CMC (Carboxymethyl Cellulose)

CMC is the most common water soluble cellulose ether, which:

• Suspends solids,
• Control viscosity of the aqueous solutions,
• Forms strong and though films,
• Retain water

CMC is mainly consumed in

• Detergent,
• Wall paper adhesive,
• Paint,
• Textile,
• Pulp and paper,
• Ceramics,
• Oil drilling industries.

CHEMISTRY OF CMC

Cellulose is a water-insoluble polymer of vegetable origin such as wood (eucalyptus, poplar, pine) or cotton.The cellulose molecule consists of  a large number of glucose anhydride rings linked in chain formation.Each  polymer chain consists of 100 to 6000 glucose anhydride units.

n:Degree of Polymerization

(Number of anhydroglucose units)

CMC (Carboxymethyl cellulose) is produced by reaction between alkali cellulose and sodium monocholora acetate under  controlled conditions.

Rcell-OH + NaOH + ClCH2COONa ---  Rcell-O-CH2COONa + NaCl +H2O

The following 4 basic factors determine properties of  CMC Grades

1- DEGREE OF SUBSTITUTION (D.S.) :

The D.S is defined as the avarage number of carboxymethyl (which may also be considered as carboxymethyl ) groups introduced per anhydroglucose unit in the cellulose. For example if 7 carboxymethylated  of 10  anhydroglucose unit ; D.S is 0,7. CMC is commercially available in the DS range from 0,4 to 0,9. D.S  determines some of properties such as solubility, chemical and bacterial resistance , film strength and  reology. D.S should be chosen carefully for  industrial application.
 
2- DEGREE OF POLYMERIZATION(D.P) :

Degree of polymerization or chain length. CMC is derived from cellulose which may have a DP as high as 5000. Generally, cellulose products of high avarage DP have better film strength properties than those of lower average of DP.Also as DP increases, the viscosity of CMC solutions  increases.

3- UNIFORMITY :

Distribution of Carboxymethylated hydroxyl group in the anhyroglucose unit determines uniformity of CMC polymer chain.
A wide variety of processes are used to produce CMC.Uniformity  influenced by processes methods and conditions  is so important for industrial applications. 

4- PURITY:

When producing CMC, a side reaction occcurs to form sodium glycolate and sodium chloride, simultaneously.        
2NaOH+ClCH2COOH----HOCH2CCONa+NaCl+H2O 

CMC is produced depends on reaction conditions and desired D.S. The average purity of techical CMC is about 60-80 percent. High purified CMC (% 98-% 99,5) can produced  to wash techical CMC with alcohol.