PAN Carbon Fibers Research Articles

Raman spectroscopic stress mapping of single high modulus carbon fibre composite fragmentation in compression

Fragmentation of high modulus carbon fibres is relevant to the failure mechanisms of advanced polymer matrix composites in compression. In situ spatially-resolved Raman spectroscopy during the fragmentation of model single fibre composites is used to map local stress distributions during failure events. The characteristic graphitic band (the G band) located around 1580 cm−1 is associated with the in-plane carbon-carbon bonds; this band shifts its position, and can be calibrated, with the local axial stress in the fibre. The analysis maps the evolution of local stresses with increasing overall composite compression strain, identifying a series of critical events, including fibre fracture, interfacial debonding, and the formation of inter-fragment ‘wedges’. Fitting shear lag models provides interfacial shear strength values. Multiple failure maps of two examples of high modulus PAN carbon fibres (M46J and M55J) demonstrate the possibility of local fragment bending due to fragment end contact. A timeline of potential fragmentation events is proposed for carbon fibres undergoing compression.

Splitting Mode-I fracture toughness of carbon fibers using nanoindentation

In this study, we conducted a thorough experimental and computational investigation to extend the pillar-splitting technique, developed initially for ceramics, to brittle fibers in reinforced composites. In pillar-splitting methodology, micropillars with circular cross-sections are tested to evaluate the load required to cause instability. The instability load is then correlated with the fracture toughness using the parameter γ which is evaluated using the cohesive zone finite element method (CZ-FEM). In reinforced composites, a unique opportunity arises due to the existence of already present micropillars (reinforcing fibers) for fracture toughness evaluation. In this work, the authors successfully applied the pillar-splitting technique to carbon fibers by investigating the effects of fiber/matrix assembly and the shape of the fiber upon the error in instability load. The minimum height required to avoid matrix effects is found to be equal to the diameter of the fiber reinforcements for a fiber–matrix system with a perfect interface. By contrast, the required protruding height is reduced to zero for a weak fiber–matrix interface. A new parameter, β, is introduced to quantify the deviation of the cross-sectional shape from circularity. An effective γ is then evaluated and used in the pillar-splitting experiments to correlate the instability load to Mode I fracture toughness. Finally, the results are validated experimentally, and the Mode I fracture toughness is evaluated for a range of Toray PAN carbon fibers. Fracture toughness is found to decrease as the modulus of the carbon fibers increases.

Powder-impregnated carbon fibers with lithium iron phosphate as positive electrodes in structural batteries

A structural battery is a multifunctional battery that can carry a load while storing energy. Structural batteries have been a cutting-edge research focus in the last decade and are mainly based on polyacrylonitrile (PAN)-carbon fibers (CFs). In this work, positive electrodes based on PAN-carbon fibers were manufactured with powder impregnation (siphon impregnation) technique using a water-based slurry containing lithium iron phosphate (LFP) as the active electrode material and the water-soluble binder polyethylene glycol (PEG). Different coating compositions, electrode-drying temperatures, and coating parameters were investigated to optimize the coating uniformity and the electrochemical performances. Scanning electron microscopy results showed that the electrode materials coat the CFs uniformly, conformably, and individually. Electrochemical characterization of pouch cells shows that the electrodes containing 6 wt% PEG dried at 140 °C have the best battery performance, delivering a first discharge capacity of 151 mAh g−1 and capacity retention higher than 80% after 100 cycles. Moreover, excellent capacity reversibility was achieved when the electrodes were cycled at multiple C-rates attesting to their stability. The results demonstrate that CFs perform excellently as current collectors in positive electrodes.

Acid Treatment of Carbon Fiber Surface

The paper describes the modification conducted for the PAN carbon fiber surfaces in the solutions of nitric and sulphuric acids. The authors studied the impact of modification parameters such as temperature, acid concentration, time and ratio of the nitrosulphuric acid on the occurrence of reactive groups on the fiber surface. The authors revealed the presence of carboxylic and ketone reactive groups in the range of 1663-1798 and 1568 cm-1 in the IR spectra of carbon fibers. The use of the nitrosulphuric acid did not identify sulfur-containing functional groups on the carbon fiber IR spectra. Preliminary acid treatment of the carbon fiber surface led to the formation of uniform continuous coating of a SiO2 barrier being 127 ± 30 μm by a sol-gel method.

