Pitch Carbon Fibers Research Articles

Synergistic effect of spinning drawing and preoxidation stretching on the orientation structure of mesophase pitch carbon fibers

Mesophase pitch carbon fiber has shown remarkable prospects in specialty carbon material. The mechanical properties of mesophase pitch carbon fiber (CF) cannot be precisely controlled because of the difficulty of forming process regulation. The early forming of carbon fiber (precursor fiber (PF) and pre-oxidation fiber (OF)) is difficult to regulate, such as carbon microcrystal and carbon layer texture, while cause the irreversible growth of carbonization process. Herein, a synergy strategy of spinning drawing and preoxidation stretching is developed to optimize orientation structure, eliminate morphology defects and improve mechanical properties. A synergistic effect of superior spinning drawing and suitable preoxidation stretching is beneficial to adjust the more order rearrangement of carbon microcrystals. The tensile strength of carbon fibers with spinning drawing and preoxidation stretching is increased by 1.7 times, and their defects are reduced by 40%. The results show that the excellent mechanical property of carbon fiber is contributed by the extrusion stress caused by high oxidation crosslinked surface layer under tension, and the micro-flow and rearrangement of carbon microcrystals induced by extrusion stress. A mechanical strengthening mechanism of carbon fiber is proposed, which provides guidance for high-performance mesophase pitch carbon fiber.

Tuning Microstructure of Mesophase Pitch Carbon Fiber by Altering the Carbonization Ramp Rate

The microstructure of mesophase pitch carbon fibers (CFs) are tuned by varying ramp rates from 1 to 50 °C min−1 up to 1000 °C to study the effect of ramp rate on CFs’ microstructure, thermal and mechanical properties with the goal of offsetting the cost by decreasing cycle time. The ramp rates represent carbonization times ranging from 16.4 to 1.17 h, not including cool down. Differential scanning calorimetry, thermogravimetric analysis, and derivative thermogravimetry are used to investigate the impact ramp rate has on the thermal properties of mesophase pitch. It is found that lower ramp rates are endothermic in nature with a lower temperature onset and maximum weight loss. Higher ramp rates possess an exothermic nature with higher temperatures resulting in maximal weight loss over a smaller range of temperatures. Mechanical testing shows varying CF strengths and moduli dependent on ramp rate and an optimized process is developed to produce the strongest CF. Microstructural characterization revealed that faster ramp rates lead to smaller interplanar spacings and larger crystallites but possessed greater disorder.

High stiffness 3D-printed continuous pitch carbon fiber reinforced polymer composites

This study presents a method for 3D printing very high stiffness pitch-based carbon fiber (CF) reinforced polylactic acid (PLA) composites using a modified open-source 3D printer. The fused filament fabrication (FFF) technique was used to fabricate the samples with alternating layers of PLA and PLA-coated pitch CF. The tensile Young’s modulus of the 3D-printed composite samples was measured to characterize the effect of different grades and volume fractions of pitch CF on the behaviour of the printed composites. Three grades of pitch CF which have different Young’s modulus were used with volume fractions ranging from 2.4 to 8.4%. Tensile tests showed that the K1392U CF reinforced composite with a 7.3% volume fraction demonstrated the highest improvement in Young’s modulus of 850% compared to neat 3D-printed PLA. This improvement is notably higher than any previous 3D-printed carbon-based composites at a relatively low volume fraction of CF. Statistical analysis showed increased Young’s modulus in all of 3D-printed composite samples tested. The experimental values were compared to the Halpin-Tsai model and suggest that some degree of fibre breakage occurred during the 3D printing process owing to the relative stiffness of the pitch-based fibers. Future directions and suggestions for process improvements are discussed.

High thermal conductivity continuous pitch carbon fiber 3D printed using a 6-axis robot arm

High thermal conductivity continuous pitch carbon fiber 3D printed using a 6-axis robot arm

Stabilization time and temperature influence on the evolution of the properties of mesophase pitch stabilized fibers and carbon fibers

