Polyamide Fibres - manmade artificial fibres

A group of fully synthetic fiber materials, which are manufactured in a melt spinning process. Characteristics: highly elastic, tear and abrasion free, low humidity absorption capability, fast drying, no loss of solidity in a wet condition, crease-free, rot and seawater proof. Application: fine stockings (for example nylon), outer sporting and motorcycle garments (for example Tactel, Cordura), female underclothes (for example Perlon), parachutes. In the middle of the 1930s nylon, a polyamide, was brought to the market by the American chemical company DuPont. It was the first material fully obtained from basic chemical elements. A sure sign for the economic breakthrough of synthetic fine chemical fibers was the triumph of nylon stockings at the beginning of the 1950s. The textile industry concentrated above all on space research and during the years of the Cold War on equipment for soldiers. At the end of this, the industry had to look for new sales markets. During the last ten years a series of new synthetic textiles and techniques for processing textiles has been developed, in which war and space technology has been matched with innovative novelties from design laboratories. A milestone: the active breathing microfibers (such as Gore-Tex).

The two main types of fibre are polyamide 6, usually known as Perlon, and polyamide 6.6, which is generally called Nylon to distinguish it from Perlon. The number or numbers after the word ‘polyamide’ indicate how many carbon atoms there are in each molecule making up the polyamide. The fact that there is only one number in one instance and two in the other shows that polyamide 6 contains only one basic module and polyamide 6.6 contains two, with six carbon atoms in each molecule.

Nylon 6 and 6.6

Polyamide 6 is made from caprolactam, and polyamide 6.6 from hexamethyldiamine and adipic acid. For fibre production, the resulting polyamide has to have the capacity to be spun into filaments, i.e.

• it must have the capacity to be melted without decomposing and to be forced through a jet
• the molten mass must be such that the filaments that are still ductile when formed do not break during cooling. Certain conditions must be met, one of them being a minimum prescribed length for the macromolecule

These nylon polymers form strong, tough, and durable fibers useful in a wide variety of textile applications. The major differences in the fibers are that nylon 6,6 dyes lighter, has a higher melting point, and a slightly harsher hand than nylon 6.

Aramid Fibers

The aramid polyamide fibers are formed from a long chain of synthetic polyamides in which at least 85% of the amide linkages are attached to aromatic rings. These essentially fully aromatic polyamides are characteristically high melting and have excellent property retention at high temperatures and excellent durability. They are unaffected by moisture and most chemicals and are inherently flame retardant. The fibers have high strength and can be used in a number of unique high-strength applications.

Common trade names for aramid fibers include Nomex and Kevlar (duPont). Aramid fibers are extremely strong and heat resistant. Fabrics from the aramids have a high luster with a fair hand and adequate draping properties. The fibers are light yellow unless bleached and exhibit moderate moisture absorption characteristics. The fibers recover readily from stretching and bending deformation and are extremely abrasion resistant. They do tend to pill due to the high strength of the fiber.

Other Polyamides

Several other polyamides have been introduced for use as fibers in specialty applications where certain combinations of properties are desired. The major specialty nylons include Qiana, nylon 4, nylon 11, nylon 6,10, and biconstituent nylon-polyester.

The molten mass is forced through the holes in the spinneret by pressure pumps and metering pumps, after which it is pulled off in the form of filaments. They cool rapidly in the (air) blasting chamber and are then either baled or wound onto bobbins at a constant speed. The macromolecules are still randomly distributed in the filaments, which is why they are stretched so that molecules are more longitudinally oriented. Once they have this orientation, the filaments take on their characteristic physical properties and can be cut to the lengths needed to make the fibres. Then the filaments of staples are prepared to ensure that they retain their processing properties.