Transcript Polyethylene

Polyethylene
27 April 2001
Jamila Richardson
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Starting Up
 Polyethylene was first produced by British company
Imperial Chemical Industries. Preparation required
temperatures up to 200 deg C and pressures up to
2000atm.
 Karl Ziegler prepared a high molecular weight
polyethylene at room temperature in 1952 while working
at Dacron Industries.
 ICI polyethylene had shorter, branched chains, and was
waxy and easily deformed. Ziegler’s puppy was had and
rigid, and could easily be easily drawn into fibers.
 Giulio Natta extended Ziegler’s research, eventually
showing how the geometry of polyethylene could be
controlled
by certain catalysts
(produced by Ziegler).
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Ethylene, the interesting
molecule
 Ethylene, because of its double bond, is more
reactive than ethane. Double bonded carbons
make molecule more susceptible to bonding with
other molecules.
 When approached by another molecule, the
double bond splits; the carbons are joined by a
single bond, leaving the the molecule free to
bond with both carbons.
 Ethylene is used in the ripening of fruit; it
stimulates the metabolic processes of the fruit by
dissolving into the cell membrane, therefore
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increasing its permeability
Formation and Structure
 Ethylene-Ethylene
bond yields
polyethylene
(CH2CH2)n
polyethylene
 Crystalline regions lie
in alternating fashion
with amorphous
regions, which creates
scattering of light
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Pure
polyethylene, low-
and high-density
polyethylene
(LDPE, HDPE)
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High-Density Polyethylene
 Absence of branching results in a more closely
packed structure, more crystalline, higher density,
and chemical resistance slightly higher than that
of LDPE.
 Resists alcohols, acids, bases, esters, and
aldehydes
 Specific Gravity: 0.94 to 0.97
 Melting point 130 to 135 deg C
 Carbon chains can are 10,000 to 100,000 carbon
atoms long
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
Translucent
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Low-density Polyethylene
(LDPE)
 Small amount of branching on the chain gives a
more open structure
 Melting point of 109 to 125 deg C
 Does not react at room temperature
 Resists alcohols, esters, acids, and bases.
Limited resistance to aldehydes.
 Translucent to opaque
 Used for plastic food or garment bags, spray
bottles, plastic lids.
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Pure Polyethylene
 Low density arises from minimal amount of
branching in chain, gives a more open structure.
 Translucent to opaque
 Resists acids, bases, esters, alcohols,
hydrocarbons. Limited resistance to aldehydes.
 Does not react at room temperature
 Translucent to opaque.
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Properties
 Poylethylene is a solvent
for fats, oils, and grease.
Dissolving occurs slowly.
 Electrons are tightly
trapped in their C-C and
C-H bonds, which results
in an inability of electrical
current to flow.
 Also results in inability
for water and ions to
penetrate interior of solid.
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Thin film of polyethylene photographed
using polarized light. The pattern arises
form the presence of spherulites, or
regions where the polymer molecules
have aggregated into spheres.
Picture and caption from Molecules
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Other (Fun) Facts
 Polyethylene is a
thermoplastic. That is, it
becomes soft and
malleable when heated,
and hard and solid when
cooled. (So, basically, it’s a plastic. Wow.)
 Polyethylene is an
addition polymer. The
double bonds allow for
splitting and bonding with
other molecules.
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R-E-C-Y-C-L-E, Recycle. . .
 Polyethylene does not
biodegrate unless first
oxidized.
 Polyeofins are highly
susceptible to
photooxidation, or
oxidation caused by the
exposure to light.
Hindered-amine light
stabilizers are then used
to prevent
photooxidation.
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Polyethylene film, which is widely used for
packaging, is formed by extruding the molten
plastic through a ring-like gap and inflating it like a
balloon.
Photo and caption from Molecules
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Well, that’s it.
I hope you enjoyed my presentation.
BYE!
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