Mesophase Pitch-based Carbon Fibers Research Articles

Vertically aligned and conformal BN-coated carbon fiber to achieve enhanced thermal conductivity and electrical insulation of a thermal interface material

Due to excellent thermal conductivity, high aspect ratio, and low density, mesophase pitch-based carbon fibers (MPCFs) are highly desired in electronic packaging. However, their thermal conductivity is hard to present in the polymer matrix because of the disordered stacking and low filling. Moreover, few researches are focused on the enhancement of the electrical insulation performance for MPCFs. Herein, we report vertically aligned and insulating boron nitride (BN) coated carbon fiber (CF) powders as significant fillers for polymer composites, endowing markedly improved thermal conductivity and electrical insulation. The high-quality BN coating layer on the surface of the CF is produced by a cooling precipitation method and high-temperature treatment with ingenious use of solubility properties, exhibiting a conformal, dense, and highly crystalline structure. This preparation method overcomes the limitations of coating thickness and particle agglomeration, resulting in a 31-fold enhancement of the electrical resistivity of the CF powders. After orientation treatment in a silicone rubber matrix, such CF@BN-filled pads exhibit good thermal conductivity, significantly improved insulation performance, and excellent mechanical properties. Among them, the optimized pad achieves a thermal conductivity of 12.06 W m−1 K−1, a volume resistivity of 50 × 108 Ω cm and a breakdown voltage of 3100 V mm−1, exceptional flexibility, and a favorable compression ratio (@45 psi) of 41.7 %. This work provides unique insights into constructing carbon fiber fillers as well as the preparation of high thermal conductivity composites, thereby expanding the application scenarios of carbon fiber powder in electronic packaging.

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.

Preparation of spinnable mesophase pitch from pyrolyzed fuel oil by pressurized heat treatment and its application of carbon fiber

Petroleum residues are produced as by-products of petroleum refining. Recently, various effective non-fuel uses of petroleum residues have been considered toward a carbon-neutral society. Pyrolysis fuel oil (PFO) is one of the petroleum residues. Advanced utilization of PFO for future non-combustion applications is required. In this study, Mesophase pitch-based carbon fibers (MPCF) were successfully produced from PFO. Spinnable mesophase pitch (SMP), a precursor of MPCF, was prepared using PFO as a raw material through the pressurized heat treatment at 420°C-430 °C. PFO is from the naphtha catalytic cracking process for ethylene production and is mainly composed of 2–4 condensed polycyclic aromatic hydrocarbons (PAHs). The high temperature pressurized heat treatment could result in the PFO-derived SMPs with yield of 23.0 wt% and excellent spinnability. On the other hand, without pressurized heat treatment, the yield was 8.5 wt%. This indicates that pressurized heat treatment significantly contributed to the yield improvement. In addition, the preference for the conversion of PFO molecules into highly condensed PAHs via cata-condensation during pressurized heat treatment at 420°C-430 °C was observed, which may be the main reason for the high yield and excellent spinnability of the resulting SMPs. As a result, the obtained PFO-derived SMPs though the such high-temperature pressurized heat treatment provided the typical radial-random transversal textures and general mechanical performances of MPCF: The tensile strength and Young's modulus of the PFO-derived MPCF graphitized at 2400 °C showed high values of 1.9–2.7 GPa and 554–635 GPa, respectively.

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.

Small-angle x-ray scattering analysis of carbon fiber voids considering void length distribution

The analysis method proposed by Ruland et al. is widely used to analyze the void lengths in carbon fibers, but it could not apply to mesophase pitch-based carbon fibers. We thought that the reason for the inability to analyze pitch-based carbon fibers was the length distribution of voids that Ruland neglected. We investigated an analytical method that considers the length distribution of voids in carbon fibers. The proposed new method could be applied to various carbon fibers from polyacrylonitrile and mesophase pitch. The analysis results revealed that the average length of voids in mesophase pitch-based carbon fibers is not only long but also widely distributed. On the other hand, the voids of carbon fibers tend to be longer as the crystallite length is longer in both polyacrylonitrile-based and mesophase-based carbon fibers. It suggests that the growth of void length is strongly influenced by the growth of crystallites in the plane direction.

Preparation, Microstructure and Thermal Properties of Aligned Mesophase Pitch-Based Carbon Fiber Interface Materials by an Electrostatic Flocking Method.

