Soap is mainly composed of Sodium Aliphatate, which is essentially an anionic surfactant. Unlike other cosmetic formulations, it has a variety of functional ingredients.
Soap factories basically use soap-base to produce soap. In theory, soap base can be used for cleaning. However, consumers not only are satisfied with this but also usually want a more outstanding soap. No matter to improve its decontamination ability, enhances its moisturizing, or has a better appearance, cheaper price, and longer shelf life. So, this is what soap factories do: add other ingredients for secondary processing in order to improve its performance.
Sodium aliphatate
It is prepared by reaction of sodium hydroxide with natural oil by soap boiling method or continuous saponification method.
There are many kinds, but due to the different molecular structures (mainly the length of the carbon chain), the properties of each are different. The longer the carbon chain is, the more delicate the foam is, and the decontamination ability is strong, but the foaming is slow and not rich. The shorter the carbon chain, the larger the foam and the faster the foaming, but the decontamination ability is worse.
It can be said that the quality of sodium aliphatate is directly related to the detergency of soap. Today, soap ingredients are mixtures of several or even more aliphatate, in order to obtain a better decontamination effect and skin feeling.
Sodium stearate(C18)
CAS: 822-16-2. Poor water solubility, poor resistance to hard water, poor foaming, but delicate foam, and best detergency in warm water. It can increase the hardness of soap.
Sodium palmitate(C16)
CAS: 408-35-5. Solubility becomes worse in cold water, the increase of water temperature can improve it, poor foaming, poor resistance to hard water, and decontamination ability become better when in warm water. It can increase the hardness of the soap.
Sodium myristate(C14)
CAS: 822-12-8. The solubility in cold water is worse than sodium laurate, good foaming, the detergency is worse than other long-chain fatty acids, but better than sodium laurate.
Sodium laurate(C12)
CAS: 629-25-4. Good solubility in cold water, good resistance to hard water, strong foaming, stable foam, but worse detergency than long-chain fatty acids.
Sodium oleate(C18)
CAS: 143-19-1. Better solubility and foaming, good resistance to hard water, and good decontamination, even in cold water. So it must be used with other Sodium Aliphatate. Low irritation to skin but worse hardness.
| fatty acid/ performance | Solubility in cold water | foaming | cleaning | hardness |
| stearate acid | ⭐⭐ | ⭐⭐ | ⭐⭐⭐⭐⭐ | ⭐⭐⭐⭐⭐ |
| palmitate acid | ⭐⭐⭐ | ⭐⭐⭐ | ⭐⭐⭐⭐ | ⭐⭐⭐⭐ |
| myristate acid | ⭐⭐⭐⭐ | ⭐⭐⭐⭐ | ⭐⭐⭐ | ⭐⭐⭐ |
| laurate acid | ⭐⭐⭐⭐⭐ | ⭐⭐⭐⭐⭐ | ⭐⭐ | ⭐⭐⭐ |
| oleate acid | ⭐⭐⭐⭐ | ⭐⭐⭐⭐ | ⭐⭐⭐⭐ | ⭐⭐ |
Solubilizer
These ingredients are more often found in mel&pour soap, since the soap base needs to be dissolved and recreated, adding these solvents can achieve uniqueness of appearance and performance, such as making transparent soap, or make more moisturizing soap.
Below are the common solvents, they are often used together to achieve the best results.
Glycerol
CAS: 56-81-5. It can be said that this is the most important additive with the best moisturizing, low cost, high-temperature resistance, and no discoloration. In production, its proportion is the highest. However, it is very thick, affecting the fluidity of the soap solution, and it is easy to make the solution turn yellow if it is not used with propylene glycol.
Propylene glycol
CAS: 57-55-6. Similar to glycerin, it is moisturizing and can replace glycerin to a certain extent. But it is thinner than glycerin, so it can reduce the viscosity of soap solution.
Sucrose
CAS: 57-50-1. The main function is to make soap transparent, with the best performance. But it will also make the soap liquid become viscous, and supersaturation will precipitate, thus the liquid is not easy to form, can’t add too much, and is often used with sorbitol. It should be noted that sugar must be used with glycerin to make soap transparent.
Sorbitol
CAS: 50-70-4. The same function as sucrose, used together with glycerin to make soap transparent. Because it contains more water, compared with sucrose, it makes the soap solution more fluid, has a more sufficient reaction, and the solution is better formed. In addition, it is cheaper than sucrose, which can be used together to reduce costs. Technically, it is available but not needed
Superfatting agent
The alkali content of soap-base is high, which is degreasing and irritating to the skin. In order to reduce these side effects, superfatting agents are added to neutralize alkalinity and leave on the skin after washing to make the skin moist and smooth.
The following are commonly used fat agents, these additives have good compatibility with soap, do not affect the normal forming process, and have no side effects on washing and decontamination. Which can be used alone or mixed, and the dosage is generally 1% – 5%.
Stearic acid
CAS: 57-11-4. A kind of fatty acid widely exists in nature. Almost all oils contain stearic acid with different contents, have good lubrication and emulsification effects. In the production of soap-base, too much stearic acid is often added, so when the saponification is complete, extra stearic acid remains and becomes a lubricant.
Coconut oil fatty acid
CAS: 61788-47-4. It is a mixture of various natural fatty acids, mainly lauric acid. Like stearic acid, it is the main raw material for making soap. Excess fatty acid gives soap fat.
Lanolin
CAS: 8006-54-0. Lanolin is a kind of secreted oil attached to wool. It is an excellent moisturizing material, which can soften and recover dry or rough skin due to a lack of natural moisture. It maintains the normal moisture by delaying, rather than completely preventing, the passage of water through the epidermis.
Other additives
Colorants
Soaps without colorants are dark gray or brown. Regular soap manufacturers will use FDA-approved pigments and strictly follow their dosage requirements. Generally, the total content shall not exceed 0.1%. In addition, as a whitening agent, titanium dioxide is often added to milled soap, but consumers generally have low acceptance of it.
Odorant
Odorant can mask the taste of soap-based, the total content is generally 1-3%. You should choose a fragrance that with a long retention time, alkali resistance, and color fastness in light. Fragrance oil is used most widely, but some people advocate the use of essential oil, which is no problem, but the price is expensive.
Chelating agent
In order to prevent the automatic catalytic and oxidation of soap caused by the trace metals of soap-base, the metal chelating agent EDTA-2Na is often added, generally 0.1% – 0.2%.
In addition, in order to achieve a certain effect, the soap will also be added with antioxidants to prevent rancidity, bactericides to achieve a bactericidal, walnut particles to achieve exfoliating, and so on.
But generally, soap does not add preservatives, because the pH can reach more than 9, and bacteria can not survive in this environment. you can add it if you don’t mind, so the soap will last longer.
Also, it does not need to add any other surfactant. If you see SLS on a soap, it is a detergent, not a soap.
