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POLYMERS “Plastics”
D14 - Describe combustion reactions of hydrocarbons and their resulting by-products.
D15 - Explain the general formation and structure of carbon-based polymers, including synthetic polymers, such as polyethylene, and biopolymers, such as carbohydrate.
D17 - Explain how the chemical structure of polymers affects their physical properties.
D14, D15, D17
Any of numerous natural and synthetic compounds consisting of up to millions of repeated linked simple Carbon based molecule called monomers.
What is a Polymer?
Monomers are simple carbon molecules Polymerization is the process of combining
many small molecules known as monomers into a covalently bonded chain.
Polymerization
Natural Polymers(Biopolymers)
Examples:Cellulose Shellac Amber Proteins Nucleic Acids Hair and Fur
Synthetic Polymers
Examples:NylonNeoprenePVCPolystyreneSiliconeSilly Putty ® Plastics
Some Common PolymersName(s) Formula Monomer Properties Uses
Polyethylenelow density (LDPE) –(CH2-CH2)n–
ethyleneCH2=CH2
soft, waxy solid film wrap, plastic bags
Polyethylenehigh density (HDPE) –(CH2-CH2)n–
ethyleneCH2=CH2
rigid, translucent solid electrical insulationbottles, toys
Polypropylene(PP) different grades –[CH2-CH(CH3)]n–
propyleneCH2=CHCH3
atactic: soft, elastic solidisotactic: hard, strong solid
similar to LDPEcarpet, upholstery
Poly(vinyl chloride)(PVC) –(CH2-CHCl)n–
vinyl chlorideCH2=CHCl strong rigid solid pipes, siding, flooring
Poly(vinylidene chloride)(Saran A) –(CH2-CCl2)n–
vinylidene chlorideCH2=CCl2
dense, high-melting solid seat covers, films
Polystyrene(PS) –[CH2-CH(C6H5)]n–
styreneCH2=CHC6H5
hard, rigid, clear solidsoluble in organic solvents
toys, cabinetspackaging (foamed)
Polyacrylonitrile(PAN, Orlon, Acrilan) –(CH2-CHCN)n–
acrylonitrileCH2=CHCN
high-melting solidsoluble in organic solvents
rugs, blanketsclothing
Polytetrafluoroethylene(PTFE, Teflon) –(CF2-CF2)n–
tetrafluoroethyleneCF2=CF2
resistant, smooth solid non-stick surfaceselectrical insulation
Poly(methyl methacrylate)(PMMA, Lucite, Plexiglas) –[CH2-C(CH3)CO2CH3]n–
methyl methacrylateCH2=C(CH3)CO2CH3
hard, transparent solid lighting covers, signsskylights
Poly(vinyl acetate)(PVAc) –(CH2-CHOCOCH3)n–
vinyl acetateCH2=CHOCOCH3
soft, sticky solid latex paints, adhesives
cis-Polyisoprenenatural rubber –[CH2-CH=C(CH3)-CH2]n–
isopreneCH2=CH-C(CH3)=CH2
soft, sticky solid requires vulcanizationfor practical use
Polychloroprene (cis + trans)(Neoprene)
–[CH2-CH=CCl-CH2]n–chloropreneCH2=CH-CCl=CH2
tough, rubbery solid synthetic rubberoil resistant
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.
Resin Identification Code
Properties of Polymers (6) Polymers can be very resistant to
chemicals that can break down other materials.
Polymers can be both thermal and electrical insulators.
Generally, polymers are very light in weight with significant degrees of strength.
Properties of Polymers cont.
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 cannot be made from other materials.
1. Chain length2. Chain branching3. Inter-chain
bonding (cross-links)
The three factors that influence the degree of stiffness of a plastic are:
As a rule, mechanical properties such as ductility, tensile strength, and hardness rise and eventually level off with increasing chain length.
The importance of the first two factors is nicely illustrated by the differences between HDPE and LDPE.
HDPE vs LDPE High Density Polyethylene
(HDPE) is composed of very long unbranched hydrocarbon chains.
These materials, while being relatively strong and stiff, retain a degree of flexibility.
Low Density Polyethylene (LDPE) is composed of smaller and more highly branched chains.
This material is therefore softer, weaker, less dense and more easily deformed than HDPE.
Linear vs. Branched
•Thermoplastic Polymers
•Thermoset Polymers
There are two Plastic Types
Thermoplastic PolymersA Thermoplastic is a polymer in which the molecules
are held together by weak forces.
These 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.
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 durable and strong
They are used extensively in automobiles and construction including applications such as adhesives, inks, and coatings.
The most common thermoset is a rubber tire
Thermoset Polymers
Recycling Thermoplastics vs. Thermosets
Thermoplastic: these are polymers that can be repeatedly softened or melted by heatingThese can be recycled by heating and reforming.
Thermoset: cross-linked polymers that do NOT soften when heated because strands are not free to move.More cross-links = greater strengthThese are not easy to recycle and can only be cut or chopped into smaller pieces
Thermoset: Vulcanized Rubber used to make strong tires
Thermoplastics Remember the
analogy to a plate of cooked spaghetti
http://farm1.static.flickr.com/203/496621094_3db122a493_o.jpg
What happens when we are done using a polymer product??
Durables vs. Non-Durables 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
1. Disposal in a landfill
2. Incineration3. Recycling
ACTION: Polymers take a very long time to decompose if just buried in a landfill.
CONSEQUENCE: Polymers placed in a landfill take up a lot of space and could possibly react with other materials to result in compounds that could be potentially harmful to the environment.
Disposal in a landfill
IncinerationACTION: Incineration is the burning
(combustion) of polymers.
CONSEQUENCE: Incineration produces harmful gases that are toxic to the environment.
The Chemical Reaction for CombustionHydrocarbon + O2 CO2 + H2O
The complete combustion of hydrocarbons results in two products – Carbon dioxide and water.
Why is incineration dangerous?
Complete combustion results in the release of CO2, which is a greenhouse gas
Incomplete combustion occurs if oxygen is in insufficient supply. This results in the release of CO (carbon monoxide) which is dangerous for organisms.
Products of Incineration
ACTION: Recycling is a process during which waste materials are re-used in different ways to form new products.
CONSEQUENCE: Recycling prevents waste of potentially useful materials, and reduces the consumption of fresh raw materials.
Recycling
Recycle - The best choice!
Mechanical RecyclingFeedstock RecyclingSource Reduction
Mechanical RecyclingOnce collected, plastics are sorted and then
chopped into flakes, washed to remove contaminants and sold to manufacturers to make new products.
Feedstock RecyclingThis is where the plastics are chemically reacted to form
new substances that are used for another purpose than producing the original material.
One way in which is this done is through Pyrolysis (heating without oxygen) . This process changes polymers such as PET or nylon into new starting materials.
Source Reduction Use less materials! 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?
What is the best choice?
