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A thermoset is a polymer that solidifies irreversibly when heated. Similar to the relationship between a raw and a cooked egg, once heated, a thermoset polymer can t be softened again; the egg can t reverts back to its original form. During the initial processing, thermosetting resins undergo a chemical reaction that results in an insoluble network. Essentially, the entire heated, finished article becomes one large molecule. For example, the polymer used in making a fiber-reinforced laminate for a golf club undergoes a cross-linking reaction when it is molded at a high temperature.

Any amount of heat does not soften the material to the point where it can be reworked and indeed may serve only to break it down. Hence, thermosetting substances must have sufficient cross-linking of their chains to prevent molecular motion on heating. Thermosets are therefore valued for their durability and strength and are primarily used in vehicles and construction.

Polyurethanes: mattresses, insulation, toys

Unsaturated Polyesters: varnishes, furniture, boat hulls

Epoxies: glues, coating for electrical circuits, helicopter blades.

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