Thermal Properties of polymers presentation

Thermal characterization of polymers

1. Thermal Properties of Polyurethanes Dr. Siddhesh Mestry

2. 2 Introduction Any measurement of a change in properties as the temperature changes qualifies as a thermal analysis technique. When performing thermal analysis procedures, usually a controlled temperature program heats or cools a sample at a certain rate, and physical or chemical property changes are monitored as a function of temperature. Some of the measured properties include mass, temperature, heat flow, size, malleability, sound transmission, magnetic characteristics, optical characteristics, electrical conductivity, and tensile strength. Thermal analysis techniques give useful information about polymers, inorganic compounds, alloys, drugs, and other organic materials.

3. Techniques in this category include TG or TGA : thermal gravimetric analysis or thermogravimetry. Measures the mass change of the sample with a thermobalance. A variation on this is DTG , or derivative thermogravimetry, which measures the slope or derivative of the mass change with temperature, dm/dt . DSC : differential scanning calorimetry, and a related technique, differential thermal analysis. DSC measures the amount of heat flowing into the sample (endothermic, +dH/dt ) or out of the sample (exothermic, - dH/dt ), 3 FR Properties: Flame retardant properties

4. Terminologies

5. Terminologies

6. Differential Scanning Calorimetry (DSC) is concerned with the measurement of energy changes in materials. It is thus the most generally applicable of all thermal analysis methods, since every physical or chemical change involves a change in energy. Small, flat samples are contained in shallow pans, with the aim of making a good thermal contact between sample, pan and heat flux plate. Symmetrical heating of the cell, and therefore S and R , is achieved by constructing the furnace from a metal of high thermal conductivity. Note the provision for establishing a gas flow through the cell , to sweep away volatiles, provide the required atmosphere, and to assist in heat transfer.

7. Traditional Heat Flux DSC: Cell Schematic Diagram Dynamic Sample Chamber Reference Pan Sample Pan Lid Gas Purge Inlet Chromel Disc Heati ng Block Chromel Disc Alumel Wire Chromel Wire T h erm o cou p le Junction Thermoelectric Disc (C o nsta n ta n)

8. DSC working range: typically up to 700°C, and down to -140°C with a liquid nitrogen cooling system. -Temperature calibration is carried out by running standard materials, usually very pure metals with accurately known melting points. -Energy calibration may be carried out by using either known heats of fusion for metals, commonly indium, or known heat capacities. - DSC: operational details

9. A variety of sample pans can be used for different purposes. The best quantitative results for polymers are obtained from thin samples crimped flat between the pan and a lid. Hermetically-sealed pans capable of holding a few atmospheres pressure are used for liquids, or when it is necessary to retain volatiles. Very high-pressure seals can be achieved using O-ring or screw- threaded seals. For materials that react with aluminium, or for higher temperatures, pans may be made from stainless steel, inconel, gold, alumina, graphite, silica or platinum. Typical purge gases are air and nitrogen, though helium is useful for efficient heat transfer and removal of volatiles. Argon is preferred as an inert purge when examining samples that can react with nitrogen. The experiment can also be carried out under vacuum or under high pressure using instruments of the appropriate design.

10. Differential Scanning Calorimetry (DSC) measures the temperatures and heat flows associated with transitions in materials as a function of time and temperature in a controlled atmosphere. These measurements provide quantitative and qualitative information about physical and chemical changes that involve endothermic or exothermic processes, or changes in heat capacity. DSC: The Technique

11. DSC: What DSC Can Tell You? Glass Transitions Melting and Boiling Points Crystallization time and temperature Percent Crystallinity Heats of Fusion and Reactions Specific Heat / Heat Capacity Oxidative/Thermal Stability Rate and Degree of Cure Reaction Kinetics Purity

12. Polyurethane structure

13. Typical DSC Transitions Temperature Heat Flow Glass Transition Crystallization M e lti n g C r oss -L i nk i ng (Cure) O x i dat i on or D eco m pos i t i on Exothermic:

14. Understanding DSC Signals Heat Flow Where: = measured heat flow rate dH dt Cp = sample heat capacity = specific heat (J/g°C) x mass (g) dT = measured heating rate dt f (T,t) = heat flow due to kinetic processes (evaporation, crystallization, etc.)

