Taking the odour out of clothes
23 Mar 2001
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 odour-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.
The research team, headed by Dr. Alan Tonelli, said that 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.
In the new process, Tonelli and his students first formed an inclusion compound, which is a high-temperature crystal that containing the desired polymer additives.
This 'host crystal' is said to be made of cyclodextrins, cyclic starch molecules composed of interlocked glucose sugar rings. Cyclodextrin molecules have a hole in their centres and naturally stack one on top of another to form long tubes into which the additives are imbedded.
After Tonelli and his students formed the cyclodextrin-inclusion compound, they melt-pressed the crystals into a polyester film. Tests are reported to 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,' said Tonelli. 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 are said to lose protection with repeated washing.
Tonelli suggests there are medical uses as well, including medical gowns and sutures made with antibacterial polymer imbedded fibres.
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 fibres that were exposed to the E.coli bacteria. Laboratory tests found the treated films and fibres 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 favourable, 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.'
