Academia and Industry fostering new devlopments in non-wovens
Research of Electrospinning at TANDEC
Peter P. Tsai
Electrospinning is a process to make nanofibers with fiber diameters in the range of about 10 nm to 10 ?m from polymer solution through electrostatic force. When a droplet of polymer solution is subject to a high electrical voltage, as shown in Figure 1, the charges drag the solution to form fibers if the chare repelling force overcomes the solution surface tension. Nanofibers have the potential of numerous applications including high efficiency filter media, protective clothing material, drug release membrane, nanotube material, chemical catalytic apparatus, bio-transplant material, and hydrogen storage tank for fuel cell, etc.
The fibers carry charges to form uniform fabric as shown in Figure 2. However, the charges also repel the fibers into separate zones on the stationary fiber collector for two spinning nozzles as shown in Figure 3. When three nozzles spin on a rotating collector, three stripes of fabric are formed as shown in Figure 4. However, this uneven phenomena can be removed by mechanical and electrical forces developed at ANDEC. The charges in the fibers such a nylon and PEO of polar materials may be depleted right after the fiber spinning while nonpolar materials such as PS and PC carry the residual charges for a lengthy period of time as shown in Figure 5. The residual charges stored in the fibers can be beneficial for the end use of the materials, e.g., negatively-charged material for bio-material as wound dressing. The charged media for improving the filtration efficiency is another example of the contribution of the charges to the final applications. If the residual charges are redundant, two techniques to either neutralize the charges or to spin the fibers that does not generate the charges since the fibers are formed from the nozzles have been developed at TANDEC.
Weak strength is a deawbsck of electropun fibers. TANDEC in cooperation with the department of ECE is awarded by NSF a grant working on a project to increase the strength and to improve the surface tension by treating the fabrics using one atmosphere uniform glow discharge plasma as shown in Figure 6 developed at TANDEC and ECE. A porous electrode is newly developed to effectively and uniformly inject a large variety of gases into the plasma reactor as working gases.
Figure 7 shows the comparison of a nylon electrospun nanofiber (70 nm) and a nylon meltblown microfiber (7 ?m) fabrics and Figure 8 compares the fiber diameters of electropun nano PU (0.9 ?m) and meltblown micro PU (20 ?m). Compared in Table I is the filtration efficiency of the nylon nanofibers and the microfibers. It is observed that the electrospun nanofibers had significantly higher filtration efficiency than the MB microfibers. Figure 9 shows the TANDEC technology to embed the micro activated carbon particles into the PUnanofabrics.
Electrospinning from a plurality of nozzles and from devices
other than nozzles are the subjects of research at TANDEC to produce the
nanofibers at the speed of mass production.
Figure 1. Sketch of an Electrospinning process.
Figure 2. Uniform fabric formed by the charge repellence among the fibers.
Figure 3. Fibers split into two zones from two nozzles.
Figure 4. Fibers form into three stripes on a rotating collector.
Fig. 6. One atmosphere uniform glow discharge plasma. SB – SpunBonding, MB – MeltBlowing, ES - Electrospinning
Fig. 8. Comparison of MB micro (L, 146X), in which a human fiber is included for reference, and electrospun nano PU (R, 1,310X) fibers.