- 2066 Shrawan (old course) · 2+6 marks
Thermoplastics versus thermosetting plastics
Short answer
A polymer is a large molecule made of repeating monomers; polymerization is the process of joining monomers, by addition or condensation. Thermoplastics soften on heating and harden on cooling, can be remoulded and recycled, with linear chains (e.g. PVC, polyethylene). Thermosetting plastics set permanently on first heating with cross-linked networks, cannot be remoulded, and are harder and more heat-resistant (e.g. Bakelite, epoxy).
Define polymer and polymerization. Differentiate between thermoplastics and thermosetting plastics.
Polymer and polymerization
A polymer is a large molecule made of many repeating small units (monomers) joined by chemical bonds. Polymerization is the chemical process by which monomers combine to form the polymer, by addition polymerization (no by-product, e.g. ethylene to polyethylene) or condensation polymerization (water or another small molecule is released, e.g. Bakelite).
Difference between thermoplastics and thermosetting plastics
| Point | Thermoplastics | Thermosetting plastics |
|---|---|---|
| Effect of heat | Soften when heated, harden on cooling; repeatable | Set permanently on first heating |
| Molecular structure | Linear or slightly branched chains | Cross-linked three-dimensional network |
| Reshaping | Can be remoulded | Cannot be remoulded |
| Recycling | Can be recycled | Hard to recycle |
| Strength and hardness | Softer, less rigid | Harder, more rigid, brittle |
| Heat and chemical resistance | Lower | Higher |
| Polymerization | Mostly addition | Mostly condensation |
| Moulding | Injection moulding, extrusion | Compression moulding |
| Examples | PVC, polyethylene, polystyrene, acrylic | Bakelite, melamine, epoxy, polyester |
| Uses | Pipes, sheets, tanks, insulation | Switches, laminates, adhesives, GRP |
✓ Answer checked by Claude Opus 5.5 (high effort)
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