POLYCHAR 22 - Short Course DYNAMIC-MECHANICAL and CALORIMETRIC PROPERTIES OF POLYMERS

1. POLYCHAR 22 - Short CourseDYNAMIC-MECHANICAL and CALORIMETRICPROPERTIES OF POLYMERS Michael Hess Thanks to Dr. Kevin Menard, University of North Texas and Perkin Elmer for some of the examples

2. Calorimetric Analysis of Polymers • course of polymerization • transreactions • chain scission • radiation induced degradation • thermal degradation • chain stripping leaving carbonaceous residue • curing of thermosets • ... • phase behaviour (estimation of a phase diagram) • mesophase behaviour • (processing) history • (themoreversible) gelation • thermal transitions (Tg, Tm, Tcr...) • bound water in hydrogels • crystallization and ordering • ...

3. Dynamic-Mechanical Analysis mechanical properties of (polymeric) materials under the influence of dynamic load and temperature mechanical modulus as a function of load, temperature, time transitions, relaxations, service range (temperature), service time

4. Thermal Transitions transition temperatures, transition enthalpie glass transition cold crystallization • recrystallization • crystallization melting • brittle/viscous • miscibility • thermal history • polymorphism • mesophases • phase diagram • kinetics • degree of crystallization • purity

8. DTA DSC DT Wel (DT=0)

9. poly(dimethyl siloxane) (PDMS) heat flux or cp melting Tm (end) enthalpy relaxation cold crystallization Tg Tm (onset) Tm (rate max)

10. Dynamic-mechanical analysis - rheology the modern machines can rapidly change the measuring device so that solid and fluid samples can be measured and many different modes can be applied Thermomechanical Analysis Stress-Strain Curves Creep Recovery Stress Relaxation Dynamic Mechanical Analysis Solvent Immersed testing

11. simple deformations in a solid simple shear deformation (also in liquids possible) simple extension

12. simple stress in a shear deformation 22 21 12 23 2 32 1 11 3 13 31 33 The total stress ijis a second rank tensor composed of normal and shear components

13. (ideal) energy elasticity • caused by deformation of bond angles and bond length at small deformations • the energy is stored and completely released after the load is removed • there is no (internal) friction • =strain;  = uniaxial deformation ratio;  = shear (angle); F = force [N]; A0 =initial area E = Young modulus [Pa]; G = shear modulus [Pa]; J = compliance [Pa-1]

14. elongation The stress [Pa = N/m2] refers to the initial cross section Stress and strain are principally time-dependent stress can “relax” (at constant strain) elongation can “creep” (at constant stress)

15. ideal stress-strain diagram in the Slope: elastic (Young-) modulus E

16. the major types of moduli extension  Young modulus E shear  shear modulus G compression  bulk modulus B bending*  bending modulus Eb *three-point bending, 4 point bending The lateral strain elat is the strain normal to the uniaxial deformation. the different moduli can be converted into one another, see D. Ferry

17. so that for elastomers: The volume change on deformation is for most elastomers negligible so that m=0.5 (isotropic, incompressible materials). In a sample under small uniaxial deformation!! The lateral strain elat is the strain normal to the uniaxial deformation.

18. dilatant structural viscous s slope = h . g shear in an ideal (Newtonian) liquid ideal liquid between two parallel plates = shear rate an ideal liquid shows no elasticity  = dynamic viscosity [Pa s]; 1 centipoise = 1 mPa s

19. important rheometer types for viscous samples torque plate-plate cone-plate Couette constant shear rate along the radius

20. a combination of both: visco-elastic behaviour James Clerk Maxwell, Phil. Trans. Roy. Soc. London 157 (1867) 52 single relaxation time  spectrum of relaxation times i There is mater that shows elastic and viscous behaviour (e.g. pitch): fast deformation rather elastic, slow deformation rather viscous response

21. major response types on deformational stress

22. storage and loss of energy dissipated energy saved energy damping (factor)

23. 'simple' static stress-strain experiment tensile strength stress  tensile strength yield strength elongation at break brittleness B*): tensile strength elongation at break *) according to Brostow et al., J. Mater. Sci 21 (2006) 2422 not to be confused with the bulk modulus B (compression modulus) strain 

24. DYNAMIC is important!! time frequency dependence of damping temperature depending properties (elasticity, flow…) long term prediction, fatigue… temperature TTS superposition

