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With the development of miniaturization of automobiles, high performance of electronic and electrical equipment and lightweight of mechanical equipment, the demand for nylon will be increasing. In particular, as a structural material, nylon requires high strength, heat resistance and cold resistance. The inherent shortcomings of nylon are also an important factor limiting its application. Especially PA6 and PA66, compared with PA46, PAl2 and other varieties, have a strong price advantage, although some properties can not meet the requirements of the development of related industries. Therefore, it is necessary to improve some properties of a certain application field through modification to expand its application field. PA has strong polarity, strong hygroscopicity and poor dimensional stability, but it can be improved by modification.
1. enhanced PA
Adding 30% glass fiber to PA can obviously improve the mechanical properties, dimensional stability, heat resistance, aging resistance and fatigue resistance of PA.
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The strength is 2.5 times that of unreinforced. The molding process of glass fiber reinforced PA is basically the same as that of unreinforced PA, but the fluidity ratio is worse than that before reinforcement. Therefore, the injection pressure and speed should be appropriately increased, and the barrel temperature 10-40℃ should be increased. Because the glass fiber will be oriented along the flow direction in the injection molding process, the mechanical properties and shrinkage will be enhanced in the orientation direction, which will lead to the deformation and warping of the product. Therefore, when designing the mold, the position and shape of the gate should be reasonable, which can technically improve the temperature of the mold. After the product is taken out, it will be slowly cooled in hot water. In addition, the greater the proportion of glass fiber, the greater the wear of plasticizing parts of injection molding machine, and it is best to use bimetallic screw and barrel.
2. Flame retardant PA
Due to the addition of flame retardants to PA, most of the flame retardants are easy to decompose at high temperature, releasing acidic substances, which have corrosive effects on metals. Therefore, plasticized parts (screws, rubber shoes, rubber shoes, rubber shoes, flanges, etc. ) Hard chromium plating is required. In the process, try to control the barrel temperature not to be too high and the injection speed not to be too fast, so as to avoid the discoloration of the product and the decline of mechanical properties caused by the decomposition of rubber due to too high temperature.
3. Transparent PA
It has good tensile strength, impact strength, rigidity, wear resistance, chemical resistance, surface hardness and other properties, and has high light transmittance, which is similar to optical glass. The processing temperature is 300-365,438 05℃. In the molding process, the barrel temperature should be strictly controlled. If the melt temperature is too high, the product will change color due to degradation, and if the temperature is too low, the transparency of the product will be affected due to poor plasticization. The mold temperature should be kept as low as possible. If the mold temperature is high, the transparency of the product will be reduced due to crystallization.
4. weather-resistant PA
Adding additives such as carbon black to absorb ultraviolet rays into PA greatly enhances the self-lubricating property of PA and the abrasion of metal, which will affect the blanking and abrasion of parts during molding. Therefore, the combination of screw, barrel, rubber-passing head, rubber-passing ring and rubber-passing ring with strong feeding ability and high wear resistance must be adopted. A polymer in which the repeating structural units in the polyamide molecular chain are amide groups.
To sum up, the main changes are as follows:
① Improve the water absorption of nylon and the dimensional stability of the product.
② Improve the flame retardancy of nylon and meet the requirements of electronic, electrical and communication industries.
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③ Improve the mechanical strength of nylon, reach the strength of metal material and replace metal.
④ Improve the low temperature resistance of nylon and enhance its ability to resist environmental strain.
⑤ Improve the abrasion resistance of nylon, so as to adapt to occasions with high abrasion resistance requirements. ⑥ Improve the antistatic performance of nylon to meet the requirements of mine and its mechanical application.
⑦ Improve the heat resistance of nylon to adapt to the field of high temperature conditions such as automobile engines.
⑧ Reduce the cost of nylon and improve the competitiveness of products.
In a word, through the above improvements, the high performance and functionalization of nylon composite materials have been realized, and then the products of related industries have been promoted to develop in the direction of high performance and high quality.
