Plastic composites: structure, types, properties and applications
Plastic composites combine plastics with fibres, metals or other materials. More about structure, advantages, types and applications.
Plastic composites combine plastics with other materials in order to achieve properties that a single material alone cannot offer, or can only offer to a limited extent. Depending on the structure, for example strength, stiffness, temperature resistance, dimensional stability or electrical properties can be specifically influenced.
Typical plastic composites consist of a plastic matrix and reinforcing fibres, metallic inserts, functional layers or lightweight core materials. This creates material systems that can be tailored very precisely to industrial requirements.
For designers and developers, plastic composites therefore offer interesting possibilities when classic plastic materials reach their technical limits or when several requirements must be met at the same time.
What are plastic composites?
A plastic composite consists of at least two different material components that are permanently bonded to one another. Unlike a simple mixture, the individual constituents retain their respective function within the composite.
The plastic often takes on the role of the matrix. It bonds the other components to one another, determines the outer shape and protects embedded materials from environmental influences.
Additional materials take on further tasks. Reinforcing fibres, for example, can increase strength and stiffness. Metallic inserts enable, among other things, greater dimensional stability or electrical conductivity. Foam cores, in turn, can reduce weight while at the same time enabling high flexural stiffness.
The property profile of a plastic composite therefore does not depend solely on the plastic used. Equally important are:
- type and proportion of the additional materials
- orientation of fibres or layers
- adhesion between the individual components
- structure and geometry of the composite
- manufacturing process
- temperature and media exposure
- mechanical stress on the later component
Plastic composites are therefore not a single material group with fixed properties, but individually constructed material systems.
How is a plastic composite structured?
Many plastic composites consist of a matrix and one or more additional components.
Plastic matrix
The matrix forms the basic structure of the composite. Both thermoplastic and thermosetting plastics can be used as matrix material.
Thermoplastics offer advantages in shaping, processing and, in some cases, also in recycling. Depending on the application, for example polyamide, polypropylene, PEEK or other engineering plastics are used.
Thermosetting matrix systems are used, among other things, when high stiffness, dimensional stability or temperature resistance is required.
Modified plastics also play an important role. Fibres, fillers or functional additives allow the property profile of a base polymer to be specifically adapted to the respective application.
Reinforcing and functional components
The second component often determines the particular performance of the composite.
Typical materials are:
- glass fibres
- carbon fibres
- aramid fibres
- natural fibres
- mineral fillers
- metal
- plastic films
- foams
- functional coatings
Which combination makes sense depends on the requirements of the component.
What types of plastic composites are there?
Depending on the material combination and structure, various groups can be distinguished.
| Composite type | Typical structure | Typical properties |
|---|---|---|
| Fibre-reinforced plastics | plastic matrix with glass, carbon or other fibres | high strength and stiffness at low weight |
| Sandwich composites | lightweight core with solid cover layers | high flexural stiffness at low weight |
| Metal-plastic composites | combination of metal and plastic | high stability, functional integration and corrosion protection |
| Multilayer composites | several plastic or functional layers | barrier, protective or surface properties that can be specifically combined |
| Particle-reinforced plastics | plastic with mineral or functional fillers | adapted mechanical, thermal or electrical properties |
| Hybrid composites | combination of different reinforcement and matrix systems | individually tailored property profile |
Fibre-reinforced plastics
In fibre-reinforced plastics, fibres are embedded in a plastic matrix. Glass fibre-reinforced plastics (GFRP) and carbon fibre-reinforced plastics (CFRP) are particularly well known.
The fibres take on a substantial share of the mechanical load, while the plastic matrix positions the fibres and bonds them to one another.
The properties depend heavily on fibre type, fibre content and fibre orientation. Short fibre-reinforced thermoplastics, for example, behave differently from components with long or continuous fibres.
Detailed information on GFRP, CFRP and their differences can be found in our article on fibre-reinforced plastics.
Sandwich composites
Sandwich structures typically consist of two load-bearing cover layers and a lightweight core.
The core can, for example, consist of a foam or a honeycomb structure. The cover layers absorb a large part of the tensile and compressive loads.
This structure makes it possible to achieve high flexural stiffness at comparatively low weight. Sandwich composites are therefore particularly suitable for large-area components and lightweight constructions.
Metal-plastic composites
Metal-plastic composites combine the properties of metallic materials with the advantages of plastics.
Metallic components can absorb high mechanical loads, while the plastic, for example:
- protects against corrosion,
- provides electrical insulation,
- reduces weight,
- takes on sealing functions,
- enables complex geometries or
- integrates additional functions.
