Polyacrylonitrile Precursor Research Articles

Large‐scale synthesis of hollow carbon fibers with ultra‐large diameter by thermally controlled pyrolysis

AbstractHollow carbon fibers (HCF) with ultra‐large diameter have been synthesized and the versatility to convert them into the corresponding carbon‐based composites has been demonstrated. The hollow carbon fibers were fabricated by thermal controlled carbonization of electrospun polyacrylonitrile fibers. For the existence of inorganic silica shell during pyrolysis, heat release will be blocked at the boundary, driving the polyacrylonitrile precursor fiber to form hollow structure. The diameter of the as‐prepared hollow carbon fibers can exceed 150 nm. Sol‐gel‐derived Fe3O4 nanoparticles can grow on the outer‐surface and the inner‐surface of hollow carbon fibers. The microwave absorption performance of ternary HCF@Fe3O4@PPy composite is testified and the values of reflection loss exceeding −10 dB can be obtained in the frequency of 3.3‐11.3 GHz. The large diameter of hollow carbon fibers can have inner and outer interfaces in the corresponding composites, which make them great potential for a variety of applications in future.

Chemical and Morphological Transition of Poly(acrylonitrile)/Poly(vinylidene Fluoride) Blend Nanofibers during Oxidative Stabilization and Incipient Carbonization.

Thermally stabilized and subsequently carbonized nanofibers are a promising material for many technical applications in fields such as tissue engineering or energy storage. They can be obtained from a variety of different polymer precursors via electrospinning. While some methods have been tested for post-carbonization doping of nanofibers with the desired ingredients, very little is known about carbonization of blend nanofibers from two or more polymeric precursors. In this paper, we report on the preparation, thermal treatment and resulting properties of poly(acrylonitrile) (PAN)/poly(vinylidene fluoride) (PVDF) blend nanofibers produced by wire-based electrospinning of binary polymer solutions. Using a wide variety of spectroscopic, microscopic and thermal characterization methods, the chemical and morphological transition during oxidative stabilization (280 °C) and incipient carbonization (500 °C) was thoroughly investigated. Both PAN and PVDF precursor polymers were detected and analyzed qualitatively and quantitatively during all stages of thermal treatment. Compared to pure PAN nanofibers, the blend nanofibers showed increased fiber diameters, strong reduction of undesired morphological changes during oxidative stabilization and increased conductivity after carbonization.

Multi-wavelength Raman microspectroscopic studies of modified monwoven carbon scaffolds for tissue engineering applications

The articular cartilage is almost a non-vascular tissue, therefore it has a very low ability to heal itself. The analyzed carbon nonwoven material, obtained by polyacrylonitrile precursor carbonization, seem to be a new option for the complementation of cartilage losses due to a unique ability of this material to restore of cartilage tissue. The analyzed carbon material may be a new option to supplement cartilage defects due to the ability of this material to restore cartilage tissue. This study presents several examples of surface modification of nonwoven carbon fibers materials forming scaffold using ceramic nanoparticles, nanosilica and nanohydroksyapatite. Surface structural changes were examined by SEM observations, composition was assessed by EDS. The results indicate that the apatite phase on the surface of nonwoven fibers is formed, and its composition depends on the type of surface. The obtained multiwavelength Raman microspectroscopy results, G-band dispersion course and also the ID/IG intensity ratio dispersion, allowed to indicate the nanocrystaline graphite organization of the fibers with the presence of certain disorder. In this way, the resulting ordering in the tested materials also indicates the material’s production parameters. All scaffolds were evaluated by examining the ability of apatite to form on the materials incubated in simulated body fluids (SBF).

Углеродное волокно. Получение, модификация, свойства, области применения.

The main methods for producing a polyacrylonitrile precursor, methods for producing carbon fiber, its properties, and applications are presented. Patent research in the field of polyacrylonitrile precursor and carbon fiber. Technological problems in the subject area are identified, namely the development of technologies and equipment for producing high-strength carbon fiber, the development of technologies and equipment to reduce the cost of carbon fiber production, the development of technologies for improving the quality of carbon fiber-based composites, and the main ways to solve them are given. Ways to solve them are developing a technology for producing a polyacrylonitrile precursor for producing high-strength carbon fibers by the wet spinning method, developing a “dry-wet” method for producing polyacrylonitrile, developing high-performance equipment for producing technical polyacrylonitrile precursor in the form of bundles, developing technologies and equipment for efficient regeneration and utilization waste, heat and emissions from the production of carbon fibers, the development of new compositions of precursors and the transition to materials with a higher linear density, optimization of the structure of carbon fiber reinforced plastic to increase strength, the development of technologies and the creation of production of modern types of binders, including the addition of nanoparticles. The main methods for modifying the surface of a carbon fiber that are currently existing are considered.

