Carbon Black Network Research Articles

Carbon Black Networking in Elastomers Monitored by Dynamic Mechanical and Dielectric Spectroscopy

AbstractThe morphological structure of CB networks in elastomers and their flocculation dynamics under heat treatment and especially during vulcanization are analyzed by dynamic mechanical and dielectric spectroscopy. Dielectric spectra in the MHz range show that nanoscopic gaps between adjacent CB particles develop during heat treatment or vulcanization. These gaps are maintained by immobilized polymer layers acting as flexible bonds between the particles. Low‐frequency dielectric data indicate that the static percolation model qualitatively describes the dielectric properties of the conducting CB network on large length scales, but a superimposed kinetic aggregation process takes place on smaller length scales.magnified image

Influence of mixing conditions on rheological behavior and electrical conductivity of polyamides filled with carbon black

The introduction of carbon black in a polyamide matrix allows one to obtain conductive materials because of the formation of a filler network. Resulting electrical properties depend, among others, on the processing conditions. In a first part, we investigate the influence of mixing conditions (rotor speed, temperature, mixing time) on electrical conductivity. Then, in a second part, we try to characterize the conducting network by rheological measurements and to establish relationships between rheological parameters and electrical properties. For that purpose, we propose to perform successive strain sweep experiments at constant frequency, from 0.5 to 100%, then from 100 to 0.5%, and finally, again, from 0.5 to 100%. Between two successive strain sweeps, we observe a drop in the moduli values that can be attributed to the breakdown of the carbon black network. A clear relationship is established between rheological and electrical properties of the compounds. Moreover, we propose a presentation of the rheological data that permits to rank the samples according to the strength of the carbon black network.

Time–temperature dependence of the electrical resistivity of high‐density polyethylene/carbon black composites

AbstractSeveral carbon blacks with surface areas from 105 to 1353 m2/g were used to produce composites through melt compounding with a high‐density polyethylene matrix. The electrical behavior of the obtained composites was investigated by the measurement of their resistivity as a function of the carbon black content and type at various temperatures and times during isothermal annealing treatments. The percolation threshold markedly decreased as the carbon black surface area increased, reaching a minimum value of 1.8 vol % for the carbon black with a surface area of 1353 m2/g. The resistivity passed through a maximum as the test temperature increased. Moreover, the analysis of the experimental data evidenced that the host high‐density polyethylene matrix and the conductive carbon black network rearranged during the isothermal thermal treatments, causing a resistivity decrease. This rearrangement became less and less important as the carbon black surface area increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Electrical and Mechanical Properties of Some Butadiene Rubber Composites in the Vicinity of the Percolation Threshold

The electrical and mechanical properties of NBR/SBR blends with different compositions were studied before the addition of carbon black. The increase in permittivity ϵ′ and dielectric loss ϵ″ noticed by increasing NBR content is due to the increase in C ≡ N dipoles. The mechanical properties which include tensile and elongation at yield and rupture are also found to be increased. This work also includes the compatibility study, which was carried out using different tools and techniques (Heat of mixing, dielectric and scanning electron microscope). This study led to a conclusion that both blends are incompatible. The electrical as well as the mechanical properties were carried out on NBR, SBR and NBR/SBR blend (50/50) to be loaded with different concentrations of high abrasion furnace black (HAF) in order to find out the percolation thresholds in relation to the net work formation. The electrical conductivity of carbon-black-filled composites is increased from pure polymer to that of pure carbon, through the change in the different composites. Up till certain concentration of HAF (30 phr for both NBR and SBR) and 20 phr for NBR/SBR blends the conductivities of the composites are approximately the same and closed to that of the pure, electrically insulating polymer matrix. These concentrations are called percolation thresholds. Above such concentrations, the conductivity increases many orders of magnitude with very little increase in the filler amount. With this increase the tendency of conductivity chain formation increases through the aggregation of the carbon black particles network. The change in conductivity beyond the percolation threshold is expressed according to the percolation theory with straight line when plotted graphically versus P-Pc; Pc is the volume fraction of carbon black at the percolation threshold. In addition to the conductivity term, the data of permittivity ϵ′ and dielectric loss ϵ″ given at different frequencies from 100 Hz up to 100 kHz show an abrupt increase at 30 phr HAF for NBR & SBR and 20 phr HAF for NBR/SBR. More over, the relaxation times obtained from the analyses of these data using Fröhlich and Havriliak-Nagami functions, which ascribe the orientation of the large aggregates caused by the movement of the main chain also show an abrupt increase at the same concentration of HAF. The mechanical properties, which investigated through the measurements of tensile and elongation at yield and rupture indicate an abrupt increase at the same concentration of HAF found in the case of electrical measurements. This result gives evidence to the good applicability between both mechanical and electrical investigations through the network formations. Any how, the percolation threshold found in case of NBR/SBR blend is less than that for NBR itself. This result is attributed to the uneven distribution of the filler in the incompatible blend matrix.

