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Polyester is a category of that contain the in their main chain. As a specific , it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include naturally occurring chemicals, such as in the of , as well as synthetics such as . Natural polyesters and a few synthetic ones are , 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. -polyester blends (polycotton) can be strong, wrinkle and tear-resistant, and reduce shrinking. using polyester have high water, wind and environmental resistance compared to plant-derived fibers. They are less and can melt when ignited.

(2005). 9780743272865, Simon and Schuster. .

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 ).

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.


Types
Depending on the chemical structure, polyester can be a or . There are also cured by hardeners; however, the most common polyesters are thermoplastics.
(2019). 9781856174312, Elsevier. .
Examples of thermoset polyesters include the Desmophen brand from Bayer. The OH group is reacted with an functional compound in a 2 component system producing coatings which may optionally be pigmented. Polyesters as thermoplastics may change shape after the application of heat. While combustible at high temperatures, polyesters tend to shrink away from flames and self-extinguish upon ignition. Polyester fibers have high tenacity and E-modulus as well as low water absorption and minimal shrinkage in comparison with other industrial fibers.

(UPR) are thermosetting . They are used in the liquid state as materials, in sheet molding compounds, as laminating resins and in non-metallic auto-body fillers. They are also used as the thermoset polymer matrix in . Fiberglass-reinforced unsaturated polyesters find wide application in bodies of yachts and as body parts of cars.

According to the composition of their main chain, polyesters can be:

AliphaticHomopolymer of
Ring-opening polymerization of
Ring-opening polymerization of
Copolymer
Polycondensation of with 1,4-butanediol
of 3-hydroxybutanoic acid and 3-hydroxypentanoic acid,
, and (oligomeric as a catalyst)
Semi-aromaticCopolymerPolycondensation of terephthalic acid with
Polycondensation of terephthalic acid with 1,4-butanediol
Polycondensation of terephthalic acid with 1,3-propanediol
Polycondensation of at least one dicarboxylic acid with ethylene glycol
Polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid

Increasing the aromatic parts of polyesters increases their glass transition temperature, melting temperature, , chemical stability...

Polyesters can also be like the polycaprolactone diol (PCL) and the polyethylene adipate diol (PEA). They are then used as .


Uses and Applications
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 .

Polyesters are also used to make bottles, films, , canoes, liquid crystal displays, , filters, film for , film insulation for and . Polyesters are widely used as a finish on high-quality wood products such as , and vehicle/yacht interiors. 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.


Industry

Basics
Polyester is a synthetic polymer made of purified terephthalic acid (PTA) or its dimethyl ester dimethyl terephthalate (DMT) and monoethylene glycol (MEG). With 18% market share of all plastic materials produced, it ranges third after (33.5%) and (19.5%).

The main raw materials are described as follows:

Purified terephthalic acid (PTA) CAS-No. 100-21-0
Synonym
Dimethylterephthalate (DMT) CAS-No. 120-61-6
Synonym
Mono-ethylene glycol (MEG) CAS No. 107-21-1
Synonym

To make a polymer of high a catalyst is needed. The most common catalyst is antimony trioxide (or antimony tri-acetate):

Antimony trioxide (ATO) CAS-No. 1309-64-4
mol. weight

In 2008, about 10,000 tonnes Sb2O3 were used to produce around 49 million tonnes polyethylene terephthalate.

Polyester is described as follows:

Polyethylene terephthalate CAS-No. 25038-59-9
Synonyms/abbreviations

There are several reasons for the importance of polyester:

  • The relatively easy accessible raw materials PTA or DMT and MEG
  • The very well understood and described simple chemical process of polyester synthesis
  • The low toxicity level of all raw materials and side products during polyester production and processing
  • The possibility to produce PET in a closed loop at low emissions to the environment
  • The outstanding mechanical and chemical properties of polyester
  • The recyclability
  • The wide variety of intermediate and final products made of polyester.

In the following table, the estimated world polyester production is shown. Main applications are polyester, bottle polyester resin, film polyester mainly for and specialty polyesters for engineering plastics. According to this table, the world's total polyester production might exceed 50 million tons per annum before the year 2010.

+ World polyester production by year ! Product type ! 2002 (million tonnes/year) ! 2008 (million tonnes/year)
Textile-PET2039
Resin, bottle/A-PET916
Film-PET1.21.5
Special polyester12.5


Raw material producer
The raw materials PTA, DMT, and MEG are mainly produced by large chemical companies which are sometimes integrated down to the crude oil refinery where is the base material to produce PTA and liquefied petroleum gas (LPG) is the base material to produce MEG.


