Continuous twisted nanofiber yarns fabricated by double conjugate electrospinning

In order to fabricate continuously twisted nanofiber yarns, double conjugate electrospinning had been developed using two pairs of oppositely charged electrospinning nozzles. The principle and process of this novel yarn spinning method were analyzed, and the effect of applied voltage, nozzle distance between positive and negative, solution flow rate and funnel rotating speed on the diameters, twist level and mechanical properties of resultant PAN nanofiber yarns were investigated in this paper. The results indicated that electrospun nanofibers aggregated stably and bundled continuously at the applied voltage of 18 kV, the nozzle distance of 17.5 cm between positive and negative, the overall flow rate of 3.2 ml/h and the flow ratio of 5/3 for positive and negative nozzles. The resultant nanofiber yarns had favorable orientation and uniform twist distribution, and the twist level of nanofiber yarns increased with the increase of the ratio of funnel rotating speed and winding speed. The diameters and mechanical properties of nanofiber yarns depended on their twist level. The diameters of prepared PAN nanofiber yarns ranged from 50 µm to 200 µm, and the strength and elongation of PAN nanofiber yarns at break were 55.70 MPa and 41.31%, respectively, at the twist angle of 41.8 °. This method can be also used to produce multifunctional composite yarns with two or more components.     

Investigation of Parameters for Preparing Nanofiber Yarn via a Stepped Airflow-assisted Electrospinning

Electrospinning is a simple and cost-effective method to prepare fiber with nanometer scale. More importantly, 3D flexible nanofiber yarns that fabricated by electrospinning have shown excellent application prospects in smart textiles, wearable sensors, energy storage devices, tissue engineering, and so on. However, current methods for preparing electrospinning nanofiber yarns had some limitations, including low yarn yield and poor yarn structure. In this paper, a stepped airflow-assisted electrospinning method was designed to prepare continuously twisted nanofiber yarn through introducing stepped airflow into traditional electrospinning system. The stepped airflow could not only help to improve nanofiber yield, but also good for controlling the formed nanofibers to be deposited in a small area. In addition, the experimental methods of single factor variables were used to study the effects of stepped airflow pressure, applied voltage, spinning distance, solution flow rate, air pumping volume and friction roller speed on nanofiber yarn yield, nanofiber diameter, yarn twist and mechanical property. The results showed that prepared nanofiber yarns exhibited perfect morphologies and the yield of nanofiber yarn could reach to a maximum of 4.207 g/h. The breaking strength and elongation at break of the prepared yarn could reach to 23.52 MPa and 30.61 %, respectively.     

Mechanical properties and in vitro degradation of PLGA suture manufactured via electrospinning

The current research discusses the efforts to achieve a Poly(lactide-co-glycolide)(PLGA) nanofiber yarn using two differently charged nozzles with potential application as surgery suture. First, electrospinning parameters such as solution concentration, applied voltage, feed rate were optimized to produce yarn with smooth nanofibers. In order to improve the properties of produced suture, heat setting setup was developed. Two heat setting techniques, including hot water and dry heat were applied, and the influence of the heat setting process on the mechanical properties of yarn was studied. The results showed that heat setting with boiling water was the best method. At first strength, E-modulus and extension of prepared suture were 36.6 MPa, 0.9 GPa and 68.8 % respectively. After improvement with heat setting, strength and E-modulus increased to 63.7 MPa, 2.7 GPa respectively and extension decreased to 29.7 %. Finally, in order to analyze knot performance, two types of surgical knot (square and surgeon) were used, and mechanical properties were investigated. The presence of knot lessens mechanical properties for each two type. Square knot showed better mechanical properties than surgeon’s knot. With square knot strength, E-modulus and extension were 62.1 MPa, 2.1 GPa, 28.6 %, respectively. In vitro study of nanofiber yarn degradation behavior showed that the mechanical properties were decreased. This could be due to greater surface area of nanofibers exposed to surrounding environment.     

