Polyacrylonitrile Fibers Research Articles

Investigation of the Microstructure of PAN Precursor Fibers Obtained at Various Processing Stages

The production of high-performance carbon fibers relies heavily on the structural transformations of polyacrylonitrile (PAN) fiber during processing. In this article differential scanning calorimetry (DSC), synchrotron small-angle X-ray scattering (SAXS), and synchrotron wide-angle X-ray diffraction (WAXD) were used to study the changes of the thermal properties, voids and crystal structure of the PAN precursor fibers on industrial lines during the continuous processing stages, i.e., after the treatment in the coagulation bath, after stretching in boiling water and after stretching in high-temperature steam. The findings of this study suggest that after boiling water stretching the molecular chain motion of the PAN precursor fiber weaken, resulting in the expansion of the voids. After high-temperature steam stretching the voids became elliptical and oriented in the stretching direction. Although the boiling water stretching process partially damaged the (100) crystal planes of the PAN precursor fibers, it does not hinder their overall crystalline structure. The high stretching ratio primarily affected the orientation of the molecular chains. This orientation, even in the context of partial crystal plane disruption, further promoted the crystallization of the (100) crystal planes in the fibers. These experiments explored the correlation between the processing technology and fiber structure transformation of PAN-based carbon fibers, resulting in producing a guide for the preparation of high-performance carbon fibers with fewer defects.

Occupational health risk for workers in the production of synthetic polyacrylonitrile fibers

The high proportion of workers in the chemical industry working in hazardous working conditions and the justification of measures to preserve their health are an urgent task in the field of protecting the health of the working population, however, aspects of the formation of occupational risks in the production of chemical fibers remain insufficiently studied. The article presents the results of prospective cohort comprehensive studies of working conditions and health status of 137 workers in the production of polyacrylonitrile fibers. The factors of the working environment (chemical, microclimate, noise), the severity and intensity of the labor process, the first identified and chronic non-infectious morbidity for 2017–2021 were studied. It has been established that workers work under the influence of a complex of factors harmful to their health, including chemicals of hazard classes 1–4 (acrylonitrile, methyl acryate, hydrocyanide, sulfuric acid, caustic alkalis, ethylene glycol, isopropyl alcohol), industrial noise, physical and neuro-emotional overloads, the levels of which, to varying degrees, exceed the hygienic standards, forming harmful working conditions (classes 3.1–3.4). In the structure of the accumulated chronic morbidity of workers, the leading ranking places belonged to diseases of the musculoskeletal system and connective tissue (24.3 %), the circulatory system (16.04 %), and the genitourinary system (15.0 %). As a result of the assessment of cause-and-effect relationships of health disorders with work, the production conditionality of diseases of the musculoskeletal system and connective tissue, represented by dorsalgia of various levels, of an average degree (RR = 1.893; EF = 47.183 %; CI = 1.192–3.007) was established. Quantitative assessment of group occupational risk corresponded to the category of «high risk» (4.780 × 10–2), indicating the need to reduce it to an acceptable level. The limitation of the study was the study of occupational risk factors for health disorders among employees of one enterprise. The results obtained were used to develop measures to reduce occupational health risks for workers in the production of synthetic polyacrylonitrile fibers.

A vertically translating collection system to facilitate roll-to-roll centrifugal spinning of highly aligned polyacrylonitrile nanofibers

Centrifugal spinning is a fiber spinning method capable of producing fibers in the nanoscale diameter range from a multitude of polymers, including polyacrylonitrile (PAN). With a traditional centrifugal spinner, fiber can be rapidly spun and collected on static collection posts. However, the use of posts inevitably forms a dense fiber “ring” that is incompatible with roll-to-roll manufacturing processes. In this work, factors that influence throughput and scalability of highly aligned centrifugally spun PAN fibers are explored. A custom centrifugal setup is used to vertically translate collected fibers during the spinning process to distribute them over a large surface area. In addition, factors that affect PAN fiber diameter during the spinning process are investigated, including spinneret to collector distance, rotational speed, and humidity. Resulting data demonstrates that these factors can be independently optimized to reliably produce quality PAN fiber in the nanoscale diameter range. Furthermore, the fiber mass collection rate can be increased without affecting sample quality when the vertical translation speed is increased. This work demonstrates the potential scalability of centrifugal spinning to quickly produce large amounts of highly aligned nanofiber in a cheap, efficient, and reliable manner, and also lends the ability to be collected in a roll-to-roll fashion.

