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7/26/2019 MME - Polymers 1
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Mechanics, Materials and
Machine Elements (MME M1)
Polymers 1
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ADVANTAGES OF PLASTICS VS STEEL
Low density and high specific strength
Electrical and thermal insulation
Design flexibility
Easy to shape
Coloring possibilities
Reduced total energy cost
Easy processing/forming
Cheaper
Corrosion resistance Chemical resistance
Tailored properties
Transparency (in some cases)
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Relatively low maximum allowable service temperatures
Moderate creep resistance and specific stiffness
Significant influence of temperature on mechanical
properties
Flammability
UV resistance (for some materials)
Higher thermal expansion rate
DISADVANTAGES OF PLASTICS
VS STEEL
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6Source: http://www.sciencedirect.com/science/article/pii/S0141391004001776
http://www.google.dk/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=Fyzd4n38plAQYM&tbnid=-9yUp84dVC_0SM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0141391004001776&ei=67BvUe3SMMHfswb38YHQDw&bvm=bv.45368065,d.Yms&psig=AFQjCNHZw_ColUK45PpI0W68hlpMYInlPA&ust=13663605999821377/26/2019 MME - Polymers 1
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DENSITY
8
Why lower
density than
metals?
Lighter
atoms
Largerinteratomic
space
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WHAT IS A POLYMER?
Poly merosmany unit
10
C C C C C C
HHHHHH
HHHHHH
Polyethylene (PE)
ClCl Cl
C C C C C C
HHH
HHHHHH
Poly(vinyl chloride) (PVC)
HH
HHH H
Polypropylene (PP)
C C C C C C
CH3
HH
CH3CH3H
monomer monomer monomer
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DEGREE OF POLYMERIZATION, DP
DP= average number of repeat units per chain
11
C C C C C C C CH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
C C C C
H
H
H
H
H
H
H
H
H( ) DP= 6
DP can be as high as 100.000, depending on plastic type.
POLYMER COMPOSITION
Most polymers backbone contain C, sometimes combined
with O and/or N. Other elements can be attached to the
backbone, e.g. H, N, Cl, and F, or groups of elements.
"Backbone" should probably be called monomer!
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POLYMERS
12
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POLYMERS
13
Naturally occurred polymers:
rubber
cotton
wool leather
silk
wood
proteins
enzymes, starches, cellulose
Synthetic produced
polymers:
plastics
rubbers fiber materials
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BULK OR COMMODITY POLYMERS
14
Again, repeat unit = monomer!
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BULK OR COMMODITY POLYMERS
15
Repeat unit = monomer!
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BULK OR COMMODITY POLYMERS
Repeat unit = monomer!
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POLYMERS
17
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POLYMERS
Thermoplastics
Can be re-melted
Low melting temperature
Long chains of monomers
Can be recycled
Little crosslinking
Ductile
Soften w/heating
Ex.: polyethylene, polypropylene,
polycarbonate, polystyrene
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Thermosets
Cannot be re-melted
Strong cross-linked, 3D intermolecular
bonds => one large molecule
Are only partially polymerized beforeprocessing
Significant crosslinking (10 to 50% of
repeat units)
Hard and brittle
Do NOT soften w/heating
Ex.: vulcanized rubber, epoxies,
polyester resin, phenolic resin
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INTERATOMIC BONDS
Covalent bonding
The atoms get a stableouter shell by sharingelectrons. Ex. CH4.
In thermosets between
molecules. In thermoplastics within
molecules.
19
Secondary bonding In thermoplastics between the molecule chains.
Types: van der Waals, hydrogen, dipole.
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THERMOPLASTICS
20
Amorphous
Can not be 100% crystalline.
High crystallinity:
Increase of density
Higher melting point
Higher E-modulus
Higher tensile strength
Lower ductility
Better resistance against
organic solvents.
Semicrystalline
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SEMICRYSTALLINE POLYMERS
Polyethylene (PE) :
Polyetrafluoroethylene (PTFE) (Teflon)
21
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SEMICRYSTALLINE POLYMERS
Polyamide (PA)
Polyoxymethylene (POM)
Polypropylene (PP)
22
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AMORPHOUS POLYMERS
Polystyrene (PS)
23
PS art by Tara Donovan
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AMORPHOUS POLYMERS
Polystyrene (PS)
Polyvinylchloride (PVC)
24
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AMORPHOUS POLYMERS
Acrylonitrile butadiene styrene (ABS)
Poly(methyl methacrylate) (PMMA)
Polycarbonate (PC)
25
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MOLECULAR STRUCTURES FOR
POLYMERS
26
Branched Cross-Linked NetworkLinear
secondarybonding
Linear: HDPE, PVC, PS, PA
higher density; can be easier close packed
Branched: LDPE.
less density
Cross-linked: Rubbers
Network: Polyurethanes, epoxies, polyesters, etc. (thermosets)
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COPOLYMERS
Two or more monomerspolymerized together
randomA and B randomlypositioned along chain
alternatingA and B
alternate in polymer chain blocklarge blocks of A units
alternate with large blocks ofB units
graftchains of B unitsgrafted onto A backbone
A B
27
random
block
graft
alternating
TEMPERATURE BEHAVIOR OF
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TEMPERATURE BEHAVIOR OF
AMORPHOUS VS. SEMICRYSTALLINE
PLASTICS
TgC TmC
PE -120 137
PP -15 176
POM -50 180
PA 50 225
PBT 55 225
PMMA 100 205-230
PVC 80 200-220
ABS 110 230-270PC 149 290-320
PS 100 204-251
Amorphous
Semicrystalline
Rubberyor
Viscoelasticstate
Temperature
Semicrystalline
Tg
morphous
T
g
E-Modulus
Semicrystalline
Tm
Glassy state Meltstate
Data not 100% reliable!
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POLYMER ADDITIVES
31
Improve mechanical properties, processability, durability, etc.
Fillers
Added to improve tensile strength & abrasion resistance,toughness & decrease cost
ex: carbon black, silica gel, wood flour, glass, limestone,
talc, etc. Plasticizers
Added to reduce the glass transition temperature Tgbelow room temperature
Presence of plasticizer transforms brittle polymer into aductile one
Commonly added to PVC - otherwise it is brittle
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POLYMER ADDITIVES (CONT.)
32
Stabilizers
Antioxidants
UV protectants
Lubricants
Added to allow easier processing Polymer slides through dies easier ex: sodium
stearate
Colorants
Dyes and pigments
Flame Retardants
Substances containing chlorine, fluorine, and boron
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33
PLASTIC
IDENTIFICATION
CODE
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