Composite yarns fabricated from continuous needleless electrospun nanofibers

In this work, a spinning metal wire collector was employed to continuously collect polyacrylonitrile (PAN) nanofibers produced by a disc fiber generator and coil them around a polyethylene terephthalate (PET) yarn. The obtained composite yarns exhibited a core/shell structure (PET yarn/PAN nanofibers) with nanofibers orderly arranged on the surface of the PET yarn. The electric field analysis showed that the position of metal wire had insignificant effect on the formed electric field and high intensity electric field was formed at the disc circumferential area, which provided a constant electric field for the production of uniform nanofibers. The spinning solution, spinning speed of metal wire, and winding speed were found to play an important role in producing good quality nanofiber yarns, in terms of morphology, strength, and productivity. Pure nanofiber yarns were obtained after dissolving the core yarns in a proper solvent. This method has shown potential for the mass production of nanofiber yarns for industrial applications.

Ethanol chemiresistor with enhanced discriminative ability from acetone based on Sr-doped SnO2 nanofibers

We demonstrated a new metal oxides based chemiresistor (MOC), which exhibits fast response/recovery behavior, large sensitivity, and good selectivity to ethanol, enabled by Sr-doped SnO2 nanofibers via simple electrospinning and followed by calcination. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS) were carefully used to characterize their morphology, structure, and composition. The ethanol sensing performances based on Sr-doped SnO2 nanofibers were investigated. Comparing with the pristine SnO2 nanofibers, enhanced ethanol sensing performances (more rapid response/recovery behavior and larger response values) have been achieved owing to the basic SnO2 surface caused by Sr-doping, whereas the acetone sensing performances have been weakened. Thus, good discriminative ability to ethanol from acetone has been realized. Additionally, Sr-doped SnO2 nanofibers also exhibit good selectivity.

Scaling up the production rate of nanofibers by needleless electrospinning from multiple ring

Mass production of nanofibers is crucial in both laboratory research and industry application of nanofibers. In this study, multiple ring spinnerets have been used to generate needleless electrospinning. Multiple polymer jets were produced from the top of each ring in the spinning process, resulting in thin and uniform nanofibers. Production rate of nanofibers increased gradually with the increase of the number of rings in the spinneret. Spinning performance of multiple ring electrospinning, namely the quality and production rate of the as-spun nanofibers, was dependent on experimental parameters like applied voltage and polymer concentration. Electric field analysis of multiple ring showed that high concentrated electric field was formed on the surface of each ring. Fiber diameter together with production rate of needleless electrospinning was dependent on the strength and distribution of the electric field of the spinneret. Needleless electrospinning from multiple ring can be further applied in both laboratory research and industry where large amount of nanofibers must be employed simultaneously. © 2014 The Korean Fiber Society and Springer Science+Business Media Dordrecht.

Green electrospun pantothenic acid/silk fibroin composite nanofibers: fabrication, characterization and biological activity

Silk fibroin (SF) from Bombyx mori has many established excellent properties and has found various applications in the biomedical field. However, some abilities or capacities of SF still need improving to meet the need for using practically. Indeed, diverse SF-based composite biomaterials have been developed. Here we report the feasibility of fabricating pantothenic acid (vitamin B5, VB5)-reinforcing SF nanofibrous matrices for biomedical applications through green electrospinning. Results demonstrated the successful loading of D-pantothenic acid hemicalcium salt (VB5-hs) into resulting composite nanofibers. The introduction of VB5-hs did not alter the smooth ribbon-like morphology and the silk I structure of SF, but significantly decreased the mean width of SF fibers. SF conformation transformed into β-sheet from random coil when composite nanofibrous matrices were exposed to 75% (v/v) ethanol vapor. Furthermore, nanofibers still remained good morphology after being soaked in water environment for five days. Interestingly, as-prepared composite nanofibrous matrices supported a higher level of cell viability, especially in a long culture period and significantly assisted skin cells to survive under oxidative stress compared with pure SF nanofibrous matrices. These findings provide a basis for further extending the application of SF in the biomedical field, especially in the personal skin-care field.

Electrospun granular hollow SnO2 nanofibers hydrogen gas sensors operating at low temperatures

In this paper, we present H2 gas sensors based on hollow and filled, well-aligned electrospun SnO2 nanofibers, operating at a low temperature of 150 C. SnO2 nanofibers with diameters ranging from 80 to 400 nm have been successfully synthesized in which the diameter of the nanofibers can be controlled by adjusting the concentration of polyacrylonitrile in the solution for electrospinning. The presence of this polymer results in the formation of granular walls for the nanofibers. We discussed the correlation between nanofibers morphology, structure, oxygen vacancy contents and the gas sensing performances. X-ray photoelectron spectroscopy analysis revealed that the granular hollow SnO2 nanofibers, which show the highest responses, contain a significant number of oxygen vacancies, which are favorable for gas sensor operating at low temperatures. © 2014 American Chemical Society.

