Electromagnetic interference shielding behavior of poly(trimethylene terephthalate)/multi-walled carbon nanotube composites

Poly(trimethylene terephthalate) [PTT]/multiwalled carbon nanotube [MWCNT] composites having varying amounts of MWCNTs were fabricated with an aim to investigate the potential of such composites as an effective light weight electromagnetic interference (EMI) shielding material in the frequency range of 12.4-18 GHz (Ku-band). PTT/MWCNT composite with shielding effectiveness (SE) of 36-42 dB was obtained at 10% (w/w) MWCNT loading. Shielding mechanism was studied by resolving the total SE into absorption (SE_A) and reflection loss (SE_R). PTT/MWCNT composite showed absorption dominated shielding; thus it can be used as microwave, radar absorbing and stealth material. The effect of MWCNT loadings on electrical conductivity (σ) and dielectric properties of PTT and the correlation among conductivity, tan δ, absorption loss and reflection loss were also studied.     

Reduced graphene oxide deposited carbon fiber reinforced polymer composites for electromagnetic interference shielding

Reduced graphene oxide deposited carbon fiber (rGO-CF) was prepared by introducing GO onto CF surface through electrophoretic deposition method, following by reducing the GO sheets on CF with NaBH₄ solution. The rGO-CF was found to be more effective than CF to improve the electromagnetic interference (EMI) shielding property of unsaturated polyester (UP) based composites. With 0.75% mass fraction of rGO-CF, the shielding effectiveness of the composite reached 37.8 dB at the frequency range of 8.2–12.4 GHz (x-band), which had 16.3% increase than that of CF/UP composite (32.5 dB) in the same fiber mass fraction. The results suggest that rGO-CF is a good candidate for the use as a light-weight EMI shielding material.     

Microwave probing of nanocarbon based epoxy resin composite films: Toward electromagnetic shielding

We report on the comparative study of the electromagnetic shielding effectiveness provided by different forms of nanocarbon dispersed in epoxy resin in low concentration (0.5 wt.%). A series of pre-percolative carbon black and close-to-percolation threshold carbon nanotube (CNT) samples were investigated in microwave frequencies in order to evaluate the shielding effectiveness of epoxy resin widely used for aerospace applications. The data of theoretical simulation on the basis of generalized Maxwell Garnett theory prove that the shielding effectiveness of the investigated composites in microwaves is determined mostly by the conductivity of nanocarbon inclusions. Consequently, utilizing well purified defect-free or chemically modified CNT we can improve drastically the shielding effectiveness of such a composite, without changing the volume fraction of nanocarbon inclusions.     

Graphene foam/carbon nanotube/poly(dimethyl siloxane) composites for exceptional microwave shielding

Highly porous poly(dimethyl siloxane) (PDMS) composites containing cellular-structured microscale graphene foams (GFs) and conductive nanoscale carbon nanotubes (CNTs) are fabricated. The unique three-dimensional, multi-scale hybrid composites with inherent percolation and a high porosity of 90.8% present a remarkable electromagnetic interference shielding effectiveness (EMI SE) of ∼75 dB, a 200% enhancement against 25 dB of the composites made from GFs alone with the same graphene content and porosity. The corresponding specific EMI SE measured against the composite density is 833 dB cm³/g. These values are among the highest for all carbon filler/polymer composites reported thus far. Significant synergy arises from the hybrid reinforcement structure of the composites: the GFs drive the incident microwaves to be attenuated by dissipation of the currents induced by electromagnetic fields, while the CNTs greatly enhance the dissipation of surface currents by expanding the conductive networks and introducing numerous interfaces with the matrix.     

Fabrication and characterization of fully biodegradable natural fiber-reinforced poly(lactic acid) composites

Polymer composites were fabricated with poly(lactic acid) (PLA) and cellulosic natural fibers combining the wet-laid fiber sheet forming method with the film stacking composite-making process. The natural fibers studied included hardwood high yield pulp, softwood high yield pulp, and bleached kraft softwood pulp fibers. Composite mechanical and thermal properties were characterized. The incorporation of pulp fibers significantly increased the composite storage moduli and elasticity, promoted the cold crystallization and recrystallization of PLA, and dramatically improved composite tensile moduli and strengths. The highest composite tensile strength achieved was 121 MPa, nearly one fold higher than that of the neat PLA. The overall fiber efficiency factors for composite tensile strengths derived from the micromechanics models were found to be much higher than that of conventional random short fiber-reinforced composites, suggesting the fiber–fiber bond also positively contributed to the composites’ strengths.     

