Baiscs of Polymers

8/7/2019 Baiscs of Polymers

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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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Baiscs of Polymers

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