Conductive Carbon Black Research Articles

Neoalkoxy Titanate and Zirconate Coupling Agent Additives in Thermoplastics

Ti or Zr coupling agents chemically bridge two dissimilar species such as an inorganic filler/particulate and organic polymer via proton coordination on non-silane reactive substrates such as CaCO3 and carbon black without the need of water of condensation as with silanes. Minor amounts of thermally stable neoalkoxy titanate and zirconate additives provide a means for post reactor, in-situ metallocene-like repolymerization catalysis of a filled or unfilled polymer during the plastication phase resulting in: significantly faster thermoplastic processing at lower temperatures; lower polymer recrystallization time; and the copolymerization of dissimilar polymers. Examples: both 40% CaCO3 filled and unfilled PP compounds experienced respective reductions of 35.5% and 42% in injection mold cycle time and 22% and 11% in process temperature; 17% “pyrophosphato titanate coupled conductive carbon black (CB)” in LDPE provides the same Positive Temperature Coefficient effect as 25% untreated CB; a 39.7% reduction in the recrystallization time of PPS; a ten-fold increase in the elongation of a PET/PC regrind alloy; and the regeneration of recycled blends of LDPE and PP regrinds. The catalysis effect is shown to be permanent and recyclable. Coupling agent liquid, powder and pellet forms; dosage; data and applications methodology in compounding, injection and blow molding are discussed. New and novel transparent and permanent antistatic agents based on the formation of bipolar layers of dissimilar trineoalkoxy zirconates are shown to be non-blooming, non-moisture dependent providing volume as well as surface ESD effects.

Electrical Conductivity of High Impact Polystyrene/Liquid Crystalline Polymer/ Carbon Black Ternary Systems

AbstractElectrically conductive immiscible polymer blends containing high impact polystyrene (HIPS), liquid crystalline polymer (LCP) and a low content of conductive carbon black (CB) were studied to establish and understand the correlation between composition, electrical properties and the morphology of filaments produced at different melt flow conditions. The HIPS/LCP/CB blend containing 30% LCP and at least 2 phr CB reveals a stable resisitivity throughout the shear rate range applied in a capillary rheometer. Interesting structure alterations were observed for the LCP and CB components as a result of melt flow processing. Unusual sensing properties of liquids were found for the blends containing LCP.

Specific Conductive Carbon Blacks in Plastics Applications

New developments in knowledge of conductive carbon blacks and their conduction mechanisms have led to new plastics compounds. Conductive carbon blacks enable us to make polymers conductive at a ‘low’ or ‘very low’ loading, leading to better mechanical property retention. The ‘in-mixture’ dispersion and the resulting ultimate dispersion quality also influence the final properties. This study shows the impact of conductive carbon blacks (high structure, low and high surface area) on plastics performance, and especially on electrical properties. Some guidelines for compounding are also covered. This understanding gives rise to new applications and provides the tool to select the most appropriate carbon black to fit the application demand.

Radiation Grafting of Polyethylene onto Conductive Carbon Black and Application as a Novel Gas Sensor

Radiation grafting of polyethylene (PE) onto carbon black was carried out by γ-ray irradiation of PE-adsorbed carbon black. The percentage of PE grafting and decomposition temperature of PE grafted onto the surface were determined by thermogravimetric analysis. At low irradiation temperature, the percentage of grafting was very small in spite of higher irradiation dose. On the contrary, at high temperatures near or above the melting point of PE, the grafting of PE onto the carbon black surface proceeded and the percentage of grafting exceeded 90% when the irradiation dose reached to 200 kGy. The results indicate that the adsorbed PE was completely grafted onto the carbon black surface. The decomposition temperature of the grafted PE on the surface was higher than both free (unadsorbed) PE and adsorbed PE on the carbon black surface, indicating that there is a covalent bond between the carbon black and PE molecule. Using the PE-grafted carbon black and PE, conductive PE/PE-grafted carbon black composite was prepared. Electric resistance suddenly increased in cyclohexane vapor over 104 times, and returned to initial resistance when transferred to air, indicating that the composite can be used as a novel gas sensor.

