---
title: "Define borosilicate glass and thermoplastic"
subject: "Civil Engineering Materials"
chapter: 10
key: "semester_3/civil_engineering_materials:thermoplastic-define"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/thermoplastic-define
site: BCT Engineering
---

# Define borosilicate glass and thermoplastic

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

- Asked in: 2074 Chaitra, 2 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/thermoplastic-define
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-10

## Question

Define borosilicate glass and thermoplastic.

## Short answer

Borosilicate glass contains silica and boron trioxide, giving it very low thermal expansion and high chemical resistance, used for laboratory glassware and ovenware. A thermoplastic softens when heated and hardens on cooling repeatedly because its polymer chains are linear, allowing remoulding; examples: PVC, polyethylene, polystyrene.

## Answer

#### Borosilicate glass

**Borosilicate glass** is a glass containing silica (about 80%) and boron trioxide (about 13%), with some soda and alumina. It has a very low coefficient of thermal expansion, high chemical resistance and can withstand sudden temperature changes. Example: Pyrex. It is used for laboratory glassware, pipes, ovenware and lighting.

#### Thermoplastic

A **thermoplastic** is a plastic that softens on heating and hardens on cooling, and this can be repeated many times without chemical change because the polymer chains are linear and not cross-linked. They can be remoulded and recycled. Examples: PVC, polyethylene, polystyrene, acrylic (PMMA), nylon.

## Check yourself

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

1. How does a thermoplastic behave on heating and cooling?
   A. It sets permanently on the first heating
   B. It softens on heating and hardens on cooling, repeatably
   C. It hardens on heating and softens on cooling
   D. It chars on the first heating
   Answer: B. Thermoplastics can be softened and hardened again and again without chemical change. (Key point: Thermoplastic behaviour)

2. Why can a thermoplastic be remoulded and recycled?
   A. Its chains are heavily cross-linked
   B. It contains boron trioxide
   C. Its polymer chains are linear and not cross-linked
   D. It is made only by condensation polymerization
   Answer: C. Linear, non-cross-linked chains can slip when heated, so the material can be reshaped repeatedly. (Key point: Why remouldable)

3. Which composition describes borosilicate glass?
   A. About 80% silica and 13% boron trioxide, with some soda and alumina
   B. About 13% silica and 80% boron trioxide
   C. Silica only, with no other oxides
   D. Polished flat glass silvered on one side
   Answer: A. Borosilicate glass (e.g. Pyrex) is about 80% silica and 13% boron trioxide with soda and alumina. (Key point: Borosilicate glass composition)

4. Why is borosilicate glass used for laboratory glassware and ovenware?
   A. It has a high thermal expansion
   B. It is soft and easily remoulded
   C. It has a very low thermal expansion and withstands sudden temperature changes
   D. It is cheaper than all other glasses because it has no silica
   Answer: C. Its very low coefficient of thermal expansion lets it survive sudden temperature changes. (Key point: Borosilicate property)