differential scanning calorimetry - uab · pdf filethermal analysis techniques technique...

Differential Scanning Calorimetry

Derrick DeanUniversity of Alabama at Birmingham

2

Agenda

• Brief overview of polymers• DSC Basics• Applications

– Melting transitions, Tm– The glass transition, Tg– Thermal Stability

• Modulated DSC, MDSC• Variations in DSC

• Quality Control• Characterization• Processing• End Use Application

Thermal Analysis Useful For

Most Commonly Used Thermal Analysis Techniques

Technique Parameter Measured

DifferentialScanningCalorimetry(DSC)

dH/dT

Thermogravimetry (TGA) Mass

Derivative Thermogravimetry(DTGA)

dM/dT

Thermomechanical Analysis (TMA)(Dilatometry; Penetration)

Deformation, Volume or Length

Dynamic MechanicalAnalysis(DMA)

Modulus/ Damping

Dielectric Analysis (DEA) Permitivity/ Loss Factor

Major Polymer Transitions

• Glass Transition, Tg– Indicates minimum/maximum service temperature

– Very important in amorphous polymers

• Melting temperature, Tm– Defines minimum processing andmaximum service temperature

Two Main Transitions in Thermoplastic Polymers

Transitions and RelaxationsWhy Important?

Range at which properties change Modulus Brittleness Impact strength Wear Permeability Thermal conductivity Strength Dielectric constant Stress‐strain properties Electrical conductivity

Transitions and RelaxationsIf we examine polymer properties with respect to temperature and/or frequencywe find that there is a range over which the properties change(eg., Silly Putty)

Log E

Log

Log E

T

• At high frequencies no motion ‐> unrelaxed• At low frequencies it flows ‐> relaxed

If T is changed instead of , same features result.

Relaxation – significant “sharp” or “steep” change in properties in a relatively narrow temperature or frequency range.

Transitions and RelaxationsRelaxation – significant “sharp” or “steep” change in properties in a relatively narrow temperature or frequency range.

Can be related to various types of polymer motion :

1. Side chain rotation ( PP, PMMA or PS)

2. Small segments as in PE :

3. Longer segments(20‐30 carbon atoms, as at Tg)

‐- CH2 - C -

‐CH3

C=O‐‐

O

CH3

- CH2 - CH -CH3

-

‐

- CH2 - CH -

Transitions and Relaxations

• Includes changes of state:• Crystalline‐to‐amorphous‐ Tm• Crystalline1‐to‐crystalline2 – polymorphism• Amorphous‐to‐glass – Tg

• At a transition there will be a discontinuous change in thermodynamic properties, which can be observed to define the transition temperature.

• Specific volume• Heat capacity• Specific heat(Enthalpy)

Transition – a discontinuous change in thermodynamic propertiesof a material.


v

T

Cp

T

T

Tm is a first ordertransition

V

T

1st Order Transition – Transition for which the first order derivative of free energy is a thermodynamic function that is discontinuous when plotted vs. temperature.

2nd Order Transition – Transition for which the second order derivative of free energy is a thermodynamic function that is discontinuous when plotted vs. temperature.

Tg is a second ordertransition

Tg is a second ordertransition


Change is greatest at Tm and Tg, and less so at lower temperature relaxations. Many polymers become brittle below Tg‐ no means to absorb energy of impact(PS, PMMA) Some remain ductile(PC, PET), because of a large secondary relaxation at T < Tg which can absorb energy and become brittle at much lower T, below the secondary relaxation.

Relative Sensitivity of Thermal Analysis Instruments

Technique Property Measured Relative Signal Change at Tg

Differential Scanning Calorimetry

Heat flow(heat capacity) 0.2

Thermomechanical Analysis Expansion Coefficient; Dimension Change or Softening

3

Dielectric Analysis Permittivity and dielectric loss

100

Dynamic Mechanical Analysis

Mechanical strength and energy loss

200

14

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

• Speed of operation• Ease of operation• Small sample size

Popularity of DSC Technique

Information Obtained from DSC

•Glass Transition temperatures• Melting points and boiling points• Crystallization time and temperature• Percent crystallinity• Heats of fusion and reaction• Specific heat• Oxidative stability• Rate of cure• Degree of cure• Reaction kinetics• Purity• Thermal stability

Types of DSC

Heat Flux Power Compensation

Same heat flows into both samples; T =0.When a change occurs(endo or exo) a Tsignal is generated which is proportional tothe heat flow difference.

When a T is detected, an additional circuit will increase or decrease heating power Of sample furnace. This compensating heating power, P, is proportional to heat absorbed or released.

