Thermally conductive nylon 6,6 and polycarbonate based resins. I. Synergistic effects of carbon fillers

Increasing the thermal conductivity of typically insulating polymers, such as nylon 6,6, opens new markets. A thermally conductive resin can be used for heat‐sink applications. This research focused on performing compounding runs followed by injection molding and thermal conductivity testing of carbon filled nylon 6,6 and polycarbonate based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a milled pitch‐based carbon fiber. For each polymer, conductive resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 2³ factorial design and a complete replicate in each polymer. The objective of this article was to determine the effects and interactions of each filler on the thermal conductivity properties of the conductive resins. From the through‐plane thermal conductivity results, it was determined that for both nylon 6,6 and polycarbonate based resins, synthetic graphite particles caused the largest increase in composite thermal conductivity, followed by carbon fibers. The combination of synthetic graphite particles and carbon fiber had the third most important effect on composite thermal conductivity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 112–122, 2003     

Thermal conductivity of silicone rubber filled with ZnO

Thermal conductivities of silicone rubber filled with ZnO in a wide volume range were measured in order to study the effect of formed conductive particle chains on thermal conductivities. With the increasing of content of ZnO particles in silicone rubber, the amount of formed conductive chains increases and the conductive chains tend linearly to increase the thermal conductivity of the composite. The experimental results obtained were also analyzed using the Nielsen and Agari models to explain the effect of ZnO filler on the formation of thermal conductive networks. Thermal conductivities of a polymer filled with high volume content of particles evidently increased with the adding of small size fillers. The scanning electron microscopy (SEM) showed that percolation threshold has been reached at 31.4 vol% ZnO filler loading, and the hybrid fillers are more densely packed than single fillers in the silicone rubber matrix. There occurs a positive temperature coefficient (PTC) phenomenon in thermal resistance in composites of silicone rubber filled with ZnO. POLYM. COMPOS., 28:125–130, 2007. © 2007 Society of Plastics Engineers     

Effects of carbon fillers on the thermal conductivity of highly filled liquid‐crystal polymer based resins

The thermal conductivity of insulating polymers can be increased by the addition of conductive fillers. One potential market for these thermally conductive resins is for fuel cell bipolar plates. In this study, various amounts of three different carbon fillers (carbon black, synthetic graphite particles, and carbon fiber) were added to Vectra A950RX liquid crystal polymer. Because the resulting composites were anisotropic, they were tested for both through‐plane and in‐plane thermal conductivities. The effects of single fillers and combinations of the different fillers were studied via a factorial design. Each single filler caused a statistically significant increase in composite through‐plane and in‐plane thermal conductivities at the 95% confidence level, with synthetic graphite causing the largest increase. All of the composites containing combinations of the different fillers caused statistically significant increases in the composite through‐plane and in‐plane thermal conductivities. It is possible that thermally conductive pathways were formed that linked these carbon fillers, which resulted in increased composite thermal conductivity. Composites containing 70, 75, and 80 wt % synthetic graphite and the composite containing all three fillers (2.5 wt % carbon black, 65 wt % synthetic graphite, and 5 wt % carbon fiber) had in‐plane thermal conductivities of 20 W m^?1 K^?1 or higher, which is desirable for bipolar plates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synergistic effect of carbon fillers in electrically conductive nylon 6,6 and polycarbonate based resins

The electrical conductivity of polymeric materials can be increased by the addition of carbon fillers, such as carbon fibers, carbon black, and synthetic graphite. The resulting composites could be used in applications such as electromagnetic and radio frequency interference shielding and electrostatic dissipation. A significant amount of work has been conducted varying the amount of single conductive fillers in a composite material. In contrast, very limited work has been conducted concerning the effect of combinations of various types of conductive fillers. In this study, three different carbon fillers were used: carbon black, synthetic graphite pareticles, and pitch based carbon fiber. Two different polymers were used: nylon 6,6 and polycarbonate. The goal of this project was to determine the effect of each filler and combinations of different fillers on the electrical conductivity of conductive resins. A 2³ factorial design was analyzed to determine the effects of the three different carbon fillers in nylon 6,6 and polycarbonate. The results showed that carbon black caused the largest increase in composite electrical conductivity. The factorial design analysis also showed that combinations of different carbon fillers do have a positive synergistic effect, thereby increasing the composite electrical conductivity.     

