Electrospinning of polyacrylonitrile fibers from ionic liquid solution

We developed a temperature-controlled electrospinning apparatus specially for the polymers/IL system with high viscosity and surface tension and investigated the electrospinning of polyacrylonitrile (PAN)/1-butyl-3-methyl-imidazolium bromide ([BMIM][Br]) solutions. The rheological behaviors, surface tensions and conductivities of PAN/[BMIM]/[Br] solutions at different temperatures indicated that appropriately increasing the temperature is beneficial to their spinnability. It is also shown that PAN/[BMIM]/[Br] with a concentration of 3 wt%, 4 wt% and 5 wt% can be electrospun to fibers by increasing their temperatures to 70°C, 75°C or 85°C, respectively. A rotating drum composed of a dacron mesh was used as a collector in order to avoid the contraction of the wet fibers. This present study provides an alternative method for electrospinning polymer fibers.     

Electrospinning Mechanism for Producing Nanoscale Polymer Fibers

Electrospinning provides a straightforward method to produce polymer fibers with nanoscale diameters. Although the setup for electrospinning is simple and convenient, the spinning mechanism itself is quite complicated. A complete understanding of this mechanism remains to be elucidated and the factors that govern fiber formation are not well understood. In this study, we investigate the electrospinning instabilities by observing the electrospinning jet behaviors with various photographic exposure times ranging from 1/100 to 1/10,000 of a second and the corresponding fiber depositions. We propose an electrospinning mechanism responsible for producing nanoscale fibers and their deposition patterns.     

Electrospun cross linked rosin fibers

In this study, we describe the first reported preparation of rosin in fiber form through use of an electrospinning technique utilizing various solvent systems. The polymer concentration of the formed fiber was studied by using various solvents such as chloroform, ethanol, N-N dimethylformamide (DMF), tetrahydrofuran (THF), acetone, and methylene chloride (MC). An electrospray of the solution resulted in the beaded form of the rosin. By varying the polymer concentration with MC, we were then able to obtain uniform fibers. However, the fibers exhibited large diameter. We believe that it is possible to reduce the diameter of the rosin fibers through appropriate selection of electrospinning parameters. In addition, the morphological transitions from beads, to beaded fiber, to fiber were studied at different polymer concentrations. We propose a possible physical cross linking mechanism for the formation of rosin fibers during the electrospinning process. Our results demonstrate the feasibility of producing fiber nanostructures of rosin by using an electrospinning technique.     

Manufacture and Characterization of Poly (butylene terephthalate) Nanofibers by Electrospinning

Poly (butylene terephthalate) (PBT) nanofiber mats were prepared by electrospinning, being directly deposited in the form of a random fibers web. The effect of changing processing parameters such as solution concentration and electrospinning voltage on the morphology of the electrospun PBT nanofibers was investigated with scanning electron microscopy (SEM). The electrospun fibers diameter increased with rising concentration and decreased by increasing the electrospinning voltage, thermal and mechanical properties of electrospun fibers were characterized by DSC and tensile testing, respectively.     

Production of nanofibers by electrospinning under pressurized CO2

Electrospinning is one of the simple technical methods for the production of polymer nanoparticles and nanofibers. Various polymers have been successfully electrospun into ultrafine particles and fibers in recent years mostly in solvent solution and some in melt form. In this work, near- and supercritical CO₂ were used as media for this process. At these conditions, the solubility can be tuned by controlling the temperature and pressure. Therefore, it is possible to form particles and fibers within a thermodynamic window where the biopolymer has been softened, but not dissolved. The experiments were conducted by using electrospinning under pressurized CO₂ system at pressures of ～ 8.0 MPa and temperature of 313 K to produce several polymers fibers. Polyvinylpyrrolidone was used as the starting material. During the electrospinning process, the applied voltage was 10–17 kV and the distance of nozzle and collector was 8 cm. The concentration of polymer solution was 4 wt%. The morphology- and structure-produced fibers were observed by scanning electron microscopy. The results showed that temperature and pressure affected the morphology of fibers produced by electrospinning in pressurized CO₂. This suggests that the thermal behavior of the polymer can be optimized by adjusting the polymer through the adjustment of pressure and temperature by using CO₂ as a solvent.     

