Microfibrillation Processing as an Industry‐Relevant Strategy for Upcycling Mixed Post‐Consumer Polyolefin Waste

Post‐consumer polyolefin waste streams frequently contain immiscible polyethylene (PE) and polypropylene (PP) mixtures that exhibit poor interfacial adhesion and limited mechanical performance, restricting their recycling potential. In this work, microfibrillation processing was investigated as a low‐cost strategy to upgrade recycled PE/PP blends without relying on extensive compatibilization. Blends containing 75 wt.% PE and 25 wt.% PP were processed as conventional non‐drawn systems and as microfibrillar composites (MFCs), with and without commercial compatibilizers. The effects of morphology development on the thermal, mechanical, and fracture behavior of the materials were systematically evaluated. Scanning electron microscope observations confirmed the in situ transformation of the dispersed PP phase into elongated microfibrils after drawing, while differential scanning calorimetry and Fourier transform infrared spectroscopy analyses indicated that neither microfibrillation nor compatibilizer addition significantly altered the crystallinity or chemical structure of the blends. Microfibrillated systems exhibited higher stiffness than the corresponding non‐drawn blends, together with a remarkable increase in fracture toughness, reaching improvements of up to 125%. Compatibilizers promoted fibril refinement and improved interfacial interactions; however, their influence on the final mechanical performance of the MFCs was limited. The results demonstrate that morphology control through microfibrillation is an effective approach for enhancing the performance of recycled immiscible PE/PP blends, providing a simple and economically attractive route for the high‐value reutilization of mixed polyolefin waste streams within a circular economy framework.