"Cellulose is the most abundant renewable resource polymer on earth. It forms the structure of all plants," says Margaret Frey, an assistant professor of textiles and apparel at Cornell. "Although researchers have predicted that fibers with strength approaching Kevlar could be made from this fiber, no one has yet achieved this. We have developed some new solvents for cellulose, which have allowed us to produce fibers using the technique known as electrospinning."
Frey is collaborating on the research with Yong Joo, an assistant professor, and Choo-won Kim, a graduate student, both in chemical engineering at Cornell. Frey reports on the development Sept. 9 at the annual meeting of the American Chemical Society in New York City.
The technique of electrospinning cellulose on the nanoscale was successfully used for the first time a few months ago. It involves dissolving cellulose in a solvent, squeezing the liquid polymer solution through a tiny pinhole and applying a high voltage to the pinhole. (Nanoscale refers to measurements often at the molecular level; a nanometer is one billionth of a meter, or three times the diameter of a silicon atom.)
"The technique relies on electrical rather than mechanical forces to form fibers. Thus, special properties are required of polymer solutions for electrospinning, including the ability to carry electrical charges," says Frey.
The charge pulls the polymer solution through the air into a tiny fiber, which is collected on an electrical ground, explains Frey. "The fiber produced is less than 100 nanometers in diameter, which is 1,000 times smaller than in conventional spinning," she says. The new technique is now possible because of a new group of solvents that can dissolve cellulose, Frey says. The Cornell researchers currently are using experimental solvents to find one that will produce fibers with superior properties.
Whenever cotton is converted to fabric and garments, fiber (cellulose) is lost to scrap or waste. At present it is largely discarded or used for low-value products, such as cotton balls, yarns and cotton batting.
"Producing a high-performance material from reclaimed cellulose material will increase motivation to recycle these materials at all phases of textile production and remove them from the waste stream," notes Frey. She says that electrospinning typically produces nonwoven mats of nanofibers, which could provide nanoscale pores for industrial filters.
"Producing ultra-small diameter fibers from cellulose could have a wide variety of applications that would exploit the enormous surface area of nonwoven mats of nanofibers and the possibility of controlling the molecular orientation and crystalline structures of nanoscale fibers," says Frey. If successful, possible applications might include air filtration, protective clothing, agricultural nanotechnology and biodegradable nanocomposites.
"Another application we foresee is using the biodegradable electrospun cellulose mats to absorb fertilizers, pesticides and other materials. These materials would then release the materials at a desired time and location, allowing targeted application," says Joo.
While Frey's group prepared the novel solvents for cellulose, Joo's group conducted the electrospinning studies.
Frey notes that the United States produces 20 million 480-pound bales of fiber a year; world annual production is 98 million bales. At every step in the process of converting harvested cotton to fabric and garments, some fiber is lost to scrap or waste, Frey says. In opening and cleaning, for example, 4 to 8 percent of the fiber is lost; up to 1 percent is lost during drawing and roving; and up to 20 percent during combing and yarn production.
The research is supported by the New York State College of Human Ecology at Cornell.
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