Courtesy: NovaComp Inc. 2006

In recent years, the term "nanotechnology" has spread across the globe like wildfire. Millions of dollars in research grants and investments are being devoted to making products less than 100 nanometers in size. Unlike many other aspects of the traditional textile industry in the United States which is said to be on death's door, "nanotechnologies" are generating quite a bit of interest. Within the past decade, it has been "rediscovered" that you can produce extremely small fibers (nano-fibers) using a process called electrospinning.

Electrospinning is not by any means a new discovery. Its roots go back to the early 1930's when the first patent was issued. Simply stated, Electrospinning is a process that uses the electrostatic attraction between a charged polymer and a grounded or oppositely charged collection plate to produce extremely fine fibers ranging in diameter from a few nanometers (<10) to several micrometers (>50). Recent developments have shown that it can be performed on polymers in both the molten state as well as in solution.

The polymer is held in a syringe or other type container as shown in Figure 1.

The charge can be applied directly to the syringe so that when polymer passes through, the polymer receives a surface charge similar to that applied to the syringe. As the voltage to the system is increased, the electric field's strength being generated eventually becomes greater than the viscoelastic properties and surface tension of the polymer and a tiny cone, often referred to as a Taylor Cone is formed.

Further increasing the electric field's strength will deform the Taylor Cone until a fine fiber is extruded from the cone's apex. When working with solutions, this strand will continue as a stable jet for a short period of time before the instability or whipping region occurs as seen in Figure 1. This region further decreases the fibers diameter as the solvent evaporates from the solution leaving an extremely small fiber. It is important to note that due to a much higher viscosity and lack of solvent evaporation, fibers electrospun from the melt do not undergo an instability region and as a result have much larger fiber diameters.

Electrospun fibers produced have typically been collected as a random nonwoven mat seen in Figure 2 and most the applications being developed today reflect this configuration. However, advancements in collection techniques continue to be a major focus of research and as a result, it is possible to collect aligned continuous fibers that be twisted to form yarns composed of nanofibers.

It is one thing to successfully produce nanofibers but it is more important from an economic standpoint to find a suitable application for them. One of the main goals for producing nanofibers was the theoretical strength they should possess. In conventional fibers being produced today, there are fairly defined limitations to the percent of crystallinity that can be obtained in a fiber/yarn form. Along these same lines, another potential benefit of nanofibers technology is the tremendous increase in surface area to weight or volume ratios. The lure of nanotechnology stems from the possibility of re-defining these limitations.