Dielectric properties of medium thermal black-polyethylene systems

The dielectric properties of thermoplastic and cross-linked polyethylene compounds with a low structure medium thermal carbon black are described in the frequency range between 30 and 8000 kHz as a function of frequency, temperature, and carbon black loading. Very high values of the dielectric constant were obtained for the conductive samples. The systems investigated are shown to follow percolative type models with experimental critical exponents in good agreement with the predicted values. The dielectric constant increases slowly with the carbon black concentration up to roughly the percolation concentration, then increases rapidly, and subsequently decreases at the higher black loadings. The dissipation factor-concentration curves show maximum values in the vicinity of the percolation concentration. The dielectric properties of these systems are discussed in terms of interfacial Maxwell-Wagner polarization effects.     

Dielectric and magnetic properties of random and segregated ferrite polystyrene composites

The dielectric and magnetic properties of polystyrene composites containing barium or nickel-zinc ferrites were studied as function of the ferrite concentration and field frequency. The composites were prepared by methods yielding a random distribution of the ferrite particles or segregated structures. Barium ferrite-poly-styrene composites exhibited a typical insulator behavior, and only above 60% ferrite were high values of the dielectric properties noted at the lower frequencies, decreasing gradually with frequency to the low values typical of the higher frequencies. The mode of barium ferrite particle distribution did not affect the dielectric properties. The nickel-zinc ferrite systems demonstrated a conductor type behavior. An apparent insulator-conductor transition was observed, having lower values for segregated than for random distributions. The magnetic permability of barium ferrite-polystyrene composites above 10% ferrite increases with the ferrite concentration, whereas the magnetic dissipation factor steeply increases with concentration above 40% ferrite.     

Dielectric behavior of carbon black filled polymer composites

This paper reports results on the dielectric properties of carbon black filled crosslinked polyethylene composites. These systems are shown to follow percolative type models. The dielectric constant increases slowly, with carbon black concentration, up to roughly the percolation concentration and then increases rapidly over the whole concentration ranges studied. The dissipation factor-concentration curves are bell-shaped with maximum values at approximately the percolation concentration. The dielectric properties of these systems are discussed in terms of interfacial Maxwell-Wagner polarization effects.     

Dielectric properties of isotactic polypropylene/nitrile rubber blends: Effects of blend ratio,filler addition,and dynamic vulcanization

The dielectric properties of isotactic polypropylene/acrylonitrile–butadiene rubber blends have been investigated as a function of frequency with special reference to the effect of blend ratio. The dielectric properties measured were volume resistivity, dielectric constant (ϵ′), dissipation factor (tan δ), and loss factor (ϵ″). At high frequencies, a transition in relaxation behavior was observed whereby the dielectric constant of the blends decreased with frequency, whereas the loss tangent and loss factor increased on reaching a maximum. The variation of the dielectric properties with blend composition was correlated with blend morphology, and relationships were established with reference to blend composition. Experimental ϵ′ values were compared with theoretical predictions. The effect of the addition of fillers on the dielectric properties was also investigated for different fillers and filler loadings. It was found that silica filler increases the dissipation factor, whereas carbon black and cork gave a reverse trend. The variation in dielectric properties upon dynamic vulcanization of the rubber phase using different vulcanizing agents (such as sulfur, peroxide, and mixed systems) was also investigated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 255–270, 1999     

Dielectric properties of aluminum–epoxy composites

Dielectric properties of Al–epoxy composites were characterized as a function of composition, frequency, and temperature. The dielectric constant increased smoothly with an increase in the concentration of aluminum. An increase in dielectric constant was also observed with an increase in temperature as well as with a decrease in frequency. In general, dissipation factor values for composites with higher concentrations of aluminum were greater than those with lower volume content of aluminum. Also, the dissipation factor showed an increase both with a decrease in frequency and an increase in temperature. The increase in values of dielectric constant and dissipation factor with an increase in concentration of aluminum was attributed to interfacial polarization. The absence of any discontinuity in the plot of dielectric constant versus composition was ascribed to the absence of continuous aluminum chains in the composition range investigated. The increase in dielectric constant with a rise in temperature was attributed to the segmental mobility of the polymer molecules. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3602–3608, 2003     

Effect of a carbon black surface treatment on the microwave properties of poly(ethylene terephthalate)/carbon black composites

