Extrusion International 3-2020

41 Extrusion International 3/2020 RECYCLING – FROM RESEARCH More than 60 odorous substances were identified using com- bined chemo-analytical methods. The information gained pro- vides a targeted strategy for avoiding off-odors. The results of this collaborative study with the Chair of Aroma and Smell Re- search at the Friedrich-Alexander-Universität Erlangen-Nürn- berg (Germany) and the University of Alicanet (Spain) have now been published. In order tomeet the targets of the new EU Packaging and Pack- aging Waste Directive concerning the recycling of packaging waste, new markets for recyclates produced from waste plas- tic packaging must be found. Recyclates produced from waste plastic packaging must have no off-odors if they are to be used as secondary raw materials for the manufacture of high-quality consumer products. Indeed, the off-odors in plastic recyclates prevent a closed cycle for the recycling of plastic packaging ma- terials. Currently, there is aparticularlyhigh reusage rate for recy- clates produced frompolyethylene terephthalate (PET) bottles. LDPE packaging waste in focus The Sensory Analytics department at the Fraunhofer IVV char- acterizes and optimizes plastics and recyclates. The odorants in HDPE waste and the recyclates produced from packaging from bodycare products and detergents have already been analyzed. Low density polyethylene (LDPE) is one of the most commonly used plastics. It is widely used for packaging materials 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 col- lection strategy on the sensory impairment of thewaste. Identification of odorants – the key step Identification of the substances causing off-odors is essential in order to be able to take measures for odor optimization. Most of the odorants identified in the study are typical metabolites of microorganisms. Many of thesemetabolites had a cheese-like or feces-like odor. The odorants included carboxylic acids and sul- fur-containingandnitrogen-containing components. The chem- ical 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 onwhich 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 newodorants. Odorant reduction via separate collection in the yellow bag The study showed that theway the packagingwaste is collected has a large bearing on the odor quality of plastic shopping bags. Thereare significant benefits by separate collection in the yellow bag. Waste collected in this way had a significantly lower over- all odor. In contrast, the waste fraction collected in the general household waste had more intense cheesy-like, sulfur-like, and feces-likeodors. Thehigher organic fraction in thegeneral waste favors the formation of thesemicrobial degradation products. It was also demonstrated that the post-consumer LDPE shopping bags from the separate collection that were washed at 60 de- grees had fewer odorants and a reduced overall odor than the unwashed bags. Methods for odor identification in plastic waste The Fraunhofer IVV scientists used sensory analytics to identify the odors. Sensory evaluation of the sample materials was first undertaken by a trained sensory panel. The odorants were then identified using chemo-analytical methods such as gas chroma- tography – olfactometry and with two-dimensional coupling with mass spectrometry. This enabled the chemical structures to be determined and also possible formation pathways and sourc- es of the odorants to be identified. These key findings can now be used to develop customized solutions for optimization of the odor of plastic recyclates, starting at thewaste collection stage. Fraunhofer Institute for Process Engineering and Packaging IVV Giggenhauser Str. 35, 85354 Freising, Germany Dr. Philipp Denk, philipp.denk@ivv.fraunhofer.de www.ivv.fraunhofer.de Plastic recyclates produced fromwaste packaging have tomeet high sensory requirements in order to be used for newproducts. Plastic recyclates often have off-odors, some of which have not hitherto been identified. The Fraunhofer Institute for Process Engineering and Packaging IVV (Germany) has analyzed the sensory properties of post-consumer shopping bags made of low density polyethylene (LDPE) and originating fromdifferent collection systems Reduced Off-Odor of Plastic Recyclates via Separate Collection of Packaging Waste Separate collection is beneficial for the sensory properties of the plastic waste and hence the quality of the resulting recyclates (© Fraunhofer IVV)