The mesophase pitch-based carbon fiber interface material (TIM) with a vertical array was prepared by using mesophase pitch-based short-cut fibers (MPCFs) and 3016 epoxy resin as raw materials and carbon nanotubes (CNTs) as additives through electrostatic flocking and resin pouring molding process. The microstructure and thermal properties of the interface were analyzed by using a scanning electron microscope (SEM), laser thermal conductivity and thermal infrared imaging methods. The results indicate that the plate spacing and fusing voltage have a significant impact on the orientation of the arrays formed by mesophase pitch-based carbon fibers. While the orientation of the carbon fiber array has a minimal impact on the shore hardness of TIM, it does have a direct influence on its thermal conductivity. At a flocking voltage of 20 kV and plate spacing of 12 cm, the interface material exhibited an optimal thermal conductivity of 24.47 W/(m·K), shore hardness of 42 A and carbon fiber filling rate of 6.30 wt%. By incorporating 2% carbon nanotubes (CNTs) into the epoxy matrix, the interface material achieves a thermal conductivity of 28.97 W/(m·K) at a flocking voltage of 30 kV and plate spacing of 10 cm. This represents a 52.1% increase in thermal conductivity compared to the material without TIM. The material achieves temperature uniformity within 10 s at the same heat source temperatures, which indicates a good application prospect in IC packaging and electronic heat dissipation.

Tensile failure mechanisms investigation of mesophase pitch-based carbon fibers based on continuous defective graphene nanoribbon model

Mesophase pitch (MPP)-based carbon fibers exhibit outstanding mechanical properties, notably an exceptionally high Young’s modulus. Despite extensive investigations into the microstructure of MPP-based carbon fibers, the influence of these factors on deformation mechanisms under tension remains unclear. This study employs the continuous defective graphene nanoribbons (dGNR) atomistic structure model for molecular dynamics simulations to explore the tensile failure mechanisms of MPP-based carbon fibers. In the simulation model, the structure of the defective region was generated through high-temperature annealing, and a transition region was introduced to prevent distortion and damage to the active graphene edges. The simulation reveals the evolutionary process of the microstructure of MPP-based carbon fibers under tension and achieves Young’s modulus predictions with greater accuracy than theoretical models. Additionally, the study shows that different strengths of interactions between adjacent graphene nanoribbons can lead to two distinct failure modes. Models with larger crystallite dimensions along the fiber axis and lower average defective concentrations exhibit geometric deformation coordination between adjacent nanoribbons, potentially elucidating the increasing strength trend in MPP-based carbon fibers with rising graphitization levels. Our simulations provide insights into the tensile failure mechanisms of MPP-based carbon fibers, offering valuable guidance for regulating their microstructure to enhance mechanical performance.

Analysis of transverse thermal conductivity for mesophase pitch-based carbon fibers and the through-thickness heat conduction of their composites

A quantitative analysis method for the transverse thermal conductivity (TC) of carbon fiber is developed, which consists of three steps including TC and morphology characterization of unidirectional composite laminate, fiber contour extraction, and finite element inverse analysis. Two different pitch-based carbon fibers with folded-radial and onion-skin microstructure are characterized, and the influences of fiber volume fraction and microstructure on the heat conduction of their composites are investigated. The equivalent transverse TCs of TC–HC–800 and PCF-1 carbon fibers are measured to be 9.27 and 2.87 W m−1 K−1, respectively. The through-thickness TC of unidirectional composite exhibits rapid growth with the increase in fiber volume fraction. The finite element analysis reveals that more continuous heat conduction paths are formed with the increase in fiber volume fraction. Benefited from the bigger graphitization degree, larger cross-sectional area, and bigger aspect ratio, TC–HC–800 unidirectional composite shows higher through-thickness TC than PCF-1 composite at the same fiber volume fraction.

Study on the ablation performance of SiC-coated high thermal conductivity three-dimensional C/C composites

Carbon/carbon composites were prepared by densifying a three-dimensional preform made of mesophase pitch-based carbon fiber woven fabric lamination and PAN-based carbon fiber z-pin. Afterwards, SiC coating was prepared on them by pack cementation, and their ablation performances were investigated. Results show that the stacked of pitch-based carbon fiber woven fabrics in Z direction induces a high thermal conductivity of composites in in-plane direction and a sawtooth-structured surface of SiC coating, which helps to decrease the surface temperature (from 1778 to 1614 ℃) and the thermal stress of coating during ablation. Thus, a greatly improved ablation resistance is obtained for the coating in the X-Z plane, showing a mass ablation rate of − 0.01 mg/s and a linear ablation rate of − 0.12 µm/s, respectively, 90.9% and 105.2% lower than that of the X-Y plane. Our findings can provide a meaningful way for the development of high-performance ablation-resistant C/C composites.

