Fabrication of nanofibers by a modified air-jet electrospinning method

A modified air-jet electrospinning (MAE) setup was demonstrated for contributing to the large-scale nanofibers production. With this single nozzle air-jet electrospinning device, the productivity of nanofibers can be increased more than forty times as compared with using the single-needle electrospinning (SNE) setup. When compared with other needle-less electrospinning setups, the benefits of this setup include ability to keep stable concentration of electrospun solution and to produce more uniform and thinner fibers, controlling of the jets formed speed and position, higher throughput, lower critical voltage, easier assembling, simpler operation, and so on. Four different parts of the fiber generator were, respectively, charged as electrospun electrodes to produce fibers. The distributions of the electric field with different electrodes were simulated and investigated for explaining the experimental results including the fibers productivity, the deposition area of nanofiber mats, as well as the surface morphology of the fibers. When the whole nozzle was charged, as compared with charging other electrodes, the MAE system produced thinner fibers with larger standard deviation on a much larger scale. By reduction of charged area, the received fibers presented lower productivity and thicker diameter with lower standard deviation. Especially, when a half of the nozzle was charged, the deposition area of nanofiber mats was larger than charging other electrodes. Besides, when a half of the nozzle was charged, the influences of electrospinning parameters such as applied voltage, collecting distance and the flow rate of air on nanofibers morphology were also investigated. Furthermore, based on this spinning unit, multi-nozzle air-jet electrospinning setup can be designed for larger production of nanofibers.     

Effect of experimental parameters on needleless electrospinning from a conical wire coil

In this study, a conical wire coil was used as spinneret to launch a novel needleless electrospinning. Multiple polymer jets were observed on the surface of the coil in the electrospinning process. Productivity of the nanofibers can be enhanced to >2.5 g/h by using this novel nozzle. The fiber productivity and diameter together with diameter distribution were dependent on the concentration of the polymer solution, applied voltage, and collecting distance. This novel concept of using wire coil as the electrospinning nozzle depicts a model of large‐scale needleless electrospinning system for nanofiber production. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of air blowing on the morphology and nanofiber properties of blowing‐assisted electrospun polycarbonates

Polycarbonate (PC) nanofibers are prepared using the air blowing‐assisted electrospinning process. The effects of air blowing pressure and PC solution concentration on the physical properties of fibers and the filtration performance of the nanofiber web are investigated. The air blowing‐assisted electrospinning process produces fewer beads and smaller nanofiber diameters compared with those obtained without air blowing. Uniform PC nanofibers with an average fiber diameter of about 0.170 μm are obtained using an applied voltage of 40 kV, an air blowing pressure of 0.3 MPa, a PC solution concentration of 16%, and a tip‐to‐collection‐screen distance (TCD) of 25 cm. The filtration efficiency improvement of the air blowing‐assisted electrospun web can be attributed to the narrow distribution of fiber diameter and small mean flow pore size of the electrospun web. Performance results show that the air blowing‐assisted electrospinning process can be applied to produce PC nanofiber mats with high‐quality filtration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

熔体直写电纺聚己内酯纤维有序沉积工艺

目前聚合物熔体电纺技术制备的纤维大多以杂乱无序的无纺布形式存在,限制了电纺技术在组织工程支架以及机器人等需要有序结构领域的应用。本文将熔体电纺技术与三维运动平台相结合,采用自主设计的熔体电纺可控成型实验装置,对聚己内酯（PCL）进行熔体直写静电纺丝,获得了有序纤维。研究了喷头移动速度、接收距离和纺丝电压对熔体直写电纺纤维沉积形貌的影响。结果表明,纤维直径随着喷头移速、接收距离和纺丝电压的增大而减小,其中接收距离的改变对直径的影响最为显著;接收距离的增大虽然有利于纤维的细化,但是距离过大会使纤维沉积的有序性变差;当射流下落速度与喷头移动速度相匹配时,射流才能实现有序沉积;增大接收距离和纺丝电压会引起射流鞭动,需要相应地增大喷头移动速度才能实现有序沉积。     

