Electromagnetic interference shielding effectiveness and microwave absorption properties of thermoplastic polyurethane/montmorillonite‐polypyrrole nanocomposites

In this work, thermoplastic polyurethane‐filled montmorillonite‐polypyrrole (TPU/Mt‐PPy) was prepared through melt mixing process for using in electromagnetic shielding applications. The effect of conducting filler content and type, sample thickness, and X‐band frequency range on the electromagnetic interference shielding effectiveness (EMI SE) and EMI attenuation mechanism was investigated. A comparative study of electrical and microwave absorption properties of TPU/Mt‐PPy nanocomposites and TPU/PPy blends was also reported. The total EMI SE average and electrical conductivity of all Mt‐PPy.Cl or Mt‐PPy.DBSA nanocomposites are higher than those found for TPU/PPy.Cl and TPU/PPy.DBSA blends. This behavior was attributed to the higher aspect ratio and better dispersion of the nanostructured Mt‐PPy when compared with neat PPy. Moreover, the presence of Mt‐PPy into TPU matrix increases absorption loss (SE_A) mechanism, contributing to increase EMI SE. The total EMI SE values of nanocomposites containing 30 wt% of Mt‐PPy.DBSA with 2 and 5 mm thickness were approximately 16.6 and approximately 36.5 dB, respectively, corresponding to the total EMI of 98% (75% by absorption) and 99.9% (88% by absorption). These results highlight that the nanocomposites studied are promising materials for electromagnetic shielding applications.     

EMI shielding and microwave absorption behavior of Au‐MWCNT/polyaniline nanocomposites

Electrically conducting Au‐multiwalled carbon nanotube/polyaniline (Au‐MWCNT/PANi) nanocomposites were synthesized by two different ways: (1) by direct mixing of MWCNT/PANi and Au nanoparticles (Au‐MWCNT/PANi‐1) and (2) by in situ polymerization of aniline in the presence of both MWCNTs and Au nanoparticles (Au‐MWCNT/PANi‐2). The higher electrical conductivity of Au‐MWCNT/PANi‐2 compared with the other samples (PANi, MWCNT/PANi, Au‐MWCNT/PANi‐1) is supported by the red shifts of the UV‐vis bands (polaron/bipolaron), the high value of the –NH+= stretch peak (Fourier transform infrared spectroscopy studies), the high % crystallinity (X‐ray diffraction analysis) and more uniform dispersion of the Au NPs in the material. The performance of the samples in electromagnetic interference (EMI) shielding and microwave absorption was studied in the X‐band (8–12 GHz). For all the samples, absorption was the dominant factor contributing toward the EMI shielding. Au‐MWCNT/PANi‐2 showed the best performance with a total shielding effectiveness of ?16 dB [averaged over the X‐band (GHz)] and a minimum reflection loss of ?56.5 dB. The higher dielectric properties resulting from the heterogeneities because of the presence of nanofillers and the high electrical conductivity lead to the increased EMI shielding and microwave absorption. The results show the significance of both Au nanoparticles and method of synthesis on the EMI shielding performance of MWCNT/PANi composites. Copyright © 2016 John Wiley & Sons, Ltd.     

Intrinsically conducting polymers for electromagnetic interference shielding

This paper summarizes and reviews the research on electromagnetic interference (EMI) shielding with intrinsically conducting polymers (ICPs), mainly polyaniline (PANI) and polypyrrole (PPY), and their composites in various frequency ranges. ICPs are new alternative candidates for EMI shielding applications due to their lightweight, corrosion resistance, ease of processing, and tunable conductivities as compared with typical metals. More importantly, the dominant shielding characteristic of absorption other than that of reflection for metals render ICPs more promising materials in applications requiring not only high EMI shielding effectiveness but also shielding by absorption, such as in stealth technology. Copyright © 2005 John Wiley & Sons, Ltd.     

Recent progress in MXene and graphene based nanocomposites for microwave absorption and electromagnetic interference shielding

