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© 2018 Malvern Panalytical
Capillary Rheometry – A Method to Predict Flow Properties under Processing Conditions
Torsten Remmler, Malvern Panalytical GmbH
Zwick testXpo 2018
© 2018 Malvern Panalytical
Overview
• Range of Applications for Capillary Rheometry
• Introduction into capillary rheometry: Principle of Operation and theoretical background
• Test results on LDPE: Complete Capillary Characterisation
• Advanced Test Types: Relaxation, Thermal Degradation etc.
© 2018 Malvern Panalytical
Capillary Rheometry: Main Applications
© 2018 Malvern Panalytical
Typical Shear Rates
Rotational-Rheometer
High Pressure Capillary-RheometerSample: Water up to high viscousResults: Shear-Viscosity, Elongational-Viscosity, Wall Slip...
10-110-3
Levelling, Sagging Sedimentation
104101
Extrusion, Pumping
100 102
Dipping, Brushing, Mixing
103 106
Roller Coating, Spraying
Sample: Water up to solidsResults: Shear-Viscosity, Yield Stesses, Visco-Elasticity, Relaxation...
s-1
© 2018 Malvern Panalytical
Principle of OperationGiven quantity: piston speed wall shear rate
Measured quantity: pressure drop wall shear stress
Bore
L
Fully developed flow region
entry
P1
Pw
00 L
Z
P
v
2R
Entrance pressure drop
Shear pressure drop
Full pressure drop
=
+
small ram extruder
© 2018 Malvern Panalytical
Laminar Pipe Flow
Isothermal, stationary Flow of an incompressible fluid
3app
Q4
R
.
2
P R
Lapp
Newtonian
-R R0
-R 0 R
0
Newtonian
Non-Newtonian
Q=Volume Flux, R= Die Radius
L=Die Length, P=Pressure Drop
© 2018 Malvern Panalytical
What are we doing to get flow curves?
measurement :v
t t
Ramp in steps p
true
.
true3app
Q4
R
.
2
P R
Lapp
corrections
© 2018 Malvern Panalytical
Correction: Entrance zone of a capillary die
Aim of the test: to separate entrance pressure and shear pressure drop!
Pressure transducer Capillary die
Convergent Flow
© 2018 Malvern Panalytical
Rosand Twin Bore Principle
Pfull
v
2R
Pfull= Pshear + Pentrance left: capillary right: orifice
v
L pshear
pentrance pentrance
© 2018 Malvern Panalytical
How do we getthe Extensional Viscosity?
Cogswell`s Convergent Flow Model Extensional Viscosity
=9 (n+1)2 (Pe)2
32 2.
10-1 - 103 s-1.
n =d (log )
d (log )
F. Cogswell, “Polymer Melt Rheology”, Woodhead Publishing Limited (1981)
Non-Newtonian Index (Ostwald-de Waele)
Pfull= Pshear + Pentrance
Zatloukal, Vlcek, Tzoganakis, Saha J. Non-Newtonian Fluid Mech. 107 (2002) 13–37
• Special Orifice Die according to Uni Zlin Model enables characterisationof very small extensional rates too.
© 2018 Malvern Panalytical
Example LDPE
LDPE at 190°C
1,0E+01
1,0E+02
1,0E+03
1,0E+04
1,0E+05
1,0E-04 1,0E-02 1,0E+00 1,0E+02 1,0E+04 1,0E+06
Shear Rate / Extensional Rate (1/s)
Shea
r Vis
cosi
ty /
Exte
nsio
nal V
isco
sity
(Pas
) Low Shear Test Zero ShearViscosity
Low Shear 2.0mm
Standard Shear 1mm
Standard Shear Melt Fracture
High Shear 0.5mm
Low Extension 2.0mm
Standard Extension 1mm
Standard Extension MeltRupture
High Extension 0.5mm
© 2018 Malvern Panalytical
Extensional Rheology of LDPE
Blow Moulding
Blow Moulding is mainly influenced by Extension!
