Polyacrylonitrile-based Carbon Fibers Research Articles

A comparative analysis of polyacrylonitrile-based carbon fibers: (Ⅱ) Relationship between the microstructures and properties

A comparative analysis of polyacrylonitrile-based carbon fibers: (Ⅱ) Relationship between the microstructures and properties

Submicron Corrugation оf Polyacrylonitrile-Based Carbon Fiber by High-Fluence Ion Irradiation

Submicron Corrugation оf Polyacrylonitrile-Based Carbon Fiber by High-Fluence Ion Irradiation

Polyacrylonitrile-Based Carbon Fiber as Anode for Manganese Electrowinning: Anode Slime Emission Reduction and Metal Dendrite Control

The traditional lead-based anodes used in industrial electrolysis process trigger the high energy consumption, lead pollution and hazardous anode slime discharge. In this work, an original undecorated Polyacrylonitrile (PAN)-based carbon fiber was employed as anode material (CF anode) to evaluate its electrochemical performance and feasibility, aiming at fundamentally reducing the energy consumption and pollution emissions for the manganese electrolysis. The results shown that the CF anode exhibited excellent electrocatalytic activity and delivered a current density of 350 A m–2 at an overpotential decreased by 112 mV for oxygen evolution reaction (OER) compared with commercial lead-based alloy anode (Pb anode). We also found CF anode exhibited favorable performance with average current efficiency increased by 4.30%, energy consumption decreased by 8.36%, and a noteworthy abatement of anode slime by 80% compared with Pb anode in MnSO4 electrolyte. Additionally, the growth of manganese dendrites on the cathode edge which directly affected the electrolytic efficiency has also been effectively controlled and the possible mechanisms were also discussed. This work displayed the excellent electrocatalytic effect of CF anode serviced as a promising candidate for green and efficient electrolysis process.

Innovative Solutions for Improving the Heat Exchange in Closed-Loop Shallow Geothermal Systems

Thermal conductivity, hydraulics properties and potential use in low-enthalpy geothermal applications of single and double U geothermal probes enhanced with carbon fibre are discussed in this work. Although the efficiency of a shallow geothermal installation is chiefly based on chemical and physical characteristics of rocks and hydrogeological aspects of the subsurface, the total heat extracted from the subsoil also depends on the intrinsic thermal characteristics of probes. New configurations and solutions aimed at enhancing the performance of components are therefore of considerable interest in this field of research. As a consequence of the economic and versatility advantages of the components, geothermal probes have been generally developed with materials like polyethylene, which presents, however, isolating behaviour that does not allow ideal heat exchange in ground source heat pump systems (GSHP). Innovative combinations of different materials are therefore necessary in order to improve thermal conductivity and to preserve the exceptional workability and commercial advantages of the finest elements available on the market. This work presents results coming from experimental tests involving standard polyethylene geothermal probes integrated with radial rings of polyacrylonitrile-based carbon fibre (PAN). Our evaluations are aimed at finding the best solutions for thermal exchange and adaptability with respect to traditional systems. Hydraulic and thermal performances and the response in a geo-exchange system have been verified. The new solutions appear to be highly suitable as geothermal exchangers in shallow geothermal systems and contribute to significantly reduce the total costs pertaining to the drilling operations.

Effect of carbon nanotexture on the synthesis, initial growth mechanism and photoluminescence properties of SiC nanowires

Although the spontaneous vapor–solid growth of SiC nanowires is a well-established phenomenon, the exact mechanism by which nanowires grow on substrates is still poorly understood. Here, we studied the initial growth of SiC nanowires on carbon sources with different nanotextures via a catalyst-free vapor reaction between a polyacrylonitrile-based carbon fiber and a silicon powder. The results revealed that the SiC nanowires were preferentially formed on the carbon fiber with a higher degree of graphitization. Detailed analyses suggested that the growth behavior of the underlying SiC film formed on the carbon fibers, which is strongly affected by the microstructures of the carbon fibers, plays an important role in the formation of nanowires. In addition, the photoluminescence spectrum of SiC nanowires showed strong ultraviolet–visible emission peaks at an excitation wavelength of 250 nm, which may provide potential applications in the field of optoelectronic devices.

A comparative analysis of polyacrylonitrile-based carbon fibers: (II) Relationship between the microstructures and properties

The relationships between the mechanical properties and the microstructures of typical polyacrylonitrile-based carbon fibers were studied on the basis of the elastic wrinkle model and Griffith microcrack theory. The effects of microcrystallite structure and its preferred orientation on tensile modulus, the effects of microvoids and mass density changes on the tensile strength, and the effects of internal residual compressive stress on the strain to failure, were analyzed, based on which the structural factors played a key role in determining the mechanical properties of the fibers.