15. Calibration of Differential Scanning Calorimeters Differential Scanning Calorimeters are almost universally calibrated for temperature and enthalpy using the melting temperatures of highly pure metals. Recommended values for the melting temperature (Tm) and heat of fusion (Hf) are given below. Many of these substances will react with standard aluminum crucibles. This may be overcomes by annealing the empty crucible (and lid) air above 400°C in order to build up a protective layer of aluminum oxide. Calibration of Differential Scanning Calorimeters Material Tm (°C) Hf (J/g) Mercury - 38 . 8344 11.469 Gallium 29 . 7646 79.88 Indium 156 . 5985 28.62 Tin 231 . 298 7.170 Bismuth 271.40 53.83 Lead 327 . 462 23.00 Zinc 419 . 527 108.6 Aluminum 660 . 323 398.1

16. Different ASTM Methods for Thermal Analysis using DSC E0537-02 - Thermal Stability of Chemicals by DSC E0928-03 - Purity by DSC E0968-02 - Heat Flow Calibration of DSCs E1269-05 - Specific Heat Capacity by DSC E1356-03 - Glass Transition Temperatures by DSC and DTA E0793-01 - Heats of Fusion and Crystallization by DSC D6604-00 - Glass Transition Temperatures of Hydrocarbons by DSC E2009-02 - Oxidation Onset Temperature by DSC E2046-03 - Reaction Induction Time by DSC E2070-03 - Isothermal Kinetics by DSC E2160-04 - Heats of Reaction by DSC

17. Second Order Transitions: Tg The DSC curve may show a step change, as at S in the curve, reflecting a change in heat capacity not accompanied by a discrete enthalpy change. The most common example, and a major application area of DSC, is the glass transition (Tg) seen in amorphous polymers. This important region, in which the material changes from a rigid glassy state to a rubber, or very viscous liquid state, may be analyzed to give a wealth of information about the material. Te m pe r a t u r e Heat Flow Glass T r ans i t i on Melting Crystallization Cross- Linking ( C u r e) O x i da t i on or Decomposition Exo up

18. Examples: The amount or effectiveness of a plasticizer may be judged by how much it reduces Tg or affects the shape of the transition. Examination of the transitions in polymer blends gives information as to their compatibility. Curing reactions result in an increase in Tg and measurements can be used to monitor the extent of cure. Tg also varies with chain length for a related group of polymers. Additional features occurring in the glass transition region, often a superimposed endothermic peak, are related to the aging undergone by the material in the glassy state. 15 The temperature Tg may be used to identify polymers, as it varies over a wide range for commonly used materials.

19. Peaks may be characterized by: Position (i.e., start, end, extrapolated onset and peak temperatures) Size (related to the amount of material and energy of the reaction) Shape (which can be related to the kinetics of the process) Enthalpy Changes (first order transition) The DSC/DTA curve may show an exothermic or endothermic peak,. The enthalpy changes associated with the events occurring are given by the area under the peaks. In general, the heat capacity will also change over the region, and problems may arise in the correct assignment of the baseline. In many cases the change is small, and techniques have been developed for reproducible measurements in specific systems.

