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.     

Electrical conductivity and shielding effectiveness of poly(trimethylene terephthalate)/multiwalled carbon nanotube composites

Poly(trimethylene terephthalate) (PTT)/multiwalled carbon nanotube (MWCNT) composites have been fabricated to evaluate the potential of PTT composites as electromagnetic interference (EMI) shielding material. The room temperature electrical conductivity, complex permittivity, and shielding effectiveness (SE) of PTT/MWCNT composites were studied in the frequency range of 8.2–12.4 GHz (X-band). The dc conductivity (σ) of composites increased with increasing MWCNT loading and a typical percolation behavior was observed at 0.48 vol% MWCNT loading. The highest EMI SE of PTT/MWCNT composites was ~23 decibel (dB) at 4.76 vol% MWCNT loading which suggest that these composites can be used as light weight EMI shielding materials. The correlation among the SE, complex permittivity, and electrical conductivity was also studied. The EMI shielding mechanism of PTT/MWCNT composites was studied by resolving the total EMI SE into absorption and reflection loss.     

Rheologic and mechanical properties of multiwalled carbon nanotubes-reinforced poly(trimethylene terephthalate) composites

This paper investigates the rheologic and mechanical properties of melt-blended poly(trimethylene terephthalate) (PTT)/multiwalled carbon nanotube (MWCNT) composites and the effect of acid treatment of MWCNT on these properties. The microstructure of the composites was studied by SEM and TEM in terms of the dispersion state of the nanotubes and the polymer–nanotube interaction. Incorporation of MWCNTs into PTT matrix resulted in an increase in both complex viscosity and moduli than those of neat PTT. A dramatic increase in the melt viscosity of composites observed with loading of MWCNT in the range of 0.5 and 2 wt% showed the formation of interconnected network of MWCNT in the polymer matrix at a rheologic percolation threshold. Acid treatment of MWCNT showed significant effect on the rheologic properties of PTT and led to the enhancement of both complex viscosity and moduli due to strong interfacial interaction between acid-treated MWCNT and PTT matrix. The effect of acid treatment was also evident by mechanical properties of the PTT/MWCNT composites. The untreated MWCNT showed only increase in modulus of PTT matrix; whereas, after acid treatment, both tensile strength and modulus of PTT matrix enhanced significantly.     

The effect of multi-wall carbon nanotubes on electromagnetic interference shielding of ceramic composites

Multi-wall carbon nanotubes (MWCNTs)-3?mol% yttria-stabilized zirconia (3Y-TZP) (MWCNTs-3Y-TZP) composite was prepared by spark plasma sintering. The complex permittivities of the composite have been measured in the Ku-band range (12.4-18?GHz) and it is found that both the real and imaginary permittivities of the composite increase with the increasing content of MWCNTs. The effect of the content of MWCNTs on the electromagnetic interference (EMI) shielding effectiveness (SE) of the composite has been evaluated, and it is found that the EMI SE of the composite increases with the increasing content of MWCNTs. An EMI SE value as high as 25-30?dB has been achieved in the Ku-band range for the composite with 9?wt% content of MWCNTs, indicating that the MWCNTs-3Y-TZP composite can be used as an effective EMI shielding material.     

Morphological,electrical, electromagnetic interference (EMI) shielding,and tribological properties of functionalized multi-walled carbon nanotube/poly methyl methacrylate (PMMA) composites

The functionalized multi-walled carbon nanotubes (MWCNTs) had been prepared via Friedel–Crafts acylation with maleic anhydride. X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) confirmed the functionalization of MWCNTs. The composites with maleic anhydride modified MWCNTs (Mah-g-MWCNTs) and poly (methyl methacrylate) were then prepared by the in situ and ex situ solution polymerization system. The Electromagnetic Interference (EMI) shielding effectiveness (SE) of Mah-g-MWCNTs/PMMA composites increased with the increasing of the Mah-g-MWCNTs content, and the in situ system shows higher EMI SE value. The wear resistance was enhanced while the loading of the Mah-g-MWCNTs was above the percolation threshold, and the in situ system provides higher efficiency than that of ex situ system.     

Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.     

Effect of multi-walled carbon nanotubes on mechanical and rheological properties of poly(trimethylene terephthalate)

This paper investigates rheological and mechanical properties of poly(trimethylene terephthalate) (PTT) in presence of multi-walled carbon nanotubes (MWCNTs). Morphological characterization by scanning electron microscope and transmission electron microscope showed uniform distribution of MWCNTs in the PTT matrix. Incorporation of MWCNTs into PTT matrix resulted in higher complex viscosity (η), storage (G′) and loss modulus (G″) than those of neat PTT, especially in low-frequency region. The dramatic increase in melt viscosity of PTT observed upon incorporation of MWCNTs in the range of 0.25–1 wt% could be due to the formation of interconnected network of MWCNTs in the polymer matrix, and thus, this can be regarded as rheological percolation threshold concentration. Cole–Cole plot showed change in slope and also shift in G′ versus G″ plot, which suggested change in microstructure upon MWCNT addition. The reinforcing effect of MWCNTs was also confirmed by dynamic mechanical analysis, where, by adding CNTs, a noticeable increase in storage modulus of PTT was observed. However, addition of MWCNTs showed no significant effect on the tensile properties of PTT due to poor interfacial interaction between CNTs and polymer matrix.     

