hidrocarbon groups. polymer = many mers polymer microstructure
TRANSCRIPT
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HIDROCARBON GROUPS
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• Polymer = many mers
C C C C C CHHHHHH
HHHHHH
Polyethylene (PE)
mer
ClCl Cl
C C C C C CHHH
HHHHHH
Polyvinyl chloride (PVC)
mer
Polypropylene (PP)
CH3
C C C C C CHHH
HHHHHH
CH3 CH3
mer
POLYMER MICROSTRUCTURE
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POLYMER MATERIALS
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POLYMER MATERIALS
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Branched Cross-Linked NetworkLinear
secondarybonding
• Covalent chain configurations and strength:
Direction of increasing strength
MOLECULAR STRUCTUREHomopolymers
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MOLECULAR STRUCTURECopolymers
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MOLECULAR STRUCTURECopolymers
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• Molecular weight, Mw: Mass of a mole of chains.
smaller Mw larger Mw
• Tensile strength (TS): --often increases with Mw. --Why? Longer chains are entangled (anchored) better.
• % Crystallinity: % of material that is crystalline. --TS and E often increase with % crystallinity. --Annealing causes crystalline regions to grow. % crystallinity increases.
crystalline region
amorphous region
MOLECULAR WEIGHT & CRYSTALLINITY
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CRYSTALLINITY
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POLYMER CRYSTALS
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6
• Compare to responses of other polymers: --brittle response (aligned, cross linked & networked case) --plastic response (semi-crystalline case)
TENSILE RESPONSE: ELASTOMER CASE
initial: amorphous chains are kinked, heavily cross-linked.
final: chains are straight,
still cross-linked
0
20
40
60
0 2 4 6
(MPa)
8
x
x
x
elastomer
plastic failure
brittle failure
Deformation is reversible!
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• Decreasing T... --increases E --increases TS --decreases %EL
20
40
60
80
00 0.1 0.2 0.3
4°C
20°C
40°C
60°Cto 1.3
(MPa)
Data for the semicrystalline polymer: PMMA (Plexiglas)
T AND STRAIN RATE: THERMOPLASTICS
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• Stress relaxation test:
Er(t)
(t)o
--strain to and hold.--observe decrease in stress with time.
• Relaxation modulus:
• Data: Large drop in Er
for T > Tg.(amorphouspolystyrene)
TIME DEPENDENT DEFORMATION
time
strain
tensile test
o
t( )
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VULCANIZATION
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0
unload/reload
0
brittle failure
plastic failure
20
40
60
2 4 6
(MPa)
x
x
semi- crystalline
case
amorphous regions elongate
crystalline regions align
crystalline regions
slide
8
onset of necking
aligned, cross- linked case
networked case
Initial
Near Failure
near failure
TENSILE RESPONSE: BRITTLE & PLASTIC
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CRYSTALLIZATION, MELTING AND GLASS TRANSITION PHENOMENA IN POLYMERS
Dependence of polymer properties as well as melting and glass transition temperatures on molecular weight
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POLYMER TYPES
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FORMING TECHNIQUES FOR PLASTICS
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FORMING TECHNIQUES FOR PLASTICS
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