Tyre rubbers

About two-thirds of the N2 produced industrially is supplied as a gas, mainly in pipes but also in cylinders under pressure. The remaining one-third is supplied as liquid N2 since this is also a very convenient source of the dry gas. The main use is as an inert atmosphere in the iron and steel industry and in many other metallurgical and chemical processes where the presence of air would involve fire or explosion hazards or unacceptable oxidation of products. Thus, it is extensively used as a purge in petrochemical reactors and other chemical equipment, as an inert diluent for chemicals, and in the float glass process to prevent oxidation of the molten tin (p. 370). It is also used as a blanketing gas in the electronics industry, in the packaging of processed foods and pharmaceuticals, and to pressurize electric cables, telephone wires, and inflatable rubber tyres, etc. 

Bulgin, D., Static electricity on rubber tyred vehicles, Brit. J. Applied Phys. Supplement No. 2, S83-S87. 

Meuzelaar and co-workers [90] have described an on-line high pressure TG-GC-MS system which requires only very small amounts (10-100 mg) of sample and can be operated at high pressure under different atmospheres (N2, He, H2, etc.). The system has been used in recycling lower grade post-consumer polymers, as coloured polyethylene and polystyrene or used rubber tyres, by co-processing with coal. The main characteristics of non-simultaneous methods, TG-GC and techniques requiring a cold trap, are given in Table 1.2. 

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. 

Cement The cement industry lobbied for process emissions and won this fairly easy case. However, they also lobbied that the use of shredded rubber tyres as a fuel in cement kilns should be considered process emissions, but this argument was turned down. 

Likewise, Orr et al.29,30 have explored the possible use of tyre pyrolysis oil as a solvent for coal liquefaction. The potential of this alternative was demonstrated by the fact that coal-TPO mixtures were transformed with higher conversion than when coal was reacted directly with ground waste rubber tyres. It is proposed that the polyaromatic compounds present in the TPO favour coal dissolution during liquefaction. Treatment of coal-TPO mixtures (50/50%) at 430 °C under 68 atm of cold-hydrogen pressure in the presence of a Mo catalyst led to a high coal conversion in just 10 min of reaction. From electron probe microanalysis of the coal particles after the reaction, the authors conclude that TPO favours the catalyst dispersion and its contact with coal, which results in enhanced coal conversion. 

Figure 4.6. A rubber-tyred front-end loader and a dump truck (by courtesy of Volvo Construction Equipment GB Ltd.)...

A relatively recent trend is to install in-pit crushers (Fig. 4.7). These may be fed directly from the quarry face by rubber-tyred shovels in a load-and-carry operation. The crushed rock is transported to the processing plant by conveyers, which generally have lower capital and operating costs than dump trucks. 

The painting process for VR differs from that used for new cars. While new car bodies can be heated at 120-140°C to cure the OEM paint system, a car for repair, complete with a tank of petrol, electronic equipment, rubber tyres and other heat-sensitive components, must be treated with care. Hence, cure temperatures of 60°C maximum are used for VR coatings. The solvent systems used must be capable of providing the necessary solubility, application, viscosity and flow characteristics. It must also evaporate quickly enough to enable the bodyshop to complete the repair as soon as possible, often under widely varying temperature and humidity conditions. 

The polishing machine (see Figure 2.5) has a metal wheel called the road wheel. This is 406 mm in diameter and holds the test specimens and the stone control specimens around its rim. The number of specimens placed around the wheel is 14 in total. The wheel rotates at 320 revolutions per minute during the test. The rubber-tyred wheel has a static contact force with the moulds of 725 N. For the first 3 h of the test, corn emery is fed onto the wheel at a rate of 27 7 g/min together with a sufficient amount of water. The corn emery has a gradation with 98%-100% of the particles passing through the 0.600 mm sieve. 

After the first 3 h, the second rubber-tyred wheel is fitted and the test is repeated for another 3 h using flour emery. The emery flour rate is 3 1 g/min with the rate of water approximately twice that of the emery flour. 

The disadvantages of coloured bitumens/asphalts are as follows (a) steep price owing to the high cost of the pigment and (b) the fact that the only truly stable colour that can be achieved is red, which, depending on the traffic, type of asphalt and ambient temperatures, gets dirty (due to rubber tyre traces left on the surface). 

Some paint formulations include casein where it functions as a thickener and stabiliser [15]. Other applications are in leather finishing and in reinforcing and stabilising rubber tyres, as a component of animal and pet foods and for softening and waterproofing of textiles [16] ... 

Figure 5.31 Natural rubber tyre after 40 years exposure to sea water. (Courtesy of the publisher Tun Abdul Razak Research Centre, Brickendonbury, Hertford, England.)...

Figure 5.37 shows the elfects of the water immersion test (distilled and salt water) on peel strength of NR and CR rubbers for 30 days at ambient temperature. The result is then compared with the dry sample of NR and CR rubbers. Within the 30-day period there is no sign of deterioration of the peel strength. The amount of water absorbed is relatively negligible and for this reason the peel strength is relatively unalfected. This is consistent with the findings of Ab-Malek et al.f who reported that the rubber tyre had absorbed about 5% of sea water after 42 years of immersion. 

Rubber tyre cord adhesion W J VAN OOlJ Adhesion to brass-coated steel Rubber-based adhesives J M MARTfN MARTInEZ General introduction Rubber-based adhesives compounding J M MARTIN MARTfNEZ Formulations, etc. 

---