20 Polymers II
-
Upload
kiran-babu-satuluri -
Category
Documents
-
view
215 -
download
0
Transcript of 20 Polymers II
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 1/49
Polymers II/ Objectives1. Explain the basis for polymer crystallinity.
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 2/49
Polymers II/ Objectives1. Explain the basis for polymer crystallinity.
2. Explain the effects of crystallinity on physical andmechanical properties.
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 3/49
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.
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 4/49
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.
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 5/49
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.
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 6/49
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.
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 7/49
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.
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 8/49
Physical Properties of Polymers
1. Non conducting - electrically
(except polyacetylene)
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 9/49
Physical Properties of Polymers
1. Non conducting - electrically
(except polyacetylene)
2. Good thermal insulators
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 10/49
Physical Properties of Polymers
3. Free volume varies with temp
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 11/49
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
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 12/49
Heat Capacity
ThermosetsAmorphous polymers
Tg : cure – exotherm
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 13/49
Heat Capacity
Semi-crystalline polymersTg : weak
Crystallization – exotherm
Melting - endotherm
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 14/49
Heat Capacity
GeneralWater vaporization – endotherm
Additive vapor – endotherm
Decomposition - exotherm
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 15/49
Glass Transition Temp.
1. Breakdown of Van Der Waals Forces
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 16/49
Glass Transition Temp.
1. Breakdown of Van Der Waals Forces
2. Onset of large scale molecular
motions
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 17/49
Glass Transition Temp.
1. Breakdown of Van Der Waals Forces
2. Onset of large scale molecular
motions3. Important in amorphous polymers
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 18/49
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
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 19/49
Modulus & Temperature
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 20/49
Effect of Crosslinking on Modulus
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 21/49
Complex Modulus:
E (t) = E ’(t) + i E ”(t)
E’ – Storage Modulus
(~elastic)
E” – Loss Modulus
(~viscous dissipation)
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 22/49
Transitions from Tan = E’’/E’
Tan =
E’’/E’
TG
Tallest is TG
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 23/49
Tg in Semicrystalline Polymers
1. May show where “brittle” behavior begins
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 24/49
Tg in Semicrystalline Polymers
1. May show where “brittle” behavior begins
2. Not a predictor of service temperature
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 25/49
Tg in Semicrystalline Polymers
1. May show where “brittle” behavior begins
2. Not a predictor of service temperature
3. Crystals maintain high E + SY
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 26/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 27/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 28/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 29/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 30/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 31/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 32/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 33/49
Fracture Processes
1. Two Deformation Process for Thermoplastics
a. Crazing
(amorphous material )
a. Shear Yielding
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 34/49
Craze Process Zone
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 35/49
Fracture Process Zone: PE
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 36/49
Ductile Thermoplastic Fracture at Different
Strain Rates
A
B
C
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 37/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 38/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 39/49
Fracture Processes
3. Fatigue
a. Macroscopically brittle
b. Same mechanismsc. Viscoelasticity complicates picture
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 40/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 41/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 42/49
Effect of 2nd Phase Tougheners
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 43/49
Environmental Effects on Polymers
1. Permeable to many gases & H2O vapor
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 44/49
Environmental Effects on Polymers
1. Permeable to many gases & H2O vapor
2. Inorganic Acids & Bases – fairly resistant
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 45/49
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
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 46/49
Environmental Effects on Polymers
4. Moisture absorption
-Polar polymers (PC, Nylon)
-lowers modulus and yield strength
-problem in processing
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 47/49
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 48/49
Environmental Effects on Polymers
5. UV & Visible light
-Chain scission
-UV stabilizers may be added
7/31/2019 20 Polymers II
http://slidepdf.com/reader/full/20-polymers-ii 49/49
Environmental Effects on Polymers
6. Heat
-Chemical Aging
-Physical Aging