1. Micro Rheology Compounder
MiniLab
Thermo Haake
Micro Rheology Compounder

2. MiniLab Micro Rheology Compounder
Conical twin-screw compounder:
co- and counter rotating possible
automatic bypass operation for extrusion/recirculation
viscosity measurement integrated in backflow channel
pneumatic feeding
inert gas flush (feeding area + extruder barrel)
digital and graphic data display
manual and computer control possible
co- and counter rotating possible Two different screw designs (counter- and co-rotating screws) are available The gearbox can be switched (by the user) from counter- to co-rotating
automatic bypass operation for extrusion/recirculation The by-pass valve is pneumatic controlled and can be easily switched by just pressing a button.
viscosity measurement integrated in backflow channel (more details later in the presentation)
pneumatic feeding
inert gas flush (feeding area + extruder barrel)
digital and graphic data display
manual and computer control possible Via the display or using the Windows Software

3. MiniLab Micro Rheology Compounder
The view inside the opened extruder barrel.
You see the co-rotating conical screws, the by-pass valve
and the two pressure transducers in the back flow channel.

4. MiniLab Micro Rheology Compounder
Backflow channel with rheological slit capillary die p1 p2
Bypass valve
The extruder has two operation modes:
The bypass valve is set to the cycle mode and the material is flowing through the backflow channel. So the residence time of the material inside of the extruder can be controlled. The backflow channel is housing two pressure transducers which can give us rheological information during the extrusion process. The details on that will follow at the end of this presentation.
The bypass valve is set to flush mode. The material will flow out through the output channel. The extruded material can either be collected as a strand, or a little mould for a small injection moulding machine can be filled.
Output channel

5. MiniLab Micro Rheology Compounder
Application:
Micro sample-amount (5 g)
Development of new polymers
Testing of expensive materials
Material studies at universities
Rheological studies
Reactive extrusion
Sample preparation for further testing
Sample preparation in combination with a micro injection moulding machine
Micro sample-amount (5 g)
Development of new polymers (because usually you are short in material)
Testing of expensive materials
Material studies at universities Small sample amount
Rheological studies Because of it‘s rheological backflow channel
Reactive extrusion (Due to the recirculation mode you can prolong the residence time in the extruder. A long residence time is nessesaty for reactive extrusions. More details and an example later in the presentation)
Sample preparation for further testing
Sample preparation in combination with a micro injection moulding machine (Which can be used to make first speciems for i.e. tensile tests)

6. MiniLab Possible screw design
Co-rotating
Counter-rotating
Shows the two operation modes for the MiniLab.
Co-rotating setup is the standard.
Counter-rotating is an option.
More see next chart...

7. Twinscrew Extruder Counter-rotating twinscrew design:
Defined residence time (good for i.e. fast degradating material)
Forced extrusion – defined volume flow ( important for rheological measurement)
Self-cleaning
High shearing
High pressure built-up
Co-rotating twinscrew design:
Mixing of shear sensitive material (i.e. PE / PP)
Best compounding behaviour (i.e. for the preparation of Masterbatches)
Lower shearing

8. Characteristics of MiniLab screw types
- Resident time distribution narrow: The resident time for each part of the melt is app. the same.
- Resident time distribution wide: Parts of the melt may stay longer in the extruder than other parts.
Forced extrusion: The melt is forced through the extruder. It has no chance to flow back.
Cleaning: How easy is it to clean the extruder screw after the test. mThis has nothing to do with the selfcleaning effect of the screws.
Extruded amount: How much is the output after the test, compared to the input. How much remains on the screws.
Blending of sensitive products: Co-rotating screws are mixing with lower shear.
High shear despersing: Counter-rotating screws are mixing with higher shear. Good for breaking up aglomerates.
Rheological measurement: For this test, we need to know the volume flow through the back flow channel. Because of their force feeding effect, this is better with the counter-rotating screws.
Blending: Co-rotating screws have a much better mixing effect.

9. MiniLab Micro Rheology Compounder
.. as a micro compounder

10. MiniLab Compounding Example:
With the counter-rotating screws it took app. 7 minutes to get an absolutely mixed compound.
Due to experience the compounding behaviour of co-rotating screws is app. 5 to 10 times better.

11. Constant speed - Constant torque
Comparison of output:
Constant speed Constant torque
This chart shows the difference between the constant speed- and the constant torque- mode.
Both test were done with the same material at the same conditions.
After the test, the bypass valve was set on flushing and the output was measured against the time.
The red curve shows the test with constant speed. It shows a high output in the beginning, but a drop in output at the end of the test.
The blue curve shows the test with constant torque (the screw speed is adjusted to keep the torque constant).
This curve shows a consistent and homogenic output. The extruded strand has a more uniform shape and it takes less time to empty the extruder.

12. MiniLab Extrusion/Output Ratio
This table should show the relation between the material input and the output after the test (because some material will stay on the screws and in the backflow channel.)
The results in the table show, that the co-rotating screws have a better output/input relation than the counter rotating screws.
This relation is not depending on the filling rate.

