Polymeric Materials for Automotive Applications

The applications of high-performance plastic are playing an important role in the automotive industry these days. It is constantly increasing and this trend is expected to continue. The main aspect in choosing the high-performance plastic materials in relation to other materials used in automobiles are the design of automobiles, their functionality and more economic manufacture, as well as reduced fuel consumption. It is estimated that every 10% reduction in vehicle weight results in a 5% to 7% reduction in fuel usage.

Current economic and environmental concerns make the creation of more fuel-efficient vehicle a top priority in the automotive industry. Although the minimization of the mass of parts is the main reason of choosing high performance plastic materials, the future rise of their usage will result in new applications in automobiles related to comfort, safety and possibility of parts integration. The application of high-performance plastic materials allows more freedom in design, and in many cases only these materials can allow safe geometrical or economic solution for the construction of parts. Some other advantages of increased applications of plastic materials in transport vehicles include:

• Minimal corrosion, allowing for longer vehicle life

• Substantial design freedom, allowing advanced creativity and innovation

• Flexibility in integrating components

• Safety, comfort and economy

• Recyclability

KINDS AND TYPES OF POLYMERIC MATERIALS FOR THE MANUFACTURE OF AUTOMOTIVE PARTS[1,2,3,4,5]

The average vehicle uses about 150-300 kg of plastics and plastic composites versus 1163 kg of iron and steel – currently it is moving around 15-20 % of total weight of the car, over 2,000 parts and components of all shapes and sizes. Although up to 13 different polymers may be used in a single car model (see Table), just three types of plastics make up to about 66 % of the total plastics used in a car:

·       polypropylene (32%),

·       polyurethane (17 %),

·       PVC (16 %).

Plastics and composites used in vehicles has risen from 100 kg in 1990, to 140kg in 2000, to 150 kg in 2010, to 200 kg in 2020.Today’s plastics typically make up 50% of the volume of a new light vehicle but less than 10% of its weight, which helps make cars lighter and more fuel efficient, resulting in lower greenhouse gas (GHG) emissions

In addition to plastics and composites, light vehicles use an average of 120 kg of rubber, 25 kg of manufactured fibres (almost entirely synthetic fibres) and 17 kg of coatings on a dry weight basis, Every light vehicle contains an average of $3,246 of chemistry (chemical products and chemical processing). This includes antifreeze and other fluids, catalysts, plastic instrument panels and other components, rubber tyres and hoses, upholstery fibres, coatings and adhesives.Plastics and polymer composites is the largest value component at $442, or 24.0% of the materials cost and 13.6% of the total chemistry value including chemical processing, according to the ACC (American Chemistry Council).

Polycarbonate (PC)

Polycarbonates are often used for the application in automotive industry. They are applied mainly in non-reinforced condition, and their main application in automobiles is for the manufacture of various parts of light assemblies, such as lights and lenses of the front and rear lights.

It features the following properties:

·       Resistant to high temperatures (up to 148°C), whereas high-temperature polycarbonate (PC- HT) is resistant to temperatures (from 160-220 ºC);

·       Transparent with possibility of being painted into any nuance;

·       Modulus in tension up to 2300 MPa;

·       High dimensional stability, precision and good properties of toughness;

·       Good electric insulation properties.

Applications: Bumpers, headlamp lenses, security screens, aircraft panels, spectacle lenses, headlamp lenses, helmets and bullet-proof glass substitutes.

Polyamide (PA, Nylon 6/6, Nylon 6)

Polyamide is known as nylon 6.6 or nylon 6. It is a general-purpose nylon that can be both molded and extruded. Nylon 6/6 has good mechanical properties and wear resistance. They are frequently used when a low cost, high mechanical strength, rigid and stable material is required. They also absorb water easily and components in wet or humid conditions will expand, precluding their use in applications where dimensional stability is required. The main application of polyamide is the manufacture of parts which are under the engine hood, mainly using the types of polyamide (PA) reinforced by fiberglass.

Applications: Gears, bushes, cams, bearings, weather proof coatings

Acrylonitrile/butadiene/styrene (ABS)

Acrylonitrile Butadiene Styrene is a durable thermoplastic. It is a copolymer built by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The styrene gives the plastic a shiny, impervious surface. The butadiene, a rubbery substance, provides resilience even at low temperatures. A variety of modifications can be made to improve impact resistance, toughness, heat resistance, weather and some chemicals resistance.