Electrospinning Instabilities in the Drop Formation and Multi-Jet Ejection Part II: Various Nozzle Diameters for PVA (Polyvinyl Alcohol) Polymer Solution

Electrospinning is recognized as a simple and easy method to produce fibers with nanoscale diameters. However, the methods for controlling the shape, structure, and uniformity of electrospun fibers have not yet been fully investigated. In this research, the electrospinning jet behavior, corresponding nanofiber deposition, and average fiber diameter are examined for various nozzle diameters. Fluctuations in the sequence of drop growing, electrospinning, and/or termination of electrospinning are analyzed. We propose two different fluctuations according to nozzle diameter. The multi-jet ejections, that are closely related to the amount of nanoweb deposition and the deposition pattern, are explored.     

Synthesis and characterization of micro/nanoscopic Pb(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript> fibers by electrospinning

Micro/nanoscopic Pb(Zr_0.52Ti_0.48)O₃ fibers were synthesized from commercially available zirconium n-pro-poxide, titanium isopropoxide, and lead 2-ethylhexanoate. Using xylene as a solvent, they were mixed to form a precursor solution with a suitable viscosity for electrospinning. The solution was analyzed using thermo-gravimetric and differential thermal methods. Ultra-fine fibers and mats were electrostatically drawn from the precursor solution. The as-deposited materials were sintered for 2 h at 400, 500, 600, 700 and 800 °C, respectively. Sintered mats or fibers were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), Raman micro-spectrometry and scanning-probe microscopy (SPM). The SEM results revealed that the fibers had diameters varying from hundreds of nanometers to 10 m. Using AES, the elements Pb, Zr, Ti and O, as well as residual C, were detected on the surface of the fibers. Raman and XRD spectra indicated that the precursors began to transform into the intermediate pyrochlore phase at 400 °C, followed by the perovskite Pb(Zr_0.52Ti_0.48)O₃ phase above 600 °C. Scanning-probe microscopy (SPM), operated in the piezo-response imaging mode, revealed spontaneous polarization domains in the fibers, with diameters ranging from 100 to 500 nm. PACS 61.46.+w; 77.90.+k; 81.07.-b; 81.16.-c     

Electrospinning Instabilities in the Drop Formation and Multi-Jet Ejection Part I: Various Concentrations of PVA (Polyvinyl Alcohol) Polymer Solution

The electrospinning technique has attracted significant research attention because of its various potential applications and simplicity of manufacturing fibers of diameter from several micrometers to nanometer range. However, the methods for controlling the shape, structure, and uniformity of electrospun fibers have not yet been fully investigated. In this research electrospinning instabilities, such as cyclical electrospinning fluctuation and multi-jet ejections, which are closely related to the corresponding nanofiber deposition, were investigated for various polymer solution concentrations. The cyclical electrospinning fluctuation was evaluated with an image analysis program integrated with an image acquisition system that we developed. Two different drop size fluctuations of the cyclical process of the drop formation were observed.     

Preparation of TiO<Subscript>2</Subscript>-loaded electrospun fibers of polylactide/poly(vinylpyrrolidone) blends for use as catalysts in epoxidation of unsaturated oils

Nanofibers of polylactide (PLA)/poly(vinylpyrrolidone) (PVP) blends, loaded with TiO₂ nanoparticles, have been prepared by an electrospinning method. The electrospun fiber mats were characterized by ATR-FTIR, X-ray diffraction (XRD), SEM, EDX, and UV-visible spectroscopy to examine structures, functional groups, crystallinity, surface morphology, and UV absorptivity. It is clearly observed that TiO₂ particles are embedded on the filaments. All PLA-based spun fibers are completely amorphous in nature. The surface morphology of those blended with PVP is smoother and more uniform than the corresponding samples without PVP. Neat PLA fibers show a UV absorption band at around 200 nm, whereas the fibers loaded with TiO₂ nanoparticles show an additional absorption band covering the 200–380-nm region. Photo-degradation of the fiber samples are conducted in phosphate buffer solution (PBS) under UVA light. The results indicate that the PVP component dissolves into the PBS solution, and the PLA matrix degrades as a function of time. The fibers are then applied as a catalytic system for epoxidation of unsaturated sunflower oil (SFO), for use as additives or plasticizers for biopolymers, employing a performic acid oxidizing agent. The fibers, especially those containing PVP, can effectively enhance the epoxidation yield of oils with a slow rate of undesirable side reactions, which break ester bonds of triglycerides to generate free fatty acids.     