Epoxy nanocomposites containing magnetite-carbon nanofibers aligned using a weak magnetic field

Abstract Novel magnetite-carbon nanofiber hybrids (denoted by Fe3O4@CNFs) have been developed by coating carbon nanofibers (CNFs) with magnetite nanoparticles in order to align CNFs in epoxy using a relatively weak magnetic field. Experimental results have shown that a weak magnetic field (∼mT) can align these newly-developed nanofiber hybrids to form a chain-like structure in the epoxy resin. Upon curing, the epoxy nanocomposites containing the aligned Fe3O4@CNFs show (i) greatly improved electrical conductivity in the alignment direction and (ii) significantly higher fracture toughness when the Fe3O4@CNFs are aligned normal to the crack surface, compared to the nanocomposites containing randomly-oriented Fe3O4@CNFs. The mechanisms underpinning the significant improvements in the fracture toughness have been identified, including interfacial debonding, pull-out, crack bridging and rupture of the Fe3O4@CNFs, and plastic void growth in the polymer matrix.

High-performance supercapacitor electrode materials from cellulose-derived carbon nanofibers

Nitrogen-functionalized carbon nanofibers (N-CNFs) were prepared by carbonizing polypyrrole (PPy)-coated cellulose NFs, which were obtained by electrospinning, deacetylation of electrospun cellulose acetate NFs, and PPy polymerization. Supercapacitor electrodes prepared from N-CNFs and a mixture of N-CNFs and Ni(OH)2 showed specific capacitances of ∼236 and ∼1045 F g(-1), respectively. An asymmetric supercapacitor was further fabricated using N-CNFs/Ni(OH)2 and N-CNFs as positive and negative electrodes. The supercapacitor device had a working voltage of 1.6 V in aqueous KOH solution (6.0 M) with an energy density as high as ∼51 (W h) kg(-1) and a maximum power density of ∼117 kW kg(-1). The device had excellent cycle lifetime, which retained ∼84% specific capacitance after 5000 cycles of cyclic voltammetry scans. N-CNFs derived from electrospun cellulose may be useful as an electrode material for development of high-performance supercapacitors and other energy storage devices.

Nerve guidance conduits from aligned nanofibers: improvement of nerve regeneration through longitudinal nanogrooves on a fiber surface

A novel fibrous conduit consisting of well-aligned nanofibers with longitudinal nanogrooves on the fiber surface was prepared by electrospinning and was subjected to an in vivo nerve regeneration study on rats using a sciatic nerve injury model. For comparison, a fibrous conduit having a similar fiber alignment structure without surface groove and an autograft were also conducted in the same test. The electrophysiological, walking track, gastrocnemius muscle, triple-immunofluorescence, and immunohistological analyses indicated that grooved fibers effectively improved sciatic nerve regeneration. This is mainly attributed to the highly ordered secondary structure formed by surface grooves and an increase in the specific surface area. Fibrous conduits made of longitudinally aligned nanofibers with longitudinal nanogrooves on the fiber surface may offer a new nerve guidance conduit for peripheral nerve repair and regeneration.

Studies on the crosslinking of electrospun starch nanofibers

The starch nanofiber mats were prepared by electrospinning, and crosslinked by deal with glutaraldehyde vapor in a sealed containers. The morphology and structure of the fibers (before and after crosslinking) were characterized by SEM and FT-IR, and the properties of the product were measured by tensile test and contact angle measurements. Test results show that, acetalization reaction occurred between the intermolecular of glutaraldehyde and starch, the morphology of crosslinked fibers can be grossly preserved compared with the uncrosslinked starch fibers, and tensile properties and water resistance of the fiber mats have been greatly improved after glutaraldehyde crosslinking.

Hydrogel properties of electrospun polyvinylpyrrolidone and polyvinylpyrrolidone/poly(acrylic acid) blend nanofibers

Hydrogel nanofibers with high water-absorption capacity and excellent biocompatibility offer wide use in biomedical areas. In this study, hydrogel nanofibers from polyvinylpyrrolidone (PVP) and PVP/poly(acrylic acid) (PAA) blend were prepared by electrospinning and by subsequent heat treatment. The effects of post-electrospinning heat treatment and PVP/PAA ratio on hydrogel properties of the nanofibers were examined. Heat treatment at a temperature above 180°C was found to play a key role in forming insoluble and water-absorbent nanofibers. Both PVP and PVP/PAA nanofibers showed high morphology stability in water and excellent water retention capacity. The swelling ratio of PVP/PAA nanofibers declined with increasing heating temperature and decreasing PVP/PAA unit ratio. In comparison with dense casting films, these nanofiber membranes showed nearly doubled swelling ratio.

