Pitch Fibers Research Articles

Exploring oxygen migration and capacitive mechanisms: Crafting oxygen-enriched activated carbon fiber from low softening point pitch

A green pitch fiber from coal tar distillation residue, with a softening point of 190 °C, was used to make activated carbon fiber through an in-situ oxygen-doped method. Oxygen-rich pitch-based activated carbon fibers (OPACFs) were successfully created with a three-stage stabilization process using this low softening point pitch fiber. The OPACFs exhibit a moderate pore size distribution and high surface oxygen content (20.83 at%). The migration and transformation of oxygen during this process were studied. Due to the formation of stable oxygen-containing functional groups (CO), the resulting material shows excellent electrochemical performance. It achieved a specific capacitance of 334 F/g at 0.5 A/g and maintained good rate capacity (73.7 %, 0.5–50 A/g) in a 6 M KOH electrolyte. The assembled supercapacitor displayed exceptional cycle stability, retaining 91.4 % capacitance at 1 A/g after 10,000 cycles. Further investigation revealed that the specific capacitance includes both surface-controlled and diffusion-controlled capacitance, with oxygen doping significantly enhancing the latter.

Mesophase pitch-based high performance carbon fiber production using coal extracts from mild direct coal liquefaction

Mild direct coal liquefaction (autogenous pressure, no catalyst, no H2 gas) of Springfield coal in fluid catalytic cracking decant oil is shown to effectively produce coal extract precursors to spinnable mesophase pitch. This work demonstrates that the coal extract can be thermally treated to obtain mesophase pitch in a facile one-step process, bypassing the production of an intermediate isotropic pitch. Furthermore, the presence of 25 wt.% coal in the initial slurry can increase the yield to mesophase pitch nearly twofold and yield to carbon fiber by approximately 70%. The coal extract-derived mesophase pitch was melt-spun and heat treated to produce carbon fiber with graphitic texture, high modulus (>400 GPa) and tensile strength up to 943 MPa. Overall, this work demonstrates that coal can be effectively utilized to markedly amplify the mesophase pitch and carbon fiber yield from fluid catalytic cracking decant oil by relatively simple processing, while conserving utility as a precursor to high performance carbon fiber and potentially other high value graphitic products.

Impact of thermal lensing on the TMI threshold powers in rod-type Yb-doped fiber amplifiers

The impact of thermal lensing (TL) on the transverse mode instability (TMI) threshold power in rod-type fiber amplifiers is investigated. Simulations are conducted with a 3D coupled mode analysis on a set of five scaled large pitch fiber (LPF) amplifiers. The LPF fibers are represented by surrogate step-index fibers (SIFs) with scaled cladding diameters, core diameters, and numerical apertures for a fixed normalized frequency V equal to 3.0 and scaled modal field overlap integrals with the core and cladding. It is found that thermal lensing decreases the TMI threshold powers due to increases in the TMI nonlinear gain. This gain increase is attributed to an increase in the nonlinear gain overlap integrals that occurs with the reduction in the fundamental mode effective area. Estimates for the TMI threshold power are in good agreement with measurements; however, the simulations overestimate the mode shrinkage factor. This discrepancy is tentatively attributed to the representation of the LPF by an effective SIF. These results may offer opportunities for fiber designs that increase the TMI threshold powers.

Understanding the Molecular Arrangement and Orientation Characteristics of Mesophase Pitch and Its Fibers via a Polarized Light Microscope.

