Nylon 6 and Nylon 66

OVERVIEW

The term nylon is used to describe a family of organic polymers called the polyamides that contain the amide (-CONH) group. The members of the family are distinguished from each other by a numbering system indicating the chemical composition of the polymer molecule. The two most important nylons are nylon 6 and nylon 66 which, between them, account for nearly all of the nylon produced in the United States. Other nylons that are produced in much smaller amounts include nylon 11, nylon 12, nylon 46, and nylon 612.

The polyamides are thermoplastic polymers. The term "thermoplastic" means that the polymer can be repeatedly melted and hardened by alternate heating and cooling. By contrast, certain other types of polymers, known as thermosetting plastics, can not be re-melted once they have hardened.

KEY FACTS

FORMULA:

Nylon 6: -[-CO(CH₂)₅NH-]-_n; Nylon 66: -[-CO(CH₂)₄CO-NH(CH₂)₆NH-]-_n

ELEMENTS:

Carbon, hydrogen, oxygen, nitrogen

COMPOUND TYPE:

Polymer (organic)

STATE:

Solid

MOLECULAR WEIGHT:

Very large

MELTING POINT:

Nylon 6: 223°C (433°F); Nylon 66: 265°C (509°C)

BOILING POINT:

Decomposes above melting point

SOLUBILITY:

Insoluble in water and most organic solvents; soluble in strong acids

Nylon was invented in 1935 by Wallace Carothers (1896–1937), an employee of the DuPont Chemical Corporation at the time. Carothers was searching for a synthetic substitute of silk because natural supplies were insufficient to meet growing demands for that fiber. Using coal, water, and air as raw materials, Carothers developed a synthetic product that could be stretched into a fiber and that got stronger and silkier as it was stretched. Nylon first appeared in commercial products in 1938, first in toothbrushes with nylon bristles, and later in women's stockings. During World War II, the U.S. military found a number of uses for the compound, especially the manufacture of parachutes. Today, nylon is used in a very wide array of products.

HOW IT IS MADE

Nylon 66 is still made commercially by the procedure originally developed by Carothers in 1935. The process is initiated with the reaction between adipic acid (HOOC(CH₂)₄COOH) and hexamethylenediamine (H₂N(CH₂)6NH₂), which results in the formation of the monomer (-[-CO(CH₂)_4-CONHCH₂)₆-]-) from which the polymer develops. That monomer has active groups at both ends of the molecule, allowing it to react with others of its kind to form long chains that make up the polymer. Methods for preparing the other polyamides can differ quite significantly from the Carothers procedure. For example, nylon 6 is made by the polymerization of aminocaproic acid (H₂N(CH₂)₅COOH). The polymer formed in this reaction also has blocks of methylene (-CH₂) groups joined by amide (CONH) groups, although the specific structure is somewhat different than it is for nylon 66.

COMMON USES AND POTENTIAL HAZARDS

Production of nylon 6 and nylon 66 for 2006 in the United States was estimated to be about 1.6 million kilograms (3.5 mil-lion pounds). About three-quarters of that production is used for the manufacture of fibers used in industrial operations and for textiles. Fabrics made from nylon are strong, resistant to abrasion, resistant to alkaline materials, and capable of taking most dyes. The clothing industry uses nylon fibers to make a variety of fabric types, including fleece, velvet, satin, taffeta, lace, and seersucker. Nylon clothing is lightweight, silky, attractive and smooth. Since it does not absorb moisture or odors readily, it is in demand for the production of athletic clothing. Nylon is also used in the manufacture of home textiles, such as furniture covering. Nylon rope is twice as strong as rope made from natural fibers such as hemp and weighs less.

Interesting Facts

• The term nylon has never been trademarked. The name itself has no specific meaning. The -on suffix was chosen, however, to suggest a comparison with other fibers, such as cotton and rayon.
• DuPont originally thought of calling nylon No-Run. They abandoned that plan, however, when they realized that nylon stockings do, in fact, run.

About 15 to 20 percent of all nylon produced in the United States goes to the manufacture of molded plastics, such as those used in automobile and truck parts, housing for electrical devices, and consumer articles. The next largest application for nylon is in tubing, pipes, films, and coatings. Some specific articles made from nylon 6 and nylon 66 include the following:

• Reinforcing cord for tires;
• Fuel tanks for automobiles;
• Tennis rackets;
• Fishing nets and lines;
• Towlines for gliders;
• Women's stockings;
• Sutures for surgical procedures;

• Bristles for toothbrushes, hairbrushes, and paint brushes;
• Parachutes;
• Pen tips; and
• Artificial turf for athletic fields.

One of the most important uses for nylon historically was the manufacture of women's stockings. Silk stockings were an essential item of a well-dressed woman's ensemble in the 1920s and 1930s. They made a woman's legs look smooth and sleek, and they were the ideal accompaniment to short skirts and high heels. In the 1920s, women spent millions of dollars on silk stockings. The DuPont company began the search for a silk substitute because it hoped to develop a product that could be used to make stockings that looked and felt as if they were made of silk, but that cost less. Nylon stockings became commercially available in 1939, and by 1941, some sixty million pairs had been sold. Both nylon and silk stockings were difficult to get during World War II because the fibers were being used for military applications. As soon as the war was over, however, women began buying nylon stockings in large quantities once again.

Words to Know

POLYAMIDE

An organic polymer that contains the amide (-CONH) group.

POLYMER

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

THERMOPLASTIC

Capable of being heated so that it can be reshaped, then cooled so that it hardens.

THERMOSETTING

Capable of being heated so that it hardens.

FOR FURTHER INFORMATION

Hermes, Matthew E. Enough for One Lifetime: Wallace Carothers, Inventor of Nylon. Philadelphia: Chemical Heritage Foundation, 1996.

"Nylons (Polyamides)." MatWeb. http://www.matweb.com/reference/nylon.asp (accessed on October 24, 2005).

"Nylon Stockings." The Great Idea Finder. http://www.ideafinder.com/history/inventions/story062.htm (accessed on October 24, 2005).

"Polyamide 6-Nylon 6-PA 6." Azom.com. http://www.azom.com/details.asp?ArticleID=442 (accessed on October 24, 2005).

"Polyamides." Chemguide. http://www.chemguide.co.uk/organicprops/amides/polyamides.html (accessed on October 24, 2005).