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What are Plastics

Plastics are macromolecules, formed by Polymerization and having the ability to be shaped by the application of the reasonable amount of heat and pressure or some other form of force.


Polymerization is the process by which individual units of similar or different molecules ("mers") combine together by chemical reactions to form large or macromolecules in the form of long chain structures, having altogether different properties than those of starting molecules ("mers"). Several hundred, and even thousands of "mers" combine together to form the macromolecules, or what we call, Polymers.


Depending upon their nature and properties, the polymers are classified as Plastics, Rubbers or Elastomers and Fibres.


If the polymer chains are very flexible, the inter molecular forces of attraction low and the chains do not fit to a regular lattice structure easily, the material will tend to retract upon when external tension is released. This is the state typical for a Rubber or Elastomer.

In the other extreme, if the polymer chains are inherently rigid, the intermolecular forces intense and the molecules fit readily into a crystal lattice, then the crystallinity once induced, will tend to be permanent. Such a material would be a typical Fibre. In the intermediate case, when the intermolecular forces of attractions are neither too high nor too low, the polymer is called Plastic. 

Generally speaking, a plastic material should possess sufficient rigidity, dimensional stability and mechanical strength at room temperature to serve as a useful household article, gadget or structural part and still be of such a character that it may be molded to shape by the application of reasonable temperature and pressure.


There are no intrinsic differences among Rubbers, Plastics, and Fibres. Any apparent difference is a matter of degree.


Polymers can be classified into two categories : -


Natural Polymers and Synthetic Polymers.

Examples of Natural Polymer: Starch, Natural Rubber, Gelatin, Protein, Shellac, Cellulose etc.


Examples of Synthetic Polymers :

Polyethylenes - Low-Density Polyethylene, High-Density Polyethylene, Linear Low-Density Polyethylene, Polypropylene, Polystyrene, Styrene Butadiene Rubber(SBR), Nylon etc.


Polymers may also be subclassified into two categories: 

Organic Polymers 
Inorganic Polymers


In Organic Polymers, the main constituent is Carbon Atom along with any one or more of the following constituents: Hydrogen, Oxygen, Nitrogen, Halogens etc.

Examples: Polyethylene, Polyvinyl Chloride, Nylon etc.


In inorganic Polymers, the main constituents are other than carbon, like Silicon, Boron etc.

Examples : Polysilanes, Polysiloxanes etc.


Types of Plastics:


There are mainly two types of Plastics: 

Thermoplastics and Thermosetting Plastics


Thermoplastics are those, which once shaped or formed, can be softened by the application of heat and can be reshaped repeatedly, till it loses its property.

Example: Polyethylene, Polypropylene, Nylon, Polycarbonate etc.

Applications are Polyethylene Buckets, Polystyrene Cups, Nylon ropes etc.


Thermosetting Plastics are those, which once shaped or formed, cannot be softened by the application of heat. Excess heat will char the material.

Example: Phenol formaldehyde, Urea Formaldehyde, Melamine Formaldehyde, Thermosetting Polyester etc.

Applications are - Bakelite Electrical switches, Formica / sermica table tops, melamine Cutlery etc.

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