There is widespread use of telecommunication and microwave technology in modern society, and raised the electromagnetic interference (EMI) issue to alarming situation due to apprehensive demand and growth of 5G technology undesirably disturbing the human health. The two dimensional (2D) materials including graphene and MXenes are already been used for variety of electronic devices due to their exceptional electrical, mechanical, optical, chemical, and thermal properties. MXene is composed of metal carbides, in which mainly metals are the building blocks for dielectrics, semiconductors, or semimetals. However, the strong interfaces with electromagnetic waves (EM) are variable from terahertz (THz) to gigahertz (GHz) frequency levels and are widely used in EMI and Microwave absorption (MA) for mobile networks and communication technologies. The use of different organic materials with metal, organic, inorganic fillers, polymers nanocomposite and MXene as a novel material has been studied to address the recent advancement and challenges in the microwave absorption mechanism of 2D materials and their nanocomposites. In this concern, various techniques and materials has been reported for the improvement of shielding effectiveness (SE), and theoretical aspects of EMI shielding performance, as well stability of 2D materials particularly MXene, graphene and its nanocomposites. Consequently, various materials including polymers, conducting polymers, and metal–organic frameworks (MOF) have also been discussed by introducing various strategies for improved MA and control of EMI shieling. Here in this comprehensive review, we summarized the recent developments on material synthesis and fabrication of MXene based nanocomposites for EMI shielding and MA. This research work is a comprehensive review majorly focuses on the fundamentals of EMI/MA.  The recent developments and challenges of the MXene and graphene based various structures with different polymeric composites are described in a broader perspective.     

Multi-layered graphene-Fe3O4/poly (vinylidene fluoride) hybrid composite films for high-efficient electromagnetic shielding

A flexible and multi-layered graphene nanosheets (GNSs)-Fe₃O₄/poly (vinylidene fluoride) hybrid composite film with high-efficient electromagnetic interference (EMI) shielding was fabricated via a facile layer-by-layer coating. The well-designed multi-layered and hybrid electromagnetic fillers endow the prepared film with good surface impedance matching and prominent internal multiple absorption, which forms “absorb-reflect-reabsorb” electromagnetic transmission pattern and results in highly efficient electromagnetic shielding effectiveness (EMI SE). The resultant composite film exhibits an exceptional EMI SE of 52.0 dB at a thickness of 0.3 mm. What is more important is that the prepared film exhibits excellent flexibility and EMI stability, and the retention rate of efficient EMI SE is high as 91.9% after 1000 bending-release cycles. This study provides a feasible strategy for designing high-efficient EMI shielding film with excellent flexibility and ultra-thin thickness that suitable for next-generation intelligent protection devices.     

Electromagnetic Interference Shielding Polymers and Nanocomposites - A Review

Intrinsically conducting polymers (ICP) and conductive fillers incorporated conductive polymer-based composites (CPC) greatly facilitate the research in electromagnetic interference (EMI) shielding because they not only provide excellent EMI shielding but also have advantages of electromagnetic wave absorption rather than reflection. In this review, the latest developments in ICP and CPC based EMI shielding materials are highlighted. In particular, existing methods for adjusting the morphological structure, electric and magnetic properties of EMI shielding materials are discussed along with the future opportunities and challenges in developing ICP and CPC for EMI shielding applications.     

Current trends in spinel based modified polymer composite materials for electromagnetic shielding

The present article deals with current trends in spinel based modified polymer composite materials for applications in the field of electromagnetic shielding. The interaction between the various spinel based materials and polymers is an emerging field of studies among various researchers. The thermal stability, electrical conductivity, the bonding between the metal ferrites and the polymer plays an important role in the interaction of electromagnetic radiation. These properties also effect the mechanism of the EM waves for the shielding applications. Considering these all properties, polyaniline appears to be an suitable polymer for electromagnetic shielding applications. Polyaniline composites not only reinforced the properties of spinel materials but also enhanced the dielectric properties of the composite material. When carbon based materials such as graphene, graphene oxide and CNT was added along with spinel material in polyaniline based composite, they accelerate the electrical properties and enhances the shielding applications. In this paper the various synthesis methods, fabrication methods of polyaniline, and the properties of polyaniline based composites have been discussed. In addition, the various salient features and futuristic challenges of polyaniline based composite materials for EMI shielding applications were attempted to make a well equipped material for radar absorption.     

Synthesis of composite of ZnO spheres with polyaniline and their microwave absorption properties

Three-dimensional (3D) ZnO microspheres with the composite of polyaniline (PANI) have been successfully synthesized by one-pot solvothermal and in-suit polymerization method. The obtained microspheres were uniform having the diameter of 4 μm–7 μm. These microspheres, inside cushion of PANI polymer, exhibit excellent microwave absorption properties. Composite of ZnO microspheres with PANI increased the complex permeability and enhanced the dielectric loss. Thus, the microwave absorption properties of the composite have been intensified. Despite the fact that the composite of ZnO with PANI herein dissipate the microwaves by dielectric loss, their performance is admirable compared to most of PANI-based composites reported. The morphological, structural and spectral properties have been investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and the Fourier transform infrared (FT-IR). It is found that the maximum reflection loss value of [email protected] reaches ?41 dB at 14 GHz with a thickness of 3.5 mm that is superior to the previously reported composite of PANI with other materials.     

