Function Of Carbon Black Content Research Articles

Fabrication and Characterization of Gelatin/Carbon Black–Based Scaffolds for Neural Tissue Engineering Applications

Abstract Neural tissue engineering has recently emerged as an alternative strategy to repair nerve damage and promote nerve regeneration. It involves the fabrication of scaffolds with properties mimicking those of the natural extracellular matrix for guiding a three-dimensional (3D) neural regeneration. These engineered constructs, in addition to mechanical support, should be also capable of providing proper chemical and electrical stimuli for adhesion, migration, and proliferation of the neural cells. In this study, we developed conductive composite hydrogel films based on gelatin and carbon black (CB) as scaffolds for neural tissue engineering applications. The presented hydrogel constructs were fabricated in the form of films using the solvent casting method after dispersing several concentrations of CB in a 5 % (w/v) gelatin solution along with (3-glycidoxypropyl)trimethoxysilane (GPTMS) as the crosslinking agent at a concentration of 1.84 % (v/v). The CB concentrations of 0.3 %, 0.5 %, 0.7 %, and 0.9 % (w/w) with respect to the gelatin amount were chosen. The morphological, compositional, swelling, dissolution, electrical, mechanical, and wettability properties together were characterized as function of CB content and compared with those of pure gelatin-based hydrogel. Results demonstrated that the incorporation of different quantities of CB relatively reduced the water uptake capability of the films and increased the stability in water of the gelatin matrix. Findings from the mechanical tests revealed that composite hydrogels have a lower elastic modulus with respect to the pure gelatin matrix. Moreover, it was found that the incorporation of incremental CB concentrations kept the wettability surface property unchanged while the electrical characterization of the proposed structures showed a reduction of the electrical impedance. Overall, the study suggests that the composite structures could be used as a potential candidate for fabrication of scaffolds for neural regeneration with tunable electrical and mechanical properties by varying the CB concentration in a finite range.

New antistatic charge and electromagnetic shielding effectiveness from conductive epoxy resin/plasticized carbon black composites

AbstractRecently, there is an increasing interest in electromagnetic interference shielding due to the rapid increase in electromagnetic pollution and the wide use of commercial and military products. Conducting polymer composites were prepared in the presence of epoxy resin and plasticized carbon black (CB). The structural characteristics of the composites were examined by means of scanning electron microscopy, cross linking density, and interparticle distance among conductive particles. The mechanical properties such as Young's modulus, elongation at break, and hardness of the composites were investigated as a function of CB content. The results indicated that CB could improve the composite microstructure. The higher mechanical behavior than green epoxy can be attributed to the interaction between CB particles and epoxy resin. The conductivity, mobility carriers, and number of charges of the composites at room temperature were found to be dependent on CB content. The applicability of the composites to antistatic charge dissipation was examined. Dependence of the microwave properties of the epoxy/CB composites on the volume fraction of CB particles and frequency were studied. Moreover the permittivity as a function of frequency of the composites was studied. The electromagnetic wave shielding of epoxy/CB composites is dominant by both reflection and absorption. Composites can find applications in antistatic charge dissipation and in suppression of electromagnetic interference and stealth technology. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers

Dry friction and sliding wear of EPDM rubbers against steel as a function of carbon black content

The dry friction and sliding wear of ethylene/propylene/diene rubbers (EPDM) were studied against steel as a function of the carbon black (CB) content using various testing configurations, such as pin(steel)-on-plate(rubber) (POP) and ring(steel)-on-plate(rubber) (ROP). The EPDM rubbers were characterized using tensile, compression tests and dynamic-mechanical thermal analysis (DMTA). The coefficient of frictions (COF) and specific wear rates of the EPDMs were determined. It was found that with increasing CB content the specific wear rate was reduced. A similar tendency was found for the COF in ROP tests. Both COF and wear rates of the EPDM mixes strongly depended on the test configurations. The wear mechanisms were concluded by inspecting the worn surfaces in scanning electron microscopy (SEM) and discussed. Albeit several rubber characteristics follow the same trend as the COF and wear rate, at least for this EPDM formulation, further investigations are needed to deduce eventual correlations between them.

