Most CMC problems in production come from how the solution behaves, not from the powder. These are the characteristics that matter when you dissolve and use CMC.
Viscosity and concentration
Viscosity rises steeply with concentration: doubling the concentration can raise viscosity several times. That is why grades are specified at a stated concentration (1% or 2%) and temperature (usually 25 °C), and why results at different concentrations cannot be compared directly.
Shear thinning and thixotropy
CMC solutions are pseudoplastic: viscosity drops under stirring, pumping or spreading and recovers at rest. Lower-DS grades can also be thixotropic, with a slow recovery that gives a gel-like structure at rest.
Temperature
Viscosity falls as temperature rises and returns on cooling, as long as the solution is not held hot for long. CMC does not gel on heating, unlike MC and HPMC. Prolonged heating, especially at low or high pH, slowly shortens the chains and lowers viscosity permanently.
pH
| pH range | Behaviour |
|---|---|
| About 7–9 | Highest, most stable viscosity |
| About 4–7 | Slightly lower viscosity; high-DS grades stay stable |
| Below about 3 | Free acid form may precipitate |
| Above about 10 | Gradual viscosity loss over time |
Salts
Monovalent salts such as sodium chloride screen the charges on the chain and lower viscosity. Divalent ions (calcium, magnesium) can cause haze or gels, and trivalent ions (aluminium, iron) can precipitate CMC. Higher-DS grades tolerate salts better, which is why polyanionic cellulose (PAC) is used in salt muds.
Storage of solutions
CMC is biodegradable, so solutions can lose viscosity when microbes grow. Prepare solutions fresh or add a preservative if they are stored for more than a day or two. Keep the powder dry; it absorbs moisture from humid air.
FAQ
Why did my CMC solution lose viscosity overnight?
Most often microbial attack or contact with an oxidiser. Use clean water, prepare fresh solutions or add a preservative.
How do I avoid lumps when dissolving CMC?
Add the powder slowly into the vortex of well-stirred water, or pre-mix it with sugar, salt or another dry ingredient, or wet it first with alcohol or glycerol.
