Parameters &
Properties
Solid CMC has a white to beige, amorphous appearance and is well soluble in cold and warm water. It acts as thickener, stabiliser, retention aid, suspension aid, water binder, fixing aid etc. All these functions are based on parameters that define the versatile properties of CMC.
Degree of Substitution (DS)
Degree of Polymerisation (DP)
Active Content (AC)
Viscosity
Particle Size
pH & Charge Density
define
/affect
Rheology & thickening
Solubility - dissolution speed
Water retention
Adhesion & binding
Stabilisation properties
Interaction with chemicals/surfaces
Degree of Polymerisation (DP) & Molecular Weight (MW)
The length of one CMC molecule is described by the DP related to the number of average anhydroglucose units (AGU). This is directly proportional to the MW which ranges typically from 20 000 - 1 000 000 g/mol.
Degree of Substitution (DS)
The extend of etherification is measured by its DS value and is defined as average number of carboxymethyl groups per AGU.
The DS correlates with the charge density and provides CMC's water affinity.
Active Content (AC)
The percentage of CMC in the final product is defined by the AC. In technical grades it ranges from 50 - 75 %, in purified grades it is typically defined to be > 98 %.
Viscosity
The most common parameter of CMC is its viscosity level at certain concentration and temperature. Furthermore the viscosity depends on AC, DP, and DS.
Particle Size
The appearance as granule or powder is measured by the product sieve or average particle size distribution. The preference of powder or granule is dependent on the application.
pH and Charge Density
CMC in water acts as a weak base, its pH value in solutions is generally neutral. Excess alkalinity especially in technical grades lead to water pH values in the slight alcalic area.
The charge density is correlated to the amount of negatively charged carboxymethyl groups and is directly derived from the DS.
Rheology & Thickening
CMC is cold water soluble and forms viscous solutions. Their properties are described in rheology as non-Newtonian fluids.
The measured viscosity depends to a high extend on several influences:
CMC is used as thickener where its thixotropycal effects are utilised.
Water Retention & Solubility
CMC is a water loving (hygroscopic) molecule that absorbs water from its environment and binds it. The water retention increases proportionally with the DS level.
CMC is well soluble in water at any temperature and forms transparent to translucent solutions. High DS levels improve the solubility.
CMC is soluble in a quite broad pH range between 3 and 12, keeping stable viscosity levels over pH 5.
Binding, Suspending and Stabilising
CMC is capable of suspending and stabilising sensitive compounds in a colloidal water system due to its charged and polymeric character.
In addition these features also allow CMC to act as a binder and network former in solid materials.
Film Forming & Adhesives
CMC forms thin mechanical- and chemical-resistant films on different surfaces. They can be further plasticised and are resistant to oil, grease, and organic solvents.
This abilty is utilised in many applications where either strong adhesion or dense barriers are needed.
Interactions
CMC shows affinity to a broad range of chemicals and surfaces. It interacts on the one hand because of its negative charge, on the other hand due to its short range intermolecular forces like hydrogen bonds and van der Waals interactions.
The synergy of cationic chemicals as well as the adsorption to different surfaces is extensively used in different industrial applications e.g. strength properties in paper Industry.