Handbook of Thermal Analysis and Calorimetry (eBook)

Applications to Polymers and Plastics

Stephen Z.D. Cheng (Herausgeber)

eBook Download: PDF

2002 | 1. Auflage
858 Seiten
Elsevier Science (Verlag)
978-0-08-052740-6 (ISBN)

Infos

"As a new and exciting field of interdisciplinary macromolecular science and engineering, polymeric materials will have a profound presence in 21st century chemical, pharmaceutical, biomedical, manufacturing, infrastructure, electronic, optical and information technologies. The origin of this field derived from an area of polymer science and engineering encompassing plastic technologies. The field is rapidly expanding to incorporate new interdisciplinary research areas such as biomaterials, macromolecular biology, novel macromolecular structures, environmental macromolecular science and engineering, innovative and nano-fabrications of products, and is translating discoveries into technologies.

?Unique in combining scientific concepts with technological aspects
?Provides a comprehensive and broad coverage of thermodynamic and thermal behaviours of various polymeric materials as well as methodologies of thermal analysis and calorimetry
?Contributions are from both pioneering scientists and the new generation of researchers"

Inhalt

Cover 1
CONTENTS 10
Foreword 6
Preface 8
Contributors 28
CHAPTER 1. HEAT CAPACITY OF POLYMERS 32
1. MEASUREMENT OF HEAT CAPACITY 32
2. THERMODYNAMIC THEORY 36
3. QUANTUM MECHANICAL DESCRIPTION 36
4. THE HEAT CAPACITY OF SOLIDS 41
5. COMPLEX HEAT CAPACITY 45
6. THE ADVANCED THERMAL ANALYSIS SYSTEM, ATHAS 47
7. EXAMPLES OF THE APPLICATION OF ATHAS 59
8. TEMERATURE-MODULATED CALORIMETRY 65
9. CONCLUDING REMARKS 76
ACKNOWLEDGMENTS 77
REFERENCES 77
CHAPTER 2. THE GLASS TRANSITION: ITS MEASUREMENT AND UNDERLYING PHYSICS 80
1. INTRODUCTION 80
2. THE APPARENT THERMODYNAMIC BEHAVIOR 81
3. KINETICS OF GLASS FORMATION 89
4. MICROSCOPIC THEORIES RELATED TO THE GLASS TRANSITION 107
5. MEASUREMENT OF Tg 112
6. PHYSICAL AGING EFFECTS 126
7. CONCLUDING REMARKS 135
ACKNOWLEDGMENTS 135
REFERENCES 135
CHAPTER 3. MECHANICAL RELAXATION PROCESSES IN POLYMERS 142
1. WHAT DO WE MEAN BY THE RELAXATION PROCESS 142
2. INTERMOLECULAR COOPERATIVITY 150
3. CHEMICAL STRUCTURE AND Tg 155
4. VISCOELASTICITY DATA ANALYSIS 158
5. BEYOND LINEAR VISCOELASTICITY 174
REFERENCES 176
CHAPTER 4. DIELECTRIC ANALYSIS OF POLYMERS 178
1. INTRODUCTION 178
2. POLAR AMORPHOUS POLYMERS 181
3. NONPOLAR POLYMERS 188
4. MISCIBILITY OF POLYMER BLENDS 190
5. COLD CRYSTALLIZATION OF AMORPHOUS POLYMERS ABOVE Tg 192
6. FREQUENCY-TEMPERATURE RELATIONSHIPS 194
ACKNOWLEDGMENTS 195
REFERENCES 195
CHAPTER 5 . CRYSTALLIZATION AND MELTING OF METASTABLE CRYSTALLINE POLYMERS 198
1 . INTRODUCTION 198
2 . THERMODYNAMIC DEFINITIONS OF THE PHASE AND PHASE TRANSITIONS 198
3 . POLYMERCRYSTALLIZATION AND MORPHOLOGY 206
4. POLYMER CRYSTAL MELTING 214
5. CONCLUDING REMARKS 222
ACKNOWLEDGMENTS 223
REFERENCES 223
CHAPTER 6. CRYSTALLIZATION, MELTING AND MORPHOLOGY OF HOMOGENEOUS ETHYLENE COPOLYMERS 228
1. INTRODUCTION 228
2. ETHYLENE-PROPYLENE COPOLYMERS 231
3. ETHYLENE- 1-BUTENE COPOLYMERS 250
