Types of Plastics and their Properties

Plastics may be classified into two broad groups based on their behaviour with respect to heat, viz., thermo plastics and thermoset plastics.

1. Thermo Plastics

These are the plastics which become soft when heated and become hard when cooled. These plastics can sustain repeated softening and hardening for indefinite time. Old scrap and worn-out materials of this type can be effectively used again.

Some of the important thermo plastics are: acrylic, cellulose acetate, polythene, perspex and poly vinyl chlorides.

Acrylic contains methyl metha crylate. Acrylics are transparent, rough and strong and withstand impacts. It is used for doors, windows and as safety glass in automobile and aircrafts.

Cellulose acetate is made from cotton seed. It is used for electric cables, hard rails, etc.

Polythene is transparent and chemically unaffected by temperature and moisture. This is mainly used for preparing pipes, covers, waterproof packing, etc.

Perspex is strong enough and are made in the form of sheets. This is used for electrical fittings for decorative purposes.

Poly vinyl chloride (PVC) is a product obtained from vinyl chloride and acetate. It is acid proof, light and withstands wear and tear. It is used for drainage pipes, floor finishing, etc.

2. Thermoset Plastics

These plastics become rigid due to chemical changes when moulded under pressure and temperature. These plastics once cooled and take a form, can not be changed further due to the application of heat.

Some of the commonly used thermoset plastics are phenol formaldehyde, phenol furfuraldehyde, urea formaldehyde and bakelite.

Phenol formaldehyde is formed by heating phenol and benzene with a suitable catalyst. Phenol furfuraldehyde is formed by digesting husks of rice, oat, groundnut with sulphuric acid, distilling the mixture to separate the furaldehyde vapour and then permitting the vapours to chemically react with phenol with a suitable catalyst.

Urea formaldehyde is formed by reacting urea with formaldehyde in the presence of a catalyst.

Bakelite is made by heating equal amount of phenol and formaldehyde with a base. This is orange in colour which is used with fillers to form different materials.

Thermoset plastics are used for various purposes such as dishes, plates, cabinets for electrical appliances, etc.