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Polyester is a synthetic fiber derived from coal, air, water, and petroleum. Polyester fibers are formed from a chemical reaction between an acid and alcohol, and is developed in a 20th-century laboratory. In the formation of polyester reaction, two or more molecules combine to make a large molecule whose structure repeats throughout its length. Polyester fibers can form very long molecules that are very stable and strong.
Polyester has been considered to have several advantages over traditional fabrics such as cotton. One of its most important quality is that it does not absorb moisture, but does absorb oil; this quality makes polyester the perfect fabric for the application of water-, soil-, and fire-resistant finishes. It’s another quality, that is, low absorbency also makes it naturally resistant to stains. Polyester is used in the manufacture of many products, including clothing, home furnishings, industrial fabrics, computer and recording tapes, and electrical insulation.
As we go along further, we would see the various uses of polyester in all the several fields such as clothing, furnishing, etc. Fabrics woven from polyester thread or yarn are used extensively in apparel and home furnishings, from shirts and pants to jackets and hats, bed sheets, blankets and upholstered furniture. Industrial polyester fibers, yarns and ropes are used in 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.
We would discuss in detail the history of polyester, the method of manufacturing of polyester, its various uses, and its importance in our day to day life, how much we use polyester in our life without really noticing that it is polyester we are using.
In short we can say that polyester is a category of polymers which contain the ester functional group in their main chain. Even though there are many types of polyester, the term “polyester” as a specific material most commonly refers to polyethylene terephthalate (PET).
Polyesters include naturally-occurring chemicals. Naturally occurring chemicals include that are found in nature and are not man-made such as in the cut in of plant cuticles. An example of synthetic fiber is synthetics through step-growth polymerization such as polycarbonate and polybutyrate. Generally natural polyesters and even a few synthetic ones are biodegradable, that is, they can break down or decay naturally without any special treatment, and can therefore be thrown away without causing pollution. Whereas on the other hand, most synthetic polyesters, which are more commonly used, are not biodegradable.
Polyester is a term often defined as “long-chain polymers chemically composed of at least 85% by weight of an ester and a dihydric alcohol and a terephthalic acid”. In simpler terms, it means that polyester is the linking of several esters within the fibers. Reaction of alcohol with carboxylic acid results in the formation of esters.
Polyester also refers to the various polymers in which the backbones are formed by the “esterification condensation of polyfunctional alcohols and acids”.
Polyester can also be classified as saturated and unsaturated polyesters.
Saturated polyesters refer to that family of polyesters in which the polyester backbones are saturated. They are thus not as reactive as unsaturated polyesters. The saturated polyesters consist of low molecular weight liquids used as plasticizers and as reactants in forming urethane polymers, and linear, high molecular weight thermoplastics such as polyethylene terephthalate (Dacron and Mylar). Usual reactants for the saturated polyesters are a glycol and an acid or anhydride.
Unsaturated polyesters refer to that family of polyesters in which the backbone consists of alkyl thermosetting resins characterized by vinyl unsaturation. They are mostly used in reinforced plastics. These are the most widely used and economical family of resins.
Characteristics of polyester
- Polyester fabrics and fibers are extremely strong and thus durable.
- Polyester is very durable: it is resistant to most chemicals, stretching and shrinking, wrinkle resistant, mildew and abrasion resistant.
- Polyester is hydrophobic in nature, that is, these molecules and quick drying. It can be used for insulation by manufacturing hollow fibers.
- Polyester’s quality to retain its shape is good for making outdoor clothing for harsh climates.
- Polyester can be easily washed and dried, without the added tension of ironing and all because it does not form wrinkles.
HISTORY OF POLYESTER:
Polyester became famous for – Scrunch it, pull it, and wash it – without any wear and wrinkles. Polyester was the fabric of choice in an economy that was changing in terms of speed, efficiency and convenience. The textile industry’s answer to food industry producing fries and coke was the production of Polyester – quick, cheap and easy.
It was W.H.Carothers who discovered that alcohols and carboxyl acids could be successfully mixed to create fibers. Carothers was working for DuPont at the time and unfortunately when he discovered Nylon, polyester took a back seat.