Effect of graphitization temperature on microstructure, mechanical and ablative properties of C/C composites with pitch and pyrocarbon dual-matrix

Two graphitized C/C composites with a density of 1.83 g/cm3 were fabricated by CVI, high-pressure liquid-phase carbonization, and graphitization process. After graphitization at 2500 and 3000 °C, the graphitization degree of carbon phases in both composites shows a trend of pitch carbon > pyrocarbon > PAN carbon fiber. With increasing graphitization temperature, the orderly arrangement and growth of the graphite microcrystals cause the improved graphitization degree of the composites. Therefore, the thermal conductivity increases from 68.78 to 126.09 W/(m·K) in the transverse direction and 31.09 to 75.60 W/(m·K) in the thickness direction. Meanwhile, the increase in micro-cracks and pores formed at the interface induced the declined flexural and compressive strength, with the corresponding strength reducing to 104.17 and 113.92 MPa, respectively. During the first 22 s of ablation, the improved graphitization degree and higher thermal conductivity can transfer the heat rapidly, resulting in a lower surface temperature and a higher backside temperature. After 30 s ablation, the mass ablation rate decreases from 0.0030 to 0.0018 g/s, while the linear ablation rate increases from 0.0040 to 0.0093 mm/s due to the increased open porosity and defects under higher graphitization temperature.

The effects of fiber radius and fiber shape deviations and of matrix void content on the strengths and failure mechanisms of UD composites by computational micromechanics

Manufacturing plays an important role in the properties of composites, which may lead to two types of uncertainties: (1) carbon fiber manufacturing deviations, such as the bean-shaped PAN carbon fibers, the lognormal-distributed fiber radius, etc. (2) composites manufacturing deviations, such as the inter-fiber voids and matrix voids. Although several experiments have been conducted to assess their effects on the mechanical properties of composites, a satisfactory result of quantitative characterization of fiber radius and fiber shape deviations and of matrix void content have not been obtained. In this paper, a parametric study based on the computational micromechanics is conducted to reveal the effects of fiber radius and fiber shape deviations and of matrix void content on the strengths and failure mechanisms of UD composites under four loading conditions, i.e. the transverse tension, compression, shear and longitudinal shear. Firstly, the constitutive laws of constituents, i.e. carbon fiber, matrix and interface, are established to characterize their mechanical responses. Then, the UD RVEs with fiber radius and fiber shape deviations and with matrix void are modeled individually based on experimental observation and statistical distribution. After qualitative validation of failure modes and quantitative validation of stress-strain curves, the methodology is applied to predict the stress-strain curves and failure modes of UD RVE with manufacturing uncertainties and the results show that not all manufacturing uncertainties have a detrimental effect on the mechanical properties of UD composites.

Hollow “graphene” microtubes using polyacrylonitrile nanofiber template and potential applications of field emission

We report a simple process to connect graphene sheets forming graphene hollow microtubes (GHMs), where the tube diameter can be adjusted in the 100–500 nm range by changing reaction conditions. We discovered that graphene sheets can be seamlessly linked to each other if C atoms are substituted for N atoms at the edges of the sheets during annealing of graphene oxide(G-O)-coated electrospun PAN carbon fibers in ammonia atmosphere. The G-O/carbon hybrid nanofibers framework served as a confining template around which graphene sheets curved to form tubular structures. The GHMs formed by this process are similar to (very) large diameter carbon nanotubes (CNTs) with relatively low curvature whose electron field-emission properties include a low turn-on voltage of 0.18 V/μm (at J = 10 μA/cm2), low threshold field of 0.35 V/μm (at J = 10 mA/cm2), and high field-emission stability. This process to produce GHMs can be scaled up to fabricate GHMs of variable diameter in bulk quantities.

