Isotropic Pitch-based Carbon Fiber Research Articles

Controllable synthesis of naphthalene-derived isotropic pitch with linear molecular structure via Blanc chloromethylation–dechlorination reaction

Isotropic pitches with high softening points were controllably synthesized using naphthalene (NAP) via Blanc chloromethylation–dechlorination. Under mild conditions, chloromethyl was introduced into the NAP ring in the presence of chloromethylation reagent. The chloromethylation products of NAP are mainly composed of 1-chloromethylnaphthalene (1-CMNP) and a small amount of 1,4-dichloromethylnaphthalene (1,4-DCMNP). The results of the thermodynamic and kinetic calculations confirmed that the alpha-hydrogen on the NAP ring was more susceptible to being substituted by chloromethyl during chloromethylation, resulting in the formation of 1-CMNP and 1,4-DCMNP. High-quality isotropic pitches with linear methylene-bridged NAP ring structures, characterized by high purity, a high H/C ratio, 100 % solubility in quinoline, and excellent spinnability, were obtained after thermal dechlorination polymerization. Due to their homogeneous isotropic phase, appropriate viscosity, and outstanding spinnability, the as-synthesized pitches were adopted as precursors to prepare isotropic pitch-based carbon fibers via melt spinning. Additionally, the investigation of the carbonization behavior of the as-synthesized pitches showed that the naphthalene-derived isotropic pitch obtained at a polymerization temperature of 380 °C had a 57 % carbon yield at 800 °C, and its derived semi-cokes displayed an isotropic texture, even when carbonized at 550 °C.

Co‑carbonization of coal tar pitch and brominated industrial methylnaphthalene for the production of isotropic pitch-based carbon fibers with enhanced tensile strength

The co‑carbonization of refined coal tar pitch (RCTP) and brominated industrial methyl naphthalene (BIMNP) employing benzoyl chloride (BC) as a catalyst has been explored to create an isotropic spinnable pitch for carbon fibers with notable tensile strength. BIMNP is derived from industrial methyl naphthalene (IMNP) via photo-bromination assisted by visible light using N-bromosuccinimide (NBS) as a brominating agent. This research investigates the impact of the mass ratio of RCTP and BIMNP on the composition, molecular structure, and thermophysical characteristics of the co‑carbonized pitch. A tentative elucidation of the co‑carbonization mechanism involving RCTP, BIMNP, and BC is presented. Adjusting the NBS-to-IMNP mass ratio leads to the complete conversion of 1-methylnaphthalene (1-MNP) and 2-methylnaphthalene (2-MNP) in IMNP into 1-bromomethylnaphthalene (1-BMNP) and 2-bromomethylnaphthalene (2-BMNP), respectively. The co‑carbonized pitch exhibits enhanced pitch production, increased thermal stability, and improved spinnability compared to pitch synthesized via thermal polycondensation. The resulting carbon fibers experience a rise in tensile strength by 947 MPa and an increase in Young's modulus by 41.3 GPa as BIMNP content varies from 10% to 30%. Using BIMNP as a co‑carbonization agent offers a promising avenue for producing pitch-based carbon fibers meeting automotive industry requirements.

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.

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.

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.

Stress graphitization in carbon/carbon composites reinforced with isotropic pitch-based carbon fiber felt

Stress graphitization in carbon/carbon composites reinforced with isotropic pitch-based carbon fiber felt

Correlating thermal conductivity of carbon fibers with mechanical and structural properties

Thermal conductivity of carbon fibers (CFs), being one of the important properties, is not easily quantified due to practical difficulties in measuring it. We suggest a universal correlation between the thermal conductivity of CFs and their electrical and mechanical properties in order to estimate it without direct measurement. Crystalline structural information did not show a clear correlation with thermal conductivity, especially for commercially available polyacrylonitrile- or isotropic pitch-based CFs that have less than a few nanometers of La and Lc. However, in a correlation between tensile modulus and thermal conductivity, there are three distinct regions and two properties increase with a different inclination in each region. We envisage tensile modulus to be utilized to estimate thermal conductivity without a direct measurement for all kinds of CFs.

