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1.1 Stress-Strain Curves
1.2 Definition and Classes
 Plastic (thermoplastic)
 Any material which undergoes a permanent change
of shape (plastic deformation) when strained
b
beyond
d a certain
t i point
i t (yield
( i ld point)
i t)
 Plastics can be identified and characterized by
the shape of their stress-strain curves
Modulus (psi)
Percent Elongation
Crystallinity
Polymer example
Elastomers
15 - 150
100 - 1000
Low
Natural rubber
Plastics
1,500 - 200,000
20 - 100
Moderate
Polyethylene
Fibers
150,000 - 1,500,000
< 10
High
Nylon
1.3 Definition and Classes
 Hard = high modulus (steep slope)
 Tough = high elongation before break, large area
under stress-strain curve
 Hard-tough
 Hard-strong
g
 Soft-tough
 Hard-brittle
 Soft-weak
1.4 Hard and Tough
 High density polyethylene, HDPE
 Fairly high crystallinity (Tm = 135 oC, Tg = -90 oC )
 Polypropylene,
Polypropylene PP
 Tm = 175 oC, Tg = -18 oC
 Slightly harder, higher tensile modulus than HDPE.
Why?
 Poly(ethylene
y( y
terephthalate),
p
) PET
 Tm = 265 oC, Tg = 70 oC
 Stiffer, higher tensile modulus than HDPE. Why?
 Typical applications
1
1.5 Definition and Classes
 Hard = high modulus (steep slope)
 Strong = moderate elongation and high modulus
1.6 Hard and Strong
 Poly(vinyl chloride), PVC
 Tm = 212 oC, Tg = 85 oC
 Would you expect this polymer to be brittle or pliable
at 0 oC?
 How can you change the flexibility of PVC?
 Typical applications
1.7 Definition and Classes
 Soft = low modulus (shallow slope)
 Tough = high elongation
1.8 Soft and Tough
 Low-Density Polyethylene, LDPE
 Tm = 115 oC, highly branched, lower crystallinity
 Linear Low-Density Polyethylene, LLDPE
 Moderate degree of branching
 More crystalline than LDPE?
 Higher tensile strength (stronger) than LDPE
 Typical applications
2
1.9 The Three PE’s
1.10 The Three PE’s
Stress-strain curves – Which is which?
1.11 Definition and Classes
 Hard = high modulus (steep slope)
 Brittle = low elongation
1.12 Hard and Brittle
 Polystyrene, PS
 Properties
 Tm = 240 oC, Tg = 100 oC
 Typical applications
3
2.1 Requirements for Fibers
2.2 Spinning of Fibers
 High tensile strength/modulus (tenacity)
 Relatively low elongation
g melting
gp
point ((esp.
p for clothing)
g)
 High
 Tm > 200 oC (iron without damage) but < 300 oC to
enable spinning from melt
 Tg < 100 oC so fibers soften when ironed at 150 oC
 Creases removed
Polymer
P
l
PET
Nylon 6,6
PAN
PP
o
Tg ( C)
70
60
105
-5
o
Tm ( C)
265
265
320
165
2.3 Requirements for Fibers
2.4 Requirements for Fibers
 Symmetrical, unbranched polymer
 Rigid backbone
structures
 High crystallinity promotes linear molecular
alignment – this is critical
 Strong intermolecular forces
 High tenacity, fiber strength, low elongation
hydrogen bonding:
H
C N
O
O
+
C O
O
H
H
O H
CH
cellulosics
C N
O
proteins, nylons
+
C O
O
polyesters
CH2
CH2
CH2
CH2
C
CH2
CH2
CH2
CH2
CH2
NH
CH2
 Aramids ((aromatic
polyamides)
 high stiffness
 heat resistance
dipole-dipole:
CH
O
NH
CH

+ C N
-
 Compete with wire
and glass fibers
 Form linear, rodlike
polymers
NH
NH
CH2
C
CH2
CH2
n
O
NH
NH
n
O
C
CH2
C
C
O
O
n
+
C N
CH
acrylics
C
O
O
NH
NH C
O
C
n
4
2.5 Important Fibers
 Nylon
NH
(CH2)5
O
O
C
C
n
2.6 Important Fibers
 Polyester
O
(CH2)4
C NH
(CH2)6
NH
n
O
O
C
C O CH2
CH2
O
n
nylon 6,6
nylon 6
 Fiber strength achieved by…
 Fiber strength achieved by…
 Properties
 Properties
 Dyeable, somewhat hydrophilic (absorbs water)
 Typical applications
 Choice of diacid (o, m, p) can vary tensile and elongation
properties
 Relatively hydrophobic
 Typical applications
2.7 Important Fibers
 Polypropylene
CH3
(CH2
CH)n
 Fiber strength achieved by…
by
 Properties
3.1 Properties of Elastomers
 Requirements for elastomers
 Completely amorphous, used above their Tg
 Low intermolecular forces allow for flexibility
 Large reversible extensions (several hundred
percent)
 High localized chain movements, low overall movement of chains
relative to one another
 Cross-linked chains can help prevent slip
 Low density (0.91 g/cc) yields lightweight fiber
 Chemical and abrasion resistance
 Hydrophobic
 Typical Applications
stress
applied
Stress
removed
slip
5
3.2 Properties of Elastomers
3.3 Important Elastomers
 Possess high molar mass to allow for chain
entanglements or are cross-linked
 Natural Rubber
H
CH3
C
 Cross-linked with sulfur
 Reaction at allylic hydrogens
C
H
H3C
C
CH2
Sx
C
n
CH2)n
CH2
C
H2C
H
n
H
C C
H
H2C
C
CH2
Free-radical polymerization
Tg = -110 oC
Primaryy use is auto tires
Also belts, hoses, gaskets
 Polybutadiene
H
Sy
CH2
C
(CH2
CH2
Biological polymerization
Agricultural crop
Tg = -70 oC
Pi
Primary
use iis auto
t titires
 Cis-1,4-polyisoprene
(CH2
C
CH2)n
CH2
n
y = 1 or 2
3.4 Fiber or Elastomer
Why is the Tg 40 oC lower than that of natural rubber?
Fiber Properties
Polymer
Cellulose
Cotton
Rayon
High-tenacity rayon
Cellulose diacetate
Cellulose triacetate
Proteins
Silk
Wool
N l 6
Nylon
6,6
6
Polyester
Polyacrylonitrile (acrylic)
Polyurethane (Spandex)
Polypropylene (polyolefin)
Asbestos
Glass
Tenacity Tensile Strength Elongation
2
(g/denier)
(%)
(kg/cm )
2.1-6.3
1.5-2.4
3.0-5.0
1.1-1.4
1.2-1.4
3000-9000
2000-3000
5000-6000
1000-1500
1000-1500
3-10
15-30
9-20
25-45
25-40
2.8-5.2
1.0-1.7
4560
4.5-6.0
4.4-5.0
2.3-2.6
0.7
7
1.3
7.7
3000-6000
1000-2000
4000 6000
4000-6000
5000-6000
2000-3000
630
5600
2100
2100
13-31
20-50
26
19-23
20-28
575
25
25
3
6