Thermosetting Plastics Design and Manufacture

Thermosetting Plastics These plastics are formed by chemical reactions which leave them in a relatively fixed state. Thermosetting plastics are formed and ‘set’ in a single operation when a chemical reaction leaves them ‘fixed’ in the shape of the mould. They cannot be softened or reformed when reheated. Although thermosets can withstand high temperatures, excess heat will simply cause the material to decompose. An egg yolk is a good analogy for this. When a yolk is raw, it is in a soft liquid state. But if it is heated, it becomes hard and is no longer capable of becoming soft. Thermosetting plastics are often used when a product needs resistance to extremes in temperature, electrical current, chemicals and wear.

Thermosetting Plastics

Thermosetting Plastics Name Properties and working characteristics Uses Glass reinforced plastics (GRP) Strengthened by glass fibres, mats of glass fibre being sandwiched between layers of polyester plastics Boat hulls, bodies and some structural components of high-performance cars and aircrafts Carbon-fibre plastics (GFRP) Strong, lightweight, higher strength to weight ratio, durable, very expensive Modern bicycles, sailboats

Epoxy resin (ER) USES for bonding of other materials PROPERTIES COMMON NAME: Araldite Many adhesives (glues) are thermosetting plastics. A good example is ‘Araldite’ which is an epoxy resin that hardens when a second chemical is added (a catalyst). It will bond most materials including woods and metals as well as some plastics USES for bonding of other materials PROPERTIES Good electrical insulator hard brittle unless reinforced resists chemicals well

Melamine formaldehyde (MF) COMMON NAME: Formica or Melaware Used in the production of plastic laminates because of its smooth surface and hygienic qualities. PROPERTIES waterproof odourless mark and scratch resistance USES worktops buttons electrical insulation

Urea formaldehyde COMMON NAME: Aerolyte or Cascamite Used in homes as an adhesive resin in pressed wood products PROPERTIES good adhesive qualities stiff, hard and brittle good electrical insulator USES electrical fittings paper and textile coating wood adhesive

Polyester resin COMMON NAME: Orel or Beetle PROPERTIES Stiff, hard and brittle Resilient as laminated GRP Formed without heat and pressure USES panels for car bodies and boat hulls casting embedding

GRP One way on reinforcing plastic is to add fibred glass to it. This makes it much stronger and is generally referred to as G.R.P. (glass reinforced plastic). GRP is used in car body repairs, sailing boats, corrugated sheet because of its lightness, toughness and resistance to water.