Carbon-filled polymer blends electrical conductivities

The electrical conductivities of injection-molded, CNT-filled polymer blends are summarized in Table 12.4. For comparison. Table 12.4 also includes the literature value of conductivities of neat polymers used in this study. For each polymer blend, electrical conductivities are measured in two directions (i.e.. Directions I and II in Fig. 12.2) to determine whether the specimen is isotropic or not. It is found that there is large difference in conductivity between Directions I and II. For the CNT-filled PET/PVDF, PET/PP, and PET/HDPE, the conductivity in Direction I is about 4-8 times higher than that in Direction II. For the CNT-filled PET/nylon 6,6, the conductivity difference in the two directions is even larger, with Direction I having more than 22 times higher conductivity than Direction II. The anisotropy found in all the specimens is related to the partial alignment of carbon nanotubes in the... 

In spite of the substantial progress made with the concept of carbon-filled polymer blends containing a triple-continuous structure, the carbon-filled polymer blends studied so far only contain relatively low carbon concentrations. As a result, their electrical conductivities are still far below the desired values (such as >100 S cm ) for the application of PEM fuel cell bipolar plates. Therefore, it is imperative to investigate (a) whether such a triple-continuous structure can still be injection molded for polymer blends with high carbon concentrations (e.g., >30 vol% carbon) and (b) whether the polymer blends with high carbon concentrations and a triple-continuous structure, if injection moldable, still possess superior electrical conductivity and mechanical properties. Both issues will be the topics of future studies. 

The effectiveness of carbon-filled polymer blends in improving simultaneously the electrical conductivity and the mechanical strength has been demonstrated by Shaw. Carbon-filled polymer blends with a triple-continuous structure, consisting of... 

Gubbels, F., Blacher, S., Vanlathem, E., Jerome, R., Deltour, R., Brouers, F., and Teyssie, Ph. (1995) Design of electrical conductive composites key role of the morphology on the electrical properties of carbon black filled polymer blends. Macromolecules, 28, 1559-1566. 

Given that all of the CNT-filled polymer blends in this study are prepared with 50 vol% of the CNT-filled PET phase (with 12 vol% CNTs) plus 50 vol% of the second immiscible polymer phase (with no CNTs), it is reasonable to assume that both the CNT-fiUed PET phase and the second immiscible neat polymer phase have formed self-continuous 3D networks in the polymer blends. This expectation is confirmed by the microstructure examination (see Sect. 12.1), which reveals that the area fractions of the CNT-filled region and the CNT-free region are both near 50%. Furthermore, the electrical conductivity data suggest that the carbon nanotubes within the PET phase have also formed a 3D conductive path because the electrical resistivity has been reduced from the neat polymer blends to the CNT-filled polymer blends by about 12 orders of magnitude. With such a triple-continuous structure, the conductive CNT-filled PET network and the non-conductive second polymer phase can be treated as parallel conductors, and the resulting resistivity, p, of the CNT-filled polymer blend can be estimated using the statistical percolation model proposed by Bueche [61] ... 

Finally, it is important to compare the electrical conductivities of the CNT-filled polymer blends with that of the CNT-filled polymers. Figure 12.7 shows the resistivities of the CNT-filled PET/PVDF and CNT-filled PET as a function of the carbon... 

F. Gubbels, S. Blacher, E. Vanlanthem, R. Jerome, R. Deltour, F. Brouers, and P. Teyssid, Design of Electrical Conductive Composites Key Role of the Morphology on the Electrical Properties of Carbon Black Filled Polymer Blends, Macromolecules 28, 1559-1566 (1995). 

Meincke O, Kaempfer D, Weickmann H, Friedrich C, Vathauer M, Warth H (2004). Mechanical properties and electrical conductivity of carbon-nanotube filled polyamide-6 and its blends with acrylonitrile/butadiene/styrene. Polymer 45 739-748. 

The electrical conductivity of two-phase, incompatible polymer blends containing carbon black has been shown to depend on the relative affinity of the conductive particles to each of the polymer components in the blend, the concentration of carbon black in the filler-rich phase, and the structural continuity of this phase [82]. Hence, by judicious manipulation of the phase microstructure, these three-phase filled composites can exhibit double percolation behaviour. 

Sumita, M., Sakata, K., Asai, S., Miyasaka, K., and Nakagawa, H. 1991. Dispersion of fillers and the electrical-conductivity of polymer blends filled with carbon-black. Polymer Btdletin 25 265-271. 

