Adding CA to rebatched soap to lower PH

[Warriorgal]

Hello. I have been making soaps for over a year now and I have been put off shampoo bars until now because of the high PH content. I know some people add ACV as a rinse but I wanted to delve into the possibility of reducing PH in a post saponified shampoo bar maybe with adding CA in a re-batch. ? ie a bit more neutral bar to 5- 6 ph? Would anyone have any thoughts on this please?

 

[Maple_Street_Bath]

Hair soap has been discussed many times on the forum - you'll likely find that it's triggering for some, and most members don't recommend soap for hair due to the pH being damaging.
You cannot lower the pH to 5-6 range and still have it be soap (it's a chemistry thing: soap is soap at 9-12 pH).
If you want a lower pH, you'll have to make proper shampoo bars using surfactants.

 

[AliOop]

Hello. I have been making soaps for over a year now and I have been put off shampoo bars until now because of the high PH content. I know some people add ACV as a rinse but I wanted to delve into the possibility of reducing PH in a post saponified shampoo bar maybe with adding CA in a re-batch. ? ie a bit more neutral bar to 5- 6 ph? Would anyone have any thoughts on this please?

I agree with @Maple_Street_Bath's answer, above. No matter what you read on the Internet, the pH of real soap cannot be lowered under 9. You can certainly try rebatching with citric acid to see what happens, but here is the spoiler alert: your soap will split into an oily mess of free fatty acids. In other words, it will no longer be soap.

Also, don't be fooled by the cheap and inaccurate pH test strips, which often read several points lower than the actual pH. Proper pH testing involves dissolving the substance to be tested (soap in this case) in distilled water to create a 10% solution, and using a properly calibrated pH tester to test it.

There are plenty of older threads here where people share their "hair soap" recipes, which work well for them and their users. There are also plenty of threads here that detail the terrible damage many other people suffered to their hair as a result of using hair soap. In the end, it's a very personal decision; you have to decide whether the risks are worth it to you.

 

[DeeAnna]

Yes, you can lower the pH of lye-based soap by adding an acid, whether citric, acetic (vinegar), or other acid. The problem that most people don't understand is you can't just lower the pH -- other chemistry processes are going to happen in response to the lowered pH.

When the pH of a given lye-based soap is lowered below it's "natural" pH, the soap will begin to break down into fatty acids.

By the time you add enough acid to drop the pH by 0.5 to 1.5 unit, the soap will have decomposed into mostly fatty acids. That means it is basically non-functional as soap.

Given that soap will have a "natural" pH from 9.5 to 11.5 depending on the fatty acids in the soap, that means the mixture will still be quite alkaline even when it's mostly fatty acids. If you decide to lower the pH into the acid region (pH below 7), the "soap" will be entirely fatty acids.

 

[Warriorgal]

Thank you everyone for your feedback here. I am guessing trying this would be in vain due to the decomposition. I did read notes from somewhere suggesting that ph only exists in an aqueous solution. The suggestion was also to add CA powder to un-saponified oils and then add this to the batter before pouring, the theory behind the suggestion was the soap would have CA granules that could neutralise the ph once added to water when in use. Im thinking that maybe not a safe method? I am thinking the limitations of the composition would make things quite soggy. I might try to experiment the limitations of decomposition vs quantities of CA for the purposes of curiosity and also compare the ph. Unless this has been tried?

 

[AliOop]

Many of us do use CA in our soap, but we increase the NaOH to compensate for the fact that citric acid reacts with NaOH to form sodium citrate, a chelator (not a pH reducer). That means whether the CA is added to your lye solution, your oils, or your mixed batter, all you do is decrease the amount of NaOH available to saponify the oils, and thus increase the final superfat of the soap.

I believe, but am not positive, that Kevin Dunn has completed experiments showing how soap decomposes as you try to lower the pH.

 

[paradisi]

It has been tried again and again and..

The question you might ask yourself is why you want to try to force soap to do something it can't, when there are better alternatives.

Syndets replaced soap for haircare many decades ago because of their superior results and ability to include moisturizing and conditioning agents. Soap (true soap) can't do that.

 

[DeeAnna]

...The suggestion was also to add CA powder to un-saponified oils and then add this to the batter before pouring, the theory behind the suggestion was the soap would have CA granules that could neutralise the ph once added to water when in use...

Frankly, there's no real science behind this advice. Not sure where these ideas are coming from -- facebook maybe? -- but I'd be pretty leery of taking this person's advice at all seriously.