A polarized light microscope (PLM) was utilized to examine the optical textures of mesophase pitch (MP) and MP-derived fibers, which aimed to reveal the arrangement and orientation characteristics of pitch molecules and to clarify the evolution and transformation mechanism of carbonaceous microcrystalline from pitch fibers to graphitized fibers. The results found that there were distinct optical textures in MP, where one side exhibited a transition from a flattening plane to a mountain-like undulating plane. This transition corresponded to the arrangement of pitch molecules, resembling stacked lamellar structures reminiscent of curved paper. Meanwhile, the optical textures of fibers revealed that the blue substance was wrapped around the red grain-like domains in the longitudinal section and confirmed that the red part belonged to the pyridine insoluble fraction of MP and the blue part belonged to its pyridine-soluble fraction. After graphitization, the red part was transformed into graphite sheets and the blue part was transformed into an amorphous carbon layer which was wrapped around the graphite sheets, forming a carbonaceous microcrystalline package-like bag. Therefore, this study provided a comprehensive interpretation of the structural evolution mechanism of MP and MP-derived fibers based on their macro-optical textures and micro-nanostructures.

Improving the mechanical properties and thermal conductivity of mesophase-pitch-based carbon fibers by controlling the temperature in industrial spinning equipment

Mesophase-pitch-based carbon fibers (MPCFs) were prepared using industrial equipment with a constant extrusion rate of pitch while controlling the spinning temperature. The influence of spinning temperature on their microstructures, mechanical properties and thermal conductivities was investigated. SEM images of the fractured surface of MPCFs show that the graphite layers have a radiating structure at all spinning temperatures, but change from the fine-and-folded to the large-and-flat morphology when increasing the spinning temperature from 309 to 320 oC. At the same time the thermal conductivity and tensile strength of the MPCFs respectively increase from 704 W·m−1·K−1 and 2.16 GPa at 309 oC to 1 078 W·m−1·K−1 and 3.23 GPa at 320 oC. The lower viscosity and the weaker die-swell effect of mesophase pitch at the outlets of the spinnerets at the higher spinning temperature contribute to the improved orientation of mesophase pitch molecules in the pitch fibers, which improves the crystallite size and orientation of the MPCFs.

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.

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.

Isotropic coal tar pitch-based carbon fibers: Effect of nitric acid towards elimination of air-stabilization step

The remarkable properties exhibited by carbon fibers have generated considerable interest in seeking alternative approaches to replace time-consuming, energy-intensive, and multi-step procedures for their synthesis. Among the various stages involved in carbon fiber synthesis, the stabilization step plays a crucial role as it necessitates an extended duration to transform thermoplastic pitch-fibers into thermosetting fibers, thus preventing them from melting during high-temperature treatments. In this study, isotropic coal tar pitch (ICTP) was transformed into pitch fibers through melt-spinning process and subsequently subjected to chemical treatment for stabilization using varying concentrations (ranging from 5% to 50% v/v) of aqueous nitric acid (HNO3) solutions. The objective was to determine the optimal concentration for effective stabilization. Consequently, this research eliminates the conventional, time-consuming air-stabilization process by treating the pitch fibers with nitric acid prior to carbonization. To produce carbon fibers, all chemically stabilized pitch fibers were directly carbonized at 1000 °C. Comprehensive characterizations including Rheology, Elemental analysis, FTIR, TGA, FE-SEM, XRD, Raman, and XPS were conducted to investigate the chemical and structural transformations occurring during the fiber processing. It was observed that aqueous nitric acid solutions ranging from 15% to 30% (v/v) exhibited superior structural, morphological, and mechanical properties compared to other concentrations of HNO3.

The effect of the molecular structure of naphthalene-based mesophase pitch on the properties of carbon fibers derived from it

