Polyester is one of the most widely-used synthetic fabrics in the world today. Fabrics, packaging, automobiles and other industries rely on it for their many uses, and because of its versatility and strength it is a ubiquitous part of everyday life. But if you want to really appreciate polyester and its role in popular use, you need to know a little about the chemistry of this synthetic material.
Polyester, particularly polyethylene terephthalate (PET), is created by chemical reactions that turn crude materials such as petroleum and natural gas into a strong, flexible, highly durable fabric. In learning more about the chemical makeup of polyester, how polyester is polymerised, its physics and chemical structure, and its uses, we begin to understand why polyester is so common, and why polyester is different by virtue of its chemistry.
We will explore the chemical composition of polyester, how polyester is melted, physical and chemical attributes that are responsible for its unique qualities, and the multitude of applications that make it an indispensable product in our lives.
1. Chemical Composition of Polyester
a. Basic Structure
Polyester is a synthetic polymer, that is, a mixture of long chains of molecules that are chemically joined together. Polyester is not made from natural fibres (derived from plant or animal materials), but from petroleum-derived chemicals. Polyester polyethylene terephthalate (PET) is the most widely used polyester in textiles and packaging, although other types of polyester have different chemical compositions and properties.
Polyesters are synthesized by a chemical reaction called polymerisation, in which small molecules (monomers) are chemically attached to long chains. Polyester’s chemical structure essentially consists of a repeating unit anchored to two monomers: ethylene glycol and terephthalic acid. These monomers interact with one another through a carefully designed chemical process to produce ester bonds, creating a polymer chain.
The simple formula for a polyester polymer is:
–(C₆H₄(CO₂H)₂–C₂H₆O₂)–
–(C₆H₄(CO₂H)₂–C₂H₆O₂)–
This configuration means that the polyester chain contains repeating ester groups (–COO–) formed in the reaction of ethylene glycol (C2H6O2) and terephthalic acid (C6H4(CO2H)2). It is these ester bonds that make polyester strong and durable.
b. Types of Polyester
There are many varieties of polyester, each with its own specialities, but they all start with the same fundamental chemical framework of polyester molecules.
Polyethylene Terephthalate (PET)
PET is the most widely-used polyester. It appears in everything from fabrics and apparel to water bottles and packaging. PET is created by polymerizing ethylene glycol and terephthalic acid through esterification and polycondensation to create long polymer chains.
PET is extremely strong, moisture-resistant, and will retain its strength and pigmentation over time. We usually use it for T-shirts, sportswear, and upholstery fabric as it resists shrinkage, stretch, and wrinkles.
PCDT (Poly-1,4-Cyclohexylene-Dimethylene Terephthalate)
A relatively rare polyester compound known as PCDT is used for products that need more elasticity and toughness. It is produced by polymerizing cyclohexanedimethanol with terephthalic acid. The polymer chains that form are more flexible than PET, and can be applied to materials that require flexibility and stretch (for example, upholstery and some forms of sportswear).
Recycled Polyester (rPET)
Recycled polyester (rPET) is more sustainable than PET. It is made from post-consumer plastic waste, including plastic bottles and containers, which is sanitised, shrunk and turned into fibers. This not only conserves the environment by keeping plastic out of landfills but also reuses existing materials. Recycled polyester has the same chemical structure as virgin PET and the resultant fabric has many of the same positive attributes.
Biopolyesters
Biopolyesters are a rapidly developing category of polyesters produced from renewable resources like corn, sugarcane or plant materials. Such polyesters are designed to minimize the footprint of polyester production using renewable feedstocks rather than fossil-fuel chemicals. Some biopolyesters are biodegradable or easily recycled, so they are more environmentally friendly than polyester.
2. Polymerization Process
Polyester is produced using two distinct chemical reactions: esterification and polycondensation. These steps create the polymer chains that comprise the fabric.
a. Step 1: Esterification
The initial phase of polymerisation is esterification, which occurs when a diol (ethylene glycol) reacts with a dicarboxylic acid (terephthalic acid). In this step, the hydroxyl (-OH) group from the ethylene glycol reacts with the carboxyl (-COOH) group from the terephthalic acid to form an ester bond. The reaction also releases water molecules as a byproduct.