Electrical conductivity of thermal carbon blacks: Influence of surface chemistry

The electrical conductivity of thermal and conductive carbon blacks with different chemistry was determined by impedance spectroscopy. Thermal blacks are suitable compounds for studying the influence of the chemistry on the conductivity since they have similar structures and surface areas, which strongly influence the conductivity. The conductivity was related to the carbon chemistry characterised by surface spectroscopic methods (ESCA and SIMS) and Raman spectroscopy, respectively. In general, the conductivity increases with decreasing concentration of surface oxygen and sulphur functional groups. However, different conductivities were observed for some samples with similar concentration of surface oxygen and sulphur functional groups. The conductivity correlated best with the polyaromatic character of the carbon black surface characterised by the C 2H −/C 2 − peak ratio of the static SIMS spectra. The surface probed by SIMS is more important for the conductivity than the surface-near region probed by the asymmetry of the ESCA carbon peak. No correlation between the carbon black electrical conductivity and the carbon black bulk structure studied by Raman spectroscopy was found.

Rheo-dielectric Behavior of Carbon Black Suspensions.

Rheo-dielectric behavior was examined for suspensions of two types of carbon black (CB) particles in varnish. For one type of CB particles having plain carbon surfaces, an agglomerated network was fully developed to exhibit low-frequency elasticity (under small strains) and high electrical conductance. This conductance decreased significantly under flow, reflecting flow-induced rupture of the network structure. This rheo-dielectric change well corresponded to the pseudo-plastic, non-Newtonian behavior of the viscosity η. In contrast, for the other type of CB particles having oxidized carbon surface, only fragmented aggregates were formed. Correspondingly, this CB exhibited just moderate rheo-dielectric changes and weak nonlinearities in its η. These results demonstrated the usefulness of the rheo-dielectric method for detecting the connectivity of the network composed of conductive CB particles.

Electrically conductive thermosetting resins containing low concentrations of carbon black

A cured vinyl ester resin containing electrically conductive carbon black (CB) particles shows electrical percolation at very low CB concentration (<0.5 phr). CB particles have a strong tendency to agglomerate in a low-viscosity resin, such as vinyl ester, unsaturated polyester resin, and epoxy resins. The agglomeration process in the low-viscosity vinyl ester resin generates electrically conductive paths already in the resin's liquid state, which undergo partial fixation by room temperature curing and full fixation by hot postcuring. The fully cured castings containing CB concentrations above percolation are characterized by a constant, temperature-independent conductivity, over a wide temperature range. The current–voltage relationships of the cured vinyl ester/CB castings obey a power-law dependency. The presence of the continuous CB paths in the vinyl ester casting is clearly observed in fracture surfaces formed at 100°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1165–1170, 2000

Effects of carbon blacks on electrical properties of EPDM compounds

The correlations between mechanical and electrical properties of ethylene propylene diene terpolymer (EPDM) compounds and carbon black types and levels applied are studied. Tensile strength increases with an increase of the carbon black, especially for carbon black with higher surface area. Tracking resistance of EPDM compounds improves when a small amount of relatively nonconductive carbon blacks are added to EPDM compounds, whereas conductive carbon blacks decrease both dielectric properties and tracking resistance of EPDM compounds. Possible reasons for these results are discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2540–2546, 2000

Polyurethane/conducting carbon black composites: Structure, electric conductivity, strain recovery behavior, and their relationships

The polyurethane composites with conducting carbon black (CB) were prepared by a solution-precipitation process, which was followed by melt compression molding. The polyurethane used has good shape memory effect. The morphology of CB fillers in polyurethane matrix and the resulting conductivity of the composites were investigated. It has been found that CB fillers exist in the forms of aggregates. The percolation threshold is achieved at the CB concentration of 20 wt %. The presence of CB fillers decreases the degree of crystallinity of polycaprolactone (PCL) soft segments of the polyurethane. However, the composites still have enough soft-segment crystals of polyurethane to fulfil the necessary condition for the shape memory properties. Dynamic mechanical data show that CB is an effective filler for the reinforcement of the polyurethane matrix, but does not deteriorate the stable physical cross-link structure of the polyurethane, which is necessary to store the elastic energy in the service process of the shape memory materials. Addition of CB reinforcement in the polyurethane has influenced the strain recovery properties, especially for those samples with CB concentrations above the percolation threshold. The response temperature of the shape memory effect Tr has not been affected too much. Strain fixation Sf, which expresses the ability of the specimens to fix their strain, has been improved in the presence of the CB fillers. The final recovery rates Rf and strain recovery speeds Vr of the shape memory measurements, however, have decreased evidently. It is expectedly ascribed to the increased bulk viscosity as well as the impeding effect of the inter-connective structure of CB fillers in the polymer matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 68–77, 2000

