Polyester

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Polyester

For the cinema film, see the article Polyester (film)''.

Polyester is a category of polymers, or, more specifically condensation polymers, which contain the ester functional group in their main chain. Usually, polyester refers to cloth woven from polyester fiber. Polyester clothing is generally considered to have a "less natural" feeling to it compared to natural fibers. Polyester fibers are often spun together with fibers of cotton, producing a cloth with some of the better properties of each.

Although polyesters do exist in nature, polyester generally refers to the large family of synthetic polyesters (plastics) which includes polycarbonate and above all polyethylene terephthalate (PET). PET is one of the most important thermoplastic polyesters.

Extreme care with fire around polyester should be exercised, as polyester is extremely flammable and flames can leap from a match to polyester at a range of at least three inches (7.5 cm).

Applications

Polyester is the most widely used manufactured fiber in the U.S. Woven fabrics are used for apparel and home furnishings. These include bed sheets, bedspreads, curtains and draperies. Polyester used in knitted fabrics include shirts and blouses. Fiberfill is also used to stuff pillows, comforters and cusion padding.

The first synthetic polyester, glycerine phthalate, was used in the First World War for waterproofing. Natural polyesters have been known since around 1830.

Polyesters are used to make bottles, films, liquid crystal displays, holograms, filters, dielectric film for capacitors, film insulation for wire and insulating tapes.

Liquid crystalline polyesters are among the first industrially used liquid crystalline polymers. In general they have extremely good mechanical properties and are extremely heat resistant. For that reason, they can be used as an abradable seal in jet engines.

Thermosetting polyester resins are commonly used as casting materials, fiberglass laminating resins, and non-metallic auto-body fillers. In such applications, polymerization and cross-linking are initiated through an exothermic reaction involving an organic peroxide, such as methyl ethyl ketone peroxide or benzoyl peroxide.

Properties

Polyester has excellent durability, abrasion resistance, tenacity and high elongation. The fiber also has high appearance retention, dimensional stability, elastic recovery and excellent resiliency. It remains very strong when it is wet. However, polyester ranks very poorly in comfort and absorbency.

Filament fibers can be bright, delustered, or have high or low tenacity. Staple fibers can range in deniers as well as the degree in which they pill.

Aesthetics

The fiber blends well with other fibers and maintains a natural look. Polyester can be engineered to be very similar in appearance and hand to wool, linen and silk.

The low absorbency causes the fabric to be very uncomfortable. This can be improved through blending it with other fibers. Static can be controlled through additives and changes in the compound.

Environmental impact

The impact is very similar to that of nylon. Polyester is extensively recycled, and less pollution is created when the recycled fibers are reengineered than when new ones are created.

History

Terylene was the first polyester fiber and was produced in England. It was brought to the U.S. in 1951 by Dupont under the trade name Dacron.

Synthesis

Synthesis of polyesters is generally achieved by a polycondensation reaction. See "condensation reactions in polymer chemistry".

Azeotrope esterification

In this classical method an alcohol and a carboxylic acid react to form a carboxylic ester. To assemble a polymer, the water formed by the reaction must be continually removed by azeotrope distillation.

Alcoholic transesterification

See main article on transesterification.

O \\ C - OCH₃ + OH^* / ^* O \\ C - O^* + CH₃OH / ^*

	$\leftrightarrow$
(ester-terminated oligomer + alcohol-terminated oligomer)		(larger oligomer + methanol)

Acylation (HCl method)

The acid begins as an acid chloride, and thus the polycondensation proceeds with emission of hydrochloric acid (HCl) instead of water. This method can be carried out in solution or as an enamel.

Silyl method

In this variant of the HCl method, the carboxylic acid chloride is converted with the trimethyl silyl ether of the alcohol component; trimethyl silyl chloride is produced.

Acetate method (esterification)

Silyl acetate method

Ring-opening polymerization

Aliphatic polyesters can be assembled from lactones under very mild conditions, catalyzed anionically, cationically or metallorganically.

References

Textiles, by Sara Kadolph and Anna Langford. 8th Edition, 1998.

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