Comprehensive Explanation, Unveiling the Selection and Use of Plastics in Cars!

Currently, the main direction of world automotive material technology development is lightweight and eco-friendly. Automotive plastics have a low relative density, and replacing steel with plastic for exterior parts can reduce the weight of the car, achieving energy-saving purposes. Reducing the car’s own weight is one of the most effective measures to reduce vehicle emissions and improve combustion efficiency. It is estimated that for every 10% reduction in the weight of the car itself, fuel consumption can be reduced by 6% to 8%.

Plastic Introduction

Types of Plastics

1.     Based on usage characteristics, plastics are divided into general plastics, engineering plastics, and special plastics. General plastics refer to those with large production volumes, wide usage, good moldability, and low cost, such as polyethylene, polypropylene, and phenolics. Engineering plastics are capable of withstanding certain external forces, have good mechanical properties, high and low-temperature resistance, and better dimensional stability, and can be used as engineering structural plastics, such as polyamides and polysulfones. Special plastics have specific functions, such as fluoroplastics and silicones.

2.     Based on physical and chemical properties, they can be divided into thermosetting plastics and thermoplastics. Thermosetting plastics refer to plastics that can solidify or become insoluble (unmeltable) under heat or other conditions. The advantages of thermosetting plastics are their strength and heat resistance, and they are not easily deformed under pressure; the disadvantage is that the molding process is complex and production efficiency is low. Thermoplastics can be repeatedly heated to soften and cooled to harden within a specific temperature range. Their advantages are simple molding processes, high production rates, certain mechanical properties, and recyclability; the downside is poor heat resistance and lower rigidity.

Composition of Plastics

Plastics primarily consist of synthetic resins, with a suitable amount of additives to improve their processability and performance. Additives include fillers and reinforcing materials, plasticizers, curing agents, stabilizers, lubricants, antistatic agents, flame retardants, etc.

Modified Plastics

The characteristics of plastics are reflected in their light weight, corrosion resistance, good impact resistance, high transparency, good wear resistance and insulation, low thermal conductivity, generally good moldability and colorability, and low processing costs. A large amount of plastic is used in car design, which can reflect the requirements for car design performance, such as lightweight, safety, anti-corrosion, aesthetic appearance, and comfort, and is beneficial for reducing costs and saving material resources. However, due to poor dimensional stability, high thermal expansion rate, flammability, and aging of ordinary plastics, many properties cannot compare with metal materials. Therefore, plastics used in cars are not a single variety but are modified, also known as “modified plastics.”

Lightweight Features of Automotive Plastics

Products made from elastomers and foamed plastics that can absorb impact and vibration energy, such as dashboards, seats, and headrests, can reduce injury to the human body during collisions and improve the safety factor of cars. Structural parts often use high-strength engineering plastics to reduce weight, lower costs, simplify processes, such as fuel tanks, engines, and some parts on the chassis.

Personalized Development of Automotive Plastics

The use of automotive plastics also aids in the personal development of cars. Plastic products have a large degree of design freedom, can be made transparent, semi-transparent, or opaque, and have a variety of appearances. Additionally, plastics have good processing performance, complex products can be molded in one go, mass-produced, with high efficiency, low cost, and significant economic benefits. If calculated by unit volume, the cost of producing plastic parts is only one-tenth of that of non-ferrous metals.

Application of Nanocomposite Materials

Thermoplastic polyolefin (TPO base) nanocomposite materials are used in automotive interior and exterior decorative parts, with advantages such as light weight, high dimensional stability, high strength, and good low-temperature impact resistance. TPO series nanocomposite automotive footboards, used in General Motors’ sedans, have higher hardness, light weight, do not become brittle at low temperatures, and are easy to recycle.

Toyota has used nanopolypropylene composite materials for car front and rear bumpers, reducing the original bumper thickness from 4mm to 3mm and the weight by about one-third. Toyota has also successively introduced polypropylene nanocomposite materials for automotive interior parts.

The involvement of nanoparticles not only improves the strength, rigidity, and toughness of polymers but also helps to improve the light transmittance, barrier properties, heat resistance, and UV resistance of polymers. Due to the simplicity of processing and significant effects, the industry is optimistic about the market prospects of polymer nanocomposite materials.

