Application of Modified Plastics in Automobiles under The Background of Lightweight

Lightweight is an effective way for automobiles to achieve energy saving and emission reduction, and it is of great significance to the sustainable development of the automobile industry and human beings. Automobile lightweight mainly includes three aspects: lightweight materials, advanced technology, and structural optimization. Among them, the application of lightweight materials is the most direct way to achieve automobile weight reduction. Modified plastic has become an important lightweight material in the automotive field due to its good cost advantage, perfect weight reduction effect, and excellent comprehensive performance. Mastering the application research status of modified plastics in automobiles is very important for the further research and application of automotive plastics and automotive lightweight materials.

1. Overview of modified plastics for vehicles

Modified plastic is a material with a uniform appearance obtained by using primary form resin as the main component, additives that can improve the performance of the resin as auxiliary components, and through technical means such as filling, toughening, strengthening, blending, and alloying. Modified plastic is a symbol of high technology, high performance and high grade in plastic products, and is widely used in aerospace, automobile manufacturing, household appliances and other fields.

In terms of varieties, the plastic varieties with more consumption include polypropylene (PP), polyurethane (PUR), polyamide (PA), polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene plastic (ABS), Polycarbonate (PC), etc., among which PP, PA, and ABS are the most abundant in automotive modification. From the application point of view, modified plastics are widely used in interior and exterior parts, structural parts and functional parts of automobiles. Among them, the interior parts include the center console, instrument panel, and decorative panels; the exterior parts include air intake grilles, bumpers and decorative parts; the structural parts include front-end frames and column skeletons; functional parts include car lights, intake manifolds, fuel tanks, etc., which are all auto parts with a large amount of modified plastics.

2. Automotive use and modification of PP

PP is considered to be the lightest plastic and is an ideal lightweight material for automobiles. PP is suitable for various modifications such as copolymerization, cross-linking, filling, and reinforcement, and is the most used and fastest-growing variety of automotive plastics. Ordinary PP has poor aging resistance, flammability, large molding shrinkage, easy warping of products, toughness and strength to be improved, so it must be modified to meet the use requirements of auto parts.

Typical modifications and applications of automotive PP include:

① Reinforced and toughened PP can be obtained by combining elasticity and inorganic fillers with PP. Among them, the elastomers include EPDM or ethylene-octene copolymer (POE), and the inorganic fillers include talcum powder, calcium carbonate, kaolin, etc. . Reinforced and toughened PP is mainly used for automotive parts with large volume, many materials, and good impact resistance, such as bumpers, instrument panels, and door trim panels.

② Long glass fiber reinforced PP (LGFPP) can be made by combining long glass fiber (10-25 mm) with PP. Compared with short glass fibers, LGFPP has better creep resistance and lower density than metal and thermosetting composite materials, and the weight of the same parts can be reduced by 20% to 50%. LGFPP is often used in automotive front-end modules, dashboard frames, battery brackets, seat brackets, door frames, etc. Among them, the all-plastic front-end module can form injection molding parts with multiple metal parts, which can reduce the weight by 30% to 40% while simplifying the front-end structure.

③Using PP as the matrix and chemical foaming agent as the gas source, through injection foaming, blow molding foaming, extrusion foaming and other micro-foaming processes, micro-cells of 80-350 μm can be obtained in the product. Foaming modified PP can reduce the weight of plastic products by 10% to 20%, which is more than 50% lighter than metal and other materials. It can be used for automobile tailgates, ceilings, air ducts and other components.

④Scratch-resistant PP can be obtained by adding silicone and amide scratch-resistant agents, which are mainly used for automotive interior parts such as car consoles, instrument panels, and door inner panels.

3. Automotive use and modification of PA

PA has good mechanical properties, heat resistance, wear resistance, chemical resistance and self-lubrication, and has certain flame retardancy, easy to process and shape, and is widely used in automobiles, electrical appliances, special equipment and other fields. Among them, PA6 and PA66 are the main varieties of automotive PA. Although PA has good performance, there are still deficiencies in water absorption, dimensional stability and toughness, and the flame retardancy needs to be further improved.

The typical modification and application of automotive PA are:

① Add 20% to 40% GF to PA66 to make PA66/GF, its bending strength can reach 310 MPa, the notched impact strength is about 25.4 J/m, the water absorption is about 0.9%, and the molding shrinkage rate is only 0.3%. With excellent overall performance, it is often used in heat-resistant functional parts such as engine hoods, air intake pipes, and radiators;

②Using the composite flame retardant system of halogenated flame retardants and antimony trioxide can improve the flame retardant grade of PA6, and the flame retardant modified PA6 is often used in electric vehicle power battery shells, brackets, cover plates, etc.

③ Use polymer blending or add montmorillonite, silica and other inorganic particles to strengthen and toughen PA11 and PA12. After modification, it not only has low water absorption, good oil resistance, but also has good strength and toughness. It is an ideal material for automobile oil pipelines such as fuel pipes and brake oil pipes.

