All about thermosets: chemical structure and properties explained
What are thermosets?
Definition of thermosets
Thermosets are plastics that, once cured, can no longer be melted or reshaped. They are formed by a chemical reaction in which monomers are crosslinked via covalent bonds into a tightly meshed, three-dimensional network.
GOBA manufactures insulation and moulded parts from thermoset materials and supplies insulation materials for electrical engineering applications.
How do thermosets differ from thermoplastics?
Thermosets:
- Tightly meshed, irreversible crosslinking
- Not meltable, only thermally decomposable
- Examples: epoxy resins, polyester resins, Bakelite
Thermoplastics:
- Linear or branched polymer chains
- Meltable and re-formable
- Examples: polyethylene (PE), polypropylene (PP)
Which groups belong to the thermosets?
Thermosets are divided into three main groups:
- Epoxy resins: For adhesives, coatings, technical applications
- Polyester resins: Often used in composite materials such as GFRP
- Polyurethanes: For foams, paints and elastomers
How are thermosets formed and manufactured?
Thermosets are produced by chemical reactions such as:
- Polyaddition: Monomers react forming covalent bonds (e.g. in epoxy resins)
- Polycondensation: By-products such as water are formed (e.g. in polyester resins)
What are the steps in the manufacture of thermosets?
- Raw material selection: Monomers, hardeners and additives such as fillers or colour pigments
- Prepolymers: Formation of partially crosslinked molecules (intermediate products)
- Curing: Complete crosslinking under heat or with catalysts
Which chemical processes are involved in manufacturing?
Chemical crosslinking is based on covalent bonds that link the molecular chains into a stable network. This structure makes thermosets hard and brittle as well as resistant to high temperatures and chemicals.
What properties do thermosets have?
How do thermosets behave at high temperatures?
Thermosets are thermally stable and resist temperatures up to 300 °C depending on composition. Under extreme heat, however, they decompose as the covalent bonds break.
What makes thermosets hard and brittle?
The tightly meshed crosslinking of the molecular chains prevents mobility, which increases mechanical strength but also produces brittleness. Under mechanical load they are prone to cracks or fractures.
What resistance do thermosets show to chemicals?
Thermosets are resistant to many chemicals, including oils, solvents and acids. This makes them ideal for applications in the chemical industry and in demanding environments.
Which types of thermosets are there?
What are the differences between epoxy resins and polyester resins?
Epoxy resins: Higher mechanical strength, chemical resistance and adhesion. Frequently used in coatings and adhesives.
Polyester resins: More cost-effective, less chemically resistant, but ideal for large-surface applications such as GFRP components.
How are polyurethanes integrated into thermosets?
Through specific curing processes, polyurethanes can be used both as elastic materials (e.g. foams) and as rigid thermosets.
What role do synthetic resins play in thermosets?
Synthetic resins such as Bakelite or melamine resin are classic thermosets used as electrical insulation, in household goods or for kitchen worktops.
How do thermosets react to mechanical stresses?
How do thermosets behave under mechanical stresses?
Thermosets are very stiff and withstand high loads. Their brittleness, however, makes them susceptible to cracks under extreme localized loading.
What happens when thermosets develop cracks or fractures?
Cracks can propagate through the entire structure, since the tightly meshed crosslinking permits no flexibility. Reinforcements with glass fibres or other additives can prevent this.
Where are thermosets used?
In which industries are thermosets frequently used?
- Automotive industry: Engine covers, body parts
- Electrical engineering: Insulation, enclosures for electrical devices
- Construction industry: Pipes, window frames
- Aerospace: High-strength components made of composite materials
Which properties make thermosets suitable for specific applications?
- Thermal resistance: Ideal for applications at high temperatures
- Chemical resistance: Use in corrosive environments
- Mechanical strength: Suitable for load-bearing components
How do thermosets influence component quality?
Thermosets increase the service life and reliability of components, since they neither melt nor deform under heat or chemical load.
GOBA Takeaway
Thermosets are indispensable for numerous industries that require durable, resilient and thermally stable materials. Their tightly meshed crosslinking makes them ideal for demanding applications, from the automotive industry to electrical engineering. With their high chemical and mechanical resistance, they provide solutions that withstand even extreme conditions.