Do you know about polyamide fiber among synthetic fibers?

Nylon is the trade name of polyamide fiber, also known as nylon (nylon), which is a large A general name for a type of fiber with CO—NH groups in the molecular chain.

Aliphatic polyester amine is commonly used, and the main varieties are polyamide 6 and polyamide 66. The former is mainly composed of polycaprolactam, and the latter is mainly composed of polyhexamethylene adipamide. Nylon fiber is mainly filament, and a small amount of short fiber is mainly used for blending with cotton, wool or other chemical fibers. Nylon filaments are widely used in deformation processing to make elastic yarns as raw materials for weaving or knitting.

Nylon fiber is generally made by melt spinning, and its cross-section and longitudinal shape are similar to polyester. The density is smaller, 1.14g/cm3.

Nylon fiber has the best moisture absorption capacity among synthetic fibers. Under normal atmospheric conditions, the moisture regain can reach about 4.5%. Some varieties such as nylon fiber 4 up to 7%. It has good dyeing performance and can be dyed with acid dyes, disperse dyes and other dyes.

Nylon fiber is resistant to alkali but not acid. The strength loss after treatment with NaOH (10%) at 95°C for 16 hours is negligible. The amide group is easily acidolyzed, causing the amide bond to break and the degree of polymerization to decrease. Nylon is dissolved in 59% sulfuric acid and hot formic acid and acetic acid. Nylon 6 and nylon 66 were dissolved in 15% and 20% hydrochloric acid respectively.

Nylon fiber has high strength, strong elongation ability and good elasticity. The strength of nylon 6 and nylon 66 fibers is 4~5.3cN/dtex (high-strength polyester can reach more than 7.9cN/dtex), and the elongation is 18%~45%. When the elongation is 3% to 6%, its elastic recovery rate is close to 100%.

The abrasion resistance and fatigue resistance of nylon fiber are the best among common fibers. According to measurements, the abrasion resistance of nylon fiber is 10 times that of cotton fiber. times, 20 times that of wool, and 50 times that of viscose. However, nylon fiber has low modulus, poor wrinkle resistance, poor fabric shape retention, and soft fabric feel.

▲nylon fiber

The glass transition temperature of nylon 6 and nylon 66 is low, about 45~60°C in dry state, and the glass transition temperature in water can drop below room temperature. Nylon has poor heat resistance. The melting point of nylon 6 is 210~215℃, and it decomposes at 300℃. The maximum heat-resistant temperature is 93℃; the melting point of nylon 66 is 255℃, and the maximum heat-resistant temperature is 130℃. The heat resistance is better than nylon 6, but the thermal stability is worse than nylon 6. Nylon can easily melt into small holes when exposed to fire and even burn the human body.

The end groups of polyamide macromolecules are sensitive to light, heat and oxygen, resulting in poor light resistance of nylon. Under long-term exposure to light, It will turn yellow and become brittle, and its strength will decrease. Therefore, nylon fabrics should not be exposed to the sun for long periods of time.

Nylon is the earliest variety of industrially produced synthetic fibers. It is used for general civilian weaving of socks, scarves, clothing, toothbrush bristles, etc., and can also be used to weave carpets; for industrial use, it can be used to make tire cords, ropes, fishnets, etc.; in the national defense industry, it is used to weave parachutes, etc..