Such hybrid constructions are used, among other things, in vehicle construction, mechanical engineering and electrotechnical applications.
Multilayer plastic composites
Multilayer systems combine different plastics or functional layers with one another.
A single plastic therefore no longer has to fulfil all requirements. One layer can, for example, provide mechanical stability, while another forms a barrier against moisture or gases.
Multilayer composites are used, among other things, in films, technical coatings, protective systems and packaging.
What advantages do plastic composites offer?
The essential advantage of plastic composites lies in the fact that different materials can not only be combined with one another, but functionally matched to one another.
High strength at low weight
In particular, fibre-reinforced and sandwich-type composites enable very high specific strengths and stiffnesses.
This is particularly interesting when the component weight is to be reduced. Further information on this topic can be found in our article on weight reduction through plastic components.
Individually adjustable properties
The composition can be specifically adapted to the application.
Depending on the material system, the following, for example, can be influenced:
- strength
- stiffness
- impact strength
- wear behaviour
- thermal expansion
- electrical conductivity
- electrical insulation
- thermal conductivity
- temperature resistance
- chemical resistance
This makes plastic composites particularly interesting for applications in which several technical requirements must be met at the same time.
Corrosion resistance
Plastics do not corrode like many metallic materials. In suitable composite systems, they can therefore protect metallic components against moisture or aggressive media.
The actual resistance, however, always depends on the polymer used, the other components and the specific operating conditions.
Functional integration
Plastic composites can combine several functions within a single component.
A composite component can, for example, simultaneously fulfil load-bearing, insulating, protective and optical functions. As a result, under certain conditions, components can be consolidated and complex assemblies simplified.
Great design freedom
Plastic-based composite materials enable complex component geometries and targeted local reinforcement.
Material can therefore be used where it is structurally required. Particularly in lightweight construction, this opens up possibilities that would be difficult to realise with homogeneous materials.
What disadvantages and limits do plastic composites have?
Despite their advantages, plastic composites are not automatically the best solution for every application.
More complex material selection
Since several materials are combined with one another, their interactions must also be taken into account.
Different thermal expansion, moisture absorption or adhesion between the components can influence component behaviour.
Material selection should therefore always be based on the actual operating conditions.
Anisotropic material behaviour
In fibre-reinforced plastics, the mechanical properties can depend on the fibre direction.
A material can therefore be particularly load-bearing in one direction and significantly less stiff or strong in another. This direction dependence must be taken into account already during design.
More complex machining
Reinforcing fibres or different material layers can make mechanical machining more difficult.
Tools, cutting parameters and machining strategy must therefore be matched to the specific material. For technically demanding components, specialised plastic machining is particularly important.
Recycling
Composite materials are often more difficult to recycle than homogeneous plastics, because different materials are permanently bonded to one another.
How well a material cycle is possible depends heavily on the structure of the composite. Thermoplastic systems offer advantages in some cases, because the plastic matrix can in principle be heated and processed again.
Further information on the entrepreneurial handling of resources can be found on our page on the topic of sustainability.
Plastic composite or modified plastic – what is the difference?
The terms are sometimes used similarly, but do not describe exactly the same thing.
In a modified plastic, the property profile of a base polymer is changed by additives, fillers or reinforcing materials.
In a plastic composite, the interaction of several material components or layers is more the focus.
The boundaries can be fluid. A short glass fibre-reinforced polyamide, for example, can be regarded both as a modified plastic and as a fibre-reinforced plastic composite.
For technical material selection, therefore, the category of the term is less relevant than the question of which material system fulfils the requirements of the specific component.
Where are plastic composites used?
Plastic composites become interesting wherever low weight, high load capacity or several functional requirements are to be combined with one another.
Mechanical and plant engineering
In mechanical and plant engineering, reinforced or functionally modified plastics can be used for guides, mounts, housings, structural components and other technical components.
Advantages arise in particular in applications where weight, corrosion resistance, wear behaviour or electrical properties play a role.
Vehicle construction
In vehicle construction, lightweight construction is an important field of application for plastic composites.
Possible applications range from structural and trim parts to housings and functional components. Suitable material combinations allow weight, mechanical properties and functional integration to be matched to one another.
Aerospace
In aerospace, the lowest possible component weight is particularly relevant.
Fibre-reinforced high-performance materials and sandwich constructions enable designs with high specific stiffness and strength. At the same time, particularly high requirements for material quality, temperature behaviour and reliability must be taken into account in this industry.
Electrical industry
In the electrical industry, plastic composites can combine mechanical stability and electrical insulation.
Depending on the material structure, specifically electrically conductive or dissipative materials are also possible.
