Characterization of Polymeric

1
Characterization of Polymeric Industrial
Materials by Thermal Analysis Techniques

• Prepared by Kadine Mohomed, Ph.D.
• Thermal Applications Chemist
• TA Instruments

2
Agenda

• 900 - 945 am TGA Theory, Interpretation of
  Results and Kinetic Analysis
• 945 - 1000am Morning Break
• 1000-1100am DSC Theory, Calibration and
  Applications
• 1100-1130am Modulated DSC
• 1130-1200 Open Session/ Questions and Answers,
  Hands-On Training

3
What We Will Accomplish

• Introduction to techniques
• How you can utilize thermal analysis for
  materials characterization
• Amorphous Structure
• Glass Transition
• Crystalline Structure
• Melting
• Crystallization
• Reactions and Processes
• Thermal Stability
• Physical Properties
• Composition and Identification

4
Techniques Available

• Thermogravimetric Analysis (TGA)
• Weight
• Calorimetry
• Differential Scanning Calorimetry (DSC)
• Heat Flow
• Thermal Mechanical Analysis (TMA)
• Length
• Dynamic Mechanical Analysis (DMA)
• Modulus (Stiffness)

5
TGA TrainingTheory, Operation, Calibration and
Data Interpretation
6
Thermogravimetric Analysis (TGA)

• Thermogravimetric Analysis (TGA) measures amount
  and rate of weight change vs. temperature or time
  in a controlled atmosphere
• Used to determine composition and thermal
  stability up to 1500C (depending on exact
  instrument)
• Characterizes materials that exhibit weight loss
  or gain due to decomposition, volatilization,
  oxidation, or dehydration
• TGA is ideal technique to use first on unknown
  samples

7
What TGA Can Tell You

• Volatile Content
• Thermal Stability
• Oxidative Stability
• Composition of Multi-component system
• Decomposition Kinetics
• Estimated Lifetime
• Effect of Reactive atmospheres

Extremely important when running DSC
8
Mechanisms of Weight Change in TGA

• Weight Loss
• Decomposition The breaking apart of chemical
  bonds.
• Evaporation The loss of volatiles with elevated
  temperature.
• Reduction Interaction of sample to a reducing
  atmosphere (hydrogen, ammonia, etc).
• Desorption.
• Weight Gain
• Oxidation Interaction of the sample with an
  oxidizing atmosphere.
• Absorption.
• All of these are kinetic processes (i.e. there is
  a rate at which they occur).

9
Features of the Q500 TGA

• 1. Q Series Two Point Mass Adjustment
• 200mg range
• 1000mg. range
• No need to do a mass recalibration
• when switching from regular Pt pans to
• Pt pans with Aluminum pans.
• Mass Loss Reference Materials
• Materials with nominal 2, 50 and 98
• mass loss are available for verification of TGA
• weight calibration.
• 2. Curie Point Transition Temperature
• Calibration
• ASTM 1582
• Curie Temperature Reference Materials
• TA Instruments is the exclusive worldwide
• distributor for a set of six certified and
  traceable
• Curie temperature materials developed by ICTAC

10
TGA How the balance works

• The balance operates on a null-balance principle.
  At the zero, or null position equal amounts of
  light shine on the 2 photodiodes.
• If the balance moves out of the null position an
  unequal amount of light shines on the 2
  photodiodes. Current is then applied to the
  meter movement to return the balance to the null
  position.
• The amount of current applied is proportional to
  the weight loss or gain.

11
TGA Purge Gas Flow
10ml/min
40ml/min
90ml/min
60ml/min
EGA Furnace
Standard Furnace
12
Typical Methods

• Ramp (heating) experiment ex. Ramp 20C/min.
  to 800C (Thermal Stability)
• Ramp (heating) and Isothermal Hold ex. Ramp
  20C/min. to 200C Iso 60 min.

13
Method Segments
14
TGA Curves are not Fingerprint Curves
Because most events that occur in a TGA are
kinetic in nature (meaning they are dependent on
absolute temperature and time spent at that
temperature), any experimental parameter that can
effect the reaction rate will change the shape /
transition temperatures of the curve. These
things include

• Pan material type, shape and size.
• Ramp rate.
• Purge gas.
• Sample mass, volume/form and morphology.

