10/6/2010

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Biopolymer Solutions

Thermal Analysis of Polysaccharides

Mechanical Methods

John Mitchell

Mechanical Methods

John.Mitchell@biopolymersolutions.co.uk

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Topics Covered

• Introduction to polymer viscoelasticity– Examples

• Thermal transitions in polysaccharide containing sweets, cellulose powders and solutions of ethyl p ycellulose

• Rapid viscosity analyser• Temperature induced swelling of particulates

– ExamplesExamples » xanthan gum and cellulose particles

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Stress Relaxation Experiment

Force

Rubber

Time

Bread dough

Time

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Response of high molecular weight amorphous polymer

Transition

Log force

Transition zone

Plateau ( )∫∞

∞−

= tdttG ln0η

Relationship to zero shear viscosity

gor

Log modulus (G(t) in shear)

Glassy state

Terminal zone

Introduction of crosslinks

Log time

Terminal zone

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What has this to do with temperature?

Transitionlog force or

log modulus (G(t) in shear)

Transition zone

Plateau

Glassy state

Terminal zone

Measured at a single time after deforming sample

Temperature

Terminal zone

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Time Temperature Superposition

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

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( )tωγγ sin0=

The Oscillation Experiment

( )γγ 0

( )δωσσ += tsin0

( )tiδ + ( )tcossin ωδσResolve stress into components in phase with strain and 90o out of phase

0 5 10 15 20

ωt / rad

- - (7)

=σ ( )tsincos ωδσ 0 + ( )tcossin ωδσ 0

“in phase”component

“out of phase”component

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Some parameters from the oscillation experiment

δγσ cos' 0=GShear Storage Modulusγ 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

The loss modulus is given by the ratio of the amplitude of the component of the stress 900 out of phase with the strain. For a given strain G’’ gives the proportion of the energy supplied to the system which is dissipated

δγσ sin''

0

0=G

- - (8)

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’

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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 Log

Terminal zone

Glassy state

G’

to short times.

Where G’ changes slowly with frequency behaviour more elastic. Energy dissipation low and G’’ less G’’

gG’or G’’

Log frequency

dissipation low and G less than G’

G

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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

uli)

I II III IV

G'

Log

(mod

u

Tan δ

1

G''

FrequencyMolecular weightLow

LowHigh

High

Temperature

Concentration

Kasapis, S p 235 in Functional Properties of Food Macromolecules Edited Hill, S et al., (1998) Aspen, Maryland

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Dynamic Mechanical Thermal Analysis (DMTA))

• Extensively used to characterise synthetic polymers

• Good for solid samples N t f d t ll diff t f• Not fundamentally different from oscillatory rheometry in rotation

• ExamplesGummy sweets– Gummy sweets

– Cellulose powder

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Dynamic Mechanical Thermal Analysis (DMTA)Dynamic Mechanical Thermal Analysis (DMTA)

bending mode

1-2mm

5-8mm

~20mm

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Gum tested in single cantilever bending mode

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Determination of Tg from DMTA for Gellan Based Gum

O E’ 34°C

108

109

1010

1.0

1.2

1.4

1.6

()

a]

tan_

Peak Tan δ = -10°COnset E’ = -34°C

106

107

0 2

0.4

0.6

0.8

E' (

)

[Pa]

E"

[P

_delta ()

[ ]Peak E” = -31 °C

-60.0 -50.0 -40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0105 0.0

0.2

Temp [°C]

Data of Marcin Deszczynski

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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

uli)

I II III IV

G'

Log

(mod

u

Tan δ

1

G''

FrequencyMolecular weightLow

LowHigh

High

Temperature

Concentration

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“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 measurementsmeasurements

Paes, S ,Sun, S, MacNaughtan, W, Ibbett, R., Ganster, J., Foster TJ. and Mitchell, J.(2010) Cellulose 17, 693-709

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DMTA – Pocket Technique

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DMTA – Ball Milled Amorphous Cellulose

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Glass Transition of Amorphous Cellulose and Starch

Data of Sun and Paes

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Association in Ethyl Cellulose Solutions on Heating

Original observation from Jena group g g pon 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, 1743-1752

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Is rheology consistent with visual observation?2% Ethyl Cellulose Random Substitution

(1Hz. 2 % strain 1OCmin-1)

103Heating

Cooling

Pa

b

( )

101

102

Heating

Cooling

G' G"

G',

G" /

0 10 20 30 40 50 60 70 80 90100

Temperature / oC

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101

b

Is rheology consistent with visual observation?2% Ethyl Cellulose Regular Substitution

100

Cooling

CoolingG" /

Pa

b

10-1

Heating

g

Heating

G'G"

G',

G

0 10 20 30 40 50 60 70 80 9010-2

G

Temperature / oC

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Large Differences in Cloud Point

Sample were held at these temperatures for 5 minutes.

Observations from University of Jena

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Rapid Viscosity Analyser

- - (24)

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Typical Viscosity Response to the Pasting Experiment

ViscosityIncrease due to granule Set back primarily due to

Viscosity

Temperature

granule swelling

Decrease due to granule disruption

network formation as a result of amylose retrogradation

Temperature

- - (25)

under heat and shear

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“Pasting” Curve for Physically Modified Xanthan (2% xanthan 0.4 %NaCl)

Data of Fuad Hajji and Woroud Alsanei

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Effect of Preheating in the Rapid Viscosity Analyser on Viscosity Development of Cellulose Particles in

LiCl/Urea/Water Solutions

400

500

600

700

μ T

cP)

70

80

90

100

Temp

0

100

200

300

400

Vis

cosi

ty (c

20

30

40

50

60

70 perature ( oC)

Data of Dr. Ivana Tatárová

0 10 20 30 40 50 600

Time (min)

20

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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

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