TECHNOLOGY | PET RECYCLING
Typical set-up of a Coperion recycling system for processing PET flakes into PET pellets that can be used to manufacture bottles. 1 SWB (Smart Weigh Belt) feeder; 2 ZSK twin screw extruder; 3 Addition of PET flakes; 4 Devolatilisation of volatile components; 5 Discharge via gear pump and filter; 6 Water bath; 7 Strand drying; 8 Strand pelletising
Below: Coperion ZSK twin screw extruders are used for PET bottle-to-bottle recycling
followed by a 29% share of the rPET taken by food contact bottles (the remainder is used in fibres, strapping and small-scale applications). Plastics Recyclers Europe and its partners say: “Driven by producers’ pledges, who have made a range of commitments and goals to incorporate recycled content within their bottles, and with the mandatory recycled content targets – the share of food-grade rPET in PET beverage bottle produc- tion is set to continue to grow rapidly.” The report says that by 2025 there are expected to be 19 EU Member States with PET bottle DRS capacity. At the moment, seven countries with established DRS achieve sorted-for-recycling rates of 83% or higher. Collection rates, as well as quality, are likely to increase substantially, it says, due to the EU Single Use Plastics Directive’s requirements for member states to achieve a 77% collection rate for beverage bottles by 2025 and 90% by 2029. The associations say: “The significant increase in
PET collection and recycling sends a positive signal to the market and will boost confidence in further accelerating PET’s circularity.” For PET recycling to continue making
progress, the report says further R&D and innovation are needed in almost all stages
IMAGE: COPERION
of the value chain. Technology suppliers in PET recycling are indeed working on innovation in various areas, particularly in PET bottle and tray recycling. Coperion says rPET flakes can now be pro- cessed without pre-drying into pellets using its ZSK twin screw extruders. In a bottle-to-bottle process, the pellets are condensed in a Solid State Polycon- densation (SSP) reactor, and processed into bottles again with the quality of virgin material. Coperion has received clearance for this process for food- contact uses from the US Food and Drug Adminis- tration (FDA). The company says other technologies require
pre-drying, crystallization or agglomeration of the rPET flakes following washing. But that is not necessary when the shredded PET is fed directly into the ZSK twin screw extruder and compounded. Coperion says that in its bottle-to-bottle process, rPET flakes are fed into the ZSK extruder using high-accuracy Smart Weigh Belt feeders or gravimetric feeders from Coperion K-Tron. Other regrind materials, new materials, or mixtures can be added. It says melting, intensive devolatilisation, and complete homogenisation take place in the ZSK process section before the melt is transferred via a gear pump and filter with an automatic screen pack changer to a strand or underwater pelletiser for pellet production. The pellets are then con- densed in an SSP reactor. The company says: “Thanks to the highly
efficient plastification within the ZSK extruder, Coperion systems for this bottle-to-bottle recycling process achieve throughput rates between 2 and 8 tonnes 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.” The bottle-to-bottle process is very gentle on the
material, says Coperion. “The residence time in the ZSK extruder is very short and dispersion is very
32 PLASTICS RECYCLING WORLD | March/April 2022
www.plasticsrecyclingworld.com
IMAGE: COPERION
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