Polyester is any of a certain group of widely used plastics materials. One of the most important polyesters, polyethylene terepthalate (PET), can be spun into fiber, extruded (pushed through an opening) to make film, or combined with other materials and molded into plastic parts. PET is a _thermoplastic—_that is, it softens and melts at high temperatures. Polycarbonates are an important group of thermoplastic polyesters (see Plastics (Types of plastics) ).
Polyesters are synthetic polymers. A polymer is a long, chainlike molecule. The “links” are repeating patterns of simple groups of atoms called monomers. In most polyesters, the monomers connect to each other by ester groups, units made of one carbon atom and two oxygen atoms.
PET fiber is one of the most widely produced synthetic fibers. It appears in such products as tire cords and clothing. It is strong and flexible, and it resists wrinkling and mildew. Much PET fiber is sold under the name Dacron, a registered trademark of the DuPont Company. Uses of PET film include magnetic tapes and shrink wrap. PET is also used to make plastic soft drink bottles, which, like PET film, are clear and tough, and resist water and chemicals.
Other important polyesters are the unsaturated polyesters. The monomers in these materials contain unsaturated acids, which are hydrocarbon acids with two carbon atoms joined by double bond (see Hydrogenation ). Manufacturers use these polymers to make thermosetting plastics, which do not soften when heated. Polyester “thermosets” can be combined with fiberglass (glass threads) to make a strong rigid material used for automobile body parts, boats, and bowling balls.
Polyester thermoplastics are easy to recycle. The thermosetting materials are difficult to recycle, but can be ground into powders and used as fillers.
Researchers discovered the chemistry of polyesters in the 1930’s. In the 1940’s, the aircraft industry began to use unsaturated polyesters. In the 1950’s, PET fiber became a major product.