5. Nano nylon
According to Toray Chemical Company of Japan, the company has successfully developed a new technology of nano-scale monofilament structure, which is two digits smaller than the previous superfine fiber diameter, and achieved the limit of fiber fineness by controlling the nano-structure technology. Toray Chemical Company said that nano nylon fibers with a diameter of 10μm and a monofilament of more than1.4000 were developed by using this new technology. Compared with the previous products, the surface area of this fiber is about 1000 times that of the previous products, and it has high surface activity. [ 1]
6.super nylon
Triangle-Raleigh nylon fiber has many uses, from clothing and carpets to ropes to data lines of microcomputers. Researchers at the Textile College of the University of North Carolina are working hard to improve this fiber, and it is reported that the strongest aliphatic nylon fiber has been developed.
Dr. Tonelli, a scientist professor of polymers, and Dr. Richard Ketak, an assistant professor of textile engineering, chemistry and natural science, are studying a method to produce nylon fibers with higher strength without expensive and complicated processes. They used aliphatic nylon or nylon for research. The carbon auxiliary of this kind of nylon is connected by straight chain or spending chain, which emphasizes the large acyclic chain.
Stronger aliphatic nylon can be used in ropes, loading and unloading belts, parachutes and automobile tires, or to produce synthetic materials suitable for high temperature utilization. This discovery was presented at the annual meeting of American Chemical Science in Philadelphia and published in the journal Polymer.
This kind of fiber is made of polymers or long-chain molecules including many units. When these polymer chains are arranged neatly, this polymer will become crystalline.
These crimped polymers need to be stretched, and if they are to be made into stronger fibers, their elasticity needs to be eliminated. Hydrogenation on nylon chain can prevent stretching, so overcoming this combination is the key factor to produce stronger nylon fiber.
Superfibers, such as Kevlar fibers, are made of aromatic nylon polymers, which are very hard and have long chains with cyclic chains. Aromatic nylon is difficult to manufacture, so it is expensive.
Therefore, Professor Tonelli and Dr Ketak used polyamide 66 (nylon 66) for research. This material is a commercial thermoplastic material, which is easy to manufacture, but difficult to stretch and arrange. At the same time, the elasticity of nylon 66 is difficult to offset.
This discovery solved the problem that nylon 66 can be dissolved in gallium trichloride and effectively broke the hydrogen bond problem. Allowing the polymer chain to extend.
7.PA nylon
The mechanical properties of PA, such as tensile strength and compressive strength, change with temperature and hygroscopicity, so water is the plasticizer of PA. After adding glass fiber, its tensile and compressive strength can be improved by about 2 times, and its temperature resistance is also improved accordingly. PA itself has very high wear resistance, so it can run without lubrication. If you want to obtain special lubrication effect, you can add sulfide to PA.
Suitable for plastic products: all kinds of gears, turbines, racks, cams, bearings, propellers and transmission belts.
Others: shrinkage 1-2%, pay attention to the dimensional change of moisture absorption after molding.
Water absorption: 100% can absorb 8% when the relative moisture absorption is saturated.
Suitable wall thickness: 2-3.5mm.
8.PA66
High fatigue strength and rigidity, good heat resistance, low friction coefficient and good wear resistance, but high hygroscopicity and insufficient dimensional stability.
Application: medium load, working temperature
PA6
The fatigue strength, rigidity and heat resistance are lower than those of nylon 66, but it has good elasticity and good vibration and noise reduction ability. white
Application: Wear-resistant stress transmission parts with no or little lubrication and low noise working under light load and medium temperature (80- 100).
PA6 10
The strength, rigidity and heat resistance are lower than those of nylon 66, but the hygroscopicity is low and the wear resistance is good. Khaki
Usage: Like nylon 6, it is suitable for gears with relatively precise requirements and parts with large humidity changes under working conditions.
PA 10 10
The strength, rigidity, heat resistance and hygroscopicity are lower than those of nylon 66 and nylon 6 10, respectively. Good molding process and good wear resistance.
Application: Parts working under light load, low temperature, great humidity change and no or little lubrication.
