PETpla.net Insider 06 / 2020

MATERIALS / RECYCLING PETplanet Insider Vol. 21 No. 06/20 www.petpla.net 27 Separate collection of packaging waste Reduced off-odour of plastic recyclates Plastic recyclates produced from waste packaging have to meet high sensory requirements in order to be used for new products. Plastic recyclates often have off-odours, some of which have not hitherto been identified. Recycling Special The Fraunhofer Institute for Pro- cess Engineering and Packaging IVV has analysed the sensory proper- ties of post-consumer shopping bags made of low density polyethylene (LDPE) and originating from differ- ent collection systems. More than 60 odorous substances were identified using combined chemo-analytical methods. The information gained pro- vides a targeted strategy for avoiding off-odours. The results of this collabo- rative study with the Chair of Aroma and Smell Research at the Friedrich- Alexander-Universität Erlangen-Nürn- berg and the University of Alicante have now been published. In order to meet the targets of the new EU Packaging and Packag- ing Waste Directive concerning the recycling of packaging waste, new markets for recyclates produced from waste plastic packaging must be found. Recyclates produced from waste plastic packaging must have no off-odours if they are to be used as secondary raw materials for the manufacture of high-quality consumer products. Indeed, the off-odours in plastic recyclates prevent a closed cycle for the recycling of plastic pack- aging materials. Currently, there is a particularly high reusage rate for recy- clates produced from polyethylene terephthalate (PET) bottles. LDPE packaging waste in focus The Sensory Analytics department at the Fraunhofer IVV characterises and optimises plastics and recyclates. The odorants in HDPE waste and the recyclates produced from packaging from bodycare products and deter- gents have already been analysed. Low density polyethylene (LDPE) is one of the most commonly used plastics. It is widely used for packaging materi- als such as plastic shopping bags. Via various collection systems these bags end up as packaging waste. Part of the current study on post-consumer LDPE shopping bags concerned the effect of the collection strategy on the sensory impairment of the waste. Identification of odorants - the key step Identification of the substances causing off-odours is essential in order to be able to take measures for odour optimisation. Most of the odor- ants identified in the study are typical metabolites of microorganisms. Many of these metabolites had a cheese- like or feceslike odour. The odorants included carboxylic acids and sulfur- containing and nitrogencontaining components. The chemical structures of the odorants gave key insight into their origin. Using this information, the pathways into the packaging waste and via the recycling process into the recyclate were identified. Depending on which process step cannot remove an odorant or even results in a new odorant, targeted measures can be taken to reduce odorants or avoid the formation of new odorants. Odorant reduction via separate collection in the yellow bag The study showed that the way the packaging waste is collected has a large bearing on the odour quality of plastic shopping bags. There are significant benefits by separate col- lection in the yellow bag. Waste col- lected in this way had a significantly lower overall odour. In contrast, the waste fraction collected in the general household waste had more intense cheesy-like, sulfur-like, and feces-like odours. The higher organic fraction in the general waste favours the forma- tion of these microbial degradation products. It was also demonstrated that the post-consumer LDPE shop- ping bags from the separate collection that were washed at 60 degrees had fewer odorants and a reduced overall odour than the unwashed bags. Methods for odour identification in plastic waste The Fraunhofer IVV scientists used sensory analytics to identify the odours. Sensory evaluation of the sample materials was first under- taken by a trained sensory panel. The odorants were then identified using chemo-analytical methods such as gas chromatography - olfactometry and with two-dimensional coupling with mass spectrometry. This enabled the chemical structures to be deter- mined and also possible formation pathways and sources of the odorants to be identified. These key findings can now be used to develop custom- ised solutions for optimisation of the odour of plastic recyclates, starting at the waste collection stage. www.ivv.fraunhofer.de/en