Bloomed chemicals? 1

[joysop]

Hi guys,
You can call me a rookie because I registerd here a few minites ago and this would be my first thing I do here.
The thing I want to get answered from you is bellow.

NBR rubber was bloomed after curing.
I analyzed it with EDX and found the bloomed chemical was kinds of sulfur-compound.
Could be just sulfur? Or curing activator?

 

[edine]

Most NBR compounds are sulfur cured. The bloom is likely a combination of accelerator fragments, but may contain just free sulfur.

You didn't give too much detail so it is a little hard to tell if you are a molder or an end user. Bloom is basically a solubility issue. This could be just normal for this compound or represent a compounding error or the part could be slightly undercured. If you have access to the data, take a look at the rheometer cure and the durometer of the part and see if anything looks out of the ordinary.

Hope this helps.

 

[joysop]

Dear edine,
Thank you for your kind reply.
It looks free sulfur from a compounding error. I checked hardness of the bloomed final product and could determine that this problem wouldn't be from uncuring because hardness was the same as a normal one. Too much sulfur seems to be mixed with NBR.
Your advice was very helpful to detect the cause of the problem.
Many thanks!!

 

[hoidap]

Not only Sulfur can bloom, but also the aid process agent; too much filler, or anti-stick agent to prevent rubber preform attaching each other. these chemical don't link to any rubber chain.

For the case of sulfur, it is important to check the Rheometer curve, not fully cured or over-cured also cause blooming.
Do you re-use the rubber draft with the new compound, the re-use is partly crosslinked, so the hardness of the product can be the same, but less of crosslink reaction, and uncured sulfur will bloom.
last, check your compound, can change to less sulfur compound for safe.