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.     

Preparation and characterization of nanoscaled poly(vinyl alcohol) fibers via electrospinning

Nanoscaled PVA fibers were prepared by electrospinning. This paper described the electrospinning process, the processing conditions, fiber morphology, and some potential applications of the PVA nano-fibers. PVA fibers with various diameters (50–250 nm) were obtained by changing solution concentration, voltage and tip to collector distance (TCD). The major factor was the concentration of PVA solution which affected the fiber diameter evidently. Increasing the concentration, the fiber diameter was increased, and the amount of beads was reduced even to 0%. The fibers were found be efficiently crosslinked by glyoxal during the curing process. Phosphoric acid was used as a catalyst activator to reduce strength losses during crosslinking. Scanning electron micrograph (SEM) and differential scanning calorimetric (DSC) techniques were employed to characterize the morphology and crosslinking of PVA fibers. It was found that the primary factor which affected the crosslinking density was the content of chemical crosslinking agent.     

Electrospun Sericin/PVA/Clay nanofibrous mats for antimicrobial air filtration mask

In this study, Sericin/Poly Vinyl Alcohol (PVA)/Clay (Cloisite 30B) nanofibrous mats are prepared by electrospinning technique for antimicrobial air filtration mask. The process parameters of electro-spinning machine such as acceleration voltage, nozzle flow rate and nozzle & collector distance are optimised on the basis of morphology of fibre observed through scanning electron microscopy (SEM). The optimum conditions for producing nanofibrous mat without bead are acceleration voltage 27.5 kV, nozzle collector distance 8 cm and flow rate 0.8 ml/hr using 10 % (w/v) solution of Sericin/PVA (1:1 wt/wt). The process parameters of electro-spinning machine for the processing of Sericin/PVA/Clay nanofibrous mats with varied clay concentrations ranging from 0.1-0.75 % are also optimized. The spun fibre diameter varied from 300-400 nm at different specified conditions. These nanofibrous mats are characterized for its structural, mechanical and antimicrobial properties. Respirable Suspended Particulate Matter (RSPM) test was conducted to check the particulate matter (PM 2.5) absorption capacity of nanofibrous mats. Results shows that sericin/PVA/clay nanofibrous mat would be a promising material for making protecting clothing based air filtration mask.     

Comparison study on transparent composites with different patterns of nanofiber reinforcement

In this work, PA-6 core and PMMA shell composite nanofiber mats together with pure PMMA and PA-6 nanofibrous membranes were obtained through electrospinning. Two kinds of transparent composites were fabricated by hot pressing multilayers of the composite nanofiber mats and of the interlaced pure PA-6 with PMMA nanofibrous membranes, respectively, under the same processing condition and with the same amount of PA-6 nanofiber content. Tensile properties and visible light transmittances of the two transparent composites were characterized. It has been found that both the tensile behavior and the visible light transmittance of the composites obtained from the composite nanofiber mats were better than the counterparts from the interlaced pure PA-6 and PMMA nanofibrous membranes. With a minor loss of less than 10 % in the transparency, a maximal increase of around 20 % in the tensile modulus and tensile strength has been recognized for a transparent composite from the composite nanofibers. Although less efficient, the tensile strengths of the composites from the interlaced nanofibrous membranes were all higher than that of a transparent panel processed from the pure PMMA nanofibers.     

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.     

Effect of hot-stretching on morphology and mechanical properties of electrospun PMIA nanofibers

Well-aligned PMIA nanofiber mats were fabricated by electrospinning and then hot-stretching along the fiber axis was used to improve the mechanical properties of nanofibers in this paper. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Differential scanning calorimetry (DSC) were used to characterize the morphology and properties of nanofibers. The results showed that the nanofibers became thinner and better alignment than the as-spun nanofibers after hotstretching, and the average diameter of the nanofibers decreased with the increasing of the tensile force. In the same time, hotstretching improved the crystallinity and T _g of the as-spun PMIA nanofibers. The tensile strength and modulus of the hotstretched nanofiber mats peaked at ca.50 % and ca.196 % respectively at the tensile force of 12 N compared with the as-spun nanofiber mats.     

Preparation of poly(vinyl alcohol)/ZrO2 composite nanofibers via co-axial electrospinning with higher ZrO2 particle content

Poly(vinyl alcohol) (PVA)/zirconium oxide (ZrO₂) composite nanofibers with a skin-core structure were prepared and the effect of ZrO₂ particle content on uniform web formation was investigated. The optimized polymer concentration, tip to collector distance, and applied voltage for electrospinning were 11 wt%, 12 cm, and 20 kV, respectively. Skin-core PVA/ZrO₂ composite nanofibers containing up to 12 wt% ZrO₂ were successfully prepared, but it was difficult to obtain PVA/ZrO₂ composite nanofiber webs via conventional electrospinning. Increasing the amount of ZrO₂ caused the morphology of the PVA/ZrO₂ composite nanofibers to become a non-uniform nanoweb with irregular nanofiber diameters. While it was difficult to obtain a uniform nanofiber web containing a content of ZrO₂ over 6 wt% for conventional electrospinning, a more uniform nanofiber web could be obtained at up to 9 wt% ZrO₂ using a skin-core dual nozzle. More uniform webs could also be obtained when ZrO₂ was in the skin rather than the core.     

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.     

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.     

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.     

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.     

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.     

