Nylon is a name for polyamide fiber (nylon). Nylon is the first synthetic fiber in the world. Nylon was developed by American scientist Carothers and a research team under his leadership.

The emergence of nylon has brought a new look to textiles. Its synthesis is a major breakthrough in the synthetic fiber industry and also a very important milestone in polymer chemistry.

Structure

Polyamide, commonly known as nylon, is a general term for thermoplastic resins containing repeating amide groups ([NHCO]) on the main chain of the molecule, including aliphatic PA, aliphatic-aromatic PA and aromatic PA. Among them, aliphatic PA has many varieties, large output and wide application, and its name is determined by the specific number of carbon atoms in the synthetic monomer.

Molecular structure

Commonly used nylon fibers can be divided into two categories.

One type is polydiacid diamine obtained by polycondensation of diamine and diacid, and the chemical structure of its long chain molecule is:

H-[HN(CH2)xNHCO(CH2)yCO]-OH

The relative molecular weight of this type of nylon is generally 17000-23000. Different nylon products can be obtained according to the different carbon atoms of the diamine and dibasic acid used, and can be distinguished by the numbers added after the nylon, where the first number is the carbon number of the diamine and the second number is the carbon number of the dibasic acid. For example, nylon 66 means that it is made by polycondensation of hexamethylenediamine and adipic acid; nylon 610 means that it is made by hexamethylenediamine and sebacic acid.

The other type is obtained by lactam polycondensation or ring-opening polymerization, and the chemical structure of its long-chain molecule is:

H-[NH(CH2)xCO]-OH

Different types of fibers are named according to the number of carbon atoms in their unit structures. For example, nylon 6 means that it is obtained by ring-opening polymerization of caprolactam containing 6 carbon atoms.

Nylon 6, nylon 66 and other aliphatic nylons are composed of linear macromolecules with amide bonds (-NHCO-). Nylon molecules contain -CO- and -NH- groups, which can form hydrogen bonds between or within molecules, and can also combine with other molecules, so nylon has good moisture absorption capacity and can form a good crystal structure.

The -CH2- (methylene) in the nylon molecule can only produce weak van der Waals forces, so the molecular chain curling degree of the -CH2- segment is relatively large. The different numbers of -CH2- in various nylons make the hydrogen bonding forms between molecules different, and the probability of molecular curling is also different. In addition, some nylon molecules have directionality. The different molecular directions will result in different structural properties of the fibers.

Morphological structure

The morphological structure of nylon made by melt spinning has a round cross section and no special longitudinal structure observed under a microscope. Under an electron microscope, filamentous fibril tissue can be observed, and the fibril width of nylon 66 is about 10-15nm. If a special-shaped spinneret is used, nylon with various special cross-sectional shapes can be made, such as polygonal, multi- lobed, hollow and other special-shaped cross-sections. Its focused state structure is closely related to the stretching and heat treatment of the spinning process. The main chains of the macromolecules of different nylons are connected by carbon atoms and nitrogen atoms.

Special-shaped fibers can change the elasticity of fibers, make them have special luster and bulkiness, and improve the fiber’s cohesion and covering ability as well as anti -pilling and anti-static properties. For example, triangular fibers have a flashing effect; pentaflobal fibers have a luster like fat light, feel good, and are anti-pilling; hollow fibers have a cavity inside, low density, and good warmth retention.

Polyamide (PA, commonly known as nylon) is a resin first developed by DuPont in the United States for fiber, and industrialized in 1939. In the 1950s, it began to develop and produce injection molded products to replace metals to meet the requirements of lightweight and cost-reducing downstream industrial products. The main chain of polyamide contains many repeated amide groups. When used as a plastic, it is called nylon. When used as a synthetic fiber, the company calls it nylon. Polyamide can be prepared from diamines and dibasic acids, or it can be synthesized from ω- amino acids or cyclic lactams. Depending on the number of carbon atoms contained in diamines, dibasic acids or amino acids, a variety of different polyamides can be produced. There are dozens of polyamide varieties, among which polyamide-6, polyamide-66 and polyamide-610 are the most widely used.

The chain structures of polyamide-6, polyamide-66 and polyamide-610 are [NH(CH2)5CO], [NH(CH2)6NHCO(CH2)4CO] and [NH(CH2)6NHCO(CH2)8CO] respectively. Polyamide-6 and polyamide-66 are mainly used for spinning synthetic fibers, called nylon-6 and nylon-66. Nylon-610 is a thermoplastic engineering plastic with excellent mechanical properties.

