New and Improved Screw Technology
for Processing INGEO™ PLA
Timothy W. Womer
TWWomer & Associates, LLC
Introduction
Since ...
Figure 1, shows a photograph of the (11)
pressure transducers used to generate an
axial screw/barrel pressure profile of t...
the chart shows, Lube “B” had the best overall
performance in both throughput and melt
temperature. As shown in the chart,...
the outcome of the Lube “B” providing the
best overall results.
This improved screw design technology can
also be incorpor...
Power Consumption & Power Efficiency
12

90

11

80
10

70
60

9

50
8

40
30

7

20
6

10
0

be
Lu

Power Efficiency (#/h...
Upcoming SlideShare
Loading in...5
×

New and Improved Screw Technology for Processing INGEO™ PLA

1,204

Published on

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.

Published in: Business, Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
1,204
On Slideshare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
29
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

New and Improved Screw Technology for Processing INGEO™ PLA

  1. 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 • • • • • • • • • • 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. 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: • • • • 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: • • • • 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. 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. 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 e ub 415 ", "A L e ev l1 L e ub ", "A L el ev 2 L e ub ", "A L e ev l3 Lu be Additve Package Figure 3 " "B at Ne In o 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. 5. Power Consumption & Power Efficiency 12 90 11 80 10 70 60 9 50 8 40 30 7 20 6 10 0 be Lu Power Efficiency (#/hr/hp) Power Consumption (HP) 100 5 " "A 1 el ev ,L be Lu " 2 el ev ,L A" be Lu " el ev ,L A" 3 be Lu " "B N t ea I ™ eo ng 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

×