4. ETHYLENE-1-OCTENE COPOLYMERS 256
5. OVERVIEW 270
ACKNOWLEDGMENTS 271
REFERENCES 271
CHAPTER 7. RECENT ADVANCES IN THERMAL ANALYSIS OF THERMOTROPIC MAIN-CHAIN LIQUID CRYSTALLINE POLYMERS 276
1. INTRODUCTION 276
2. LIQUID CRYSTALS AND LIQUID CRYSTALLINE POLYMERS 278
3. THERMODYNAMIC TRANSITION BEHAVIORS 284
4. ENANTIOTROPIC AND MONOTROPIC BEHAVIORS 290
5. EFFECTS OF MESOGENIC GROUPS AND SPACERS ON THE LIQUID CRYSTALLINE ORDERS AND STABILITY 294
6. CONCLUDING REMARKS 299
REFERENCES 299
CHAPTER 8 . POLYMER BLENDS AND COPOLYMERS 304
1. INTRODUCTION 304
2. BACKGROUND 304
3. POLYMERBLENDS 305
ACKNOWLEDGMENTS 322
REFERENCES 323
CHAPTER 9. THERMOSETS 326
1. INTRODUCTION 326
2. GENERAL CONCEPTS 327
3. CHEMISTRY AND APPLICATIONS OF THERMOSETTING POLYMERS 332
4. DETERMINATION OF EXTENT OF CURE 339
5. GLASS TRANSITION TEMPERATURE 346
6. REACTION KINETICS 361
7. PHOTO-INITIATED POLYMERIZATION 369
8. MODULATED TEMPERATURE DSC 379
9. CONCLUDING REMARKS 381
ACKNOWLEDGMENTS 382
REFERENCES 382
CHAPTER 10. THERMAL ANALYSIS OF POLYMER FILMS 386
1. INTRODUCTION 386
2. GENERAL EXPERIMENTAL CONSIDERATIONS IN THERMAL ANALYSIS OF POLYMER FILMS 391
3. THERMAL ANALYSIS OF SPECIFIC POLYMER FILMS 400
4. CONCLUDING REMARKS 435
REFERENCES 435
CHAPTER 11. THERMAL ANALYSIS OF POLYMER FIBERS 440
1. INTRODUCTION 440
2. FIBER STRUCTURE AND ITS DETERMINATION 448
3. THERMAL ANALYSIS OF FIBER 457
4. CONVENTIONAL FIBERS AND THEIR MODIFICATIONS 470
5. HIGH PERFORMANCE FIBERS 494
6. CONCLUDING REMARKS 513
REFERENCES 513
CHAPTER 12. THERMAL PROPERTIES OF HIGH TEMPERATURE POLYMER MATRIX FIBROUS COMPOSITES 522
1. INTRODUCTION 522
2. RESULTS AND DISCUSSION 526
3. CONCLUDING REMARKS 547
REFERENCES 548
CHAPTER 13. THERMAL ANALYSIS AND CALORIMETRY OF ELASTOMERS 550
1. INTRODUCTION 550
2. CLASSES OF ELASTOMER 557
3. SINGLE ELASTOMERS 560
4. BLENDS 569
5. ADDITIVES 575
6. CURING 587
7. STABILITY 597
8. QUALITY CONTROL 607
9. FUTURE OPPORTUNITIES 609
REFERENCES 611
CHAPTER 14. POLYMER DEGRADATION 618
1. INTRODUCTION 618
2. GENERAL PHYSICAL, STRUCTURAL AND THERMODYNAMIC CONSIDERATIONS 620
3. GENERAL THERMAL DEGRADATION MECHANISMS 624
4. GENERAL THERMO-OXIDATIVE MECHANISMS 639
5. GENERAL HYDROLYSIS MECHANISMS 644
6. LIFETIME PREDICTION OF POLYMERS BY THERMAL ANALYSIS 645
7. SOME SPECIFIC EXAMPLES OF DEGRADATION 647
8. COPOLYMERS, BLENDS, MIXTURES 662
9. CONCLUDING REMARKS 672
10. BIBLIOGRAPHY 672
11. REFERENCES 676
CHAPTER 15. THERMALLY STIMULATED CURRENTS: RECENT DEVELOPMENTS IN CHARACTERIZATION AND ANALYSIS OF POLYMERS 684
1. INTRODUCTION 684
2. EXPERIMENTAL SECTION 688
3. ANALYSIS OF TSC-TS DATA 691
4. INTERPRETATION OF GLOBAL TSC RESULTS 698
5. INTERPRETATION OF TSC-THERMAL SAMPLING (TSC-TS) RESULTS 705
6. TSC APPLICATIONS 728
7. CONCLUDING REMARKS 737
ACKNOWLEDGMENTS 739
REFERENCES 739
CHAPTER 16. TEMPERATURE MODULATED DIFFERENTIAL SCANNING CALORIMETRY (TMDSC) –BASICS AND APPLICATIONS TO POLYMERS 744
1. INTRODUCTION 744
2. DIFFERENTIAL SCANNING CALORIMETRY (DSC) – BASIC CONSIDERATIONS 748
3. TEMPERATURE MODULATED DIFFERENTIAL SCANNING CALORIMETRY (TMDSC) 753
4. APPLICATIONS 799
5. CONCLUDING REMARKS 832
ACKNOWLEDGMENTS 833
REFERENCES 833
INDEX 842