PA has good comprehensive properties, including mechanical properties, heat resistance, wear resistance, chemical resistance and self-lubrication, and has a low friction coefficient, certain flame retardancy, and is easy to process. It is suitable for filling and reinforcing modification with glass fiber and other fillers to improve performance and expand the scope of application.

There are many varieties of PA, including PA6, PA66, PAll, PA12, PA46, PA610, PA612, PA1010, etc., as well as many new varieties such as semi-aromatic nylon PA6T and special nylon developed in recent years. Nylon-6 plastic products can use metal sodium, sodium hydroxide, etc. as the main catalyst, N- acetyl caprolactam as the co-catalyst, and make δ-caprolactam directly in the model through negative ion ring-opening polymerization, which is called cast nylon. This method is convenient for manufacturing large plastic parts.

Use

Polyamide is mainly used for synthetic fibers. Its most prominent advantage is that it has higher wear resistance than all other fibers. It is 10 times more wear-resistant than cotton and 20 times more wear-resistant than wool. Adding a little polyamide fiber to blended fabrics can greatly improve its wear resistance. When stretched to 3-6%, the elastic recovery rate can reach 100%; it can withstand tens of thousands of folds and bends without breaking.

The strength of polyamide fiber is 1-2 times higher than cotton, 4-5 times higher than wool, and 3 times higher than viscose fiber. However, polyamide fiber has poor heat resistance and light resistance, and its retention is not good. Clothes made of it are not as crisp as polyester. In addition, nylon- 66 and nylon-6 used for clothing have the disadvantages of poor moisture absorption and dyeability. For this reason, new varieties of polyamide fibers have been developed -nylon-3 and nylon-4 new polyamide fibers, which are light, wrinkle-resistant, breathable, and have good durability, dyeability and heat setting, and are therefore considered to have great development prospects.

This kind of product has a wide range of uses. It is a good material to replace steel, iron, copper and other metals with plastics. It is an important engineering plastic. Cast nylon widely replaces wear-resistant parts of mechanical equipment and replaces copper and alloys as wear-resistant parts of equipment. It is suitable for making wear-resistant parts, transmission structural parts, household appliance parts, automobile manufacturing parts, screw rods to prevent mechanical parts, chemical machinery parts, and chemical equipment. Such as turbines, gears, bearings, impellers, cranks, instrument panels, drive shafts, valves, blades, screw rods, high-pressure washers, screws, nuts, seals, shuttles, sleeves, sleeve connectors, etc.

Replace copper and other metals

Since polyamide is non-toxic, lightweight, has excellent mechanical strength, wear resistance and good corrosion resistance, it is widely used to replace copper and other metals in the manufacture of bearings, gears, pump blades and other parts in the machinery, chemical, instrumentation, automobile and other industries. After polyamide is melt-spun into yarn, it has high strength and is mainly used as synthetic fiber and medical suture.

Used in various medical and knitwear products

In civilian use, it can be blended or spun into various medical and knitted products. Nylon filaments are mostly used in knitting and silk industries, such as single stockings, elastic stockings and other wear-resistant nylon stockings, nylon scarves, mosquito nets, nylon lace, elastic nylon outerwear, various nylon silks or interwoven silk products. Nylon staple fibers are mostly used to blend with wool or other chemical fiber wool products to make various wear-resistant and durable clothing materials.

In industry, nylon is used in large quantities to make cords, industrial fabrics, cables, conveyor belts, tents, fishing nets, etc. In national defense, it is mainly used as parachutes and other military fabrics.

R&D History

In 1927, the largest chemical industry company in the United States decided to pay $250,000 per year in research expenses and began to hire chemical researchers.

In 1928, the company established the Institute of Basic Chemistry, and Dr. Carothers, who was only 32 years old, was hired as the director of the institute. He mainly engaged in research on polymerization reactions. He first studied the polycondensation reaction of bifunctional molecules, and synthesized long-chain polyesters with high molecular weight through the esterification condensation of diols and dicarboxylic acids. In less than two years, Carothers made important progress in the preparation of linear polymers, especially polyesters, and increased the relative molecular weight of polymers to 10,000-25,000. He called polymers with a relative molecular weight higher than 10,000 superpolymers.

