Transcript Flow Behavior

Rheology
of food materials
www.anton-paar.com
Food products: life cycle
2
Food products
Rheological characterization
Formulation
-- Composition,
additives and
stabilizers
Viscosity and flow behavior of
formulation
Production
Flow behavior, viscosity, elasticity
Storage
Sedimentation stability, thermal
stability
Application (usage)
Flow behavior under shear
conditions, Thixotropy
Rheology road
Rheology road and measuring system
3
Overview
- Measuring systems for rotational and oscillatory rheometers
- Flow and viscosity curves in a wide shear rate range
Examples: Water; Polymer solutions (polysaccharide); Emulsions; Binder solutions
- Special measuring systems: measuring with the ball measuring system
Examples: Marmalade, Bolognese sauce with meat chunks
- Yield point in flow curves (via rotational tests)
Examples: Creams; Ketchups
-Yield point as the limiting value of the linear-elastic deformation range (via rotational tests)
Example: Ketchup
-Structure at rest as G’ value (via oscillatory tests: amplitude and frequency sweeps)
Examples: 1) Butter; 2) Starch gels; 3) Pudding; 4) Milk drinks; 5) Emulsions
- Structure regeneration of coatings, leveling, sagging behavior and layer thickness
- Step tests (oscillatory and rotational tests)
Example: Ketchup
- Temperature-dependent behavior during heating, softening, melting, cooling, solidification,
crystallization (using rotational and oscillatory tests)
Examples: Chocolate; Ice creams; Spreading cheese and melting cheese
-Gel formation (using time-dependent and temperature-dependent rotational and oscillatory tests)
Examples: Corn starch; Gelatin
4
Typical shear rates
Shear rate range [s-1]
Examples of application
Sedimentation (fine particles in
a suspension)
10-6 to 10-4
Salad dressing, fruit juice
Leveling
- due to surface tension
10-2 to 10-1
Coatings, printing inks,
lacquers, chocolate
Process
Dip coating
Chewing, swallowing
Pouring from a bottle
5
1 to 100
10 to 100
Cheese, yogurt, chocolate
Transport in tubes, pipe flow,
pumping, filling into
containers
1 to 104
Blood, crude oils, paints, juices
Mixing, stirring
10 to 104
Emulsion, plastisol, polymer
blends
Brushing, painting, spraying,
blade coating
100 to 104
Brush coating, tooth paste,
butter
Viscosity values
6
Materials
Shear viscosity 
Gases / air
0.01 to 0.02 / 0.018 mPas
Water at 20°C
(at 0 / 40 / 60 / 80 / 100°C)
1.0 mPas
(1.8 / 0.65 / 0.47 / 0.35 / 0.28 mPas)
Milk, coffee creams
2 to 10 mPas
Olive oil
approx. 100 mPas
Glycerin
1480 mPas
Polymer melts (T=+100 to +200°C
and at shear rates of 10 to 1000 1/s)
10 to 10 000 Pas
Polymer melts (zero-shear viscosity)
1 kPas to 1MPas
Bitumen (T = +80 / +60 / +40 /
+20 / +0°C)
200 Pas / 1 kPas / 20 kPas /
0.5 MPas / 1 MPas
Typically used measuring systems
Cone - plate and plate - plate systems
Use sandblasted or profiled measuring systems for oily and fatty substances !
Gel-like samples G‘ > G‘‘ and temperature tests
Profiled geometries for mozarrella type of cheeses,
sandblasted for cream cheese
Viscoelastic, high viscous, caution to particles and
structures sizes
Paste like, sticky and almost not flowing
Viscoelastic, medium viscosity (free flowing and
significantly above 100 mPas (1000mPas)
(larger particles or super structures )
Viscoelastic, medium viscosity (free flowing and
significantly above 100 mPas (1000mPas)
Flowing liquid but larger super-structures (CP50-2)
PP25
CP25-1, CP25-2, CP2
PP50
CP50-1
Low viscosity
CP75-0,5
7
CPxx: Cone & Plate
Cone truncation
Cone with truncation:
cone truncation
=
measuring gap
Crash!!
Name
-
Cone Truncation
[µm]
CP25-1
CP25-2
CP25-3
CP35-3
CP50-0.5
CP50-1
CP50-2
CP50-3
CP60-0.5
CP60-1
CP60-2
CP75-1
CP75-2
50
105
170
240
50
100
210
345
60
120
250
150
315
+ Shear rate and shear strain constant
+ Easy to clean
- Measurement of friction if particles are below the tip of the cone
8
Standards: ISO 3219, DIN53019, DIN53018
Double Cone BI-C60-1°
Applications: Food, Cosmetics, Pharma
 precise determination of melting and crystallization temperature
 homogenous heating and cooling
 low temperature measurements without condensation (inert, dry)
 no evaporation of water or solvents
Peltier-hood
heating & cooling
by convection
and radiation
N2
Peltier basis-control by conduction
9
modular
Bi-cone
for inset-Peltier
PTD – Peltier Temperature Device
Excellent temperature control from the bottom to the top
 unique combination of
radiation, convection (frost protection) & conductive heating & cooling
 homogenous heating and cooling
 low temperature measurement without having
 condensation (inert, dry)
 frost formation
optional
evaporation
blocker
Peltier-Hood
Heating / Cooling
by Convection
and Radiation
Peltier Basis Temp.-Control by Conduction
10
Sealing the Gap: PP & CP
Applications: Food, cosmetics, coatings
 evaporation of solvent / water ?
 skin formation ?
2 - guard ring
oil (10 mPas Si-Oil)
11
Sealing the Gap: PP & CP
Applications: Food, cosmetics, coatings
 evaporation of solvent / water ?
 skin formation ?
1a - solvent trap
solvent
sample
12
Typically used measuring systems
Concentric cylinders systems
Above 1000mPas (100mPas)
 CC27
Above 10mPas and below 1000mPas
 CC39
Above 10mPas and below 100mPas with super-structures
 DG27 (same dimensions like CC27), gap size = 1mm
Below 10mPas und homogenous, small structure
 DG26.7, gap size = 0.4mm