The simple esterification reaction could be expressed as follows:
C₂H₆O₂ + C₆H₄(CO₂H)₂
⟶
HO-C₂H₄-O-C(O)-C₆H₄-C(O)-O-C₂H₄-OH
C₂H₆O₂ + C₆H₄(CO₂H)₂⟶HO-C₂H₄-O-C(O)-C₆H₄-C(O)-O-C₂H₄-OH
In this reaction, the ester bond (-COO-) between the molecules of ethylene glycol and terephthalic acid is produced. The water molecules that leak out during this reaction are expunged to accelerate the reaction.
b. Step 2: Polycondensation
After esterification, the polyester is processed by polycondensation, wherein the monomers obtained in the esterification process are further converted into long polymer chains. The esterification process persists during polycondensation, only now the growing polymer chains react with additional monomers, yielding water or methanol as byproducts. This produces extremely long, high molecular weight polyester polymers.
Polycondensation can be represented as:
𝑛
(
HO-C₂H₄-O-C(O)-C₆H₄-C(O)-O-C₂H₄-OH
)
⟶
[
–C₂H₄-O-C(O)-C₆H₄-C(O)-O-C₂H₄–
]
𝑛
+
𝑛
H₂O
n(HO-C₂H₄-O-C(O)-C₆H₄-C(O)-O-C₂H₄-OH)⟶[–C₂H₄-O-C(O)-C₆H₄-C(O)-O-C₂H₄–]
n
+nH₂O
In this reaction, polymer chains expand via ester bonding between monomers. This reaction produces polyethylene terephthalate (PET), a very tough and versatile material.
3. The Chemical and Physical Analysis of Polyester
a. Physical Properties
The chemical structure of polyester creates a special set of physical properties that make polyester an ideal material for many uses.
Strength and Durability
Polyester is known for its high tensile strength, which keeps it from stretching and shrinking. Long polymer chains generated during polycondensation make polyester fabrics tough enough to withstand the abuses of washing. The anti-abrasion qualities of polyester also make it suitable for high-impact environments such as upholstery and outdoor wear.
Moisture Resistance
Polyester is not a water-retaining material. That feature makes polyester a good candidate for applications that require water resistance. Polyester repels water and maintains its strength and structure when damp or wet. Also, it quickly dries, so activewear and sportswear usually use it.
Thermal Resistance
Polyester melts relatively quickly, around 250°C (482°F). This renders it heat resistant and a significant step up from most natural fibers like cotton, which burn or degrade at low temperatures. Polyester’s heat resistance makes it ideal for a wide variety of industrial and commercial applications, such as automotive upholstery and safety clothing.
Lightweight
Polyester is less dense than other natural fibres such as cotton, so it is lightweight and comfortable to wear. This feature is particularly crucial in applications like clothes, which require comfort and mobility. Furthermore, polyesters are often used for outdoor products like tents and sleeping bags due to their thinness.
b. Chemical Properties
Polyester, too, has several essential chemical characteristics that make it very suitable for various applications.
Resistance to Chemicals
Polyester is chemically inert, which keeps most acids and alkalis at bay. This makes it a great option for applications where chemicals might be an issue, like industrial environments. Polyester fibers do not absorb most cleaning, oil, or solvents, thus helping to extend the useful life of polyester fabrics.
Thermoplasticity
Polyester is a thermoplastic, which means that it can be melted and cut up and again without losing much of its properties. The ability to shape polyester into any desired shape in the manufacturing process, as well as polyester being recyclable, makes polyester malleable. Polyester textiles can be destroyed after usage, and reprocessed to make new materials, including recycled polyester (rPET).
UV Resistance
Polyester is resistant to ultraviolet (UV) radiation, allowing it to retain its colour and durability when left in the sunlight. This UV protection is particularly relevant for outdoor uses including tent fabrics, outdoor furniture and sun wear. It also protects the fabric from stretching or flaking during long-time exposure to the sun.
4. Manufacturing Process
Polyester fabric is produced in several steps, all of which are critical to making the finished product that is used in an array of industries. This involves starting from the formation of polyester fibers from the raw materials and then processing into the manufacturing, dyeing, and finishing of the fabric. Let’s look at each step in detail.
a. Fiber Production
Polyester fabric is made by preparing polyester fibres. These fibers are the building blocks from which fabrics will be weaved or knitted. The fiber production process is a highly structured set of steps that produces good quality polyester fibres that meet the strength, durability and appearance requirements for textile applications.
Melt Spinning
Polyester fibres are manufactured by melt spinning, in which the polyester polymer (usually polyethylene terephthalate, or PET) is melted into a liquid and pushed out of it using a machine called a spinneret. The spinneret has a series of small holes through which the molten polymer is pulled, creating continuous threads of polyester fibre.
Melt spinning is a great way to create fiber because you don’t need solvents or other chemicals to spin it. It also enables greater control over the diameter and profile of the fibres. The boiling polyester gets blown out into cool air, where it hardens into filaments. These filaments are twisted into spools for further application.