In 1930, Carothers’ assistant discovered that the molten polyester made from diols and dicarboxylic acids through polycondensation reaction could be drawn into threads like cotton candy, and that the fibrous filaments could continue to stretch even after cooling, with the stretching length reaching several times the original. After cooling and stretching, the strength, elasticity, transparency and glossiness of the fibers were greatly increased.

The unique properties of this polyester made them feel that it might have great commercial value and that it might be possible to spin fibers from the molten polymer. However, further research showed that obtaining fibers from polyester was only of theoretical significance. Because high polyester melts below 100°C and is particularly soluble in various organic solvents, it is only slightly more stable in water, so it is not suitable for textile use.

Carothers then conducted in-depth research on a series of polyester and polyamide compounds. After many comparisons, he selected polyamide-66 (the first 6 represents the number of carbon atoms in the diamine and the second 6 represents the number of carbon atoms in the diacid ) which he first synthesized from hexamethylenediamine and adipic acid on February 28, 1935. This polyamide is insoluble in common solvents and has a melting point of 263°C, which is higher than the commonly used ironing temperature. The drawn fiber has the appearance and luster of silk, and is also close to natural silk in structure and properties. Its wear resistance and strength exceed any fiber at the time. Considering its properties and manufacturing costs, it is the best choice among known polyamides. Then, the problem of industrial sources of raw materials for the production of polyamide 66 was solved.

On October 27, 1938, the world’s first synthetic fiber was officially announced, and the synthetic fiber polyamide 66 was named nylon. Nylon later became the general name for all polyamides synthesized from coal, air, water or other substances, with wear resistance and flexibility and a protein-like chemical structure in English.

After it was industrialized in 1939, it was named Nylon and was the earliest synthetic fiber variety to be industrialized.

The synthesis of nylon laid the foundation for the synthetic fiber industry, and the emergence of nylon gave textiles a new look. Nylon stockings woven from this fiber are both transparent and more durable than silk stockings.

When nylon stockings were put on sale on October 24, 1939, they caused a sensation and were regarded as rare and valuable items. Many women at the bottom of society could not buy stockings, so they had to draw patterns on their legs with pens to pretend they were stockings. People praised this fiber as ” thin as spider silk, strong as steel wire, and beautiful as silk “. By May 1940, nylon fiber fabrics were sold all over the United States.

From the outbreak of World War II until 1945, the nylon industry was turned to parachutes, aircraft tire cord fabrics, military uniforms and other military products. Due to the characteristics and wide range of uses of nylon, it developed very rapidly after World War II, and various nylon products appeared in countless ways, from stockings and clothes to carpets, ropes, fishing nets, etc. Nylon is one of the three major synthetic fibers.

In April 1958, the first batch of Chinese caprolactam test samples were finally successfully trial-produced at the Jinxi Chemical Plant in Liaoning Province (now Huludao, Liaoning Province ). The product was sent to the Beijing Fiber Factory and successfully spun at once, marking the beginning of China’s synthetic fiber industry. Because it was born in the Jinxi Chemical Plant (now Huludao, Liaoning Province), this synthetic fiber was later named “nylon”. Since nylon had important national defense and military uses in the early days of the founding of the impoverished New China, the significance of its birth is self-evident.

Nylon fiber is the raw material for many kinds of man-made fibers. Hard nylon is used in the construction industry. Hot air balloons made of nylon can be made very large.

Technical Parameters

Cleanability and antifouling properties

The two properties are affected by the cross-sectional shape of the fiber and the subsequent antifouling treatment, while the strength and hardness of the fiber itself have little effect on cleaning and antifouling properties.

Melting point and elasticity

The melting point of nylon 6 is 220℃ and that of nylon 66 is 260℃. However, this is not a difference in terms of the temperature conditions of carpet use. The lower melting point makes nylon 6 have better resilience, fatigue resistance and thermal stability than nylon 66.

Color fastness

Color fastness is not a property of nylon; it is the dye in the nylon, not the nylon itself, that fades when exposed to light.

Wear resistance and dust resistance

Clemson University in the United States conducted a two-and-a-half-year experiment at Tampa International Airport using Zeftron 500 nylon 6 carpet and Antron XL nylon 66 carpet. The carpet was subject to extremely high traffic, and the results showed that BASF Zeftron 500 nylon was slightly better than Antron XL in terms of color retention and pile wear resistance. There was no difference in the dust resistance of the two yarns.

