large lye solution hydroxide soap

[LazerBottle]

I heard a while ago service personnel (soldiers) are provided with lye soap ranging to =>70% lye solution. Obviously those personnel need to be clean in a hurry with the most potent soap there is.

Is this lye concentration to speed up the saponification process to increase soap yeild or to enhance its cleaning ability?

 

[earlene]

You cannot make a 70% lye solution with NaOH. It will not all dissolve. I don't know where you heard what you heard, but it cannot be right. 50% lye solution is all that is possible for the NaOH to dissolve in water. 1:1 lye to water is a 50% lye solution.

If you want to test that out yourself, just give it a try.

 

[LazerBottle]

They could have used non common fats/chemicals mixtures which could be proprietary to obtain high lye ratio.

Doesen't a high lye content mixture shorten saponification duration?

 

[earlene]

Lye concentration means the mix of lye to water. It does not relate to the mix of oils at all.

Here are some references about lye concentration:

https://www.modernsoapmaking.com/lye-solution-in-soapmaking/

https://classicbells.com/soap/waterInSoap.asp

 

[LazerBottle]

Lye content depends on fats employed.
Page 431

...The density of the lye necessary to saponify with a fat depends on the type of fatty acids it contains ; coconut oil, for instance, requires a stronger concentration of lye than tallow to accomplish saponification because of its high lauric acid content. Residues of lye which have not entered into a chemical compound with the fatty acids often remain in the cheaper grades of soap as fillers. In toilet soap such residues should be completely eliminated because they are very irritating to the skin. Sodium lyes are always used in producing hard soaps, while potash lyes are needed for soft soap; it is therefore the type of lye and not the consistency of the soap fat which ultimately determines the consistency of the soap, although the hardness of the fat adds by certain degree...​

Thereby demonstrating the army had a specific fat mixture to employ such a high lye ratio.

 

[earlene]

While that is true that the amount of lye needed for each specific oil may be somewhat different, that has no bearing on how lye solution is made. Lye solution is made by mixing lye and water (or another liquid that contains water). The lye solution is added to the oils to start the saponification process.


Again, lye concentration refers to the lye to water ratio; not the lye to oil ratio.

 

[steffamarie]

If you don't trust earlene, try it for yourself as she suggested. Try to mix your own 70% solution. It won't work. Even as hot as the water gets, it cannot accept much more than its own weight in the alkali. The maximum amount that 100g of water could accept, as told on a research forum, is 111g. This is around 52% concentration. See this link for science-y details.

Most soapers, myself included, use around a 33% lye concentration (that is, 2 parts water to 1 part lye) to make soap. It's possible to use up to a 50% solution and it can speed up the time it takes for the soap to harden. It will have less water to evaporate off and it can cause trace to be faster since there's less water to help the batter stay thin. This is obviously ideal for large-scale production where design doesn't matter. But 70% will not work no matter how hard you try. Not with water. If they truly used a 70% concentration they may have used an alternative solvent, but I'm not sure what that would do to the saponification process.

 

[IrishLass]

I think we might be getting hung up on semantics.

What we as soap-makers refer to as being a 'lye solution' is the mixture of lye and water.

What we refer to as being a 'lye concentration' is the ratio of how much lye to water, which we often speak of in terms of percent. For example, a 1:1 ratio is a 50% lye concentration. The higher the lye:water concentration, the quicker the soap will trace and set up/harden, but that has nothing to do with the lye to fat ratio. That's looked at as a separate thing.

The ratio of lye to fat is what we term as being a 'superfat'. Basically, a low superfat (more lye to oils) will make for a more cleansing (harsh) soap, and a high superfat (less lye to oils) will make for a less cleansing (more gentle feeling) soap.

In any given soap recipe, the lye amount is calculated according to the individual SAP# (saponification number) and amount of each oil/fat in the given recipe, i.e., how much lye is needed to turn any given oil/fat into soap. In a perfect world, if you set your superfat level at 0% when making your calculations, in theory you would have the exact amount of lye to 100% completely saponify all your oils with no oils or lye left over.

But the world is not perfect and SAP#'s are not set-in-stone. Since SAP #'s vary depending on where your oils/fats were sourced, it's very possible for one to end up with a lye heavy soap with a 0% superfat, or maybe a slightly superfatted soap at the other end of the spectrum. Because of this fact, online lye calculators base their SAP#'s for each oil/fat on the average SAP range for whichever individual oil/fat. And since lye-heavy soaps are very unpleasant on the skin, online lye calculators have also set up their superfat box with a built-in default 5% superfat level (which you can change if you desire), which insures against lye heavy soaps.



IrishLass