Have you ever made a lotion and it ended up separating months or maybe weeks later?
Are you noticing just a little bit of liquid on the top of your lotion weeks or months later?
This is happening because the emulsion has failed.
Emulsions don't last forever, but as cosmetic formulators it is our job to make them last as long as possible especially, if you are selling that emulsified product. If you want more information about emulsions go watch my video titled “Introduction to Emulsions for Beginners”
Co-Emulsifiers
Co-emulsifiers are used along side emulsifiers to help keep the emulsion more stable and to help thicken the emulsion. Co-emulsifiers are oil soluble and are included in the heated oil phase of your formula. They often come in small waxy white to off-white beads, flakes, or pellets. Often times Co-emulsifiers can already be found in our all-in-one emulsifiers, but I always recommend adding an additional co-emulsifier to every emulsion, because in my experience, it creates a much more stable product.
Examples of Co-Emulsifiers
All of these will add a different sensory feel to your product, spreadability, and viscosity. My go to is Cetyl alcohol. It's basically the co emulsifier I use in most emulsion. For you, I'd recommend purchasing a few different co-emulsifiers and trying them in your lotion recipe to see which one you like the most.
Typically for co-emulsifiers I will use them anywhere between 1% to 5%. Again do some experiments to see which percent is perfect for you. It is so important to do small batch experiments as a formulator because you learn from your mistakes & your experiences. So even if you end up with lots of failed formulas, it's OK because you will learn from that.
Polymers
So what if you want to stabilize your emulsion, but you still want to keep it thinner? Because typically with co-emulsifiers they will thicken. So what's the alternative?
This is where Polymers come in. There are natural & synthetic polymers.
Polymers, unlike co-emulsifiers are water soluble. Polymers could also be described as gelling agents because they thicken and gel water. So adding a gelling agent/polymer will thicken the water phase into a gel making it harder for the oils to separate out. (Adding a polymer in the water phase creates a double layer around the dispersed phase which creates a more stable emulsion.)
There are a lot of different polymers/gelling agents out there that you could choose from.
Natural Polymers
These are xanthan gum, Tara Gum (Caesalpinia Spinosa Gum), and Guar Gum to name a few, but make sure it’s xanthan gum soft. I don’t recommend other xanthan gums for this. Natural Gums can sometimes feel tacky on the skin though, so if you do choose to use one of these use it at less than 0.5%. You may notice xanthan gum in a lot of Store bought lotions. And if you do choose to sell a lotion I do recommend adding in at least 0.1% xanthan gum to your heated water phase to help with stability. Xanthan gum soft is very inexpensive and like I said, it's so commonly used in lotions that I think it's the perfect go to natural polymer to help with emulsion stability. Xanthan gum is considered natural and it's Ecocert, so it makes a lot of people happy. If you want to add xanthan gum into your emulsion, I recommend first mixing it with glycerin before adding in the distilled water. Xanthan gum likes to clump up in water so it works best when its first mixed with a solvent like Glycerin Propanediol or Propylene Glycol.
If you have any of these other gums on hand you can try using them in your water phase. I would mix them with the glycerin first then add in your water. Try different percentages of your natural polymer to see what works the best for your emulsion.
Synthetic Polymers
The other section of polymers/gelling agents you could use to help stabilize the emulsion would be synthetic polymers. There are so many different types of synthetic polymers, but to name a few, you could use Sepimax Zen, Sepinov EMT 10, Carbomer, or Aristoflex AVC.
Except with these polymers you would add them to the oil phase. Usually synthetic polymers have a much better sensory feel on the skin. So you can use these at higher percentages in your emulsions. They feel more like water on the skin and don’t leave a film on your skin unlike the “natural” gums/gelling agents do. So if you want a very light sensory feel or tend to find products to be tacky or sticky then stick with a synthetic polymers. But if you are only using a small amount of xanthan gum, like 0.1%, this will not make the lotion tacky or sticky,
Each of these synthetic polymers are very different from another. For example Sepimax Zen & Sepinov EMT 10 can actually emulsify oil and water together on their own. So these two specifically could make a great gel moisturizer or gel cream without the addition of an all-in-one emulsifier. Which I can actually make an entire video talking about gel creams, so let me know if you wanna see that.
Sepimax zen claims to emulsify up to 25% oils, while Sepinov EMT 10 claims to emulsify up to 50% oils. So these are actually two ingredients I could talk a lot about. But for now what I'm going to say is that if you do decide to use these alongside your are all in one emulsifiers to increase emulsions stability, add them into the oil phase, even though they are technically water soluble. You only need a small amount, like 0.1% to 0.5%. These are more expensive ingredients so unless you want to make a gel moisturizer or gel cream I think Xanthan Gum is the better option here or maybe even carbomer, but when using carbomer you need to have your product be in a pH around 6 for it to thicken. If you use sodium carbomer it does the pH adjusting for you.
Something to keep in mind when you are working with these synthetic polymers is that they don’t really work with all ingredients. Sometimes certain ingredients can thin them out, but not always. It really can depend on the overall formulation, but here are a few ingredients that might cause some issues for you. It doesn’t mean they will, but it’s possible. High amounts of aloe vera, hydrolyzed proteins, sodium PCA, sodium lactate, and cationic surfactants. Now I have used aloe vera with sepimax zen with no problem, but I do know it can cause issues with carbomer, so it could cause issues with these other polymers as well. And by issues I mean, it thins it out.
Chelating Agents
The simplest way to explain Chelating agents is that they help get rid of metals that may be in our products. These metals can improve the overall stability of the product.
Metals can get into your products during manufacturing, from the ingredients we use, & from hard waters that we use. Using a chelating agent is almost always essential because they can help improve the preservation of your product, stabilize an emulsion, help keep the products color from changing, help keep pH from drifting, and help with reducing soap scum in cleansing products.
Some reasons you may not want a chelating agent, is in cationic based products, like conditioners.
Also if you are working with electrolyte sensitive polymers such as carbomer. I actually have a whole post about dealing with electrolytes while formulating. Again the ions in a chelating agent can reduce the stability of these electrolyte sensitive polymers and cause them not to work.
Examples of Chelating Agents;
Hopefully this information will help you create a more stable emulsion.
Sources;
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