General Purpose Carbon Fibers Research Articles

Enhancing spinnability and properties of carbon fibers through modification of isotropic coal tar pitch precursor

Producing general-purpose carbon fibers (GPCFs) with excellent properties using an economical raw material such as coal tar pitch (CTP) holds significant importance. To synthesize carbon fibers, the spinnability of precursor material plays an important role. However, the CTP impedes flowability during the spinning process due to possessing high molecular weight complex aromatic structures. To address this limitation, CTP was blended with varying proportions of petroleum pitch (5, 10 and 20 %) and spinnability and flow behavior were analyzed using Rheology measurements. The distinct constitutional properties of petroleum pitch also contributed to alterations in both the stabilization and carbonization processes. Carbon fibers produced from 10PP showed the highest tensile strength and modulus of ∼784 MPa and ∼47 GPa, respectively. The impact of oxidative and carbonization treatments on the resultant microstructural and mechanical properties of carbon fibers was thoroughly examined using various techniques such as FTIR, XPS, XRD, SEM, Raman and UTM. The results showed that the composition of petroleum pitch influenced the stabilization of fibers which eventually affected the carbonization process and resultant properties of carbon fibers. This study offers an understanding of the connection between the precursor's composition, stabilization conditions, and mechanical properties of the resultant carbon fibers.

Effect of carbonization conditions on microstructural properties of isotropic coal tar pitch-based general-purpose carbon fibers

The microstructures of carbon fibers can be significantly modified by understanding the carbonization conditions which improves the properties of fibers. The carbonization is a complex process of converting pitch fibers into carbon fibers through the evolution of gases and arrangement of molecules by polymerization reactions. Hence, the present study focuses on the synthesis of isotropic pitch-based carbon fibers and the investigation of microstructural properties with varying carbonization conditions at 1000 °C. The isotropic pitch is derived from coal-tar pitch through the utilization of a vacuum distillation technique. Various properties of isotropic pitch are studied to determine the flowability and optimum temperature range for melt-spinning into fibers. Subsequently, the stabilization process is conducted in an open atmosphere to retain fibers shape by introducing oxygen-containing functional groups. Time-dependent carbonization parameters such as heating rate and holding/soaking periods are used to optimize the conditions that yield superior microstructural properties. This research reveals that slower heating rates enhance the crystallite sizes while reducing defects. Conversely, longer holding times at carbonization temperature showed adverse effects on the microstructural properties. To assess microstructural, thermal and physical properties of the pitch and fibers, various characterizations are performed, including DSC, TGA, rheology, FTIR, XPS, Raman, XRD, and SEM.

Chlorination–dechlorination of coal liquefaction residue using benzyl chloride for general-purpose carbon fiber synthesis

Chlorination–dechlorination of coal liquefaction residue using benzyl chloride for general-purpose carbon fiber synthesis

Direct electrochemical grafting of crystalline PAEK macromolecule on carbon fiber to enhance the interfacial properties of PEEK/CF composites

Electrochemical grafting of diazonium salts have been applied to improve interfacial properties of carbon fiber and matrix resin. However, these graft modifications are still limited to general-purpose carbon fiber reinforced resin matrix composites such as epoxy. In this research, the direct grafting of Poly (aryl ether ketone) (PAEK) macromolecule on carbon fiber was achieved with mild condition. Firstly, aniline was introduced into Poly (ether ether ketone) (PEEK) as pendent group to improve solubility and amino terminated group was introduced as precursor of diazonium salt. Then the graft was conduct through diazonium salt reduction. After modification, the aniline side group could be hydrolyzed off to recover crystallinity. To further analyze the graft, single molecular-force spectroscopy was introduced to investigate the surface of carbon fiber. Impressively, the extension curve suggested the PAEK macromolecule had been attached to surface through strong interaction. Combined this with XPS data, it was believed that the graft was a success. As a result, the grafted polymer along with the polymer that physically absorbed on carbon fiber in electrolyte can cooperate to strengthen the interface. The interfacial shear strength of the grafted carbon fiber and PEEK increased from 42.27 MPa to 97.33 MPa by 130.26%. The improvement mainly originated from the covalent bonding that connected the carbon fiber and the graft coating layer as well as the great compatibility between the graft coating layer and the matrix resin. These results also demonstrated the possibility to graft high performance polymers on carbon fiber through one-step modifications.

