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In this contribution, we propose a new approach to enhance the ablation properties of carbon/carbon (C/C) composites. 2.5D CFMP/C composites were obtained by mesophase pitch-based carbon fiber (CFMP) as the reinforcing carbon fibers, which facilitates the high aerodynamic heat flow near the stagnation to be rapidly guided to the low heat flow region at the rear of the structure. The results show that the surface temperature of 2.5D CFMP/C composites is 100 °C lower than that of 2.5D CFPAN/C composites prepared by traditional PAN-based carbon fiber (CFPAN), and the mass ablation rate and linear ablation rate of 2.5D CFMP/C composites decreased from 3.307 mg/s to 1.412 mg/s and from 3.067 µm/s to 0.501 µm/s, respectively. In addition, the mechanical properties of the 2.5D CFMP/C composites are outstanding, which will lay the foundation for their stability in ablative environments. Our work will bring new blessings for the further development of C/C composites in the aerospace field. [ABSTRACT FROM AUTHOR]

In this contribution, we propose a new approach to enhance the ablation properties of carbon/carbon (C/C) composites. 2.5D CFMP/C composites were obtained by mesophase pitch-based carbon fiber (CFMP) as the reinforcing carbon fibers, which facilitates the high aerodynamic heat flow near the stagnation to be rapidly guided to the low heat flow region at the rear of the structure. The results show that the surface temperature of 2.5D CFMP/C composites is 100 °C lower than that of 2.5D CFPAN/C composites prepared by traditional PAN-based carbon fiber (CFPAN), and the mass ablation rate and linear ablation rate of 2.5D CFMP/C composites decreased from 3.307 mg/s to 1.412 mg/s and from 3.067 µm/s to 0.501 µm/s, respectively. In addition, the mechanical properties of the 2.5D CFMP/C composites are outstanding, which will lay the foundation for their stability in ablative environments. Our work will bring new blessings for the further development of C/C composites in the aerospace field. [ABSTRACT FROM AUTHOR]

Polyacrylonitrile (PAN) gels create significant obstacles in industrial fiber spinning by forming insoluble networks that compromise solution stability and uniformity. This study investigates the rheological properties of PAN/dimethyl sulfoxide (DMSO) solutions, examining how aging time, moisture content, and polymer concentration affect gelation behavior. Dynamic rheological analysis revealed that both physical and chemical crosslinks play crucial roles in gel formation, with gelation accelerating markedly when moisture content exceeds 3% and aging progresses. Under heat treatment at 80 °C, samples with increased moisture content demonstrated rapid transitions to solid-like states, indicating a critical moisture threshold for enhanced gelation kinetics. Additionally, reductions in polymer concentration disrupted physical crosslink density, thereby mitigating gel formation. These results underscore the importance of precisely controlling moisture and concentration parameters in PAN solutions to stabilize solution properties and minimize gel formation, thus enhancing process efficiency and quality in PAN-based carbon fiber production. [ABSTRACT FROM AUTHOR]

Thermal protection systems (TPS) are vital for re-entry vehicles for their safe passage into the atmosphere from space. Hence, researchers took a keen interest in improving the thermal and ablative properties of composites to be used in making thermal protection systems. Therefore, an attempt was made to improve the thermal and ablative properties of composites made of carbon fibers (Cf) and resorcinol formaldehyde phenolic (Ph) resin with the incorporation of silicon carbide (SiC) particles. The filler was added in various percentages (0 wt% - blank, 1 wt%, 3 wt%, and 5 wt%), and the composites were tested for ablative, thermal and mechanical properties. The results demonstrate that the SiC-modified PAN-based carbon fiber reinforced phenolic (SiC-PANCf-Ph) composite with 3 wt% SiC enhancement exhibited ideal properties. The post-ablation phase composition and microstructure were examined through X-ray diffraction (XRD), Scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The surface morphology evidences the formation of a silicon dioxide (SiO2) layer on the composites. The SiC-PANCf-Ph composites demonstrated the lowest ablation rate, enhancing their potentiality for effective TPS applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

While carbon fibers (CFs) are still the most attractive reinforcement material for lightweight structures, they are mostly manufactured using crude oil-based process chains. To achieve a higher eco-efficiency, the partial substitution of polyacrylonitrile (PAN) by renewable materials, such as lignin, is investigated. So far, this investigation has only been carried out for batch manufacturing studies, neglecting the transfer and validation to continuous CF manufacturing. Therefore, this work is the first to investigate the possibility of partial substituting lignin for PAN in a continuous process. Lignin/PAN-blended CFs with up to 15 wt.-% lignin were able to attain mechanical properties comparable to unmodified PAN-based carbon fibers, achieving tensile strengths of up to 2466 MPa and a Young's Modulus of 200 Pa. In summary, this study provides the basis for continuous Lignin/PAN-blended CF manufacturing. [ABSTRACT FROM AUTHOR]

The article evaluates the HexTow 85 Polyacrylonitrile (PAN) carbon fiber from Hexcel Corporation which is utilized for manufacturing ablative carbon-carbon structures in various applications.

Polyacrylonitrile (PAN) copolymers are important precursors for the preparation of high-performance PAN-based carbon fibers. In this study, different ratios of P(AN-co-AMPS) and P(AN-co-MA-co-AMPS) were prepared by solution polymerization. The compositional structure, thermal, and crystallization properties of P(AN-co-AMPS) and P(AN-co-MA-co-AMPS) were characterized. The results show that an increase in the AMPS feeding ratio is beneficial for improving the thermal stability and crystallization ability of the PAN copolymer; however, it also reduces the molecular weight of the copolymer and increases the cyclization exothermic peak temperature, which is not conducive to the preparation of high-performance carbon fibers. This problem is avoided in P(AN-co-MA-co-AMPS), which maintains its high thermal stability and crystallization properties when appropriate amounts of MA and AMPS are introduced, and P(AN-co-MA-co-AMPS) has smoother cyclization exothermic rates, lower onset exothermic temperatures and lower peak exothermic temperatures. The structural changes of PAN, P(AN-co-MA), and P(AN-co-MA-co-AMPS) during thermal stabilization were investigated in detail using Fourier-transform infrared spectroscopy and it was found that P(AN-co-MAco-AMPS) formed more stable structures at lower temperatures. Furthermore, when the AN:MA:AMPS mass ratio is 97.5:1.5:1, P(AN-co-MA-co-AMPS) has the best overall performance. Our results suggest that the P(AN-co-MA-co-AMPS) has potential as a precursor for carbon fibers. [ABSTRACT FROM AUTHOR]

