Reinflating Tire Recycling
Oct 30, 2014, 15:36 PM
January/February 2000
Tire recycling hit the skids recently due to setbacks in its major market—tire-derived fuel. But experts predict it will be rolling again soon.
By Aaron B. Pryor
Aaron B. Pryor is associate editor of Scrap.
After rolling steadily upward for most of the 1990s, the U.S. scrap tire market—like most recycling markets—headed downhill in 1998.
While the number of scrap tires generated grew from 266 million in 1996 to 270 million in 1998, the number of tires reused or recycled slipped from 202 million to about 178 million—a 12-percent decline, according to the Scrap Tire Management Council (STMC) (Washington, D.C.). As a result, the scrap tire recovery rate decreased from about 76 percent in 1996 to 66 percent in 1998.
Much of the decline can be attributed to unfavorable changes in the fuel market, which consumed about 75 percent of scrap tires in 1996 and 64 percent in 1998, STMC reports. Most other scrap tire markets either stayed the same or increased in the same period.
These developments served as a wakeup call for the scrap tire industry and gave it a candid challenge: Expand existing markets and create new ones or face possible continued declines.
The Fuel Factor
What fuels scrap tire recovery? In short, tire-derived fuel, or TDF, which is used in cement kilns, dedicated scrap tire-to-energy facilities, and boilers in pulp and paper mills, utilities, and industrial operations. One tire contains the equivalent of seven gallons of oil, which makes it an enviable fuel source. According to STMC, one pound of scrap tire rubber can provide 15,000 Btus of energy.
Though TDF qualifies as energy recovery rather than recycling, it’s the most efficient way to consume scrap tires, and burning them is easier than developing new markets. Not surprisingly, then, TDF applications are expanding into wood-fired operations in California and Michigan as well as other industries, says John Serumgard, executive vice president of STMC.
While the cement kiln industry is “still very strong in its use of tires,” Serumgard notes, overall TDF use declined in 1998 “principally because of sold-out conditions in the cement industry and because certain kilns lose some production when they use tires.” And there were other factors, such as the end of some state subsidy programs for TDF, plus the fact that crude oil was a relatively cheap fuel source.
The result was that TDF usage declined 25 percent between 1996 and 1998, going from about 151 million to 114 million units, STMC reports.
This downtrend won’t continue, however, STMC says, suggesting that the conditions that caused the recent decline may subside in the next two years. Why? “There continues to be an improvement in the efficiency to collect and process scrap tires, the processors who remain in business have developed strong localized markets, and new innovations and markets continue to be examined and tested,” the group says.
Robert Davis, president and CEO of tire recycler GreenMan Technologies Inc. (Lynnfield, Mass.), agrees: “I think it’s solid, growing, and the biggest market going. As markets develop for products, then you’ve got the economic decisions to make, but the majority of the markets are in the energy fields. The economics will take care of where the markets go to. Right now, TDF will go to the majority of the market.”
Developing new markets for TDF is time-consuming but essential, Davis says. His company knows it can’t rely on government-subsidized markets because the subsidies always run out. “You have to go out and work with people,” he states.
“If you’ve got a large coal-consuming body of plants there and you have to go within your market area, you start knocking on doors and asking people for their consideration.”
Building Other Markets
Beyond TDF, the main scrap tire markets include civil engineering applications; ground rubber; punched and/or stamped products; agricultural uses; and other smaller miscellaneous markets.
Civil Actions. Among the non-TDF markets, civil engineering is the largest and represents a promising growth sector for scrap tires. In fact, that market doubled from 1996 to 1998, jumping from 10 million to 20 million units for an 11-percent share of the market.
There are three contributing factors to this growth, says STMC:
- The American Society for Testing and Materials (West Conshohocken, Pa.) completed work on a new “Standard Practice for Use of Scrap Tires in Civil Engineering Applications”;
- The Federal Highway Administration distributed “Design Guidelines to Minimize Internal Heating of Tire Shred Fills”; and
- Educational seminars held through the country raised public awareness among civil engineers and public works officials.
Common civil engineering applications include use of shredded tires as backfill behind retaining walls and lightweight fill and insulation in projects such as roadbeds.
Shredded tires are also used as surfacing for playgrounds, as leachfield materials for septic systems, and in landfill construction. In these uses, Serumgard says, “we’ve found out that, from an operational and installation standpoint, tire shreds bring some value to the table,” noting that “they weigh less and don’t damage the ground as much.”
There are other creative engineering-related uses for whole tires as well: In Taos, N.M., Solar Survival Architecture takes advantage of tires’ durability and ability to retain heat to build homes that it calls “Earthships.” When packed with earth in the foundation of a building, the tires create a strong building block and provide excellent insulation. The tires store heat through the winter and release it during the summer.
On the Ground Floor. Behind the civil engineering market comes ground, or crumb, rubber. In 1998, 15 million tires were processed into ground rubber, up 15 percent from the almost 13 million processed in 1996, according to STMC.
Crumb rubber is used in many applications. Carsonite International (Carsonite, S.C.), for one, uses crumb rubber to make highway sound barriers—lightweight tongue-and-groove panels of reinforced composite material filled with the rubber.
The product has received honorable mention for environmental excellence from the Federal Highway Administration. According to Pat Ladolcetta, vice president of sales, marketing, and engineering, the barriers are easier and cheaper to install than other barriers, take less space for construction, and attenuate noise better than concrete. The barriers, which have been on the market for about five years, are installed in about 14 states.
Another example: Rumber Materials Inc. (Austin, Texas) uses ground rubber to make polymer products such as buckets, highway signs, livestock feeders, plastic pallets, trailer bed floors, and dumpster and garbage pail lids.