18

DSC Heat Flow

t)(T,dtdT Cp

dtdH f

signal flowheat DSC dtdH

Weight SampleHeat x Specific Sample CapacityHeat Sample Cp

Rate Heating dtdT

(kinetic) re temperatuabsolutean at timeoffunction is that flowHeat t)(T, f

Typical DSC Output: Transitions of Interest in a DSC

Temperature

Heat Flow ‐>

exothermic

GlassTransition Crystallization

Melting

Cross‐Linking(Cure)

Oxidation or

Decomposition

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

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

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

21

DSC: Terminology

Amorphous Phase - The portion of material whose molecules are randomly oriented in space. Liquids and glassy or rubbery solids. Thermosets and some thermoplastics.Crystalline Phase - The portion of material whose molecules are regularly arranged into well defined structures consisting of repeat units. Very few polymers are 100% crystalline.Semi-crystalline Polymers - Polymers whose solid phases are partially amorphous and partially crystalline. Most common thermoplastics are semi-crystalline.Endothermic - A transition which absorbs energy.Exothermic - A transition which releases energy.Melting - The endothermic transition upon heating from a crystalline solid to the liquid state. This process is also called fusion. The melt is another term for the polymer liquid phase.Crystallization - The exothermic transition upon cooling from liquid to crystalline solid. Crystallization is a function of time and temperature.Cold Crystallization - The exothermic transition upon heating from the amorphous rubbery state to the crystalline state. This only occurs in semi-crystalline polymers that have been quenched (very rapidly cooled from the melt) into a highly amorphous state.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.

Physical Origins of Peaks in DSC

Endothermic ExothermicCrystalline Transition X X

Fusion X

Crystallization X

Vaporization X

Sublimation X

Adsorption X

Desorption X

Glass Transition Baseline Change, No peaks

Liquid Crystal transition X

Physical Aging X

Chemical Origin of Peaks in DSC

Endothermic ExothermicChemisorption X

Dehydration X

Decomposition X X

Oxidative Degradation

X

Oxidation in Gaseous Atmosphere

X

Adsorption X

Solid State reaction X XCombustion X

Polymerization XCuring X

• 5 to 15 mg for thermoplastics or elastomers• Might no be able to determine TG of highly crosslinked sample

• Melting/Crystallizing– Less than 10 mg– Heat of reaction

• As small as can be accurately measured

• Composites: Depends on filler loading

Sample Size

• Calbration: ASTM E967, E968, D3417, D3418– Same heating rate as experiment– Same atmosphere and purge flow rates(50cc/min)– Same temperature range as experiment

• Pan:– Flat bottom– Good sample –to‐pan contact– Inert to reactive samples

• Reference:– Same pan as sample, but it should be empty

• Pan‐Cell Contact:– Symmetric placement of reference and sample

General Experimental Setup

• Identification of all substances and their sources• Details of material histories, pretreatments, purities, etc.

• Calibration procedures, temperatures, cell constants used.

• Details of any preconditioning• Temperature program• Method for detrmining Tg, Tm • Instrument used

Reporting DSC DataASTM E472, D3418

250.61°C

236.86°C48.50J/g

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

Hea

t Flo

w (W

/g)

160 180 200 220 240 260 280 300

Temperature (°C)Exo Up Universal V3.8B TA Instruments

% Xtallinity = Hexp/ HoWhere Hexp is Heat of fusion for the polymer

H0 is Heat of fusion for 100% crystalline polymer

Tm and Crystallinity Measurement by Differential Scanning Calorimetry, DSC

Melting and Crystallization

• Melting is the endothermic transition from a crystalline solid to a liquid amorphous state

• Crystallization is the exothermic transition from amorphous to crystalline (normally from liquid to solid during cooling)

• Cold‐Crystallization is the exothermic transition during heating from a solid amorphous state to a solid crystalline state.

Typical DSC Output: Transitions of Interest in a DSC

Temperature

Heat Flow ‐>

exothermic

GlassTransition Crystallization

Melting

Cross‐Linking(Cure)

Oxidation or

Decomposition

Measurement of Melting

221.83°C271.52°C

256.26°C-0.8930W/g

242.65°C-77.27J/g

12.28°C

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

Hea

t Flo

w (W

/g)

160 180 200 220 240 260 280 300 320 340

Temperature (°C)Exo Up

StartEnd

Extrapolated Onset & Integrated Area

Width @ Half height

Peak & Height

Measurement of Melting

256.26°C

242.65°C-77.27J/g

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

Hea

t Flo

w (W

/g)

160 180 200 220 240 260 280 300 320 340


DSC Melting

• Polymers– The peak temperature is the melt point– Between the extrapolated onset and the peak, crystal perfection

may be occurring– Between the peak and the end the sample is finished melting

and returning to the DSC temperature• Pure, low molecular weight materials (mw<500g/mol) (small molecules)– The extrapolated onset is the melting temperature– All of the crystals are melted at the peak– Between the peak and the end the sample is finished melting

and returning to the DSC temperature

Tm is affected by:• Mwt• Chemical Structure• Additives

• Can disrupt packing of serve as nucleating sites

•Effect of heating/cooling rate

•Crystallization kinetics

•Effects of polymer structure/composition

•Effects of thermal/mechanical processing

34

Effect of Aromaticity on Melting

Polymer % Aromatic Melting Range

-CH2 - CH2 - 0 105 - 135°CPET 39 250 - 275°C-(Ph)-O- 62 300 - 315°C-(Ph)-S- 70 300 - 360°C

35

Effect of Branching on Melting

Polyolefin Branching Tm

LDPE irregular ~ 105°Crandom lengths

LLDPE irregular ~ 127°Cfixed lengths

HDPE none ~ 135°C

PP regular ~ 150°Cfixed lengths

36

Effect of Polymer Type on Melting

Class Structure Melting RangePolyolefins -CH -CH - 85 - 174°CPolyamides -CH -NH-C(O)-CH - 190 - 265°CPolyesters -CH -O-C(O)-CH - 220 - 270°CPolyphenylene