PET & Terylene
The incomplete research of Carothers had not advanced to investigating the polyester formed from mixing ethylene glycol and terephthalic acid. Whinfield and Dickson – 2 British scientists are the ones who patented PET or PETE in 1941. Polyethylene terephthalate (PET) forms the basis for synthetic fibers like Dacron, Terylene and polyester.
Later that year, the first polyester fiber – Terylene – was created by Whinfield and Dickson along with Birtwhistle and Ritchiethey. Terylene was first manufactured by Imperial Chemical Industries or ICI.
It was in 1946 that DuPont bought all legal rights from ICI, that is, Imperial Chemical Industries. In 1950, the Dealware property of DuPont manufactured another polyester fiber, which they named Dacron. Mylar was introduced in 1952. Polyester was first introduced to the American public in 1951 as the magical fabric that needed no ironing! PET and PEN are DuPont trademarks that have turned the use and consumption of Polyester around.
Polyester Becomes Popular
Subsequent to the development of Terylene and Dacron, Kodel was developed by Eastman Chemical Products, Inc in 1958.
The polyester market underwent rapid expansion and textile mills emerged everywhere. Many of the mills were located at small gas stations and produced cheap polyester apparel. The inexpensive and durable fiber became very popular and the industry expanded rapidly till the 1970s. Unfortunately, the infamous double-knit polyester image hit the industry and polyester soon came to be known as the uncomfortable fabric.
The Phoenix Rises
Today, polyester is largely regarded as a cheap fabric that is rather uncomfortable for sensitive human skin to wear. It is also not preferred because of its highly inflammable properties.
However, the emergence of luxury fibers like polyester microfiber and various polyester blends, the polyester industry is once again on its way to a grand come back. The Tennessee Eastman Company and the Man-Made Fiber Producers’ Association’s (MMFPA) Polyester Fashion Council played a significant role in the revival of polyester. The Tennessee Eastman Company started a YES campaign for “polYESter” and popularized it via radio and television. The main idea was to focus on the wash and go properties of polyester rather than sell it as a cheap fabric.
Hoechst Fibers Industries also played a part in the history of polyester. They conducted various studies from 1981 to 1983 and found that 89% of people could not distinguish between polyester and other natural fibers like cotton, wool and silk. Also, it was found that people were more interested in the appearance of the apparel than the fabric it was made of.
Today, the biggest contributor to the appeal of polyester is the discovery of microfibers. Microfibers give polyester the feel of silk and are rapidly becoming the choice of fabric. With an expensive tag to match, the cheap image of polyester seems to be on its way out. Here’s to heralding a new era in the history of polyester!
MANUFACTURING OF POLYESTER:
Polyester fibers or the synthetic fibers are long chain polymers which are derived from coal, air, water, and petroleum. They are formed through chemical reaction between an acid and alcohol, which forms ester. In this reaction, two or more molecules combine to make a large molecule whose structure repeats throughout its length. These molecules are very stable and strong. There are variations in the compositions and therefore in the properties of polyester fibers.
Types of Polyester
PHYPERLINK “http://www.teonline.com/fibers-yarns-threads/polyester-fiber.html”olyester fibers are generally available in two varieties- PET (polyethylene terephthalate) and PCDT (poly-1, 4-cyclohexylene-dimethylene terephthalate). PET is the most common production of polyester. It is stronger than PCDT, while PCDT has more elasticity and resilience. Another advantage of PET is that it can be used alone or blended with other fabrics for making wrinkle free and stain resistant clothing that can retain its shape. PCDT is more suitable for heavier applications. These heavier applications include draperies and furniture coverings. Modifications can be introduced in each of these varieties for obtaining specific properties.
Polyester is a chemical term which can be broken into poly, meaning many, and ester, a basic organic chemical compound. The principle ingredient used in the manufacture of polyester is ethylene, which is derived from petroleum. In this process, ethylene is the polymer, the chemical building block of polyester, and the chemical process that produces the finished polyester is called polymerization.
