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1.
    
Adding conductive carbon fillers to insulating resins increases the composite electrical and thermal conductivity. Often, enough of a single type of carbon filler is added to achieve the desired conductivity while still allowing the material to be molded into a bipolar plate for a fuel cell. In this study, various amounts of three different carbons (carbon black, synthetic graphite particles, and carbon fiber) were added to Vectra A950RX liquid‐crystal polymer. The rheological properties of the resulting single‐filler composites were measured. In addition, the rheological properties of composites containing combinations of different carbon fillers were studied via a factorial design. In all cases, the viscosity increased with increasing filler volume fraction and followed a shear‐thinning power‐law model. The factorial design results indicated that each of the single fillers and all the filler combinations caused a statistically significant increase in the composite viscosity when compared at a shear rate of 500 s?1 or at a stress of 105 Pa. For composites containing synthetic graphite particles and/or carbon fiber, the viscosity variation with the volume fraction of carbon followed a modified Maron–Pierce equation. When compared at a constant volume fraction of carbon, composites containing carbon black showed viscosity enhancement above and beyond that shown by the other composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

2.
    
Thermally conductive resins are needed for bipolar plates in fuel cells. Currently, the materials used for these bipolar plates often contain a single type of graphite in a thermosetting resin. In this study, varying amounts of two different types of polyacrylonitrile based carbon fibers, Fortafil 243 and Panex 30, were added to a thermoplastic matrix (Vectra A950RX Liquid Crystal Polymer). The resulting single filler composites were tested for thermal conductivity and a simple exponential thermal conductivity model was developed for the square root of the product of the in‐plane and through‐plane thermal conductivity . The experiments showed that the through‐plane thermal conductivity was similar for composites up to 40 vol % fiber. However, at higher loadings, the Panex 30 samples exhibited higher thermal conductivity. The experiments also showed that the in‐plane thermal conductivity of composites containing Panex 30 was higher than those containing Fortafil 243 for all volume fractions studied. Finally, the model agreed very well with experimental data covering a large range of filler volume fraction (from 0 to 55 vol % for both single filler systems). The model can be used with existing through‐plane thermal conductivity models to predict in‐plane thermal conductivity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5456–5462, 2006  相似文献   

3.
    
Electrically conductive resins may have applications as fuel cell bipolar plates. The current trend in this technology is a thermosetting polymer as the matrix containing high concentrations of various types of fillers. These fillers are carbon based and electrically conductive powders, particles, or fibers. In this study, we utilized two composite formulations of polyacrylonitrile fibers (Fortafil 243 and Panex 30) in a liquid crystal polymer (Vectra A950RX) with increasing concentrations. Electrical conductivity tests were performed and modified Mamunya and additive models were applied to the experimental data. These models fit the entire range of data for each composite tested. Four alternate models were also produced: linear, quadratic, exponential, and geometric, with a restricted range of electrical conductivity data greater than 10?2 S/cm. The exponential and the geometric resulted in the best fits over this restricted data range. These particular models may allow researchers to extrapolate beyond the maximum filler concentrations studied here. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007  相似文献   

4.
    
Electrically conductive resins are needed for bipolar plates used in fuel cells. Currently, the materials for these bipolar plates often contain a single type of graphite powder in a thermosetting resin. In this study, various amounts of two different types of carbon, carbon black and synthetic graphite, were added to a thermoplastic matrix. The resulting single‐filler composites were tested for electrical conductivity, and electrical conductivity models were developed. Two different models, the Mamunya and additive electrical conductivity models, were used for both material systems. It was determined how to modify these models to reduce the number of adjustable parameters. The models agreed very well with experimental data covering a large range of filler volume fractions (from 0 to 12 vol % for the carbon black filled composites and from 0 to 65 vol % for the synthetic graphite filled composites) and electrical conductivities (from 4.6 × 10?17 S/cm for the pure polymer to 0.5 S/cm for the carbon black filled composites and to 12 S/cm for the synthetic graphite filled composites). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3293–3300, 2006  相似文献   

5.
    
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  相似文献   

6.
    