A surface treatment was applied to carbon black to improve the electrical and microwave properties of poly(ethylene terephthalate) (PET)-based composites. Three different formamide solutions with 1, 2, and 3 wt % concentrations were prepared to modify the surface chemistry of carbon black. Microwave properties such as the absorption loss, return loss, insertion loss, and dielectric constant were measured in the frequency range of 8–12 GHz (X-band range). Composites containing formamide-treated carbon black exhibited enhancements in the electrical conductivity, electromagnetic interference (EMI) shielding effectiveness, and dielectric constant values when compared to composites with untreated carbon black. In addition, increases in the formamide solution concentration and carbon black content of composites resulted in an increase in the electrical conductivity, EMI shielding effectiveness, and dielectric constant values. The percolation threshold concentration of PET composites shifted from a 3 to 1.5 wt % carbon black composition with the surface treatment. The best EMI shielding effectiveness was around 27 dB, which was obtained with the composite containing 8 wt % carbon black treated with a 3 wt % formamide solution. Moreover, this composition gave the lowest electrical resistivity and the highest dielectric constant among the produced composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

BaTiO3／环氧树脂／玻璃纤维复合材料介电性能研究

本文运用热压工艺制备了BaTiO3（BT）／环氧树脂／玻璃纤维和BaTiO3／炭黑／环氧树脂／玻璃纤维复合材料,研究了温度、填料含量和交流频率对复合材料的介电性能的影响。结果表明,复合材料的介电常数（εr）和介电损耗（tanδ）随肌体积分数的增加而升高。当肌体积分数为17％时,复合材料在1MHz下的εr和tanδ分别为7.88和0.027。当炭黑的含量为1.0％时,明含量为17％的复合材料εr和tanδ分别为11.0和0.035。随着频率的升高,复合材料的εr降低,而介电损耗升高。复合材料的εr随温度升高而增加。     

Dielectric properties of epoxy‐dielectrics‐carbon black composite for phantom materials at radio frequencies

In order to develop new dry phantom materials that can simulate the effect of electromagnetic wave on human tissues, the dielectric properties of the phantom materials composed of dielectrics, carbon black, and epoxy resin were investigated. For dielectrics/epoxy composite, the dielectric constants increased with the content of dielectric powder and were independent of frequency at the measured frequency range. The dielectric constants and conductivity of carbon black/epoxy composite also increased with the carbon black, but it showed the frequency dependence that the complex dielectric constants decreased with increasing frequency. The dielectric constants and conductivity corresponding to human tissues could be obtained by combining the frequency dependence of carbon black/epoxy composite with the dielectric properties of dielectrics/epoxy composite and by adjusting the composition ratios of carbon black, dielectrics, and epoxy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1294–1302, 2000     

Dielectric and microwave properties of carbon nanotubes/carbon black filled natural rubber composites

Abstract

Natural rubber (NR) based nanocomposites containing a constant amount (50 phr) of standard furnace carbon black and carbon nanotube (CNT) at a concentration from 1 to 5 phr have been prepared. Their dielectric (dielectric permittivity and dielectric loss) and microwave properties (coefficients of absorption and reflection of the electromagnetic waves and electromagnetic interference shielding effectiveness) have been investigated in the 1–12 GHz frequency range. The results achieved allow recommending CNTs as second filler for NR based composites to afford specific absorbing properties.     

改性炭黑对复合材料介电性能的影响

为提高复合材料的介电性能,采用硅烷偶联剂KH550对炭黑表面进行改性,并与聚偏氟乙烯、钛酸钡制成复合材料,研究了复合材料介电性能.结果表明,硅烷偶联剂KH550改变了炭黑表面结构,使炭黑/聚偏氟乙烯复合材料的介电常数在104 Hz时提高了15％以上,填充钛酸钡后介电常数进一步增加,介电损耗可控制在较低的范围.     

Electrical properties of natural-fiber-reinforced low density polyethylene composites: A comparison with carbon black and glass-fiber-filled low density polyethylene composites

The electrical properties of sisal fiber-low density polyethylene (LDPE) and coir fiber-LDPE composites have been studied. The dielectric constant progressively increases with increase of fiber loading and decreases with increase of frequency in the case of all composites. The dielectric constant of sisal-LDPE composites has been studied as a function of fiber length. Volume resistivity values decrease with fiber content. The increase of dielectric constant with fiber loading is more predominant at low frequencies in both the sisal fiber-LDPE and coir fiber-LDPE composites. The results of the natural-fiber-filled composites were compared to those of the carbon and glass-fiber-filled LDPE composites. The dielectric constant of carbon-black-loaded LDPE composites increases with carbon content, and the increase is sharper at high carbon content. This is associated with the network formation of carbon black in LDPE matrix. © 1997 John Wiley & Sons, Inc.     

