Matrix materials

in Composite Lightweight Construction

Composite materials consist of two main components: the fibers, which determine the mechanical strength and stiffness, and the matrix, which surrounds, protects the fibers, and distributes the forces within the material.

The choice of the right matrix material is crucial for the overall performance of the composite, as it significantly influences the thermal, chemical, and mechanical properties of the material. 

Matrix systems in composite materials can generally be divided into two main groups: thermosets (thermosetting plastics) and thermoplastics. Both material classes have specific properties that make them suitable for different applications.

Thermosets (Thermosetting Plastics) as Matrix Materials

Thermosets are plastics that harden during processing and form a solid, irreversible structure. This curing process means they cannot be reshaped or melted once hardened. They are characterized by high temperature and chemical resistance, as well as low creep tendency.

The most important thermoset matrix materials include:

1. Epoxy Resins (EP Resins)

Epoxy resins are the most commonly used thermoset matrix systems in high-performance composites. They offer an excellent combination of mechanical strength, chemical resistance, and adhesion to the fibers.

Typical applications:

Epoxy resins are commonly used in aerospace, motorsports, wind turbines, medical technology, and boat building.

Advantages

  • High mechanical strength and stiffness
  • Very good adhesion to fibres, especially carbon fibres
  • Low shrinkage during curing, leading to precise component geometries
  • High temperature resistance and chemical resistance

Disadvantages

  • Higher costs compared to polyester or phenolic resins
  • Curing times can be relatively long
  • Sensitivity to UV radiation without special protective measures

2. Unsaturated Polyester Resins (UP Resins)

UP resins are cost-efficient and widely used thermoset matrix systems with good mechanical properties and high chemical resistance. They are particularly attractive for applications where cost-effectiveness is a key factor.

Typical applications:

UP resins are commonly used in boat building, the automotive industry, construction, and the production of leisure and sports equipment.

Advantages

  • Cheaper than epoxy resins
  • Good chemical resistance
  • Fast processing and curing
  • Wide availability and easy processing

Disadvantages

  • Mechanical strength and fibre adhesion are lower than in epoxy resins
  • Higher shrinkage during curing
  • Emissions of styrene during processing can be harmful to health

3. Phenolic Resins (PF Resins)

Phenolic resins are particularly known for their high heat resistance and excellent fire-retardant properties. They are often used in safety-critical applications.

Typical applications:

Phenolic resins are commonly used in aerospace, rail vehicle construction, fire protection panels, and high-temperature applications.

Advantages

  • Very high temperature resistance
  • Excellent fire resistance and smoke resistance
  • Good chemical resistance

Disadvantages

  • Lower mechanical strength than epoxy and polyester resins
  • Long curing times
  • Processing can be more demanding

Thermoplastics as Matrix Materials

In contrast to thermosets, thermoplastics remain thermally formable even after processing. This allows for faster and more efficient processing as well as better recyclability. Thermoplastic matrix systems offer high toughness, making them particularly resistant to impact and shock loads.

Properties of Thermoplastics: 

  • Reformability by heating
  • Short processing times, as no chemical curing is required
  • High impact toughness and elongation at break
  • Good recyclability