One emerging market for thermally and electrically conductive resins is bipolar plates for use in fuel cells. Adding carbon fillers to thermoplastic resins increases the composite thermal and electrical conductivity. These fillers have an effect on the composite tensile and flexural properties, which are also important for bipolar plates. In this study, various amounts of three different types of carbon (carbon black, synthetic graphite particles, and carbon fibers) were added to Vectra A950RX liquid‐crystal polymer. In addition, composites containing combinations of fillers were also investigated via a factorial design. The tensile and flexural properties of the resulting composites were then measured. The objective of this study was to determine the effects and interactions of each filler with respect to the tensile and flexural properties. The addition of carbon black caused the tensile and flexural properties to decrease. Adding synthetic graphite particles caused the tensile and flexural modulus to increase. The addition of carbon fiber caused the tensile and flexural modulus and ultimate flexural strength to increase. In many cases, combining two different fillers caused a statistically significant effect on composite tensile and flexural properties at the 95% confidence level. For example, when 40 wt % synthetic graphite particles and 4 wt % carbon black were combined, the composite ultimate tensile and flexural strength increased more than what would be expected from the individual additive effect of each single filler. It is possible that linkages were formed between the carbon black and synthetic graphite particles that resulted in improved ultimate tensile and flexural strength. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

7.
    
There is an emerging market for conductive resins for use in fuel cell bipolar plates. This research focuses on developing a finite element model of a capillary rheometer. Comsol Multiphysics 3.2b was used to model the flow of a remeltable thermoplastic matrix material, Vectra A950RX Liquid Crystal Polymer, with varying amounts of either a carbon black or synthetic graphite filler, to obtain the velocity profile and pressure drop of these composites within the capillary. Previous experimental results have shown that the molten composites obey a shear‐thinning power law behavior. When comparing the model predicted pressure drops from the model with the experimental data, very good agreement was obtained. This signifies that the rheological behavior of the composites can be described by a power law relationship, using parameters specific to each composite. When comparing the modeled velocity profile with the theoretical profile, it was found for all composite formulations that the velocity becomes fully developed within a length of 0.05 times the diameter of the tube, independent of the power law parameters n and m. This work is a necessary first step in developing 2D or 3D mold filling simulations for fuel cell bipolar plate applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007  相似文献   

8.
    
Thermally conductive resins are needed for bipolar plates in fuel cells. Currently, the materials used for these bipolar plates often contain a single type of graphite in a thermosetting resin. In this study, varying amounts of four different types of polyacrylonitrile carbon fillers (Ketjenblack carbon black, Thermocarb synthetic graphite, Fortafil 243 carbon fiber, and Panex 30 carbon fiber) were added to a thermoplastic matrix (Vectra A950RX Liquid Crystal Polymer), with the resulting resins tested for through‐plane and in‐plane thermal conductivity. There are two unique contributions of this work. The first contribution is the use of the Nielsen model for the through‐plane thermal conductivity as a function of the single filler volume fraction. The model fits the data for all composites well. The second contribution is the development of a new, accurate, empirical model to predict the in‐plane thermal conductivity for all resins containing synthetic graphite or carbon fiber. Both of these models will form the basis for the development of new thermal conductivity models for composites with multiple fillers for fuel cell bipolar plate applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007  相似文献   

9.
The physical properties, thermal stability, rheology and tensile properties of a commercial semi-crystalline and an amorphous thermotropic liquid crystalline polymer (TLCP) have been investigated. Analysis by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) confirm the presence of a small melting endotherm and a glass transition in the former material. The as-received amorphous TLCP exhibits no obvious melting endotherm and a strong glass transition is detected. The flow and tensile properties of the semicrystalline polymer are dominated by the presence of the crystalline to nematic transition temperature. The properties of the amorphous TLCP appear to be governed by increasing mobility afforded by increasing temperature. Based on flow behaviour and further DSC analysis it has been shown that under appropriate annealing conditions the as-received amorphous TLCP can develop solid crystalline order.  相似文献   

10.
    
The temperature–conductivity characteristics of poly(3‐hexylthiophene) (P3HT) composites filled with P3HT‐grafted indium tin oxide (ITO) particles were investigated in this work. The ITO particles were first treated with a silane coupling reagent of 3‐aminopropyltriethoxysilane (APS), and then thiophene rings were introduced through a condensation reaction between the ending amino groups of APS and the carboxylic groups of thiophene‐3‐acetic acid. The composites were prepared by the polymerization filling of the 3‐hexylthiophene (3HT) monomer with the thiophene‐ring‐introduced ITO particles. Elemental analysis, Fourier transform infrared, and X‐ray photoelectron spectroscopy were used to confirm the grafting reaction on the ITO surface. The longer the polymerization time was or the higher the 3HT/ITO feeding ratio was, the more P3HT was grafted. The influence of the grafted amount on the electrical properties of ITO particles was attributed to the wrapping effect formed by the grafted P3HT on the surface of the ITO particles. The conductivity change of the P3HT‐grafted ITO/P3HT composites was proved to be subject to the change in the average gap width of ITO interparticles, which was determined by the filling ratio of P3HT to ITO in the polymerization and the volume expansion effect of a P3HT thin film between neighboring ITO particles during the heating process. In comparison with the ungrafted ITO/P3HT composites, the grafting treatment enhanced the interaction between the particles and polymer matrix, and this was helpful for obtaining a more homogeneous dispersion structure for the composites and thus afforded a higher positive temperature coefficient intensity and better reproducibility. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1881–1888, 2006  相似文献   