Effects of high-temperature thermal reduction on thermal conductivity of reduced graphene oxide polymer composites

The graphitic crystalline structure of reduced graphene oxide (rGO) can be improved by high-temperature thermal reduction at various heat-treatment temperatures ranging from 1000 to 2500 °C. The crystallinity significantly increased with increasing heat-treatment temperature. The electrical conductivities of the rGOs heat-treated at 2000 and 2500 °C (h-rGO-2000 and h-rGO-2500, respectively) were similar to those of commercial graphite. The isotropic thermal conductivity of rGO/epoxy composite with 10 wt% h-rGO-2500 (2.56 W/mK) was 11.6 times higher than that of pristine rGO (p-rGO; 0.22 W/mK) and significantly superior to those of epoxy composites with commercial graphite (0.82 W/mK) and mesophase pitch-based carbon fibers (MPCFs; 1.29 W/mK). Moreover, owing to the synergistic effect operating in the MPCF–h-rGO hybrid filler in epoxy composites, this combination of fillers increased the thermal conductivity to a greater extent than the MPCF–p-rGO hybrid filler. Optimum synergistic effects on the isotropic and in-plane thermal conductivities were achieved with an MPCF:h-rGO-2000 weight ratio of 49:1 (11.90 and 17.93 W/mK, 1.48 and 1.85 times higher than 8.02 and 9.69 W/mK for MPCF–p-rGO, respectively). Finally, a machine learning method that could predict and optimize the properties of rGOs based on their heat-treatment temperatures and material compositions was developed.

Effect of secondary gas-phase reactions (SGR) in pyrolysis of carbon feedstocks for anisotropic carbon materials production – 3: Modifying non-coking coal tar through co-pyrolysis of coal with linear low-density polyethylene and high-impact polystyrene

This work focuses on co-pyrolysis experiments of Utah Sufco coal with linear low-density polyethylene (LLDPE) and high-impact polystyrene (HIPS). These two plastic types have differing pyrolysis chemistries and have different hydrogen transfer behavior. Similar to earlier work in this series of papers, controlled secondary gas-phase reactions during pyrolysis were used to induce cracking and condensation reactions among the pyrolytic tar species. Co-pyrolysis tests were performed with feed plastic percentages ranging from 10 to 20 wt % and pyrolysis SGR temperatures ranging from 800 to 900° C. Analyses of the intermediate tar products showed that oxygen contents and aromaticity were substantially different, depending on the plastic, and resulting pitch softening points and mesophase contents also varied greatly depending on the starting plastic feedstock used. Most of the synergies observed in the co-pyrolysis results were negative, except for the oxygen content. Oxygen contents were higher than expected when LLDPE was used, resulting in reactive pitches with softening points >350° C. On the other hand, oxygen contents were lower than expected when HIPS was used, resulting in less reactive pitches. Ultimately, only the HIPS/coal samples created at the SGR temperature of 900° C had reasonable softening points at or under 350° C, making them the only samples created in this work potentially suitable for mesophase pitch-based carbon fiber production. The success in creating fusible mesophase pitches from co-pyrolyzing HIPS with Utah Sufco coal is likely attributed to the fact that polystyrene is a stronger hydrogen acceptor rather than donor, which should facilitate more cracking rather than stabilizing tar oxygen functional groups, making the tar species ultimately less reactive during thermal conversion to mesophase pitch.

Influences of fracture toughness and thermal conductivity on the ablation behavior of SiC-ZrC-MPCFs composite modified by mesophase-pitch-based carbon fibers

A novel SiC-ZrC-MPCFs composite was successfully prepared by introducing short-cut mesophase-pitch-based carbon fibers (MPCFs) into SiC-ZrC ceramics. Results show that the MPCFs improved the fracture toughness of SiC-ZrC-MPCFs composite to 4.97 ± 0.47 MPa m1/2, which was 58.06 % higher than that of SiC-ZrC ceramics. Due to the reinforcement of MPCFs, no cracks were formed on the composite during ablation, thus preventing the direct diffusion of oxidizing atmospheres into the interior. Moreover, the MPCFs also worked as thermally conductive channels and provided a thermal conductivity of 68.10 ± 0.68 W/(m K) for the composite, compared to 39.48 ± 1.25 W/(m K) for SiC-ZrC ceramics. The heat could rapidly transfer from ablation center to other areas through the MPCFS, leading to low ablation center temperatures. The COMSOL simulation indicates that the ablation center temperature of SiC-ZrC-MPCFs composite was 1094 °C after 2300 °C plasma ablation for 20 s, while that of SiC-ZrC ceramics was up to 1543 °C, which was confirmed by the actual back temperatures. Therefore, the improved fracture toughness and high thermal conductivity ensured the excellent ablation property of SiC-ZrC-MPCFs composite. After ablation for 20 s, the ablation rates of the composite were − 0.048 ± 0.007 mg/s and − 0.715 ± 0.056 µm/s, respectively.

