Carbon Nanofiber Precursor Research Articles

Sustainable Lignin-Based 3D Porous Carbon Nanofibers As a Na-Ion Battery Anode

Rechargeable lithium-ion batteries (LIBs) have been increasingly popular in recent years in response to the growing need for large-scale energy storage applications and systems. However, due to the scarcity of lithium resources and their unequal distribution in the earth's crust, the present energy crisis has encouraged research into producing greener and more sustainable alternatives. Due to the relatively high abundance of sodium compared to lithium, sodium-ion batteries (SIBs) raise hope as an alternative and more sustainable chemistry.[1] Unfortunately, it is typically found that anode materials for LIBs are not suited for SIBs. Graphite, which is frequently used as an anode material in commercial LIBs, is incapable of achieving efficient Na+ insertion/extraction due to a lack of interlayer spacing (Na+ has a radius 39% bigger than Li+) and high energy involved in the formation of Na-C bonds..[2] So, to develop mechanically flexible electrode materials that combine high electrochemical performance with low-cost is still a challenge for its applications in a world subjected to severe shortage of resources and various environmental issues. The problem can be solved by selecting "green" and economically viable precursors and synthesis procedures. Carbon nanofibers derived from renewable biomass materials exhibit great potential as electrode materials with obvious cost and environmental benefits. Lignin, a heterogeneous and amorphous polymer found in many plants, and it is estimated that annual natural lignin production is 5-36×108 tons, of which more than 70 million tons are commercialized mainly from the paper industry as a by-product, is a possible choice as the precursor for carbon nanofibers due to its low cost and bio-renewable nature.In this work, mechanically flexible and 3D interconnected lignin/polylactic acid (PLA) carbon nanofibers with different amounts of lignin were prepared by electrospinning, then stabilized and carbonized. The obtained carbon nanofibers were characterized by scanning electron microscopy and transmission electron microscopy to investigate their morphology. To determine the carbon yield thermogravimetric analysis has been performed. Surface area, pore radius and volume values were obtained by performing BET analysis from N2 sorption isotherms. The obtained carbon nanofibers were tested as anode materiasl in 1 mol/L NaCF3SO3 in diethylene glycol dimethyl ether (DEGDME) electrolyte. Results show that lignin derived carbon nanofibers deliver a high reversible capacity of 330 mAhg-1 at the current density of 100 mAg-1 in the first cycle. Additionally, these carbon nanofibers showed excellent cycling and high-rate performance and maintained a capacity of up to 200 mAhg-1 for over 200 cycles. It is therefore, demonstrated that lignin derived carbon nanofibers prepared under appropriate conditions are promising anode material candidates for sodium-ion batteries.

Magnetic carbon nanofiber composite adsorbent through green in-situ conversion of bacterial cellulose for highly efficient removal of bisphenol A

A magnetic carbon nanofiber sorbent was facilely synthesized from bio-based bacterial cellulose and FeCl3via impregnation, freeze-drying, followed by pyrolysis at 700 °C, without additional activation or nanofiber fabrication. The obtained material possessed intrinsic 3D naturally fibrous and porous structure with good magnetization. The adsorption results showed that the adsorption capacity of the prepared adsorbent towards bisphenol A (BPA) was as high as 618 mg/g, outperforming other adsorbents. Moreover, recycling the adsorbent for 10 consecutive cycles retained 96% of initial adsorption efficiency. The magnetic sorbent can maintain good magnetic properties even with recycling. Hence, the use of bacterial cellulose as a renewable carbon nanofiber precursor and FeCl3 as a source of magnetic particles, and a green pore generating agent in the present protocol, lead to a superior magnetic carbon nanofiber adsorbent with sustainable characteristics.

Catalytic graphitization of bacterial cellulose–derived carbon nanofibers for stable and enhanced anodic performance of lithium-ion batteries

Bacterial cellulose (BC) produced through microbial fermentation has emerged as a viable precursor for carbon nanofibers (CNF) anode used in lithium-ion batteries. However, the low capacity and fading behavior of BC-derived CNFs render their usage in its pure form. Tuning the microstructure of CNFs in such cases plays an essential role in overcoming these negative ramifications and improves battery performance. In this study, the fermentation media used for BC production is modified by the addition of an iron catalyst, which can induce graphitization in the derived CNFs. Pure BC and catalyst-incorporated BC are pyrolyzed at 900 °C and 1800 °C to obtain CNFs, and the properties of derived CNFs are compared for understanding the role of incorporated catalyst. The structural, morphological, and electrochemical properties of CNFs are analyzed through X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, impedance spectroscopy, galvanostatic charge-discharge studies, and cyclic voltammogram studies. By possessing a higher graphitic content, catalyst-incorporated BC–derived CNFs exhibit an enhanced rate performance with a reversible capacity of 529 mAh g−1 after 100 continuous charge/discharge cycles at a current density of 0.2C.

