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.^[1] Of the 290 million, 45 million of these scrap tires were used to make automotive and truck tire re-treads.^[2] 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.

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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.^[3] 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.^[4] Since vulcanization links the molecules it is difficult to separate these molecules again to recycle, meaning the product cannot be re-melted.^[5] 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.^[6] 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%.^[7] Use of synthetic rubber surpasses that of natural rubber for the first time.^[8] 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 1980s, 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.^[9] 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.^[10].

Landfill Disposal

Tires are not desired at landfills due to their large volumes, 75% void space, which quickly consumes valuable space.^[11] 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.^[12] 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.^[13] 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 recurred and molded into new rubber products.

Markets

As of 2003 markets existed for 80.4% of scrap tires, about 233 million tires per year. These markets are for: Tire Derived Fuel (TDF) 44.7% (130 million), Civil Engineering Projects 19.4% (56 million), Ground Rubber turned into molded rubber products 7.8% (18 million), Ground Rubber turned into rubber-modified asphalt (4.3% (12 million), Exported 3.1% (9 million), Cut/Stamped/Punched Products 2.0% (6.5 million), and Agricultural and Misc. uses 1.7% (3 million).^[14]

Tire Recycling Supply Chain

The Tire Recycling Supply Chain is divided into three stages:

Collection and processing stage

The number of tires being made available for recycle is growing, as attention and demand for tire derived products increases. In addition, state and government programs exist to clean-up scrap tire stockpiles and illegal dumping sites with a long-term goal of no scrap tires sent to the landfill. The tire processing stage is sorted into four operations: whole tires, stamped (cut) tires, chipped (shredded) tires, and ground (crumb) rubber.

Tire-derived products stage

Second stage of tire recycling involves the production of alternate products for sale. New products derived from waste tires generate more economic activity than combustion or other low multiplier production, while reducing waste stream without generating excessive pollution and emissions from recycling operations.^[15].

Tire-derived products

• Whole tires can be reused in many different ways. One way, although not recycling, is for a Steel mill to burn the tires for carbon replacement in steel manufacturing. Tires are also bound together and used as different types of barriers such as: collision reduction, erosion control, rainwater runoff, wave action- that protects piers and marshes, and sound barriers between roadways and residences. Entire homes can be built with whole tires by ramming them full of earth and covering them with concrete, known as Earthships.

Some Artificial reefs are built using tires that are bonded together in groups, there is some controversy on how effective tires are as an artificial reef system, an example is The Osborne Reef Project.

• The process of stamping and cutting tires is used in some apparel products, such as sandals and as a road sub-base, by connecting together the cut sidewalls to form a flexible net.

• Chipped and shredded tires are used as Tire Derived Fuel (TDF); once again not recycling, but TDF helps to eliminate tires from our waste stream and produces a fuel source. Also used in civil engineering applications such as: sub grade fill and embankments, backfill for walls and bridge abutments, sub grade insulation for roads, landfill projects, and septic system drain fields

• Ground and crumb rubber, also known as size-reduced rubber, can be used in both paving type projects and in moldable products. These types of paving are: Rubber Modified Asphalt (RMA), Rubber Modified Concrete, and as a substitution for an aggregate. Examples of rubber-molded products are: Carpet padding or underlay, flooring materials, dock bumpers, patio decks, railroad crossing blocks, livestock mats, sidewalks, rubber tiles and bricks, moveable speed bumps, and curbing/edging. Then there is plastic and rubber blend molded products like pallets and railroad ties. Athletic and recreational areas can also be paved with the shock absorbing rubber-molded material. Rubber from tires is sometimes ground into medium-sized chunks and used as rubber mulch.

Ground up tires even find their way back to your car in the form of automotive parts, like: exhaust hangers, brake pads and shoes, acoustic insulation, and even low percentages go into making new tires.

Distribution and demand stage

For the third stage the production of new products is so dependant on a distribution network and marketing efforts to ensure sales, that transporters and processors of tires are expected to keep focusing on their upstream activity. In order to create new products companies are more likely to merge or link with distributors and retailers to ensure product sales and satisfy customers. Consolidation up and down the tire recycling supply chain must occur to increase the probability of a healthy business. Integrating supply chains can reduce costs, and prices, placing producers closer to their customers. The challenge remaining is to realize supply chain consolidation without increasing prices or decreasing product and service quality. It may be unlikely that companies will keep prices low when consolidation creates larger organizations that take advantage of economies of scale and increased market power.^[16].

Environmental Concerns

Due to heavy metals and other pollutants in tires there is a potential risk for the leaching (leachate) of toxins into the groundwater when placed in wet soils. This impact on the environment varies according to the Ph level and conditions of local water and soil. Research has shown that very little leaching occurs when shredded tires are used as light fill material, however limitations have been put on use of this material; each site should be individually assessed determining if this product is appropriate for given conditions.^[17]

State and Local Government

State laws and regulations dealing with scrap tires are currently enacted in 48 states. Here are some common features of state programs that deal with scrap tires: source of funding for the program, licensing or registration of scrap tire haulers, processors, and end users, manifests for scrap tire shipments, limitations on who may handle scrap tires, financial assurance requirements for scrap tire handlers, and market development activities.^[18] Some state programs are now supported by fees charged to the consumer at purchase or disposal of each tire. These fees sometimes called “tipping fees” help to support recycling costs. When the disposal rates charged to consumers are set high this in turn discourages landfill disposal, a simple solution encouraging more affordable tire recycling programs.

References

See also

• Vulcanization/Devulcanization
• Pyrolysis
• Recycle
• Tire
• Rubber
• Tire fire
• Landfill
• Landfill liner
• Waste Management
• Artificial reef
• Re-tread
• Katy Trail (Dallas)
• Rubber mulch
• Mousepad
• Underlay
• Railroad tie
• Rubberized asphalt