A new method of recycling PET into pellets or directly into extruded sheet is said to save time and energy by combining crystallizing and drying with size reduction in one piece of equipment. Residence time is only 20 minutes instead of hours with conventional methods. Operating cost is 30-50% less (only 9-12¢/lb), reports Manfred Hackl, polyester project manager at Erema Recycling Maschinen und Anlagen GmbH in Austria, which developed the process.
To crystallize and dry the PET, the method requires only the frictional heat generated by rotating knives in Erema's shredder-compactor unit. Normally, PET is ground up first and then crystallized with hot air in tall hoppers for several hours.
Erema (represented here by Erema North America, Topsfield, Mass.) sold one of the first two systems to Lenaers Plastik Verpakkingen in Borgloon, Belgium. It will recycle post-consumer PET bottle flake directly into sheet for blister packs. The flake contains 0.5-0.8% moisture and has an initial I.V. of 0.76-0.77. Erema says the final I.V. will be only 3% lower at 0.73-0.75.
The other new system goes to a U.K. recycler for pelletizing reclaimed PET film. Material starting at 0.62-0.63 I.V. is said to lose at most 3% of that value.
Erema says its process has passed a European test for direct food contact similar to that used by the U.S. FDA. It is suitable for pellets for food-grade bottle-to-bottle recycling.
Pump up the vacuum
The line in Belgium is interesting because grinding, crystallizing, and extrusion take place under very high vacuum. A valve feeds the shredder-compactor without releasing the vacuum. An agitator in the crystallizing shredder-compactor keeps hot flake from sticking.
Densified, crystallized material feeds from the shredder-compactor to a 35:1 L/D extruder that has two vacuum vents side by side and a new screw optimized for PET. Dual-vent degassing is said to remove up to 50 ppm of PVC contamination. Next is a backflushing screen changer that cleans itself in small increments. A melt pump holds pressure fluctuations at the die to ±0.2 bar.