Products and Types

With the acceleration of the miniaturization of automobiles, the high performance of electronic and electrical equipment, and the lightweighting of mechanical equipment, the demand for nylon will be higher and greater. In particular, as a structural material, nylon has high requirements for its strength, heat resistance, cold resistance, etc. The inherent shortcomings of nylon are also an important factor limiting its application, especially for the two major varieties of PA6 and PA66, which have a strong price advantage compared with varieties such as PA46 and PAl2, although some performance cannot meet the requirements of the development of related industries.

Therefore, it is necessary to expand its application field by modifying and improving some of its properties for a certain application field. Due to the strong polarity of PA, it has strong hygroscopicity and poor dimensional stability, but this can be improved through modification.

Enhanced PA

Adding 30% glass fiber to PA can significantly improve the mechanical properties, dimensional stability, heat resistance and aging resistance of PA, and the fatigue strength is 2.5 times that of unreinforced PA. The molding process of glass fiber reinforced PA is roughly the same as that of unreinforced PA, but because the flow is worse than before reinforcement, the injection pressure and injection speed should be appropriately increased, and the barrel temperature should be increased by 10-40℃. Since the glass fiber will be oriented along the flow direction during the injection molding process, the mechanical properties and shrinkage rate will be enhanced in the orientation direction, resulting in deformation and warping of the product. Therefore, when designing the mold, the position and shape of the gate should be reasonable. The temperature of the mold can be increased in the process, and the product can be taken out and placed in hot water to cool slowly. In addition, the greater the proportion of glass fiber added, the greater the wear on the plasticizing components of the injection molding machine. It is best to use a bimetallic screw and barrel.

Flame retardant PA

Since flame retardants are added to PA, most of them are easy to decompose at high temperatures, releasing acidic substances that are corrosive to metals. Therefore, plasticizing components (screws, rubber heads, rubber rings, rubber washers, flanges, etc.) need to be hard chrome plated. In terms of technology, try to control the barrel temperature not too high and the injection speed not too fast to avoid discoloration of the product and degradation of mechanical properties due to decomposition of the rubber material due to excessively high temperature.

Transparent PA

It has good tensile strength, impact resistance, rigidity, wear resistance, chemical resistance, surface hardness and other properties, high light transmittance, similar to optical glass, processing temperature is 300-315℃, during molding, the barrel temperature must be strictly controlled, too high melt temperature will cause product discoloration due to degradation, too low temperature will affect the transparency of the product due to poor plasticization. The mold temperature should be as low as possible, high mold temperature will reduce the transparency of the product due to crystallization.

Weather-resistant PA

Addition of carbon black and other UV- absorbing additives to PA greatly enhances the self- lubricity and wear of PA to metals, which will affect material feeding and wear parts during molding. Therefore, it is necessary to use a screw, barrel, rubber head, rubber ring, and rubber gasket combination with strong feeding capacity and high wear resistance. The repeating structural unit on the polyamide molecular chain is a type of polymer with amide group.

In summary, the modifications are mainly carried out in the following aspects:

1. Improve the water absorption of nylon and improve the dimensional stability of the product.
2. Improve the flame retardancy of nylon to meet the requirements of the electronics, electrical, communications and other industries.
3. Improve the mechanical strength of nylon to achieve the strength of metal materials and replace metal
4. Improve nylon’s resistance to low temperatures and enhance its ability to withstand environmental strain.
5. Improve the wear resistance of nylon to meet the occasions with high wear resistance requirements.
6. Improve the antistatic property of nylon to meet the requirements of mines and their mechanical applications.
7. Improve the heat resistance of nylon to adapt to high temperature resistant fields such as automobile engines.
8. Reduce the cost of nylon and improve product competitiveness.

In short, through the above improvements, the high performance and functionalization of nylon composite materials can be achieved, thereby promoting the development of related industry products towards high performance and high quality.

Nano Nylon

According to Toray Chemical Co., Ltd. of Japan, the company has successfully developed a new ” nano fiber ” technology with a nano-scale monofilament structure whose diameter is two digits smaller than that of previous ultra-fine fibers, and has reached the limit of fiber fineness by controlling nanostructure technology. Toray Chemical Co., Ltd. said that the company has used this new technology to develop nano nylon fibers composed of more than 1.4 million monofilaments with a diameter of 10 μm. Compared with previous products, this fiber has a surface area of ​​about 1,000 times that of previous products and has a high surface activity.

Super strong nylon

Triangle-Raleigh nylon fibers are used in everything from clothing and carpeting to ropes and computer data cables. Researchers at the University of North Carolina’s College of Textiles are working to improve the fibers and report that they have developed the strongest aliphatic nylon fibers.

