Definition

Adjective: 1. Permanently hardening when heated: Describing a material, especially a synthetic polymer or plastic, that undergoes an irreversible chemical change when heated or cured, becoming hard, rigid, and infusible. Once set, it cannot be remelted or reshaped by reheating.

Usage

• This term is primarily used in industrial, manufacturing, and materials science contexts to classify polymers and describe their properties.
• It is often used attributively (before a noun) to modify words like , , , or .
• The process is called .

Examples

• Attributive use:

  • Epoxy is a classic thermoset adhesive used in construction and aerospace.
  • The electrical switch housing is made from a durable thermoset plastic.
  • Bakelite was one of the first commercially successful thermoset polymers.

• Predicative use:

  • Once cured, the resin becomes completely thermoset.
  • This type of plastic is thermoset, so you cannot recycle it by melting it down.

Advanced Usage

• Thermoset vs. Thermoplastic: This is a fundamental dichotomy in polymer science. A (e.g., epoxy, vulcanized rubber, polyurethane foam) permanently hardens. A (e.g., polyethylene, PVC, nylon) softens when heated and hardens when cooled, allowing it to be remolded repeatedly.
  • Example: For this application, we need a thermoset material for its high heat resistance, not a thermoplastic.

Variants and Related Words

• Thermosetting (adj): The process or property of becoming thermoset. Often used interchangeably with "thermoset" as an adjective.
  • Example: Phenolic resins have strong thermosetting properties.
• Thermoset (noun): A material that has this property.
  • Example: Fiberglass is often combined with a thermoset like polyester resin.

Synonyms

• Heat-set
• Thermohardening
• Irreversible (in this specific context)

Antonyms

• Thermoplastic (a polymer that becomes pliable or moldable above a specific temperature and solidifies upon cooling, allowing repeated reshaping)

Adjective

1. having the property of becoming permanently hard and rigid when heated or cured
   • the phenol resins and plastics were the original synthetic thermosetting materials