AbstractMesophase pitch-based carbon fibers (MPCFs) have a high modulus of elasticity, low electrical resistivity and high thermal conductivity, so can be used in many fields. Carbon fibers were prepared from two naphthalene-based mesophase pitches, one synthesized by a HF/BF3 catalytic one-step method (AR-MP) and the other by an AlCl3 catalytic two-step method (N-MP). The mesophase pitches, spun pitch fibers, pre-oxidized fibers, carbonized fibers and graphitized fibers produced from them were characterized by TG-MS, FT-IR, 13C-NMR, MALDI-TOF-MS, XRD, SEM and elemental analysis. The molecular structures and properties of mesophase pitches were compared, and the effects of molecular structures on the structures and properties of the carbon fibers produced from them were measured. In comparison to N-MP, AR-MP has a rod-like semi-rigid molecular configuration containing more naphthenic structures and methyl side chains. The pre-oxidized fibers derived from AR-MP have a better carbon layer orientation, so that their graphitized fibers have a higher thermal conductivity of 716 W/(m·K). N-MP has a higher aromaticity with a disc-like rigid molecular configuration, so that the graphitized fibers prepared from it have a higher tensile strength of 3.47 GPa due to fewer defects being formed during preparation. The molecular structures of AR-MP and N-MP have an obvious influence on the structures and properties of their graphitized fibers.

Study of mesophase pitch based carbon fibers: Structural changes as a function of anisotropic content

This study investigates the synthesis of mesophase pitch (MP) with varying anisotropic (mesophase) content of 19–74% by thermal soaking of isotropic coal tar pitch for different time intervals at 410 °C without using any catalyst/additive and pre-treatment processing. These mesophase pitches were converted into continuous pitch fibers by melt spinning process, then stabilized in air and carbonized at 1000 °C to obtain the carbon fibers. The anisotropic (mesophase) content increases with increasing soaking time period from 11 to 15 h and as a result, alter the various microstructural properties of carbon fibers. Physio-chemical and microstructural properties of prepared MP were systematically studied with TGA, FTIR, Raman spectroscopy, XRD and 1H‐NMR. The overall result suggested enhancement in aromaticity and naphthenic hydrogen with increased anisotropy. Rheological studies were carried out to understand the spinning behavior of MPs. Furthermore, transformation of mesophase pitch into carbon fibers at 1000 °C, showed a decline in the microcrystal properties due to the evolution of gases which create disorderness in the lattice structure. It was observed that the increased anisotropic content improves the microstructure of the mesophase pitch and their resultant carbon fibers as the microstructure attained during mesophase formation is retained during its carbonization.

Evaluating of the oxidative behaviors of isotropic pitch fractions for optimal the mechanical properties of isotropic pitch-based carbon fibers

Oxidative stabilization plays an extremely important role in maintaining shape and structural integrity and preventing inter-filament fusing of isotropic pitch fibers during the subsequent carbonization. However, the actual chemical processes and mechanism of the stabilization reaction are complex and as yet poorly defined because of the complexity of the isotropic pitch. In the study, an isotropic pitch synthesized through the co-carbonization of aromatic-rich distillate oil and polyethylene glycol was fractioned into seven fractions by n-heptane, toluene, and their mixtures. The chemical structure and oxidative reaction features of each pitch fraction were systematically analyzed and investigated by FT-IR, 13C NMR, TG-DSC, SEM, etc. The results revealed that the light pitch fractions with more and longer alky side chains attached to the aromatic nucleus exhibit higher oxidative reactivity and appear to induce a higher content of oxygen uptake to achieve stabilization as compared with the heavy pitch fractions. The stabilization reactions of the pitch fractions were carried out in multiple stages, which was confirmed by the conversion of oxygen-containing functional groups ketones and aldehydes to anhydrides and esters as oxidation temperature increased from 150 ℃ to 290 ℃. Three commercial isotropic pitches produced from petroleum-based raw material were oxidized under different conditions. The results confirmed that it is feasible to predict and optimize the stabilization process by tailoring the pitch components.

In-Situ Doping B4C Nanoparticles in Mesophase Pitch for Preparing Carbon Fibers with High Thermal Conductivity by Boron Catalytic Graphitization.