Formation of SiC in the Isotropic Pitch-Based Carbon Fiber and Its C/C Composites

Formation of SiC in the Isotropic Pitch-Based Carbon Fiber and Its C/C Composites

Controlling spinning pitch property by tetrahydrofuran-soluble fraction of coal tar pitch co-carbonization with petrolatum

Isotropic pitch-based carbon fiber was successfully prepared from tetrahydrofuran-soluble fraction of coal tar pitch co-carbonization with petrolatum by air-blowing. The effects of reaction temperature and time, amount of petrolatum added on the composition and spinning properties of resultant pitches were investigated. It indicated that petrolatum could effectively improve the softening point, aromaticity, hydrogen content and molecular weight of the resultant pitches by promoting cross-linking and dehydrogenation polymerization reactions at low air-blowing temperature. Moreover, more aliphatic and naphthenic structures had been introduced into resultant pitches as addition of petrolatum and also inhibited the generation of quinoline-insoluble particles. The obtained green fibers were facile to be stabilized and carbonized and the resultant carbon fibers showed fully isotropic and finer, uniform diameter with smooth surface and higher tensile strength of up to 0.92 GPa. It provided a facile chemical modification method for isotropic pitch-based carbon fiber production. Spinnable pitches and isotropic pitch-based carbon fiber with higher tensile strength prepared from CTP-THFS co-carbonization with petrolatum by air-blowing.

Facile Preparation and Characterization of Carbon Fibers with Core-Shell Structure from Graphene-Dispersed Isotropic Pitch Compounds.

In this study, isotropic pitch-based carbon fibers were prepared from a mixture of petroleum residue and graphene nanoplatelets with different contents. The softening point and synthetic yield of synthesized isotropic pitches were analyzed and compared to characterize the nature of the pitches. The surface and thermal characteristics of the fibers were observed using scanning electron microscopy and thermogravimetric analysis (TGA), respectively. From the results, it was observed that the prepared carbon fibers had an interesting core-shell structure. In the TGA analysis with air, the carbon fiber having 0.1 wt.% of graphene showed a higher residue yield than that of the sample having 1.0 wt.% of graphene. This result can be explained due to the graphene being placed on the surface region of the carbon fibers and directly helping to increase the surface area of the carbon fibers, resulting in rapid oxidation due to the enhanced contact area with oxygen.

Structural evolution of pitch fibers during low temperature carbonization

Isotropic pitch-based carbon fibers (IPCFs) were prepared at various carbonization temperatures from 400 to 1200 °C using pitch fibers stabilized at 290 °C to investigate their structural evolution during the carbonization process. The chemical structure changes of IPCFs as a function of carbonization temperature were thoroughly analyzed using various characterization tools, such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and laser desorption/ionization time-of-flight mass spectrometry. The characterization results were systematically compared with those of the ordering structures obtained from Raman spectroscopy and X-ray diffraction. The results demonstrated that the transformation of the chemical structure, ordering structure, and physical properties of IPCFs proceeds with three distinct steps depending on the carbonization temperature: fusion of small aromatic structures of pitch, random stacking of the fused structure and conversion into mostly disordered carbon structures. In addition, we found a correlation of the chemical and ordering structure changes with the enhancement of physical properties, such as density, tensile modulus, and strength.

Analyses of oxidation process for isotropic pitch-based carbon fibers using model compounds

Isotropic pitch-based carbon fiber has been utilized for various applications such as thermal insulation materials for high-temperature furnace and additives for slide member, but the structure of the carbon fiber is still under debate. This is because the precursor pitch contains various aromatic compounds in addition to the complicated oxidation and carbonization reaction during production process of carbon fiber. In this work, oxidation processes of model compounds of pitch such as pyrene (sp2CH with zigzag-like edges), triphenylene (sp2CH with armchair edges), fluorene (pentagon with sp3CH2), and 9-methylanthracene (hexagon with sp3CH3) were analyzed using mass spectrometry, elemental analysis, infrared (IR), Raman, and X-ray photoelectron spectroscopy (XPS) in addition to calculation such as molecular dynamic simulation with a reactive force field (ReaxFF) and simulation of IR, Raman, and XPS spectra (Gaussian09). Combination of calculations and experiments revealed that oxidation proceeded in the order of zigzag-like edges > sp3CH3 > sp2CH2 > armchair edges, and the quinone formed by oxidation worked as a precursor for a crosslinking reaction. It is expected that the results of this work, which revealed the origin of the crosslinking, could lead to improve properties as well as to estimate the detailed structures of isotropic pitch-based carbon fiber.

