Thickening the hand wash with betaine - viscosity issue.

Hello everyone,

I am trying to thicken a hand wash which contains ALS 30% with betaine. I get the viscosity in spec (7,000 - 9,000 cPs), but the batch thins out significantly when I adjust pH with Sodium Citrate to be 5.0-5.5... it basically crashes... previously the pH range was 4.5 - 5.0 but they added preservatives such as Benzyl Alcohol at 0.5% and Phenoxyethanol at 0.9% apart from potassium sorbate which was in the formula previously. It must be pH related issue as I went very slowly with betaine and did not overshoot.. what to do? Should I set pH to be 4.5-5.0 regardless preservatives efficacy? I needed a lot of sodium citrate to bring it up to be 5.0-5.5 and maybe that is why the batch crashed? 

Comments

  • Celeste7878Celeste7878 Member
    edited April 15
    Ingredients are: water, citric acid, potassium sorbate, phenoxyethanol, cocamide DEA, ammonium lauryl sulphate, cocamidopropyl betaine, sodium citrate, jojoba oil, olive oil, benzyl alcohol, glycerine BP grade, tea tree oil, fragrance. 
  • As soon as you Google benzyl alcohol, one of the first functions which appears alongside preservative, fragrance and solvent is viscosity-thinning agent - this may be the problem. Are you able to try the formulation without benzyl alcohol and have its preservative efficacy tested? You may not need it. 

    Also, I believe phenoxyethanol works well over a wide pH range so you should be fine with a target pH of 4.5 - 5.0. Potassium sorbate should be effective under pH 5.5, but more so the lower the pH as more of the ingredient will convert to its preserving counterpart - sorbic acid.
  • Celeste7878Celeste7878 Member
    edited April 15
    @klangridge thank you very much for your advice. I will make the batch without the benzyl alcohol and see what I get. Sure, I can microtest the batch too. 
  • PerryPerry Administrator, Professional Chemist
    The other question is have you done a salt curve analysis?  
    You may be able to use sodium chloride to adjust the viscosity without otherwise changing your formula.
  • ozgirlozgirl Member, PCF student
    This definitely sounds like a salt curve issue. It appears you have added too much sodium citrate. The salt curve for ALS is narrower than that for SLS/SLES and it is easy to add too much salt and reduce viscosity.

    I noticed that you are adding citric acid. Why not just reduce this to get the desired pH.

    Why are you using sodium citrate to adjust pH? It is not great for pH adjustment.
  • BelassiBelassi Member, PCF student
    ozgirl has the best answer. Sodium citrate is an electrolyte, you overshot the salt curve. they added preservatives such as Benzyl Alcohol at 0.5% and Phenoxyethanol at 0.9% overkill. We use sodium benzoate at 0.4% and pH 5 and have never had a problem. Don't use potassium sorbate, the shampoo will turn yellow.
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • Celeste7878Celeste7878 Member
    edited April 17
    @Perry did the salt curve analysis. I needed 2.4% of betaine to get the viscosity in spec. (total was listed as 6% on the formula - I know this is a huge amount). I got the viscosity and then when I added sodium citrate the batch thinned out. 

    removing benzyl alcohol did not change anything. Apparently, this is not the issue with that.. 

    @ozgirl why is it not great to use Sodium Citrate for pH adjustments? From the manufacturing point of view, it’s easy to use for compounders. 
    You are right, it’s pointless to have citric acid in this formula if we aim for pH 5.0-5.5...I moved Sodium Citrate to the water phase where is added at the start and removed citric acid... we will see what I can get... 

    @Belassi I discussed the use of Sodium Benzoate with my supervisor. Was thinking to replace those preservatives with Potassium Sorbate & Sodium Benzoate combination, but apparently Sodium Benzoate is an irritant and the customer does not want this in the formula... we don’t mind the yellow colour as the fragrance blend used gives the batch a yellow colour anyway. 
  • Belassi said:
    ozgirl has the best answer. Sodium citrate is an electrolyte, you overshot the salt curve. they added preservatives such as Benzyl Alcohol at 0.5% and Phenoxyethanol at 0.9% overkill. We use sodium benzoate at 0.4% and pH 5 and have never had a problem. Don't use potassium sorbate, the shampoo will turn yellow.
    what did you mean by the preservative overkill?
  • BelassiBelassi Member, PCF student
    what did you mean by the preservative overkill?
    -- Too much.
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
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