静电纺丝制备聚丙烯腈纳米纤维及其预氧化

利用聚丙烯腈／二甲基甲酰胺纺丝溶液由静电纺丝制备了聚丙烯腈纳米纤维,纳米纤维的直径在220～760nm。随着聚合物溶液浓度和纺丝施加电压的升高,纳米纤维的直径变大。采用热分析和热重分析研究了纳米纤维的热性能,还用红外光谱对纳米纤维预氧化过程分子化学结构的变化进行了表征,结果表明,纳米纤维有一个很尖锐的放热峰,是聚丙烯腈均聚物典型的放热峰。随着预氧化温度的升高,纤维的内部分子结构发生了变化,表现在红外光谱上最突出的是C≡N在2243～2241cm^-1峰的降低,以及C—H在1684cm^-1峰的降低。     

Graphitic carbon nanofibers developed from bundles of aligned electrospun polyacrylonitrile nanofibers containing phosphoric acid

Graphitic carbon nanofibers (GCNFs) with diameters of approximately 300 nm were developed using bundles of aligned electrospun polyacrylonitrile (PAN) nanofibers containing phosphoric acid (PA) as the innovative precursors through thermal treatments of stabilization, carbonization, and graphitization. The morphological, structural, and mechanical properties of GCNFs were systematically characterized and/or evaluated. The GCNFs made from the electrospun PAN precursor nanofibers containing 1.5 wt.% of PA exhibited mechanical strength that was 62.3% higher than that of the GCNFs made from the precursor nanofibers without PA. The molecules of PA in the electrospun PAN precursor nanofibers initiated the cyclization and induced the aromatization during stabilization, as indicated by the FT-IR and TGA results. The stabilized PAN nanofibers possessed regularly oriented ladder structures, which facilitated the further formation of ordered graphitic structures in GCNFs during carbonization and graphitization, as indicated by the TEM, XRD, and Raman results.     

Comparative investigation on the thermal degradation and stabilization of carbon fiber precursors

Thermal degradation and stabilization of two kinds of polyacrylonitrile (PAN) fibers have been investigated by a combination of FT-IR, differential scanning calorimetry (DSC), modulated DSC, thermogravimetry (TG), thermal shrinkage behavior, in situ mass spectrometry (MS), and tensile property examinations. The two types of precursor fibers exhibit distinct properties after oxidative stabilization, but they can both make carbon fibers with equivalent mechanical properties. Compared with PAN/itaconic acid precursor fibers, the fibers containing acrylamide comonomers show a doublet appearance, broader exothermic peak, lower threshold degradation temperature, and more amount of heat evolved in DSC thermogram, which is favorable to obtain uniform microstructures in oxidative stabilization process. The two types of samples produce different ring structures in the thermal degradation and stabilization process, as evidenced by results from tensile test, TG–MS and thermal shrinkage behavior analyses. In addition, the molecular rearrangement or melting of ordered structures accompanying with nitrile polymerization was also detected from modulated DSC.     

Processing and characterization of carbon nanofibers obtained from PAN/lignin blends processed by electrospinning

Blankets based on blends with different PAN/lignin ratios (10 and 50% wt. of lignin) were processed via electrospinning. Then, the blankets obtained were thermally treated in order to produce samples of carbon nanofibers. The thermo-oxidative stabilization parameters were defined based on a 2³-factorial design. The samples, after stabilization, were analyzed by differential scanning calorimetry (DSC), thermogravimetry (TGA), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR) techniques. Based on the results, the best parameters for the stabilization of electrospun, blankets were selected, and subsequently, the most adequate carbonization parameters were established to obtain the carbon blankets. The carbonized blankets were characterized for electrical conductivity by impedance spectroscopy, chemical structure (Raman and FT-IR spectroscopies), crystallographic ordering by X-ray diffraction (XRD), and morphology (SEM). The results showed the feasibility of producing carbon blankets based on PAN/lignin blends. However, carbonized blankets showed low carbon yield (10–56%) and a decrease of up to 70% in fiber diameter. XRD and Raman spectroscopy showed that the structural ordering of carbon blankets presents different values according to the heat treatment parameters used (45–57%) and a poorly ordered structure, indicated by the ID/IG ratio.     

