Molecular interactions between ethylene-vinyl alcohol copolymers and functionalized tie layers for recyclable multilayer films

Abstract

The increasing demand for recyclable multilayer polymer packaging requires a deeper understanding of the interactions between barrier and tie-layer materials to enable circular design strategies. In this study, the compatibility between polyethylene–co–vinyl alcohol (EVOH) copolymer and typical tie-layer copolymers—polyethylene–co–ethyl acrylate, polyethylene–co–vinyl acetate, and a polyethylene–co–methacrylic acid ionomer partially neutralized with sodium—was investigated. EVOH crystalline nanoaggregates were prepared and embedded in the different matrices to evaluate physical and thermal interactions. Differential Scanning Calorimetry revealed a pronounced melting temperature depression of EVOH crystals when blended with functionalized matrices, particularly with the ionomer, indicating strong intermolecular interactions. In contrast, non-interacting systems retained their original melting behaviour, confirming the absence of chemical affinity. Fourier Transform Infrared Spectroscopy further corroborated these findings, showing hydrogen-bonding interactions between the hydroxyl groups of EVOH and the carbonyl or carboxylate groups of the functionalized tie layers. The combination of the results obtained from the different techniques provides a comprehensive understanding of the molecular mechanisms governing compatibility, offering valuable insights for the eco-design and recyclability enhancement of polyolefin-based multilayer packaging materials.