Scientists at North Carolina State University have found new ways to make protective fabrics -- such as those used in flame-retardant children’s clothing or odor-inhibiting socks and shirts -- last longer and work better.
Instead of treating the surface of the fabrics with protective polymer coatings that can wear thin and lose effectiveness from use or repeated washing, the NC State researchers are imbedding the polymers that make up the fabric itself with various additives. Laboratory tests show that fabrics and films made this way provide greater protection and retain their flame-retardant or antibacterial qualities longer than materials treated with conventional surface coatings.
The new process could be used on fabrics and films in a wide range of products, from children’s clothing and odor-inhibiting socks and shirts, to antibacterial medical gowns, dressings and sutures.
The research team is headed by Dr. Alan Tonelli, KoSa professor of polymer science at NC State’s College of Textiles.
In the new process, Tonelli and his students first form an inclusion compound -- a high-temperature crystal that contains the desired polymer additives. This "host crystal," as Tonelli calls it, typically is made of cyclodextrins, cyclic starch molecules composed of interlocked glucose sugar rings. Cyclodextrin molecules have a hole in their centers, much like doughnuts, and naturally stack one on top of another to form long tubes into which the additives are imbedded.
After Tonelli and his students form the cyclodextrin-inclusion compound, they melt-press the crystals into a polyester film. Tests have shown a significant increase in the flame retardancy of polyester films created this way.
"We were convinced, just based on these results, that this is much better, much more effective and should provide longer lasting protection," Tonelli said. Since the crystals are part of the film or fabric, washing would have far less of an impact on its effectiveness than typical flame retardants, which lose protection with repeated washing.
Another possible application for the process is the use of antibacterial polymers. Fibers imbedded with antibacterial cyclodextrin-inclusion compound crystals could be used in socks or shirts, or any other fabric that is exposed to perspiration, to reduce the likelihood of body odors.
Tonelli suggests there are medical uses as well, including medical gowns and sutures made with antibacterial polymer imbedded fibers. "If the sutures were antibacterial -- that would be great, you’d never get any infection around the wound, whether it’s internal or external," Tonelli said.
In one test, Tonelli’s students used polyesters embedded with the cyclodextrin-inclusion compound formed with the active ingredient from Neosporin first aid cream to make polyester films and fibers that were exposed to the E.coli bacteria. Laboratory tests found the treated films and fibers prevented the growth of the bacteria.
The researchers are also investigating ways of laminating fabrics with polymers containing cyclodextrin-inclusion compounds. The crystal inclusion compound containing the antibacterial is ground up into a powder, mixed with a polymer powder, and then sprinkled onto a fabric. A second layer of fabric is laid on top, then exposed to heat and pressure. Tonelli is encouraged by this technique.
"In our experience the lamination route seems to be very, very favorable, just by virtue of how it’s done," he said. "It ought to make the fabrics antibacterial, it ought to do a nice job in flame retardancy, it might be good for who knows what else, and the additives don’t necessarily have to be released from the embedded cyclodextrin inclusion compound crystals."
An underlying aim of Tonelli’s research is to uncover more about how polymers behave. The imbedding technique he and his students have devised allows scientists to isolate polymers, even those that are normally bunched together, inside the narrow channels formed by the stacked cyclodextrins. "We like to study the properties of these individual polymer chains that are trapped inside. How is that behavior different from when you have a collection of polymer chains?" Tonelli said. Learning more about the behaviors of long-chain polymers could enable scientists to develop computer models that would allow them to more easily identify the proper polymer needed for a given application, he explains.
Tonelli’s research is sponsored by the U.S. Army and the National Textiles Center, a consortium of textiles colleges funded by the U.S. Department of Commerce.
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