13
Easy to prevent sample from drying-out (oil film on top of sample)
No trimming
Good solution for all kind of liquids in rotational mode
CC: not recommended for oscillation; DG: also recommended for oscillation
CC: Helical groove if phase separation or vertical profiling to prevent slippage
Standards: ISO 3219, DIN53019, DIN53018
Flow Behavior: ideally viscous behavior
water
10
1000
mPa
mPas
10
lg 
1
lg t
constant viscosity
1
0.1
0.1
0.01
1
10
s-1
100
lg

Double-gap measuring systems are special systems designed
for low - viscosity liquids.
14
DG 42
(double gap MS)
T = +20°C
Natural Food Products
Measure natural product without destroying the initial structure
by cutting into the sample structure
A special measuring system for:
E.g. natural yoghurt
 ST22-4V-40 measuring system
 aluminum cup
 or stainless steel cup
Advantages:
 allows measurement of brittle, natural materials
 excellent penetration characteristics
 dimensions similar to standard CC27
 alternative: combination with flexible cup holder - >
15
Special Geometries
CC with Surface Treatment or Vanes, Stirrers, Propellers
Coarse disperse materials
 Building materials
 Slurries
 Food (Yoghurt)
 Better grip
 No slip
More Stirrers on request:
- User defined
- Brookfield Spindels
- Krebs Stormer
Spindels
16
- ...
Special Geometries (Relative Values)
Helix 1
Helix 2
Blade
Anchor
Ball Measuring System
All these stirrers are
relative measuring systems
Stirrer for
Building Materials
17
Starch
Stirrer
Rheometry with special Geometries
Ball Measuring System (BMS)
for dispersions containing
coarse-grained particles
(showing a diameter up to 10mm)
Example: Marmalade
containing fruit pieces
18
Rheometry with special Geometries
Ball Measuring System (BMS)
Flow and Viscosity
Curves
ofCurves
two Marmalade
Flow- and
Viscosity
of Jams at 23 °C
Measured with the Ball Measuring System
Preparations
1,000
1,000
Pa
Pa·s
100
100
blueberry
KMS-3 /Q1; d=0 mm
Shear Stress
Viscosity
lemon
10
10
KMS-3 /Q1; d=0 mm
Shear Stress
Viscosity
1
0.1
1
10
Shear Rate
.
Anton Paar GmbH
19
1/s
1
100
Rheometry with special Geometries
Ball Measuring System (BMS)
Flow and Viscosity Curves of a
Sauce Bolognese
3
4
10
10
Pa·s
Pa
3
meat sauce
10
KMS - 1M
2
10
t shear stress
2
t
10
 viscosity

