Nylon is the general term for a group of synthetic products. These products are made from chemicals derived from coal, petroleum, agricultural by-products, and natural gas. Nylon is one of the most important chemical discoveries. It is a tough elastic substance that can be formed into fibers, bristles, sheets, rods, and tubes. It also can be made in powdered form for use in molding operations.
Nylon fibers and fabrics are noted for their strength, ability to be dyed, low shrinkage, silklike appearance, and resistance to abrasion, mildew, and insects. They are not harmed by most kinds of oil and grease or by household cleaning fluids. Nylon fabrics dry rapidly because nylon absorbs little water.
Uses.
Nylon is used primarily in fibers and fabrics. It was the first synthetic fabric thought to be superior to natural fabrics. Nylon hosiery came on the market in 1939. Since then, many uses have been found for nylon. Carpets, tires, upholstery, dresses, underwear, bathing suits, lace, and parachutes are among the many nylon products. Single threads of nylon are used for fishing line and for bristles in brushes. Surgeons use nylon thread to sew up wounds.
Nylon is also important in the plastics industry. Nylon plastics are noted for their electrical properties, toughness, and resistance to chemicals and wear. They are used in such products as electrical equipment, gears, tubing, and sporting equipment. Plastic nylon body panels have replaced steel on some automobiles.
How nylon is made.
Most nylon produced in the United States is made from two chemical compounds—hexamethylenediamine and adipic acid. Both of these compounds contain carbon and hydrogen. Manufacturers combine the compounds to form hexamethylene-diammonium-adipate, commonly called nylon salt.
Most nylon factories make the substance by placing a solution of nylon salt in a machine called an autoclave. The autoclave heats the solution under pressure. The water is removed, and the molecules that make up each of the compounds combine to form very large molecules. This process of making large molecules from smaller ones is called polymerization. In some factories, the newly formed nylon comes out of the machine as a plastic ribbon. The ribbon is cooled, hardened, and cut into chips that are used in making a variety of nylon products. See Plastics (How plastics are made) .
Nylon fibers are made by forcing molten nylon through tiny holes in a device called a spinneret. In some factories, the molten nylon travels to the spinneret as soon as the polymerization process is completed. Other factories melt nylon chips and pump the melted nylon through the spinneret. The streams of nylon harden into filaments when they strike the air. Then they are wound onto bobbins. From 1 to as many as 2,520 filaments are united into a textile nylon yarn.
Nylon fibers are drawn (stretched) after they cool. Some factories draw nylon after it has been spun into yarn. Others spin and draw the yarn in one operation. Drawing involves unwinding the yarn or filaments from one spool and winding them onto another. The winding rate is four or more times as fast as the unwinding rate. The pull between the spools stretches the fibers. Drawing makes the molecules in each filament fall into parallel lines. This process gives the fiber strength and elasticity. After being drawn, the yarn may be twisted a few turns per yard or per meter as it is wound onto spools. It may also be treated to give it a special texture or bulk.
The size of nylon yarn is measured in denier. A denier is the weight in grams of 9,000 meters (9,843 yards) of the yarn. For example, if 9,000 meters of a nylon yarn weigh 15 grams, the yarn is called 15-denier yarn.
History.
Wallace H. Carothers, a chemist of the DuPont Company, was a leader in the development of nylon. In the late 1920’s, he began to experiment with polymerization. He used a machine called the “molecular still,” which made it possible to make longer molecules than had been made before. Carothers found that many of the fibers made from compounds that he polymerized could be pulled out to several times their original length after they were cooled. This pulling process made the fibers much stronger and more elastic.
But most of the compounds that Carothers had made so far melted at a temperature too low to make them practical for textiles that must be ironed. Then, in 1935, Carothers polymerized hexamethylenediamine and adipic acid. The product was called polyhexamethylene adipamide. This material had a melting point of 482 °F (250 °C), which is satisfactory for textiles. The new fiber was named nylon and was hailed as a great discovery. Later, chemists referred to this original kind of nylon as nylon 66 because both chemicals used in making it had six carbon atoms.
Before nylon could be produced for the public market, scientists had to find a way to make large amounts of hexamethylenediamine and adipic acid. Researchers at DuPont eventually developed a method for making these chemicals from petroleum, natural gas, and agricultural by-products. The production of nylon began in 1938, and the first products made from nylon were introduced in 1939.
Most manufacturers in the United States have continued to produce nylon 66. However, other types of nylon have also been developed. Nylon 6, made from a six-carbon chemical called caprolactam, is a major fiber produced in the United States and numerous other countries.
