Electrospinning is a spinning technique from polymer solutions
or melts by using the electrostatic force.
Electrospun fibers have very thinner diameter (from nanometer to micrometer) than those obtained from conventional spinning processes (melt spinning, solution spinning and so on).
It is possible to produce a nonwoven fabric made of very thin fibers (Fig.1).
The very thin diameter provides a large surface area to volume ratio and unique characteristics that makes a number of applications, for example, filtration for submicron or nano-materials, separator, tissue scaffolding, drug delivery system, artificial organ and so on.
We are studying the both cases of solution electrospinning and melt electrospinning. There are two apparatuses to perform the electrospinning of polymer solutions and melts in our laboratory.
Additionally, it is possible to adjust our electrospinning apparatus for any kinds of experimental cases.
The advantage of solution electrospinning is able to make very thin fibers easily (average fiber diameter is about 75nm to 500nm), since the viscosity of many polymer solutions is very low. The lower viscosity of sample makes an elongational deformation easily.
However, the instability of elongational deformation increases with growing deformation of low viscosity polymer solutions.
This phenomenon is one of serious problems in solution electrospinning, namely, 'beads formation'. Beads are more easily formed as the fiber diameter decreases (Fig 2). Beads formation decreases the surface area of fabrics and deteriorates the function of nonwoven products.
Therefore, it is very difficult to make beads-less fibers with the very thin fiber diameter.
In our previous works, we researched the beads formation in solution electrospinning. We used many polymers, such as poly vinyl alcohol (PVA), polystyrene (PS), poly methyl methacrylate (PMMA) and others. We investigated the effect of many spinning and sample conditions on the beads formation.
From the results of previous data, we found that “controlling the relaxation time of sample” and “controlling the electric charges” are essential parameters for beads formation in solution electrospinning.
Consequently, we achieve to make the beads-less fiber as the average fiber diameter is not changed at the time of beads formation (Fig 3).
While, Melt elctrospinning, we use commercial polymers. The polymer in a syringe is raised to high temperature over the melting point or glass transition temperature of samples. The Melts nanofibers are thicker than the Solution ones, so it hasn’t noticed these days. But recently these become to draw attentions as discussion the sample’s spinning process without effects of solvents.