Sulfides -Ph-S- 300 - 360°C

2 2

2 2

2 2

37

Effect of Molecular Weight on Melting

Olefin Formula Mole. Wt. Tm(g/mol) (°C)

C12H26 170 -10C24H50 339 54C30H62 423 66C35H72 493 75

38

Effect of Hydrogen Bonding on Melting

Polyamide Tm H BondingNylon 12,2 236 LeastNylon 10,2 242Nylon 8,2 279Nylon 6,2 326 Most

Nylon x,y where:x = carbons in diamine sectiony = carbons in diacid section

Effect of Processing on Crystallinity

for PP

167.94°C

152.08°C77.88J/g

168.21°C

152.84°C91.62J/g

167.52°C

150.18°C88.10J/g

166.25°C

153.18°C95.98J/g

-2.0

-1.5

-1.0

-0.5

0.0

0.5

Hea

t Flo

w (W

/g)

60 80 100 120 140 160 180 200

Temperature (°C)

PP Pellet––––––– PP Cup– – – – PP Quenched from Melt––––– · PP Slow Cooled––– – –

Exo Up Universal V4.4A TA Instruments

First heat vs. second heat

Observation of Crystallization

•Crystallization is a two step process:NucleationGrowth

•The extrapolated onset is the nucleation temperature

•The peak maximum is the crystallization temperature

Observation of Crystallization

160.65°C

183.75°C14.68J/g

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Hea

t Flo

w (W

/g)

0 50 100 150 200 250


Extrapolated Onset & Integrated Area

Peak

0.0

0.5

1.0

1.5

2.0

Hea

t Flo

w (W

/g)

40 50 60 70 80 90 100 110 120 130 140 150 160Temperature (°C)Exo Up

POLYPROPYLENEWITH NUCLEATING AGENTS

POLYPROPYLENEWITHOUT NUCLEATING AGENTS

-1.5

-1.0

-0.5

0.0

Hea

t Flo

w (W

/g)

60 80 100 120 140 160 180 200Temperature (°C)Exo Up

crystallization

melting

Effect of Nucleating Agents

43

DSC: Applications

Effect of heating/cooling rate

Crystallization kinetics

Effects of polymer structure/composition

Effects of thermal/mechanical processing

44

DSC: Effect of Heating Rate onNylon 66 Melting Behavior

1 2 3 4Temperature (°C)

endo

H

EA

T F

LO

W

exo

240 260 280 300

0.2 mW

1 mW

5 mW

5 mW

10 mW

50°C/min

20°C/min

10°C/min

2°C/min

0.5°C/min• Heat transfer rates; thermal gradients• Increased heating rate causes:

• Can change appearance ofcurve

• Can cause Tm increase and beless accurate

• If heating rate is low, sample may anneal as it is tested.

Effect of Sample Mass

46

DSC: Crystallization Kinetics

Two step process Nucleation Crystal growthNucleation may be Natural Induced (using nucleation agents)Thermally influenced process Natural nucleation Crystal growth Modeled by Isothermal Kinetics using the

Autocatalytic Model

47

DSC: Isothermal Crystallization Procedure

Heat to 10°C above Tm

Hold for 5 minutes to remove local order

Cool rapidly to below melt onset (DO NOT OVERSHOOT TEMP)

Hold isothermally

Record time to crystallization peak (t )

48

DSC: Isothermal Crystallization ofPolyethylene Terephthalate

0 1 2 3 4 5 6

Time (min)

T

T1

T2

T3T4

Blank run

T1<T2<T3<T4

49

Effect of AnnealingPoly(ethyletherketone) (PEEK) on Melting

Heat Flow

(W/g)

260 280 300 320 340 360 380‐0.3

‐0.2

‐0.1

0.0

Temperature (°C)

PEEK annealed@ 300°C

PEEK

303.61°C

50

Effect of Draw Ratio on Crystallinity for HDPE Fibers

104 J/g

120 J/g

160 J/g

-2

0

2

4

6

Hea

t Flo

w (W

/g)

80 100 120 140 160

Temperature (°C)

HDPE 115%.001 HDPE 115%––––––– HDPE 240.001 HDPE 240%– – – – HDPE 700 HDPE 700%––––– ·


51

Melting and Crystallization -Summary

Melting and crystallization are phase changes from organized solid to amorphous phases and vice-versa.

Melting is a one-step process while crystallization involves nucleation and crystal growth.

The enthalpy of melting can be used to measure crystallinity or filler.

Any process that makes it easier for molecules to be organized will raise the melting temperature.

The Glass Transition Temperature, Tg

• Observed in amorphous thermoplastics but not all semicrystalline thermoplastics

• Observed in thermosets– Exceptions:

• Extremely high crosslink densities• Very rigid backbones

The Glass Transition

• The Glass Transition is 1.) the reversible change of the amorphous region of a polymer from, or to, a viscous or rubbery condition to, or from, a hard and relatively brittle one. 2.) onset of large scale, cooperative motion of the polymer chains.

