Details
Material hierarchy: Polymer
Thermosets, also called thermosetting polymers or thermosetting resins, and abbreviated by TS, cannot tolerate repeated heating cycles as thermoplastics can. When initially heated, they soften and flow for molding, but the elevated temperatures also produce a chemical reaction that hardens the material into an infusible solid. If reheated, thermosetting polymers degrade and char rather than soften.
Among plastic materials, thermosetting materials generally provide one or more of the following advantages:
- high thermal stability
- resistance to creep and deformation under load and high dimensional stability, and
- high rigidity and hardness
These advantages are coupled with the light weight and excellent electrical insulating properties common to all plastics. The compression and transfer molding methods by which the materials are formed, together with the more recent evolution of thermoset injection molding techniques, offer low processing cost and mechanized production.
Thermosetting molding compounds consist of two major ingredients: (1) a resin system, which generally contains such components as curing agents, hardeners, inhibitors, and plasticizers; and (2) fillers and/or reinforcements, which may consist of mineral or organic particles, inorganic or organic fibers, and/or inorganic or organic chopped cloth or paper.
The resin system usually exerts the dominant effect, determining to a great extent the cost, dimensional stability, electrical qualities, heat resistance, chemical resistance, decorative possibilities, and flammability. Fillers and reinforcements affect all these properties to varying degrees, but their most dramatic effects are seen in strength and toughness and, sometimes, electrical qualities.