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| Author | Topic: Reprocessing HDPE with EVOH |
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sbromm Senior Member Posts: 5 |
posted February 15, 2005 12:03 PM
  
We are trying to reprocess a HDPE with 3-5% EVOH but get a poor chattery surface finish. Is there anything we can do to eliminate the cosmetic look? The functionality of the part it great, we just need it to look better. Thanks for your help in advance. IP: Logged |
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Tom C Moderator Posts: 465 |
posted February 15, 2005 10:47 PM
One of two things are happening; 1) The EVOH is overheating, degrading and foaming. In either case lowering the screw RPMs, should help. If that provides too low of an output rate, please contact my company about extrusion optimization services.
Tom Cunningham
Extrusion Technical Services [This message has been edited by Tom C (edited February 15, 2005).] IP: Logged |
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sbromm Senior Member Posts: 5 |
posted February 16, 2005 09:16 AM
Thanks Tom, We have adjusted screw speed and temps, but this doesn't seem to work. The EVOH surfaces everytime, even if we blend it with a natural. Any other suggestions? IP: Logged |
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Tom C Moderator Posts: 465 |
posted February 16, 2005 10:10 AM
Do you feel you are expereinceing foaming, melt fracture, incompatibility, or something else? ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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sbromm Senior Member Posts: 5 |
posted February 16, 2005 10:33 AM
Tom, It is melt fracture. The part's surface finish looks "chunky" so to speak. It is a regrind that we are attempting to reprocess, so the screw was around 35 RPM I am told. Feel free to email me direct at scottb@polyflexinc.com IP: Logged |
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Steve H Moderator Posts: 344 |
posted February 16, 2005 02:25 PM
Is there an EVA tie layer in the structure you are granulating and then re-extruding? I've experianced a similar thing with an anti-static MBX that uses EVA as a carrier. You could try running a fluropolymer additive through the extruder before running the EVOH/HDPE material, to try and get a "non stick" layer built up on the flow surfaces of your die. Are you drying the EVOH/HDPE before reprocessing? ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
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sbromm Senior Member Posts: 5 |
posted February 16, 2005 02:50 PM
Steve Thanks for the reply. I am not sure if there is a tie layer. The material is a regrind from a gas tank manufacturer, so the EVOH is a layer they use in forming the tank. We are not drying the material, although that has been discussed because it is our understanding that this material is very hydroscopic. In the summer when it is humid I am not sure that would even help. By adding the non stick layer, will that smooth out he surface finish? That truly is our only issue, the cosmetic results. IP: Logged |
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Steve H Moderator Posts: 344 |
posted February 16, 2005 10:32 PM
quote: The effect that you're getting is a slip/stick one, and that might improve the situation. The costly way to do it, would be a co-ex, and encapsulate the regrind with a virgin layer. It's my understanding that EVOH is hydroscopic, but if you're not getting any sign of it in the product, it may not be an issue. ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
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zabielski Senior Member Posts: 352 |
posted February 17, 2005 06:00 AM
In general, the EVOH people will tell (and sell) you a compatilizer. They offer two grades. EVOH is hygroscopic - but not that bad when it's embedded. However, depending on the MI of the HDPE, you can get a better flow by just adding some Dow-DuPont elastomer (Grade POE 8999). POE is PolyOlefin Elastomer. Percentage is up to you, but your flow will be smooth once you reach the right percentage. An added side benifit to this is that you'll have a significant resistance to impact. Let us know how your progress goes, eh? [This message has been edited by zabielski (edited February 17, 2005).] [This message has been edited by zabielski (edited February 17, 2005).] IP: Logged |
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sbromm Senior Member Posts: 5 |
posted February 17, 2005 09:27 AM
Where can I get some of this elastomer to try it out? IP: Logged |
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zabielski Senior Member Posts: 352 |
posted February 20, 2005 03:33 PM
Dow Chemicals. Previously developed when they were called Dow-DuPont Chemicals. IP: Logged |
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felix Senior Member Posts: 45 |
posted February 20, 2005 05:57 PM
quote: We have had a great deal of success in using K05 coating for eliminating melt fracture in our blown film lines. Perhaps it could be of use here as well: http://www.dualspiralsystems.com/extrusion_die_coatings.html IP: Logged |
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