Goodyear Patents Devulcanizing Process
AKRON, Ohio, Sept. 8 - Most people don't know it, but tires are a lot like cakes -- you can't "unbake" a cake into flour, eggs and other ingredients.
It's been the same way with tires ever since the inventor of vulcanization, Charles Goodyear, mixed and baked sulfur and rubber together, creating a tough, cured compound that could withstand the heat, stress and strain demanded of tires.
The Goodyear Tire & Rubber Company, the world's largest tiremaker has patented a process for devulcanizing cured rubber products.
For years, conventional wisdom has held that reversing the vulcanization process was as implausible as retrieving the raw eggs from baked goods.
"The recycling of cured rubber has proven to be very challenging because once vulcanized, rubber cannot be easily melted and reformed into other products," said Goodyear's Larry Hunt, section head, who discovered the process with co-inventor Ron Kovalak, master chemical technician, analytical sciences at corporate headquarters.
Vulcanization, discovered by Charles Goodyear in 1839, is the process of heating and hardening rubber compounds to make them serviceable and is similar to baking a cake.
"A number of devulcanization techniques have been developed over the years, but none have been commercially viable," Hunt said. "This process, however, appears to offer considerably higher recovery rates than any earlier attempts and could ultimately reduce the amounts of petroleum and natural rubber needed to manufacture rubber goods."
Earlier methods devulcanized by using everything from microwaves, cryogenic processes, pyrolysis, ultrasonic waves, alkali metals to organic solvents, which typically yielded 1 to 2 percent recovery, Kovalak said. "We believed we could substantially increase the amount of recovered material."
Goodyear's process preserves the rubber's chemical composition and molecular weight, leaving the rubber suitable for recompounding and recuring into new products. It uses an environmentally friendly, recyclable solvent.
"Initial tests resulted in a 40 percent recovery rate of the raw polymer with its structure essentially preserved, and through process improvements, we've been able to achieve an 80 percent recovery level. This demonstrates that the chemistry to recover polymer close to its original state is possible."
Currently the process only has been used to recover laboratory quantities, however if it can be fully developed, it could offer a viable solution to the recycling of more than 800 million scrap tires in North America alone. In addition, the process could provide a means of increasing recycled content in automotive components, a priority for automakers.
Goodyear's experimentation with using recovered raw polymer in other items is the latest step in the company's decades of innovative recycling technologies for worn out rubber products.
During the 1990s, Goodyear championed the controlled combustion of scrap tires for energy with electric utilities and nurtured a network for scrap tire collection through its retail network.
In 1989, Goodyear spearheaded the formation of the Scrap Tire Management Council, a division of the Rubber Manufacturers' Association, to focus intense efforts on scrap tire management. At the time, only 10 percent of scrap tires in the United States were utilized in some fashion compared with 81 percent recovered in 1998, a level exceeding the 63 percent recycle rate of aluminum cans.
Earlier in the '80s, Goodyear invested in an enterprise to use scrap tires in the concrete and paper manufacturing industries paved the way for scrap tires to be used as supplemental fuel and added fuel sources to reduce the nation's energy dependency and conserve national resources. Tires have more energy value per pound than coal and burning a passenger car tire generates the heat value of almost two gallons of fuel oil.
Goodyear pioneered scrap tire initiatives in the 1970s that included protective shore barriers, fish habitats, highway impact barriers and playground equipment. The company also explored using ground scrap tires in asphalt road surfaces and supported the construction of a pyrolysis plant to recover oil, carbon black and steel.