Introduction to 1.

Polyamide (PA), commonly known as nylon, is obtained by polycondensation of dibasic acids and diamines or amino acids. It is a general term for resins containing repeated amide groups-NHCO-on the molecular chain. Nylon is the basic resin with the largest output, the most widely used and excellent comprehensive performance among the five general-purpose engineering plastics. Among the nylon series varieties, the output and consumption of PA6 and PA66 are the largest, accounting for about 90% of the nylon output. The reason why nylon can rank first among the five major engineering plastics is mainly due to its many excellent properties, such as mechanical properties, chemical properties, and thermal properties.

Nylon is a kind of high performance engineering plastics, because of its outstanding weather resistance, low temperature flexibility and corrosion resistance and other characteristics, widely used in automotive, communications, machinery, electronics, textile, aerospace, military, sporting goods and other fields, is the current domestic and foreign nylon industry focus on research and development direction. Due to the rapid development of China's automobile, electronics, machinery and other industries, the demand for nylon is also increasing. Among them, the automobile industry has the largest demand, accounting for about 50% of the market share. It is mainly used to manufacture oil pipelines and clutch hoses, replacing the original copper pipes, reducing the hidden dangers of oil leakage and fire caused by collision and wear between metal pipes. It not only improves the safety of the car, but also reduces the quality of the car and saves energy consumption.

Nylon, as an important engineering plastic, is being continuously modified by physical and chemical properties. At present, many fields have put forward new requirements for the high temperature resistance of materials. In order to meet these requirements, people have done a lot of research in the development of new high-temperature nylon, and high-temperature nylon is becoming a research hotspot in the current market.

Definition of 2. high temperature nylon

High temperature nylon (HTPA) is a kind of heat-resistant polyamide, which can be used in 150 ℃ environment for a long time. It is a semi-aromatic polyamide made by the polycondensation of terephthalic acid and 1,6-hexanediamine. Good performance in thermal, electrical, physical and chemical resistance. Especially at high temperature still has high rigidity and high strength and excellent dimensional accuracy and stability.

Characteristics of 3. high temperature nylon

1. High temperature resistance.The heat deflection temperature was 280°C (1.8MPa) and the continuous use temperature was 180°C.

2. Creep performance.The high crystallinity of HTPA allows it to maintain excellent rigidity at high temperatures (greater than 120°C), with the same strength as aluminum, the same hardness as steel, and the same flexibility, ductility and impact resistance as rubber.

3. Excellent dimensional accuracy and stability.In the molecular structure of HTPA, the molecular chain segment contains aromatic rings, the molecular structure is more regular, and the chain is shorter and more difficult to move.

4. Chemical resistance.Polyamide-based materials have good resistance to most chemicals. Like other polyamide materials, HTPA is no exception, especially at high temperature oil and grease resistance is very good.

5, hygroscopicity.HTPA fiber reinforced products have low moisture absorption, and their water absorption is only half of the equivalent glass fiber reinforced PA46 products. This low moisture absorption can save customers more drying costs, and the dimensional stability of the product is better.

6. Resilience.The excellent impact toughness of HTPA makes it the material of choice for highly demanding fabrication.

Production and molding process of 4. nylon

Taking PA66 as an example, PA66 is formed by condensation polymerization of adipic acid and hexamethylene diamine. Its production process mainly has three processes: monomer synthesis, PA66 salt preparation and polycondensation.

4.1 monomer synthesis

(1) Preparation of adipic acid

There are mainly phenol method, cyclohexane method and acrylonitrile dimerization method.

Phenol method is based on phenol as raw material, using Raney nickel as catalyst, at 140 ~ l50 ℃ and 2 ~ 3MPa pressure, hydrogenation to produce cyclohexanol, and then with 60% ~ 65% concentration of nitric acid, in the presence of copper or vanadium catalyst, at 55~60 ℃ oxidation to adipic acid.

Cyclohexane method is based on cyclohexane as raw material, in the presence of cobalt naphthenate or boric acid catalyst, air pressure liquid phase oxidation, generating a mixture of cyclohexanone and cyclohexanol, and then 60% concentration of nitric acid at 45~60 ℃ oxidation to adipic acid.

