Plastic
Plastics are synthetic resins which are rapidly becoming important in everyday life. These are classified into two types:Thermoplastics
Thermosetting plastics
Thermoplastics
These
are the plastics which can easily be softened when heated and become
hard when cooled with a little change in their properties. When heated
they melt and form a fluid which can be moulded into any desired shape
and then cooled to get the desired product. Common examples are
polythene, polypropylene, polyvinyl chloride etc.
Thermosetting Plastics
These
are the plastics which undergo permanent change on heating. When heated
they get highly cross linked to form hard, infusible products. Common
examples are bakelite, melamine etc.
Methods of preparation and uses of plastics
Polythene
It is prepared by the polymerization of ethjfrie under high pressure and in the presence of traces of oxygen (0.01 %)
nCH2 = CH2 ► —{-H2C— CH2)t-
It is used in the manufacture of pipes, laboratory apparatus, bottles, buckets, toys and electrical insulators.
Polyvinyl chloride (PVC)
It is prepared by the polymerization of vinyl chloride (CH2=CHCI) in an autoclave
PVC is used:
in the manufacture of rain coats and hand bags.
for artificial flooring.
as a good insulating material for wires and other electrical goods.
Polystyrene
It
is prepared by the polymerization of styrene in the presence of benzoyl
neroxide. It is resistant to shock and chemical action.
It is used for:
making hot drink cups, toys, combs, etc.
making radio and television bodies.
Making tiles to be used in covering ceilings and floors.
Teflon (Polytetrafluoroethylene)
It is prepared by the polyemerization oftetrafluoroethylene.
Pressure
It is used in the manufacture of non-stick utensils.
Bakelite
It is prepared by the polymerization of phenol and formaldehyde.
It is used for making combs, fountain pens, formica, tabletops and electrical goods.
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