Fabrication of poly(vinyl alcohol) nanofibers by wire electrode-incorporated electrospinning

Wire electrodes for needleless electrospinning consist of stainless steel wires in place of cylinder electrodes. The effects of different numbers of constituent stainless steel wires on the morphology and diameter of polyvinyl alcohol (PVA) fibers are examined. With 1, 2, 3, or 4 stainless steel wires being twisted as wire electrodes, an 8, 10, or 12 wt.% polyvinyl alcohol (PVA) solution is electrospun into PVA nanofibers by using a needleless electrospinning machine. The morphology and diameter of PVA nanofibers is observed by scanning electron microscopy. The combination of the number of stainless steel wires (two), PVA solution (10 wt.%), and the collecting distance (10 cm) results in the finest diameter and an evenly formed fiber morphology. In addition, the nanofibers exhibit a wide range of diameters when electrospun with an electrode consisting of more than two stainless steel wires. Compared with the cylinder electrode, the use of a wire electrode can form nanofibers, which results in a more even morphology.     

Electrospinning of silk nanofibers. I. An investigation of nanofiber morphology and process optimization using response surface methodology

Ultra fine fibers were electrospun from regenerated silk fibroin/formic acid solution. Effect of some process parameters on the morphology, diameter and variation in fiber diameter of electrospun fibers were experimentally investigated. Scanning electron microscope was used for the measurement of fiber diameter. Fibers with diameter ranging from 80 to 210 nm were collected depending on the solution concentration and the applied voltages. Response surface methodology (RSM) was used to obtain a quantitative relationship between selected electrospinning parameters and the average fiber diameters and its distribution. It was shown that concentration of silk fibroin solution had a significant effect on the fiber diameter and the standard deviation of the fiber diameter. Applied voltage had no significant effect on the fiber diameter and its standard deviation.     

Optimization of elecrospinning process of zein using central composite design

Biodegradable edible sub-micron electrospun zein fibers were prepared using acetic acid as solvent. The solution concentration at three levels: 22, 26 and 30 w/v %, the electrospinning voltage at three levels: 10, 20 and 30 kV, the solution flow rate at three levels: 4, 8 and 12 ml/h and the distance between needle tip and collector at three levels: 10, 15 and 20 cm were studied. Central composite design (CCD) was utilized to modeling the effect of electrospinning parameters of zein solution on average fiber diameters and the data were analyzed using response surface methodology (RSM). Coefficient of determination, R², of fitted regression model was higher than 0.9 for response. The analysis of variance table showed that the lack of fit was not significant for response surface model at 95 %. Therefore, the model for response variable was highly adequate. Results also indicated that the solution concentration had significant influence (P<0.0001) on morphology and diameter of fibers. By increasing the solution concentration, uniform and bead-free fibers were obtained. As the solution concentration was increased, the average fiber diameters were also increased. Furthermore, the electrospinning voltage had significant effect (P<0.0001) on average fiber diameters. By increasing the electrospinning voltage, the average fiber diameters increased. The solution flow rate and the distance between needle tip and collector had no significant influence on the average fiber diameters. According to model optimization, the minimum average fiber diameter of electrospun zein fiber is given by following conditions: 24 w/v % zein concentration, 10 kV of the applied voltage, 10 cm of needle tip to collector distance, and 4 ml/h of solution flow rate.     

Electrospinning PVA solution-rheology and morphology analyses

This study investigates the electrospinning (ES) of poly(vinyl alcohol) (PVA). All of the electrospinning process or property parameters, including the concentration effect, the molecular weight effect, the pH effect, the salt effect, electrode voltage, surface tension, shear viscosity and extensional viscosity were examined. The pH variation had an insignificant effect on the formation of fibers. An increase in electrode voltage and salt concentration negatively affects the ES process. The salt concentration that yields an acceptable ES membrane without droplets was below 0.001 N. Also, the decrease in elongation viscosity rather than the variation in electric conductivity or surface tension was the main cause of the negative effect on the fiber formation when the salt was added to a PVA solution. The salt negative effects follow the order CaCl₂ < NaCl < NaI < KBr < KI. Experimental results show that the ES processability of PVA solution depends mainly on the concentration and secondly on the molecular weight of the dissolved polymer. The PVA solution prepared with a larger molecular weight had a lower concentration window in the ES process. The concentration window of PVA solution with an MW of 88,000 in the ES process ranged between 6 and 14 wt%. Additionally, experimental results demonstrated that the upper limitation on PVA concentration depends strongly on the extension viscosity of the spun solution. Whenever the power law index n determined by extension test exceeds one, spinning is unfeasible, regardless of whether the index of the power law for shearing is within the normal range. Briefly, this work indicates that the extension viscosity can be adopted as a good indicator for predicting ES processability.     