Applications: Automotive body parts, dashboards, wheel covers manufacture of housings, Covers and linings

Thermoplastic alloy

For the manufacture of automobile parts often thermoplastics alloy PC+ acrylonitrile/butadiene/styrene (PC+ABS) is used, and the thermoplastics alloy acrylonitrile/butadiene/styrene+polyamide (ABS+PA)

The alloys allow combining of mechanical, thermal and rheological properties of materials. The thermoplastic alloy of polycarbonate+ acrylonitrile/butadiene/styrene (PC+ ABS) is used to manufacture the internal and external decorative parts and small bodywork parts, and features the following properties

·       it is opaque, has high surface polish;

·        resistance to temperature between ABS and PC;

·       high dimension stability and reaches high precision in the production of small parts;

·       slight tendency to distortion and humidity absorption;

·       features good electric insulation properties;

·       modulus in tension from 1800-2750 MPa, and fibre glass reinforced 3900-5900 MPa.

Applications: Thermoplastic alloy acrylonitrile/butadiene/styrene+ polyamide (ABS+PA) is used for the manufacture of unpainted parts in the car interior, such as: housings for radios and navigation systems, sliding roof supports, air nozzles and air conditioning grates,gear level linings, steering wheels, etc., and also for the manufacture of painted external parts: hub covers, grilles and fenders.

Polyvinyl chloride (PVC)

This is a material used in automotive industry for the manufacture of the protection for the bottom floor in the car, for internal lining and coating of electric cables in the vehicle, and features the following properties;

·       low thermal resistance at high temperatures;

·       good absorbent of impacts and vibrations, low flammability;

·       diversity of manufacturing procedures, easy to weld, paste, and print.

Applications: automobile instruments panels, sheathing of electrical cables, pipes, doors, waterproof clothing, and chemical tanks.

Polypropylene (PP)

Polypropylene properties vary according to molecular weight, method of production, and the copolymers involved. Polypropylene has demonstrated certain advantages in improved strength, stiffness and higher temperature capability over polyethylene. Polypropylene has been very successfully applied to the forming of fibers due to its good specific strength which is why it is the single largest use of polypropylene Is one of the lightest plastics available with a d=0.905 g/cm3. It is extremely chemically resistant and almost completely impervious to water. Black has the best UV resistance.

Applications: automotive bumpers, chemical tanks, cable insulation, battery boxes, bottles, Petrol cans, indoor and outdoor carpets, carpet fibers.

Polyurethane (PUR)

Polyurethanes are a large family of polymers with wide range of properties and uses all based on the reaction product of an organic isocyanate with compounds containing a hydroxyl group. Polyurethanes may be thermosetting or thermoplastic, rigid and hard or flexible and soft, solid or cellular with great property variances. Principal applications are in coatings, elastomers and foams. Polyurethane has excellent abrasion resistance but high hysteresis. Rigid polyurethane foams have become widely used as insulation materials because of their combination of low heat transfer and good cost effectiveness. Use as insulation and other applications are restricted by an upper temperature capability of about 250°F. Polyurethanes do not survive well in direct sunlight or in contact with most organic solvents. Two types of polyurethane are common: polyester based and polyether based, with these backbone structures actually comprising a significant part of a so-called polyurethane resin.

Applications: Flexible foam seating, foam insulation panels, elastomeric wheels and tires, automotive suspension bushings, cushions, electrical potting compounds, hard plastic parts.

PS (Polystyrene)

Polystyrene is an amorphous, glassy polymer that is generally rigid and relatively inexpensive. Unfilled polystyrene has a sparkle appearance and is often referred to as crystal PS or general purpose polystyrene (GPPS). High impact polystyrene grades (HIPS) are produced by adding rubber or butadiene copolymer which increases the toughness and impact strength of the polymer.