meat sauce (new sample)
KMS - 1M
1
t shear stress
10
1
10
0
0
10
10
-4
10
-3
10
-2
10
Shear rate
-1
0
10
10
1
10
.

Copyright (C) 1999 Physica Meßtechnik GmbH
20
2
1/s 10
 viscosity
Spaghetti Sauce
containing meat pieces
(testing reproducibility)
Further measuring systems/ temperature
control systems
 Starch (pressure) measuring cell
 Tribology cell
 Penetration measurements
 Interfacial rheology (IRS)
 Sentmanat extensional rheology(SER)
 Flexible Toolholder
 Rheo-Microscopy
21
Flow Behavior
Rheo - Microscopy
water / oil emulsion
lg
22

dispersions
Size and shape
of the droplets
are depending
on shear rate
and
“shear history”.
Shear-Thinning flow Behavior
rest
high shear rates
Suspension 1:
Orientation of particles
(needle shaped)
Suspension 2:
Agglomerated particles
Break-up of agglomerates
Emulsion:
Deformation and break-up of
droplets
high viscosity
23
low viscosity
Shear-Thickening flow Behavior
At low shear load:
The rod inclines slowly.
Low viscosity
24
At high shear load:
Solidification of the liquid
due to shear thickening.
High viscosity
Flow Behavior
Shear-thickening Behavior
dispersions
Suspensions
shear - thickening
of suspensions at
- high solid concentrations
- high shear loads
1
f ... volume fraction of solid particles
25
Flow Behavior
Yield Point
High stress
…sample starts moving
Low stress
…no movement
t2
t1
The applied force is
higher than the
structural force
Flow Curves on a
linear scale
Yield Point as a limiting value of the shear stress
Break of the structure - at - rest.
Super - structure by a chemical - physical
network via interactive forces.

t
2
1
ty

1 without a yield point
2 having a yield point ty
Examples: Pastes, concentrated dispersions, suspensions, ketchups, mayonnaises, chocolate
melts, butter, gels
26
Flow behavior: yield point
Flow curve
showing a yield point
(on a linear scale)
Pa
2500
2000
1500
t
Ketchup
t shear stress
1000
500
Yield point can hardly be
read-off
0
0
200
400
shear rate
27
600

s-1
1000
Flow Behavior
Yield Point, comparison lin / log diagrams (2)
food
104
Flowcurve
showing a Yield Point
(on a logarithmic scale)
Pa
1000
lg t
Ketchup
100
yield point ty = 48 Pa
10
1
10
lg
28