Water-resistant Lignin/Poly(vinyl alcohol) Blend Fibers for Removal of Hexavalent Chromium

Lignin is the second most abundant renewable biomass-derived natural resource that has been used to replace traditional petrochemical-based materials. However, fabricating the lignin component into the various forms required for practical application is still challenging. In this work, we fabricated water-resistant lignin/poly(vinyl alcohol) (PVA) blend fibers by wet spinning and glutaraldehyde crosslinking methods. The effect of the lignin/PVA blend ratio and glutaraldehyde crosslinking process on the physicochemical properties of wet-spun lignin/PVA blend fibers were studied using maximum draw ratios, hydrolytic degradation profiles, and mechanical properties. Furthermore, the hexavalent chromium [Cr(VI)] removal behavior of lignin/PVA blend fibers was investigated according to the effect of pH, initial Cr(VI) concentration, and contact time. The wet-spun lignin/PVA blend fiber achieved excellent water stability through glutaraldehyde crosslinking and exhibited notable Cr(VI) adsorption capacity (350.87 mg/g) and good regeneration ability. These findings demonstrate that glutaraldehyde-crosslinked lignin/PVA blend fibers could be promising adsorbents for the remediation of heavy metal species containing textile wastewater.     

Preparation of Cu-BTC/PVA Fibers with Antibacterial Applications

In this study, a metal-organic framework (MOF)/polymer electrospun fiber was prepared. The MOF, copper-1,3,5- benzenetricarboxylate (Cu-BTC), was synthesized using a sonochemical method at 25 °C, with a 1:1:1 mixture of dimethylformamide, ethanol, and deionized water as solvent. The sonication time was shown to have a pronounced effect on the morphology and structure of the Cu-BTC. A square pyramid shape with sides of 100 nm was obtained after 2 h of sonication. Extending the sonication time provided a lower amount of unknown phase and produced a uniform Cu-BTC framework. The Cu-BTC-modified PVA fibers were then fabricated by electrospinning. The effect of the Cu-BTC and PVA concentration was investigated at 25 kV, a flow rate of 10 μl/min, and a working distance of 150 mm. FTIR spectra and FESEM images showed good dispersion of the Cu-BTC on the PVA fiber. The as-prepared Cu-BTC-modified PVA fibers exhibited excellent antibacterial effectiveness against S. aureus.     

Electrospun poly(tetrafluoroethylene) nanofiber membranes from PTFE-PVA-BA-H<Subscript>2</Subscript>O gel-spinning solutions

As a kind of high-performance fibers, PTFE fiber has been widely used in many fields because of its unique characteristics. In this study, the poly(tetrafloroethylene) (PTFE) nanofibers manufactured by electrospinning method was reported. The gel-spinning solution of poly(tetrafluoroethylene)/poly(vinyl alcohol)/boric acid (PTFE/PVA/BA), which was prepared by the gel process of the mixture of PTFE, PVA, BA and redistilled water, was electrospun to form PTFE/PVA/BA composite nanofibers. After calcinating, the PTFE nanofibers with diameters of 200 nm to 1000 nm were obtained. The fibers before and after calcinating were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), FT-IR spectrum analysis and X-ray photoelectron spectroscopy (XPS), respectively, and the mechanical and hydrophobic properties of the fibers were also investigated. The results showed that the PTFE nanofiber membranes could be electrospun effectively used the gel-spinning solution of PTFE/PVA/BA, and may realize the applications in the fields of high-temperature filtration, catalyst supports, battery separator and so on.     