Force field in coagulation bath at low temperature induced microfibril evolution within PAN nascent fiber and precursor fiber

AbstractThe coagulation process was vital for the microfibril evolution and mechanical properties of polyacrylonitrile (PAN) fibers. The PAN nascent fibers and precursor fibers were prepared by controlling drawing ratio of coagulation bath at low temperature during the dry‐jet wet spinning process. The microfibril morphological changes induced by force fields in coagulation bath were investigated by scanning electron microscopy and high‐resolution transmission electron microscopy. During the coagulation process, the spinning solution evolved into an interconnected network composed of random microfibrils and tie joints as a building block of the network. At low drawing ratio, the random interconnected network existed in nascent fibers. Increasing drawing ratio, the fiber filaments underwent shrinkage and the network was transformed into the transverse lamellae. Furthermore, the lamellar thickness also decreased. After the treatment of post‐spinning, similar transverse lamellae were formed in all of precursor fibers, and random microfibrillar network was stretched and oriented to develop into the aligned microfibrils in precursor fibers. The transverse fold‐chain crystal layers were densely stacked in the microfibrils. Increasing drawing ratio, the lamellae and microfibrils in precursor fibers were packed more densely and orderly. Consequently, the order and homogeneity of microfibrils in nascent fibers and precursor fibers were improved by increasing drawing ratio, which were benefit to increase fiber tensile strength and modulus.

Microstructural evolution and mechanical investigation of hot stretched graphene oxide reinforced polyacrylonitrile nanofiber yarns

To reveal the enhancement effect of graphene oxide (GO) in polymer nanofiber yarns, polyacrylonitrile (PAN)/GO nanofibers with different GO content (0.1‐0.5 wt%) were electrospun. The alignment of PAN chains and GO in nanofibers was enhanced by hot stretching of the yarn in dry conditions. The microstructure of the composite nanofiber yarns was investigated through X‐ray diffraction, polarized Fourier transform infrared spectroscopy and transmission electron microscopy. The results demonstrated that the hot stretching above Tg of PAN precursor lead to the increased orientation‐induced crystallization and alignment of PAN chain and GO. The yarn with 0.1 wt% GO and stretched by 4 times its length obtained the highest strength and modules (310.88 ± 24.68 MPa and 7.24 ± 0.55 GPa), which were 600% and 500% higher than those of the as‐electrospun pure PAN yarn. The most promising tensile properties found in hot stretched yarns with low GO content was because the strong interaction occurred between PAN molecules and oxygen‐containing functional groups. Indirect evidence of GO aggregation was also presented, which adversely affected the mechanical properties at higher GO content. Composite nanofiber yarns were sewable and weavable, and could be used as a new generation of composite reinforcement after pyrolysis.

Nebulized jet-based printing of bio-electrical scaffolds for neural tissue engineering: a feasibility study

In this paper we investigate the application of a direct writing technique for printing conductive patterns onto a biocompatible electrospun-pyrolysed carbon-fibre-based substrate. The result is a first study towards the production of bio-electrical scaffolds that could be used to enhance the promotion of efficient connections among neurons for in vitro studies in the field of neural tissue engineering. An electrospinning process is employed for production of the materials derived from the precursor polyacrylonitrile, in which the embedding of carbon nanotubes (CNTs) is also investigated. Subsequently, the methodology of research into suitable parameters for the printed electronics, using a commercial silver nanoparticle (Øavg,particle size ∼ 100 nm) ink, is described. The results show values of 2 Ω cm for the resistivity of the carbon-fibre materials and conductive printed lines of resistance ∼50 Ω on glass and less than ∼140 Ω on carbon-fibre samples. Biocompatibility results demonstrate the possibility of using electrospun-pyrolysed mats, also with embedded CNTs, as potential neural substrates for spatially localized electrical stimulation across a tissue. In addition, the data concerning the potential toxicity of silver suspensions are in accordance with the literature, showing a dose-dependent behaviour. This work is a pioneering feasibility study of the use of the flexible and versatile printed electronic approach, combined with engineered biocompatible substrates, to realize integrated bio-electrical scaffolds for in vitro neural tissue engineering applications.

