Rubber has very special properties compared to other materials. It's also very resistant to age, tolerates temperature fluctuations and UV radiation, insulates against electricity, heat and cold, ensures good drainage and is lightweight, has a porous surface on which microorganisms thrive and can even bind with other materials, including with the help of co-polymers.
Rubber is produced nowadays from rubber trees (natural rubber, which also has a very weak smell) and industrially (synthetic). To ensure all the properties needed, other substances are added such as carbon black, oil etc. The key to a stable, formable and resistant material is vulcanising. The word comes from using sulphur (found in volcanoes) to create very hard chemical bindings within the material. Thanks to its stability, tyre rubber does not emit uncontrolled amounts of substances to the environment or organisms, and migration to air or water is extremely limited. Even in the laboratory using very strong solvents, it is difficult to extract or even to detect all the substances it contains. Its stability is also a positive factor when it comes to impact on humans and the environment, which means that recycling the component parts of tyre rubber can be a challenge, although a number of processes have been developed that are being scaled up for commercial use. These include devulcanising, i.e. breaking the sulphur bindings using microwaves, chemicals, bacteria or pyrolysis, i.e. vaporising the rubber to extract oils, carbon black, steel and textiles without the presence of acids.
When used tyres are recycled, the result is material that to a large extent retains its technical properties. It's soft, elastic and returns to its original shape after being compressed. Such properties have been used to produce products with unique abilities, such as those that can be deformed without breaking, that dampen vibrations, or that can absorb impulses and reproduce them in a controlled manner.
In the long run, tyre rubber will probably be used for the manufacture of new tyres, but given that each manufacturer works with its own optimised and constantly improved formula designed to increase such factors as grip in the wet and lifetime, reduced vehicle rolling resistance and energy consumption and optimising new vehicles such as electric cars, a competitor's tyre or older generations of tyre rubber cannot be introduced into new tyre production. However there are several manufacturers working on solutions to this issue.