Preparation of poly(ether sulfone) nanofibers by gas‐jet/electrospinning

Poly(ether sulfone) (PES) nanofibers were prepared by the gas‐jet/electrospinning of its solutions in N,N‐dimethylformamide (DMF). The gas used in this gas‐jet/electrospinning process was nitrogen. The morphology of the PES nanofibers was investigated with scanning electron microscopy. The process parameters studied in this work included the concentration of the polymer solution, the applied voltage, the tip–collector distance (TCD), the inner diameter of the needle, and the gas flow rate. It was found from experimental results that the average diameter of the electrospun PES fibers depended strongly on these process parameters. A decrease in the polymer concentration in the spinning solutions resulted in the formation of nanofibers with a smaller diameter. The use of an 18 wt % polymer solution yielded PES nanofibers with an average diameter of about 80 nm. However, a morphology of mixed bead fibers was formed when the concentration of PES in DMF was below 20 wt % during gas‐jet/electrospinning. Uniform PES nanofibers with an average diameter of about 200 nm were prepared by this electrospinning with the following optimal process parameters: the concentration of PES in DMF was 25 wt %, the applied voltage was 28.8 kV, the gas flow was 10.0 L/min, the inner diameter of the needle was 0.24 mm, the TCD was 20 cm, and the flow rate was 6.0 mL/h. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Influence of electric field interference on double nozzles electrospinning

The low production rate of electrospinning process may limit the industrial use of single needle system. To meet high yield requirement and uniform fibers, a bottom‐up multiple jets electrospinning nozzle was designed, each nozzle can emit 6–18 jets. The influence of electric field interference on jet path, membrane shape, and fiber morphology were investigated. Experiment finds that electrical field strength in the closer part of two nozzles is weakened because of electric field interference when the distance between two nozzles is 30 mm, making the jet hard to emit in this section, and closer part of electrospun fiber webs has fewer fibers. The spinning in far side part of two nozzles is similar to that of single nozzle. While in middle part of one nozzle, the jet path is short, elongation of jets smaller, the formed fibers thicker, solvent evaporation less sufficient. When the distance of two nozzles is increased to 50 mm, influence of electric field interference is weaker, the electrospun fiber web and average diameter of fibers are almost the same as that of single nozzle electrospinning. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fabrication of continuous nanofiber yarn using novel multi‐nozzle bubble electrospinning

A novel multi‐nozzle bubble electrospinning apparatus, including spinning unit, metering pump, constant flow pump, metal funnel and yarn winder, was designed for the preparation of continuous twisted polyacrylonitrile nanofiber yarns, and the principle of nanofiber yarn spinning was studied. An innovative spinning unit consisting of nozzle and air chamber was used to improve the production of nanofibers. Double conjugate electrospinning was developed using two pairs of oppositely charged spinning units to neutralize the charges. The effects of applied voltage, air flow rate, overall solution flow rate and funnel rotary speed on the fiber diameter, production rate and mechanical properties of the nanofiber yarns were analyzed. Nanofibers could be aggregated stably and bundled continuously, then twisted into nanofiber yarns uniformly at an applied voltage of 34 kV, air flow rate of 1200 mL min^?1 and overall solution flow rate of 32 mL h^?1. With an increase in the funnel rotary speed, the twist angle of the nanofiber yarns gradually increased when the take‐up speed was constant. The yarn tensile strength and elongation at break showed an increasing trend with increasing twist angle. Nanofiber yarns obtained using this novel method could be produced at a rate from 2.189 to 3.227 g h^?1 with yarn diameters ranging from 200 to 386 µm. Nanofiber yarns with a twist angle of 49.7° showed a tensile strength of 0.592 cN dtex^?1 and an elongation at break of 65.7%. © 2013 Society of Chemical Industry     

Effects of some electrospinning parameters on morphology of natural silk‐based nanofibers

Natural silk, from Bombyx mori solutions were electrospun into nanofibers, with diameters ranged from 60 to 7000 nm. The effects of electrospinning temperature, solution concentration and electric field on the formation nanofibers were studied. Optical and scanning electron microscope were used to study the morphology and diameter of electrospun nanofibers. It was observed that the nanofibers became flattened with ribbon‐like shape with increasing the electrospinning temperature. The nanofiber diameter increases with the increase in the concentration of silk solution at all electrospinning temperature. With increasing the voltage of electric field at 50°C, morphology of the nanofibers changes from ribbon‐like structure to circular cross section. Referring to the literature the probable mechanism responsible for the change of morphology is pointed out. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mass‐Production of Electrospun Carbon Nanofiber Containing SiOx for Lithium‐Ion Batteries with Enhanced Capacity

In this study, electrospun carbon nanofibers hybridized with silicon oxide (SiO_x) are prepared by using a syringeless electrospinning system of polyacrylonitrile (PAN) solution containing tetraethylorthosilicate (TEOS) via a sequential pyrolysis process. The syringeless electrospinning system provides a large number of composite nanofibers in a short time, and the obtained composite nanofibers exhibit uniform diameter and morphology. The composite nanofiber is converted into a carbon nanofiber containing SiO_x via a simple pyrolysis. The obtained SiO_x‐carbon nanofiber mat exhibits higher charge/discharge capacity than a general carbon nanofiber, and it provides more stable retention than single crystalline silicon materials. Thus, the mass‐production of a SiO_x‐carbon nanofiber from syringeless electrospinning is a promising method to produce anodic materials for Li‐ion batteries.     