Scientists Dr. Tonelli, professor of polymers, and Dr. Richard Cuttack, assistant professor of textile engineering, chemistry and natural sciences, are working on a way to create stronger nylon fibers without the need for expensive, complex processes. They are working with aliphatic nylons, or nylons, which have carbon fibers that are connected in straight or open- chain chains, rather than large, ring-shaped chains.

Stronger aliphatic nylons could be used in ropes, loading straps, parachutes and car tires, or to create synthetic materials suitable for high-temperature applications. The discovery was presented at the annual meeting of the American Chemical Society in Philadelphia and published in the journal Polymer Journal.

The fibers are made from polymers, or long chains of molecules consisting of many units. When these polymer chains are aligned, the polymer becomes crystalline.

These coiled polymers need to be stretched, and their elasticity needs to be eliminated if they are to be made into stronger fibers. Adding hydrogen to nylon chains prevents stretching, so overcoming this bonding is a key factor in creating stronger nylon fibers.

Super-strong fibers, such as Kevlar, are made from aromatic nylon polymers. They are very stiff, with long chains containing rings. Aromatic nylon is difficult to make and therefore very expensive.

So Professor Tonelli and Dr Cuttack used polyamide 66 (nylon 66), a commercial thermoplastic that is easy to make but difficult to stretch and align. It is also difficult to remove the elasticity of nylon 66.

This discovery could solve the problem of nylon 66 being able to dissolve in gallium trichloride, effectively breaking the hydrogen bonds and allowing the polymer chain to extend.

PA Nylon

The mechanical properties of PA, such as tensile and compressive strength, change with temperature and moisture absorption, so water is relatively a plasticizer for PA. After adding glass fiber, its tensile and compressive strength can be increased by about 2 times, and its temperature resistance is also improved accordingly. PA itself has very high wear resistance, so it can operate continuously without lubrication. If you want to get a special lubrication effect, you can add sulfide to PA.

Suitable plastic products: various gears, turbines, racks, cams, bearings, propellers, transmission belts.

Others: Shrinkage rate is 1-2%. Please pay attention to the dimensional changes due to moisture absorption after molding.

Water absorption rate : 100% relative moisture absorption saturation can absorb 8%.

Suitable wall thickness: 2-3.5mm

PA66

It has high fatigue strength and rigidity, good heat resistance, low friction coefficient, and good wear resistance, but it has high hygroscopicity and insufficient dimensional stability.

Application: medium load, operating temperature ≈100-120 degrees, wear-resistant transmission parts working under no or little lubrication conditions.

PA6

Fatigue strength and heat resistance are lower than nylon 66, but it has good elasticity and good vibration and noise reduction capabilities. White

Application: Wear-resistant transmission parts that work under light load, medium temperature (80-100°C), no lubrication or little lubrication, and low noise.

PA610

Strength, rigidity and heat resistance are lower than nylon 66, but it has low moisture absorption and good wear resistance.

Application: Same as nylon 6, suitable for gears that require relatively high precision and parts with large changes in humidity in working conditions.

PA1010

The strength, rigidity and heat resistance are lower than nylon 66, the moisture absorption is lower than nylon 610, the molding process is good, and the wear resistance is good.

Application: Parts working without or with little lubrication under light load, low temperature, large humidity changes, and other conditions

MCPA

Strength, fatigue resistance, heat resistance, and rigidity are better than PA6 and PA66, hygroscopicity is lower than PA6 and PA66, wear resistance is good, can be directly polymerized in the model, suitable for casting large parts. Application: high load, high operating temperature (below 120) without lubrication or less lubrication. Milky white

Cast Nylon

Cast nylon ( MC nylon ), also known as monomer cast nylon, is a product obtained by directly polymerizing caprolactam monomer in a mold under the action of a strong base (such as NaOH ) and some co-catalysts. Since the polymerization and molding processes are combined together, it is easy to mold, requires less equipment investment, and is easy to manufacture large machine parts. Its mechanical and physical properties are higher than those of nylon 6. It can manufacture gears, turbines, bearings, etc. weighing dozens of kilograms.

Nylon 1010

Nylon 1010 is a kind of engineering plastics created in China. It is made from castor oil, decanediamine and sebacic acid, and then condensed. It has low cost, good economic effect, excellent self-lubrication and wear resistance, good oil resistance, low brittle transition temperature (about -60℃), high mechanical strength, and is widely used in mechanical parts, chemical and electrical parts.

