Citric acid as a chelator

[TeresaT]

I don't understand 95% of what you're talking about, but I love the geek talk. I love the fact that you are so excited about the science of your hobby and not just the hobby itself. The science never gets boring, does it? AND you are so willing to share your knowledge and dumb it down for the likes of me. If we were at a coffee shop, I could just picture you excitedly going at it and my head going back and forth like a tennis tournament. It reminds me of a friend and me with "fiber talk" at gatherings.

 

[The Efficacious Gentleman]

See now, swirling and colours and all that jazz I can take or leave - but this sort of thing gets my eyebrows raised and the pipe removed from my mouth in interest.

 

[DeeAnna]

Well, I'm glad Galaxy and I are entertaining y'all.

I feel rather clueless at the moment, and that's not especially comfortable place for me, but feeling unsure is all part of the process of solving problems and learning stuff. I really hope something will come of this group discussion and experimentation that will benefit all of us.

 

[galaxyMLP]

You all are making me want to get home as soon as possible to try this but I know I cant get to it till around 8:30 pm tonight (6 1/2 hours away!)

 

[Susie]

I am not much into the swirling and such, either. But I am following every word here. I am off today and doing house/yard work, but SMF is up on the computer so I can catch up every time I come inside.

 

[galaxyMLP]

My experiments are sitting now.

I don't see a difference or separation in the palm/olive recipe ones so far. I've got a control w/ just DI water, one with just SC added, and one with BS and SC. I added the SC at 2% or the soap paste. For the one with added BS, I added BS to the water w/ SC to reach a pH of 10 on my test strips. These 3 are still diluting.

I already had diluted Castile so I thought I'd give it a go. I made a boo boo and added the SC at 2% of the diluted soap! The one with SC in it got SUPER thick, gloppy and gel like. The one with BS and SC stayed liquid but was completely cloudy. This was a Castile diluted for a foam pump @ 1:6. What was very interesting is that the gel like Castile soap lathers amazingly and leaves hands free of that hard water scum feeling. Might actually be a good finding in this case.

I'll report back about the other soaps that are diluting tomorrow.

 

[DeeAnna]

Thanks, Galaxy -- you're amazing!

 

[Saponista]

I use a solution of sodium citrate to thicken my liquid soap. I use it instead of salt as I figured it would add some chelation. Unfortunately as it was only for me I didn't really measure it, I diluted some (a few tbsp) in distilled water then added it but by bit until the soap was at the consistency I wanted. It didn't cause any cloudiness or separation.

 

[DeeAnna]

"... I made a boo boo and added the SC at 2% of the diluted soap! The one with SC in it got SUPER thick, gloppy and gel like...."

That's pretty much what I'm seeing, Galaxy. The SC definitely thickens the diluted soap. Eventually the gel will turn opaque white with enough SC. If you put this thickened soap into an excess of water (as if you were going to wash dishes), the water-soap solution will show separation as well, if my experience is any indication.

My thought is the white color change is the soap is breaking down in response to the added SC. That would be the downside to using SC to thicken liquid soap vs. table salt (NaCl). Table salt won't cause this breakdown.

Much different outcome compared with adding an excess of EDTA.

 

[ngian]

"... I made a boo boo and added the SC at 2% of the diluted soap! The one with SC in it got SUPER thick, gloppy and gel like...."

That's pretty much what I'm seeing, Galaxy. The SC definitely thickens the diluted soap. Eventually the gel will turn opaque white with enough SC. If you put this thickened soap into an excess of water (as if you were going to wash dishes), the water-soap solution will show separation as well, if my experience is any indication.

My thought is the white color change is the soap is breaking down in response to the added SC. That would be the downside to using SC to thicken liquid soap vs. table salt (NaCl). Table salt won't cause this breakdown.

Well it must be something in the way that the SC is made with BS that makes it cloudy. Maybe impurities in BS or some CA leftovers...

Anyway I had the same experience with Saponista. I did try to dilute my one year old soap paste (was kept in the refrigerator all the time) with store bought SC 4%, EDTA 0,5% and EDTA 1% without any cloudiness problem. Unfortunately I didn't make a dilution without any chelating agents as a control sample just for comparison.

The paste was:
(65% Olive, 25% Coconut, 10% Castor, 3% Lye Discount)
KOH 3:1 (ratio of water/glycerin to KOH)
and the water for dilution was 80% of the paste's weight.

[ame]https://www.youtube.com/watch?v=QXpMyM4iMS4[/ame]

It seems that Sodium Citrate apart from being a chelating agent, it can also build up viscosity. I tried all three of them and they produced really nice bubbles, but the one with SC has also that perfect honey-like viscosity!

I need to make a new liquid soap so as to test Sodium Chloride vs Sodium Citrate and their affect to viscosity and bubbles...

 

[DeeAnna]

"...it must be something in the way that the SC is made with BS that makes it cloudy..."

You may indeed be right, Nikos. I thought of that too, but didn't have commercial sodium citrate to compare with the homemade. I'm glad you shared your results!

 

[galaxyMLP]

I think both of you are right about the baking soda+ SC

I think my explanation wasn't clear. My results were as follows (I'm working from memory after reading my old post):

Homemade SC only (from baking soda and CA)- clear, thickened soap, no noticeable lather reduction.

Homemade SC plus additional baking soda added- Cloudy and separated. The mix was also very low viscosity.

So even with my homemade SC, as long as additional baking soda is not added, it should act as you saw with commercial SC and work as a thickener.

I also just tried it last week with some commercial SC and it worked quite well.

 

[DeeAnna]

So it sounds like the culprit is excess baking soda causing the soap to dissociate. Makes sense.

