A thermoset is a polymer that can only be used once and which becomes infusible and insoluble after polymerisation. Once hardened the shape can no longer be changed.
The polymerisation can triggered by an increase in temperature, the action of radiation, or chemicals (catalysts, hardeners etc.).
After polymerisation and hardening the product cannot be restored to its initial state (liquid or paste) by re-heating.
Most resins used in the composites industry are thermosets.
The main ones are:
• unsaturated polyesters;