Plastics

A . Plastic is a common name for polymers: materials made of long strings of carbon and other elements. Each unit in a string is called a monomer, and is a chemical derived from oil, coal or natural gas. Monomers are made into polymers by joining the carbon atoms together.

There are many different types of plastic, depending on:

• The starting monomer selected

• The length of the polymer chains

• The type of modifying compounds added

There are two main groups of plastics: thermoplastics soften with heat and harden with cooling, while thermosets are cured or hardened by heat.

The disposal of plastics causes major environmental problems. Efforts to reduce the environmental impact of waste plastics are:•source reduction-using less material to manufacture a product•biodegradable plastics-developing plastics that will disintegrate•Incineration- some plastics can be burned through this is strictly regulated because of hazardous air emissions and other pollutants•recycling plastics-making the plastics into new products•collecting and sorting used plastics

B. Life would be different without plastics, as their features make them indispensable.

A selection of plastic products

ruler

milk bottle

refrigerator linerplastic bag

electric cables

bucketballpoint pen audio cassette

shoes soles water pipes

Features of plastics

attractive

good insulators of heat or electricity

lightweight non-rusting

hard and slippery hygienic

cheapeasy to shape and

colourflexible

soft and rubbery

tough and slippery

C. Plastics are made into shapes in many ways. Here are some of the processes used.

Extrusion-hot molten plastic is squeezed through a nozzle to make long lengths of special shapes like pipes.

Blow extrusion-used for making plastic films and bags.

Injection moulding-lots of everyday articles like washers or bowls are made this way.

Blow moulding-many bottles and toys are made this way.

Reaction injection moulding-used to make car bumpers and the meat trays in supermarkets.

Fabrication-used to make acrylic signs and displays, and industrial thanks and equipment.