A polymeric solid can be thought of as a material that contains
many chemically bonded parts or units which themselves are bonded
together to form a solid. The word polymer literally means "many
parts." Two industrially important polymeric materials are
plastics and elastomers. Plastics are a large and varied group
of synthetic materials which are processed by forming or molding
into shape. Just as there are many types of metals such as aluminum
and copper, there are many types of plastics, such as polyethylene
and nylon. Elastomers or rubbers can be elastically deformed a
large amount when a force is applied to them and can return to
their original shape (or almost) when the force is released.
Polymers have many properties that make them attractive to use
in certain conditions. Many polymers:
- are less dense than metals or ceramics,
- resist atmospheric and other forms of corrosion,
- offer good compatibility with human tissue, or
- exhibit excellent resistance to the conduction of electrical
polymer plastics can be divided into two classes, thermoplastics
and thermosetting plastics, depending on how they are structurally
and chemically bonded. Thermoplastic polymers comprise the four
most important commodity materials – polyethylene, polypropylene,
polystyrene and polyvinyl chloride. There are also a number of
specialized engineering polymers. The term ‘thermoplastic’
indicates that these materials melt on heating and may be processed
by a variety of molding and extrusion techniques. Alternately,
‘thermosetting’ polymers can not be melted or remelted.
Thermosetting polymers include alkyds, amino and phenolic resins,
epoxies, polyurethanes, and unsaturated polyesters.
Rubber is a natural occurring polymer. However, most polymers
are created by engineering the combination of hydrogen and carbon
atoms and the arrangement of the chains they form. The polymer
molecule is a long chain of covalent-bonded atoms and secondary
bonds then hold groups of polymer chains together to form the
polymeric material. Polymers are primarily produced from petroleum
or natural gas raw products but the use of organic substances
is growing. The super-material known as Kevlar is a man-made polymer.
Kevlar is used in bullet-proof vests, strong/lightweight frames,
and underwater cables that are 20 times stronger than steel.