A comparative analysis of polyacrylonitrile-based carbon fibers: (I) Microstructures

X-ray wide angle diffraction/small angle scattering, Raman spectroscopy and high resolution transmission electron microscopy were used to characterize the crystalline structure, pore structure, radial structural heterogeneity, degree of graphitization, internal residual stress, crystalline orientation and fractal phenomena of various grades (T and MJ) of polyacrylonitrile-based carbon fibers made by Toray Inc, Japan. Results showed that compared with the T series fibers, theMJ series fibers had a significantly lower internal residual stress, better structural orientation and a much higher degree of graphitization, but the dimensions of the microvoids and the radial inhomogeneity were increased, which revealed the significant influence of graphitization conditionsin making MJ series fibers on the microstructures of carbon fibers.

Towards designing strong porous carbon fibers through gel spinning of polymer blends

Blends of polyacrylonitrile (PAN) with three different sacrificial polymers: poly (acrylic acid) (PAA), poly (methyl methacrylate) (PMMA), and poly (styrene-co-acrylonitrile) (SAN), were gel spun, oriented through the drawing process, stabilized and carbonized to obtain porous carbon fibers. Carbon fibers with an average pore diameter of 15 nm, 31 nm, 37 nm and 115 nm have been obtained from PAN-PAA (90/10), PAN-PMMA (90/10), PAN-SAN (90/10) and PAN-SAN (80/20) precursor fibers, respectively. The variation in pore size caused by the differences in compatibility between PAN and the sacrificial polymer was evaluated experimentally through blend rheology and theoretically using interaction parameter values. Despite their porosity, carbon fibers from PAN-PAA (90/10) and PAN-PMMA (90/10) exhibited tensile strength (∼1.6 GPa) comparable to that of the non-porous PAN based carbon fibers, processed under similar conditions. Specific tensile modulus of the porous carbon fibers was 15–40% higher than that for the PAN based carbon fibers, and the electrical conductivity was as high as 74 kS/m due to high graphitic ordering. Porous channels presented in this study were obtained by combining phase separation in the nano/micro scale range, with pore orientation and elongation achieved through gel spinning.

Nitrate Ion Adsorption Characteristics of Activated Carbon Fibers with and without Quaternary Nitrogen Effective for Anion Adsorption.

By comparing the two types of activated carbon fibers (ACFs), characteristics of adsorption sites for nitrate ion other than quaternary nitrogen (N-Q) were investigated. Using phenol resin as precursors, activation with ZnCl2 was performed, and then heat treatment at 950 °C was carried out to prepare ACFs without N-Q, while ACFs with N-Q was prepared in the same method using polyacrylonitrile-based carbon fiber as precursors. We assessed the amount of functional groups, elemental composition, porous properties, and model of unit crystal size of graphene. For both ACFs with N-Q and without N-Q, equilibrium adsorption amount was not always simply proportional to surface area, but to the average number of benzene rings (Bz-rings) of graphene universally. PhR-5.0Z4 had only 20 benzene rings per graphene unit, but after heat treatment at 950 °C, the number drastically increased to 1088 (PhR-5.0Z4-9.5HT30). However, when the ACFs contained a large amount of oxygen, the number of Bz-rings was limited to 792 (PhR-5.0Z4-Ox-9.5HT30) even after heat treatment at 950 °C, and did not increase sufficiently. Cπ sites are more susceptible to oxygen inhibition than N-Q in adsorbing nitrate ions. For ACFs having Cπ sites as main adsorption sites, the heat treatment at 950 °C without oxidation can enhance the nitrate ion adsorption capacity.

Potassium-insertion in polyacrylonitrile-based carbon fibres for multifunctional energy storage, morphing, and strain-sensing

By increasing the number of functions a structure performs it is possible to save weight and volume on a systems level. Ion-insertion in carbon fibres (CFs) is a way to create multifunctional structures for energy storage, morphing, and strain-sensing. Previous studies have focussed on lithium- and sodium-insertion to create multifunctionality. However, with a larger ionic radius and a chemistry more amenable to insertion in polyacrylonitrile (PAN)-based CFs, potassium-insertion is a promising way forward. Here, a study is conducted to examine potassium-insertion in intermediate modulus PAN-based CFs for multifunctionality. Electrochemical cycling shows a maximum reversible capacity of 170 mAh/g, with ex-situ mechanical testing showing a small impact on the CFs’ mechanical properties post-cycling. Operando measurements show a maximum reversible CF expansion during potassium-insertion of 0.24%, and analytical modelling illustrates that such strains can generate significant deformations in a morphing structure. A voltage-strain coupling of 0.26 V/unit strain is also found. Results are compared with previous work on lithium- and sodium-insertion, with the conclusion that potassium-insertion is more promising than sodium-insertion, but less so than lithium-insertion for multifunctional structures.

