2004 Training SeminarsDSC

5

MDSC®

What it’s all about & how to get better results

What Does MDSC® Measure? • MDSC separates the Total heat flow of DSC into two

parts based on the heat flow that does and does not respond to a changing heating rate

• MDSC applies a changing heating rate on top of a linear heating rate in order measure the heat flow that responds to the changing heating rate

• In general, only heat capacity and melting respond to the changing heating rate.

• The Reversing and Nonreversing signals of MDSC should never be interpreted as the measurement of reversible and nonreversible properties

Modulated DSC® Theory

• MDSC® uses two simultaneous heating rates– Average Heating Rate

• This gives Total Heat Flow data which is equivalent to standard DSC @ same average heating rate

– Modulated Heating Rate• Purpose is to obtain heat capacity information at the

same time as heat flow

Note that temperature is not decreasing during Modulation i.e. no cooling

Modulate +/- 0.42 °C every 40 secondsRamp 4.00 °C/min to 290.00 °C

52

54

56

58

60

62

Mo

du

late

d T

em

pe

ratu

re (

°C)

52

54

56

58

60

62

Te

mp

era

ture

(°C

)

13.0 13.5 14.0 14.5 15.0

Time (min)

Average & Modulated Temperature

Modulated Temperature

Average Temperature

(Heat-Iso)

Note that temperature is not decreasing during Modulation i.e. no cooling

Modulate +/- 0.42 °C every 40 secondsRamp 4.00 °C/min to 290.00 °C

52

54

56

58

60

62

Modula

ted T

em

pera

ture

(°C

)

52

54

56

58

60

62

Tem

pera

ture

(°C

)

13.0 13.5 14.0 14.5 15.0

Time (min)

Average & Modulated Temperature

54.5

55.0

55.5

56.0

56.5

57.0

Mo

du

late

d T

em

pe

ratu

re (

°C)

54.5

55.0

55.5

56.0

56.5

57.0

Te

mp

era

ture

(°C

)

13.70 13.75 13.80 13.85 13.90 13.95 14.00 14.05

Time (min)

Modulated Temperature

Average Temperature

Amplitude

(Heat-Iso)

Average & Modulated Heating Rate

Note That Heating Rate isNever Negative (no cooling)

AverageHeating Rate

ModulatedHeating Rate

0

2

4

6

8

10

De

riv.

Mo

du

late

d T

em

pe

ratu

re (

°C/m

in)

0

2

4

6

8

10

De

riv.

Te

mp

era

ture

(°C

/min

)

13.0 13.5 14.0 14.5 15.0

Time (min)

Period

MDSC® Raw Signals

Modulated Heat Flow(Response)

Modulated Heating Rate (Stimulus)

MDSC Raw Data Signals for 13.54mg Quenched PET;+/-0.48;60sec;3°C/minNote that all transitions are visible in MHF signal

Glass Transition

Cold Crystallization

Melting

Crystal Perfection

0

4

8

12

16

20

24

Deri

v. M

odu

late

d T

em

pe

ratu

re (

°C/m

in)

-12

-8

-4

0

Mo

du

late

d H

ea

t F

low

(m

W)

0 50 100 150 200 250 300

Temperature (°C)Exo Up

Modulated DSC® Theory

• MDSC® Heat Flow & Signals

t)(T, dt

dT Cp

dt

dHf

Total = Reversing + Nonreversing

Modulated DSC® Theory• MDSC® Data Signals

t)(T, dt

dT Cp

dt

dHf

Total = Reversing + Nonreversing

Reversing Transitions

•Heat Capacity•Glass Transition•Most Melting

Modulated DSC® Theory• MDSC® Data Signals

t)(T, dt

dT Cp

dt

dHf

Total = Reversing + Nonreversing

Nonreversing Transitions

•Enthalpic Recovery•Evaporation•Crystallization•Thermoset Cure•Protein Denaturation•Starch Gelatinization•Decomposition•Some Melting

MDSC® of Quench-Cooled PET

Nonreversing

Reversing

Total

-0.4

-0.2

0.0

No

nre

v H

ea

t F

low

(W

/g)

