Additive-Free Compatibilization of Commodity Polypropylene/Polyethylene via Partial Melting and Recrystallization.

Mixed polyethylene (PE) and polypropylene (PP) generate roughly 250 million tons of plastic waste annually, yet their mechanical recycling still relies on additive- and reactive chemistry-based compatibilization, raising costs and complicating waste streams that can obstruct circularity at scale. Here, we report an additive-free, thermal solvent immersion annealing strategy that compatibilizes PP/PE blends post-manufacturing. Elevated temperatures partially melt crystalline regions while the solvent selectively swells amorphous domains, broadening PP/PE interfaces and promoting local chain mixing. Upon solvent removal, chain recrystallization generates entangled intercrystallite loops that bridge PP and PE domains, enabling efficient stress transfer and transforming brittle blends into tough, strain-hardening materials. We demonstrate broad applicability across PP/PE compositions and molecular identities, supported by experiments and molecular dynamics simulations that directly track loop formation and its role in stress transfer during sample deformation. This work establishes a new compatibilization pathway based on entangled intercrystallite loop formation, enabled by partial melting and recrystallization, and offers a scalable route to mechanical recycling of plastic waste via phase-specific engineering.