Next‐Generation Sustainable Polyolefin Packaging Manufactured Using Flow‐Induced Crystallization

The replacement of non‐recyclable multilayer films with high‐performance, monolithic polymer films represents a critical goal for a circular economy. This feasibility study investigates melt mastication (MM), a novel processing technique that utilizes flow‐induced crystallization (FIC) to enhance the mechanical and barrier properties of high‐density polyethylene (HDPE). The MM process, particularly at low shear rates, fundamentally alters the semicrystalline morphology, increasing the bulk crystallinity to an exceptional level of 85%. This unique, non‐spherulitic, granular morphology results in a dramatic enhancement of mechanical properties, with a greater than 240% increase in elastic modulus and a 340% increase in tensile strength compared to conventional controls. A detailed, multi‐scale characterization using thermal analysis (DSC), X‐ray scattering (WAXS/SAXS), solid‐state NMR, and electron microscopy (SEM) elucidates the structure responsible for this performance. The resulting morphology is a direct product of an FIC pathway that occurs above the nominal melting temperature. While the oxygen barrier performance shows a complex dependence on the interplay between crystalline and amorphous structures, the most highly crystalline MM films demonstrate promising properties. This work establishes MM as a powerful pathway for upcycling commodity polymers and provides a model for understanding how chaotic shear can create non‐equilibrium structures with enhanced performance.