Problems associated with landfilling of scrap tires
Landfilling of scrap tires causes serious environmental pollution and health problems. Of the 283 million scrap
tires generated in the United States in 2003, nearly one-fourth wound up in landfills. This is in addition to
more than 300 million tires already stockpiled across the country. The estimated cost of cleaning up the existing
tire stockpiles in the United States is in the range of $800 million to $1 billion. The most obvious hazard with
the stockpiling of scrap tires is the potential for large uncontrolled fires. Scrap tires are petroleum-rich
products, and as tires burn, they release particulate pollutants to the atmosphere and hazardous chemicals into
groundwater. Several uncontrolled fires have recently occurred in tire stockpiles (e.g. California, 1999), which
have posed tremendous hazards to the environment. Tire piles are also prime breeding grounds for mosquitoes and
other vermin, which are vectors for human diseases such as Dengue fever, Malaria, and West Nile virus. The World
Health Organization estimates that over two billion people live in areas at risk for epidemic transmission of
these diseases.
Problems associated with current use of scrap tires
In an effort to address these problems, about three-fourths of the 283 million scrap tires generated in the United States were subjected to recycling processing in 2003. Scrap tires were mainly used in one of three major applications, namely, tire-derived fuel (TDF), civil engineering (CE) applications and ground rubber applications. In addition to these three major applications, about 5% of the scrap tires are sold as used tires to underdeveloped countries. The downside of exporting used tires is that the receiving countries end up with a disproportionate amount of scrap tires and the accompanying environmental problems and pollution.
The first of the three major applications, TDF or incineration of scrap tires, is a reasonable solution to reduce
the tire landfill rates; however, it is not a viable option. The reason is that TDF application recovers only
one-fourth of the energy invested in the production of tires.
The second method, CE applications, use tires mainly as a replacement for conventional construction materials, e.g., road fill, crushed rock or sand. Together, these two methods use 55% of the total scrap tires generated in the United States. Both TDF and CE are considered "low-value" applications; moreover, the economic feasibility of these two methods has depended heavily on subsidized support in the form of "tipping fees," paid by some states to recyclers for consuming scrap tires.
The third recycling approach, ground rubber application, is the highest value-added use of scrap tires. In 2003, only
13% of the scrap tires generated in United States were used in this application. Ground rubber application is a
component in the production of rubber particles for incorporation in a variety of products such as asphalt modifications,
molded products, sport surfacing and manufacturing of new tires. The use of scrap tires in ground rubber applications
makes far more economic and environmental sense than TDF and CE applications. Therefore, it is a necessity to expand
further this third approach, the use of ground rubber applications.
Problems associated within the ground rubber application
The ground rubber particles can be used in various ways such as incorporation in raw rubber or plastic mix to form usable products. One advantage of this approach is to cut the raw material cost in half as compared to virgin rubber material. The amount of rubber powder that can be added to a raw rubber mix during rubber production depends on the size and shape of the rubber particles. Superfine rubber particles, in the size range of 80-200 mesh can be added in significantly higher amounts than larger particles without sacrificing the performance. Production of superfine rubber particles is generally accomplished through the use of an expensive cryogenic process. In the cryogenic process, rubber is subjected to extremely low temperatures (below -80°C) so it becomes nearly as brittle as glass, and thereby can be easily crushed into very fine particles. Because of the high energy required to cool the rubber to a sufficiently low temperature, production of fine rubber particles by the cryogenic process is not economical. In the United States, there currently is a limited market for the subsequent high cost superfine rubber particles. Non-cryogenic grinding of the rubber results in production of large particles in the size range of 10-40 mesh. The large rubber particles are generally used in the production of high-volume, low-performance rubber products such as livestock mats, railroad crossings, removable speed bumps and athletic rubber mats.
One alternative approach to incorporate a larger amount of rubber particles regardless of their size range is to
chemically modify the particles. It has been reported that surface modification enables incorporation of up to 75% of
the rubber particles into raw rubber mix. Rubber particles can be also modified to increase their compatibility with a
thermoplastic polymer. This can further expand the use of rubber particles in production of thermoplastic elastomer
composite materials. The other approach is to convert the vulcanized rubber back to its original unvulcanized state
through a devulcanization process. This offers the advantage of rendering the rubber suitable for being revulcanized to
form new rubber articles. Chemical, thermal and wave treatments are the alternative devulcanization techniques. These
devulcanization techniques have various disadvantages. Some results in the reduction of original properties of the rubber.
Others are environmentally undesirable or economically not feasible. Therefore, companies in the United States do not
engage in devulcanization processes, and reclaimed rubber is imported from overseas.
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Opportunity
The objective of this project is to design a sustainable technology to produce "high-value-added' products from scrap tire materials. The proposed approach combines a cost-effective solid state shear extrusion (SSSE) pulverization technology, with a new particle modification (PPIPN) technology to enhance the properties of rubber particles and enable their use in aqueous media. To learn more about this, visit the Technology page. (return to top)
Benefits
Benefits to People
- Reducing the number of tire stockpiles that create human health problems such as the spread of disease-carrying mosquitoes (e.g., the west Nile virus).
- Helping global nations to solve the present problem of tire disposal without compromising the ability of future generations to meet their own needs.
- Providing safe sports facilities by utilizing recycled rubber particles to reduce the risk of impact-induced injuries.
- Lowering the disposal fee that has traditionally passed back to owners, by increasing the demand for scrap tire materials.
- Lowering the use of hazardous organic compounds in coating applications by developing environmentally benign products.
- Securing financial savings by lowering disposal costs of scrap tires that are estimated as much as US$400 million a year in the United States alone.
- Securing significant savings on raw material costs by substituting recycled rubber materials for virgin rubber.
- Reducing the number of scrap tire monofill sites (dedicated landfills) that are costly to create and hazardous to maintain.
- Providing more favorable long-term cost benefits by increasing the useful life cycle of scrap rubber materials.
- Increasing prosperity in a community through remediation of existing and prevention of new scrap tire stockpiles that pollute the land.
- Reducing costs associated with environmentally related health problems.
- Conserving natural and synthetic sources of petroleum-rich rubber materials by reutilizing existing scrap tires.
- Lowering the risk of polluting the atmosphere and groundwater by possible uncontrollable fires in stockpiles of scrap tires.
- Lowering environmental pollutants by consuming a greater volume of scrap tires and producing environmentally benign products.
- Preventing global environmental degradation caused by scrap tire disposal by creating new large-use applications.