Preparation of Isotropic Carbon Fibers from Kerosene-Purified Coal Tar Pitch by Co-Carbonization with Pyrolysis Fuel Oil.

An inexpensive and general-purpose carbon fiber was prepared using coal tar pitch. In contrast to the solvent extraction process employing expensive solvents, a low-cost centrifugal separation method facilitated the reduction of loss due to the pitch purification and an overall yield increase. The coal tar pitch purified by centrifugation and subsequently co-carbonized with pyrolysis fuel oil improved in spinnability. Moreover, the resulting spinnable pitch had a softening point of 250 °C. The obtained carbon fibers were heat-treated at 1000 °C for 5 min, resulting in a tensile strength of approximately 1000 MPa and an average diameter of 9 μm. In this study, we present an effective method for obtaining low-cost general-purpose isotropic carbon fibers.

Melt spinning of poly(acrylonitrile)-co-styrene copolymer

The search for alternative processes and high performance materials precursors for carbon fibers, has been continuously the aim for use in the aerospace, automotive, energy and sports goods market. The reduction in the precursor production cost is then essential to allow the installation of an industrial plant to produce a general purpose carbon fiber. Polyacrylonitrile has been the main precursor for carbon fiber production. It has been produced by the wet and dry spinning process since it has been discovered in the beginning of the forties. Nowadays, the extrusion process of PAN fibers shows potential of cost reduction in relation to the wet spinning method. This innovative technology enables spinning by melting PAN polymer by using glycerin as the primary plasticizer, avoiding the use of highly toxic solvents. In the present work, PAN copolymer was copolymerized by conventional aqueous suspension. Its characterization was performed by FT-IR, GPC and DSC analysis. The fibers obtained by extrusion process were characterized by SEM, DSC/TGA analysis and kinetics of the thermal stabilization process was studied by Kissinger method. The results showed that styrene monomer was suitable for polymerization with PAN leading to a molecular weight Mn= 46,000 g/mol and Mw = 138,000 g/mol. The PAN-co-Styrene copolymer was suitable for obtaining extruded PAN fibers continuously with morphological and thermal properties having properties similar to commercial PAN fibers.

Preparation of isotropic spinnable pitch with high-spinnability by co-carbonization of coal tar pitch and bio-asphalt

Co-carbonization of coal tar pitch (CTP) with bio-asphalt (BA) was performed to prepare spinnable pitch with suitable softening point and excellent spinnability for general purpose carbon fiber. The co-carbonization mechanism and the correlation between spinnability and molecular structure of prepared pitch were clarified. BA produced from the pyrolysis of biomass is abundant of aliphatic units and oxygen-containing groups, leading to high reactivity during carbonization. The co-carbonization reactions mainly depend on the mutual cross-linking among CTP and BA molecules, which are principally triggered by active oxygen-containing groups of BA. The formed cross-linked macromolecules could further promote the polymerization degree of pitch molecules; thus, the spinnable pitch with suitable softening point could be obtained by simply thermal treatment of blended pitches at a relatively moderate condition (<350 °C). The properties of the pitch could be optimized by changing the blending ratio of CTP to BA. Moreover, the prepared carbon fibers demonstrated distinct features, especially surface profiles. It is expected to provide a new strategy for the preparation of isotropic spinnable pitch in a relatively simple approach.

Controllable synthesis of isotropic pitch precursor for general purpose carbon fiber using waste ethylene tar via bromination–dehydrobromination

Nowadays, the substantial amount of waste ethylene tar (ET) lacks a clean and efficient route for utilization. In this work, a feasible approach was developed to fabricate general purpose carbon fiber (GPCF) using ET as a raw material. The method of bromination–dehydrobromination was used to synthesize controllably isotropic pitch precursor for GPCF. The results show that bromination–dehydrobromination reaction promotes the cyclization and aromatization of small molecules and relatively low molecular weight components and also prevents excess condensation during thermal treatment. The molecular structure of pitch precursor generated from bromination–dehydrobromination reaction has more linear and cross-linked structures as more naphthenic groups and the side chain of aromatic rings. The spinnability of pitch precursors and the mechanical performance of GPCFs are optimized when 10 wt% of bromine is introduced in synthetic reaction. The tensile strength, Young’s modulus, and elongation property of the final GPCF are 1072 ± 66 MPa, 47 ± 7 GPa, and 2.3%, respectively, with the diameter of 10.3 ± 0.5 μm.

