Thermal charactrization of polymer

Thermal analysis of Polymer , DSC, TGA , DTA , TMA , principle and mechanism

1. Bharati vidyapeeth university poona college of pharmacy THERMAL CHARACTERIZATION OF POLYMERS Guided by : Dr.V.B.Pokharkar (Head of Pharmaceutics dept.) Presented by: Sharad Ghodake First Year M.Pharm

2. Content Polymer characterization technique. General terms of Thermodynamics. Thermal behavior of polymers( Tg,Tm,Tc ). Technique of Thermal characterization DSC, DTA,TGA,TMA. Reference.

3. POLYMER AND POLYMER MORPHOLOGY Polymers are large macromolecules consisting of repeating structural units. The morphology of most polymers is semi-crystalline. That is, they form mixtures of small crystals and amorphous material and melt over a range of temperature instead of at a single melting point. Thermoplasts : Polymers soften when heated and harden when cooled. Thermosets: These polymers become permanently hard when cooled. They do not soften during subsequent heating.

4. Polymer characterization Techniques Chemical Properties . Thermal Properties. Rheological Properties. Morphology. Mechanical and dielectric properties.

5. Thermal Analysis/ Characterization The term thermal analysis (TA) is frequently used to describe analytical experimental techniques which investigate the behaviour of a sample as a function of temperature. IUPAC definition - a group of techniques in which a physical property is measured as a function of temperature , while the sample is subjected to a controlled temperature programme.

6. Types of Thermal analytical techniques THERMAL TECHNIQUE PROPERTY USES Thermogravimetry (TG) Mass Decomposition, oxidation reactions Differential Thermal Analysis (DTA) Temperature difference Phase change reactions Differential Scanning Calorimetry (DSC) Heat flow Heat capacity, phase change reactions Thermo mechanical Analysis (TMA) Deformations Softening, Expansion Dynamic mechanical Analysis (DMA) Deformations Phase changes Di-electrical Thermal Analysis (DETA) Electrical Phase changes

7. General terms of Thermodynamics Temperature : it is the average kinetic energy of the atoms or molecules of the system . Heat : Heat is a form of energy, which in spontaneous processes flows from a higher - temperature body to a lower - temperature body. heat flow can be defined as a process in which two thermodynamic systems exchange energy. The flow of heat continues until the temperature of the two systems or bodies becomes equal. This state is called thermal equilibrium There are three major forms of heat flow : conduction, convection, and thermal radiation

8. Latent Heat :The latent ( “ hidden ” ) heat is the amount of heat absorbed or emitted by a material during a phase transition. the current term is the heat of transition Enthalpy: Enthalpy is the measurement of energy in a  thermodynamic system. The quantity of enthalpy equals to the total content of heat of a system , H ≡ U + pV H is the enthalpy SI unit Joule. Entropy : The measure of the level of disorder in a closed but changing system, a system in which energy can only be transferred in one direction from an ordered state to a disordered state

9. Heat Capacity : Heat capacity indicates how much heat is needed to increase the sample temperature by 1 °C . The heat capacity of a unit mass of a material is called specific heat capacity . The SI units for heat capacity are J /( K · mol ) or J /( K · kg ).

10. Crystallisation Temperature :( Tc) When polymers fall into these crystalline arrangements, they give off heat to the system, thus the process is exothermic. In fact the heat flow drops as one can note from the big dip in the plot of (q/t) vs. T

11. Glass Transition Temperature : A glass transition temperature ( Tg ) is the temperature above which material changes from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased. Each polymer with an amorphous structure has its own unique glass transition temperature.

12. Melting Point : The melting point ( Tm ) is the temperature at which a crystalline solid changes to an isotropic liquid . Upon melting the polymers absorb heat, thus melting is an endothermic transition . From a DSC curve the melting point of a low molecular mass , high - purity substance can be determined as the point of intersection of the leading edge of the melting peak with the extrapolated baseline. This determination of the melting point is not suitable for low - molecular - mass substances of low purity and semi crystalline polymers

13. Differential Scanning Calorimetry Differential scanning calorimetry or DSC is a  thermoanalytical  technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature These measurements provide quantitative and qualitative information about physical and chemical changes that involve endothermic or exothermic processes, or changes in heat capacity.

