ppp dsc 1 thermal analysis fundamentals of analysis
TRANSCRIPT
Thermal Analysis of Polymers
Thermal Analysis of Polymers
By
Muhammad Zafar Iqbal
P.E. Physical Properties of Polymers
AgendaAgenda
• Introduction to Butyl Rubbers• Introduction to some important physical and chemical
properties of butyl rubbers• Typical Applications based on the above properties• Introduction to Thermoplastic elastomers• Some important applications of TPEs
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Thermal AnalysisThermal AnalysisDefinitionThe term thermal analysis (TA) is frequently used to describe analytical
experimental techniques which investigate the behavior of a sample as a function of temperature.
This (TA) includes the following techniques:
1. Differential Scanning Calorimeter (DSC)
2. Differential Thermal Analyzer (DTA)
3. Thermo-gravimetric analyzer (TGA)
4. Thermo-mechanical analyzer (TMA)
5. Dynamic Mechanical Analyzer
The operational simplicity of TA instruments belies the subtlety of techniques which, if improperly practiced, can give rise to misleading or erroneous results.
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Characteristics of TA techniquesCharacteristics of TA techniquesThe advantages of TA instruments over other techniques include but
not limited to:
(I) The sample can be studied over a wide temperature range using various temperature programmes.
(II) Almost any physical form of sample (solid, liquid or gel) can be accommodated using a variety of sample vessels or attachments
(III) A small amount of sample (0.1 μg-10 mg) is required
(IV) The atmosphere in the vicinity of the sample can be standardized
(V) The time required to complete an experiment ranges from several minutes to several hours
(VI) TA instruments are reasonably priced.
In polymer science, preliminary investigation of the sample transition temperatures and decomposition characteristics is routinely performed using TA before spectroscopic analysis is begun.
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• The recorded data are influenced by experimental parameters such as the sample dimensions and mass, the heating/cooling rate, the nature and composition of the atmosphere in the region of the sample and the thermal and mechanical history of the sample.
• The sensitivity and precision of TA instruments to the physicochemical changes occurring in the sample are relatively low compared with spectroscopic techniques.
• TA is not a passive experimental method as the high-order structure of a sample (for example crystallinity, network formation, morphology) may change during the measurement.
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Variants of DSCVariants of DSC• Heat flux
– 1955 Boersma– 1 large (30 – 100 g) furnace
• Power compensated– Separate small (1 g) microheaters for sample and
reference• Hyper DSC
– Very fast scan rates 500°C/min– Mimic processing conditions
• StepScan DSC– Short dynamic and isothermal scan steps– Separate reversible and irreversible effects
DSCDSC
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Heat Flux DSCHeat Flux DSCSet-up is similar to DTA: analysis sample and reference sample.
Heat-Flow DSC: each sample is surrounded by an inner ring and an outer ring of thermocouples. The average temperature difference between the two measures the heat flow into or out of the sample.
Outer ring of 30 thermocouples
Inner ring of 30 thermocouples
Reference
Analysis
Output of DSCOutput of DSC
Temperature, K
Thermogram
dH/d
t, m
J/s
Glass transition
crystallization
melting
exo
endo
Glass TransitionGlass Transition
• Step in thermogram
• Transition from disordered solid to liquid
• Observed in glassy solids, e.g., polymers
• Tg, glass transition temperature
Temperature, K
Thermogram
dH/d
t, m
J/s
Glass transition
Tg
CrystallizationCrystallization
• Sharp positive peak
• Disordered to ordered transition
• Material can crystallize!
• Observed in glassy solids, e.g., polymers
• Tc, crystallization temperature
Temperature, K
Thermogram
dH/d
t, m
J/s
Crystallization
Tc
MeltingMelting
• Negative peak on thermogram
• Ordered to disordered transition
• Tm, melting temperature
• Melting happens to crystalline polymers; glassing happens to amorphous polymers
Temperature, K
Thermogram
dH/d
t, m
J/s Melting
Tm
ConclusionConclusion
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SamplingSampling
• Pan– Al– Au– Glass capillary tubes
• Maximize contact between sample and pan– Thin films– Fine granules of uniform size
• Grind!
CruciblesCrucibles
Choice of crucible is critical.
• Thermal properties of crucible.
• Reactive properties with samples.
• Catalytic behaviour with samples.
Aluminum: inexpensive, low temp
Copper: used as catalyst (testing polymers)
Gold: higher temp, expensive
Platinum: still higher temp, expensive.
Alumina (Al2O3): very high temp
Sapphire: crystalline alumina, more chemically resistant than amorphous Al2O3.
CalibrationCalibration• Calibrants
– High purity– Metals
• In 156.4°C• Sn 231.9°C• Pb 327.4°C• Zn 419.5°C• Al 660.4°C
– Inorganics• KNO3 128.7°C• KClO4 299.4°C
– Organics• Triphenylmethane• Polystyrene 105°C• Higher thermal conductivity
than metals
– Accurately known enthalpies• EX: indium (5 – 10 mg) H(fusion) = 6.80 cal/g, mp
156.4°C– K * (Area/mass) =
H(fusion) = 6.80 cal/g
– Not hygroscopic– Not light sensitive– High thermal stability– Relatively unreactive
• Pan• Atmosphere
What Can You Measure with DSC?What Can You Measure with DSC?
• Qualitative analysis– Fingerprinting of minerals, clays, polymers
• Sample purity– Melting points
• Heat capacity, cp
• Glass transition temperature, Tg
• Crystallization temperature, Tc
• Phase diagrams
Most Important to RememberMost Important to Remember
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Where Used?Where Used?
• Pharmaceutical industry– Purity
• Food industry– Characterization of fats and oils
• Polymer industry– Synthetic blends
Poly (Lactic Acid)Glass transition temperature, Tg.
30 40 50 60 70 80 90-800
-600
-400
-200 GlassTransition, T
g
DD
SC
, W
/min
DS
C,
W
Temperature, oC
-40
0
40
80
120
160
200
240
DSC
DDSC
DSC traces for melting and crystallization
of a polymer sample.
DSC traces of Low Crystallinity PLA treated in Water at 70C and 100C. The higher the crystallinity achieved
at 100 C, the higher and the less defined the Tg
0 50 100 150 200
-2000
0
2000
1hr@ 70oC
1hr@100oC
Weak Tg
Strong TgDS
C1
00
C W
Temperature, oC
-1000
0
1000
CrystallizationBefore Melting
Same MeltingPattern
Weak ColdCrystallization
Me
ltin
g
DS
C7
0C W
Melting of two semicrystalline HDPE samples.
110 120 130 140 150-20.0k
-15.0k
-10.0k
-5.0k
0.0
EN
DO
H: 165 mj/mg
H: 132 mj/mg
134oC
132oC
DS
C, W
Temperature, oC
HDPE Detergent Bottles HDPE Milk Bottles
Considering H = 200 mJ/mg as the enthalpic change for the melting of a 100% crystalline HDPE sample, from DSC data of these two recyclable HDPE it can be found that:
• the polymer derived from detergent bottles was (132/200)x100 = 66% crystalline
• the polymer used for milk bottles was (165/200)x100 = 82.5% crystalline.
Sample PreparationSample Preparation
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Temperature Gradient in SampleTemperature Gradient in Sample
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Mass of SampleMass of Sample
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Why should we work on micro level..?
Why should we work on micro level..?
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Sample PackingSample Packing
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Scanning RateScanning Rate
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