Which statement correctly describes thermoset plastics?

• A. Thermoplastics can be heated and formed; thermosets cannot be reheated and reformed.
• B. Thermosets can be reheated and reformed.
• C. Thermoset plastics are always biodegradable.
• D. Thermoset plastics cannot be reheated and reformed.

Answer: (D)

Thermoset plastics form a permanent crosslinked network when they cure, which makes them behave like a rigid, non-melting structure. Once set, the bonds between chains are so extensive that heating don’t make them flow; instead, they tend to degrade or char. That’s why they cannot be reheated and reformed into a new shape—their structure is permanently locked in place. This is the defining behavior of thermosets and is what the statement correctly describes.

In contrast, thermoplastics don’t have those permanent crosslinks, so they soften when heated and can be reshaped and remolded. The other idea about thermosets being biodegradable isn’t inherently true for all of them; biodegradability varies and isn’t a defining trait of thermosets, so that option isn’t correct either.