Polyester is a category of
polymerA polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties.Due to the extraordinary...
s which contain the
esterEsters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
functional groupIn organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part...
in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to
polyethylene terephthalatePolyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P), is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...
(PET). Polyesters include naturally-occurring chemicals, such as in the
cutinCutin is one of two waxy polymers that are the main components of the plant cuticle which covers all aerial surfaces of plants. The other major cuticle polymer, which is much more readily preserved in the fossil record, is cutan...
of
plant cuticlePlant cuticles are a protective waxy covering produced only by the epidermal cells of leaves, young shoots and all other aerial plant organs without periderm...
s, as well as synthetics through
step-growth polymerizationStep-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers. Many naturally occurring and some synthetic polymers are produced by step-growth...
such as
polycarbonatePolycarbonates are a particular group of thermoplastic polymers. They are easily worked, moulded, and thermoformed; as such, these plastics are very widely used in the modern chemical industry. Their interesting features position them between commodity plastics and engineering plastics...
and
polybutyratePolybutyrate is a biodegradable aliphatic-aromatic polyester plastic....
. Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not.
Depending on the chemical structure polyester can be a
thermoplasticA thermoplastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through weak Van der Waals forces ; stronger dipole-dipole interactions and hydrogen bonding ;...
or thermoset, however the most common polyesters are thermoplastics.
Woven polyester fabrics are used in apparel and home furnishings such as bed sheets, beds, table sheets, curtains and draperies. Similarly, industrial polyesters are used in tyre reinforcements, ropes, fabrics for conveyor belts, safety belts, coated fabrics and plastic reinforcements with high energy absorption. Polyester fibers are also used to stuff pillows, comforters and cushion padding.
Polyester fabrics are claimed to have a "less natural" feel when compared to similarly-woven fabrics made from natural fibers (i.e.
cottonCotton is a soft, staple fiber that grows in a form known as a boll around the seeds of the cotton plant, a shrub native to tropical and subtropical regions around the world, including the Americas, India and Africa. The fiber most often is spun into yarn or thread and used to make a soft,...
in textile uses). However, polyester fabrics may exhibit other advantages over natural fabrics, such as improved wrinkle resistance. As a result, polyester fibers are sometimes spun together with natural fibers to produce a cloth with blended properties.
Polyesters are also used to make bottles, films,
tarpaulinA tarpaulin or tarp is a large sheet of strong, flexible, water-resistant or waterproof material, often cloth such as canvas or polyester coated with urethane, or made of plastics such as polyethylene. In some places such as Australia, and in military slang, a tarp may be known as a hootchie...
, canoes,
liquid crystal displayA liquid crystal display is a thin, flat panel used for electronically displaying information such as text, images, and moving pictures...
s, holograms,
filterIn chemistry and common usage, a filter is a device that is designed to physically block certain objects or substances while letting others through. Filters are often used to remove solid substances suspended in fluids, for example to remove air pollution, to make water drinkable, and to prepare...
s,
dielectricA dielectric is a nonconducting substance, i.e. an insulator. The term was coined by William Whewell in response to a request from Michael Faraday...
film for
capacitorA capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force...
s,
film insulationAn insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate...
for
wireA wire is a single, usually cylindrical, string of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various wire gauges...
and insulating tapes.
Liquid crystalline polyesters are among the first industrially-used liquid crystalline 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.
Polyesters are widely used as a finish on high-quality wood products such as
guitarThe guitar is a musical instrument with ancient roots that adapts readily to a wide variety of musical styles. It typically has six strings, but four-, seven-, eight-, ten-, eleven-, twelve-, thirteen- and eighteen-string guitars also exist. The size and shape of the neck and the base of the guitar...
s,
pianoThe piano is a musical instrument which is played by means of a keyboard. Widely used in Western music for solo performances, ensemble use, chamber music, and accompaniment, the piano is also very popular as an aid to composing and rehearsal...
s and vehicle / yacht interiors.
Burns GuitarsBurns London is a guitar-making company originally formed in 1960 as Ormston Burns Ltd. It was founded by James Ormston Burns , who has been described as the British Leo Fender...
, Rolls Royce and
SunseekerSunseeker International, is a UK luxury motor yacht manufacturer. Their headquarters and assembly factory is in Poole Harbour, at Poole in Dorset, England. The company has been making motor boats since 1979.-Profile:...
are a few companies that use polyesters to finish their products. 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.
Types
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.
Thermosetting polyesters are used as
castingIn metalworking, casting involves pouring a liquid metal into a mold, which contains a hollow cavity of the desired shape, and then is allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
materials, and chemosetting
polyester resinPolyester resins are unsaturated resins formed by the reaction of dibasic organic acids and polyhydric alcohols. Among other uses, it is the basic component of sheet moulding compound, bulk moulding compound and the toner of laser printers....
s are used as
fiberglassFiberglass, , is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer or glass-reinforced plastic , is called "fiberglass" in popular usage...
laminating resins and non-metallic auto-body fillers. Fiberglass-reinforced unsaturated polyesters find wide application in bodies of yachts and as body parts of cars.
