Sodium carboxymethyl cellulose (CMC, sodium CMC, CAS 9004-32-4) is a water-soluble cellulose ether supplied here as a fine white to cream powder at 99.5% minimum purity, with a degree of substitution of 0.7-0.9 and a 1% solution viscosity of 2500-3000 mPa.s. It is the general-purpose grade used for thickening, stabilising, suspending and binding across food, detergent, oilfield, paper, textile and battery applications.
Specification
| Parameter | Limit | Why it matters |
|---|---|---|
| Appearance | Fine, white to cream powder | Colour deviation suggests residual salts or inconsistent washing |
| Purity | 99.5% min | Active content – the balance is moisture, sodium chloride and sodium glycolate from the etherification |
| Viscosity (1% solution, 25 deg C, dry basis) | 2500 – 3000 mPa.s | A mid-to-high viscosity grade. The figure is only meaningful with the concentration, temperature and basis stated together |
| pH (1% solution, 25 deg C) | 6.0 – 8.5 | Outside this window the solution can gel, precipitate or corrode; also indicates residual alkali |
| Degree of substitution (DS) | 0.7 – 0.9 | The average number of carboxymethyl groups per anhydroglucose unit – the parameter that governs solubility, salt tolerance and compatibility |
| Moisture | 8% max | CMC is hygroscopic; excess moisture causes caking and viscosity drift |
| Heavy metals | 20 ppm max | Food and pharmaceutical compliance gate |
| Arsenic | 3.0 ppm max | Elemental impurity |
| Lead | 2.0 ppm max | Elemental impurity |
| Cadmium | 1.0 ppm max | Elemental impurity |
| Mercury | 1.0 ppm max | Elemental impurity |
| Coliforms | 0 cfu/g | Microbiological limit for food-grade use |
| E. coli | 0 cfu/g | As above |
| Yeast and mould | 100 cfu/g max | As above |
| Salmonella | 0 cfu/g | As above |
What the two defining numbers mean
| Parameter | What it controls | Practical consequence |
|---|---|---|
| Degree of substitution 0.7-0.9 | How many carboxymethyl groups sit on each anhydroglucose unit, and therefore how much negative charge and how much water-binding capacity the molecule carries | Below about 0.4 the polymer is not fully water-soluble; 0.7-0.9 is the general-purpose water-soluble band; above about 1.0 salt tolerance and acid stability improve markedly |
| Viscosity 2500-3000 mPa.s at 1%, 25 deg C | Chain length combined with DS, measured under defined conditions | Sets the dose rate and the pumpability. A 5 deg C change in temperature can move the reading by tens of percent, so the test conditions are part of the specification |
Behaviour in use
- Dissolves in cold water, not in hot. The standard technique is to disperse the powder in cold water with agitation before it can lump, or to dry-blend it with other powders first. Hot water causes the particles to swell and skin over without dissolving.
- Pseudoplastic flow. Solutions thin under shear and thicken again at rest, which is useful for suspending solids but has to be allowed for when sizing pumps and mixers.
- Anionic. CMC carries a negative charge, so it is incompatible with cationic surfactants and cationic polymers – the two precipitate each other. This matters in detergent and water-treatment formulations.
- Electrolyte sensitivity. Salt tolerance depends on DS; a 0.7-0.9 grade tolerates modest electrolyte levels, and higher-DS grades are needed in hard or saline systems.
- Film forming and binding. Used as a binder and film former in tableting, ceramics, coatings and electrodes.
Applications
| Sector | Function | Detail |
|---|---|---|
| Food | Thickener, stabiliser, suspending agent (E466) | Ice cream and frozen desserts, bakery, sauces, beverages, dietary products |
| Detergents | Anti-redeposition agent | Keeps soil suspended in the wash liquor so it does not settle back on the fabric |
| Oil and gas drilling | Fluid-loss control and viscosity modification | Drilling muds and workover fluids |
| Paper and board | Surface sizing and coating binder | Improves surface strength and printability |
| Textiles | Sizing agent | Warp sizing, removable by washing |
| Batteries | Electrode binder | Commonly paired with SBR in anode formulations |
| Pharmaceutical and personal care | Suspending, binding, thickening | Oral suspensions, tablets, toothpaste |
| Ceramics and construction | Green strength and water retention | Extrusion aids, tile adhesives |
Packaging, storage and documentation
| Item | Detail |
|---|---|
| Packaging | 25 kg paper sacks with PE liner; bulk bags on request |
| Storage | Cool, dry, sealed. CMC is hygroscopic: a damp store causes caking and a viscosity reading that no longer matches the certificate |
| Documentation | Batch COA (purity, viscosity, DS, pH, moisture, heavy metals, microbiology) plus SDS |
| Grade statement | Food-grade (E466) compliance on request; confirm the specific market’s requirements before labelling |
For the technical background and how the parameters interact, see the sodium CMC technical guide, and for the parameter that decides most formulation problems, the degree of substitution explained.