Thermal properties of acrylonitrile/itaconic acid polymers in oxidative and nonoxidative atmospheres

Thermal stabilization of polyacrylonitrile (PAN) fibers is an indispensable process in the manufacture of carbon fibers. The effects of acidic comonomers on the thermal properties of PAN have attracted much attention because of their importance in the fibers spinning and heat treatment process. In this study, oxidative and nonoxidative atmospheres are adopted in differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) test to disclose the key effects of oxygen on the thermal properties of PAN/itaconic acid (IA) polymers. The DSC results under oxidative atmosphere are consistence to the reports by previous researchers: the exothermic curves of copolymers containing 0.6 wt % and 1.0 wt % IA exhibit lower initiation temperature and more broaden shapes than that of PAN homopolymer, indicating that IA facilitates both cyclization and oxidation reactions. However, copolymers containing the same content of IA shows no apparent improving effect on the thermal properties under inert atmosphere, which has not been mentioned in the published literature. TGA indicates that oxygen remarkably increases the thermal stability of AN/IA copolymers structure, and will bring high carbon yield in the eventual carbon fibers. The influential mechanisms of oxidative and nonoxidative atmospheres on thermal stabilization reactions of PAN were discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of electrospun Ag/polyacrylonitrile composite nanofibers

Novel composite nanofibers consisting of Ag nanoparticles and polyacrylonitrile (PAN) were fabricated successfully. The Raman properties of these Ag/PAN nanofibers were studied at low temperatures, which showed good Raman characteristics. In the process, a PAN solution containing Ag ions was directly electrospun to obtain nanofiber films containing Ag ions, and the Ag ions of resulting composite nanofibers were reduced to Ag nanoparticles in N₂H₅OH aqueous solution. Then, we treated Ag/PAN composite nanofibers at 100 °C, 200 °C, 400 and 600 °C, respectively. The Ag/PAN nanocomposite film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) patterns and surface-enhanced Raman scattering (SERS) spectroscopy.     

Thermo-chemical reactions occurring during the oxidative stabilization of electrospun polyacrylonitrile precursor nanofibers and the resulting structural conversions

Thermo-chemical reactions occurring during the oxidative stabilization of electrospun polyacrylonitrile (PAN) precursor nanofibers with diameters of approximately 300 nm were investigated as well as the resulting structural conversions, and the results were compared to those of conventional SAF 3K (Courtaulds) precursor fibers. The study revealed that: (1) the nitrile groups in the electrospun nanofibers possessed a higher reactivity than those in the SAF 3K fibers; (2) the macromolecules in the electrospun nanofibers predominantly underwent inter-molecular cyclization/crosslinking while those in the SAF 3K fibers underwent intra-molecular cyclization during the early stages of stabilization; and (3) under the same stabilization conditions, the structural conversion from linear macromolecules to aromatic ring/ladder structures in the electrospun nanofibers occurred faster and more thoroughly than in the SAF 3K fibers. These characteristics combined with other properties, including small diameter and high degree of structural perfection, suggest that electrospun PAN precursor nanofibers may be used to develop continuous nano-scale carbon fibers with superior mechanical strength, especially if the electrospun nanofibers could be further aligned and stretched.     