Xu, Z., Zhao, C., Gu, A., Fang, Z., and Tong, L. (2008) Effect of morphology on the electric conductivity of binary polymer blends filled with carbon black. J. pL Polym. ScL, 106, 2008. 

Zhou and co-workers [28] measured the electrical conductivity/resistivity of carbon black filled linear low-density polyethylene (LLDPE) and blends of LLDPE with ethylene-methylacrylate (EMA). The percolation threshold of the blended polymer composite was significantly lower than that of the LLDPE composite, although in an EMA composite the threshold is higher. This effect was due to preferential absorption of the carbon black into the LLDPE due to phase separation and immiscibility in low-density polyethylene (LDPE)/EMA blends. The viscosity of polymers in the blend... 

Electrical conductivity measurements have been reported on a wide range of polymers including carbon nanofibre reinforced HOPE [52], carbon black filled LDPE-ethylene methyl acrylate composites [28], carbon black filled HDPE [53], carbon black reinforced PP [27], talc filled PP [54], copper particle modified epoxy resins [55], epoxy and epoxy-haematite nanorod composites [56], polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) blends [57], polyacrylonitrile based carbon fibre/PC composites [58], PC/MnCli composite films [59], titanocene polyester derivatives of terephthalic acid [60], lithium trifluoromethane sulfonamide doped PS-block-polyethylene oxide (PEO) copolymers [61], boron containing PVA derived ceramic organic semiconductors [62], sodium lanthanum tetrafluoride complexed with PEO [63], PC, acrylonitrile butadiene [64], blends of polyethylene dioxythiophene/ polystyrene sulfonate, PVC and PEO [65], EVA copolymer/carbon fibre conductive composites [66], carbon nanofibre modified thermotropic liquid crystalline polymers [67], PPY [68], PPY/PP/montmorillonite composites [69], carbon fibre reinforced PDMS-PPY composites [29], PANI [70], epoxy resin/PANI dodecylbenzene sulfonic acid blends [71], PANI/PA 6,6 composites [72], carbon fibre EVA composites [66], HDPE carbon fibre nanocomposites [52] and PPS [73]. 

Mallette J G, Quej L M, Marquez A and Manero O (2001) Carbon black-filled PET/HDPE blends Effect of the CB structure on rheological and electric properties, J Appl Polym Sci 81 562-569. Xu X B, Li Z M, Dai K and Yang M B (2006) Anomalous attenuation of the positive temperature coefficient of resistivity in a carbon-black-filled poljoner composite with electrically conductive in situ microfibrils, Appl Phys Lett 89 032105. 

Composites prepared by filling with carbon black natural rubber/polyethylene or polystyrene/ethylene-propylene random copolymer blends have an electrical conductivity much higher than that for the individual components at the same loading level (Geuskens et al. 1987). The addition of carbon black to these immiscible polymers lowered the size of the dispersed phase. 

Geuskens G., Gielens J.L., Geshef D., and Deltour R. The electrical conductivity of polymer blends filled with carbon-black. Eur. Polym. J. 23 no. 12 (1987) 993-995. 

Conductive polymer composites can be defined as insulating polymer matrices which have been blended with filler particles such as carbon black, metal flakes or powders, or other conductive materials to render them conductive. Although the majority of applications of polymers in the electrical and electronic areas are based on their ability to act as electrical insulators, many cases have arisen more recently when electrical conductivity is required. These applications include the dissipation of electrical charge from rubber and plastic parts and the shielding of plastic boxes from the effects of electromagnetic waves. Consequently, materials scientists have sought to combine the versatility of polymers with the electrical properties of metals. The method currently used to increase the electrical conductivity of plastics is to fill them with conductive additives such as metallic powders, metallic fibres, carbon black and intrinsically conducting polymers such as polypyrrole. 

It is known that carbon-black filled polymers conduct electric current only with the concentration of carbon black exceeding the threshold of percolation ((p ). In heterogeneous polymer blends carbon black is distributed nonuniformly between polymer phases. If the concentrations of carbon black in both phases of a blend are lower than (p, the blend can conduct electric current only subject to the condition that the part of carbon black is localized at the interface and its concentration here reaches the percolation threshold [12]. So if the concentration of carbon black in both phases of a blend is only slightly lower than (p, even a minor accumulation of carbon black at the interface confers conductivity on the polymer blend. This enables the extent of carbon black aggregation at the interface to be judged by the conductivity value. 

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