First cellulose react with caustic to form alkali cellulose then react with mono chloro acetic acid or it’s salt from sodium carboxy methyl cellulose. During the reaction of alkali cellulose with etherification agents and in the subsequent reactions, sodium chloride (common salt) is produced as a major by-product. This is washed out together with any other byproducts or, in the case of technical-grade NaCMC, left in the product. The dried cellulose ethers are then processed into granular or powder products and in some cases modified with other additives. NaOH
Generally the reaction are as follows
Solvent Cellulose + caustic - alkali cellulose
Alkali cellulose + MCA ------ Na CMC + NaCl
CMC dissolves rapidly in cold water and mainly used for controlling viscosity without gelling (CMC, at typical concentrations, does not gel even in the presence of calcium ions). As its viscosity drops during heating, it may be used to improve the volume yield during baking by encouraging gas bubble formation. Its control of viscosity allows use as thickener, phase and emulsion stabilizer (e.g. with milk casein), and suspending agent. CMC can be also used for its water-holding capacity as this is high even at low viscosity; particularly when used as the Ca2+ salt. Thus, it is used for retarding staling and reducing fat uptake into fried foods.
The average chain length and degree of substitution are of great importance; the more-hydrophobic lower substituted CMC's are thixotropic but more-extended higher substituted CMC's are pseudoplastic. At low pH, CMC may form cross-links through lactonization between carboxylic acid and free hydroxyl groups.
Unit Operations