Nylon material modification technology for automobile and its application
Nylon (PA), as one of the most commonly used engineering plastics, has higher mechanical properties and heat resistance than general-purpose plastics, as well as excellent abrasion resistance, fatigue resistance, corrosion resistance, electrical insulation and ease of processing, etc., and is widely used in automotive, mechanical and other engineering fields.
In all kinds of automotive parts, compared to polypropylene (PP), PA is more often used in parts with higher performance requirements, such as engine peripheral parts, various pipelines, etc. Therefore, PA needs to be modified to enhance the mechanical properties of PA, heat resistance, and to make the PA to obtain more functional properties, so that it can better meet the automotive structural components, functional parts of the application requirements.
Most of the modification of PA is physical modification, including fiber reinforced modification, inorganic particle filling modification, blending modification, foam modification, etc. For high temperature PA, copolymerization modification is also a commonly used modification method.
First, automotive general PA modification technology research
1. Fiber reinforced modification
Fiber reinforced modification is one of the most commonly used modification technology, its main purpose is to enhance the mechanical properties of PA, the reinforcing fibers used are mainly glass fiber (GF) and carbon fiber (CF). The mechanical properties of fiber-reinforced PA are closely related to the type, length, content of fibers and the interfacial bonding state of fibers and PA, and are also strongly influenced by the preparation process. Compared with short fibers, continuous fibers and fiber braids enhance the mechanical properties of PA more, but their preparation process is more complicated, and the adequate impregnation of continuous fibers and fiber braids with PA resin is the key factor for the successful preparation of these fiber-reinforced modified PA composites.
Compared with short fibers, continuous fiber-reinforced thermoplastic composites have higher comprehensive mechanical properties, and have become a research hotspot and development focus in the fields of automobile manufacturing, rail transportation and aerospace.
Compared with single fibers, fiber braids can reinforce thermoplastic composites in multiple directions in two or three dimensions, and relative to thermoset composites, fiber braids reinforced thermoplastic composites have shorter molding cycles, thus their manufacturing costs are relatively low, and they can be recycled many times, so they are increasingly used in automotive and other fields.
In addition to CF and GF, basalt fiber (BF) can also be used to reinforce PA, some researchers have prepared PA6/BF composites with natural and environmentally friendly BF as the reinforcing material, in order to solve the problem of poor interfacial bonding between BF and resin matrix.
2. Inorganic particle filling modification
Inorganic particles are widely available, inexpensive, and can enhance certain properties of plastics, most of which are used for filler modification of plastics. However, most of the inorganic particles are poorly compatible with the resin matrix in plastics, and it is generally necessary to carry out surface modification, or add capacitance enhancers to improve the interfacial compatibility. Adding surface-treated inorganic particles to PA, or adding a bulking agent to the inorganic particle-filled PA system can significantly improve the mechanical properties of PA, which can be used in automotive manufacturing and other fields. In addition, inorganic particles can also be added to the fiber reinforced PA system to play the role of synergistic modification of inorganic particles and fibers.
Silica is added to PA6 to improve the mechanical properties of PA6, and this modification of silica helps to improve the performance of PA products applied in the field of automotive parts.
Talc is utilized to modify PA6 materials for automotive applications to reduce material costs and enhance material properties. The processing properties of PA6 composites can be significantly improved and the tensile properties can be significantly enhanced, while the flexural and thermal properties of pure PA6 are maintained.
Graphene nanosheets are added to PA610, which can be used to enhance the mechanical and thermal properties of automotive PA610 materials.
3. Foaming modification
Lightweight is currently one of the main directions of automobile development. The use of foaming technology to prepare PA-based microporous foam materials can not only obtain a better lightweight effect, the presence of microbubble holes can also make PA materials to obtain such characteristics as sound insulation, heat insulation, etc., which enhances the potential for the application of PA materials in automobiles.
4.Blending modification
A researcher prepared a new energy vehicle high-voltage connector with halogen-free flame retardant reinforced PA66/PA6 alloy, using the compound flame retardant system for the diethyl phosphonic acid aluminum and aluminum phosphite, reinforcing system for the GF. found that the effect of PA6 on the alloy's flame retardant properties is very small, with the increase in the content of PA6 alloy alloy, the alloy strength and modulus decreased, the notched impact strength has increased. After aging at 85℃/85% relative humidity for 1000h, the water absorption of the alloy increased with the increase of PA6 content, and the electrical insulation properties under high temperature conditions gradually decreased with the increase of PA6 content in the alloy.
In addition, PA6/ABS color-bearing alloy materials for automobiles were prepared by blending acrylonitrile-butadiene-styrene copolymer (ABS) high gum powder with PA6. In addition, the rate of color change of the material after thermo-oxidative aging was reduced by adding titanium dioxide. The prepared PA6/ABS gray alloy material has been successfully applied to automotive child seat parts.
5. Heat-resistant modification
A study synthesized four kinds of maleic anhydride copolymerization heat-resistant agent, respectively, containing a rigid structure of poly (N-phenylmaleimide-alt-styrene) (PNS), carboxyl group-containing PNS (PCS), fluorine group-containing PNS (PFS) and contain a cross-linking structure of poly (N-(4-carboxyphenyl) maleimide-alt-triallyl isocyanate) (PCT), to investigate the effect of these four kinds of heat-resistant agent on the PA6/ABS gray alloy material has been successfully applied to automotive child seat parts. 4 heat-resistant agents on the heat-resistant properties of PA6. The results showed that the heat resistance of PCT-modified PA6 was the best, followed by PFS (10%) modified PA6 (182.3°C), again PCS (10%) modified PA6 (164.8°C), and finally PNS (15%) modified PA6 (138.5°C).