An experimental study was performed to investigate damage sensing and fracture toughness of multifunctional conductive glass fiber composites under dynamic mode-I fracture loading. Carbon nanotubes (CNTs) were dispersed within the epoxy matrix using a shear mixing and sonicating process. An electrostatic wet flocking process was used to reinforce milled short PAN-based carbon fibers onto each of the layers of glass fiber fabric along the thickness direction in the composites. These layers of flocked fabric were stacked, and a vacuum infusion process was employed to fabricate the composites. The parametric study consisted of two carbon fiber lengths (80 μm and 150 μm) and two fiber densities (1000 fibers/mm2 and 2000 fibers/mm2) and was performed to investigate the damage sensing capabilities of a three-dimensional conductive network generated through CNTs and carbon fibers. A double cantilever beam (DCB) configuration was considered, and a modified Hopkinson pressure bar setup along with a high-speed camera was used to investigate dynamic fracture toughness of the composites. The piezo-resistance response of the composites during dynamic fracture was measured using a modified system of four probes. For comparison, composites were also characterized for fracture toughness and piezo-resistance under quasi-static fracture loading conditions. The addition of short, milled PAN-based carbon fibers significantly increased the fracture toughness of glass/epoxy composites. The piezo-resistance response of the composites was easily correlated with instances of sudden crack growth during static fracture loading. [ABSTRACT FROM AUTHOR]

The demand for revolutionizing the lightweight design of Li‐ion batteries has become inevitable due to the ever‐increasing development of electric transportation modes. Integration of structural and energy storage functionalities into a single structural battery device can be a smart way to improve the overall performance of electric vehicles. In this study, we propose a facile and cost‐effective approach to develop a prospective anode for structural Li‐ion batteries through electrophoretic deposition of silicon (Si) particles onto polyacrylonitrile (PAN)‐based carbon fiber. The synthesis method is able to selectively deposit small‐sized silicon particles on the surface of carbon fiber, producing a thin, continuous, and porous coating of silicon nanoparticles on commercial PAN‐based carbon fiber. The synthesized Si/PAN‐based carbon fiber electrode exhibits remarkable mechanical properties, delivering a tensile strength of 2.57 GPa and a tensile modulus of 118.2 GPa. Benefitting from the morphology of the deposited silicon, the discharge capacity of silicon/PAN‐based carbon fiber anode can reach 565 mAh g−1 with 81 % capacity retention after 50 cycles. This work highlights the potential of silicon‐modified carbon fiber electrodes obtained via a simple and cost‐effective deposition method for structural Li‐ion battery applications. [ABSTRACT FROM AUTHOR]

The main objective of the work was to create a layer of carbon nanofibre on the surface of the NiTi shape memory alloy. The coating process was carried out in three stages. First, polyacrylonitrile was deposited by electrospinning. Then it was stabilized at temperatures up to 250°C. The last stage was the carbonization performed below 1000°C. The microstructure of the obtained coatings was observed using a scanning electron microscope. The X-ray diffraction techniques were applied to analyze the coating structure. After the polyacrylonitrile deposition, the fibers had an average diameter of about 280 nm, and the final fibers were almost twice as tiny. The applied steps also changed the phase and crystalline state of the fibers, finally leading to the formation of amorphous-nanocrystalline graphite. [ABSTRACT FROM AUTHOR]

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Polyacrylonitrile (PAN) carbon fibers are often used to prepare high-performance paper-based materials owing to their high strength, good electrical and thermal conductivity, and superior comprehensive properties. In this study, a novel method for preparing PAN-based carbon fibers by centrifugal spinning was developed, and a stable and homogeneous PAN carbon fiber paper was successfully obtained. Subsequently, the formation process, microscopic morphology, electrical conductivity, electrochemical performance and hydrophobicity of the PAN carbon fiber paper were studied and evaluated. The results showed that the electrical conductivity of the PAN carbon fiber paper prepared via this method reached 43.250 s·cm−1, resistivity was as low as 0.023–0.033 Ω·cm, and contact angle exceeded 140°. This study adopted a new method to prepare PAN carbon fiber paper, which provided another method for the preparation of high-performance fiber paper. [ABSTRACT FROM AUTHOR]

Composite materials based on magnesium–lithium (MgLi) and magnesium–yttrium (MgY) matrices reinforced with unidirectional carbon fibers were prepared using the gas pressure infiltration method. Two types of carbon fibers were used, high-strength PAN-based T300 fibers and high-modulus pitch-based Granoc fibers. The PAN-based carbon fibers have an internal turbostratic structure composed of crystallites. The pitch-based carbon fibers have a longitudinally aligned graphite crystal structure. The internal carbon fiber structure is crucial in the context of the interfacial reaction with the alloying element. There are various mechanisms of bonding to carbon fibers in the case of magnesium–lithium and magnesium–yttrium alloys. This paper presents the use of the DMA method for the characterization of the role of alloying elements in the quality of interfacial bonding and the influence on the complex modulus at increasingly elevated temperatures (50–250 °C). The complex modulus values of the composites with T300 fibers were in the range of 118–136 GPa. The complex modulus values of the composites with Granoc fibers were in the range of 198–236 GPa. The damping capacity of magnesium-based unidirectionally aligned carbon fiber composites is related to the quality of the interfacial bonding. [ABSTRACT FROM AUTHOR]