Unveiling Carbon Ring Structure Formation Mechanisms in Polyacrylonitrile-Derived Carbon Fibers.

As the demand for electric vehicles (EVs) and autonomous vehicles (AVs) rapidly grows, lower-cost, lighter, and stronger carbon fibers (CFs) are urgently needed to respond to consumers' call for greater EV traveling range and stronger safety structures for AVs. Converting polymeric precursors to CFs requires a complex set of thermochemical processes; a systematic understanding of each parameter in fiber conversion is still, to a large extent, lacking. Here, we demonstrate the effect of carbonization temperature on carbon ring structure formation by combining atomistic/microscale simulations and experimental validation. Experimental testing, as predicted by simulations, exhibited that the strength and ductility of PAN CFs decreased, whereas the Young's modulus increased with increasing carbonization temperature. Our simulations unveiled that high carbonization temperature accelerated the kinetics of graphitic phase nucleation and growth, leading to the decrease in strength and ductility but increase in modulus. The methodology presented herein using combined atomistic/microscale simulations and experimental validation lays a firm foundation for further innovation in CF manufacturing and low-cost alternative precursor development.

Wear behavior of medical grade PEEK and CFR PEEK under dry and bovine serum conditions

Wear is among the main factors affecting the performance of artificial couplings in joint arthroplasty. In the attempt of investigating the applicability of PEEK and CFR PEEK in such applications, wear behavior of three medical grade PEEK formulations (unfilled PEEK, 30% wt. pitch carbon fiber reinforced PEEK and 30% wt. PAN carbon fiber reinforced PEEK) have been tested under dry and bovine serum lubricated conditions in a pin on flat test against Al2O3 1/8″ spheres, replicating physiological conditions whereas possible. The crystallinity and the resulting mechanical properties of the three selected material were differentiated by annealing treatments performed at 200, 250, and 300 °C. All the specimens were tested under both lubrication regimes.The observed coefficient of friction variations, as well as the calculated volumetric wear rate, displayed an improved wear behavior of the reinforced formulations in both dry and bovine serum. Correlation among the modified material properties by annealing and the wear behavior was possible. The formation of a lubricating film was identified as responsible for an improved wear performance of PEEK and CFR PEEK formulations.

Copolymerization of Acrylonitrile/1-Vinyl-3-Ethylimidazolium Bromide and Rheological, Thermal Properties of the Copolymer

Acrylonitrile(AN)/1-vinyl-3-ethylimidazolium bromide (VIMB) copolymer was prepared via solution polymerization using dimethyl sulfoxide (DMSO) as a solvent and azodiisobutyronitrile as an initiator. The effects of comonomer VIMB on the polymerization, rheological properties of the polymer solution and thermal properties of the copolymer were investigated. The ionic liquid VIMB resulted in higher polymerization conversion ratio and higher average molecular weight when copolymerized with AN than itaconic acid (ITA). Rheological measurements indicated that the transition shear rate increased linearly with increasing temperature for P(AN/ITA)/DMSO solution, while an exponential growth with temperature was observed for P(AN/VIMB)/DMSO solution. The exothermic peaks of DSC curves in N2 appeared at 276.67 and 257.34 °C for P(AN/VIMB) and P(AN/ITA), respectively. As a potential comonomer of AN for PAN carbon fibers, the VIMB resulted in about 7% higher char yield in N2, and 23.7% less weight loss at 600 °C in air than ITA copolymer.

Investigations on neutron irradiated 3D carbon fibre reinforced carbon composite material