Poly(m‐Phenylene Isophthalamide) Ultrafine Fibers from an Ionic Liquid Solution by Dry‐Jet‐Wet‐Electrospinning

Ultrafine poly(m‐phenylene isophthalamide) (PMIA) fibers from PMIA solution in an ionic liquid via dry‐jet‐wet electrospinning technology are described. The morphology of the fibers with and without treatment in a coagulation water bath in the dry‐jet‐wet‐electrosinning process was observed by scanning electrical microscopy (SEM) and a high resolution optical microscope. The crystal structure of the fibers was analyzed by wide angle X‐ray diffraction (WAXD). The differences of morphologies and properties between the ultrafine fibers obtained by the electrospinning process and fibers from conventional wet‐spinning technology are discussed. The thermal properties of the ultrafine PMIA fibers were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).     

Poly (Vinyl Alcohol)/Chitosan/Akermanite Nanofibrous Scaffolds Prepared by Electrospinning

Abstract

Electrospinning, as an effective method for preparation of scaffolds for cell growth templates, has attracted great attention. In this study electrospinning was used to prepare poly (vinyl alcohol) (PVA)/chitosan scaffolds for bone tissue engineering. In order to improve the bioactivity and mechanical properties of the fibrous scaffolds, 0.5, 1 and 2?wt% akermanite, a calcium silicate based bioceramic, was added to the electrospinning solution. The morphology of the electrospun scaffolds was observed by using field emission-scanning electron microscopy and their mechanical strengths were analyzed by tension tests. The results showed that the formed scaffolds consisted of fibers with less than 100?nm diameter. In the case of the composite containing 1?wt% akermanite, the fibers were more homogeneous and no beads were formed during electrospinning, while in the composite containing 2?wt% akermanite a considerable number of beads were formed which we attribute to an improper viscosity of the electrospinning solution. Among the different compositions, the composite containing 1?wt% akermanite showed higher ultimate tensile strength (10.6?MPa) and fracture strain (9%). These values were increased by crosslinking the scaffold by reaction with glutaraldehyde, up to 13?MPa and 9.4%, respectively.     

Vibrational spectroscopy of self‐assembling aromatic peptide derivates

Peptides can assemble to supramolecular structures, of which fibers are of special biochemical and medical relevance. We employed Raman and infrared spectroscopy to elucidate the chemical integrity of fibers built from peptides and peptide derivates that contain the aromatic side groups fluorenyl and phenyl. Because the observed spectra compare very well with simulation results of the respective single molecules in vacuum, we were able to assign all observed vibrations. We found the main differences between solid phase and single molecule for O‐H and N‐H stretching and bending vibrations, owing to hydrogen bonding in solids. The fluorenyl and phenyl residues cause π‐stacking of the molecules, which barely manifests in the spectra, but clearly in the structures. Whereas hydrogen bonds provide the principal stability of the fiber backbone, aromatic π‐stacking supports the assembly to fibers, especially when electrospinning assists the molecular alignment. Copyright © 2012 John Wiley & Sons, Ltd.     

Electrospinning of Continuous,Large Area,Latticework Fiber onto Two‐Dimensional Pin‐array Collectors

The fiber spinning technique of electrospinning has been optimized in order to prepare unidirectionally aligned and structurally oriented fibers. For this paper, we designed a new device based on a 2D period collector fabrication and electrostatic fields analysis to obtain a large area latticework fibers pattern. The pattern was composed of polyvinylpyrrolidone (PVP)‐based sub‐micron fibers with diameters ranging from 910 nm to 1300 nm, which have potential applications in tissue cell cultures.     

Predicting Polymorphism of Electrospun Polyvinylidene Fluoride Membranes by Their Morphologies

Although electrospinning of polyvinylidene fluoride (PVDF) has been studied for more than 10 years, the crystalline phase differentiation of the electrospun mats is still normally through the combination of different characterization techniques, and the relationship between polymorphism and morphology of the fibers in electrospun PVDF membranes has never been reported. Here, we show their close relationships by conducting room-temperature electrospinning experiments on various polymer/solvent systems. The electrospun membranes full of bead-free fibers have a very high fraction of β-phase, F(β), over 90%, and high orientation, whereas the membranes comprising beads and/or a large number of beaded fibers most often result in a low fraction of β-phase (F(β) normally below 50%) and low orientation. On the other hand, electrospun membranes consisting of both bead-free fibers and a very limited number of beaded fibers showed a medium high fraction of β-phase, F(β) more than 70% but less than 90%. These findings suggest the feasibility of intuitively predicting the crystalline phase of electrospun PVDF membranes directly by their morphologies, which is obviously simple, inexpensive and convenient for future investigations.     

