On the ‘curiosity’ of electrical self‐heating,static charge and electromagnetic shielding effectiveness from carbon black/aluminium flakes reinforced epoxy‐resin composites

This paper shows the wide application range (such as electrical self‐heating and electromagnetic shielding effectiveness) of composites consisting of conductive carbon black/aluminum flakes (CBA) filler and epoxy insulative matrix. The effect of CBA content on the network structure of epoxy matrix was investigated in detail. Static electrical conductivity increases linearly with the increase of filler concentration at the interface in epoxy composites. The large decrease of the conductivity as a function of the temperature is analyzed in terms of the negative temperature coefficient of conductivity (NTCC) effect. The influence of viscosity, surface energy and barrier highest energy on the NTCC behaviour in the composite is also considered. Based on these results, a new interpretation is proposed to explain the NTCC phenomena by computing the swelling force among conductive phases. The correlations of conductivity during the temperature cycling and activation energy were analyzed. The effects of dynamic ageing at various temperatures on the resistivity are reported. Current–voltage–temperature characteristics for epoxy with different contents of CBA were examined in detail. A model based on the law of energy conservation is proposed to calculate the specific heat and amount of heat dissipation. The static charge of the epoxy–CBA composites was estimated. The correlation between electromagnetic wave‐shielding effectiveness (EMS), conductivity and frequency of epoxy composites with different filler contents is also discussed. Furthermore, the effect of annealing on EMS of epoxy composites was examined. © 2002 Society of Chemical Industry     

导电炭黑及与沥青基碳纤维并用对NBR导电、导热性能的影响

研究了导电炭黑(VXC72)用量及与沥青基短切碳纤维(CF)并用对丁腈橡胶(NBR)的力学性能及导电、导热性能的影响;并用扫描电镜(SEM)观察填料的分散状态,同时考察了双辊开炼机对CF长径比的剪切破破坏程度。结果表明,随VXC72用量的增加,NBR/VXC72硫化胶的拉伸强度、撕裂强度和导热系数基本呈线性增加;体积电阻率呈阶梯形下降,逾渗阈值为25 phr。随VXC72/CF并用比的增大,NBR硫化胶的拉伸强度和撕裂强度明显降低,体积电阻率略有减小,而导热系数有一定程度的增加。填充20 phr CF时,NBR的导热系数较填充VXC72时提高了约30%。混炼使CF的长径比L/D剧烈降低,由原来的600降低到10-20,这也许是CF对NBR体积电阻率降低幅度不大的主要原因。     

Effect of some service conditions on the electrical resistivity of conductive styrene–butadiene rubber–carbon black composites

Conductive polymer composites were prepared using vulcanized styrene–butadiene rubber as a matrix and conductive carbon black as a filler. The filler loading was varied from 10 to 60 phr. The volume resistivity was measured against the loading of the carbon black to verify the percolation limit. The electrical conductivity of filled polymer composites is attributed to the formation of some continuous conductive networks in the polymer matrix. These conductive networks involve specific arrangements of conductive elements (carbon black aggregates) so that the electrical paths are formed for free movement of electrons. The effects of temperature and pressure on the volume resistivity of the composites were studied. The volume resistivity of all the composites increased with increase in temperature, and the rate of increase in the resistivity against temperature depended on the loading of carbon black. The change in volume resistivity during the heating and cooling cycle did not follow the same route, leading to the phenomena of electrical hysteresis and electrical set. It was found that the composites with 40 and 60 phr carbon black become more conductive after undergoing the heat treatment. Generally, all the composites showed a positive temperature coefficient of resistivity. The volume resistivity of all the composites decreased with increase in pressure. The relaxation characteristic of the volume resistivity of the composites was studied with respect to time under a constant load. It was found that the volume resistivity of the compressed specimen of the composites decreased exponentially with time. It was observed that initially a faster relaxation process and later a slower relaxation process occurred in these composites. Some mechanical properties of these composites were also measured to confirm the efficacy of these composites for practical applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2179–2188, 2004     

Thermal conductivity and electromagnetic shielding effectiveness of composites based on Ag‐plating carbon fiber and epoxy