-0.4

-0.2

0.0

0.2

0.4

Re

v H

ea

t F

low

(W

/g)

-0.4

-0.2

0.0

0.2

He

at

Flo

w (

W/g

)

0 50 100 150 200 250 300

Temperature (°C)Exo Up

When & Why to Run MDSC®

• Always run a standard DSC @ 10°C/min first

• If you’re looking for a glass transition --– If the glass transition is detectable and can be routinely

analyzed, then you don’t need to use MDSC

– However, if the Tg is hard to detect, or has an enthalpic recovery, then run MDSC

When & Why to Run MDSC®

• If looking at melting and crystallization –– If the melting process looks normal (single

endothermic peak) and there is no apparent crystallization of the sample as it is heated, then there is no need to use MDSC

– However, if melt is not straightforward, or it is difficult to determine if crystallization is occurring as the sample is heated, use MDSC

When & Why to Run MDSC®

• If you want heat capacity (Cp) – run MDSC– To get Cp by normal DSC (Q1000 is an

exception due to Direct Cp)• Use High heating rates, >10°C/min

• Three experiments required– Baseline

– Reference (sapphire)

– Sample

The Natural Limitations of DSC

• The next several slides discuss some of the natural limitations of DSC & how they are solved by MDSC®. This is by no means a complete list, just some of the more significant limitations.

The Natural Limitations of DSC1. It is not possible to optimize both sensitivity and

resolution in a single DSC experiment.

• Sensitivity is increased by increasing weight or heating rate

• Although increased sample size or heating rate improves sensitivity, they decrease resolution by causing a larger temperature gradient within the sample

• MDSC® solves this problem because it has two heating rates: the average heating rate can be slow to improve resolution, while the modulated heating rate can be high to improve sensitivity

t)(T,dt

dT Cp

dt

dHf

Sensitivity & Resolution

PC-PEE Blend 16.13mg MDSC® .424/40/1

Natural Limitations of DSC (cont.)

2. Baseline curvature and drift limit the sensitivity of DSC for detecting weak transitions

• MDSC® eliminates baseline curvature and drift in the Heat Capacity and Reversing signals by using the ratio of two measured signals rather than the absolute heat flow signal as measured by DSC.

K x Rate Heating Mod Amplitude

FlowHeat Mod Amplitude Cp

Rate Heating Avg x Cp Reversing

Where’s the Tg?

Tablet Binder, 44%RH 3.08mg MDSC® 1/60/5 Vented pan

Here’s the Tg!

Natural Limitations of DSC (cont.)

3. Transitions are often difficult to interpret because DSC can only measure the Sum of Heat Flow within the Calorimeter

• MDSC® minimizes this problem by providing not only the Total Heat Flow signal but also the heat capacity and kinetic components of it

Complicated Example

Quenched Xenoy 14.79mg 10°C/min

MDSC® Aids Interpretation

Xenoy 13.44 mg MDSC .318602

Natural Limitations of DSC (cont.)

4. It is often difficult to accurately measure the crystallinity of polymers by DSC because the crystallinity increases as the sample is being heated in the DSC cell. – To measure the correct crystallinity requires

the ability to:• determine the true heat capacity (no transitions) baseline

• quantitatively measure how much crystallinity developed during the heating process

DSC of Amorphous PET/PC Mixture…Where is the PC Tg ?

120.00°C 170.00°C

30.74J/g

215.00°C270.00°C

42.95J/g

120.00°C 270.00°C

13.31J/g

Standard DSC @ 10°C/min57% PET; 43% PC

DSC Heat Flow AnalyzedTwo Different Ways

-16

-12

-8

-4

0

4

[ ––––– · ] H

eat F

low

(m

W)

-22

-18

-14

-10

-6

-2

Heat F

low

(m

W)

50 100 150 200 250

Temperature (°C)

Sample: Quenched PET and PCSize: 13.6000 mgMethod: DSC@10Comment: DSC@10; PET13.60/PC 10.40/Al film 0.96mg

