Vulcanizing Accelerators

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An ASTM definition for vulcanization reads as follows "An irreversible process during which a rubber compound through a change in its chemical structure (for example, cross-linking) becomes less plastic and more resistant to swelling by organic liquids while elastic properties are conferred, improved, or extende over a greater range of temperature."

Vulcanization is very important in Rubber Technology as it gives the real rubber property to the so called Rubber. Again the term of "curing" and "vulcanizing" are used interchangeably.

Four types of curing systems are in common use. The are

1. Sulfur systems 2. Peroxides 3. Urethane crosslinkers 4. Metallic oxides

By far the most common vulcanizing methods are those dependent on sulfur.

Sulfur, by itself, is a slow vulcanizing agent. Large amounts of sulfur are necessary, high temperatures and long heating periods and one obtains an unsatisfactory crosslinking efficiency with unsatisfactory strength and aging properties. Only with vulcanization accelerators the quality corresponding to today's level of technology can be achieved. The multiplicity of vulcanization effects demanded cannot be achieved with one universal substance, a large number of divers materials is necessary.

[edit] Classification

Since a high number of commercial products are available, accelerators are best classfied according to their chemical structure. There are also a number of speciality products that are difficult to classify.

The most imprtant organi accelerators are 1. Merkapto accelerators 2. Sulfenamid accelerators 3. Thiuram accelerators 4. Dithiocarbamate accelerators 5. Dithiocarbamylsulfenamide 6. Xanthate accelerators 7. Guanidine accelerators 8. Amine Accelerators 9. Thiourea Accelerators 10. Dithiophosphate accelerators

Accelerators can also be classified according to the way they speed up the process. They can be classified as 1. Ultra fast 2. Fast 3. Medium Fast 4. Delayed Action 5. Slow