MCPA
Strength, fatigue resistance, heat resistance and rigidity are better than PA6 and PA66, and hygroscopicity is lower than PA6 and PA66, so it has good wear resistance. Can be directly aggregated in the model, suitable for casting large parts. Application: High load, high working temperature (below 120), no or little lubrication. elephant's tusk
Cast nylon
Casting nylon (MC nylon), also known as monomer casting nylon, is a product body obtained by direct polymerization of caprolactam monomer with a mold under the action of strong alkali (such as NaoH) and some cocatalysts. Due to the combination of polymerization and molding technology, the molding is convenient, the equipment investment is low, and it is easy to manufacture large machine parts. Its mechanical properties and physical properties are higher than those of nylon 6. It can manufacture dozens of kilograms of gears, turbines, bearings and so on.
Nylon 10 10
Nylon 10 10 is an original engineering plastic in China, which is condensed from castor oil, decylamine and sebacic acid. Low cost, good economic effect, excellent self-lubrication and wear resistance, good oil resistance, low ductile-brittle transition temperature (about -60℃) and high mechanical strength, which are widely used in mechanical parts and chemical electrical parts.
Modified nylon
Modified nylon is a kind of engineering plastics, which is a granular product based on nylon raw materials and formed by changing its physical properties. The output of such products is adjusted according to the different needs 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: glass transition temperature (Tg) and melting point (TM); High heat distortion temperature (HDT); Long-term use of high temperature (UL-746b); The use temperature range is large; Low thermal expansion coefficient. 2. Mechanical properties: high strength, high mechanical modulus, low creep, strong wear resistance and fatigue resistance. 3. Others: good chemical resistance, resistance, flame retardancy, weather resistance and dimensional stability. The output of this kind of products is modified according to the different needs 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. Modified nylon has many characteristics, so it is widely used in automobiles, electrical equipment, mechanical parts, transportation equipment, textiles, paper machinery and so on [2].
Aromatic nylon
Aromatic nylon, also known as polyaramid, is a new kind of nylon with high temperature resistance, radiation resistance and corrosion resistance, which was first developed by DuPont Company in the 1960s. Any nylon molecule containing aromatic ring structure belongs to aromatic nylon. If only the diamine or diacid of synthetic nylon is replaced by aromatic diamine or aromatic diacid respectively, the obtained nylon is semi-aromatic nylon, and the nylon synthesized from aromatic diacid and aromatic diamine is fully aromatic nylon. Brittle temperature of aromatic nylon can reach -70℃, and Vicat softening temperature can reach 270℃. It has high temperature resistance, radiation resistance, corrosion resistance, wear resistance and self-extinguishing, and can maintain high electrical properties in wet state. Aromatic nylon can be extruded, molded, laminated and impregnated, and can be used to manufacture fibers, films, impregnated films, decorative laminates, glass fiber reinforced laminates, high-temperature radiation-resistant conduits, firewalls and the like. Semi-aromatic nylons that have been commercialized mainly include MXD6, PA6T and PA9T, and fully aromatic nylons mainly include poly (p-phenylene terephthalamide), poly (m-phenylene terephthalamide) and poly (p-toluamide).
All-aromatic nylon was successfully developed and industrialized by DuPont in 1960s and 1970s. Fully aromatic nylon is widely used in the production of synthetic fibers because of its high melting point, high modulus and high strength. PPTA is prepared from p-phenylenediamine and terephthaloyl chloride by low temperature solution polymerization developed by DuPont. PPTA has excellent properties such as high strength, high modulus, high temperature resistance and low density. Mainly used as raw material for synthetic fiber spinning; PPTA fiber can also be used as rubber reinforcing material and plastic reinforcing agent. However, PPTA has the shortcomings of fatigue resistance and pressure resistance, and PPTA can not realize melt extrusion molding.
