This 2007 presentation gives an overview on some aspects of the Cambridge Multipass Rheometer (MPR)

1. “The Cambridge Multipass Rheometer”
By
Malcolm Mackley
Department of Chemical Engineering
University of Cambridge

2. The Cambridge MultiPass Rheometer
(MPR)
Pressure variation mode Rheology flow mode
Cross-slot flow mode

3. Key issues for Processing in general
Temperature Pressure Flow Time
Key features of MPR
Temperature -10 to 210 Centigrade
Pressure 1 to 200 bar
Flow 1 to 100000 reciprocal seconds
Time ms to hours
Enclosed small volume

4. Cambridge MPRs
MPR3
MPR2
MPR4

5. J Rheology 1995

7. J Rheology 1995

8. Ice cream
a complex composite material:
Ice cream is a 3 phase material: diameter range -5°c
–ice crystals 25µm to 40 µm 15%
–air bubbles 20µm to 60 µm 50%
–matrix 35%
Conventional ice cream microstructure:
Air cells
Ice Crystals
Matrix
100µm x300

9. Ice cream matrix with foam inclusion
100000
10000 φ = 0.6
Apparent viscosity (Pa.s)

 φ = 0.5
1000  φ = 0.4
φ = 0.0
100
10
1
Parallel Plates MPR-3
0
0.01 0.1 1 10 100 1000 10000 100000
Shear stress (Pa)

10. Ice cream matrix and foam inclusion
Visualisation; Linkam CSS (Cambridge Shear System)

11. Optical Flow birefringence
Rudy Valette CEMEF Sophia
Antipolis
France
Dr David Hassell

12. Multi-Pass Rheometer (MPR)
top piston
heating jacket
pressure transducer
slit die or
capillary inserts
bottom piston

13. Case Study 1. Rudy Valette CMEF
Pressure difference vs time Flow curve
10000
differential pressure
1000
time Predicted
η * (Pa.s)
RDS
MPR2, L/D=2.5
MPR2, L/D=5
MPR2, L/D=20
MPR4, L/D=2.5
MPR4, L/D=4
MPR4, L/D=5
100
0.01 0.1 1 -1 10 100 1000 10000
shear rate (s )
FLOW

14. LLDPE Experiment and matching simulation

15. Pressure drop vs Time
MPR4
12
10
8
Pressure drop (Bars)
Experiment
6 Compressible Rolie Poly
Compressible Carreau
Incompressible Rolie Poly
4
2
0
0 0,5 1 1,5 2 2,5 3 3,5 4
Time (s)
LLDPE differential pressure responses

16. Rheo-X-RAY
Piston X-Ray 2D detector
Sample
Beryllium capillary
Beam stop
Detector
X-Ray positioning rail
source

18. The Cambridge Multipass
Rheometer (MPR)
Pressure variation mode Rheology flow mode Cross-slot flow mode

19. Foaming Tri Tuladhar, Nitin Nowjie
Top piston
Pressure Thermocouple
transducer
Thermal Capillary/ Optical window
insulation
Bleed valve
Heating circuit
Bottom piston
5

20. Growth profiles for different bubbles
5
Initial Final 4
41.94 – 149.89 – 6.83 PT – TT – XT 4.07 – 149.89 – 0.12 2
41.47 – 149.99 – 8.25 PB – TB – XB 4.44 – 150.01 – 1.38
450
1
400 3
Bottom barrel pressure (0.1 x bar)
350
Equivalent bubble radius (µ m)
300
250
200 Bubble 1
Bubble 2
150
Bubble 3
Bubble 4
Piston speed = 0.5 mm/s
100
Bubble 5
50 P-bot
0
0 500 1000 1500 2000 2500
Time (s)
12

21. Model matching with experimental data
400
Best fit conditions:
350 T = 150°C, Pf = 4.0 bar, Ro = 0.1 µm,
co = 30wt%, η o= 1×105 Pa s,
300 Dw = 6×10-16 m2/s, ρ = 1500 kg/m3,
σ = 0.05 N/m, KH = 1×10-8 Pa-1
Bubble radius ( µ m)
250 B u b b le 1
B u b b le 2
200 B u b b le 3
B u b b le 4
B u b b le 5
150
M o d e l - S o = 6 0 m ic ro n s , D w = 1E - 11 m 2 / s
M o d e l - S o = 6 0 m ic ro n s , D w = 6 E - 16 m 2 / s
100 M o d e l - S o = 5 0 m ic ro n s , D w = 6 E - 16 m 2 / s
50
0
0.001 0.01 0.1 1 10 100 1000 10000
Time (s)
15

22. Starch melt rheology in the MPR
1.0E+05
Apparent viscosity (η app) of
starch melt at 70 bar pressure
Viscosity (Pa s)
1.0E+04
1.0E+03
1.0E+02
1.0E-01 1.0E+00 1.0E+01
shear rate (s-1)
Capillary: 12mm diameter, 56mm length
30% moisture content potato starch
T = 140oC 19

23. Viscoelastic behaviour of starch melt
1.0E+05
Initial pressure
maintained at 70 bar
1.0E+04
G', G'', η *
1.0E+03
Storage modulus, G’
Loss modulus, G’’
Complex viscosity, η*
1.0E+02
1.0E-01 1.0E+00 1.0E+01 1.0E+02
Frequency (Hz)
Capillary: 12mm diameter, 56mm length
25% moisture content potato starch
T = 141.9oC 20

24. Cross Slot, Kris Coventry
• The MPR action was
modified for cross-slot flow
• Pistons move out of phase
and force polymer through
a cross-slot geometry
• New inserts were
fabricated for cross-slot
flow

25. Flow Pattern
Cross-Slot flow
• The aim is to generate
a hyperbolic flow
pattern as shown.
• Near the walls the flow
deviates from ideal.
• Along the symmetry axes
we have rotation free pure extensional flow.

26. Apparatus
• Molten polymer is Servo-hydraullically
driven through a driven piston
central section by
two servo-
hydraulically driven
pistons. Slave piston
1.5 mm
0.75 mm
radius
Slave piston
• Air pressure is driven by air
pressure
driven by air
pressure
used to return it so 1.5 mm
that multiple
experiments can
be carried out on
the same
Servo-hydraullically
driven piston
apparatus

27. Apparatus

28. Centre Section
3 cm

29. Typical Result
-Dow PS680E
-Piston velocity of 0.5
mm/s (maximum
extension rate =4.3/s).
-Inlet slit
width=1.5mm
-Section depth=10mm
- T=180°C.

30. Pom-Pom Simulation
Flowsolve
8 mode
Pom-Pom
Constitutive
Equation.

31. Filament stretch

32. DEP + 1 wt% PS +2.5 wt% PS + 5.0 wt%
1.2 mm
t-ts = -20 ms -17 ms -17 ms -11 ms
t-ts = -1 ms 0 ms 0 ms 5 ms
t-ts = 1 ms 1 ms 2 ms 6 ms

33. 5000
4500
Stretch velocity (mm/s)
4000 10 30 50 80
Mid filament diameter (µm)
100 130 150 180
3500 200 250 300
3000
2500
2000
Piston stop time,
tstop = 150 ms
1500
1000
tstop = 50 ms
500
0 tstop = 30 ms
0 20 40 60 80 100 120 140
Time (ms)
Piston diameter = 5 mm
Filament initially stretched to 1.5 mm on each side

34. 1.2 mm