Characterization of organo-montmorillonite (OMMT) modified wood flour and properties of its composites with poly(lactic acid)

In this research, sodium-montmorillonite (Na-MMT) at four different concentrations (0.5%, 1.0%, 2.0% and 4.0%) and didecyl dimethyl ammonium chloride (DDAC) were used to modify wood flour (WF) in a two-step process to form organo-montmorillonite (OMMT) inside the WF. Then the WFs with three sizes were mixed with poly(lactic acid) (PLA) to produce WF/PLA composites. The treated WF was characterized and some physical and mechanical properties of the composites were tested. The results showed that: (1) Na-MMT was successfully transformed to OMMT and uniformly distributed inside WF; (2) at 0.5% MMT concentration, water repellency, flexural and tensile properties of the composites were improved significantly. However, after introducing more OMMT, the enhancements diminished because of poor interfacial adhesion caused by OMMT agglomeration; (3) the composites with the maximum size of WF showed the most significant improvements among all, suggesting bigger WF was more suitable for this modification process.     

纤维复合材料电磁屏蔽效能分层多尺度计算

为建立复合材料宏细观尺度之间电磁响应的关联性,将分层多尺度计算方法应用于纤维复合材料电磁屏蔽效能计算。为准确描述复合材料宏细观之间的联系,以电磁屏蔽效能为衡量标准,确定了复合材料细观结构的代表性体积单元(RVE)。根据电磁场媒质本构方程计算了RVE的等效电磁参数。采用分层多尺度方法计算复合材料宏观构件的电磁屏蔽效能。结果表明工作频率越高则复合材料的RVE越小;所设计的纤维复合材料结构在工作频率2～18GHz范围内具有38dB以上的电磁屏蔽效能,且电磁屏蔽效能随工作频率增加而下降。研究方法适用于求解细观结构相分散均匀或分布有规律的任意形状复合材料宏观构件电磁屏蔽效能。     

Segregated poly(vinylidene fluoride)/MWCNTs composites for high-performance electromagnetic interference shielding

Conductive polymer composites (CPCs) that contain a segregated structure have attracted significant attentions because of their promising for fulfilling low filler contents with high electromagnetic interference (EMI) properties. In the present study, segregated poly(vinylidene fluoride) (PVDF)/multi-walled carbon nanotubes (MWCNTs) composites were successfully prepared by mechanical mixing and hot compaction. The PVDF/MWCNTs samples with 7 wt% filler content possess high electrical conductivities and high EMI shielding effectiveness (SE), reaching 0.06 S cm⁻¹ and 30.89 dB (in the X-band frequency region), much higher than lots of reported results for CNT-based composites. And the EMI SE greatly increased across the frequency range as the sample thickness was improved from 0.6 to 3.0 mm. The EMI shielding mechanisms were also investigated and the results demonstrated absorption dominating shielding mechanism in this segregated material. This effective preparation method is simple, low-cost, and environmentally-friendly and has potential industrial applications in the future.     

单壁碳纳米管无纺布/环氧树脂复合材料的电磁屏蔽性能

采用一种导电材料预制体-单壁碳纳米管(Single-wall carbon nanotube,SWCNT)无纺布与环氧树脂复合制备了电磁屏蔽复合材料,并对所制复合材料的电磁屏蔽性能进行了表征。结果表明:所制复合材料对电磁波的屏蔽效率随SWCNT无纺布厚度的增加而增加。在较低的SWCNT无纺布填加量下所制复合材料可以实现对低频电磁波较高的屏蔽效率。不同于填加粉体导电材料所制电磁屏蔽复合材料,作为导电材料预制体使用的SWCNT无纺布是一个独立的整体导电薄膜,可以直接引入到基体当中,不存在分散问题。并且通过简单的导电预制体多层叠加的方式即可实现复合材料更高的屏蔽效率。     

Study on short ramie fiber/poly(lactic acid) composites compatibilized by maleic anhydride

Short ramie fiber reinforced poly(lactic acid) (PLA) composites without and with maleic anhydride (MA) were developed. The influence of PLA-g-MA as a compatibilizer on the properties of the composites was studied. The tensile, flexural and impact strength of the composites have improvements with the addition of PLA-g-MA. The morphology of fracture surface evaluated by SEM indicates that the composites with the addition of PLA-g-MA can get better adhesion between the fiber and the matrix. And the Vicat softening temperature and the degradation temperature of the composites are increased with the addition of PLA-g-MA. However, PLA-g-MA leads the glass transition temperature (T_g) decrease according to the DSC results.     

