Chemistry Of Cmc

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. 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.
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01

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.
02

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.
03

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.
04

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.

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