14. Involves general measurement of heat flow in and out of the system i.e. endothermic and exothermic reaction. Endothermic reaction on a DSC occurs from: Melting Glass transitions Decompositions (rarely) Exothermic reaction measured by DSC is indicative of: Condensation Molecular reorganizations like crystallization.

15. Types of DSC: HEAT FLUX DSC : Here the difference in heat flow into the sample and reference is measured while the sample temperature is changed at a constant rate. More popular, more stable baseline. The sample and reference are enclosed in the same furnace The difference in energy required to maintain them at a nearly identical temperature is provided by the heat changes in the sample

16. Power compensating DSC •Each sample has own heater. • Temperature of samples controlled independently. • Less power required with endotherm Sample. In this the power needed to maintain the sample temperature equal to the reference temperature is measured. It has lower sensitivity but response time is more and high resolution.

17. Instrumentation: Heat is transferred through the discs and up into the material through pans. The differential heat into the two pans is directly proportional to the difference in the outputs of the two thermocouple junctions. The sample temperature is measured by the chromel and alumel junction under the sample

18. Reference Material Reference should have same physical properties as sample Reference should not have any transformations during heating Commonly used, SiC , Al2O3, empty crucible

19. The Heat capacity ( Cp ) of the system is the quantity of heat required to raise the temperature of the system by 1°C. Units Joules /°C. Cp = q/ Δ T Heat flux is given by: Δ H = Cp Δ T (or) dH / dt = Cp dT / dt + f( T,t ) where: Cp = specific heat capacity (J/K/ mol ) T = temperature (°C) H = Enthalpy (J / mol ) dH / dt = heat flow (J/min.) dT / dt = heating rate (°C/min.) f( T,t ) = Kinetic response of the sample ( J/ mol ) DSC : HEAT CAPACITY MEASUREMENT

20. APPLICATIONS: Inorganic materials, salts and complexes has been measured to study their physical properties, chemical changes and qualitative thermal behavior . One special use of DSC for physical changes is the determination of purity . Quantitative applications include determination of heats of fusion, crystallisation of materials. Glass transition temperatures and melting points are useful for qualitative estimation of materials, although thermal methods alone cannot be used for identification.

21. In this DSC profile, exothermic heat flow is measured versus temperature.

22. Here the endothermic heat flow is measured versus temperature.

23. Possible Transitions in a DSC Curve

24. Tg ( glass transition temperature): Seen in an amorphous material. No latent heat associated with it, and such transitions are referred to as second order transitions. All amorphous polymers undergo a change from glassy state to rubbery state and vice versa at certain temperature. Characteristic for each polymer. Glassy plastics, Tg > RT Rubbery material, Tg < RT Ex. Tg for polystyrene= 373K Tg for polyvinyl alcohol= 358K

25. Variants of DSC Conventional – linear temperature (cooling, heating) programme Fast scan DSC – very fast scan rates (also linear) MTDSC (modulated temperature DSC) –more complex temperature programmes, particularly useful in the investigation of glass transitions ( amorphous materials) HPDSC (high pressure DSC) – stability of materials, oxidation processes

26. DIFFERENTIAL THERMAL ANALYSIS (DTA ) Differential Thermal Analysis (DTA) measures the temperatures and temperature differences (between sample and reference) associated with transitions in materials as a function of time and temperature in a controlled atmosphere. This differential temperature is then plotted against time, or against temperature (DTA curve or   thermogram ). Changes in the sample, either exothermic or endothermic, can be detected relative to the inert reference . A DTA curve provides data on the transformations that have occurred, such as glass transitions, crystallization, melting and sublimation.

