Tyres, additives Carbon-black

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. 

The effect of the different components present in used tyres on the generation of free radicals on coal has been studied by Ibrahim and Seehra22 through ESR experiments. Figure 6.10 shows that the addition of carbon black or SBR to coal at 420 °C leads to a significant increase in the free radical intensity. Likewise, it was observed that the tyre tread and its components lower the temperature of coal thermal cracking, favouring the formation of free radicals on the coal. 

Mastral et al.23,24 have also investigated the effect of the main components present in tyres (carbon black, styrene-butadiene copolymer and polybutadiene) on the liquefaction of coal. Coprocessing of coal and carbon black confirmed the catalytic role of the latter, as it promotes hydrocracking reactions leading mainly to the formation of gaseous products. The addition of SBR to coal improves the yield of gases, oil and asphalt fractions, even at relatively low temperatures (350-375 °C). It is proposed that SBR favours the stabilization of the radicals involved in the process through alkylation reactions... 

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. 

The major user of black is the rubber industry, particularly for tyres, where addition of carbon black contributes to reinforcement and resistance to tearing, abrasion, flex, and fatigue. In the USA it is estimated that a little less than 0.5 lb (0.25 kg) of black on average is used for every 1 lb of rubber used. Plastics are the largest and fastest-growing non-elastomer use for carbon black. 

Improved methods of vulcanization, and the addition of fillers, most often carbon black powder, to dilute the ruhher, reduced the price and improved the reliability of the product. The issue grew in importance with the coming of World War II. Rubber became scarce while the need increased. In Germany the situation was critical. A synthetic rubber, known as Buna (from the starting monomer, Mtadiene and the metallic sodium, in German watrium, used to initiate polymerization), had been produced on a laboratory scale, but it was expensive and its properties were far from ideal. A more complex polymer, with two mixed types of monomer unit, polymerized by improved procedures, gave better results. Some material was produced in the infamous Buna factory in Auschwitz. The preferred material for tyres proved later to be a polymer made from styrene and butadiene ... 

Although natural rubber has satisfactory properties in many applications there are now many synthetic alternatives available. Natural rubber is rather prone to chemical degradation by ozone and has poor resistance to solvents. Synthetic rubbers are usually better in these respects. The most important use of rubbers is in motor vehicle tyres in which styrene-butadiene rubber (a random copolymer, SBR), is mainly used along with a variety of additives such as carbon black. This reinforces the rubber and improves the strength, stiffness and abrasion resistance. 

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