Textauszug

Chapter 1

Heat capacity of polymers*

B. Wunderlich    Department of Chemistry, The University of Tennessee, Knoxville, TN 37996-1600, USA; and the Chemical and Analytical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6197, USA

Heat capacity is the basic quantity derived from calorimetric measurements and is used in the description of its thermodynamics. For a full description of a system, heat capacity information is combined with heats of transition, reaction, etc. In the present Chapter the measurement and theory of heat capacity are discussed which leads to a description of the Advanced THermal Analysis System, ATHAS [1]. This system was developed over the last 30 years to increase the precision of thermal analysis of linear macromolecules and related small molecules.

1 MEASUREMENT OF HEAT CAPACITY

In a measurement of heat capacity one measures the heat, dQ, required to increase the temperature of the sample by dT:

p≡dQdT=∂H∂Tp,n,

  (1)

where H represents the enthalpy and p and n, are pressure and composition, which are kept constant. Classically, the measurement is done with an adiabatic calorimeter [2]. Even today, adiabatic calorimetry is the most precise method of measurement in the temperature range from 10 to 150 K.

In an adiabatic calorimeter an attempt is made to follow step-wise temperature changes of an internally heated calorimeter in a well-controlled, adiabatic enclosure. Due to loss of heat caused by deviations from the adiabatic condition, corrections must be made to the heat added to the calorimeter, ΔQ. Similarly, the measured increase of temperature, ΔT, must be corrected for the temperature drifts of the calorimeter. The calculations are then given by:

p=ΔQcorrected−C′ΔTcorrectedmΔTcorrected,

  (2)

where the specific heat capacity cp (in J K− 1 g− 1) is calculated by subtracting the heat capacity of the empty calorimeter, its “water value” C′, and dividing by the mass of the sample, m. The evaluation of the corrections is time consuming, but at the heart of good calorimetry.

Modern control and measurement technology permitted some 30–40 years ago to miniaturize the calorimeter to measure down to milligram quantities in a differential scanning mode (DSC) [3]. In a symmetric setup, the difference in extraneous heat flux can be minimized and the remaining imbalance corrected for. Under the usual condition where sample and reference calorimeters (often aluminum pans) are identical and the reference pan is empty, one finds the heat capacity as:

cp=KΔTβ+KΔTβ+CpldΔT/dTr1−dΔT/dTr≈KΔTβ,

  (3)

where K is the Newton’s law constant, ΔT is the temperature difference between reference and sample (Tr - Ts), and β is the constant heating rate (in K min− 1)’: The left equation is exact, the right approximation neglects the difference in heating rates between reference and sample due to a slowly changing heat capacity of the sample. This limits the precision to ± 3% or less.

In the more recently developed temperature-modulated DSC (TMDSC) [4], a sinusoidal or other periodic change in temperature is superimposed on the underlying heating rate. The heat capacity is now given by:

cp=AΔAKω2+Cp′2,

  (4)

where AΔ and A are the maximum amplitudes of the modulation found in the temperature difference and sample temperature, respectively, and ω is the modulation frequency 2π/p (p = modulation period in seconds). The equation represents the reversing heat capacity. In case there is a difference between the result of the last two equations, this is called a nonreversing heat capacity, and is connected to processes within the sample that cannot be modulated properly, such as the change of temperature in the glass transition region, irreversible crystallization or reorganization, or heat losses.