100
s-1
1000
Flow behavior: yield point
Flow curves on a logarithmic scale
ty
29
ty
Yield point analysis
in the low-shear range,
Yield point analysis
in the low-shear range,
e.g. read off
on the t- axis
e.g. read off
at  = 0.01 s-1
Flow behavior: yield point
Mathematical curve fitting
for flow curves on a linear scale (approximation, "regression")
examples:
models
according to
Bingham: flow curve of a
material with a yield stress other often used models:
and a constant viscosity
- Casson
(food or cosmetics)
blood, food
tB - “yield point acc. to
Bingham“
B - “Bingham viscosity“
30
-Herschel / Bulkley
materials with a yield
stress and shear thinning or shear
thickening behavior
Windhab:chocolate and
other cocoa products
t0 - yield point
t1 - linear yield point
 - “high-shear viscosity“
Flow Behavior
Yield Point
food
Analysis using Approximation Functions for Flow Curves
here: according to Casson (OICC 1973), and Windhab (IOCCC 2001 / ICA)
300
Pa
250
Chocolate
Melts
Zartbitter
(T2 =
200
t
+40°C)
Schubspannung
Bitter
150
Weiße 1; A4...A4
100
1,200
50
Pa
Schubspannung
White
Cream 1
Vollmilch; A4...A4
t
Shear Stress
Schubspannung
0
0
Analysis
Bitter
White
Whole Milk
31
Whole
CreamMilk
2
800
10
20
shear rate.
Scherrate
Casson
t0 (Pa)
15
19
21
30
40
t
Anton Paar GmbH
Windhab
t0 (Pa)
18
25
23
1/s
50
t
Shear Stress
600
Cream 1 Herschel-Bulkley
400
tau0 = 705.01 Pa; b = 11.503; p =
Summary:
200
t
Shear Stress
Cream 2 Herschel-Bulkley
Yield0Points are not material
constants,
tau0 = 31.224 Pa; b = 4.7648; p =
1/s 100 on the measuring
since 0they are50depending
t Shear Stress
method and on the analysis method.
Viscoelastic Behavior
Yield Point (using a
 / t - Diagram)
Yield point as the
limiting value
of the shear stress:
The sample starts to flow
not before the external
forces are exceeding the
network-of-forces of the
internal structure.
Testing with controlled shear stress
lg 
lg 
Below the yield point
there is
elastic deformation.
lg t
yield point ty using the
best fit straight line (“ tangent“)
in the linear-elastic deformation range
32
lg t
yield point ty using the
„tangent crossover“ method
Viscoelastic Behavior
Yield Point (using a
 / t - Diagram)
food
Comparison of two Ketchups
106
%
without binder
yield point 13.5 Pa
104
lg 
deformation
with binder
yield point 114 Pa
102
100
10-2
0.1
1
shear stress
33
10
lg t
100
Pa
1000
Introduction
Viscoelastic Behavior
viscous
G'' >> G'