• The Glass Transition Temperature is a temperature taken to represent the temperature range over which the glass transition takes place

• Detected by DSC as an increase in Cp

Tg Measurement by DSCTg of PMMA

109.58°C(H)

103.43°C

115.78°C

-0.40

-0.35

-0.30

-0.25

-0.20

-0.15

Hea

t Flo

w (W

/g)

40 60 80 100 120 140 160

Temperature (°C)

Sample: PMMA sampleSize: 10.6500 mgMethod: Ramp

DSCFile: J:...\MSE 430-Fall 2010\Team 2\PMMA.001Operator: AHRun Date: 01-Oct-2010 12:51Instrument: DSC Q100 V9.8 Build 296


Measurement of Tg

93.01°C(H)0.04705W/g

88.27°C

98.33°C

53.49°C

125.49°C

-0.35

-0.30

-0.25

-0.20

-0.15

Hea

t Flo

w (W

/g)

20 40 60 80 100 120 140 160


Start

End

Extrapolated Onset

Extrapolated End

Midpoint & Change

Measurement of Tg

93.01°C(H)

-0.35

-0.30

-0.25

-0.20

-0.15

Hea

t Flo

w (W

/g)

20 40 60 80 100 120 140 160


Some Properties Affected at Tg

Physical property Response on heating through Tg

Specific Volume Increases

Modulus Decreases

Coefficient of thermal expansion

Increases

Specific Heat Increases

Enthalpy Increases

Entropy Increases Temperature

V,1/E,

CTE

CpH &S

Tg

Tg is Affected by:

• Heating rate• Molecular weight• Chemical structure• Crystallinity• Crosslinking• Plasticizer• Physical Aging• Blends/copolymers• Composites

Anything that effects the mobility of the molecules, affects the Heat Capacity, which in

turn affects the Tg

59

DSC: Heating Rate

Heating Rate Sensitivity Reproducibility(°C/min)

5 poor very good20* good good40 very good poor

* Recommended heating rate for measuring Tg.

Effect of Heating Rate on the Tg

Optimizing Measurement of Tg

• If Tg is hard to see:– Use larger sample weight– Use higher heating rate– Use MDSC®

Factors that Affect the Tg Molecular Weight

Redrawn from the data of T.G. Fox and P.J. Flory, J.Appl. Phys., 1950, 21, 581

63

Effect of Molecular Weighton the Tg (for Styrene Oligomers/Polymers)

Molecular Weight Tg104 -138°C524 - 40°C

2,210 40°C3,100 62°C

15,100 86°C36,000 94°C

170,000 100°C

Turi, pg 249 Kumler, 1977

- CH2 - CH2 -Tg ~ ‐ 800C

Tg ~ ‐ 100C

Tg ~ 1000C

Polyethylene

Atactic Polystyrene

- CH2 - CH -CH3

-‐

- CH2 - CH -

Atactic Polypropylene

Bulky Substituents

Flexible Substituents‐

- CH2 - C -‐CH3

C=O‐

‐

OCH3

CH2 - CH3

‐

- CH2 - C -

‐CH3

C=O

‐‐

O

‐

- CH2 - C -

‐CH3

C=O

‐‐

O

(CH2)2 - CH3

‐

- CH2 - C -

‐CH3

C=O

‐‐

O

(CH2)3 - CH3

‐

- CH2 - C -

‐CH3

C=O‐

‐O

(CH2)7 - CH3

‐

- CH2 - C -

‐CH3

C=O

‐‐

O

(CH2)11 - CH3

Poly(methyl methacrylate)

Poly(ethyl methacrylate)

Tg ~ 1050C

Poly(propyl methacrylate)Poly(butyl methacrylate)

Poly(octyl methacrylate)Poly(dodecyl methacrylate)

Tg ~ 650C

Tg ~ 350C Tg ~ 200C Tg ~ ‐200C Tg ~ ‐650C

The Effect of Intermolecular Interactions

Tg ~ ‐ 100C- CH2 - CH -

CH3

-

Atactic Polypropylene

Tg ~ 870C- CH2 - CH -Cl

-PVC

67

Effect of Hydrogen Bondingon the Tg

Polyamide Tg (°C) HBondingNylon 12,2 59 LeastNylon 10,2 56Nylon 8,2 93Nylon 6,2 159 Most

The Effect of Cross - Linking

The Effect of Crystallization

The Effect of Plasticizer on Tg

Polymer + Solventor Plasticizer

109.86°C(H)

103.45°C

116.47°C

67.19°C(H)

64.39°C

70.04°C

52.85°C(H)

48.80°C

56.83°C

45.26°C(H)

38.89°C

51.72°C

-0.4

-0.2

0.0

0.2

0.4

Hea

t Flo

w (W

/g)

0 20 40 60 80 100 120 140 160

Temperature (°C)

Pure Polystyrene––––––– 10%––––––– 20%––––––– 30%–––––––


The Effect of Plasticizer on Tg

-0.006

-0.004

-0.002

0.000

0.002

Der

iv. H

eat F

low

(W/(g

·°C

))

