Sodium carboxymethyl cellulose (CMC) is a carboxymethylated derivative of cellulose, also known as cellulose gum, and is the most important ionic cellulose gum. CMC is usually an anionic polymer compound obtained by reacting natural cellulose with caustic alkali and monochloroacetic acid. The molecular weight of the compound ranges from tens of millions to several millions.
【Properties】White powder, odorless, soluble in water to form a high viscosity solution, insoluble in ethanol and other solvents.

【Application】It has the functions of suspension and emulsification, good cohesion and salt resistance, and is known as “industrial monosodium glutamate”, which is widely used.

Preparation of CMC

According to the different etherification medium, the industrial production of CMC can be divided into two categories: water-based method and solvent-based method. The method of using water as the reaction medium is called the water-borne method, which is used to produce alkaline medium and low-grade CMC; the method of using an organic solvent as the reaction medium is called the solvent method, which is suitable for the production of medium and high-grade CMC. Both of these reactions are carried out in a kneader, which belongs to the kneading process and is the main method for producing CMC at present.

1
water-based method

The water-borne method is an earlier industrial production process, which is to react alkali cellulose with an etherifying agent in the condition of free alkali and water. During the alkalization and etherification process, there is no organic medium in the system. The equipment requirements of the water-borne method are relatively simple, with less investment and low cost. The disadvantage is that there is a lack of a large amount of liquid medium, and the heat generated by the reaction increases the temperature, which accelerates the speed of side reactions, resulting in low etherification efficiency and poor product quality. This method is used to prepare middle and low-grade CMC products, such as detergents, textile sizing agents, etc.

2
solvent method

The solvent method is also known as the organic solvent method. Its main feature is that the alkalization and etherification reactions are carried out under the condition that the organic solvent is used as the reaction medium (diluent). According to the amount of reaction diluent, it is divided into kneading method and slurry method. The solvent method is the same as the reaction process of the water-based method, and it also consists of two stages of alkalization and etherification, but the reaction medium of these two stages is different. The solvent method eliminates the processes inherent in the water-based method, such as soaking, squeezing, pulverizing, aging, etc., and the alkalization and etherification are all carried out in a kneader. The disadvantage is that the temperature controllability is relatively poor, the space requirement and the cost are high. Of course, for the production of different equipment layouts, it is necessary to strictly control the system temperature, feeding time, etc., so that products with excellent quality and performance can be prepared. Its process flow chart is shown in Figure 2.

3
Status of Preparation of Sodium Carboxymethyl Cellulose from Agricultural By-products

Crop by-products have the characteristics of variety and easy availability, and can be widely used as raw materials for the preparation of CMC. At present, CMC’s production raw materials are mainly refined cellulose, including cotton fiber, cassava fiber, straw fiber, bamboo fiber, wheat straw fiber, etc. However, with the continuous promotion of CMC applications in all walks of life, under the existing raw material processing resources, how to use cheaper and wider sources of raw materials for CMC preparation will definitely become a focus.

Outlook

Sodium carboxymethyl cellulose can be used as emulsifier, flocculant, thickener, chelating agent, water-retaining agent, adhesive, sizing agent, film-forming material, etc. It is widely used in electronics, leather, plastics, printing, ceramics, daily use Chemical and other fields, and because of its excellent performance and wide range of uses, it is still constantly developing new application fields. Nowadays, under the widespread dissemination of the concept of green chemical production, foreign research on CMC preparation technology focuses on the search for cheap and easy-to-obtain biological raw materials and new methods for CMC purification. As a country with large agricultural resources, my country is in cellulose modification In terms of technology, it has the advantages of raw materials, but there are also problems such as inconsistency in the preparation process caused by various sources of biomass cellulose fibers and large differences in components. There are still deficiencies in the adequacy of the utilization of biomass materials, so further achievements in these areas need to be carried out extensive research