Sodium carboxymethylcellulose (CMC), also called cellulose gum, is a carboxymethylated derivative of cellulose and a major type of anionic cellulose ether.

It is an anionic polymeric substance synthesized from natural cellulose via reaction with caustic soda and monochloroacetic acid, with molecular weights ranging from thousands to millions.

CMC appears as white or off-white fibrous powder or granules, with a density of 0.5–0.7 g/cm³. It is nearly odorless, tasteless and hygroscopic. It disperses readily in water to form clear colloidal solutions, while being insoluble in organic solvents such as ethanol.

A 1% aqueous solution features a pH value of 6.5–8.5. Its viscosity drops sharply when pH exceeds 10 or falls below 5, and optimal performance is achieved at pH=7.

The product possesses good thermal stability. Its viscosity increases rapidly below 20°C and changes moderately at 45°C. Prolonged heating above 80°C will cause colloid denaturation, leading to obvious loss of viscosity and performance.

CMC dissolves easily in water to yield transparent solutions. It remains stable in alkaline media but is prone to hydrolysis under acidic conditions. Precipitation takes place at pH 2–3; precipitation can also occur through reactions with multivalent metal salts.