Typical applications are found, for example, in housings, insulators, mounts and technical components.
Construction industry
In the construction industry, plastic composites are used, among other things, for profiles, sheets, façade elements, reinforcing components and structural applications.
Low weight, corrosion resistance and weather resistance can represent important advantages here.
How are plastic composites manufactured?
The suitable manufacturing process depends on the matrix material, reinforcement, component geometry and required quantity.
Compounding
In compounding, for example fibres, fillers or functional additives are added to a plastic.
This produces materials with specifically modified properties, which can then be further processed using classic plastic processing methods.
Injection moulding
Short and long fibre-reinforced thermoplastic compounds can often be processed by injection moulding.
The orientation of the fibres within the component is of particular importance here, as it influences the mechanical properties.
Extrusion
In extrusion, plastic is continuously passed through a shaping tool.
The process is suitable, among other things, for the production of technical profiles and semi-finished products. Depending on the application, modified or reinforced plastic grades can be processed.
Laminating
In laminating, several material layers are bonded to one another.
This technique is used in particular for fibre-reinforced components and multilayer composite structures.
Pultrusion
Pultrusion, or the strand drawing process, serves for the continuous production of fibre-reinforced profiles.
Reinforcing fibres are passed through a matrix system and then cured in a defined profile geometry.
The process is particularly suitable for long components with a constant cross-section.
Which criteria are important when selecting a plastic composite?
Selection should not be based exclusively on individual characteristic values. For a reliable component, all relevant operating conditions must be taken into account.
Important questions are:
- What mechanical loads occur? Tension, compression, bending, impact loads and continuous loads place different demands on the composite.
- What temperatures are to be expected? In addition to the maximum temperature, continuous load and temperature changes must also be taken into account.
- Is there contact with chemicals or moisture? Matrix, reinforcement and interfaces must be resistant to the media present.
- How important is weight? If lightweight construction has priority, fibre-reinforced or sandwich-type systems can offer advantages.
- Which electrical properties are required? Depending on their composition, plastic composites can be set to be insulating, antistatic, dissipative or conductive.
- Which production and post-processing is planned? Material and manufacturing process must be matched to geometry, quantity, tolerances and surface requirements.
- What requirements exist regarding service life and cost-effectiveness? The material price alone is not relevant. Machining, assembly, maintenance, weight and service life also influence the total costs.
Selecting plastic composites specifically for industrial components
Plastic composites open up great possibilities when the properties of a single material are not sufficient for an application.
Their ability to combine different functions within a single material system is particularly interesting. Fibres can increase mechanical load capacity, functional fillers can change electrical or tribological properties, and multilayer structures can take on different tasks within a component.
For a plastic composite to actually play to its advantages, material, design and production must be considered together.
Martan Plastics supports you in selecting suitable materials as well as in the realisation of industrial plastic components. For individual requirements, you can contact us directly via our enquiry page.
FAQ on plastic composites
What is meant by a plastic composite?
A plastic composite combines a plastic with at least one further material component. These include, for example, reinforcing fibres, metals, foams or additional plastic layers. The aim is to combine the properties of different materials in a single material system.
What types of plastic composites are there?
The most important groups include fibre-reinforced plastics, sandwich composites, metal-plastic composites, multilayer plastic systems as well as particle-reinforced and hybrid composite materials.
What is the difference between GFRP and CFRP?
In GFRP, glass fibres are used as reinforcement, in CFRP carbon fibres. Both belong to the fibre-reinforced plastics, but differ with regard to stiffness, weight, electrical properties and costs. A detailed comparison can be found in our article on fibre-reinforced plastics.
What advantages do plastic composites have over metals?
Depending on the material system, plastic composites can offer lower weight, high specific strength, corrosion resistance, electrical insulation and greater design freedom. Whether a plastic composite is actually more advantageous, however, always depends on the specific application.
Are plastic composites recyclable?
Recyclability depends on the structure of the composite. The separation of permanently bonded different materials is particularly difficult. Thermoplastic composite systems can offer advantages over thermosetting systems, since the thermoplastic matrix can be heated and processed again.
Which plastics are suitable for plastic composites?
Numerous thermoplastics and thermosetting plastics are possible as the matrix. Typical thermoplastic base materials are, for example, polyamide, polypropylene and various high-performance plastics. The selection depends on mechanical load, temperature, media contact, electrical requirements and the intended manufacturing process.
When are fibre-reinforced plastics worthwhile?
Fibre-reinforced plastics are particularly interesting when higher stiffness or strength is required without unnecessarily increasing the component weight. Which fibre, matrix and reinforcement form is suitable must be determined on the basis of the specific load.