15
Effect of Sample Size on Decomposition
Temperature of Polystyrene
16
Effect of Heating Rate on Decomposition
Temperature of Polystyrene
17
Mass Effect Semi-crystalline PE
18
Optimizing TGA Resolution

• Means of Enhancing Resolution
• Slower Heating Rate - longer runs.
• Reduced Sample Size - detection of small weight
  losses compromised.
• Change Purge Gas - not applicable in all cases.
• Pin-hole Hermetic Pans
• - not applicable in all cases.

19
DSC Pinhole Pans Used in a Gypsum TGA Experiment
20
Resolution Enhancement by Changing Purge
PET
gas switch
N2 Air N2 w/ switch to air
21
Comparison of 1C/min, 20C/min Hi-Res TGA
22
Acetaminophen Std TGA Vs. Hi-Res
23
PET w/ Carbon Black Filler
How much Carbon Black was in this sample?
24
PET
25
Comparison of Filled Un-Filled PET
26
Calcium Oxalate Standard Analysis

• Although Calcium Oxalate is not generally
  accepted as a Standard Material, it does have
  practical utility for INTRA-laboratory use
• Carefully control the experimental conditions
  i.e. pan type, purge gases/flowrates, heating
  rate
• Particularly control the amount (5mg) and the
  particle size of the sample and how you position
  it in the pan

27
Calcium Oxalate Standard Analysis

• Perform multiple runs, enough to do a statistical
  analysis
• Analyze the weight changes and peak temperatures
  and establish the performance of YOU and YOUR
  instrument
• When performance issues come up -- repeat

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Calcium Oxalate Decomposition

• 1st Step CaC2O4H2O (s) CaC2O4 (s) H2O (g)
• Calcium Oxalate Monohydrate Calcium
  Oxalate
• 2nd Step CaC2O4 (s) CaCO3 (s) CO (g)
• Calcium Oxalate Calcium Carbonate
• 3rd Step CaCO3 (s) CaO (s) CO2 (g)
• Calcium Carbonate Calcium Oxide

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Calcium Oxalate Repeatability
Overlay of 8 runs, same conditions
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Thermal Stability

• Thermal Stability
• Can be studied by multiple techniques
• May be studied w/ inert or oxidizing atmospheres
• TGA Best choice
• Weight loss
• DSC
• Change in heat flow (typically exothermic)
• DSC cell can be contaminated
• Can also see the effect in other techniques like
  DMA TMA

31
TGA Profile In Nitrogen and Air

• First Step in Materials Characterization
• Look for
• Thermal Stability
• Volatilization/Decomposition Temperature
• Weight Loss Profile
• Number of Steps
• Chemical Identification using FTIR, MS
• Residue
• Char/Ash/Filler Presence

32
TGA Gives Upper Limit for DSC
PTFE 8.91mg N2 Purge _at_ 10C/min
Decomposition products can include Hydrogen
fluoride!
33
Filled Polymer Analysis

Inert filler
Inert filler
Inert filler
34
Kinetic Analysis

• The rate at which a kinetic process proceeds
  depends not only on the temperature the specimen
  is at, but also the time it has spent at that
  temperature.
• Typically kinetic analysis is concerned with
  obtaining parameters such as activation energy
  (Ea), reaction order (k), etc. and/or with
  generating predictive curves.

35
Kinetic Analysis, cont.
Activation energy (Ea) can be defined as the
minimum amount of energy needed to initiate a
chemical process.
Ea
State 1
State 2
With Modulated TGA, Ea can be measured directly.
36
TGA Kinetics

• 1st Order Kinetics based on Flynn and Wall method
• Lifetime Estimation based on Toops and Toops
  method
• PTFE tested at 1, 5, 10 and 20 deg/min
• Sample sizes constant
• Nitrogen purge
• Conversion levels selected at 1, 2.5, 5, 10 and
  20

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Common Thermogram with TGA Scans
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Log Heating Rate versus 1/T
Check for linearity
1000/T (K)
39
Activation Energy by MTGA
40
Questions on TGA?Break 15min
41
Q100 DSC Theory, Operation, Calibration, Data
Interpretation and Modulated DSC
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What Does a DSC Measure?