Acrylonitrile dimerization method is based on acrylonitrile as raw material, using electrolytic reduction method to dimerize adiponitrile, and then in dilute sulfuric acid aqueous solution heating hydrolysis to obtain adipic acid.

(2) Preparation of hexamethylene diamine

There are mainly adipic acid method and butadiene method.

The adipic acid method is based on adipic acid as a raw material, in the presence of a dehydration catalyst such as dibutyl phosphate, at a temperature of 280 to 300 ℃ for ammoniation and dehydration to obtain adiponitrile, which is then hydrogenated in acetic acid under a Raney nickel catalyst at 90 ℃ and a pressure of 2.8MPa to obtain hexamethylene diamine.

The butadiene method is to chlorinate butadiene to form a mixture of dichlorobutene isomers, then cyanate it with hydrocyanic acid or sodium cyanide in acidic aqueous solution to butene dicyanide isomers, then treat it with sodium oxyoxide to convert all isomers into l, 4-dicyanobutene -2, and after purification, use palladium carbon as catalyst to hydrogenate hexamethylene diamine at 300 ℃.

Preparation of 4.2 PA 66 salt

When nylon is prepared from dibasic acid and diamine, it is necessary to strictly control the ratio of raw materials to equimolar ratio in order to obtain polymers with higher molecular weight. Therefore, adipic acid and hexamethylene diamine must be mixed to make PA66 salt in production. The preparation of PA66 salt is to stir and mix the ethanol solution of hexamethylene diamine and the ethanol solution of adipic acid at a temperature above 60 ℃, neutralize into salt, precipitate, filter, wash with alcohol and dry, and finally prepare about 63% aqueous solution for polycondensation.

4.3 polycondensation

The polycondensation of PA66 salt needs to be carried out at high temperature, and the continuous method is used to generate linear high molecular weight PA66. About 88% of nylon 66 is processed into various parts by injection molding, and about 12% of nylon 66 is processed into corresponding products by extrusion, blow molding, etc.

PA66 production process

5. traditional high temperature nylon

5.1 PA46

PA46 is an aliphatic polyamide formed by polycondensation of butanediamine and adipic acid. Compared with PA6 and PA66,PA46 has more amides per chain of given length and more symmetrical chain structure, which makes its crystallinity as high as 70% and gives it a very fast crystallization speed.

The melting point of PA46 is 295 ℃, the HDT (thermal deformation temperature) of unreinforced PA46 is 160 ℃, and after glass fiber reinforcement, its HDT can be as high as 290 ℃, and the long-term use temperature is 163 ℃.

The unique structure of PA46 gives unique properties that other materials cannot achieve. As the full owner of PA46 property rights, DSM company is gradually its excellent performance through continuous modification and industrialization. While ensuring its high temperature resistance, various special applications such as ultra-wear resistance, ultra-high rigidity, and ultra-high mobility have been continuously developed.

In terms of high temperature resistance, DSM introduced its new high-performance STAN YL Diablo in Chinaplas 2008. It has long-term heat resistance stability and can work normally at 230 ℃ for more than 3000h, while its mechanical properties decrease by less than 15%.

5.2 PA6T

PA6T is a typical representative of semi-aromatic nylon, which is formed by polycondensation of hexamethylene diamine and terephthalic acid. The melting point of pure PA6T is as high as 370 ℃. At this temperature, nylon has been degraded and cannot be thermoplastic molded. Therefore, the PA6T in the market is a copolymer or compound that reduces the melting point after copolymerization with other monomers.

PA6T introduces a large number of benzene rings on the basis of aliphatic chains. Compared with traditional PA6 and PA66, PA6T has higher Tg, low water absorption, dimensional stability and high heat resistance. Because PA6T needs to introduce other monomers for copolymerization to reduce the melt processing temperature, different monomer ratios become the key to PA6T modification, so it can be said that the high temperature resistance modification of PA6T has a lot of room for development.