Stabilization and Incipient Carbonization of Electrospun Polyacrylonitrile Nanofibers Fixated on Aluminum Substrates

Polyacrylonitrile (PAN) nanofibers, prepared by electrospinning, are often used as a precursor for carbon nanofibers. The thermal carbonization process necessitates a preceding oxidative stabilization, which is usually performed thermally, i.e., by carefully heating the electrospun nanofibers in an oven. One of the typical problems occurring during this process is a strong deformation of the fiber morphologies—the fibers become thicker and shorter, and show partly undesired conglutinations. This problem can be solved by stretching the nanofiber mat during thermal treatment, which, on the other hand, can lead to breakage of the nanofiber mat. In a previous study, we have shown that the electrospinning of PAN on aluminum foils and the subsequent stabilization of this substrate is a simple method for retaining the fiber morphology without breaking the nanofiber mat. Here, we report on the impact of different aluminum foils on the physical and chemical properties of stabilized PAN nanofibers mats, and on the following incipient carbonization process at a temperature of max. 600 °C, i.e., below the melting temperature of aluminum.

Polyacrylonitrile Nanofiber Optimization as Precursor of Carbon Nanofibers for Supercapacitors

Polyacrylonitrile (PAN) nanofibers are one of the primary precursors in the production of carbon nanofibers. The nanofiber morphology is significantly affected by the process parameters such as polymer concentration, distance, applied voltage and feed rate during the production of PAN nanofibers obtained by the solution-based electrospinning method, and these parameters should be optimized properly. In this study, firstly PAN nanofiber production parameters were optimized, and then homogeneous and thin PAN nanofibers produced in optimum conditions were used as the precursor in the production of carbon nanofibers. PAN nanofibers with a diameter of 233 nm were obtained at 7.5% PAN concentration in N,N-dimethylformamide (DMF), 28 kV applied voltage, 17.5 cm nozzle to collector distance, 2 ml/h feed rate and 500 rpm rotation speed of the aluminum drum. The carbon nanofiber diameters produced after the stabilization and carbonization processes were measured as 200 and 140 nm, respectively. The morphological, chemical and thermal properties of the produced nanofibers were characterized by field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR), thermogravimetric analyzer (TGA). Carbon nanofibers, which are made from optimized electrospun PAN nanofibers, can be used to construct supercapacitors in future studies.

Thermally Treated Graphene Oxide/Polyacrylonitrile Based Electrospun Carbon Nanofiber Precursor

Graphene oxide (GO) included polyacrylonitrile (PAN) composite electrospun nanofiber webs were fabricated, and thermal oxidation of PAN/GO composite nanofibers were performed at different temperatures (25, 250, 280, and 300 °C) for different time intervals (0, 1 and 3 h.) to investigate the oxidation process of PAN/GO nanofibers. The thermal oxidation process of PAN has a complex mechanism through the cyclization and dehydrogenation steps. For all oxidized samples, Electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared-Attenuated Total Reflectance (FTIR-ATR) Spectroscopic results were comparatively evaluated to investigate the effect of GO addition onto the nanofiber webs. After heat treatment, change in C1s spectra from virgin PAN to oxidized form was detected and sp² carbon is developed. The presence of GO accelerated the oxidation and development of the final structure. At shorter heat treatment time, less oxidized forms are obtained. The cyclization of nitrile pendant groups of PAN forming polyimine type structure is the main reaction occurs during stabilization. In addition to the imine sequences with three to six units long, the presence of polar groups C═O, OH and COOH in the chains facilitates the initiation of the cyclization process through a nucleophilic attack and accelerates the subsequent oxidative ring closure reactions which these newly formed bonds during thermal oxidation and stabilization steps play an essential role on the carbonization process as an intermediate form of PAN based structures.

