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Background
Polyethylene terephthalate polyester (PETP) is the most common thermoplastic polyester and is often called just “polyester”. This often causes confusion - not only is the chemically similar polybutylene terephthalate (PBT) also a (thermoplastic) polyester, the most common resin system used in GRP is also a polyester system - and also often called just “polyester”. (In this latter case, however, the polyesters are chemically unsaturated and are “free-radical polymerised” into a thermoset).
General Properties
Polyethylene terephthalate (PET) is a hard, stiff, strong, dimensionally stable material that absorbs very little water. It has good gas barrier properties and good chemical resistance except to alkalis (which hydrolyse it). Its crystallinity varies from amorphous to fairly high crystalline. It can be highly transparent and colourless but thicker sections are usually opaque and off-white.
Polyethylene Terephthalate Films
It is widely known in the form of biaxially oriented and thermally stabilised films usually referred to by their main brand names Mylar, Melinex or Hostaphan. Strictly speaking, these names should be used only for this type of film whose properties are different from, and in several respects superior to, those of “ordinary” polyethylene terephthalate (PET) film.
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