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Sodium Carboxymethyl Cellulose (Na-CMC) is a water-soluble anionic linear polymer derived from cellulose, the most abundant natural polysaccharide.
It is produced through the chemical modification of cellulose with chloroacetic acid in the presence of an alkali, leading to the substitution of hydroxyl groups with carboxymethyl groups.
The resulting compound is a sodium salt of carboxymethyl cellulose.
Na-CMC is widely used in various industries such as food, pharmaceuticals, cosmetics, oil drilling, detergents, and paper due to its thickening, stabilizing, and film-forming properties.
CAS Number: 9004-32-4
Synonyms:
CMC-Na,Sodium cellulose glycolate,Cellulose gum,Sodium salt of carboxymethyl cellulose
Sodium cellulose carboxymethyl ether
Historical Development
The development of sodium carboxymethyl cellulose dates back to the early 20th century, when cellulose derivatives began to gain industrial importance. I
n 1918, Dreyfus patented a process for producing cellulose ethers. Commercial production of Na-CMC started in the 1940s, and its applications expanded rapidly due to its versatility and biodegradability compared to synthetic polymers.
Today, Na-CMC is among the most widely used cellulose derivatives worldwide.
Importance
Na-CMC plays a crucial role in multiple sectors because of its ability to modify the rheological properties of aqueous systems, provide stability to emulsions and suspensions, and improve texture and consistency.
Its biocompatibility and non-toxic nature make it a preferred polymer for food and pharmaceutical formulations.
Chemical and Physical Properties
Chemical Formula and Structure
Empirical Formula: C₆H₇O₂(OH)₂OCH₂COONa
Molecular Weight: Variable (depending on the degree of polymerization and substitution, typically 90,000–700,000 g/mol)
Functional Groups: Carboxymethyl (-CH₂COONa), hydroxyl (-OH)
Na-CMC consists of β-D-glucose units linked by β-(1→4)-glycosidic bonds.
The carboxymethyl groups replace some of the hydroxyl groups in the cellulose chain, imparting solubility and anionic character to the polymer.
Degree of Substitution (DS)
The degree of substitution (DS) refers to the average number of hydroxyl groups substituted per anhydroglucose unit.
It typically ranges between 0.4 and 1.4 for industrial Na-CMC. DS determines solubility, viscosity, and performance in various applications.
Physical Properties
Appearance: White to off-white powder or granules
Solubility: Soluble in cold and hot water; insoluble in organic solvents such as ethanol, acetone, and ether
pH (1% solution): 6.0–8.5
Viscosity (1% solution, 25°C): 10–10,000 mPa·s (depending on molecular weight)
Density: 0.5–0.9 g/cm³
Moisture Content: ≤10%
Thermal Stability: Decomposes above 200°C
Ionic Character
Na-CMC is an anionic polymer due to the presence of carboxylate groups.
This property allows it to interact with cationic species and influence electrostatic stabilization in colloidal systems.
Rheological Behavior
Na-CMC exhibits pseudoplastic (shear-thinning) behavior.
As shear rate increases, viscosity decreases, making it ideal for applications such as coatings and liquid detergents where ease of flow under stress is desirable.
Production and Manufacturing Process
Raw Materials
Cellulose (derived from wood pulp or cotton linters)
Sodium hydroxide (NaOH)
Monochloroacetic acid (CH₂ClCOOH) or its sodium salt
Reaction Steps
Step 1: Alkalization
Cellulose is treated with sodium hydroxide to produce alkali cellulose:
Cellulose+
