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.     

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 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.     

The influence of graphene reinforced electrospun nano-interlayers on quasi-static indentation behavior of fiber-reinforced epoxy composites

The aim of this research is to investigate the development and evaluation of hybrid multi-scale aramid/epoxy composites interleaved with electrospun graphene nanoplatelets/nylon 66 (GNPs/PA66) mats. The reinforced nanofiber mats were explored for their best mechanical properties and PA66 nanofibers with 1 wt% GNPs were selected for composite production. Quasi-static indentation tests were performed on both pristine and nanofiber-modified composites. The experimental results revealed that the introduction of reinforced interleaves within the interlaminar interfaces of composites promotes fracture toughness compared to pristine interleaves. It is shown that there is a particular interleaf thickness for optimum toughening effect of nanofibers. The optimum thicknesses for pristine and reinforced interleaves are 35 and 17.5 μm, respectively.     

Electrospinning of <Emphasis Type="Italic">Bombyx mori</Emphasis> silk fibroin nanofiber mats reinforced by cellulose nanowhiskers

Cellulose nanowhisker (CNW) reinforced electrospun Bombyx mori silk fibroin (SF) nanofibers were fabricated. The morphology, structure, and mechanical properties of nanofibers were investigated by FE-SEM, TEM, FTIR, and tensile testing. It was found that the nanofiber size decreased obviously from 250 nm in the unreinforced mat to 77–160 nm in the CNW reinforced mats depending on the CNW content due to the increased conductivity of spinning dope. In the reinforced mats, the CNWs were embedded in the SF matrix separated from each other, and aligned along the fiber axis. There was a positive correlation between the CNW content and the tensile strength and Young’s modulus of reinforced mats. However the strain at break dropped gradually with the increase of CNW. When the CNW content was 2 w/w%, the tensile strength and Young’s modulus of reinforced SF nanofiber mats were about 2 times higher than those of unreinforced mat.     

Fabrication and characterization of mechano-modulated PET/BPU nanofibrous mats as potential vascular grafts materials

Polyethylene terephthalate (PET)/biomedical polyurethane (BPU) composite nanofibers with modulated mechanical properties are electrospun by varying the weight ratios of PET and BPU polymers in the mixture. The effect of BPU content on the morphology, porosity, thermal properties, and crystalline structures are systematically investigated. It is shown that uniform PET/BPU nanofibers can be formed through optimization. When the content of BPU is low (0?C7 %), better elongation of the nanofibrous mats is obtained with the increase of BPU content, whereas further increasing the BPU polymer (up to 15 %) results in a decreased breaking elongation as well as the mechanical strength of composites. The formed nanofibrous mats may find potential applications in tissue engineering and vascular graft.     

Electrospinning of cellulose nanofibers mat for laminated epoxy composite production

In this study, a new approach consisting of chemical treatment steps followed by electrospinning process was applied to produce cellulose nanofibers from wheat straws. Wheat straws were initially pretreated by NaOH solution to open the complex structure of raw materials and remove non-cellulosic materials. Then, acid and alkali hydrolysis was separately performed to eliminate hemicellulose and soluble lignin. Also, bleaching processes were implemented to remove the insoluble lignin. Cellulose nanofibers were produced by electrospinning of various concentrations of cellulose in different solvents including sodium hydroxide/urea/thiourea, pure trifluoroacetic acid (TFA), and TFA/methylene chloride. Images obtained by Scanning Electron Microscope (SEM) showed long and uniform nanofibers produced from electrospinning of cellulose/TFA/methylene chloride solution. An epoxy based laminated composite was prepared by a lamina of cellulose microfiber and electrospun nanofiber mat using hand lay-up composite manufacturing method. The fracture surface of the epoxy nanocomposite was analyzed by SEM images. In addition, the mechanical properties of laminated epoxy composites were compared with pure epoxy by conducting tensile and impact tests. Tensile test results showed that the ultimate tensile strength, elongation, and modulus of laminated epoxy nanocomposites were significantly increased. Moreover, it was found that by adding a nanofiber lamina in the epoxy composite, the impact resistance was significantly improved as a result of crack growth prevention.     