Preparation and properties of antibacterial Poly(vinyl alcohol) nanofibers by nanoparticles

Poly(vinyl alcohol) (PVA)/Ag-zeolite nanofiber webs were prepared with different concentrations of Ag-zeolite nanoparticles by the electrospinning technique. Scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Instron, and antibacterial activities analysis were utilized to characterize the morphology and properties of the PVA/Ag-zeolite nanofiber webs. The study results showed that the polymer concentration, applied voltages and tip-to-collector distances were the main factors influencing the morphology of the electrospun nanofiber webs. The introduction of Ag-zeolite nanoparticles improved the mechanical properties and thermal stability of the PVA nanofiber webs. TEM data demonstrated that the Ag-zeolite nanoparticles were well distributed within the nanofiber. FTIR revealed a possible interaction between the PVA matrix and the Ag-zeolite nanoparticles. These fibers showed an antibacterial efficacy of 99.8 % and over against Staphylococcus aureus and Klebsiella pneumoniae at Ag-zeolite concentrations of 1 % and over, because of the presence of the silver nanoparticles in the zeolite.     

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.     

The study on the air volume fraction of electrospun nanofiber nonwoven mats

Electrospinning is an efficient method to produce polymer fibers with a diameter range from nanometers to a few microns using an electrically driven jet. Electrospun nanofiber nonwoven fabrics can be applied into different areas with higher air volume fraction, especially applied into textile materials with good warmth retention property. In this article, the air volume fraction in nonwoven mats made of electrospun nanofibers was verified by studying fiber volume fraction in the mats. Then the relationship between fiber volume fraction and fiber diameter was derived, and the fiber volume fraction is in direct ratio to the square of fiber radius. By experimental verification, to get electrospun PAN nanofiber nonwoven mats with high air volume fraction about 99 %, it can fix the polymer concentration on 8 %. The voltage fixed on 20 kV, the tip-to-collector distance on 15 cm. The experiment is in accordance with the theory excellently.     

Fabrication of continuous nanofiber core-spun yarn by a novel electrospinning method

Continuously twisted polyacrylonitrile/viscose nanofiber core-spun yarns were fabricated through novel self-designed multi-nozzle air jet electrospinning set-up. The effect of voltage, solution flow rate, air flow rate and funnel rotating speed on coating rate of core-spun yarn, nanofiber diameter, twist level and mechanical property were discussed. The results showed that polyacrylonitrile/viscose nanofiber core-spun yarns with perfect nanofiber orientation and uniform twist distribution could be obtained at voltage of 32 KV, solution flow rate of 32 ml/min and air flow rate of 1000 ml/min, and the spinning speed could reach to 235.5 cm/min. The diameters of outer coated nanofiber distributed from 100 nm to 300 nm, and nanofiber coating rate could reach to 70.4 %. In addition, the strength and elongation at break increased from 30.82 MPa to 69.65 MPa and from 28.34 % to 43.29 % at the twist angle of 46.6 °, respectively.     

Fabrication and characterization of PET nanofiber hollow yarn

In this study, various concentrations of polyethylene terephthalate (PET) polymeric solution were investigated to produce hollow nanofiber yarn. First, the electrospining apparatus was designed in a way that to put PVA multifilament in the core and to twist PET nanofibers onto multifilament yarn as a sheath simultaneously, followed by dissolving PVA yarn in hot water, PET hollow nanofiber yarn was produced. In this survey, it has been observed that the average thickness of sheath increased by increasing concentrations of PET polymeric solution. Results showed that maximum efficiency of extracting the PVA multifilament from the hollow yarn under certain conditions (concentration of 18 % (w/v) of PET, applied voltage of 10 kV, and flow rate of 0.0526 ml/h) was more than 85 %. The mechanical and physical properties of PET hollow yarns were investigated and indicated that the hollow nanofiber yarns at concentration of 30 % and 18 % polymeric solution had the lowest strength and the highest regain moisture, respectively.     

