---
title: "Thermoplastics versus thermosetting plastics"
subject: "Civil Engineering Materials"
chapter: 10
key: "semester_3/civil_engineering_materials:thermoplastics-vs-thermosetting"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/thermoplastics-vs-thermosetting
site: BCT Engineering
---

# Thermoplastics versus thermosetting plastics

Civil Engineering Materials · Chapter 10: Asphalt, Bitumen, Tar and Miscellaneous Materials

- Asked in: 2066 Shrawan (old course), 2+6 marks
- Video: [Thermoplastics and Thermosetting plastics | Meaning, Difference, Uses | uses of plastics](https://www.youtube.com/watch?v=A_UWQuXIOWM) — Gourav educator
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/thermoplastics-vs-thermosetting
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-10

## Question

Define polymer and polymerization. Differentiate between thermoplastics and 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).

## Answer

#### 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 |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is a polymer?
   A. A chemical process that joins monomers
   B. A large molecule made of many repeating small units (monomers)
   C. A catalyst used in moulding
   D. A small molecule released during condensation
   Answer: B. A polymer is the large molecule built from repeated monomer units; the joining process is polymerization. (Key point: Definition of polymer)

2. What distinguishes condensation polymerization from addition polymerization?
   A. Condensation gives no by-product
   B. Addition releases water
   C. Condensation releases a small molecule such as water, addition does not
   D. Addition is used only for Bakelite
   Answer: C. Condensation polymerization releases water or another small molecule; addition (e.g. ethylene to polyethylene) has no by-product. (Key point: Addition vs condensation polymerization)

3. Which pairing of structure is correct?
   A. Thermoplastics: cross-linked network; thermosets: linear chains
   B. Thermoplastics: linear or slightly branched chains; thermosets: cross-linked 3D network
   C. Both have cross-linked networks
   D. Both have only linear chains
   Answer: B. Thermoplastics have linear or slightly branched chains, thermosets a three-dimensional cross-linked network. (Key point: Molecular structure difference)

4. Compared with thermoplastics, thermosetting plastics are generally:
   A. Softer and easier to recycle
   B. Harder, more rigid, brittle, and more heat and chemical resistant
   C. Mostly made by injection moulding and extrusion
   D. Able to be remoulded after cooling
   Answer: B. Thermosets are harder, more rigid and brittle with higher heat and chemical resistance, and are hard to recycle. (Key point: Property comparison)

## Related in Civil Engineering Materials

- [Polymer versus polymerization](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Apolymer-vs-polymerization) — Civil Engineering Materials, chapter 10

## Related in other subjects

- [Thermosetting vs thermoplastics; polymers for ropes, utensils](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Athermo-nylon-teflon) — Engineering Chemistry, chapter 4
- [Thermosetting vs thermoplastics; Bakelite](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Athermosetting-bakelite) — Engineering Chemistry, chapter 4
- [Thermosetting polymer; uses of epoxy resin](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Athermosetting-epoxy-uses) — Engineering Chemistry, chapter 4