For manufacturing PET Polyester, the main raw material is ethylene derived from petroleum. This ethylene is oxidized to produce a glycol monomer dihydric alcohol which is further combined with another monomer, terephthalic acid at a high temperature in a vacuum. Polymerization, the chemical process that produces the finished polyester, is done with the help of catalysts. Catalysts are used to speed up the rate of a reaction. Then a colorless molten polyester is formed which then flows from a slot in a vessel on to a casting wheel and takes shape of a ribbon as it cools to hardness. The polymer thus produced by this process is then cut into very small chips, dried to remove all moisture and blended to make it uniform for getting it ready for spinning into yarn.
This variation of polyester is made by condensing terephthalic acid with 1, 4-cyclohexane-dimethanol to form poly-1, 4-cyclohexylene-dimethylene terephthalate or the PCDT Polyester. As for PET Polyester, PCDT is processed for melt spinning.
Polymer chips are melted at 500-518Â°F (260-270Â°C) to form a syrup-like solution. The polymer, which is now in a molten form, is then extruded through a spinneret and the filaments are subsequently drawn into the desired polyester fiber. Variations are introduced to obtain desired end results.
Spinnerets having hole of different shapes such as round, trilobal, pentalobal, hexalobal or octalobal can be used for special effects like opacity, luster or its suppression, wicking, comfort or feel. Hollow fibers may be produced to make it lightweight and for providing greater cushioning or insulative properties. Crepe effect can be obtained through crimps. Certain additives may also be combined with the spinning solutions for specific properties. Delusterant can be added to make the fiber dull, a flame retardant may be added or certain other antistatic substance may also be included.
The product stream divides into two different application areas which are mainly textile applications and packaging applications, after the first stage of polymer production in the melt phase. In the table shown below, the main applications of textile and packaging polyester are listed.
Staple fiber (PSF)
Bottles for CSD, Water, Beer, Juice, Detergents
Filaments POY, DTY, FDY
Technical yarn and tire cord
Non-woven and spun bond
BO-PET Biaxial oriented Film
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;
After extrusion from the spinneret, the fibers are drawn or elongated, with the help of godet wheels. The polyester fibers are usually drawn up to five times its original length, depending upon the desired properties. The filaments are drawn to a greater extent, for higher tenacity. When the fibers come in contact with the air, they solidify. Generally, the PET fibers are drawn hot as it produces more uniform fibers. PCDT fibers are drawn at higher temperature because of their higher melting point. During the drawing process itself, fibers may be textured which saves time, efforts and production cost and also gives greater quality control over the finished fibers. After the polyester yarn is drawn, it is wound on large bobbins or flat-wound packages, ready to be woven into material.
Types of Polyester Yarns
Polyester yarns have a wide range of diameters and staple lengths. The yarns are made basically as monofilament yarns, multifilament yarns and spun yarns.
PET Polyester is used to make filament yarns either in monofilament or multifilament forms. The direction and amount of twists are decided by the desired end use. The properties are also pre-determined. There are various types of such yarns. There is the bright, regular tenacity polyester yarn having light, stretch and sag resistance, used for sheer lightweight fabrics like tulle, voile and organdy. The regular tenacity semi dull yarn used for various apparels including lingerie. Its duller version is used for shirts and blouses. Polyester yarns resistant to various chemicals, and micro organisms are produced from high tenacity fibers for such industrial uses as conveyor belts, ropes and nets etc.
These yarns are made of PET multifilament’s. Texturizing is either done along with the drawing process or afterwards during throwing or texturizing process.
Spun yarns are made of staple or cut PET or PCDT polyester fibers. The staple may be bright, semi dull or dull and tenacity may be regular, mid or high. It may be polished to reduce crimp and increase luster. It may either be spun alone or blended with other staple such as cotton, wool or rayon and then spun into yarn.
Manufacturing Staple Fiber
In making polyester staple fiber, polymerization, drying, and melt spinning are much the same as in the manufacture of filament yarn. However, in the melt spinning process, the spinneret has many more holes when the product is staple fiber. The rope-like bundles of polyester that emerge are called tow.