Carboxyl and polyamine groups functionalized polyacrylonitrile fibers for efficient recovery of copper ions from solution.

Heavy metals (e.g., Cu) in wastewater are attractive resources for diverse applications, and adsorption is a promising route to recovery of heavy metals from wastewater. However, high-performance adsorbents with high adsorption capacity, speed, and stability remain challenging. Herein, chelating fibers were prepared by chemically grafting amine and carboxyl groups onto the polyacrylonitrile fiber surface and used in the wastewater's adsorption of Cu2+. The adsorption behavior of Cu2+ on the fibers was systematically investigated, and the post-adsorption fibers were comprehensively characterized to uncover the adsorption mechanism. The results show that chelated fiber has a 136.3mg/g maximum capacity for Cu2+ adsorption at pH = 5, and the whole adsorption process could reach equilibrium in about 60min. The adsorption process corresponds to the quasi-secondary kinetic and Langmuir models. The results of adsorption, FTIR, and XPS tests indicate that the synergistic coordination of -COOH and -NH2 plays a leading role in the rapid capture of Cu2+. In addition, introducing hydrophilic groups facilitates the rapid contact and interaction of the fibers with Cu2+ in the solution. After being used five times, the fiber's adsorption capacity remains at over 90% of its original level.

A simplified numerical simulation of uniaxial compression for polyacrylonitrile fiber reinforced permeable concrete based on CT images

For fiber reinforced permeable concrete, numerical simulation method have been applied to reduce the time consumption of physical experiments and to study the mesostructure of the material. In this paper, polyacrylonitrile fiber reinforced permeable concrete (PANFRPC) is considered to consist of aggregate, mortar (containing fibers inside), interface transition zone (ITZ) and pores in 3D mesostructure model generated from computer tomography (CT) images. For the numerical simulation of the, material properties of each component in the model are assigned according to physical experimental results. The failure curve of the mortar in PANFRPC is determined by physical test results to reflect the effect of fibers. The simulation results show that the model has similar mechanical properties to the actual specimen and can be used to simulate the elastic stage of the uniaxial compression process and predict the strength with an error of less than 15% despite the simplification of fiber. the accuracy and reliability of the model have also been verified by the distribution pattern of vertical caraks and x-shaped shear cracks from macro and meso perspectives.

Application of dynamic image analysis to the optical characterisation of fibrous bulk material

Dynamic image analysis provides an automated evaluation method to determine the size and shape of multiple particles. This method represents a common application for ordinary bulk material. The latest draft of ISO 13322–2:2021 describes the state of the art, but lacks instructions for handling fibrous bulk material. Interlocking fibres complicate the measurement conditions and require a disentanglement of fibrous samples during a pre-dispersion step. A further error source includes the fibre orientation inside the measurement zone of the device. If the thresholding algorithm fails to differentiate between the fibre projection area and the background, a subsequent image optimisation solves the problem. This article addresses the mentioned problems by analysing cotton cellulose and polyacrylonitrile fibres. Besides the execution of a pre-dispersion step, the experiments compare the discrepancies between dry and wet dispersion. Here, the software packages PAQXOS and ImageJ perform the image evaluation. In this case, the wet dispersion setup with a subsequent image evaluation by ImageJ provides comprehensible results.

Controlled preparation and chemical actuation of polyacrylonitrile fibers

Pure polyacrylonitrile (PAN) fibers with diameter size at micrometric scale were obtained and collected radially using an immersion-jet wet spinning .system. This technique is a fast and easy approach to fabricate micrometric PAN fibers. The diameter of the fiber can be easily controlled by adjusting the size of the spinneret. Uniform, smooth and continuous PAN microfibers were suitable modified by thermal stabilization and alkaline saponification to obtain pH-sensitive fibers. The effect of diameter size fiber on the chemical actuation behavior was investigated in terms of length change characteristics under the influence of pH solution. The microfibers showed expanding/contracting behavior and force generation stimulated by changes in the environment pH. The fibers structural and chemical properties were characterized using the FT-IR spectroscopy and SEM microscopy techniques.