Hydrophobization and evaluation of absorption capacity of Aloe vera,Opuntia ficus-indica and Gelidium for oil spill cleanup

Natural sorbent materials have practical advantages for the oil spill cleanup, whose advantages are their low-cost, feasibility for real-life applications and environmental adaptability. In this work, absorption capacity was determined for lyophilized aloe, nopal and agar and their composites with silica, Fe₃O₄/polysterene and multi-wall carbon nanotubes (MWCNTs). Freeze-drying was performed in order to preserve the structure and increase the internal volume of sorbents. The structures of lyophilized sorbents and composites were analyzed by scanning electron microscopy (SEM). SEM images for lyophilized sorbents show a tridimensional arrangement formed by plant-derived materials, which allows the oil absorption. The composites keep their tridimensional structure after freeze-drying and composite formation and exhibit coupling between both materials. Absorption capacity of aloe, nopal and agar are 9?g/g, 3?g/g, and 26?g/g, respectively without any pretreatment. Composites with Fe₃O₄/polysterene own capacities of 5.8?g/g, 2.8?g/g, and 14?g/g, respectively. Finally, for MWCNT composites, capacities are 7.8?g/g, 2.9?g/g and 23?g/g. A significant difference of adsorption capacity between lyophilized sorbents and composites is attributed to lyophilized materials absorbing oil, water and other compounds. Meanwhile, for composites the absorption is a more selective process, since the hydrophobization does not allow the absorption of water.     

Advancement in cellulose-based multifunctional high conductive PNIPAAm/PPy hydrogel/cotton composites for EMI shielding

Exploitation of cotton fabric as electromagnetic interference (EMI) shielding substrates have attracted a growing interest due to their desirable low carbon footprint, economic feasibility, and sustainability. Herein, a facile strategy was proposed for preparing a cellulose-based multifunctional PNIPAAm/PPy hydrogel/cotton (PPHC) EMI shielding composites with simultaneous high-efficient electro-photo-thermal conversion and comfort regulation functions. The PPHC was fabricated via in situ polymerization conductive PPy hydrogel on cotton substrate followed by deposition of PNIPAAm. Benefiting from the unique interconnected three-dimensional networked conductive structure of PPy hydrogel, the obtained PPHC composites exhibited high conductivity (15 mS/cm), and EMI shielding effectiveness (EMI SE?~?40 dB) in the frequency of 8.2–12.3 GHz. Moreover, the PNIPAAm coating endowed the composite fabrics with adjustable wettability performance in response to external temperature, leading to excellent comfort regulation performance. This work provided feasible avenue toward low cost and sustainability cotton-based EMI shielding composites with efficient EMI shielding and comfort regulation performance.

Graphical abstract

     

Segregated reduced graphene oxide polymer composite as a high performance electromagnetic interference shield

Herein, we report the synthesis of a graphene/polymer composite via a facile and straightforward approach for electromagnetic interference (EMI) shielding applications. Polystyrene (PS) beads were added in graphene oxide (GO)/water solution followed by the addition of hydroiodic acid (HI) for in situ reduction of GO. The composite solution (rGO/PS) was filtered, hot compressed and tested for EMI shielding and dielectric measurements. A 2-mm thick segregated rGO/PS sample with 10 wt% filler loading delivered a high EMI shielding effectiveness (SE) of 29.7 dB and an AC electrical conductivity of 21.8 S m^?1, which is well above the commercial requirement for EMI shielding applications. For comparison with the segregated rGO/PS composite, a control polymer composite sample utilizing a thermally reduced graphene oxide was synthesized by following a conventional coagulation approach. The as-synthesized conventional rGO/PS yield an EMI SE of 14.2 dB and electrical conductivity of 12.5 S m^?1. The high EMI shielding of segregated rGO/PS is attributed to the better filler-to-filler contact among graphene layers surrounded by PS beads and also to the better reduction and preservation of graphene structure during reduction process that makes the low temperature chemically reduced segregated rGO/PS approach a viable route compared to high temperature thermally reduced conventional rGO/PS approach.     

Microwave Absorption and Infrared Stealth Characteristics of Bamboo Charcoal/Silver Composites Prepared by Chemical Reduction Method

Bamboo charcoal coated with silver (BC/Ag) was prepared by activation and chemical reduction processes at different AgNO₃ contents (10‐30 wt.%). The spectroscopic characterizations of the formation processes of BC/Ag composites were studied using X‐ray diffraction, scanning electron microscopy and transmission electron microscopy. These composites were introduced in epoxy resin to be a microwave absorber and mixed polyethylene to be an infrared stealth plate. Microwave absorbing properties were investigated by measuring complex permittivity, complex permeability and reflection loss in the 2‐18 and 18‐40 GHz microwave frequency range using the free space method. The thermal extinction measurements in the 3‐5 and 8‐12 μm were done to evaluate the shielding affectivity of infrared. The results showed that a significant thermal extinction and a wider absorption frequency range could be obtained by adding silver to bamboo charcoal.     