Fig. 1 illustrates a heat-capacity measurement with a DSC. Central is the evaluation of the calibration constant at each temperature of measurement. Three consecutive runs must be made. The sample run (S) is made on the unknown, enclosed in the customary aluminum pan and an empty, closely-matched aluminum reference pan. The width of the temperature interval is dictated by the quality of the isothermal base line. In the example of Fig. 1 the initial isotherm is at 500 K and the final isotherm, at 515 K. Typical modern instrumentation may permit intervals as wide as 100 K. Measurements can also be made on cooling instead of heating. The cooling mode is particularly advantageous in the glass transition region since it avoids hysteresis. When measurements are made on cooling, all calibrations must necessarily also be made on cooling, using liquid-crystal transitions which do not supercool, for example, for temperature calibration [5]. As the heating is started, the DSC recording changes from the initial isotherm at 500 K in an exponential fashion to the steady-state amplitude on heating at constant rate β. After completion of the run, at time tf, there is an exponential approach to the final isotherm at 515 K. The area between base line and the DSC run, called AS, is the integral over the amplitude, as. A reference run (R) with a matched, second, empty aluminum-pan, instead of the sample, yields the small correction area AR which may be positive or negative. Finally, a calibration run (C) with sapphire crystals (A12O3) completes the experiment (area AC). The difference between the two areas, AS – AR, is a measure of the uncalibrated integral of the sample heat capacity:

′/β=WCc¯pCΔTAC−AR.

  (5)

Fig. 1 Measurement and calibration by DSC.

For a small temperature interval at constant heating rate β in the region of steady state in Fig. 1, it is sufficient to define an average heat capacity over the temperature range of interest to simplify the integral, as indicated. The uncalibrated heat capacity of A12O3 is similarly evaluated using Ac – AR. The proportionality constant, K′,can now be evaluated as:

0tfCpSβdt=C¯pSΔT=K′AS−AR/β.

  (6)

The specific heat capacity of sapphire, cp(Al2O3), is well known, and the weight of sapphire used, W(C) = W(Al203), must be determined with sufficient precision (± 0.1%) so as not to affect the accuracy of the measurement (± 1% or better).

The initial and final exponential changes to steady state are sufficiently similar in area so that one may compute the heat capacities as a function of temperature directly from the amplitudes as(T), aR(T), and aC(T) in the region of steady state. Eq. (7) and Eq. (8) outline the computations involved in the calibration:

0tfCpSβdt=CpSΔT=K′aS−aR/βand

  (7)

′/β=WCcpCΔTaC−aR.

  (8)

In a typical DSC experiment, a sample may weigh 20 mg and show a heat capacity of about 50 mJ K 1. For a heating rate of 10 K min 1 there would be, under steady-state conditions, a lag between the measured temperature and the actual temperature of about 0.4 K. This is an acceptable value for heat capacity that changes slowly with temperature. If necessary, lag corrections can be included in the computation. The typical instrument precision is reported to be ± 0.04 mJ s− 1 at 700 K. Heat capacities can thus be measured to a precision of ± 0.25%, respectable for such fast measurements. For TMDSC, sample mass and modulation parameters are chosen to modulate the whole sample with the same amplitude, checked by measuring with varying sample masses [6], or calibration as a function of frequency is necessary.

2 THERMODYNAMIC THEORY

The importance of heat capacity becomes obvious when one realizes that by integration it is linked to the three basic quantities of thermodynamics, namely the enthalpy or energy (H, U), the Gibbs energy or free energy (G, F), and the entropy (S). Naturally, in cases where there are transitions in the temperature range of interest, their heats and entropies need to be added to the integration. The enthalpy or energy of a system can be linked to the total amount of thermal motion and interaction on a microscopic...

Produkt-Details

• Erscheint lt. Verlag: 9.12.2002
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Biologie
• Themenwelt: Naturwissenschaften ► Chemie ► Technische Chemie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Angewandte Physik
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Thermodynamik
• Themenwelt: Technik ► Maschinenbau
• ISBN-10: 0-08-052740-X / 008052740X
• ISBN-13: 978-0-08-052740-6 / 9780080527406