Efficient removal of U(VI) from wastewater by a sponge-like 3D porous architecture with hybrid electrospun nanofibers

Removal of uranium(VI) from nuclear wastewater is urgent due to the global nuclear energy exploitation. This study synthesized novel sponge-like 3D porous materials for enhanced uranium adsorption by combining electrospinning and fibrous freeze-shaping techniques. The materials possessed an organic–inorganic hybrid architecture based on the electrospun fibers of polyacrylonitrile (PAN) and SiO2. As a supporting material, the surface of fibrous SiO2 could be further functionalized by cyano groups via (3-cyanopropyl)triethoxysilane. All the cyano groups were turned into amidoxime (AO) groups to obtain a amidoxime-functionalized sponge (PAO/SiO2-AO) through the subsequent amidoximation process. The proposed sponge exhibited enhanced uranium adsorption performance with a high removal capacity of 367.12 mg/g, a large adsorption coefficient of 4.0 × 104 mL/g, and a high removal efficiency of 97.59%. The UO22+ adsorption kinetics perfectly conformed to the pseudo-second-order reaction. The sorbent also exhibited an excellent selectivity for UO22+ with other interfering metal ions.

Interaction between thermal stabilization temperature program, oxidation reaction, and mechanical properties of polyacrylonitrile (PAN) based carbon fibers

Thermal stabilization is a very time-consuming process from PAN fibers to carbon fibers and seriously affects the structure and properties of the final carbon fibers. In this study, the thermal stabilization of PAN fibers is accomplished through two steps, taking 12 k PAN fibers as an example. That is, firstly, the preliminary thermal stabilization is done by optimizing the temperature range (220–240 °C) to achieve the rapid establishment of the trapezoidal structure. Then, the completed thermal stabilization is done by holding at a lower temperature (240 °C) to refine the oxidized structure. Discussions focused on the establishment of the optimized temperature range in the preliminary thermal stabilization and the effect of insulating at different temperatures during the completed thermal stabilization on the development of the structure and properties of the carbon fibers. It was confirmed that the use of this process to accomplish thermal stabilization of PAN fibers reasonably reduced the process time and energy consumption for thermal stabilization and improved the mechanical properties of the final carbon fibers. Moreover, it is applicable to optimize the thermal stabilization temperature program for all commercially available PAN fibers with different tow specifications and properties without any additional conditions.

Recyclable bispyridine functionalized polyacrylonitrile fibers as ligand of Cu(II) for A3 coupling reaction

Developing an effective and economical technology to achieve the recovery of catalysts in the process of organometallic synthesis has attracted significant attention. Herein, a novel functional fiber catalyst with bispyridine structure was successfully constructed by modifying the commercial polyacrylonitrile fiber. Modified bidentate ligand fiber-based can be used to efficiently complexe Cu(II). The functional fibers were fully characterized by FTIR, ICP, XPS, XRD, SEM, and TGA. To verify the catalytic activity of PANbis(Py)-Cu(II)F, A3 coupling reaction was applied in this work. The results showed that only 0.1 mol% catalyst dosage was needed and the maximum isolated yield was up to 99%. Recycle experiments showed that PANbis(Py)-Cu(II)F has fine recycling performance, and there is no decrease in catalytic efficiency during the first six cycles. Consequently, as a recyclable functional fiber catalyst based on commercial polyacrylonitrile fiber, it provided a new insight for green synthesis and industrial production.

