# pH reduction experiment, Free Fatty Acids

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#### galaxyMLP

Supporting Member

Not sure if this belongs in its own thread, in this section, or in the other thread. I hope it's ok to post this here. If not, I'm happy to delete this and post it elsewhere.

I spent about 20 minutes doing math before I started making the soap. This is math heavy but I bold the parts that are important. Feel free to only read the parts in bold.

I went ahead and did my own FFA pH reduction experiment to see if I could lower the pH of a soap with FFA or if it was the same as SFing with straight oil (triglycerides).

In order to get free fatty acids in a soap, I needed to add an acid after cooking the soap via HP. This is because the soap will already have reacted with the lye to give FFA salts and glycerin. When I add an acid, it will give back the FFAs themselves, increasing the SF of the soap.

I didn't realize the original post was in the liquid soap forum so I made this as a bar soap. I used a 100% coconut oil recipe with a 20% SF.

According to soapee, 20% SF.

200 g coconut oil
29.3 g Sodium Hydroxide
Some amount of water

I knew that I would need to add acid into the soap with FFAs so I needed to do the same with the triglyceride soap in a way that won't generate FFAs.

I wanted to add the equivalent NaOH to give 20% left over FFAs. That meant I needed to add 20%/100% * 29.3g NaOH = 5.9 g more NaOH to the batch and 5.9/.64 (grams of lye per 1 gram of citric acid neutralized) = 9.2 g Citric acid to neutralize that extra lye. That gives me a net change of zero SF for the soap. Meaning it stays at 20%.

I decided to use a 2:1 Water: NaOH/CA ratio

That meant for both batches I needed to use:
200 g coconut oil
35.2 g NaOH
9.2 g CA
89 g water

The difference in the two batches would be the ingredient order.

Triglyceride (Oil) soap

1. 160 g of coconut oil melted in slow cooker
2. Made my lye solution by adding 9.2 g CA to 89 g water. Then I added the 35.2 g NaOH very slowly to clarity.

I mixed the lye and oil together to trace and cooked it. After it reached the paste stage (finished cooking) I added 40 g coconut oil. It was very brittle so I added 10 more g of water. Important part: Left with 20% unreacted oil

FFA Soap

1. 200 g coconut oil melted in slow cooker
2. Made lye solution by adding 35.2 g NaOH to 70.6 g water

I mixed the lye and oil together to trace and cooked it. After it reached the paste stage, I added 9.2 g CA dissolved in 18.4 g water. After mixing, I added another 10 g water to match the triglyceride batch. Important part: Left with 20% FFA

Observations

Triglyceride Soap
- Difficult to trace (could be due to high salt content)
- Separated in the pot after ~20 minutes (also could be high salt content)
-Took a while to come together
-When it did, it solidified almost instantly
-Didnt change much when I added 40 g of coconut oil
-Finally loosened some with additional 10 g water
- Difficult to get into the mold
-Very crumbly and hardened super fast.

-Very opaque soap

pH in 1% solution of distilled water by test strips: 9-10; ~9.5

FFA Soap
-Came to trace in expected time frame
-Did not separate
- More fluid at paste stage
-Smelled funky when I added the CA solution
- Became VERY fluid!!
- Easy to pour and did not solidify quickly

- Took longer to solidify
- More transluscent soap
- Had more bubbles and held bubbles for longer than the triglyceride soap

pH in 1% solution with distilled water by test strips: 9-10; ~9.5

Thoughts on what this all means:

1. So, it didn't seem to effect pH. However, it did make other, important differences. I also don't have proper pH testing materials. I wonder what a pH meter would read. Please note during the time I was writig this TOMH posted that the referenced experiments were done at 40% SF. I will be re-doing this experiment at this level to see whether pH is affected. I do not have HCl to try with. I will stick to citric acid. There may be some equilibrium issues with this.

2. Maybe adding yogurt or other acidic foods after cooking in HP works so well because it creates FFAs and that's what actually makes the soap more fluid! This is definitely something to look into! It could also be why fluid HP seems so variable. I wonder if some FFAs contribute to fluidity more than others.

3. Why does the FFA soap give off substantially more bubbles that also last longer? Most likely glycerin! The FFA soap has a higher glycerin amount because the glycerin has been formed from saponifiying all of the oil. The soap that has the oil added at the end has all glycerin bound up within the triglycerides. After adding the acid to the FFA soap, the glycerin is still free and present.

4. Why the smell in the FFA soap? Some FFAs have a scent whereas most triglycerides do not. The scent is not particularly pleasant but its not terrible either. It could probably be covered up by a fragrance.

5. Things I will be looking for in the coming weeks:

I will be using the soaps at 1 week, 4 weeks and 8 weeks to determine differences.

Let me know if you find any mistakes or have other questions to add.

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This is extremely fascinating and I appreciate you posting it!

4. Why the smell in the FFA soap? Some FFAs have a scent whereas most triglycerides do not. The scent is not particularly pleasant but its not terrible either. It could probably be covered up by a fragrance.

This tidbit caught my eye. I had a similar experience making liquid soap with fatty acids instead of oils and using a lye discount. The result looked like any other liquid soap, but the smell was different and stronger.

Some fatty acids have more of an odor than others, and I think the culprit in my experiment was oleic acid. Judging by ingredient lists, it seems the commercial producers may be adding stearic acid to make a milder product instead of acidifying. Stearic is stable and doesn't add odor.