Simulation of Electrical Resistivity of Carbon Black Filled Rubber under Elongation

It has been known that the carbon black (CB) network is responsible for the electrical and mechanical behaviors of filled rubber. Due to the complexity involved in the filled rubber in relation to the conductive mechanism of the CB network, there has been little work concerned with simulation of the electrical behavior at large strains. Based upon an infinite circuit model, the electrical resistivity of CB filled rubber under elongation is simulated. For CB (N330) filled natural rubber with volume fraction of 27.5%, the simulated electrical resistivity increases with elongation at small stains, corresponding to the breakup of the agglomerates. The reduction in resistivity at larger strains corresponds to the decrease of the junction width, which results in a decrease of the contact resistance. Good agreement is found between the simulations and the experimental data available in the literature. The simulated results confirm the effects of the breakdown of the CB network and the alignment of CB aggregates under strain on the electrical resistivity.

Investigation of Carbon Black Network in Natural Rubber with Different Bound Rubber Contents

A new method was applied to modify the surface activity of virginal carbon black (VCB). LA‐57, one kind of hindered amine light stabilizer, was adsorbed onto the carbon black surface through a strong shear force induced by the screws of a HAAKE internal mixer. The modified carbon black (MCB) was characterized by FT‐IR and thermogravimetric analysis (TGA). The bound rubber content of the natural rubber (NR) compounded with MCB and VCB varied with the fraction of LA‐57 on the MCB surface. The nonlinear effect at small strains, generally referred as the Payne effect, was investigated in the rubber compounds based on the different bound rubber contents. The NR compound containing the lowest bound rubber content had an obvious Payne effect. Based on the bound rubber content, the types of filler network varied from direct contact mode to the joint rubber shell mechanism.

Carbon-matrix composites with continuous glass fiber and carbon black for maximum strain sensing

Electrically conductive glass-fiber-reinforced polymer composites have been prepared by adding carbon black, and carbonization processes have been applied to the resulting matrices. The carbonized composites were found to show characteristic changes in resistance during cyclic tensile tests, in which the resistance increased in the loaded state was retained even after unloading. Pyrolysis temperature dependence of the residual phenomena was investigated in order to understand the effects of the carbonized matrix and the carbon black network. The residual behavior became more pronounced with increasing pyrolysis temperature until 500 °C, while that diminished over 600 °C. The thermal decomposition of the matrix was almost completed up to 500 °C, and the shrunk matrix coexisting with glass fibers had a residual tensile stress along the fiber direction. The matrix carbonized at higher than 600 °C showed an increase in conductivity, which disrupted the strain-sensitive percolation network and hence the resistance response. These results showed that irreversible change in the carbon black network under the internal tensile stress provided the residual phenomena.