-0.3

-0.2

-0.1

0.0

0.1

Hea

t Flo

w (W

/g)

0 20 40 60 80 100 120

Temperature (°C)

Sample: 30%DGDSize: 11.1000 mgMethod: Ramp

DSCFile: J:...\jasmine\P&J.DGD\30%Operator: PreciousRun Date: 06-Mar-2012 14:36Instrument: DSC Q100 V9.8 Build 296


-0.015

-0.010

-0.005

0.000

0.005

Der

iv. H

eat F

low

(W/(g

·°C

))

-0.1

0.0

0.1

0.2

Hea

t Flo

w (W

/g)

0 20 40 60 80 100 120

Temperature (°C)

Sample: 10%DGDSize: 10.1000 mgMethod: Ramp

DSCFile: J:...\jasmine\P&J.DGD\10%Operator: PreciousRun Date: 06-Mar-2012 13:08Instrument: DSC Q100 V9.8 Build 296


72

Effect of Plasticizer on the Tg

for Polyamides

Water Content (%) Tg (°C)0.35 940.70 841.17 711.99 562.70 454.48 406.61 2310.33 6

Physical Aging--Relaxation and Recovery

Specific Vo

lume

Tg

A

B Temperature

Melt

Glass

• Thermally reversible•Involves changes below Tg• Associated with non‐equilibrium from melt state

• Affects the amorphous phase only• Volume and enthalpy change with time• The change in enthalpy with time is called relaxation or physical aging

74

Effect of Aging on the GlassTransition [M. Todoki, Polymer Data Handbook]

0 50 100 150Temperature (°C)

Glass TransitionCold Crystallization

As-Spun

2 days

28 days

196 days3 years and2 months

4 years and11 months

75

DSC: Effect of Aging Time at 95°Con Shape of Polystyrene Tg

80 90 100 110 120 130- 0. 25

- 0. 20

- 0. 15

- 0. 10

- 0. 05

Temper at ur e ( ° C)

Heat

Flo

w (W

/g)

0. 00Anneal Times = 0, 10, 100 & 1000 minutes

Physical Aging

Heating the material above the Tg then cooling it through the Tg at a rate equal to or greater than the final heating rate reduces the relaxation effect.

Physical AgingEffect on Mechanical

Properties

• General loss of ductility• Modulus increases• Yield strength increases• Impact strength, elongation, fracture energy decrease

Single Phase

Two Phase

Temperature

Endo

therm

Tg1Tg2

Tgmixture

Effect of Miscible and Immiscible Blends on Tg

Curing of ThermosetsCrosslinking

Thermosetting Polymers• Curing reaction can be followed by

monitoring a wide variety of physical properties including:– Heat of reaction– Heat capacity– Viscosity– Modulus– Others

DSC Thermoset Cure: First and Second Heat

0 50 100 150 200 250 300-0.24

-0.20

-0.16

-0.12

-0.08

-0.04

Temperature (°C)

Hea

t Flo

w (W

/g)

Tg

Tg

155.93°C

102.64°C20.38J/g

Residual Cure

First

Second

Isothermal Cure of Epoxy Resin

20

40

60

80

100

Tem

pera

ture

(°C

)

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

Hea

t Flo

w (W

/g)

0 5 10 15 20 25Time (min)


Oxidative Induction Time

Oxidative Induction Time

Heatflow

Time

MDSC Theory

85

Heat Flow Equation

),( tTfdtdTCp

dtdH

dHdt

= Total Heat Flow measured by the calorimeter

Cp = Specific Heat Capacity dTdt = Underlying Heating Rate

f(T,t) = kinetic response of sample

86

Heat Flow Due to Heat Capacity

87

Kinetic Heat Flow

time0 t t1 2

Hea

t Flo

w

The magnitude of measured kineticheat flow is a function of time at aconstant temperature.

Isothermal Temperature

88

Standard DSC Measures the Sum of Heat Flow

Temperature

Hea

t Flo

w

Heat Flow due toHeat Capacity

Heat Flow due toKinetic Events

89

Heat Flow Can Be Separated

Heat Flow due toHeat Capacity

Heat Flow due toKinetic Events

f(T,t)

Cp dTdt

Temperature

Hea

t Flo

w

90

General Theory of MDSC

Heat flow from DSC experiments is composed of two partsbut DSC can only measure the sum of the two.

dH/dt = Cp (dT/dt) + f (T,t)

Total = Heat Capacity + KineticHeat Flow Component Component(DSC) = Heating Rate + Time Dependent Dependent

= MDSC Reversing + MDSC Nonreversing

91

Distribution of Transitions in MDSC Experiments

Total = Heat Capacity + KineticComponent Component

= Reversing Heat Flow + Nonreversing Heat Flow

glass transition melting (some)

enthalpic relaxationevaporationcrystallizationdecompositioncuremelting (some)

92

Physical Measurement Technique

Apply Stimulus Measure ResponseStimulus Response

FTIR IR Radiation AbsorbanceWavelength

NMR Magnetic Field ResonanceFrequency

X-Ray Diffraction X-Ray Radiation Angle ofDiffraction

MDSC SinusoidalHeating Rate

Amplitude ofHeat Flow

93

Raw Signals in MDSC

TimeModulated Temperature (Stimulus)Modulated Heat Flow (Response)

All Modulated DSC Signals are derived fromthree measured parameters.