So glad it's not too hard to follow!

TOMH, it was instant too. The moment I added the acid, it started to smell. In this case I think it was the lauric acid. According to Wikipedia it smells somewhat like bay laurel but I have never smelled that so I can't say for sure!

So glad it's not too hard to follow!

TOMH, it was instant too. The moment I added the acid, it started to smell. In this case I think it was the lauric acid. According to Wikipedia it smells somewhat like bay laurel but I have never smelled that so I can't say for sure!

I have a big bag of lauric acid and it smells like nothing botanical. I could hand you containers of stearic, lauric and myristic acids and you could not tell the difference by eye. In my recollection they smell very similar too -- and not much -- but I haven't specifically tried to distinguish them that way.

Getting into the spirit of it, I thought I might try making the standard 100% CO with 20% lye discount along with a version superfatted with stearic acid. Maybe I should make one with lauric acid also. I have more of it than I can use!

Please let us know how that goes! I'm particularly interested in the lauric acid SF one.

I was on Reddit not too long ago and there was someone posting questions on the soap making subreddit about using soy wax in shaving soap. I answered a few questions and another soaper came back with a comment/response to me.

He/she was saying that stearin mono and di glycerides feel terrible and sticky on the skin whereas stearic acid itself feels smooth and emollient. It's been having me think a lot about the chemical nature of soap. Like the fact that too much castor oil in soap makes a sticky soap (maybe it's from left over mono-diglycerides?)

He/she also mentioned that when we SF soap in CP, we are left with the mono and diglycerides at around double of the expected "SF" amount because of chemical equilibrium. So a soap that we intend to SF at 5% triglyceride content, actually contains around 10% mixed mono-diglyceride content.

Not much happens on that sub but that was a pretty neat revelation for me. I wanted to try making two shaving soaps, one with the CP method and one with FFAs. I didn't really have a way to do it before but now I think I'll try with this acid neutralization method in some way.

You might find this interesting.

OCR version:

PDF image:

Also there is a liquid soap patent just like what I did with the incomplete saponification of a fatty acid composition:

That last one includes the statement, "Fully neutralized potassium soap compositions, when measured as a 1% solution based on total fatty acids, have a pH of about 10.3.The compositions herein have a pH of from about 8.7 to 9.7 when measured on a 1% total fatty acids solution basis."

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Thank you for that! My favorite part was that it's says that shorter chained, unsaturated fatty acids are more likely to be acidified than the monger chained and saturated fatty acids. That's a very important insight and it may be what I was smelling in the coconut was the small amount of capric/caprylic FFA found in coconut.

Now I really want to try making a tallow/coconut shaving soap using acidification. I have stearic acid but I don't know if it's palm/tallow stearin or actual stearic acid as I got it for free and I don't have labels for it. I'll stick to citric acid since I won't be salting out and the citric acid helps both with preservation and with chelating.

You lost me at "math heavy." Actually, I read it and I think I understand what's going on. Neat looking soaps, by the way. The triglyceride soap looks like my standard HP soaps. So, if I could get my HP soap to look like the FFAs, I'm all for it. However, I'm exhausted and am marking this thread so I can read it when I've got coffee in my system and drops in my eyes. I'm probably going to be dreaming about the letters "CA" and "NaOH" running after "FFA" with a knife or something. Those poor FFAs are gonna be screaming, "Help me...help me!!!" Just like on "The Fly." (Good night, all.)

He/she also mentioned that when we SF soap in CP, we are left with the mono and diglycerides at around double of the expected "SF" amount because of chemical equilibrium. So a soap that we intend to SF at 5% triglyceride content, actually contains around 10% mixed mono-diglyceride content.

I really wonder how much mono and diglycerides are left in soap particularly when using a regular superfat. They are considered emulsifiers and you would expect them to react with the lye faster than triglycerides.

I have stearic and lauric acids. I might do some testing.

Alright, I know I haven't done a great job updating this thread. In fact I've done a terrible job. Thank you to everyone who PM'ed me to remind me to update! I wasn't trying to shoo you away or ignore you. I wanted to have done some more experimenting with this but life kept getting in the way! I was never able to do the 40% experiment. These are the results of my experiment/observations.

I don't have a pH meter, only pH paper. So my readings are as best as I can do with that.

A 1% solution in distilled water of each of the 2 soaps both gave a pH of 10 according to my paper.

However, if I tested the soap directly (no dilution, just smearing the paper onto the wet soap) I got a pH reading of 10 on the regular soap and a pH reading of 8 on the one with FFA. The only thing I can think of that would cause this is that more of the soap is coming off of the FFA soap and causing a lower amount of OH- generation (more soap per water amount means less of the soap is dissolving) giving an artificially lower pH. I wonder if it has any effect on the skin.

The tests of the soap on my skin resulted in pretty much identical feeling. I couldn't tell a difference in the irritation or softeness of my skin between either soap.

The FFA soap was significantly softer and more translucent than the non-FFA soap. It also produced a lot more bubbles.

The FFA soap has a really terrible smell and it seems to be smelling more prominent as it ages. Plus, it sticks to the skin. Not good!!

I really really want to try it at 40% and also with true stearic acid as the FFA to see if I could get a higher bubble, lower pH soap that didn't smell.

For those of you that want to test the 2 soaps yourselves, pm me and I can send you some for you to try it yourself and see if you see a difference.

Edit: shop to shoo (darn autocorrect!)

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