Comprehensive Rheological Study of Post-Consumer Recycled Polypropylene: Analyzing the Influence of Waste Origin on Material Flow Properties

Abstract

Recycling of post-consumer waste has emerged as a key strategy to reduce environmental impact and conserve resources, particularly in the production of sustainable polymers. The development of high-quality recycled polypropylene (rPP) from household waste, such as the Systalen recyclate produced by Der Grüne Punkt (Green Dot), exemplifies this progress. Systalen is manufactured using a patented purification and recycling process designed to produce consistent, high-quality rPP from post-consumer waste streams, significantly reducing CO₂ emissions compared to virgin plastics. This study provides a comprehensive rheological characterization of Systalen rPP, focusing on the influence of its waste origin on the material's flow properties. Advanced rheological methods, including oscillatory shear and rotation rheometry, were used to evaluate viscoelastic properties, flow stability, and processing behavior. Results reveal notable variations in flow characteristics due to the heterogeneous composition and potential contaminants inherent to post-consumer waste, impacting shear thinning behavior, complex viscosity, and relaxation times. This research highlights the necessity of optimized processing strategies tailored to such recyclates to ensure their consistent performance. The findings emphasize the potential of Systalen rPP as a reliable secondary raw material for a wide range of applications (e.g., textile industry), supporting circular economy initiatives and reducing reliance on virgin resources.