Thermosetting polymers have a rigid molecular structure that prevents them from being reformed and experience permanent deformation under load. They are ideal for permanent applications that require structural resistance to heat and a high material strength (although brittle). They are typically formed through 'curing' which involves the heating of a powdered/liquid resin within a mold until hardened, although a chemical reaction can be used
Epoxy Resin (ER), also known as polyepoxides, is a highly reactive plastic available in a liquid state. It is combined chemically with a catalyst, known as a hardener, which cures the resin creating cross-linked molecular chains. The epoxide content of the resin determines the quantity of hardener required to cure the resin. Chemically the reaction is 'exothermic' as heat is released when the two elements are mixed together. This reaction can occur at room temperature using products such a Araldite or at around 150 °C for other applications
Although commercially found as widely available adhesive, Epoxy Resin is widely used industrially as a coating, predominantly in the electronics industry. It is used for its excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties and very good electrical insulating properties
Melamine-formaldehyde (MF), or melamine resin, is a hard thermosetting polymer used to form cross-link bonds with other resins for use in surface coatings. Typically it is used for it's high durability, surface hardness and excellent fire/heat resistance due to the release of nitrogen when burnt. MF is found in a range of products such as kitchenware, laminates, overlay materials, particleboards, and floor tiles. Melamine is widely used in the manufacture of particleboards as a hard wearing, fire proof coating that protects the decorative finished layer below, such as; faux wood grain, marble, or singe colour
MF is also available as a foam for use in soundproofing, insulation and in cleaning products to remove dirt an fine abrasions
Urea-formaldehyde (UF), or aminoplasts, is a strongly linked thermosetting polymer that has a very high strength, is cost effective and rapidly cures (hardens) within 2 seconds. Like MF, UF is widely used by the wood industry for the manufacture of particle board (chipboard) and in MDF and plywood as the resin bond between particles. It is one of the most popular amino resins with over 1 million tonnes produced annually accounting for 80% of the industry. Due to a poor moisture resistance, UF is only used for internal applications
In the electronics industry UF is used widely for; plugs, sockets and switches due its - low cost and high strength/ heat resistance and insulating properties
Phenol-formaldehyde (PF) if one of the earliest commercially available synthetic polymers as it formed the basis of Bakelite. This was first developed in 1909 and quickly became the material of choice for the growing electronics and automotive industry. It's ability to be moulded quickly into structures that were smooth, retained their shape and were resistant to heat, scratches, and destructive solvents made it a popular replacement for sheet metal/timber. Primarily, as with all plastics since, it's low electrical conductivity and insulating properties were crucial to it's early success. Now widely replaced by thermoplastics, PF is found in particleboard and plywood much like other thermosetting plastics for it's use as a resin
Polyester resin (PR) is a thermosetting polymer unlike Polyester. It is often confused with fiberglass as it is the main resin reinforcement used. It is the lowest cost option of the thermosetting resins and has a high chemical resistance/strength. PR is almost always combined with a filler or with reinforcing material due to it being highly brittle and having a low viscosity (runny) in it's unsaturated form. Combined with glass fibres it is found commonly in insulation, boats, hot tubs, baths, water tanks, piping, roofing and cladding
Polyurethane (PU) is a versatile thermosetting polymer developed from two monomors; diisocyanate & polyol. It can be manufactured directly as a solid, liquid or foam product, with resulting products referred to as 'urethanes'. PU is incredibly elastic allowing it to be stretched substantially before permanent deformation, as well as maintaining high impact/wear resistance. Polyurethanes are a large family of polymers and as such can have a range of properties to suit different applications, such as - footwear, upholstery foam, insulation, varnishes, adhesives, sealants textiles, paint rollers, earplugs etc.
Although versatile, PU is flammable, cannot be recycled, damaged by solvents and degrades quickly in direct U.V light if untreated. There are also toxicity concerns regarding the use of isocyanates in the manufacture of PU as they are irritants to eyes and the respiratory system. Developments are seeking to replace this component in PU.