Octadecanoic acid, as we often call it, is actually called stearic acid. Its salt formed with metal ions is called stearate. There are three common kinds: zinc stearate, calcium stearate and barium stearate. Today we'll talk about the characteristics, uses and preparation methods of these three stearates.

Calcium stearate

In appearance, calcium stearate is a white fine powder, which is easily soluble in hot pyridine, slightly soluble in hot alcohol, hot vegetable oil and mineral oil, and insoluble in water, aldehyde, chloroform, acetone and cold alcohol. Calcium stearate is often used as a non-toxic heat stabilizer for PVC; Non toxic soft products such as food packaging films and medical appliances; Because of its good non-toxic heat stabilizer and lubricant, it is also a smoothing agent and water resistant agent for adhesives and coatings. It is widely used in chemical production processes such as plastics and rubber.

There are many preparation methods of calcium stearate recorded in the book. The common double decomposition methods are as follows: dissolve stearic acid in 20 times the mass of hot water, add saturated caustic soda solution, and conduct saponification reaction at about 75 ℃ to produce dilute sodium stearate solution. Then add the calcium oxide solution with the content of 1074kg / m3 to the sodium stearate solution, carry out the double decomposition reaction at about 65 ℃, and the product calcium stearate is precipitated. Then, after filtration, water washing and drying at about 90 ℃, the finished product is obtained.

Zinc stearate

Zinc stearate is a white powder, insoluble in water, soluble in hot organic solvents such as alcohol, benzene, toluene and turpentine, and decomposes into stearic acid and corresponding salts when encountering acid. It has various uses, mainly as stabilizer, lubricant, grease, accelerator and thickener, which is convenient for storage and transportation.

There are two methods to produce stearic acid: water method and melting method. Generally speaking, zinc stearate produced by water method is acidic and molten method is alkaline. Water method: (also known as wet method) under the condition of water as the medium, add the catalyst, control a certain temperature and pressure, then add metal hydroxide, replace the metal ions on the catalyst through the catalyst, and then replace the metal ions on the stearic acid through the catalyst itself, so as to achieve the purpose of generating metal salts.

Acid source: stearic acid is usually slightly excessive in aqueous production, so the finished product is acidic after reaction. Melting method: (also known as dry method) in the molten stearic acid, metal oxide is directly added, a certain temperature, pressure and stirring speed are controlled, and stearate is obtained through reaction.

Alkaline source: due to the existence of catalyst, the products produced by dry method can get complete reaction in general reaction results, and the metal oxide is slightly excessive. Therefore, the products are alkaline when tested.

Barium stearate

Barium stearate is a white or slightly yellow powder crystal. It has water absorption in the air. It is soluble in hot ethanol, benzene, toluene and other nonpolar solvents, but insoluble in water. Barium stearate is a good heat stabilizer in the copolymer of polyvinyl chloride and vinyl chloride. It has good long-term heat resistance and lubricant. The stabilization effect is greater than that of calcium stearate, but less than that of lead stearate. In some industrial fields, it can be used as high temperature resistant release agent and high temperature lubricant. At the same time, it can also be used for transparent film, sheet, artificial leather, hard plate and pipe, etc.

For example, it is used in combination with zinc soap in the formula of vulcanized artificial leather, and it is often used in combination with basic lead salt and lead soap in pipes and cables. If used together with cadmium soap, zinc soap or epoxy compound, the electrical properties of the products can be effectively improved.

The synthesis method of barium stearate is relatively simple. Stearic acid is added to the reaction gold, and 20 times the mass of hot water is added while stirring to dissolve it. Add caustic soda at 80 ℃ to form a dilute sodium stearate solution. When the temperature of the reaction solution drops to 70 ℃, barium oxide solution is added to produce double decomposition reaction. Barium stearate is precipitated in the form of sediment. After filtering and washing the sediment, it is dried to obtain the finished product of barium stearate.

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