Preparation of pitch-based general purpose carbon fibers from catalytic slurry oil

Preparation of high-value pitch-based carbon fiber from catalytic slurry oil is of great importance, but is very difficult with traditional routes. In this work, a new route studied on the development of suitable pitch precursor from catalytic slurry oil was carried out using the techniques of thermal polymerization to increase the content of heavy components, centrifugal separation to remove the quinoline insolubles (QI), solvent extraction to remove light components and vacuum distillation to remove extractant. The effects of the above treatment processes on the QI particles size distribution, thermo-gravimetry, other properties of asphalt, micro-structure of pitch fibers and mechanical properties of carbon fibers were investigated. The result showed that thermal polymerization could significantly improve the contents of heavy components, accelerate the conversion of active components (alkenes, heterocycles, etc) into QI, and greatly increase QI particles size. The process of solvent extraction could effectively remove the light components and increase the softening points of asphalt. With increasing the time of thermal polymerization, QI particles became bigger and more easily removable, the micro-structures of pitch fibers were much smoother, and the mechanical properties of carbon fibers were more uniform.

Stabilization of pitch-based carbon fibers accompanying electron beam irradiation and their mechanical properties

Carbon fibers are prepared by stabilizing pitch fibers accompanying electron beam (E-beam) irradiation. The carbon fibers pretreated by E-beam irradiation achieve a higher stabilization index than the carbon fibers that are only heat-stabilized. In addition, the carbon fibers subjected to E-beam irradiation in the stabilization step exhibit a comparable tensile strength to that of general purpose carbon fibers. The carbon fibers pretreated with an absorbed dose of 3000 kGy have a tensile strength of 0.54 GPa for a similar fiber diameter. Elemental, Fourier-transform infrared spectroscopy, and thermogravimetric analyses indicate that Ebeam irradiation is an efficient oxidation and dehydrogenation treatment for pitch fibers by showing that the intensity of the aliphatic C?H stretching and aromatic CH2 ben

Graphene Nanoribbons as an Advanced Precursor for Making Carbon Fiber

Graphene oxide nanoribbons (GONRs) and chemically reduced graphene nanoribbons (crGNRs) were dispersed at high concentrations in chlorosulfonic acid to form anisotropic liquid crystal phases. The liquid crystal solutions were spun directly into hundreds of meters of continuous macroscopic fibers. The relationship of fiber morphology to coagulation bath conditions was studied. The effects of colloid concentration, annealing temperature, spinning air gap, and pretension during annealing on the fibers' performance were also investigated. Heat treatment of the as-spun GONR fibers at 1500 °C produced thermally reduced graphene nanoribbon (trGNR) fibers with a tensile strength of 378 MPa, Young's modulus of 36.2 GPa, and electrical conductivity of 285 S/cm, which is considerably higher than that in other reported graphene-derived fibers. This better trGNR fiber performance was due to the air gap spinning and annealing with pretension that produced higher molecular alignment within the fibers, as determined by X-ray diffraction and scanning electron microscopy. The specific modulus of trGNR fibers is higher than that of the commercial general purpose carbon fibers and commonly used metals such as Al, Cu, and steel. The properties of trGNR fibers can be further improved by optimizing the spinning conditions with higher draw ratio, annealing conditions with higher pretensions, and using longer flake GONRs. This technique is a new high-carbon-yield approach to make the next generation carbon fibers based on solution-based liquid crystal phase spinning.

Preparation of General Purpose Carbon Fibers by the Two-Step Method from Ethylene Tar Pitch

In this paper, besides the single method of air blowing and thermal condensation, a new two-step combining method was taken to modulate the pitch precursor for carbon fibers: the ethylene tar pitch was first air-blown under 280 °C for 10 h, and then thermal-condensed in nitrogen under 380 °C. Then group composition, elemental and thermal analysis, FT-IR, SEM and polarized optical micrographs were used in this paper, and the influence of different methods of modulation on the performance of pitches was discussed. The results revealed that neither in the method of air blowing nor thermal treatment can the pitch with a high softening point and coking value but no mesophase be produced. However, isotropic spinnable pitch with high softening point (286 °C), coking value (80.2%) and superior thermal stabilities can be synthesized in the two-step combining method. Carbon fibers from such pitches had been produced through melt-spinning, stabilization and carbonization, they showed uniform diameters (about 15.5 μm) with smooth and homogeneous surfaces. After stabilization and carbonization, the shrinkage of carbon fibers’ diameter was limited to 6%.

