ppp dsc 1 thermal analysis fundamentals of analysis

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

14

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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