94

MDSC Raw Signal

MODULATED HEAT FLOW(Response) CRYSTALLIZATION DURING MELTING

MELTING

GLASS TRANSITION

COLD CRYSTALLIZATION

NOTE: ALL TRANSITIONS OFINTEREST ARE CONTAINED INMDSC RAW DATA SIGNALS

MODULATED HEATING RATE(Stimulus)

50 100 150 200 250 300

0

2

4

6

8

-0.6

-0.4

-0.2

0.0

0.2

Temperature (°C)

Deriv. Modulated Temp (°C/min)

Modulated Heat Flow (W/g)

95

Temperature Change (MDSC)

200

210

220

230

240

Mod

ulat

ed T

emp

(°C

)

200

210

220

230

240

Tem

pera

ture

(°C

)

38 39 40 41 42 43 44 45

Time (min)

Exo Up Universal V2.5D TA Instruments

ACTUAL MEASURED TEMPERATURE

CALCULATED AVERAGETEMPERATURE

PA

96

MDSC Signals: Total Heat Flow

The average value of the modulated heat flow signal. This signal is qualitatively and quantitatively equivalent to the heat flow signal from conventional DSC at the same average heating rate.

Definition: The sum of all thermal events in the sample

Calculation: Fourier Transformation analysis of the modulated heat flow signal is used to continuously calculate its average value

97

Total Heat Flow: Average of Modulated Heat Flow Signal

50 100 150 200 250 300-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

-0.4

-0.2

0.0

0.2

Temperature (°C)


Heat Flow (W/g)

98

MDSC Signals: Heat Capacity

Where:AMHF = Amplitude of Modulated Heat FlowAMHR = Amplitude of Modulated Heating Rate

K = Heat Capacity Calibration Factor

Definition: The amount of heat required to raise the temperature of a material 1°C.

Calculation: The basis for making the heat capacity measurement in MDSC can be explained from a series of conventional DSC experiments at different heating rates.

K x AA Cp

MHR

MHF

99

Conventional DSC Cp Measurement

x wtRateHeat HF– HFK x Cp MTS

HF

endo

0HFMT

HFS

Temp.

Where:K = Calibration constantHFS = Differential heat flow

with sampleHFMT = Differential heat flow

with empty panswt = weight of sample

100

Alternative DSC Cp Measurement

HF

endo

0HFHR1

HFHR2

Temp.

wt)HR– (HRHF– HFK x Cp

12

HR1HR2

Where:K = Calibration constantHFHR1 = Differential heat flow of

sample at HR1

HFHR2 = Differential heat flow of sample at HR2

HR2 = Heating rate 2 HR1 = Heating rate 1wt = weight of sample

101

Heat Capacity from MDSC Raw Signals

50 100 150 200 250 300

0

5

10

-0.6

-0.2

0.2

0.6

Temperature (°C)

Deriv. Modulated Temp (°C/min)


4

2

0

2

4

6

Complex Cp (J/g/°C)HEAT CAPACITY

MODULATED HEAT FLOW

MODULATED HEATING RATE

102

MDSC Signals - Reversing Heat Flow (Heat Capacity Component)

Reversing Heat Flow is the heat capacity component of the total heat flow. It is calculated by converting the measured heat capacity into a heat flow signal using the classical heat flow equation as a theoretical basis.

Reversing Heat Flow = Cp x Avg. Heat Rate

t)(T, dtdT Cp

dtdH f

Basis for Calculation

ing)(Nonrevers process kinetic from flowheat t)(T,

)(Reversingcomponent capacity heat dtdT Cp

rate heating average dtdT

capacityheat measured Cp

flowheat total dtdH

:Where

f

103

Reversing Heat Flow from MDSC Raw Signals

50 100 150 200 250 300-8

-4

0

4

8

-0.25

-0.15

-0.05

0.05

0.15

Temperature (°C)

Com

plex

Cp

(J/g

/°C)

Rev

Hea

t Flo

w (W

/g)

HEAT CAPACITY

REVERSING HEAT FLOW

104

Quench Cooled PET: Total vs. Reversing Heat Flow

50 100 150 200 250 300-0.3

-0.2

-0.1

0.0

0.1

-0.25

-0.15

-0.05

0.05

0.15

Temperature (°C)

Hea

t Flo

w (W

/g)

[

]Rev

Hea

t Flo

w (W

/g)

TOTAL

REVERSING

105

MDSC Signals - Nonreversing Heat Flow (Kinetic Component)

Nonreversing Heat Flow is the kinetic component of the total heat flow. It is calculated by subtracting the heat capacity component from the total heat flow using the classical heat flow equation as a theoretical basis.

