Thermal Analysis of Polysaccharides Mechanical Methods

Transcription

1 Biopolymer Solutions Thermal Analysis of Polysaccharides Mechanical Methods John Mitchell 1

2 Topics Covered Introduction to polymer viscoelasticity Examples Thermal transitions in polysaccharide containing sweets, cellulose powders and solutions of ethyl cellulose Rapid viscosity analyser Temperature induced swelling of particulates Examples» xanthan gum and cellulose particles 2

3 Stress Relaxation Experiment Rubber Force Bread dough Time 3

4 Response of high molecular weight amorphous polymer Log force or Log modulus (G(t) in shear) Glassy state Transition Relationship to zero shear zone viscosity Plateau η 0 tg() t d ln Terminal zone = t Introduction of crosslinks Log time 4

5 What has this to do with temperature? log force or log modulus (G(t) in shear) Transition zone Plateau Measured at a single time after deforming sample Glassy state Terminal zone Temperature 5

6 Time Temperature Superposition An Introduction to Polymer Viscoelasticity: Aklonis, J.J. and MacKnight, W.J. (1983) Wiley-Interscience page 44 6

7 The Oscillation Experiment γ = γ 0 sin ( ωt ) ( ω δ ) σ = σ sin t ωt / rad Resolve stress into components in phase with strain and 90 o out of phase σ = σ 0 cos δ sin ( ω t ) + σ sin δ cos ( ω t ) σ 0 in phase component out of phase component - - (7) 7

8 Some parameters from the oscillation experiment Shear Storage Modulus σ G = cos δ γ ' 0 γ 0 The storage modulus is given by the ratio of the amplitude of the component of the stress in phase with the strain to the strain amplitude. G gives the proportion of the energy supplied to the system which is stored elastically during each cycle of oscillation. Shear Loss Modulus σ '' 0 G = sin δ γ 0 The loss modulus is given by the ratio of the amplitude of the component of the stress 90 0 out of phase with the strain. For a given strain G gives the proportion of the energy supplied to the system which is dissipated during viscous flow during each cycle of oscillation. Loss tangent tanδ= G /G - - (8) 8

9 Response of high molecular weight amorphous polymer Dependence of real part of dynamic modulus on frequency mirror image of stress relaxation modulus on time. High frequencies correspond to short times. Where G changes slowly with frequency behaviour more elastic. Energy dissipation low and G less than G Log G or G Terminal zone G G Glassy state Log frequency 9

10 Master curve of storage and loss modulus, and their ratio (tan δ = G"/G') as a function of frequency, polymer concentration and molecular weight, and temperature at the terminal zone (I), plateau (II), glass transition (III), and glassy region (IV). I II III IV G' Log (modu uli) G'' 1 Tan δ Low High Frequency Molecular weight Concentration Temperature Kasapis, S p 235 in Functional Properties of Food Macromolecules Edited Hill, S et al., (1998) Aspen, Maryland High Low 10

11 Dynamic Mechanical Thermal Analysis (DMTA)) Extensively used to characterise synthetic polymers Good for solid samples Not fundamentally different from oscillatory rheometry in rotation Examples Gummy sweets Cellulose powder 11

12 Dynamic Mechanical Thermal Analysis (DMTA) bending mode ~20mm 5-8mm 1-2mm 12

13 Gum tested in single cantilever bending mode 13

14 Determination of Tg from DMTA for Gellan Based Gum Onset E = -34 C Peak Tan δ = -10 C ( ) a] E" [P E' ( ) [Pa] Peak E = -31 C tan delta ( ) [ ] Temp [ C] Data of Marcin Deszczynski 14

15 Master curve of storage and loss modulus, and their ratio (tan δ = G"/G') as a function of frequency, polymer concentration and molecular weight, and temperature at the terminal zone (I), plateau (II), glass transition (III), and glassy region (IV). I II III IV G' Log (modu uli) G'' 1 Tan δ Low High Frequency Molecular weight Concentration Temperature High Low 15

16 Amorphous Cellulose Powder Attempt to measure mechanically, glass transition of small quantities of ball milled cellulose powder Mechanical measurements of transition much more sensitive than calorimetric measurements Paes, S,Sun, S, MacNaughtan, W, Ibbett, R., Ganster, J., Foster TJ. and Mitchell, J.(2010) Cellulose 17,

17 DMTA Pocket Technique 17

18 DMTA Ball Milled Amorphous Cellulose 18

19 Glass Transition of Amorphous Cellulose and Starch Data of Sun and Paes 19

20 Association in Ethyl Cellulose Solutions on Heating Original observation from Jena group on cloud point observed after heating at indicated temperature for five minutes. Can solution rheology follow this transtion? Sun, S., Foster, T., MacNaughtan, W., Mitchell, J., Fenn, D., Koschella, A. and Heinze, T. (2009) Journal of Polymer Science Part B Polymer Physics 47,

21 Is rheology consistent with visual observation? 2% Ethyl Cellulose Random Substitution b (1Hz. 2 % strain 1 O Cmin -1 ) 10 3 Heating Pa G', G" / G' G" Cooling Cooling Heating Temperature / o C 21

22 Is rheology consistent with visual observation? 2% Ethyl Cellulose Regular Substitution 10 1 b G', G" / Pa G' G" 10-2 Cooling Cooling Heating Heating Temperature / o C 22

23 Large Differences in Cloud Point Sample were held at these temperatures for 5 minutes. Observations from University of Jena 23

24 Rapid Viscosity Analyser - - (24) 24

25 Typical Viscosity Response to the Pasting Experiment Viscosity Viscosity Temperature Increase due to granule swelling Set back primarily due to network formation as a result of amylose retrogradation Decrease due to granule disruption under heat and shear Temperature - - (25) 25

26 Pasting Curve for Physically Modified Xanthan (2% xanthan 0.4 %NaCl) Data of Fuad Hajji and Woroud Alsanei 26

27 Effect of Preheating in the Rapid Viscosity Analyser on Viscosity Development of Cellulose Particles in LiCl/Urea/Water Solutions μ T Viscosity (c cp) Temp perature ( o C) Time (min) Data of Dr. Ivana Tatárová 27

28 References An Introduction to Polymer Viscoelasticity: Aklonis, J.J. and MacKnight, W.J. (1983) Wiley-Interscience Dynamic Mechanical Analysis: A Practical Introduction: Menard K.P. (1999) CRC Press An Introduction to Rheology. Barnes, H.A., Hutton, J.F. and Walters, K. (1989) Elesevier, Amsterdam Viscoelastic Properties of Polymers 3rd Edition: Ferry, J.D. (1980) Wiley 28

29 Thank you for listening 29