18 November 2009

Polystyrene


The invention: A clear, moldable polymer with many industrial
uses whose overuse has also threatened the environment.
The people behind the invention:
Edward Simon, an American chemist
Charles Gerhardt (1816-1856), a French chemist
Marcellin Pierre Berthelot (1827-1907), a French chemist
Polystyrene Is Characterized
In the late eighteenth century, a scientist by the name of Casper
Neuman described the isolation of a chemical called “storax” from a
balsam tree that grew in Asia Minor. This isolation led to the first report
on the physical properties of the substance later known as “styrene.”
The work of Neuman was confirmed and expanded upon
years later, first in 1839 by Edward Simon, who evaluated the temperature
dependence of styrene, and later by Charles Gerhardt,
who proposed its molecular formula. The work of these two men
sparked an interest in styrene and its derivatives.
Polystyrene belongs to a special class of molecules known as
polymers.Apolymer (the name means “many parts”) is a giant molecule
formed by combining small molecular units, called “monomers.”
This combination results in a macromolecule whose physical
properties—especially its strength and flexibility—are significantly
different fromthose of its monomer components. Such polymers are
often simply called “plastics.”
Polystyrene has become an important material in modern society
because it exhibits a variety of physical characteristics that can be
manipulated for the production of consumer products. Polystyrene
is a “thermoplastic,” which means that it can be softened by heat
and then reformed, after which it can be cooled to form a durable
and resilient product.
At 94 degrees Celsius, polystyrene softens; at room temperature,
however, it rings like a metal when struck. Because of the glasslike
nature and high refractive index of polystyrene, products made from it are known for their shine and attractive texture. In addition,
the material is characterized by a high level of water resistance and
by electrical insulating qualities. It is also flammable, can by dissolved
or softened by many solvents, and is sensitive to light. These
qualities make polystyrene a valuable material in the manufacture
of consumer products.
Plastics on the Market
In 1866, Marcellin Pierre Berthelot prepared styrene from ethylene
and benzene mixtures in a heated reaction flask. This was the
first synthetic preparation of polystyrene. In 1925, the Naugatuck
Chemical Company began to operate the first commercial styrene/
polystyrene manufacturing plant. In the 1930’s, the Dow Chemical
Company became involved in the manufacturing and marketing of
styrene/polystyrene products. Dow’s Styron 666 was first marketed
as a general-purpose polystyrene in 1938. This material was
the first plastic product to demonstrate polystyrene’s excellent mechanical
properties and ease of fabrication.
The advent ofWorldWar II increased the need for plastics. When
the Allies’ supply of natural rubber was interrupted, chemists sought
to develop synthetic substitutes. The use of additives with polymer
species was found to alter some of the physical properties of those
species. Adding substances called “elastomers” during the polymerization
process was shown to give a rubberlike quality to a normally
brittle species. An example of this is Dow’s Styron 475, which
was marketed in 1948 as the first “impact” polystyrene. It is called
an impact polystyrene because it also contains butadiene, which increases
the product’s resistance to breakage. The continued characterization
of polystyrene products has led to the development of a
worldwide industry that fills a wide range of consumer needs.
Following World War II, the plastics industry revolutionized
many aspects of modern society. Polystyrene is only one of the
many plastics involved in this process, but it has found its way into
a multitude of consumer products. Disposable kitchen utensils,
trays and packages, cups, videocassettes, insulating foams, egg cartons,
food wrappings, paints, and appliance parts are only a few of
the typical applications of polystyrenes. In fact, the production of polystyrene has grown to exceed 5 billion pounds per year.
The tremendous growth of this industry in the postwar era has
been fueled by a variety of factors. Having studied the physical
and chemical properties of polystyrene, chemists and engineers
were able to envision particular uses and to tailor the manufacture
of the product to fit those uses precisely. Because of its low cost of
production, superior performance, and light weight, polystyrene
has become the material of choice for the packaging industry. The
automobile industry also enjoys its benefits. Polystyrene’s lower
density compared to those of glass and steel makes it appropriate
for use in automobiles, since its light weight means that using
it can reduce the weight of automobiles, thereby increasing gas
efficiency.
Impact
There is no doubt that the marketing of polystyrene has greatly
affected almost every aspect of modern society. Fromcomputer keyboards
to food packaging, the use of polystyrene has had a powerful
impact on both the quality and the prices of products. Its use is not,
however, without drawbacks; it has also presented humankind
with a dilemma. The wholesale use of polystyrene has created an
environmental problem that represents a danger to wildlife, adds to
roadside pollution, and greatly contributes to the volume of solid
waste in landfills.
Polystyrene has become a household commodity because it lasts.
The reciprocal effect of this fact is that it may last forever. Unlike natural
products, which decompose upon burial, polystyrene is very
difficult to convert into degradable forms. The newest challenge facing
engineers and chemists is to provide for the safe and efficient
disposal of plastic products. Thermoplastics such as polystyrene
can be melted down and remolded into new products, which makes
recycling and reuse of polystyrene a viable option, but this option
requires the cooperation of the same consumers who have benefited
from the production of polystyrene products.

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marinacurtis17 said...

great share, Polystyrene is the amazing product developed so far. Without polystyrene we cannot think about our growth which we get now with the use of this product. polystyrene blocks and sheets are the best example of polystyrene daily use.

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