Electrochemical treatment has a significant effect on the properties of carbon fibers (CFs). In this study, the effect of mild electric field action on the microstructure and properties of polyacrylonitrile (PAN)-based high-modulus CFs (HMCFs) and high-strength CFs (HSCFs) was investigated. Under the action of a mild electric field, CFs did not show obvious defects, but their microstructure, mechanical properties and electrical properties were affected. For HMCFs, the graphitization degree in both axial and radial directions of the fibers had a decreasing trend, the grain spacing increased, and the grain size and degree of orientation decreased, which led to a decrease in the tensile strength, tensile modulus and axial conductivity. However, for HSCFs, the pattern of change was exactly opposite to that of HMCFs. The results of this study can provide useful guidance for optimizing the production process and surface modification of CFs.

Carbon nanotube (CNT) fibers were synthesized in this study under a hydrogen atmosphere using the floating-catalyst chemical vapor deposition (CVD) technique. Acetone, ferrocene, and thiophene served as the sources of carbon, catalyst, and promoter, respectively. By adjusting the amount of thiophene, the sulfur molar ratio in the CVD reactor was varied to study its impact on the morphology and composition of the CNT fibers. Raman and TEM analyses showed that the structural properties of the CNTs, especially the production of single-walled CNTs (SWCNTs) with a high Raman IG/ ID ratio of approximately 23.8, can be finely tuned by altering the sulfur content, which also affects the accumulation of spherical carbonaceous particles. Moreover, it was established that the electrical conductivity of the CNT fibers is significantly influenced by their specific components—SWCNTs, multi-walled CNTs (MWCNTs), and spherical carbonaceous particles. The ratios of these components can be adjusted by modifying the molar ratios of catalyst and promoter in the precursor mixture. Remarkably, SWCNTs with enhanced crystallinity were found to substantially improve the electrical conductivity of the CNT fibers, despite the presence of numerous spherical carbon impurities.

This study introduces a novel method for synthesizing carbon nanotube (CNT) fibers using floating catalyst chemical vapor deposition (FC-CVD) in an open-atmosphere without the need for hydrogen as a carrier gas. Traditional FC-CVD techniques depend on hydrogen gas and require a harvest box with inert gas purging, which restricts scalability. Our approach utilizes nitrogen gas as the sole carrier, allowing for CNT fiber production without a harvest box. To understand the spinning process mechanism in an open-atmosphere, we conducted thermodynamic and computational fluid dynamics (CFD) analyses. Methanol was selected as the carbon source based on thermodynamic calculations, which revealed that at high temperatures, methanol forms CO and H2 as thermodynamically stable species instead of carbon (C), thereby preventing soot formation. Moreover, methanol undergoes catalytic cracking exclusively in the presence of catalysts, further preventing soot formation. This approach allows operation at high partial pressure, even above the upper explosive limit (UEL), effectively preventing combustion. A 600 mm cooling zone was incorporated into the reactor to lower the outlet gas temperature below methanol's auto-ignition point, mitigating combustion risks. CFD calculations were employed to determine the necessary cooling zone length. Additionally, we developed a predictive model using the XGBoost machine learning method to efficiently map the parameter space for CNT fiber spinning, achieving an accuracy of 95.24%. The resulting CNT fibers demonstrate high electrical conductivity (240 ± 24 S/cm) and a low ID/ IG ratio, indicating a high degree of crystallinity.

To further increase the mechanical properties of polyacrylonitrile-based carbon fibers, a multiple stretching technique was applied. Carbon fibers were multiple stretched at 2200 °C and characterizations such as SEM, Raman, XRD, and TEM were used to investigate the evolution of microstructure of carbon fibers. It was found that the grooves on the surface of carbon fibers along the fiber axis direction became more obvious and the cross-section of fibers were twisted from nearly circular to elliptical after multiple stretching. Growth and slippage of graphite microcrystals along the fiber axis direction resulted decrease in disordered structure and defects in the carbon fibers and increase in the degree of graphitization. The multiple stretching effectively enhanced the length-to-width ratio of microcrystals. An increase of 75 GPa in tensile modulus and a retention rate of 0.95 in tensile strength were realized for carbon fibers multiple stretched at 2200 °C.

