Electrical properties of carbon black filled crosslinked polyethylene

The electrical resistivity of peroxide and radiation crosslinked polyethylene/carbon black compounds was studied as a function of black concentration and, temperature in heating/cooling cycles. Different carbon blacks in compounds with polyethylene responded differently, regarding electrical resistivity, to the effect of crosslinking. In one case (fine black) the resistivity and PTC (positive temperature coefficient) effect did not significantly change, whereas in another case (coarse black) the effect of crosslinking-was to significantly increase the resistivity and reduce the PTC effect. The main advantages of crosslinking were to give compounds having good electrical reproducibility and to practically eliminate the NTC (negative temperature coefficient) effect in compounds containing fine, coarse, or mixtures of carbon blacks. Crosslinked compounds containing mixtures of carbon blacks have shown good conductivity, electrical reproducibility, and switching properties.     

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     

Effect of carbon black structure on low‐strain conductivity of polypropylene and low‐density polyethylene composites

The influences of carbon black (CB) structure on the percolation threshold, mechanical properties, and strain‐resistivity response of polymer composites are studied. Low‐density polyethylene (LDPE) and polypropylene (PP) samples were blended with five different types of CB differing in structure. Relatively low strains were studied; the maximum strain was 10%. It was found that the CB concentration for maximum strain‐sensitivity of the electrical conductivity is higher for low structure carbon blacks but is essentially independent of the CB structure for medium‐ to high‐structure carbon blacks. However, the composite containing the largest particle size carbon black clearly showed the highest strain‐sensitivity to electrical conduction. The mechanical properties and sensitivity of electrical resistivity to tensile strain of the filled composites examined in the study are also presented and discussed. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Electrothermal study of carbon loaded ethylene-vinylacetate copolymer

Temperature dependence of resistance of carbon black loaded ethylene-vinylacetate (EVA) copolymer was studied from ?100 to 250°C in a modified differential scanning calorimeter (DSC) apparatus. Both room temperature resistivity and positive temperature coefficient of resistance (PTC) effects can be correlated with carbon black parameters (structure, surface area, porosity). Room temperature resistivity and the degree of increase of resistivity, (ratio of maximum to minimum) progressively decrease with carbon black structure if occlusion of polymer by carbon black is considered in calculating the volume fraction. An integrated surface areastructure-porosity equivalence of the carbon black is derived by introducing factors proportional to the volume and porosity of the black used. Any black parameter that increases conductivity (loading, surface area, structure, porosity) decreases the PTC effect. A cable compounder can therefore minimize the undesirable impact of PTC by suitable choice of black-parameters. The necessary considerations for other uses, where PTC effect is used for microswitches, heaters, etc., will be just the opposite. The modified DSC method provides a quick scanning tool for determining the suitability of semicrystalline polymer recipes, either for cable or for any other material using the PTC effect.     

Effect of concentration and temperature on the electrical conductivity of butyl rubber loaded with different types of carbon black

In this study we are interested in the effect of concentration and temperature on the electrical resistivity of butyl rubber (IIR) loaded with two types of carbon black, (namely, high abrasion furnace black (HAF), and fast extrusion furnace black (FEF)). It was found that the conductivity at low carbon black concentrations is mainly achieved by thermal activation of carriers. Tunneling mechanism at low termperature followed by thermal activation at relatively high temperature is found to be predominant for moderate concentrations for both carbon blacks. The metal-like behaviour which was observed in highly loaded compounds was attributed to both, the thermal expansion of the tunneling paths between carbon-carbon agglomerates and the breakdown of carbon agglomerates with temperature.     