The physicomechanical characteristics of PAN-based carbon fibers were investigated by SEM-EDS, XRD, TEM and AFM analysis while the mechanical properties of the composites were studied by tensile, flexural and Charpy impact tests with ASTM standards. Regarding the tensile test of carbon fiber fabric, the average tensile strength of CF-I, CF-II and CF-III fibers were around 147 MPa, 137 MPa and 225 MPa and the tensile modulus of those were 12.8 GPa, 13.2 GPa and 12.8 GPa, respectively. Later, the nanostructure of carbon fiber was recognized not as a pure graphite carbon structure because they mixed with graphite and amorphous structures. The higher tensile strength and modulus of CF-III fiber fabric was lower interlayer spacing (d002) because it consisted of more graphene layers in the graphite structure when compared with CF-I and CF-II fiber fabrics. Concerning AFM analysis's results, CF-I fiber fabric has higher surface roughness (Ra) of 34.8 nm and more in-depth with wider pit lines along the fiber axis, which caused higher mechanical properties among the three composites. According to this article, the nanostructure of carbon fibers had a lower impact on CFRP composite because the interfacial bonding between fiber and epoxy matrix, which obtained the higher mechanical properties in the composite, was directly enhanced by the higher surface roughness of the fibers. [ABSTRACT FROM AUTHOR]

Carbon fibers (CFs) are made mostly from a non-environmentally friendly polyacrylonitrile (PAN) and little from rayon. PAN-based CFs, require huge amount of energy for its production aside its contributions to the global CO2 emission. Therefore, there is recourse to a more environmentally friendly sources of CFs biomass. Recently lignin has been recognized as a potential renewable raw material for carbon fibers to replace PAN-based. The magnitude and quality of CO2 emission of lignin-based CFs are dependent on the processing route. On this premise; this review examines the various lignin-based CFs processing route adopted by researcher in the recent past to establish the most viable route with minimum carbon footprint emission. Outcome of the review shows that the major advantages of aromatic polymer (AP) generated precursor over PAN is the presence of higher quantity of guaiacyl units and oxygen content which makes the stabilization phase efficient and faster requiring less energy. Though there are several methods and options for the various stages of conversion of lignocellulosic biomass into CFs as highlighted in the study, establishing an optimum processing route will be a trade-off amongst various issues of concern; carcinogenic risk, carbon footprint emission, CFs Yield and mechanical strength of the CFs. Inferences from the study shows that the L-CF significantly produced reduced climatic impact in terms of CO2 emission. [ABSTRACT FROM AUTHOR]

Carbon fibers were successfully fabricated via the electrospinning technique, followed by stabilizing and carbonizing electrospun PAN fibers. A wide range of analytical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), vibrating sample magnetometer (VSM) techniques, and Hall effect were performed to study of the effect of carbonization temperature on the physical and chemical characterization of carbon fibers. The SEM images of the PAN precursor exhibit a smooth outer surface, after the stabilization and carbonization process, along with a broken fiber at higher carbonization temperature about 1400 °C. Morphological characterization based on the recorded TEM images of carbonized fibers at 1000 °C and 1400 °C, showed that the obtained morphology can be classified as fiber structures, where their diameters ranged from 196 to 331 nm. The XRD patterns of PAN-based carbon fibers confirm the structural changes from linear structure into a graphite-like structure. The DRS study indicates the possible π–π*/σ–π* and n–π* transitions. The presence of the surface functional groups and different trapped radiative recombination on the emission bands is confirmed by the PL. VSM results shows the weak ferromagnetic nature of the carbon fibers. [ABSTRACT FROM AUTHOR]

Gas-phase chlorination of carbon fiber based on polyacrylonitrile was performed and active chlorine-containing precursors were obtained, in which chlorine can be replaced by sulfur-containing functional groups. It is shown that chlorination of carbon fiber samples with carbon tetrachloride at temperatures of 300, 450 and 6000C in an argon stream leads to the introduction of 0.2-1.7 mmol g-1 of chlorine into the surface layer of the fiber. The thermodesorption properties of the modified carbon fiber samples were investigated by thermogravimetry and thermoprogrammed desorption with mass spectrometric registration of products. It was established that the obtained samples exhibit a relatively high thermal stability. The study conducted by means of thermoprogrammed desorption method showed that chlorine is desorbed from the surface in a wide temperature range (up to 8000C). It was found that the treatment of chlorinated samples with sulfur-containing reagents with subsequent oxidation produce the samples of carbon fiber with a concentration of sulfo-groups up to 0.3 mmol g-1, which are catalytically active in the dehydration reaction of isopropyl alcohol in the gas phase. The temperature of 50% conversion of isopropyl alcohol to propylene was used as a measure of catalytic activity. It was found that pre-chlorination leads to an increase in the catalytic activity of the fiber modified with sulfur-containing reagents: the temperature of 50% conversion of isopropyl alcohol to propylene is 215-2900C, depending on the concentration of sulfo-groups. [ABSTRACT FROM AUTHOR]

For the improvement of the processing of melt‐spun lignin‐based fibers, the use of a spinning oil is necessary. The use of spinning oils is standard for the processing of PAN based carbon fiber precursors. Since no commercial spinning preparations for lignin fibers are available on the market, a study on different oils, such as technical oils, food‐grade oils or spinning avivages, is performed. A stepwise approach with applied tests (viscosity measurement, fiber etching, melt‐spinning, stabilization, carbonization) was developed to eliminate oils which are not suitable. The physical properties of the tested oils are determined and spectroscopic studies of these avivages are performed. Mechanical properties are characterized for as‐spun lignin fibers, stabilized lignin‐based fibers and lignin‐based carbon fibers with and without a spinning preparation. Four of seven tested spinning oils improve the handling during the processing of lignin‐based fibers but only two spinning oils lead to good quality carbon fibers and improve even the tensile strength of the resulting carbon fibers. [ABSTRACT FROM AUTHOR]

Thermal‐oxidative stabilization of the polyacrylonitrile (PAN) precursor was performed employing a multi‐step heat treatment strategy in an air circulating furnace. In this approach, the applied temperature was gradually increased from 200°C to 250°C employing several stages for different stabilization durations. Fifteen percent guanidine carbonate (GC) was found as optimum to incorporate with the PAN precursor fibers to accelerate the thermal‐oxidative stabilization process. Characterization techniques, including X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), tensile strength, volume density, linear density, fiber thickness, and burning test have been performed to monitor the changes in PAN structure. Test results of the stabilized samples were compared with the reference sample results to demonstrate the accelerating effect of GC integration. Findings showed that GC pretreatment enhanced and accelerated the cyclization of nitrile groups in the PAN polymer structure and allowed the quicker formation of a thermally stable structure. The analysis of the experimental results revealed that GC integration and employing the multi‐step heat treatment strategy helps greatly to cut the overall PAN‐based carbon fiber production cost. [ABSTRACT FROM AUTHOR]

