Capillary Rheometry - ZwickRoell Materials Testing · 2021. 1. 26. · F. Cogswell, “Polymer Melt Rheology” , Woodhead Publishing Limited (1981) Non-Newtonian Index (Ostwald-de

© 2018 Malvern Panalytical

Capillary Rheometry – A Method to Predict Flow Properties under Processing Conditions

Torsten Remmler, Malvern Panalytical GmbH

Zwick testXpo 2018


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.


Capillary Rheometry: Main Applications


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


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


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


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


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


Rosand Twin Bore Principle

Pfull

v

2R

Pfull= Pshear + Pentrance left: capillary right: orifice

v

L pshear

pentrance pentrance


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.


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


Extensional Rheology of LDPE

Blow Moulding

Blow Moulding is mainly influenced by Extension!


Surface Instabilities LDPE

Cooling air

Surface shape


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


Another Example: Co-Extrusion

High acceleration

Low acceleration

Similar instabilites


LDPE in Co-Extrusion Die

Instabilities caused by Extensional Flow Behaviour of LDPE

Zatloukal et. al. Journal of Applied Polymer Science, 98 (2005) 153


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


Equilibrium Pressure: Homogeneity

Pressure drop is important

For polymer blens, filled polymers, suspensions, emulsions, composites etc.

homogeneous inhomogeneous


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 )


Stick-Slip

Flow Instabilities

What is the max processing pressure / Shear Rate?

Melt fracture

v

t

Linear Ramp


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)

?


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)


Rheometer Types

Benchtop RH2000 and Floor Standing RH7/10


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: [email protected]

Documents

Capillary Rheometry - ZwickRoell Materials Testing · 2021. 1. 26. · F. Cogswell, “Polymer Melt Rheology” , Woodhead Publishing Limited (1981) Non-Newtonian Index (Ostwald-de