Tire recycling

Tire recycling

by Bob

link back: http://en.wikipedia.org/wiki/Tire_recycling

Tire recycling is the process of recycling vehicles tires (or tyres) that are no longer suitable for use on vehicles due to wear or irreparable damage (such as punctures). These tires are among the largest and most problematic sources of waste, due to the large volume produced and their durability. Those same characteristics which make waste tires such a problem also make them one of the most re-used waste materials, as the rubber is very resilient and can be reused in other products. Approximately one tire is discarded per person per year. The U.S. Environmental Protection Agency reports 290 million scrap tires were generated in 2003.Of the 290 million, 45 million of these scrap tires were used to make automotive and truck tire re-treads. With landfills minimizing their acceptance of whole tires and the health and environmental risks of stockpiling tires, many new markets have been created for scrap tires. Growing markets exist for a majority of scrap tires produced every year, being supported by State and Local Government.

History

Rubber recycling dates back to about the time when industrial rubber manufacturing began. A machine called a Masticator or a "pickle", invented by Thomas Hancock around 1820, which ground up rubber scraps into shreds that could then be mashed into blocks and reused. Due to the high cost of rubber (equal in cost per ounce to silver), starting in 1910 and continuing well into the 20th century, 50% of rubber content was recycled. This type of rubber recycling was very basic and easy, but short-lived. In 1843 Charles Goodyear invented vulcanization, a process of weather proofing rubber by linking all the molecules in a rubber product into one big molecule preventing separation, receiving a patent on June 24, 1844. Since vulcanization links the molecules it is difficult to separate these molecules again to recycle, meaning the product cannot be re-melted. Vulcanized rubber could still be shredded and ground, but had to be mixed with natural rubber to reuse. A shortage of natural rubber caused by the need for tires during World War II, led to the building of synthetic rubber plants around the world in 1945. In the 1960s cheap oil imports and an increased use of synthetic rubber brought down manufacturing costs making the tire and rubber industry's recycled rubber content drop to 20%. Use of synthetic rubber surpasses that of natural rubber for the first time. The 1960s also brought about steel-belted radial tires, which made recycling even more difficult; the steel now would have to be removed after slicing and grinding. A national wave of Tire-Derived Fuel (TDF) development occurs in the mid 1980's, although not recycling, eliminates tires and provides a fuel for utilities. In 1990 markets are shown to exist for 17% of used tires, growing to 78% in 2001 and up to 80.4% in 2003. Due to safety issues, tire industry's recycled rubber content drops to 5-15%, new tires must be manufactured primarily from virgin rubber. The tire recycling industry is currently developing methods of devulcanization or rubber molecule separation by: Pyrolysis, Bacteria, Ultrasound, Thermal, or Mechanical means.

Tire Life Cycle

The tire life cycle can be identified by the following six steps: 1) Product developments and innovations increase tire life, increments of replacement, consumer safety, and reduce tire waste. 2) Proper manufacturing and quality of delivery reduces waste at production. 3) Direct distribution through retailers, reduces inventory time and ensures that the life span and the safety of the products are explained to customers. 4) Consumers use and maintenance choices like tire rotation affect tire wear and safety of operation. 5) Manufacturers and retailers set policies on return, re-tread, and replacement to reduce the waste generated from tires and assume responsibility for taking the ‘tire to its grave’ or to its reincarnation. 6) Recycling tires by developing strategies that combust or process waste into new products, creates viable businesses, and fulfilling public policies.

Landfill Disposal

Tires are not desired at landfills due to their large volumes, 75% void space, which quickly consumes valuable space. Tires can trap methane gases causing them to become buoyant, or ‘bubble’ to the surface. This ‘bubbling’ effect can damage landfill liners that has been installed to help keep landfill contaminants from polluting local surface and ground water. Shredded tires are now being used in landfills, replacing other construction materials, for a light weight backfill in gas venting systems, leachate collection systems, and operational liners. Shredded tire material may also be used to cap, close, or daily cover landfill sites. Scrap tires as a backfill and cover material is also more cost effective, since tires can be shredded on site instead of hauling in other fill materials. In 2003, 38 states banned whole tires from landfills, 35 allowed shredded tires, 11 banned all tires from landfills, 17 allowed processed tires in mono-fills, and 8 states had no restrictions on scrap tires in landfills (Rubber Manufacturers Association, 2003).

Stockpiles and Illegal Dumping

Tire stockpiles create a great health and safety risk. Tire fires can occur easily, burning for months, creating substantial pollution in the air and ground, becoming Superfund cleanup sites. By recycling tires it helps to reduce the number of tires in storage. The United States has decreased the number of waste tires in storage from 700-800 million in 1994, down to 275 million tires in 2004 primarily due to state scrap management programs (Rubber Manufacturers Association 2004). An additional health risk, tire piles provide harborage for vermin and a breeding ground for mosquitoes that may carry diseases. Illegal dumping of scrap tires pollutes ravines, woods, deserts, and empty lots; which has led many states to pass scrap tire regulations requiring proper management. Tire amnesty day events, in which community members can deposit a limited number of waste tires free of charge, can be funded by state scrap tire programs, helping decrease illegal dumping and improper storage of scrap tires.

Ultrasound recycling

High power ultrasound is applied to the cured rubber during extrusion and the high pressure, heat and mechanical energy break the crosslinks which make the extrudate a gum rubber like new material, that can be recured and molded into new rubber products.