Antibacterial effect of carbon nanofibers containing Ag nanoparticles

Silver nanoparticles imbedded in polyacrylonitrile (PAN) nanofibers and converted into carbon nanofibers by calcination was obtained in a simple three-step process. The first step involves conversion of silver ions to metallic silver nanoparticles, through reduction of silver nitrate with dilute solution of PAN. The second step involves electrospinning of viscous PAN solution containing silver nanoparticles, thus obtaining PAN nanofibers containing silver nanoparticles. The third step was converting PAN/Ag composites into carbon nanofibers containing silver nanoparticles. Scanning electron microscopy (SEM) revealed that the diameter of the nanofibers ranged between 200 and 800 nm. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) showed silver nanoparticles dispersed on the surface of the carbon nanofibers. The obtained fiber was fully characterized by measuring and comparing the FTIR spectra and thermogravimetric analysis (TGA) diagrams of PAN nanofiber with and without imbedded silver nanoparticles, in order to show the effect of silver nanoparticles on the electrospun fiber properties. The obtained carbon/Ag composites were tested as gram-class-independent antibacterial agent. The electrosorption of different salt solutions with the fabricated carbon/Ag composite film electrodes was studied.     

Microstructures and electrical properties of composite films based on carbon nanotube and para-aramid containing cyano side group

We report the microstructures and electrical properties of poly(2-cyano-1,4-phenylene terephthalamide) (cyPPTA)-based composite films including pristine multi-walled carbon nanotube (MWCNT) of 0.3-10.0 wt%, which were manufactured by ultrasonication-based solution mixing and casting techniques. FT-IR spectra of the composite films revealed the existence of specific interaction between cyPPTA and MWCNT. Accordingly, the pristine MWCNTs were found to be dispersed uniformly in the cyPPTA matrix, as confirmed by TEM images. The electrical resistivity of the composite films decreased considerably from ~10¹⁰ Ω cm to ~10⁰ Ω cm with the increase of the MWCNT content by forming a conductive percolation threshold at ~0.525 wt%. The composite films with 3.0-10.0 wt% MWCNT contents, which have sufficiently low electrical resistivity of ~10²-10⁰ Ω cm, exhibited excellent electric heating performance by attaining high maximum temperatures and electric power efficiency under given applied voltages of 10-100 V. Since the thermal decomposition of the composite films took place at 520-600 °C under air atmosphere, cyPPTA/MWCNT composite films could be used for high performance electric heating, antistatic, and EMI shielding materials.     

Shape memory properties of electrospun nafion nanofibers

Nanoscaled non-woven fibers with shape memory effect are successfully fabricated via electrospinning method from Nafion solutions consisting of a little poly(ethylene oxide) (PEO). Scanning electron microscopy (SEM) investigation shows the electrospun nanofibers with average diameters in the range 170–410 nm. The electrospun nanofibers exhibit excellent shape memory properties. When deformed Nafion nanofibers are stimulated upon heat, the temporary shape responds rapidly, and then recovers to the permanent shape in less than one minute. The shape recovery ratios and shape fixity ratios of Nafion nanofibers with 0.3 wt%, 0.5 wt% and 0.7 wt% PEO are all above 90 %. In shape memory cycle, fibrous structure is stable after the stretching recovery. Shape memory Nafion nanofibers have various potential applications in smart structures and materials in the future.     

Fabrication of electrospun antimicrobial nanofibers containing metronidazole using nanospider technology

Nanospider technology as a modified electrospinning technique was used for the fabrication of electrospun nanofibers based on poly(vinyl alcohol) (PVA)/poly(ethylene oxide) (PEO) blend as drug delivery system (DDS) for metronidazole (MTZ) as an antimicrobial drug. Electrospun PVA/PEO/MTZ composite nanofibers were stabilized against disintegration in water by heating in oven at 110°C, or by soaking in isopropyl alcohol for 6 hrs. Incorporation of MTZ into electrospun nanofibers was confirmed by SEM, FT-IR spectra and TGA. The drug release results showed that the burst release was suppressed with stabilized electrospun nanofibers compared with non-stabilized ones. Electrospun PVA/PEO/MTZ composite nanofibers exhibited remarkable antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger, Penicillium notatum and Aspergillus flavus which varies with the species of the tested organisms.     

