Plastics

Plastics

Plastics are cross linked polymers and are very tough. Lac is a natural plastic.

Chemically plastic can be of two types :
(i) Thermoplastic
(ii) Thermosetting plastics

Thermoplastic

These are the polymers which can be easily softened repeatedly when heated and hardened when cooled with little change in their properties.
Examples : Polyethylene, polystyrene, polyvinyl chloride, teflon, etc.

Thermoplastic

These are the polymers which undergo permanent change on heating. On heating they undergo extensive cross linking in moulds and become hard and infusible therefore, they can not be reused.
Examples : Bakelite, glyptal, terrylene etc.

Bakelite (Phenol-formaldehyde resins)

It is a condensation polymer and is obtained from phenol and formaldehyde in presence of either an acid or a base catalyst. It is used for making combs, fountain pens, photographs records, electrical goods etc.