Virgin blends do not accurately predict the properties of recycled plastics

Virgin materials, particularly virgin binary blends (VBBs), are widely used to model the properties of mechanically recycled plastics. However, it is assumed rather than proved that these results accurately represent real post-consumer recyclates (PCRs). This study is focused on polypropylene (PP) and high-density polyethylene (HDPE), the dominant polymers in rigid packaging. VBBs were manufactured using application-specific grades, realistic cross-contamination levels and appropriate processing techniques to mimic real waste as closely as possible. Despite this, they failed to predict the mechanical behavior of real PCRs. VBBs systematically overestimate the technical performance of PCRs, which reflects the complexity of recyclates containing multiple polymer subtypes, heterogeneous contamination at different levels, degradation history, and prior (mis)use. Matching single polymer contamination levels alone is insufficient to reproduce the application-relevant PCR behavior. Future assessments should prioritize testing with real PCRs or develop refined model systems that better capture both compositional complexity and use-phase chemical changes.