Basics
Polyester is a synthetic polymer made of purified
terephthalic acidTerephthalic acid is the organic compound with formula C
6H
42. This colourless solid is a commodity chemical, used principally as a precursor to the polyester PET, used to make clothing and plastic bottles. Several billion kilograms are produced annually...
(PTA) or its dimethyl ester
dimethyl terephthalateDimethyl terephthalate is an ester of terephthalic acid and methanol and is used in the production of polyesters, including polyethylene terephthalate and polytrimethylene terephthalate...
(DMT) and
monoethylene glycolEthylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet tasting liquid....
(MEG). With 18% market share of all plastic materials produced, it ranges third after
polyethylenePolyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons. Its primary use is within packaging .- Description :Polyethylene is a thermoplastic polymer consisting of long chains of the monomer ethylene...
(33.5%) and
polypropylenePolypropylene or polypropene is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and...
(19,5%).
The main raw materials are described as follows:
- Purified Terephthalic Acid – PTA – CAS-No.: 100-21-0
- Synonym: 1,4 Benzenedicarboxylic acid,
- Sum formula; C6H4(COOH)2 , mol weight: 166,13
- Dimethylterephthalate – DMT- CAS-No: 120-61-6
- Synonym: 1,4 Benzenedicarboxylic acid dimethyl ester
- Sum formula C6H4(COOCH3)2 , mol weight: 194,19
- Mono Ethylene Glycol – MEG – CAS No.: 107-21-1
- Synonym: 1,2 Ethanediol
- Sum formula: C2H6O2 , mol weight: 62,07
More information about polyester raw materials can be found for PTA ,DMT and MEG , at the webpage INCHEM "Chemical Safety Information from Intergovernmental Organizations".
To make a polymer of high molecular weight a catalyst is needed. The most common catalyst is
antimony trioxideAntimony trioxide is the inorganic compound with the formula Sb2O3. It is the most important commercial compound of antimony. It is found in nature as the minerals valentinite and senarmontite...
(or antimony tri acetate):
Antimony trioxide – ATO – CAS-No.: 1309-64-4
Synonym: non, mol weight: 291,51
Sum formula: Sb2O3
In 2008 about 10 000 t Sb2O3 were used to produce around 49 Mio t polyethylene terephthalate.
Polyester is described as follows:
Polyethylene Terephthalate CAS-No.: 25038-59-9
Synonym / abbreviations: polyester, PET, PES
Sum Formula: H-[C10H8O4]-n=60-120 OH, mol unit weight: 192,17
There are several reasons for the importance of PTA:
- 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 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 table 1 the estimated world polyester production for
textileA textile is a flexible material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw wool fibres, linen, cotton, or other material on a spinning wheel to produce long strands...
polyester, bottle polyester resin, film polyester mainly for packaging and specialty polyesters for engineering plastics, which are the main fields of application, can be seen. According to this table, the world's total polyester production might exceed 50 million tons per annum before the year 2010.
Table 1: World polyester production
|
Market size per year |
| Product Type |
2002 [Mio t/a] |
2008 [Mio t/a] |
| Textile-PET |
20 |
39 |
| Resin, Bottle/A-PET |
9 |
16 |
| Film-PET |
1.2 |
1.5 |
| Special Polyester |
1 |
2.5 |
| TOTAL |
31.2 |
49 |
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
P-Xylenep-Xylene is an aromatic hydrocarbon, based on benzene with two methyl substituents. The “p” stands for para, identifying the location of the methyl groups as across from one another....
is the base material to produce PTA and liquefied petroleum gas (LPG) is the base material to produce MEG.
Large PTA producers are for instance BP, Reliance, Sinopec, SK-Chemicals, Mitsui and Eastman Chemicals. MEG production is in the hand of about 10 global players which are headed by MEGlobal a JV of DOW and PIC Kuweit followed by Sabic.
Among the world's largest polyester producers are the following companies:
Artenius, Advansa, DAK, DuPont, Eastman/Voridian, Hyosung, Huvis, Indorama, Invista, Jiangsu Hengli Chemical Fiber, Jiangsu Sanfangxian Industry, M&G Group, Mitsui, Mitsubishi, NanYa Plastics, Reichhold, Reliance, Rongsheng, Sabic, Teijin, Toray, Trevira, Tuntex, Wellman, Yizheng Sinopec, Zhejiang Hengi Polymerization.
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 figure 2 the main applications of textile and packaging polyester are listed.
Table 2: Textile and packaging polyester application list
| POLYESTER-BASED POLYMER (MELT or PELLET) |
TextileA textile is a flexible material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw wool fibres, linen, cotton, or other material on a spinning wheel to produce long strands...
|
Packaging |
| Staple fiber (PSF) |
Bottles for CSD, Water, Beer, Juice, Detergents |
| Filaments POY, DTY, FDY |
A-PET Film |
| Technical yarn and tire cord |
Thermoforming |
| Non-woven and spunbond |
BO-PET Biaxial oriented Film |
| Mono-filament |
Strapping |
Abbreviations:
PSF = Polyester Staple Fiber;
POY = Partially Oriented Yarn;
DTY = Draw 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 (<< 1 Million t/a) of polyester is used to produce engineering plastics and masterbatch.
