Synergistic effects of carbon fillers on tensile and flexural properties in liquid‐crystal polymer based resins

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     

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     

Electrical conductivity of carbon‐filled polypropylene‐based resins

Adding conductive carbon fillers to insulating thermoplastic resins increases composite electrical conductivity. Often, as much of a single type of carbon filler is added to achieve the desired conductivity and still allow 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 nanotubes) were added to polypropylene resin. The resulting single‐filler composites were tested for electrical resistivity (1/electrical conductivity). The effects of single fillers and combinations of the different carbon fillers were studied via a factorial design. The percolation threshold was 1.4 vol % for the composites containing only carbon black, 2.1 vol % for those containing only carbon nanotubes, and 13 vol % for those containing only synthetic graphite particles. The factorial results indicate that the composites containing only single fillers (synthetic graphite followed closely by carbon nanotubes and then carbon black) caused a statistically significant decrease in composite electrical resistivity. All of the composites containing combinations of different fillers had a statistically significant effect that increased the electrical resistivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrical and thermal conductivity and tensile and flexural properties of carbon nanotube/polycarbonate resins

Adding conductive carbon fillers to insulating thermoplastic polymers increases the resulting composite's electrical conductivity. Carbon nanotubes (CNTs) are very effective at increasing composite electrical conductivity at low loading levels without compromising composite tensile and flexural properties. In this study, varying amounts (2–8 wt %) of CNTs were added to polycarbonate (PC) by melt compounding, and the resulting composites were tested for electrical conductivity (1/electrical resistivity), thermal conductivity, and tensile and flexural properties. The percolation threshold was less than 1.4 vol % CNT, likely because of CNTs high aspect ratio (1000). The addition of CNT to PC increased the composite electrical and thermal conductivity and tensile and flexural modulus. The 6 wt % (4.2 vol %) CNT in PC resin had a good combination of properties for electrical conductivity applications. The electrical resistivity and thermal conductivity were 18 Ω‐cm and 0.28 W/m · K, respectively. The tensile modulus, ultimate tensile strength (UTS), and strain at UTS were 2.7 GPa, 56 MPa, and 2.8%, respectively. The flexural modulus, ultimate flexural strength, and strain at ultimate flexural strength were 3.6 GPa, 125 MPa, and 5.5%, respectively. Ductile tensile behavior is noted in pure PC and in samples containing up to 6 wt % CNT. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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

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     

Effect of hybridization and compatibilization on the mechanical properties of recycled polypropylene‐hemp composites

Hemp fibers and particles, with different sizes and contents, were used to make hybrid composites based on recycled polypropylene (PP). In particular, the effect of maleated polypropylene (MAPP) addition on the morphology and mechanical properties is reported. The results show that better adhesion is obtained with MAPP addition. In general, fiber content and size had a substantial effect on the tensile, flexural, torsion, and impact properties of the resulting composites. Although, adding MAPP to the samples improved the impact strength of the composites, the values were always lower than neat PP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of soybean‐oil‐based polyurethane composites containing industrial and agricultural residual wastes as fillers

Thermosetting composites were prepared from soybean‐oil‐based polyols (hydroxyl number = 190 mg of KOH/g, [OH]/[NCO] for 2,4‐toluene diisocyanate = 0.9) and fillers (10 wt %) from industrial and agricultural residual wastes. Different types of inexpensive residual wastes were used: black rice husk ash, coconut husk ash, calcined retorted oil shale, and retorted oil shale. The fillers were characterized by thermogravimetric analysis and measurements of particle size distribution, specific surface area, and pore size distribution. The fillers were microporous materials with different chemical compositions, with average particle diameters varying from 5.6 to 76.6 μm, specific surface areas varying between 6 and 165 m²/g, and thermal stability at the polyurethane cure temperature (65°C). All composites were characterized by dynamic mechanical analysis, flexural tests, Shore A hardness tests, thermogravimetric analysis, and scanning electron microscopy analysis. Coconut husk ash, rice husk ash, and retorted oil shale presented better mechanical properties; nevertheless, coconut husk ash and rice husk ash had higher particle sizes, which caused bad dispersion of the filler in the matrix and resulted in nonhomogeneous composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Morphology and tensile properties of polypropylene‐multiwalled carbon nanotubes composite fibers

