Thermoplastic materials: identify the correct definition and behavior under heat and pressure Consider the behavior of thermoplastic polymers during heating, forming, cooling, and any associated chemical change. Choose the most accurate description of thermoplastics.
-
AAre formed into shape under heat and pressure and result in a permanently hard product
-
BDo not become permanently hard by heat and pressure; they soften on heating, harden on cooling, and undergo no chemical change
-
CAre inherently flexible and can withstand considerable wear under suitable conditions
-
DAre used specifically as friction linings for clutches and brakes
Answer
Correct Answer: Do not become permanently hard by heat and pressure; they soften on heating, harden on cooling, and undergo no chemical change
Explanation
Given
- Definition-centric question about thermoplastic behavior.
ConceptThermoplastics soften and become formable when heated and solidify when cooled, without a chemical curing reaction. They can be reheated and reshaped multiple times. In contrast, thermosets cure irreversibly into a permanently hard product upon heat and pressure.
ReasoningThermoplastic: softens ⇄ hardens with temperature cycling; no cross-linking reaction.Thermoset: permanent set due to chemical cross-linking under heat/pressure.
Eliminate optionsOption (a) describes thermosets. Options (c) and (d) are application-specific and not defining features.
Final AnswerDo not become permanently hard by heat and pressure; they soften on heating, harden on cooling, and undergo no chemical change