tfcallahan1
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How to remove excess sulfer from latex
I have a problem with some latex that has excess sulfer.
I am a novice so please bear with me if what follows is not entirely correct.
We receive a latex soup containing latex, water, ammonia, sulfer, and some other compounds.
We then apply this in open air as a backing to some textiles.
As the the soup dries it vulcanizes.
We got a batch of latex that had excess sulfer (confirmed by testing) - perhaps as much as 3x normal.
So, when the latex soup dried all of the sulfer was not used in the vulcanization process and so remained in the dried latex.
Then, apparently moisture (water) from the textiles reacts with the excess sulfer causing H2S gas to be released and a rotten egg smell that
accompanies it, especially if the product is wrapped up or bagged.
So, the questions are:
1. Is there any way to easily neutralize the excess sulfer?
2. What are the potential impacts of the excess sulfer on the latex? e.g. durability, etc.
Thanks,
Tim
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neutrino
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Give us some more information about this 'soup'. Is it polar or nonpolar? Is the sulfur in a true solution, a fine suspension, or is it a coarser
powder that is just mixed in?
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Mr. Wizard
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The latex doesn't vulcanize when it dries, it only precipitates or comes out of solution as the ammonia is lost from the water solution. Vulcanization
takes heat, and sulfur. BTW this latex solution is available in the US in stores that carry carpet supplies and even in many lumber yards. It is
sold to treat the edge of cut carpets to keep them from unravelling.
I would ask the same question as neutrino. How is the sulfur carried in the solution? Is it as ammonium sulfide, elemental sulfur, or what? On a
small scale the sulfur could be removed by adding a correct amount of colloidal copper metal. This will form a very black stable sulfide.
You could also use the latex by diluting the stuff with non sulfur bearing latex solution, to give the correct mix. How much quantity are we talking
about here... 10 grams, 10 kilograms, 10,000 kilograms?
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tfcallahan1
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The "soup" is probably very much like what is commerically available for treating edges of carpets. Not sure about the answer to polar v. non-polar.
We have analyzed some of the "bad" dried latex mixture and it has a concetration of Sulfer ICP of .48%.
The "good" latex has a concetrnation of about .18% when in liquid form - still waiting for the test results of the concentration of the "good" latex
in dried form.
Our problem is that the dried "bad" latex which is backing some textiles, is emitting a "rotten egg" smell (presumably H2S) after it has been wrapped.
Our hypothesis is that moisture from the fibers is reacting with the excess S to make the H2S.
So - questions are:
1. Could the hypothesis be correct?
2. Is there anyway to neutralize the S in the already dried latex?
We get the mixture in 275 Gallon drums.
Thanks again for the help.
Tim
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Mr. Wizard
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If it smells like H2S it probably is ;-)
I can't think of any way to remove S from coagulated latex. Do you heat the latex onto the back of the fabric? Maybe a little more heat would bond
up the free sulfur? What process makes the H2S? Is the material damp and undergoing bacterial decomposition? Is the rubber acidic after you apply
it? Any free acid may lead to H2S being liberated. It is such a weak acid, anything will displace it. You might try adding a little calcium carbonate
or lime to the rubber and see if it stops the problem. Are we talking about removing the smell from an existing lot of carpet, or some to be
manufactured in the future with this faulty latex? Does the smell continue after the carpet is in use or is it just a temporary thing as it's
unrolled?
I can't think of any way to remove the Sulfur in the rubber, but you might look for something that would oxidize the H2S to a less stinky SO2. We can
smell very small amounts of H2S , but I don't think we could detect the same concentration of SO2. Maybe a 'judicious' i.e., unknown amount, of ozone
from a room deodorizer would remove the stink, by oxidizing the H2S to SO2. Unfortunately Ozone also really likes to degrade latex rubber. You might
also try hydrogen peroxide or the "Oxyclean" detergent, (Sodium Carbonate : H2O2 ?- The one with the irritating salesman).
Maybe there is some metallic oxide or hydroxide that could be painted on the rubber backing to react with the H2S to form a harmless sulfide? Maybe
someone knows of common quickly forming sulfide, besides Lead, Mercury, Copper and other toxic metals. Most sulfides will release H2S when wet or
acidic though :-(
Sorry about the 'shotgun' answers, I'm just throwing out ideas.
[Edited on 11-4-2006 by Mr. Wizard]
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tfcallahan1
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Thanks Mr. Wizard.
No worries on the "shotgun" responses - any help is welcome!
The latex is not heated on the back of the fabric - it just dries (with the aid of some airflow.)
Not sure of what process makes the H2S - there is some residual mositure in the fabric. Tests have shown that there is no bacteria however.
We are trying to remove the smell from already manufactured goods and are not trying to correct any bad, unused latex.
The smell seems to be temporary in that it dissipates after the goods are unsealed. But, there is concern that it might re-appear in say a closed
environment or if additional moisture is applied, etc.
Thanks for the possible suggestions on how to remedy the situation - we might be able to test some of those.
I'll post any new information I get.
Thanks again.
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chemoleo
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Well if it is just about fuming out the goods, why don't you vent it for a few days/weeks in a well-circulated area? If it still stinks after that
time, try a slightly elevated temperature. Or, use a scavenger for H2S in your venting room, even a large pan iwth dilute NaOH will do. Or purge the
venting chamber with ammonia gas. Both act as H2S scavengers.
If moisture is an issue, that is easily tested, just spray H2O on it, and measure if more H2S is emitted than before. It looks like you have
some analytical tools at hand, so you can most certainly try that.
Another workaround would be to add a scavenger to the packages, i.e. similar to silica packs in electronic goods etc which keep the moisture out. One
could modify this and use i.e. a base of some sort.
Finally, I don't think that elemental sulphur is a fault for generating H2S. Even a pot of pure sulphur only very faintly smells of H2S. I should
rather think the smell is generated by organic mercaptides that decompose, or something along those lines, but not elemental sulphur that is present
in the latex.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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tfcallahan1
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Thanks for the ideas on the scavengers chemoleo - that's very helpful.
The issue with the goods is that many have been wrapped and shipped and are warehoused (many, many locales) so we are looking for the easiest solution
to address these as well as the potential long term affect on durability, etc.
They are custom goods so are not easily replaced or replicated.
We're still struggling with the source of the H2S so we will investigate the organic component.
We are a bunch of (non-chemical) engineers trying to do chemistry  or maybe more
like 
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tfcallahan1
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Further information that may help:
1. The textiles that the latex is backing are dyed yarns (wool, etc.) that are dyed with an acid based dye and finished with an acid rinse (can get
the details if needed.)
2. We tested the only the liquid latex for bacteria and there was none. But, there is the possibility that some bacteria may be in the fibers but
based on "bad products" it seems this is unlikely (the latex lot is the common factor, not any yarn lots.)
3. We now suspect that there is a chemical reaction with the acidic yarns and the excess sulfer - what about this theory?
4. Could the excess sulfur be left over from the vulcanization if there was too much sulfur to begin with?
Thanks again,
Tim
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