Recycling of Polystyrene/Polyethylene Micro/Nanolayered Films: Effect of Melt Rheological Properties Mismatch on Induced Morphological and Mechanical Performances

ABSTRACT In the latest decade, intensive research work was dedicated to multi‐micro/nanolayer systems as an alternative to classical multilayer systems, aiming to reduce the number of constituents. However, limited attention has been paid to their recyclability. The present study aimed to evaluate a novel eco‐design approach for the valorization of polystyrene‐based multilayer films as an alternative to conventional PS/PE multilayer systems. To facilitate their recyclability, films were prepared with a limited number of constituents, avoiding the use of tie layers. The forced assembly coextrusion technology was employed to manufacture multi‐micro/nanolayer films composed of polystyrene and low‐density polyethylene (PS/LDPE), as well as polystyrene and linear low‐density polyethylene (PS/LLDPE), with a volumetric ratio of 90/10 mimicking the composition encountered in the packaging field. PS/PE multilayer systems were tailored based on their rheological properties (i.e., different viscosity and elasticity ratios between the polymer constituents) in order to control their morphology, even throughout the recycling process. Firstly, the effect of mechanical recycling steps (grinding and melt blending by twin‐screw extrusion) on the evolution of the mechanical properties was investigated. Interestingly, it was found that the initial multi micro/nanolayered structure was transformed into a multi‐micro/nanofibrillar or lamellar morphology, making it possible to obtain recycled films with a good compromise between rigidity and ductility. Furthermore, the Young's modulus was higher for 256L, 1024L, and 2048L prepared at DDR5 in comparison to 32‐layer films with low confinement and interfacial area, whatever the recycling cycle. Overall, Young's modulus measurements suggest that the mechanical properties were preserved over multiple recycling cycles and, in some cases, even improved. The results demonstrated that eco‐design through the recycling of multi‐micro/nanolayer structures can represent a promising sustainable strategy to improve the recyclability of multilayer packaging films as produced. This approach reduces the number of components used in the multilayer system and supports the transition toward mono‐materials in order to reduce environmental impact.