DSCFile: C:...\Len\Crystallinity\qPET-PCdsc.001

Exo Up Universal V3.8A TA Instruments

MDSC® Shows Two Tgs in Polymer Mixture

Decrease in Heat CapacityDue to Cold Crystallization

Glass Transitionof Polycarbonate

True Onset of Melting

Cold Crystallization PeakSeen Only in Total Signal

Total Heat Flow

Reversing Heat Flow

-3.2

-3.0

-2.8

-2.6

-2.4

-2.2

-2.0

[ –

––

––

· ]

Re

v H

ea

t F

low

(m

W)

-3.2

-3.0

-2.8

-2.6

-2.4

-2.2

-2.0

He

at

Flo

w (

mW

)

50 100 150 200 250

Temperature (°C)

Sample: Quenched PET and PCSize: 13.6000 mgMethod: MDSC .318/40@3Comment: MDSC 0.318/40@3; PET13.60/PC 10.40/Al film 0.96mg

DSCFile: C:\TA\Data\Len\Crystallinity\qPET-PC.002

Exo Up Universal V3.8A TA Instruments

MDSC® .318/40/3

MDSC® Gives Correct Crystallinity of Zero

Optimization of MDSC® Conditions

• Proper selection of the three experimental parameters is important in order to maximize the quality of the results.– In general, temperature is controlled to either

provide or not provide cooling during the temperature modulation

– Cooling is desirable for heat capacity transitions– Cooling is undesirable for melting &

crystallization

Select Modulated Mode

Select signals to store

Select Test (Template)

MDSC® Heat-Cool Modulation

Heating Rate goes below 0°C/min

Heating & Cooling

MDSC® Heat-Iso Modulation

Heating Rate never goes below 0°C/min

No Cooling

MDSC® Heat-Iso Amplitudes

40 50 60 70 80 90 100

0.1 0.011 0.013 0.016 0.019 0.021 0.024 0.027

0.2 0.021 0.027 0.032 0.037 0.042 0.048 0.053

0.5 0.053 0.066 0.080 0.093 0.106 0.119 0.133

1.0 0.106 0.133 0.159 0.186 0.212 0.239 0.265

2.0 0.212 0.265 0.318 0.371 0.424 0.477 0.531

5.0 0.531 0.663 0.796 0.928 1.061 1.194 1.326

HHeeaattiinngg

RRaattee

Period (sec)

This table is additive, i.e. the heat only amplitude for a period of 40 sec & a heating rate of 2.5°C/min is the sum of the values for 2.0°C/min & 0.5°C/min

Amplitude (40s,2.5°C/min)=0.212+0.053=0.265°C

No Cooling

MDSC® Conditions for Q Series DSC

Glass Transitions (Tg)Glass Transitions (Tg)• For “standard Tg”:

Sample Size: 10 – 15 mg Amplitude*: 2X Table

Period: 40 seconds Heating Rate: 3°C/min

• If Tg is Hard to Detect Sample Size: 10 – 20 mg Amplitude*: 4X TablePeriod: 60 seconds Heating Rate: 2°C/min

• If Tg has Large Enthalpic Relaxation Sample Size: 5 – 10 mg Amplitude*: 1.5X TablePeriod: 40 seconds Heating Rate: 1°C/min

*Use a minimum of 0.5°C amplitude

MDSC® Conditions for Q Series DSC

Heat Capacity (Cp)Heat Capacity (Cp)

• Heating Rate; isothermal up to 5ºC/min

• Modulation Period– 100 seconds with crimped pans– 120 seconds with hermetic pans

• Modulation Amplitude; 1.5X Table Value with a minimum of 0.5ºC

• Sample Size; 10-15mg

MDSC® Conditions for Q Series DSC

Melting and crystallinity:Melting and crystallinity:• Sample Size; 10-15mg

• Period– 40 sec. with crimped pans

– 60 sec. With hermetic pans

• Heating Rate– Slow enough to get a minimum of 4-5 cycles at half-height

of the melting peaks

• Amplitude– Use “Heat-Iso” amplitude which provides no cooling

during temperature modulation (see Table)