Thermally conductive and electromagnetic interference shielding composites comprising low content of Ag‐plating carbon fiber (APCF) were fabricated as electronic packing materials. APCF as conductive filler consisting of carbon fiber (CF) employed as the structural component to reinforce the mechanical strength, and Ag enhancing electrical conductivity, was prepared by advanced electroless Ag‐plating processing on CF surfaces. Ag coating had a thickness of 450 nm without oxide phase detected. The incorporation of 4.5 wt % APCF into epoxy (EP) substrate yielded thermal conductivity of 2.33 W/m·K, which is approximately 2.6 times higher than CF–EP composite at the same loading. The APCF–EP composite performed electromagnetic shielding effectiveness of 38–35 dB at frequency ranging from 8.2 to 12.4 GHz in the X band, and electromagnetic reflection was the dominant shielding mechanism. At loading content of APCF up to 7 wt %, thermal conductivity of APCF–EP composites increased to 2.49 W/m·K. Volume resistivity and surface resistivity decreased to 9.5 × 10³ Ω·cm and 6.2 × 10² Ω, respectively, which approached a metal. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42306.     

Mechanical,Thermal and Electrical Resisitivity Properties of Thermoplastic Composites Filled with Carbon Fibers and Carbon Particles

Composites consisting of carbon fibers (CF) and carbon particles (CP) in polypropylene (PP) matrix were melt-compounded. Composites were analyzed for their mechanical, electrical and thermal properties. Results indicate that the addition of these fillers improved the mechanical properties of the composites. Thermal conductivity was enhanced as the concentration of fillers was increased. Carbon fibers render the composites electrically conductive so we observed a percolation threshold near 10 wt.% of CF for PP/CF (PP and CF composite) and near 25 wt.% of CP for PP/CP (PP and carbon particle composite). All the results indicated that carbon fibers are more effective in improving the properties as compare to the carbon particles.     

High performance thermoplastic composites: Study on the mechanical,thermal, and electrical resistivity properties of carbon fiber‐reinforced polyetheretherketone and polyethersulphone

High temperature processing thermoplastic polymers, polyetheretherketone (PEEK) and polyethersulphone (PES), were melt blended with carbon fibers (CFs) to make composites. These composites were investigated for their mechanical, thermal, and electrical properties. Mechanical properties that are expressed in terms of storage modulus, loss, and damping were enhanced with the addition of CFs. Thermal properties were determined by DSC and TGA. These methods help to understand the effects of fiber content and fiber–matrix adhesion in the composites. Composites were also tested for their electrical and thermal conductivity because CFs leave the composites thermally and electrically conductive. CFs enhanced the crystallinity of the PEEK appreciably that in turn influenced thermal conductivity, electrical resistivity, and the stiffness of PEEK/CF (composites of PEEK with CFs). PES/CF (composites of PES with CF) shows a different behavior due to the amorphous nature of PES. The work involves one filler and two different matrices, and so it provides an interesting comparison of how matrix morphology can influence the properties of composites. POLYM. COMPOS. 28:785–796, 2007. © 2007 Society of Plastics Engineers.     

Measurement of AC conductivity and dielectric properties of flexible conductive styrene–butadiene rubber‐carbon black composites

Flexible conductive polymer composites were prepared using styrene–butadiene rubber (SBR) as a matrix and conductive carbon black as filler. The filler loading was varied from 10 to 60 phr. The effect of frequency, filler loading, temperature, and applied pressure on the AC conductivity, permittivity, and loss factor of the composites was studied. The AC conductivity of low and high loaded composites was found to be frequency dependent and independent respectively. The permittivity and the loss factor were continuously decreasing with increasing frequency. The increase in filler loading increased the AC conductivity, dielectric constant, and loss factor of the composites. Increase in temperature imposed increase in conductivity and permittivity of the composites. With increasing applied pressure the properties showed exponential increase. The effect of time under a constant compressive stress was studied and dielectric relaxation times were evaluated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 986–995, 2007     

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.     

