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Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

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Page 1: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Analysis of Materials (Polymers) by Thermal Methods:

DSC, TG/DTA

Instructor: Ioan I. Negulescu

CHEM 4010Tuesday,October 29, 2002

Page 2: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Thermal Methods:

Thermal methods are based upon the measurement of the dynamic relationship between temperature and some property of the system such as mass and heat absorbed or evolved by/from it.

Page 3: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

• Differential Scanning Calorimetry, DSC

• Differential Thermal Analysis, DTA

• Thermogravimetry, TG

are the most important thermal methods used in characterization of polymers.

Page 4: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

The temperature increase, T, of a body which is heated is directly proportional to the amount of heat absorbed, Q, and inversely proportional to its mass, m, and its capacity C to store heat:

T = Q/m C Eq. 1

Page 5: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Consider the temperature increase of two different samples of the same mass

m1 = m2

for which the same amount of heat was given

Q1 = Q2

If their heat capacities are different

C1 C2

they do not experience the same temperature increase, i.e.,

T1 T2

Page 6: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

A greater heat flow (dQ/dt, where t is time)

will always flow into the sample whose heat capacity is higher, in order that the steady-state heating rate be maintained.

The heat capacity at constant pressure (Cp)

of a material is defined as the temperature increase of a unit of substance (mass) as a result of the supply of a unit of heat at

constant pressure.

Page 7: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

For the same substance, Cp is dependent upon its aggregation state, i.e., it is different for the liquid state as compared to loose gaseous or to more compact solid state.

Page 8: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

A polymeric material has different heat capacities for amorphous or crystalline morphologies. For amorphous polymers, the heat capacity for the glassy state (i.e., below glass transition, Tg, where only vibrations of atomic groups occur) is different from that characterizing the leathery (short range diffusional motion, i.e., of chain segments), rubbery (retarded long-range motions), rubbery flow (slippage of long-range entanglements) or liquid state.

Page 9: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Figure 1. Temperature - molecular mass diagram for amorphous polymers: (1) Glass transition (Tg); (2)

Diffuse transition zone; and (3) Thermal decomposition.

Page 10: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Figure 2. Temperature - Molecular Mass diagram for (semi) -crystalline polymers: (1) Glass transition (Tg); (2) Melting point (Tm); (3) Diffuse transition zone; and (4) Thermal decomposition.

Page 11: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

For amorphous polymers, the glass-rubber transition temperature is of considerable importance technologically. It (Tg) determines the lower use limit of a rubber (e.g., polydienes, Tg -50°C) and the upper limit use of an amorphous thermoplastic material(e.g., polystyrene, Tg 100 ° C).

Page 12: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

In the case of (semicrystalline) linear polymers it is possible to identify a melting temperature (Tm). Above this temperature the polymer may be liquid, viscoelastic or rubbery according to its molecular mass, but below it, at least in the high molecular mass range, it will tend to be leathery and tough down to the glass transition temperature.

Page 13: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

POLYHYDROXYALKANOATES

R can be hydrogen or hydrocarbon chains of up to around C13 in length, and x can range from 1 to 3 or more. Varying x and R effect hydrophobicity, Tg, Tm, and level of crystallinity

Page 14: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

POLYHYDROXYALKANOATES

Fig 4: The Family of PHAs has Physical Characteristics that Allow it to be Used Across a Wide Spectra of Applications

Page 15: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Detailed information on glass transition, crystallization, and melting, is therefore critically important in formation, processing and utilization of polymers.

Differential thermal methods (DTA and DSC) have been widely applied to the study and characterization of polymeric materials.

Page 16: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

In DTA the heat absorbed or emitted by a system is observed by measuring the temperature difference (T) between that system (the sample) and an inert reference material (often alumina), as the temperature of both is increased at a constant rate (usually 5-10 C/min).

Page 17: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Figure 3. Schematic diagram of a typical DTA apparatus.

Page 18: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

• In DSC, the sample and the reference are also subjected to a continuously increasing or decreasing temperature.

• In the scanning operation the sample and the reference show different temperature independent heat capacities.

• Heat (dQ/dt) is added to the sample or to the reference as necessary to maintain the two identical temperatures.

Page 19: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Bottom: (b) measured curve. m is the measured heat flux. bl is the heat flux corresponding to the base line and t is time.

Page 20: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

• The ordinate is usually represented by the heat flux (denominated as or dQ/dt) or by the variation of the heat capacity.

