CMC Makes Cleaner Cotton

Winston B. Strickland.

Wherever washday Monday is a tradition and cleanliness is a virtue, news will be welcomed of a simple washtub treatment for cotton goods that speeds soil removal in the tub and leaves a soil-resistant finish.

Because resistance to soiling is so important in many uses of cotton, the Agricultural Research Administration of the Department of Agriculture accepted the responsibility and authorized the expenditure of funds in a Research and Marketing contract research project at the Institute of Textile Technology, Charlottesville, Va., to study the problem.

The treatment developed there consists merely of adding to the water each time the goods are washed a solution of a commercially available compound, carboxymethyl cellulose, known as CMC. The solution coats the fibers and yarns in the fabric with a film much like that caused by starch. In ordinary amounts, CMC does not noticeably stiffen the cloth, although when it is used in larger amounts it gives stiffening if desired. The film protects the fabrics in use from a great deal of the dirt and grease that would otherwise be deposited. During the next washing it dissolves and acts to suspend the soil particles in the soapy water so that they cannot be redeposited. Thus it acts as a detergent aid. The treatment has no adverse effects on the wearing quality of the fabric.

Also, CMC, by almost completely removing dirt, eliminates the need of bleaching in home laundering and reduces the amount of bleach required in commercial laundries. Since the usual chlorine bleach shortens the service life of cotton materials, CMC-rinsed articles give extra wear.

White clothes rinsed in CMC keep their whiteness and colored goods come out brighter and do not "bleed" and discolor white things in the wash.

Some CMC-rinsed materials can be ironed in less time. CMC also washes out underarm perspiration odors, increases resistance to creasing and mussing, and removes iron stains.

CMC has long been sold on the wholesale market. Several detergents on the market contain a small amount of CMC (0.5 percent) as a detergent aid. During the Second World War, the inclusion of CMC in soap powder was mandatory in some parts of Europe, as a means of conserving fats. CMC is also regularly used as a thickener for pastes in textile printing, as a sizing agent, and in similar uses.

In their preliminary investigations, scientists at the Institute of Textile Technology learned that soil particles are trapped in the irregularities of the fiber surfaces and between the fibers and yarns in cotton fabrics. They discovered this by examining, under the microscope, short-length cotton fibers soiled with lampblack. They found that when a small amount of dirt or grease was already attached, a second deposit adhered more easily, because there tended to be a build-up of soil particles at vulnerable points.

CMC smooths the fiber surface by coating over the irregularities to insulate or block them so that soil particles, while the article is in use, cannot find a lodging place. It suspends the soil particles in the wash water, so that they cannot, after removal, be redeposited on the cloth.

TO TEST its effectiveness, the treatment was applied to strips of purified and bleached cotton cloth, and the strips were immersed in a CMC solution, passed through squeeze rolls, and dried. The samples were then soiled artificially by dipping into a dispersion of carbon black, and the amount of carbon black needed in the bath to soil the sample was measured. The determination was made by measurements of the whiteness judged by a reflectance method. A reflectometer is an instrument in which a beam of light is directed upon a material and the amount of light it reflects measured. Magnesium oxide has a high degree of whiteness its reflectance reading is 100 percent and it was selected as the standard in the reflectance tests. The untreated bleached cloth, when compared to magnesium oxide, has a reflectance reading of about 85 percent. Samples treated with only 0.5 to 1 percent CMC required almost three times as much carbon black as untreated cloth for both to show a reflectance of 25 percent.

A very dilute solution of CMC can be added to the wash during the last rinse to give an antisoil finish that will remain on the article until the next wash to help in soil removal. A much stronger solution can be applied as a sizing instead of starch.

CMC comes in powder form, and before it is added to the water in the machine it must be mixed with water, with the help, say, of an ordinary kitchen food mixer, or by adding boiling water to the proper amount of CMC and allowing the mixture to continue boiling for 5 to 10 minutes.

For convenience, a large quantity of a stock solution can be mixed and kept for several days' use by heating a gallon of water almost to the boil and stirring in 7 ounces of technical grade CMC powder as rapidly as possible. Stirring is continued for 5 to 10 minutes longer, or until a uniform, smooth, sirupy solution is obtained. This makes a 4-percent concentration of pure CMC.

To impart the nonstiffening soil-resistant finish in the home type of washing machine of average capacity (8 gallons), 3 cupfuls of the stock solution is sufficient. In use as a size, good results will be obtained with 2 to 4 cupfuls of the stock solution.

Mrs. W. L. R., who supervises the laundering of articles used in tourist cabins, tried out CMC in the suds operation she used 2 cups of the stock solution with one-half cup of her regular soap, in place of the 1 1/2 cups which she generally used. She found that pillowcases, sheets, bath towels, wash-rags, and aprons, even though some had become quite gray, when rinsed in CMC all cleared to a beautiful white, without either bleach or alkali.

Two commercial laundries, after several uses of 1 quart of the 4-percent stock solution for each 100 pounds` of clothes, added to the wash wheel after most of the sour-blue water had been emptied, reported a definite increase in the visible whiteness of the washed articles.

Nevertheless, the applications of CMC require further research: What is the place of alkali in detergency when CMC is added to the detergent? What can be learned about the action of CMC in causing clothes to resist the deposition of iron oxide from contaminated water and the effect of the hardness of water on the use of CMC? How does the CMC treatment affect dyeing properties of cotton? Can CMC be modified by other chemicals to control the film-forming properties in such a way as to make the treatment perform as a superior finish? What is the proper ratio of CMC to the usual commercial soaps or to synthetic detergents to obtain the highest detergency efficiency?

WINSTON B. STRICKLAND, a former member of the staff of the Bureau of Agricultural and Industrial Chemistry, is technical sales representative of a commercial firm. He lives in Charlotte, N. C.