Friday, November 9, 2018

a little bit of chemistry: introduction to emulsifiers

Today I will make a simple introduction to emulsification because I think one of the most difficult chapters in lotion making is to decide which is the right emulsifier to use. For so many years, I have understood that choosing an emulsifier or a combination of emulsifiers is a matter that depends on too many factors. It depends on the texture you want to give to your cream, the ingredients you use, the percentage of oils and water ingredients etc.

As you already know, the emulsions are made of 2 phases:
  • the oily phase &
  • the aqueous phase
To homogenise these two phases we use emulsifiers. Our main goal in emulsion formation is to stabilize it; not to separate the water from the oil phase. Emulsifiers are therefore surfactants or surfactant combinations that stabilize, preserve and determine the final form and type of product.

In addition to choosing the right emulsifier in the right amount, in order to achieve emulsification, it is possible to heat our components (thermal emulsification) or stir them until they get homogenized (mechanical emulsification).

The percentage and way of using an emulsifier depends on the result we want for our cream, for example what kind of product do I want? milk, cream or lotion; What texture do I want to give? is it suitable for body or for face; what is the type of skin?

There are many types of emulsifiers available in the market and we use them according to the type of cream we want to make:
  • For emulsions O/W (oil in water), we select an emulsifier that can disperse and trap oil drops in the aqueous phase, giving fine-grained products such as body milks or lotions
  • For emulsions W/O (water in the oil), we select an emulsifier that disperses fine particles of water into the oil phase, giving more fat and rich products.
But this is not necessarily the rule.

Generally, emulsifiers are applied to 20% of the oil phase, but there are some that perform better in smaller or larger concentrations of oil. At the same time, by reducing the amount of emulsifier, we can add other stabilizing agents to achieve the desired viscosity in our cream. The amount of oil that we use, plays a big role in the choice of emulsifier because some emulsifiers work best in a small percentage of oils (5-10%), others work at a higher oil concentration (12-25%) while there are emulsifiers at much higher oil levels. Therefore, depending on the percentage of water or fat phase, we modify our formulas with the appropriate emulsifier.

The stability, texture and appearance of the cream also depends on the pH, and here the emulsifier is very important in combination with the preservative that we use. If the cream has low pH and the emulsifier works better at higher pH, then it is not the proper emulsifier. Many products require special emulsifiers and other stabilizing agents in order to have a satisfactory result.

The emulsifiers may be in the form of flakes where they must be melted to be useful such as BTMS and Polawax or they may be in a liquid form such as Polysorbate 20 and Polysorbate 80 which I recently used to make body mist because I wanted to incorporate essential oils into water.

This is because each emulsifier has its own HLB (Hydrophilic-Lipophyllic Balance) system. As can be seen from the above, emulsifiers consist of:
  • the hydrophilic part, consisting of water-soluble elements
  • and lipophilic part consisting of alcohols and fatty acids

By following the HLB system, we can see if an emulsifier is hydrophilic or lipophilic:
  • if the HLB value is high, then the emulsifier is suitable for emulsions O/W (oil in water)
  • if the HLB value is low, then the emulsifier is intended for emulsions W/O (water in oil)
Therefore, according to the HLB system, coconut oil has an HLB value of 8. The emulsifiers must have a value or a sum of 8 also.

In conclusion, I want to emphasize that we can not use only one emulsifier if we want to make an emulsion or a cream but we combine more than one together to ensure the product’s stability without the risk of separation. I would like to recommend dosages, but this is not feasible, as the right amount is defined by continuous experimentation.

As you can see, it’s not so easy to make cream. For me it is a little Russian roulette every time because it’s never sure if I will be able to homogenise my mixture and keep it stable. Here’s a link for you, to read more about emulsification and the HLB system: 

In future posts, we will discuss about the emulsifiers we have already tried, about  beeswax (is it an emulsifier or not?), cold process emulsifiers and other co-emulsifiers, stabilizing agents and thickeners.

Stella Crown©