## Friday, December 5, 2014

### Weekday Wonderings: Using polysorbates and separation? Exact recipe?

In this post, using polysorbates in your products, Lisa asks: I've tried the bath oil recipe, but I noticed that the polysorbate 80 starts to separate from the oil after letting it sit for a while. Everytime I want to use it, I have to shake it up. Is there anything I can add to prevent it from separating?

From this post: How do oils in a serum stay combined? It's about specific gravity!

Specific gravity is a way of measuring if something weighs more or less than water.  Pure water at 4 Celsius is our baseline for specific gravity and everything else is compared to it. Water weighs 1000 grams per litre - 1 kg per litre - or 1 gram per millilitre. So a teaspoon or 5 ml of water weighs 5 grams. A tablespoon or 15 ml of water weighs 15 grams. A cup of water at 250 ml weighs 250 grams.

If something is listed as being less than 1, its volume is more than water per gram. If something is more than 1, its volume is less than water per gram.  If something has a specific gravity of 1.03, it means it weighs 1.03 grams for every 1 millilitre or 1030 grams per litre.

Specific gravity is the reason that oil floats on top of water. A lot of the oils we use have a specific gravity of 0.90 to 0.95, which means they are lighter than water, so they float to the top of our product while the water settles on the bottom.

Let's say we make a facial serum with four oils - safflower oil (0.90), olive oil (0.91), cottonseed oil (0.88), and peanut oil (0.92), and a few oil soluble ingredients like Vitamin E (0.955) and calendula oil (0.91) they will eventually settle into layers with the heaviest oil at the bottom and the lightest oil at the top. (Order from the bottom, Vitamin E, peanut oil, calendula and olive oil, safflower oil, and cottonseed oil.)

So to answer your question - polysorbate 80 has a different specific gravity than your oils at 1.06 to 1.10, so it separates. Shaking it up before you use it is the easiest way to keep it emulsified.

In this post, BTMS-50 in solid scrub bars, Melanie asks: How do you get the sodium lactate in when there is no water to dissolve it in? I used a little water to dissolve it before adding it and mine is totally separated-salt to the bottom, oil on top.It wouldn't stay mixed long enough to get it into molds. It kept going into oil on top of salt. Oh also, I tried siliconyl beeswax because I had some and wanted to try it. otherwise, your recipe.

I need to say something out loud for a moment...when you change something in one of my recipes, it isn't my recipe any more. It's a different recipe. There's nothing wrong with changing the recipe - you know I encourage experimentation! - but saying to me that you followed my recipe isn't accurate if you changed something. Even something as small as 2% of this or 0.5% of that can change the chemistry and make the skin feel different. This is why I insist that you include the recipe you followed in percentages and the process you followed so I can trouble shoot easier.

I have found that if you pour this product too warm, it will separate into layers as you pour it into the molds. My suggestion is to let it cool a bit, add the sugar, and let it sit for a bit, until it is hardening around the edges. Then add it. This seems to work for me. Make sure, too, that you are adding enough sugar to make a paste out of the product!

What about dissolving sodium lactate in a scrub bar? When we include an emulsifier in a scrub bar - in this case, I'm using Incroquat BTMS-50 - we can add a bit of water to the mix. It doesn't take much to dissolve sodium lactate - it's incredibly soluble at 1.5 g/mL (reference) - so you can get away with dissolving it in some panthenol or hydrolyzed protein or other liquid you plan to include in the bar. You can heat the liquid slightly to make it more soluble. Having said this, I use liquid sodium lactate, so I don't worry about it dissolving.

As a quick aside, someone asked the other day how my solid conditioner bar could work with water soluble ingredients in it. Yes, the bar is based on oil soluble ingredients, but most of those oil soluble ingredients are emulsifiers in the form of Incroquat BTMS-50. That emulsifier allows me to add water soluble ingredients like panthenol or honeyquat to the bar.

Join me tomorrow for more fun with cosmetic chemistry!

#### 1 comment:

Lisa said...

Hi Susan,

Thanks for looking into my question. I actually have looked into the gravity before, and you're right. Polysorbate 80 is a lot denser than the oils. I was doing research, and I've read that I have to use a lipophilic emulsifier with a hydrophilic one so that the oil stay in suspension with the emulsifier. They suggested polysorbate 80 with a lipophilic emulsifier like a product called Span. I'm not sure, but I may have to experiment with it in the future.