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Depending on the chemical structure, polyester can be a thermoplastic or thermoset. There are also polyester resins cured by hardeners; however, the most common polyesters are thermoplastics. Examples of thermoset polyesters include the Desmophen brand from Bayer. The OH group is reacted with an Isocyanate functional compound in a 2 component system producing coatings which may optionally be pigmented. ( Taken from lead section - add to types section)

Polyester is a category of polymers that contain the ester functional group in their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include naturally occurring chemicals, such as in the cutin of plant cuticles, as well as synthetics such as polybutyrate. Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not. The material is used extensively in clothing.

Polyester fibers are sometimes spun together with natural fibers to produce a cloth with blended properties. Cotton-polyester blends (polycotton) can be strong, wrinkle and tear-resistant, and reduce shrinking. Synthetic fibers using polyester have high water, wind and environmental resistance compared to plant-derived fibers. They are less fire resistant and can melt when ignited.

Polyester blends have been renamed so as to suggest their similarity or even superiority to natural fibers (for example, China silk, which is a term in the textiles industry for a 100% polyester fiber woven to resemble the sheen and durability of insect-derived silk).

Liquid crystalline polyesters are among the first industrially used liquid crystal polymers. They are used for their mechanical properties and heat-resistance. These traits are also important in their application as an abradable seal in jet engines

Natural polyesters could have played a significant role in the origins of life. Long heterogeneous polyester chains are known to easily form in a one-pot reaction without catalyst under simple prebiotic conditions.

Uses and Applications
Fabrics woven or knitted from polyester thread or yarn are used extensively in apparel and home furnishings, from shirts and pants to jackets and hats, bed sheets, blankets, upholstered furniture and computer mouse mats. Industrial polyester fibers, yarns and ropes are used in car tire reinforcements, fabrics for conveyor belts, safety belts, coated fabrics and plastic reinforcements with high-energy absorption. Polyester fiber is used as cushioning and insulating material in pillows, comforters and upholstery padding. Polyester fabrics are highly stain-resistant—in fact, the only class of dyes which can be used to alter the color of polyester fabric are what are known as disperse dyes. Polyesters are also used to make bottles, films, tarpaulin, canoes, liquid crystal displays, holograms, filters, dielectric film for capacitors, film insulation for wire and insulating tapes. Polyesters are widely used as a finish on high-quality wood products such as guitars, pianos and vehicle/yacht interiors. Thixotropic properties of spray-applicable polyesters make them ideal for use on open-grain timbers, as they can quickly fill wood grain, with a high-build film thickness per coat. Cured polyesters can be sanded and polished to a high-gloss, durable finish.

Polyester is also used to manufacture high strength ropes, thread, hoses, sails, floppy disk liners, power belting and much more in industries.

History
In 1926, United States-based E.I. du Pont de Nemours and Co. began research on large molecules and synthetic fibers. This early research, headed by W.H. Carothers, centered on what became nylon, which was the first synthetic fiber. Carothers was working for duPont at the time. Carother’s research was incomplete and had not advanced to investigating the polyester formed from mixing ethylene glycol and terephthalic acid. The project was revived by British scientists Whinfield and Dickson who patented PET or PETE in 1941. Polyethylene terephthalate forms the basis for synthetic fibers like Dacron, Terylene and polyester. In 1946, duPont bought all legal rights from Imperial Chemical Industries (ICI) In 1950.

Environmental Concern

Polyester is a synthetic petroleum-based fibre, and is therefore a non-renewable carbon-intensive resource. Nearly 70 million barrels of oil are used each year to make polyester around the world, which is now the most commonly used fiber in our clothing. But it takes more than 200 years to decompose.