Reversible electrical behavior with strain for a carbon black‐filled rubber

Most unfilled elastomers exhibit a high electrical resistance. Fillers are usually added to elastomers to enhance their mechanical properties. Frequently the filler type used is an electrically conductive carbon black and the inclusion of such fillers reduces the resistivity of the elastomer compound. Previous work has shown that for elastomers containing high abrasion furnace, carbon black fillers such as N330 (or N300 series) at a volume fraction above the percolation threshold the resistivity changes with strain, the precise resistivity versus strain behavior being nonlinear and irreversible for conventional carbon black fillers. A strain‐measuring device, deriving strain directly from a measure of the resistivity, requires that the behavior be reversible and reproducible from cycle to cycle. This work presents the electrical resistivity behavior of a natural rubber (NR) compound filled with Printex XE2 carbon black. This type of filler has a significantly different morphology to the N300 series blacks examined previously. The Printex was incorporated into the rubber at a volume fraction above its percolation threshold and its behavior is contrasted to that observed with N300 series carbon black‐filled NR. Here, and for the first time, reversible electrical resistivity dependence with strain is reported for an elastomer filled with Printex XE2. This reversible behavior under strain opens up the possibility of applications, such as a flexible load sensor, pressure sensor, or switch. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of composite preparation techniques on electrical and mechanical properties and morphology of nylon 6 based conductive polymer composites

Nylon 6/carbon black conductive composites were prepared using two different methods, masterbatch dilution and melt mixing. Their effect on the size and distribution of carbon black agglomerates in the matrix was studied in terms of electrical and mechanical properties and morphology. The electrical resistivity of composites prepared by both methods decreased with increasing filler composition. The electrical resistivity of the diluted masterbatch composites and the melt mixed composites was reduced from the resistivity of pure nylon 6, 10¹⁵ “ohm, cm”, to 10⁷ “ohm, cm” at 1 and 6 wt % of carbon black, respectively. As the filler content increased, elongation at break and impact strength decreased, but tensile modulus increased. Masterbatch dilution method provided smaller carbon black clusters in composites compared to melt mixing method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2520–2526, 2006     

炭黑对不饱和聚酯/玻纤复合材料导电性能的影响

在纤维增强不饱和聚酯复合材料中填加不同种类和不同数量的炭黑、ZnO非导电填料及金属导电铝粉进行复合材料电学及力学性能改性研究，通过对体积电阻率和弯曲强度的变化研究，得出乙炔炭黑对材料电学和力学性能综合改性效果较好，非导电填料ZnO用量为15份时改善的导电性能最佳，金属铝粉的填加量在一定范围内既可提高电阻率，又可提高弯曲强度。     

Torrefied agro-industrial residue as filler in natural rubber compounds

This study explored the feasibility of using torrefied biomass as a reinforcing filler in natural rubber compounds. Carbon black was then replaced with the torrefied biomass in elastomer formulations for concentrations varying from 0% to 100% (60 parts per hundred rubber or phr total). Their influence on the curing process, dynamic properties, and mechanical properties was investigated. Results were compared with the properties of vulcanizates containing solely carbon black fillers. Time to cure (t₉₀) for compounds with torrefied biomass fillers increased, while filler-filler interactions (ΔG') decreased, compared to carbon black controls. At low strains, the tan δ values of the torrefied fillers vulcanizates were similar to the controls. Incorporation of torrefied biomass into natural rubber decreased compound tensile strength and modulus but increased elongation. Replacement with torrefied fillers resulted in a weaker filler network in the matrix. Still, results showed that moderate substitution concentrations (~20 phr) could be feasible for some natural rubber applications.     

