baiscs of polymers
TRANSCRIPT
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Basics of PolymersBasics of Polymers
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Solid Materials
e a s eram cso ymer
ThermoplasticsThermo -settings Elastomers
Commodity Engineering Specialty
Amor hous Semi- Cr stallineCr stalline
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ADVANTAGES OF PLASTICS
Fire retardant
suit the needsGood strength/weight ratio
Do not rust/corrode.Resistant to microbes
Tough & durable
Non toxic
Attractive colours
Good weatherabilityEasy Processability
Chemical/Moisture Resistant
Practically maintenance free
Reusable / Recyclable
At Much Cheaper Price !!!
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POLYMERS: INTRODUCTION
Pol mer: Hi h molecular wei ht molecule made u of a
small repeat unit (monomer). A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A
Monomer: Low molecular weight compound that can beconnected together to give a polymer
Copolymer: polymer made up of 2 or more monomers
Random co ol mer: A-B-B-A-A-B-A-B-A-B-B-B-A-A-B Alternating copolymer: A-B-A-B-A-B-A-B-A-B-A-B-A-B Block copolymer: A-A-A-A-A-A-A-A-B-B-B-B-B-B-B-B
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COMMON POLYOLEFINSMonomer Polymer
EthyleneH
3C 3
n Repeat unitPolyethylene
CH 33
n
CH3 CH3 CH3 CH3 CH3 CH 3CH 3
Propylene
Polypropylene
PhCH3
n
Ph Ph Ph Ph Ph PhPhStyrene
Polystyrene
ClCH3
n
Cl Cl Cl Cl Cl ClClVinyl Chloride
Poly(vinyl chloride)
F2C CF
2
TetrafluoroethyleneF3C
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF2
CF 3n
Poly(tetrafluoroethylene): Teflon
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Pol esters Amides and UrethanesMonomer Polymer
O O H HCO 2HHO2C HO HO O C C O
nTerephthalicacid
Ethyleneglycol
Poly(ethylene terephthalate
H
Ester
HO OH4
H2N NH24Adipic Acid 1,6-Diaminohexane Nylon 6,6
HO NH
NH
H4 4
n
Amide
CO 2HHO 2C
Terephthalicacid
NH2H2N
1,4-Diaminobenzene
Kevlar
O
HO
OHN
HN H
n
HOOH
Ethylenel col
H2COCN NCO
4,4-diisocyantophenylmethane Spandex
H2C
HN
HN
O
HO
O
OH2C
H2C O H
n
Urethane linkage
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What Makes Pol mers Uni ue?Really big molecules (macromolecules) like polymers havever different ro erties than small molecules
Chain entanglement: Long polymerchains get entangled with each other.
When the polymer is melted, the
chains can flow past each other. e ow e me ng po n , e c a ns
can move, but only slowly. Thusthe plastic is flexible, but cannot beeasily stretched.
Below the glass transition point,
polymer is rigid
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Ph sical Pro ertiesLinear Polymer
Stretch
The chains can be stretched, which causes. ,the polymer will not return to its original form.Cross-Linked Polymer
Stretch
The cross-links hold the chains together.When released, the polymer will return to it'soriginal form.
Relax
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Polymer Microstructure
Polyolefins with side chains have stereocenters on every other carbon
CH3nCH3 CH3 CH3 CH 3 CH3 CH3CH3
With so many stereocenters, the stereochemistry can be complex.There are three main stereochemical classifications for polymers.
: erna ng s ereoc em s ry
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Why is this important?
Tacticity affects the physical properties
Atactic polymers will generally be amorphous, soft,flexible materials so ac c an syn o ac c po ymers w e more
crystalline, thus harder and less flexible
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Polymer Synthesis There are two major classes of polymer formation mechanisms
Addition polymerization: The polymer grows by sequentialaddition of monomers to a reactive site
Maximum molecular weight is obtained early in the
reaction Step-Growth polymerization: Monomers react together to
make small oligomers. Small oligomers make bigger ones,
. Chain growth is exponential
reaction
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Addition Pol merizationPropagation
nAIn A A A A
nA*In*
A
InitiationIn A A A A*
*A A A A Am*A A A A A
mA
A A A A Am
In A A A An
A
Combination
In A A A An
A
B A A A Am
In A A A An
A
A*Disproportionation
TerminationReactive site is consumed
Chain TransferNew reactive siteis produced
MW k propagation
ter min ation
% conversion0 100
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Ste -Growth Pol merizationStage 1
n nConsumptionof monomer
Stage 2
Combinationof small fragments
Stage 3
Reaction ofoligomers to give
high molecularweight polymer
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TERMINOLOGY
Thermoplastics Polymers
heated and harden when cooledThermosetting Polymers
Thermosets are resins that undergo chemical changes
during processing to become permanently insoluble and-linked network structure when heat is applied.
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Various Thermo lastics Various Thermo lasticsPI
SpecialtySpecialtyPolymersPolymers PSU
PESPPSU
LCPPTFE
HPPA
EngineeringEngineeringPolymersPolymers POM
PA
PET PBT
PC
CommoditiesCommoditiesPSPS
ABSABS PMMAPMMAPPPP--GFGF PEPE--UHMWUHMW
TPE
AMORPHOUSAMORPHOUS CRYSTALLINECRYSTALLINE
SANSAN PPPP PEPE--HDHDPEPE--LDLD
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CODE FOR RECYLCING
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POLYMER PROPERTIES
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Amorphous vs. Crystalline Thermoplastics
Amorphous (a-morphous = without shape) - Thepolymer chains are in random arrangement. Molecularstructure is incapable of forming regular order
regularly stacked in crystal-like fashion. Molecular
arrangement is randomly twisted, kinked and coiled.
Crystalline - The polymer chains form a regular pattern.
molecules or portions of molecules regularly stacked incrystal-like fashion. Molecular arrangement is arrangedn an or ere as on.
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Amorphous vs. Crystalline Thermoplastics
Properties Crystalline Amorphous
Transparent NO Yes
Chemical Resistance Excel PoorStress-craze No Yes
Shrinkage High Low
Tensile Strength andmodulus High Low (exception in PC)
Melt Temperature Yes No
CriticalTemperature/Time
Yes No
Specific Gravity Higher LowerDuctility and elongation Lower Higher
Resistance to creep Higher Lower
Max. Usage Temperature Higher Lower
Flow Higher Lower
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Effect of Crystallinity on Properties
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Glass Transition Temperature (Tg)
The temperature below, which a polymer is hard and abovew c t s so t, s ca e t e g ass trans t on temperature g).The hard, brittle state is known as the glassy state and thesoft flexible state as rubber or viscous state.
OrThe molecular mobility is just starts at that temperature called
.
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