Modified nylon

Modified nylon is a type of engineering plastics. It is a granular product formed by changing the physical properties of nylon raw materials. The output of this type of product is modified according to the different requirements of some manufacturers.

Modified nylon generally includes: reinforced nylon, toughened nylon, wear-resistant nylon, halogen-free flame retardant nylon, conductive nylon, flame retardant nylon and so on.

1. Thermal properties: high glass transition temperature (Tg), melting point (Tm), heat deformation temperature ( HDT ); high long-term use temperature (UL-746B); wide use temperature range; small thermal expansion coefficient.
2. Mechanical properties: high strength, high mechanical modulus, low latent deformation, strong wear resistance and fatigue resistance.
3. Others: Good chemical resistance, electrical resistance, flame resistance, weather resistance and dimensional stability.

Aromatic Nylon

Aromatic nylon, also known as polyaromatic amide, is a new type of nylon that was successfully developed in the 1960s. It is resistant to high temperature, radiation and corrosion. All nylon molecules that contain aromatic ring structures belong to aromatic nylon. If only the diamine or dibasic acid of synthetic nylon is replaced by aromatic diamine or aromatic diacid, the nylon obtained is semi-aromatic nylon, and the nylon synthesized by aromatic diacid and aromatic diamine is fully aromatic nylon. The embrittlement temperature of aromatic nylon can reach -70℃, and the Vicat softening temperature can reach 270℃. It is resistant to high temperature, radiation, corrosion and wear, has self-extinguishing properties, and can maintain high electrical properties in a humid state. Aromatic nylon can be extruded, molded, laminated, and impregnated. It can be used to make fibers, films, impregnated films, decorative laminates, glass fiber reinforced laminates, high temperature radiation tubes, firewalls, etc. The semi-aromatic nylons that have been commercialized mainly include MXD6, PA6T and PA9T, and the fully aromatic nylons mainly include poly(p-phenylene terephthalamide) ( PPTA ), poly(m-phenylene isophthalamide) (MPIA) and poly(p-phenylene terephthalamide) (PBA).

Fully aromatic nylon was successfully developed and industrialized in the 1960s and 1970s. Fully aromatic nylon is widely used in the production of synthetic fibers due to its high melting point, high modulus and high strength. PPTA is made from p-phenylenediamine and terephthaloyl chloride by low-temperature solution polymerization. PPTA has excellent properties such as high strength, high modulus, high temperature resistance and low density. It is mainly used as a raw material for synthetic fiber spinning; PPTA fiber can also be used as a reinforcing agent for rubber reinforcement and plastics. However, PPTA has shortcomings in fatigue resistance and pressure resistance, and PPTA cannot be melt extruded.

MXD6

MXD6 is a crystalline nylon resin synthesized by Lum et al. in the 1950s using m-phenylenediamine and adipic acid as raw materials through polycondensation reaction. Mitsubishi Gas Chemical Company of Japan synthesized MXD6 by direct polycondensation method and Toyobo Co., Ltd. synthesized MXD6 by nylon salt method. The uses of MXD6 obtained by these two different polymerization methods are also different: MXD6 synthesized by direct polycondensation method can be used to manufacture barrier materials or engineering structural materials; MXD6 synthesized by nylon salt method can be used to produce fiber-grade MXD6 resin. As a crystalline semi-aromatic nylon, MXD6 has the characteristics of low water absorption, high heat deformation temperature, high tensile strength and bending strength, small molding shrinkage, and good barrier properties to gases such as O2 and CO2. Due to its wide processing temperature, MXD6 can be co-extruded with polypropylene ( PP ) and co -extruded with high-density polyethylene (HDPE) for blow molding. In industry, MXD6 is mainly used as packaging materials and as an engineering structural material to replace metal. The former includes food and beverage packaging, instrument and equipment packaging (moisture-proof, vibration-absorbing cushions and foaming materials ); the latter includes high-heat-resistant Reny, MXD6/PPO alloy, vibration-resistant Reny, etc. In addition, MXD6 is also used in magnetic plastics, transparent adhesive, etc.

