Chemically Recyclable Polyester Miscible with HDPE Transforms Contamination into Functional Enhancement

High-density polyethylene’s (HDPE) chemical inertness, the foundation of its commercial success, renders it nearly impossible to chemically recycle. Furthermore, strict purity requirements limit mechanical recycling rates to ∼30% despite the legislative targets being 75%. Chemically recyclable polyolefin mimics containing cleavable ester linkages offer a solution, but their compatibility with commodity polyethylene waste streams remains unexplored, raising concerns that contamination could worsen rather than solve the global recycling crisis. Here, we demonstrate that HDPE-like polyesters (HDPE-like) exhibit complete miscibility with HDPE across all compositions (20–80 wt %), a crucial result given the expected difficulty to separate the HDPE-like from HDPE waste streams. Single melting transitions, cocrystallized lamellar structures, and retention of ductility confirm molecular-level mixing without mechanical failure. Strikingly, incorporation of just 20 wt %HDPE-like increases adhesion to aluminum by more than 10-fold (from 0.4 to 4.4 MPa), an effect that persists in postconsumer recycled HDPE, enabling upcycling of low-value waste into metal-laminate applications. Both components retain their recycling pathways: HDPE undergoes mechanical reprocessing, while HDPE-like achieves quantitative methanolysis to monomers that repolymerize with full property retention. By demonstrating that chemically recyclable polyesters can be miscible with, and functionally beneficial to, commodity polyolefins, this work establishes a dual-recycling framework where a contamination becomes a useful additive.