Transcript POLYMERS “Plastics” Third Generation CAPT Science Preparation for Strand II: Chemical Structures and Properties What is a Polymer? Any of numerous natural and synthetic compounds of usually high.

POLYMERS
“Plastics”
Third Generation
CAPT Science Preparation for
Strand II: Chemical Structures and
Properties
What is a Polymer?
Any of numerous natural and synthetic
compounds of usually high molecular
weight consisting of up to millions of
repeated linked units (monomers), each a
relatively light and simple molecule.
Polymerization
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Polymerization is the process of combining
many small molecules known as
monomers into a covalently bonded chain.
Natural Polymers
(Biopolymers)
Examples:
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Cellulose
Shellac
Amber
Proteins
Nucleic Acids
Synthetic Polymers
Examples:
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Nylon
Neoprene
PVC
Polystyrene
Silicone
Silly Putty ®
Some Common Addition Polymers
Name(s)
Formula
Monomer
Properties
Uses
Polyethylene
low density (LDPE)
–(CH2-CH2)n–
ethylene
CH2=CH2
soft, waxy solid
film wrap, plastic bags
Polyethylene
high density (HDPE)
–(CH2-CH2)n–
ethylene
CH2=CH2
rigid, translucent solid
electrical insulation
bottles, toys
Polypropylene
(PP) different grades
–[CH2-CH(CH3)]n–
propylene
CH2=CHCH3
atactic: soft, elastic solid
isotactic: hard, strong solid
similar to LDPE
carpet, upholstery
Poly(vinyl chloride)
(PVC)
–(CH2-CHCl)n–
vinyl chloride
CH2=CHCl
strong rigid solid
pipes, siding, flooring
Poly(vinylidene chloride)
(Saran A)
–(CH2-CCl2)n–
vinylidene chloride
CH2=CCl2
dense, high-melting solid
seat covers, films
Polystyrene
(PS)
–[CH2-CH(C6H5)]n–
styrene
CH2=CHC6H5
hard, rigid, clear solid
soluble in organic solvents
toys, cabinets
packaging (foamed)
Polyacrylonitrile
(PAN, Orlon, Acrilan)
–(CH2-CHCN)n–
acrylonitrile
CH2=CHCN
high-melting solid
soluble in organic solvents
rugs, blankets
clothing
Polytetrafluoroethylene
(PTFE, Teflon)
–(CF2-CF2)n–
tetrafluoroethylene
CF2=CF2
resistant, smooth solid
non-stick surfaces
electrical insulation
Poly(methyl methacrylate)
(PMMA, Lucite, Plexiglas)
–[CH2-C(CH3)CO2CH3]n–
methyl methacrylate
CH2=C(CH3)CO2CH3
hard, transparent solid
lighting covers, signs
skylights
Poly(vinyl acetate)
(PVAc)
–(CH2-CHOCOCH3)n–
vinyl acetate
CH2=CHOCOCH3
soft, sticky solid
latex paints, adhesives
cis-Polyisoprene
natural rubber
–[CH2-CH=C(CH3)-CH2]n–
isoprene
CH2=CH-C(CH3)=CH2
soft, sticky solid
requires vulcanization
for practical use
Polychloroprene (cis + trans)
(Neoprene)
–[CH2-CH=CCl-CH2]n–
chloroprene
CH2=CH-CCl=CH2
tough, rubbery solid
synthetic rubber
oil resistant
Resin Identification Code
Symbol
Abbreviation Polymer Type
PET or PETE
Polyethylene Terephthalate
HDPE
High Density Polyethylene
PVC
Polyvinyl Chloride or Vinyl
LDPE
Low Density Polyethylene
PP
Polypropylene
PS
Polystyrene
Other
Polymers or blends of
polymers that do not fall into
the other 6 classifications.
Properties of Polymers
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Polymers can be very resistant to
chemicals.
Polymers can be both thermal and
electrical insulators.
Generally, polymers are very light
in weight with significant degrees
of strength.
Properties of Polymers cont.