Carbon fibers (CFs) have been considered as a next-generation material in high-performance applications such as aerospace, defense, sporting goods, wind energy, automobiles, electronics, and civil engineering industries due to their superior mechanical properties including high tensile strength and modulus and characteristics such as low density, good corrosion and low impact resistance, low coefficient of thermal expansion, and high electric conductivity. In this paper, we introduced the brief overview of the most widely produced and used polyacrylonitrile(PAN)-based CFs. In particular, the studies on developing high performance CFs by theoretical and experimental approaches were presented. Theoretical tensile strength of CFs can be ideally up to 100 GPa with the perfectly developed graphitic structure and its orientation along fiber direction. However, commercially available CFs reveal only tensile strength of 7 GPa because of the existing defects, misordered carbon crystals, and turbostratic structure. Those originate from manufacturing processes such as spinning, stabilization, and carbonization, which generate significant morphological and structural defects in both exterior and interior of CFs. The review covered the research on parameters related with the tensile properties and optimizing processes to increase the tensile strength of PAN-based CFs. [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of carbon nanotubes (CNTs) on the tensile properties of polyacrylonitrile (PAN)-based carbon fiber epoxy impregnated bundle composites was investigated. To grow CNTs on the carbon fibers, the following catalysts were selected: Ferrocene ([Fe(C5H5)2]) catalyst applied to the bundles using chemical vapor deposition (CVD), and iron (III) nitrate nonahydrate ([Fe(NO3)3•9H2O]) catalyst applied by dipping the bundles in ethanol solutions of different concentrations ranging from 0.01 to 0.5 M. For bundle composites with Fe(C5H5)2-catalyzed CNTs, the Weibull modulus was 29% higher than the as-received state, although the tensile strength is almost unchanged. The Weibull modulus is 9–39% higher than the as-received state for Fe(NO3)3•9H2O catalyst solutions in the range 0.01–0.3 M, while it decreases by 22–32% for 0.4–0.5 M solutions. The tensile strength is lower in both cases; 4–7% lower for 0.01–0.3 M solutions and 14–17% lower for 0.4–0.5 M solutions. Fe(NO3)3•9H2O catalysts 0.1 M solutions gives the best combination of tensile strength and Weibull modulus improvement. The results also show that for each type of CNT-grafted and as-received PAN-based carbon fibers, an almost linear relation between the Weibull modulus and average tensile strength on the log-log scale is observed. This relation indicates that Fe(C5H5)2 catalyst-grafting of CNTs gives better tensile strength and Weibull modulus results. [ABSTRACT FROM AUTHOR]

Through comparing carbons in the graphite allotrope family, namely isotropic graphite (IG), exfoliated-graphite-based flexible graphite (FG), graphite-flake thick film (not sintered), carbon fibers (PAN, pitch) and highly-oriented pyrolytic graphite (HOPG), all differing in the microstructure, this work addresses for the first time the factors (including the structure-property relationship) that govern the electric permittivity (kHz frequency) of carbons. The permittivity is more sensitive to the microstructural heterogeneities than the resistivity, which only slightly influences the permittivity. Smaller crystallite dimensions promote the permittivity. PAN-based carbon fibers exhibit higher permittivity than pitch-based carbon fibers, IG, FG or HOPG. The crystallographic preferred orientation is not influential to the permittivity, though it influences the resistivity. Interfaces (e.g., the grain boundaries in IG and the interface between the carbon layer ribbons in a fiber) promote the permittivity, being sites for the carrier-atom interaction that enables the polarization. A large number of sites is more important than a large site size for promoting the permittivity. The fiber diameter is not influential to both permittivity and resistivity. The thick film exhibits the highest relative permittivity (5 × 105), due to its low electrical connectivity. IG (grain size 12 μm) gives the lowest relative permittivity (5 × 102), due to its coarse microstructure. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, the effects of different spinning methods including traditional wet and dry‐jet wet spinning, and newly developed dry‐jet gel spinning, on the structures and performances of polyacrylonitrile fibers, as well as the structural evolution during stabilization and carbonization, are compared in detail. The structural differences along radial direction, surface roughness, and chain orientation of carbon fibers are inherited from their precursor fibers, and these factors are determined by spinning technologies and processing conditions. Among all spinning methods, dry‐jet gel spinning could prepare fibers with the best chain orientation, the highest tensile properties, and the lowest surface roughness, which would be favorable for achieving higher mechanical performance. Additionally, for the resultant carbon fibers, the surface modification of dry‐jet gel spun carbon fibers is easier than dry‐jet wet spun carbon fibers, and comparable to wet spun carbon fibers. Overall, dry‐jet gel spinning is promising to make carbon fibers with both excellent tensile properties and good interfacial adhesion with epoxy matrix. [ABSTRACT FROM AUTHOR]

Polyacrylonitrile (PAN)-based carbon fibers have been in full-scale industrialization for more than 50 years, during which time it has grown at an annual rate of 10–20 % for half a century, a trend that is expected to continue. Throughout this period, the carbon fiber industry has supported the composites industry through a stable global supply and improved fiber quality. Here, we show PAN-based carbon fibers' history and future for this 50-year milestone. The industrialization of carbon fiber began in 1959, when Shindo discovered how to stabilize PAN. The later discovery of comonomers based on the Morita-Baylis-Hilman reaction by Morita in 1966 further enabled industrialization. In addition to the innovativeness of this breakthrough, progress was made in converging technologies which intensified competition and encouraged incremental innovation. In recent years, microstructure control has become increasingly precise: down to the molecular level through incremental innovations, with tensile strength reaching 8.0 GPa and named T1200. Evaluating the carbon fibers' intrinsic strength by the loop method, where evaluation size is reduced to the order of tens of micrometers, shows that the maximum value of T1200 is very high at 18 GPa. This is almost consistent with the value of 19 GPa predicted using molecular dynamics. Even higher strength can be expected by reducing defects. These performance improvements have already contributed toward carbon neutrality in aircraft and wind power generation. PAN-based carbon fibers will continue to be an important material in the future as further performance improvements and increased mass production are realized. [ABSTRACT FROM AUTHOR]