In order to produce the polyester melt with a high efficiency, high-output processing steps like staple fiber (50–300 t/d per spinning line) or POY /FDY (up to 600 t/d split into about 10 spinning machines) are meanwhile more and more horizontal, integrated, direct processes. This means the polymer melt is directly converted into the textile fibers or filaments without the common step of pelletizing. We are talking about full horizontal integration when polyester is produced at one site starting from crude oil or distillation 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 introduced at first the idea to close the chain from PX to PET resin with their so-called INTEGREX process. The capacity of such horizontal, integrated productions sites is >1000 t/d and can easily reach 2500 t/d.
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 annum, depending on the world region. Useful information about the polyester industry can be found under where a “Who is Producing What in the Polyester Industry” is gradually being developed.
Synthesis
Synthesis of polyesters is generally achieved by a polycondensation reaction. See "
condensation reactionA condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule. When this small molecule is water, it is known as a dehydration reaction; other possible small molecules lost are hydrogen chloride,...
s 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 ---> HO[ROOCR´COO]
nROH + 2n H
2O
Azeotrope esterification
In this classical method, an
alcoholIn chemistry, an alcohol is any organic compound in which a hydroxyl group is bound to a carbon atom of an alkyl or substituted alkyl group. An important group of acohols is formed by the simple acyclic alcohols, the general formula for which is C
nH
2n+1OH...
and a
carboxylic acidCarboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the formula -COH, usually written -COOH or -CO2H. Carboxylic acids are Brønsted-Lowry acids — they are proton donors. Salts and anions of carboxylic acids are called...
react to form a carboxylic ester.
To assemble a polymer, the water formed by the reaction must be continually removed by
azeotropeAn azeotrope is a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation...
distillation.
Alcoholic transesterification
O
\\
C - OCH3 + OH[Oligomer2]
/
[Oligomer1] |
|
O
\\
C - O[Oligomer2] + CH3OH
/
[Oligomer1] |
| (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 acidHydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong mineral acid and has major industrial uses. It is found naturally in gastric acid....
(HCl) instead of water. This method can be carried out in solution or as an
enamelIn a discussion of material science, enamel is the colorful result of fusing powdered glass to a substrate by firing, usually between 750 and 850 degrees Celsius. The powder melts and flows and hardens to a smooth, durable vitreous coating on metal, glass or ceramic...
.
- 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
Ring-opening polymerization
Aliphatic polyesters can be assembled from
lactoneIn chemistry, a lactone is a cyclic ester which can be seen as the condensation product of an alcohol group -OH and a carboxylic acid group -COOH in the same molecule...
s under very mild conditions, catalyzed
anionicIn chemistry, an anionic species is one that contains a full negative charge. These types of compounds can range in reactivity, but most are fairly reactive....
ally, cationically or metallorganically.
Thermosetting
resinResin is a hydrocarbon secretion of many plants, particularly coniferous trees. It is valued for its chemical constituents and uses, such as varnishes and adhesives, as an important source of raw materials for organic synthesis, or for incense and perfume. Fossilized resins are the source of amber...
s are generally copolymers of unsaturated polyesters with
styreneStyrene, also known as vinyl benzene as well as many other names , is an organic compound with the chemical formula C
6H
5CH=CH
2. This aromatic hydrocarbon is a colorless oily liquid that evaporates easily and has a sweet smell, although high concentrations confer a...
. Polyester saturation is governed through the use of
maleic acidMaleic acid or -butenedioic acid or cis-butenedioic acid. is an organic compound that is a dicarboxylic acid...
or
fumaric acidFumaric acid or trans-butenedioic acid, is the chemical compound with the formula HO2CCH=CHCO2H.
This white crystalline compound is one of two isomeric unsaturated dicarboxylic acids, the other being maleic acid, wherein the carboxylic acid groups are cis. It has a...
. In vinyl esters, saturation (or lack thereof) is found in the alcohol group of the polyester. The double bond of unsaturated polyester reacts with styrene resulting in a 3-D cross-linked structure. This structure acts as a thermoset. The
cross-linkCross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...
ing is initiated through an
exothermicIn thermodynamics, the term exothermic describes a process or reaction that releases energy usually in the form of heat, but also in the form of light , electricity , or sound. Its etymology stems from the Greek prefix ex- and the Greek word thermein...
reaction involving an
organic peroxideOrganic peroxides are organic compounds containing the peroxide functional group . If the R' is hydrogen, the compound is called an organic hydroperoxide. Peresters have general structure RCOOR....
, such as
methyl ethyl ketone peroxideMethyl ethyl ketone peroxide is an organic peroxide, a high explosive similar to acetone peroxide. MEKP is a colorless, oily liquid whereas acetone peroxide is a white powder at STP; MEKP is slightly less sensitive to shock and temperature, and more stable in storage.Dilute solutions of 30 to 60%...
or
benzoyl peroxideBenzoyl peroxide is an organic compound in the organic peroxide family. It consists of two benzoyl groups joined by a peroxide group. Its structural formula is [C
6H
5C]
2O
2. It is one of the most important organic peroxides in terms of applications and...
.
External links