Microstructure and mechanical properties of polyurethane fibrous membrane

A series of PU fibrous membranes were fabricated by using electrospinning method. The microstructure of the membranes was characterized by field-emission scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectrum. Their mechanical properties were tested by dynamic mechanical thermal analysis and stress-strain behaviors. The solution concentration, the applied voltage and the tip-collector distance had an effect on the crystallinity degree and molecular orientation of PU, the size and distribution of the fiber diameter and the point-bonded structures between the fibers, leading to the change in the microstructure and the mechanical properties of the fibrous membrane. Fibers with a smaller diameter had higher strength but lower ductility. The fibrous membranes indicated the similar stress-strain behaviors, which slopes in the initial stage were low and that in the later stage were high. The initial elastic behavior with the low Young’s modulus were attributed to the network structure of the fibrous membranes and that with the high Young’s modulus was from the electrospun PU fibers.     

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.     

Investigation on the Biodegradability and Antibacterial Properties of Nanohybrid Suture Based on Silver Incorporated PGA-PLGA Nanofibers

Polyglycolic acid-poly lactic glycolic acid (PGA-PLGA) electrospun nanofibers containing silver nanoparticles have been produced and twisted into the nanofibrous yarn. The morphology of nanofibers and produced yarns, as well as the mechanical properties of the yarns, were investigated. Furthermore, in vitro antibacterial properties and in vitro degradation behavior of yarns containing various silver nanoparticles were studied. SEM images confirmed that the addition of the silver nanoparticles into the polymer solution increases the fiber diameters. The result of the mechanical test of the yarns alone and used in two different forms of the knots was measured and results showed that the strength of the yarns without the knot was significantly more than that of others. The biodegradability test showed that the mechanical properties and the weight of the yarns were quickly reduced after subjecting to in vitro condition. The result of the antibacterial test indicated that the nanofiber yarns containing %3 silver nanoparticles were the most appropriate sample with a considerably antibacterial activity against both gram-positive bacterium Staphylococcus aureus and gram-negative bacterium Escherichia Coli with inhibition zones of 8.1 and 9.5 mm, respectively; which demonstrated that silver nanoparticles retained their effectiveness after the electrospinning process. Therefore the nanofibrous yarns containing silver nanoparticles could be successfully produced by the electrospinning process with the proper antibacterial property as a candidate for the surgical sutures.     

Application of electrospun polyurethane web to breathable water-proof fabrics

Electrospun web may possibly be widely applied to protective garments or specialty textiles due to its high level of protection as well as comfort. Of particular interest in this study is to develop waterproof-breathable fabric by applying electrospun web of polyurethane directly onto the substrate fabric. The optimal electrospinning condition was examined with regards to the concentration, applied voltage and tip-to-collector distance. Solvent-electospinning of polyurethane was performed at the optimum condition, using N,N-dimethylacetamide as solvent. The thickness of 0.02 mm of electrospun web was applied onto the polyester/nylon blended fabric. For comparison, the polyester/nylon fabrics were coated with 0.02 mm thickness of polyurethane resin membranes adopting four different conditions. The electrospun PU web/fabric was compared to resin coated fabrics in terms of water-proof and breathable properties. The electrospun web applied fabric showed higher air permeability, vapor transmission, and thermal insulation properties than resin coated fabrics, which can be translated as greater comfort sensation of electrospun applied fabrics. However, water resistance value of electrospun web applied fabric did not reach that of resin coated fabrics.     

Electrospun nanostructures based on polyurethane/MWCNTs for strain sensing applications

Electrically conductive nanofibers were fabricated from elastic polyurethane (PU) and PU/multiwalled carbon nanotubes (MWCNTs) nanocomposite by electrospinning method. The nanocomposites were electrospun at various MWCNTs loading. Electron microscopy was used to investigate nanofibers morphology and dispersion of MWCNTs in the electrospun nanofibers. The results showed that the presence of the MWCNTs promoted the creation of fibrous structures in comparison with the PU without MWCNTs. On the other hand, increasing the MWCNTs content resulted in a slight increase in the average fiber diameter. TEM micrographs and mechanical properties of the electrospun mats indicated that the homogeneous dispersion of MWCNTs throughout PU matrix is responsible for the considerable enhancement of mechanical properties of the nanofiber mats. Electrical behavior of the conductive mats was also studied, in view of possible sensor applications. Cyclic experiments were conducted to establish whether the electrical properties were reversible, which is an important requirement for sensor materials.     