20. Process Exothermic Endothermic Solid-solid transition * * Crystallization * Melting * Vaporization * Sublimation * Adsorption * Desorption * Desolvation (drying) * Decomposition * * Solid-solid reaction * * Solid-liquid reaction * * Solid-gas reaction * * Curing * Polymerization * Catalytic reactions *

21. Applications Thermoplastics Thermosets Heat Capacity Glass Transition Melting and Crystallization

22. Thermoplastic Polymers Semi-Crystalline or Amorphous Crystalline Phase melting temperature Tm (endothermic peak) Amorphous Phase glass transition temperature (Tg) (causing  Cp) Tg < Tm Crystallizable polymer can crystallize on cooling from the melt at Tc (Tg < Tc < Tm)

23. DSC of Thermoplastic Polymers Tg Melting Crystallization Oxidative Induction Time General Recommendations – 10-15mg in crimped pan – @ 10°C/min

24. The Glass Transition (Tg) The glass transition is a step change in molecular mobility (in the amorphous phase of a sample) that results in the change of many physical properties The material is rigid below the glass transition temperature and rubbery above it. Amorphous materials flow , they do not melt The change in heat capacity at Tg is a measure of the amount of amorphous phase in the sample. Enthalpic recovery at Tg is a measure of order in the amorphous phase. Annealing or storage at temperatures just below Tg permit development of order as the sample moves towards equilibrium

25. Advantages of DSC Techniques Differential Scanning Calorimetry Most common technique for Tg Small sample size Faster analysis (fast heating, automation)

26. Typical Polymer Tg by DSC 92.87°C(H) 0.2638mW - 1 . 5 - 1 . - . 5 . Heat Flow (mW) -2.0 20 40 60 120 140 160 8 100 Temperature (°C) Sa m pl e: PMMA S i ze: 10.47mg Heating Rate: 10°C/min

27. Effect of Plasticizer on Tg Plasticizers are generally low molecular weight organic additives which are used to soften rigid polymers Plasticizers are typically added to a polymer for two reasons: 1. To lower the glass transition to make a rigid polymer become soft and rubbery. 2. To make the polymer easier to process. Plasticizers make it easier for a polymer to change molecular conformation. Therefore plasticizers will have the effect lowering and broadening the glass transition.

28. C r ystall iz ation Crystallization is a kinetic process which can be studied either while cooling, heating or isothermally Differences in crystallization temperature or time (at a specific temperature) between samples can affect end-use properties as well as processing conditions Isothermal crystallization is the most sensitive way to identify differences in crystallization rates

29. Crystallization Crystallization is a two step process: Nucleation Growth The onset temperature is the nucleation (T n ) The peak maximum is the crystallization temperature (T c )

30. Effect of Cooling Rate on Crystallization A temperature shift is seen in the cooling data on the next slide. In this example, the samples were cooled from 285 ° C to room temperature at 2 to 16 ° C/min. The higher rates of temperature change broaden the crystallization process and shift it further in temperature from the starting point.

31. Sample must be pure material, not copolymer or filled Must know enthalpy of melting for 100% crystalline material (  H literature ) You can use a standard  H literature for relative Calculation of % Crystallinity crystallinity For standard samples: % crystallinity = 100*  H m /  H literature For samples with cold crystallization: % crystallinity = 100* (  H m -  H c )/  H lit

32. Crystallinity Calculation 78.99°C(I) 75.43°C 80.62°C 134.62°C 127.72°C 53.39J/g 256.24°C 242.91°C 74.71J/g - 1 . - . 5 . . 5 1 . Heat Flow (W/g) 250 300 -1.5 5 10 15 20 Temperature (°C) 140 100   74.71  53.39   15% % crystallinity = 100* (  H m -  H c )/  H lit

33. Melting Definitions Melting – the process of converting crystalline structure to a liquid amorphous structure Thermodynamic Melting Temperature – the temperature where a crystal would melt if it had a perfect structure (large crystal with no defects) Metastable Crystals – Crystals that melt at lower temperature due to small size (high surface area) and poor quality (large number of defects)

34. Melting of PET 249.70°C 236.15°C 52.19J/g PET 6.79mg 10 ° C / m i n -7 -6 -5 -4 -3 -2 -1 Heat Flow (mW) 200 210 250 260 Exo Up 270 Universal V4.0B TA Instruments E xt rapo l a t ed Onset T e m pera t u r e Peak Temperature 22 23 240 Temperature (°C) Heat of Fusion For polymers, use Peak as Melting Temperature

