Q. Discuss the classifications of plastics.
OR
Discuss the general properties and classification of plastics.
OR
Give a brief introduction of plastic technology and classify the plastics.
Ans. Today plastics play an important role both for industrial and domestic applications because of their excellent properties and merits. These are very popular because of their high specific strength and stiffness, corrosion resistance, good electrical and thermal insulating properties, low coefficient of friction, toughness and resilience with good vibration damping capacities, ease of fabrication and inexpensiveness. Compared to other metals on volume basis.
However they have some limitations like low operating temperature, high thermal expansion, low strength in compression to metal and inflameability.
The whole range of plastics is based on various ways of combining carbon, hydrogen and oxygen atoms to produce molecules which have characteristics quite different from other elements.
Plastics may defined as organic materials can be easily moulded or shaped by mechanical or chemical action to give non-crystalline substance that are solids of ordinary temperatures.
Classification of plastics : All the plastics are broadly classified into two main groups are under :
1. Thermosetting plastics : Those plastics which are hardened by heat, effecting a non-reversible chemical change are called thermosetting. In other words, plastics are those who acquire a permanent shape when heated and pressed and cannot be softened by reheating. They are also known as heat setting or thermosetting plastics.
2. Thermoplastics : Those plastics which can be softened again and again by heating are called thermoplastics. Thus, they can be heated and reshaped by pressing many times. On cooling, they become hard. They are also known as cold-setting materials. They can be shaped into bars, tubes, sheets, films and many other shapes.