Phenoxyehtanol severely changed shampoo viscosity

Hi all,

I've been formulating a shampoo, the surfactant blend is Sodium C14-16 Olefin sulfonate and cocamidopropyl betaine, viscosity is around 3000 adjusted by NaCl. It's a very simple formulation, the rest is a 0.35% fragrance and 0.01% of dye, and water.

Initially I was using 0.5% Methylchloroisothiazolinone and Methylisothiazolinone as the preservatives, but the shampoo failed the preservative challenge, so we decided to move to phenoxyethanol. However, with the exact shampoo formulation, the viscosity dropped to ~500, and no matter how we adjust the salt, the viscosity just won't come up. We also tried benzyl alcohol as the preservative, same viscosity drop. 

Later, I tried to use an other surfactant blend with SLES, same thing with the viscosity drop with phenoxyethanol and benzyl alcohol. I also tried to add a thickener, a methyl cellulose, but it doesn't help much unless I add a lot of it (over 2%, budget won't allow).

I've been searching around but I couldn't find any relevant content. My guess is the benzene ring in these two preservatives somehow disturbed the surfactant aggregates. But I don't know if it's true or how to fix this problem.

I'm wondering if anyone has seen similar phenomenon or have any suggestions. Much appreciated!

Comments

  • BelassiBelassi Member, PCF student
    Almost anything you add affects the viscosity. I should also advise, your original choice of preservative is horrible, don't risk being sued by clients when their skin erupts.
    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.
  • Dear jenny,
    1. you're not mentioning HOW MUCH phenoxyethanol you are using.
    i know it's common to use between 0.5%-1.1%.  are you using more?

    2.how much SLES you are using?  my experince shows that if you use too little, the formulation is very weak and sensitive to problems such as you mentioned.
  • JennycatJennycat Member
    edited January 2020
    Hi asafvarlix,

    Thank you so much for your reply! I was using 1% of phenoxyethanol, or 1% of benzyl alcohol.

    I was using up to 20% of a blend that contains 40% of SLES and 15% CAPB. I'll try to boost it up a little more but the budget won't allow me to add much more.

    I am wondering if adding sequence would play a role? Most of the time I add the preservatives in the end, especially when I use hot water to blend methyl cellulose in the formulation.

    Dear jenny,
    1. you're not mentioning HOW MUCH phenoxyethanol you are using.
    i know it's common to use between 0.5%-1.1%.  are you using more?

    2.how much SLES you are using?  my experince shows that if you use too little, the formulation is very weak and sensitive to problems such as you mentioned.

  • JennycatJennycat Member
    edited January 2020
    Thank you! The thiazolinons were truly a poor choice, and I'm glad that we are making the change to another preservative system that works better and cause less irritation.

    However the viscosity drop really bothered me to move forward. Considering phenoxyehtanol such a common preservative these days, I am just curious if anyone has seen it before or have seen similar phenomenon or have a solution for it.

    Belassi said:
    Almost anything you add affects the viscosity. I should also advise, your original choice of preservative is horrible, don't risk being sued by clients when their skin erupts.

  • ozgirlozgirl Member, PCF student
    I have definitely seen Phenoxyethanol drop the viscosity like that in surfactant formulations. We had to reformulate our products when we changed from MCI/MI preservatives.

    You may need to increase your surfactant concentration. We achieve a viscosity of around 4000 with a ALS/CAPB/Cocamide MEA blend and a phenoxyethanol based preservative so it is possible.

    Just remember that adding too much salt can also cause a decrease in viscosity.


  • This is super helpful information!!! Thank you so much!

    Did you have to add a thickener in addition to a higher surfactant concentration?

    ozgirl said:
    I have definitely seen Phenoxyethanol drop the viscosity like that in surfactant formulations. We had to reformulate our products when we changed from MCI/MI preservatives.

    You may need to increase your surfactant concentration. We achieve a viscosity of around 4000 with a ALS/CAPB/Cocamide MEA blend and a phenoxyethanol based preservative so it is possible.

    Just remember that adding too much salt can also cause a decrease in viscosity.



  • ozgirlozgirl Member, PCF student
    No we didn't add any dedicated thickeners but it does include Lamesoft PO65 (Coco glucoside and Glyceryl Oleate) which does have a small thickening effect.
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