Nylon 6 induced morphological developments and electrical conductivity improvements of polypropylene/carbon black composites

In this study, a polar conductive filler [carbon black (CB)], a nonpolar polymer [polypropylene (PP)], and a polar polymer [nylon 6 (PA6)] were chosen to fabricate electrically conductive polymer composites by melt blending and compression molding. The morphological developments of these composites were studied. Scanning electron microscopy results showed that in a CB‐filled PP/PA6 (CPA) composite, CB particles were selectively dispersed in PA6 phases and could make the dispersed particles exist as microfiber particles, which could greatly improve the electrical conductivity. The PA6 and CB contents both could affect the morphologies of these composites. The results of electrical resistivity measurements of these composites proved the formation of conductive networks. The resistivity–temperature behaviors of these composites were also studied. For CB‐filled PP (CP) composites, there were apparent positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects and an unrepeatable resistivity–temperature characteristic. However, for CPA composites, there were no PTC or NTC effects from room temperature to 180°C, and the resistivity–temperature behavior showed a repeatable characteristic; this proved that CB particles were selectively dispersed in the PA6 phase from another point of view. All experimental results indicated that the addition of PA6 to a CP composite could lead to an expected morphological structure and improve the electrical conductivity of the CP composite. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of adding carbon fiber on conductive stability of acrylonitrile‐butadiene rubber composites

In this work, the conductive composites of acrylonitrile‐butadiene rubber (NBR) and conductive carbon black (CCB) were prepared. The volume resistivity of NBR/CCB composites became stable when the addition content of CCB reached 12 wt %. However, when carbon fiber (CF) was added into the composites, the volume resistivity of NBR/CCB/CF composites continued to decrease with the increase of CF addition, which resulted from the formation of the three‐dimensional conductive network in composite matrix. In addition, the effect of acid oxidation of CF surface on the mechanical proprieties and conductive stability of NBR/CCB/CF composites was studied. The results indicated the acid oxidation of CF surface improved the bond structure between NBR and CF, which further decreased the resistance and significantly improved the mechanical properties of the composites. It was demonstrated that the conductive stability of NBR composites after cyclic mechanical and temperature fatigues was remarkably enhanced with the addition of CF. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46668.     

Improved stability of volume resistivity in carbon black/ethylene-vinyl acetate copolymer composites by employing multi-walled carbon nanotubes as second filler

Semiconductive polymer shielding layers of power cable require stable volume resistivity to protect the insulation layer from stress enhancements when carbon black (CB)/polymer composite undergoes thermal cycles. For the CB-filled polymer composites, CB would often re-aggregate when temperature is close to the melting point of polymer matrix, so that the conductive network would be destroyed. Re-distribution of CB and re-formation of conductive CB network under thermal cycles might be the main reason for the instability of volume resistivity. In this work, the re-aggregation of CB in the CB/polymer composites was disclosed. Besides, a small amount of multi-walled carbon nanotubes (MWNTs) was employed as cofiller with CB to improve the stability of volume resistivity of the polymer composites under thermal cycles. The total weight fraction of conductive fillers (CB or CB cofilled with MWNTs) was set as 35 wt%. Compared with the polymer composites loaded with CB solely, the volume resistivity of the composites filled with CB-MWNTs was much more stable with changing temperature. This can be attributed to the enhancement of conductive networks when the MWNTs are employed as second conductive filler.     

聚合物基导热复合材料的性能及导热机理

采用不同品种、粒径的导热填料和基体树脂,以熔融共混方法制备聚合物/填料体系导热功能复合材料。研究了复合材料热导率λ和体积电阻率ρ_v随不同填料、粒径等因素的变化规律及其内在原因。不同填充体系的热导率均随填料粒径的减小而降低,而电导率则相反;复合体系热导率随填料含量的增加始终呈逐步上升趋势,未表现出电导率那样的急剧变化。研究表明：复合体系热导率和电导率变化的差异主要是由于二者具有不同的传导机理;复合材料热导率的变化规律可以用热弹性复合增强机制进行合理解释。     

