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| Author | Topic: PET extrusion |
| esskayplastics Member Posts: 1 |
 posted September 25, 2004 12:09 AM    
I have a single screw extruder being used to recycle PP,HDPE,LDPE waste.I need to recycle PET bottle waste to granules.What changes need to be made to make the same screw suitable for this?? The l/d ratio of this 65 mm screw is 30:1. Detailed information about PET extrusion parameters would be welcome or even if someone points out suitable resources on the net I would be obliged. IP: Logged |
| Tom C Moderator Posts: 392 |
posted September 25, 2004 08:36 AM
PET is extremely sensitive to moisture. Ideally the regrind should be dried to below 0.025% moisture content before extrusion. Many extrude regrind without drying, becasue of the difficulty in drying it. This technique requires a vacuum vent on the extruder. Under these conditions the viscosity can be maintained on average, but there will be a lot of varibility. Without out drying and/or a vacuum vent the results will be poor. One of the most difficult challanges is just getting the regind into the extruder if you are using flake. A regular extruder hopper will not work as the material compresses and locks up. In the extruder a high compression ratio screw will work best. Extruder zone temperatures run 520-540F. Tom Cunningham IP: Logged |
| Bob Cunningham Senior Member Posts: 92 |
posted September 28, 2004 04:29 PM
You may want to consider contacting Erema- http://www.erema.at/ . Their Vacurema was designed specifically for this purpose. Even if you are not looking to purchase a machine, you can look at how it is done. You will see that there is much more than just a screw involved- they preheat the material, pre-dry it, size-reduce the material, apply a vacuum to the whole system, cram it into the screw, and use a vent on the screw. -Bob Cunningham [This message has been edited by Bob Cunningham (edited September 28, 2004).] IP: Logged |
| Tom C Moderator Posts: 392 |
posted September 28, 2004 09:27 PM
Apparently we Cunnighams have this one covered. Tom IP: Logged |
| Steve H Moderator Posts: 320 |
posted September 29, 2004 05:29 AM
quote: Well not quite boys Steve [This message has been edited by Steve H (edited September 29, 2004).] IP: Logged |
| Tom C Moderator Posts: 392 |
posted September 29, 2004 07:40 AM
Exactly how does the Erema process work? To my surprise, there are no pictures or process descriptions on the web site. From what I have seen in the past they use a mechanical shearing system to work the flakes, drive the moisture out, and feed the extruder. A nice process if it works. A similar concept has been developed to use on fully intermeshing corotating twin screw extruders. The material is worked in it's solid state and water is vented out. The polymer is then melted, vacuum vented and extruded. Tom Cunningham www.ExtrusionTech.com IP: Logged |
| Steve H Moderator Posts: 320 |
posted September 29, 2004 03:22 PM
quote: Pretty close, Tom. The hopper where this is taking place is under a vacuum. It's an elegant solution to recycling APET. Processing APET on a vented extruder without predrying lowers it's IV, while this may not be much of a problem first time round, it will become a problem on subsequent reuses. With the Erema process, there is no loss in IV, and when used with chain extenders, the materials IV is raised. Erema are using their process to injection mould preforms for bottle blow moulding. The other plus with the Erema process is that it has FDA approval to recycle for food contact applications. IP: Logged |
| TomBlack Moderator Posts: 55 |
posted September 30, 2004 06:01 PM
While agree w/ what's been mentioned so far, I wouldn't necessarily consider it to be mutually exclusive. Many processors I've worked w/ will pre-dry/crystallize PET to maintain IV and avoid feed problems, then vacuum vent as well (as an insurance policy for IV degradation). ------------------ www.ppsincorp.com IP: Logged |
| Bob Cunningham Senior Member Posts: 92 |
posted September 30, 2004 07:15 PM
In one of their machines spefically designed for PET (i.e. their "bottle to bottle" machines), their repelletizing process will actually increase the IV, so that you can re-use the pellets in new bottles. They expose the flake to vacuum and heat for long periods, and the screw is very low sheer (with a few special tricks). And no, they don't use any chain extenders or anything. The PET that you put in is the PET that you get out (except for the moisture/volitiles, etc., that come out under vacuum), with a higher IV. They also have processes for PET fiber (which have more oils, etc.). -Bob Cunningham IP: Logged |
| mik henson Member Posts: 1 |
 posted October 26, 2004 04:45 AM
we extruded recycled bottles ,main thing is you need a good dryer/crystalizer good feed section and a screen IP: Logged |
esskay, I dislike the vented approach to processing/reprocessing APET.All times are ET (US) |
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