35. Comparison of Melting 249.70°C 236.15°C 52.19J/g 156.60°C 28.50J/g Indium 5.7mg 10 ° C / m i n PET 6.79mg 10 ° C / m i n - 25 -20 157.01°C - 15 - 10 -5 Heat Flow (mW) 140 160 180 240 260 20 220 Temperature (°C) Exo Up 280 Universal V4.0B TA Instruments

36. Thermosetting Polymers: polymerization Rxn Thermosetting polymers react (cross-link) irreversibly. A+B will give out heat (exothermic) when they cross-link (cure). After cooling and reheating C will have only a glass transition Tg. A + B C GLUE

37. DSC Thermoset Cure: First and Second Heat 50 2 50 3 - . 2 - . 2 4 - . 1 6 - . 1 2 - . 8 - . 4 1 1 5 2 Temperature (°C) Heat Flow (W/g) T g T g 155.93°C 102.64°C 20.38J/g Residual Cure F i r s t Second General Recommendations 10-15 mg in crimped pan if solid; hermetic pan if liquid @ 10°C/min

38. Determination of % Cure

39. 90 o C https://doi.org/10.1007/s00289-020-03450-7 91.8% 88.7% 87.9% WPUD

40. WPUD1 was thermally stable

41. 71.8% https://doi.org/10.1016/j.mtcomm.2023.107259

42. Microphase Separation Tg of Soft and Hard segments Increased thermal stability at latter stages of degradation

43. DIM0 DIM5 DIM10 DIM15

44. TGA (ASTM E 1131) 47 TGA measures the amount & rate of change in the mass of a sample as a function of temperature or time in controlled atmosphere. TGA can tell us : Compositional analysis of multi- component materials or blends Thermal stability Oxidative stability Estimation of product lifetime Effect of reactive atmospheres on material Filler content of material Moisture & volatiles content

45. APPARATUS TEST SPECIMEN 4 to 5mg TEST PROCEDURE 48

46. Thermogravimetric Analysis (TGA) PRINCIPLE INSTRUMENTATION FACTORS AFFECTING RESULTS ADVANTAGES AND DISADVANTAGES PHARMACEUTICAL APPLICATIONS

47. TGA – Thermal Gravimetric Analysis Principle : Measure the weight loss of the material with change in temperature Mechanism Weight Loss: Decomposition: The breaking apart of chemical bonds. Evaporation: The loss of volatiles with elevated temperature. Weight Gain: Oxidation: Interaction of the sample with an oxidizing atmosphere. Absorption or Adsorption.

48. TGA – Working Furnace Auto Sampler Balance

49. Typical TGA Curve of additive polymer system

50. Principle TGA measures the amount and the rate of weight change of a material with respect to temperature or time in controlled environments. The mass of a sample in a controlled atmosphere is recorded continuously as a function of temperature (or time) as the temperature of the sample is increased. TGA thermogram : -A plot of mass percent as a function of time or temperature. TGA measures the change in weight of a sample as it is heated, cooled or held at constant (isothermal) temperature .

51. PRINCIPLE A large number of chemical substances invariably decompose upon heating, and this heating a sample & observing weight change is the principle of thermogravimetric analysis (TGA). TGA may be sub-divided into two heads, namely : (a) Static (or Isothermal) Thermogravimetric Analysis, and (b) Dynamic Thermogravimetric Analysis. Static (Isothermal) Thermogravimetric Analysis The sample under analysis is maintained at a constant temperature for a period of time during which any changes in weight are observed carefully. Dynamic Thermogravimetric Analysis Sample is subjected to conditions of predetermined, carefully controlled continuous increase in temperature that is invariably found to be linear with time.