The boron carbide (B4C) nanoparticles doping mesophase pitch (MP) was synthesized by the in-situ doping method with tetrahydrofuran solvent, and the corresponding MP−based carbon fibers (CFs) were successfully prepared through the melt−spinning, stabilization, carbonization and graphitization processes. The structural evolution and properties of boron−containing pitches and fibers in different processes were investigated for exploring the effect of B4C on mechanical, electrical and thermal properties of CFs. The results showed that the B4C was evenly dispersed in pitch fibers to provide active sites of oxygen, resulting in a homogeneous stabilization and ameliorating the split−ting microstructures of CFs. Moreover, the thermal conductivity of B1−MP−CF prepared with 1 wt.% B4C increased to 1051 W/m•K, which was much higher than that of B0−MP−CF prepared without B4C (659 W/m•K). While the tensile strength of B4C−doped CFs was lower than that of pristine CFs. In addition, a linear relationship equation between the graphite microcrystallite parameter (ID/IG) calculated from Raman spectra and the thermal conductivity (λ) calculated according to the electrical resistivity was found, which was beneficial to understand the thermal properties of CFs. Therefore, the doping B4C nanoparticles in MP did play a significant role in reducing the graphitization temperatures due to the boron catalytic graphitization but decreasing the mechanical properties due to the introduction of impurities.

Modification of isotropic pitch by tailoring chemical structure and fraction contents for enhancing carbon fiber mechanical properties

The composition of isotropic pitch (IP) is the key factor to determine the performance of carbon fibers (CFs). It is necessary to investigate the effect of chemical structure of pitch and compositions change on the performance of CFs. An isotropic pitch was fractionated into seven fractions by solvent fractionation to characterize the molecular structural features by FT-IR, 1H NMR etc. The oxidative reactivity of pitch fibers, mechanical properties, microstructure and morphology of CFs derived from four IPs with different components were characterized and evaluated. The results revealed that with the removal of light fractions, the synergistic effect between pitches components in melting significantly decreased, leading to the decrease of spinnability of pitch and deteriorating the uniformity of carbon fiber microstructure. The oxidative reactivity of the pitch fibers gradually decreased with the removal of light fractions. The reason was that these light fractions contained more alkyl side chains, which were preferentially attacked by oxygen at the low oxidation temperature, than that of these heavy fractions. The mechanical properties of CFs showed an increase first and then decrease with the removal of these light fractions. Especially, the carbon fiber derived from the isotropic pitch (H80-T20I) exhibited an excellent high tensile strength of 1190 MPa.

Extrusion Dwell Time and Its Effect on the Mechanical and Thermal Properties of Pitch/LLDPE Blend Fibres

Mesophase pitch-based carbon fibres have excellent resistance to plastic deformation (up to 840 GPa); however, they have very low strain to failure (0.3) and are considered brittle. Hence, the development of pitch fibre precursors able to be plastically deformed without fracture is important. We have previously, successfully developed pitch-based precursor fibres with high ductility (low brittleness) by blending pitch and linear low-density polyethylene. Here, we extend our research to study how the extrusion dwell time (0, 6, 8, and 10 min) affects the physical properties (microstructure) of blend fibres. Scanning electron microscopy of the microstructure showed that by increasing the extrusion dwell from 0 to 10 min the pitch and polyethylene components were more uniformly dispersed. The tensile strength, modulus of elasticity, and strain at failure for the extruded fibres for different dwell times were measured. Increased dwell time resulted in an increase in strain to failure but reduced the ultimate tensile strength. Thermogravimetric analysis was used to investigate if increased dwell time improved the thermal stability of the samples. This study presents a useful guide to help with the selection of mixes of linear low-density polyethylene/pitch blend, with an appropriate extrusion dwell time to help develop a new generation of potential precursors for pitch-based carbon fibres.

