Question

A material that can be deformed permanently by heat and pressure is called a:

• A. Thermoplastic
• B. Thermoset
• C. Chemical compound
• D. Polymer

Hint:

This type of plastic cross-links permanently the first time it is heat-moulded.

Answer 1

The Correct Option is B

Step 1: Polymers used as plastics are broadly divided into two types based on how they behave on heating: thermoplastics and thermosetting plastics, thermosets.

Step 2: Thermoplastics have linear or slightly branched chains held together only by weak intermolecular forces. On heating they soften and can be moulded again and again, and on cooling they harden again. This softening and reshaping is reversible, so the change is not permanent.

Step 3: Thermosetting plastics are shaped once while soft, under heat and pressure. During this shaping, extensive cross-linking, covalent bonds, forms between the polymer chains, locking them into a rigid, three dimensional network.

Step 4: Once this cross-linked network sets, the material cannot be softened and remoulded again by heating. The shape given during the original heat and pressure moulding becomes permanent, and if heated strongly afterward, the material chars or decomposes instead of melting.

Step 5: Chemical compound and polymer are both far too general and do not specifically describe this permanent, heat and pressure set behaviour.

Answer: The material that deforms permanently under heat and pressure is a thermoset, option B.