Mechanical recycling of polypropylene (PP) often causes chain scission resulting in diminishing performance in crystallinity and mechanical toughness. To address this challenge and enable the use of low molecular weight PP in a circular economy, we demonstrate a solvent annealing approach for enhancing the mechanical properties of PP blends of distinct molecular weights, which could enable effective use of post-consumer recycled polypropylene. Our method works by swelling the amorphous regions of high molecular weight PP, reorganizing the semicrystalline structures of lower molecular weight polymers, and creating entanglements between high and low molecular weight species. Upon drying, the material retains its initial dimensions prior to swelling and demonstrates enhanced crystallinity, elevated glass transition temperature, improved toughness, and a unimodal melting transition. This method enables the incorporation of brittle, low molecular weight PP into a commodity PP material with comparable performance to the virgin material. We anticipate the ability to restructure the amorphous and crystalline regions of PP blends will become instrumental in developing new technologies to effectively upcycle a variety of post-consumer recycled polyolefins.