G'' > G'
liquid - like
structure
with
tand = G'' / G'
34
tand >> 1

tand > 1
viscoelastic
G'' = G'
„at the gel
point“
tand = 1

G' > G''
elastic
G' >> G''
gel - like
structure
tand < 1
tand << 1
0
Application
Shear Modulus
Material Stiffness and Shear Moduli
Example: different types of cheese
cheese
type
example
shear modulus
(around)
1 cream
Philadelphia
1 kPa
2 soft
French
Camembert
10 kPa
Holland Gouda
(young)
0.1 MPa
Swiss
Emmentaler
0.5 MPa
Italian
Parmigiano
1 MPa
3 semi-hard
4 hard
5 extra hard
35
1
2
5
4
Viscoelastic Behavior
Amplitude Sweeps
Gel Strength, Dependence on the Binder - Concentration
food
10,000
Pa
15 w-%
Starch Gel
(in water)
1000
10 w-%
Summary:
Gel strength
is dependent
on the binder
concentration
lg G'
7.5 w-%
100
5% w-%
10
First check in the LVE range:
tand < 1 for all samples ( = gel structure) ? Yes !
1
lg tand
0.1
0.1
36
1
10
strain lg 
%
100
ω = 10 rad/s
T = +23°C
loss factor
tand = G‘‘ / G‘
Viscoelastic Behavior
Amplitude Sweeps
food
Temperature Dependence of Butter
10
MPa
T = +10°C
1
Summary:
cold butter shows
brittle break,
hence
poor spreadability
lg G'
0.1
lg G''
T = +23°C
0.01
ω = 10 rad/s
0.01
0.1
1
strain lg 
37
%
10
Amplitude Sweep /CSD /CSS
Margarine as semi-solid material with flow point
5
10
Pa
G'
10
10
Pa
4
Margarine CSD
10
G'' 10
10
10
0,001
0,01
0,1
Deformation
1
5
10
10
10
% 100
0
G'
Speichermodul
G''
Verlustmodul
Schubspannung
-1
10
Pa
4
10
2
Margarine css
CP 50-2; d=0,05 mm
G'' 10
3
10
2
10
0,001
0,01
0,1
Deformation
1
10
am03014
CSD
CP 50-2; d=0,05 mm
3
am03014
10
Pa
38
1
3
2
G'
3
10
% 100
1
0
CSS
G'
Speichermodul
G''
Verlustmodul
Schubspannung
Application
Sedimentation, Long-term Storage Stability
dispersions
Stability of Dispersions
Example: Salad Dressings
in the beginning
after 15min
Behavior in the low-shear range or at rest, respectively
39
Frequency Sweep
Stability of suspensions
1
2
Time dependent structural strength
1
t = 1 / omega
G‘
G‘‘
- Long term behavior =
Fluid -like
- Strength of the structure
G’ decreases
- Good flow
characteristics
- Low stability
G’ constant, light
decreasing
- Long time structural
strength G‘
- Bad flow characteristics
- High stability
2
2
1
w=1/Time
40
G’ decreasing
Amplitude Sweep
Sedimentation-Stability
Milk: Geometry DG26.7*




Mechanical storage
stability
41
Pure milk
Chocolate Milk Plus
Chocolate Milk Budget
Ca enriched Mill
Amplitude Sweep
Structural strength G´ as function of stress
TAULVE = Yield stress = External force to overcome the structure at rest
-1
10
Pure Milk (no G‘ )
Pa
CHOC budget
CA Milk
CHOC plus
-2
10
G'
-3
10
-4
10
0,0001
42
tLVE
0,001
Shear stress
*) Strain-Test, plottet as function of strain
tLVE
tLVE
0,01
t
Pa
0,1
Frequency Sweep
Sedimentation Stability
Measurement of structural strength at rest or mechanical stability of milk
10
0
Pure milk
Pa
10
DG 26.7
G'
-1
Choc milk, plus
DG 26.7
G'
G'
10
-2
Choc milk, Std.
DG 26.7
G'
10
-3
CA-Milk
DG 26.7
G'
10
-4
0,1
1
10
w
43
1/s
100
Amplitude Sweep
Representation as function of stress to determine the flow points
Spread cheese
Temperature behavior
 Flow point = Spreadability as crossover point at G‘ = G“

5
10
Spread cheese 5°C
G'
G''
Spread cheese 20°C
G'
G''
Spread cheese 36°C
G'
G''
Pa
G'
4
10
G''
5°C
20°C
36°C
3
10
2
10
3
4
10
10
t Pa
44
Penetration measurements
Soft cheese
 Presetting 0.3N contact pressure
 Temperature 60°C
 Temperature of cheese before test ca. 25°C
Penetration Test
60
10
Start
Depth
°C
mm
40
d
6
30
4
20
End
2
10
0
0
0
2
4
6
8
Zeit t
Time
Anton Paar GmbH
45
10
12 min 14
T
Penetration measurement
Margarine
 Presetting: Penetration velocity down/up = 2000µm/s
 Alternatively: Normal force controlled testing
down
2
2.000
µm/s
N
1.000
1
FN
500
0
0,5
stop
-500
0
-1.000
-0,5
-1.500
up
-2.000
-1
0
46
5
10
Zeit t
Time
15
20
s
25
v
Flow Behavior
Temperature - dependent Behavior
softening and melting,
or solidification and crystallization

preset: constant shear conditions
(shear rate or shear stress)
T
result: viscosity / temperature curve
with steadily decreasing or increasing
viscosity values, respectively
gel formation and curing

preset: constant shear conditions
(shear rate or shear stress)
min
result: viscosity / temperature curve
showing a viscosity minimum
T
47
Flow Behavior
Temperature - dependent Behavior
food
10
Cooling process:
Crystallization Temperature
of Cocoa Butter
Pas
8

