Extrusion International 4-2021

32 Extrusion International 4/2021 INDUSTRY NEWS Innovative Process for Bottle-to-Bottle Recycling „ Polyethylene terephthalate (PET) is a high-value material that is on course to take over a key function in the plastics industry’s path toward a circular economy. PET flakes can now be processed without pre-dry- ing into pellets using Coperion ZSK twin screw extruders. Next they are condensed in the SSP (Solid State Polycondensation) reactor, and re- processed back into bottles again with the quality of virgin material. PET recyclate manufactured using this innovative process has received approval from the United States Food and Drug Administration (FDA) for food-contact uses. Thanks to the highly efficient plastification within the ZSK ex- truder, Coperion systems for this bottle-to-bottle recy- cling process achieve throughput rates between 2 and 8 tons per hour, therefore recycling companies profit from very high product quality, reduced operating and logistic expenses as well as from energy cost savings up to 30% in comparison to conventional PET recycling methods. PET plays an ever more important role in recycling, due to the large volume of packaging materials in use today. PET is a very high-value material, possessing extremely good properties for reprocessing. Its continuously expanding use in single- and reusable bottles, as well as its recovery via deposit systems, add to its value. Correspondingly, it can be lucrative for companies to focus on PET recycling. Before PET can be reprocessed, it must first be shredded to flakes and then cleaned. Ordinary technologies require pre-drying, crystallization or agglomeration of the PET flakes following washing. However, using the specialized technology from Coperion, the shredded PET can be fed directly into the ZSK twin screw extruder and compound- ed. The shredded flakes are reliably fed into the ZSK extruder using high-accuracy SWB (Smart Weigh Belt) feeders or gravimetric feeders from Coperion K-Tron. In addition, other regrind materials, new materials, or mixtures can be added. Melting, intensive devolatilization, and complete homogenization take place in the ZSK process section be- fore the melt is transferred via a gear pump and filter with an automatic screen pack changer to a strand or under- water pelletizer for pellet production. Pellets are then condensed in an SSP reactor. The pellets’ quality meets the requirements of virgin material. With this direct processing of PET into bottles, recyclers profit particularly from the very high end product qual- ity. Product handling in the bottle-to-bottle process is very gentle. The residence time in the ZSK extruder is very short and dispersion is very good. The ZSK extruders’ high torque enables processing at low temperatures and with almost no viscosity loss. ZSK extruders’ self-cleaning en- ables rapid recipe and color changes. Thanks to the ZSK twin screw extruder’s very good devolatilization options, volatile components such as monomers, oligomers, and water are reliably removed and channeled away from the exhaust flow in suitable separators before discharging the process section. Coperion GmbH www.coperion.com CoperionZSK twin screwextruders provide verygooddevolatilization with short residence times in theprocess sectionaswell as veryhighdispersion, contributing signi fi cantly tohighend product quality (Photo: Coperion) Typical set-upof a recycling systemfor economicallyprocessingPET fl akes intoPETpellets that canbeused in turn tomanufacturebottles: 1) SWB (SmartWeighBelt) feeder; 2) ZSK twin screwextruder; 3) Additionof PET fl akes; 4)Devolatilizationof volatile components; 5)Discharge viagear pumpand fi lter; 6)Water bath; 7) Stranddrying; 8) Strandpelletizing (Image: Coperion) 1 2 3 4 5 6 7 8