Bacterial cellulose as a carbon nano-fiber precursor: Enhancement of thermal stability and electrical conductivity

Bacterial cellulose was selected as a potential precursor for the production of carbon nanofiber because of its high purity and crystallinity. Diammonium phosphate ((NH4)2HPO4) as a flame retardant was used to impregnate the cellulosic nanofiber sheet precursor in order to increase its thermal stability during the thermal processing. Also, the effect of heating rate on the stabilization and carbonization processes of cellulosic nanofiber samples was investigated. The precursor and resulted carbon nanofiber sheets were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and electrical characteristics. The results showed that the simultaneous usage of flame retardant (diammonium phosphate) and low heating rate in the stabilization process (2 °C min-1) increases thermal stability of cellulosic nanofiber sheets and the carbon yield. The presence of a flame retardant acts like a low heating rate effect but does not significantly affect the high heating rate of the stabilization process. As carbonization temperature increased, electrical conductivity and crystallite size were increased for impregnated samples. The carbonization process at 1200 °C, with a heating rate of 2 °C min-1, makes bacterial cellulose precursor an appropriate candidate for producing carbon nanofiber sheets with proper electrical characteristics.

Thermal stabilization of poly(acrylonitrile-co-itaconic acid) nanofibers as carbon nanofiber precursor

The thermal treatment of poly (acrylonitrile-co-itaconic acid), (P (AN-co-IA)) and polyacrylonitrile (PAN) under the oxygen atmosphere has a complex mechanism which strongly affects the properties of final product carbon nanofiber. Not only precursor composition but also oxidation treatment parameters play a key role in the achievement of the desired properties of the end product; carbon nanofiber. PAN and P (AN-co-IA) based nanofibers were fabricated via electrospinning technique and later treated at different temperatures to investigate the oxidation procedure in the presence of itaconic acid as a copolymer form. Description of the oxidation (thermal stabilization) route of nanofibers is challenging thus powerful characterization tools such as electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and FTIR-ATR are used for characterization and evaluated dependently. All obtained results are pointed out that; IA addition has a positive effect on the oxidation process in nanoscale in terms of reduction of applied temperature and time compared to homopolymer PAN. Spectroscopic results were also correlated with the equivalent Circuit Parameters of Electrochemical Impedance Spectroscopic Measurements, where oxidation and carbonization stages can be followed easily due to the formation of heterocyclic and conjugated structures by thermal treatments.

Nanocomposite structures of polypyrrole derivatives and poly (acrylonitrile‐co‐itaconic acid) produced by in situ polymerization as carbon nanofiber precursor

This study aimed to produce nanoparticles of poly (acrylonitrile‐co‐itaconic acid) (P (AN‐co‐IA)) containing conjugated polymers of pyrrole, N‐Methylpyrrole, 2,5‐dimethylpyrrole, and 1‐(Triisopropylsilyl)pyrrole which were synthesized by emulsion polymerization. Nanocomposite structures of P (AN‐co‐IA)/polypyrrole and polymer of pyrrole derivatives were produced via in situ polymerization, and the nanoparticle formation were followed by morphologic and ultraviolet‐visible (UV‐Vis) spectroscopic methods. Characterizations were made by Fourier transform infrared‐attenuated total reflectance (FTIR‐ATR) and Raman spectroscopy. Atomic force microscopy (AFM) was used for investigating the surface characteristics of the nanoparticles. Characterization results revealed that nanoparticles containing conjugated polymers had rougher surface than P (AN‐co‐IA) nanoparticles. It was also observed that the nanoparticles were well‐distributed although having some agglomerates. Moreover, depending on the type of monomer of conjugated polymer, the shape and size of the produced nanoparticles differed by conjunction with their polymerization rate. These findings can be used as a startup information for production of carbon nanofibers (CNFs) with desired properties after oxidation and carbonization, and as a high‐performance and cost‐effective flame and heat‐resistant material (oxidized copolymers of polyacrylonitrile nanofiber).

A Novel Carbon Nanofiber Precursor: Poly(acrylonitrile-co-vinylacetate-co-itaconic acid) Terpolymer.