Drawing
After extrusion, the fibres go through the drawing process where they are pushed to several times their original length. Drawing aligns the polymer chains within the fibers, enhancing their strength and pliability. This stretching is crucial, since it converts the loose, amorphous polymer chains into more crystalline, orderly shapes that increase the mechanical strength of the fibre.
These drawn fibers are denser, softer, and more tensile, making them ideal for a wide range of applications, from clothing to industrial fabrics. Drawn levels may vary depending on use, since stretched fibres are generally thicker and more rigid, whereas drawn fibers are usually thicker and more pliable.
Texturizing
The second step of fiber making is texturizing, whereby the fibres are made to have a texture to make them bulkier, more supple, and more appealing. This is especially useful for fibers that are going to be spun into woven or knitted cloth, as it renders the fabric more comfortable and pleasing to the eye.
Texturizing is typically accomplished by crimping or twisting the fibers. The crimping creates tiny waves or bends in the fibers, bulking them up and making them more textured. Also insulating are textured polyester fibres, where crimping opens up more air between the fibers to make the fabric warmer. In products including activewear, upholstery and carpets, they use textured polyester fibres.
b. Fabric Production
After polyester fibers are produced, the final step in manufacturing them is weaving or knitting them into cloth. This is where the fibres get turned into the all-purpose textiles that populate most consumer goods.
Weaving and Knitting
The polyester filaments are either woven or knitted into fabrics, depending on the properties of the final product.
Weaving involves knitting two sets of yarns (warp and weft) together at a right angle to make a garment. Through weaving, the fabric is both strong and durable, which makes it ideal for everything from garments to furniture.
Knitting involves looping yarns to make a garment. Knitted fabrics are generally more pliable and stretchy than knit fabrics, and they are applied to activewear, tees and sportswear where movement and comfort are required.
Wringing and knitting can be used on polyester fibers to weave all sorts of different types of fabric. Fabric is produced based on fiber content, weave/knit composition, and finishes.
Dyeing and Finishing
Once the polyester fabric is woven or knitted, it goes through the dyeing and finishing stages, which are necessary for the proper color, feel, and performance properties.
Polyester fabric can be dyed with disperse dyes, which work extremely well on synthetic fibers such as polyester. Disperse dyes are put in a hot, watery solution to make sure the dye molecules pass through the fabric and attach to the fibers. Dyeing can occur in several stages, for example, solution dyeing, stock dyeing, or piece dyeing, based on the end result.
After the fabric is dyed, it goes through finishing and additional treatments are done to make the fabric perform better. These finishes can include:
Softening Finishes: To soften and soften the fabric to the touch.
Anti-slip finishes: To make the fabric resistant to water.
Finishes that repel flame: In order to give the fabric a stronger resistance to fire, used for safety and protective wear.
Antimicrobial finishes: To stop bacteria and fungi from invading the fabric, which makes them more clean and odor-free.
These finishes can significantly enhance the function and appearance of polyester fabric and make it suitable for a multitude of uses, from clothing and textiles to industrial and medical.
5. Applications of Polyester Fabric
Polyester fabric has been widely used in almost all sectors because of its durability, strength, and adaptability. Polyester permeates every aspect of modernity, from fashion to interior decor and business use. The following are some of the major uses of polyester cloth.
a. Fashion and Apparel
Polyester dominates the fashion and apparel industry because its qualities make it ideal for a variety of clothing.
Sportswear and Activewear
Polyester is highly prized in the manufacture of sportwear and activewear because of its wicking and quick-drying qualities. Polyester fibers don’t hold water, and therefore do not absorb it. Rather, they draw the moisture from the body and immediately expel it in the air. This is why polyester is perfect for workout attire, running shirts, leggings, and gym clothing where wicking away moisture is essential for ease.
Casual Wear
Polyester also finds its way into t-shirts, dresses, and other casual clothes. It is often paired with cotton in order to produce fabrics that are as soft and comfortable as cotton but as strong and wrinkle-resistant as polyester. High-street and budget collections all feature woven materials.
Formal Wear
Polyester is typically used in suits, dresses, and other formal clothes. Poly-polyester mixtures are commonly found in formal wear, particularly suiting fabrics where the material’s strength and ability to resist wrinkles and shrinkage are highly regarded. Polyester’s softness and ability to hold its shape also contribute to the elegant look of a suit.
b. Home Furnishings
Apart from clothes, polyester fabric is widely used in home furnishings because of its longevity and easy maintenance.