99/03147 Effect of thermal treatment on crystallization and PTC properties of conductive PVDFI/CB composite

The conduction mechanism in the organic positive temperature coefficient of resistance (PTC) materials composed of conductive carbon black (CB) particles and an insulating polymer matrix was investigated at the nanolevel using a scanning probe microscope. The atomic force microscope (AFM) observation showed the CB particles as circular projections of about 50–100 nm in diameter. On the other hand, nanoscopic current measurements conducted by scanning an Au-coated AFM tip on the sample surface revealed that some of these projections also appear as bright spots in the current-mode image, suggesting that these parts are electrically connected through the sample to a conductive substrate. Moreover, the area of the bright regions was observed to increase significantly with increasing applied voltages. These data suggest that the governing mechanism for these organic PTC compounds may be the electron tunneling or hopping processes through the dispersed CB particles rather than the electron transport through the contacted CB particles.

Reduced percolation thresholds of immiscible conductive blends

The DC conductivity of polymer blends composed of poly(ethylene-co-vinyl acetate) (EVA) and high density polyethylene (HDPE), where a conductive carbon black (CB) had been preferentially blended into the HDPE, were investigated to establish the percolation characteristics. The blends exhibited reduced percolation thresholds and enhanced conductivities above that of the individually carbon filled HDPE and EVA. The percolation threshold of the EVA/HDPE/CB composites was between 3.6 and 4.2 wt % carbon black, where the volume resistivity changed by 8 orders of magnitude. This threshold is at a significantly lower carbon content than the individually filled HDPE or EVA. At a carbon black loading of 4.8 wt %, the EVA/HDPE/CB composite exhibits a volume resistivity which is approximately 14 and 11 orders of magnitude lower than the HDPE/CB and EVA/CB systems, respectively, at the same level of incorporated carbon black. The dielectric response of the ternary composites, at a temperature of 23°C and frequency of 1 kHz, exhibited an abrupt increase of ca. 252% at a carbon concentration of 4.8 wt %, suggesting that the percolation threshold is somewhat higher than the range predicted from DC conductivity measurements. Percolating composites with increasing levels of carbon black exhibit significantly greater relative permittivity and dielectric loss factors, with the composite containing 6 wt % of carbon black having a value of ∈' 79 and ∈ 14.

The interrelation between morphology, resistivity, and flow properties of carbon black-containing HIPS/EVA blends

Immiscible polymer blends based on high-impact polystyrene/ethylene vinyl acetate (HIPS/EVA) are interesting host multiphase systems for the incorporation of low concentrations of carbon black (CB). The conductive filler CB tends to accumulate preferentially within the EVA phase, forming segregated structures, and thus conductivity of the blends is only obtained when double percolation is realized. Material properties such as surface tension and crystallinity of the CB-containing polymer are found to influence filler distribution, accordingly affecting the electrical conductivity. A rheological-electrical method is presented, whereupon extrudates of CB-containing binary immiscible polymer blends are produced by a capillary rheometer, and the effect of shear level on the extrudates' structure and resultant resistivity is determined. A descriptive model was derived, illustrating the effect of shear on double percolation at various blend compositions. The flow behavior of the CB-containing compounds was studied in regard to the filler packing factor, Φ m , and related to the electrical properties of the extrudates. Blend composition, CB content, and shear level were considered as significant parameters, determining the structure and the resultant electrical properties.