An investigation on structure characterization of thermally stabilized polyacrylonitrile precursor fibers pretreated with guanidine carbonate prior to carbonization

Thermal stabilization of polyacrylonitrile (PAN) precursor fiber was performed with a pretreatment of an aqueous guanidine carbonate solution and its structure was thoroughly characterized using a combination of infrared spectroscopy (IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), density, elemental analysis, and X‐ray diffraction measurements. The use of guanidine carbonate pretreatment of polyacrylonitrile precursor fiber was found to be very useful for the acceleration of thermal stabilization of polyacrylonitrile precursor fiber prior to the carbonization stage. The results obtained from density, thermal analysis (TGA and DSC), infrared‐spectroscopy and X‐ray diffraction methods suggested an accelerated thermally stable aromatic ladder structure formation resulting in much reduced thermal stabilization time. X‐ray observations showed the transformation of the original structure from a highly ordered phase to a totally disordered amorphous phase which seemed to be a direct consequence of the crosslinked and cyclized structure present in the stabilized fibers. The results obtained from the infrared spectra of thermally stabilized samples showed a rapid and simultaneous cyclization and dehydrogenation reactions aided by the oxygen uptake in the form of oxygen containing functional groups. Guanidine carbonate pretreated and thermally stabilized PAN precursor fibers showed a carbon yield of 52.5% at 1100°C obtained from TGA measurements. The use of guanidine carbonate pretreatment is expected to significantly increase the productivity of carbon fiber manufacturing at a substantially reduced cost by significantly reducing the time necessary for thermal stabilization of polyacryonitrile fiber. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Ferric Chloride Assisted Thermal Stabilization of Polyacrylonitrile Precursor Fibers Prior to Carbonization

The effect of ferric (Fe³⁺) ion incorporation on the thermal stabilization of polyacrylonitrile (PAN) fibers was investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction analysis and infrared spectroscopy methods. The results obtained from the DSC and TGA measurements indicated that there was an improvement in thermal stability when Fe³⁺ ions were incorporated into the polymer structure. TGA thermograms showed a relative improvement in thermal stability as indicated by increasing carbon yield with progressing time. The degree of lateral order and apparent crystallite size estimated by X-ray diffraction decreased with increasing stabilization time. Incorporation of Fe³⁺ induced distinct changes in the infrared spectra of the thermally stabilized PAN fibers. The spectral changes appeared to be due to the formation of coordination bonds between the nitrogen atom of the nitrile group and Fe³⁺. The formation of ferric ion-nitrile coordination bonds accelerated thermal stabilization by catalyzing the occurrence of dehydrogenation, cyclization and oxidation reactions.     

Structure and thermo-chemical properties of continuous bundles of aligned and stretched electrospun polyacrylonitrile precursor nanofibers collected in a flowing water bath

Continuous bundles of aligned and stretched electrospun polyacrylonitrile (PAN) precursor nanofibers were prepared in an attempt to develop carbon nanofibers with superior strength. The bundles were prepared through collection of electrospun nanofibers with a flowing water bath followed by stretching in water at 97 °C. Their morphologies, structures, and thermo-chemical properties were characterized by SEM, XRD, and DSC. The shrinkages in boiling water and the amounts of residual solvent were also measured. The results indicated that, the nanofibers in the bundles were uniform with smooth surfaces and small variations in diameters; after stretching the bundles by 4 times, the average fiber diameter was reduced to 56%, while the crystallinity of PAN was improved by 72%. The post-spinning stretching process facilitated the stabilization of PAN, as evidenced by the shift of the cyclization reaction to a lower temperature with smaller activation energy and larger enthalpy change. In comparison with the commonly adopted nanofiber collection method of a rotating drum, the flowing water bath method results in higher degree of uni-axial alignment and more desired structures of nanofibers.     