Hybrid multi-scale basalt fiber-epoxy composite laminate reinforced with Electrospun polyurethane nanofibers containing carbon nanotubes

In this study, we report the fabrication and evaluation of a hybrid multi-scale basalt fiber/epoxy composite laminate reinforced with layers of electrospun carbon nanotube/polyurethane (CNT/PU) nanofibers. Electrospun polyurethane mats containing 1, 3 and 5 wt% carbon nanotubes (CNTs) were interleaved between layers of basalt fibers laminated with epoxy through vacuum-assisted resin transfer molding (VARTM) process. The strength and stiffness of composites for each configuration were tested by tensile and flexural tests, and SEM analysis was conducted to observe the morphology of the composites. The results showed increase in tensile strength (4–13 %) and tensile modulus (6–20 %), and also increase in flexural strength (6.5–17.3 %) and stiffness of the hybrid composites with the increase of CNT content in PU nanofibers. The use of surfactant to disperse CNTs in the electrospun PU reinforcement resulted to the highest increase in both tensile and flexural properties, which is attributed to the homogeneous dispersion of CNTs in the PU nanofibers and the high surface area of the nanofibers themselves. Here, the use of multi-scale reinforcement fillers with good and homogeneous dispersion for epoxy-based laminates showed increased mechanical performance of the hybrid composite laminates.     

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.     

Facile fabrication of carbon nanotubes/polystyrene composite nanofibers for high-performance electromagnetic interference shielding

Polystyrene (PS) composites with nanofibrous structure consisting of multi-walled carbon nanotubes (MWCNTs) with 0-10 wt.% of nanofiller have been fabricated via electrospinning technique. The surface morphology and thermal properties of the composites were evaluated by scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA). The SEM analysis of the composite nanofibers samples revealed that the average diameter of the nanofibers increases with increasing MWCNTs content. The resultant MWCNTs/PS composite nanofibers diameters were in the range of 391±63 to 586±132 nm. The thermal stability of composites was increased after addition of MWCNTs to PS matrix. The electrical conductivity of the composites with different weight percentage of MWCNTs was investigated at room temperature. Electrical conductivity of MWCNTs/PS composite nanofiber followed percolation theory having a percolation threshold V _c= 0.45 vol% (~0.75 wt. %) and critical exponent q=1.21. The electrical conductivity and thermal properties confirmed the presence of good dispersion and alignment MWCNTs encapsulated within the electrospun nanofibers. The electromagnetic interference (EMI) shielding effectiveness of the MWCNTs/PS composites was examined in the measurement frequency range of 8.2-12.4 GHz (X-band). The total EMI shielding efficiency of MWCNTs/PS composite nanofibers increased up to 32 dB. The EMI shielding results for MWCNTs/PS composite nanofibers showed that absorption loss was the major shielding mechanism and reflection was the secondary mechanism. The present study has shown the possibility of utilizing MWCNTs/PS composite nanofibers as EMI shielding/absorption materials.     

Electrospun grape seed polyphenols/gelatin composite fibers contained silver nanoparticles as biomaterials

GSP/gelatin composite nanofiber membranes containing silver nanoparticles were successfully fabricated as a novel biomaterial by electrospinning. The silver nanoparticles (AgNPs) were synthesized with the grape seed polyphenols (GSP) as reducing agent in aqueous solution of gelatin, and then the GSP/gelatin/AgNPs mixed solution was electrospun into nanofibers at 55 °C. The scanning electron microscopy (SEM) confirmed that the composite fibers were uniform and the average fiber diameter ranged between 150 nm and 230 nm with an increase in applied potentials from 14 kV to 22 kV. And the transmission electron microscopy (TEM) showed that silver nanoparticles distributed individually in the fibers with the average particle size of about 11 nm. Furthermore, the ultraviolet visible spectrophotometer (UV-vis spectroscopy) test demonstrated that all of Ag⁺ converted to Ag⁰ when the concentration of gelatin was 24 wt% and the mass ratio of GSP to AgNO₃ was about 5:2. The antibacterial activities of the fiber membranes against E.coli and S.aureus were measured via a shake flank test and demonstrated good performance after the importation of silver nanopaticles. Cytotoxicity testing also revealed that fiber membranes contained silver nanoparticles had no cyto-toxic. All the results indicated that the GSP was effective for the formation and stabilization of silver nanoparticles in composite nanofibers mats which had the potential for applications in antimicrobial tissue engineering and wound dressing.     