Ground rubber is also a component in rubber-modified asphalt. Though this is a competitive market—because many other recycled commodities vie to be used as adjuncts in pavement mixtures—there has been some growth in the market for rubber, Serumgard says.
“Tennessee has done some extensive testing that we think will be helpful in expanding its use, as well as in Arizona and Southern California,” he says. “Los Angeles County has a technology transfer center funded by the state to increase the use of rubber asphalt in the state.”
Though ground rubber potentially offers the highest return on investment among scrap tire markets, it has been limited by overcapacity and limited markets, says STMC. Another limiting factor is that it takes up to three years to develop a new end-use market for ground rubber.
Whether the market can eventually overcome these challenges remains to be seen. Plus, capacity continues to be added, potentially exacerbating the situation. “There’s a new large-scale crumb rubber processor coming online in South Carolina, and that will expand the crumb rubber available,” Serumgard notes. “Whether or not the market will be able to absorb it remains to be seen.”
Best of the Rest. Of the remaining scrap tire markets, an estimated 8 million tires were used to make punched and/or stamped products in 1998, while 15 million were exported—both virtually the same as in 1996, STMC reports.
Solving the Devulcanization Puzzle
If there’s a Holy Grail in scrap tire circles, it’s the quest to develop a process that can truly devulcanize rubber—that is, return it to its virgin state.
Problem is, devulcanizing rubber is like trying to unbake a cake.
That’s the simile Goodyear Tire & Rubber Co. (Akron, Ohio) offers to drive home how difficult it is to devulcanize tires. Vulcanization is a baking process designed to make tires durable. It forms a bond between the rubber’s carbon and sulfur molecules and makes it virtually impossible to return the rubber to its pristine state.
But Goodyear has patented a process that appears to unbake the cake. According to the company, its process can recover up to 80 percent of the rubber in a tire. And the recovered material reportedly retains the rubber’s chemical composition and molecular weight.
As with many discoveries, this one occurred largely by accident. Goodyear researchers Larry Hunt and Ron Kovalak were attempting to dissolve rubber polymers from a cured rubber compound. They put some rubber crumbs into a finger-sized steel pipe, sealed it, and used a pressure pump to inject the solvent through thin tubes. After a 20-minute heating stage, what was left were clumps of sulfur-free rubber. They had found that 2-butanol—an alcohol-based rubber solvent—recovered polymers with all their virgin properties. From an initial recovery rate of 40 percent, the researchers eventually doubled their success to 80 percent.
“Under certain pressures and conditions, we can extract polymer out of the rubber, though it was all done in a laboratory setting. The discovery leads to hope, but it doesn’t solve the problem in one fell swoop,” says Ron Dill, director of analytical and materials testing for Goodyear’s research division.
Goodyear is far from taking the process to a commercial scale. First, it has to make sure the process is cost-effective and develop usable products from it.
“We’re making a lot of attempts to scale it up,” says Dill. “We haven’t been able to determine if it can be scaled up. But it does have the potential to recover polymers from cured rubber, and it extracts them in an intact state.”
In Serumgard’s view, Goodyear’s discovery would be a major advance in tire recycling, though he echoed the company’s caution that it’s still only at the laboratory stage. “As they say, they do a wonderful job on pencil eraser-sized pieces,” he says. “There are a couple of technical issues to overcome. Tires are multiple rubbers. There can be as many as four or five rubbers in a tire, and they have to work on the technology to separate the individual polymer streams. They think they can do that.”
Of course, the big questions are: “Can they do it in a fashion where it makes economic sense, and is there a real possibility that the material derived is capable of being used?” Serumgard asks.
Goodyear isn’t the only company seeking the devulcanization prize.
Take, for example, Ultramer Inc. (Massillon, Ohio) and the U.S. Army Tank Automotive and Armaments Command (TACOM). They are researching a process that uses an ultrasonic horn to exert high-frequency pressure waves on tire parts, reportedly breaking the sulfur crosslinks between rubber molecules and reverting the rubber into a viscous, fluid, virgin-like material.
The company is about “a step or two beyond research,” says engineer Tim Barbor. Thus far, the company has used some of its recovered material in demonstration products, such as prototype automotive parts including floor mats, body plugs, brake pedals, and tire retreads.
American Rubber Technologies Inc. (Jacksonville, Fla.) is another seeker with its ReVived rubber product. In its process, scrap rubber is ground to 40-mesh size then run through a proprietary treatment step that produces ReVived rubber, which reportedly retains most of its original properties. “It still looks like crumb to the naked eye, but it’s not. It’s been treated,” says A.C. Thomas, chairman. This product, he says, can be added at proportions up to 10 to 20 percent with virgin materials in tire treads.
Currently, the process hasn’t been commercialized, though three tire companies are reportedly testing the product. “It takes about a year to a year-and-a-half to get through all the testing in the companies,” Thomas states, adding, “We do think one of those companies will be making tires for the test track.”
TIRE TIDBITS
What did the U.S. scrap tire market look like in 1998? The following statistics from the Scrap Tire Management Council paint the picture:
Scrap tires generated: 270 million
Scrap tires in stockpiles: 500 million
Scrap tires recovered: 177.5 million
Used for fuel: 114 million
Used in civil engineering applications: 20 million
Processed into ground rubber: 15 million
Punched/stamped into new products: 8 million
Scrap tires exported: 15 million
Number of new products that contain scrap tire rubber: 110 and counting
Fastest-growing scrap tire markets: playground cover, soil amendments, flooring/matting
Tire recycling hit the skids recently due to setbacks in its major market—tire-derived fuel. But experts predict it will be rolling again soon.