Preparation,characterization of antibacterial PLA/TP nanofibers

Polylactic acid (PLA)/Tea polyphenol (TP) composite nanofilms were prepared using an electrospinning process. The mixed dichloromethane (DCM) and N,N-dinethylformamide (DMF) (70:30, v/v) was found to be the most suitable solvent for electrospinning. Various blends of PLA/TP solutions were formed. The morphology of the electrospun nano-scale fibers was investigated by scanning electron microscope (SEM), and the antibacterial performance was tested using shake flask method. The average diameter of the fibers is between 380 and 850 nm. It was found that the fiber diameter decreases as TP content increases, however the fibers may become brittle when the blend ratio of PLA and TP reached 50/50 (w/w). The antibacterial performance can be improved at the beginning when TP content increased. But it gradually gets impaired when TP content surpasses a certain value. The highest inhibitory rate against Escherichia coli and Staphylococcus aureus are 96.9 and 97.6 % respectively.     

The effect of salt on the roller electrospinning of polyurethane nanofibers

In this study, we investigated the effect of tetraethylammoniumbromide (TEAB) salt on the spinnability of polyurethane nanofibers via roller electrospinning method. At first, solution properties, spinnability and fiber properties were determined and then all the results were analyzed. According to the results, TEAB salt concentration has an important effect on the conductivity, viscosity, spinning performance, fiber diameter and morphology. It was found that all these parameters increased with salt concentration. Also it was indicated that viscosity decreased with shear rate. Polyurethane including 1.82 wt % TEAB gives the best spinning performance although 0.87 wt % TEAB is the optimum value related to fiber properties such as diameter, uniformity and morphology given the ideal polyurethane nano web structure.     

Effects of PLGA nanofibrous scaffolds structure on nerve cell directional proliferation and morphology

Electrospinning has been recognized as an efficient technique for the fabrication of neural tissue engineering scaffolds. Many approaches have been developed on material optimization, electrospinning techniques, and physical properties of scaffolds to produce a suitable scaffold for tissue engineering aspects. In this study, structural properties of scaffolds were promoted by controlling the speed of fiber collection without any post-processing. PLGA scaffolds, in two significantly different solution concentrations, were fabricated by the electrospinning process to produce scaffolds with the optimum nerve cell growth in a desired direction. The minimum, intermediate and maximum rate of fiber collection (0.4, 2.4, 4.8 m/s) formed Random, Aligned and Drown-aligned fibers, with various porosities and hydrophilicities. The scaffolds were characterized by fiber diameter, porosity, water contact angle and morphology. Human nerve cells were cultured on fiber substrates for seven days to study the effects of different scaffold structures on cell morphology and proliferation, simultaneously. The results of MTT assay, the morphology of cells and scaffold characterization recommend that the best structure to promote cell direction, morphology and proliferation is accessible in an optimized hydrophilicity and porosity of scaffolds, which was obtained at the collector linear speed of 2.4 m/s.     

The role of Na-montmorillonite on thermal characteristics and morphology of electrospun PAN nanofibers

Polymer organic-inorganic hybrid nanofibers constitute a new class of materials in which the polymeric nanofibers are reinforced by uniformly dispersed inorganic particles having at least one dimension in nanometer-scale. In the present study, polyacrylonitrile (PAN) and PAN/Na-montmorillonite (PAN/Na-MMT) nanofibers were conducted via electrospinning process. Electrospun PAN and PAN/Na-MMT fibers with the respective mean fiber diameter of about 220 and 160 nm were prepared. The influence of the clay-montmorillonite on the morphology and diameter of nanofibers was investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The microscopic techniques propose that the PAN/Na-MMT composite nanofibers show lower mean fiber diameter than the neat PAN nanofibers. Besides, the difference in nanoclay-content has a slight effect on the distribution of fibers diameter. Thermogravimetric analysis (TGA) results suggest that introduction of clay-nanomaterials improves the thermal characteristics of fibers.     

Effect of fiber diameter on surface morphology,mechanical property,and cell behavior of electrospun poly(ε-caprolactone) mat

In this study, electrospinning of poly(ε-caprolactone) (PCL) and its optimum preparation conditions were examined in detail using various solvent systems, such as formic acid, dichloromethane/dimethyl formamide (DMF), chloroform/DMF, and dichloroethane. The average fiber diameter of the electrospun PCL mat was controlled by the solvent used with a proper concentration of PCL dope solution. Different fiber sizes (0.1, 0.8, 1.9, and 3.4 μm) of uniform PCL mats were fabricated and the effects of fiber size on surface morphology, tensile properties and cell behavior were investigated. Here, we manipulated much broader range of average fiber diameter of the mats, from nano to several micron size of fiber. It was found that the fiber diameter greatly affected topology (surface roughness) and mechanical properties of the electrospun PCL mat and consequently, they influenced the cell behavior (adhesion and proliferation) significantly. We expect that these results will provide more feasible application of electrospun PCL scaffold in tissue engineering through the co-relations in structure and property of PCL fiber mat on cell behavior.     

