Polyethylene terephthalate (PET) flakes can now be processed without pre-drying into pellets, using Coperion ZSK twin screw extruders.
Next they are condensed in the SSP (Solid State Polycondensation) reactor, and reprocessed 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 efficient plastification within the ZSK extruder, Coperion systems for this bottle-to-bottle recycling process achieve throughput rates between two and eight tons per hour.
Coperion estimates this can generate cost savings from reduced operating and logistics expenses as well as energy cost savings of up to 30 percent 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.
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 compounded.
The shredded flakes are fed 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.
Melting, intensive devolatilization, and complete homogenization 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 pelletizer for pellet production.
Pellets are then condensed in an SSP reactor. The pellet quality meets the requirements of virgin material. They have received FDA Letter of Non Objection which certifies 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 profit particularly from the very high end product quality. 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. They are self-cleaning to enable rapid recipe and colour changes.
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.
“With FDA certification, we have officially confirmed the high product quality of the PET recyclates,” said Jochen Schofer, business segment manager, recycling and direct extrusion at Coperion.
“With the Coperion solution, we make a technology available to recyclers that is economical and at the same time allows them to make a decisive contribution to the plastic industry’s path towards a circular economy.”
Coperion designs, develops, manufactures and maintains systems, machines and components for the plastics, chemicals, pharmaceutical, food and minerals industries. Within its two divisions – Polymer and Strategic Markets / Aftermarket Sales and Service – Coperion has 2,500 employees and nearly 30 sales and service companies worldwide.