Activated carbon fibers (ACFs) have emerged as promising adsorbents for environmental applications in the removal, separation, and modification of organic compounds in liquid and gas phases. Recent research has focused on enhancing the effectiveness of ACFs via precursor and surface modification, aiming to enhance their affinity for specific pollutants. Hence, the present review reports recent research advances in this area, focusing on ACF production and modification techniques, along with their respective advantages and disadvantages. After a brief description of ACFs, their state-of-the-art surface modification techniques are systematically summarized, divided into two categories: (i) type of precursor [e.g., polyacrylonitrile (PAN), pitch, phenolic resin (e.g., novoloid), biomass] and (ii) type of surface modification (wet or dry). In short, this review presents recent advances in the preparation and modification of ACFs for the removal of organic compounds from aqueous and gas phases; various fabrication techniques and the adsorption mechanisms of organic compounds are also discussed in detail.

One of the key challenges for the commercialization of carbon nanotube fibers (CNTFs) is their large-scale economic production. Among CNTF spinning methods, surfactant-based wet spinning is one of the promising techniques for mass producing CNTFs. Here, we investigated how the coagulation bath composition affects the spinnability and the properties of CNTFs in surfactant-based wet spinning. We used acetone, DMAc, ethanol, and IPA as coagulants and analyzed the relationship between coagulation bath composition and the properties of CNTFs in terms of kinetic and thermodynamic coagulation parameters. From a kinetic perspective, we found that a low mass transfer rate difference (MTRD) is favorable for wet spinning. Based on this finding, we mixed the coagulant bath with solvent in a proper ratio to reduce the MTRD, which generally improved the wet spinning. We also showed that the coagulation strength, a thermodynamic parameter, should be considered. We believe that our research can contribute to establishment of surfactant-based wet spinning of CNTFs.

In this study, polyimide (PI)-based activated carbon fibers (ACFs) were prepared for application as electrode materials in electric double-layer capacitors by varying the steam activation time for the PI fiber prepared under identical cross-linking conditions. The surface morphology and microcrystal structural characteristics of the prepared PI-ACFs were observed by field-emission scanning electron microscopy and X-ray diffractometry, respectively. The textural properties (specific surface area, pore volume, and pore size distribution) of the ACFs were calculated using the Brunauer–Emmett–Teller, Barrett–Joyner–Halenda, and non-local density functional theory equations based on N2/ 77 K adsorption isotherm curve measurements. From the results, the specific surface area and total pore volume of PI-ACFs were determined to be 760–1550 m2/ g and 0.36–1.03 cm3/ g, respectively. It was confirmed that the specific surface area and total pore volume tended to continuously increase with the activation time. As for the electrochemical properties of PI-ACFs, the specific capacitance increased from 9.96 to 78.64 F/g owing to the developed specific surface area as the activation time increased.

Carbon fibers of polyacrylonitrile (PAN) type were coated with nickel nanoparticles using a chemical reduction method in alkaline hydrazine bath. The carbon fibers were firstly heated at 400 °C and then chemically treated in hydrochloric acid followed by nitric acid to clean, remove any foreign particles and functionalized its graphitic surfaces by introducing some functional groups. The functionalized carbon fibers were coated with nickel to produce 10 wt% Cf/Ni nanocomposites. The uncoated heat treated and the nickel coated carbon fibers were investigated by SEM, EDS, FTIR and XRD to characterize the particle size, morphology, chemical composition and the crystal structure of the investigated materials. The nickel nanoparticles were successfully deposited as homogeneous layer on the surface of the functionalized carbon fibers. Also, the deposited nickel nanoparticles have quazi-spherical shape and 128–225 nm median particle size. The untreated and the heat treated as well as the 10 wt% Cf/Ni nanocomposite particles were further reinforced in ethylene vinyl acetate (EVA) polymer separately by melt blending technique to prepare 0.5 wt% Cf-EVA polymer matrix stretchable conductive composites. The microstructures of the prepared polymer composites were investigated using optical microscope. The carbon fibers as well as the nickel coated one were homogenously distributed in the polymer matrix. The obtained samples were analyzed by TGA. The addition of the nickel coated carbon fibers to the EVA was improved the thermal stability by increasing the thermal decomposition temperature Tmax1 and Tmax2. The electrical and the mechanical properties of the obtained 10 wt% Cf/Ni nanocomposites as well as the 0.5 wt% Cf-EVA stretchable conductive composites were evaluated by measuring its thermal stability by thermogravimetric analysis (TGA), electrical resistivity by four probe method and tensile properties. The electrical resistivity of the fibers was decreased by coating with nickel and the 10 wt% Cf/Ni nanocomposites has lower resistivity than the carbon fibers itself. Also, the electrical resistivity of the neat EVA is decreased from 3.2 × 1010 to 1.4 × 104 Ω cm in case of the reinforced 0.5 wt% Cf/Ni-EVA polymer composite. However, the ultimate elongation and the Young’s modulus of the neat EVA polymer was increased by reinforcing with carbon fibers and its nickel composite.

