Increasing the PP-recyclate quality by enhanced mechanical processing of post-consumer packaging waste
Nikolai Kuhn, Moritz Mager, Joerg Fischer, Gerald Koinig, Alexia Tischberger-Aldrian
Abstract
Achieving higher recycling targets requires recyclates with consistent qualities. However, mixed recycling of different packaging types (e.g., caps and bottles) reduces recyclate quality, limiting substitutability for virgin materials. In this study, we present an industrially scalable and ready-to-deploy process for polypropylene (PP) packaging waste, which includes sorting, shredding, washing, and extrusion. We demonstrate that sensor-based sorting on article and flake level according to opacity (white-PP) and translucency (clear-PP) alters the mechanical properties and processability of PP-recyclates. White-PP recyclate exhibited a nearly twofold higher melt flow rate (17 vs. 9 g/10 min) and greater stiffness (Young's modulus 1424 MPa vs. 1154 MPa) than that of clear-PP recyclate. These differences can be attributed to variations in crystallinity of white-PP compared to clear-PP. Our results highlight the economic and environmental benefits of advanced sorting method to increase PP-recyclate quality – enabling higher-value applications for PP recyclates and supporting the transition towards a circular plastics economy.