The Worlds of Plastics

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CHAPTER 9 The Worlds of Plastics
In order to have a better understanding of the
topics discussed in these notes, you may want to
read the related chapters from the book. In the
exams you are responsible only sections of the
book which are discussed in the lecture notes.
This information and advice is valid for all
chapters
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Fig.09.02
a) Representation of three types of monomers
b) Representation of polymer formed from one type
of monomers
c) Representation of polymer formed from two
types of monomers
Polymers are large molecules made up of long
chains of monomers (smallest same unit).
Polymers can also be referred as macromolecules,
since they contain thousands of atoms.
Synthetic polymers are often referred to by the
word PLASTIC, which means capable
of being molded. Natural polymers are found i
n animals and plants wood, wool, cotton, starch,
skin, hair.
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6
You are expected to know the structures of
monomers and polymers made of those structures,
including teflon (see slide 6) exception PET
(next slide last polymer)
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Fig.09.01b
All the polymers listed in this table are also
characterized as thermoplastic, which
means they can be melted and shaped, and all tend
to be flexible. Plasticizers are often
added to improve the flexibility of the
polymers, which also enhances performance.
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Fig.09.02
Functional groups are distinctive arrangements of
groups of atoms that import characteristics phys
ical and chemical properties to the molecules
that contain them.
Common functional groups in chemistry
alcohol
acid
Anti-cancer drug
You are expected to know the structures and names
of functional groups presented.
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Addition polymerization adding same unit over
and over again to form the polymer
From the same monomer of PVC, you may have PVC
with 3 different properties, since there are 3
different ways of the orientation of the monomer
Head-to-tail, head-to-head, and random. This is
the reason having PVC for stiff polymers such as
credit cards, toys as well as for flexible
polymers such as shower curtain, electrical
wiring.
Both the jewel CD cases and Styrofoam coffee
cups are chemically identical, only difference is
cups are made by expansion molding using CO2 to
make bubbles
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Fig.09.06
A plastic bag can be stretched until it necks.
Dispersion forces causes to hold
of molecules together. Necking is unlike rubber
band non reversible. Dispersion forces
are intermolecular forces between large polymer
molecules. Longer the each polymer
unit more stretchy and stronger the product out
of that polymer will be, since longer
the polymer molecule more dispersion forces
between the polymer units.
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One way of controlling the physical properties of
the polymer is to regulate the branching of the
polymer chain. This approach produces two types
of PE (polyethylene) HDPE (high density PE) and
LDPE (low density PE) LDPE is branched polymer
, usually consist of 500 monomer per polymer
unit, is soft, stretchy, transparent and not very
strong. Modifying the extent and the location of
branching in LDPE causes different physical
properties too. Common uses plastic grocery
bags, stretch plastic wrap. Has lower melting
point than HDPE, which makes unsafe for
dishwashers.
HDPE is linear polymer, usually
consist of 10000 monomer per polymer unit, is ri
gid, dense, opaque, and strong. Having high melt
ing point makes them good use for dishwashers.
Common uses toys, pipes, containers,
electrical insulator.
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H2O

ester group
alcohol
acid
Addition of monomers
Condensation polymerization more than one
monomer units joined together by eliminating a
small molecule, often water. Each time ethylene
glycol (dialcohol) and tetraphthalic acid reacts,
a water (H2O) molecule is given out and O-CO
(ester) functional group forms between acid and
alcohol. That is why polyethylene terephthlate
(PET) is classified as polyester. Common uses
clothing, soft-drink bottles, video tapes,
artificial heart parts, medical supplies.
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Proteins, which make up our skin, hair, muscle,
and silk, are macromolecules and
polymers of amino acids. An amino acid molecule
contains an amine group (NH2),
an acid group (HO-CO). There are 20 naturally
occurring amino acids which are
differing in the R position shown on the
structure on the left. Amino acids are the
monomers of the proteins. Analogous to polyester
formation, NH2 reacts with HO-CO to form amide
linkage, also called peptide bond. The reaction
shown below can be repeated many times using 20
amino acids in different order to make different
proteins. The order of the amino acids in a
protein is stored in DNA as a code.