The structure of a mesophase pitch carbon fiber is primarily developed during the fiber spinning process and is refined in stabilization and carbonization steps. Stabilization of mesophase pitch filaments was performed in a thermogravimetric apparatus (TGA) using a multivariate approach to investigate the influence of the initial and final temperature of stabilization and the step time on the changes that occur during the stabilization stage. Different levels of stabilization were observed: insufficient, proper, and over-oxidation. Through Fourier Transform Infrared Spectroscopy (FTIR), Energy-Dispersive X-ray Spectroscopy (EDX), and X-ray Photoelectron Spectroscopy (XPS), it was found that the chemical composition of the stabilized fibers was highly dependent on the mass evolution of this thermal treatment. Excessive stabilization induced defects in the structure of the fibers that negatively reflected on their tensile strength and modulus. Stabilization at lower final temperatures led to low mass increase but in turn provided carbon fibers with the highest modulus. Carbon fibers differing solely in their initial stabilization temperature did not exhibit statistically different tensile strength and modulus, proving that industrial stabilization can be shortened without compromising the fibers' properties.

Hydrogenation of coal tar pitch for improved mesophase pitch molecular orientation and carbon fiber processing

The high softening point and mosaic optical textures of coal tar pitch (CTP)-derived mesophase pitches are the main factors limiting their application in high performance carbon fibers. Spinnable mesophase pitch was prepared using CTP hydrogenation process, and the effect of hydrogenation process on the preparation of mesophase pitch and the crystal structure of carbon fibers was investigated. Molecular structure characterization results show that the naphthenic structures and the aliphatic groups in hydrogenated CTP were generated by the hydrogen addition reaction of aromatic rings and the subsequent naphthenic cracking reactions, respectively. The naphthenic structures and aliphatic groups introduced during the CTP hydrogenation process of CTP have a significant effect on improving the homogeneity of anisotropic textures, molecular weight distributions and the molecular stacking heights of mesophase pitches. The prepared mesophase pitch has lower viscosity and enhanced flowability, significantly improving its spinning stability and the molecular orientation of their as-spun pitch fibers. Benefits from this, the optimized carbon fibers present distorted graphite lamellar structures and possess a larger crystal size than commercial coal tar-based carbon fibers K13D2U. The work provides some valuable insights for enhancing crystal structures of carbon fibers via molecular structure regulations of their precursors.

Influence of Oxygen Uptake on Pitch Carbon Fiber.

Carbon fiber precursor materials, such as polyacrylonitrile, pitch, and cellulose/rayon, require thermal stabilization to maintain structural integrity during conversion into carbon fiber. Thermal stabilization mitigates undesirable decomposition and liquification of the fibers during the carbonization process. Generally, the thermal stabilization of mesophase pitch consists of the attachment of oxygen-containing functional groups onto the polymeric structure. In this study, the oxidation of mesophase pitch precursor fibers at various weight percentage increases (1, 3.5, 5, 7.5 wt%) and temperatures (260, 280, 290 °C) using in situ differential scanning calorimetry and thermogravimetric analysis isinvestigated. The results areanalyzed to determine the effect of temperature and weight percentage increase on the stabilization process of the fibers, and the fibers aresubsequently carbonized and tested for tensile mechanical performance. Thefindings provide insight into the relationship between stabilization conditions, fiber microstructure, and mechanical properties of the resulting carbon fibers.

Thermal conductivity of 3D-printed continuous pitch carbon fiber composites

Thermal conductivity of 3D-printed continuous pitch carbon fiber composites

Evolution of the Composition and Melting Behavior of Spinnable Pitch during Incubation.

The physical and chemical properties of spinnable pitch showed a huge impact on the performance of resultant pitch carbon fiber even if its physical and chemical properties were slightly changed. Various polycyclic aromatic compounds and abundant free radicals existed in spinnable pitch, and there are many interactions among molecules and free radicals. The molecular structure and composition of spinnable pitch were investigated during incubation, and the effect of molecular evaluation on rheological properties of spinnable pitch was illustrated using various characterization methods in this work. It indicated that n-hexane soluble fraction mainly occurred condensation or cleavage, and a small number of heavy components were generated after a long period. The fraction of n-hexane insoluble/toluene soluble underwent molecular condensation and cross-linking in the presence of oxygen-containing radicals and aromatic hydrocarbon radicals, while toluene insoluble/tetrahydrofuran soluble fraction tended to change in large molecules of polycyclic aromatic hydrocarbons. Lastly, tetrahydrofuran insoluble fraction was condensed due to its high aromaticity during the incubation process, and the content of aromatic carbon increased. These changes of composition and structure of spinnable pitch led to its softening point, increase in viscosity and flow activation energy, and deterioration of the rheological property.