Controlling the architecture of nanofiber‐coated microfibers using electrospinning

This study shows that electrospinning nanofibers onto single microfibers allows for careful tailoring of material properties that may suit a wide variety of applications. The nanofiber‐coated microfibers are created by electrospinning nanofibers alongside a microfiber toward a collector that rotates around the microfiber. This force the nanofibers to be collected around the microfiber, creating a hierarchical structure that can be modified at nano scale. In this study, control of nanofiber diameters, nanofiber alignment, and nanofiber loading was evaluated. It was seen that varying polymer concentration affected the nanofiber diameters, collecting the nanofiber‐coated microfibers at different speeds changed the degree of alignment of the nanofibers and that changing the polymer feeding rate affected the loading density of the nanofibers collected. The carefully designed nanofiber‐coated microfibers have great potential in creation of highly porous materials with tailored properties down to nano scale. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Production of Synthetic,Para‐Aramid and Biopolymer Nanofibers by Immersion Rotary Jet‐Spinning

Nanofiber production platforms commonly rely on volatile carrier solvents or high voltages. Production of nanofibers comprised of charged polymers or polymers requiring nonvolatile solvents thus typically requires customization of spinning setup and polymer dope. In severe cases, these challenges can hinder fiber formation entirely. Here, a versatile system is presented which addresses these challenges by employing centrifugal force to extrude polymer dope jet through an air gap, into a flowing precipitation bath. This voltage‐free approach ensures that nanofiber solidification occurs in liquid, minimizing surface tension instability that results in jet breakup and fiber defects. In addition, nanofibers of controlled size and morphology can be fabricated by tuning spinning parameters including air gap length, spinning speed, polymer concentration, and bath composition. To demonstrate the versatility of our platform, para‐aramid (e.g., Kevlar) and biopolymer (e.g., DNA, alginate) nanofibers are produced that cannot be readily produced using standard nanofiber production methods.

     

Solution blow spinning: A new method to produce micro‐ and nanofibers from polymer solutions

A solution blow spinning technique was developed using elements of both electrospinning and melt blowing technologies as an alternative method for making non‐woven webs of micro‐ and nanofibers with diameters comparable with those made by the electrospinning process with the advantage of having a fiber production rate (measured by the polymer injection rate) several times higher. The diameters of fibers produced ranged from 40 nm for poly(lactic acid) to several micrometers for poly(methyl methacrylate). This solution blow spinning method uses a syringe pump to deliver a polymer solution to an apparatus consisting of concentric nozzles whereby the polymer solution is pumped through the inner nozzle while a constant, high velocity gas flow is sustained through the outer nozzle. Analysis of the process showed that pressure difference and shearing at the gas/solution interface jettisoned multiple strands of polymer solution towards a collector. During flight, the solvent component of the strands rapidly evaporates forming a web of micro and nanofibers. The effect of injection rate, gas flow pressure, polymer concentration, working distance, and protrusion distance of the inner nozzle was investigated. Polymer type and concentration had a greater effect on fiber diameter than the other parameters tested. Injection rate, gas flow pressure, and working distance affected fiber production rate and/or fiber morphology. Fibers were easily formed into yarns of micro‐ and nanofibers or non‐woven films that could be applied directly onto biological tissue or collected in sheets on a rotating drum. Indeed, virtually any type of target could be used for fiber collection. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Needleless electrospinning of nanofibers with a conical wire coil

In this article, we have demonstrated a novel needleless electrospinning of PVA nanofibers by using a conical metal wire‐coil as spinneret. Multiple polymer jets were observed to generate on the coil surface. Up to 70 kV electric voltage can be applied to this needleless electrospinning nozzle without causing “corona discharge.” Compared with conventional needle electrospinning, this needleless electrospinning system produced finer nanofibers on a much larger scale, and the fiber processing ability showed a much greater dependence on the applied voltage. Finite element calculation indicates that the electric field intensity profiles for the two systems are also quite different. This novel concept of using wire coil as the electrospinning nozzle will contribute to the further development of new large‐scale needleless electrospinning system for nanofiber production. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Transparent poly(methyl methacrylate‐co‐butyl acrylate) nanofibers

