They behave very differently from thermoplastics. When first heated, the polymer softens and can be shaped under pressure. However, due to the heat, a chemical reaction begins in which the molecules become permanently bonded. This reaction is known as degradation. As a consequence the polymer becomes permanently rigid and if heated it will not soften but will be destroyed.
Some examples of thermosets:
BAKELITE (phenolic resins)
It was the first plastic to be artificially manufactured from chemicals. It was named after the man who first manufactured it (Leo Baekeland).It is a hard and brittle plastic, with a dark, shiny color. It is a thermosetting plastic, so it resists heat without softening, but up to a certain temperature, because at very high temperatures it decomposes and becomes carbonized.
Bakelite is a good thermal and electrical insulator, hence its uses and applications in electrical accessories, to make handles for pots and pans, kitchen knobs, handles for soldering irons, etc.
MELAMINE (FORMALDEHYDE)
It is a colorless polymer, which can be dyed with color pigments. It is harder than Bakelite, has no taste or odor and is a good thermal and electrical insulator.It is used for the manufacture of unbreakable tableware, door handles, kitchen countertops....etc.
POLYESTER
It is in the form of resin and must be mixed with a product called hardener. It solidifies and forms a rigid, hard and fragile plastic.To give it more resistance, it is reinforced with a layer of fiberglass.Applications: fiberglass coatings (airplanes, boats, swimming pools...) and as transparent plates for roofs and roofing.