Preparation of isotropic pitch precursor for pitch-based carbon fiber through the co-carbonization of ethylene bottom oil and polyvinyl chloride

For the first time, polyvinyl chloride (PVC) was used as an easily-handled chlorine source for preparation of isotropic pitch-based carbon fiber (IPCF) incorporating ethylene bottom oil (EO) as a raw material. Pitch precursors were prepared by the chlorination–dehydrochlorination triggered by chlorine radicals originated from PVC; aromatization and poly-condensation reactions occurred by polyene-type radicals from PVC. Radical production and co-carbonization were facilitated by pretreatments of EO through vacuum distillation, bromination, and additional heat treatment. Pitches were prepared by the co-carbonization of pretreated EO and EO containing 20wt% PVC, and had higher yields and better spinnability than those by simple distillation.

Effects of stabilization variables on mechanical properties of isotropic pitch based carbon fibers

Optimization of the stabilization process for manufacturing low-cost carbon fibers was performed. By simply varying both heating rate (0.5–10°C/min) and starting temperature (25–230°C), the resulting fibers possessed different properties such as densities, oxygen contents, and weight gains due to the oxygen up-takes. Subsequent oxidative reactions led to changes in chemical compositions of the fibers. Therefore, this study suggests that more concerned design with complementary parameters such as starting temperature and heating rate, significantly reducing stabilization time down to 56.5min with the comparable mechanical properties of the conventional isotropic pitch based CFs.

Effect of carbonization temperature on crystalline structure and properties of isotropic pitch-based carbon fiber

carbonized at temperatures ranging from 800 to 1600oC to investigate their crystalline structure and physical properties as a function of the carbonization temperature. The in-plane crystallite size (La) of the carbonized pitch fiber from X-ray diffraction increased monotonously by increasing the ca...

等方性ピッチ系炭素繊維フェルトを用いた炭素繊維／炭素複合材料における応力黒鉛化

等方性ピッチ系炭素繊維フェルトを用いた炭素繊維／炭素複合材料における応力黒鉛化

Preparation of pitch based carbon fibers using Hyper-coal as a raw material

A cost-effective method for producing an isotropic pitch-based carbon fiber using the 1-methylnaphthalene (MN) soluble fraction of Hyper-coal (HPC) was newly developed. The extent of MN fractionation was controlled by altering the fractionation temperatures. The MN soluble fraction obtained from HPC at 60 °C had excellent spinnability after the removal of volatile matter by thin layer evaporation. Additionally, the fiber that was subsequently derived from the MN soluble fraction had satisfactory mechanical properties with an averaged tensile strength of 1150 MPa after heating to 800 °C for 5 min.

等方性ピッチ系炭素繊維の構造と空気酸化挙動

等方性ピッチ系炭素繊維の構造と空気酸化挙動

Enhancing the tensile strength of isotropic pitch-based carbon fibers by improving the stabilization and carbonization properties of precursor pitch

A unique isotropic pitch composed of linear chains of polycondensed aromatic molecules was synthesized through the bromination and subsequent dehydrobromination of mixed naphtha-cracked oil (NCO) and quinoline-insoluble free coal tar (CT). Isotropic pitch-based carbon fibers obtained from the co-carbonization of an NCO/CT mixture via bromination and dehydrobromination exhibited an unprecedentedly high tensile strengths and elongations at break of 1800 and 2050 MPa, and 3.2 and 2.8% following carbonization at 800 and 1100 °C for 5 min, respectively. The aromatic components derived from the co-carbonization process were primarily condensed cyclic compounds containing four or five aromatic rings. These substructures enhanced the tensile strength of the carbon fibers up to 2050 MPa, which is a level much higher than that reported for carbon fibers derived from naphtha-cracked oil-based isotropic pitch. TOF-MS analyses indicated that the molecular weight of the NCO/CT derived pitch was higher than that of the NCO derived pitch. Both isotropic pitches exhibited Bingham behavior above their softening temperatures. However, the linear chains of the higher aromatic units of the NCO/CT derived pitch resulted in a higher degree of shear-thinning than was observed with the NCO derived pitch, resulting in a higher degree of molecular orientation during spinning.

Preparation of isotropic pitch-based carbon fiber using hyper coal through co-carbonation with ethylene bottom oil

A spinnable pitch was developed from the tetrahydrofuran-soluble fractions (THFS) of hyper coal (HPC) and used to prepare carbon fibers. THFS-derived pitch from bituminous coal-derived HPC showed excellent spinnability and the obtained carbon fibers had a tensile strength of over 800MPa with a diameter of 13μm following heat treatment at 800°C for 5min. Thus, HPC was shown to be a useful alternative precursor for the preparation of low-cost and general-performance carbon fibers.