Promoting photo-Fenton reactions by anchoring Fe doped g-C3N4 onto an amidoxime-functionalized fibrous support for organic contaminants removal

Fe-doped graphitic carbon nitride (g-C3N4) represents an attractive photo-Fenton catalyst for organic contaminants removal, but the practical performances still need to be improved for large-scale application. Herein, we developed a high-efficiency photo-Fenton catalyst by anchoring Fe-g-C3N4 onto an amidoxime-functionalized polyacrylonitrile fiber (AP) substrate through a simple hydrothermal approach. Comprehensive characterizations demonstrate the strong catalyst-support interaction via the axial coordination bonding between -OH groups and Fe3+, which could induce electric polarization of Fe-g-C3N4 to promote the H2O2 adsorption and activation. The fibrous support could also accelerate the photoelectrons transfer from g-C3N4 to Fe3+ by strengthening the d-π conjugated large π bond, as well as alleviate the backflow recombination from Fe3+ to g-C3N4 through the electron sink effect. These synergistic qualities resulted in superior photo-Fenton performance for organic contaminants removal, which delivered 4.0-fold higher degradation kinetics than that of the Fe doped g-C3N4 powder catalyst and exhibited unexpected high activity at strong basic environment (pH = 12). Our work demonstrates an ingenious and simple way to design exceptional photo-Fenton catalysts for environmental remediation.

Investigating the Effect of Fixation Tension on the Thermal Analysis Process and Crystal Structure of Polyacrylonitrile (PAN) Fibers

Thermal analysis of polyacrylonitrile (PAN) fibers is commonly employed to assess the chemical and physical changes occurring during the pre-oxidation stage. However, in actual pre-oxidation processes, PAN fibers are stretched to a certain extent (approximately 5%) to prevent fiber shrinkage. Consequently, the pre-oxidation process of PAN fiber is influenced not only by temperature and atmosphere but also by the stretching tension. In this study, two types of PAN fiber samples with different crystal structures were utilized alongside four different processing methods (PAN powder, unfixation, physical fixation, and chemical fixation) to generate three degrees of fixed stretching. These included PAN powder and unfixed PAN fiber samples (without fixation tension), physically fixed PAN fiber with relatively weak fixation tension, and chemically fixed PAN fiber with strong fixation. Through a comparison of these samples, it was observed that the fixation tension aided in preserving the crystal structure during the heating process, significantly reducing the cyclization rate of the PAN fibers. The cyclization reaction rate of PAN fiber A, initially at 85% without any fixation, decreased to 66% after physical fixation and dropped to 56% after chemical fixation. For PAN fibers with distinct crystal morphologies, the impact of the fixation tension was more prominent for PAN fibers with larger crystal sizes and lower orientation. Additionally, the presence of crystal orientation facilitated the occurrence of the cyclization reactions.

Chemical reaction and phase transformation mechanism of electrospun iron (III) acetylacetonate-polyacrylonitrile fibers during pre-oxidation process

Low-temperature pre-oxidation of electrospun metal-compound-incorporated carbon fibers can involve phase transitions and chemical reactions. However, their mechanics remain unclear. In this work, a mixture of polyacrylonitrile (PAN) and iron acetylacetonate is subjected to electrospinning followed by a pre-oxidation process at 230 °C, producing PAN fibers loaded with iron compounds. Our detailed investigations shed light on the mechanisms of phase transitions and associated chemical reactions during the pre-oxidation process. Our findings reveal that PAN undergoes cyclization during pre-oxidation, and that crystalline iron acetylacetonate within PAN fibers transforms into amorphous FeO and Fe2O3.

Research on Improving the Pre‐Oxidation Process of the Excellent Mechanical Strength Carbon Fiber

AbstractThis study uses synchrotron wide‐angle X‐ray diffraction (WAXD) and synchrotron small angle X‐ray scattering (SAXS) to carry out an in situ study of the pre‐oxidation process of polyacrylonitrile (PAN) fibers with two different preparation processes. Through analysis of 2D WAXD/SAXS data, this study divides the evolution of PAN fiber's crystal and microporous structures during pre‐oxidation into three and two stages, respectively. The evolution of PAN fiber's crystal structure during pre‐oxidation can be divided into three stages: 1) Initial stage: small‐sized crystals melt, crystal orientation decreases, and no cyclization reactions occur. 2) Intermediate stage: cyclization reactions happen in the amorphous region, leading to increased crystal size, crystal orientation, and crystallinity. 3) Final stage: cyclization reactions occur in the crystal region, resulting in reduced crystal size and orientation. The evolution of microporous structure can be divided into two stages: microporous shrinkage stage and microporous expansion stage. These features are analyzed using 2D WAXD/SAXS techniques. This study provides valuable references and guidance for the industrial production of PAN fibers by exploring the mechanism of the pre‐oxidation process in‐depth.

