What is HLB? To start with, HLB stands for hydrophilic-lipophilic balance.
Say what? Don’t worry – you’re not alone. Many lotion makers are unaware of HLB and why it is important to understand when creating a lotion formula. This article will explain the mysteries of HLB and help you to better understand how to create a stable emulsion for your lotion.
To begin with, the HLB system is in place to help match the oils used with appropriate emulsifiers. As you know, emulsions are combinations of oil and water held together by a bridge (an emulsifier) that has a water-loving and an oil-loving end.
Several factors can influence the stability of your emulsions. Think of your emulsion as a lava lamp. You have colorful oil droplets drifting around inside the water. Similarly, depending upon whether you are making an oil in water (O/W) emulsion or a water in oil (W/O) emulsion, your lotion’s emulsion consists of small droplets of one material (either oil or water) dispersed amongst the larger body of the other material (either oil or water).
In order to keep your emulsion stable, you must use the correct amount and type of emulsifier. This keeps the small droplets dispersed properly. One rule of thumb to keep in mind:
For O/W emulsions: one part oil to 2 parts water
For W/O emulsions: one part water to 2 parts oil
These are maximum measurements. Tighter emulsions are formed when using less than these amounts. Try to stay to a ratio of 1:3 or 1:4 or more.
Each oily material requires a different strength of emulsifier to ensure stability. This is referred to as the HLB requirement for that oil. Vegetable oils are the easiest to emulsify, mineral oils are moderately difficult, while silicone oils are the most difficult to stabilize. Typical requirements are shown in Table A.
Emulsifiers have HLB values. The HLB value of an emulsifier is determined by the ratio of the weight of the hydrophilic (water-loving) portion of the molecule to the lipophilic (oil-loving) molecules. Typical values are shown in Table B.
So, You Say You Want to Design A Lotion Recipe?
The first step in creating a new lotion formula is determining the HLB requirement of the oil phase. Each oil used brings its own special needs. Vegetable oils, being easily emulsified, reduce the overall requirement. Silicone oils, on the other end of the spectrum, increase the demand.
Determine how much of each oil you will be using by breaking them down into fractions of the whole oil amount. Then, using this simple equation, you can determine the HLB requirement for your oil mixture.
HLB requirement = (HLB req. A x Fraction A) + (HLB req. B x Fraction B) + …
Continue adding the HLB requirements and fractions until you have finished accounting for all of the oils you will be using in your oil mixture.
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To ensure that you are using the correct emulsifier/s given the outcome of the above calculation, you must figure which combination of emulsifiers is appropriate. Do not be fooled into thinking that just because you use only one or two vegetable oils that one emulsifier will do. Even emulsifying wax (e-wax) is a combination of more than one emulsifier.
Here is the generalized equation you must solve in order to determine the ratios of emulsifying agents to be used in your specific formula:
HLB requirement = (HLB A x Fraction A) + (HLB B x Fraction B) + …
This equation is easy to solve for sinple systems but becomes more complex as the number of emulsifiers increases. For a two emulsifier system, use this equation:
(HLB req – HLB B) / (HLB A – HLB B) = amount (fraction) of material A required
The amount of material B required equals 1 – A (amount of material A required, as calculated above).
As we mentioned previously, the more emulsifiers used, the more complex the equation becomes. Fortunately, there are ways to make the equations easier to solve. Up to three emulsifier systems are easily solved using the above and trial calculations and adjustment. The “official” mathematical name for this process is iterative solution.
Here are some ideas to help you out:
- Typical use rates for primary emulsifiers, such as glyceryl monostearate (GMS) are 35-55% of the total emulsifier content.
- Secondary emulsifiers such as stearic acid should be kept in the 5-15% range to avoid excessive “drag” and poor “feel” issues.
- Using a “high” HLB emulsifier such as polysorbate as part of the emulsification system will greatly enhance the ease of satisfying the HLB requirement of the oils.
Once the emulsifier ratios have been determined, it’s time to figure out emulsifier usage rates.
Many common emulsification systems obey the “20% rule”. This rule states that the total emulsifier content should be 20% of the oil weight. E-wax and GMS both fall into this category.
Some manufacturers, such as Croda, have developed proprietary emulsification systems that use synthetic polymers and other materials. These may be used at less than 20%. Consult the manufacturer for details.
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Oh, But There’s More!
The HLB match is not your only consideration. Several other factors may influence the stability of an emulsion.
Thermal Inversion Phenomena
This issue can come into play in both processing and stability in use.
Under normal circumstances, the emulsifier molecule will stay oriented in the correct direction. That is to say, the water-loving end (polar) stays in the water while the oil-loving end (non-polar) stays in the oil. Each end of the emulsifier molecule may have minor solubility in the opposite phase. Usually, they stay put, preferring to be with their own.
Generally, solubility (the ability to leave its own and break out of the emulsion) increases as temperature increases. Once this inversion begins, the emulsion becomes unstable and breaks apart. The specific temperature at which this destabilization takes place is known as the “phase inversion temperature.”
Low phase inversion temperatures can limit processing as an emulsion will not form. This is why we recommend processing at no more than 140F. We have all seen the result of summer’s heat on a lotion – especially those left to simmer in a closed car.
What About Those Droplets?
Remember droplets? We talked about them in the beginning. Droplets are the so-called inner phase. They are the opposite of the “continuous phase”. Droplets can be either oil or water, depending upon the type of emulsion you are creating.
Larger droplets are less stable than smaller droplets. Because of their size, they also have a greater chance of “running into each other” and combining. A slight imperfection in the emulsifer’s coat or shell can cause the emulsion to fall apart. The larger the droplet size, the more likely this event will occur.
So, how can we get smaller droplets? High shear mixing is the key. Using manual mixing devices, such as a fork or whisk does not provide the energy required to keep an emulsion in place. Using a high shear mixer such as a stick blender or kitchen blender will provide the amount of force required to keep the emulsion together.
What About Beeswax and Borax?
Beeswax and borax emulsions are water in oil (W/O) emulsions. These do not obey the HLB system well, but are usually stable when prepared correctly.
The beeswax is emulsified by the borax to yield fatty acid borates (salts) and fatty alcohols. It’s kind of like making a soap out of borax. The borax actually makes the emulsifier. It is difficult to predict the exact amount of emulsifier that will be produced, so trial and error is your best method. Write everything down so you can duplicate your results another time.
It’s OK To Be Confused
There’s a lot to learn and understand about HLB. Most lotion makers don’t get it all the first time. And that’s OK. Just bear in mind that products such as emulsifying wax are compound emulsifiers and can take a lot of the math and guesswork out of lotion making.
Take your time, experiment and remember, write everything down. Drop us a line if you have questions.
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