Introduction:

The exclusive use of sulfur for curing is both time-consuming and ineffective. A typical sulfur cure requires 5-20 phr (parts per hundred rubber) of sulfur and takes 5-15 hours to complete at temperatures ranging from 266-320°F. This slow reaction occurs due to the need for numerous sulfur atoms to form crosslinks with the rubber. Undoubtedly, the process of sulfur curing could greatly benefit from the incorporation of additives that accelerate crosslink formation.

An accelerator is a chemical compound incorporated into a rubber mixture with the purpose of expediting the vulcanization process, enabling it to take place at reduced temperatures and with improved efficiency. More than 150 different chemicals from various compositional classes are known to function as accelerators for rubber vulcanizates, with approximately 50 accelerators being commonly used in the rubber industry. There is a wide range of accelerators available for compounders. To facilitate understanding, accelerators can be classified based on their chemical structure. One such classification, established by the ASTM, includes the following categories: 

1. Thiazoles (Mercapto), 

2. Sulfenamides, 

3. Guanidines, 

4. Dithiocarbamates, 

5. Thiurams,