Design and Synthesis Strategies: 2D Materials for Electromagnetic Shielding/Absorbing

Two-dimensional (2D) materials possess special physical and chemical properties. They have been proved to have potential application advantage in the microwave absorption (MA) and electromagnetic interference (EMI) shielding. Particularly, they exhibit positive shielding and absorbing response to EMI. Here, the research progress of preparation, electromagnetic performance and microwave shielding/absorbing mechanisms of 2D composite materials are introduced. Effective preparation routes including introducing heteroatoms, constructing unique structures and 2D composite materials are described. Furthermore, the application prospects and challenges for the development of novel EMI materials are expatiated.     

Fabrication,characterization and X-band microwave absorption properties of PAni/Fe3O4/PVA nanofiber composites materials

This work presents a study of microwave absorption properties of PAni/Fe₃O₄/PVA nanofiber composites with different ratio of Fe₃O₄ nanoparticles. The morphology of the composites nanofibers study by Field Emission Scanning Electron Microscopes (FESEM) and Transmission Electron Microscope (TEM) showed that the low content of Fe₃O₄ nanoparticles presence in the composites nanofibers indicates very much uniform surface, in the composites nanofiber without many bends, but some bends develop at higher content of Fe₃O₄ nanoparticles as indicated in the TEM image. Image-J software was used to further investigate the diameter of the composites nanofiber and found to be in the range of 152 to 195 nm. The nanofiber composites show excellent electric and magnetic properties and therefore vary with the addition of Fe₃O₄ nanoparticles in the composites nanofiber. In addition the PAni/Fe₃O₄/PVA composites nanofibers were further characterized by X-ray diffraction spectra (XRD) and Four Transformation infrared spectra (FTIR). The XRD pattern shows the presence of PAni nanotubes containing Fe₃O₄ nanoparticles by indicating peaks at 23.4⁰ and 35.43⁰ which was further supported by FTIR analysis. Microwave vector network analyzers (MVNA) were used to estimate the microwave absorption properties of the composites nanofibers. The absorption parameters was found to be −6.4 dB at 12.9 GHz within the range of X-band microwave absorption frequency, this reflection loss is attributed to the multiple absorption mechanisms as a result of the improved of impedance matching between dielectric and magnetic loss of the absorbent materials demonstrating that these materials can be used as protective material for electromagnetic radiation.     

Significantly enhanced electromagnetic interference shielding effectiveness of montmorillonite nanoclay and copper oxide nanoparticles based polyvinylchloride nanocomposites

In the present study, montmorillonite (MMT) nanoclay and copper oxide (CuO) nanoparticles (NPs) reinforced polyvinylchloride (PVC) based flexible nanocomposite films were prepared via solvent casting technique. Using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA), the structural, morphological and thermal properties of PVC/MMT/CuO nanocomposite films with various loadings of CuO NPs and MMT were investigated. These studies suggested that by the addition of dual nanofillers in the polymer matrix some structural modifications occurred owing to the homogenous dispersion of MMT and CuO NPs within the PVC matrix. The TGA results reveal that the addition of CuO NPs and MMT considerably improved the thermal stability of the nanocomposites. The EMI shielding effectiveness (SE) of nanocomposites was examined in the X-band (8–12 GHz) and Ku-band (12–18 GHz) frequency regions. The EMI SE values were found to be −30 dB (X-band) and −35 dB (Ku-band) for nanocomposites containing 0.3 wt% of CuO NPs and 4.7 wt% of MMT respectively while the shielding was found to be absorption dominant. These results emphasize that PVC/MMT/CuO nanocomposite films can be used as a potential EMI shielding material.     

