Plastics

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Plastics
The origin of the word "plastics" comes from
Greek. Its original Greek root means "to form."
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Plastics are polymers.

• What is a polymer?

Polymer is something made of many units. Think of
a polymer as a chain. Each link of the chain is
the "mer" or basic unit that is made of carbon,
hydrogen, oxygen, and/or silicon.
To make the chain, many links or "mers" are
hooked or polymerized together.
Polymerization can be demonstrated by linking
strips of construction paper together to make
paper garlands or hooking together hundreds of
paper clips to form chains.
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Polymers

• Tiny molecules strung in long repeating chains
  form polymers.

A very good website for information
is http//www.teachingplastics.org/hands_on_plast
ics/intro_to_plastics/teachers.html
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Why should you care?

• Well for one thing, your body is made of them.
  DNA, the genetic blueprint that defines people
  and other living things, is a polymer.

So are the proteins and starches in the foods we
eat, the wheels on our skateboards and in-line
skates, and the tires on our bikes and cars.
In fact, we are surrounded by polymers every day,
everywhere we go.
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Monomer vs. polymer
Propylene monomer
Polypropylene A polymer
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History of Polymers
Polymers have been with us since the beginning of
time. Natural polymers include such things as
tar and shellac, tortoise shell and horns, as
well as tree saps that produce amber and latex.
These polymers were processed with heat and
pressure into useful articles like hair ornaments
and jewelry.
Natural polymers began to be chemically modified
during the 1800s to produce many materials. The
most famous of these were vulcanized rubber, gun
cotton, and celluloid.
The first synthetic polymer produced was Bakelite
in 1909 and was soon followed by the first
semi-synthetic fiber, rayon, which was developed
in 1911.
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Characteristics of Polymers
Polymers can be very resistant to chemicals.
Consider all the cleaning fluids in your home
that are packaged in plastic. Many of these
chemicals are very corrosive and abrasive agents.
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Characteristics of Polymers
Polymers can be both thermal and electrical
insulators. Consider all the appliances, cords,
electrical outlets, and general wiring that are
made of or covered with polymeric materials.
Thermal resistance is evident in the kitchen
with pot and pan handles made of polymers, with
the foam core of refrigerators and freezers, and
with insulated cups, coolers, and microwave
cookware.
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Characteristics of Polymers
Generally, polymers are very light in mass with
varying degrees of strength. Consider the range
of applications from a dime store toy to the
frame structure of space stations, or from
delicate nylon fiber used to make pantyhose to
Kevlar, which is used in bulletproof vests.
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Characteristics of Polymers
Polymers can be processed in various ways to
produce thin fibers or very intricate parts.
Plastics can be molded into bottles or the body
of a car, or can be mixed with solvents to become
an adhesive or paint. Elastomers and some
plastics stretch and are very flexible. Other
polymers can be foamed, like polystyrene
(Styrofoam) and urethane, to give just two
examples.
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Intermolecular forces
The attractive forces between polymer chains
play a large part in determining a polymer's
properties. These inter-chain forces are
amplified far beyond the attractions between
conventional molecules. Also, longer chains are
more amorphous (randomly oriented). Polymers can
be visualised as tangled spaghetti chains -
pulling any one spaghetti strand out is a lot
harder the more tangled the chains are. These
stronger forces typically result in high tensile
strength and melting points. The intermolecular
forces in polymers are determined by dipoles in
the monomer units. Polymers containing amide
groups can form hydrogen bonds between adjacent
chains the positive hydrogen atoms in N-H groups
of one chain are strongly attracted to the oxygen
atoms in CO groups on another. These strong
hydrogen bonds result in, for example, the high
tensile strength and melting point of kevlar.
Polyesters have dipole-dipole bonding between the
oxygen atoms in CO groups and the hydrogen atoms
in H-C groups. Dipole bonding is not as strong as
hydrogen bonding, so ethene's melting point and
strength are lower than kevlar's, but polyesters
have greater flexibility. Ethene, however, has
no permanent dipole. The attractive forces
between polyethene chains arise from weak van der
Waals forces. Molecules can be thought of as
being surrounded by a cloud of negative
electrons. As two polymer chains approach, their
electron clouds repel one another. This has the
effect of lowering the electron density on one
side of a polymer chain, creating a slight
positive dipole on this side. This charge is
enough to actually attract the second polymer
chain. Van der Waals forces are quite weak,
however, so polyethene melts at low temperature.
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Polymers
Polymers are materials with a seemingly limitless
range of possible characteristics, and colors.
Polymers have many inherent properties that can
be enhanced by a wide range of additives to
broaden their use and application. The ability to
design or engineer the polymer for each specific
application makes plastics unique among basic
material types.