Process Optimization for Preparing High Performance PAN-based Carbon Fibers

wet spun polyacrylonitrile (PAN) fiber precursors. The process variables chosen were treatment temperature, applied tension in stabilization process. The temperature profile of the stabilization was set on the basis of exothermic peaks of the differential scanning calorimetry (DSC) result. Both tensile strength and modulus increased with holding at onset temperatures of the exothermic peaks for extended duration, and with a higher heating rate up to the onset temperatures at a given applied tension among the experimental conditions. The increase in load monotonously increased the tensile modulus, on the other hand, the tensile strength was maximum at the load of 15 mg/filament (T15). The load 20 mg/ filament (T20) was considered to be exceeded to form oriented crystalline structure, possibly introducing more defects in the fiber than under load of T15. The sample CP3-T15 O5 H30 showed the best tensile properties among the samples experimented whose tensile properties are compatible with the commercialized grade of general purpose carbon fibers even at low carbonization temperature such as <TEX>$800\;{^{\circ}C}$</TEX> (the carbonization temperature in the commercial process. 1300∼<TEX>$1500\;{^{\circ}C}$</TEX>).

FORMATION OF CARBON NANOSTRUCTURES DURING PYROLYSIS OF POLYMERS

Carbon nanomaterials have been of great interest in nanoscience and nanotechnology because of their very small size with unique properties and simplicity in structure having only one chemical element. In our laboratory, attempts were made to synthesize carbon nanomaterials through different routes such a CCVD and pyrolysis of solids carbonaceous precursors. Pyrolysis of polyacrylonitrile fibers in presence of a suitable catalyst resulted in formation of straight as well as coil type long carbon nanofibers and tubes along with general-purpose carbon fibers. Similarly, growth of carbon nanotubes was also observed in the coke deposits during pyrolysis of pitches. The yield of CNTs formed was found to increase if the precursors are impregnated with a suitable catalyst solution. These carbon nanostructures have been characterized using XRD, TEM, SEM and TGA.

Biopitch-based general purpose carbon fibers: Processing and properties

Eucalyptus tar pitches are generated on a large scale in Brazil as by-products of the charcoal manufacturing industry. They present a macromolecular structure constituted mainly of phenolic, guaiacyl, and siringyl units common to lignin. The low aromaticity (60–70%), high O/C atomic ratios (0.20–0.27%), and large molar mass distribution are peculiar features which make biopitches behave far differently from fossil pitches. In the present work, eucalyptus tar pitches are evaluated as precursors of general purpose carbon fibers (GPCF) through a four-step process: pitch pre-treatment and melt spinning, and fiber stabilization and carbonization. Homogeneous isotropic fibers with a diameter of 27 μm were obtained. The fibers had an apparent density of 1.84 g/cm 3, an electrical resistivity of 2 × 10 −4 Ω m, a tensile strength of 130 MPa, and a tensile modulus of 14 GPa. Although the tensile properties advise against using the produced fibers as structural reinforcement, other properties give rise to different potential applications, as for example in the manufacture of activated carbon fibers or felts for electrical insulation.

Preparation of carbon fiber from heavy oil residue through bromination

A pitch precursor for a general purpose carbon fiber was prepared by condensation of pyrolized fuel oil (petroleum residual oil) with bromine under nitrogen blowing. Such a condensation raised the softening point of the pitch from 40°C to 265°C with a yield of 43%. The pitch precursor showed an enhanced aromaticity and enlarged molecular size, which led to a reduction in molecular mobility and optical isotropy. The precursor was spun into fibers of 20 µm diameter at a take-up speed of 700 m/min. The fiber was stepwise stabilized in air and carbonized in Ar gas to obtain an isotropic carbon fiber. The carbon fiber exhibited tensile strengths of 500–800 MPa though the fiber was formed via a crude method. The electric conductivity of the carbon fiber was relatively high, 2.2×102 S/cm, sufficient to be used as electrode materials.

