The word plastics come from the Greek word Plastikos which means ‘to shape’ or ‘able to be moulded’. All plastics are man-made polymers containing repeat units of the same group called monomer. The process by which plastics are made is called polymerization. The starting materials from which plastics are made are obtained from natural gas and crude oil.
The first plastic was made in the 19th century, by a German scientist Friedrik Schonbein. He accidentally produced a highly combustible substance — nitrocellulose by reacting cotton with nitric acid. Since then several others have been made; among them are polythene, polystyrene, polyvinyl chloride (PVC), polypropylene, polyurethane, nylon and polyester. All these plastics have different monomeric units with specific characteristics.
Plastics can be divided into two major groups— thermosetting and thermoplastics— depending upon the way they behave when heated. Thermoplastics such as nylon and polyethylene become soft when heated and harden on cooling and hence can be recycled many times. But thermosetting plastics such as bakelite cannot he softened or melted once they are set.