Nonreversing = Total – Reversing

Basis for Calculation

ing)(nonreverscomponent kinetic t)(T,

)(reversingcomponent capacity heat dtdT Cp

flowheat total dtdH

t)(T, dt dT Cp

dtdH

f

f

106

Quench-Cooled PET: Deconvoluted Signals

50 100 150 200 250 300-0.25

-0.15

-0.05

0.05

0.15

0.25

-0.25

-0.15

-0.05

0.05

0.15

0.25

Temperature (°C)

Hea

t Flo

w (W

/g)

Rev

Hea

t Flo

w (W

/g)

-0.2

-0.1

0.0

0.1

Non

rev

Hea

t Flo

w (W

/g)

NONREVERSING

TOTAL

REVERSING

107

Glass Transition of Polymer Resin

108

MDSC: Glass Transition of Epoxy Coating

109

MDSC: Glass Transition of Epoxy Coating

110

PET/ABS Blend –Conventional DSC

-0.2

-0.3

-0.4

-0.5

-0.6

-0.7

-0.8

Temperature (°C)50 100 150 200 250

Hea

t Flo

w (W

/g)

first heat on molded part

(Curve shifted on Y axis to avoid overlap)second heat after 10°C/min cooling

120.92°C67.38°C

70.262°C (H)235.36°C

111.82°C9.016J/g

22.63J/g

249.75°C

9.22 mg sample, nitrogen purge 10°C/minute heating rate

111

PET/ABS - MDSC

8.46mg sample nitrogen purge 2°C/minute heating rate, ±1°C amplitude, 60 second period

first heat on molded part

PET Tg

ABS Tg

-0.10

-0.11

-0.12

-0.13

-0.14

-0.15

Temperature (°C)40 60 100 120 140

Hea

t Flo

w (m

W)

20 80 160

-0.02

-0.03

-0.04

-0.05

-0.06

-0.04

-0.05

-0.06

-0.07

-0.08

-0.09

(

) N

onre

v. H

eat F

low

(W/g

)

(

) R

ev. H

eat F

low

(W/g

)

67.00°C+72.89°C (H)

104.45°C107.25°C (H)

180 200

112

DSC of Polymer Blend

113

MDSC of Polymer Blend

114

MDSC: Detection of Two GlassTransitions in PC/PEE Blend

40 60 80 100 120 140 160

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

-0.005

-0.004

-0.003

-0.002

-0.001

Temperature (°C)

Rev

Hea

t Flo

w (W

/g)

Der

iv. R

ev H

eat F

low

(W/g

/min

)3 CONSECUTIVE HEATING RUNS AFTER 2deg/min COOLING

DERIVATIVE

NOTE 81°C WIDTH OF GLASS TRANSITION

3

2

1

62. 58° C

141. 45° C

MDSC ±0.424°C, 40 sec. period4°C/min underlying ramp rate

++

115

FAST MDSC ON THE Q1000

1

1

1

1

1

1

1

1

11

1

2

2

2

2

2

2

2

2

2

22

2

1

1

1

1 1

1

1

1

1 1

1

1

2

2

2

2

2

2

2

2

2

22 2

First HeatSecond Heat

First Heat Shows SmallTg Near 70c

Residual Cure Occurs at Low Temperature Tg of First Heat

MDSC Conditions:30 sec. period+/- 0.3c amplitude10 cpm

-0.35

-0.30

-0.25

-0.20

-0.15

[ –––

– –

] H

eat F

low

(W/g

)

1.0

1.2

1.4

1.6

1.8

2.0

[ –––

––––

] R

ev C

p (J

/g/°C

)

0 50 100 150 200 250Temperature (°C)

1––––––2––––––

Exo Up Universal V3.1B TA Instruments

116

MDSC: Heat Capacity for PET DuringIsothermal Steps

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.01.0

1.2

1.4

1.6

60

80

100

120

140

Time (day)

Hea

t Cap

acity

(J/g

/°C)

Tem

pera

ture

(°C

)

PLOT vs TIME

Heat Capacity

Temperature

MDSC ±0.30°C, 40 sec. period1°C isothermal steps

117

MDSC: PET Heat CapacityDuring GlassTransition &

Cold Crystallization

60 70 80 90 100 110 120 130

1.1

1.2

1.3

1.4

1.5

1.6

Temperature (°C)

Hea

t Cap

acity

(J/g

/°C)

COLD CRYSTALLIZATION(First-Order Transition)

GLASS TRANSITION(Second-Order Transition)

MDSC ±0.30°C, 40 sec. period1°C isothermal steps

118

Isothermal Epoxy Cure

H of Cure6

4

2

0

Time (min)5 10 20 25 30

Non

rev.

Hea

t Flo

w (m

W)

Heat Capacity

Isothermal 80°C helium purge ±0.5°C amplltude 60 second period

DMA 1Hz

0 15 35 40

30

20

10

0

(

) H

eat C

apac

ity (m

J/°C

)

14.5

14.0

13.5

13.0

12.5

12.0

11.5

(

) E

' (G

Pa)

119

MDSC: Heat Capacity vs. Cure TimeTM =Epoxy-Amine System MDSC Result at 70°C Cure

Thermochimica Acta, 268, 121-142 (1995), Dr. B. Van Mele, et alat Vrije Universiteit Brussels (Belgium)

=

0 100 200 3000

30

60

90

120

1.0

1.5

2.0

2.5

Time (min)

(

) N

onre

vers

ing

Hea

t Flo

w (m

W/g

)

(

)

Hea

t Cap

acity

(J/g

/K)

exo

t1/2 Cp

t1/2 Cp

vit

= 97 miX = 0.53

Nonreversing Heat Flow

Heat Capacity

120

MDSC: Experimental Considerations

Modulation Period?