• A DSC measures the difference in heat flow rate
  (mW mJ/sec) between a sample and inert
  reference as a function of time and temperature

43
Endothermic Heat Flow

• Heat Flow
• Endothermic heat flows into the sample as a
  result of either heat capacity (heating) or some
  endothermic process (Tg, melting, evaporation,
  etc.)

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Exothermic Heat Flow

• Heat Flow
• Exothermic heat flows out of the sample as a
  result of either heat capacity (cooling) or some
  exothermic process (crystallization, cure,
  oxidation, etc.)

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• Typical DSC Transitions

Composite graph
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What DSC Can Tell You

• Identification of amorphous crystalline
  material
• Identification of phase transitions and changes
  of state
• Specific Heat Capacity measure of molecular
  mobility
• Heats of fusion reactions
• Oxidative/Thermal Stability
• Reaction Kinetics

47
Temperature

• What temperature is being measured and displayed
  by the DSC?
• Sensor Temp used by most DSCs. It is measured
  at the sample platform with a thermocouple,
  thermopile or PRT.

48
DSC Heat Flow
49
How does a DSC Measure Heat Flow?
DSC comprises two nominally identical
calorimeters in a common enclosure that are
assumed to be identical.

• Advantages of a twin calorimeter
• Noise reduction by cancellation of common
  mode noise.
• Simplified heat flow rate measurement.
• Cancellation of calorimeter and pan heat
  capacities.
• Cancellation of heat leakages.

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How do we Measure Heat Flow?
QSeries DSC
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Tzero Heat Flow Measurement - T4
Thermal Resistance Imbalance
Heating Rate Difference
Principal DSC Heat Flow
Heat Capacity Imbalance
The four term Tzero heat flow rate measurement
includes effects of the thermal resistance and
heat capacity imbalances as well as the
difference in the heating rates of the sample and
reference calorimeters. When the assumptions of
conventional DSC are applied, only the first term
remains and the conventional heat flow rate
measurement is obtained.
52
Thoughts on Calibration

• Calibration
• Use Calibration Mode (collect uncorrected data)
• Calibrate upon installation
• Re-calibrate every ????
• Verification
• Determine how often to verify data
• Run a standard as a sample (std mode)
• Compare results vs. known
• If results are within your tolerance system
  checks out and doesnt re-need calibration
• If results are out of tolerance, then re-calibrate

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DSC Calibration

• Heat Flow (Cell Constant)
• ASTM E-968
• Temperature Calibration
• ASTM E-967
• Baseline (depending on instrument)

54
Traceable Calibration Materials

• NIST DSC calibration materials
• SRM 2232 Indium Tm 156.5985C
• SRM 2220 Tin Tm 231.95C
• SRM 2222 Biphenyl Tm 69.41C
• SRM 2225 Mercury Tm -38.70C
• NIST Gaithersburg, MD 20899-0001
• Phone [phone]
• Fax [phone]
• Email SRMINFO_at_nist.gov
• Website http//ts.nist.gov/srm

55
Traceable Calibration Materials

• LGC DSC Calibration Materials
• LGC2601 Indium (TA p/n 915060-901)
• LGC2608 Lead
• LGC2609 Tin
• LGC2611 Zinc
• Laboratory of the Government Chemist, UK
• Phone [phone]
• Fax [phone]
• Email orm_at_lgc.co.uk

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To begin calibration start DSC Calibration Wizard
57
Select Heat flow signal type of cooler
Q1000 T4P Q100 T4 Q10 T1
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Select which calibration to perform
Tzero Calibration
59
Enter parameters for first run (empty cell)
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Start experiment
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Enter weight of sapphire samples
62
When run is completed, capacitance resistance
are plotted and saved
63
Always run Indium for Cell Constant
Enter parameters for Indium sample
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Enter temperatures for Indium run
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Start experiment
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Data is analyzed automatically
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(No Transcript)
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Verify Calibration

• Instead of automatically re-calibrating at some
  interval, consider verification
• If it aint broke dont fix it theory
• Empty cell baseline
• Indium verification

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Verifying Baseline

• After completion of calibration routine, run
  baseline
• Standard mode
• Empty cell, -90C-400C (w/ RCS)
• Plot mw vs. temperature on a 1mw scale
• Should look fairly flat on this scale
• To verify performance in the future re-run