Electrical,dielectric, and electromagnetic shielding properties of polypropylene‐graphite composites

The conducting polymer composite material is desired to have a high dielectric constant and high dissipation factor in low and high frequency ranges, so that it can be used in charge storing devices, decoupling capacitors, and electromagnetic interference (EMI) shielding applications. Currently, on‐going research is trying to enhance the dielectric constant of ceramic powder‐polymer, metal powder‐polymer, and nanotube‐polymer composites in the low frequency region. In this article, we present the dielectric properties of polypropylene (PP)‐graphite (Gr) composites in low and radio frequency ranges. Furthermore, the EMI shielding properties of these composites are examined in the radio frequency range. The PP‐Gr composites were prepared by mixing and the hot compression mold technique. The electrical conductivity and dielectric constant of PP‐Gr composites with graphite volume fraction follow the power law model of percolation theory. The percolation threshold of the composites is estimated to be 0.0257 (～ 5wt % of Gr). The current of PP‐Gr composites as a function of voltage shows a nearly ohmic behavior above the percolation threshold. Shore‐D hardness of the composites is decreased with the addition of conducting filler. The PP‐Gr composites exhibit a high dielectric constant and high dissipation factor with the addition of graphite in low frequency and radio frequency regions, so they can be used in the proposed applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dielectric properties and stress–strain measurements of chloroprene rubber based on different carbon black fillers

A systematic dielectric study of 1 kHz was carried out on chloroprene rubber, mixed with different types of carbon black and different concentrations. The measurements were carried out at room temperature (25°C). It was found that better dielectric properties cannot be achieved when the carbon black concentration exceeds 60% for MT, 40% for SRF, and 20% for both HAF and SAF. In addition, the relation between the dielectric constant ε and the modulus of elasticity E for the different mixes were studied. From this study it was found that, up to certain carbon black volume concentration (depending on the filler type), the modulus equation E_f = E₀ (1 + 0.67φC + 1.62φ²) can be used to relate the dielectric properties ε_f and ε_o of carbon black filled and unfilled rubber compounds. The dielectric measurements were also related to the particle size and the structure of carbon black.     

Influence of carbon‐based nanofillers on the electrical and dielectric properties of ethylene vinyl acetate nanocomposites

A comparative study of ethylene vinyl acetate nanocomposites based on expanded graphite, multiwalled carbon nanotubes, and carbon nanofibers has been carried out to investigate the effect of different carbon nanofillers on the electrical properties of the corresponding composites. The composites were prepared by ultrasonic dispersion of fillers in ethylene vinyl acetate solution, followed by casting and compression molding. The dependence of AC conductivity and dielectric constant on the frequency and filler concentration was investigated. Carbon nanofibers provided maximum conductivity as well as lowest percolation threshold (8.2 vol%) compared to expanded graphite and multiwalled carbon nanotubes filled composites. The improvement in both electrical conductivity and dielectric constant was attributed to the high filler aspect ratio and the formation of conducting networks. The relationship of dielectric constant with filler volume fraction for all the composite systems is estimated using a power law. The pressure sensing capability of the composites at respective percolation thresholds was also compared. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Electrical properties of nanostructured interpenetrating polymer networks based on natural rubber (NR)/polystyrene (PS)

The electrical properties of nanostructured sequential interpenetrating polymer networks from natural rubber (NR) and polystyrene (PS) have been studied in the frequency range of 10²–10⁷ Hz. The permittivity, volume resistivity, dielectric loss factor, and dissipation factor were analyzed as a function of frequency, blend composition, crosslinking level, and initiating system. It was found that the volume resistivity and dissipation factor first increase, reach a maximum around 10³–10⁵ Hz, and then decrease gradually with the increase of frequency. As the NR content is increased from 30 to 70%, the dissipation factor (tan δ) increases. On increasing the extent of the PS phase crosslinking, the permittivity increases. However, at higher levels of PS crosslinking, the permittivity values decrease due to the agglomeration of PS phase arising from excessive crosslinking. The morphology studies using a scanning electron microscope confirmed the agglomeration of PS phase at high crosslinking level. The permittivity values are maximum at 4% of crosslinking content. The influence of initiating system on the dielectric properties was not very significant. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2017–2026, 2005     