Citric acid is very soluble in water for one thing, so even if it stays in solid form while mixed with fat, once you add that fat to the lye solution, the citric acid is going to dissolve and then will quickly react with lye to form sodium citrate.

 

[Warriorgal]

Frankly, there's no real science behind this advice. Not sure where these ideas are coming from -- facebook maybe? -- but I'd be pretty leery of taking this person's advice at all seriously.

Citric acid is very soluble in water for one thing, so even if it stays in solid form while mixed with fat, once you add that fat to the lye solution, the citric acid is going to dissolve and then will quickly react with lye to form sodium citrate.

Thank you DeeAnna, I am guessing if there was an easy way it would have been done by now. Undissolved citric acid probably isnt a good idea and I am guessing there is a limit when CA is added when it comes to solubility. I am very grateful for everyone thoughts on this. The source of the information I found was from a website called `chemists corner` but it was part of a general discussion.

 

[Elise]

Yes, you can lower the pH of lye-based soap by adding an acid, whether citric, acetic (vinegar), or other acid. The problem that most people don't understand is you can't just lower the pH -- other chemistry processes are going to happen in response to the lowered pH.

When the pH of a given lye-based soap is lowered below it's "natural" pH, the soap will begin to break down into fatty acids.

By the time you add enough acid to drop the pH by 0.5 to 1.5 unit, the soap will have decomposed into mostly fatty acids. That means it is basically non-functional as soap.

Given that soap will have a "natural" pH from 9.5 to 11.5 depending on the fatty acids in the soap, that means the mixture will still be quite alkaline even when it's mostly fatty acids. If you decide to lower the pH into the acid region (pH below 7), the "soap" will be entirely fatty acids.

Do you mean that some fatty acids make a more alkaline soap than others? Is there a chart or a list somewhere you could point me to? I'd live to read more about that.

 

[paradisi]

Thank you DeeAnna, I am guessing if there was an easy way it would have been done by now. Undissolved citric acid probably isnt a good idea and I am guessing there is a limit when CA is added when it comes to solubility. I am very grateful for everyone thoughts on this. The source of the information I found was from a website called `chemists corner` but it was part of a general discussion.

The mods there are professional cosmetic chemists and pharmacists etc. However.. advice from them on lowering pH *for syndets or other non soap products* isn't intended for or applicable to soap.

 

[DeeAnna]

Do you mean that some fatty acids make a more alkaline soap than others? Is there a chart or a list somewhere you could point me to? I'd live to read more about that.

Yes, some fatty acids make soap more alkaline than others. There's a good discussion of this in Kevin Dunn's book Scientific Soapmaking. He may also have it on his Caveman Chemistry website, but I haven't looked to confirm that. I also cover this topic in my articles about soap pH and alkalinity: https://classicbells.com/soap/pH.asp and https://classicbells.com/soap/alkalinity.asp

"... I am guessing there is a limit when CA is added when it comes to solubility..."

I consult Wikipedia rather than guess; it's a quick and legit resource to get basic chemical properties.

In water at room temp (20C/68F), Wikipedia tells me you can dissolve about 62 grams of citric acid in 100 grams of water. Yes, that's a limit, but that's a really high limit -- citric acid would be a "highly soluble" chemical in water to most chemistry folks. https://en.wikipedia.org/wiki/Citric_acid

The amounts of citric acid normally used as a chelator in soap are far, far lower than this.

...advice from them on lowering pH *for syndets or other non soap products* isn't intended for or applicable to soap.

I strongly second this!

 

[Elise]

Yes, some fatty acids make soap more alkaline than others. There's a good discussion of this in Kevin Dunn's book Scientific Soapmaking. He may also have it on his Caveman Chemistry website, but I haven't looked to confirm that. I also cover this topic in my articles about soap pH and alkalinity: https://classicbells.com/soap/pH.asp and https://classicbells.com/soap/alkalinity.asp

"... I am guessing there is a limit when CA is added when it comes to solubility..."

I consult Wikipedia rather than guess; it's a quick and legit resource to get basic chemical properties.

In water at room temp (20C/68F), Wikipedia tells me you can dissolve about 62 grams of citric acid in 100 grams of water. Yes, that's a limit, but that's a really high limit -- citric acid would be a "highly soluble" chemical in water to most chemistry folks. https://en.wikipedia.org/wiki/Citric_acid

The amounts of citric acid normally used as a chelator in soap are far, far lower than this.



I strongly second this!

Thank you. I just read your two articles and they aswer all the questions I had or didn't know I had on PH