a bit of an 'out there' question

[Sandra@SS]

Forgive me if I don't explain this idea well, I have mulled over a few parts, but am not sure of the feasibility of the whole.
I am hoping the brains trust will show me where I am right, and where I am wrong in my thinking, and the all important...why I am wrong or right.

salt water soap
I am trying to formulate a soap which will have some cleansing abilities in sea water, but also in brackish bore, or river water.

so...here is my idea

a) Sodium hydroxide soap is less soluble in saline waters due to the production of ...what?

b) In high metal salt (ie calcium, magnesium ions) containing water, soap molecules become bound to the metals and form insoluble salts (soap scum).

ie post saponification exchange of ions can occur.

c) Potassium hydroxide soap does lather well/better in high sodium water, as the potassium salts are more soluble in high sodium water.

d) Potassium hydroxide is difficult to source for me, not impossible (I hope) but difficult.

e) Dual Lye soaps lather better/best for all water options.

f) I use sodium chloride at a rate of 1% of soap weight, to enable earlier hardening of olive based soaps. I use a 25% solution w/w to add to the batter after lye.

g) adding this extra sodium may repress lathering/cleansing ability of my soap in saline waters due to the increased concentration of sodium ions in the soap

h) potassium chloride is readily available for me.

so....

i)... if I added potassium chloride solution to my oils would this increase in potassium ion concentration, possibly drive some of the fatty acids to attach to potassium ions rather than sodium ions, thus increase (somewhat) the soaps ability to lather/cleans in saline waters.

j) The free sodium ions stay in solution and harden the bar as before...but the sodium donor has changed.

k) what will any free potassium ions do



has anyone even tried this? Google is completely unhelpful here.

I look forward to hearing peoples thoughts

thanks for your time

Sandra

 

[penelopejane]

I can’t help with most of your questions except to say I think CO is good for soap in brackish water.

But KOH is available at cleaning supply stores. Just look up some local ones and ring around. I buy 1kg at a time.

Or ring chemical supply shops - you have to buy 25kg through them but they will tell you who they supply locally and you can go from there.

Where in Australia are you?

 

[shunt2011]

Salt Bars work great in Sea and most other types of water. High Coconut oil is what makes it work along with the salt. I make them with NAOH as I think KOH would be too soluble and too soft and probably not able to add salt except to the water.

 

[dixiedragon]

I can't answer your sciency questions, but for salt water and brackish water, I suggest a 100% coconut oil bar with a 20% superfat. I actually like a 95% coconut, 5% castor (still 20% superfat).

 

[DeeAnna]

It is true that soap in general is less soluble in salty water, but there's salty water and there's salty water. Sea water is only about 3% salt, if memory serves me right, and brackish water has even less salt. 3% is not anywhere close to a saturated solution, which is roughly a 25% sodium chloride solution, again speaking from memory.

You have to get the salt concentration close to saturation to get a coconut oil soap to "salt out" (in other words, become insoluble in the salt brine.) Since sea water isn't anywhere close to a saturated solution, I think you may be overthinking this issue.

IMO, Shari (shunt) and Dixie are correct -- if you want to make a bar soap for use in sea or brackish water, then just make a 100% coconut soap with NaOH and be done with it. Coconut oil soap made with NaOH is highly soluble in this type of water. I don't know anything about bore water, unless you mean what I'd call "well water." If so, coconut oil soap with NaOH should still work well.

***

As far as making NaOH soap and then adding a source of potassium ions in the hope that the potassium will replace some of the sodium on the soap --

It's not very likely this will happen. The ability of one kind of ion to "bump off" another ion is based on the radius of the ions. Of the ions being discussed here (sodium, potassium, calcium, magnesium), the smaller ions will be more "aggressive" than the larger ions in their ability to bump other ions off the soap molecule.

The radius of a sodium ion is smaller than that of a potassium ion. This means sodium ions are able to easily bump potassium ions off soap molecules, but the reverse is not nearly as likely to happen.

I'm speaking about probabilities here, not absolutes, so I can't say it absolutely won't happen, but it's not likely. Also if you add only a small amount of potassium salt to a sodium soap, the chance of making a measurable change is even smaller.

Calcium and magnesium ions have ionic radii that are smaller yet, compared to sodium. So they are able to bump sodium and potassium ions off the soap molecules and take their place, thus forming relatively insoluble soap scum. Soap scum made from coconut oil soap is somewhat more soluble than soap scum made from other types of soap. Any kind of soap scum won't clean as well as soap, but coconut oil scum will still rinse off somewhat better.

 

[Sandra@SS]

Where in Australia are you?

South Australia

 

[penelopejane]

Ace chemicals, Adelaide sells potassium hydroxide for 500g for $19 + GST
5kg for $45 + GST. 25kg is probably not much more. They like to kill the little guy.

Adelaide Cleaning Supplies sells it for 5kg (minimum) $39.60 (including GST)

CTSS doesn't sell it.

You have to ring around all the smaller cleaning supply companies and ask as they never list it on their websites. I get 1kg for $14 (including GST) near Sydney so I am sure you can get it cheaper than those above.

 

[Sandra@SS]

thanks Penelope

 

[Sandra@SS]

Thanks DeeAnna, I appreciate your expert opinion. The first trial bars are curing atm

 

[KimT2au]

You have to ring around all the smaller cleaning supply companies and ask as they never list it on their websites. I get 1kg for $14 (including GST) near Sydney so I am sure you can get it cheaper than those above.

I am in Perth and also get mine from a local bulk cleaning shop. I pay the same as @penelopejane .