(4)Polymeric Materials

8/14/2019 (4)Polymeric Materials

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Stru

ctu

res

Processes

Proper

ties

Performance

Metals

CeramicsPolymers

Composites

Polymeric Materials

2nd semester 2006


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Composites

Dept of Mat Eng 2

Outline: Polymeric Materials

Definition Classification of Polymer

Polymerization

Structure-Property Relationship Effect of Temperature on Thermoplastics

Polymer Processing

Strain-induced Crystalline Additives


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Dept of Mat Eng 3

Polymeric Materials in Everyday Life


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Dept of Mat Eng 4

Polymer Applications

Plastics: two typesof plastic arethermoplasticandthermosetting

Elastomers: consistof linear polymerchain that are lightlycross-linked & high

degree of elasticity
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Dept of Mat Eng 5


Fibers: be capable ofbeing drawn into longfilament having atleast a 100:1 length-to

diameter ratio. Ex. PA(nylon), PES (dacron),and PAN (acrylicfibers).

Adhesives: used tojoin together thesurfaces of twosolid materials
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Dept of Mat Eng 6


Foams: containingvolume percentageof small pores

Films: havingthicknessesbetween 0.025 0.125 mm and used

as packagingproduct


7/44Dept of Mat Eng 7

Definition

POLYMER (Greek root)

poly = many meros = part

substance containing high-molecular-

weight molecules, consisting of repeating unit

which are bond to each other

MONOMER

mono = one meros = part



Classification: Source

Natural polymers :wood, rubber, cotton,wool, leather, andsilk.

Synthetic polymers :PE, PP, PVC, PS, andPET.
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Classification: Structure &Physical Property

ThermoplasticThermoplasticLinear or branched polymers in which

chains of molecules are not interconnected toone another.

Polymer can be soften or molten andreformed into new shapes. Process can bereheated.




ThermosettingThermosettingPolymers that are heavily cross-linked to

produce a strong three dimensional network

structure.Polymer cannot be soften or molten and

reshaped.




ElastomerElastomerThese are polymers that have an elastic

deformation > 200%Material resumes its original shape when

stretched or compressed and then released.


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Dept of Mat Eng 12

Differences between Thermoplastic & Elastomer

2003Brooks /

Cole,ad

ivisionofThomson

Learning,Inc .

ThomsonLearning

isa

trademarkused

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license.

ThermoplasticThermoplastic ElastomerElastomer


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Dept of Mat Eng 13

Vulcanization

Cross-linking elastomer chains by introducingsulfur or other chemicals

Polyisoprene
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Dept of Mat Eng 14

Properties of Thermoplastic Polymers


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Dept of Mat Eng 15

Properties of Thermosetting Polymers


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Dept of Mat Eng 16

Properties of Elastomers


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Dept of Mat Eng 17

Design/Materials Selection

Design the type of polymeric materialyou might select for the followingapplications:

A surgeons gloveA beverage containerA car bumper


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Dept of Mat Eng 18

Polymerization

Polymerization:

The process that monomer

units are bonded bycovalent bonds to generate

giant molecules.

Polymerization

Monomer Polymer

PolymerPolymer

Petroleum ProductsPetroleum Products

MonomerMonomer

Crude Oil or Natural GasCrude Oil or Natural Gas


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Dept of Mat Eng 19

Addition Polymerization

Process by which polymer chains are builtup by adding monomers together without

creating a byproduct.

Unsaturated Bond: the double- or even

triple- covalent bond joining together in an

organic molecule

Functionality: the average no. of reactive

functional groups (sites) per monomer


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Dept of Mat Eng 20


1. Initiation

orDisproportionation

2. Propagation

3. Termination

Combination

Note:-Addition polymerizationis used in the synthesis

of PE, PP, PVC, and PS,as well as many of thecopolymers.


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Dept of Mat Eng 21


2003Bro

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(a) producing free radicals from initiators such as benzoyl peroxide

(b) attachment of a polyethylene repeat unit to one of the initiator radicals

(c) attachment of additional repeat units to propagate the chain.


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Dept of Mat Eng 22

Condensation Polymerization

A polymerization mechanism in which a smallmolecule (e.g., H2O, CH

3OH, etc.) is

condensed out as a byproduct. The thermosetting polyesters and phenol-

formaldehyde,nylons, and PCare producedby condensationpolymerization.


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Dept of Mat Eng 23


2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.


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Dept of Mat Eng 24


Hexamethylene diamine

+

Adipic acid

Water

+

H O C C C C C CO H H H H O

O H

H H H H

N C C C

HH

H H

C C C

H

H

H

H

H H

H H

N

H

C C C C

O

H H H

C C O H

O

H

HHHHH

H

N C C C

HH

H HC C C

H

H

H

H

H H

H H

NH

H H

H

H2O

6,6-Nylon

N C C C

HH

H H

C C C

H

H

H

H

H H

H H

N

H

C C C C

O

H H H

C C

O

H

HHHHH

n


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Dept of Mat Eng 25

Degree of Polymerization

Ex. Calculate the degree of polymerization if polyethylene (PE)has a molecular weight of 56,000 g/mol.

Degree of Polymerization =Average molecular weight of the polymer

Molecular weight of the repeating unit

The degree of polymerization refers to the totalnumber of repeat units in the chain.

