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Conclusion

	Economic Feasibility	Market Scale	Established Technology	Expectation	Development in '90	Comment
Thermal Recycling	C	A+	A	B	A	Currently well established.
Whole Tire Application	B	C	A	C	B	Market scale is small.
Retreading	A	C	A	B	C	Depends on the development of passenger market.
Processed Tire Application	C	B	B	B	B	Variety of markets.
Rubber Asphalt	A	B	B	B	A	Depends on funding support by government.
Pyrolysis	D	D	C	C	B	Depends on the development of new technology.
Export	A	B	--	D	B	Not a true solution.

A--Excellent, B--Good, C--Neutral, D--Poor

Waste Tire Management:
In the United States, waste tire management has been successfully conducted and developed over the last ten years. The number of stockpiled tires decreased from 2 billion to 500 million, and the recycling rate has increased from 44.2 % to 75.8 %. This success is primarily due to government-level efforts such as law enforcement, funding, and education. Pressure from growing public concern was the driving force behind government programs, and the motivation for industry.
However, no progress has been observed in increasing the annual recycling rate from 1996 to 1998. It appears that current waste tire management practices may be reaching a limitation. The stagnation and decline in TDF usage has arisen from environmental concerns and the relatively low market price of oil and coal.

Above table provide a summary of the recycling technologies discussed in this report. Grading is based on data and discussions given in earlier sections, and the grading is as follows:

Economic feasibility: A...Beneficial technology. B...No financial support necessary. C...Financial support is required to compete with alternatives. D...No commercial success.
Market scale: A...Large market existing. B...Large but developing market. C...Small or difficult market. D...No market existing.
Established technology: A...No new development is necessary for plant scale application. B...Further development will contribute to expand the market. C...Technological breakthrough is required. D...No technological basis existing.
Expectation: A...Will solve waste tire problem. B...Will be an important recycling technology. C...Will not be main stream. D...Not a true solution.
Development in '90s: A...Successfully conducted. B...R&D has been done. C...No progress. D...Failed.

This report has shown that the development of other technologies will reduce the heavy reliance on TDF, and will stabilize the market demand for waste tire recycling. The growing markets for crumb rubber applications (including rubber asphalt) will soon occupy more than 20 % of the annual recycling rate. Large scale whole tire applications such as dams and construction materials are receiving increased attention.
Pyrolysis has been studied as a new technology for waste tire recycling. It is not economically feasible at the present time. Technological developments may make it possible to recover more valuable chemicals from waste tires in the future, but price competition with conventionally produced chemicals will not be easy.

Economic feasibility is always a major problem for all recycling technologies. Except for retreading, the economic feasibility of all technologies is based on government subsidy (approximately $0.6 per tire).

TDF:
TDF applications constitute 70 -80 % of the waste tire 'recovery' rate, but TDF is frequently not considered as 'recycling'. For some solid wastes, incineration is the best alternative. However, the incineration of waste materials is often not performed under controlled conditions, since their energy value is not significant as a fuel source. Waste tire incineration was first proposed as an inexpensive alternative for conventional fuel sources such as coal and petroleum. This approach has been adopted by paper/pulp manufacturers to reduce their boiler heating costs. The high energy content of waste tires has been recognized by other industries looking for cheap energy alternatives. Cement kilns already have sufficient capacity to consume the entire annual waste tire generation.

Retread:
Retreading has proven to be reliable and economically feasible, particularly for large tires used on buses, trucks, airplanes, off-the-road vehicles and racing cars. These applications presently constitute almost 100 % of the retreading market. One major reason for the negligible amount of passenger tire retreading is related to the negative image of recycled materials. Proper education and marketing could lower this barrier.
Passenger radial tires typically possess low aspect ratio ((side wall height / tread width)*100 = aspect ratio), light weight and low rolling resistance. A low aspect ratio allows a vehicle to accept high capacity brake equipment, and gives high speed stability. Light weight contributes in many ways to improving vehicle performance with regard to fuel efficiency, stability, product life, acceleration, etc.
Since retreading is not significant for passenger tires in today's market, tire manufacturers have not considered this possibility in the design and manufacture of new tires. Some unsuitable aspects for retreading include the relatively thin casing layer, which makes repair difficult, and heat damage which may occur during the recuring process. Special rubber compounds require additional care when they are recured, since many non-sulfur based crosslinking agents have been used in the original formulations. This makes passenger tires more difficult and expensive to retread compared to truck/bus tires.

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