* 1: Newly-formed tow is quickly cooled in cans that gather the thick fibers. Several lengths of tow are gathered and then drawn on heated rollers to three or four times their original length.
* 2: Drawn tow is then fed into compression boxes, which force the fibers to fold like an accordion, at a rate of 9-15 crimps per inch (3-6 per cm). This process helps the fiber hold together during the later manufacturing stages.
*3: After the tow is crimped, it is heated at 212-302Â°F (100-150Â°C) to completely dry the fibers and set the crimp. Some of the crimp will unavoidably be pulled out of the fibers during the following processes.
* 4: Following heat setting, tow is cut into shorter lengths. Polyester that will be blended with cotton is cut in 1.25-1.50 inch (3.2-3.8 cm) pieces; for rayon blends, 2 inch (5 cm) lengths are cut. For heavier fabrics, such as carpet, polyester filaments are cut into 6 inch (15 cm) lengths.
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 RÂ´ (COOH) 2 —> HO [ROOCRÂ´COO] n ROH + 2n H2O
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.
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.
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
Aliphatic polyesters can be assembled from lactones under very mild conditions, catalyzed anionically, cationically or metallorganically.
Unsaturated polyesters are thermosetting resins. They are generally copolymers prepared by polymerizing one or more diol with saturated and unsaturated dicarboxylic acids (maleic acid, fumaric acid…) or their anhydrides. The double bond of unsaturated polyesters reacts with a vinyl monomer mainly the styrene, resulting in a 3-D cross-linked structure. This structure acts as a thermoset. The cross-linking is initiated through an exothermic reaction involving an organic peroxide, such as methyl ethyl ketone peroxide or benzoyl peroxide.
APPLICATION OF POLYESTER:
Polyester is used in manufacturing of many products, such as clothing, home furnishings, industrial fabrics, computer, recording tapes, and electrical insulation. It has several advantages over traditional fabrics as it does not absorb moisture. Its low absorbency also makes it naturally resistant to stains. Polyester clothing can be preshrunk in the finishing process. This makes it resist shrinking and it doesn’t stretch out of shape. The fabric can be dyed easily, and is mildew resistant too. Textured polyester fibers are an effective, nonallergenic insulator, thus it is used for filling pillows, quilting, outerwear, and sleeping bags.
Because of their many desirable qualities, polyester fibers and fabrics have many uses.
Polyester is often used in outerwear because of its high tenacity and durability. It is a strong fiber and consequently can withstand strong and repetitive movements. Its hydrophobic property makes it ideal for garments and jackets that are to be used in wet or damp environments–coating the fabric with a water-resistant finish intensifies this effect.
Many jackets and quilted garments are made of polyester. Since polyester can be molded into almost any shape, certain insulating properties can be built-in to the fiber. One method is to create hollow fibers:
This process traps air inside the fiber which is then heated by the body. The warm air stays inside and helps warm the body in cool weather. A second method is to use crimped polyester in a fiberfill. The crimp helps keep in warm air. Polyester is an ideal fiber to use for this since it will retain its shape, unlike its cotton and wool counterparts that tend to flatten out over time, significantly reducing their ability to trap warm air.
Polyester is often used in pants, shirts, suits, and bed sheets either by itself or as a blend, because of its wrinkle-resistant property and its ability to retain its shape. Since these garments are frequently worn and washed, its stain-resistancy and durability are also desirable.
Polyester also has industrial uses as well, such as carpets, filters, synthetic artery replacements, ropes, and films. The pie chart below, taken from Fiber Science by Kathryn L. Hatch, summarizes many of polyester’s uses:
When the world thinks of plastic films, it thinks of PET.
Polyester film is used in many types of packaging applications ranging from food and drugs to industrial and consumer goods. As plain or metalized, formable, heat-shrinkable and/or coated for barrier, metal adhesion, laminating adhesion, extrusion coating adhesion, printing or sealing, PET film offers excellent characteristics for the packaging market – easy machinability, strength, high- and low-temperature resistance, crystal clarity, and printability.
