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Silica in anhydrous skincare
Hi, I am working in an anhydrous sunscreen formula, using Zinc Oxide and Silica to reduce the oily feeling and improve rheology. I have some doubts when it comes to dispersing them homogeneously in solution. I first disperse Zinc Oxide since Silica “gels” the mixture, making any further mixing more difficult. The problem is, that I sometimes find “agglomerates” or “chunks”, but I don’t know if these are from Zinc oxide or silica. Any recommendations to improve dispersion of these in solution? The formula is mainly composed of oils and waxes, plus antioxidants.
I have also tried Moroccan clays for rheology, do these form oxides that could harm the purpose of sunscreen? Thank you. -
6 Replies
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I’d suggest you use a shear mixer to disperse the zinc oxide and silica, if you don’t already; if you still have the problem, omit one or the other and see if the problem still occurs
clays are chemically inert silicate minerals, can’t see them causing a problem
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I am using a high shear mixer. Thank you, I will try ommiting one or the other.
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First, the fact that you can’t easily mix your material after adding silica tells me that you have a low-shear and/or underpowered or undersized mixer - increase your shear considerably, using a either a long time with a high-shear mixer (homogenizer) or a shorter time with a very high shear mixer (3-roll mill, colloid mill or micro-fluidizer).
The thicker the mixture, the better, for the purposes of dispersion. You really need a dispersant in your formula, as well. Something like Ganex WP-660.
Also, looking at your agglomerates under a microscope should tell you if they’re zinc oxide or silica.
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which type of microscope works better for this purpose?
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Would clay form breeding grounds for microorganisms in anhydrous products? Using anhydrous preservatives and antioxidants. Would this depend on the concentration used? 1%, 10% clay?
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Just an ordinary light microscope should do.
Clay will not breed microbes in anhydrous products. No water = no growth. Concentration of clay isn’t an issue, unless it caries a lot of water in with it - dry powdered clay typically has little to no water. Mold is a problem whether you have clay or not.
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