 

[KristaY]

So I'm trying to boil all this amazing chemisty down to the nuts and bolts. Anyone who can correct any errors and answer any questions, please do so.

1. By using sodium citrate (as opposed to citric acid) no extra KOH or NaOH is needed. The pH of trisodium citrate is 7.5-9.0 so there's no worry of "breaking" the paste by accidentally lowering the pH too much. Plus, a small percentage is used so final pH shouldn't be a lot lower anyway?

2. Sodium citrate was used by ngian at 4% paste weight, galaxy at 2% paste weight so it was added during the dilution phase. Is the difference just in personal preference based on water quality in the home, viscosity desired in the final soap, a combo of the 2 or other factors?

3. Is it safe to assume the water needed for dilution was measured out, SC dissolved in that, then the whole added to the paste? What if I start at 2% SC but decide I want to add more. Will it need to be dissolved into water before adding to the diluted soap? I couldn't find a dilution ratio when I did a quick search so don't know how much water it takes to fully dissolve SC.

4. I know sodium citrate and citric acid can be purchased through many soap supply sites but did a google search for fun and the majority of the results are in the food industry. So is food grade SC and what is used in soap making the same purity?

5. Another topic included in this thread: Susie stated she's used up to 40% NaOH + 60% KOH to make LS paste. Why is that? What does the combo of hydroxides bring to the LS party?

I apologize if some of this was covered and I missed it but I'm just trying to get a clearer picture in my head. Thanks to any and all for help!

 

[Susie]

5. Another topic included in this thread: Susie stated she's used up to 40% NaOH + 60% KOH to make LS paste. Why is that? What does the combo of hydroxides bring to the LS party?

I apologize if some of this was covered and I missed it but I'm just trying to get a clearer picture in my head. Thanks to any and all for help!

People mistakenly think that you can get thicker liquid soap by adding NaOH to the KOH when you make the paste. You can't.

 

[ngian]

2. Sodium citrate was used by ngian at 4% paste weight, ...

I used SC 4% of the final liquid soap weight (paste & water). In the specific experiment, the weight of the paste was 89gr so I added ~71gr water (80% of paste weight) and that made a total of 160gr. 4% SC is 6,4gr so that was the amount that I diluted in 71gr of water prior inserting it into the paste.

Generally I account the % of each additive as follows:

In liquid soaps (KOH): % of the total weight of paste and water used for dilution, as water will remain whole in the product when it will be used.
In bar soaps (NaOH): % of the weight of oils only, as part of the water in a recipe will evaporate by the time of a full cure.

That's my logic...

 

[KristaY]

People mistakenly think that you can get thicker liquid soap by adding NaOH to the KOH when you make the paste. You can't.

Good to know! I had a feeling that might be the thinking behind it. Other than not getting a thicker LS, did you notice a difference in the soap itself? Different lather, different viscosity, different ratio of water needed for dilution, etc?

I used SC 4% of the final liquid soap weight (paste & water). In the specific experiment, the weight of the paste was 89gr so I added ~71gr water (80% of paste weight) and that made a total of 160gr. 4% SC is 6,4gr so that was the amount that I diluted in 71gr of water prior inserting it into the paste.

Generally I account the % of each additive as follows:

In liquid soaps (KOH): % of the total weight of paste and water used for dilution, as water will remain whole in the product when it will be used.
In bar soaps (NaOH): % of the weight of oils only, as part of the water in a recipe will evaporate by the time of a full cure.

That's my logic...

Thanks ngian! Now I understand the direction and method you used. Since I never know exactly how much water it's going to take to dilute the paste, I guess I'll have to make an educated guess. Here's another thought I just had: did you add any EO or FO to your diluted LS? If so, did it behave any differently than batches without SC? Also, I use PS80 mixed with EO/FO when scenting. Will the SC interfere with that in any way?

 

[ngian]

did you add any EO or FO to your diluted LS? If so, did it behave any differently than batches without SC?

I will try and add some EO in the honey-like SC liquid soap and see how it will behave. As far as I know from my very little experience on the matter, some EOs affect a little on the viscosity of LSs.


What I'm also thinking right now is that maybe in bar soaps (with NaOH) SC will act also as a hardening agent similar with salt, so salt (or any other sodium eg. sodium lactate) is not needed if we want a hard bar.

Although we are in a LS thread, now that I'm thinking about it in a wider perspective I guess the following are correct for a soap bar:

Sodium Chloride (salt): gives only a hard bar (and maybe cuts down some bubbles because of its physical hardness)
Sodium Lactate: gives a hard bar (and maybe adds a few bubbles)
Sodium Citrate: gives a hard bar and acts as a chelating agent
Sodium Acetate: gives only a hard bar (topofmurrayhill maybe can tell us if the soap with sodium acetate cuts down the bubbles, and it is because of the physical hardness of the bar that needs more abrasion to produce the same amount of lather).

In the world of LS I guess the above are true too, but instead of "hard bar" the more appropriate world would be "build up viscosity".

 

[topofmurrayhill]

Sodium Acetate: gives only a hard bar (topofmurrayhill maybe can tell us if the soap with sodium acetate cuts down the bubbles, and it is because of the physical hardness of the bar that needs more abrasion to produce the same amount of lather).

Both sodium lactate and sodium acetate appear to increase lather.

http://www.soapmakingforum.com/showpost.php?p=587205&postcount=31

 

[Susie]

Good to know! I had a feeling that might be the thinking behind it. Other than not getting a thicker LS, did you notice a difference in the soap itself? Different lather, different viscosity, different ratio of water needed for dilution, etc?

It diluted differently, less water, if I recall correctly. I stopped using dual lye just because it was more work for no appreciable benefit before I started keeping really detailed notes.