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Polymers can be processed in various
ways.
Polymers are materials with a seemingly
limitless range of characteristics and
colors.
Polymers are usually made of petroleum,
but not always.
Polymers can be used to make items that
have no alternatives from other
materials.
Three factors that influence the degree of
crystallinity (or “stiffness”) are:
• Chain length
• Chain branching
• Interchain bonding
The importance of the first two factors is nicely
illustrated by the differences between HDPE and LDPE.
HDPE vs LDPE
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HDPE is composed of very long
unbranched hydrocarbon chains. These
pack together easily in crystalline domains
that alternate with amorphous segments,
and the resulting material, while relatively
strong and stiff, retains a degree of
flexibility.
In contrast, LDPE is composed of smaller
and more highly branched chains which
do not easily adopt crystalline structures.
This material is therefore softer, weaker,
less dense and more easily deformed than
HDPE. As a rule, mechanical properties
such as ductility, tensile strength, and
hardness rise and eventually level off with
increasing chain length.
Two Plastic Types
Based on Processing
•Thermoplastic Polymers
•Thermosetting Polymers
Thermoplastic Polymers
A Thermoplastic is a polymer in which the molecules are held
together by weak secondary bonding forces that soften when
exposed to heat and return to its original condition when cooled
back down to room temperature. When a thermoplastic is
softened by heat, it can then be shaped by extrusion, molding,
or pressing.
Examples include milk jugs and carbonated soft drink bottles.
Thermoset Polymers
A Thermoset is a polymer that solidifies or “sets”
irreversibly when heated or cured. A thermoset
polymer can’t be softened once “set”. Thermosets are
valued for their durability and strength and are used
extensively in automobiles and construction including
applications such as adhesives, inks, and coatings.
The most common thermoset is the rubber truck and
automobile tire.
The End Life of Polymers
Durables vs. Non-Durables
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Products with a useful life of three years
or more are referred to as durables.
They include appliances, furniture,
consumer electronics, automobiles, and
building and construction materials.
Products with a useful life of less than
three years are generally referred to as
non-durables. Common applications
include packaging, trash bags, cups,
eating utensils, sporting and recreational
equipment, toys, medical devices and
disposable diapers.
What do we do with Polymers
when they are no longer useful?
Three Options
and their consequences
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Disposal
in a landfill
Incinerate
Recycle
Disposal in a landfill
Polymers are fairly resistant to chemicals
and therefore would take a very long time
to decompose if just buried in a landfill.
In the meantime, the waste polymers take
up a lot of space and could possibly
decompose or react with other materials
that might eventually result in compounds
that could be potentially harmful to the
environment.
Incinerate
The burning (combustion) of polymers produces
harmful gases that are toxic to the environment.
Recycle - The best choice!
Mechanical Recycling
 Feedstock Recycling
 Source Reduction
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Mechanical Recycling
Once collected, reclamation is the next step where the
plastics are chopped into flakes, washed to remove
contaminants and sold to end users to manufacture
new products such as bottles, containers, clothing,
carpet, plastic lumber, etc.
Feedstock Recycling
Pyrolysis (heating without oxygen) and other
chemical recycling is a special case where
condensation polymers such as PET or nylon
are chemically reacted to form starting
materials.
Source Reduction Use less!
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Redesign products and packaging that uses less polymer
material.
Reduce the amount the amount of polymer products that are
purchased.
Clean and Reuse the polymer products that have been
purchased.
What is the first question you are asked at
the grocery store checkout: paper or plastic?
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Paper bags can be recycled. Plastic bags are being
recycled in many places, with about 50% of
supermarkets now having recycling programs for
plastic bags.
However, a stack of 1,000 paper bags is 46 inches
high and weigh 140 pounds. A stack of 1,000 plastic
bags is only 4 inches tall and weighs 16 pounds. That
is a 124 pound savings.
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When you translate these weight and volume
differences into transportation efficiencies, it
takes seven trucks to haul the same number of
paper bags as can be hauled by only one truck
carrying plastic ones.