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Carboxymethyl cellulose is an anionic, linear, water-soluble cellulose ether, and a derivative obtained from the chemical modification of natural cellulose with chloroacetic acid. Its aqueous solution has functions such as thickening, film formation, adhesion, moisture retention, colloid protection, emulsification, and suspension. It can be used as a flocculant, chelating agent, emulsifier, thickener, water retention agent, sizing agent, film-forming material, etc., and is widely used in the fields of food, medicine, electronics, pesticides, leather, plastics, printing, ceramics, daily chemicals, and so on.
Carboxymethyl cellulose is generally a powdery solid, sometimes appearing in granular or fibrous form, and its color is white or light yellow. It has no special odor, is a macromolecular chemical substance, has high hygroscopicity, dissolves in water, and forms a highly transparent viscous solution in water. It is insoluble in general organic solvents such as ethanol, ether, chloroform, and benzene, but it can dissolve in water.
The dissolution rate in water is relatively slow, but the solubility is very high, and its aqueous solution has a certain viscosity. The solid is relatively stable under normal conditions and can be stored for a long time in a dry environment because of its certain water absorption and hygroscopicity.
The aqueous method is one of the earlier production processes for carboxymethyl cellulose industrial preparation. In this process, alkali cellulose and etherifying agents react in an aqueous solution containing free oxygen anions, with water serving as the reaction medium and no organic solvents involved. This method is a traditional process in the carboxymethyl cellulose production.
The solvent method, or organic solvent method, was developed based on the aqueous method. It uses organic solvents instead of water as the reaction medium. In this process, alkali cellulose and monochloroacetic acid undergo alkali reaction and etherification in an organic solvent. Depending on the amount of reaction medium used, it can be divided into the kneading method and the slurry method.
The amount of organic solvent used in the slurry method is much greater than that in the kneading method. The kneading method uses an organic solvent volume-to-weight ratio relative to the amount of cellulose, while the slurry method uses an organic solvent volume-to-weight ratio relative to the amount of cellulose.
In the preparation of carboxymethyl cellulose by the slurry method, the reactive solids are in a slurry-like or suspended state within the system, so the slurry method is also known as the suspension method. This method improves the uniformity and efficiency of the reaction in the carboxymethyl cellulose production.
The slurry method is the latest process for the carboxymethyl cellulose production. The slurry method can not only produce high-purity carboxymethyl cellulose but also prepare carboxymethyl cellulose with a high and uniform degree of substitution. The production process of the slurry method is roughly as follows: the powdered cotton pulp is sent to a vertical alkalizer containing isopropanol, and a sodium hydroxide solution is added while stirring to carry out alkalization at a temperature of about 20°C.
After alkalization, the material is pumped into a vertical etherifier, where a solution of chloroacetic acid in isopropanol is added, and etherification is carried out at about 65°C. The alkalization concentration, alkalization time, amount of etherifying agent, and etherification time, among other process parameters, can be adjusted according to the specific product's purpose and quality requirements. The slurry method achieves higher purity and uniformity in the carboxymethyl cellulose production and is an advanced process in current carboxymethyl cellulose production.
Through the above three carboxymethyl cellulose production processes, the carboxymethyl cellulose production has been continuously optimized to meet the high-performance requirements of products in different fields.
