Cellulose Xanthate

OVERVIEW

Cellulose xanthate (SELL-you-lohs ZAN-thate) is a compound produced from cellulose in the viscose process for making rayon. The subscript "n" in the chemical formula indicates that many molecules chain together to make up the polymer. In this case, between 200 and 400 C₆H₇O₂ (OH)₂OCS₂Na molecules combine to make a molecule of cellulose xanthate.

KEY FACTS

OTHER NAMES:

Viscose rayon; xanthate rayon

FORMULA:

[C₆H₇O₂(OH)₂ OCS₂Na]_n

ELEMENTS:

Carbon, hydrogen, oxygen, sulfur, sodium

COMPOUND TYPE:

Polymer

STATE:

Solid

MOLECULAR WEIGHT:

Very large (50,000 to 100,000 g/mol)

MELTING POINT:

Not applicable

BOILING POINT:

Not applicable

SOLUBILITY:

Soluble in aqueous caustic solutions

Although rayon is made from a naturally-occurring material, cellulose, it is regarded as a synthetic product. It was the first synthetic fiber made by humans. The method for making rayon was discovered in about 1891 by three English chemists, Charles Frederick Cross (1855–1935), Edward John Bevan (1856–1921), and Clayton Beadle (1868–1917). The discovery occurred while the three chemists were looking for a way of making artificial silk. Although silk is an excellent fiber for making clothes and other materials, it had to be exported from Japan and was, therefore, very expensive.

The first plant for the manufacture of rayon in the United States was built in 1910 by the newly-formed Viscose Corporation of America. Sales of the new product were slow at first, but by 1925, rayon had become more popular than silk. Today, the Cross-Bevan-Beadle method of making rayon is only one of four processes used by the industry to make the fiber.

HOW IT IS MADE

The process to make rayon begins with wood pulp or wood chips, usually from spruce or pine trees. The wood is treated with carbon disulfide (CS₂), which converts cellulose in the wood to cellulose xanthate. The purpose of this step is to change an insoluble material (cellulose) into a soluble material (cellulose xanthate). The cellulose xanthate is then dissolved in sodium hydroxide (NaOH), a strong alkali, forming a thick, viscous solution. The viscosity of the solution is responsible for the name given to this method of making rayon, the viscose process.

Interesting Facts

Rayon was first sold in the United States as "artificial silk." But manufacturers thought the word "artificial" would not appeal to consumers. So they held a contest with a $1,000 prize to choose a better name for the fabric. More than 10,000 names were suggested, but the committee appointed to choose a winner rejected all of the names. Finally, a member of the committee suggested the word rayon, French for "a ray of light."

The cellulose xanthate solution is then allowed to stand for eight to ten hours in a "ripening room." During this period, the cellulose xanthate slowly gives up its carbon disulfide and reverts to cellulose. The end result of these steps is the recovery of cellulose in a form that is easier to work with and from which long fibers can be made. The fibers are produced by forcing cellulose from the viscous solution through plates called spinnerettes with many small holes in them.

COMMON USES AND POTENTIAL HAZARDS

Rayon has many properties that make it a desirable fabric. It has a soft, silky feel that is comfortable to the skin. Its fibers are strong, abrasion resistant, easy to dye, and resistant to bleaches and most chemicals. Electric charges do not collect on the fiber, allowing it to remain static-free and to hang smoothly from the body. Rayon does have some disadvantages. It tends to wrinkle easily, shrinks when it gets wet, and is very flammable. Among the many products made from rayon are the following:

• Clothing, such as suits, dresses, sports shirts, ties, lingerie, and work clothes;
• Domestic textiles, such as upholstery, curtains, drapes, bedspreads, sheets, and blankets; and
• Industrial textiles, such as reinforcing threads in rubber products, such as tires, hoses, and conveyor belts; braided cords; and tapes.

Words to Know

ALKALI

A strong base.

AQUEOUS SOLUTION

A solustion that consists of some material dissolved in water.

CAUSTIC

Strongly basic or alkaline, capable of irritating or corroding living tissue.

POLYMER

A compound consisting of very large molecules made of one or two small repeated units called monomers.

VISCOUS

Syrupy material that flows slowly.

Rayon is very flammable, probably its greatest disadvantage in commercial products. During the late 1940s and early 1950s, a number of accidents were reported in which rayon clothing caught fire, resulting in injury or death to wearers. In response to this problem, the U.S. Congress passed the Flammable Fabrics Act of 1953 (FFA), banning the sale of any fabric (such as rayons) likely to catch fire. Since passage of the FFA, manufacturers who use rayon in their products must treat the fiber in some way to prevent it from catching fire.

FOR FURTHER INFORMATION

"Rayon Fiber (Viscose)." Fibersource. http://www.fibersource.com/f-tutor/rayon.htm (accessed on September 14, 2005).

"Rayon Fibers." Raghavendra R. Hegde, Atul Dahiya, and M. G. Kamath. http://www.engr.utk.edu/mse/pages/Textiles/Rayon%20fibers.htm (accessed on September 14, 2005).

"Rayon Viscose." http://www.swicofil.com/viscose.html (accessed on September 14, 2005).

See AlsoCellulose, Cellulose Nitrate