27. The temperature difference is finite only when: Heat is evolved or absorbed due to exothermic or endothermic activity in the sample or Heat capacity of the sample is changing abruptly. Temperature difference is directly proportional to the heat capacity , hence curves resemble specific heat curves, but are inverted: Heat evolution is registered as an upward peak Heat absorption as a downward peak

28. A DTA consists of a sample holder comprising thermocouples, sample containers and a ceramic or metallic block; a furnace; a temperature programmer; and a recording system. The key feature is the existence of two thermocouples connected to a voltmeter. One thermocouple is placed in an inert material such as   Al 2 O 3 , while the other is placed in a sample of the material under study.

29. A DTA curve plots the temperature difference as a function of temperature (scanning mode) or time (isothermal )

30. DTA : Applications In the study of polymeric materials: Physical changes and thermal transitions Chemical reactions like: dehydration, degradation and curing, etc.

31. THERMOGRAVIMETRIC ANALYSIS (TGA) Changes in weight with temperature are measured. Mostly solid samples are used. Ideal sample: small, powdered and evenly spread in crucible (usually platinum pan). The sample is kept in definite environment and changes in temperature are tuned to preprogrammed rate. Initial sample range: 7-8 to 10-11mg.

32. General considerations Suitable samples for TG are solids that undergo one of the two general types of reaction: Processes occuring without change in mass (e.g., the melting of a sample) obviously cannot be studied by TG. Reactant(s)  Product(s)+Gas (a mass loss) Gas+Reactant (s)  Product(s) (a mass gain)

33. Instrumentation

34. The electro balance and its controller The furnace and temperature sensor The programmer or a computer Data acquisition device/ recorder/ plotter A sensitive vacuum reading balance with sensitivity of 0.1 μ m is used to follow the weight change. Sample weight is recorded under pressure of 10 -4 mm to 1 atm. Now a days, coupled with IR or MS to measure chemical nature of the evolved gases being lost from sample. Instrumentation

35. The sample is placed in a small electrically heated oven with a thermocouple to accurately measure the temperature. The atmosphere may be purged with an inert gas to prevent oxidation or other undesired reactions.

36. The environment of furnace can be changed as desired. Ex. Air, nitrogen, inert atmosphere of Ar, etc. with use of gas inlet and outlet chutes. Dynamic and static modes can be applied. Results represented as TG curves, variation of the apparent mass of sample Vs. temperature is plotted. Mass generally represented as: mass loss Where, Wo = initial mass Wt = mass at a given temperature Typical plots are usually of one/two/three or even multi-step uturned S type of curves.  

37. In order to ascertain steps in TGA traces, the derivative thermogravimetric (DTG) curves are frequently constructed. DTG curve is represented by: Rate of mass change per pre-selected temperature interval, dm / dt Vs. temperature DTG curve has well defined peaks superimposing on rapid fall in the mass loss as observed in TGA curve.

38. TGA(weight changes) and DSC (heat flow).

39. Ti : Lowest temperature at which the onset of a mass change can be detected Tf : Lowest temperature by which the process responsible for the mass change has been completed

40. Thermogravimetric analysis (TGA): Uses Typical applications include: Pharmaceutical engineering research & in industrial quality control . Assessment of thermal stability. Assessment of decomposition temperature. Extent of cure in condensation polymers. Composition and some information on sequence distribution in copolymers. Composition of filled polymers. Used for drug stability studies and the kinetics of decomposition.

41. Thermomechanical Analysis (TMA) Measurement of mechanical response of a polymer system as temperature is changed. These responses include: expansion and extension of materials or changes in viscoelastic properties and heat distortions, such as shrinking. The temperature range used is: -150 C to 700 C.

42. Instrumentation: Probe assembly(generally quartz glass) Furnace Recorder(LVDT) Thermocouple The furnace, containing the sample and probe, controls the temperature. Any motion due to expansion, melting, or other physical change(in test sample) delivers an electric signal to a recorder .

43. Uses: Measurement of: Penetration or heat deflection Torsion modulus Stress-strain behavior Mechanical and Viscoelastic properties of hair and stratum corneum of the skin (Humphries et al.) To look at polymer films and coatings used in pharmaceutical processes.