Novel carbon foam composites derived from various pitch precursors have been fabricated and characterized. This paper specifically focuses on developing an effective process for fabricating the carbon foam composites from Polyacrylonitrile (PAN)-based carbon felt as a reinforcement and various readily available pitch matrix such as petroleum pitch, coal tar pitch, and mesophase pitch. The paper endeavors to develop the carbon foam composites and to carry out detailed morphological, thermal, and mechanical characterization. Traditional carbon foams have been known to offer poor mechanical performance, and hence, in this paper, the pitch-based carbon foams were innovatively reinforced with the PAN-based carbon fiber felt. Carbon foam composites were subjected to partial oxidation, and their morphological and mechanical response after the heat treatment was studied thoroughly. Thermal gravimetric analysis and thermal mechanical analysis techniques reveal an appreciable thermo-physical and thermo-mechanical response at elevated temperatures. Also, it was found out that the factors such as volatile content and quinoline insoluble fraction affect the morphology as well as the physical robustness on the composite foams. [ABSTRACT FROM AUTHOR]

The thermal stabilization of polyacrylonitrile fibers (FPAN) is one of the most important steps in the production of carbon fibers (CFs). In this paper, new precursor polymers from PAN have been synthesized with different chemical characteristics using a solution polymerization, and FPAN was obtained using an unconventional wet spinning system in the drying and collapsing steps. The effect of different operation conditions, comonomers, and termonomers on the properties of precursor polymers, polymerization reactions, mechanical properties, structural characteristics, and stabilization of the FPAN was studied and analyzed. FTIR and optical microscopy were used to analyze structural changes of FPAN in the thermal stabilization. The impact of the chemical composition of the precursor polymers on the physicochemical characteristics of FPAN and their behavior in the thermal stabilization process were evaluated. In particular, itaconic acid termonomer improved the tensile strength of the fibers from 8.07 to 16.87 cN/dtex, and the extent stabilization increased from 1.81 to 4.6. FTIR indicated that the reaction of stabilization of the terpolymer developed was initiated at a lower temperature compared to that of a commercial precursor polymer. [ABSTRACT FROM AUTHOR]

Effects of different electrolytes on the surface structure and interfacial property with epoxy resin of PAN-based carbon fiber are evaluated, which is used to find out the key factor that affects the improvement in the interfacial adhesion. It is found that the carbon fiber treated in H2SO4 electrolyte owns the most abundant oxidative groups but bonds relatively weak with epoxy resin by the maximum interlaminar shear strength of 60 MPa. The carbon fiber oxidized in NaOH electrolyte and then restored in HCl solution owns less oxidative groups but shows a strongest bonding with epoxy resin by the maximum interlaminar shear strength of 69 MPa. We conclude this phenomenon is mainly ascribed to the graphene layers covering on the fiber surface that are formed during carbonization and connect weakly with the substrate of carbon fiber, thus called weak layers. The weak layers can be peeled off effectively in NaOH electrolyte but not in H2SO4 electrolyte. An attempt for modification is tried by removing the weak layers in NaOH electrolyte and adding more oxygen groups in H2SO4 electrolyte. The interlaminar shear strength of the fiber with epoxy resin is not increased as expected; however, it shows oxidation in H2SO4 electrolyte does not generate weak layers on carbon fiber surface. [ABSTRACT FROM AUTHOR]

Carbon fiber (CF) is a versatile material renowned for its excellent mechanical, thermal, and electrical properties. Polyacrylonitrile (PAN)-based CFs dominate the market in part due to their high tensile strength, rendering them suitable for structural applications in a wide variety of applications ranging from sporting goods to aerospace. Over five decades of commercial development of PAN-based CF has resulted in a range of varieties with different tensile moduli and tensile strengths. The microstructures, nanostructures, and crystal structures of PAN-based CF all play pivotal roles in the macroscale properties of this material. In particular, the crystal structure and crystallite orientation in CF is closely related to the mechanical properties. The crystal structure of PAN-based CF generally consists of turbostratic carbon, a disordered form of graphite, the characteristics of which can be effectively characterized in a bulk format through wide-angle x-ray diffraction (WAXD). In this work, we employed a three-part approach to the analysis of WAXD patterns collected from four intermediate modulus PAN-based CFs. The approach incorporates a Scherrer analysis, a Debye analysis, and an orientational analysis to provide precise estimates of crystallite sizes, crystallite distributions, and crystallite orientations with the fiber axis. The results presented here suggest that intermediate modulus PAN-based CF mostly consists of small turbostratic crystallites (<4 nm), with larger crystallites having increased orientation with the fiber axis. The results here imply the presence of curvature and/or wrinkling of the turbostratic layers within the CF structure. [Display omitted] [ABSTRACT FROM AUTHOR]

An experimental setup for 3ω method with a constant current source and two differential amplifiers was built to measure the thermal conductivity and the volumetric heat capacity of single polyacrylonitrile (PAN)-based carbon fiber. In complement to a well-known analytical thermal model, a numerical one was developed that can check the validity of the analytical one and can also take into account the effect of convective heat loss on the measurements. A detailed sensitivity analysis of the unknown parameters was presented that would finally help in the better design of the setup for 3ω method. The tests were performed under vacuum and atmospheric pressure for chromel wire as a reference sample and under vacuum for two types of PAN-based carbon fiber. Detailed measurements were performed displaying the influence of convective loss and the thermal contact resistance between fiber and copper electrodes on the estimation of thermal properties of carbon fiber. [ABSTRACT FROM AUTHOR]