炭黑/碳纤维/ABS电磁屏蔽复合材料的制备及其性能研究

采用硅烷偶联剂KH550改性炭黑(CB),浓硝酸氧化碳纤维(CF),将表面处理前后的炭黑和碳纤维与丙烯腈-丁二烯-苯乙烯(ABS)树脂通过混炼挤出制备了电磁屏蔽复合材料,考察了炭黑、碳纤维含量及表面处理对复合材料体积电阻率和屏蔽效能的影响。实验结果表明,采用KH550改性炭黑可以达到改性目的,浓硝酸氧化碳纤维后,其表面接上了羰基和羧基。随着炭黑含量增加,复合材料的体积电阻率逐渐下降,且变化规律符合渗滤效应,在100～1800MHz频率范围内,屏蔽效能逐渐增加,采用1%KH550改性炭黑后,导电性能和屏蔽效能均得到提高。加入碳纤维后,复合材料的导电性能和屏蔽效能均有较大提高,且含量为2%时,分别达到最大值,采用浓硝酸氧化碳纤维后,导电性能得到进一步提高,屏蔽效能提高了1dB左右。     

Effect of diisocyanates as compatibilizer on the properties of ramie/poly(lactic acid) (PLA) composites

Ramie/PLA composites with the diisocyanates as compatibilizer were fabricated by extrusion and injection molding. The influence of different diisocyanates and various diisocyanate content on the mechanical properties and thermal properties of the composites was investigated. The presence of the diisocyanates in the composites lead to the improvements in mechanical properties and thermal properties of the composites. The morphologies of fracture surface using scanning electron microscopy (SEM) provided evidence of improved interfacial adhesion between ramie and PLA from the addition of the diisocyanates. The composites containing isophorone diisocyanate (IPDI) showed the best mechanical properties. The comparison of various IPDI content showed that the composites with 1.5% IPDI could get the optimum mechanical properties, and the excess diisocyanate content resulted in the decrease in the mechanical properties of the composites. However, IPDI content had almost no effect on the crystallization and melting behavior of the ramie/PLA composites.     

Electromagnetic interference shielding effectiveness of nanoreinforced polymer composites deposited with conductive metallic thin films

The effect of using conductive metallic thin films deposited on high density polyethylene (HDPE) and styrene butadiene copolymer (SBC) in conjunction with carbon nanofiber (CNF) reinforcement of HDPE and SBC was investigated in order to improve the electromagnetic interference shielding effectiveness (EMI SE) of the structures. Thin films of copper, silver and aluminum were deposited by thermal evaporation onto the polymeric matrices and its composites (0-20 wt.% of CNFs). Results show a synergistic effect of the two approaches (metallic coating and CNF reinforcement) toward improving the EMI SE. The chemical composition, surface morphology, carbon nanofiber distribution, thickness and microstructure of metallic coated polymers are examined using X-Ray Diffraction and Scanning Electron Microscopy.     

Aerosol based fabrication of a Cu/polymer and its application for electromagnetic interference shielding

The effect of a catalytic surface activation on the electromagnetic interference shielding of Cu deposited polymer substrates was investigated. The surface of polymer substrates was catalytically activated by different methods respectively adopted Pd aerosol nanoparticles and Sn-Pd wet chemical processes. Although both activations initiated the deposition of Cu on the substrates, differences such as morphology (Pd aerosol: ~80 nm vs Sn-Pd: ~ 140 nm, in Cu grain size) and composition (Pd aerosol: Cu and Pd vs Sn-Pd: Cu, Pd, Sn, and Cl) of Cu deposits were presented. Specimens activated using Pd aerosol nanoparticles showed a higher range of shielding effectiveness by about 4-10 dB than those activated by Sn-Pd processes in 2-18 Ghz frequencies.     

可生物降解聚乳酸/纳米纤维素复合材料的亲水性和降解性

采用溶液浇铸法制备可生物降解聚乳酸(PLA)/纳米纤维素复合材料。测试了该复合材料的吸水性,在37℃的磷酸缓冲溶液中及在土壤中的降解性。并用扫描电子显微镜(SEM)观察了降解前后复合材料的表面形貌。结果表明,随着复合材料中纳米纤维素质量分数的增加,复合材料的吸水性和降解性均随之提高,明显优于纯的聚乳酸。从SEM的图片中看出,降解后,在磷酸缓冲溶液中的复合材料表面有孔洞,而在土壤中的则有明显被侵蚀的痕迹。     

Composite electromagnetic interference shielding materials for aerospace applications

