Nylon
History of Nylon Fiber
The inventor of the method for producing nylon fiber was Wallace H. Carothers in 1928, a professor who had taught at Harvard University. He was interested in polymer theory involving molecules linked together in long chains, and found that a compound formed between dibasic acid and polyhydric alcohol, when heated, combines to form polyester with large molecules linked together that can form fibers. However, the fiber discovered at that time was not yet in a condition suitable for use as textile fiber, so it was improved until it could be produced as a textile in 1939.
The first type of nylon successfully produced for use was Nylon 6.6, sold as nylon stockings and it became widely popular; other types of nylon were also produced, such as Nylon 6,10, Nylon 6, and so on.
Nylon refers to the general name for fibers synthesized from large amide molecules linked together in long chains. These amide groups must combine into a single molecule and must have properties that allow them to be formed into fiber. Therefore, nylon is not the name of one specific fiber, but rather a collective name for materials synthesized from amide compounds in general.
Production of Nylon Fiber
The basic raw materials for producing nylon fiber are coal, air, and water. These are combined in a high-pressure autoclave, producing a reaction that forms adipic acid and hexamethylenediamine. Each substance is separated out and then combined in equal proportions, causing a reaction that forms nylon salt, which links together into long chains and large molecules. The reaction takes place in a pressure autoclave that rotates, with heat and pressure controlled until the substances combine into sufficiently large molecules. This melting process is called Melt Spinning.
The nylon fiber produced is very glossy and translucent. To make it into fabric, the fiber must be made opaque by adding titanium dioxide to the liquid nylon solution, which is then extruded into a flat, ribbon-like strand. Once dried and hardened, it is ground into powder, then heated until it melts and extruded into fiber. To prevent nylon from losing its properties, oxygen gas must be completely removed from the melting tank during the melting process.
The nylon fiber obtained at this stage has low tenacity, only about 1.0-1.3 grams per denier, and the fiber is still opaque, so it must go through a stretching process called cold drawn. Stretching it by 400% makes the fiber clear, increases its tenacity to 5.8 grams per denier, and gives it 17% elongation.
Nylon is a fiber with long molecules, a straight chain of polyamide. A polymer that can be made into fiber must have an average molecular weight of 12,000-20,000; if lower than 6,000 it cannot be made into fiber because the fiber would be brittle, but if higher than 20,000 it would melt, making it unsuitable for use as fiber.
Properties of Nylon Fabric (Nylon 6.6, Nylon 6)
Physical Properties of the Fiber
1. Shape
Nylon fiber is smooth and glossy. Viewed in cross-section it is round, except for Nylon 6.6, which has the trade name Antron and a rounded triangular shape. Viewed lengthwise, it appears as a smooth, even strand throughout its length, is fairly clear, and has small dots scattered throughout.
2. Tenacity
This varies depending on the intended use of production. For industrial applications requiring very high tenacity, elongation is reduced; for example, a tenacity of 8.8 grams per denier gives 18% elongation, while a tenacity of 4.3 grams per denier gives 45% elongation. Tenacity when wet decreases slightly, to about 80-90% of the dry tenacity, which is a good property.
3. Elasticity and Elongation
Nylon is a fiber with very good elasticity; for example, if stretched 8%, it will recover 100%, and if stretched 16%, it will recover 91%. Nylon can stretch up to as much as 22% before reaching the breaking point. This property is useful in applications requiring elasticity, such as industrial uses and clothing that needs to fit the body closely.
4. Moisture Absorption
Nylon absorbs very little moisture compared to natural fibers, but among synthetic fibers, nylon absorbs moisture the best. Under standard conditions, Nylon 6.6 absorbs 4.2-4.5% moisture, while Nylon 6 absorbs 3.5-5.0% moisture.
5. Heat Resistance
Nylon fiber is classified as a Thermoplastic fiber (melts before burning). Nylon 6.6 melts at a temperature of 250C, while Nylon 6 melts at approximately 210C.
Chemical Properties of the Fiber
Nylon fiber withstands alkaline substances better than acids. Mineral acids such as HCL, HNO3, and H2SO2 can dissolve nylon, and certain organic solvents such as phenol, meta-cresol, and formic acid can dissolve the fiber as well.
Dry-cleaning fluids or stain-removing solvents used on fabric will not damage nylon fabric.
Biological Properties of the Fiber
Nylon is fairly resistant to mold and bacteria. If nylon fabric is finished with starch sizing, it can become susceptible to mold growth. Insects and moths do not eat nylon fabric, but if it is folded and stored for a long time, ants or insects may chew along the fold lines.
Nylon Fiber and Its Uses
Nylon fabric has good properties for making many kinds of clothing and accessories that are durable and do not tear easily. It is often blended with other fibers to enhance its properties, both in terms of dimensional and shape stability and abrasion resistance. However, nylon has low moisture absorption, so if it is to be used for clothing, fabric with a looser, less tight weave or knit should be chosen to allow air and body moisture to evaporate easily, so it does not feel stuffy or too hot when worn. Knitted nylon fabric is durable, has good elasticity, holds its shape well, and allows for comfortable body movement, making it suitable for sportswear. Nylon fabric woven with a tight, smooth construction is suitable for making waterproof umbrella fabric, and if finished to prevent water penetration, it can be used very effectively. Nylon fiber is also suitable for making carpets, upholstery, and rope. Nylon fiber is easy to care for, whether made into fabric or other items; it can be used with soap, detergent, and bleach, and washed using ordinary wet-washing methods. However, nylon fabric should not be left in sunlight for long periods, as the color fades easily and the fabric loses strength.
Today, nylon fiber is produced in many types to meet the varied needs of users, such as:
Nylon 4 is produced by Polymerizing 2 pyrrolidone, adding properties similar to natural fibers, namely good moisture absorption and higher heat resistance than Nylon 6.
Nylon 5 Polyvalerolactam has properties similar to Nylon 6.6 and is produced in America.
Nylon 7 polyheptanoamide, with the trade name Enant, has properties similar to Nylon 6.6 and Nylon 6, but has higher heat resistance and a higher melting point, though it absorbs less moisture; it is produced in Russia.
Nylon 6 T or Nomex has a high melting point (370C) and greater density than Nylon 6 and Nylon 6.6, but has lower elongation.
Qiana nylon is produced in small quantities and is expensive, with a luxurious fabric feel and texture similar to silk. It resists wrinkling very well, dyes and prints beautifully, and its colors do not fade. It is produced into the finest knitting yarns.
Nylon 6, 10 is often used to make carpets, fur-like fabrics, or fabrics requiring a special texture.
Nylon 11 named Rilsan is similar to Nylon 6 and Nylon 6, 6. It absorbs little moisture, melts at a low temperature, has low density, and is often produced as soft, fluffy yarn.
Nylon 22 has the property of not accumulating static electricity, is glossy like silk, has very good elasticity, does not soil easily, and white fabric retains its whiteness excellently.
Within the polyamide fiber group, there is also a newly discovered fiber produced by the DuPont company in 1963, under the name Nomex nylon. Later, in 1973, another type was produced called Kevlar. Both of these are known by the generic name aramid. Aramid fiber has several properties superior to nylon fiber: it does not burn, is very strong and durable, and the fabric is relatively lightweight, with a specific gravity of about 1.38-1.44 grams per cubic centimeter and moisture absorption of 4.5-7%. The fiber resists acids, alkalis, and organic solvents well, but is not resistant to sunlight. Aramid fiber is used to make clothing and equipment for astronauts, as well as curtains, pillows, bed sheets, rope, carpets, heat-resistant pads, and equipment materials requiring heat resistance.