What is a common characteristic of thermoplastic polymers?

Thermoplastic polymers are characterized by their ability to be molded and reshaped multiple times upon heating. This property arises because thermoplastics do not undergo any chemical change during this process; instead, they soften, allowing them to be formed into different shapes and sizes. When cooled, they solidify but can again be re-heated and re-molded. This versatility makes thermoplastics a popular choice in various applications, from packaging to automotive parts.

The statement about thermoplastics becoming permanently rigid when cooled refers more to thermosetting polymers, which undergo a chemical change during the curing process, creating a rigid structure that cannot be reshaped. The option concerning biodegradability is not universally applicable to all thermoplastic polymers, as many are synthetic and not biodegradable. Lastly, while some thermoplastics may have low melting points, this characteristic is not definitive for all, as thermoplastic polymers can vary widely in thermal properties.