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Yes, B6650LN must be dried in a desiccant drier for best processing and property performance. We recommend 100°C for 3-4 hours. Acceptable moisture content of pellets prior to processing is ≤0.04%. A moisture analyzer is a good tool to have to verify pellet moisture is in an acceptable range. See the attached drying curves for B6550LN.
It’s critical to get quantitative moisture data prior to processing because excessive moisture has the potential to affect tensile strength, elongation, abrasion resistance, and tear strength. Elastollan® TPU is hygroscopic, so, when it’s exposed to the atmosphere, it rapidly absorbs moisture.
We recommend a moisture level of less than or equal to 0.02% during processing (as shown in Figure 1). A common mistake is that many people don’t use moisture analysis prior to production. They purge material from the barrel, say “looks good” and set up a process. There often aren’t any visual indications during processing that the moisture levels aren’t acceptable. Unacceptable moisture levels are mostly undetectable to the human eye.
Dryer settings vary by hardness so it’s important to check the recommendations on the Technical Datasheet for your grade.
Elastollan® TPU is sensitive to moisture and can absorb excessive moisture in 20 minutes in warm/humid conditions. I strongly recommend that every production floor should have a simple hydrometer and temperature gage near its production press. This will remind processing technicians of the critical residence time that Elastollan® TPU spends between the outlet of the desiccant dryer and the feed throat of the extruder. At a standard room temperature of 73°F and 50% relative humidity Elastollan® TPU can absorb excessive moisture for processing in 20 minutes, which will affect mechanical properties (see results for abrasion testing). Conveying Elastollan® TPU to a properly sized extruder hopper with dry desiccant air is always preferred over production floor ambient air.
Processing Elastollan® TPU uses common screw and barrel designs, so special designs aren’t necessary. Elastollan® TPU is a shear sensitive material, and for this reason, a 3-section screw design with a L/D ratio of 24-30 and a compression ratio 1:2.5 to 1:2.7 is recommended. The following graph shows the maximum recommended RPM depending on your screw size.
Download brochures about Ellastolan® products in our resources area.
Download brochures about Ellastolan® products in our resources area.
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