Synthetic polyisoprene rubbers tyres

Rubber tyres are by far the most visible of rubber products. Identification is trivial and collection is well organized. Recycling and disposal, however, are less evident. A major route for tyres is their use as a supplemental fuel in cement kilns. Major compounds in tyres are styrene-butadiene rubber (SBR), synthetic and natural polyisoprene rubber, steel cord, carbon black, zinc oxide, sulphur and vulcanization-controlling chemicals. Tyres can be retreaded, which is economic for large sizes (truck tyres), or ground to crumb or powder (cryogenic grinding). Such materials have some limited market potential as an additive in asphalt, and in surfaces for tennis courts or athletics. 

In view of the wide application of Py—GC in industry and research, the development of techniques and equipment for automatic analysis by this method is of great practical interest. An automatic Py—GC system was developed by Coulter and Thompson [69] for Curie-type cells with a filament for specific application in the tyre industry. A typical analysis involves the identification and determination of polymers in a tyre material sample. The material of a tyre is essentially a mixture of polymers, most often natural rubber (polyisoprene), synthetic polyisoprene, polybutadiene and butadiene-styrene copolymer. A tube is normally made of a material based on butyl rubber and a copolymer of isobutylene with small amounts of isoprene. In addition to the above ingredients, the material contains another ten to twelve, such as sulphur, zinc oxide, carbon black, mineral oil, pine pitch, resins, antioxidants, accelerators and stearic acid. In analysing very small samples of the tyre material, the chemist must usually answer the following question on the basis of which polymers is the tyre made and what is their ratio The problem is not made easier by the fact that cured rubber is not soluble in any solvent. 

As for natural rubber the most important single outlet is in tyre production but benefits may be obtained in the manufacture of products as diverse as elastic bands, bridge bearings, conveyor belts and pharmaceutical goods. Certain specific attributes of synthetic polyisoprenes have made them attractive to manufacturers. For example, the lack of non-rubbers allows higher resistivity values to be reached in electrical applications and the low modulus provides easy extensibility and therefore comfort for items such as respirator masks and bathing hats. 

This also shows that the lower compound green strength associated with the synthetic polyisoprenes relative to natural rubber is not an insurmountable problem. However, the incipient problem has been generally avoided by not making a total replacement of the natural rubber in tyre compounds which are subject to substantial deformation during building operations. 

Isoprene rubber (IR) or Polyisoprene is a synthetic copy of natural rubber (NR) and approaches NR in its properties. Besides for tyres, IR is, because of its good flow properties, suitable for injection moulding. 

Elastomers are used in a wide range of industrial, transportation, domestic, construction and aerospace end-applications. The major consumer of both natural and synthetic rubber is the tyre industry. Five types natural rubber (NR), styrene butadiene rubber (SBR), polybutadiene, polyisoprene and the butyl (and halobutyl) rubbers are used in massive quantities around the world. Smaller applications for rubbers include conveyor belting, footwear, pharmaceutical closures, plant lining, hoses, extruded goods, flooring, power cables, gaskets and seals, and many, many other applications. 

Natural rubber, as extracted from a tree, flows under its own weight (albeit slowly) and as such it is not very useful. However, Charles Goodyear discovered in 1839 that it can be vulcanized, by adding sulphur and heating. This material has the properties we are familiar with in car tyres etc. i.e. it is elastic and does not flow under normal conditions. Vulcanization corresponds to the crosslinking of polyisoprene chains by sulphur atoms (Goodyear was not aware of the molecular mechanism). This process is sketched in Fig. 2.27. Natural rubber is predominantly ds-1,4-polyisoprene (Fig. 2.9). Although synthetic rubbers have been developed (especially copolymers of polystyrene and polybutadiene), natural rubber is still very widely used due to its excellent properties as an elastomer and its ready availability. 

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