Polyamides are polymers, which contain recurring amide groups as essential parts of the main polymer chains. Polyamides were the first synthetic polymer developed through research by Wallace Carothers at DuPont laboratories. Naturally occurring polyamides include the protein fibers, e.g., silk and wool fibers. Synthetic polyamide fibers form one of the most important of all classes of textile fiber, which we know today as nylon fiber. Nylon is one of the most common polymers used as a textile fiber.

Besides, Nylon is now known by a more generic name, polyamide, because it is made out of amide-based chemicals. Polyamides are available in many forms, including compliant textiles and rigid, durable resistant materials. In textiles, there are several forms of nylon depending upon chemical synthesis such as nylon 4, 6, 6.6, 6.10, 6.12, 8, 10 and 11 types. The most common nylon are 6 and 6.6 types. Nylon 6 (nylon Z type) and nylon 66 (nylon XY type) are the two most manufactured polyamides, which are commonly used in a wide range of applications from apparels, ropes, carpets, tyre cords to technical textile applications.

Microscopic View of Polyamide Fiber

Properties of Polyamide Fiber

The physical and mechanical properties of polyamide fibers depend on their peculiar molecular structure. These fibers exhibit a great breaking length (40–50 km), high elasticity (complete recovery amounts to 35–40% of the total elongation); the recovery of nylon 66 is equal to 100% after stretching it by approximately 8%. The high abrasion resistance of polyamide fibers is an extremely valuable property in practical textile use. The abrasion resistance of polyamide fibers excels that of natural and other man-made synthetic fibers. The behavior of polyamide fibers in water is somewhat specific and distinctive. Swelling of polyamide fibers in water is not considerable and their strength in the wet state is very slightly reduced (by about 5–10%). At a relative humidity of 65%, these fibers absorb 3.5–4% of moisture content. This is probably due to the low content of hydrophilic chemical groups. Polyamides belong to thermoplastic polymers and melt without decomposition: nylon 6 at 215°C, nylon 66 at 255°C, nylon 7 at 225°C and nylon 11 at 186–187°C. As compared with nylon 6, nylon 66 melts at a considerably higher temperature, which is due to its greater crystallinity and to the larger number of hydrogen bonds between amide chemical groups.

Common properties of polyamide fiber are given below:

• Absorbency: Polyamide is not absorbent, and most of the moisture remains on the surface of the fabric material. The material is generally smooth, so it dries quickly as the water either runs off easily or stays on the surface for the air to evaporate it naturally.
• Resilience: It possesses excellent elasticity and resilience. In spun and knitted polyamide products, however, resilience and elasticity are reduced slightly.
• Strength: Polyamide is one of the strongest fibers (aramid and glass are stronger, though), and it does not deteriorate with time or usage.
• Draping: It has excellent draping qualities regardless of the weight of the textile fabric.
• Insulating: Polyamide is warm and often used in outdoor clothing and apparel.
• Abrasion: Because it has high abrasion resistance, it can withstand excessive rubbing, wringing and scraping without breaking or any loss of strength or durability.
• Lightweight: The degree of its lightness varies based upon the denier of the fiber but it is still considered to be lightweight and comfortable.
• Resistance: Polyamide is resistant to most chemicals, mildew, perspiration and insect damage.
• Susceptible: Polyamide will melt if an iron is too hot; therefore, the irons should be set on their lowest temperature settings. Cold, concentrated solutions of mineral acids, such as hydrochloric, sulphuric and nitric acids, can decompose polyamide. The low absorption rate of polyamides can be problematic because it can make wearers feel clammy in warm, humid environments. Also of note: white nylon can yellow in sunlight exposure.