Wang Peigang and others have studied the polymerization process and heat resistance of PA6T/66 copolymer with different aromatic ring content in China. And Shanghai Jie Jie Jie company has also successfully issued the PA6T series of high temperature resistant nylon, and has been put into production.

5.3 PA9T

PA9T is developed by the Japanese Kuraray company alone, is nonyl diamine and terephthalic acid polycondensation. Although the same as semi-aromatic nylon, PA9T does not need to be modified by copolymerization to reduce the melting point like PA6T before processing, and the melting point of pure PA9T is 306 ℃. PA9T high glass transition temperature (125 ℃) and high crystallinity, giving it good toughness in high temperature environment.

At the same time, it also has incomparable chemical resistance to other PA materials, second only to PPS, and its water absorption rate is only 0.17, which is the lowest among all PA. The comprehensive performance of PA9T is undoubtedly a better one in the traditional heat-resistant nylon, and with the continuous expansion of production scale, its cost will be close to the cost of ordinary PA, so PA9T is a variety with great development potential.

6. Newest High Temperature Nylon

6.1 PA66

Although compared with traditional high-temperature nylon, PA66 has a relatively low Tm and Tg, which seems to limit its use in high-temperature fields, but the French company Rhodia believes that it can still be used as a high-end application material. InAt the German K Exhibition in 2007, Rhodia Company introduced the PPA alternative material TECHNYL Heat Performance(HP) in high temperature environment., This PA66 can meet the performance requirements of the car hood under the rising temperature environment.

It is said that the material also maintains the processing performance of nylon 66 at the cost level of nylon 66. This technology has brought new development to PA66 materials in the field of high temperature resistance, but at present only Rhodia has mastered the technology.

6.2 PA4T

As the world's leading producer of high-temperature nylon (PA46), DSM has the world's only industrial solution for butylenediamine. Butylenediamine is the key raw material for the synthesis of PA46, and this technical advantage has led DSM to develop PA4T products as raw materials.

This 21st century's first new polymer, with excellent space stability, lead-free soldering compatibility, high melting point, in the case of temperature rise with high hardness and mechanical strength, and compared to DSM's original PA46 products, even PA9T, it shows ultra-low water absorption.

The comprehensive and excellent performance of PA4T will make it occupy an important share in the future high-temperature applications such as electronics and automobiles. The invention of PA4T is also a manifestation of higher requirements for performance materials due to market miniaturization and centralization of electronic products.

6.3 PA10T

Cao Ming, Zhang Mingqiu and others in China have carried out a systematic study on the synthesis and copolymerization modification of PA10T, and the results show that pure PA10T has a high melting point of 319.1 degrees C, and its excellent heat resistance makes PA10T show potential commercial value. The leading domestic plastic modification enterprise-blonde technology has commercialized this technology.

At the rubber and plastic exhibition in 2009, Blonde Company solemnly introduced PA10T product with brand name Vicnyl. It has excellent heat resistance, ultra-low water absorption, better dimensional stability, lead-free solder temperature up to 280 ℃, excellent chemical resistance and injection molding processing performance.

Moreover, it is said that nearly half of the raw materials of PA10T resin come from castor, which is a bio-based environmental protection material with excellent comprehensive performance and strong market competitiveness. The commercialization of PA10T products has filled the gap of independent research and development of new high-temperature nylon materials in our country, and Blonde Company has also become the second domestic unit with high-temperature nylon industrialization technology after Shanghai Jieshajie Company.

6.4 other PPA materials

PPA (semi-aromatic nylon) is prepared by polycondensation of aliphatic diamine or diacid with aromatic ring diacid or diamine. In addition to the above mentioned PA4T, PA6T, PA9T, PA10T and other materials, there are PAMXD6, PA12T and many other PPA varieties. Because these nylon materials have aromatic ring structure in the chemical structure, the thermal deformation temperature is increased to varying degrees. Among them, DuPont synthesized PA12T with dimethyl terephthalate (DMT) and dodecylamine (DDMD), with a melting point of 296.6 ℃, which has a strong application value.