WASHING | TECHNOLOGY


maintaining quality. Solutions to process laminated materials are also needed and where possible separate them, into aluminium layers and bio- based plastics for example. Rigid plastic streams coming from separate plastic waste collection is another area of potential improvement. Recovery of plastics from laminated cartons, as well as processing of pulped waste, are also streams that can contain valuable raw materials that can be returned into the cycle. Process solutions have already passed several trial rounds with very promising outcomes, he says. Herbold Meckesheim is concentrating on film lines and has recently installed one in the US and one in Europe. In addition to the standard steps of pre-washing, wet grinding, centrifugal and thermal drying, both include hot washing steps, hydrocy- clone separation and agglomerators. The company adds that it optimises plant performance both by mechanical improvements and advanced process control to ease operation and maximise through- put and uptime. Recent technical developments at Herbold


Meckesheim have included a larger centrifugal dryer, HVST step dryers, introduction of hot washing from PET into film, larger SB-granulators (force-fed machines), and improved label removers for PET bottle treatment. Herbold adds that future developments will include bigger films lines, more combined with NIR sorting and washing lines. There will also continue to be more integration of the different recycling technologies of sorting, separation, cleaning and granulation. Converters and virgin material producers will also continue to be looking at upgrading recyclate properties. There will also be more pre-processing for chemi- cal recycling, predicts Herbold. Herbold Meckesheim says that its hot washing is


a practical complement to existing washing technology and represents an important process


step for increasing quality. Herbold meets this challenge of producing high recycling quality in large quantities by integrating this process step, which originated in the recycling of PET bottles, into other areas of the plastic recycling process. Initially, this involved just pre-washing used PET bottles. However, the procedure is also used for other items, such as thermoformed foils, trays and foil used in the packaging industry, and has also been developed for polyolefin foils. With optimum temperatures, a suitable dwell time and optimum use of additives, Herbold says that its hot washing process yields excellent cleaning results. The company says that the main advantage of hot washing is the cleanliness of the flakes. Fatty impurities, for example from body lotions, cooking oil or sun cream, are dissolved and washed away, as are residues from labels and their adhesives. The clean flake material has reduced odour, is clear and does not yellow. Herbold adds that just how clean the material is can be demonstrated by the melt filter in the extrusion system. While the industry standard for filtering out foreign particles in the melt filtration process is 80-110 microns, hot washed flake material achieves just 40 microns. The origin of the material being recycled – discarded items from normal domestic waste – is no longer detectable in the end result. Different types of waste present different demands of the preparation stages. When quality is the main focus, Herbold’s customers rely on the hot washing system’s recommended process integration, in a discontinuous process. The reason for this is the recyclate’s important and more controllable dwell time in separate tanks with agitators. If using multiple tanks in alternating operation, the process step becomes more or less continuous, and can be integrated into continu- ously running machinery. In PET recycling, the improvements to the


www.plasticsrecyclingworld.com


Above: Jörg Schneeberger, CEO of WKR Walter, and Karlheinz Herbold, Executive Director of Herbold Meckesheim, in front of the centrifuge of the new washline


Left: Post- consumer waste input


July/August 2019 | PLASTICS RECYCLING WORLD 27


PHOTO: HYDRODYN


PHOTO: HERBOLD


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