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Polyethylene Terephthalate

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Fabrics are used to make the clothes we wear on a daily basis. Fabrics are composed up of fibers that come from both natural and man-made sources. Natural fibers such as wool, silk, and cotton are examples of natural fibers, while synthetic fibers such as polyesters and terylene are examples of synthetic fibers. Fibers are also utilized to create a wide range of home items. Natural fibers such as cotton, wool, silk, and others are derived from plants or animals. Humans are the ones who create synthetic fibers. Synthetic and plastic fibers, like natural fibers, are made up of extremely big units. 

Polymers refer to the bigger units. These are made up of several little components that are identical or distinct. Monomers are the smallest units. Natural fibers come from plants and animals, while synthetic fibres are made from petrochemicals that have been chemically processed. Before heading toward PET. Let us now discuss some concepts related to this.

What is Plastics?

The arrangement of units in all plastics is not the same. It is linear in some cases and cross-linked in others. Plastic can be recycled, repurposed, colored, melted, rolled into sheets, or wired. That is why it has so many applications.

Depending on how they interact with heat, plastics can be divided into two groups.

  • Thermoplastics: Thermoplastics are plastics that distort easily when heated and maybe bent with ease. Thermoplastics include materials such as polythene and PVC. These are utilized in the production of toys, combs, and various containers.
  • Thermosetting plastic: Thermosetting Plastics are plastics that cannot be softened by heating after being molded once. Bakelite and melamine, for example.

Characteristics of Plastics are:

  • Plastic is light, strong, and durable.
  • Plastic is non-reactive.
  • Plastic is light, strong,
  • Plastic is a poor conductor of electricity.

Polyethylene Terephthalate (PET)

A polyethylene terephthalate is a terephthalic acid and ethylene glycol condensation polymer. Water is a by-product of the reaction that produces this molecule, hence it is an example of step-growth polymerization or condensation.

There are two types of polymerization based on this mechanism. Step-growth and chain-growth polymerization are the two types. The monomer units are joined to each other by their numerous bonds in chain-growth polymerization, also known as addition polymerization. Polymerization of ethylene, for example, results in the creation of polyethylene polymer, also known as polythene.

This polymerization procedure consists of three steps. In the first phase, free radicals are formed in the presence of some initiators, such as peroxide. A free-radical is a chemical entity that has one or more free electrons.

R-O-O-R         ⇢        2 R-O

These free radicals go through initiation processes and combine with monomer units to produce fresher free radicals, which start the polymer chain. The monomer double bond units then break and bind to free radicals, resulting in additional free radicals.

Structure of PET

Protonation of terephthalic acid occurs in an acidic medium, where it combines with ethylene glycol to generate an intermediate that rearranges and forms a polyethylene terephthalate polymer due to the transfer of OH- ions.

Structure of PET

Overall, the two monomer units are linked together by an ester linkage, resulting in a polyester. It’s a chemical substance utilized in the production of fiber and plastic. The polycondensation of ethylene glycol and terephthalic acid produces this.

Preparation of PET

PET/PETE stands for polyethylene terephthalate, which is mostly utilized in the production of food packaging materials such as fruit and drink containers. It’s lightweight, translucent, and comes in a variety of colors. It is a member of the ester family and is therefore also known as polyester. It’s a thermoplastic polymer having stiffness, functional strength, ductility, and hardness that can be recycled. As a result, injection molding, vacuum forming, blow molding, and compression molding are all viable options.

PET / PETE can also be recycled into polyester fibers and returned to its original ingredients. Polyester fibers are utilized in the production of synthetic garments, carpets, and other textile items. Because PET fibers are less expensive and wrinkle-free, they are frequently combined with natural fibers. It’s also employed in the production of microwavable trays and the packaging of microwaveable meals in containers for pharmaceutical and cosmetic products.

Applications of PET

Polyethylene Terephthalate (PET) is used in a variety of packaging applications, the most common of which are listed below.

  • PET plastic bottles are commonly used for carbonated soft drinks and mineral water because of the outstanding water and moisture barrier properties of Polyethylene Terephthalate.
  • Polyethylene Terephthalate films are suited for use in tape applications because of their great mechanical strength.
  • Thermoforming non-oriented PET polymer sheet can be used to create packaging blisters and trays.
  • Its chemical inertness, along with other physical qualities, has made it particularly appropriate for food packaging applications.
  • Microwavable containers, hard cosmetic jars, transparent films, and a variety of other packaging applications are just a few examples.
  • PET polymer is being used successfully in a variety of automotive applications. Wiper arm and gear housings, engine covers, headlight retainers, and connector housings are among the applications where it is now used.

Sample Problems

Problem 1: What are synthetic fibers? 

Solution:

Synthetic fibres are human-made fibres that are created chemically. Coal, petroleum, and natural gas supply the majority of synthetic fibres. Synthetic fibres include nylon and rayon, for example. 

Problem 2: How do plastics impact the environment?

Solution:

  • Plastic takes a long time to disintegrate and is therefore not environmentally friendly.
  • It pollutes the environment.
  • The synthetic material’s burning process is lengthy, and it does not simply burn fully.
  • It emits a large amount of harmful gases into the environment, resulting in air pollution.

Problem 3: Define types of plastics.

Solution:

Depending on how they interact with heat, plastics can be divided into two groups.

  1. Thermoplastics- Thermoplastics are plastics that distort easily when heated and may be bent with ease. Thermoplastics include materials such as polythene and PVC. These are utilised in the production of toys, combs, and various containers.
  2. Thermosetting plastic- Thermosetting Plastics are plastics that cannot be softened by heating after being moulded once. Bakelite and melamine, for example.

Problem 4: Suggest solutions to mitigate the negative consequences of plastic disposal.

Solution:

There are two strategies to mitigate the negative consequences of plastic disposal.

  1. Cutting down on the use of plastics
  2. Plastics recycling and reuse.

Problem 5: Why is it recommended that you don’t wear synthetic clothing in a laboratory or when working with a fire in the kitchen?

Solution:

When heated, the synthetic fibres melt. With synthetic fibres, this is actually a negative. It can be highly dangerous if the material catches fire. The fabric melts and adheres to the person who is wearing it. As a result, synthetic clothing should not be worn in a laboratory or when working with fire in the kitchen.


Last Updated : 17 Aug, 2021
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