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January 1, 2008
1 Min Read
It is common practice throughout Europe when extruding amorphous polyethylene terephthalate (APET) sheet to apply a 5% polyethylene (PE) laminate prior to thermoforming a food container to effect an efficient lid seal for modified atmosphere packaging (MAP) applications, particularly for trays for meat and chicken.
This results in some 40% APET / PE regrind being generated from edge trim and skeletal waste that conventional crystallisers can not process, since the PE melts below the APET crystallising temperature, causing discoloration and sticking, with the result that thermoformers are left with huge stocks of valuable material that can not be processed.
Based on the success achieved to date by auxiliary equipment manufacturer UPM (Slough, Berkshire, England; www.upm.co.uk) with its infrared dryer (IRD), an unidentified, multinational PET sheet and food tray packaging processor supplied 1000 kilos of its APET / PE regrind to enable trials to be carried out in UPM’s demonstration facility to determine if infrared technology could offer a solution based on its lower operating temperatures and residence times in comparison to a normal crystallizer for APET. PET drying requires at least one hour at 140°C and continuous agitation.
According to UPM, its infrared dryer (IRD) trials on APET / PE led to crystallinity of 33% after only 4 minutes at 115o C without any discoloration or sticking, allowing the material to be used in PET sheet extrusion as the core layer in a coextruded sheet construction with a 25 micron coating top and bottom. UPM officials reckon this test could lead to increased use of IR dryers to crystallize APET / PE scrap and thus help processors re-use more of their scrap.
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