Carboxymethyl cellulose

Carboxymethyl cellulose, or CMC, is a cellulose derivative with carboxymethyl groups (-CH2-COOH) bound to some of the hydroxyl groups of the glucopyranose monomers that make up the cellulose backbone.

Preparation
It is synthesized by the alkali-catalyzed reaction of cellulose with chloroacetic acid. The polar (organic acid) carboxyl groups render the cellulose soluble and chemically reactive.

The functional properties of CMC depend on the degree of substitution of the cellulose structure (i.e., how many of the hydroxyl groups have taken part in the substitution reaction), chain length of the cellulose backbone structure.

Uses
CMC is used in food science as a viscosity modifier or thickener, and to stabilize emulsions, for instance in ice cream. It has E number E466. It is also a constituent of many non-food products, such as K-Y Jelly, toothpaste, laxatives, diet pills, water-based paints, detergents, and various paper products. They have high viscosity, are not toxic, and are generally non-allergenic. CMC is used as a lubricant in non-volatile eye drops (artificial tears). Sometimes it is methylcellulose (MC) which is used, but its non-polar methyl groups (-CH3) do not add any solubility or chemical reactivity to the base cellulose.