Thermoset VS Thermoplastic Composites: What's the Difference?

In a basic sense, a thermoplastic composite is a melt-processable plastic (a heat-treated material). Plastic liquefies (softens enough to handle) when enough heat is added to bring it above its melting point. When the heat source is removed and the temperature of the plastic drops below the melting point, the plastic solidifies (or freezes) into a glass-like solid. This process can be repeated, and the plastic melts and solidifies when the temperature is above and below the melting temperature, respectively. However, the molten state of the material gets worse and worse, so there is a practical limit to the number of times this reprocessing can be done before material properties start to suffer. Many thermoplastic polymers are addition-type, capable of producing very long molecular chain lengths (very high molecular weights).

   Thermosets, basically, are materials that undergo a chemical reaction (curing) and change from a liquid to a solid. In its uncured form, the material has very small unlinked molecules (called monomers). The addition of a second material (catalyst) and/or heat or some other activating influence will initiate a chemical reaction. During this reaction, the molecules cross-link and form significantly longer molecular chains, allowing the material to cure. This change is permanent and irreversible. Subsequently, exposure to high temperatures causes the material to degrade without melting. This is because these materials typically degrade below the temperature at which they can be melted.

  Each material has its place in the market. In broad terms, thermosets tend to be around for a long time (have a good place in the market), generally have lower raw material costs, and are generally easier to wet the reinforcing fibers and form part geometries (easier to machine). Thermoplastic composites tend to be tougher (less brittle), can have better chemical resistance, do not require refrigeration (as uncured thermosets often do), and can be recycled and repaired more easily.