Electrochemical Behaviors of Sulfurized-Polyacrylonitrile with Synthesized Polyacrylonitrile Precursors Based on the Radical Polymerization Through Monomer Acrylonitrile

Polyacrylonitrile (PAN) precursors have been polymerized at different radical polymerization temperatures for preparing sulfurized-polyacrylonitrile (S-PAN) composite cathodes in rechargeable lithium sulfur battery. The physical properties of these composites have been investigated using X-ray diffraction, Fourier transform infrared spectrometry, Raman spectroscopy, Brunner-Emmet-Teller measurement and Gel permeation chromatography analysis. The electrochemical performance of the S-PAN composite cathodes made from the PAN precursor was investigated. The results showed that the molecular weight distribution of the PAN precursors affected the electrochemical performance of the S-PAN made from the PAN precursor. S-PAN composites derived from PAN with a narrower molecular weight distribution at 65 °C were exhibit the best electrochemical performance in lithium-sulfur battery.

A novel methodology for designing thermal processes in order to optimize stabilization of polyacrylonitrile (PAN) fibers

AbstractThe aim of this work is to describe a novel methodology for optimizing the stabilization of polyacrylonitrile (PAN) fibers, through designing of proper thermal treatment. The methodology is based on a set of design rules and the procedure for implementing them, utilizing the time‐temperature‐transition (TTT) and the maximum permittable stress (max.stress) plots. The proposed approach is implemented in order to optimize the stabilization of commercial PAN fibers, resulting in a series of multistage thermal treatments. The changes of both physical and chemical structures of PAN during the progress of the multistage treatments were investigated and showed that the fibers were progressively converted into completely stabilized material; this gradual transformation permitted improvement of fiber annealing and minimized the effect of the decomposition reactions. The proposed methodology can be universally applied for achieving the global optimum of the stabilization process for any PAN precursor.

Effect of the Ionic Liquid Structure on the Melt Processability of Polyacrylonitrile Fibers.

The production of high-strength carbon fibers is an energy-intensive process, where a significant cost involves the wet or dry-spinning of polyacrylonitrile (PAN) fiber precursors. Melt-spinning PAN fibers would allow for significant reduction in the production cost and production hazards. Ionic liquids (ILs) are an attractive fiber-processing medium because of their negligible vapor pressure and low toxicity. In addition, they are carbon-forming precursors; upon carbonization, residual ILs can enhance the carbon yield, although primarily useful for plasticized melt-spinning of PAN precursor fibers. In this research, we investigated the influence of the molecular structure of ILs and the control of plasticizing interactions with PAN during melt-spinning. The structural, thermal, and mechanical properties of the melt-spun PAN fibers were obtained by a combination of various characterization methods, such as differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and mechanical testing. These results demonstrated that the IL structure and counteranions influence the PAN fiber formation. More specifically, ILs containing bromide counteranions produced PAN precursor fibers with increased mechanical properties compared to ILs containing chloride anions. Our research can provide a foundation to understand the influence of ILs on melt-spinning of PAN fibers and provides us the guidelines for a higher cost-/energy-efficient production of PAN-based carbon fibers.

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.

Singular properties of boron-doped diamond/carbon fiber composite as anode in Brilliant Green dye electrochemical degradation

Carbon fiber (CF) and boron doped diamond/carbon fiber (BDD/CF) were applied as anodes for the Brilliant Green dye electrochemical degradation process. CF substrates were obtained from polyacrylonitrile precursor heat treated at 1000 °C in a nitrogen atmosphere. BDD films were grown on CF substrates by hot filament chemical vapor deposition with boron source from an additional hydrogen line passing through a bubbler containing B2O3 dissolved in methanol solution with B/C ratio of 15,000 ppm. The electrodes were characterized by field emission gun-scanning electron microscopy images, Raman spectroscopy, and electrochemical impedance spectroscopy showing notable tridimensional characteristics besides their high diamond quality. They were applied to electrochemical degradation of Brilliant Green dye at different current densities using a concentration of 100 mg L−1. Their electrolysis efficiency was analyzed by UV/Vis spectrophotometry technique. The results showed that BDD/CF electrodes were efficient in the solution color removal, regardless of the current density value. BDD/CF electrode under the lowest current density of 10 mA·cm−2 presented the best performance with higher kinetic constant and color removal percentage associated to its low energetic consumption.