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Verifying Baseline
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Verifying Baseline
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Verifying Baseline
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Verifying Baseline
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Verifying Heat Flow Temperature

• Run Indium as a sample (i.e. in std mode not cal
  mode)
• Analyze melt and record melt onset heat of
  fusion
• Compare to known values
• Melting of In 156.598C
• Heat of Fusion 28.71J/g

75
Verifying Heat Flow Temperature
Temp is within 0.04C Heat of fusion is within
0.11J/g
76
Selecting Optimum Experimental Conditions

• "Always" do TGA experiments before beginning DSC
  tests on new materials
• Heat approximately 10mg sample at 10C/min to
  determine
• Volatile content
• Unbound water or solvent is usually lost over a
  broader temperature range and a lower temperature
  than a hydrate/solvate
• Decomposition temperature
• DSC results are of little value once the sample
  has lost 5 weight due to decomposition (not
  desolvation)
• Decomposition is a kinetic process (time
  temperature dependent). The measured
  decomposition temperature will shift to lower
  temperatures at lower heat rates

77
Selecting Optimum Experimental Conditions (cont.)

• Use TGA data to help select DSC experimental
  conditions
• Crimped vs. Hermetic (sealed) Pan
• Use hermetic pan if sample loses approximately
  0.5 or more
• Maximum Temperature
• Excessive decomposition will contaminate DSC cell
  between runs
• When comparing samples, always use the same
  experimental conditions

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• Optimization of DSC Conditions

• Sample Preparation
• Keep thin cut rather than crush
• Weight of 10-15mg for polymers 3-5mg for metal
  or chemical melting
• Goal is to achieve a change of 0.1-10mW heat flow
  in going through the transition
• If sample contains volatiles, put 5-10 pinholes
  in the lid of the pan before crimping in order to
  permit a continuous evaporation process

79

• Optimization of DSC Conditions

• Experimental Conditions (cont.)
• Select an end-temperature which does not cause
  decomposition of the sample to occur in the DSC.
  Decomposition products can condense in the cell
  and cause either corrosion of the cell or
  baseline problems
• Use sealed glass ampoules or stainless steel
  pans, which can take high pressure (gt1000psi), in
  order to study decomposition by DSC

80

• Optimization of DSC Sensitivity or Resolution

Basic Heat Flow Equation dQ/dT
Cp x dT/dt f(T,t) heat flow
heat capacity x heating rate kinetic
component
Parameters
To Increase Sensitivity
To Increase Resolution
Sample Weight
Increase
Decrease
Heating Rate
Increase
Decrease
81
Sample Pans

• Type of pan depends on-
• Sample form
• Volatilization
• Temperature range
• Use lightest, flattest pan possible
• Always use reference pan of the same type as
  sample pan

82
Standard DSC Pans (Crimped)

• Used for solid non-volatile samples
• Always use lid (see exceptions)
• Lid improves thermal contact
• Keeps sample from moving
• Exceptions to using a lid
• Running oxidative experiment
• Running PCA experiment

83
Standard DSC Pans (Crimped)

• Crimped pans are available in
• Aluminum - up to 600C
• Copper - up to 725C (in N2)
• Gold - up to 725C
• Standard Pans without lids
• Graphite - up to 725C (in N2)
• Platinum - up to 725C

84
Hermetic Pans (Sealed)

• Used for liquid samples and samples with
  volatiles
• Always use lid (same exceptions as before)

85
Hermetic Pans (Sealed)

• Hermetic Pans are available in
• Aluminum lt600C lt3 atm (300 kPa gage)
• Alodined Aluminum - lt600C lt3 atm (300 kPa gage)
• (For aqueous samples)
• Gold lt725C, lt6 atm (600 kPa gage)
• Specialized Sealed Pans
• High Volume - 100µL lt250C 600 psig(4.1 MPa)
• High Pressure - 35µL lt300C 1450 psig(10 MPa)
• Note 3 atm is approximately 44 psig

86
Keeping the DSC Cell Clean

• One of the first steps to ensuring good data is
  to keep the DSC cell clean
• How do DSC cells get dirty?
• Decomposing samples during DSC runs
• Samples spilling out of the pan
• Transfer from bottom of pan to sensor