11.
    
This report describes how the degree of deacetylation and molecular weight of chitosan and the concentrations of sodium chloride and malic acid affect the formation of lyotropic chitosan liquid crystals. Chitosan samples of various degrees of deacetylation were prepared from β‐chitin that was isolated from squid pens. They were degraded by ultrasonic irradiation to various molecular weights. The critical concentrations forming chitosan liquid crystals were determined with a polarized microscope. A chitosan sample with a degree of deacetylation of 67.2–83.6% formed cholesteric lyotropic liquid crystals when it was dissolved in 0.37–2.59M malic acid. The critical concentrations increased with increasing degrees of deacetylation of chitosan. They decreased with increasing molecular weights or increasing concentrations of sodium chloride and malic acid. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007  相似文献   

12.
    
Ethyl‐cyanoethyl cellulose [(E–CE)C]/poly(acrylic acid) (PAA) composite films were prepared by photopolymerizing acrylic acid (AA) in (E–CE)C/AA cholesteric liquid crystalline solutions. With the selection of suitable concentrations, (E–CE)C/PAA composite films showed vivid colors due to the selective reflection property of the cholesteric phase. It was found that the wavelength of reflection was a function of the concentration of (E‐CE)C, and the reflectivity was increased with increasing thickness of the film. The selective reflection of the composite holds well upon heating at temperatures below 160°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 213–217, 2004  相似文献   

13.
    
A semirigid and amorphous commercial liquid‐crystalline copolyester (Rodrun) was filled with mica and calcium carbonate (up to 25 wt %) by direct injection molding. The fillers led to decreases in the processability, as observed by torque increases, but maintained the thermal resistance of Rodrun. The effects of the two fillers on the modulus of elasticity, ductility, and tensile strength were the same or very similar. The decrease in the tensile strength (20% for a 10% filler content) was compensated by a generally slight increase in the modulus of elasticity, whatever the filler content was. This balance of properties found in these new liquid‐crystalline‐polymer‐based materials and the important savings that the fillers bring may spread the applications of these materials' matrices. © 2003 Wley Periodicals, Inc. J Appl Polym Sci 88: 998–1003, 2003  相似文献   

14.
    
The microencapsulated red phosphorus (MRP) filled polypropylene (PP) composites were prepared using a twin‐screw extruder. The effects of load and temperature on the extrudate swell behavior of the PP/MRP composite melts were investigated by means of a melt flow indexer. The test temperatures and loads were varied from 180 to 205°C and from 2.16 to 12.5 kg, respectively. The results showed that the die‐swell ratio (B) of the composite melts increased roughly linearly with increasing load while decreased slightly with a rise of test temperature. The sensitivity of the die‐swell ratio of the composite melts to load was significant. When the test temperature or load was constant, the values of the B of the composite melts decreased slightly with increasing MRP weight fraction. The findings can provide useful information for processing of these composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

15.
    
A thermotropic liquid‐crystalline polymer (TLCP), a copolyester with a 60/40 molar ratio of p‐hydroxy benzoic acid and poly(ethylene terephthalate), was blended with a styrene/ethylene butylene/styrene thermoplastic elastomer with a twin‐screw extruder. The rheological behavior, morphology, and mechanical properties of the extruded strands of the blends were investigated. The rheological measurements were performed on a capillary rheometer in the shear rate range of 5–2000 s?1 and on a plate‐and‐plate rheometer in the frequency range of 0.6–200 rad s?1. All the neat components and blends exhibited shear thinning behavior. Both the shear and complex viscosities of all the blends decreased with increasing TLCP contents, but the decrease in the shear viscosity was more pronounced. The best fibrillar morphology was observed in the extruded strands of a blend containing 30 wt % TLCP, and a lamellar structure started to form at 40 wt % TLCP. With an increasing concentration of TLCP, the tensile modulus of the blends was greatly enhanced, whereas the tensile strength was almost unchanged. The elongation at break of the blends first slightly decreased with the addition of TLCP and then sharply dropped at 40 wt % TLCP. The tension set measured at 200% deformation slightly increased with increasing TLCP contents up to 30 wt %, over which the set value was unacceptable for a thermoplastic elastomer. A remarkable improvement in the dynamic mechanical properties of the extruded strands was observed in the blends with increasing amounts of TLCP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2676–2685, 2003  相似文献   