Preparation and characterization of PVA/PU blend nanofiber mats by dual-jet electrospinning

A series of blend nanofiber mats comprising poly(vinyl alcohol) (PVA) and polyurethane (PU) were prepared by dual-jet electrospinning in various parameters. Orthogonal experimental design was used to investigate how those parameters affected on fiber diameters and fiber diameter distribution. Altogether three parameters having three levels each were chosen for this study. The chosen parameters were tip-to-collector distance (TCD), voltage and tip-to-tip distance (TTD). Fiber diameters, thermal properties, mechanical properties and hydrophilicity of the blend nanofiber mats were examined by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), tensile test, contact angle and water absorption test, respectively. The results showed that the optimum conditions for PVA/PU blend nanofiber mats fabricated by dual-jet electrospinning were TCD of 20 cm, voltage of 18 kV and TTD of 4 cm. Besides, the thermal stability of PVA/PU blend nanofiber mats had been improved compared with pure nanofibers. Furthermore, the elongation and tensile strength of the blend nanofiber mats were significantly increased compared with pure PVA and pure PU, respectively. And the blend nanofiber mats exhibited well hydrophilicity.     

Effects of wet-spinning conditions on structures,mechanical and electrical properties of multi-walled carbon nanotube composite fibers

A series of composite fibers composed of multi-walled carbon nanotube (MWCNT) and poly(vinyl alcohol) (PVA) are prepared by varying co-flowing wet-spinning conditions such as spinning geometry and PVA concentration, which affect aligning shear stress for MWCNTs during the wet-spinning. Then, structural features, mechanical and electrical performances of MWCNT/PVA composite fibers are investigated as a function of the aligning shear stress of the wet-spinning process. SEM images of the composite fibers exhibit that MWCNTs are wetted effectively with PVA chains. Polarized Raman spectra confirm that the alignment of MWCNTs is enhanced along the composite fiber axis with increasing the aligning shear stress of the spinning process. Accordingly, initial moduli and tensile strengths of the composite fibers are significantly increased with the increment of the aligning shear stress. In addition, it is found that electrical conductivities of MWCNT/PVA composite fibers increase slightly with the aligning shear stress, which is associated with the formation of efficient electrical conduction paths caused by well-aligned MWCNTs along the composite fiber axis.     

Study of synthesizing energy storage microcapsules in PVA spinning solution and thermal regulating fibers prepared by this solution

Thermal regulating fiber has been a research hotspot worldwide recently. In this paper, the energy storage microcapsules composed of silicon dioxide (SiO₂) as shell and paraffin as core were synthesized in the spinning solution of polyvinyl alcohol (PVA). This solution was used to prepare thermal regulating PVA fibers by wet spinning directly. Orthogonal experiment was conducted to optimize the synthetic conditions of the microcapsules. Chemical structure and morphology of the fibers were characterized by Fourier transform infrared-attenuated total reflectance (FTIR-ATR) and scanning electron microscope (SEM) respectively. The thermal properties of the fibers were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Results present that energy storage microcapsules are successfully synthesized in PVA spinning solution with a mean particle size of 1.39 µm. The fibers containing such microcapsules show a high latent heat storage density of 45.39 J g^?1, which also achieve a relatively better thermal stability.     

Fabrication and characterization of polyamide6-room temperature ionic liquid (PA6-RTIL) composite nanofibers by electrospinning

In the present work, polyamide6-room temperature ionic liquid (PA6-RTIL) composite nanofibers and membranes were successfully prepared for the first time by an electrospinning technique. The surface morphology, component analysis, mechanical properties, thermal properties and conductivity of the PA6-RTIL composite membranes were investigated by field-emission scanning electron microscope (FE-SEM), fourier transform infrared spectrometer (FT-IR), tensile testing, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and digit multimeter, respectively. The morphology, fiber diameter, mechanical strength of the obtained fibers can be controlled by changing experimental parameters for electrospinning, especially the content of RTIL in original electrospun mixture solution. The composite fibrous membranes showed ideal mechanical properties and significantly enhanced conductivity, which may be attributed to intrinsic high mechanical strength of PA6 and conductivity of RTIL.     