In this study, the influence of type of carbon fiber, sizing amount on the fiber surface and the degree of compaction on the through-thickness electrical resistivity of dry unidirectional carbon fiber tows is investigated to validate the conduction pathways and mechanisms proposed by our previously reported micromechanics electrical resistivity model. An automated experimental setup has been developed and implemented, which measures the electrical resistivity and fiber volume fraction of carbon fiber tows under compression in real time. An extensive experimental study is conducted with five types of commercial PAN-based carbon fibers which vary in fiber diameter, number of fibers in a tow including two unsized fibers and three sized fibers with sizing amount of 0.25% and 1.0% by weight. The fiber volume fraction was increased by compacting the fiber tows using a mechanical testing system (Instron, Norwood, MA). The results show that the fiber sizing and fiber volume fraction impact the through-thickness electrical resistivity of carbon fiber tows. Sized fibers demonstrate 1–2 orders of magnitude higher electrical resistivity than the unsized fibers at lower fiber volume fractions (below 45%), while at higher fiber volume fraction (60%–70%), the electrical resistivity of the two fiber systems tends to be of similar magnitude. Fibers with more sizing (1 wt.%) demonstrated 10 times larger through-thickness resistivity than those with less sizing (0.25 wt.%), indicating the significant impact of fiber sizing on electrical resistivity. The results show good agreement with our micromechanics electrical resistivity model. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to prepare a spherical modifier-modified activated carbon fiber of high specific capacitance intended for electrode materials of supercapacitor. Design/methodology/approach: In this study, phenolic-based microspheres are taken as modifiers to prepare PAN-based fiber composites by electrospinning, pre-oxidation and carbonization. Pearl-chain structures appear in RFC/ACF composites, and pure polyacrylonitrile fibers show a dense network. The shape and cross-linking degree are large. After the addition of the phenolic-based microspheres, the composite material exhibits a layered pearlite chain structure with a large porosity, and the RFC/ACF composite material is derived because of the existence of a large number of bead chain structures in the composite material. The density increases, the volume declines and the mass after being assembled into a supercapacitor as a positive electrode material decreases. The specific surface area of RFC/ACF composites is increased as compared to pure fibers. The increase in specific surface area could facilitate the diffusion of electrolyte ions in the material. Owing to the large number of bead chains, plenty of pore channels are provided for the diffusion of electrolyte ions, which is conducive to enhancing the electrochemical performance of the composite and improving the RFC/ACF composite and the specific capacitance of the material. The methods of electrochemical testing on symmetric supercapacitors (as positive electrodes) are three-electrode cyclic voltammetry, alternating current impedance and cycle stability. Findings: The specific capacitance value of the composite material was found to be 389.2 F/g, and the specific capacitance of the electrode operating at a higher current density of 20 mA/cm2 was 11.87 F/g (the amount of the microsphere modifier added was 0.3 g). Using this material as a positive electrode to assemble into asymmetrical supercapacitor, after 2,000 cycles, the specific capacitance retention rate was 87.46 per cent, indicating excellent cycle stability performance. This result can be attributed to the fact that the modifier embedded in the fiber changes the porosity between the fibers, while improving the utilization of the carbon fibers and making it easier for electrolyte ions to enter the interior of the composites, thereby increasing the capacitance of the composites. Originality/value: The modified PAN-based activated carbon fibers in the study had high specific surface area and significantly high specific capacitance, which makes it applicable as an efficient and environment-friendly absorbent, as well as an advanced electrode material for supercapacitor. [ABSTRACT FROM AUTHOR]

Graphical abstract The oxygen diffusion distance (the skin width) was homogeneous in every direction for the single circular carbon fibers, while it was inhomogeneous for the commercially elliptical carbon fibers. The inhomogeneity of the oxygen diffusion distances was induced not by the surface or cross-sectional morphologies but by the density difference at the edge of a single PAN precursor fiber, which was caused by the nonuniform stress on the surface of the gel fiber. Highlights • The skin widths of PAN-based carbon fibers were proposed to assess the oxygen diffusion distances. • The oxygen diffusion distances are uniform for the commercial carbon fibers with the circular sections, while they are unequal for those with the non-circular sections. • Inhomogeneity of the oxygen diffusion distances is proposed to result from density difference at the edge of a single PAN precursor fiber, which is caused by the nonuniform stress on the surface of the gel fiber. • This study not only deepens understanding of the effect of the shapes of PAN precursor fibers on oxygen diffusion during stabilization, but also provides an opportunity for optimizing stabilization. Abstract Accurate measurement of oxygen diffusion distances (ODDs) is important but difficult in the production of polyacrylonitrile (PAN)-based carbon fibers. Traditionally, the ODDs were deemed to be homogeneous in a single fiber and paid no attention. Herein, the skin widths of carbon fibers with the skin-core structure were proposed to assess the ODDs, and the ODDs were investigated by transmission electron microscopy. The ODDs were first found to be homogeneous for the commercially noncircular carbon fibers, while they were uniform in every direction for the circular single carbon fibers. The inhomogeneity of the ODDs was unrelated to the surface and cross-sectional morphologies of carbon fibers, and it was considered to result from the density difference at the edge of a single PAN precursor fiber. These findings not only deepen the understanding of the effect of the PAN precursor fiber shapes on the oxygen diffusion during stabilization, but also provide an opportunity for optimizing the stabilization conditions according to the density difference at the edges of single PAN precursor fibers. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The as-prepared polymer precursor delivers a turning morphology including microspheres and mint leaf-like structure. • This work reported the synthesis of the mint leaf-like morphology based on PAN through a precipitation polymerization method. • The obtained 2D carbon nanosheets possess an ultrahigh specific surface area up to 3292.3 m2 g−1. Abstract A facile and effective approach to design and obtain polyacrylonitrile-based electrode materials with shape-controlled and high surface area structure is highly critical and stringent to the development of supercapacitors. To solve this problem, for the first time, the mint leaf-like polyacrylonitrile is prepared via a one-step precipitation polymerization. After pyrolysis and activation process, hierarchical porous carbon nanosheets with a high specific surface area of 3292.3 m2 g−1 is successfully fabricated. As the electrode material for supercapacitors, it shows a high specific capacitance of 331 F g−1 at 0.5 A g−1 and good rate performance of 220 F g−1 at 50 A g−1 in 6 M KOH electrolyte. The assembled all-solid-state asymmetric device present a specific capacitance of 147 F g−1 coupled with an energy density of 52.27 Wh kg−1 at a power density of 800.68 W kg−1 and excellent cyclability with 89.5% capacity retention after 10,000 bending cycles. The synthetic strategy can be easily implemented, without complicated procedure and particular template, and thus opens up a new window towards the simple and highly efficient synthesis of well-designed carbon-based materials for supercapacitor applications. [ABSTRACT FROM AUTHOR]