Design of a novel all-carbon multi-layer structure with excellent thermal protection performance based on carbon/carbon composites and carbon foam

In order to obtain high-performance thermal protection materials, a novel all-carbon triple-layer structure was designed by orderly combining high thermal conductivity carbon/carbon composites (HTC-C/C), polyacrylonitrile-based carbon fiber reinforced composites (PAN-C/C) and carbon foam. During exposure to the oxyacetylene torch, compared with the multi-layer structure made of PAN-C/C and carbon foam, the maximum surface temperature of the triple-layer structure was lowered from 2348 °C to 2215 °C, and the mass ablation rate was reduced by 90.0%, attributed to the excellent heat-dissipation performance and the higher anti-oxidation property of HTC-C/C. When compared with the multi-layer structure composed of HTC-C/C and PAN-C/C, the back surface temperature of the triple-layer structure is further decreased by 700 °C, proving the effective thermal insulation of carbon foam; meanwhile, by isolating the air structure of the intermediate layer made of PAN-C/C was protected from oxidation.

Investigating the effective carbon material for thermal chemical vapor deposition using aniline to enhance As(V) adsorption capacity of activated carbon

To enhance the arsenic(V) adsorption capacity in the wide pH range, thermal chemical vapor deposition (tCVD) using aniline was conducted on various raw materials to prepare nitrogen-doped activated carbon samples. Phenol resin, polyacrylonitrile-based carbon fiber, cellulose-based activated carbon fiber, petroleum-derived beads-shaped activated carbon, and plant-based activated carbon powder were used as activated carbon precursors. We conducted the consecutive treatment (CVD) of steam activation as a pretreatment (8ST30), aniline tCVD (8ANL10), steam activation (8ST50), and heat treatment (9.5HT30). Steam activation was performed to improve tCVD efficiency and specific surface area. The annealing process at 950 °C was conducted to form quaternary nitrogen (N-Q) and reduce oxygen-containing acidic functional groups on the surface. The best result was obtained when we used cellulose-based activated carbon fiber as a precursor (KF-CVD). KF-CVD showed 0.172 mmol/g of the arsenic adsorption capacity, and it was at least 46% larger than that of all prepared samples. KF-CVD also indicated the highest adsorption capacity at any pH range. We assessed porous properties, elemental composition, nitrogen configuration by X-ray photoelectron spectroscopy, the number of surface functional groups by Boehm titration, and pHpzc of the prepared samples. Based on these surface characteristic studies; the increased specific surface area and the highest N-Q content of KF-CVD would enhance the arsenic adsorption in all pH ranges.

Evaluation of the stability of polyacrylonitrile-based carbon fiber electrode for hydrogen peroxide production and phenol mineralization during electro-peroxone process

This study evaluated the stability of polyacrylonitrile-based carbon fiber cathode for hydrogen peroxide (H2O2) production and phenol mineralization during multiple cycles of electro-peroxone (E-peroxone) process. Results show that the oxidation of bulk carbon fiber by electro-generated H2O2 and bubbled ozone (O3) is negligible during the E-peroxone process. Nevertheless, the carbon fiber surface was oxidized to some extent as the cathode was repeatedly used in the multi-cycle E-peroxone process. Due to the oxidation by H2O2 and O3, nitrogen-containing groups on the carbon fiber surface were converted from pyridinic-N to pyridonic-N during the E-peroxone process. These changes resulted in an increase in the activity of the cathode for oxygen reduction reaction (ORR), but a decrease in the selectivity of the cathode for two-electron ORR to H2O2. After the carbon fiber cathode was used for 30 cycles of the E-peroxone treatment of phenol solutions, the cathodic potentials for ORR shifted positively by ~450 mV, which is beneficial to reduce the energy consumption of electrochemical H2O2 production. Nevertheless, the apparent current efficiency (ACE) for H2O2 production decreased from ~91.5% for the virgin cathode to ~48.2% for the used cathode. Despite the decrease in the ACE for H2O2 production, sufficient amounts of H2O2 could still be produced during the E-peroxone process with the used cathode. Therefore, complete phenol mineralization was maintained during all 30 cycles of the E-peroxone treatment of phenol solutions. These results suggest that the polyacrylonitrile-based carbon fiber is a promising cathode material for long-term E-peroxone operations.