Conductive polymeric compositions

In most low-strength applications, plastics offer cost, maintenance, and density advantages over metals. Major deficiencies of plastics, however, are low thermal and electrical conductivities. Various studies have dealt with these problems, and it has been found that thermal conductivity and electrical conductivity can both be increased by the addition of conductive fillers to the polymer. The two parameters that most significantly affect the increase in conductivity of the resulting composite are volume loading of filler and filler shape. Fibrous conductors improve conductivity much-more significantly than spheres, flakes, or irregular particulates. The effect of fillers on thermal and electrical conductivities is not the same. The maximum increase in thermal conductivity that can reasonably be expected over the base polymer is 100:1. Electrical conductivity, on the other hand, can be increased by a factor of 10¹⁵. One particularly attractive technique for increasing the electrical conductivity of polymers is electroless plating of metals onto glass fibers which are then incorporated into the polymer. Such a composite can he made electrically conductive with as little as 6 volume percent metal.     

Thermally conductive nylon 6,6 and polycarbonate based resins. II. Modeling

Increasing the thermal conductivity of typically insulating polymers opens new markets. A thermally conductive resin can be used for heat‐sink applications. This research focused on extruding followed by injection molding and thermal conductivity testing of carbon filled nylon 6,6 and polycarbonate‐based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a milled pitch‐based carbon fiber. For each polymer, conductive resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 2³ factorial design and a complete replicate in each polymer. These through‐plane thermal conductivity experimental results were then compared to results predicted by several different thermal conductivity models. An improved thermal conductivity model was developed that fit the experimental results well for resins that contained single fillers and combinations of different fillers. This improved model was based on the original Nielsen model. A single value for the shape parameter, A (which is needed in Nielsen's model), was used for all three different fillers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 123–130, 2003     

Tensile properties of carbon filled liquid crystal polymer composites

Electrically and thermally conductive resins can be produced by adding carbon fillers. Mechanical properties such as tensile modulus, ultimate tensile strength, and strain at ultimate tensile strength are vital to the composite performance in fuel cell bipolar plate applications. This research focused on performing compounding runs followed by injection molding and tensile testing of carbon filled Vectra A950RX liquid crystal polymer composites. The four carbon fillers investigated included an electrically conductive carbon black, thermocarb synthetic graphite particles, and two carbon fibers (Fortafil 243 and Panex 30). For each different filler type, resins were produced and tested that contained varying amounts of these single carbon fillers. The carbon fiber samples exhibited superior tensile properties, with a large increase in tensile modulus over the base polymer, and very low drop in the ultimate tensile strength as the filler volume fraction was increased. The strain at the ultimate tensile strength was least affected by the addition of the Panex carbon fiber but was significantly affected by the Fortafil carbon fiber. In general, composites containing synthetic graphite did not perform as well as carbon fiber composites. Carbon black composites exhibited poor tensile properties. POLYM. COMPOS., 29:15–21, 2008. © 2007 Society of Plastics Engineers     

Visualisation of conductive filler distributions in polymer composites using voltage and energy contrast imaging in SEM

Semiconductive composites have been examined using advanced scanning electron microscopy (SEM). For the first time, voltage contrast and energy contrast between the conductive filler and the polymer matrix have been revealed using a secondary electron detector placed inside the lens system and an energy selective backscattering detector respectively. Critical parameters, including loading level, distribution, dimension and shape of conductive fillers, correlating to the electrical conductivities of the composites, have been investigated and quantitatively determined. These parameters are essential for performance predictions, product quality control and new product development. The volume fractions of the conductive fillers in the two investigated composites were determined as 20.9% and 14.2% respectively. Higher frequency of distribution distance between the conductive filler aggregates within the ranges of 20–100 nm was revealed for the composite with volume fraction of 20.9%. The aggregates of conductive fillers showed mainly branched shapes. The information obtained provides further insight into the conductivity mechanism of conductive filler loaded polymer composite.     

