Sulfur vulcanisation diene rubbers

These polyolefin rubbers are produced in two main types the saturated co-polymers, ethylene propylene rubber (EPM), and the unsaturated ethylene-propylene diene terpolymer (EPDM). The monomers are co-polymerised in ziegler natta type catalysts. The EPDM types are capable of sulfur vulcanisation as they contain, in addition to olefins, a non coagulated diene as the third monomer. 

Some of these chemical agents (e.g., the amine/thiol mixtures) were used in the chemical probe rubber chemistry research work being undertaken at TARRC in the 1950s and 1960s to establish the chemical nature and processes involved during the sulfur vulcanisation of diene rubbers, such as NR. 

The accelerated sulfur vulcanisation of general purpose diene rubbers (e.g., natural rubber (NR), Styrene butadiene rubber (SBR), and butadiene rubber (BR)) in the presence of organic accelerators and other rubbers, which are vulcanised by closely related technology (e.g., ethylene-propylene-diene terpolymer (EPDM) rubber, butyl rubber (HR), halobutyl rubber (XIIR), nitrile rubber (NBR)) comprises more than 90% of all vulcanisations. 

Most accelerators used in the sulfur vulcanisation of other high diene rubbers are not applicable to the metal oxide vulcanisation of CR. An exception is the use of a so-called mixed curing system for CR, in which metal oxide and accelerated sulfur vulcanisation are combined. Along with the metal oxides, TMTD, DOTG and sulfur are used. This is a good method to obtain high resilience and dimensional stability. 

In this chapter, some of these uses are explored in greater detail. Goodyear and Hancock in 1847 discovered that, when natural rubber was heated with a small amount of sulfur, the physical properties of the resultant rubber were improved the material became tougher and more resistant to changes in temperature. This process of vulcanisation is also useful for the treatment of synthetic rubbers, and as well as sulfur, many sulfur donors such as symmetrical diphenylthiourea, tetraalkylthiuram disulfides (1) and 2-mercaptobenzothia-zole (2) (Figure 1) can be used.1 These compounds act as accelerators of the process of polymerisation of the diene monomers in synthetic rubbers for this purpose, the additional presence of zinc oxide and preferably a carboxylic acid, e.g. stearic acid, is required. 

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