Phosphate ion adsorption properties of PAN-based activated carbon fibers prepared with K2CO3 activation

Adsorbents for phosphate ion removal were prepared with K2CO3 activation and heat treatment at 950 °C from polyacrylonitrile-based carbon fiber (PAN-CF). Comparative tests for specific surface area and pore structures, elemental and nitrogen species analysis, and phosphate ion adsorption experiments demonstrated that K(3)-Δ, which was activated with K2CO3/PAN-CF weight ratio of 3 and then treated at 950 °C, exhibited larger amount of quaternized-nitrogen (0.46 wt%) and equilibrium adsorption amount (0.23 mmol/g) among the prepared adsorbents. The experimental data for phosphate adsorption of K(3)-Δ was well fitted to Langmuir adsorption isotherms and pseudo-second-order kinetic model. As for regeneration performance, K(3)-Δ still remained more than 60% adsorption amount of the fresh adsorbent after rejuvenation treatment.

Fiber-reinforced Mechanism and Mechanical Performance of Composite Fibers Reinforced Concrete

To understand the enhancing effect and fiber-reinforced mechanism of composite fibers reinforced cement concrete, the influences of composite fibers on micro-cracks and the distribution of composite fibers were evaluated by optical electron micrometer (OEM) and scanning electron microscope (SEM). Three kinds of fiber, such as polyacrylonitrile-based carbon fiber, basalt fiber, and glass fiber, were used in the composite fibers reinforced cement concrete. The composite fibers could form a stable structure in concrete after the liquid-phase coupling treatment, gas-liquid double-effect treatment, and inert atmosphere drying. The mechanical properties of composite fibers reinforced concrete (CFRC) were studied by universal test machine (UTM). Moreover, the effect of composite fibers on concrete was analyzed based on the toughness index and residual strength index. The results demonstrated that the composite fibers could improve the mechanical properties of concrete, while the excessive amount of composite fibers had an adverse effect on the mechanical properties of concrete. The composite fibers could significantly improve the toughness index of CFRC, and the increment rate is more than 30%. The composite fibers could form a mesh structure, which could promote the stability of concrete and guarantee the excellent mechanical properties.

Oxidation Modification of Polyacrylonitrile-Based Carbon Fiber and Its Electro-Chemical Performance as Marine Electrode for Electric Field Test

A novel sensor for ocean electric field testing has been fabricated by polyacrylonitrile-based on carbon fibers with electro-chemical oxidation. The surface profile characteristics of the carbon fibers were characterized by scanning electron microscope, Fourier transform infrared spectra and contact angle. Cyclic voltammetry and Tafel curves have been used to study its electrochemical performances. Two identical electrodes in sea water as the electric field sensor will swiftly respond to applied electric field which causes positive and negative ions to move in opposite direction, resulting in a electric potential difference (ΔE). Test result indicates that the offset potential is typically below 1 mV with a drift of 60-170 μVd−1. Typical self noise level is 1.07nV/√Hz@1Hz. The electric field response indicates that the modified electrode pair shows better response to AC sine signal of amplitude and frequency (5mV and 1 mHz) respectively than its blank. The electric field response model of the modified electrodes is creatively presented according to its electric double layer capacitance and Faraday pseudo-capacitance. Many advantages of the carbon fiber electric field electrode will make it have potential application prospect.

Thermal Analysis and Crystal Structure of Poly(Acrylonitrile-Co-Itaconic Acid) Copolymers Synthesized in Water.

The composition and structure of polyacrylonitrile (PAN) precursors play an important role during thermal stabilization, which influences the properties of the resulting carbon fibers. In this paper, PAN homopolymer and PAN-itaconic (IA) copolymers with different IA contents were synthesized by aqueous phase precipitation polymerization. The effects of IA content on the structure and thermal properties were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The morphology of PAN polymers showed that the average size of the PAN particles increased with the increase of IA content in the feed. The content of the IA comonomer on the copolymers was quantitatively characterized by the relative absorbance intensity (A1735/A2243) in FTIR spectrum. With the increase of IA content in the feed, PAN-IA copolymers exhibited lower degree of crystallinity and crystal size than the control PAN homopolymer. The results from DSC curves indicated that PAN-IA1.0 copolymers had lower initial exothermic temperature (192.4 °C) and velocity of evolving heat (6.33 J g−1 °C−1) in comparison with PAN homopolymer (Ti = 238.1 °C and ΔH/ΔT = 34.6 J g−1 °C−1) in an air atmosphere. TGA results suggested that PAN-IA1.0 copolymers had higher thermal stability than PAN homopolymer, which can form a ladder structure easier during thermal processing. Therefore, PAN-IA1.0 copolymers would be a suitable candidate for preparing high performance PAN based carbon fibers.

