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7/31/2019 20 Polymers II
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Polymers II/ Objectives1. Explain the basis for polymer crystallinity.
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Polymers II/ Objectives1. Explain the basis for polymer crystallinity.
2. Explain the effects of crystallinity on physical andmechanical properties.
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Polymers II/ Objectives1. Explain the basis for polymer crystallinity.
2. Explain the effects of crystallinity on physical andmechanical properties.
3. Explain the mechanisms underlying elastic, viscoelastic,
and plastic deformation in polymers.
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Polymers II/ Objectives1. Explain the basis for polymer crystallinity.
2. Explain the effects of crystallinity on physical andmechanical properties.
3. Explain the mechanisms underlying elastic, viscoelastic,
and plastic deformation in polymers.
4. Identify the regions of behavior on a TSModulus/Temperature curve.
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Polymers II/ Objectives1. Explain the basis for polymer crystallinity.
2. Explain the effects of crystallinity on physical andmechanical properties.
3. Explain the mechanisms underlying elastic, viscoelastic,
and plastic deformation in polymers.
4. Identify the regions of behavior on a TSModulus/Temperature curve.
5. Explain the mechanism of temperature and rate
dependence of polymer modulus, and yield.
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Polymers II/ Objectives1. Explain the basis for polymer crystallinity.
2. Explain the effects of crystallinity on physical andmechanical properties.
3. Explain the mechanisms underlying elastic, viscoelastic,
and plastic deformation in polymers.
4. Identify the regions of behavior on a TSModulus/Temperature curve.
5. Explain the mechanism of temperature and rate
dependence of polymer modulus, and yield.
6. Summarize the major environmental variables whichimpact polymer failure in TP’s and TS’s.
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Polymers II/ Objectives1. Explain the basis for polymer crystallinity.
2. Explain the effects of crystallinity on physical andmechanical properties.
3. Explain the mechanisms underlying elastic, viscoelastic,
and plastic deformation in polymers.
4. Identify the regions of behavior on a TSModulus/Temperature curve.
5. Explain the mechanism of temperature and rate
dependence of polymer modulus, and yield.
6. Summarize the major environmental variables whichimpact polymer failure in TP’s and TS’s.
7. Describe the basic mechanisms of failure in TP and TS
polymers.
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Physical Properties of Polymers
1. Non conducting - electrically
(except polyacetylene)
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Physical Properties of Polymers
1. Non conducting - electrically
(except polyacetylene)
2. Good thermal insulators
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Physical Properties of Polymers
3. Free volume varies with temp
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Physical Properties of Polymers
1. Non conducting - electrically
(except polyacetylene)
2. Good thermal insulators
3. Free volume varies with temp
4. Optically crystalline/ semi-crystalline
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Heat Capacity
ThermosetsAmorphous polymers
Tg : cure – exotherm
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Heat Capacity
Semi-crystalline polymersTg : weak
Crystallization – exotherm
Melting - endotherm
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Heat Capacity
GeneralWater vaporization – endotherm
Additive vapor – endotherm
Decomposition - exotherm
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Glass Transition Temp.
1. Breakdown of Van Der Waals Forces
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Glass Transition Temp.
1. Breakdown of Van Der Waals Forces
2. Onset of large scale molecular
motions
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Glass Transition Temp.
1. Breakdown of Van Der Waals Forces
2. Onset of large scale molecular
motions3. Important in amorphous polymers
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Glass Transition Temp.
1. Breakdown of Van Der Waals Forces
2. Onset of large scale molecular
motions3. Important in amorphous polymers
4. Upper service temperature
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Modulus & Temperature
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Effect of Crosslinking on Modulus
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Complex Modulus:
E (t) = E ’(t) + i E ”(t)
E’ – Storage Modulus
(~elastic)
E” – Loss Modulus
(~viscous dissipation)
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Transitions from Tan = E’’/E’
Tan =
E’’/E’
TG
Tallest is TG
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Tg in Semicrystalline Polymers
1. May show where “brittle” behavior begins
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Tg in Semicrystalline Polymers
1. May show where “brittle” behavior begins
2. Not a predictor of service temperature
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Tg in Semicrystalline Polymers
1. May show where “brittle” behavior begins
2. Not a predictor of service temperature
3. Crystals maintain high E + SY
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Fracture Processes
1. Two Deformation Process for Thermoplastics
a. Crazing
(amorphous material )
a. Shear Yielding
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Craze Process Zone
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Fracture Process Zone: PE
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Ductile Thermoplastic Fracture at Different
Strain Rates
A
B
C
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Fracture Processes
3. Fatigue
a. Macroscopically brittle
b. Same mechanismsc. Viscoelasticity complicates picture
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Effect of 2nd Phase Tougheners
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Environmental Effects on Polymers
1. Permeable to many gases & H2O vapor
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Environmental Effects on Polymers
1. Permeable to many gases & H2O vapor
2. Inorganic Acids & Bases – fairly resistant
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Environmental Effects on Polymers
3. Organic Solvents – can be very sensitive
-Crosslinks, crystallinity improves resistance
-Polarity of polymer & solvent important
-Solvents swell, dissolve, crack polymers
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Environmental Effects on Polymers
4. Moisture absorption
-Polar polymers (PC, Nylon)
-lowers modulus and yield strength
-problem in processing
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Environmental Effects on Polymers
5. UV & Visible light
-Chain scission
-UV stabilizers may be added
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Environmental Effects on Polymers
6. Heat
-Chemical Aging
-Physical Aging
