Soap is widely used not only for washing clothes but also for the textile industry. The sodium salt of high-grade fatty acids is usually used most, which is generally called hard soap; its potassium salt is called soft soap, which is mostly used for hair washing and shaving. Its ammonium salt is often used to make the cream. According to the composition of soap, considering the fatty acid part, the soap made of saturated fatty acid is relatively hard; on the contrary, the soap made of unsaturated fatty acid is relatively soft. The main raw material of soap is grease with a high melting point. Considering the length of the carbon chain, generally speaking, the carbon chain of fatty acids is too short, and the soap made is too soluble in water; if the carbon chain is too long, the solubility is too small. Therefore, only C10-C20 fatty acid potassium salt or sodium salt is suitable for making soap. In fact, sodium salt containing c16-c18 fatty acid is the most.
Soap usually also contains a lot of water. After adding spices, dyes, and other fillers to the finished product, all kinds of soap can be obtained.
Commonly used yellow laundry soap is generally blended with rosin. Rosin is added in the form of sodium salt. Its purpose is to increase the solubility and foam of soap and is also cheaper as a filler.
The white laundry soap is added with sodium carbonate and water glass (up to 12%), and the general composition of laundry soap contains about 30% water. If the white laundry soap is dried and cut into thin pieces, the soap pieces are obtained for washing high-grade fabrics.
The medicated soap can be obtained by adding a proper amount of mixture of phenol and cresol (antiseptic, bactericidal) or boric acid into the soap. Soap needs high-grade raw materials, for example, the soap made by mixing butter or palm oil with coconut oil, smashing, drying to about 10-15% water content, adding spices and dyes, and then pressing.
Liquid potassium soap is often used as shampoo, etc. it is usually made from coconut oil.