With the miniaturization of automobiles, the higher performance of electronic and electrical equipment, and the acceleration of the process of lightweight mechanical equipment, the demand for nylon will be higher and greater. Especially nylon, as a structural material, puts forward high requirements on its strength, heat resistance, and cold resistance. The inherent shortcomings of nylon are also important factors that limit its application. Especially for the two major varieties of PA6 and PA66, they have a strong price advantage compared with varieties such as PA46 and PAl2, although some properties cannot meet the development requirements 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 it can be improved by modification.
Enhanced PA
30% glass fiber is added to PA, the mechanical properties, dimensional stability, heat resistance, and aging resistance of PA are significantly improved, and the fatigue strength is 2.5 times that of unreinforced. The molding process of glass fiber reinforced PA is roughly the same as that when it is not reinforced, 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°C. Since the glass fiber is oriented along the flow direction during the injection molding process, the mechanical properties and shrinkage rate will increase in the orientation direction, resulting in deformation and warpage of the product. Therefore, when designing the mold, the position and shape of the gate should be reasonable, and the process can be improved. The temperature of the mold, put the product in hot water after taking it out, and let it cool down 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 better to use bimetallic screws and barrels.
Flame retardant PA
Because flame retardants are added to PA , most flame retardants are easy to decompose at high temperature, release acidic substances, and have a corrosive effect on metals. Therefore, plasticizing components (screw, rubber head, rubber ring, rubber Washers, flanges, etc.) need to be hard chrome plated. In terms of technology, try to control the temperature of the barrel not to be too high and the injection speed not to be too fast to avoid discoloration of the product and degradation of mechanical properties due to the decomposition of the rubber material due to the high temperature.
Transparent PA
It has good tensile strength, impact strength, rigidity, abrasion resistance, chemical resistance, surface hardness and other properties, high light transmittance, similar to optical glass, processing temperature is 300-315 ℃, when molding processing, it needs Strictly control the temperature of the barrel. Too high melt temperature will cause discoloration of the product due to degradation, and 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
Adding carbon black and other auxiliaries that absorb ultraviolet rays to PA greatly enhances the self-lubricity of PA and the wear to metal, which will affect the blanking and wear of parts during the molding process. Therefore, it is necessary to use a combination of screw, barrel, rubber head, rubber ring, and rubber gasket with strong feeding capacity and high wear resistance. The repeating structural unit on the polyamide molecular chain is a type of polymer with amide groups.
To sum it up, it is mainly modified in the following aspects:
①Improve the water absorption of nylon and improve the dimensional stability of products.
②Improve the flame retardancy of nylon to meet the requirements of electronics, electrical, communications and other industries. ③Improve the mechanical strength of nylon to achieve the strength of metal materials and replace metal
④Improve the low temperature resistance of nylon and enhance its ability to withstand environmental strains.
⑤Improve the abrasion resistance of nylon to adapt to the occasions with high requirements for abrasion resistance. ⑥Improve the antistatic property of nylon to meet the requirements of mines and their mechanical applications.
⑦Improve the heat resistance of nylon to adapt to areas with high temperature conditions such as automobile engines.
⑧Reduce the cost of nylon and improve product competitiveness.
In short, through the above improvements, the high performance and functionalization of nylon composite materials will be realized , and the products of related industries will be promoted to develop in the direction of high performance and high quality.
Nano nylon
According to Toray Chemical Company of Japan, the company has successfully developed a new technology of " nano fiber " with a nanometer monofilament structure with a diameter of two digits smaller than that of the previous ultra-fine fibers. The nanometer structure technology is controlled to reach the limit of fiber fineness. . Toray Chemical Company said that the company has developed nano-nylon fibers composed of more than 1.4 million monofilaments with a diameter of 10 μm 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.
Super Nylon
Triangle-Raleigh nylon fiber has many uses, from clothing, carpets to ropes to data lines of microcomputers can use this kind of fiber. Researchers at the University of North Carolina's School of Textiles are working hard to improve this fiber, and it is reported that the strongest aliphatic nylon fiber has been developed.
Scientist Polymer Professor-Dr. Tonelli and Dr. Richard Cuttack, Assistant Professor of Textile Engineering, Chemistry and Natural Sciences, are working on a way to produce higher yields without the need for expensive and complicated processes Strong nylon fiber. They used aliphatic nylon or nylon for research. The carbon aid of this nylon was connected by straight or open branched chains before, emphasizing that the chain is not large.
Stronger aliphatic nylon can be applied to ropes, loading and unloading belts, parachutes and car tires, or to produce synthetic materials that can be used in high temperatures. This discovery was presented at the American Chemical Science Annual Conference in Philadelphia and published in the Journal of Polymers.
This kind of fiber is made of polymers or long-chain molecules consisting of many units. When these polymer chains are neatly arranged, this polymer will become crystalline.