52. Thermogram: TG curve of a single stage Two Temperatures: Ti: initial lowest temperature at which the onset of a mass change is detected, procedural decomposition temperature Tf : Final T decomposition appear to be complete Ti- Tf difference : reaction interval

53. INSTRUMENT Instrument: is“Thermobalance ” Data recorded in form of curve known as ‘ Thermogram ’. A TGA consists of three major parts (1) A sensitive analytical balance : Range : up to 100 mg. Sample holder is in furnace. However, the rest of the balance must be thermally isolated from the furnace. (2) furnace: Heating Device Temperature range: up to 1500°C. (3) Unit for temperature measurement & control (4) Recorder: automatic recording unit for the mass and temperature changes purge gas system : For prevention of oxidation: N 2 Ar , He, etc. For oxidation: O 2 or air.

54. BLOCK DIAGRAM OF THERMOBALANCE

55. Thermobalance components. The balance beam is shown as A. The sample cup and holder are B; C is a counterweight. D is a lamp and photodiodes, E is a magnetic coil, and F is a permanent magnet. The computer data-acquisition, data-processing, and control systems are components G, H, and I. Component J is the printer and display unit. Oven/heater for heating, ceramic rod/pan, and balance.

56. The TGA instrument continuously weighs a sample as it is heated to temperatures of up to 2000 ° C for coupling with FTIR and Mass spectrometry gas analysis.

57. Balances Basic : accuracy, sensitivity, reproducibility, and capacity Two types : (a) Null-point Type : incorporates a sensing element which detects a deviation of the balance beam from its null position A sensor detects the deviation and triggers the restoring force to bring the balance beam to back to the null position. The restoring force is directly proportional to the mass change. (b) Deflection Type : conversion of the balance beam deflection about the fulcrum into a suitable mass change trace by (a) photographic recording i.e change in path of a reflected beam of light available of photographic recording, (b) recording electrical signals generated by an appropriate displacement measurement transducer, and (c) using an electro-chemical device. The different balances used in TG instruments are having measuring range from 0.0001 mg to 1 g depending on sample containers used.

58. FURNACE The furnace and control system must be designed to produce linear heating at over the whole working temperature range of the furnace and provision must be made to maintain any fixed temperature. A wide temperature range generally 150-2000°C of furnaces is used in different instruments. The range of furnace basically depends on the types of heating elements are used. The temperature control of the furnace is satisfactorily achieved via a thermocouple mounted very close to the furnace-winding. The maximum operational temperature may be obtained by using different thermocouples as indicated below :

59. Temperature measurement are commonly done using thermocouples , chromal – alumel thermocouple are often used for temperature up to 1100 °C whereas Pt/(Pt–10% Rh ) is employed for temperature up to 1750 °C. Temperature may be controlled or varied using a program controller with two thermocouple arrangement, the signal from one actuates the control system whilst the second thermocouple is used to record the temperature. Temperature Measurement and Control

60. Recorder The recording device must be such so as to : ( i ) record both temperature and weight continuously, and ( ii) make a definite periodic record of the time. Graphic recorders are preferred to meter type recorders. X-Y recorders are commonly used as they plot weight directly against temperature. Facilitate microprocessor controlled operation and digital data acquisition and processing using personal computer with different types recorder and plotter for better presentation of data.

61. In this diagram, whole of the balance system is housed in a glass to protect it from dust and provide inert atmosphere. There is a control mechanism to regulate the flow of inert gas to provide inert atmosphere and water to cool the furnace. The temperature sensor of furnace is linked to the programme to control heating rates, etc. The balance output and thermocouple signal may be fed to recorder to record the TG Curve. schematic diagram of the specific balance and furnace assembly as a whole to better understand the working of a thermobalance .

62. Thermogravimetric Curves Quantitative aspects of TG TG curves represent the variation in the mass ( m) of the sample with the temperature (T) or time (t). Sometime we also record derivative thermogravimetric (DTG) Curves. A DTG curve presents the rate of mass change (d m/ dt ) as a function of temperature, or time (t) against T on the abscissa (x axis) as shown in Fig. when substance is heated at uniform rate. In this figure, the derivatives of the Curve is shown by dotted lines.