Mechanical properties,thermal stability,sound absorption,and flame retardancy of rigid PU foam composites containing a fire‐retarding agent: Effect of magnesium hydroxide and aluminum hydroxide

Isocyanate, polyether polyol, a flame retardant (10 wt%), and aluminum hydroxide/magnesium hydroxide (0, 5, 10, 15, and 20 wt%) are used to form the rigid polyurethane (PU) foam, while nylon nonwoven fabrics and a polyester aluminum foil are combined to serve as the panel. The rigid PU foam and panel are combined to form the rigid foam composites. The cell structure, compressive stress, combustion resistance, thermal stability, sound absorption, and electromagnetic interference shielding effectiveness (EMI SE) of the rigid foam composites are evaluated, examining the effects of using aluminum hydroxide and magnesium hydroxide. Compared with magnesium hydroxide, aluminum hydroxide exhibits superior performance to the rigid foam composites. When aluminum hydroxide is 20 wt%, the rigid foam composite has an optimal density of 0.153 g/cm³, an average cell size of 0.2466 mm, a maximum compressive stress of 546.44 Kpa, an optimal limiting oxygen index (LOI) of 29.5%, an optimal EMI SE of 40 dB, and excellent thermal stability and sound absorption.     

Polymerization and characterization of high conductivity and good adhension polypyrrole films for electromagnetic interference shielding

<正>Polypyrrole(PPy) shows a favorable application in the electromagnetic interference(EMI) shielding due to its good electrical conductivity and outstanding air stability.Conducting PPy films with high conductivity and good adhesion were successfully polymerized on the surface of insulating epoxy resin substrates using chemical polymerization.The factors affecting the properties of PPy films,such as the surface morphology,adhesion between PPy film and substrate,electrical conductivity,EMI shielding effectiveness(SE),were investigated.The adhesion was improved significantly through a three-step surface pretreatment of epoxy resin substrates including removing impurities,roughening,and surface modification with silane coupling agent.An enhancement in the conductivity of PPy films of about one order of magnitude was achieved by adding dopant in FeCl_3 solution.The higher the conductivity,the better the shielding effectiveness.Taking sodium p-toluenesulfonate doped PPy film as example,EMI SE was in the practically useful range of about 30 dB over a wide frequency range from 30 MHz to 1500 MHz.The PPy film samples were characterized by scanning electron microscopy (SEM),infrared spectra(IR),X-ray photoelectron spectroscopy(XPS) and the flange coaxial transmission device.The fourpoint probe method was used to measure conductivity of PPy films.     

高导电聚苯胺薄膜的制备及其电磁屏蔽性能的研究

随着电器制品、电子器件的商用、军事用和科学应用的迅速增长 ,产生了亟待解决的电磁干扰 (也称作电磁环境污染 )问题 ,电磁干扰屏蔽日益受到关注 .本文从聚苯胺掺杂工艺角度出发 ,通过改变掺杂剂用量和溶剂种类 ,制备出高导电的聚苯胺薄膜 ,并对其电磁屏蔽特性进行了初步的测试与理论分析 ,将屏蔽效能的实测结果与理论计算值进行了比较     

Progress in the Foaming of Polymer-based Electromagnetic Interference Shielding Composites by Supercritical CO2

As a critical action plan formulated for peaking carbon dioxide emissions, polymeric electromagnetic interference (EMI) shielding materials based on CO₂ foaming technology have recently been attracting widespread attention in both research and industry, attributable to their efficient use of CO₂, high specific strength, corrosion resistance and low-cost characteristics. In the past decade, the emergence of novel design concepts and preparation techniques for CO₂ foaming technology has led to the development of new high-performance EMI shielding materials in this field. This review summarizes the research progress made to date on the fabrication of EMI shielding composite foams by supercritical carbon dioxide (scCO₂) foaming. We also explore the structure-activity relationships between the component/distribution and EMI shielding properties. Additionally, the application prospects and development challenges of new EMI shielding composite foams are described.     

Preparation of graphene/BaFe12O19–Ni0.8Zn0.2Fe2O4 nanocomposite and its microwave absorbing properties

BaFe₁₂O₁₉–Ni_0.8Zn_0.2Fe₂O₄/graphene nanocomposites were prepared by a deoxidation technique. The structure, morphology and electromagnetic properties of the samples were detected by means of X-ray diffraction, scanning electron microscope, transmission electron microscopy, Raman, thermogravimetric analysis. Results show that the BaFe₁₂O₁₉–Ni_0.8Zn_0.2Fe₂O₄ nanoparticles dispersed on the graphene sheets. The magnetic properties of the composites decreased with the increasing of graphene contents, However, the electrical conductivity is in the contrary. Measurement of electromagnetic parameters shows that when the mass ratio of BaFe₁₂O₁₉–Ni_0.8Zn_0.2Fe₂O₄ to graphene is 5:1, it can be matched well. The microwave absorption property of it is below ?10 dB at 6.8–8.2 GHz and the minimum loss value is ?19.63 dB at 7.2 GHz. The introduction of graphene can increase the dielectric loss and has an important effect on the microwave absorption properties.