What happens to thermoplastics when heated?

Thermoplastics are a category of plastics that become pliable or moldable at a certain elevated temperature and solidify upon cooling. When thermoplastics are heated, they undergo a physical change: they soften, which allows them to be reshaped or molded into new forms. This property is what makes thermoplastics highly versatile and widely used in various applications, from packaging materials to automotive components.

As the temperature of thermoplastics increases, the molecular structure begins to move more freely, breaking the intermolecular forces that hold the plastic in a rigid form. This process continues until the thermoplastic reaches its melting point, at which it can be processed and shaped without significant degradation. Once cooled, it retains its new shape. This characteristic contrasts with thermosetting plastics, which undergo a chemical change when heated that permanently hardens their structure.

The other options do not accurately describe the behavior of thermoplastics under heating. Thermoplastics do not decompose at lower temperatures; they only begin decomposition at much higher temperatures. They do not harden upon heating; rather, they soften. Lastly, they do not maintain their shape when heated since the primary characteristic of thermoplastics is their ability to change shape when subjected to heat.