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What is Carboxymethylcellulose (CMC)?

10/25/2013 9:27:02 AM | by Anonymous


Carboxymethylcellulose (CMC) also known as cellulose gum is a type of cellulose derivative with carboxymethyl groups. They are bounded to some of the hydroxyl groups of the glucopyranose monomers that makes up the cellulose backbone. It is oftenly used as a sodium salt. It is synthesized by the catalysed reaction of cellulose. The polar carboxyl groups render the cellulose soluble and are chemically reactive.


CMC’s functional properties are dependent on the degree of substitution of the cellulose structure as well as the chain length of the cellulose back bone structure together with the degree of clustering of the carboxymethyl substituents.


CMC is used for a variety of uses. It is used in food science as a viscosity thickener or modifier as well as to stabilize emulsions in various products including ice cream. Being a food additive, it contains the E number, E466. On top of that, it is also a constituent of many non food products typically, laxative diet pills, detergents, personal lubricants, toothpaste, water based paints, various paper products and textile sizing.


It is always primarily used due to the fact that it has high viscosity, non toxic and is considered to be hypoallergic as the major source fiber is either cotton linter or softwood pulp. CMC is also used extensively in reduced fat food products and gluten free products. It is also used as a soil suspension polymer designed to deposit onto cotton and other cellulosic fabrics in laundry detergents. They also create a negative charged barrier to soils in the wash solution. Cmc can also be used as a lubricant in eye drops.


After the initial reaction, the resultant mixture would produce about 40% salts inclusive of sodium glycolate and sodium chloride as well as 60% CMC. The product is the technical CMC used in detergents. A more elaborate purification process is used to remove the salts to produce the pure CMC that is used for toothpaste, food and pharmaceutical applications.


Carboxymethylcellulose is also used in pharmaceuticals as a thickening agent. In the oil drilling industry, it is used as an ingredient of drilling mud where it acts as a viscosity modifier and water retention agent. Insoluble micro granular CMC is used as a cation exchange resin for purification of proteins. The level of derivatization is much lower so the solubility properties are retained while adding sufficient charged carboxylate groups to bind the positively charged proteins.


On top of that, CMC is also used in ice packs to form a mixture that results in a lower freezing point. Therefore, it has a cooler capacity than ice. Aqueous solutions of CMC have also been used to disperse carbon nanotubes. The long CMC molecules are thought to be wrapped around the nanotubes. This allows then to be dispersed in water. It can also be used as fixatives or adhesives.


Last but not least, Carboxymethylcellulose is used to achieve cold stability in wine. This innovation helps to save megawatts of electricity used to chill wine in warm climates. It is more stable and very effective in inhibiting tartrate precipitation. It has also been reported that KHT crystals grow slower and changes their morphology in the presence of CMC. Their shape also becomes flatter because they lose 2 of their 7 faces that change their dimension.


Carboxymethylcellulose molecules are negatively charged to interact with the electropositive surface of the crystals at which the potassium ions are accumulated. The slower growth of the crystals and modification are caused by the competition happening between the molecules and the bitartrate ions for binding to the KHT crystals.

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