Zinc rash cream
Hi I am formulating a zinc cream for rash application and it is a great consistency, however it will only emulsify at lower temperatures ~50C and above that is split into water and oil. In stability testing it has split when heated after a couple of weeks (not immediately) but has not split in freeze thaw or centrifuge testing.
I have never experienced something not emulsifying until it reaches a low temp so feel a bit out of my depth here. The HLB is balanced with an overall HLB of around 8.
An outline of the formula is as follows:
Water <30% Zinc Oxide 15% Castor Oil <15% Apricot Kernel Oil <10% Glycerin ~5% Glyceryl Stearate Citrate SE 4% Mango Butter <5% Vegan Lanolin <5% Calendula infused oil (olive oil), borage seed oil, isoamyl laurate, aloe vera oil, MCT oil <10% Sorbitan Olivate 3% Pomegranate Extract <5% Rice Bran wax <5% Silica <5% Plantaserv A 1% Glyceryl Caprylate <1% I am wondering a few things:
- Do i add some xanthan to the water phase to thicken it to help stop splitting?
- Do i try adding a liquid solubiliser like Polysorbate 60 or Soya Lecithin?
- What could be causing it to only emulsify at low temp - is it due to stopping mixing as it cools or water and oil phase at different temps?
- Should i ignore the splitting in stability testing in an oven (~40C) as it wont be exposed to that heat for weeks on end (note it did not split until week 3 in an oven, all other samples at room and fridge are perfect after over a month) and i have other samples at room temp that have been fine for over 6 months
- The product needs to be filled at below 50C so i cannot wait until it is completely cool to fill which is another issue.
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