Electric conductivity of PS/PA6/carbon black composites

AbstractPolystyrene (PS)/nylon6 (PA6)/carbon black (CB) composites were prepared in Haake rheometer. The factors influencing the electric conductivity of PS/PA6/CB composites were investigated. Results showed that CB particles only distribute in PA6 phase because of the strong polarity of PA6. The CB content in PA6 phase and the morphology of PA6/CB phase affect the electric conductivity of PS/PA6/CB composites. No matter the PA6/CB phase is continuous or dispersed, the electric conductivity of PS/PA6/CB composites increases with the increase of CB content in the PA6 phase; higher continuous degree of PA6/CB phase leads to higher electric conductivity. A new term, statistical average critical distance (SACD), was defined to explain the electric mechanism of PS/PA6/CB composites, which is a function of CB content in PA6. The SACD of PS/PA6/CB composites, in which CB content is 23 wt % in PA6, was quantitatively counted, which is about 54 nm. Keeping the CB content in composites at 5.67 wt %, the optimum mass ratio of PS/PA6 for the composites having the highest electric conductivity is 80 : 20, resulting from the competitive result of the earlier two factors (that is the CB content in PA6 phase and the morphology of PA6/CB phase). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1042–1047, 2007

Mechanical and rheological properties of poly(ethylene‐co‐ethyl acrylate) as a function of carbon black content

AbstractCarbon black (CB) filled poly(ethylene‐co‐ethyl acrylate) (EEA‐CB) is used as conductive phase in conductive polymer composites (CPC). Electrical conductivity of CPC obtained from blends of immiscible polymers results from CB particles localization within the material, which depends on composition and processing conditions. It is particularly important to control viscosity of such systems as this parameter determines both the phase morphology and conductive pathway structure. The small scale, at which CB particle aggregation/dispersion phenomena occur within CPC, makes direct observations difficult. But the effect of carbon black particles/polymers interactions is clearly visible by means of rheological measurements.A strong reinforcing effect of CB on CPC in both solid and liquid states has been noticed. This phenomenon has been analyzed using classical models as a function of temperature and CB content. The results confirm the necessity of CPC rheology control especially during the process to achieve good reproducibility of electrical properties.

A novel way of enhancing the electrical and thermal stability of conductive epoxy resin–carbon black composites via the Joule heating effect for heating‐element applications

AbstractThe influence of Joule heating treatments and carbon black (CB) on the electrical and thermal behavior of epoxy resin composites is well described in this article. The effect of CB and Joule heating on network structure characteristics, such as shrinkability, interparticle distance between conductive particles, crosslinking density, hardness, thermoelectric power, thermal conductivity, the thermal expansion coefficient, and scanning electron microscopy, of epoxy composites was investigated. The electrical conductivity (σ) of epoxy resin correlated with the volume fraction of CB and Joule heating treatment. σ increased continuously with increasing CB content, and Joule heating increased the level of σ, which makes it attractive for electronic utilization. The σ for fresh and Joule heating samples was recorded during heating–cooling cycles. The conduction mechanism of σ for epoxy composites was identified. The activation energy and hopping energy for two batches of epoxy as a function of CB content were estimated. The hopping distance, the state density at the Fermi level, and the radius of localized wave function versus CB content were evaluated. The current–voltage–temperature characteristics of fresh and Joule heating samples of epoxy composites were demonstrated. The thermal reliability was tested by means of temperature–time characteristics when certain applied power was on and off for several cycles. The specific heat and amount of heat transfer by radiation and convection were calculated based on the energy balance model for two batches. The results indicate that the Joule heating effect is a very effective and prospective way of enhancing the electrical and thermal stability of epoxy–CB composites for consumer use as heaters and in other electronic areas such as electromagnetic shielding effectiveness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 97–109, 2003

Electrical properties and stability of epoxy reinforced carbon black composites

The conductivity of an insulating epoxy matrix increases continuously with carbon black (CB) content and is well explained by percolation theory. The effects of CB content and sintering on the electrical conductivity ( σ) of epoxy composite as a function of temperature during heating and cooling cycles were discussed. The current–voltage–temperature ( I– V– T) and working power–temperature ( P– T) characteristics of these composites as a function of CB content were investigated. The thermal stability was tested by means of temperature–time ( T– t) curve at certain applied power on and off for one cycle.

