3. End-of-life Tyre Properties
3.1 Definition of End-of-life Tyre
An end-of-life tyre is a used tyre that cannot or is not reused for its originally intended purpose and is not retreaded. Such tyres may have a further use as a raw material for other processes or be destined for final disposal. End-of-life tyres are called "scrap tires" in the United States.
3.2 Physical Properties
Tyres consist of a rubber compound usually reinforced with steel and textile. Depending on their size and utilisation, tyres vary in design, construction and total weight. The weight of a used passenger car tyre in Europe is about 6.5 kg and that of a truck tyre is about 53 kg. [Basel Convention Working Group (1999)"Basel Convention Technical Guidelines on the Identification and Management of Used Tyres". Basel Convention on the control of transboundary movements on hazardous wastes and their disposal. Document No. 10.] Passenger car and truck tyres make up approximately 85% of the total tyres manufactured globally. [Ibid.]
3.3 Chemical Composition
Approximately 80% of the weight of car tyres and 75% of truck tyres is rubber compound. [Ibid.] The compositions of tyres produced by different manufacturers are reported to be similar. Table 3.1 shows the material composition of passenger car and truck tyres from the European Union (EU) as well as the composition of tyre rubber from Canada.
Table 3.1: Comparison of material composition of passenger car and truck tyres in the EU as well as tyre rubber in Canada
| Material |
Car tyre [Ibid.] |
Truck tyre [Ibid.] |
Tyre rubber [O'Shaughnessy VO and Garga VK. (2000) Tire-Reinforced Earthfill. Part 3: Environmental Assessment.Canadian Geotechnical Journal37: 117-131.] |
|---|---|---|---|
| Rubber/elastomers |
47% |
45% |
62% |
| Carbon black* |
21.5% |
22% |
31% |
| Metal |
16.5% |
25% |
NA |
| Textile |
5.5% |
- |
NA |
| Zinc oxide |
1% |
2% |
2% |
| Sulphur |
1% |
1% |
1% |
| Additives |
7.5% |
5% |
4% |
Note:
* Part of the carbon black may be replaced by silica in certain types of tyres.
3.4 Hazardous Waste Composition
Tyres contain a total of approximately 1.5% by weight of hazardous waste compounds listed in Annex 1 of the Basel Convention. These compounds, outlined in Table 3.2, are encased in the rubber compound or present as an alloying element.
Table 3.2: Hazardous waste constituents [Basel Convention Working Group (1999)"Basel Convention Technical Guidelines on the Identification and Management of Used Tyres". Basel Convention on the control of transboundary movements on hazardous wastes and their disposal. Document No. 10.]
| Chemical name |
Remarks |
Content |
|---|---|---|
| Copper compounds |
Alloying constituent of metallic reinforcing material |
Approximately 0.02% |
| Zinc compounds |
Zinc oxide, retained in the rubber matrix |
Approximately 1% |
| Cadmium |
On trace levels, as cadmium compounds attendant substance of the zinc oxide |
Maximum 0.001% |
| Lead |
On trace levels, as attendant substance of the zinc oxide |
Maximum 0.005% |
| Acidic solutions or acids in solid form |
Stearic acid, in solid form |
Approximately 0.3% |
| Organohalogen compounds |
Halogen butyl rubber (tendency: decreasing) |
Maximum 0.1% |
3.5 Thermal Properties
The net calorific value of a tyre is between 26 and 34 GJ/tonne, [MWH New Zealand Ltd (June 2003)"Development of a Regional Waste Recovery / Processing Sector". A report prepared for the Wellington City Council, Ministry for the Environment and Ministry of Economic Development.] which is similar to that of common fuel sources such as coal (Figure 3.1). A tyre is difficult to ignite. It burns almost completely at 650°, producing principally carbon dioxide and water, plus inert resides such as ash and slag.
