Using chitosan as a thickener for electrospinning dilute PVA solutions to improve fibre uniformity

Chitosan was added to PVA aqueous solutions as a thickener to improve the electrospinning process. The presence of a small amount of chitosan considerably improved the uniformity of as-spun nanofibres. This improvement is attributed to its significant effect on the solution viscosity and conductivity, with only a slight impact on the surface tension. The concentration of the PVA required to produce bead-free and uniform nanofibres was reduced with the increase in chitosan concentration. The chitosan thickener suppressed the jet break-up and facilitated the jet stretching so that fine and uniform fibres could be electrospun even from a dilute PVA solution.

Large-scale electrospinning of polymer nanofibers using needleless nozzle

In this study, we have demonstrated that a rotating metal wire coil can be used as a nozzle to electrospin nanofibers on a large-scale. Without using any needles, the rotating wire coil, partially immersed in a polymer solution reservoir, can pick up a thin layer of charged polymer solution and generate a large number of nanofibers from the wire surface simultaneously. This arrangement significantly increases the nanofiber productivity. The fiber productivity was found to be determined by the coil dimensions, applied voltage and polymer concentration. The dependency of fiber diameter on the polymer concentration showed a similar trend to that for a conventional electrospinning system using a syringe needle nozzle, but the coil electrospun fibers were thinner with narrower diameter distribution. The profiles of electric field strength in the coil electrospinning was calculated and showed concentrated electric field intensity on the wire surface.

Wire coil needleless electrospinning of polymer nanofibers

Elcctrospinning is a very useful technique to produce polymeric nanofibers for diverse applications. The conventional needle-based electrospinning system has VCIY limited fiber productivity and a key challenge has been to develop electrospinning systems that can produce uniform nanofibcrs on a large scale l-3.
In this study, we have demonstrated that a rotating metal wire coil can be used as a nozzle to eiectrospin nanofibers on a large-scale. Without using any needles, the rotating wire coil, partially immersed in a polymer solution reservoir, can pick up a thin layer of charged polymer solution and generate a large number of nanofibers from the wire surface simultaneously. This arrangement significantly increases the nanofiber productivity.
The fiber productivity was found to be determined by the coil dimensions, such as wire diameter, coil radius and distance, and coil length. The effects of applied voltage, the distance bctv,lcen the coil nozzle and collector, and polymer concentration on the fiber
morphology were examined. The dependency of fiber diameter on the polymer concentration showed a similar trend to that for a conventional electrospinning system using a syringe needle nozzle, but the diameter distribution was narrower for the
coil electrospun fibers.
The profiles of electric fIeld strength in coil electrospinning was calculated and showed
concentrated electrical field intensity on the top wire surface. This novel concept of using wire coil as the electrospinning nozzle will contribute to the further development of new large-scale needleless electrospinning systems for nanofiber production.

The charge effect of cationic surfactants on the elimination of fibre beads in the electrospinning of polystyrene

Polystyrene nanofibres were electrospun with the inclusion of cationic surfactants, dodecyltrimethylammonium bromide (DTAB) or tetrabutylammonium chloride (TBAC), in the polymer solution. A small amount of cationic surfactant effectively stopped the formation of beaded fibres during the electrospinning. The cationic surfactants were also found to improve the solution conductivity, but had no effect on the viscosity. Only DTAB had an effect on the surface tension of the polymer solution, the surface tension decreasing slightly with an increase in the concentration of DTAB.

The formation of beaded fibres was attributed to an insufficient stretch of the filaments during the whipping of the jet, due to a low charge density. Adding the cationic surfactants improved the net charge density that enhanced the whipping instability. The jet was stretched under stronger charge repulsion and at a higher speed, resulting in an exhaustion of the bead structure. In addition, a polymer/surfactant interaction was found in the polystyrene–DTAB solution system, while this interaction was not found in the polystyrene–TBAC system. The polymer/surfactant interaction led to the formation of thinner fibres than those formed in the absence of the interaction.

The effects of a non-ionic surfactant, Triton X-405, on the electrospun fibres were also studied. The addition of Triton X-405 did not eliminate the fibre beads, but reduced the bead numbers and changed the morphology. Triton X-405 slightly improved the solution conductivity, and had a minor effect on the surface tension, but no effect on the viscosity.

