Home Cosmetic Science Talk Formulating Physical Sunscreens and Dispersion

  • Physical Sunscreens and Dispersion

    Posted by arctat on December 4, 2013 at 11:21 pm

    I am wanting to make a “natural” (mineral) sunscreen formulation for my friends, most of whom lean toward the hippie side (can’t help it, I live in San Fran :) ). I’ve read several blog posts regarding the difficulty of formulating an effective physical/mineral sunscreen. Of course, if I decided to sell such product I would get SPF and other kinds of formal testing done. But is it true that using a regular handheld stick blender will not adequately disperse Zinc Oxide powder in a base, as suggested by the following blog post? If so, which homogenizer you would recommend buying to an entry level chemist for this purpose? I probably need one anyway for down the road. My typical batch sizes are currently quite small (anywhere from 3 to 14 oz or so).

    ChemWizard replied 10 years, 5 months ago 3 Members · 3 Replies
  • 3 Replies
  • alchemist

    December 5, 2013 at 12:05 am

    I’ve yet to discover where people are getting this “natural” zinc oxide from.

    If you’re making a zinc cream (a product that remains white or coloured when applied - essentially like paint) you may get away with it.  If you’re making a product that appears relatively transparent when applied then dispersion (and the stability of the dispersion over time) will be critical.  In the lab you’d use a Silverson or similar homogeniser - It takes a lot of energy to get it dispersed, and a little bit of magic to make it stay dispersed.  ;)  
  • arctat

    December 5, 2013 at 12:24 am

    :) Yes, I would be using a regular Zinc Oxide powder, probably the one from KOBO Products (ZNO-C). The idea among these people is that physical sunscreens (non-nano) are “safer” and “more natural” than chemical blockers.

    Keeping it dispersed is key - how does one accomplish such a thing?
  • ChemWizard

    December 7, 2013 at 8:19 pm

    Does Pre-dispersed ZnO (for eg SPD-Z5 from Shinetsu) also need severe Homogenization ?

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