• The glass-to-rubber transition, or shortly the glass transition (Tg) is a phase change reminiscent of a thermodynamic second order transition (melting and crystallization being first order transitions) for which a plot of specific heat versus temperature shows a sudden jump.

• The first order transitions appear

as peaks.

Page 21: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

DSC curve of a polymeric sample: (1), (3) and (5) are base lines; (2) is glass-to-rubber transition, Tg; (4) is the interpolated base line; and (6) is the first order transition peak.

Page 22: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

The glass transition region in cooling (a) and subsequent heating (b) mode showing some commonly used definitions of glass transition, Tg.

Page 23: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Poly(Lactic Acid)

-[-O-CH(CH3)-CO-]n

Two of the most attractive features of poly(lactic acid), PLA, polymers are:

• they are easily synthesized from renewable resources (corn!)

• they are both hydro- and biodegradable

Page 24: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

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

Page 25: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

DSC traces for melting and crystallization

of a polymer sample.

Page 26: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Melting of polyoxymethylene with superheating.

Page 27: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

DSC analysis of a poly(ethylene terephthalate) sample quenched from the melt.

Page 28: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

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

Page 29: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

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

Page 30: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

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.

Page 31: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Determination of the HDPE content in a blend with inorganic filler from DSC data.

40 60 80 100 120 140 160 180

-10

-5

0

EN

DO

%HDPE=(H/H100

)x100H

100=132 mj/mg

%HDPE=(106/132)x100 HDPE = 80.3%

132.8oC

H = 106 mJ/mg

He

at

Flo

w (

mW

)

Temperature, oC

HDPE Detergent Bottles

Page 32: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Polyhydroxylated Nylons

Similarity of Nylon 6,6 and the poly hydroxylated counterpart:

Page 33: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

DSC Thermal Transitions in Polyhydroxylated Nylon 6,6

0 20 40 60 80 100 120 140 160 180 200

0.0

500.0

1.0k

1.5k

2.0k

2.5k

3.0k

3.5k

H

Decomposition

Tm

Tg

DDSC

DSC

D

SC

, W

Temperature, oC

-2k

-1k

0

1k

2k

3k

4k

5k

6k

D

DS

C, W

/min

Page 34: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Thermogravimetric (TG) analysis is concerned with the change in weight of a material as its temperature changes. This indicates:

• the temperature at which the material loses weight through evaporation or decomposition

• the temperature at which no weight loss takes place is revealed, which indicates stability of the material.

Page 35: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

TG Measurement Principle of Seiko TG/DTA Thermobalance

Page 36: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Thermal Degradation of Polyhydroxylated Nylon 6,6

0 100 200 300 400 500 600

-100

-80

-60

-40

-20

0

100oC -6.3%

150oC -6.9%

200oC -19.0%

235oC -50.0%

205oC

425oC

DTG

TG

DT

G

We

igh

t L

oss

(T

G),

%

Temperature, oC

0.0

5.0k

10.0k

15.0k

Page 37: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Poly (4-dodecyl-1-4-aza heptamethylene-D-glucaramide). Thermal decomposition.

0 100 200 300 400 500 600

-100

-80

-60

-40

-20

0

TG

(%

Wei

ght L

oss)

Temperature, oC

TGpercent

0

2

-97.5%@400oC

-1.3%@150oC

188oC

0.6%/oC

372oC

1.3%/oC

166oC

DT

G (

%/o C

)

Page 38: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Initial decomposition of linear polymers.

Initial sample weight: 10 mg. Heating rate:

5C/min.

Page 39: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Thermogravimetric analysis of a polymeric blend containing HDPE and an inorganic filler (phosphogypsum)

0 100 200 300 400 500 600 700 800

-60

-50

-40

-30

-20

-10

0

-62.8%

% w

eig

ht

loss

Temperature, oC

TGpercentL

Page 40: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Almost any measurement that can be done at different temperatures can be expanded into thermal analysis; and any series of thermal analysis techniques can be combined with other non-thermal technique for valuable multiple-parameter information.

Page 41: Analysis of Materials (Polymers) by Thermal Methods: DSC, TG/DTA Instructor: Ioan I. Negulescu CHEM 4010 Tuesday, October 29, 2002

Coupled techniques, such as Thermogravimetry, Differential Thermal Analysis and Mass Spectrometry (TG-DTA-MS) or evolved gas analysis of polymers by coupled Thermogravimetry, Gas Chromatography, Fourier Transform Infrared and Mass Spectrometry (TG-GC-FTIR-MS) are just two examples often used in industrial laboratories.