“The Cambridge Multipass Rheometer”

By

Malcolm MackleyDepartment of Chemical Engineering University of Cambridge

The Cambridge MultiPass Rheometer (MPR)

Pressure variation mode Rheology flow modeCross-slot flow mode

Key issues for Processing in general Temperature Pressure Flow Time

Key features of MPR

Temperature -10 to 210 CentigradePressure 1 to 200 bar Flow 1 to 100000 reciprocal secondsTime ms to hoursEnclosed small volume

Cambridge MPRs

MPR2

MPR4

MPR3

J Rheology 1995

J Rheology 1995

Conventional ice cream microstructure:

100m x300

Ice Crystals

Matrix

Air cells

Ice creama complex composite material:

Ice cream is a 3 phase material: diameter range -5°c

–ice crystals 25m to 40 m 15%–air bubbles 20m to 60 m 50%–matrix 35%

= 0.6 = 0.5

= 0.4

= 0.0

0

1

10

100

1000

10000

100000

0.01 0.1 1 10 100 1000 10000 100000

Shear stress (Pa)

Ap

par

ent

visc

osi

ty (

Pa.

s)

Parallel Plates MPR-3

= 0.6 = 0.5

= 0.4

= 0.0

0

1

10

100

1000

10000

100000

0.01 0.1 1 10 100 1000 10000 100000

Shear stress (Pa)

Ap

par

ent

visc

osi

ty (

Pa.

s)

Parallel Plates MPR-3

Ice cream matrix with foam inclusion

Ice cream matrix and foam inclusion

Visualisation; Linkam CSS (Cambridge Shear System)

Optical Flow birefringence

Rudy Valette CEMEF Sophia Antipolis

France

Dr David Hassell

Multi-Pass Rheometer (MPR)top piston

heating jacket

pressure transducer

slit die orcapillary inserts

bottom piston

time

diff

ere

nti

al p

ressu

re

FLOW

100

1000

10000

0.01 0.1 1 10 100 1000 10000shear rate (s-1)

*

(Pa.

s) PredictedRDSMPR2, L/D=2.5MPR2, L/D=5MPR2, L/D=20MPR4, L/D=2.5MPR4, L/D=4MPR4, L/D=5

Pressure difference vs time Flow curve

Case Study 1. Rudy Valette CMEF

LLDPE Experiment and matching simulation

Pressure drop vs TimeMPR4

0

2

4

6

8

10

12

0 0,5 1 1,5 2 2,5 3 3,5 4

Time (s)

Pre

ssu

re d

rop

(B

ars)

Experiment

Compressible Rolie Poly

Compressible Carreau

Incompressible Rolie Poly

LLDPE differential pressure responses

Rheo-X-RAY

X-Ray source

X-Ray 2D detector

Sample

Piston

Beam stop

Beryllium capillary

Detector positioning rail

The Cambridge Multipass Rheometer (MPR)

Pressure variation mode Rheology flow mode Cross-slot flow mode

Foaming Tri Tuladhar, Nitin Nowjie

Thermocouple

Capillary/ Optical window

Heating circuit

Bottom piston

Top piston

Pressure transducer

Thermal insulation

Bleed valve

5

Growth profiles for different bubbles

12

1

2

3

4

5

Initial FinalPT – TT – XT

PB – TB – XB

41.94 – 149.89 – 6.83

41.47 – 149.99 – 8.254.07 – 149.89 – 0.12

4.44 – 150.01 – 1.38

Piston speed = 0.5 mm/s

0

50

100

150

200

250

300

350

400

450

0 500 1000 1500 2000 2500

Time (s)

Bo

tto

m b

arr

el p

res

su

re (

0.1

x b

ar)

Eq

uiv

ale

nt

bu

bb

le r

ad

ius

(m

)

Bubble 1

Bubble 2

Bubble 3

Bubble 4

Bubble 5

P-bot

0

50

100

150

200

250

300

350

400

0.001 0.01 0.1 1 10 100 1000 10000

Time (s)

Bu

bb

le r

adiu

s (

m)

Bubble 1

Bubble 2

Bubble 3

Bubble 4

Bubble 5

Model - So = 60microns, Dw = 1E-11 m2/s

Model - So = 60microns, Dw = 6E-16 m2/s

Model - So = 50microns, Dw = 6E-16 m2/s

Model matching with experimental data

15

Best fit conditions:

T = 150°C, Pf = 4.0 bar, Ro = 0.1 m,

co = 30wt%, o= 1105 Pa s,

Dw = 610-16 m2/s, = 1500 kg/m3,

= 0.05 N/m, KH = 110-8 Pa-1

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E-01 1.0E+00 1.0E+01

shear rate (s-1)

Vis

cosi

ty (

Pa

s)

19

Capillary: 12mm diameter, 56mm length

30% moisture content potato starch

T = 140oC

Apparent viscosity (app) of starch melt at 70 bar pressure

Starch melt rheology in the MPR

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E-01 1.0E+00 1.0E+01 1.0E+02

Frequency (Hz)

G',

G'',

*

20

Capillary: 12mm diameter, 56mm length

25% moisture content potato starch

T = 141.9oC

Viscoelastic behaviour of starch melt

Storage modulus, G’Loss modulus, G’’Complex viscosity, *

Initial pressure maintained at 70 bar

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

Flow PatternCross-Slot flow

• The aim is to generatea hyperbolic flowpattern as shown.

• Near the walls the flowdeviates from ideal.

• Along the symmetry axeswe have rotation free pure extensional flow.

Apparatus

• Molten polymer is driven through a central section by two servo-hydraulically driven pistons.

• Air pressure is used to return it so that multiple experiments can be carried out on the same apparatus Servo-hydraullically

driven piston

Servo-hydraullically driven piston

Slave piston driven by air pressure

Slave piston driven by air pressure

1.5 mm

1.5 mm0.75 mm radius

Apparatus

Centre Section

3 cm

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.

Pom-Pom SimulationFlowsolve

8 mode Pom-Pom Constitutive Equation.

Filament stretch

DEP + 1 wt% PS +2.5 wt% PS + 5.0 wt%

t-ts = -20 ms -17 ms -17 ms -11 ms1.2 mm

t-ts = -1 ms 0 ms 0 ms 5 ms

t-ts = 1 ms 1 ms 2 ms 6 ms

Piston diameter = 5 mm

Filament initially stretched to 1.5 mm on each side

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 20 40 60 80 100 120 140

Time (ms)

Mid

fila

men

t di

amet

er (

µm

) 10 30 50 80

100 130 150 180

200 250 300

Stretch velocity (mm/s)

Piston stop time,tstop = 150 ms

tstop = 50 ms

tstop = 30 ms

1.2 mm1.2 mm