Plastics- Chemistry Guide for Class 8

Palstics- Class 8 Science Guide

Information about Plastics


Plastics and the Environment


Class 8


Class 8 Chemistry

Topics Covered

  • Synthetic Fibres
  • Different Synthetic Fibres
  • Rayon or Artificial Silk
  • Nylon
  • Terylene
  • Poly Ethene Tetraphthalate (PET)
  • Acrvlic Fibres (Acrvlon)
  • Advantages of Synthetic Fibre
  • Disadvantages of Synthetic Fibres


Plastics are polymers of simple molecules (monomers). The arrangement of simple molecules, in different polymers, is not of the same type. There are certain plastics where monomers are arranged in a straight chain. Such plastics are said to have linear arrangement of molecules; they are generally known as thermoplastics.

In some other plastics, the monomers are cross-linked. Such plastics are said to have cross-linked arrangement; they are generally known as thermosetting plastics.

Characteristics of Synthetic Plastics

  1. Light weight: Synthetic plastic materials are very light in weight as compared to natural plastic materials.
  2. High tensile strength: Synthetic plastics can hold a lot of weight without breaking. For example, a thread of synthetic plastic can withstand more weight as compared to a thread of cotton of the same thickness.
  3. Resistance to chemicals: Synthetic plastics are not easily affected by strong chemicals, such as acids and alkalis. 
  4. Non-biodegradable: Synthetic plastics are not biodegradable, that is, they do not wither like natural plastics.
  5. Lustrous and colourful: Synthetic plastic materials can be made more shiny and bright. They can be made in any desired colour or texture; they are, therefore, often used for making a large variety of household products.
  6. Non-conductors: They are poor conductors of heat and electricity.

  • Teflon is a special plastic on which oil and water do not stick. It is used for providing a 'non-stick coating' on cookwares. 
  • Synthetic fibres/plastics generally catch fire easily. However, melamine is a plastic which is flame resistant. It is, therefore, coated on the uniforms of firemen. 

Types of Synthetic Plastics

Synthetic plastics are classified as:
  1. Thermoplastics
  2. Thermosetting plastics

1. Thermoplastics

  • Plastics, which have a linear arrangement of molecules, are thermoplastics.
  • These plastics can be deformed easily on heating and can be remoulded into a new shape.
  • Polyethene, Polyvinyl Chloride (PVC), nylon, polystyrene and terylene are among the well-known examples of thermoplastics.

2. Thermosetting plastics

  • Plastics, which have a cross-linked arrangement of molecules, are called thermosetting plastics.
  • These plastics cannot be deformed on heating and therefore, cannot be remoulded again.
  • Bakelite and melamine are examples of thermosetting plastics.
  • Bakelite is a poor conductor of heat and electricity and is used in making electrical switches, handles of cooking utensils, etc. 
  • Melamine resists fire and can tolerate heat better than other plastics. It is used for making kitchenware and fabrics which resist fire.

Plastics and the Environment

When we go to the market for purchasing items of daily need, we should, but usually do not, take a cotton or jute carrybag with us. The shopkeeper may then give us the items in polythene carrybags. Also most of the materials, being sold, are wrapped in polythene.

  • Synthetic polymers, by and large, have some common characteristics:
  • These are resistant to heat and chemicals like acids and alkalis.
  • Their inertness makes them useful but has also created numerous environmental problems.
  • All these carrybags, or wrappers, ultimately find their way to the garbage can.
  • The disposal of all such plastic garbage is a major problem all over the world. It is because plastic does not get decomposed by natural processes, such as action of bacteria.
  • Materials which get decomposed through natural processes (such as action of bacteria) are called biodegradable.
    Parts and skins of vegetables and fruits, leftover food stuff, paper, cotton, wood, etc., are examples of biodegradable materials.
  • Materials, that do not decompose through natural processes and take a very long time to degrade, are called non-biodegradable.
    Plastic bags, plastic buckets, etc., are examples of non-biodegradable materials.

Damages caused by Plastic Waste

  • Plastic carrybags and other articles clog the city drainage system, thereby, causing a lot of inconvenience.
  • Stray cows and other animals, in the process of eating the food waste, may also swallow materials like polythene bags and wrappers. This can choke the digestive tract of animals and can cause their death.
  • Plastics take several years to decompose; they are not environmental friendly and cause environmental pollution.
  • Plastics, if burnt, produce harmful gases which pollute air. 

Measures to Control the Damage caused by Plastic Waste

  1. We should not throw plastic wrappers carelessly on road. They then generally get carried into the city sewage system resulting in clogging of drainage.
  2. Biodegradable and non-biodegradable wastes should be collected separately and disposed off separately.
  3. We should make use of bags made of cotton or jute when we go out for shopping. This will reduce the use of plastics.
  4. As a responsible citizen we need to remember the 4 R's principle:
  5. We need to develop habits that help to preserve the environment. 
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