Hydrogen peroxide modified polyacrylonitrile-based fibers and oxidative stabilization under microwave and conventional heating – The 1st comparative study

Polyacrylonitrile (PAN) precursor was modified with hydrogen peroxide, and oxidative stabilisation studies were carried out using conventional and microwave heating. Wetting property, bulk density, Fourier transform infrared spectroscopy (FT-IR), extent of reaction (EOR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and mechanical properties were also investigated. Results show that PAN fibers have excellent wettability with hydrogen peroxide. Hydrogen peroxide modification can shorten the oxidation stabilisation time of PAN fibers. The FT-IR spectrum shows that the stabilised fibers modified by hydrogen peroxide have a conjugated structure, and the EOR value of hydrogen peroxide-modified PAN fibers stabilised by microwave heating is the largest. XRD analysis shows that hydrogen peroxide-modified fibers stabilised by microwave heating have low stack domains and height of the interlayer spacing. The SEM and Raman spectra indicate that hydrogen peroxide can improve the surface finish of the fibers and reduce defects. In addition, hydrogen peroxide-modified fibers stabilised by microwave heating exhibit excellent mechanical properties, with fineness of 0.78 dtex, strength of 1.60 dtex, and elongation at break of 3.49%.     

Electrospun magnetic fibrillar polyarylene ether nitriles nanocomposites reinforced with Fe‐phthalocyanine/Fe3O4 hybrid microspheres

The electrospinning method has been employed to fabricate ultrafine nanofibers of high‐performance polyarylene ether nitriles (PEN) and PEN/Fe‐phthalocyanine/Fe₃O₄ nanocomposite fibers for the first time. Through optimizing the operational conditions, such as polymer concentration, applied electric voltage, federate, and distance between needle tip and collector, bead‐free and uniform fibers with smooth surfaces and certain diameters were obtained. The morphology of the PEN nanofibers is correlated to the corresponding rheological behaviors of the polymer solutions. The nanocomposite fibers showed a beads‐in‐string structures without agglomeration after introducing the Fe‐phthalocyanine/Fe₃O₄ hybrid microspheres in the polymer fibers. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) reveal an enhanced thermal stability of the nanocomposite fibers after introducing the hybrids. The glass transition temperature (T_g) of the nanocomposite fibers increases by 10°C with 30 wt % hybrid microspheres, compared with those of the pure PEN fibers. The magnetic properties of the PEN/Fe‐phthalocyanine/Fe₃O₄ nanocomposite fibers are different from those of the hybrid microspheres. The hybrid microspheres in the composite nanofibers become magnetically harder with a much larger coercivity than that of the fillers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Air permeability of electrospun polyacrylonitrile nanoweb

Ultrafine fibers were spun from polyacrylonitrile (PAN) solution in N,N‐dimethylformamide using a homemade electrospinning setup. Fibers with diameter ranging from 80 to 340 nm were obtained. Fiber size and fiber size distribution were investigated for various concentration, applied voltage, and tip‐to‐collector distance using image analysis. The diameters of the electrospun fibers increase when increasing the solution concentration and decrease slightly when increasing the voltage and needle tip‐to‐collector distance. Porosity and air permeability are vital properties in applications of electrospun nanofibrous structures. In this study, effects of process parameters on the porosity and air permeability of electrospun nanoweb were investigated as well. Results of statistical analysis showed that solution concentration and applied voltage have significant influences on pore diameters. It was concluded that nanofiber diameter played an important role on the diameter of pores formed by the intersections of nanofibers. A more realistic understanding of porosity was obtained and a quantitative relationship between nanoweb parameters and its air permeability was established by regression analysis. Two separate models were constructed for predicting air permeability in relation to process parameters. Optimization of electrospinning process for producing nanoweb with desirable air permeability is well achieved by these models. The models presented in this study are of high importance for their ability to predict the air permeability of PAN nanoweb both by process or structure parameters. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 with tunable morphologies via polyacrylonitrile as a template and applications in lithium‐ion batteries