Study on the Crystallization Behavior of PAN Fibers during Hot-Drawing Process in Supercritical Carbon Dioxide Fluid with Different Strain

Hot-drawing of polyacrylonitrile (PAN) fibers is an important step in the production of carbon fibers. In this article, we investigated the effect of strain on the crystallization behavior and mechanical properties of PAN fibers treated in supercritical carbon dioxide (Sc-CO2) fluid. We mainly used the methods of X-ray diffraction (XRD), monofilament strength analysis and differential scanning calorimeter (DSC) to study the crystallization behavior, mechanical properties and thermal behavior of PAN fibers during hot-drawing process. The experimental results showed that the crystallinity and mechanical properties of PAN fibers both increased a lot under the action of strain during hot-drawing in Sc-CO2 fluid. This provides an important method for preparation of higher performance PAN precursor for PAN-based carbon fibers.

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.

Preparation and characterization of KOH-treated electrospun nanofiber mats as electrodes for iron-based redox-flow batteries

Abstract A series of electrospun nanofiber mats have been fabricated from polyacrylonitrile (PAN) precursor, followed by treatments with pyrolytic heat and KOH solutions. The heat & KOH-treated electrospun nanofiber mats were investigated to serve as electrodes for iron-based redox-flow batteries (RFBs). The morphology, porosity, wettability, and cyclic voltammetry have been studied for the treated electrospun nanofiber mats. The KOH treatment effectively reduced the fiber diameter, increased the mat porosity, and enhanced the surface wettability. Specifically, the heat & 4 M KOH-treated electrospun nanofiber mat has ~300 nm of fiber diameter, 92% of porosity, and 20° of contact angle. Compared with the electrospun nanofiber mat treated with heat alone, the heat & 4 M KOH-treated electrospun mat increases the anodic peak current in cyclic voltammogram of Fe3+/Fe2+ redox by 60% at the same scan rate, implying considerably increased specific surface area. The KOH treatment does not seem to change the peak separation: around 120 mV is observed at 10 mV/s of scan rate on all electrospun nanofiber mats, regardless of treatment with heat alone or heat & KOH solutions. Such peak separation of those electrospun nanofiber mats is substantially narrower than that of a commercial carbon felt (977 mV at 3 mV/s), indicating much improved redox activity. The narrow peak separation and reasonably high current suggest that the treated electrospun nanofiber mats are promising candidates as electrodes for iron-based RFBs and other aqueous batteries.

Microfibril alignment induced by stretching fields during the dry-jet wet spinning process: Reinforcement on polyacrylonitrile fiber mechanical properties

The high-quality polyacrylonitrile (PAN) precursor fibers are indispensable for the manufacture of high-performance carbon fibers. For the purpose of regulating microfibril structures and improving fiber quality, scanning electron microscopy, high-resolution transmission electron microscopy and the nitrogen adsorption measurement were carried out to investigate the microfibril alignment evolution in PAN fibers, which was obtained by different stretching fields during dry-jet wet spinning process. The interconnected microfibrillar network forming in coagulation bath was plastically elongated and gradually developed into the oriented microfibrils while the transverse lamellae formed. Then break-reorganization of the lamellae brought the remarkable enhancement of fiber crystallinity during the hot-treatment process. Finally, the well-aligned and regular microfibrils appeared due to the deep plastic deformation. There were three stages in the total evolution of microfibril alignment: the plastic deformation of microfibrillar network, the fragmentation of the original lamella, and the formation and development of regular microfibrils. The microfibrils in PAN fibers were stacked by crystal layers in an order and tightly manner. Served as excellent reinforcing elements, aligned microfibrils could efficiently improve the fiber mechanical properties. Compared with nascent fiber, the tensile strength of PAN precursor fiber increased by 1492% and its tensile modulus enhanced by 574%.