Copper-coated carbon fibers have excellent conductivity and mechanical properties, making them a promising new lightweight functional material. One of the main challenges to their development is the poor affinity between carbon fiber and metals. This paper selects different carbon fibers for copper electroplating experiments to study the effect of carbon fiber properties on the interface bonding performance between the copper plating layer and carbon fibers. It has been found that the interfacial bonding performance between copper and carbon fiber is related to the degree of graphitization of carbon fiber. The lower the degree of graphitization of carbon fiber, the smaller the proportion of carbon atoms with sp2 hybrid structure in carbon fiber, the stronger the interfacial bonding ability between carbon fiber and copper coating. Therefore, carbon fiber with lower graphitization degree is conducive to reducing the falling off rate of copper coating and improving the quality of copper coating, and the conductivity of copper-plated carbon fibers increases with the decrease of graphitization degree of carbon fibers. The conductivity of copper-plated carbon fibers increases by more than six times when the graphitization degree of carbon fibers decreases by 23.9%. This work provides some benchmark importance for the preparation of highquality copper-plated carbon fibers.

Evaporative emissions, a major cause of air pollution, are primarily produced by automobiles and can be recovered using adsorbents. This study investigated the effect of the textural properties of polyimide (PI)-based activated carbon fibers (PIACFs) on the adsorption and desorption performance of n-butane, which are a type of evaporative emissions. PI-ACFs were prepared by varying the activation time while maintaining the identical crosslinking and carbonization conditions. The surface morphology and microstructural properties of the ACFs were examined using a field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD), respectively. The textural properties of ACF (specific surface area, pore volume, and pore size distribution) were analyzed using N2/ 77 K adsorption and desorption isotherm curves. The n-butane adsorption and desorption performance were evaluated according to modified ASTM D5228. From the results, the specific surface area and total pore volume of ACFs were determined to be 680–1480 m2/ g and 0.28–1.37 cm3/ g, respectively. Butane activity (BA) of the ACFs increased from 14.1% to 37.1% as the activation time increased, and especially it was found to have highly correlated with pore volume in the 1.5–4.0 nm range.

In this study, we utilized a multi-step stabilization method, incorporating dry-oxidation, to produce high-density polyethylene (HDPE)-based activated carbon fibers. This stabilization was achieved through electron-beam irradiation, sulfonation, and dry oxidation. The stabilized fibers were carbonized and activated at 900 ℃. The crystallite characteristics of the activated carbon fibers were observed using X-ray diffraction, and their surface morphologies were analyzed through scanning electron microscopy. The textural properties were analyzed using N2/ 77 K adsorption–desorption isothermal curves. And leveraging the microdomain model, we explored the influence of these stabilization methods on the HDPE-based activated carbon fibers texture properties. The results show that HDPE fibers treated with sulfonation only at 100 ℃ for 60 min were not sufficiently cross-linked and were completely decomposed during the carbonization stage. However, the sulfonated fibers treated with the new dry-oxidation process maintained their shapes and were successfully activated. The specific surface area of the resulting activated carbon fibers was as much as 2000 m2/ g.