44. Reference: Hatakeyama T., Quinn F.X., Thermal Analysis Fundamentals and Applications to Polymer Science, Second Edition, John Wiley & Sons Ltd . , 1999. JOSEPH D. MENCZEL, R. BRUCE PRIME, THERMAL ANALYSIS OF POLYMERS Fundamentals and Applications, A JOHN WILEY & SONS, INC., PUBLICATION ,2009. H. K. D. H. Bhadeshia, Differential Scanning Calorimetry, University of Cambridge, Materials Science & Metallurgy.

45. RESEARCH PAPER Characterization of Cellulose Acetate Phthalate (CAP ) P. Roxin , Anders Karlsson , Satish K. Singh Dept . of Pharmaceutical Analytical Chemistry, Pharmacia and Upjohn AB, S-751 82 Uppsala, Sweden. Drug Development and Industrial Pharmacy, 24(1 I), Page .1025-1041 ( 1998). www.dekker.com Copyright 1998 by Marcel Dekker, Inc.

46. ABSTRACT Cellulose acetate phthalate (CAP) is a commonly used enteric coating polymer . CAP powder has been studied by various methods to determine characteristics that have an influence on its functionality. Other characteristics, such as the molecular mass distribution, have not been reported earlier . Fourier transform infrared spectroscopy (FTIR ), nuclear magnetic resonance (NMR), and thermal analysis have also been performed on fresh samples, as well as samples stored under various temperature und humidity conditions

47. INTRODUCTION Cellulose acetate phthalate is a commonly used tablet coating material employed to produce so-called enteric films , which resist prolonged contact with the strongly acidic gastric fluid, but soften, swell, and finally dissolve in the mildly acidic or neutral intestinal environment . In this work, they report an examination of some of the polymer characteristics, including the effect of storage. While a number of these characteristics have been studied earlier, others (such as the molecular mass distribution ) have not been reported . new methods have also been developed to enable a more rapid examination of these characteristics than that allowed by the pharmacopoeia methods, for instance.

48. Materials and Methods CAP was obtained from Eastman Chemical Company Sr.No . Batch No. 1) 50103 2) 50105 3) 50106 4) 40706 5) 50104

49. Methods Thermo gravimetric Analysis: Mettler TA4000 system using a TGA5O analyzer. Mass of sample : 20mg Sample Pan: Al2O3 crucibles. heating rate : 5°C/min temperature interval : 50°C-600°C. Nitrogen atmosphere was used in the temperature range 50°C-600°C , and oxygen was used over 500°C .

50. DSC CAP powder samples were subject to differential scanning calorimetry (DSC) on a Mettler TA4000 system using a DSC30 analyser. Sample masses of approximately 10mg were placed in aluminium pans with crimped lids and also lids with pinholes. The scanning rate was 10 ° C/min over the range 50 ° C-300 ° C . Nitrogen flow rate was 50ml/min .

51. Results and discussion: CAP samples were analysed by TGA to obtain separated vaporization and thermal degradation steps , such that absolute values of water content , degree of substituents measured in acetic and phthalic acid, and pyrolysis products were know. A TGA thermogram is shown in next slide for a fresh CAP sample Batch no.40706 . DSC was used to measure the glass transition temperature Tg of the CAP powders. A typical thermogram is shown in next slide, in which both water loss and glass transition phenomena are clearly visible. Batch No. Tg ("C) 50103 174 50105 173 50106 172 40706 172 50104 172

52. On examining the storage data in Table , it is seen that only the storage at the most severe conditions (40°C 65.6 mbar 89% RH) seems to have any measurable effect on this parameter. From the analysis of total acetic and phthalic content above, we know that, under this storage condition, CAP loses a large fraction of substituents in 15 weeks , so we are essentially measuring a different polymeric material along with free acetic and phthalic acids serving as plasticizers.

53. Cellulose acetate phthalate powder has been studied by various methods. New methods have been developed to examine free-acid content, substituent composition, and molecular mass distribution; FTIR, NMR, and thermal analysis have also been performed on fresh samples, as well as samples stored under various temperature and humidity conditions . Glass transition temperatures of CAP samples were measured. However, this characteristic of the polymer is judged not to be as sensitive to the loss of substituents as the molecular weight . Conclusion