Home Cosmetic Science Talk Formulating Carboxylic acid pH.

  • Carboxylic acid pH.

    Posted by belassi on April 10, 2020 at 2:32 am

    I ran out of liquid soap today for the house, So I decided to make more. Most of the lab materials are packed, but I found some AKYPO RLM-45CA, and decided to use that, along with some Stepan APB and Plantapon LGC-Sorb. (It came out fine, but that’s not the issue.)
    RLM-45CA is supplied as a pure carboxylic acid. I measured the pH and it was around 2.5. The NaOH and KOH being packed, I decided to neutralise it with some TEA that I’ve been using to make sanitiser.
    As supplied, RLM is a thin clear liquid with a high (70% I think) ASM. It has a pleasant fruity odour. I began titrating TEA while stirring and taking frequent pH readings. First it turns milky, then clarifies. At pH 4, clear again, the viscosity went way up. Like syrup. I continued titrating with TEA and at pH 4.5 or so, the viscosity suddenly dropped again and remained fairly low until pH 5.5 which was my target pH, so I stopped there.
    I should perhaps add, that RLM is not a salt-thickening surfactant; it tends to be cationic or anionic depending on pH. With acid pH it’s anionic. 
    I’m unsure as to why the viscosity was so pH dependent over such a narrow range. It’s annoying because it makes the effect useless for thickening; I don’t want a soap with a pH of 4.

    belassi replied 3 years, 11 months ago 1 Member · 1 Reply
  • 1 Reply
  • belassi

    Member
    April 10, 2020 at 2:46 am

    In case anyone is interested, the “whatever’s in the first packing case” formulation turned out to be:
    Water Q/S 100%
    AKYPO RLM-45CA 10%
    TEA Q/S for pH = 5.5
    Stepan APB 10%
    CAPB 9%
    Plantapon LGC Sorb 2%
    Glycerine 1%
    Silsense DW-16 soluble silicone ester 1%
    Fragrance 0.2% (Poison)
    Methyl parabens 0.3%

    Notes. The RLM-45CA is highly acidic and so can be mixed with the Stepan APB without causing problems. Under no circumstances mix TEA with APB because ammonia will be produced. Keep pH less than or equal to 6.

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