Sprayable and Non-paint Plastics

The conductive polyphenylene ether/polyamide material developed by General Electric (GE) allows plastic body parts to undergo cathodic electrodeposition (i.e., full online spraying) together with metal stamping parts, thereby eliminating the color difference problem between non-metal and metal parts of the car body.

In addition, PC/PBT materials and SLX films used to manufacture car body panels, front and rear fenders, and rear trunk doors through in-mold decoration injection molding process can achieve the effect of paint, reducing production costs. This technology has begun to be used in the production of car body panels abroad.

Plastic Optics and Plastic Glass

Special polycarbonate produced by General Electric (GE) used for headlight optics is coated with a scratch-resistant coating, brighter than glass lenses, more shatter-resistant, and more accurate in optical processing.

In the United States, the tri-layer safety glass of car windshields is laminated with a 20μm thick polyurethane film. Most buses in the United States use acrylic resin panels, and the plasticization of windshield glass can achieve energy saving and protect passengers’ safety.

Fiber Reinforced Thermoplastics

Long fiber reinforced thermoplastics (LFRT) are a new type of lightweight, high-strength engineering structural material that is developing rapidly in automotive applications due to its lightweight, low cost, and recyclability.

Manufacturing car body parts from natural fibers such as flax and jute reinforced plastics has been recognized in the automotive industry. Using flax-reinforced polypropylene to make car body floor panels, the material’s tensile strength is higher than steel, stiffness is not lower than glass fiber reinforced materials, and the parts are easier to recycle. For operators, it eliminates skin rashes and respiratory diseases caused by glass fibers. Some enterprises in Jiangyin, China, have begun to produce such materials.

Application in Power Transmission Systems

Engine valve covers and oil pans are molded or pressed from glass fiber reinforced plastics such as polyamide, reaction injection molded polyurethane, epoxy resin, etc.; engine cylinder liners and gaskets use high-performance or traditionally produced synthetic rubber, including CR and FRM; wear-resistant polypropylene molding materials are applied to gears, shafts, and other wear-resistant molded products.

In vans and trucks, composite material (glass and carbon fiber) drive shafts replace metal shafts, reducing weight, noise, and vibration, and making operation smoother. GKN Technology in the UK manufactures drive shafts from fiber-reinforced plastics, reducing weight by 50% to 60%, with torsional strength 1.0 times higher than steel, and bending stiffness 1.5 times higher. DuPont has developed a composite glass fiber reinforced nylon 66 for the active assembly plastic ventilation system of the V6 engine.

Plastics in Car Body Applications

The application of plastics in car bodies mainly has three modes: (1) Both outer coverings and structural parts are made of plastics: mainly used in high-end sports cars, with carbon fiber reinforced plastics for skeleton structural parts and glass fiber reinforced plastics for outer coverings, which are very costly. (2) Metal skeleton and all-plastic outer coverings combined with the body: the body uses glass fiber reinforced thermoplastic polyester injection molding, with equipment being an 8800t injection molding machine, which is expensive. (3) Partial use of plastic outer coverings: some luxury cars use metal for the skeleton structure, while partial outer coverings are made of plastic parts.

Development of Plastic Functional Parts

Glass fiber reinforced thermoplastics (GMT) are used to manufacture brackets, supports, and multifunctional parts. Using plastics to make intake manifolds can reduce weight by 40% to 60%, and the smooth surface and low flow resistance can improve engine performance, fuel efficiency, and reduce vibration and noise. Developing “composite conductive plastics” by incorporating conductive fillers into the base polymer and “conductive polymers” with inherent conductivity, for their high functionality for automotive production selection.

Dashboard and Interior System

Many car manufacturers use foam polyurethane to make door panels, not only to reduce weight and strength but also to improve sound absorption and safety performance. Polypropylene, due to its low cost, is widely used in the American automotive market, not only replacing ABS but also some car models use polypropylene for all interiors.

Currently, dashboards used in China can be divided into hard dashboards and soft dashboards. Hard dashboards are generally made of modified used in economy cars. Soft dashboards are made of polyurethane reaction foam molding, usually used in mid-to-high-end sedans.

The innovative application of plastic materials will be a key focus and attention in . In addition to relying on engine and new material innovations, cars will significantly depend on the development of plastic technology in the face of energy shortages and increasing environmental concerns. Whoever can lead in material selection and application can gain greater benefits.


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