87
How do we keep DSC cells clean?

• DO NOT DECOMPOSE SAMPLES IN THE DSC CELL!!!
• Run TGA to determine the decomposition
  temperature
• Stay below that temperature!
• Make sure bottom of pans stay clean
• Use lids
• Use hermetic pans if necessary

88
TGA Gives Decomposition Temperature
89
Cleaning Cell Q Series

• Use solvent slightly damp swab w/ appropriate
  solvent
• Heat cell to 200C for 10 min to drive off any
  remaining solvent
• If the cell is still dirty

90
Cleaning Cell Q Series

• If the cell is still dirty
• Clean w/ brush
• Brush gently both sensors and cell if necessary
• Be careful with the Tzero thermocouple
• Blow out any remaining particles

91
Before Cleaning
92
Brushing the Sample Sensor
93
After Cleaning Sample Sensor
Fibers in cell from cleaning brush need to be
removed
94
Cleaning Cell Q Series

• Bake out (Use as a last resort)
• Air purge
• Open lid
• Heat _at_ 20C/min to appropriate temp (max of
  550C) No Isothermal _at_ the upper temperature
• Cool back to room temp brush cell again
• Check for improved baseline performance

95
DSC APPLICATIONS Amorphous Materials

• Amorphous Structure
• Randomly oriented molecules
• No long-range order
• Liquids, glassy or rubbery solids
• Most polymers are either amorphous or
  semi-crystalline

96
Characterization of Amorphous Structure

• Glass Transition (Tg)
• Due to amorphous (non-crystalline) structure
• Due to macro-molecular motion (translational)
  i.e., the entire molecule is free to move
  relative to adjacent molecules.
• Extremely important transition because the
  significant change in molecular mobility at Tg
  causes significant changes in physical and
  reactive properties.

97
Changes at the Tg
Polystyrene - Modes of Molecular Motion/Mobility
Translation
Rotation
Vibration
98
Characterization of Amorphous Structure

• Glass Transition
• Detectable by DSC due to a step increase in heat
  capacity
• Detectable by TMA as an increase in rate of
  expansion
• Detectable by DMA as a decrease in modulus

99
Glass Transition Analysis

• Reporting the Glass Transition (Tg) Temperature
• Tg is always a temperature range and never a
  single temperature
• When reporting a single temperature, it is
  necessary to state
• What point in the step change (onset, midpoint,
  end, etc.) is being measured
• The experimental conditions used to measure Tg
  such as technique (DSC, DMA, TMA, DEA etc.),
  heating rate, sample size or weight, modulation
  conditions, etc.

100
Tg by DSC

• DSC
• Most common technique for Tg
• Small sample size
• Faster analysis (fast heating, automation)
• MDSC
• Can separate kinetic and heat capacity related
  events

101
Tg by DSC
Polystyrene - 9.67mg 10C/min
Selected Start
Extrapolated Onset Temperature
? Heat Flow or Cp Used to Calculate Amorphous
Midpoint at ½ Cp or Heat Flow Change
Selected End
102
Glass Transition Analysis
Polystyrene - 9.67mg 10C/min
Same data file, same limits, only Tg by infection
103
What Affects the Tg by DSC?

• Heating Rate
• Heating Cooling
• Aging
• Molecular Weight
• Plasticizer
• Filler

• Crystalline Content
• Copolymers
• Side Chains
• Polymer Backbone
• Hydrogen Bonding

Anything that effects the mobility of the
molecules, affects the Heat Capacity, and in turn
the Glass Transition
104
General DSC Recommendations for Tgs

• 10 mg sample weight
• 10C/min rate (H-C-H)
• Remember - Thermal History can change results

105
Effect of Heating Rate on the Tg
10.04mg PMMA
106
Glass Transition Detection

• The Tg is a low energy transition
• Due only to amorphous structure
• Can be hard to detect in semi-crystalline
  samples.
• To increase sensitivity
• DSC
• Use larger (gt10mg) samples and higher (gt10C/min)
  heating rates
• Quench cool sample from above the melt
• Use MDSC
• Use TMA or DMA

107
MDSC Separates the Total Heat Flow Signal of DSC
into Two Parts
108
Measuring Amorphous Structure
MDSC Conditions

• For standard Tg
• Sample Size 10 15 mg Amplitude 0.6-0.8C
• Period 60 seconds Heating Rate 3C/min
• If Tg is Hard to Detect Sample Size 10 20
  mg Amplitude 1.0C-1.25CPeriod 80 seconds
  Heating Rate 2C/min
• If Tg has Large Enthalpic Relaxation Sample
  Size 5 10 mg Amplitude
  0.3C-0.5CPeriod 60 seconds Heating
  Rate 1C/min

With Tzero pans standard hermetic pans. You
can subtract 20 sec for low mass
Tzero pans standard crimped pans.
Add 20 sec for 2900
series MDSC
109
Is it a Tg?