Analysis of carbon black networking in elastomers by dielectric spectroscopy

The dielectric response of various series of cross-linked and non-cross-linked solution-styrene-butadiene-rubber and/or carbon black composites is investigated in the frequency range from $0.1\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$ up to $10\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$. Two types of rubber, differing in vinyl content, and two carbon black grades, differing in particle size, are considered. The dielectric spectra are analyzed in the framework of percolation theory, describing the effect of structural disorder of the conducting carbon black network on the diffusive charge transport. Various deviations from the predictions of percolation theory are observed, which are related to a superimposed kinetic aggregation or flocculation process. It is demonstrated that due to the heat treatment during vulcanization, a pronounced flocculation of filler particles takes place in the rubber matrix, especially in the case of a small particle size, leading to a drastic modification of the dielectric spectra. In particular, the percolation threshold decreases significantly and a second high-frequency relaxation transition appears, which is traced back to the tunneling of charge carriers over small gaps between adjacent carbon black particles. The gap size is found to be independent of the carbon black concentration in the range of $2--5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.

Simulation of Carbon Black Network in Filled Rubber

Carbon black (CB) is one of the most important fillers for rubber and plastics materials. How to describe the CB network is a fundamental problem for establishing relationships between the CB network and the mechanical properties of filled rubber. In view of the electrical conductivity of CB, an infinite circuit consisting of numerous contact resistors, interconnected with each other, is proposed to simulate the CB network in filled rubber; the resistances were determined by considering the tunneling conduction mechanism and a Gaussian distribution for the CB aggregate junction width. As an example, the electrical resistivity of CB (N330) filled natural rubber during uniaxial deformation was studied. It was found that the logarithm of resistivity was an approximately linear function of the extension ratio, and the resistivity increased with the increase of average number of primary particles per aggregates. Additionally, some published experimental points lie between the curves calculated for five primary particles and for seven primary particles per aggregate at extension ratios below 1.2. The calculations suggested that the average number of primary particles per aggregate for CB type N330 might be between five and seven.

Nanoparticle induced network self-assembly in polymer–carbon black composites

A novel percolation phenomenon with inorganic nanoparticle loading in polyamide 6-carbon based nanoparticle hybrids was identified. Percolation threshold substantially shifts to lower carbon black (CB) volume fractions in the presence of optimum concentration of chemically modified montmorillonite (organoclay) while the effective organoclay concentration can be optimized to lower the slope of percolation curve maintaining electrical conductivity within static dissipative 10−6–10−9Scm−1 range. Organoclay/CB ‘nano-unit’ morphology was found in polyamide 6 ternary hybrids. It is composed of stacked organo-montmorillonite platelets that deform to wrap partially around one or two primary CB aggregates. This elementary nano-unit structure induces CB network self-assembly within polyamide 6 matrices. The structure was found to be prevalent throughout the polymer matrix. This morphology remains robust under wide range of thermal-deformation histories due to the strong preferred organoclay/polyamide 6/CB interactions that partially blocks the electron conduction and hopping mechanisms with clay ‘walls’ thereby reducing the slope of the percolation curve. Organoclay can be used as a dispersion control agent in these polymer–carbon systems to induce self-assembly of CB network at low CB content, simultaneously, partial blocking the electron hopping pathways to level the slope of percolation curves. High order exfoliation and nano-scale dispersion of organoclay is essential to induce this advanced percolation phenomenon.

Visualisation of carbon black networks in rubbery matrix by skeletonisation of 3D-TEM image

The first visualization of nanofiller networking due to association of carbon black in natural rubber is achieved by a transmission electron microscopy combined with computerised tomography (3D-TEM), and the resulted skeleton displays the characteristics of the filler network, which has long been assumed on the percolation behaviour in electron conductivity and on the mechanical behaviours of filled rubbers.

Critical Role of Polymeric Binders on the Electronic Transport Properties of Composites Electrode

The role of the polymeric binder nature and composition on the electronic transport properties of composite electrodes based on , carbon black (CB), and poly(ethylene oxide) (PEO)/poly(vinylidene difluoride)-co-hexafluoropropylene/ethylene carbonate–propylene carbonate (EC–PC)/Li bis(trifluoromethansulfon)imide binders were examined. The variation of the electrical conductivity vs CB volume fraction is typical of tunneling-percolation systems. Lower percolation threshold found for preplasticized binders is related to a more efficient CB dispersion due to the presence of EC–PC in the liquid suspension at the time of the composite processing. Above the conductivity is a unique function of the PEO to CB concentration ratio in the suspension, . This ratio controls the amount of polymer that adsorbs at the surface of the CB particles before the CB conducting network forms. The insertion behavior was studied at low current rate, for which ionic conductivity is not a limiting factor. The electrochemical capacity sharply increases at . However, for CB content typical of practical composite electrodes, the electronic conductivity of the CB network is not the only parameter that governs the electrode performance. It depends also on the electronic wiring at the interface, which is improved when adding EC–PC and lithium salt in the formulation.

