When rubber was first commercially produced in Europe during the
nineteenth century, it rapidly became a very important commodity,
particularly in the fields of transportation and electricity. However,
during the twentieth century a number of new synthetic materials, called
plastics, superseded natural rubber in all but a few applications.
Rubber is a polymer—a compound containing large molecules that are
formed by the bonding of many smaller, simpler units, repeated over and
over again. The same bonding principle—polymerization—underlies the
creation of a huge range of plastics by the chemical industry.
The first plastic was developed as a result of a competition in the
USA. In the 1860s, $10,000 was offered to anybody who could replace
ivory—supplies of which were declining—with something equally good as a
material for making billiard balls. The prize was won by John Wesley Hyatt
with a material called celluloid. Celluloid was made by dissolving
cellulose, a carbohydrate derived from plants, in a solution of camphor
dissolved in ethanol. This new material rapidly found uses in the
manufacture of products such as knife handles, detachable collars and
cuffs, spectacle frames and photographic film. Without celluloid, the film
industry could never have got off the ground at the end of the 19th
century.
Celluloid can be repeatedly softened and reshaped by heat, and is
known as a thermoplastic. In 1907, Leo Baekeland, a Belgian chemist working
in the USA, invented a different kind of plastic, by causing phenol and
formaldehyde to react together. Baekeland called the material Bakelite, and
it was the first of the thermosets—plastics that can be cast and moulded
while hot, but cannot be softened by heat and reshaped once they have set.
Bakelite was a good insulator, and was resistant to water, acids and
moderate heat. With these properties it was soon being used in the
manufacture of switches, household items such as knife handles, and
electrical components for cars.
Soon chemists began looking for other small molecules that could be
strung together to make polymers. In the 1930s British chemists discovered
that the gas ethylene would polymerize under heat and pressure to form a
thermoplastic they called polythene. Polypropylene followed in the
1950s. Both were used to make bottles, pipes and plastic bags. A small
change in the starting material—replacing a hydrogen atom in ethylene with
a chlorine atom—produced PVC (polyvinyl chloride), a hard, fireproof
plastic suitable for drains and gutters. And by adding certain chemicals, a
soft form of PVC could be produced, suitable as a substitute for rubber in
items such as waterproof clothing. A closely related plastic was Teflon,
or PTFE (polytetrafluoroethylene). This had a very low coefficient
of friction, making it ideal for bearings, rollers, and non-stick frying
pans. Polystyrene, developed during the 1930s in Germany, was a
clear, glass-like material, used in food containers, domestic appliances
and toys. Expanded polystyrene—a white, rigid foam—was widely used in
packaging and insulation. Polyurethanes, also developed in Germany,
found uses as adhesives, coatings, and—in the form of rigid foams—as
insulation materials. They are all produced from chemicals derived from
crude oil, which contains exactly the same elements—carbon and hydrogen—as
many plastics.
The first of the man-made fibres, nylon, was also created in the
1930s. Its inventor was a chemist called Wallace Carothers, who worked for
the Du Pont company in the USA. He found that under the right conditions,
two chemicals— hexamethylenediamine and adipic acid—would form a polymer
that could be pumped out through holes and then stretched to form long
glossy threads that could be woven like silk. Its first use was to make
parachutes for the US armed forces in World War H. In the post-war years
nylon completely replaced silk in the manufacture of stockings.
Subsequently many other synthetic fibres joined nylon, including Orion,
Acrilan and Terylene. Today most garments are made of a blend of natural
fibres, such as cotton and wool, and man-made fibres that make fabrics
easier to look after.
The great strength of plastic is its indestructibility. However, this
quality is also something of a drawback: beaches all over the world, even
on the remotest islands, are littered with plastic bottles that nothing can
destroy. Nor is it very easy to recycle plastics, as different types of
plastic are often used in the same items and call for different treatments.
Plastics can be made biodegradable by incorporating into their structure a
material such as starch, which is attacked by bacteria and causes the plastic
to fall apart. Other materials can be incorporated that gradually decay in
sunlight—although bottles made of such materials have to be stored in the
dark, to ensure that they do not disintegrate before they have been used.
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