Conductive polymers/polyacrylonitrile composite fibers: Fabrication and properties

Polypyrrole/polyacrylonitrile, polyaniline/polyacrylonitrile, and poly(3,4‐ethylenedioxythiophene)/polyacrylonitrile composite fibres were fabricated successfully by in situ polymerization. The morphologic observations confirmed the uniformly‐covered polyacrylonitrile fiber surface by conductive conjugated polymers. These composite fibers exhibited conductivity in the range of 1.4 × 10⁻² to 5.2 × 10⁻¹ S cm⁻¹. Improved thermal stability of the composite fibers was observed from thermogravimetric analysis results. Structural analysis indicated that the interactions of both hydrogen‐bonding and the electrostatic attraction existed between polyacrylonitrile chains and conjugated polymers. These novel composite fibers still possessed original fibrillar morphology and strength properties and showed a good stability to atmosphere and washing. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Modified resistivity–strain behavior through the incorporation of metallic particles in conductive polymer composite fibers containing carbon nanotubes

Eutectic metal particles and carbon nanotubes are incorporated into a thermoplastic polyurethane matrix through a simple but efficient method, melt compounding, to tune the resistivity–strain behavior of conductive polymer composite (CPC) fibers. Such a combination of conductive fillers is rarely used for CPCs in the literature. To characterize the strain‐sensing properties of these fibers, both linear and dynamic strain loadings are carried out. It is noted that a higher metal content in the fibers results in higher strain sensitivity. These strain‐sensing results are discussed through a morphological study combined with a model based on the classic tunneling model of Simmons. It is suggested that a high tunneling barrier height is preferred in order to achieve higher strain sensitivity. Copyright © 2012 Society of Chemical Industry     

Tensile modulus modeling of carbon‐filled nylon 6,6 and polycarbonate‐based resins

Electrically and thermally conductive resins can be produced by adding conductive fillers to insulating polymers. Mechanical properties, such as tensile modulus, are also important. This research focused on performing compounding runs followed by injection molding and tensile testing of carbon‐filled nylon 6,6 and polycarbonate‐based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a milled pitch–based carbon fiber. For each polymer, resins were produced and tested that contained varying amounts of these single‐carbon fillers. In addition, combinations of fillers were investigated by conducting a full 2³ factorial design and a complete replicate in each polymer. These tensile modulus experimental results were then compared to results predicted by several different models. For the composites containing only one filler type, the Nielsen model with the modified Ψ term provided the best prediction of the actual experimental values. For the composites containing more than one filler type, a new parameter, which includes the vibrated bulk density (VBD) of the fillers, was incorporated into the Nielsen model with the modified Ψ term. This model with the new VBD parameter provided the best estimate of experimental tensile modulus for composites containing multiple‐filler types. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1716–1728, 2003     

A three-dimensional Monte Carlo model for electrically conductive polymer matrix composites filled with curved fibers

A three-dimensional (3-D) Monte Carlo model is developed for predicting electrical conductivity of polymer matrix composites filled with conductive curved fibers. The conductive fillers are modeled as a 3-D network of finite sites that are randomly positioned. The percolation behavior of the network is studied using the Monte Carlo method, which leads to the determination of the critical fiber volume fraction (or the percolation threshold). The effect of fiber curliness on the percolation behavior is incorporated in the current model by using 3-D arm-shaped fibers, each of which needs five independent geometrical parameters (i.e., three coordinates for its vertex and two orientation angles) for its identification. There are three controlling parameters for such fibers, namely the fiber arm length, the fiber aspect ratio, and the fiber arm angle. The new model also considers the sample size and scaling effects. The simulation results reveal an exponential relationship between the fiber aspect ratio and the percolation threshold: the higher the aspect ratio, the lower the threshold. It is also found that the curliness largely influences the percolation threshold: the more curved the fiber, the higher the threshold. However, the effect of curliness diminishes with the increase of the fiber aspect ratio. With the percolation threshold obtained from the Monte Carlo model, the effective electrical conductivity of the composite is then determined by applying the theory of percolation. The numerical results indicate that the composite conductivity decreases as the fibers become more curved and as the fiber aspect ratio decreases. These predicted trends of the percolation threshold and composite conductivity are in good agreement with existing experimental and simulation results.     