Evaluation of the effect of ruthenium oxide on the properties of composite electrodes used in cathodic protection

Results have been presented of potentiodynamic and impedance investigations of conducting polymeric composites based on the polyethylene matrix with addition of DuPont vinyl acetate (Elvax 450). High conducting carbon black was the main conducting component of investigated polymeric composites. Improvement of the current output of composite electrodes was realised by introduction of active ruthenium dioxide. Statistical analysis was carried out of potentiodynamic dependencies allowing determination of relations of the current output of designed electrodes in the function of the percentage of introduced oxide. An improvement of electrochemical parameters has been shown characterising polymeric composites with increase of the percentage of ruthenium oxide.

Conductive polymer blends with low carbon black loading: High impact polystyrene/thermoplastic elastomer (styrene‐isoprene‐styrene)

AbstractElectrical resistivity and morphology of high impact polystyrene (HIPS)/styrene‐isoprene‐styrene copolymer (SIS)/carbon black (CB) blends were studied. Conductive CB particles locale preferentially within the HIPS phase of the HIPS/SIS blends. The blends studied remain conductive as long as HIPS maintains a continuous phase and the effective CB concentration within HIPS surmounts its percolation threshold. Thus, blends containing 2 phr CB depict significant changes in resistivity with the HIPS/SIS composition, transforming from insulative to conductive. SIS/CB mixtures exhibit an unusual behavior, explained by a physical model suggested in this paper and extended to the HIPS/SIS/CB systems.

High-Dilution Carbon-Black/Polymer Composites: Hierarchical Percolating Network Derived from Hz to THz ac Conductivity

We have studied conducting carbon-black (CB) composites with a percolation threshold $({p}_{c})$ of $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ in volume fraction. The low ${p}_{c}$ is explained in terms of a fractal distribution of CB aggregates. To prove this model we measured the frequency dependence of the complex conductivity (up to 0.6 THz) for various CB concentrations. Two successive scaling regimes are found, the first dominated by the infinite percolating cluster and the second by finite clusters. We extend the anomalous diffusion model to explain this observation and show the parameters found to be consistent with the proposed structure.

Nanoscopic analysis of the conduction mechanism in organic positive temperature coefficient composite materials

The conduction mechanism in the organic positive temperature coefficient of resistance (PTC) materials composed of conductive carbon black (CB) particles and an insulating polymer matrix was investigated at the nanolevel using a scanning probe microscope. The atomic force microscope (AFM) observation showed the CB particles as circular projections of about 50–100 nm in diameter. On the other hand, nanoscopic current measurements conducted by scanning an Au-coated AFM tip on the sample surface revealed that some of these projections also appear as bright spots in the current-mode image, suggesting that these parts are electrically connected through the sample to a conductive substrate. Moreover, the area of the bright regions was observed to increase significantly with increasing applied voltages. These data suggest that the governing mechanism for these organic PTC compounds may be the electron tunneling or hopping processes through the dispersed CB particles rather than the electron transport through the contacted CB particles.

Conductive carbon black

Conductive carbon black

Fabrication and electrical properties of carbon/ polyesterimide thick resistive films

The preparation, morphology and basic electrical properties of carbon/polyesterimide (PEI) thick film resistors are presented. SEM observations have been used for microstructure investigation. The influence of carbon (conductive carbon black (CB) or graphite (G)) and the effect of an inorganic filler (TiO 2) on sheet resistance, normalized temperature dependence of resistance, durability to thermal shocks and moisture behaviour of two- and three-component systems are discussed.

Evidence for superlocalization on a fractal network in conductive carbon-black-polymer composites.

The dc conductivity of carbon-black-polymer composites has been measured as a function of carbonblack concentration from just above the percolation threshold p c up to 33p c , and in the temperature range from 4 to 300 K. To explain the temperature dependence we have modified the Mott-Deutscher model for variable-range hopping between superlocalized states on a fractal by assuming Coulomb-dominated hopping. Our data then yield the first experimental evidence of electron superlocalization, with a superlocalization exponent ζ=1.94±0.06, close to theoretical estimates

Electric conduction property and structure of highly conductive carbon black

Electric conduction property and structure of highly conductive carbon black