Nanofibers of n‐Butyl Acrylate/Methyl Methacrylate copolymer [P(BA‐co‐MMA)] were produced by electrospinning in this study. P(BA‐co‐MMA) was synthesized by emulsion polymerization. The structural and thermal properties of copolymers and electrospun P(BA‐co‐MMA) nanofibers were analyzed using Fourier transform infrared spectroscopy–Attenuated total reflectance (FTIR–ATR), Nuclear magnetic spectroscopy (NMR), and Differential scanning calorimetry (DSC). FTIR–ATR spectra and NMR spectrum revealed that BA and MMA had effectively participated in polymerization. The morphology of the resulting nanofibers was investigated by scanning electron microscopy, indicating that the diameters of P(BA‐co‐MMA) nanofibers were strongly dependent on the polymer solution dielectric constant, and concentration of solution and flow rate. Homogeneous electrospun P(BA‐co‐MMA) fibers as small as 390 ± 30 nm were successfully produced. The dielectric properties of polymer solution strongly affected the diameter and morphology of electrospun polymer fibers. The bending instability of the electrospinning jet increased with higher dielectric constant. The charges inside the polymer jet tended to repel each other so as to stretch and reduce the diameter of the polymer fibers by the presence of high dielectric environment of the solvent. The extent to which the choice of solvent affects the nanofiber characteristics were well illustrated in the electrospinning of [P(BA‐co‐MMA)] from solvents and mixed solvents. Nanofiber mats showed relatively high hydrophobicity with intrinsic water contact angle up to 120°. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4264–4272, 2013     

Processing of continuous poly(amide‐imide) nanofibers by electrospinning

Continuous poly(amide‐imide) nanofibers were fabricated using a novel electrospinning method with rotating and re‐collecting cylindrical collectors. The nanofilaments were modified using various post‐treatments, i.e. glycerol treatment and thermal imidization under tension, for possible application as high‐performance reinforcements. Morphological and mechanical properties of continuous poly(amide‐imide) nanofibers prepared by the electrospinning process and various post‐treatments were measured. Severe adhesion between individual nanofibers within fiber bundles was inhibited through surface treatment of the electrospun nanofiber bundles by spraying with glycerol. The morphological and mechanical properties of the continuous poly(amide‐imide) nanofibers and thermal stability were improved using thermal imidization at high temperature under tension. The morphological and mechanical properties of the continuous electrospun nanofibers were improved significantly by post‐treatments after electrospinning because uniform and complete thermal imidization occurred through the core region of the nanofibers. Copyright © 2009 Society of Chemical Industry     

Molecular orientation and mechanical property size effects in electrospun polyacrylonitrile nanofibers

Electrospinning of polymeric solutions entails high jet velocities which could orient the polymer molecules along the jet direction. Polarized Fourier Transform IR spectroscopy (FTIR), Wide angle X-ray diffraction (WAXD) and Microelectromechanical System (MEMS)-based single nanofiber mechanical property experiments were employed to investigate the molecular orientation and crystallinity in electrospun polyacrylonitrile (PAN) nanofibers produced under different electrospinning conditions with diameters mainly varying between 100 and 300 nm. FTIR measurements with nanofibers fabricated at three different electrospinning distances, but under the same electric field intensity, revealed an enhanced molecular orientation only for the longest electrospinning distance. At long electrospinning distances the fiber solvent content is substantially reduced resulting in high viscosity, and, therefore, sustained shear stresses, which, in turn, allows for permanent molecular orientation. The orientation factors from polarized FTIR were in good agreement with the mechanical property trends obtained from individual nanofibers, where high elastic moduli and yield strengths were recorded from nanofibers with diameters smaller than 300 nm, which were fabricated at the longest electrospinning distance. WAXD studies on bundles of aligned PAN nanofibers showed small crystallinity which did not follow the trends in the mechanical properties and varied rather non-monotonically from 7%, for fibers spun at the shortest distance, to 17% for fibers spun at the longest distance used in this study.     