Effect of Polyaniline (Emeraldine Base) Addition on α to β Phase Transformation in Electrospun PVDF Fibers

A facile and effective transformation of α to β phase in electrospinning of PVDF was demonstrated by adding emeraldine base polyaniline (PANI). Results from FTIR and X-ray studies revealed that a very large amount of the electraoctive β-phase can be obtained by controlling the amount of PANI loading and the electrospinning parameters, whereas the γ-phase normally showed a very tiny amount, much lower than the β-phase, for all samples with PANI loading. The above results indicate that the addition of PANI into the PVDF solution during electrospinning is a powerful way to enhance the electroactive β-phase of the fibers, which is significant for developing high-performance fiber-based piezoelectric devices.     

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.     

Electrospinning of non-woven poly(styrene-co-acrylonitrile) nanofibrous webs for corrosive chemical filtration: Process evaluation and optimization by Taguchi and multiple regression analyses

Nano-fibrous ultra-filtration membranes of poly(styrene-co-acrylonitrile) were produced from n-butanone solution by electrospinning. Effects of governing parameters on morphology and variation in diameter of the electrospun fibers were experimentally investigated by orthogonal experimental design. The process parameters were selected by Taguchi's method. Multiple regression analysis was used to obtain a quantitative relationship between selected electrospinning parameters and average fiber diameter and ANOVA was used to identify the statistically significant parameters and set the optimal level for each parameter. Confirmation experiment revealed a good agreement between the predicted values of the response obtained from optimum level parameters and the observed experimental values.     

Preparation of LiCoO2 nanofibers by electrospinning technique

Using a sol-gel processing and electrospinning technique, extrathin fibers of PVA (polyvinyl alcohol)/lithium chloride/cobalt acetate composite were prepared. After calcinations of the above precursor fibers at 600°C, LiCoO₂ nanofibers with a diameter of 100-150 nm, were successfully obtained. Measurements of TG/DTA, IR, XRD, Raman, SEM, EDS, respectively, were performed to characterize the properties of the as-prepared materials. We observed a strong correlation between crystalline phase and morphology of the fibers and calcinations temperature.     

Electrospinning of Poly(Hydroxybutyrate-co-hydroxyvalerate) Fibrous Scaffolds for Tissue Engineering Applications: Effects of Electrospinning Parameters and Solution Properties

Electrospinning, a technology capable of fabricating ultrafine fibers (microfibers and nanofibers), has been investigated by various research groups for the production of fibrous biopolymer membranes for potential medical applications. In this study, poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), a natural, biocompatible, and biodegradable polymer, was successfully electrospun to form nonwoven fibrous mats. The effects of different electrospinning parameters (solution feeding rate, applied voltage, working distance and needle size) and polymer solution properties (concentration, viscosity and conductivity) on fiber diameter and morphology were systematically studied and causes for these effects are discussed. The formation of beaded fibers was investigated and the mechanism presented. It was shown that by varying electrospinning parameters within the processing window that was determined in this study, the diameter of electrospun PHBV fibers could be adjusted from a few hundred nanometers to a few microns, which are in the desirable range for constructing “biomimicking” fibrous scaffolds for tissue engineering applications.     

Two-nozzle electrospinning of (MWNT/PU)/PU nanofibrous composite mat with improved mechanical and thermal properties

Composite nanofibrous mat composed of neat polyurethane (PU) and multiwalled carbon nanotubes/polyurethane (MWNT/PU) nanofibers have been fabricated by one-step angled two-nozzle electrospinning. The morphological, thermal, and mechanical properties of the electrospun nanofibers were evaluated. The diameters of electrospun neat PU and composite nanofibers ranged from 239 to 1058 nm. The two-nozzle electrospun (MWNT/PU)/PU composite nanofibers showed curly, and randomly-oriented fibers with interfiber bonding, and were generally bigger in size than single-nozzle electrospun nanofibers. The tensile strength of the neat PU composite nanofiber mat obtained from two-nozzle electrospinning was 25% higher than that obtained from neat PU single-nozzle electrospinning. The incorporation of MWNTs in the composite nanofiber increased the tensile strength by as much as 64% without reducing elongation, made the composite nanofiber more thermally stable, and improved the melting zone. The present results showed that side-by-side angled two-nozzle electrospinning can improve the quality of the electrospun nanofibers that could have potential application in different fields such as filtration, protective clothing and tissue engineering.