Compatibilization of Low Molecular Weight Polypropylene in High Molecular Weight Matrix Via Solvent Swelling.

Mechanical recycling of polypropylene (PP) causes chain scission during high-temperature, high-shear processing, resulting in lower molecular weight (MW) fragments, which contain fewer tie chains between crystalline lamellae. This change can lead to significantly reduced mechanical performance, making the use of post-consumer recycled PP in new materials particularly challenging, especially as recent government policies mandate the use of recycled content at increasing levels. Previous strategies in addressing these needs rely on chemically crosslinking or introducing additives, which can be time-consuming, cost-prohibitive at scale, and/or further complicate waste streams. In this work, we demonstrate a solvent immersion annealing method that swells PP blends containing high and low MW fractions, promoting their co-crystallization, which leads to significantly improved mechanical performance of the blended materials. Specifically, our results show an over 6-fold increase in extensibility of PP blends, effectively enabling their reuse and extended lifetime. This work presents an innovative and straightforward method to address the recycling challenges of low MW PP without the need for additives, potentially opening new avenues for future research in blend compatibilization for addressing plastic circularity challenges.