Preparation and properties of highly thermal conductive C/C-SiC

A kind of highly thermal conductive silicon carbide matrix composites (c-1000/C-SiC, c-600/C-SiC) reinforced with chopped mesophase pitch-based carbon fibers (c-MPCF) including 1000 W/(m·K) and 600 W/(m·K) were successfully prepared by the phenolic resin precursor impregnation pyrolysis and liquid silicon infiltration (LSI) method. Quasi-isotropic c-MPCF/C-SiC composites demonstrate excellent thermophysical properties, including average flexure strength of 111.5 MPa of c-1000/C-SiC and 123.0 MPa of c-600/C-SiC, average high thermal conductivity of 101.33 W/(m·K) and 93.94 W/(m·K) at room temperature, low coefficient of thermal expansions of 2.942 ppm/K and 3.147 ppm/K at room temperature, which provides a new strategy for preparing isotropic silicon carbide ceramic matrix composites with comprehensive properties and dimensional stability.

Effects of high thermal conductivity chopped fibers on ablation behavior of pressureless sintered SiC–ZrC ceramics

As one of the most promising thermal protection materials, the ablation performance of SiC–ZrC ceramics is strongly influenced by thermal conductivity. In this work, the high thermal conductivity mesophase pitch-based carbon fibers (MPCFs) were uniformly added into a mixture of SiC and ZrC powders, which were pressureless sintered to form a MPCFs modified SiC–ZrC ceramics. The relationship between thermal conductivity and MPCFs content was investigated in detail. Both theoretical calculations and experimental results showed that the SiC–ZrC ceramics modified by adding 4.81 vol% MPCFs gained the highest thermal conductivity of 68.10±0.68 W/(m⋅K). The simulation shows that the temperatures at ablation center and backside of the ceramics were 1094 °C and 446 °C, respectively, after plasma ablation at 2300 °C for 20 s. And the actual backside temperature was detected to be 438 °C and that agreed with the simulation results. The high thermal conductivity leads to a lower ablation temperature because the heat is rapidly transferred from the high temperature part to the low region. Due to the low ablation temperature, the 4.81 vol% MPCFs modified SiC–ZrC ceramics exhibited the lowest mass ablation rate (−0.048±0.007 mg/s) and linear ablation rate (−0.715±0.056 μm/s). This research presents a novel insight for designing and fabricating excellent ablation-resistance ultra-high temperature ceramics (UHTCs).

Investigation of the Tendency of Carbon Fibers to Disintegrate into Respirable Fiber-Shaped Fragments

Recent reports of the release of large numbers of respirable and critically long fiber-shaped fragments from mesophase pitch-based carbon fiber polymer composites during machining and tensile testing have raised inhalation toxicological concerns. As carbon fibers and their fragments are to be considered as inherently biodurable, the fiber pathogenicity paradigm motivated the development of a laboratory test method to assess the propensity of different types of carbon fibers to form such fragments. It uses spallation testing of carbon fibers by impact grinding in an oscillating ball mill. The resulting fragments were dispersed on track-etched membrane filters and morphologically analyzed by scanning electron microscopy. The method was applied to nine different carbon fiber types synthesized from polyacrylonitrile, mesophase or isotropic pitch, covering a broad range of material properties. Significant differences in the morphology of formed fragments were observed between the materials studied. These were statistically analyzed to relate disintegration characteristics to material properties and to rank the carbon fiber types according to their propensity to form respirable fiber fragments. This tendency was found to be lower for polyacrylonitrile-based and isotropic pitch-based carbon fibers than for mesophase pitch-based carbon fibers, but still significant. Although there are currently only few reports in the literature of increased respirable fiber dust concentrations during the machining of polyacrylonitrile-based carbon fiber composites, we conclude that such materials have the potential to form critical fiber morphologies of WHO dimensions. For safe-and-sustainable carbon fiber-reinforced composites, a better understanding of the material properties that control the carbon fiber fragmentation is imperative.

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.