High conductivity and stability intercalated carbonaceous conductors

• Copper chloride intercalation is scalable and stable up to 500K • It enhances electrical conductivity of different carbonaceous conductors by 10X • Intercalated carbon fibers achieve a 10MS/m electrical conductivity • Intercalation results in a one-step impurity purification and conductivity enhancement • Conduction in CNT yarns is hampered significantly by internal junction resistances Carbonaceous conductors have attracted great interest due to their low density and superior mechanical and chemical properties. Metal halide intercalation is an effective approach for enhancing the electrical conductivity of these conductors. This paper investigates the microstructure, composition, electrical, and mechanical properties of different carbonaceous conductors (pitch carbon fiber, three types of carbon nanotube yarns, and graphene fiber) intercalated with copper chloride. Temperature-dependent conductivity measurements along with Raman spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy reveal the degree of intercalation in different samples. Intercalated specimens exhibit electrical conductivities at least seven-fold higher than their pristine counterparts, including a 10 MS/m conductivity for intercalated carbon fibers. Interestingly, the intercalation process results in a one-step impurity purification and conductivity enhancement in CNT yarns. Electrical conductivity measurements over cryogenic and elevated temperature ranges (30-500 K) explain conduction mechanisms and demonstrate intercalant stability. This study informs future applications of lightweight conductors by presenting a library of different carbon-based conductors and their structural and property variations. :

A comprehensive investigation on the chemical structure character of spinnable pitch for improving and optimizing the oxidative stabilization of coal tar pitch-based fiber

Oxidative stabilization is the critical step to maintain the fibrous morphology of pitch fiber and affects mechanical properties of resultant carbon fiber, but the detailed oxidation mechanism is still unclear because of the complex polycyclic aromatic hydrocarbons composition in pitch fiber. In here, pitch fiber was obtained from coal tar pitch followed by air-blowing and spinning. The chemical structure character of corresponding fibers before and after oxidative stabilization at different temperatures (260–320 °C) and durations (2–12 h) were analyzed. The results indicated that aromatic nucleus in spinnable pitch was gradually increased, while aliphatic chains were gradually shorten with prolongation of air-blowing time. The spinnable pitch obtained by air-blowing at 330 °C for 4 h showed excellent spinning performance, and the as-spun pitch fiber displayed a higher oxidative stabilization efficiency because the lower oxygen content was introduced and more C-O-C groups were formed in the resultant oxidative stabilized pitch fiber. The obtained pitch-based carbon fiber, after carbonizing at 1000 °C, showed excellent mechanical properties with tensile strength of 1068.7 ± 100.0 MPa and Young's modulus of 52.5 ± 9.8 GPa. This work provided a facile approach to improve and optimize the oxidative stabilization efficiency for pitch carbon fiber preparation.

Carbon Fiber-Silica Aerogel Composite with Enhanced Structural and Mechanical Properties Based on Water Glass and Ambient Pressure Drying.

The article presents the synthesis of silica aerogel from a much cheaper precursor of water glass that was reinforced with short pitch carbon fiber by way of ambient pressure drying. Before being added to the silica gel, the carbon fibers were surface modified to increase adhesion at the interfacial border. We were able to obtain stable structures of the composite with the amount of fibers above 10% by volume. The presence of fibers in the silica matrix resulted in lower synthesis time of the composite, improved adhesion of fibers to the aerogel nanostructure, and increased mechanical and structural parameters. An additional effect of the presence of fibers in excess of 10% by volume was a new function of the nanocomposite—the ability to conduct electric current. The most optimal parameters of the composite, however, were obtained for silica aerogel reinforced with 10 vol.% of carbon fibers. This material indicated relatively low density and good physical parameters. The paper also analyzes the results on the synthesis of fiber-reinforced silica aerogels that have appeared in recent years and compares these to the results gained in presented work.

Impact of spinning conditions on the diameter and tensile properties of mesophase petroleum pitch carbon fibers using design of experiments

The structure of a mesophase pitch carbon fiber evolves in spinning and is perfected through stabilization and carbonization. Thus, it is crucial to control extrusion variables to form standard carbon fibers. Design of experiments was employed in melt spinning to investigate the influence of three process variables on the diameter of petroleum-derived pitch filaments. Optimized conditions were validated in an experiment that produced filaments with average diameter of 14 μm. Pitch filaments with different thickness were thermally treated to verify structure discrepancies and quantify the relation between mechanical properties and fiber’s diameters. Diameters smaller than 45 μm could be stabilized in air. Thinner fibers reached average strength of 1.4 GPa and 150 GPa modulus, thicker fibers only supported 120 MPa with 65 GPa modulus.