This study aimed to produce poly(acrylonitrile-co-vinylacetate-co-itaconic acid) (poly(AN-co-VAc-co-IA)) terpolymer as a carbon nanofiber precursor. In this respect, terpolymer samples with different IA amounts were synthesized by free radical polymerization. Produced terpolymer samples were electrospun in order to obtain nanofibers which were then converted to carbon nanofibers. Obtained electrospun nanofibers were oxidized at different temperatures between 200-325 °C. After the oxidation process, carbonization process was applied at 1100 °C in the presence of N₂. Viscosity and molecular weight distribution of produced samples were measured with ubbelohde viscosimeter and gel permeation chromatography (GPC), respectively. Thermal features of the ter-polymer samples were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Spectroscopic characterization of terpolymer samples, oxidized and carbonized nanofibers were performed by Fourier transform infrared-attenuated total reflectance (FTIR-ATR). Original electrospun nanofibers, oxidized and carbonized nanofibers were investigated morphologically by scanning electron microscope (SEM). Inclusion of IA had considerable effect on terpolymer properties and electrospun nanofibers. Moreover, it was proven that oxidation temperature was a crucial parameter for carbon nanofiber production from terpolymer. Both morphology and color of the produced nanofiber mats changed when carbonization process was accomplished. It was observed that poly(AN-co-VAc-co-IA) terpolymer has lower initiation temperature when compared to poly(AN-co-VAc) and poly(AN-co-IA) copolymers, giving the opportunity to obtain carbon nanofibers easier, and poly(AN-co-VAc-co-IA) terpolymer can be used as an effective precursor for carbon nanofiber production.

Synthesis of special acrylic nanofibers as an appropriate precursor for conductive carbon nanofibers

Electrospinning technique is a significant approach used for producing special acrylic nanofibers (SANFs) through applying electrostatic field. SANFs were electrospun from polyacrylonitrile (PAN) copolymer solutions to be used as a precursor for carbon nanofibers (CNFs). The Box–Benkhen design (BBD) was used to elucidate the effects of the acrylic concentration (wt%), electrospinning voltage (kV), and spinning distance (cm) on the SANFs surface morphology and optimize these parameters. Based on BBD model the optimum SANFs diameter of 292 nm and 14.20% coefficient of variation, were collected at 9.3 wt% PAN concentration, 14 kV applied voltage, and 20 cm spinning distance. The optimized SANFs manufactured under BBD settings were specified by scanning electron microscope (SEM), mechanical tester, and differential scanning calorimeter (DSC). The optimized SANFs was stabilized in air and then carbonized in inert atmosphere at 800, 1000, and 1200 °C, respectively. The electrical conductivity of CNFs samples obtained from SANFs at 800 °C carbonization temperature is 2.31 × 10−2 S/cm, which is increased to 2.60 × 10+1 S/cm at 1200 °C. The results indicated that, the optimized SANFs possessed the most desired morphological properties, mechanical characteristics, and thermal stability; and thus they are appropriate for the development of high-performance CNFs.

Fabrication of carbon nanofiber electrodes using poly(acrylonitrile-co-vinylimidazole) and their energy storage performance

For electrodes in electrochemical double-layer capacitors, carbon nanofibers (CNFs) were prepared by thermal treatment of precursor polymer nanofibers, fabricated by electrospinning. Poly(acrylonitrile-co-vinylimidazole) (PAV) was employed as a precursor polymer of carbon nanofibers due to the effective cyclization of PAV polymer chains during thermal treatment compared to a typical precursor, polyacrylonitrile (PAN). PAV solutions with different comonomer compositions were prepared and electrospun to produce precursor nanofibers. Surface images obtained from scanning electron microscopy showed that their nanofibrous structure was well preserved after carbonization. It was also confirmed that electrospun PAV nanofibers were successfully converted to carbon nanofibers after the carbonization step by Raman spectroscopy. Carbon nanofiber electrodes derived from PAV showed higher specific capacitances and energy/power densities than those from PAN, which was tested by coin-type cells. It was also shown that PAV with an acrylonitrile/vinylimidazole composition of 83:17 is most promising for the carbon nanofiber precursor exhibiting a specific capacitance of 114 F/g. Their energy and power density are 70.1 Wh/kg at 1 A/g and 9.5 W/kg at 6 A/g, respectively. In addition, pouch cells were assembled to load the higher amount of electrode materials in the cells, and a box-like cyclic voltammetry was obtained with high capacitances.

Oxidative stabilization of polyacrylonitrile nanofibers and carbon nanofibers containing graphene oxide (GO): a spectroscopic and electrochemical study.

In this study, a precursor for carbon nanofibers (CNF) was fabricated via electrospinning and carbonized through a thermal process. Before carbonization, oxidative stabilization should be applied, and the oxidation mechanism also plays an important role during carbonization. Thus, the understanding of the oxidation mechanism is an essential part of the production of CNF. The oxidation process of polyacrylonitrile was studied and nanofiber webs containing graphene oxide (GO) are obtained to improve the electrochemical properties of CNF. Structural and morphological characterizations of the webs are carried out by using attenuated total reflectance Fourier transform infrared spectroscopy and Raman spectroscopy, scanning electron microscopy, atomic force microscopy and transmission electron microscopy. Mechanical tests are performed with a dynamic mechanical analyzer, and thermal studies are conducted by using thermogravimetric analysis. Electrochemical impedance spectroscopy, and cyclic voltammetry are used to investigate capacitive behavior of the products. The proposed equivalent circuit model was consistent with charge-transfer processes taking place at interior pores filled with electrolyte.

