Upcycling of Mixed Polyolefins via a Grafting-Dynamic Cross-Linking Strategy

Abstract The differences in molecular chain structure, polarity, and crystallinity among mixed polyolefins severely weaken interfacial adhesion in their blends, posing a critical barrier to the efficient upcycling of mixed waste polyolefin plastics. Herein, a solvent-free, one-pot reactive extrusion process is developed, which enables dynamic covalent cross-linking modification of polyolefin blends-including post-consumer plastic waste-using two commercially available bio-sourced additives (itaconic anhydride and D-sorbitol) as modifiers. This integrated process simultaneously accomplishes chain grafting and dynamic cross-linking, achieving enhanced interfacial adhesion without requiring presynthesized small-molecule compatibilizers, thereby greatly simplifying the process. PP/PE blends modified by this process exhibit a 247% increase in elongation at break and a 5-fold enhancement in fracture toughness, while the material retains considerable mechanical performance even after three reprocessing cycles. This modification strategy is demonstrated to be universally applicable to mixed polyolefin systems with different compositions, indicating broad potential for practical application. This work establishes a scalable, green, and potentially cost-effective technical system for the high-value circular utilization of plastic waste, providing a novel pathway for the upcycling of waste polyolefin plastics.