Since the early 1990’s INGEO™ resins have made enormous improvements in the process ability of their bio-polymer resins. In the early days, when the resin was first being manufactured at pilot plant levels, extrusion processing of INGEO™ was very difficult. Today, natural additives are being used to improve the process ability of these resins. Several new lubricant additive packages were tested to determine which package produced the best overall performance and process improvements. The process data was used to quantify the process ability of the various additive packages. The data was then compared to the internal pressure data that was collected to analyze and determine the best overall additive package.

1. New and Improved Screw Technology
for Processing INGEO™ PLA
Timothy W. Womer
TWWomer & Associates, LLC
Introduction
Since the early 1990’s INGEO™ resins have
made enormous improvements in the process
ability of their bio-polymer resins. In the early
days, when the resin was first being
manufactured at pilot plant levels, extrusion
processing of INGEO™ was very difficult.
Today, natural additives are being used to
improve the process ability of these resins.
Several new lubricant additive packages were
tested to determine which package produced
the best overall performance and process
improvements. The process data was used to
quantify the process ability of the various
additive packages.
The data was then compared to the internal
pressure data that was collected to analyze
and determine the best overall additive
package.
The New Technology
The new screw technology which was used
during this study had a much different melting
mechanism than previous screw design
concepts. The idea behind the concept was
an effort to design a barrier-type screw which
would not only deliver excellent throughput
rates, but also low melt temperatures and low
power consumption. Much work was done in
the laboratory to develop this new technology;
now there is actual performance data
available to show the capabilities of this new
screw design concept.
This paper will present process data for PLA,
for which this new screw technology has been
tested. This new design finally allows older
low power extruders to be able to produce an
additional 10 to 15% more output with the
existing drive systems.
Equipment Used
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NRM Corp. 90mm (3.5") x 24:1 L/D
Extruder, 112 Kw (150HP) DC Drive,
243 Ampsmax and 129RPMmax
5 Zone water cooled, 7 Die Zones
New Concept Barrier / Mixing Screw
90mm (3 1/2") Screen Changer
11 Kw (15HP) Drive Melt Pump
EDI Ultraflex R-75 28" wide sheet die
Conair GB 22X Gravimetric Blender
NRM 3 Roll Stack w/ 305mm (12”)
Dia. X 1372mm (54”) face Rolls
Conair CD-200 Desiccant Dryer
Fluke NetDAQ data acquisition system
The NetDAQ data acquisition system was the
key to understanding what was happening
over the length of the extrusion screw. The
NetDAQ system was able to collect the
following information:
1. Records data every tenth of a second.
2. Records internal barrel pressures every 2
L/D, (11 total locations) along the axial
length of the barrel including head
pressure.
3. Motor amperage (243 full load amps).
4. Resin melt temperatures.
5. Actual barrel zone temperatures.
The data was recorded and charted to
observe the pressures being generated by the
screw with each respective resin blend.

2. Figure 1, shows a photograph of the (11)
pressure transducers used to generate an
axial screw/barrel pressure profile of the
screw at every 2 L/D down the processing
length of the screw.
This enables us to “look” inside the barrel and
determine how the screw is performing and if
there are any problem areas regarding the
screw design. This instrumentation will enable
us to graph a pressure profile of the particular
screw and resin being processed.
The final essential piece of process
equipment used in the study was a three-roll
down-stack sheetline. By using the roll stack,
the quality of the extruded sheet could be
examined to ensure the quality of the PLA
sheet.
channel to the melt channel as shown in
Figure 2.
With today’s math modeling, it was conceived
that if a given amount of resin was allowed to
pass through the barrier section as partially
melted polymer the overall bulk temperature
of the polymer would be lower than if the
polymer was 100% melted.
The pre-determined amount of semi-melted
polymer, which would have a lower
temperature, would be blended with the
higher temperature of the melted polymer
which had passed over the barrier flight.
Therefore, by blending the semi-melted
polymer with the melted polymer, the overall
bulk temperature would be lower than what
would normally be obtained from the original
barrier-type screw concept.
Resin Tested
The base resin that was tested during the
trials was a NATUREWORKS INGEO™ PLA
with the following characteristics:
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5-7 Melt Index
1.24 Specific Gravity
1.12 Melt Density
.019% moisture content (190 ppm
dried)
The neat INGEO™ 4032 PLA resin was
tested first and used for the baseline
reference. Then the neat base resin was the
gravimetrically blended with various levels of
lubricates as follows:
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Lube “A”, level 1
Lube “A”, level 2
Lube “A”, level 3
Lube “B”
Finally, in order to deliver a homogenous melt
at the end of the screw, an extended
distributive mixer was used to finalize the
melting of the semi-melted polymer and
produce a lower overall melt temperature
extrudate.
Note that “Lube B” had the highest throughput
rate (Figure 4) and lowest melt temperature.
The only material processed which had higher
internal pressures at the end of the feed
section of the screw was the neat PLA resin.
This new design concept also made it
possible to reduce the typical drive motor load
approximately 10 to 15% because much of
the melting was being completed by
convection instead of mechanical shear. This
was demonstrated numerous times in the
laboratory when comparing the old screw
technology to the new design concept.
Screw Technology: Old Versus New
Process Data
When barrier-type screws were originally
developed back in the 1960’s, the basic
concept was that by the time that polymer
reached the end of the barrier section all of
the material had been transfer from the solids
The following is actual process data gathered
while processing the various PLA blends with
various lubricants.
In Figure 3, all of the process data was
summarized at a screw speed of 120 rpm. As