Electrical response of Poly(styrene)/carbon black conductive polymer composites (CPC) to methanol, toluene, chloroform and styrene vapors as a function of filler nature and matrix tacticity

We have studied the sensing properties of several conductive polymer composites (CPC) to saturated solvent vapors (methanol, toluene, chloroform and styrene) as a function of carbon black (CB) structure and poly(styrene) PS crystal Unity. It appears that the combination of these two previous parameters allows obtaining very different electrical signature for the four vapors studied, confirming the importance of the carbon black conductive pathways morphologies structuring during the process. This study shows that selectivity of the CPC toward the vapors can be obtained not only by changing the matrix chemical nature but also by tailoring the morphology of the CB network.

Investigation of the Carbon‐Black Network in Natural Rubber Under Cyclic Deformation

Carbon‐black (CB) filled rubbers are often subjected to cyclic deformation in service, particularly in tire applications. To improve resistance to fatigue, better understanding of how the meso‐ or microstructures evolve under cyclic loading is necessary. The presence of a CB network for reinforcement of rubber has been proposed. We describe the study of a CB network in natural rubber by an analysis of the impedance spectrum. The characteristic frequency of the filled rubber is used to characterize the junction width of the CB network. As the junction width of the CB network decreases, theoretically the characteristic frequency will increase. When the CB concentration was less than 10%, the nonfatigued rubbers had normal frequency characteristics, i.e., the measured frequency increased with an increase of the CB concentration. However, rubber with higher CB loading had an abnormal frequency response, whose the origin has been unclear until now. Much work will be done to clarify it. By examining the characteristic frequency, the dependence of the CB network in natural rubbers on the deformation cycle was studied. In general, the higher the number of fatigue cycles, the lower the characteristic frequency that was obtained. Although the rubber specimens showed little change in length in the tension direction before and after the fatigue cycles, the predicted change (different from the recoverable change) in the CB network did occur.

Electrical and mechanical behavior of filled elastomers. I. The effect of strain

AbstractElectrical and mechanical property tests have been used to examine the changes in the carbon black network structure that occur in a filled elastomer at large strains in tension and compression. These changes have been examined both in materials that have no previous loading history and in test pieces that have been subjected to a specific known prestrain. When a previously unstrained, filled elastomer specimen is stretched to moderate extensions, the electrical resistivity increases. This is ascribed to the breakdown of the carbon black network structure. At higher tensile extensions, the resistivity decreases. This reduction in the electrical resistivity is attributed to the alignment of the shaped carbon black aggregates under strain. During unloading, the resistivity behavior is different from that during loading, with the final unloaded electrical resistivity being significantly higher than that measured in the unstrained elastomer. This dramatic change in the electrical properties after unloading is in marked contrast to the relatively modest changes observed in the mechanical behavior. After the first cycle, the electrical behavior becomes much more reversible, and this indicates that the bulk of the damage experienced by the carbon black network is developed during the first cycle. After unloading from a large strain, the electrical anisotropy is small, whereas the mechanical anisotropy is more marked. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2079–2089, 2003

Dynamic properties of carbon black filled chlorinated polyethylene/hindered phenol blends

