Why add surfactants?

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Romiriam

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Hello expert soap-makers!
I am new to soap making and I love researching the chemistry related facts about it (science teacher here).
I came across a home-made soap bar that listed SLS and other surfactants amongst the ingredients, but I know that soap is itself a surfactant.
I also know that sodium citrate acts as sequestrant when it's added to home-made laundry soap to prevent fats left in the bar from sticking to clothes, so my questions are:

Why add surfactants to hand-soap bars at all?🤔
Is there a reason it's added to liquid soap or shampoos?
What's the difference between Sodium Lauryl Sulfate, sodium citrate and normal soap (besides the fact that SLS is usually made from palm oil 😠)?

Thank you in advance for your wisdom!

Romiriam
 
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lsg

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I do not add surfactants to my bar soap. Surfactants can be added to CP soap to boost lather, but I prefer to use Castor oil, coconut oil and or palm kernel oil for lather. Here is a thread about adding sodium lauryl sulfoactetate to soap. Many add Tetrasodium EDTA or Sodium Gluconate to soap if they have hard water problems.


 
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Romiriam

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I so nor add surfactants to my bard soap. Surfactants can be added to CP soap to boost lather, but I prefer to use Castor oil, coconut oil and or palm kernel oil for lather. Here is a thread about adding sodium lauryl sulfoactetate to soap. Many add Tetrasodium EDTA or Sodium Gluconate to soap if they have hard water problems.


Thank you, Isg, for the info! I checked the forums, since I live in Denmark and we have hard water, I might consider adding Tetrasodium EDTA in my soap too... Maybe it'll feel better on my skin! We shall see!
 

DeeAnna

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Sodium citrate is not a surfactant; it is a chelator. It sequesters multivalent metal ions when added to soap to prevent rancidity and soap scum. You really can't compare chelators to either soap or synthetic detergents (syndets).

Syndets are added to a mostly soap cleanser so the cleanser lathers better, forms less soap scum, and makes the cleanser milder to the skin than just soap alone. Your choice of syndet and the amount used will greatly affect these qualties, however, so don't assume all syndets will provide these benefits.

Soap is added to a mostly syndet cleanser to make the product easier to form into bars, reduce softening and mushing during use, and to reduce the cost. These are mainly concerns you'll find in industrial manufacturing, not so much the handcrafted world.

As far as I know, not many handcrafted soap makers make combination cleansers. A few, but not many. The commercial soap making industry is an entirely different situation -- combination cleansing products, both bars and liquids, are fairly common.

As far as combining syndets and soap to function as a shampoo -- Some people's hair can tolerate being cleaned with soap, but the high alkalinity of soap (and also of some syndets) damages many people's hair. I would not make a soap and syndet combination for washing hair. I recommend using only low pH syndets for shampoo.
 

Romiriam

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Sodium citrate is not a surfactant; it is a chelator. It sequesters multivalent metal ions when added to soap to prevent rancidity and soap scum. You really can't compare chelators to either soap or synthetic detergents (syndets).

Syndets are added to a mostly soap cleanser so the cleanser lathers better, forms less soap scum, and makes the cleanser milder to the skin than just soap alone. Your choice of syndet and the amount used will greatly affect these qualties, however, so don't assume all syndets will provide these benefits.

Soap is added to a mostly syndet cleanser to make the product easier to form into bars, reduce softening and mushing during use, and to reduce the cost. These are mainly concerns you'll find in industrial manufacturing, not so much the handcrafted world.

As far as I know, not many handcrafted soap makers make combination cleansers. A few, but not many. The commercial soap making industry is an entirely different situation -- combination cleansing products, both bars and liquids, are fairly common.

As far as combining syndets and soap to function as a shampoo -- Some people's hair can tolerate being cleaned with soap, but the high alkalinity of soap (and also of some syndets) damages many people's hair. I would not make a soap and syndet combination for washing hair. I recommend using only low pH syndets for shampoo.
Thank you so much for the thorough explanation!
I researched further in your soapy stuff articles, and this is what I concluded:
1. I got confused between surfactants and sequestrants, hihihi
2. Sequestrants, like trisodium citrate, have better effects in hand soap if you are looking for more than their anti-rancidity properties.
3. Surfactants are not that awesome, unless you really need to enhance foaming. I'll stay away from SLS for now.
4. Better using washing soda to reduce water hardness with homemade laundry soap.

I don't use normal soap as shampoo, that would burn my hair!
I just read about people adding SLS to liquid shampoos to thicken it, but I was wondering what other effects it has on the skin and what it does at a chemical level.

Thank you!
 

violets2217

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I watched a YouTube video about a soaper adding SLS noodles to cold processed soap. I guess there was a controversial conversation bout it on a forum somewhere! Lol! She was like “ it can be done,SEE! I’m just not sure why you would want to!” It did make it sudsy, but it didn’t really change the ph of the soap any, so it definitely didn’t make it any safer for hair.
 

DeeAnna

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Yes, you can use some syndets to thicken liquid soap (soap made with KOH rather than NaOH). If you're using the syndet just for thickening, you do not need to add much -- maybe 1-2% or a bit more. In that case, the character of the cleanser would be mostly the soap, and very little from the syndet.

If you wanted the syndet to really change the properties of the cleanser besides just thickening, I'd say you would need to use more syndet -- 10-30% perhaps?

To be honest, I think there are other syndets that are more desirable than sodium lauryl sulfate if you are a hand crafter wanting to experiment with combination cleansers. SLS has an alkaline pH and is an extremely efficient cleanser. If you want to pick a syndet for adding to soap to increase mildness, SLS is not a good candidate for these reasons.
 
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