Electrospun composite nanofibre supercapacitors enhanced with electrochemically 3D printed current collectors

Abstract Carbonised electrospun nanofibres are attractive for supercapacitors due to their relatively high surface area, facile production routes and flexibility. With the addition of materials such as manganese oxide (MnO), the specific capacitance of the carbon nanofibres can be further improved through fast surface redox reactions, however this can reduce the electrical conductivity. In this work, electrochemical 3D printing is used as a novel means of improving electrical conductivity and the current collector-electrode interfacial resistance through the deposition of highly controlled layers of copper. Neat carbonised electrospun electrodes made with a 30 wt% manganese acetylacetonate (MnACAC) and polyacrylonitrile precursor solution have a hydrophobic nature preventing an even copper deposition. However, with an ethanol treatment, the nanofibre films can be made hydrophilic which enhances the copper deposition morphology to enable the formation of a percolating conductive network through the electrode. This has the impact of increasing electrode electronic conductivity by 360% from 10 S/m to 46 S/m and increasing specific capacitance 110% from 99 F/g to 208 F/g at 5 mV/s through increased utilisation of the pseudocapacitive active material. This novel approach thus provides a new route for performance enhancement of electrochemical devices using 3D printing, which opens new design possibilities.

Development of a cost model for the production of carbon fibres

Carbon fibre composites offer considerable potential for mass reduction in automotive applications. However, raw material cost is one of the major factors that constraints its extensive use in this mass market. Here we report a systematic study that presents the cost contributors by considering the entire process chain of the carbon fibre manufacturing. The sensitivity analysis revealed that the final cost of Polyacrylonitrile (PAN) precursor and carbon fibres were strongly influenced by tow size. It was observed that a prompt decrease in the precursor and carbon fibre cost per kg for tow sizes from 3k to 12k, later this decrement was gradual and almost became stable above 50k. Moreover, with an increase in tow size from 3k to 50k, the contribution of the precursor on the final carbon fibre cost decreased from 76.6% to 49.6%. On the other hand, the contribution of the other factors increased with increase in the tow size, for instance, labour (9.86%–17.78%), Energy (2.49%–6.48%) and Depreciation (6.11%–11.01%). Nevertheless, precursor holds the major share in determining the final price of the carbon fibres.

Visualization of microfibrillar elements in cross-section of polyacrylonitrile fiber along the fiber spinning line.

The microfibrils served as the structural elements in polyacrylonitrile (PAN) fiber, which played an important role in the quality of the PAN precursor fibers. Their morphologies were examined by the scanning electron microscopy (SEM), atomic force microscopy (AFM) and high-resolution transmission electron microscope (HRTEM). The microfibrils existed in all of PAN fibers and arranged evenly in the cross-sections. Furthermore, the pores existed between the microfibrils. The unoriented microfibrillar network was already formed in nascent fiber during coagulated process. Although the microfibrillar network was elongated and the microfibrils oriented along the fiber longitudinal direction during the spinning process, the interconnected microfibrillar network was still existed in the fiber transverse section. Furthermore, the transverse connection of the microfibrils was reinforced and the small microfibrils were tended to aggregate into the large fibrils. For mechanical performance of PAN fibers, their tensile strength increased to 708 MPa and the elongation at break decreased to 15.5%. PAN fibers exhibited ductile rupture during the mechanical test and the microfibrils served as reinforcing elements.

Preparation, Stabilization and Carbonization of a Novel Polyacrylonitrile-Based Carbon Fiber Precursor.

The quality of polyacrylonitrile (PAN) precursor has a great influence on the properties of the resultant carbon fibers. In this paper, a novel comonomer containing the sulfonic group, 2-acrtlamido-2-methylpropane acid (AMPS), was introduced to prepare P(AN-co-AMPS) copolymers using itaconic acid (IA) as the control. The nanofibers of PAN, P(AN-co-IA), and P(AN-co-AMPS) were prepared using the electrospinning method. The effect of AMPS comonomer on the carbon nanofibers was studied using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Raman spectrum. The structural evolutions of PAN-based nanofibers were quantitatively tracked by FTIR and XRD during the thermal oxidative stabilization (TOS) process. The results suggested that P(AN-co-AMPS) nanofibers had the lower heat release rate (ΔH/ΔT = 26.9 J g−1 °C−1), the less activation energy of cyclization (Ea1 = 26.6 kcal/mol and Ea2 = 27.5 kcal/mol), and the higher extent of stabilization (Es and SI) during TOS process, which demonstrated that the AMPS comonomer improved the efficiency of the TOS process. The P(AN-co-AMPS) nanofibers had the better thermal stable structures. Moreover, the carbon nanofibers derived from P(AN-co-AMPS) precursor nanofibers had the better graphite-like structures (XG = 46.889). Therefore, the AMPS is a promising candidate comonomer to produce high performance carbon fibers.