- Vulcanizing Accelerators
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 systems2. Peroxides3. Urethane crosslinkers4. 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.
Since a high number of commercial products are available, accelerators are best classified according to their chemical structure. There are also a number of speciality products that are difficult to classify.
The most important organi accelerators are1. Merkapto accelerators2. Sulfenamid accelerators3. Thiuram accelerators4. Dithiocarbamate accelerators5. Dithiocarbamylsulfenamide6. Xanthate accelerators7. Guanidine accelerators8. Amine Accelerators9. Thiourea Accelerators10. Dithiophosphate accelerators
Accelerators can also be classified according to the way they speed up the process. They can be classified as1. Ultra fast2. Fast3. Medium Fast4. Delayed Action5. Slow
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