Polyethylene terephthalate (PET) has a crystalline structure and good chemical resistance to mineral oils, acids and solvents but not to bases. It has good electrical resistance, low moisture absorption; it resists combustion and is self-extinguishing.
PET exists both as an amorphous (transparent) and a semi-crystalline (opaque and white) thermoplastic, and can be made into either a resin or a film. The semi-crystalline PET has good strength, stiffness and hardness while the amorphous PET has better ductility.
PET can be made into a resin, fibre or film. The largest outlet is synthetic fibres, followed by bottle resin. PET film is used in electrical applications and packaging.
In the manufacture of PET resins, purified terephthalic acid (PTA) and monoethylene glycol (MEG) are reacted to make a basic ester which is polymerised in a melt phase, polycondensation finishing reactor.
Dimethyl terephthalate (DMT) is an alternative feedstock to PTA but the PTA route is preferred. The molten polymer is extruded, cut into chips and cooled. The chips pass to a solid state polycondensation unit to form the PET resin.