Phosphate Accelerators In the Vulcanization of Etylene Propylene Based EPDM Elastomers

Vulcanization of ethylene propylene based terpolymer (EPDM rubber) using sulfur and organic accelerators is facilitated by the presence of crosslinks in the ethylene norbornene units.  The low degree of unsaturation, usually in the order of 1 to 10%, has traditionally necessitated use of ultra-fast accelerators such as tetramethyl thiuram disulfide (TMTD) or zinc dimethyldithiocarbamate (ZMDC). Such accelerators can potentially form nitrosamines which may be undesirable.

There are a number of alternatives to thiuram and dithiocarbamate cure systems. Due to the absence of nitrogen, phosphate accelerators can provide a platform for development of cure systems. Phosphate accelerators may bring a number of advantages to EPDM polymer compound cure systems. For example, zinc dialkylphosphorodithiates have an inhibiting effect on anaerobic oxidation and thermal breakdown of rubber vulcanization networks, i.e. they provide reversion resistance. Dialkyldiphosphorothiate disulfide can be used in rubber in conjunction with various other accelerators to obtain a high state of cure and good mechanical properties without encountering short scorch time constraints. This study explores the use of such cure systems in the vulcanization of EPDM rubber compounds, and is intended to provide a starting point for further development work.