Improvement of the dirt suspending power of CMC

Abstract

AbstractThe salts of carboxymethylcellulose (CMC) are used in large quantities to improve the dirt‐suspending power of synthetic detergents and soaps. Hardly any attention has been given to the question as to which properties they should have to obtain the greatest suspending power. They exert their specific influence because they are adsorbed by cellulose fibers from their solutions in water. Theoretical considerations are given, showing that: (1) The degree of substitution (DS) should probably be about 0.5. (2) The substitution should be as uniform as possible. (3) The cellulose chains should be neither too short nor too long. Normally only the average degree of substitution, DS, is determined. The fiber contents, FC, i.e., the percentage of insoluble and partly swollen fibers in 1/20 N NaOH can be taken as a measure of the uniformity of the substitution. Technical products differ greatly in pH and salt contents; therefore the viscosity of solutions of the technical products containing 1% of the cellulose ether, to which 2.5% Na2CO3 and 2.5% NaHCO3 have been added, is taken as a measure of the length of the cellulose chains. The easiest way to obtain uniformly substituted products is by dispersing cellulose and reagents in a suspending liquid, e.g., an alcohol or a hydrocarbon. FC's smaller than 2 to 4% are obtained. Then the dirt‐suspending power was greatest with a DS between 0.48 and 0.53; and a viscosity measured as above with a Hoeppler standard viscometer between 11 and 29 c.p.s. The substitution in general is much less uniform when CMC is prepared according to the customary method by mixing cellulose, NaOH, and ClCH2COONa or ClCH2COOH and a little water. Then the results were best with an average DS between 0.51 and 0.60, and an FC between 6 and 16%, said viscosity being 20 to 30 c.p.s.