The surface characteristics of organoclays and their effect on the properties of poly(trimethylene terephthalate) nanocomposites

Biobased materials developed in conjunction with nanotechnology are poised to achieve a significant presence in the world market for polymeric materials. An example of an engineering polymer that can be partially derived from biomass is poly(trimethylene terephthalate). One of its raw materials, 1,3-propanediol, can be derived from corn sugar. In the present study we used a fully petroleum-based resin as an analog to the biobased material. Five organically modified montmorillonite clays were characterized via moisture uptake studies to determine the hydrophilic/hydrophobic nature of their surfaces. Nanocomposites were produced via melt compounding followed by injection molding with 5 wt.% organoclay loading to determine which modification gave the best balance of mechanical and thermal properties. It was found that the tensile modulus increased by up to 35% and the tensile stress at break by up to 50%. The heat deflection temperature of the nanocomposites versus the neat polymer increased by up to 33 °C. From these results, one organoclay was selected for detailed study over a loading range of 0–5 wt.%. The testing revealed that over this range, changes in the mechanical properties may go through a maximum (e.g. strength) or increase/decrease to a plateau (e.g. modulus, elongation at break). X-ray diffraction and transmission electron microscopy were also used to characterize the nature of the organoclay/polymer interaction. Biobased poly(trimethylene terephthalate)/organoclay nanocomposites are expected to exhibit properties similar to the petroleum-based resin.     

屏蔽电磁干扰高分子磁性复合材料的研究

与铁氧化比较，二茂铁高分子磁性材料（OPM）在100MHz以下，其频率－磁导率（f-μ′）及温度－磁导率（T－μ′）变化不大，研究了金属纤维及碳纤维填充的OPM复合材料及其配位金属（Cu,Co,Ni)类型，屏蔽形式对屏蔽效果（SE）的影响。     

Morphology development and size control of poly(trimethylene terephthalate) nanofibers prepared from poly(trimethylene terephthalate)/cellulose acetate butyrate in situ fibrillar composites

Formation of nano-fibrillar composite structures provides an effective method for preparing thermoplastic nanofibers. By mixing two immiscible thermoplastic polymers in a twin screw extruder, poly(trimethylene terephthalate) (PTT) formed nano-fibrillar morphology in cellulose acetate butyrate (CAB) matrix, and then PTT nanofibers were obtained from PTT/CAB in situ fibrillar composites after removing the matrix phase of CAB. Blend ratio, shear rate, and draw ratio were three important parameters in the extrusion process, which could affect the shape and size of nanofibers. By varying the process conditions, average diameter of PTT nanofibers could be controlled in the range of 80–400 nm. Besides this, the mechanism of nano-fibrillar formation in PTT/CAB blends was also studied by collecting samples at different stages in the extruder. The morphology developmental trends of PTT dispersed phase with different blend ratios were nearly the same. From initial to metaphase and later phase development, the PTT dispersed component undergo the formation of sheets, holes, and network structures, then the size reduction and formation of nanofibers.     

铁镍合金对复合电磁屏蔽材料性能的影响

在导电组分中添加磁性合金粉末,利用复合效应增加电磁屏蔽材料的吸收损耗,以获得较好的屏蔽效能。通过在12%体积分数的金属镍粉中添加不同体积分数的FeNi合金,研究了复合材料中FeNi合金对电磁屏蔽效能的影响。实验结果表明,当加入4%体积分数的FeNi合金时,屏蔽效能最好。分析得出FeNi合金粉末的加入能够增加材料的磁导率,增加材料对电磁波的吸收,在提升屏蔽效能的同时达到低二次污染的目的。     

The effect of nanotube surface oxidation on the electrical properties of multiwall carbon nanotube/poly(vinylidene fluoride) composites

Carbon nanotube/poly(vinylidene fluoride) (CNT/PVDF) composites were prepared using CNT with different oxidation and thermal treatments. The oxidation procedure leads to CNT with the most acidic characteristics that lower the degree of crystallinity of the polymer and contribute to a large increase of the dielectric constant. The surface treatments, in general, increase the percolation threshold and decrease conductivity. The surface treatments do not seem to affect CNT interactions and similar degrees of dispersion are achieved in all cases, as shown by the SEM results. The maximum value of the dielectric constant is ~630. It is demonstrated that the composite conductivity can be attributed to a hopping mechanism that is strongly affected by the surface treatment of the CNT.     

Miscibility and melting properties of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) blends

The miscibility and melting properties of binary crystalline blends of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) (PEN/PTT) have been investigated with differential scanning calorimetry (DSC). The glass transition and cold crystallization behaviors indicated that in PEN/PTT blends, there are two different amorphous phases and the PEN/PTT blends are immiscible in the amorphous state. The polymer–polymer interaction parameter, , calculated from equilibrium melting temperature depression of the PEN component was −1.791 × 10⁻⁵ (300 °C), revealing miscibility of PEN/PTT blends in the melt state.     