Electrical and mechanical properties of melamine‐formaldehyde–based laminates with shungite filler

Processing issues and the electrical and mechanical properties of a novel combination of a natural carbonaceous filler, Karelian shungite, and a water soluble thermosetting polymer, melamine‐formaldehyde, were investigated. Two types of shungite with different carbon contents were investigated and compared to a commercial carbon black. The larger particle size and chemically more active surface of the shungites compared to carbon black leads to easy handling with little dusting and allows water to be used as dispersant. Laminates of melamine‐formaldehyde reinforced with random cellulose fibers and filler were prepared by film stacking. The layered structure results in anisotropic resistivities for the shungites with fairly low in‐plane percolation thresholds and a dissipative resistivity above the percolation transition. In comparison, carbon black had a lower percolation threshold and a low isotropic resistivity above the percolation transition. The mechanical properties of the composites were slightly deteriorated by all three fillers, indicating poor interfacial adhesion. The results of Fourier transform infrared (FTIR) measurements are interpreted as indicating hydrogen bonding and thus relatively weak adhesion between filler and polymer. Aqueous mixtures of melamine‐formaldehyde and shungite filler had lower viscosities than corresponding melamine‐formaldehyde and carbon black filler mixtures. POLYM. COMPOS., 26:552–562, 2005. © 2005 Society of Plastics Engineers     

Mechanical,thermal and electrical properties of multi‐walled carbon nanotube/aluminium nitride/polyetherimide nanocomposites

A series of polyimide‐based nanocomposites containing polyimide‐grafted multi‐walled carbon nanotubes (PI‐g MWCNTs) and silane‐modified ceramic (aluminium nitride (AlN)) were prepared. The mechanical, thermal and electrical properties of hybrid PI‐g MWCNT/AlN/polyetherimide nanocomposites were investigated. After polyimide grafting modification, the PI‐g MWCNTs showed good dispersion and wettability in the polyetherimide matrix and imparted excellent mechanical, electrical and thermal properties. The utilization of the hybrid filler was found to be effective in increasing the thermal conductivity of the composites due to the enhanced connectivity due to the high‐aspect‐ratio MWCNT filler. The use of spherical AlN filler and PI‐g MWCNT filler resulted in composite materials with enhanced thermal conductivity and low coefficient of thermal expansion. Results indicated that the hybrid PI‐g MWCNT and AlN fillers incorporated into the polyetherimide matrix enhanced significantly the thermal stability, thermal conductivity and mechanical properties of the matrix. Copyright © 2012 Society of Chemical Industry     

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     

Thermoset/graphene polymer composites—A review of processing and properties

Polymer-carbon nanocomposites incorporate the exceptional properties of both the polymer matrices, such as low cost and simple processing, with the distinctive features of the carbon-based fillers, such as high electrical and thermal conductivities, and excellent mechanical properties. Various fillers like carbon black (CB), graphite, expanded graphite (EG), and carbon nanotubes (CNTs) are being used to produce materials with advanced properties. However, at high filler loading, these filler materials have some major challenges such as filler agglomeration. Recently, graphene has gained increased interest as an alternative filler to produce polymer nanocomposites with advanced characteristics. Thermosetting polymer composites with graphene fillers are being considered for multiple applications and are a subject of interest for researchers because of enhanced properties like excellent corrosion resistance and low density. This review outlines studies to improve the mechanical, electrical, and thermal properties of thermoset/graphene composites.     

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.     

Electrical properties of composites in the vicinity of the percolation threshold

The electrical response of thermoplastic composites composed of carbon black and high‐density polyethylene near the electrical percolation threshold (p_c) has been investigated through the study of the volume resistivity and complex permittivity. The change in conductivity beyond p_c exhibited a critical exponent that was greater than predicted from percolation theory. Composites with carbon black contents slightly larger than p_c exhibited the greatest sensitivity in volume resistivity with temperature variations under the melting point of polyethylene. In addition, percolating composites with low carbon black contents exhibited significant “negative temperature coefficient” (NTC) effects and improvements in conductivity with annealing. Maxwell–Wagner interfacial polarization resulted in moderate increases in both the permittivity (ϵ′) and dielectric loss factor (ϵ″) below p_c, while at percolation, an abrupt and dramatic increase was observed for both components of the complex permittivity. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1573–1582, 1999     

Dynamic mechanical and Raman spectroscopy studies on interaction between single‐walled carbon nanotubes and natural rubber