High-temperature axial stress evolution mechanism of polyacrylonitrile-based carbon fiber

Temperature and stretching are important factors in the high-temperature treatment of carbon fiber. The axial stress during carbon-fiber high-temperature treatment affects its ability to stretch. The high-temperature axial stress evolution mechanism of polyacrylonitrile-based carbon fiber was studied through in situ tension tests, Raman spectroscopy, X-ray diffractometry, elemental analysis, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, thermal expansion coefficient tests, and density methods. The high-temperature axial stress evolution of polyacrylonitrile-based carbon fiber involved three stages: rapid increase, rapid decrease, and relaxation. The highest stress and relaxation temperatures of the polyacrylonitrile-based carbon fiber were 1600°C and 1950°C, respectively. The main factors that affected the fiber axial stress included carbon-structure rearrangement and the effect of thermal expansion and cold shrinkage on fiber length. During the first stage ( T < 1600°C), carbon-structure rearrangement after nitrogen atom removal increased the fiber axial stress. In the second stage (1600 ⩽ T ⩽ 1950°C), the difference in the thermal expansion of fibers that entered the graphite furnace and the cold shrinkage of fibers that exited the graphite furnace increased gradually, which resulted in a decrease in fiber axial stress by up to 1950°C, where the fiber relaxed and the third stage ( T > 1950°C) began. The difference between expansion and shrinkage increased significantly, which increased fiber relaxation. Carbon fibers with fewer nitrogen atoms and more regular structures had a lower axial stress during high-temperature treatment, but the trend and characteristic temperature remained unchanged. The corresponding fiber high-temperature maximum stretching ratio and axial stress showed opposite trends below 1950°C. The ability to stretch the carbon fiber increased above 1950°C, which differed from the axial stress relaxation.

Kinetics of the cyclization and isomerization reactions in polyacrylonitrile based carbon fiber precursors during thermal‐oxidative stabilization

ABSTRACTThe kinetics of reactions in polyacrylonitrile (PAN) based carbon fiber (CF) production should be of significance to the guidance of process control, fiber structure formation. PAN precursor fibers were isothermally stabilized at 210, 225, 240, 255, and 270 °C, respectively, for 10 to 100 min in an air oven to study the kinetics of the cyclization and isomerization reactions. The structural evolution of PAN precursor fibers during thermal‐oxidative stabilization was characterized by Fourier transform infrared (FTIR) spectroscopy and solid state 13C nuclear magnetic resonance (13C NMR). The results indicate that the FTIR absorbance of CN (the resultant of the cyclization) in PAN shows a trend of first increasing and then decreasing. And then the NMR peak assigned to the carbon atoms linking imino groups (NH) proves the isomerization of CN into NH in pyridone structure. Based upon the FTIR absorbance method, the entire process of the cyclization and isomerization reactions is considered as a consecutive first‐order reaction. A kinetic model for the consecutive reaction has been established via the evaluation of the reaction rate constants of two single reactions. According to the model, the simulated kinetic curves of the characteristic groups (CN, CN, and NH) conform to the FTIR absorbance trends of these groups based on experimental data. This study is expected to furnish in‐depth information on the crucial reaction kinetics during stabilization of PAN precursors, which is of advantage to the process optimization of the CF production. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48819.

Electret behavior of unpoled carbon fiber with and without nickel coating

Unpoled continuous polyacrylonitrile-based carbon fiber is an electret, as tested along the fiber direction of a 12,000-fiber tow. The open-circuit DC electric field before (E1) and after (E2) polarity reversal are opposite in sign, with │E2│ slightly less than E1, which is contributed by voltmeter-current-induced polarization. Both E1 and │E2│increase linearly with inter-electrode distance l, with E1 varying with l more significantly. At l = 140 mm,│E2│ is 5.5 × 10−5 V/m. The short-circuit current density is 3.5 A/m2. Both E1 and │E2│ decrease to zero upon discharge (short-circuited) and recover upon charge (open-circuited), though E1 is partly contributed by polarization. For l = 140 mm, discharge-charge testing gives participating charge density 1.8 × 103 C/m3, participating carrier density 1.2 × 1022 m−3, fraction of carriers that participate 1.7 × 10−3 and volumetric power density 1.9 × 10−4 W/m3. Discharge and charge in multiple cycles behave similarly. During discharge/charge, the electric field changes faster than the charge amount. Nickel coating increases the participating charge density, volumetric/gravimetric power density and current density, but decreases the electric field and the time for discharge completion divided by the participating charge. These results and previously reported inverse proportionality of capacitance with l support modeling an electret as electric dipoles of length much smaller than l in series electrically.