The electric permittivity is a fundamental material property concerning the dielectric behavior. Colossal permittivity (relative permittivity exceeding 10,000) is attractive for capacitors, sensors, actuators and mechanical energy harvesters. It was discovered in this work in continuous polyacrylonitrile (PAN) based carbon fiber (Teijin's Tenax HTS45) along the fiber axis. This is the first report of colossal permittivity in carbon materials. The relative permittivity (12230 ± 990, 2 kHz) is much higher than that of mesophase-pitch-based carbon fiber (Cytec's Thornel P-25, 4384 ± 257, 2 kHz). The two fibers exhibit similar resistivity (1.52 × 10−3 and 1.24 × 10−3 Ω.cm for the PAN-based and pitch-based fibers, respectively). For both fibers, the permittivity is high, due to the physical continuity and mobile charge carriers. The higher permittivity of the PAN-based fiber compared to the pitch-based fiber is attributed to the higher degree of graphitization (as indicated by the lower interplanar spacing) of the PAN-based fiber. However, the smaller crystallite sizes and larger azimuthal spread of the carbon layers around the fiber axis cause the PAN-based fiber to be not higher in conductivity than the pitch-based fiber, in spite of the higher degree of graphitization. The smaller crystallite sizes and larger azimuthal spread are detrimental more to the conductivity than the polarization. Image 103662 [ABSTRACT FROM AUTHOR]

Polyacrylonitrile (PAN) fibers containing up to 40 wt% cellulose nanocrystals (CNC) have been successfully stabilized and carbonized to make carbon fibers. Under the batch process, PAN/CNC based carbon fibers exhibit a tensile strength in the range of 1.8–2.3 GPa, and tensile modulus in the range of 220–265 GPa, which are comparable to the control PAN-based carbon fibers. Based on the transmission electron microscopy study, individually distributed CNC regions surrounded by PAN matrix were observed in the stabilized and carbonized fibers. Carbonized fibers show two distinct stabilized and carbonized regions. This study shows that biphasic carbon fibers can be made from the PAN/CNC system. Image 1 [ABSTRACT FROM AUTHOR]

The influence of stabilized fibre structure and skin-core formation induced by rapid thermal stabilization of polyacrylonitrile (PAN) on the tensile properties of carbon fibres was investigated. Three sets of samples were prepared by stabilizing PAN fibres under three temperature profiles using a continuous carbon fibre processing line. Initially, the chemical structure and density variations in stabilized fibres were examined with respect to process conditions using Fourier Transform Infrared Spectroscopy (FTIR) and density column methods. Interestingly, while the cyclization and dehydrogenation indices are similar for all the stabilized fibres irrespective of temperature profiles used, the densities of these fibres varied from 1.34 to 1.366 g/cc. Micro-Raman studies showed the existence of structural heterogeneity in the fibres from low temperature (LT) carbonization (I(D)/I(G) ratio of core was ~5.6% higher than the skin) that eventually reduced with high temperature (HT) carbonization because of uniform sp3 to sp2 hybridization of carbons. However, modulus mapping revealed heterogeneous storage modulus distribution in the HT carbon fibre cross-section from Trial-2 (storage modulus of core was ~23 GPa less than the skin). Interestingly, this heterogeneity did not show a significant effect on the bulk properties of carbon fibres suggesting skin-core formation is an effect rather than a defect. [ABSTRACT FROM AUTHOR]

[Display omitted] • PAN-based carbon fibers with highly developed microstructures via calcium-assisted thermal treatments is reported. • The catalytic effect of Ca compounds on CF graphitization at low temperatures of 1600 °C was observed. • The effect of Ca on the structural changes of CFs was investigated via AIMD simulations. • We suggest a new and affordable methodology to manufacture CF with significantly higher conductivities and moduli. Graphitized carbon fibers are attractive materials because of their high tensile modulus and thermal and electrical conductivities. These attributes derive from their crystalline structures that develop during heat treatments of up to 3000 °C. Despite the costly thermal processes, there is a structural limit for achieving these sought-after properties for polyacrylonitrile-based carbon fibers. Herein, the preparation of polyacrylonitrile-based carbon fibers with highly developed microstructures via calcium-assisted thermal treatments of up to 2700 °C is reported. Carbon fibers hydrothermally immersed in a solution of calcium carbonate were heat-treated and their chemical structures traced to investigate the calcium-assisted catalytic graphitization mechanism. Graphitic structures appeared at 1400 °C, accompanied by intermediate complexes of carbon and calcium on the carbon fibers surfaces. Further heat treatment of the calcium compounds at 1600 °C to incorporate carbon fibers resulted in an interlayer spacing of 0.3360 nm, which was unachievable solely through heat treatment at 2700 °C. In addition, the achieved tensile modulus and electrical conductivity of 480 GPa and 1.7 × 103 S/cm, respectively, were significantly higher than those of pure carbon fibers. The calcium ions penetrating the internal structure of the carbon fibers aligned the non-uniform graphene structure and developed the graphite structure of the carbon fibers by acting as catalysts, even at low temperatures. [ABSTRACT FROM AUTHOR]

The effects of concentration of dimethyl sulfoxide (DMSO) in the coagulation bath, draw ratio and extrusion speed on surface roughness of polyacrylonitrile (PAN) fibers prepared by wet spinning and dry-jet wet spinning were investigated. The surface roughness was much higher for PAN fibers produced by wet spinning than dry-jet wet spinning. The surface roughness of the fiber increased linearly with increasing concentration of DMSO in the coagulation bath. Higher roughness was observed at higher draw ratios during spinning. The surface roughness of the PAN fibers decreased initially until at 90m/h, then increased with further increases in extrusion speed. A mechanism for formation of PAN fiber surface morphology based on deformation of the soft skins of single fibers during solidification of PAN/DMSO solution caused by stress perpendicular to the fiber axis is proposed. The stress results from recovery of the aligned PAN macromolecules due to shear in the spinneret during extrusion. [ABSTRACT FROM AUTHOR]