PA6T

PA6T is a semi-aromatic nylon synthesized from aromatic diacids and aliphatic diamines. PA6T has excellent heat resistance and dimensional stability. Since PA6T has a high melting point, it can be prepared by solid phase polymerization or interfacial polymerization. It can be used for fiber manufacturing, mechanical parts and film products. The modified PA6T developed by Mitsui Chemicals of Japan has the characteristics of high rigidity, high strength and low water absorption. It is mainly used for automotive internal combustion engine parts, heat-resistant electrical parts, transmission parts and electronic assemblies. It is precisely because of the high melting point of PA6T that it cannot be injection molded like ordinary aliphatic nylon, which limits the application of PA6T to a certain extent.

PA9T

PA9T is obtained by melt polycondensation of nonanediamine and terephthalic acid. PA9T has good heat resistance and melt processability, and its water absorption rate is only 0.17%, which is 1/10 of PA46 (1.8%). It has good dimensional stability and other characteristics, and has been widely used in electronic and electrical, information equipment, automotive parts, etc. When the number of carbon atoms of the diamine in the repeating unit chain is 6, the melting point of PA6T is 370℃, which exceeds its thermal decomposition temperature of about 350℃. Therefore, if the third or even fourth component is not added to reduce the melting point, nylon cannot be used in practical applications (the melt processing temperature of nylon is generally below 320℃). However, if other components are added to reduce the melting point, it will inevitably lead to a decrease in the properties of PA6T such as crystallinity, dimensional stability and chemical resistance. Therefore, increasing the number of carbon atoms of diamine has become another research hotspot, and the structure of PA9T has become an ideal structure with both heat resistance and melt processability. However, the synthesis route of nonanediamine, the main raw material for synthesizing PA9T, is relatively complicated: butadiene undergoes chemical reactions such as hydration, transposition, hydroxylation, and amination reduction to finally obtain nonanediamine. This results in high production costs for PA9T, which in turn limits the large-scale production and application of PA9T.

Polyphthalamide​

Polyphthalamide ( PPA ) is a blend of polymers formed by polycondensation of isophthalic acid, terephthalic acid, adipic acid and hexamethylenediamine. It is a semi-crystalline, semi-aromatic nylon. PPA resin is generally produced in batches. PPA has good heat resistance, excellent mechanical properties and dimensional stability, low water absorption and excellent molding processability, as well as good electrical properties and chemical resistance. PPA can be processed by injection molding and extrusion molding. PPA is widely used in the fields of automobiles, electronic appliances and general industrial machinery.

Poly (m-phenylene isophthalamide)

Polyisophthalamide (MPIA) is a new type of polyaromatic amide successfully developed in the 1960s. It is made of metaphenylenediamine and isophthaloyl chloride and can be synthesized by low-temperature solution polycondensation and interfacial polymerization. The outstanding feature of MPIA is its long heat-resistant life. In addition, it also has the advantages of high modulus, wear resistance, flame retardancy, and high-temperature dimensional stability. However, the light resistance of MPIA is slightly poor, and an anti-ultraviolet agent needs to be added. MPIA is mainly used for work clothes in industrial and flammable and explosive high-temperature environments, high-temperature resistant industrial filter materials, parachutes, high-temperature conveyor belts, electrical insulation materials, etc. MPIA can also be processed into rods, plates and fibers. With its excellent heat resistance, sliding and radioactive resistance, it is used in aerospace, atomic energy industry, electrical and automotive industries.

Polyparaben

Poly -p-benzamide (PBA) was successfully developed in the 1970s. Its synthesis route is: p -nitrotoluene is oxidized by air in the liquid phase to obtain p-nitroformic acid, p-nitroformic acid is subjected to an amination reduction reaction to obtain p -aminoformic acid, p-aminobenzoic acid is converted into the hydrochloride of p- aminobenzoyl chloride or p-sulfinamidebenzoyl chloride, and finally PBA is obtained by polycondensation. PBA has the characteristics of high modulus and high strength, and can be used in rocket engine casings, high-pressure containers, sports goods, and coated fabrics in industry.

Development Trend

The latest development of modified PA products

Glass fiber reinforced PA was studied in the 1950s, but it was not industrialized until the 1970s. Since the development of super-tough PA66 in 1976, major companies in various countries have developed new modified PA products. The United States, Western Europe, Japan, the Netherlands, Italy and other countries have vigorously developed reinforced PA, flame retardant PA, and filled PA, and a large number of modified PA have been put on the market.

In the 1980s, the successful development of compatibilizer technology promoted the development of PA alloys. Countries around the world have successively developed thousands of alloys such as PA/PE, PA/PP, PA/ABS, PA/PC, PA/PBT, PA/PET, PA/PPO, PA/PPS, PA/PA, etc., which are widely used in automobiles, locomotives, electronics, electrical machinery, textiles, sporting goods, office supplies, home appliance parts and other industries.