Samples of 0.4Li₂MnO₃·0.6LiNi_1/3Co_1/3Mn_1/3O₂ (LMO) with tunable morphologies were synthesized via polyacrylonitrile (PAN) as a template. The starting PAN/N,N‐dimethylformamide (DMF) ratios, including 1:9, 1:10, 1:12, and 1:14, were optimized for the fiber morphologies and electrochemical performance. Through electrospinning, metal salts were well dispersed in the PAN fibers. The crystal structure and morphologies of the PAN/LMO fibers were characterized by X‐ray diffraction, scanning electron microscopy, and thermal analysis. Along with the decrease in the concentration of PAN in the precursor, the diameters of the PAN/LMO fibers decreased. On the other hand, at the highest and lowest concentrations, 1:9 and 1:14, of PAN with DMF, micrometer PAN fibers were electrospun, whereas ratios of PAN to DMF of 1:10 and 1:12 resulted in the electrospinning of millimeter‐long fibers of PAN. In the interface of PAN and metal salts, LMOs were grown and accompanied the decomposition of PAN, and the crystal morphologies of LMO quite depended on the diameter and length of the PAN/LMO nanofibers. During heat treatment, the morphologies of the PAN fibers controlled the removal of small molecules and the crystal morphologies of LMOs. The charge/discharge results indicate that LMO with a tubular structure delivered a capacity of 262.3 mAh/g at a cutoff voltage of 2.5–4.8 V at a 0.1 C rate. Benefitting from a unique hollow and nanocrystalline architecture, it also exhibited good rate and cycling performances. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43022.     

Study of electrospun polyacrylonitrile fibers with porous and ultrafine nanofibril structures: Effect of stabilization treatment on the resulting carbonized structure

Electrospun polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) with high surface area have been of promising interest because of their potential for applications in various fields, especially energy devices. In this study, PAN nanofibers with porous and ultrafine nanofiber structures were prepared by electrospinning PAN/poly(vinyl pyrrolidone) (PVP) immiscible solutions and then selectively removing the PVP component from the electrospun PAN/PVP bicomponent nanofibers. The chemical reaction and microstructure of the PAN fibers with porous and ultrafine nanofibril structures in the stabilization process were investigated. The results revealed the effects of PAN fibers with porous and ultrafine nanofibril structures on the crosslinking reaction, microstructure, and morphology during the stabilization process. According to the in situ Fourier transform infrared spectroscopy results, the intermolecular and intramolecular reactions of the nitrile group for the PAN fibers with ultrafine nanofibril structures exhibited slower reaction rates than those for the neat PAN fibers during stepwise and isothermal heating. Selecting a good stabilization temperature for ultrafine PAN-crosslinked nanofibrils can enhance the surface area and carbonized structure of CNFs. The possible applications of CNFs with porous and ultrafine nanofibril structures in supercapacitors were also evaluated. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48218.     

Co-axial electrospinning with sodium thiocyanate solution for preparing polyacrylonitrile nanofibers

A modified co-axial electrospinning process including electrolyte solution as sheath fluid for preparing high quality polymer nanofibers is investigated. A series of polyacrylonitrile (PAN) nanofibers were fabricated utilizing the modified process with sodium thiocyanate solutions in N, N-dimethylacetamide (DMAc) as sheath fluids. Field-emission scanning electron microscopy results demonstrated that the sheath sodium thiocyanate solutions had significant influence on the quality of PAN nanofibers. High quality PAN nanofibers in terms of fiber diameters and their distributions, surface morphology and structure have been successfully produced. The diameters of nanofibers (D, nm) could be manipulated simply by adjusting the concentrations of sodium thiocyanate (C, mg ml^-1) in the sheath fluids with a scaling law of D = 324 C ^-0.1806. The mechanism about the influence of sodium thiocyanate solutions on the formation of PAN fibers is discussed and it is felt that co-axial electrospinning with electrolyte solution is a facile process for achieving high quality polymer nanofibers.     

