Automotive Plastics: Properties, Manufacturing, and Recycling

Advantages of Plastic in Automotive Construction

• Weight reduction
• Impact recovery and resistance
• Resistant to oxidation
• Easily moldable

How Plastics Are Formed

Plastics are formed by large polymer molecules, also known as macromolecules.

Four Steps in Plastic Manufacturing

1. Obtaining raw materials
2. Synthesis of polymers
3. Adding molding and additives
4. Finishing

Polycondensation vs. Polyaddition

In polycondensation, monomers unite in a chain formation, while in polyaddition, formed chains bind to each other, similar to the general polymerization process.

Polymer Structures

Polymers can have various structures:

• Linear: Long chains of monomers linked by primary bonds.
• Branched: Secondary chains attached to the main chain.
• Reticulated (Crosslinked): One or more polymer chains linked by secondary chains.

Characteristics of Thermoplastics

Polypropylene (PP)

• Easily recovers from impacts.
• Rigid, with good elasticity.
• Temperature resistance up to 130°C.
• Pets.
• Often used with plastic strengtheners.

Acrylonitrile Butadiene Styrene (ABS)

• Rigid structure.
• Functions well at ambient temperatures.
• Below 10°C, it is prone to cracking.
• Resistant to weld temperatures up to 110°C.

Polyethylene (PE)

• Very elastic structure with good impact recovery.
• Resistant to most solvents.
• Good casting qualities.
• Maintains properties when deformation exceeds 87%.

Thermoset Polymer Chain Structures

Thermosetting materials exhibit specific chain structures:

• Linear Chains: Long chains of monomers linked by primary bonds.
• Branched Chains: Secondary chains attached to the main chain.
• Reticulated (Crosslinked): One or more polymer chains linked by secondary chains.

Advantages of Thermosetting Materials

• High thermal stability and high stiffness.
• Low weight.
• Resistance to deformation under load.
• Good properties as thermal and electrical insulation.

Characteristics of Thermosetting Plastics

Polyurethane (PU)

• Can exist as a thermostable material, or even as a thermoplastic elastomer.
• Can have rigid, semi-rigid, or flexible structures.
• Resistant to acids and solvents.
• Supports heat well.
• Can be repaired with adhesive systems.

Unsaturated Polyester Resin (UPR)

• Good electrical and physical properties.
• Good strength and dimensional stability.
• High rigidity.

Structure of a Thermosetting Plastic

Thermosetting plastics are made up of highly branched polymer chains and cross-links that form three-dimensional structures.

Advantages of Resin Injection Molding

• Many parts can be produced simultaneously.
• Useful for manufacturing complicated parts.

Hybrid Technology in Automotive Design

This technique can increase the resistance of a steel structure with plastic reinforcement beyond what can be achieved with a welded reinforcement plate.

Characteristics of Composite Materials

• Possess good mechanical resistance (both tensile and compressive).
• Great lightness.
• High resistance to acids and solvents.
• Low water absorption or production.
• Their production cycles are short.

Chemical Recycling Processes

Pyrolysis

Plastic molecules undergo cracking after heat treatment.

Hydrogenation

Plastics are subjected to heat and hydrogen.

Gasification

Plastic is heated with air or oxygen.