Give classification of plastics and also the differences between them.

Plastics are materials (containing carbon as common element) that have organic substances of high molecular weight and are able of being formed in required shape throughout or after their manufacture. The organic substances are termed as resins polymers and are derived from natural gas and petroleum. The polymers are mixed along with other materials to change their properties. There are two kinds of plastics: thermoplastics, thermosettings.

Thermoplastic materials:-

The properties of these plastic materials do not change considerably if they are melted and then cooled and solidify. They are deformable at higher temperature.

Thermoplastic materials: The properties of such plastic materials do not change considerably when they are melted and after that cooled and solidify. They can be repeatedly dissolved or melted in various solvents. They are additional elastic, less brittle and do not lose elasticity while subjected to prolonged heating. They are less apt to age thermally. Again and again they can be remoulded in any shape after heating. Several of them possess extraordinary high insulating properties and they are water repellent. They are polymers of linear structure that is their molecules are elongated and are like thread. This, kind of structure is soluble, fusible, highly plastic, able of forming thin flexible threads as well as films. Illustrations are Polytetra Flouroethylene (P.T.F.E. or Teflon) and Polyvinyl Chloride (P.V.C.)

Thermosetting Plastic Materials: They are either softening or originally soft upon heating but harden permanently on more heating and they cannot be resoftened when they have set and hardened.

They undergo huge changes while subjected to high temperatures for rather sometimes. They are called as baked and no longer can melt or be dissolved. They are more brittle, less elastic and lose their elasticity while subjected to prolonged heating. Therefore they cannot be remoulded in various shapes once they are hardened and set. They are used, while insulation is to withstand high temperatures without losing or melting its shape and also mechanical strength. Thermosetting plastic substances are space-polymers and the molecules branch off in different directions throughout polymerisation. Such structure makes them extremely rigid, fusible, poorly soluble, and enable of forming elastic films and threads. Examples are Phenol formaldehyde (i.e. Bakelite), Epoxy resins.