Phase inversion of w/o emulsion?

We are having some instability issues with a diaper rash cream (w/o emulsion, 13% zinc oxide). It is a new formula for us. The lab batches I’ve made and the pilot batch we did for stability turned out perfect and after 3 months 40C no separation or changes in the product, still looks great. However, we are having issues with the scaled up production batch. The first set of samples pulled to be tested looks great, however when they moved the product to the hopper to fill tubes, it fell apart. The first picture is how it initially looked, the second picture is what was poured from the tubes, third picture is product from the hopper.  They pump they used to move it to the hopper was just air. Could too much shear be causing the emulsion to break or phase inversion possibly? Not familiar with w/o emulsion but want to try to prevent this from happening on our next batch if anyone has some input they could share. Thank you!


  • EVchemEVchem Member
    You could try taking a sample and pushing it through syringe to see if you can replicate separation on small scale from shear. 

    Is the liquid pool in the third picture water or oil?
  • mhart123mhart123 Member
    That is water 
  • PharmaPharma Member, Pharmacist
    My guess would also be on too much shear. It's a common issue with w/o.
  • chemicalmattchemicalmatt Member, Professional Chemist
    Could be a shear issue (too much or too little) or heating on transfer (was Tygon hose used?) or something else. Without more formula details I could only speculate. I will say that virtually all inverse-phase emulsions are entropically unstable and will separate eventually, but not THAT fast.
  • mhart123mhart123 Member
    @chemicalmatt they had made the batch on a Thursday but waited until Monday to fill it.  I was told they had only reheated to ~35-40C and it was transferred using a diaphragm pump. Chances are it could have heated way past 40C.  But I took some leftover product from the stability batch, heated to 60C with pretty high shear and then cooled and it did not show any separation, although that was only about 500 g. 


    Phase A : Deionized Water, Magnesium Sulfate, Glycerin, Aloe Vera, Euxyl PE 9010, Potassium Hydroxide 

    Phase B: Mineral Oil, Microcrystalline Wax, Sorbitan Sesquioleate, White Beeswax, White Petrolatum, Vitamin E Acetate, Dimethicone

    Phase C: Zinc Oxide 

    Would it be better to add zinc into the oil phase then add water, instead of adding after the two phases are combined? 

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