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Discussion Starter · #1 ·
Either the pre-mixed reciepes (Stan's, Eclipse) and the modelling Liquid latex have the unmistakable smell of ammonia. This is just a curiosity but...what is it used for?
Reduced evaporation? FAster vulcanization? Preservation? Does any Chemistry PhD or NCIS guy have any idea? Thanks, Fab
 

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Discussion Starter · #2 ·
Well, browsing through the net I have found the reply to my own question... In case anyone is interested:
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Rubber trees are usually tapped for latex by making a spiral cut through the bark of the tree on alternate days, although the frequency and method of tapping vary. The latex is collected in cups hung on the tree below the cuts. (...). Ammonia is usually added as a preservative. Ammonia disrupts the particles of rubber and produces a two-phase product consisting of 30 to 40% solids. This product is further concentrated to 60% solids, resulting in ammoniated latex concentrate, which contains 1.6% ammonia by weight. A low-ammonia latex concentrate (0.15 to 0.25% ammonia) is also available. The low-ammonia concentrate requires the addition of a secondary preservative to the latex to avoid coagulation and contamination. Secondary preservatives include sodium pentachlorophenate, tetramethylthiuram disulphide, sodium dimethyldithiocarbamate and zinc oxide.
 

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I work in a factory that makes different glues for home and industry use. these glues look
(and smell) alot like a tire sealant. we sometimes add ammonia to lower the pH,
if its too high and dosen't complie with the specs. the pH level, among with other qualities,
determines behavior and performance of the glue, according to usage.
 

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Discussion Starter · #4 ·
Right, in fact I also found out that the opposite effect (faster coagulation) can be obtained adding acids. You ever stop learning!
 

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Ausable said:
Well, browsing through the net I have found the reply to my own question... In case anyone is interested:
Quote
Rubber trees are usually tapped for latex by making a spiral cut through the bark of the tree on alternate days, although the frequency and method of tapping vary. The latex is collected in cups hung on the tree below the cuts. (...). Ammonia is usually added as a preservative. Ammonia disrupts the particles of rubber and produces a two-phase product consisting of 30 to 40% solids. This product is further concentrated to 60% solids, resulting in ammoniated latex concentrate, which contains 1.6% ammonia by weight. A low-ammonia latex concentrate (0.15 to 0.25% ammonia) is also available. The low-ammonia concentrate requires the addition of a secondary preservative to the latex to avoid coagulation and contamination. Secondary preservatives include sodium pentachlorophenate, tetramethylthiuram disulphide, sodium dimethyldithiocarbamate and zinc oxide.
Wow, freaky! I was watching that How is it made show the other night and they had this on the show as a topic. They showed them tapping the trees and everything.

Nothing important, just thought the coincidence was freaky, that's all.
 

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Ausable said:
Well, browsing through the net I have found the reply to my own question... In case anyone is interested:
Quote
Rubber trees are usually tapped for latex by making a spiral cut through the bark of the tree on alternate days, although the frequency and method of tapping vary. The latex is collected in cups hung on the tree below the cuts. (...). Ammonia is usually added as a preservative. Ammonia disrupts the particles of rubber and produces a two-phase product consisting of 30 to 40% solids. This product is further concentrated to 60% solids, resulting in ammoniated latex concentrate, which contains 1.6% ammonia by weight. A low-ammonia latex concentrate (0.15 to 0.25% ammonia) is also available. The low-ammonia concentrate requires the addition of a secondary preservative to the latex to avoid coagulation and contamination. Secondary preservatives include sodium pentachlorophenate, tetramethylthiuram disulphide, sodium dimethyldithiocarbamate and zinc oxide.
Yeah, I've looked it up in the past myself. It sounds like the ammonia just keeps the latex dispersed in the mixture (acting like an anti-coagulant). Why? Beats me, although it's probably related to the pH of the dispersion. I have a phd in chemistry, and I doubt too many chemists could tell you off the top of their heads why latex mixtures require the ammonia.
 

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Discussion Starter · #7 ·
Another interesting question would be how the coagulation is triggered when you punture the tire. I bet it's not just the evaporation of solvent (water), should be something related to pressure drop or a quick change of the dispersion's entropic state
 

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Ausable said:
Another interesting question would be how the coagulation is triggered when you punture the tire. I bet it's not just the evaporation of solvent (water), should be something related to pressure drop or a quick change of the dispersion's entropic state
Well, my guess would be that the latex coagulates when the pH drops. The ammonia holds the pH around 10 (or something like that, I'm not about to measure it), and as the solvent evaporates, the ammonia also evaporates, resulting in a drop in pH (to 7 or so), triggering coagulation.
 

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Discussion Starter · #9 ·
Fat Elvis, I think you are right. In fact ammonia has a boiling temperature of -33 degrees Celsius. It evaporates much faster than water. When air is flowing out of a puncture, the evaporation of ammonia is furtherly accelerated- So the PH drops, the latex coagulates and the puncture is instantly sealed. Why we dind't think of that in 1994??? fab
 

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Ausable said:
Fat Elvis, I think you are right. In fact ammonia has a boiling temperature of -33 degrees Celsius. It evaporates much faster than water.
Yup, liquid ammonia is cool stuff; back when I was in grad school I got to do some reactions with it. It dissolves alkali metals and form beautiful, deep blue solutions. Ah, good times. Not really.
 
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