Plastics -composition, classification and uses | The Mechanical post

The Mechanical post is back with a fresh post on "Everything you need to know about plastics". Plastics are the most widely used material in almost every aspect of life. Be it baby products to wheelchairs for the aged, plastics are everywhere. Plastic is one of the best and the most harmful invention by men. How ironical, isn't it ?

Plastics -composition, classification and uses | The Mechanical post
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Plastics are very useful and they have a lot of advantages like they are inexpensive, waterproof, resistant to electricity, have low friction, easily mouldable etc.

But the problem arises when plastics are not in use i.e. when they are discarded. It is non-degradable and harms the environment a lot. Recently I read an article which stated that scientist have found plastics at great depth in the oceans.

Well let's come back to the topic. Plastics are made up of polymers.

What are polymers ?

"Poly" which means many and "mers' which means parts. Polymers are organic material and have carbon as a common element in them.

Polymers comprise of large number of similar units called monomers. Put it like this " A large number of monomers come together to form a long chain called polymer". 

The process of linking of monomers to form polymers is called as polymeriszation. Plastics, rubbers and fibre material are types of synthetic polymers.

Basic characteristic of polymer

  1. Low density.
  2. It is resistant to corrosion. 
  3. They have low co-efficient of friction.
  4. They can be muolded easily.
  5. It is inexpensive.
  6. Good surface finish.
  7. Can be produced in desired type of colours.
  8. Electrical resistant.
Plastics are broadly classified into two categories.
  1. Thermoplastic polymers.
  2. Thermosetting polymers.


Thermoplastics material are those plastics which can be softned and reshaped by applying heat. When cooled they set to their moulded shape. This process of heating and cooling can be done numerous times.

But there is a condition, that the thermoplastic material should not be heated above their decomposition temperatures.

Properties of thermoplastic :

  • They are long chain, straight or slightly branched molecules held close to each other. However, the forces holding them are weak. Thus, when heat is applied they easily break.
  • They can be easily reshaped.
  • They have low melting temperatures.
  • Since they can be reshaped, these type of plastics are recycleable.

Commonly and widely used thermoplastics in the industry are:

  • Nylon.
  • Vinyl.
  • Acrylics.
  • Acrylonitrile butadiene styrene (ABS).

Uses of thermoplastics

  • Thermoplastics like polyvnyl chloride (PVC) are used to manufacture coatings for wire, cables, water pipes, water storage tanks etc.
  • Nylons are used to manufacture fibre and yarn for clothes, bearings, gears, ropes etc.
  • Acrylics are used to manufacture fibre optics, contact lenses, roof lights, sinks and baths etc.
  • Polycarbonate is used to make CD's, modern smartphones, water bottles.
  • Acrylonitrile butadiene styrene (ABS) is used for making sports equipments, toys, car bumpers etc.

    Thermosetting plastics

    As their name suggests, thermosetting plastics are the type of plastics which initially  are soft during their 1st heating, then they become permanently hard when cooled. These plastics cannont be reshaped by application of heat. Thus, they are not recycleable.

    Properties of thermosetting plastics

    • They cannot be reshaped and reused.
    • They are rigid, have high strength and heat resistance as compared to thermoplastics.
    • If heated to high temperatures it decomposes.
    • Thermosetting plastics have high molecular weight.
    • Their resistant to chemicals.
    • It is abrasion resistant.

    Commonly and widely used thermosetting in the industry are:

    • Bakelite (Phenol formaldehyde)
    • Melamin.
    • Epoxy resins.
    • Silicone.
    • Polyurethane.

    Uses of thermosetting plastics

    • Thermosetting plastics like Bakelite are used for heat resistant handles, electrical connection and switches etc.
    • Melamin resin is used for manufacturing utensils.
    • Epoxy resins are used for making adhesives, paints, glues for plywood etc.
    • They are used for manufacturing rain coats, gum boots, gloves etc.

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