• If not sure if a transition is a Tg
• Run Heat-Cool-Heat (H-C-H)
• If transition is a Tg then it should be present
  on cooling curve and 2nd heat
• Run MDSC
• A Tg will always show up in the Reversing Curve
  of a MDSC experiment
• Run TMA or DMA

110
Is this a Tg or a Melt?
111
Now Is this a Tg or a Melt?
Sample was annealed (aged) for 130 hours _at_ 135C
Cool
2nd Heat
1st Heat
112
Enthalpic Relaxation/Recovery at Tg

• Enthalpic relaxation, or aging, is the process of
  amorphous material approaching equilibrium
  (never reached). Energy is released as a function
  of time and temperature
• Enthalpic recovery is the endothermic transition
  seen at the end of a glass transition in DSC
  experiments. It is the recovery of energy that
  was dissipated during aging
• In traditional DSC, enthalpic recovery can appear
  as a melt and make measurement of Tg difficult
• Since enthalpic recovery is a kinetic event, it
  can be separated from the change in heat capacity
  by MDSC or the change in length by MTMA

113
Effect of Aging on Amorphous Structure
2 Equal Masses of Amorphous Material
Max Tg
Temp. Above Tg
Storage
Same
Properties
time
V
Quench Cooled in Liquid N2
H
Cooled At 1C Per Day
Equilibrium
Liquid
M
H
S
Equilibrium
Temp. 20C Below Tg
Glass
Different Properties
Kauzmann
Temp Lowest Tg
(Entropy of Crystal)
Temperature
After 1 Year Storage _at_ Tg -20C
Where H HIGH relative cooling rate
Temp. 20 Below Tg
Similar Properties
M MODERATE relative cooling rate
S SLOW relative cooling rate
114
MDSC of Aged Polycarbonate
Sample was annealed (aged) for 130 hours _at_ 135C
115
Importance of Enthalpic Relaxation

• Is enthalpic recovery at the glass transition
  important?
• Sometimes!
• If two samples of finished product have
  significantly different size enthalpic recovery
  peaks (differ by 0.5 J/g or more), they can be
  expected to show differences in some physical
  properties (size, hardness, impact resistance,
  etc.)
• Differences in the size of the enthalpic recovery
  peak for raw materials that will be processed at
  temperatures above Tg are not important
• The thermal history of raw materials is usually
  not controlled
• These samples should be compared after they are
  heated to a temperature above Tg which removes
  the previous thermal history

116
PMMA Annealed _at_ 90C
117
2 Tgs?
Is this a Tg?
What about this?
118
1 Tg
Thermoplastic Elastomer -- MDSC 0.48/60_at_3
Yes!
No!
Tgs occur in Rev Heat Flow 1st transition
clearly is a Tg 2nd one isnt
119
Wheres the Tg
4.1 mg Cellulose Acetate in Vented Pan
120
Very Clear by MDSC
4.1 mg Cellulose Acetate in Vented Pan
121
DSC of Complex Polymer Blend
Quenched Xenoy -- 13.44mg -- DSC _at_ 10C/min
122
MDSC of Complex Polymer Blend
Quenched Xenoy -- 13.44mg -- MDSC
0.318/60_at_2C/min
123
Partially Miscible Amorphous Phases

• If not miscible then Tgs dont shift
• If completely miscible then one Tg in the middle

ABS-PC Copolymer Alloy
124
Semi-Crystalline Polymers

• Crystalline Structure
• Molecules arranged in well defined structures
• Consists of repeating units
• Polymers can have crystalline phases
• Length of molecules prevents complete
  crystallization
• Semi-crystalline Polymers
• Both amorphous crystalline solid phases
• Examples are most common thermoplastics
• Polyethylene, Polypropylene, etc

