Engineering 45
Polymer
Applications
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering-45: Materials of Engineering
1
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Learning Goals – Polymer Apps
 Learn How Microstructure affects Room
Temperature Tensile Stress Behavior
 Understand Hardening, Anisotropy, and
Annealing in Polymers
 How the elevated-temperature
mechanical-response for PolyMers
compares to Ceramics and Metals
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
PolyMer Tensile σ-ε Response

PolyMers Exhibit 3
Basic Types of
Tensile Response
A. Brittle → Glass-Like
•
•
Linear-Elastic
Very Small Strain
at Fracture
B. Elastic-Plastic →
Metal-Like
•
•
Well-Defined
Yielding
Significant Strain at
Fracture
Engineering-45: Materials of Engineering
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C. Elastomeric →
Rubber-Like
•
•
Completely Elastic; all
the way to fracture
Very Large Strains
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Tensile Response – Brittle & Plastic
Near Failure
s(MPa)
brittle failure
x
60
40
Initial
20
onset of
necking
plastic failure
x
unload/reload
0
0
2
6
4
aligned,networked
crosscase
linked
case
8
e
crystalline
regions
slide
semicrystalline
case
Engineering-45: Materials of Engineering
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near
failure
amorphous
regions
elongate
crystalline
regions align
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Tensile Response – Elastomers
s(MPa)
60 xbrittle failure
plastic failure
40
x
20
0
0
initial: amorphous chains are
kinked, heavily cross-linked.
x
elastomer
2
4
6
e
final: chains
are straight,
8
still
cross-linked
Deformation
is reversible!
 Compare Elastomers to responses of other polymers:
• BRITTLE response (aligned, cross-linked & networked case)
• PLASTIC response (semi-crystalline case)
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
T & StrainRate - ThermoPlastics
 DEcreasing Temp
• Increases E
• Increases TS
• Decreases %EL
 INcreasing Strain
Rate...
• Same effects as
decreasing
Temperature
Engineering-45: Materials of Engineering
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s(MPa)
80 4°C
Data for the
semicrystalline
polymer: PMMA
20°C (Plexiglas)
60
40
40°C
to 1.3
20
0
0
60°C
0.1
0.2
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
e 0.3
PreDeformation by Drawing
 Drawing
• stretches the polymer prior to use
• aligns chains to the stretching direction
 Results of drawing
• Increases the elastic modulus (E) in the
stretching direction
• Increases the tensile strength (TS) in the
stretching direction
• Decreases ductility (%EL)
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Vulcanization
 Chemically Induced Cross-Linking Process in
Elastomers is called VULCANIZATION
• An Irreversible Chemical Reaction Performed at
Elevated Temperature
Thru a Cross Linking
Agent; Typically Sulfur
 Typically Requires
More than ONE S-atom per Cross-Link
 Vulcanization at the 1-5 wt%-S level improves
Elastomer Properties Including
Wear & Strength (e.g., Tires)
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Time Dependent Deformation
 Stress Relaxation
Test
• Rapidly deform to
Strain ε0, and Hold
• Measure
Hold-Stress as a
Function of Time
 The Hold-Stress
Decreases with
Time Due to
“unkinking” of the
PolyMer chains
s (t )  s 0 e
 t /
• Where
– σ0  Stress at time-0
–   Time Constant;
i.e., the time required
for the stress to
drop by 63%
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Relaxation Modulus
 Given Stress
Relaxation
 Define a TimeDependent
RELAXATION
Modulus
Engineering-45: Materials of Engineering
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s (t )
Er (t ) 
eo
 Next Pick a
BaseLine time, Say
10s, and Vary
Temperature to
s (10 s )
Er10 (T ) 
e o tempT
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Relaxation Modulus vs Temperature
 Glassy State
• Material is RIGID and
BRITTLE
• ELASTIC Stretching of
Bonds
 Leathery State
• some Sliding of chains
over one another
• some Permanent
deformation
• deformation will be timedependent and not totally
recoverable
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Relaxation Modulus vs Temp cont.1
 Rubbery Plateau
• deforms in a
rubbery manner
• both elastic and
viscous behavior
• straightening out of
polymer chains gives
large strains
• strain is reversible due
to crosslinks and
entanglements
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Relaxation Modulus vs Temp cont.2
 Rubbery flow and
Viscous flow
• high temperature states
• polymer chains slide
over each other
• permanent deformation
is possible (molding)
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Glass Transition Temperature
 Notice on the Er
vs T curve the
almost VERTICAL
Slope at the Center
of the Leathery, or
Tough Regime
 This marks the Transition from a
Brittle, amorphous State to a
ViscoElastic Condition
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Specific Volume = 1/ρ (cu-m/kg)
The Glass Transition Temp
Note
Change in
Slope
 NonCrystalline Material
Tg
Engineering-45: Materials of Engineering
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Tm
• T < Tg → Rigid, Glass-Like
• Tg < T < Tm → Rubbery
or Leathery
• T > Tm → Melted, Liquid
Temperature
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Structure-Property Relationships
 Ease of MOVEMENT of molecular
chains affects properties
• crystallinity (ability to pack efficiently)
• Tg (onset of
large-scale
molecular motion)
• Glass-forming
ability
• Strength vs.
Flexibility
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
Structure-Property Relns cont.
 STRUCTURAL factors that inhibit
Crystalline
molecular motion:
• Complexity of the Mer
• Size of Side Groups
• Branching,
Crosslinking
Region
Amorphous
Tie Region
• Configuration
• Bonding
• Entanglements
Engineering-45: Materials of Engineering
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Possible organization of
PolyEthylene polymer chains
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
WhiteBoard Work
 Prob Similar to 15.24
 Vulcanize PolyIsoPrene with Sulfur
• Given
– 57 wt%-S combined with the polymer
– Six Sulfur atoms per CrossLink on Average
• Determine CrossLinks per Isoprene Mer
Natural rubber (cispolyisoprene) before
vulcanizing with sulfur
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
IsoPrene Polymerization
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt
σ-ε vs. T for FluoroPolymer
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-30_Polymer-Apps.ppt