Emulsion stability

Hi everyone.
I need your help on this stability issue: I made an emulsion that passed centrifuge. Also it passed 7 cycles of freeze/thaw (24 hours freeze then 24 hours RT, repeated 7 times). However , it started to show signs of separation in the incubator at 45C . Any clue as to what  might be the reason ? Which test would you rely on in that case? TIA

Comments

  • PharmaPharma Member, Pharmacist
    I don't like incubators too much regarding emulsion stability. They're okay regarding chemical stability or if you produce for very hot climatate. However, without knowing your formulations and certain features of it, it's impossible to say whether or not the 45°C have any meaning.
  • ShamsShams Member
    Thanks @Pharma
    I use stearic acid 5%
    Emulgade 1000 1%
    Cetearyl alcohol 1%
    Variety of oils 18%
    Ultrez 10 0.1%
    Hyaluronic acid 0.5%
    The rest is water , water-based actives and extracts
  • chemicalmattchemicalmatt Member, Professional Chemist
    @Shams To address your immediate question: 45C is too high for ACC testing, 38 - 43C is more relevant.(That 'ol Arrhenius equation bedevils again!) Also, MANY formulations are unstable at 40C+ for extended periods; it doesn't necessarily reflect RT instability in the long term though, as @Pharma expressed. Your entropic stability test (centrifuge) tells you your formula is holding up well.  On another matter: what alkali did you employ to saponify stearic acid/neutralize Ultrez? That has much to do with your product's integrity.
  • ShamsShams Member
    @chemicalmatt I used NaOHto neutralise stearic to pH around 7. Then homogenised. Then at the end I adjusted the final pH to 6.5 . Does this sound good or bad?

    If you will put the samples under 40C as you said, how long incubation can predict a 3 year shelf life
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