TECHNOLOGY | WASHING


There is now significant market demand to


recycle polypropylene and polyethylene to render them suitable for high-grade re-use. Following extensive trials in its plant’s own washing system, Krones says it was able to demonstrate that it is possible to treat these polyolefins to create top-quality recyclates – in a process that is both ecologically and economically viable.


Polymer densities vs water (g/cm³) PET: 1.38-1.40 Polyolefins: < 1 PP: 0.90-0.915 LDPE: 0.915-0.935 HDPE: 0.94-0.97


Below: Herbold Meckesheim installed this washing line for WKR Walter in Austria


One of the main characteristics of polyolefins is their density of lower than one, which allows them to float on the the surface of water, while PET is significantly heavier than water meaning that it sinks to the bottom (see table). Krones adds that the relatively low density of polyolefins and their resulting ability to float are particularly helpful in the washing process for PET when it comes to separating cap material from the PET itself. In the washing process for polyolefins, this material characteristic requires some procedural adjust- ment. However, the overall concept continues to be based on the experience gathered in the field of PET washing technology. Units were adapted to suit polyolefins and in-house trials produced good washing quality. Washing results were confirmed in external laboratories and validated in the produc- tion of test specimens. One problem encountered with polyolefins is


material collection and resulting side effects. “The packaging we are talking about here is collected in household garbage or in separate bins or sacks for plastics,” says Esmarch. “Because this material is


Krones’ MetaPure W-PO washing module recycles polypropylene and polyethylene suitable for re-use


usually not cleaned before recycling, it is invariably in contact with organic residues such as ketchup, mayonnaise, oil, yoghurt, shampoo, soap, house- hold cleaning agents and many other substances. This creates an enormous biological and chemical loading, with an unpleasant smell. That in turn renders it relatively difficult to make sure the end-product is odour-neutral. However, with the standard washing module used in the in-house pilot plant, optimum results in regard to cleanliness and odour-neutrality could indeed be achieved.” According to Daniel Zeiler, Vice President, Sales


at Herbold Meckesheim, there is increasing interest in film recycling at present in the industry. “Rigid plastics are in good hands in many coun- tries, but film scrap is often out of recycling,” he says. “In order to achieve European Union recycling targets, packaging waste, in particular, in sorting plants needs further treatment to allow higher qual- ity recycling. Plant upgrades are required and new streams need adapted processing solutions. We also see the need to treat PET trays separately. It is brittle and therefore a more demanding product. We have run several trials to improve the washing technologies and recovery rates for this material – minimising losses in fines is the key,” he says. “As far as the end markets are concerned, there is a higher demand for improved recycling process- es and quality recyclates. If plastic converters want or are forced to replace more virgin material by r-pellets, then they need r-pellets of a quality that is closer to virgin. In recycling process efficiency, the main trends are to reduce the loss of fines in the processing of hard and brittle plastics, as well as reducing energy use in size reduction and drying.” Zeiler also highlights some other areas where new solutions are required in plastics recycling and washing technologies. These include the process- ing of larger amounts of stretch film, with films continuing to get thinner. Bigger recycling lines are also required – for 2-5 tonnes per hour – while


26 PLASTICS RECYCLING WORLD | July/August 2019 www.plasticsrecyclingworld.com


PHOTO: KRONES


PHOTO: HERBOLD MECKESHEIM


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