Curing, rubber accelerator classes

ZnDBC is commonly referred to as an ultra-accelerator because the dithiocarba-mate class of rubber accelerators is known for imparting a very fast cure rate (just like the thiuram accelerator class). 

Chemically, the dithiocarbamate class of rubber accelerators is actually salts of the thiurams. And just as with the thiuram class, the dithiocarbamates can also emit nitrosamines during the curing process, which can pose a health risk to workers. This is why over the years there has been some shifting of use in rubber accelerators away from the dithiocarbamates. 

Classed as ultra accelerators, xanthates are among the fastest of accelerators available to the rubber compounder. Their speed is such that they find only limited application in solid rubber product manufacture but they are used in low temperature curing of latex articles. 

Cure system species, accelerators and their reaction products This class of additive can present problems as they are often thermally labile, reactive and, in some cases, have a degree of ionic character (e.g. zinc dithiocarbamate salts). In these cases LC-MS is a more appropriate technique than GC-MS. It is also easier to use LC-MS with a number of the approved food simulants as they can be injected directly into the instrument, being compatible with the mobile phase. In some cases the reaction products (e.g. aniline from diphenyl guanidine, and benzothiazole from thiazole and sulphonamide accelerators) are stable and so GC and GC-MS can be used. Peroxides are popular curatives for food use rubbers and the stable, breakdown products of these can be easily detected by GC-MS. 

It is common practice in the rubber industry for a compoimder to use combinations of several accelerators in developing a cure system. Typically, these cure systems comprise a primary accelerator and one or more secondary types. Primary accelerators are generally the thiazole and sulfenamide classes the secondary accelerators are the thiurams, dithiocarbamates, guanidines, and to a much lesser extent, certain amines and the dialkylphosphorodithioates (32). Typically, secondary accelerators are more basic than the primary or major accelerator. 

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