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 and characterization of nylon-6/gelatin composite nanofibers via electrospinning for biomedical applications

Easy fabrication, porosity, good mechanical properties, and composition controllable of the electrospun nanofiber mat make this material a promising candidate for wound dressing applications. In the present study, nylon6/gelatin electrospun nanofiber mats are introduced as novel wound dressing materials. The introduced mats were synthesized by electrospinning of nylon6 and gelatin mixtures, three mats containing different gelatin content were prepared; 10, 20 and 30 wt%. Interestingly, addition of the gelatin did not affect the mechanical properties of the nylon 6, moreover the mat containing 10 wt% gelatin revealed higher mechanical properties due to formation of spider-net like structure from very thin nanofibers (～10 nm diameter) bonding the main nanofibers. Biologically study indicates that gelatin incorporation strongly enhances the bioactivity performance as increasing the gelatin content linearly increases the MC3T3-E1 cell attachment. Overall, the obtained results recommend exploiting the introduced mats as wound dressing material.     

Fabrication of hollow nanofibrous structures using a triple layering method for vascular scaffold applications

This study aims to develop a new approach for fabricating hollow nanofibrous yarns by engineering a triple-layer structure (polyvinyl alcohol (PVA) multifilament core surrounded by a layer of PVA nanofibers and a polylactic acid (PLA) nanofiber outer layer). After fabrication of this 3-layer structure, the core portion was extracted, leaving the outer layer intact after dissolving the PVA nanofibers in water. To determine the optimum thickness of the outer layer, hollow nanofiber yarns with five different thicknesses were produced. A hollow nanofiber yarn was also produced using a common method to enable comparison of the methods. In the common method, a core sheath yarn consisting of a PVA multifilament core and a PLA nanofiber outer layer was fabricated, and a hollow yarn was produced by placing the core yarn in hot water. The results revealed facilitation of core extraction from the yarn body of the new 3-layer structure, which occurred due to rapid dissolution of the middle layer. The wicking behavior in the hollow yarn fabricated using the novel method followed the Locus Washburn equation and that of the hollow yarn produced from the core sheath yarn deviated from it. The results demonstrated that tensile properties of hollow nanofiber yarns were improved by increasing the thickness. Furthermore, hemolysis and cytotoxicity assays indicated that the fabricated hollow nanofibrous structure is non-toxic and blood compatible, indicating its potential for use in biomedical applications such as vascular scaffolds.     

Yarn formation of nanofibers prepared using electrospinning

In this study, the process of electrospinning was used on nanofiber yarn formation. The parameters in the study were flow rate and twist multiplier, which were discussed their effect on yarn formation. Further, a normal yarn was used as the core yarn, which was wrapped with nanofibers to form a new type of composite yarn. In this part of the experiment, the parameters were flow rate and collector width, which were discussed in terms of their effect on the yarn quality of nanofibrous composite yarn. The experiment result showed the diameter of the nanofiber was between 220 nm to 260 nm. When the collector width was 5 mm, there was a high quality wrapping resulting in good yarn, with the nanofiber composite yarn having a strength of 3.25 (cN/dtex).     

Preparation of electrospun silk fibroin/Cellulose Acetate blend nanofibers and their applications to heavy metal ions adsorption

Silk fibroin (SF)/Cellulose Acetate (CA) blend nanofibrous membranes were prepared by electrospinning and their heavy metal absorbabilities were examined in an aqueous solution after ethanol treatment. The electrospun nanofibrous membranes were comprised of randomly oriented ultrafine fibers of 100–600 nm diameters. As a result of field emission electron microscope (FEEM), the anti-felting properties of the blend nanofibrous membranes were markedly improved after treatment with 100 % ethanol when SF was blended with CA. Metal ion adsorption test was performed with Cu²⁺ as a model heavy metal ion in a stock solution. The SF/CA blend nanofiber membranes showed higher affinity for Cu²⁺ in an aqueous solution than pure SF and pure CA nanofiber membranes. Especially, the blend nanofibrous membranes with 20 % content of CA had an exceptional performance for the adsorption of Cu²⁺, and the maximum milligrams per gram of Cu²⁺ adsorbed reached 22.8 mg/g. This indicated that SF and CA had synergetic effect. Furthermore, the parameters affecting the metal ions adsorption, such as running time and initial concentration of Cu²⁺, had been investigated. The results showed that the adsorption of the Cu²⁺ sharply increased during the first 60 min, the amount of metal ions adsorbed increased rapidly as the initial concentration increased and then slope of the increase decreased as the concentration further increased. This study provides the relatively comprehensive data for the SF/CA blend nanofibrous membranes application to the removal of heavy metal ion in wastewater.     