Disk-electrospinning of PVA nanofibres

In this study, we demonstrated that a thin aluminium disk can be used as nozzle to electrospin PVA nanofibres on a large-scale. A schematic of this electrospinning system and a SEM image of as-spun PVA nanofibers are shown in Figure 1. The lower part of the disk is inside a bath containing the polymer solution, which is connected to a high voltage powder supply. During electrospinning, the disk rotates and picks up a thin layer of electrically charged PVA solution. A large number of fibres are then electrospun simultaneously from two sides of tile disk and deposited on the electrode collector.
With the small prototype unit we used, the fibre production rate can be as high as 6.0 which is about 270 times higher than that of a corresponding normal needle electrospinning system (0.022g/hr). The effects of appliedb voltage, the distance between the disk nozzle and collector, and PVA concentration on the fibre morphology were examined. The dependency of fibre diameter on the PVA concentration showed a similar trend to that for a conventional electrospinning system using a syringe needle nozzle, but the diameter distribution was wider for the disk electrospun fibres in this study.
The profiles of electric field strength in disk electrospinning showed considerable dependence on the disk thickness, with a thin disk exhibiting similar electric field profile to
that of a needle electrospinning system, but a thick disk (cylinder) exhibiting levelled electric field between the disk and the collector. PVA nanofibres electrospun from disk electrospinning were compared to that electrospun from syringe needle and metal cylinder nozzles.

Needleless electrospinning. I. A comparison of cylinder and disk nozzles

In this study, we demonstrated the needleless electrospinning of poly(vinyl alcohol) (PVA) nanofibers with two nozzles, a rotating disk and a cylinder, and examined the effect of the nozzle shape on the electrospinning process and resultant fiber morphology. The disk nozzle needed a relatively low applied voltage to initiate fiber formation, and the fibers were mainly formed on the top disk edge. Also, the PVA concentration had little influence on the disk electrospinning process (up to 11 wt %). In comparison, the cylinder electrospinning showed a higher dependence on the applied voltage and polymer concentration. The fibers were initiated from the cylinder ends first and then from the entire cylinder surface only if the applied voltage were increased to a certain level. With the same polymer solution, the critical voltage needed to generate nanofibers from the disk nozzle was lower than that needed to generate nanofibers from the cylinder. Both electrospinning systems could produce uniform nanofibers, but the fibers produced from the disk nozzle were finer than those from the cylinder when the operating conditions were the same. A thin disk (8 cm in diameter and 2 mm thick) could produce nanofibers at a rate similar to that of a cylinder of the same diameter but 100 times wider (i.e., 20 cm long). Finite element analysis of electric field profiles of the nozzles revealed a concentrated electric field on the disk edge. For the cylinder nozzle, an uneven distribution of the electric field intensity profile along the nozzle surface was observed. The field lines were mainly concentrated on the cylinder ends, with a much lower electric field intensity formed in the middle surface area. At the same applied voltage, the electric field intensity on the disk edge was much higher than that on the cylinder end. These differences in the electric field intensity profiles could explain the differences in the fiber fineness and rate of the nanofibers produced from these two nozzles. These findings will benefit the design and further development of large-scale electrospinning systems for the mass production of nanofibers for advanced applications.

Needleless electrospinning : developments and performances

Electrospinning technique has attracted a lot of interests recently, although it was invented in as early as 1934 by Anton (Anton, 1934). A basic electrospinning setup normally comprises a high voltage power supply, a syringe needle connected to power supply, and a counter-electrode collector as shown in Fig. 1. During electrospinning, a high electric voltage is applied to the polymer solution, which highly electrifies the solution droplet at the needle tip (Li & Xia, 2004). As a result, the solution droplet at the needle tip receives electric forces, drawing itself toward the opposite electrode, thus deforming into a conical shape (also known as “Taylor cone” (Taylor, 1969)). When the electric force overcomes the surface tension of the polymer solution, the polymer solution ejects off the tip of the “Taylor cone” to form a polymer jet. The charged jet is stretched by the strong electric force into a fine filament. Randomly deposited dry fibers can be obtained on the collector due to the evaporation of solvent in the filament. There are many factors affecting the electrospinning process and fiber properties, including polymer materials (e.g. polymer structure, molecular weight, solubility), solvent (e.g. boiling point, dielectric properties), solution properties (e.g. viscosity, concentration, conductivity, surface tension), operating conditions (e.g. applied voltage, collecting distance, flow rate), and ambient environment (e.g. temperature, gas environment, humidity).

Transport properties of multi-layer fabric based on electrospun nanofiber mats as a breathable barrier textile material

Layered fabric systems with an electrospun nanofiber web layered onto a sandwich of woven fabric were developed toexamine the feasibility of developing breathable barrier textile materials. Some parameters of nanofiber mats, including thetime of electrospinning and the polymer solution concentration, were designed to change and barrier properties ofspecimens were compared. Air permeability, water vapor transmission, and water repellency (Bundesmann and hydrostaticpressure tests) were assessed as indications of comfort and barrier performance of different samples. These performancesof layered nanofiber fabrics were compared with a well-known water repellent breathable multi-layered fabric(Gortex).Multi-layered electrospun nanofiber mats equipped fabric (MENMEF) showed better performance in windproof propertythan Gortex fabric. Also, water vapor permeability of MENMEF was in a range of normal woven sport and work clothing.Comparisons of barrier properties of MENMEF and the currently available PTFE coated materials showed that, thoseproperties could be achieved by layered fabric systems with electrospun nanofiber mats.

