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Issue 06/2018

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From Science & Research

From Science & Research PLA in the post-consumerrecycling stream The constant increase in global production capacities of biobased plastics [1] results in a variety of products made of biobased plastics that reach the established disposal streams as post-consumer wastes after being used. In Germany, one of these disposal streams is the collection and disposal of lightweight packaging waste by the yellow bin or the yellow bag system. KNOTEN WEIMAR and TU Chemnitz have investigated the behaviour of biobased plastic products in the sorting of lightweight packaging wastes at operating plants and pointed out possible options for material recycling. The research project was carried out on behalf of the German Federal Ministry of Food and Agriculture (BMEL) and funded by the project management organization Fachagentur für nachwachsende Rohstoffe (FNR) [2]. The scheme in Fig. 1 gives an overview of the various disposal routes and the recycling and disposing processes of various packaging waste as well as the recyclable material fractions produced. Products made of biobased plastics can also be integrated into this system. Sensor-based sorting with near-infrared (NIR) devices is a key element of modern sorting plants and enables the sorting of different types of plastics. Drop-in solutions such as biobased PET and PE, are sorted out together with conventional equivalents. However, biobased novel plastics (e.g. PLA, PLA blends or starch based materials) can also be detected and sorted out due to their characteristic NIR spectra. It can be concluded that the sorting of e.g. PLA blends as representatives of biobased novel plastics as single fraction is technologically viable. Impurities of the sorted fractions can thus be kept to a minimum. In preparation for a practical field test in a conventional sorting plant, the NIR spectra of several different PLA blends (plastic yoghurt cups, sheets but also dishes, cups and bottles) were scanned in the existing NIR devices. In order to determine the current initial quantity, a sorting test was first run for lightweight packaging sorting with approx. 25 tonnes of lightweight packaging input material. The result showed that the current quantity of products made from PLA/PLA blends and starch blends in all of the analysed material streams is predominantly below 1.1 ‰. A further sorting test (three subtests) investigated the detectability and sortability or material output of PLA products/wastes at an operating plant in more detail. The goal was to determine where PLA materials remain under unchanged sorting conditions (without positive sorting of PLA or without activating the PLA spectrum on the NIR devices) and to test the detectability and sortability of PLA materials from the post-consumer stream. Cups, forks and dessert cups were used as PLA input material. Subsequent to material mixing (Fig. 2) the material was fed into the sorting process. Three sorting tests were carried out (see above), the Fig. 1 Disposal paths and recycling, reutilization and disposal processes of separate packaging wastes Taking back systems for packaging waste Deposit systems PET -Bottles Light weight packaging via dual systems (yellow bin/bag) e.g. cups, bowls, bottles, films etc. Sorting -/Pre-treatment plants (Disposal company), Sorting dry Process steps a.o. crushing, sieving, metal separation, sensor-based sorting (NIR), air separation, manual control Products: relevant enriched reusable materials (incl. impurities caused by sorting performance, material-compounds / -mixtures, residues and pollutants)* PET PS PE / PP Films MP RDF** Residues Final recipient plant, Conditioning wet-dry- Process steps (per material): a.o metal separation, sensor-based sorting (NIR), crushing, washing, sink-float separation (separation by density), drying, if any extruding Sinking fraction (ρ > 1) e.g. PET Swimming fraction Sinking fraction e.g. PE / PP Swimming fraction (ρ < 1) Final recipient plant, Conditioning dry Process steps (per material): a.o. metal separation, crushing, sieving, air separation, sorting, if any agglomeration e.g. Mixed plastics (MKS) Thermal treatment (MVA ) PET a.o. residues a.o. residues PE / PP z.B. PO Recyclates, e.g. PET, PO, PS (material recycling) Reductant, gases and oils (raw material recycling e.g. steel plant) Fuel (energetic utilisation e.g. cement and CHP station) Energy (disposal, if possible energetic utilisation***) *Specification for individual recyclable material available; **classification as final recipient plant for RDF-production; ***MVA if possible energetic utilisation 18 bioplastics MAGAZINE [06/18] Vol. 13

From Science & Research By: Jasmin Bauer,Carola Westphalen KNOTEN WEIMAR Internationale Transferstelle Umwelttechnologien GmbH Weimar, Germany Tobias Hartmann, Roman Rinberg,,Lothar Kroll Technische Universität Chemnitz Chemnitz, Germany material first underwent the automated sorting process and was then manually separated from the fractions. The following results were achieved: • Detecting and, in particular, separation of PLA materials as individual material fraction in a state-of-the-art plant is possible. • Sorting under normal conditions for lightweight packaging (PLA detection not active) approx. 9 % of the PLA input goes into the PVC fraction. Hence, PLA is classified as PVC if no PLA spectrum is active. • Small scale adaption was made by adjusting the plant technology by scanning the PLA spectra. • Positive sorting on PLA results in a sorting rate of 55%. • Positive sorting on PLA+PE/PP extracted 46% of PLA input. The generated test material (PLA fraction) was grinded, washed and the grist was purified to 90 % PLA with the help of Hamos GmbH (Penzberg, Germany) in the company’s own pilot plant. The purification took place in three stages: air separation, metal separation and plastic-plastic separation. The main contamination after the cleaning process was adhesive label residues from the yoghurt cup. As not enough input material was available for the final regranulation on an industrial plant, a test material (~ 0.8 t) Fig. 2 Input material (left), automated sorting process (right) was mixed analogous to the purified fraction. This grist was regranulated at Sysplast GmbH&Co. KG in Nürnberg, Germany on a Coperion ZSK 50MC with an Ettlingen rotary filter ERF (sieve width 250 µm) with throughputs of up to 400 kg per hour. The impurities were separated effectively and a green regranulate was obtained (see Fig. 3). The mechanical testing revealed the following losses with regard to the virgin material (Ingeo 2003D from NatureWorks): Young’s modulus -1 % tensile strength -24 % Charpy unnotched -31 % Charpy notched -17.4 % All the tests and results mentioned, as well as further experiments on the recycling of PLA, including a life cycle assessment, are detailed in the final report of the research alliance “Nachhaltige Verwertungsstrategien für Produkte und Abfälle aus biobasierten Kunststoffen” funded by BMEL in which eight partners from science and industry participated [3]. A quick overview of the most important results, as well as further links to the joint project and the partners, are summarised in the results paper “PLA in the waste stream” (download link see [4]). References: [1] European Bioplastics, nova-Institut (2017). [2] [3] [4] documents/press-releases/2017/pla-in-the-waste-stream.pdf | Fig. 3: seperates impurities (left) and green PLA regranulate (right) bioplastics MAGAZINE [06/18] Vol. 13 19

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