Fatigue resistance of ultra-high-modulus pitch-based carbon fiber/epoxy composites under tensile loading

Pitch-based carbon fiber reinforced epoxy composites are used in specialized applications for their high-modulus and thermal conductivity; however, little data on their fatigue performance are available in the open literature. In this study, fatigue behaviors of ultra-high-modulus pitch-based carbon fiber and standard-modulus polyacrylonitrile (PAN)-based carbon fiber were compared in woven quasi-isotropic epoxy matrix composites subject to uniaxial tension. It was found that the pitch fiber composite possessed higher normalized tensile fatigue strength and that its stress-life ( S-N) curve is less steep. Extrapolation suggests the pitch fiber composite is more fatigue-resistant in higher cycle regimes (specifically, N > 107). Cyclic loading of the pitch fiber composite resulted in minimal matrix damage, and the eventual fractures were localized and fiber-dominated for all stress levels. Cyclic loading of the PAN fiber composites resulted in widespread matrix cracking and delamination. The difference in fatigue behavior is attributed to the different strain levels attained at similar stress levels and the consequent difference in matrix damage development.

Mesophase Pitch-Based Carbon Fibers: Accelerated Stabilization of Pitch Fibers under Effective Plasma Irradiation-Assisted Modification.

Stabilization is the most complicated and time-consuming step in the manufacture of carbon fibers (CFs), which is important to prepare CFs with high performance. Accelerated stabilization was successfully demonstrated under effective plasma irradiation-assisted modification (PIM) of mesophase pitch fibers (PFs). The results showed that the PIM treatment could obviously introduce more oxygen-containing groups into PFs, which was remarkably efficient in shortening the stabilization time of PFs with a faster stabilization heating rate, as well as in preparing the corresponding CFs with higher performance. The obtained graphitized fiber (GF-5) from the PF-5 under PIM treatment of 5 min presented a higher tensile strength of 2.21 GPa, a higher tensile modulus of 502 GPa, and a higher thermal conductivity of 920 W/m·K compared to other GFs. Therefore, the accelerated stabilization of PFs by PIM treatment is an efficient strategy for developing low-cost pitch-based CFs with high performance.

Measurement Technique of Oxygen Concentration in Narrow Channels of PEFCs Based on Transmission Laser Absorption Spectroscopy

Oxygen transport at cathodes of polymer electrolyte fuel cells (PEFCs) is one of the key factors for determining their power generation performance. To maintain their stable operations, it’s necessary to establish a technique for real-time monitoring of oxygen concentration inside cathode channels of operational cells. In the previous works, the measurements of oxygen distribution within gas channels of operating PEFCs have been conducted using gas chromatograph (GC) [1], oxygen-quenching of fluorescence and phosphorescence [2], and tunable diode laser absorption spectroscopy (TDLAS) [3]. GC techniques provide better accuracy for gas detection in flow channels, however, it takes a long time (at least a few minutes) to collect a gas sample and identify a species. On the other hand, TDLAS enables the non-invasive in-situ monitoring of chemical species inside cells with a high time resolution of 100 milliseconds. Fujii et al. [3] applied the single-ended TDLAS sensor to measure the oxygen concentration in a PEFC channel. In their experiments, since the laser beam is injected perpendicular to the flow direction, the optical path length is extremely short and the sensitivity is insufficient. The detection sensitivity of oxygen is relatively low due to the weak infrared absorption. Therefore, the optical path needs to be lengthened to measure its concentration with high accuracy. In this study, to solve the above-mentioned problem, we developed the fiber-optic transmission TDLAS system and applied it to the quantitative measurement of oxygen concentration in the narrow channel of a simulated cell.Fig. 1 shows the experimental apparatus for measuring the oxygen concentration in a simulated flow cell using the fiber-optic transmission TDLAS system. TDLAS is one of the high sensitive absorption spectroscopy techniques which measure the absorbance of a chemical species and identify its concentration using infrared diode laser. The triangular modulated beam emitted from a DFB laser diode (wavelength: 764 nm) is directly injected into the straight narrow channel (width and depth: 1.0 or 1.5 mm, length: 50 mm) through the single-mode optical fiber. To collimate the laser beam at the channel inlet, a GRIN lens is attached at the top of the pitch fiber. The injected beam passes one or two channels along the flow direction. In the case of passing two channels, the beam transmitted through the first channel is turned 180 degrees by a triangular prism at the bend section (length: 5 mm). The returned beam is passed through the second channel and detected at a photodiode. The output signal is transmitted to a lock-in amplifier, and then the second harmonic (2f) absorption spectrum can be obtained by phase-sensitive detection. In the experiments, the mixed gas of oxygen and nitrogen was supplied to the channel at 100 ml/min. The oxygen concentration in the channels was adjusted to 0 to 100% by controlling each gas flow rate. This measurement was performed at 25 oC and 1 atm.Fig. 2 presents the 2f absorption signals of oxygen in the narrow channel of the simulated flow cell. The incident laser beam passed two straight channels (channel width and depth: 1.5 mm, optical path: 105 mm). The oxygen mole fraction was varied from 0 to 100%. Although the TDLAS measurements were performed inside the narrow channels, the optical fringe noise was hardly observed and the 2f spectra were clearly obtained. It was also noted that the peak-valley height of 2f spectrum increased with an increase in oxygen mole fraction. The oxygen concentration in fuel cell channels can be quantitatively estimated from only the 2f spectrum data using the fiber-optic transmission TDLAS technique.

