Polymers II/ Objectives

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Polymers II/ Objectives

• Explain the basis for polymer crystallinity.

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Polymers II/ Objectives

• Explain the basis for polymer crystallinity.
• Explain the effects of crystallinity on physical
  and mechanical properties.

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Polymers II/ Objectives

• Explain the basis for polymer crystallinity.
• Explain the effects of crystallinity on physical
  and mechanical properties.
• Explain the mechanisms underlying elastic,
  viscoelastic, and plastic deformation in polymers.

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Polymers II/ Objectives

• Explain the basis for polymer crystallinity.
• Explain the effects of crystallinity on physical
  and mechanical properties.
• Explain the mechanisms underlying elastic,
  viscoelastic, and plastic deformation in
  polymers.
• Identify the regions of behavior on a TS
  Modulus/Temperature curve.

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Polymers II/ Objectives

• Explain the basis for polymer crystallinity.
• Explain the effects of crystallinity on physical
  and mechanical properties.
• Explain the mechanisms underlying elastic,
  viscoelastic, and plastic deformation in
  polymers.
• Identify the regions of behavior on a TS
  Modulus/Temperature curve.
• Explain the mechanism of temperature and rate
  dependence of polymer modulus, and yield.

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Polymers II/ Objectives

• Explain the basis for polymer crystallinity.
• Explain the effects of crystallinity on physical
  and mechanical properties.
• Explain the mechanisms underlying elastic,
  viscoelastic, and plastic deformation in
  polymers.
• Identify the regions of behavior on a TS
  Modulus/Temperature curve.
• Explain the mechanism of temperature and rate
  dependence of polymer modulus, and yield.
• Summarize the major environmental variables which
  impact polymer failure in TPs and TSs.

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Polymers II/ Objectives

• Explain the basis for polymer crystallinity.
• Explain the effects of crystallinity on physical
  and mechanical properties.
• Explain the mechanisms underlying elastic,
  viscoelastic, and plastic deformation in
  polymers.
• Identify the regions of behavior on a TS
  Modulus/Temperature curve.
• Explain the mechanism of temperature and rate
  dependence of polymer modulus, and yield.
• Summarize the major environmental variables which
  impact polymer failure in TPs and TSs.
• Describe the basic mechanisms of failure in TP
  and TS polymers.

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Physical Properties of Polymers

• Non conducting - electrically
• (except polyacetylene)

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Physical Properties of Polymers

• 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

• 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

• Thermosets
• Amorphous polymers
• Tg cure exotherm

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Heat Capacity
Semi-crystalline polymers Tg weak Crystallizatio
n exotherm Melting - endotherm
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Heat Capacity
General Water vaporization endotherm Additive
vapor endotherm Decomposition - exotherm
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Glass Transition Temp.

• Breakdown of Van Der Waals Forces

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Glass Transition Temp.

• Breakdown of Van Der Waals Forces
• Onset of large scale molecular motions

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Glass Transition Temp.

• Breakdown of Van Der Waals Forces
• Onset of large scale molecular motions
• Important in amorphous polymers

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Glass Transition Temp.

• Breakdown of Van Der Waals Forces
• Onset of large scale molecular motions
• Important in amorphous polymers
• 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
TG
Tan ? E/E
?
?
?
Tallest is TG
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Tg in Semicrystalline Polymers

• May show where brittle behavior begins

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Tg in Semicrystalline Polymers

• May show where brittle behavior begins
• Not a predictor of service temperature

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Tg in Semicrystalline Polymers

• May show where brittle behavior begins
• Not a predictor of service temperature
• Crystals maintain high E SY

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Fracture Processes

• 1. Two Deformation Process for Thermoplastics
• Crazing
• (amorphous material )
• 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
2. Thermoset Deformation Process a. Crazing
suppressed b. Shear Yielding only option
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Fracture Processes
3. Fatigue a. Macroscopically brittle b. Same
mechanisms c. Viscoelasticity complicates picture
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Effect of 2nd Phase Tougheners
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Environmental Effects on Polymers

• Permeable to many gases H2O vapor

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Environmental Effects on Polymers

• Permeable to many gases H2O vapor
• 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