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.

Self-crimping bicomponent nanofibres electrospun from polyacrylonitrile and elastomeric polyurethane

Two polymer solutions were brought together via a microfluidic device and subjected to an electrospinning process. The two polymer solutions flowed into the microfluidic channel side-by-side with very little intermixing due to their laminar nature. High speed stretching of the polymer solutions resulted in side-by-side bicomponent fibres. The electrospun nanofibres exhibited an extremely high propensity to self-crimp when an elastomeric polymer (polyurethane) and a normal polymer (polyacrylonitrile PAN) were involved in the electrospinning process. The formation of self-crimping fibre morphology was attributed to the differential shrinkage of the two polymers.

Effects of MWNT nanofillers on structures and properties of PVA electrospun nanofibres

In this study, we have electrospun poly(vinyl alcohol)(PVA) nanofibres and PVA composite nanofibres containing multi-wall carbon nanotubes (MWNTs) (4.5 wt%), and examined the effect of the carbon nanotubes and the PVA morphology change induced by post-spinning treatments on the tensile properties, surface hydrophilicity and thermal stability of the nanofibres. Through differential scanning calorimetry (DSC) and wide-angle x-ray diffraction (WAXD) characterizations, we have observed that the presence of the carbon nanotubes nucleated crystallization of PVA in the MWNTs/PVA composite nanofibres, and hence considerably improved the fibre tensile strength. Also, the presence of carbon nanotubes in PVA reduced the fibre diameter and the surface hydrophilicity of the nanofibre mat. The MWNTs/PVA composite nanofibres and the neat PVA nanofibres responded differently to post-spinning treatments, such as soaking in methanol and crosslinking with glutaric dialdehyde, with the purpose of increasing PVA crystallinity and establishing a crosslinked PVA network, respectively. The presence of carbon nanotubes reduced the PVA crystallization rate during the methanol treatment, but prevented the decrease of crystallinity induced by the crosslinking reaction. In comparison with the crosslinking reaction, the methanol treatment resulted in better improvement in the fibre tensile strength and less reduction in the tensile strain. In addition, the presence of carbon nanotubes reduced the onset decomposition temperature of the composite nanofibres, but stabilized the thermal degradation for the post-spinning treated nanofibres. The MWNTs/PVA composite nanofibres treated by both methanol and crosslinking reaction gave the largest improvement in the fibre tensile strength, water contact angle and thermal stability.

Needleless-electrospinning of PVA nanofibres

In this paper, we demonstrated that a thin metal disk can be used as nozzle to electrospin PVA nanofibres on a large-scale. With the rotation of a disk covered with a thin layer of electrically charged PVA solution, a large number of fibres were electrospun simultaneously from two sides of the disk and deposited on the electrode collector. The fibre production rate can be as high as 6.0 glhr, which is about 270 times higher than that of a corresponding normal needle based electrospinning system (0.022 g/hr). The effects of applied 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 PV A concentration showed a similar trend to that for a conventional electrospinning system using a syringe needle nozzle, but the diameter distribution was slightly wider for the disk electrospun fibres. The profiles of electric field strength in disk electrospinning showed considerable dependence on the disk thickness, with a thin disk exhibiting similar electric field strength profile to that of a needle electrospinning system.

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.

Electrospinning of nanofibres for construction of vital organ replacements

This paper described the production of a novel biosynthetic material using the manufacturing technique of electro spinning for the construction of scaffold for organ replacement. This electrostatic technique uses an electric field to control the deposition of polymer fibres onto a specific substrate to fabricate fibrous polymer constructs composed of fibre diameters ranging from several microns down to 100 nm or less. Two areas of research, in particular, heart valve leaflets and blood vessel will be discussed. Here, a sandwich structure nanofibre mesh was used to construct materials for leaflets of heart valve and blood vessel. In the case of heart valve leaflet, the randomly oriented polyurethane nanofibres were prepared as the first layer, followed by gelatin-chitosan complex layer. Complex nanofibres were initially used to spin on the PU layer with cross orientation to mimic the fibrosa layer. A gelatin and chitosan complex was then spun onto the other side of PU nanofibre mesh to mimic the ventricularis layer. This particular sandwich structure using the PU layer was designed to simulate the mechanical properties of natural tissue. In addition, this design was aimed to provide good biocompatibility and improved cellular environment to assist in adhesion and proliferation. Smooth muscle cells adhered and flattened out onto the surface of the gelatin-chitosan complex as early as 1 day post seeding. There is great potential for this biosynthetic biocompatible nanofibrous material to be developed for various clinical applications.

Carbon nanotube polymer composites and nanofibres

This study examined how carbon nanotubes (CNTs) in electrospun polymeric nanofibres influenced the polymer morphology, and how polymer morphology change induced by different post-electrospinning treatments influenced CNT-polymer interaction and nanofibre properties. The results showed that both the polymer structure and morphology played important roles in determining the composite and nanofibre properties.

Electrospun nanofibres

This research contributes new knowledge to fundamental understanding and applications of nanofibre materials made by the electrospinning technique. An innovative method was developed to visualise the fibre thinning, and the nanofibres with improved mechanical properties and controlled surface wettability were prepared. These nanofibres have shown significant potential in wound dressing application.