Synthesis and characterization of poly (acrylonitrile‐co‐acrylic acid) as precursor of carbon nanofibers

Synthesis of a co‐polymer of polyacrylonitrile (PAN) producing a carbon nanofiber out of PAN and co‐polymer of PAN and comparison between these products were examined. Free‐radical solution copolymerization of acrylonitrile (AN) with acrylic acid (AA) was studied. In this perspective, AA, and AN were used as a precursor for polymerization reactions; then copolymers were synthesized by using ammonium persulfate (APS) as an oxidant and carried in water/dimethylformamide (DMF) mixture. These polymers were used to obtain corresponding electrospun nanofibers. Synthesized P(AN‐co‐AA) was investigated by Fourier transform infrared spectroscopy‐attenuated total reflection (FTIR‐ATR) spectroscopy, and characteristic peaks for AN unit, AA were achieved. Thermal behavior was examined by using differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA), and results indicated that addition of monomers to AN unit reduced the Tg value of homopolymer PAN compared to P(AN‐co‐AA), which provides improvement to the cyclization and the formation of a thermally stable aromatic ladder polymer chain formation. In order to prevent the shrinkage and maintain the molecular orientation on nanofiber webs during stabilization, tension was applied to the samples, and thermal oxidation varies at 200–300°C for different duration of times. Surface morphology of the fibers was observed with scanning electron microscope (SEM), and average nanofiber diameter was found 550 nm, and after carbonization it was reduced to 320 nm for homopolymer PAN, and for poly(AN‐co‐AA) average nanofiber diameter was found as 220 nm and reduced to 130 nm, respectively. Copyright © 2016 John Wiley & Sons, Ltd.

Electrospun precursor carbon nanofibers optimization by using response surface methodology

Ultrafine fibers were electrospun from Polyacrylonitrile and N,N-dimethylformamide solution to be used as a precursor for carbon nanofibers. An electrospinning set-up was used to collect fibers with diameter ranging from 104 nm to 434 nm. Morphology of fibers and its distribution were investigated by varying Berry's number, charge density, spinning angle, spinneret diameter and collector area. A more systematic understanding of process parameters was obtained and a quantitative relationship between electrospinning parameters and average fiber diameter was established by using response surface methodology. It was concluded that; Berry's number, charge density and spinneret diameters played an important role to the diameter of nanofibers and its standard deviation. Spinning angle and collector area had no significant impact. Based on response surface methodology the optimum Polyacrylonitrile average fiber diameter of 280 nm and 28 nm standard deviation, were collected at 1.6 kV/cm charge density, 8 Berry's number and 0.9 mm spinneret diameter.

Electrospun Nanofibers of Acrylonitrile and Itaconic Acid Copolymers and their Stabilization

(APS) as an oxidant in the aqueous medium,and nanofibers produced by electrospinning . Electrospun nanofiber mats were by treated heat under air atmosphere to be stabilized. Nanofiber production from AN-IA copolymers and suitability of the nanofiber as carbon nanofiber precursor is discussed. Copolymer are characterized using Fourier Transform Infrared - Attenuated Total Reflectance spectrometer (FTIR-ATR), Nuclear Magnetic Resonance Spectroscopy (1H-NMR), differential scanning calorimeter (DSC), thermal gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The effect of IA content on the spectroscopic and thermal properties of AN-IA copolymers was investigated. Increasing IA content confirmed by spectroscopic methods seriously affects thermal properties which is important for carbon nanofiber production. IA provides a catalytic effect on stabilization process by decreasing initiation cyclization reaction temperature from 202 to 195 oC. Elecrospinning from the AN-IA copolymer solutions in dimethyl foramide (DMF) was performed, morphology of nanofibers was monitored using Scanning Electron Microscopy (SEM). Bead free nanofibers were produced from AN-IA copolymer solutions under same conditions. Average nanofiber diameter decreases from 878±18 to 376±7 nm according to increasing IA content in copolymers. The nanofiber mats produced were treated at high temperature under air atmosphere for oxidative stabilization. Stabilized nanofibers were characterized using FTIR-ATR spectrometer and a new structure was monitored as a result of cyclization reactions. The stabilized nanofibers were also characterized mophologically using SEM. Volume loss occurring after heat treatment calculated based on the nanofiber diameter changes. Consequently, electrospun nanofibers can be suggested as a carbon nanofiber precursor due to suitability for electrospinning and stabilization process.