In this work, we analyzed tensile properties of polypropylene‐multiwalled carbon nonotubes composite fibers. The multiwalled carbon nanotubes (MWCNTS) were used in different contents of 0, 1, 2, 3, 4, and 5 wt %. Dispersing agents were used to disperse MWCNTs in polypropylene matrix. After the dispersing agent was removed, the mixture was melt mixed. The fibers were spun by a home‐made melt spinning equipment and stretching was done at a draw ratio of 7.5. By using 1–5 wt % of MWCNTs, the modulus of composite fibers increased by 69–84% and tensile strength increased about 39% when compared with the virgin polypropylene fibers. In addition, the MWCNTs dispersion in the matrix was monitored by scanning electron microscopy and transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The influence of carbon‐based fillers on the flammability of polypropylene‐based co‐extruded wood‐plastic composite

Comparative analysis of the effect of carbon‐based fillers with different particle sizes and morphologies on the flammable properties of a co‐extruded wood‐plastic composite is performed. Five carbon‐based fillers, namely carbon black, carbon nanotubes, graphite, expandable graphite, and carbon fibers were loaded into the shell layer of the composite. The flammability was characterized by using the cone calorimeter technique. The nanosized fillers, carbon black and carbon nanotubes, had a larger impact on the peak of the heat release rate, decreasing it by 16% and 17%, respectively. The samples with graphite, expandable graphite, and carbon fibers, decreased the peak of the heat release rate by 10%, 6%, and 11%, respectively. The total heat release decreased slightly for all the samples, except for the carbon fibers–wood‐plastic composite. The effective heat of combustion decreased also slightly, and carbon monoxide production increased for all the studied composites. Copyright © 2015 John Wiley & Sons, Ltd.     

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     

Tensile and flammability properties of polypropylene‐based RTPO/clay nanocomposites for cable insulating material

Nanocomposites of polypropylene‐based RTPO with organically modified clays were prepared by melt compounding of three components, that is, polypropylene‐based RTPO, maleic anhydride‐grafted polypropylene oligomer (PPgMA), and organically modified clay. Their morphologies, tensile behaviors, and flammability properties were investigated. In the clay nanocomposites, the silicate layers were dispersed at the nanometer level, which was confirmed by X‐ray diffraction and transmission electron microscopy. The tensile yield strength of nanocomposites containing 10 wt % clay exhibited 2.8 times higher value compared with that of neat resin. The combustion behavior of the nanocomposites was evaluated by measuring the heat release rate (HRR) using cone calorimetry. The peak HRR was lowered greatly and the char yield was very high compared with those of neat resin. However, these flame retardant properties of clay are not sufficient as a flame retardant used alone in cable applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2375–2381, 2005     

Modification of dry‐spun Suplon polyimide fibers by mixed‐acid oxidation and their effects on the properties of polypropylene‐resin‐based composites

In this study, the effects of mixed‐acid oxidation on the contents of surface elements, morphology, fiber fineness, mechanical properties, mass change rate, chemical structure, and microaggregate structure of dry‐spun Suplon polyimide (PI) fibers were systematically investigated with wet chemical treatment with HNO₃/H₂SO₄. Experiments investigating both the improvement in the O/C ratio of the fiber surface elements and the changes in other performance features were conducted through the functional modification of the fibers. Meanwhile, the causes of specific changes in the mechanical properties of the oxidized PI‐fiber‐reinforced polypropylene‐resin‐based composites were studied and are discussed. The results of this study demonstrate that the treatment of the fibers with HNO₃/H₂SO₄ mixed‐acid oxidation resulted in significant changes in the properties of the fibers; these changes included an uneven surface, increased specific surface area and surface roughness, a locally etched surface, increased surface energy and O/C ratio, an enhanced wettability, an increased fiber fineness, reduced mechanical properties, and a mass gain in the fibers. Although the chemical structures of the fibers treated by oxidized HNO₃/H₂SO₄ were not significantly changed compared to those of the untreated fibers, the microscopic aggregation of the treated fibers changed to some degree, and the ratio of the amorphous regions significantly increased. Taken together, the functional modification of the PI fiber surface was achieved efficiently through the use of a suitable HNO₃/H₂SO₄ oxidation process and with other performance features of the fibers taken into account. This was favorable for the enhancement of the interfacial properties of the polypropylene fibers and the matrix resins, and thus, the modification improved the mechanical properties of the composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44932.     