Release of Respirable Fibrous Dust from Carbon Fibers Due to Splitting along the Fiber Axis

ABSTRACT The aim of this report is to sensitize to the fact that some types of carbon fibers can split along the fiber axis during machining processes, thus becoming a source of respirable fibrous fragments in high concentrations. The risk of releasing respirable fiber dust must be assessed both in terms of carbon fiber materials and handling processes. We present an analysis of fiber concentrations released during mechanical processing of carbon fiber reinforced polymers at two different workplaces together with measurements from abrasion testing in a closed laboratory setup with inherent bulk sample analysis. During workplace measurements of the machining of polymer composites that were reinforced with pitch-based carbon fibers, concentrations of 830,000 WHO-fiber m–3 were observed 15 cm from the source and of 33,000 WHO-fiber m–3 at about 3 m distance. An explanation for such a high release propensity for respirable fibers with diameters below 3 µm is a fiber splitting along the axis of the studied fiber type. Comparative abrasion experiments of pitch and polyacrylonitrile-based carbon fiber reinforced polymer composites revealed that their fracture behavior differs from another. The studied polyacrylonitrile-based carbon fibers broke primarily perpendicular to their axis, whereas the studied pitch-based carbon fibers show fiber splicing and splitting along the fiber axis. In order to predict and manage health risks of the large variety of existing carbon fiber materials, the understanding of the relation between fiber microstructure, fracture morphology and WHO-fiber release propensity must be urgently improved. In the meantime, all handling and processing steps of pitch-based carbon fibers have to be accompanied by precautionary or exposure measurement-controlled safety measures to protect the employees.

The Interaction between Electricigens and Carbon Nanotube Forest and Electricity Generation Performance in MFC

AbstractCarbon nanotube forest (CNTFs) is grown vertically on the surface of highly conductive mesophase pitch carbon fibers (Pitch‐CFs) in the chemical vapor deposition method. Then the CNTFs‐modified CFs (CNTFs‐Pitch‐CF) as an anode material is assembled into the single chamber microbial fuel cells (MFCs). Interaction between electricigens and carbon nanotubes (CNTs) is investigated. The toxicity of the CNTs can make electricigens expend energy or electrons to produce exopolysaccharid (EPS) as much as possible. Accordingly, this leads to low voltage and the long start up time for the CNTFs‐Pitch‐CF anode in the early period. When the activity of electricigens with the EPS reaches a stable state over time, the output voltage rises rapidly and the maximum power density of the CNTFs‐Pitch‐CF‐equiped MFC is increased to 1112 mW/m2, which is approximately 1.55‐fold higher than Pitch‐CF‐equiped MFC. And the CNTFs‐Pitch‐CF‐equiped MFC can keep high electricity generation performance of MFCs for a long time, which is 75 % larger than the Pitch‐CF‐equiped MFC. This method of the CNTFs modifying the CFs provides a new idea for increasing the electricity generation performance of the MFCs.

Enhancement of bioelectricity generation by synergistic modification of vertical carbon nanotubes/polypyrrole for the carbon fibers anode in microbial fuel cell

Enhancing microbial electrocatalysis through novel anode design is essential to the efficient and stable operation of microbial fuel cells. Carbon fibers modified by the vertical carbon nanotubes/polypyrrole composites can give full play to their advantages, exhibiting excellent conductivity of the vertical carbon nanotubes and good biocompatibility of the polypyrrole. The carbon nanotubes are vertically grown on the carbon fibers by the chemical vapor deposition method, increasing the transfer efficiency of extracellular electron transfer. And then pyrrole is in-situ polymerized on the exterior and interior of the vertical carbon nanotubes, which can not only avoid direct contact between the vertical carbon nanotubes and electricigens to reduce the damage of the vertical carbon nanotubes to electricigens, but also enhance the positive electricity of anode. The modification of the vertical carbon nanotubes/polypyrrole for mesophase pitch carbon fibers anode improves the electricity generation performances of the microbial fuel cells. In this study, the obtained maximum power density is 1876.62 mW m−2, which is approximately 2.63-fold higher than unmodified carbon fiber brush anode. The results show that the vertical carbon nanotubes/polypyrrole composite anode has demonstrated the high potential for the use of microbial fuel cells.

