RECYCLING LINES | TECHNOLOGY


that it achieves a quality equivalent to that of primary material. The technologies and the various processes for recycling plastics continue to improve to make this feasible, as well as being more economic and energy efficient.” To meet these requirements, Coperion has developed plastics recycling technology that enables processing despite residual moisture. Before plastics can be recycled, they must be first shredded to flakes and cleaned. Conventional technologies then require pre-drying, crystallisa- tion and partial agglomeration. However, with Coperion’s solution the plastic flakes can be fed directly to a ZSK twin-screw extruder, where they are compounded and all residual moisture is safely removed via degassing domes, vent ports or the ZS-EG side degassing system. The result is recy- clate of a high product quality, equivalent to virgin material. The company says that this can be demonstrated by PET recyclate produced through this process. This recyclate recently received approval from the US Food and Drug Administra- tion (FDA) for direct food contact – proof of high compound quality produced from plastic flakes even with residual moisture. Coperion highlights other developments that


can provide significant benefits in recycling processes. These include Feed Enhancement Technology (FET). Plastic flakes that are fed into an extruder have a low bulk density. This is the same for additives, fillers and reinforcing materials that are mixed in during recycling to achieve the desired property profile of the recyclate. Both the flakes and additives are often feed-limited and therefore difficult to feed into the extruder. With FET, the feeding zone of the extruder is equipped with a porous, gas-permeable wall to which a vacuum is applied from externally. The result of the FET equipment is significantly improved feeding and throughput rates during recycling. In addition, the company says that if volatile substances and unpleasant odours generated during the recycling of plastics cannot be sufficient- ly removed via degassing domes and atmospheric vent ports, the ZS-EG twin-screw side degassing unit is a reliable, efficient solution. With its large free cross-section for degassing, the ZS-EG keeps the melt in the process section even at maximum specific torque of the extruder. The quality of the recyclate increases significantly. Non-product-contact devices in gravimetric


feeders, such as the Bulk Solid Activator ActiFlow, can also have a key role in plastics recycling, says Coperion K-Tron. Many bulk materials used in recycling processes, such as film flakes, regrind,


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fibres or fine powders, have a low bulk density. They are cohesive and do not flow consistently out of the supply hopper during the feeding process into the extruder. Such poor flow properties can lead to the formation of material bridges, making it difficult to accurately deliver these materials to the process. The Coperion K-Tron ActiFlow system for gravimetric feeders applies gentle vibrations to the hopper wall that carefully activate the contained material and ensures ideal flow in the hopper and maintains high feeding accuracy. Also suitable for recycling and recompounding


applications, the SWB Smart Weigh Belt Feeder is considered a comparatively simple model of gravimetric feeders. It features high accuracy and efficient process control. SWB Smart Weigh Belt Feeders can reliably feed large bulk material volumes and materials with different flow properties, as they weigh the bulk material before discharge and actively adjust the belt speed based on this. KraussMaffei has developed extrusion solutions for a wide range of plastics recycling, including technologies for the plasticising, compounding and degassing process steps, for pure regranulation and for recompounding. “The most important advantage KraussMaffei offers is the wide variety of line concepts, which are customised for each individual recycling application,” says Carl-Philip Pöpel, Director of Global Application & Product Ownership – Extrusion Technology. “Depending on the specific requirements, we can design these lines as stand- alone or cascade solutions with almost unlimited output rates. Another plus point is the option to use a system solution composed of a single-screw extruder and a twin-screw extruder, especially when it comes to solvent-based plastics recycling.” “The KraussMaffei EdelweissCompounding technology is based on two extruders operating in cascade arrangement,” says Franz-Xaver Keilbach,


Above: KraussMaffei EdelweissCom- pounding technology provides a cascade


solution for processing and compounding sorted plastics scrap in a single cycle


October 2021 | PLASTICS RECYCLING WORLD 33


IMAGE: KRAUSSMAFFEI


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