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The present work explores the shear and extensional rheology of immiscible multi-micro/nanolayered systems comprising low-density polyethylene (LDPE) paired with polystyrene (PS) and polycarbonate (PC) obtained from forced-assembly multilayer coextrusion. Firstly, miscible multilayer references based on LDPE/LLDPE layers were prepared with their miscibility characterized by shear and elongational measurements. Their strain hardening behaviors were found to be intricately linked to the number of layers and confinement. Secondly, for immiscible LDPE/PS and LDPE/PC multilayers with symmetric (50/50) and asymmetric (10/90) compositions, negative deviation of complex viscosities from neat polymers was highlighted because of the heightened confinement of LDPE chains by PS or PC and reduced entanglements at polymer–polymer interfaces. Intriguingly, LDPE/PC systems exhibited no strain hardening irrespective of layer configuration, while the geometric confinement imposed by PS layers facilitated interactions between single chains with long-chain branching (LCB), leading to strain hardening under specific conditions. Furthermore, the extensional viscosities were predicted using the Macosko model (C.W. Macosko et al. Journal of Rheology. 63 2019), accurately describing the behavior of 1024 layered films for both asymmetric (10/90) LDPE/PS and LDPE/PC systems, but not for 32 layers due to a limited number of interfaces. This study provides insights into quantifying interfacial tension properties in micro/nano-layered systems with high mismatched viscoelastic polymers, shedding light on their strain hardening properties in the presence of increased interfacial area. [ABSTRACT FROM AUTHOR]

This paper describes a future-oriented approach for the valorization of polyethylene-based multilayer films. The method involves going from eco-design to mechanical recycling of multilayer films via forced assembly coextrusion. The originality of this study consists in limiting the number of constituents, reducing/controlling the thickness of the layers and avoiding the use of tie layers. The ultimate goal is to improve the manufacturing of new products from recycled multilayer materials by simplifying their recyclability. Within this framework, new structures were developed with two polymer systems: polyethylene/polypropylene and polyethylene/polystyrene, with nominal micro- and nanometric thicknesses. Hitherto, the effect of the multi-micro/nanolayer architecture as well as initial morphological and mechanical properties was evaluated. Several recycling processes were investigated, including steps such as: (i) grinding; (ii) monolayer cast film extrusion; or (iii) injection molding with or without an intermediate blending step by twin-screw extrusion. Subsequently, the induced morphological and mechanical properties were investigated depending on the recycling systems and the relationships between the chosen recycling processes or strategies, and structure and property control of the recycled systems was established accordingly. Based on the results obtained, a proof of concept was demonstrated with the eco-design of multi-micro/nanolayer films as a very promising solution for the industrial issues that arise with the valorization of recycled materials. [ABSTRACT FROM AUTHOR]