Testing Vinegar/Sodium Acetate In Soap - Phase II

[topofmurrayhill]

I have been testing the hypothesis that sodium acetate has an effect on soap comparable to the hardening effect of sodium lactate.

One of the implications would be that you can get the benefits of SL by simply replacing all or part of your lye water with vinegar. The acetic acid in vinegar promptly reacts with sodium hydroxide to produce sodium acetate.

There was a gentleman named Leonard M. Liddle who wrote a short piece for a chemical engineering journal on this subject. Almost 100 years ago, he filed a patent for the use of sodium lactate and sodium acetate to harden soap. I think some of you will find it very interesting. You can see it here:

https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US1377843.pdf

My original thread on this subject, which includes initial testing and any numbers and calculations you might be interested in, is located here:

http://www.soapmakingforum.com/showthread.php?t=57991

TeresaT recently did a relevant experiment by substituting apple cider vinegar for water. This thread describes the enhanced hardness and easy demolding of the resulting soap:

http://www.soapmakingforum.com/showthread.php?t=59092
There will be some additional results posted at the end of the week when I get back from a business trip. Here however is something I did on the way out of town.

I tested chunks of the 2 test soaps from the original experiment using a soil penetrometer. A penetrometer tests the hardness of something by poking into it. Higher numbers signify greater hardness, meaning more force required to poke into the soap to a depth of 1/4 inch.

I tested each soap sample at one end and on one face and averaged two readings from each location. The end was harder than the face for both soaps.

Plain soap, face: 2.8 kg/cm2
Plain soap, end: 3.3 kg/cm2

Sodium acetate, face: 4.3 kg/cm2
Sodium acetate, end: > 4.5 kg/cm2 (exceeded the maximum reading)

 

[Susie]

I love this forum! All of these experiments make my inner mad scientist very happy without me having to do them. Using real scientific method and everything!

 

[The Efficacious Gentleman]

I agree - as SL is really not easy to get hold of over here, I am very interested in this.

 

[galaxyMLP]

Very cool! Thank you for sharing.

 

[Seawolfe]

This is pretty exciting! Thanks for compiling your results so far.

 

[ngian]

Thank you for informing us with all the data you have gained.

Wouldn't salt give the same hardening property?

I guess I'm lucky to have available in my town sodium lactate (100ml at 1,5€) and lactic acid 85% (1 litre at 5,5€).

 

[songwind]

Do you have any plans/ability to compare the hardness of sodium acetate and sodium lactate soaps?

 

[TeresaT]

I just want to make one tiny correction to TOMH's post. I did not have ACV at home so I used white vinegar in my experiment. However, I did get similar results to his. When I did not add the extra lye to my batch to compensate for the acidity in the vinegar, the bar was rock hard when I unmolded it. It literally fell out of the mold. I think this vinegar lye solution will be very beneficial for high OO/soft oil soaps. (I'm thinking Castile-types and Bastille.) My next experiment (since I did this one with lard) is to use 100% OO instead. Someone mentioned salt being a factor in the hardening process. I could do one bar with salt as my hardener instead of the vinegar. I'll post those experiments with the other thread that I had started. I need to stop at the store on my way home, so I'll pick up some ACV and compare it to white vinegar, as well. As an aside, I wish I had searched the forum better regarding "vinegar" because TOMH's original thread would have been the perfect answer to my questions. But then again, I wouldn't have been able to learn quite as well and I would have missed DeeAnna's awesome explanation of how vinegar and lye react together. (It takes a lot of vinegar to neutralize a little bit of lye. 28:1 ratio. You definitely don't want to toss a little vinegar on your lye spill to neutralize it. It's just going to heat up and burn you worse!)

ETA: Wow! I'm glad I didn't read that thread first. I never would have experimented with the vinegar. I just weighed out my vinegar and weighed out my lye and dumped the lye in vinegar and stirred. I knew it heated up more than a regular water solution did, but I didn't do anything special for it. I replaced 100% of the water, too. Dangerous soaping going on in my house!

 

[topofmurrayhill]

Do you have any plans/ability to compare the hardness of sodium acetate and sodium lactate soaps?

Yes, I already have some testers made with nothing, sodium acetate and sodium lactate. I'm away but will be returning home on Thursday night.

Thank you for informing us with all the data you have gained.

Wouldn't salt give the same hardening property?

I guess I'm lucky to have available in my town sodium lactate (100ml at 1,5€) and lactic acid 85% (1 litre at 5,5€).

Salt has a hardening property, but I'm not experienced with it. I don't know if the effect is the same or somewhat different from SL. I always assumed it was different.

The effects of sodium lactate that I've gathered so far is that it increases the hardness and/or brittleness of bar soap, helps solubilize potassium soap, and adds fluidity to neat soap in the hot process. I think it might be that the lactate and acetate are equivalent in how they work and produce the same effects to one degree or another. It's not for certain, but at first glance they seem pretty similar.