As against conventional graphite materials carbon-carbon (C/C) composite materials are now being contemplated as the promising candidate materials for the high temperature and fusion reactor owing to their high thermal conductivity and high thermal resistance, better mechanical/thermal properties and irradiation stability. The current need is for focused research on novel carbon materials for future new generation nuclear reactors. The advantage of carbon-carbon composite is that the microstructure and the properties can be tailor made. The present study encompasses the irradiation of 3D carbon composite prepared by reinforcement using PAN carbon fibers for nuclear application.The carbon fiber reinforced composite was subjected to neutron irradiation in the research reactor DHRUVA. The irradiated samples were characterized by Differential Scanning Calorimetry (DSC), small angle neutron scattering (SANS), XRD and Raman spectroscopy. The DSC scans were taken in argon atmosphere under a linear heating program. The scanning was carried out at temperature range from 30 °C to 700 °C at different heating rates in argon atmosphere along with reference as unirradiated carbon composite. The Wigner energy spectrum of irradiated composite showed two peaks corresponding to 200 °C and 600 °C. The stored energy data for the samples were in the range 110–170 J/g for temperature ranging from 30 °C to 700 °C. The Wigner energy spectrum of irradiated carbon composite did not indicate spontaneous temperature rise during thermal annealing. Small angle neutron scattering (SANS) experiments have been carried out to investigate neutron irradiation induced changes in porosity of the composite samples. SANS data were recorded in the scattering wave vector range of 0.17 nm−1 to 3.5 nm−1. Comparison of SANS profiles of irradiated and unirradiated samples indicates significant change in pore morphology. Pore size distributions of the samples follow power law size distribution with different exponent. Narrowing of SANS profile of the irradiated sample indicates creation of significant number of larger pores due to neutron irradiation.

Разработка полимерных композиционных материалов на основе политетрафторэтилена и пан-углеродных волокон

Разработка полимерных композиционных материалов на основе политетрафторэтилена и пан-углеродных волокон

High-strength lignin-based carbon fibers via a low-energy method.

Bio-renewable carbon fibers are fabricated and employed as high-strength composite materials in many fields. In this work, a facile and low energy consumption method was developed to fabricate high-strength lignin-based carbon fibers. Using iodine treatment, the thermodynamic stability of the lignin-based precursor fibers increased significantly, and thus energy consumption during the preparation of the carbon fibers was reduced. The influence of the iodine treatment on fibers was analyzed by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), Raman spectroscopy, tension testing, etc. The resulting iodine lignin-based carbon fibers had better tensile strength (89 MPa) than that of PAN carbon fibers produced by electrospinning technology.

Effect of Gamma and electron beam irradiation on PAN-carbon fiber composite

The aim of this study was to evaluate the effects of irradiation on structural, mechanical and thermal properties of PAN- carbon fiber composite. The overall applied doses were 250, 500, 750, and 1000 kGy. Irradiated and non-irradiated samples were characterized by Scanning electron microscopy, Fourier transform infrared spectroscopy and differential scanning calorimetry. Tensile strength test was conducted in order to measure mechanical properties. Scanning electron microscopy was used to evaluate microstructural behavior. Thermal behavior of the samples was studied by thermogravimetric analysis and differential scanning calorimetry. The results showed that by increase in Gamma and Electron doses the thermal behavior of the composite indicated higher decomposition degree as a function of temperature. Electron irradiated relatively smoothed surface of carbon fibers than that of virgin fibers and after γ treatment the bulges were decreased and surface was unrough.

Super-strong and highly conductive carbon nanotube ribbons from post-treatment methods

In this study, we present a simple and effective mechanical densification method that uses carbon nanotube (CNT) fibers synthesized via a floating-catalyst technique to produce highly dense CNT ribbons. After being infiltrated with epoxy, the resulting cross-linked CNT ribbons exhibited impressive improvements of an increase in strength by 13.5 times and an increase in stiffness by more than 63 times, the best improvement factors reported in the literature. The strength and stiffness of the post-treated fibers reached as high as 5.2 GPa and 444 GPa respectively, while their electrical conductivity reached up to 12,000 S/cm. The knot-strength efficiency of the cross-linked CNT ribbons approached 78%, which is much higher than that of many commercial high-strength fibers. The performance of the post-treated ribbons was comparable to that of commercial PAN carbon fibers, suggesting that our combined post-treatment of CNT fibers is a promising method for achieving cost-effective mass production of high-performance CNT fibers.

