replacing TBSI 2

[Metten]

I have a formulation (NR, for thicker articles, compression moulding) where TBSI is used.
I cannot find TBSI, so I wondered if anyone knew a (possible) replacement.

 

[stancom]

Let’s be clear, in my own mind as much as in anybody else’s, Santocure TBSI is N-t-butyl-2-benzothiazole sulfenimide, not to be confused, as it sometimes is, with N-t-butyl-2-benzothiazole sulfenamide (TBBS). It was introduced to give curing characteristics sulfenamides could not easily provide, namely a long scorch time and relatively slow rate of cure, coupled with improved reversion resistance. Hence, its suitability for thick components.
Perhaps the nearest sulfenamide contender is the dicyclohexyl derivative, DCBS, but this is very slow curing and not very efficient in terms of crosslink density. Replacing TBSI by CBS, TBBS or MBS (assuming nitrosamines is not a problem) ought to be possible with the aid of a retarder, but maybe not PVI because this does not reduce cure rate. A more conventional retarder such as salicylic acid may be more suitable. However, no advice can really be given unless more information on the rest of the formulation, the intended application and key vulcanizate properties is provided. For instance, is the vulcanizing system a conventional high sulfur one or is it a semi EV?
I am not aware of any other commercially available sulfenimdes.

 

[Metten]

Stancom, thank you for the answer. I can't disclose much information as it is regarded as confidential.
The vulcanizing system is a high sulfur (2.2phr) one. The application is for thick parts which need a high crosslink density.

 

[stancom]

Appreciate conventional system is used, presumably for desired vulcanizate properties, so the focus needs to be on minimizing reversion. Rather than trying to mimic TBSI, I wonder whether a better solution is to change the cure conditions, ie by either preheating the moulded blank or by reducing the vulcanization temperature. Some bulky products are cured at temperature below 14O C, and may need a cure time of several hours, with advantage being taken of the reduced rate of reversion. Partly because of that and the increased efficiency of crosslinking a relatively high crosslink density should result. With this approach adding a retarder (ie to ape TBSI) serves little purpose and a long scorch time may do more harm than good.

Another possibility to ensure use of a higher cure temperature is to use a post vulcanization stabiliser such as Duralink HTS, but I have no personal experience of these.