Leveraging a Dynamic Physical Cross-Linking Architecture to Enable Recycled PET with Exceptional Thermoplasticity and Toughness

The recycling of poly(ethylene terephthalate) (PET) is vital for environmental sustainability, yet achieving recycled PET (rPET) and its composites with optimal processability and flexibility remains a challenge. This study presents a solvent-free reactive extrusion method to extend the chains of rPET using a macromolecular chain extender (i.e., methyl methacrylate-glycidyl methacrylate copolymer, marked as PMG) rich in epoxy groups and to produce rPET/recycled polyethylene (rPET/rPE) composites. The resulting composites exhibit excellent thermoplasticity and controllable mechanical properties, such as the rPET/rPE composite (70:30 by mass), with a tensile strength of 39.2 MPa and an elongation at a break of 81.4%. After five extrusion cycles, their mechanical properties just encounter a subtle decline, indicating robust sustainability and cycle performance. The formation of a dynamic physical cross-linking network arises from the distinct polarity, hydrophobicity, and melt viscosity of rPET and rPE, where the hard spherical rPET phase is evenly dispersed in the soft rPE matrix with PMG acting as an interfacial compatibilizer. This innovative approach not only enhances the properties of the recycled composites but also promotes their cost-effectiveness and environmental benefits, thus broadening the potential applications of rPET and rPE as partial substitutes for virgin PET and PE.