Why are thermosetting plastics difficult to recycle by remelting?

Thermosetting plastics are difficult to recycle by remelting because of their unique molecular structure, which is formed during their initial processing. Unlike thermoplastics, which consist of separate molecules that can flow past one another when heated, thermosets undergo a chemical reaction that creates a highly cross-linked, three-dimensional network.123

Essentially, this process turns the entire finished article into one large, interconnected molecule. Because of this extensive cross-linking, thermosets do not undergo a solid-melt transformation when heated. Instead of softening to a point where they can be reshaped, they remain dimensionally stable until they reach temperatures high enough to cause chemical degradation or decomposition. Consequently, they cannot be reprocessed or remolded like thermoplastics.1243