Aspects on prestretching of PAN precursor: Shrinkage and thermal behavior

Polyacrylonitrile (PAN) fibers of a special grade have been modified by a method of prestretching with various stretching ratios from negative to positive before the onset of stabilization. The effect of such pretreatments on the thermorhelogical and thermal behaviors of PAN fibers was followed by free shrinkage experiments and differential scanning calorimetry (DSC) analyses. It was found that prestretching had a significant influence on the physical shrinkage of PAN fibers. DSC results of PAN fibers showed dependence not only on atmospheric conditions but also on the extent of prestretching. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1185–1190, 1998     

Characterization of polyacrylonitrile,poly(acrylonitrile‐co‐vinyl acetate), and poly(acrylonitrile‐co‐itaconic acid) based activated carbon nanofibers

In this study, three different acrylonitrile (AN)‐based polymers, including polyacrylonitrile (PAN), poly(acrylonitrile‐co‐vinyl acetate) [P(AN‐co‐VAc)], and poly(acrylonitrile‐co‐itaconic acid) [P(AN‐co‐IA)], were used as precursors to synthesize activated carbon nanofibers (ACNFs). An electrospinning method was used to produce nanofibers. Oxidative stabilization, carbonization, and finally, activation through a specific heating regimen were applied to the electrospun fibers to produce ACNFs. Stabilization, carbonization, and activation were carried out at 230, 600, and 750 °C, respectively. Scanning electron microscopy, thermogravimetric analysis (TGA), and porosimetry were used to characterize the fibers in each step. According to the fiber diameter variation measurements, the pore extension procedure overcame the shrinkage of the fibers with copolymer precursors. However, the shrinkage process dominated the scene for the PAN homopolymer, and this led to an increase in the fiber diameter. The 328 m²/g Brunauer–Emmett–Teller surface area for ACNFs with PAN precursor were augmented to 614 and 564 m²/g for P(AN‐co‐VAc) and P(AN‐co‐IA), respectively. The TGA results show that the P(AN‐co‐IA)‐based ACNFs exhibited a higher thermal durability in comparison to the fibers of PAN and P(AN‐co‐VAc). The application of these copolymers instead of AN homopolymer enhanced the thermal stability and increased the surface area of the ACNFs even in low‐temperature carbonization and activation processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44381.     

Variety of photoluminescence intensity of fluorescent whitening agents introduced into polyacrylonitrile nanofibers

The major objective in this study was the preparation of polyacrylonitrile (PAN) nanofibers composed of 1,4‐bis(o‐cyanostyryl)benzene (ER) and 1‐(o‐cyanostyryl)‐4‐(p‐cyanostyryl)benzene (EB), two kinds of fluorescent whitening agents widely used in the textile industry. The scanning electron microscopy images revealed that the diameters of ER/PAN and EB/PAN fibers ranged from 78 to 154 nm. The IR spectra indicated that the peaks of the ? CN group blueshift and the generation of a shoulder peak were obviously due to the interaction between ER or EB and PAN. Furthermore, the UV spectra demonstrated that the distributive status of ER or EB tended toward the molecular state in PAN nanofibers. Finally, the most interesting finding in this study was that the photoluminescence intensity of EB/PAN nanofibers increased magnificently, whereas that of ER/PAN nanofibers decreased remarkably. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2382–2386, 2007     

Electrospinning of pure polymer-derived SiBCN nanofibers with high yield

In this paper, we have discussed the synthesis of nanoscale silicoboron carbonitride (SiBCN) nanofibers by electrospinning of novel polyborosilazane precursor solutions, which were synthesized from boron trichloride, tris(dichloromethylsilylethyl)borane and hexamethyldisilazane using a one-pot method, followed by pyrolysis at 1000 °C under nitrogen atmosphere. The influence of the processing procedure (solution concentration, feeding rate and spinning voltage) of the electrospum fibers was also investigated. TGA and FT-IR experiments were employed to study the polymer-to-ceramic conversion and SEM was used to characterize the final materials. Combining the precursor derived ceramics route and electrospinning process enables to product SiBCN nanofibers for industrial applications.