Characterizing Heterogeneity in Post‐Consumer Rigid PP Packaging Waste: Implications for Object and Property‐Based Flake Sorting

ABSTRACT

Meeting the recycled content targets of the Packaging and Packaging Waste Regulation requires significant improvements in recyclate quality for high‐performance rigid polypropylene (PP) packaging. However, the post‐consumer rigid PP stream is highly heterogeneous, resulting in intermediate recyclate properties when processed as a single stream. This study provides a comprehensive characterization of 20 representative rigid PP packaging products from an Austrian sorting facility, combining rheological, mechanical, thermal, molecular, and chemical analyses to derive a product‐property matrix and sorting implications. The results reveal substantial variability in melt flow rate, stiffness, impact strength, crystallinity, and molecular weight distribution, driven by polymer design and degradation during primary processing. Additional heterogeneity arises from chemical loads, particularly between food and non‐food products, as well as inconsistent stabilizer packages and barrier layers. These findings highlight inherent limitations of object‐based sorting, which cannot reliably infer material properties from external product attributes. Conversely, correlations between spectral‐relevant properties underscore the potential of property‐based flake sorting to classify materials by intrinsic characteristics. A systemic combination of both strategies is proposed: isolating food‐contact materials at the object stage and generating application‐specific recyclate fractions through flake sorting. Developing robust spectral‐property prediction models for PP remains a critical step towards substituting virgin grades.