MXD6
MXD6 is a crystalline nylon resin synthesized by condensation polymerization of m-xylylenediamine and adipic acid by Lum et al in 1950s. MXD6 was synthesized by direct polycondensation of Mitsubishi Gas Chemical Company of Japan and nylon salt method of Toyo Textile Company. The uses of MXD6 obtained by these two different polymerization methods are also different: MXD6 synthesized by direct polycondensation can be used to make barrier materials or engineering structural materials; MXD6 synthesized by nylon salt method can be used to produce fiber-grade MXD6 resin. As a kind of crystalline semi-aromatic nylon, MXD6 has the characteristics of low water absorption, high thermal deformation temperature, high tensile strength and bending strength, small molding shrinkage, and good barrier to gases such as O2 and CO2. MXD6 can be extruded with polypropylene (PP) and blown with high density polyethylene (HDPE) because of its wide processing temperature. In industry, MXD6 mainly replaces metal as packaging material and engineering structure material. The former includes food and beverage packaging and equipment packaging (moisture-proof, shock-absorbing pads and foaming materials); The latter includes high heat-resistant Raney, MXD6/PPO alloy, anti-vibration Raney and so on. In addition, MXD6 is also used in magnetic plastics, transparent adhesives and so on.
PA6T
PA6T is a semi-aromatic nylon synthesized from aromatic diacid and aliphatic diamine. PA6T has excellent heat resistance and dimensional stability. Because of its high melting point, PA6T can be prepared by solid-state polymerization or interfacial polymerization. It can be used in fiber manufacturing, mechanical parts and film products. The modified PA6T developed by Mitsui Chemical Co., Ltd. in Japan has the characteristics of high rigidity, high strength and low water absorption, and is mainly used in automobile internal combustion engine parts, heat-resistant electrical parts, transmission parts and electronic components. 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.
PA9T
PA9T is formed by melt polycondensation of nonylenediamine and terephthalic acid, which was first developed by Japan Cola Company. PA9T has good heat resistance and melt processability, and its water absorption is only 0. 17%, which is110 of PA46( 1.8%), and its dimensional stability is good. It is widely used in electronic and electrical, information equipment, auto parts and other fields. When the number of carbon atoms of diamine in the repeating unit chain is 6, the melting point of PA6T is 370℃, which is about 350℃ higher than its thermal decomposition temperature. Therefore, if the third or even fourth component is not added to lower the melting point, it is impossible to obtain practical nylon (the melting processing temperature of nylon is generally below 320℃). However, if other components are added to lower the melting point, the crystallinity, dimensional stability and chemical resistance of PA6T will inevitably decrease. Therefore, increasing the number of carbon atoms in 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 synthetic route of nonane diamine, the main raw material for the synthesis of PA9T, is complicated: nonane diamine can be obtained through chemical reactions such as hydration, translocation, hydroxylation, ammoniation and reduction of butadiene. This leads to the high production cost of PA9T, which further limits the large-scale production and application of PA9T.
Polyphenyldiamide
Polyphenyldiamide (PPA) is a semi-crystalline semi-aromatic nylon, which is a polymer mixture formed by polycondensation of isophthalic acid, terephthalic acid, adipic acid and hexamethylenediamine. PPA resin is usually produced in batch mode. PPA has good heat resistance, excellent mechanical properties and dimensional stability, low water absorption and excellent 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 terephthalamide)
Poly (p-phenylene terephthalamide) (MPIA) is a new type of polyaramid developed by DuPont Company in 1960s. It is synthesized by m-phenylenediamine and m-phthaloyl chloride through low temperature solution polycondensation and interfacial polymerization. MPIA's outstanding features are long heat-resistant life, in addition, it also has the advantages of high modulus, wear resistance, flame retardancy, high-temperature dimensional stability and so on. However, MPIA's light resistance is a little poor, so it is necessary to add anti-ultraviolet agents. MPIA is mainly used in work clothes, high-temperature industrial filter materials, parachutes, high-temperature conveyor belts, electrical insulation materials and so on. In industrial and flammable and explosive high temperature environment. MPIA can also be processed into rods, plates and fibers, which are used in aerospace, atomic energy industry, electrical and automobile industries because of its excellent heat resistance, sliding resistance and radiation resistance.
Poly (p-benzamide)
Poly (p-benzamide, PBA for short) was successfully developed by DuPont in 1970s. Its synthetic route is as follows: p-nitrotoluene is oxidized by air in liquid phase to obtain p-nitroformic acid, and then p-nitroformic acid is obtained by ammoniation reduction reaction, and p-aminobenzoic acid is converted into hydrochloric acid of p-aminobenzoyl chloride or p-thioamide benzoyl 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 shells, high-pressure vessels, sporting goods and coated fabrics in industry.