Investigation of the Effect of Needle Diameter and the Solution Flow Rate on Fiber Morphology in the Electrospinning Method

Abstract In the study, the morphological properties of polyacrylonitrile (PAN) fibers produced by electrospinning at different needle diameters and solution flow rates were investigated. For this purpose, 20G and 22G diameter needles were used. The fibres were produced at flow rates of 0.5 ml/hr, 1 ml/hr and 1.5 ml/hr. Scanning electron microscopy (SEM) was used to measure nanofiber diameters. Statistical analyzes were made with the help of the SPSS program. It was observed that finer fibers were obtained as the needle diameter decreased. As the solution flow rate increased, thicker fibers were obtained. In addition, it was observed that the needle diameter and flow rate affect the fiber arrangement and interfiber spacing.

Integrating V-doped CoP on Ti3C2Tx MXene-incorporated hollow carbon nanofibers as a freestanding positrode and MOF-derived carbon nanotube negatrode for flexible supercapacitors

Novel architectural electrode materials that are freestanding and exhibit improved electrochemical performances in flexible asymmetric supercapacitors are urgently needed; however, designing these materials is challenging. Herein, a Ti3C2TX MXene-aligned hollow carbon fiber (MX/HCF) is engineered and vanadium-doped cobalt phosphide nanorod arrays are grown on it (V-CoP@MX/HCF) and applied for supercapacitor positrode. V doping modulates the surface structure and electronic environment of CoP nanorods grown over conductive and flexible MX/HCFs. As expected, the optimized V-CoP@MX/HCF exhibits a better electrochemical performance (1896.8Fg−1) than that of CoP@MX/HCF and CoP@HCF. For the negative electrode, zeolitic imidazolate framework-67 (ZIF-67) grown on electrospun polyacrylonitrile (PAN) fibers is converted to cobalt nanoparticle-encapsulated nitrogen-doped carbon nanotubes at carbon nanofibers (Co-CNT@CNF) by a simple heat treatment without the burden of external catalysts and reducing gases. The as-designed freestanding Co-CNT@CNF delivers a specific capacitance of 405.5Fg−1 with superior cycling stability. A flexible asymmetric supercapacitor (V-CoP@MX/HCF//Co-CNT@CNF) is designed that unveil remarkable electrochemical properties, such as a high energy density of 72.4 Wh kg−1 at 800.12 W kg−1 and good capacitance retention (91.4 %) after 10,000 charge/discharge cycles. Furthermore, the device can maintain a consistent performance regardless of the bending degree. More importantly, this work provides new opportunities to rationally design novel freestanding cathodes and anodes for high-performance flexible asymmetric supercapacitors.

Effect of structural evolution in high‐temperature thermal oxidative stabilized polyacrylonitrile fibers on carbonized fibers

AbstractThe effect of structure and properties of polyacrylonitrile (PAN) fibers during thermal oxidative stabilization (TOS) stage (especially high‐temperature TOS stage at 270–300°C) on the skin‐core structure of carbonized fibers was studied. The work clarified the reasons for selecting the highest TOS temperature, and also determined the optimal TOS temperature range of obtaining structurally stable carbonized fibers. The changes of chemical groups were quantitatively calculated by a combination of peak‐fitting and second‐order derivative methods. The results showed that the cyclization was dominant in the early TOS stage, oxidation reaction mainly occurred in the post‐TOS stage, and crosslinking structure significantly increased after 250°C. In the high‐temperature TOS stage, cyclization reaction was basically completed, the growth rate of oxygen content slowed down, and dehydrogenation index continued to increase. The microstructure observation found that the grooves on the fiber surface were gradually smooth after low‐temperature and high‐temperature carbonization. The radial structure of A285‐1350 and A300‐1350 fibers have obvious heterogeneity, and diameter dropped below 5 μm. Therefore, carbonized fibers have obvious structural defects when the TOS temperature is above 285°C. The TOS temperature between 200 and 285°C is more conducive to obtain structurally stable carbonized fibers.