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     

Use of pyrolysed oil shale as filler in poly(ethylene‐co‐vinyl alcohol)

The pyrolysed oil shale (POS) obtained from the pyrolysis of bituminous rock was used as filler in poly(ethylene‐co‐vinyl alcohol) (EVAL). The effects of vinyl alcohol content in the EVAL and the particle size of pyrolysed oil shale in the mechanical properties were investigated. The EVAL was prepared by hydrolysis of poly(ethylene‐co‐vinyl acetate) (EVA) with 8 and 18 wt % of vinyl alcohol content. The composites were prepared in a rotor mixer at 180°C with concentration of pyrolysed oil shale up to 5 wt %. Stress–strain plots of compression‐molded composites showed a synergic behavior in the mechanical properties for low concentrations (1–5 wt %) of POS in all particle sizes and EVAL used. Such behavior indicates a close packing and strong interactions between the inorganic filler and the polymer. Increasing of the vinyl alcohol content of EVAL improved the compatibility between the polymer and filler, but decreasing the POS particle size had no effect on the properties. The modulus and the ultimate tensile strength also increased in all concentrations of POS for both EVAL. Mechanical properties and dynamic mechanical analysis also demonstrated the compatibility between EVAL and POS. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1658–1665, 2004     

Nielsen thermal conductivity model for single filler carbon/polypropylene composites

In this study, three different carbon fillers (Thermocarb TC‐300 synthetic graphite, Ketjenblack EC‐600 JD carbon black, and Hyperion Catalysis International's FIBRIL? carbon nanotubes) were added to a polypropylene matrix to produce single filler composites with filler concentrations of up to 80 wt % synthetic graphite (61.6 vol %), 15 wt % carbon black (8.1 vol %), and 15 wt % carbon nanotubes (7.4 vol %). The through‐plane thermal conductivity for each formulation was measured. For the synthetic graphite, carbon black, and carbon nanotubes composites, the Nielsen model was applied to the experimental through‐plane thermal conductivity data. The Nielsen Model presented in this work showed very good agreement with experimental data. The model parameters were similar to those used in the literature for these fillers in other polymers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical properties and viscoelastic behavior of basalt fiber‐reinforced polypropylene

In the present article, a series of commercial‐grade polypropylenes (PP) filled with different contents of short basalt fibers were studied. This composite material presented deterioration of both mechanical characteristics, for example, stress and strain at yield with increasing of the fiber content. On the other hand, the impact strength was fourfold higher than that of unfilled PP. A poor adhesion between the PP matrix and the basalt fibers was detected. This is why interfacial interactions were promoted by the adding of poly(propylene‐g‐maleic anhydride) (PP‐g‐MA). It was observed that the tensile properties of the obtained materials and their impact strengths increased significantly with increasing of the amount of PP‐g‐MA in the blend. The adhesion improvement was confirmed by scanning electron microscopy as well. Fourier transform infrared spectroscopy was applied to assess if any chemical interactions in the system PP/PP‐g‐MA/basalt fibers exist. Dynamic mechanical thermal analysis data showed an increase of the storage modulus with increasing fiber content. The conclusion was made that the modification of the PP matrix led to a higher stiffness but its value remained constant, irrespective of the PP‐g‐MA content. With increasing fiber content, damping in the β‐region decreased, but increase of the coupling agent content restored its value back to that of PP. The loss modulus spectra presented a strong influence of fiber content on the α‐relaxation process of PP. The position of the peaks of the above‐mentioned relaxation processes are discussed as well. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 523–531, 1999     

From morphology of attrited copper/MWCNT hybrid fillers to thermal and mechanical characteristics of their respective polymer‐matrix composites: An analytical and experimental study