BTW, the old-time soapy term for what SL does is that it shortens soap. I think this is borrowed from baking, where shortening is used for products like pie crusts that are supposed to be hard and crispy rather than flexible.

Your prices are pretty good. In the States we can get 1 gallon or 7 lb SL for $18.99 from Soaper's Choice, which comes out to 50 cents for 100 ml plus a variable shipping cost. The same amount of lactic acid 88% from Essential Wholesale is $26.75. Other suppliers might charge much more, but those two sources happen to be very good.

 

[RobertBarnett]

What acidity levels are your vinegars? This could/would have an Impact on the experiments. Like other thank you all for your hard (no pun intended) work.

Robert

 

[topofmurrayhill]

What acidity levels are your vinegars? This could/would have an Impact on the experiments. Like other thank you all for your hard (no pun intended) work.

Robert

5 percent. All the relevant calculations for using vinegar are here:

http://www.soapmakingforum.com/showthread.php?t=57991

If this technique turns out to be useful, I'll post simpler instructions for people who aren't into the math and aren't looking to be super exacting.

 

[FlybyStardancer]

Yes, I already have some testers made with nothing, sodium acetate and sodium lactate. I'm away but will be returning home on Thursday night.

How are you controlling for the amount of additive? Are you aiming for the same amount of Sodium acetate and Sodium lactate by weight? Same molar amount (or an equivalent measure)?

 

[TeresaT]

5 percent. All the relevant calculations for using vinegar are here:

http://www.soapmakingforum.com/showthread.php?t=57991

If this technique turns out to be useful, I'll post simpler instructions for people who aren't into the math and aren't looking to be super exacting.

That would be me. You know, "Sux-at-math." You should have see my eyes glaze over when I got to the math part of your thread. Yeah, not so much. It was like shoving toothpicks under my nails.

 

[RobertBarnett]

I would also like know if you have to replace all of the water with vinegar or can you get a similar hardening effect with a couple of tablespoons, or if a cup, part of a cup, etc. will work.

Robert

 

[topofmurrayhill]

How are you controlling for the amount of additive? Are you aiming for the same amount of Sodium acetate and Sodium lactate by weight? Same molar amount (or an equivalent measure)?

I wasn't sure whether to do it by weight or molar amount, so I chose weight. If the two additives truly work the same way, there's a good chance molar amount might be the actual equivalence. Or so I would think, but other opinions would be interesting.

The question, for people not familiar with the terminology, is how you could best compare the effects of the two additives relative to each other. Do you use equal weights, for example 1 g sodium lactate and 1 g sodium acetate, or do you use essentially the same number of molecules of each? That would be 1 g lactate and 0.73 g acetate, because a sodium acetate molecule has less mass than a sodium lactate molecule.

 

[FlybyStardancer]

Weight is certainly easier to calculate out.

I wonder how it would do by molar, though... Since three soap hardener all contain sodium (Sodium lactate, Sodium acetate, Sodium chloride), I would guess that the extra sodium has something to do with it, and would want to keep the sodium levels introduced the same (and I would include salt as a fourth tester).

 

[TeresaT]

"Molar" weight. Is that new terminology, because when I was in school I'm pretty sure it was "molecular" weight. Of course, I am 50, forgetful and haven't had a science class since 1982. I believe I was dodging dinosaurs on my way to school.

 

[topofmurrayhill]

"Molar" weight. Is that new terminology, because when I was in school I'm pretty sure it was "molecular" weight. Of course, I am 50, forgetful and haven't had a science class since 1982. I believe I was dodging dinosaurs on my way to school.

It's been molar forever. The general subject is called stoichiometry. You are right though that it's directly connected to molecules and molecular mass.

Excerpt from Wikipedia:

The mole is widely used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions. For example, the chemical equation 2 H2 + O2 → 2 H2O implies that 2 mol of dihydrogen (H2) and 1 mol of dioxygen (O2) react to form 2 mol of water (H2O). The mole may also be used to express the number of atoms, ions, or other elementary entities in a given sample of any substance. The concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution.

 

[TeresaT]

Oh. That must be college stuff. I never made it that far. I only got as far as lighting alcohol on fire on the lab table to watch everyone freak out in my freshman year of HS. Got nicknamed "Pyro" for that stunt and was never allowed to sit in the back of a science lab again. Somehow the teacher didn't believe my "accident" explanation. Must have been the mischievous twinkle in my eyes and the devious little smile on my face.

 

[topofmurrayhill]

Oh. That must be college stuff. I never made it that far. I only got as far as lighting alcohol on fire on the lab table to watch everyone freak out in my freshman year of HS. Got nicknamed "Pyro" for that stunt and was never allowed to sit in the back of a science lab again. Somehow the teacher didn't believe my "accident" explanation. Must have been the mischievous twinkle in my eyes and the devious little smile on my face.

Pyros are cool.