In 1930, Nylon, a synthetic polymer similar to
proteins (contains amide linkage) is formed from
polymerization of adipic acid and
hexamethyleneadiamine. Nylon was introduced as a
substitute for silk in stockings, since it is
superior in strength, stability, and resistance.
Today it is used in clothing, kitchen and camping
equipment and more.
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A newspaper after staying 37 years in landfill
Relative volumes of 1000 plastic bags vs paper b
ags
Composition of municipal solid waste
The source of the monomers used for the synthesis
of polymers are derived from oil.
So we can basically say polymers (plastics) are
coming from oil, which creates
dependence on oil again different than energy.
56 of waste into landfills, 30 recycled, 14 i
ncinerated. 100 billion pounds of plastic produce
d in US yearly. 5 strategies for reducing the
reliance on landfills 1) incineration 2) biodeg
radation, 3) reuse, 4) recycle, 5)source
reduction.
Listen following radio links
Paper or plastic http//www.npr.org/templates/sto
ry/story.php?storyId11954271 http//www.npr.org/
templates/story/story.php?storyId4615730
How much green? http//www.npr.org/templates/story
/story.php?storyId11756093
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1) Incineration Since polymers are mostly
carbons and hydrogen, burning them is an excelle
nt way to dispose plastics. According to a
German study, incineration is less damaging to
environment than any other disposal method. Inci
neration can decrease the volume of plastics
headed to landfills by 90 and will produce
energy too. Drawbacks produce of CO2 (global war
ming gas) and other chemicals
added into plastics which may become toxic with
burning. If carefully controlled, incineration o
f plastics will generate energy, reduce the
plastic waste and have little impact on
environment. 2) Biodegradation Letting bacteri
a degrade the polymers. Problem is
bacteria and fungi is lack of chemicals to break
down plastics. Even tough they can decompose natu
ral polymers that is also difficult sometimes,
since landfills are lack of oxygen, which is not
a good environment for bacteria and fungi to liv
e around. Chemist came up with new polymers
which are biodegradable, which has sites
susceptible to bacterial digestion. But still mu
ch to be done before these become widely used,
such impact to environment.
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3) Reuse is another way to divert plastic from
landfill. But not every plastic is reusable. Som
e bottles can be reused after cleaning them.
80 of Americans reuse their plastic products,
such food storage containers and refillable bott
les. 50 of plastic car parts reused in US.
Germany requires to design and built all the cars
so plastic parts of cars should be able to reuse
d when the car has to be discarded. 11 of the
cars are plastic, which makes a lot of sense to
try to reuse them if possible.
4) Recycle It helps to reduce the amount of new
plastic entering to waste. However, recycling,
in contrast to incineration, requires input of
energy. If the plastic is dirty, or low quality
it requires more energy to recycle than to make
a new plastic. 23 of all plastics in US is
recycled, which is far behind other developed cou
ntries. Recycled milk and water
jugs are transformed to Tyvek, a material used in
clothing, insulating wrap. PET plastics are easi
est to recycle and US recycles only less than
20 of those type plastics. Recycled PET can be
converted into polyester Fabrics, including fleec
e, carpets, t-shirts. Five 2-L bottles can be
converted into a T-shirt.
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5) Source reduction using less material in the
first will generate less waste, which is the sim
plest and the most direct way. Advantages are
many resources will be conserved pollution will
be reduced, toxic materials will be minimized. O
ne way is to reduce the amount of
polymer used per product by technology, such as
2-L soda bottle now Uses 25 less plastic than 2
0 years ago and 1gal milk jug weighs 30
less than a decade ago. Other way of source
reduction is substituting plastic with other sou
rces. This option is more complicated than it
sounds. Some substitutions may increase the
negative environmental impact rather than decrea
sing. Eg. 2 lb plastic is enough to hold 8 gal of
juice, however 3 lb aluminum, 8 lb of steel, or
27 of glasses is needed for the same job. But re
placing plastic grocery bags with reusable
plastic bags will reduce the waste generation.
Is paper cup a environmentally better
alternative to Styrofoam cup?
Listen the radio link placed in the following page
http//www.npr.org/templates/story/story.php?story
Id5027659
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Fig.09.03