Analysis of trade-offs of post-sorting plastic packaging

Article Analysis of trade-offs of post-sorting plastic packaging https://doi.org/10.1038/s41586-026-10606-4 Received: 22 August 2025 Alexandra Schmuck1, Tiago G. A. Belé2, Daniël Withoeck3, Kevin M. Van Geem3, Kim Ragaert4 & Steven De Meester1 ✉ Accepted: 28 April 2026 Published online: xx xx xxxx Open access Check for updates Increasing recycling rates requires not only better technologies but also smarter collection of plastic packaging waste1. Source separation—sorting materials such as plastics and metals at the household level—captures substantial waste volumes2,3, yet significant quantities still remain in the residual household waste fraction owing to misthrows and non-participation4,5. Post-sorting of mixed waste has been proposed as a one-bin alternative to boost capture6,7, despite concerns that contamination could compromise recycling quality7–9. Here we show, based on samples collected from one single material recovery facility, that bale purity, expressed as percent target polymer, is similar across source-separation and post-sorting pathways, but post-sorted bales contain more contaminants, including prohibited metals such as cadmium and lead. Post-sorted samples have higher moisture and dirt content8, which can lead to increased complex volatile organic compounds and necessitate additional washing. Concentrations of metals and halogens are elevated owing to non-packaging items, potentially compromising recycling quality and further complicating both mechanical and chemical recycling processes10,11. Although post-sorting can be a useful supplement, it should not replace source separation. Our results demonstrate that post-sorting can increase feedstock for recycling, but it also acts as a pathway for certain contaminants to enter plastic packaging waste, raising concentrations above typical levels, with potential risks to human health if these contaminants are not removed before recyclate production. As post-sorting of residual waste becomes crucial to meet circularity targets, these findings are particularly relevant. Global plastic production exceeded 413.8 Mt in 202412, but only about 9% is recycled13. Collection and sorting remain key bottlenecks1, driven by low collection-system efficacy3,14, public non-compliance and limitations of material recovery facilities (MRFs). As a result, up to 65% of European plastic packaging waste (PPW) is diverted to mixed residual streams comprising both recyclable and non-recyclable plastic packaging4,5. Collection and sorting strategies vary widely. In source-separation systems, households separate recyclables, typically as multi-material stream (for example, plastic packaging, metals and drinking cartons (PMD)) or via single- or dual-stream systems. In contrast, mixed-waste systems collect all waste together and depend on downstream post-sorting. Globally, plastic recycling still relies on mixed waste collection followed by post-sorting (PoSo), ranging from informal recovery to mixed-waste MRFs15, often achieving recycling rates below 15% in countries such as China16, Brazil17 and Australia18. In the USA, multiple collection systems coexist, but often target only polyethylene terephthalate (PET) bottles and high-density polyethylene (HDPE) containers, contributing to similarly low overall plastic recycling rates (<15%)19,20. By contrast, countries with established source-separation systems, for example, Belgium, the Netherlands and Germany, achieve collection rates above 70% (refs. 3,14) and recycling rates above 50%. However, even these systems retain 7–30% non-target material in PMD streams owing to household misplacement21,22, and losses during sorting and processing create a gap between collection and recycling rates. These limitations, combined with advances in post-sorting technologies, raise the question of whether post-sorting, or hybrid approaches, could outperform source separation6,7. Although discussions often prioritize recycling volumes, recyclate quality is critical for substituting virgin materials23. Here ‘recyclate quality’ refers to the expected mechanical and technical properties determining functionality in end-market products. As this concept is context dependent24–27, it is not measured but inferred from feedstock quality indicators. Post-sorting processes heterogeneous streams, including nonpackaging plastics, potentially increasing contamination and reinforcing the quantity–quality trade-off3. Although feedstock heterogeneity is known to limit recyclate quality3,28, comparative analyses across collection systems remain scarce7,29. A previous study8 showed only minor differences in low-density polyethylene (LDPE) and polypropylene (PP) 1 Laboratory for Circular Process Engineering (LCPE), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Kortrijk, Belgium. 2Chair of Aroma and Smell Research, Department of Chemistry and Pharmacy, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany. 3Laboratory for Chemical Technology (LCT), Department of Materials, Textiles and Chemical Engineering, Faculty of Engineering and Architecture, Ghent University, Ghent, Belgium. 4Circular Plastics, Department of Circular Chemical Engineering, Faculty of Science and Engineering, Maastricht University, Maastricht, the Netherlands. ✉e-mail: Nature | www.nature.com | 1 Article a b 100 Composition (%) 80 60 40 20 LDPE HDPE PP film PP rigid PET Others So Po PM D M ix So rig id PP Textiles Paper WEEE c M ix Po PM D So PE PP rig id rig id Po PM D Po rig id PE PE LD LD PE PM D So 0 Metals Rubber Toys LAMD PMD (filled) 0 100 PoSo (open) This study (large) Other studies (small) Fig. 1 | Polymer composition and LAMD. a, Dry-weight polymer composition and associated LAMD of sorted plastic waste bales. Polymer fractions are reported in wt% (dry basis) for LDPE, PE rigid, PP rigid and mixed plastic bales collected from source-separated (PMD) and post-sorting (PoSo) systems. ‘Others’ includes all other polymer types, for example, polystyrene, PVC and polyamide. The mix PoSo composition combines data from identification of polymer fraction through Fourier transform infrared spectroscopy and nonpackaging fraction (textiles, paper, WEEE, metals, rubber, toys) through visual inspection. Non-packaging fraction sums up to 15.7 wt% of the total mix PoSo sample. b, Examples of non-packaging plastic items included in the sorted mixed plastic bale (from top to bottom): textiles (shoes, heavy-duty cloths), WEEE (console), metals and toys. c, Ternary plot comparing bale composition by target polymer (right axis; 40–100%), non-target polymer (left axis, 0–60%) and contamination (bottom axis; 0–60%). Large symbols denote bales analysed in this study and small symbols denote literature values. Bale categories include HDPE bale (blue circles), rigid PP bale (orange squares), film bale (predominantly LDPE, purple triangles) (...truncated)