Electrospinning of nanofibres with parallel line surface texture for improvement of nerve cell growth

Nanofibres having a parallel line surface texture were electrospun from cellulose acetate butyrate solutions using a solvent mixture of acetone and N,N'-dimethylacetamide. The formation mechanism of the unusual surface feature was explored and attributed to the formation of voids on the jet surface at the early stage of electrospinning and subsequent elongation and solidification of the voids into a line surface structure. The fast evaporation of a highly volatile solvent, acetone, from the polymer solution was found to play a key role in the formation of surface voids, while the high viscosity of the residual solution after the solvent evaporation ensured the line surface to be maintained after the solidification. Based on this principle, nanofibres having a similar surface texture were also electrospun successfully from other polymers, such as cellulose acetate, polyvinylidene fluoride, poly(methyl methacrylate), polystyrene and poly(vinylidene fluoride-co-hexafluoropropene), either from the same or from different solvent systems. Polarized Fourier transform infrared spectroscopy was used to measure the polymer molecular orientation within nanofibres. Schwann cells were grown on both aligned and randomly oriented nanofibre mats. The parallel line surface texture assisted in the growth of Schwann cells especially at the early stage of cell culture regardless of the fibre orientation. In contrast, the molecular orientation within nanofibres showed little impact on the cell growth.

Mass production of nanofibers from a spiral coil

In this study, we have demonstrated that a rotating metal wire coil can be used as a nozzle to electrospin nanofibers on a large-scale. Without using any needles, the rotating wire coil, partially immersed in a polymer solution reservoir, can pick up a thin layer of charged polymer solution and generate a large number of nanofibers from the wire surface simultaneously. This arrangement significantly increases the nanofiber productivity. The fiber productivity was found to be determined by the coil dimensions, applied voltage and polymer concentration. The dependency of fiber diameter on the polymer concentration showed a similar trend to that for a conventional electrospinning system using a syringe needle nozzle, but the coil electrospun fibers were thinner with narrower diameter distribution. The profiles of electric field strength in the coil electrospinning was calculated and showed concentrated electric field intensity on the top wire surface.

Effects of polymer concentration and cationic surfactant on the morphology of electrospun polyacrylonitrile nanofibres

PAN nanofibres were prepared via an electrospinning process. The effect of polymer concentration on the fibre morphology was studied. At a very dilute solution, no fibres were obtained in the electrospinning process. As the concentration increased, the fibre morphology evolved from a beads-on-string structure to a uniform fibre structure with increasing fibre diameters. However, when the same electrospinning process was conducted with the addition of a cationic surfactant, the formation of disconnected beads was prevented, and the number of beads-on-string structures reduced significantly. In addition, the presence of cationic surfactant reduced the average diameter of the electrospun PAN nanofibres.

A novel polymer membrane for extraction applications

In this study, a new type of Aliquat 336/PVC membrane has been made for extraction experiments. This new membrane is capable of holding more Aliquat 336 than previously developed extraction membranes, hence overcoming a major problem that has confronted many researchers for a long time. The new membrane has been used to investigate the rate of extraction for the Cd(II) ion in 2.0 M HCl solution and the effect of membrane thickness on the rate of extraction. The experimental results have shown this new membrane has a promising future in relevant industrial applications. A new method is also used in this study to qualitatively identify the oily substance on the surface of membrane after the extraction experiment was completed. This oily substance has been found to be Aliquat 336.

Electroless synthesis of nano-structured gold particles using conducting polymer nanoparticles

In this study, gold nanoparticles were synthesized by electroless recovery of [AuCl4]− from an acidic aqueous solution using nano-structured conducting polymer, polypyrrole nanoparticles, as active surface. The formation of gold nanoparticles was confirmed by TEM, SEM and EDX measurements. The effects of the initial Au(III) concentration on the gold uptake was examined. The recovery capability and gold particle morphology prepared from polypyrrole nanoparticle were compared to that from cast PPy film counterpart.

Characterization and application of conducting polymer coated textiles

This paper reports on some physical properties of a conducting polymer, polypyrrole, coated textiles. Polypyrrole was coated on textiles chemically through in-situ solution or vapor polymerisation to produce conducting textiles. The effects of the conductive coating on the physical and mechanical properties of the fibrous materials are presented. The coating durability and conductivity of the textiles have also been examined.