C C

H H

H H

n

Polyethylene (PE)

Mrepeat unit = 2(atomic wt. of C) + 4(atomic wt. of H)= 2(12) + 4(1) = 28

Degree of Polymerization = 56,000/28 = 2,000


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Dept of Mat Eng 26

Ex. Structure-Property Relationship

PropertyLow DensityPolyethylene

High DensityPolyethylene

Branches many few

Density 0.195 - 0.925 g/cm3 0.945 - 0.965 g / cm3

Crystallinity 55% - 75% 80% - 95%

Hardness, Flexibility soft, pliable harder, stiff

Glass transition temp.Melting Point

about 75 oCabout 110 oC

about 100 oCabout 130 oC

Typical Uses food wrapping, film, flexiblebottles, garbage bags

milk jugs, bleach bottles,pipes, an excellentelectrical insulator

Solubility softens and swells inhydrocarbon solvent

Insoluble in most organicsolvents


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Dept of Mat Eng 27


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Dept of Mat Eng 28

Effect of Temperature on Thermoplastics

Glass Temperature (Tg): the temp. rangebelow which the amorphous polymer assumesa rigid glassy structure

Melting Temperature (Tm): the temp. rangeabove which molecules transform formordered to disordered molecular states.

Degradation Temperature: the temp. abovewhich a polymer burns, chars, ordecomposes.


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Dept of Mat Eng 29


2003Broo

ks/Cole,adivisionofT

homsonLea

rning,Inc.Thomson

Learning

isatrademarkusedhere i

nunderlicense.


30/44

Dept of Mat Eng 30


2003Brooks /

Cole,ad

ivisionofThomson

Learning,Inc .

ThomsonLearning

isa

trademarkused

hereinunder

lic

ense.


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Dept of Mat Eng 31

Processing

Thermoplastic Injection Molding

Extrusion

Blow Molding Compression Molding

Themosetting

Reaction InjectionMolding (RIM)

Compression Molding

Elastomer Extrusion

Compression Molding

Fiber

Spinning


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Dept of Mat Eng 32

Injection Molding

Injection molding is the most widely usedtechnique for fabricating thermoplasticmaterials.

Probably the most outstanding feature ofthis technique is the speed with which piecescan be produce due to cycle times are short(commonly within the range of 10 30 s)


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Dept of Mat Eng 33

Injection Molding Machine

Injection Unit- Hopper

- Barrel, Heater

- Nozzle- Screw

Mold Unit- Stationary Mold

- Movable Mold

Clamping Unit


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Dept of Mat Eng 34

Reaction Injection Molding (RIM)

Thermosetting polymers may also be injection molded;curing takes place while the material is under pressure ina heated mold.

A process likes

injection molding. Twoor more kinds of fluid

plastics are mixed,

often without heating,and injected into a

mould where the

mixture solidifies.


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Dept of Mat Eng 35

Extrusion

The extrusion process is simply injection moldingof a viscous thermoplastic through an open-endeddie, similar to the extrusion of metals.

The technique is especially adapted to producingcontinuous lengths having constant cross-sectionalgeometries.

Ancillary Equipmenti.e. Bonding, Cutting,

Printing,


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Dept of Mat Eng 36

Extrusion

Major type of Extrusion Products Profile Pipe

Sheet Film Wire Covering

Filament
http://www.materials-careers.org.uk/gfx/plastic.gif


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Dept of Mat Eng 37

Blown Film Extrusion

This process related to the extruder is fitted withan annular die, pointing (usually) upwards. The tubeproduced is inflated with air and at the same time isdrawn upwards in a continuous process.


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Dept of Mat Eng 38

Fiber Forming

The process bywhich fibers are

formed from bulk

polymer material istermedspinning.

The strength of

fibers is improved by

a post forming

process called

drawing.


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Dept of Mat Eng 39

Blow Molding

Injection Blow MoldingInjection Blow Molding

Extrusion Blow MoldingExtrusion Blow Molding


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Dept of Mat Eng 40

Compression Molding

Compression molding is almost exclusivelyused for thermosetting and elastomer.

Step1. Place and preheat compound or preform

between male & female mold

2. The mold is closed, heat & pressure are applied

3. The mold is opening
http://abalone.cwru.edu/tutorial/enhanced/files/polymers/apps/graphics/tire.gifhttp://abalone.cwru.edu/tutorial/enhanced/files/polymers/apps/graphics/tire.gif


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Dept of Mat Eng 41

Strain-induced CrystallineStrain-induced Crystalline

when a rubbery polymer is stretched, themolecules become aligned, which leads tocrystallization (non-permanent)non-rubbery polymers can be stretched to

increase their crystalline proportionpermanently stretching in two directions simultaneously

induces biaxially oriented crystallization e.g. biaxially stretched PET, PVC, PP: goodstrength with high clarity (no opticalinterference)


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Dept of Mat Eng 42


(c) 2003 Brooks/Cole Publishing / Thomson

Learning

This figure shows a schematic of the blow-stretch process used for fabrication of a standardtwo-liter PET (polyethylene terephthalate) bottlefrom a preform. The stress induced crystallizationleads to formation of small crystals that helpreinforce the remaining amorphous matrix.


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Dept of Mat Eng 43



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Additives

Fillers: to improve mechanical propertiesand reduce cost.

Plasticizers:to improve flexibility,ductility, and toughness of polymers. Theirpresence also produces reductions in

hardness and stiffness. Stabilizers: to protect againstatmospheric oxidation or UV radiation.

Colorants: to classify application ofmaterials.

Flame retardants: may function byinterfering with the combustion processthrough the gas phase, or by initiating achemical reaction that causes a cooling ofthe combustion region.
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(4)Polymeric Materials

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