Polystyrenes possess good flow properties at temperatures safely below degradation ranges, and can easily be extruded, injection moulded, or compression moulded. Considerable quantities of polystyrene are produced in the form of heat-expandable beads containing a suitable blowing agent which ultimately results in familiar foamed polystyrene articles. Naturally clear, polystyrene shows excellent chemical and electrical resistance. Special high gloss and high impact grades are widely available. This easy to manufacture plastic has poor resistance to UV light.

Applications: equipment housings, buttons, car fittings, display bases.

Polyoxymethylene (POM)

POM (Polyoxymethylene), also known as Acetal, Polyacetal and Polyformaldehyde, is a high performance engineering polymer. It used in precision parts which require high stiffness, low friction and excellent dimensional stability. These properties are stable in low temperatures. POM also is highly chemical and fuel resistant.

Applications: interior and exterior trims, fuel systems, small gears, window guides, speaker grills, zips, lighters, aerosol valves, fasteners and furniture components.

Acrylic (PMMA)

PMMA (Acrylic) is a transparent thermoplastic; it is often used as a lightweight or shatter-resistant alternative to glass and good UV and weather resistance, high optical quality and surface finish with a huge colour range. It’s cheaper than PC but is also more prone to scratching and shattering.

Applications: windows, displays, screens.

Polybutylene terephthalate (PBT)

Polybutylene terephthalate has good chemical resistance and electrical properties, hard and tough material with water absorption, very good resistance to dynamic stress, thermal and Dimensional stability, They are easy to manufacture due to fast crystallization and fast cooling.

Applications: Fog lamp housings and bezels, sun-roof front parts, locking system housings, door handles, bumpers, carburettor components etc.

Polyethylene Terephthalate (PET)

Polyethylene terephthalate has similar conditions as PBT, good thermal stability, good electrical properties, very low water absorption and excellent surface properties. It is mostly used to create synthetic fibres and plastic bottles. You may recognize it on clothing labels under the name “polyester”.

Applications: Wiper arm and their gear housings, headlamp retainer, engine cover, connector housings etc.

Acrylonitrile Styrene Acrylate (ASA)

ASA (Acrylonitrile styrene acrylate) material has great toughness and rigidity, good chemical Resistance and thermal stability, outstanding resistance to weather, aging and yellowing, and High gloss. Be careful not to burn this material. It will cause a toxic smoke.

Applications: Housings, profiles, interior parts and outdoor applications.

Technology Activities and Properties in Four Key Areas

Plastics industry is very important in supporting the automotive industry. Automobile engineers are working together closely to optimize other systems and to meet the important challenges associated with enhancing automotive safety. Automotive and plastics producers, along with their suppliers, have identified a preliminary research plan and set of priorities. The Technology Integration Workshop Report presents R&D priorities in four automotive areas that together capture the broad range of plastics applications in vehicles (see Figure). These four areas are Interiors, Bodies and Exteriors, Power train and Chassis Components, and Light weighting:

• Interior: Priorities for improving safety in the passenger compartment include making safety advances affordable through innovative design and more efficient manufacturing capabilities, designing for increased vehicle compatibility, accommodating an aging driver population, including more safety features in reduced package space, and enhancing safety belt designs.

• Body & Exterior: From bumpers to body panels, laminated safety glass to rear parking assists, research activities must include energy management technologies that resist vehicle intrusion, impede roof crush, and reduce body and exterior weight without compromising safety performance.

• Power train & Chassis: Research in this area focuses on components that generate and deliver power and include the frame and its working parts. R&D priorities include pursuing significant advancements in engineering and research capabilities for designing with plastics, exploring new ways to optimize safety and fuel efficiency, expanding predictive modelling capabilities for composite materials, and developing the new safety components that will be required for future alternative vehicles and power train options.

• Light weighting: The transition to lightweight materials from conventional ones requires research activities that will increase the overall value of plastics in automobiles; develop new, high-performance components that lower the centre of gravity of a vehicle; improve crash avoidance and performance systems; and enhance pedestrian safety.