125
Melting

• Melting The process of converting solid
  crystalline structure to liquid amorphous
  structure
• Melting shows up as an endothermic peak in a DSC
  scan
• The energy required to melt the crystalline phase
  is proportional to the amount of crystalline
  phase
• In most cases sensitivity isnt an issue with
  melting transitions
• Heating rate doesnt effect the onset of melting
  (much), but will effect resolution

126
Definitions

• Thermodynamic Melting Temperature The
  temperature where a perfect crystal would melt
• Metastable Crystals Crystals that melt at lower
  temperature due to imperfections
• Crystal Perfection The process of metastable
  crystals melting at a temperature below their
  thermodynamic melting point and then (re)
  crystallizing into larger, more perfect crystals
  that will melt again at a higher temperature

127
Definitions (cont.)

• True Heat Capacity Baseline (Thermodynamic
  baseline) the measured baseline (usually in heat
  flow rate units of mW) with all crystallization
  and melting removed.
• Assumes no interference from other latent heat
  over the crystallization/melting range.
• Such as polymerization, cure, evaporation, etc.

128
Definitions (cont.)

• Crystallization The process of converting
  either solid amorphous structure (cold
  crystallization on heating) or liquid amorphous
  structure (cooling) to a more organized solid
  crystalline structure
• Enthalpy of Melting/Crystallization - The heat
  energy required for melting or released upon
  crystallization. This is calculated by
  integrating the area of the DSC peak on a time
  basis.

129
Melting of Indium
Extrapolated Onset Temperature
Heat of Fusion
For pure, low molecular weight materials (mwlt500
g/mol) use Extrapolated Onset as Melting
Temperature
Peak Temperature
130
Melting of PET
For polymers, use Peak as Melting Temperature
Extrapolated Onset Temperature
Heat of Fusion
Peak Temperature
131
Melting Recommendations

• 10 mg sample weight (most polymers)
• Run Heat-Cool-Heat Method
• 10C/min heating/cooling rate
• Remember - Thermal History can change results

132
If a melt is questionable

• If hard to see
• Larger sample
• Faster rate
• If hard to separate from another transition
• Slower heating rate
• Try MDSC
• Is it really a melt?
• Try H-C-H
• Try different heating rates
• Try MDSC

133
Measurement of a Melt by DSC
134
Heat-Cool-Heat of PET
135
Baseline Type
136
Calculation of Crystallinity

• Sample must be pure material, not copolymer or
  filled
• Must know enthalpy of melting for 100
  crystalline material (DHlit)

137
ATHAS Databank
The ATHAS Databank is a source for the DHf for
common polymers
138
ATHAS Summary Page for PET
DHf in kJ/mol
139
PET Bottle Resin Cold Crystallization
Temperature Ramp at 3C/min. Frequency 1
Hz Strain 0.025
a- transition Tg 88.0C
G
Cold Crystallization
G
b- transition -56.62C
tan d
DMA Rheology provide information how molecular
structure is changing as a material is
crystallizing
140
PET Bottle Resin
Before and After DMA Scan
Pressed PET Bottle Resin
PET After Temperature Ramp Scan (Cold
Crystallization)
141
PET Bottle Resin - 2nd Run
142
Dynamic Mechanical Analysis (DMA)
143
What Does DMA Measure?

• DMA Solids Rheometer
• Deforms a sample mechanically measures the
  response
• Deformation can be applied
• Sinusoidally (oscillatory) most common
• Fixed stress or strain (creep/stress relaxation)
• Constant stress or strain rate
• Response monitored as function of temperature,
  time, and frequency

144
What DMA Can Tell You

• Transition Temperatures
• Glass transitions
• Secondary transitions
• Mechanical Properties and Viscoelastic
  information
• Modulus
• Damping

145
Polymer Structure

• The mechanical properties of a polymer are a
  consequence of
• Chemical Composition of the Polymer
• Dictates where changes in mechanical properties
  occur
• Physical Molecular Structure of the Polymer
• Dictates how changes in mechanical properties
  will occur
• A DMA can be used to measure the mechanical
  properties of a polymer material and relate them
  to differences in composition and molecular
  structure (chemical and physical differences).