Core-sheath polyurethane-carbon nanotube nanofibers prepared by electrospinning

The core-sheath nanofibers consisting of polyurethane (PU) core and PU composites sheath with multi-walled carbon nanotubes (MWNTs) were prepared by electrospinning. At low MWNT concentration, MWNTs appeared highly aligned along the fiber axis with some curving in nanotubes, whereas in case of high concentration, some aggregation of MWNTs appeared due to difficulty in full dispersion of nanotubes. In comparison of the single component nanofiber webs, the core-sheath nanofiber webs showed much better mechanical properties of modulus and breaking stress, including an exceptional elongation-at-break. It indicates that the CNT-incorporated core-sheath structure is very effective for enhancing the mechanical properties of nanofiber webs. In addition, the core-sheath nanofibers demonstrated the fast shape recovery, compared with one component fibers of pure shape memory PU and PU/MWNTs, which provides the possibility of fabricating more sensitive intelligent materials.     

Effect of Electric Field on the Directly Electrospun Nanofiber Yarns: Simulation and Experimental Study

Electric field plays a key role in electrospinning process for nanofiber and nanofiber yarn producing. The electric field distribution of the yarn manufacturing system is simulated by using finite element method analysis. The effects of electric field distribution and intensity were studied to analyze the influence of the electric field on the electrospun nanofiber yarn surface morphology, mechanical, thermal and water absorption properties. The results show that the morphology and diameters of nanofiber and yarn were obviously affected by the electric field with changing the needle distance and applied voltage, which further influence the mechanical performance of the yarn. The needle distance does not much affect the thermal property of the PSA electrospun yarn, whereas the yarn obtains better thermal resistance properties at voltage of 25 kV. The nanoyarn electrospun and assembled under higher applied voltage is proved to have a better wicking property in our research.     

EDC/NHS crosslinked electrospun regenerated tussah silk fibroin nanofiber mats

The tussah silk fibroin (TSF) nanofibers with 611 nm diameters were prepared by electrospinning with the solvent hexafluoroisopropanol (HFIP). And then, the TSF nanofibers were crosslinked by 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide/N-Hydroxysuccinimide (EDC/NHS) crosslinking agent. The morphology and microstructure of the crosslinked TSF nanofibers were characterized by scanning electron microscopy (SEM), Fourier transforms infrared analysis (FTIR), X-ray diffraction, Instron electronic strength tester, and cell culture. After treatment with EDC/NHS crosslinking agent, the TSF nanofibers swelled and its average diameter increased from 611 to 841 nm. FTIR and X-ray diffraction results demonstrated that random coil, ??-helix, and ??-sheet co-existed in the TSF nanofiber mats, but the content of ??-sheet increased from 25.26 to 45.34 %, and the random coil content decreased from 32.47 to 24.94 %. Compared with the electrospun pure TSF nanofiber mats, the crosslinked TSF nanofiber mats exhibited a lower breaking tenacity and initial modulus, which were 5.51 MPa and 9.86 MPa, respectively. At the same time, the extension at break of the crosslinked TSF nanofiber achieved 109.38 %. In cell culture evaluation, the crosslinked TSF nanofibers were found to support cell adhesion and spreading fibroblast L373 and bone marrow mesenchymal stem cells (BMSCs), which had potential utility in a range of tissue engineering.     

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.     

Gallium arsenide (GaAs) nanofibers by electrospinning technique as future energy server materials

Gallium arsenide (GaAs) does have superior electronic properties compared with silicon. For instant, it has a higher saturated electron velocity and higher electron mobility. Weak mechanical properties and high production cost are the main drawbacks of this interesting semiconductor. In this study, we are introducing production of GaAs nanofibers by electrospinning methodology as a very low cost and yielding distinct product technique. In general, nano-fibrous shape is strongly improving the physical properties due to the high surface area to volume ratio of this nanostructure. The mechanical and environmental properties of the GaAs compound have been modified since GaAs nanofibers have been produced as a core inside a poly(vinyl alcohol) (PVA) shell. GaAs/PVA nanofibers were prepared by electrospinning of gallium nitrate/PVA solution in presence of arsenic vapor. The whole process was carried out in a closed hood equipped with nitrogen environment. FT-IR, XPS, TGA and UV-Vis spectroscopy analyses were utilized to confirm formation of GaAs compound. Transmission electron microscope (TEM) analysis has revealed that the synthesized GaAs compound is crystalline and does have nano-fibrous shape as a core inside PVA nanofibers. To precisely recommend the prepared GaAs nanofiber mats to be utilized in different applications, we have measured the electric conductivity and the band gap energies of the prepared nanofiber mats. Overall, the obtained results affirmed that the proposed strategy successfully remedied the drawbacks of the reported GaAs structures and did not affect the main physical properties of this important semiconductor.     

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.     

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.     

Palladium immobilized on aminated polyacrylonitrile nanofiber as an efficient heterogeneous catalyst for Heck reaction

Aminated polyacrylonitrile (PAN-NH) nanofiber mats prepared by electrospinning and then aminated by multiamines with different chemical structures have been used for the immobilization of palladium. The PAN-NH fiber morphologies were characterized by scanning electron microscopy (SEM) and the dispersion of palladium particles on the PAN-NH fiber were examined by transmission electron microscopy (TEM). The catalytic activity and recyclability of the prepared heterogeneous palladium catalysts have been evaluated by the Heck reaction of iodobenzene with n-butyl acrylate. It was found that the catalytic activities of PAN-NH-Pd catalysts could be correlated with the chelating energies of the PAN-NH fiber mats with Pd active species.