Second, the study of modification technology of high temperature resistant PA for automotive use
Compared with conventional PA (PA66 and PA6, etc.), high-temperature-resistant PA can withstand higher temperatures, has better heat-resistant properties, and is more suitable for the manufacture of automotive parts that require higher heat-resistant properties. However, the melting point of high-temperature resistant PA is higher, the molding processability is poor, generally need to copolymerize with other monomers to obtain good processing performance.
Through the high temperature and high pressure solution polycondensation method, in the polymerization kettle for PA6T and PA66 mixed into salt, and then through the direct polycondensation of PA6T / 66 copolymer. It is characterized by excellent heat resistance and good processability and can be used for automotive connectors.
Prepared by high-temperature solution polymerization method, a semi-biobased high-temperature copolymer PA - poly(terephthalic acid) - pentylenediamine / adipic acid - pentylenediamine (PA5T/56), this semi-biobased high-temperature copolymer PA has a better thermal decomposition stability than PA6T/66 and carbon formation, and the mechanical properties with the PA6T/66 equivalent This semi-bio-based high-temperature copolymerized PA has better thermal decomposition stability and char formation than PA6T/66, and its mechanical properties are comparable to those of PA6T/66.
Through the first solution polymerization and then solid-phase polycondensation of hexylenediamine, copolymerization of diamine and dibutyl oxalate for polymerization, produced a high heat-resistant PA62 copolymer materials. This type of material has a wide range of application prospects in fields requiring high heat resistance such as automobile engine periphery.
In view of the excellent barrier properties, mechanical properties, heat resistance and low water absorption of poly(hexanediyl m-toluene dimethylamine) (PAMXD6), the use of GF reinforced modified PAMXD6, and at the same time adding antioxidant 1098 and lubricant TAF101, to prepare a GF-reinforced PAMXD6 composite material, which has high strength, excellent dimensional stability, excellent surface properties (no floating fiber) and other characteristics.
Third, the application of modified PA in automobile research
3.1 Piping parts
Piping parts in the automobile occupies a very important position, and its types are many, including oil pipeline, coolant pipe, brake pipeline and so on. Automotive piping parts in addition to requiring the corresponding material has good mechanical properties, should also have excellent hydrolysis resistance, weather resistance, high temperature resistance and other characteristics.
PA is a commonly used material for automotive piping parts, but the shorter carbon chain PA (such as PA6 and PA66) amide bond density, easy to absorb water, easily affecting the strength and hydrolysis resistance of the material.
Controlling the water absorption of PA becomes an important factor in improving the performance of automotive PA tubes. In addition, the heat resistance of PP is relatively poor, which will adversely affect the high temperature resistance of PA. Specialty engineering plastics have better heat resistance, and some varieties also have lower water absorption, such as polyphenylene sulfide (PPS), the combination of PPS and PA can be obtained with excellent heat resistance and hydrolysis resistance of the composite pipe, which can be used in automotive coolant pipes.
Relative to short carbon chain PA (PA6, PA66), long carbon chain PA (PA12, PA612, PA11, PA1010, PA1012) amide bond density is lower, with lower water absorption, has become the most commonly used PA materials for piping parts. Long carbon chain PA pipe processing methods are mostly extrusion molding, molding process has a very important impact on the performance of long carbon chain PA pipe.
PA can be made into a water pipe, used in new energy vehicles on the water cooling system, PA can also be used to make automotive air conditioning hose barrier material.
3.2 Other automobile parts
In addition to piping parts, PA materials in the automotive engine peripheral components are also more and more widely used, including the supercharged air cooler, intake manifold, air intake heat shield, turbine pipe resonator, hot side turbine air ducts and other components.
GF reinforced PA has excellent performance and can be applied to a variety of automotive components, such as through the inorganic mineral filling and GF reinforced composite modification technology, and then add toughening agents, antioxidants, lubricants and other components, after careful formulation, the resulting modified PA6 can be applied to automotive hood; GF reinforced PA6 has been used in the steering column module of the new BMW 3 to 7 series cars, which can reduce the GF reinforced PA6 has been applied in the steering column module of the new BMW 3 to 7 series cars, which can reduce the mass by 20%; GF reinforced PA66 has good mechanical properties and low water absorption, which can be applied in the production of automotive connectors.
In addition, a variety of functionalized modified PA materials in automotive parts are increasingly widely used, such as the use of high thermal conductivity PA materials produced by the radiator can be applied to automotive rear fog lamps, which compared to the traditional aluminum radiator, not only reduces the quality of the reduction of 30%, but also to meet the requirements of LED rear fog lamp heat dissipation and mechanical properties, the cost of production has also been reduced to achieve the automotive fog lamp radiator “Plastic instead of aluminum”.
By matching the appropriate viscosity of PA and different types of polyolefin-based graft elastomers, can obtain low-temperature resistant high-flow PA66 material, which can be applied to the manufacture of automotive ties. PA can also be used in new energy vehicle powertrain suspension system, compared with the metal material suspension system, the quality of the reduction of about 37% to 50%, the cost is reduced by about 10% to 28%, and the effect of vibration damping is relatively good.