Improving the interlaminar bonding and thermal conductivity of polymer composites by using split-radial mesophase pitch-based carbon fiber as reinforcement

Mesophase-pitch-based carbon fiber (MPCF) reinforced polymer (MPCFRP) have excellent properties such as high thermal conductivity and high modulus, but the significant anisotropy and surface inertness of MPCF result in the poor interlaminar thermal conductivity and interface bonding of MPCFRP, which greatly limits its application. To address this issue, MPCF-A with split-radial structure was prepared through fiber structure modulation. Compared with the conventional skin-core fiber (MPCF-B), the higher surface roughness and chemical activity of MPCF-A contribute to stronger mechanical locking and chemical bonding between fibers and resin, meanwhile open wedge crack and better graphite microcrystalline structure of MPCF-A play a positive role in increasing the contact points and reducing the phonon scattering in the heat transfer. Therefore, the interlaminar shear strength (40.7 MPa) and interlaminar thermal conductivity (2.09 W/(m·K)) of MPCFRP-A are 9.12% and 27.4% higher than those of MPCFRP-B, respectively, on the basis of the excellent in-plane thermal conductivity (322.8 W/(m·K)). This study provides a reliable guide to improve the interlayer performance of MPCFRP by tailoring the fiber microstructure.

Electroless copper plating mechanism of mesophase pitch-based carbon fibers by the grafting modification of silane couple agents

Electroless copper plating mechanism of mesophase pitch-based carbon fibers (CFs) by the novel silane couple agents (SCAs) sensitization method was investigated based on the three different functional groups of SCAs (KH550, KH570, KH792). The results showed that relatively stable oligomer films could be formed on the surface of CFs after the sensitization treatment with three kinds of SCAs, which promoted adhesion of CFs with copper plating. Besides, a larger crystalline size, lower resistivity, more uniform and continuous coated copper layers were observed in the copper-plated CFs with KH550 grafting modification (Cu@CF-KH550), in comparison with the copper-coated CFs prepared with KH570 or KH 792 grafting modification (Cu@CF-KH570, Cu@CF-KH792). Moreover, Cu@CF-KH550 had the higher thermal stability than Cu@CF-KH570 and Cu@CF-KH792.

Stretching modification on mesophase-pitch-based fibers during carbonization process: From laboratory batch experiments to pilot continuous production

Mesophase-pitch-based carbon fibers (MPCFs) have excellent physical performance and are widely used in many cutting-edge fields. The regulation and control of temperature-dependent crystalline structure is very vital for improving their physical properties. Herein, a stretching technique was applied in the carbonization process to produce performance-improved MPCFs, through testing initially in laboratory batch experiments, and then upgrading into a pilot continuous production. For batch carbonization stretching on a bundle of fixed-length fibers, it is found that applying an appropriate tension helps improve their crystalline structure and physical properties. Compared to the “one-stage” constant tension, the “two-stage” variable tension is more conducive to the growth and orientation of graphite microcrystals in MPCFs and the improvement of their physical properties owing to the good match of tension and temperature. For continuous carbonization stretching on a bundle of long filaments, the optimal condition is under a suitable stretching ratio of 0.965 at 500–780 °C for 40 min. The tensile strength and modulus of the 3000°C-graphitized large-diameter MPCFs rise by ∼35% and ∼10%, respectively. The axial electrical resistivity (1.66 μΩ m) decreases by ∼25%, while the thermal conductivity (759.64 W/m K) increases by ∼33%. The effect of the continuous carbonization stretching has been verified to be well accordant with that of the batch in this work, which will pave the road for the wide application of hot-stretching in industrial production of high-performance MPCFs.

Pressure-Strengthened Carbon Fibers from Mesophase Pitch Carbonization Processes.

Little attention has been devoted to studying the pressures during the mesophase pitches carbonization processes and their effects on the as-produced carbon fibers' mechanical properties. Herein, we study the pressure-enhanced graphitization of mesophase pitch and the promoted tensile stresses of the produced carbon fibers using full atomistic simulations based on reactive force fields. Results show that pressures increase the tensile stress of as-produced fibers by 3.7-11 times under 1-6 GPa isotropic compressing pressure. The highest tensile stress can reach 4.39 GPa in carbonized coal tar pitch at 4000 K under 6 GPa. In experimental work, the pressurized laser-processed mesophase pitch generates less gas and shows more ordered carbonized structures in Raman spectra. This work provides a fundamental understanding of the reaction mechanism of carbon fiber production under pressure, and also illustrates a promising method to manufacture mesophase pitch-based carbon fibers with exceptional mechanical properties.