AbstractAggregates of carbon black (CB) in a polymer matrix have a tendency to form a CB network. The dynamic mechanical properties of binary systems of chlorinated polyethylene (CPE) and CB or 3,9‐bis{1,1‐dimethyl‐2[β‐(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl)propionyloxy]ethyl}‐2,4,8,10‐tetraoxaspiro[5,5]‐undecane (AO‐80) and their ternary systems were investigated. It was found that the dynamic mechanical properties of those systems depend on the colloidal properties, surface oxides, and surface modification of CB. For binary systems of CPE and CB, oxidized CB gives a high modulus at low strain amplitude and a large Payne effect compared with untreated CB. In contrast, the reverse effect was observed for their ternary systems. Consequently, a good micro‐dispersion is obtainable by surface modification due to physical adsorption of AO‐80 on oxidized CB particles via hydrogen bonds.© 2003 Society of Chemical Industry

Dynamic percolation phenomenon of poly(methyl methacrylate)/surface fluorinated carbon black composite

AbstractThe electrical resistivity of polymer filled with conductive filler, such as carbon black (CB) particles, is greatly decreased by incorporating the conductive filler. This is called the percolation phenomenon and the critical CB concentration is called the percolation threshold concentration (Φ*). For CB particle–filled insulating polymer composite at lower than Φ*, the conductive CB network is constructed in the polymer matrix when the composite is maintained at a temperature higher than the glass‐transition temperature or the melting temperature of the polymer matrix. This phenomenon is called dynamic percolation and the time to reach the substantial decrease in resistivity is called percolation time (tp). To investigate the relationship between the dynamic percolation process and the surface state of CB particles, we used three kinds of carbon black particles such as original carbon black (CB0) and fluorinated carbon black (FCB010 and FCB025)–filled poly(methyl methacrylate) (PMMA). It was observed that the dynamic percolation curves for CB0‐filled PMMA and FCB‐filled PMMA composites shifted to a shorter percolation time with increases in both the annealing temperature and the filler concentration. However, the dynamic percolation curves of FCB‐filled PMMA showed a gradually decreasing trend compared to that of CB0‐filled PMMA composites. The activation energy calculated from an Arrhenius plot of the tp against the inverse of the annealing temperature was decreased by surface fluorine treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1151–1155, 2003

Fusion mechanism in rigid PVC

AbstractA classic approach for studying network effects in carbon‐black‐containing rubber was applied to PVC with stabilizer. This approach involves measuring the shear modulus with increasing strain. In carbon‐black‐containing rubber, the modulus drops dramatically at a critical strain level. This is known as the Payne effect and is associated with the breakup of the carbon black network. Rigid PVC that is fused to different levels in a bowl mixer shows exactly the same behavior, and the drop point correlates very well with the fusion peak in the mixing bowl. The relationship between network effects and fusion in PVC is discussed.

Alternating electric field induced agglomeration of carbon black filled resins

This letter reports on our observation that an alternating electric field is able to induce the formation of an electrically conducting network in carbon black (CB) filled resins well below the zero-field percolation threshold. Compared with the recently presented dc method, the ac agglomeration is more efficient in two respects: it proceeds significantly faster under equivalent conditions and is still effective at higher ionic concentration. In contrast to the ramified form of dc-induced CB networks, ac agglomeration favors the formation of parallel CB chains. The experimental results can be explained taking into account ionic conductivities of the matrices as well as charges and field induced dipoles on the CB particles.

Electric and elastic properties of conductive polymeric nanocomposites on macro- and nanoscales

In the past several years, the macroscopic electric and elastic properties of conductive polymeric composites have been studied from the viewpoint of such applications as thermistors and pressure sensors. In particular, we studied carbon black (CB) polymeric nanocomposites on macro- and nanoscales, using polyisoprene as the composite matrix. The filler component was an extra conductive carbon black (PRINTEX XE2, DEGUSSA) with a primary particle diameter of about 30 nm. A very strong reversible tensoresistive effect of electric resistance dependence on uniaxial tension deformation was observed in composites with the 10 carbon black mass parts added to 100 mass parts of polyisoprene. A conductive-type atomic force microscope (AFM) was used for the mapping of carbon black conductive network into an insulating matrix, while for studying the nanomechanical properties of composites, a tapping mode atomic force microscope was applied. A correlation between macroscopic and nanoscopic—both electric and elastic—properties was observed.