3. the chart shows, Lube “B” had the best overall
performance in both throughput and melt
temperature. As shown in the chart, the new
screw concept produced 376 kg/hr (830 lb/hr)
at a melt temperature of 214° (418° while
C
F)
processing the PLA with the Lube “B”
additive.
As mentioned earlier in this paper, this new
screw design concept requires lower power
consumption. In Figure 4, a summary of the
four different blends of additives and also the
neat base PLA at 120 rpm, show a
comparison of the power consumption of
each material. As shown in Figure 4, the
Lube “B” consumed almost as much power as
the neat PLA, but this is due to the higher
throughput rate which was achieved. The
significant piece of data is the Power
Efficiency of the pounds per hour per
horsepower (lb/hr/hp). As shown in this chart
it can be seen that Lube “B” only requires
10.4 lb/hr/hp. This result is much higher than
what had been typically witnessed during
previous trials using conventional barrier-type
screws.
Another attribute of the new screw design
concept is the low melt temperature that was
obtained while processing the PLA blends.
As shown in Figure 5, there was
approximately an average of 12° difference
C
in melt temperature over the total speed
range of the study, which was from 30 rpm to
120 rpm screw speed. This low increase in
melt temperature is attributed to the lower
overall shear rate induced on the PLA
throughout the entire length of the screw. As
mentioned earlier, the new design concept
which allows this to be obtained is the fact
that by combining the semi-melted material in
exiting the solids channel of the barrier
section with the completely melted resin
existing the melt channel of the barrier section
produces a lower overall bulk temperature of
the PLA.
The final completion of melting the semimelted material is done by homogenizing the
two dissimilar melt pools into one
homogenous melt by convection heat as the
material is pumped through the extended
distributive mixer which produces the lower
overall bulk melt temperature of the extrudate.
Since the additives which were used during
this study were of a lubricant form, solids
conveying was also very significant in
maximizing the throughput rate of the screw.
By utilizing the NetDAQ data acquisition
system, the internal pressures were studied to
observe the maximum pressure developed in
the feed section of the screw. As can be
seen in Figure 6, a typical pressure trace is
shown of all of the blends.
As earlier noted, Lube “B” obtained the
highest throughput rate which was very
similar to the throughput rate of the neat PLA
resin; and just as the Figure 6 shows, these
two materials had very similar internal
pressure profiles. Both material exhibited
higher internal pressures at the end of the
feed section of the screw, just prior to
entering the barrier section. As can be seen
in the chart, both of these had approximately
twice the internal pressure at the same point
as the other PLA blends, 800 psi (55 bar)
versus 400 psi (28 bar). This is primarily due
to the higher coefficient of friction in the feed
section between the material and the metal
surfaces of the screw and barrel, plus the
coefficient of friction of the polymer itself. The
higher the coefficient of friction, the higher the
solids conveying rate. Based on a slightly
modified feed section geometry of the new
screw design concept, this was obtained.
Without utilizing the NetDAQ data acquisition
system to collect the internal pressure profile
of the screw, this observation would not have
been able to be achieved.
Conclusion
The new screw design concept exhibited
excellent overall performance for processing
the NatureWorks INGEO™ PLA. With the
use of the new screw design concept and the
NetDAQ data acquisition system it was
possible to determine how the various
attributes of the new design concept affected

4. the outcome of the Lube “B” providing the
best overall results.
This improved screw design technology can
also be incorporated in the processing of
various other resins which have tendencies of
requiring higher drive torque and produce
higher undesirable melt temperatures.
Resins and compounds are continually
changing as requirements for plastic products
continue to evolve. Therefore, the way that
screws are designed to process these more
sophisticated resins also needs to evolve and
improve.
Figure 1
Barrier Section Schematic
References
Figure 2
Throughput Rates & Melt Temperature
of Various Lubricants at 120 RPM
425
830
424
810
423
790
422
770
421
750
420
730
419
710
418
690
417
670
416
650
L
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415
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ub
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Additve Package
Figure 3
"
"B
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Ne
In
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ge
™
3
40
2
Rate
Melt Temp
Melt Temperature (F)
850
Throughput Rate (lb/hr)
1. Dr. E. Bernhardt, Processing of
Thermoplastic Materials, Robert E.
Krieger Publishing Co., FLA. 1959
2. C. Rauwendaal, Polymer Extrusion,
Hanser Publishers, NY, 1986
3. W. Smith, L. Miller, T. Womer, R.
Sickles, An Experimental Investigation
Into Solids Feeding Characteristics of
a Single Piece barrel Vs a Two Piece
Barrel Configuration, ANTEC 2007
4. C. Chung, Extrusion of Polymers,
Hanser Publishers, NY, 2000
5. Z. Tadmor and I. Klein, Engineering
Principles of Plasticating Extrusion,
Reinhold, NY, 1970
6. F.
Henson,
Plastics
Extrusion
Technology, Hanser Publishers, NY,
1997.
7. Spirex
Corporation,
“Plasticating
Components
Technology”,
Youngstown, Ohio (© 1992)

5. Power Consumption & Power Efficiency
12
90
11
80
10
70
60
9
50
8
40
30
7
20
6
10
0
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Power Efficiency (#/hr/hp)
Power Consumption (HP)
100
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32
40
HP (req'd)
Eff. (#/hr/hp)
Additive Package
Figure 4
Melt Temperature Measured 3 Ways
On PLA Blend
250
Melt Temperature (C)
200
196
201
211
206
203
209
204
211
213
211
212
217
150
100
50
0
30
60
90
120
Screw Speed (RPM)
IR Gun
Mlet Probe
Immersion Probe
Figure 5
Internal Pressures of Various Additive
Packages
2000
1800
1600
1400
Pressure (PSI)
Lube "A", Level 1
1200
Lube "A", Level 2
Lube "A", Level 3
1000
Lube "B"
Neat Ingeo™ 4032
800
600
400
200
0
0
2
4
6
8
Pressure Transducer Location
Figure 6
10
12