63. METHODOLOGY The ‘ thermogram ’ for calcium oxalate monohydrate (CaC 2 O 4 .H 2 O). The successive plateaus correspond to the anhydrous oxalate (100-250°C), calcium carbonate (400-500°C), and finally calcium oxide (700-850°C). In other words, these plateaus on the decomposition curve designate two vital aspects, namely : ( a) clear indication of constant weight, and ( b) stable phases within a specified temperature interval. The chemical reactions involved may be summarized as follows :

64. Interpretation of Thermogram the thermogravimetric evaluation of CaC 2 O 4 .H 2 O, it is ensured that the weight of this product decreases in several stages, namely :

65. Stage 1 : The water of hydration (or crystallization) from calcium oxalate monohydrate is lost which corresponds to 2.46 mg (12.3%) equivalent to 1 mole of H 2 O in the temperature range 100-250°C. Actually, the 12.3% weight loss that took place between 100-250°C should correspond to 12.3% of the original formula weight for CaCO 3 H 2 O (FW = 146). Hence, the product being lost has a formula weight of 0.123 × 146 = 17.958 (~_ 18.0), and it corresponds to H 2 O. Stage 2 : One mole of carbon monoxide is evolved subsequently from calcium oxalate, corresponding 2 to 3.84 mg (19.2%) in the temperature range 400-500°C. The 19.2% weight loss that occurred between 400-500°C should correspond to 19.2% of the original formula weight of 146. Therefore, the product being given out has a formula weight of 0.192 × 146 = 28.0, that corresponds to CO. Stage 3 : Finally, a mole of CO 2 is evolved from calcium carbonate that corresponds to 6.02 mg (3.01%) in the temperature range 700-850°C.

66. FACTORS AFFECTING TG CURVE These factors may be due to instrumentation or nature of sample: 1. Instrumental factors: i ) Furnace heating rate. ii) Recording or chart speed iii) Furnace atmosphere iv) Geometry of Sample holder/ location of sensors v) Sensitivity of recording mechanism. vi) Composition of sample container. 2 . Sample Characteristics: a) Amount of sample b) Solubility of evolved gases in sample. c) Particle size d) Heat of reaction e) Sample packing f) Nature of sample g) Thermal conductivity.

67. Furnace heating rate At a given temperature, the degree of decomposition is greater at the slower heating rate, and thus it follows that the shape of the TG curve can be influenced by the heating rate. For a single stage endothermic reaction it has been found that F and S indicate fast and slow heating rate polystyrene decomposes 10% by mass when heating rate is 1°C per min by 357 °C and 10% by mass when heating rate is 5 °C per min by 394 °C. Ti & Tf will decrease with decrease in heating rate and the TG curve will be shifted to the left. The appearance of an inflection in a TG curve at a fast heating rate may well be resolved into a plateau at a slower heating rate. Therefore, in TGA there is neither optimum no standard heating rate, but a heating rate of 3 °C per min. gives a TG curve with maximum meaningful resolution.

68. Recording or chart speed The chart speed on the recording of the TG curve of rapid or slow reaction effects greatly on the shape of the TG curves. For a slow decomposition reaction: Low chart speed for recording the TG curve because at high chart speed the curve will be flattened and it will not show the sharp decomposition temperature. For a slow reaction followed by a rapid one: at the lower chart speed the curve will show less separation in the two steps than the higher chart speed curve. For fast-fast reaction followed by slower one similar observation are observed in shorter curve plateaus.

