Thermoplastics are polymers that can be repeatedly softened by heating and hardened by cooling. Which statement best describes this property?

• A. They can be remelted and reshaped multiple times
• B. They harden permanently after initial forming
• C. They decompose when heated
• D. They are always biodegradable

Answer: (A)

Thermoplastics can be softened by heating and hardened by cooling, which means they can be remelted and reshaped many times. This happens because their polymer chains have few or no permanent crosslinks; when heated above their glass transition or melting temperature, the chains gain mobility and can flow. Upon cooling, they solidify again into a new shape. Because there isn’t a permanent network holding the chains in place, this reshaping cycle can be repeated, enabling recycling and reprocessing.

The idea that they harden permanently after initial forming describes thermosetting plastics, not thermoplastics. Saying they decompose when heated is about degradation under high heat rather than the normal, reversible softening. And being always biodegradable is not a defining property of thermoplastics.