Effect of collector temperature and conductivity on the chain conformation of nylon 6 electrospun nanofibers

Electrospinning is a versatile process used to prepare micro- and nano- sized fibers from various polymer solution. Here, we dealt with the variation in the morphology of nylon 6 electrospun nanofibers and their polymorphism depending on the type and physical state of the collectors. SEM study showed that the fiber diameter was increased from 80 to 103 nm while it was collected in water bath. Similarly the fiber diameter and bonding was increased 103 to 115 nm with the temperature whereas it was linearly decreased 103 to 90 nm with the conductivity of the water bath. Spectroscopic analysis (FT-Raman, FT-IR) showed that the polymorphism of nylon 6 depended on the types of collector (aluminum sheet and water bath). Nylon 6 electrospun nanofibers display theγ-phase while collected in aluminum sheet andα-phase while collection in water bath. The extent of transformation fromγ- toα-phase was linearly increased with temperature and conductivity of the water bath.     

Electrical conductive and structural characterization of electrospun aligned carbon nanofibers membrane

In the paper, the membrane with aligned carbon nanofibers (CNFs) was prepared by electrospinning, stabilization and carbonization. The electrical conductivity of the membrane was examined. The effect of stabilization temperature and drum rotating speed on the conductivity of aligned CNFs membrane was discussed. The study on stabilization temperature showed that 250 °C was optimum parameter for preparing fibrous aligned CNFs membrane with uniform diameter, but 270 °C was benefit to fiber conglutination which could improve the electrical conductivity of the final CNFs membrane. The study on drum rotating speed showed that when drum rotating speed reached 2500 rpm, graphitic structures with parallel graphene sheets could be observed and 1000, 1500 and 2000 rpm CNFs membranes presented desirable conductivity with only 1.3 Ω·cm in the parallel directions and 2.0 Ω·cm in the perpendicular direction.     

Preparation of inorganic silica nanofibers containing silver nanoparticles

Silica nanofibers containing silver nanoparticles were successfully prepared using sol-gel chemistry and electro-spinning technique. Solution of tetraethly orthosilicate in ethanol containing silver nitrate was aged to have sufficient viscosity and electrospun to form nanofibers. Upon thermal treatment, the gelation reaction between silanols was completed in the prepared silica nanofibers, and at the same time, silver ions in the nanofiber changed to metallic silver or silver oxides. The reduction of silver ions could be also achieved by UV irradiation, and the generated silver nanoparticles were present preferentially on the surface of the silica nanofibers. On testing release behavior of silver ions, it was found that most of silver remained in the silica nanofiber. The silica nanofibers containing silver nanoparticles exhibited excellent antibacterial and deodorant properties.     

Transport properties of layered fabric systems based on electrospun nanofibers

Layered fabric systems with electrospun polyurethane fiber web layered on spunbonded nonwoven were developed to examine the feasibility of developing protective textile materials as barriers to liquid penetration using electrospinning. Barrier performance was evaluated for layered fabric systems, using pesticide mixtures that represent a range of surface tension and viscosity. Air permeability and water vapor transmission were assessed as indications of thermal comfort performance. Protection performance and air/moisture vapor transport properties were compared for layered fabric systems and existing materials for personal protective equipment (PPE). Layered fabric systems with electrospun nanofiber web showed barrier performance in the range between microporous materials and nonwovens used for protective clothing. Layered fabric structures with the web area density of 1.0 and 2.0 g/m² exhibited air permeability higher than most PPE materials currently in use; moisture vapor transport was in a range comparable to nonwovens and typical woven work clothing fabrics. Comparisons of layered fabric systems and currently available PPE materials indicate that barrier/transport properties that may not be attainable with existing PPE materials could be achieved from layered fabric systems with electrospun nanofibrous web.     

Effect of purification method on the electrical properties of the carbon nanotube fibers

We purified as-received CNT fibers (CNTFs) with four different methods and systematically examined effects of various purifications on the morphology, structure, and electrical conductivity of the resultant CNTFs, respectively. The purified CNTFs were characterized by an optical microscope, transmission electron microscope (TEM) coupled with an energy dispersive X-ray spectrometer (EDS), Raman spectroscopy, and multiple source meters. Optical images showed that morphology of CNTFs did not largely change after purification. TEM images and EDS results showed that the Fe impurities, 21.9 wt%, in CNTFs were decreased to 0.17-1.20 wt% and were nearly eliminated by acid and alkali purifications, respectively. Raman results identified the I_D/I_G ratio of CNTFs was 0.71, while those of HCl treatment after steam with heat (HSCNTFs-HCl), NaOCl treatment after steam with heat (HSCNTFs-NaOCl), and NaOH treatment with heat without steam (NaOH-HCNTFs) were 0.45, 0.49, and 0.57, respectively, which means that purification methods of CNTFs performed in this study are thought to be satisfactory for manufacturing high-purity CNTFs. Electrical conductivity (1.4×10⁴ S/m) of NaOH-HCNTFs (one-step procedure) was twice as high as that (7.3×10³ S/m) of CNTFs, but lower than those (2.1-2.3×10⁴ S/m) of HSCNTFs-HCl and HSCNTFs-NaOCl (two-step processes), which demonstrates that two-step processes rather than one-step procedure would have a positive effect on the electrical conductivity of the resultant CNTFs.     

