With mountains of used tires marring the landscape and creating environmental hazards, methods to remove old tires from the waste stream have become an important component in the battle to save the environment.

Drew Williams, a doctoral student in polymer science and engineering at UMass, told NewsFactor that recent studies indicate there are about two billion scrap tires currently piled up in U.S. landfills. More than 273 million new tires reaching the waste stream each year, 60 million of which end up in landfills.

Mosquitoes, Rodents and Fire

"Scrap tires can fill with water and provide a breeding ground for mosquitoes and rodents," Williams told NewsFactor. "They also present a serious fire hazard, as large tire fires are difficult to extinguish and spew toxins into the air as they burn."

While rubber is one the most useful materials of the modern age, it also represents a particularly vexing recycling problems, said Richard Farris, professor of polymer science in the engineering department at UMass.

"Rubber is difficult to recycle because it is chemically cross-linked, and those links will not melt and will not dissolve, unlike aluminum or glass," Farris told NewsFactor.

So, the current method for disposing of tires is that about 40 percent are burned for fuel, 40 percent end up in landfills, and the rest of them are chipped or ground into powder for use as industrial filler or to make synthetic turfs for playing fields.

Heat and Pressure

As an alternative to the current methods, a team of researchers led by Farris turned to a process introduced way back in 1853 by Goodyear. The tire company used a method in which the recycled rubber is ground into a fine powder and mixed with unvulcanized rubber.

The mixture is then vulcanized, which, in essence, means that it is heated and new cross-links are formed by adding sulfur or other chemicals to restore its strength and elasticity.

Farris discovered that by subjecting the cross-linked powder to high pressure (1,000 psi) and high and temperatures (200 degrees Celsius or 400 degrees Fahrenheit), the powder forms a solid rubber material.

"At high temperatures, the thermal energy breaks the chemical bonds and re-forms them, creating a rubber material containing 100 percent reclaimed rubber without significantly compromising the material's quality," Farris said.

Typically, the new material retains 50 percent to 70 percent of the original rubber's strength and elasticity, he added.

While the new material is not fit for use in making car tires, Farris said, it could potentially be used for the soles and heels of shoes, flooring materials and tires for lawn tractors.

Asphalt Extreme

Williams is involved in a related project to create a rubber-asphalt composite using the same high temperature-high pressure process as the rubber recycling project.

Unlike traditional asphalt that gets soft and tacky at high temperatures and brittle at low temperatures, Williams said the new material remains stable and flexible at both extremes.

"It could be used in shingles and possibly in paving surfaces if a company could create a way to roll it out on a road," he suggested.

"With this process, we can reduce the amount of materials in our landfills," Williams said, "and develop a starting material for new products -- and it's cost-effective, because all we are doing is heating the scrap rubber and subjecting it to high pressure."