Critical Electrospinning Parameters for Synthesis Control of Stabilized Polyacrylonitrile Nanofibers.

Polyacrylonitrile (PAN) fibers are widely used as precursors in the manufacture of high-conducting and mechanically resistant carbon fibers. The modulation of such fibers is carried out through electrospinning. In this work, we show the production and control of the morphology of nanometric-range PAN fibers for their potential use as precursors for high-electrical-conductivity carbon fibers. PAN samples dissolved in dimethylformamide (DMF) were prepared at 6, 10, and 12% w/w, at 15 and 25 kV. The impact of the rotation of the collector drum at 100, 300, and 500 RPM was also studied. It was found that the percentage of PAN in the solution proportionally affects the diameter of the fibers and that the preparation potential affects the morphology. The rotation speed, when increased, decreases the diameter, and it has a negative impact on the morphology. Fibers prepared with 6% w/w at 15 kV and 500 RPM show 90 nm diameters, the smallest diameter of all the samples.

Обоснование закона распределения и статистических характеристик длины нитей фибры для армирования асфальтобетонной смеси

The paper describes the distribution of polyacrylonitrile roving filaments lengths in terms of risk theory by the normal distribution law. We identify the optimal fiber length experimentally. However, it depends on the type of fibrous material, its optimal dosage as a percentage by weight of asphalt concrete mixture, and fiber density. Also research dwells on the statistical methods of identifying the standard deviation of the cut length of fibre filaments on special cutting equipment which provides the substantiation of the law of distribution of fibre filament lengths. The results ensure the risk assessments and reliability of reinforcement of asphalt concrete mixture with polyacrylonitrile fiber. Moreover, according to the research, density of polyacrylonitrile fiber filaments affects the spread of the distribution law of the lengths of the filaments as follows: the higher the density, the lower the standard deviation of the cut fibre lengths; the denser the polyacrylonitrile fibre filaments, the lower the variability of the cut filament lengths.

Improving flame retardancy, fume suppression and mechanical properties of SBS modified binder using nano-porous fibers prepared by electrospinning

The current study utilizes polyacrylonitrile (PAN) as the foundational material, augmented with multi-walled carbon nanotubes (MWCNTs) and nano-calcium carbonate (nCC) as additives. Utilizing electrospinning techniques, micro-nanoscale composite fibers possessing elevated surface areas (MCE-PAN) were synthesized. Experimental data indicate that MCE-PAN enhances both the flame-retardant and mechanical attributes of the modified asphalt binder. Specifically, MCE-PAN elevates the limiting oxygen index (LOI) of the modified asphalt binder by 25.24%, increases smoke suppression efficiency by 10.67%, elevates the decomposition temperature by 105℃, and substantially curtails smoke emission. MCE-PAN manifests significant hydrophobic characteristics, thus augmenting the interfacial interactions between PAN fibers and the asphalt binder. Additionally, at an ambient temperature of 46℃, the complex modulus (G*) of the MCE-PAN/SBS/MA modified asphalt binder, with a 0.1% loading, surged by 52% relative to the SBS modified asphalt binder (SBS/MA); the storage modulus (G') escalated by 101.4%, and the loss modulus (G'') increased by 75.6%. Under low-temperature conditions, the MCE-PAN/SBS/MA modified asphalt binder demonstrates enhanced resistance to crack propagation. This investigation not only introduces an innovative approach to fiber synthesis but also elucidates its applicability in augmenting the performance and flame retardancy of asphalt pavements. It thereby holds significant practical, environmental, and energy-saving implications for sustainable, flame-retardant asphalt pavement, particularly in tunnel applications and high-temperature settings.