Upholstery
Polyester is a upholstery fabric found in furniture. It is stain, fade and scratch resistant, making it perfect for sofas, chairs and cushions that are exposed to the elements regularly. Polyester upholstery fabrics are also easily cleanable and maintenance-free, making them ideal for both residential and commercial uses.
Curtains and Drapes
The most commonly used fabrics for curtains and drapes is polyester because it’s resistant to staining and wrinkles. Polyester fabric resists shrinkage, fade, and wrinkles so curtains and drapes do not look the same after multiple washes.
Bedding
Polyester is used in mattresses, pillowcases, blankets and comforters. Polyester’s suppleness, sturdiness, and ability to resist wrinkles and shrinkage are perfect for bedspreads that have to be comfortable and durable.
c. Industrial Applications
Polyester’s strength, chemical resistance and hardness make it a must-have material in a number of industrial settings.
Automotive Industry
Polyester is commonly used in automotive seat covers, seat belts, and interior linings because it’s tear-resistant, as well as heat and UV-sensitive. Polyester’s toughness and ease of care make it a great material for the automobile industry, where materials must withstand extreme weather conditions.
Safety Gear
Polyester is also used to make safety clothing, including hi-vis vests, harnesses, and personal protective equipment. It’s strong and wear resistant, making it a good option for safety applications requiring strong materials. Polyesters can be glazed with flame retardants for further protection in dangerous situations.
Geotextiles
Polyester fibers are often found in geotextiles, which are the fabric materials used in building and landscaping to stabilize the ground. Geotextiles made of polyester resist deterioration, making them suitable for use in road building, drainage and erosion control.
6. Environmental Impact
Polyester, though common, poses major ecological risks, mostly because it is made from petroleum products and is not biodegradable. But we are also developing remedies and innovations to address these problems.
a. Sustainability Challenges
Petroleum-Based Origin
Polyester is chemically based on petroleum, which means it requires non-renewable resources. This presents a sustainability issue, since the petrochemical sector is one of the largest greenhouse gas emitters. Further, the production of petroleum involves environmental consequences ranging from habitat loss to pollution.
Non-Biodegradability
One of polyester’s greatest hurdles is its non-biodegradability. Polyester fabrics can take hundreds of years to decay in landfill, contributing to the ever-escalating textile problem. As polyester fabrics decompose, they also release microplastics into the environment, which will add to pollution.
Microplastics
In the washing process, polyester clothes spit out microscopic fibres called microplastics that can leak into waterways and oceans and kill fish and end up in food supply.
b. Solutions and Innovations
Recycled Polyester (rPET)
Recycled polyester (rPET) is one of the most promising alternatives to polyester in terms of its environmental footprint. rPET is produced by melting up recycled plastic bottles or other polyester waste into new fibers. The process avoids virgin polyester production and lowers plastic waste from the landfills.
Bio-Based Polyesters
Scientists are also looking into bio-based polyesters, which are derived from renewable materials such as plants, corn or sugarcane. These bio-based substitutes are better alternatives to petroleum-based polyester because they are less dependent on non-renewable resources and may have a lower carbon footprint.
Closed-Loop Systems
Another solution could be the creation of closed loops in polyester manufacturing. In such systems, polyester fabric is gathered, regenerated and reconstituted back into fibres of high quality for the production of new textiles. The process mimics the natural cycle and helps establish a circular economy for polyester goods.
7. Future of Polyester Fabric
The future for polyester fabric is rosy, with innovations constantly underway that aim to enhance sustainability and performance.
Advancements in Recycling
Chemical recycling is becoming increasingly popular as a way to decompose polyester back into its original monomers and create a more desirable version of polyester from the material recycled. This will improve the ecological footprint of polyester production by promoting use of recycled material.
Sustainable Alternatives
Biodegradable, bio-based polyesters are being developed. These alternatives could soon supplant traditional polyester and offer textiles a cleaner alternative that is less destructive to the environment.
Smart Textiles
Finally, smart textiles are one of the rapidly growing areas of research in polyester fabric design. They can use sensors and conductive fabrics to build wearable technologies — health monitors or interactive garments, for example. Polyester’s tenacity and elasticity make it the perfect canvas for these high-tech textile uses.
Yashvi Jain, a writer by day and reader by night, is an accomplished content writer and published author of ‘Mind Under Construction. Yashvi possesses extensive knowledge of fabrics, sustainability, and literature. On occasions, you would catch her scripting for her YouTube channel, engrossed in fiction, or ardently dedicating her time to research and storytelling.