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Plastic (Short Note)

2nd Year Chemistry Notes


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Old 03-18-2010, 09:44 AM   #1 (permalink)
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Default Plastic (Short Note)

Plastic (Short Note)

Definition

Plastics are macromolecules, which are formed by the polymerization of simple molecules.


Explanation

In other words we can say that plastic are the polymers formed from monomers. The phenomenon in which simple and smaller molecules are combined together to form complex and large molecules, is called polymerization. The simple and smaller molecules are called monomers and the large and complex molecules are called polymers.
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Types of Plastic

There are the following two types of plastics.
1. Thermo Plastic
2. Thermosetting Plastic

1. Thermo Plastic
Thermo plastic is also known as Thermo-softening plastic. This type of plastic is manufactured by heating, softening melding and cooling the raw materials, this process can be repeated and it does not effect the properties of plastic.

2. Thermosetting Plastic
Thermosetting plastics are those materials, which cannot be heated, only once before they set, i.e. they cannot be reworked.


Examples of Plastic

1. Polyethene (Polythene)
In presence of traces of oxygen, when ethene is heated at 200C, under 100 atm pressure then polymerization takes place. As a result, polyethene is formed, which is commonly known as polythene.
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Uses
Polythene is the most common plastic used to form polythene bags and to package food.

2. Poly Vinyl Chloride (PVC)
PVC or Poly Vinyl Chloride is the polymer of vinyl chloride. When vinyl chloride is heated at 80C in the presence of catalyst hydrogen peroxide, then polymerization takes place. As a result, Poly Vinyl Chloride is formed.

Uses
PVC is used for insulating covering for electrical cables, for the manufacture of gramophone, records, suitcase covering etc.

3. Poly Vinyl Acetate (PVA)
Poly Vinyl Acetate (PVA) is the polymer of vinyl acetate.

Uses
PVA is used in the manufacture of chewing gums and in the water proofing of textiles.

4. Bakelite
Bakelite is a polymer of phenol and formaldehyde. By the condensation of two molecules of phenol with formaldehyde, a polymer Bakelite is obtained.
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Uses
Bakelite is used to make buttons, switches, electrical boards, camera, radio, telephone etc.


Quality of Plastics

During the polymerization, some other components are also mixed to improve the quality of the plastic. For example, plasticizer is mixed with the polymer. It reduces the brittleness and improves the elasticity of plastic. Fillers are also mixed with the polymer, which usually increases the mechanical strength of plastics, Some pigments or dyes are added to get various coloured plastics.


Plastic Industry of Pakistan

The plastic industry in Pakistan essentially consists of moulding of plastic powders into various articles of daily use

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