Advancing mechanical recycling of polypropylene: lessons from sorting, washing, and life cycle assessment
Moritz Mager, Lukas Zeilerbauer, Alexander Felgel-Farnholz, Sandra Czaker, Jörg Fischer, Sander H.J. Postema, Johann B. Kasper, Marcel C.P. van Eijk
Abstract
European legislation, particularly the Packaging and Packaging Waste Regulation (PPWR), is rapidly increasing the demand for high-quality recycled polypropylene (PP) in packaging applications. Achieving such qualities through mechanical recycling remains challenging due to the heterogeneity of post-consumer waste, while the role of intensified washing in the overall decontamination remains debated. This study evaluates the influence of additional sorting and washing intensity on material properties, product performance, and environmental impacts in mechanical recycling of Dutch post-consumer rigid PP. White, clear, and colored fractions were processed under cold and hot wash conditions, extruded, and converted into cups by injection molding and thermoforming. Sorting effectively reduced feedstock heterogeneity, while hot washing slightly improved oxidation stability and ductility. Cup testing showed that the investigated recyclates achieved 77-88 % of virgin polypropylene top load performance. Hot washing removed surface contamination but did not significantly reduce volatile organic compounds or migration levels. A Life cycle assessment (LCA) was performed in openLCA using Ecoinvent background data. The results showed that advanced mechanical recycling, despite higher energy and chemical demand, remained environmentally advantageous, achieving significantly lower climate change impacts compared to virgin PP. However, the recyclate substitution rate in final products was identified as the dominant driver of environmental benefits. Overall, maximizing substitution and sorting efficiency proved more effective for achieving sustainable, high-quality PP recycling than intensifying washing.