Influences of dielectric and conductive fillers on dielectric and mechanical properties of solid silicone rubber composites

Dielectric elastomers are materials being used for electromechanical transduction applications. Their electromechanical response depends on permittivity, Young’s modulus and electric breakdown strength. A factor that limits its application is high operating voltages that can be reduced through improvement in permittivity. One of the methods is by incorporating high permittivity fillers into polymer matrix to obtain dielectric–dielectric composites (DDC).These composites show high permittivity at the cost of reduced flexibility. An alternative solution is development of composites by incorporating organic or inorganic conductive fillers into polymer matrix. These composites show high permittivity with high dielectric loss and low breakdown strength. To overcome both the above limitations both dielectric and conductive fillers are incorporated into dielectric polymer matrix to obtain conductor–dielectric composites (CDC). In this study, high temperature vulcanized solid silicone rubber as matrix has been used to prepare DDC composites with barium titanate (BT) filler and CDC composites with both BT as dielectric and ketjenblack as conductive fillers, using Taguchi design of experiments. The effect of factors such as amount of fillers and curing agent, mixing time in roll mill and curing temperature on the dielectric and mechanical properties are reported. Lichtenecker model predicts the permittivity of the DDC composite more accurately. For the CDC composites permittivity increased by 390%, effective resistivity decreased by 80%, Young’s modulus increased by 368% and Shore A hardness increased by 90% as compared to those of reference matrix. Important interaction effects are observed among both the fillers that are uniformly dispersed without any aggregation.

     

Mechanical and shape‐memory behavior of shape‐memory polymer composites with hybrid fillers

Shape‐memory polymer (SMP) materials have several drawbacks such as low strength, low stiffness and natural insulating tendencies, which seriously limit their development and applications. Much effort has been made to improve their mechanical properties by adding particle or fiber fillers to reinforce the polymer matrix. However, this often leads to the mechanical properties being enhanced slightly, but the shape‐memory effect of reinforced SMP composites being drastically reduced. The experimental results reported here suggested that the mechanical resistive loading and thermal conductivity of a composite (with hybrid filler content of 7.0 wt%) were improved by 160 and 200%, respectively, in comparison with those of pure bulk SMP. Also, the glass transition temperature of the composite was enhanced to 57.28 °C from the 46.38 °C of a composite filled with 5.5 wt% hybrid filler, as determined from differential scanning calorimetry measurements. Finally, the temperature distribution and recovery behavior of specimens were recorded with infrared video in a recovery test, where a 28 V direct current circuit was applied. The effectiveness of carbon black and short carbon fibers being incorporated into a SMP with shape recovery activated by electricity has been demonstrated. These hybrid fillers were explored to improve the mechanical and conductive properties of bulk SMP. Copyright © 2010 Society of Chemical Industry     

Thermal conductivity of a polymer composite

A prediction equation for thermal conductivity of polymer composites reported in our previous papers has been revised in terms of two view points: (1) estimation of thermal conductivity of a composite using an idea of reduced thermal conductivity; and (2) the effect of ease in forming conductive filler chains on thermal conductivity is related to the CVF value in electric conductivity of the composite. The new equation was confirmed to be adaptable to thermal conductivities of varieties of polymer composite systems filled with spherical or irregular fillers. The equation was also considered to explain thermal conductivity of polymer composites filled with fibers. Further, it was found that thermal conductivities of fiber composites can be estimated by introducing a factor of the CVF value or aspect ratio (L/D) into the new equation. © 1993 John Wiley & Sons, Inc.     

