Direct PET processing
Economical and FDA-compliant recycling of PET flakes – 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 flakes without predrying into pellets. The flakes are then condensed in the SSP (solid state polycondensation) reactor and reprocessed back into bottles, with virgin material quality.
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 efficient plastification within the ZSK extruder enables bottle-to-bottle 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 efficiency
Before PET can be reprocessed, it must first be shredded to flakes and then cleaned. Ordinary technologies require pre-drying, crystallisation or agglomeration of the PET flakes 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 flakes 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 filter 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 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 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 flow in suitable separators before discharge from the process section.
As well as high product quality, direct processing of PET flakes offers further advantages including reduced operating costs and energy consumption as well as lower logistic expense, according to Mr Jochen Schofer, Business Segment Manager, Recycling & Direct Extrusion at Coperion.
“With FDA certification, we have officially confirmed the high product quality of the PET recyclates. 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 is an international market and technology leader in compounding and extrusion systems, feeding and weighing technology, bulk materials handling systems and services. It has 2,500 employees and nearly 30 sales and service companies worldwide.
