Classification and properties of nylon fibers
Nylon (Nylon) fibers are known as polyamide (polyamide) fibers. They were originally the trade name of polyadipic adipic diamine produced by DuPont Company, which is commonly known as Nylon 66. Polyamide fiber is the first commercial synthetic fiber product of synthetic polymer. It was invented by Caa rothers of DuPont Company in 1937, which opened the first page of synthetic fiber. It is still the representative of polyamide fiber.
Polyamide can be synthesized by amino acid polycondensation, lactam ring-opening polycondensation or by corresponding dibasic acid and dibasic amine polycondensation, which is a step-by-step polymerization reaction.
Polyamide varieties: mainly PA6, PA66, PA11, PA12, PA610, PA1010, PA46, nylon 6T, nylon 9T and so on. Polyamides are named in four ways according to their raw materials:
(1) Nylon, which is ring-opening polymerization of lactam, is called nylon n, abbreviated as PAn. For example, the polymer obtained by ring-opening polymerization of caprolactam is called PA6.
(2) Polymers obtained by polycondensation of diamines and dicarboxylic acids are called nylon m n, which is abbreviated as PAmn. m is the number of carbon atoms in the duplicate unit, and N is the number of carbon atoms in the duplicate unit. Such as: 1,6-hexanediamine and 1,6-adipic acid polycondensation polymer called PA66. Polycondensation of 1,4-butanediamine and 1,6-adipic acid yields a polymer called PA46.
(3) Repeated diamines or diacids are abbreviated as nylon MXD6, hexamethylene diamine and terephthalic acid, 6T and 9T respectively.
Polyamides can be divided into aliphatic polyamides, semi-aromatic polyamides, all-aromatic polyamides, heterocyclic aromatic polyamides and alicyclic polyamides.
Properties of polyamide fibers
Wear resistance: The wear resistance of polyamide fibers is the best of all textile fibers. Under the same conditions, the wear resistance of polyamide fibers is 10 times that of cotton and 20 times that of wool. If 15% polyamide fibers are mixed into wool or cotton spinning, the wear resistance of polyamide fibers is 3 times higher than that of pure wool or cotton.
FRACTURE STRENGTH: The FRACTURE STRENGTH of polyamide filament for clothing use is 5.0-6.4 g/d, while that of high strength filament for industrial use is 7-9.5 g/d or even higher. The FRACTURE STRENGTH in wet state is about 85%-90% of that in dry state.
Breaking extensibility: The breaking extensibility of polyamide fibers varies according to the variety. The extensibility of strong filaments is lower than 10-25%, and that of general clothing yarns is 25-40%. The breaking extensibility of wet filaments is about 3-5% higher than that of dry filaments.
Elastic recovery rate: Polyamide fibers have excellent resilience. When the elongation of long fibers is 10%, the elastic recovery rate is 99%, while polyester is 67% in the same condition, while the elongation of long fibers is only 32%.
Fatigue resistance: Due to the good elastic recovery rate of polyamide fibers, the fatigue resistance of polyamide fibers is also good. The fatigue resistance of polyamide fibers is similar to that of polyester fibers, but higher than that of other chemical fibers and natural fibers. Under the same test conditions, the fatigue resistance of polyamide fibers is 7-8 times higher than that of cotton fibers.
Hygroscopicity: The hygroscopicity of polyamide fibers is lower than that of natural fibers and yarns, but the hygroscopicity of polyamide fibers is higher than that of other synthetic fibers only after polyvinyl chloride alcohol (PVA, vinylon). The moisture content of Nylon 66 is 3.4-3.8 at 20 degrees Celsius and 65% relative humidity, and that of Nylon 6 is 3.4-5.0. Therefore, the hygroscopicity of polyamide 6 is slightly higher than that of polyamide hexane.
Dyeability: The dyeability of polyamide fibers is more difficult than that of natural fibers, but it is still easier to dye than other synthetic fibers, usually with acid dyes.
Optical properties: Polyamide fibers have birefringence. The birefringence varies greatly with the elongation ratio. After fully elongation, the longitudinal and transverse refractive index of Nylon 66 fibers are 1.528 and 1.519 respectively. The longitudinal and transverse refractive index of Nylon 66 fibers are 1.580 and 1.530 respectively. The surface gloss of polyamide fibers is high, and titanium dioxide is usually added to extinction in polymerization.
Optical rotation resistance: Polyamide fibers have poor optical rotation resistance. The optical rotation resistance of polyamide fibers can be improved by adding light resistance agent into the fibers during polymerization.
Heat resistance: Polyamide fibers have poor heat resistance. They turn yellow after 5 hours at 150 degrees Celsius, soften at 170 degrees and begin to melt at 215 degrees. Nylon 66 has better heat resistance than Nylon 6. Its safety temperatures are 130 and 90 degrees respectively. The highest heat setting temperature can not exceed 150 degrees, preferably below 120 degrees. However, polyamide fibers have good low temperature resistance. Even at low temperatures below 70 degrees, the elastic recovery rate of polyamide fibers has little change.
Chemical resistance: Polyamide fibers have good alkali resistance, but poor acid resistance. Under normal room temperature adjusting parts, it can withstand 7% hydrochloric acid, 20% sulfuric acid, 10% nitric acid, 50% caustic soda soaking, the results are not corroded. Therefore, polyamide fibers are suitable for anti-corrosion work clothes. In addition, polyamide fibers can be used as fishing nets. They are not afraid of seawater erosion. The life of nylon fishing nets is 3-4 times longer than that of ordinary fishing nets.
Main uses of polyamide fibers
Its main uses can be divided into clothing, industrial and decorative carpet three aspects:
Clothing fibers
Polyamide filaments can be woven into pure fabrics or used as raw materials for woven fabrics, knitted fabrics and weft knitted fabrics after elastic and fluffy processing.
Industrial fibers
With high wet and dry strength and corrosion resistance, it is an ideal material for manufacturing industrial filter cloth and paper felt.
Polyamide cord tire occupies an important position in the automobile manufacturing industry. Compared with other kinds of cord fabric, polyamide cord tire can withstand the test of speed, weight and rough road surface in high-speed driving and is not easy to cause tire rupture because of its high strength, large elongation and large breaking work.
Wear-resistant, soft, light weight, can be used