An investigation on the effects of twist on geometry of the electrospinning triangle and polyamide 66 nanofiber yarn strength

The formation of a symmetric electrospinning triangle zone (E-triangle) via a technique based on using two oppositely charged nozzles is described for fabricating continuous twisted nanofiber yarn of polyamide (Nylon 66). This study shows how changing the dimensions and geometry of the E-triangle influences the distribution of nanofiber tension and diameter in this zone, and consequently how it affects the nanofiber yarn strength. The twist effect on the E-triangle geometry was investigated by changing the rotational speed of the twister plate of values of 96, 160, 224 and 288 rpm. The results showed that by increasing the twist rate, the apex angle of the E-triangle increased, whereas the height and width of the Etriangle decreased. An energy method was adopted to study the distribution of tension on nanofibers in the E-triangle. Considering a constant spinning tension, it was observed that the gradient of the nanofiber tension curve was steeper and the extreme values of tension on nanofibers were increased by increasing the twist rate. Furthermore, the mean diameter reduction of nanofibers confirmed these results. It is concluded that mechanical properties of nanofiber yarn have been considerably improved by increasing the twist rate and changing the shape of the E-triangle.     

Metal ion adsorbability of electrospun wool keratose/silk fibroin blend nanofiber mats

In this study, electrospun wool keratose (WK)/silk fibroin (SF) blend nanofiber was prepared and evaluated as a heavy metal ion adsorbent which can be used in water purification field. The WK, which was a soluble fraction of oxidized wool keratin fiber, was blended with SF in formic acid. The electrospinnability was greatly improved with an increase of SF content. The structure and properties of WK/SF blend nanofibers were investigated by SEM, FTIR, DMTA and tensile test. Among various WK/SF blend ratios, 50/50 blend nanofiber showed an excellent mechanical property. It might be due to some physical interaction between SF and WK molecules although FTIR result did not show any evidence of molecular miscibility. As a result of metal ion adsorption test, WK/SF blend nanofiber mats exhibited high Cu²⁺ adsorption capacity compared with ordinary wool sliver at pH 8.5. It might be due to large specific surface area of nanofiber mat as well as numerous functional groups of WK. Consequently, the WK/SF blend nanofiber mats can be a promising candidate as metal ion adsorption filter.     

RSM and ANN approaches for modeling and optimizing of electrospun polyurethane nanofibers morphology

This paper focused on using response surface methodology (RSM) and artificial neural network (ANN) to analyze polyurethane (PU) nanofibers morphology synthesized by electrospinning. The process was characterized in detail by using experimental design to determine the parameters that may affect the nanofibers morphology such as polymer concentration, a tip to collector distance and applied voltage. It was concluded that solution concentration plays an important role (relative importance of 79.85 %) against nanofibers diameter and its standard deviation. Based on the results, applied voltage has a different effect on the nanofiber diameter at low and high solution concentrations. Moreover, the tip to collector distance parameter has no significant impact on the average nanofiber diameter. The finest PU nanofiber (201 nm) was obtained from experimental under conditions of: 9 w/v% polymer concentrations, 12 cm tip to collector distance and 16 kV applied voltage. The results show a very good agreement between the experimental and modeled data. It was demonstrated that both models (specially, in case of neural network) are excellent for predicting diameter of PU nanofibers. Furthermore, numerical optimization has been performed by considering desirability function to access the region in design space that introduces minimum average diameter.     

Preparation and characterization of (polyurethane/nylon-6) nanofiber/ (silicone) film composites <Emphasis Type="Italic">via</Emphasis> electrospinning and dip-coating

This paper reports on the preparation and characterization of nanofibers and nanofiber/film composites fabricated by electrospinning and dip-coating. The polymers in this study consist of polyurethane, nylon-6, and silicone. Scanning electron microscopy (SEM), fiber distribution, X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR) and tensile tests were conducted. The electrospun nylon-6 nanofiber/dip-coated silicone film (dried for 5 min) showed the optimum tensile strength and strain results, showing an increase in tensile strength of 63 % compared to pure nylon-6 nanofiber alone. XRD and FTIR verified the presence of individual polymers in the composite matrix. The electrospun PU nanofiber produced the biggest fiber diameter, while electrospun nylon-6, and PU/nylon-6 produced uniform fiber diameters, with PU/nylon-6 obtaining very random and curved fiber morphology.     