Influence of High-Concentration LLDPE on the Manufacturing Process and Morphology of Pitch/LLDPE Fibres

A high modulus of elasticity is a distinctive feature of carbon fibres produced from mesophase pitch. In this work, we expand our previous study of pitch/linear low-density polyethylene blend fibres, increasing the concentration of the linear low-density polyethylene in the blend into the range of from 30 to 90 wt%. A scanning electron microscope study showed two distinct phases in the fibres: one linear low-density polyethylene, and the other pitch fibre. Unique morphologies of the blend were observed. They ranged from continuous microfibres of pitch embedded in linear low-density polyethylene (occurring at high concentrations of pitch) to a discontinuous region showing the presence of spherical pitch nodules (at high concentrations of linear low-density polyethylene). The corresponding mechanical properties—such as tensile strength, tensile modulus, and strain at failure—of different concentrations of linear low-density polyethylene in the pitch fibre were measured and are reported here. Thermogravimetric analysis was used to investigate how the increased linear low-density polyethylene content affected the thermal stability of linear low-density polyethylene/pitch fibres. It is shown that selecting appropriate linear low-density polyethylene concentrations is required, depending on the requirement of thermal stability and mechanical properties of the fibres. Our study offers new and useful guidance to the scientific community to help select the appropriate combinations of linear low-density polyethylene/pitch blend concentrations based on the required mechanical property and thermal stability of the fibres.

Manufacturing Pitch and Polyethylene Blends-Based Fibres as Potential Carbon Fibre Precursors.

The advantage of mesophase pitch-based carbon fibres is their high modulus, but pitch-based carbon fibres and precursors are very brittle. This paper reports the development of a unique manufacturing method using a blend of pitch and linear low-density polyethylene (LLDPE) from which it is possible to obtain precursors that are less brittle than neat pitch fibres. This study reports on the structure and properties of pitch and LLDPE blend precursors with LLDPE content ranging from 5 wt% to 20 wt%. Fibre microstructure was determined using scanning electron microscopy (SEM), which showed a two-phase region having distinct pitch fibre and LLDPE regions. Tensile testing of neat pitch fibres showed low strain to failure (brittle), but as the percentage of LLDPE was increased, the strain to failure and tensile strength both increased by a factor of more than 7. DSC characterisation of the melting/crystallization behaviour of LLDPE showed melting occurred around 120 °C to 124 °C, with crystallization between 99 °C and 103 °C. TGA measurements showed that for 5 wt%, 10 wt% LLDPE thermal stability was excellent to 800 °C. Blend pitch/LLDPE carbon fibres showed reduced brittleness combined with excellent thermal stability, and thus are a candidate as a potential precursor for pitch-based carbon fibre manufacturing.

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.