In situ network structure, electrical and thermal properties of conductive epoxy resin–carbon black composites for electrical heater applications

Epoxy composites at high carbon black (CB) concentration exhibited good electrical and thermal stability, which can make them attractive for consideration in heating devices and conducting composite applications. The effect of CB on the network structure of epoxy composites, like volume fraction of epoxy network ( V r), the extent of CB reinforcing ( γ), interparticle distance between conductive particles (IPD), epoxy–solvent interaction parameter ( χ), average number molecular weight between cross-links ( M c), number of elastically effective chains (NEC), cross-linking density (CLD) and scanning electron microscope (SEM), was investigated in details. The conductivity of an insulating epoxy matrix increases continuously with CB content and is well explained by percolation theory. The effects of different concentration of CB and sintering on the electrical conductivity of epoxy composite as a function of temperature during heating and cooling cycles were discussed. The conduction mechanism and negative temperature coefficient of conductivity (NTCC) of epoxy–CB composites were analyzed. The current–voltage–temperature and working power–temperature characteristics of these composites as a function of CB content were investigated. We attempt to contribute to a better understanding of the negative resistance phenomena in epoxy–CB composites. The nonlinear coefficient ( α), the size of conductive particles (SCP) and hopping distance ( a h) of charge carriers in epoxy–CB composites were evaluated. The thermal stability was tested by means of temperature–time curve at certain applied power, on and off, for one cycle. The characteristic thermal properties, like characteristic time growth τ g, decay τ d and current t i constants of epoxy as a function of CB content, were estimated. The specific heat ( C p) and amount of heat transferred by radiation and convection ( h r) were calculated based on energy balance concept as a function of CB content. The thermoelectric power (TEP) and thermal conductivity ( λ) as a function of temperature of epoxy–CB composite were discussed. In conclusion, the epoxy–CB composites show good thermal stability and they can be used as heating devices for consumer products.

Percolation phenomena in carbon black–filled polymeric concrete

AbstractPercolation in carbon black‐filled polymeric concrete, is discussed based on the measured changes in electrical conductivity and morphology of the composite at different concentrations of carbon black. The percolation threshold ranged between 6 and 7 wt% (based on resin weight) of carbon black. Above this concentration, the filler particles formed agglomerates in contact with each other, suggesting that the conduction process is nearly ohmic in nature. A power law predicted by percolation theory described the behavior of the conductivity as a function of carbon black content. Microscopic analysis showed the presence of a continuous structure formed by the polyester resin and carbon black, in which silica particles were embedded.

Sorption and diffusion of a brake fluid in EPDM elastomers

This article reports on an investigation into how the morphology of four commercially available ethylene propylene diene monomer (EPDM) elastomers was affected by exposure to a brake fluid. The sorption and diffusion coefficients as a function of carbon-black content as well as the EPDM type were determined at 23°C, 60°C, 100°C and 150°C. It was found that variation in carbon-black loading showed an effect on the transport characteristics of EPDM elastomers. The sorption data at room temperature were not reported since these took too long a time. The leaching out of the indigenous additives might be due to the paraffin oil migrating to the surface of the specimens. The diffusion of the brake fluid in the EPDM membranes follows non-Fickian transport. The results of this investigation are discussed in terms of the morphological differences in the EPDM formulations. The diffusion coefficients showed a dependence on the morphology of EPDM, as studied by the glass-transition temperature of the elastomers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 000–000, 2001

Solid-state13C-NMR and equilibrium-swelling studies of filled, TBBS-accelerated sulfur vulcanization of natural rubber

