What are Fatty Acids?
Oil and fats are made up of fatty acids. They are simply the building blocks of soap and each fatty acid creates a different soap with different qualities.
Triglycerides are present in every oil or fat used in soap making. A triglyceride has a glycerol molecule which is like a tree trunk and three fatty acids which are like its branches. Every fatty is made up of a unique chemical composition that adds different characteristics to the functioning and structure of the end fatty acid salt.
There are only eight primary fatty acids that we need to know to formulate a soap based on our desired properties, performance and appearance. A bar of soap is a unique combination of thousands of individual solid soap molecules that form a crystalline structure.
Properties of Different Types of Fatty Acids
Two Type of Fatty Acids
1. Saturated Fatty Acids
Lauric and Myristic fatty acids are more soluble in water and are excellent cleansers as they have shorter carbon chains. This also allows them to produce a fast-forming, full and bubbly lather. However, it will not create a long-lasting bar as it will “melt” in the shower more quickly than desired and its high cleansing power may cause your skin to be a little dry.
The common usage rate of 20-30% assures the qualities of Lauric / Myristic fatty acids, but in a low enough percentage so that users will not find it too harsh. Other oils should also be added to make the bar last longer.Palmitic and Stearic fatty acids will create a hard bar with a stable and creamy lather as well as increased lifespan because they have longer saturated carbon chains. Stearic acid is a must for shaving soap and also good for hardening soaps that are high in olive oil.
Oils High in Fatty Acids
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Myristic Acids
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Lauric acids
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Palmitic acids
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Stearic acids
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2. In general, unsaturated fatty acids are less soluble and will produce a milder and creamier lather as it has long hydrophobic tails. It is also softer which makes it harder to solidify into solid crystals due to its shape.
Oleic and Linoleic acid contributes to a hard bar with conditioning and moisturizing properties but it is not as long-lasting as bar soaps with Palmitic and Stearic acid. Most soapmakers cap oils high in Linoleic at about 15% to reduce rancidity and DOS (Dead Orange Spot).
Linolenic acid is valued for its rich, silky and conditioning properties. Oils containing Linolenic acids should be limited to 15% or less to ensure they do not cause rancidity in the soap.
An interesting point to note is that, unlike the other three unsaturated fatty acids, Ricinoleic has an OH (hydroxyl) group which increases the solubility of the soap. This fatty acid is only found in castor oil and it increases the rate of lather formation, trace and reaction rate.
Oils High in Fatty Acids
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Oleic acids
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Linoleic acids
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Linolenic acids
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Ricinoleic acids
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Selecting Fatty Acids
As we have known more about the properties of each fatty acid. It is recommended to use a blend of fatty acids to create a soap bar of your desired properties.
Tips for Improving Bar Soap
Add amino acid surfactant to improve foam, mildness and hard water tolerance.