Synthesis,analysis and simulation of carbonized electrospun nanofibers infused carbon prepreg composites for improved mechanical and thermal properties

This paper reports the fabrication, characterization and simulation of electrospun polyacrylonitrile (PAN) nanofibers into pre-impregnated (prepreg) carbon fiber composites for different industrial applications. The electrospun PAN nanofibers were stabilized in air at 270 °C for one hour and then carbonized at 950 °C in an inert atmosphere (argon) for another hour before placing on the prepreg composites as top layers. The prepreg carbon fibers and carbonized PAN nanofibers were cured together following the prepreg composite curing cycles. Energy dispersive X-ray spectroscopy (EDX) was carried out to investigate the chemical compositions and elemental distribution of the carbonized PAN nanofibers. The EDX results revealed that the carbon weight % of approximately 66 (atomic % 72) was achieved in the PAN-derived carbon nanofibers along with nitrogen and lower amounts of nickel, oxygen and other impurities. Thermomechanical analysis (TMA) exhibited the glass transition regions in the prepreg nanocomposites and the significant dependence of coefficient of thermal expansion on the fiber directions. The highest value of coefficient of thermal expansion was observed in the temperature range of 118-139 °C (7.5×10^-8 1/°C) for 0 degree nanocomposite scheme. The highest value of coefficient of thermal expansion was observed in the temperature range of 50-80 °C (37.5×10^-6 1/°C) for 90 degree nanocomposite scheme. The test results were simulated using ANSYS software. The test results may be useful for the development of structural health monitoring of various composite materials for aircraft and wind turbine applications.     

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.     

Three-layer composite filter media containing electrospun polyimide nanofibers for the removal of fine particles

Polyimide (P84) nanofibers of 200-500 nm were deposited uniformly on needle punched aramid felt with basis weight of 260-350 g/m² by optimized electrospinning. High temperature adhesive was then electro-sprayed on the nanofiber side deliberately to bind a thin protective layer made of temperature-resistant non-wovens. The three layer structure was afterwards enforced by hot pressing to form composite filter media. The application of the adhesive was tailored not to affect the permeability of the substrate felt while exerting adhesion strength of over 1000 kPa for the media to be suitable for flue gas dust treatment under 240 ºC. When 0.3-10 μm NaCl aerosols were used as the simulated dusts, it was found that even a small amount of P84 nanofibers could obviously elevate the filtration efficiency. The composite showed 100 % removal efficiency of particles equal and greater than 2.0 μm, and 99.5 % for particles 1.0-2.0 μm in diameter.     

Enhanced spinnability of carbon nanotube fibers by surfactant addition

A surfactant is used to enhance spinnability of carbon nanotube (CNT) fibers during direct spinning via chemical vapor deposition (CVD). In this study, the non-ionic surfactant, polysorbate, is used due to its good solubility in the CNT synthesis solution. The addition of the surfactant increased the specific strength and electrical conductivity of CNT fibers. Due to these enhanced properties, CNT fibers can be spun at higher speeds which results in lower linear density. These enhancements are due to the reduced agglomeration of iron catalysts during the synthesis of CNT fibers via CVD. This simple approach may create new applications for CNT fibers, such as for artificial muscles and power cables.     

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

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

Enhanced mechanical and dielectric properties of poly(vinylidene fluoride)/polyurethane/multi-walled carbon nanotube nanocomposites

Multi-walled carbon nanotubes (MWNTs) nanocomposites with the polymer matrix composed of blends of poly(vinylidene fluoride) (PVDF) and polyurethane (PU) were prepared via functionalization of 3,4,5-triflouroaniline (TFA) on MWNTs. The MWNTs/polymer nanocomposites showed a dominantly enhanced elongation due to incorporation of PU molecules in PVDF matrix and the improved MWNTs dispersion in the polymer matrix resulting from functionalization of MWNTs with TFA. The functionalization of TFA on MWNTs was confirmed by the measurements of Raman, FT-IR spectra, SEM, and TEM images. In addition, the dielectric constant of nanocomposites increased with an increase of TFA-functionalized MWNTs in PVDF/PU/MWNTs nanocomposites. The polymer blend nanocomposites incorporating MWNTs may be available as an alternative potential route for the actuator materials.     