Electric properties of carbon black–epoxy resin composites at microwave frequencies

This present paper is a study of the dielectric behavior of carbon black–epoxy resin composites at the microwave frequencies 9.5 and 35 GHz. The results of this research have shown that the complex propagation constant γ_g for these mediums depends on the frequency F, on the volume concentration ϕ of the conducting medium, and on the particle size. Numerical simulations allow us to fit the dependence of the measures upon the sample thickness, but we have to assign dielectric and diamagnetic properties of the heterogeneous medium. The permittivity and the permeability depend on the particle concentration, and the real part of the permeability is always smaller than unity. © 1996 John Wiley & Sons, Inc.     

Optimal compositions of molded phenolic resins and its properties

Phenolic resins [commercial (CP), pure (PP), and woodflour-filled (WP)] containing different levels of hexamine, were evaluated in terms of curing behavior as well as thermal, electrical, and mechanical properties. The degree and rate of curing increase markedly with the rise of the hexamine content; however, the dielectric constant, dielectric loss, and dissipation factor decrease gradually. Dielectrical values decrease with the increase of the applied frequency. When the ratios of hexamine to phenolics are increased, samples become harder and experience increased molding shrinkage. With the increase of molding time or temperature, the surface hardness and molding shrinkage improve. The optimal hexamine contents of WP and PP are determined with respect to the above properties.     

Studies on Epdm/Nr Blends. I. Dielectric and Mechanical Properties

Ethylene-propylene-diene terpolymer rubberlnatural rubber blends (EPDM/NR) in different proportions (100 : 0, 75 : 25, 50 : 50, 25 : 75, and 0 : 100) reinforced with 20 phr semireinforcing furnace carbon black have been studied. The permittivity ?' and dielectric loss ?″ for these samples were determined in the frequency range 10²–10⁷ Hz. Also, their physico-mechanical properties were investigated.

The EPDM/NR blend (75 : 25) possessed the best mechanical properties and stability against aging. Thus, it was chosen to explore the effect of adding carbon black in different quantities up to 50 phr on its electrical and mechanical properties. Three different types of carbon black. namely high-abrasion furnace black, fast-extrusion furnace black, and medium thermal black, were used. At a certain concentration of carbon black, referred to as the threshold percolation concentration, an abrupt increase in ?′ and ?″, which depends on its type, was detected. This could be attributed to some sort of interaction between the blend and the carbon black at higher concentrations.     

The electrical conductivity of polypropylene and nickel-coated carbon fiber composite

The effect of filler content, temperature, and frequency of the applied electric field on DC and AC electrical conductivities of composites of nickel-coated carbon fibers and polypropylene are considered. The impedance behavior and the dielectric properties of these composites were studied in the low frequency range 10 Hz–30 kHz. It was found that the volume electrical resistivity shows filler content and temperature dependence. The calculated activation energy of the thermal rate-process decreases with the filler concentration, while the shielding effectiveness increases. The overall observed permittivity of the composites increases with the filler concentration, and the dielectric behavior is discussed in terms of the space charge, electronic and interfacial polarization within the covered frequency range. It was observed that the AC conductivity is nearly independent of the frequency below 100 Hz and increases with frequency above this range. Finally, it was concluded that addition of nickel-coated carbon fibers could alter the electrical conduction mechanism and the polarization process of the polymeric matrix.     

Thermal and dielectric behavior of flexible polycarbonate/lead zirconate titanate composite system

Polycarbonate (PC)/Lead Zirconate Titanate (PZT) composites were prepared using solution mixing method followed by hot pressing. The volume fraction of PZT particles was varied from 0 to 27.5%. SEM showed good dispersion of PZT in the PC matrix. XRD confirmed the perovskite structure of PZT and amorphous structure of polycarbonate. The dielectric constant of the composites measured at 1 kHz, increased ～3.5‐fold compared with pure PC. The modified Lichtenecker equation agreed well with the experimental data. There was no dispersion in the dielectric constant of the composites for the frequency range of 1 kHz to 10 MHz. However, at frequencies higher than 10 MHz significant drop in dielectric constant was observed. The dissipation factor of the composites was found below 0.02. However, above 1 MHz, an abrupt increment in the dissipation factor was observed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39913.