© 2018 Malvern Panalytical
Surface Instabilities LDPE
Cooling air
Surface shape
© 2018 Malvern Panalytical
How can the process be improved?
Dehnviskosität - Vergleichskurven zwischen Homopolymer PE und Polymerblend PE-PP
1,0E+02
1,0E+03
1,0E+04
1,0E+05
1,0E-04 1,0E-02 1,0E+00 1,0E+02 1,0E+04 1,0E+06
Extensional Rate (1/s)
Ext
ensi
onal
Vis
cosi
ty (P
as)
Sample 2
Sample 2
Sample 2
Sample 2
Sample 1
© 2018 Malvern Panalytical
Another Example: Co-Extrusion
High acceleration
Low acceleration
Similar instabilites
© 2018 Malvern Panalytical
LDPE in Co-Extrusion Die
Instabilities caused by Extensional Flow Behaviour of LDPE
Zatloukal et. al. Journal of Applied Polymer Science, 98 (2005) 153
© 2018 Malvern Panalytical
Further Applications: Wall Slip
• Wall Slip Velocity of chromium catalyzed HDPE at 190°C
Wall slip velocity increases dramatically at just above 0.1 MPa.
Wandgleitgeschwindigkeit bei 190°C
-0,1
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
0 50 100 150 200 250 300 350 400
Shear Stress (kPa)
Wal
l Slip
Vel
ocity
(m/s
)Wall Slip according to MooneyModel
Critical Stress
critical stress 120 kPa
Vmax Vmax
Vw = 0Vw = 0
No wall slip Wall slip
© 2018 Malvern Panalytical
Equilibrium Pressure: Homogeneity
Pressure drop is important
For polymer blens, filled polymers, suspensions, emulsions, composites etc.
homogeneous inhomogeneous
© 2018 Malvern Panalytical
Thermal degradation / Curing
Gives maximum process times under high temperatures
v
t
Prinzip:
Thermischer Abbau at 260°C
0
1
2
3
4
5
6
0 1000 2000 3000 4000 5000 6000
real time (sec)
Pres
sure
(MPa
)
0
10
20
30
40
50
60
70
Pressure Drop
Shear Rate
Extruded Volume
Shea
r Rat
e (/s
) / E
xtru
ded
Volu
me
(cm
3 )
© 2018 Malvern Panalytical
Stick-Slip
Flow Instabilities
What is the max processing pressure / Shear Rate?
Melt fracture
v
t
Linear Ramp
© 2018 Malvern Panalytical
Melt Fracture
Unstable flow, poor product quality.
1,000s-10.1
1
10
100
0 50 100 150 200 250 300Time
Pre
ssur
e (M
pa)
PO PC
10000
100000
1000000
1 10 100
Shear Rate (1/s)
Shea
r Str
ess
(Pa)
?
© 2018 Malvern Panalytical
Relaxation LDPE
What happens after processing
inner stresses can lead to surface crack (automotive industry)
v
t
Prinzip:
Relaxation 190°C LDPE
0
5
10
15
20
25
0 50 100 150 200 250 300 350 400Real Time (sec)
Pres
sure
Dro
p (M
Pa)
0
2000
4000
6000
8000
10000
12000
Online Pressure Drop
Shear Rate
Thermal Equilibrium Time
Relaxation Time= 26.75 sec
( Mono-exp. Decay)
© 2018 Malvern Panalytical
Rheometer Types
Benchtop RH2000 and Floor Standing RH7/10
© 2018 Malvern Panalytical
Summary
• Capillary Rheometry gives correlation with processing flow properties
• Calculation of extensional viscosity according Cogswell method
• Flow curves up to very high shear end extensional rates
• Prediction of flow instabilities
• Correlation with structural changes during processing
Thank you for your attention.
Email: torsten.remmler@malvernpanalytical.com
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