The properties that make PET film ideal for packaging applications include:
- High strength for high speed processes, higher tensions, and higher temperatures
- Chemical surface treatment during manufacturing or post-manufacturing to enhance characteristics, such as barrier, adhesion, printability, metal adhesion, and release
- High clarity Strength and resistance to tear
- Dimensional stability over a very wide range of temperatures and humidity
- Resistance to attack by moisture and most common solvents
- Excellent barrier to both oxygen and water vapor to extend shelf- life.
- Flexible packaging – PET film is an excellent laminating substrate for flexible packaging structures, i.e. stand-up pouches, offering excellent flex and puncture resistance.
- Lidding – PET film maintains its strength at both, freezer and oven temperatures, for leak-resistant wraps, lidding, and peelable seals in a wide range of food and nonfood applications.
- Can laminations – Co polyester film is laminated to metal for can applications.
- Metallized packaging – Metallized PET film is used for high barrier, decoration, and embossed holographic applications.
- Susceptors – lightly Metallized PET film is used in microwave Susceptors constructions for browning and cooking food in microwave ovens.
The unique combination of optical, physical, thermal, and chemical properties of polyester film has made it the film of choice for many imaging applications. Some of the major applications include x-ray, photographic, printing, microfilm, photoresist/phototool, overhead projection transparencies, and drafting/reprographics. Currently, these applications account for about 30% of the total PET film consumption. Recent developments in electronic imaging may cause some decline in the use of PET film in some of these applications, but the impact is not expected to be very significant in the near future.
The properties that make PET film ideal are its:
- Brilliantly clear nature
- Very smooth and glossy surface
- be translucent, opaque, or colored (with suitable additives)
- have a desired rough or matt finish (with filler additives or coatings)
- be chemically surface treated during manufacture to enhance adhesion to subsequent coatings
Strength and resistance to tear
- Excellent flatness (freedom from curl and cannot be creased easily)
- Dimensional stability over a very wide range of temperatures and humidity
- Resistance to attack by moisture (or most of the common solvents)
- Non-aging characteristics
- Shelf life (can be stored for a long time)
Out of the total PET film usage for imaging applications, more than 30% goes into x-ray base. Typically, a blue-tinted 175 micron PET film is coated with a gelatin-based photosensitive coating and is used as medical x-ray film.
Generally, 100 micron and 175 micron PET film is coated with silver-sensitized layers for photographic applications mainly in professional photographic films and instant photographic applications.
PET film is used for printing applications such as in layout, masking, pre-press proofing, plate mounting, and photopolymer plates. PET film is also widely used as a base to print on for displays, signage, posters, labels, etc.
Originals and duplicates of micro-images of documents, records, drawings, etc., are produced on suitably coated PET film for easy storage, space saving, and retrieval.
Photoresist & Phototool
PET film is used in the plating or etching processes for production of rigid and flexible printed circuits.
Overhead Projection Transparencies
Coated PET film is used for making overhead projection transparencies in plain paper copying machines. Overhead projection transparencies can be printed by other techniques and written on, as well.
Drafting & Reprographic
PET base film is coated with matt or diazo-sensitized or silver-sensitized lacquers, and is widely used for drafting and in the duplication of engineering drawings. This drawing office film is considered to be more convenient for making subsequent changes in designs, and it can also be used for storage.
Industrial & Specialty Applications
Polyester film’s thermal, chemical, and dimensional stability coupled with its high tensile strength, durability, flex resistance, and clarity promote broad utilization in Industrial and Specialty applications.
Polyester film can be produced in a wide range of thickness (from one to several hundred microns) and visible light transmission from essentially 0% to 99+%. Polyester film’s ability to be customized through both polymer and surface modification to fit the specific application adds to its versatility and value as a film of choice.