The effective network chain density (νe) and the density of the chains between sulfurizations (2[S]chem) for natural rubber vulcanized with N-t-butyl benzothiazole sulfenamide (TBBS) in different levels of HAF–HS (N347) carbon black were determined by equilibrium swelling and solid-state 13C-NMR measurements, respectively. The proportion of the intermolecular crosslinks over a whole range of sulfurized products (Ec) for the gum stock was estimated by the comparison of the chemical network chain density (νchem) calculated from νe using Mullins's approach with 2[S]chem. Ec increases with cure, reaches a maximum at an optimum cure state (trpar;, and decreases during an overcuring. It was observed from the NMR results that the total amount of chemical sulfurization reactions occurring in the rubber is almost independent of the level of carbon black loading. Based on the assumption that the amount of the intermolecular crosslinking reactions is also constant with the carbon black content, the amount of physical crosslinks (vent) in filled formulations was determined by subtracting the estimated νchem from the νe. The linear relationship obtained from the plot of the vent at the optimum cure state (t90) as a function of carbon black content postulates that the physical adsorption plays a major role in the polymer–filler interactions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1391–1399, 1998

Solid‐state 13C‐NMR and equilibrium‐swelling studies of filled, TBBS‐accelerated sulfur vulcanization of natural rubber

The effective network chain density (νe) and the density of the chains between sulfurizations (2[S]chem) for natural rubber vulcanized with N-t-butyl benzothiazole sulfenamide (TBBS) in different levels of HAF–HS (N347) carbon black were determined by equilibrium swelling and solid-state 13C-NMR measurements, respectively. The proportion of the intermolecular crosslinks over a whole range of sulfurized products (Ec) for the gum stock was estimated by the comparison of the chemical network chain density (νchem) calculated from νe using Mullins's approach with 2[S]chem. Ec increases with cure, reaches a maximum at an optimum cure state (trpar;, and decreases during an overcuring. It was observed from the NMR results that the total amount of chemical sulfurization reactions occurring in the rubber is almost independent of the level of carbon black loading. Based on the assumption that the amount of the intermolecular crosslinking reactions is also constant with the carbon black content, the amount of physical crosslinks (vent) in filled formulations was determined by subtracting the estimated νchem from the νe. The linear relationship obtained from the plot of the vent at the optimum cure state (t90) as a function of carbon black content postulates that the physical adsorption plays a major role in the polymer–filler interactions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1391–1399, 1998

Broadband ac conductivity of conductor-polymer composites

The electrical conductivity of a composite model system formed by highly structured carbon black (CB) filled, within an amorphous polymer, poly(ethylene terephtalate) composite is studied. The dc conductivity as a function of CB content follows a scaling law of the type $\ensuremath{\sigma}\ensuremath{\propto}(p\ensuremath{-}{p}_{c}{)}^{t}$ yielding for the percolation concentration, ${p}_{c}=0.011$ and for the exponent, $t=2.17$. The analysis of the temperature dependence of the conductivity suggests that for temperatures larger than 45 K, conduction can be ascribed to thermal fluctuation induced tunneling of the charge carriers through the insulating layer of polymer separating two CB aggregates. At lower temperatures, conductivity becomes temperature independent, which is typical of conventional tunneling. The frequency dependence of the conductivity is also studied between dc and ${10}^{9}$ Hz. By the introduction of a shift factor ${a}_{p},$ a procedure for the construction of a master curve based on a ``time-length equivalence principle'' is proposed. Finally, a model is introduced to describe the frequency dependence of the conductivity of CB-filled composites based on the behavior of charge carriers placed in a fractal object.

Electrical properties of crosslinked polyethylene/carbon black switching composites as a function of morphology and structure of the carbon black

AbstractThe electrical resistivity of a radiation‐crosslinked polyethylene/carbon black switching composite was investigated as a function of carbon black content and temperature. Carbon blacks of different morphology and microstructure behaved differently regarding the electrical resistivity. A HG black, highly porous and structured, imparts high conductivity to its composite mixture at a low degree of loading, whereas nonporous acetylene EQ black of like structure requires a higher degree of loading to impart the same conductivity. The PTC (positive temperature coefficient) effect anomaly was smaller for HG black than for EQ black. It was found that the PTC anomaly was heightened when a combination of the two different carbon blacks was mixed into the composites. Suggestions as to the causes for this particular behavior are made with reference to the electron micrography and other parameters for microstructure of the two carbon blacks.