Influence of dispersing additives on the conductivity of carbon black pigment dispersion

The influence of dispersing additives on the electrical conductivity of carbon black pigments dispersed in an organic medium was studied. Two dispersing additives were examined in combination with two different carbon blacks, a conductive carbon black and a nonconductive one. These carbon blacks differ in the size of their aggregates and in the amounts of surface oxygen groups. Both of the additives form a monolayer when adsorbed on either of the pigment surfaces. FTIR studies showed that chemical bonding of one of the additives on the surfaces of both pigments had occurred. Conductivity decreases with increasing additive concentration, but in the case of the chemically bonded additive, the conductivity of the dispersion remained high even at higher additive loadings. This study helps in understanding the effects such additives have on the specific conductivity of composite materials that contain dispersed carbon black pigment particles.     

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     

Thermal aging of carbon black filled rubber compounds. I. Experimental evidence for bridging flocculation

An extensive work was performed to analyze how and why electrical properties of carbon black filled rubber compounds change during thermal aging. Several compounds were prepared using different polymer matrices and a broad range of carbon black types. Electrical resistivity of cured and uncured samples was measured, under different conditions, during thermal aging at constant temperature. Other experimental techniques, like transmission electron microscopy, bound rubber measurements and gamma irradiation were also used. Contrary to previous works, it was found that the changes of the electrical resistivity might be explained without any movement of carbon black aggregates during aging. Additionally, a new dependence of the variation of electrical resistivity with carbon black loading is reported and analyzed. This dependence could be the source of the contradictory data and conclusions in previous works. A correlation between the increment of electrical conductivity and the increment of bound rubber during thermal aging was found. This fact suggests that polymer chains and polymer-filler interaction are responsible for the changes during thermal aging instead of aggregate movement.     

Properties and thermo-switch behaviour of LDPE mixed with carbon black,zinc metal and paraffin wax

This paper reports on the presence of wax and radiation-induced crosslinking on the morphology, thermal and mechanical properties, as well as electrical conductivity and thermo-switch properties of LDPE containing different amounts of carbon black (CB) or carbon black plus zinc metal as filler. Although the filler was generally well dispersed in the polymer or polymer/wax blend, there were clear indications of the formation of conductive pathways. Different combinations of polymer, wax, CB and zinc filler and radiation induced crosslinking gave rise to different extents of crystallinity and/or chain immobilization, which had an influence on the mechanical and thermo-mechanical properties, and on the electrical conductivity and thermo-switch behaviour. Most importantly, the presence of wax, and CB and CB/Zn fillers, gave rise to increased electrical conductivity. The thermal expansion in the composites did not seem to play a significant role in obtaining larger values of the positive temperature coefficient of resistivity (PTC). We found that the presence of a small amount of paraffin wax significantly increased the PTC coefficients of the LDPE based conductive composites, and that γ-radiation induced crosslinking provided the thermo-mechanical stability of the amorphous regions in LDPE needed to obtain a high PTC intensity, which would provide a cheap material with good thermo-switch functionality, which is something not observed before.     

Investigation of multi‐walled carbon nanotube‐reinforced high‐density polyethylene/carbon black nanocomposites using electrical,DSC and positron lifetime spectroscopy techniques

BACKGROUND: The positive temperature coefficient (PTC) effect on material properties has attracted much attention in recent years due to the prospects of many applications like temperature sensors, thermistors, self‐regulating heaters, etc. It has been suggested that incorporation of multi‐walled carbon nanotubes (MWNTs) into carbon black (CB)‐filled polymers could improve the electrical properties of composites due to high conductivity and network structure and significantly reduce the required CB loading. RESULTS: We observed no change in melting temperature and crystalline transition temperature on addition of MWNTs. However, the heat of fusion decreases as the amount of conducting carboxylated MWNT (c‐MWNT) filler increases and the resistivity of the composite decreases. The free volume shows an increase up to 1.5 wt% of c‐MWNT content and then decreases. CONCLUSION: Well‐developed crystals could not be formed due to restricted chain mobility as filler content increases. This results in minimum intermolecular interactions, and thus a decreased heat of fusion. A composite with c‐MWNT content of 0.5 wt% showed the highest PTC and higher resistivity at 150 °C possibly due to the formation of flocculated structures at elevated temperature. For filler content greater than 1.5 wt%, the decrease in free volume may be due to restricted chain mobility. Copyright © 2009 Society of Chemical Industry     

