Mechanical Recycling of Mixed Plastics by Supramolecular Dynamic Cross-Linking Strategy

Mechanical recycling of waste plastics is one of the main strategies for addressing plastic pollution, but most waste plastics exist as incompatible mixed plastics that undergo phase separation, making their direct mechanical recycling challenging. Here, a supramolecular dynamic cross-linking strategy using only a small amount of supramolecular dynamic small-molecule cross-linkers was designed to compatibilize and directly mechanically recycle a variety of nonpolar/nonpolar, nonpolar/polar, and polar/polar polymer blends. These difunctional small-molecule cross-linkers contain functional groups with supramolecular dynamic cross-linking capability and functional groups that can be easily grafted to various polymers. Under industrial processing conditions (reactive extrusion using a twin-screw extruder), these small-molecule cross-linkers can be grafted to both components of the mixed plastics. This leads to the in situ formation of a dynamic-cross-linked network that significantly improves the mechanical properties of the blends. More importantly, this strategy achieved the large-scale and multiple recycling/reuse of postconsumer mixed plastics using commercially available small-molecule cross-linkers.