In Situ Compatibilization of Polyethylene/Polypropylene Blends Enabled by Supramolecular Dynamic Cross-Linking for Efficient Upcycling

Polyolefins are integral to modern society but pose a severe environmental crisis due to their persistent accumulation. While mechanical recycling is widely adopted for its scalability, it often suffers from “downcycling” due to phase immiscibility and performance deterioration in mixed plastic streams. Herein, we address these challenges by applying a supramolecular dynamic cross-linking strategy to upcycle blended polyolefins. Moving beyond general compatibilization, this study systematically investigates the upcycling of high-density polyethylene/isotactic polypropylene (HDPE/iPP) binary blends across varying composition ratios and, crucially, elucidates the synergistic mechanism in elastomer-toughened ternary systems (rPE-rPP/POE). Comprehensive characterization reveals that the reactive small-molecule cross-linker (M1) not only constructs a dynamic supramolecular network at the interface but also synergizes with the elastomer phase to regulate phase morphology, significantly enhancing mechanical toughness. This strategy offers a low-cost, robust solution for upcycling complex postconsumer polyolefin waste into high-performance materials, effectively reducing the reliance on commercial toughening agents.