Characterization of pitches by an ultrasonic method: Change in the molecular aggregation state during air-blowing

The air blowing reaction has been used to modify the chemical structure and molecular aggregation of pitches for general-purpose carbon fiber on an industrial scale. The purpose in this study is to obtain fundamental ultrasonic data so that one can monitor in situ the change in chemical structure and molecular aggregation state in air blowing reaction. For this purpose, the effects of heat-treatment, oxygen (or air), and distillation (or low pressure) on the ultrasonic properties were separately examined. It was found that the ultrasonic measurements give the temperature dispersion curve characteristic to the structure, which was quite consistent to previous studies by ESR and NMR.

Influences of Stabilization Extent on the Properties of General Purpose Carbon Fiber and Activated Carbon Fiber from Isotropic Air-blown Coal Tar Pitch

The influences of stabilization extent were examined on the yield, strength and surface area of general purpose carbon and activated carbon fibers, respectively, prepared from isotropic air-blown coal tar pitch. The stabilization extent was described by the content of oxygen uptake after the stabilization. The amounts of oxygen uptake optimum for the high tensile strength, elongation, and surface area were found 10, 9 and 13wt%, respectively for the carbon and activated carbon fibers. Larger extent of stabilization reduced the yield of both fibers. The stabilization introduced oxygen into the pitch in forms of carbonyl, ketone, and phenol types of functional groups and accelerated the dehydrogenative condensation and aromatization as well. The volatilization also took place during the stabilization, becoming very marked above 350°C by evolving cracked gas. The cross-linkage can stabilize the pitch not to deform the fiber shape and maintain the axis-alignment of component aromatic planes induced at the spinning to give the strength of carbon fiber. An optimum oxygen uptake for the highest elongation may moderate cross-linkage to form linear chains of aromatic sheets leaving some flexibility among the chains.In contrast, optimum oxygen uptake for the largest surface area by activation was higher than that for the highest strength. Sufficient three-dimensional cross-linkage may induce the voids among the aromatic planes during the carbonization and gas evolution which contribute to form large surface area by limited burn off.Excess stabilization increases the number of oxygen functional groups, all of which leave as cracked gas at the carbonization, reducing the yield.Thus the optimum stabilization extents must be carefully achieved for the best performances of resultant pitch based fiber materials.

Influence of Properties of Coal Tars on Preparation of Isotropic Pitch Precursor, General Purpose Carbon Fiber and Activated Carbon Fiber

The isotropic precursor pitches for general purpose carbon fibers and activated carbon fibers were prepared from coal tars of various origins through air-blowing reaction. The coal tars and isotropic pitches were characterized by means of solvent fractionation and NMR spectroscopy. The quality of the isotropic pitches was evaluated in terms of their spinning continuity, stabilization reactivity, strength of the resultant carbon fibers and yield of activated carbon fibers. The coal tar carrying higher aliphatic carbon content was found to produce the general purpose carbon fibers of high quality at a lower yield. In contrast all tars provided the activated carbon fiber of the same surface area at the same yield of 9% on coal tar base regardless of their variable properties.

The Desirable Condition of the Air-blowing Reaction on Isotropic Pitch Precursor for General Purpose Carbon Fiber

Coal tar pitch was air-blown under the various pressures and temperatures to investigate their roles on the properties of isotropic pitch fiber precursor derived from the pitch. The quality of the precursor pitches was evaluated in terms of their spinning continuity, stabilization reactivity and strength of the resultant carbon fibers. The pitches were also characterized by means of solvent fractionation and NMR spectroscopy. Lower pressure and temperature were confirmed to produce better precursor pitches for the general purpose carbon fiber of higher quality. Although the yield of the pitch was low. Efficient removal of lighter fraction without excess condensation of heavier fraction favored the quality of the pitch. The distillation before the air-blowing to remove lower boiling substances was found also effective to give better precursor pitch for the general purpose cabon fiber of higher quality. In contrast, the prehydrogenation allowed development of mesophase and decreased the 13-resin content in the air-blown pitch, being not recommended in the pretreatment.