In the 1990s, new varieties of modified nylon continued to increase. During this period, modified nylon was commercialized, forming a new industry and developing rapidly. By the end of the 1990s, the world’s nylon alloy production reached 1.1 million tons/year.

In terms of product development, the main directions are high-performance nylon PPO/PA6, PPS/PA66, toughened nylon, nano nylon, and halogen-free flame-retardant nylon; in terms of application, major progress has been made in the development of automotive components and electrical components. For example, high-flow modified nylon for automobile intake manifolds has been commercialized. The plasticization of such complex structural components is not only of great significance in application, but more importantly, it prolongs the life of the components and promotes the development of engineering plastics processing technology.

Development trend of modified nylon

As the largest and most important variety of engineering plastics, nylon has strong vitality, mainly because it can achieve high performance after modification. Secondly, the automotive, electrical, communications, electronics, machinery and other industries have increasingly strong requirements for high performance of their products. The rapid development of related industries has promoted the process of high performance of engineering plastics. The future development trends of modified nylon are as follows.

1. The market demand for high-strength and high-rigidity nylon is increasing, and new reinforcement materials such as inorganic whisker – reinforced and carbon fiber -reinforced PA will become important varieties, mainly used in automotive engine parts, mechanical parts and aviation equipment parts.
2. Nylon alloying will become the mainstream of the development of modified engineering plastics. Nylon alloying is an important way to achieve high performance of nylon, and it is also the main means to manufacture special nylon materials and improve nylon performance. By mixing with other polymers, the water absorption of nylon can be improved, and the dimensional stability, low-temperature brittleness, heat resistance and wear resistance of the product can be improved. Therefore, it is suitable for the use of different requirements of vehicle types.
3. The manufacturing technology and application of nano-nylon will develop rapidly. The advantages of nano-nylon are that its thermal properties, mechanical properties, flame retardancy and barrier properties are higher than those of pure nylon, while its manufacturing cost is comparable to that of ordinary nylon. Therefore, it has great competitiveness.
4. The flame-retardant nylon used in electronics, electrical appliances and electrical appliances is increasing day by day, and green flame-retardant nylon is receiving more and more attention from the market.
5. Antistatic, conductive nylon and magnetic nylon will become the preferred materials for electronic equipment, mining machinery and textile machinery.
6. The research and application of processing aids will promote the functionalization and high performance of modified nylon.
7. The application of comprehensive technologies and refinement of products are the driving force for the development of the industry.

Polyamide fiber is a general term for a type of fiber with -CO-NH- groups on the macromolecular chain. Commonly used aliphatic polyamide fibers are mainly polyamide 6 and polyamide 66, and the commercial names in China are nylon 6 and nylon 66. 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 filament is widely used for deformation processing to make stretch yarn as a raw material for weaving or knitting. Nylon fiber is generally spun by melt spinning. The strength of nylon 6 and nylon 66 fibers is 4-5.3cN/dtex, and high-strength polyester can reach more than 7.9cN/dtex, with an elongation of 18%-45%, and an elastic recovery rate of more than 90% at 10% elongation. According to measurements, the wear resistance of nylon fiber is 20 times that of cotton fiber, 20 times that of wool, and 50 times that of viscose. Fatigue resistance ranks first among all kinds of fibers. In civilian use, it is widely used to process socks and other blended products to improve the wear resistance of fabrics. However, nylon fiber has a low modulus and its wrinkle resistance is not as good as that of polyester, which limits the application of nylon in the field of clothing. The life of nylon cord is 3 times longer than that of viscose, and its impact absorption is large, so the tire can run on bad roads. However, due to the large elongation of nylon cord, when the car stops, the tire deforms and produces flat spots, and the car jumps violently at the beginning of starting. Therefore, it can only be used for truck tires, and is not suitable for passenger car tire cords.

The surface of nylon fiber is smooth, and the friction coefficient of the fiber without oil is very high. Nylon oil is easy to lose its effectiveness after long-term storage, and it is necessary to add oil again during textile processing.

Nylon fiber has higher moisture absorption than polyester. The moisture regain of nylon 6 and nylon 66 under standard conditions is 4.5%, which is second only to vinylon among synthetic fibers. It has good dyeing performance and can be dyed with acid dyes, disperse dyes and other dyes.