The Weekly Newsmagazine of Science
Volume 155, Number 18 (May 1, 1999)
By P. Weiss
Old tires never die. Of more than 265 million discarded each year in the United States, some get shredded and recycled into products such as mulch, mats, and shoe soles. Most, however, end up as litter that clutters vacant lots and landfills indefinitely.
Borrowing from technology related to cotton ginning, scientists at the Department of Agriculture have developed a machine that may reduce the flow of old tires and their parts into landfills. The device will allow "a far greater fraction of the tires to be recycled into something useful," predicts inventor W. Stanley Anthony of USDA's Cotton Ginning Research Unit in Stoneville, Miss.
In a typical recycling plant, machines chop up tires into pieces that contain rubber, synthetic fibers, and steel. Then they grind up the pieces or freeze and pulverize them. Magnets extract the steel before vibrating wire-mesh filters separate rubber from fiber as best they can. Anthony says that about 15 to 50 percent by weight of an average 9-kilogram tire emerges from this process as a useless rubber-fiber blend, which gets buried in a landfill.
His group's prototype machine takes that waste, 80 percent of which is rubber, and turns out nearly pure, usable rubber and fiber, Anthony says. The machine mimics cotton-industry equipment that cleans raw cotton of leaves and other plant parts before the ginning separates fibers from seeds.
The new machine bites into the rubber-fiber waste with rotating, steel-toothed cylinders that push the material against gratings, forcing 97 percent of the rubber off the fiber. The recovered rubber contains only about 1 percent fiber, making it marketable for most uses.
No market exists yet for the fiber, but a preliminary search for customers turned up a Korean textile firm that wanted to buy 36,000 kg, Anthony says.
The USDA group intends to install two demonstration machines in tire-recycling plants this year.
"If in any way, shape, or form, I can get that equipment in here, I'd love to," says Max Daughtrey, co-owner and vice president of operations of Four D Corp. in Duncan, Okla. The plant spends up to $8,000 per month to put rubber-fiber waste in landfills.
"I hate to landfill anything," Daughtrey says. "Why put sellable material in a landfill if you can find a use for it?"
From Science News, Vol. 155, No. 18, May 1, 1999, p. 276. Copyright © 1999, Science Service.
Copyright © 1999 Science Service