Magnetic‐field‐assisted electrospinning highly aligned composite nanofibers containing well‐aligned multiwalled carbon nanotubes

Composite nanofiber meshes of well‐aligned polyacrylonitrile (PAN)/polyvinylpyrrolidone (PVP) nanofibers containing multiwalled carbon nanotubes (MWCNTs) were successfully fabricated by a magnetic‐field‐assisted electrospinning (MFAES) technology, which was confirmed to be a favorable method for preparation of aligned composite nanofibers in this article. The MFAES experiments showed that the diameters of composite nanofibers decreased first and then increased with the increase of voltage and MWCNTs content. With the increase of voltage, the degree of alignment of the composite nanofibers decreased, whereas it increased with increasing MWCNTs concentration. Transmission electron microscopy observation showed that MWCNTs were parallel and oriented along the axes of the nanofibers under the low concentration. A maximum enhancement of 178% in tensile strength was manifested by adding 2 wt % MWCNTs in well‐aligned composite nanofibers. In addition, the storage modulus of PAN/PVP/MWCNTs composite nanofibers was significantly higher than that of the PAN/PVP nanofibers. Besides, due to the highly ordered alignment structure, the composite nanofiber meshes showed large anisotropic surface resistance, that is, the surface resistance of the composite nanofiber films along the fiber axis was about 10 times smaller than that perpendicular to the axis direction. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41995.     

Solution blowing of thermoplastic polyurethane nanofibers: A facile method to produce flexible porous materials

Solution blowing (SB) is a promising and scalable approach for the production of nanofibers. Air pressure, solution flow‐rate, and nozzle‐collector distance were determined as effective process parameters, while solution concentration was also reported as a material parameter. Here we performed a parametric study on thermoplastic polyurethane/dimethyl formamide (TPU/DMF) solutions to examine the effect of such parameters on the resultant properties such as fiber diameter, diameter distribution, porosity, and air permeability of the nanofibrous webs. The obtained solution blown thermoplastic polyurethane (TPU) nanofibers had average diameter down to 170 ± 112 nm, which is similar to that observed in electrospinning. However, the production rate per nozzle can be 20 times larger, which is primarily dependent on air pressure and solution flow rate (20 mL/h). Moreover, it was even possible to produce nanofibers polymer concentrations of 20%; however, this increased the average nanofiber diameter. The fibers produced from the TPU/DMF solutions at concentrations of 20% and 10% had average diameters of 671 ± 136 nm and 170 ± 112 nm, respectively. SB can potentially be used for the industrial‐scale production of products such as nanofibrous filters, protective textiles, scaffolds, wound dressings, and battery components. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43025.     

Polymeric nanofibers via flat spinneret electrospinning

Electrospun nanofibers are most often produced by needle electrospinning process, which has inherent disadvantages like clogging and low efficiency. In this study, an alternative needleless electrospinning process is reported for the fabrication of nanofibers based on a novel spinneret. Firstly, a spinneret with a 0.5‐mm diameter hole in the middle of a flat plastic cap was custom‐made that may be readily scaled up for mass production. Then, polyethylene oxide (PEO) aqueous solution with 6.0 wt% concentration was used to demonstrate the needleless electrospinning process. The processing window for the jet formation in the flat spinneret electrospinning process was determined. The relationships between various processing parameters (applied voltage, working distance, and flow rate) and the resultant PEO nanofibers were also investigated. It was found that stable fluid jet launched from the tip of the coned droplet anchored at the rim of the hole and formed fibers. The morphology and diameter of electrospun fibers were examined using scanning electron microscopy. The results show that PEO nanofibers produced by this needleless electrospinning have similar structure and morphology to those from the single needle source. Finally, the hole number of spinneret was increased to four holes, which was still able to produce smooth nanofibers with a higher production rate. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Sea‐island polyurethane/polycarbonate composite nanofiber fabricated through electrospinning

Sea‐island polyurethane (PU)/polycarbonate (PC) composite nanofibers were obtained through electrospinning of partially miscible PU and PC in 3 : 7 (v/v) N,N‐dimethylformamide (DMF) and tetrahydrofuran (THF) mixture solvent. Their structures, mechanical, and thermal properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric (TG), and differential scanning calorimetry (DSC). The structures and morphologies of the nanofibers were influenced by composition ratio in the binary mixtures. The pure PC nanofiber was brittle and easy to break. With increasing the PU content in the PU/PC composite nanofibers, PU component not only facilitated the electrospinning of PC but improved the mechanical properties of PU/PC nanofibrous mats. In a series of nanofibrous mats with varied PU/PC composition ratios, PU/PC 70/30 showed excellent tensile strength of 9.60 Mpa and Young's modulus of 55 Mpa. After selective removal of PC component in PU/PC composite nanofibers by washing with acetone, the residual PU maintained fiber morphology. However, the residual PU nanofiber became irregular and contained elongated indents and ridges along the fiber surface. PU/PC composite fibers showed sea‐island nanofiber structure due to phase separation in the spinning solution and in the course of electrospinning. At PC content below 30%, the PC domains were small and evenly dispersed in the composite nanofibers. As PC content was over 50%, the PC phases became large elongated aggregates dispersed in the composite nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010