Why salicylic acid is reducing viscosity of cleanser and how to avoid it?

I made 3 different facewash products with different Surfactants and ratios, all with high enough viscosity but adding salicylic acid 1% and 2% reduced the viscosity a lot and made it thin and undesirable viscosity in all three facewash.

Composition of one face wash in active percentage

SLES 6%
CAPB 1%
Lauryl glucoside 1%
Glyceryl oleate 0.5% (one formula without it)
Xanthan gum 0.1%
Formalin 0.1%
pH 5.1 with citric acid

Salicylic acid 1%
Sodium hydroxide 10% 2.9%

I used these methods
1. Made the product, dissolved salicylic acid in sodium hydroxide and then addid to complete face wash. Viscosity decreased from thick to very runny and thin.

2. Dissolved salicylic with sodium hydroxide in water, added the rest of ingredients and made the product. viscosity didn't increase with up to adding 5% NACL.

What is the problem here and how to thicken salicylic acid 2% cleanser?




Comments

  • CamelCamel Member
    edited April 13
    I didn't experience a reduction in viscosity when adding salicylic acid at 2% to my face wash. I tried both of your methods, but used HPMC at 1 and 2% as the thickener (the 2% was actually a bit too thick but still good). They were just as viscous as the versions without the salicylic acid.

    As you know, I'm not an expert, so I'm interested in what others will have to say. 
  • Camel said:
    I didn't experience a reduction in viscosity when adding salicylic acid at 2% to my face wash. I tried both of your methods, but used HPMC at 1 and 2% as the thickener (the 2% was actually a bit too thick but still good). They were just as viscous as the versions without the salicylic acid.

    As you know, I'm not an expert, so I'm interested in what others will have to say. 
    Thanks. 
    That was helpful. 

    I forgot to mention i used 3% NACL to adjust viscosity.
    Maybe salicylic acid and NACL doesn't work together :#
  • @Abdullah What's the final pH of your product? It might be due to a pH drift. Betaine usually interacts with SLES to form higher micellar structures. The interaction between the two is better when CAPB behaves as a cationic (pH close or below 5). When you are at a higher pH, the interaction is different, and thicker products can show a reduction in viscosity. When you mix SA with NaOH, you have a basic salt, and that one increases your solution pH. Try reducing the pH of the product you already made to see if viscosity increases.
  • ketchito said:
    @Abdullah What's the final pH of your product? It might be due to a pH drift. Betaine usually interacts with SLES to form higher micellar structures. The interaction between the two is better when CAPB behaves as a cationic (pH close or below 5). When you are at a higher pH, the interaction is different, and thicker products can show a reduction in viscosity. When you mix SA with NaOH, you have a basic salt, and that one increases your solution pH. Try reducing the pH of the product you already made to see if viscosity increases.
    pH is always 5.1. 
    0.29% sodium hydroxide increases the pH of 1% salicylic acid to ~5. So there is no change in pH.
  • Did you check the final pH of the solution after adding the salicylic acid? My guess is that the salicylic acid in the prepared pre-solution is not completely dissolved, and it continues to dissolve after adding surfactants, which causes a significant lowering of the pH value. According to information from salicylic acid supplier I got, if you want to convert salicylic acid to salicylate to make it water-soluble, you need to raise the pH to at least 10. If that doesn't help, try thickening with Peg-120 methyl glucose dioleate or its equivalent.
  • AbdullahAbdullah Member
    edited April 16
    Did you check the final pH of the solution after adding the salicylic acid? My guess is that the salicylic acid in the prepared pre-solution is not completely dissolved, and it continues to dissolve after adding surfactants, which causes a significant lowering of the pH value. According to information from salicylic acid supplier I got, if you want to convert salicylic acid to salicylate to make it water-soluble, you need to raise the pH to at least 10. If that doesn't help, try thickening with Peg-120 methyl glucose dioleate or its equivalent.
    As i am still making samples of 400g, yes salicylic acid is completely dissolved after adding surfactants and receiving high shear but pH is around 5. 

    I made shampoo sample with gum and it thickened well. It just didn't thicken with NACL.

    I am currently selling serum with 2% salicylic acid at pH 5. You dont need pH 10 for it to dissolve. Just a homogenizer.
  • Have you tried without Lauryl glucoside?
  • Have you tried without Lauryl glucoside?
    Yes  

    That formula was SLES+CAPB+SSL
  • we have salicylic acid 2% face wash. SLES+CAPB+CDEA. not having any problem of viscosity. we don't useformalin.
  • @amitvedakar what % surfactants and NACL do you have in formula?

    Do you have any other type of thickener too? 
  • I think 4% CDEA works as thickener in our formula. I think nacl requirement depends of brands of surfactants.   As my CAPB comes with SB. 
  • I think 4% CDEA works as thickener in our formula. I think nacl requirement depends of brands of surfactants.   As my CAPB comes with SB. 
    That is a lot of DEA.
    How much total surfactant do you have?

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