This study aimed to fabricate composites with high thermal conductivity using diglycidyl ether of bisphenol-A (DGEBA), incorporating carbon fiber cloth (CFC) and graphene as reinforcing agents. Notably, the dispersion of graphene within the DGEBA matrix was enhanced through surface modification via a silane coupling agent. The effects of CFC and graphene addition on the impact strength, thermal conductivity, and morphology of the composites were examined. The experimental results showed that the incorporation of 6 wt% CFC resulted in a substantial (16-fold) increase in impact strength. Furthermore, the introduction of 6 wt% CFCs along with 20 wt% graphene led to a remarkable enhancement in thermal conductivity to 5.7 W/(m K), which was approximately 22 and 4 times higher than the intrinsic thermal conductivities of pristine DGEBA and the CFC/DGEBA composite, respectively. The increased impact strength is ascribed to the incorporation of CFC and silane-modified graphene. Additionally, the gradual increase in thermal conductivity can be attributed to the enhanced interaction between the acidic silane-modified graphene and the basic epoxy–amine hardener within the system studied.

A thorough knowledge and understanding of the structure–property relationship between thermal conductivity and C-fiber morphology is important to estimate the behavior of carbon fiber components, especially under thermal loading. In this paper, the thermal conductivities of different carbon fibers with varying tensile modulus were analyzed perpendicular and parallel to the fiber direction. Besides the measurement of carbon fiber reinforced polymers, we also measured the thermal conductivity of single carbon fibers directly. The measurements clearly proved that the thermal conductivity increased with the tensile modulus both in fiber and perpendicular direction. The increase is most pronounced in fiber direction. We ascribed the increase in tensile modules and thermal conductivity to increasing anisotropy resulting from the orientation of graphitic domains and microvoids.

Cellulose has experienced a renaissance as a precursor for carbon fibers (CFs). However, cellulose possesses intrinsic challenges as precursor substrate such as typically low carbon yield. This study examines the interplay of strategies to increase the carbonization yield of (ligno-) cellulosic fibers manufactured via a coagulation process. Using Design of Experiments, this article assesses the individual and combined effects of diammonium hydrogen phosphate (DAP), lignin, and CO2 activation on the carbonization yield and properties of cellulose-based carbon fibers. Synergistic effects are identified using the response surface methodology. This paper evidences that DAP and lignin could affect cellulose pyrolysis positively in terms of carbonization yield. Nevertheless, DAP and lignin do not have an additive effect on increasing the yield. In fact, combined DAP and lignin can affect negatively the carbonization yield within a certain composition range. Further, the thermogravimetric CO2 adsorption of the respective CFs was measured, showing relatively high values (ca. 2 mmol/g) at unsaturated pressure conditions. The CFs were microporous materials with potential applications in gas separation membranes and CO2 storage systems.

To improve the thermophysical properties of Al alloy for thermal management materials, the Cu-coated carbon fibers (CFs) were used as reinforcement to improve the thermal conductivity (TC) and the coefficient of thermal expansion (CTE) of Al-12Si. The CFs reinforced Al matrix (CFs/Al) composites with different CFs contents were prepared by stir casting. The effects of the CFs volume fraction and Cu coating on the microstructure, component, TC and CTE of CFs/Al composites were investigated by scanning electron microscopy with EDS, X-ray diffraction, thermal dilatometer and thermal dilatometer. The results show that the Cu coating can effectively improve the interface between CFs and the Al-12Si matrix, and the Cu coating becomes Al2Cu with Al matrix after stir casting. The CFs/Al composites have a relative density greater than 95% when the volume fraction of CFs is less than 8% because the CFs uniform dispersion without agglomeration in the matrix can be achieved by stir casting. The TC and CTE of CFs/Al composites are further improved with the increased CFs volume fraction, respectively. When the volume fraction of CFs is 8%, the CFs/Al composite has the best thermophysical properties; the TC is 169.25 W/mK, and the CTE is 15.28 × 10– 6/K. The excellent thermophysical properties of CFs and good interface bonding are the main reasons for improving the thermophysical properties of composites. The research is expected to improve the application of Al matrix composites in heat dissipation neighborhoods and provide certain theoretical foundations.