Fabrication and characterization of nano Al<Subscript>2</Subscript>O<Subscript>3</Subscript> filled PVA:NH<Subscript>4</Subscript>SCN electrolyte nanofibers by electrospinning

Present paper reports a method of preparing polymer composite electrolyte nanofiber mat using polyvinyl alcohol (PVA), ammonium thiocynate (NH₄SCN) salt, and aluminium oxide (Al₂O₃) nano particles based on electrospinning technique. Two-stage process of preparation of nanofibers, namely, preparation of nano particles filled PVA electrolyte gel solution followed by its electrospinning has been used. The so obtained nanofibers have been characterized by XRD, DSC, SEM, and Conductivity measurements. XRD patterns affirm the formation of nanocomposite while SEM pictures reveal formation of fibers on a nano scale format (300–800 nm). Fibers of the electrolytes are seen to be thermally stable. Ionic conductivity of electrolyte fiber is seen to improve in the presence of nano filler at room temperature with a maximum at 5.31×10⁻³ Scm⁻¹ for 4 wt% filler concentration, which is comparable to that for corresponding dried gel electrolyte films.     

Solution blowing nylon 6 nanofiber mats for air filtration

Solution blowing process is a new nanofiber fabricating method with high productivity. In the present study, nylon 6 nanofiber mats were solution blown and the effects of spinning conditions on nanofibers morphology were investigated. The fiber diameter ranged from 150 to 750 nm which was affected by solution concentration, gas pressure and solution feeding rate. The solution blown fibers were three-dimensional curly which made loose construction in bulk. The filtration performance of solution blown mats was evaluated. The tested solution blown nanofiber mats showed high filtration efficiency of 83.10 % to 93.45 % for 0.3 µm particles filtration and extremely low pressure drop of 15.37 to 30.35 Pa. The results indicate the solution blown nanofiber mats will find potential application of high efficiency and low resistance filter.     

Preparation of self-clustering highly oriented nanofibers by needleless electrospinning methods

Polyacrylonitrile (PAN) oriented nanofibers were produced by homemade needleless electrospinning device. Spiral coils were adopted to replace the traditional spinning needles in this equipment. The tracks of multi-jets were controlled by adjusting the microcurrent during the eletrospinning process. The microcurrent value and the motion track of the spinning jet during the spinning process were observed, the fiber morphology and the mechanical properties of fiber membranes were measured. The results revealed that the average diameters of the electrospun fibers were increased from 490 nm to 740 nm. with the addition of organic salt. Meanwhile, the self-clustering phenomenon was obviously observed, and the mechanical properties of obtained fibers were also altered, the tensile strength was improved from 3.63 MPa to 23.90 MPa, while the strain decreased from 74.6 % to 27.1 %.     

Preparation of electrospun affinity membrane and cross flow system for dynamic removal of anionic dye from colored wastewater

In this research, poly(vinyl alcohol) (PVA)/chitosan electrospun nanofibrous membrane (ENM) was prepared by electrospinning method in order to investigate its dye removal ability from colored wastewater. The morphology and average fiber diameter of the membranes were investigated by scanning electron microscopy (SEM), image analysis and atomic force microscopy (AFM). The chemical characterization was studied by Fourier transform infrared spectroscopy (FTIR). The permeability of the membranes was evaluated by measuring pure water flux (PWF). In order to investigate the performance of the prepared membranes they were used in the batch adsorption and membrane separation for dye removal from colored wastewater. The effect of pH, number of membranes and dye concentration on the dye removal ability of the ENM was investigated. Response surface methodology (RSM) was used to achieve multi-objective optimization and equations of adsorption capacity and breakthrough time regarding operating conditions. The results demonstrated the potential of using PVA/chitosan nanofiber membrane as a microfiltration (MF) membrane for dye removal. Moreover, the recoverability property of prepared membranes was noticeable.