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Topic: How do I form a stable emulsion?

posed by  Last edited: 11 December 2013 At 8:39am
I read Dave Dickey's response on "How do you create an emulsion?" and I would like to ask some follow up questions. I am working with O/W emulsions for cosmetic products and don’t have access to a vacuum-planetary mixer that is the standard in the industry. Instead, I’ve been using an axial flow turbine and a tank, but I am getting stability issues. My internal phase ranges between 20 and 30% and I use emulsifiers that are solid at room temperature. I calculated the tip speed of my impeller and found it is around 0.05 m/sec, which eventually I could double; but I am limited by the high vortex produced by higher speeds that eventually promotes air inclusion. Would a saw-tooth disk improve significantly the stability of my emulsions? Also, if I want to obtain drop sizes of 1 micron, would I need a rotor-stator device?
  • Avatar Dave Dickey Forum Moderator 279 Posts

    Re: How do I form a stable emulsion?

    The tip speed of the current mixer could be the primary source of stability problems.  The current axial flow turbine probably is creating too much flow, which is causing the air entrainment problems.  A saw-tooth disk impeller will definitely reduce the liquid circulation and may reduce air entrainment, depending on the impeller size, fluid viscosity, and impeller coverage.  Simply replacing the impeller may not do enough to create a stable emulsion, the rotational speed of the mixer may need to be increased.
     
    To form a stable emulsion, the tip speed may need to be 0.5 to 1.5 m/sec.  The saw-tooth disk should not be more than 1/3 the tank diameter.  The final viscosity of the product and the melting or dissolution of the emulsifiers will all affect the emulsion stability, not just the mixer tip speed.

    The answers by this expert are based on the best available interpretation of the information provided.  The consequences of the application of this information are the responsibility of the user.  If clarification is needed, please submit a further question.

  • Avatar Jane Barber Community Member 2 Posts

    Re: How do I form a stable emulsion?

    Last edited: 2 January 2014 at 10:50am
    Dave - would you recommend a saw-tooth disk impeller for a high viscosity o/w lotion? or would a bow tie or anchor mixer be better? My internal phase varies - usually around 35%. Unfortunately I do not have the budget for a homogenizer or rotor stator mixer.
  • Avatar Dave Dickey Forum Moderator 279 Posts

    Re: How do I form a stable emulsion?

    A bowtie or anchor impeller will do almost nothing to disperse your o/w.  They will simply move the two phases around inside your vessel and not create an emulsion, stable or not.  A saw-tooth disk impeller can mix a high-viscosity emulsion, but will require high-speed and high-horsepower.  A combination of a high-shear saw-tooth disk impeller and an anchor impeller may provide the combination you need, but you are back to about the same equipment and cost of a vacuum planetary mixer.
     
    If you don't have the budget for a homogenizer or rotor-stator mixer, you may not have the budget for a large saw-tooth disk impeller either.  About the only way to reduce equipment cost is to reduce the size of your tank, which will eventually cost more in the amount of time and number of batches you need to produce.

  • Avatar Jane Barber Community Member 2 Posts

    Re: How do I form a stable emulsion?

    Last edited: 8 January 2014 at 6:34pm
    Thanks so much Dave for your response. I'm actually only making 2kg batches (for personal use) so I'm not yet at the stage of purchasing professional mixers but instead looking for suitable drill attachments like the ones from INDCO - http://www.indco.com/shop/impellers/lab-scale-impellers. I have so far been using model boat propellors attached to a drill and/or a stick blender. I'm presuming the boat propellor is similar to the bow tie so it's not suitable ?? You mention using an anchor as well as a saw-tooth disk - would the anchor be used after the emulsion has formed? Thanks again for your kind help.