MATERIALS / RECYCLING PETplanet Insider Vol. 22 No. 10/21 www.petpla.net 26 PET recyclate manufactured using this process has received approval from the United States Food and Drug Administration (FDA) for food-contact uses. Coperion says that the effi cient plastifi cation within the ZSK extruder enables bottle-tobottle recycling at throughput rates between 2 t/h and 8 t/h. The company asserts that recycling companies will gain from high product quality, reduced operating and logistic expenses, and from energy cost savings up to 30% lower than conventional PET recycling methods. Increased effi ciency Before PET can be reprocessed, it must fi rst be shredded to fl akes and then cleaned. Ordinary technologies require pre-drying, crystallisation or agglomeration of the PET fl akes following washing. However, Coperion says that its specialised technology enables shredded PET to be fed directly into the ZSK twin screw extruder and compounded. The shredded fl akes are fed reliably into the ZSK extruder using high-accuracy SWB (Smart Weigh Belt) feeders or gravimetric feeders from Coperion K-Tron. Other regrind materials, new materials, or mixtures can be added at this stage. Melting, intensive devolatilisation and complete homogenisation take place in the ZSK process section before the melt is transferred, via a gear pump and fi lter with an automatic screen pack changer, to a strand or underwater pelletiser for pellet production. Pellets are then condensed in an SSP reactor. The pellets’ quality meets the requirements of virgin material. They have received FDA Letter of Non Objection which certifi es that they meet the standards for food-safe plastics and thus, can be processed into bottles once again. With this direct processing of PET into bottles, recyclers profi t particularly from the high product quality. Product handling in the bottle-to-bottle process is very gentle. Residence time in the ZSK extruder is short and dispersion is good. The ZSK extruders’ high torque enables processing at low temperatures and with almost no viscosity loss and their self-cleaning capacity enables rapid recipe and colour changes, states the company. The machines’ devolatilisation options mean that volatile components such as monomers, oligomers, and water are reliably removed and channelled away from the exhaust fl ow in suitable separators before discharge from the process section. High-accuracy Coperion K-Tron SWB feeder that feeds PET fl akes into the extruder. (Photo: Coperion K-Tron, Niederlenz, Switzerland) Economical and FDA-compliant recycling of PET fl akes Direct PET processing Coperion Gmbh, headquartered in Stuttgart, Germany, says that the drive towards a circular economy for PET has taken another step with its Coperion ZSK twin screw extruders, which can process PET fl akes without predrying into pellets. The fl akes are then condensed in the SSP (solid state polycondensation) reactor and reprocessed back into bottles, with virgin material quality. Coperion ZSK twin screw extruders are claimed to provide good devolatilisation with short residence times in the process section as well as high dispersion. (Photo: Coperion, Stuttgart) RECYCLING
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