Upcycling Recycled Polyethylene into Reprocessable, Creep-Resistant, High-Strength, and Thermally Conductive Composites via Dynamic Cross-Linking and Solid-State Stretching

Abstract

Postconsumer recycled polyethylene (rPE) is commonly downcycled because degradation and mixed waste histories compromise its mechanical reliability, creep resistance, and functional performance. Here, we report an integrated upcycling strategy that combines dynamic covalent cross-linking, solid-state shear milling (S3M), and solid-state stretching to convert rPE into reprocessable, creep-resistant, high-strength, and thermally conductive composites. Dynamic cross-linking reduced the maximum creep strain at 80 °C from 1.66% for rPE to 0.50% for the optimized cross-linked sample. After adding 5 wt % graphite nanosheets and applying a 3-fold stretching ratio, the optimized composite achieved a tensile strength of 108.7 MPa and an in-plane thermal conductivity of 2.55 W/(m·K), approximately 4.2 and 6.1 times higher than the corresponding rPE-derived controls. The dynamic network enabled remolding with high property retention, while the oriented graphite/polyethylene structure improved resistance to photo-oxidative aging. This scalable route provides a practical approach for producing durable functional materials from recycled polyolefins.