With a strive to develop light-weight material for automotive and aerospace applications, aluminum-based hybrid nanocomposites (AHNCs) were manufactured utilizing the compocasting approach in this study. Chopped carbon fibers (CFs) are reinforced along with different weight fractions of nanoclay (1–5%) in the matrix of AA6026 forming AHNCs. The AHNCs specimens were examined by microstructural analysis, mechanical characterization, fatigue, and corrosion strength as per ASTM guidelines. Electroless plating method is adopted for coating CFs with copper to improve the wettability with matrix. SEM pictures of manufactured composites reveal thin inter-dendritic aluminum grains with precipitate particle of eutectic at intergranular junctions, as well as nanoclay particles that have precipitated in the matrix. Tensile strength (TS) rises with inclusion of nanoclay up to a maximum of 212.46 MPa for 3% nanoclay reinforcement, after which the TS is reduced due to non-homogeneity in distribution, agglomeration and de-bonding of nanoparticles. Similarly, micro-hardness increases with addition of 3% nanoclay after which it decreases. Higher energy absorption was achieved with 3% nanoclay reinforced hybrid and a significant improvement in flexural strength was obtained. With addition of both CFs and nanoclay, the fatigue strength of the hybrid composite tends to increase due to flexible CFs and high surface area nanoclays which strengthen the grain boundaries until 3% addition. Addition of nanoclay lowers the corrosion rate with nanoclays filling the crevices and voids in the matrix.

The evolvement in the microstructure and electrical properties of PAN-based carbon fibers during high-temperature carbonization were investigated. The study showed that as the heat treatment temperature increases, the change of carbon fiber resistivity around 1100 °C can be divided into two stages. In the first stage, the carbon content of the fiber increased rapidly, and small molecules such as nitrogen were gradually released to form a turbostratic of carbon crystal structure. The resistivity dropped rapidly from 3.19 × 10− 5 Ω·m to 2.12 × 10− 5 Ω·m. In the second stage, the carbon microcrystalline structure gradually became regular, and the electron movement area gradually became larger. At this time, the resistivity further decreases, from 2.12 × 10− 5 Ω·m to 1.59 × 10− 5 Ω·m. During carbonization, the tensile strength of carbon fiber first increased and then decreased. This is because the irregular and disordered graphite structure is formed first. As the temperature rose, the graphite layer spacing decreased and the grain thickness gradually increases. The modulus also gradually increased.

The pitch-based activated carbon fibers (ACFs) were prepared from ethylene tar-derived pitches containing nickelocene (CNi) or nickel nitrate (NiN). The effects of different anions and contents of metal salts on the microstructure and surface chemical properties of fibers were investigated. The results revealed that Ni2+ from CNi mainly remained its pristine molecule in the organometal salt-derived pitch (OP-xCNi), while Ni2+ from NiN occurred complexation reaction with polycyclic aromatic hydrocarbons (PAHs) in the inorganic metal salt-derived pitch (IP-xNiN) due to the weaker binding ability between anions and Ni2+ of CNi than CNi. The XRD and SEM results confirmed that IP-3NiN-ACF contained Ni, NiO, Ni2O3 nanoparticles with different size distributions, while OP-3CNi-ACF only contained more uniformly distributed Ni nanoparticles with small size. Furthermore, OP-3.0CNi-ACF presented higher specific surface area of 1862 m2/ g and a pore volume of 1.69 cm3/ g than those of IP-3.0NiN-ACF due to the formation of pore structure during the in-situ catalytic activation of different metal nanoparticles. Therefore, this work further pointed out that the desired pore structure and surface chemistry of pitch-based ACFs could be obtained through regulating and controlling the interaction of anion species, metal cations and PAHs during the synthesis of pitch precursors.

To address the need for a suitable thermoplastic resin-based sizing agent for accommodating the increasing demands of carbon fiber-reinforced plastic, in this work, alcohol-soluble polyamide 6 (PA6) and silane were chemically combined in a certain ratio to improve the mechanical interface properties of the carbon fiber/PA6 composite, and the enhancement in the mechanical interface strength of the final composite according to the treatment time was confirmed. Carbon fiber surface properties were analyzed through ultrahigh-resolution field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy, and Fourier transform infrared spectrometry. The tensile strength of carbon fibers before and after hybrid sizing treatment and the mechanical interfacial shear strength of the final composite were analyzed using tensile and universal testing machines, respectively. After the hybrid sizing treatment, the introduction of the sizing agent to the carbon fiber surface was confirmed through FE-SEM, and a simultaneous increase in the surface roughness was observed. Moreover, the interfacial adhesion was confirmed to increase significantly, as compared to that of the desized carbon fiber. Therefore, this modified sizing agent treatment serves as an effective method for improving the mechanical interfacial adhesion between the carbon fiber and the PA6 matrix.