Dynamic mechanical characterization for nonlinear behavior of single carbon fibers

In the work presented here, small amplitude in-situ dynamic loads are superimposed onto quasi-static tensile tests, to obtain storage and loss modulus as a function of global strain for deforming single PAN carbon fibers. This technique allows for the measurement of carbon fiber modulus at unprecedented resolution without the need for compliance correction, which is difficult to implement as carbon fibers have a non-linear modulus dependency with strain. The relationship of the elastic modulus with strain is quantified to evaluate the single fiber nonlinearity during extension. Fibers with initially higher modulus are shown to have greater nonlinear dependency on strain amplitude, even for fibers taken from the identical tow. The strong correlation between tensile modulus with strain and its initial modulus indicates that the measured mechanical properties describe a fundamental structure of carbon fibers.

Ion-beam erosion of carbon fibers of the composites

The results of experimental studies of the structural and morphological changes of the surface of carbon PAN fibers of a carbon-carbon KUP-VM (1D) composite as a result of high-dose irradiation (1018–1019 ion/cm2) with Ne+ and Ar+ ions with an energy of 10–30 keV are presented. The threshold values of radiation damage, resulting in an amorphization of the PAN carbon fibers at room temperature and ion-induced crimping at temperatures greater than the annealing temperature of the radiation damage, are determined.

Investigation of Rheological Characteristics of Carbon Fiber Modified Asphalt Binder

The performance of asphalt concrete is strongly dependent on the rheological properties of asphalt binders. In this paper, PAN carbon fiber was employed to improve the conductivity of asphalt mixture. To better understand the performance of conductive asphalt mixture, the present study investigated the rheological characteristics of asphalt binders containing PAN carbon fiber. Additionally, scanning electron microscopy (SEM) was used to elucidate the microstructure and interface reaction between the asphalt and the PAN carbon fiber. Experimental results showed that carbon fibers in the asphalt can overlap each other and form a three-dimensional space structure, which could transfer and buffer the stress. Moreover, the addition of PAN carbon fiber increases the complex shear modulus of modified asphalt binders, which means higher resistance to the permanent deformation. Furthermore, the reduction of phase angle implied the increment of elastic portion in the visco-elastic of carbon modified asphalt binder.

2D SAXS/WAXD analysis of pan carbon fiber microstructure in organic/inorganic transformation

Structure of PAN fibers during pre-oxidation and carbonization was studied using two dimensional small angle X-ray scattering/wide angle X-ray diffraction (2D SAXS/WAXD). The SAXS results show that during pre-oxidation between 180 °C and 275 °C, the volume content of microvoids increases with the temperature increasing, which may be one of reasons for the decrease of tensile strength of pre-oxidized fibers. 253 °C was the critical transition temperature, the length, diameter, aspect ratio and orientation distribution of microvoids increased with temperature before this temperature and decreased after this temperature. After the high temperature carbonization, lots of spindly microvoids formed. WAXD patterns demonstrate that the crystallite size of PAN fibers first increased before 230 °C and then decreased with the increase of temperature during the pre-oxidation. The diffraction peak of PAN fibers at 2θ ≈ 17° almost disappeared at the end of preoxidation while the diffraction peak of aromatic structure at 2θ ≈ 25° appeared at 253 °C. During carbonization, the peak intensity at 2θ ≈ 25° increased apparently due to the formation of graphite structure. The results obtained give a deep understanding of the microstructure development in the PAN fibers during pre-oxidation and carbonization, which is important for the preparation of high performance carbon fibers.

聚丙烯腈碳纤维原丝上油的研究分析

在碳纤维生产过程中，油剂对提高原丝、碳丝的性能有着重要影响，因此研究分析油剂及上油工艺对聚丙烯腈原丝及碳纤维工业化生产具有重要意义。为了提高产品质量，本文从上油工艺、上油设备、油剂成分等方面分析了现有生产工艺的不足。 In the production process of the carbon fiber, the finish oil has an important effect on improving the per- formance of the PAN precursor and carbon fiber. Thus, the study on the finish oil and oil technology is of great signifi- cance to the industrialized production of the PAN precursor and carbon fiber. In this research, in order to improve the quality of products, from oil technology, oil equipment, oil composition, the deficiencies in the current production process were discussed.