Figure 2: Summary of Highest-Priority Research and Development Needed to Enhance Future Automotive Safety with Plastics

Manufacturing Procedures of Automotive Parts Made of Polymeric Materials

Injection moulding: is the most important cyclic procedure of processing polymers and it is the most widely applied procedure in manufacturing automobile parts. Injection moulding of polymers is a process of shaping by injecting the polymeric substance of a required shear viscosity from the preparation units into the temperature regulated mould cavity. By polyreaction and/or cross linking or cooling the product, the mould part becomes suitable for demoulding. The injection moulding procedure can be automated and it is suitable for manufacturing moulded parts of high dimensional stability and complexity, as well as of different sizes. Injection moulding can be applied for low viscous liquids (e.g. integral-polyurethane foams) or polymeric melts (e.g. thermoplastic melts). Elastomers can also be injection moulded, and elasto-thermoplastics are injection moulded in compliance with the rules of injection moulding of thermoplastics.

Blow moulding: is a cyclic procedure of forming a preform into a product, hollow body which strengthens its shape by cooling. Blow moulding is a very important processing procedure, meant for production of hollow articles or one-side open hollow bodies. In the first phase of the production of hollow bodies by blow moulding a preform is produced by extrusion or injection moulding. In the second phase the work piece is shaped.

Heat forming: the films, foils or plates cut from extruded or calendared strips are used as preforms for heat forming. The preforms are also made by direct and indirect pressing, casting and compression forming of polypropylene. Many thermoplastics are suitable for heat forming. In order to be formed, the preform must be in rubber state. Therefore sometimes the still non-cooled strip is conducted directly to the forming machine, but more often the preform must be heated, usually by exposing it to infrared beams or by contact with heated part of the machine. Out of the heat forming procedures stretching is most widely used, that can be caused by mechanical compression, air pressure or sub-pressure action, and combination thereof. The most frequent are the following forming procedures by stretching:

• Free stamp forming, unheated preform is formed freely (i. e. without matrix) by pressing the heated stamp.

• Forming by compressed air, the heated preform is printed by compressed air into the matrix. • Free forming by compressed air.

• Forming in the matrix with sub-pressure, the perform is drawn into the matrix due to the sub-pressure in it.

• Forming in the matrix with stamp and sub-pressure, the preform is stamp printed into the matrix from which the air is drawn out, and the preform clings closely to the matrix.

• Forming on stamp with sub-pressure, the perform is stretched by stamp in which there is sub-pressure and it clings along the stamp and acquires its shape.

Extrusion is the most widely used processing procedure of polymeric materials. Extrusion is used to produce the socalled continuous products or semi- products (extrudates), i.e. such products whose dimensions are not all final nor precisely defined (such as e.g. rigid and flexible pipes, sticks and coated cables). Extrusion is a procedure of continuous primary shaping, by pressing the liquefied polymers through nozzles. The extruded polymer hardens in the product, extrudate by cooling, cross- linking or polymerization. Extrudate is stacked or winded. The cyclic piston pressing is called extrusion. The thermo-sets and thermoplastic poly (tetraphluorethylene) are extruded

Javier Echave

PhD. Chemical Engineer

References:

[1] https://matmatch.com/resources/blog/four-reasons-why-plastic-is-used-in-car-manufacturing/

[2]Akshat Patil et.al./ Materials Today: Proceedings 4 (2017) 3807–3815

[3]N. Strumberger, A. Gospocic, C. Bra tu lie: Polymeric Materials in Automobiles, Promet-Traffic- Traffico, Vol. 17, 2005, No. 3, 149-160

[4] https://www.gpca.org.ae/2021/08/09/plastics-in-us-autos-surge/

[5] https://www.automotiveplastics.com/wp-content/uploads/Plastics-and-Polymer-Composites-in-Light-Vehicles-2019-REV-Sm.pdf

Tables:

Table 1: Akshat Patil et.al./ Materials Today: Proceedings 4 (2017) 3807–3815

Table 2: https://www.automotiveplastics.com/wp-content/uploads/Plastics-and-Polymer-Composites-in-Light-Vehicles-2019-REV-Sm.pdf

Table 3: https://www.automotiveplastics.com/wp-content/uploads/Plastics-and-Polymer-Composites-in-Light-Vehicles-2019-REV-Sm.pdf

Figures:

Figure 1: http://adapt.mx/plastics-in-the-automotive-industry-which-materials-will-be-the-winners-and-losers/

Figure 2: Akshat Patil et.al./ Materials Today: Proceedings 4 (2017) 3807–3815