The effects of the incorporation of single‐walled carbon nanotubes (SWNTs) on the physical and mechanical properties of natural rubber (NR) are described. Characterization of these new materials has been performed by dynamic mechanical analysis, differential scanning calorimetry, and Raman spectroscopy to obtain information about of the possible interactions between both materials as well as the dispersion of SWNTs on elastomer matrix. The results are then compared with those obtained for NR–carbon black composites. Dynamic mechanical analysis indicates a stronger filler–matrix interaction in the case of SWNTs incorporation, showing a noticeable decrease of the height of tan δ peak, as well as a marked shift of T_g towards higher temperatures. In particular, the increase of the storage modulus indicates a beneficial effect of SWNTs incorporation with respect to NR filled with carbon black and the pristine polymer matrix. In addition, calorimetric analysis indicates that both fillers accelerate the NR vulcanization reaction, this effect being more evident when SWNTs are added into the matrix. Raman spectroscopy indicates that SWNTs dispersion into the elastomer matrix creates residual strain on the nanotubes bundle. We demonstrate that the Raman microprobe technique provides a means for load transfer effectiveness of SWNTs. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3394–3400, 2004     

Preparation and Characterization of Natural Rubber Composites Comprising Conductive Carbon Black/Magnetite Hybrid Fillers Obtained by Impregnation Technology

Hybrid fillers have been prepared of conductive carbon black/magnetite at various ratios of the phases: 90:10, 70:30, and 50:50. The fillers have been characterized and their effect on the curing, mechanical, electric, and dynamic properties of natural rubber–based vulcanizates has been also investigated. The macrohomogeneity of the composites has been evaluated by ohmic resistivity measurements and correlation analysis. It has been established that all properties studied are dependent on the ratio between the filler’s phases. Viewing their composition, we conclude that the hybrid fillers are expected to exhibit both high dielectric and magnetic losses and may find application in the manufacturing of microwave absorbers.     

Improving the performance of carbon/graphite composites through the synergistic effect of electrostatic self-assembled carbon nanotubes and nano carbon black

Superior performance fillers are considered as an effective means to enhance the performance of carbon/graphite composites. However, poor interfacial properties and incomplete filler networks limit the performance enhancement of the composites. In this study, a new method was proposed to weaken this impact through the synergistic effect of the electrostatic self-assembly of nano carbon black (NCB) onto carbon nanotubes (CNTs). The results showed that the synergistic effect between NCB and the CNTs significantly improved the mechanical and electrical properties of the composites. NCB reduces the porosity of the composites and increases the interaction between the CNTs and matrix. The compressive strength of the composite was 143.2 Mpa, and the flexural strength was 46.3 MPa, which is 210% higher than that of the pristine carbon/graphite composites. Moreover, NCB and CNTs form a globally connected synergistic network in the carbon skeleton. Composites filled with CNTs/NCB exhibited the lowest resistivity and highest thermal conductivity, with a resistance that was 42% lower than that of pristine carbon/graphite composites at 44.8 μΩ m. All of these results suggest that the synergistic effect of CNTs/NCB show great potential to improve the performance of carbon/graphite composites.     

Effect of different types of filler and filler loadings on the properties of carboxylated acrylonitrile–butadiene rubber latex films

The effects of different types of fillers and filler loadings on the properties of carboxylated nitrile rubber (XNBR) latex were identified. Silica, mica, carbon black (CB; N330), and calcium carbonate (CaCO₃) were used as fillers with filler loadings of 10, 15, and 20 parts per hundred rubber. Furnace ashing and Fourier transform infrared analysis proved that interaction existed between the fillers and XNBR latex films. The morphology of the filled XNBR films was significantly different for different types of fillers. Mica and CaCO₃ fillers showed uneven distribution within the XNBR film, whereas other fillers, such as silica and CB, showed homogeneous distribution within the films. In the observation, silica and mica fillers also illustrated some degree of agglomeration. The mechanical properties (e.g., tensile and tear strengths) showed different trends with different types of fillers used. For silica and mica fillers, the mechanical properties increased with filler loadings up to a certain loading, and decreased with higher filler loadings. For CB filler, the mechanical properties increased gradually with increasing filler loadings. CaCO₃ fillers did not increase the mechanical properties. The crosslinking density of the XNBR films increased when they were incorporated with fillers because of the presence of elastomer–filler and filler–filler interactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Improvement in physical and electrical properties of poly(vinyl alcohol) hydrogel conductive polymer composites