Wear behavior of medical grade PEEK and CFR PEEK under dry and bovine serum conditions

Wear is among the main factors affecting the performance of artificial couplings in joint arthroplasty. In the attempt of investigating the applicability of PEEK and CFR PEEK in such applications, wear behavior of three medical grade PEEK formulations (unfilled PEEK, 30% wt. pitch carbon fiber reinforced PEEK and 30% wt. PAN carbon fiber reinforced PEEK) have been tested under dry and bovine serum lubricated conditions in a pin on flat test against Al2O3 1/8″ spheres, replicating physiological conditions whereas possible. The crystallinity and the resulting mechanical properties of the three selected material were differentiated by annealing treatments performed at 200, 250, and 300 °C. All the specimens were tested under both lubrication regimes.The observed coefficient of friction variations, as well as the calculated volumetric wear rate, displayed an improved wear behavior of the reinforced formulations in both dry and bovine serum. Correlation among the modified material properties by annealing and the wear behavior was possible. The formation of a lubricating film was identified as responsible for an improved wear performance of PEEK and CFR PEEK formulations.

Thermal numerical simulation for metal matrix composite design: Application to weight saving in electronic packaging for aeronautics

This design study aims at replacing aluminium alloy in electronic packaging for aeronautics with a weigh saving objective. In a first time, a classical materials selection method is applied to the problem, showing the most suitable material would be an aluminium alloy reinforced by pitch carbon fibres. In order to define an optimal composite for this application, the thermal dissipation function of the packaging is detailed. An accurate simulation of the heat transfers in the casing was operated thanks to simplified numerical model using finite elements in which the complex geometry of the part has been brought back to a rectangular plate. As a result, the study enhances the interest of anisotropic material, and defines specific directions in which high thermal conductivities are needed.

Thermal response of carbon fiber epoxy laminates with metallic and nonmetallic protection layers to simulated lightning currents

Nonlinear finite element (FE) simulations to characterize lightning‐induced thermal damage in AS4/3506 carbon/epoxy composites with metallic and nonmetallic protection layers were performed and then compared with those for unprotected composites. In this study, FE estimates of matrix thermal decomposition in composites subjected to 40 kA peak currents were performed. Two protection layers were considered: (1) a traditional copper mesh (CM) commonly used for aircraft lightning strike protection and (2) a single layer of highly conductive pitch carbon fiber paper (PCFP). Temperature‐dependent material properties of each constituent were used to predict the matrix thermal decomposition induced by simulated lightning current waveforms. The lightning strike FE models suggest that both the CM and the PCFP lightning protection layers successfully mitigated thermal damage development in the underlying composites as a consequence of reduced through‐thickness electrical current flow/heat conduction. The CM provided excellent protection from thermal damage; the predicted matrix decomposition only penetrated the first AS4/3506 ply. Similarly, the PCFP outer layer limited thermal damage to the top three composite plies, while the predicted matrix decomposition of the unprotected composite penetrated the sixth ply. Improved PCFP protection layers appear possible to design by varying the in‐plane and through‐thickness electrical conductivities, as well as the PCFP‐to‐first ply gap conductance. This suggests that PCFP outer layers or similar lightweight carbon‐based layers may serve as efficient lightning protection layers. POLYM. COMPOS., 39:E2149–E2166, 2018. © 2017 Society of Plastics Engineers

Effect of phenoxy-based coating resin for reinforcing pitch carbon fibers on the interlaminar shear strength of PA6 composites

Carbon fiber-reinforced thermoplastic composites have not been considered as constituent materials for structural parts due to the poor interfacial adhesion between the fiber and the thermoplastic matrix. In this work, polyamide 6 (PA6) composites with pitch carbon fibers (pCF) were fabricated by alternatively stacking PA6 films and pCF fabrics followed by being pressed. In order to improve the interfacial adhesion, phenoxy resin-based materials were coated on the surface of the fiber. The surface analyses of the fiber were carried out by XPS, TGA and dynamic contact angle method. Interlaminar shear strength (ILSS) of the composites was measured to evaluate the effect of the coating materials. The results showed that the composites with the coated pCF had higher ILSS than that with neat pCF by more than 20%. This indicated that a proper coating material can improve mechanical properties of the PA6 composites, which can be applied to the structural parts.