The relationship of carbon black dispersion to electrical resistivity and vulcanizate physical properties

The degree of dispersion of carbon black in rubber is known to be a determining factor in the physical properties of the composite. It is important, therefore, to have a reliable, quantitative technique for assessing carbon black dispersion. It has been known for some time that the degree of dispersion of carbon black is reflected in its electrical resistivity. A resistivity instrument, developed by B. Boonstra, has been redesigned and constructed for use in this study. Factors that influence resistivity (i.e., black type, volume loading, and mixing time) are examined. Physical property and dynamic mechanical measurements are made, and their relationship to black dispersion is investigated. Light microscopy is also used to evaluate dispersion, and these data are compared to the resistivity results.     

Electrical and thermal conductivity and tensile and flexural properties: Comparison of carbon black/polycarbonate and carbon nanotube/polycarbonate resins

Adding conductive carbon fillers to thermoplastic polymers increases the resulting composite's electrical conductivity. Carbon black (CB) is very effective at increasing composite electrical conductivity at low loading levels. In this study, varying amounts (2 to 10 wt %) CB were added to polycarbonate (PC) and the resulting composites were tested for electrical conductivity (1/electrical resistivity), thermal conductivity, and tensile and flexural properties. These results were compared with prior work done for carbon nanotubes (CNT) in polycarbonate. The percolation threshold was ～ 2.3 vol % CB compared to between 0.7 and 1.4 vol % CNT. At 8 wt % filler, the CNT/PC composite had an electrical resistivity of 8 ohm‐cm compared to 122 ohm‐cm for the CB/PC composite. The addition of CB to polycarbonate increased the composite electrical and thermal conductivity and tensile and flexural modulus. The 8 wt % (5.5 vol %) CB in polycarbonate composite had a good combination of properties for semiconductive applications. Ductile tensile behavior is noted in pure polycarbonate and in samples containing up to 8 wt % CB. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

CO2处理对N990炭黑及其复合材料电性能的影响

以高温(工沁处理的改性N990炭黑与PE-H。熔融混合制备正温度系数(PTC)电阻(率)复合材料。采用氮气吸附比表面积、扫描电镜和X射线光电子能谱表征处理炭黑的结构,研究G毛处理对N990炭黑的结构和导电性及其复合材料PTC特性的影响。结果表明,C姚处理后的N990炭黑内部结构基本不变,导电率可增加1倍以上,比表面积增加4倍以上,表面10--30人孔径的孔容增加6倍以上,表面的氧元素含量下降36.6%。以无处理PE-HD/N990炭黑复合材料的电阻率比未处理的下降了0.6-3个数量级,PTC强度下降了0-60.1%,但适当选择处理的N990炭黑含量的复合材料同时具有低的室温电阻率和较高的PTC强度。     

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     

Temperature dependence of electrical resistivity for carbon black filled ultra-high molecular weight polyethylene composites prepared by hot compaction

In this article, the temperature dependence of electrical resistivity is studied for carbon black (CB)/ultra-high molecular weight polyethylene (UHMWPE) composites. A new positive temperature coefficient (PTC) material with a very low percolation threshold is produced by the hot compaction method. The very low percolation threshold can be attributed to the segregation of CB in the interfacial regions of UHMWPE particles. The percolation threshold decreases with the increase of the molecular weight of UHMWPE, and with the decrease of the particle size of CB. For CB filled lower molecular weight UHMWPE (145M) composites, the PTC temperature, at which a sharp increase in the resistivity of the composite occurs, decreases with the increase of CB size. However, for a higher molecular weight UHMWPE (630M) filled with CB, the second PTC effect is observed and the negative temperature coefficient (NTC) effect is eliminated. A mechanism is proposed to explain these phenomena based on the optical microscopy and TEM observations. It can be concluded that the degree of the intermixing between CB and UHMWPE particles plays an important role in determining the electrical properties of the composites.     