146
Dynamic Mechanical Testing
147
DMA Viscoelastic Parameters
The Modulus Measure of materials overall
resistance to deformation.
E Stress/Strain
The Elastic (Storage) Modulus Measure of
elasticity of material. The ability of the
material to store energy.
E' (stress/strain)cos?
The Viscous (Loss) Modulus The ability of the
material to dissipate energy. Energy lost as
heat.
E" (stress/strain)sin?
Tan Delta Measure of material damping - such
as vibration or sound damping.
Tan ?? E"/E'
148
Typical DMA Data
Glassy Region
Transition Region
Rubbery Plateau Region
Terminal Region
Viscoelastic liquid
Log E and E
Very hard and rigid solid
Stiff to Soft rubber
Storage Modulus (E' or G')
Loss Modulus (E" or G")
Temperature/Time/Frequency-1
149
Variety of Clamps Available

• Bending
• Cantilever
• 3-Point Bending
• Tension
• Film/fiber
• Shear
• Compression

150
The Importance of the Glass Transition Measurement

• Below the glass transition temperature, many
  amorphous polymers are hard, rigid glasses
• modulus is gt 109 Pa
• In the glassy region, thermal energy is
  insufficient to surmount the potential barriers
  for translational and rotational motions of
  segments of the polymer molecules. The chain
  segments are frozen in fixed positions.
• Above Tg, the amorphous polymer is soft and
  flexible.
• modulus in this rubbery region is about 105 or
  106 Pa.
• Because of the four orders of magnitude change in
  modulus between the glassy and rubbery state, the
  Tg can be considered the most important material
  characteristic of a polymer.

Nielsen, Lawrence E., Mechanical Properties of
Polymers and Composites, Marcel Dekker, Inc., New
York, 1974, p. 19.
151

• E' Onset, E" Peak, and tan ? Peak

• E' Onset Occurs at lowest temperature - Relates
  to mechanical Failure

• E" PeakOccurs at middle temperature - more
  closely related to the physical property changes
  attributed to the glass transition in plastics.
  It reflects molecular processes - agrees with the
  idea of Tg as the temperature at the onset of
  segmental motion.

• tan d Peak Occurs at highest temperature - used
  historically in literature - a good measure of
  the "leatherlike" midpoint between the glassy and
  rubbery states - height and shape change
  systematically with amorphous content.

Reference Turi, Edith, A, Thermal
Characterization of Polymeric Materials, Second
Edition, Volume I., Academic Press, Brooklyn, New
York, P. 980.
152

• PSA Glass Transition Measurement

153
Structure-Property Relationships
Effects of Crystallinity, Molecular Weight, and
Crosslinking on Modulus
Increasing Crystallinity
Amorphous
Crystalline
log Modulus
Cross-linked
3 decade drop in modulus at Tg
Tm
Increasing MW
Temperature
154

• The Glass Secondary Transitions

• Glass Transition - Cooperative motion among a
  large number of chain segments, including those
  from neighboring polymer chains
• Secondary Transitions
• Local Main-Chain Motion - intramolecular
  rotational motion of main chain segments four to
  six atoms in length
• Side group motion with some cooperative motion
  from the main chain
• Internal motion within a side group without
  interference from side group.
• Motion of or within a small molecule or diluent
  dissolved in the polymer (eg. plasticizer.)

Reference Turi, Edith, A, Thermal
Characterization of Polymeric Materials, Second
Edition, Volume I., Academic Press, Brooklyn, New
York, P. 487.
155
Nylon Temperature Ramp
Nylon Fiber Film Clamp 8.94mm x 0.15mm
3C/min - 20µm _at_ 1Hz
156
Nano Clay Composite
Nylon Fiber w/ Clay nano composite
Film Clamp 8.94mm x 0.15mm -
3C/min - 20µm _at_ 1Hz
157
Overlay of the Two Results
Clay Nano Composite has Higher Modulus
158
Effect of Fiber Orientation
Carbon Composite
159
What if I need help?

• On-site training e-Training courses - see
  Website
• Call the TA Instruments Applications Hotline
• 302-427-4070 M-F 8-430 Eastern Time
• mailto thermalsupport_at_tainstruments.com
• Call the TA Instruments Service Hotline
• 302-427-4050 M-F 8-430 Eastern Time
• Check our Website
• www.tainstruments.com