16.
《国际聚合物材料杂志》2012,61(3-4):243-248
Abstract

In this article emphasis will be placed on selectively from 45 papers presented at the spring meeting and 33 papers also presented at the fall meeting.  相似文献   

17.
The interfacial properties of polymer blends of the engineering thermoplastics (TPs) polycarbonate (PC) and polyethersulfone (PES) with thermotropic liquid crystalline polymers (TLCPs) were studied using FTIR and DSC. The TLCP/TP blend systems were mainly immiscible. The viscosity properties of the TLCP/TP blends were analysed. The mechanism of the viscosity variation of the blends is discussed. Based on the assumptions given in this paper, a reasoned theoretical formula of the blend viscosity is derived to express the viscosity reduction of the TLCP/TP blends.  相似文献   

18.
    
A novel concept of improving shear‐induced fibrillation of liquid crystalline polymer (LCP) in LCP/thermoplastic blend systems was introduced. Silica fillers (SiO2) were added to an LCP/polypropylene (PP) system to serve as a viscosity thickening agent and to improve the fibrillation of the LCP phase. The formation of LCP fibrils was found to enhance with the incorporation of 5–15 wt % of fillers. The presence of LCP fibrils improved the flow properties of the LCP/PP/SiO2 composites. It was evident from the rheological and morphological studies that the addition of silica led to an increase of the aspect ratio of the LCP fibrils, which, in turn, should improve their effectiveness as reinforcements and/or toughening agents. Substantial improvement in LCP aspect ratio was achieved by the introduction of hydrophobic SiO2 fillers in the PP/LCP blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2070–2078, 2002  相似文献   

19.
    
Polypropylene (PP) was melt‐blended in a single‐screw extruder with a thermotropic Vectra B‐950 liquid crystalline polymer (LCP) in different proportions. The mechanical properties of such blends were compared in respect of their Young's moduli, ultimate tensile strength (UTS), percent elongation at break, and toughness to those of pure PP. The thermal properties of these blends were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The morphology was studied by using a polarizing light microscope (PLM) and a scanning electron microscope (SEM) while the rheological aspects of the blends and the pure PP were studied by a Haake Rheowin equipment. Mechanical analysis (tensile properties) of the blends showed pronounced improvement in the moduli and the UTS of the PP matrix in the presence of 2–10% of LCP incorporation. TGA of all the blends showed an increase in the thermal stability for all the blends with respect to the matrix polymer PP, even at a temperature of 410°C, while PP itself undergoes drastic degradation at this temperature. DSC studies indicated an increase in the softening range of the blends over that of PP. Morphological studies showed limited mixing and elongated fibril formation by the dispersed LCP phase within the base matrix (PP) at the lower ranges of LCP incorporation while exhibiting a tendency to undergo gross phase separation at higher concentrations of LCP, which forms mostly agglomerated fibrils and large droplets. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 767–774, 2003  相似文献   

20.
    
Liquid crystalline chitin/poly(acrylic acid) composite, with its unique optical properties, was fabricated by the free‐radical photopolymerization of acrylic acid in an aligned mesophase. Alignment of the mesophase was achieved by unidirectional shearing. The developed composites, coated on calcium fluoride (CaF2) substrate, were transparent, and the alignment was retained depending on the mesophase composition of the ternary dispersion (chitin microfibrils, water, acrylic acid). According to studies from polarized FTIR spectroscopy, both the degree of orientation and the molecular interactions were strongly affected by respective mesophase behavior. The average molecular chains of chitin microfibrils were oriented along the shear direction. A high dichroic ratio value of about 25, observed in composites of chitin/poly(acrylic acid) with a w/w ratio of 55:45, opens an interesting avenue to prepare a new chitin‐based optically anisotropic composite. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1932–1940, 2003  相似文献   

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