With an aim to develop anti‐electrostatic discharge materials based on biodegradable polymers, poly(vinyl alcohol) films composited with two different conductive fillers (carbon black and aluminium) at various fillers contents (20?60%wt), were manufactured using solvent‐casting technique. The mechanical properties of such the films were investigated through tensile stress‐strain tests. Wettability and morphology of the composite films were performed by water contact angle measurement and SEM, respectively. Young's modulus of the composite films can be increased with the addition of conductive fillers. The surface of the composite films showed non‐homogeneous appearance, in which the phase boundary within the composites was clearly observed and the conductive fillers formed aggregation structure at high filler concentration. In addition, the composite films exhibited better hydrophobicity when higher conductive filler content was added. TGA results suggested that both carbon black and aluminum have proven their efficiency to enhance thermal stability of poly(vinyl alcohol). Investigation of cross‐cut adhesion performance of the prepared composite films revealed that carbon black‐filled composites exhibited excellent adhesion strength. The effect of conductive filler content on surface resistivity of the composite films was also examined. The experimental results confirmed that both the fillers used in this study can improve the electrical conductivity of poly(vinyl alcohol) hydrogel. The surface resistivity of the composite films was reduced by several orders of magnitude when the filler of its critical concentration was applied. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42234.     

Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

Relation between electrical and mechanical properties of conducting polymer composites

The influence of the carbon black content on the mechanical and electrical properties of polypropylene/carbon black composites prepared by different processing procedures was investigated. The formation of a continuous conducting network in the insulating matrix and, consequently, the percolation threshold depend strongly on the processing route and influence both the mechanical and electrical properties of the prepared composites. An interesting coincidence of the dependencies of conductivity and elongation at break on the filler content was found. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1903–1906, 2001     

Effect of carbon‐based nanoparticles on the cure characteristics and network structure of styrene–butadiene rubber vulcanizate

The network structure of styrene–butadiene rubber (SBR) in the presence of carbon black (CB) with two different structures and multi‐walled carbon nanotubes (MWCNTs) was investigated. Swelling behaviour, tensile properties at various strain rates and cure kinetics were characterized. Experimental data were analysed using the Flory–Rehner model as well as the tube model theory. It is found that the network structure of CB‐filled SBR follows a three‐phase composite model including rigid particles, semi‐rigid bound rubber and matrix rubber. This bound rubber is postulated to be critical for the mechanical and deformational properties, development of crosslinking density in matrix rubber and polymer–filler interaction. For MWCNT‐filled SBR, the bound rubber does not show a substantial contribution to the network structure and mechanical performance, and these properties are greatly dominated by the higher aspect ratio and polymer–filler interaction. Additionally it is deduced that the crosslinking density of matrix rubber increases on incorporation of the fillers compared to unfilled matrix rubber. Copyright © 2012 Society of Chemical Industry     

Mechanical and physical properties of epoxy composites reinforced by vapor grown carbon nanofibers

Epoxy/vapor grown carbon nanofiber composites (VGCF) with different proportions of VGCF were fabricated by the in situ process.The VGCFs were well dispersed in both of the low and high viscosity epoxy matrices, although occasional small aggregates were observed in a high viscosity epoxy of 20 wt.%. The dynamic mechanical behavior of the nanocomposite sheets was studied. The storage modulus and the glass transition temperature (T_g) of the polymer were increased by the incorporation of VGCFs.The electrical and mechanical properties of the epoxy-VGCFs nanocomposite sheets with different weight percentages of VGCFs were discussed. The results were that both had maximum tensile strength and Young’s modulus at 5 wt.% for both materials and reduced the fracture strain with increasing filler content. The electrical resistivity was decreased with the addition of filler content. Mechanical, electrical and thermal properties of low viscosity epoxy composites were resulted better than that of the high viscosity composites.     

Effect of different carbon fillers on the properties of PP composites: Comparison of carbon black with multiwalled carbon nanotubes

Polypropylene (PP)/carbon composites were prepared via melt blending PP with carbon fillers, including multiwalled carbon nanotubes (MWNTs) and carbon black (CB). Field‐emission scanning electron microscopy was used to research the morphology and dispersion of fillers in the PP matrix. The electrical properties, mechanical properties, and crystallization behaviors of PP/carbon composites were also investigated. The results show that the influence of MWNTs on the properties of PP composites is different with CB, which can be ascribed to the structure and aspect ratio difference between MWNTs and CB. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4823–4830, 2006