2种导电炭黑复合橡胶体系的导热性能研究

研究了2种导电炭黑复合天然橡胶材料的导热性能随着温度和填料用量的变化规律。结果表明,温度对于导电炭黑复合体系导热性能的影响不大。乙炔黑复合体系具有极高的导热性能,随着炭黑用量的增加,其导热性能优势越加明显。据透射电镜观察填料的微观形态,乙炔黑链枝状结构丰富,聚集体之间以面接触为主,这是其复合橡胶导热性能优异的原因,乙炔黑复合材料的热导率与炭黑体积分数呈线性关系。40B2复合体系的热导率与炭黑体积分数呈现逾渗规律,逾渗阈值在炭黑体积分数8.30%至13.63%之间。据扫描电镜观察复合材料的微观结构,逾渗现象与炭黑在基体内的分布密切相关。为更精确地描述填料用量与复合体系热导率的关系,对2种复合体系的热导率与炭黑的体积分数进行了回归。     

Effect of temperature,pressure, and composition on DC resistivity and AC conductivity of conductive styrene–butadiene rubber–particulate metal alloy nanocomposites

Conductive nanocomposites were prepared using styrene butadiene rubber as the polymer matrix and nanosized powder of copper–nickel (Cu–Ni) alloy as the filler. The filler loading was varied from 0 to 40 phr. The electrical conductivity of filled polymer composites is due to the formation of some continuous conductive networks in the polymer matrix. Atomic force microscopy was used to determine the particle size of the nanofiller and its nature of dispersion in the rubber matrix. The DC volume resistivity was measured against the loading of the nanofiller to check the percolation limit. The effect of temperature, applied pressure, time duration under constant compressive stress on the DC resistivity and AC conductivity of the composites with different filler loading were investigated. The change in DC resistivity and AC conductivity against temperature of these composites exhibited positive coefficient of temperature. With the change in applied pressure and time duration under constant compressive stress the DC resistivity undergoes an exponential decrease. The effect of AC field frequency on the AC conductivity was investigated. POLYM. COMPOS. 28:696–704, 2007. © 2007 Society of Plastics Engineers     

High electrical conductivity of nylon 6 composites obtained with hybrid multiwalled carbon nanotube/carbon fiber fillers

The synergetic effect of multiwalled carbon nanotubes (MWNTs) and carbon fibers (CFs) in enhancing the electrical conductivity of nylon 6 (PA6) composites was investigated. To improve the compatibility between the fillers and the PA6 resin, we grafted γ‐aminopropyltriethoxy silane (KH‐550) onto the MWNTs and CFs after carboxyl groups were generated on their surface by chemical oxidation with nitric acid. Fourier transform infrared spectroscopy and thermogravimetric analysis proved that the KH‐550 molecules were successfully grafted onto the surface of the MWNTs and CFs. Scanning electron microscopy and optical microscopy showed that the obtained modified fillers reduced the aggregation of fillers and resulted in better dispersion and interfacial compatibility. We found that the electrical percolation threshold of the MWNT/PA6 and CF/PA6 composites occurred when the volume fraction of the fillers were 4 and 5%, respectively. The MWNT/CF hybrid‐filler system exhibited a remarkable synergetic effect on the electrically conductive networks. The MWNT/7% CF hybrid‐filler system appeared to show a second percolation when the MWNT volume fraction was above 4% and a volume resistivity reduction of two orders of magnitude compared with the MWNT/PA6 system. The mechanical properties of different types of PA6 composites with variation in the filler volume content were also studied. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40923.     

Conductive rubbers made by adding conductive carbon black to EVA,EPDM, and EVA–EPDM blends

Abstract

Electrically conductive rubbers have been prepared by the incorporation of conductive carbon black into ethylene/vinyl acetate (EVA) copolymers, ethylene/propylene/diene monomer (EPDM) terpolymers, and a 50 : 50 EVA–EPDM blend. The electrical and mechanical properties of these composites have been studied. The percolation limit for high conductivity in the filled rubbers depends on their compatibility as well as the viscosity and polarity of the rubbers. The electrical resistivity decreases with increasing temperature and the activation energy for conduction decreases with increasing filler loading. The temperature dependence of resistivity can be correlated with data from DSC, XRD, and DMTA measurements. Electrical set and electrical hysteresis have been observed during heating–cooling cycles. The change in resistivity with applied pressure is also reported.     