69. Furnace Atmosphere The effect of atmosphere on the TG curve depends on ( i ) The types of the reaction (ii) The nature of the decomposition products (iii) Type of the atmosphere employed. The effect of the atmosphere on TG curve may be illustrated by taking the example of thermo-decomposition of a sample of monohydrates of calcium oxalate in dry O 2 and dry N 2 as shown in fig. The small difference is due to difference in the nature/composition of CaCO 3 formed in the two atmospheres. This is due to the particle size, surface area, lattice defects or due to the other physical characteristics of CaCO 3 formed

70. Sample Holder Range from flat plates to deep crucible of various capacities. The shape of the TG curve vary as the sample will not be heated in identical condition. Generally, it is preconditioning that the thermocouple is placed on near the sample as possible and is not dipped into the sample because it might be spoiled due to sticking of the sample to the thermocouple on heating. So actual sample temperature is not recorded, it is the temperature at some point in the furnace near the sample. Thus it leads to source of error due to the thermal lag and partly due to the finite time taken to cause detectable mass change. If the sensitivity of recording mechanism is not enough to record the mass change of the sample then this will also cause error in recording the weight change of the sample. If the composition of the sample is such that it reacts either with the sample, or product formed or the evolved gases then this will cause error in recording the mass change of the sample.

71. Effect of Sample Mass The sample mass affects the TG curve in following i ) The endothermic and exothermic reactions of the sample will cause sample temperature to deviate from a linear temperature change. ii) The degree of diffusion of evolved gases through the void space around the solid particles. iii) The existence of large thermal gradients throughout the sample particularly, if it has a low thermal conductivity. Thus, it is preferable to use as small a sample as possible depending on the sensitivity of the balance.

72. Effect of Sample Particle Size The particle size will cause a change in the diffusion of the evolved gases which will alter the reaction rate and hence the curve shape. The smaller the particle size, greater the extent of decomposition at any given temperature. The use of large crystal may result in apparent vary rapid mass loss during heating. This may be due to the mechanical loss of part of the sample by forcible ejection from the sample container, when the accumulated evolved gases within the coarse grains are suddenly released.

73. Effect of Heat of Reaction The heat of reaction will affect the extent to which sample temperature proceeds or succeeds the furnace temperature. This depends on whether the reaction is exothermic or endothermic and consequently the extent of decomposition will also be affected. The other sample characteristics such as sample packing, nature of the sample and its thermal conductivity will also affect the shape of TG curves. If the sample is packed loosely then the evolved gases may diffuse more easily than if the sample packed tightly. If the sample reacts with the sample container on heating then it will not give the mass of the product formed so the sample will change. We can avoid this effect by a sensible choice of sample container.

74. ADVANTAGES DISADVANTAGES Any type of solid can be analyzed With minimal sample preparation (at least 0.1mg) eg : powders, pellets, flakes • TGA has high accuracy of balance used as well as precise control of heating/cooling rate and atmospheric condition • TGA may be convenient and time saving, performance of technique does suffer due to construction requirements • Easy sample changing and easy change of sample holder • Fast heating rate with good resolution can be maintained • In TGA one can hold the furnace at 1000°C without any balance drift, which is not balanced in other thermobalance • Solid sample only must be used in quantitative and qualitative analysis • Data interpretation is not always straight forward • Very small Amount of samples are used but non-homogeneous material cannot be tested • Sensitive to heating rate and sample masses results in shift in temperature • Limited to sample which undergoes weight change.

75. APPLICATIONS Purity and thermal stability. Solid state reactions. Decomposition of inorganic and organic compounds. Determining composition of the mixture. Corrosion of metals in various atmosphere. Pyrolysis of coal, petroleum and wood. Roasting and calcinations of minerals. Reaction kinetics studies. Evaluation of gravimetric precipitates. Oxidative and reductive stability. Determining moisture, volatile and ash contents. Desolvation , sublimation, vaporizations , sorption, desorption , chemisorptions .

76. Examples

77. Effect of structure of Aromatic Diisocyanate

78. Aliphatic PU and Aromatic PU

79. Spherical aluminium oxide/Hexagonal boron nitride (ABN)