25. frequency range and applied technique

27. Free damping experiment logarithmic decrement amplitude shear (storage) modulus G'(f, T) loss modulus G''(f, T) loss factor D (tangent)

28. stress and strain are in phase in an idealenergy-elastic material, phase angle  = 0° stress strain stress and strain are out of phase in an ideal viscous material, phase angle  = 90°

29. The modulus of a visco-elastic material is a complex physical entity dissipated (loss) stored

30. Correlation between moduli and phase angle (damping) in the Gaussian plane of complex numbers the complex shear modulus G*, the Young modulus E* and the complex viscosity * can be visualized as the damping factor D is then given by the tan of the loss angle  D shows a behaviour similar to 

31. Modulus, damping and their correlation with molecular motions  or tan  (rubber)  or tan 

32. a thermodynamic view at the 'glass transition' There is not only one glass. The type of glass depends on the thermal history. slowly heating can cause annealing

33. G' The glass transition in a dynamic experiment tan G'' T glassy visco-elastic rubbery

34. DMA and different molecular parameters

35. Tg are easily seen, as in PET Film

36. Tg by DMA and DSC DH/(J/g)  DCp Tf Temperature /C Onset Inflection Point Heat flow/mW differential scanning calorimetry Peak Tan d = 140.5°C Onset E’ = 133.1 °C Peak E” = 136.7 °C Tan d Modulus/Pa Onset E” = 127.3 °C Onset Tan d = 130.0 °C Temperature/C (a) (b)

37. Operating Range by DMA Operating range Operating range (a) Beta (b) Tg Operating range modulus is ok toughness is ok (c) leather-like state

38. blow forming temperature of use vacuum forming extrusion injection moulding 'leather' rigid shear modulus rubber viscous amorphous semicrystalline thermoplasts temperature of use extrusion injection moulding cold forming vacuum forming shear modulus blow forming

39. Cold Crystallization in PET seen by DMA and DSC Tm Tg Cold Crystallization DSC

40. Higher Order Transitions affect toughness Good Impact Strength b Transitions Tg Poor Impact was good if Tg/Tb was 3 or less.

41. stress-relaxation in a silicone rubber DMTA Tg DSC Cold Crystallization Left: silicon rubber with a glass transition at –117°C and a melting transition at –40°C. Beyond the melting temperature this crosslinked (vulcanised) material shows rubber-elasticity with modulus that increases with the temperature. Right: also a silicone rubber that contains silicone oil as diluent, as plasticizer. The oil causes a stress-relaxation at the beginning of the melting transition around –47°C.

42. Polymer A Both Tgs E’ Block Copolymers Graft Copolymers Immiscible Blends E’ Temperature/K Temperature/K = + Single Tg Polymer B Random Copolymers & Miscible Blends E’ E’ Exact T depends on concentration of A and B Blends and Copolymers Temperature/K Temperature/K

43. The frequency-dependence of dynamic experiments Temperature dependency of E' and tan of PVC at different frequencies, after Becker, Kolloid-Z.140 (1955) 1

44. Time-Temperature-Superposition Principle(TTS) experimental window experimental window NBS-poly(isobutylene, after A. Tobolski

45. The glass transition temperature seen by viscosity lg  empirical WLF equation Tg+50K Arrhenius-type Temperature-dependence of the viscosity of PMMA (M=63.000 g/mol) after Bueche Williams-Landel-Ferry (WLF) equation

46. TTS gives the frequency-dependence of the glass transition temperature: An increase of the measuring frequency  (heating rate) by a factor 10 (or a decrease of the time frame by a factor of 10) near Tg the glass-transition temperature is found about 3 K higher.

47. Master Curves*) extend the range • We can collect data from 0.01 to 100 Hz. • If we do this at many temperatures, we can “superposition” the data. • After TTS, our range is 1e-7 to 1e9 Hertz (1/sec) • Then x scale (frequency) can then be inverted to get time TTS *) modulus or compliance; compliance = (modulus)-1

48. BUT... TTS assumes that: “all relaxation times are equally affected by temperature.” THIS IS KNOWN TO OFTEN BE INVALID. J. Dealy

49. Failure of TTS Log J* compliance J = 1/E

50. experiment at a constant heating rate time-temperature-transition diagram after Gillham