What is plastic ?
Plastics are macromolecules, which are formed by the polymerization of simple molecules.
In other words we can say that plastic are the polymers formed from monomers. The phenomenon in which simple and smaller molecules are combined together to form complex and large molecules, is called polymerization. The simple and smaller molecules are called monomers and the large and complex molecules are called polymers.
Types of Plastic:
There are the following two types of plastics.
- Thermo Plastic.
- Thermosetting Plastic
1. Thermo Plastic:
Thermo plastic is also known as Thermo-softening plastic. This type of plastic is manufactured by heating, softening melding and cooling the raw materials, this process can be repeated and it does not effect the properties of plastic.
2. Thermosetting Plastic:
Thermosetting plastics are those materials, which cannot be heated, only once before they set, i.e. they cannot be reworked.
Examples of Plastic:
1. Polyethene (Polythene):
In presence of traces of oxygen, when ethene is heated at 200ºC, under 100 atm pressure then polymerization takes place. As a result, polyethene is formed, which is commonly known as polythene. It is the type of addition reaction is one in which two or more molecules join together to give a single product.
Polythene is the most common plastic used to form polythene bags and to package food.
2. Poly Vinyl Chloride (PVC) :
PVC or Poly Vinyl Chloride is the polymer of vinyl chloride. When vinyl chloride is heated at 80ºC in the presence of catalyst hydrogen peroxide, then polymerization takes place. As a result, Poly Vinyl Chloride is formed.
PVC is used for insulating covering for electrical cables, for the manufacture of gramophone, records, suitcase covering etc.
3. Poly Vinyl Acetate (PVA) :
Poly Vinyl Acetate (PVA) is the polymer of vinyl acetate.
PVA is used in the manufacture of chewing gums and in the water proofing of textiles. It is colorless, non-toxic resin. The resin has characteristic odour. It is mostly used as an adhesive material and as a binder for emulsion paints.
Bakelite is a polymer of phenol and formaldehyde. Phenol reacts with formaldehyde (methanol) in the presence of acid or alkali to give hydroxyl benzyl alcohol which on further reaction with other phenol molecules yields a polymer called Bakelite.
Bakelite is used to make buttons, switches, electrical boards, camera, radio, telephone etc.