Synergistic effect of copper and multiwalled carbon nanotube on thermal and mechanical properties of high‐density polyethylene (HDPE)‐matrix composite was evaluated. Attrition mill was employed to prepare the hybrid powder. Reinforcing the polymer‐matrix was carried out using different contents of simultaneously (Sim) and separately (Sep) milled powders as hybrid fillers. X‐ray diffraction and microscopy results show different trends of particle size for Sep and Sim affected by both milling time and volume fraction ratio. Thermal characterization indicates that conductivity was enhanced by 90% and thermal expansion was reduced to 53% of neat HDPE. Young's modulus and tensile strength were improved by 7.8 and 1.22 times of neat HDPE, respectively. Also, characteristics of Sim‐reinforced composites exhibited better correlated relation with milling time compared with erratic behavior of Sep. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45397.     

Microstructure dependent properties of polypropylene‐clay nanocomposites

The mechanical properties of melt processed polypropylene‐montmorillonite nanocomposites were studied as a function of clay content. The measurement of tensile properties at room temperature and dynamic mechanical properties over a wide temperature range reveal a decrease in modulus and tensile strength of the composite with increasing clay content. The origins of this anomalous result were examined in detail using X‐ray diffraction and differential scanning calorimeter, which averaged the microstructure over reasonable specimen volumes. Micromechanical models could be used to adequately describe the composite properties, provided appropriate properties for the matrix and particle were used. The matrix properties were found to affect the average properties significantly. © Wiley Periodicals, Inc. J Appl Polym Sci 103: 204–210, 2007     

Tensile and impact properties of carbon filled nylon‐6,6 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 stress, strain at ultimate tensile stress, and notched Izod impact strength are also important and cannot be ignored. This study focused on performing compounding runs, followed by injection molding and evaluation of tensile and impact properties of carbon filled nylon‐6,6 based resins. The three carbon fillers investigated include an electrically conductive carbon black, synthetic graphite particles, and a surface treated polyacrylonitrile (PAN) based carbon fiber. Resins containing varying amounts of these single carbon fillers were produced and tested. In addition, combinations of fillers were investigated by conducting a full 2³ factorial design and a complete replicate. The addition of carbon fiber increased the composite tensile modulus, ultimate tensile stress, and impact strength. Also, in many cases, combining two or three different fillers caused a statistically significant effect at a 95% confidence level. When comparing the results of this study with prior work, it appears that increased heteroatoms present on the carbon fiber surface likely improve composite ultimate tensile stress and impact strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2881–2893, 2004     

Recycling of polypropylene‐based eco‐composites

BACKGROUND: Renewable resources and recyclable thermoplastic polymers provide an attractive eco‐friendly quality as well as environmental sustainability to the resulting natural fibre‐reinforced composites. The properties of polypropylene (PP)‐based composites reinforced with rice hulls or kenaf fibres were investigated with respect to their recyclability. Rice hulls from rice processing plants and natural lignocellulosic kenaf fibres from the bast of the plant Hibiscus cannabinus represent renewable sources that could be utilized for composites. Maleic anhydride‐grafted PP was used as a coupling agent to improve the interfacial adhesion between fillers and matrix. Composites containing 30 wt% reinforcement were manufactured by melt mixing and their mechanical and thermal properties were determined. The composites were then pelletized and reprocessed by melt mixing. Finally, structure/properties relationships were investigated as a function of the number of reprocessing cycles. RESULTS: It is found that the recycling processes do not induce very significant changes in flexural strength and thermal stability of the composites. In particular PP‐based composites reinforced with kenaf fibres are less sensitive to reprocessing cycles with respect to PP‐based composites reinforced with rice hulls. CONCLUSION: The response of PP‐based composites reinforced with rice hulls or kenaf fibres is promising since their properties remain almost unchanged after recycling processes. Moreover, the recycled composites are suitable for applications as construction materials for indoor applications. In fact, the flexural strength and modulus of these materials are comparable to those of conventional formaldehyde wood medium‐density fibreboards. Copyright © 2008 Society of Chemical Industry