Prediction of diameter in blended nanofibers of polycaprolactone-gelatin using ANN and RSM

Fabrication of nanofibers with a defined diameter is a primary purpose of the electrospinning process. The diameter of nanofiber is directly related to its individual features, such as mechanical property and porosity. The motivation to conduct the current study was to explore the diameter of hybrid nanofibers of polycaprolactone-gelatin (PCL-GT) as one of the most attractive scaffolds employed in various research fields, such as tissue engineering and industrial fields. We have developed two predictive models describing the electrospinning process of PCL-GT using response surface methodology (RSM) and artificial neural network (ANN). The effect of 4 variables on diameter was analyzed, including total polymer concentration, ratio of PCL to Gel, voltage, and tip-to-collector distance. The individual and interactive effects of the mentioned factors were analyzed using RSM. The total polymer concentration had the most significant individual effect on the diameter of PCL-Gel nanofiber, whereas the other three factors showed less strong individual effects, although, the interactive effects of these factors were more remarkable. It was demonstrated that both models, especially the ANN model, could accurately predict the diameter of PCL-GT nanofiber (regression coefficient > 0.92, mean absolute percentage error < 5.7). The represented predictive models could facilitate construction of electrospun nanofibers from PCL-Gel with wellcontrolled diameter required for any intended purpose.     

Ultrasound-mediated preparation and evaluation of a collagen/PVP-PCL micro- and nanofiber scaffold electrospun from chloroform/ethanol mixture

In this study, to improve the cellular biocompatibility of PVP-PCL micro- and nanofiber scaffold, a novel electrospun collagen/PVP-PCL micro- and nanofiber scaffold was sucessfully prepared assisted by ultrasonic irradiation using chloroform/ethanol mixtures as solvent. The micro- and nanofibers of the electrospun PCL-PVP scaffolds still presented compact inter-fiber entanglement and three-dimensional netlike network with some certain range of pore space after introducing collagen. The incorporated collagen phase was dispersed as inclusions within the electrospun fibers, and then could be easily released by immersing the scaffold in Hanks simulated body fluid. Meanwhile, the integral triple helix structure of collagen could be maintained after blending with the PVP-PCL mixture due to the weak intermolecular interactions. Furthermore, the suitable mechanical and degradation properties of the PVP-PCL scaffold were still reserved after introducing collagen, and the introduction of collagen could further promote the thermostability of the PVP-PCL scaffold. Above all, the collagen/PVP-PCL scaffold showed no cytotoxicity, better cell proliferation, and improved viability of primary fibroblasts than the PVP-PCL scaffold. In conclusion, blending collagen with the PVP-PCL mixture in this study has potential for promoting the biocompatibility of PVP-PCL micro- and nanofiber scaffolds for tissue engineering.     

Crystallization of PVDF in graphene-filled electrospun PVDF/PMMA nanofibers processed at three different conditions

In this study, the morphology and crystal polymorphism of electrospun blend nanocomposite of graphene filled-polyvinylidene fluoride (PVDF)/poly(methyl methacrylate) (PMMA) nanofibers were investigated. The preparation of the nanofibers was carried out by synthesis of PMMA/graphene as a masterbatch through in-situ polymerization, and then followed by compounding with PVDF solution in the different ratios. The process of electrospinning was done at three selective conditions of temperature, moist and ordinary environment. Crystallinity, morphology and thermal properties of nanofibers were characterized by X-ray diffraction spectroscopy (XRD), differential scanning calorimetric (DSC), Transmittance Electron Microscopy (TEM), Thermogravimetric Analyses (TGA), and Field Emission Scanning Electron Microscopic (FE-SEM). The enhancement of β crystal formation in the electrospun graphene-filled blend nanofibers was confirmed by XRD and DSC results. This can be ascribed by the benefits of solution casting, mechanical stretching, high electric field, PMMA interactions and graphene restrictions, altogether in one simple process. Also, presence of water molecules during the electrospinning causes the orientation of fluorine atoms in PVDF due to polar-polar interactions which enhance the polar conformation even in the pure PVDF nanofibers.