13. MiniLab Micro Rheology Compounder
.. as a reactive extruder

14. MiniLab – Reaction monitoring
This chart shows an example for the use of the MiniLab as an reactive extruder.
The graph shows the polymerisation of a Polylactide (a very expensive (up to 5000,- US$/g), biodegradable polymer, used in the pharmaceutical industry) from a basic Lactide (monomer) with additives.
With a normal extruder it would be very difficult to achieve the required long reaction times for this reaction.
By the possibility of running the reaction mixture (monomer and catalyst) in a circulation loop, the required reaction times can be set. At the end of the test the polymer is extruded as rod. This rod can be used in sample specimens for decomposition tests in different media.
The graph displays the melt temperature, screw torque and the pressure values against the test time.
Due to the low viscosity of the monomer no pressure signal can be detected in the beginning of the test.
The reaction starts at app. 7,5 min with a pressure signal at pressure transducer 1 (p-D1).
An increasing torque and pressure signal at the second pressure transducer (p-D2) can be noticed a bit later (the back flow channel is now filled completely with polymer).
After 20 minutes the constant pressures p-D1 and p-D2 show the reaction is finished. The pressure drop between the sensors p-D1 and p-D2 of 15 bar correlates to with increased viscosity of the melt in the back flow channel.
This test shows the sensitivity of the instrument. Although torque signal is only about 3% of the whole measuring range (maximum: 5,5 Nm) and is less suitable for evaluation, the reaction can be monitored with the more sensitive pressure signals.
In contrast to conventional glass reactors, the temperature (TM) of the highly viscous melt can also be controlled exactly, because of the large relation of the metal extruder block compared to the small amount of sample. It acts like a heat sink and ensures isothermal test condition.

15. MiniLab Micro Rheology Compounder
.. as a relative viscometer

16. MiniLab Micro Rheology Compounder
Backflow channel with rheological slit capillary die p2 p1
Bypass valve
Output channel

17. Rheology Newtonian plate model
Area A
Force F dy dv
Shear Stress:
Some basic information on Rheology:
Viscosity is the inner friction of a liquid and cannot be measured directly.
Only the effects of the viscosity can be measured.
The viscosity is defined as the shear stress (the force applied over a certain area; F/A) in relation to the shear rate (the deformation in relation to the position in the shear gap; dv/dy).
So for the viscosity measurement we actually measure the shear stress and the shear rate. t h =
Viscosity: g . g . dv =
Shear Rate: dy

18. Rheological backflow channel
pressure
pressure drop dp dl
channel length W H
To measure the viscosity with the MiniLab, we measure the pressure difference between the two pressure transducers in the back flow channel.
This back flow channel has the geometry of a slit capillary.
Details see next slide... P3 T2 P1
sensor ports

19. Slit Capillary Channel Calculations for Newtonian liquids
Pressure Gradient: Shear Rate:
Volume flow: Viscosity:
Shear stress: = 6 Q W H g . h t
To get the viscosity value we need to know the shear rate and the shear stress.
To get the shear stress, we measure the pressure in the beginning and at the end of the backflow channel.
From the pressure difference and distance between the two pressure sensors we do get the pressure gradient. From the pressure gradient and the slit geometry (height) we can calculate the shear stress.
The shear rate is calculated from the volume flow (the volume that passes through the capillary in a certain time) and the geometry of the capillary.
The viscosity is the shear stress divided by the shear rate.
A limitation of the MiniLab is the determination of the volume flow. This volume flow is correlated to the screw speed. This is not an absolute measurement. Therefore the shear rate is not an absolute value. So the resulting viscosity value is a relative (instrument depending) value.
Nevertheless the viscosity measured with the MiniLab is very close to the real viscosity values.

20. Results Viscosity curve Flow curve Shear rate [1/s] Viscosity [Pas]10
100
1000
10000
Shear rate [1/s]
Shear Stress [Pa]
Viscosity [Pas]
Flow curve
Viscosity curve
As a result of the test we get a viscosity function as shown in the graph.
For the viscosity function the extruder runs at different screw speeds (we start at a low speed and sep by step go up in speed).
At each speed step, the pressure drop is measured (the shear stress calculated; the red curve).
From the calculated shear stress and the shear rate (correlated to the screw speed) we calculate the viscosity (the blue curve).
So step by step we get the viscosity curve.
Example: see next chart

21. MiniLab - Relative Rheology:
This graph shows the test results of two viscosity measurements with the MiniLab.
The measurement was done with a Polypropylene (PP) sample.
The first viscosity measurement (1:µ-app) was done directly after feeding and melting of the PP sample.
Then the sample was kept inside the MiniLab for ten more minutes. After this time a second viscosity measurement was done (2:µ-app).
Comparing the viscosity curves of this both measurements shows, that the PP sample had degradated during the extrusion process and therefore the viscosity was reduced.