There are two main classes of polyester, thermoplastics and thermosets. The largest difference between the two is thermosets once molded can not be reshaped. Of course when heated the thermoset polyester will become soft but it can not be molded into a new or different shape; because of this thermosets must be made and formed in one step. Thermoplastics, the most popular class of polyesters by far, becomes malleable and formable each time it becomes hot enough. Thermoplastic polyesters typically are made and formed into parts in separate steps. Another big difference is that thermoplastics are more agreeable to being recycled then thermosets, making them much more popular for green applications.
The production of polyesters can become a bit complicated but simply put it is the polycondensation reaction of a glycol and a carboxylic acid. Depending on what alcohol and acid are used in production a variety of polyesters can be made. The most popular are polybutylene terephthalate (PBT), polyethylene terephthalate (PET) and polycarbonate (PC). The differences between the listed polyesters will be examined in separate essays.
Thermoplastic polyesters are considered high performance engineering resins, with good thermal resistance and hardwearing mechanical properties. Thermoplastic polyesters are crystalline/semi-crystalline; high molecular weight polymers which flow readily when melted and crystallized rapidly making them very good molding resins.
Polyesters come filled and unfilled, fillers or reinforcements typically make up a sizable amount of a polymer anywhere from 5% to +50%. The filling, usually glass fiber, adds strength, mechanical resistance and electrical properties to the polyester. For stiffness glass and mineral fillers can be used and for decreased wear and friction fillers such as graphite and floropolymers are used.
Many additives or modifiers are used in polyesters not just fillers. Modifiers are added for better chemical resistance also modifiers are used to increase polymer toughness. Flame retardants and drip suppressants are used to insure safety in case of electrical shorts or fires; these products keep the polymer from burning when exposed to flame. This keeps the television or fan that short circuits from burning the house down, yes the t.v or fan will melt and burning plastic stinks something terrible but if no combustibles are able to touch the flame it will burn itself without causing additional damage. Polyesters can be made in any color, and can be made to have a shiny or textured surface.
Thermoplastic polyesters are typically made into things such as equipment and belongings by being melted and molded, extruded or drawn and spun (last method is used mainly for the production of fabric). Thermoset polyesters are produced and made into things through foams, compression molding, pultrusin and resin injection molding.
You can find polyesters in many things such as soda bottles, clothing, carpets, film, and varies brushes such as tooth and paint brushes. But polyesters uses do not end there, you will find polyester in cars, shiny Mylar balloons and even furniture. Hey don’t forget polyesters can also be found in boat hulls, building components, storage tanks, bathroom tubs and showers and athletic equipment.
Polyesters are in may parts of our lives, in many forms with many uses. While polyesters along with other plastics have made our lives better we need to remain vigilant in producing them in the most green manner as possible and recycling them every chance we get.