These coiled polymers need to be stretched, and if they are to be made into stronger fibers, their elasticity needs to be eliminated. Adding hydrogen to the nylon chain can prevent stretching, so overcoming this combination is a key factor in producing stronger nylon fibers.
Super-strong fiber, taking Kevlar fiber as an example, is made from aromatic nylon polymer. It is very stiff, and its long chain contains cyclic chains. It is difficult to make aromatic nylon and therefore very expensive.
Therefore, Professor Tonelli and Dr. Ketak used polyamide 66 (nylon 66) for research. This material is a commercial thermoplastic material that is easy to make, but difficult to stretch and arrange. At the same time, it is difficult to cancel the elasticity of nylon 66.
This discovery can solve the problem that nylon 66 can be dissolved in gallium trichloride and can effectively break the problem of hydrogen bonding. Allow polymer chain extension.
PA nylon
Among the mechanical properties of PA, the tensile and compressive strength changes with temperature and moisture absorption, so water is relatively PA plasticizer . After adding glass fiber, its tensile and compressive strength can be increased by about 2 times, and the temperature resistance is also Correspondingly, the wear resistance of PA itself is very high, so it can be operated continuously without lubrication. If you want a special lubricating effect, you can add sulfide to PA.
Suitable plastic products: various gears, turbines, racks, cams, bearings, propellers, transmission belts.
Others: shrinkage rate of 1-2%, pay attention to the dimensional change of moisture absorption after molding.
Water absorption rate: 100% relative moisture absorption can absorb 8% when saturated.
Suitable wall thickness: 2-3.5mm
PA66
The fatigue strength and rigidity are high, the heat resistance is good, the friction coefficient is low, the wear resistance is good, but the moisture absorption is large, and the dimensional stability is not enough.
Application: Medium load, wear-resistant force transmission parts that work under the conditions of no lubrication or less lubrication at a temperature of <100-120 degrees.
PA6
Fatigue strength, rigidity and heat resistance are lower than nylon 66, but it has good elasticity, good vibration absorption and noise reduction capabilities. White
Application: Light load, medium temperature (80-100), wear-resistant force transmission parts that work under conditions with no or little lubrication and low noise requirements.
PA610
Strength. Rigidity and heat resistance are lower than nylon 66, but it has low moisture absorption and good abrasion resistance. Khaki
Application: Same as nylon 6, suitable for gears requiring more precision and parts with large changes in working conditions and humidity.
PA1010
Strength, rigidity and heat resistance are lower than nylon 66, moisture absorption is lower than nylon 610, molding process is good, and abrasion resistance is good.
Application: parts that work under light load, low temperature, large humidity changes, and no or less lubrication
MCPA
Strength, fatigue resistance, heat resistance, rigidity are better than PA6 and PA66, moisture absorption is lower than PA6 and PA66, good wear resistance, can be directly polymerized in the model, suitable for casting large parts. Application: under high load, high use temperature (below 120) without lubrication or less lubrication. milky
Cast nylon
Casting nylon (MC nylon) is also called monomer cast nylon. It uses caprolactam monomer under the action of strong alkali (such as NaOH) and some co-catalysts to directly polymerize the product with a mold to obtain the rough part of the product. The molding process is integrated, so the molding is convenient, the equipment investment is small, and it is easy to manufacture large machine parts. Its mechanical properties and physical properties are higher than nylon 6. It can manufacture gears, turbines, bearings, etc. of dozens of kilograms.
Nylon 1010
Nylon 1010 is a kind of original engineering plastic in our country. It is made from castor oil as raw material, extracting decanediamine and sebacic acid and then condensing it. Low cost, good economic effect, excellent self-lubrication and wear resistance, good oil resistance, low brittleness transition temperature (about -60 ℃), high mechanical strength, 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 as the base material. The output of this type of product 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.
1. Thermal properties: glass transition temperature (Tg), melting point (Tm), heat distortion temperature (HDT) are high; long-term use temperature is high (UL-746B); use temperature range is large; thermal expansion coefficient is small.
2. Mechanical properties: high strength, high mechanical modulus, low creep, strong wear and fatigue resistance.
3. Others: chemical resistance, electrical resistance, flame resistance, weather resistance, and good dimensional stability.
Aromatic nylon
Aromatic nylon, also known as polyaramid , is a new variety of nylon with high temperature resistance, radiation resistance and corrosion resistance developed in the 1960s. Anything that contains an aromatic ring structure in the nylon molecule belongs to the aromatic nylon. If only the diamine or dibasic acid of synthetic nylon is replaced by aromatic diamine or aromatic diacid respectively, the nylon obtained is semi-aromatic nylon, and the nylon synthesized by aromatic diacid and aromatic diamine is Fully aromatic nylon. Aromatic nylon embrittlement temperature can reach -70℃, Vicat softening temperature can reach 270℃, high temperature resistance, radiation resistance, corrosion resistance, abrasion resistance, self-extinguishing, and can maintain high electrical performance in a humid state . Aromatic nylon can be extruded, molded, laminated, impregnated, and can be used to manufacture 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. The fully aromatic nylons mainly include polyparaphenylene terephthalamide (PPTA), polymetaphenylene isophthalamide (MPIA) and poly P-benzamide (PBA) and so on.
