Soap

Soap began to be made in ancient civilizations, such as Sumer and Babylon (about 2800 BC). A description of the technology for the production of soap was found in Mesopotamia on clay tablets dating back to about 2200 BC. e.

The ancient Egyptians used soda for hygiene. Also, Ebers papyrus (1550 BC) mentions a certain soap-like substance from animals (goose) and vegetable fats with the addition of lead ( galena extract) or sodium carbonate (extracted from the Nile) ^[1] .

Such detergents were widely used in ancient Rome , where the first mention of soap ( lat. Sapo , then converted into many Romance languages ) by Pliny the Elder in " Natural History ". In ancient Russian literature, soap is mentioned in Domostroy ( XVI century ).

It is proved that oils of biological origin well remove dirt from the surface of the skin. This is easy to notice when eating fatty foods with your hands, for example, roasted meat on a fire. While in the southern latitudes it was easier to use vegetable oil for washing, in the northern latitudes this could be difficult due to the high cost of raw materials. And melted animal fat is much easier to get in the north. Given that open fire was often used for heating, mixing melted fat with ash or sand was a matter of time. In the future, it was only necessary to select the optimal composition of fats to obtain a homogeneous mixture.

In 1808, the French chemist Michel Eugene Chevreul (1786−1889) at the request of the owners of the textile factory established the composition of the soap. As a result of the analysis, it turned out that soap is a mixture of sodium salts of higher fatty (carboxylic) acids.

In Europe and the USA, the continuous soap-making process was developed at the end of the 1930s together with the continuous process of hydrolysis (splitting) of fats by water and high-pressure steam in soap towers.

Chemically, the main component of solid soap is a mixture of soluble salts of higher fatty acids . Typically, these are sodium , less commonly, potassium and ammonium salts of acids such as stearic , palmitic , myristic , lauric and oleic ^[2] .

One of the variants of the chemical composition of solid soap is C ₁₇ H ₃₅ COONa (liquid - C ₁₇ H ₃₅ COOK).

Additionally, the soap may contain other substances that have a detergent effect, as well as flavorings , dyes, and powders.

As raw materials for obtaining the main component of soap, animal and vegetable fats , fat substitutes ( synthetic fatty acids , rosin , naphthenic acids , tall oil ) can be used.

The preparation of soap is based on a saponification reaction — hydrolysis of fatty acid esters (in particular fats) with alkalis , resulting in the formation of alkali metal salts and alcohols.

In special containers (digesters) heated fats are saponified with caustic alkali (usually sodium hydroxide ). As a result of the reaction, a homogeneous viscous liquid is formed in the digesters, thickening upon cooling - soap glue , consisting of soap and glycerin. The content of fatty acids in soap obtained directly from soap glue is usually 40-60% ^[2] . Such a product is called “ glue soap ”. The method of producing glue soap is called the "direct method".

The “indirect method” of soap production is the further processing of soap glue, which is subjected to shredding - treatment with electrolytes (solutions of caustic alkali or sodium chloride ), as a result, the liquid is stratified: the top layer, or soap core , contains at least 60% fatty acids; the lower layer is the soapstone , an electrolyte solution with a high glycerol content (also contains contaminants contained in the feedstock). The soap obtained as a result of the indirect method is called “ sound ”.

The highest grade of soap is sawn , obtained by grinding the dried sound soap on the rollers of the sawing machine. In this case, the content of fatty acids in the final product rises to 72–74%, the structure of soap, its resistance to drying, rancidity, and the effect of high temperatures during storage improve ^[3] .

When caustic soda is used as alkali, solid sodium soap is obtained. Mild or even liquid potassium soap is formed when potassium hydroxide is used .

Laundry soap

When sodium soap is cooled , a laundry soap is obtained. A solid soap contains 40–72% of the basic substance, 0.1–0.2% of free alkali, 1–2% of free Na or K carbonates, and 0.5–1.5% of a water-insoluble residue.

As a thickener

In technology, calcium and lithium soap are widely used as a thickener for lubricants. So, the well-known grease grease is a petroleum oil thickened with calcium soap, and lithol is the same oil thickened with lithium soap (lithium salt of stearic acid).

Handmade Soap

Soap can be produced manually in several ways. At the same time, essential oils, grated nuts, ground coffee, coconut oil, etc., perfumes and fragrances can be added to it.

One of the methods is grinding and melting of a finished soap (for example, children's soap). A bar of soap is ground on a grater or knife, diluted with water or another desired liquid (for example, decoctions of herbs), then the whole mass is melted in a water bath. When the mass becomes homogeneous, it is removed from the fire and essential oils and other ingredients are added as desired. The difficulty of this method is that the finished soap used by the soap maker is rather refractory and the process of its digestion is long. This method is used by beginners in soap making, since it does not require significant financial costs.

Handmade soap can also be made from a special soap base sold in specialized stores. The base can also be melted in a water bath or in a microwave. Unlike industrial-made soaps, handmade soaps are worse washed because the ingredients in the soap base are more gentle and softer. For the same reason, it expends faster than industrial soap of the same weight.

Soap made directly from alkali and fats by hand requires a soap-worker to comply with safety precautions when working with alkali. On the other hand, full control over the process of creating soap allows the soap-maker to create exactly the product that he needs. For the manufacture of solid soaps, alkali NaOH ( sodium hydroxide ), fatty oils and water are used. To make the soap firm enough, with good foam and not dry the skin, you need to choose the right oil and carefully calculate how much alkali and water will be needed to saponify the selected amount of oil, for this a soap calculator is used ^[4] . Soap must contain:

• oils that make the soap solid (for example, palm oil , cocoa, coconut, olive, shea, cupuasu, murumuru, etc.) - up to 65%;
• foam-forming and foam-stabilizing oils (coconut, babassu, palm kernel, castor (castor oil is not foam-forming, but only foam-stabilizing)) - up to 35%,
• oils that care for the skin, which provide good conditioning properties to the soap, soften its effect on the skin - up to 25% (for example, avocado, almond, mango, macadamia, grape seed, etc.).
• Soap cooked 90-100% from coconut oil, subject to complete saponification, has very high washing properties, does not salted out, so it is washed with salt water.

The ancient method is cooking soap from improvised materials (using non-resinous tree ash, animal fat), the mixture of which is boiled over an open fire.

Reuse remnants

In Cambodia , the practice of making soap from remnants is common. Samir Lakhani, an American student, organized the production of affordable soap from soap residues in large hotels. The Eco-Soap Bank company he organized for 2016 collects remnants in 170 hotels and processes them, supplying cheap soap to more than 600 thousand rural residents who did not have the opportunity to buy soap before ^[5] .

The consistency is a viscous liquid . The chemical composition of most varieties of liquid soap differs markedly from solid soap and closer to shampoos , in particular, include synthetic surfactants , as well as skin softeners and fragrances. Liquid soap is used as a detergent, for washing hands, as a gel for body care and antibacterial. Liquid soap is easy to make with your own hands ^[6] .

• Molodchikov S.I., Malina E.V. Soaps // Chemical Encyclopedia: 5 t / Knunyants I.L. - M .: Big Russian Encyclopedia , 1992. - T. 3: Copper — Polymer. - S. 155-156. - 639 p. - 48,000 copies. - ISBN 5-85270-039-8 .
• Khlopin G.V. Soap // Brockhaus and Efron Encyclopedic Dictionary : 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.