Chocolate Melt
6

4

2
crystallization
0
20
25
30
temperature T
48
35
°C
40
Starch gelling
 Electrical heated cell
 Watercooling
 Fast heating and cooling
rate
 Stirrer acts against
sedimentation of particles
49
Viscoelastic Behavior
Temperature - dependent Behavior
melting or crystallization process
preset: constant shear conditions (amplitude and frequency)
(with an amplitude in the LVE-range, and mostly with ω = 10 rad/s)
result:
steep decrease or increase, resp.,
in a narrow temperature range
Tk ... crystallization temperature
50
Viscoelastic Behavior
Temperature - dependent Behavior
food
Comparison of two Ice Creams
8
10
1 Old Freezer
2 New Freezer
1
Pa
6
Advantages of icecream 2:
1) better separable at –20°C
2) less cold - feel when melting
3) creamier feel at molten state
10
lg G'
5
10
lg G''
2
4
10
3
melting 
10
2
10
-20
-15
-10
-5
temperature T
51
0
5
°C
10
preset:
 = 0.02 %
ω = 10 rad/s
T = T(t)
Crystallization of a Vegetable Fat
Rheo-Microscopy
=1 % w=10 1/s
2
75
°C
70
10
Pa
65
1
60
10
55
G'
50
G''
0
45
10
40
35
-1
10
30
0
20
40
Time t
60
Vegetable Fat 10%
G'
Storage Modulus
Anton Paar GmbH
52
80
min
G''
Loss Modulus
T
Temperature
100
T
Viscoelastic Behavior
Time - dependent Structure Recovery
Different Behavior of two Ketchup Samples
fast
structure recovery
for coatings:
high wet-layer thickness,
good film stability
53
slow
structure recovery
for coatings:
small wet-layer thickness,
good levelling
Viscoelastic Behavior
Time - dependent Structure Recovery
Step test with 3 intervals, as oscillation / rotation / oscillation
(measuring „thixotropic behavior“)
preset:
1 low - shear conditions
(strain in the LVE-range, oscillation)
2 high - shear conditions (rotation)
3 low - shear conditions
(strain in the LVE-range, oscillation)
measuring result:
1 state of rest
2 structure decomposition
3 structure regeneration
2nd test interval:
liquid, at high shear rates
1st & 3rd test interval:
G‘ > G‘‘ („gel-like structure“ at rest)
54
Viscoelastic behavior: time - dependent
structure recovery
Step test: oscillation / rotation / oscillation
1000
Pas
Pa
G'
Ketchup
1.0
100

G'
0.8
G''
G''
0.6

0.4
1 = 3 = 0.3 %
10
0
50
100
time
150
200
s 250
ω = 10 rad/s
 =100 s-1
T = +23°C
t
www.anton-paar.com
Interfacial Rheology System (IRS)
MCR Rheometer + Interfacial Rheology System (IRS)
H1 = 22,5 mm
H2 = 45 mm
R = 40 mm
R2 = 34,14 mm
2  = 10°
P. Erni et. al.
J.Rev.Sci.Instr., 74(11), 4916-4924 (2003)
56
IRS: Film Formation of a Coffee Sample at
different Concentrations
 0.1% strain, frequency 1Hz
 0.05g, 0.15g, and 0.3g coffee powder / 114ml double distilled water
0
10
Pa·m
-2
G i'
10
-3
10
Gi''
Gi´= 3*10-5 Pa*m
-4
10
-5
10
-6
10
57
0
200
400
Time t
600 min 800