Mechanical and Thermal Structure–Property Relationships of Recycled PP-Based Thermoplastics Under Environmental Aging
Abstract
The present study aims to investigate the performance of regenerated polymers obtained after the mechanical recycling of two distinct polypropylene (PP)-derived materials (dustpan and tram seat) collected from the post-consumer waste stream, in line with circular economy principles. The primary goal is to determine the potential of these secondary raw materials for evaluation as value-added products in high-performance applications. To this end, the chemical, thermal, and mechanical stabilities of the secondary raw materials were analyzed in detail, establishing a scientific basis for their potential use in demanding applications. Specifically, the chemical (FTIR, XRD), morphological (SEM-EDS), thermal (TGA, DSC), and mechanical (tensile, flexural) properties of the materials were thoroughly examined. Furthermore, environmental aging tests were applied to assess the suitability of these materials for potential outdoor applications. XRD, SEM-EDS, and TGA analyses confirmed that the tram seat sample is a complex composite containing flame retardants (Br/Sb) and calcium carbonate (CaCO₃) filler, while the dustpan sample contains a purer PP matrix. Environmental aging tests revealed contrasting and critical changes in material performance: a significant increase in tensile strength of up to 27.8% (embrittlement/stiffening) was observed in the dustpan sample, whereas the tram seat sample showed a sharp decrease of 35.1% in tensile strength due to accelerated oxidative degradation. The findings indicate that the long-term stability of recycled polymers is critically dependent on the type of additives they contain, rather than solely on the polymer type. Finally, it was concluded that the tram seat material is suitable for 3D printer filament production, and the dustpan sample can be utilized in new products due to its high mechanical stability. This work provides a scientific foundation for the valorization of urban waste into the circular economy.