Plastics are used to make a wide range of materials,
including furniture, computers, and toys. Plastics are not found in nature, but
are created from the products of coal, oil, and natural gas. They are made up
of carbon, hydrogen, and other atoms linked in long-chained molecules
called POLYMERS. Plastics are so useful because they are strong,
light and can withstand heat and chemicals better than many materials. They can
also be moulded into practically any shape or size.
Modern plastics can be created with precise properties that suit a
particular use. Mylar® is a plastic used to insulate space shuttles. It
is a shiny, strong, and light polyester film made in very thin sheets. It
reflects the intense heat generated when a space shuttle re-enters
Earth’s atmosphere, protecting the craft and its crew.
Plastic bowls are often shaped by injection moulding. Plastic
pellets are heated until they have melted. The liquid plastic is then pushed,
or injected, into a mould, held in place by a clamp. After the plastic in the
mould has cooled and hardened, the finished product is pushed out. This process
is used to mass-produce items such as bowls, butter tubs, and yoghurt pots.
Polyvinylchloride, or PVC for short, is the plastic used to make
credit cards and waterproof clothes. It is tough, flexible, cheap to produce,
and easy to print on.
There are two types of polythene. Low-density polythene is used to
make lightweight plastic bags. High-density polythene is stronger and is used
to make plastic milk bottles.
Polystyrene can be either rigid or foamed. Rigid polystyrene is
used to make toys and containers. Foamed polystyrene is used for fast food
packaging.
Polyethylene terephthalate, more commonly called PET, is a strong
plastic used to make fizzy drinks bottles. It can be recycled into carpets and
ribbons for video cassettes.
Polypropylene, or PP, is a plastic with a relatively high melting
point of 160°C (320°F). It is used to make camera film and
dishwasher-proof plastic objects.
Polyamide, or PA for short, is the plastic used to package oily
food such as cheese and meats. It is also known as nylon, and is used in
clothing, ropes, carpets, and bristles for brushes.
All plastics are synthetic polymers. Polymers are
substances whose molecules are made of simpler molecules called monomers joined
together in long, winding chains. The monomers contain carbon and hydrogen, and
sometimes other elements such as oxygen and nitrogen. Synthetic polymers can be
divided into two groups, thermoplastics and thermosets.
