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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
Polymer Applications
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
http://images.google.com/imgres?imgurl=www.homeportfolio.com/kravet/images/fabric.jpg&imgrefurl=http://www.homeportfolio.com/kravet/TopIndex.jhtml&h=180&w=180&prev=/images%3Fq%3Dfabric%26svnum%3D10%26hl%3Dth%26sa%3DG8/14/2019 (4)Polymeric Materials
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Dept of Mat Eng 6
Polymer Applications
Foams: containingvolume percentageof small pores
Films: havingthicknessesbetween 0.025 0.125 mm and used
as packagingproduct
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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
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Classification: Source
Natural polymers :wood, rubber, cotton,wool, leather, andsilk.
Synthetic polymers :PE, PP, PVC, PS, andPET.
http://seasiancrafts.com/spiritworld/silk.jpghttp://images.google.com/imgres?imgurl=www.rmconnection.com/images/nf10771.jpg&imgrefurl=http://www.rmconnection.com/tnfshoe.htm&h=315&w=360&prev=/images%3Fq%3Dsport%2Bshoes%26svnum%3D10%26hl%3Dthhttp://www.gristmagazine.com/grist/images/consumers/cotton.jpghttp://seasiancrafts.com/spiritworld/silk.jpghttp://www.weber-schaer.com/images/2_1f.jpghttp://www.youngsdairy.com/images/wool.h2.gif8/14/2019 (4)Polymeric Materials
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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.
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Classification: Structure &Physical Property
ThermosettingThermosettingPolymers that are heavily cross-linked to
produce a strong three dimensional network
structure.Polymer cannot be soften or molten and
reshaped.
8/14/2019 (4)Polymeric Materials
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Classification: Structure &Physical Property
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
hereinunder
license.
ThermoplasticThermoplastic ElastomerElastomer
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Dept of Mat Eng 13
Vulcanization
Cross-linking elastomer chains by introducingsulfur or other chemicals
Polyisoprene
http://www.key.ca/resources/Petro/isoprene.gif8/14/2019 (4)Polymeric Materials
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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
Addition Polymerization
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
Addition Polymerization
2003Bro
oks/Cole,adivision
ofThom
sonLearni n
g,Inc.
ThomsonL
earning
isatradem
arkused
hereinund
erlicense
.
(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
Condensation Polymerization
2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.
8/14/2019 (4)Polymeric Materials
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Dept of Mat Eng 24
Condensation Polymerization
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
Effect of Temperature on Thermoplastics
2003Broo
ks/Cole,adivisionofT
homsonLea
rning,Inc.Thomson
Learning
isatrademarkusedhere i
nunderlicense.
8/14/2019 (4)Polymeric Materials
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Dept of Mat Eng 30
Effect of Temperature on Thermoplastics
2003Brooks /
Cole,ad
ivisionofThomson
Learning,Inc .
ThomsonLearning
isa
trademarkused
hereinunder
lic
ense.
8/14/2019 (4)Polymeric Materials
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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
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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.gif8/14/2019 (4)Polymeric Materials
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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
Strain-induced CrystallineStrain-induced Crystalline
(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
Strain-induced CrystallineStrain-induced Crystalline
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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.
http://www.rtpcompany.com/products/structural/glass.jpghttp://www.sc.ehu.es/powgep99/polymat/masterbatch.gif