Electromagnetic interference (EMI) occurs when electronic devices are subject to electromagnetic radiation from unwanted sources at the same frequency ranges that these devices operate. Metals typically serve as excellent EMI shielding agents, but their heavy weight, high cost and susceptibility to forms of environmental degradation make them an undesired choice for many current electronic devices. Conversely fibre reinforced polymeric (FRP) composite materials are normally light weight, and can be cheaper to produce, but typically lack the inherent EMI shielding capabilities that may be required. This research work addresses the viability FRP composite materials for use as EMI shielding structures, specifically for aerospace applications. It was found that carbon fibre could suffice this purpose, but likely required filler materials to enhance electrical conductivity and shielding effectiveness (SE).     

Additive manufacturing of mechanical testing samples based on virgin poly (lactic acid) (PLA) and PLA/wood fibre composites

3D printing in additive manufacturing is considered as one of key technologies to the future high-precision manufacturing in order to benefit diverse industries in building construction, product development, biomedical innovation, etc. The increasing applications of 3D printed components depend primarily on their significant merits of reduced weight, minimum used materials, high precision and shorter production time. Furthermore, it is very crucial that such 3D printed components can maintain the same or even better material performance and product quality as those achieved by conventional manufacturing methods. This study successfully fabricated 3D printed mechanical testing samples of PLA and PLA/wood fibre composites. 3D printing parameters including infill density, layer height and the number of shells were investigated via design of experiments (DoE), among which the number of shells was determined as the most significant factor for maximising tensile strengths of PLA samples. Further, DoE work evaluated the effect of material type (i.e., neat PLA and PLA/wood fibres) and the number of shells on tensile, flexural and impact strengths of material samples. It is suggested that material type is the only predominant factor for maximising all mechanical strengths, which however are consistently lower for PLA/wood fibre composites when compared with those of neat PLA. Increasing the number of shells, on the other hand, has been found to improve almost all strength levels and decrease infill cavities. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0211-3     

Effect of heat treatment temperature on microstructure and electromagnetic shielding properties of graphene/SiBCN composites

Three-dimensional (3D) graphene/SiBCN composites (GF/SiBCN) were prepared by depositing SiBCN ceramics in 3D graphene foam via the chemical vapor infiltration technique. The effect of the heat treatment temperature on the microstructure, phase composition, and electromagnetic properties of the GF/SiBCN composite was investigated. The SiBCN ceramics maintained an amorphous structure in the composite below 1400 °C above which the crystallinity of the free carbon phase gradually increased. While the Si₃N₄ and B₄C phases started to crystallize at 1500 °C and their crystallinity increased with temperature, SiC was observed at 1700 °C. The electromagnetic shielding effectiveness of GF/SiBCN increased with the heat treatment temperature.     

Molecular relaxations in the composites of liquid crystalline cellulose derivatives with poly(acrylic acid)

The molecular relaxation phenomena of the specific polymer composites obtained by photopolymerisation of the oriented lyotropic liquid-crystalline systems composed of cellulose derivatives dissolved in photopolymerisable acrylic acid are studied. We have investigated the composites based on two cellulose derivatives, which differ by the length of their side-chains and consequently by their physical properties. In this work, the molecular relaxations of such anisotropic composites were studied by dielectric relaxation spectroscopy and by thermooptical analysis. In the dielectric relaxation spectroscopy two representations were analysed: temperature dependences of dielectric loss ɛ"(T) and of electric modulus M "(T). The electric modulus representation is especially convenient to monitor the relaxations in a high temperature range where the ionic conductivity dominates the dielectric response. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000     

Preparation and properties of self-reinforced poly(lactic acid) composites based on oriented tapes

The inherent brittleness and poor thermal resistance of poly(lactic acid) (PLA) are two main challenges toward a wider industrial application of this bioplastic. In the present work, through the development of self-reinforced PLA (SR-PLA) or “all-PLA” composites, the high brittleness and low heat deflection temperature (HDT) of PLA have been overcome, while simultaneously improving the tensile strength and modulus of SR-PLA. The obtained composites are fully biobased, recyclable and under the right conditions compostable. For the creation of SR-PLA composites, first a tape extrusion process was optimized to ensure superior mechanical properties. The results show that SR-PLA composites exhibited enhanced moduli (2.5 times) and tensile strengths (2 times) and showed 14 times increase in impact energy compared to neat PLA. Finally, the HDT of SR-PLA was also increased by about 26 °C compared to neat PLA, mainly as a result of an increase in modulus and crystallinity.