Shielding effectiveness of carbon-filled nylon 6,6

Electrically conductive resins can be made by adding electrically conductive fillers to typically insulating polymers. Resins with an electrical resistivity of approximately 10⁰ ohm-cm or less can be used for electromagnetic and radio frequency interference shielding applications. This research focused on performing compounding runs followed by injection molding and shielding effectiveness testing of carbon filled nylon 6,6 based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a surface-treated polyacrylonitrile (PAN)-based carbon fiber. Conductive resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 2³ factorial design and a complete replicate. The objective of this paper was to determine the effects and interactions of each filler on the shielding effectiveness properties of the conductive resins. Carbon fiber caused the largest increase in shielding effectiveness. Also, all the single fillers and combinations of fillers were statistically significant at the 95% confidence level, except the composite containing carbon black and synthetic graphite particles tested at 800 MHz. Polym. Compos. 25:407–416, 2004. © 2004 Society of Plastics Engineers.     

Potassium persulfate-mediated preparation of conducting polypyrrole/polyacrylonitrile composite fibers: Humidity and temperature-sensing properties

Conducting polypyrrole (PPy)/polyacrylonitrile (PAN) composite fibers were prepared by the polymerization of pyrrole in the presence of PAN fibers with potassium persulfate in an acidic aqueous solution. We obtained composite fibers containing concentrations of PPy as high as 1.14% and having surface resistivities as low as 0.6 kΩ/cm² by changing the polymerization parameters, including the temperature and concentrations of pyrrole and oxidant. The tensile strength of 10.02 N/m² and breaking elongation of 32.68% for the pure PAN fiber increased up to 10.45 N/m² and 33.23%, respectively, for the composite fiber containing 0.13% PPy. The change in the resistivity of the PPy/PAN composite fiber during heating–cooling cycles in the temperature range of +5 to 120°C was examined. Scanning electron microscopy and optical microscopy images of the composite fibers showed that the PPy coating was restricted to the surfaces of the PAN fibers. Surface resistivity measurements, Fourier transform infrared spectroscopy, and thermogravimetric analysis techniques were also used to characterize the composite fibers. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrical conductivity of poly(vinyl chloride) plastisol–short carbon fiber composite

In this work, short carbon fibers were blended with poly(vinyl chloride) (PVC) plastisol forming a conductive network of the fibers in the composite. The effects of concentration and initial length of the carbon fibers on the conductivity of the network were studied. For an initial fiber length of 3 mm (L/D = 428), the volume resistivity of the network decreased rapidly from 4.3 × 10⁵ to 5.1 × 10⁰ Ω-m for a change in the fiber concentration of 0.5 to 1.0 phr. The samples prepared by the plastisol method also showed excellent antistatic properties at very low fiber concentration (e.g. 1.0 phr), better than the samples that were prepared by mill mixing. Observation of the morphology showed that the short carbon fibers maintained their initial length in the PVC plastisol-carbon fiber composite, without obvious breakage. This is why a conductive network in the plastisol-carbon fiber composite can be formed at very low fiber concentrations.     

Synergistic effects of carbon fillers on tensile and impact properties in nylon 6,6 and polycarbonate based resins

Electrically and thermally conductive resins can be produced by adding conductive fillers to insulating polymers. Mechanical properties such as tensile modulus, ultimate tensile strength, strain at ultimate tensile strength, and notched Izod impact strength are also important and cannot be ignored. This research focused on performing compounding runs followed by injection molding and tensile and impact property testing of carbon filled nylon 6,6 and polycarbonate based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a milled pitch based carbon fiber. For each polymer, resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 2³ factorial design and a complete replicate in each polymer. The objective of this paper was to determine the effects and interactions of each filler on the tensile and impact properties. The results showed that, in many cases, combining two and three different fillers caused a statistically significant effect at the 95% confidence level. Polym. Compos. 25:172–185, 2004. © 2004 Society of Plastics Engineers.     

导电复合橡胶研究进展

介绍了导电复合橡胶的两大导电机理,即导电通路学说和量子力学隧道效应学说;对炭系、金属系、颗粒表面镀金属、本征导电聚合物填充制备导电复合橡胶的研究进展状况进行了综述;并从聚合物并用、温度、压力等方面对复合型导电橡胶导电性能的影响因素进行了综述。