Dithiodimorpholine cure systems

Sulfur cures do not always use elemental sulfur. Sometimes with special EV (efficient vulcanization) cure systems no elemental sulfur is used at all. Instead a sulfur donor chemical is used. The most common sulfur donor is dithiodimorpholine (DTDM), which donates two sulfur atoms from the center of its molecule to participate in the sulfur vulcanization process. These EV cures are more expensive than conventional sulfur cures based on elemental sulfur. This is because sulfur donors such as DTDM are more expensive per pound than sulfur itself. Elowever, the EV cure will usually impart better air aging resistance than that of a conventional sulfur cure system using a significant concentration of elemental sulfur. 

TMTD is used as a sulfur donor in EV cure systems to improve the rubber compound s aging properties. TMTD imparts less scorch safety time than dithiodimorpholine (DTDM) when used as a sulfur donor in an EV cure. Also, TMTD is commonly used as a very fast accelerator in conventional sulfur cures. It is also used as a secondary accelerator (a kicker ) in conjunction with a conventional primary accelerator. 

The choice of accelerator will influence the length of crosslinks, but this can be further controlled by adjusting the accelerator sulfur ratio. Increasing this ratio progressively favors shorter crosslinks. This can be alternatively accomplished by using sulfur donors in place of most or all of the elemental sulfur for vulcanization. The thiuram accelerators, particularly the disulfides, and dithiodimorpholine are commonly used for this purpose. The use of a cure system designed to form predominately short crosslinks is referred to as efficient vulcanization (EV). 

Rhenocure SDT (Rhein Chemie), a dialkyl dithiophosphate polysulphide sulphur donor, was evaluated in curing systems for the vulcanisation of thick NR parts. It was found that a curing system based on a dithiophosphate accelerator and the dithiophosphate sulphur donor was superior to a system based on a sulphenamide and dithiodimorpholine. A substantially higher amount of short sulphur bridges was generated, leading to improved reversion resistance and superior heat... 

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