Thermoplastics soften when heated while thermosets are permanently hardened.
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Thermoplastics are polymers whose chains are not chemically crosslinked, so they soften when heated and harden again on cooling. This allows them to be remelted, reshaped and recycled, as with polyethylene, PVC and polystyrene. Thermosets, such as Bakelite and epoxy resins, form a three-dimensional network of covalent crosslinks during curing, which makes them rigid, heat resistant and insoluble. Once cured, thermosets cannot be remelted because heating causes decomposition before melting. The distinction therefore determines how each type of plastic is processed and disposed of.
Key ideas: Thermoplastics (polyethylene, PVC, polystyrene, nylon) have linear or branched chains held by weak forces, soften on heating and can be remolded and recycled. Thermosets (Bakelite, epoxy, vulcanized rubber, melamine) have covalent crosslinks formed on curing, so they char rather than melt and cannot be reshaped.
Common mistakes and connections: Students think thermosets are stronger just because they are hard; they are brittle and hard to recycle. Light crosslinking gives elastomers such as rubber. Crystallinity raises density and melting point in thermoplastics. Links to polymer structure, recycling and composites.
Approximate melting points of common thermoplastics. Unlike thermosets, they can be remelted and reshaped because their chains are not crosslinked. The interactive lesson shows this as a live animation or chart.
Epoxy adhesive sets permanently as its crosslinked network forms, and it cannot be melted down to reuse it.
Thermoplastics soften when heated while thermosets are permanently hardened.
Thermoplastics and Thermosets is a intermediate topic in Biochemistry, Environment & Industry. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Biochemistry, Environment & Industry first: Chemistry of Cooking, Cosmetic Chemistry, Plastics.
The next topics in Biochemistry, Environment & Industry are Polyethylene and PVC.
Yes. The interactive lesson includes a self-check question on Thermoplastics and Thermosets, and the Biochemistry, Environment & Industry quiz draws on every topic in this area.
Thermoplastics and Thermosets is topic 53 of 127 in Biochemistry, Environment & Industry.
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