Modulation Amplitude?

Sample Dimensions?

Purge Gas?

Sample Preparation?

Phase Correction?

Calibration?

Modulated DSCIsothermal approach

• The approach assumes that the reaction follows autocatalyzed exothermic systems and obeys the general rate equation:

• where d/dt = reaction rate (1/sec) = fractional conversion k(T) = specific rate constant at temperature T

• This approach requires three or more isothermal experiments to generate the kinetic parameters : – Activation energy (Ea), Pre‐exponential factor Z Heat of reaction (H), Reaction order (n, m) Rate constant (k)

m( ) 1 nd k Tdt

121

Isothermal DSC Thermograms at 120 °C for Neat resin and Nanocomposites

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

Hea

t Flo

w (W

/g)

0 50 100 150 200 250

Time (min)

1% F-MWCNT EPON 828––––––– 1% COOH-MWCNT EPON 828– – – – Neat Epoxy––––– ·

Exo Up Universal V4.5A TA I

122

Activation Energies and Rate Constant for the Neat Resin and Nanocomposites

Sample Average (H) J/g

EakJ/mol

Rate constant min-1

TIso120 °C

Neat Epoxy 319.6 47.5 0.0428

1.0 % COOH-MWCNT/EPON 828 239.8 61.7 0.0390

1.0 % F-MWCNT/EPON 828 263.4 47.7 0.0428

123

Isothermal Cure Behavior of Neat Epoxy Resin and Nanocomposites at

120 °C

0 1000.0 2000.0 3000.0 4000.0 5000.0 6000.0 7000.0 8000.0time (s)

0.1000

1.000

10.00

100.0

1000

10000

1.000E5

1.000E6

1.000E7

G' (

Pa)

Neat Epoxy1% F-MWCNT EPON8281% COOH-MWCNT EPON828

124

Gelation, Vitrification and Degree of Conversion and of the Neat Resin and

Nanocomposites

Sample

Gel point time (min)

°C

tvitr(min) Tg (°C)Degree of

Conversion (%)

Neat Epoxy 81.4 149 119 95

1.0 % COOH-MWCNT/EPON 828 58 185 120 96

1.0 % F-MWCNT/EPON 828 78.5 160 119 96

125

Heat Capacity

148.61min

185.11min

158.94min

1.4

1.8

Rev

Cp

(J/(g

·°C

))

0 50 100 150 200 250

Time (min)

Neat Epoxy––––––– 1% COOH-MWCNT EPON828– – – – 1% F-MWCNT EPON828––––– ·

Universal V4.5A TA Instruments

Carbon Nanotube Reaction Schemes

F H2N R NH2

HN

R NH2

+

NH

R

NH2 + CH RH2CO

CH CH2

O

NH

R N CH2 RCHOH

CH CH2

O

A)

B)CO

CO

O CH2 CHOH

R

OH + CH RH2CO

CH CH2

O

CH CH2

O

F H2N R NH2

HN

R NH2

+

NH

R

NH2 + CH RH2CO

CH CH2

O

NH

R N CH2 RCHOH

CH CH2

O

A)

B)CO

CO

O CH2 CHOH

R

OH + CH RH2CO

CH CH2

O

CH CH2

O

A)

B)CO

CO

O CH2 CHOH

R

OH + CH RH2CO

CH CH2

O

CH CH2

O

127

128

MDSC: Sample Preparation

Thin, Low Mass SamplesMinimize Thermal GradientsAllow for Faster Periods, Larger Modulation Amplitudes

Thicker, Heavier SamplesMinimize Baseline CurvatureImprove Sensitivity

129

Low, Consistent Mass Best Choice for MDSC Measurements Solids, Powders, Films Volatility may be an issue

MDSC: Sample Pans Standard Crimped

130

MDSC: Sample Pans Standard Hermetic

Use for liquid/volatile samples Higher Mass, Less Sensitivity Use Heat Sink Compound

131

NitrogenEconomicalWide Operating RangeProvides Good Sensitivity

HeliumHigher Thermal ConductivityFacilitates Wider Range of Modulation

ConditionsReduces Baseline Curvature

MDSC: Purge Gas

132

MDSC: Purge GasFlow Rates

Use Purge Gas Flow Rate of 50 mL/min. (N2) & 25 ml/min (He)

Faster rates increase noise Slower rates decrease sensitivity, increase baseline curvature

Flow Purge Gas through Vacuum Portat 50 mL/min.

Improves response of furnace Facilitates wider range of modulation

parameters

133

MDSC: Heat Capacity Calibration

Provides for Accurate Heat Capacity MeasurementsUse Either Sapphire Disc (wide temperature range) or HDPE (polymer melt)Choose one‐point or average valuesEffects of Experimental Conditions

Variations in DSC

• Pressure DSC• Photo DSC

differential scanning calorimetry - uab · pdf filethermal analysis techniques technique...

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