Electromagnetic interference (EMI) shielding of single-walled carbon nanotube epoxy composites

Single-walled carbon nanotube (SWNT)-polymer composites have been fabricated to evaluate the electromagnetic interference (EMI) shielding effectiveness (SE) of SWNTs. Our results indicate that SWNTs can be used as effective lightweight EMI shielding materials. Composites with greater than 20 dB shielding efficiency were obtained easily. EMI SE was tested in the frequency range of 10 MHz to 1.5 GHz, and the highest EMI shielding efficiency (SE) was obtained for 15 wt % SWNT, reaching 49 dB at 10 MHz and exhibiting 15-20 dB in the 500 MHz to 1.5 GHz range. The EMI SE was found to correlate with the dc conductivity, and this frequency range is found to be dominated by reflection. The effects of SWNT wall defects and aspect ratio on the EMI SE were also studied.     

Pickering乳液技术制备纤维素纳米纤丝-还原氧化石墨烯/聚甲基丙烯酸甲酯电磁屏蔽复合材料

利用纤维素纳米纤丝（CNF）和氧化石墨烯（GO）共稳定的含有聚甲基丙烯酸甲酯（PMMA）的Pickering乳液法,并经抽滤、还原、热压等工艺制备高性能的纤维素纳米纤丝-还原氧化石墨烯/聚甲基丙烯酸甲酯（CNF-rGO/PMMA）电磁屏蔽复合材料。通过调节油相中聚合物的质量浓度、水油体积比,从而调控GO在复合材料中的质量分数。研究GO还原方式、质量分数及热压过程对所制备的CNF-rGO/PMMA电磁屏蔽复合材料的形貌结构与性能的影响。CNF-rGO/PMMA电磁屏蔽复合材料中GO经水合肼处理后有效还原为rGO,热压工艺使包裹在PMMA颗粒外的CNF-rGO片层与PMMA颗粒紧密堆积并形成交联的三维导电网络从而具有优异的导电率,在X波段不同频率（8.2~12.4 GHz）下具有良好的电磁屏蔽效能及稳定性,电磁屏蔽效能可达20 dB以上,可用于民用电磁屏蔽材料。      

A comparative study of EMI shielding properties of carbon nanofiber and multi-walled carbon nanotube filled polymer composites

Electromagnetic interference shielding properties of carbon nanofiber- and multi-walled carbon nanotube-filled polystyrene composites were investigated in the frequency range of 8.2-12.4 GHz (X-band). It was observed that the shielding effectiveness of composites was frequency independent, and increased with the increase of carbon nanofiber or nanotube loading. At the same filler loading, multi-walled carbon nanotube-filled polystyrene composites exhibited higher shielding effectiveness compared to those filled with carbon nanofibers. In particular, carbon nanotubes were more effective than nanofibers in providing high EMI shielding at low filler loadings. The experimental data showed that the shielding effectiveness of the composite containing 7 wt% carbon nanotubes could reach more than 26 dB, implying that such a composite can be used as a potential electromagnetic interference shielding material. The dominant shielding mechanism of carbon nanotube-filled polystyrene composites was also discussed.     

A study of the electromagnetic properties of Cobalt-multiwalled carbon nanotubes (Co-MWCNTs) composites

Electroless plating was utilized to deposit Cobalt (Co) on the surface of multi-walled carbon nanotubes (MWCNTs), and the technological parameters of electroless plating were optimized. To obtain optimized processing parameters, field-emission scanning electron microscope (FESEM) as well as energy dispersive spectroscopy (EDS) results were presented to show the morphology, components of as-prepared Co-MWCNTs. Based on the optimized processing parameters, Co-MWCNTs were prepared and filled into the epoxy resin to fabricate Co-MWCNTs composites. The electromagnetic properties of pure MWCNTs composites and Co-MWCNTs composites were studied. To sum up, the pure MWCNTs composites with a filler concentration of 2 wt% had an intense absorbing peak at 15.20 GHz, where the highest reflection loss (R) reached −21.41 dB. Compared to the pure MWCNTs composite at the same concentration, the Co-MWCNTs composites showed a higher impedance which implies a better potential absorbing property and makes Co-MWCNTs probable to be utilized in electromagnetic absorbing field.     

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。     

DC electrical conductivity of poly(methyl methacrylate)/carbon black composites at low temperatures

The study deals with the dc electrical conduction of poly(methyl methacrylate)/carbon black composites of different carbon black (CB) filler concentrations (2, 6, 12 wt%). The dc electrical conductivity was studied as a function of filler concentration, and temperature in the range (20–290 K). It was found that the composites exhibit negative temperature coefficient of resistivity (NTCR) at low temperatures and enhancement in the dc electrical conductivity with both temperature and CB concentration. The observed increase of conductivity with CB concentration was interpreted through the percolation theory. The dependence of the electrical conductivity of the composites in low temperatures was analyzed in term of a formula in consistence with Mott variable rang hopping (VRH) mechanism. The observed overall mechanism of electrical conduction has been related to the transfer of electrons through the carbon black aggregations distributed in the polymer matrix.