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 reinforcing materials and plastics. However, PPTA has the shortcomings of fatigue resistance and pressure resistance, PPTA can not achieve melt extrusion molding.
MXD6
MXD6 is a crystalline nylon resin synthesized by Lum et al. in the 1950s using meta-xylylenediamine and adipic acid as raw materials through polycondensation. 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 distortion temperature, high tensile and bending strength, low molding shrinkage, and good barrier properties to gases such as O 2 , CO 2 and so on. Because of its wide processing temperature, MXD6 can be co-extruded with polypropylene (PP) and co-extruded with high-density polyethylene (HDPE). In industry, MXD6 is mainly used for packaging materials and instead of metal as engineering structural materials. The former includes food and beverage packaging, equipment packaging (moisture-proof, vibration-absorbing cushions and foam materials); the latter includes high heat-resistant grade Reny, MXD6/PPO alloy, vibration-resistant Reny, etc. In addition, MXD6 is also used in magnetic plastics, transparent adhesives, etc.
PA6T
PA6T is a semi-aromatic nylon synthesized from aromatic diacids and aliphatic diamines. PA6T has excellent heat resistance and dimensional stability. Due to the high melting point of PA6T, it can be prepared by solid-phase polymerization or interfacial polymerization. It can be used in 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 automobile internal combustion engine parts, heat-resistant electrical parts, transmission parts and electronic assembly parts. 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 obtained by melt polycondensation of nonanediamine and terephthalic acid . PA9T has good heat resistance and melt processability, water absorption is only 0.17%, which is 1/10 of PA46 (1.8%), and has good dimensional stability. It is quickly used in electronic and electrical, information equipment, and automotive parts. It has been widely used. When the number of carbon atoms of the diamine in the repeating unit chain is 6, the melting point of PA6T is 370°C, which exceeds its thermal decomposition temperature by about 350°C. Therefore, if the third is not added, it is even The fourth component to lower the melting point is a nylon that cannot be used in practical applications (the nylon melt processing temperature is generally below 320°C), but if other components are added to lower the melting point, it will inevitably bring PA6T properties such as crystallinity and dimensional stability. Therefore, increasing the number of diamine carbon atoms has become another research hotspot. The structure of PA9T has become an ideal structure, which has both heat resistance and melt processability. However, The synthesis route of nonanediamine, the main raw material for the synthesis of PA9T, is more complicated: butadiene undergoes hydration, transposition, hydroxylation, and ammonia reduction and other steps of chemical reactions to finally obtain nonanediamine. This results in the production cost of PA9T. The high level further limits the mass production and application of PA9T.
Polyphthalamide
Polyphthalamide (PPA) is a blend of polymers formed by polycondensation between isophthalic acid , terephthalic acid , adipic acid and hexamethylene diamine . 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(metaphenylene isophthalamide)
Poly-metaphenylene isophthalamide (MPIA) is a new type of polyaramid which was successfully developed in the 1960s. It is made of meta-phenylene diamine and isophthaloyl chloride . It can be polycondensed by low-temperature solution. And interfacial polymerization method synthesis. The outstanding feature of MPIA is its long heat-resistant life. In addition, it also has the advantages of high modulus, wear resistance, flame-retardant, and high-temperature dimensional stability. However, the light resistance of MPIA is slightly poor, and an anti-ultraviolet agent is required. MPIA is mainly used in industrial and flammable and explosive high-temperature working clothes, high-temperature industrial filter materials, parachutes, high-temperature conveyor belts, electrical insulation materials, etc. MPIA can also be processed into rods, plates and fibers, and is used in aerospace, atomic energy industry, electrical and automotive industries due to its excellent heat resistance, sliding properties and radiation resistance.
Polyparabenzamide
Poly(p-benzamide, referred to as PBA) was successfully developed in the 1970s. Its synthesis route is: p-nitrotoluene undergoes liquid phase air oxidation to obtain p-nitroformic acid, and p-nitroformic acid undergoes liquid-phase air oxidation. Amidation reduction reaction produces p-carbamic acid, which converts p-aminobenzoic acid into p-aminobenzoyl chloride hydrochloride or p-thionamide benzoyl chloride, and finally PBA is prepared by polycondensation. PBA has high modulus and high strength It can be used in industry for rocket engine shells, high-pressure vessels, sporting goods and coated fabrics.
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