Improvement of thermo-electrical properties of polymer composites filled with multiwall carbon nanotubes decorated carbon fillers

To enhance the thermo-electrical properties of liquid silicone rubber (LSR) in applications, the carbon fibres (CFs) modified by multiwall carbon nanotubes (MWCNT) on the surfaces were used as the fillers. The MWCNT-modified CFs (MPCFs) were analysed by Fourier transform infrared spectra, thermogravimetric analysis, scanning electron micrograph and energy dispersive X-ray spectroscopy. It was found that MWCNT were successfully adsorbed onto the surface of CFs. The MPCFs functioned as conductive fillers in LSR for thermal and electrical conductivity application and exhibited significant enhancement. The effects of MPCFs loading on thermal conductivity and volume resistivity of LSR composites were investigated in detail. Results of this work revealed that the MPCFs/LSR composites possessed a thermal conductivity of 0.73?W?m^?1?K^?1 with 14?vol.-% filler loading, approximately 3.48-fold higher than that of pure LSR substrate. And with the increase of MPCFs loading, the least volume resistivity of MPCFs/LSR composites is 10?Ω?cm. Besides, compared with that of neat LSR, the tensile strength of MPCFs/LSR composites increased 0.913?MPa.     

Effect of axial stretching on electrical resistivity of short carbon fibre and carbon black filled conductive rubber composites

The variation of electrical resistivity of carbon black and short carbon fibre (SCF) filled rubber composites was studied against the degree of strain at constant strain rate. It was found that both the degree of strain and strain rate affect the electrical resistivity of the composites. The change in resistivity against the strain and strain rate depends both on the concentration and the type of conductive filler. The incorporation of short carbon fibres (SCF) imparts higher conductivity to the composite than carbon black at the same level of loading. Composites filled with carbon black exhibit better mechanical properties than SCF filled composites. Electrical setting, ie a permanent change in electrical resistivity, was observed during extension–retraction cycles. A good correlation was found between the mechanical response and the electrical response towards strain sensitivity. The results of different experiments are discussed in the light of breakdown and formation of conductive networks in the filled rubber composites. © 2002 Society of Chemical Industry     

Effects of carbon fillers on the rheology of highly filled liquid‐crystal polymer based resins

Adding conductive carbon fillers to insulating resins increases the composite electrical and thermal conductivity. Often, enough of a single type of carbon filler is added to achieve the desired conductivity while still allowing the material to be molded into a bipolar plate for a fuel cell. In this study, various amounts of three different carbons (carbon black, synthetic graphite particles, and carbon fiber) were added to Vectra A950RX liquid‐crystal polymer. The rheological properties of the resulting single‐filler composites were measured. In addition, the rheological properties of composites containing combinations of different carbon fillers were studied via a factorial design. In all cases, the viscosity increased with increasing filler volume fraction and followed a shear‐thinning power‐law model. The factorial design results indicated that each of the single fillers and all the filler combinations caused a statistically significant increase in the composite viscosity when compared at a shear rate of 500 s^?1 or at a stress of 10⁵ Pa. For composites containing synthetic graphite particles and/or carbon fiber, the viscosity variation with the volume fraction of carbon followed a modified Maron–Pierce equation. When compared at a constant volume fraction of carbon, composites containing carbon black showed viscosity enhancement above and beyond that shown by the other composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Correlated electrical conductivity and mechanical property analysis of high-density polyethylene filled with graphite and carbon fiber

The development of conductive polymer composites remains an important endeavor in light of growing energy concerns. In the present work, graphite (G), carbon fiber (CF) and G/CF mixtures are added to high-density polyethylene (HDPE) to discern if mixed fillers afford appreciable advantages over single fillers. The effects of filler type and composition on electrical conductivity, composite morphology and mechanical properties have been examined and correlated to establish structure-property relationships. The threshold loading levels required for G and CF to achieve measurable conductivity in HDPE have been identified. Addition of CF to HDPE/G composites is found to increase the conductivity relative to that of HDPE/G composites at the same filler concentration. This observed increase depends on CF length and becomes more pronounced at and beyond the threshold loading of the HDPE/G composite. Scanning electron microscopy is employed to elucidate the morphology of these multicomponent composites, whereas dynamic mechanical analysis reveals that filler concentration, composition and CF length impact both the magnitude and temperature dependence of the dynamic storage modulus.