Acrylonitrile/vinyl acetate copolymer nanofibers with different vinylacetate content

AbstractIn this study, free radical copolymerization of acrylonitrile (AN)–vinyl acetate (VAc) was performed for five different feed ratio of VAc (wt %) by using ammonium persulfate (APS) in the aqueous medium. The effect of VAc content on the spectrophotometric and thermal properties of AN–VAc copolymers was investigated by Fourier Transform Infrared–Attenuated Total Reflectance spectrophotometer (FTIR–ATR), differential scanning calorimeter (DSC), and thermal gravimetric analyzer (TGA). Thermal stability of homopolymer of AN is improved after being copolymerized. The electrospun P(AN‐co‐VAc) nanofibers were fabricated and the effect of VAc content on the morphologic properties of nanofibers was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The viscosity of the solution had a significant effect on P(AN‐co‐VAc) electrospinning and the nanofiber morphology. The average diameters of P(AN‐co‐VAc) nanofibers decreased 3.4 times with increasing feed ratio of VAc wt %. The P(AN‐co‐VAc) electrospun nanofiber mats, with the feed ratio of 30 wt % VAc, can be used as a nanofiber membrane in filtration and as a carbon nanofiber precursor for energy storage applications due to high surface to volume ratio, high thermal stability, homogeneous, and thinner nanofiber distribution. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Preparation of Carbon Nanofibers from Polyacrylonitrile Nanofibers by Electrospinning

Ultrafine fibers were electrospun from polyacrylonitrile (PAN)/N,N-dimethyl formamide (DMF) solution as a precursor of carbon nanofibers. The effects of solution concentration, applied voltage and flow rate on preparation and morphologies of electrospun PAN fibers were investigated. Morphologies of the green fibers, stabilized fibers and carbonized fibers were compared by scanning electron microscope (SEM). The diameter of PAN nanofibers is about 450nm and the distribution of diameter is well-proportioned. Characterization of the elements changes of fibers were performed by X-ray photoelectron spectroscopy (XPS).

Pre-Oxidation Nanofibers from Acrylonitrile-Acrylamide Copolymers Synthesized by Solvent-Water Polymerization

Solvent-water suspension free-radical polymerization method was used to synthesize acrylonitrile(AN)-acrylamide(AM) copolymers in this paper. The copolymerization was carried out with azobisisobutyronitrile (AIBN) as an initiator and dimethysulfoxide (DMSO)/ water solution as solvents at a constant monomer ratio (AN:AM(wt)=85:15). The ratio(wt) AN:AM=100:0 was also be used for a comparison. The structure and properties of the copolymers was studied by fourier transform infrared (FT-IR), X-ray diffraction (XRD) and thermogravimetry(TG). The nanofibers were obtained by electrospinning AN-AM copolymer solution with N,N-Dimethyl acetamide(DMAc) as a solvent. Then, the fibers were pre-oxidized in relaxation state and in air by using an oven. The structure of pre-oxidized nanofibers was investigated by scanning electron microscopy (SEM) and FT-IR. The results showed that the ratio of dimethysulfoxide (DMSO)/water 50/50(v) was optimum for the copolymer properties and nanofiber spinnability as a carbon nanofiber precursor. The copolymer fibers only needed lower preoxidation temperature and shorter preoxidation time to reach the same degree of cyclization due to the introduction of AM.

An investigation on the stabilization of special polyacrylonitrile nanofibers as carbon or activated carbon nanofiber precursor

This paper reports the effect of the conditions of stabilization process on the properties of special polyacrylonitrile nanofibers (SAF) with an average diameter of 467 nm. Stabilization constitutes an important pretreatment for the production of either carbon fibers or activated carbon fibers. It was found that the higher the stabilization temperature, the lower the initial induction time and the total reaction time. Extent of reaction increases with both treatment time and temperature of stabilization process. Crystallinity index and crystal size of stabilized nanofibers decreases as a result of stabilization. Special polyacrylonitrile nanofibers containing itaconic acid shows a higher capability for stabilization process. Potassium permanganate as a catalyst leaves a positive effect on the extent of reaction of stabilization. The diameter of nanofibers decreases by about 20% as a result of stabilization at 250 °C. Thermally stabilized nanofiber shows a wider exothermic peak with a lower height.