Use of airflow to improve the nanofibrous structure and quality of nanofibers from needleless electrospinning

Mass production of nanofibers from needleless electrospinning shows great potential in research and development of nanofibers. However, how to improve the electrospinning performance so as to achieve high quality nanofibers is still of great challenge. In this study, airflow has been applied to optimize upward needleless electrospinning from ring spinneret. Effects of airflow speed and the position of airflow on the nanofiber quality and production rate have been investigated. It has been found that thinner and more uniform nanofibers were produced when airflow was applied to needleless electrospinning system. It also improved the collected nonwoven membrane, resulting in better nanofibrous structure of the as-spun nanofibers. Application of airflow on needleless electrospinning would further benefit the development of mass production of nanofibers from needleless electrospinning.

Capsular polypyrrole hollow nanofibers: an efficient recyclable adsorbent for hexavalent chromium removal

Capsular polypyrrole hollow nanofibers (PPy-HNFs) were fabricated via in situ polymerization of pyrrole on an organic-inorganic template, followed by acid etching. Their application in removing hexavalent chromium (Cr(vi)) from aqueous solution was then investigated. The morphologies of the capsular PPy-HNFs were studied by both scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which showed that the PPy-HNFs had a capsular structure in the walls of hollow nanofibers. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) data confirmed the adsorption of Cr on capsular PPy-HNFs. The adsorption capacity increased with reduced pH of the initial solution and the adsorption process can be described using the pseudo-second-order model. These capsular PPy-HNFs showed a high Cr(vi) adsorption capacity up to 839.3 mg g-1. This adsorption capacity was largely retained even after five adsorption/desorption cycles. Electrostatic attraction between Cr and PPy-HNFs was studied using a proposed adsorption mechanism. The capsular PPy-HNFs formed a flexible membrane, which allowed easy handling during application. This study has demonstrated the possibilities of using this capsular PPy-HNF membrane for heavy metal removal from aqueous solution.

Influence of processing conditions on polymorphic behavior, crystallinity, and morphology of electrospun poly(VInylidene fluoride) nanofibers

The polymorphism and crystallinity of poly(vinylidene fluoride) (PVDF) membranes, made from electrospinning of the PVDF in pure N,N-dimethylformamide (DMF) and DMF/acetone mixture solutions are studied. Influence of the processing and solution parameters such as flow rate, applied voltage, solvent system, and mixture ratio, on nanofiber morphology, total crystallinity, and crystal phase content of the nanofibers are investigated using scanning electron microscopy, wide-angle X-ray scattering, differential scanning calorimetric, and Fourier transform infrared spectroscopy. The results show that solutions of 20% w/w PVDF in two solvent systems of DMF and DMF/acetone (with volume ratios of 3/1 and 1/1) are electrospinnable; however, using DMF/acetone volume ratio of 1/3 led to blockage of the needle and spinning process was stopped. Very high fraction of β-phase (∼79%-85%) was obtained for investigated nanofiber, while degree of crystallinity increased to 59% which is quite high due to the strong influence of electrospinning on ordering the microstructure. Interestingly, ultrafine fibers with the diameter of 12 and 15 nm were obtained in this work. Uniform and bead free nanofiber was formed when a certain amount of acetone was added in to the electrospinning solution.

High-performance supercapacitor electrode from cellulose-derived, inter-bonded carbon nanofibers

Carbon nanofibers with inter-bonded fibrous structure show high supercapacitor performance when being used as electrode materials. Their preparation is highly desirable from cellulose through a pyrolysis technique, because cellulose is an abundant, low cost natural material and its carbonization does not emit toxic substance. However, interconnected carbon nanofibers prepared from electrospun cellulose nanofibers and their capacitive behaviors have not been reported in the research literature. Here we report a facile one-step strategy to prepare inter-bonded carbon nanofibers from partially hydrolyzed cellulose acetate nanofibers, for making high-performance supercapacitors as electrode materials. The inter-fiber connection shows considerable improvement in electrode electrochemical performances. The supercapacitor electrode has a specific capacitance of ∼241.4 F g-1 at 1 A g-1 current density. It maintains high cycling stability (negligible 0.1% capacitance reduction after 10,000 cycles) with a maximum power density of ∼84.1 kW kg-1. They may find applications in the development of efficient supercapacitor electrodes for energy storage applications.