Polyester processing
After the first stage of polymer production in the melt phase, the product stream divides into two different application areas which are mainly textile applications and packaging applications. In the following table, the main applications of textile and packaging of polyester are listed.

+ Textile and packaging polyester application list (melt or pellet) ! Textile ! Packaging
Staple fiber (PSF)Bottles for CSD, water, beer, juice, detergents, etc.
Filaments POY, DTY, FDYA-PET film
Technical yarn and tire cordThermoforming
Non-woven and spunbondbiaxial-oriented film (BO-PET)
Mono-filamentStrapping

Abbreviations:

PSF
Polyester-staple fiber;
POY
Partially oriented yarn;
DTY
Drawn textured yarn;
FDY
Fully drawn yarn;
CSD
Carbonated soft drink;
A-PET
Amorphous polyester film;
BO-PET
Biaxial-oriented polyester film;

A comparable small market segment (much less than 1 million tonnes/year) of polyester is used to produce engineering plastics and .

In order to produce the polyester melt with a high efficiency, high-output processing steps like staple fiber (50–300 tonnes/day per spinning line) or POY /FDY (up to 600 tonnes/day split into about 10 spinning machines) are meanwhile more and more vertically integrated direct processes. This means the polymer melt is directly converted into the textile fibers or filaments without the common step of . We are talking about full vertical integration when polyester is produced at one site starting from crude oil or products in the chain oil → benzene → PX → PTA → PET melt → fiber/filament or bottle-grade resin. Such integrated processes are meanwhile established in more or less interrupted processes at one production site. Eastman Chemicals were the first to introduce the idea of closing the chain from PX to PET resin with their so-called INTEGREX process. The capacity of such vertically integrated production sites is >1000 tonnes/day and can easily reach 2500 tonnes/day.

Besides the above-mentioned large processing units to produce staple fiber or yarns, there are ten thousands of small and very small processing plants, so that one can estimate that polyester is processed and recycled in more than 10 000 plants around the globe. This is without counting all the companies involved in the supply industry, beginning with engineering and processing machines and ending with special additives, stabilizers and colors. This is a gigantic industry complex and it is still growing by 4–8% per year, depending on the world region.


Synthesis
Synthesis of polyesters is generally achieved by a polycondensation reaction. See "condensation reactions in polymer chemistry". The general equation for the reaction of a diol with a diacid is :
(n+1) R(OH)2 + n R´(COOH)2 → HOROOCR´COOnROH + 2n H2O


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


Alcoholic transesterification

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 .
Silyl method
In this variant of the HCl method, the carboxylic acid chloride is converted with the trimethyl silyl ether of the alcohol component and production of trimethyl silyl chloride is obtained


Acetate method (esterification)
Silyl acetate method


Ring-opening polymerization
polyesters can be assembled from under very mild conditions, catalyzed , or . A number of catalytic methods for the copolymerization of epoxides with cyclic anhydrides have also recently been shown to provide a wide array of functionalized polyesters, both saturated and unsaturated.


History
In 1926, United States-based began research on large molecules and synthetic fibers. This early research, headed by W.H. Carothers, centered on what became , 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 or PETE in 1941. Polyethylene terephthalate forms the basis for synthetic fibers like , Terylene and polyester. In 1946, duPont bought all legal rights from Imperial Chemical Industries (ICI).


Biodegradation
The house was made of fibreglass-reinforced polyester plastic; polyester-polyurethane, and poly(methylmethacrylate) one of them was found to be degrading by and .


Cross-linking
Unsaturated polyesters are thermosetting resins. They are generally copolymers prepared by polymerizing one or more with saturated and unsaturated dicarboxylic acids (, ...) or their . The double bond of unsaturated polyesters reacts with a monomer, usually , resulting in a 3-D cross-linked structure. This structure acts as a thermoset. The reaction is initiated through a , usually an such as methyl ethyl ketone peroxide or .


Environmental concerns

Pollution of freshwater and seawater habitats
A team at Plymouth University in the UK spent 12 months analysing what happened when a number of synthetic materials were washed at different temperatures in domestic washing machines, using different combinations of detergents, to quantify the microfibres shed. They found that an average washing load of 6 kg could release an estimated 137,951 fibres from polyester-cotton blend fabric, 496,030 fibres from polyester and 728,789 from acrylic. Those fibers add to the general pollution.O'Connor, Mary Catherine (27 October 2014) Inside the lonely fight against the biggest environmental problem you've never heard of. The Guardian


Non Renewable
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.


See also


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


External links

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