Key properties of PET:
- Dimensional stability, both thermal and moisture
- Chemical and solvent resistant
- Strength, tear, and flexual resistance
- Broad light transmission: optically clear to opaque
- Surface treatable for adhesion to a variety of materials
- Broad thickness availability
- Printable surfaces
Few, if any, flexible films available today provide the broad array of performance properties for use in the Industrial and Specialty application market. PET film provides exceptional value in a wide variety of applications.
Polyester film itself is used as electrical insulation. It is also used as a laminate with other substrates, such as non-woven polyester matt (DMD), and organic and inorganic papers, such as aramid paper, silica paper, and mica paper. Polyester film can be used in UL registered electrical systems rated as high as Class F (155Â°C). Laminates can be used in systems rated as high as Class R (220Â°C).
In motor applications, polyester film is used for ground insulation as slot liners and wedges, as well as phase insulation. The high electrical breakdown voltage, coupled with polyester film’s high resistance to degradation, makes it ideal for mechanical barriers in wire and cable applications. In transformer and high-voltage distribution equipment applications, polyester film is used to wrap the conductors. Polyester film, with lower extractable content, is effective for use in hermetic applications, such as refrigerator and air conditioner motor/compressor assemblies. PEN polyester film is used where higher temperature performance is required, either in the fabrication stage or in the end-use operating conditions.
Thin polyester films (two micron and below) are an integral component of capacitors, where polyester’s high dielectric constant and its physical properties enable the component design to be optimized and miniaturized.
The physical properties of polyester film (such as dimensional stability, thermal stability at elevated temperatures, and coefficient of friction) combined with its mechanical properties (such as tensile break strength, tensile yield strength, and elongation at break) and its chemical and electrical resistance; make it the preferred material for a wide variety of electrical insulation applications.
Polyester film is used in a variety of magnetic media, including video, camcorder and audio tapes, and data storage applications such as floppy disks and computer tapes. For all magnetics applications, the base film is further coated with a magnetically receptive coating layer. Polyester film has the excellent dimensional stability required to ensure that the heavy coating layer does not distort and faithfully records the images, sound, or data.
The largest volumes of PET film for the magnetic market sector are consumed at present in conventional video and audio tapes. Once again, the dimensional stability of polyester, plus the ability to have a magnetic coating layer adhere to the film, are key to these new applications, which are reaching exceptionally high information densities with corresponding reductions in size and faster data access times.
The dynamic nature of this market segment, with new applications growing as others mature, is typical of the innovation that exists in the polyester film industry.
Use of polyester in garments
Polyester is used in the manufacturing of all kinds of clothes and home furnishings like bedspreads, sheets, pillows, furniture, carpets and even curtains. The disco clothing of the 70s with all its jazz and flash was made of polyester.
Hydrophobic nature: High tenacity and good durability makes polyester the choice of fabric for high stress outdoors use. Polyester is also a strong fiber that is hydrophobic in nature. It is thus ideal for clothing to be used in wet and damp environments. The fabric is also coated with a water-resistant finish and further intensifies the hydrophobic nature.
Being the most heavily recycled polymer worldwide, it is also used by climbers. Climbing suits, parkas, sleeping bags and other outdoor gear are using the new insulating polyester fiberfill products. One can also do winter windsurfing wearing dry suits lined with polyester fleece.
Creating insulation: By creating hollow fibers it is also possible to build insulation into the polyester fiber. Air is trapped inside the fiber, which is then warmed by the heat of the body. This keeps the body warm in cold weather. Another method to build insulation is to use crimped polyester in a fiberfill. The crimp helps keep the warm air in. Polyester is an ideal fabric for this kind of insulation because it retains its shape. Cotton and wool tend to flatten over a period of time and loose the warming effect.
Wrinkle resistant: Polyester is also wrinkle resistant and is used very often in everyday clothing like pants, shirts, tops, skirts and suits. Used either by itself or as a blend, it is also stain resistant and hence very popular.
Polyester care tips
- Taking care of polyester clothing is really easy and very time efficient.
- Polyester clothing can be machine washed and dried. Adding a fabric softener generally helps
- Dry the fabric at low temperatures to get maximum usage from the clothing.
- Though polyester does not require much ironing, if
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