Dyeing properties of nylon 66 nano fiber with high molecular mass acid dyes

Research and development of nano fiber products is very active over the world. Physical characteristics and dyeing properties of nylon 66 nano fiber were investigated in this study. X-ray diffraction, DSC, analysis of amino end group, and water absorption were performed to get information concerning physical properties of nano fiber. Nylon 66 nano fiber was dyed with high molecular mass acid dyes. Effects of dyeing temperature, pH of dyeing solution, and concentration of acid dyes on dyeing properties such as rate of dyeing and the extent of exhaustion, were examined and compared to those of regular fiber. It was found that nano fiber adsorbed acid dyes at lower temperature, got rapidly dyed, and its extents of exhaustion at specific dyeing temperature were higher than regular fiber. It was also observed that nano fiber could adsorb a large amount of acid dye without a significant loss in the extent of exhaustion. Washing fastness of the dyed nano fiber was lower by 1/2∼1 grade, light fastness by 1 grade than the dyed regular fiber.     

Enhanced dielectric properties of electrospun titanium dioxide/polyvinylidene fluoride nanofibrous composites

Titanium dioxide/polyvinylidene fluoride (TiO₂/PVDF) composite was prepared by electrospinning process to enhance the dielectric properties for application as a gate insulator in organic thin-film transistors (OTFTs). Scanning electron microscopy, thermogravimetric analysis, and X-ray diffraction were employed to characterize the as-prepared samples, and then their dielectric constants were investigated by impedance analysis. The impedance results show that the dielectric constant of the electrospun TiO₂/PVDF nanofibers is higher than those of other samples, demonstrating that electrospun TiO₂/PVDF composite can be a proper candidate for gate insulators in OTFTs.     

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.     

Physical and comfort properties of the hoisery knit product containing intermingled nylon elastomeric yarn

There are several studies related with knitted fabric containing elastomeric yarn. These studies have been carried out only on fabrics containing naked elastomeric yarn, i.e., without intermingling. And most of them have focused on dimensional and extension-recovery properties of the fabric. Of course, intermingling yarn parameters such as number of knots and draw-ratio will affect the properties and performance of the fabrics. This paper presents a study about the effect of draw-ratio and number of knots, which are important parameters in intermingled nylon-elastomeric yarns, on the physical and comfort properties of hosiery knit products. To see the relationship and significance, bivariate correlation analysis and analysis of variance have been carried out. It has been seen that increase of draw ratio and number of knots lead to an increase in dimensional change, stitch density, fabric weight, and lead to a decrease in fabric spirality, abrasion, fabric wicking (wickability in course direction is less than that of wale direction). Fabric thickness increases with an increase in draw ratio and a decrease in number of knots. The number of knots and the draw-ratio do not affect the fabric drying rate. However, an increase in the draw ratio and the number of knots result in an increase in initial water content before beginning the drying process. But, an increase in initial water content is not so high as to affect the drying rate.     

Morphology and properties of polyacrylonitrile/single wall carbon nanotube composite films

Composite films were prepared by casting the solution of polyacrylonitrile (PAN) and single wall nanotube (SWNT) in DMF subsequent to sonication. The SWNTs in the films are well dispersed as ropes with 20–30 nm thickness. Moreover, AFM surface image of the composite film displays an interwoven fibrous structure of nanotubes which may give rise to conductive passways and lead to high conductivity. The polarized Raman spectroscopy is an ideal characterization technique for identification and the orientation study of SWNT. The well-defined G-peak intensity at 1580 cm⁻¹ shows a dependency on the draw ratio under cross-Nicol. The degree of nanotube orientation in the drawn film was measurable from the sine curve obtained by rotating the drawn film on the plane of cross-Nicol of polarized Raman microscope. The threshold loading of SWNT for electrical conductivity in PAN is found to be lower than 1 wt% in the composite film. The electrical conductivity of the SWNT/PAN composite film decreased with increasing of draw ratio due to the collapse of the interwoven fibrous network of the nanotubes with uniaxial orientation.