Tyre rubbers, stability

Sonnier R., E. Leroy, L. Clerc, A. Bergeret, and J.M. Lopez-Cuesta. 2006. Compatibilization of polyethylene ground tyre rubber blends by gamma irradiation. Polym Degradat. Stability. 91 2375-79. 

Soimier, R., Leroy, E., Clerc, L., Bergeret, A., Lopeztyre rubber blends by y irradiation. Polymer Degradation and Stability 2006,91,2375-2379. 

Roy and co-workers [57] at the Indian Institute of Technology have evaluated the performance and the chemical behaviour of a range of disulfide compounds when applied to waste tyre rubber. The DR that were obtained in each case were revulcanised to assess their cure characteristics, and then samples tested to determine their mechanical properties, morphology, dynamic properties and thermal stability. 

Resin cures utilise phenol-formaldehyde resins with reactive methylene groups and a small added amount of either a chlorinated rubber, e.g., polychloroprene, or stannous chloride. If halogenated phenolic resins are used the additional source of a halogen may not be required. Resin cures give butyl compounds excellent heat stability and are used to good effect where this is required, e.g., in tyre curing bags which have to resist service at 150 °C in a steam atmosphere. 

Radiation cross-linking affects different characteristics of polymers like mechanical behaviour, chemical stability, thermal and flame resistance. Until now, radiation cross-linking is limited to only a few industrial applications cross-linking of rubber or polymers for tyres, cables, pipes (e.g. in under floor heating systems), and heat-shrinkable tubes. Nevertheless, there exist industrial facilities like electron accelerators and gamma plant. Some of these radiation sources are operated by research institutes. 

The main use of NR is in automobiles. In developed countries nearly 60% of all rubber consumed is for automobile tyres and tubes. The superior heat build-up and tensile strength of NR makes it indispensable in the manufacture of aviation tyres. In heavy-duty tyres such as those for tractors and trucks, the major portion of the rubber used is NR. In addition to tyres, a modern automobile has more than 300 components made out of rubber. Many of these are processed from NR. NR is also widely used in the manufacture of hoses, footwear, battery boxes, foam mattresses, balloons, toys, etc. In addition to this, NR now finds extensive use in soil stabilization, in vibration absorption and in road construction. A variety of NR-based engineering products have been developed for use in these fields. Seismic isolators, bridge bearings and dock fenders are niche products relying on the superior properties of NR. 

NR is primarily utilized in the tyre industry because of its ideal properties. However, it has poor stability due to the existence of many double or unsaturated bonds. To improve the ambient stability of NR, synthetic rubber was chosen for blending. Zhang and coworkers blended and vulcanized NR and chloroprene rubber at a weight ratio of 75/25 by using a two-roll mill. The NR/ chloroprene rubber blends had improved mechanical properties in terms of their elongation strength and Shore A hardness. Moreover, the vulcanized chloroprene rubber blends had excellent oil resistance, thermal stability, selfextinguishing ability and ozone resistance. 

Yagneswaran and co-workers [25] incorporated mechanically devulcanised waste tyre powder into a vinyl ester resin matrix at various levels of addition and characterised the resulting materials using physical tests, DSC and TGA. As the level of rubber powder increased the composites were found to have reduced heat stability and flexural strength, but increased flexural modulus. 

Sulphur curing systems provide long service in air at 100°C or less quinoid systems give vulcanisates with greater stability than sulphur systems and are suitable for short-term or intermittent service in air at temperatures up to ISO C extended service in air at 150-200 °C demands resin cures. Tyre curing bladders, for example, are virtually always made from resin cured butyl rubber. However, at high temperatures in the absence of air, e.g. in super heated, deaerated steam, properly cured butyl rubbers perform exceptionally well, irrespective of curing system. 

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