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16

2022

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02

The production method of sodium carboxymethyl cellulose


  CMC is usually an anionic polymer compound prepared by reacting natural cellulose with caustic alkali and monochloroacetic acid, with a molecular weight of 6400 (±1 000). The main by-products are sodium chloride and sodium glycolate. CMC belongs to natural cellulose modification. At present, the United Nations Food and Agriculture Organization (FAO) and the World Health Organization (WHO) have officially called it "modified cellulose".
  (1) The production method of carboxymethyl cellulose is to react cellulose with sodium hydroxide to generate alkali cellulose, and then carry out carboxymethylation with monochloroacetic acid. The preparation method can be divided into a water-based method in which the reaction is carried out with water as a medium and a solvent method in which the reaction is carried out in a solvent such as isopropanol, ethanol, and acetone.
  (2) Immerse the degreasing and bleached cotton thread in 35% concentrated lye solution in proportion, soak for about 30 minutes and take it out. The liquid caustic soda can be recycled. The soaked cotton short thread is weighed on the flat press, and the lye liquid is pressed out at a pressure of 14 MPa to obtain alkalized cotton. Put the alkali cotton into the etherification kettle, add 15 parts of alcohol, slowly add the chloroacetic acid alcohol solution under stirring, and finish at 30 °C for 2 h. After adding, stir at 40 °C for 3 h to obtain etherified cotton. Add 120 parts of alcohol (70%) in etherified cotton, stir for 0.5 h, and add hydrochloric acid to adjust the pH to 7. Wash twice with alcohol, filter out the alcohol, blow dry at 80 °C, and pulverize to obtain the finished product.
  (3) Treat cellulose with sodium hydroxide to form alkali cellulose, mix with sodium monochloroacetate, and mature for several days (20~30℃) to obtain the product
(C6H9O4OH)n+nNaOH→(C6H9O4ONa)n[ClCH2COOH]→(C6H9O4OCH2COONa)n
  The processes used in China include the traditional water-based method with water as the medium and the solvent method with an organic solvent as the reaction medium.
  Traditional water-based method
  Spray the kneader with 18%~19% lye solution, alkalize the refined cotton at 30~35℃ to form alkali cellulose, and then knead and etherify with solid sodium chloroacetate. The temperature in the first 1 to 2 hours is controlled below 35 °C; the temperature in the last 1 hour is controlled at 45 to 55 °C. After a period of aging (to make etherification complete), it is dried and pulverized to obtain the finished product.
  Solvent method
  The cotton is refined in a kneader, and the lye is sprayed into the kneader at a certain flow rate to fully expand the cellulose. At the same time, an appropriate amount of ethanol is added, and the alkalization temperature is controlled at 30-40°C, and the time is 15-25min. After the alkalization is complete, spray into the chloroacetic acid ethanol solution, and etherify it at 50~60℃ for 2h. Neutralize and wash with ethanolic hydrochloric acid solution to remove sodium chloride, use a centrifuge to remove alcohol and remove water, and then dry and pulverize to obtain the finished product.