With the gradual deepening of automotive PA to replace metal parts, high fluidity, high heat resistance, halogen-free flame retardant PA has become a research hotspot in the industry. High fluidity can not only improve the production efficiency of PA parts, reduce processing costs, but also improve the appearance quality of auto parts; High heat-resistant PA is not only suitable for high-temperature working environments above 200 °C, but also requires good high-temperature performance retention; Although halogen-based flame retardants have high flame retardant efficiency and have little effect on the mechanical properties of materials, they will produce dense smoke and harmful gases when burned, while phosphorus-based, nitrogen-based, inorganic metal and nano-halogen-free flame-retardant PAs will be more environmentally friendly and safe.

4. Automotive use and modification of ABS

ABS is moderately priced and is widely used in machinery, automobiles, electronic appliances and other fields. ABS parts are flexible in design, easy to form, and convenient for electroplating, painting, and welding. They are widely used in interior and exterior trims and structural parts of automobiles. The amount of ABS used in automobiles accounts for about 8% of the total amount of plastics used in automobiles. ABS contains side phenyl groups, cyano groups and unsaturated double bonds, which create favorable conditions for blending modification. The development and production of its blends is the most active branch of polymer blending modification.

In addition to heat-resistant, fiber-reinforced and flame-retardant modifications, typical alloy modifications and applications of automotive ABS include:

①ABS/PC alloy has excellent fluidity, low-temperature impact resistance and thermal deformation temperature, and is often used in instrument panel frames, decorative strips, heat dissipation grills, etc.;

②ABS/PA alloy has low density, good toughness, easy forming and high temperature resistance, and can be used for air-conditioning outlets, instrument panels and exterior decorations, etc.;

③ABS/PVC alloy is not only low temperature resistant, impact resistant, easy to form, but also has good flame retardancy and corrosion resistance, and is often used in automotive dashboards, door and window seals;

④ABS/polybutylene terephthalate (PBT) alloy has dimensional stability, chemical resistance, impact resistance, and excellent fluidity, which is of great significance to large plastic parts of automobiles and can be used for automobile dashboards and bumpers, seats, etc.

With the wide application of modified ABS parts in automobiles, especially the advancement of the full plasticization process of automobile interiors, antibacterial, antistatic, and low-noise automotive ABS has become an emerging hot spot in the industry.

5. Vehicle use and modification of other plastics

In addition to the above three automotive plastics with various modifications and abundant applications, the modification and special uses of PUR, PC, PE, and POM are also fully displayed in automobiles.

PUR materials include foam, coatings, adhesives, etc., while modified PUR for vehicles is mainly low-VOC, flame-retardant foam and synthetic leather, such as bumper energy-absorbing blocks, door roof fillers, seat fabrics, etc.

PC has good impact resistance, dimensional stability, easy processing and molding, but poor corrosion resistance, its application in automobiles is often based on alloys, such as elastomer toughened PC/PBT alloys and PC/polyethylene terephthalate (PET) alloys for automobile door frames, side guards, fenders, etc. At the same time, PC also has a unique high light transmittance, high refractive index, high heat-resistant PC and PC/polymethyl methacrylate (PMMA) alloy are often used in automobile lights and windows.

PE has good low temperature resistance, chemical stability and chemical corrosion resistance, while cross-linked PE has a network structure and is thermosetting, and its wear resistance, stress crack resistance, weather resistance and heat resistance are all improved.

POM is the toughest thermoplastic resin, its hardness, strength and rigidity are comparable to metal. At the same time, POM also has good chemical corrosion resistance, self-lubrication, and oil resistance. After its strengthening and toughening modification, it often replaces copper, aluminum, zinc and other metal materials to make automotive bearings, gears and other parts;

With the implementation of multiple plastic pollution control policies around the world, biodegradable plastics such as modified polylactic acid (PLA), polybutylene succinate (PBS), and polyhydroxyalkanoate (PHA) are expected to become new favorites for automotive plastics. The raw material of PLA is lactic acid, which is a typical representative of bio-based degradable plastics. It is mainly synthesized from biomass resources such as corn starch, and is often used in the automotive field in the form of fiber-reinforced modification. The price of PBS is relatively low, and it is also an important variety for the research and development and application of biodegradable plastics at home and abroad, with a good market prospect. PHA is currently mainly used in the form of textiles for car floor mats and seat covers. In the future, it is expected to be modified in terms of low VOC, antistatic, flame retardant and mechanical properties, so as to further promote its application in the automotive field.

6. Conclusion

Lightweight is not only an effective way to achieve energy saving and emission reduction of automobiles, but also an important way to enhance the independent innovation capability of the national automobile industry. Modified plastic has become an indispensable lightweight material for automobiles due to its good cost advantage, perfect weight reduction effect, and excellent comprehensive performance. "Three highs and one low" PP, high fluidity, high heat resistance, halogen-free flame retardant PA are widely used in automobiles. Antibacterial, anti-static, and low-noise automotive ABS have produced a large number of achievements. The modification and special application of PUR, PC, PE, and POM are also fully demonstrated in automobiles, and the era of biodegradable plastics for automobiles is coming.

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