposite films were prepared via a simple and versatile solution casting method. The morphological, thermal and electrical properties of h-BNNPs/PVDF nanocomposite films were elucidated. The electromagnetic interference (EMI) shielding properties of prepared nanocomposite films were investigated in the X-band frequency regime (8–12 GHz). The EMI shielding effectiveness (SE) was increased from 1 dB for the PVDF film to 11.21 dB for the h-BNNPs/PVDF nanocomposite film containing 25 wt% h-BNNPs loading. The results suggest that h-BNNPs/PVDF nanocomposite films can be used as lightweight and low-cost EMI shielding materials.     

SiC encapsulated Fe@CNT ultra-high absorptive shielding material for high temperature resistant EMI shielding

Carbon nanotubes (CNTs) decorated with ferromagnetic materials have promising potential in electromagnetic interference (EMI) shielding applications. In this work, CNT sponges with increasing density were fabricated by filling them with magnetic Fe nanowires of mutative filling ratios via chemical vapor deposition (CVD). Results indicated that Fe@CNT composites with the highest density endowed the most remarkable average SE_T value of 70.01 dB (more than 99.99999% absorption), showing an ultra-high EMI shielding performance. However, the susceptibility to oxidation of carbon materials has restricted its further development in high-temperature EMI shielding applications. Therefore, the Fe@CNT composites were encapsulated by silicon carbide (SiC) with satisfactory oxidation resistance. Thereafter, the average SE_T value of SiC encapsulated a higher density Fe@CNT sponge decreased to an adequate value of 36.48 dB due to the huge loss of electrical conductivity. However, the SE_T value of it only dropped by about 1.20 as the temperature went up from 25 to 600 °C, demonstrating an excellent stability under high temperature conditions. As a proof of concept, the Fe@CNT/SiC composites with adequate EMI shielding performance and satisfactory oxidation resistance suggest its prospect in high temperature resistant EMI shielding.     

Enhanced Dielectric Constant for Efficient Electromagnetic Shielding Based on Carbon-Nanotube-Added Styrene Acrylic Emulsion Based Composite

An efficient electromagnetic shielding composite based on multiwalled carbon nanotubes (MWCNTs)-filled styrene acrylic emulsion-based polymer has been prepared in a water-based system. The MWCNTs were demonstrated to have an effect on the dielectric constants, which effectively enhance electromagnetic shielding efficiency (SE) of the composites. A low conductivity threshold of 0.23 wt% can be obtained. An EMI SE of ~28 dB was achieved for 20 wt% MWCNTs. The AC conductivity (σ _ac) of the composites, deduced from imaginary permittivity, was used to estimate the SE of the composites in X band (8.2–12.4 GHz), showing a good agreement with the measured results.