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

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. • Pre-formed EVOH crystalline nanoaggregates used as molecular probes of polymer compatibility. • DSC reveals a clear hierarchy of EVOH–matrix interactions: EMANa > EVA > EEA >> PCL. • Strong interactions suppress EVOH crystal thickening, indicating restricted chain mobility. • FTIR confirms hydrogen bonding and ionic contributions at the EVOH/tie-layer interface. • Combined DSC–FTIR analysis guides eco-design of recyclable polyolefin multilayer films.