Measuring tensile strength of nanofibers using conductive substrates and dynamic mechanical analyzer

Though the tensile strength of nanofibers is essential to determine their application fields, few studies have been conducted on this topic, due to the difficulties involved in the preparation of single nanofiber tensile specimens, the manipulation of the clamping device, and the sensing of the nano- force and strain. A bundle testing method was employed in this work to measure the tensile strength of nanofibers. For this purpose, a conductive substrate was designed to hold several thousand nanofibers extruded from a spinning nozzle and align them uniaxially during the electrospinning process. This substrate was designed for a dynamic mechanical analyzer (DMA), because most DMAs are equipped with fine sensors sensitive enough to measure a very small force and strain. Nylon 6 nanofibers were electrospun and collected on the substrate. Then, they were elongated simultaneously in the DMA until they were fractured, showing that the aligned nanofibers have superior tensile strength and modulus compared to their counterpart microfibers and thus suggesting that polymeric nanofibers have the potential to be used as reinforcement fibers for composite materials.     

Effect of thermal annealing on mechanical properties of polyelectrolyte complex nanofiber membranes

Optimization of mechanical properties is required in the applications of tissue-engineered scaffolds. Thermal annealing strategy is proposed to improve the mechanical properties of polyelectrolyte complex nanofiber membranes. The effects of annealing on the structural and mechanical properties of electrospun chitosan-gelatin (CG) nanofiber membranes were investigated using tensile tests, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Tensile test results showed that annealing processing at 90 °C produced 1.3-fold and 1.1-fold increase on Young’s modulus and tensile strength, respectively. By scanning electron microscopy (SEM) observation, it was found there was a formation of partial interfiber bonding when annealing temperature was elevated over the glass transition temperature (T _g ) of CG nanofibers. FTIR results showed enhanced molecular interactions within fibers, suggesting that annealing treatment promoted the conjunction between chitosan and gelatin. In contrast, no detectable changes in crystallinity for CG nanofiber specimens were exhibited on XRD patterns following annealing treatment. In addition, thermal annealing induced the improvement in thermal stability, aqueous stability and swelling capacity. Therefore, annealing is proved to be an effective strategy for mechanical enhancement of polyelectrolyte complex nanofibrous scaffolds. The enhanced stiffness and strength is mainly attributed to the formation of interfiber bonding and strengthened molecular interactions between chitosan and gelatin.     

Preparation of porous PVDF nanofiber coated with Ag NPs for photocatalysis application

The porous Polyvinylidene fluoride (PVDF) nanofibers were prepared by leaching method using polyethylene oxide (PEO) as porogen for the first time. The influences of the molecular weight (MW) and concentration of PEO, and the leaching solution on the morphology and the surface area of the porous PVDF nanofiber were systematically investigated. Polyethylene glycol 6000 (PEG6000) showed a better pore-forming effect. Optimized preparation parameters were obtained. With the ratio of PEG6000/PVDF reaching 1:1, the surface area of the resulting porous PVDF nanofiber was about three times higher than that of the pure PVDF nanofiber. Moreover, NaClO solution as leaching solution showed a very limited influence on the surface area of porous PVDF nanofiber. Afterwards, Ag NPs coated PVDF (Ag/PVDF) nanofiber was prepared by physical adsorption of Ag ions and in-situ reduction reaction using sodium borohydride as reductant. The photoactivity of Ag/PVDF nanofiber was evaluated by the photodegradation of methyl orange (MO) under visible light irradiation. Ag/PVDF nanofiber showed a better photoactivity than PVDF-Ag nanofiber prepared by the ex-situ blending method.     

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.