Polyethylene Terephthalate

What is Polyethylene Terephthalate?

Polymers are macromolecules that form by specific repeating units. These repeating units are known as monomers. Monomers contain some functional groups that react with each other to form a long polymeric chain. The chemical bonds that existed between monomer units are usually covalent bonds that are formed due to the addition between condensation or some unsaturated monomer units between two different functional groups such as -NH2, -COOH, -OH, and so on.

The formation of polymers process from monomer units is referred to as a polymerization process. Polymerization occurs because of the addition reaction between condensation or unsaturated monomer units between two different monomers by the elimination of certain small molecules such as carbon dioxide, water, and so on.


Definition of Polyethylene Terephthalate

“A polyethylene terephthalate is a condensation polymer of both terephthalic acid and ethylene glycol.” The reaction’s by-product to create this compound is water, and so it is an example of step-growth polymerization or condensation.

Based on this mechanism, there are two types of polymerization. They are the step-growth and chain-growth polymerization. Chain growth polymerization is further known as addition polymerization where the monomer units are bonded with each other through their multiple bonds. For example, polymerization of ethylene leads to the formation of polyethylene polymer that is otherwise known as polythene.

This is a three-step polymerization process. In the first step, there is the formation of free radicals in the presence of some initiators like peroxide. We already know that a free-radical is a chemical species with a free electron.

R-O-O-R --> 2 R-O

These free radicals involve initiation steps and form newer free radicals with monomer units that begin the polymer chain. Then, the monomer double bond units break and attach with free radicals to form new free radicals.


Polyethylene Terephthalate Structure

According to the acidic medium, protonation of terephthalic acid happens that reacts with ethylene glycol to form an intermediate that rearranges and due to the transfer of OH- ions forms a polyethylene terephthalate polymer.

The structure of Polyethylene Terephthalate is represented in the following figure.

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Overall the two monomer units are joined together with ester linkage, which is commonly called a polyester. It is a chemical compound that is used to produce fibre and plastic. This is formed by the polycondensation of ethylene glycol and terephthalic acid.


Polyethylene Terephthalate Preparation

Polyethylene Terephthalate, which otherwise abbreviated as PET / PETE, is mainly used in the manufacturing of food products packaging material such as fruit and drink containers. It is a lightweight, transparent, and also available in various colours. It is one of the members of the ester family so also known as polyester. It is a recyclable thermoplastic polymer with stiffness, functional strength, ductility, and hardness. Therefore, it can be processed through injection moulding, vacuum forming, blow moulding, and compression moulding.

Also, the PET / PETE can be recycled back to its original elements and into the polyester fibres as well. These polyester fibres are used to manufacture synthetic clothing, synthetic carpets, and other textile products. PET fibres are less expensive and wrinkle-free and often therefore mixed with natural fibres. It is also used to manufacture microwavable trays and for the packaging of microwavable meals in containers for pharmaceutical products and cosmetic products.


What are The Properties of Polyethylene Terephthalate?

The physical and chemical properties of polyethylene terephthalate are tabulated below.

Property

Value

Technical Name

Polyethylene terephthalate (PET or PETE)

Chemical Formula

(C10H8O4)n

Melting point

500°F (260°C)

Typical Injection Mold Temperature

74 - 91 °C (165 - 195 °F) ***

Heat Deflection Temperature (HDT)

70 °C (158 °F) at 0.46 MPa (66 PSI) **

Tensile Strength

152 MPa (22000 PSI) *** W/ 30% of Glass Fiber

Flexural Strength

221 MPa (32000 PSI) *** W/ 30% of Glass Fiber

Specific Gravity

1.56

Shrink Rate

0.1 - 0.3 % (.001 - .003 in/in) ***


Pet Plastic Applications

Polyethylene Terephthalate is used in various packaging applications, and the main ones are mentioned below.

  • Due to the excellent water and moisture barrier material of Polyethylene Terephthalate, the plastic bottles are made from PET, and those are widely used for carbonated soft drinks and mineral water

  • The high mechanical strength having in it makes Polyethylene Terephthalate films ideal for its use in tape applications.

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  • Non-oriented PET polymer sheet can be thermoformed to make packaging blisters and trays

  • Together with other physical properties, its chemical inertness has made it particularly suitable for food packaging applications

  • Other various packaging applications include microwavable containers, rigid cosmetic jars, transparent films, and many more.

PET monofilament is primarily used for the production of mesh fabrics for screen printing, bracing wires for agricultural applications (greenhouses), filters for oil and sand filtration, woven/knitted ties, filter cloths, and other related industrial applications.

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PET/PETE has a wide range of applications in the textile industry. Polyester fabrics exhibit strong, flexible, and offer the additional benefit of fewer wrinkles and shrinkage over cotton. Polyester fabrics are reduced-wind, lightweight, drag-resistant, and more resistant to tears.

Thanks to high structural and dimensional stability, good electrical insulating properties, polyethylene terephthalate are widely used in the electrical and electronics industry. It is an effective polymer to replace thermosets and die casts metals in applications such as solenoids, smart meters, electrical encapsulation, photovoltaic parts, solar junction boxes, and more. The outstanding flow characteristics of polymers enable design freedom and miniaturization to produce high-performance parts.

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PET polymer is being used successfully in several applications in the automotive industry. It is currently being employed in the applications, including wiper arm and gear housings, engine cover, headlamp retainer, and connector housings.

FAQ (Frequently Asked Questions)

1. Mention Some of The Important Properties of Polyethylene Terephthalate?

  • Crystal clear polymer - It is a crystal clear polymer with good health and purity. We must have seen the sparkling PET bottles with brilliant glass-clear presentations which attract us.

  • Purity - The PET products taste good and comply with international food contact regulations.

  • Safe - The objects made from PET, such as bottles, are tough and virtually unbreakable. Therefore they can be easily used for storage and transportation. It’s tensile strength, and high impact makes it ideal for carbonated products.

  • Good barrier - PET products have low permeability to carbon dioxide, oxygen, and water. It, therefore, maintains the integrity of products with good shelf life.

  • Lightweight - The PET products lightweight reduce shipping costs compared to glass products.

  • No Leakage or damage - Because of the absence of a weld line in the base, PET bottles are free from damage and leakage.

  • Recyclable - PET polymer is completely recyclable and can be reshaped to different shapes.

  • Good resistance power - PET products have good resistance against different chemicals like acids, bases, and more.

2. List the Polyethylene Terephthalate Uses?

A few of the polyethylene terephthalate uses are given below.

  • Manufacturing water bottles, shopping bags, videotapes

  • Manufacturing containers and bags

  • Manufacturing housing material and clothes

  • Manufacturing microwaves containers, and carpets

  • Manufacturing of packaging films

  • PET polymer is used as a substrate in thin-film solar cells

  • It is also used as a waterproofing barrier in undersea cables

  • Terylene (a trademark formed by polyethylene and terephthalate inversion) is spliced into bell rope tops that helps to prevent wear on the ropes because they pass through the ceiling

  • The PET polymer is used since late 2014’s as liner material in type IV composite high-pressure gas cylinders and works much better barrier to oxygen than earlier used (LD)PE

  • PET polymer is also used as a 3D printing filament and in the 3D printing plastic PETG as well.