Acronitrile butadiene styrene/polycaprolactam/nano carbon black composites: Selective percolation,glass transition and temperature dependence of electrical conductivity

Preferential percolation is a promising strategy to develop conducting composites at lower loading of conducting filler; however, little information is available on temperature dependence of conductivity of such composites. This study reports synthesis and positive temperature coefficient (PTC) behavior of a novel multiphase polymer composite in which conducting filler preferentially percolates in a composite containing two incompatible polymers, both having glass transition in the temperature range of study. High electrical conductivity and good mechanical behavior was demonstrated by acrylonitrile butadiene styrene (ABS)/polycaprolactam (PCL)/nano carbon black (NCB) composites, which was dependent on blend composition as well as on the extent of NCB loading. PTC intensity was considerably less for ternary composites than it was for binary ABS/NCB or PCL/NCB composites. Theoretical analysis of the dispersion state of NCB in this phase separated system revealed preferential distribution of NCB at the interfacial region. PTC effect was also found to decrease significantly with increase in NCB content. ABS/PCL/NCB (1:1:2) composites showed no significant temperature dependence (zero positive coefficients) up to 413 K while ABS/NCB 30 wt% NCB composites showed highest PTC. A sudden rise was observed in the glass transition region of polymers for all composites; however, the effect was less pronounced for ternary composites. POLYM. COMPOS., 37:481–487, 2016. © 2014 Society of Plastics Engineers     

Electrical properties of carbon black filled polyethylene

Resistivity and dielectric constant of polyethylene/carbon black compounds were measured from room temperature to 140°C. Within the polyethylene melting region a PTC/NTC (positive followed by negative temperature coefficients) phenomenon is observed, whose intensity depends on the type of carbon black, its concentration and other parameters. Reproducibility of the PTC phenomenon in polyethylene compounds containing a single type of carbon black is rather low. However, by using mixtures of carbon blacks differing appreciably in their particle size, remarkable reproducibility improvements can be achieved. Several other aspects are also discussed in the present paper covering current-voltage relationships in these materials, comparison of PTC curves with DSC thermograms upon heating and cooling, and dielectric constant-temperature relations. The carbon black concentration giving the optimum PTC intensity can be predicted approximately from room temperature data.     

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     

Influence of radiation structures on positive‐temperature‐coefficient and negative‐temperature‐coefficient effects of irradiated low‐density polyethylene/carbon black composites

The electrical‐resistivity/temperature behaviors of low‐density polyethylene (LDPE)/carbon black (CB) composites irradiated with ⁶⁰Co γ rays were studied. The experimental results showed that the irradiated composites could be separated into insoluble crosslinking networks with CB (gel) and soluble components (sol) by solvent‐extraction techniques. When the sol of an irradiated LDPE/CB composite was extracted, the electrical conductivity of the system increased. The positive‐temperature‐coefficient (PTC) and negative‐temperature‐coefficient (NTC) intensities of the gels of the irradiated composites became extremely small and independent of the radiation dose. The sols and gels of the irradiated LDPE/CB composites, which had different thermal behaviors, played important roles in the appearances of the PTC and NTC effects. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 700–704, 2005     

Studies on the electrical conductivity of carbon black filled polymers

The conductivity mechanism for a carbon black (CB) filled high-density polyethylene (HDPE) compound was investigated in this work. From the experimental results obtained, it can be seen that the relation between electrical current density (J) and applied voltage across the sample (V) coincides with Simmons's equation (i.e., the electrical resistivity of the compound decreases with the applied voltage, especially at the critical voltage). The minimum electrical resistivity occurs near the glass transition temperature (T_g) of HDPE (198 K). It can be concluded that electron tunneling is an important mechanism and a dominant transport process in the HDPE/CB composite. A new model of carbon black dispersion in the matrix was established, and the resistivity was calculated by using percolation and quantum mechanical theories. © 1996 John Wiley & Sons, Inc.