Batch experiments were conducted to investigate the capacity and mechanisms for adsorbing Cd2+ from aqueous solutions by the composite material. The composite material was manufactured with Plesiomonas shigelloides strain H5 and modified polyacrylonitrile-based carbon fiber. Experimental results showed that the surface areas of modified polyacrylonitrilebased carbon fiber increased by 58.54% and pore width increased by 40.19% compared with unmodified polyacrylonitrile-based carbon fiber. Boehm's titration results show the surface acid sites of composite material were increased by 712% compared with unmodified polyacrylonitrilebased carbon fiber. The field emission scanning electron microscope results show P. shigelloides H5 can be grown on the surface of modified polyacrylonitrile-based carbon fiber closely. The equilibrium removal rate and sorption quantity of composite material were 71.56% and 7.126 mg g-1, respectively. With the pH value of aqueous solution increased, the removal rate of Cd ions was also increased, but the change of temperature and ionic strength had no significant effect on the removal rate. Furthermore, the results showed the whole sorption process was a good fit to Lagergren pseudo-second-order model and Freundlich isotherms model. Therefore, the results infer that there was a heterogeneous distribution of active sites, and then the sorption process was chemical adsorption and multilayer adsorption. In a word, microbial composite carbon fiber material can adsorb Cd2+ ions from aqueous solution effectively, which might be helpful in wastewater treatment in the future. [ABSTRACT FROM AUTHOR]

The stress analysis and fracture toughness of high tensile strength polyacrylonitrile (PAN)-based (T1000GB, IMS60, and T300), high modulus PAN-based (M60JB), high modulus pitch-based (K13D), and high ductility pitch-based (XN-05) single carbon fibers were investigated using notched specimens and a focused ion beam. The maximum stress of T1000GB, IMS60, T300, M60JB, K13D, and XN-05 single fibers was calculated as 30.5, 29.4, 25.6, 44.3, 68.6, and 15.5 GPa, respectively. The critical stress intensity factor of T1000GB, IMS60, T300, M60JB, K13D, and XN-05 single carbon fibers was calculated as 1.91, 1.82, 1.67, 3.09, 4.84, and 1.02 MPa m 1/2 , respectively. The critical energy release rate of T1000GB, IMS60, T300, M60JB, K13D, and XN-05 single carbon fibers was calculated as 478, 502, 763, 3064, 13266, and 237 J/m 2 , respectively. These results indicate that a linear relationship exists between the fracture toughness (critical stress intensity factor and critical energy release rate) and tensile modulus and maximum stress. The results indicate that the maximum stress is an effective parameter for evaluating the fracture toughness of PAN-based and pitch-based single carbon fibers. [ABSTRACT FROM AUTHOR]

A simple rubbing treatment was used to mechanochemically modify the surface of polyacrylonitrile-based carbon fibers and its effect on their surface structure and functional groups was studied using several surface characterization techniques. To control the mechanochemical effect, the shear forces accompanying rubbing were kept constant. Scanning electron microscopy tests and the peak positions and widths of the main Raman spectroscopy bands indicated that there were no morphological changes to the carbon fibers following rubbing. In contrast, X-ray photoelectron spectroscopy showed an increase in oxygen-containing functional groups; in addition to hydroxyl species, the main groups introduced were alkoxide, carbonyl, and carboxyl groups. The ratio of carboxyl groups on the carbon fiber surface increased with the shear force magnitude, indicating carbon surface oxidation. The difference between the Raman and X-ray photoelectron spectroscopy results indicates that the modification was confined to the first few atomic layers; therefore, this rubbing method is capable of producing efficient mechanochemical surface modification of carbon fibers. This technique is simple, is relatively inexpensive, and is applicable to carbon fiber-reinforced plastic processing techniques. [ABSTRACT FROM AUTHOR]

A kind of dry mixing and pressing process was introduced to prepare expanded graphite/carbon fiber cement composites (EG-CFRC). Significant effect of moisture on the thermoelectric properties of EG-CFRC was observed. The higher the moisture content is, the greater the absolute Seebeck coefficient. The maximum of absolute Seebeck coefficient 11.59 μV/°C was obtained with moisture of 14.98% at 33 °C. Simultaneously, the maximum of electrical conductivity 0.78 S cm −1 was got with moisture of 11.44%. Furthermore, the largest power factor 7.85×10 −4 µW m −1 K −2 was calculated at 33 °C with moisture of 11.44%. The carrier scattering, polarization effects and high density defects interface of EG-CFRC are attributed to the enhancement of thermoelectric properties in the case of higher moisture content. [ABSTRACT FROM AUTHOR]

A polyacrylonitrile (PAN)-based carbon fiber (CF) manufacturing cost estimation model driven by mass is presented in this study. One of the biggest limiting factors in the large-scale use of carbon fiber (CF) in manufacturing is its high cost. The costs involved in manufacturing the carbon fiber have been formalized into a cost model in order to facilitate the understanding of these factors. This can play a key role in manufacturing CF in a cost-effective method. This cost model accounts for the fixed and variable costs involved in all the stages of manufacturing, in addition to accounting for price elasticity. [ABSTRACT FROM AUTHOR]

Humic acid is creatively selected as an anode material in sodium ion batteries. Bio-based carbon fibers (H-CF) are fabricated from polyacrylonitrile (PAN) − humic acid (HA) via simple eletrospinning followed by stabilization and carbonization. The heat-treatment temperature (HTT) is optimized based on analysis of material structures and electrochemical performances. Due to unique composite networks and oxygenic functionalities, the H-CF anode obtained at 1300 °C has a large reversible capacity of 261.3 mAh g −1 (current density: 0.02 A g −1 , initial efficiency: 69.6%). The anode also presents good cycle stability (249.6 mAh g −1 reversible capacity at 0.1 A g −1 with capacity retention of 92.8% over 100 cycles) and good rate capability (208.6 mAh g −1 at 0.2 A g −1 and 81.7 mAh g −1 at 1 A g −1 ). It is proved that humic acid can serve as a robust precursor for high-performance anode of sodium ion batteries. [ABSTRACT FROM AUTHOR]